IGF-1 protects against dexamethasone-induced cell death in insulin secreting INS-1 cells independent of AKT/PKB phosphorylation.
Appropriate insulin secretion depends on beta-cell mass that is determined by the balance between cell proliferation and death. IGF-1 stimulates proliferation and protects against apoptosis. In contrast, glucocorticoids promote cell death. In this study we examined molecular interactions of the glucocorticoid dexamethasone (dexa) with IGF-1 signalling pathways in insulin secreting INS-1 cells. IGF-1 (50 ng/ml) increased the growth rate and stimulated BrdU incorporation, while dexa (100 nmol/l) inhibited cell growth, BrdU incorporation and induced apoptosis. Dexa-induced cell death was partially antagonized by IGF-1. This protection was further increased by LY294002 (10 micromol/l), an inhibitor of PI3 kinase. In contrast, MAP kinase inhibitor PD98059 (10 micromol/l) significantly reduced the protective effect of IGF-1. The analysis of signalling pathways by Western blotting revealed that dexa increased IRS-2 protein abundance while the expression of PI3K, PKB and ERK remained unchanged. Despite increased IRS-2 protein,IRS-2 tyrosine phosphorylation stimulated by IGF-1 was inhibited by dexa. Dexa treatment reduced basal PKB phosphorylation. However, IGF-1-mediated stimulation of PKB phosphorylation was not affected by dexa, but ERK phosphorylation was reduced. LY294002 restored IGF-1-induced ERK phosphorylation. These data suggest that dexa induces apoptosis in INS-1 cells by inhibiting phosphorylation of IRS-2, PKB and ERK. IGF-1 counteracts dexa-mediated apoptosis in the presence of reduced PKB but increased ERK phosphorylation.
Avram
Diana
D
Institute of Physiology, University of Tübingen, Germany.
Ranta
Felicia
F
Hennige
Anita M
AM
Berchtold
Susanne
S
Hopp
Sabine
S
Häring
Hans-Ulrich
HU
Lang
Florian
F
Ullrich
Susanne
S
D000818:Animals; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D019610:Cytoprotection / Q000187:drug effects*; D003907:Dexamethasone / Q000494:pharmacology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D000078790:Insulin Secretion; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats
D003907:Dexamethasone; D048049:Extracellular Signal-Regulated MAP Kinases; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; C526299:Irs2 protein, rat