| Research Abstract |
Cells expressing the NS3 protein of hepatitis C virus, which were more resistant against actinomycin D-induced apoptosis, expressed a decreased level of p53 tumor suppressor protein than that of the control cells. Therefore, possible interaction between NS3 and p53 was studied. The full-size NS3 (NS3F) and a C-terminally truncated form of NS3 (NS3DELTAC), both of which were localized in the cytoplasm and the nucleus when expressed alone, were shown to be colocalized with p53 almost exclusively in the nucleus. On the other hand, NS3DELTANDELTAC, which lacks N-terminal 174 amino acid (aa) residues of NS3DELTAC, was not colocalized with p53. Immunoprecipitation analysis revealed that NS3F and NS3DELTAC, but not NS3DELTANDELTAC, coprecipitated with p53, suggesting that NS3 and p53 can form a complex through an N-terminal portion of NS3. A mutant form of NS3DELTAC that lacks N-terminal 28 aa residues still formed a complex with p53, although it did not form a complex with NS4A.This result indicates that p53-binding domain of NS3 is different from the NS4A-binding domain, supporting our observation that complex formation between NS3 and p53 takes place even in the presence of NS4A.Whereas an N-terminally truncated form of p53 bbund to NS3, C-terminal 93 aa-deleted p53 did not bind to NS3. Taken together, these results suggest that a portion near the N-terminus of NS3 (aa 1055 - 1200) and a C-terminal portion of p53 (aa 301 - 393), the latter of which contains p53 polymerization domain, are important for the complex formation between the two molecules. By using a CAT reporter plasmid that carries a p53-responsive promoter, NS3F and NS3DELTAC, but not NS3DELTANDELTAC, were shown to suppress transactivating function of p53, further implying the possible involvement of NS3 in hepatocarcinogenesis by hepatitis C virus.
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