FIG. 1.

Cleavage of influenza virus HA by coexpression with TMPRSS2 (left panel) and HAT (right panel). A549 cells were cotransfected with pCAGGS-HA (lanes 2 to 5) and empty pCAGGS vector (lanes 2 and 3), pCAGGS-TMPRSS2 or pCAGGS-HAT (lane 4), and pCAGGS-TMPRSS2(S441A) (lane 5, left panel). Mock transfections were done with empty pCAGGS plasmid (lane 1). We analyzed cell lysates prepared 48 h after transfection by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting as described in the text. For a positive control of HA cleavage, transfected cells were incubated with 10 μg of TPCK (tolylsulfonyl phenylalanyl chloromethyl ketone)-trypsin (Sigma)/ml for 20 min at 37°C prior to lysis (lane 3).