Signal regulatory protein α negatively regulates mast-cell activation following FcεRI aggregation

Mast cells elicit allergic reaction through degranulation and release of proinflammatory mediators after aggregation of the IgE receptor FcεRI. Here we provide evidence to show that signal regulatory protein α (SIRPα), an ITIM-containing receptor, is an endogenous regulator of IgE-Ag induced mast-cell activation. SIRPα expression is promptly reduced in mast cells in response to FcεRI aggregation. Impaired expression of SIRPα in mast cells facilitates FcεRI-evoked degranulation and de novo synthesis of cytokines (IL-4, IL-13, IL-6, and TNF-α). We further demonstrate that SIRPα knockdown in mast cells accelerates calcium mobilization and affects cytoskeletal rearrangement (F-actin disassembly and polymeric tubulin formation) after FcεRI aggregation. Mechanistic studies highlight the prolonged activation of NF-κB and MAPKs as well as PLC-γ after FcεRI stimulation as a consequence of the inhibition of SIRPα expression in mast cells. Immunoprecipitation analysis shows that SIRPα knockdown markedly increases IgE-induced SHP2 interaction with PI3K regulatory subunit PI3Kp85 or IKK-β in mast cells, indicating that SIRPα may accomplish this through its association and sequestration of SHP2. Collectively, our results strongly indicate that SIRPα is a biological important regulator of FcεRI signaling.