MRC AMED - The HDAC6/USP7 axis in enveloped RNA viral infection

Influenza A virus (IAV) causes annual epidemics and occasional pandemics with continuous threat of emerging and potentially lethal strains derived from reassortment with avian or swine IAV. In addition to development of a universal influenza vaccine, a deeper understanding of cell biology of IAV infections is needed to discover antiviral strategies that target cellular proteins and pathways. Viral uncoating is an early step in infection that is poorly understood, but we think that the host cell factors involved can be targeted effectively as an antiviral strategy.

IAV entry and uncoating is well-studied compared to many enveloped RNA viruses. Uncoating requires a ubiquitin-mediated, misfolded protein degradation pathway known as aggresome processing. Here, the key host player, the cytosolic histone deacetylase 6 (HDAC6), senses misfolded protein 'tags' and activates a cellular pathway that helps to break apart the viral shell during entry. In this study we will address the interplay between HDAC6 and ubiquitin-modifying enzymes, and target multiple host factors to block viral uncoating and thus block infectivity. Our findings may contribute to the understanding of general viral uncoating pathways and lead to conceptualisation of a broad spectrum antiviral that can combat emerging and re-emerging viruses of medical importance.

Influenza A virus (IAV) causes annual epidemics and occasional pandemics with continuous threat of emerging and potentially lethal strains derived from reassortment with avian or swine IAV. In addition to development of a universal influenza vaccine, a deeper understanding of cell biology of IAV infections is needed to discover antiviral strategies that target cellular proteins and pathways. Viral uncoating is an early step in infection that is poorly understood but highly druggable. As an example, adamantanes that were once used in human flu patients blocks IAV uncoating by inhibiting the M2 ion channel.

IAV entry and uncoating is well-studied compared to many enveloped RNA viruses. Uncoating requires a ubiquitin-mediated, misfolded protein degradation pathway known as aggresome processing. Here, the key host player, histone deacetylase 6 (HDAC6), senses unanchored ubiquitin chains packaged within the virion via the HDAC6 zinc finger ubiquitin-binding domain (ZnF-UBP). In this study we will address the interplay between HDAC6 and a novel host factor, the deubiquitinase USP7, and analyse their role in IAV entry. Furthermore based on knowledge that HDAC6 can be hijacked by multiple viruses, we will test a panel of emerging and re-emerging enveloped RNA viruses on their dependence on HDAC6 and USP7.

Our strategy is to use IAV as a prototype enveloped RNA virus. Our findings may contribute to the understanding of general viral uncoating pathways and lead to conceptualisation of a broad spectrum antiviral that can combat emerging and re-emerging viruses of medical importance.

Emerging and re-emerging viral infections are a true burden to our society, to the government, and most of all to infants and the elderly. Many of these so-called old or new viruses are categorised into having an envelope (a lipid bilayer derived from the cells of our bodies) and having an RNA genome (instead of DNA). Examples are Dengue virus (kills many people in South East asia), Zika virus (causes microcephaly in newborns), Ebola virus (prevalence in Africa), MERS virus etc. Our research tries to tackle these viral infections by first understanding how our bodies inadvertently assist these viruses into infecting. Viruses are obligatory parasites and depend on our bodily functions to reproduce offspring. By deeply understanding how our cells in our body assists the virus, we may be able to tweak this cellular function so that the viruses can no longer infect us.

In this research we propose to study two cellular proteins of interest. One is a unique and cytosolic histone deacetylase (HDAC), the other is a deubiquitinating enzyme (DUB), that is, an enzyme that is capable of removing a ubiquitin (small protein that modifies other proteins) from a conjugated protein. HDACs are known to deacetylate their targets and to regulate their function. We believe that some HDACs and DUBs work together in order to support viruses enter our cells and to infect them. By understanding the mechanism of the cellular functions we can in the future try to inhibit this mechanism to block infections. We are also aware that targeting our own proteins and their functions can have off-target effects, but we should also appreciate that many cancer drugs target our own cellular proteins and functions. Thus, the logic goes that for devastating viral infections we should not be afraid to do the same, based on concrete biology and mechanistic understanding.

When our research is completed, we believe we will have a very good handle on how to combat enveloped RNA viral infection by targeting one or two enzymes that exist in our own bodies. Our approach may not immediately become therapeutics in real patients, but will nevertheless give researchers and doctors a lot of valuable insight into how viruses enter and infect our bodies and could lead to the development of new strategies of antiviral interventions in the future.