Fmlp stimulates arachidonic acid release in dibutyryl cyclic amp treated u937 cells

Undifferentiated U937 cells contain high amounts of cytosolic phospholipase A2 (cPLA2) but do not release arachidonic acid (AA) when stimulated with calcium ionophores. Treatment with dibutyryl cyclic AMP (cAMP) causes cell surface receptor expression of fMLP receptors (10,000receptors/cell). These cAMP treated cells release AA but not oleic or linoleic acids in response to exogenous fMLP or ionomycin(IM) as determined by gas chromatography using electron capture detection. FMLP treatment resulted in a dose dependent release of AA. When cAMP treated cells are incubated with Pertussis Toxin prior to stimulation with fMLP, AA release is inhibited by 72%. Treated U937 cells also form the oxidative AA metabolite PGE2 but not LTB4 after stimulation with either fMLP or IM. This data suggests that fMLP stimulation of AA release is a receptor and G-protein mediated event. In contrast, untreated U937 cells failed to release AA after IM or fMLP treatment. Immunoblot analysis of U937 lysates from both treated and untreated cells showed no difference in cPLA2 levels. When Fura-2 loaded cells were measured for calcium influx, there was no difference in cAMP treated cells versus untreated cells after stimulation with IM. While expression of the fMLP receptor can explain the fMLP induced stimulation of AA release in treated cells, IM stimulated AA release suggests the development of additional regulatory elements in cAMP treated cells.

Duke Scholars

Author James Robert Burke Neurology, Behavioral Neurology