title: Physical interaction of human T-cell leukemia virus type 1 Tax with cyclin-dependent kinase 4 stimulates the phosphorylation of retinoblastoma protein.
abstract: The Tax oncoprotein of human T-cell leukemia virus type 1 (HTLV-1) induces leukemia in transgenic mice and permanent T-cell growth in vitro. In transformed lymphocytes, it acts as an essential growth factor. Tax stimulates the cell cycle in the G(1) phase by activating the cyclin-dependent kinase (CDK) CDK4 and CDK6 holoenzyme complexes. Here we show that Tax directly interacts with CDK4. This binding to CDK4 was specific, since Tax did not bind to either CDK2 or CDK1. The interaction with CDK4/cyclin D complexes was observed in vitro, in transfected fibroblasts, in HTLV-1-infected T cells, and in adult T-cell leukemia-derived cultures. Binding studies with several point and deletion mutants indicated that the N terminus of Tax mediates the interaction with CDK4. The Tax/CDK complex represented an active holoenzyme which capably phosphorylates the Rb protein in vitro and is resistant to repression by the inhibitor p21(CIP). Binding-deficient Tax mutants failed to activate CDK4, indicating that direct association with Tax is required for enhanced kinase activity. Tax also increased the association of CDK4 with its positive cyclin regulatory subunit. Thus, protein-protein contact between Tax and the components of the cyclin D/CDK complexes provides a further mechanistic explanation for the mitogenic and immortalizing effects of this HTLV-1 oncoprotein.
authors.affiliation: Institut für Klinische und Molekulare Virologie, D-91054 Erlangen, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Haller
authors.forename: Yalin
authors.initials: Y
authors.lastname: Wu
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Derow
authors.forename: Iris
authors.initials: I
authors.lastname: Schmitt
authors.forename: Kuan-Teh
authors.initials: KT
authors.lastname: Jeang
authors.forename: Ralph
authors.initials: R
authors.lastname: Grassmann
mesh_terms: D002478:Cells, Cultured; D056742:Cyclin D2; D056743:Cyclin D3; D051358:Cyclin-Dependent Kinase 4; D051361:Cyclin-Dependent Kinase 6; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D005347:Fibroblasts / Q000502:physiology; D016356:Gene Products, tax / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1 / Q000378:metabolism*; D006801:Humans; D008214:Lymphocytes / Q000378:metabolism; D010766:Phosphorylation; D011233:Precipitin Tests; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism*
chemical_list: C080336:CCND2 protein, human; C534696:CCND3 protein, human; C493956:CDKN1A protein, human; C534697:Ccnd3 protein, mouse; D056742:Cyclin D2; D056743:Cyclin D3; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D016356:Gene Products, tax; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; D016160:Retinoblastoma Protein; 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