Arf1 facilitates mast cell proliferation via the mTORC1 pathway.

Mast cells are one of major players in allergic responses. Mast cell activation via the high affinity IgE receptor (FcεRI) causes degranulation and release of de novo synthesized proinflammatory cytokines in a process that involves vesicle trafficking. Considering that the GTPase ADP-ribosylation factor 1 (Arf1) orchestrates and maintains membrane traffic and organelle structure, it seems likely that Arf1 contributes to mast cell activation. Actually, it has been reported that pharmaceutical blockade of the Arf1 pathway suppresses cytokine secretion and mast cell degranulation. However, physiological roles of Arf1 in mast cells remain elusive. Here, by using a genetic approach, we demonstrate that Arf1 is required for optimal mTORC1 activation upon IL-3 and facilitates mast cell proliferation. On the other hand, contrary to our expectation, Arf1-deficiency had little impact on FcεRI-induced degranulation nor cytokine secretion. Our findings reveal an unexpected role of Arf1 in mast cell expansion and its potential as a therapeutic target in the mast cell proliferative disorders.