Central role for phosphatidylinositide 3-kinase in the repression of glucose-6-phosphatase gene transcription by insulin.
Transcription of the gene encoding the catalytic subunit of glucose-6-phosphatase (G6Pase) is stimulated by glucocorticoids and strongly repressed by insulin. We have explored the signaling pathways by which insulin mediates the repression of G6Pase transcription in H4IIE cells. Wortmannin, a phosphatidylinositide 3-kinase (PtdIns 3-kinase) inhibitor blocked the repression of G6Pase mRNA expression by insulin. However, both rapamycin, which inhibits p70S6 kinase activation, and PD98059, an inhibitor of mitogen-activated protein kinase activation, were without effect. Insulin inhibited dexamethasone-induced luciferase expression from a transiently transfected plasmid that places the luciferase gene under the control of the G6Pase promoter. This effect of insulin was mimicked by the overexpression of a constitutively active PtdIns 3-kinase but not by a constitutively active protein kinase B. Taken together, these data demonstrate that PtdIns 3-kinase activation is both necessary and at least partly sufficient for the repression of G6Pase expression by insulin, but neither mitogen-activated protein kinase nor p70S6 kinase are involved. In addition, activation of protein kinase B alone is not sufficient for repression of the G6Pase gene. These results imply the existence of a novel signaling pathway downstream of PtdIns 3 kinase that is involved in the regulation of G6Pase expression by insulin.
Dickens
M
M
Department of Biochemistry, School of Medical Sciences, University of Bristol, BS8 1TD, United Kingdom.
Svitek
C A
CA
Culbert
A A
AA
O'Brien
R M
RM
Tavaré
J M
JM
D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter / Q000235:genetics; D005952:Glucose-6-Phosphatase / Q000235:genetics*; D007328:Insulin / Q000494:pharmacology*; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012097:Repressor Proteins / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection / Q000235:genetics; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D000730:Androstadienes; D003907:Dexamethasone; D005952:Glucose-6-Phosphatase; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D012097:Repressor Proteins; D000077191:Wortmannin