Association between HTLV-1 Tax and I kappa B alpha is dependent on the I kappa B alpha phosphorylation state.
Biological, molecular, and epidemiological data have demonstrated that human T cell leukemia virus type 1 (HTLV-1) encoded Tax protein plays a central role in the initiation of T cell malignancy. The 40-kDa Tax oncoprotein serves as a potent transcriptional activator that induces viral gene expression driven by the HTLV-1 long terminal repeats and also stimulates multiple cellular genes involved in T cell activation, cell cycle regulation, and gene activation. Since Tax has been shown to interact directly and indirectly with the NF-kappa B/I kappa B regulatory proteins, we examined the significance of an in vivo association between Tax and the I kappa B alpha inhibitor. Using GST affinity chromatography, Tax was shown to interact with the I kappa B alpha ankyrin repeats which are essential for interaction with the NF-kappa B/Rel proteins. In vivo, using I kappa B alpha mutants and co-immunoprecipitation, a preferential interaction between HTLV-1 Tax and N-terminally hypophosphorylated I kappa B alpha was detected. Tax also enhanced binding of I kappa B alpha to the proteasome subunit HsN3, resulting in a Tax-enhanced, constitutive degradation of wild-type and mutated forms of I kappa B alpha in the absence of phosphorylation and ubiquitination. Binding of I kappa B alpha to proteasome subunit HC9 was also observed, but this interaction occurred independently of Tax. Taken together, these results suggest a role for Tax as a viral chaperone resulting in the enhanced constitutive turnover of I kappa B alpha. The association of Tax with hypophosphorylated I kappa B alpha may prevent I kappa B alpha from binding to NF-kappa B and also target I kappa B alpha to the proteasome for degradation via a phosphorylation-independent pathway.
Petropoulos
L
L
Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis-Jewish General Hospital, Montréal, Québec, Canada.
Hiscott
J
J
D016475:3T3 Cells; D000818:Animals; D017487:Ankyrins / Q000378:metabolism; D001665:Binding Sites; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D016356:Gene Products, tax / Q000378:metabolism*; D015368:Human T-lymphotropic virus 1; D006801:Humans; D020672:I-kappa B Proteins; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011485:Protein Binding; D011487:Protein Conformation; D013329:Structure-Activity Relationship; D015533:Transcriptional Activation
D017487:Ankyrins; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C000606205:Nfkbia protein, mouse; D000072000:NF-KappaB Inhibitor alpha; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex