Inhibitory effect of IGF-I on type 2 nitric oxide synthase expression in Ins-1 cells and protection against activation-dependent apoptosis: Involvement of phosphatidylinositol 3-kinase

Abstract

Challenge of Ins-1 cells, a rat β-pancreatic cell line, with lipopolysaccharide (LPS) and interferon-γ (IFN-γ) promoted the expression of type 2 nitric oxide synthase (NOS-2) in a cooperative way. Treatment of Ins-1 cells with IGF-I significantly inhibited the expression of NOS-2, especially at subsaturating concentrations of LPS and IFN-γ. The inhibitory effect of IGF-I on NOS-2 expression was abrogated when cells were incubated with wortmannin or LY294002, two inhibitors of phosphatidylinositol 3-kinase. Transient expression of the p110 subunit of phosphatidylinositol 3-kinase impaired the LPS and IFN-γ-dependent NOS-2 promoter activity in cells transfected with a 1-kb fragment corresponding to the 5'-flanking region of the NOS-2 gene. However, expression of a dominant negative form of p85 abolished the inhibitory action of IGF-I on the NOS-2 promoter activity. Analysis of the decreased NOS-2 promoter activity in cells incubated with IGF-I showed a lower nuclear factor κB binding as determined by electrophoretic mobility shift assays. The synthesis of NO, produced after LPS and IFN-γ challenge, triggered an apoptotic response in these cells. IGF-I reduced apoptosis mainly through the decreased synthesis of NO. However, in activated cells treated with N-[3- (aminomethyl)benzyl]acetamidine, a specific NOS-2 inhibitor, IGF-I completely abolished the NO-independent apoptosis. This protection from apoptosis was dependent on phosphatidylinositol 3-kinase activity. These results suggest an important anti-inflammatory and anti-apoptotic role for IGF-I in β- pancreatic cells, with both actions depending on the activation of phosphatidylinositol 3-kinase.