The cellular target for the plasminogen activator, urokinase, in human fibroblasts - 66 000 dalton protein.

The effects of urokinase, the plasminogen activator of human urine, on the isolated substratum-attached pericellular matrices of cultured human lung fibroblasts were studied in serum-free conditions. Pericellular matrices were prepared from dense cultures of human lung fibroblasts after labelling of the cultures with radioactive glycine. Extraction of the cultures with sodium deoxycholate and hypotonic buffer gave a reproducible pattern of polypeptides when analyzed in polyacrylamide gels. The isolated pericellular matrix was subsequently exposed to affinity chromatography-purified urokinase. Urokinase affected a 66000-dalton protein but none of the other matrix polypeptides. The appearance of a 62000-dalton protein that remained attached to the matrix was seen concomitantly suggesting that it was derived from the 66000-dalton protein. The 66000-dalton protein is the first known cellular target for urokinase.