Synergistic activation of mutant TERT promoter by Sp1 and GABPA in BRAF-driven human cancers.

The activating TERT promoter mutations and BRAF mutation are well-established oncogenic alterations in human cancers. Coexistence of BRAF and TERT promoter mutations is frequently found in multiple cancer types, and is strongly associated with poor patient prognosis. Although the BRAF-elicited activation of ERK has been demonstrated to contribute to TERT reactivation by maintaining an active chromatin state, it still remains to be addressed how activated ERK is selectively recruited to mutant TERT promoter. Here, we report that transcription factor GABPA mediates the regulation of BRAF/MAPK signaling on TERT reactivation by selectively recruiting activated ERK to mutant TERT promoter, where activated ERK can phosphorylate Sp1, thereby resulting in HDAC1 dissociation and an active chromatin state. Meanwhile, phosphorylated Sp1 further enhances the binding of GABPA to mutant TERT promoter. Taken together, our data indicate that GABPA and Sp1 synergistically activate mutant TERT promoter, contributing to tumorigenesis and cancer progression, particularly in the BRAF-driven human cancers. Thus, our findings identify a direct mechanism that bridges two frequent oncogenic alterations together in TERT reactivation.