A phosphatidylinositol 3-Kinase/p70 ribosomal S6 protein kinase pathway is required for the regulation by insulin of the p85alpha regulatory subunit of phosphatidylinositol 3-kinase gene expression in human muscle cells.
Insulin acutely up-regulates p85alpha phosphatidylinositol 3-kinase (p85alphaPI 3-K) mRNA levels in human skeletal muscle (Laville, M., Auboeuf, D., Khalfallah, Y., Vega, N., Riou, J. P., and Vidal, H. (1996) J. Clin. Invest. 98, 43-49). In the present work, we attempted to elucidate the mechanism of action of insulin in primary cultures of human muscle cells. Insulin (10(-7) M, 6 h of incubation) induced a 2-fold increase in p85alphaPI 3-K mRNA abundances (118 +/- 12 versus 233 +/- 35 amol/microgram total RNA, n = 5, p < 0.01) without changing the expression levels of insulin receptor, IRS-1, glycogen synthase, and Glut 4 mRNAs in differentiated myotubes from healthy subjects. The effect is most probably due to a transcriptional activation of the p85alphaPI 3-K gene because the half-life of the mRNA was not affected by insulin treatment (4.0 +/- 0.8 versus 3.1 +/- 0.4 h). PD98059 (50 microM) did not modify the insulin response but increased p85alphaPI 3-K mRNA levels in the absence of insulin, suggesting that the mitogen-activated protein kinase pathway exerts a negative effect on p85alphaPI 3-K mRNA expression in the absence of the hormone. On the other hand, the insulin effect was totally abolished by LY294002 (10 microM) and rapamycin (50 nM). In addition, overexpression of a constitutively active protein kinase B increased p85alphaPI 3-K mRNA levels. These results indicate that the phosphatidylinositol 3-kinase/PKB/p70S6 kinase pathway is required for the stimulation by insulin of p85alphaPI 3-K gene expression in human muscle cells.
Roques
M
M
INSERM U449, Faculté de Médecine René Laënnec, Université Claude Bernard Lyon-1, F-69372, Lyon, France. roques@laennec.univ-lyon1.fr
Vidal
H
H
D000328:Adult; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006006:Glycogen Synthase / Q000235:genetics; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D008875:Middle Aged; D009025:Morpholines / Q000494:pharmacology; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics* / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011972:Receptor, Insulin / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects
D002867:Chromones; D003609:Dactinomycin; D004791:Enzyme Inhibitors; D005419:Flavonoids; D006006:Glycogen Synthase; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D011972:Receptor, Insulin; D011993:Recombinant Fusion Proteins; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; C526292:IRS1 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one