Differential expression on matriptase by THP-1 and U937 cells. (A) RNA was isolated from THP-1 and U937 cells, reverse transcribed, and subjected to qRT-PCR. Values are corrected for RNA content by comparison with 18S ribosomal RNA and shown as mean ± SD (n = 3). (B) Cell lysates (lys, 10 μg protein) and concentrated conditioned medium (CM, 10 μL) were isolated from THP-1 and U937 cells in the presence of protease inhibitor cocktail, subject to 10% SDS-PAGE, and probed with an antibody to matriptase (M32). The mobility of matriptase is consistent with the molecular weight of the form proteolytically processed at Gly149,²⁵  but this does not lead to shedding of the protease as it is not detectable in the cell-conditioned medium.