Modulation of apoptosis by the cyclin-dependent kinase inhibitor p27Kip1
Keiju Hiromura, … , James M. Roberts, Stuart J. Shankland
Keiju Hiromura, … , James M. Roberts, Stuart J. Shankland
Published March 1, 1999
Citation Information: J Clin Invest. 1999;103(5):597-604. https://doi.org/10.1172/JCI5461.
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Article

Modulation of apoptosis by the cyclin-dependent kinase inhibitor p27Kip1

Abstract

Proliferation and apoptosis are increased in many types of inflammatory diseases. A role for the cyclin kinase inhibitor p27Kip1 (p27) in limiting proliferation has been shown. In this study, we show that p27–/– mesangial cells and fibroblasts have strikingly elevated rates of apoptosis, not proliferation, when deprived of growth factors. Apoptosis was rescued by restoration of p27 expression. Cyclin A–cyclin-dependent kinase 2 (CDK2) activity, but not cyclin E–CDK2 activity, was increased in serum-starved p27–/– cells, and decreasing CDK2 activity, either pharmacologically (Roscovitine) or by a dominant–negative mutant, inhibited apoptosis. Our results show that a new biological function for the CDK inhibitor p27 is protection of cells from apoptosis by constraining CDK2 activity. These results suggest that CDK inhibitors are necessary for coordinating the cell cycle and cell-death programs so that cell viability is maintained during exit from the cell cycle.

Authors

Keiju Hiromura, Jeffrey W. Pippin, Matthew L. Fero, James M. Roberts, Stuart J. Shankland

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Figure 7

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Effect of suppressing CDK2 activity on apoptosis in p27–/– fibroblasts i...
Effect of suppressing CDK2 activity on apoptosis in p27–/– fibroblasts in response to serum starvation. (a) p27–/– cells transfected with a dominant–negative mutant CDK2 (dnk2) plasmid were identified by cotransfection with a GFP plasmid (green nuclei). (b) Apoptosis (measured by Hoechst staining) was not detected in dnk2-transfected cells (thick arrow), but was detected in nontransfected cells (thin arrow). (c) p27–/– cells cotransfected with wild-type CDK2 (wtk2) plasmid and GFP were identified as green. (d) wtk2 did not protect p27–/– fibroblasts from apoptosis (arrow). (e) Quantitation of apoptosis. The percentage of apoptotic cells was evaluated in 200 cells. *P < 0.001 vs. nontransfected p27–/– fibroblasts (p27–/– alone) and wtk2-transfected cells. Similar results were obtained in p27–/– mesangial cells.