Eugene Dempsey

Molecular footprints reveal the impact of the protective HLA-A*03 allele in hepatitis C virus infection

Background and aims CD8 T cells are central to the control of hepatitis C virus (HCV) although the key features of a successful CD8 T cell response remain to be defined. In a cohort of Irish women infected by a single source, a strong association between viral clearance and the human lecucocyte (HLA)-A*03 allele has been described, and the aim of this study was to define the protective nature of the associated CD8 T cell response. Methods A sequence-led approach was used to identify HLA-A*03-restricted epitopes. We examine the CD8 T cell response associated with this gene and address the likely mechanism underpinning this protective effect in this special cohort, using viral sequencing, T cell assays and analysis of fitness of viral mutants. Results A strong ‘HLA footprint’ in a novel NS3 epitope (TVYHGAGTK) was observed. A lysine (K) to arginine (R) substitution at position 9 (K1088R) was seen in a significant number of A*03-positive patients (9/12) compared with the control group (1/33, p=0.0003). Threonine (T) was also substituted with alanine (A) at position 8 (T1087A) more frequently in A*03-positive patients (6/12) compared with controls (2/33, p=0.01), and the double substitution of TK to AR was also observed predominantly in HLA-A*03-positive patients (p=0.004). Epitope-specific CD8 T cell responses were observed in 60% of patients three decades after exposure and the mutants selected in vivo impacted on recognition in vitro. Using HCV replicons matched to the viral sequences, viral fitness was found to be markedly reduced by the K1088R substitution but restored by the second substitution T1087A. Conclusions It is proposed that at least part of the protective effect of HLA-A*03 results from targeting of this key epitope in a functional site: the requirement for two mutations to balance fitness and escape provides an initial host advantage. This study highlights the potential protective impact of common HLA-A alleles against persistent viruses, with important implications for HCV vaccine studies.

5-AZA-2'-deoxycytidine induced demethylation influences N-glycosylation of secreted glycoproteins in ovarian cancer.

Glycosylation is the most common posttranslational modification of proteins and is highly reflective of changes in the environment of a cell. Epigenetic modifications to the genome are stably transmitted to daughter cells without the requirement for genetic sequence alterations. Aberrant regulation of both epigenetic programming and glycosylation patterning are integral aspects of carcinogenesis. The objective of this study was to determine the interplay between these two complex cellular processes. We demonstrate that global DNA methylation changes in ovarian cancer epithelial cells (OVCAR3) resulted in significant alterations in the glycosylation of secreted glycoproteins. These changes included a reduction in core fucosylation, increased branching and increased sialylation. We further show that the change in core fucose levels was mirrored by altered expression of GMDS and FX, key enzymes in fucose biosynthesis. Alterations in the expression of key glycosyltransferase enzymes such as MGAT5 reflect the changes seen in the branching and sialylation of secreted glycans. Overall, our results highlight that modifications to the epigenetic machinery have a profound effect on the glycan structures generated by cells, which may be a key step in understanding metastasis and drug resistance during cancer progression.

Overexpression of the microRNA miR-433 promotes resistance to paclitaxel through the induction of cellular senescence in ovarian cancer cells

Annually, ovarian cancer (OC) affects 240,000 women worldwide and is the most lethal gynecological malignancy. High‐grade serous OC (HGSOC) is the most common and aggressive OC subtype, characterized by widespread genome changes and chromosomal instability and is consequently poorly responsive to chemotherapy treatment. The objective of this study was to investigate the role of the microRNA miR‐433 in the cellular response of OC cells to paclitaxel treatment. We show that stable miR‐433 expression in A2780 OC cells results in the induction of cellular senescence demonstrated by morphological changes, downregulation of phosphorylated retinoblastoma (p‐Rb), and an increase in β‐galactosidase activity. Furthermore, in silico analysis identified four possible miR‐433 target genes associated with cellular senescence: cyclin‐dependent kinase 6 (CDK6), MAPK14, E2F3, and CDKN2A. Mechanistically, we demonstrate that downregulation of p‐Rb is attributable to a miR‐433‐dependent downregulation of CDK6, establishing it as a novel miR‐433 associated gene. Interestingly, we show that high miR‐433 expressing cells release miR‐433 into the growth media via exosomes which in turn can induce a senescence bystander effect. Furthermore, in relation to a chemotherapeutic response, quantitative real‐time polymerase chain reaction (qRT‐PCR) analysis revealed that only PEO1 and PEO4 OC cells with the highest miR‐433 expression survive paclitaxel treatment. Our data highlight how the aberrant expression of miR‐433 can adversely affect intracellular signaling to mediate chemoresistance in OC cells by driving cellular senescence.

The role of chemokines in acute and chronic hepatitis C infection

Hepatitis C imposes a significant burden on global healthcare. Chronic infection is associated with progressive inflammation of the liver which typically manifests in cirrhosis, organ failure and cancer. By virtue of elaborate evasion strategies, hepatitis C virus (HCV) succeeds as a persistent human virus. It has an extraordinary capacity to subvert the immune response enabling it to establish chronic infections and associated liver disease. Chemokines are low molecular weight chemotactic peptides that mediate the recruitment of inflammatory cells into tissues and back into the lymphatics and peripheral blood. Thus, they are central to the temporal and spatial distribution of effector and regulatory immune cells. The interactions between chemokines and their cognate receptors help shape the immune response and therefore, have a major influence on the outcome of infection. However, chemokines represent a target for modulation by viruses including the HCV. HCV is known to modulate chemokine expression in vitro and may therefore enable its survival by subverting the immune response in vivo through altered leukocyte chemotaxis resulting in impaired viral clearance and the establishment of chronic low-grade inflammation. In this review, the roles of chemokines in acute and chronic HCV infection are described with a particular emphasis placed on chemokine modulation as a means of immune subversion. We provide an in depth discussion of the part played by chemokines in mediating hepatic fibrosis while addressing the potential applications for these chemoattractants in prognostic medicine.

Hepatitis C virus – T-cell responses and viral escape mutations

Hepatitis C virus (HCV) is a small, enveloped RNA virus and the number of HCV‐infected individuals worldwide is estimated to be approximately 170 million. Most HCV infections persist, with up to 80% of all cases leading to chronic hepatitis associated with liver fibrosis, cirrhosis, and hepatocellular carcinoma. HCV–host interactions have a crucial role in viral survival, persistence, pathogenicity of infection, and disease progression. Maintenance of a vigorous, sustained cellular immune response recognizing multiple epitopes is essential for viral clearance. To escape immune surveillance, HCV alters its epitopes so that they are no‐longer recognized by T cells and neutralizing antibodies, in addition to interfering with host cell cellular components and signaling pathways. The generation of escape variants is one of the most potent immune evasion strategies utilized by HCV. A large body of evidence suggests that single or multiple mutations within HLA‐restricted epitopes contribute to viral immune escape and establishment of viral persistence. Further elucidation of the molecular mechanisms underlying immune escape will aid in the design of novel vaccines and therapeutics for the disease.

A new microtubule-targeting compound PBOX-15 inhibits T-cell migration via post-translational modifications of tubulin

The ordered, directional migration of T-lymphocytes is a key process during immune surveillance, immune response, and development. A novel series of pyrrolo-1,5-benzoxazepines have been shown to potently induce apoptosis in variety of human chemotherapy resistant cancer cell lines, indicating their potential in the treatment of both solid tumors and tumors derived from the hemopoietic system. Pyrrolobenzoxazepine 4-acetoxy-5-(1-naphtyl)naphtho[2,3-b]pyrrolo[1,2-d][1,4]-oxazepine (PBOX-15) has been shown to depolymerize tubulin in vitro and in the MCF7 breast cancer cell line. We hypothesized that this may suggest a role for this compound in modulating integrin-induced T-cell migration, which is largely dependent on the microtubule dynamics. Experiments were performed using human T lymphoma cell line Hut78 and peripheral blood T-lymphocytes isolated from healthy donors. We observed that human T-lymphocytes exposed to PBOX-15 have severely impaired ability to polarize and migrate in response to the triggering stimulus generated via cross-linking of integrin lymphocyte function associated antigen-1 receptor. Here, we show that PBOX-15 can dramatically impair microtubule network via destabilization of tubulin resulting in complete loss of the motile phenotype of T-cells. We demonstrate that PBOX-15 inhibitory mechanisms involve decreased tubulin polymerization and its post-translational modifications. Novel microtubule-targeting effects of PBOX-15 can possibly open new horizons in the treatment of overactive inflammatory conditions as well as cancer and cancer metastatic spreading.

Acute phase glycoproteins: bystanders or participants in carcinogenesis?

Acute phase proteins (APPs) are a group of serum proteins that undergo dramatic changes in concentration during times of inflammation. Many APPs are heavily glycosylated, and their sugar content and complexity change in the presence of cancer‐induced chronic inflammation. These changes in glycosylation are currently being exploited in the search for novel biomarkers of cancer. Like other posttranslational modifications, such as phosphorylation, changes in glycosylation can profoundly alter the function of a protein. We hypothesize that besides being a rich source of potential biomarkers APPs may also play an active role in tumorigenesis. The glycan content of the APPs haptoglobin and kininogen, for example, is altered in many types of cancer. These APPs can interact with a number of receptors on macrophages in the tumor microenvironment, potentially modulating macrophage activity and thereby contributing to tumor cell survival, growth, and metastasis.

Leukocyte Function-associated Antigen-1/Intercellular Adhesion Molecule-1 Interaction Induces a Novel Genetic Signature Resulting in T-cells Refractory to Transforming Growth Factor-β Signaling

Background: Transforming growth factor-β (TGF-β) plays crucial regulatory roles in the immune homeostasis. Results: Leukocyte function-associated antigen-1 (LFA-1) stimulation induces a genetic signature in T-cells, resulting in their refractoriness to TGF-β signaling. Conclusion: T-cells stimulated via LFA-1 are programmed to become refractory to TGF-β functions. Significance: Findings are important for understanding local inflammatory response and in designing immunotherapies. The immunesuppressive cytokine TGF-β plays crucial regulatory roles in the induction and maintenance of immunologic tolerance and prevention of immunopathologies. However, it remains unclear how circulating T-cells can escape from the quiescent state maintained by TGF-β. Here, we report that the T-cell integrin leukocyte function-associated antigen-1 (LFA-1) interaction with its ligand intercellular adhesion molecule-1 (ICAM-1) induces a genetic signature associated with reduced TGF-β responsiveness via up-regulation of SKI, E3 ubiquitin-protein ligase SMURF2, and SMAD7 (mothers against decapentaplegic homolog 7) genes and proteins. We confirmed that the expression of these TGF-β inhibitory molecules was dependent on STAT3 and/or JNK activation. Increased expression of SMAD7 and SMURF2 in LFA-1/ICAM-1 cross-linked T-cells resulted in impaired TGF-β-mediated phosphorylation of SMAD2 and suppression of IL-2 secretion. Expression of SKI caused resistance to TGF-β-mediated suppression of IL-2, but SMAD2 phosphorylation was unaffected. Blocking LFA-1 by neutralizing antibody or specific knockdown of TGF-β inhibitory molecules by siRNA substantially restored LFA-1/ICAM-1-mediated alteration in TGF-β signaling. LFA-1/ICAM-1-stimulated human and mouse T-cells were refractory to TGF-β-mediated induction of FOXP3+ (forkhead box P3) and RORγt+ (retinoic acid-related orphan nuclear receptor γt) Th17 differentiation. These mechanistic data suggest an important role for LFA-1/ICAM-1 interactions in immunoregulation concurrent with lymphocyte migration that may have implications at the level of local inflammatory response and for anti-LFA-1-based therapies.

Hepatitis C virus targets the T cell secretory machinery as a mechanism of immune evasion

T cell activation and the resultant production of interleukin (IL‐2) is a central response of the adaptive immune system to pathogens, such as hepatitis C virus (HCV). HCV uses several mechanisms to evade both the innate and adaptive arms of the immune response. Here we demonstrate that liver biopsy specimens from individuals infected with HCV had significantly lower levels of IL‐2 compared with those with other inflammatory liver diseases. Cell culture–grown HCV particles inhibited the production of IL‐2 by normal peripheral blood mononuclear cells, as did serum from HCV‐infected patients. This process was mediated by the interaction of HCV envelope protein E2 with tetraspanin CD81 coreceptor. HCV E2 attenuated IL‐2 production at the level of secretion and not transcription by targeting the translocation of protein kinase C beta (PKCβ), which is essential for IL‐2 secretion, to lipid raft microdomains. The lipid raft disruptor methyl‐β‐cyclodextrin reversed HCV E2‐mediated inhibition of IL‐2 secretion, but not in the presence of a PKCβ‐selective inhibitor. HCV E2 further inhibited the secretion of other cytokines, including interferon‐γ. Conclusion: These data suggest that HCV E2–mediated disruption of the association of PKCβ with the cellular secretory machinery represents a novel mechanism for HCV to evade the human immune response and to establish persistent infection. (HEPATOLOGY 2011;)

Conjugated Linoleic Acid Targets β2 Integrin Expression To Suppress Monocyte Adhesion

Chronic recruitment of monocytes and their subsequent migration through the activated endothelium contribute to atherosclerotic plaque development. Integrin-mediated leukocyte adhesion is central to this process. Conjugated linoleic acid (CLA) has the unique property of inducing regression of pre-established murine atherosclerosis via modulation of monocyte/macrophage function. Understanding the mechanisms through which CLA mediates its atheroprotective effect may help to identify novel pathways that limit or reverse atherosclerosis. In this study, we identified a novel mechanism through which CLA alters monocyte function. We show that CLA inhibits human peripheral blood monocyte cell adhesion to activated endothelial cells via loss of CD18 expression, the β2 chain of LFA-1 and Mac-1 integrins. In addition, using a static-adhesion assay, we provide evidence that CLA prevents monocytes from binding to ICAM-1 and subsequently reduces the capacity of these cells to polarize. CXCL12–CXCR4 interactions induce a conformational change in β2 integrins, facilitating leukocyte adhesion. In this study, we demonstrate that CLA inhibits CXCR4 expression, resulting in a failure of monocytes to directionally migrate toward CXCL12. Finally, using intravital microscopy, we show that, during CLA-induced regression of pre-established atherosclerosis in ApoE−/− mice, there is reduced leukocyte adhesion and decreased CD18 expression on Gr1+/CD115+ proinflammatory monocytes. In summary, the data presented describe a novel functional role for CLA in the regulation of monocyte adhesion, polarization, and migration.