Possible regulation of telomerase activity by transcription and alternative splicing of telomerase reverse transcriptase in human melanoma

To investigate the regulatory mechanisms of telomerase activity in human me lanoma cells, we assessed the enzyme's catalytic activity and the expressio n of the telomerase subunits, the human telomerase RNA, the human telomeras e-associated protein, and the human telomerase reverse transcriptase, in 52 melanoma lesions. Eight normal skin specimens were also studied. Telomeras e activity was detected in 84.6% of melanomas, whereas all skin specimens w ere telomerase negative. Human telomerase-associated protein mRNA and human telomerase RNA were constitutively expressed in all melanoma and skin spec imens. Although at a variable level of expression, human telomerase reverse transcriptase mRNA was detected in all but one melanomas, whereas it was n ever present in skin samples. Reverse transcriptase-polymerase chain reacti on experiments were performed using primers within the reverse transcriptas e domain of human telomerase reverse transcriptase and revealed the presenc e of multiple alternatively spliced transcripts in melanoma specimens. Amon g the 44 telomerase-positive melanomas, one showed the full-length transcri pt alone whereas in all other specimens a full-length message was present w ith different combinations of alternatively spliced variants. In these tumo rs the expression of the full-length transcript was generally equal to or h igher than that of the alternatively spliced variants. The ratio full-lengt h transcript to alternatively spliced species ranged from 0.6 to 5.26, with a median value of 1.18. Among the seven telomerase-negative melanomas, one displayed the beta deletion transcript alone, whereas in the remaining six tumors weak expression of the full-length transcript and a more abundant l evel of alternatively spliced transcripts were found. In these cases human telomerase reverse transcriptase ratio ranged from 0.09 to 1.1, with a medi an value of 0.40. The results suggest that transcription and alternative sp licing of human telomerase reverse transcriptase are regulatory mechanisms controlling telomerase activity in melanoma.