Disparate effects of telomere attrition on gene expression during replicative senescence of human mammary epithelial cells cultured under different conditions

Abstract

Telomere shortening in populations of human mammary epithelial cells (HMECs) that survive early replicative arrest (M0) by the inactivation of p16INK4A during cell culture on plastic dishes leads to a state of permanent replicative arrest termed senescence. While culture of HMECs on feeder layers abrogates M0 and p16 INK4A inactivation, progressive telomere attrition in these cells also eventually results in permanent replicative arrest. Expression of telomerase prevents both senescence on plastic (S-P) and senescence on feeder layers (S-FL) in HMECs, as it does also in cultured primary human fibroblasts. We report here that the gene expression profiles of senescence in HMECs of the same lineage maintained under different culture conditions showed surprisingly little commonality. Moreover, neither of these senescence-associated profiles in HMECs resembles the profile for senescence in human fibroblasts. These results indicate that senescence-associated alterations in gene expression resulting from telomere attrition are affected by culture conditions as well as by cell origins, and argue that replicative senescence at the molecular level is a diverse rather than unique cellular process.

Smurf2 up-regulation activates telomere-dependent senescence

“…1A, WS1 and WI38), the Smurf2 level remained constant in populations of human mammary epithelial cells (HMECs) (Fig. 1A, 48R and 184) during their progression to replicative senescence-consistent with earlier evidence that senescence occurs by fundamentally different pathways in these two kinds of cells (Romanov et al 2001;Zhang et al 2003Zhang et al , 2004. Consistent with our Northern blot results, two isoforms of a protein recognized by anti-Smurf2 antibody were elevated three-to sixfold during replicative senescence in fibroblasts (Fig.…”

“…This view is supported by the dramatically disparate alterations in gene expression observed during replicative senescence in human fibroblasts versus human mammary epithelial cells (HMECs) (Zhang et al 2003(Zhang et al , 2004. Even HMECs of the same origin cultured under different conditions can display disparate gene expression patterns when entering senescence (Zhang et al 2004), providing further evidence that senescence is a diverse cellular process. Consistent with such observations, Smurf2 elevation was not seen during telomere-dependent senescence in either post-selection HMECs (Fig.…”

Enhanced control of proliferation in telomerized cells

“…The life of normal cells is accompanied by many changes in gene expression, which are not related to genetic modification, as exemplified by cell senescence (Zhang et al, 2003(Zhang et al, , 2004. It was shown by us and other researchers that the telomerized cells preserved all normal mechanisms of growth regulation and their spontaneous transformation was never recorded in our laboratory during seven years of observations.…”

Molecular mechanisms of neoplasia

“…Then CCL5 interacts Indukcja starzenia się w pewnych komórkach może być opóźniona lub nawet wyeliminowana dzięki polepszeniu warunków stworzonych wewnątrz kultury. Pierwotne komórki świeżo wyizolowane z tkanki w celu zapoczątkowania hodowli tkankowej mogą rozrastać się bez przeszkód, aż do momentu kryzysu i do indukcji apoptozy zapoczątkowanej przez krytycznie skrócone telomery [46,47,48,49]. Starzenie się indukowane przez nadmierne lub niestabilne sygnalizowanie onkogenne jest mechanizmem obronnym przed nowotworzeniem, który ma swój początek w wielorakich odchyleniach od normy dotyczących proliferacji, w wysokich poziomach sygnalizacji kancerogernnej i w skróceniu telomerów.…”

“…The induction of ageing in certain cells can be delayed or even eliminated by improving conditions created within the culture. Primary cells newly isolated from the tissue to initiate tissue culture can grow unhindered until a crisis and the induction of apoptosis initiated by critically shorted telomeres [46,47,48,49]. Ageing induced by excessive or unstable oncogenic signalling is a defence mechanism against neoplasia, which has its origins in multiple deviations from the norm of proliferation, in high levels of carcinogenic signalling, and telomere shortening.…”