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Elevated hepatic multidrug resistance‐associated protein 3/ATP‐binding cassette subfamily C 3 expression in human obstructive cholestasis is mediated through tumor necrosis factor alpha and c‐Jun NH2‐terminal kinase/stress‐activated protein kinase–signaling pathway

Multidrug resistance‐associated protein 3 (MRP3, ABC subfamily C [ABCC]3) plays an important role in protecting hepatocytes and other tissues by excreting an array of toxic organic anion conjugates, including bile salts. MRP3/ABCC3 expression is increased in the liver of some cholestatic patients, but the molecular mechanism of this up‐regulation remains elusive. In this report, we assessed liver MRP3/ABCC3 expression in patients (n = 22) with obstructive cholestasis caused by gallstone blockage of bile ducts and noncholestatic patient controls (n = 22). MRP3/ABCC3 messenger RNA (mRNA) and protein expression were significantly increased by 3.4‐ and 4.6‐fold, respectively, in these cholestatic patients where elevated plasma tumor necrosis factor alpha (TNFα) (4.7‐fold; P < 0.01) and hepatic specificity protein 1 transcription factor (SP1) and liver receptor homolog 1 expression (3.1‐ and 2.1‐fold at mRNA level, 3.5‐ and 2.5‐fold at protein level, respectively) were also observed. The induction of hepatic MRP3/ABCC3 mRNA expression is significantly positively correlated with the level of plasma TNFα in these patients. In HepG2 cells, TNFα treatment induced SP1 and MRP3/ABCC3 expression in a dose‐ and time‐dependent manner, where increased phosphorylation of c‐Jun NH2‐terminal kinase/stress‐activated protein kinase (JNK/SAPK) was also detected. These inductions were significantly reduced in the presence of the JNK inhibitor, SP600125. TNFα treatment enhanced HepG2 cell nuclear extract‐binding activity to the MRP3/ABCC3 promoter, but was abolished by SP600125, as demonstrated by electrophoretic mobility shift assay (EMSA). An increase in nuclear protein‐binding activity to the MRP3/ABCC3 promoter, consisting primarily of SP1, was also observed in liver samples from cholestatic patients, as assessed by supershift EMSA assays. Conclusions: Our findings indicate that up‐regulation of hepatic MRP3/ABCC3 expression in human obstructive cholestasis is likely triggered by TNFα, mediated by activation of JNK/SAPK and SP1. (HEPATOLOGY 2012)