Figure 2. Hypothetical roles for LAB-dependent positive signaling.

Engagement of FcεRI (shown) or other receptors, such as FcγRI, BCR, and TREM-1/2, results in activation of various tyrosine kinases, such as Fyn, Lyn, and/or Syk, leading to phosphorylation of LAB, which can then recruit the Grb2-Sos complex, resulting in Ras-MAPK activation and IL-3 production, which promotes survival. Phosphorylated LAB may also recruit a Grb2-PLCγ complex, resulting in partial Ca²⁺ responses. Lastly, phospho-LAB may be involved in the LAT-independent Fyn-Gab2-PI3K pathway described previously, resulting in PKC activation and degranulation. It is through this pathway that the direct phosphorylation of LAB by KIT may potentiate FcεRI-derived signals. ?, Unknowns in these pathways.