title: GAIP, GIPC and Galphai3 are concentrated in endocytic compartments of proximal tubule cells: putative role in regulating megalin's function.
abstract: Megalin is the most abundant endocytic receptor in the proximal tubule epithelium (PTE), where it is concentrated in clathrin-coated pits (CCPs) and vesicles in the brush border region. The heterotrimeric G protein alpha subunit, Galphai3, has also been localized to the brush border region of PTE. By immunofluorescence GIPC and GAIP, components of G protein-mediated signaling pathways, are also concentrated in the brush border region of PTE and are present in megalin-expressing cell lines. By cell fractionation, these signaling molecules cosediment with megalin in brush border and microvillar fractions. GAIP is found by immunoelectron microscopy in CCPs, and GIPC is found in CCPs and apical tubules of endocytic compartments in the renal brush border. In precipitation assays, GST-GIPC specifically binds megalin. The concentration of Galphai3, GIPC, and GAIP with megalin in endocytic compartments of the proximal tubule, where extensive endocytosis occurs, and the interaction between GIPC and the cytoplasmic tail of megalin suggest a model whereby G protein-mediated signaling may regulate megalin's endocytic function and/or trafficking.
authors.affiliation: *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California.
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Lou
authors.affiliation: *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California.
authors.forename: Tammie
authors.initials: T
authors.lastname: McQuistan
authors.affiliation: *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Orlando
authors.affiliation: *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California.
authors.forename: Marilyn Gist
authors.initials: MG
authors.lastname: Farquhar
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D004847:Epithelial Cells / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D019204:GTP-Binding Proteins / Q000502:physiology*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000502:physiology*; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000502:physiology*; D008297:Male; D016253:Microscopy, Immunoelectron; D008871:Microvilli / Q000378:metabolism; D009479:Neuropeptides / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014018:Tissue Distribution
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; C492008:Gipc1 protein, rat; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D009479:Neuropeptides; D019204:GTP-Binding Proteins