The expression of the core gene of two different hepatitis C virus (HCV) isolates was analyzed. In the presence of its downstream E1 envelope protein sequence, two major core protein products with molecular masses of 21 kDa (P21) and 19 kDa (P19) and a minor protein product with molecular mass of 16 kDa (P16) were detected. In the absence of its downstream E1 envelope protein sequence, P21 and P19 remained the major protein products expressed from the core gene of the HCV-RH isolate, whereas P16 became the major protein product of the core gene of the HCV-1 isolate. Analysis of the amino-terminal sequences of P21 and P16 expressed in Escherichia coli revealed that P21 and P16 were co-amino terminal. Deletion-mapping analysis indicated that P16 lacked the carboxy-terminal sequence of P21. Immunofluorescence analysis of the subcellular localization of different HCV core proteins indicated that P21 and P19 displayed a reticular and punctate staining pattern typical of endoplasmic reticulum-associated proteins, while P16 was localized to the nucleus. The distinct subcellular localization of P16 raises the possibility that P16 may have a biological function very different from those of P21 and P19.

More than twenty years of study has provided a better understanding of hepatitis C virus (HCV) life cycle, including the general properties of viral RNA and proteins. This effort facilitates the development of sensitive diagnostic tools and effective antiviral treatments. At present, serologic screening test is recommended to perform on individuals in the high risk groups and nucleic acid tests are recommended to confirm the active HCV infections. Quantization and genotyping of HCV RNAs are important to determine the optimal duration of anti-viral therapy and predict the likelihood of response. In the early 2000s, pegylated interferon plus ribavirin became the standard anti-HCV treatment. However, this therapy is not ideal. To 2014, boceprevir, telaprevir, simeprevir, sofosbuvir and Harvoni are approved by Food and Drug Administration for the treat of HCV infections. It is likely that the new all-oral, interferon-free, pan-genotyping anti-HCV therapy will be available within the next few years. Majority of HCV infections will be cured by these antiviral treatments. However, not all patients are expected to be cured due to viral resistance and the high cost of antiviral treatments. Thus, an efficient prophylactic vaccine will be the next challenge in the fight against HCV infection. Core tip: Understanding the general properties of hepatitis C virus (HCV) viral RNA and proteins facilitates the development of sensitive diagnostic tools and effective antiviral treatments. At present, serologic screening test is recommended to perform on individuals in the high risk groups and nucleic acid tests are recommended to confirm the active HCV infections. To 2014, in addition to pegylated interferon and ribavirin, boceprevir, telaprevir, simeprevir, sofosbuvir and Harvoni are approved by Food and Drug Administration to treat HCV infections. The majority of HCV infections can be cured by these anti-viral treatments. An efficient prophylactic vaccine will be the next challenge in the fight against HCV infection. REVIEWSubmit a

In addition to being a structural protein that packages the viral genomic RNA, hepatitis C virus (HCV) core protein possesses regulatory functions. In this report, we demonstrate that the HCV core protein could enhance the gene transactivation activity of the tumor suppressor p53, regardless of whether p53 was derived from an exogenous or an endogenous gene. The activation of p53 by the HCV core protein was supported by the observation that the HCV core protein could enhance the expression of p21(waf1/Cip1), a downstream effector gene of p53, in a p53-dependent manner. Further studies indicated that the HCV core protein could also suppress hepatocellular growth via p53. The HCV core protein and p53 could bind to each other in vitro, which was evidenced by the coimmunoprecipitation, the GST pull-down, and the Far-Western blot assays. The deletion-mapping analysis indicated that the carboxy-terminal sequence of p53 located between amino acids 366 and 380 was required for the core protein binding. These results raised the possibility that the HCV core protein might activate p53 through direct physical interaction. The persistent perturbation of p53 activity by the HCV core protein during chronic infection may have important consequences in HCV pathogenesis.

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Hepatitis C virus (HCV) core protein is a multifunctional protein. We examined whether it can interact with cellular proteins, thus contributing to viral pathogenesis. Using the HCV core protein as a bait to screen a human liver cDNA library in a yeast two-hybrid screening system, we have isolated several positive clones encoding cellular proteins that interact with the HCV core protein. Interestingly, more than half of these clones encode the cytoplasmic domain of lymphotoxin-␤ receptor (LT ␤ R), which is a member of the tumor necrosis factor receptor family. Their binding was confirmed by in vitro glutathione S-transferase fusion protein binding assay and protein-protein blotting assay to be direct and specific. The binding sites were mapped within a 58-amino-acid region of the cytoplasmic tail of LT ␤ R. The binding site in the HCV core protein was localized within amino acid residues 36 to 91 from the N terminus, corresponding to the hydrophilic region of the protein. In mammalian cells, the core protein was found to be associated with the membrane-bound LT ␤ R. Since the LT ␤ R is involved in germinal center formation and developmental regulation of peripheral lymphoid organs, lymph node development, and apoptotic signaling, the binding of HCV core protein to LT ␤ R suggests the possibility that this viral protein has an immunomodulating function and may explain the mechanism of viral persistence and pathogenesis of HCV.

Severe acute respiratory syndrome-associated coronavirus (SARS-CoV) structural proteins (S, E, M, and NC) localize in different subcellular positions when expressed individually. However, SARS-CoV M protein is co-localized almost entirely with S, E, or NC protein when co-expressed in the cells. On the other hand, only partial co-localization was observed when S and E, S and NC, or E and NC were co-expressed in the cells. Interactions between SARS-CoV M and other structural proteins but not interactions between S and E, S and NC, or E and NC were further demonstrated by co-immunoprecipitation assay. These results indicate that SARS-CoV M protein, similar to the M proteins of other coronaviruses, plays a pivotal role in virus assembly. The cytoplasmic C-terminus domain of SARS-CoV M protein was responsible for binding to NC protein. Multiple regions of M protein interacted with E and S proteins. A model for the interactions between SARS-CoV M protein and other structural proteins is proposed. This study helps us better understand protein-protein interactions during viral assembly of SARS-CoV.

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