Discovering innate immunity genes using differential display: a story of RNA helicases

Contemporary Strategies and Current Trends in Designing Antiviral Drugs against Dengue Fever via Targeting Host-Based Approaches

Dengue virus (DENV) is an arboviral human pathogen transmitted through mosquito bite that infects an estimated ~400 million humans (~5% of the global population) annually. To date, no specific therapeutics have been developed that can prevent or treat infections resulting from this pathogen. DENV utilizes numerous host molecules and factors for transcribing the single-stranded ~11 kb positive-sense RNA genome. For example, the glycosylation machinery of the host is required for viral particles to assemble in the endoplasmic reticulum. Since a variety of host factors seem to be utilized by the pathogens, targeting these factors may result in DENV inhibitors, and will play an important role in attenuating the rapid emergence of other flaviviruses. Many experimental studies have yielded findings indicating that host factors facilitate infection, indicating that the focus should be given to targeting the processes contributing to pathogenesis along with many other immune responses. Here, we provide an extensive literature review in order to elucidate the progress made in the development of host-based approaches for DENV viral infections, focusing on host cellular mechanisms and factors responsible for viral replication, aiming to aid the potential development of host-dependent antiviral therapeutics.

A plasmid-based reporter system for live cell imaging of dengue virus infected cells

Cell culture models are used widely to study the effects of dengue virus (DENV) on host cell function. Current methods of identification of cells infected with an unmodified DENV requires fixation and permeablization of cells to allow DENV-specific antibody staining. This method does not permit imaging of viable cells over time. In this report, a plasmid-based reporter was developed to allow non-destructive identification of DENV-infected cells. The plasmid-based reporter was demonstrated to be broadly applicable to the four DENV serotypes, including low-passaged strains, and was specifically cleaved by the viral protease with minimal interference on viral production. This study reveals the potential for this novel reporter system to advance the studies of virus-host interactions during DENV infection.

Inflammatory and innate immune responses in dengue infection: protection versus disease induction

Dengue disease is a mosquito-borne viral disease of expanding geographical range and incidence. Infection by one of the four serotypes of dengue virus induces a spectrum of disease manifestations, ranging from asymptomatic to life-threatening Dengue hemorrhagic fever/dengue shock syndrome. Many efforts have been made to elucidate several aspects of dengue virus-induced disease, but the pathogenesis of disease is complex and remains unclear. Understanding the mechanisms involved in the early stages of infection is crucial to determine and develop safe therapeutics to prevent the severe outcomes of disease without interfering with control of infection. In this review, we discuss the dual role of the innate and inflammatory pathways activated during dengue disease in mediating both protection and exacerbation of disease. We show that some mediators involved in each of these responses differ substantially, suggesting that interfering in disease-associated immune pathways may represent a potential therapeutic opportunity for the treatment of severe dengue.

RNA helicases: emerging roles in viral replication and the host innate response

RNA helicases serve multiple roles at the virus-host interface. In some situations, RNA helicases are essential host factors to promote viral replication; however, in other cases they serve as a cellular sensor to trigger the antiviral state in response to viral infection. All family members share the conserved ATP-dependent catalytic core linked to different substrate recognition and protein-protein interaction domains. These flanking domains can be shuffled between different helicases to achieve functional diversity. This review summarizes recent studies, which have revealed two types of activity by RNA helicases. First, RNA helicases are catalysts of progressive RNA-protein rearrangements that begin at gene transcription and culminate in mRNA translation. Second, RNA helicases can act as a scaffold for alternative protein-protein interactions that can defeat the antiviral state. The mounting fundamental understanding of RNA helicases is being used to develop selective and efficacious drugs against human and animal pathogens. The analysis of RNA helicases in virus model systems continues to provide insights into virology, cell biology and immunology, and has provided fresh perspective to continue unraveling the complexity of virus-host interactions.

Gene expression analysis during dengue virus infection in HepG2 cells reveals virus control of innate immune response

OBJECTIVES

Liver damage occurs during Dengue Virus infection and constitutes a characteristic of severe forms of the disease. The present study was focused on the modulation of gene expression in a human hepatic cell lineage, HepG2, in response to Dengue Virus infection.

METHODS

The global gene expression changes in HepG2 cells after 6, 24 and 48h of infection with Dengue Virus were investigated using a new tool of microarray data analysis and real-time PCR.

RESULTS

HepG2 cells infected with Dengue Virus showed alterations in several signaling pathways involved in innate immune response. The analysis of pattern recognition pathways genes demonstrated that TLR3, TLR8, RIG-I and MDA5 mRNAs were up-regulated during Dengue Virus infection along with an increase in the expression of the type I interferon, IFN-beta and pro-inflammatory cytokines IL-6, IL-8 and RANTES genes.

CONCLUSIONS

Our results suggest that innate immune pathways are involved in the recognition of Dengue Virus by HepG2 cells. These observations may contribute to the understanding of the inflammatory responses induced by Dengue Virus-hepatocytes interaction during dengue diseases.

Molecular profiling of T-helper immune genes during dengue virus infection

In this study, we provide a comprehensive molecular profiling of the involvement of T- helper (Th) genes during dengue virus infection of different cell types. The Th gene profiles of three human cell types (monocytes, T-cells and hepatocytes) were analyzed simultaneously via array-based RT-PCR upon infection with dengue virus. Differential regulation of 41 Th genes was identified and of which 20 of those genes may contribute to immuno-pathogenesis of dengue virus infection by regulating inflammation, thrombocytopenia and vascular permeability. Among the strongly up-regulated genes were the RANTES, CC-CKR3, IRF4, CLEC2C, IL-6 and TLR6, which are potent inducer of inflammation and vascular permeability. Profiling genes obtained from this study may serve as potential biomarkers and the modulation of Th immune responses during dengue virus infection has important implications in disease outcome.

Efficient dengue virus (DENV) infection of human muscle satellite cells upregulates type I interferon response genes and differentially modulates MHC I expression on bystander and DENV-infected cells

Dengue virus (DENV) is a mosquito-borne flavivirus that causes an acute febrile disease in humans, characterized by musculoskeletal pain, headache, rash and leukopenia. The cause of myalgia during DENV infection is still unknown. To determine whether DENV can infect primary muscle cells, human muscle satellite cells were exposed to DENV in vitro. The results demonstrated for the first time high-efficiency infection and replication of DENV in human primary muscle satellite cells. Changes in global gene expression were also examined in these cells following DENV infection using Affymetrix GeneChip analysis. The differentially regulated genes belonged to two main functional categories: cell growth and development, and antiviral type I interferon (IFN) response genes. Increased expression of the type I IFN response genes for tumour necrosis factor-related apoptosis-inducing ligand (TRAIL), melanoma-derived antigen 5 (MDA-5), IFN-gamma-inducible protein 10 (IP-10), galectin 3 soluble binding protein (LGals3BP) and IFN response factor 7 (IRF7) was confirmed by quantitative RT-PCR. Furthermore, higher levels of cell-surface-bound intracellular adhesion molecule-1 (ICAM-1) and soluble ICAM-1 in the cell-culture medium were detected following DENV infection. However, DENV infection impaired the ability of the infected cells in the culture medium to upregulate cell-surface expression of MHC I molecules, suggesting a possible mechanism of immune evasion by DENV. The findings of this study warrant further clinical research to identify whether muscle cells are targets for DENV infection during the acute stage of the disease in vivo.