Characterization of a glycine N‐methyltransferase gene knockout mouse model for hepatocellular carcinoma: Implications of the gender disparity in liver cancer susceptibility

Abstract

Hepatocellular carcinoma (HCC) is the fifth common cancer in the world and it mainly occurs in men. Glycine N-methyltransferase (GNMT) participates in one-carbon metabolism and affects DNA methylation by regulating the ratio of S-adenosylmethionine to S-adenosylhomocystine. Previously, we described that the expression of GNMT was diminished in human HCC. Here, we showed that 50% (3/6) male and 100% (7/7) female Gnmt2/2 mice developed HCC, and their mean ages of HCC development were 17 and 16.5 months, respectively. In addition, 42.9% (3/7) of female Gnmt2/2 mice had hemangioma. Wnt reporter assay demonstrated that Gnmt is a negative regulator for canonical Wnt signaling pathway. Beta-catenin, cyclin D1 and c-Myc, genes related to Wnt pathway, were upregulated in the liver tissues from both 11 weeks and HCC stage of Gnmt2/2 mice. Furthermore, global DNA hypomethylation and aberrant expression of DNA methyltransferases 1 and 3b were found in the early and late stages of HCC development. Hierarchical cluster analysis of 6,023 transcripts from microarray data found that gene expression patterns of HCC tumors from male and female Gnmt2/2 mice were distinctively different. Real-time PCR confirmed that Gadd45a, Pak1, Mapk3 and Dsup3 genes of mitogen-activated protein kinase (MAPK) pathway were activated in Gnmt2/2 mice, especially in the female mice. Therefore, GNMT is a tumor suppressor gene for liver cancer, and it is associated with gender disparity in liver cancer susceptibility. '

Glycine N-Methyltransferase Deficiency Affects Niemann-Pick Type C2 Protein Stability and Regulates Hepatic Cholesterol Homeostasis

“…In this study, we showed that Gnmt -/-mice had signs of hepatic steatosis with increased cholesterol deposition in liver tissues, as well as inflammatory infiltration before HCC formation ( Figure 1). According to our previous report, 50% male and 100% female Gnmt -/-mice developed HCC spontaneously (26), suggesting that loss of GNMT is associated with gender disparity of liver cancer susceptibility. It is important to note that the percentages of female Gnmt -/-mice with fatty change were higher than in male Gnmt -/-mice at 11 wks and 9 months (Supplementary Table 5).…”

“…According to genotypic analyses, the loss of heterozygosity at the GNMT locus in paired tumor and tumor-adjacent tissues from HCC patients ranges from 36% to 47% (24). Previously, we generated a GNMT knockout (Gnmt -/-) mice and reported on their tendencies toward chronic hepatitis, glycogen storage, hypercholesterolemia, fatty nodules and HCC (25,26). In this study, we showed that Gnmt -/-mice impaired cholesterol metabolism and developed steatohepatitis.…”

“…GNMT deficiency in mice results in chronic hepatitis, fatty liver and HCC spontaneously (25,26,30). Recently, several putative metabolites identified in Gnmt -/-mice serum closely resemble those of NAFLD patients (31).…”

Reply

“…Then, after our discovery of HCC in our GNMT-/-animals, the Chen group found that their GNMT-/-animals also developed HCC at about 17 months of age. 4 Most surprising in Dr. Chen's letter is the contention that our GNMT knockout mouse is not a complete knockout based on the dubious designation of a 51-nucleotide to 52-nucleotide sequence as a gene "promoter" with no documentation to justify this. They contend that our mouse model generates a protein truncated by 73 amino acids.…”

“…We know from both the Botnia and Malmö feasibility studies that the best clinical predictors for future diabetes are current smoking status; family history of diabetes, hypertension, and increased body mass index (BMI); and increased triglyceride, apolipoprotein A-I, and liver enzyme levels. 2,3,4 In the baseline patient characteristics, we could only find triglyceride, baseline liver enzyme levels, baseline hyper-…”