Ets-1 Protects Vascular Smooth Muscle Cells from Undergoing Apoptosis by Activating p21WAF1/Cip1

The cyclin-dependent kinase inhibitor (CKI) p21WAF1/Cip1 is regulated at the level of transcription by nuclear factors such as the co-activator p300. It is presently unknown whether the Ets family of transcription factors control p21WAF1/Cip1 gene expression. Ets-1 inhibits apoptosis in vascular smooth muscle cells as determined by both fluorescein isothiocyanate-linked annexin V/propidium iodide staining of cells and fluorescence-activated cell sorting analysis and quantitative cytoplasmic histone-associated internucleosomal DNA fragmentation. p21WAF1/Cip1 can play a mitogenic and anti-apoptotic role in smooth muscle cells. Using transient transfection and Western blot analysis, we determined that Ets-1 activates p21WAF1/Cip1 transcription and protein expression. Electrophoretic mobility shift assays revealed that Ets-1 interacts selectively with the -1350GGAA-1347 Ets element in the p21WAF1/Cip1 promoter. Mutation of this element reduced basal and Ets1-inducible p21WAF1/Cip1 promoter-dependent expression. In contrast, the -1577GGAT-1574 motif mediates basal but not Ets-1 activation of the p21WAF1/Cip1 promoter. Co-immunoprecipitation and co-transfection analysis showed that Ets-1 binds p300 and cooperatively activates p21WAF1/Cip1 transcription. The phenotypic importance of Ets-1 regulation of p21WAF1/Cip1 was demonstrated by the capacity of antisense p21WAF1/Cip1 strategies to block Ets-1-inhibition of apoptosis and inhibit Ets-1-induction of proliferation.