Differential targeting of the HSV1 vhs endoribonuclease - preferential degradation of cellular transcripts on the endoplasmic reticulum?

Lead Research Organisation: University of Surrey
Department Name: Microbial & Cellular Sciences


Herpes simplex virus (HSV) is an important human pathogen of medical and economic impact. HSV infection is life-long and once acquired it remains dormant in the body, poised to re-emerge and cause disease. It is the causative agent of recurring oral and genital herpes, both of which have profound effects on the quality of life of sufferers. Upon activation, HSV can also have much more serious consequences. For example, it is a pioneer infection for human immunodeficiency virus (HIV), making individuals more susceptible to HIV infection. It is the major cause of infectious blindness, and viral encephalitis that results in death or devastating brain damage. In developing countries neonatal herpes remains a cause of death in newborns. Individuals who have a suppressed immune system, such as transplant, cancer chemotherapy, and AIDS patients, are particularly susceptible to complications of HSV. With 24 million new cases globally each year, this virus is a huge economic burden on our health systems. However, efforts to develop an HSV vaccine have, without exception, failed. Moreover, although drug treatments for HSV have existed for decades, their use has made no impact on this HSV epidemic and resistance is growing. It is therefore vital that new ways to treat HSV are identified.

To understand how to treat virus infections, it is first important to understand how they cause disease. HSV produces a number of factors that are considered non-essential for infection in cells in the lab, but are vital for the virus to cause disease in the host animal. These factors represent new targets for therapuetic intervention. One of these is virion host shutoff (vhs), which has a role in controlling the global cellular environment to make it favourable for efficient virus growth. Nonetheless, it is not yet clear how vhs activity influences the outcome of the disease process in a balanced fashion, such that it does not create a hostile environment for the virus. Using a global approach to look at cellular changes in HSV1 infection, we have discovered that vhs appears to target specific groups of cellular factors involved in pathways that determine the make-up of the environment outside the cell. Here, we propose to use state-of-the-art technology to define in detail the targets that are highly susceptible to vhs activity. New tools will be developed to identify the infected cell components that interact with vhs to understand how vhs is targeted to its site of action. Finally, we will determine if the activity of vhs prepares the cell to make large numbers of virus structual components thereby enabling the efficient production of new virus particles. In this way we aim to unravel the complexities of vhs activity to further our understanding of its role in virus infection and identify target interactions to potentially inhibit therapeutically.

Technical Summary

Herpes simplex virus type 1 (HSV1) virion host shutoff (vhs) protein is an endoribonuclease that specifically targets mRNAs by binding to the translation initiation machinery at the 5' end of the mRNA, but the subtlety of its specificity remains to be delineated. Using RNAseq of infected human fibroblasts we have recently shown that cellular mRNAs exhibit a wide range of susceptibility to vhs activity during HSV1 infection, ranging from no effect to a 1000-fold reduction after 12 hours. Pathway analysis of transcripts reduced by more than 30-fold has revealed a surprising enrichment in pathways related to the extracellular environment, particularly the remodeling of the extracellular matrix. Furthermore, the most vhs-susceptible transcripts were determined to be enriched in transcripts encoding membrane/secreted proteins in general. This proposal therefore aims to test the novel hypothesis that vhs specifically targets transcripts that are translated on the endoplasmic reticulum (ER), resulting in important alterations to the extracellular environment. The specificity of vhs activity against ER bound transcripts will be delineated using differential expression analysis of total and ER-bound cellular transcriptomes from cells infected with Wt and vhs- viruses. Vhs-induced alterations in the extracellular proteomes will be assessed using tandem mass tagging mass spectrometry of similar infections. Additionally, the vhs interactome will be defined to determine the nature of vhs targeting to specific subsets of mRNAs. Finally, the role of vhs in paving the way for HSV1 glycoprotein translation - the most abundant transcripts present at later times in infection - will be determined. These studies will further our understanding of the molecular consequences of HSV vhs activity within the cell and its impact on the global make-up of the cell, data that will impact on other alphaherpesviruses and viruses in general that encode endoribonucleases.

Planned Impact

The immediate goal of this research is to delineate the fundamental biology of the vhs protein of HSV and as such, its short-term impact will be to advance scientific knowledge on herpes simplex virus and animal herpesviruses of veterinary importance that have vhs homologues.

The project also has the potential to impact on future research leadership, as the appointed postdoctoral researcher will be trained in specialist transferable skills such as RNAseq, confocal microscopy and proteomics. This individual will have the potential to become a virology leader of the future. Moreover, the interdisciplinary nature of the research has the capacity to impact a wider research community than the field of virology alone, including RNA metabolism and protein translation fields.

In the longer term, this research has the potential to impact on the understanding and development of new antiviral treatments of HSV infection. HSV is the causative agent of oral and genital herpes and although not life-threatening, the quality of life of individuals who suffer from frequent reactivation of HSV could be greatly improved by new anti-HSV treatment. HSV is also a major cofactor in the transmission of HIV, and is a particular problem in Africa. Prevention of HSV spread would be predicted to reduce HIV infection rates. As a consequence, deaths from HIV would be significantly reduced. HSV is the major viral cause of encephalitis, resulting in severe brain damage or death. The ability to block reactivation of HSV could greatly reduce the occurrence of both the frequent symptoms and the more serious outcomes of HSV infection. New treatments of HSV could also lead to a reduction in levels of blindness caused by HSV keratitis. Death or serious disease from neonatal herpes, a result of transmission from mother to baby at birth, could be prevented. Immunosuppressed transplant or cancer patients will be less susceptible to serious complications of HSV infection.

In addition, because other alphaherpesviruses express homologues of vhs, the work has the potential to impact patients with varicella zoster virus or animals with alphaherpesviruses, thereby also contributing to the health of the population and the One Health agenda in general. Our research will therefore contribute to the University of Surrey School of Biosciences Strategic Aims to optimise human health and tackle global disease burden.

Development of new treatments for HSV and VZV could impact on the work of clinical virologists, who are involved in treating and caring for individuals with serious complications, have an economic impact on health services both in the UK and worldwide. Fewer patients will present with serious HSV-related illness, or other infections, so fewer resources will be required to care for them. A reduction in virus transmission through the population would result in fewer drugs being needed to treat individuals, relieving the economic burden of these drugs on the health service. Globally, a reduction in HIV transmission would reduce the cost to health services of caring and treating HIV patients, and would relieve the economic burden of anti-retroviral drugs.

This project could contribute to the economic competitiveness of the UK through the development of drugs that target HSV or VZV, or treatments for animal alphaherpesvirus infections. Our discoveries would be commercialized by existing companies in the UK, with the potential for enhanced wealth generation and employment opportunities.