Our lab focuses on virus-host interactions of positive-sense RNA viruses, including coronaviruses (CoVs), dengue virus and hepatitis C virus (HCV). We have projects focused on viral entry, replication and pathogenesis with a view to developing host-targeting antiviral strategies. Some of our research questions are as follows:

Antiviral mechanisms of cyclophilin inhibitors

Cyclophilin inhibitors such as cyclosporine A (CsA) have broad-spectrum activity against a diverse array of viruses. We are characterizing the antiviral mechanism(s) of CsA against positive-sense RNA virus infections (HCV, dengue virus, and common cold coronaviruses). We have shown that CsA inhibits human CoV-229E infection in part by activating the transcription factor IRF1, thereby upregulating expression of antiviral genes that inhibit viral replication (Mamatis et al. (2023) Antiviral Res.). We are currently investigating how CsA activates IRF1. We are also evaluating the roles of cyclophilin A (CypA) – a cellular protein that is a main target of CsA – in HCV infection. We recently showed that HCV requires CypA to evade cellular innate immune responses (Colpitts et al. (2020) eLife). We are now studying the mechanisms to understand how CypA contributes to HCV immune evasion. Overall, these studies may inform the repurposing of cyclophilin inhibitors as broadly-acting antivirals.

ER stress and positive-sense RNA virus infection

We also study endoplasmic reticulum stress and how this is induced or regulated by HCV and human common cold CoV (HCoV-229E and -OC43) infection. Viral infection places a burden on the ER, through excessive protein synthesis at the ER and remodelling of ER membranes by HCV and CoV non-structural proteins to form viral replication organelles, which are the site of viral RNA replication. ER stress leads to activation of the unfolded protein response (UPR), comprised of three pathways (ATF6, IRE1 and PERK) that function to restore ER homeostasis through diverse mechanisms. We are studying how these UPR pathways affect HCV and HCoV-229E replication, and how viral proteins modulate the UPR. In addition, chemical inducers of ER stress, such as thapsigargin, have potent, long-lasting, and broad-spectrum antiviral activity. We are currently characterizing the antiviral mechanisms to understand how induction of ER stress confers antiviral activity.

Roles of viral glycoproteins in pathogenesis

Viral glycoproteins, such as coronavirus spike and dengue virus NS1, have been shown to activate the pattern recognition receptor TLR4, triggering induction of pro-inflammatory cytokines and contributing to the ‘cytokine storm’ that is associated with severe viral disease (Halajian & LeBlanc et al. (2022) Front. Microbiol.). Since the classic ligand of TLR4 is bacterial lipopolysaccharide, it is unclear how these viral glycoproteins activate TLR4. We are characterizing the viral and cellular determinants that are required for TLR4 activation by viral glycoproteins, which could inform new therapeutic strategies to counteract viral cytokine storm.

We are grateful to NSERC, CIHR, CFI, ORF, the J.P. Bickell Foundation, the Banting Research Foundation, and Queen’s University for grants supporting our research.