title: Cyclin A-CDK phosphorylates Sp1 and enhances Sp1-mediated transcription.
abstract: Cyclin A-mediated activation of cyclin-dependent kinases (CDKs) is essential for cell cycle transversal. Cyclin A activity is regulated on several levels and cyclin A elevation in a number of cancers suggests a role in tumorigenesis. In the present study, we used a modified DNA binding site selection and PCR amplification procedure to identify DNA binding proteins that are potential substrates of cyclin A-CDK. One of the sequences identified is the Sp1 transcription factor binding site. Co-immunoprecipitation experiments show that cyclin A and Sp1 can interact physically. In vitro and in vivo phosphorylation studies indicate that cyclin A-CDK complexes can phosphorylate Sp1. The phosphorylation site is located in the N-terminal region of the protein. Cells overexpressing cyclin A have elevated levels of Sp1 DNA binding activity, suggesting that cyclin A-CDK-mediated phosphorylation augments Sp1 DNA binding properties. In co-transfection studies, cyclin A expression stimulated transcription from an Sp1-regulated promoter. Mutation of the phosphorylation site abrogated cyclin A-CDK-dependent phosphorylation, augmentation of Sp1 transactivation function and DNA binding activity.
authors.affiliation: Department of Medical Microbiology and Immunology, University of California, Davis, CA 95616, USA.
authors.forename: P
authors.initials: P
authors.lastname: Fojas de Borja
authors.forename: N K
authors.initials: NK
authors.lastname: Collins
authors.forename: P
authors.initials: P
authors.lastname: Du
authors.forename: J
authors.initials: J
authors.lastname: Azizkhan-Clifford
authors.forename: M
authors.initials: M
authors.lastname: Mudryj
mesh_terms: D016475:3T3 Cells; D000818:Animals; D019925:Cyclin A / Q000502:physiology*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000502:physiology; D004247:DNA / Q000378:metabolism; D004790:Enzyme Induction; D005786:Gene Expression Regulation / Q000502:physiology*; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D010766:Phosphorylation; D010768:Phosphoserine / Q000737:chemistry; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011494:Protein Kinases / Q000502:physiology*; D011499:Protein Processing, Post-Translational; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012045:Regulatory Sequences, Nucleic Acid; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis / Q000235:genetics; D015533:Transcriptional Activation / Q000502:physiology*; D014162:Transfection
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D016329:Sp1 Transcription Factor; D010768:Phosphoserine; D004247:DNA; D013762:Tetrahydrofolate Dehydrogenase; D011494:Protein Kinases; C102333:histone H1 kinase