Abstract B12: GABP selectively binds and activates the mutant TERT promoter across multiple cancer types

Abstract

Reactivation of telomerase reverse transcriptase (TERT) expression enables cells to overcome replicative senescence and escape apoptosis, fundamental steps in the initiation of human cancer. Multiple cancer types, including up to 83% of glioblastomas (GBM), harbor highly recurrent mutations in the TERT promoter specific to two nucleotide positions. The common mutation sites, G228A and G250A, may create de-novo ETS family transcription factor binding sites, but the precise mechanism of how these mutations confer increased TERT expression has been elusive. Here, we demonstrate the de-novo ETS motif to be critical for mutant TERT activation by site directed mutagenesis. A focused siRNA screen of the many ETS transcription factors expressed in GBM identifies GABPA as the single ETS factor to selectively regulate the mutant but not the wild type TERT promoter. Single molecule binding assays and ChIP-qPCR analysis reveal that GABPA is exclusively recruited to the mutant allele in vitro and in vivo respectively. Furthermore, this allelic recruitment is consistent across four tested cancer types, highlighting a shared mechanism underlying mutant TERT promoter activation. Tandem flanking native ETS motifs critically cooperate with these mutations to activate TERT, likely by facilitating GABP heterotetramer binding. GABP thus directly links TERT promoter mutations to aberrant expression and may provide a novel therapeutic target for multiple cancers. Citation Format: Robert J.A Bell, H. Tomas Rube, Alex Kreig, Andrew Mancini, Shaun F. Fouse, Raman P. Nagarajan, Serah Choi, Chibo Hong, Daniel He, Melike Pekmezci, John K. Wiencke, Margaret R. Wrensch, Susan M. Chang, Kyle M. Walsh, Sua Myong, Jun S. Song, Joseph F. Costello. GABP selectively binds and activates the mutant TERT promoter across multiple cancer types. [abstract]. In: Proceedings of the AACR Special Conference: Advances in Brain Cancer Research; May 27-30, 2015; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2015;75(23 Suppl):Abstract nr B12.

Implications of TERT promoter mutations and telomerase activity in urothelial carcinogenesis

“…Convincing experimental evidence exists that both these mutations create novel binding sites for the heterotetrameric GA-binding protein (GABP) transcription factor,[Au:Are you referring to a specific subunit or the whole factor "GA-binding protein"?] resulting in increased transcription of TERT and activation of telomerase 97,103,113 . In a study published in 2015, researchers introduced the common TERT promoter mutations into human embryonic stem cells (hESCs) and demonstrated that these mutations prevented down-regulation of the TERT promoter and telomerase activity during differentiation of these mutant hESCs but not wild-type hESCs 131 .…”

ABO Blood Group Antigens as a Model of Studying Protein-Protein Interactions

“…The possibility of an inhibitory effect on a gene expressing telomerase was predicted. About 85% of cancer cells acquire unlimited replicative potential due to the reactivation of a specific telomerase enzyme [12].…”