Figure 4.

A fraction of the extracellular S1P is imported directly into cells.A–C, WT and PLPP1–3 TKO HAP1 cells were labeled with 0.2 μCi [³²P]Pi or 0.2 μCi [³²P]S1P for 3 h in the presence of 1% bovine serum albumin. After washing the cells, lipids were extracted, separated by TLC, and detected (A) and quantified (B and C) using an imaging analyzer BAS2500. Values represent the means ± SD of the radioactivity of [³²P]PE (B) or [³²P]PS/PI (C) relative to that in respective [³²P]Pi-labeled WT cells, from three independent experiments (∗p < 0.05; ∗∗p < 0.01; Tukey's test). PE, phosphatidylethanolamine; Pi, orthophosphoric acid; PI, phosphatidylinositol; PS, phosphatidylserine; SM, sphingomyelin; S1P, sphingosine-1-phosphate; TKO, triple KO; #unidentified lipid.