title: A bipartite signal regulates the faithful delivery of apical domain marker podocalyxin/Gp135.
abstract: Podocalyxin/Gp135 was recently demonstrated to participate in the formation of a preapical complex to set up initial polarity in MDCK cells, a function presumably depending on the apical targeting of Gp135. We show that correct apical sorting of Gp135 depends on a bipartite signal composed of an extracellular O-glycosylation-rich region and the intracellular PDZ domain-binding motif. The function of this PDZ-binding motif could be substituted with a fusion construct of Gp135 with Ezrin-binding phosphoprotein 50 (EBP50). In accordance with this observation, EBP50 binds to newly synthesized Gp135 at the Golgi apparatus and facilitates oligomerization and sorting of Gp135 into a clustering complex. A defective connection between Gp135 and EBP50 or EBP50 knockdown results in a delayed exit from the detergent-resistant microdomain, failure of oligomerization, and basolateral missorting of Gp135. Furthermore, the basolaterally missorted EBP50-binding defective mutant of Gp135 was rapidly retrieved via a PKC-dependent mechanism. According to these findings, we propose a model by which a highly negative charged transmembrane protein could be packed into an apical sorting platform with the aid of its cytoplasmic partner EBP50.
authors.affiliation: Department of Internal Medicine, National Taiwan University Hospital, National Taiwan University College of Medicine, Taipei, 100 Taiwan.
authors.forename: Chun-Ying
authors.initials: CY
authors.lastname: Yu
authors.forename: Jen-Yau
authors.initials: JY
authors.lastname: Chen
authors.forename: Yu-Yu
authors.initials: YY
authors.lastname: Lin
authors.forename: Kuo-Fang
authors.initials: KF
authors.lastname: Shen
authors.forename: Wei-Ling
authors.initials: WL
authors.lastname: Lin
authors.forename: Chung-Liang
authors.initials: CL
authors.lastname: Chien
authors.forename: Martin B A
authors.initials: MB
authors.lastname: ter Beest
authors.forename: Tzuu-Shuh
authors.initials: TS
authors.lastname: Jou
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D016764:Cell Polarity; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004285:Dogs; D004705:Endocytosis; D006031:Glycosylation; D021962:Membrane Microdomains / Q000378:metabolism; D008954:Models, Biological; D009154:Mutation; D011493:Protein Kinase C / Q000378:metabolism; D021382:Protein Sorting Signals / Q000235:genetics; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000235:genetics; D012795:Sialoglycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D000099149:Ezrin
chemical_list: D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D011493:Protein Kinase C; D021382:Protein Sorting Signals; D034741:RNA, Small Interfering; D012795:Sialoglycoproteins; D000099149:Ezrin; C001643:podocalyxin