Effect of the 5′ non-translated region on self-assembly of hepatitis C virus genotype 1a structural proteins produced in insect cells

Optimum ribavirin exposure overcomes racial disparity in efficacy of peginterferon and ribavirin treatment for hepatitis C genotype 1

OBJECTIVES

Peginterferon and ribavirin treatment is less effective for hepatitis C virus (HCV) genotype 1 infections in African Americans (AA) compared with Caucasian Americans (CA). Host genetic variability near the interleukin-28B (IL28B) gene locus is partly responsible. We investigated the relationship between ribavirin drug exposure and week 24 and 72 (sustained virologic response, SVR) responses (undetected serum HCV RNA) in 71 AA and 74 CA with HCV genotype 1 who received >90% of the prescribed peginterferon and weight-based ribavirin (1,000 or 1,200 mg per day) from week 1 to 24.

METHODS

Ribavirin plasma levels were measured at weeks 1, 2, 4, 8, 12 and 24; ribavirin area under the concentration vs. time curve (AUC) was calculated using the linear trapezoidal rule.

RESULTS

Compared with CA, AA had lower week 24 (WK24VR) (57.8 vs. 78.1; P<0.05) and week 72 (SVR) (36.6% vs 54.8%; P<0.05) response rates. AA also had significantly lower ribavirin exposure (AUC) from week 1 to 12 (P<0.05). Ribavirin exposures ≥4,065 and ≥4,480 ng/ml/day in the first week (AUC(0-7)) were thresholds for WK24VR and SVR in receiver-operating characteristic curve analyses. AA were less likely to have a threshold ribavirin AUC(0-7) level than CA (P<0.05). There were no significant racial differences in WK24VR (AA: 77 vs. CA: 84%) and SVR (AA: 52 vs. CA: 60%) rates in patients who met the ribavirin AUC(0-7) thresholds. Ribavirin AUC(0-7) predicted WK24VR and SVR independently of IL28B single-nucleotide polymorphism rs12979860 genotype. Yet, achieving threshold AUC(0-7) levels increased response rates primarily in AA with the less favorable non-C/C genotypes.

CONCLUSIONS

Standard weight-based dosing leads to suboptimal ribavirin exposure in AA and contributes to the racial disparity in peginterferon and ribavirin treatment efficacy for HCV genotype 1.

Single nucleotide polymorphism upstream of interleukin 28B associated with phase 1 and phase 2 of early viral kinetics in patients infected with HCV genotype 1

BACKGROUND & AIMS

We studied the relationship between IL28B gene-related SNP rs12979860 and early viral kinetics (day 0-28) during peginterferon and ribavirin treatment, in 173 African Americans (AA) and 188 Caucasian Americans (CA) with HCV genotype 1.

METHODS

We studied the relationship between IL28B 16 gene-related SNP rs12979860 and early viral kinetics (day 0-28) 17 during peginterferon and ribavirin treatment, in 171 African 18 Americans (AA) and 188 Caucasian Americans (CA) with HCV 19 genotype 1.

RESULTS

Compared to non-C/C genotypes, C/C was associated with greater declines in serum HCV RNA during phase 1 (day 0-2), phase 2 (day 7-28), and day 0-28 and higher response (undetected HCV RNA) rates at weeks 4 and 12 in AA and CA. A static phase and increases in HCV RNA from day 2 to 7 were more common in patients with non-C/C genotypes. C/C was also associated with higher week 24, 48, and 72 response rates in CA (p<0.01) but not in AA. At baseline, SNP genotype was the only independent predictor of phase 1; SNP genotype and phase 1 were independent predictors of phase 2 (p<0.001). There were no racial differences in HCV RNA declines during phase 1, day 2-7, phase 2, and day 0-28 with the same SNP genotype. AA with C/C and C/T genotypes had lower week 24, 48, and 72 (SVR) rates than did CA (p=0.03). SNP C/C predicted higher SVR rates in AA and CA with high baseline HCV RNA (≥ 600,000 IU/ml), and in CA with ≥ 1 log(10)IU/ml decrease in HCV RNA from day 0 to 28.

CONCLUSIONS

SNP rs12979860 is strongly associated with both phase 1 and phase 2 HCV RNA kinetics in AA and CA with HCV genotype 1.

Cellular models for the screening and development of anti-hepatitis C virus agents

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible, reliable and consistent manner. Many different models based on different forms of virions and hepatoma or other cell types have been described including virus-like particles, pseudotyped particles, subgenomic and full length replicons, virion productive replicons, immortalised hepatocytes, fetal and adult primary human hepatocytes. This review focuses on these different cellular models, their advantages and disadvantages at the biological and experimental levels, and their respective use for evaluating the effect of antiviral molecules on different steps of HCV biology including virus entry, replication, particles generation and excretion, as well as on the modulation by the virus of the host cell response to infection.

Evidence for cellular uptake of recombinant hepatitis C virus non-enveloped capsid-like particles

Although the hepatitis C virus (HCV) is an enveloped virus, naked nucleocapsids have been reported in the serum of infected patients, and most recently novel HCV subgenomes with deletions of the envelope proteins have been identified. However the significance of these findings remains unclear. In this study, we used the baculovirus expression system to generate recombinant HCV capsid-like particles, and investigated their possible interactions with cells. We show that expression of HCV core in insect cells can sufficiently direct the formation of capsid-like particles in the absence of the HCV envelope glycoproteins and of the 5' untranslated region. By confocal microscopy analysis, we provide evidence that the naked capsid-like particles could be uptaken by human hepatoma cells. Moreover, our findings suggest that they have the potential to produce cell-signaling effects.

Signal Peptide Peptidase-catalyzed Cleavage of Hepatitis C Virus Core Protein Is Dispensable for Virus Budding but Destabilizes the Viral Capsid

The capsid of hepatitis C virus (HCV) particles is considered to be composed of the mature form (p21) of core protein. Maturation to p21 involves cleavage of the transmembrane domain of the precursor form (p23) of core protein by signal peptide peptidase (SPP), a cellular protease embedded in the endoplasmic reticulum membrane. Here we have addressed whether SPP-catalyzed maturation to p21 is a prerequisite for HCV particle morphogenesis in the endoplasmic reticulum. HCV structural proteins were expressed by using recombinant Semliki Forest virus replicon in mammalian cells or recombinant baculovirus in insect cells, because these systems have been shown to allow the visualization of HCV budding events and the isolation of HCV-like particles, respectively. Inhibition of SPP-catalyzed cleavage of core protein by either an SPP inhibitor or HCV core mutations not only did not prevent but instead tended to facilitate the observation of viral buds and the recovery of virus-like particles. Remarkably, although maturation to p21 was only partially inhibited by mutations in insect cells, p23 was the only form of core protein found in HCV-like particles. Finally, newly developed assays demonstrated that p23 capsids are more stable than p21 capsids. These results show that SPP-catalyzed cleavage of core protein is dispensable for HCV budding but decreases the stability of the viral capsid. We propose a model in which p23 is the form of HCV core protein committed to virus assembly, and cleavage by SPP occurs during and/or after virus budding to predispose the capsid to subsequent disassembly in a new cell.

Baculovirus as versatile vectors for protein expression in insect and mammalian cells

Today, many thousands of recombinant proteins, ranging from cytosolic enzymes to membrane-bound proteins, have been successfully produced in baculovirus-infected insect cells. Yet, in addition to its value in producing recombinant proteins in insect cells and larvae, this viral vector system continues to evolve in new and unexpected ways. This is exemplified by the development of engineered insect cell lines to mimic mammalian cell glycosylation of expressed proteins, baculovirus display strategies and the application of the virus as a mammalian-cell gene delivery vector. Novel vector design and cell engineering approaches will serve to further enhance the value of baculovirus technology.