title: T-loop deletion of CDC2 from breast cancer tissues eliminates binding to cyclin B1 and cyclin-dependent kinase inhibitor p21.
abstract: The eukaryotic cell cycle is regulated by a highly conserved family of protein kinases, the cyclin-dependent kinases (CDKs). Monomeric free CDKs do not possess enzymatic activity, largely due to the steric hindrance caused by the T-loop at the entrance of the catalytic cleft, making ATP inaccessible to the substrate. Binding of a cyclin, primarily to the NH2-terminal lobe of the CDK that surrounds the PSTAIRE helix, induces a large conformational change in the PSTAIRE helix of the CDK and also causes the T-loop to move out of the way of the catalytic cleft. We identified from breast cancer tissues a novel variant of human CDC2, termed CDC2deltaT, that lacks 171 nucleotides corresponding to 57 amino acids, which compose most of the T-loop. CDC2deltaT was detected in 10 of 14 breast cancer tissues analyzed, whereas it was not detectable in diploid human fibroblast cell lines or in interleukin 2-stimulated normal human lymphocytes. CDC2deltaT protein is unable to complex with cyclin B1 and lacks histone H1 kinase activity. CDC2deltaT also fails to bind to the CDK inhibitor p21. These results indicate that the T-loop not only plays a key role in keeping a free CDK in its inactive state but also in facilitating CDK activation by promoting cyclin binding.
authors.affiliation: First Department of Surgery, St. Marianna University School of Medicine, Kawasaki, Japan. tomo@imap.unc.edu
authors.forename: T
authors.initials: T
authors.lastname: Ohta
authors.forename: K
authors.initials: K
authors.lastname: Okamoto
authors.forename: F
authors.initials: F
authors.lastname: Isohashi
authors.forename: K
authors.initials: K
authors.lastname: Shibata
authors.forename: M
authors.initials: M
authors.lastname: Fukuda
authors.forename: S
authors.initials: S
authors.lastname: Yamaguchi
authors.forename: Y
authors.initials: Y
authors.lastname: Xiong
mesh_terms: D017398:Alternative Splicing; D001483:Base Sequence; D001943:Breast Neoplasms / Q000378:metabolism*; D016203:CDC2 Protein Kinase / Q000737:chemistry* / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D005260:Female; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D006656:Protamine Kinase / Q000378:metabolism; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics; D012334:RNA, Neoplasm / Q000235:genetics; D017384:Sequence Deletion; D013329:Structure-Activity Relationship; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
chemical_list: C534699:CCNB1 protein, human; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; D008869:Microtubule-Associated Proteins; D012333:RNA, Messenger; D012334:RNA, Neoplasm; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D006656:Protamine Kinase; D016203:CDC2 Protein Kinase