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Impaired cAMP-mediated gene expression and decreased cAMP response element binding protein in senescent cells
J H Chin1, M Okazaki, J S Frazier
1Department of Medicine, Stanford University School of Medicine, California, USA.
Abstract:
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.
Insights
Senescence impairs the expression of c-fos and junB mRNA in response to cyclic adenosine monophosphate (cAMP) signaling. This is linked to reduced levels and phosphorylation of the cAMP response element binding protein (CREB).
Area of Science:
- Cellular senescence
- Molecular biology
- Gene regulation
Background:
- Senescence is associated with diminished growth factor-induced c-fos expression.
- Aging also blunts adenosine 3',5'-cyclic monophosphate (cAMP)-mediated responses.
Purpose of the Study:
- To investigate if cAMP-induced c-fos gene expression is impaired in senescent cells.
- To explore the role of cAMP response element binding protein (CREB) in this process.
Main Methods:
- Utilized IMR fibroblasts, comparing young and senescent cells.
- Measured mRNA abundance of c-fos and junB using prostaglandin E1 (PGE1) and forskolin.
- Assessed CREB protein levels and phosphorylation via Western blotting and gel retardation assays.
Main Results:
- PGE1 and forskolin increased c-fos and junB mRNA abundance more in young than senescent cells.
- Senescent cells showed markedly decreased CREB abundance in whole cell and nuclear extracts.
- PGE1-induced CREB phosphorylation by protein kinase A was attenuated in senescent cells.
Conclusions:
- Senescence leads to a marked decrease in CREB expression.
- Diminished CREB expression may contribute to altered cAMP-mediated gene regulation in senescent cells.