Hyperglycemia stimulates p62/PKCζ interaction, which mediates NF-κB activation, increased Nox4 expression, and inflammatory cytokine activation in vascular smooth muscle

Hyperglycemia leads to vascular smooth muscle cell (VSMC) dedifferentiation and enhances responses to IGF-I. Prior studies showed that hyperglycemia stimulated NADPH oxidase 4 (Nox4) synthesis, and IGF-I facilitated its recruitment to a signaling complex where it oxidized src, leading to AKT and MAPK activation. To determine the mechanism that led to these changes, we analyzed the roles of p62 (sequestrosome1) and PKC zeta. Hyperglycemia induced a 4.9 +/- 1.0-fold increase in p62/PKC zeta association, and disruption of PKC zeta/p62 using a peptide inhibitor or p62 knockdown reduced PKC zeta activation (786 +/- 6%). 3-Phosphoinoside-dependent protein kinase 1 was also recruited to the p62 complex and directly phosphorylated PKC zeta, leading to its activation (3.1 +/- 0.4-fold). Subsequently, activated PKC zeta phosphorylated p65 rel, which led to increased Nox4 synthesis. Studies in diabetic mice confirmed these findings (6.0 +/- 0.4-fold increase in p62/PKC zeta) and their disruption of attenuated Nox4 synthesis (7669% reduction). PKC zeta/p62 activation stimulated inflammatory cytokine production and enhanced IGF-I-stimulated VSMC proliferation. These results define the molecular mechanism by which PKC zeta is activated in response to hyperglycemia and suggest that this could be a mechanism by which other stimuli such as cytokines or metabolic stress function to stimulate NF-kappa B activation, thereby altering VSMC sensitivity to IGF-I.