UNESTERIFIED LONG-CHAIN FATTY-ACIDS INHIBIT THE BINDING OF SINGLE-CHAIN UROKINASE TO THE UROKINASE RECEPTOR

The interaction of single chain urokinase with its receptor accelerate s plasminogen activator activity on cell surfaces and induces intracel lular signalling in several cell types. To date, no physiologic inhibi tor of this binding has been identified. We report that the binding of scuPA to its cellular receptor is inhibited by long chain fatty acids such as oleic acid (C18,Delta 9) at physiological plasma concentratio ns. Inhibition of single chain urokinase binding to human trophoblasti c cells by long chain fatty acids was dose-dependent and saturable. Fi fty percent of the binding was inhibited at an oleic acid concentratio n of 27 mu M, while inhibition was maximal (75%) at 150 mu M oleic aci d. The inhibitory potency of oleic acid was unaffected by fatty acid f ree albumin or human plasma. Inhibition of single chain urokinase bind ing by free fatty acid analogues was critically dependent on chain len gth (>C-14 required for inhibition) and was proportional to the extent of unsaturation. Only the fraction of specific scuPA binding to troph oblasts that was dependent on uPAR was susceptible to inhibition by ol eic acid, while binding of scuPA to vitronectin, thombospondin, and th e alpha(2)-macroglobulin receptor/low-density lipoprotein-related rece ptor was not. [H-3]Oleic acid bound specifically to recombinant solubl e uPAR in a 1:1 molar ratio in the presence or absence of plasma and t otally blocked its specific binding to a cell line expressing glycosyl phosphatidylinositol-linked single chain urokinase. These results ind icate that oleic acid and other unsaturated long chain free fatty acid s may serve as physiologic regulators of proteolytic events and intrac ellular signalling that depend upon the interaction of urokinase with its receptor.