INHIBITORY EFFECT OF A SYNTHETIC PROSTACYCLIN ANALOG, BERAPROST, ON UROKINASE-TYPE PLASMINOGEN-ACTIVATOR EXPRESSION IN RC-K8 HUMAN LYMPHOMA-CELLS

Plasminogen activation by urokinase-type plasminogen activator (uPA) i s implicated in tumor invasion and metastasis by the breakdown of extr acellular matrix. We have recently demonstrated the inhibitory effect of cAMP on uPA gene transcription in RC-K8 human lymphoma cells (Bioch im Biophys Acta 1268: 293-9, 1995). Prostacyclin produced by endotheli al cells is shown to increase cellular cAMP levels by activating adeny late cyclase. We, therefore, examined the effect of a stable analogue of prostacyclin, Beraprost, on uPA production in RC-K8 cells. uPA acti vity gradually increased in the conditioned medium with time. Berapros t (0.1 nM-1.0 mu M) inhibited uPA accumulation in a dose-dependent man ner without affecting cell viability. Fibrin-zymography demonstrated t hat high and low molecular forms of uPA were present in the conditione d medium and that after Beraprost-treatment all forms of uPA decreased and no PA/PA inhibitor complex was present. Northern blot analysis re vealed that after exposure to Beraprost, uPA mRNA levels increased tra nsiently and then rapidly decreased to below control levels. Treatment with Beraprost resulted in a rapid activation of cellular cyclic AMP- dependent protein kinase (PKA). Beraprost completely negated uPA gene expression induced by phorbol myristate acetate, an activator of prote in kinase C (PKC). These results suggest that Beraprost inhibits uPA p roduction by suppressing uPA gene expression through the PKA pathway a nd that PKA-mediated signals are dominant in uPA gene expression as co mpared to those medicated by PKC. This inhibition of uPA expression by a prostacyclin analogue may be an important fact to explain the mecha nism of anti-metastatic effects of prostacyclin.