Fig. 3. SphK1 and CERK in mast cell functions. Crosslinking of the high affinity IgE receptor FcRI on mast cells translocates and activates SphK1, increasing S1P formation. S1P in turn transactivates S1P₁ and S1P₂ receptors, leading to mast cell degranulation and cell motility. Furthermore, CERK may also regulate degranulation of mast cells.