SARS-CoV-2 envelope-protein corruption of homeostatic signaling mechanisms in mammalian cells

Schulze, Tobias; Hartel, Andreas; Höler, Sebastian; Hemming, Clara; Lehn, Robert; Tandl, Dominique; Greiner, Timo; Bertl, Adam; Shepard, Kenneth; Moroni, Anna; Thiel, Gerhard; Rauh, Oliver

During a SARS-CoV2 infection, host cells produce large amounts of the viral envelope protein (Ep-CoV2). Ep-CoV2 is partially inserted into the membrane of nascent viral particles and into cellular membranes. To mimic the pathophysiological impact of the cellular protein fraction, Ep-CoV2 was overexpressed in mammalian cells and effects on key signaling parameters were monitored. By tagging with green fluorescent protein (GFP), we found that Ep-CoV2 protein is mostly present in the endoplasmic reticulum with additional trace amounts in the plasma membrane. We observed that wild-type Ep-CoV2 and, to a lesser extent, its mutants (N15A, V25F) corrupted some of the most important homeostatic mechanisms in cells. The same was observed with isolated transmembrane domains of the protein. The Ep-CoV2-evoked elevation of intracellular Ca2+ and pH as well as the induced membrane depolarization produced by the presence of the protein interfere with major signal transduction cascades in host cells. These functions of Ep-CoV2, which likely contribute to the pathogenesis of the viral protein, result from the ion-channel activity of the viral protein. Two independent assays, a functional reconstitution of Ep-CoV2 protein in artificial membranes and a rescue of K+-deficient yeast mutants, confirm that Ep-CoV2 generates a cation-conducting channel with a low unitary conductance and a complex ion selectivity. The data presented here suggest that specific channel function inhibitors of Ep-CoV2 can provide cell protection and virostatic effects.