Telomerase reactivation

B. Accelerated Aging Process in Nontransformed RER+ Cells Possible Role of Very Early Telomerase Reactivation in Senescence Rescue and Possible Impact on Karyotype... 

Telomeres are nucleoprotein structures located at the ends of eucaryotic chromosomes. They protect chromosome ends from fusion and degradation and ensure complete replication of chromosomal DNA. In human somatic cells, telomeres have 1.000 to 3,000 repeats. They gradually shorten with every cell division. This shortening i.s thought to limit their proliferative capacity. Cancer cells, in contrast, can maintain their telomere length and thus become immortalized. They do this by reactivating telomerase, a specific reverse transcriptase with an endogenous RNA template. ... 

A reactivation of telomerase activity has been reported in 8 of 24 normal colonic mucosa samples from patients affected by Lynch syndrome, a phenomenon marginally observed in only one of the non-Lynch controls (Cheng et al., 1998). This observation is unique for Lynch syndrome patients, be-... 

The human genes expressing the telomerase protein and the telomerase-associated RNA are active in germ cells but are turned off in most adult tissues, in which cells replicate only rarely. However, these genes are reactivated in most human cancer cells, where telomerase is required for the multiple cell divisions necessary to form a tumor. This phenomenon has stimulated a search for inhibitors of human telomerase as potential therapeutic agents for treating cancer. I... 

Cells that do divide regularly, such as stem cells and the cells that give rise to sperm, have active telomerase. They have no problem with shrinking telomeres either. Even circulating immune cells, which do not express telomerase when quiescent, reactivate it when stimulated to proliferate by bacteria. In other words, if our immune cells need to undergo many rounds of cell division, they have all the telomeres they need. All... 

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