DNA Methylation Suppresses Expression of the Urea Cycle Enzyme Carbamoyl Phosphate Synthetase 1 (CPS1) in Human Hepatocellular Carcinoma

Abstract

Carbamoyl phosphate synthetase 1 (CPS1) is a liverspecific, intramitochondrial, rate-limiting enzyme in the urea cycle. A previous study showed that CPS1 is the antigen for hepatocyte paraffin 1 antibody, a commonly used antibody in surgical pathology practice; and CPS1 expression appears to be down-regulated in liver cancer tissue and cell lines. The aim of this study is to understand how the CPS1 gene is regulated in liver carcinogenesis. In this report, we show that human hepatocellular carcinoma (HCC) cells do not express CPS1, whereas cultured human primary hepatocytes express abundant levels. In addition, CPS1 was silenced or down-regulated in liver tumor tissues compared with the matched noncancerous tissues. The expression of CPS1 in HCC cells was restored with a demethylation agent, 5-azacytidine. We show that two CpG dinucleotides, located near the transcription start site, and a CpG-rich region in the first intron were hypermethylated in HCC cells. The hypermethylation of the two CpG dinucleotides was also detected in HCC tumor tissues compared with noncancerous tissues. Further molecular analysis with mutagenesis indicated that the two CpG dinucleotides play a role in promoter activity of the CPS1 gene. In conclusion, our study demonstrates that DNA methylation is a key mechanism of silencing CPS1 expression in human HCC cells, and CPS1 gene hypermethylation of the two CpG dinucleotides is a potential biomarker for HCC.

Role of CPS1 in Cell Growth, Metabolism, and Prognosis in LKB1-Inactivated Lung Adenocarcinoma

“…CPS1 is expressed mainly in intestinal epithelial cells and liver cells, as well as several types of cancer including liver, colorectal, stomach, cervical, and pancreatic cancer (29)(30)(31)(32)(33)(34)(35)(36)(37). Although expression of CPS1 protein has not been well studied in lung cancer, Kaufman ARTICLE (38).…”

Homocitrullination Is a Novel Histone H1 Epigenetic Mark Dependent on Aryl Hydrocarbon Receptor Recruitment of Carbamoyl Phosphate Synthase 1

“…However, P4501A1 inducibility, which does not rely on CPS1, confirmed that AhR functionality persisted over the 3-week culture period. In complementary studies, CPS1 expression was re-established in AML12 cells using 5-aza-2Ј-deoxycitidine (5-Aza) to hypomethylate the CPS1 promoter (24). TCDD-inducible hcit formation only occurred in the 5-Aza-treated CPS1-positive cells (Fig.…”

Linking metabolism and epigenetic regulation in development of hepatocellular carcinoma

“…Epigenetic biomarkers based on promoter hypermethylation have been developed as diagnostic tools to detect liver cirrhosis and HCC (Table 1). 4–10 Many studies have shown that progressive promoter methylation accumulates throughout HCC development and is associated with tumor recurrence and prognosis. 27, 28, 30–32 …”

“…4–10 Many of the DNA methylation biomarkers identified distinguish between normal healthy tissue and cirrhotic tissue, however the distinction between cirrhotic tissue and HCC is less clear. Many gene promoters which are methylated in HCC are also methylated in the surrounding cirrhotic tissue (Table 1).…”

“…The causes of HCC are heterogeneous, with both genetic and epigenetic alterations associated with tumor progression. 3–10 Infection with hepatitis C (HCV) and hepatitis B (HBV ) are major risk factors, as are exposure to aflatoxin (found in stored peanut products) and chronic alcohol abuse. 2 The liver produces metabolites essential for epigenetic processes.…”