title: Human T-cell leukemia virus type 1 Tax releases cell cycle arrest induced by p16INK4a.
abstract: The human T-cell leukemia virus type 1 (HTLV-1) Tax oncoprotein causes cellular transformation by deregulating important cellular processes such as DNA repair, transcription, signal transduction, proliferation, and growth. Although it is clear that normal cell cycle control is deregulated during HTLV-1-induced cellular transformation, the effects of Tax on cell cycle control are not well understood. Flow cytometric analyses of human T cells indicate that cell cycle arrest in late G1, at or before the G1/S restriction point, by p16INK4a is relieved by Tax. Furthermore, Tax-dependent stimulation of 5-bromo-2'-deoxyuridine incorporation and transcriptional activation is inhibited by p16INK4a. This result suggests that p16INK4a is able to block Tax-dependent stimulation of DNA synthesis and cell cycle progression into S phase. In vitro binding assays with recombinant glutathione S-transferase fusion proteins and [35S]methionine-labeled proteins indicate that Tax binds specifically with p16INK4a but not with either p21cip1 or p27kip1. Furthermore, sequential immunoprecipitation assays with specific antisera and [35S]methionine-labeled cell lysates subsequent to coexpression with Tax and p16INK4a indicate that the two proteins form complexes in vivo. Immunocomplex kinase assays with cyclin-dependent kinase 4 antiserum indicate that Tax blocks the inhibition of cdk4 kinase activity by p16INK4a. This study identifies p16INK4a as a novel cellular target for Tax and suggests that the inactivation of p16INK4a function is a mechanism of cell cycle deregulation by Tax.
authors.affiliation: Laboratory of Cell Signaling, New England Biolabs, Beverly, Massachusetts 01915, USA. low@neb.com
authors.forename: K G
authors.initials: KG
authors.lastname: Low
authors.forename: L F
authors.initials: LF
authors.lastname: Dorner
authors.forename: D B
authors.initials: DB
authors.lastname: Fernando
authors.forename: J
authors.initials: J
authors.lastname: Grossman
authors.forename: K T
authors.initials: KT
authors.lastname: Jeang
authors.forename: M J
authors.initials: MJ
authors.lastname: Comb
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D002460:Cell Line; D002461:Cell Line, Transformed; D002522:Chlorocebus aethiops; D051358:Cyclin-Dependent Kinase 4; D019941:Cyclin-Dependent Kinase Inhibitor p16; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism*; D016356:Gene Products, tax / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D015368:Human T-lymphotropic virus 1; D006801:Humans; D019169:Jurkat Cells; D051379:Mice; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase; D015398:Signal Transduction / Q000502:physiology*; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
chemical_list: D002352:Carrier Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004791:Enzyme Inhibitors; D016356:Gene Products, tax; D011518:Proto-Oncogene Proteins; D011993:Recombinant Fusion Proteins; C495900:CDK4 protein, human; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases