Regulated processing of hepatitis C virus core protein is linked to subcellular localization

Abstract

Posttranslational processing and subcellular localization of the HCV core protein are critical steps involved in the assembly of hepatitis C virus (HCV). In this study, both of these events were investigated by in vitro translation and transient COS-1 cell transfection of core protein expression constructs. Mutations at amino acid residues 173 to 174 and 191 to 192 disrupted processing events at the two putative cleavage sites in the C-terminal hydrophobic region of the core protein, indicating that these residues are implicated in the pathway of core protein maturation. As a result, two forms of core protein, C173 and C191, were detected by immunoblotting. Indirect immunofluorescence experiments showed that core proteins C173 and C191, when produced from HCV full-length protein or various polyprotein precursors, displayed a cytoplasmic localization. The C173 species, however, was translocated to the nucleus when expressed in the absence of C191. These findings indicate that preferential cleavage may occur during core protein maturation and that the association of the C191 with the C173 species may contribute to the distinct subcellular distribution of core protein. This may provide a possible mechanism for the control of the diverse biological functions of core protein during HCV replication and assembly.

Continuous human cell lines inducibly expressing hepatitis C virus structural and nonstructural proteins

“…[45][46][47] In addition, there is a striking similarity with the staining pattern observed for NS1, NS2B, and NS3 proteins in cells infected with the related flavivirus Kunjin. 48 In contrast with previous reports investigating full-length and especially truncated forms of core and NS3 proteins, 20,25,[49][50][51][52] there was no evidence of nuclear localization of these proteins in the context of a full-length HCV ORF expression construct in UHCV cells. The opportunity to observe HCV structural and nonstructural proteins in the context of a complete viral ORF allowed us to perform double immunostaining studies for the various viral proteins.…”

Role of hepatitis C virus proteins (C, NS3, NS5A) in hepatic oncogenesis

“…The core protein representing aa 1-173 (C173) expressed in the absence of C191 is able to translocate into the nucleus. 110 The nuclear localization of the C protein of the incomplete protein molecule has been demonstrated by other authors. 19,60,114 The nuclear localization of the core protein has been finally confirmed as being caused by the presence of a nuclear localization signal (NLS) of the basic aa cluster at the N terminus of the core protein by other authors.…”

“…8,[107][108][109] Several forms of the core protein of variable molecular weights (17-23 kDa) were demonstrated. 16,[110][111][112][113] In the HCV-infected human liver, the molecular mass of core protein was 20 kDa, which corresponds to the mature form from recombinant sources. 49 The mature core protein corresponded to the product of 173 aa of the HCV open reading frame.…”

Immature Core protein of hepatitis C virus induces an unfolded protein response through inhibition of ERAD‐L in a yeast model system

“…Alternatively, amino acid substitution in the HCV protein may be due to the highly frequent error ratio of the RNA replicase. Some artificial amino acid substitutions in the C-terminal peptide resulted in inhibition of the processing (Liu et al 1997;Okamoto et al 2008;Pene et al 2009). Our results showed that the conservation of the cellular response to Core in yeast and mammalian cells, as indicated by UPR, may be induced by Core-dependent perturbation of ER luminal protein homeostasis in HCV-infected hepatocytes.…”

“…After the production of the Core region (aa 1 to aa 191, Core191), Core 191 is furthermore processed by signal peptide peptidase (SPP) in the C-terminal signal peptide region (McLauchlan et al 2002). Several cleavage sites of the later processing have been determined between aa 173 and aa 182 (Hussy et al 1996;Liu et al 1997;Ogino et al 2004;Okamoto et al 2008), although aa 1 to aa 177 of Core (Core177) is needed for virus production (Kopp et al 2010). We speculated that some of the Cores with different C-termini except Core177 may eventually remain in cells and may affect cellular homeostasis.…”