Direct association and nuclear import of the hepatitis B virus X protein with the NF-kappaB inhibitor IkappaBalpha.
The X protein of hepatitis B virus (HBV) is a transcriptional activator which is required for infection and may play an important role in HBV-associated hepatocarcinogenesis. It has been suggested that X acts as a nuclear coactivator or stimulates several signal transduction pathways by acting in the cytoplasm. One of these pathways leads to the nuclear translocation of NF-kappaB. A recent report indicates that X activates NF-kappaB by acting on two cytoplasmic inhibitors of this family of transcription factors: IkappaBalpha and the precursor/inhibitor p105. We demonstrate here that X directly interacts with IkappaBalpha, which is able to transport it to the nucleus by a piggyback mechanism. This transport requires a region of IkappaBalpha (the second ankyrin repeat) which has been demonstrated to be involved in its nuclear import following NF-kappaB activation. Using deletion mutants, we showed that amino acids 249 to 253 of IkappaBalpha (located in the C-terminal part of the sixth ankyrin repeat) play a critical role in the interaction with X. This small region overlaps one of the domains of IkappaBalpha mediating the interaction with the p50 and p65 subunits of NF-kappaB and is also close to the nuclear export sequence of IkappaBalpha, therefore providing a potential explanation for the nuclear accumulation of IkappaBalpha with X. This association can also be observed upon the induction of endogenous IkappaBalpha by tumor necrosis factor alpha (TNF-alpha) treatment of Chang cells expressing X. In accordance with this observation, band shift analysis indicates that X induces a sustained NF-kappaB activation following TNF-alpha treatment, probably by preventing the reassociation of newly synthesized nuclear IkappaBalpha with DNA-bound NF-kappaB complexes.
Weil
R
R
Unité de Biologie Moléculaire de l'Expression Génique, URA 1773 Centre National de la Recherche Scientifique, Institut Pasteur, 75724 Paris Cedex 15, France.
Sirma
H
H
Giannini
C
C
Kremsdorf
D
D
Bessia
C
C
Dargemont
C
C
Bréchot
C
C
Israël
A
A
D000818:Animals; D001483:Base Sequence; D001693:Biological Transport, Active; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism / Q000821:virology; D015342:DNA Probes / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006515:Hepatitis B virus / Q000378:metabolism* / Q000472:pathogenicity; D006801:Humans; D020672:I-kappa B Proteins; D009154:Mutation; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D014764:Viral Proteins / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins
D015342:DNA Probes; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D015534:Trans-Activators; D014409:Tumor Necrosis Factor-alpha; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D000072000:NF-KappaB Inhibitor alpha