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EMBO J. 1999 Mar 15;18(6):1571-83.

The p21(Cip1) and p27(Kip1) CDK 'inhibitors' are essential activators of cyclin D-dependent kinases in murine fibroblasts.

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1
Department of Tumor Cell Biology, St Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105, USA.

Abstract

The widely prevailing view that the cyclin-dependent kinase inhibitors (CKIs) are solely negative regulators of cyclin-dependent kinases (CDKs) is challenged here by observations that normal up-regulation of cyclin D- CDK4 in mitogen-stimulated fibroblasts depends redundantly upon p21(Cip1) and p27(Kip1). Primary mouse embryonic fibroblasts that lack genes encoding both p21 and p27 fail to assemble detectable amounts of cyclin D-CDK complexes, express cyclin D proteins at much reduced levels, and are unable to efficiently direct cyclin D proteins to the cell nucleus. Restoration of CKI function reverses all three defects and thereby restores cyclin D activity to normal physiological levels. In the absence of both CKIs, the severe reduction in cyclin D-dependent kinase activity was well tolerated and had no overt effects on the cell cycle.

PMID:
10075928
PMCID:
PMC1171245
DOI:
10.1093/emboj/18.6.1571
[Indexed for MEDLINE]
Free PMC Article
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