Activation-Inactivation Cycling of Rab35 and ARF6 Is Required for Phagocytosis of Zymosan in RAW264 Macrophages

J Immunol Res. 2015:2015:429439. doi: 10.1155/2015/429439. Epub 2015 Jul 1.

Abstract

Phagocytosis of zymosan by phagocytes is a widely used model of microbial recognition by the innate immune system. Live-cell imaging showed that fluorescent protein-fused Rab35 accumulated in the membranes of phagocytic cups and then dissociated from the membranes of newly formed phagosomes. By our novel pull-down assay for Rab35 activity, we found that Rab35 is deactivated immediately after zymosan internalization into the cells. Phagosome formation was inhibited in cells expressing the GDP- or GTP-locked Rab35 mutant. Moreover, the simultaneous expression of ACAP2-a Rab35 effector protein-with GTP-locked Rab35 or the expression of plasma membrane-targeted ACAP2 showed a marked inhibitory effect on phagocytosis through ARF6 inactivation by the GAP activity of ACAP2. ARF6, a substrate for ACAP2, was also localized on the phagocytic cups and dissociated from the membranes of internalized phagosomes. In support of the microscopic observations, ARF6-GTP pull-down experiments showed that ARF6 is transiently activated during phagosome formation. Furthermore, the expression of GDP- or GTP-locked ARF6 mutants also suppresses the uptake of zymosan. These data suggest that the activation-inactivation cycles of Rab35 and ARF6 are required for the uptake of zymosan and that ACAP2 is an important component that links Rab35/ARF6 signaling during phagocytosis of zymosan.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ADP-Ribosylation Factor 6
  • ADP-Ribosylation Factors / metabolism*
  • Animals
  • Cell Line
  • Cell Membrane / metabolism
  • Cell Tracking / methods
  • GTPase-Activating Proteins / metabolism
  • Macrophages / immunology*
  • Macrophages / metabolism*
  • Mice
  • Phagocytosis / physiology*
  • Phagosomes / metabolism
  • Zymosan / immunology*
  • rab GTP-Binding Proteins / metabolism*

Substances

  • ACAP2 protein, mouse
  • ADP-Ribosylation Factor 6
  • GTPase-Activating Proteins
  • Zymosan
  • Rab35 protein, mouse
  • ADP-Ribosylation Factors
  • Arf6 protein, mouse
  • rab GTP-Binding Proteins