The nascent truncation of FcϵRIβ confers calmodulin binding which is essential for microtubule formation and degranulation in human mast cells (177.17)

Abstract

Abstract The gene locus containing the MS4A2 gene (encoding FcϵRIβ) has strong linkage to allergy susceptibility. MS4A2 was considered as a candidate gene, but studies on the functional consequence of mutations in FcϵRIβ have been disappointing. We have identified a truncation of FcϵRIβ (t-FcϵRIβ) in humans. In this study we sought to identify the function of this variant. We determined that t-FcϵRIβ forms a complex with Fyn kinase and Gab2 in the cytosol and that the truncation of FcϵRIβ exposes a calmodulin (CaM) binding domain. Using co-IPs we show that in the presence of Ca2+, CaM binds to the t-FcϵRIβ complex, allowing phosphorylation of Fyn and Gab2, which are involved in microtubule formation. Confocal microscopy revealed translocation of the t-FcϵRIβ complex to a tubulin-rich region after cell activation. Deconvolution and 3D modeling of the imaging data demonstrated that the translocated complex surrounds the centrosome, forming an intricate network with microtubules. Utilizing lentiviral shRNA to silence the FcϵRIβ variants, we identified that knockdown of t-FcϵRIβ attenuated microtubule formation, degranulation and cytokine production in response to thapsigargin. Ca2+ influx and PGD2 production were unaffected. These data suggest that t-FcϵRIβ propagates Ca2+ signals by binding CaM and initiating microtubule formation which is essential for mast cell degranulation and cytokine release. Thus, targeting t-FcϵRIβ may offer a novel approach to treatment of allergic diseases.