Renewed DNA synthesis in senescent WI-38 cells by expression of an inducible chimeric c-fos construct.
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.
Phillips
P D
PD
Center for Gerontological Research, Medical College of Pennsylvania, Philadelphia 19129.
Pignolo
R J
RJ
Nishikura
K
K
Cristofalo
V J
VJ
D000375:Aging / Q000378:metabolism* / Q000502:physiology; D015152:Blotting, Northern; D001973:Bromodeoxyuridine / Q000378:metabolism; D016923:Cell Death / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002478:Cells, Cultured; D002678:Chimera / Q000235:genetics / Q000502:physiology*; D004247:DNA / Q000096:biosynthesis* / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism* / Q000502:physiology; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D007124:Immunoenzyme Techniques; D008668:Metallothionein / Q000235:genetics / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000502:physiology*; D016755:Proto-Oncogene Proteins c-jun / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014162:Transfection; D015032:Zinc / Q000494:pharmacology
D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D004247:DNA; D008668:Metallothionein; D001973:Bromodeoxyuridine; D015032:Zinc; D013936:Thymidine