Alterations of tumor suppressor and tumor-related genes in the development and progression of gastric cancer

MicroRNA-146a is down-regulated in gastric cancer and regulates cell proliferation and apoptosis

Aberrant expression of microRNA-146a (miR-146a) has been reported to be involved in development and progression in various types of cancers, but its role in gastric cancer has not been fully elucidated. The purpose of this study was to investigate the levels of miR-146a expression and its function in human gastric cancer. Quantitative real-time polymerase chain reaction was used to detect the levels of miR-146a expression in gastric cancer tissue samples and cell lines. The cell growth rate of MKN-45 gastric cancer cells transfected with miR-146a mimics was examined by MTT assay. The effects of miR-146a on cell cycle and apoptosis were assessed by FACS analyses in MKN-45 cells. Thirty-six of 43 gastric cancer tissue samples (84%) showed decreased expression of miR-146a. We found low expression of miR-146a was correlated with increased tumor size (P = 0.006) and poor differentiation (P = 0.010) in gastric cancer. Overall survival time of patients with high miR-146a expression was significantly longer than that of patients with low expression of miR-146a (P = 0.011). The MTT assay showed that introduction of miR-146a inhibited cell proliferation in MKN-45 cells (P < 0.05). The proportion of apoptotic cells induced by transfection of miR-146a mimics were greater than that induced by transfection of the negative control mimics (11.9 vs. 5.9%). Our results suggested that miR-146a has potential as a novel suppressor gene in gastric cancer and its down-regulation may promote the progression of gastric cancer.

Down-regulation of NDRG2 gene expression in human colorectal cancer involves promoter methylation and microRNA-650

The expression of N-myc downstream-regulated gene 2 (NDRG2) is present in normal tissues but low or undetectable in various cancers and thus poses a potential tumor suppressor gene. However, the expression of NDRG2 in colorectal tissues remains unknown. Here, our results showed that NDRG2 was down-regulated in colorectal cancer compared to benign colorectal tissues by using immunohistochemical staining and semi-quantitative RT-PCR analyses. Bisulfite sequencing analysis showed that the reduced NDRG2 expression was accompanied by de novo DNA methylation at the NDRG2 promoter. We also found that microRNA-650 (miR-650) targets a homologous DNA region in the promoter region of the NDRG2 gene and represses its expression at the transcriptional level. Reporter assay with 3'untranslated region of NDRG2 cloned downstream of the luciferase gene showed reduced luciferase activity in the presence of miR-650, providing strong evidence that miR-650 is a direct regulator of NDRG2. In conclusion, these results suggest that NDRG2 expression is regulated by promoter methylation and miR-650 in human colorectal cancer cells, and endogenous small noncoding RNA induced control of transcription may be a potential system for expressional regulation in human colorectal cancer cells.

Hypermethylation of tumor-related genes in Tunisian patients with gastric carcinoma: clinical and biological significance

BACKGROUND

Promoter hypermethylation is an alternative mechanism of gene silencing in cancers including gastric carcinoma (GC). Its affects genes with crucial functions as tumor suppressor.

METHODS

DNA methylation in the promoter of P16INK4a, DAPK, retinoic acid receptor β (RARβ2), RASSF1A, and CDH1 genes was investigated in 79 Tunisian patients with GC using methylation-specific PCR.

RESULTS

The methylation frequencies vary from 31.6% for P16INK4a to 65.8% for RARβ2. Hypermethylation of DAPK and CDH1 was associated with tumor grade and age (P = 0.04 and 0.034) respectively, while hypermethylation of RASSF1A correlated with TNM stage (P = 0.027). The distribution of the methylated DNA at P16INK4a, DAPK, and CDH1 promoters were different in the intestinal and diffuse histotypes of GC according to TNM. Moreover, the survival rate of patients with P16INK4a methylated status was shorter than that of patients with the unmethylated status (P log rank = 0.009). On the other hand, the hypermethylation of RARβ2 correlated with COX-2 expression (P = 0.001).

CONCLUSION

We showed that methylation of P16INK4a is predictive of poor prognosis and could be a useful marker. Moreover, the association between RARβ2 methylation and COX-2 expression suggests a functional link between these two proteins in gastric carcinogenesis.

Clinicopathological and patient characteristics of early gastric neoplasia endoscopically resected with loss of Mlh1 expression

Hypermethylation of the promoter region of the MLH1 gene leads to loss of Mlh1 protein expression and plays a key role in the development of gastric cancer. Little is known about the association between Mlh1 expression and the clinicopathological and patient characteristics in early gastric neoplasia, particularly in endoscopically resected tumors. Immunohistochemistry was used to examine Mlh1 expression in 140 early gastric neoplasias obtained by endoscopic resection and comprising 31 gastric adenomas (GAs) and 109 early gastric cancers (EGCs), and compared them to corresponding clinicopathological and patient data. P53 expression and phenotypic profiles were also analyzed. The rate of reduced Mlh1 expression and P53 overexpression was 9.6 and 6.5% in GAs, and 27.5 and 27.5% in EGCs, respectively. In elderly patients (≥65 years of age), the aberrant expression of Mlh1 in EGCs was more significant in female than in male patients (59.9 vs. 29.8%; P=0.016). In addition, the frequency of aberrant Mlh1 expression in EGCs increased significantly in patients with oncological family histories and elevated gross type (P=0.033 and P=0.04, respectively). Moreover, a significant correlation was observed among aberrant Mlh1, P53-negative and HGM expression. The present findings suggest that loss of Mlh1 expression is associated with age, gender, oncological family history and tumor growth pattern in EGC. Patient and tumor characteristics are key factors in the screening, surveillance and diagnosis of early gastric neoplasia, particularly in elderly individuals.

Up-regulation of activation-induced cytidine deaminase causes genetic aberrations at the CDKN2b-CDKN2a in gastric cancer

BACKGROUND & AIMS

The DNA/RNA editing enzyme activation-induced cytidine deaminase (AID) is mutagenic and has been implicated in human tumorigenesis. Helicobacter pylori infection of gastric epithelial cells leads to aberrant expression of AID and somatic gene mutations. We investigated whether AID induces genetic aberrations at specific chromosomal loci that encode tumor-related proteins in gastric epithelial cells.

METHODS

Human gastric epithelial cell lines that express activated AID and gastric cells from AID transgenic mice were examined for DNA copy number changes and nucleotide alterations. Copy number aberrations in stomach cells of H pylori-infected mice and gastric tissues (normal and tumor) from H pylori-positive patients were also analyzed.

RESULTS

In human gastric cells, aberrant AID activity induced copy number changes at various chromosomal loci. In AID-expressing cells and gastric mucosa of AID transgenic mice, point mutations and reductions in copy number were observed frequently in the tumor suppressor genes CDKN2A and CDKN2B. Oral infection of wild-type mice with H pylori reduced the copy number of the Cdkn2b-Cdkn2a locus, whereas no such changes were observed in the gastric mucosa of H pylori-infected AID-deficient mice. In human samples, the relative copy numbers of CDKN2A and CDKN2B were reduced in a subset of gastric cancer tissues compared with the surrounding noncancerous region.

CONCLUSIONS

H pylori infection leads to aberrant expression of AID and might be a mechanism of the accumulation of submicroscopic deletions and somatic mutations in gastric epithelial cells. AID-mediated genotoxic effects appear to occur frequently at the CDKN2b-CDKN2a locus and contribute to malignant transformation of the gastric mucosa.

Molecular analysis of gastric differentiated-type intramucosal and submucosal cancers

Identification of the molecular characteristics of intramucosal (IMCs) and submucosal cancers (SMCs) is essential to our understanding of early gastric carcinogenesis. However, little is known regarding the differences between the 2 lesions. One hundred and forty-eight patients with primary early gastric cancer [IMC, 106; SMC, 42] were characterized for expression of cell cycle-related proteins and loss of heterozygosity (LOH). We also examined microsatellite instability (MSI) and methylation status. For LOH and methylation studies, we used a panel of 17 microsatellite markers (3p, 4p, 5q, 9p. 13q, 17p, 18q and 22q) and promoter regions of 9 genes (MLH-1, RUNX3, p16, HPP1, RASSF2A, SFRP1, DKK-1, ZFP64 and SALL4) that are frequently altered or methylated in gastric cancers. Overexpression of p53 and cyclin D1 was observed in SMC. In addition, low expression of p27 was more frequent in SMC than in IMC. Frequencies of 4p, 9p, 13q and 22q were significantly higher in SMC than in IMC. The SALL4 gene was frequently methylated in SMC compared with IMC. However, other gene methylations were common in both IMC and SMC. The frequency of LOH-high status/methylation-low status was significantly higher in SMC than in IMC. However, LOH-low status/methylation-high status in SMC was more frequently found in IMC. Our data confirm that methylation of cancer-related genes plays a major role in the development of IMCs. Importantly, the results also show that gastric submucosal progression is characterized by the accumulation of specific genetic alterations. In addition, changes of cell cycle-related proteins are associated with cancer progression.

TSLC1 tumour-suppressor gene expression in canine mast cell tumours

Tumour suppressor in lung cancer-1 (TSLC1) is a tumour-suppressor gene coding for an adhesion molecule that is expressed by mast cells. Reduced TSLC1 expression is associated with a poor prognosis in several human tumours, and this study sought to investigate if TSLC1 expression could be used to predict outcome in dogs with mast cell tumours (MCTs). Sections of MCTs of different tumour grades from 45 dogs (Group 1) were immunohistochemically assessed for TSLC1 and Ki67 expression. In addition, 35 intermediate-grade MCTs (Group 2) from dogs with known clinical follow-up were immunohistochemically stained for TSLC1 and Ki67. The TSLC1 staining intensity was found to strongly inversely correlate with tumour grade for Group 1 (P = 0.002857). For Group 2 there was a trend towards dogs with lower TSLC1 scores being more likely to die from MCT-related disease (P = 0.058). The intensity of TSLC1 staining inversely correlated with Ki67 expression for both groups.

Genomic profiling of cell-free DNA in blood and bone marrow of prostate cancer patients

PURPOSE

To advance the characterization of tumor-associated cell-free DNA in blood and bone marrow (BM), a rapid profiling method using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) was established. MS-MLPA detects genetic and epigenetic aberrations of 37 tumor suppressor genes (TSG) in a single reaction and might, therefore, avoid the cumbersome single gene analyses.

METHODS

The validity of MS-MLPA for using cell-free plasma DNA was assessed by analyzing blood and BM samples of 91 patients with prostate cancer. As reference analyses, the methylation patterns of 4 genes (CD44, E-cadherin, CDKN2A and PTEN) chosen from the TSG set of the MS-MLPA kit were investigated in single reactions by sodium bisulfite DNA sequencing.

RESULTS

Copy number changes and aberrant DNA methylation of 37 circulating TSG could be analyzed in BM and blood of 30 and 13 of the 91 patients, respectively, whereas the DNA content in the remaining samples was too low (<50 ng/μl of eluted DNA). The copy number of 28 of the 37 TSG was altered, and most changes were found for APC, CHFR, TP73 and GSTP1 genes in BM plasma. Statistical evaluations showed an association between copy number changes of TP73 and a positive resection margin of the prostate (p = 0.05). Both MS-MLPA and sodium bisulfite sequencing techniques showed that all genes were unmethylated.

CONCLUSIONS

Our results demonstrate the potential and limitation of MS-MLPA for multiplex characterization of TSG in cell-free plasma DNA as a new non-invasive approach to obtain information on the molecular tumor biology of individual cancer patients.

Aberrant methylation impairs low density lipoprotein receptor-related protein 1B tumor suppressor function in gastric cancer

DNA methylation plays a significant role in tumor progression. In this study, we used CpG microarray and differential methylation hybridization approaches to identify low density lipoprotein receptor-related protein 1B (LRP1B) as a novel epigenetic target in gastric cancer. LRP1B was hypermethylated in four gastric cancer cell lines, and low LRP1B mRNA expression was associated with high methylation levels in gastric cancer cell lines. Addition of a DNA methylation inhibitor (5-Aza-dC) restored the mRNA expression of LRP1B in these cell lines, indicating that DNA methylation is involved in regulating LRP1B expression. In 45 out of 74 (61%) clinical samples, LRP1B was highly methylated; LRP1B mRNA expression was significantly lower in 15 out of 19 (79%, P < 0.001) gastric tumor tissues than in corresponding adjacent normal tissues. In addition, ectopic expression of mLRP1B4 in gastric cancer cell lines suppressed cell growth, colony formation and tumor formation in nude mice. These results collectively indicate that LRP1B is a functional tumor suppressor gene in gastric cancer and that is regulated by DNA methylation.

CDKN2A promoter methylation is related to the tumor location and histological subtype and associated with Helicobacter pylori flaA(+) strains in gastric adenocarcinomas

Promoter hypermethylation of CDKN2A (p16INK4A protein) is the main mechanism of gene inactivation. However, its association with Helicobacter pylori infection is a controversial issue. Therefore, we examined a series of gastric adenocarcinomas to assess the association between p16INK4A inactivation and H. pylori genotype (vacA, cagA, cagE, virB11 and flaA) according to the location and histological subtype of the tumors. p16INK4A expression and CDKN2A promoter methylation were found in 77 gastric adenocarcinoma samples by immunohistochemistry and methylation-specific PCR, respectively. Helicobacter pylori infection and genotype were determined by PCR. A strong negative correlation between immunostaining and CDKN2A promoter region methylation was found. In diffuse subtype tumors, the inactivation of p16INK4A by promoter methylation was unique in noncardia tumors (p=0.022). In addition, H. pylori-bearing flaA was associated with non-methylation tumors (p=0.008) and H. pylori strain bearing cagA or vacAs1m1 genes but without flaA was associated with methylated tumors (p=0.022 and 0.003, respectively). Inactivation of p16INK4A in intestinal and diffuse subtypes showed distinct carcinogenic pathways, depending on the tumor location. Moreover, the process of methylation of the CDKN2A promoter seems to depend on the H. pylori genotype. The present data suggest that there is a differential influence and relevance of H. pylori genotype in gastric cancer development.

MicroRNA-650 targets ING4 to promote gastric cancer tumorigenicity

MicroRNAs (miRNAs) are non-coding RNAs that regulate the expression of target mRNAs. Altered expression of specific miRNAs in human gastric cancer progression has been reported; however, the role of miR-650 in gastric cancer is poorly understood. In this study, we show that miR-650 is involved in lymphatic and distant metastasis in human gastric cancer, and we find that ectopic expression of miR-650 promotes tumorigenesis and proliferation of gastric cancer cells. A luciferase reporter assay demonstrates that Inhibitor of Growth 4 (ING4) is a direct target of miR-650. Collectively, our study demonstrates that over-expression of miR-650 in gastric cancer may promote proliferation and growth of cancer cells, at least partially through directly targeting ING4. These findings help clarify the molecular mechanisms involved in gastric carcinogenesis and indicate that miR-650 modulation may be a bona fide miRNA-based treatment of gastric cancer.

The presence of JC virus in gastric carcinomas correlates with patient's age, intestinal histological type and aberrant methylation of tumor suppressor genes

JC virus (JCV) is a neurotropic polyomavirus and the causative agent of progressive multifocal leukoencephalopathy. A role for JCV in gastrointestinal malignancies has been recently suggested. This study was carried out to determine the prevalence of polyomaviruses including JCV, BKV and SV40 in gastric cancers in Tunisia and to determine the clinicopathological characteristics of virus-associated gastric carcinomas. The presence of polyomaviruses DNA sequences was surveyed in 61 cases of primary gastric carcinomas and in 53 paired non-tumor gastric mucosa by PCR. Findings were correlated to clinicopathological parameters, p53 expression and methylation status of 11 tumor-related genes. Using PCR assays, JCV T-antigen sequence was more frequently detected in gastric carcinomas than in non-tumor gastric mucosa (26 vs 6%, P=0.03), while those of SV40 and BKV were not detected in any cases. Correlation analysis showed that JCV had higher frequency in patients older than 55 years (P=0.034) and in the intestinal histological type (P=0.04). With regard to methylation status, P16 and P14 showed significantly higher methylation frequencies in JCV-positive gastric carcinomas than in JCV-negative cases (P=0.007 and P=0.003, respectively). Moreover, the mean of the methylation index was significantly higher in JCV-positive than in JCV-negative cases (P=0.024). In multivariate logistic regression analysis, age of patients and the methylation index are only the two independent factors associated with JCV infection. Kaplan-Meier survival analysis showed a trend toward better survival for JCV-associated gastric carcinomas patients (log-rank, P=0.11). Our study suggests a role of JCV as cofactor in the pathogenesis of the intestinal type of gastric carcinomas in older persons.

MAGE-A antigens in lesions of the oral mucosa

Oral squamous cell carcinoma develops continuously out of predamaged oral mucosa. For the physician and pathologist, difficulties arise in distinguishing precancerous from cancerous lesions. MAGE-A antigens are tumor antigens that are found solely in malignant transformed cells. These antigens might be useful in distinguishing precancerous from cancerous lesions. The aim of this study was to verify this assumption by comparing MAGE-A expression in benign, precancerous, and cancerous lesions of the oral mucosa. Retrospectively, biopsies of different oral lesions were randomly selected. The lesions that were included are 64 benign oral lesions (25 traumatic lesions (oral ulcers), 13 dental follicles, and 26 epulis), 26 oral lichen planus, 123 epithelial precursor lesions (32 epithelial hyperplasia found in leukoplakias, 24 epithelial dysplasia found in leukoplakias, 26 erythroplasia with oral epithelial dysplasia, and 41 carcinomas in situ in erythroleukoplakias). The lesions were immunohistochemically stained with the poly-MAGE-A antibody 57B, and the results were compared. Biopsies of oral lichen planus, oral ulcers, dental follicles, epulis, and leukoplakia without dysplasia showed no positive staining for MAGE-A antigens. Leukoplakia with dysplasia, dysplasia, and carcinomata in situ displayed positive staining in 33%, 65%, and 56% of the cases, respectively. MAGE-A antigens were not detectable via immunohistochemistry in benign lesions of the oral mucosa. The staining rate of dysplastic precancerous lesions or malignant lesions ranged from 33% to 65%. The MAGE-A antigens might facilitate better differentiation between precancerous and cancerous lesions of the oral mucosa.

Development of the human cancer microRNA network

BACKGROUND

MicroRNAs are a class of small noncoding RNAs that are abnormally expressed in different cancer cells. Molecular signature of miRNAs in different malignancies suggests that these are not only actively involved in the pathogenesis of human cancer but also have a significant role in patients survival. The differential expression patterns of specific miRNAs in a specific cancer tissue type have been reported in hundreds of research articles. However limited attempt has been made to collate this multitude of information and obtain a global perspective of miRNA dysregulation in multiple cancer types.

RESULTS

In this article a cancer-miRNA network is developed by mining the literature of experimentally verified cancer-miRNA relationships. This network throws up several new and interesting biological insights which were not evident in individual experiments, but become evident when studied in the global perspective. From the network a number of cancer-miRNA modules have been identified based on a computational approach to mine associations between cancer types and miRNAs. The modules that are generated based on these association are found to have a number of common predicted target onco/tumor suppressor genes. This suggests a combinatorial effect of the module associated miRNAs on target gene regulation in selective cancer tissues or cell lines. Moreover, neighboring miRNAs (group of miRNAs that are located within 50 kb of genomic location) of these modules show similar dysregulation patterns suggesting common regulatory pathway. Besides this, neighboring miRNAs may also show a similar dysregulation patterns (differentially coexpressed) in the cancer tissues. In this study, we found that in 67% of the cancer types have at least two neighboring miRNAs showing downregulation which is statistically significant (P < 10-7, Randomization test). A similar result is obtained for the neighboring miRNAs showing upregulation in specific cancer type. These results elucidate the fact that the neighboring miRNAs might be differentially coexpressed in cancer tissues as that of the normal tissue types. Additionally, cancer-miRNA network efficiently detect hub miRNAs dysregulated in many cancer types and identify cancer specific miRNAs. Depending on the expression patterns, it is possible to identify those hubs that have strong oncogenic or tumor suppressor characteristics.

CONCLUSIONS

Limited work has been done towards revealing the fact that a number of miRNAs can control commonly altered regulatory pathways. However, this becomes immediately evident by accompanying the analysis of cancer-miRNA relationships in the proposed network model. These raise many unaddressed issues in miRNA research that have never been reported previously. These observations are expected to have an intense implication in cancer and may be useful for further research.

Contrasting activity of Hedgehog and Wnt pathways according to gastric cancer cell differentiation: relevance of crosstalk mechanisms

Gastric cancer displays different biological behaviors according to histological differentiation. The different biological behavior might involve the activation of distinct signaling pathways necessary for the growth and survival of cancer cells in gastric cancer. We investigated the differentiation-related signal interaction between Hedgehog and Wnt pathways in gastric cancer cells. Differentiation of gastric cancer cells was induced by sodium butyrate. The sonic Hedgehog (SHH) signal expressions were increased during cellular differentiation. In contrast, the expression of Wnt signaling was decreased during differentiation. Ectopic expression of glioma-associated oncogene-1 (GLI1) increased the level of secreted frizzled related protein-1 (SFRP1) transcript, whereas inhibition of GLI1 reduced the level of SFRP1 transcript. ChIP assay showed that GLI1 induced the transcriptional regulation of SFRP1 gene expression. Ectopic expression of GLI1 decreased the nuclear beta-catenin staining, but the inhibition of GLI1 induced the reversal of nuclear beta-catenin overexpression. Ectopic expression of beta-catenin also decreased the expression of GLI1 in the butyrate treated cancer cells. SHH and GLI1 immunoexpression was greater in well differentiated gastric cancer tissues compared to poorly differentiated tissues, and nuclear beta-catenin immunoexpression was lower in well differentiated compared to poorly differentiated tissues. The SHH and Wnt pathways are differentially involved according to gastric cancer cell differentiation.

Helicobacter pylori and EBV in gastric carcinomas: Methylation status and microsatellite instability

AIM: To verify the methylation status of CDH1, DAPK, COX2, hMLH1 and CDKN2A genes and to evaluate their association with Helicobacter pylori (H. pylori)-cagA⁺ and Epstein Barr virus (EBV) infections in gastric adenocarcinomas.

METHODS: Methylation-specific PCR (MSP) assay was performed in 89 primary gastric carcinomas (intestinal and diffuse types). Microsatellite instability (MSI) analysis was performed using the BAT26 primer set and PCR products were analyzed with the ABI PRISM 3100 Genetic Analyzer using Genescan 3.7 software (Applied Biosystems). Detection of H. pylori and genotyping were performed by PCR, using specific primers for ureaseC and cagA genes. The presence of EBV was assessed by in situ hybridization. Statistical analyses were performed using the χ² or Fisher’s exact test.

RESULTS: The most frequent hypermethylated gene was COX-2 (63.5%) followed by DAPK (55.7%), CDH1 (51%), CDKN2A (36%) and hMLH1 (30.3%). Intestinal and diffuse adenocarcinomas showed different methylation profiles and there was an association between methylation of E-CDH1 and H. pylori-cagA⁺ in the intestinal adenocarcinoma type. MSI was correlated with hMLH1 methylation. There was an inverse correlation between DAPK hypermethylation and MSI.

CONCLUSION: We found a strong association between CDH1 methylation and H. pylori-cagA⁺ in intestinal-type gastric cancer, association of MSI and better prognosis and an heterogeneous COX-2 overexpression.

Evaluation of radiation-induced chromosome instability in subjects with a family history of gastric cancer

Gastric cancer (GC) shows a familiar predisposition which is largely unexplained. In this study the hypothesis that radiation sensitivity is implicated in the familiar predisposition to GC was investigated by means of the cytokinesis-block micronucleus assay. Data indicate that a family history of GC is not associated with any of the biomarkers investigated and does not interact with the demographic variables considered. When study subjects were dichotomized around the median age, a significant prevalence of micronuclei was observed in older subjects. Age and both spontaneous and radiation-induced micronuclei were linearly correlated. The effect of age was not modified by gender or smoking habits.

Cancer proteomics by quantitative shotgun proteomics

A major scientific challenge at the present time for cancer research is the determination of the underlying biological basis for cancer development. It is further complicated by the heterogeneity of cancer's origin. Understanding the molecular basis of cancer requires studying the dynamic and spatial interactions among proteins in cells, signaling events among cancer cells, and interactions between the cancer cells and the tumor microenvironment. Recently, it has been proposed that large-scale protein expression analysis of cancer cell proteomes promises to be valuable for investigating mechanisms of cancer transformation. Advances in mass spectrometry technologies and bioinformatics tools provide a tremendous opportunity to qualitatively and quantitatively interrogate dynamic protein-protein interactions and differential regulation of cellular signaling pathways associated with tumor development. In this review, progress in shotgun proteomics technologies for examining the molecular basis of cancer development will be presented and discussed.

Down-regulated miR-9 and miR-433 in human gastric carcinoma

Background

MircoRNAs(miRNAs) are short, endogenously non-coding RNAs. The abnormal expression of miRNAs may be valuable for the diagnosis and treatment of tumors.

Methods

To screening the special miRNAs in gastric carcinoma, expression level of miRNAs in gastric carcinoma and normal gaster samples were detected by miRNA gene chip. Then, the expressions of miR-9 and miR-433 in gastric carcinoma tissue and SGC7901 cell line were validated by qRT-PCR. GRB2 and RAB34, targets of miR-433 and miR-9 respectively, were detected by Western blot.

Results

We found 19 miRNAs and 7 miRNAs were down-regulated and up-regulated respectively. Compared with normal gaster samples, our data showed that miR-9 and miR-433 were down-regulated in gastric carcinoma. Meanwhile, we also found that miR-433 and miR-9 regulated the expression levels of GRB2 and RAB34 respectively.

Conclusion

Our data show miR-9 and miR-433 was down-regulated in gastric carcinoma. The targets of miR-433 and miR-9 were tumor-associated proteins GRB2 and RAB34 respectively. This result provided the related information of miRNAs in gastric carcinoma.

Checkpoint with forkhead-associated and ring finger promoter hypermethylation correlates with microsatellite instability in gastric cancer

AIM: To examine the methylation status of the promoter region of the checkpoint with forkhead-associated and ring finger (CHFR) and microsatellite mutator status in 59 primary gastric cancers.

METHODS: We investigated the promoter methylation of CHFR in 59 cases of gastric cancer using methylation-specific PCR. Five microsatellite loci were analyzed using high-intensity microsatellite analysis reported previously, and p53 gene mutations were investigated by direct sequencing.

RESULTS: Twenty cases (33.9%) showed promoter methylation and no relation was observed with the clinicopathological factors. We found that the promoter methylation of CHFR was frequently accompanied with microsatellite instability (MIN). Seven of 20 (35.0%) cases showed MIN in hypermethylation of the CHFR tumor, while three of 39 (7.7%) cases showed MIN in the non-methylated CHFR tumor (P < 0.01). However, we failed to find any relationship between CHFR methylation and p53 mutation status.

CONCLUSION: The coordinated loss of both the mitotic check point function and mismatch repair system suggests the potential to overcome the cell cycle check point, which may lead to an accumulation of mutations. However, the p53 mutation was not related to hypermethylation of the CHFR promoter and MIN, which indicates that an abnormality in p53 occurs as an independent process from the mismatch repair deficiency in carcinogenesis.

Expression and promoter methylation status of mismatch repair gene hMLH1 and hMSH2 in epithelial ovarian cancer

OBJECTIVE

The purpose of this study is to determine the relationship between methylation and loss of hMLH1 and hMSH2 expression in ovarian cancer.

METHODS

We examined the methylation status of hMLH1 and hMSH2 promoter region by methylation-specific polymerase chain reaction (MSP) in 56 primary ovarian cancer tissues and 20 normal ovarian tissues, the relationship between the methylation status of these two genes and clinicopathological characteristics were analysed. We then treated SKOV3 and 3AO ovarian cancer cell lines with the demethylating agent 5-aza-2'-deoxycytidine (5-aza-dc). The hMLH1 and hMSH2 methylation was further assessed by MSP, and their mRNA expression was compared by reverse transcription polymerase chain reaction (RT-PCR) before and after 5-aza-dc treatment in these two cell lines.

RESULTS

The methylation frequency of hMLH1 and hMSH2 was 30.4% (17 of 56) and 51.7% (29 of 56) in ovarian cancers, respectively, while no methylation was detected in normal ovarian tissues (P=0.015). There is a significant correlation between hMLH1 promoter hypermethylation and histological grade (P=0.028) as well as lymphatic metastasis (P=0.003). Methylation of hMSH2 correlated with histological grade (P=0.035) and lymphatic metastasis (P=0.015). Besides, the methylation rates of hMSH2 were significantly higher in endometrioid adenocarcinoma tissues than in other pathological types of ovarian cancer. After 5-aza-dc treatment, the expression of hMLH1 and hMSH2 was reversed in two cell lines.

CONCLUSION

Our results indicate that promoter hypermethylation is an important mechanism for loss of hMLH1 and hMSH2 expression in human ovarian cancer and may be a potential prognostic factor in ovarian cancer.

Biological significance of promoter hypermethylation of tumor-related genes in patients with gastric carcinoma

BACKGROUND

DNA promoter hypermethylation is a potential means of inactivating tumor-related genes in several types of cancers.

METHODS

We investigated aberrant promoter hypermethylation of eleven tumor-related genes in 68 gastric carcinomas and 53 adjacent non-tumor tissues using methylation-specific PCR, and we correlated the findings with clinico-pathological features.

RESULTS

In gastric carcinoma tissues, hypermethylation frequencies of the investigated genes were 61.8% for RASSFIA, 52.9% for APC, 36.8% for MGMT, 30.9% for DAPK, 29.4% for P16, 26.5% for P14, 25% for SHP1, 23.5% for RAR-beta2, 20.6% for GSTP1, 13.2% for TIMP3, and 8.8% for hMLH1. For adjacent non-tumor samples, the frequencies of methylation were respectively 5.7, 37.7, 5.7, 24.5, 3.8, 5.7, 20.8, 5.7, 1.9, 3.8, and 0%. Hypermethylation of P16 correlates with intestinal subtype and cardiac location (P = 0.044 and P = 0.004, respectively), whereas methylation of GSTP1 correlates with diffuse subtype (P = 0.050). Methylation of SHP1 was associated with EBV infection (P = 0.014). Methylation of APC and RAR-beta2 genes were significantly associated with improved patient's outcome (P = 0.007 and P = 0.042, respectively).

CONCLUSIONS

Our data suggest that methylation of multiple genes may be involved in the pathogenesis and correlated with the prognosis of gastric carcinomas.

Loss of Rad51c leads to embryonic lethality and modulation of Trp53-dependent tumorigenesis in mice

RecA/Rad51 protein family members (Rad51, Rad51b, Rad51c, Rad51d, Xrcc2, and Xrcc3) are essential for DNA repair by homologous recombination, and their role in cancers has been anticipated. Here we provide the first direct evidence for a tumor suppressor function for a member of the Rad51 family. We show that Rad51c deficiency leads to early embryonic lethality, which can be delayed on a Trp53-null background. To uncover the role of Rad51c in tumorigenesis, we have exploited the fact that Rad51c and Trp53 are both closely located on the mouse chromosome 11. We have generated double heterozygous (DH) mice carrying mutant alleles of both genes either on different (DH-trans) or on the same chromosome (DH-cis), the latter allowing for a deletion of wild-type alleles of both genes by loss of heterozygosity. DH-trans mice, in contrast to DH-cis, developed tumors with latency and spectrum similar to Trp53 heterozygous mice. Strikingly, Rad51c mutation in DH-cis mice promoted the development of tumors of specialized sebaceous glands and suppressed tumors characteristic of Trp53 mutation. In addition, DH-cis females developed tumors significantly earlier than any other group.

Reprimo as a potential biomarker for early detection in gastric cancer

PURPOSE

Gastric cancer is a curable disease if diagnosed at early stage. However, most cases are diagnosed at advanced stage because of the lack of screening programs. Therefore, the identification of plasma biomarkers for early detection is necessary.

EXPERIMENTAL DESIGN

To search for these biomarkers, we evaluated the DNA methylation patterns of 24 genes by Methylation-specific PCR in primary tissues from 32 retrospectively collected gastric cancer cases (testing group). Correlation between methylation and gene expression was evaluated in the MKN-45 cell line after treatment with 5-aza-2'-deoxycytidine. The most frequently hypermethylated genes were next evaluated in primary tissues and plasma samples from 43 prospectively collected gastric cancer cases as well as plasma samples from 31 asymptomatic age- and gender-matched controls (validation group).

RESULTS

In the testing group, 11 genes were hypermethylated in at least 50% of cases (APC, SHP1, E-cadherin, ER, Reprimo, SEMA3B, 3OST2, p14, p15, DAPK, and p16). Eight genes (BRCA1, p73, RARbeta, hMLH1, RIZI, RUNX3, MGMT, and TIMP3) were statistically associated with a particular variant of gastric cancer, the signet-ring cell type (P = 0.03). Seven genes (APC, SHP1, E-cadherin, ER, Reprimo, SEMA3B, and 3OST2) were next evaluated in the validation group. We confirm the high frequency of methylation in primary tumors for all seven genes. However, only APC and Reprimo were frequently methylated in pair plasma samples. In asymptomatic controls, only Reprimo was infrequently methylated in comparison with plasma from gastric cancer cases (P < 0.001).

CONCLUSION

Our results identified specific methylation profile associated to signet-ring cell-type histology and aberrant hypermethylation of Reprimo as a potential biomarker for early detection of gastric cancer.

Expression of cell adhesion molecule CD44 in gastric adenocarcinoma and its prognostic importance

AIM: To evaluate the relation of cluster of differentiation 44 (CD44) expression with clinicopathological features of gastric adenocarcinoma, and also its effect on prognosis with an emphasis on the differences between intestinal and diffuse types.

METHODS: From 2000 to 2006, 100 patients with gastric adenocarcinoma, who had undergone total or subtotal gastrectomy without any prior treatment, were studied. Haematoxylin & eosin (HE) staining was used for histological evaluation, including the type (Lauren’s classification) and grading of the tumor. The expression of CD44 in the gastric adenocarcinoma mucosa and the adjacent mucosa were determined by immunohistochemistry. The survival analysis was obtained using the Kaplan-Meier test.

RESULTS: Of 100 patients, 74 (74%) patients were male. The tumors were categorized as intestinal type (78%) or diffuse type (22%). Sixty-five percent of patients were CD44-positive. CD44 expression was not detected in normal gastric mucosa. Rather, CD44 was more commonly expressed in the intestinal subtype (P = 0.002). A significant relation was seen between the grade of tumor and the expression of CD44 (P = 0.014). The survival analysis showed a poor prognosis of patients with CD44-positive tumors (P = 0.008); and this was more prominent in the intestinal (P = 0.001) rather than diffuse type.

CONCLUSION: Cell adhesion molecule CD44 is highly expressed in gastric adenocarcinoma. CD44 expression is correlated with a poor prognosis in patients with the intestinal type of gastric adenocarcinoma. CD44 can, therefore, be utilized as a prognostic marker for this group of patients.

Early gastric cancer shows different associations with adipose tissue volume depending on histological type

BACKGROUND

Visceral obesity is known to be a risk factor for diabetes and cardiovascular disease. Cancer of the gastric cardia has been shown to have a close association with obesity in Western countries. In order to examine the possible relationship between fat volume and the development of gastric cancer (GC), we quantified visceral and subcutaneous fat areas of computed tomography (CT) images of patients with early GC.

METHODS

A total of 210 patients who underwent endoscopic resection or surgical gastrectomy and whose disease was pathologically diagnosed as early GC were investigated for total fat area (TFA), visceral fat area (VFA), and subcutaneous fat area (SFA) with Fat Scan software, using a CT slice at the umbilical level, and the relationships of these findings with clinical and pathological data were analyzed. The same analysis was performed in 147 patients with early colorectal cancer (CRC).

RESULTS

TFA, VFA, and SFA values in GC patients were not significantly different from the values in CRC patients. These values did not differ with the location of the GC. However, patients with undifferentiated-type GC had significantly smaller VFAs and SFAs than those with differentiated-type GC. Among the patients with undifferentiated GC, TFA and SFA values in the patients with submucosal cancer were significantly smaller than those in the patients with mucosal cancer.

CONCLUSION

GC has different associations with adipose tissue volume according to its histological type. As compared with differentiated GC, lower adipose tissue volume may be a preferential environment for the development and progression of undifferentiated GC.

Suppression of gastric cancer growth by baculovirus vector-mediated transfer of normal epithelial cell specific-1 gene

AIM: To study the inhibitory effect of baculovirus-mediated normal epithelial cell specific-1 (NES1) gene therapy on gastric cancer (GC) in vitro and in vivo.

METHODS: We first constructed recombinant baculovirus vectors and then transfected them into gastric cancer cells (SGC-7901). Efficiency of the baculovirus for gene transfer into SGC-7901 cells and cell growth curves were detected by fluorescence microscopy, Western blot and 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay in vitro, respectively. The therapeutic effect of this gene therapy on GC was confirmed in xenografted nude mice. Tumor growth was determined by tumor volume, and expression of NES1 in tumor was analyzed by immunohistochemistry.

RESULTS: Baculovirus vectors were successfully transfected into SGC-7901 cells. SGC-7901 cells transfected with the NES1 gene inhibited cell growth. In the Bac-NES1 treated group, tumor growth was significantly reduced with a high level of NES1 expression

CONCLUSION: Baculovirus-mediated NES1 gene can be used in gene therapy for GC.

Cancer-associated splicing variants of the CDCA1 and MSMB genes expressed in cancer cell lines and surgically resected gastric cancer tissues

BACKGROUND

Alternative splicing is a molecular mechanism by which different combinations of exons can be alternatively spliced to produce different mRNA isoforms. Recently, several databases have been published to predict the alternative splicing of mRNA; cancer-specific alternative splicing has also been predicted with these databases. Those variants may be potentially useful targets for cancer therapy, however, the accuracy and veracity of these databases have yet to be confirmed.

METHODS

In this study, we analyzed 17 genes by reverse transcriptase-polymerase chain reaction (RT-PCR) that were predicted to have cancer-specific alternative splicing by using the splicing database, the Alternative Splicing Annotation Project (ASAP) by Lee et al, between 38 cancer cell lines from various organs and 9 corresponding normal tissues. By designing 2 types of primer sets for RT-PCR including (1) primers flanking the alternatively spliced exons and (2) primers spanning the exon/exon junctions, cancer-associated splicing variants were investigated.

RESULTS

The alternatively splicing events were detected in 15 of 17 genes (88%); 35 of 43 variants (81%) were detected successfully with RT-PCR. Among these variants, M-RIP, HYAL2, CDCA1, and MSMB genes showed differential expressions between cancer cell lines and corresponding normal tissues. Furthermore, RT-PCR with surgically resected gastric cancer tissues (diffuse type, 6; intestinal type, 4) confirmed that 2 variants of CDCA1 were upregulated in cancer tissues, whereas both variants of MSMB were expressed predominantly in normal tissues.

CONCLUSION

Alternative splicing variants, especially in CDCA1, were detected in this study and may be potentially useful as diagnostic markers and/or novel targets for anticancer therapy.

Overexpression of the receptor tyrosine kinase EphA4 in human gastric cancers

AIM: To clarify the expression and role of Ephrin receptor A4 (EphA4) in gastric cancer in relation to clinicopathological characteristics and the expression of fibroblast growth factor receptor 1 (FGFR1) and ephrin ligands.

METHODS: Eleven gastric carcinoma cell lines, 24 paired surgical fresh specimens of gastric adenocarcinoma and adjacent nontumor tissue, 74 conventional formalin-fixed, paraffin-embedded tumor specimens, and 55 specimens spotted on tissue microarray (TMA) were analyzed. Reverse transcription-PCR (RT-PCR), real-time RT-PCR, immunohistochemistry, and cell growth assays were performed.

RESULTS: Overexpression of EphA4 mRNA expression was observed in 8 (73%) of 11 gastric cancer cell lines and 10 (42%) of 24 gastric cancer tissues. Overexpression of EphA4, analyzed by immunohistochemistry, was observed in 62 (48%) of 129 gastric cancer tissues. EphA4 overexpression, at the protein level, was significantly associated with depth of invasion and recurrence. EphA4 overexpression was also correlated with FGFR1 overexpression. Patients with EphA4-positive cancer had significantly shorter overall survival periods than did those with EphA4-negative cancer (P = 0.0008). The mRNAs for ephrin ligands were coexpressed in various combinations in gastric cancer cell lines and cancer tissues. Downregulation of EphA4 expression by siRNA in EphA4-overexpressing gastric cancer cell lines resulted in a significant decrease in cell growth.

CONCLUSION: Our results suggest that overexpression of EphA4 plays a role in gastric cancer.

Mechanism and pathobiologic implications of CHFR promoter methylation in gastric carcinoma

AIM: To investigate the aberrant methylation of CHFR promoter in human gastric cancer (GC) and its impact on the expression of CHFR mRNA and protein, as well as its correlation with clinical and histological features of human GC.

METHODS: Methylation-specific polymerase chain reaction (MSPCR) was used to detect the methylation status of CHFR promoter in 20 primary GC samples and paired normal gastric mucosa. The CHFR mRNA and protein expressions were investigated both by RT-PCR and by Western blotting. The CHFR protein expression in 69 GC samples was immunohistochemically examined.

RESULTS: The DNA methylation of the CHFR gene was found in 9 of the 20 GC samples (45%) and the down-regulation of CHFR mRNA and protein was significantly associated with the methylation status of the CHFR gene (P = 0.006). In 20 samples of corresponding non-neoplastic mucosa, no DNA methylation of the CHFR gene was detected. The CHFR gene methylation in poorly differentiated GC samples was significantly higher than that in well-differentiated GC samples (P = 0.014). Moreover, the negative CHFR protein expression rate in paraffin-embedded GC samples was 55.07% (38/69), the positive rate in poorly differentiated GC samples was 36.73% (18/49), which was significantly lower than 65.00% (13/20) in well-differentiated GC samples (χ² = 4.586, P = 0.032).

CONCLUSION: Aberrant methylation of the CHFR gene may be involved in the carcinogenesis and development of GC, and is the predominant cause of down-regulation or loss of CHFR mRNA or protein expression. As aberrant methylation of CHFR promoter is correlated with tumor differentiation, it may help to predict the prognosis of GC and CHFR may become a novel target of gene therapy for GC in the future.

Genomic investigation of alpha-synuclein multiplication and parkinsonism

OBJECTIVE

Copy number variation is a common polymorphic phenomenon within the human genome. Although the majority of these events are non-deleterious they can also be highly pathogenic. Herein we characterize five families with parkinsonism that have been identified to harbor multiplication of the chromosomal 4q21 locus containing the alpha-synuclein gene (SNCA).

METHODS

A methodological approach using fluorescent in situ hybridization and Affymetrix (Santa Clara, CA) 250K SNP microarrays was used to characterize the multiplication in each family and to identify the genes encoded within the region. The telomeric and centromeric breakpoints of each family were further narrowed using semiquantitative polymerase chain reaction with microsatellite markers and then screened for transposable repeat elements.

RESULTS

The severity of clinical presentation is correlated with SNCA dosage and does not appear to be overtly affected by the presence of other genes in the multiplicated region. With the exception of the Lister kindred, in each family the multiplication event appears de novo. The type and position of Alu/LINE repeats are also different at each breakpoint. Microsatellite analysis demonstrates two genomic mechanisms are responsible for chromosome 4q21 multiplications, including both SNCA duplication and recombination.

INTERPRETATION

SNCA dosage is responsible for parkinsonism, autonomic dysfunction, and dementia observed within each family. We hypothesize dysregulated expression of wild-type alpha-synuclein results in parkinsonism and may explain the recent association of common SNCA variants in sporadic Parkinson's disease. SNCA genomic duplication results from intraallelic (segmental duplication) or interallelic recombination with unequal crossing over, whereas both mechanisms appear to be required for genomic SNCA triplication.

Epigenetic alterations of CDH1 and APC genes: relationship with activation of Wnt/beta-catenin pathway in invasive ductal carcinoma of breast

Activation of canonical Wnt/beta-catenin pathway in Invasive Ductal Carcinoma of Breast (IDCs) was recently reported from our laboratory. Herein, we analyzed promoter methylation status of CDH1 and Adenomatous polyposis coli (APC) genes in 50 IDCs and correlated with expression of E-cadherin (E-CD) and APC proteins and with activation of oncogenic Wnt/beta-catenin signaling pathway components, Dvl, beta-catenin and CyclinD1. Further, Wnt/beta-catenin driven epithelial mesenchymal transition (EMT) was investigated by correlating the expression of Dvl, beta-catenin and CyclinD1 with vimentin expression in these IDCs. Promoter hypermethylation was observed in 25/50 (50%) IDCs for CDH1 and in 11/50 (22%) tumors for APC, associated with loss of expression of E-CD and APC proteins; concordant hypermethylation of these genes was observed in paired patients' sera. Further, 57% of tumors harboring CDH1 methylation and 50% tumors harboring the methylated APC gene showed nuclear localization of beta-catenin, suggesting activation of the canonical Wnt/beta-catenin pathway. Our study demonstrates significant association between vimentin expression and nuclear beta-catenin (p=0.001; Odds ratio (OR)=25.6) and Dvl (p=0.023; OR=8.0), suggesting that EMT may be driven by Wnt/beta-catenin activation in IDCs. In conclusion, we demonstrate correlation of CDH1 and APC promoter methylation with loss of E-CD and APC proteins and with activation of Wnt/beta-catenin signaling pathway. Association of nuclear Dvl and beta-catenin with vimentin expression suggests the importance of Wnt/beta-catenin pathway driven EMT in IDCs. The concordance between CDH1 and APC methylation in IDCs and paired circulating DNA underscores the utility of serum DNA as a non-invasive tool for methylation analysis in IDC patients.

Molecular staging of gastric cancer

Gastric cancer has traditionally been staged using purely histological methods, but these methods provide little information about the biology of gastric cancer and have limited predictive power. Recent studies have shown that clinically relevant gastric cancer subtypes have distinct gene expression profiles. This approach, termed molecular staging, can lead to the discovery of novel diagnostic and prognostic biomarkers of gastric cancers. This update reviews advances in molecular staging of gastric cancer and discusses their implications for the prognosis and diagnosis of this complex disease. Technologies used in molecular staging as well as future directions for the optimization of molecular staging of gastric cancer are also discussed.

Detection of RASSF1A promoter hypermethylation in serum from gastric and colorectal adenocarcinoma patients

AIM: To evaluate the diagnostic role of serum RASSF1A promoter hypermethylation in gastric and colorectal adenocarcinoma.

METHODS: Methylation-specific polymerase chain reaction (MSPCR) was used to examine the promoter methylation status of the serum RASSF1A gene in 47 gastric adenocarcinoma patients, 45 colorectal adenocarcinoma patients, 60 patients with benign gastrointestinal disease (30 with benign gastric disease and 30 with benign colorectal disease), and 30 healthy donor controls. A paired study of RASSF1A promoter methylation status in primary tumor, adjacent normal tissue, and postoperative serum were conducted in 25 gastric and colorectal adenocarcinoma patients who later were underwent surgical therapy.

RESULTS: The frequencies of detection of serum RASSF1A promoter hypermethylation in gastric (34.0%) and colorectal (28.9%) adenocarcinoma patients were significantly higher than those in patients with benign gastric (3.3%) or colorectal (6.7%) disease or in healthy donors (0%) (P < 0.01). The methylation status of RASSF1A promoter in serum samples was consistent with that in paired primary tumors, and the MSPCR results for RASSF1A promoter methylation status in paired preoperative samples were consistent with those in postoperative serum samples. The serum RASSF1A promoter hypermethylation did not correlate with patient sex, age, tumor differentiation grade, surgical therapy, or serum carcinoembryonic antigen level. Although the serum RASSF1A promoter hypermethylation frequency tended to be higher in patients with distant metastases, there was no correlation between methylation status and metastasis.

CONCLUSION: Aberrant CpG island methylation within the promoter region of RASSF1A is a promising biomarker for gastric and colorectal cancer.

Cytogenetic and molecular aspects of gastric cancer: clinical implications

Gastric cancer is of major importance world-wide being the second most common cause of cancer-related death in the world. According to Lauren's histological classification gastric cancer is divided in two groups, the better differentiated intestinal carcinomas and the poorly differentiated diffuse-type cancers. The genetic changes underlying the initiation and progression of gastric cancer are not well defined. Gastric carcinogenesis is a multistep process involving a number of genetic and epigenetic factors. Although it has been proposed that different genetic pathways exist for differentiated and undifferentiated carcinomas, the two histological subtypes of gastric cancer share some common genetic alterations. Currently, tumor histology and pathologic stage are the major prognostic variables used in the clinical practice for gastric cancer patients. However, it is known that tumors with similar morphology may differ in biological aggressiveness, prognosis and response to treatment. Molecular genetic analysis of gastric cancer revealed a number of associations of certain genetic changes with pathological features, tumor biological behavior and prognosis of gastric cancer patients, suggesting that these genetic abnormalities might play an important role in gastric tumorigenesis. Increasing evidence suggests that the molecular genetic changes could be helpful in the clinical setting, contributing to prognosis and management of patients. Regarding epigenetic events in gastric tumorigenesis, a number of methylating markers have been proposed for risk assessment, prognostic evaluation and as therapeutic targets. However, further research is required in order to systematically investigate the genetic changes in gastric cancer estimating also their usefulness in the clinical practice. A good understanding of the genetic changes underlying gastric carcinogenesis may provide new perspectives for prognosis and screening of high risk individuals. Some of the genetic alterations could definitely improve tumor classification and management of gastric cancer patients. Also, based on molecular data identified in gastric cancer novel therapeutics might help to improve the treatment of this disease.

CDH1 gene polymorphisms, smoking, Helicobacter pylori infection and the risk of gastric cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC-EURGAST)

Despite declining incidence rates, gastric cancer (GC) is a major cause of death worldwide. E-Cadherin is an adhesion molecule that is thought to be involved in GC. Germline mutations in the E-Cadherin gene (CDH1) have been identified in hereditary diffuse GC. Also, a promoter polymorphism at position -160 C/A has been suggested to lead to transcriptional down regulation and has been shown to affect GC risk in some studies. However, very little information exists on the GC risk association of other CDH1 polymorphisms and it is unclear whether any associations may be different by GC anatomical sites or histological types. Thus, a case-control study (cases=245/controls=950) nested within the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort was conducted to assess the GC risk association of eight CDH1 gene polymorphisms. None of the CDH1 polymorphisms or haplotypes analysed were associated with GC risk and no differences of effect were observed by Helicobacter pylori infection status. However, three CDH1 polymorphisms in the same haplotype block, including the CDH1-160C/A, interacted with smoking to increase GC risk in smokers but not in never smokers. These findings should be confirmed in larger independent studies.

Frequent epigenetic inactivation of hSRBC in gastric cancer and its implication in attenuated p53 response to stresses

hSRBC is a putative tumor suppressor located at 11p15.4, at which frequent genomic loss has been observed in several human malignancies. To explore the candidacy of hSRBC as a suppressor of gastric tumorigenesis, we analyzed the expression and mutation status of hSRBC in gastric tissues and cell lines. hSRBC transcript was expressed in all normal and benign tumor tissues examined, but undetectable or very low in 73% (11/15) cancer cell lines and 41% (46/111) primary tumors. Loss or reduction of hSRBC expression was tumor-specific and correlated with stage and grade of tumors. While allelic loss or somatic mutations of the gene were infrequent, its expression was restored in tumor cells by 5-aza-2'-deoxycytidine treatment and aberrant hypermethylation of 23 CpG sites in the promoter region showed a tight association with altered expression. Transient or stable expression of hSRBC led to a G(1) cell cycle arrest and apoptosis of tumor cells, and strongly suppresses colony forming ability and xenograft tumor growth. In addition, hSRBC elevated apoptotic sensitivity of tumor cells to genotoxic agents, such as 5-FU, etoposide and ultraviolet. Interestingly, hSRBC increased the protein stability of p53 and expression of p53 target genes, such as p21(Waf1), PUMA and NOXA, while hSRBC-mediated cell cycle arrest and apoptosis were abolished by blockade of p53 function. Our findings suggest that hSRBC is a novel tumor suppressor whose epigenetic inactivation contributes to the malignant progression of gastric tumors, in part, through attenuated p53 response to stresses.

Crosstalk of hedgehog and Wnt pathways in gastric cancer

Morphogenic signals like Hedgehog (Hh) and Wnt are reported to play critical roles in the progression of gastric cancer. We aimed to assess the relationship between Hh and Wnt signaling pathways. In 58 gastric cancer specimens, Wnt pathway activation was inversely correlated with Hh pathway activation. When AGS gastric cancer cells, in which Wnt signaling was constitutively active, were used as a target cell line, Gli1 overexpression suppressed Wnt transcriptional activity, nuclear beta-catenin accumulation and proliferation of AGS cells. Knock-down of beta-catenin by siRNA suppressed Wnt pathway activity and proliferation of AGS cells. Our data may provide some clues for the treatment of gastric cancer associated with Wnt signaling activation.

Patterns of genomic instability in gastric cancer: clinical implications and perspectives

In gastric cancer (GC) the loss of genomic stability represents a key molecular step that occurs early in the carcinogenesis process and creates a permissive environment for the accumulation of genetic and epigenetic alterations in tumor suppressor genes and oncogenes. It is widely accepted that GC can follow at least two major genomic instability pathways, microsatellite instability (MSI) and chromosome instability (CIN). MSI is responsible for a well-defined subset of GCs. CIN represents a more common pathway comprising heterogeneous subsets of GC. In addition to MSI and CIN, the CpG islands methylator phenotype (CIMP) plays an important role in gastric carcinogenesis. CIMP may lead to the transcriptional silencing of various genes in gastric carcinogenesis. Intriguingly, more recently in addition to CpG island hypermethylation, a global DNA demethylation, that precedes genomic damage, has been observed in GC. Thus, epigenetic alterations may play a relevant role in gastric carcinogenesis as alternative mechanisms. Evidence suggests that although MSI, CIN and CIMP phenotypes can be distinguished from one another, there might be some degree of overlap. This review describes our current knowledge of the instability pathways in gastric carcinogenesis and the potential clinical applications for different forms of genomic instability in GC.

Lysophosphatidic acid (LPA) promotes E-cadherin ectodomain shedding and OVCA429 cell invasion in an uPA-dependent manner

OBJECTIVES

To evaluate the role of LPA in regulating E-cadherin cell surface expression, adhesion, and invasion in epithelial ovarian carcinoma (EOC) cells.

METHODS

E-cadherin mRNA expression in OVCA429 and IOSE-29 cells was evaluated by real-time RT-PCR. Immunofluorescence and Western blot analysis were performed to determine cell surface expression and shedding of E-cadherin 80-kDa soluble fragment by LPA. Kinetics of LPA-induced uPA activity was followed with a colorimetric enzymatic assay. Invasion assays were performed in a modified Boyden chamber where cells were allowed to migrate to the bottom compartment through a porous filter coated with collagen. Additionally we measured the 80-kDa form from the ascites of women with stage III/IV EOC.

RESULTS

LPA induces E-cadherin shedding of a soluble 80-kDa fragment. We found that this process is mediated by the uPA proteolytic cascade. High levels of soluble E-cadherin were found in the ascites from women with advanced stage EOC. LPA and a soluble recombinant E-cadherin-Fc chimera promotes invasion of OVCA429 cells.

CONCLUSIONS

LPA induces shedding of an 80-kDa E-cadherin-soluble fragment in an uPA-dependent manner and promotes in vitro invasion. High levels of soluble E-cadherin in malignant ascites may also affect ovarian metastasis.

Expression of pituitary homeobox 1 gene in human gastric carcinogenesis and its clinicopathological significance

AIM: To investigate the effect of pituitary homeobox 1 (PITX1) expression in cases of human gastric cancer on cancer differentiation and progression, and carcinogenesis.

METHODS: Using polyclonal PITX1 antibodies, we studied the expression of PITX1 in normal gastric mucosa, atypical hyperplasia, intestinal metaplasia, and cancer tissue samples from 83 gastric cancer patients by immunohistochemistry. Moreover, semi-reverse transcription polymerase chain reaction (semi-RT-PCR) was performed to detect the mRNA level of PITX1 in three gastric cancer cell lines and a normal gastric epithelial cell line. Subsequently, somatic mutations of the PITX1 gene in 71 gastric cancer patients were analyzed by a combination of denaturing high performance liquid chromatography (DHPLC) and DNA sequencing.

RESULTS: Immunohistochemistry showed that PITX1 was strongly or moderately expressed in the parietal cells of normal gastric mucosa (100%), while 55 (66.3%) out of 83 samples of gastric cancers showed decreased PITX1 expression. Moreover, PITX1 expression was reduced in 20 out of 28 cases (71.5%) of intestinal metaplasia, but in only 1 out of 9 cases (11%) of atypical hyperplasia. More importantly, PITX1 expression was significantly associated with the differentiation, position and invasion depth of gastric cancers (r = -0.316, P < 0.01; r = 0.213, P < 0.05; r = -0.259, P < 0.05, respectively). Similarly, levels of PITX1 mRNA were significantly decreased in 2 gastric cancer cell lines, BGC-823 and SGC-7901, compared with the normal gastric epithelial cell line GES-1 (0.306 ± 0.060 vs 0.722 ± 0.102, P < 0.05; 0.356 ± 0.081 vs 0.722 ± 0.102, P < 0.05, respectively). Nevertheless, no somatic mutation of PITX1 gene was found in 71 samples of gastric cancer by DHPLC analysis followed by sequencing.

CONCLUSION: Down-regulation of PITX1 may be a frequent molecular event in gastric carcinogenesis. Aberrant levels of PITX1 expression may be closely correlated with the progression and differentiation of gastric cancer.

Phosphoinositide 3-kinase/Akt pathway plays an important role in chemoresistance of gastric cancer cells against etoposide and doxorubicin induced cell death

The major obstacle to successful treatment of gastric cancer is chemotherapy resistance. Our study was designed to investigate the role of phosphoinositide 3-kinase (PI3K)/Akt pathway in the development of chemoresistance in gastric cancer. In the present study, elevated Akt expression and Akt phosphorylation (Ser 473), as well as decreased PTEN expression were observed in 28 cases of gastric cancer tissues. Etoposide and doxorubicin stimulated Akt and PI3K activities in 2 gastric cancer cell lines (BGC-823 and SGC-7901), and the activities were concentration and time-dependent. Up-regulation of PTEN expression in BGC-823 cells by PEAK8-PTEN transient transfection obviously decreased the basal and anticancer drugs induced Akt activities, then sensitized BGC-823 cells to etoposide and doxorubicin. Pretreatment of BGC-823 and SGC-7901 cells with wortmannin, a PI3K inhibitor, attenuated cells's resistance to etoposide and doxorubicin. In addition, pretreatment of wortmannin blocked etoposide and doxorubicin induced IkappaB-alpha degradation, NFkappaB activation, phosphorylation of Akt, MDM-2 and forkhead transcription factors. Wortmannin pretreatment also promoted the accumulation of p27/Kip, but inhibited the Mcl-1 expression. Furthermore, wortmannin promoted etoposide and doxorubicin induced caspase-3, caspase-9 activation and poly ADP-ribose polymerase cleavage. Taken together, the observations indicate the PI3K/Akt pathway plays an important role in the chemoresistance of gastric cancer cells. A new strategy for combined chemotherapy of gastric cancer should be designed to more specifically block PI3K/Akt pathway and then decrease the amount of resistant cells.

Frequent loss of Brm expression in gastric cancer correlates with histologic features and differentiation state

The mammalian SWI/SNF chromatin remodeling complex, an essential epigenetic regulator, contains either a single Brm or BRG1 molecule as its catalytic subunit. We observed frequent loss of Brm expression but not of BRG1 in human gastric cancer cell lines. Treatment with histone deacetylase inhibitor rescued Brm expression, indicating epigenetic regulation of this gene, and an RNA interference-based colony formation assay revealed antioncogenic properties of Brm. Brm immunostaining of 89 primary gastric cancers showed an obvious reduction in 60 cases (67%) and a severe decrease in 37 cases (42%). Loss of Brm is frequent in the major gastric cancer types (well- or moderately-differentiated tubular adenocarcinoma and poorly-differentiated adenocarcinoma) and positively correlates with the undifferentiated state. Among the minor gastric cancer types, Brm expression persists in signet-ring cell carcinoma and mucinous adenocarcinoma, but a marked decrease is observed in papillary adenocarcinoma. Intestinal metaplasia never shows decreased expression, indicating that Brm is a valid marker of gastric oncogenesis. In contrast, BRG1 is retained in most cases; a concomitant loss of BRG1 and Brm is rare in gastric cancer, contrary to other malignancies. We further show that Brm is required for villin expression, a definitive marker of intestinal metaplasia and differentiation. Via regulating such genes important for gut differentiation, Brm should play significant roles in determining the histologic features of gastric malignancy.

Genome-wide combination profiling of copy number and methylation offers an approach for deciphering misregulation and development in cancer cells

Copy number changes and DNA methylation alterations are crucial to gene regulation in mammals. Recently, a number of microarray studies have been based on copy number and DNA methylation alterations in order to find clinical biomarkers of carcinogenesis. In this study, we attempted to combine profiles of copy number and methylation patterns in four human cancer cell lines using BAC microarray-based approaches and we detected several clinically important genes which showed genetic and epigenetic relationships. Within the clones analyzed, many contained cancer-related genes involved in cell cycle regulation, cell division, signal transduction, tumor necrosis, cell differentiation, and cell proliferation. One clone included the FHIT gene, a well-known tumor suppressor gene involved in various human cancers. Our combined profiling techniques may provide a method by which to find new clinicopathologic cancer biomarkers, and support the idea that systematic characterization of the genetic and epigenetic events in cancers may rapidly become a reality.

Coexpression of receptor-tyrosine-kinases in gastric adenocarcinoma-a rationale for a molecular targeting strategy?

AIM: To define the (co-)expression pattern of target receptor-tyrosine-kinases (RTK) in human gastric adenocarcinoma.

METHODS: The (co-)expression pattern of VEGFR1-3, PDGFRα/β and EGFR1 was analyzed by RT-PCR in 51 human gastric adenocarcinomas. In addition, IHC staining was applied for confirmation of expression and analysis of RTK localisation.

RESULTS: The majority of samples revealed a VEGFR1 (98%), VEGFR2 (80%), VEGFR3 (67%), PDGFRα (82%) and PDGFRβ (82%) expression, whereas only 62% exhibited an EGFR1 expression. 78% of cancers expressed at least four out of six RTKs. While VEGFR1-3 and PDGFRα revealed a predominantly cytoplasmatic staining in tumor cells, accompanied by an additional nuclear staining for VEGFR3, EGFR1 was almost exclusively detected on the membrane of tumor cells. PDGFRβ was restricted to stromal pericytes, which also depicted a PDGFRα expression.

CONCLUSION: Our results reveal a high rate of receptor-tyrosine-kinases coexpression in gastric adenocarcinoma and might therefore encourage an application of multiple-target RTK-inhibitors within a combination therapy.

Aberrant DNA methylation in non-neoplastic gastric mucosa of H. Pylori infected patients and effect of eradication

BACKGROUND

Gene promoter methylation is an epigenetic event leading to gene silencing. This mechanism is particularly relevant in cancer since it can interfere with the activity of specific "suppressor" genes.

AIM

To evaluate promoter methylation of CDH1, p16, APC, MLH1, and COX2 in patients with H. pylori (Hp) infection before and after eradication.

METHODS

Fifty-seven dyspeptic outpatients who had never performed previous endoscopy or Hp testing and treatment underwent clinical interview, endoscopy with three paired gastric biopsy specimens from the antrum, angulus, and corpus, and (13)C-urea breath test (UBT). Biopsies were scored for the presence of Hp and intestinal metaplasia (IM). DNA methylation of five tumor-related genes (CDH1, p16, MLH1, APC, and COX2) was evaluated by methylation-specific PCR in each biopsy. Infected patients were given a standard eradicating treatment and, after 1 yr, underwent endoscopy with biopsies and UBT.

RESULTS

Hp infection was found in 45 patients. IM was detected in 17 out of 45 (38%) infected patients. Mean number of methylated genes was 0, 1.1 +/- 0.9, and 1.6 +/- 0.9 among the 12 Hp-/IM-, the 28 Hp+/IM-, and the 17 Hp+/IM+ patients, respectively (P < 0.0001). Specifically, promoter hypermethylation of CDH1, p16, APC, MLH1, and COX2 was found in 68%, 25%, 7%, 0%, and 14% of Hp+/IM- patients and in 71%, 29%, 35%, 12%, and 12% of Hp+/IM+ patients. No significant difference was found among the three groups of patients as far as age, smoking, alcohol, meat and vegetable consumption, and family history of gastric cancer were considered. Twenty-three out of 45 (51%) infected patients underwent the 1-yr follow-up endoscopy: 17 out of 23 (74%) were successfully eradicated. After Hp eradication, CDH1, p16, and APC methylation significantly decreased while COX2 methylation completely disappeared. Conversely, MLH1 methylation did not change significantly in patients with IM.

CONCLUSION

Hp infection is associated with promoter methylation of genes which are relevant in the initiation and progression of gastric carcinogenesis. While CDH1 methylation seems to be an early event in Hp gastritis, MLH1 methylation occurs late along with IM. Hp eradication is able to significantly reduce gene methylation thus delaying or reversing Hp-induced gastric carcinogenesis.

Is gastric cancer part of the tumour spectrum of hereditary non-polyposis colorectal cancer? A molecular genetic study

BACKGROUND

Gastric cancer is the second most common extracolonic malignancy in individuals with hereditary non-polyposis colorectal cancer (HNPCC)/Lynch syndrome. As gastric cancer is relatively common in the general population as well, it is not clear whether or not gastric cancer is a true HNPCC spectrum malignancy.

AIM

To determine whether or not gastric cancer is a true HNPCC spectrum malignancy.

SUBJECTS AND METHODS

The molecular and clinicopathological profiles of gastric cancers (n = 13) from HNPCC mutation carriers were evaluated and compared with the profiles of sporadic gastric cancers (n = 46) stratified by histology and microsatellite instability (MSI) status.

RESULTS

This study on sporadic and HNPCC gastric cancers revealed several important universal associations. Loss of heterozygosity in the adenomatous polyposis coli (APC) region was associated with intestinal histology regardless of the MSI (p = 0.007). KRAS-mutations (p = 0.019) and frameshift mutations in repeat tracts of growth-regulatory genes (p<0.001) were associated with MSI tumours being absent in microsatellite stable (MSS) tumours. The average number of methylated tumour suppressor gene loci among the 24 genes studied (methylation index) was higher in MSI than in MSS tumours regardless of histology (p<0.001). Gastric cancers from HNPCC mutation carriers resembled sporadic intestinal MSI gastric cancers, except that MLH1 promoter methylation was absent (p<0.001) and the general methylation index was lower (p = 0.038), suggesting similar, but not identical, developmental pathways. All these lacked the mismatch repair protein corresponding to the germline mutation and displayed high MSI.

CONCLUSION

The present molecular evidence, combined with the previous demonstration of an increased incidence relative to the general population, justify considering gastric cancers as true HNPCC spectrum malignancies.

Protein expression of checkpoint with fork head associated and ring finger and mutant p53 and their clinicopathological significances in gastric cancer

AIM: To investigate the relationship between the expression of checkpoint with fork head associated and ring finger (CHFR) and P53 protein in gastric cancer (GC) and the clinicopathologic characteristics, and to explore the correlated molecular mechanism of CHFR and p53 genes in gastric carcinogenesis.

METHODS: Five paraffin blocks of tissue microarray were constructed using a Tissue Array Machine (Steve Leighton Beecher Instruments, USA), including 151 cases of primary GC (101 cases with matched normal mucosa, intestinal metaplasia or dysplasia). Envision immunohistochemical method was employed to detect the protein expression of CHFR and mutant p53 in GC and precancerous tissues mentioned above.

RESULTS: The positive rate of CHFR protein expression in GC (49.67%, 75/151) was significantly lower than that in normal gastric mucosa (85.25%, 52/61)(P < 0.05). The down-regulation or absence of mitotic checkpoint CHFR protein expression was correlated with the sex of GC patients. The absent rate of CHFR protein expression in the female GC patients was significantly higher than that in the male GC ones (64% vs 43.56%, P < 0.05). The absent rates was also significantly different between GC patients of Borrmann Ⅲ + Ⅳ and Ⅰ + Ⅱ types (57.14% vs 34.78%, P < 0.05). In the present study, though CHFR protein expression showed no significant difference among various histological types of GC, the absent rate of CHFR protein expression was the highest (71.43%) in signet ring cell carcinoma. The absent expression of CHFR protein was not related to the depth of invasion and lymph node metastasis of GC. In addition, no correlation was found between the expression of CHFR and P53 protein expression in GC (P > 0.05).

CONCLUSION: Down-regulation or absence of mitotic checkpoint CHFR protein expression is frequent events in GC and may take a part in gastric carcinogenesis. Abnormal expression of CHFR may be of more importance in the development of female patients and diffuse-type GC.