engleski

Cadmium increases the expression of multidrug resistance P-glycoprotein in rat kidney proximal tubule cells through an oxidative mechanism

Multidrug resistance P-glycoprotein (mdr1) is a membrane protein of 150-170 kD that catalyzes the ATP-driven efflux of hydrophobic, potentially cytotoxic endogenous and xenobiotic compounds from cells. Expressed in many apithelial tissues, including the kidney proximal tubule (PT), the mdr1 protein provides major routes of detoxification. We found that cadmium (Cd), a well-known environmental hazard with a potent nephrotoxic action, increases mdr1 expression in the brush-border of PT from the kidney cortex of Cd-intoxicated rats. The S1- and S2-segments of the PT from control rats had a weak apical expression of mdr1, as determined by indirect immunofluorescence of cryostat sections from kidney cortex and by Western blotting of isolated brush-border membranes (BBM) wiht mdr1 antibodies (C219 and anti-pgp 389). In rats, which had been treated in vivo with 2 mg Cd/kg b. w. for 14 days, mdr1 expression was increased in the brush-border of PT from kidney cortex. These observations were confirmed in vitro with an immortalized cell line (WKPT 0293 Cl.2) derived from the S1-segment of rat PT. Control cells expressed low levels of mdr1. Following incubation of WKPT 0293 Cl.2 cells with 5um CdCl2 for 3 days, the expression of mdr1 was clearly increased, but Cd-induced increase of mdr1 expression was prevented by co-incubation with the thiol antioxidants N-acetylcysteine (30 mM) or pyrollidenedithiocarbamate (0.1 mM). Mdr1 expression levels in WKPT 1293 Cl.2 cells also correlated well with a functional assay for mdr1-mediated transport, which measures the intracellular accumulation of the fluorescent probe calcein. The data indicate that Cd increases mdr1 expression in brush-border membranes of the S1- and S2- segments of rat kidney PT through an oxidative mechanism.

mdr1; cadmium; proximal tubule cell; rat

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