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Paulusma CC, Lamers W, Broer S, van de Graaf SFJ. Amino acid metabolism, transport and signalling in the liver revisited. Biochem Pharmacol 2022; 201:115074. [PMID: 35568239 DOI: 10.1016/j.bcp.2022.115074] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2022] [Revised: 04/28/2022] [Accepted: 04/29/2022] [Indexed: 11/02/2022]
Abstract
The liver controls the systemic exposure of amino acids entering via the gastro-intestinal tract. For most amino acids except branched chain amino acids, hepatic uptake is very efficient. This implies that the liver orchestrates amino acid metabolism and also controls systemic amino acid exposure. Although many amino acid transporters have been identified, cloned and investigated with respect to substrate specificity, transport mechanism, and zonal distribution, which of these players are involved in hepatocellular amino acid transport remains unclear. Here, we aim to provide a review of current insight into the molecular machinery of hepatic amino acid transport. Furthermore, we place this information in a comprehensive overview of amino acid transport, signalling and metabolism.
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Affiliation(s)
- Coen C Paulusma
- Tytgat Institute for Liver and Intestinal Research, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, Netherlands; Department of Gastroenterology and Hepatology, Amsterdam University Medical Centers, Amsterdam, Netherlands; Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam University Medical Centers, Amsterdam, The Netherlands
| | - Wouter Lamers
- Tytgat Institute for Liver and Intestinal Research, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, Netherlands; Department of Gastroenterology and Hepatology, Amsterdam University Medical Centers, Amsterdam, Netherlands; Department of Anatomy & Embryology, Maastricht University, Maastricht, The Netherlands
| | - Stefan Broer
- Department of Gastroenterology and Hepatology, Amsterdam University Medical Centers, Amsterdam, Netherlands; Research School of Biology, Australian National University, Canberra, Australia
| | - Stan F J van de Graaf
- Tytgat Institute for Liver and Intestinal Research, Amsterdam University Medical Centers, University of Amsterdam, Amsterdam, Netherlands; Department of Gastroenterology and Hepatology, Amsterdam University Medical Centers, Amsterdam, Netherlands; Amsterdam Gastroenterology Endocrinology Metabolism, Amsterdam University Medical Centers, Amsterdam, The Netherlands; Department of Anatomy & Embryology, Maastricht University, Maastricht, The Netherlands.
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2
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Holeček M. Serine Metabolism in Health and Disease and as a Conditionally Essential Amino Acid. Nutrients 2022; 14:nu14091987. [PMID: 35565953 PMCID: PMC9105362 DOI: 10.3390/nu14091987] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 05/02/2022] [Accepted: 05/06/2022] [Indexed: 02/04/2023] Open
Abstract
L-serine plays an essential role in a broad range of cellular functions including protein synthesis, neurotransmission, and folate and methionine cycles and synthesis of sphingolipids, phospholipids, and sulphur containing amino acids. A hydroxyl side-chain of L-serine contributes to polarity of proteins, and serves as a primary site for binding a phosphate group to regulate protein function. D-serine, its D-isoform, has a unique role. Recent studies indicate increased requirements for L-serine and its potential therapeutic use in some diseases. L-serine deficiency is associated with impaired function of the nervous system, primarily due to abnormal metabolism of phospholipids and sphingolipids, particularly increased synthesis of deoxysphingolipids. Therapeutic benefits of L-serine have been reported in primary disorders of serine metabolism, diabetic neuropathy, hyperhomocysteinemia, and amyotrophic lateral sclerosis. Use of L-serine and its metabolic products, specifically D-serine and phosphatidylserine, has been investigated for the therapy of renal diseases, central nervous system injury, and in a wide range of neurological and psychiatric disorders. It is concluded that there are disorders in which humans cannot synthesize L-serine in sufficient quantities, that L-serine is effective in therapy of disorders associated with its deficiency, and that L-serine should be classified as a “conditionally essential” amino acid.
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Affiliation(s)
- Milan Holeček
- Department of Physiology, Faculty of Medicine in Hradec Králové, Charles University, Šimkova 870, 500 03 Hradec Králové, Czech Republic
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3
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Bhutia YD, Mathew M, Sivaprakasam S, Ramachandran S, Ganapathy V. Unconventional Functions of Amino Acid Transporters: Role in Macropinocytosis (SLC38A5/SLC38A3) and Diet-Induced Obesity/Metabolic Syndrome (SLC6A19/SLC6A14/SLC6A6). Biomolecules 2022; 12:biom12020235. [PMID: 35204736 PMCID: PMC8961558 DOI: 10.3390/biom12020235] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 01/24/2022] [Accepted: 01/27/2022] [Indexed: 02/06/2023] Open
Abstract
Amino acid transporters are expressed in mammalian cells not only in the plasma membrane but also in intracellular membranes. The conventional function of these transporters is to transfer their amino acid substrates across the lipid bilayer; the direction of the transfer is dictated by the combined gradients for the amino acid substrates and the co-transported ions (Na+, H+, K+ or Cl−) across the membrane. In cases of electrogenic transporters, the membrane potential also contributes to the direction of the amino acid transfer. In addition to this expected traditional function, several unconventional functions are known for some of these amino acid transporters. This includes their role in intracellular signaling, regulation of acid–base balance, and entry of viruses into cells. Such functions expand the biological roles of these transporters beyond the logical amino acid homeostasis. In recent years, two additional unconventional biochemical/metabolic processes regulated by certain amino acid transporters have come to be recognized: macropinocytosis and obesity. This adds to the repertoire of biological processes that are controlled and regulated by amino acid transporters in health and disease. In the present review, we highlight the unusual involvement of selective amino acid transporters in macropinocytosis (SLC38A5/SLC38A3) and diet-induced obesity/metabolic syndrome (SLC6A19/SLC6A14/SLC6A6).
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Placenta-specific Slc38a2/SNAT2 knockdown causes fetal growth restriction in mice. Clin Sci (Lond) 2021; 135:2049-2066. [PMID: 34406367 PMCID: PMC8410983 DOI: 10.1042/cs20210575] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2021] [Revised: 08/12/2021] [Accepted: 08/18/2021] [Indexed: 12/30/2022]
Abstract
Fetal growth restriction (FGR) is a complication of pregnancy that reduces birth weight, markedly increases infant mortality and morbidity and is associated with later-life cardiometabolic disease. No specific treatment is available for FGR. Placentas of human FGR infants have low abundance of sodium-coupled neutral amino acid transporter 2 (Slc38a2/SNAT2), which supplies the fetus with amino acids required for growth. We determined the mechanistic role of placental Slc38a2/SNAT2 deficiency in the development of restricted fetal growth, hypothesizing that placenta-specific Slc38a2 knockdown causes FGR in mice. Using lentiviral transduction of blastocysts with a small hairpin RNA (shRNA), we achieved 59% knockdown of placental Slc38a2, without altering fetal Slc38a2 expression. Placenta-specific Slc38a2 knockdown reduced near-term fetal and placental weight, fetal viability, trophoblast plasma membrane (TPM) SNAT2 protein abundance, and both absolute and weight-specific placental uptake of the amino acid transport System A tracer, 14C-methylaminoisobutyric acid (MeAIB). We also measured human placental SLC38A2 gene expression in a well-defined term clinical cohort and found that SLC38A2 expression was decreased in late-onset, but not early-onset FGR, compared with appropriate for gestational age (AGA) control placentas. The results demonstrate that low placental Slc38a2/SNAT2 causes FGR and could be a target for clinical therapies for late-onset FGR.
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Castillo-Castrejon M, Yamaguchi K, Rodel RL, Erickson K, Kramer A, Hirsch NM, Rolloff K, Jansson T, Barbour LA, Powell TL. Effect of type 2 diabetes mellitus on placental expression and activity of nutrient transporters and their association with birth weight and neonatal adiposity. Mol Cell Endocrinol 2021; 532:111319. [PMID: 33989714 PMCID: PMC8206039 DOI: 10.1016/j.mce.2021.111319] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/28/2021] [Revised: 05/06/2021] [Accepted: 05/07/2021] [Indexed: 11/19/2022]
Abstract
AIMS Infants born to women with Type 2 Diabetes Mellitus (T2DM) are at risk of being born large for gestational age due to excess fetal fat accretion. Placental nutrient transport determines fetal nutrient availability, impacting fetal growth. The aims of the study were to evaluate the effect of T2DM on placental insulin signaling, placental nutrient transporters and neonatal adiposity. METHODS Placentas were collected from BMI-matched normoglycemic controls (NGT, n = 9) and T2DM (n = 9) women. Syncytiotrophoblast microvillous (MVM) and basal (BM) plasma membranes were isolated. Expression of glucose (GLUT1, -4), fatty acid (FATP2, -4, -6, FAT/CD36), amino acid (SNAT1, -2, -4, LAT1, -2) transporters, insulin signaling, and System A transporter activity was determined. Neonatal fat mass (%) was measured in a subset of neonates born to T2DM women. RESULTS GLUT1 protein expression was increased (p = 0.001) and GLUT4 decreased (p = 0.006) in BM from T2DM. MVM FATP6 expression was increased (p = 0.02) and correlated with birth weight in both T2DM and NGT groups (r = 0.65, p = 0.02). BM FATP6 expression was increased (p = 0.01) in T2DM. In MVM of T2DM placentas, SNAT1 expression was increased (p = 0.05) and correlated with birth weight (r = 0.84, p = 0.004); SNAT2 was increased (p = 0.01), however System A transporter activity was not different between groups. MVM LAT1 expression was increased (p = 0.01) in T2DM and correlated with birth weight (r = 0.59, p = 0.04) and neonatal fat mass (r = 0.76, p = 0.06). CONCLUSION In pregnancies complicated by T2DM placental protein expression of transporters for glucose, amino acids and fatty acids is increased, which may contribute to increased fetal growth and neonatal adiposity.
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Affiliation(s)
- Marisol Castillo-Castrejon
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA.
| | - Kyohei Yamaguchi
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA; Department of Obstetrics and Gynecology, Mie University, Mie, Japan
| | - Rachel L Rodel
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Kathryn Erickson
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Anita Kramer
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Nicole M Hirsch
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Kristy Rolloff
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Thomas Jansson
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Linda A Barbour
- Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA; Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
| | - Theresa L Powell
- Department of Obstetrics and Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA; Department of Pediatrics, Section of Neonatology, University of Colorado Anschutz Medical Campus, Aurora, CO, 80045, USA
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6
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James-Allan LB, Teal S, Powell TL, Jansson T. Changes in Placental Nutrient Transporter Protein Expression and Activity Across Gestation in Normal and Obese Women. Reprod Sci 2020; 27:1758-1769. [PMID: 32072607 DOI: 10.1007/s43032-020-00173-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Accepted: 02/03/2020] [Indexed: 11/26/2022]
Abstract
Fetal growth and development are dependent on placental nutrient transport. The syncytiotrophoblast (ST) and its two polarized plasma membranes, the maternal-facing microvillous membrane (MVM) and fetal-facing basal membrane (BM), represent the primary barrier in the human placenta, controlling transplacental transfer of small solutes. MVM and BM nutrient transporter expression and activity are increased in obese mothers delivering large babies. However, placental nutrient transporter expression and activity in early gestation in normal and obese women are largely unknown. Placentas from normal BMI and obese women at 6-24 weeks of gestation, and term placentas from normal BMI women, were collected and ST plasma membranes isolated. The activity and protein expression of amino acid, glucose, and fatty acid transporters was assessed. No significant differences were observed in placental nutrient transporter protein expression between normal BMI and obese women in early pregnancy. In the MVM, system A amino acid activity (p = 0.02), SNAT2 (p < 0.0001), SNAT4 (p < 0.001), and GLUT1 (p = 0.01) protein expression were higher at term compared with early gestation. In contrast, MVM system L activity (p = 0.001), FATP4 (p = 0.03), and FATP6 (p = 0.009) protein expression were lower at term compared with early pregnancy. In the BM, there was no change in system L activity across gestation; however, BM FATP6 (p = 0.002) protein expression was lower at term compared with early pregnancy. These results suggest that placental transport of amino acids, glucose, and fatty acids are subjected to coordinated regulation across gestation to meet a fetal nutrient demand that changes with advancing pregnancy.
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Affiliation(s)
- Laura B James-Allan
- Department of Obstetrics/Gynecology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA.
| | - Stephanie Teal
- Department of Obstetrics/Gynecology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Theresa L Powell
- Department of Obstetrics/Gynecology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
- Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
| | - Thomas Jansson
- Department of Obstetrics/Gynecology, University of Colorado Anschutz Medical Campus, Aurora, CO, USA
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7
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Menchini RJ, Chaudhry FA. Multifaceted regulation of the system A transporter Slc38a2 suggests nanoscale regulation of amino acid metabolism and cellular signaling. Neuropharmacology 2019; 161:107789. [PMID: 31574264 DOI: 10.1016/j.neuropharm.2019.107789] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Revised: 09/16/2019] [Accepted: 09/20/2019] [Indexed: 02/07/2023]
Abstract
Amino acids are essential for cellular protein synthesis, growth, metabolism, signaling and in stress responses. Cell plasma membranes harbor specialized transporters accumulating amino acids to support a variety of cellular biochemical pathways. Several transporters for neutral amino acids have been characterized. However, Slc38a2 (also known as SA1, SAT2, ATA2, SNAT2) representing the classical transport system A activity stands in a unique position: Being a secondarily active transporter energized by the electrochemical gradient of Na+, it creates steep concentration gradients for amino acids such as glutamine: this may subsequently drive the accumulation of additional neutral amino acids through exchange via transport systems ASC and L. Slc38a2 is ubiquitously expressed, yet in a cell-specific manner. In this review, we show that Slc38a2 is regulated at the transcriptional and translational levels as well as by ions and proteins through direct interactions. We describe how Slc38a2 senses amino acid availability and passes this onto intracellular signaling pathways and how it regulates protein synthesis, cellular proliferation and apoptosis through the mechanistic (mammalian) target of rapamycin (mTOR) and general control nonderepressible 2 (GCN2) pathways. Furthermore, we review how this extensively regulated transporter contributes to cellular osmoadaptation and how it is regulated by endoplasmic reticulum stress and various hormonal stimuli to promote cellular metabolism, cellular signaling and cell survival. This article is part of the issue entitled 'Special Issue on Neurotransmitter Transporters'.
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Affiliation(s)
| | - Farrukh Abbas Chaudhry
- Department of Molecular Medicine, University of Oslo, Oslo, Norway; Department of Plastic and Reconstructive Surgery, Oslo University Hospital, Oslo, Norway
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8
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Stretton C, Lipina C, Hyde R, Cwiklinski E, Hoffmann TM, Taylor PM, Hundal HS. CDK7 is a component of the integrated stress response regulating SNAT2 (SLC38A2)/System A adaptation in response to cellular amino acid deprivation. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2019; 1866:978-991. [PMID: 30857869 PMCID: PMC6456927 DOI: 10.1016/j.bbamcr.2019.03.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/01/2018] [Revised: 03/04/2019] [Accepted: 03/06/2019] [Indexed: 12/31/2022]
Abstract
Extracellular amino acid (AA) withdrawal/restriction invokes an integrated stress response (ISR) that induces global suppression of protein synthesis whilst allowing transcription and translation of a select group of genes, whose protein products facilitate cellular adaptation to AA insufficiency. Transcriptional induction of the System A/SNAT2 AA transporter represents a classic adaptation response and crucially depends upon activation of the General Control Nonderepressible-2 kinase/Activating transcription factor 4 (GCN2/ATF4) pathway. However, the ISR may also include additional signalling inputs operating in conjunction or independently of GCN2/ATF4 to upregulate SNAT2. Herein, we show that whilst pharmacological inhibition of MEK-ERK, mTORC1 and p38 MAP kinase signalling has no detectable effect on System A upregulation, inhibitors targeting GSK3 (e.g. SB415286) caused significant repression of the SNAT2 adaptation response. Strikingly, the effects of SB415286 persist in cells in which GSK3α/β have been stably silenced indicating an off-target effect. We show that SB415286 can also inhibit cyclin-dependent kinases (CDK) and that roscovitine and flavopiridol (two pan CDK inhibitors) are effective repressors of the SNAT2 adaptive response. In particular, our work reveals that CDK7 activity is upregulated in AA-deprived cells in a GCN-2-dependent manner and that a potent and selective CDK7 inhibitor, THZ-1, not only attenuates the increase in ATF4 expression but blocks System A adaptation. Importantly, the inhibitory effects of THZ-1 on System A adaptation are mitigated in cells expressing a doxycycline-inducible drug-resistant form of CDK7. Our data identify CDK7 as a novel component of the ISR regulating System A adaptation in response to AA insufficiency. Roscovitine and flavopiridol (CDK inhibitors) block the System A adaptive response. Extracellular amino acid (AA) withdrawal induces CDK7 activation. Pharmacological inhibition of GCN2 represses CDK7 activation in AA-deprived cells. Targeted suppression of CDK7 represses ATF4 expression and System A adaptation.
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Affiliation(s)
- Clare Stretton
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Christopher Lipina
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Russell Hyde
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Emma Cwiklinski
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Thorsten M Hoffmann
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Peter M Taylor
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Harinder S Hundal
- Division of Cell Signalling and Immunology, Sir James Black Centre, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
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Anandam KY, Srinivasan P, Subramanian VS, Said HM. Molecular mechanisms involved in the adaptive regulation of the colonic thiamin pyrophosphate uptake process. Am J Physiol Cell Physiol 2017; 313:C655-C663. [PMID: 28931541 DOI: 10.1152/ajpcell.00169.2017] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A considerable amount of the thiamin generated by gut microbiota exists in the form of thiamin pyrophosphate (TPP). We have previously shown that human colonocytes possess an efficient carrier-mediated uptake process for TPP that involves the SLC44A4 system and this uptake process is adaptively regulated by prevailing extracellular TPP level. Little is known about the molecular mechanisms that mediate this adaptive regulation. We addressed this issue using human-derived colonic epithelial NCM460 cells and mouse colonoids as models. Maintaining NCM460 cells in the presence of a high level of TPP (1 mM) for short (2 days)- and long-term (9 days) periods was found to lead to a significant reduction in [3H] TPP uptake compared with cells maintained in its absence. Short-term exposure showed no changes in level of expression of SLC44A4 protein in total cell homogenate (although there was a decreased expression in the membrane fraction), mRNA, and promoter activity. However, a significant reduction in the level of expression of the SLC44A4 protein, mRNA, and promoter activity was observed upon long-term maintenance with the substrate. Similar changes in Slc44a4 mRNA expression were observed when mouse colonoids were maintained with TPP for short- and long-term periods. Expression of the transcription factors ELF3 and CREB-1 (which drive the SLC44A4 promoter) following long-term exposure was unchanged, but their binding affinity to the promoter was decreased and specific histone modifications were also observed. These studies demonstrate that, depending on the period of exposure, different mechanisms are involved in the adaptive regulation of colonic TPP uptake by extracellular substrate level.
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Affiliation(s)
- Kasin Yadunandam Anandam
- Department of Medical Research, VA Medical Center , Long Beach, California.,Departments of Medicine and Physiology/Biophysics, University of California School of Medicine , Irvine, California
| | - Padmanabhan Srinivasan
- Department of Medical Research, VA Medical Center , Long Beach, California.,Departments of Medicine and Physiology/Biophysics, University of California School of Medicine , Irvine, California
| | - Veedamali S Subramanian
- Department of Medical Research, VA Medical Center , Long Beach, California.,Departments of Medicine and Physiology/Biophysics, University of California School of Medicine , Irvine, California
| | - Hamid M Said
- Department of Medical Research, VA Medical Center , Long Beach, California.,Departments of Medicine and Physiology/Biophysics, University of California School of Medicine , Irvine, California
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10
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Hellsten SV, Hägglund MG, Eriksson MM, Fredriksson R. The neuronal and astrocytic protein SLC38A10 transports glutamine, glutamate, and aspartate, suggesting a role in neurotransmission. FEBS Open Bio 2017; 7:730-746. [PMID: 28593130 PMCID: PMC5458457 DOI: 10.1002/2211-5463.12219] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Revised: 03/03/2017] [Accepted: 03/08/2017] [Indexed: 12/21/2022] Open
Abstract
In brain cells, glutamine transporters are vital to monitor and control the levels of glutamate and GABA. There are 11 members of the SLC38 family of amino acid transporters of which eight have been functionally characterized. Here, we report the first histological and functional characterization of the previously orphan member, SLC38A10. We used pairwise global sequence alignments to determine the sequence identity between the SLC38 family members. SLC38A10 was found to share 20–25% transmembrane sequence identity with several family members, and was predicted to have 11 transmembrane helices. SLC38A10 immunostaining was abundant in mouse brain using a custom‐made anti‐SLC38A10 antibody and colocalization of SLC38A10 immunoreactivity with markers for neurons and astrocytes was detected. Using Xenopus laevis oocytes overexpressing SLC38A10, we show that SLC38A10 mediates bidirectional transport of l‐glutamine, l‐alanine, l‐glutamate, and d‐aspartate, and efflux of l‐serine. This profile mostly resembles system A members of the SLC38 family. In conclusion, the bidirectional transport of glutamine, glutamate, and aspartate by SLC38A10, and the immunostaining detected in neurons and astrocytes, suggest that SLC38A10 plays a role in pathways involved in neurotransmission.
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Affiliation(s)
- Sofie V Hellsten
- Department of Pharmaceutical Bioscience, Molecular Neuropharmacology Uppsala University Sweden
| | - Maria G Hägglund
- Department of Neuroscience, Functional Pharmacology Uppsala University Sweden
| | - Mikaela M Eriksson
- Department of Pharmaceutical Bioscience, Molecular Neuropharmacology Uppsala University Sweden
| | - Robert Fredriksson
- Department of Pharmaceutical Bioscience, Molecular Neuropharmacology Uppsala University Sweden
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11
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Pantham P, Rosario FJ, Weintraub ST, Nathanielsz PW, Powell TL, Li C, Jansson T. Down-Regulation of Placental Transport of Amino Acids Precedes the Development of Intrauterine Growth Restriction in Maternal Nutrient Restricted Baboons. Biol Reprod 2016; 95:98. [PMID: 27605346 PMCID: PMC5178152 DOI: 10.1095/biolreprod.116.141085] [Citation(s) in RCA: 44] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Accepted: 08/24/2016] [Indexed: 12/17/2022] Open
Abstract
Intrauterine growth restriction (IUGR) is an important risk factor for perinatal complications and adult disease. IUGR is associated with down-regulation of placental amino acid transporter expression and activity at birth. It is unknown whether these changes are a cause or a consequence of human IUGR. We hypothesized that placental amino acid transport capacity is reduced prior to onset of reduced fetal growth in baboons with maternal nutrient restriction (MNR). Pregnant baboons were fed either a control (n = 8) or MNR diet (70% of control diet, n = 9) from Gestational Day 30. At Gestational Day 120 (0.65 of gestation), fetuses and placentas were collected. Microvillous (MVM) and basal (BM) plasma membrane vesicles were isolated. System A and system L transport activity was determined in MVM, and leucine transporter activity was assessed in BM using radiolabeled substrates. MVM amino acid transporter isoform expression (SNAT1, SNAT2, and SNAT4 and LAT1 and LAT2) was measured using Western blots. LAT1 and LAT2 expression were also determined in BM. Maternal and fetal plasma amino acids concentrations were determined using mass spectrometry. Fetal and placental weights were unaffected by MNR. MVM system A activity was decreased by 37% in MNR baboon placentas (P = 0.03); however MVM system A amino acid transporter protein expression was unchanged. MVM system L activity and BM leucine transporter activity were not altered by MNR. Fetal plasma concentrations of essential amino acids isoleucine and leucine were reduced, while citrulline increased (P < 0.05) in MNR fetuses compared to controls. In this primate model of IUGR, placental MVM system A amino acid transporter activity is decreased prior to the onset of reduction in the fetal growth trajectory. The reduction in plasma leucine and isoleucine in MNR fetuses may be caused by reduced activity of MVM system A, which is strongly coupled with system L essential amino acid uptake. Our findings indicate that reduced placental amino acid transport may be a cause rather than a consequence of IUGR due to inadequate maternal nutrition.
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Affiliation(s)
- Priyadarshini Pantham
- Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado
| | - Fredrick J Rosario
- Department of Obstetrics & Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado
| | - Susan T Weintraub
- Department of Biochemistry, University of Texas Health Science Center San Antonio, San Antonio, Texas
| | - Peter W Nathanielsz
- Department of Animal Science, University of Wyoming, Laramie, Wyoming.,Southwest National Primate Research Center, San Antonio, Texas
| | - Theresa L Powell
- Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado
| | - Cun Li
- Department of Animal Science, University of Wyoming, Laramie, Wyoming.,Southwest National Primate Research Center, San Antonio, Texas
| | - Thomas Jansson
- Department of Obstetrics & Gynecology, Division of Reproductive Sciences, University of Colorado Anschutz Medical Campus, Aurora, Colorado
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The Glutamine Transporters and Their Role in the Glutamate/GABA-Glutamine Cycle. ADVANCES IN NEUROBIOLOGY 2016; 13:223-257. [PMID: 27885631 DOI: 10.1007/978-3-319-45096-4_8] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Glutamine is a key amino acid in the CNS, playing an important role in the glutamate/GABA-glutamine cycle (GGC). In the GGC, glutamine is transferred from astrocytes to neurons, where it will replenish the inhibitory and excitatory neurotransmitter pools. Different transporters participate in this neural communication, i.e., the transporters responsible for glutamine efflux from astrocytes and influx into the neurons, such as the members of the SNAT, LAT, y+LAT, and ASC families of transporters. The SNAT family consists of the transporter isoforms SNAT3 and SNAT5 that are related to efflux from the astrocytic compartment, and SNAT1 and SNAT2 that are associated with glutamine uptake into the neuronal compartment. The isoforms SNAT7 and SNAT8 do not have their role completely understood, but they likely also participate in the GGC. The isoforms LAT2 and y+LAT2 facilitate the exchange of neutral amino acids and cationic amino acids (y+LAT2 isoform) and have been associated with glutamine efflux from astrocytes. ASCT2 is a Na+-dependent antiporter, the participation of which in the GGC also remains to be better characterized. All these isoforms are tightly regulated by transcriptional and translational mechanisms, which are induced by several determinants such as amino acid deprivation, hormones, pH, and the activity of different signaling pathways. Dysfunctional glutamine transporter activity has been associated with the pathophysiological mechanisms of certain neurologic diseases, such as Hepatic Encephalopathy and Manganism. However, there might also be other neuropathological conditions associated with an altered GGC, in which glutamine transporters are dysfunctional. Hence, it appears to be of critical importance that the physiological and pathological aspects of glutamine transporters are thoroughly investigated.
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Regulation of amino acid transporter trafficking by mTORC1 in primary human trophoblast cells is mediated by the ubiquitin ligase Nedd4-2. Clin Sci (Lond) 2015; 130:499-512. [PMID: 26608079 DOI: 10.1042/cs20150554] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 11/25/2015] [Indexed: 12/11/2022]
Abstract
Changes in placental amino acid transfer directly contribute to altered fetal growth, which increases the risk for perinatal complications and predisposes for the development of obesity, diabetes and cardiovascular disease later in life. Placental amino acid transfer is critically dependent on the expression of specific transporters in the plasma membrane of the trophoblast, the transporting epithelium of the human placenta. However, the molecular mechanisms regulating this process are largely unknown. Nedd4-2 is an ubiquitin ligase that catalyses the ubiquitination of proteins, resulting in proteasomal degradation. We hypothesized that inhibition of mechanistic target of rapamycin complex 1 (mTORC1) decreases amino acid uptake in primary human trophoblast (PHT) cells by activation of Nedd4-2, which increases transporter ubiquitination resulting in decreased transporter expression in the plasma membrane. mTORC 1 inhibition increased the expression of Nedd4-2, promoted ubiquitination and decreased the plasma membrane expression of SNAT2 (an isoform of the System A amino acid transporter) and LAT1 (a System L amino acid transporter isoform), resulting in decreased cellular amino acid uptake. Nedd4-2 silencing markedly increased the trafficking of SNAT2 and LAT1 to the plasma membrane, which stimulated cellular amino acid uptake. mTORC1 inhibition by silencing of raptor failed to decrease amino acid transport following Nedd4-2 silencing. In conclusion, we have identified a novel link between mTORC1 signalling and ubiquitination, a common posttranslational modification. Because placental mTORC1 is inhibited in fetal growth restriction and activated in fetal overgrowth, we propose that regulation of placental amino acid transporter ubiquitination by mTORC1 and Nedd4-2 constitutes a molecular mechanisms underlying abnormal fetal growth.
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Aye ILMH, Jansson T, Powell TL. TNF-α stimulates System A amino acid transport in primary human trophoblast cells mediated by p38 MAPK signaling. Physiol Rep 2015; 3:3/10/e12594. [PMID: 26508738 PMCID: PMC4632960 DOI: 10.14814/phy2.12594] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Maternal obesity and gestational diabetes mellitus (GDM) increase the risk of delivering infants that are large for gestational age with greater adiposity, who are prone to the development of metabolic disease in childhood and beyond. These maternal conditions are also associated with increased levels of the proinflammatory cytokine TNF-α in maternal tissues and the placenta. Recent evidence suggests that changes in placental amino acid transport contribute to altered fetal growth. TNF-α was previously shown to stimulate System A amino acid transport in primary human trophoblasts (PHTs), however the molecular mechanisms remain unknown. In this study, we tested the hypothesis that TNF-α regulates amino acid uptake in cultured PHTs by a mitogen-activated protein kinase (MAPK)-dependent mechanism. Treatment of PHTs with TNF-α significantly increased System A amino acid transport, as well as Erk and p38 MAPK signaling. Pharmacological antagonism of p38, but not Erk MAPK activity, inhibited TNF-α stimulated System A activity. Silencing of p38 MAPK using siRNA transfections prevented TNF-α stimulated System A transport in PHTs. TNF-α significantly increased the protein expression of System A transporters SNAT1 and SNAT2, but did not affect their mRNA expression. The effects of TNF-α on SNAT1 and SNAT2 protein expression were reversed by p38 MAPK siRNA silencing. In conclusion, TNF-α regulates System A activity through increased SNAT1 and SNAT2 transporter protein expression in PHTs. These findings suggest that p38 MAPK may represent a critical mechanistic link between elevated proinflammatory cytokines and increased placental amino acid transport in obese and GDM pregnancies associated with fetal overgrowth.
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Affiliation(s)
- Irving L M H Aye
- Division of Reproductive Sciences, Department of Obstetrics and Gynecology, University of Colorado Anschutz Medical Campus, Aurora, Colorado
| | - Thomas Jansson
- Division of Reproductive Sciences, Department of Obstetrics and Gynecology, University of Colorado Anschutz Medical Campus, Aurora, Colorado
| | - Theresa L Powell
- Division of Reproductive Sciences, Department of Obstetrics and Gynecology, University of Colorado Anschutz Medical Campus, Aurora, Colorado Section of Neonatology, Department of Pediatrics, University of Colorado Anschutz Medical Campus, Aurora, Colorado
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Hägglund MGA, Hellsten SV, Bagchi S, Philippot G, Löfqvist E, Nilsson VCO, Almkvist I, Karlsson E, Sreedharan S, Tafreshiha A, Fredriksson R. Transport of L-glutamine, L-alanine, L-arginine and L-histidine by the neuron-specific Slc38a8 (SNAT8) in CNS. J Mol Biol 2014; 427:1495-1512. [PMID: 25451601 DOI: 10.1016/j.jmb.2014.10.016] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 09/30/2014] [Accepted: 10/17/2014] [Indexed: 11/19/2022]
Abstract
Glutamine transporters are important for regulating levels of glutamate and GABA in the brain. To date, six members of the SLC38 family (SNATs) have been characterized and functionally subdivided them into System A (SNAT1, SNAT2 and SNAT4) and System N (SNAT3, SNAT5 and SNAT7). Here we present the first functional characterization of SLC38A8, one of the previous orphan transporters from the family, and we suggest that the encoded protein should be named SNAT8 to adhere with the SNAT nomenclature. We show that SLC38A8 has preference for transporting L-glutamine, L-alanine, L-arginine, L-histidine and L-aspartate using a Na+-dependent transport mechanism and that the functional characteristics of SNAT8 have highest similarity to the known System A transporters. We also provide a comprehensive central nervous system expression profile in mouse brain for the Slc38a8 gene and the SNAT8 protein. We show that Slc38a8 (SNAT8) is expressed in all neurons, both excitatory and inhibitory, in mouse brain using in situ hybridization and immunohistochemistry. Furthermore, proximity ligation assay shows highly similar subcellular expression of SNAT7 and SNAT8. In conclusion, the neuronal SLC38A8 has a broad amino acid transport profile and is the first identified neuronal System A transporter. This suggests a key role of SNAT8 in the glutamine/glutamate (GABA) cycle in the brain.
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Affiliation(s)
- Maria G A Hägglund
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Sofie V Hellsten
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Sonchita Bagchi
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Gaëtan Philippot
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Erik Löfqvist
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Victor C O Nilsson
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Ingrid Almkvist
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Edvin Karlsson
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Smitha Sreedharan
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Atieh Tafreshiha
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
| | - Robert Fredriksson
- Department of Neuroscience, Functional Pharmacology, Uppsala University, Husargatan 3, SE-75124 Uppsala, Sweden.
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Lee IP, Evans AK, Yang C, Works MG, Kumar V, De Miguel Z, Manley NC, Sapolsky RM. Toxoplasma gondii is dependent on glutamine and alters migratory profile of infected host bone marrow derived immune cells through SNAT2 and CXCR4 pathways. PLoS One 2014; 9:e109803. [PMID: 25299045 PMCID: PMC4192591 DOI: 10.1371/journal.pone.0109803] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2014] [Accepted: 09/12/2014] [Indexed: 01/16/2023] Open
Abstract
The obligate intracellular parasite, Toxoplasma gondii, disseminates through its host inside infected immune cells. We hypothesize that parasite nutrient requirements lead to manipulation of migratory properties of the immune cell. We demonstrate that 1) T. gondii relies on glutamine for optimal infection, replication and viability, and 2) T. gondii-infected bone marrow-derived dendritic cells (DCs) display both “hypermotility” and “enhanced migration” to an elevated glutamine gradient in vitro. We show that glutamine uptake by the sodium-dependent neutral amino acid transporter 2 (SNAT2) is required for this enhanced migration. SNAT2 transport of glutamine is also a significant factor in the induction of migration by the small cytokine stromal cell-derived factor-1 (SDF-1) in uninfected DCs. Blocking both SNAT2 and C-X-C chemokine receptor 4 (CXCR4; the unique receptor for SDF-1) blocks hypermotility and the enhanced migration in T. gondii-infected DCs. Changes in host cell protein expression following T. gondii infection may explain the altered migratory phenotype; we observed an increase of CD80 and unchanged protein level of CXCR4 in both T. gondii-infected and lipopolysaccharide (LPS)-stimulated DCs. However, unlike activated DCs, SNAT2 expression in the cytosol of infected cells was also unchanged. Thus, our results suggest an important role of glutamine transport via SNAT2 in immune cell migration and a possible interaction between SNAT2 and CXCR4, by which T. gondii manipulates host cell motility.
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Affiliation(s)
- I-Ping Lee
- Department of Biology, Stanford University, Stanford, California, United States of America
- * E-mail:
| | - Andrew K. Evans
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Cissy Yang
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Melissa G. Works
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Vineet Kumar
- School of Biological Sciences, Nanyang Technological University, Singapore, Republic of Singapore
| | - Zurine De Miguel
- Department of Biology, Stanford University, Stanford, California, United States of America
| | - Nathan C. Manley
- Department of Biology, Stanford University, Stanford, California, United States of America
- Department of Neurosurgery, Stanford University School of Medicine, Stanford, California, United States of America
- Stanford Stroke Center and Stanford Institute for Neuro-Innovation and Translational Neurosciences, Stanford University School of Medicine, Stanford, California, United States of America
| | - Robert M. Sapolsky
- Department of Biology, Stanford University, Stanford, California, United States of America
- Department of Neurosurgery, Stanford University School of Medicine, Stanford, California, United States of America
- Stanford Stroke Center and Stanford Institute for Neuro-Innovation and Translational Neurosciences, Stanford University School of Medicine, Stanford, California, United States of America
- Department of Neurology and Neurological Sciences, Stanford University School of Medicine, Stanford, California, United States of America
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Torrente M, Guetg A, Sass JO, Arps L, Ruckstuhl L, Camargo SMR, Verrey F. Amino acids regulate transgene expression in MDCK cells. PLoS One 2014; 9:e96823. [PMID: 24797296 PMCID: PMC4010483 DOI: 10.1371/journal.pone.0096823] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Accepted: 04/11/2014] [Indexed: 11/18/2022] Open
Abstract
Gene expression and cell growth rely on the intracellular concentration of amino acids, which in metazoans depends on extracellular amino acid availability and transmembrane transport. To investigate the impact of extracellular amino acid concentrations on the expression of a concentrative amino acid transporter, we overexpressed the main kidney proximal tubule luminal neutral amino acid transporter B0AT1-collectrin (SLC6A19-TMEM27) in MDCK cell epithelia. Exogenously expressed proteins co-localized at the luminal membrane and mediated neutral amino acid uptake. However, the transgenes were lost over few cell culture passages. In contrast, the expression of a control transgene remained stable. To test whether this loss was due to inappropriately high amino acid uptake, freshly transduced MDCK cell lines were cultivated either with physiological amounts of amino acids or with the high concentration found in standard cell culture media. Expression of exogenous transporters was unaffected by physiological amino acid concentration in the media. Interestingly, mycoplasma infection resulted in a significant increase in transgene expression and correlated with the rapid metabolism of L-arginine. However, L-arginine metabolites were shown to play no role in transgene expression. In contrast, activation of the GCN2 pathway revealed by an increase in eIF2α phosphorylation may trigger transgene derepression. Taken together, high extracellular amino acid concentration provided by cell culture media appears to inhibit the constitutive expression of concentrative amino acid transporters whereas L-arginine depletion by mycoplasma induces the expression of transgenes possibly via stimulation of the GCN2 pathway.
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Affiliation(s)
- Marta Torrente
- Institute of Physiology and Zurich Center of Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Adriano Guetg
- Institute of Physiology and Zurich Center of Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Jörn Oliver Sass
- Division of Clinical Chemistry & Biochemistry, University Children's Hospital, Zurich, Zurich, Switzerland
| | - Lisa Arps
- Institute of Physiology and Zurich Center of Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Lisa Ruckstuhl
- Institute of Physiology and Zurich Center of Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - Simone M. R. Camargo
- Institute of Physiology and Zurich Center of Integrative Human Physiology, University of Zurich, Zurich, Switzerland
| | - François Verrey
- Institute of Physiology and Zurich Center of Integrative Human Physiology, University of Zurich, Zurich, Switzerland
- * E-mail:
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18
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Kavitha JV, Rosario FJ, Nijland MJ, McDonald TJ, Wu G, Kanai Y, Powell TL, Nathanielsz PW, Jansson T. Down-regulation of placental mTOR, insulin/IGF-I signaling, and nutrient transporters in response to maternal nutrient restriction in the baboon. FASEB J 2013; 28:1294-305. [PMID: 24334703 DOI: 10.1096/fj.13-242271] [Citation(s) in RCA: 92] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The mechanisms by which maternal nutrient restriction (MNR) causes reduced fetal growth are poorly understood. We hypothesized that MNR inhibits placental mechanistic target of rapamycin (mTOR) and insulin/IGF-I signaling, down-regulates placental nutrient transporters, and decreases fetal amino acid levels. Pregnant baboons were fed control (ad libitum, n=11) or an MNR diet (70% of controls, n=11) from gestational day (GD) 30. Placenta and umbilical blood were collected at GD 165. Western blot was used to determine the phosphorylation of proteins in the mTOR, insulin/IGF-I, ERK1/2, and GSK-3 signaling pathways in placental homogenates and expression of glucose transporter 1 (GLUT-1), taurine transporter (TAUT), sodium-dependent neutral amino acid transporter (SNAT), and large neutral amino acid transporter (LAT) isoforms in syncytiotrophoblast microvillous membranes (MVMs). MNR reduced fetal weights by 13%, lowered fetal plasma concentrations of essential amino acids, and decreased the phosphorylation of placental S6K, S6 ribosomal protein, 4E-BP1, IRS-1, Akt, ERK-1/2, and GSK-3. MVM protein expression of GLUT-1, TAUT, SNAT-2 and LAT-1/2 was reduced in MNR. This is the first study in primates exploring placental responses to maternal undernutrition. Inhibition of placental mTOR and insulin/IGF-I signaling resulting in down-regulation of placental nutrient transporters may link maternal undernutrition to restricted fetal growth.
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Affiliation(s)
- Jovita V Kavitha
- 2Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, Mail Code 7836, 7703 Floyd Curl Dr., San Antonio, TX 78229-3900, USA.
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19
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The SLC38 family of sodium-amino acid co-transporters. Pflugers Arch 2013; 466:155-72. [PMID: 24193407 DOI: 10.1007/s00424-013-1393-y] [Citation(s) in RCA: 153] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Revised: 10/16/2013] [Accepted: 10/20/2013] [Indexed: 12/13/2022]
Abstract
Transporters of the SLC38 family are found in all cell types of the body. They mediate Na(+)-dependent net uptake and efflux of small neutral amino acids. As a result they are particularly expressed in cells that grow actively, or in cells that carry out significant amino acid metabolism, such as liver, kidney and brain. SLC38 transporters occur in membranes that face intercellular space or blood vessels, but do not occur in the apical membrane of absorptive epithelia. In the placenta, they play a significant role in the transfer of amino acids to the foetus. Members of the SLC38 family are highly regulated in response to amino acid depletion, hypertonicity and hormonal stimuli. SLC38 transporters play an important role in amino acid signalling and have been proposed to act as transceptors independent of their transport function. The structure of SLC38 transporters is characterised by the 5 + 5 inverted repeat fold, which is observed in a wide variety of transport proteins.
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20
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Gaccioli F, White V, Capobianco E, Powell TL, Jawerbaum A, Jansson T. Maternal overweight induced by a diet with high content of saturated fat activates placental mTOR and eIF2alpha signaling and increases fetal growth in rats. Biol Reprod 2013; 89:96. [PMID: 24006279 DOI: 10.1095/biolreprod.113.109702] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
The mammalian target of rapamycin (mTOR) and the eukaryotic initiation factor 2 (eIF2) signaling pathways control protein synthesis in response to nutrient availability. Moreover, mTOR is a positive regulator of placental nutrient transport and is involved in the regulation of fetal growth. We hypothesized that maternal overweight, induced by a diet with high saturated fat content, i) up-regulates placental mTOR activity and nutrient transport, resulting in fetal overgrowth; ii) inhibits phosphorylation of eIF2 at its alpha subunit (eIF2alpha); and iii) leads to placental inflammation. Albino Wistar female rats were fed a control or high-saturated-fat (HF) diet for 7 wk before mating and during pregnancy. At gestational day 21, the HF diet significantly increased maternal and fetal triglyceride, leptin, and insulin (but not glucose) levels and maternal and fetal weights, and placental weights trended to increase. Phosphorylated 4EBP1 (T37/46 and S65) was significantly higher, and phosphorylated rpS6 (S235/236) tended to increase, in the placentas of dams fed an HF diet, indicating an activation of mTOR complex 1 (mTORC1). Phosphorylation of AMPK and eIF2alpha was reduced in the HF diet group compared to the control. The expression and activity of placental nutrient transporters and lipoprotein lipase (LPL), as well as the activation of inflammatory pathways, were not altered by the maternal diet. We conclude that maternal overweight induced by an HF diet stimulates mTORC1 activity and decreases eIF2alpha phosphorylation in rat placentas. We speculate that these changes may up-regulate protein synthesis and contribute to placental and fetal overgrowth.
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Affiliation(s)
- Francesca Gaccioli
- Center for Pregnancy and Newborn Research, University of Texas Health Science Center, San Antonio, Texas
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21
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Jansson N, Rosario FJ, Gaccioli F, Lager S, Jones HN, Roos S, Jansson T, Powell TL. Activation of placental mTOR signaling and amino acid transporters in obese women giving birth to large babies. J Clin Endocrinol Metab 2013; 98:105-13. [PMID: 23150676 PMCID: PMC3537112 DOI: 10.1210/jc.2012-2667] [Citation(s) in RCA: 209] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
CONTEXT Babies of obese women are often large at birth, which is associated with perinatal complications and metabolic syndrome later in life. The mechanisms linking maternal obesity to fetal overgrowth are largely unknown. OBJECTIVE We tested the hypothesis that placental insulin/IGF-I and mammalian target of rapamycin (mTOR) signaling is activated and amino acid transporter activity is increased in large babies of obese women. DESIGN AND SETTING Pregnant women were recruited prospectively for collection of placental tissue at a university hospital and academic biomedical center. PATIENTS OR OTHER PARTICIPANTS Twenty-three Swedish pregnant women with first trimester body mass index ranging from 18.5 to 44.9 kg/m(2) and with uncomplicated pregnancies participated in the study. INTERVENTIONS There were no interventions. MAIN OUTCOME MEASURES We determined the phosphorylation of key signaling molecules (including Akt, IRS-1, S6K1, 4EBP-1, RPS6, and AMPK) in the placental insulin/IGF-I, AMPK, and mTOR signaling pathways. The activity and protein expression of the amino acid transporter systems A and L were measured in syncytiotrophoblast microvillous plasma membranes. RESULTS Birth weights (range, 3025-4235 g) were positively correlated to maternal body mass index (P < 0.05). The activity of placental insulin/IGF-I and mTOR signaling was positively correlated (P < 0.001), whereas AMPK phosphorylation was inversely (P < 0.05) correlated to birth weight. Microvillous plasma membrane system A, but not system L, activity and protein expression of the system A isoform SNAT2 were positively correlated to birth weight (P < 0.001). CONCLUSIONS Up-regulation of specific placental amino acid transporter isoforms may contribute to fetal overgrowth in maternal obesity. This effect may be mediated by activation of insulin/IGF-I and mTOR signaling pathways, which are positive regulators of placental amino acid transporters.
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Affiliation(s)
- Nina Jansson
- Department of Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA
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22
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Rosario FJ, Kanai Y, Powell TL, Jansson T. Mammalian target of rapamycin signalling modulates amino acid uptake by regulating transporter cell surface abundance in primary human trophoblast cells. J Physiol 2012; 591:609-25. [PMID: 23165769 DOI: 10.1113/jphysiol.2012.238014] [Citation(s) in RCA: 139] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Abnormal fetal growth increases the risk for perinatal complications and predisposes for the development of obesity, diabetes and cardiovascular disease later in life. Emerging evidence suggests that changes in placental amino acid transport directly contribute to altered fetal growth. However, the molecular mechanisms regulating placental amino acid transport are largely unknown. Here we combined small interfering (si) RNA-mediated silencing approaches with protein expression/localization and functional studies in cultured primary human trophoblast cells to test the hypothesis that mammalian target of rapamycin complex 1 (mTORC1) and 2 (mTORC2) regulate amino acid transporters by post-translational mechanisms. Silencing raptor (inhibits mTORC1) or rictor (inhibits mTORC2) markedly decreased basal System A and System L amino acid transport activity but had no effect on growth factor-stimulated amino acid uptake. Simultaneous inhibition of mTORC1 and 2 completely inhibited both basal and growth factor-stimulated amino acid transport activity. In contrast, mTOR inhibition had no effect on serotonin transport. mTORC1 or mTORC2 silencing markedly decreased the plasma membrane expression of specific System A (SNAT2, SLC38A2) and System L (LAT1, SLC7A5) transporter isoforms without affecting global protein expression. In conclusion, mTORC1 and mTORC2 regulate human trophoblast amino acid transporters by modulating the cell surface abundance of specific transporter isoforms. This is the first report showing regulation of amino acid transport by mTORC2. Because placental mTOR activity and amino acid transport are decreased in human intrauterine growth restriction our data are consistent with the possibility that dysregulation of placental mTOR plays an important role in the development of abnormal fetal growth.
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Affiliation(s)
- Fredrick J Rosario
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, Mail Code 7836, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
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Fike CD, Sidoryk-Wegrzynowicz M, Aschner M, Summar M, Prince LS, Cunningham G, Kaplowitz M, Zhang Y, Aschner JL. Prolonged hypoxia augments L-citrulline transport by system A in the newborn piglet pulmonary circulation. Cardiovasc Res 2012; 95:375-84. [PMID: 22673370 DOI: 10.1093/cvr/cvs186] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
AIMS Pulmonary arterial endothelial cells (PAECs) express the enzymes needed for generation of l-arginine from intracellular l-citrulline but do not express the enzymes needed for de novo l-citrulline synthesis. Hence, l-citrulline levels in PAECs are dependent on l-citrulline transport. Once generated, l-arginine can be converted to l-citrulline and nitric oxide (NO) by the enzyme NO synthase. We sought to determine whether hypoxia, a condition aetiologically linked to pulmonary hypertension, alters the transport of l-citrulline and the expression of the sodium-coupled neutral amino acid transporters (SNATs) in PAECs from newborn piglets. METHODS AND RESULTS PAECs isolated from newborn piglets were cultured under normoxic and hypoxic conditions and used to measure SNAT1, 2, 3, and 5 protein expression and (14)C-l-citrulline uptake. SNAT1 protein expression was increased, while SNAT2, SNAT3, and SNAT5 expression was unaltered in hypoxic PAECs. (14)C-l-citrulline uptake was increased in hypoxic PAECs. Studies with inhibitors of System A (SNAT1/2) and System N (SNAT3/5) revealed that the increased (14)C-l-citrulline uptake was largely due to System A-mediated transport. Additional studies were performed to evaluate SNAT protein expression and l-citrulline levels in lungs of piglets with chronic hypoxia-induced pulmonary hypertension and comparable age controls. Lungs from piglets raised in chronic hypoxia exhibited greater SNAT1 expression and higher l-citrulline levels than lungs from controls. CONCLUSION Increased SNAT1 expression and the concomitant enhanced ability to transport l-citrulline in PAECs could represent an important regulatory mechanism to counteract NO signalling impairments known to occur during the development of chronic hypoxia-induced pulmonary hypertension in newborns.
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Affiliation(s)
- Candice D Fike
- Department of Pediatrics, University School of Medicine, Vanderbilt University Medical Center, 2215 B Garland Ave., Nashville, TN 37232-0656, USA.
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Rosario FJ, Schumacher MA, Jiang J, Kanai Y, Powell TL, Jansson T. Chronic maternal infusion of full-length adiponectin in pregnant mice down-regulates placental amino acid transporter activity and expression and decreases fetal growth. J Physiol 2012; 590:1495-509. [PMID: 22289908 DOI: 10.1113/jphysiol.2011.226399] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Maternal adiponectin levels are inversely correlated to birth weight, suggesting that maternal adiponectin limits fetal growth. We hypothesized that full-length adiponectin (fADN) infusion in pregnant mice down-regulates placental amino acid transporters and decreases fetal growth. Starting at embryonic day (E) 14.5, fADN (0.62 ± 0.02 μg (g body weight)(−1) day(−1), n = 7) or vehicle (control, n = 9) were infused in pregnant C57/BL6 mice by mini-osmotic pump. At E18.5, dams were killed and placental homogenates and trophoblast plasma membrane (TPM) vesicles were prepared. Infusion of fADN elevated maternal serum fADN by 4-fold and decreased fetal weights by 18%. Adiponectin receptor 2, but not adiponectin receptor 1, was expressed in TPM. fADN infusion decreased TPM System A (–56%, P < 0.001) and System L amino acid transporter activity (–50%, P < 0.03). TPM protein expression of SNAT1, 2 and 4 (System A amino acid transporter isoforms) and LAT1 and LAT2, but not CD98, (System L amino acid transporter isoforms) was down-regulated by fADN infusion. To identify possible mechanisms underlying these changes we determined the phosphorylation of proteins in signalling pathways known to regulate placental amino acid transporters. fADN decreased phosphorylation of insulin receptor substrate-1 (Tyr-608), Akt (Thr-308 and Ser-473), S6 kinase 1 (Thr-389), eukaryotic initiation factor 4E binding protein 1 (Thr-37/46 and Thr-70) and ribosomal protein S6 (Ser-235/236) and increased the phosphorylation of peroxisome proliferator-activated receptor α (PPARα) (Ser-21) in the placenta. These data suggest that maternal adiponectin decreases fetal growth by down-regulation of placental amino acid transporters, which limits fetal nutrient availability. This effect may be mediated by inhibition of insulin/IGF-I and mTOR signalling pathways, which are positive regulators of placental amino acid transporters. We have identified a novel physiological mechanism by which the endocrine functions of maternal adipose tissue influence fetal growth.
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Affiliation(s)
- Fredrick J Rosario
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, Mail Code 7836, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
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Nakanishi T, Tamai I. Solute Carrier Transporters as Targets for Drug Delivery and Pharmacological Intervention for Chemotherapy. J Pharm Sci 2011; 100:3731-50. [DOI: 10.1002/jps.22576] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2011] [Revised: 03/29/2011] [Accepted: 03/31/2011] [Indexed: 01/11/2023]
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Corallini S, Taranta A, Bellomo F, Palma A, Pastore A, Emma F. Transcriptional and posttranscriptional regulation of the CTNS gene. Pediatr Res 2011; 70:130-5. [PMID: 21508882 DOI: 10.1203/pdr.0b013e3182200187] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Cell cysteine (Cys) levels and/or the [Cys/CySS] redox potential have been shown to regulate mRNA levels of the CTNS gene, which encodes for a lysosomal cystine (CySS) carrier that is defective in cystinosis. To investigate the mechanisms involved CTNS mRNA regulation, different portions of the CTNS promotor were cloned into a luciferase vector and transfected in HK2 cells. A 1.5-2.4-fold increase in luciferase activity was observed when cells were incubated in culture medium containing low CySS concentrations. Conversely, CTNS mRNA levels decreased by 47-56% in the presence of N-acetyl-L-cysteine (NAC). Chase experiments with actinomycin D (ActD) demonstrated a 3-fold stabilization of the CTNS mRNA when cells were cultured in low CySS medium for 48 h. Treatment of control cells with cyclohexamide (CHX) increased CTNS mRNA levels, suggesting that CHX blocked the synthesis of proteins involved in mRNA degradation or in repression of the CTNS gene. Finally, in vitro binding assays showed increased binding (30-110%) of the Sp-1 transcription factor to two regions of the CTNS promotor when cells were incubated in low CySS medium. These results indicate that the CTNS gene is actively regulated at the transcriptional and posttranscriptional levels and suggest that CTNS plays a pivotal role in regulating cell thiol concentrations.
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Affiliation(s)
- Serena Corallini
- Division of Nephrology and Dialysis, Bambino Gesù Children's Hospital and Research Institute, 00165 Rome, Italy
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Protein kinase C-mediated phosphorylation of a single serine residue on the rat glial glutamine transporter SN1 governs its membrane trafficking. J Neurosci 2011; 31:6565-75. [PMID: 21525297 DOI: 10.1523/jneurosci.3694-10.2011] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Molecular mechanisms involved in the replenishment of the fast neurotransmitters glutamate and GABA are poorly understood. Glutamine sustains their generation. However, glutamine formation from the recycled transmitters is confined to glial processes and requires facilitators for its translocation across the glial and neuronal membranes. Indeed, glial processes are enriched with the system N transporter SN1 (Slc38a3), which, by bidirectional transport, maintains steady extracellular glutamine levels and thereby furnishes neurons with the primary precursor for fast neurotransmitters. We now demonstrate that SN1 is phosphorylated by protein kinase Cα (PKCα) and PKCγ. Electrophysiological characterization shows that phosphorylation reduces V(max) dramatically, whereas no significant effects are seen on the K(m). Phosphorylation occurs specifically at a single serine residue (S52) in the N-terminal rat (Rattus norvegicus) SN1 and results in sequestration of the protein into intracellular reservoirs. Prolonged activation of PKC results in partial degradation of SN1. These results provide the first demonstration of phosphorylation of SN1 and regulation of its activity at the plasma membrane. Interestingly, membrane trafficking of SN1 resembles that of the glutamate transporter GLT and the glutamate-aspartate transporter GLAST: it involves the same PKC isoforms and occurs in the same glial processes. This suggests that the glutamate/GABA-glutamine cycle may be modified at two key points by similar signaling events and unmasks a prominent role for PKC-dependent phosphorylation. Our data suggest that extracellular glutamine levels may be fine-tuned by dynamic regulation of glial SN1 activity, which may impact on transmitter generation, contribute to defining quantal size, and have profound effects on synaptic plasticity.
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Rosario FJ, Jansson N, Kanai Y, Prasad PD, Powell TL, Jansson T. Maternal protein restriction in the rat inhibits placental insulin, mTOR, and STAT3 signaling and down-regulates placental amino acid transporters. Endocrinology 2011; 152:1119-29. [PMID: 21285325 PMCID: PMC3858644 DOI: 10.1210/en.2010-1153] [Citation(s) in RCA: 133] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The mechanisms underlying reduced fetal growth in response to maternal protein restriction are not well established. Maternal levels of insulin, IGF-I, and leptin are decreased in rats fed a low protein (LP) diet. Because these hormones stimulate placental amino acid transporters in vitro, we hypothesized that maternal protein restriction inhibits placental leptin, insulin/IGF-I, and mammalian target of rapamycin signaling and down-regulates the expression and activity of placental amino acid transporters. Pregnant rats were fed either an isocaloric low protein (LP, 4% protein) or control diet (18% protein) and studied at gestational day (GD)15, GD19, or GD21 (term 23). At GD19 and GD21, placental expression of phosphorylated eukaryotic initiation factor 4E binding protein 1 (Thr-36/46 or Thr-70) and phosphorylated S6 ribosomal protein (Ser-235/236) was decreased in the LP group. In addition, placental expression of phosphorylated S6 kinase 1 (Thr-389), phosphorylated Akt (Thr-308), and phosphorylated signal transducer and activator of transcription 3 (Tyr-705) was reduced at GD21. In microvillous plasma membranes (MVM) isolated from placentas of LP animals, protein expression of the sodium-coupled neutral amino acid transporter (SNAT)2 and the large neutral amino acid transporters 1 and 2 was reduced at GD19 and GD21. MVM SNAT1 protein expression was reduced at GD21 in LP rats. SNAT4 and 4F2 heavy chain expression in MVM was unaltered. System A and L amino acid transporter activity was decreased in MVM from LP animals at GD19 and GD21. In conclusion, maternal protein restriction inhibits placental insulin, mammalian target of rapamycin signaling, and signal transducer and activator of transcription 3 signaling, which is associated with a down-regulation of placental amino acid transporters. We speculate that maternal endocrine and metabolic control of placental nutrient transport reduces fetal growth in response to protein restriction.
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Affiliation(s)
- Fredrick J Rosario
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center San Antonio, Mail Code 7836, 7703 Floyd Curl Drive, San Antonio, Texas 78229-3900, USA
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Carr EL, Kelman A, Wu GS, Gopaul R, Senkevitch E, Aghvanyan A, Turay AM, Frauwirth KA. Glutamine uptake and metabolism are coordinately regulated by ERK/MAPK during T lymphocyte activation. THE JOURNAL OF IMMUNOLOGY 2010; 185:1037-44. [PMID: 20554958 DOI: 10.4049/jimmunol.0903586] [Citation(s) in RCA: 542] [Impact Index Per Article: 38.7] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Activation of a naive T cell is a highly energetic event, which requires a substantial increase in nutrient metabolism. Upon stimulation, T cells increase in size, rapidly proliferate, and differentiate, all of which lead to a high demand for energetic and biosynthetic precursors. Although amino acids are the basic building blocks of protein biosynthesis and contribute to many other metabolic processes, the role of amino acid metabolism in T cell activation has not been well characterized. We have found that glutamine in particular is required for T cell function. Depletion of glutamine blocks proliferation and cytokine production, and this cannot be rescued by supplying biosynthetic precursors of glutamine. Correlating with the absolute requirement for glutamine, T cell activation induces a large increase in glutamine import, but not glutamate import, and this increase is CD28-dependent. Activation coordinately enhances expression of glutamine transporters and activities of enzymes required to allow the use of glutamine as a Krebs cycle substrate in T cells. The induction of glutamine uptake and metabolism requires ERK function, providing a link to TCR signaling. Together, these data indicate that regulation of glutamine use is an important component of T cell activation. Thus, a better understanding of glutamine sensing and use in T cells may reveal novel targets for immunomodulation.
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Affiliation(s)
- Erikka L Carr
- Department of Cell Biology and Molecular Genetics, Maryland Pathogen Research Institute, University of Maryland, College Park, MD 20742, USA
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Drummond MJ, Glynn EL, Fry CS, Timmerman KL, Volpi E, Rasmussen BB. An increase in essential amino acid availability upregulates amino acid transporter expression in human skeletal muscle. Am J Physiol Endocrinol Metab 2010; 298:E1011-8. [PMID: 20304764 PMCID: PMC2867366 DOI: 10.1152/ajpendo.00690.2009] [Citation(s) in RCA: 161] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Essential amino acids (EAA) stimulate skeletal muscle mammalian target of rapamycin complex 1 (mTORC1) signaling and protein synthesis. It has recently been reported that an increase in amino acid (AA) transporter expression during anabolic conditions is rapamycin-sensitive. The purpose of this study was to determine whether an increase in EAA availability increases AA transporter expression in human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis of seven young adult subjects (3 male, 4 female) before and 1-3 h after EAA ingestion (10 g). Blood and muscle samples were analyzed for leucine kinetics using stable isotopic techniques. Quantitative RT-PCR, and immunoblotting were used to determine the mRNA and protein expression, respectively, of AA transporters and members of the general AA control pathway [general control nonrepressed (GCN2), activating transcription factor (ATF4), and eukaryotic initiation factor (eIF2) alpha-subunit (Ser(52))]. EAA ingestion increased blood leucine concentration, delivery of leucine to muscle, transport of leucine from blood into muscle, intracellular muscle leucine concentration, ribosomal protein S6 (Ser(240/244)) phosphorylation, and muscle protein synthesis. This was followed with increased L-type AA transporter (LAT1), CD98, sodium-coupled neutral AA transporter (SNAT2), and proton-coupled amino acid transporter (PAT1) mRNA expression at 1 h (P < 0.05) and modest increases in LAT1 protein expression (3 h post-EAA) and SNAT2 protein expression (2 and 3 h post-EAA, P < 0.05). Although there were no changes in GCN2 expression and eIF2 alpha phosphorylation, ATF4 protein expression reached significance by 2 h post-EAA (P < 0.05). We conclude that an increase in EAA availability upregulates human skeletal muscle AA transporter expression, perhaps in an mTORC1-dependent manner, which may be an adaptive response necessary for improved AA intracellular delivery.
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Affiliation(s)
- Micah J Drummond
- University of Texas Medical Branch, Department of Physical Therapy, Division of Rehabilitation Sciences, Sealy Center on Aging, 301 Univ. Blvd., Galveston, TX 77555-1144, USA
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Brand A, Greenwood S, Glazier J, Bennett E, Godfrey K, Sibley C, Hanson M, Lewis R. Comparison of l-serine uptake by human placental microvillous membrane vesicles and placental villous fragments. Placenta 2010; 31:456-9. [DOI: 10.1016/j.placenta.2010.01.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Revised: 01/27/2010] [Accepted: 01/28/2010] [Indexed: 12/18/2022]
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Lewis RM, Greenwood SL, Cleal JK, Crozier SR, Verrall L, Inskip HM, Cameron IT, Cooper C, Sibley CP, Hanson MA, Godfrey KM. Maternal muscle mass may influence system A activity in human placenta. Placenta 2010; 31:418-22. [PMID: 20206993 DOI: 10.1016/j.placenta.2010.02.001] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Revised: 01/28/2010] [Accepted: 02/01/2010] [Indexed: 11/28/2022]
Abstract
During pregnancy, nutrient partitioning between the mother and fetus must balance promoting fetal survival and maintaining nutritional status of the mother for her health and future fertility. The nutritional status of the pregnant woman, reflected in her body composition, may affect placental function with consequences for fetal development. We investigated the relationship between maternal body composition and placental system A amino acid transporter activity in 103 term placentas from Southampton Women's Survey pregnancies. Placental system A activity was measured as Na(+)-dependent uptake of 10 mumol/L (14)C-methylaminoisobutyric acid (a system A specific amino acid analogue) in placental villous fragments. Maternal body composition was measured at enrollment pre-pregnancy; in 45 infants neonatal body composition was measured using dual-energy x-ray absorptiometry. Term placental system A activity was lower in women with smaller pre-pregnancy upper arm muscle area (r = 0.27, P = 0.007), but was not related to maternal fat mass. System A activity was lower in mothers who reported undertaking strenuous exercise (24.6 vs 29.7 pmol/mg/15 min in sedentary women, P = 0.03), but was not associated with other maternal lifestyle factors. Lower placental system A activity in women who reported strenuous exercise and had a lower arm muscle area may reflect an adaptation in placental function which protects maternal resources in those with lower nutrient reserves. This alteration may affect fetal development, altering fetal body composition, with long-term consequences.
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Affiliation(s)
- R M Lewis
- Institute of Developmental Sciences, School of Medicine, University of Southampton, UK.
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Niu L, Qiao W, Li G, Li Q, Huang Q, Gong J, Zhu W, Li N, Li J. Different alterations in rat intestinal glutamine transport during the progression of CLP- and LPS-induced sepsis. J Surg Res 2009; 169:284-91. [PMID: 20338592 DOI: 10.1016/j.jss.2009.11.732] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2009] [Revised: 11/09/2009] [Accepted: 11/23/2009] [Indexed: 11/28/2022]
Abstract
BACKGROUND A marked deficiency of glutamine in clinical critical illness is correlated with mortality in the intensive care unit. Though intestinal glutamine transport was reported to be impaired in late sepsis, we hypothesized that there might be a different alteration in the early stage, with differential effects on the Na(+)-dependent glutamine transporters B(0)AT1, ATB(0,+), and ATA2. MATERIALS AND METHODS Sepsis was induced by cecal ligation and puncture or lipopolysaccharide intraperitoneal injection in Sprague Dawley rats, and the samples were collected at 0, 2, 6, 12, 24h. Small intestinal brush border glutamine transport was studied by a rapid filtration technique. The relative contributions of the three main transporter, B(0)AT1, ATB(0,+), and ATA2, were determined by competitive inhibition. The mRNA level of each transporter was analyzed by RT-PCR, and an extra immunohistochemistry analysis was performed to detect the localization of ATA2 protein in small intestine. Serum TNF-α and IL-10 concentrations were quantitated by ELISA. RESULTS Intestinal glutamine transport showed a biphasic change with an early increase and a late decrease in both CLP and LPS group. The early increase of glutamine transport was mainly attributable to the increased contributions of ATA2 and ATB(0,+). The transport activities of B(0)AT1, ATB(0,+) altered mainly because of the number of transporters (mRNA level as an indicator), while turned to ATA2, the redistribution was also found to be involved. The plasma TNF-α and IL-10 levels, especially the former, showed similar changing profiles to glutamine transport and, thus, may have relevance to it. CONCLUSION Rat intestinal glutamine transport showed an early increase and a late decrease in sepsis, and may provide some information for sepsis treatment.
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Affiliation(s)
- Lingying Niu
- Research Institute of General Surgery, Jinling Hospital, Medical School of Nanjing University, Nanjing, PR China
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34
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Kilberg MS, Shan J, Su N. ATF4-dependent transcription mediates signaling of amino acid limitation. Trends Endocrinol Metab 2009; 20:436-43. [PMID: 19800252 PMCID: PMC3587693 DOI: 10.1016/j.tem.2009.05.008] [Citation(s) in RCA: 421] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2009] [Revised: 05/18/2009] [Accepted: 05/19/2009] [Indexed: 01/28/2023]
Abstract
Mammals respond to dietary nutrient fluctuations; for example, deficiency of dietary protein or an imbalance of essential amino acids activates an amino acid response (AAR) signal transduction pathway, consisting of detection of uncharged tRNA by the GCN2 kinase, eIF2alpha phosphorylation and ATF4 expression. In concert with heterodimerization partners, ATF4 activates specific genes via a CCAAT-enhancer binding protein-activating transcription factor response element (CARE). This review outlines the ATF4-dependent transcriptional mechanisms associated with the AAR, focusing on progress during the past 5 years. Recent evidence suggests that maternal nutrient deprivation not only has immediate metabolic effects on the fetus, but also triggers gene expression changes in adulthood, possibly through epigenetic mechanisms. Therefore, understanding the transcriptional programs initiated by amino acid limitation is crucial and timely.
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Affiliation(s)
- Michael S Kilberg
- Department of Biochemistry and Molecular Biology, Box 100245, University of Florida, Gainesville, Florida 32610-0245, USA.
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Grewal S, Defamie N, Zhang X, De Gois S, Shawki A, Mackenzie B, Chen C, Varoqui H, Erickson JD. SNAT2 amino acid transporter is regulated by amino acids of the SLC6 gamma-aminobutyric acid transporter subfamily in neocortical neurons and may play no role in delivering glutamine for glutamatergic transmission. J Biol Chem 2009; 284:11224-36. [PMID: 19240036 PMCID: PMC2670127 DOI: 10.1074/jbc.m806470200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2008] [Revised: 02/06/2009] [Indexed: 01/24/2023] Open
Abstract
System A transporters SNAT1 and SNAT2 mediate uptake of neutral alpha-amino acids (e.g. glutamine, alanine, and proline) and are expressed in central neurons. We tested the hypothesis that SNAT2 is required to support neurotransmitter glutamate synthesis by examining spontaneous excitatory activity after inducing or repressing SNAT2 expression for prolonged periods. We stimulated de novo synthesis of SNAT2 mRNA and increased SNAT2 mRNA stability and total SNAT2 protein and functional activity, whereas SNAT1 expression was unaffected. Increased endogenous SNAT2 expression did not affect spontaneous excitatory action-potential frequency over control. Long term glutamine exposure strongly repressed SNAT2 expression but increased excitatory action-potential frequency. Quantal size was not altered following SNAT2 induction or repression. These results suggest that spontaneous glutamatergic transmission in pyramidal neurons does not rely on SNAT2. To our surprise, repression of SNAT2 activity was not limited to System A substrates. Taurine, gamma-aminobutyric acid, and beta-alanine (substrates of the SLC6 gamma-aminobutyric acid transporter family) repressed SNAT2 expression more potently (10x) than did System A substrates; however, the responses to System A substrates were more rapid. Since ATF4 (activating transcription factor 4) and CCAAT/enhancer-binding protein are known to bind to an amino acid response element within the SNAT2 promoter and mediate induction of SNAT2 in peripheral cell lines, we tested whether either factor was similarly induced by amino acid deprivation in neurons. We found that glutamine and taurine repressed the induction of both transcription factors. Our data revealed that SNAT2 expression is constitutively low in neurons under physiological conditions but potently induced, together with the taurine transporter TauT, in response to depletion of neutral amino acids.
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Affiliation(s)
- Sukhjeevan Grewal
- Neuroscience Center, Louisiana State University Health Science Center, New Orleans, Louisiana 70112, USA
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Hundal HS, Taylor PM. Amino acid transceptors: gate keepers of nutrient exchange and regulators of nutrient signaling. Am J Physiol Endocrinol Metab 2009; 296:E603-13. [PMID: 19158318 PMCID: PMC2670634 DOI: 10.1152/ajpendo.91002.2008] [Citation(s) in RCA: 224] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Amino acid transporters at the surface of cells are in an ideal location to relay nutritional information, as well as nutrients themselves, to the cell interior. These transporters are able to modulate signaling downstream of intracellular amino acid receptors by regulating intracellular amino acid concentrations through processes of coupled transport. The concept of dual-function amino acid transporter/receptor (or "transceptor") proteins is well established in primitive eukaryotes such as yeast, where detection of extracellular amino acid deficiency leads to upregulation of proteins involved in biosynthesis and transport of the deficient amino acid(s). The evolution of the "extracellular milieu" and nutrient-regulated endocrine controls in higher eukaryotes, alongside their frequent inability to synthesize all proteinaceous amino acids (and, hence, the requirement for indispensable amino acids in their diet), appears to have lessened the priority of extracellular amino acid sensing as a stimulus for metabolic signals. Nevertheless, recent studies of amino acid transporters in flies and mammalian cell lines have revealed perhaps unanticipated "echoes" of these transceptor functions, which are revealed by cellular stresses (notably starvation) or gene modification/silencing. APC-transporter superfamily members, including slimfast, path, and SNAT2 all appear capable of sensing and signaling amino acid availability to the target of rapamycin (TOR) pathway, possibly through PI 3-kinase-dependent mechanisms. We hypothesize (by extrapolation from knowledge of the yeast Ssy1 transceptor) that, at least for SNAT2, the transceptor discriminates between extracellular and intracellular amino acid stimuli when evoking a signal.
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Affiliation(s)
- Harinder S Hundal
- Division of Molecular Physiology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.
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Nickel A, Klein U, Weitz D, Daniel H. L-Proline transport into renal OK epithelial cells: a second renal proline transport system is induced by amino acid deprivation. Amino Acids 2009; 38:753-61. [PMID: 19333719 DOI: 10.1007/s00726-009-0280-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2008] [Accepted: 03/13/2009] [Indexed: 11/28/2022]
Abstract
Influx of [(3)H]-L-proline into renal OK cells revealed that basal transport was mediated by the transporter SIT1. When cells were submitted for 8 h to amino acid deprivation, uptake of L-proline was now dominated by a low-affinity system with an apparent K (m) of 4.4 +/- 0.6 mM and a V (max) of 10.2 +/- 0.6 nmol/mg of protein/min operating in addition to the high-affinity SIT1 system with a K (m) of 0.12 +/- 0.01 mM and a V (max) of 0.28 +/- 0.04 nmol/mg of protein/min. The low- and high-affinity proline transporting systems were sensitive to inhibitors of JNK and PI-3 kinases, whereas a GSK-3 inhibitor affected only the upregulated transport system. Ion-replacement studies and experiments assessing substrate specificities for both systems provided strong evidence that SNAT2, that showed two- to threefold increased mRNA levels, is the responsible transporter mediating the increased proline influx under conditions of amino acid deprivation.
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Affiliation(s)
- A Nickel
- Molecular Nutrition Unit, Technical University of Munich, Am Forum 5, 85350 Freising-Weihenstephan, Germany
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38
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Roos S, Kanai Y, Prasad PD, Powell TL, Jansson T. Regulation of placental amino acid transporter activity by mammalian target of rapamycin. Am J Physiol Cell Physiol 2009; 296:C142-50. [DOI: 10.1152/ajpcell.00330.2008] [Citation(s) in RCA: 115] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The activity of placental amino acid transporters is decreased in intrauterine growth restriction (IUGR), but the underlying regulatory mechanisms have not been established. Inhibition of the mammalian target of rapamycin (mTOR) signaling pathway has been shown to decrease the activity of the system L amino acid transporter in human placental villous fragments, and placental mTOR activity is decreased in IUGR. In the present study, we used cultured primary trophoblast cells to study mTOR regulation of placental amino acid transporters in more detail and to test the hypothesis that mTOR alters amino acid transport activity by changes in transporter expression. Inhibition of mTOR by rapamycin significantly reduced the activity of system A (−17%), system L (−28%), and taurine (−40%) amino acid transporters. mRNA expression of isoforms of the three amino acid transporter systems in response to mTOR inhibition was measured using quantitative real-time PCR. mRNA expression of l-type amino acid transporter 1 (LAT1; a system L isoform) and taurine transporter was reduced by 13% and 50%, respectively; however, mTOR inhibition did not alter the mRNA expression of system A isoforms (sodium-coupled neutral amino acid transporter-1, -2, and -4), LAT2, or 4F2hc. Rapamycin treatment did not significantly affect the protein expression of any of the transporter isoforms. We conclude that mTOR signaling regulates the activity of key placental amino acid transporters and that this effect is not due to a decrease in total protein expression. These data suggest that mTOR regulates placental amino acid transporters by posttranslational modifications or by affecting transporter translocation to the plasma membrane.
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Desforges M, Mynett KJ, Jones RL, Greenwood SL, Westwood M, Sibley CP, Glazier JD. The SNAT4 isoform of the system A amino acid transporter is functional in human placental microvillous plasma membrane. J Physiol 2008; 587:61-72. [PMID: 19015196 PMCID: PMC2667314 DOI: 10.1113/jphysiol.2008.161331] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Placental system A activity is important for the supply of neutral amino acids needed for fetal growth. There are three system A isoforms: SNAT1, SNAT2 and SNAT4, but the contribution of each to system A-mediated transport is unknown. Here, we have used immunohistochemistry to demonstrate that all three isoforms are present in the syncytiotrophoblast suggesting each plays a role in amino acid transport across the placenta. We next tested the hypothesis that the SNAT4 isoform is functional in microvillous plasma membrane vesicles (MVM) from normal human placenta using a method which exploits the unique property of SNAT4 to transport both cationic amino acids as well as the system A-specific substrate MeAIB. The data show that SNAT4 contribution to system A-specific amino acid transport across MVM is higher in first trimester placenta compared to term (approx. 70% and 33%, respectively, P < 0.01). Further experiments performed under more physiological conditions using intact placental villous fragments suggest a contribution of SNAT4 to system A activity in first trimester placenta but minimal contribution at term. In agreement, Western blotting revealed that SNAT4 protein expression is higher in first trimester MVM compared to term (P < 0.05). This study provides the first evidence of SNAT4 activity in human placenta and demonstrates the contribution of SNAT4 to system A-mediated transport decreases between first trimester and term: our data lead us to speculate that at later stages of gestation SNAT1 and/or SNAT2 are more important for the supply of amino acids required for normal fetal growth.
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Affiliation(s)
- M Desforges
- Maternal and Fetal Health Research Group, University of Manchester, St Mary's Hospital, Hathersage Road, Manchester M13 0JH, UK.
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Specificity of amino acid regulated gene expression: analysis of genes subjected to either complete or single amino acid deprivation. Amino Acids 2008; 37:79-88. [PMID: 19009228 DOI: 10.1007/s00726-008-0199-2] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Accepted: 10/17/2008] [Indexed: 12/20/2022]
Abstract
Amino acid deprivation activates the amino acid response (AAR) pathway that enhances transcription of genes containing an amino acid response element (AARE). The present data reveal a quantitative difference in the response to deprivation of individual amino acids. The AAR leads to increased eukaryotic initiation factor 2alpha (eIF2alpha) phosphorylation and ATF4 translation. When HepG2 cells were deprived of an individual essential amino acid, p-eIF2alpha and activating transcription factor 4 were increased, but the correlation was relatively weak. Complete amino acid starvation in either Earle's balanced salt solution or Krebs-Ringer bicarbonate buffer (KRB) resulted in activation of transcription driven by a SNAT2 genomic fragment that contained an AARE. However, for the KRB, a proportion of the transcription was AARE-independent suggesting that amino acid-independent mechanisms were responsible. Therefore, activation of AARE-driven transcription is triggered by a deficiency in any one of the essential amino acids, but the response is not uniform. Furthermore, caution must be exercised when using a medium completely devoid of amino acids.
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41
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Jones HN, Woollett LA, Barbour N, Prasad PD, Powell TL, Jansson T. High-fat diet before and during pregnancy causes marked up-regulation of placental nutrient transport and fetal overgrowth in C57/BL6 mice. FASEB J 2008; 23:271-8. [PMID: 18827021 DOI: 10.1096/fj.08-116889] [Citation(s) in RCA: 227] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Maternal overweight and obesity in pregnancy often result in fetal overgrowth, which increases the risk for the baby to develop metabolic syndrome later in life. However, the mechanisms underlying fetal overgrowth are not established. We developed a mouse model and hypothesized that a maternal high-fat (HF) diet causes up-regulation of placental nutrient transport, resulting in fetal overgrowth. C57BL/6J female mice were fed a control (11% energy from fat) or HF (32% energy from fat) diet for 8 wk before mating and throughout gestation and were studied at embryonic day 18.5. The HF diet increased maternal adiposity, as assessed by fat pad weight, and circulating maternal leptin, decreased serum adiponectin concentrations, and caused a marked increase in fetal growth (+43%). The HF diet also increased transplacental transport of glucose (5-fold) and neutral amino acids (10-fold) in vivo. In microvillous plasma membranes (MVMs) isolated from placentas of HF-fed animals, protein expression of glucose transporter 1 (GLUT1) was increased 5-fold, and protein expression of sodium-coupled neutral amino acid transporter (SNAT) 2 was elevated 9-fold. In contrast, MVM protein expression of GLUT 3 or SNAT4 was unaltered. These data suggest that up-regulation of specific placental nutrient transporter isoforms constitute a mechanism linking maternal high-fat diet and obesity to fetal overgrowth.
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Affiliation(s)
- Helen N Jones
- Department of Obstetrics and Gynecology, College of Medicine, University of Cincinnati, 231 Albert Sabin Way, Cincinnati OH 45267, USA.
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42
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Kashiwagi H, Yamazaki K, Takekuma Y, Ganapathy V, Sugawara M. Regulatory mechanisms of SNAT2, an amino acid transporter, in L6 rat skeletal muscle cells by insulin, osmotic shock and amino acid deprivation. Amino Acids 2008; 36:219-30. [PMID: 18330498 DOI: 10.1007/s00726-008-0050-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2007] [Accepted: 02/15/2008] [Indexed: 10/22/2022]
Abstract
Several studies have demonstrated that the activity of system A is upregulated by insulin, osmotic shock and amino acid deprivation. However, the mechanisms are not clear. We carried out studies using L6 rat skeletal muscle cells to clarify the mechanisms of upregulation of system A activity by insulin, osmotic shock and amino acid deprivation. The upregulation was found to be due to an increase in Vmax, not Km. Chloroquine and wortmannin inhibited the upregulation induced by insulin stimulation and amino acid deprivation but not that induced by osmotic shock. On the other hand, cycloheximide and actinomycin D inhibited the upregulation by each stimulation. Moreover, PD98059 and SP600125 inhibited only amino acid deprivation-induced upregulation and SB202190 inhibited only insulin-induced upregulation. Our findings indicate that the mechanisms of upregulation of system A activity by insulin, osmotic shock and amino acid deprivation are different in L6 cells. Western blot and RT-PCR analysis showed an increase in system A at the protein and mRNA levels with each stimulation.
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Affiliation(s)
- Hitoshi Kashiwagi
- Department of Pharmacy, Hokkaido University Hospital, Sapporo, Hokkaido, Japan
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43
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Parrott MS, von Versen-Hoeynck F, Ness RB, Markovic N, Roberts JM. System A amino acid transporter activity in term placenta is substrate specific and inversely related to amino acid concentration. Reprod Sci 2008; 14:687-93. [PMID: 18000230 DOI: 10.1177/1933719107306895] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Using intact villous fragments from normal term placentas, the authors characterize the effect of reduced amino acid availability on amino acid uptake via the system A amino acid transporter. Villous fragments deprived of amino acids demonstrate increased system A activity compared with those incubated in an amino acid-sufficient medium (P < .05). Similarly, placental villous fragments exposed to media containing only amino acids not specifically transported by system A have a significant increase in system A activity compared with villous fragments incubated in an amino acid-sufficient medium containing only substrates of system A (P < .05). There is a significant trend for increasing system A activity as the concentrations of the system A amino acid substrates are decreased (P < .01). Collectively, these data indicate that normal placentas can increase system A amino acid transporter activity in a substrate-specific and dose-dependent manner as a means to ensure optimal fetal growth in the presence of amino acid limitation.
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Affiliation(s)
- Meredith Snook Parrott
- Magee-Womens Research Institute, Department of Obstetrics and Gynecology and Reproductive Sciences, University of Pittsburgh, Pittsburgh, Pennsylania 15213, USA.
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Abstract
Animals reject diets that lead to indispensable amino acid (IAA) depletion or deficiency. This behavior is adaptive, as continued IAA depletion is incompatible with maintenance of protein synthesis and survival. Following rejection of the diet, animals begin foraging for a better IAA source and develop conditioned aversions to cues associated with the deficient diet. These responses require a sensory system to detect the IAA depletion and alert the appropriate neural circuitry for the behavior. The chemosensor for IAA deprivation is in the highly excitable anterior piriform cortex (APC) of the brain. Recently, the well-conserved general AA control non-derepressing system of yeast was discovered to be activated by IAA deprivation via uncharged tRNA in mammalian APC. This system provides the sensory limb of the mechanism for recognition of IAA depletion that leads to activation of the APC, diet rejection, and subsequent adaptive strategies.
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Affiliation(s)
- Dorothy W Gietzen
- Department of Anatomy, Physiology and Cell Biology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
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Hyde R, Cwiklinski EL, MacAulay K, Taylor PM, Hundal HS. Distinct sensor pathways in the hierarchical control of SNAT2, a putative amino acid transceptor, by amino acid availability. J Biol Chem 2007; 282:19788-98. [PMID: 17488712 DOI: 10.1074/jbc.m611520200] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian nutrient sensors are novel targets for therapeutic intervention in disease states such as insulin resistance and muscle wasting; however, the proteins responsible for this important task are largely uncharacterized. To address this issue we have dissected an amino acid (AA) sensor/effector regulon that controls the expression of the System A amino acid transporter SNAT2 in mammalian cells, a paradigm nutrient-responsive process, and found evidence for the convergence of at least two sensor/effector pathways. During AA withdrawal, JNK is activated and induces the expression of SNAT2 in L6 myotubes by stimulating an intronic nutrient-sensitive domain. A sensor for large neutral AA (e.g. Tyr, Gln) inhibits JNK activation and SNAT2 up-regulation. Additionally, shRNA and transporter chimeras demonstrate that SNAT2 provides a repressive signal for gene transcription during AA sufficiency, thus echoing AA sensing by transceptor (transporter-receptor) orthologues in yeast (Gap1/Ssy1) and Drosophila (PATH). Furthermore, the SNAT2 protein is stabilized during AA withdrawal.
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Affiliation(s)
- Russell Hyde
- Division of Molecular Physiology, Sir James Black Centre, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
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Ericsson A, Säljö K, Sjöstrand E, Jansson N, Prasad PD, Powell TL, Jansson T. Brief hyperglycaemia in the early pregnant rat increases fetal weight at term by stimulating placental growth and affecting placental nutrient transport. J Physiol 2007; 581:1323-32. [PMID: 17430988 PMCID: PMC2170823 DOI: 10.1113/jphysiol.2007.131185] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
In pregnant women with type 1 diabetes, suboptimal glucose control in the first trimester is a strong predictor for giving birth to a large fetus. However, the mechanisms underlying this association are unknown. We hypothesized that transient hyperglycaemia in early pregnancy results in (1) increased placental growth and (2) an up-regulation of placental nutrient transport capacity, which leads to fetal overgrowth at term. In order to test this hypothesis, pregnant rats were given intraperitoneal injections of glucose (2 g kg(-1), resulting in a 50-100% increase in blood glucose level during 90 min) or saline (control) in either early or late gestation using four different protocols: one single injection on gestational day (GD) 10 (n=5), three injections on GD 10 (n=8-9), six injections on GD 10 and 11 (n=9-11) or three injections on GD 19 (n=7-8). Multiple injections were given approximately 4 h apart. Subsequently, animals were studied on GD 21. Three glucose injections in early pregnancy significantly increased placental weight by 10%, whereas fetal weight was found to be increased at term in response to both three (9% increase in fetal weight, P<0.05) and six glucose injections (7%, P=0.05) in early gestation. A single glucose injection on GD 10 or three injections of glucose on GD 19 had no effect on placental or fetal growth. In groups where a change in feto-placental growth was observed, we measured placental system A and glucose transport activity in the awake animals on GD 21 and placental expression of the glucose and amino acid transporters GLUT1, GLUT3, SNAT2 (system A), LAT1 and LAT 2 (system L). Placental system A transport at term was down-regulated by six glucose injections in early pregnancy (by -33%, P<0.05), whereas placental mRNA and protein levels were unchanged. No long-term alterations in maternal metabolic status were detected. In conclusion, we demonstrate that transient hyperglycaemia in early pregnancy is sufficient to increase fetal weight close to term. In contrast, brief hyperglycaemia in late pregnancy did not stimulate fetal growth. Increased fetal growth may be explained by a larger placenta, which would allow for more nutrients to be transferred to the fetus. These data suggest that maternal metabolic control in early pregnancy is an important determinant for feto-placental growth and placental function throughout the remainder of gestation. We speculate that maternal metabolism in early pregnancy represents a key environmental cue to which the placenta responds in order to match fetal growth rate with the available resources of the mother.
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MESH Headings
- Amino Acid Transport System A
- Amino Acid Transport System y+/metabolism
- Amino Acid Transport Systems/metabolism
- Amino Acid Transport Systems, Neutral/genetics
- Amino Acid Transport Systems, Neutral/metabolism
- Animals
- Blood Glucose/metabolism
- Diabetes, Gestational/blood
- Diabetes, Gestational/chemically induced
- Diabetes, Gestational/metabolism
- Diabetes, Gestational/pathology
- Disease Models, Animal
- Female
- Fetal Nutrition Disorders/blood
- Fetal Nutrition Disorders/etiology
- Fetal Nutrition Disorders/metabolism
- Fetal Nutrition Disorders/pathology
- Fetal Weight
- Fusion Regulatory Protein 1, Light Chains/metabolism
- Gestational Age
- Glucose
- Glucose Transport Proteins, Facilitative/genetics
- Glucose Transport Proteins, Facilitative/metabolism
- Glucose Transporter Type 1/metabolism
- Glucose Transporter Type 3/metabolism
- Hyperglycemia/blood
- Hyperglycemia/chemically induced
- Hyperglycemia/complications
- Hyperglycemia/metabolism
- Hyperglycemia/pathology
- Insulin/blood
- Large Neutral Amino Acid-Transporter 1/metabolism
- Maternal-Fetal Exchange
- Organ Size
- Placenta/metabolism
- Placenta/pathology
- Pregnancy
- RNA, Messenger/metabolism
- Rats
- Rats, Sprague-Dawley
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Affiliation(s)
- Anette Ericsson
- Perinatal Center, Institute of Neuroscience and Physiology, Gothenburg University, Box 432, s-405 30 Gothenburg, Sweden.
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Jansson N, Pettersson J, Haafiz A, Ericsson A, Palmberg I, Tranberg M, Ganapathy V, Powell TL, Jansson T. Down-regulation of placental transport of amino acids precedes the development of intrauterine growth restriction in rats fed a low protein diet. J Physiol 2007; 576:935-46. [PMID: 16916910 PMCID: PMC1892642 DOI: 10.1113/jphysiol.2006.116509] [Citation(s) in RCA: 142] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Intrauterine growth restriction (IUGR) represents an important risk factor for perinatal complications and for adult disease. IUGR is associated with a down-regulation of placental amino acid transporters; however, whether these changes are primary events directly contributing to IUGR or a secondary consequence is unknown. We investigated the time course of changes in placental and fetal growth, placental nutrient transport in vivo and the expression of placental nutrient transporters in pregnant rats subjected to protein malnutrition, a model for IUGR. Pregnant rats were given either a low protein (LP) diet (n = 64) or an isocaloric control diet (n = 66) throughout pregnancy. Maternal insulin, leptin and IGF-I levels decreased, whereas maternal amino acid concentrations increased moderately in response to the LP diet. Fetal and placental weights in the LP group were unaltered compared to control diet at gestational day (GD) 15, 18 and 19 but significantly reduced at GD 21. Placental system A transport activity was reduced at GD 19 and 21 in response to a low protein diet. Placental protein expression of SNAT2 was decreased at GD 21. In conclusion, placental amino acid transport is down-regulated prior to the development of IUGR, suggesting that these placental transport changes are a cause, rather than a consequence, of IUGR. Reduced maternal levels of insulin, leptin and IGF-1 may link maternal protein malnutrition to reduced fetal growth by down-regulation of key placental amino acid transporters.
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Affiliation(s)
- Nina Jansson
- Perinatal Center, Institute of Neuroscience and Physiology, Göteborg University, Sweden.
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48
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Jones HN, Ashworth CJ, Page KR, McArdle HJ. Expression and adaptive regulation of amino acid transport system A in a placental cell line under amino acid restriction. Reproduction 2006; 131:951-60. [PMID: 16672359 DOI: 10.1530/rep.1.00808] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Trans-placental transport of amino acids is vital for the developing fetus. Using the BeWo cell line as a placental model, we investigated the effect of restricting amino acid availability on amino acid transport system type A. BeWo cells were cultured either in amino acid-depleted (without non-essential amino acids) or control media for 1, 3, 5 or 6 h. System A function was analysed using alpha(methyl-amino)isobutyric acid (MeAIB) transcellular transport studies. Transporter (sodium coupled neutral amino acid transporter (SNAT1/2)) expression was analysed at mRNA and protein level by Northern and Western blotting respectively. Localisation was carried out using immunocytochemistry. MeAIB transcellular transport was significantly (P < 0.05) increased by incubation of the cells in amino acid-depleted medium for 1 h, and longer incubation times caused further increases in the rate of transfer. However, the initial response was not accompanied by an increase in SNAT2 mRNA; this occurred only after 3 h and further increased for the rest of the 6-h incubation. Similarly, it took several hours for a significant increase in SNAT2 protein expression. In contrast, relocalisation of existing SNAT2 transporters occurred within 30 min of amino acid restriction and continued throughout the 6-h incubation. When the cells were incubated in medium with even lower amino acid levels (without non-essential plus 0.5 x essential amino acids), SNAT2 mRNA levels showed further significant (P < 0.0001) up-regulation. However, incubation of cells in depleted medium for 6 h caused a significant (P = 0.014) decrease in the expression of SNAT1 mRNA. System L type amino acid transporter 2 (LAT2) expression was not changed by amino acid restriction, indicating that the responses seen in the system A transporters were not a general cell response. These data have shown that placental cells adapt in vitro to nutritional stress and have identified the physiological, biochemical and genomic mechanisms involved.
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Affiliation(s)
- H N Jones
- Maternal-Fetal Physiology, Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen AB21 9SB, UK
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López A, Torres N, Ortiz V, Alemán G, Hernández-Pando R, Tovar AR. Characterization and regulation of the gene expression of amino acid transport system A (SNAT2) in rat mammary gland. Am J Physiol Endocrinol Metab 2006; 291:E1059-66. [PMID: 16787963 DOI: 10.1152/ajpendo.00062.2006] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Amino acid transport via system A plays an important role during lactation, promoting the uptake of small neutral amino acids, mainly alanine and glutamine. However, the regulation of gene expression of system A [sodium-coupled neutral amino acid transporter (SNAT)2] in mammary gland has not been studied. The aim of the present work was to understand the possible mechanisms of regulation of SNAT2 in the rat mammary gland. Incubation of gland explants in amino acid-free medium induced the expression of SNAT2, and this response was repressed by the presence of small neutral amino acids or by actinomycin D but not by large neutral or cationic amino acids. The half-life of SNAT2 mRNA was 67 min, indicating a rapid turnover. In addition, SNAT2 expression in the mammary gland was induced by forskolin and PMA, inducers of PKA and PKC signaling pathways, respectively. Inhibitors of PKA and PKC pathways partially prevented the upregulation of SNAT2 mRNA during adaptive regulation. Interestingly, SNAT2 mRNA was induced during pregnancy and to a lesser extent at peak lactation. beta-Estradiol stimulated the expression of SNAT2 in mammary gland explants; this stimulation was prevented by the estrogen receptor inhibitor ICI-182780. Our findings clearly demonstrated that the SNAT2 gene is regulated by multiple pathways, indicating that the expression of this amino acid transport system is tightly controlled due to its importance for the mammary gland during pregnancy and lactation to prepare the gland for the transport of amino acids during lactation.
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Affiliation(s)
- Adriana López
- Departamento de Fisiología de la Nutrición, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico
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Palii S, Thiaville M, Pan YX, Zhong C, Kilberg M. Characterization of the amino acid response element within the human sodium-coupled neutral amino acid transporter 2 (SNAT2) System A transporter gene. Biochem J 2006; 395:517-27. [PMID: 16445384 PMCID: PMC1462688 DOI: 10.1042/bj20051867] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The neutral amino acid transport activity, System A, is enhanced by amino acid limitation of mammalian cells. Of the three gene products that encode System A activity, the one that exhibits this regulation is SNAT2 (sodium-coupled neutral amino acid transporter 2). Fibroblasts that are deficient in the amino acid response pathway exhibited little or no induction of SNAT2 mRNA. Synthesis of SNAT2 mRNA increased within 1-2 h after amino acid removal from HepG2 human hepatoma cells. The amino acid responsive SNAT2 genomic element that mediates the regulation has been localized to the first intron. Increased binding of selected members of the ATF (activating transcription factor) and C/EBP (CCAAT/enhancer-binding protein) families to the intronic enhancer was established both in vitro and in vivo. In contrast, there was no significant association of these factors with the SNAT2 promoter. Expression of exogenous individual ATF and C/EBP proteins documented that specific family members are associated with either activation or repression of SNAT2 transcription. Chromatin immunoprecipitation analysis established in vivo that amino acid deprivation led to increased RNA polymerase II recruitment to the SNAT2 promoter.
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Affiliation(s)
- Stela S. Palii
- Department of Biochemistry and Molecular Biology, Shands Cancer Center, and the Genetics Institute, University of Florida College of Medicine, Gainesville, FL 32610, U.S.A
| | - Michelle M. Thiaville
- Department of Biochemistry and Molecular Biology, Shands Cancer Center, and the Genetics Institute, University of Florida College of Medicine, Gainesville, FL 32610, U.S.A
| | - Yuan-Xiang Pan
- Department of Biochemistry and Molecular Biology, Shands Cancer Center, and the Genetics Institute, University of Florida College of Medicine, Gainesville, FL 32610, U.S.A
| | - Can Zhong
- Department of Biochemistry and Molecular Biology, Shands Cancer Center, and the Genetics Institute, University of Florida College of Medicine, Gainesville, FL 32610, U.S.A
| | - Michael S. Kilberg
- Department of Biochemistry and Molecular Biology, Shands Cancer Center, and the Genetics Institute, University of Florida College of Medicine, Gainesville, FL 32610, U.S.A
- To whom correspondence should be addressed (email )
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