Canonical and Noncanonical G-Protein Signaling Helps Coordinate Actin Dynamics To Promote Macrophage Phagocytosis of Zymosan

Abstract

Both chemotaxis and phagocytosis depend upon actin-driven cell protrusions and cell membrane remodeling. While chemoattractant receptors rely upon canonical G-protein signaling to activate downstream effectors, whether such signaling pathways affect phagocytosis is contentious. Here, we report that Gα_i nucleotide exchange and signaling helps macrophages coordinate the recognition, capture, and engulfment of zymosan bioparticles. We show that zymosan exposure recruits F-actin, Gα_i proteins, and Elmo1 to phagocytic cups and early phagosomes. Zymosan triggered an increase in intracellular Ca²⁺ that was partially sensitive to Gα_i nucleotide exchange inhibition and expression of GTP-bound Gα_i recruited Elmo1 to the plasma membrane. Reducing GDP-Gα_i nucleotide exchange, decreasing Gα_i expression, pharmacologically interrupting Gβγ signaling, or reducing Elmo1 expression all impaired phagocytosis, while favoring the duration that Gα_i remained GTP bound promoted it. Our studies demonstrate that targeting heterotrimeric G-protein signaling offers opportunities to enhance or retard macrophage engulfment of phagocytic targets such as zymosan.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.00325-14.

ACKNOWLEDGMENTS

We thank David Stephany and Kevin Holmes (Research Technologies Branch, NIAID) for help with some of the flow cytometry experiments. We gratefully acknowledge Juraj Kabat (Core Imaging Facility, NIAID) for his quantification and modeling of some of the imaging data and Hyeseon Cho (NIAID) for making the PTX-resistant YFP-Gα_i2 construct. We also thank Anthony Fauci for his continued support.

This research was supported by the intramural program of the National Institute of Allergy and Infectious Diseases.