title: Phagosomes fuse with late endosomes and/or lysosomes by extension of membrane protrusions along microtubules: role of Rab7 and RILP.
abstract: Nascent phagosomes must undergo a series of fusion and fission reactions to acquire the microbicidal properties required for the innate immune response. Here we demonstrate that this maturation process involves the GTPase Rab7. Rab7 recruitment to phagosomes was found to precede and to be essential for their fusion with late endosomes and/or lysosomes. Active Rab7 on the phagosomal membrane associates with the effector protein RILP (Rab7-interacting lysosomal protein), which in turn bridges phagosomes with dynein-dynactin, a microtubule-associated motor complex. The motors not only displace phagosomes in the centripetal direction but, strikingly, promote the extension of phagosomal tubules toward late endocytic compartments. Fusion of tubules with these organelles was documented by fluorescence and electron microscopy. Tubule extension and fusion with late endosomes and/or lysosomes were prevented by expression of a truncated form of RILP lacking the dynein-dynactin-recruiting domain. We conclude that full maturation of phagosomes requires the retrograde emission of tubular extensions, which are generated by activation of Rab7, recruitment of RILP, and consequent association of phagosomes with microtubule-associated motors.
authors.affiliation: Division of Cell Biology, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada M5G 1X8.
authors.forename: Rene E
authors.initials: RE
authors.lastname: Harrison
authors.forename: Cecilia
authors.initials: C
authors.lastname: Bucci
authors.forename: Otilia V
authors.initials: OV
authors.lastname: Vieira
authors.forename: Trina A
authors.initials: TA
authors.lastname: Schroer
authors.forename: Sergio
authors.initials: S
authors.lastname: Grinstein
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D022081:Cell Surface Extensions / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D000072159:Dynactin Complex; D004398:Dyneins / Q000378:metabolism; D011992:Endosomes / Q000502:physiology*; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008247:Lysosomes / Q000502:physiology*; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D010588:Phagosomes / Q000502:physiology*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000090802:rab7 GTP-Binding Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D000072159:Dynactin Complex; D008164:Luminescent Proteins; D008869:Microtubule-Associated Proteins; D011994:Recombinant Proteins; C498920:Rilp protein, mouse; D000090802:rab7 GTP-Binding Proteins; C000716465:rab7 GTP-binding proteins, mouse; D049452:Green Fluorescent Proteins; D004398:Dyneins; D020691:rab GTP-Binding Proteins