GEF-H1 Transduces FcεRI Signaling in Mast Cells to Activate RhoA and Focal Adhesion Formation during Exocytosis

When antigen-stimulated, mast cells release preformed inflammatory mediators kept in cytoplasmic granules. This happens using a robust exocytosis mechanism termed degranulation. Our previous studies says RhoA and Rac1 are activated during mast cell antigen stimulation and therefore are needed for mediator release. Here, we reveal that the RhoGEF, GEF-H1, functions like a signal transducer of antigen stimulation to activate RhoA and promote mast cell distributing via focal adhesion (FA) formation. Cell distributing, granule movement, and exocytosis counseled me reduced in antigen-stimulated mast cells when GEF-H1 was depleted by RNA interference. GEF-H1-depleted cells also demonstrated a substantial decrease in RhoA activation, leading to reduced stress fiber formation without altering lamellipodia formation. Ectopic expression of the constitutively active RhoA mutant restored normal morphology in GEF-H1-depleted cells. FA formation during antigen stimulation needed GEF-H1, suggesting it’s a downstream target from the GEF-H1-RhoA signaling axis. GEF-H1 was activated by phosphorylation along with antigen stimulation. Syk kinase is from the FceRI signaling path and also the Syk inhibitor, GS-9973, blocked GEF-H1 activation as well as covered up cell distributing, granule movement, and exocytosis. We figured that during FceRI receptor stimulation, GEF-H1 transmits signals to RhoA activation and FA formation to facilitate the exocytosis mechanism.