Caspase-1 is a Direct Target Gene of ETS1 and Plays a Role in ETS1-induced Apoptosis

ETS1, the founding member of Ets transcriptional factor family, plays an important role in cell proliferation, differentiation, lymphoid cell development, transformation, angiogenesis, and apoptosis. Previous work has shown that ETS1 represses tumorigenicity of colon carcinoma cells in vivo, and that the p42-ETS1 protein bypasses a defect in apoptosis in colon carcinoma cells through the up-regulation of caspase-1 expression. In this report, we show that expression of p42-ETS1 inhibits tumorigenicity of colon cancer DLD-1 cells through induction of apoptosis in vivo. In support of the hypothesis that caspase-1 might be a target involved in the sensitization of DLD-1 cells to Fas-induced apoptosis by ETS1, overexpression of caspase-1 bypasses Fas-induced apoptosis in these cells as well. Furthermore, ETS1-mediated apoptosis was observed in MOP8 cells, a transformed mouse NIH3T3 cell line. To determine whether ETS1 activates the transcription of caspase-1, luciferase reporters driven by the wild-type and mutant caspase-1 promoters were generated. Both p51-ETS1 and p42-ETS1 transactivated the caspase-1 transcription and a functional Ets binding site is identified in the caspase-1 promoter. Wild-type caspase-1 promoter (pGL3-ICE) was strongly transactivated by ETS1 and this transactivation was dramatically diminished by the mutation of the potential Ets binding site (-525 bp). In addition, electrophoretic mobility shift assay and chromatin immunoprecipitation assay showed complex formation between this binding site and ETS1 proteins. Taken together, ETS1 transcriptionally induces the expression of caspase-1; as such, the regulatory control of caspase-1 expression by ETS1 may underlie the apoptotic susceptibility modulated by ETS1 in specific tumor cells.