Interaction of retroviral Tax oncoproteins with tristetraprolin and regulation of tumor necrosis factor-alpha expression

J Natl Cancer Inst. 2003 Dec 17;95(24):1846-59. doi: 10.1093/jnci/djg118.


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.

Conclusion: 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Cattle
  • DNA, Complementary / analysis
  • DNA-Binding Proteins*
  • Gene Expression Regulation, Neoplastic*
  • Gene Products, tax / metabolism*
  • Human T-lymphotropic virus 1*
  • Humans
  • Immediate-Early Proteins / genetics
  • Immediate-Early Proteins / metabolism*
  • Leukemia Virus, Bovine*
  • Microscopy, Confocal
  • Mutation
  • Neoplasms / metabolism*
  • Neoplasms / virology
  • Plasmids
  • Polymerase Chain Reaction
  • Precipitin Tests
  • Transfection
  • Tristetraprolin
  • Tumor Necrosis Factor-alpha / metabolism*
  • Up-Regulation
  • beta-Galactosidase / metabolism


  • DNA, Complementary
  • DNA-Binding Proteins
  • Gene Products, tax
  • Immediate-Early Proteins
  • Tristetraprolin
  • Tumor Necrosis Factor-alpha
  • ZFP36 protein, human
  • beta-Galactosidase