Cadmium impairs albumin reabsorption by down-regulating megalin and ClC5 channels in renal proximal tubule cells.

Content Provider	Europe PMC
Author	Gena, Patrizia Calamita, Giuseppe Guggino, William B.
Copyright Year	2010
Abstract	BackgroundCadmium (Cd) is a potent nephrotoxicant that impairs the reabsorptive and secretory functions of the renal proximal tubule, leading to albuminuria.ObjectivesTo gain insights into the mechanisms of Cd-induced albuminuria, we investigated effects of Cd on the expression of megalin and chloride channel 5 (ClC5), two key players in albumin- receptor–mediated endocytosis.MethodsWe used quantitative polymerase chain reaction, Western blotting, the albumin endocytosis assay, and confocal microscopy to evaluate effects of Cd on the expression and regulation of megalin and ClC5 in cultured LLC-PK1 cells, a pig proximal tubular cell model.ResultsTen micromolar cadmium chloride (CdCl2) caused a significant time- and dose-dependent decrease in both mRNA and protein levels of megalin and ClC5, whereas no changes resulted from exposure to other divalent metals (zinc chloride, manganese chloride, magnesium chloride, and nickel chloride). After inhibiting protein synthesis using cycloheximide (CHX), we found that levels of both megalin and ClC5 were lower in Cd-challenged cells than in cells treated with Cd or CHX only, which is consistent with reduced translation and/or posttranslational down-regulation. Moreover, Cd-induced degradation of megalin and ClC5 was abolished by the lysosomal pathway inhibitor bafilomycin A-1 but not by the proteasome system blocker MG-132, suggesting that the enhanced proteolysis was occurring via lysosomes. Using confocal microscopy, we observed a remarkable reduction of fluoroisothiocyanate (FITC)-labeled albumin uptake after Cd exposure.ConclusionsWe found that Cd reduced the transcriptional expression of megalin and ClC5 and, at the same time, increased the degradation of megalin and ClC5 proteins via the lysosomal pathway in an in vitro model of renal proximal tubular cells. Overall, these results provide valuable insights into the molecular mechanisms by which Cd impairs luminal protein reabsorption by renal proximal tubules.
ISSN	00916765
Journal	Environmental Health Perspectives
Volume Number	118
PubMed Central reference number	PMC2974692
Issue Number	11
PubMed reference number	20576581
e-ISSN	15529924
DOI	10.1289/ehp.0901874
Language	English
Publisher	National Institute of Environmental Health Sciences
Publisher Date	2010-11-01
Access Restriction	Open
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Subject Keyword	albuminuria cadmium ClC5 heavy metals megalin nephrotoxicity renal proximal tubules
Content Type	Text
Resource Type	Article
Subject	Health, Toxicology and Mutagenesis Public Health, Environmental and Occupational Health