Identification of hepatitis C virus (HCV) subtype 1b strains that are highly, or only weakly, associated with hepatocellular carcinoma on the basis of the secondary structure of an amino-terminal portion of the HCV NS3 protein

From viruses to cancer: exploring the role of the hepatitis C virus NS3 protein in carcinogenesis

Hepatitis C virus (HCV) chronically infects approximately 170 million people worldwide and is a known etiological agent of hepatocellular carcinoma (HCC). The molecular mechanisms of HCV-mediated carcinogenesis are not fully understood. This review article focuses on the oncogenic potential of NS3, a viral protein with transformative effects on cells, although the precise mechanisms remain elusive. Unlike the more extensively studied Core and NS5A proteins, NS3's roles in cancer development are less defined but critical. Research indicates that NS3 is implicated in several carcinogenic processes such as proliferative signaling, cell death resistance, genomic instability and mutations, invasion and metastasis, tumor-related inflammation, immune evasion, and replicative immortality. Understanding the direct impact of viral proteins such as NS3 on cellular transformation is crucial for elucidating HCV's role in HCC development. Overall, this review sheds light on the molecular mechanisms used by NS3 to contribute to hepatocarcinogenesis, and highlights its significance in the context of HCV-associated HCC, underscoring the need for further investigation into its specific molecular and cellular actions.

Occurrence of late relapse of hepatitis C virus confirmed by molecular analysis after sustained virologic response to interferon-ribavirin-based therapy

AIM

The optimal duration of follow-up for patients who achieve sustained virologic responses (SVR) has become an important issue. Reports on long-term follow-up of SVR have indicated that 99% of patients maintained SVR. However, the limitations of a majority of studies include small patient numbers, short study periods, and lack of molecular analysis of hepatitis C virus (HCV) genome. The present study sought to evaluate the late relapse rate in long-term follow-up of patients who achieved SVR, with molecular analysis of HCV.

METHODS

A total of 224 patients with chronic hepatitis C who were treated by interferon and ribavirin-based therapy and achieved SVR were enrolled. All patients were recommended for follow-up every 6 or 12 months.

RESULTS

The mean follow-up period was 6.0 years (range, 1.0-13.6 years). Cumulative 5- and 10-year follow-up rates of the patients after SVR were 87.8% and 78.8%, respectively. Cumulative 5- and 10-year follow-up rates of serum HCV RNA after SVR were 85.5% and 52.6%, respectively. Two patients had detectable serum HCV RNA at 20 and 30 months, respectively, after SVR. Phylogenetic analyses of core, non-structural protein 3, and 5A regions of HCV strains from late relapse patients confirmed the same strain was present at baseline and late relapse.

CONCLUSIONS

Two of 224 patients developed late relapse of HCV by the original strain, which was confirmed by direct sequencing analysis. Although few patients may develop late relapse, SVR achieved with interferon and ribavirin-based therapy is durable for prolonged periods.

Polymorphisms of the NS3 Proteins of Hepatitis C Virus Genotype 1b Are Associated with Liver Cirrhosis

Polymorphisms of the hepatitis C virus (HCV) core protein and NS3 have been described to be associated with liver cirrhosis (LC) and/or hepatocellular carcinoma in patients with chronic hepatitis C genotype 1b (HCV 1b). Here, we determine whether there is an association between LC and polymorphisms of viral core protein and NS3 in patients in Hubei province, China. A total of 42 patients with chronic HCV 1b (21 patients with LC and 21 with chronic hepatitis [CH]) were enrolled, amino acid sequence of the core protein and N-terminus of NS3 were obtained by direct sequencing and compared with the prototype strain HCV-J. No significant difference of amino acid polymorphisms was observed between isolates from LC and CH patients in the core protein. However, in the N-terminus of NS3, amino acid polymorphisms at positions A1072T (Ala 1072 chronic Thr 1072 cirrhosis), I1074V (Ile 1074 chronic Val 1074 cirrhosis), and T1098N/I (Thr 1098 chronic Asn or Ile 1098 cirrhosis) correlated significantly with LC. These findings indicate that the polymorphisms of HCV at these sites may be the risk factors for the development of LC in patients with chronic HCV 1b.

Duplication of the V3 domain in hepatitis C virus (1b) NS5A protein: Clonal analysis and physicochemical properties related to hepatocellular carcinoma occurrence

BACKGROUND

Hepatitis C virus non-structural protein 5A is known to play a role in development of hepatocellular carcinoma (HCC) via interactions with host cell pathways.

OBJECTIVES

Hepatitis C virus genotype 1b strains presenting a wide insertion of 31 amino acids in the non-structural protein 5A V3 domain (V3 DI) were studied to determine whether this V3-like additional domain (V3 DII) was associated with HCC occurrence.

STUDY DESIGN

Seventy-four patients' sera were screened for V3 DII presence regarding clinical status.

RESULTS

Three strains with duplicated V3 were detected among patients with progression to HCC (n=28), two strains among patients with liver cirrhosis (Ci, n=27) and none among patients with chronic hepatitis (Chr, n=19). Phylogenetic trees built from V3 DI and V3 DII sequences indicated that the latter clustered separately. In between-group clonal analysis, V3 DII sequences from the HCC group were found to be more distant from HCV-J than V3 DI sequences (p<0.0001). Between-group comparisons showed significant differences in genetic distances from HCV-J, in HCC V3 DI and HCC V3 DII compared to Ci V3 DI and Ci V3 DII sequences (p<0.0001). HCC V3 DII domain and its junction with V3 DI exhibited higher Shannon entropy values and enrichment in disorder-promoting residues.

CONCLUSIONS

Taken together, our results suggest that V3 DII evolution may differ in strains associated with HCC occurrence. The presence of an intrinsically "disordered" V3 duplicate may alter the NS5A protein network. Further investigations are necessary to elucidate the potential impact of V3 duplication in the context of carcinogenesis.

Polymorphisms of the core, NS3, and NS5A proteins of hepatitis C virus genotype 1b associate with development of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the common sequelae of hepatitis C virus (HCV) infection. It remains controversial, however, whether HCV itself plays a direct role in the development of HCC. Although HCV core, NS3, and NS5A proteins were reported to display tumorigenic activities in cell culture and experimental animal systems, their clinical impact on HCC development in humans is still unclear. In this study we investigated sequence polymorphisms in the core protein, NS3, and NS5A of HCV genotype 1b (HCV-1b) in 49 patients who later developed HCC during a follow-up of an average of 6.5 years and in 100 patients who did not develop HCC after a 15-year follow-up. Sequence analysis revealed that Gln at position 70 of the core protein (core-Gln(70) ), Tyr at position 1082 plus Gln at 1112 of NS3 (NS3-Tyr(1082) /Gln(1112) ), and six or more mutations in the interferon/ribavirin resistance-determining region of NS5A (NS5A-IRRDR≥6) were significantly associated with development of HCC. Multivariate analysis identified core-Gln(70) , NS3-Tyr(1082) /Gln(1112) , and α-fetoprotein (AFP) levels (>20 ng/L) as independent factors associated with HCC. Kaplan-Meier analysis revealed a higher cumulative incidence of HCC for patients infected with HCV isolates with core-Gln(70) , NS3-Tyr(1082) /Gln(1112) or both than for those with non-(Gln(70) plus NS3-Tyr(1082) /Gln(1112) ). In most cases, neither the residues at position 70 of the core protein nor positions 1082 and 1112 of the NS3 protein changed during the observation period.

CONCLUSION

HCV isolates with core-Gln(70) and/or NS3-Tyr(1082) /Gln(1112) are more closely associated with HCC development compared to those with non-(Gln(70) plus NS3-Tyr(1082) /Gln(1112) ).

Decreased apoptosis in advanced-stage/high-grade hepatocellular carcinoma complicating chronic hepatitis C is mediated through the downregulation of p21 ras

OBJECTIVE AND BACKGROUND

Although p21 ras has been reported to be upregulated in hepatocellular carcinoma complicating chronic hepatitis C type I, p21 ras has a different role in advanced stages, as it has been found to be downregulated. The goal of this study was to investigate the status of p21 ras in early-stage/low-grade and late-stage/high-grade hepatocellular carcinoma and its possible link to apoptosis.

MATERIAL AND METHODS

Thirty-five cases each of chronic HCV hepatitis type 4 (group I) and cirrhosis with hepatocellular carcinoma (HCC) complicating chronic HCV hepatitis (groups II and III) were immunohistochemically evaluated using a p21 ras polyclonal antibody. The apoptotic index was determined in histologic sections using the terminal deoxynucleotidyl transferase-mediated d-UTP biotin nick end labeling (TUNEL) assay.

RESULTS

Significant differences (P=0.001) were detected in p21 ras protein expression between the three groups. A near 2-fold increase in p21 ras staining was observed in the cirrhotic cases compared to the hepatitis cases, and p21 ras expression was decreased in the HCC group. p21 ras expression correlated with stage (r=0.64, P=0.001) and grade (r=(-)0.65, P=0.001) in the HCC group and grade in the HCV group (r=0.44, P=0.008). Both p21 ras expression and TUNEL-LI were significantly lower in large HCCs compared to small HCCs (P=0.01 each). The TUNEL values were negatively correlated with stage in the HCC group (r=(-)0.85, P=0.001). The TUNEL values were also negatively correlated with grade in both the HCV and HCC groups (r=0.89, P=0.001 and r=(-)0.53, P=0.001, respectively). The p21 ras scores were significantly correlated with the TUNEL-LI values in the HCC group (r=0.63, P=0.001) and HCV group (r=0.88, P=0.001).

CONCLUSIONS

p21 ras acts as an initiator in HCC complicating type 4 chronic HCV and is downregulated with HCC progression, which most likely promotes tumor cell survival because it facilitates the downregulation of apoptosis with tumor progression.

Amino acid substitutions in the hepatitis C Virus core region and lipid metabolism are associated with hepatocarcinogenesis in nonresponders to interferon plus ribavirin combination therapy

BACKGROUND

Substitution of amino acid 70 and/or 91 in the core region of hepatitis C virus (HCV) genotype 1b (HCV-1b) is an important predictor of hepatocellular carcinoma (HCC), but its impact on HCC in nonresponders to interferon (IFN) and ribavirin (RIB) combination therapy is not clear.

METHODS

A total of 292 patients with HCV-1b-related chronic liver disease who did not achieve a sustained virological response to 24-48 weeks of IFN+RIB combination therapy were included in a follow-up study to investigate the risk factors for HCC.

RESULTS

Sixteen patients developed HCC during the follow-up. The cumulative HCC rates were 5.0, 13.1 and 16.9% at the end of 3, 5 and 7 years, respectively. Multivariate analysis identified substitution of core amino acid 70 (Gln70/His70; hazard ratio 4.64, p = 0.018) and low serum levels of high-density lipoprotein cholesterol (<50 mg/dl; hazard ratio 9.35, p = 0.041) as determinants of HCC. Gender, stage of fibrosis and interleukin-28B showed no such relationship.

CONCLUSIONS

Amino acid substitution in the core region of HCV-1b and low serum levels of high-density lipoprotein cholesterol are significant and independent predictors of HCC in nonresponders to IFN+RIB combination therapy. These results emphasize the importance of viral and lipid metabolic factors in the development of HCC after combination therapy.

Secondary structure of the amino-terminal region of HCV NS3 and virological response to pegylated interferon plus ribavirin therapy for chronic hepatitis C

The aim of the study was to identify a predictive marker for the virological response in hepatitis C virus 1b (HCV-1b)-infected patients treated with pegylated interferon plus ribavirin therapy. A total of 139 patients with chronic hepatitis C who received therapy for 48 weeks were enrolled. The secondary structure of the 120 residues of the amino-terminal HCV-1b non-structural region 3 (NS3) deduced from the amino acid sequence was classified into two major groups: A and B. The association between HCV NS3 protein polymorphism and virological response was analyzed in patients infected with group A (n = 28) and B (n = 40) isolates who had good adherence to both pegylated interferon and ribavirin administration (>95% of the scheduled dosage) for 48 weeks. A sustained virological response (SVR) representing successful HCV eradication occurred in 33 (49%) in the 68 patients. Of the 28 patients infected with the group A isolate, 18 (64%) were SVR, whereas of the 40 patients infected with the group B isolate only 15 (38%) were SVR. The proportion of virological responses differed significantly between the two groups (P < 0.05). These results suggest that polymorphism in the secondary structure of the HCV-1b NS3 amino-terminal region influences the virological response to pegylated interferon plus ribavirin therapy, and that virus grouping based on this polymorphism can contribute to prediction of the outcome of this therapy.

Management of hepatitis C; Report of the Consensus Meeting at the 45th Annual Meeting of the Japan Society of Hepatology (2009)

The consensus meeting for the diagnosis, management and treatment for hepatitis C was held in 45(th) annual meeting for the Japan Society of Hepatology (JSH) in June 2009 where the recommendations and informative statements were discussed including organizers and presenters. The Several important informative statements and recommendations have been shown. This was the fourth JSH consensus meeting of hepatitis C, however, the recommendations have not been published in English previously. Thus, this is the first report of JSH consensus of hepatitis C. The rate of development of hepatocellular carcinoma (HCC) in HCV-infected patients in Japan is higher than in the USA, because the average age of the HCV-infected patients is greater and there are more patients with severe fibrosis of the liver than in the USA. In Japan, more than 60% of HCV-infected patients are genotype 1b infection, and they show lower response to perinterferon and ribavirin combination treatment. To improve the response rate is also an important issue in our country. To establish the original recommendations and informative statements to prevent the development of HCC is a very important issue in Japan.

Sustained virological response in a patient with chronic hepatitis C treated by monotherapy with the NS3-4A protease inhibitor telaprevir

Here, we describe for the first time a case of sustained virological response (SVR) achieved in a patient with chronic hepatitis C (CH-C) by monotherapy with a NS3-4A protease inhibitor, telaprevir, without interferon therapy. A 59-year-old treatment-naïve Japanese man was enrolled in a phase II trial of telaprevir by repeat oral administration at a dose of 750mg every 8h for 24 weeks. At the start of treatment, he exhibited a low-level viremia with genotype 1b of the hepatitis C virus (HCV). After the first week of treatment with telaprevir, serum HCV RNA was undetectable, and negativity remained until the end of treatment. Moreover, he was evaluated as having a SVR after the post-treatment 24-week follow-up program. Two characteristics may explain the strong antiviral activity of telaprevir in the present case. First, although pre-treatment PCR-direct sequencing and cloning for the N-terminal in the NS3 region showed a protease inhibitor-resistant variant (T54A) in 1 of 32 independent clones, the T54A substitution has only a low-level resistance to protease inhibitors and his viral load was low. Second, when compared to a consequence sequence of 35 treatment-naïve patients with HCV genotype 1b, R130K and Q195K substitutions were unique to the present case. Although it is presently unknown whether the R130K and Q195K substitutions are related to SVR, this case suggests that long-term telaprevir monotherapy may be effective in CH-C patients with genotype 1 and a low viral load.

Conservation of hepatitis C virus nonstructural protein 3 amino acid sequence in viral isolates during liver transplantation

As a consequence of selective pressure exerted by the immune response during hepatitis C virus (HCV) infection, a high rate of nucleotide mutations in the viral genome is observed which leads to the emergence of viral escape mutants. The aim of this study was to evaluate the evolution of the amino acid (aa) sequence of the HCV nonstructural protein 3 (NS3) in viral isolates after liver transplantation. Six patients with HCV-induced liver disease undergoing liver transplantation (LT) were followed up for sequence analysis. Hepatitis C recurrence was observed in all patients after LT. The rate of synonymous (dS) nucleotide substitutions was much higher than that of nonsynonymous (dN) ones in the NS3 encoding region. The high values of the dS/dN ratios suggest no sustained adaptive evolution selection pressure and, therefore, absence of specific NS3 viral populations. Clinical genotype assignments were supported by phylogenetic analysis. Serial samples from each patient showed lower mean nucleotide genetic distance when compared with samples of the same HCV genotype and subtype. The NS3 samples studied had an N-terminal aa sequence with several differences as compared with reference ones, mainly in genotype 1b-infected patients. After LT, as compared with the sequences before, a few reverted aa substitutions and several established aa substitutions were observed at the N-terminal of NS3. Sites described to be involved in important functions of NS3, notably those of the catalytic triad and zinc binding, remained unaltered in terms of aa sequence. Rare or frequent aa substitutions occurred indiscriminately in different positions. Several cytotoxic T lymphocyte epitopes described for HCV were present in our 1b samples. Nevertheless, the deduced secondary structure of the NS3 protease showed a few alterations in samples from genotype 3a patients, but none were seen in 1b cases. Our data, obtained from patients under important selective pressure during LT, show that the NS3 protease remains well conserved, mainly in HCV 3a patients. It reinforces its potential use as an antigenic candidate for further studies aiming at the development of a protective immune response.

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

In recent years, the effects of hepatitis C virus (HCV) proteins on hepatocarcinogenesis have undergone intense investigations. The potentially oncogenic proteins include at least three HCV proteins: core (C) protein, NS3, and NS5A. Several authors indicated relationships between subcellular localization, concentration, a specific molecular form of the proteins (full length, truncated, phosphorylated), the presence of specific domains (the nuclear localization signal homologous to e.g. Bcl-2) and their effects on the mechanisms linked to oncogenesis. The involvement of all the proteins has been described as being in control of the cell cycle, through interactions with key proteins of the process (p53, p21, cyclins, proliferating cell nuclear antigen), transcription factors, proto-oncogenes, growth factors/cytokines and their receptors, and proteins linked to the apoptotic process. Untilnow, the involvement of the core protein of HCV in liver carcinogenesis is the most recognized. One of the most common proteins affected by HCV proteins is the p53 tumor-suppressor protein. The p21/WAF1 gene is a major target of p53, and the effect of HCV proteins on the gene is frequently considered in parallel. The results of studies on the effects of HCV proteins on the apoptotic process are controversial. This work summarizes the information collected thus far in the field of HCV molecular virology and principal intracellular signaling pathways in which HCV oncogenic proteins are involved.

Amino acid substitutions in the hepatitis C virus core region are the important predictor of hepatocarcinogenesis

We showed previously that amino acid (aa) substitutions in hepatitis C virus core region (HCV-CR) are negative predictors of virologic response to pegylated interferon (IFN) plus ribavirin therapy. HCV-CR induces hepatocellular carcinoma in transgenic mice, but the clinical impact is still unclear. To evaluate the impact of aa substitutions in HCV-CR on hepatocarcinogenesis, we performed a follow-up study on 313 noncirrhotic consecutive naïve patients infected with HCV genotype 1b who received IFN monotherapy. The median follow-up was 14.7 years. A sustained virologic response (SVR) after the first IFN was achieved by 65 patients (20.8%) (group A). Of 248 patients (79.2%) of non-SVR after first IFN, 112 (35.8%) did not receive additional IFN (group B), and the remaining 136 (43.5%) received multicourse IFN monotherapy (group C). As a whole, cumulative hepatocarcinogenesis rates in double wild-type (arginine at aa 70/leucine at aa 91) of HCV-CR were significantly lower than those in nondouble wild-type. Multivariate analyses identified 3 parameters (fibrosis stage 3, nondouble wild-type of HCV-CR, and group B) that tended to or significantly influenced hepatocarcinogenesis independently. With regard to hepatocarcinogenesis rates in group C according to HCV-CR and the mean alanine aminotransferase (ALT) during IFN-free period, significantly higher rates were noted in patients of nondouble wild-type with ALT levels of more than 1.5 times the upper limit of normal (25.7%) compared with the others (2.4%).

CONCLUSION

Amino acid substitutions in the HCV-CR are the important predictor of hepatocarcinogenesis. In multicourse IFN therapy to nondouble wild-type, we emphasize the importance of reducing the risk of hepatocarcinogenesis by mean ALT during an IFN-free period below 1.5 times the upper limit of normal.

Is hepatitis C virus NS3 protease quasispecies heterogeneity predictive of progression from cirrhosis to hepatocellular carcinoma?

We investigated whether an HCV NS3 protease quasispecies heterogeneity was associated with progression from viral cirrhosis to hepatocellular carcinoma (HCC). The NS3 protease quasispecies structure of 10 HCV-1b cirrhotic patients (controls) was compared with that of 10 paired HCV-1b cirrhotic patients who displayed progression to HCC (cases). NS3 protease genetic complexity and diversity did not differ significantly between cases and controls. Amino acid substitutions were detected at 20 (11%) and 25 (14%) sites in at least two variants of the NS3 protease in cases and controls, respectively. Significant differences in the percentage of substituted clones were observed for 10 NS3 sites. Mutations Y56F, I71V, T72I, Q86P, P89S, S101G/D, R117H, S122G/T/N, V132I and V170I were more frequently observed in the NS3 protease sequences of controls than in those of cases. Residue V107 was substituted in NS3 cases but not in controls. However, these differences did not allow the definition of a specific NS3 profile related to HCC occurrence. The NS3 secondary structure B1-1 previously identified as potentially predictive of HCC was identified with a higher frequency in cases quasispecies (84.2%) than in controls (55.9%; P < 0.05). Our results suggest that there may be a relationship to fibrosis progression when diversity parameters are considered together with secondary structure profiles. Further investigations are required to determine the cellular interactions of HCV NS3 protease in the context of carcinogenesis.

NS3 protein of Hepatitis C virus associates with the tumour suppressor p53 and inhibits its function in an NS3 sequence-dependent manner

The N-terminal 198 residues of NS3 (NS3-N) of Hepatitis C virus (HCV) subtype 1b obtained from 29 patients, as well as full-length NS3 (NS3-Full), were analysed for their subcellular localization, interaction with the tumour suppressor p53 and serine protease activity in the presence and absence of the viral cofactor NS4A. Based on the subcellular-localization patterns in the absence of NS4A, NS3-N sequences were classified into three groups, with each group exhibiting either dot-like, diffuse or a mixed type of localization. Chimeric NS3-Full sequences, each consisting of an individual NS3-N and a shared C-terminal sequence, showed the same localization patterns as those of the respective NS3-N. Site-directed mutagenesis experiments revealed that a single or a few amino acid substitutions at a particular position(s) of NS3-N altered the localization pattern. Interestingly, NS3 of the dot-like type, either NS3-N or NS3-Full, interacted with p53 more strongly than that of the diffuse type, in both the presence and the absence of NS4A. Moreover, NS3-N of the dot-like type suppressed trans-activating activity of p53 more strongly than that of the diffuse type. Serine protease activity did not differ significantly between the two types of NS3. In HCV RNA replicon-harbouring cells, physical interaction between NS3 and p53 was observed consistently and p53-mediated transcriptional activation was suppressed significantly compared with HCV RNA-negative control cells. Our results collectively suggest the possibility that NS3 plays an important role in the hepatocarcinogenesis of HCV by interacting differentially with p53 in an NS3 sequence-dependent manner.

Genetic similarity of hepatitis C virus and fibrosis progression in chronic and recurrent infection after liver transplantation

The effect of hepatitis C virus (HCV) genetic heterogeneity on clinical features of post-transplantation hepatitis C is controversial. Different regions of the HCV genome have been associated with apoptosis, fibrosis, and other pathways leading to liver damage in chronic HCV infection. Besides, differences in immunodominant regions, such as NS3, may influence HCV-specific immune responses and disease outcome. In the liver transplant setting, a recent study has reported a positive association between HCV-1b Core region genetic relatedness 5-year post-transplantation and histological severity of recurrent hepatitis C. We have compared nucleotide sequences of HCV Core, NS3 and NS5b regions in HCV-1b-infected patients 3 years post-transplantation (n = 22). A cohort of nontransplanted patients (n = 22) was used as control of natural chronic HCV-1b infection. Histological evaluation was used to define the rate of fibrosis progression. Molecular variance analysis did not show significant differences in HCV sequences between transplanted and nontransplanted patients, or between those with fast or slow fibrosis progression. The same results were obtained when analysing phylogenetic trees for Core, NS3 and NS5b regions. A more appropriate clustering method (using minimum spanning networks) revealed a significant positive relationship between HCV genetic similarity in Core (r = 0.550, P < 0.01) and NS5b regions (r = 0.847, P < 0.01) and the yearly rate of fibrosis progression in nontransplanted patients which, in contrast, was not observed in transplanted patients. Our results indicate that some strains of HCV-1b might be more pathogenic in the natural course of chronic infection by this virus subtype. In the liver transplant setting, when the immune response is severely compromised, other mechanisms are probably more important in determining hepatitis C progression.

Single-point mutations of hepatitis C virus NS3 that impair p53 interaction and anti-apoptotic activity of NS3

The N-terminal domain of NS3 of hepatitis C virus (HCV) possesses serine protease activity, which is essential for virus replication. This portion is also implicated in malignant transformation of hepatocytes. We previously demonstrated that an N-terminal portion of NS3 formed a complex with the tumor suppressor p53 and suppressed actinomycin D-induced apoptosis. We report here that single-point mutations of NS3 at position 106 from Leu to Ala (L106A), and position 43 from Phe to Ala (F43A) to a lesser extent, significantly impaired complex formation with p53. Moreover, the L106A mutation impaired an otherwise more distinct anti-apoptotic activity of NS3. F43A and L106A mutations also inhibited serine protease activity of NS3. These results collectively suggest the possibility that Leu106 and Phe43 are involved in p53 interaction and serine protease activity, and therefore, can be a good target for certain low-molecular-weight compound(s) to inhibit both oncogenic and replicative abilities of HCV.

Hepatitis C virus core variants isolated from liver tumor but not from adjacent non-tumor tissue interact with Smad3 and inhibit the TGF-beta pathway

Hepatitis C virus (HCV) is a major risk factor for human hepatocellular carcinoma (HCC) but the mechanisms underlying HCV-induced carcinogenesis are still poorly understood. We have hypothesized that viral variants, selected during long-term infection, might contribute to cellular transformation. To address this issue, we have investigated the effect of natural HCV core variants isolated from liver tumors (T), or their non-tumor (NT) counterparts, on the tumor growth factor-beta (TGF-beta) pathway, a major regulator of cellular proliferation, differentiation and apoptosis. We have found a significant reduction in TGF-beta reporter gene activity with the expression of core sequences isolated from liver tumors. In contrast, moderate or no effects were observed with non-tumor mutants or a core reference sequence. The molecular mechanisms have been characterized and involved the inhibition, by tumor-derived cores, of the DNA-binding activity of the Smad3/4 transcription factors complex. This inhibition occurs through a direct interaction between the central domain (amino acids 59-126) of tumor-derived core and the MH1 DNA-binding domain of Smad3, thus preventing its binding to DNA. We have therefore identified a new cell-signaling pathway targeted by HCV core and inhibited by tumor-derived core sequences. These results suggest that during chronic infection, there is selection of viral variants that may promote cell transformation by providing, to clonally expanding cells, resistance to TGF-beta antiproliferative effects.

Hepatitis C virus NS3 protein interacts with ELKS-δ and ELKS-α, members of a novel protein family involved in intracellular transport and secretory pathways

The NS3 protein of hepatitis C virus (HCV) has a serine protease activity in its N-terminal region, which plays a crucial role in virus replication. This region has also been reported to interact not only with its viral cofactor NS4A, but also with a number of host-cell proteins, which suggests a multifunctional feature of NS3. By means of yeast two-hybrid screening using an N-terminal region of NS3 as bait, a human cDNA encoding a region of ELKS-δ, a member of a novel family of proteins involved in intracellular transport and secretory pathways, was molecularly cloned. Using co-immunoprecipitation, GST pull-down and confocal and immunoelectron microscopic analyses, it was shown that full-length NS3 interacted physically with full-length ELKS-δ and its splice variant, ELKS-α, both in the absence and presence of NS4A, in cultured human cells, including Huh-7 cells harbouring an HCV subgenomic RNA replicon. The degree of binding to ELKS-δ varied with different sequences of the N-terminal 180 residues of NS3. Interestingly, NS3, either full-length or N-terminal fragments, enhanced secretion of secreted alkaline phosphatase (SEAP) from the cells, and the increase in SEAP secretion correlated well with the degree of binding between NS3 and ELKS-δ. Taken together, these results suggest the possibility that NS3 plays a role in modulating host-cell functions such as intracellular transport and secretion through its binding to ELKS-δ and ELKS-α, which may facilitate the virus life cycle and/or mediate the pathogenesis of HCV.

Activation of c-Jun NH2-terminal kinase (JNK) signaling pathway is essential for the stimulation of hepatitis C virus (HCV) non-structural protein 3 (NS3)-mediated cell growth

Hepatitis C virus (HCV) non-structural protein 3 (NS3) has been shown to affect cellular functions and is thought to contribute to the development of HCV-related hepatocarcinogenesis. In this study, we delineated part of the mechanisms whereby NS3 protein stimulates cell growth in liver (HepG2) and non-liver (HeLa) cells. The expression of NS3 protein enhanced cell growth, c-jun NH(2)-terminal kinase (JNK) activation, DNA binding activities of the transcription factors AP-1 and ATF-2, and c-jun expression, but not the activation of extracellular signal-regulated kinase (ERK) or p38(MAPK). Whereas co-expression of NS3 with its cofactor NS4A inhibited NS3-mediated cell growth without to influence NS3-mediated JNK activation, or to affect the basal activities of ERK or p38(MAPK). Pre-treatment of NS3 protein-expressing cells with JNK inhibitor, SP600125, abolished activation of AP-1 and ATF-2 and inhibited c-jun expression and induced cell growth, suggesting that JNK activation is essential for the stimulation of NS3-mediated cell growth.

Suppression of hepatitis C virus replicon by RNA interference directed against the NS3 and NS5B regions of the viral genome

RNA interference (RNAi) is a phenomenon in which small interfering RNA (siRNA), an RNA duplex 21 to 23 nucleotides (nt) long, or short hairpin RNA (shRNA) resembling siRNA, mediates degradation of the target RNA molecule in a sequence-specific manner. RNAi is now expected to be a useful therapeutic strategy for hepatitis C virus (HCV) infection. In the present study we compared the efficacy of a number of shRNAs directed against different target regions of the HCV genome, such as 5'-untranslated region (5'UTR) (nt 286 to 304), Core (nt 371 to 389), NS3-1 (nt 2052 to 2060), NS3-2 (nt 2104 to 2122), and NS5B (nt 7326 to 7344), all of which except for NS5B are conserved among most, if not all, HCV subtype 1b (HCV-1b) isolates in Japan. We utilized two methods to express shRNAs, one utilizing an expression plasmid (pAVU6+27) and the other utilizing a recombinant lentivirus harboring the pAVU6+27-derived expression cassette. Although 5'UTR has been considered to be the most suitable region for therapeutic siRNA and/or shRNA because of its extremely high degree of sequence conservation, we observed only a faint suppression of an HCV subgenomic replicon by shRNA against 5'UTR. In both plasmid-and lentivirus-mediated expression systems, shRNAs against NS3-1 and NS5B suppressed most efficiently the replication of the HCV replicon without suppressing host cellular gene expression. Synthetic siRNA against NS3-1 also inhibited replication of the HCV replicon in a dose-dependent manner. Taken together, the present results imply the possibility that the recombinant lentivirus expressing shRNA against NS3-1 would be a useful tool to inhibit HCV-1b infection.

Hepatitis C virus NS5A protein interacts with 2′,5′-oligoadenylate synthetase and inhibits antiviral activity of IFN in an IFN sensitivity-determining region-independent manner

The non-structural protein 5A (NS5A) of hepatitis C virus (HCV) has been implicated in inhibition of antiviral activity of IFN. While previous studies have suggested an interaction between NS5A and the double-stranded RNA-dependent protein kinase (PKR), the possibility still remains that interaction with another molecule(s) is involved in the NS5A-mediated inhibition of IFN. In the present study, we investigated a possible interaction between NS5A and 2′,5′-oligoadenylate synthetase (2-5AS), another key molecule in antiviral activity. We observed that NS5A physically interacted with 2-5AS in cultured cells, with an N-terminal portion of NS5A [aa 1–148; NS5A(1–148)] and two separate portions of 2-5AS (aa 52–104 and 184–275) being involved in the interaction. Single point mutations at residue 37 of NS5A affected the degree of the interaction with 2-5AS, with a Phe-to-Leu mutation (F37L) augmenting and a Phe-to-Asn mutation (F37N) diminishing it. Virus rescue assay revealed that the full-length NS5A (NS5A-F) and NS5A(1–148), the latter of which contains neither the IFN sensitivity-determining region (ISDR) nor the PKR-binding domain, significantly counteracted the antiviral activity of IFN. Introduction of a F37N mutation into NS5A(1–148) impaired the otherwise more significant IFN-inhibitory activity of NS5A(1–148). It was also found that the F37N mutation was highly disadvantageous for the replication of an HCV RNA replicon. Taken together, our results suggest the possibility that NS5A interacts with 2-5AS and inhibits the antiviral activity of IFN in an ISDR-independent manner.