Human liver methionine cycle: MAT1A and GNMT gene resequencing, functional genomics, and hepatic genotype-phenotype correlation.
The "methionine cycle" plays a critical role in the regulation of concentrations of (S)-adenosylmethionine (AdoMet), the major biological methyl donor. We set out to study sequence variation in genes encoding the enzyme that synthesizes AdoMet in liver, methionine adenosyltransferase 1A (MAT1A) and the major hepatic AdoMet using enzyme, glycine N-methyltransferase (GNMT), as well as functional implications of that variation. We resequenced MAT1A and GNMT using DNA from 288 subjects of three ethnicities, followed by functional genomic and genotype-phenotype correlation studies performed with 268 hepatic biopsy samples. We identified 44 and 42 polymorphisms in MAT1A and GNMT, respectively. Quantitative Western blot analyses for the human liver samples showed large individual variation in MAT1A and GNMT protein expression. Genotype-phenotype correlation identified two genotyped single-nucleotide polymorphisms (SNPs), reference SNP (rs) 9471976 (corrected p = 3.9 × 10(-10)) and rs11752813 (corrected p = 1.8 × 10(-5)), and 42 imputed SNPs surrounding GNMT that were significantly associated with hepatic GNMT protein levels (corrected p values < 0.01). Reporter gene studies showed that variant alleles for both genotyped SNPs resulted in decreased transcriptional activity. Correlation analyses among hepatic protein levels for methionine cycle enzymes showed significant correlations between GNMT and MAT1A (p = 1.5 × 10(-3)) and between GNMT and betaine homocysteine methyltransferase (p = 1.6 × 10(-7)). Our discovery of SNPs that are highly associated with hepatic GNMT protein expression as well as the "coordinate regulation" of methionine cycle enzyme protein levels provide novel insight into the regulation of this important human liver biochemical pathway.
Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, MN 55905, USA.
Yuan
Y
Ji
Kendra K S
KK
Nordgren
Yubo
Y
Chai
Scott J
SJ
Hebbring
Gregory D
GD
Jenkins
Ryan P
RP
Abo
Yi
Y
Peng
Linda L
LL
Pelleymounter
Irene
I
Moon
Bruce W
BW
Eckloff
Xiaoshan
X
Chai
Jianping
J
Zhang
Brooke L
BL
Fridley
Vivien C
VC
Yee
Eric D
ED
Wieben
Richard M
RM
Weinshilboum
D001741:Black or African American / Q000235:genetics; D044466:Asian People / Q000235:genetics; D001706:Biopsy; D015153:Blotting, Western; D005492:Folic Acid / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D056726:Genetic Association Studies; D023281:Genomics / Q000379:methods; D005838:Genotype; D050938:Glycine N-Methyltransferase / Q000235:genetics* / Q000378:metabolism*; D057809:HEK293 Cells; D056945:Hep G2 Cells; D006801:Humans; D008099:Liver / Q000201:enzymology*; D008715:Methionine / Q000378:metabolism*; D008716:Methionine Adenosyltransferase / Q000235:genetics* / Q000378:metabolism*; D010641:Phenotype; D020641:Polymorphism, Single Nucleotide; D012436:S-Adenosylmethionine / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014162:Transfection; D044465:White People / Q000235:genetics
D012436:S-Adenosylmethionine; D005492:Folic Acid; D008715:Methionine; C494510:GNMT protein, human; D050938:Glycine N-Methyltransferase; C506577:MAT1A protein, human; D008716:Methionine Adenosyltransferase