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Endocytosis and signaling of angiotensin II type 1 receptor. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2023; 194:141-157. [PMID: 36631190 DOI: 10.1016/bs.pmbts.2022.08.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
A vasoactive octapeptide angiotensin II (Ang II) hormone is the key regulator of the renin-angiotensin system (RAS). It binds with the two different plasma membrane receptors like angiotensin II type 1 (AT1) and type 2 (AT2) and consequence various biological responses occur. Further, AT1 has two subtypes such as AT1A and AT1B. These angiotensin receptors are classified to be G protein-coupled receptors (GPCRs). The main constituent of RAS is the AT1 receptor (AT1R), and its activation, signal transduction, and regulation have been extensively studied. After Ang II stimulation, the ligand-receptor complexes internalized and trafficked through the early endosome, recycling endosome, and some receptors skipped the recycling endosome and trafficked to the lysosome for metabolic degradation. Moreover, some short sequence motifs located in the carboxyl-terminus (CT) of the receptor play a vital role in the internalization, phosphorylation, subcellular trafficking, signaling, and desensitization. Furthermore, in endocytosis, the various proteins interact with the CT region of the receptor. This chapter highlights the basic mechanism of AT1 receptor internalization, trafficking and signaling in both physiological and pathophysiological conditions.
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Abd Alla J, Quitterer U. The RAF Kinase Inhibitor Protein (RKIP): Good as Tumour Suppressor, Bad for the Heart. Cells 2022; 11:cells11040654. [PMID: 35203304 PMCID: PMC8869954 DOI: 10.3390/cells11040654] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Revised: 02/08/2022] [Accepted: 02/11/2022] [Indexed: 02/04/2023] Open
Abstract
The RAF kinase inhibitor protein, RKIP, is a dual inhibitor of the RAF1 kinase and the G protein-coupled receptor kinase 2, GRK2. By inhibition of the RAF1-MAPK (mitogen-activated protein kinase) pathway, RKIP acts as a beneficial tumour suppressor. By inhibition of GRK2, RKIP counteracts GRK2-mediated desensitisation of G protein-coupled receptor (GPCR) signalling. GRK2 inhibition is considered to be cardioprotective under conditions of exaggerated GRK2 activity such as heart failure. However, cardioprotective GRK2 inhibition and pro-survival RAF1-MAPK pathway inhibition counteract each other, because inhibition of the pro-survival RAF1-MAPK cascade is detrimental for the heart. Therefore, the question arises, what is the net effect of these apparently divergent functions of RKIP in vivo? The available data show that, on one hand, GRK2 inhibition promotes cardioprotective signalling in isolated cardiomyocytes. On the other hand, inhibition of the pro-survival RAF1-MAPK pathway by RKIP deteriorates cardiomyocyte viability. In agreement with cardiotoxic effects, endogenous RKIP promotes cardiac fibrosis under conditions of cardiac stress, and transgenic RKIP induces heart dysfunction. Supported by next-generation sequencing (NGS) data of the RKIP-induced cardiac transcriptome, this review provides an overview of different RKIP functions and explains how beneficial GRK2 inhibition can go awry by RAF1-MAPK pathway inhibition. Based on RKIP studies, requirements for the development of a cardioprotective GRK2 inhibitor are deduced.
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Affiliation(s)
- Joshua Abd Alla
- Molecular Pharmacology, Department of Chemistry and Applied Biosciences, ETH Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland;
| | - Ursula Quitterer
- Molecular Pharmacology, Department of Chemistry and Applied Biosciences, ETH Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland;
- Department of Medicine, Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
- Correspondence: ; Tel.: +41-44-632-9801
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Aditama APR, Ma'arif B, Laswati H, Agil M. In vitro and in silico analysis of phytochemical compounds of 96% ethanol extract of semanggi ( Marsilea crenata Presl.) leaves as a bone formation agent. J Basic Clin Physiol Pharmacol 2021; 32:881-887. [PMID: 34214308 DOI: 10.1515/jbcpp-2020-0515] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2020] [Accepted: 03/25/2021] [Indexed: 11/15/2022]
Abstract
OBJECTIVES Osteoporosis is the result of an imbalance in the rate of bone resorption and bone formation due to a decrease in estrogen. Phytoestrogens are plant compounds with structures and functions similar to estrogen. Phytoestrogens that bind to estrogen receptors in bone cells are able to modulate bone formation. Semanggi (Marsilea crenata Presl.) is a plant that contains phytoestrogens. The purpose of this study was to observe the expression of osteocalcin and predict the content of extract phytoestrogens through a computer simulation study to study the bone formation activity of the 96% ethanol extract of M. crenata leaves on hFOB 1.19 cells. METHODS hFOB 1.19 cells were cultured in 24-well microplates, and 96% ethanol extract of M. crenata Presl. leaves was added at 62.5, 125 and 250 ppm. The expression of osteocalcin was analyzed using CLSM immunocytochemistry. Using PyRx 0.8 software and 1ERE protein for molecular docking, the compound was analyzed by computer. RESULTS The 96% ethanol extract of M. crenata Presl. leaves can increase the expression of osteocalcin, the optimal dose is 125 ppm, and p<0.05 is 881.658 AU. In silico study was obtained six compounds that showed similar activity 17β-estradiol as ER-β agonists. CONCLUSIONS The 96% ethanol extract of M. crenata Presl. leaves contain six compounds that are thought to be phytoestrogens and ER-β agonists, and play a role in increasing bone formation activity and have the potential to be used as an oral drug.
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Affiliation(s)
- Agnis P R Aditama
- Faculty of Pharmacy, Universitas Airlangga, Surabaya, Indonesia.,Department of Pharmacy, Pharmacy Academy of Jember, Jember, Indonesia
| | - Burhan Ma'arif
- Department of Pharmacy, Faculty of Medical and Health Science, Maulana Malik Ibrahim State Islamic University, Malang, Indonesia
| | - Hening Laswati
- Department of Physical Medicine and Rehabilitation, Universitas Airlangga, Surabaya, Indonesia
| | - Mangestuti Agil
- Department of Pharmacognosy and Phytochemistry, Faculty of Pharmacy, Universitas Airlangga, Surabaya, Indonesia
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Vandenberg LN, Colborn T, Hayes TB, Heindel JJ, Jacobs DR, Lee DH, Shioda T, Soto AM, vom Saal FS, Welshons WV, Zoeller RT, Myers JP. Hormones and endocrine-disrupting chemicals: low-dose effects and nonmonotonic dose responses. Endocr Rev 2012; 33:378-455. [PMID: 22419778 PMCID: PMC3365860 DOI: 10.1210/er.2011-1050] [Citation(s) in RCA: 1961] [Impact Index Per Article: 163.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 02/07/2012] [Indexed: 02/08/2023]
Abstract
For decades, studies of endocrine-disrupting chemicals (EDCs) have challenged traditional concepts in toxicology, in particular the dogma of "the dose makes the poison," because EDCs can have effects at low doses that are not predicted by effects at higher doses. Here, we review two major concepts in EDC studies: low dose and nonmonotonicity. Low-dose effects were defined by the National Toxicology Program as those that occur in the range of human exposures or effects observed at doses below those used for traditional toxicological studies. We review the mechanistic data for low-dose effects and use a weight-of-evidence approach to analyze five examples from the EDC literature. Additionally, we explore nonmonotonic dose-response curves, defined as a nonlinear relationship between dose and effect where the slope of the curve changes sign somewhere within the range of doses examined. We provide a detailed discussion of the mechanisms responsible for generating these phenomena, plus hundreds of examples from the cell culture, animal, and epidemiology literature. We illustrate that nonmonotonic responses and low-dose effects are remarkably common in studies of natural hormones and EDCs. Whether low doses of EDCs influence certain human disorders is no longer conjecture, because epidemiological studies show that environmental exposures to EDCs are associated with human diseases and disabilities. We conclude that when nonmonotonic dose-response curves occur, the effects of low doses cannot be predicted by the effects observed at high doses. Thus, fundamental changes in chemical testing and safety determination are needed to protect human health.
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Affiliation(s)
- Laura N Vandenberg
- Tufts University, Center for Regenerative and Developmental Biology, Department of Biology, 200 Boston Avenue, Suite 4600, Medford, Massachusetts 02155, USA.
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Abstract
Constitutively active mutants (CAMs) of G-protein-coupled receptors mimic the active conformation of the receptor in their ability to activate second messenger systems in the absence of agonist. They have revealed novel properties of drugs that reverse the basal levels of constitutive activity, indicating that the drugs have the inverse agonist activity. Internalization plays an important role in receptor endocytosis and signal transduction. The present chapter provides the investigation of the internalization behavior of CAM N111G of Angiotensin II type 1 (AT(1)) receptor and correlates the result with the mechanism of constitutive activity of the mutant. Both wild-type (WT) and N111G mutant receptors were transiently expressed in COS-7 cells and total inositol phosphate production was measured in presence and absence of the angiotensin II receptor blockers (ARBs). The binding affinities toward agonist and ARBs were also determined. We found that the ARBs have the inverse agonist activity in CAM N111G of AT(1) receptor. The internalization of the mutant, which was much lower than WT receptor, was significantly increased in presence of the ARBs. The results indicate that internalization of CAM N111G of AT(1) receptor is induced by the ARBs, which may be an important characteristic of inverse agonist activities of the ARBs in N111G.
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Bhuiyan MA, Hossain M, Miura SI, Nakamura T, Ozaki M, Nagatomo T. Constitutively Active Mutant N111G of Angiotensin II Type 1 (AT1) Receptor Induces Homologous Internalization Through Mediation of AT1-Receptor Antagonist. J Pharmacol Sci 2009; 111:227-34. [DOI: 10.1254/jphs.09202fp] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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Bodenstein J, Sunahara RK, Neubig RR. N-terminal residues control proteasomal degradation of RGS2, RGS4, and RGS5 in human embryonic kidney 293 cells. Mol Pharmacol 2007; 71:1040-50. [PMID: 17220356 DOI: 10.1124/mol.106.029397] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Regulator of G protein signaling (RGS) proteins modulate G protein-coupled receptor (GPCR) signaling. The N termini of some RGS4-family proteins provide receptor specificity and also contain an N-end rule determinant that results in ubiquitylation and decreased protein expression. The relevance of these mechanisms to other RGS proteins is not fully understood. Thus we examined function, receptor specificity, and expression of R4 subfamily RGS proteins (RGS2, -3, -4, -5, and -8). Although the N terminus plays a key role in protein stability in human embryonic kidney (HEK) 293 cells, we were unable to demonstrate specificity of RGS2, -3, -4, -5, or -8 for muscarinic receptors (M(1), M(3), and M(5)). However, cellular RGS activity (8 = 3 > 2) was strongly correlated with expression; RGS4 and -5 had minimal expression and activity. Stabilizing mutations of RGS4 and -5 (C2S) enhanced expression and function with a greater influence on RGS4 than on RGS5. We were surprised to find that a predicted destabilizing mutation in RGS8 (A2C) did not markedly affect expression and had no effect on function. In contrast, a destabilizing mutation in RGS2 (RGS2-Q2L) recently identified as a rare N-terminal genetic variant in a Japanese hypertensive cohort (J Hypertens 23:1497-1505, 2005) showed significantly reduced expression and inhibition of angiotensin II (AT(1)) receptor-stimulated accumulation of inositol phosphates. We were surprised to find that RGS2-Q2R, also predicted to be destabilizing, showed nearly normal expression and function. Thus, proteasomal regulation of RGS expression in HEK293 cells strongly controls RGS function and a novel RGS2 mutation with decreased protein expression could be relevant to the pathophysiology of hypertension in humans.
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Affiliation(s)
- Johannes Bodenstein
- Department of Pharmacology, 1301 MSRB III/Box 0632, 1150 W. Medical Center Drive, University of Michigan Medical School, Ann Arbor, MI 48109-0632, USA
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Cook JL, Mills SJ, Naquin RT, Alam J, Re RN. Cleavage of the angiotensin II type 1 receptor and nuclear accumulation of the cytoplasmic carboxy-terminal fragment. Am J Physiol Cell Physiol 2006; 292:C1313-22. [PMID: 17122414 DOI: 10.1152/ajpcell.00454.2006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Our published studies show that the distribution of the ANG II type 1 (AT(1)) receptor (AT(1)R), expressed as a enhanced yellow fluorescent fusion (YFP) protein (AT(1)R/EYFP), is altered upon cellular treatment with ANG II or coexpression with intracellular ANG II. AT(1)R accumulates in nuclei of cells only in the presence of ANG II. Several transmembrane receptors are known to accumulate in nuclei, some as holoreceptors and others as cleaved receptor products. The present study was designed to determine whether the AT(1)R is cleaved before nuclear transport. A plasmid encoding a rat AT(1)R labeled at the amino terminus with enhanced cyan fluorescent protein (CFP) and at the carboxy terminus with EYFP was employed. Image analyses of this protein in COS-7 cells, CCF-STTG1 glial cells, and A10 vascular smooth muscle cells show the two fluorescent moieties to be largely spatially colocalized in untreated cells. ANG II treatment, however, leads to a separation of the fluorescent moieties with yellow fluorescence accumulating in more than 30% of cellular nuclei. Immunoblot analyses of extracts and conditioned media from transfected cells indicate that the CFP domain fused to the extracellular amino-terminal AT(1)R domain is cleaved from the membrane and that the YFP domain, together with the intracellular cytoplasmic carboxy terminus of the AT(1)R, is also cleaved from the membrane-bound receptor. The carboxy terminus of the AT(1)R is essential for cleavage; cleavage does not occur in protein deleted with respect to this region. Overexpressed native AT(1)R (nonfusion) is also cleaved; the intracellular 6-kDa cytoplasmic domain product accumulates to a significantly higher level with ANG II treatment.
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Affiliation(s)
- Julia L Cook
- Ochsner Clinic Foundation, Ochsner Health System, 1516 Jefferson Hwy., New Orleans, LA 70121, USA.
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9
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Kalatskaya I, Schüssler S, Seidl C, Jochum M, Faussner A. C-terminal fusion of eGFP to the bradykinin B2 receptor strongly affects down-regulation but not receptor internalization or signaling. Biol Chem 2006; 387:603-10. [PMID: 16740132 DOI: 10.1515/bc.2006.077] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A functional comparison was made between the wild-type bradykinin B2 receptor (B2wt) and the chimera B2eGFP (enhanced green-fluorescent protein fused to the C-terminus of B2wt), both stably expressed in HEK 293 cells. There was almost no difference in terms of ligand-inducible receptor phosphorylation and internalization, signal transduction (accumulation of inositol phosphates) or expression and affinity. However, stimulation for up to 8 h with 10 microM bradykinin (BK) resulted in a strong decrease in surface receptors (by 60% within 5 h) in B2wt, but not in B2eGFP. When the expression levels of both constructs where comparably reduced using a weaker promoter, long-term stimulation resulted in a reduction in surface receptors for B2wt(low) to less than 20% within 1 h, whereas the chimera B2eGFP(low) still displayed 50% binding activity after 2 h. A 1-h incubation in the absence of BK resulted in a recovery of 60% of the binding in B2wt(low) after 1-h stimulation with BK, but of only 20% after 7-h stimulation. In contrast, B2eGFP(low) levels were restored to more than 70%, even after 7-h stimulation. These data indicate that although the fusion of eGFP to B2wt does not affect its ligand-induced internalization, it strongly reduces the down-regulation, most likely by promoting receptor recycling over degradation.
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Affiliation(s)
- Irina Kalatskaya
- Abteilung für Klinische Chemie und Klinische Biochemie, Ludwig-Maximilians-Universität München, Nussbaumstrasse 20, D-80336 München, Germany
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10
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Zhai P, Yamamoto M, Galeotti J, Liu J, Masurekar M, Thaisz J, Irie K, Holle E, Yu X, Kupershmidt S, Roden DM, Wagner T, Yatani A, Vatner DE, Vatner SF, Sadoshima J. Cardiac-specific overexpression of AT1 receptor mutant lacking G alpha q/G alpha i coupling causes hypertrophy and bradycardia in transgenic mice. J Clin Invest 2006; 115:3045-56. [PMID: 16276415 PMCID: PMC1265872 DOI: 10.1172/jci25330] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2005] [Accepted: 08/30/2005] [Indexed: 12/25/2022] Open
Abstract
Ang II type 1 (AT1) receptors activate both conventional heterotrimeric G protein-dependent and unconventional G protein-independent mechanisms. We investigated how these different mechanisms activated by AT1 receptors affect growth and death of cardiac myocytes in vivo. Transgenic mice with cardiac-specific overexpression of WT AT1 receptor (AT1-WT; Tg-WT mice) or an AT1 receptor second intracellular loop mutant (AT1-i2m; Tg-i2m mice) selectively activating G(alpha)q/G(alpha)i-independent mechanisms were studied. Tg-i2m mice developed more severe cardiac hypertrophy and bradycardia coupled with lower cardiac function than Tg-WT mice. In contrast, Tg-WT mice exhibited more severe fibrosis and apoptosis than Tg-i2m mice. Chronic Ang II infusion induced greater cardiac hypertrophy in Tg-i2m compared with Tg-WT mice whereas acute Ang II administration caused an increase in heart rate in Tg-WT but not in Tg-i2m mice. Membrane translocation of PKCepsilon, cytoplasmic translocation of G(alpha)q, and nuclear localization of phospho-ERKs were observed only in Tg-WT mice while activation of Src and cytoplasmic accumulation of phospho-ERKs were greater in Tg-i2m mice, consistent with the notion that G(alpha)q/G(alpha)i-independent mechanisms are activated in Tg-i2m mice. Cultured myocytes expressing AT1-i2m exhibited a left and upward shift of the Ang II dose-response curve of hypertrophy compared with those expressing AT1-WT. Thus, the AT1 receptor mediates downstream signaling mechanisms through G(alpha)q/G(alpha)i-dependent and -independent mechanisms, which induce hypertrophy with a distinct phenotype.
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MESH Headings
- Animals
- Apoptosis/genetics
- Bradycardia/genetics
- Bradycardia/metabolism
- Bradycardia/pathology
- Cells, Cultured
- Electrocardiography
- Extracellular Signal-Regulated MAP Kinases/metabolism
- Fibrosis/genetics
- Fibrosis/metabolism
- GTP-Binding Protein alpha Subunits, Gi-Go/deficiency
- GTP-Binding Protein alpha Subunits, Gi-Go/genetics
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- GTP-Binding Protein alpha Subunits, Gq-G11/deficiency
- GTP-Binding Protein alpha Subunits, Gq-G11/genetics
- GTP-Binding Protein alpha Subunits, Gq-G11/metabolism
- Hypertrophy, Left Ventricular/genetics
- Hypertrophy, Left Ventricular/metabolism
- Hypertrophy, Left Ventricular/pathology
- Mice
- Mice, Transgenic
- Mutation
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/pathology
- Phenotype
- Protein Kinase C-epsilon/metabolism
- Rats
- Rats, Wistar
- Receptor, Angiotensin, Type 1/deficiency
- Receptor, Angiotensin, Type 1/genetics
- Receptor, Angiotensin, Type 1/metabolism
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Affiliation(s)
- Peiyong Zhai
- Cardiovascular Research Institute, Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103, USA
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11
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Gilbert JS, Lang AL, Nijland MJ. Maternal nutrient restriction and the fetal left ventricle: decreased angiotensin receptor expression. Reprod Biol Endocrinol 2005; 3:27. [PMID: 16018810 PMCID: PMC1187921 DOI: 10.1186/1477-7827-3-27] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/26/2005] [Accepted: 07/14/2005] [Indexed: 12/21/2022] Open
Abstract
BACKGROUND Adequate maternal nutrition during gestation is requisite for fetal nutrition and development. While a large group of epidemiological studies indicate poor fetal nutrition increases heart disease risk and mortality in later life, little work has focused on the effects of impaired maternal nutrition on fetal heart development. We have previously shown that 50% global nutrient restriction from 28-78 days of gestation (early to mid-pregnancy; term = 147 days) in sheep at mid-gestation retards fetal growth while protecting growth of heart and results in hypertensive male offspring at nine months of age. In the present study, we evaluate LV gene transcription using RNA protection assay and real-time reverse transcriptase polymerase chain reaction, and protein expression using western blot, of VEGF and AT1 and AT2 receptors for AngII at mid-gestation in fetuses from pregnant ewes fed either 100% (C) or 50% (NR) diet during early to mid-gestation. RESULTS No difference between the NR (n = 6) and C (n = 6) groups was found in gene transcription of the AngII receptors. Immunoreactive AT1 (1918.4 +/- 154.2 vs. 3881.2 +/- 494.9; P < 0.01) and AT2 (1729.9 +/- 293.6 vs. 3043.3 +/- 373.2; P < 0.02) was decreased in the LV of NR fetuses compared to C fetuses. The LV of fetuses exposed to NR had greater transcription of mRNA for VEGF (5.42 +/- 0.85 vs. 3.05 +/- 0.19; P < 0.03) than respective C LV, while no change was observed in immunoreactive VEGF. CONCLUSION The present study demonstrates that VEGF, AT1 and AT2 message and protein are not tightly coupled, pointing to post-transcriptional control points in the mid gestation NR fetus. The present data also suggest that the role of VEGF and the renin-angiotensin system receptors during conditions inducing protected cardiac growth is distinct from the role these proteins may play in normal fetal cardiac growth. The present findings may help explain epidemiological studies that indicate fetuses with low birth weight carry an increased risk of mortality from coronary and cardiovascular disease, particularly if these individuals have reduced cardiovascular reserve due to an epigenetic decrease in vascularization.
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Affiliation(s)
- Jeffrey S Gilbert
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
- Department of Zoology and Physiology, University of Wyoming, Laramie, WY, USA
| | - Alvin L Lang
- Department of Zoology and Physiology, University of Wyoming, Laramie, WY, USA
| | - Mark J Nijland
- Center for Pregnancy and Newborn Research, Department of Obstetrics and Gynecology, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
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12
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Schumann M, Nakagawa T, Mantey SA, Tokita K, Venzon DJ, Hocart SJ, Benya RV, Jensen RT. Importance of amino acids of the central portion of the second intracellular loop of the gastrin-releasing Peptide receptor for phospholipase C activation, internalization, and chronic down-regulation. J Pharmacol Exp Ther 2003; 307:597-607. [PMID: 12970386 DOI: 10.1124/jpet.103.055087] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Little is known about the function of the central portion of the second intracellular loop (i2 loop) of peptide receptors in activation of downstream pathways and receptor modulatory processes such as receptor internalization or chronic down-regulation (DR). Recent data suggest a role for i2 loop hydrophobic amino acids in these processes. We used site-directed mutagenesis to address these issues with the gastrin-releasing peptide receptor (GRP-R). Each i2 loop residue from 142 to 148 was mutated and the receptors were expressed in Balb 3T3 cells. Two mutants showed a minimal (<2-fold) decrease in affinity. Five mutants showed decreased efficacy for activating phospholipase C (PLC). Two double mutants (IM143.147AA and VM144.147AA) showed a minimal decrease in affinity but had a decreased ability to fully activate PLC. Only the IM double mutation had decreased maximal internalization, whereas the R145A single mutant showed an increase, suggesting a tonic inhibitory role for Arg-145 in internalization. Three single and both double mutants showed decreases in receptor DR. There was a weak correlation between the extent of GRP-R internalization and the maximal PLC activation, whereas changes in the maximal PLC activation were significantly (p = 0.008) coupled to receptor DR. This study shows that amino acids of the i2 loop of the GRP-R are important in activation of PLC, internalization and down-regulation, but not for affinity. Our results support the proposal that internalization and chronic down-regulation have differing dependence on PLC and are largely independent processes, because some mutants showed no changes in internalization, but significant alterations in down-regulation.
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Affiliation(s)
- Michael Schumann
- Digestive Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Building 10, Rm. 9C-103, 10 Center Drive, MSC 1804, Bethesda, MD 20892, USA.
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13
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Licht T, Tsirulnikov L, Reuveni H, Yarnitzky T, Ben-Sasson SA. Induction of pro-angiogenic signaling by a synthetic peptide derived from the second intracellular loop of S1P3 (EDG3). Blood 2003; 102:2099-107. [PMID: 12763936 DOI: 10.1182/blood-2002-12-3634] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The G-protein-coupled receptors of the endothelial differentiation gene (EDG) family mediate pro-angiogenic activities, such as endothelial cell proliferation, chemotaxis, and vessel morphogenesis. We synthesized and tested the effects of a 9-amino acid peptide (KRX-725), derived from the second intracellular loop of S1P3 (EDG3). KRX-725 mimics the effects of sphingosine 1-phosphate (S1P), the natural ligand of S1P3, by triggering a Gi-dependent MEK-ERK (mitogen-activated protein kinase kinase and extracellular signal-regulated kinase) signal transduction pathway. Using aortic rings as an ex vivo model of angiogenesis, vascular sprouting was assessed in the presence of KRX-725 or S1P. KRX-725 induced extensive and dense vascular sprouts, which contain an elaborated organization of endothelial and smooth muscle layers, including lumen formation. When KRX-725 or S1P was combined with proangiogenic factors, such as basic fibroblast growth factor (bFGF), stem cell factor, or vascular endothelial growth factor, the effect was synergistic, leading to further enhancement of vascular sprouting. KRX-725 also initiated neovascularization in a mouse corneal pocket assay in vivo and showed synergism with bFGF. The specificity of KRX-725 was demonstrated via peptide-induced receptor internalization of S1P3 but not S1P1. The ability of a short peptide to stimulate extensive angiogenesis and to synergize with pro-angiogenic factors suggests that KRX-725 may serve as a useful agent in treating pathologic conditions such as peripheral vascular disease, cardiac ischemia, or tissue grafts.
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MESH Headings
- Animals
- Aorta/cytology
- Cells, Cultured
- Dose-Response Relationship, Drug
- Drug Synergism
- Endothelial Growth Factors/pharmacology
- Endothelium, Vascular/cytology
- Fibroblast Growth Factor 2/pharmacology
- GTP-Binding Protein alpha Subunits, Gi-Go/metabolism
- Humans
- I-kappa B Proteins/chemistry
- I-kappa B Proteins/genetics
- I-kappa B Proteins/metabolism
- Intercellular Signaling Peptides and Proteins/pharmacology
- Lymphokines/pharmacology
- MAP Kinase Signaling System/drug effects
- MAP Kinase Signaling System/physiology
- Mice
- Mice, Inbred C57BL
- Mitogen-Activated Protein Kinases/metabolism
- Muscle, Smooth, Vascular/cytology
- NF-KappaB Inhibitor alpha
- Neovascularization, Physiologic/drug effects
- Neovascularization, Physiologic/physiology
- Peptide Fragments/chemical synthesis
- Peptide Fragments/pharmacology
- Protein Structure, Tertiary
- Receptors, Lysophospholipid
- Stem Cell Factor/pharmacology
- Transfection
- Umbilical Veins/cytology
- Vascular Endothelial Growth Factor A
- Vascular Endothelial Growth Factors
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Neef M, Biecker E, Heller J, Schepke M, Nischalke HD, Wolff M, Spengler U, Reichen J, Sauerbruch T. Portal hypertension is associated with increased mRNA levels of vasopressor G-protein-coupled receptors in human hepatic arteries. Eur J Clin Invest 2003; 33:249-55. [PMID: 12641544 DOI: 10.1046/j.1365-2362.2003.01131.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
BACKGROUND The contractile response of human splanchnic vessels to different vasoconstrictors is attenuated in cirrhosis. Functional studies indicate a cellular signalling defect upstream of the G-protein level. The aim of the present study was to analyze expression and mRNA levels of the following most relevant vasopressor receptors in the smooth musculature of human hepatic arteries: alpha1 adrenoceptor (AR) subtypes a, b and d, angiotensin II type 1 receptor (AT1), arginine vasopressin receptor type 1a (V1a), endothelin receptor type A (ETA) and B (ETB). MATERIALS AND METHODS Hepatic arteries were collected from 10 donors (noncirrhotic) and 14 recipients (cirrhotic) at liver transplantations. Real-time-PCR was performed to quantify steady-state levels of receptor mRNAs. RESULTS alpha 1aAR mRNA levels showed no significant difference between the cirrhotic arteries and the controls while the mRNA levels of the other vasoactive receptors were significantly higher in the cirrhotic hepatic arteries (alpha 1bAR: 4-fold, P = 0.013; AT1: 16-fold, P = 0.024; V1a: 23-fold, P = 0.001; ETA: 4-fold, P = 0.02; ETB: 8-fold, P = 0.008). No mRNA for the alpha 1dAR was detected either in the donor or recipient hepatic arteries. CONCLUSION We conclude that vascular hyporeactivity to the most relevant endogenous vasoconstrictors of cirrhotic hepatic arteries is not caused by a receptor down-regulation at mRNA levels. In contrast they were up-regulated.
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MESH Headings
- Adult
- Female
- Hepatic Artery/metabolism
- Humans
- Hypertension, Portal/metabolism
- Male
- Middle Aged
- Polymerase Chain Reaction/methods
- RNA, Messenger/isolation & purification
- RNA, Messenger/metabolism
- Receptors, Adrenergic, alpha/metabolism
- Receptors, Angiotensin/metabolism
- Receptors, Cell Surface/metabolism
- Receptors, Endothelin/metabolism
- Receptors, Vasopressin/metabolism
- Transcription, Genetic
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Affiliation(s)
- M Neef
- Department of Internal Medicine I, University of Bonn, Bonn, Germany.
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Seta K, Nanamori M, Modrall JG, Neubig RR, Sadoshima J. AT1 receptor mutant lacking heterotrimeric G protein coupling activates the Src-Ras-ERK pathway without nuclear translocation of ERKs. J Biol Chem 2002; 277:9268-77. [PMID: 11777928 DOI: 10.1074/jbc.m109221200] [Citation(s) in RCA: 120] [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
Angiotensin II (Ang II) type 1 receptors (AT1Rs) activate tyrosine kinases, including Src. Whether or not tyrosine kinase activation by AT1R occurs independently of heterotrimeric G protein coupling and, if so, the cellular function of such a mechanism are unknown. To address these questions, we used an AT1aR intracellular second loop mutant, which lacks heterotrimeric G protein coupling (AT1a-i2m). Surprisingly, Ang II-induced Src activation was preserved in AT1a-i2m, which was not attenuated by inhibiting protein kinase C and Ca(2+) or by inhibiting Galpha(i) or Galpha(q) in CHO-K1 cells. By contrast, Ang II-induced Src activation was abolished in a C-terminally truncated AT1a-(1--309), where Ang II-induced inositol phosphate response was preserved. Ang II activates ERKs via a Src-Ras-dependent mechanism in AT1a-i2m. ERKs activated by AT1a-i2m phosphorylate their cytoplasmic targets, including p90(RSK), but fail to translocate into the nucleus or to cause cell proliferation. Ang II-induced nuclear translocation of ERKs by wild type AT1aR was inhibited by overexpression of nuclear exportin Crm-1, while that by AT1a-i2m was restored by leptomycin B, an inhibitor of Crm-1. In summary, while Src and ERKs are activated by Ang II even without heterotrimeric G protein coupling, the carboxyl terminus of the AT1 receptor is required for activation of Src. Interestingly, ERKs activated by heterotrimeric G protein-independent mechanisms fail to phosphorylate nuclear targets due to lack of inhibition of Crm-1-induced nuclear export of ERKs. These results suggest that heterotrimeric G protein-dependent and -independent signaling mechanisms play distinct roles in Ang II-mediated cellular responses.
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Affiliation(s)
- Koichi Seta
- Cardiovascular Research Institute, Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey 07103, USA
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