Phosphorylation‐dependent degradation of the cyclin‐dependent kinase inhibitor p27Kip1
摘要：
The p27Kip1 protein associates with G1-specific cyclinCDK complexes and inhibits their catalytic activity. p27Kip1 is regulated at various levels, including translation, degradation by the ubiquitin/proteasome pathway and non-covalent sequestration. Here, we describe point mutants of p27 deficient in their interaction with either cyclins (p27c), CDKs (p27k) or both (p27ck), and demonstrate that each contact is critical for kinase inhibition and induction of G1 arrest. Through its intact cyclin contact, p27k associated with active cyclin ECDK2 and, unlike wild type p27, p27c or p27ck, was efficiently phosphorylated by CDK2 on a conserved C-terminal CDK target site (TPKK). Retrovirally expressed p27k was rapidly degraded through the proteasome in Rat1 cells, but was stabilized by secondary mutation of the TPKK site to VPKK. In this experimental setting, exogenous wild-type p27 formed inactive ternary complexes with cellular cyclin ECDK2, was not degraded through the proteasome, and was not further stabilized by the VPKK mutation. p27ck, which was not recruited to cyclin ECDK2, also remained stable in vivo. Thus, selective degradation of p27k depended upon association with active cyclin ECDK2 and subsequent phosphorylation. Altogether, these data show that p27 must be phosphorylated by CDK2 on the TPKK site in order to be degraded by the proteasome. We propose that cellular p27 must also exist transiently in a cyclin-bound non-inhibitory conformation in vivo.
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DOI：
10.1093/emboj/16.17.5334
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年份：
2014
Nature
Wiley
Semantic Scholar
万方医学
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