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Catechol O-methyltransferase pharmacogenomics: human liver genotype-phenotype correlation and proximal promoter studies.

ABSTRACT: Catechol O-methyltransferase (COMT) is expressed as both soluble (S) and membrane-bound (MB) isoforms, with S-COMT predominantly expressed in the liver. A common nonsynonymous single nucleotide polymorphism (SNP), 472G > A (108/158Val > Met, S/MB), has been associated with variation in levels of COMT enzyme activity and thermal stability. We set out to test the hypothesis that additional COMT polymorphisms might also be associated with phenotypic variation.We phenotyped 268 liver biopsy samples for S-COMT activity and thermal stability, resequenced a portion of the gene that had not been resequenced earlier, and genotyped DNA from these same samples for 16 COMT polymorphisms.There was a significant association between the two COMT phenotypes and genotype at the codon 108 SNP. A haplotype-based approach was then used to assess the possible association of other polymorphisms with phenotype. Specifically, the codon 108 SNP explained 20.4% of variance in enzyme activity (P < 10), and 59% of variance in thermal stability (P < 10). Haplotypes that included SNPs at cDNA nucleotides 408 and 472 explained additional variance in enzyme activity (up to 24.4%), and the addition to the haplotype of a SNP at intron 2 (51) explained a total of 27.5% of the variance. However, no SNPs beyond that at the nucleotide 472G > A polymorphism were associated with variation in thermal stability. We also observed a three-fold variation in the ability of reporter gene constructs for 'proximal promoter' haplotypes to drive transcription.The common COMT 108Val > Met polymorphism is associated with human liver S-COMT activity and thermal stability, but additional COMT SNPs also contribute to variation in activity.

SUBMITTER: Zhang J

PROVIDER: S-EPMC3052748 | biostudies-literature | 2009 Aug

REPOSITORIES: biostudies-literature

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Catechol O-methyltransferase pharmacogenomics: human liver genotype-phenotype correlation and proximal promoter studies.

Zhang Jianping J Ji Yuan Y Moon Irene I Pelleymounter Linda L LL Ezequel Salavaggione Oreste O Wu Yanhong Y Jenkins Gregory D GD Batzler Anthony J AJ Schaid Daniel J DJ Weinshilboum Richard M RM

Pharmacogenetics and genomics 20090801 8

<h4>Objectives</h4>Catechol O-methyltransferase (COMT) is expressed as both soluble (S) and membrane-bound (MB) isoforms, with S-COMT predominantly expressed in the liver. A common nonsynonymous single nucleotide polymorphism (SNP), 472G > A (108/158Val > Met, S/MB), has been associated with variation in levels of COMT enzyme activity and thermal stability. We set out to test the hypothesis that additional COMT polymorphisms might also be associated with phenotypic variation.<h4>Methods</h4>We p ...[more]

PMID: 19641441

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Project description:Betaine-homocysteine methyltransferase (BHMT) catalyzes the remethylation of homocysteine. BHMT is highly expressed in the human liver. In the liver, BHMT catalyzes up to 50% of homocysteine metabolism. Understanding the relationship between BHMT genetic polymorphisms and function might increase our understanding of the role of this reaction in homocysteine remethylation and in S-adenosylmethionine-dependent methylation. To help achieve those goals, we measured levels of BHMT enzyme activity and immunoreactive protein in 268 human hepatic surgical biopsy samples from adult subjects as well as 73 fetal hepatic tissue samples obtained at different gestational ages. BHMT protein levels were correlated significantly (p<0.001) with levels of enzyme activity in both fetal and adult tissues, but both were decreased in fetal tissue when compared with levels in the adult hepatic biopsies. To determine possible genotype-phenotype correlations, 12 tag SNPs for BHMT and the closely related BHMT2 gene were selected from SNPs observed during our own gene resequencing studies as well as from HapMap. These SNPs data were used to genotype DNA from the adult hepatic surgical biopsy samples, and genotype-phenotype association analysis was performed. Three SNPs (rs41272270, rs16876512, and rs6875201), located 28kb upstream, in the 5'-UTR and in intron 1 of BHMT, respectively, were significantly correlated with both BHMT activity (p=3.41E-8, 2.55E-9 and 2.46E-10, respectively) and protein levels (p=5.78E-5, 1.08E-5 and 6.92E-6, respectively). We also imputed 230 additional SNPs across the BHMT and BHMT2 genes, identifying an additional imputed SNP, rs7700790, that was also highly associated with hepatic BHMT enzyme activity and protein. However, none of the 3 genotyped or one imputed SNPs displayed a "shift" during electrophoretic mobility shift assays. These observations may help us to understand individual variation in the regulation of BHMT in the human liver and its possible relationship to variation in methylation.

Project description:AimTo determine whether cellular apoptosis is a suitable phenotypic trait for pharmacogenomics studies by evaluating caspase 3/7-mediated activity in lymphoblastoid cell lines after treatment with six chemotherapeutic agents: 5'-deoxyfluorouridine, pemetrexed, cytarabine, paclitaxel, carboplatin, and cisplatin.Materials and methodsUsing monozygotic twin pair and sibling pair lymphoblastoid cell lines, we identified conditions for measurement of caspase 3/7 activity in lymphoblastoid cell lines. Genome-wide association studies were performed with over 2 million single nucleotide polymorphisms (SNPs) and cisplatin-induced apoptosis in HapMap CEU cell lines (n=77).ResultsAlthough treatment with 5'-deoxyfluorouridine and pemetrexed for up to 24 h resulted in low levels of apoptosis or interindividual variation in caspase-dependent cell death; paclitaxel, cisplatin, carboplatin, and cytarabine treatment for 24 h resulted in 9.4-fold, 9.1-fold, 7.0-fold, and 6.0-fold increases in apoptosis relative to control, respectively. There was a weak correlation between caspase activity and cytotoxicity (r(2)=0.03-0.29) demonstrating that cytotoxicity and apoptosis are two distinct phenotypes that may produce independent genetic associations. Estimated heritability (h(2)) for apoptosis was 0.57 and 0.29 for cytarabine (5 and 40 μmol/l, respectively), 0.22 for paclitaxel (12.5 nmol/l), and 0.34 for cisplatin (5 μmol/l). In the genome-wide association study using the HapMap CEU panel, we identified a significant enrichment of cisplatin-induced cytotoxicity SNPs within the significant cisplatin-induced apoptosis SNPs and an enrichment of expression quantitative trait loci (eQTL). Among these eQTLs, we identified several eQTLs with known function related to apoptosis and/or cytotoxicity.ConclusionOur study identifies apoptosis as a phenotype for pharmacogenomic studies in lymphoblastoid cell lines after treatment with paclitaxel, cisplatin, carboplatin, and cytarabine that may have utility for discovering biomarkers to predict response to certain chemotherapeutics.

Dataset Information

Catechol O-methyltransferase pharmacogenomics: human liver genotype-phenotype correlation and proximal promoter studies.

Publications

Catechol O-methyltransferase pharmacogenomics: human liver genotype-phenotype correlation and proximal promoter studies.

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