Concurrent expression of aryl hydrocarbon receptor and CYP1A1 but not CYP1A1 MspI polymorphism is correlated with gastric cancers raised in Dalian, China

Inflammation-Related Genes Serve as Prognostic Biomarkers and Involve in Immunosuppressive Microenvironment to Promote Gastric Cancer Progression

Gastric cancer (GC) is a typical inflammatory-related malignant tumor which is closely related to helicobacter pylori infection. Tumor inflammatory microenvironment plays a crucial role in tumor progression and affect the clinical benefit from immunotherapy. In recent years, immunotherapy for gastric cancer has achieved promising outcomes, but not all patients can benefit from immunotherapy due to tumor heterogeneity. In our study, we identified 29 differentially expressed and prognostic inflammation-related genes in GC and normal samples. Based on those genes, we constructed a prognostic model using a least absolute shrinkage and selection operator (LASSO) algorithm, which categorized patients with GC into two groups. The high-risk group have the characteristics of "cold tumor" and have a poorer prognosis. In contrast, low-risk group was "hot tumor" and had better prognosis. Targeting inflammatory-related genes and remodeling tumor microenvironment to turn "cold tumor" into "hot tumor" may be a promising solution to improve the efficacy of immunotherapy for patients with GC.

Evaluation of aryl hydrocarbon receptor expression in oral squamous cell carcinoma and normal oral mucosa using western blot

Background

Aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that acts as a binding site for toxic chemicals, particularly the dioxin group of chemicals. Elevated levels of AHR have been observed in various human cancers, including lung carcinomas, hepatic carcinomas and in mammary tumors. However, the expression of AHR in oral squamous cell carcinoma (OSCC) patients who are tobacco users are less explored.

Aims and Objectives

The aim of the present study is to evaluate and compare AHR levels in OSSC patients and in normals using Western blot technique in an attempt to explore the possible role of AHR in oral carcinogenesis.

Materials and Methods

The study sample consisted of ten oral squamous cell carcinoma cases which were diagnosed clinically and confirmed histopathologically as OSCC and four samples of the normal oral mucosa. AHR protein expression was evaluated using Western blot technique and chemiluminescence detection kit. The densitometry was performed on a Microtek scan maker MSP flatbed scanner and quantified using Image J software. Mean AHR protein levels were calculated and compared between OSCC and normal oral mucosa using Student's t-test.

Results

The mean AHR protein level in OSCC samples (n = 10) was 2878.90 ± 1231.27 and 975.75 ± 227.27 in the normal oral mucosa (n = 4). The OSCC samples showed significantly higher levels of AHR protein compared to the normal oral mucosa (P = 0.008).

Conclusion

The study showed a significantly higher expression of AHR in oral squamous cell carcinoma samples when compared to the normal oral mucosa, suggesting a possible role of AHR in the initiation, promotion and progression of oral squamous cell carcinoma.

How the AHR Became Important in Cancer: The Role of Chronically Active AHR in Cancer Aggression

For decades, the aryl hydrocarbon receptor (AHR) was studied for its role in environmental chemical toxicity i.e., as a quirk of nature and a mediator of unintended consequences of human pollution. During that period, it was not certain that the AHR had a “normal” physiological function. However, the ongoing accumulation of data from an ever-expanding variety of studies on cancer, cancer immunity, autoimmunity, organ development, and other areas bears witness to a staggering array of AHR-controlled normal and pathological activities. The objective of this review is to discuss how the AHR has gone from a likely contributor to genotoxic environmental carcinogen-induced cancer to a master regulator of malignant cell progression and cancer aggression. Particular focus is placed on the association between AHR activity and poor cancer outcomes, feedback loops that control chronic AHR activity in cancer, and the role of chronically active AHR in driving cancer cell invasion, migration, cancer stem cell characteristics, and survival.

Elevated exposure to polycyclic aromatic hydrocarbons (PAHs) may trigger cancers in Pakistan: an environmental, occupational, and genetic perspective

Polycyclic aromatic hydrocarbons (PAHs) are carcinogenic compounds which are emitted through incomplete combustion of organic materials, fossil fuels, consumption of processed meat, smoked food, and from various industrial activities. High molecular mass and mobility make PAHs widespread and lethal for human health. A cellular system in human detoxifies these toxicants through specialized enzymatic machinery called xenobiotic-metabolizing (CYP450) and phase-II (GSTs) enzymes (XMEs). These metabolizing enzymes include cytochromes P450 family (CYP1, CYP2), glutathione s-transferases, and ALDHs. Gene polymorphisms in XMEs encoding genes can compromise their metabolizing capacity to detoxify ingested carcinogens (PAHs etc.) that may lead to prolong and elevated exposure to ingested toxicants and may consequently lead to cancer. Moreover, PAHs can induce cancer through reprograming XMEs' gene functions by altering their epigenetic markers. This review article discusses possible interplay between individual's gene polymorphism in XMEs' genes, their altered epigenetic markers, and exposure to PAHs in cancer susceptibility in Pakistan.

Prognostic Role of Aryl Hydrocarbon Receptor Interacting Protein (AIP) Immunohistochemical Expression in Patients with Resected Gastric Carcinomas

Aryl hydrocarbon receptor (AHR) interacting protein (AIP) is a chaperone which binds to inactive AHR in the cell cytoplasm. AHR is best known for mediating the toxicity of halogenated aromatics, but it has also been linked to carcinogenesis and tumor progression in several tumor types. Our aims are to assess the features of AIP immunohistochemical (IHC) staining and to evaluate its possible role as a prognostic marker in gastric cancer (GC). Retrospective study of 147 cases of resected GC. Clinicopathological features were collected, tissue microarrays were constructed for AIP IHC and statistical analysis were performed. AIP staining was observed in 50.3% of tumors. All AIP-positive cases exhibited cytoplasmic or membranous staining, variably associated with nuclear co-staining. 93.2% of AIP-positive tumors showed AIP immunoreactivity in 100% of cells. Staining intensity was mild, moderate and intense in 33.8%, 13.5% and 52.7% of cases. Tumors were stratified according to AIP staining intensity into low expression (no or mild AIP immunoreactivity) and high expression (moderate or intense AIP immunoreactivity). 36.6% of our cases showed high AIP expression. High AIP expression was significantly and independently correlated to tumor progression and cancer death. Tumors with high AIP expression showed lower survival and higher progression rates. AIP expression might be useful for determining GC prognosis. More studies are needed to clarify the role of AHR pathway in GC, AIP expression and its potential use as a surrogate marker for selecting patients for AHR modulation therapy.

Aryl hydrocarbon receptor and intestinal immunity

Aryl hydrocarbon receptor (AhR) is a member of the basic helix-loop-helix-(bHLH) superfamily of transcription factors, which are associated with cellular responses to environmental stimuli, such as xenobiotics and oxygen levels. Unlike other members of bHLH, AhR is the only bHLH transcription factor that is known to be ligand activated. Early AhR studies focused on understanding the role of AhR in mediating the toxicity and carcinogenesis properties of the prototypic ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). In recent years, however, it has become apparent that, in addition to its toxicological involvement, AhR is highly receptive to a wide array of endogenous and exogenous ligands, and that its activation leads to a myriad of key host physiological functions. In this study, we review the current understanding of the functions of AhR in the mucosal immune system with a focus on its role in intestinal barrier function and intestinal immune cells, as well as in intestinal homeostasis.

Cytochrome P450 1A1 gene polymorphisms and digestive tract cancer susceptibility: a meta-analysis

Cytochrome P450 1A1 (CYP1A1) is a phase I enzyme that regulates the metabolism of environmental carcinogens and alter the susceptibility to various cancers. Many studies have investigated the association between the CYP1A1 MspI and Ile462Val polymorphisms and digestive tract cancer (DTC) risk in different groups of populations, but their results were inconsistent. The PubMed and Embase Database were searched for case–control studies published up to 30th September, 2015. Data were extracted and pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated to assess the relationship. Totally, 39 case–control studies (9094 cases and 12,487 controls) were included. The G allele in Ile/Val polymorphism was significantly associated with elevated DTC risk with per‐allele OR of 1.24 (95% CI = 1.09–1.41, P = 0.001). Similar results were also detected under the other genetic models. Evidence was only found to support an association between MspI polymorphism and DTC in the subgroups of caucasian and mixed individuals, but not in the whole population (the dominant model: OR = 1.19, 95% CI = 0.94–1.91, P = 0.146). In conclusion, our results suggest that the CYP1A1 polymorphisms are potential risk factors for DTC. And large sample size and well‐designed studies with detailed clinical information are needed to more precisely evaluate our founding.

Meta-analysis of association studies of CYP1A1 genetic polymorphisms with digestive tract cancer susceptibility in Chinese

BACKGROUND

A great number of studies have shown that cytochrome P450 1A1 (CYP1A1) genetic polymorphisms, CYP1A1 Msp I and CYP1A1 Ile/Val, might be risk factors for digestive tract cancers, including esophageal cancer (EC), gastric cancer (GC), hepatic carcinoma (HC), as well as colorectal cancer (CC), but the results are controversial. In this study, a meta-analysis of this literature aimed to clarify associations of CYP1A1 genetic polymorphisms with digestive tract cancer susceptibility in Chinese populations.

MATERIALS AND METHODS

Eligible case-control studies published until December 2013 were retrieved by systematic literature searches from PubMed, Embase, CBM, CNKI and other Chinese databases by two investigators independently. The associated literature was acquired through deliberate search and selection based on established inclusion criteria. Fixed- effects or random-effects models were used to estimate odds ratios (ORs and 95%CIs). The meta-analysis was conducted using Review Manager 5.2 and Stata 12.0 softwares with stability evaluated by both stratified and sensitivity analyses. Moreover, sensitivity analysis and publication bias diagnostics confirmed the reliability and stability.

RESULTS

Eighteen case control studies with 1, 747 cases and 2, 923 controls were selected for CYP1A1 MspI polymorphisms, and twenty case-control studies with 3, 790 cases and 4, 907 controls for the CYP1A1 Ile/ Val polymorphisms. Correlation associations between CYP1A1 Ile/Val polymorphisms and digestive tract cancers susceptibility were observed in four genetic models in the meta-analysis (GG vs AA:OR= 2.03, 95%CI =1.52- 2.72; AG vs AA: OR=1.26, 95%CI =1.07-1.48; [ GG+AG vs AA] :OR =1.42, 95%CI=1.20-1.68, [GG vs AA+AG ]:OR=1.80, 95%CI =1.40-2.31). There was no association between CYP1A1 Msp I polymorphisms and digestive tract cancer risk. Subgroup analysis for tumor type showed a significant association of CYP1A1 Ile/Val genetic polymorphisms with EC in China. However, available data collected by the study failed to reveal remarkable associations of GC or HC with CYP1A1 Ile/Val genetic polymorphisms and EC, GC or CC with CYP1A1 MspI genetic polymorphisms.

CONCLUSIONS

Our results indicated that CYP1A1 Ile/Val genetic polymorphisms, but not CYP1A1 Msp I polymorphisms, are associated with an increased digestive tract cancer risk in Chinese population. Additional well-designed studies, with larger sample size, focusing on different ethnicities and cancer types are now warranted to validate this finding.

The effect of CYP1A1 and CYP1A2 polymorphisms on gastric cancer risk among different ethnicities: a systematic review and meta-analysis

Potential Cytochrome P450s (CYPs) 1A1 MspI, 1A1 Ile462Val, 1A2*1 F, and/or 1A2*1C polymorphisms have been implicated in gastric cancer risk among different ethnicities. We aimed to explore the effect of CYP 1A1 MspI, 1A1 Ile462Val, 1A2*1 F, and/or 1A2*1C polymorphisms on the susceptibility to gastric cancer among different ethnicities through a systematic review and meta-analysis. Each initially included article was scored for quality appraisal. Desirable data were extracted and registered into databases. A number of 11 studies were ultimately eligible for the meta-analysis of CYP1A1 MspI polymorphism, eight studies for the meta-analysis of 1A1 Ile462Val polymorphism, and two studies for the meta-analysis of 1A2*1 F polymorphism. None of genetic model was evidently suggested, and thus all the genetic models were presented. Potential sources of heterogeneity were sought out via subgroup and sensitivity analyses, and publication biases were estimated. In our meta-analysis, significant results could be found in mutational heterozygous CT genotype, compared with wild TT genotype, among large sample size subgroup for CYP1A1 MspI polymorphism. Regarding CYP1A1 Ile462Val polymorphism, no statistically significant results could be found. For CYP1A2*1 F polymorphism, mutational heterozygous AC genotype, compared with wild-type AA, has deleterious effects, whereas mutational homozygous CC genotype, compared with mutational heterozygous type AC, has protective effects but lacks statistically significant difference despite its a proximity to 0.05. Combined mutational homozygous CC genotype and wild-type homozygous AA, compared with mutational heterozygous AC genotype, has protective effects. Our meta-analysis suggests no associations between CYP1A1 Ile462Val polymorphism and gastric cancer, but possible associations between CYP1A1 MspI and CYP1A2*1 F polymorphisms and gastric cancer, which needs to be further reinforced or refuted among different ethnicities in well-designed large-scale high-quality studies.

Aryl hydrocarbon receptor as a new therapeutic target for cancer and immune disorders

The aryl hydrocarbon receptor (AhR) was discovered more than three decades ago, and initially was characterized as a transcription factor with a role in xenobiotic metabolism. However, based on subsequent observations that AhR remains active under physiological conditions, exhibits constitutive expression during development, and has a high degree of conservation among species, it was hypothesized that AhR is responsible for functions in addition to its role in detoxification. Correspondingly, recent studies have elucidated novel physiological roles for this ligand-dependent transcription factor that link it to several pathways associated with disease development. In this review, studies are presented that support a role for AhR in cell proliferation, apoptosis, and immune homeostasis, thereby highlighting the therapeutic potential of this receptor for cancer and immune disorders.

Liver hypertrophy: a review of adaptive (adverse and non-adverse) changes--conclusions from the 3rd International ESTP Expert Workshop

Preclinical toxicity studies have demonstrated that exposure of laboratory animals to liver enzyme inducers during preclinical safety assessment results in a signature of toxicological changes characterized by an increase in liver weight, hepatocellular hypertrophy, cell proliferation, and, frequently in long-term (life-time) studies, hepatocarcinogenesis. Recent advances over the last decade have revealed that for many xenobiotics, these changes may be induced through a common mechanism of action involving activation of the nuclear hormone receptors CAR, PXR, or PPARα. The generation of genetically engineered mice that express altered versions of these nuclear hormone receptors, together with other avenues of investigation, have now demonstrated that sensitivity to many of these effects is rodent-specific. These data are consistent with the available epidemiological and empirical human evidence and lend support to the scientific opinion that these changes have little relevance to man. The ESTP therefore convened an international panel of experts to debate the evidence in order to more clearly define for toxicologic pathologists what is considered adverse in the context of hepatocellular hypertrophy. The results of this workshop concluded that hepatomegaly as a consequence of hepatocellular hypertrophy without histologic or clinical pathology alterations indicative of liver toxicity was considered an adaptive and a non-adverse reaction. This conclusion should normally be reached by an integrative weight of evidence approach.

Meta-analysis of the association of CYP1A1 polymorphisms with gastric cancer susceptibility and interaction with tobacco smoking

The association of two cytochrome P4501A1 (CYP1A1) polymorphisms, m1 (T6235C transition) and m2 (A4889G transition), with gastric cancer risk is inconclusive. We conducted a meta-analysis of all available studies to evaluate the potential role of the polymorphisms and their interactions with tobacco smoking in gastric cancer susceptibility. Published literature from PubMed was retrieved by two investigators independently. Fourteen case-control studies with 2,032 gastric cancer cases and 5,099 controls were selected. A fixed effects model or a random-effects model was used to estimate the odds ratio (OR) for the CYP1A1 polymorphisms and the occurrence of gastric cancer. Significant associations between CYP1A1 m1 and m2 polymorphisms and gastric cancer susceptibility were not observed in all genetic models in the overall analyses. Subgroup analyses by ethnicity and source of controls did not reveal significant associations with gastric cancer risk. Stratification analysis by smoking status found that carriers of the heterozygous and homozygous m1 genotypes decreased the susceptibility of gastric cancer among ever-smokers (pooled OR = 0.56, 95 % CI 0.36-0.89, fixed effects). In contrast, the m2 genotypes (G/G and A/G) did not show any relevance to gastric cancer risk among the smoking population (pooled OR = 1.30, 95 % CI 0.84-2.00, fixed effects). Overall, we found that the CYP1A1 polymorphism itself, either m1 or m2, did not represent an independent genetic risk factor influencing gastric cancer. However, subgroup analyses suggest that carriers of the heterozygous and homozygous m1 genotype who are exposed to tobacco smoke have a significantly lower risk of developing gastric cancer. To explain the observed reduction of gastric cancer risk, we proposed a novel hypothesis of "observation bias". This hypothesis is also applicable to explain the combined effects of other genetic polymorphisms and environmental factors on the risk of developing cancers, and the rationality of the hypothesis needs to be further investigated.

Expression patterns and potential roles of SIRT1 in human medulloblastoma cells in vivo and in vitro

Medulloblastoma is a primitive neuroectodermal tumor, which originates in the cerebellum, presumably due to the alterations of some neurogenetic elements. Sirtuin 1 (SIRT1), a class III histone deacetylase (HDAC), regulates differentiation of neuronal stem cells but its status in medulloblastomas remains largely unknown. The current study aimed to address this issue by checking SIRT1 expression in noncancerous cerebellar tissues, medulloblastoma tissues and established cell lines. The roles of SIRT1 in proliferation and survival of UW228-3 medulloblastoma cells were analyzed by SIRT1 small interfering RNA (siRNA) transfection and SIRT1 inhibitor nicotinamide treatment. The results revealed that the frequency of SIRT1 expression in medulloblastoma tissues was 64.17% (77/120), while only one out of seven tumor-surrounding noncancerous cerebellar tissues showed restricted SIRT1 expression in the cells within the granule layer. Of the three morphological subtypes, the rates of SIRT1 detection in the large cell/anaplastic cell (79.07%; 34/43) and the classic medulloblastomas (60.29%; 41/68) are higher than that (22.22%; 2/9) in nodular/desmoplastic medulloblastomas (P<0.01 and P<0.05, respectively). Heterogeneous SIRT1 expression was commonly observed in classic medulloblastoma. Inhibition of SIRT1 expression by siRNA arrested 64.96% of UW228-3 medulloblastoma cells in the gap 1 (G1) phase and induced 14.53% of cells to apoptosis at the 48-h time point. Similarly, inhibition of SIRT1 enzymatic activity with nicotinamide brought about G1 arrest and apoptosis in a dose-related fashion. Our data thus indicate: (i) that SIRT1 may act as a G1-phase promoter and a survival factor in medulloblastoma cells; and (ii) that SIRT1 expression is correlated with the formation and prognosis of human medulloblastomas. In this context, SIRT1 would be a potential therapeutic target of medulloblastomas.

Quantitative assessment of the associations between CYP1A1 polymorphisms and gastric cancer risk

A great number of studies regarding the association between MspI and Ile462Val polymorphisms in the CYP1A1 gene and gastric cancer have been published. However, the results have been inconsistent. In this study, a meta-analysis was performed to investigate the associations. Published literature from PubMed, ISI Web of Science and other Chinese databases were searched for eligible publications. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated using random or fixed effect model. Nine studies (860 cases/2183 controls) for CYP1A1 MspI polymorphism and nine studies (1161 cases/3273 controls) for CYP1A1 Ile462Val polymorphism were included in this meta-analysis. MspI polymorphism was not associated with gastric cancer risk (dominant model, OR = 0.95, 95%CI 0.80-1.14; recessive model, OR = 1.01, 95%CI 0.76-1.35; CC vs. TT, OR = 1.03, 95%CI 0.76-1.41; TC vs. TT, OR = 0.95, 95%CI 0.78-1.15). Similarly, there was no association between Ile462Val polymorphism and gastric cancer risk (dominant model, OR = 0.93, 95%CI 0.79-1.10; recessive model, OR = 1.34, 95%CI 0.90-2.00; GG vs. AA, OR = 1.27, 95%CI 0.84-1.90; AG vs. AA, OR = 0.87, 95%CI 0.71-1.07). In the subgroup analysis, no significant association was found in ever smokers, never smokers, Asians and Caucasians. This meta-analysis suggested that there were no associations between CYP1A1 polymorphisms and gastric cancer.

Effect of combined genetic polymorphisms on lung cancer risk in northern Thai women

Lung cancer is a major cause of cancer-related death in developed countries, and its incidence in developing countries is increasing. In Thailand, cancer incidences differ greatly from region to region, and lung cancer is the most common cancer in the northern Thai population. The polymorphic frequency of 10 genetic susceptibility genes and their association with lung cancer were examined in a northern Thai population: CYP1A1 (MspI), CYP1A1 (Ile462Val), CYP2E1 (PstI), CYP2E1 (DraI), GSTM1, GSTT1, MPO (AciI), OGG1 (Ser326Cys), TP53 (Arg72Pro), and MMP1(AluI). The 173 subjects were 91 lung cancer patients and 82 healthy volunteers. Although no significant association between any single genetic variant and lung cancer risk was observed, when genetic variants were analyzed in combination, a significant effect on lung cancer risk was found for the variant allele in a combination of five genes involved in oxidative stress and inflammatory response: GSTM1 (null), MPO (-463A), OGG1 (326Cys), TP53 (72Pro) (alias p53), MMP1 (2G). With a reference group of individuals carrying at least two wild-type genotypes of these five genes, it was found that an individual carrying three or more variant genotypes is at significantly higher risk of developing lung cancer with the increasing of odds ratios (OR) in concurrence with the number of variant genes. The OR was 2.41 (95% CI = 0.76-7.64), 3.90 (95% CI = 1.23-12.34), and 5.20 (95% CI = 1.31-20.54) for individuals carrying three, four, and five variants, respectively. After stratifying by sex, the OR was higher for women: OR 4.05 (95% CI = 0.44-36.94), 9.00 (95% CI = 0.95-84.89) and 18.00 (95% CI = 1.49-216.62) for three, four, and five variant genotypes, respectively. This augmented effect on lung cancer risk of variant genes involved in oxidative stress and inflammatory response in women with a low prevalence of smoking indicates their modifying effect on other risk factors, such as environmental cigarette smoke, air pollution, radon radiation, or infection of the airway. Confirmation would require further investigations with larger sample sizes.

Aryl hydrocarbon receptor pathway activation enhances gastric cancer cell invasiveness likely through a c-Jun-dependent induction of matrix metalloproteinase-9

Background

Abberant aryl hydrocarbon receptor (AhR) expression and AhR pathway activation are involved in gastric carcinogenesis. However, the relationship between AhR pathway activation and gastric cancer progression is still unclear. In present study, we used 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD), a classic and most potent ligand of AhR, to activate AhR pathway and investigated the effect of AhR pathway activation on human gastric cancer AGS cell invasion and explored the corresponding mechanism.

Results

To determine whether AhR pathway can be activated in AGS cells, we examined the expression of CYP1A1, a classic target gene of AhR pathway, following TCDD exposure. RT-PCR and western blot analysis showed that both CYP1A1 mRNA and protein expression were increased in a dose-dependent manner following TCDD treatment and AhR antagonist resveratrol (RSV) could reverse this TCDD-induced CYP1A1 expression. To determine whether TCDD treatment of AGS cells results in an induction of MMP-9 expression, we detected MMP-9 mRNA using RT-PCR and detected MMP-9 enzymatic activity using gelatin zymography. The results showed that both MMP-9 mRNA expression and enzymatic activity were gradually increased with the concentration increase of TCDD in media and these changes could be reversed by RSV treatment in a dose-dependent manner. To examine whether AhR activation-induced MMP-9 expression and activity in AGS cells results in increased migration and invasion, we performed wound healing migration assay and transwell migration and invasion assay. After TCDD treatment, the migration distance and the migration and invasion abilities of AGS cells were increased with a dose-dependent manner. To demonstrate AhR activation-induced MMP-9 expression is mediated by c-Jun, siRNA transfection was performed to silence c-Jun mRNA in AGS cells. The results showed that MMP-9 mRNA expression and activity in untreated control AGS cells were very weak; After TCDD (10 nmol/L) treatment, MMP-9 mRNA expression and activity were significant increased; This TCDD-induced MMP-9 expression and activity increase could be abolished by c-Jun siRNA transfection.

Conclusion

AhR pathway activation enhances gastric cancer cell invasiveness likely through a c-Jun-dependent induction of MMP-9. Our results provide insight into the mechanism and function of the AhR pathway and its impact on gastric cancer progression.

Potential therapeutic significance of increased expression of aryl hydrocarbon receptor in human gastric cancer

AIM: To determine the functional significance of aryl hydrocarbon receptor (AhR) in gastric carcinogenesis, and to explore the possible role of AhR in gastric cancer (GC) treatment.

METHODS: RT-PCR, real-time PCR, and Western blotting were performed to detect AhR expression in 39 GC tissues and five GC cell lines. AhR protein was detected by immunohistochemistry (IHC) in 190 samples: 30 chronic superficial gastritis (CSG), 30 chronic atrophic gastritis (CAG), 30 intestinal metaplasia (IM), 30 atypical hyperplasia (AH), and 70 GC. The AhR agonist tetrachlorodibenzo-para-dioxin (TCDD) was used to treat AGS cells. MTT assay and flow cytometric analysis were performed to measure the viability, cell cycle and apoptosis of AGS cells.

RESULTS: AhR expression was significantly increased in GC tissues and GC cell lines. IHC results indicated that the levels of AhR expression gradually increased, with the lowest levels in CSG, followed by CAG, IM, AH and GC. AhR expression and nuclear translocation were significantly higher in GC than in precancerous tissues. TCDD inhibited proliferation of AGS cells via induction of growth arrest at the G1-S phase.

CONCLUSION: AhR plays an important role in gastric carcinogenesis. AhR may be a potential therapeutic target for GC treatment.

Omeprazole stimulates the induction of human insulin-like growth factor binding protein-1 through aryl hydrocarbon receptor activation

5-Methoxy-2-{(4-methoxy-3,5-dimethyl-pyridin-2-yl)methylsulfinyl}-3H-benzoimidazole (omeprazole), a benzoimidazole-derived gastric H(+)/K(+)-ATPase proton pump inhibitor (PPI) extensively prescribed for the treatment of gastroesophageal acid reflux disease, can stimulate the expression of CYP1A1 via activation of the human aryl hydrocarbon receptor (hAhR) in an apparent nonligand-binding manner. Here, we have examined the effect of nonclassical, i.e., nonligand binding, AhR activation by omeprazole upon human insulin-like growth factor binding protein (hIGFBP)-1, a secreted phosphoprotein involved in regulation of insulin-like growth factor-I/II bioavailability and mitogenic activity. Analysis of the proximal promoter of the hIGFBP-1 gene reveals the presence of an aryl hydrocarbon binding/dioxin response element (DRE). Quantitative mRNA analysis revealed hIGFBP-1 expression to be responsive to both ligand (TCDD) and nonligand (omeprazole) modes of hAhR activation in the human hepatocarcinoma HepG2 cell line. Furthermore, mutagenesis of the DRE renders the hIGFBP-1 promoter unresponsive to both compounds in HepG2 cells. Likewise, small interfering RNA-mediated hAhR ablation inhibits TCDD and omeprazole-dependent hIGFBP-1 induction, as determined by quantitative mRNA analysis. Cotreatment with cycloheximide further suggests a direct transcriptional role for hAhR at the hIGFBP-1 promoter. Omeprazole exposure prompted a significant increase in both hIGFBP-1 mRNA and secreted protein from HepG2 cells. In addition, we present in vitro evidence indicating that omeprazole at a concentration comparable with that found circulating in subjects undergoing PPI therapy can stimulate the expression of hIGFBP-1. These data demonstrate that activation of hAhR by pharmaceuticals such as omeprazole can alter IGFBP-1 expression and thus may influence IGFBP-1-dependent physiological processes.