The nuclear receptor CAR (NR1I3) is responsible for the increase in hepatic drug metabolism that results from exposure to diverse xenobiotics. These include the well known inducer phenobarbital, which functions as an indirect CAR activator and a large number of species-specific agonist or inverse agonist ligands. CAR activation also induces an acute, but strictly limited proliferative response, and blocks apoptosis. In accord with this, phenobarbital is a well studied liver non-genotoxic carcinogen and tumor promoter, and we demonstrated that CAR mediates these effects. The ability of CAR to drive liver tumorigenesis suggests, by analogy with hormone dependent estrogen and androgen receptor driven breast and prostate cancers, that antagonizing CAR could have beneficial effects in cancer treatment and chemoprevention. Our preliminary results strongly support this: the mouse CAR inverse agonist androstanol can inhibit hepatocyte proliferation and tumor growth, and may actually shrink established tumors. Additional preliminary results demonstrate a powerful functional synergy between CAR and ?-catenin that results in both unlimited hepatocyte growth and hepatocarcinogenesis. The current proposal addresses two specific hypotheses: 1) CAR and ?-catenin function synergistically to drive hepatocyte proliferation and tumorigenesis. 2) Reversing CAR transcriptional activation by inverse agonists exerts anti-proliferative effects in normal hepatocytes and liver tumors, and will have chemopreventative effects in hepatocarcinogenesis.
Three specific aims address these hypotheses: 1. Characterize the molecular basis for the proliferative and anti-proliferative effects of CAR agonists and inverse agonists in cell culture and in vivo. 2. Define the mechanisms for the synergistic impact of combined CAR and ?-catenin activation in acute liver growth and chronic hepatocarcinogenesis. 3. Critically test the ability of CAR inverse agonists to treat and prevent liver cancer. These studies will provide important new insights into the molecular mechanisms that lead to liver cancer. More importantly, they will identify specific therapeutic strategies that will have direct relevance to human health.

Public Health Relevance

This project is based on understanding the functional roles of the nuclear receptor CAR in health and disease. We have identified potential therapeutic strategies for liver cancer that target CAR. Our goal is to develop these strategies at the levels of both mechanistic understanding and of near term clinical application.

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Molecular and Cellular Endocrinology Study Section (MCE)
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Margolis, Ronald N
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Baylor College of Medicine
Anatomy/Cell Biology
Schools of Medicine
United States
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Park, Young Joo; Lee, Eun Kyung; Lee, Yoon Kwang et al. (2012) Opposing regulation of cytochrome P450 expression by CAR and PXR in hypothyroid mice. Toxicol Appl Pharmacol 263:131-7
Sberna, Anne-Laure; Assem, Mahfoud; Xiao, Rui et al. (2011) Constitutive androstane receptor activation decreases plasma apolipoprotein B-containing lipoproteins and atherosclerosis in low-density lipoprotein receptor-deficient mice. Arterioscler Thromb Vasc Biol 31:2232-9
Smetanina, Mariya A; Pakharukova, Mariya Y; Kurinna, Svitlana M et al. (2011) Ortho-aminoazotoluene activates mouse constitutive androstane receptor (mCAR) and increases expression of mCAR target genes. Toxicol Appl Pharmacol 255:76-85
Wagner, Martin; Moore, David D (2011) Endoplasmic reticulum stress and glucose homeostasis. Curr Opin Clin Nutr Metab Care 14:367-73
Dong, Bingning; Saha, Pradip K; Huang, Wendong et al. (2009) Activation of nuclear receptor CAR ameliorates diabetes and fatty liver disease. Proc Natl Acad Sci U S A 106:18831-6
Hernandez, J P; Mota, L C; Huang, W et al. (2009) Sexually dimorphic regulation and induction of P450s by the constitutive androstane receptor (CAR). Toxicology 256:53-64
Dong, Bingning; Qatanani, Mohammed; Moore, David D (2009) Constitutive androstane receptor mediates the induction of drug metabolism in mouse models of type 1 diabetes. Hepatology 50:622-9
Merrell, Matthew D; Jackson, Jonathan P; Augustine, Lisa M et al. (2008) The Nrf2 activator oltipraz also activates the constitutive androstane receptor. Drug Metab Dispos 36:1716-21
Blanco-Bose, William E; Murphy, Mark J; Ehninger, Armin et al. (2008) C-Myc and its target FoxM1 are critical downstream effectors of constitutive androstane receptor (CAR) mediated direct liver hyperplasia. Hepatology 48:1302-11
Baskin-Bey, Edwina S; Huang, Wendong; Ishimura, Norihisa et al. (2006) Constitutive androstane receptor (CAR) ligand, TCPOBOP, attenuates Fas-induced murine liver injury by altering Bcl-2 proteins. Hepatology 44:252-62

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