Enterokinase Enhances Influenza A Virus Infection by Activating Trypsinogen in Human Cell Lines

Abstract

Cleavage and activation of hemagglutinin (HA) by trypsin-like proteases in influenza A virus (IAV) are essential prerequisites for its successful infection and spread. In host cells, some transmembrane serine proteases such as TMPRSS2, TMPRSS4 and HAT, along with plasmin in the bloodstream, have been reported to cleave the HA precursor (HA0) molecule into its active forms, HA1 and HA2. Some trypsinogens can also enhance IAV proliferation in some cell types (e.g., rat cardiomyoblasts). However, the precise activation mechanism for this process is unclear, because the expression level of the physiological activator of the trypsinogens, the TMPRSS15 enterokinase, is expected to be very low in such cells, with the exception of duodenal cells. Here, we show that at least two variant enterokinases are expressed in various human cell lines, including A549 lung-derived cells. The exogenous expression of these enterokinases was able to enhance the proliferation of IAV in 293T human kidney cells, but the proliferation was reduced by knocking down the endogenous enterokinase in A549 cells. The enterokinase was able to enhance HA processing in the cells, which activated trypsinogen in vitro and in the IAV-infected cells also. Therefore, we conclude that enterokinase plays a role in IAV infection and proliferation by activating trypsinogen to process viral HA in human cell lines.

Hemagglutinin Cleavability, Acid Stability, and Temperature Dependence Optimize Influenza B Virus for Replication in Human Airways

“…In contrast, activation of A/H1N1 and A/H3N2 HA was largely limited to TMPRSS2 and TMPRSS11D/HAT and to TMPRSS4 in the case of A/H1N1. We saw no evidence for a role of TMPRSS15/enterokinase (70) or KLK5, KLK12 (71,72) or of any other kallikrein. It is possible that the KLK levels attained in our cell systems were below those applied during incubation with recombinant KLKs (71).…”

Smoking and COVID‐19: Similar bronchial ACE2 and TMPRSS2 expression and higher TMPRSS4 expression in current versus never smokers

“…Padj and FC values were generated by GEO2R. Figures were prepared using GraphPad Prism v.8.4.2 and are both implicated in the activation and cell entry of H3N2 influenza A and influenza B viruses, so that TMPRSS4 allows cell infection in the albescence of the host TMPRSS2 gene (Bertram et al, 2010;Chaipan et al, 2009;Harbig et al, 2020;Hayashi et al, 2018;Kühn et al, 2016;Zmora et al, 2017). Both TMPRSS2 and TMPRSS4 play a role in lung cancer metastasis (Martin & List, 2019); high levels of TMPRSS4 were observed in several malignancies and were associated with epithelial to mesenchymal cell transition, invasion and metastasis (de Aberasturi & Calvo, 2015).…”

The Cytotoxicity of RNase-Derived Peptides

“…Host proteases play an important role in determining the cell or tissue tropism of different viruses [ 48 ]. Lung epithelial cells express matrix metalloproteinases (MMPs) and type II transmembrane serine proteases (TTSPs); among them transmembrane serine protease 4 (TMPRSS4) and 15 (TMPRSS15) are found in A549 cells though at a low expression level [ 49 , 50 , 51 ]. Both proteases regulate physiological processes as well as tumor development and progression notably in lung, pancreatic, thyroid, colon, and gastric cancers [ 52 ].…”