p62 Binding to Protein Kinase C ζ Regulates Tumor Necrosis Factor α-Induced Apoptotic Pathway in Endothelial Cells

Objective-Protein kinase C (PKC) zeta is a key pathological mediator of endothelial cell apoptosis. p62 is a scaffold protein that regulates several cell signaling pathways by binding to target proteins. Because PKC zeta and p62 contain Phox/Bem1p (PB1) modules that mediate protein protein interactions, we hypothesized that an interaction between p62 and PKC is required for tumor necrosis factor alpha-induced PKC zeta signaling in endothelial cells. Methods and Results-In human umbilical vein endothelial cell, tumor necrosis factor alpha (10 ng/mL) enhanced the interaction between p62 and PKC zeta. Transfection with p62 small interfering RNA reduced the activation of both PKC zeta and its downstream targets JNK and caspase 3, suggesting that p62 is necessary for PKC zeta signaling. Overexpression of only the PB1 domain of p62 inhibited p62-PKC zeta interaction, showing that binding of these 2 proteins is mediated by their PB1 domains. Furthermore, overexpression of the p62 PB1 domain suppressed tumor necrosis factor alpha-induced PKC zeta activation and subsequent activation of JNK and caspase 3. Finally, transfection of either p62 small interfering RNA or the PB1 domain of p62 inhibited human umbilical vein endothelial cell apoptosis. Conclusion-Our results suggest a novel function of p62 that regulates the activity of PKC by binding to PKC, thereby activating the PKC zeta-JNK-caspase 3 apoptotic pathway in endothelial cells. (Arterioscler Thromb Vasc Biol. 2012;32:2974-2980.)