The common Arg ⁹⁷² polymorphism in insulin receptor substrate‐1 causes apoptosis of human pancreatic islets

Abstract

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.

Kallikrein/Kinin Protects against Myocardial Apoptosis after Ischemia/Reperfusion via Akt-Glycogen Synthase Kinase-3 and Akt-Bad·14-3-3 Signaling Pathways

“…Phosphorylation of Bad provides an important link between extracellular survival factors and the intrinsic cell death pathway. The primary role of 14-3-3 proteins is to inhibit apoptosis; they bind to phosphorylated Bad, which prevents the formation of the Bad⅐Bcl-xL complex (35). Phosphorylation of different residues of the Bad proteins appears to have distinct consequences.…”

G972R IRS-1 Variant Impairs Insulin Regulation of Endothelial Nitric Oxide Synthase in Cultured Human Endothelial Cells

“…16 -20 Thus, it has been demonstrated that the presence of the Gly3 Arg change at codon 972-IRS-1 causes a specific defect in binding of the p85 regulatory subunit of PI3-K to the IRS-1 variant. 16,20 This results in a decrease in IRS-1-associated PI3-K activity and in the subsequent reduced activation of the Ser/Thr kinase-Akt, a key enzyme linking PI3-K activation to multiple biological functions of insulin, including glucose transport, glycogen synthesis, and eNOS activation. [17][18][19][20] In HUVECs naturally expressing the G972R-IRS-1 variant, we observed cell-specific impairment of insulin action, as revealed by defective insulin-stimulated eNOS activation and expression.…”

“…16,20 This results in a decrease in IRS-1-associated PI3-K activity and in the subsequent reduced activation of the Ser/Thr kinase-Akt, a key enzyme linking PI3-K activation to multiple biological functions of insulin, including glucose transport, glycogen synthesis, and eNOS activation. [17][18][19][20] In HUVECs naturally expressing the G972R-IRS-1 variant, we observed cell-specific impairment of insulin action, as revealed by defective insulin-stimulated eNOS activation and expression. Indeed, we observed that in the cells carrying the G972R-IRS-1 variant, the IRS-1/PI3-K/PDK-1/protein kinase B/Akt insulin-signaling cascade was impaired (as documented by reduced IRS-1-associated PI3K activity and reduced insulin-stimulated Akt phosphorylation), whereas MAPK pathway activity was increased.…”

Induction of apoptotic death in cells via Bad gene expression by infectious pancreatic necrosis virus infection

“…12 Insulin can prevent pancreatic b cell apoptotic death through the involvement of sequential induction of IRS-1-associated PI 3-kinase activity, Akt activity, and Bad phosphorylation at Ser-112 and Ser-136. 13 On occasion, Bad up-regulation has been reported to lead to cell death as a result of drug treatment. 14 The infectious pancreatic necrosis virus (IPNV) is a fishderived pathogen and is the prototype of the Birnaviridae virus family.…”