Phosphorylation-dependent degradation of the cyclin-dependent kinase inhibitor p27Kip1

摘要: The p27(Kip1) protein associates with G1-specific cyclin-CDK complexes and inhibits their catalytic activity. is regulated at various levels, including translation, degradation by the ubiquitin/proteasome pathway non-covalent sequestration. Here, we describe point mutants of p27 deficient in interaction either cyclins (p27(c-)), CDKs (p27(k-)) or both (p27(ck-)), demonstrate that each contact critical for kinase inhibition induction G1 arrest. Through its intact cyclin contact, p27(k-) associated active E-CDK2 and, unlike wild type p27, p27(c-) p27(ck-), was efficiently phosphorylated CDK2 on a conserved C-terminal CDK target site (TPKK). Retrovirally expressed rapidly degraded through proteasome Rat1 cells, but stabilized secondary mutation TPKK to VPKK. In this experimental setting, exogenous wild-type formed inactive ternary cellular E-CDK2, not proteasome, further VPKK mutation. which recruited also remained stable vivo. Thus, selective depended upon association subsequent phosphorylation. Altogether, these data show must be order proteasome. We propose exist transiently cyclin-bound non-inhibitory conformation