Signaling Pathway Inhibitor Library Screening Reveals B-Catenin/TCF4 as a Novel Telomerase Regulator in Cancer cell lines

Abstract

Well-defined signaling pathway (Wnt, EGFR and JAK/STAT) inhibitors that are known to play important roles in cancer progression were screened to identify new telomerase regulators. Hits from the inhibitors libraries were verified in a wide range of cancer cell lines (stomach adenocarcinoma: AGS, breast cancer: MCF7, colorectal cancer: HCT116/LS174T) and are therefore expected to be general TA inhibitors for some of the major types of cancer. ?-catenin/TCF4 complex was identified as a novel TA regulator from the screen and was later found to inhibit TA via transcription regulation of hTERT (human TERT). Activation of the Wnt pathway either by Wnt ligand (Wnt-3a) or LiCl (activates Wnt signaling by inhibiting GSK-3?) treatment as well as overexpression of a constitutively active form of ?-catenin (?-N ?-catenin) up regulated hTERT mRNA expression and telomerase activity (TA) in cancer cell lines. On the other hand, knocking down of endogenous ?-catenin via shRNA reduces hTERT mRNA expression and TA. In addition, a ?-catenin/TCF4 consensus binding sequence from -659bp to -653 bp (5?-TGCAAAG-3?) upstream of transcription start site in hTERT promoter was also found and evidences from promoter studies, electrophoretic mobility shift assay, and chromatin immunoprecipitation assay, showed that ?-catenin/TCF4 bind to hTERT promoter in vivo and in vitro. Taken together, this is the first study has shown that Wnt signaling regulates telomerase via the transcription regulation of hTERT.