Transition of apoptotic resistant vascular smooth muscle cells to troptotic sensitive state is correlated with downregulation of c-FLIP

Fas and its ligand, FasL, are a receptor-ligand pair identified as promotin g cell death in several tissues. Vascular smooth muscle cells (VSMCs) are r esistant to FasL or anti-Pas antibody (Ab) signal, and a number of in vitro studies show that VSMC death can only be induced by anti-Pas Ab or FasL in the presence of protein inhibitor or additional inflammatory mediators. It remains to be clarified whether known, constitutively expressed cytoprotec tive molecules are reduced by protein inhibitor, thereby accounting for sen sitization to cell death by Fas/FasL signaling. We found that Pas mRNA and protein exist in several primary VSMCs, as previously reported. We also dem onstrated (1) that critical death-signaling molecules, such as FADD, caspas e-1/ICE, and caspase-3/YAMA, are present in these VSMCs, (2) that human VSM Cs contain high concentrations of c-FLIP (3) and that following treatment w ith the protein inhibitor, CHX, cell extracts showed a decrease in c-FLIP p rotein that was dose- and time-dependent on the degree of apoptosis and inv ersely correlated with both caspase-8 and -3 activity. in contrast, there w as neither a change nor an even modest upregulation of Bcl-2 family, even a fter 12 h of treatment with CHX, Taken together, these results may provide a novel insight into atherogenesis and suggest that c-FLIP may contribute t o an apoptosis-resistant state of VSMC, and that a downregulation of c-FLIP may render VSMCs susceptible to apoptosis. Copyright (C) 2000 S. Karger AG , Basel.