Telomere dynamics and telomerase activity in cell senescence and cancer

Human somatic cells have a mortal phenotype that is under stringent genetic control and is dominant over unlimited proliferation. Reversal of this phenotype (immortality) may be required for tumour growth. Somatic cell division is accompanied by a decrease in telomeric DNA resulting in progressively shorter telomeres, a process that has been implicated in the control of the proliferative lifespan of cells. Conversely, telomere stabilization and expression of telomerase, the enzyme that elongates telomeric DNA, have been proposed as crucial to cell immortalization and tumour growth. This review discusses the data supporting this hypothesis, focusing on human cells, and addresses their implications for the management of cancer.