Surface Enhanced Visible Absorption of Dye Molecules in the Near-Field of Gold Nanoparticles

Surface enhanced absorption is a plasmonic effect parenting to surface enhanced fluorescence and Raman scattering, and it was clearly reported to occur in the infrared region of the spectrum of light. In this paper, we unambiguously show that it also occurs in the visible region of the spectrum by using a dye; i.e. an azo-dye, which exhibits a good light absorption in that region, and gold nanoparticles, which act as plasmonic nanoantennas that capture and re-radiate light, when the azo-dyes and the nanoparticles are incorporated in the bulk of solid films of polymer. In such a configuration, it is possible to use a dye concentration much larger than that of the nanoparticles and absorption path lengths much larger than those of the molecularly thin layers used in surface enhanced effects studies. In addition, the dye undergoes shape and orientation change; i.e. isomerization and reorientation, upon polarized light absorption; and the observation of surface enhanced visible absorption is done by two separate experiments; i.e. UV-visible absorption spectroscopy and photo-induced birefringence, since the signals detected from both experiments are directly proportional to the extinction coefficient of the dye. Both the dye's absorption and photoorientation are enhanced by the presence of the nanoparticles.

Tripartite Motif Containing 24 Acts as a Novel Coactivator of the Constitutive Active/Androstane Receptor

The constitutive androstane receptor (CAR) is a nuclear receptor that acts as a transcription factor for a variety of genes, including genes encoding xenobiotic, steroid, and drug-metabolizing enzymes and transporters. Transactivation of a target gene by a transcription factor is generally mediated through the concerted and stepwise recruitment of various proteins termed coregulators, including coactivators and corepressors. In this study, TRIM24 (also known as transcriptional intermediary factor 1 alpha) was found to interact with the CAR. TRIM24 enhanced the CAR-dependent transactivation in reporter assays using the direct repeat-4 motif, a binding site of the CAR. This enhancement was synergistically augmented in the presence of steroid receptor coactivator (SRC) 1 or SRC2, both of which are coactivators of the CAR. In addition, TRIM24 was recruited to the CAR-binding element of the CYP2B6 promoter together with the CAR. We also noted that knockdown of TRIM24 suppressed CAR-induced CYP2B6 mRNA expression in HepTR/CAR and HepaRG cells and suppressed CAR-induced CYP3A4 mRNA expression in HepaRG cells but not HepTR/CAR cells. From these results, we suggest that TRIM24 is a novel coactivator of the CAR that is involved in cell- and/or promoter- selective transactivation.

Alisol B 23-acetate from the rhizomes of Alisma orientale is a natural agonist of the human pregnane X receptor

BACKGROUND

Pregnane X receptor (PXR) is a key regulator of the induction of drug metabolizing enzymes. PXR has been studied for its importance in drug-drug or herb-drug interactions, and it is also a molecular target for the treatment of inflammatory and metabolic diseases.

PURPOSE

This study aims to determine new natural PXR-ligands from traditional plant medicines.

METHODS

The PXR activation activity was measured by a mammalian one hybrid assay of PXR. Identification of the active compound from Alisma rhizome (the rhizomes of Alisma orientale) was carried out by bioassay-guided fractionation method. The transcriptional activity of the liver-enriched nuclear receptors was measured by the luciferase reporter assay. The interaction between the SRC-1 and PXR was measured by a mammalian 2-hybrid assay. The expression of endogenous CYP3A4 mRNA in both cultured hPXR-overexpressing hepatoma cells and human primary hepatocytes were measured by quantitative RT-PCR method.

RESULTS

The extract of Alisma rhizome showed the most potent activation activity by screening of a library of medicinal plant extracts. Alisol B 23-acetate (ABA) was identified to be the active compound of Alisma rhizome. ABA caused a concentration-dependent increase on the PXR-dependent transactivation of a luciferase reporter gene, but did not affect the ligand binding activity of the liver-enriched nuclear receptors, such as CAR, LXR, FXR, PPARα, PPARδ and PPARγ, emphasizing that ABA is a potent and specific agonist of PXR. With ABA treatment, the direct interaction between the ligand-binding domain of PXR and the receptor interaction domain of SRC1 was observed. ABA also induced the expression of endogenous CYP3A4 mRNA in both cultured hPXR-overexpressing hepatoma cells and human primary hepatocytes.

CONCLUSION

Since the rhizomes of Alisma orientale are used for a wide range of ailments in traditional Chinese medicine and Japanese Kampo medicine, this study could possibly extend into the clinical usage of these medicines via the mechanism of PXR activation.

Light-tunable Fano resonance in metal-dielectric multilayer structures

High-Q optical Fano resonances realized in a variety of plasmonic nanostructures and metamaterials are very much promising for the development of new potent photonic devices, such as optical sensors and switches. One of the key issues in the development is to establish ways to effectively modulate the Fano resonance by external perturbations. Dynamic tuning of the Fano resonance applying the mechanical stress and electric fields has already been demonstrated. Here, we demonstrate another way of tuning, i.e., photo-tuning of the Fano resonance. We use a simple metal-dielectric multilayer structure that exhibits a sharp Fano resonance originating from coupling between a surface plasmon polariton mode and a planar waveguide mode. Using a dielectric waveguide doped with azo dye molecules that undergo photoisomerization, we succeeded in shifting the Fano resonance thorough photo-modulation of the propagation constant of the waveguide mode. The present work demonstrates the feasibility of photo-tuning of the Fano resonance and opens a new avenue towards potential applications of the Fano resonance.

Androgen receptor functions as a negative transcriptional regulator of DEPTOR, mTOR inhibitor

It has been noticed that crosstalk between androgen receptor (AR) and mammalian target of rapamycin (mTOR) signaling pathways plays a crucial role in the proliferation of prostate cancer cells. To clarify this mechanism, we focused on DEPTOR, a naturally occurring inhibitor of mTOR. The treatment of a human AR-positive prostate cancer cell line, LNCaP, with the AR-agonist dihydrotestosterone (DHT) repressed DEPTOR mRNA expression in a time-dependent manner. This repression was abrogated by treatment with the AR-antagonist bicalutamide. Knockdown of DEPTOR mRNA by siRNA resulted in the increased phosphorylation of 70 kDa ribosomal protein S6 kinase 1 (S6K), a substrate of mTORC1, accompanied by the elevated expression of cyclin D1, a positive regulator of cell proliferation. Furthermore, the ChIP assay demonstrated that AR could bind to AR-responsible element-like region within the 4th intron of the DEPTOR gene. The amount of acetylated histone H3 (Lys9, Lys14) was reduced by the DHT treatment in this region. Taken together, these results propose that AR-dependent prostate cancer cell proliferation requires decreased DEPTOR transcription directly controlled by AR.

[Structure and Function of the Nuclear Receptor Constitutive Androstane Receptor]

Animal defense mechanisms against both endogenous and exogenous toxic compounds function mainly through receptor-type transcription factors, including the constitutive androstane receptor (CAR). Following xenobiotic stimulation, CAR translocates into the nucleus and transactivates its target genes including oxygenic and conjugative enzymes and transporters in hepatocytes. We identified subcellular localization signals in the rat CAR: two nuclear localization signals (NLS1 and 2); two nuclear export signals (NES1 and 2); and a cytoplasmic retention region. The nuclear import of CAR is regulated by the importin-Ran system and microtubule network. Five splice variants (SV1-5) were identified in rat liver in addition to wild-type CAR. When expressed in immortalized cells, their artificial transcripts were inactive as transcription factors. A CAR mutant with three consecutive alanine residues inserted into the ligand-binding domain of CAR showed ligand-dependent activation of target genes in immortalized cells, which is in marked contrast to the constitutive transactivating nature of wild-type CAR. Using this assay system, androstenol and clotrimazole, both of which are inverse agonists of CAR, were classified as an antagonist and weak agonist, respectively. A member of the DEAD box DNA/RNA helicase family (DP97) and protein arginine methyltransferase 5 (PRMT5) were found to be gene (or promotor)-specific coactivators of CAR. The expression of the CAR gene might be under the control of clock genes mediated by the nuclear receptor Rev-erb-α.

Protein arginine methyltransferase 5 (PRMT5) is a novel coactivator of constitutive androstane receptor (CAR)

The constitutive androstane receptor (CAR) plays a key role in the expression of xenobiotic/steroid and drug metabolizing enzymes and their transporters. In this study, we demonstrated that protein arginine methyltransferase 5 (PRMT5) is a novel CAR-interacting protein. Furthermore, the PRMT-dependent induction of a CAR reporter gene, which was independent of methyltransferase activity, was enhanced in the presence of steroid receptor coactivator 1 (SRC1), peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) or DEAD box DNA/RNA helicase DP97. Using tetracycline inducible-hCAR system in HepG2 cells, we showed that knockdown of PRMT5 with small interfering RNA suppressed tetracycline -induced mRNA expression of CYP2B6 but not of CYP2C9 or CYP3A4. PRMT5 enhanced phenobarbital-mediated transactivation of a phenobarbital-responsive enhancer module (PBREM)-driven reporter gene in co-operation with PGC-1α in rat primary hepatocytes. Based on these findings, we suggest PRMT5 to be a gene (or promoter)-selective coactivator of CAR by mediating the formation of complexes between hCAR and appropriate coactivators.

Molecular Cloning and Expression of aStreptomycesSarcosine Oxidase Gene inStreptomyces lividans

A genomic library of Streptomyces sp. KB210-8SY, prepared in the plasmid vector pACYC184, was screened to obtain the gene encoding sarcosine oxidase with probes based on the amino acid sequence of the protein. A plasmid pSOXS13, which was isolated from a clone identified by hybridization with the probes, contained a 8.4-kb insert of Streptomyces DNA. When the 2.0-kb MIuI/EcoRV DNA fragment of pSOXS13 was inserted into the Streptomyces vector pIJ680 and introduced into S. lividans, the transformants produced 100-fold more sarcosine oxidase intracellularly than KB210-8SY. The nucleotides of the 1.7-kb fragment containing the sarcosine oxidase gene were sequenced. An open reading frame encoded a mature sarcosine oxidase consisting of 388 amino acids, with a calculated molecular mass of 42,107 daltons.

Nigramide J is a novel potent inverse agonist of the human constitutive androstane receptor

The constitutive androstane receptor (CAR, NR1I3) is very important for drug development and for understanding pharmacokinetic drug-drug interactions. We screened by mammalian one hybrid assay among natural compounds to discover novel ligands of human constitutive androstane receptor (hCAR). hCAR transcriptional activity was measured by luciferase assay and mRNA levels of CYP2B6 and CYP3A4 in HepTR-hCAR cells and human primary hepatocytes were measured by real-time RT-PCR. Nigramide J (NJ) whose efficacy is comparable to those of hitherto known inverse agonists such as clotrimazole, PK11195, and ethinylestradiol. NJ is a naturally occurring cyclohexane-type amide alkaloid that was isolated from the roots of Piper nigrum. The suppressive effect of NJ on the CAR-dependent transcriptional activity was found to be species specific, in the descending order of hCAR, rat CAR, and mouse CAR. The unliganded hCAR-dependent transactivation of reporter and endogenous genes was suppressed by NJ at concentrations higher than 5 μmol/L. The ligand-binding cavity of hCAR was shared by NJ and CITCO, because they were competitive in the binding to hCAR. NJ interfered with the interaction of hCAR with coactivator SRC-1, but not with its interaction with the corepressor NCoR1. Furthermore, NJ is agonist of human pregnane X receptor (hPXR). NJ is a dual ligand of hCAR and hPXR, being an agonist of hPXR and an inverse agonist of hCAR.

Pd(ii)-catalyzed ligand controlled synthesis of pyrazole-4-carboxylates and benzo[b]thiophene-3-carboxylates

A simple change of the ligand and solvent allows controlled, effective switching between cyclization–carbonylation–cyclization-coupling (CCC-coupling) and cyclization–carbonylation reactions.

TO901317, a potent LXR agonist, is an inverse agonist of CAR

The basal transcriptional activity of unliganded human constitutive androstane receptor (hCAR) was shown to be repressed by the potent liver X receptor (LXR) agonist, TO901317, in a concentration-dependent manner using a reporter assay in cultured cells. TO901317 also repressed the basal transcriptional activity of both mouse and rat CAR. The certified hCAR agonist, CITCO, partially reversed this repressive effect of TO901317 on hCAR basal activity. Unlike hCAR, a three alanine insertion mutant and the splice variant 2 of hCAR require agonists, such as CITCO, to become transcriptionally active and the CITCO-induced reporter activity was repressed by TO901317. As has been previously shown for the typical hCAR inverse agonist, PK11195, TO901317 blocked the interaction of hCAR with steroid receptor co-activator 1 (SRC1). In contrast, the interaction between hCAR and nuclear receptor corepressor 1 (NCoR1) was promoted by PK11195 and TO901317. Furthermore, the hCAR-mediated basal induction of endogenous cytochrome P450 2B6 (CYP2B6) mRNA was adversely affected by co-treatment with TO901317.

Changes in monoclonal antibody productivity of recombinant BHK cells immobilized in collagen gel particles

Animal cell perfusion high density culture is often adopted for the production of biologicals in industry. In high density culture sometimes the productivity of biologicals has been found to be enhanced. Especially in immobilized animal cell culture, significant increase in the productivity has been reported. We have found that the specific monoclonal antibody (MAb) productivity of an immobilized hybridoma cell is enhanced more than double. Several examples of enhancing productivities have been also shown by collagen immobilized cells. Immobilized cells involve some different points from non-immobilized cells in high density culture: In immobilized culture, some cells are contacted together, resulting in locally much higher cell concentration more than 10(8) cells/ml. Information originating from a cell can be easily transduced to the others in immobilized culture because the distance between cells is much nearer. Here we have performed collagen gel immobilized culture of recombinant BHK cells which produce a human IgG monoclonal antibody in a protein-free medium for more than three months. In this high density culture a stabilized monoclonal antibody production was found with around 8 times higher specific monoclonal antibody productivity compared with that in a batch serum containing culture. No higher MAb productivity was observed using a conditioned medium which was obtained from the high density culture, indicating that no components secreted from the immobilized cells work for enhancing monoclonal antibody production. The MAb productivity by the non-immobilized cells obtained by dissolving collagen using a collagenase gradually decreased and returned to the original level in the batch culture using a fresh medium. This suggests that the direct contact of the cells or a very close distance between the cells has something to do with the enhancement of the MAb productivity, and the higher productivity is kept for a while in each cell after they are drawn apart.

DP97, a DEAD box DNA/RNA helicase, is a target gene-selective co-regulator of the constitutive androstane receptor

The constitutive androstane receptor (CAR) plays a key role in the expression of xenobiotic/steroid and drug metabolizing enzymes and their transporters. In this study, we demonstrated that DP97, a member of the DEAD box DNA/RNA helicase protein family, is a novel CAR-interacting protein. Using HepG2 cells expressing human CAR in the presence of tetracycline, we showed that knockdown of DP97 with small interfering RNAs suppressed tetracycline-inducible mRNA expression of CYP2B6 and UGT1A1 but not CYP3A4. Thus, DP97 was found to be a gene (or promoter)-selective co-activator for hCAR. DP97-mediated CAR transactivation was synergistically enhanced by the co-expression of SRC-1 or PGC1α, therefore it might act as mediator between hCAR and appropriate co-activators.

[Mechanism for subcellular localization of nuclear receptor CAR]

Animals including human beings have defense mechanisms against the toxicity of xenobiotics such as medicinal compounds and environmental pollutants. Receptor-type transcriptional factors, such as aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR) and pregnane X receptor (PXR), play important roles in the defense against xenobiotic toxicities. In the absence of stimuli, these receptors are distributed predominantly in the cytoplasmic compartment. Following xenobiotic stimuli, receptors translocate into the nucleus and transactivate its target genes. However, the exogenously expressed CAR translocates spontaneously into the nucleus in immortal cells. Previously, we identified subcellular localization signals in rat CAR: nuclear localization signal (NLS), nuclear export signal (NES) and cytoplasmic retention region (CRR). Lack of CRR function might be responsible for the spontaneous nuclear accumulation of CAR in immortal cells. Further, the nuclear import of CAR is regulated by the importin-Ran system, which is required for maintaining an intact microtubule network. Clarifying the mechanisms underlying the nuclear translocation of CAR would be useful for the establishment of novel assay systems for the screening of ligands and activators of CAR using immortal cells without sacrificing animals.

5-aminoimidazole-4-carboxamide-1-beta-ribofuranoside (AICAR) prevents nuclear translocation of constitutive androstane receptor by AMP-activated protein kinase (AMPK) independent manner

The nuclear receptor superfamily consists of ligand-dependent transcription factors. Among them, constitutive androstane receptor (CAR) plays a key role in the detoxification of xenobiotics, inducing various drug-metabolizing enzymes including human CYP2B6 and its homologues of other species. AMP-activated protein kinase (AMPK) acts as an important energy sensor, being activated by an increased AMP/ATP ratio. CAR is activated by phenobarbital (PB) treatment. It has been recently reported that AMPK is involved in PB-mediated CYP2B induction both in vitro and in vivo. We investigated the relationship between the functions of AMPK and CAR in rat primary hepatocyte. The AMPK-activator 5-aminoimidazole-4-Carboxamide-1-beta-Ribofuranoside (AICAR) unexpectedly repressed PB-induced CYP2B mRNA expression as well as AMPK-inhibitor compound C. In contrast, both the AMPK-activator metformin and the constitutive active form of AMPK enhanced PB-induced PB-responsive enhancer module-driven reporter gene expression. We demonstrated that AICAR prevented nuclear translocation of CAR in an AMPK-independent manner in rat primary hepatocytes. AICAR might be a convenient probe for studying the mechanisms of PB-induced activation, especially nuclear translocation, of CAR in rat primary hepatocytes.

Mechanism of variable structural colour in the neon tetra: quantitative evaluation of the Venetian blind model

The structural colour of the neon tetra is distinguishable from those of, e.g., butterfly wings and bird feathers, because it can change in response to the light intensity of the surrounding environment. This fact clearly indicates the variability of the colour-producing microstructures. It has been known that an iridophore of the neon tetra contains a few stacks of periodically arranged light-reflecting platelets, which can cause multilayer optical interference phenomena. As a mechanism of the colour variability, the Venetian blind model has been proposed, in which the light-reflecting platelets are assumed to be tilted during colour change, resulting in a variation in the spacing between the platelets. In order to quantitatively evaluate the validity of this model, we have performed a detailed optical study of a single stack of platelets inside an iridophore. In particular, we have prepared a new optical system that can simultaneously measure both the spectrum and direction of the reflected light, which are expected to be closely related to each other in the Venetian blind model. The experimental results and detailed analysis are found to quantitatively verify the model.

The inhibitory effect of aryl hydrocarbon receptor repressor (AhRR) on the growth of human breast cancer MCF-7 cells

The variant cell lines stably expressing aryl hydrocarbon receptor repressor (AhRR), MCFRR1 and MCFRR4, were established from human breast cancer MCF-7 cells by transfecting with AhRR-expression construct followed by selection, in order to analyze the effect of AhRR on the cell growth and expression of cell cycle-related genes. The variant cells showed higher levels of AhRR mRNA compared with the parental cells. MCFRR4 cells grew slowly compared with MCF-7 in both cell number and proliferation rate measured by the MTS method. Among cell cycle-related genes such as E2F, cyclin E1, cyclin D1, PCNA, p53, Rb, c-myc and p27Kip1, and estrogen responsive genes such as cathepsin D and hsp27, the expression levels of E2F, cyclin E1, PCNA and cathepsin D mRNA in MCFRR4 cells were lower than those in MCF-7 cells, while those of Rb, p27Kip1, c-myc and hsp27 mRNA were not significantly affected and that of cyclin D1 mRNA was enhanced in variant cells. Based on these results, AhRR might be suppressive on cell growth of MCF-7 by disturbing the transcriptional and/or posttranscriptional regulations of estrogen-responsive and cell cycle-related genes.

Femtosecond laser nano-ablation in fixed and non-fixed cultured cells

To understand the onset and morphology of femtosecond laser submicron ablation in cells and to study physical evidence of intracellular laser irradiation, we used transmission electron microscopy (TEM). The use of partial fixation before laser irradiation provides for clear images of sub-micron intracellular laser ablation, and we observed clear evidence of bubble-type physical changes induced by femtosecond laser irradiation at pulse energies as low as 0.48 nJ in the nucleus and cytoplasm. By taking ultrathin sliced sections, we reconstructed the laser affected subcellular region, and found it to be comparable to the point spread function of the laser irradiation. Laser-induced bubbles were observed to be confined by the surrounding intracellular structure, and bubbles were only observed with the use of partial pre-fixation. Without partial pre-fixation, laser irradiation of the nucleus was found to produce observable aggregation of nanoscale electron dense material, while irradiation of cytosolic regions produced swollen mitochondria but residual local physical effects were not observed. This was attributed to the rapid collapse of bubbles and/or the diffusion of any observable physical effects from the irradiation site following the laser exposure.

Suppressive effect of aryl hydrocarbon receptor repressor on transcriptional activity of estrogen receptor alpha by protein-protein interaction in stably and transiently expressing cell lines

Aryl hydrocarbon receptor repressor (AhRR) suppressed, in a ligand independent manner, the ability of estrogen receptor alpha (ERalpha) to enhance the transcription of heterologous estrogen-responsive reporter plasmids in transient transfection assays, as well as of endogenous estrogen-responsive genes in human breast cancer MCF-7 cells. AhRR repressed ERalpha-mediated trans-activation by interfering allosterically with the ligand-independent function of AF-1. The direct interaction between AhRR and ERalpha at the multipartite binding site of ERalpha, which ranges from a DNA binding domain to a ligand binding domain, but did not include the AF-1 moiety was confirmed by a coimmunoprecipitation assay. The AhRR/ERalpha complex was formed in the nuclear compartment and was entrapped by a cis-element in the promoter of E2-responsive genes, as determined in a chromatin immunoprecipitation assay. AhRR might play a role of co-repressor on the transcriptional activity of the ERalpha homodimer.

Difference in nucleocytoplasmic shuttling sequences of rat and human constitutive active/androstane receptor

Fluorescence recovery after photobleaching (FRAP) in spontaneous multinuclear cells shows that both rat and human constitutive active/androstane receptors (CARs) are shuttling proteins with both nuclear localization signals (NLSs) and nuclear export signals (NESs). We previously identified two NLSs in rat CAR: NLS1 in the hinge region (residues 100-108) and NLS2 in the ligand-binding domain (residues 111-320). In the present study, we compared the intracellular localization signals between rat and human CARs. There was a marked difference in their intracellular localization in COS-7 cells because, unlike rat CAR, human CAR does not contain NLS1 due to an amino acid change at position 106. A CRM1-dependent leucine-rich NES, which is sensitive to an inhibitory effect of leptomycin B, was found in the cytoplasmic retention region previously identified within the ligand-binding domain of rat CAR (residues 220-258). We found that human CAR instead has a NES in the ligand-binding domain between residues 170 and 220. Also, we detected CRM1-independent C-terminal NESs between residues 317-358 of rat and human CARs. Removal of NLS1 by N-terminal truncation and mutation of xenochemical response signal caused rat CAR to localize in the cytoplasm of COS-7 cells, which we suspect is due to the masking of NLS2.

Effects of carbocisteine on sialyl-Lewis x expression in an airway carcinoma cell line stimulated with tumor necrosis factor-alpha

Carbocisteine is a mucoregulatory drug normalizing sialic acid and fucose contents in mucins through the regulation of glycosyltransferase activities. Tumor necrosis factor (TNF)-alpha-induced overexpression of sialyl-Lewis x epitopes, containing sialic acid and fucose, in mucins were previously reported to be regulated by glycosyltransferase mRNAs expression through phosphatidyl inositol-specific phospholipase C (PI-PLC) signaling pathways [Ishibashi, Y., Inouye, Y., Okano, T., Taniguchi, A., 2005. Regulation of sialyl-Lewis x epitope expression by TNF-alpha and EGF in an airway carcinoma cell line. Glycoconj. J. 22, 53-62]. To investigate the mechanism behind the mucoregulatory action of carbocisteine, the present study evaluated the effects of carbocisteine on TNF-alpha-induced overexpression of sialyl-Lewis x epitopes in NCI-H292 cells. 100 mug/ml of carbocisteine was able to inhibit the TNF-alpha-induced expression of hST3GallV mRNA, FUT3 mRNA, C2/4GnT mRNA and sialyl-Lewis x epitopes as well as the TNF-alpha-induced activity of PI-PLC in NCI-H292 cells. These findings suggest that carbocisteine may normalize the sialyl-Lewis x epitopes expression in mucins through the inhibition of cellular PI-PLC activity in vivo.

Primary Structure and Organ-Specific Expression of the Rat Aryl Hydrocarbon Receptor Repressor Gene

The aryl hydrocarbon receptor repressor (AhRR) is a member of the basic helix-loop-helix/Per-Arnt-Sim (bHLH/PAS) family of transcription factors, providing a negative feedback loop with a xenobiotic or endogenous ligand-dependent signal transduction mediated by the AhR. We sequenced full-length AhRR mRNA extracted from the heart of a male Wistar rat injected intraperitoneally with 3-methylcholanthrene (3-MC) 24 h before. The 95.6 kb-long AhRR genome was clarified to consist of 11 exons and 10 introns. The constitutive expression of AhRR mRNA was prominent in males when compared with females in parallel with the sexual difference in AhR expression. Although AhRR was ubiquitously expressed in all tissues tested, the levels of AhRR expression were higher in the small intestine, where the 3-MC-dependent induction of CYP1A1 transcription was less significant, than in the heart, lung, liver, and kidney. The dose-dependent suppression of AhR-dependent transcriptional activation in both the presence and absence of 3-MC was observed in rat liver-derived RL-34 cells transiently transfected with the expression plasmid for AhRR in combination with the reporter plasmid.

Expression of constitutive androstane receptor splice variants in rat liver and lung and their functional properties

The mammalian constitutive androstane receptor (CAR) is a transcription factor that participates in controlling the expression of xenobiotic metabolizing and transporting genes in response to xenobiotics in an organ-specific manner. In addition to the wild-type CAR (CAR WT) mRNA, mRNAs for five splice variants (SVs) could be detected in the liver of 7-week-old male Wistar rats by RT-PCR using primer pairs covering a full-length mRNA derived from 9 exons; insertion of 18 bp at the 5'-end of intron 8 with or without deletion of 3 bp from the 5'-end of exon 7 (CAR SV1 or SV2), deletion of 4 bp from the 5'-end of exon 8 (CAR SV3), insertion of 195 bp intron 7 (CAR SV4), and insertion of 91 bp intron 6 (CAR SV5). In contrast, only CAR SV5 was detected in lung. Due to the introduction of novel stop codons, all the SVs were considered to code for premature proteins. The liver homogenate gave two protein bands in the vicinity of 37 kDa on Western blotting. They were attributable to CAR WT and SV-complex, respectively, based on their putative molecular weights in descending order. Upon cotransfection with the reporter plasmid, only the cells transfected with the CAR SV4-expression plasmid showed enhanced luciferase activity similar to the WT-transfected cells, for which the further splicing of the remaining intron 7 seemed to be responsible. The transactivation-defective SVs downregulated CAR WT-induced luciferase activity to some extent in the cotransfection experiments.

Characterization of nuclear localization signals and cytoplasmic retention region in the nuclear receptor CAR

The constitutive androstane receptor (CAR) is a ligand/activator-dependent transactivation factor that resides in the cytoplasm and forms part of an as yet unidentified protein complex. Upon stimulation, CAR translocates into the nucleus where it modulates the transactivation of target genes. However, CAR exogenously expressed in rat liver RL-34 cells is located in the nucleus even in the absence of activators. By transiently transfecting RL-34 cells with various mutated rat CAR segments, we identified two nuclear localization signals: a basic amino acid-rich sequence (RRARQARRR) between amino acids 100 and 108; and an assembly of noncontiguous residues widely spread over amino acid residues 111 to 320 within the ligand binding domain. A C-terminal leucine-rich segment corresponding to a previously reported murine xenochemical response signal was not found to exhibit nuclear import activity in cultured cells. Using rat primary hepatocytes transfected with various CAR segments, we identified the region required for the cytoplasmic retention of CAR. Based on these results, the intracellular localization of CAR would be determined by the combined effects of nuclear localization signals, the xenochemical response signal, and the cytoplasmic retention region.

A study of the metabolism of methamphetamine and 4-bromo-2,5-dimethoxyphenethylamine (2C-B) in isolated rat hepatocytes

The metabolism of methamphetamine (MA) and 4-bromo-2,5-dimethoxyphenethylamine (2C-B) in freshly isolated rat hepatocytes was investigated, and compared with in vivo results. A suspended hepatocyte culture, established from male Wistar rats using a collagenase perfusion technique, was incubated in the presence of MA or 2C-B. After enzymatic hydrolysis of the conjugated forms, the metabolites were extracted by liquid-liquid partition and analyzed by gas chromatography/mass spectrometry (GC/MS). Amphetamine, p-hydroxymethamphetamine and p-hydroxyamphetamine were detected in the culture fluids of the rat hepatocytes inoculated with MA. The alcohol derivative, carboxylic acid derivative, 2-O-desmethyl-2C-B, 2-O-desmethyl-N-acetyl-2C-B and 5-O-desmethyl-N-acetyl-2C-B were detected in the case of 2C-B. The major metabolite of MA in rat hepatocytes was p-hydroxymethamphetamine. This is in good agreement with the urinary excretion profile for rats that were fed MA. 2-O-Desmethyl-2C-B and the carboxylic acid derivative were the major recovered metabolites of 2C-B in the rat hepatocyte culture, a slight deviation from the in vivo findings, in which 5-O-desmethyl-N-acetyl-2C-B was found to be the main component. Metabolites with a hydroxy group were largely present in their conjugated forms in the culture fluids, except for 2-O-desmethyl-2C-B. Taking these results into consideration, a primary hepatocyte culture system has the potential to provide a quick and handy method for estimating the in vivo metabolic fate of abused drugs.

Regulation of sialyl-Lewis x epitope expression by TNF-α and EGF in an airway carcinoma cell line

Sialyl-Lewis x epitopes and MUC5AC protein are known to be overexpressed in mucins secreted by patients suffering from various respiratory diseases. To investigate the mechanisms by which airway inflammatory agents mediate the expression of sialyl-Lewis x epitopes and MUC5AC mucin, we examined the effects of tumor necrosis factor (TNF)-alpha and epidermal growth factor (EGF) in the human lung carcinoma cell line, NCI-H292. Basal expression levels of hST3GalIV, FUT3 and C2/4GnT mRNA, involved in the biosynthesis of sialyl-Lewis x, were higher than those of other glycosyltransferases in NCI-H292 cells. TNF-alpha induced expression of hST3GalIV, FUT3, C2/4GnT and MUC5AC mRNAs in NCI-H292 cells. When cells were pretreated with U73122, a phosphatidylinositol-phospholipase C (PI-PLC) inhibitor, the expression of these glycosyltransferase mRNAs was suppressed. Treating cells with EGF induced the down-regulation of these glycosyltransferase mRNAs and sialyl-Lewis x epitopes, while inducing an increase in expression of MUC5AC mRNA. These EGF-mediated effects on the glycosyltransferase and MUC5AC mRNAs were blocked when cells were first exposed to AG1478, an EGF receptor tyrosine kinase inhibitor. These findings suggest that the expression of sialyl-Lewis x epitopes, which is regulated separately from the expression of MUC5AC protein, may be controlled through pathways such as the EGF receptor tyrosine kinase and PI-PLC signaling cascades in NCI-H292 cells.

Diurnal difference in CAR mRNA expression

Background

The constitutive androstane receptor (CAR, NR1I3) plays a key role in the transcriptional activation of genes that encode xenobiotic/steroid and drug metabolizing enzymes.

Results

The expression of CAR mRNA throughout the circadian rhythm is reported for the first time in phase with the clock gene Bmal1 and in antiphase with the clock-controlled gene Rev-erbα mRNAs, with a peak at Zeitgeber time (ZT) 20 and a trough at ZT8, and a peak/trough ratio of 2.0. The diurnal difference in CAR mRNA expression might underlie the 1.7-fold difference in the magnitude of the PB-dependent induction of CYP2B1/2 mRNA.

Conclusion

The circadian oscillation of xenosensor gene CAR mRNA expression is partially responsible for chronopharmacokinetics and chronopharmacology in disease.