Expression of TMPRSS2 mutants Δex4/5 and Δex5 in A549 cells and coexpression of Δex4/5 and Δex5 with HA. (A) A549 cells were transfected with plasmids encoding either TMPRSS2, enzymatically inactive TMPRSS2 mutant S441A, Δex4/5, or Δex5, each with a C-terminal FLAG epitope. Cells transfected with empty pCAGGS were used as mock controls. At 24 h posttransfection, cell lysates were analyzed by SDS-PAGE and Western blotting using a FLAG-specific antibody. Zymogens and the mature form are indicated. A nonspecific band is indicated by an asterisk. (B) A549 cells were transfected with pCAGGS (mock) or cotransfected with pCAGGS-HA and either empty pCAGGS or pCAGGS plasmids encoding either TMPRSS2, S441A, Δex4/5, or Δex5. Cell lysates were subjected to SDS-PAGE and Western blot analysis using antibodies against HA.