Interplay between TERT promoter mutations and methylation culminates in chromatin accessibility and TERT expression

PLoS One. 2020 Apr 8;15(4):e0231418. doi: 10.1371/journal.pone.0231418. eCollection 2020.

Abstract

The telomerase reverse transcriptase (TERT) gene is responsible for telomere maintenance in germline and stem cells, and is re-expressed in 90% of human cancers. CpG methylation in the TERT promoter (TERTp) was correlated with TERT mRNA expression. Furthermore, two hotspot mutations in TERTp, dubbed C228T and C250T, have been revealed to facilitate binding of transcription factor ETS/TCF and subsequent TERT expression. This study aimed to elucidate the combined contribution of epigenetic (promoter methylation and chromatin accessibility) and genetic (promoter mutations) mechanisms in regulating TERT gene expression in healthy skin samples and in melanoma cell lines (n = 61). We unexpectedly observed that the methylation of TERTp was as high in a subset of healthy skin cells, mainly keratinocytes, as in cutaneous melanoma cell lines. In spite of the high promoter methylation fraction in wild-type (WT) samples, TERT mRNA was only expressed in the melanoma cell lines with either high methylation or intermediate methylation in combination with TERT mutations. TERTp methylation was positively correlated with chromatin accessibility and TERT mRNA expression in 8 melanoma cell lines. Cooperation between epigenetic and genetic mechanisms were best observed in heterozygous mutant cell lines as chromosome accessibility preferentially concerned the mutant allele. Combined, these results suggest a complex model in which TERT expression requires either a widely open chromatin state in TERTp-WT samples due to high methylation throughout the promoter or a combination of moderate methylation fraction/chromatin accessibility in the presence of the C228T or C250T mutations.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alleles
  • Cell Line
  • Chromatin / chemistry
  • Chromatin / metabolism*
  • Chromatin Assembly and Disassembly
  • CpG Islands
  • DNA Methylation*
  • Humans
  • Keratinocytes / cytology
  • Keratinocytes / metabolism
  • Melanoma / genetics
  • Melanoma / pathology
  • Mutation
  • Promoter Regions, Genetic
  • Protein Binding
  • RNA, Messenger / metabolism
  • Skin Neoplasms / genetics
  • Skin Neoplasms / pathology
  • Telomerase / genetics
  • Telomerase / metabolism*
  • Transcription Factors / chemistry
  • Transcription Factors / metabolism

Substances

  • Chromatin
  • RNA, Messenger
  • Transcription Factors
  • TERT protein, human
  • Telomerase

Grants and funding

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the grant agreement No 641458 (http://melgen.org/). RN is supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No 667787 (UM Cure 2020 project, https://www.umcure2020.org/en/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.