title: Interaction of retroviral Tax oncoproteins with tristetraprolin and regulation of tumor necrosis factor-alpha expression.
abstract: BACKGROUND
  The Tax oncoproteins are transcriptional regulators of viral expression involved in pathogenesis induced by complex leukemogenic retroviruses (or delta-retroviruses, i.e., primate T-cell leukemia viruses and bovine leukemia virus). To better understand the molecular pathways leading to cell transformation, we aimed to identify cellular proteins interacting with Tax.
  
  
  METHODS
  We used a yeast two-hybrid system to identify interacting cellular proteins. Interactions between Tax and candidate interacting cellular proteins were confirmed by glutathione S-transferase (GST) pulldown assays, co-immunoprecipitation, and confocal microscopy. Functional interactions between Tax and one interacting protein, tristetraprolin (TTP), were assessed by analyzing the expression of tumor necrosis factor-alpha (TNF-alpha), which is regulated by TTP, in mammalian cells (HeLa, D17, HEK 293, and RAW 264.7) transiently transfected with combinations of intact and mutant Tax and TTP.
  
  
  RESULTS
  We obtained seven interacting cellular proteins, of which one, TTP, was further characterized. Tax and TTP were found to interact specifically through their respective carboxyl-terminal domains. The proteins colocalized in the cytoplasm in a region surrounding the nucleus of HeLa cells. Furthermore, coexpression of Tax was associated with nuclear accumulation of TTP. TTP is an immediate-early protein that inhibits expression of TNF-alpha at the post-transcriptional level. Expression of Tax reverted this inhibition, both in transient transfection experiments and in stably transfected macrophage cell lines.
  
  
  CONCLUSIONS
  Tax, through its interactions with the TTP repressor, indirectly increases TNF-alpha expression. This observation is of importance for the cell transformation process induced by leukemogenic retroviruses, because TNF-alpha overexpression plays a central role in pathogenesis.
authors.affiliation: Biologie cellulaire et moléculaire, Faculté Universitaire des Sciences Agronomiques, Gembloux, Belgium.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Twizere
authors.forename: Véronique
authors.initials: V
authors.lastname: Kruys
authors.forename: Laurent
authors.initials: L
authors.lastname: Lefèbvre
authors.forename: Alain
authors.initials: A
authors.lastname: Vanderplasschen
authors.forename: Delphine
authors.initials: D
authors.lastname: Collete
authors.forename: Christophe
authors.initials: C
authors.lastname: Debacq
authors.forename: Wi S
authors.initials: WS
authors.lastname: Lai
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Jauniaux
authors.forename: Lori R
authors.initials: LR
authors.lastname: Bernstein
authors.forename: O John
authors.initials: OJ
authors.lastname: Semmes
authors.forename: Arsène
authors.initials: A
authors.lastname: Burny
authors.forename: Perry J
authors.initials: PJ
authors.lastname: Blackshear
authors.forename: Richard
authors.initials: R
authors.lastname: Kettmann
authors.forename: Luc
authors.initials: L
authors.lastname: Willems
mesh_terms: D000818:Animals; D002417:Cattle; D018076:DNA, Complementary / Q000032:analysis; D004268:DNA-Binding Proteins; D015972:Gene Expression Regulation, Neoplastic; D016356:Gene Products, tax / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D001909:Leukemia Virus, Bovine; D018613:Microscopy, Confocal; D009154:Mutation; D009369:Neoplasms / Q000378:metabolism* / Q000821:virology; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011233:Precipitin Tests; D014162:Transfection; D051816:Tristetraprolin; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D015854:Up-Regulation; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D017874:Immediate-Early Proteins; D051816:Tristetraprolin; D014409:Tumor Necrosis Factor-alpha; C497552:ZFP36 protein, human; D001616:beta-Galactosidase