Differential mitogenic signaling in insulin receptor-deficient fetal pancreatic beta-cells.
Insulin receptor (IR) may play an essential role in the development of beta-cell mass in the mouse pancreas. To further define the function of this signaling system in beta-cell development, we generated IR-deficient beta-cell lines. Fetal pancreata were dissected from mice harboring a floxed allele of the insulin receptor (IRLoxP) and used to isolate islets. These islets were infected with a retrovirus to express simian virus 40 large T antigen, a strategy for establishing beta-cell lines (beta-IRLoxP). Subsequently, these cells were infected with adenovirus encoding cre recombinase to delete insulin receptor (beta-IR(-/-)). beta-Cells expressed insulin and Pdx-1 mRNA in response to glucose. In beta-IRLoxP beta-cells, p44/p42 MAPK and phosphatidylinositol 3 kinase pathways, mammalian target of rapamycin (mTOR), and p70S(6)K phosphorylation and beta-cell proliferation were stimulated in response to insulin. Wortmannin or PD98059 had no effect on insulin-mediated mTOR/p70S(6)K signaling and the corresponding mitogenic response. However, the presence of both inhibitors totally impaired these signaling pathways and mitogenesis in response to insulin. Rapamycin completely blocked insulin-activated mTOR/p70S(6)K signaling and mitogenesis. Interestingly, in beta-IR(-/-) beta-cells, glucose failed to stimulate phosphatidylinositol 3 kinase activity but induced p44/p42 MAPKs and mTOR/p70S(6)K phosphorylation and beta-cell mitogenesis. PD98059, but not wortmannin, inhibited glucose-induced mTOR/p70S(6)K signaling and mitogenesis in those cells. Finally, rapamycin blocked glucose-mediated mitogenesis of beta-IR(-/-) cells. In conclusion, independently of glucose, insulin can mediate mitogenesis in fetal pancreatic beta-cell lines. However, in the absence of the insulin receptor, glucose induces beta-cell mitogenesis.
Guillen
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Institute of Biochemistry/Department of Biochemistry and Molecular Biology, Joint Center Consejo Superior Investigacion Cientifica/Universidad Complutense, School of Pharmacy, Complutense University, Madrid, Spain.
Navarro
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Robledo
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Valverde
A M
AM
Benito
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M
D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005333:Fetus / Q000166:cytology*; D005419:Flavonoids / Q000494:pharmacology; D005947:Glucose / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D050417:Insulin-Secreting Cells / Q000166:cytology*; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D011972:Receptor, Insulin / Q000172:deficiency / Q000502:physiology*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases
D048049:Extracellular Signal-Regulated MAP Kinases; D005419:Flavonoids; D005947:Glucose; D007328:Insulin; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D011972:Receptor, Insulin; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C546843:mTOR protein, mouse; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one