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Distinct and opposing roles for R ab27a/ M lph/ M yo V a and R ab27b/ M unc13‐4 in mast cell secretion
Author(s) -
Singh Rajesh K.,
Mizuno Koichi,
Wasmeier Christina,
WavreShapton Silene T.,
Recchi Chiara,
Catz Sergio D.,
Futter Clare,
Tolmachova Tanya,
Hume Alistair N.,
Seabra Miguel C.
Publication year - 2013
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.12081
Subject(s) - degranulation , microbiology and biotechnology , secretion , biology , knockout mouse , rab , mast cell , actin , immunology , gtpase , biochemistry , receptor
Mediator release from mast cells is a critical step in allergic and inflammatory disease. However, the processes regulating the latter stages of granule release are yet to be fully understood. Rab27 small GTP ases regulate release of secretory lysosomes in a variety of cells, including mast cell granules. In the present study, using murine bone marrow‐derived mast cells ( BMMC ) from Rab27‐deficient mutant mice, we found that, in contrast to Rab27b, Rab27a primarily plays an inhibitory role in regulating degranulation. Immunofluorescence analysis revealed that resting Rab27a‐deficient ( ashen ) BMMC s display abnormal cortical F‐actin distribution. Actin disassembly prior to IgE cross‐linking increased wild‐type BMMC secretion to ashen levels, suggesting that changes in the integrity of cortical F‐actin underlie the ashen phenotype. Comparison of the secretory impairment of Rab27b knockout and Rab27a / b double knockout BMMC s highlighted a secondary positive role for Rab27a in enhancing degranulation. Rab27 is known to interact with actin via its effectors melanophilin (Mlph) and myosin Va (MyoVa) in other cell types. To better understand the differing roles of Rab27 proteins, we analysed the secretory phenotype of BMMC s derived from mice lacking Rab27 effector proteins. These experiments revealed that the phenotype of BMMC s deficient in Mlph ( leaden ) and BMMC s deficient in MyoVa ( dilute ) resembles the hyper‐secretion of ashen BMMC s, while Munc13‐4‐deficient ( jinx ) BMMC s phenocopy the Rab27b knockout and double Rab27a / b knockout secretory impairment. We conclude that Rab27a and Rab27b regulate distinct steps in the BMMC degranulation pathway, with Rab27a/Mlph/MyoVa regulating cortical actin stability upstream of Rab27a/b/Munc13‐4‐dependent granule exocytosis.