Breast cancer resistance protein (BCRP/ABCG2) is known to actively transport various anticancer drugs and to restrict the uptake of the food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine from the gut lumen. The present study reveals that BCRP is involved in the transport of phase-2 metabolites of the carcinogen benzo[a]pyrene (BP) in the human intestinal cell line Caco-2. Treatment with the selective BCRP inhibitor Ko 143 (5 microM) inhibited the apical transport of BP-3-sulfate (BP3S) to 83% of control levels in TC7 cells and to 64% of control levels in Caco-2 cells. The apical transport of BP-3-glucuronide was inhibited by Ko 143 to 76% of control levels in TC7 cells. Furthermore, the expression of BCRP is most likely aryl hydrocarbon receptor (AhR) dependent, as treatment of Caco-2 cells with known AhR agonists including 2,3,7,8-tetrachlorodibenzo-p-dioxin, BP, indolo[3,2-b]carbazole and benzo[k]fluoranthene increased both mRNA and protein levels of BCRP. Induced BCRP protein was found to be functionally active, since pre-treatment of TC7 cells with oltipraz, indolo[3,2-b]carbazole or benzo[k]fluoranthene increased the amount of apically transported BP3S to as much as 180% of that in the controls. The induction of BCRP (mRNA and protein expression) by indolo[3,2-b]carbazole was inhibited in Caco-2 cells by co-incubation with the AhR antagonist PD98059 (2'-amino-3'-methoxyflavone). In summary, this study provides strong evidence that BCRP is an important part of the intestinal barrier protecting the body from food-associated contaminants such as the carcinogen BP.

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ABSTRACT:The Caco-2 cell line and its subclone TC7 are frequently used for studying human intestinal transport and metabolism of xenobiotics. We have investigated the expression of soluble sulfotransferases (SULT) in parental Caco-2 and TC7 cells by immunoblotting. SULT1A1, SULT1A2, SULT1A3, SULT1B1, SULT1C1, SULT1C2, and SULT2A1 were expressed in both cell lines. SULT2B1a, SULT2B1b, and SULT4A1 were absent. SULT1E1 protein was found in TC7 but not in Caco-2 cells. Other differences in SULT between the cell lines were minor. More important was the influence of differentiation. Expression of the various SULT forms was low or not detectable in cultures just reaching confluence but then increased strongly. Likewise, the rate of sulfation of the model substrate 3-hydroxybenzo

We have previously reported that breast cancer resistance protein (BCRP) is involved in the transport of phase II metabolites of the food carcinogen benzo[a]pyrene (BP) in the human intestinal cell line Caco-2. Furthermore, the expression of BCRP seemed most likely to be aryl hydrocarbon receptor (AhR) dependent. Since numerous plant-derived anticarcinogens with AhR-agonistic activity have been identified to date, in the present study we investigated the effects of naturally occurring dietary compounds and tert-butyl hydroquinone (TBHQ) for their effects on BCRP expression. In Caco-2 cells, the most pronounced induction of BCRP expression could be observed after treatment with TBHQ (100 microM), dibenzoylmethane (DBM, 50 microM), and quercetin (25 microM), while green tea component (-)-epicatechin (50 microM) decreased BCRP expression. On mRNA level, quercetin, chrysin, flavone, and indole-3-carbinol showed a strong inducing effect, while genistein had no effect on BCRP mRNA expression. Curcumin and resveratrol showed a strong effect on BCRP induction in MCF-7 wild-type cells but no response in AhR-deficient MCF-7AHR(200) cells, supporting our hypothesis that BCRP is regulated via AhR-dependent signaling pathways. Inhibition of proteasome-mediated degradation of ligand-activated AhR caused a "superinduction" of BCRP mRNA. Antioxidant responsive element activators sulforaphane and diethylmaleate (DEM) had no inducing effect on BCRP mRNA expression. Caco-2 cells pretreated with quercetin or DBM showed an enhancement of apically transported benzo[a]pyrene-3-sulfate, indicating that induced BCRP was functionally active. In conclusion, apart from the modulation of detoxifying enzymes in the intestine, induction of BCRP by dietary constituents may contribute to the detoxification of food-derived procarcinogens such as BP.

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Dicarbonyl/L-xylulose reductase (DCXR; SDR20C1), a member of the short-chain dehydrogenase/reductase (SDR) superfamily catalyzes the reduction of α-dicarbonyl compounds and monosaccharides. Its role in the metabolism of L-xylulose has been known since 1970, when essential pentosuria was found to be associated with DCXR deficiency. Despite its early discovery, our knowledge about the role of human DCXR in normal physiology and pathophysiology is still incomplete. Sporadic studies have demonstrated aberrant expression in several cancers, but their physiological significance is unknown. In reproductive medicine, where DCXR is commonly referred to as 'sperm surface protein P34H', it serves as marker for epididymal sperm maturation and is essential for gamete interaction and successful fertilization. DCXR exhibits a multifunctional nature, both acting as a carbonyl reductase and also performing non-catalytic functions, possibly resulting from interactions with other proteins. Recent observations associate DCXR with a role in cell adhesion, pointing to a novel function involving tumour progression and possibly metastasis. This review summarizes the current knowledge about human DCXR and its orthologs from mouse and Caenorhabditis elegans (DHS-21) with an emphasis on its multifunctional characteristics. Due to its close structural relationship with DCXR, carbonyl reductase 2 (Cbr2), a tetrameric enzyme found in several non-primate species is also discussed. Similar to human DCXR, Cbr2 from golden hamster (P26h) and cow (P25b) is essential for sperm-zona pellucida interaction and fertilization. Because of the apparent similarity of these two proteins and the inconsistent use of alternative names previously, we provide an overview of the systematic classification of DCXR and Cbr2 and a phylogenetic analysis to illustrate their ancestry.

Carbonyl reduction is a central metabolic process that controls the level of key regulatory molecules as well as xenobiotics. Carbonyl reductase 3 (CBR3; SDR21C2), a member of the short-chain dehydrogenase/reductase (SDR) superfamily, has been poorly characterized so far, and the regulation of its expression is a complete mystery. Here, we show that CBR3 expression is regulated via Nrf2, a key regulator in response to oxidative stress. In human cancer cell lines, CBR3 mRNA was expressed differentially, ranging from very high (A549, lung) to very low (HT-29, colon; HepG2, liver) levels. CBR3 protein was highly expressed in SW-480 (colon) cells but was absent in HCT116 (colon) and HepG2 cells. CBR3 mRNA could be induced in HT-29 cells by Nrf2 agonists [sulforaphane (SUL, 7-fold) and diethyl maleate (DEM, 4-fold)] or hormone receptor ligand Z-guggulsterone (5-fold). Aryl hydrocarbon receptor agonist B[k]F failed to induce CBR3 mRNA after incubation for 8 h but elevated CBR3 levels after 24 h, most likely mediated by B[k]F metabolites that can activate Nrf2 signaling. Inhibition of Nrf2-activating upstream kinase MEK/ERK by PD98059 weakened DEM-mediated induction of CBR3 mRNA. Proteasome inhibitors MG-132 (5 μM) and bortezomib (50 nM) dramatically increased the level of CBR3 mRNA, obviously because of the increase in the level of Nrf2 protein. While siRNA-mediated knockdown of Nrf2 led to a decrease in the level of CBR3 mRNA in A549 cells (30% of control), Keap1 knockdown increased the level of CBR3 mRNA expression in HepG2 (9.3-fold) and HT-29 (2.7-fold) cells. Here, we provide for the first time evidence that human CBR3 is a new member of the Nrf2 gene battery.