Fig. 1.

Different type-II transmembrane serine proteases (TTSPs) can activate SARS-2-S in transfected cells. (a) The indicated TTSPs equipped with an N-terminal C-MYC antigenic tag were transiently expressed in 293T cells and expression analyzed by immunoblot with anti-C-MYC antibody. Detection of ß-actin (ACTB) served as loading control. Similar results were obtained in three biological replicates. (b) BHK-21 cells transiently expressing ACE2 and one of the indicated TTSPs (or empty vector) were pre-incubated with either 50 mM ammonium chloride or DMSO (control, indicated by dashed line) for 2 h, before they were inoculated with particles pseudotyped with SARS-2-S. At 16 h post inoculation, SARS-2-S-driven cell entry of viral pseudotypes was analyzed by measuring the activity of virus-encoded luciferase activity in cell lysates. Data were further normalized and entry efficiency in the absence of ammonium chloride was set as 100 % (indicated by dashed line). Shown are the average (mean) data obtained from three biological replicates, each performed with four technical replicates. Error bars indicate the standard error of the mean (SEM). Statistical significance of differences in entry efficiency in the presence of ammonium chloride was analyzed by two-way analysis of variance (ANOVA) with Dunnett's posttest (P values, from left to right: 0.0001; 0.9999; 0.0620; 0.9140; 0.4900; 0.0685; 0.0001; 0.0001; 0.0001; 0.0001).