The role of telomeres and telomerase in human cancer.

Human cancers/malignant transformation of normal cells occur from multiple independent genetic changes/mutations that can subvert the normal growth controls of cells, leading to distinct phenotypic changes and immortalization. Normal human somatic cells have limited proliferative capacity both in vitro and in vivo and undergo senescence. Recent studies have implicated telomeres and telomerase in the regulation of lifespan of cells. Telomeres are the stretches of DNA consisting of tandem repeats of nucleotide sequences that cap chromosomes and prevent its degradation and play a role, both in normal control of cell proliferation and abnormal growth of cancers. They are highly conserved during evolution. Telomerase, the novel reverse transcriptase enzyme that synthesizes telomeric DNA is repressed in most human somatic cells, it results in telomere shortening with each cell division, leading to a process thought to contribute to senescence. Recent research proposes that activation of telomerase is important for cells to proliferate indefinitely and that all human cancer cells require activation of this enzyme to maintain telomeric DNA, to overcome cellular senescence and to attain immortality. Thus telomeres and telomerase offer potential for diagnostics, cancer therapy as well as for understanding the process of aging.