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Title: The role of Rab27 in inflammation
Author: Singh, Rajesh Kumar
ISNI:       0000 0004 2706 8064
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2011
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Rab27 is a member of the Rab family of Ras-like GTPases and is expressed in two isoforms, Rab27a and Rab27b that share 72% amino acid identity. Previous studies have suggested Rab27a and Rab27b to regulate inflammation through exocytosis in a variety of leukocytes including T lymphocytes, NK cells, mast cells and neutrophils. A key process in inflammation is mast cell secretion, a process in which Rab27b has been established as a positive regulator but the role of Rab27a remains unclear. In this study we confirm that in response to IgE crosslinking, Rab27a appears to play a negative role in secretion, however Rab27a was observed to promote secretion in absence of Rab27b, so this effect is likely due to abnormally distributed cortical F-actin and enhanced granule docking in absence of Rab27a. Furthermore Rab27a may exert this regulation through effector Melanophilin. We also confirm that the effector Munc13-4 is important for promoting mast cell secretion, likely through interaction with both Rab27a and Rab27b. Rab27 has also been suggested to regulate inflammation by promoting granule secretion in neutrophils. Here we find that Rab27a was localised to structures at the uropod and that Rab27a deficient neutrophils display defective chemotaxis due to impaired uropod release. Inhibition of extracellular serine proteases inhibited wild-type but not Rab27a deficient neutrophil chemotaxis suggesting that defective protease secretion may underlie Rab27a deficient neutrophil chemotaxis defect. Analysis of αMβ2 integrin subunit CD11b after chemokine stimulation revealed that CD11b surface expression was sustained on Rab27a deficient neutrophils compared to wild-type, suggesting that cleavage of CD11b may be impaired. Inhibition of other proteins known to promote primary granule secretion, Rab27b and Rab27 effectors Slp1 and Munc13-4 also impaired neutrophil chemotaxis. Together these data suggest that Rab27a promotes uropod detachment through release of proteases contained in primary granules to promote neutrophil chemotaxis.
Supervisor: Seabra, Miguel Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral