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Fructose Consumption Affects Glucocorticoid Signaling in the Liver of Young Female Rats. Nutrients 2020; 12:nu12113470. [PMID: 33198224 PMCID: PMC7698302 DOI: 10.3390/nu12113470] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2020] [Revised: 10/28/2020] [Accepted: 11/04/2020] [Indexed: 02/06/2023] Open
Abstract
The effects of early-life fructose consumption on hepatic signaling pathways and their relation to the development of metabolic disorders in later life are not fully understood. To investigate whether fructose overconsumption at a young age induces alterations in glucocorticoid signaling that might contribute to development of metabolic disturbances, we analysed glucocorticoid receptor hormone-binding parameters and expression of its target genes involved in gluconeogenesis (phosphoenolpyruvate carboxykinase and glucose-6-phosphatase) and lipid metabolism (lipin-1), as well as redox and inflammatory status in the liver of female rats subjected to a fructose-rich diet immediately after weaning. The fructose diet increased hepatic corticosterone concentration, 11β-hydroxysteroid dehydrogenase type 1 level, glucocorticoid receptor protein level and hormone-binding activity, as well as lipin-1 level. The expression of glucose-6-phosphatase was reduced in fructose-fed rats, while phosphoenolpyruvate carboxykinase remained unaltered. The fructose-rich diet increased the level of fructose transporter GLUT2, while the expression of fructolytic enzymes fructokinase and aldolase B remained unaltered. The diet also affected pro-inflammatory pathways, but had no effect on the antioxidant defence system. In conclusion, a fructose-rich diet applied immediately after weaning promoted lipogenesis and enhanced hepatic glucocorticoid signaling, possibly to protect against inflammatory damage, but without an effect on gluconeogenesis and antioxidant enzymes. Yet, prolonged treatment might ultimately lead to more pronounced metabolic disturbances.
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2
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Seo K, Shin SM. Induction of Lipin1 by ROS-Dependent SREBP-2 Activation. Toxicol Res 2017; 33:219-224. [PMID: 28744353 PMCID: PMC5523558 DOI: 10.5487/tr.2017.33.3.219] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Revised: 05/30/2017] [Accepted: 06/12/2017] [Indexed: 01/26/2023] Open
Abstract
Lipin1 was identified as a phosphatidate phosphatase enzyme, and it plays a key role in lipid metabolism. Since free radicals contribute to metabolic diseases in the liver, this study investigated the effects of free radicals on the regulation of Lipin1 expression in Huh7 and AML12 cells. Hydrogen peroxide induced mRNA and protein expression of Lipin1 in Huh7 cells, which was assayed by quantitative RT-PCR and immunoblotting, respectively. Induction of Lipin1 by hydrogen peroxide was confirmed in AML12 cells. Hydrogen peroxide treatment significantly increased expression of sterol regulatory element-binding protein (SREBP)-2, but not SREBP-1. Moreover, nuclear translocation of SREBP-2 was detected after hydrogen peroxide treatment. Hydrogen peroxide-induced Lipin1 or SREBP-2 expression was significantly reduced by N-acetyl-l-cysteine treatment, indicating that reactive oxygen species (ROS) were implicated in Lipin1 expression. Next, we investigated whether the hypoxic environments that cause endogenous ROS production in mitochondria in metabolic diseases affect the expression of Lipin1. Exposure to hypoxia also increased Lipin1 expression. In contrast, pretreatment with antioxidants attenuated hypoxia-induced Lipin1 expression. Collectively, our results show that ROS activate SREBP-2, which induces Lipin1 expression.
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Affiliation(s)
- Kyuhwa Seo
- College of Pharmacy, Chosun University, Gwangju, Korea
| | - Sang Mi Shin
- College of Pharmacy, Chosun University, Gwangju, Korea
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3
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Kok BPC, Dyck JRB, Harris TE, Brindley DN. Differential regulation of the expressions of the PGC-1α splice variants, lipins, and PPARα in heart compared to liver. J Lipid Res 2013; 54:1662-1677. [PMID: 23505321 DOI: 10.1194/jlr.m036624] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Peroxisome proliferator-activated receptor α (PPARα) and PPARγ coactivator 1α (PGC-1α) are crucial transcriptional regulators for genes involved in FA oxidation. Lipin-1 is essential for this increased capacity for β-oxidation in fasted livers, and it is also a phosphatidate phosphatase involved in triacylglycerol and phospholipid synthesis. Little is known about the regulation of these proteins in the heart during fasting, where there is increased FA esterification and oxidation. Lipin-1, lipin-2, lipin-3, carnitine palmitoyltransferase-1b (Cpt1b), and PGC-1α-b mRNA were increased by glucocorticoids and cAMP in neonatal rat cardiomyocytes. However, Cpt1b upregulation was caused by increased PPARα activation rather than expression. By contrast, the effects of PPARα in fasted livers are mediated through increased expression. During fasting, the expressions of PGC-1α-b and PGC-1α-c are increased in mouse hearts, and this is explained by increased cAMP-dependent signaling. By contrast, PGC-1α-a expression is increased in liver. Contrary to our expectations, lipin-1 expression was decreased and lipin-2 remained unchanged in hearts compared with increases in fasted livers. Our results identify novel differences in the regulation of lipins, PPARα, and PGC-1α splice variants during fasting in heart versus liver, even though the ultimate outcome in both tissues is to increase FA turnover and oxidation.
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Affiliation(s)
- Bernard P C Kok
- Signal Transduction Research Group, University of Alberta, Edmonton, Alberta, Canada
| | - Jason R B Dyck
- Department of Biochemistry, and Cardiovascular Research Centre, University of Alberta, Edmonton, Alberta, Canada; Department of Pediatrics, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada
| | - Thurl E Harris
- Department of Pharmacology, University of Virginia School of Medicine, Charlottesville, Virginia
| | - David N Brindley
- Signal Transduction Research Group, University of Alberta, Edmonton, Alberta, Canada; Department of Pediatrics, Mazankowski Alberta Heart Institute, University of Alberta, Edmonton, Alberta, Canada.
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4
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Kok BPC, Venkatraman G, Capatos D, Brindley DN. Unlike two peas in a pod: lipid phosphate phosphatases and phosphatidate phosphatases. Chem Rev 2012; 112:5121-46. [PMID: 22742522 DOI: 10.1021/cr200433m] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Affiliation(s)
- Bernard P C Kok
- Signal Transduction Research Group, Department of Biochemistry, School of Translational Medicine, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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5
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Ghosh PM, Shu ZJ, Zhu B, Lu Z, Ikeno Y, Barnes JL, Yeh CK, Zhang BX, Katz MS, Kamat A. Role of β-adrenergic receptors in regulation of hepatic fat accumulation during aging. J Endocrinol 2012; 213:251-61. [PMID: 22457517 PMCID: PMC3539306 DOI: 10.1530/joe-11-0406] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Excessive fat accumulation in liver (hepatic steatosis) predisposes to hepatic functional and structural impairment and overall metabolic risk. Previous studies noted an association between hepatic steatosis and age in humans and rodents. However, the mechanisms leading to age-associated hepatic fat accumulation remain unknown. Earlier work from our group showed that β-adrenergic receptor (β-AR) levels and β-AR-stimulated adenylyl cyclase activity increase in rat liver during aging. Here we investigated whether age-associated increases in β-AR signaling play a role in augmenting hepatic lipid accumulation. We demonstrate an increase in hepatic lipid content during senescence and a significant correlation between hepatic fat content and stimulation of adenylyl cyclase activity by the β-AR agonist isoproterenol in rat liver. Isoproterenol administration to young and old rodents in vivo increased hepatic lipid accumulation. Furthermore, in vitro overexpression of β1- and β2-AR subtypes in hepatocytes from young rodents increased cellular lipid content, whereas inhibition of β-ARs by receptor subtype-specific inhibitors reduced lipid levels in hepatocytes from senescent animals. Isoproterenol-induced hepatic lipid accumulation in vivo was prevented by the β-AR nonselective blocker propranolol, suggesting a novel therapeutic effect of this class of drugs in hepatic steatosis. Acipimox, which inhibits adipose tissue lipolysis, did not alter isoproterenol-mediated hepatic fat accumulation; thus β-AR responsive hepatic lipid accumulation does not appear to be related primarily to altered lipolysis. These findings suggest that augmented hepatic β-AR signaling during aging may increase lipid accumulation in liver and advocate a possible role for β-adrenergic blockers in preventing or retarding the development of hepatic steatosis.
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MESH Headings
- Adenylyl Cyclases/metabolism
- Adrenergic beta-Agonists/pharmacology
- Adrenergic beta-Antagonists/pharmacology
- Aging
- Animals
- Cells, Cultured
- Enzyme Activation/drug effects
- Fats/metabolism
- Hepatocytes/drug effects
- Hepatocytes/metabolism
- Imidazoles/pharmacology
- Isoproterenol/pharmacology
- Lipids/analysis
- Liver/metabolism
- Male
- Mice
- Mice, Inbred C57BL
- Propanolamines/pharmacology
- Propranolol/pharmacology
- Rats
- Rats, Inbred F344
- Receptors, Adrenergic, beta/genetics
- Receptors, Adrenergic, beta/metabolism
- Receptors, Adrenergic, beta-1/genetics
- Receptors, Adrenergic, beta-1/metabolism
- Receptors, Adrenergic, beta-2/genetics
- Receptors, Adrenergic, beta-2/metabolism
- Signal Transduction/drug effects
- Time Factors
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Affiliation(s)
- Paramita M Ghosh
- Geriatric Research, Education and Clinical Center (182), Audie L. Murphy Division, South Texas Veterans Health Care System, 7400 Merton Minter Boulevard, San Antonio, Texas 78229, USA
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Khalil MB, Sundaram M, Zhang HY, Links PH, Raven JF, Manmontri B, Sariahmetoglu M, Tran K, Reue K, Brindley DN, Yao Z. The level and compartmentalization of phosphatidate phosphatase-1 (lipin-1) control the assembly and secretion of hepatic VLDL. J Lipid Res 2009; 50:47-58. [DOI: 10.1194/jlr.m800204-jlr200] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
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7
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Zhang P, O'Loughlin L, Brindley DN, Reue K. Regulation of lipin-1 gene expression by glucocorticoids during adipogenesis. J Lipid Res 2008; 49:1519-28. [PMID: 18362392 DOI: 10.1194/jlr.m800061-jlr200] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Lipin-1 deficiency in the mouse causes generalized lipodystrophy, characterized by impaired adipose tissue development and insulin resistance. Lipin-1 expression in differentiating preadipocytes is required for normal expression of adipogenic transcription factors, including peroxisome proliferator-activated receptor gamma and CCAAT enhancer binding protein alpha, and for the synthesis of triacylglycerol. The requirement of lipin-1 for adipocyte differentiation can be explained, in part, by its activity as the sole adipocyte phosphatidic acid phosphatase-1 enzyme, which converts phosphatidate to diacylglycerol, the immediate precursor of triacylglycerol. Here we identify glucocorticoids as the stimulus for the induction of lipin-1 expression in differentiating adipocytes, and characterize a glucocorticoid response element (GRE) in the Lpin1 promoter. The Lpin1 GRE binds to the glucocorticoid receptor and leads to transcriptional activation in adipocytes and hepatocytes, as demonstrated by reporter gene transcription, electrophoretic mobility shift, and chromatin immunoprecipitation assays. This represents the first gene regulatory element identified to directly influence lipin-1 expression levels, and may modulate lipin-1 mRNA levels in adipose tissue and liver in conditions associated with increased local glucocorticoid concentrations in vivo, such as obesity and fasting.
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Affiliation(s)
- Peixiang Zhang
- Department of Human Genetics and Medicine, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, CA 90095, USA
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8
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Manmontri B, Sariahmetoglu M, Donkor J, Bou Khalil M, Sundaram M, Yao Z, Reue K, Lehner R, Brindley DN. Glucocorticoids and cyclic AMP selectively increase hepatic lipin-1 expression, and insulin acts antagonistically. J Lipid Res 2008; 49:1056-67. [PMID: 18245816 DOI: 10.1194/jlr.m800013-jlr200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Glucocorticoids (GCs) increase hepatic phosphatidate phosphatase (PAP1) activity. This is important in enhancing the liver's capacity for storing fatty acids as triacylglycerols (TAGs) that can be used subsequently for beta-oxidation or VLDL secretion. PAP1 catalyzes the conversion of phosphatidate to diacylglycerol, a key substrate for TAG and phospholipid biosynthesis. PAP1 enzymes in liver include lipin-1A and -1B (alternatively spliced isoforms) and two distinct gene products, lipin-2 and lipin-3. We determined the mechanisms by which the composite PAP1 activity is regulated using rat and mouse hepatocytes. Levels of lipin-1A and -1B mRNA were increased by dexamethasone (dex; a synthetic GC), and this resulted in increased lipin-1 synthesis, protein levels, and PAP1 activity. The stimulatory effect of dex on lipin-1 expression was enhanced by glucagon or cAMP and antagonized by insulin. Lipin-2 and lipin-3 mRNA were not increased by dex/cAMP, indicating that increased PAP1 activity is attributable specifically to enhanced lipin-1 expression. This work provides the first evidence for the differential regulation of lipin activities. Selective lipin-1 expression explains the GC and cAMP effects on increased hepatic PAP1 activity, which occurs in hepatic steatosis during starvation, diabetes, stress, and ethanol consumption.
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Affiliation(s)
- Boripont Manmontri
- Signal Transduction Research Group, Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
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9
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Roy S. Melanin, melanogenesis, and vitiligo. FORTSCHRITTE DER CHEMIE ORGANISCHER NATURSTOFFE = PROGRESS IN THE CHEMISTRY OF ORGANIC NATURAL PRODUCTS. PROGRES DANS LA CHIMIE DES SUBSTANCES ORGANIQUES NATURELLES 2007; 88:131-85. [PMID: 17302180 DOI: 10.1007/978-3-211-49389-2_3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Shyamali Roy
- Institute of Natural Products, 8, J. N. Roy Lane, Kolkata 700006, India.
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Martinez Agosto JA, McCabe ER. Conserved family of glycerol kinase loci in Drosophila melanogaster. Mol Genet Metab 2006; 88:334-45. [PMID: 16545593 PMCID: PMC2807631 DOI: 10.1016/j.ymgme.2006.01.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2006] [Accepted: 01/10/2006] [Indexed: 10/24/2022]
Abstract
Glycerol kinase (GK) is an enzyme that catalyzes the formation of glycerol 3-phosphate from ATP and glycerol, the rate-limiting step in glycerol utilization. We analyzed the genome of the model organism Drosophila melanogaster and identified five GK orthologs, including two loci with sequence homology to the mammalian Xp21 GK protein. Using a combination of sequence analysis and evolutionary comparisons of orthologs between species, we characterized functional domains in the protein required for GK activity. Our findings include additional conserved domains that suggest novel nuclear and mitochondrial functions for glycerol kinase in apoptosis and transcriptional regulation. Investigation of GK function in Drosophila will inform us about the role of this enzyme in development and will provide us with a tool to examine genetic modifiers of human metabolic disorders.
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Affiliation(s)
- Julian A. Martinez Agosto
- Department of Pediatrics, David Geffen School of Medicine at UCLA; and Mattel Children’s Hospital at UCLA, USA
| | - Edward R.B. McCabe
- Department of Pediatrics, David Geffen School of Medicine at UCLA; and Mattel Children’s Hospital at UCLA, USA
- Department of Human Genetics, David Geffen School of Medicine at UCLA; UCLA Molecular Biology Institute; and UCLA Biomedical Engineering Interdepartmental Training Program, USA
- Corresponding author. Fax: +1 310 267 2045. (E.R.B. McCabe)
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11
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Iida S, Sato Y, Nakaya A, Shinohara Y, Hayashi Y, Sawada A, Nagata H, Kaji N, Kamiya H, Baba Y, Harashima H. Genome Wide Expression Analysis of White Blood Cells and Liver of Pre-diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) Rats Using a cDNA Microarray. Biol Pharm Bull 2006; 29:2451-9. [PMID: 17142981 DOI: 10.1248/bpb.29.2451] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In a prior study, we reported on a significant decrease in calpain10 gene expression in white blood cells (WBC) as well as the major insulin-target tissues including liver and adipose tissue, before the onset of diabetes in Otsuka Long-Evans Tokushima Fatty (OLETF) rats. In this study, we extended our hypothesis that some type 2 diabetes mellitus (NIDDM) susceptible genes are up/down-regulated before the onset in WBC of OLETF rats, reflecting their up/down-regulation in major insulin-target tissues, such as the liver. We tested this hypothesis using rat cDNA microarrays. The findings show that 1080 genes are up/down-regulated by more than 2-fold compared to the controls, Long-Evans Tokushima Otsuka rats, before the onset in WBC and liver under fasted or insulin administered condition. Fifty-seven of the 1080 genes were up/down-regulated in both WBC and the liver. More than half have been reported to NIDDM susceptible genes and the remainder have not been reported to be related to NIDDM. These results indicate that there some NIDDM related genes are up/down-regulated in WBC before the onset of diabetes.
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Affiliation(s)
- Shinya Iida
- Laboratory for Molecular Design of Pharmaceutics, Graduate School of Pharmaceutical Sciences, Hokkaido University, Japan
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12
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Westergaard N, Madsen P, Lundgren K. Characterization of glycerol uptake and glycerol kinase activity in rat hepatocytes cultured under different hormonal conditions. BIOCHIMICA ET BIOPHYSICA ACTA 1998; 1402:261-8. [PMID: 9606984 DOI: 10.1016/s0167-4889(98)00016-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Glycerol uptake and glycerol kinase activity were studied in primary cultures of rat hepatocytes in the presence of either 1 nM insulin, 1 nM glucagon, or 100 nM dexamethasone, alone or in combination in the culture medium. Glycerol uptake exhibited saturation kinetic with K(m) values (microM) and Vmax (nmol/min x mg protein) ranging from 250-402, and 7.9-10.1, respectively. The corresponding K(m) and Vmax values for glycerol kinase activity were 36-46 and 8.7-12.7. Using the metabolic uncoupler 2,4-dinitrophenol, glycerol uptake and the cellular content of glycerol phosphorylated metabolites were reduced 33% and 43%, respectively, whereas no decrease in the cellular content of glycerol was seen. The glycerol analogues monoacetin, monobutyrin and dihydroxypropyl dichloroacetate were able in a concentration-dependent manner to inhibit glycerol uptake into hepatocytes with the two latter having IC50 values of approximately 1 mM. Moreover, it was demonstrated that the three glycerol analogues were substrates for glycerol kinase, which indicates a competitive mode of inhibition. The kinetic parameters for these substrates were calculated by using glycerol kinase from Candida Mycoderma. Monobutyrin was found to be 4 times lees efficient as substrate compared to the other substrates. Overall, these results indicate that independently of the culture conditions, glycerol uptake is the rate-limiting step in glycerol metabolism, and that the investigated glycerol analogues are metabolized via the same route as glycerol.
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13
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Burns K, Opas M, Michalak M. Calreticulin inhibits glucocorticoid- but not cAMP-sensitive expression of tyrosine aminotransferase gene in cultured McA-RH7777 hepatocytes. Mol Cell Biochem 1997; 171:37-43. [PMID: 9201693 DOI: 10.1023/a:1006865108833] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Calreticulin is a ubiquitously expressed Ca2+ binding protein of the endoplasmic reticulum which inhibits DNA binding and transcriptional activation by steroid hormone receptors. In this study the effects of calreticulin on tyrosine aminotransferase (TAT) gene expression in cultured McA-RH7777 hepatocytes was investigated. McA-RH7777 cells were stably transfected with calreticulin expression vector to generate cells overexpressing the protein. The transcriptional activity of the TAT gene, which is glucocorticoid-sensitive and cAMP-dependent, was investigated in the mock transfected McA-RH7777 and in cells overexpressing calreticulin (designated McA-11 and McA-17). In the presence of dexamethasone or the cAMP analog (CTP-cAMP) expression of the TAT gene was induced in mock transfected McA-RH7777 cells by approximately 4.5 and 5 fold, respectively. In McA-11 and McA-17 cells, overexpressing calreticulin, glucocorticoid-sensitive expression of the TAT gene was significantly inhibited, however, the CTP-cAMP-dependent expression of the TAT gene was not affected. The ability of calreticulin to inhibit glucocorticoid-sensitive TAT gene expression but not the cAMP-dependent expression of the gene suggests that the protein affects specifically the action of transcription pathways involving steroid receptors or transcription factors containing KxFF(K/R)R-like motifs. Calreticulin may play an important role in the regulation of glucocorticoid-sensitive pathway of expression of the hepatocytes specific genes during development.
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Affiliation(s)
- K Burns
- MRC Group in Molecular Biology of Membranes, University of Alberta, Edmonton, Canada
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Pittner RA. Lack of effect of calcitonin gene-related peptide and amylin on major markers of glucose metabolism in hepatocytes. Eur J Pharmacol 1997; 325:189-97. [PMID: 9163566 DOI: 10.1016/s0014-2999(97)00132-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Effects of amylin and calcitonin gene-related peptide on several processes involved in carbohydrate metabolism were investigated in rat hepatocytes, non-parenchymal cells (Kupffer, Ito and endothelial cells) and alveolar macrophages. In hepatocytes, cAMP levels were increased 25-fold by glucagon (10 nM), less than 2-fold by calcitonin gene-related peptide (100 nM) and not at all by amylin (100 nM). In non-parenchymal cells and cultured alveolar macrophages, calcitonin gene-related peptide potently, and amylin weakly, stimulated cAMP levels. In hepatocytes neither amylin nor calcitonin gene-related peptide affected glycogen phosphorylase activity, glucose output, lactate uptake, glycogen synthesis, glycogen mass or tyrosine aminotransferase activity. The density of calcitonin gene-related peptide specific binding sites in parenchymal cells was 10-fold less then seen in non-parenchymal cells. We found no significant evidence of specific amylin binding sites. These results are consistent with the notion that amylin does not exert a direct effect in hepatocytes. However, we do not rule out that amylin may affect hepatic glucose output indirectly through Cori cycling of lactate derived from skeletal muscle or from interactions through non-parenchymal cells.
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Affiliation(s)
- R A Pittner
- Amylin Pharmaceuticals, Inc., San Diego, CA 92121-3027, USA.
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Dixon MC, Yeaman SJ, Agius L, Day CP. Transforming growth factor beta increases the activity of phosphatidate phosphohydrolase-1 in rat hepatocytes. Biochem Biophys Res Commun 1997; 230:365-9. [PMID: 9016785 DOI: 10.1006/bbrc.1996.5965] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Phosphatidic acid (PA) is a potent second messenger arising from growth factor-induced stimulation of phospholipase D which hydrolyses phosphatidylcholine. PA is hydrolysed to diacylglycerol by PA phosphohydrolase (PAP) which exists in two forms: PAP-1 and PAP-2. In rat hepatocyte cultures, overnight (20h) incubation with transforming growth factor (TGF) beta (1 ng/ml) increased PAP-1 activity two-fold. This effect was concentration and time dependent and was greatest at low cell density. The TGFbeta effect on PAP-1 was additive to stimulation induced by dexamethasone but not by glucagon and it reversed the inhibition by insulin. Epidermal growth factor had no effect on PAP-1 activity. None of the above hormones or growth factors affected the subcellular distribution of PAP-1. Stimulation of PAP-1 by TGFbeta may be involved in mediating some of its biological effects.
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Affiliation(s)
- M C Dixon
- Department of Medicine, Medical School, University of Newcastle, Framlington Place, Newcastle upon Tyne, United Kingdom
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16
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Chakraborty DP, Roy S, Chakraborty AK. Vitiligo, psoralen, and melanogenesis: some observations and understanding. PIGMENT CELL RESEARCH 1996; 9:107-16. [PMID: 8888309 DOI: 10.1111/j.1600-0749.1996.tb00098.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Since the etiology of vitiligo is still unknown, we searched for some abnormal biochemical parameters, if any, in subjects with vitiligo. Higher urinary excretion of indole metabolites in vitiliginous patients have been noted, in association with higher dioxygenase, superoxide dismutase, and tyrosine aminotransferase activity in their serum. Similar results have also been found in an animal model, Bufo melanostictus, during induced tyrosinase inhibition. Treatment with psoralen can reverse the parameters, except tyrosine aminotransferase, to a normal level. Although psoralens are not the magic bullet for the therapy of vitiligo, they are still being used as a chemotherapeutic agent against vitiligo on a major scale to date. Tryptophan was found to participate in the pathway of melanogenesis, as a precursor as well as a positive regulator of tyrosinase. Its behavior in this regard is much more similar to the conventional substrates tyrosine and dopa (dihydroxyphenylalanine). In consideration of combined participation of tyrosine and tryptophan in the synthesis of melanin and its breakdown, the possible influence of different enzymatic reactions, like mono-oxygenase, dioxygenase, and deamination, has been suggested.
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17
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Wang CN, McLeod RS, Yao Z, Brindley DN. Effects of dexamethasone on the synthesis, degradation, and secretion of apolipoprotein B in cultured rat hepatocytes. Arterioscler Thromb Vasc Biol 1995; 15:1481-91. [PMID: 7670964 DOI: 10.1161/01.atv.15.9.1481] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Oversecretion of apoB and decreased removal of apoB-containing lipoproteins by the liver results in hyperapobetalipoproteinemia, which is a risk factor for atherosclerosis. We investigated how dexamethasone, a synthetic glucocorticoid, affects the synthesis, degradation, and secretion of apoB-100 and apoB-48. Primary rat hepatocytes were incubated with dexamethasone for 16 hours. Incorporation of [35S]methionine into apoB-48 and apoB-100 was increased by 36% and 50%, respectively, with 10 nmol/L dexamethasone, despite a 28% decrease of incorporation into total cell proteins. However, Northern blot analysis revealed that dexamethasone (1 to 1000 nmol/L) did not significantly alter the steady-state concentrations of apoB mRNA, suggesting that the net increase in apoB synthesis may involve increased translational efficiency. The intracellular retention and the rate and efficiency of apoB secretion were determined by pulse-chase experiments in which the hepatocytes were labeled with [35S]methionine for 10 minutes or 1 hour, and the disappearance of labeled apoB from the cells and its accumulation in the medium were monitored. Degradation of labeled apoB-100 after a 3-hour chase in both protocols was decreased from about 50% to 30%, whereas degradation of apoB-48 was decreased from 30% to 10% to 20% by treatment with 10 or 100 nmol/L dexamethasone. Additionally, the half-life of decay (time required for 50% of labeled cell apoB-100 to disappear from the peak of radioactivity following a 10-minute pulse) was increased by treatment with 10 nmol/L dexamethasone from 77 to 112 minutes, and the value for apoB-48 increased from 145 to 250 minutes. Treatment with 100 nmol/L dexamethasone also stimulated secretion of 35S-labeled apoB-100 and apoB-48 by twofold and 1.5-fold, respectively. The increased secretion of apoB-100 and apoB-48 after dexamethasone treatment was confirmed by immunoblot analysis for apoB mass, and the effect was relatively specific since albumin secretion was not significantly changed. We conclude that glucocorticoids promote the secretion of hepatic apoB-containing lipoproteins by increasing the net synthesis of apoB-100 and apoB-48 and by decreasing the intracellular degradation of newly synthesized apoB. An increased action of glucocorticoids coupled with a decreased ability of insulin to suppress these effects in insulin resistance can lead to hyperapobetalipoproteinemia and an increased risk of atherosclerosis.
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Affiliation(s)
- C N Wang
- Department of Biochemistry, University of Alberta, Edmonton, Canada
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18
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Marra CA, de Alaniz MJ. Regulatory effect of various steroid hormones on the incorporation and metabolism of [14C]stearate in rat hepatoma cells in culture. Mol Cell Biochem 1995; 145:1-9. [PMID: 7659072 DOI: 10.1007/bf00925706] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have examined the incorporation and metabolism of [14C] stearic acid within the total lipids of HTC rat-hepatoma cells in suspension culture in presence and in absence of steroidal hormone stimulation. Both, glucocorticoids (dexamethasone, cortisol and corticosterone) and mineralocorticoids (deoxycorticosterone and aldosterone) as well as the estrogen beta-estradiol and the androgen testosterone enhanced the extent of delta 9 desaturation to oleic acid of the saturated precursors, whereas only the two mineralocorticoids affected the incorporation rate of the exogenous acid into total cellular lipids, thus promoting a little stimulation. Furthermore, all the hormones tested increased the radiolabelling of the total cellular phospholipids except deoxycorticosterone and testosterone, the former having no effect and the latter exerting a moderate inhibition. On the other hand, the incorporation of 14C into neutral lipids was stimulated by testosterone, in contrast to the inhibition of this parameter observed exclusively with either the mineralocorticoids or the estrogen. Within the phospholipid subclasses, the radiolabelling of phosphatidylcholine was augmented by means of all the steroids tested save deoxycorticosterone and testosterone, whereas phosphatidylethanolamine exhibited a decrease only in the presence of testosterone. In a similar fashion, within the neutral lipids, the predominating triglyceride fraction was preferentially labelled--at the expense of other subclasses of lesser abundance--upon treatment with the steroids except aldosterone, which exerted no effect. The results obtained were correlated with those changes observed in the mass distribution of the different lipid subclasses either with or without prior hormonal stimulation.
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Affiliation(s)
- C A Marra
- Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP), CONICET-UNLP, Facultad de Ciencias Médicas, Argentina
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19
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Höer A, Oberdisse E. Characterization of a phosphatidic acid phosphatase from rat brain cell membranes. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1994; 350:653-61. [PMID: 7708122 DOI: 10.1007/pl00004905] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We have characterized a phosphatidic acid phosphatase (PAP, EC 3.1.3.4) that is associated with cell membranes from rat brain using [32P]phosphatidic acid as substrate in a simple assay. The enzyme could be activated by Triton X-100, cholic acid and Chaps and inhibited by Lubrol PX and sodium dodecyl sulfate. The optimal pH was between 6.0 and 7.0 Mg2+ was not essential for enzyme activity. The enzyme activity was decreased by about 50% by Ca2+ at concentrations of 0.1 to 1 mmol/l. Zn2+ inhibited the enzyme by 50% at concentrations of about 10 mumol/l in the absence of, and 100 nmol/l in the presence (3 mmol/l) of, Triton X-100. NaF decreased the activity by about 50% at concentrations between 0.3 and 1 mmol/l when Triton X-100 was added, but did not inhibit the enzyme if the detergent was not present. N-Ethylmaleimide (NEM) did not affect the enzyme. In the absence of Triton X-100, propranolol and metoprolol enhanced the PAP activity. In the presence of 3 mmol/l Triton X-100, the enzyme was inhibited by about 50% by propranolol at a concentration of 10 mmol/l, whereas metoprolol caused only a slight inhibition of PAP. The Km for phosphatidic acid was 150 mumol/l and was changed to 20 mumol/l by 3 mmol/l Triton X-100 without the Vmax being changed. Enzyme activity could be solubilized by 1-5% (w/v) Triton X-100. Gel filtration chromatography showed a M(r) of 320,000. This membrane-associated PAP from neuronal tissue probably belongs among the NEM-insensitive forms of PAP enzymes which have been proposed to play a role in transmembrane signal transduction via phospholipase D.
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Affiliation(s)
- A Höer
- Institut für Pharmakologie, Freien Universität Berlin, Germany
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20
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Day CP, Yeaman SJ. The biochemistry of alcohol-induced fatty liver. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1215:33-48. [PMID: 7948006 DOI: 10.1016/0005-2760(94)90089-2] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- C P Day
- Department of Biochemistry, Medical School, University of Newcastle, UK
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21
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Byrne CD, Wareham NJ, Brown DC, Clark PM, Cox LJ, Day NE, Palmer CR, Wang TW, Williams DR, Hales CN. Hypertriglyceridaemia in subjects with normal and abnormal glucose tolerance: relative contributions of insulin secretion, insulin resistance and suppression of plasma non-esterified fatty acids. Diabetologia 1994; 37:889-96. [PMID: 7806018 DOI: 10.1007/bf00400944] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Although plasma insulin and triglyceride concentrations are positively correlated in many studies, the relationships between insulin resistance, insulin secretion and hypertriglyceridaemia remain unclear. To study these associations, subjects between the ages of 40 and 64 were randomly selected from a general practice register and invited to attend for a standard oral glucose tolerance test for measurement of insulin, triglyceride and non-esterified fatty acid concentrations. The study comprised 1122 subjects who were not previously known to have diabetes and who completed the test. Using the World Health Organisation criteria, 51 subjects were classified to have non-insulin-dependent diabetes mellitus, 188 had impaired glucose tolerance and 883 subjects had normal glucose tolerance. Triglyceride concentrations in subjects with glucose intolerance were elevated compared to those in control subjects, even after adjustment for age, obesity and gender (p < 0.001 for subjects with diabetes and p < 0.01 for those with impaired glucose tolerance compared to normal subjects). In separate multiple regression analyses for males and females, the most important determinants of the plasma triglyceride concentration were the area under the non-esterified fatty acid suppression curve (p < 0.001 in both genders) and the waist-hip ratio (p < 0.001 for men and < 0.01 for women). The fasting insulin concentration was independently associated with triglyceride concentration in women only (p < 0.01). The most important determinant of the area under the non-esterified fatty acid suppression curve in men was the 30-min insulin increment, a measure of insulin secretion, (p < 0.001) whereas for women age (p < 0.001) and the body mass index (p < 0.01) were the most important.
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Affiliation(s)
- C D Byrne
- University Department of Clinical Biochemistry, Addenbrooke's Hospital, Cambridge, UK
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22
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Day CP, James OF, Brown AS, Bennett MK, Fleming IN, Yeaman SJ. The activity of the metabolic form of hepatic phosphatidate phosphohydrolase correlates with the severity of alcoholic fatty liver in human beings. Hepatology 1993; 18:832-8. [PMID: 8406356 DOI: 10.1002/hep.1840180413] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Increased esterification of fatty acids to triglyceride is common to most of the mechanisms proposed to explain the causation of alcoholic fatty liver. However, it is unclear whether this is caused by increased substrate supply or whether direct stimulation of the enzymes of the esterification pathway occurs after excessive alcohol intake. The rate-limiting step in triglyceride synthesis is catalyzed by the enzyme phosphatidate phosphohydrolase, which is present in the cytosol and microsomes and is sensitive to inhibition by N-ethylmaleimide. This enzyme is physically distinct from a second form of phosphatidate phosphohydrolase that is located predominantly in the plasma membrane, is insensitive to N-ethylmaleimide inhibition and has a putative role in cell-signaling. We have investigated whether the activity of the N-ethylmaleimide-sensitive ("metabolic") form of phosphatidate phosphohydrolase is increased in patients with alcoholic liver disease and whether any increased activity correlates with the severity of steatosis. N-ethylmaleimide-sensitive and -insensitive phosphatidate phosphohydrolase activities were measured in needle liver biopsy specimens from 42 alcoholic patients and 6 patients with primary biliary cirrhosis and in wedge biopsy specimens from 6 normal patients undergoing routine cholecystectomy. Steatosis was "scored" on coded slides from 0 to 3. N-ethylmaleimide-sensitive activity was higher in alcoholic biopsy specimens scoring 3 (3.25 +/- 0.4 units/mg protein, n = 10) than in those scoring either 0 (1.21 +/- 0.2, n = 14) or 1 to 2 (1.58 +/- 0.2, n = 18), and it was also higher than in biopsy specimens from normal and primary biliary cirrhosis patients (1.65 +/- 0.3, n = 12; p < 0.0001, analysis of variance).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- C P Day
- Department of Biochemistry and Genetics, Medical School, University of Newcastle, United Kingdom
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23
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Affiliation(s)
- C A Seymour
- Department of Clinical Biochemistry and Metabolism, St George's Hospital Medical School, London, UK
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24
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Skarlatos SI, Rao R, Kruth HS. Accelerated development of human monocyte-macrophages cultured on Plastek-C tissue culture dishes. ACTA ACUST UNITED AC 1992. [DOI: 10.1007/bf01409100] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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25
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Gomez-Muñoz A, Hamza EH, Brindley DN. Effects of sphingosine, albumin and unsaturated fatty acids on the activation and translocation of phosphatidate phosphohydrolases in rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1127:49-56. [PMID: 1320939 DOI: 10.1016/0005-2760(92)90200-f] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The activities of two phosphatidate phosphohydrolases were measured in cultured rat hepatocytes incubated with 0.1 mM albumin. The activity, which is inhibited by N-ethylmaleimide (PAP-1) is located in the cytosolic and membrane fractions. PAP-1 activity is stimulated by Mg2+ and it can be translocated from the cytosol to the membranes by relatively low (0.5-1 mM) concentrations of fatty acids. In addition, higher concentrations (1-3 mM) of fatty acids cause an increase in the total PAP-1 activity. Translocation of PAP-1 activity in the hepatocytes is preferentially promoted by unsaturated fatty acids (C18:1, C18:2, C18:3, C20:4 and C20:5), rather than by saturated acids (C14:0, C16:0, C18:0). Increasing the extracellular concentration of albumin from 30 microM to 1 mM displaces PAP-1 activity from the membrane fraction. Sphingosine, but not staurosporine, can inhibit the redistribution of PAP-1 activity induced by oleate. The amphiphilic amines, sphingosine, chlorpromazine and propranolol, also decrease membrane-bound PAP-1 activity in the absence of fatty acids, but they do not alter, significantly, the activity of the cytosolic PAP-1. In the presence of 1 mM oleate, sphingosine, chlorpromazine and propranolol decrease the translocation of PAP-1 from the cytosol to the membranes. The phosphohydrolase activity, which is insensitive to N-ethylmaleimide (PAP-2), is specifically located in the plasma membrane (Jamal, Z., Martin, A., Gomez-Muñoz, A. and Brindley, D.N. (1991) J. Biol. Chem. 266, 2988-2996) and it is not stimulated by Mg2+. Saturated fatty acids, albumin, sphingosine and propranolol have no significant effects on PAP-2 activity. However, chlorpromazine decreases PAP-2 activity by about 14%. Linolenate, arachidonate and eicosapentaenoate at 1 mM also produced small (7-10%) decreases in PAP-2 activity. It is proposed that both PAP-1 and PAP-2 activities may be involved in signal transduction, although the main function of PAP-1 seems to be involved in the synthesis of glycerolipids.
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Affiliation(s)
- A Gomez-Muñoz
- Department of Biochemistry, University of Alberta, Edmonton, Canada
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26
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Pandis N, Heim S, Bardi G, Limon J, Mandahl N, Mitelman F. Improved technique for short-term culture and cytogenetic analysis of human breast cancer. Genes Chromosomes Cancer 1992; 5:14-20. [PMID: 1384657 DOI: 10.1002/gcc.2870050103] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Various growth media and procedures for tissue disaggregation and culturing were tested with regard to cell attachment, the type of cells to grow out, and the emergence of cytogenetically abnormal clones in cultures of 20 primary breast carcinomas. Clonal chromosome abnormalities were detected in 16 cases (80%). Our findings allow us to suggest a series of modifications of existing culturing and chromosome preparation techniques for breast cancer cytogenetic analysis. The improvements include: (1) combined mechanical and enzymatic disaggregation of the tumor samples, (2) initiation of short-term cultures in plastic flasks that have a Primaria-modified tissue culture surface or have been coated with Vitrogen 100, (3) use of serum-free growth medium, CDM-5, but with temporary (24 hours) enrichment with 20% FBS if rapid cell attachment is not achieved, (4) partial and sequential harvesting of the cultures, and (5) use of minimal volumes of hypotonic and fixative solutions during harvesting.
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Affiliation(s)
- N Pandis
- Department of Clinical Genetics, Lund University Hospital, Sweden
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27
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Pittner RA, Spitzer JA. Endotoxin and TNF alpha directly stimulate nitric oxide formation in cultured rat hepatocytes from chronically endotoxemic rats. Biochem Biophys Res Commun 1992; 185:430-5. [PMID: 1599481 DOI: 10.1016/s0006-291x(05)81003-4] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
We examined the effects of endotoxin on nitric oxide formation in isolated rat hepatocytes in primary culture. Endotoxin was administered either in vivo, by continuous infusion for 30 or 3 h, or in vitro, on cultured cells. The spontaneous production of nitrites in hepatocytes from in vivo ET-infused rats was lower than equivalent saline controls in the absence of added stimuli. However in vitro addition of endotoxin in culture to hepatocytes from 30 h ET-infused rats greatly enhanced production relative to saline controls. This effect was mimicked by TNF alpha, and activators of protein kinase C (PMA and Ca2+ ionophore A23187). The effects of ET were blocked by NMMA, dexamethasone and protein synthesis inhibitors Actinomycin D and cycloheximide. No in vitro effect of ET was observed in the 3 h infusion model. The results show that chronic exposure to sub-lethal levels of ET primes liver parenchymal cells for the production of nitric oxide, when exposed in vitro to ET or TNF alpha.
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Affiliation(s)
- R A Pittner
- Louisiana State University Medical Center, Department of Physiology, New Orleans 70112-1393
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28
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Stals HK, Mannaerts GP, Declercq PE. Factors influencing triacylglycerol synthesis in permeabilized rat hepatocytes. Biochem J 1992; 283 ( Pt 3):719-25. [PMID: 1590762 PMCID: PMC1130945 DOI: 10.1042/bj2830719] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Rat hepatocytes were treated with Staphylococcus aureus alpha-toxin to permeabilize their plasma membrane for low-molecular-mass compounds. During incubation with 1 mM labelled fatty acid, phosphatidate and, less clearly, lysophosphatidate rapidly reached a steady state, whereas labelled diacylglycerol accumulated to some extent, at least in the absence of exogenous CDP-choline. Esterification and oxidation were linearly related to the fatty acid concentration, and there was no indication for saturation with acyl-CoA. However, when permeabilized cells were incubated with labelled sn-glycerol 3-phosphate and 1 mM unlabelled fatty acid, glycerolipid synthesis and the level of esterification intermediates reached a plateau between 0.25 and 0.50 mumol of the triose phosphate/ml. The synthesis of phosphatidylcholine was dependent on addition of CDP-choline. In presence of the latter, diacylglycerol no longer accumulated and triacylglycerol synthesis was suppressed, although the sum of synthesized diacylglycerol, triacylglycerol and phosphatidylcholine remained constant. This indicates that the same pool of diacylglycerol is shared by choline-phosphotransferase and diacylglycerol acyltransferase and that the relative activity of these enzymes depends on the CDP-choline supply. Comparison of the levels of the esterification intermediates with the activity of the respective steps of the pathway reveals that, at a fixed fatty acid concentration, glycerophosphate acyltransferase determines the esterification rate, whereas lysophosphatidate acyltransferase and, at low CDP-choline levels, diacylglycerol acyltransferase approach saturation at elevated sn-glycerol 3-phosphate concentration. There is, however, no indication for a regulatory role of phosphatidate phosphohydrolase in this system. The significance of these findings for the regulation of triacylglycerol synthesis under conditions in vivo is discussed.
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Affiliation(s)
- H K Stals
- Katholieke Universiteit Leuven, Belgium
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29
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Pittner RA, Fain JN. Ethanol is a potent stimulator of phosphatidylcholine breakdown in cultured rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1992; 1133:316-20. [PMID: 1737064 DOI: 10.1016/0167-4889(92)90053-e] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Addition of ethanol (17 to 340 mM) to cultured rat hepatocytes stimulated the breakdown of phosphatidylcholine phospholipases D and C as measured by an increase in the rate of release of choline and phosphocholine into the medium. The effects of ethanol were mimicked by propanol, dimethylsulfoxide and to a lesser extent methanol. The magnitude of the stimulation seen with ethanol was equivalent to and additive to that produced by glucagon vasopressin, norepinephrine, A23187 or PMA. In contrast, ethanol (340 mM) stimulated PI-specific phospholipase C activity by less than 20%. An equivalent stimulation of PC-specific phospholipase D and C was seen with as little as 20 mM ethanol and a 100% increase was seen with 340 mM ethanol. Ethanol did not significantly affect the ability of vasopressin, norepinephrine, ATP or A23187 to stimulate PI-specific phospholipase C. It is concluded that while ethanol is only a weak stimulator of PI-specific phospholipase C, it is a potent stimulator of phosphatidylcholine breakdown in rat hepatocytes.
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Affiliation(s)
- R A Pittner
- Department of Biochemistry, University of Tennessee, Memphis
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30
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Byrne CD, Brindle NP, Wang TW, Hales CN. Interaction of non-esterified fatty acid and insulin in control of triacylglycerol secretion by Hep G2 cells. Biochem J 1991; 280 ( Pt 1):99-104. [PMID: 1660268 PMCID: PMC1130605 DOI: 10.1042/bj2800099] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The role of insulin in the regulation of plasma triacylglycerol is poorly understood. Conflicting actions of insulin on rat liver cells have been reported, insulin inhibiting triacylglycerol secretion in short incubations (less than 24 h) and stimulating triacylglycerol secretion in longer incubations (48-72 h). The present study was undertaken to examine regulation of triacylglycerol secretion by insulin and investigate the interaction between insulin and non-esterified fatty acid over 72 h in human hepatoblastoma (Hep G2) cells. Insulin inhibited triacylglycerol secretion throughout the 72 h period. The inhibition increased from 66% in the first 24 h to 88% in the final 24 h. Increasing the initial concentration of oleic acid from 200 microM to 1000 microM resulted in a 358% increase in triacylglycerol secretion and a 712% increase in accumulation over 24 h. Oleic acid uptake by the cells was rapid, with only 2.4% of the initial concentration (500 microM) remaining after 24 h. Supplementation of the medium with oleic acid to maintain the concentration between 750 microM and 1000 microM throughout a 5 h period resulted in a 350% increase in triacylglycerol secretion. Supplementation also decreased the insulin-induced inhibition of triacylglycerol secretion (18.2 to 7.8%; P less than 0.001). These results demonstrate that there is not a biphasic action of insulin on triacylglycerol secretion by Hep G2 cells. Experiments of this nature have not previously taken into account the rapid uptake of non-esterified fatty acid by hepatocytes and have consequently underestimated the effect of a sustained concentration on triacylglycerol metabolism. Oleic acid is therefore an even more potent stimulus to triacylglycerol synthesis and secretion than has previously been recognized. In addition, in the presence of a sustained increase in oleic acid concentration, there is a decrease in the action of insulin to inhibit triacylglycerol secretion.
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Affiliation(s)
- C D Byrne
- University Department of Clinical Biochemistry, Addenbrooke's Hospital, Cambridge, U.K
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31
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Hermier D, Hales P, Brindley DN. Biphasic effects of glucagon and cyclic AMP on the synthesis and secretion of lipids by rat hepatocytes. Biochem J 1991; 279 ( Pt 3):705-9. [PMID: 1659386 PMCID: PMC1151503 DOI: 10.1042/bj2790705] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Cultured rat hepatocytes were preincubated with glucagon or a cyclic AMP analogue for up to 24 h and lipid synthesis and secretion were determined during the next 2 h. Glucagon or cyclic AMP did not change the incorporation of choline or glycerol into phosphatidylcholine, or choline into sphingomyelin, in the cells after 0-12 h of preincubation. After 12 h these incorporations were increased. Incorporations into hepatic lysophosphatidylcholine were decreased after preincubation with glucagon or cyclic AMP for 0-12 h, but by 24 h they increased. There was no change in the lysophosphatidylcholine in the medium after preincubation with glucagon or cyclic AMP for up to 6 h, but increases occurred after preincubation from 12 to 24 h. The secretion of triacylglycerol was decreased after preincubation for 0-1 h, but it returned to control values after 4 h. After preincubation for 18-24 h the incorporation of glycerol into secreted triacylglycerol was increased. The results are discussed in relation to the control of lipid metabolism in starvation and diabetes.
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Affiliation(s)
- D Hermier
- Department of Biochemistry, Faculty of Medicine, University of Alberta, Edmonton, Canada
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32
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Hermier D, Hales P, Brindley DN. Effects of the lipase inhibitors, Triton WR-1339 and tetrahydrolipstatin, on the synthesis and secretion of lipids by rat hepatocytes. FEBS Lett 1991; 286:186-8. [PMID: 1864367 DOI: 10.1016/0014-5793(91)80970-e] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The lipase inhibitors, Triton WR-1339 and tetrahydrolipstatin, were incubated with rat hepatocytes. Triton WR-1339 increased the recovery of triacylglycerol in the hepatocytes and incubation medium by 31% and 38%, respectively. Tetrahydrolipstatin decreased the accumulation of newly synthesized, and of total triacylglycerol in the medium. This compound might be useful in determining mechanisms involved in intracellular triacylglycerol metabolism and the secretion of very low density lipoproteins.
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Affiliation(s)
- D Hermier
- Department of Biochemistry, Faculty of Medicine, University of Alberta, Edmonton, Canada
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33
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Pittner RA, Fain JN. Activation of membrane protein kinase C by glucagon and Ca(2+)-mobilizing hormones in cultured rat hepatocytes. Role of phosphatidylinositol and phosphatidylcholine hydrolysis. Biochem J 1991; 277 ( Pt 2):371-8. [PMID: 1859365 PMCID: PMC1151243 DOI: 10.1042/bj2770371] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We found that glucagon stimulated membrane protein kinase C (PKC) activity and phosphatidylcholine hydrolysis in 24 h-cultured rat hepatocytes. Phorbol myristate acetate, 8-bromo cyclic AMP, vasopressin, noradrenaline and the Ca2+ ionophore A23187 also stimulated membrane PKC activity. However, only vasopressin and noradrenaline stimulated inositol phosphate accumulation, whereas all agonists stimulated the rate of release of water-soluble choline metabolites into the medium. Choline, and to a much lesser extent phosphocholine, were released, suggesting predominantly phospholipase D activation. This was supported by the finding that the accumulation of phosphatidate and diacylglycerol was enhanced by the agents in [3H]myristate-labelled hepatocytes, as was [32P]phosphatidylethanol formation. Since the time courses for the release of choline into the medium and the accumulation of phosphatidate and diacylglycerol caused by vasopressin and glucagon were similar, the more rapid activation of PKC by vasopressin probably reflects diacylglycerol formation from phosphoinositide breakdown. The inability of glucagon to stimulate inositol phosphate production was not due to the prolonged culture, since similar results were obtained in 4 h cultures. We conclude that the stimulation of membrane PKC activity by glucagon correlates with accumulation of diacylglycerol and phosphatidate derived from the hydrolysis of phosphatidylcholine.
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Affiliation(s)
- R A Pittner
- Department of Biochemistry, University of Tennessee, Memphis
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34
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Henly DC, Berry MN. Relationship between the stimulation of citric acid cycle oxidation and the stimulation of fatty acid esterification and inhibition of ketogenesis by lactate in isolated rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1092:277-83. [PMID: 1828700 DOI: 10.1016/s0167-4889(97)90001-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Isolated hepatocytes from fasted rats were used to study the effects of lactate on palmitate metabolism. Lactate was found to stimulate fatty acid esterification and citric acid cycle oxidation and to inhibit ketone body synthesis. These effects of lactate were largely maintained when gluconeogenesis was inhibited with either quinolinate or perfluorosuccinate, but were overcome by alpha-cyano-4-hydroxycinnamate. However, the responses of hepatocytes to lactate could be restored in the presence of alpha-cyano-4-hydroxycinnamate by the further addition of propionate. The stimulation of triacylglycerol synthesis by lactate was not associated with an increase in the concentration of glycerol 3-phosphate. Rather, there was a correlation between flux through the citric acid cycle and the rate of triacylglycerol synthesis. In all instances reduction of ketone body formation in the presence of lactate was accompanied by a stimulation of citric acid cycle oxidation.
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Affiliation(s)
- D C Henly
- Department of Medical Biochemistry, Flinders University of South Australia, Bedford Park
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35
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Gomez-Muñoz A, Hales P, Brindley DN. Unsaturated fatty acids activate glycogen phosphorylase in cultured rat hepatocytes. Biochem J 1991; 276 ( Pt 1):209-15. [PMID: 2039470 PMCID: PMC1151166 DOI: 10.1042/bj2760209] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Oleate, linoleate, linolenate, arachidonate and eicosapentaenoate, but not myristate, palmitate and stearate, stimulated glycogen phosphorylase activity by 2-8-fold when added to cultured rat hepatocytes. Addition of BSA or Ca2- to the incubation medium decreased the stimulating effects of the unsaturated fatty acids. The combination of oleate or linolenate, with corticosterone, testosterone or estradiol produced synergistic stimulations of phosphorylase activity. The stimulation of glycogen phosphorylase activity by linolenate was inhibited by staurosporine or sphingosine. Staurosporine (80 nM) alone also decreased basal phosphorylase activities by about 60%. The results show that unsaturated fatty acids can be used as model agonists to stimulate phosphorylase activity by a mechanism that probably involves protein kinase C. On the basis of the fatty acid: BSA ratios used, this stimulation should only occur in vivo at high fatty acid concentrations when accompanied by hypoalbuminaemia.
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Affiliation(s)
- A Gomez-Muñoz
- Department of Biochemistry, University of Alberta, Edmonton, Canada
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36
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Marra CA, de Alaniz MJ. Inhibition of arachidonate biosynthesis in hepatoma tissue culture cells by 11-deoxycorticosterone-induced factor. Mol Cell Biochem 1991; 103:63-71. [PMID: 1906979 DOI: 10.1007/bf00229594] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
In this work it was demonstrated that the incubation of hepatoma cultured cells (HTC 7288 c) with 11-deoxycorticosterone (DOC) ranging from 0 to 10(-4) M concentration provoked a dose-dependent inhibition in the conversion of [1-14C] eicosatrienoic acid to arachidonic acid. This steroid also produced an increase in the uptake of exogenous 20:3 (n-6) acid. The depressive effect evoked by DOC on delta 5 desaturating activity was reflected on the fatty acid composition changes of the hepatoma cells. The delta 5 desaturase activity was inhibited by a soluble factor that would be induced by the hormone and that was present in the cytosol fraction from DOC-treated cells, corresponding to a low molecular mass below 25 kDa. Presently we report that an 11-beta-OH group on the steroid molecule is not an essential requirement for the production of a delta 5 desaturase inhibitory factor.
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Affiliation(s)
- C A Marra
- Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP), CONICET-UNLP, Facultad de Ciencias Médicas, Argentina
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37
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Graham A, Zammit VA, Christie WW, Brindley DN. Sexual dimorphism in the preferential secretion of unsaturated lysophosphatidylcholine by rat hepatocytes but no secretion by sheep hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1081:151-8. [PMID: 1998732 DOI: 10.1016/0005-2760(91)90020-i] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
(1) Rat and ovine hepatocytes were incubated in monolayer culture with various fatty acids to determine their effects on the composition of the lysophosphatidylcholine that was secreted. (2) No lysophosphatidylcholine was detected in the medium from the ovine hepatocytes even though these cells were hormonally responsive and they secreted phosphatidylcholine and triacylglycerol in very-low-density lipoprotein. (3) Lysophosphatidylcholine was readily detected in the incubation medium of rat hepatocytes. The predominant fatty acids in this lipid were unsaturated. Stearate and arachidonate contributed 15 and 34%, and 24 and 26% of the total fatty acids when hepatocytes from male and female rats were used, respectively. The relative proportions of stearate and arachidonate in the phosphatidylcholine secreted from the hepatocytes were 20 and 14%, and 28 and 21% for the males and females, respectively. The equivalent values for stearate and arachidonate for phosphatidylcholine in the hepatocytes were 18 and 17% and 33 and 22% for male and female rats. These results provide further indications of sex differences in hepatic phospholipid metabolism and extend this to the secretion of phosphatidylcholine and lysophosphatidylcholine. (4) The addition of 1 mM stearate to the incubation medium did not significantly decrease the proportion of arachidonate in the lysophosphatidylcholine obtained from the hepatocytes of the male rats. However, the relative proportion of arachidonate was decreased in incubations that contained 1 mM oleate or linoleate. (5) The results provide evidence that the preferential secretion of unsaturated lysophosphatidylcholine by the liver may provide a system for transporting unsaturated fatty acids and choline to other organs in non-ruminant animals. However, this mechanism may not operate for ruminants.
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Affiliation(s)
- A Graham
- Department of Biochemistry and Lipid, Faculty of Medicine, University of Alberta, Canada
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38
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Dunlop ME, Larkins RG. Insulin-dependent contractility of glomerular mesangial cells in response to angiotensin II, platelet-activating factor and endothelin is attenuated by prostaglandin E2. Biochem J 1990; 272:561-8. [PMID: 2268285 PMCID: PMC1149745 DOI: 10.1042/bj2720561] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Culture of glomerular mesangial cells in the absence of insulin decreased the degree of contraction of individual cells in response to vasoconstrictive agonists, angiotensin II, platelet-activating factor and endothelin 1, as compared with cells cultured in the presence of insulin (0.7 nM). This change was associated with a decreased sensitivity of the intracellular Ca2+ response to vasoactive agents in fura-2-loaded cells and with an increase in the basal level of prostanoid [prostaglandins (PG) E1 and E2] production estimated by radioimmunoassay. Addition of exogenous PGE2 to insulin-exposed cells decreased the contractile response to that observed in insulin-deficient cells. Inclusion of 8-bromo cyclic AMP had a similar effect. In 45Ca2(+)-release studies it was shown that, in saponin-permeabilized insulin-exposed cells, preincubation with exogenous PGE2 or 8-bromo cyclic AMP decreased the sensitivity of 45Ca2+ release in response to Ins(1,4,5)P3, as demonstrated by an increase in the EC50 (concn. giving half-maximal effect) to 0.182 +/- 0.024 microM and 0.457 +/- 0.031 microM respectively, as compared with untreated permeabilized cells (EC50 0.091 +/- 0.021 microM). A similar decrease in Ins(1,4,5)P3-sensitive 45Ca2+ release was seen in permeabilized cells from insulin-free conditions of culture (EC50 0.20 +/- 0.061 microM). As altered glomerular haemodynamics are found in insulinopaenic diabetic conditions, it is proposed that a decrease in intracellular Ca2+ availability in response to vasoactive agonists and consequent decrease in mesangial-cell contractility contributes to the hyperfiltration seen in this condition.
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Affiliation(s)
- M E Dunlop
- University of Melbourne, Department of Medicine, Royal Melbourne Hospital, Parkville, Victoria, Australia
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39
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Metcalfe HK, Cohen RD, Monson JP. Hormonal modulation of hepatic plasma membrane lactate transport in cultured rat hepatocytes. Biosci Rep 1990; 10:573-7. [PMID: 2085671 DOI: 10.1007/bf01116618] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Hormonal modulation of hepatic plasma membrane lactate transport was studied in primary cultures of isolated hepatocytes from fed rats to examine the mechanism for the known enhancement of lactate transport in starvation and diabetes. Total cellular lactate entry was increased by 14% in the presence of dexamethasone; this was accounted for by an approximately 40% increase in the carrier-mediated component of entry with no effect on diffusion. A trend of similar magnitude was evident with glucagon. The effects of dexamethasone and glucagon on lactate transport constitute an additional potential mechanism for enhancement of gluconeogenesis by these hormones.
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Affiliation(s)
- H K Metcalfe
- Cellular Mechanisms Group, London Hospital Medical College, U.K
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40
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Schoonderwoerd K, Broekhoven-Schokker S, Hülsmann WC, Stam H. Properties of phosphatidate phosphohydrolase and diacylglycerol acyltransferase activities in the isolated rat heart. Effect of glucagon, ischaemia and diabetes. Biochem J 1990; 268:487-92. [PMID: 2163615 PMCID: PMC1131459 DOI: 10.1042/bj2680487] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Myocardial triacylglycerol hydrolysis is subject to product inhibition. After hydrolysis of endogenous triacylglycerols, the main proportion of the liberated fatty acids is re-esterified to triacylglycerol, indicating the importance of fatty acid re-esterification in the regulation of myocardial triacylglycerol homoeostasis. Therefore, we characterized phosphatidate phosphohydrolase (PAP) and diacylglycerol acyltransferase (DGAT) activities, enzymes catalysing the final steps in the re-esterification of fatty acids to triacylglycerols in the isolated rat heart. The PAP activity was mainly recovered in the microsomal and soluble cell fractions, with an apparent Km of 0.14 mM for both the microsomal and the soluble enzyme. PAP was stimulated by Mg2+ and oleic acid. Oleic acid, like a high concentration of KCl, stimulated the translocation of PAP activity from the soluble to the particulate (microsomal) fraction. Myocardial DGAT had an apparent Km of 3.8 microM and was predominantly recovered in the particulate (microsomal) fraction. Both enzyme activities were significantly increased after acute streptozotocin-induced diabetes, PAP from 15.6 +/- 1.1 to 28.1 +/- 3.6 m-units/g wet wt. (P less than 0.01) and DGAT from 2.23 +/- 0.11 to 3.01 +/- 0.11 m-units/g wet wt. (P less than 0.01). In contrast with diabetes, low-flow ischaemia during 30 min did not affect PAP and DGAT activity in rat hearts. Perfusion with glucagon (0.1 microM) during 30 min did not affect total PAP activity, but changed the subcellular distribution. More PAP activity was recovered in the particulate fraction. DGAT activity was lowered by glucagon treatment from 0.37 +/- 0.03 to 0.23 +/- 0.02 m-unit/mg of microsomal protein (P less than 0.05). The role of PAP and DGAT activity and PAP distribution in the myocardial glucose/fatty acid cycle is discussed.
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Affiliation(s)
- K Schoonderwoerd
- Department of Biochemistry I, Medical Faculty, Erasmus University Rotterdam, The Netherlands
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41
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Spydevold O, Sørensen H, Clausen OP, Gautvik KM. Dexamethasone inhibition of rat hepatoma cell growth and cell cycle traverse is reversed by insulin. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1052:221-8. [PMID: 2182131 DOI: 10.1016/0167-4889(90)90080-w] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
(1) The growth of 7800 C1 Morris hepatoma cells was inhibited by dexamethasone. The inhibition was detectable at 1 nM and half-maximal effect was obtained with approx. 13 nM dexamethasone. About 80% growth inhibition was obtained with 250 nM of the hormone and the growth rate was normalized on cessation of treatment. (2) These hepatoma cells contain dexamethasone receptors with equilibrium dissociation constant of 0.24 nM and a capacity of 24 fmol/mg cell protein. Treatment of the cells with insulin did not change these dexamethasone binding properties. Binding experiments showed that 2, 10 and 100% of the receptors were occupied when the cells were incubated with 1 nM, 7 nM and 250 nM dexamethasone, respectively. (3) Insulin completely counteracted the growth inhibition by dexamethasone and antagonized the induction of peroxisomal acyl-CoA oxidase and tyrosine aminotransferase caused by the glucocorticoid. (4) Micro-flow fluorometry showed that the cultures had a major diploid DNA stem line and a minor tetraploid stem line. Changes in diploid, tetraploid and S phase cells of the diploid stem line were scored. Dexamethasone reduced the proportion of cells in S phase and of tetraploid cells. Insulin partly reversed the action of dexamethasone in S phase, but prevented the reduction in tetraploid cells caused by dexamethasone. (5) The mitotic rate was significantly reduced by dexamethasone and this effect was reversed by insulin. (6) Continuous [3H]methyl-thymidine labelling showed a growth fraction of unity in all treatment groups. (7) It is concluded that dexamethasone induces growth inhibition by reducing the G1-S transition. Insulin is able to counteract this effect and increase the rate of DNA synthesis.
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Affiliation(s)
- O Spydevold
- Institute of Medical Biochemistry, University of Oslo, Norway
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42
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Pittner RA, Fain JN. Vasopressin and norepinephrine stimulation of inositol phosphate accumulation in rat hepatocytes are modified differently by protein f1nase C and protein kinase A. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1043:211-7. [PMID: 2107881 DOI: 10.1016/0005-2760(90)90298-c] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Rat hepatocytes were maintained in primary monolayer culture for 24 h in the presence of serum. Treatment of hepatocytes with 1 microM 4 beta-phorbol 12 beta-myristate 13 alpha-acetate (PMA) for 5-15 min increased membrane-associated protein kinase C activity and concomitantly decreased soluble activity. Membrane protein kinase C activity returned to basal values within 1 h then decreased by more than 50% within 2 h. Prolonged (2-18 h) incubation with PMA did not further decrease protein kinase C activity. Pretreatment of hepatocytes with PMA for 5-15 min had little effect on the subsequent actions of 100 nM vasopressin but abolished the stimulation of inositol phosphate accumulation by 3 nM vasopressin and 20 microM norepinephrine. Long-term exposure (2-18 h) of hepatocytes to 1 microM PMA actually enhanced the effects of vasopressin and 20 microM norepinephrine. The stimulation by norepinephrine (20 microM) of inositol phosphate accumulation was abolished by the alpha 1-adrenergic antagonist prazosin (1 microM), whereas the beta-adrenergic antagonist propranolol (30 microM) had little effect. Addition of 8Br-cAMP (100 microM) or glucagon (10 nM) for 5 min or 8 h had no significant effect alone, but enhanced the subsequent vasopressin stimulation of inositol phosphate accumulation. There was no effect of 8Br-cAMP or glucagon on norepinephrine stimulation of phosphoinositide breakdown. These data indicate that the stimulation of phospholipase C activity in rat hepatocytes by 3 nM vasopressin is enhanced by cyclic AMP-dependent kinase but inhibited by protein kinase C. In contrast, down regulation of protein kinase C markedly enhanced the maximal phosphoinositide response due to both vasopressin and norepinephrine.
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Affiliation(s)
- R A Pittner
- Department of Biochemistry, University of Tennessee, Memphis 88163
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43
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Pittner RA, Fain JN. Effects of insulin on inositol phosphate production in cultured rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1990; 1043:218-24. [PMID: 2180488 DOI: 10.1016/0005-2760(90)90299-d] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Addition of vasopressin (100 nM) to rat hepatocytes prelabelled with [3H]inositol stimulated the production of inositol phosphates in the presence of 20 mM Li+. Preincubation of hepatocytes with insulin (50 nM) or glucagon (10 nM) had no significant effect alone but enhanced the effects of vasopressin after a lag period of at least 1 min. The effects of insulin and glucagon appeared additive in this respect. Insulin also enhanced the norepinephrine-mediated stimulation of inositol phosphate accumulation. The enhancement by insulin of the effects of vasopressin required at least 0.5-5 nM insulin and did not involve changes in [3H]inositol lipid labelling or IP3 phosphatase activity. The effect of insulin appeared insensitive to prior treatment of hepatocytes with pertussis toxin (200 ng/ml for 18-24 h) or cholera toxin (100 ng/ml for 3-4 h). The glucagon enhancement of the effects of vasopressin was not affected by pertussis toxin but was mimicked by cholera toxin. The response of hepatocytes to vasopressin in the absence of Li+ was smaller and more transient. Under these conditions a 5 min prior incubation with insulin inhibited the stimulation by vasopressin of inositol phosphate accumulation. A similar inhibitory effect of prior insulin exposure on the transient activation by vasopressin of exogenous phosphatidylinositol 4,5-bisphosphate breakdown by hepatocyte homogenates was also seen. These data indicate that insulin, although having no effect on basal inositol phosphate accumulation, can either enhance or antagonise the effects of vasopressin in primary rat liver hepatocyte cultures depending on the experimental conditions.
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Affiliation(s)
- R A Pittner
- Department of Biochemistry, University of Tennessee, Memphis 38163
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44
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Niemann R. The effects of xenobiotics on hepatic lipid and lipo-protein metabolism. EXPERIMENTAL PATHOLOGY 1990; 39:213-32. [PMID: 2257927 DOI: 10.1016/s0232-1513(11)80188-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The liver occupies a central position in lipid and lipo-protein metabolism. Its function includes lipid and lipoprotein biosynthesis, assembly, packaging, transport, secretion, uptake and degradation of lipoproteins. In addition, enzymes synthesized and secreted by the liver into the blood stream or remaining bound to the endothelial cells in the capillaries, affect lipoprotein metabolism in the circulation. Xenobiotics may influence each of these steps. The mechanisms include more specific actions such as hormone or transmitter agonism and antagonism, membrane effects (stabilization or changes in trans-membrane gradients), influence on protein synthesis, influence on lipid metabolism by induction or inhibition of involved enzymes, or more general actions such as disturbances or damage of cellular membranes and cellular function. Some of these effects can easily be described as pharmacological actions, more or less independent of specific requirements in the chemical structure of the xenobiotics. Others are linked to specific chemical substituents such as carboxyl or alcoholic hydroxyl groups allowing the formation of lipid-xenobiotic-conjugates and/or the channeling of xenobiotics into lipid metabolism. This review will give a short overview of the mechanisms of xenobiotic-influenced hepatic lipid and lipoprotein metabolism.
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Affiliation(s)
- R Niemann
- A. Nattermann & Cie. GmbH, Cologne, FRG
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45
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Kaloyianni M, Freedland RA. Effect of diabetes and time after in vivo insulin administration on ketogenesis and gluconeogenesis in isolated rat hepatocytes. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1990; 22:159-64. [PMID: 2185062 DOI: 10.1016/0020-711x(90)90178-6] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
1. Diabetic rats had elevated rates of gluconeogenesis and ketone body production. 2. Four hours after insulin administration the rate of gluconeogenesis returned to normal and the rate of ketogenesis decreased with certain substrates, but did not return to normal. 3. Eight hours after insulin treatment ketogenesis from all substrates was significantly reduced, but still significantly higher than normal.
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Affiliation(s)
- M Kaloyianni
- Laboratory of Animal Physiology, Science School, Aristotelian University of Thessaloniki, Greece
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46
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Salter AM, Ekins N, al-Seeni M, Brindley DN, Middleton B. Cholesterol esterification plays a major role in determining low-density-lipoprotein receptor activity in primary monolayer cultures of rat hepatocytes. Biochem J 1989; 263:255-60. [PMID: 2604696 PMCID: PMC1133416 DOI: 10.1042/bj2630255] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
1. We have previously shown that the capacity for specific binding of human 125I-labelled low-density lipoprotein (LDL) to rat hepatocytes increases with time in culture [Salter, Bugaut, Saxton, Fisher & Brindley (1987) Biochem. J. 247, 79-84]. 2. In the present study we show that this up-regulation is accompanied by a rise in the cholesterol ester content of the cells. 3. Inhibition of cholesterol esterification with the drug 58-035 (Sandoz) significantly decreases the time-dependent 'up-regulation' of LDL receptors. 4. Incubation of hepatocytes with LDL itself has little effect on subsequent LDL binding. However, when cholesterol esterification is inhibited, incubation with LDL decreases binding below that attained with the drug alone. 5. Inhibition of cholesterol synthesis with Lovastatin significantly increases LDL binding and antagonizes the effect of 58-035. 6. We conclude that in hepatocytes the rate of cellular cholesterol esterification can become the major determinant of LDL-receptor activity.
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Affiliation(s)
- A M Salter
- Department of Biochemistry, University of Nottingham Medical School, Queens Medical Centre, U.K
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47
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Gomez-Muñoz A, Hales P, Brindley DN, Sancho MJ. Rapid activation of glycogen phosphorylase by steroid hormones in cultured rat hepatocytes. Biochem J 1989; 262:417-23. [PMID: 2803260 PMCID: PMC1133284 DOI: 10.1042/bj2620417] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Testosterone (40-300 microM), oestradiol (20-500 microM), progesterone (20-500 microM), dexamethasone (10 nM-1 microM) and corticosterone (1-10 microM) activate glycogen phosphorylase rapidly when added directly to hepatocytes. The activation of phosphorylase was concentration-dependent and occurred after 10 min for dexamethasone, 30 min for testosterone and 60 min for oestradiol and progesterone. This rapid effect does not appear to be dependent on a stimulation of protein synthesis, it is independent of an increase in cyclic AMP, and it is not diminished by the presence of ornithine decarboxylase inhibitors. The stimulation of phosphorylase activity is diminished by depleting the incubation medium of Ca2+ in the presence of 0.5 mM-EGTA, and therefore it may involve changes in the distribution of Ca2+ in the hepatocytes. These results may explain some of the pharmacological effects of sex steroids, and also might contribute to the physiological actions of glucocorticoids.
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Affiliation(s)
- A Gomez-Muñoz
- Department of Biochemistry, University of Alberta, Edmonton, Canada
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48
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Tijburg LB, Geelen MJ, van Golde LM. Regulation of the biosynthesis of triacylglycerol, phosphatidylcholine and phosphatidylethanolamine in the liver. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1004:1-19. [PMID: 2663077 DOI: 10.1016/0005-2760(89)90206-3] [Citation(s) in RCA: 191] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- L B Tijburg
- Laboratory of Veterinary Biochemistry, University of Utrecht, The Netherlands
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49
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Pittner RA, Fain JN. Vasopressin transiently stimulates phospholipase C activity in cultured rat hepatocytes. BIOCHIMICA ET BIOPHYSICA ACTA 1989; 1010:227-32. [PMID: 2536285 DOI: 10.1016/0167-4889(89)90165-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Vasopressin stimulated phospholipase C activity in primary cultures of rat hepatocytes maintained for 18-24 h under serum free conditions. Soluble and membrane-associated phospholipase C activity was determined using exogenous [3H]phosphatidylinositol 4,5-bisphosphate ([3H]PIP2) in the presence of cholate, deoxycholate and NaCl. Exposure of hepatocytes for 5 s to vasopressin (100 nM) stimulated both membrane-associated and soluble phospholipase C activity by 30% and 40%, respectively. However, by 15 s this stimulation had disappeared. Addition of vasopressin to hepatocytes, previously labelled with [3H]inositol, stimulated inositol phosphate production within 5 s, but little further increase was seen over a 5-min incubation. These results indicate that vasopressin rapidly stimulates both soluble and membrane-associated phospholipase C activity.
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Affiliation(s)
- R A Pittner
- Department of Biochemistry, University of Tennessee, Memphis 38163
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50
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Pittner RA, Fain JN. Exposure of cultured hepatocytes to cyclic AMP enhances the vasopressin-mediated stimulation of inositol phosphate production. Biochem J 1989; 257:455-60. [PMID: 2539087 PMCID: PMC1135601 DOI: 10.1042/bj2570455] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Isolated rat hepatocytes in primary monolayer culture were maintained for 18-24 h in the presence of 10% (v/v) serum and [3H]inositol. Vasopressin (100 nM) stimulated the production of inositol mono-, bis- and tris-phosphates (IP1, IP2, and IP3). Prior exposure of hepatocytes to 8-bromo cyclic AMP (8Br-cAMP; 100 microM), but not 8-bromo cyclic GMP, enhanced the vasopressin-mediated stimulation of inositol phosphate accumulation, but had no significant effect on their formation in the absence of vasopressin. The effect of the cyclic AMP analogue was mimicked by glucagon (10 nM), and was seen whether cyclic AMP or glucagon was added 5 min or 12 h before the addition of vasopressin. An 8 h incubation with dexamethasone (100 nM) enhanced the accumulation of IP3, but not that of IP2 or IP1, in the presence of 8Br-cAMP and vasopressin. Cycloheximide or actinomycin D had little effect on the vasopressin stimulation of inositol phosphate accumulation, after an 8 h incubation in the presence or absence of 8Br-cAMP.
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Affiliation(s)
- R A Pittner
- Department of Biochemistry, University of Tennessee, Memphis 38163
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