Arylamine N-acetyltransferase 1 deficiency inhibits drug-induced cell death in breast cancer cells: switch from cytochrome C-dependent apoptosis to necroptosis.

PURPOSE: Arylamine N-acetyltransferase 1 (NAT1) deficiency has been associated with drug resistance and poor outcomes in breast cancer patients. The current study aimed to investigate drug resistance in vitro using normal breast cancer cell lines and NAT1-deficient cell lines to understand the changes induced by the lack of NAT1 that resulted in poor drug response. METHODS: The response to seven chemotherapeutic agents was quantified following NAT1 deletion using CRISPR-Cas 9 in MDA-MB-231 and T-47D cells. Apoptosis was monitored by annexin V staining and caspase 3/7 activity. Cytochrome C release and caspase 8 and 9 activities were measured by Western blots. Caspase 8 was inhibited using Z-IETD-FMK and necroptosis was inhibited using necrostatin and necrosulfonamide. RESULTS: Compared to parental cells, NAT1 depleted cells were resistant to drug treatment. This could be reversed following NAT1 rescue of the NAT1 deleted cells. Release of cytochrome C in response to treatment was decreased in the NAT1 depleted cells, suggesting suppression of the intrinsic apoptotic pathway. In addition, NAT1 knockout resulted in a decrease in caspase 8 activation. Treatment with necrosulfonamide showed that NAT1 deficient cells switched from intrinsic apoptosis to necroptosis when treated with the anti-cancer drug cisplatin. CONCLUSIONS: NAT1 deficiency can switch cell death from apoptosis to necroptosis resulting in decreased response to cytotoxic drugs. The absence of NAT1 in patient tumours may be a useful biomarker for selecting alternative treatments in a subset of breast cancer patients.

NAT2 knockdown inhibits the development of colorectal cancer and its clinical significance.

OBJECTIVE: This study aims to explore the correlation between N-acetyltransferase 2 (NAT2) expression in colorectal cancer (CRC) tissues and the progression and prognosis of CRC. Through in vitro and in vivo experiments, the biological functions of NAT2 in the occurrence and development of CRC were explored. PATIENTS AND METHODS: Immunohistochemical (IHC) staining, reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and Western blot were used to detect the difference of NAT2 expression in CRC tissues and normal tissues. The role of NAT2 in the cell proliferation, apoptosis, migration, invasion, and tumorigenesis and development of CRC was analyzed by cell counting kit-8 (CCK-8), colony formation, flow cytometry, transwell cell invasion, wound-healing assays and construction of nude mouse xenograft model. The correlation between the expression level of NAT2, and the overall survival and clinicopathological characteristics of CRC patients were statistically analyzed to preliminarily determine the clinical significance of NAT2 in the diagnosis and prognosis of CRC. RESULTS: The expression level of NAT2 was notably upregulated in CRC. NAT2 knockdown inhibited the proliferation, migration, invasion and in vivo tumor formation of CRC cells, and promoted cell apoptosis. High NAT2 expression was associated with TNM stage, differentiation degree, tumor size, distant metastasis, lymph node metastasis and poor prognosis in CRC patients. CONCLUSIONS: This study showed that the expression level of NAT2 in CRC tissues was increased and closely related to the metastasis and prognosis of CRC. In addition, NAT2 can be used as a new prognostic biomarker and therapeutic target for CRC.

Critical Roles of Translation Initiation and RNA Uridylation in Endogenous Retroviral Expression and Neural Differentiation in Pluripotent Stem Cells.

Previous studies have suggested that the loss of the translation initiation factor eIF4G1 homolog NAT1 induces excessive self-renewability of naive pluripotent stem cells (PSCs); yet the role of NAT1 in the self-renewal and differentiation of primed PSCs is still unclear. Here, we generate a conditional knockout of NAT1 in primed PSCs and use the cells for the functional analyses of NAT1. Our results show that NAT1 is required for the self-renewal and neural differentiation of primed PSCs. In contrast, NAT1 deficiency in naive pluripotency attenuates the differentiation to all cell types. We also find that NAT1 is involved in efficient protein expression of an RNA uridyltransferase, TUT7. TUT7 is involved in the neural differentiation of primed PSCs via the regulation of human endogenous retrovirus accumulation. These data demonstrate the essential roles of NAT1 and TUT7 in the precise transition of stem cell fate.

Arylamine N-Acetyltransferase 1 Regulates Expression of Matrix Metalloproteinase 9 in Breast Cancer Cells: Role of Hypoxia-Inducible Factor 1-α.

Arylamine N-acetyltransferase 1 (NAT1) is a drug-metabolizing enzyme that influences cancer cell proliferation and survival. However, the mechanism for these effects is unknown. Because of previous observations that NAT1 inhibition decreases invasiveness, we investigated the expression of the metalloproteinase matrix metalloproteinase 9 (MMP9) in human breast cancer samples and in cancer cells. We found a negative correlation between the expression of NAT1 and MMP9 in 1904 breast cancer samples. Moreover, when NAT1 was deleted in highly invasive breast cancer cells, MMP9 mRNA and protein significantly increased, both of which were reversed by reintroducing NAT1 into the knockout cells. After NAT1 deletion, there was an increased association of acetylated histone H3 with the SET and MYND-domain containing 3 (SMYD3) element in the MMP9 promoter, consistent with an increase in MMP9 transcription. NAT1 deletion also up-regulated hypoxia-inducible factor 1-α (HIF1-α). Treatment of the NAT1 knockout cells with small interfering RNA directed toward HIF1-α mRNA inhibited the increased expression of MMP9. Taken together, these results show a direct inverse relationship between NAT1 and MMP9 and suggest that HIF1-α may be essential for the regulation of MMP9 expression by NAT1. SIGNIFICANCE STATEMENT: The expression of the enzyme NAT1 was found to be negatively correlated with MMP9 expression in tumor tissue from breast cancer patients. In cells, NAT1 regulated MMP9 expression at a transcriptional level via HIF1-α. This finding is important as it may explain some of the pathological features associated with changes in NAT1 expression in cancer.

A readout of metabolic efficiency in arylamine N-acetyltransferase-deficient mice reveals minor energy metabolism changes.

Recent studies have revealed a possible link between the activities of polymorphic arylamine N-acetyltransferases (NATs) and energy metabolism. We used a Nat1/Nat2 double knockout (KO) mouse model to demonstrate that ablation of the two Nat genes is associated with modest, intermittent alterations in respiratory exchange rate. Pyruvate tolerance tests show that double KO mice have attenuated hepatic gluconeogenesis when maintained on a high-fat/high-sucrose diet. Absence of the two Nat genes also leads to an increase in the hepatic concentration of coenzyme A in mice fed a high-fat/high-sucrose diet. Our results suggest a modest involvement of NAT in energy metabolism in mice, which is consistent with the absence of major phenotypic deregulation of energy metabolism in slow human acetylators.

Loss of human arylamine N-acetyltransferase I regulates mitochondrial function by inhibition of the pyruvate dehydrogenase complex.

Human arylamine N-acetyltransferase 1 (NAT1) has been widely reported to affect cancer cell growth and survival and recent studies suggest it may alter cell metabolism. In this study, the effects of NAT1 deletion on mitochondrial function was examined in 2 human cell lines, breast carcinoma MDA-MB-231 and colon carcinoma HT-29 cells. Using a Seahorse XFe96 Flux Analyzer, NAT1 deletion was shown to decrease oxidative phosphorylation with a significant loss in respiratory reserve capacity in both cell lines. There also was a decrease in glycolysis without a change in glucose uptake. The changes in mitochondrial function was due to a decrease in pyruvate dehydrogenase activity, which could be reversed with the pyruvate dehydrogenase kinase inhibitor dichloroacetate. In the MDA-MB-231 and HT-29 cells, pyruvate dehydrogenase activity was attenuated either by an increase in phosphorylation or a decrease in total protein expression. These results may help explain some of the cellular events that have been reported recently in cell and animal models of NAT1 deficiency.

Mechanism by which arylamine N-acetyltransferase 1 ablation causes insulin resistance in mice.

A single-nucleotide polymorphism in the human arylamine N-acetyltransferase 2 (Nat2) gene has recently been identified as associated with insulin resistance in humans. To understand the cellular and molecular mechanisms by which alterations in Nat2 activity might cause insulin resistance, we examined murine ortholog Nat1 knockout (KO) mice. Nat1 KO mice manifested whole-body insulin resistance, which could be attributed to reduced muscle, liver, and adipose tissue insulin sensitivity. Hepatic and muscle insulin resistance were associated with marked increases in both liver and muscle triglyceride (TAG) and diacylglycerol (DAG) content, which was associated with increased PKCε activation in liver and increased PKCθ activation in skeletal muscle. Nat1 KO mice also displayed reduced whole-body energy expenditure and reduced mitochondrial oxygen consumption in white adipose tissue, brown adipose tissue, and hepatocytes. Taken together, these studies demonstrate that Nat1 deletion promotes reduced mitochondrial activity and is associated with ectopic lipid-induced insulin resistance. These results provide a potential genetic link among mitochondrial dysfunction with increased ectopic lipid deposition, insulin resistance, and type 2 diabetes.

Nat1 Deficiency Is Associated with Mitochondrial Dysfunction and Exercise Intolerance in Mice.

We recently identified human N-acetyltransferase 2 (NAT2) as an insulin resistance (IR) gene. Here, we examine the cellular mechanism linking NAT2 to IR and find that Nat1 (mouse ortholog of NAT2) is co-regulated with key mitochondrial genes. RNAi-mediated silencing of Nat1 led to mitochondrial dysfunction characterized by increased intracellular reactive oxygen species and mitochondrial fragmentation as well as decreased mitochondrial membrane potential, biogenesis, mass, cellular respiration, and ATP generation. These effects were consistent in 3T3-L1 adipocytes, C2C12 myoblasts, and in tissues from Nat1-deficient mice, including white adipose tissue, heart, and skeletal muscle. Nat1-deficient mice had changes in plasma metabolites and lipids consistent with a decreased ability to utilize fats for energy and a decrease in basal metabolic rate and exercise capacity without altered thermogenesis. Collectively, our results suggest that Nat1 deficiency results in mitochondrial dysfunction, which may constitute a mechanistic link between this gene and IR.

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.

Effects of human arylamine N-acetyltransferase I knockdown in triple-negative breast cancer cell lines.

Expression of human arylamine N-acetyltransferase I (NAT1) has been associated with various cancer subtypes and inhibition of this enzyme with small molecule inhibitors or siRNA affects cell growth and survival. Here, we have investigated the role of NAT1 in the invasiveness of breast cancer cells both in vitro and in vivo. We knocked down NAT1 using a lentivirus-based shRNA approach and observed marked changes in cell morphology in the triple-negative breast cancer cell lines MDA-MB-231, MDA-MB-436, and BT-549. Most notable was a reduction in the number and size of the filopodia protrusions on the surface of the cells. The loss of filopodia could be rescued by the reintroduction of NAT1 into the knockdown cells. NAT1 expression was localized to the lamellipodia and extended into the filopodia protrusions. In vitro invasion through Geltrex was significantly inhibited in both the MDA cell lines but not in the BT-549 cells. The expression of Snail increased when NAT1 was knocked down, while other genes associated with mesenchymal to epithelial transition (vimentin, cytokeratin-18, and Twist) did not show any changes. By contrast, both N-cadherin and ß-catenin were significantly reduced. When MDA-MB-231 cells expressing shRNA were injected in vivo into BALB/c nu/nu nude mice, a significant reduction in the number of colonies that formed in the lungs was observed. Taken together, the results show that NAT1 can alter the invasion and metastatic properties of some triple-negative breast cancer cells but not all. The study suggests that NAT1 may be a novel therapeutic target in a subset of breast cancers.

Paradoxical attenuation of autoimmune hepatitis by oral isoniazid in wild-type and N-acetyltransferase-deficient mice.

Isoniazid (INH) treatment can cause serious liver injury and autoimmunity. There are now several lines of evidence that INH-induced liver injury is immune mediated, but this type of liver injury has not been reproduced in animals, possibly because immune tolerance is the dominant response of the liver. In this study, we immunized mice with isonicotinic acid (INA)-modified proteins and Freund's adjuvant, which led to mild experimental autoimmune hepatitis (EAH) with an increase in cells staining positive for F4/80, CD11b, CD8, CD4, CD45R, and KI67. We expected that subsequent treatment of mice with oral INH would lead to more serious immune-mediated liver injury, but paradoxically it markedly attenuated the EAH caused by immunization with INA-modified hepatic proteins. In addition, patients of the slow acetylator phenotype are at increased risk of INH-induced liver injury. Treatment of arylamine N-acetyltransferase-deficient Nat1/2(-/-) mice with INH for up to 5 weeks produced mild increases in glutamate and sorbitol dehydrogenase activities, but not severe liver injury. Female Nat1/2(-/-) mice treated with INH for 1, 3, or 7 days developed steatosis, an increase in Oil Red O staining, and abnormal mitochondrial morphology in the liver. A decrease in M1 and an increase in M2a and M2b macrophages was observed in female Nat1/2(-/-) mice treated with INH for 1, 3, or 7 days; these changes returned to baseline levels by day 35. These data indicate that INH has immunosuppressive effects, even though it is also known to induce autoantibody production and a lupus-like autoimmune syndrome in humans.

RNAi-mediated knock-down of arylamine N-acetyltransferase-1 expression induces E-cadherin up-regulation and cell-cell contact growth inhibition.

Arylamine N-acetyltransferase-1 (NAT1) is an enzyme that catalyzes the biotransformation of arylamine and hydrazine substrates. It also has a role in the catabolism of the folate metabolite p-aminobenzoyl glutamate. Recent bioinformatics studies have correlated NAT1 expression with various cancer subtypes. However, a direct role for NAT1 in cell biology has not been established. In this study, we have knocked down NAT1 in the colon adenocarcinoma cell-line HT-29 and found a marked change in cell morphology that was accompanied by an increase in cell-cell contact growth inhibition and a loss of cell viability at confluence. NAT1 knock-down also led to attenuation in anchorage independent growth in soft agar. Loss of NAT1 led to the up-regulation of E-cadherin mRNA and protein levels. This change in E-cadherin was not attributed to RNAi off-target effects and was also observed in the prostate cancer cell-line 22Rv1. In vivo, NAT1 knock-down cells grew with a longer doubling time compared to cells stably transfected with a scrambled RNAi or to parental HT-29 cells. This study has shown that NAT1 affects cell growth and morphology. In addition, it suggests that NAT1 may be a novel drug target for cancer therapeutics.

Association of cytochrome P450, glutathione S-transferase and N-acetyl transferase 2 gene polymorphisms with incidence of acute myeloid leukemia.

The objective of the paper was to study the association of polymorphisms of phases I and II xenobiotic metabolizing enzyme genes cytochrome P450 (CYP-4501A1*2A, *2B, *2C and *4 alleles, CYP-4502D6*4 allele), glutathione-S-transferase (GSTM1 and GSTT1 null genotypes) and N-acetyl transferase 2 (NAT2*6B and *7A alleles) with the incidence of acute myeloid leukemia (AML) in an eastern Indian population. Polymerase chain reaction and restriction fragment length polymorphism of genomic DNA from peripheral blood cells were used to detect CYP-450 and NAT2 gene polymorphisms in 110 AML patients and 144 racially and geographically matched normal controls. Polymerase chain reaction was also applied to detect GST gene polymorphisms in both groups. A statistically significant difference between the AML group and the normal group was observed in the case of glutathione-S-transferase M1 null (odds ratio 3.25, 95% confidence interval 1.9-5.58, P<0.001) and N-acetyl transferase 2*6B (odds ratio 3.04, 95% confidence interval 1.79-5.16, P<0.001) genotypes. Combined deficiency of N-acetyl transferase 2 and glutathione-S-transferase M1 genes produced an odds ratio of 11.91 (95% confidence interval 4.06-34.96, P<0.001). The effect of N-acetyl transferase 2*6B (P<0.001) is significant only at ages

Confirmation of the role of N-acetyltransferase 2 in teratogen-induced cleft palate using transgenics and knockouts.

Previous work on Dilantin- and hydrocortisone-induced cleft palate and cleft lip with or without cleft palate using congenics for the N-acetyltransferase loci (Nat1 and Nat2 are closely linked) and recombinant inbred lines implicated the Nat1,2 region in susceptibility to teratogen-induced orofacial clefting. Since Nat1 does not differ between the two strains, Nat2 appeared to be responsible. We have now tested this conclusion using transgenics and knockouts. Transgenics for human NAT1 (equivalent to mouse Nat2) and knockouts for Nat2 were tested for susceptibility to Dilantin, hydrocortisone, and 6-aminonicotinamide-induced orofacial clefting. We found that Nat2 greatly influences teratogen-induced orofacial clefting on the A/J background but not on the C57BL/6J background. The magnitude and direction of the effects depended on which teratogen was used. The Nat2 knockout did not make C57BL/6J susceptible or A/J (already with very low activity) more susceptible but significantly decreased sporadic clefting in the A/J strain. We conclude that only the A/J strain, with several loci affecting orofacial clefting, is influenced by Nat2.

Effect of arylamine acetyltransferase Nat3 gene knockout on N-acetylation in the mouse.

Arylamine N-acetyltransferases (NAT) catalyze the biotransformation of many important arylamine drugs and procarcinogens. NAT can either detoxify or activate procarcinogens, complicating the manner in which these enzymes may participate in enhancing or preventing toxic responses to particular agents. Mice possess three NAT isoenzymes: Nat1, Nat2, and Nat3. Whereas Nat1 and Nat2 can efficiently acetylate many arylamines, few substrates appear to be appreciably metabolized by Nat3. We generated a Nat3 knockout mouse strain and used it along with our double Nat1/2(-/-) knockout strain to further investigate the functional role of Nat3. Nat3(-/-) mice showed normal viability and reproductive capacity. Nat3 expression was very low in wild-type animals and completely undetectable in Nat3(-/-) mice. In contrast, greatly elevated expression of Nat3 transcript was observed in Nat1/2(-/-) mice. We used a transcribed marker polymorphism approach to establish that the increased expression of Nat3 in Nat1/2(-/-) mice is a positional artifact of insertion of the phosphoglycerate kinase-neomycin resistance cassette in place of the Nat1/Nat2 gene region and upstream of the intact Nat3 gene, rather than a biological compensatory mechanism. Despite the increase in Nat3 transcript, the N-acetylation of p-aminosalicylate, sulfamethazine, 2-aminofluorene, and 4-aminobiphenyl was undetectable either in vivo or in vitro in Nat1/2(-/-) animals. In parallel, no difference was observed in the in vivo clearance or in vitro metabolism of any of these substrates between wild-type and Nat3(-/-) mice. Thus, Nat3 is unlikely to play a significant role in the N-acetylation of arylamines either in wild-type mice or in mice lacking Nat1 and Nat2 activities.

In vivo and in vitro metabolism of arylamine procarcinogens in acetyltransferase-deficient mice.

Arylamine N-acetyltransferases (NATs) catalyze the biotransformation of a number of aromatic and heterocyclic amines, many of which are procarcinogenic agents. Interestingly, these enzymes are binary in nature, participating in both detoxification and activation reactions, and thus it is unclear what role NATs actually play in either preventing or enhancing toxic responses. The ultimate direction may be substrate-specific and dependent on its tissue-specific metabolism by competing, but genetically variable, drug-metabolizing enzymes. To investigate the effect of N-acetylation on the metabolism of some classical procarcinogenic arylamines, we have used our double knockout Nat1/2(-/-) mouse model to test both in vitro activity and the in vivo clearance of some of these agents. As expected, N-acetylation activity was undetectable in tissue cytosol preparations from Nat1/2(-/-) mice for 4-aminobiphenyl (ABP) and 2-aminofluorene (AF), whereas significant levels were measured in all wild-type tissue cytosols tested, indicating the widespread metabolism of these agents. Nat1/2(-/-) mice displayed a variable response with respect to in vivo pharmacokinetics. AF appeared to be most severely compromised, with a 3- to 4-fold increased area under the curve (AUC), whereas the clearance of ABP was found to be less dependent on N-acetylation, with no difference in ABP-AUC between wild-type and knockout animals. 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine was neither N-acetylated nor was its clearance affected by NAT genotype, signifying a dependence on other drug-metabolizing enzymes. The elucidation of the role that N-acetylation plays in the clearance of procarcinogenic agents is the first step in attempting to correlate metabolism by NATs to toxic outcome prevention or augmentation.

The microcell-mediated transfer of human chromosome 8 restores the deficient N-acetylytransferase activity in skin fibroblasts of Mucopolysaccharidosis type IIIC patients.

The candidate gene for Mucopolysaccharidosis (MPS) type IIIC has been localized to the pericentric region of the chromosome 8 by the linkage disequilibrium analysis. To validate the localization of the gene, we rescued the deficient acetyl-coenzyme A: alpha-glucosaminide-N-acetylytransferase activity in the cultured cells of MPS IIIC patients by functional complementation via microcell-mediated chromosome transfer. The introduction of the target human monochromosome completely restored the activity confirming functional localization of the candidate gene on human chromosome 8.

[Dapsone-induced agranulocytosis. The role of xenobiotic-metabolizing enzymes demonstrated by a case report]. / Dapson-induzierte Agranulozytose. Die Rolle fremdstoffmetabolisierender Enzyme am Beispiel einer Kasuistik.

A 34-year-old female patient with a three year history of generalized granuloma annulare was treated systemically with dapsone (DADPS). Six weeks after the onset of treatment, the patient developed an extensive tonsillitis of the base of the tongue with fever and malaise. Routine laboratory work showed a leukocytopenia with agranulocytosis. Further investigation revealed a marked decrease of the enzyme activity of N-acetyltransferase 2, which plays an important role in dapsone metabolism. Treatment included the cessation of dapsone, antibiotic coverage, and G-CSF leading to the rapid improvement of symptoms and normalization of leukocyte counts. Dapsone-induced angina agranulocytotica is a rare event and is interpreted as an idiosyncratic reaction. Depending on genetic polymorphisms of various enzymes, dapsone can be metabolized to immunologically or toxicologically relevant intermediates. Because of the risk of severe hematologic reactions, dapsone should only be employed for solid indications and with appropriate monitoring.

Pharmacogenetic screening and therapeutic drugs.

BACKGROUND: Pharmacogenetics is the science of the influence of heredity on pharmacological response. ISSUES: The cost of severe adverse drug reactions in individuals has been estimated in the US alone to be in excess of US$4 billion. It has been argued that in a significant proportion of cases, the efficacy and toxicity profiles of drug therapy would be substantially improved in individuals if characteristics due to genetic variation were taken into account. Methods are now available, which make screening for susceptibility feasible. CONCLUSIONS: There are several therapeutic areas in which screening may give rise to significant improvements in outcome with cost-benefits to both the individual and the community. However, there is currently a lack of data on which cost-benefit analysis can be based. The challenge is to provide this information for new drugs, and for drugs with established therapeutic roles.