NADPH Oxidase Activation in Pancreatic Cancer Cells Is Mediated through Akt-dependent Up-regulation of p22phox

We recently showed that Nox4 NADPH oxidase is highly expressed in pancreatic ductal adenocarcinoma and that it is activated by growth factors and plays a pro-survival, antiapoptotic role. Here we investigate the mechanisms through which insulin-like growth factor I and serum (FBS) activate NADPH oxidase in pancreatic cancer (PaCa) cells. We show that in PaCa cells, NADPH oxidase is composed of Nox4 and p22(phox) catalytic subunits, which are both required for NADPH oxidase activity. Insulin-like growth factor I and FBS activate NADPH oxidase through transcriptional up-regulation of p22(phox). This involves activation of the transcription factor NF-kappa B mediated by Akt kinase. Up-regulation of p22(phox) by the growth factors results in increased Nox4-p22(phox) complex formation and activation of NADPH oxidase. This mechanism is different from that for receptor-induced activation of phagocytic NADPH oxidase, which is mediated by phosphorylation of its regulatory subunits. Upregulation of p22(phox) represents a novel pro-survival mechanism through which growth factors and Akt inhibit apoptosis in PaCa cells.