title: Differential regulation of the cyclin-dependent kinase inhibitors p21(Cip1) and p27(Kip1) by phosphorylation directed by the cyclin encoded by Murine Herpesvirus 68.
abstract: Members of the gamma2-herpesvirus family encode cyclin-like proteins that have the ability to deregulate mammalian cell cycle control. Here we report the key features of the viral cyclin encoded by Murine Herpesvirus 68, M cyclin. M cyclin preferentially associated with and activated cdk2; the M cyclin/cdk2 holoenzyme displayed a strong reliance on phosphorylation of the cdk T loop for activity. cdk2 associated with M cyclin exhibited substantial resistance to the cdk inhibitor proteins p21(Cip) and p27(Kip). Furthermore, M cyclin directed cdk2 to phosphorylate p27(Kip1) on threonine 187 (T187) and cellular expression of M cyclin led to down-regulation of p27(Kip1) and the partial subversion of the associated G1 arrest. Mutation of T187 to a non-phosphorylatable alanine rendered the p27(Kip1)-imposed G1 arrest resistant to M cyclin expression. Unlike the related K cyclin, M cyclin was unable to circumvent the G1 arrest associated with p21(Cip1) and was unable to direct its associated catalytic subunit to phosphorylate this cdk inhibitor. These results imply that M cyclin has properties that are distinct from other viral cyclins and that M cyclin expression alone is insufficient for S phase entry.
authors.affiliation: Division of Cell and Molecular biology, Faculty of Natural Sciences, Imperial College London, South Kensington, London, SW7 2AZ, UK.
authors.forename: Aliaksandr
authors.initials: A
authors.lastname: Yarmishyn
authors.forename: Emma S
authors.initials: ES
authors.lastname: Child
authors.forename: Lucy M
authors.initials: LM
authors.lastname: Elphick
authors.forename: David J
authors.initials: DJ
authors.lastname: Mann
mesh_terms: D000818:Animals; D020134:Catalytic Domain / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics / Q000378:metabolism*; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004279:DNA, Viral / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics; D004789:Enzyme Activation / Q000235:genetics; D015967:Gene Expression Regulation, Viral / Q000235:genetics; D018816:Genes, cdc / Q000502:physiology; D006566:Herpesviridae Infections / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics; D018144:Rhadinovirus / Q000235:genetics* / Q000378:metabolism; D016196:S Phase / Q000235:genetics; D013912:Threonine / Q000378:metabolism; D014412:Tumor Virus Infections / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004279:DNA, Viral; C411568:M cyclin, gamma-herpesvirus 68; D014764:Viral Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D013912:Threonine; D051357:Cyclin-Dependent Kinase 2