Regulation of prostaglandin E 2 binding to a murine macrophage cell line, P388D 1, by insulin

Abstract

Preincubation of murine macrophage-like P388D 1 cells with physiological amounts of insulin resulted in an increase in prostaglandin E 2 binding to these cells, by approximately 2-fold, when compared to untreated cells. Scatchard analysis of the binding of PGE 2 to insulin-treated cells indicated that the enhanced binding was due to an increase in receptor number (from 0.30 ± 0.02 to 0.63 ± 0.03 fmol/10 6 cells for the high affinity receptor binding sites, and from 2.4 ± 0.31 to 5.0 ± 0.41 fmol/10 6 cells for the low affinity receptor binding sites) rather than to an increase in the affinity of the binding sites. The insulin-stimulation of PGE 2 binding appeared to be associated with a lowering of the cAMP level in these cells; treatment of cells with insulin lowered the cAMP level by increasing the cAMP phosphodiesterase activity of both the membrane and cytosolic fractions. However, enhanced PGE 2 binding to the cells resulted in an increase in cAMP level in the cells. This increase in cAMP level may help to enhance the immunosuppressive action of this prostanoid, as PGE 2 is known to suppress many steps in the immune response, including interleukin-1 expression, by raising cAMP levels via activation of receptor-linked adenylate cyclase. Our data suggest that insulin at physiological concentrations may enhance the immunosuppressive action of PGE 2.