Debanjana Mondal, Queen's University

Authors: Debanjana Mondal and Che C. Colpitts. Affiliation: Department of Biomedical and Molecular Sciences, Queen's University

Fighting & Responding

The COVID-19 pandemic highlighted the need for new broad spectrum antiviral drugs. Thapsigargin (Tg), which induces ER stress and the unfolded protein response (UPR) by inhibiting the sarco/endoplasmic reticulum calcium ATPase (SERCA), exhibits broad antiviral activity against multiple viruses, including human coronaviruses (HCoVs). However, its antiviral mechanisms are still unclear. Therefore, we aimed to test the role of the UPR and SERCA in the antiviral activity of Tg against HCoV infection. Using A549 alveolar epithelial cells infected with HCoV-229E and HCoV-OC43, we confirmed that Tg is antiviral at concentrations that do not affect cell viability. Tg inhibits HCoV transcription/replication, as shown by reduced HCoV-229E and HCoV-OC43 gene expression. Interestingly, Tg also exhibits antiviral activity against the murine CoV MHV-1 in L2 cells, opening perspectives for in vivo testing in mice. To test the role of UPR activation in the antiviral effect of Tg, we used tunicamycin, which activates UPR by inhibiting N-linked glycosylation and causing the accumulation of misfolded proteins in ER. Interestingly, we found that tunicamycin only minimally inhibits HCoV transcription/replication compared to Tg. On the other hand, we also observed an inhibition of UPR activation post infection. These findings suggest additional mechanisms beyond UPR activation contribute to the antiviral activity of Tg. This creates an opportunity to investigate the role of SERCA in the antiviral activity of Tg. Currently, we are generating SERCA knockdown cell lines to test the role of SERCA. Overall, these findings help to define the antiviral mechanisms of Tg against HCoVs.