title: The human vaccinia-related kinase 1 (VRK1) phosphorylates threonine-18 within the mdm-2 binding site of the p53 tumour suppressor protein.
abstract: The tumour suppressor p53 protein integrates multiple signals regulating cell cycle progression and apoptosis. This regulation is mediated by several kinases that phosphorylate specific residues in the different functional domains of the p53 molecule. The human VRK1 protein is a new kinase related to a poxvirus kinase, and more distantly to the casein kinase 1 family. We have characterized the biochemical properties of human VRK1 from HeLa cells. VRK1 has a strong autophosphorylating activity in several Ser and Thr residues. VRK-1 phosphorylates acidic proteins, such as phosvitin and casein, and basic proteins such as histone 2b and myelin basic protein. Because some transcription factors are regulated by phosphorylation, we tested as substrates the N-transactivation domains of p53 and c-Jun fused to GST. Human c-Jun is not phosphorylated by VRK1. VRK1 phosphorylates murine p53 in threonine 18. This threonine is within the p53 hydrophobic loop (residues 13-23) required for the interaction of p53 with the cleft of its inhibitor mdm-2. The VRK1 C-terminus domain (residues 268-396) that contains a nuclear localization signal targets the protein to the nucleus, as determined by using fusion proteins with the green fluorescent protein. We conclude that VRK1 is an upstream regulator of p53 that belongs to a new signalling pathway.
authors.affiliation: Centro de Investigación del Cáncer, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones Científicas, Universidad de Salamanca, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Lopez-Borges
authors.forename: P A
authors.initials: PA
authors.lastname: Lazo
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D047388:Casein Kinases; D020134:Catalytic Domain; D002467:Cell Nucleus / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000145:classification / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D011506:Proteins; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D011993:Recombinant Fusion Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013379:Substrate Specificity; D013912:Threonine / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D011506:Proteins; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D016159:Tumor Suppressor Protein p53; D014764:Viral Proteins; D013912:Threonine; D012694:Serine; C497206:MDM2 protein, human; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D011494:Protein Kinases; D047388:Casein Kinases; D017346:Protein Serine-Threonine Kinases; C109890:VRK1 protein, human