Regulation of urokinase plasminogen activator (uPA) activity by E-cadherinand hormones in mammary epithelial cells

Urokinase plasminogen activator (uPA) is involved in proteolysis of extrace llular matrix during development and tumor cell invasion. In the present st udy, we examined the regulation of uPA in hormone-responsive, noninvasive m ammary epithelial cells by using fibrinolytic and caseinolytic enzyme activ ity assays. Urokinase PA expression was activated after contact with fibrin and initiation of cell-cell interactions that were mediated by E-cadherin. Fibrinolysis occurred in zones surrounding cellular aggregates. Stromal ma trix proteins that disrupted aggregation or anti-E-cadherin antibodies that inhibited cellular compaction inhibited fibrinolysis perhaps by increasing cell-matrix adhesion or preventing E-cadherin signaling, respectively. Agg regation required the presence of divalent cations and was inhibited by ser um and ethylene diaminetetraacetic acid, whereas serine protease inhibitors reduced uPA activity without affecting aggregation. inhibitors of PA (type 2; PAI-2) and a specific antisense uPA oligonucleotide also reduced enzyma tic activity, suggesting that fibrinolysis depends on translational regulat ion of uPA. In addition, the activation of plasmin from plasminogen was inh ibited by anti-E-cadherin antibodies and PAI-2, consistent with a role for uPA. The data also support a role for transcriptional regulation of uPA act ivity because treatment of cells with progesterone, hydrocortisone, or dexa methasone inhibited uPA activation on fibrin without affecting cellular agg regation. Estradiol and insulin did not alter, whereas human chorionic gona dotropin and prolactin increased uPA activity. The expression of the 55-kDa uPA activity was consistent with specific hormone action and correlated wi th protein expression by immunoblotting. Therefore, the alteration of downs tream signaling events by hormones may affect uPA production. These results indicate that uPA is an enzyme that may be important in the degradation of extracellular matrix during development and that specific E-cadherin inter actions and hormones can regulate its activity, investigation of the regula tion of uPA in these cells may be useful in understanding and manipulating mammary gland remodeling. J. Cell. Physiol. 181:7-13, 1999. Published 1999 Wiley-Liss, Inc.