Glycine-N methyltransferase expression in HepG2 cells is involved in methyl group homeostasis by regulating transmethylation kinetics and DNA methylation

Yi Cheng Wang, Feng Yao Tang, Shih Yin Chen, Yi Ming Chen, En Pei Isabel Chiang

研究成果: 雜誌貢獻文章

25 引文 斯高帕斯(Scopus)

摘要

Glycine-N methyltransferase (GNMT) is a potential tumor suppressor that is commonly inactivated in human hepatoma. We systematically investigated how GNMT regulates methyl group kinetics and global DNA methylation. HepG2 cells (GNMT inactive, GNMT-) and cells transfected with GNMT expressed vector (GNMT+) were cultured in low (10 μmol/L), adequate (100 μmol/L), or high (500 μmol/L) L-methionine, each with 2.27 μmol/L folate. Transmethylation kinetics were studied using stable isotopic tracers and GC-MS. Methylation status was determined by S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH) levels, SAM:SAH ratio, DNA methyltransferase (DNMT) activity, and methylated cytidine levels in DNA. Compared with GNMT- cells, GNMT+ cells had lower homocysteine and greater cysteine concentrations. GNMT expression increased methionine clearance by inducing homocysteine transsulfuration and remethylation metabolic fluxes when cells were cultured in high or adequate L-methionine. In contrast, homocysteine remethylation flux was lower in GNMT+ cells than in GNMT- cells and homocysteine transsulfuration fluxes did not differ when cells were cultured in low methionine, suggesting that normal GNMT function helps to conserve methyl groups. Furthermore, GNMT expression decreased SAM and increased SAH levels and reduced DNMT activity in high or adequate, but not low, methionine cultures. In low methionine cultures, restoring GNMT in HepG2 cells did not lead to sarcosine synthesis, which would waste methyl groups. Methylated cytidine levels were significantly lower in GNMT- cells than in GNMT+ cells. In conclusion, we have shown that GNMT affects transmethylation kinetics and SAM synthesis and facilitates the conservation of methyl groups by limiting homocysteine remethylation fluxes.
原文英語
頁(從 - 到)777-782
頁數6
期刊Journal of Nutrition
141
發行號5
DOIs
出版狀態已發佈 - 五月 1 2011
對外發佈Yes

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics

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