Cubilin is an albumin binding protein important for renal tubular albumin reabsorption
Henrik Birn, … , Søren K. Moestrup, Erik I. Christensen
Henrik Birn, … , Søren K. Moestrup, Erik I. Christensen
Published May 15, 2000
Citation Information: J Clin Invest. 2000;105(10):1353-1361. https://doi.org/10.1172/JCI8862.
View: Text | PDF
Article

Cubilin is an albumin binding protein important for renal tubular albumin reabsorption

Abstract

Using affinity chromatography and surface plasmon resonance analysis, we have identified cubilin, a 460-kDa receptor heavily expressed in kidney proximal tubule epithelial cells, as an albumin binding protein. Dogs with a functional defect in cubilin excrete large amounts of albumin in combination with virtually abolished proximal tubule reabsorption, showing the critical role for cubilin in the uptake of albumin by the proximal tubule. Also, by immunoblotting and immunocytochemistry we show that previously identified low–molecular-weight renal albumin binding proteins are fragments of cubilin. In addition, we find that mice lacking the endocytic receptor megalin show altered urinary excretion, and reduced tubular reabsorption, of albumin. Because cubilin has been shown to colocalize and interact with megalin, we propose a mechanism of albumin reabsorption mediated by both of these proteins. This process may prove important for understanding interstitial renal inflammation and fibrosis caused by proximal tubule uptake of an increased load of filtered albumin.

Authors

Henrik Birn, John C. Fyfe, Christian Jacobsen, Francoise Mounier, Pierre J. Verroust, Hans Ørskov, Thomas E. Willnow, Søren K. Moestrup, Erik I. Christensen

×

Figure 5

Options: View larger image (or click on image) Download as PowerPoint
Immunological cross-reaction and colocalization of antibodies raised aga...
Immunological cross-reaction and colocalization of antibodies raised against cubilin and antibodies against previously identified albumin binding proteins (ABP). (a) Immunoblotting using polyclonal anti-ABP antibody on affinity purified rat cubilin and rat kidney cortex. Both the IF-B12 and albumin affinity purified cubilin, as well as a similar band in rat kidney cortex, were recognized by the anti-ABP. (b and c) Fluorescent double labeling reveals identical labeling using rabbit anti-ABP (1:3,000) and monoclonal mouse anti-cubilin (1:5,000) on the same section of rat cortex followed by secondary TRITC labeled anti-rabbit IgG (red fluorescent in b) and FITC-labeled anti-mouse IgG (green fluorescent in c). The antibodies colocalize along the brush border and apical cytoplasm, as well as in vesicular structures in the proximal tubules. (d and e) Inhibition of labeling with anti-ABP by preincubation with IF-B12 affinity purified cubilin. Immunocytochemical labeling using anti-ABP (1:8,000) on cryosections of kidney cortex reveals proximal tubule apical labeling (d) that is clearly inhibited when the anti-ABP is preincubated with affinity purified cubilin (e). ×700.