Cellular asymmetric catalysis by UDP-glucuronosyltransferase 1A8 shows functional localization to the basolateral plasma membrane

Identification of selective inhibitors of uridine 5'-diphospho-glucuronosyltransferase (UGT) 1A3 and UGT1A8 and their application in UGT reaction phenotyping studies in human liver and intestinal microsomes

Uridine 5'-diphospho-glucuronosyltransferase (UGT) reaction phenotyping studies have posed significant challenges due to the limited availability of isoform-selective inhibitors. This recognized gap in reagent availability impedes the accurate determination of the contribution of specific UGT isoforms to the metabolism of UGT substrates. To address this challenge, 9 antibiotics were evaluated for their potential inhibitory effects on UGT isoforms. We identified 2 macrolide antibiotics, troleandomycin and erythromycin, as potent and selective inhibitors of UGT1A3 and UGT1A8, respectively. The mechanism of UGT inhibition by troleandomycin and erythromycin was investigated using recombinant UGT1A3 (mefenamic acid as probe substrate) and UGT1A8 (7-hydroxy-4-(trifluoromethyl)coumarin and apigenin as probe substrates). The results revealed a mixed-type inhibition mechanism, where troleandomycin and erythromycin allosterically inhibit UGT1A3 and UGT1A8, respectively. A slight positive cooperativity between erythromycin and substrate binding to UGT1A8 and a slight negative cooperativity between troleandomycin and substrate binding to UGT1A3 was observed. At saturating inhibitor concentrations, greater than 90% inhibition of glucuronidation catalyzed by UGT1A3 and UGT1A8 was observed. To validate these findings in human liver microsomes and human intestinal microsomes, telmisartan, a selective substrate of UGT1A3 and UGT1A8, was utilized. Similar to the results in expressed UGT isoforms, troleandomycin selectively inhibited UGT1A3 in human liver microsomes and erythromycin selectively inhibited UGT1A8 in human intestinal microsomes. The identification of these UGT isoform-selective inhibitors provides researchers with important new tools expanding the utility of in vitro UGT reaction phenotyping studies. SIGNIFICANCE STATEMENT: Identification of uridine 5'-diphospho-glucuronosyltransferase (UGT)1A3 (troleandomycin) and UGT1A8 (erythromycin) selective inhibitors addresses an important and heretofore unmet need for in vitro reaction phenotyping studies by facilitating the determination of the contribution of these enzymes to drug glucuronidation in humans.

The odorant metabolizing enzyme UGT2A1: Immunolocalization and impact of the modulation of its activity on the olfactory response

Odorant metabolizing enzymes (OMEs) are expressed in the olfactory epithelium (OE) where they play a significant role in the peripheral olfactory process by catalyzing the fast biotransformation of odorants leading either to their elimination or to the synthesis of new odorant stimuli. The large family of OMEs gathers different classes which interact with a myriad of odorants alike and complementary to olfactory receptors. Thus, it is necessary to increase our knowledge on OMEs to better understand their function in the physiological process of olfaction. This study focused on a major olfactory UDP-glucuronosyltransferase (UGT): UGT2A1. Immunohistochemistry and immunogold electronic microscopy allowed to localize its expression in the apical part of the sustentacular cells and originally at the plasma membrane of the olfactory cilia of the olfactory sensory neurons, both locations in close vicinity with olfactory receptors. Moreover, using electroolfactogram, we showed that a treatment of the OE with beta-glucuronidase, an enzyme which counterbalance the UGTs activity, increased the response to eugenol which is a strong odorant UGT substrate. Altogether, the results supported the function of the olfactory UGTs in the vertebrate olfactory perireceptor process.

Bloom Syndrome Protein Activates AKT and PRAS40 in Prostate Cancer Cells

Purpose

Prostate cancer (PC) is a common malignant tumor and a leading cause of cancer-related death in men worldwide. In order to design new therapeutic interventions for PC, an understanding of the molecular events underlying PC tumorigenesis is required. Bloom syndrome protein (BLM) is a RecQ-like helicase, which helps maintain genetic stability. BLM dysfunction has been implicated in tumor development, most recently during PC tumorigenesis. However, the molecular basis for BLM-induced PC progression remains poorly characterized. In this study, we investigated whether BLM modulates the phosphorylation of an array of prooncogenic signaling pathways to promote PC progression.

Methods

We analyzed differentially expressed proteins (DEPs) using iTRAQ technology. Site-directed knockout of BLM in PC-3 prostate cancer cells was performed using CRISPR/Cas9-mediated homologous recombination gene editing to confirm the effects of BLM on DEPs. PathScan® Antibody Array Kits were used to analyze the phosphorylation of nodal proteins in PC tissue. Immunohistochemistry and automated western blot (WES) analyses were used to validate these findings.

Results

We found that silencing BLM in PC-3 cells significantly reduced their proliferative capacity. In addition, BLM downregulation significantly reduced levels of phosphorylated protein kinase B (AKT (Ser473)) and proline-rich AKT substrate of 40 kDa (PRAS40 (Thr246)), and this was accompanied by enhanced ROS (reactive oxygen species) levels. In addition, we found that AKT and PRAS40 inhibition reduced BLM, increased ROS levels, and induced PC cell apoptosis.

Conclusions

We demonstrated that BLM activates AKT and PRAS40 to promote PC cell proliferation and survival. We further propose that ROS act in concert with BLM to facilitate PC oncogenesis, potentially via further enhancing AKT signaling and downregulating PTEN expression. Importantly, inhibiting the BLM-AKT-PRAS40 axis induced PC cell apoptosis. Thus, we highlight new avenues for novel anti-PC treatments.

Investigation of the Endoplasmic Reticulum Localization of UDP-Glucuronosyltransferase 2B7 with Systematic Deletion Mutants

UDP-Glucuronosyltransferase (UGT) plays an important role in the metabolism of endogenous and exogenous compounds. UGT is a type I membrane protein, and has a dilysine motif (KKXX/KXKXX) in its C-terminal cytoplasmic domain. Although a dilysine motif is defined as an endoplasmic reticulum (ER) retrieval signal, it remains a matter of debate whether this motif functions in the ER localization of UGT. To address this issue, we generated systematic deletion mutants of UGT2B7, a major human isoform, and compared their subcellular localizations with that of an ER marker protein calnexin (CNX), using subcellular fractionation and immunofluorescent microscopy. We found that although the dilysine motif functioned as the ER retention signal in a chimera that replaced the cytoplasmic domain of CD4 with that of UGT2B7, UGT2B7 truncated mutants lacking this motif extensively colocalized with CNX, indicating dilysine motif-independent ER retention of UGT2B7. Moreover, deletion of the C-terminal transmembrane and cytoplasmic domains did not affect ER localization of UGT2B7, suggesting that the signal necessary for ER retention of UGT2B7 is present in its luminal domain. Serial deletions of the luminal domain, however, did not affect the ER retention of the mutants. Further, a cytoplasmic and transmembrane domain-deleted mutant of UGT2B7 was localized to the ER without being secreted. These results suggest that UGT2B7 could localize to the ER without any retention signal, and lead to the conclusion that the static localization of UGT results from lack of a signal for export from the ER.

Differential Impact of Flavonoids on Redox Modulation, Bioenergetics, and Cell Signaling in Normal and Tumor Cells: A Comprehensive Review

SIGNIFICANCE

Flavonoids can interact with multiple molecular targets to elicit their cellular effects, leading to changes in signal transduction, gene expression, and/or metabolism, which can, subsequently, affect the entire cell and organism. Immortalized cell lines, derived from tumors, are routinely employed as a surrogate for mechanistic studies, with the results extrapolated to tissues in vivo. Recent Advances: We review the activities of selected flavonoids on cultured tumor cells derived from various tissues in comparison to corresponding primary cells or tissues in vivo, mainly using quercetin and flavanols (epicatechin and (-)-epigallocatechin gallate) as exemplars. Several studies have indicated that flavonoids could retard cancer progression in vivo in animal models as well as in tumor cell models.

CRITICAL ISSUES

Extrapolation from in vitro and animal models to humans is not straightforward given both the extensive conjugation and complex microbiota-dependent metabolism of flavonoids after consumption, as well as the heterogeneous metabolism of different tumors.

FUTURE DIRECTIONS

Comparison of data from studies on primary cells or in vivo are essential not only to validate results obtained from cultured cell models, but also to highlight whether any differences may be further exploited in the clinical setting for chemoprevention. Tumor cell models can provide a useful mechanistic tool to study the effects of flavonoids, provided that the limitations of each model are understood and taken into account in interpretation of the data.

Interplay of Efflux Transporters with Glucuronidation and Its Impact on Subcellular Aglycone and Glucuronide Disposition: A Case Study with Kaempferol

Glucuronidation is a major process of drug metabolism and elimination that generally governs drug efficacy and toxicity. Publications have demonstrated that efflux transporters control intracellular glucuronidation metabolism. However, it is still unclear whether and how efflux transporters interact with UDP-glucuronosyltransferases (UGTs) in subcellular organelles. In this study, kaempferol, a model fluorescent flavonoid, was used to investigate the interplay of glucuronidation with transport at the subcellular level. Human recombinant UGTs and microsomes were utilized to characterize the in vitro glucuronidation kinetics of kaempferol. The inhibition of UGTs and efflux transporters on the subcellular disposition of kaempferol were determined visually and quantitatively in Caco-2/TC7 cells. The knockout of transporters on the subcellular accumulation of kaempferol in liver and intestine were evaluated visually. ROS and Nrf2 were assayed to evaluate the pharmacological activities of kaempferol. The results showed that UGT1A9 is the primary enzyme responsible for kaempferol glucuronidation. Visual and quantitative data showed that the UGT1A9 inhibitor carvacrol caused a significant rise in subcellular aglycone and reduction in subcellular glucuronides of kaempferol. The inhibition and knockout of transporters, such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance-associated proteins (MRPs), exhibited a marked increase in subcellular kaempferol and decrease in its subcellular glucuronides. Correspondingly, inhibition of UGT1A9 and transporters led to increased kaempferol and, consequently, a significantly enhanced ROS scavenging efficiency and nuclear translocation of Nrf2. In conclusion, the interplay of efflux transporters (P-gp, BCRP, and MRPs) and UGTs govern the subcellular exposure and corresponding pharmacological activity of kaempferol.

TUFT1 is expressed in breast cancer and involved in cancer cell proliferation and survival

Tuftelin 1 (TUFT1), which plays an important role in the initial stages of the mineralization of ectodermal enamel, is widely expressed in different embryonic and adult tissues and some tumor cells. However, since the roles of this gene have not been thoroughly investigated in tumors, its function in the development of breast cancer remains unclear. We proved both human specimens studies and cell line studies, that TUFT1 expression levels are increased in breast cancer samples, and the increased expression of TUFT1 was shown to be positively correlated with tumor size, histological grade, lymph node metastasis rate, and poor prognosis. Further in vitro studies showed that the inhibition of TUFT1 expression in T-47D and MDA-MB-231 breast cancer cells significantly affected cell proliferation, induced apoptosis, and led to G1-phase cell cycle arrest. Moreover, reduced TUFT1 expression restrained tumor growth compared with the control group in vivo. Furthermore, microarray and pathway analysis demonstrated that TUFT1 inhibition led to significant changes of several signaling pathways and semi-quantitative western blot analysis showed that a decrease in TUFT1 expression was accompanied by changes in MAPK signaling pathway components. The obtained results suggest that TUFT1 may represent a novel breast cancer marker and a potentially effective therapeutic target.

Gender and geographical variability in the exposure pattern and metabolism of deoxynivalenol in humans: a review

Deoxynivalenol (DON, also known as vomitoxin) is a common mycotoxin found worldwide, especially in contaminated food. DON is toxic to a variety of cells and tissues in humans. Three kinds of conjugated products (DON-3-glucuronide, DON-15-glucuronide and DON-7-glucuronide) can be found as major metabolites in human urine. Females and males show different patterns of exposure levels, and human exposure to DON also shows some geographical differences because of different DON levels in cereal-based foods, food intake habits and UDP-glucuronosyltransferase expression. Specifically, the C12, 13-deepoxy metabolite was found predominantly in French adults but was rarely detected in UK adults. However, a cohort of Spanish individuals demonstrated even lower DON levels than the levels in the UK populations, whereas a very high DON exposure level was detected in South Africa and Linxian, China. Recent publications have further indicated that DON could be detected in the urine of pregnant women from different countries, which suggests that there is a potential risk to both mothers and foetuses. Additionally, phytochemicals have been shown to be less toxic to cells and laboratory animals in research studies and may also be used as food additives for reducing the toxic effects of DON. In this review, we provide global information on DON metabolism, human exposure and gender differences in humans. Also, control strategies for this mycotoxin are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

Glycosyltransferases and non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the most common form of chronic liver disease and its incidence is increasing worldwide. However, the underlying mechanisms leading to the development of NAFLD are still not fully understood. Glycosyltransferases (GTs) are a diverse class of enzymes involved in catalyzing the transfer of one or multiple sugar residues to a wide range of acceptor molecules. GTs mediate a wide range of functions from structure and storage to signaling, and play a key role in many fundamental biological processes. Therefore, it is anticipated that GTs have a role in the pathogenesis of NAFLD. In this article, we present an overview of the basic information on NAFLD, particularly GTs and glycosylation modification of certain molecules and their association with NAFLD pathogenesis. In addition, the effects and mechanisms of some GTs in the development of NAFLD are summarized.