Phosphorylation of SNAP-23 by IκB kinase 2 regulates mast cell degranulation

Mast cells are known to play a pivotal role in allergic diseases. Cross-linking of the high-affinity receptor for IgE (Fc epsilon RI) leads to degranulation and allergic inflammation; however, the regulatory mechanisms of IgE-dependent exocytosis remain unknown. We show here that I kappa B kinase (IKK) 2 in mast cells plays critical roles in IgE-mediated anaphylaxis in vivo, and IgE-mediated degranulation in vitro, in an NF-kB-independent manner. Upon Fc epsilon RI stimulation, IKK2 phosphorylates SNAP-23, the target membrane soluble N-ethylmaleimide-sensitive fusion factor attachment protein receptor (SNARE), and ectopic expression of a phospho-mimetic mutant of SNAP-23 partially rescued the impaired IgE-mediated degranulation in IKK2-deficient mast cells. These results suggest that IKK2 phosphorylation of SNAP-23 leads to degranulation and anaphylactic reactions. While this reaction is NF-kB-independent, we additionally show that IKK2 also regulates late-phase allergic reactions promoted by the release of proinflammatory cytokines in an NF-kB-independent manner. The findings suggest that IKK2 is a central player in allergic reactions.