title: TOK-1, a novel p21Cip1-binding protein that cooperatively enhances p21-dependent inhibitory activity toward CDK2 kinase.
abstract: A p21(Cip1/Waf1/Sdi1) is known to act as a negative cell-cycle regulator by inhibiting kinase activity of a variety of cyclin-dependent kinases. In addition to binding of the cyclin-dependent kinase to the N-terminal region of p21, p21 is also bound at its C-terminal region by proliferating cell nuclear antigen (PCNA), SET/TAF1, and calmodulin, indicating the versatile function of p21. In this study, we cloned cDNA encoding a novel protein named TOK-1 as a p21 C-terminal-binding protein by a two-hybrid system. Two splicing isoforms of TOK-1, TOK-1alpha and TOK-1beta, comprising 322 and 314 amino acids, respectively, were co-localized with p21 in nuclei and showed a similar expression profile to that of p21 in human tissues. TOK-1alpha, but not TOK-1beta, directly bound to the C-terminal proximal region of p21, and both were expressed at the G(1)/S boundary of the cell cycle. TOK-1alpha also preferentially bound to an active form of cyclin-dependent kinase 2 (CDK2) via p21, and these made a ternary complex in human cells. Furthermore, the results of three different types of experiments showed that TOK-1alpha enhanced the inhibitory activity of p21 toward histone H1 kinase activity of CDK2. TOK-1alpha is thus thought to be a new type of CDK2 modulator.
authors.affiliation: Graduate School of Pharmaceutical Sciences, College of Medical Technology, Hokkaido University, Kita-ku, Sapporo 060, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Ono
authors.forename: H
authors.initials: H
authors.lastname: Kitaura
authors.forename: H
authors.initials: H
authors.lastname: Ugai
authors.forename: T
authors.initials: T
authors.lastname: Murata
authors.forename: K K
authors.initials: KK
authors.lastname: Yokoyama
authors.forename: S M
authors.initials: SM
authors.lastname: Iguchi-Ariga
authors.forename: H
authors.initials: H
authors.lastname: Ariga
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D042846:CDC2-CDC28 Kinases; D019556:COS Cells; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D002453:Cell Cycle; D018797:Cell Cycle Proteins; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003001:Cloning, Molecular; D018388:Codon, Terminator; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000737:chemistry / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins; D010770:Phosphotransferases / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism; D011485:Protein Binding; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D013997:Time Factors; D014018:Tissue Distribution; D020798:Two-Hybrid System Techniques
chemical_list: C415366:BCCIP protein, human; C493956:CDKN1A protein, human; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D018388:Codon, Terminator; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D018076:DNA, Complementary; D009687:Nuclear Proteins; D018809:Proliferating Cell Nuclear Antigen; D020033:Protein Isoforms; D011994:Recombinant Proteins; D005982:Glutathione Transferase; D010770:Phosphotransferases; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases