Loss of IkappaB alpha-mediated control over nuclear import and DNA binding enables oncogenic activation of c-Rel.
The IkappaB alpha protein is able both to inhibit nuclear import of Rel/NF-kappaB proteins and to mediate the export of Rel/NF-kappaB proteins from the nucleus. We now demonstrate that the c-Rel-IkappaB alpha complex is stably retained in the cytoplasm in the presence of leptomycin B, a specific inhibitor of Crm1-mediated nuclear export. In contrast, leptomycin B treatment results in the rapid and complete relocalization of the v-Rel-IkappaB alpha complex from the cytoplasm to the nucleus. IkappaB alpha also mediates the rapid nuclear shuttling of v-Rel in an interspecies heterokaryon assay. Thus, continuous nuclear export is required for cytoplasmic retention of the v-Rel-IkappaB alpha complex. Furthermore, although IkappaB alpha is able to mask the c-Rel-derived nuclear localization sequence (NLS), IkappaB alpha is unable to mask the v-Rel-derived NLS in the context of the v-Rel-IkappaB alpha complex. Taken together, our results demonstrate that IkappaB alpha is unable to inhibit nuclear import of v-Rel. We have identified two amino acid differences between c-Rel and v-Rel (Y286S and L302P) which link the failure of IkappaB alpha to inhibit nuclear import and DNA binding of a mutant c-Rel protein to oncogenesis. Our results support a model in which loss of IkappaB alpha-mediated control over c-Rel leads to oncogenic activation of c-Rel.
Biochemistry Department, University of Missouri-Columbia, Columbia, Missouri 65212, USA.
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D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D002467:Cell Nucleus / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005347:Fibroblasts; D019084:Fluorescent Antibody Technique, Indirect; D020672:I-kappa B Proteins; D007700:Kinetics; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors; D020572:Oncogene Proteins v-rel; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D020569:Proto-Oncogene Proteins c-rel; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D015682:Retroviridae Proteins, Oncogenic / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; D020572:Oncogene Proteins v-rel; D011518:Proto-Oncogene Proteins; D020569:Proto-Oncogene Proteins c-rel; D011994:Recombinant Proteins; D015682:Retroviridae Proteins, Oncogenic; D000072000:NF-KappaB Inhibitor alpha