title: MAGI-1 is a component of the glomerular slit diaphragm that is tightly associated with nephrin.
abstract: MAGUK with inverted domain structure-1 (MAGI-1) is a membrane-associated protein with one guanylate kinase, six PSD-95/Dlg-A/ZO-1 (PDZ), and two WW domains and is localized at tight junctions in epithelial cells. MAGI-1 interacts with various proteins and is proposed to function as a scaffold protein. In the previous study, we discovered a MAGI-1-interacting cell adhesion molecule junctional adhesion molecule 4 (JAM4). Both proteins are highly expressed in glomerular podocytes in the kidney and partially colocalized. In this study, we have further searched for a binding partner of MAGI-1 in the kidney through yeast two-hybrid screening and obtained nephrin. Nephrin is a cell adhesion molecule specifically localized at the slit diaphragm between neighboring foot processes of podocytes. Biochemical studies reveal that nephrin directly binds to the middle PDZ domains of MAGI-1 through its carboxyl terminus but does not bind to ZO-1. MAGI-1 forms a tripartite complex with nephrin and JAM4 in vitro. Immunoelectron microscopy shows that the localization of MAGI-1 is restricted to the slit diaphragm, whereas JAM4 is also distributed on apical membranes of podocytes. In puromycin aminonucleoside-induced nephrotic podocytes, MAGI-1 is localized with nephrin at the displaced slit diaphragm. These data indicate that MAGI-1 is a component of the slit diaphragm and tightly interacts with nephrin and JAM4 in vivo. MAGI-1 may play a role in determining the boundary between the apical and the bosolateral domain at the level of slit diaphragm.
authors.affiliation: Department of Medical Biochemistry, Graduate School of Medicine, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Hirabayashi
authors.forename: Hiroki
authors.initials: H
authors.lastname: Mori
authors.forename: Ai
authors.initials: A
authors.lastname: Kansaku
authors.forename: Hidetake
authors.initials: H
authors.lastname: Kurihara
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Sakai
authors.forename: Fujio
authors.initials: F
authors.lastname: Shimizu
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Kawachi
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Hata
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D019556:COS Cells; D015815:Cell Adhesion Molecules / Q000378:metabolism* / Q000648:ultrastructure; D002522:Chlorocebus aethiops; D019084:Fluorescent Antibody Technique, Indirect; D005920:Glomerular Mesangium / Q000378:metabolism* / Q000648:ultrastructure; D051528:Guanylate Kinases; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism* / Q000648:ultrastructure; D016253:Microscopy, Immunoelectron; D009401:Nephrosis / Q000139:chemically induced / Q000378:metabolism* / Q000473:pathology; D010750:Phosphoproteins / Q000378:metabolism; D050199:Podocytes / Q000201:enzymology* / Q000648:ultrastructure; D011485:Protein Binding; D051381:Rats; D019108:Tight Junctions / Q000201:enzymology; D020798:Two-Hybrid System Techniques; D062826:Zonula Occludens-1 Protein
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D015815:Cell Adhesion Molecules; C492399:Igsf5 protein, rat; D008565:Membrane Proteins; D010750:Phosphoproteins; C569042:TJP1 protein, human; C569043:Tjp1 protein, mouse; C569044:Tjp1 protein, rat; D062826:Zonula Occludens-1 Protein; C113267:nephrin; D051528:Guanylate Kinases; C493280:Magi1 protein, mouse