A novel role of the tumor suppressor GNMT in cellular defense against DNA damage.
Glycine N-methyltransferase (GNMT) is a folate binding protein commonly diminished in human hepatoma yet its role in tumor development remains to be established. GNMT binds to methylfolate but is also inhibited by it; how such interactions affect human carcinogenesis is unclear. We postulated that GNMT plays a role in folate-dependent methyl group homeostasis and helps maintain genome integrity by promoting nucleotide biosynthesis and DNA repair. To test the hypothesis, GNMT was over-expressed in GNMT-null cell lines cultured in conditions of folate abundance or restriction. The partitioning of folate dependent 1-carbon groups was investigated using stable isotopic tracers and GC/MS. DNA damage was assessed as uracil content in cell models, as well as in Gnmt wildtype (Gnmt(+/+)), heterozygote (Gnmt(+/-)) and knockout (Gnmt(-/-)) mice under folate deplete, replete, or supplementation conditions. Our study demonstrated that GMMT 1) supports methylene-folate dependent pyrimidine synthesis; 2) supports formylfolate dependent purine syntheses; 3) minimizes uracil incorporation into DNA when cells and animals were exposed to folate depletion; 4) translocates into nuclei during prolonged folate depletion. In conclusion, loss of GNMT impairs nucleotide biosynthesis. Over-expression of GNMT enhances nucleotide biosynthesis and improves DNA integrity by reducing uracil misincorporation in DNA both in vitro and in vivo. To our best knowledge, the role of GNMT in folate dependent 1-carbon transfer in nucleotide biosynthesis has never been investigated. The present study gives new insights into the underlying mechanism by which GNMT can participate in tumor prevention/suppression in humans.
Department of Food Science and Biotechnology, National Chung Hsing University, Taichung, Taiwan, Republic of China.
Yi-Cheng
YC
Wang
Wei-Li
WL
Lin
Yan-Jun
YJ
Lin
Feng-Yao
FY
Tang
Yi-Ming
YM
Chen
En-Pei Isabel
EP
Chiang
D000241:Adenosine / Q000378:metabolism; D000818:Animals; D002250:Carbon Radioisotopes; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004249:DNA Damage; D019175:DNA Methylation; D019587:Dietary Supplements; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D005492:Folic Acid / Q000494:pharmacology*; D050938:Glycine N-Methyltransferase / Q000502:physiology*; D022781:Hepatocytes / Q000378:metabolism / Q000473:pathology*; D006710:Homocysteine / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000378:metabolism / Q000473:pathology*; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008297:Male; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP) / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D015778:Minor Histocompatibility Antigens; D021381:Protein Transport; D011687:Purines / Q000378:metabolism; D011743:Pyrimidines / Q000378:metabolism; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D013763:Tetrahydrofolates; D014498:Uracil / Q000378:metabolism
D002250:Carbon Radioisotopes; D015778:Minor Histocompatibility Antigens; D011687:Purines; D011743:Pyrimidines; D013763:Tetrahydrofolates; D006710:Homocysteine; D014498:Uracil; D012436:S-Adenosylmethionine; D005492:Folic Acid; D012435:S-Adenosylhomocysteine; C539735:MTHFD1 protein, human; D008754:Methylenetetrahydrofolate Dehydrogenase (NADP); D050938:Glycine N-Methyltransferase; D000241:Adenosine; C005984:5-methyltetrahydrofolate
glycine-N methyltransferase; nuclear folate metabolism; purine synthesis; pyrimidine synthesis; stable isotopic tracer studies; transmethylation metabolic kinetics; uracil misincorporation