Hepatitis C Virus Core Protein Selectively Inhibits Synthesis and Accumulation of p21/Waf1 and Certain Nuclear Proteins

Abstract

By using a vaccinia virus‐T7 expression system, possible effects of hepatitis C virus (HCV) core protein on synthesis and accumulation of host cellular proteins transiently expressed in cultured cells were analyzed. Immunoblot and immunofluorescence analyses revealed that synthesis and accumulation of certain nuclear proteins, such as p21/Waf1, p53, proliferating cell nuclear antigen and c‐Fos, were strongly inhibited by HCV core protein. On the other hand, synthesis and accumulation of cytoplasmic proteins, such as 2′‐5′‐oligoadenylate synthetase (2′‐5′‐OAS), RNase L and MEK1, were barely affected by HCV core protein. Northern blot analysis showed that the degrees of mRNA expression for those proteins did not differ between HCV core protein‐expressing cells and the control, suggesting that the inhibition occurred at the post‐transcription level. Pulse‐labeling analysis suggested that HCV core protein strongly inhibited synthesis of p21/Waf1 at the translation level. Once being accumulated in the nucleus, p21/Waf1 stability was not significantly affected by HCV core protein. Mutants of HCV core protein C‐terminally deleted by 18 or 41 amino acids (aa), which were localized almost exclusively in the nucleus, lost their ability to inhibit synthesis/accumulation of p21/Waf1 whereas another mutant C‐terminally deleted by 8 aa still maintained the same properties (subcellular localization and the inhibitory effect) as the full‐length HCV core protein of 191 aa. Taken together, our present results suggest that expression of HCV core protein in the cytoplasm selectively inhibits synthesis of p21/Waf1 and some other nuclear proteins at the translation level.

p21/Wafl/Cipl cellular expression in chronic long-lasting hepatitis C: correlation with HCV proteins (C, NS3, NS5A), other cell-cycle related proteins and selected clinical data.

“…On the other hand, we have noted that expression of NS3 protein was directly related to expressions of p21 and cyclin D1. We have not been able to confirm the in vitro results demonstrating positive [20,21] or negative relationships [22,24] between core protein and p21 protein. We also couldn't demonstrate any correlation between NS5A protein and p21 protein expression [26,27].…”

“…The cytoplasmic form of core protein augmented p21 expression (via activation of p53) and the mature form in the cell nucleus inhibited it (the p53-independent pathway) [23]. In an another study inhibition of p21 synthesis was demonstrated by the core protein situated in the cytoplasm [24]. Out of the non-structural HCV proteins, NS3 can promote growth [25] but NS5A protein can either promote [26] or inhibit growth via up-regulation of p21 [27].…”

Suppression of Hepatitis C Virus Replicon by RNA Interference Directed against the NS3 and NS5B Regions of the Viral Genome

“…Immunoblotting was performed as described previously (36). In brief, Huh7-FK2884Gly-1 cells were lysed in a buffer consisting of 50 mM Tris-HCl (pH 8.0), 150 mM NaCl, 0.2% sodium azide, 0.1% sodium dodecyl sulfate (SDS), 0.1% NP-40, and 0.5% sodium deoxycholate.…”

Physical and functional interactions between hnRNP K and PRMT family proteins

“…Controversial observations have been reported about the effects of HCV Core protein on p53 and p21 expressions because of the different subcellular localizations for its nascent or mature forms [19][20][21][22]. Our previous study demonstrated that hnRNP K protein might serve as a p53 coactivator in the non-stress condition [10].…”