Impaired cAMP-mediated gene expression and decreased cAMP response element binding protein in senescent cells.

The capacity of various growth factors to induce c-fos expression is diminished with senescence. Because adenosine 3',5'-cyclic monophosphate (cAMP)-mediated responses are also blunted with aging, we wondered whether cAMP-induced c-fos gene expression might be impaired with senescence. Using IMR fibroblasts, we found that prostaglandin E1 (PGE1) and forskolin, stimulators of cAMP accumulation in young and senescent cells, increased abundance of c-fos and junB mRNA more in young than senescent cells. The abundance of the cAMP response element binding protein (CREB), a transcription factor which enhances gene expression when phosphorylated by protein kinase A, was markedly decreased in both whole cell and nuclear extracts of senescent cells, in both Western blotting and in gel retardation assays. Also, PGE1-induced phosphorylation of CREB by protein kinase A was markedly attenuated in senescent cells. There is a marked decrement in expression of CREB with senescence, and the results suggest the possibility that the diminished expression of CREB may contribute to altered cAMP-mediated regulation of gene expression with senescence.