title: Differential phosphorylation of T-47D human breast cancer cell substrates by D1-, D3-, E-, and A-type cyclin-CDK complexes.
abstract: The cyclin-dependent kinases (CDKs) promote cell cycle transitions in mammalian cells by phosphorylation of key substrates. To characterize substrates of the G1 and S phase cyclin-CDK complexes, including cyclin D1-CDK4, cyclin D3-CDK4, cyclin D3-CDK6, cyclin E-CDK2, and cyclin A-CDK2, which are largely undefined, we phosphorylated T-47D breast cancer cell nuclear lysates partially purified by ion-exchange chromatography with purified baculovirus expressed cyclin-CDK complexes. A comparison of the substrates that were phosphorylated by the different cyclin D-CDKs revealed some common as well as specific substrates. Hence, cyclin D1-CDK4 specifically phosphorylated a 38-kDa protein while cyclin D3-CDK4 specifically phosphorylated proteins of 105, 102, and 42 kDa. A 24-kDa protein was phosphorylated by both complexes. Cyclin D3-CDK6 exhibited similar substrate preferences to cyclin D3-CDK4, phosphorylating the 105- and 102-kDa proteins but not the 24-kDa protein. Hence, both the cyclin D1 and D3 as well as CDK4 and CDK6 subunits can confer substrate specificity on the overall cyclin D-CDK complex. Cyclin E-CDK2 and cyclin A-CDK2 phosphorylated a greater number of substrates than the cyclin D-CDKs, ranging in size from 10 kDa to over 200 kDa. Twenty-two substrates were common to both complexes, while six were specific for cyclin A-CDK2 and only one protein of 34 kDa was specific for cyclin E-CDK2. These studies indicate that cyclins E and A modulate the specificity of CDK2 and have demonstrated substrates that may be important for the specific roles of these cyclin-CDKs during G1 and S phase progression. Protein sequencing of one of the cyclin-CDK substrates characterized in this study identified this protein as nucleolin, a previously characterized CDC2 (CDK1) substrate, thus indicating the utility of this approach in identifying cyclin-CDK targets. These results show that both the cyclin and CDK subunits can regulate the substrate specificity of the overall cyclin-CDK complex and have demonstrated numerous substrates of D-, E-, and A-type cyclin-CDK complexes potentially involved in regulating transit through the G1 and S phases of the cell cycle.
authors.affiliation: Cancer Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Darlinghurst, New South Wales 2010, Australia. b.sarcevic@garvan.unsw.edu.au
authors.forename: B
authors.initials: B
authors.lastname: Sarcevic
authors.forename: R
authors.initials: R
authors.lastname: Lilischkis
authors.forename: R L
authors.initials: RL
authors.lastname: Sutherland
mesh_terms: D000595:Amino Acid Sequence; D001943:Breast Neoplasms / Q000378:metabolism; D002384:Catalysis; D019925:Cyclin A / Q000378:metabolism*; D056741:Cyclin D; D056743:Cyclin D3; D019927:Cyclin E / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000378:metabolism*; D005260:Female; D016193:G1 Phase; D006801:Humans; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D016196:S Phase; D014407:Tumor Cells, Cultured
chemical_list: C534696:CCND3 protein, human; D019925:Cyclin A; D056741:Cyclin D; D056743:Cyclin D3; D019927:Cyclin E; D016213:Cyclins; D046911:Macromolecular Substances; D011518:Proto-Oncogene Proteins; D017346:Protein Serine-Threonine Kinases; C495900:CDK4 protein, human; C495911:CDK6 protein, human; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases