Sphingosylphosphorylcholine and lysophosphatidylcholine are ligands for the G protein-coupled receptor GPR4.

Sphingosylphosphorylcholine (SPC) and lysophosphatidylcholine (LPC) are bio active lipid molecules involved in numerous biological processes. We have r ecently identified ovarian cancer G protein-coupled receptor 1 (OGR1) as a specific and high affinity receptor for SPC, and G2A as a receptor with hig h affinity for LPC, but low affinity for SPC. Among G protein-coupled recep tors, GPR4 shares highest sequence homology with OGR1 (51%). In this work, we have identified GPR4 as not only another high affinity receptor for SPC, but also a receptor for LPC, albeit of lower affinity. Both SPC and LPC in duce increases in intracellular calcium concentration in GPR4-, but not vec tor-transfected MCF10A cells. These effects are insensitive to treatment wi th BN52021, WEB-2170, and WEB-2086 (specific platelet activating factor (PA F) receptor antagonists), suggesting that they are not mediated through an endogenous PAF receptor. SPC and LPC bind to GPR4 in GPR4-transfected CHO c ells with K-d/SPC = 36 nM, and K-d/LPC = 159 nM, respectively. Competitive binding is elicited only by SPC and LPC. Both SPC and LPC activate GPR4-dep endent activation of serum response element reporter and receptor internali zation. Swiss 3T3 cells expressing GPR4 respond to both SPC and LPC, but no t sphingosine 1-phosphate (SIP), PAF, psychosine (Psy), glucosyl-beta1'1-sp hingosine (Glu-Sph), galactosyl-beta1'1-ceramide (GalCer), or lactosyl-beta 1'1-ceramide (Lac-Cer) to activate extracellular signal-regulated kinase mi togen-activated protein kinase in a concentration- and time-dependent manne r. SPC and LPC stimulate DNA synthesis in GPR4-expressing Swiss 3T3 cells. Both extracellular signal-regulated kinase activation and DNA synthesis sti mulated by SPC and LPC are pertussis toxin-sensitive, suggesting the involv ement of a G(i)-heterotrimeric G protein. In addition, GPR4 expression conf ers chemotactic responses to both SPC and LPC in Swiss 3T3 cells. Taken tog ether, our data indicate that GPR4 is a receptor with high affinity to SPC and low affinity to LPC, and that multiple cellular functions can be transd uced via this receptor.