Caveolin-1, cellular senescence and pulmonary emphysema.

Caveolae are vesicular invaginations of the plasma membrane. Caveolin-1 is the structural protein component of caveolae. Caveolin-1 participates in signal transduction processes by acting as a scaffolding protein that concentrates, organizes and functional regulates signaling molecules within caveolar membranes. Cigarette smoke, a source of oxidants, is an environmental hazard that causes pulmonary emphysema. Recently, we reported that the development of cigarette smoking-induced pulmonary emphysema was inhibited in caveolin-1 null mice, which do not express caveolin-1. We demonstrated that lack of caveolin-1 expression in lung fibroblasts dramatically inhibited premature senescence induced by oxidants contained in cigarette smoke. Mechanistically, we uncovered that premature senescence of lung fibroblasts induced by oxidative stress occurred through activation of an ataxia telangiectasia-mutated (ATM)/p53-depedent pathway following sequestration of the catalytic subunit of protein phosphatase 2A (PP2A-C), an inhibitor of ATM, by caveolin-1 into caveolar membranes. We propose caveolin-1 as a key player of a novel signaling pathway that links cigarette smoke to premature senescence of lung fibroblasts and development of pulmonary emphysema.