Megalin Antagonizes Activation of the Parathyroid Hormone Receptor

doi:10.1074/jbc.274.9.5620

Megalin Antagonizes Activation of the Parathyroid Hormone Receptor*

From the ^‡Franz-Volhard-Clinic, Humboldt-University and ^§Max-Delbrueck Center for Molecular Medicine, 13125 Berlin, Germany, Departments of ^¶Medical Biochemistry and ^‖Cell Biology, University of Aarhus, 8000 Aarhus, Denmark

Abstract

Parathyroid hormone (PTH) is predominantly cleared from the circulation by glomerular filtration and degradation in the renal proximal tubules. Here, we demonstrate that megalin, a multifunctional endocytic receptor in the proximal tubular epithelium, mediates the uptake and degradation of PTH. Megalin was purified from kidney membranes as the major PTH-binding protein and shown in BIAcore analysis to specifically bind full-length PTH and amino-terminal PTH fragments (K _d 0.5 μm). Absence of the receptor in megalin knockout mice resulted in 4-fold increased levels of amino-terminal PTH fragments in the urine. In F9 cells expressing both megalin and the PTH/PTH-related peptide receptor (PTH/PTHrP receptor), uptake and lysosomal degradation of the hormone was mediated through megalin. Blocking megalin-mediated clearance of PTH resulted in 3-fold increased stimulation of the PTH/PTHrP receptor. These data provide evidence that megalin is involved in the renal catabolism of PTH and potentially antagonizes PTH/PTHrP receptor activity in the proximal tubular epithelium.

Footnotes

↵* This work was supported in part by grant Wi 1158/3-1 and a Heisenberg fellowship (to T. E. W.) from the Deutsche Forschungsgemeinschaft and by the Danish Medical Research Council and the Novo Nordic Foundation.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵** To whom correspondence should be addressed: Max-Delbrueck Center, R.-Roessle-Strasse 10, D-13125 Berlin, Germany. Tel.: 49-30-9406-2569; Fax: 49-30-9406-2110; E-mail: willnow{at}mdc-berlin.de.
↵2 A. Nykjaer, H. Vorum, D. Dragun, D. Walther, C. Jacobsen, J. Herz, F. Melsen, E. I. Christensen, and T. E. Willnow, manuscript submitted for publication.
↵3 J. Hilpert, A. Nykjaer, C. Jacobsen, G. Wallukat, R. Nielsen, S. K. Moestrup, H. Haller, F. C. Luft, E. I. Christensen, and T. E. Willnow, unpublished observations.
Abbreviations:

PTH

parathyroid hormone

LDL

low density lipoprotein

CHAPS

3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid

DMEM

Dulbecco’s modified Eagle’s medium

RAP

receptor-associated protein

GST

glutathione S-transferase

PAGE

polyacrylamide gel electrophoresis

IGF

insulin-like growth factor
- Received October 8, 1998.
- Revision received November 23, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.