Ian Gaël Rodrigue-Gervais

RNA interference blocks gene expression and RNA synthesis from hepatitis C replicons propagated in human liver cells

RNA interference represents an exciting new technology that could have therapeutic applications for the treatment of viral infections. Hepatitis C virus (HCV) is a major cause of chronic liver disease and affects >270 million individuals worldwide. The HCV genome is a single-stranded RNA that functions as both a messenger RNA and replication template, making it an attractive target for the study of RNA interference. Double-stranded small interfering RNA (siRNA) molecules designed to target the HCV genome were introduced through electroporation into a human hepatoma cell line (Huh-7) that contained an HCV subgenomic replicon. Two siRNAs dramatically reduced virus-specific protein expression and RNA synthesis to levels that were 90% less than those seen in cells treated with negative control siRNAs. These same siRNAs protected naive Huh-7 cells from challenge with HCV replicon RNA. Treatment of cells with synthetic siRNA was effective >72 h, but the duration of RNA interference could be extended beyond 3 weeks through stable expression of complementary strands of the interfering RNA by using a bicistronic expression vector. These results suggest that a gene-therapeutic approach with siRNA could ultimately be used to treat HCV.

The Nlrp3 Inflammasome Suppresses Colorectal Cancer Metastatic Growth in the Liver by Promoting Natural Killer Cell Tumoricidal Activity

The crosstalk between inflammation and tumorigenesis is now clearly established. However, how inflammation is elicited in the metastatic environment and the corresponding contribution of innate immunity pathways in suppressing tumor growth at secondary sites are poorly understood. Here, we show that mice deficient in Nlrp3 inflammasome components had exacerbated liver colorectal cancer metastatic growth, which was mediated by impaired interleukin-18 (IL-18) signaling. Control of tumor growth was independent of differential cancer cell colonization or proliferation, intestinal microbiota effects, or tumoricidal activity by the adaptive immune system. Instead, the inflammasome-IL-18 pathway impacted maturation of hepatic NK cells, surface expression of the death ligand FasL, and capacity to kill FasL-sensitive tumors. Our results define a regulatory signaling circuit within the innate immune system linking inflammasome activation to effective NK-cell-mediated tumor attack required to suppress colorectal cancer growth in the liver.

Activation of MEK1 or MEK2 isoform is sufficient to fully transform intestinal epithelial cells and induce the formation of metastatic tumors

BackgroundThe Ras-dependent ERK1/2 MAP kinase signaling pathway plays a central role in cell proliferation control and is frequently activated in human colorectal cancer. Small-molecule inhibitors of MEK1/MEK2 are therefore viewed as attractive drug candidates for the targeted therapy of this malignancy. However, the exact contribution of MEK1 and MEK2 to the pathogenesis of colorectal cancer remains to be established.MethodsWild type and constitutively active forms of MEK1 and MEK2 were ectopically expressed by retroviral gene transfer in the normal intestinal epithelial cell line IEC-6. We studied the impact of MEK1 and MEK2 activation on cellular morphology, cell proliferation, survival, migration, invasiveness, and tumorigenesis in mice. RNA interference was used to test the requirement for MEK1 and MEK2 function in maintaining the proliferation of human colorectal cancer cells.ResultsWe found that expression of activated MEK1 or MEK2 is sufficient to morphologically transform intestinal epithelial cells, dysregulate cell proliferation and induce the formation of high-grade adenocarcinomas after orthotopic transplantation in mice. A large proportion of these intestinal tumors metastasize to the liver and lung. Mechanistically, activation of MEK1 or MEK2 up-regulates the expression of matrix metalloproteinases, promotes invasiveness and protects cells from undergoing anoikis. Importantly, we show that silencing of MEK2 expression completely suppresses the proliferation of human colon carcinoma cell lines, whereas inactivation of MEK1 has a much weaker effect.ConclusionMEK1 and MEK2 isoforms have similar transforming properties and are able to induce the formation of metastatic intestinal tumors in mice. Our results suggest that MEK2 plays a more important role than MEK1 in sustaining the proliferation of human colorectal cancer cells.

Dendritic Cell Inhibition Is Connected to Exhaustion of CD8+ T Cell Polyfunctionality during Chronic Hepatitis C Virus Infection

Although chronic viral infections have evolved mechanisms to interfere with aspects of pathogen recognition by dendritic cells (DCs), the role that these APCs play in virus-specific T cell exhaustion is unclear. Herein we report that NS3-dependent suppression of Toll/IL-1 domain-containing adapter-inducing IFN-β– and IFN-β promoter stimulator-1– but not MyD88-coupled pathogen-recognition receptor–induced synthesis of proinflammatory cytokines (IL-12 and TNF-α) from DCs by hepatitis C virus (HCV) is a distinctive feature of a subgroup of chronically infected patients. The result is decreased CD8+ T cell polyfunctional capacities (production of IFN-γ, IL-2, TNF-α, and CD107a mobilization) that is confined to HCV specificities and that relates to the extent to which HCV inhibits DC responses in infected subjects, despite comparable plasma viral load, helper T cell environments, and inhibitory programmed death 1 receptor/ligand signals. Thus, subjects in whom pathogen-recognition receptor signaling in DCs was intact exhibited enhanced polyfunctionality (i.e., IL-2-secretion and CD107a). In addition, differences between HCV-infected patients in the ability of CD8+ T cells to activate multiple functions in response to HCV did not apply to CD8+ T cells specific for other immune-controlled viruses (CMV, EBV, and influenza). Our findings identify reversible virus evasion of DC-mediated innate immunity as an additional important factor that impacts the severity of polyfunctional CD8+ T cell exhaustion during a chronic viral infection.

Poly(I:C) and Lipopolysaccharide Innate Sensing Functions of Circulating Human Myeloid Dendritic Cells Are Affected In Vivo in Hepatitis C Virus-Infected Patients

ABSTRACT The role of peripheral dendritic cells (DCs) in hepatitis C virus (HCV) infection is unclear. To determine if persistent infection exerts an inhibitory pressure on HCV-specific innate responses, we analyzed DC function in blood through quantification of cell-associated HCV RNA levels in conjunction with multiparametric flow cytometry analysis of pathogen recognition receptor-induced cytokine expression. Independently of the serum viral load, fluorescence-activated cell sorter-purified total DCs had a wide range of cell-associated HCV genomic RNA copy numbers (mean log10, 5.0 per 106 cells; range, 4.3 to 5.8). Here we report that for viremic patients with high viral loads in their total DCs, the myeloid DC (MDC) subset displayed impaired expression of interleukin-12 (IL-12) and tumor necrosis factor alpha (TNF-α) but normal IL-6 or chemokine CCL3 expression in response to poly(I:C) and lipopolysaccharide (LPS). IL-6-expressing cells from this subgroup of viremic patients demonstrated a significant increase (sixfold more) in TNF-α− IL-12− cell frequency compared to healthy donors (mean, 38.8% versus 6.5%; P < 0.0001), indicating a functional defect in a subpopulation of cytokine-producing MDCs (∼6% of MDCs). Attenuation of poly(I:C) and LPS innate sensing was HCV RNA density dependent and did not correlate with viremia or deficits in circulating MDC frequencies in HCV-infected patients. Monocytes from these patients were functionally intact, responding normally on a per-cell basis following stimulation, independent of cell-associated HCV RNA levels. Taken together, these data indicate that detection of HCV genomic RNA in DCs and loss of function in the danger signal responsiveness of a small proportion of DCs in vivo are interrelated rather than independent phenomena.

Distinct antiviral signaling pathways in primary human hepatocytes and their differential disruption by HCV NS3 protease

BACKGROUND & AIMS Molecular sensors recognize viral nucleic acids and initiate events that subsequently enable cells to control and clear infection. Hepatitis C Virus (HCV) can interfere with the innate host response and the NS3/4A protease was reported to specifically block antiviral signaling pathways, a finding that had yet to be studied in human primary hepatocytes. METHODS Freshly isolated human primary hepatocytes, transduced with a lentiviral vector expressing HCV NS3/4A were stimulated with extracellular and intracellular double-stranded RNA (dsRNA) and the innate immune antiviral genes were quantified by quantitative PCR and microarrays analysis. RESULTS We demonstrate that sensing receptors of human hepatocytes in primary cultures are stimulated following recognition of either mode of dsRNA delivery, inducing transcriptional up-regulation (over 100-fold) of multiple immune genes, either selectively or independently of recognition pathways. We also report that the intracellular dsRNA-activated innate response is severely compromised upon ectopic expression of the HCV NS3/4A protease gene in normal human primary hepatocytes, and completely restored by treatment with the NS3/4A protease specific inhibitor BILN2061. CONCLUSIONS The present study indicates that NS3/4A has a wider protease-dependent effect on the intracellular Pathogen Recognition Receptor (PRR)-mediated immune response than on its extracellular counterpart, which underlies the major role of cytosolic dsRNA receptors in HCV recognition by primary human hepatocytes.

An N-Ethyl-N-Nitrosourea (ENU)-Induced Dominant Negative Mutation in the JAK3 Kinase Protects against Cerebral Malaria

Cerebral malaria (CM) is a lethal neurological complication of malaria. We implemented a genome-wide screen in mutagenized mice to identify host proteins involved in CM pathogenesis and whose inhibition may be of therapeutic value. One pedigree (P48) segregated a resistance trait whose CM-protective effect was fully penetrant, mapped to chromosome 8, and identified by genome sequencing as homozygosity for a mis-sense mutation (W81R) in the FERM domain of Janus-associated kinase 3 (Jak3). The causative effect of Jak3W81R was verified by complementation testing in Jak3W81R/− double heterozygotes that were fully protected against CM. Jak3W81R homozygotes showed defects in thymic development with depletion of CD8+ T cell, B cell, and NK cell compartments, and defective T cell-dependent production of IFN-γ. Adoptive transfer of normal splenocytes abrogates CM resistance in Jak3W81R homozygotes, an effect attributed to the CD8+ T cells. Jak3W81R behaves as a dominant negative variant, with significant CM resistance of Jak3W81R/+ heterozygotes, compared to CM-susceptible Jak3+/+ and Jak3+/− controls. CM resistance in Jak3W81R/+ heterozygotes occurs in presence of normal T, B and NK cell numbers. These findings highlight the pathological role of CD8+ T cells and Jak3-dependent IFN-γ-mediated Th1 responses in CM pathogenesis.

Genetics of inflammasome-associated disorders: A lesson in the guiding principals of inflammasome function

Human genetics research has had a great impact on the genesis of the inflammasome field and the treatment of certain inflammasomopathies. The identification of mutations causing rare autoinflammatory syndromes, reproductive wastage disorders and of single nucleotide polymorphisms influencing susceptibility to complex diseases such as vitiligo, sepsis, and Crohns disease has not only led to the characterization of novel proteins involved in NOD‐like receptor‐coupled inflammatory signaling pathways but also to greater insights into pathogenic mechanisms.

Intact dendritic cell pathogen-recognition receptor functions associate with chronic hepatitis C treatment-induced viral clearance.

Although studies have addressed the exhaustion of the hosts immune response to HCV and its role in treatment, there is little information about the possible contribution of innate immunity to treatment-induced clearance. We hypothesized that because intact myeloid dendritic cell (MDC) pathogen sensing functions are associated with improved HCV-specific CD8+ T cell functionality in some chronically infected patients, it might enhance HCV clearance rate under standard interferon therapy. To investigate this hypothesis, TLR-induced MDC activation and HCV-specific CD8+ T cell response quality were monitored longitudinally at the single-cell level using polychromatic flow cytometry in chronically infected patients undergoing interferon therapy. We correlated the immunological, biochemical and virological data with response to treatment. We demonstrate that the clinical efficacy of interferon-induced viral clearance is influenced by the extent to which HCV inhibits MDC functions before treatment, rather than solely on a breakdown of the extrinsic T cell immunosuppressive environment. Thus, viral inhibition of MDC functions before treatment emerges as a co-determining factor in the clinical efficacy of interferon therapy during chronic HCV infection.

The mitochondrial protease HtrA2 restricts the NLRP3 and AIM2 inflammasomes.

Activation of the inflammasome pathway is crucial for effective intracellular host defense. The mitochondrial network plays an important role in inflammasome regulation but the mechanisms linking mitochondrial homeostasis to attenuation of inflammasome activation are not fully understood. Here, we report that the Parkinson’s disease-associated mitochondrial serine protease HtrA2 restricts the activation of ASC-dependent NLRP3 and AIM2 inflammasomes, in a protease activity-dependent manner. Consistently, disruption of the protease activity of HtrA2 results in exacerbated NLRP3 and AIM2 inflammasome responses in macrophages ex vivo and systemically in vivo. Mechanistically, we show that the HtrA2 protease activity regulates autophagy and controls the magnitude and duration of inflammasome signaling by preventing prolonged accumulation of the inflammasome adaptor ASC. Our findings identify HtrA2 as a non-redundant mitochondrial quality control effector that keeps NLRP3 and AIM2 inflammasomes in check.