Insulin induces heme oxygenase-1 through the phosphatidylinositol 3-kinase/Akt pathway and the Nrf2 transcription factor in renal cells

Heme oxygenase-1 catalyzes the breakdown of heme and is protective in models of kidney transplantation. In this study we describe the induction of heme oxygenase-1 mRNA and protein by insulin. Following treatment with insulin, a five-fold increase in heme oxygenase-1 mRNA and a fourfold increase in protein expression were observed in renal adenocarcinoma cells; insulin-induced heme oxygenase-1 expression was also demonstrated in mouse primary tubular epithelial cells. The induction of heme oxygenase-1 in renal adenocarcinoma cells was blocked by actinomycin D and cycloheximide and was abolished by the phosphatidylinositol 3-kinase inhibitor, LY294002, but not by the inactive analog LY303511. Over-expressing a dominant-negative form of Akt abrogated the heme oxygenase-l-inducing effects of insulin, whereas cells transfected with a constitutively active Akt construct demonstrated an increase in heme oxygenase-1 promoter activity and protein expression. The transcription factor NF-E2-related factor-2 was found to translocate to the nucleus following insulin treatment in a phosphatidylinositol 3-kinase-dependent manner. Pretreatment with NF-E2-related factor-2 small-interfering RNA abolished insulin-induced heme oxygenase-1 induction. Insulin was also found to activate the mitogen-activated protein kinase cascades p38 and extracellular signal-related kinase; however, inhibition of these pathways with SB202190 and PD98059 did not alter insulin-induced heme oxygenase-1 expression. Thus, insulin induces heme oxygenase-1 mRNA and protein expression in renal cells in a phosphatidylinositol 3-kinase/Akt and NF-E2-related factor-2-dependent manner.