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Genome-wide chromatin accessibility analysis in colorectal cancer PDC (ATAC-Seq)

ABSTRACT: Transcriptional reactivation of hTERT is the limiting step in tumorigenesis. While mutations in hTERT promoter in 19% of cancers are recognized as key drivers of hTERT reactivation, mechanisms by which wildtype hTERT (WT-hTERT) promoter is reactivated, in majority of human cancers, remain unknown. Using primary colorectal cancers (CRC) we identify, Tert INTeracting region 2 (T-INT2), the critical chromatin region essential for reactivating WT-hTERT promoter in CRCs. T-INT2 is essential for the formation of a unique chromatin architecture needed for the reactivation of WT-hTERT. This cancer-cell-specific WT-hTERT reactivation is mediated by -catenin and JunD signalling via T-INT2. Pharmacological screens uncovered Salinomycin, which inhibits WT-hTERT reactivation by blocking T-INT2 mediated formation of chromatin architecture essential for WT-hTERT promoter reactivation. Our results provide a framework for therapeutic targeting of WT-hTERT, specifically in cancer cells and explain, for the first time how known CRC alterations, such as APC lead to WT-hTERT promoter reactivation during oncogene-induced stepwise-transformation.

ORGANISM(S): Homo sapiens

PROVIDER: GSE163075 | GEO | 2023/01/08

REPOSITORIES: GEO

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Project description:Human telomerase reverse transcriptase (hTERT) is a rate-limiting catalytic subunit of the enzyme telomerase, which plays a central role in maintaining replicative immortality in normal stem cells and many cancer cells. Mostly silenced in normal somatic cells, hTERT is reactivated in cancer commonly through highly recurrent hot spot point mutations in the hTERT promoter. Bladder cancer has a 60-70% hTERT promoter mutation prevalence, commonly at -124 bp from the translation start site, and this is associated with increased hTERT expression and poor patient prognosis. Identifying targetable signaling pathways that drive hTERT transcription from the mutant promoter could lead to therapies with reduced effects on normal progenitors. Here we describe a new platform that probes endogenous hTERT regulation by allele-specific insertion of GFP at either wild-type or mutant promoter allele within human bladder cancer cells harboring a heterozygous mutation. Using cells expressing the GFP-hTERT fusion protein, we performed a pooled CRISPR-Cas9 Kinome KO genetic screen to identify regulators of mutant hTERT promoter activity. We identified TRIM28 as an activator and TRIM24 as a suppressor of hTERT expression. Similar to hTERT, TRIM28 expression stratifies patient outcome and inhibits promotes cell growth both in vitro and in vivo, supporting their clinical relevance. TRIM28 and TRIM24 get recruited to the mutated promoter through GABPA, where TRIM24 interacts with TRIM28 and inhibits its activity as a transcriptional activator. TRIM28 phosphorylation causes its release from TRIM24 and activates hTERT transcription. mTOR phosphorylates TRIM28 through the mTORC1 complex leading to hTERT expression, while mTORC1 inhibition with rapamycin analog Ridaforolimus suppresses the phosphorylation and promoter binding of TRIM28, resulting in reduced hTERT expression and lower cell viability. This study uses a bespoke platform to identify a novel therapeutically tractable regulatory pathway for cancers harboring mutant hTERT promoters.

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Genome-wide chromatin accessibility analysis in colorectal cancer PDC (ATAC-Seq)

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