TRIM28 is a transcriptional activator of the mutant TERT promoter in human bladder cancer

Menée in vitro et à l'aide de xénogreffes de cancer humain de la vessie sur des modèles murins, cette étude démontre que le facteur TRIM28 est un activateur transcriptionnel du promoteur muté du gène TERT

Résumé en anglais

Telomerase reverse transcriptase (hTERT) is involved in immortalization and survival of cancer cells. Recurring mutations in its promoter often lead to its reexpression in cancer. Therapies targeting hTERT activity have been challenging to develop, and none are in routine use. Using targeted functional genomics knockout screening in a human bladder cancer model, we found that transcription factor TRIM28 activates hTERT expression preferentially from the mutant promoter allele. We also revealed a therapeutically targetable mechanism whereby mTORC1-mediated phosphorylation of TRIM28 is required to activate hTERT transcription. This study describes an approach to functional screening of endogenous promoters and insights into TERT regulation, and it may aid clinicians in making informed decisions for precision therapy of cancer patients harboring hTERT promoter mutations.Bladder cancer (BC) has a 70% telomerase reverse transcriptase (TERT or hTERT in humans) promoter mutation prevalence, commonly at −124 base pairs, and this is associated with increased hTERT expression and poor patient prognosis. We inserted a green fluorescent protein (GFP) tag in the mutant hTERT promoter allele to create BC cells expressing an hTERT-GFP fusion protein. These cells were used in a fluorescence-activated cell sorting–based pooled CRISPR-Cas9 Kinome knockout genetic screen to identify tripartite motif containing 28 (TRIM28) and TRIM24 as regulators of hTERT expression. TRIM28 activates, while TRIM24 suppresses, hTERT transcription from the mutated promoter allele. TRIM28 is recruited to the mutant promoter where it interacts with TRIM24, which inhibits its activity. Phosphorylation of TRIM28 through the mTOR complex 1 (mTORC1) releases it from TRIM24 and induces hTERT transcription. TRIM28 expression promotes in vitro and in vivo BC cell growth and stratifies BC patient outcome. mTORC1 inhibition with rapamycin analog Ridaforolimus suppresses TRIM28 phosphorylation, hTERT expression, and cell viability. This study may lead to hTERT-directed cancer therapies with reduced effects on normal progenitor cells.RNA-seq data have been deposited in the Gene Expression Omnibus (GSE181461). All other study data are included in the article and/or supporting information.