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  • Title: Renewed DNA synthesis in senescent WI-38 cells by expression of an inducible chimeric c-fos construct.
    Author: Phillips PD, Pignolo RJ, Nishikura K, Cristofalo VJ.
    Journal: J Cell Physiol; 1992 Apr; 151(1):206-12. PubMed ID: 1560044.
    Abstract:
    As normal human cells approach the end of their proliferative lifespan in vitro they lose responsiveness to a variety of growth factors, to which they respond with DNA replication when they are young. Recently it has been reported that the protooncogene c-fos is not expressed in senescent cells (Seshadri and Campisi, 1990). In this study we have found that both c-jun and jun B, partners of c-fos in heterodimeric transactivating complexes, are equivalently expressed in young and senescent cells at both early (1-6 hr) and late (12 or 16 hr) time points following serum stimulation of quiescent cells. We have also investigated the effect of the enforced expression of c-fos in senescent WI-38 cells using an inducible construct carrying the murine c-fos gene under the control of the sheep metallothionein promoter. We have found that the transient transfection and subsequent activation of the conditional promoter with Zn++ stimulated DNA synthesis in a significant fraction of senescent cells which had completed 90%-95% of their proliferative lifespan. However, populations which had completed 100% of their proliferative life span and nondividing cultures which had been selected with BrdU did not respond to the expression of the c-fos gene. These results demonstrate that one of the primary events associated with senescence in human cells is the suppression of c-fos gene expression, but additional phenotypic changes must also occur in order to explain the ultimate loss of proliferative responsiveness of these cells.
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