Figure 4.

Lymphoma cells produce free, active matriptase. Raji BL cells were induced to activate matriptase (lanes 2) by exposing cells to 150 mmol/L phosphate buffer, pH 6.0, for 20 minutes or 200 μmol/L CoCl₂ in basal medium overnight, or basal medium as a nonactivation control (lanes 1). The shed proteins were analyzed by immunoblot for total matriptase using mAb M24 (MTP) and for activated matriptase using mAb M69 (activated MTP). The shed proteins collected from matriptase activation were immunoprecipitated using the activated matriptase mAb M69. The total shed protein (lanes L), unbound (lanes UB), and the proteins eluted from the M69 antibody (lanes E) were analyzed for matriptase gelatinolytic activity by gelatin zymography and by measuring amidolytic activity against a synthetic fluorescent substrate.