SECRETION OF UROKINASE AND METALLOPROTEINASE-9 INDUCED BY STAUROSPORINE IS DEPENDENT ON A TYROSINE KINASE PATHWAY IN MAMMARY-TUMOR CELLS

Urokinase-type plasminogen activator (uPA) is a key serine protease in volved in invasion and metastasis. We had shown that overproduction of uPA in tumor cells is controlled by a phospholipase D-protein kinase C-dependent pathway, Now we studied whether other signaling pathways p articipate in the regulation of constitutive uPA and metalloproteinase (MMP) overproduction in tumor cells. Staurosporine, a protein kinase inhibitor, stimulated uPA and MMP-9 secretion as measured by radial ca seinolysis, zymography and Western blotting. Genistein, a specific tyr osine kinase inhibitor, reduced the constitutive and staurosporine-ind uced uPA and MMP-9 secretion. Interestingly, the phosphatase inhibitor vanadate stimulated uPA secretion, Verapamil, a calcium channel block er, inhibited both endogenous and PMA-stimulated secretion of uPA but was unable to inhibit staurosporine-induced secretion. The alcohol n-b utanol, a phospholipase D and protein kinase C inhibitor, besides inhi biting constitutive uPA secretion, blocked staurosporine-induced secre tion. Our results suggest that constitutive and staurosporine-induced uPA and MMP-9 secretion by LM3 murine mammary tumor cells is controlle d by an endogenous tyrosine kinase pathway and probably involves prote in phosphatases, in addition, the staurosporine-induced signal regulat ing urokinase secretion is independent of extracellular calcium but de pendent on phospholipase (C) 1998 Wiley-Liss, Inc.