Tumorogensis: The Dual Role of Telomerase

Carcinogenesis is a multistep process characterized by the gradual accumulation of genetic changesthat ultimately lead to cancer. These genetic mutations can impart limitless replicative potential tothe cancer cells making them immortal. Telomeres are repeat nucleotide sequence TTAGGG thatare present at the end of chromosomes. Its functions are to protect the chromosomal ends and toensure that these ends are not recognized as DNA strand break by the polymerase enzyme. Theyalso act as a clock like mechanism to count the number of times a cell divides. These telomeresare maintained in the cell by an enzyme called as telomerase. The function of telomerase enzymeis to protect the cells from telomere erosion and senescence. Thus, the cell can become immortaland replicate forever. This is called as the canonical function of telomerase. Normally telomeraseis present in stem cells, germ cells and blood cells only and the somatic cells usually do not expresstelomerase. However, a very high concentration of telomerase has been identified in various cancercells. A few years back it was observed that low levels of telomerase are present in the S phase ofcell cycle of somatic cells at levels that are not sufficient to maintain telomeres lengths. Additionallyit was observed that ectopic expression of telomerase causes stem cell division, mobilization andmigration, increased wound repair and an increased tumor burden. Based on these facts it hasbeen deduced that telomerase has at least one non-canonical and elongation-independent function.Both canonical and non-canonical functions of telomerase are considered to play important roles indevelopment and progression of tumorogensis.