Abstract 4979: The role of Tel in repression of BCL-XL transcription in tumor cells

Abstract

Abstract Study of Bcl-xl and hepatocyte growth factor (HGF) receptor c-Met demonstrates that ETS transcription factors influence the transcriptional control of Bcl-xl in multiple tumors. The phosphorylation of Tel, a transcriptional repressor in the ETS family, by activated c-Met is required to increase Bcl-xl transcription in addition to activation of ETS2, a transcriptional activator. Our data indicate that stimulation by HGF causes the activation of ERK and leads to the nuclear export of Tel. In order to determine whether ERK is responsible for the phosphorylation of Tel after HGF stimulation, physical interaction between Tel and ERK was detected using I.P. (Tel)-western blotting (ERK). To determine if blocking MAP kinase could prevent Tel's phosphorylation after HGF exposure, we again used I.P. Western to compare the phosphorylation of Tel under specific ERK kinase inhibitors, after HGF exposure, to the phosphorylation of Tel in the absence of inhibitors, after HGF exposure. A His-Tel 213mutant (phosphorylation sites mutants) was created. The Tel 213 mutant did not undergo phosphorylation induced by c-Met activation, as demonstrated by I.P. Western blot. Nuclear localization of mutated His-Tel was detected under HGF/EGF exposure via fluorescent microscopy using FITC labeled anti-his antibody, indicating that phosphorylation of Tel is also required for nuclear export. A luciferase reporter assay shows that the transient expression of Tel 213 mutant in cancer cell lines results in further repression of Bcl-xl promoter activity. Indeed, Tel 213's repressive function is independent of c-Met stimulation, as determined by comparing with wild type Tel cDNA transfected cells. Consequently, Tel 213 transfection results in much stronger reduction in Bcl-xl mRNA and protein expression levels in the presence of HGF, as compared to transfection with wild-type Tel cDNAs in the presence of HGF. Furthermore, a CHIP assay demonstrates that the activation of c-Met reduced the binding of wild-type Tel to the Bcl-xl promoter, while the binding of Tel 213 to bcl-xl promoter was not affected. Finally, transfection of Tel 213 leads to increased cell proliferation inhibition and apoptosis. Taken together, these findings are supportive of a role for Tel, through a c-Met aixs, as an inhibitor of Bcl-xl transcription. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4979.