EXPRESSION OF FUNCTIONAL GLUCAGON RECEPTORS ON LYMPHOID-CELLS

The objective of the present studies was to determine whether the exis tence of functional glucagon receptors could be established on lymphoi d cells. The glucagon receptor, which positively regulates adenylate c yclase, is a member of the superfamily of seven transmembrane domain G -protein coupled receptors. Previously reported specific binding with [I-125]-glucagon to a variety of lymphoid and myeloid cell preparation s suggests that glucagon receptors are expressed within the immune sys tem. In the present study, Northern analysis of polyA RNA isolated fro m primary mouse and rat derived lymphoid tissues and lymphoid cell lin es EL-4.IL-2, Jurkat E6-1, CH12LX, and BCL1-3B3 cells were probed with a P-32-labeled human hepatic glucagon receptor. Mouse spleen and thym us, rat spleen, and the B cell line, CH12LX, all possessed a single 1. 5 kb fragment (BCL1-3B3, 1.4 kb) which hybridized to the glucagon rece ptor cDNA probe, as compared to mouse liver which exhibited a 2.8 kb f ragment. EL-4.IL-2 and Jurkat E6-1 cells possessed a 3.7 kb fragment w ith an additional 2.75 kb band present in Jurkat E6-1 cells. Treatment of mouse splenocytes and T- and B-lymphoma cells with glucagon (0 - 1 00 nM) produced a dose-dependent enhancement in intracellular cAMP whi ch was maximal at 5 min post treatment followed by a gradual decline. Direct addition of glucagon to spleen cell cultures over a broad conce ntration range produced no effect on either lymphoproliferation follow ing stimulation with anti-CD3 mAb, or LFS nor on the antibody forming cell (AFC) response to sRBC. Conversely, glucagon effectively reversed the suppression of the sRBC AFC response produced by Delta(9)-tetrahy docannabinol (Delta(9)-THC), and partially reversed the suppression pr oduced by 2',3'-dideoxyadenosine, both of which are potent inhibitors of adenylate cyclase. These studies confirm the expression of function al glucagon receptors on lymphoid cells.