In renal proximal tubule, multidrug resistance protein 2 (Mrp2) actively transports many organic anions into urine, including drugs and metabolic wastes. Upon exposure to nephrotoxicants or during endotoxemia, both Mrp2 activity and expression are up-regulated. This may result from induced de-novo synthesis of Mrp2 or post-transcriptional events involving specific signaling pathways. Here we investigated glucocorticoid signaling to Mrp2 in killifish renal proximal tubules, a model system in which transport activity can be measured using a fluorescent substrate and confocal imaging. Exposure of tubules to dexamethasone rapidly increased Mrp2-mediated fluorescein methotrexate (FL-MTX) transport. Other glucocorticoid receptor (GR)-ligands, cortisol and triamcinolone acetonide, also stimulated Mrp2-mediated transport. The GR-antagonist, RU486, abolished stimulation by all three ligands, whereas the mineralocorticoid receptor antagonist, spironolactone, was ineffective. Consistent with action through a nongenomic mechanism, dexamethasone stimulation of Mrp2-mediated transport was insensitive to cycloheximide and actinomycin D, and immunohistochemistry revealed no alterations in Mrp2 expression at the luminal membrane. K252a, an inhibitor of the tyrosine kinase TRK subfamily, reduced the dexamethasone effect, as did the specific c-Met receptor tyrosine kinase inhibitor, PHA-665752. Hepatocyte growth factor (HGF), endogenous ligand for c-Met, stimulated Mrp2-mediated transport. This effect was reversed by PHA-665752 but not by RU486. Inhibition of MEK1/2 also abolished the effects of dexamethasone and HGF. Our results disclose a novel mechanism by which glucocorticoids acting through GR, c-Met and MEK1/2 cause rapid, nongenomic stimulation of Mrp2-mediated transport in renal proximal tubules. This up-regulation may be nephroprotective, enhancing efflux of metabolic wastes and toxicants during cell and tissue stress.
- Received January 20, 2011.
- Revision received April 20, 2011.
- Accepted April 21, 2011.
- The American Society for Pharmacology and Experimental Therapeutics