Cytokines have been implicated in the pathogenesis of inflammatory cholestasis. This is due to transcriptional down-regulation of hepatic transporters including the Na ؉ /bile acid cotransporter, ntcp, and the multispecific organic anion exporter, mrp2. We have recently shown that ntcp suppression by lipopolysaccharide in vivo is caused by down-regulation of transactivators including the previously uncharacterized Footprint B-binding protein. Both the ntcp FpB element and the mrp2 promoter contain potential retinoid-response elements. We hypothesized that retinoic acid receptor (RAR) and retinoid X receptor (RXR) heterodimers would activate these two genes and that cytokines that reduce bile flow might do so by suppressing nuclear levels of these transactivators. Retinoid transactivation and interleukin-1␤ down-regulation of the ntcp and mrp2 promoters were mapped to RXR␣:RAR␣-response elements. Gel mobility shift assays demonstrated specific binding of RXR␣: RAR␣ heterodimers to the ntcp and mrp2 retinoid-response elements. The RXR␣:RAR␣ complex was downregulated by IL-1␤ in HepG2 cells. An unexpected finding was that an adjacent CAAT-enhancer-binding protein element was required for maximal transactivation of the ntcp promoter by RXR␣:RAR␣. Taken together, these studies demonstrate regulation of two hepatobiliary transporter genes by RXR␣:RAR␣ and describe a mechanism which likely contributes to their down-regulation during inflammation.

1 Monochloroacetic acid (MCAA) and its sodium salt, sodium monochloroacetate (SMCA) are widely used in chemical industries as intermediates in the synthesis of carboxymethylcellulose, phenoxyacetic acid, thio-glycolic acid, glycine, indigoid dyes and others. More-over, MCAA has been found as a by-product of the chlorination disinfection of drinking water and as an environmental contaminant of the atmosphere from the photodechlorination reactions of chlorinated hydrocarbons. Little is known about the mode of action of both compounds on the cellular level. From cases of accidental poisoning of man it is known that MCAA accumulates in liver and kidney. 2 In this study, the cytotoxicity of SMCA on cultured liver (Chang liver cells) and kidney epithelial cells of the proximal tubule (Opossum kidney cells) was investigated and its effect on metabolism, ultrastruc-ture and organization of cytoskeleton was examined. 3 Independent from the growth state of the cells (proliferating or quiescent), the results clearly show that SMCA causes a dose-dependent decrease in cell viability after an exposure period of 24 h. In all experiments, proliferating cells were more sensitive than quiescent and confluent cells. Liver cells were less sensitive against SMCA treatment than kidney epithe-lial cells. In contrast to liver cells, kidney cells exhibited a dose-dependent decrease in cell volume. The decrease in cell viability was accompanied by an increase of lactate and pyruvate concentrations released into the culture medium. In the case of Opossum kidney cells, lactate and pyruvate levels increased 5-6-fold, whereas in the case of Chang liver cells the increase was approximately twofold. While the ultrastructure of liver cells remained unaltered after drug treatment, kidney cells exhibited cytoplas-mic vacuolization, membraneous disruption and especially mitochondrial alterations. In accordance with the changes in the ultrastructure of Opossum cells, was the reorganization of cytoskeletal elements with an increased stress fiber network at the basolat-eral surface as well as a partial depolymerization of microtubules and vimentin filaments. A cytoskeletal reorganization was not observed for Chang liver cells after SMCA treatment. 4 The results demonstrate that SMCA causes a dose-dependent cytotoxicity which is accompanied by metabolic, mitochondrial and cytoskeletal alterations in the cells.