RabGEF1 regulates stem cell factor/c‐Kit‐mediated signaling events and biological responses in mast cells

We recently reported that RabGEF1 is a negative regulator of FcεRIdependent mast cell activation and that mice lacking RabGEF1 developed severe skin inflammation and increased numbers of dermal mast cells. To extend our understanding of how RabGEF1 can regulate signaling events and biological responses in mast cells, we examined the responses of bone marrow‐derived cultured mast cells (BMCMCs) from wild‐type (+/+) and Rabgef1 knockout (−/−) mice after stimulation with the c‐Kit ligand, stem cell factor (SCF), an important regulator of mast cell development, survival, proliferation and activation. We found that activation of Ras and Erk was enhanced and prolonged, and IL‐6 secretion was significantly elevated, in RabGEF1‐deficient BMCMCs after stimulation with SCF. SCF‐induced activation of JNK was increased in Rabgef1 −/− BMCMCs, but without corresponding significant increases in SCF‐induced migration or adhesion. SCF‐mediated activation of the survival‐enhancing kinase, Akt, was also increased in Rabgef1 −/− BMCMCs, and these cells had a survival advantage over their +/+ counterparts in vitro . Despite enhancement of the Ras pathway in the absence of RabGEF1, SCF‐induced proliferation was lower in Rabgef1 −/− vs . +/+ BMCMCs. Finally, we found that c‐Kit internalization was delayed in the absence of RabGEF1, reflecting a positive role for RabGEF1 in the regulation of endocytic events, and infection of Rabgef1 −/− BMCMCs with a lentiviral introduced RabGEF1 expression construct normalized c‐Kit internalization to the levels seen in +/+ BMCMCs. Thus, RabGEF1 plays a critical role in the regulation of SCF/c‐Kit‐mediated signaling events and biological responses in mast cells.