FIGURE 4.

E₂ but not EGF stimulates release of S1P and dihydro-S1P from MCF-7 cells. MCF-7 cells were stimulated with vehicle (open circles) or 20 nm E₂ (filled squares) for the indicated times (A and C), for 5 min with the indicated concentrations of E₂ or EGF (B), or with 10 ng/ml of EGF (filled triangles) for the indicated times (C and D). S1P (A–C) and dihydro-S1P (D) released into the medium were measured by LC-ESI-MS/MS. Data are expressed as picomole of phosphorylated sphingoid base/ml and are mean ± S.D. Levels of S1P and dihydro-S1P in the cells at zero time (7.4 ± 1 and 2.8 ± 0.2 pmol/ml, respectively) were subtracted from all values. *, p < 0.01 compared with vehicle. Similar results were obtained in three independent experiments.