Rab27a Regulates Exocytosis of Tertiary and Specific Granules in Human Neutrophils

Abstract

The correct mobilization of cytoplasmic granules is essential for the proper functioning of human neutrophils in host defense and inflammation. In this study, we have found that human peripheral blood neutrophils expressed high levels of Rab27a, whereas Rab27b expression was much lower. This indicates that Rab27a is the predominant Rab27 isoform present in human neutrophils. Rab27a was up-regulated during neutrophil differentiation of HL-60 cells. Subcellular fractionation and immunoelectron microscopy studies of resting human neutrophils showed that Rab27a was mainly located in the membranes of specific and gelatinase-enriched tertiary granules, with a minor localization in azurophil granules. Rab27a was largely absent from CD35-enriched secretory vesicles. Tertiary and specific granule-located Rab27a population was translocated to the cell surface upon neutrophil activation with PMA that induced exocytosis of both tertiary and specific granules. Specific Abs against Rab27a inhibited Ca2+ and GTP-γ-S activation and PMA-induced exocytosis of CD66b-enriched tertiary and specific granules in electropermeabilized neutrophils, whereas secretion of CD63-enriched azurophil granules was scarcely affected. Human neutrophils lacked or expressed low levels of most Slp/Slac2 proteins, putative Rab27 effectors, suggesting that additional proteins should act as Rab27a effectors in human neutrophils. Our data indicate that Rab27a is a major component of the exocytic machinery of human neutrophils, modulating the secretion of tertiary and specific granules that are readily mobilized upon neutrophil activation.

Rab27a Supports Exosome-Dependent and -Independent Mechanisms That Modify the Tumor Microenvironment and Can Promote Tumor Progression

“…Similar observations have recently been published on the B16F10 melanoma cell line (12), where Rab27a shRNA decreased secretion of exosomes and also of some angiogenic growth factors (placenta growth factor, platelet-derived growth factor), while increasing secretion of protease inhibitors (tissue inhibitor of metalloproteinase 1). Complex roles of Rab27a in regulated secretion have been described in various secretory cells (26)(27)(28)(29). Further studies will be required to determine the molecular mechanisms responsible for Rab27a-regulated expression and/or secretion by tumor cells of some cytokines and we are currently conducting such analyses for proteinases (C. Recchi, M. Seabra and colleagues, in preparation).…”

A neutrophil intrinsic impairment affecting Rab27a and degranulation in cystic fibrosis is corrected by CFTR potentiator therapy

“…45 Rab27a interacts with its effector protein Munc13-4, 46 and the SNARE protein complex reportedly required for release of secondary and tertiary granules is composed of VAMP2 on the granule membrane and SNAP23 and syntaxin 4 (STX4) on the plasma membrane. [47][48][49] To rule out differential protein expression as a possible cause for impaired degranulation, expression levels of Rab27a, Munc13-4, and the SNAREs VAMP2, SNAP23, and STX4 were determined by immuno-blotting ( Figure 3A).…”

“…Collectively, these results demonstrate that Rab27a regulation and activation is altered in CF neutrophils, which could contribute significantly to impaired degranulation of secondary and tertiary granules. 45 …”

An immunohistochemical analysis of Rab27B distribution in fetal and adult tissue

“…Also Rab3 family proteins and Rab27A are present on mast cell secretory granules (Mizuno et al, 2007). Rab27A is detected on primary, secondary and tertiary granules in neutrophils (Herrero-Turrion et al, 2008).…”