Insulin-stimulated glycogen synthesis in cultured hepatoma cells: differential effects of inhibitors of insulin signaling molecules.
In rat HTC hepatoma cells overexpressing human insulin receptors, insulin stimulated glycogen synthesis by 55-70%. To study postreceptor signaling events leading to insulin-stimulated glycogen synthesis in these cells, we have employed pathway-specific chemical inhibitors such as LY294002, rapamycin and PD98059 to inhibit phosphatidylinositol-3-kinase (PI3K), p70 ribosomal S6 kinase and mitogen-activated protein kinase (MAPK) kinase/MAPK, respectively. LY294002 (50 microM) completely abolished insulin-stimulated glycogen synthesis whereas rapamycin (2-20 nM) partially inhibited it. Neither LY294002 nor rapamycin significantly affected the basal glycogen synthesis. However, PD98059 (100 microM) significantly inhibited the basal glycogen synthesis without affecting insulin-stimulated glycogen synthesis. In these cells, insulin at 100 nM decreased glycogen synthase kinase 3 alpha (GSK3 alpha) activity by 30-35%. LY294002, but neither rapamycin nor PD98059, abolished insulin-induced inactivation of GSK3 alpha. These data suggest that insulin-stimulated glycogen synthesis in rat HTC hepatoma cells is mediated mainly by PI3K-dependent mechanism. In these cells, inactivation of GSK3 alpha, downstream of PI3K, may play a role in insulin-stimulated glycogen synthesis.
Sung
C K
CK
Department of Physiology and Biophysics, University of Southern California, School of Medicine, Los Angeles 90033, USA.
Choi
W S
WS
Scalia
P
P
D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D002867:Chromones / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006003:Glycogen / Q000096:biosynthesis*; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D008113:Liver Neoplasms / Q000378:metabolism*; D008969:Molecular Sequence Data; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D051381:Rats; D020123:Sirolimus / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism
D002867:Chromones; D005419:Flavonoids; D007328:Insulin; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D014443:Tyrosine; D006003:Glycogen; D019869:Phosphatidylinositol 3-Kinases; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus