Telomerase in cutaneous carcinogenesis.

Telomerase is a ribonucleoprotein enzyme that catalyses the addition of telomeric repeats to telomeres. Since the shortening of telomeres is thought to act as a mitotic clock, activation of telomerase is crucial for the continued growth of cancer cells. Telomerase is frequently activated in premalignant and malignant skin tumors and even in normal skin from sun-exposed sites. Normal epidermis contains a subpopulation with telomerase activity, although those might not be stem cells. Telomerase activity correlates closely with the expression of human telomerase catalytic subunits. The effects of acute and chronic UV exposure on telomerase activity and their mechanisms should be studied in relevance to UV-carcinogenesis and photoaging.