G Protein Coupled Receptor 4 (GPR4)

GPR4 is a high-affinity receptor for the sphingosylphosphorylcholine (SPC) signaling molecule. Zhu et al. showed that cells expressing GPR4 are stimulated to produce increased calcium by both SPC and LPC, a ligand for G2A . RNA dot blot analysis revealed highest expression of GPR4 in ovary, liver, lung, kidney, lymph node, and subthalamic nucleus; in contrast, OGR1 is most highly expressed in lung, placenta, spleen, testis, small intestine, and peripheral blood leukocytes. Binding analysis determined that GPR4 interacts with SPC with high affinity and with LPC with lower affinity. Both ligands enhanced proliferation and ERK mitogen-activated protein kinase activation in a GPR4-dependent and pertussis toxin (PTX)-sensitive manner, whereas ERK activation is PTX-insensitive in OGR1-mediated signaling.