Expression of telomerase genes correlates with telomerase activity in human colorectal carcinogenesis

The human telomerase enzyme is composed of two essential components, hTR, w hich acts as a template for reverse transcription, and hTERT, which is the putative catalytic subunit for the enzyme. Recent studies have demonstrated a good correlation between hTERT expression and telomerase activation, whe reas RT-PCR results seemed to reveal that hTR is ubiquitously expressed in all cells. These observations left unclear the role of hTR, and to a lesser extent hTERT, in the regulation of telomerase activation. In the present s tudy, the correlation of telomerase activity and the expression of these ge nes was examined in a total of 70 colorectal tissues (25 adenocarcinomas, 3 0 adenomas, and 15 samples of normal colorectal mucosa). Total RNA for RT-P CR analysis and cell extracts for TRAP assay mere obtained from consecutive sections and histological control was simultaneously performed. To avoid f alse-positive results, due to the fact that hTR cDNA and genomic hTR DNA ar e identical (the gene has no introns), extensive DNase digestion was perfor med before cDNA synthesis. RT-PCR analysis revealed that hTERT mRNA was exp ressed in all cancers and in 13 of 14 telomerase-positive adenomas, but nev er in telomerase-negative colorectal tissues. hTR transcripts mere observed in all telomerase-positive samples but also in three telomerase-negative s amples, two adenomas, and one normal colonic mucosa. It is concluded that h TERT and hTR expression is strongly correlated with telomerase activity. hT R transcripts, however, also occur in some telomerase-negative tissues and these results are in keeping with the concept that hTERT expression is a ma jor regulator of telomerase activity. Copyright (C) 2000 John Wiley & Sons, Ltd.