The negative regulatory role of ORMDL3 in antigen-induced cytokine production, cyclooxygenase-2 expression, and chemotactic response in mast cells (IRM11P.637)

Single-nucleotide polymorphism studies have linked the chromosome 17q12-q21 region, where human ORMDL3 gene is localized, to the risk of asthma and other inflammatory diseases. Although mast cells are involved in development of these diseases, the contribution of ORMDL3 to mast cell physiology is unknown. In this study we examined the role of ORMDL3 in mouse bone marrow-derived mast cells with reduced or enhanced ORMDL3 expression. Our data show that in antigen-activated mast cells, reduced expression of the ORMDL3 protein had no effect on degranulation, calcium response, and sarco/endoplasmic reticulum Ca2+ ATPase 2b expression, but significantly enhanced phosphorylation of the IκBα and translocation of the NF-κB p65 subunit into the nucleus. These events were followed by an increased expression of pro-inflammatory cytokines (TNF-α, IL-6, and IL-13), chemokines (CCL3 and CCL4), and cyclooxygenase-2, an enzyme involved in the synthesis of prostanoids. Antigen-mediated chemotaxis was also enhanced in ORMDL3-deficient cells, whereas adhesion and spreading on fibronectin were decreased. On the other hand, increased expression of ORMDL3 had no significant effect on mast cell signaling events, except for reduced antigen-mediated chemotaxis. Our data provide the evidence that ORMDL3 in mast cells acts as a non-inducible suppressor of NF-kB-directed signaling pathways and chemotaxis.