ArylamineN-acetyltransferases

Environmental sulfonamides pollution and microbial adaptation: Genome, transcriptome, and toxicology reveal Bacillus sp. HC-1 biotransformation and antibiotic resistance mechanisms

Sulfonamides (SAs) residue in the environment presents significant challenges to both environmental safety and medical security. Currently, the reaction and transformation mechanisms of microorganisms in the presence of SAs remain unclear. This study employed multiomics to investigate the gene response and enzymatic transformation mechanisms of Bacillus sp. HC-1 under SAs exposure conditions. Strain HC-1 demonstrated the ability to transform sulfaquinoxaline (SQX), sulfamethoxazole (SMX), and sulfamethazine (SMZ) into their respective N4-acetylated products. Within 12 hours, the transformation rates of SQX, SMX, and SMZ reached 51.7 %, 44.7 %, and 42.70 % respectively. Transcriptome analysis revealed that differentially expressed genes (DEGs) related to cellular transport, membrane channel activity, and various metabolic pathways were significantly enriched in strain HC-1 exposed to SQX. Through genomic analysis, we identified three types of arylamine N-acetyltransferases (NATs), which were named BaNATA, BaNATB, and BaNATC. Their highest homologies with reported NATs were 35.29 %, 40.82 %, and 35.32 %, respectively. Resistance and toxicological assessments indicated that NATs functioned as resistance genes against SAs, and the toxicity of transformation products to microorganisms and plant seeds was diminished. This study offers a valuable reference for a more in-depth understanding of microbial reactions, potential resistance, and transformation mechanisms in antibiotic-contaminated environments.

A review of the known MTA-cooperative PRMT5 inhibitors

Protein arginine methyltransferase 5 (PRMT5), an epigenetic target with significant clinical potential, is closely associated with the occurrence and development of a range of tumours and has attracted considerable interest from the pharmaceutical industry and academic research communities. According to incomplete statistics, more than 10 PRMT5 inhibitors for cancer therapy have entered clinical trials in recent years. Among them, the second-generation PRMT5 inhibitors developed based on the synthetic lethal strategy demonstrate considerable clinical application value. This suggests that, following the precedent of poly ADP ribose polymerase (PARP), PRMT5 has the potential to become the next clinically applicable synthetic lethal target. However, due to the inherent dose-limiting toxicity of epigenetic target inhibitors, none of these PRMT5 inhibitors has been approved for marketing to date. In light of this, we have conducted a review of the design thoughts and the structure-activity relationship (SAR) of known methylthioadenosine (MTA)-cooperative PRMT5 inhibitors. Additionally, we have analysed the clinical safety of representative first- and second-generation PRMT5 inhibitors. This paper discusses the in vivo vulnerability of the aromatic amine moiety of the second-generation PRMT5 inhibitor based on its structure. It also considers the potential nitrosamine risk factors associated with the preparation process.

Cascading Detection of Hydrogen Sulfide and N-Acetyltransferase 2 in Hepatocellular Carcinoma Cells Using a Two-Photon Fluorescent Probe

Hydrogen sulfide (H2S), a critical gas signaling molecule, and N-acetyltransferase 2 (NAT2), a key enzyme in drug metabolism, are both known active biomarkers for liver function. However, the interactions and effects of H2S and NAT2 in living cells or lesion sites remain unknown due to the lack of imaging tools to achieve simultaneous detection of these two substances, making it challenging to implement real-time imaging and precise tracking. Herein, we report an activity-based two-photon fluorescent probe, TPSP-1, for the cascade detection of H2S and NAT2 in living liver cells. Continuous conversion from TPSP-1 to TPSP-3 was achieved in liver cells and tissues. Significantly, leveraging the outstanding optical properties of this two-photon fluorescent probe, TPSP-1, has been effectively used to identify pathological tissue samples directly from clinical liver cancer patients. This work provides us with this novel sensing and two-photon imaging probe, which can be used as a powerful tool to study the physiological functions of H2S and NAT2 and will help facilitate rapid and accurate diagnosis and therapeutic evaluation of hepatocellular carcinoma.

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.

How Can Drug Metabolism and Transporter Genetics Inform Psychotropic Prescribing?

Many genetic variants in drug metabolizing enzymes and transporters have been shown to be relevant for treating psychiatric disorders. Associations are strong enough to feature on drug labels and for prescribing guidelines based on such data. A range of commercial tests are available; however, there is variability in included genetic variants, methodology, and interpretation. We herein provide relevant background for understanding clinical associations with specific variants, other factors that are relevant to consider when interpreting such data (such as age, gender, drug-drug interactions), and summarize the data relevant to clinical utility of pharmacogenetic testing in psychiatry and the available prescribing guidelines. We also highlight areas for future research focus in this field.

Functional expression of human arylamine N-acetyltransferase NAT1*10 and NAT1*11 alleles: a mini review

The arylamine N-acetyltransferase (NAT) nomenclature committee assigns functional phenotypes for human arylamine N-acetyltransferase 1 (NAT1) alleles in those instances in which the committee determined a consensus has been achieved in the scientific literature. In the most recent nomenclature update, the committee announced that functional phenotypes for NAT1*10 and NAT1*11 alleles were not provided owing to a lack of consensus. Phenotypic inconsistencies observed among various studies for NAT1*10 and NAT1*11 may be owing to variable allelic expression among different tissues, the limitations of the genotyping assays (which mostly relied on techniques not involving direct DNA sequencing), the differences in recombinant protein expression systems used (bacteria, yeast, and mammalian cell lines) and/or the known inherent instability of human NAT1 protein, which requires very careful handling of native and recombinant cell lysates. Three recent studies provide consistent evidence of the mechanistic basis underlying the functional phenotype of NAT1*10 and NAT1*11 as 'increased-activity' alleles. Some NAT1 variants (e.g. NAT1*14, NAT1*17, and NAT1*22) may be designated as 'decreased-activity' alleles and other NAT1 variants (e.g. NAT1*15 and NAT1*19) may be designated as 'no-activity' alleles compared with the NAT1*4 reference allele. We propose that phenotypic designations as 'rapid' and 'slow' acetylator should be discontinued for NAT1 alleles, although these designations remain very appropriate for NAT2 alleles.

Identification of the anti-mycobacterial functional properties of piperidinol derivatives

Background and Purpose

Tuberculosis (TB) remains a major global health threat and is now the leading cause of death from a single infectious agent worldwide. The current TB drug regimen is inadequate, and new anti‐tubercular agents are urgently required to be able to successfully combat the increasing prevalence of drug‐resistant TB. The purpose of this study was to investigate a piperidinol compound derivative that is highly active against the Mycobacterium tuberculosis bacillus.

Experimental Approach

The antibacterial properties of the piperidinol compound and its corresponding bis‐Mannich base analogue were evaluated against M. smegmatis and Gram‐negative organisms. Cytotoxicity studies were undertaken in order to determine the selectivity index for these compounds. Spontaneous resistant mutants of M. smegmatis were generated against the piperidinol and corresponding bis‐Mannich base lead derivatives and whole genome sequencing employed to determine the genetic modifications that lead to selection pressure in the presence of these compounds.

Key Results

The piperidinol and the bis‐Mannich base analogue were found to be selective for mycobacteria and rapidly kill this organism with a cytotoxicity selectivity index for mycobacteria of >30‐fold. Whole genome sequencing of M. smegmatis strains resistant to the lead compounds led to the identification of a number of single nucleotide polymorphisms indicating multiple targets.

Conclusion and Implications

Our results indicate that the piperidinol moiety represents an attractive compound class in the pursuit of novel anti‐tubercular agents.

Linked Articles

This article is part of a themed section on Drug Metabolism and Antibiotic Resistance in Micro‐organisms. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.14/issuetoc

Identification of cancer chemopreventive isothiocyanates as direct inhibitors of the arylamine N-acetyltransferase-dependent acetylation and bioactivation of aromatic amine carcinogens

Aromatic amines (AAs) are chemicals of industrial, pharmacological and environmental relevance. Certain AAs, such as 4-aminobiphenyl (4-ABP), are human carcinogens that require enzymatic metabolic activation to reactive chemicals to form genotoxic DNA adducts. Arylamine N-acetyltransferases (NAT) are xenobiotic metabolizing enzymes (XME) that play a major role in this carcinogenic bioactivation process. Isothiocyanates (ITCs), including benzyl-ITC (BITC) and phenethyl-ITC (PEITC), are phytochemicals known to have chemopreventive activity against several aromatic carcinogens. In particular, ITCs have been shown to modify the bioactivation and subsequent mutagenicity of carcinogenic AA chemicals such as 4-ABP. However, the molecular and biochemical mechanisms by which these phytochemicals may modulate AA carcinogens bioactivation and AA-DNA damage remains poorly understood.

This manuscript provides evidence indicating that ITCs can decrease the metabolic activation of carcinogenic AAs via the irreversible inhibition of NAT enzymes and subsequent alteration of the acetylation of AAs. We demonstrate that BITC and PEITC react with NAT1 and inhibit readily its acetyltransferase activity (k_i = 200 M⁻¹.s⁻¹ and 66 M⁻¹.s⁻¹ for BITC and PEITC, respectively). Chemical labeling, docking approaches and substrate protection assays indicated that inhibition of the acetylation of AAs by NAT1 was due to the chemical modification of the enzyme active site cysteine. Moreover, analyses of AAs acetylation and DNA adducts in cells showed that BITC was able to modulate the endogenous acetylation and bioactivation of 4-ABP. In conclusion, we show that direct inhibition of NAT enzymes may be an important mechanism by which ITCs exert their chemopreventive activity towards AA chemicals.

Identification and validation of N-acetyltransferase 2 as an insulin sensitivity gene

Decreased insulin sensitivity, also referred to as insulin resistance (IR), is a fundamental abnormality in patients with type 2 diabetes and a risk factor for cardiovascular disease. While IR predisposition is heritable, the genetic basis remains largely unknown. The GENEticS of Insulin Sensitivity consortium conducted a genome-wide association study (GWAS) for direct measures of insulin sensitivity, such as euglycemic clamp or insulin suppression test, in 2,764 European individuals, with replication in an additional 2,860 individuals. The presence of a nonsynonymous variant of N-acetyltransferase 2 (NAT2) [rs1208 (803A>G, K268R)] was strongly associated with decreased insulin sensitivity that was independent of BMI. The rs1208 "A" allele was nominally associated with IR-related traits, including increased fasting glucose, hemoglobin A1C, total and LDL cholesterol, triglycerides, and coronary artery disease. NAT2 acetylates arylamine and hydrazine drugs and carcinogens, but predicted acetylator NAT2 phenotypes were not associated with insulin sensitivity. In a murine adipocyte cell line, silencing of NAT2 ortholog Nat1 decreased insulin-mediated glucose uptake, increased basal and isoproterenol-stimulated lipolysis, and decreased adipocyte differentiation, while Nat1 overexpression produced opposite effects. Nat1-deficient mice had elevations in fasting blood glucose, insulin, and triglycerides and decreased insulin sensitivity, as measured by glucose and insulin tolerance tests, with intermediate effects in Nat1 heterozygote mice. Our results support a role for NAT2 in insulin sensitivity.

Arylamine N-acetyltransferases: from drug metabolism and pharmacogenetics to drug discovery

Arylamine N-acetyltransferases (NATs) are polymorphic drug-metabolizing enzymes, acetylating arylamine carcinogens and drugs including hydralazine and sulphonamides. The slow NAT phenotype increases susceptibility to hydralazine and isoniazid toxicity and to occupational bladder cancer. The two polymorphic human NAT loci show linkage disequilibrium. All mammalian Nat genes have an intronless open reading frame and non-coding exons. The human gene products NAT1 and NAT2 have distinct substrate specificities: NAT2 acetylates hydralazine and human NAT1 acetylates p-aminosalicylate (p-AS) and the folate catabolite para-aminobenzoylglutamate (p-abaglu). Human NAT2 is mainly in liver and gut. Human NAT1 and its murine homologue are in many adult tissues and in early embryos. Human NAT1 is strongly expressed in oestrogen receptor-positive breast cancer and may contribute to folate and acetyl CoA homeostasis. NAT enzymes act through a catalytic triad of Cys, His and Asp with the architecture of the active site-modulating specificity. Polymorphisms may cause unfolded protein. The C-terminus helps bind acetyl CoA and differs among NATs including prokaryotic homologues. NAT in Salmonella typhimurium supports carcinogen activation and NAT in mycobacteria metabolizes isoniazid with polymorphism a minor factor in isoniazid resistance. Importantly, nat is in a gene cluster essential for Mycobacterium tuberculosis survival inside macrophages. NAT inhibitors are a starting point for novel anti-tuberculosis drugs. Human NAT1-specific inhibitors may act in biomarker detection in breast cancer and in cancer therapy. NAT inhibitors for co-administration with 5-aminosalicylate (5-AS) in inflammatory bowel disease has prompted ongoing investigations of azoreductases in gut bacteria which release 5-AS from prodrugs including balsalazide.

Immunohistochemical determination of the miR-1290 target arylamine N-acetyltransferase 1 (NAT1) as a prognostic biomarker in breast cancer

Background

There are many molecular differences between estrogen receptor α (ERα)-positive and ER-negative breast cancers. Recent analyses have shown that the former can be divided into two subtypes, luminal A and luminal B. These differ in response to endocrine therapy and chemotherapy, and in prognosis. In a previous study, we found that microRNA (miR)-1290 that was significantly down-regulated in luminal A tumors and its potential target arylamine N-acetyltransferase 1 (NAT1). The aim of the present study was to determine whether NAT1 is a bona fide target of miR-1290, and to investigate the impact of NAT1 on breast cancer prognosis.

Methods

Luciferase reporter assays were employed to validate NAT1 as a putative miR-1290 target gene. Expression of NAT1, ERα, progesterone receptor (PgR) and HER2 was analyzed in 394 breast cancer samples by immunohistochemistry.

Results

NAT1 was confirmed to be a direct target of miR-1290. Levels of expression of NAT1 were positively correlated with those of ERα (P < 0.0001) and PgR (P < 0.0001), but negatively correlated with both tumor grade and size (P < 0.0001). Kaplan-Meier analysis showed that the presence of NAT1 was significantly associated with increased overall survival (OS) (P = 0.0416) in these patients. Similarly, significant associations of NAT1 with disease-free survival (DFS) (P = 0.0048) and OS (P = 0.0055) in those patients who received adjuvant endocrine therapy with tamoxifen (n = 176) were found. Moreover, NAT1 was also significantly associated with increased DFS (P = 0.0025) and OS (P = 0.0007) in the subset of lymph node-positive patients (n = 147). Univariate and multivariate analyses showed significant associations between levels of NAT1 and DFS (P = 0.0005 and 0.019, respectively).

Conclusions

We report that miR-1290 directly targets the NAT1 3′-UTR and that NAT1 protein expression is correlated with improved OS of breast cancer patients. NAT1 is a possible prognostic biomarker for lymph node-positive breast cancer. Thus, miR-1290 and its target NAT1 are associated with important characteristics of breast cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-990) contains supplementary material, which is available to authorized users.

From arylamine N-acetyltransferase to folate-dependent acetyl CoA hydrolase: impact of folic acid on the activity of (HUMAN)NAT1 and its homologue (MOUSE)NAT2

Acetyl Coenzyme A-dependent N-, O- and N,O-acetylation of aromatic amines and hydrazines by arylamine N-acetyltransferases is well characterised. Here, we describe experiments demonstrating that human arylamine N-acetyltransferase Type 1 and its murine homologue (Type 2) can also catalyse the direct hydrolysis of acetyl Coenzyme A in the presence of folate. This folate-dependent activity is exclusive to these two isoforms; no acetyl Coenzyme A hydrolysis was found when murine arylamine N-acetyltransferase Type 1 or recombinant bacterial arylamine N-acetyltransferases were incubated with folate. Proton nuclear magnetic resonance spectroscopy allowed chemical modifications occurring during the catalytic reaction to be analysed in real time, revealing that the disappearance of acetyl CH₃ from acetyl Coenzyme A occurred concomitantly with the appearance of a CH₃ peak corresponding to that of free acetate and suggesting that folate is not acetylated during the reaction. We propose that folate is a cofactor for this reaction and suggest it as an endogenous function of this widespread enzyme. Furthermore, in silico docking of folate within the active site of human arylamine N-acetyltransferase Type 1 suggests that folate may bind at the enzyme’s active site, and facilitate acetyl Coenzyme A hydrolysis. The evidence presented in this paper adds to our growing understanding of the endogenous roles of human arylamine N-acetyltransferase Type 1 and its mouse homologue and expands the catalytic repertoire of these enzymes, demonstrating that they are by no means just xenobiotic metabolising enzymes but probably also play an important role in cellular metabolism. These data, together with the characterisation of a naphthoquinone inhibitor of folate-dependent acetyl Coenzyme A hydrolysis by human arylamine N-acetyltransferase Type 1/murine arylamine N-acetyltransferase Type 2, open up a range of future avenues of exploration, both for elucidating the developmental role of these enzymes and for improving chemotherapeutic approaches to pathological conditions including estrogen receptor-positive breast cancer.

Rapid birth-and-death evolution of the xenobiotic metabolizing NAT gene family in vertebrates with evidence of adaptive selection

Background

The arylamine N-acetyltransferases (NATs) are a unique family of enzymes widely distributed in nature that play a crucial role in the detoxification of aromatic amine xenobiotics. Considering the temporal changes in the levels and toxicity of environmentally available chemicals, the metabolic function of NATs is likely to be under adaptive evolution to broaden or change substrate specificity over time, making NATs a promising subject for evolutionary analyses. In this study, we trace the molecular evolutionary history of the NAT gene family during the last ~450 million years of vertebrate evolution and define the likely role of gene duplication, gene conversion and positive selection in the evolutionary dynamics of this family.

Results

A phylogenetic analysis of 77 NAT sequences from 38 vertebrate species retrieved from public genomic databases shows that NATs are phylogenetically unstable genes, characterized by frequent gene duplications and losses even among closely related species, and that concerted evolution only played a minor role in the patterns of sequence divergence. Local signals of positive selection are detected in several lineages, probably reflecting response to changes in xenobiotic exposure. We then put a special emphasis on the study of the last ~85 million years of primate NAT evolution by determining the NAT homologous sequences in 13 additional primate species. Our phylogenetic analysis supports the view that the three human NAT genes emerged from a first duplication event in the common ancestor of Simiiformes, yielding NAT1 and an ancestral NAT gene which in turn, duplicated in the common ancestor of Catarrhini, giving rise to NAT2 and the NATP pseudogene. Our analysis suggests a main role of purifying selection in NAT1 protein evolution, whereas NAT2 was predicted to mostly evolve under positive selection to change its amino acid sequence over time. These findings are consistent with a differential role of the two human isoenzymes and support the involvement of NAT1 in endogenous metabolic pathways.

Conclusions

This study provides unequivocal evidence that the NAT gene family has evolved under a dynamic process of birth-and-death evolution in vertebrates, consistent with previous observations made in fungi.

N-Acetyltransferase 1 (NAT1) Genotype: A Risk Factor for Urinary Bladder Cancer in a Lebanese Population

In Lebanon, bladder cancer is the second most incident cancer among men. This study investigates a possible association between N-acetyltransferase 1 (NAT1) genotype, a drug-metabolizing enzyme coding gene, and bladder cancer in Lebanese men. A case-control study (54 cases and 105 hospital-based controls) was conducted in two major hospitals in Beirut. Cases were randomly selected from patients diagnosed in the period of 2002–2008. Controls were conveniently identified and selected from the same settings. Data was collected using interview questionnaire and blood analysis. NAT1 genotypes were determined by PCR-RFLP. Statistical analysis revolved around univariate, bivariate, and multivariate logistic regression models, along with checks for effect modification. Results showed NAT1^∗14A allele, smoking, occupational exposure to combustion fumes, and prostate-related symptoms, to be risk factors for bladder cancer. The odds of carrying at least one NAT1^∗14A allele are 7 times higher in cases compared to controls (OR = 7.86, 95% CI: 1.53–40.39). A gene-environment interaction was identified for NAT1^∗14A allele with occupational exposure to combustion fumes. Among carriers of NAT1^∗14A allele, the odds of bladder cancer dropped to 2.03 from 3.72. Our study suggests NAT1^∗14A allele as a possible biomarker for bladder cancer. Further research is recommended to confirm this association.

N-Acetylation of p-aminobenzoic acid and p-phenylenediamine in primary porcine urinary bladder epithelial cells and in the human urothelial cell line 5637

N-Acetyltransferases (NAT) are important enzymes in the metabolism of certain carcinogenic arylamines, as N-acetylation decreases or prevents their bioactivation via N-hydroxylation. To study such processes in the bladder, cell culture models may be used, but metabolic competence needs to be characterized. This study focused on the N-acetylation capacity of two urothelial cell systems, using p-aminobenzoic acid (PABA) and the hair dye precursor p-phenylenediamine (PPD), two well-known substrates of the enzyme NAT1. The constitutive NAT1 activity was investigated using primary cultures of porcine urinary bladder epithelial cells (PUBEC) and in the human urothelial cell line 5637 to assess their suitability for further in vitro studies on PABA and PPD-induced toxicity. N-Acetylation of PABA and PPD was determined by high-performance liquid chromatography (HPLC) analysis in cytosols of the two cell systems upon incubation with various substrate levels for up to 60 min. The primary PUBEC revealed higher N-acetylation rates (2.5-fold for PABA, 5-fold for PPD) compared to the 5637 cell line, based on both PABA conversion to its acetylated metabolite and formation of mono- and diacetylated PPD. The urothelial cell systems may thus be useful as a tool for further studies on the N-acetylation of aromatic amines via NAT1.

Characterization of genetic variation and natural selection at the arylamine N-acetyltransferase genes in global human populations

Functional variability at the arylamine N-acetyltransferase genes is associated with drug response in humans and may have been adaptive in the past owing to selection pressure from diet and exposure to toxins during human evolution.

AIMS

We have characterized nucleotide variation at the NAT1 and NAT2 genes, and at the NATP1 pseudogene in global human populations, including many previously under-represented African populations, in order to identify potential functional variants and to understand the role that natural selection has played in shaping variation at these loci in globally diverse populations.

MATERIALS & METHODS

We have resequenced approximately 2800 bp for each of the NAT1 and NAT2 gene regions, as well as the pseudogene NATP1, in 197 African and 132 nonAfrican individuals.

RESULTS & CONCLUSION

We observe a signature of balancing selection maintaining variation in the 3'-UTR of NAT1, suggesting that these variants may play a functional role that is currently undefined. In addition, we observed high levels of nonsynonymous functional variation at the NAT2 locus that differs amongst ethnically diverse populations.

Sequence and structural characterization of tbnat gene in isoniazid-resistant Mycobacterium tuberculosis: identification of new mutations

The present study was carried out to investigate the presence of polymorphism in the N-acetyltransferase gene of 41 clinical isolates of Mycobacterium tuberculosis, that were resistant to isoniazid (INH) with no mutations in the hot spots of the genes previously described to be involved in INH resistance (katG, inhA and ahpC). We observed single nucleotide polymorphisms (SNPs) in ten of these, including the G619A SNP in five isolates and an additional four so far un-described mutations in another five isolates. Among the latter SNPs, two were synonymous (C276T, n=1 and C375G, n=3), while two more non-synonymous SNPs were composed of C373A (Leu→Met) and T503G (Met→Arg) were observed in respectively one and two isolates. Molecular modeling and structural analysis based in a constructed full length 3D models of wild type TBNAT (TBNAT_H37Rv) and the isoforms (TBNAT_L125M and TBNAT_M168R) were also performed. The refined models show that, just as observed in human NATs, the carboxyl terminus extends deep within the folded enzyme, into close proximity to the buried catalytic triad. Analysis of tbnat that present non-synonymous mutations indicates that both substitutions are plausible to affect enzyme specificity or acetyl-CoA binding capacity. The results contribute to a better understanding of structure-function relationships of NATs. However, further investigation including INH-sensitive strains as a control group is needed to get better understanding of the possible role of these new mutations on tuberculosis control.

Analysis of β-amino alcohols as inhibitors of the potential anti-tubercular target N-acetyltransferase

The synthesis and inhibitory potencies of a novel series of β-amino alcohols, based on the hit-compound 3-[3'-(4''-cyclopent-2'''-en-1'''-ylphenoxy)-2'-hydroxypropyl]-5,5 dimethylimidazolidine-2,4-dione as specific inhibitors of mycobacterial N-acetyltransferase (NAT) enzymes are reported. Effects of synthesised compounds on growth of Mycobacterium tuberculosis have been determined.

Polymorphisms in NAT2 gene and atherosclerosis in an Algerian population

BACKGROUND AND AIMS

The etiology of atherosclerosis is multifactorial. Genetic and environmental factors are involved in the development of atherosclerosis. Human arylamine N-acetyltransferase 2 (NAT2) is an important metabolizing enzyme that exhibits genetic polymorphisms and modifies individual response and/or toxicity to many xenobiotics. We undertook this study to investigate the NAT2 polymorphisms in patients with atherosclerosis.

METHODS

Genotyping for NAT2 alleles was performed using polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) in 285 Algerian patients with atherosclerosis and 286 controls.

RESULTS

There was no association between NAT2 polymorphisms and atherosclerosis risk. However, the haplotype NAT2(*)5F decreased susceptibility to the disease (p = 0.005, OR = 0.55, 95% CI = 0.37-0.84). The frequency of the slow acetylator phenotype was approximately 50% in both cases and controls.

CONCLUSIONS

These results suggest that NAT2 polymorphisms may not be involved in the pathogenesis of atherosclerosis.

N-acetyltransferase 2 (Nat2) polymorphism in the sand rat Psammomys obesus

Human arylamine N-acetyltransferase 1 (NAT1) and its homologue in rodents (Nat2) are polymorphic xenobiotic metabolizing enzymes and also seem to play a role in endogenous metabolism. NAT1 and Nat2 polymorphism was associated to cancers under xenobiotic procarcinogens metabolism as well as under endogenous substrate metabolism. This study investigated the p-aminobenzoic acid (PABA) -Nat2 catalytic activity and its polymorphism in liver homogenates of adult sand rats Psammomys obesus Cretzschmar, 1828. These Saharian sand rats develop high incidence of spontaneous cancers under standard laboratory diet. The average value of PABA-Nat2 specific activity tested in nine sand rats was significant (2.96 ± 2.16 nmoles/min/mg). The N-acetylation exhibited a bimodal distribution. There was a significant difference (p<0.01) between PABA-Nat2 activity in the fast acetylators group (4.10 ± 1.67 nmol/min/mg) and slow acetylators group (0.7 ± 0.27 nmol/min/mg). The percentage of the fast acetylator group was 66.66%. These results support the presence of Nat2 polymorphism in the liver of the strain sand rats Psammomys obesus. This strain is useful for investigating the role of Nat2 polymorphisms in susceptibility to cancers related to arylamine carcinogen exposures as well as to endogenous substrate metabolism.

Small molecule colorimetric probes for specific detection of human arylamine N-acetyltransferase 1, a potential breast cancer biomarker

The identification, synthesis, and evaluation of a series of naphthoquinone derivatives as selective inhibitors of human arylamine N-acetyltransferase 1 and mouse arylamine N-acetyltransferase 2 are described. The compounds undergo a distinctive color change (red --> blue) upon binding to these human and mouse NAT isoenzymes driven by a proton transfer event. No color change is observed in the presence of functionally distinct but highly similar isoenzymes which are >70% identical. These molecules may be used as sensors to detect the presence of human NAT1 in cell lysates.

Isoform-selective inactivation of human arylamine N-acetyltransferases by reactive metabolites of carcinogenic arylamines

Human arylamine N-acetyltransferases (NATs) are expressed as two polymorphic isoforms, NAT1 and NAT2, that have toxicologically significant functions in the detoxification of xenobiotic arylamines by N-acetylation and in the bioactivation of N-arylhydroxylamines by O-acetylation. NAT1 also catalyzes the N-acetylation of 4-aminobenzoylglutamic acid, a product of folic acid degradation, and is associated with endogenous functions in embryonic development. On the basis of earlier studies with hamster NAT1, hamster NAT2, and human NAT1, we proposed that human NAT2 would be more susceptible than NAT1 to inactivation by N-arylhydroxamic acid metabolites of arylamines. Kinetic analyses of the inactivation of recombinant NAT1 and NAT2 by the N-arylhydroxamic acid, N-hydroxy-2-acetylaminofluorene (N-OH-AAF), as well as the inactivation of NAT2 by N-hydroxy-4-acetylaminobiphenyl (N-OH-4-AABP), resulted in second-order inactivation rate constants (k(inact)/K(I)) that were several fold greater for NAT2 than for NAT1. Mass spectrometric analysis showed that inactivation of NAT2 in the presence of the N-arylhydroxamic acids was due to formation of a sulfinamide adduct with Cys68. Treatment of HeLa cells with N-OH-4-AABP and N-OH-AAF revealed that the compounds were less potent inactivators of intracellular NAT activity than the corresponding nitrosoarenes, but unexpectedly, the hydroxamic acids caused a significantly greater loss of NAT1 activity than of NAT2 activity. Nitrosoarenes are the electrophilic products responsible for NAT inactivation upon interaction of the enzymes with N-arylhydroxamic acids, as well as being metabolic products of arylamine oxidation. Treatment of recombinant NAT2 with the nitrosoarenes, 4-nitrosobiphenyl (4-NO-BP) and 2-nitrosofluorene (2-NO-F), caused rapid and irreversible inactivation of the enzyme by sulfinamide adduct formation with Cys68, but the k(inact)/K(I) values for inactivation of recombinant NAT2 and NAT1 did not indicate significant selectivity for either isoform. Also, the IC(50) values for inactivation of HeLa cell cytosolic NAT1 and NAT2 by 4-NO-BP were similar, as were the IC(50) values obtained with 2-NO-F. Treatment of HeLa cells with low concentrations (1-10 microM) of either 4-NO-BP or 2-NO-F resulted in preferential and more rapid loss of NAT1 activity than NAT2 activity. Because of its wide distribution in human tissues and its early expression in developing tissues, the apparent high sensitivity of intracellular NAT1 to inactivation by reactive metabolites of environmental arylamines may have important toxicological consequences.

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.

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.

Activation of aminoimidazole carcinogens by nitrosation: mutagenicity and nucleotide adducts

2-Amino-3-methylimidazo[4,5-f]quinoline (IQ) and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline(MeIQx) are heterocyclic amines (HCAs) derived from high temperature cooking of meat and thought to cause colon cancer in humans. Reactive nitrogen oxygen species, which are mediators of the inflammatory response, can convert these amines to the corresponding N-nitrosamines, N-NO-IQ and N-NO-MeIQx. This study was designed to evaluate whether these N-nitrosamines are genotoxic and could be responsible, in part, for the high incidence of colon cancer in individuals with colitis. Such an association would counsel reduced intake of well-done red meat by colitis patients. Mutagenicity was evaluated by reversion of a lacZ frameshift allele in three different E. coli strains. Strains DJ701 and DJ702 express recombinant(S. typhimurium) aromatic amine N-acetyltransferase (NAT); DJ702 also expresses recombinant human cytochrome P450 1A2 and NADPH-P450 reductase; and DJ2002 served as an N-acetyltransferase negative control. In strain DJ701, N-NO-IQ and N-NO-MeIQx elicited dose-dependent mutagenicity,which was not further increased in DJ702. Neither nitrosamine was mutagenic in strain DJ2002. While both N-nitrosamines are stable for >4 h (pH 7.4, 37 degrees C), they react with DNA or 2'-deoxyguanosine 3'-monophosphate at lower pH (5.5) to form adducts. HOCl, a component of the inflammatory response,increased adduct formation, as measured by 32P-postlabeling. Following treatment with nuclease P1and separation by two-dimensional thin-layer chromatography and then HPLC, N-NO-IQ and N-NOMeIQxwere shown to form the same adducts as those formed by N-OH-MeIQx or N-OH-IQ, namely N-(deoxyguanosin-8-yl) adducts. In summary, these N-nitrosamines are genotoxic and might be alternatives to their hydroxylamine analogues as activated intermediates leading to initiation of colon cancer in individuals with colitis.

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.

Temperature stability of proteins essential for the intracellular survival of Mycobacterium tuberculosis

In Mycobacterium tuberculosis, the genes hsaD (2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid hydrolase) and nat (arylamine N-acetyltransferase) are essential for survival inside of host macrophages. These genes act as an operon and have been suggested to be involved in cholesterol metabolism. However, the role of NAT in this catabolic pathway has not been determined. In an effort to better understand the function of these proteins, we have expressed, purified and characterized TBNAT (NAT from M. tuberculosis) and HsaD (2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid hydrolase) from M. tuberculosis. Both proteins demonstrated remarkable heat stability with TBNAT and HsaD retaining >95% of their activity after incubation at 60 degrees C for 30 min. The first and second domains of TBNAT were demonstrated to be very important to the heat stability of the protein, as the transfer of these domains caused a dramatic reduction in the heat stability. The specific activity of TBNAT was tested against a broad range of acyl-CoA cofactors using hydralazine as a substrate. TBNAT was found to be able to utilize not just acetyl-CoA, but also n-propionyl-CoA and acetoacetyl-CoA, although at a lower rate. As propionyl-CoA is a product of cholesterol catabolism, we propose that NAT could have a role in the utilization of this important cofactor.

Selective small molecule inhibitors of the potential breast cancer marker, human arylamine N-acetyltransferase 1, and its murine homologue, mouse arylamine N-acetyltransferase 2

The identification, synthesis and evaluation of a series of rhodanine and thiazolidin-2,4-dione derivatives as selective inhibitors of human arylamine N-acetyltransferase 1 and mouse arylamine N-acetyltransferase 2 is described. The most potent inhibitors identified have submicromolar activity and inhibit both the recombinant proteins and human NAT1 in ZR-75 cell lysates in a competitive manner. (1)H NMR studies on purified mouse Nat2 demonstrate that the inhibitors bind within the putative active site of the enzyme.

Genetic polymorphism in N-Acetyltransferase (NAT): Population distribution of NAT1 and NAT2 activity

N-Acetyltransferases (NAT) are key enzymes in the conjugation of certain drugs and other xenobiotics with an arylamine structure. Polymorphisms in NAT2 have long been recognized to modulate toxicity produced by the anti-tubercular drug isoniazid, with molecular epidemiologic studies suggesting a link between acetylator phenotype and increased risk for bladder cancer. Recent evidence indicates that the other major NAT isozyme, NAT1, is also polymorphic. The current analysis characterizes the main polymorphisms in both NAT2 and NAT1 in terms of their effect on enzyme activity and frequency in the population. Multiple NAT2 alleles (NAT2*5, *6, *7, and *14) have substantially decreased acetylation activity and are common in Caucasians and populations of African descent. In these groups, most individuals carry at least one copy of a slow acetylator allele, and less than 10% are homozygous for the wild type (fast acetylator) trait. Incorporation of these data into a Monte Carlo modeling framework led to a population distribution of NAT2 activity that was bimodal and associated with considerable variability in each population assessed. The ratio of the median to the first percentile of NAT2 activity ranged from 7 in Caucasians to 18 in the Chinese population. This variability indicates the need for more quantitative approaches (e.g., physiologically based pharmacokinetic [PBPK] modeling) to assess the full distribution of internal dose and adverse responses to aromatic amines and other NAT2 substrates. Polymorphisms in NAT1 are generally associated with relatively minor effects on acetylation function, with Monte Carlo analysis indicating less interindividual variability than seen in NAT2 analysis.

Multiple advantageous amino acid variants in the NAT2 gene in human populations

BACKGROUND

Genetic variation at NAT2 has been long recognized as the cause of differential ability to metabolize a wide variety of drugs of therapeutic use. Here, we explore the pattern of genetic variation in 12 human populations that significantly extend the geographic range and resolution of previous surveys, to test the hypothesis that different dietary regimens and lifestyles may explain inter-population differences in NAT2 variation.

METHODOLOGY/PRINCIPAL FINDINGS

The entire coding region was resequenced in 98 subjects and six polymorphic positions were genotyped in 150 additional subjects. A single previously undescribed variant was found (34T>C; 12Y>H). Several aspects of the data do not fit the expectations of a neutral model, as assessed by coalescent simulations. Tajima's D is positive in all populations, indicating an excess of intermediate alleles. The level of between-population differentiation is low, and is mainly accounted for by the proportion of fast vs. slow acetylators. However, haplotype frequencies significantly differ across groups of populations with different subsistence.

CONCLUSIONS/SIGNIFICANCE

Data on the structure of haplotypes and their frequencies are compatible with a model in which slow-causing variants were present in widely dispersed populations before major shifts to pastoralism and/or agriculture. In this model, slow-causing mutations gained a selective advantage in populations shifting from hunting-gathering to pastoralism/agriculture. We suggest the diminished dietary availability of folates resulting from the nutritional shift, as the possible cause of the fitness increase associated to haplotypes carrying mutations that reduce enzymatic activity.

Human arylamine N-acetyltransferase 1: in vitro and intracellular inactivation by nitrosoarene metabolites of toxic and carcinogenic arylamines

Arylamines (ArNH 2) are common environmental contaminants, some of which are confirmed risk factors for cancer. Biotransformation of the amino group of arylamines involves competing pathways of oxidation and N-acetylation. Nitrosoarenes, which are products of the oxidation pathway, are electrophiles that react with cellular thiols to form sulfinamide adducts. The arylamine N-acetyltransferases, NAT1 and NAT2, catalyze N-acetylation of arylamines and play central roles in their detoxification. We hypothesized that 4-nitrosobiphenyl (4-NO-BP) and 2-nitrosofluorene (2-NO-F), which are nitroso metabolites of arylamines that are readily N-acetylated by NAT1, would be potent inactivators of NAT1 and that nitrosobenzene (NO-B) and 2-nitrosotoluene (2-NO-T), which are nitroso metabolites of arylamines that are less readily acetylated by NAT1, would be less effective inactivators. The second order rate constants for inactivation of NAT1 by 4-NO-BP and 2-NO-F were 59200 and 34500 M (-1) s (-1), respectively; the values for NO-B and 2-NO-T were 25 and 23 M (-1) s (-1). Densitometry quantification and comparisons of specific activities with those of homogeneous recombinant NAT1 showed that NAT1 constitutes approximately 0.002% of cytosolic protein in HeLa cells. Treatment of HeLa cells with 4-NO-BP (2.5 microM) for 1 h caused a 40% reduction in NAT1 activity, and 4-NO-BP (10 microM) caused a 50% loss of NAT1 activity within 30 min without affecting either glyceraldehyde 3-phosphate dehydrogenase (GAPDH) or glutathione reductase (GR) activities. 2-NO-F (1 microM) inhibited HeLa cell NAT1 activity by 36% in 1 h, and a 10 microM concentration of 2-NO-F reduced NAT1 activity by 70% in 30 min without inhibiting GAPDH or GR. Mass spectrometric analysis of NAT1 from HeLa cells in which NAT1 was overexpressed showed that treatment of the cells with 4-NO-BP resulted in sulfinamide adduct formation. These results indicated that exposure to low concentrations of nitrosoarenes may lead to a loss of NAT1 activity, thereby compromising a critical detoxification process.

Downregulation of hepatic acetylation of drugs in chronic renal failure

Drug metabolism can be affected by chronic renal failure (CRF). Although it is known that several drugs that are known to be acetylated accumulate in CRF, the effect of CRF on N-acetyltransferase (NAT), the enzyme responsible for this acetylation, is unknown. Herein is reported that protein and gene expression of both Nat isoforms in the liver was reduced by >30% and Nat2 activity was reduced by 50% in rats with CRF compared with control rats. Incubation of hepatocytes with serum from rats with CRF suggested that a circulating factor is responsible for the decrease in protein and gene expression. For testing the hypothesis that parathyroid hormone may be this factor, CRF was induced in parathyroidectomized rats; downregulation of Nat expression and activity was not observed in these rats. Furthermore, addition of parathyroid hormone to cultured hepatocytes induced a decrease in Nat2 protein and gene expression. In conclusion, liver acetylation of drugs in a rat model of CRF is reduced by a downregulation of Nat1 and Nat2 isoforms, secondary to decreased gene expression. Parathyroid hormone seems to be an important mediator of this phenomenon.

Structure/function evaluations of single nucleotide polymorphisms in human N-acetyltransferase 2

Arylamine N-acetyltransferase 2 (NAT2) modifies drug efficacy/toxicity and cancer risk due to its role in bioactivation and detoxification of arylamine and hydrazine drugs and carcinogens. Human NAT2 alleles possess a combination of single nucleotide polymorphisms (SNPs) associated with slow acetylation phenotypes. Clinical and molecular epidemiology studies investigating associations of NAT2 genotype with drug efficacy/toxicity and/or cancer risk are compromised by incomplete and sometimes conflicting information regarding genotype/phenotype relationships. Studies in our laboratory and others have characterized the functional effects of SNPs alone, and in combinations present in alleles or haplotypes. We extrapolate this data generated following recombinant expression in yeast and COS-1 cells to assist in the interpretation of NAT2 structure. Whereas previous structural studies used homology models based on templates of N-acetyltransferase enzyme crystal structures from various prokaryotic species, alignment scores between bacterial and mammalian N-acetyltransferase protein sequences are low (approximately 30%) with important differences between the bacterial and mammalian protein structures. Recently, the crystal structure of human NAT2 was released from the Protein Data Bank under accession number 2PFR. We utilized the NAT2 crystal structure to evaluate the functional effects of SNPs resulting in the protein substitutions R64Q (G191A), R64W (C190T), I114T (T341C), D122N (G364A), L137F (A411T), Q145P (A434C), E167K (G499A), R197Q (C590A), K268R (A803G), K282T (A845C), and G286E (G857A) of NAT2. This analysis advances understanding of NAT2 structure-function relationships, important for interpreting the role of NAT2 genetic polymorphisms in bioactivation and detoxification of arylamine and hydrazine drugs and carcinogens.

Arylamine N-acetyltransferases in mycobacteria

Polymorphic Human arylamine N-acetyltransferase (NAT2) inactivates the anti-tubercular drug isoniazid by acetyltransfer from acetylCoA. There are active NAT proteins encoded by homologous genes in mycobacteria including M. tuberculosis, M. bovis BCG, M. smegmatis and M. marinum. Crystallographic structures of NATs from M. smegmatis and M. marinum, as native enzymes and with isoniazid bound share a similar fold with the first NAT structure, Salmonella typhimurium NAT. There are three approximately equal domains and an active site essential catalytic triad of cysteine, histidine and aspartate in the first two domains. An acetyl group from acetylCoA is transferred to cysteine and then to the acetyl acceptor e.g. isoniazid. M. marinum NAT binds CoA in a more open mode compared with CoA binding to human NAT2. The structure of mycobacterial NAT may promote its role in synthesis of cell wall lipids, identified through gene deletion studies. NAT protein is essential for survival of M. bovis BCG in macrophage as are the proteins encoded by other genes in the same gene cluster (hsaA-D). HsaA-D degrade cholesterol, essential for mycobacterial survival inside macrophage. Nat expression remains to be fully understood but is co-ordinated with hsaA-D and other stress response genes in mycobacteria. Amide synthase genes in the streptomyces are also nat homologues. The amide synthases are predicted to catalyse intramolecular amide bond formation and creation of cyclic molecules, e.g. geldanamycin. Lack of conservation of the CoA binding cleft residues of M. marinum NAT suggests the amide synthase reaction mechanism does not involve a soluble CoA intermediate during amide formation and ring closure.

Identification of the xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 as a new target of cisplatin in breast cancer cells: molecular and cellular mechanisms of inhibition

Arylamine N-acetyltransferase 1 (NAT1) is a phase II xenobiotic-metabolizing enzyme that plays an important role in the biotransformation of aromatic drugs and carcinogens. NAT1 activity has long been associated with susceptibility to various cancers. Evidence for a role of NAT1 in malignant progression has also been obtained, particularly for breast and prostate cancer. Cisplatin is widely used in chemotherapy against human cancers, and it is thought to act principally by forming DNA adducts. However, recent studies have suggested that some of the pharmacological and/or toxicological effects of cisplatin may be due to the direct targeting and inhibition of certain cellular enzymes. We show here that the exposure of breast cancer cells, known to express functional NAT1 enzyme, to therapeutically relevant concentrations of cisplatin impairs the catalytic activity of endogenous NAT1. Endogenous NAT1 was also found to be inactivated, in vivo, in the tissues of mice treated with cisplatin. Mechanistic studies with purified human NAT1 indicated that this inhibition resulted from the irreversible formation of a cisplatin adduct with the active-site cysteine residue of the enzyme. Kinetic studies suggested that NAT1 interacts rapidly with cisplatin, with a second-order rate inhibition constant of 700 M(-1) min(-1). This rate constant is one the highest ever reported for the reaction of cisplatin with a biological macromolecule. Few enzymes have been clearly shown to be inactivated by cisplatin. We provide here molecular and cellular evidence suggesting that NAT1 is one of the targets of cisplatin in cells.

Current trends in N-acetyltransferase research arising from the 2007 International NAT Workshop

Arylamine N-acetyltransferase (NAT) research has been influenced in recent years by the rapid progress in genomics, proteomics, structural genomics and other cutting-edge disciplines. To keep up with these advancements, the NAT scientific community has fostered collaboration and exchange of know-how between its members. As a specialized event bringing together experts from many different laboratories, the triennial International NAT Workshop has been instrumental in maintaining this culture over the past ten years. The 2007 Workshop took place in Alexandroupolis, Greece, and covered ongoing research on the structure and enzymatic function of human NATs, the prokaryotic and eukaryotic models for NAT, the mechanisms of NAT gene regulation and expression, the frequencies and effects of polymorphisms in the human NAT genes, and the involvement of NATs in multifactorial diseases, including cancer, allergic conditions, endometriosis and endemic nephropathies. Gene nomenclature issues were also addressed and the participants discussed current trends in the field.

Mouse N-acetyltransferase type 2, the homologue of human N-acetyltransferase type 1

There is increasing evidence that human arylamine N-acetyltransferase type 1 (NAT1, EC 2.3.1.5), although first identified as a homologue of a drug-metabolising enzyme, appears to be a marker in human oestrogen receptor positive breast cancer. Mouse Nat2 is the mouse equivalent of human NAT1. The development of mouse models of breast cancer is important, and it is essential to explore the biological role of mouse Nat2. We have therefore produced mouse Nat2 as a recombinant protein and have investigated its substrate specificity profile in comparison with human NAT1. In addition, we have tested the effects of inhibitors on mouse Nat2, including compounds which are endogenous and exogenous steroids. We show that tamoxifen, genistein and diethylstilbestrol inhibit mouse Nat2. The steroid analogue, bisphenol A, also inhibits mouse Nat2 enzymic activity and is shown by NMR spectroscopy, through shifts in proton peaks, to bind close to the active site. A three-dimensional structure for human NAT1 has recently been released, and we have used this crystal structure to generate a model of the mouse Nat2 structure. We propose that a conformational change in the structure is required in order for ligands to bind to the active site of the protein.

Mouse arylamine N-acetyltransferase 2 (Nat2) expression during embryogenesis: a potential marker for the developing neuroendocrine system

Arylamine N-acetyltransferase (NAT) genes in humans and in rodents encode polymorphic drug metabolizing enzymes. Human NAT1 (and the murine equivalent mouse Nat2) is found early in embryonic development and is likely to have an endogenous role. We report the detailed expression of the murine gene (Nat2) and encoded protein in mouse embryos, using a transgenic mouse model bearing a lacZ transgene inserted into the coding region of mouse Nat2. In mouse embryos, the transgene was expressed in sensory epithelia, epithelial placodes giving rise to visceral sensory neurons, the developing pituitary gland, sympathetic chain and urogenital ridge. In Nat2+/+ mice, the presence and activity of Nat2 protein was detected in these tissues and their adult counterparts. Altered expression of the human orthologue in breast tumours, in which there is endocrine signalling, suggests that human NAT1 should be considered as a potential biomarker for neuroendocrine tissues and tumours.

Divergence of cofactor recognition across evolution: coenzyme A binding in a prokaryotic arylamine N-acetyltransferase

Arylamine N-acetyltransferase (NAT) enzymes are widespread in nature. They serve to acetylate xenobiotics and/or endogenous substrates using acetyl coenzyme A (CoA) as a cofactor. Conservation of the architecture of the NAT enzyme family from mammals to bacteria has been demonstrated by a series of prokaryotic NAT structures, together with the recently reported structure of human NAT1. We report here the cloning, purification, kinetic characterisation and crystallographic structure determination of NAT from Mycobacterium marinum, a close relative of the pathogenic Mycobacterium tuberculosis. We have also determined the structure of M. marinum NAT in complex with CoA, shedding the first light on cofactor recognition in prokaryotic NATs. Surprisingly, the principal CoA recognition site in M. marinum NAT is located some 30 A from the site of CoA recognition in the recently deposited structure of human NAT2 bound to CoA. The structure explains the Ping-Pong Bi-Bi reaction mechanism of NAT enzymes and suggests mechanisms by which the acetylated enzyme intermediate may be protected. Recognition of CoA in a much wider groove in prokaryotic NATs suggests that this subfamily may accommodate larger substrates than is the case for human NATs and may assist in the identification of potential endogenous substrates. It also suggests the cofactor-binding site as a unique subsite to target in drug design directed against NAT in mycobacteria.