Telomerase is a specialized enzyme that plays a crucial role in maintaining the stability and integrity of chromosomes by adding specific DNA sequence repeats, known as telomeres, to the ends of linear chromosomes. Telomeres protect the ends of chromosomes from degradation and prevent them from being recognized as damaged DNA. Over time, as cells divide, telomeres become progressively shorter. Eventually, when the telomeres are too short, the cell enters a state of senescence or undergoes apoptosis (programmed cell death). In this way, telomeres act as a molecular “clock” that limits the number of cell divisions and contributes to cellular aging.
Telomerase is a ribonucleoprotein complex composed of two main components: a catalytic subunit with reverse transcriptase activity called telomerase reverse transcriptase (TERT), and an RNA component called telomerase RNA component (TERC). TERC serves as a template for the synthesis of telomeric DNA repeats by TERT.
In most normal human cells, telomerase activity is low or absent, leading to telomere shortening and eventual cellular senescence. However, in certain cell types, such as stem cells, germ cells, and immune cells, telomerase activity is maintained to ensure their long-term functionality.
Telomerase is of particular interest in cancer research because the enzyme is reactivated in approximately 85-90% of human cancers, enabling cancer cells to maintain or even elongate their telomeres. This reactivation of telomerase provides cancer cells with unlimited replicative potential, allowing them to divide and grow uncontrollably, which is a hallmark of cancer.
The reactivation of telomerase in cancer cells has made it an attractive target for cancer therapy. Several strategies have been developed to inhibit telomerase activity, including small molecule inhibitors, immunotherapeutic approaches, and antisense oligonucleotides. While some of these approaches have shown promise in preclinical studies and early-phase clinical trials, further research is needed to optimize their efficacy, selectivity, and safety before they can become part of standard cancer treatment regimens.