The common Arg972 polymorphism in insulin receptor substrate-1 causes apoptosis of human pancreatic islets.
Molecular scanning of human IRS-1 gene revealed a common polymorphism causing Gly-->Arg972 change. Diabetic and pre-diabetic carriers of Arg972 IRS-1 are characterized by low fasting levels of insulin and C-peptide. To investigate directly whether the Arg 972 IRS-1 affects human islet cells survival, we took advantage of the unique opportunity to analyze pancreatic islets isolated from three donors heterozygous for the Arg972 and six donors carrying wild-type IRS-1. Islets from carriers of Arg972 IRS-1 showed a two-fold increase in the number of apoptotic cells as compared with wild-type. IRS-1-associated PI3-kinase activity was decreased in islets from carriers of Arg972 IRS-1. Same results were reproduced in RIN rat b-cell lines stably expressing wild-type IRS-1 or Arg972 IRS-1. Using these cells, we characterized the downstream pathway by which Arg972 IRS-1 impairs b-cell survival. RIN-Arg972 cells exhibited a marked impairment in the sequential activation of PI3-kinase, Akt, and BAD as compared with RI N-WT. Impaired BAD phosphorylation resulted in increased binding to Bcl-XL instead of 14-3-3 protein, thus sequestering the Bcl-XL antiapoptotic protein to promote survival. Both caspase-9 and caspase-3 activities were increased in RIN-Arg972 cells. The results show that the common Arg972 polymorphism in IRS-1 impairs human b-cell survival and causes resistance to antiapoptotic effects of insulin by affecting the PI3-kinase/Akt survival pathway. These findings establish an important role for the insulin signaling in human b-cell survival and suggest that genetic defects in early steps of insulin signaling may contribute to b-cell failure.
Federici
M
M
Laboratory of Molecular Medicine, Department of Internal Medicine, University of Rome-'Tor Vergata', 00133 Rome, Italy.
Hribal
M L
ML
Ranalli
M
M
Marselli
L
L
Porzio
O
O
Lauro
D
D
Borboni
P
P
Lauro
R
R
Marchetti
P
P
Melino
G
G
Sesti
G
G
D048948:14-3-3 Proteins; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001120:Arginine / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006579:Heterozygote; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007515:Islets of Langerhans / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011110:Polymorphism, Genetic / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051381:Rats; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein
D048948:14-3-3 Proteins; D001120:Arginine; D002352:Carrier Proteins; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2; D014446:Tyrosine 3-Monooxygenase; D051025:bcl-Associated Death Protein; D051020:bcl-X Protein; C494819:BAD protein, human; C494811:BCL2L1 protein, human; C494821:Bad protein, rat; C494813:Bcl2l1 protein, rat; C526292:IRS1 protein, human; C526296:Irs1 protein, rat; C494918:AKT1 protein, human; C494920:Akt1 protein, rat; C505407:CASP3 protein, human; C506433:CASP9 protein, human; C505410:Casp3 protein, rat; C506435:Casp9 protein, rat