Insulin Antiapoptotic Signaling Involves Insulin Activation of the Nuclear Factor κB-dependent Survival Genes Encoding Tumor Necrosis Factor Receptor-associated Factor 2 and Manganese-superoxide Dismutase

Abstract

We recently showed that the antiapoptotic function of insulin requires nuclear factor kappaB (NF-kappaB) activation (Bertrand, F., Atfi, A., Cadoret, A., L'Allemain, G., Robin, H., Lascols, O., Capeau, J., and Cherqui, G. (1998) J. Biol. Chem. 273, 2931-2938). Here we sought to identify the NF-kappaB-dependent survival genes that are activated by insulin to mediate this function. Insulin increased the expression of tumor necrosis factor receptor-associated factor 2 (TRAF2) mRNA and protein in Chinese hamster ovary cells overexpressing insulin receptors (IRs). This effect required (i) IR activation since it was abrogated by IR mutation at tyrosines 1162 and 1163 and (ii) NF-kappaB activation since it was abolished by overexpression of dominant-negative IkappaB-alpha(A32/36) and mimicked by overexpression of the NF-kappaB c-Rel subunit. TRAF2 contributed to insulin protection against serum withdrawal-induced apoptosis since TRAF2 overexpression mimicked insulin protection, whereas overexpression of dominant-negative TRAF2-(87-501) reduced this process. Along with its protective effect, overexpressed TRAF2 increased basal and insulin-stimulated NF-kappaB activities. All effects were inhibited by IkappaB-alpha(A32/36), suggesting that an amplification loop involving TRAF2 activation of NF-kappaB is implicated in insulin antiapoptotic signaling. We also show that insulin increased manganese-superoxide dismutase (Mn-SOD) mRNA expression through NF-kappaB activation and that Mn-SOD contributed to insulin antiapoptotic signaling since expression of antisense Mn-SOD RNA decreased this process. This study provides the first evidence that insulin activates the NF-kappaB-dependent survival genes encoding TRAF2 and Mn-SOD and thereby clarifies the role of NF-kappaB in the antiapoptotic function of insulin.