title: Human T-cell leukemia virus type 1 Tax protein binds to assembled nuclear proteasomes and enhances their proteolytic activity.
abstract: The human T-cell leukemia virus type 1 (HTLV-1) Tax protein activates the HTLV-1 long terminal repeat and key regulatory proteins involved in inflammation, activation, and proliferation and may induce cell transformation. Tax is also the immunodominant target antigen for cytotoxic T cells in HTLV-1 infection. We found that Tax bound to assembled nuclear proteasomes, but Tax could not be detected in the cytoplasm. Confocal microscopy revealed a partial colocalization of Tax with nuclear proteasomes. As Tax translocated into the nucleus very quickly after synthesis, this process probably takes place prior to and independent of proteasome association. Tax mutants revealed that both the Tax N and C termini play a role in proteasome binding. We also found that proteasomes from Tax-transfected cells had enhanced proteolytic activity on prototypic peptide substrates. This effect was not due to the induction of the LMP2 and LMP7 proteasome subunits. Furthermore, Tax appeared to be a long-lived protein, with a half-life of around 15 h. These data suggest that the association of Tax with the proteasome and the enhanced proteolytic activity do not target Tax for rapid degradation and may not determine its immunodominance.
authors.affiliation: Nuffield Department of Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom. hemelaar@pinnacle.jr2.ox.ac.uk
authors.forename: J
authors.initials: J
authors.lastname: Hemelaar
authors.forename: F
authors.initials: F
authors.lastname: Bex
authors.forename: B
authors.initials: B
authors.lastname: Booth
authors.forename: V
authors.initials: V
authors.lastname: Cerundolo
authors.forename: A
authors.initials: A
authors.lastname: McMichael
authors.forename: S
authors.initials: S
authors.lastname: Daenke
mesh_terms: D001692:Biological Transport; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D016356:Gene Products, tax / Q000737:chemistry / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000502:physiology; D006801:Humans; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex
chemical_list: D016356:Gene Products, tax; D015395:Histocompatibility Antigens Class I; D009097:Multienzyme Complexes; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex