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.

Autophagy protein microtubule-associated protein 1 light chain-3B (LC3B) activates extrinsic apoptosis during cigarette smoke-induced emphysema

“…Recent studies show that Fas can localize to plasma membrane lipid rafts (19,20). We therefore examined whether LC3B localizes to lipid rafts.…”

“…Immunoprecipitation and immunoblotting were performed essentially as previously described (6,20,24). SI Methods provides additional details.…”

Cigarette Smoke Induces Akt Protein Degradation by the Ubiquitin-Proteasome System

“…Because apoptosis and senescence are induced by cigarette smoke in vitro and in vivo (2)(3)(4)(5), and Akt is a well known signaling hub for cell survival (11)(12)(13)(14)(15)(16), suppression of Akt has been proposed to be related to cell death and dysfunction. However, only a few reports provide indirect evidence showing that Akt may be related to development of emphysema.…”

“…Although overwhelming protease activity due to persistent inflammation has long been suggested to play a pivotal role in the development of emphysema (1), recent data suggest that apoptosis, cell cycle arrest, and cellular senescence may contribute to the development of emphysema. Cigarette smoke causes apoptotic death in human lung fibroblasts and mouse lungs (2), inhibits cell proliferation, and induces cellular senescence in human lung fibroblasts, with elevation of p53 and p21 (3). Patients with emphysema have a higher percentage of type II alveolar epithelial cells and endothelial cells positive for p16 and p21, along with shortened telomeres, compared with asymptomatic smokers and nonsmokers (4).…”

“…Chronic obstructive pulmonary disease (COPD), 2 caused mainly by cigarette smoking, is characterized by emphysema, small airway remodeling, chronic bronchitis, and vascular remodeling (1). Although overwhelming protease activity due to persistent inflammation has long been suggested to play a pivotal role in the development of emphysema (1), recent data suggest that apoptosis, cell cycle arrest, and cellular senescence may contribute to the development of emphysema.…”