Small molecule inhibition of arylamine N-acetyltransferase Type I inhibits proliferation and invasiveness of MDA-MB-231 breast cancer cells

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.

Therapeutic effects of lentivirus-mediated shRNA targeting of cyclin D1 in human gastric cancer

Background

Gastric cancer is the second most common cause of cancer-related death in males and the fourth in females. Traditional treatment has poor prognosis because of recurrence and systemic side effects. Therefore, the development of new therapeutic strategies is an important issue. Lentivirus-mediated shRNA stably inhibits target genes and can efficiently transduce most cells. Since overexpressed cyclin D1 is closely related to human gastric cancer progression, inhibition of cyclin D1 using specific targeting could be an effective treatment method of human gastric cancer.

Methods

The therapeutic effect of lentivirus-mediated shRNA targeting of cyclin D1 (ShCCND1) was analyzed both in vitro and in vivo experiments.

Results

In vitro, NCI-N87 cells with downregulation of cyclin D1 by ShCCND1 showed significant inhibition of cell proliferation, cell motility, and clonogenicity. Downregulation of cyclin D1 in NCI-N87 cells also resulted in significantly increased G1 arrest and apoptosis. In vivo, stable NCI-N87 cells expressing ShCCND1 were engrafted into nude mice. Then, the cancer-growth inhibition effect of lentivirus was confirmed. To assess lentivirus including ShCCND1 as a therapeutic agent, intratumoral injection was conducted. Tumor growth of the lentivirus-treated group was significantly inhibited compared to growth of the control group. These results are in accordance with the in vitro data and lend support to the mitotic figure count and apoptosis analysis of the tumor mass.

Conclusion

The lentivirus-mediated ShCCND1 was constructed, which effectively inhibited growth of NCI-N87-derived cancer both in vitro and in vivo. The efficiency of shRNA knockdown and variation in the degree of inhibition is mediated by different shRNA sequences and cancer cell lines. These experimental results suggest the possibility of developing new gastric cancer therapies using lentivirus-mediated shRNA.

Lentivirus-mediated shRNA targeting of cyclin D1 enhances the chemosensitivity of human gastric cancer to 5-fluorouracil

Gastric cancer is one of the major public health problems. Despite new chemotherapeutic treatments, the prognosis of gastric cancer remains poor. 5-Fluorouracil (5-FU) is used as a standard chemotherapy drug in gastric cancer. However, 5-FU resistance develops frequently and is a main cause of chemotherapy failure in human gastric cancer. Overexpression of cyclin D1 is related to rapid cell growth, a poor prognosis and increased chemoresistance in several types of cancers. In this study, we investigated whether treatment of gastric cancer cells with shRNA targeting cyclin D1 (ShCCND1) or 5-FU, alone or in combination, influences the activation of phosphorylated AKT (pAKT) and pNFκB, which are markers that are increased in 5-FU chemoresistance. We also investigated the effect of combined treatment with ShCCND1 and 5-FU on cell growth and chemosensitivity to 5-FU in the gastric cancer cell line AGS. The data showed that ShCCND1-mediated cyclin D1 downregulation in AGS cells significantly inhibited cell proliferation, cell mobility and clonogenicity. In addition, combined treatment with ShCCND1 and 5-FU significantly decreased the survival rate of AGS cells, compared to single-treatment with either agent. These results demonstrated that ShCCND1 increases 5-FU chemosensitivity, a conclusion that is also supported by the concomitant reduction in expression of pAKT and pNFκB, increase of G1 arrest and induction of apoptosis. Taken together, these data provide further evidence that therapeutic strategies targeting cyclin D1 may have the dual advantage of suppressing the growth of cancer cells, while enhancing their chemosensitivity.

Carboxyl-terminal modulator protein positively regulates Akt phosphorylation and acts as an oncogenic driver in breast cancer

Akt activation has been implicated broadly in tumorigenesis, but the basis for its dysregulation in cancer cells is incompletely understood. In this study, we sought to clarify a regulatory role for the Akt-binding carboxy-terminal modulator protein (CTMP), which has been controversial. In evaluating CTMP expression in paired normal-tumor specimens of 198 patients with breast cancer, we found that CTMP was upregulated in breast tumors, where it was associated with poor patient survival. Notably, CTMP expression also correlated positively with Akt phosphorylation in breast cancer clinical specimens and cell lines. Furthermore, ectopic expression of CTMP promoted cell proliferation and enhanced the tumorigenic properties of estrogen-dependent breast cancer cells. This effect was correlated with increased sensitivity to insulin-induced Akt phosphorylation, which is mediated primarily by the phosphoinositide 3-kinase-Akt pathway. In contrast, short hairpin RNA-mediated silencing of endogenous CTMP decreased the proliferation of estrogen-dependent or estrogen-independent breast cancer cells. Mechanistic investigations defined the N-terminal domain of CTMP at amino acids 1 to 64 as responsible for Akt binding. Taken together, our results firmly corroborate the concept that CTMP promotes Akt phosphorylation and functions as an oncogenic molecule in breast cancer.

Interrogating differences in expression of targeted gene sets to predict breast cancer outcome

Background

Genomics provides opportunities to develop precise tests for diagnostics, therapy selection and monitoring. From analyses of our studies and those of published results, 32 candidate genes were identified, whose expression appears related to clinical outcome of breast cancer. Expression of these genes was validated by qPCR and correlated with clinical follow-up to identify a gene subset for development of a prognostic test.

Methods

RNA was isolated from 225 frozen invasive ductal carcinomas,and qRT-PCR was performed. Univariate hazard ratios and 95% confidence intervals for breast cancer mortality and recurrence were calculated for each of the 32 candidate genes. A multivariable gene expression model for predicting each outcome was determined using the LASSO, with 1000 splits of the data into training and testing sets to determine predictive accuracy based on the C-index. Models with gene expression data were compared to models with standard clinical covariates and models with both gene expression and clinical covariates.

Results

Univariate analyses revealed over-expression of RABEP1, PGR, NAT1, PTP4A2, SLC39A6, ESR1, EVL, TBC1D9, FUT8, and SCUBE2 were all associated with reduced time to disease-related mortality (HR between 0.8 and 0.91, adjusted p < 0.05), while RABEP1, PGR, SLC39A6, and FUT8 were also associated with reduced recurrence times. Multivariable analyses using the LASSO revealed PGR, ESR1, NAT1, GABRP, TBC1D9, SLC39A6, and LRBA to be the most important predictors for both disease mortality and recurrence. Median C-indexes on test data sets for the gene expression, clinical, and combined models were 0.65, 0.63, and 0.65 for disease mortality and 0.64, 0.63, and 0.66 for disease recurrence, respectively.

Conclusions

Molecular signatures consisting of five genes (PGR, GABRP, TBC1D9, SLC39A6 and LRBA) for disease mortality and of six genes (PGR, ESR1, GABRP, TBC1D9, SLC39A6 and LRBA) for disease recurrence were identified. These signatures were as effective as standard clinical parameters in predicting recurrence/mortality, and when combined, offered some improvement relative to clinical information alone for disease recurrence (median difference in C-values of 0.03, 95% CI of -0.08 to 0.13). Collectively, results suggest that these genes form the basis for a clinical laboratory test to predict clinical outcome of breast cancer.

Cyanamide-mediated Inhibition of N-acetyltransferase 1

Cyanamide has been used for decades for medical intentions in the treatment of alcoholism and for agricultural purposes as a plant growth regulator and bud-breaking agent. Its therapeutic effect is mediated by reversible inhibition of aldehyde dehydrogenase and it was reported to be metabolized in vivo mainly via coenzyme A dependent N-acetylation by N-acetyltransferases. Although described to be a substrate for N-acetyltransferases (NATs), cyanamide has a different molecular structure to arylamines and hydrazines, the preferred substrates for N-acetyltransferases. Therefore, a more detailed investigation of its interrelations with N-acetyltransferases was performed. We analyzed the impact of cyanamide on NAT1 activities of human monocytes (monocytic THP-1 cells) using the classical substrate p-aminobenzoic acid. We found that a 24h treatment with physiologically relevant concentrations of cyanamide decreased the NAT1 activity significantly. Based on this observation we performed additional experiments using recombinant human NAT1 and NAT2 to achieve further insights. In detail a significant dose- and time-dependent inhibition of NAT1 activity was observed for 100 and 1000μM cyanamide using recombinant human NAT1*4. However, cyanamide did not inhibit recombinant NAT2*4. Experiments testing cyanamide as substrate did not provide evidence that cyanamide is metabolized via coenzyme A dependent N-acetylation in vitro by human NAT1 or NAT2, THP-1 or human liver cytosol. Therefore we can conclude that the observed enzyme inhibition (around 50% and 25% after treatment with 0.5 and 0.25mM CA, respectively) is not based on substrate-dependent down-regulation of NAT1. Further mechanistic and kinetic studies indicated that cyanamide reacts with the active site cysteine residue of NAT1, leading to its rapid inhibition (significant inhibition after 30min and 2h for 1000 and 100μM CA, respectively). Addition of the reduction agent dithiothreitol (DTT) did not modify the effect, indicating that oxidative processes that can be reversed by 5mM DTT are not likely involved in the inhibition. Taken together our results show that cyanamide is able to inhibit NAT1 most likely via interaction with the active site cysteine residue. Thereby cyanamide might modulate NAT1 dependent detoxification and activation of arylamines.

Variable NAT1 enzyme activity in long-term cultured human HaCaT keratinocytes

Since animal testing should be avoided whenever possible, the development of in vitro tests for predicting the effect of chemicals becomes a major field. This rise of in vitro test systems led to an increased requirement for well-characterized continuously growing cell lines. Monitoring of the cells during test and routine culture is necessary to gain relevant and reproducible results. In the present study, the influence of passaging under constant culture conditions on the human keratinocyte cell line HaCaT was investigated. Data demonstrated that growth rate rose with increasing passages. Doubling times of the cells were decreased to 24 ± 0.6 h in the late passages (12-16), in comparison to 36.2 ± 1.5 h in the early passages (2-8). These data were confirmed by a fall in mRNA expression levels of keratin 1 and transglutaminase 1 within the passages. Furthermore, the activities of the xenobiotic metabolizing phase II enzyme N-acetyltransferase 1 (NAT1) were higher in the late passages compared to the early passages. These results are contrary to an expected decrease in enzyme activity and proliferation rate induced by replicative senescence or cell aging. Data also indicate that routine culture might result in significant changes in proliferation and phase II metabolism. These findings reinforce the necessity of a strict characterization and knowledge of regulation of in vitro systems, as well as the need for new biomarkers, in order to use cells for the development and evaluation of reproducible in vitro test systems.

Reduced 4-aminobiphenyl-induced liver tumorigenicity but not DNA damage in arylamine N-acetyltransferase null mice

The aromatic amine 4-aminobiphenyl (ABP) is a liver procarcinogen in mice, requiring enzymatic bioactivation to exert its tumorigenic effect. To assess the role of arylamine N-acetyltransferase (NAT)-dependent acetylation capacity in the risk for ABP-induced liver tumors, we compared 1-year liver tumor incidence following the postnatal exposure of wild-type and NAT-deficient Nat1/2(-/-) mice to ABP. At an ABP exposure of 1200 nmol, male Nat1/2(-/-) mice had a liver tumor incidence of 36% compared to 69% in wild-type males, and at 600 nmol there was a complete absence of tumors compared to 60% in wild-type mice. Only one female wild-type mouse had a tumor using this exposure protocol. However, levels of N-deoxyguanosin-8-yl-ABP-DNA adducts did not correlate with either the strain or sex differences in tumor incidence. These results suggest that female sex and NAT deficiency reduce risk for ABP-induced liver tumors, but by mechanisms unrelated to differences in DNA-damaging events.

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

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

Silencing of the IKKε gene by siRNA inhibits invasiveness and growth of breast cancer cells

Introduction

IκB kinase ε (IKKε) is a member of the IKK family that plays an important role in the activation of NF-κB. Overexpressed in more than 30% of breast cancers, IKKε has been recently identified as a potential breast cancer oncogene. The purpose of the present study is to examine the therapeutic potential of IKKε siRNA on human breast cancer cells.

Methods

Eight siRNAs targeting different regions of the IKKε mRNA were designed, and the silencing effect was screened by quantitative real-time RT-PCR. The biological effects of synthetic siRNAs on human breast cancer cells were investigated by examining the cell proliferation, migration, invasion, focus formation, anchorage-independent growth (via soft agar assay), cell cycle arrest, apoptosis (via annexing binding), NF-κB basal level, and NF-κB-related gene expressions upon the IKKε silencing.

Results

Silencing of IKKε in human breast cancer cells resulted in a decrease of focus formation potential and clonogenicity as well as in vitro cell migration/invasion capabilities. Moreover, knockdown of IKKε suppressed cell proliferation. Cell cycle assay showed that the anti-proliferation effect of IKKε siRNA was mediated by arresting cells in the G₀/G₁ phase, which was caused by downregulation of cyclin D₁. Furthermore, we demonstrated that silencing of IKKε inhibited the NF-κB basal activity as well as the Bcl-2 expression. Significant apoptosis was not observed in breast cancer cells upon the silencing of IKKε. The present study provided the first evidence that silencing IKKε using synthetic siRNA can inhibit the invasiveness properties and proliferation of breast cancer cells.

Conclusions

Our results suggested that silencing IKKε using synthetic siRNA may offer a novel therapeutic strategy for breast cancer.

The human xenobiotic-metabolizing enzyme arylamine N-acetyltransferase 1 (NAT1) is irreversibly inhibited by inorganic (Hg2+) and organic mercury (CH3Hg+): mechanism and kinetics

Human arylamine N-acetyltransferase 1 (NAT1) is a xenobiotic-metabolizing enzyme that biotransforms aromatic amine chemicals. We show here that biologically-relevant concentrations of inorganic (Hg2+) and organic (CH3Hg+) mercury inhibit the biotransformation functions of NAT1. Both compounds react irreversibly with the active-site cysteine of NAT1 (half-maximal inhibitory concentration (IC50)=250 nM and kinact=1.4x10(4) M(-1) s(-1) for Hg2+ and IC50=1.4 microM and kinact=2x10(2) M(-1) s(-1) for CH3Hg+). Exposure of lung epithelial cells led to the inhibition of cellular NAT1 (IC50=3 and 20 microM for Hg2+ and CH3Hg+, respectively). Our data suggest that exposure to mercury may affect the biotransformation of aromatic amines by NAT1.

Characterization of N-acetyltransferase 1 activity in human keratinocytes and modulation by para-phenylenediamine

N-acetyltransferase 1 (NAT1)-mediated N-acetylation in keratinocytes is an important detoxification pathway for the hair dye ingredient para-phenylenediamine (PPD). Because NAT1 can be regulated by various exogenous compounds, including some NAT1 substrates themselves, we investigated NAT1 expression in keratinocytes and the interactions between PPD and NAT1. NAT1 activity was found to be cell-cycle phase-dependent. Maximum NAT1 activities (mean: 49.7 nmol/mg/min) were estimated when HaCaT keratinocytes were arrested in G(0)/G(1) phase, whereas nonsynchronized cells showed the lowest activities (mean: 28.9 nmol/mg/min). It is noteworthy that we also found an accelerated progression through the cell cycle in HaCaT cells with high NAT1 activities. This evidence suggests an association between NAT1 and proliferation in keratinocytes. Regarding the interaction between NAT1 and PPD, we found that keratinocytes N-acetylate PPD; however, this N-acetylation was saturated with increasing PPD concentrations. HaCaT cultured in medium supplemented with PPD (10-200 microM) for 24 h showed a significant concentration-dependent decrease (17-50%) in NAT1 activity. PPD also induced down-regulation of NAT1 activity in human primary keratinocytes. Western blot studies using a NAT1-specific antibody in HaCaT showed that the loss of enzyme activity was associated with a decline in the amount of NAT1 protein, whereas no changes in the amounts of NAT1 P1 (NATb)-dependent mRNA were found by quantitative reverse transcription-polymerase chain reaction analysis, suggesting the involvement of a substrate-dependent mechanism of NAT1 down-regulation. In conclusion, these data show that overall N-acetylation capacity of keratinocytes and consequently detoxification capacities of human skin is modulated by the presence of NAT1 substrates and endogenously by the cell proliferation status of keratinocytes.