Classifying Melanoma by TERT Promoter Mutational Status

Abstract

Although TERT promoter mutations have been associated with a worsened prognosis in melanoma, the relationship between mutation status and downstream telomerase activity and telomere length remains convoluted. Using Sanger sequencing and techniques based on quantitative reverse transcriptase in real time, we evaluated 60 melanoma cell lines for TERT promoter mutational status, copy number, gene expression, and telomere length to provide a comprehensive analysis of the TERT/telomere pathway and establish a classification system whereby the associations between TERT mutations and their downstream molecular manifestations can more easily be ascertained. Mutations at positions -124/125 and -146 were associated with the highest levels of TERT gene expression but had no appreciable impact on absolute telomere length. In contrast, the common variant rs2853669 (at position -245) was significantly associated with longer telomere length via a recessive model in our cohort (P = 0.003). Our results, which are from assays performed on purified melanoma cell lines, suggest that the TERT promoter harbors a more complex mutational landscape than previously thought. Furthermore, the failure of TERT promoter mutations to consistently correlate with TERT expression and telomere length suggests an alternative method whereby tumor cells escape the critical shortening of telomeres.

Figure 1:

“TERT Classification.” Color-coded clustering of TERTp mutations in each subgroup (top) and their association with melanoma driver mutations (middle), and both TERT mRNA expression (fold change) and telomere length (kb; bottom). *Other mutations: −136C>T, - 100C>T, and −57A>C.

Figure 2:

“Effect of promoter variants on gene expression and telomere length.” Dot plots of mRNA expression (left) and telomere length (right) for each of the most commonly observed TERTp mutations broken down by variant allele count (0, 1, or 2).