title: A non-SUMOylated tax protein is still functional for NF-κB pathway activation.
abstract: Whether NF-κB promoter transactivation by the human T-cell leukemia virus type 1 (HTLV-1) Tax protein requires Tax SUMOylation is still a matter of debate. In this study, we revisited the role of Tax SUMOylation using a strategy based on the targeting of Ubc9, the unique E2 SUMO-conjugating enzyme. We show that either a catalytically inactive form of Ubc9 (Ubc9-C93S) or Ubc9 small interfering RNA (siRNA) dramatically reduces Tax conjugation to endogenous SUMO-1 or SUMO-2/3, demonstrating that as expected, Tax SUMOylation is under the control of the catalytic activity of Ubc9. We further report that a non-SUMOylated Tax protein produced in 293T cells is still able to activate either a transfected or an integrated NF-κB reporter promoter and to induce expression of an NF-κB-regulated endogenous gene. Importantly, blocking Ubc9 activity in T cells also results in the production of a non-SUMOylated Tax that is still fully functional for the activation of a NF-κB promoter. These results provide the definitive evidence that Tax SUMOylation is not required for NF-κB-driven gene induction.
  
  
  OBJECTIVE
  Human T-cell leukemia virus type 1 is able to transform CD4(+) T lymphocytes. The viral oncoprotein Tax plays a key role in this process by promoting cell proliferation and survival, mainly through permanent activation of the NF-κB pathway. Elucidating the molecular mechanisms involved in NF-κB pathway activation by Tax is therefore a key issue to understand HTLV-1-mediated transformation. Tax SUMOylation was initially proposed to be critical for Tax-induced NF-κB promoter activation, which was challenged by our later observation that a low-level-SUMOylated Tax mutant was still functional for activation of NF-κB promoters. To clarify the role of Tax SUMOylation, we set up a new approach based on the inhibition of the SUMOylation machinery in Tax-expressing cells. We show that blocking the SUMO-conjugating enzyme Ubc9 abolishes Tax SUMOylation and that a non-SUMOylated Tax still activates NF-κB promoters in either adherent cells or T cells.
authors.affiliation: INSERM, U1016, Institut Cochin, Paris, France, CNRS, UMR8104, Paris, France, and Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Pène
authors.affiliation: INSERM, U1016, Institut Cochin, Paris, France, CNRS, UMR8104, Paris, France, and Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors.forename: Laetitia
authors.initials: L
authors.lastname: Waast
authors.affiliation: INSERM, U1016, Institut Cochin, Paris, France, CNRS, UMR8104, Paris, France, and Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors.forename: Amandine
authors.initials: A
authors.lastname: Bonnet
authors.affiliation: INSERM, U1016, Institut Cochin, Paris, France, CNRS, UMR8104, Paris, France, and Université Paris Descartes, Sorbonne Paris Cité, Paris, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Bénit
authors.affiliation: INSERM, U1016, Institut Cochin, Paris, France, CNRS, UMR8104, Paris, France, and Université Paris Descartes, Sorbonne Paris Cité, Paris, France claudine.pique@inserm.fr.
authors.forename: Claudine
authors.initials: C
authors.lastname: Pique
mesh_terms: D016356:Gene Products, tax / Q000235:genetics / Q000378:metabolism*; D015490:HTLV-I Infections / Q000201:enzymology / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D015368:Human T-lymphotropic virus 1 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D016328:NF-kappa B / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D058207:Sumoylation; D015533:Transcriptional Activation; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000378:metabolism; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: D016356:Gene Products, tax; D016328:NF-kappa B; C514970:tax protein, Human T-lymphotrophic virus 1; D044763:Ubiquitin-Conjugating Enzymes; D000098843:Ubiquitin-Conjugating Enzyme UBC9