Stress‐induced premature senescence in BJ and hTERT‐BJ1 human foreskin fibroblasts

Abstract

To test the involvement of the telomeres in the senescent phenotype, we used telomerase-immortalized human foreskin ¢broblasts (hTERT-BJ1). We exposed hTERT-BJ1 and parental BJ cells to either UVB or H 2 O 2 subcytotoxic stress(-es). Both cell lines developed biomarkers of replicative senescence: loss of replicative potential, increase in senescence-associated L L-galactosidase activity, typical senescence-like morphology, overexpression of p21 WAFÀ1 and p16 INKÀ4a , and decreased level of the hyperphosphorylated form of pRb. Telomere shortening was slightly higher under stress for both BJ and hTERT-BJ1 but still much lower than that reported for other cell lines. We conclude that pathways alternative to telomere shortening must cause the appearance of the senescence phenotype. ß

Reconstitution of active telomerase in primary human foreskin fibroblasts: effects on proliferative characteristics and response to ionizing radiation

“…This is consistent with data reported previously, albeit on cells with fewer PD (Jiang et al 1999, Vaziri et al 1999, Gorbunova et al 2002. Furthermore, cell cycle checkpoint activation after other forms of DNA damage were unaffected by hTERT-mediated immortalization (Gorbunova et al 2002, De Magalhaes et al 2002. These combined data suggest that fibroblast immortalization by telomerase activation alone does not affect the response of cells to DNA damage in terms of cellular sensitivity and cell cycle response.…”

“…So, although hTERT lengthened the mean telomeric length in the fibroblasts and prevented replicative senescence during normal cell culturing (chronic stress), it did not prevent DNA damage (acute stress)-induced entry into senescence. This suggests that senescence due to end-replication problems might-at least in part-occur via separate pathways than senescence induced by DNA damage, which is in agreement with earlier observations using both ionizing radiation and/or other forms of DNA damage-inducing stresses like H 2 O 2 or UV-B (Chen et al 2001, Gorbunova et al 2002, De Magalhaes et al 2002, Matuoka and Chen 2002. It is also consistent with recent findings by te Poele et al (2002), who showed that DNA damage can induce senescence in tumour cells provided they express wild-type p53 and p21 WAF-1,CIP-1 .…”

“…Similarly, stress-induced senescence of human foreskin fibroblast by ceramide, hydrogen peroxide (H 2 O 2 ), LY294002 or trichostatin A was not altered by hTERT transfection (Matuoka and Chen 2002). Finally, it was found that p21 WAF-1,CIP-1 induction, cell growth delay and induction of senescence after ultraviolet B (UV-B) or H 2 O 2 was similar in primary and hTERT-immortalized human foreskin fibroblast (De Magalhaes et al 2002). To address these issues further and to ask whether telomerase-immortalized human fibroblasts have a normal response to ionizing radiation, active hTERT was expressed ectopically in primary human foreskin fibroblasts.…”

The tumor suppressor p16Ink4a regulates T lymphocyte survival

“…In contrast, p16 can be easily detected in cultured human and mouse mesenchymal and epithelial cells, where its expression is associated with an irreversible growth arrest status (Voorhoeve and Agami, 2003). It has been repeatedly reported that p16 expression can be induced in vitro by different forms of cell stress (Chazal et al, 2002;de Magalhaes et al, 2002;Chen et al, 2004). These and other observations suggest that p16 is a checkpoint protein that does not participate in the control of normal cell proliferation, and whose expression is triggered only in some particular circumstances such as cell stress, cell senescence or the activation of certain oncogenes (Roussel, 1999;Lowe and Sherr, 2003).…”

“…It has been reported that p16 expression can be induced by oxidative stress in cultured adherent human cells (de Magalhaes et al, 2002;Chen et al, 2004). DNA damage triggered by different agents such as UV light and chemicals can also induce p16 expression (Chazal et al, 2002), whereas p16 inactivation has been reported in gamma irradiation-induced thymic lymphomas (Malumbres et al, 1997).…”