Promoter Mutations Increase Sense and Antisense Transcription from the Promoter.

Chief among mechanisms of telomerase reverse transcriptase (TERT) reactivation is the appearance of mutations in the promoter. The two main promoter mutations are C>T transitions located -146C>T and -124C>T upstream from the translational start site. They generate a novel Ets/TCF binding site. Both mutations are mutually exclusive and -124C>T is strikingly overrepresented in most cancers. We investigated whether this mutational bias and mutual exclusion could be due to transcriptional constraints. We compared sense and antisense transcription of a panel of promoter- vectors harboring the -124C>T and -146C>T mutations alone or together. lncRNA levels were measured by RT-PCR. Both mutations generally increased transcription by 2-4-fold regardless of upstream and downstream regulatory elements. The double mutant increased transcription in an additive fashion, arguing against a direct transcriptional constraint. The -146C>T mutation, alone or in combination with -124C>T, also unleashed antisense transcription. In line with this finding, lncRNA was higher in cells with mutated promoter (T98G and U87) than in cells with wild-type promoter, suggesting that lncRNA may balance the effect of promoter mutations. : -146C>T and -124C>T promoter mutations increase sense and antisense transcription, and the double mutant features higher transcription levels. Increased antisense transcription may contain expression within sustainable levels.