title: Phosphoinositide 3-kinase enables phagocytosis of large particles by terminating actin assembly through Rac/Cdc42 GTPase-activating proteins.
abstract: Phagocytosis is responsible for the elimination of particles of widely disparate sizes, from large fungi or effete cells to small bacteria. Though superficially similar, the molecular mechanisms involved differ: engulfment of large targets requires phosphoinositide 3-kinase (PI3K), while that of small ones does not. Here, we report that inactivation of Rac and Cdc42 at phagocytic cups is essential to complete internalization of large particles. Through a screen of 62 RhoGAP-family members, we demonstrate that ARHGAP12, ARHGAP25 and SH3BP1 are responsible for GTPase inactivation. Silencing these RhoGAPs impairs phagocytosis of large targets. The GAPs are recruited to large--but not small--phagocytic cups by products of PI3K, where they synergistically inactivate Rac and Cdc42. Remarkably, the prominent accumulation of phosphatidylinositol 3,4,5-trisphosphate characteristic of large-phagosome formation is less evident during phagocytosis of small targets, accounting for the contrasting RhoGAP distribution and the differential requirement for PI3K during phagocytosis of dissimilarly sized particles.
authors.affiliation: Division of Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G1X8.|Institute of Medical Science, University of Toronto, Faculty of Medicine, 1 King's College Circle, Toronto, Ontario, Canada M5S1A8.
authors.forename: Daniel
authors.initials: D
authors.lastname: Schlam
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario, Canada M5G1X5.
authors.forename: Richard D
authors.initials: RD
authors.lastname: Bagshaw
authors.affiliation: Division of Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G1X8.
authors.forename: Spencer A
authors.initials: SA
authors.lastname: Freeman
authors.affiliation: Division of Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G1X8.
authors.forename: Richard F
authors.initials: RF
authors.lastname: Collins
authors.affiliation: Lunenfeld-Tanenbaum Research Institute, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario, Canada M5G1X5.
authors.forename: Tony
authors.initials: T
authors.lastname: Pawson
authors.affiliation: Institute of Medical Science, University of Toronto, Faculty of Medicine, 1 King's College Circle, Toronto, Ontario, Canada M5S1A8.|Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, Ontario, Canada M5B1T8.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Fairn
authors.affiliation: Division of Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G1X8.|Institute of Medical Science, University of Toronto, Faculty of Medicine, 1 King's College Circle, Toronto, Ontario, Canada M5S1A8.|Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 209 Victoria Street, Toronto, Ontario, Canada M5B1T8.
authors.forename: Sergio
authors.initials: S
authors.lastname: Grinstein
mesh_terms: D000199:Actins / Q000378:metabolism*; D020690:GTPase-Activating Proteins / Q000378:metabolism; D064368:Healthy Volunteers; D006801:Humans; D010587:Phagocytosis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D000199:Actins; D020690:GTPase-Activating Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; C085379:rho GTPase-activating protein; D019869:Phosphatidylinositol 3-Kinases; D020741:rho GTP-Binding Proteins