Absence of cancer-associated changes in human fibroblasts immortalized with telomerase

The ectopic expression of telomerase(1-2) in normal human cells results in an extended lifespan(3-4), indicating that telomere shortening regulates th e timing of cellular senescence, As telomerase expression is a hallmark of cancer, we investigated the long-term effects of forced expression of human telomerase catalytic component (hTERT) in normal human fibroblasts. In vit ro growth requirements, cell-cycle checkpoints and karyotypic stability in telomerase-expressing cells are similar to those of untransfected controls. In addition, co-expression of telomerase, the viral oncoproteins HPV16 E6/ E7 (which inactivate p53 and pRB) and oncogenic HRAS does not result in gro wth in soft agar, Thus, although ectopic expression of telomerase in human fibroblasts is sufficient for immortalization, it does not result in change s typically associated with malignant transformation.