Loss of CYP3A7 gene induction by 1,25-dihydroxyvitamin D3 is caused by less binding of VDR to the proximal ER6 in CYP3A7 gene

Cytochrome P450 3A4 and 3A7 (CYP3A4 and CYP3A7, respectively) are predominant forms in the human adult and fetal liver, respectively. 1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) is known to be a potent inducer of CYP3A4 in human colon carcinoma Caco-2 via vitamin D receptor (VDR). However, whether CYP3A7 is inducible by 1,25(OH)(2)D(3) has not yet been elucidated. In the present study, we examined the effect of 1,25(OH)(2)D(3) on CYP3A7 gene expression in Caco-2 cells, which express CYP3A4 and CYP3A7 mRNAs. 1,25(OH)(2)D(3) hardly induced the expression of CYP3A7 mRNA in contrast to the marked induction of CYP3A4 mRNA. Reporter assay using 5'-franking region CYP3A4 and CYP3A7 genes also revealed that 1,25(OH)(2)D(3) activates CYP3A4 promoter, but not CYP3A7 promoter, which has two mutations in the proximal ER6 site compared with CYP3A4 promoter. In addition, we found that the binding of VDR to the proximal ER6 in CYP3A7 gene was markedly less than that to the proximal ER6 in CYP3A4 gene using gel shift assay. Taken together, the decrease of VDR binding to the proximal ER6 caused by the mutation results in the loss of CYP3A7 gene activation by 1,25(OH)(2)D(3).     

3'-UTR polymorphism in the human CYP2A6 gene affects mRNA stability and enzyme expression

Cytochrome P450 2A6 (CYP2A6) is the major nicotine C-oxidase in human and participates in the metabolism of drugs and precarcinogens. The CYP2A6 gene is highly polymorphic and more than 22 different alleles have been described. We here focused on the polymorphism in the 3'-UTR region, in particular the common CYP2A6*1B allele, carrying an unequal crossover element from the pseudogene CYP2A7. Analysis of CYP2A6 expression in a human liver bank (n=46) revealed that the protein level and catalytic activity using coumarin as a substrate were all higher, following a linear gene-dose relationship, in livers carrying one or two copies of CYP2A6*1B, as compared to other CYP2A6 allelic variants. Different variants of the CYP2A6 3'-UTR were cloned into a modified pGL3 plasmid downstream of the luciferase reporter gene. The plasmids, having the proximal promoter of CYP2A6 gene, were transfected into HeLa cells or injected into the tail veins of male CD1 mice. In both systems, the 3'-UTR CYP2A6*1B constructs caused higher reporter gene activity and the CYP2A7 3'-UTR construct lower activity, compared to the CYP2A6*1 3'-UTR constructs. Two SNPs differentiating the 3'-UTR between CYP2A7 and CYP2A6*1B were found to be of importance for the expression in both systems. Analysis of reporter enzyme degradation in HeLa cells showed that luciferase-3'-UTR-CYP2A6*1A had a half-life of approximately 4.9h as compared to 6.3h for luciferase-3'-UTR-CYP2A6*1B. In conclusion, we identified polymorphic motifs in the CYP2A6 3'-UTR of importance for CYP2A6 mRNA stabilization and enzyme expression. Such polymorphism has been described to influence the in vivo rate of nicotine elimination and possibly the cigarette consumption and risk of smoking induced lung cancer.     

Allele and genotype frequencies of the polymorphic cytochrome P450 genes (CYP1A1, CYP3A4, CYP3A5, CYP2C9 and CYP2C19) in the Jordanian population

Drug metabolizing enzymes participate in the neutralizing of xenobiotics and biotransformation of drugs. Human cytochrome P450, particularly CYP1A1, CYP2C9, CYP2C19, CYP3A4 and CYP3A5, play an important role in drug metabolism. The genes encoding the CYP enzymes are polymorphic, and extensive data have shown that certain alleles confer reduced enzymatic function. The goal of this study was to determine the frequencies of important allelic variants of CYP1A1, CYP2C9, CYP2C19, CYP3A4 and CYP3A5 in the Jordanian population and compare them with the frequency in other ethnic groups. Genotyping of CYP1A1(m1 and m2), CYP2C9 (*2 and *3), CYP2C19 (*2 and *3), CYP3A4*5, CYP3A5 (*3 and *6), was carried out on Jordanian subjects. Different variants allele were determined using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). CYP1A1 allele frequencies in 290 subjects were 0.764 for CYP1A1*1, 0.165 for CYP1A1*2A and 0.071 for CYP1A1*2C. CYP2C9 allele frequencies in 263 subjects were 0.797 for CYP2C9*1, 0.135 for CYP2C9*2 and 0.068 for CYP2C9*3. For CYP2C19, the frequencies of the wild type (CYP2C19*1) and the nonfunctional (*2 and *3) alleles were 0.877, 0.123 and 0, respectively. Five subjects (3.16?%) were homozygous for *2/*2. Regarding CYP3A4*1B, only 12 subjects out of 173 subjects (6.9?%) were heterozygote with none were mutant for this polymorphism. With respect to CYP3A5, 229 were analyzed, frequencies of CYP3A5*1,*3 and *6 were 0.071, 0.925 and 0.0022, respectively. Comparing our data with that obtained in several Caucasian, African-American and Asian populations, Jordanians are most similar to Caucasians with regard to allelic frequencies of the tested variants of CYP1A1, CYP2C9, CYP2C19, CYP3A4 and CYP3A5.     

Modulation of human dUTPase using small interfering RNA

Analyzing the CYP2A6 gene of subjects who showed a poor metabolic phenotype toward SM-12502, we discovered a novel mutant allele (CYP2A6*4C) lacking the whole CYP2A6 gene. Using genetically engineered Salmonella typhimurium expressing a human CYP, we found that CYP2A6 was involved in the metabolic activation of a variety of nitrosamines such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) contained in tobacco smoke. Taking these results into consideration, we hypothesized that the subjects carrying the CYP2A6*4C allele had lower risk of tobacco-related lung cancer. In accordance with our hypothesis, our epidemiological studies indicated that smokers homozygous for the CYP2A6*4C allele showed much lower odds ratios toward cancer risk. Other mutant alleles reducing the CYP2A6 activity, besides CYP2A6*4C, also reduced the risk of lung cancer in smokers, particularly of squamous-cell carcinoma and small-cell carcinoma, both smoking-related cancers. 8-Methoxypsoralen, an inhibitor of CYP2A6, efficiently prevented the occurrence of adenoma caused by NNK in A/J mice.     

CYP7A1基因-204位点A/C变异对启动子活性的影响

CYP7A1（cholesterol 7α-hydroxylase ）在胆固醇向胆汁酸代谢途径中起着至关重要的作用.为研究该基因启动子区-204位点A/C多态性是否影响基因表达, 利用荧光素酶作为报告基因,将含有A或C等位基因的启动子区片段分别正向和反向插入不含启动子的pGL3 basic质粒载体中,再以重组体转染4种细胞株,采用双荧光素酶报告基因检测系统测定酶活性并进行比较.实验结果表明,2种基因型的正向序列启动子活性均高于相应的反向序列,含有A等位基因的启动子片段活性比含有C等位基因的片段低约1/3.TRANSFAC数据库分析显示,当-204位点等位基因为C时,可能存在1个Zic3结合位点.研究结果提示,CYP7A1基因启动子区-204位点A/C变异可减少启动子活性从而影响基因表达,其原因可能为1个潜在的Zic3结合位点的丧失.     

Targeted label-free approach for quantification of epoxide hydrolase and glutathione transferases in microsomes

The aim of this study was to investigate the expression and organ distribution of cytochrome P450 (CYP450) enzymes, microsomal epoxide hydrolase (MEH), and microsomal glutathione-S-transferase (MGST 1, 2, 3) in human liver, lung, intestinal, and kidney microsomes by targeted peptide-based quantification using nano liquid chromatography–tandem multiple reaction monitoring (nano LC-MRM). Applying this method, we analyzed 16 human liver microsomes and pooled lung, kidney, and intestine microsomes. Nine of the CYP450s (CYP1A2, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, 3A4, 3A5) could be quantified in liver. Except for CYP3A4 and 3A5 existing in intestine, other CYP450s had little content (<0.1 pmol/mg protein) in extrahepatic tissues. MEH and MGSTs could be quantified both in hepatic and in extrahepatic tissues. The highest concentrations of MEH and MGST 1, 2 were found in liver; conversely MGST 3 was abundant in human kidney and intestine compared to liver. The targeted proteomics assay described here can be broadly and efficiently utilized as a tool for investigating the targeted proteins. The method also provides novel CYP450s, MEH, and MGSTs expression data in human hepatic and extrahepatic tissues that will benefit rational approaches to evaluate metabolism in drug development.     

Identification of a null allele of cytochrome P450 3A7: CYP3A7 polymorphism in a Korean population

Cytochrome P450 3A7 (CYP3A7) is expressed in the human fetal liver and plays a role in the metabolism of hormones, drugs, and toxic compounds. Genetic variants of CYP3A7 are associated with serum estrone level, bone density, and hepatic CYP3A activity in adults. We analyzed the genetic variations of CYP3A7 in a Korean population. From direct sequencing of all exons and flanking regions of the CYP3A7 gene in 48 Koreans, we found five genetic variants, including three novel variants. One variant, a thymidine insertion in exon 2 (4011insT), causes premature termination of CYP3A7 translation, which may result in a null phenotype. The novel variant was assigned to the CYP3A7*3 allele by the CYP allele nomenclature committee. For further screen of this novel variant in other ethnic populations, we used pyrosequencing to analyze an additional 185 Koreans, 100 African Americans, 100 Caucasians, and 159 Vietnamese for the presence of this variant. The variant was not found in any other individuals, except for one Korean subject. The frequencies of two known functional alleles, CYP3A7*2 and CYP3A7*1C, were 26 and 0%, respectively, in Koreans. The frequencies of the functional CYP3A7 polymorphisms in Koreans were significantly different from those in Caucasians and African Americans. This is the first report of a null-type allele of the CYP3A7 gene. It also provides population-level genetic data on CYP3A7 in Koreans to reveal the wide ethnic variation in CYP3A7 polymorphism.     

Identification and characterisation of novel polymorphisms in the CYP2A locus: implications for nicotine metabolism.

The polymorphic human cytochrome P450 2A6 (CYP2A6) metabolises a number of drugs, activates a variety of precarcinogens and constitutes the major nicotine C-oxidase. A relationship between CYP2A6 genotype and smoking habits, as well as incidence of lung cancer, has been proposed. Two defective alleles have hitherto been identified, one of which is very common in Asian populations. Among Caucasians, an additional defective and frequently distributed allele (CYP2A6*3) has been suggested to play a protective role against nicotine addiction and cigarette consumption. Here, we have re-evaluated the genotyping method used for the CYP2A6*3 allele and found that a gene conversion in the 3' flanking region of 30-40% of CYP2A6*1 alleles results in genotype misclassification. In fact, no true CYP2A6*3 alleles were found among 100 Spaniards and 96 Chinese subjects. In one Spanish poor metaboliser of the CYP2A6 probe drug coumarin, we found two novel defective alleles. One, CYP2A6*5, encoded an unstable enzyme having a G479L substitution and the other was found to carry a novel type of CYP2A6 gene deletion (CYP2A6*4D). The results imply the presence of numerous defective as well as active CYP2A6 alleles as a consequence of CYP2A6/CYP2A7 gene conversion events. We conclude that molecular epidemiological studies concerning CYP2A6 require validated genotyping methods for accurate detection of all known defective CYP2A6 alleles.     

Novel Single Nucleotide Polymorphisms in Interleukin 6 Affect Tacrolimus Metabolism in Liver Transplant Patients

Background

Tacrolimus is the first-line immunosuppressant after organ transplantation. It is mainly metabolized by cytochrome P450, family 3, subfamily A (CYP3A) enzymes, but there are large individual differences in metabolism. Interleukin 6 (IL6) has been shown to cause a pan-suppression of mRNA levels of ten major CYP enzymes in human hepatocyte cultures. IL6 has been shown to provide hepatoprotection in various models of liver injury. Rs1800796 is a locus in the IL6 gene promoter region which regulates cytokine production. We speculated that IL6 rs1800796 polymorphisms may lead to individual differences in tacrolimus metabolism by affecting CYP3A enzymes levels and liver function after liver transplantation.

Methodology/Principal Findings

Ninety-six liver transplant patients receiving tacrolimus were enrolled in the study. Two single nucleotide polymorphisms (SNP), CYP3A5 rs776746 and IL6 rs1800796, were genotyped in both donors and recipients. The effects of SNPs on tacrolimus concentration/dose (C/D ratio) at four weeks after transplantation were studied, as well as the effects of donor IL6 rs1800796 polymorphisms on liver function. Both donor and recipient CYP3A5 rs776746 allele A showed association with lower C/D ratios, while donor IL6 rs1800796 allele G showed an association with higher C/D ratios. Donor CYP3A5 rs776746 allele A, IL6 rs1800796 allele C, and recipient CYP3A5 rs776746 allele A were associated with fast tacrolimus metabolism. With increasing numbers of these alleles, patients were found to have increasingly lower tacrolimus C/D ratios at time points after transplantation. Donor IL6 rs1800796 allele G carriers showed an association with higher glutamic-pyruvic transaminase (GPT) levels.

Conclusions

Combined analysis of donor CYP3A5 rs776746, IL6 rs1800796, and recipient CYP3A5 rs776746 polymorphisms may distinguish tacrolimus metabolism better than CYP3A5 rs776746 alone. IL6 may lead to individual differences in tacrolimus metabolism mainly by affecting liver function.     

The murine Cyp1a1 gene is expressed in a restricted spatial and temporal pattern during embryonic development

In adult mice the cytochrome P450 Cyp1a1 gene is not constitutively expressed but is highly inducible by foreign compounds acting through the aryl hydrocarbon (Ah) receptor. However, the expression profile of the Cyp1a1 gene in the developing embryo is not well under-stood. Using established transgenic mouse lines where 8.5 kb of the rat CYP1A1 promoter is cloned upstream of the lacZ reporter gene (1), we describe the expression of the CYP1A1-driven reporter gene in all tissues through-out stages E7-E14 of embryonic development. In contrast to the absence of constitutive Cyp1a1 and lacZ transgene expression in tissues of the adult mouse, a constitutive cell-specific and time-dependent pattern of CYP1A1 promoter activity was observed in the embryo. This expression pattern was confirmed as reflecting the endogenous gene by measuring Cyp1a1 mRNA levels and protein expression by immunohistochemistry. The number of cells displaying endogenous CYP1A1 activity could be increased in the embryo upon xenobiotic challenge, but only within areas where the CYP1A1 promotor was already active. When reporter mice were bred onto a genetic background expressing a lower affinity form of the Ah receptor (DBA allele), transgene and murine Cyp1a1 protein expression were both attenuated in the adult mouse liver upon xenobiotic challenge. By comparison, constitutive CYP1A1 promoter activity in the embryo was identical in the presence of either the high or low affinity Ah receptor. These novel data suggest that the Cyp1a1 protein may play a role in murine development and that regulation of the Cyp1a1 gene during this period is either through the action of a high affinity Ah receptor ligand or by an alternative regulatory pathway.     

Conditional disruption of the aryl hydrocarbon receptor nuclear translocator (Arnt) gene leads to loss of target gene induction by the aryl hydrocarbon receptor and hypoxia-inducible factor 1alpha

To determine the function of the aryl hydrocarbon receptor nuclear translocator (ARNT), a conditional gene knockout mouse was made using the Cre-loxP system. Exon 6, encoding the conserved basic-helix-loop-helix domain of the protein, was flanked by loxP sites and introduced into the Arnt gene by standard gene disruption techniques using embryonic stem cells. Mice homozygous for the floxed allele were viable and had no readily observable phenotype. The Mx1-Cre transgene, in which Cre is under control of the interferon-gamma promoter, was introduced into the Arnt-floxed mouse line. Treatment with polyinosinic-polycytidylic acid to induce expression of Cre resulted in complete disruption of the Arnt gene and loss of ARNT messenger RNA (mRNA) expression in liver. To determine the role of ARNT in gene control in the intact animal mouse liver, expression of target genes under control of an ARNT dimerization partner, the aryl hydrocarbon receptor (AHR), was monitored. Induction of CYP1A1, CYP1A2, and UGT1*06 mRNAs by the AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin was absent in livers of Arnt-floxed/Mx1-Cre mice treated with polyinosinic-polycytidylic. These data demonstrate that ARNT is required for AHR function in the intact animal. Partial deletion of the Arnt allele was found in kidney, heart, intestine, and lung. Despite more than 80% loss of the ARNT expression in lung, maximal induction of CYP1A1 was found, indicating that the expression level of ARNT is not limiting to AHR signaling. Cobalt chloride induction of the glucose transporter-1 and heme oxygenase-1 mRNAs was also markedly abrogated in mice lacking ARNT expression, suggesting an inhibition of HIF-1alpha activity. These studies establish a critical role for ARNT in AHR and HIF-1alpha signal transduction in the intact mouse.     

A novel single nucleotide polymorphism altering stability and activity of CYP2a6

CYP2A6 is known as a major cytochrome P450 (CYP) responsible for the oxidation of nicotine and coumarin in humans. In this study, we explored genetic polymorphisms, which reduce CYP2A6 activity in Japanese. Two novel mutations in exon 9 of the CYP2A6 gene were found. A single nucleotide polymorphism of T1412C and G1454T resulted in Ile471Thr and Arg485Leu substitution, respectively. The frequency of the former variant allele was considerably high (15.7%), while the latter variant appeared to be a rare polymorphism. Heterologous expression of CYP2A6 using a cDNA possessing C instead of T-base at codon 471 in Escherichia coli caused remarkable reduction of the stability of holoenzyme at 37 degrees C. Furthermore, this variant enzyme almost lacked nicotine C-oxidase activity, although coumarin 7-hydroxylase activity was still observed. These data suggest that individuals homozygous for the T1412C variant allele or heterozygous for this and a defect allele such as the CYP2A6*4 may be poor metabolizer of nicotine, but not coumarin.     

Characterization of variant alleles of cytochrome CYP2D6 in a Spanish population

The CYP2D6 gene codes for a P450 monooxygenase which is involved in the biotransformation of a large number of commonly prescribed drugs. Adverse drug effects and therapeutic failure can be related to abnormal CYP2D6 activity. We investigated the allele and genotype frequencies of cytochrome P4502D6 in a Spanish population to predict the prevalence of ultra-rapid and poor metabolizer phenotypes in our population and to design a feasible CYP2D6 genotyping protocol. The study included 105 healthy unrelated Spanish Caucasian volunteers. CYP2D6 genotyping was performed by a combination of long-PCR, direct sequencing and allele-specific real-time PCR. The frequency of the wild-type CYP2D6*1 allele was 31%. The alleles coding for slightly (CYP2D6*2) or moderately (*9 and *10) reduced activity showed frequencies of 40.47, 2.38 and 1.90%, respectively. Frequencies of defective alleles *3, *4, *5 and *6 were 0.95, 13.8, 3.33 and 0.95%, respectively. The defective CYP2D6 alleles *7, *8, *12, *14, *15 and *21 were not found. Duplicated CYP2D6 alleles were detected at a frequency of 4.27%. Our protocol allows the identification of the four inactive CYP2D6 alleles (*3, *4, *5 and *6) and the detection of alleles with CYP2D6 *1, CYP2D6 *2 and CYP2D6*4 gene duplications. Testing for this reduced CYP2D6 allele set would facilitate its use in clinical practice by assisting in the development of individualized pharmacotherapy.     

A distinct thyroid hormone response element mediates repression of the human cholesterol 7alpha-hydroxylase (CYP7A1) gene promoter.

We examined the molecular basis by which T3 regulates the human cholesterol 7alpha-hydroxylase gene (CYP7A1) promoter. L-T3 decreased chloramphenicol acetyltransferase activity in hepatoma cells cotransfected with a plasmid encoding the T3 receptor (TR) alpha [NR1a1] and a chimeric gene containing nucleotides -372 to +61 of the human CYP7A1 gene fused to the chloramphenicol acetyltransferase structural gene. Deoxyribonuclease I footprinting revealed that recombinant TRalpha protected two regions in this segment of the human CYP7A1 gene promoter. In EMSAs, TRalpha bound to both regions. The binding was competed by oligonucleotides bearing an idealized TRalpha binding motif and abolished by mutation of these elements. In assays of promoter function, mutation of only one of the TRalpha binding sites blocked repression by T3. The results indicate that T3-dependent repression of human CYP7A1 gene expression is mediated via a novel site in the human CYP7A1 gene promoter.