ABSTRACT
Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of COVID-19 (Coronavirus disease 19). SARS-CoV-2 causes a multisystemic infection, which frequently presents with pulmonary oedema, endothelial damage and electrolytic abnormalities. An essential physiopathological feature of SARSCoV-2 involves cleavage of its S protein by furin or furin-like enzymes. It has been shown by sequence-based evidence that the S protein polybasic aminoacid sequence is identical to the consensus sequence for furin cleavage present in the human alpha subunit of the epithelial sodium channel (ENaC). Furin and furin-like enzymes are also involved in the posttranslational regulation of ENaC in many tissues, including the lung, endothelium, and the kidney, where cleavage is associated with increased activity of the channel. ENaC is involved in the regulation of fluid clearance, Na+, K+ and acid-base homeostasis, and endothelial function. Thus, we hypothesized that the S protein competes with ENaC for furin-mediated cleavage and activation. Method(s): We injected synthetic mRNA encoding WT S protein and mutant S protein lacking the furin consensus sequence (DELTA-Spike) into X. laevis oocytes with alphabetagamma-ENaC subunits. We then performed whole-cell voltage-clamp experiments and protein analysis by western blot. Result(s): We observed an interdependent competitive effect on the cleavage of both the S protein and ENaC when co-expressed, which was partially prevented with the injection of DELTA-Spike. We also found a decrease in the amiloride-sensitive sodium current in oocytes injected with the WT S protein but not with DELTA-Spike. This suggests diminished function of ENaC in the presence of WT S protein that depends on its furin cleavage site. Conclusion(s): These findings show evidence of a competitive interaction between the S protein and ENaC for furin-like enzymes. This suggests that SARS-CoV-2 infection may impair ENaC activity in human epithelia, which gives a plausible explanation to pulmonary oedema, endothelial damage, and electrolyte disturbances in patients with COVID-19.