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p21Waf1 inhibits the activity of cyclin dependent kinase 2 by preventing its activating phosphorylation
1The Department of Molecular Biology, The Lerner Research Institute, The Cleveland Clinic Foundation, Ohio 44195, USA.
Abstract:
Prostaglandin A2 (PGA2), a potent inhibitor of the growth of many cell types, inhibits G1 phase cyclin dependent kinases (cdk). Although PGA2 suppresses cyclin D1 and elevates p21Waf1 levels, it was the failure of cdk2 to become activated by phosphorylation which correlated best with growth inhibition. In kinetic studies, cdk2 activation was inhibited efficiently only if p21Waf1 levels increased prior to the activating phosphorylation; suggesting that p21Waf1 had blocked this phosphorylation. This model was confirmed in cells from p21Waf1 knockout mice where PGA2 was completely unable to block the activating phosphorylation of cdk2, or inhibit cdk2 activity. As expected, growth inhibition of p21Waf1(-/-) cells was not observed at PGA2 concentrations which inhibited cdk2 activity and growth of p21Waf1(+/+) cells.
Insights
Prostaglandin A2 (PGA2) inhibits cell growth by blocking cyclin-dependent kinase 2 (cdk2) activation. This effect is dependent on the protein p21Waf1, which prevents cdk2 phosphorylation and activation.
Area of Science:
- Cell Biology
- Biochemistry
- Molecular Biology
Background:
- Prostaglandin A2 (PGA2) is a known inhibitor of cell proliferation.
- Cyclin-dependent kinases (cdks) regulate the cell cycle.
- p21Waf1 is a cyclin-dependent kinase inhibitor.
Purpose of the Study:
- To investigate the mechanism by which Prostaglandin A2 (PGA2) inhibits cell growth.
- To determine the role of cyclin-dependent kinase 2 (cdk2) and p21Waf1 in PGA2-induced growth inhibition.
Main Methods:
- Kinetic studies of cdk2 activation and phosphorylation.
- Analysis of cyclin D1 and p21Waf1 levels.
- Experiments using p21Waf1 knockout (p21Waf1(-/-)) and wild-type (p21Waf1(+/+)) cells.
Main Results:
- PGA2 suppressed cyclin D1 and elevated p21Waf1 levels.
- Inhibition of cdk2 activation by phosphorylation correlated with growth inhibition.
- p21Waf1 levels increased prior to cdk2 phosphorylation, suggesting p21Waf1 blocked this process.
- PGA2 failed to inhibit cdk2 activation and cell growth in p21Waf1 knockout cells.
Conclusions:
- PGA2 inhibits cell growth primarily by preventing the activating phosphorylation of cdk2.
- The protein p21Waf1 is essential for PGA2's inhibitory effect on cdk2 activation and cell proliferation.
- These findings elucidate a key molecular mechanism of PGA2 action in cell cycle regulation.