Plasminogen activator in cultured human epidermal cells

Primary cultures of human epidermal cells produce plasminogen activator (PA) as demonstrated by the ability of conditioned medium or cell lysates to hydrolyze fibrin in the presence of plasminogen, and to cleave [125I]plasminogen to characteristic fragments. The major molecular species of PA in human epidermal cells was inhibited by diisopropylfluorophosphate and comigrated in sodium dodecyl sulfate-polyacrylamide gel electrophoresis with the high molecular weight band of human urokinase (Mr 55,000). Production of PA by human epidermal cells was inhibited by cycloheximide, stimulated by colchicine, and not affected by cytochalasin B or the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. Both cholera toxin and epidermal growth factor stimulated PA activity in human epidermal cells, and PA activity was maximal at concentrations that best support in vitro growth of human epidermal cells. Examination of individual cells indicated that at least 15% of cells within a culture produced detectable amounts of PA.