Phosphatases in Mouse Mast Cells Rapid IgE Desensitization: The Role of SHIP-1

RATIONALE: Desensitization (DS) studies on murine IgE/mast cell (MC) model showed impairment of MC activation; receptor internalization, calcium mobilization, actin remodeling, degranulation, lipid mediators and cytokines production. Although, the molecular targets and underlying mechanisms behind this process remain undefined.

The inositol phosphatase SHIP acts as a “gatekeeper” and negatively regulate MC degranulation. In addition, SHIP is highly phosphorylated, rapidly recruited into the plasma membrane and colocalizes with FceRI receptors at both suboptimal and supraoptimal doses which may explain the reduction of degranulation. We hypothesize that multiple suboptimal antigen doses during DS might result in recruitment of SHIP-1 which may tip the balance between positive and negative signaling pathways that regulate degranulation.

METHODS: Sensitized murine bone marrow derived mast cells (mBMMCs) with anti-DNP IgE were either challenged or desensitized with 11 steps until target dose is reached (1ng DNP-HSA) as shown in (Sancho-Serra Mdel et al., 2011).

RESULTS: We found that SHIP-1 is phosphorylated at each step of DS, more importantly it is more phosphorylated at early steps, statistically higher at step 3 (P<0.05), at the time when the doses cannot induce β-hexosaminidase release. As opposed to Syk and p38 MAPK which are only phosphorylated at activating doses. Of the 11 DS doses, steps 2 and 3 showed significantly higher SHIP-1 phosphorylation when antigen given cumulatively as compared to single doses (P<0.05 and P<0.01, respectively).

CONCLUSIONS: DS takes advantage of SHIP-1 at the early steps when low doses cannot induce β-hexosaminidase release to dominate the inhibitory signals over activating molecules as Syk kinase.