Figure 3.

Existence of an S1P uptake mechanism independent of PLPPs.A and B, WT and PLPP1–3 TKO HAP1 cells were incubated with 5 μM ²H₇-S1P (A) or ²H₇-Sph (B) for 2 h. After separation into medium and cell fractions by centrifugation, lipids were extracted from each, and ²H₇-S1P, ²H₇-Sph, and ²H₇-ceramide levels were measured using LC-MS/MS. Values represent the means ± SD of the lipid amounts obtained from three independent experiments (∗p < 0.05; ∗∗p < 0.01; Student's t test). C, total RNA prepared from WT and PLPP1–3 TKO HAP1 cells was subjected to quantitative real-time RT-PCR using specific primers for ceramide synthases (CERS1–6) and GAPDH. Values represent the means ± SD and indicate the quantities relative to that of GAPDH from three independent reactions. Cer, ceramide; nd, not detected; PLPP, phospholipid phosphatase; S1P, sphingosine-1-phosphate; Sph, sphingosine.