Figure 2.

Sphingosine-1-phosphate-mediated signaling pathways. Intracellular S1P is synthesized from sphingosine by SphK1. S1P can be converted back to sphingosine by S1P phosphatases (SPPs) or degraded to ethanolamine-1-phosphate and hexadecenal by SPL. Intracellular S1P can directly activate various cellular signaling pathways or be exported out of cells by specific transporters in the cell membrane. Extracellular S1P exerts its biological functions through activation of five G-protein coupled receptors, which are coupled to different G proteins and activate different cellular responses.