Methiothepin downregulates SNAP-23 and inhibits degranulation of rat basophilic leukemia cells and mouse bone marrow-derived mast cells.

In the present study, we found that methiothepin (a non-selective 5-hydroxytryptamine (5-HT) receptor antagonist) inhibited antigen-induced degranulation in rat basophilic leukemia cells and mouse bone marrow-derived mast cells. Although antigen stimulation induces release of histamine and serotonin (5-HT) by exocytosis and mast cells express several types of 5-HT receptor, the detailed role of these receptors remains unclear. Here, pretreatment of cells with methiothepin attenuated increased intracellular Ca 2+ concentration, phosphorylated critical upstream signaling components: SFKs, Syk, and PLCγ1, and suppressed TNF-α secretion via inhibition of Akt and ERK phosphorylation. Furthermore, it inhibited PMA/ionomycin-induced degranulation; this finding suggested that methiothepin affected downstream signaling. IκB kinase β (IKKβ) phosphorylates synaptosomal associated protein 23 (SNAP23), which regulates the fusion events of the secretory granule/plasma membrane after mast cell activation, resulting in degranulation. We showed that methiothepin blocked PMA/ionomycin-induced phosphorylation of SNAP23 by inhibiting its interaction with IKKβ. Together with the results of selective 5-HT antagonists, it is suggested that methiothepin inhibits mast cell degranulation by downregulating upstream signaling pathways and exocytotic fusion machinery through mainly 5-HT1A receptor. Our findings provide that 5-HT antagonists may be used to relieve allergic reactions. This article is protected by copyright. All rights reserved.