Long-Range Chromatin Interactions Drive Mutant TERT Promoter Activation

Abstract

Cancer-specifi c TERT promoter mutations (-146C>T and -124C>T) have been linked to reactivation of the epigenetically silenced telomerase reverse transcriptase gene ( TERT ). Understanding how these single-nucleotide alterations drive TERT reactivation is a fundamental unanswered question and is key for making successful therapeutics. We show that unlike wild-type promoters, recruitment of the transcription factor GABPA specifi cally to mutant TERT promoters mediates long-range chromatin interaction and enrichment of active histone marks, and hence drives TERT transcription. CRISPR-mediated reversal of mutant TERT promoters, or deletion of its long-range interacting chromatin, abrogates GABPA binding and long-range interactions, leading to depletion of active histone marks, loss of POL2 recruitment, and suppression of TERT transcription. In contrast, de novo introduction of a TERT promoter mutation enables GABPA binding and upregulation of TERT via long-range interactions, acquisition of active histone marks, and subsequent POL2 recruitment. This study provides a unifying mechanistic insight into activation of mutant TERT promoters across various human cancers. SIGNIFICANCE:This study identifi es a key mechanism by which cancer-specifi c mutant TERT promoters cause reactivation of TERT . Because the mechanism uncovered here is not utilized by promoters that drive TERT in normal cells, this mechanism could be exploited to make inhibitors which have the potential to block telomerase function and hence the progression of up to 90% of human cancers.Cancer Discov; 6(11); 1276-91.

TERT biology and function in cancer: beyond immortalisation

“…Reversal of the TERT promoter mutations, or deletion of its long-range interacting chromatin, abrogates GABPA binding and long-range interactions, leading to the depletion of active histone marks, loss of POL2 recruitment and suppression of TERT transcription. In contrast, the de novo insertion of the mutation in the TERT promoter allows GABPA binding and upregulation of TERT via long-range interactions, acquisition of active histone marks and subsequent POL2 recruitment (Akıncılar et al 2016).…”

“…Recently, Akıncılar and coworkers reported in several cell lines that the mutated TERT promoter recruitment of GABPA mediates long-range chromatin interaction (Vinagre et al 2013) (Borah et al 2015) (Li et al 2015a) ) (Stern et al 2015) Presence of the mutations Patients poorer outcome Reduced disease specific survival (Griewank et al 2014) (Nagore et al 2016) (Populo et al 2014) (Batista et al 2016) (Mosrati et al 2015) (Simon et al 2015) (Yuan et al 2016) (Melo et al 2014) (Vinagre et al 2013) −124C > T mutation: Binding of GABPA Reactivation of TERT (Bell et al 2015) −146C > T mutation: Binding of NF-κB p52 Interaction with ETS factors Activation of the non-canonical NF-κB pathway Enhanced tumourigenesis Enhanced proliferation Increase of telomerase activity (Li et al 2015b) Insertion of the mutation Abrogation of TERT transcription silencing Increase of telomerase activity Impair of telomere shortening Obliterate tumour formation GABPA binding Upregulation of TERT via long-range interactions Acquisition of active histone marks POL2 recruitment (Chiba et al 2015) (Li et al 2015a) (Akıncılar et al 2016) Reversion of the mutation Decrease of telomerase activity Telomere shortening Reduced proliferation rate Abrogation of GABPA binding and long-range interaction Depletion of active histone marks Suppression of TERT transcription (Xi et al 2015) (Akıncılar et al 2016) R140 Review a pestana and others TERT biology and function in cancer 58 2 : R140 Review and enrichment of active histone marks, activating TERT transcription (Akıncılar et al 2016). Reversal of the TERT promoter mutations, or deletion of its long-range interacting chromatin, abrogates GABPA binding and long-range interactions, leading to the depletion of active histone marks, loss of POL2 recruitment and suppression of TERT transcription.…”

Activation of mutant TERT promoter by RAS-ERK signaling is a key step in malignant progression of BRAF-mutant human melanomas

“…To verify that the regulation of RAS-ERK signaling is specific to mutant TERT promoters, we analyzed isogenic BLM TERT (−146C > T) and TERT WT cells that were previously created using the CRISPR/ Cas9 genome editing tool (27). Although TERT (−146C > T) CRISPR cells displayed a similar reduction in active histone marks and Pol II recruitment during MEK inhibitor treatment (Fig.…”

TERT Promoter Mutations Enhance Telomerase Activation by Long-Range Chromatin Interactions

“…In this issue, Ak 1 nc 1 lar and colleagues (1) identify a potential mechanism of TERT reactivation that is mediated by a novel long-range chromatin interactions between the TERT promoter on chromosome 5p and a 300 kb upstream region. This permits recruitment of the transcription factor GABPA in mutant TERT promoters but not in wild-type promoters.…”

“…The TERT gene has a GC rich core promoter containing CpG islands that are mostly methylated in normal cells (1). The hypermethylation of the TERT core promoter is believed to be one of the major mechanisms for TERT repression but what changes the methylation status during fetal development is not known.…”