Apoptosis of vascular smooth muscle cells (SMC) at the sites of atherosclerotic plaques may result in plaque rupture and thrombosis. Kavurma et al. used two immortalized, but phenotypically different, SMC cell lines (WKY12-22 and WKY3M-22) to study apoptosis. WKY12-22 cells are derived from rat pup arteries and will grow in the absence of exogenous growth factors; WKY3M-22 cells are derived from adult rat arteries and are dependent on plasma-derived serum for growth. WKY12-22 cells express higher levels of the ubiquitous transcription factor Sp1 and undergo spontaneous apoptosis at a greater frequency than seen in the WKY3M-22 cells. FasL is also expressed at higher levels in the WKY12-22 cells, suggesting a possible mechanism for the increased apoptosis. Overexpression of Sp1 in either cell type increases the expression of FasL. On the basis of reporter genes assays and electrophoretic mobility shift assays, Sp1 is a transcriptional activator of FasL and binds to the Sp1 consensus site in the FasL promoter. It is noteworthy that the inhibitor of DNA topisomerase I camptothecin (CAM), a known proapoptotic chemical, enhances the phosphorylation of Sp1 and increases the production of FasL and apoptosis in these cells. Thus, Sp1, a ubiquitous transcription factor, may represent a point of control for the apoptotic pathway.
M. M. Kavurma, F. S. Santiago, E. Bonfoco, L. M. Khachigian, Sp1 phosphorylation regulates apoptosis via extracellular FasL-Fas engagement. J. Biol. Chem. 276, 4964-4971 (2001). [Abstract] [Full Text]