Characterization of prostaglandin E2 receptors expressed on human monocytic leukaemic cell line, U937

Prostaglandin E2 (PGE2) receptors of a human monocytic leukaemic cell line, U937 cells, have been identified. [3H]PGE2 binding to these cells was found to be saturable and highly specific. Scatchard analysis of binding data revealed a non-linear plot indicating the presence of two independent classes of binding sites with different affinities and capacities. The high-affinity class had Kd1 = 3.1 nM and binding capacities n1 = 0.6 fmol/10(6) cells, whereas the low-affinity class had Kd2 = 137 nM and capacities n2 = 16 fmol/10(6) cells. Incubation of U937 cells with 3 microM PGE2 stimulated a 15-fold increase in cAMP formation compared to basal levels. Prior exposure of these cells with 10 microM PGE2 for 60 min induced both homologous and heterologous desensitization of adenylate cyclase activity. PGE2 (3 microM) or histamine (100 microM) showed reduced stimulation of cAMP formation in these desensitized cells compared to controls. The desensitized cells also showed 80% reduction of specific PGE2 binding compared to control cells. Our data suggest that U937 cells have PGE2 receptors which are linked to the adenylate cyclase system.