Lipocalin-2 (24p3/Neutrophil Gelatinase-associated Lipocalin (NGAL)) Receptor Is Expressed in Distal Nephron and Mediates Protein Endocytosis

• Published in: The Journal of biological chemistry 2012-01, Vol.287 (1), p.159-169
• Main Authors: Langelueddecke, Christian, Roussa, Eleni, Fenton, Robert A., Wolff, Natascha A., Lee, Wing-Kee, Thévenod, Frank
• Format: Article
• Language: English
• Subjects: Acute-Phase Proteins - metabolism; Albumins - metabolism; Amnionless; Animals; CHO Cells; Connecting Tubules; Cricetinae; Cricetulus; Endocytosis - drug effects; Gene Expression Regulation - drug effects; Kidney Medulla - cytology; Kidney Medulla - drug effects; Kidney Medulla - metabolism; Kidney Tubules, Distal - cytology; Kidney Tubules, Distal - drug effects; Kidney Tubules, Distal - metabolism; Lipocalin-2; Lipocalins - metabolism; Male; Membrane Biology; Membrane Transport; Metal Toxicity; Metalloproteins; Metallothionein - toxicity; Oncogene Proteins - metabolism; Proteinuria; Quinolinium Compounds - metabolism; Rats; Receptor Endocytosis; Renal Physiology; Siderophores; Transferrin - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.308296

In the kidney, bulk reabsorption of filtered proteins occurs in the proximal tubule via receptor-mediated endocytosis (RME) through the multiligand receptor complex megalin-cubilin. Other mechanisms and nephron sites for RME of proteins are unclear. Recently, the secreted protein 24p3 (lipocalin-2, neutrophil gelatinase-associated lipocalin (NGAL)), which is expressed in the distal nephron, has been identified as a sensitive biomarker of kidney damage. A high-affinity receptor for 24p3 (24p3R) that is involved in endocytotic iron delivery has also been cloned. We investigated the localization of 24p3R in rodent kidney and its role in RME of protein-metal complexes and albumin. Immunostaining of kidney tissue showed expression of 24p3R in apical membranes of distal tubules and collecting ducts, but not of proximal tubule. The differential expression of 24p3R in these nephron segments was confirmed in the respective cell lines. CHO cells transiently transfected with 24p3R or distal tubule cells internalized submicromolar concentrations of fluorescence-coupled proteins transferrin, albumin, or metallothionein (MT) as well as the toxic cadmium-MT (Cd2+7-MT) complex, which caused cell death. Uptake of MT or transferrin and Cd2+7-MT toxicity were prevented by picomolar concentrations of 24p3. An EC50 of 123 ± 50 nm was determined for binding of MT to 24p3R by microscale thermophoresis. Hence, 24p3R binds proteins filtered by the kidney with high affinity and may contribute to RME of proteins, including 24p3, and to Cd2+7-MT toxicity in distal nephron segments. Background: Localization and function of the lipocalin-2/NGAL/24p3 receptor (24p3R) in the kidney are unknown. Results: 24p3R is expressed in apical plasma membranes of the distal nephron and mediates high-affinity protein endocytosis in renal cells. Conclusion: 24p3R contributes to protein endocytosis and nephrotoxicity in distal nephron segments. Significance: This is the first study to investigate localization and function of 24p3R in relevant epithelia.