Protein Kinase Cα and ζ Differentially Regulate Death-Inducing Signaling Complex Formation in Cigarette Smoke Extract-Induced Apoptosis

Abstract

Cigarette smoke, a major risk factor in emphysema, causes cell death by incompletely understood mechanisms. Death-inducing signaling complex (DISC) formation is an initial event in Fas-mediated apoptosis. We demonstrate that cigarette smoke extract (CSE) induces DISC formation in human lung fibroblasts (MRC-5) and promotes DISC trafficking from the Golgi complex to membrane lipid rafts. We demonstrate a novel role of protein kinase C (PKC) in the regulation of DISC formation and trafficking. The PKC isoforms, PKCα, ζ, ε, and η, were activated by CSE exposure. Overexpression of wild-type PKCα inhibited, while PKCζ promoted, CSE-induced cell death. Dominant-negative (dn)PKCζ protected against CSE-induced cell death by suppressing DISC formation and caspase-3 activation, while dnPKCα enhanced cell death by promoting these events. DISC formation was augmented by wortmannin, an inhibitor of PI3K. CSE-induced Akt phosphorylation was reduced by dnPKCα, but it was increased by dnPKCζ. Expression of PKCα in vivo inhibited DISC formation, caspase-3/8 activation, lung injury, and cell death after prolonged cigarette smoke exposure, whereas expression of PKCζ promoted caspase-3 activation. In conclusion, CSE-induced DISC formation is differentially regulated by PKCα and PKCζ via the PI3K/Akt pathway. These results suggest that modulation of PKC may have therapeutic potential in the prevention of smoke-related lung injury.