title: The cyclin-dependent kinase inhibitor p27(Kip1) induces N-terminal proteolytic cleavage of cyclin A.
abstract: Progression through the cell cycle is regulated in part by the sequential activation and inactivation of cyclin-dependent kinases (CDKs). Many signals arrest the cell cycle through inhibition of CDKs by CDK inhibitors (CKIs). p27(Kip1) (p27) was first identified as a CKI that binds and inhibits cyclin A/CDK2 and cyclin E/CDK2 complexes in G1. Here we report that p27 has an additional property, the ability to induce a proteolytic activity that cleaves cyclin A, yielding a truncated cyclin A lacking the mitotic destruction box. Other CKIs (p15(Ink4b), p16(Ink4a), p21(Cip1), and p57(Kip2)) do not induce cleavage of cyclin A; other cyclins (cyclin B, D1, and E) are not cleaved by the p27-induced protease activity. The C-terminal half of p27, which is dispensable for its kinase inhibitory activity, is required to induce cleavage. Mechanistically, p27 does not appear to cause cleavage through direct interaction with cyclin/CDK complexes. Instead, it activates a latent protease that, once activated, does not require the continuing presence of p27. Mutation of cyclin A at R70 or R71, residues at or very close to the cleavage site, blocks cleavage. Noncleavable mutants are still recognized by the anaphase-promoting complex/cyclosome pathway responsible for ubiquitin-dependent proteolysis of mitotic cyclins, indicating that the p27-induced cleavage of cyclin A is part of a separate pathway. We refer to this protease as Tsap (pTwenty-seven- activated protease).
authors.affiliation: Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
authors.forename: H
authors.initials: H
authors.lastname: Bastians
authors.forename: F M
authors.initials: FM
authors.lastname: Townsley
authors.forename: J V
authors.initials: JV
authors.lastname: Ruderman
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D018797:Cell Cycle Proteins; D019925:Cyclin A / Q000737:chemistry / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D018076:DNA, Complementary; D017353:Gene Deletion; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry; D010957:Plasmids; D011994:Recombinant Proteins / Q000378:metabolism; D012156:Reticulocytes / Q000378:metabolism; D015398:Signal Transduction; D025521:Tumor Suppressor Proteins
chemical_list: C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D019925:Cyclin A; D018076:DNA, Complementary; D008869:Microtubule-Associated Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases