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Colocalization of the novel plasminogen receptor, Plg‐RKT, with the epithelial sodium channel (ENaC)
Author(s) -
Chen Kevin W,
Bai Hongdong,
Kiosses William B,
Krajewski Stan,
Miles Lindsey A,
Parmer Robert J
Publication year - 2010
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.24.1_supplement.786.22
Subject(s) - colocalization , chemistry , epithelial sodium channel , plasmin , urokinase receptor , receptor , microbiology and biotechnology , confocal microscopy , biology , sodium , biochemistry , enzyme , organic chemistry
Binding of plasminogen (Plg) to cells via specific receptors markedly enhances Plg activation, and localizes the proteolytic activity of plasmin (P) on cell surfaces. Exposure of kidney tubular cells to P results in cleavage and activation of ENaC leading to increased Na + uptake, and Na + retention in nephrotic syndrome in which Plg is present in urine. We recently isolated a novel transmembrane Plg receptor, Plg‐R KT , from macrophages. Here, we examined kidney cells for the presence and subcellular localization of Plg‐R KT as a potential component of the mechanism in which P processes ENaC. Human kidney sections were stained with specific monoclonal anti‐Plg‐R KT . Strong staining was observed in distal tubular epithelium (intensity=200–256) > proximal tubular cells (intensity=140–199) ≫ glomeruli (intensity=80–139). In western blotting of MDCK cells and M1 mouse collecting duct cells Plg‐R KT was highly expressed in membrane fractions, but was not detected in cytoplasm. Using confocal microscopy, Plg‐R KT was immunodetected on the apical surface, an orientation allowing for interaction with urinary Plg. Furthermore, in merged images, Plg‐R KT colocalized with both ENaC and the urokinase receptor (uPAR). The extent of colocalization of Plg‐R KT with ENaC was 98±1% and 89±3% in MDCK and M1 cells, respectively, and with uPAR was 96±1% in both cell types. Thus, Plg‐R KT , uPAR and ENaC are present in very close proximity on the kidney tubular cell surface in an orientation to promote Plg activation and ENaC processing.