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Gastroenterology. 2018 Aug;155(2):557-571.e14. doi: 10.1053/j.gastro.2018.04.032. Epub 2018 May 5.

Mechanisms of MAFG Dysregulation in Cholestatic Liver Injury and Development of Liver Cancer.

Author information

1
Division of Digestive and Liver Diseases, Cedars-Sinai Medical Center, Los Angeles, California; Department of Gastroenterology, Xiangya Hospital, Central South University, Changsha, Hunan, China; Key Laboratory of Cancer proteomics of Chinese Ministry of Health, Xiangya Hospital, Central South University, Changsha, Hunan, China.
2
Division of Digestive and Liver Diseases, Cedars-Sinai Medical Center, Los Angeles, California.
3
Division of Digestive and Liver Diseases, Cedars-Sinai Medical Center, Los Angeles, California; Department of Geriatrics, Guangzhou First People's Hospital, Guangzhou, China; State Key Laboratory of Respiratory Diseases, The First Affiliated Hospital, Guangzhou Medical University, Guangzhou, China.
4
Division of Digestive and Liver Diseases, Cedars-Sinai Medical Center, Los Angeles, California; Institute of Pharmacy and Pharmacology, University of South China, Hengyang, China.
5
Department of Oncology, Xiangya Hospital, Central South University, Changsha, Hunan, China.
6
Department of Surgery, Cedars-Sinai Medical Center, Los Angeles, California.
7
Samuel Oschin Comprehensive Cancer Institute, Cedars-Sinai Medical Center, Los Angeles, California.
8
Division of Digestive and Liver Diseases, Cedars-Sinai Medical Center, Los Angeles, California; Comprehensive Transplant Center, Cedars-Sinai Medical Center, Los Angeles, California.
9
The Warren Alpert Medical School of Brown University, Providence, Rhode Island.
10
Department of Surgery, Cedars-Sinai Medical Center, Los Angeles, California; Comprehensive Transplant Center, Cedars-Sinai Medical Center, Los Angeles, California.
11
Center of Cooperative Research in Bioscience, Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas (Ciberehd), Technology, Park of Bizkaia, Derio, Bizkaia, Spain.
12
Division of Digestive and Liver Diseases, Cedars-Sinai Medical Center, Los Angeles, California. Electronic address: shelly.lu@cshs.org.

Abstract

BACKGROUND & AIMS:

MAF bZIP transcription factor G (MAFG) is activated by the farnesoid X receptor to repress bile acid synthesis. However, expression of MAFG increases during cholestatic liver injury in mice and in cholangiocarcinomas. MAFG interacts directly with methionine adenosyltransferase α1 (MATα1) and other transcription factors at the E-box element to repress transcription. We studied mechanisms of MAFG up-regulation in cholestatic tissues and the pathways by which S-adenosylmethionine (SAMe) and ursodeoxycholic acid (UDCA) prevent the increase in MAFG expression. We also investigated whether obeticholic acid (OCA), an farnesoid X receptor agonist, affects MAFG expression and how it contributes to tumor growth in mice.

METHODS:

We obtained 7 human cholangiocarcinoma specimens and adjacent non-tumor tissues from patients that underwent surgical resection in California and 113 hepatocellular carcinoma (HCC) specimens and adjacent non-tumor tissues from China, along with clinical data from patients. Tissues were analyzed by immunohistochemistry. MAT1A, MAT2A, c-MYC, and MAFG were overexpressed or knocked down with small interfering RNAs in MzChA-1, KMCH, Hep3B, and HepG2 cells; some cells were incubated with lithocholic acid (LCA, which causes the same changes in gene expression observed during chronic cholestatic liver injury in mice), SAMe, UDCA (100 μM), or farnesoid X receptor agonists. MAFG expression and promoter activity were measured using real-time polymerase chain reaction, immunoblot, and transient transfection. We performed electrophoretic mobility shift, and chromatin immunoprecipitation assays to study proteins that occupy promoter regions. We studied mice with bile-duct ligation, orthotopic cholangiocarcinomas, cholestasis-induced cholangiocarcinoma, diethylnitrosamine-induced liver tumors, and xenograft tumors.

RESULTS:

LCA activated expression of MAFG in HepG2 and MzChA-1 cells, which required the activator protein-1, nuclear factor-κB, and E-box sites in the MAFG promoter. LCA reduced expression of MAT1A but increased expression of MAT2A in cells. Overexpression of MAT2A increased activity of the MAFG promoter, whereas knockdown of MAT2A reduced it. MAT1A and MAT2A had opposite effects on the activator protein-1, nuclear factor-κB, and E-box-mediated promoter activity. Expression of MAFG and MAT2A increased, and expression of MAT1A decreased, in diethylnitrosamine-induced liver tumors in mice. SAMe and UDCA had shared and distinct mechanisms of preventing LCA-mediated increased expression of MAFG. OCA increased expression of MAFG, MAT2A, and c-MYC, but reduced expression of MAT1A. Incubation of human liver and biliary cancer cells lines with OCA promoted their proliferation; in nude mice given OCA, xenograft tumors were larger than in mice given vehicle. Levels of MAFG were increased in human HCC and cholangiocarcinoma tissues compared with non-tumor tissues. High levels of MAFG in HCC samples correlated with hepatitis B, vascular invasion, and shorter survival times of patients.

CONCLUSIONS:

Expression of MAFG increases in cells and tissues with cholestasis, as well as in human cholangiocarcinoma and HCC specimens; high expression levels correlate with tumor progression and reduced survival time. SAMe and UDCA reduce expression of MAFG in response to cholestasis, by shared and distinct mechanisms. OCA induces MAFG expression, cancer cell proliferation, and growth of xenograft tumors in mice.

KEYWORDS:

FXR; Obeticholic Acid; S-Adenosylmethionine; Ursodeoxycholic Acid

PMID:
29733835
PMCID:
PMC6067975
[Available on 2019-08-01]
DOI:
10.1053/j.gastro.2018.04.032
[Indexed for MEDLINE]

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