title: SNX31: a novel sorting nexin associated with the uroplakin-degrading multivesicular bodies in terminally differentiated urothelial cells.
abstract: Uroplakins (UP), a group of integral membrane proteins, are major urothelial differentiation products that form 2D crystals of 16-nm particles (urothelial plaques) covering the apical surface of mammalian bladder urothelium. They contribute to the urothelial barrier function and, one of them, UPIa, serves as the receptor for uropathogenic Escherichia coli. It is therefore important to understand the mechanism by which these surface-associated uroplakins are degraded. While it is known that endocytosed uroplakin plaques are targeted to and line the multivesicular bodies (MVBs), it is unclear how these rigid-looking plaques can go to the highly curved membranes of intraluminal vesicles (ILVs). From a cDNA subtraction library, we identified a highly urothelium-specific sorting nexin, SNX31. SNX31 is expressed, like uroplakins, in terminally differentiated urothelial umbrella cells where it is predominantly associated with MVBs. Apical membrane proteins including uroplakins that are surface biotin-tagged are endocytosed and targeted to the SNX31-positive MVBs. EM localization demonstrated that SNX31 and uroplakins are both associated not only with the limiting membranes of MVBs containing uroplakin plaques, but also with ILVs. SNX31 can bind, on one hand, the PtdIns3P-enriched lipids via its N-terminal PX-domain, and, on the other hand, it binds uroplakins as demonstrated by co-immunoprecipitation and proximity ligation assay, and by its reduced membrane association in uroplakin II-deficient urothelium. The fact that in urothelial umbrella cells MVBs are the only major intracellular organelles enriched in both PtdIns3P and uroplakins may explain SNX31's MVB-specificity in these cells. However, in MDCK and other cultured cells transfected SNX31 can bind to early endosomes possibly via lipids. These data support a model in which SNX31 mediates the endocytic degradation of uroplakins by disassembling/collapsing the MVB-associated uroplakin plaques, thus enabling the uroplakin-containing (but 'softened') membranes to bud and form the ILVs for lysosomal degradation and/or exosome formation.
authors.affiliation: Department of Cell Biology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Neide
authors.initials: N
authors.lastname: Vieira
authors.affiliation: Department of Pathology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Fang-Ming
authors.initials: FM
authors.lastname: Deng
authors.affiliation: Department of Dermatology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Feng-Xia
authors.initials: FX
authors.lastname: Liang
authors.affiliation: Department of Cell Biology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Yi
authors.initials: Y
authors.lastname: Liao
authors.affiliation: Department of Cell Biology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Chang
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Ge
authors.initials: G
authors.lastname: Zhou
authors.affiliation: Department of Cell Biology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Weiyue
authors.initials: W
authors.lastname: Zheng
authors.affiliation: Department of Cell Biology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Simon
authors.affiliation: College of Life Sciences, Peking University, Beijing, People's Republic of China.
authors.forename: Mingxiao
authors.initials: M
authors.lastname: Ding
authors.affiliation: Department of Pathology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America; Department of Urology; NYU Cancer Institute, NYU Langone Medical Center, New York University, New York, New York, United States of America; Veterans Affairs New York Harbor Healthcare Systems, Manhattan Campus, New York, New York, United States of America.
authors.forename: Xue-Ru
authors.initials: XR
authors.lastname: Wu
authors.affiliation: Institute of Cell Biology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia.
authors.forename: Rok
authors.initials: R
authors.lastname: Romih
authors.affiliation: Department of Cell Biology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America.
authors.forename: Gert
authors.initials: G
authors.lastname: Kreibich
authors.affiliation: Department of Cell Biology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America; Department of Dermatology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America; Department of Biochemistry and Molecular Pharmacology, NYU Cancer Institute, NYU Langone Medical Center, New York, New York, United States of America; Department of Urology; NYU Cancer Institute, NYU Langone Medical Center, New York University, New York, New York, United States of America.
authors.forename: Tung-Tien
authors.initials: TT
authors.lastname: Sun
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002417:Cattle; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D004285:Dogs; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism; D055786:Gene Knockout Techniques; D061985:Madin Darby Canine Kidney Cells; D008810:Mice, Inbred C57BL; D008954:Models, Biological; D057146:Multivesicular Bodies / Q000378:metabolism* / Q000648:ultrastructure; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D011485:Protein Binding; D058305:Sorting Nexins / Q000378:metabolism*; D014461:Ultracentrifugation; D060165:Uroplakins / Q000378:metabolism*; D019459:Urothelium / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D015415:Biomarkers; D018129:Phosphatidylinositol Phosphates; D058305:Sorting Nexins; D060165:Uroplakins; C055525:phosphatidylinositol 3-phosphate; D019869:Phosphatidylinositol 3-Kinases