Phosphatidylinositol 3-kinase is required for the formation of constitutive transport vesicles from the TGN.
An 85-kD cytosolic complex (p62(cplx)), consisting of a 62-kD phosphoprotein (p62) and a 25-kD GTPase, has been shown to be essential for the cell-free reconstitution of polymeric IgA receptor (pIgA-R)-containing exocytic transport vesicle formation from the TGN (Jones, S.M., J.R. Crosby, J. Salamero, and K.E. Howell. 1993. J. Cell Biol. 122:775-788). Here the p62(cplx) is identified as a regulatory subunit of a novel phosphatidylinositol 3-kinase (PI3-kinase). This p62(cplx)-associated PI3-kinase activity is stimulated by activation of the p62(cplx)-associated GTPase, and is specific for phosphatidylinositol (PI) as substrate, and is sensitive to wortmannin at micromolar concentrations. The direct role of this p62(cplx)-associated PI3-kinase activity in TGN-derived vesicle formation is indicated by the finding that both lipid kinase activity and the formation of pIgA-R-containing exocytic vesicles from the TGN are inhibited by wortmannin with similar dose-response curves and 50% inhibitory concentrations (3.5 microM). These findings indicate that phosphatidylinositol-3-phosphate (PI[3]P) is required for the formation of TGN-derived exocytic transport vesicles, and that the p62(cplx)-associated PI3-kinase and an activated GTPase are the essential molecules that drive production of this PI(3)P.
Jones
S M
SM
Department of Cellular and Structural Biology, University of Colorado School of Medicine, Denver, Colorado 80262, USA.
Howell
K E
KE
D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D003594:Cytoplasmic Granules / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006056:Golgi Apparatus / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D007070:Immunoglobulin A / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D051381:Rats; D011961:Receptors, Fc / Q000096:biosynthesis* / Q000737:chemistry; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; C045281:IgA receptor; D007070:Immunoglobulin A; D046911:Macromolecular Substances; D010750:Phosphoproteins; D011961:Receptors, Fc; D019869:Phosphatidylinositol 3-Kinases; D020558:GTP Phosphohydrolases; D000077191:Wortmannin