TCPOBOP

Expression of c-jun is not mandatory for mouse hepatocyte proliferation induced by two nuclear receptor ligands: TCPOBOP and T3.[Pubmed:21354444]

J Hepatol. 2011 Nov;55(5):1069-78.

BACKGROUND & AIMS: Mice lacking c-jun in the liver display impaired regeneration after partial hepatectomy (PH), and were reported to be more resistant to chemically-induced hepatocellular carcinoma (HCC). We investigated the role of c-jun in normal and preneoplastic hepatocyte proliferation induced by ligands of nuclear receptors, which cause liver hyperplasia in the absence of cell loss/death. METHODS: The effect of 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) on hepatocyte proliferation was determined in c-jun conditional knockout (c-jun(Deltali)) or in mouse liver where c-jun has been silenced. To study the role of c-jun in HCC development, c-jun(Deltali) and WT mice were given diethylnitrosamine (DENA) followed by repeated injections of TCPOBOP. RESULTS: Hepatocyte proliferation induced by TCPOBOP was associated with a stronger proliferative response and earlier S phase entry in c-jun(Deltali) mice, compared to WT animals. Moreover, silencing of c-jun in the liver of CD-1 mice caused increased hepatocyte proliferation. A stronger hepatocyte proliferative response of c-jun(Deltali) mice was observed also following treatment with a ligand of thyroid hormone receptor. Finally, loss of c-jun did not inhibit the development of HCC induced by DENA and promoted by TCPOBOP. CONCLUSIONS: (i) c-jun may, under certain conditions, negatively regulate proliferation of normal hepatocytes, (ii) c-jun is not an absolute requirement for DENA/TCPOBOP-induced HCC formation, suggesting that the therapeutic potential of c-jun/JNK inhibition in liver tumors might be impaired by an increased stimulation of cell growth due to blockade of the c-jun pathway.

The primary mitogen (TCPOBOP)-induced hepatocyte proliferation is resistant to transforming growth factor- beta-1 inhibition.[Pubmed:21040405]

Liver Int. 2010 Nov;30(10):1505-10.

BACKGROUND: Transforming growth factor (TGF)-beta-1 is a very efficient inhibitor of hepatocyte proliferation in various in vivo and in vitro experimental systems. However, there are no data on whether it can influence the mitogenic response induced by primary hepatocyte mitogens. AIMS: In this study, we compared the proliferative response in the liver between wild-type and transgenic mice, overexpressing active TGF-beta-1 in their liver following the treatment by a primary hepatocyte mitogen TCPOBOP (1,4-bis[2-(3,5-dichloropyridyloxy)]benzene). METHODS: The proliferative response was characterized by the immunohistochemical examination of pulse and cumulative bromodeoxyuridine labelling and by quantitative real-time polymerase chain reaction analysis of cell cycle-related genes. RESULTS: Neither of the applied techniques revealed significant differences between the two groups of mice; furthermore, we observed the upregulation of TGF-beta-1 expression following the mitogenic treatment. CONCLUSIONS: TGF-beta-1 does not inhibit the primary mitogen-induced proliferative response of the hepatocytes. This observation may provide an explanation for the divergent consequences of hepatic proliferations induced by partial hepatectomy or primary mitogenic treatment.

Identification of Candidate Target Cyp Genes for microRNAs Whose Expression Is Altered by PCN and TCPOBOP, Representative Ligands of PXR and CAR.[Pubmed:27237601]

Biol Pharm Bull. 2016 Aug 1;39(8):1381-6.

MicroRNAs (miRNAs) are small non-coding RNAs that are involved in mRNA post-transcriptional regulation. The deregulation of miRNAs affects the expression of drug-metabolizing enzymes, drug transporters, and nuclear receptors, all of which are important in regulating drug metabolism. miRNA expression can be altered by several endogenous or exogenous agents, such as steroid hormones, carcinogens, and therapeutic drugs. However, it is unclear whether hepatic miRNA expression is regulated by nuclear receptors, such as pregnane X receptor (PXR) and constitutive androstane receptor (CAR), which are indispensable for the expression of the CYPs. Here we investigated the effects of the mouse PXR and CAR ligands pregnenolone-16alpha-carbonitrile (PCN) and 1,4-bis[(3,5-dichloropyridin-2-yl)oxy]benzene (TCPOBOP) on hepatic miRNA expression in mice. We found that the expression of 9 miRNAs was increased (>2-fold) and of 4 miRNAs was decreased (>50%) in response to PCN, while TCPOBOP treatment led to the up-regulation of 8 miRNAs and down-regulation of 6 miRNAs. Using several miRNA target prediction algorithms, we found that the predicted target genes included several lesser known Cyp genes (Cyp1a1, Cyp1b1, Cyp2b10, Cyp2c38, Cyp2u1, Cyp4a12a/b, Cyp4v3, Cyp17a1, Cyp39a1, and Cyp51). We analyzed the expression of these genes in response to PCN and TCPOBOP and found changes in their mRNA levels, some of which were negatively correlated with the expression of their corresponding miRNAs, suggesting that miRNAs may play a role in regulating Cyp enzyme expression. Further studies will be required to fully elucidate the miRNA regulatory mechanisms that contribute to modulating CYP expression.

Constitutive androstane receptor agonist, TCPOBOP, attenuates steatohepatitis in the methionine choline-deficient diet-fed mouse.[Pubmed:17948939]

World J Gastroenterol. 2007 Nov 14;13(42):5635-41.

AIM: To ascertain whether constitutive androstane receptor (CAR) activation by 1,4-bis-[2-(3,5,-dichloropyridyloxy)] benzene (TCPOBOP) modulates steatohepatitis in the methionine choline-deficient (MCD) diet-fed animal. METHODS: C57/BL6 wild-type mice were fed the MCD or standard diet for 2 wk and were treated with either the CAR agonist, TCPOBOP, or the CAR inverse agonist, androstanol. RESULTS: Expression of CYP2B10 and CYP3A11, known CAR target genes, increased 30-fold and 45-fold, respectively, in TCPOBOP-treated mice fed the MCD diet. TCPOBOP treatment reduced hepatic steatosis (44.6 +/- 5.4% vs 30.4 +/- 4.5%, P < 0.05) and serum triglyceride levels (48 +/- 8 vs 20 +/- 1 mg/dL, P < 0.05) in MCD diet-fed mice as compared with the standard diet-fed mice. This reduction in hepatic steatosis was accompanied by an increase in enzymes involved in fatty acid microsomal omega-oxidation and peroxisomal beta-oxidation, namely CYP4A10, LPBE, and 3-ketoacyl-CoA thiolase. The reduction in steatosis was also accompanied by a reduction in liver cell apoptosis and inflammation. In contrast, androstanol was without effect on any of the above parameters. CONCLUSION: CAR activation stimulates induction of genes involved in fatty acid oxidation, and ameliorates hepatic steatosis, apoptosis and inflammation.

The xenobiotic compound 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene is an agonist ligand for the nuclear receptor CAR.[Pubmed:10757780]

Mol Cell Biol. 2000 May;20(9):2951-8.

A wide range of xenobiotic compounds are metabolized by cytochrome P450 (CYP) enzymes, and the genes that encode these enzymes are often induced in the presence of such compounds. Here, we show that the nuclear receptor CAR can recognize response elements present in the promoters of xenobiotic-responsive CYP genes, as well as other novel sites. CAR has previously been shown to be an apparently constitutive transactivator, and this constitutive activity is inhibited by androstanes acting as inverse agonists. As expected, the ability of CAR to transactivate the CYP promoter elements is blocked by the inhibitory inverse agonists. However, CAR transactivation is increased in the presence of 1,4-bis[2-(3, 5-dichloropyridyloxy)]benzene (TCPOBOP), the most potent known member of the phenobarbital-like class of CYP-inducing agents. Three independent lines of evidence demonstrate that TCPOBOP is an agonist ligand for CAR. The first is that TCPOBOP acts in a dose-dependent manner as a direct agonist to compete with the inhibitory effect of the inverse agonists. The second is that TCPOBOP acts directly to stimulate coactivator interaction with the CAR ligand binding domain, both in vitro and in vivo. The third is that mutations designed to block ligand binding block not only the inhibitory effect of the androstanes but also the stimulatory effect of TCPOBOP. Importantly, these mutations do not block the apparently constitutive transactivation by CAR, suggesting that this activity is truly ligand independent. Both its ability to target CYP genes and its activation by TCPOBOP demonstrate that CAR is a novel xenobiotic receptor that may contribute to the metabolic response to such compounds.

In vivo hepatocyte proliferation is inducible through a TNF and IL-6-independent pathway.[Pubmed:9747883]

Oncogene. 1998 Aug 27;17(8):1039-44.

Recent studies in mice harboring a targeted disruption of genes encoding TNF receptor 1 (TNFR-1) or Interleukin 6 (IL-6) suggested a critical role for TNF and IL-6 in initiation of liver regeneration after 2/3 partial hepatectomy. However, hepatocyte proliferation can also occur following treatment with agents that do not induce tissue loss (primary mitogens). To determine whether the above cytokines could also be involved in mitogen-induced liver cell proliferation, we studied the hepatocyte proliferative response after treatment with primary mitogens in mice knock-out for TNFR-1 or IL-6. Our results showed no difference in the proliferative response of the liver between the wild type and the knock-out mice following treatment with the mitogens 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP), or the peroxisome proliferator, ciprofibrate, suggesting that TNF or IL-6 may not play a major role in this type of proliferation. Gel shift assay indicated that TCPOBOP-induced hepatocyte proliferation is not associated with activation of STAT3 transcription factor, a major target of IL-6 and other growth factors/cytokines. Our results thus indicate that hepatocyte proliferation can be induced by at least two different pathways; compensatory regeneration being TNF and IL-6-dependent, and mitogen-induced direct hyperplasia which does not require TNF or IL-6.

TCPOBOP is a constitutive androstane receptor (CAR) agonist that induces robust hepatocyte proliferation and hepatomegaly without any liver injury or tissue loss. TCPOBOP attenuates Fas-induced murine liver injury by altering Bcl-2 proteins.

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