A splicing isoform of LPP1, LPP1a, exhibits high phosphatase activity toward FTY720 phosphate

The sphingolipid metabolite sphingosine 1-phosphate (S1P) plays an essential function in the egress of T cells from the thymus and secondary lymphoid organs. The novel immunomodulating agent FTY720 is phosphorylated in vivo to the functional form FTY720 phosphate (FTY720-P), which is structurally similar to S1P. FTY720-P inhibits the S1P-mediated T cell egress as an agonist of S1P receptors. FTY720-P is not stable in plasma and is dephosphorylated to FTY720. In the present study, we investigated activities toward FTY720-P of LPP family members (LPP1, LPP1a, LPP2, and LPP3), which exhibit broad substrate specificity. Of the four, LPP1a, the splicing isoform of LPP1, had the highest activity toward FTY720-P, and the highest affinity. Among blood-facing cells tested, only endothelial cells displayed high phosphatase activity for FTY720-P. Significant levels of LPP1a expression were found in endothelial cells, suggesting that LPP1a is important for the dephosphorylation of FTY720-P in plasma.