title: Functional characterization of a human cyclin T1 mutant reveals a different binding surface for Tat and HEXIM1.
abstract: HIV transcription is regulated at the step of elongation by the viral Tat protein and the cellular positive transcription elongation factor b (P-TEFb; Cdk9/cyclin T1). Herein, a human cyclin T1 mutant, cyclin T1-U7, which contains four substitutions and one deletion in the N-terminal cyclin box, was stably expressed in HeLa cells. HIV transcription was efficiently inhibited in HeLa-HA-CycT1-U7 stable cells. Cyclin T1-U7 bound Tat but did not modulate its expression levels, which remained high. Importantly cyclin T1-U7 failed to interact with Cdk9 or HEXIM1 and did not interfere with endogenous P-TEFb activity to stimulate MEF2C or NFkB mediated transcription. In a T cell line and primary CD4+ cells, cyclin T1-U7 also inhibited HIV transcription. We conclude that cyclin T1-U7 sequesters Tat from P-TEFb and inhibits HIV transcription. Importantly, N-terminal residues in cyclin T1 are specifically involved in the binding of cyclin T1 to HEXIM1 but not to Tat.
authors.affiliation: Department of Virology and Developmental Genetics Faculty of Health Sciences, Ben-Gurion University of the Negev, Israel.
authors.forename: Alona
authors.initials: A
authors.lastname: Kuzmina
authors.forename: Uzi
authors.initials: U
authors.lastname: Hadad
authors.forename: Koh
authors.initials: K
authors.lastname: Fujinaga
authors.forename: Ran
authors.initials: R
authors.lastname: Taube
mesh_terms: D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism / Q000821:virology; D056906:Cyclin T / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D015658:HIV Infections / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism*
chemical_list: D056906:Cyclin T; C476123:HEXIM1 protein, human; D016601:RNA-Binding Proteins; D014157:Transcription Factors; D054322:tat Gene Products, Human Immunodeficiency Virus