DNA methylation of the TERT promoter and its impact on human cancer

Telomere maintenance is a hallmark of human cancer that enables replicative immortality. Most cancer cells acquire telomere maintenance by telomerase activation through expression of telomerase reverse transcriptase (TERT), a rate-limiting component of the telomerase holoenzyme. Although multiple cancer-specific genetic alterations such as gain of TERT copy number and recurrent TERT promoter mutations (TPM) have been identified, the majority of cancers still express TERT via unknown mechanisms. In the last decade, DNA methylation of the TERT promoter emerged as a putative epigenetic regulatory mechanism of telomerase activation in cancer. Here, we comparatively discuss studies that investigated the DNA methylation landscape of the TERT promoter. We further review the biological and clinical impacts of TERT promoter hypermethylation in cancer and provide insight into future applications of this phenomenon.