title: The Phosphoinositide-Gated Lysosomal Ca(2+) Channel, TRPML1, Is Required for Phagosome Maturation.
abstract: Macrophages internalize and sequester pathogens into a phagosome. Phagosomes then sequentially fuse with endosomes and lysosomes, converting into degradative phagolysosomes. Phagosome maturation is a complex process that requires regulators of the endosomal pathway including the phosphoinositide lipids. Phosphatidylinositol-3-phosphate and phosphatidylinositol-3,5-bisphosphate (PtdIns(3,5)P2 ), which respectively control early endosomes and late endolysosomes, are both required for phagosome maturation. Inhibition of PIKfyve, which synthesizes PtdIns(3,5)P2 , blocked phagosome-lysosome fusion and abated the degradative capacity of phagosomes. However, it is not known how PIKfyve and PtdIns(3,5)P2 participate in phagosome maturation. TRPML1 is a PtdIns(3,5)P2 -gated lysosomal Ca(2+) channel. Because Ca(2+) triggers membrane fusion, we postulated that TRPML1 helps mediate phagosome-lysosome fusion. Using Fcγ receptor-mediated phagocytosis as a model, we describe our research showing that silencing of TRPML1 hindered phagosome acquisition of lysosomal markers and reduced the bactericidal properties of phagosomes. Specifically, phagosomes isolated from TRPML1-silenced cells were decorated with lysosomes that docked but did not fuse. We could rescue phagosome maturation in TRPML1-silenced and PIKfyve-inhibited cells by forcible Ca(2+) release with ionomycin. We also provide evidence that cytosolic Ca(2+) concentration increases upon phagocytosis in a manner dependent on TRPML1 and PIKfyve. Overall, we propose a model where PIKfyve and PtdIns(3,5)P2 activate TRPML1 to induce phagosome-lysosome fusion.
authors.affiliation: Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B2K3, Canada.|Molecular Science Program, Ryerson University, Toronto, Ontario, M5B2K3, Canada.
authors.forename: Roya M
authors.initials: RM
authors.lastname: Dayam
authors.affiliation: Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B2K3, Canada.|Molecular Science Program, Ryerson University, Toronto, Ontario, M5B2K3, Canada.
authors.forename: Amra
authors.initials: A
authors.lastname: Saric
authors.affiliation: Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B2K3, Canada.
authors.forename: Ryan E
authors.initials: RE
authors.lastname: Shilliday
authors.affiliation: Department of Chemistry and Biology, Ryerson University, Toronto, Ontario, M5B2K3, Canada.|Molecular Science Program, Ryerson University, Toronto, Ontario, M5B2K3, Canada.
authors.forename: Roberto J
authors.initials: RJ
authors.lastname: Botelho
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D010587:Phagocytosis; D010588:Phagosomes / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D050051:Transient Receptor Potential Channels / Q000235:genetics / Q000378:metabolism*
chemical_list: C512321:Mcoln1 protein, mouse; D010716:Phosphatidylinositols; D050051:Transient Receptor Potential Channels; D019869:Phosphatidylinositol 3-Kinases; C116930:Pikfyve protein, mouse; D002118:Calcium
keywords: calcium; lysosomes; macrophages; organelles; phagocytosis; phagosome maturation; phosphoinositides