title: Role of megalin in endocytosis of advanced glycation end products: implications for a novel protein binding to both megalin and advanced glycation end products.
abstract: Advanced glycation end products (AGE) are filtered by glomeruli and reabsorbed and metabolized by proximal tubule cells (PTC). In renal failure, decreased renal AGE metabolism likely accounts for the accumulation in serum that is related to uremic complications. In diabetes, AGE generation is increased, and the handling mechanisms in PTC are likely associated with the pathogenesis of tubulointerstitial injury. It is therefore important to clarify the mechanisms of the AGE metabolism to develop a strategy for removing AGE in uremia and to elucidate the pathogenesis of diabetic nephropathy. To this end, this study focused on the molecular analysis of megalin, a multi-ligand endocytic receptor, in PTC. AGE uptake analysis was performed using the rat yolk sac-derived L2 cell line system established for the analysis of megalin's endocytic functions. The cells mediated specific internalization and degradation of AGE, which were significantly blocked by anti-megalin IgG, indicating that megalin is involved in the cellular processes. However, cell surface AGE-binding assays and ligand blot analysis revealed no evidence that megalin is a direct AGE receptor. Affinity chromatography and ligand blot analysis originally revealed that 200-kD and 400-kD proteins in the cells bind to AGE and the 200-kD protein to megalin in a Ca(2+)-dependent manner. The binding of megalin with the 200-kD protein was suppressed by receptor-associated protein (RAP), a ligand for megalin. In conclusion, megalin functions for endocytosis of AGE via an indirect mechanism. L2 cells express novel AGE-binding proteins, one of which may interact with megalin.
authors.affiliation: Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Niigata 951-8510, Japan. akisaito@med.niigata-u.ac.jp
authors.forename: Akihiko
authors.initials: A
authors.lastname: Saito
authors.forename: Ryoji
authors.initials: R
authors.lastname: Nagai
authors.forename: Atsuhito
authors.initials: A
authors.lastname: Tanuma
authors.forename: Hitomi
authors.initials: H
authors.lastname: Hama
authors.forename: Kenji
authors.initials: K
authors.lastname: Cho
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Takeda
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Tosifusa
authors.initials: T
authors.lastname: Toda
authors.forename: Fujio
authors.initials: F
authors.lastname: Shimizu
authors.forename: Seikoh
authors.initials: S
authors.lastname: Horiuchi
authors.forename: Fumitake
authors.initials: F
authors.lastname: Gejyo
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D018240:Endodermal Sinus Tumor; D017127:Glycation End Products, Advanced / Q000493:pharmacokinetics*; D007457:Iodine Radioisotopes; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000378:metabolism*; D008970:Molecular Weight; D011485:Protein Binding / Q000502:physiology; D011817:Rabbits; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D002352:Carrier Proteins; D017127:Glycation End Products, Advanced; D007457:Iodine Radioisotopes; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D011956:Receptors, Cell Surface; D002118:Calcium