Roles for MS4A4 in FcɛRI signal transduction and store-operated calcium entry in human mast cells.

Abstract

Abstract The membrane spanning 4A (MS4A) gene family have similar topology to tetraspanins and are clustered around chromosome 11q12-13, a region linked to allergy and asthma susceptibility. However, other than the well-established roles of FcɛRIβ and CD20 in mast cell and B cell signaling, respectively, functional studies for the remaining genes in the MS4A family are lacking. We have demonstrated that MS4A4 promotes recruitment of KIT into caveolin-1-enriched microdomains and signaling through PLCγ1 in mast cells. PLCγ1 signaling and caveolin-1 are important regulators of store-operated Ca2+entry (SOCE) and caveolin-1 promotes expression of the store-operated Ca2+ channel pore-forming unit, Orai1. We thus hypothesized that MS4A4 regulates SOCE in response to FcɛRI-mediated stimulation through PLCγ1 and Orai1-dependent pathways. We began by identifying that human mast cells express a full length and truncated splice variant of MS4A4. Transfection of MS4A4 variants into HEK293 cells demonstrates that the full length variant of MS4A4 traffics to the plasma membrane, but the truncated MS4A4 variant does not. Knockdown of the full length MS4A4 variant with shRNA inhibits IgE-mediated degranulation of human mast cells, signaling through PLCγ1 and SOCE, likely through Orai1. Compound 48/80 and ionomycin stimulation were less affected by knockdown of MS4A4 or Orai1. These data suggest that MS4A4 plays an important role in FcɛRI signaling and suggest a possible novel link between KIT and FcɛRI signaling pathways.