Rab27a negatively regulates phagocytosis by prolongation of the actin-coating stage around phagosomes

J Biol Chem. 2011 Feb 18;286(7):5375-82. doi: 10.1074/jbc.M110.171702. Epub 2010 Dec 18.


Rab27a, a Rab family small GTPase, is involved in the exocytosis of secretory granules in melanocytes and cytotoxic T-cells. Rab27a mutations cause type 2 Griscelli syndrome, which is characterized by immunodeficiency, including uncontrolled macrophage activation known as hemophagocytic syndrome. However, the role of Rab27a in phagocytosis remains elusive. Here, using macrophage-like differentiated HL-60 cells and C3bi-opsonized zymosan as a pathogen-phagocyte model, we show that Rab27a negatively regulates complement-mediated phagocytic activity in association with F-actin remodeling. We found that transfection of Rab27a shRNA into HL-60 cells enhances complement-mediated phagocytosis. To clarify the mechanisms underlying the elevated phagocytosis in Rab27a knockdown cells, we analyzed the process of phagosome formation focusing on F-actin dynamics: F-actin assembly, followed by F-actin extension around the particles and the subsequent degradation of F-actin, leading to internalization of the particles enclosed in phagosomes. Microscopic analysis revealed that these actin-related processes, including F-actin coating and F-actin degradation, proceed more rapidly in Rab27a knockdown cells than in control HL-60 cells. Both elevated phagocytosis and accelerated F-actin remodeling were restored by expression of rescue-Rab27a and Rab27a-Q78L (GTP-bound form), but not by Rab27a-T23N (GDP-bound form). Furthermore, an increased accumulation of Coronin 1A surrounding F-actin coats was observed in Rab27a knockdown cells, suggesting that the function of Coronin 1A is related to the regulation of the F-actin coating. Our findings demonstrate that Rab27a plays a direct regulatory role in the nascent process of phagocytosis by prolongation of the stage of actin coating via suppression of Coronin 1A. This study may contribute to an explanation of the underlying mechanisms of excessive phagocytosis observed in Griscelli syndrome.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actins / genetics
  • Actins / metabolism*
  • Complement System Proteins / genetics
  • Complement System Proteins / metabolism
  • Gene Knockdown Techniques
  • HL-60 Cells
  • Humans
  • Immunologic Deficiency Syndromes / enzymology
  • Immunologic Deficiency Syndromes / genetics
  • Lymphohistiocytosis, Hemophagocytic
  • Macrophage Activation / genetics
  • Macrophages / enzymology*
  • Microfilament Proteins / genetics
  • Microfilament Proteins / metabolism
  • Mutation, Missense
  • Phagocytosis*
  • Phagosomes / enzymology*
  • Phagosomes / genetics
  • Piebaldism / enzymology
  • Piebaldism / genetics
  • Primary Immunodeficiency Diseases
  • rab GTP-Binding Proteins / genetics
  • rab GTP-Binding Proteins / metabolism*
  • rab27 GTP-Binding Proteins


  • Actins
  • Microfilament Proteins
  • rab27 GTP-Binding Proteins
  • coronin proteins
  • Complement System Proteins
  • RAB27A protein, human
  • rab GTP-Binding Proteins

Supplementary concepts

  • Griscelli syndrome type 2