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

Crosstalk of methylation and tamoxifen in breast cancer (Review)

Tamoxifen is a widely used anti‑estrogen drug in the endocrine therapy of breast cancer (BC). It blocks estrogen signaling by competitively binding to estrogen receptor α (ERα), thereby inhibiting the growth of BC cells. However, with the long‑term application of tamoxifen, a subset of patients with BC have shown resistance to tamoxifen, which leads to low overall survival and progression‑free survival. The molecular mechanism of resistance is mainly due to downregulation of ERα expression and abnormal activation of the PI3K/AKT/mTOR signaling pathway. Moreover, the downregulation of targeted gene expression mediated by DNA methylation is an important regulatory mode to control protein expression. In the present review, methylation and tamoxifen are briefly introduced, followed by a focus on the effect of methylation on tamoxifen resistance and sensitivity. Finally, the clinical application of methylation for tamoxifen is described, including its use as a prognostic indicator. Finally, it is hypothesized that when methylation is used in combination with tamoxifen, it could recover the resistance of tamoxifen.

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.

Upregulation of cytidine deaminase in NAT1 knockout breast cancer cells

PURPOSE

Arylamine N-acetyltransferase 1 (NAT1), a phase II metabolic enzyme, is frequently upregulated in breast cancer. Inhibition or depletion of NAT1 leads to growth retardation in breast cancer cells in vitro and in vivo. A previous metabolomics study of MDA-MB-231 breast cancer cells suggests that NAT1 deletion leads to a defect in de novo pyrimidine biosynthesis. In the present study, we observed that NAT1 deletion results in upregulation of cytidine deaminase (CDA), which is involved in the pyrimidine salvage pathway, in multiple breast cancer cell lines (MDA-MB-231, MCF-7 and ZR-75-1). We hypothesized that NAT1 KO MDA-MB-231 cells show differential sensitivity to drugs that either inhibit cellular pyrimidine homeostasis or are metabolized by CDA.

METHODS

The cells were treated with (1) inhibitors of dihydroorotate dehydrogenase or CDA (e.g., teriflunomide and tetrahydrouridine); (2) pyrimidine/nucleoside analogs (e.g., gemcitabine and 5-azacytidine); and (3) naturally occurring, modified cytidines (e.g., 5-formyl-2'-deoxycytidine; 5fdC).

RESULTS

Although NAT1 KO cells failed to show differential sensitivity to nucleoside analogs that are metabolized by CDA, they were markedly more sensitive to 5fdC which induces DNA damage in the presence of high CDA activity. Co-treatment with 5fdC and a CDA inhibitor, tetrahydrouridine, abrogated the increase in 5fdC cytotoxicity in NAT1 KO cells, suggesting that the increased sensitivity of NAT1 KO cells to 5fdC is dependent on their increased CDA activity.

CONCLUSIONS

The present findings suggest a novel therapeutic strategy to treat breast cancer with elevated NAT1 expression. For instance, NAT1 inhibition may be combined with cytotoxic nucleosides (e.g., 5fdC) for breast cancer treatment.

Retrospective study of transcriptomic profiling identifies Thai triple-negative breast cancer patients who may benefit from immune checkpoint and PARP inhibitors

Background

Triple-negative breast cancer (TNBC) is a rare and aggressive breast cancer subtype. Unlike the estrogen receptor-positive subtype, whose recurrence risk can be predicted by gene expression-based signature, TNBC is more heterogeneous, with diverse drug sensitivity levels to standard regimens. This study explored the benefit of gene expression-based profiling for classifying the molecular subtypes of Thai TNBC patients.

Methods

The nCounter-based Breast 360 gene expression was used to classify Thai TNBC retrospective cohort subgroups. Their expression profiles were then compared against the previously established TNBC classification system. The differential characteristics of the tumor microenvironment and DNA damage repair signatures across subgroups were also explored.

Results

Thai TNBC cohort could be classified into four main subgroups, corresponding to the LAR, BL-2, and M subtypes based on Lehmann's TNBC classification. The PAM50 gene set classified most samples as basal-like subtypes except for Group 1. Group 1 exhibited similar enrichment of the metabolic and hormone response pathways to the LAR subtype. Group 2 shared pathway activation with the BL-2 subtype. Group 3 showed an increase in the EMT pathway, similar to the M subtype. Group 4 showed no correlation with Lehmann's TNBC. The tumor microenvironment (TME) analysis showed high TME cell abundance with increased expression of immune blockade genes in Group 2. Group 4 exhibited low TME cell abundance and reduced immune blockade gene expressions. We also observed distinct signatures of the DNA double-strand break repair genes in Group 1.

Conclusions

Our study reported unique characteristics between the four TNBC subgroups and showed the potential use of immune checkpoint and PARP inhibitors in subsets of Thai TNBC patients. Our findings warrant further clinical investigation to validate TNBC's sensitivity to these regimens.

Arylamine N-Acetyltransferase 1 Activity is Regulated by the Protein Acetylation Status

Arylamine N-acetyltransferase 1 (NAT1) is a drug metabolizing enzyme that influences cancer cell proliferation and survival, especially in breast cancer. Lysine-acetylation is an important Post-Translational Modification (PTM) in the regulation of diverse cellular processes. Histone deacetylases (HDACs) and Sirtuins (SIRT) may have an important role on the NAT1 acetylation status, affecting its catalytic capacity and having an impact on the downstream functions of this protein. The aim of the present work is to investigate the acetylation status of NAT1 in human breast cancer. Breast cancer cell lines MDA-MB-231 (ER-, PR-, HER2-) and ZR-75-1 (estrogen receptor+, PR+, HER2+) were cultured in the presence of HDAC inhibitors (SAHA, TSA) or Sirtuin inhibitors (AGK2, EX527, Sirtinol). Under these conditions, NAT1 protein and gene expression as well as enzymatic activity were quantified. Acetylation of NAT1 protein was evaluated following an immunoprecipitation protocol and acetyl-Lysine quantification. Sirt1 and Sirt2 knockdown were performed and NAT1 protein and NAT1 mRNA expression and catalytic activity were quantified. The treatment of MDA-MB-231 or ZR-75-1 cells with increasing HDAC inhibitors resulted in 2 to 15-fold upregulation in NAT1 message expression. Finally, the catalytic activity of NAT1 in the presence of HDAC inhibition increased 2-fold. Conversely, the inhibition of Sirtuin activity did not cause significant changes in NAT1 message but produced a significant decrease in NAT1 catalytic activity. NAT1 acetylation was higher in the cells treated with HDAC inhibitors, as well as Sirtuin inhibitors. Finally, silencing of Sirt1 and Sirt2 genes by siRNA transient knockdown of each or both genes resulted in reduction of NAT1 protein expression and catalytic activity. The use of HDAC and Sirtuin inhibitors has been demonstrated as a promising powerful therapeutic alternative in various cancers. These inhibitors can significantly attenuate tumor burden by limiting tumor growth and metastasis. These compounds can also induce DNA damage, cell cycle arrest, apoptosis, and autophagy to promote cancer cell death. Several studies have shown that NAT1 is upregulated in cancer cells. The results of the present study show that the acetylation status of NAT1 is an important factor that might have a relevant role in the progression of cancer.

Deletion of arylamine N-acetyltransferase 1 in MDA-MB-231 human breast cancer cells reduces primary and secondary tumor growth in vivo with no significant effects on metastasis

Arylamine N-acetyltransferase 1 (NAT1) is frequently upregulated in breast cancer. Previous studies showed that inhibition or depletion of NAT1 in breast cancer cells diminishes anchorage-independent growth in culture, suggesting that NAT1 contributes to breast cancer growth and metastasis. To further investigate the contribution of NAT1 to growth and cell invasive/migratory behavior, we subjected parental and NAT1 knockout (KO) breast cancer cell lines (MDA-MB-231, MCF-7, and ZR-75-1) to multiple assays. The rate of cell growth in suspension was not consistently decreased in NAT1 KO cells across the cell lines tested. Similarly, cell migration and invasion assays failed to produce reproducible differences between the parental and NAT1 KO cells. To overcome the limitations of in vitro assays, we tested parental and NAT1 KO cells in vivo in a xenograft model by injecting cells into the flank of immunocompromised mice. NAT1 KO MDA-MB-231 cells produced primary tumors smaller than those formed by parental cells, which was contributed by an increased rate of apoptosis in KO cells. The frequency of lung metastasis, however, was not altered in NAT1 KO cells. When the primary tumors of the parental and NAT1 KO cells were allowed to grow to a pre-determined size or delivered directly via tail vein, the number and size of metastatic foci in the lung did not differ between the parental and NAT1 KO cells. In conclusion, NAT1 contributes to primary and secondary tumor growth in vivo in MDA-MB-231 breast cancer cells but does not appear to affect its metastatic potential.

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.

Moonlighting in drug metabolism

Drug metabolizing enzymes catalyze the biotransformation of many of drugs and chemicals. The drug metabolizing enzymes are distributed among several evolutionary families and catalyze a range of detoxication reactions, including oxidation/reduction, conjugative, and hydrolytic reactions that serve to detoxify potentially toxic compounds. This detoxication function requires that drug metabolizing enzymes exhibit substrate promiscuity. In addition to their catalytic functions, many drug metabolizing enzymes possess functions unrelated to or in addition to catalysis. Such proteins are termed 'moonlighting proteins' and are defined as proteins with multiple biochemical or biophysical functions that reside in a single protein. This review discusses the diverse moonlighting functions of drug metabolizing enzymes and the roles they play in physiological functions relating to reproduction, vision, cell signaling, cancer, and transport. Further research will likely reveal new examples of moonlighting functions of drug metabolizing enzymes.

Transfer of microRNA-221 from mesenchymal stem cell-derived extracellular vesicles inhibits atherosclerotic plaque formation

Mesenchymal stem cells (MSCs) have emerged as a cell-based therapy in many diseases including atherosclerosis (AS) due to their capability of immunomodulation and tissue regeneration. However, the pathway for MSCs' antiatherosclerotic activity remains to be elucidated. Here, we test the hypothesis that microRNA-221 (miR-221) from MSC-derived extracellular vesicles (EVs) alleviates AS. Male ApoE-/- mice were fed a high-fat diet for 12 weeks to induce AS, and were then treated with human bone marrow mesenchymal stem cell-derived EVs by tail vein injection. The expression pattern of miR-221 and N-acetyltransferase-1 (NAT1) in AS mice was characterized by quantitative RNA analysis and their interaction was identified by dual-luciferase reporter gene assay. In other studies, human arterial smooth muscle cells treated with oxidized low-density lipoprotein-were co-cultured with MSC-released EVs to evaluate the EV-mediated transfer of miR-221. NAT1 was highly expressed in atherosclerotic lesions. Adenovirus-mediated NAT1 knockdown resulted in a reduced lipid deposition in AS mice. Human bone marrow mesenchymal stem cell -derived EVs carrying miR-221 were internalized by human arterial smooth muscle cells and transferred their miR-221 contents to downregulate the target gene NAT1. Injection of miR-221-containing EVs inhibited lipid deposition in AS mice, in part by downregulating NAT1. The present study provides evidence that miR-221 shuttled by MSC-derived EVs can inhibit atherosclerotic plaque formation in AS model mice, suggesting that miR-221 may serve as a target for improving MSC-based therapeutic strategy against AS.

Prognostic and Clinicopathological Significance of X-Box-Binding Protein 1 and N-Acetyltransferase 1 in Gallbladder Cancer

Background: X-box-binding protein 1 (XBP1) and N-acetyltransferase 1 (NAT1) are involved in oncogenesis and progression of many human cancer types. However, the roles of XBP1 and NAT1 in gallbladder cancer (GBC) are never reported.

Methods: We examined XBP1 and NAT1 expression in GBC and matched adjacent non-tumor tissues via Western blotting. Then, we assayed XBP1 and NAT1 expression in 215 GBCs, including 69 squamous cell/adenosquamous carcinomas (SC/ASCs) and 146 adenocarcinomas (ACs) with immunohistochemistry. Their prognostic and clinicopathological significance was further evaluated using the χ² test or Fisher's exact test, Kaplan–Meier univariate survival analysis, and log-rank tests.

Results: XBP1 expression was upregulated, and NAT1 expression was downregulated in GBC. Immunohistochemical results showed that XBP1 expression was negatively associated with NAT1 expression in GBC, including SC/ASC and AC. The rate of patients with an age of more than 45 years, positivity of lymph node metastasis, and invasion were significantly higher in SC/ASC than those in AC (all P < 0.05). The percentage of XBP1-positive and NAT1-negative expression was significantly higher in the cases with poor differentiation, advanced tumor, nodes, and metastases (TNM) stage, lymph node metastasis, invasion, and only receiving biopsy in GBC, SC/ASC, and AC (all P < 0.05). XBP1-positive and NAT1-negative expression was positively related to larger tumor size (>3 cm) in GBC and AC. There was a negative association between XBP1 and NAT1 expression in GBC, SC/ASC, and AC (all P < 0.05). Positive XBP1 and negative NAT1 expression was closely associated with decreased overall survival in GBC, SC/ASC, and AC patients (all P < 0.05). The multivariate Cox regression analysis showed that positive XBP1 or negative NAT1 expression was an independent factor for poor prognosis in gallbladder SC/ASC and AC patients.

Conclusions: This study indicates that positive XBP1 and negative NAT1 expression are closely associated with the clinicopathological and biological behaviors and poor prognosis in GBC.

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.

MicroRNA-6744-5p promotes anoikis in breast cancer and directly targets NAT1 enzyme

Objective: Anoikis is apoptosis that is induced when cells detach from the extracellular matrix and neighboring cells. As anoikis serves as a regulatory barrier, cancer cells often acquire resistance towards anoikis during tumorigenesis to become metastatic. MicroRNAs (miRNAs) are short strand RNA molecules that regulate genes post-transcriptionally by binding to mRNAs and reducing the expression of its target genes. This study aimed to elucidate the role of a novel miRNA, miR-6744-5p, in regulating anoikis in breast cancer and identify its target gene. Methods: An anoikis resistant variant of the luminal A type breast cancer MCF-7 cell line (MCF-7-AR) was generated by selecting and amplifying surviving cells after repeated exposure to growth in suspension. MiRNA microarray analysis identified a list of dysregulated miRNAs from which miR-6744-5p was chosen for overexpression and knockdown studies in MCF-7. Additionally, the miRNA was also overexpressed in a triple-negative breast cancer cell line, MDA-MB-231, to evaluate its ability to impair the metastatic potential of breast cancer cells. Results: This study showed that overexpression and knockdown of miR-6744-5p in MCF-7 increased and decreased anoikis sensitivity, respectively. Similarly, overexpression of miR-6744-5p in MDA-MB-231 increased anoikis and also decreased tumor cell invasion in vitro and in vivo. Furthermore, NAT1 enzyme was identified and validated as the direct target of miR-6744-5p. Conclusions: This study has proven the ability of miR-6744-5p to increase anoikis sensitivity in both luminal A and triple negative breast cancer cell lines, highlighting its therapeutic potential in treating breast cancer.

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.

The role of acetyl-coA carboxylase2 in head and neck squamous cell carcinoma

Background

Acetyl-CoA carboxylase (ACC) plays an important role in the metabolism of various cancer cells, but its role in head and neck squamous cell carcinoma (HNSCC) is uncertain. Therefore, in the present study, we explored the role of ACC2 in HNSCC.

Methods

Western blot and immunohistochemistry assays were used to determine ACC2 protein expression levels in laryngocarcinoma and adjacent normal tissues derived from patients with laryngocarcinoma. ACC2 expression was knocked down in the hypopharyngeal cancer cell line FaDu to determine its effect on apoptosis. Lipid oil red staining was used to test the change of intracellular lipid.

Results

The results showed that the ACC2 protein was highly expressed in laryngocarcinoma and that the ACC2 expression level was positively associated with the clinical cancer stage and negatively associated with the degree of laryngocarcinoma cell differentiation. Kaplan-Meier analyses indicated that compared with patients having low levels of ACC2, those with high ACC2 levels had a decreased 5-year survival rate. The results of western blot and terminal deoxynucleotidyl transferase dUTP nick-end labeling assays showed that knockdown of ACC2 accelerated apoptosis in FaDu cells. Furthermore, knockdown of ACC2 significantly reduced the intracellular lipid levels in FaDu cells.

Conclusion

These findings suggest that ACC2 may be an important prognostic marker for patients with HNSCC and that ACC2 may be a potential target in the treatment of HNSCC.

Retrospective analysis of estrogen receptor 1 and N‑acetyltransferase gene expression in normal breast tissue, primary breast tumors, and established breast cancer cell lines

The expression levels of estrogen receptor 1 (ESR1), arylamine N‑acetyltransferase 1 (NAT1), and arylamine N‑acetyltransferase 2 (NAT2) are implicated in breast cancer; however, their co-expression profiles in normal breast tissue, primary breast tumors and established breast cancer cell lines are undefined. NAT1 expression is widely reported to be associated with ESR1 expression and is frequently investigated in breast cancer etiology. Furthermore, the NAT2 phenotype has been reported to modify breast cancer risk in molecular epidemiological association studies. Understanding the relationships between the expression levels of these genes is essential to understand their role in breast cancer etiology and treatment. In the present study, NAT1, NAT2 and ESR1 expression data were accessed from repositories of RNA‑Seq data covering 57 breast cancer cell lines, 1,043 primary breast tumors and 99 normal breast tissues. The relationships between gene expression, and between NAT1 activity and RNA expression in breast cancer cell lines were evaluated using non-parametric statistical analyses. Differences in gene expression in each dataset, as well as gene expression differences in normal breast tissue compared to primary breast tumors, and stratification by estrogen receptor status were determined. NAT1 and NAT2 mRNA expression were detected in normal and primary breast tumor tissues; NAT1 expression was much higher than NAT2. NAT1 and ESR1 expression were strongly associated, whereas NAT2 and ESR1 expression were not. Although NAT1 and NAT2 expression were associated, the magnitude was moderate. NAT1, NAT2, and ESR1 expression were increased in primary breast tumor tissue compared with normal breast tissue; however, the magnitude and significance of the differences were lower for NAT2. Analysis of NAT1, NAT2, and ESR1 expression in normal and primary breast tissues and breast cancer cell lines suggested that NAT1 and NAT2 expression are regulated by distinctive mechanisms, whereas NAT1 and ESR1 expression may have overlapping regulation. Defining these relationships is important for future investigations into breast cancer prevention.