TELOMERASE

Telomerase is an enzyme that elongates telomeric repeats, the speciali zed structures at the ends of chromosomes that provide genomic stabili ty and compensate for the physiologic process of telomere shortening. It has been implicated in cellular senescence, immortalization, and ca rcinogenesis. Over 85% of human tumours, and 95% of non-melanocytic sk in cancers, show telomerase activity, in contrast to the corresponding normal tissues. This suggests that telomerase activity may play an im portant role in carcinogenesis. Recent evidence shows that telomerase is active not only in embryonal and germ line tissues, but also in som e normal tissues. In the skin, this activity has been traced to the st em-cell-bearing epidermal basal cell layer, possibly reflecting the pr esence of telomerase-competent stem cells. These findings require a re consideration of our interpretation of telomerase activity in tumours of the skin and other tissues. as a causal relationship linking telome rase activity and cancer has yet not been demonstrated, some caution i s warranted.