Shufeng Liu

Tight Junction Proteins Claudin-1 and Occludin Control Hepatitis C Virus Entry and Are Downregulated during Infection To Prevent Superinfection

ABSTRACT A tight junction (TJ) protein, claudin-1 (CLDN1), was identified recently as a key factor for hepatitis C virus (HCV) entry. Here, we show that another TJ protein, occludin, is also required for HCV entry. Mutational study of CLDN1 revealed that its tight junctional distribution plays an important role in mediating viral entry. Together, these data support the model in which HCV enters liver cells from the TJ. Interestingly, HCV infection of Huh-7 hepatoma cells downregulated the expression of CLDN1 and occludin, preventing superinfection. The altered TJ protein expression may contribute to the morphological and functional changes observed in HCV-infected hepatocytes.

Fatty Acid Synthase Is Up-Regulated During Hepatitis C Virus Infection and Regulates Hepatitis C Virus Entry and Production

Hepatitis C virus (HCV) is a major human pathogen that causes serious illness, including acute and chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Using a mass spectrometry–based proteomics approach, we have identified 175 proteins from a cell culture supernatant fraction containing the HCV genotype 2a (JFH1) virus, among which fatty acid synthase (FASN), the multifunctional enzyme catalyzing the de novo synthesis of fatty acids, was confirmed to be highly enriched. Subsequent studies showed that FASN expression increased in the human hepatoma cell line, Huh7, or its derivative, upon HCV infection. Blocking FASN activity by C75, a pharmacological FASN inhibitor, led to decreased HCV production. Reduction of FASN by RNA interference suppressed viral replication in both replicon and infection systems. Remarkably, FASN appeared to be selectively required for the expression of claudin‐1, a tight junction protein that was recently identified as an entry coreceptor for HCV, but not for the expression of another HCV coreceptor, CD81. The decrease in Claudin‐1 expression resulting from FASN inhibition was accompanied by a decrease in transepithelial electric resistance of Huh7 cells, implying a reduction in the relative tightness of the cell monolayer. Consequently, the entry of human immunodeficiency virus–HCV pseudotypes was significantly inhibited in C75‐treated Huh7 cells. Conclusion: As far as we know, this is the first line of evidence that demonstrates that HCV infection directly induces FASN expression, and thus suggests a possible mechanism by which HCV infection alters the cellular lipid profile and causes diseases such as steatosis. (HEPATOLOGY 2008.)

Human apolipoprotein E peptides inhibit hepatitis C virus entry by blocking virus binding

Hepatitis C virus (HCV) entry is a multiple‐step process involving a number of host factors and hence represents a promising target for new antiviral drug development. In search of novel inhibitors of HCV infection, we found that a human apolipoprotein E (apoE) peptide, hEP, containing both a receptor binding fragment and a lipid binding fragment of apoE specifically blocked the entry of cell culture grown HCV (HCVcc) at submicromolar concentrations. hEP caused little cytotoxicity in vitro and remained active even if left 24 hours in cell culture. Interestingly, hEP inhibited neither human immunodeficiency virus (HIV)‐HCV pseudotypes (HCVpp) nor HIV and Dengue virus (DENV) infection. Further characterization mapped the anti‐HCV activity to a 32‐residue region that harbors the receptor binding domain of apoE, but this fragment must contain a cysteine residue at the N‐terminus to mediate dimer formation. The anti‐HCV activity of the peptide appears to be dependent on both its length and sequence and correlates with its ability to bind lipids. Finally, we demonstrated that the apoE‐derived peptides directly blocked the binding of both HCVcc and patient serum‐derived virus to hepatoma cells as well as primary human hepatocytes. Conclusion: apoE peptides potently inhibit HCV infection and suggest a direct role of apoE in mediating HCV entry. Our findings also highlight the potential of developing apoE mimetic peptides as novel HCV entry inhibitors by targeting HCV‐host interactions. (HEPATOLOGY 2012)

A human claudin-1-derived peptide inhibits hepatitis C virus entry.

Hepatitis C virus (HCV) entry is a complicated process that requires multiple host factors, such as CD81, scavenger receptor BI, claudin‐1 (CLDN1), and occludin. The interaction of virus and cellular entry factors represents a promising target for novel anti‐HCV drug development. In this study, we sought to identify peptide inhibitors for HCV entry by screening a library of overlapping peptides covering the four above‐mentioned entry factors. An 18–amino acid peptide (designated as CL58) that was derived from the CLDN1 intracellular and first transmembrane region inhibited both de novo and established HCV infection in vitro. Unlike previously reported peptides corresponding to CLDN1 extracellular loops, CL58 did not alter the normal distribution of CLDN1 and was not cytotoxic in vitro at concentrations nearly 100‐fold higher than the effective antiviral dose. The inhibitory effect of CL58 appeared to occur at a late step during viral entry, presumably after initial binding. Finally, overexpressed CL58 was able to interact with HCV envelope proteins. Conclusion: We identified a novel CLDN1‐derived peptide that inhibits HCV entry at a postbinding step. The findings expand our knowledge of the roles that CLDN1 play in HCV entry and highlight the potential for developing a new class of inhibitors targeting the viral entry process. (HEPATOLOGY 2012)

MCPIP1 restricts HIV infection and is rapidly degraded in activated CD4+ T cells

Significance Here, we present data showing that monocyte chemotactic protein-induced protein 1 (MCPIP1) acts as an RNase to limit HIV-1 production in resting CD4+ T cells. Unlike those previously identified factors with restrictions that tend to be overcome by virally encoded proteins, MCPIP1 becomes rapidly degraded on activation of human CD4+ T cells. These findings provide insights into the mechanisms of cellular activation-mediated HIV-1 production in CD4+ T cells and represent a breakthrough in the relevant field. HIV-1 primarily infects activated CD4+ T cells and macrophages. Quiescent CD4+ T cells, however, possess cellular factors that limit HIV-1 infection at different postentry steps of the viral life cycle. Here, we show that the previously reported immune regulator monocyte chemotactic protein-induced protein 1 (MCPIP1) restricts HIV-1 production in CD4+ T cells. While the ectopic expression of MCPIP1 in cell lines abolished the production of HIV-1, silencing of MCPIP1 enhanced HIV-1 production. Subsequent analysis indicated that MCPIP1 imposes its restriction by decreasing the steady levels of viral mRNA species through its RNase domain. Remarkably, common T-cell stimuli induced the rapid degradation of MCPIP1 in both T-cell lines and quiescent human CD4+ T cells. Lastly, blocking the proteosomal degradation of MCPIP1 by MG132 abrogated HIV-1 production in phorbol 12-myristate 13-acetate/ionomycin-stimulated human CD4+ T cells isolated from healthy donors. Overall, MCPIP1 poses a potent barrier against HIV-1 infection at a posttranscriptional stage. Although the observed HIV restriction conferred by MCPIP1 does not seem to be overcome by any viral protein, it is removed during cellular stimulation. These findings provide insights into the mechanisms of cellular activation-mediated HIV-1 production in CD4+ T cells.

The ubiquitin-like protein PLIC-1 or ubiquilin 1 inhibits TLR3-Trif signaling.

Background The innate immune responses to virus infection are initiated by either Toll-like receptors (TLR3/7/8/9) or cytoplasmic double-stranded RNA (dsRNA)-recognizing RNA helicases RIG-I and MDA5. To avoid causing injury to the host, these signaling pathways must be switched off in time by negative regulators. Methodology/Principal Findings Through yeast-two hybrid screening, we found that an ubiquitin-like protein named protein linking integrin-associated protein to cytoskeleton 1(PLIC-1 or Ubiquilin 1) interacted with the Toll/interleukin-1 receptor (TIR) domain of TLR4. Interestingly, PLIC-1 had modest effect on TLR4-mediated signaling, but strongly suppressed the transcriptional activation of IFN-β promoter through the TLR3-Trif-dependent pathway. Concomitantly, reduction of endogenous PLIC-1 by short-hairpin interfering RNA (shRNA) enhanced TLR3 activation both in luciferase reporter assays as well as in new castle disease virus (NDV) infected cells. An interaction between PLIC-1 and Trif was confirmed in co-immunoprecipitation (Co-IP) and GST-pull-down assays. Subsequent confocal microscopic analysis revealed that PLIC-1 and Trif colocalized with the autophagosome marker LC3 in punctate subcellular structures. Finally, overexpression of PLIC-1 decreased Trif protein abundance in a Nocodazole-sensitive manner. Conclusions Our results suggest that PLIC-1 is a novel inhibitor of the TLR3-Trif antiviral pathway by reducing the abundance of Trif.

Monocyte Chemotactic Protein-induced Protein 1 and 4 Form a Complex but Act Independently in Regulation of Interleukin-6 mRNA Degradation

Background: The post-transcriptional regulation of interleukin-6 (IL-6) production is critical for immune homeostasis. Results: Monocyte chemotactic protein-induced protein 1 (MCPIP1) and MCPIP4 form a complex but they act independently in regulation of IL-6 mRNA degradation. Conclusion: MCPIP1 and MCPIP4 may additively contribute to control IL-6 production. Significance: The study may help to understand the mechanisms by which MCPIP1 protein family control immune homeostasis. It was recently demonstrated that MCPIP1 is a critical factor that controls inflammation and immune homeostasis; however, the relationship between MCPIP1 and other members of this protein family is largely unknown. Here, we report that MCPIP1 interacts with MCPIP4 to form a protein complex, but acts independently in the regulation of IL-6 mRNA degradation. In an effort to identify MCPIP1-interacting proteins by co-immunoprecipitation (Co-IP) and mass-spec analysis, MCPIP4 was identified as a MCPIP1-interacting protein, which was further confirmed by Co-IP and mammalian two-hybrid assay. Immunofluorescence staining showed that MCPIP4 was co-localized with MCPIP1 in the GW-body, which features GW182 and Argonaute 2. Further studies showed that MCPIP1 and MCPIP4 act independently in regulation of IL-6 mRNA degradation. These results suggest that MCPIP1 and MCPIP4 may additively contribute to control IL-6 production in vivo.

Development of a Robust Cytopathic Effect-Based High-Throughput Screening Assay To Identify Novel Inhibitors of Dengue Virus

ABSTRACT We have developed a robust cytopathic effect-based high-throughput screening assay to identify inhibitors of dengue virus (DENV) infection. Screening of a small natural product library yielded 11 hits. Four of these were found to be potent inhibitors of DENV, although serotype differences were noted. Taken together, these data suggest that screening of larger and more complex molecule libraries may result in the identification of more potent and specific DENV inhibitors.

Identification of novel human kinases that suppress hepatitis C virus infection.

The human kinome includes between 500 and 600 known kinases and open reading frames (ORFs) that play key roles in regulating many cellular processes. Past studies adopting loss‐of‐function approaches have identified some kinases whose activities are required for hepatitis C virus (HCV) life cycle. Here, by screening a retroviral cDNA library of 192 active human kinases, we found that three of them, namely cyclin‐dependent kinases regulatory subunit 1 (CKS1B), mitogen‐activated protein kinase kinase 5 (MAP2K5) and protein kinase C and casein kinase substrate in neurons 1 (PACSIN1), potently suppressed HCV infection. The expression of these kinases did not induce the production of type I interferon (IFN) and interferon‐stimulated genes (ISGs); instead, they inhibited HCV at postentry stages. Specifically, CKS1B and MAP2K5 significantly inhibited viral RNA replication. PACSIN1, by contrast, inhibited HCV infection by decreasing the level of HCV p7. Altogether, the identification of human protein kinases that exert an anti‐HCV activity highlighted the potential of combating HCV infection by activating specific kinase‐mediated pathways, offering an alternative strategy of treatment.

Comparative Proteomics Reveals Important Viral-Host Interactions in HCV-Infected Human Liver Cells.

Hepatitis C virus (HCV) poses a global threat to public health. HCV envelop protein E2 is the major component on the virus envelope, which plays an important role in virus entry and morphogenesis. Here, for the first time, we affinity purified E2 complex formed in HCV-infected human hepatoma cells and conducted comparative mass spectrometric analyses. 85 cellular proteins and three viral proteins were successfully identified in three independent trials, among which alphafetoprotein (AFP), UDP-glucose: glycoprotein glucosyltransferase 1 (UGT1) and HCV NS4B were further validated as novel E2 binding partners. Subsequent functional characterization demonstrated that gene silencing of UGT1 in human hepatoma cell line Huh7.5.1 markedly decreased the production of infectious HCV, indicating a regulatory role of UGT1 in viral lifecycle. Domain mapping experiments showed that HCV E2-NS4B interaction requires the transmembrane domains of the two proteins. Altogether, our proteomics study has uncovered key viral and cellular factors that interact with E2 and provided new insights into our understanding of HCV infection.