1
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Goto S, Yoshida Y, Hosojima M, Kuwahara S, Kabasawa H, Aoki H, Iida T, Sawada R, Ugamura D, Yoshizawa Y, Takemoto K, Komochi K, Kobayashi R, Kaseda R, Yaoita E, Nagatoishi S, Narita I, Tsumoto K, Saito A. Megalin is involved in angiotensinogen-induced, angiotensin II-mediated ERK1/2 signaling to activate Na + -H + exchanger 3 in proximal tubules. J Hypertens 2023; 41:1831-1843. [PMID: 37682076 DOI: 10.1097/hjh.0000000000003555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/09/2023]
Abstract
BACKGROUND Kidney angiotensin (Ang) II is produced mainly from liver-derived, glomerular-filtered angiotensinogen (AGT). Podocyte injury has been reported to increase the kidney Ang II content and induce Na + retention depending on the function of megalin, a proximal tubular endocytosis receptor. However, how megalin regulates the renal content and action of Ang II remains elusive. METHODS We used a mass spectrometry-based, parallel reaction-monitoring assay to quantitate Ang II in plasma, urine, and kidney homogenate of kidney-specific conditional megalin knockout (MegKO) and control (Ctl) mice. We also evaluated the pathophysiological changes in both mouse genotypes under the basal condition and under the condition of increased glomerular filtration of AGT induced by administration of recombinant mouse AGT (rec-mAGT). RESULTS Under the basal condition, plasma and kidney Ang II levels were comparable in the two mouse groups. Ang II was detected abundantly in fresh spot urine in conditional MegKO mice. Megalin was also found to mediate the uptake of intravenously administered fluorescent Ang II by PTECs. Administration of rec-mAGT increased kidney Ang II, exerted renal extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, activated proximal tubular Na + -H + exchanger 3 (NHE3), and decreased urinary Na + excretion in Ctl mice, whereas these changes were suppressed but urinary Ang II was increased in conditional MegKO mice. CONCLUSION Increased glomerular filtration of AGT is likely to augment Ang II production in the proximal tubular lumen. Thus, megalin-dependent Ang II uptake should be involved in the ERK1/2 signaling that activates proximal tubular NHE3 in vivo , thereby causing Na + retention.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | - Ryohei Kaseda
- Department of Clinical Nephrology and Rheumatology, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata City, Niigata
| | | | | | - Ichiei Narita
- Department of Clinical Nephrology and Rheumatology, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata City, Niigata
| | - Kouhei Tsumoto
- The Institute of Medical Science and Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, Tokyo, Japan
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2
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Beenken A, Cerutti G, Brasch J, Guo Y, Sheng Z, Erdjument-Bromage H, Aziz Z, Robbins-Juarez SY, Chavez EY, Ahlsen G, Katsamba PS, Neubert TA, Fitzpatrick AWP, Barasch J, Shapiro L. Structures of LRP2 reveal a molecular machine for endocytosis. Cell 2023; 186:821-836.e13. [PMID: 36750096 PMCID: PMC9993842 DOI: 10.1016/j.cell.2023.01.016] [Citation(s) in RCA: 15] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 11/29/2022] [Accepted: 01/10/2023] [Indexed: 02/08/2023]
Abstract
The low-density lipoprotein (LDL) receptor-related protein 2 (LRP2 or megalin) is representative of the phylogenetically conserved subfamily of giant LDL receptor-related proteins, which function in endocytosis and are implicated in diseases of the kidney and brain. Here, we report high-resolution cryoelectron microscopy structures of LRP2 isolated from mouse kidney, at extracellular and endosomal pH. The structures reveal LRP2 to be a molecular machine that adopts a conformation for ligand binding at the cell surface and for ligand shedding in the endosome. LRP2 forms a homodimer, the conformational transformation of which is governed by pH-sensitive sites at both homodimer and intra-protomer interfaces. A subset of LRP2 deleterious missense variants in humans appears to impair homodimer assembly. These observations lay the foundation for further understanding the function and mechanism of LDL receptors and implicate homodimerization as a conserved feature of the LRP receptor subfamily.
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Affiliation(s)
- Andrew Beenken
- Division of Nephrology, Department of Medicine, Columbia University Vagelos College of Physicians and Surgeons, New York, NY 10032, USA
| | - Gabriele Cerutti
- Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA
| | - Julia Brasch
- Department of Biochemistry, University of Utah, Salt Lake City, UT 84112, USA
| | - Yicheng Guo
- Aaron Diamond AIDS Research Center, Columbia University, New York, NY 10032, USA
| | - Zizhang Sheng
- Aaron Diamond AIDS Research Center, Columbia University, New York, NY 10032, USA
| | - Hediye Erdjument-Bromage
- Department of Cell Biology, New York University Grossman School of Medicine, New York, NY 10016, USA
| | - Zainab Aziz
- Vagelos College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA
| | | | - Estefania Y Chavez
- Department of Pediatrics, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
| | - Goran Ahlsen
- Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA
| | - Phinikoula S Katsamba
- Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA
| | - Thomas A Neubert
- Department of Cell Biology, New York University Grossman School of Medicine, New York, NY 10016, USA
| | - Anthony W P Fitzpatrick
- Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; Department of Biochemistry and Molecular Biophysics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY 10032, USA; Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Columbia University Irving Medical Center, New York, NY 10032, USA.
| | - Jonathan Barasch
- Division of Nephrology, Department of Medicine, Columbia University Vagelos College of Physicians and Surgeons, New York, NY 10032, USA; Department of Pathology and Cell Biology, Columbia University Vagelos College of Physicians and Surgeons, New York, NY 10032, USA; Columbia University George M. O'Brien Urology Center, New York, NY 10032, USA.
| | - Lawrence Shapiro
- Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10027, USA; Aaron Diamond AIDS Research Center, Columbia University, New York, NY 10032, USA; Department of Biochemistry and Molecular Biophysics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY 10032, USA.
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3
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Arita M, Watanabe S, Aoki N, Kuwahara S, Suzuki R, Goto S, Abe Y, Takahashi M, Sato M, Hokari S, Ohtsubo A, Shoji S, Nozaki K, Ichikawa K, Kondo R, Hayashi M, Ohshima Y, Kabasawa H, Hosojima M, Koya T, Saito A, Kikuchi T. Combination therapy of cisplatin with cilastatin enables an increased dose of cisplatin, enhancing its antitumor effect by suppression of nephrotoxicity. Sci Rep 2021; 11:750. [PMID: 33437029 PMCID: PMC7804437 DOI: 10.1038/s41598-020-80853-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2020] [Accepted: 12/29/2020] [Indexed: 01/22/2023] Open
Abstract
Cisplatin, one of the most active anticancer agents, is widely used in standard chemotherapy for various cancers. Cisplatin is more poorly tolerated than other chemotherapeutic drugs, and the main dose-limiting toxicity of cisplatin is its nephrotoxicity, which is dose-dependent. Although less toxic methods of cisplatin administration have been established, cisplatin-induced nephrotoxicity remains an unsolved problem. Megalin is an endocytic receptor expressed at the apical membrane of proximal tubules. We previously demonstrated that nephrotoxic drugs, including cisplatin, are reabsorbed through megalin and cause proximal tubular cell injury. We further found that cilastatin blocked the binding of cisplatin to megalin in vitro. In this study, we investigated whether cilastatin could reduce cisplatin-induced nephrotoxicity without influencing the antitumor effects of cisplatin. Nephrotoxicity was decreased or absent in mice treated with cisplatin and cilastatin, as determined by kidney injury molecule-1 staining and the blood urea nitrogen content. Combined with cilastatin, a twofold dose of cisplatin was used to successfully treat the mice, which enhanced the antitumor effects of cisplatin but reduced its nephrotoxicity. These findings suggest that we can increase the dose of cisplatin when combined with cilastatin and improve the outcome of cancer patients.
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Affiliation(s)
- Masashi Arita
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Satoshi Watanabe
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan.
| | - Nobumasa Aoki
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Shoji Kuwahara
- Laboratory of Clinical Nutrition, Department of Nutrition, Graduate School of Human Cultures, The University of Shiga Prefecture, Hikone, Japan
| | - Ryo Suzuki
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Sawako Goto
- Department of Applied Molecular Medicine, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - Yuko Abe
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Miho Takahashi
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Miyuki Sato
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Satoshi Hokari
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Aya Ohtsubo
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Satoshi Shoji
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Koichiro Nozaki
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Kosuke Ichikawa
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Rie Kondo
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Masachika Hayashi
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Yasuyoshi Ohshima
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Hideyuki Kabasawa
- Department of Clinical Nutrition Science, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - Michihiro Hosojima
- Department of Clinical Nutrition Science, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - Toshiyuki Koya
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
| | - Akihiko Saito
- Department of Applied Molecular Medicine, Kidney Research Center, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - Toshiaki Kikuchi
- Department of Respiratory Medicine and Infectious Diseases, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachidori, Chuouku, Niigata, 951-8510, Japan
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4
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De S, Kuwahara S, Hosojima M, Ishikawa T, Kaseda R, Sarkar P, Yoshioka Y, Kabasawa H, Iida T, Goto S, Toba K, Higuchi Y, Suzuki Y, Hara M, Kurosawa H, Narita I, Hirayama Y, Ochiya T, Saito A. Exocytosis-Mediated Urinary Full-Length Megalin Excretion Is Linked With the Pathogenesis of Diabetic Nephropathy. Diabetes 2017; 66:1391-1404. [PMID: 28289043 DOI: 10.2337/db16-1031] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Accepted: 02/15/2017] [Indexed: 11/13/2022]
Abstract
Efficient biomarkers for diabetic nephropathy (DN) have not been established. Using ELISA, we found previously that urinary levels of full-length megalin (C-megalin), a multiligand endocytic receptor in proximal tubules, was positively correlated with DN progression in patients with type 2 diabetes mellitus (T2DM). Here, we found that urinary extracellular vesicle (UEV) excretion and C-megalin content in UEVs or in their exosomal fraction increased along with the progression of the albuminuric stages in patients with T2DM. Cultured immortalized rat proximal tubule cells (IRPTCs) treated with fatty acid-free BSA or advanced glycation end product-modified BSA (AGE-BSA), endocytic ligands of megalin, increased EV excretion, and their C-megalin content. C-megalin excretion from IRPTCs via extracellular vesicles was significantly blocked by an exosome-specific inhibitor, GW4869, indicating that this excretion is mainly exocytosis-mediated. AGE-BSA treatment of IRPTCs caused apparent lysosomal dysfunction, which stimulated multivesicular body formation, resulting in increased exosomal C-megalin excretion. In a high-fat diet-induced, megalin-mediated kidney injury model in mice, urinary C-megalin excretion also increased via UEVs. Collectively, exocytosis-mediated urinary C-megalin excretion is associated with the development and progression of DN in patients with T2DM, particularly due to megalin-mediated lysosomal dysfunction in proximal tubules, and hence it could be a candidate biomarker linked with DN pathogenesis.
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MESH Headings
- Acute Kidney Injury/metabolism
- Adult
- Aged
- Aged, 80 and over
- Animals
- Case-Control Studies
- Diabetes Mellitus, Type 2/complications
- Diabetes Mellitus, Type 2/metabolism
- Diabetes Mellitus, Type 2/urine
- Diabetic Nephropathies/etiology
- Diabetic Nephropathies/metabolism
- Diabetic Nephropathies/urine
- Diet, High-Fat
- Exocytosis
- Extracellular Vesicles/metabolism
- Extracellular Vesicles/ultrastructure
- Female
- Glycation End Products, Advanced/pharmacology
- Humans
- Immunoblotting
- Kidney Tubules, Proximal/drug effects
- Kidney Tubules, Proximal/metabolism
- Kidney Tubules, Proximal/ultrastructure
- Low Density Lipoprotein Receptor-Related Protein-2/metabolism
- Male
- Mice
- MicroRNAs
- Microscopy, Electron, Transmission
- Microscopy, Immunoelectron
- Middle Aged
- RNA, Messenger
- Rats
- Serum Albumin, Bovine/pharmacology
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Affiliation(s)
- Shankhajit De
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
- Department of Applied Molecular Medicine, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Shoji Kuwahara
- Department of Applied Molecular Medicine, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Michihiro Hosojima
- Department of Clinical Nutrition Science, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Tomomi Ishikawa
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Ryohei Kaseda
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Piyali Sarkar
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
- Department of Applied Molecular Medicine, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Yusuke Yoshioka
- Division of Molecular and Cellular Medicine, National Cancer Center Research Institute, Chuo-ku, Tokyo, Japan
| | - Hideyuki Kabasawa
- Department of Clinical Nutrition Science, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Tomomichi Iida
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Sawako Goto
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Koji Toba
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Yuki Higuchi
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Yoshiki Suzuki
- Health Administration Center, Niigata University, Nishi-ku, Niigata, Niigata, Japan
| | - Masanori Hara
- Department of Pediatrics, Yoshida Hospital, Tsubame, Niigata, Japan
| | - Hiroyuki Kurosawa
- Diagnostics Research Department, Life Innovation Research Institute, DENKA Innovation Center, Denka Co., Ltd., Machida, Tokyo, Japan
| | - Ichiei Narita
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
| | - Yoshiaki Hirayama
- Diagnostics Research Department, Life Innovation Research Institute, DENKA Innovation Center, Denka Co., Ltd., Machida, Tokyo, Japan
| | - Takahiro Ochiya
- Division of Molecular and Cellular Medicine, National Cancer Center Research Institute, Chuo-ku, Tokyo, Japan
| | - Akihiko Saito
- Department of Applied Molecular Medicine, Niigata University Graduate School of Medical and Dental Sciences, Chuo-ku, Niigata, Niigata, Japan
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5
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Hori Y, Aoki N, Kuwahara S, Hosojima M, Kaseda R, Goto S, Iida T, De S, Kabasawa H, Kaneko R, Aoki H, Tanabe Y, Kagamu H, Narita I, Kikuchi T, Saito A. Megalin Blockade with Cilastatin Suppresses Drug-Induced Nephrotoxicity. J Am Soc Nephrol 2017; 28:1783-1791. [PMID: 28052987 DOI: 10.1681/asn.2016060606] [Citation(s) in RCA: 97] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Accepted: 11/25/2017] [Indexed: 11/03/2022] Open
Abstract
Nephrotoxicity induced by antimicrobial or anticancer drugs is a serious clinical problem. Megalin, an endocytic receptor expressed at the apical membranes of proximal tubules, mediates the nephrotoxicity of aminoglycosides and colistin, key antimicrobials for multidrug-resistant organisms. The mechanisms underlying the nephrotoxicity induced by vancomycin, an antimicrobial for methicillin-resistant Staphylococcus aureus, and cisplatin, an important anticancer drug, are unknown, although the nephrotoxicity of these drugs and gentamicin, an aminoglycoside, is suppressed experimentally with cilastatin. In the clinical setting, cilastatin has been used safely to suppress dehydropeptidase-I-mediated renal metabolism of imipenem, a carbapenem antimicrobial, and thereby limit tubular injury. Here, we tested the hypothesis that cilastatin also blocks megalin-mediated uptake of vancomycin, cisplatin, colistin, and aminoglycosides, thereby limiting the nephrotoxicity of these drugs. Quartz crystal microbalance analysis showed that megalin also binds vancomycin and cisplatin and that cilastatin competes with megalin for binding to gentamicin, colistin, vancomycin, and cisplatin. In kidney-specific mosaic megalin knockout mice treated with colistin, vancomycin, or cisplatin, the megalin-replete proximal tubule epithelial cells exhibited signs of injury, whereas the megalin-deficient cells did not. Furthermore, concomitant cilastatin administration suppressed colistin-induced nephrotoxicity in C57BL/6J mice. Notably, cilastatin did not inhibit the antibacterial activity of gentamicin, colistin, or vancomycin in vitro, just as cilastatin did not affect the anticancer activity of cisplatin in previous studies. In conclusion, megalin blockade with cilastatin efficiently suppresses the nephrotoxicity induced by gentamicin, colistin, vancomycin, or cisplatin. Cilastatin may be a promising agent for inhibiting various forms of drug-induced nephrotoxicity mediated via megalin in the clinical setting.
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Affiliation(s)
- Yoshihisa Hori
- Departments of Respiratory Medicine and Infectious Diseases
| | - Nobumasa Aoki
- Departments of Respiratory Medicine and Infectious Diseases.,Advanced Disaster Medical and Emergency Critical Care Center and Intensive Care Units and
| | | | | | | | - Sawako Goto
- Applied Molecular Medicine.,Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - Tomomichi Iida
- Applied Molecular Medicine.,Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | - Shankhajit De
- Applied Molecular Medicine.,Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
| | | | | | | | - Yoshinari Tanabe
- Division of Infection Control and Prevention, Niigata University Medical and Dental Hospital, Niigata, Japan; and
| | - Hiroshi Kagamu
- Division of Respiratory Medicine, Saitama Medical University International Medical Center, Hidaka-shi, Japan
| | - Ichiei Narita
- Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
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6
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Abstract
Membranous nephropathy (MN) describes a histopathologic pattern of injury marked by glomerular subepithelial immune deposits and collectively represents one of the most common causes of adult nephrotic syndrome. Studies in Heymann nephritis, an experimental model of MN, have established a paradigm in which these deposits locally activate complement to cause podocyte injury, culminating in cytoskeletal reorganization, loss of slit diaphragms, and proteinuria. There is much circumstantial evidence for a prominent role of complement in human MN because C3 and C5b-9 are found consistently within immune deposits. Secondary MN often shows the additional presence of C1q, implicating the classic pathway of complement activation. Primary MN, however, is IgG4-predominant and IgG4 is considered incapable of binding C1q and activating the complement pathway. Recent studies have identified the M-type phospholipase A2 receptor (PLA2R) as the major target antigen in primary MN. Early evidence hints that IgG4 anti-PLA2R autoantibodies can bind mannan-binding lectin and activate the lectin complement pathway. The identification of anti-PLA2R antibodies as likely participants in the pathogenesis of disease will allow focused investigation into the role of complement in MN. Definitive therapy for MN is immunosuppression, although future therapeutic agents that specifically target complement activation may represent an effective temporizing measure to forestall further glomerular injury.
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Affiliation(s)
- Hong Ma
- Department of Medicine, Renal Section, Boston University School of Medicine
| | - Dana G. Sandor
- Department of Medicine, Renal Section, Boston University School of Medicine
| | - Laurence H. Beck
- Department of Medicine, Renal Section, Boston University School of Medicine
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7
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Nagai J, Takano M. Molecular-targeted approaches to reduce renal accumulation of nephrotoxic drugs. Expert Opin Drug Metab Toxicol 2010; 6:1125-38. [DOI: 10.1517/17425255.2010.497140] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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8
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Kerr ML, Gasperini R, Gibbs ME, Hou X, Shepherd CE, Strickland DK, Foa L, Lawen A, Small DH. Inhibition of Aβ aggregation and neurotoxicity by the 39-kDa receptor-associated protein. J Neurochem 2010; 112:1199-209. [DOI: 10.1111/j.1471-4159.2009.06540.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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9
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Pandey P, Pradhan S, Mittal B. LRP-associated protein gene (LRPAP1) and susceptibility to degenerative dementia. GENES BRAIN AND BEHAVIOR 2008; 7:943-50. [DOI: 10.1111/j.1601-183x.2008.00436.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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10
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DE HEER E, BRUIJN JA, HOEDEM AEKER PHJ. Heymann nephritis revisited—new insights into the pathogenesis of experimental membranous glomerulonephritis. Clin Exp Immunol 2008. [DOI: 10.1111/j.1365-2249.1993.tb08206.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Affiliation(s)
- E DE HEER
- Department of Pathology, University of Leiden, Leiden, The Netherlands
| | - J A BRUIJN
- Department of Pathology, University of Leiden, Leiden, The Netherlands
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11
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Fisher CE, Howie SEM. The role of megalin (LRP-2/Gp330) during development. Dev Biol 2006; 296:279-97. [PMID: 16828734 DOI: 10.1016/j.ydbio.2006.06.007] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2005] [Revised: 04/21/2006] [Accepted: 06/05/2006] [Indexed: 11/17/2022]
Abstract
Megalin (LRP-2/GP330), a member of the LDL receptor family, is an endocytic receptor expressed mainly in polarised epithelial cells. Identified as the pathogenic autoantigen of Heymann nephritis in rats, its functions have been studied in greatest detail in adult mammalian kidney, but there is increasing recognition of its involvement in embryonic development. The megalin homologue LRP-1 is essential for growth and development in Caenorhabditis elegans and megalin plays a role in CNS development in zebrafish. There is now also evidence for a homologue in Drosophila. However, most research concerns mammalian embryogenesis; it is widely accepted to be important during forebrain development and the developing renal proximal tubule. Megalin is also expressed in lung, eye, intestine, uterus, oviduct, and male reproductive tract. It is found in yolk sacs and the outer cells of pre-implantation mouse embryos, where interactions with cubilin result in nutrient endocytosis, and it may be important during implantation. Models for megalin interaction(s) with Sonic Hedgehog (Shh) have been proposed. The importance of Shh signalling during embryogenesis is well established; how and when megalin interacts with Shh is becoming a pertinent question in developmental biology.
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Affiliation(s)
- Carolyn E Fisher
- Centre for Inflammation Research, Queen's Research Institute, University of Edinburgh, 47 Little France Crescent, Edinburgh EH 16 4JT, Scotland, UK.
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12
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Page S, Judson A, Melford K, Bensadoun A. Interaction of Lipoprotein Lipase and Receptor-associated Protein. J Biol Chem 2006; 281:13931-8. [PMID: 16517593 DOI: 10.1074/jbc.m600995200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Receptor-associated protein (RAP) is a recognized chaperone/escort protein for members of the low density lipoprotein receptor family. In this report, we show that RAP binds to lipoprotein lipase (LPL) and may play a role in the maturation of LPL. Binding of highly purified RAP to LPL was demonstrated in vitro by solid phase assays, surface plasmon resonance, and rate zonal centrifugation. The dissociation constant for this interaction measured by the first two techniques ranged between 2.4 and 13 nM, values similar to those reported for the binding of RAP to LRP or gp330. The specificity of the interaction was demonstrated by competition with a panel of LPL monoclonal antibodies. Rate zonal centrifugation demonstrated the presence of a stable complex with an apparent Mr consistent with the formation of a complex between monomeric LPL and RAP. RAP x LPL complexes were co-immunoprecipitated in adipocyte lysates or from solutions of purified LPL and RAP. The interaction was also demonstrated in whole cells by cross-linking experiments. RAP-deficient adipocytes secreted LPL with a specific activity 2.5-fold lower than the lipase secreted by control cells. Heparin addition to cultured RAP-deficient adipocytes failed to stimulate LPL secretion in the medium, suggesting defective binding of the lipase to the plasma membrane. These studies demonstrate that RAP binds to LPL with high affinity both in purified systems and cell extracts and that RAP-deficient adipocytes secrete poorly assembled LPL. A function of RAP may be to prevent premature interaction of LPL with binding partners in the secretory pathway, namely LRP and heparan sulfate proteoglycan.
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Affiliation(s)
- Shallee Page
- Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA
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13
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Christensen EI, Nielsen R. Role of megalin and cubilin in renal physiology and pathophysiology. Rev Physiol Biochem Pharmacol 2006; 158:1-22. [PMID: 17729440 DOI: 10.1007/112_0604] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Megalin and cubilin are endocytic receptors highly expressed in the endocytic apparatus of the renal proximal tubule. These receptors appear to be responsible for the tubular clearance of most proteins filtered in the glomeruli. Cubilin is a peripheral membrane protein, and therefore it does not have an endocytosis signaling sequence. It appears that megalin is responsible for internalization of cubilin and its ligands in addition to internalizing its own ligands. The proteinuria observed in megalin-deficient mice, in dogs lacking functional cubilin, and in patients with distinct mutations of the cubilin gene illustrates the importance of the receptors.
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Affiliation(s)
- E I Christensen
- University of Aarhus, Department of Cell Biology, Institute of Anatomy, University Park, Building 234, 8000 Aarhus C, Denmark.
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14
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Oyama Y, Takeda T, Hama H, Tanuma A, Iino N, Sato K, Kaseda R, Ma M, Yamamoto T, Fujii H, Kazama JJ, Odani S, Terada Y, Mizuta K, Gejyo F, Saito A. Evidence for megalin-mediated proximal tubular uptake of L-FABP, a carrier of potentially nephrotoxic molecules. J Transl Med 2005; 85:522-31. [PMID: 15696188 DOI: 10.1038/labinvest.3700240] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Liver-type fatty acid binding protein (L-FABP) binds with high affinity to hydrophobic molecules including free fatty acid, bile acid and bilirubin, which are potentially nephrotoxic, and is involved in their metabolism mainly in hepatocytes. L-FABP is released into the circulation, and patients with liver damage have an elevated plasma L-FABP level. L-FABP is also present in renal tubules; however, the precise localization of L-FABP and its potential role in the renal tubules are not known. In this study, we examined the cellular and subcellular localization of L-FABP in the rat kidney and tried to determine from where the L-FABP in kidney tissues had originated. Immunohistochemical studies of kidney sections localized L-FABP in the lysosomes of proximal tubule cells (PTC). In rats with carbon tetrachloride (CCl4)-induced acute liver injury, we detected high levels of L-FABP in the circulation and in the kidney compared with those in the control rat by immunoblotting, while reverse transcription-polymerase chain reaction showed that the level of L-FABP mRNA expression in the kidney of CCl4-treated rats was low and did not differ from that in the control rat. When 35S-L-FABP was intravenously administered to rats, the kidneys took up 35S-L-FABP more preferentially than the liver and heart, and histoautoradiography of kidney sections revealed that 35S-L-FABP was internalized via the apical domains of PTC. Quartz-crystal microbalance analysis revealed that L-FABP bound to megalin, a multiligand endocytotic receptor on PTC, in a Ca2+-dependent manner. Degradation assays using megalin-expressing rat yolk sac tumor-derived L2 cells demonstrated that megalin mediated the cellular uptake and catabolism of 125I-L-FABP. In conclusion, circulatory L-FABP was found to be filtered by glomeruli and internalized by PTC probably via megalin-mediated endocytosis. These results suggest a novel renal uptake pathway for L-FABP, a carrier of hydrophobic molecules, some of which may exert nephrotoxic effects.
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Affiliation(s)
- Yuko Oyama
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan
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15
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Tramontano A, Makker SP. Conformation and glycosylation of a megalin fragment correlate with nephritogenicity in Heymann nephritis. THE JOURNAL OF IMMUNOLOGY 2004; 172:2367-73. [PMID: 14764706 DOI: 10.4049/jimmunol.172.4.2367] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Active Heymann nephritis (AHN), a rat model of autoimmune glomerulonephritis, is induced by immunization with autologous megalin, a 600-kDa cell surface glycoprotein isolated from crude renal extracts. Recombinant proteins containing a 563-residue N-terminal sequence of megalin were obtained from Escherichia coli and baculovirus-insect cell expression systems. Rats immunized with the soluble, secreted protein encoded by a baculovirus construct elicited high titer anti-megalin autoantibodies and developed glomerular immune deposits and elevated proteinuria consistent with AHN. Rats treated with the bacterial or nonsecreted insect cell proteins produced a milder anti-megalin response and did not develop the disease. Nephritogenicity appeared to correlate with conformational or other structural features of native megalin. All three recombinant proteins were reactive in Western blots with rabbit anti-megalin antiserum, whereas the insect cell-derived proteins reacted preferentially in Western blot and ELISA with anti-megalin autoantibodies from rats with AHN induced by native megalin. Only the secreted insect cell product was stained in a lectin blot, suggesting its specific glycosylation. These observations provide evidence that a megalin N-terminal domain includes B and T cell epitopes sufficient for a pathogenic autoimmune response and that a native-like conformation and glycosylation are essential for the induction of disease. The importance of conformational B cell epitopes for pathogenic autoantibodies recapitulates observations made in other models of organ-specific autoimmune disease. Glycosidic modifications could influence the presentation of either B or T cell epitopes in AHN, consistent with emerging evidence of the role of post-translational modifications in pathogenic autoimmune responses.
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MESH Headings
- Animals
- Autoantibodies/biosynthesis
- Autoantigens/genetics
- Autoantigens/immunology
- Autoantigens/metabolism
- Binding Sites, Antibody
- Blotting, Western
- Cloning, Molecular
- Epitopes, B-Lymphocyte/genetics
- Epitopes, B-Lymphocyte/immunology
- Epitopes, B-Lymphocyte/metabolism
- Epitopes, T-Lymphocyte/genetics
- Epitopes, T-Lymphocyte/immunology
- Epitopes, T-Lymphocyte/metabolism
- Female
- Glomerulonephritis/immunology
- Glomerulonephritis/metabolism
- Glomerulonephritis/pathology
- Glycosylation
- Immunohistochemistry
- Injections, Intradermal
- Low Density Lipoprotein Receptor-Related Protein-2/chemistry
- Low Density Lipoprotein Receptor-Related Protein-2/genetics
- Low Density Lipoprotein Receptor-Related Protein-2/immunology
- Low Density Lipoprotein Receptor-Related Protein-2/metabolism
- Peptide Fragments/chemistry
- Peptide Fragments/genetics
- Peptide Fragments/immunology
- Peptide Fragments/metabolism
- Protein Conformation
- Rats
- Rats, Inbred Lew
- Recombinant Fusion Proteins/chemistry
- Recombinant Fusion Proteins/immunology
- Recombinant Fusion Proteins/metabolism
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Affiliation(s)
- Alfonso Tramontano
- Department of Pediatrics, University of California School of Medicine, Davis, CA 95616, USA
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16
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Orlando RA. The low-density lipoprotein receptor-related protein associates with calnexin, calreticulin, and protein disulfide isomerase in receptor-associated-protein-deficient fibroblasts. Exp Cell Res 2004; 294:244-53. [PMID: 14980518 DOI: 10.1016/j.yexcr.2003.11.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2003] [Revised: 10/23/2003] [Indexed: 11/20/2022]
Abstract
The low-density lipoprotein receptor-related protein (LRP) is a large (>600 kDa) multi-ligand-binding cell surface receptor that is now known to participate in a diverse range of cellular events. To accomplish this diverse role, LRP is composed of repetitive amino acid motifs consisting of complement-type and EGF precursor-type repeats. Within these repeats are six conserved cysteine residues that form the core disulfide bond structure of each repeat. To accommodate the intricate folding that such a complex structure dictates, a specialized chaperone is present in the endoplasmic reticulum (ER) called the receptor-associated protein (RAP) that binds to LRP immediately following its biosynthesis and assists in its exocytic transport. Interestingly, RAP -/- mice show reduced LRP expression in certain cell types, but not a more global affect on LRP expression that was expected. Such a tissue-restricted effect by RAP prompted an investigation if other ER chaperones associate with LRP to assist in its complex folding requirements and compensate for the absence of RAP in RAP -/- cells. Fibroblasts obtained from RAP -/- mice demonstrate similar LRP expression levels and subcellular distribution as RAP +/+ fibroblasts. Moreover, RAP -/- cells show an identical exocytic trafficking rate for LRP as RAP +/+ cells and comparable cell surface internalization kinetics. In RAP -/- cells, three well-known ER chaperones, calnexin, calreticulin, and protein disulfide isomerase (PDI), associate with LRP and likely compensate for the absence of RAP.
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Affiliation(s)
- Robert A Orlando
- Department of Biochemistry and Molecular Biology, School of Medicine, University of New Mexico, Health Sciences Center, Albuquerque, NM 87131-5221, USA.
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17
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Nagai J, Takano M. Molecular Aspects of Renal Handling of Aminoglycosides and Strategies for Preventing the Nephrotoxicity. Drug Metab Pharmacokinet 2004; 19:159-70. [PMID: 15499183 DOI: 10.2133/dmpk.19.159] [Citation(s) in RCA: 167] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Aminoglycosides such as gentamicin and amikacin are the most commonly used antibiotics worldwide in the treatment of Gram-negative bacterial infections. However, serious complications like nephrotoxicity and ototoxicity are dose-limiting factors in the use of aminoglycosides. A relatively large amount of the intravenously administered dose is accumulated in the kidney (about 10% of dose), whereas little distribution of aminoglycosides to other tissues is observed. Aminoglycosides are taken up in the epithelial cells of the renal proximal tubules and stay there for a long time, resulting in nephrotoxicity. Acidic phospholipids are considered as a binding site for aminoglycosides in the brush-border membrane of the proximal tubular cells. More recently, it has been reported that megalin, a giant endocytic receptor abundantly expressed at the apical membrane of renal proximal tubules, plays an important role in binding and endocytosis of aminoglycosides in the proximal tubular cells. The elucidation of the aminoglycoside-binding receptor would help design a strategy to prevent against aminoglycoside-induced nephrotoxicity. In this review, we summarize recent advances in the understandings of the molecular mechanisms responsible for renal accumulation of aminoglycosides, especially megalin-mediated endocytosis. In addition, approaches toward prevention of aminoglycoside-induced nephrotoxicity are discussed, based on the molecular mechanisms of the renal accumulation of aminoglycosides.
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Affiliation(s)
- Junya Nagai
- Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical Sciences, Hiroshima University, Japan
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18
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Saito A, Nagai R, Tanuma A, Hama H, Cho K, Takeda T, Yoshida Y, Toda T, Shimizu F, Horiuchi S, Gejyo F. Role of megalin in endocytosis of advanced glycation end products: implications for a novel protein binding to both megalin and advanced glycation end products. J Am Soc Nephrol 2003; 14:1123-31. [PMID: 12707383 DOI: 10.1097/01.asn.0000062962.51879.f8] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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.
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Affiliation(s)
- Akihiko Saito
- Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, 1-757 Asahimachi-dori, Niigata 951-8510, Japan.
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19
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Verroust PJ, Birn H, Nielsen R, Kozyraki R, Christensen EI. The tandem endocytic receptors megalin and cubilin are important proteins in renal pathology. Kidney Int 2002; 62:745-56. [PMID: 12164855 DOI: 10.1046/j.1523-1755.2002.00501.x] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The molecular mechanisms controlling proximal tubule reabsorption of proteins have been much elucidated in recent years. Megalin and cubilin constitute two important endocytic receptor proteins involved in this process. Although structurally very different the two receptor proteins interact to mediate the reabsorption of a large number of filtered proteins, including carrier proteins important for transport and cellular uptake of several vitamins, lipids and other nutrients. Dysfunction of either protein results in tubular proteinuria and is associated with specific changes in vitamin metabolism due to the defective proximal tubular reabsorption of carrier proteins. Additional focus on the two receptors is attracted by the possible pathogenic role of excessive tubular protein uptake during conditions of increased filtration of proteins, and by recent findings implicating members of the low density lipoprotein-receptor family, which includes megalin, in the transduction of signals by association with cytoplasmic proteins.
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Affiliation(s)
- Pierre J Verroust
- Institut National de la Santé et de la Recherche Médicale U538, Centre Hôpitale Universitaire, St. Antoine, Paris, France
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20
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González P, Alvarez R, Reguero JR, Batalla A, Alvarez V, Cortina A, Cubero GI, García-Castro M, Coto E. Variation in the lipoprotein receptor-related protein, alpha2-macroglobulin and lipoprotein receptor-associated protein genes in relation to plasma lipid levels and risk of early myocardial infarction. Coron Artery Dis 2002; 13:251-4. [PMID: 12394648 DOI: 10.1097/00019501-200208000-00001] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
BACKGROUND The lipoprotein receptor-related protein (LRP) is an endocytic receptor for several ligands, such as alpha2-macroglobulin (alpha2 M) and apolipoprotein E. LRP is involved in the clearance of lipids from the bloodstream and is expressed in the atherosclerotic plaque. The LRP-associated protein (LRPAP in humans, RAP in mice) acts as a chaperone protein, stabilizing the nascent LRP peptide in the endoplasmic reticulum and Golgi complex. In mice, the amount of LRP activity was modulated by RAP, and RAP-null mice showed higher levels of total cholesterol. OBJECTIVE To evaluate the association between DNA polymorphisms at the LRP, LRPAP and alpha2 M genes and early myocardial infarction (MI). METHODS We genotyped 210 patients with early MI (<55 years) and 200 healthy control participants for three polymorphisms in the LRP, LRPAP and alpha2 M genes. RESULTS No association was found between these polymorphisms and plasma lipid levels in patients and control participants. Only the LRPAP-intron 1 polymorphism (a 21 bp insertion/deletion) was associated with MI (P = 0.0065; odds ratio = 2.18, 95% confidence intervals = 1.22-3.90). CONCLUSIONS According to our data, the variation at the LRPAP1 gene could contribute to the risk of developing an early episode of MI.
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Affiliation(s)
- Pelayo González
- Laboratorio de Genética Molecular-Instituto de Investigación Nefrológica (IRSIN-FRIAT), Hospital Central Asturias, Oviedo, Spain
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21
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Lou X, McQuistan T, Orlando RA, Farquhar MG. GAIP, GIPC and Galphai3 are concentrated in endocytic compartments of proximal tubule cells: putative role in regulating megalin's function. J Am Soc Nephrol 2002; 13:918-927. [PMID: 11912251 DOI: 10.1681/asn.v134918] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
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.
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Affiliation(s)
- Xiaojing Lou
- *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California
| | - Tammie McQuistan
- *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California
| | - Robert A Orlando
- *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California
| | - Marilyn Gist Farquhar
- *Department of Cellular and Molecular Medicine and †Pathology, University of California San Diego, La Jolla, California
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22
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Christensen EI, Birn H. Megalin and cubilin: multifunctional endocytic receptors. Nat Rev Mol Cell Biol 2002; 3:256-66. [PMID: 11994745 DOI: 10.1038/nrm778] [Citation(s) in RCA: 584] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The ability to take up substances from the surrounding environment not only provides cells with vital nutrients, but also enables the selective transport of substances from one compartment to another. Megalin and cubilin are two structurally different endocytic receptors that interact to serve such functions. Evidence has accumulated in recent years to indicate that these receptors have important functions in both normal physiology and pathology.
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Affiliation(s)
- Erik Ilsø Christensen
- Department of Cell Biology, University of Aarhus, University Park, Building 234, DK-8000 Aarhus C, ;
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23
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Birn H, Willnow TE, Nielsen R, Norden AGW, Bönsch C, Moestrup SK, Nexø E, Christensen EI. Megalin is essential for renal proximal tubule reabsorption and accumulation of transcobalamin-B(12). Am J Physiol Renal Physiol 2002; 282:F408-16. [PMID: 11832420 DOI: 10.1152/ajprenal.00206.2000] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Megalin has previously been shown to bind and mediate endocytosis of transcobalamin (TC)-B(12). However, the physiological significance of this has not been established, and other TC-B(12) binding proteins have been suggested to mediate renal uptake of this vitamin complex. The present study demonstrates by the use of megalin-deficient mice that megalin is, in fact, essential for the normal renal reabsorption of TC-vitamin B(12) and for renal accumulation of this highly conserved vitamin. Megalin-deficient mice excrete increased amounts of TC and B(12) in the urine, revealing a defective renal tubular uptake of TC-B(12). The urinary B(12) excretion is increased approximately 4-fold, resulting in an approximately 28-fold higher renal B(12) clearance. This is associated with an approximately 4-fold decrease in B(12) content in megalin-deficient kidney cortex. Thus megalin is important to prevent urinary loss of vitamin B(12). In addition, light- and electron-microscopic immunocytochemistry demonstrate lysosomal accumulation of B(12) in rat and mouse proximal tubules. In rats this accumulation is correlated with vitamin intake. Thus renal lysosomal B(12) accumulation is dependent on vitamin status, indicating a possible reserve function of this organelle in the rat kidney.
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Affiliation(s)
- Henrik Birn
- Department of Cell Biology, Institute of Anatomy, University of Aarhus, DK-8000 Aarhus C, Germany.
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24
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Moestrup SK, Verroust PJ. Megalin- and cubilin-mediated endocytosis of protein-bound vitamins, lipids, and hormones in polarized epithelia. Annu Rev Nutr 2001; 21:407-28. [PMID: 11375443 DOI: 10.1146/annurev.nutr.21.1.407] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Polarized epithelia have several functional and morphological similarities, including a high capacity for uptake of various substances present in the fluids facing the apical epithelial surfaces. Studies during the past decade have shown that receptor-mediated endocytosis, rather than nonspecific pinocytosis, accounts for the apical epithelial uptake of many carrier-bound nutrients and hormones. The two interacting receptors of distinct evolutionary origin, megalin and cubilin, are main receptors in this process. Both receptors are apically expressed in polarized epithelia, in which they function as biological affinity matrices for overlapping repertoires of ligands. The ability to bind multiple ligands is accounted for by a high number of replicated low-density lipoprotein receptor type-A repeats in megalin and CUB (complement C1r/C1s, Uegf, and bone morphogenic protein-1) domains in cubilin. Here we summarize and discuss the structural, genetic, and functional aspects of megalin and cubilin, with emphasis on their function as receptors for uptake of protein-associated vitamins, lipids, and hormones.
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Affiliation(s)
- S K Moestrup
- Department of Medical Biochemistry, University of Aarhus, 8000 Arhus C, Denmark.
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25
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Melman L, Cao ZF, Rennke S, Marzolo MP, Wardell MR, Bu G. High affinity binding of receptor-associated protein to heparin and low density lipoprotein receptor-related protein requires similar basic amino acid sequence motifs. J Biol Chem 2001; 276:29338-46. [PMID: 11382778 DOI: 10.1074/jbc.m103717200] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 39-kDa receptor-associated protein (RAP) is a specialized chaperone for members of the low density lipoprotein receptor gene family, which also binds heparin. Previous studies have identified a triplicate repeat sequence within RAP that appears to exhibit differential functions. Here we generated a series of truncated and site-directed RAP mutants in order to define the sites within RAP that are important for interacting with heparin and low density lipoprotein receptor-related protein (LRP). We found that high affinity binding of RAP to heparin is mediated by the carboxyl-terminal repeat of RAP, whereas both the carboxyl-terminal repeat and a combination of amino and central repeats exhibit high affinity binding to LRP. Several motifs were found to mediate the binding of RAP to heparin, and each contained a cluster of basic amino acids; among them, an intact R(282)VSR(285)SR(287)EK(289) motif is required for high affinity binding of RAP to heparin, whereas two other motifs, R(203)LR(205)R(206) and R(314)ISR(317)AR(319), also contribute to this interaction. We also found that intact motifs of both R(203)LR(205)R(206) and R(282)VSR(285)SR(287)EK(289) are required for high affinity binding of RAP to LRP, with the third motif, R(314)ISR(317)AR(319), contributing little to RAP-LRP interaction. We conclude that electrostatic interactions likely contribute significantly in the binding of RAP to both heparin and LRP and that high affinity interaction with both heparin and LRP appears to require mostly overlapping sequence motifs within RAP.
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Affiliation(s)
- L Melman
- Department of Pediatrics Washington University School of Medicine, St. Louis, Missouri 63110, USA
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26
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Christensen EI, Birn H. Megalin and cubilin: synergistic endocytic receptors in renal proximal tubule. Am J Physiol Renal Physiol 2001; 280:F562-73. [PMID: 11249847 DOI: 10.1152/ajprenal.2001.280.4.f562] [Citation(s) in RCA: 243] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The multiligand, endocytic receptors megalin and cubilin are colocalized in the renal proximal tubule. They are heavily expressed in the apical endocytic apparatus. Megalin is a 600-kDa transmembrane protein belonging to the low-density lipoprotein-receptor family. The cytoplasmic tail contains three NPXY motifs that mediate the clustering in coated pits and are possibly involved in signaling functions. Cubilin, also known as the intestinal intrinsic factor-cobalamin receptor, is a 460-kDa receptor with no transmembrane domain and no known signal for endocytosis. Because the two receptors bind each other with high affinity and colocalize in several tissues, it is highly conceivable that megalin mediates internalization of cubilin and its ligands. Both receptors are important for normal tubular reabsorption of proteins, including albumin. Among the proteins normally filtered in the glomeruli, cubilin has been shown to bind albumin, immunoglobulin light chains, and apolipoprotein A-I. The variety of filtered ligands identified for megalin include vitamin-binding proteins, hormones, enzymes, apolipoprotein H, albumin, and beta(2)- and alpha(1)-microglobulin. Loss of these proteins and vitamins in the urine of megalin-deficient mice illustrates the physiological importance of this receptor.
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Affiliation(s)
- E I Christensen
- Department of Cell Biology, Institute of Anatomy, University of Aarhus, DK-8000 Aarhus C, Denmark.
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27
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Knauer DJ, Majumdar D, Fong PC, Knauer MF. SERPIN regulation of factor XIa. The novel observation that protease nexin 1 in the presence of heparin is a more potent inhibitor of factor XIa than C1 inhibitor. J Biol Chem 2000; 275:37340-6. [PMID: 10973954 DOI: 10.1074/jbc.m003909200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In the present studies we have made the novel observation that protease nexin 1 (PN1), a member of the serine protease inhibitor (SERPIN) superfamily, is a potent inhibitor of the blood coagulation Factor XIa (FXIa). The inhibitory complexes formed between PN1 and FXIa are stable when subjected to reducing agents, SDS, and boiling, a characteristic of the acyl linkage formed between SERPINs and their cognate proteases. Using a sensitive fluorescence-quenched peptide substrate, the K(assoc) of PN1 for FXIa was determined to be 7.9 x 10(4) m(-)(1) s(-)(1) in the absence of heparin. In the presence of heparin, this rate was accelerated to 1.7 x 10(6), M(-)(1) s(-)(1), making PN1 a far better inhibitor of FXIa than C1 inhibitor, which is the only other SERPIN known to significantly inhibit FXIa. FXIa-PN1 complexes are shown to be internalized and degraded by human fibroblasts, most likely via the low density lipoprotein receptor-related protein (LRP), since degradation was strongly inhibited by the LRP agonist, receptor-associated protein. Since FXIa proteolytically modifies the amyloid precursor protein, this observation may suggest an accessory role for PN1 in the pathobiogenesis of Alzheimer's disease.
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Affiliation(s)
- D J Knauer
- Department of Developmental and Cell Biology, School of Biological Sciences, University of California, Irvine, California 92627, USA
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28
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Sarti M, Farquhar MG, Orlando RA. The receptor-associated protein (RAP) interacts with several resident proteins of the endoplasmic reticulum including a glycoprotein related to actin. Exp Cell Res 2000; 260:199-207. [PMID: 11035914 DOI: 10.1006/excr.2000.4993] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The receptor-associated protein (RAP) is a chaperone found primarily in the endoplasmic reticulum (ER) that plays a necessary role in the folding and exocytic trafficking of members of the LDL receptor gene family including megalin and the LDL receptor-related protein (LRP). Recently, RAP has been shown to interact with a growing number of proteins including several that are unrelated to the LDL receptor family as well as new members of this rapidly expanding family. Based on these observations, we have applied chemical crosslinking procedures to identify additional novel RAP-interacting proteins, and thereby better characterize the scope of RAP's ER-related function. In this study, we have identified eight proteins with molecular weights of 32, 35, 46, 55, 70, 95, 170, and 200 kDa that interact with endogenous RAP. These proteins were found to associate with RAP in multiple cell types from different species, suggesting that their expression and interactions with RAP are ubiquitous. Results of pulse-chase experiments show that most of the proteins remain sensitive to endoglycosidase-H digestion, and also remain stably associated with RAP over an extended period, suggesting that they are ER resident proteins. All of the RAP-associated proteins appear to be largely soluble as they partition into the aqueous phase following TX-114 detergent extraction. Sequence analysis and immunoblotting of the 46-kDa RAP-associated glycoprotein (gp46) shows that it is structurally and immunologically related to actin. If gp46 is also functionally related to actin as an intracellular structural protein, it may represent a novel component of the putative ER matrix.
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Affiliation(s)
- M Sarti
- Departments of Pathology and Cellular and Molecular Medicine, University of California, San Diego, La Jolla, California, 92093-0651, USA
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29
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Crisp RJ, Knauer DJ, Knauer MF. Roles of the heparin and low density lipid receptor-related protein-binding sites of protease nexin 1 (PN1) in urokinase-PN1 complex catabolism. The PN1 heparin-binding site mediates complex retention and degradation but not cell surface binding or internalization. J Biol Chem 2000; 275:19628-37. [PMID: 10867020 DOI: 10.1074/jbc.m909172199] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously described thrombin (Th)-protease nexin 1 (PN1) inhibitory complex binding to cell surface heparins and subsequent low density lipid receptor-related protein (LRP)-mediated internalization. Our present studies examine the catabolism of urinary plasminogen activator (uPA)-PN1 inhibitory complexes, which, unlike Th.PN1 complexes, bind almost exclusively through the uPA receptor. In addition, the binding site in PN1 required for the LRP-mediated internalization of Th.PN1 complexes is not required for the LRP-mediated internalization of uPA.PN1 complexes. Thus, the protease moiety of the complex partially determines the mechanistic route of entry. Because cell surface heparins are only minimally involved in the binding and internalization of uPA.PN1 complexes, we then predicted that complexes between uPA and the heparin binding-deficient PN1 variant, PN1(K7E), should be catabolized at the same rate as complexes formed with native PN1. Surprisingly, the uPA.PN1(K7E) complexes were degraded at only a fraction of the rate of native complexes. Internalization studies revealed that both uPA. PN1(K7E) and native uPA.PN1 complexes were initially internalized at the same rate, but uPA.PN1(K7E) complexes were rapidly retro-endocytosed in an intact form. By examining the pH dependence of complex binding in the range of 4.0-7.0, it was determined that the uPA.PN1 inhibitory complexes must specifically bind to endosomal heparins at pH 5.5 to be retained and sorted to lysosomes. These studies are the first to document a role for heparins in the catabolism of SERPIN-protease complexes at a point further in the pathway than cell surface binding, and this role may extend to other heparin-binding LRP-internalized ligands.
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Affiliation(s)
- R J Crisp
- Department of Developmental and Cell Biology, School of Biological Sciences, University of California, Irvine, California 92627, USA
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30
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Birn H, Vorum H, Verroust PJ, Moestrup SK, Christensen EI. Receptor-associated protein is important for normal processing of megalin in kidney proximal tubules. J Am Soc Nephrol 2000; 11:191-202. [PMID: 10665926 DOI: 10.1681/asn.v112191] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
The receptor-associated protein (RAP) has been identified as a chaperone regulating the expression and processing of the LDL receptor-related protein. RAP also binds to the related 600-kD multiligand endocytic receptor megalin expressed in many absorptive epithelia including renal proximal tubule. The present study examines the effect of RAP gene disruption on megalin expression and subcellular distribution in the proximal tubule as well as the effect on tubular protein reabsorption. It is shown that RAP is important for the normal expression and function of megalin. Megalin expression was reduced to approximately 23% estimated by immunoblotting and supported by immunocytochemistry and by the amount of megalin recovered by RAP affinity chromatography. Light- and electron microscope immunocytochemistry as well as analyses on separated membrane fractions showed significant changes in the subcellular distribution of megalin. A significant reduction in the normal brush border labeling was observed in association with increased labeling of rough endoplasmic reticulum and the smooth paramembranous endoplasmic reticulum along the basolateral membranes. RAP deficiency was associated with changes in urinary protein composition, enabling the identification of alpha-amylase as a new ligand for megalin. In addition, an increased excretion of vitamin D-binding protein, a recently identified ligand to megalin, was observed supporting changes in tubular protein reabsorption. The present data show that RAP is of crucial importance for normal processing and function of megalin, suggesting a chaperone-like function of this protein in the kidney proximal tubule.
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Affiliation(s)
- Henrik Birn
- Department of Cell Biology, Institute of Anatomy University of Aarhus, Denmark
| | - Henrik Vorum
- Institute of Medical Biochemistry, University of Aarhus, Denmark
| | - Pierre J Verroust
- Institut National de la Santé et de la Recherche Médicale U64 Hôpital Tenon, Paris, France
| | - Søren K Moestrup
- Institute of Medical Biochemistry, University of Aarhus, Denmark
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31
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Umans L, Serneels L, Lorent K, Dewachter I, Tesseur I, Moechars D, Van Leuven F. Lipoprotein receptor-related protein in brain and in cultured neurons of mice deficient in receptor-associated protein and transgenic for apolipoprotein E4 or amyloid precursor protein. Neuroscience 1999; 94:315-21. [PMID: 10613521 DOI: 10.1016/s0306-4522(99)00242-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The role of the receptor-associated protein in controlling the expression of the low-density lipoprotein receptor-related protein was analysed in brain and in cultured neurons of receptor-associated protein - / - mice. In addition, the effect of two important ligands of lipoprotein receptor-related protein in brain, i.e. apolipoprotein E and amyloid precursor protein, was examined by crossing the receptor-associated protein - / - mice with transgenic mice overexpressing these proteins specifically in neurons. The immunohistochemical localization of lipoprotein receptor-related protein and receptor-associated protein in wild-type mouse brain was demonstrated to be congruent over all structures, including the cortex and hippocampus. In primary hippocampal neurons, lipoprotein receptor-related protein was distributed somatodendritically and receptor-associated protein was concentrated perinuclearly. In hippocampal neurons from receptor-associated protein - / - mice, lipoprotein receptor-related protein was redistributed over the cell body at the expense of the dendrites. In the absence of receptor-associated protein, maturation of lipoprotein receptor-related protein is slow, resulting in accumulation of the uncleaved 600,000 mol. wt precursor. Neither the added expression of apolipoprotein E4 nor that of amyloid precursor protein in cultured neurons influenced the maturation of lipoprotein receptor-related protein, in either the presence or absence of receptor-associated protein. This result shows that receptor-associated protein is not needed to allow co-expression of lipoprotein receptor-related protein with these ligands in neurons. Furthermore, the typical ramified neuronal morphology of cultured primary neurons and the histology and architecture of the brain were normal in receptor-associated protein - / - mice and in all of the double transgenic mice. Finally, we demonstrated that the survival of receptor-associated protein - /- hippocampal neurons was normal and unaffected by the genotype of the glial feeder cells, whether they were derived from wild-type mice or from mice deficient in receptor-associated protein or apolipoprotein E. These results show that, despite the dramatic effect on maturation and cellular localization of lipoprotein receptor-related protein, the absence of receptor-associated protein did not result in any notable physiological, functional or morphological effects.
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Affiliation(s)
- L Umans
- Experimental Genetics Group, Center for Human Genetics, Flemish Institute for Biotechnology, K.U. Leuven, Belgium
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32
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Umans L, Overbergh L, Serneels L, Tesseur I, Van Leuven F. Analysis of expression of genes involved in apolipoprotein E-based lipoprotein metabolism in pregnant mice deficient in the receptor-associated protein, the low density lipoprotein receptor, or apolipoprotein E. Biol Reprod 1999; 61:1216-25. [PMID: 10529267 DOI: 10.1095/biolreprod61.5.1216] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Mice deficient in receptor-associated protein (RAP) were phenotypically normal, but in contrast to results previously reported in RAP(-/-) mice, nearly 50% of the offspring died at or shortly after birth. To attempt to determine the reason for this, we analyzed the regulation of expression of genes involved in apolipoprotein E (apoE)-based mechanisms in RAP-deficient mice and compared this to results in mice deficient in low density lipoprotein receptor (LDLR) or apoE. The major finding concerned a large increase in hepatic lipoprotein receptor-related protein (LRP) mRNA and LDLR mRNA levels in pregnant RAP knockout mice. This is in contrast to the down-regulation of LRP mRNA and LDLR mRNA, which is normally seen in wild-type mice. Also in LDLR knockout mice, a significant up-regulation in expression of LRP mRNA was demonstrated. In apoE knockout mice, hepatic LRP mRNA did not change significantly, while hepatic LDLR mRNA expression was increased. In placenta and uterus, the deficiency of RAP did not markedly affect the expression of LRP and LDLR. Lipoprotein lipase mRNA and apoE mRNA increased during pregnancy in all mice, independent of their genetic status. The current study does not directly explain the increased mortality of RAP(-/-) pups. The data demonstrate, however, important relative changes in expression of the genes analyzed, an indication that LRP and LDLR play an important role in lipid metabolism during pregnancy.
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Affiliation(s)
- L Umans
- Experimental Genetics Group, Center for Human Genetics (CME), Flemish Institute for Biotechnology (VIB), Katholieke Universiteit Leuven, Campus Gasthuisberg, B-3000 Leuven, Belgium
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33
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Muller L, Lindberg I. The cell biology of the prohormone convertases PC1 and PC2. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 1999; 63:69-108. [PMID: 10506829 DOI: 10.1016/s0079-6603(08)60720-5] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Mature peptide hormones and neuropeptides are typically synthesized from much larger precursors and require several posttranslational processing steps--including proteolytic cleavage--for the formation of the bioactive species. The subtilisin-related proteolytic enzymes that accomplish neuroendocrine-specific cleavages are known as prohormone convertases 1 and 2 (PC1 and PC2). The cell biology of these proteases within the regulated secretory pathway of neuroendocrine cells is complex, and they are themselves initially synthesized as inactive precursor molecules. ProPC1 propeptide cleavage occurs rapidly in the endoplasmic reticulum, yet its major site of action on prohormones takes place later in the secretory pathway. PC1 undergoes an interesting carboxyl terminal processing event whose function appears to be to activate the enzyme. ProPC2, on the other hand, exhibits comparatively long initial folding times and exits the endoplasmic reticulum without propeptide cleavage, in association with the neuroendocrine-specific protein 7B2. Once the proPC2/7B2 complex arrives at the trans-Golgi network, 7B2 is internally cleaved into two domains, the 21-kDa fragment and a carboxy-terminal 31 residue peptide. PC2 propeptide removal occurs in the maturing secretory granule, most likely through autocatalysis, and 7B2 association does not appear to be directly required for this cleavage event. However, if proPC2 has not encountered 7B2 intracellularly, it cannot generate a catalytically active mature species. The molecular mechanism behind the intriguing intracellular association of 7B2 and proPC2 is still unknown, but may involve conformational rearrangement or stabilization of a proPC2 conformer mediated by a 36-residue internal segment of 21-kDa 7B2.
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Affiliation(s)
- L Muller
- Department of Biochemistry and Molecular Biology, Louisiana State University Medical Center, New Orleans 70112, USA
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34
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Christensen EI, Willnow TE. Essential role of megalin in renal proximal tubule for vitamin homeostasis. J Am Soc Nephrol 1999; 10:2224-36. [PMID: 10505701 DOI: 10.1681/asn.v10102224] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Affiliation(s)
- E I Christensen
- Department of Cell Biology, Institute of Anatomy, University of Aarhus, Denmark.
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35
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Abstract
The low-density lipoprotein (LDL) receptor (LDL-R) family consists of cell-surface receptors that recognize extracellular ligands and internalize them for degradation by lysosomes. The LDL-R is the prototype of this family, which also contains very-low-density lipoprotein receptors (VLDL-R), apolipoprotein E receptor 2, LRP, and megalin. The family members contain four major structural modules: the cysteine-rich complement-type repeats, epidermal growth factor precursor-like repeats, a transmembrane domain, and a cytoplasmic domain. Each structural module serves distinct and important functions. These receptors bind several structurally dissimilar ligands. It is proposed that instead of a primary sequence, positive electrostatic potential in different ligands constitutes a receptor binding domain. This family of receptors plays crucial roles in various physiologic functions. LDL-R plays an important role in cholesterol homeostasis. Mutations cause familial hypercholesterolemia and premature coronary artery disease. LDL-R-related protein plays an important role in the clearance of plasma-activated alpha 2-macroglobulin and apolipoprotein E-enriched lipoproteins. It is essential for fetal development and has been associated with Alzheimer's disease. Megalin is the major receptor in absorptive epithelial cells of the proximal tubules and an antigenic determinant for Heymann nephritis in rats. Mutations in a chicken homolog of VLDL-R cause female sterility and premature atherosclerosis. This receptor is not expressed in liver tissue; however, transgenic expression of VLDL-R in liver corrects hypercholesterolemia in experiment animals, which suggests that it can be a candidate for gene therapy for various hyperlipidemias. The functional importance of individual receptors may lie in their differential tissue expression. The regulation of expression of these receptors occurs at the transcriptional level. Expression of the LDL-R is regulated by intracellular sterol levels involving novel membrane-bound transcription factors. Other members of the family are not regulated by sterols. All the members are, however, regulated by hormones and growth factors, but the mechanisms of regulation by hormones have not been elucidated. Studies of these receptors have provided important insights into receptor structure-function and mechanisms of ligand removal and catabolism. It is anticipated that increased knowledge about the LDL-R family members will open new avenues for the treatment of many disorders.
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Affiliation(s)
- M M Hussain
- Department of Biochemistry, MCP Hahnemann University, Philadelphia, Pennsylvania 19129, USA.
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36
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Hermo L, Lustig M, Lefrancois S, Argraves WS, Morales CR. Expression and regulation of LRP-2/megalin in epithelial cells lining the efferent ducts and epididymis during postnatal development. Mol Reprod Dev 1999; 53:282-93. [PMID: 10369389 DOI: 10.1002/(sici)1098-2795(199907)53:3<282::aid-mrd4>3.0.co;2-a] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Low density lipoprotein receptor-related protein-2/megalin (LRP-2) is a receptor belonging to the low density lipoprotein receptor family that mediates endocytosis and lysosomal degradation of a variety of ligands including apolipoprotein J (Apo J)/clusterin/SGP-2. LRP-2 has been shown to be expressed regionally in the adult rat epididymis. In this study, we describe the pattern of expression of LRP-2 in the efferent ducts and epididymis during postnatal development of the rat and examine the role of testicular luminally derived substances on its expression. The expression of LRP-2 was analyzed immunocytochemically in tissues of normal animals ranging in age from postnatal day 7-90 and in 15-day-old efferent-duct-ligated animals sacrificed at later ages. In the efferent ducts, LRP-2 expression, appearing as a dense band on the apical surface of the nonciliated epithelial cells, was noted as early as day 7, well before the entry of sperm, Sertoli-cell-derived secretory products, and high levels of androgens. Efferent duct ligation studies further revealed that expression under this condition was comparable to controls at all later ages examined, suggesting that the factor regulating its expression was not a luminally derived testicular substance. In normal untreated animals, LRP-2 expression was not apparent at any of the ages examined in the proximal initial segment of the epididymis. By comparison, the distal initial segment, although having no LRP-2 expression from 7-15 days, showed expression in principal cells by day 21 which intensified at days 29 and 39. However, by day 49 and at later ages (56 and 90), LRP-2 immunoreactivity over principal cells became spotty or with weak or moderate reactivity in some cells and none in others. LRP-2 expression in the intermediate zone, proximal caput, corpus, and cauda regions also appeared in principal cells by day 21, intensified at days 29 and 39 and persisted as such at all later ages examined, correlating with high levels of androgens shown to occur by day 39. Although LRP-2 expression in the distal caput region was evident in principal cells at days 21 and 29, it became spotty with weak, moderate, or absent reactivity over principal cells at all later ages. These data suggest that LRP-2 expression is under the influence of both stimulatory and region-specific inhibitory factors. Analysis of 15-day-old efferent-duct-ligated animals at all later ages examined revealed that there was no change in LRP-2 expression along the entire epididymis, suggesting that both the stimulatory and inhibitory factors are not luminally derived testicular substances. The observed pattern of LRP-2 expression in all regions of the epididymis, except the distal caput region, was similar to that described for Apo J internalization by principal cells during postnatal development, showing a correlation between LRP-2 expression and its ligand, Apo J. In summary, LRP-2 expression in the epididymis undergoes region-specific changes during postnatal development and appears to be influenced by both stimulatory and inhibitory factors.
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Affiliation(s)
- L Hermo
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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37
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Ranganathan S, Knaak C, Morales CR, Argraves WS. Identification of low density lipoprotein receptor-related protein-2/megalin as an endocytic receptor for seminal vesicle secretory protein II. J Biol Chem 1999; 274:5557-63. [PMID: 10026171 DOI: 10.1074/jbc.274.9.5557] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The low density lipoprotein receptor-related protein-2/megalin (LRP-2) is an endocytic receptor that is expressed on the apical surfaces of epithelial cells lining specific regions of the male and female reproductive tracts. In the present study, immunohistochemical staining revealed that LRP-2 is also expressed by epithelial cells lining the ductal region and the ampulla of the rat seminal vesicle. To identify LRP-2 ligands in the seminal vesicle, we probed seminal vesicle fluid with 125I-labeled LRP-2 in a gel-blot overlay assay. A 100-kDa protein (under non-reducing conditions) was found to bind the radiolabeled receptor. The protein was isolated and subjected to protease digestion, and the proteolytic fragments were subjected to mass spectroscopic sequence analysis. As a result, the 100-kDa protein was identified as the seminal vesicle secretory protein II (SVS-II), a major constituent of the seminal coagulum. Using purified preparations of SVS-II and LRP-2, solid-phase binding assays were used to show that the SVS-II bound to the receptor with high affinity (Kd = 5.6 nM). The binding of SVS-II to LRP-2 was inhibited using a known antagonist of LRP-2 function, the 39-kDa receptor-associated protein RAP. Using a series of recombinant subfragments of SVS-II, the LRP-2 binding site was mapped to a stretch of repeated 13-residue modules located in the central portion of the SVS-II polypeptide. To evaluate the ability of LRP-2 to mediate 125I-SVS-II endocytosis and lysosomal degradation, ligand clearance assays were performed using differentiated mouse F9 cells, which express high levels of LRP-2. Radiolabeled SVS-II was internalized and degraded by the cells, and both processes were inhibited by antibodies to LRP-2 or by RAP. The results indicate that LRP-2 binds SVS-II and can mediate its endocytosis leading to lysosomal degradation.
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Affiliation(s)
- S Ranganathan
- Cell Biology and Anatomy Department, Medical University of South Carolina, Charleston, South Carolina 29425-2204, USA
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38
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Ziak M, Kerjaschki D, Farquhar MG, Roth J. Identification of megalin as the sole rat kidney sialoglycoprotein containing poly alpha2,8 deaminoneuraminic acid. J Am Soc Nephrol 1999; 10:203-9. [PMID: 10215318 DOI: 10.1681/asn.v102203] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022] Open
Abstract
Recently, poly alpha2,8 deaminoneuraminic acid (poly alpha2,8 KDN) was demonstrated in various embryonic and adult mammalian tissues. This study reports the purification and characterization of the single poly alpha2,8 KDN-bearing glycoprotein from rat kidney. Amino acid sequences of proteolytic fragments shared homology with megalin, a member of the LDL receptor family. Immunochemical analysis supported this finding, since immunoprecipitated poly alpha2,8 KDN-bearing glycoprotein was immunoreactive with anti-megalin antibodies in Western blotting and conversely immunoprecipitated megalin was immunoreactive with the monoclonal anti-poly alpha2,8 KDN antibody. Furthermore, receptor-associated protein affinity-purified megalin reacted with the anti-poly alpha2,8 KDN antibody. By immunoelectron microscopy, labeling for both poly alpha2,8 KDN and megalin coincided in the brush border, endocytic invaginations and vesicles, and apical dense tubules of proximal convoluted tubules. Immunoreactivity for poly alpha2,8 KDN on purified megalin was abolished by beta-elimination reaction but not by N-glycosidase F treatment. These data identified megalin as the sole glycoprotein of rat kidney, which contains poly alpha2,8 KDN present on O-glycosidically linked oligosaccharides. Furthermore, this study shows that megalin carries N-glycosidically linked hybrid and complex-type oligosaccharides terminating with sialic acid. Both poly alpha2,8 KDN and sialic acids on megalin may contribute to the binding of Ca2+ and cationic ligands.
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Affiliation(s)
- M Ziak
- Department of Pathology, University of Zürich, Switzerland
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39
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Medved LV, Migliorini M, Mikhailenko I, Barrientos LG, Llinás M, Strickland DK. Domain organization of the 39-kDa receptor-associated protein. J Biol Chem 1999; 274:717-27. [PMID: 9873007 DOI: 10.1074/jbc.274.2.717] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 39-kDa receptor-associated protein (RAP) is an endoplasmic reticulum resident protein that binds to the low density lipoprotein receptor-related protein (LRP) as well as certain members of the low density lipoprotein receptor superfamily and antagonizes ligand binding. In order to identify important functional regions of RAP, studies were performed to define the domain organization and domain boundaries of this molecule. Differential scanning calorimetry (DSC) experiments revealed that the process of thermal denaturation of RAP is highly reversible and occurs in a broad temperature range with two well resolved heat absorption peaks. A good fit of the endotherm was obtained with four two-state transitions suggesting these many cooperative domains in the molecule. A number of recombinant fragments of RAP were expressed in bacteria, and their domain composition and stability were characterized by DSC, circular dichroism, and fluorescence spectroscopy. The results confirmed that RAP is composed of four independently folded domains, D1, D2, D3, and D4, that encompass residues 1-92, 93-163, 164-216, and 217-323, respectively. The first and the fourth domains preserved their structure and stability when isolated, whereas the compact structure of the fragment corresponding to D2 seems to be altered when isolated from the parent molecule. Isolated D3 was partially degraded during isolation from bacterial lysates. The isolated D4 was capable of binding with high affinity to LRP whereas neither D1 nor D2 bound. At the same time a fragment containing both D1 and D2 exhibited high affinity binding to LRP. These facts combined with the thermodynamic analysis of the melting process of the fragments containing D1 and D2 indicate that these two domains interact with each other and that the proper folding of the second domain into a native-like active conformation requires presence of the first domain.
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Affiliation(s)
- L V Medved
- Department of Biochemistry, Holland Laboratory, American Red Cross, Rockville, Maryland 20855, USA
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40
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Li Y, Wood N, Yellowlees D, Donnelly PK. Expression of alpha2-macroglobulin receptor-associated protein in normal human epidermal melanocytes and human melanoma cell lines. J Cell Biochem 1998; 71:149-57. [PMID: 9779814 DOI: 10.1002/(sici)1097-4644(19981101)71:2<149::aid-jcb1>3.0.co;2-v] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Alpha2-Macroglobulin receptor/low-density lipoprotein receptor-related protein is a multifunctional cell surface receptor known to bind and internalize a large number of ligands. alpha2-Macroglobulin receptor-associated protein acts as an intracellular "chaperone" for this receptor, and it has been shown to inhibit binding of all its known ligands. In this paper, we characterize the expression of the receptor-associated protein in both normal human epidermal melanocytes and in six different human melanoma cell lines, by the use of flow cytometry and Western blotting analysis. We show that all the melanoma cell lines and the normal melanocytes express the receptor-associated protein at similar levels, with most located intracellularly. No receptor-associated protein was detected at the cell surface in the melanocytes or in three of the cell lines. However, in two of the melanoma cell lines, large amounts of receptor-associated protein were found on the cell surface, these having the largest amounts of it reported to date; in a further melanoma cell line, there was a small amount at the cell surface. We have also shown that the melanocytes and all the melanoma cell lines express the receptor itself at a wide range of levels, the highest levels of both the cell surface receptor and the cell surface receptor-associated protein being found in one particular melanoma cell line. By growing the cell lines under controlled conditions, we have demonstrated that, although the total cellular content of the receptor is markedly increased at high cell culture density, this treatment has no effect on the level of expression of the receptor-associated protein.
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Affiliation(s)
- Y Li
- Department of Surgery, North Queensland Clinical School, University of Queensland, Townsville, Australia
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Van Leuven F, Thiry E, Stas L, Nelissen B. Analysis of the human LRPAP1 gene coding for the lipoprotein receptor-associated protein: identification of 22 polymorphisms and one mutation. Genomics 1998; 52:145-51. [PMID: 9782079 DOI: 10.1006/geno.1998.5413] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The lipoprotein receptor-associated protein (RAP) is considered a chaperone protein for the lipoprotein receptor-related protein (LRP) and for the other members of the LDL receptor family. Genetic analysis is anticipated to help in delineating groups or individuals with potential defects or problems in this regard. A combined amplification/sequencing strategy was developed to analyze the human LRPAP1 gene for polymorphisms and mutations. The LRPAP1 gene was amplified from genomic DNA in four long-range PCR amplicons, 2.4 to 7.6 kb in size. Three amplicons were finally used as templates with 14 sequencing primers to obtain the sequence of the eight exons and large portions of adjacent introns from individual DNA. This strategy, applied to sequence the LRPAP1 gene of 14 unrelated, normal individuals revealed, in total, 23 distinct mutations and polymorphisms, mostly intronic substitutions and deletions. In this small group 1 expressed mutation was encountered on one allele in 2 unrelated individuals: a G to A transition results in the replacement of valine by methionine in exon 7 at position 311 of the human RAP precursor protein.
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Affiliation(s)
- F Van Leuven
- Center for Human Genetics, Flemish Institute for Biotechnology, K. U. Leuven, Campus Gasthuisberg, Leuven, B-3000, Belgium.
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Foiani M, Ferrari M, Liberi G, Lopes M, Lucca C, Marini F, Pellicioli A, Muzi Falconi M, Plevani P. S-phase DNA damage checkpoint in budding yeast. Biol Chem 1998; 379:1019-23. [PMID: 9792433 DOI: 10.1515/bchm.1998.379.8-9.1019] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Eukaryotic cells must be able to coordinate DNA repair, replication and cell cycle progression in response to DNA damage. A failure to activate the checkpoints which delay the cell cycle in response to internal and external cues and to repair the DNA lesions results in an increase in genetic instability and cancer predisposition. The use of the yeast Saccharomyces cerevisiae has been invaluable in isolating many of the genes required for the DNA damage response, although the molecular mechanisms which couple this regulatory pathway to different DNA transactions are still largely unknown. In analogy with prokaryotes, we propose that DNA strand breaks, caused by genotoxic agents or by replication-related lesions, trigger a replication coupled repair mechanism, dependent upon recombination, which is induced by the checkpoint acting during S-phase.
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Affiliation(s)
- M Foiani
- Dipartimento di Genetica e di Biologia dei Microorganismi, Universita' degli Studi di Milano, Italy.
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Wheal HV, Chen Y, Mitchell J, Schachner M, Maerz W, Wieland H, Van Rossum D, Kirsch J. Molecular mechanisms that underlie structural and functional changes at the postsynaptic membrane during synaptic plasticity. Prog Neurobiol 1998; 55:611-40. [PMID: 9670221 DOI: 10.1016/s0301-0082(98)00026-4] [Citation(s) in RCA: 75] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The synaptic plasticity that is addressed in this review follows neurodegeneration in the brain and thus has both structural as well as functional components. The model of neurodegeneration that has been selected is the kainic acid lesioned hippocampus. Degeneration of the CA3 pyramidal cells results in a loss of the Schaffer collateral afferents innervating the CA1 pyramidal cells. This is followed by a period of structural plasticity where new synapses are formed. These are associated with changes in the numbers and shapes of spines as well as changes in the morphometry of the dendrites. It is suggested that this synaptogenesis is responsible for an increase in the ratio of NMDA to AMPA receptors mediating excitatory synaptic transmission at these synapses. Changes in the temporal and spatial properties of these synapses resulted in an altered balance between LTP and LTD. These properties together with a reduction in the inhibitory drive increased the excitability of the surviving CA1 pyramidal cells which in turn triggered epileptiform bursting activity. In this review we discuss the insights that may be gained from studies of the underlying molecular machinery. Developments in one of the collections of the cogs in this machinery has been summarized through recent studies characterizing the roles of neural recognition molecules in synaptic plasticity in the adult nervous systems of vertebrates and invertebrates. Such investigations of neural cell adhesion molecules, cadherins and amyloid precursor protein have shown the involvement of these molecules on the morphogenetic level of synaptic changes, on the one hand, and signal transduction effects, on the other. Further complex cogs are found in the forms of the low-density lipoprotein receptor (LDL-R) family of genes and their ligands play pivotal roles in the brain development and in regulating the growth and remodelling of neurones. Evidence is discussed for their role in the maintenance of cognitive function as well as Alzheimer's. The molecular mechanisms responsible for the clustering and maintenance of transmitter receptors at postsynaptic sites are the final cogs in the machinery that we have reviewed. Postsynaptic densities (PSD) from excitatory synapses have yielded many cytoskeletal proteins including actin, spectrin, tubulin, microtubule-associated proteins and calcium/calmodulin-dependent protein kinase II. Isolated PSDs have also been shown to be enriched in AMPA, kainate and NMDA receptors. However, recently, a new family of proteins, the MAGUKs (for membrane-associated guanylate kinase) has emerged. The role of these proteins in clustering different NMDA receptor subunits is discussed. The MAGUK proteins are also thought to play a role in synaptic plasticity mediated by nitric oxide (NO). Both NMDA and non-NMDA receptors are highly clustered at excitatory postsynaptic sites in cortical and hippocampal neurones but have revealed differences in their choice of molecular components. Both GABAA and glycine (Gly) receptors mediate synaptic inhibition in the brain and spinal cord. Whilst little is known about how GABAA receptors are localized in the postsynaptic membrane, considerable progress has been made towards the elucidation of the molecular mechanisms underlying the formation of Gly receptors. It has been shown that the peripheral membrane protein gephyrin plays a pivotal role in the formation of Gly receptor clusters most likely by anchoring the receptor to the subsynaptic cytoskeleton. Evidence for the distribution as well as function of gephyrin and Gly receptors is discussed. Postsynaptic membrane specializations are complex molecular machinery subserving a multitude of functions in the proper communication between neurones. Despite the fact that only a few key players have been identified it will be a fascinating to watch the story as to how they contribute to structural and functional plasticity unfold.
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Affiliation(s)
- H V Wheal
- Neuroscience Research Group, School of Biological Sciences, University of Southampton, U.K..
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Bajari TM, Lindstedt KA, Riepl M, Mirsky VM, Nimpf J, Wolfbeis OS, Dresel HA, Bautz EK, Schneider WJ. A minimal binding domain of the low density lipoprotein receptor family. Biol Chem 1998; 379:1053-62. [PMID: 9792438 DOI: 10.1515/bchm.1998.379.8-9.1053] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
As more relatives of the low density lipoprotein receptor (LDLR) are discovered, defining their minimal binding domain(s) becomes a challenge. Here we have chosen the multifunctional chicken oocyte receptor for yolk deposition (termed LR8), and the pan-receptor ligand, receptor associated protein (RAP), as model systems to characterize a minireceptor using the phage display approach. Displayed fragments derived from the entire 819 residue LR8 molecule, followed by selection via panning on RAP, led to the definition of an 80 residue stretch LR8 minireceptor. It contains 12 cysteines, and represents parts of the second, the entire third, and parts of the fourth, of the eight clustered 'ligand binding repeats' in LR8; only two of the eight stretches of negatively charged residues of LR8, i.e., EDGSDE and DSGEDEE, are present. The latter sequence is reminiscent of that in the fifth repeat of the human LDLR, thought to be most critical for interaction with positive charge clusters in ligands. Baculovirus-mediated expression of the soluble minireceptor in insect cells showed it to fold as a monomer, and sulfhydryl-reduction-sensitive interaction with RAP was demonstrated for immobilized as well as soluble minireceptor. Furthermore, the LR8-derived minireceptor provided a RAP-responsive surface when covalently coupled to the surface of a gold electrode. In addition to its use in defining minimal binding domains, the phage display approach provides powerful tools for dissection, and consequently, manipulation, of the function of receptors so as to direct their binding activity toward ligands of diagnostic and/or therapeutic interest.
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Affiliation(s)
- T M Bajari
- Department of Molecular Genetics, University of Heidelberg, Germany
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Abstract
Members of the low-density lipoprotein (LDL) receptor gene family play an important role in cellular uptake of various extracellular ligands. Recent studies have shown that a 39-kDa protein known as RAP (receptor-associated protein) serves as a molecular chaperone to assist the folding of certain LDL-receptor family proteins and their passage through the secretory pathway. In this review, the authors discuss our current understanding of the roles of RAP as a molecular chaperone/escort protein and present a model of how RAP might carry out these functions.
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Affiliation(s)
- G Bu
- Dept of Pediatrics, Washington University School of Medicine, St Louis, MO 63110, USA
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Bu G. Receptor-associated protein: a specialized chaperone and antagonist for members of the LDL receptor gene family. Curr Opin Lipidol 1998; 9:149-55. [PMID: 9559273 DOI: 10.1097/00041433-199804000-00012] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Members of the LDL receptor gene family mediate cellular uptake of various extracellular ligands, including lipoprotein particles. Ligand interactions with these receptors can be antagonized by a 39 kDa receptor-associated protein. Recent biochemical, cellular, and genetic studies have shown that receptor-associated protein is a molecular chaperone/escort protein for LDL receptor-related protein, a member of the LDL receptor gene family that binds multiple ligands. These studies indicate that receptor-associated protein interacts with LDL receptor-related protein at multiple sites and assists the proper folding and disulfide bond formation of LDL receptor-related protein within the endoplasmic reticulum. Following the completion of folding, receptor-associated protein remains associated with the receptor during its subsequent trafficking along the early secretory pathway, thereby preventing premature ligand interaction with the receptor. The ability of receptor-associated protein to universally inhibit ligand interactions with members of the LDL receptor gene family underscores the use of this protein as a tool in the study of ligand-receptor interactions.
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Affiliation(s)
- G Bu
- Department of Pediatrics, Washington University School of Medicine, St. Louis, MO 63110, USA
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Christensen EI, Birn H, Verroust P, Moestrup SK. Membrane receptors for endocytosis in the renal proximal tubule. INTERNATIONAL REVIEW OF CYTOLOGY 1998; 180:237-84. [PMID: 9496636 DOI: 10.1016/s0074-7696(08)61772-6] [Citation(s) in RCA: 127] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The renal proximal tubule exhibits a very extensive apical endocytic apparatus consisting of an elaborate network of coated pits and small coated and noncoated endosomes. In addition, the cells contain a large number of late endosomes/prelysosomes, lysosomes, and so-called dense apical tubules involved in receptor recycling from the endosomes to the apical plasma membrane. This endocytic apparatus is involved in the reabsorption of molecules filtered in the glomeruli. The process is very effective as demonstrated by the fact that although several grams of protein are filtered daily in the human glomeruli, human urine is virtually devoid of proteins under physiological conditions. Several key receptors appear to be involved in this function, which serves not only to conserve protein as such for the organism but also to reabsorb vital substances such as different vitamins in complex with their binding proteins. Recent research has established megalin, a 600-kDa protein belonging to the LDL receptor family, as probably the most important receptor in this process in the proximal tubule mediating endocytosis of a large variety of ligands and therefore classifying it as a scavenger receptor. More specific receptors like the folate receptor, IGF-II/Man-6-P receptor, and gp280/IFR, identical to the intrinsic factor receptor, are also functioning in the apical endocytic pathway of renal proximal tubules. A better understanding of these receptors will give us new insight into these very important processes for the organism.
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Christensen EI, Birn H, Verroust P, Moestrup SK. Megalin-mediated endocytosis in renal proximal tubule. Ren Fail 1998; 20:191-9. [PMID: 9574443 DOI: 10.3109/08860229809045102] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Megalin, a 600 kDa membrane protein belonging to the IDL receptor family is highly expressed in the endocytic pathway of renal proximal tubules. In addition, this receptor is found in several other epithelia facing transcellular fluids but is also expressed in the parathyroid glands. Recent studies have established this protein as probably the most important receptor for endocytosis of macromolecules filtered in the renal glomeruli. The ligands reported to bind to megalin consist of a variety of different substances including albumin, vitamin-carrier complexes, proteinases and proteinase-inhibitor complexes, lipoprotein particles, receptor associated protein (RAP), different drugs and calcium.
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Jung FF, Bachinsky DR, Tang SS, Zheng G, Diamant D, Haveran L, McCluskey RT, Ingelfinger JR. Immortalized rat proximal tubule cells produce membrane bound and soluble megalin. Kidney Int 1998; 53:358-66. [PMID: 9461095 DOI: 10.1046/j.1523-1755.1998.00766.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Megalin (gp330), a glycoprotein receptor found on renal proximal tubule cells and several other epithelial cells, is deduced to be a type I integral membrane protein, but may also exist as a cell surface form lacking a cytoplasmic domain. Furthermore, soluble megalin products have been detected in urine, and in culture medium of a rat yolk sac carcinoma cell line, combined with receptor associated protein (RAP). Permanent renal cell lines expressing megalin were unavailable until the recent description of two immortalized rat proximal tubule cell lines (IRPTC). The present study demonstrated megalin on IRPTC surface by immunofluorescence, without surface staining for RAP, which was, however, readily detected within cells. Antibodies to ectodomain megalin epitopes immunoprecipitated megalin products both from cell lysates and culture medium, whereas antibodies to cytoplasmic domain epitopes precipitated megalin only from lysates. Western blots showed two major megalin products in medium, a prominent band at approximately 200 kDa, and a fainter band above 400 kDa, slightly below intact megalin in cell lysates. Anti-receptor associated protein antibodies immunoprecipitated megalin from IRPTC lysates, but not from media. We propose that portions of megalin are spontaneously produced by IRPTC, probably either by cleavage in the ectodomain or release of forms lacking a cytoplasmic domain.
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Affiliation(s)
- F F Jung
- Pediatric Renal Research Laboratory, Massachusetts General Hospital, Boston 02114, USA
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50
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Cell Polarity and Mouse Early Development. ACTA ACUST UNITED AC 1998. [DOI: 10.1016/s1569-2558(08)60019-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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