Expression of human telomerase (hTERT) does not prevent stress-induced senescence in normal human fibroblasts but protects the cells from stress-induced apoptosis and necrosis.
Cells subjected to sub-lethal doses of stress such as irradiation or oxidative damage enter a state that closely resembles replicative senescence. What triggers stress-induced premature senescence (SIPS) and how similar this mechanism is to replicative senescence are not well understood. It has been suggested that stress-induced senescence is caused by rapid telomere shortening resulting from DNA damage. In order to test this hypothesis directly, we examined whether overexpression of the catalytic subunit of human telomerase (hTERT) can protect cells from SIPS. We therefore analyzed the response of four different lines of normal human fibroblasts with and without hTERT to stress induced by UV, gamma-irradiation, and H(2)O(2). SIPS was induced with the same efficiency in normal and hTERT-immortalized cells. This suggests that SIPS is not triggered by telomere shortening and that nonspecific DNA damage serves as a signal for induction of SIPS. Although telomerase did not protect cells from SIPS, fibroblasts expressing hTERT were more resistant to stress-induced apoptosis and necrosis. We hypothesize that healing of DNA breaks by telomerase inhibits the induction of cell death, but because healing does not provide legitimate DNA repair, it does not protect cells from SIPS.
Huffington Center on Aging, Baylor College of Medicine, Houston, Texas 77030, USA. Vera_Gorbunova@hotmail.com
Vera
V
Gorbunova
Andrei
A
Seluanov
Olivia M
OM
Pereira-Smith
D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D016922:Cellular Senescence / Q000502:physiology*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D005720:Gamma Rays; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009336:Necrosis; D016877:Oxidants / Q000494:pharmacology; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D014466:Ultraviolet Rays; D001616:beta-Galactosidase / Q000378:metabolism
D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; D016877:Oxidants; D016160:Retinoblastoma Protein; D016159:Tumor Suppressor Protein p53; D006861:Hydrogen Peroxide; D019098:Telomerase; D001616:beta-Galactosidase; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)