Abstract 1474: Hippo-mediated control of the mutant TERT promoter via MYC and GABP

Abstract

Abstract Most cancers achieve replicative immortality through reactivation of telomerase reverse transcriptase (TERT), the rate limiting subunit in telomerase activity. Tumors from more than 50 distinct cancer types reactivate TERT expression via mutations in the TERT promoter. Understanding how the mutations lead to activation and immortality is a central question in cancer research. Oncogenic signaling pathways including EGFR/AMPK, MAPK, and C-MYC/ASL, have been linked to telomere maintenance via their regulation of the mutant TERT promoter. Two mutually exclusive point mutations in the TERT promoter generate a de novo E26 Transformation Specific (ETS) binding motif that recruits the GA-Binding Protein (GABP) multimeric complex to reactivate TERT expression (Bell et al, Science 2015). Recruitment of GABP to the mutant TERT promoter facilitates the recruitment of C-MYC to the promoter (Shi et al, Mol. Cell 2022), which aids in transcriptional activation. The Hippo pathway plays a key role in development, organ size determination, and homeostasis, and has been found dysregulated in numerous cancer types. GABP is a member of the Hippo pathway, with GABP activating the promoter of the Hippo transcriptional effector Yes-associated protein (YAP1) and the Hippo pathway core kinases stimulating GABP nuclear exit (Wu et al., Cell Reports 2013). We have found that YAP and its paralogue transcriptional coactivator with PDZ-binding motif (TAZ) are linked to mutant TERT promoter activation in glioblastoma via transcriptional activation of both GABPA and MYC. These observations suggest the Hippo pathway supports tumor immortality in glioblastoma. While immortality has proven to be an elusive target, further investigations of the signaling networks that converge on the activation of the mutant TERT promoter may reveal therapeutic targets that block tumor growth and have secondary benefit by their impact on tumor immortality. Citation Format: Nicholas O. Stevers, Andrew Mancini, Joseph F. Costello. Hippo-mediated control of the mutant TERT promoter via MYC and GABP [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1474.