Chrysin, baicalein and galangin are indirect activators of the human constitutive androstane receptor (CAR)

Carazo, Alejandro; Smutný, Tomás̆; Hyršová, Lucie; Berka, Karel; Pávek, Petr

doi:10.1016/j.toxlet.2015.01.013

Cited by 35 publications

(33 citation statements)

References 48 publications

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“…CITCO, prepared in DMSO, was used as a positive control hCAR agonist ligand, and clotrimazole (in DMSO) as an inverse agonist. The LanthaScreen TR-FRET CAR Coactivator Assay was used according to the manufacturer's instructions (Invitrogen) and has been recently described (Carazo and Pavek, 2015). A dilution series of each test compound was prepared at 100Â and then diluted to 2Â with Complete TR-FRET Coregulator Buffer G. A 10-ml aliquot of each dilution was transferred to the wells of a 384-well plate in triplicate, and the glutathione S-transferase-hCAR ligand-binding-domain fusion protein (20 nM) was added to each well followed by a mixture containing 0.5 mM fluoresceinlabeled peroxisome proliferator-activated receptor gamma, coactivator 1 alpha (PGC1a) peptide, and 20 nM terbium-conjugated anti-glutathione S-transferase antibody.…”

Section: Methodsmentioning

confidence: 99%

Nonsterol Isoprenoids Activate Human Constitutive Androstane Receptor in an Isoform-Selective Manner in Primary Cultured Mouse Hepatocytes

Rondini

Duniec-Dmuchowski

Kocarek

2016

Drug Metabolism and Disposition

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Our laboratory previously reported that accumulation of nonsterol isoprenoids following treatment with the squalene synthase inhibitor, squalestatin 1 (SQ1) markedly induced cytochrome P450 (CYP)2B1 mRNA and reporter activity in primary cultured rat hepatocytes, which was dependent on activation of the constitutive androstane receptor (CAR). The objective of the current study was to evaluate whether isoprenoids likewise activate murine CAR (mCAR) or one or more isoforms of human CAR (hCAR) produced by alternative splicing (SPTV, hCAR2; APYLT, hCAR3). We found that SQ1 significantly induced Cyp2b10 mRNA (∼3.5-fold) in primary hepatocytes isolated from both CAR-wild-type and humanized CAR transgenic mice, whereas the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor pravastatin had no effect. In the absence of CAR, basal Cyp2b10 mRNA levels were reduced by 28-fold and the effect of SQ1 on Cyp2b10 induction was attenuated. Cotransfection with an expression plasmid for hCAR1, but not hCAR2 or hCAR3, mediated SQ1-induced CYP2B1 and CYP2B6 reporter activation in hepatocytes isolated from CAR-knockout mice. This effect was also observed following treatment with the isoprenoid trans,trans-farnesol. The direct agonist CITCO increased interaction of hCAR1, hCAR2, and hCAR3 with steroid receptor coactivator-1. However, no significant effect on coactivator recruitment was observed with SQ1, suggesting an indirect activation mechanism. Further results from an in vitro ligand binding assay demonstrated that neither farnesol nor other isoprenoids are direct ligands for hCAR1. Collectively, our findings demonstrate that SQ1 activates CYP2B transcriptional responses through farnesol metabolism in an hCAR1-dependent manner. Further, this effect probably occurs through an indirect mechanism.

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Section: Methodsmentioning

confidence: 99%

Nonsterol Isoprenoids Activate Human Constitutive Androstane Receptor in an Isoform-Selective Manner in Primary Cultured Mouse Hepatocytes

Rondini

Duniec-Dmuchowski

Kocarek

2016

Drug Metabolism and Disposition

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“…This binding potently inhibited EGF-mediated signaling and led to the dephosphorylation of the downstream receptor for activated C kinase 1 (RACK1) at Tyr52, which promoted dephosphorylation of the Thr38 residue of hCAR by PP2A, leading to the nuclear translocation and activation of CAR [73]. Subsequent studies with the flavonoids chrysin, baicalein, and galangin, which are known to activate CAR, found that these compounds do not bind to CAR and instead activate CAR through inhibition of EGF-mediated signaling, further validating inhibition of the EGF signaling pathway as a common mechanism for indirect CAR activation [74]. …”

Section: Constitutive Androstane Receptormentioning

confidence: 99%

Mechanisms of xenobiotic receptor activation: Direct vs. indirect

Mackowiak

Wang

2016

Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanism

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The so-called xenobiotic receptors (XRs) have functionally evolved into cellular sensors for both endogenous and exogenous stimuli by regulating the transcription of genes encoding drug-metabolizing enzymes and transporters, as well as those involving energy homeostasis, cell proliferation, and/or immune responses. Unlike prototypical steroid hormone receptors, XRs are activated through both direct ligand-binding and ligand-independent (indirect) mechanisms by a plethora of structurally unrelated chemicals. This review covers research literature that discusses direct vs. indirect activation of XRs. A particular focus is centered on the signaling control of the constitutive androstane receptor (CAR), the pregnane X receptor (PXR) and the aryl hydrocarbon receptor (AhR). We expect that this review will shed light on both the common and distinct mechanisms associated with activation of these three XRs.

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“…Indirect activation of CAR with PB or phenytoin has been well documented [105, 106] and is now understood to be a common mechanism of CAR activation, with an increasing number of indirect activators having been identified [e.g., flavonoids [107], triclosan [108], or acetaminophen [109]]. These activators do not bind directly to CAR; instead, they activate CAR by stimulating its nuclear translocation in a ligand-independent manner.…”

Section: Carmentioning

confidence: 99%

Small-molecule modulators of PXR and CAR

Chai

Cherian

Wang

et al. 2016

Biochimica et Biophysica Acta (BBA) - Gene Regulatory Mechanism

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Two nuclear receptors, the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR), participate in the xenobiotic detoxification system by regulating the expression of drug-metabolizing enzymes and transporters in order to degrade and excrete foreign chemicals or endogenous metabolites. This review aims to expand the perceived relevance of PXR and CAR beyond their established role as master xenosensors to disease-oriented areas, emphasizing their modulation by small molecules. Structural studies of these receptors have provided much-needed insight into the nature of their binding promiscuity and the important elements that lead to ligand binding. Reports of species- and isoform-selective activation highlight the need for further scrutiny when extrapolating from animal data to humans, as animal models are at the forefront of early drug discovery.

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Chrysin, baicalein and galangin are indirect activators of the human constitutive androstane receptor (CAR)

Cited by 35 publications

References 48 publications

Nonsterol Isoprenoids Activate Human Constitutive Androstane Receptor in an Isoform-Selective Manner in Primary Cultured Mouse Hepatocytes

Nonsterol Isoprenoids Activate Human Constitutive Androstane Receptor in an Isoform-Selective Manner in Primary Cultured Mouse Hepatocytes

Mechanisms of xenobiotic receptor activation: Direct vs. indirect

Small-molecule modulators of PXR and CAR

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