title: Class IA phosphatidylinositol 3-kinase p110α regulates phagosome maturation.
abstract: Of the various phosphatidylinositol 3- kinases (PI3Ks), only the class III enzyme Vps34 has been shown to regulate phagosome maturation. During studies of phagosome maturation in THP-1 cells deficient in class IA PI3K p110α, we discovered that this PI3K isoform is required for vacuole maturation to progress beyond acquisition of Rab7 leading to delivery of lysosomal markers. Bead phagosomes from THP-1 cells acquired p110α and contained PI3P and PI(3,4,5)P3; however, p110α and PI(3,4,5)P3 levels in phagosomes from p110α knockdown cells were decreased. Phagosomes from p110α knock down cells showed normal acquisition of both Rab5 and EEA-1, but were markedly deficient in the lysosomal markers LAMP-1 and LAMP-2, and the lysosomal hydrolase, β-galactosidase. Phagosomes from p110α deficient cells also displayed impaired fusion with Texas Red dextran-loaded lysosomes. Despite lacking lysosomal components, phagosomes from p110α deficient cells recruited normal levels of Rab7, Rab-interacting lysosomal protein (RILP) and homotypic vacuole fusion and protein sorting (HOPs) components Vps41 and Vps16. The latter observations demonstrated that phagosomal Rab7 was active and capable of recruiting effectors involved in membrane fusion. Nevertheless, active Rab7 was not sufficient to bring about the delivery of lysosomal proteins to the maturing vacuole, which is shown for the first time to be dependent on a class I PI3K.
authors.affiliation: Department of Medicine, Experimental Medicine Program, Division of Infectious Diseases, University of British Columbia and the Immunity and Infection Research Centre, Vancouver Coastal Health Research Institute, Vancouver, BC, Canada.
authors.forename: Emily P
authors.initials: EP
authors.lastname: Thi
authors.forename: Ulrike
authors.initials: U
authors.lastname: Lambertz
authors.forename: Neil E
authors.initials: NE
authors.lastname: Reiner
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D045744:Cell Line, Tumor; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D006801:Humans; D052118:Lysosomal-Associated Membrane Protein 1 / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D010588:Phagosomes / Q000201:enzymology / Q000378:metabolism*; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000090802:rab7 GTP-Binding Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D052118:Lysosomal-Associated Membrane Protein 1; D018129:Phosphatidylinositol Phosphates; C423317:RILP protein, human; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1; C060974:phosphatidylinositol 3,4,5-triphosphate; C055525:phosphatidylinositol 3-phosphate; D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; D058543:Class Ia Phosphatidylinositol 3-Kinase; D001616:beta-Galactosidase; D020691:rab GTP-Binding Proteins