ABCA1, ABCG1, and SR-BI: Transit of HDL-associated sphingosine-1-phosphate.

Sphingosine-1-phosphate (S1P) is a zwitterionic lysophospholipid generated by the sphingosine kinase-catalyzed phosphorylation of sphingosine. A number of the biological effects of S1P are mediated by its binding to five specific G protein-coupled receptors located on the cell surface or intracellular targets. However, the synthesis and secretion of S1P require release out of cells for binding with receptors by certain transporters and carriers. High-density lipoprotein (HDL) is an important carrier of S1P in the blood, but the mechanism by which it does so is unclear. This review discusses the mechanism how S1P is transported, and focuses particularly on how the formation of HDL-associated S1P (HDL-S1P) is mediated by certain transporters and carriers. A hypothesis that the ATP-binding cassette transporter A1 (ABCA1), ABCG1, and scavenger receptor class B memberI (SR-BI) play pivotal roles in HDL-S1P formation is also described.