Functional analysis of the human N-acetyltransferase 1 major promoter: quantitation of tissue expression and identification of critical sequence elements

Differential expression of NAT1 pharmacogene in hormone receptor positive vs. negative female breast tumors may affect drug treatment

Studies have reported overexpression of NAT1 gene for xenobiotic metabolizing arylamine N-acetyltransferase type 1 in estrogen receptor positive breast tumors, and this association has been linked to patient chemoresistance and response to tamoxifen. We probed the expression of NAT1, using quantitative reverse transcription PCR to screen clinically characterized breast cancer tissue cDNA arrays. Primers detecting all NAT1 alternative transcripts were used, and the protocol and results are reported according to consensus guidelines. The clinical information about 166 tumor samples screened is provided, including tumor stage, estrogen and progesterone receptor status and HER2 expression. NAT1 was found to be significantly (P < 0.001) upregulated in hormone receptor positive vs. negative tumors. No correlation was apparent between NAT1 and tumor stage or HER2 expression. Our findings demonstrate a strong correlation between the expression of NAT1 and steroid hormone receptors in breast tumors, supporting its possible utility as a pharmacogenetic biomarker or drug target. Of the two polymorphic NAT genes, NAT1 is the one primarily expressed in breast tissue, and is subjected to regulation by two differential promoters and more than one polyadenylation signal. Hormonal factors may enhance NAT1 gene expression at the transcriptional or epigenetic level, and tamoxifen has additionally been shown to inhibit NAT1 enzymatic activity. The outcome of tamoxifen treatment is also more favorable in patients with NAT1 overexpressing tumors. The study adds to the growing body of evidence implicating NAT1 in breast cancer and its pharmacological treatment.

Identification and characterization of potent, selective, and efficacious inhibitors of human arylamine N-acetyltransferase 1

Arylamine N-acetyltransferase 1 (NAT1) plays a pivotal role in the metabolism of carcinogens and is a drug target for cancer prevention and/or treatment. A protein-ligand virtual screening of 2 million chemicals was ranked for predicted binding affinity towards the inhibition of human NAT1. Sixty of the five hundred top-ranked compounds were tested experimentally for inhibition of recombinant human NAT1 and N-acetyltransferase 2 (NAT2). The most promising compound 9,10-dihydro-9,10-dioxo-1,2-anthracenediyl diethyl ester (compound 10) was found to be a potent and selective NAT1 inhibitor with an in vitro IC₅₀ of 0.75 µM. Two structural analogs of this compound were selective but less potent for inhibition of NAT1 whereas a third structural analog 1,2-dihydroxyanthraquinone (a compound 10 hydrolysis product also known as Alizarin) showed comparable potency and efficacy for human NAT1 inhibition. Compound 10 inhibited N-acetylation of the arylamine carcinogen 4-aminobiphenyl (ABP) both in vitro and in DNA repair-deficient Chinese hamster ovary (CHO) cells in situ stably expressing human NAT1 and CYP1A1. Compound 10 and Alizarin effectively inhibited NAT1 in cryopreserved human hepatocytes whereas inhibition of NAT2 was not observed. Compound 10 caused concentration-dependent reductions in DNA adduct formation and DNA double-strand breaks following metabolism of aromatic amine carcinogens beta-naphthylamine and/or ABP in CHO cells. Compound 10 inhibited proliferation and invasion in human breast cancer cells and showed selectivity towards tumorigenic versus non-tumorigenic cells. In conclusion, our study identifies potent, selective, and efficacious inhibitors of human NAT1. Alizarin's ability to inhibit NAT1 could reduce breast cancer metastasis particularly to bone.

Human Arylamine N-Acetyltransferase 1 (NAT1) Knockout in MDA-MB-231 Breast Cancer Cell Lines Leads to Transcription of NAT2

Many cancers, including breast cancer, have shown differential expression of human arylamine N-acetyltransferase 1 (NAT1). The exact effect this differential expression has on disease risk and progression remains unclear. While NAT1 is classically defined as a xenobiotic metabolizing enzyme, other functions and roles in endogenous metabolism have recently been described providing additional impetus for investigating the effects of varying levels of NAT1 on global gene expression. Our objective is to further evaluate the role of NAT1 in breast cancer by determining the effect of NAT1 overexpression, knockdown, and knockout on global gene expression in MDA-MB-231 cell lines. RNA-seq was utilized to interrogate differential gene expression (genes correlated with NAT1 activity) across three biological replicates of previously constructed and characterized MDA-MB-231 breast cancer cell lines expressing parental (Scrambled), increased (Up), decreased (Down, CRISPR 2–12), or knockout (CRISPR 2–19, CRISPR 5–50) levels of NAT1. 3,889 genes were significantly associated with the NAT1 N-acetylation activity of the cell lines (adjusted p ≤ 0.05); of those 3,889 genes, 1,756 were positively associated with NAT1 N-acetylation activity and 2,133 were negatively associated with NAT1 N-acetylation activity. An enrichment of genes involved in cell adhesion was observed. Additionally, human arylamine N-acetyltransferase 2 (NAT2) transcripts were observed in the complete NAT1 knockout cell lines (CRISPR 2–19 and CRISPR 5–50). This study provides further evidence that NAT1 functions as more than just a drug metabolizing enzyme given the observation that differences in NAT1 activity have significant impacts on global gene expression. Additionally, our data suggests the knockout of NAT1 results in transcription of its isozyme NAT2.

Case Study 10: A Case to Investigate Acetyl Transferase Kinetics

Major routes of metabolism for marketed drugs are predominately driven by enzyme families such as cytochromes P450 and UDP-glucuronosyltransferases. Less studied conjugative enzymes, like N-acetyltransferases (NATs), are commonly associated with detoxification pathways. However, in the clinic, the high occurrence of NAT polymorphism that leads to slow and fast acetylator phenotypes in patient populations has been linked to toxicity for a multitude of drugs. A key example of this is the observed clinical toxicity in patients who exhibit the slow acetylator phenotype and were treated with isoniazid. Toxicity in patients has led to detailed characterization of the two NAT isoforms and their polymorphic genotypes. Investigation in recombinant enzymes, genotyped hepatocytes, and in vivo transgenic models coupled with acetylator status-driven clinical studies have helped understand the role of NATs in drug development, clinical study design and outcomes, and potential roles in human disease models. The selected case studies herein document NAT enzyme kinetics to explore substrate overlap from two human isoforms, preclinical species considerations, and clinical genotype population concerns.

Acetylation of putative arylamine and alkylaniline carcinogens in immortalized human fibroblasts transfected with rapid and slow acetylator N-acetyltransferase 2 haplotypes

Exposure to alkylanilines found in tobacco smoke and indoor air is associated with risk of bladder cancer. Genetic factors significantly influence the metabolism of arylamine carcinogens and the toxicological outcomes that result from exposure. We utilized nucleotide excision repair (NER)-deficient immortalized human fibroblasts to examine the effects of human N-acetyltransferase 1 (NAT1), CYP1A2, and common rapid (NAT2*4) and slow (NAT2*5B or NAT2*7B) acetylator human N-acetyltransferase 2 (NAT2) haplotypes on environmental arylamine and alkylaniline metabolism. We constructed SV40-transformed human fibroblast cells that stably express human NAT2 alleles (NAT2*4, NAT2*5B, or NAT2*7B) and human CYP1A2. Human NAT1 and NAT2 apparent kinetic constants were determined following recombinant expression of human NAT1 and NAT2 in yeast for the arylamines benzidine, 4-aminobiphenyl (ABP), and 2-aminofluorene (2-AF), and the alkylanilines 2,5-dimethylaniline (DMA), 3,4-DMA, 3,5-DMA, 2-6-DMA, and 3-ethylaniline (EA) compared with those of the prototype NAT1-selective substrate p-aminobenzoic acid and NAT2-selective substrate sulfamethazine. Benzidine, 3,4-DMA, and 2-AF were preferential human NAT1 substrates, while 3,5-DMA, 2,5-DMA, 3-EA, and ABP were preferential human NAT2 substrates. Neither recombinant human NAT1 or NAT2 catalyzed the N-acetylation of 2,6-DMA. Among the alkylanilines, N-acetylation of 3,5-DMA was substantially higher in human fibroblasts stably expressing NAT2*4 versus NAT2*5B and NAT2*7B. The results provide important insight into the role of the NAT2 acetylator polymorphism (in the presence of competing NAT1 and CYP1A2-catalyzed N-acetylation and N-hydroxylation) on the metabolism of putative alkyaniline carcinogens. The N-acetylation of two alkylanilines associated with urinary bladder cancer (3-EA and 3,5-DMA) was modified by NAT2 acetylator polymorphism.

Arylamine N-acetyltransferase acetylation polymorphisms: paradigm for pharmacogenomic-guided therapy- a focused review

INTRODUCTION

The N-acetylation polymorphism has been the subject of comprehensive reviews describing the role of arylamine N-acetyltransferase 2 (NAT2) in the metabolism of numerous aromatic amine and hydrazine drugs.

AREAS COVERED

We describe and review data that more clearly defines the effects of NAT2 haplotypes and genotypes on the expression of acetylator phenotype towards selected drugs within human hepatocytes in vitro, within human hepatocyte cultures in situ, and clinical measures such as bioavailability, plasma metabolic ratios of parent to N-acetyl metabolite, elimination rate constants and plasma half-life, and/or clearance determinations in human subjects. We review several drugs (isoniazid, hydralazine, sulfamethazine, amifampridine, procainamide, sulfasalazine, amonafide and metamizole) for which NAT2 phenotype-guided therapy may be important. The value of pharmacogenomics-guided isoniazid therapy for the prevention and treatment of tuberculosis is presented as a paradigm for NAT2 phenotype-dependent dosing strategies.

EXPERT OPINION

Studies in human subjects and cryopreserved human hepatocytes show evidence for rapid, intermediate and slow acetylator phenotypes, with further data suggesting genetic heterogeneity within the slow acetylator phenotype. Incorporation of more robust NAT2 genotype/phenotypes relationships, including genetic heterogeneity within the slow acetylator phenotype, should lead to further advancements in both health outcomes and cost benefit for prevention and treatment of tuberculosis.

Modulation of Human Arylamine N-Acetyltransferase 1 Activity by Lysine Acetylation: Role of p300/CREB-Binding Protein and Sirtuins 1 and 2

Arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic-metabolizing enzyme that also has a role in cancer cell growth and metabolism. Recently, it was reported that NAT1 undergoes lysine acetylation, an important post-translational modification that can regulate protein function. In the current study, we use site-directed mutagenesis to identify K¹⁰⁰ and K¹⁸⁸ as major sites of lysine acetylation in the NAT1 protein. Acetylation of ectopically expressed NAT1 in HeLa cells was decreased by C646, an inhibitor of the protein acetyltransferases p300/CREB-binding protein (CBP). Recombinant p300 directly acetylated NAT1 in vitro. Acetylation of NAT1 was enhanced by the sirtuin (SIRT) inhibitor nicotinamide but not by the histone deacetylase inhibitor trichostatin A. Cotransfection of cells with NAT1 and either SIRT 1 or 2, but not SIRT3, significantly decreased NAT1 acetylation. NAT1 activity was evaluated in cells after nicotinamide treatment to enhance acetylation or cotransfection with SIRT1 to inhibit acetylation. The results indicated that NAT1 acetylation impaired its enzyme kinetics, suggesting decreased acetyl coenzyme A binding. In addition, acetylation attenuated the allosteric effects of ATP on NAT1. Taken together, this study shows that NAT1 is acetylated by p300/CBP in situ and is deacetylated by the sirtuins SIRT1 and 2. It is hypothesized that post-translational modification of NAT1 by acetylation at K¹⁰⁰ and K¹⁸⁸ may modulate NAT1 effects in cells. SIGNIFICANCE STATEMENT: There is growing evidence that arylamine N-acetyltransferase 1 has an important cellular role in addition to xenobiotic metabolism. Here, we show that NAT1 is acetylated at K¹⁰⁰ and K¹⁸⁸ and that changes in protein acetylation equilibrium can modulate its activity in cells.

Human arylamine N-acetyltransferase 2 genotype-dependent protein expression in cryopreserved human hepatocytes

Human N-acetyltransferases (NAT; EC 2.3.1.5) catalyze the N-acetylation of arylamine and hydrazine drugs and the O-acetylation of N-hydroxylated metabolites of aromatic and heterocyclic amines. Two different isoforms of this protein, N-acetyltransferase 1 (NAT1) and N-acetyltransferase 2 (NAT2), are expressed in human hepatocytes. Both are encoded by a single 870-bp open reading frame that exhibits genetic polymorphisms in human populations. NAT1 and NAT2 share more than 85% gene and protein sequence, making it challenging to produce antibodies with high specificity for NAT1 or NAT2. In the present study, we compared methods for the quantification of immunoreactive NAT1 and NAT2 with seven different antibodies and investigated the relationship of NAT2 genotype to NAT2 mRNA and protein expression in cryopreserved human hepatocytes. Sulfamethazine (NAT2-selective substrate) and NAT2 protein expression differed significantly with NAT2 acetylator genotype (p < 0.0001). NAT2 protein expression and sulfamethazine NAT2 catalytic activity correlated highly across the cryopreserved human hepatocytes of rapid, intermediate, and slow acetylator NAT2 genotypes. In conclusion, our data describe a specific analytical method for the quantification of NAT1 and NAT2 protein expression. We showed that the NAT2 activity in human hepatocytes is directly correlated to expression levels of NAT2 protein but not mRNA.

Genetic variants of N-acetyltransferases 1 and 2 (NAT1 and NAT2) in cynomolgus and rhesus macaques

In humans, polymorphic N-acetyltransferases NAT1 and NAT2 are important enzymes that metabolize endogenous and exogenous compounds, including drugs. These enzymes exhibit considerable inter-individual variability in humans. The cynomolgus macaque is a nonhuman primate species that is widely used in drug metabolism studies. NAT1/2 in these macaques have molecular and enzymatic similarities to their human orthologs; however, genetic polymorphisms in NAT1/2 have not been fully investigated in this species. In this study, the resequencing of NAT1 and NAT2 in 114 cynomolgus macaques and 19 rhesus macaques found 15 non-synonymous variants for NAT1 and 11 non-synonymous variants and 1 insertion/deletion variant for NAT2. Nine (60%) and five (33%) NAT1 variants and seven (67%) and three (25%) NAT2 variants were unique to cynomolgus and rhesus macaques, respectively. Functional characterization of the mutant enzymes was carried out using cynomolgus NAT1 and NAT2 proteins heterologously expressed in Escherichia coli. Compared with wild-type NAT1, the D122N NAT1 variant showed substantially lower acetylation activities toward p-aminobenzoic acid but had higher acetylation activities toward isoniazid. Moreover, liver cytosolic fractions from cynomolgus macaques homozygous for T98A NAT2 showed significantly lower acetylation activities toward isoniazid than wild-type NAT2; similar results were obtained for recombinant T98A NAT2. Interestingly, all the rhesus macaques analyzed were homozygous for T98A. These findings indicate that polymorphic NAT1/2 variants in cynomolgus and rhesus macaques, especially the T98A NAT2 variant, could account for the inter-animal and/or inter-lineage variabilities of NAT-dependent drug metabolism in macaques.

Population variability of rhesus macaque (Macaca mulatta) NAT1 gene for arylamine N-acetyltransferase 1: Functional effects and comparison with human

Human NAT1 gene for N-acetyltransferase 1 modulates xenobiotic metabolism of arylamine drugs and mutagens. Beyond pharmacogenetics, NAT1 is also relevant to breast cancer. The population history of human NAT1 suggests evolution through purifying selection, but it is unclear whether this pattern is evident in other primate lineages where population studies are scarce. We report NAT1 polymorphism in 25 rhesus macaques (Macaca mulatta) and describe the haplotypic and functional characteristics of 12 variants. Seven non-synonymous single nucleotide variations (SNVs) were identified and experimentally demonstrated to compromise enzyme function, mainly through destabilization of NAT1 protein and consequent activity loss. One non-synonymous SNV (c.560G > A, p.Arg187Gln) has also been characterized for human NAT1 with similar effects. Population haplotypic and functional variability of rhesus NAT1 was considerably higher than previously reported for its human orthologue, suggesting different environmental pressures in the two lineages. Known functional elements downstream of human NAT1 were also differentiated in rhesus macaque and other primates. Xenobiotic metabolizing enzymes play roles beyond mere protection from exogenous chemicals. Therefore, any link to disease, particularly carcinogenesis, may be via modulation of xenobiotic mutagenicity or more subtle interference with cell physiology. Comparative analyses add the evolutionary dimension to such investigations, assessing functional conservation/diversification among primates.

Molecular and Functional Characterization of N-Acetyltransferases NAT1 and NAT2 in Cynomolgus Macaque

Arylamine N-acetyltransferases (NATs) are drug-metabolizing enzymes essential for the metabolism of endogenous substrates and xenobiotics, and their molecular characteristics have been extensively investigated in humans, but not in cynomolgus macaques, nonhuman primate species important for drug metabolism studies. In this study, cynomolgus NAT1 and NAT2 cDNAs were isolated from livers. NAT1 and NAT2 were characterized by molecular analyses and drug-metabolizing assays. A total of 9 transcript variants were found for cynomolgus NAT1, similar to human NAT1, and contained 1-4 exons with the coding region largely conserved with human NAT1. Genomic organization was similar between cynomolgus macaques and humans. Cynomolgus NAT1 and NAT2 amino acid sequences showed high sequence homology (95% and 89%, respectively) and showed close relationships with human NAT1 and NAT2 in a phylogenetic tree. Cynomolgus NAT2 mRNA was predominantly expressed in liver among the 10 different tissues analyzed, followed by kidney and jejunum. In contrast, cynomolgus NAT1 mRNA showed more ubiquitous expression with relatively more abundant expression in liver, kidney, and jejunum, along with testis. Metabolic assays using recombinant proteins showed that cynomolgus NAT1 and NAT2 metabolized human NAT substrates, including p-aminobenzoic acid, sulfamethazine, isoniazid, and 2-aminofluorene. Interestingly, p-aminobenzoic acid and isoniazid were largely metabolized by NAT1 and NAT2, respectively, in cynomolgus macaques and humans; sulfamethazine, a human NAT2 substrate, was metabolized by both NAT enzymes in cynomolgus macaques. These results suggest molecular and enzymatic similarities of NAT1 and NAT2 between cynomolgus macaques and humans, despite some small differences in substrate specificity of the enzymes.

Comparative analysis of xenobiotic metabolising N-acetyltransferases from ten non-human primates as in vitro models of human homologues

Xenobiotic metabolising N-acetyltransferases (NATs) perform biotransformation of drugs and carcinogens. Human NAT1 is associated with endogenous metabolic pathways of cells and is a candidate drug target for cancer. Human NAT2 is a well-characterised polymorphic xenobiotic metabolising enzyme, modulating susceptibility to drug-induced toxicity. Human NATs are difficult to express to high purification yields, complicating large-scale production for high-throughput screens or use in sophisticated enzymology assays and crystallography. We undertake comparative functional investigation of the NAT homologues of ten non-human primates, to characterise their properties and evaluate their suitability as models of human NATs. Considering the amount of generated recombinant protein, the enzymatic activity and thermal stability, the NAT homologues of non-human primates are demonstrated to be a much more effective resource for in vitro studies compared with human NATs. Certain NAT homologues are proposed as better models, such as the NAT1 of macaques Macaca mulatta and M. sylvanus, the NAT2 of Erythrocebus patas, and both NAT proteins of the gibbon Nomascus gabriellae which show highest homology to human NATs. This comparative investigation will facilitate in vitro screens towards discovery and optimisation of candidate pharmaceutical compounds for human NAT isoenzymes, while enabling better understanding of NAT function and evolution in primates.

High N-Acetyltransferase 1 Expression Is Associated with Estrogen Receptor Expression in Breast Tumors, but Is not Under Direct Regulation by Estradiol, 5α-androstane-3β,17β-Diol, or Dihydrotestosterone in Breast Cancer Cells

N-acetyltransferase 1 (NAT1) is an enzyme that metabolizes carcinogens, which suggests a potential role in breast carcinogenesis. High NAT1 expression in breast tumors is associated with estrogen receptor α (ERα+) and the luminal subtype. We report that NAT1 mRNA transcript, protein, and enzyme activity were higher in human breast tumors with high expression of ERα/ESR1 compared with normal breast tissue. There was a strong correlation between NATb promoter and NAT1 protein expression/enzyme activity. High NAT1 expression in tumors was not the result of adipocytes, as evidenced by low perilipin (PLIN) expression. ESR1, NAT1, and XBP1 expression were associated in tumor biopsies. Direct regulation of NAT1 transcription by estradiol (E₂) was investigated in ERα (+) MCF-7 and T47D breast cancer cells. E₂ did not increase NAT1 transcript expression but increased progesterone receptor expression in a dose-dependent manner. Likewise, NAT1 transcript levels were not increased by dihydrotestosterone (DHT) or 5α-androstane-3β, (3β-adiol) 17β-diol. Dithiothreitol increased levels of the activated, spliced XBP1 in ERα (+) MCF-7 and T47D breast cancer cells but did not affect NAT1 or ESR1 expression. We conclude that NAT1 expression is not directly regulated by E₂, DHT, 3β-adiol, or dithiothreitol despite high NAT1 and ESR1 expression in luminal A breast cancer cells, suggesting that ESR1, XBP1, and NAT1 expression may share a common transcriptional network arising from the luminal epithelium associated with better survival in breast cancer. Clusters of high-expression genes, including NAT1, in breast tumors might serve as potential targets for novel therapeutic drug development.

Arylamine N-acetyltransferase 1 in situ N-acetylation on CD3+ peripheral blood mononuclear cells correlate with NATb mRNA and NAT1 haplotype

Human arylamine N-acetyltransferase 1 (NAT1) is responsible for the activation and elimination of xenobiotic compounds and carcinogens. Genetic polymorphisms in NAT1 modify both drug efficacy and toxicity. Previous studies have suggested a role for NAT1 in the development of several diseases. The aim of the present study was to evaluate NAT1 protein expression and in situ N-acetylation capacity in peripheral blood mononuclear cells (PBMC), as well as their possible associations with the expression of NAT1 transcript and NAT1 genotype. We report NAT1 protein, mRNA levels, and N-acetylation in situ activity for PBMC obtained from healthy donors. NAT1-specific protein expression was higher in CD3+ cells than other major immune cell subtypes (CD19 or CD56 cells). N-acetylation of pABA varied markedly among the PBMC of participants, but correlated very significantly with levels of NAT1 transcripts. NAT1*4 subjects showed significantly (p = 0.017) higher apparent pABA V _max of 71.3 ± 3.7 versus the NAT1*14B subjects apparent V _max of 58.5 ± 2.5 nmoles Ac-pABA/24 h/million cells. Levels of pABA N-acetylation activity at each concentration of substrate evaluated also significantly correlated with NAT1 mRNA levels for all samples (p < 0.0001). This highly significant correlation was maintained for samples with the NAT1*4 (p = 0.002) and NAT1*14B haplotypes (p = 0.0106). These results provide the first documentation that NAT1-catalyzed N-acetylation in PBMC is higher in T cell than in other immune cell subtypes and that individual variation in N-acetylation capacity is dependent upon NAT1 mRNA and NAT1 haplotype.

Ocular non-P450 oxidative, reductive, hydrolytic, and conjugative drug metabolizing enzymes

Metabolism in the eye for any species, laboratory animals or human, is gaining rapid interest as pharmaceutical scientists aim to treat a wide range of so-called incurable ocular diseases. Over a period of decades, reports of metabolic activity toward various drugs and biochemical markers have emerged in select ocular tissues of animals and humans. Ocular cytochrome P450 (P450) enzymes and transporters have been recently reviewed. However, there is a dearth of collated information on non-P450 drug metabolizing enzymes in eyes of various preclinical species and humans in health and disease. In an effort to complement ocular P450s and transporters, which have been well reviewed in the literature, this review is aimed at presenting collective information on non-P450 oxidative, hydrolytic, and conjugative ocular drug metabolizing enzymes. Herein, we also present a list of xenobiotics or drugs that have been reported to be metabolized in the eye.

Lipoteichoic acid isolated from Lactobacillus plantarum down-regulates UV-induced MMP-1 expression and up-regulates type I procollagen through the inhibition of reactive oxygen species generation

BACKGROUND

Ultraviolet (UV) irradiation from the sun is the primary environmental factor that causes human skin aging. UV irradiation induces the expressions of matrix metalloproteinases (MMPs) and extracellular matrix degrading enzymes. Among the members of MMP family, MMP-1 is an interstitial collagenase that degrades the collagen triple helix. We investigated the effect of Lactobacillus plantarum, well known as useful microorganism, on UV-induced-MMP-1 expression in human dermal fibroblasts.

METHODS

Human dermal fibroblasts (HDF) was pre-stimulated with lipoteichoic acid isolated from L. plantarum followed by UV irradiation. Secreted protein level of MMP-1 was evaluated by Western blot analysis. The phosphorylation of mitogen-activated protein kinases (MAPKs) and nuclear factor-kappa B (NF-κB) from the cell lysates was also examined by western blotting. Electrophoretic mobility-shift assay (EMSA) was used to detect the activated transcription factor, AP-1 and NF-κB. The detection of type 1 procollagen was carried with Procollagen type 1 C-peptide (PIP) EIA kit. The generation of reactive oxygen species (ROS) by LTA and UV irradiation was examined by Griess reagent assay and fluorescence microscope.

RESULTS

We found that lipoteichoic acid (LTA), a cell-wall component of Gram-positive bacteria, isolated from L. plantarum, inhibited MMP-1 expression. Pretreatment with LTA from L. plantarum (pLTA) reduced MMP-1 expression in a dose-dependent manner and inhibited activation of extracellular signal-regulated kinases (ERK) and c-Jun N-terminal kinases (JNK). It also led to the inhibition of DNA binding activity of activator protein-1 (AP-1) and of nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB). Furthermore, LTA promoted type 1 procollagen synthesis and reduced the generation of ROS induced by UV irradiation.

CONCLUSION

Our study demonstrates that pLTA inhibits degradation of collagen and promotes its synthesis and that pLTA contributes to a decrease in ROS production. Therefore, pLTA from L. plantarum has potential abilities to prevent and treat skin photo-aging.

Structural and Kinetic Characterization of a Novel N-acetylated Aliphatic Amine Metabolite of the PRMT Inhibitor, EPZ011652

Pharmacokinetic and metabolite identification studies were conducted to understand the clearance pathways of EPZ011652 [(2-aminoethyl)(methyl)({3-[4-(propan-2-yloxy)phenyl]-1H-pyrazol-4-yl}methyl)amine], a potent protein arginine N-methyltransferase inhibitor. Metabolic clearance was the major pathway of EPZ011652 elimination in rats with structural elucidation of metabolites via liquid chromatography - mass spectrometry (LC-MS(n)) accurate mass measurement revealing the formation of a novel aliphatic N-acetylated metabolite (M1) located on the terminal nitrogen of the ethylene-diamine side chain. EPZ015564, a synthetic standard of the N-acetyl product, was prepared and was also generated by human and rat, but not dog hepatocytes. In rat hepatocytes, on incubation with EPZ011652, the concentration of EPZ015564 initially increased before decreasing with incubation time, suggesting that the metabolite is itself a substrate for other metabolizing enzymes, in agreement with the identification of metabolites M2, M3, and M4 in rat bile, all N-acetylated metabolites, undergoing sequential phase I (demethylation, oxidation) or phase II (sulfation) reactions. Reaction phenotyping with recombinant human N-acetyltransferase (NAT) isoforms revealed that both NAT1 and NAT2 are capable of acetylating EPZ011652, although with different catalytic efficiencies. Kinetic profiles of EPZ015564 formation followed classic Michaelis-Menten behavior with apparent Km values of >1000 μM for NAT1 and 165 ± 14.1 µM for NAT2. The in vitro intrinsic clearance for EPZ011652 by NAT2 (110 μL/min/mg) was 500-fold greater than by NAT1. In summary, we report the unusual N-acetylation of an aliphatic amine and discuss the implications for drug discovery and clinical development.

Foxf genes integrate tbx5 and hedgehog pathways in the second heart field for cardiac septation

The Second Heart Field (SHF) has been implicated in several forms of congenital heart disease (CHD), including atrioventricular septal defects (AVSDs). Identifying the SHF gene regulatory networks required for atrioventricular septation is therefore an essential goal for understanding the molecular basis of AVSDs. We defined a SHF Hedgehog-dependent gene regulatory network using whole genome transcriptional profiling and GLI-chromatin interaction studies. The Forkhead box transcription factors Foxf1a and Foxf2 were identified as SHF Hedgehog targets. Compound haploinsufficiency for Foxf1a and Foxf2 caused atrioventricular septal defects, demonstrating the biological relevance of this regulatory network. We identified a Foxf1a cis-regulatory element that bound the Hedgehog transcriptional regulators GLI1 and GLI3 and the T-box transcription factor TBX5 in vivo. GLI1 and TBX5 synergistically activated transcription from this cis-regulatory element in vitro. This enhancer drove reproducible expression in vivo in the posterior SHF, the only region where Gli1 and Tbx5 expression overlaps. Our findings implicate Foxf genes in atrioventricular septation, describe the molecular underpinnings of the genetic interaction between Hedgehog signaling and Tbx5, and establish a molecular model for the selection of the SHF gene regulatory network for cardiac septation.

Atrioventricular septal defects (AVSDs) are a common severe class of congenital heart defects. Recent work demonstrates that events in the second heart field (SHF) progenitors, rather than in the heart, drive atrioventricular (AV) septation. Our laboratory has shown that both Hedgehog signaling and the T-box transcription factor, Tbx5, are required in the SHF for AV septation. To understand the molecular underpinnings of the AV septation process we investigated SHF Hedgehog-dependent gene regulatory networks. Transcriptional profiling and chromatin interaction assays identified the Forkhead box transcription factors Foxf1a and Foxf2 as SHF Hedgehog targets. Compound haploinsufficiency for Foxf1a and Foxf2 caused AVSDs in mice, demonstrating the biological relevance of this pathway. We identified a cis-regulatory element at Foxf1a that bound TBX5 and Hedgehog transcriptional regulators GLI1 and GLI3 in-vivo. Furthermore, TBX5 and Gli1 co-activate transcription of the identified cis-regulatory element in-vitro. The enhancer is expressed primarily in the pSHF in-vivo, where Tbx5 and Gli1 expression overlap. Our findings implicate Foxf1a and Foxf2 in AV septation and establish Tbx5 and Hedgehog signaling upstream of Foxf genes in a gene regulatory network for cardiac septation.

ATP8B1 gene expression is driven by a housekeeping-like promoter independent of bile acids and farnesoid X receptor

Background

Mutations in ATP8B1 gene were identified as a cause of low γ-glutamyltranspeptidase cholestasis with variable phenotype, ranging from Progressive Familial Intrahepatic Cholestasis to Benign Recurrent Intrahepatic Cholestasis. However, only the coding region of ATP8B1 has been described. The aim of this research was to explore the regulatory regions, promoter and 5′untranslated region, of the ATP8B1 gene.

Methodology/Principal Findings

5′Rapid Amplification of cDNA Ends using human liver and intestinal tissue was performed to identify the presence of 5′ untranslated exons. Expression levels of ATP8B1 transcripts were determined by quantitative reverse-transcription PCR and compared with the non-variable part of ATP8B1. Three putative promoters were examined in vitro using a reporter gene assay and the main promoter was stimulated with chenodeoxycholic acid. Four novel untranslated exons located up to 71 kb upstream of the previously published exon 1 and twelve different splicing variants were found both in the liver and the intestine. Multiple transcription start sites were identified within exon −3 and the proximal promoter upstream of this transcription start site cluster was proven to be an essential regulatory element responsible for 70% of total ATP8B1 transcriptional activity. In vitro analysis demonstrated that the main promoter drives constitutive ATP8B1 gene expression independent of bile acids.

Conclusions/Significance

The structure of the ATP8B1 gene is complex and the previously published transcription start site is not significant. The basal expression of ATP8B1 is driven by a housekeeping-like promoter located 71 kb upstream of the first protein coding exon.

Glucocorticoid receptor-mediated transcriptional regulation of N-acetyltransferase 1 gene through distal promoter

Human arylamine N-acetyltransferase 1, (HUMAN)NAT1, is a phase II xenobiotic-metabolizing enzyme that plays an important role in drug and carcinogen biotransformation and cancer development. Its gene expression has been shown to be regulated by environmental factors. The purpose of the current study is to determine the involvement of nuclear receptors in transcriptional regulation of (HUMAN)NAT1 gene. We show that among the nuclear receptors examined, including the glucocorticoid receptor, retinoid acid receptor-related orphan receptor alpha, constitutive androstane receptor, pregnane X receptor, aryl hydrocarbon receptor, and retinoic acid receptor, the glucocorticoid receptor plays a dominant role in regulating (HUMAN)NAT1 gene expression through distal promoter (P3). The involvement of the glucocorticoid receptor in transcription regulation of (HUMAN)NAT1 gene expression was demonstrated by dexamethasone treatment, reporter assay using plasmid-containing 3 kbp of 5'-end region of promoter 3, and treatment of anti-glucocorticoid RU486 in primary culture of human hepatocytes and transfected HepG2 cells. In addition, translation inhibition did not affect dexamethasone-induced gene expression through P3, suggesting that dexamethasone effect is directly mediated by glucocorticoid receptor activation. Furthermore, deletion analysis revealed the presence of multiple responsive elements within the 3 kbp fragment of P3. Transfection assays in mice using hydrodynamics-based procedure and reporter gene assay in a mouse cell line revealed that glucocorticoid-induced NAT gene expression is species dependent. Dexamethasone treatment of transfected mice and mouse cell line decreased (MOUSE)Nat2 gene expression, (HUMAN)NAT1 homologue. These results suggest that glucocorticoids serve as a modulator for (HUMAN)NAT1 gene expression via the P3-containing 5'-flanking region.

Human N-acetyltransferase 1 *10 and *11 alleles increase protein expression through distinct mechanisms and associate with sulfamethoxazole-induced hypersensitivity

OBJECTIVES

N-acetyltransferase 1 (NAT1) metabolizes drugs and environmental carcinogens. NAT1 alleles *10 and *11 have been proposed to alter protein level or enzyme activity compared with wild-type NAT1 *4 and to confer cancer risk, through uncertain pathways. This study characterizes regulatory polymorphisms and underlying mechanisms of NAT1 expression.

METHODS

We measured allelic NAT1 mRNA expression and translation, as a function of multiple transcription start sites, alternative splicing, and three 3'-polyadenylation sites in human livers (one of which was discovered in this study), B lymphocytes, and transfected cells. In a clinical study of 469 patients with HIV/AIDS treated with the NAT1/NAT2 substrate sulfamethoxazole (SMX), associations were tested between SMX-induced hypersensitivity and NAT1 *10 and *11 genotypes, together with known NAT2 polymorphisms.

RESULTS

NAT1 *10 and *11 were determined to act as common regulatory alleles accounting for most NAT1 expression variability, both leading to increased translation into active protein. NAT1 *11 (2.4% minor allele frequency) affected 3'-polyadenylation site usage, thereby increasing formation of NAT1 mRNA with intermediate length 3'-untranslated region (major isoform) at the expense of the short isoform, resulting in more efficient protein translation. NAT1 *10 (19% minor allele frequency) increased translation efficiency without affecting 3'-untranslated region polyadenylation site usage. Livers and B-lymphocytes with *11/*4 and *10/*10 genotypes displayed higher NAT1 immunoreactivity and NAT1 enzyme activity than the reference genotype *4/*4. Patients who carry *10/*10 and *11/*4 (fast NAT1 acetylators) were less likely to develop hypersensitivity to SMX, but this was observed only in individuals who are also carrying a slow NAT2 acetylator genotype.

CONCLUSION

NAT1 *10 and *11 significantly increase NAT1 protein level/enzyme activity, enabling the classification of carriers into reference and rapid acetylators. Rapid NAT1 acetylator status seems to protect against SMX toxicity by compensating for slow NAT2 acetylator status.

Functional analysis of arylamine N-acetyltransferase 1 (NAT1) NAT1*10 haplotypes in a complete NATb mRNA construct

N-acetyltransferase 1 (NAT1) catalyzes N-acetylation of arylamines as well as the O-acetylation of N-hydroxylated arylamines. O-acetylation leads to the formation of electrophilic intermediates that result in DNA adducts and mutations. NAT1*10 is the most common variant haplotype and is associated with increased risk for numerous cancers. NAT1 is transcribed from a major promoter, NATb, and an alternative promoter, NATa, resulting in messenger RNAs (mRNAs) with distinct 5'-untranslated regions (UTRs). To best mimic in vivo metabolism and the effect of NAT1*10 polymorphisms on polyadenylation usage, pcDNA5/Flp recombination target plasmid constructs were prepared for transfection of full-length human mRNAs including the 5'-UTR derived from NATb, the open reading frame and 888 nucleotides of the 3'-UTR. Following stable transfection of NAT1*4, NAT1*10 and an additional NAT1*10 variant (termed NAT1*10B) into nucleotide excision repair-deficient Chinese hamster ovary cells, N- and O-acetyltransferase activity (in vitro and in situ), mRNA and protein expression were higher in cells transfected with NAT1*10 and NAT1*10B than in cells transfected with NAT1*4 (P < 0.05). Consistent with NAT1 expression and activity, cytotoxicity and hypoxanthine phosphoribosyl transferase mutants following 4-aminobiphenyl exposures were higher in NAT1*10 than in NAT1*4 transfected cells. Ribonuclease protection assays showed no difference between NAT1*4 and NAT1*10. However, protection of one probe by NAT1*10B was not observed with NAT1*4 or NAT1*10, suggesting additional mechanisms that regulate NAT1*10B. The higher mutants in cells transfected with NAT1*10 and NAT1*10B are consistent with an increased cancer risk for individuals possessing NAT1*10 haplotypes.

NATb/NAT1*4 promotes greater arylamine N-acetyltransferase 1 mediated DNA adducts and mutations than NATa/NAT1*4 following exposure to 4-aminobiphenyl

N-acetyltransferase 1 (NAT1) is a phase II metabolic enzyme responsible for the biotransformation of aromatic and heterocyclic amine carcinogens such as 4-aminobiphenyl (ABP). NAT1 catalyzes N-acetylation of arylamines as well as the O-acetylation of N-hydroxylated arylamines. O-acetylation leads to the formation of electrophilic intermediates that result in DNA adducts and mutations. NAT1 is transcribed from a major promoter, NATb, and an alternative promoter, NATa, resulting in mRNAs with distinct 5'-untranslated regions (UTR). NATa mRNA is expressed primarily in the kidney, liver, trachea, and lung while NATb mRNA has been detected in all tissues studied. To determine if differences in 5'-UTR have functional effect upon NAT1 activity and DNA adducts or mutations following exposure to ABP, pcDNA5/FRT plasmid constructs were prepared for transfection of full-length human mRNAs including the 5'-UTR derived from NATa or NATb, the open reading frame, and 888 nucleotides of the 3'-UTR. Following stable transfection of NATb/NAT1*4 or NATa/NAT1*4 into nucleotide excision repair (NER) deficient Chinese hamster ovary cells, N-acetyltransferase activity (in vitro and in situ), mRNA, and protein expression were higher in NATb/NAT1*4 than NATa/NAT1*4 transfected cells (P < 0.05). Consistent with NAT1 expression and activity, ABP-induced DNA adducts and hypoxanthine phosphoribosyl transferase mutants were significantly higher (P < 0.05) in NATb/NAT1*4 than in NATa/NAT1*4 transfected cells following exposure to ABP. These differences observed between NATa and NATb suggest that the 5'-UTRs are differentially regulated.

Functional effects of genetic polymorphisms in the N-acetyltransferase 1 coding and 3' untranslated regions

BACKGROUND

The functional effects of N-acetyltransferase 1 (NAT1) polymorphisms and haplotypes are poorly understood, compromising the validity of associations reported with diseases, including birth defects and numerous cancers.

METHODS

We investigated the effects of genetic polymorphisms within the NAT1 coding region and the 3'-untranslated region (3'-UTR) and their associated haplotypes on N- and O-acetyltransferase catalytic activities, and NAT1 mRNA and protein levels following recombinant expression in COS-1 cells.

RESULTS

1088T>A (rs1057126; 3'-UTR) and 1095C>A (rs15561; 3'-UTR) each slightly reduced NAT1 catalytic activity and NAT1 mRNA and protein levels. A 9-bp (TAATAATAA) deletion between nucleotides 1065 and 1090 (3'-UTR) reduced NAT1 catalytic activity and NAT1 mRNA and protein levels. In contrast, a 445G>A (rs4987076; V149I), 459G>A (rs4986990; T153T), and 640T>G (rs4986783; S214A) coding region haplotype present in NAT1*11 increased NAT1 catalytic activity and NAT1 protein, but not NAT1 mRNA levels. A combination of the 9-bp (TAATAATAA) deletion and the 445G>A, 459G>A, and 640T>G coding region haplotypes, both present in NAT1*11, appeared to neutralize the opposing effects on NAT1 protein and catalytic activity, resulting in levels of NAT1 protein and catalytic activity that did not differ significantly from the NAT1*4 reference.

CONCLUSIONS

Because 1095C>A (3'-UTR) is the sole polymorphism present in NAT1*3, our data suggest that NAT1*3 is not functionally equivalent to the NAT1*4 reference. Furthermore, our findings provide biologic support for reported associations of 1088T>A and 1095C>A polymorphisms with birth defects.

Lack of association of the N-acetyltransferase NAT1*10 allele with prostate cancer incidence, grade, or stage among smokers in Finland

Genetic variations in xenobiotic metabolizing genes can influence susceptibility to many environmentally induced cancers. Inheritance of the N-acetyltransferase 1 allele (NAT1*10), linked with increased metabolic activation of pro-carcinogens, is associated with an increased susceptibility to many cancers in which cigarette- or meat-derived carcinogens have been implicated in their etiology. The role of NAT1*10 in prostate cancer is under studied. Although cigarette smoking is not considered a risk factor for prostate cancer, a recent review suggests it may play a role in disease progression. Consequently, we examined the association of NAT1*10 with prostate cancer risk, grade, and stage among 400 Finnish male smokers using a case-control study design. Following genotyping of 206 patients and 196 healthy controls, our results do not support the role of NAT1*10 in relation to prostate cancer risk (OR = 1.28; 95% CI, 0.66-2.47), aggressive disease (OR = 0.58; 95% CI, 0.13-2.67), or advanced disease (OR = 1.19; 95% CI, 0.49-2.91).

Histone deacetylase inhibitors increase human arylamine N-acetyltransferase-1 expression in human tumor cells

Arylamine N-acetyltransferase-1 (NAT1) has been associated with disorders involving folate metabolism, such as spina bifida, as well as numerous human cancers. As a result, the transcriptional and post-transcriptional regulation of NAT1 activity has been extensively studied. However, little work has been reported on the epigenetic control of NAT1 expression. Here, we demonstrate that the histone deacetylase inhibitor trichostatin A (TSA) increases NAT1 activity in human cancer cells by increasing transcription from the proximal promoter NATb. A specific Sp1 binding site was identified as essential for optimal induction of NAT1 by TSA. However, TSA did not increase the expression of Sp1 in HeLa cells. Instead, TSA increased the acetylation of histones associated with the NATb promoter. This allowed recruitment of Sp1 to the promoter along with acetylated histones. We propose that NAT1 transcription is partially repressed by the local chromatin condensation in the vicinity of NATb and that histone deacetylase inhibition leads to up-regulation of NAT1 expression via a direct change in chromatin conformation.

Structural and functional characterization of the mouse tescalcin promoter

Tescalcin, an EF-hand calcium binding protein that regulates the Na(+)/H(+) exchanger 1 (NHE1), is highly expressed in various mouse tissues such as heart and brain. Despite its potentially important role in cell physiology, the mechanisms that regulate tescalcin gene (Tesc) expression are unknown. In this study, we report two new Tesc mRNA variants (V2 and V3) and characterize the mouse Tesc promoter. The V2 and V3 transcripts result from alternative splicing of intron 5. Our results show that Tesc mRNA variants are expressed in various mouse tissues. Primer extension analysis located the transcription start site at 94 nucleotides upstream of the translation start codon. The DNA nucleotide sequence of the 5'-flanking region contained a CpG island spanning the promoter region from nucleotides -372 to +814, a canonical TATA box (-38/-32), and putative transcription factor binding sites for Sp1, EGR1, ZBP-89, KLF3, MZF1, AP2, ZF5, and CDF-1. Transient transfection of the Y1 and msc-1 cell lines with a series of 5'-deleted promoter constructs indicated that the minimal promoter region was between nucleotides -130 and -40. Electrophoresis mobility shift assays, supershift assays, and mutation studies demonstrated that Sp1 and Sp3 bind to the GC-rich motifs, a CACCC box and three GC boxes, located within the Tesc proximal promoter. Nonetheless, mutations that abolished interaction of Sp1 and Sp3 with the GC-rich motifs located within the minimal promoter region did not abrogate promoter activity in Y1 cells. Mithramycin A, an inhibitor of Sp1-DNA interaction, reduced Tesc promoter activity in msc-1 cells in a dose-dependent manner. Sp3 was a weaker transactivator compared to Sp1 in Drosophila D.mel-2 cells. However, when Sp1 and Sp3 were coexpressed, they transactivated the Tesc promoter in a synergistic manner. In Y1 cells, mutation analysis of a putative ZF5 motif located within the Tesc minimal promoter indicated that this motif was critical for activity of Tesc promoter. Taken together, the data demonstrated that Sp1 and Sp3 transcription factors cooperate positively in the regulation of Tesc promoter, and that the putative ZF5 motif is critical for its activation.

N-acetyltransferase SNPs: emerging concepts serve as a paradigm for understanding complexities of personalized medicine

Arylamine N-acetyltransferase 1 and 2 exhibit single nucleotide polymorphisms in human populations that modify drug and carcinogen metabolism. This paper updates the identity, location and functional effects of these single nucleotide polymorphisms and then follows with emerging concepts for understanding why pharmacogenetic findings may not be replicated consistently. Using this paradigm as an example, laboratory-based mechanistic analyses can reveal complexities such that genetic polymorphisms become biologically and medically relevant when confounding factors are more fully understood and considered. As medical care moves to a more personalized approach, the implications of these confounding factors will be important in understanding the complexities of personalized medicine.

Characterisation of CpG methylation in the upstream control region of mouse Nat2: evidence for a gene-environment interaction in a polymorphic gene implicated in folate metabolism

Human arylamine N-acetyltransferase 1 (NAT1), a polymorphic xenobiotic metabolising enzyme, has been investigated in relation to susceptibility and prognosis in certain types of cancer. Both human NAT1 and its murine equivalent NAT2 have previously been shown to play roles in the catabolism of folate, which is required for the synthesis of S-adenosylmethionine, the methyl donor for cellular methylation reactions. We have tested whether the expression of mouse Nat2 is subject to epigenetic regulation, specifically CpG methylation in the promoter region, by determining levels of 5-methylcytosine by bisulphite sequencing and methylation-specific PCR. Under normal conditions, methylation levels of the Nat2 promoter were low, and varied in different tissues. However, CpG methylation was significantly increased by dietary folate supplementation, and increased methylation corresponded to decreased use of the core promoter. Functional deletion of the Nat2 gene gave rise to a significant increase in Nat2 methylation, extending our previous observations that folate catabolism is decreased in Nat2 null mice. Mouse NAT2 is likely to influence epigenetic gene control, particularly of its own locus, and this is consistent with recent evidence associating aberrant mouse Nat2/human NAT1 gene expression with certain developmental malformations and cancers.

Update on the pharmacogenetics of NATs: structural considerations

The arylamine N-acetyltransferase (NAT) genes encode enzymes that catalyze the N-acetylation of aromatic amines and hydrazines and the O-acetylation of heterocyclic amines. These genes, which play a key role in cellular homeostasis as well as in gene-environment interactions, are subject to marked pharmacogenetic variation, and different combinations of SNPs in the human NAT genes lead to different acetylation phenotypes. Our understanding of the consequences of pharmacogenetic variability in NATs has recently been enhanced by structural studies showing that effects on protein folding, aggregation and turnover, as well as direct changes in active site topology, are involved. These developments pave the way for a better understanding of the role played by NATs in maintaining cellular homeostasis. In addition, the NATs represent a model for studying fundamental processes associated with protein folding and pharmacogenomic effects mediated by inheritance in human populations across a polymorphic region of the genome.

4-Aminobiphenyl downregulation of NAT2 acetylator genotype-dependent N- and O-acetylation of aromatic and heterocyclic amine carcinogens in primary mammary epithelial cell cultures from rapid and slow acetylator rats

Aromatic and heterocyclic amine carcinogens present in the diet and in cigarette smoke induce breast tumors in rats. N-acetyltransferase 1 (NAT1) and N-acetyltransferase 2 (NAT2) enzymes have important roles in their metabolic activation and deactivation. Human epidemiological studies suggest that genetic polymorphisms in NAT1 and/or NAT2 modify breast cancer risk in women exposed to these carcinogens. p-Aminobenzoic acid (selective for rat NAT2) and sulfamethazine (SMZ; selective for rat NAT1) N-acetyltransferase catalytic activities were both expressed in primary cultures of rat mammary epithelial cells. PABA, 2-aminofluorene, and 4-aminobiphenyl N-acetyltransferase and N-hydroxy-2-amino-1-methyl-6-phenylimidazo[4,5-b] pyridine and N-hydroxy-2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline O-acetyltransferase activities were two- to threefold higher in mammary epithelial cell cultures from rapid than slow acetylator rats. In contrast, SMZ (a rat NAT1-selective substrate) N-acetyltransferase activity did not differ between rapid and slow acetylators. Rat mammary cells cultured in the medium supplemented 24 h with 10muM ABP showed downregulation in the N-and O-acetylation of all substrates tested except for the NAT1-selective substrate SMZ. This downregulation was comparable in rapid and slow NAT2 acetylators. These studies clearly show NAT2 acetylator genotype-dependent N- and O-acetylation of aromatic and heterocyclic amine carcinogens in rat mammary epithelial cell cultures to be subject to downregulation by the arylamine carcinogen ABP.

Systemic functional expression of N-acetyltransferase polymorphism in the F344 Nat2 congenic rat

Rat lines congenic for the rat N-acetyltransferase 2 [(RAT)Nat2] gene were constructed and characterized. F344 (homozygous Nat2 rapid) males were mated to Wistar Kyoto (homozygous Nat2 slow) females to produce heterozygous F1. F1 females were then backcrossed to F344 males. Heterozygous acetylator female progeny from this and each successive backcross were identified by rat Nat2 genotyping and mated with F344 rapid acetylator males. After 10 generations of backcross mating, heterozygous acetylator brother/sister progeny were mated to produce the homozygous rapid and slow acetylator Nat2 congenic rat lines. p-Aminobenzoic acid (selective for rat NAT2) and 4-aminobiphenyl N-acetyltransferase activities were expressed in all tissues examined (liver, lung, esophagus, stomach, small intestine, colon, pancreas, kidney, skin, leukocytes, and urinary bladder in male and female rats and in breast of female and prostate of male rats). NAT2 expression in rat extrahepatic tissues was much higher than that in liver. In each tissue, activities were Nat2-genotype-dependent, with the highest levels in homozygous rapid acetylators, intermediate levels in heterozygous acetylators, and lowest in homozygous slow acetylators. Sulfamethazine (selective for rat NAT1) N-acetyltransferase activities were observed in all tissues examined in both male and female rats except for breast (females), bladder, and leukocytes. In each tissue, the activity was Nat2 genotype-independent, with similar levels in homozygous rapid, heterozygous, and homozygous slow acetylators. These congenic rat lines are useful for investigating the role of NAT2 genetic polymorphisms in susceptibility to cancers related to arylamine carcinogen exposures.

Quantitative tissue and gene-specific differences and developmental changes in Nat1, Nat2, and Nat3 mRNA expression in the rat

Human N-acetyltransferase 1 (NAT1) and 2 (NAT2) are important phase II enzymes involved in the biotransformation of xenobiotics. In toxicity and carcinogenicity studies, functional polymorphism of rat N-acetyltransferase is considered a model for similar human variability. To accurately quantitate expression of the three rat N-acetyltransferases, we developed sensitive, specific assays for Nat1, Nat2, and Nat3 mRNAs. In male F344 rats, tissue-specific expression varied over a limited range for both Nat1 (approximately 19-fold) and Nat2 (approximately 30-fold), with the highest expression of both genes in colon. Expression of Nat3 mRNA was at least 2 to 3 orders of magnitude less than that of Nat1 or Nat2. Comparison of Nat1 and Nat2 mRNA expression in bladder, colon, liver, and lung of male and female F344 rats detected no significant gender-specific difference. In Sprague-Dawley and F344 rats ranging in age from neonate to mature adult, colon showed a >10-fold increase in Nat2 during the first postnatal month that did not correlate with changes in Nat1. In contrast, Nat2 showed no developmental change in Sprague-Dawley or F344 liver as Nat1 increased modestly. These measures of rat Nat expression confirm that Nat3 expression is negligible and that Nat1 and Nat2 are the primary determinants of arylamine acetylation activity in all tissues tested. The findings demonstrate differential tissue-specific and developmental regulation of the rat Nat1 and Nat2 genes and contribute to more complete understanding of tissue-, gender-, and development-specific expression patterns of the cognate N-acetyltransferase genes of humans and other species.

The functional consequences of alternative promoter use in mammalian genomes

We are beginning to appreciate the increasing complexity of mammalian gene structure. A phenomenon that adds an important dimension to this complexity is the use of alternative gene promoters that drive widespread cell type, tissue type or developmental gene regulation. Recent annotations of the human genome suggest that almost one half of the protein-coding genes contain alternative promoters, including those of many disease-associated genes. Aberrant use of one promoter over another has been found to be associated with various diseases, including cancer. Here we discuss the functional consequences of use and misuse of alternative promoters in normal and disease genomes and review the molecular mechanisms regulating alternative promoter use in mammalian genomes.

Modification by N-acetyltransferase 1 genotype on the association between dietary heterocyclic amines and colon cancer in a multiethnic study

OBJECTIVE

Colorectal cancer incidence is greater among African Americans, compared to whites in the U.S., and may be due in part to differences in diet, genetic variation at metabolic loci, and/or the joint effect of diet and genetic susceptibility. We examined whether our previously reported associations between meat-derived heterocyclic amine (HCA) intake and colon cancer were modified by N-acetyltransferase 1 (NAT1) or 2 (NAT2) genotypes and whether there were differences by race.

METHODS

In a population-based, case-control study of colon cancer, exposure to HCAs was assessed using a food-frequency questionnaire with a meat-cooking and doneness module, among African Americans (217 cases and 315 controls) and whites (290 cases and 534 controls).

RESULTS

There was no association with NAT1*10 versus NAT1-non*10 genotypes for colon cancer. Among whites, there was a positive association for NAT2-"rapid/intermediate" genotype [odds ratio (OR)=1.4; 95% confidence interval (CI)=1.0, 1.8], compared to the NAT2-"slow" that was not observed among African Americans. Colon cancer associations with HCA intake were modified by NAT1, but not NAT2, regardless of race. However, the "at-risk" NAT1 genotype differed by race. For example, among African Americans, the positive association with 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP) was confined to those with NAT1*10 genotype (OR=1.8; 95% CI=1.0, 3.3; P for interaction=0.02, comparing highest to lowest intake), but among whites, an association with 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) was confined to those with NAT1-non*10 genotype (OR=1.9; 95% CI=1.1, 3.1; P for interaction=0.03).

CONCLUSIONS

Our data indicate modification by NAT1 for HCA and colon cancer associations, regardless of race. Although the at-risk NAT1 genotype differs by race, the magnitude of the individual HCA-related associations in both race groups are similar. Therefore, our data do not support the hypothesis that NAT1 by HCA interactions contribute to differences in colorectal cancer incidence between African Americans and whites.