Critical roles of IĸB kinase subunits in mast cell degranulation.

The IκB kinase (IKK) complex plays a crucial role in the activation of the transcription factor NF-κB by phosphorylating an inhibitory molecule IκBα. Recently, we showed that IKK2 (also called IKKβ), a catalytic subunit of the IKK complex, induces immunoglobulin E-mediated degranulation in mast cells by phosphorylating SNAP-23, the target-membrane soluble N-ethylmaleimide-sensitive fusion factor attachment protein receptor (SNARE). In addition to IKK2, a recent study has shown that ELKS, a regulatory subunit of the IKK complex, also induces the degranulation of rat basophilic leukemia cells. These findings indicate that the two subunits of the IKK complex, IKK2 and ELKS, function not only in NF-κB-dependent transcriptional activation but also in NF-κB-independent pathways. This review focuses on the functions of IKK2 and ELKS in mast cell degranulation.