Distinct promoter hypermethylation of p16INK4a, CDH1, and RAR-beta in intestinal, diffuse-adherent, and diffuse-scattered type gastric carcinomas

Mutational landscape of TP53 and CDH1 in gastric cancer

In this editorial we comment on an article published in a recent issue of the World J Gastrointest Surg. A common gene mutation in gastric cancer (GC) is the TP53 mutation. As a tumor suppressor gene, TP53 is implicated in more than half of all tumor occurrences. TP53 gene mutations in GC tissue may be related with clinical pathological aspects. The TP53 mutation arose late in the progression of GC and aided in the final switch to malignancy. CDH1 encodes E-cadherin, which is involved in cell-to-cell adhesion, epithelial structure maintenance, cell polarity, differentiation, and intracellular signaling pathway modulation. CDH1 mutations and functional loss can result in diffuse GC, and CDH1 mutations can serve as independent prognostic indicators for poor prognosis. GC patients can benefit from genetic counseling and testing for CDH1 mutations. Demethylation therapy may assist to postpone the onset and progression of GC. The investigation of TP53 and CDH1 gene mutations in GC allows for the investigation of the relationship between these two gene mutations, as well as providing some basis for evaluating the prognosis of GC patients.

Overexpression of Tetraspanin31 contributes to malignant potential and poor outcomes in gastric cancer

Tetraspanin has important functions in many cancers by aggregating with various proteins that interact with intracellular signaling proteins. The molecular function of Tetraspanin31 (TSPAN31), located in the 12q14 amplified region in various cancers, remains unclear in gastric cancer (GC). We tested whether TSPAN31 acts as a cancer‐promoting gene through its activation or overexpression in GC. We analyzed seven GC cell lines and 189 primary tumors, which were curatively resected in our hospital between 2011 and 2013. Overexpression of the TSPAN31 protein was frequently detected in three GC cell lines (42.9%) and 62 primary GC specimens (32.8%). Overexpression of TSPAN31 was significantly correlated with lymphatic invasion, venous invasion, more advanced pT and pN stages, and a higher recurrence rate. Moreover, TSPAN31 positivity was an independent factor predicting worse patient outcomes (p = 0.0283, hazard ratio 3.97). Ectopic overexpression of TSPAN31 facilitated cell proliferation of GC cells, and knockdown of TSPAN31 inhibited cell proliferation, migration, invasion, and epithelial–mesenchymal transition of GC cells through the PI3K‐Akt pathway and increased cell apoptosis in a TP53 mutation‐independent manner. In vivo analysis also revealed knockdown of TSPAN31 suppressed tumor progression. In addition, knockdown of TSPAN31 improved chemosensitivity to cisplatin through the suppression of ABCC2. These findings suggest that TSPAN31 plays a crucial role in tumor‐malignant potential through overexpression, highlighting its utility as a prognostic factor and a potential therapeutic target in GC.

TRIM37 contributes to malignant outcomes and CDDP resistance in gastric cancer

Background: TRIM37 (Tripartite Motif Containing 37) is an E3 ubiquitin ligase for histone H2A and inhibits transcription in several genes. However, it is not known whether it plays a role in gastric cancer (GC). In this study, we tested whether TRIM37 acts as a cancer-promoting factor by being overexpressed in GC. Methods: We analyzed GC cell lines and 124 primary tumors, which were curatively resected in our hospital between 2001 and 2003. Results: Overexpression of the TRIM37 protein was detected in almost all GC cell lines and GC samples (76 out of 124 cases) and was significantly correlated with lymphatic and venous invasion, advanced T-Stage, N-Stage, histology and high recurrence rate. Patients with TRIM37 overexpressing tumors had a worse survival rate than those with non-expressing tumors (P=0.0057). Moreover, TRIM37 positivity was identified as an independent factor predicting worse outcomes (P=0.018, Hazard ratio 3.41). The apoptotic cell analysis showed that the knockdown of TRIM37 increased apoptosis in comparison with the control. In TRIM37 overexpressing GC cells, knockdown of TRIM37 suppressed the migration and invasion. Conclusions: TRIM37 plays a crucial role in tumor malignant potential through its overexpression and highlight its usefulness as a prognostic factor and potential therapeutic target in GC.

Retinoic Acids in the Treatment of Most Lethal Solid Cancers

Although the use of oral administration of pharmacological all-trans retinoic acid (ATRA) concentration in acute promyelocytic leukaemia (APL) patients was approved for over 20 years and used as standard therapy still to date, the same use in solid cancers is still controversial. In the present review the literature about the top five lethal solid cancers (lung, stomach, liver, breast, and colon cancer), as defined by The Global Cancer Observatory of World Health Organization, and retinoic acids (ATRA, 9-cis retinoic acid, and 13-cis retinoic acid, RA) was compared. The action of retinoic acids in inhibiting the cell proliferation was found in several cell pathways and compartments: from membrane and cytoplasmic signaling, to metabolic enzymes, to gene expression. However, in parallel in the most aggressive phenotypes several escape routes have evolved conferring retinoic acids-resistance. The comparison between different solid cancer types pointed out that for some cancer types several information are still lacking. Moreover, even though some pathways and escape routes are the same between the cancer types, sometimes they can differently respond to retinoic acid therapy, so that generalization cannot be made. Further studies on molecular pathways are needed to perform combinatorial trials that allow overcoming retinoic acids resistance.

Essential updates 2017/2018: Recent topics in the treatment and research of gastric cancer in Japan

Recent developments in diagnostic technology, accumulated clinical effort and established evidence have boosted early detection and drastically improved early and long-term outcomes of gastric cancer. However, gastric cancer continues to be one of the most aggressive and life-threatening malignancies among all cancers and is a global health problem. Between January 2017 and December 2018, various fascinating reports of managements and research were published, including the new 15th Japanese Classification of Gastric Carcinoma reflecting the 8th American Joint Committee on Cancer/Union for International Cancer Control (AJCC/UICC) tumor, node and metastasis (TNM) classification (October 2017) and the new Gastric Cancer Treatment Guidelines version 5 (January 2018). Moreover, pivotal molecular features of gastric cancer were clarified by the worldwide cancer genome project, and various treatment targets and biomarkers such as circulating DNAs and microRNAs were detected. Novel treatment options using programmed cell death protein 1 immune checkpoint inhibitors have been started. In this review, we summarize the recent topics of classification, guidelines, and clinical and basic research in order to bring new insights to gastric cancer treatment.

Overexpression of ZRF1 is related to tumor malignant potential and a poor outcome of gastric carcinoma

Zuotin-related factor 1 (ZRF1) is a recently characterized epigenetic factor involved in transcriptional regulation and is highly overexpressed in several malignancies, but it is not known whether it plays a role in gastric cancer (GC). In this study, we investigated whether ZRF1 acts as a cancer-promoting gene through its activation/overexpression in GC. We analyzed five GC cell lines and 133 primary tumors, which had been curatively resected in our hospital between 2001 and 2003. Overexpression of ZRF1 was detected in GC cell lines (four out of five lines, 80.0%) and was detected in primary tumor samples of GC (52 out of 133 cases, 39.1%) and significantly correlated with differentiated histological type, venous invasion, lymphatic invasion, advanced stage and a higher recurrence rate. ZRF1-overexpressing tumors had a worse survival rate than those with non-expressing tumors (P < 0.01, log-rank test). ZRF1 positivity was independently associated with a worse outcome in the multivariate analysis (P < 0.01; hazard ratio 4.92; 95% confidence interval: 1.6-21.1). In ZRF1-overexpressing GC cells, knockdown of ZRF1 using specific siRNAs inhibited the cell proliferation, migration and invasion and induced apoptosis in a p53-dependent manner. These findings suggest that ZRF1 plays a crucial role in tumor malignant potential through its overexpression and highlight its usefulness as a prognostic factor and potential therapeutic target in GC.

Promoter hypermethylation of RAR-β tumor suppressor gene in gastric carcinoma: Association with histological type and clinical outcomes

BACKGROUND

While gastric cancer is a common cancer in the world and Iran, its molecular mechanisms are not fully understood as yet. Epigenetic modifications can lead to alteration of gene expression and development of tumorigenesis mechanisms.

METHODS

To clarify the difference in DNA methylation pattern of histological types in gastric carcinoma, CpG islands in the promoters of retinoic acid receptor β gene (RAR-β) was studied using methylation-specific PCR.

RESULTS

In gastric cancer tissues, hypermethylation frequency of RAR-β gene was respectively 61 and 33% for diffuse and intestinal type. In diffuse type, hypermethylation of RAR-β has been significantly associated with invasion (P= 0.007), differentiation (P= 0.033) and location (P= 0.012) of the tumor. However, hypermethylation of RAR-β correlated only with tumor size (P= 0.029) in intestinal type. For adjacent non-tumor samples, hypermethylation of RAR-β was not detected and there was no significant association between age of diagnosis and hypermethylation of RAR-β in both types of gastric cancer.

CONCLUSIONS

These results support previous findings denoting a distinct profile of promoter hypermethylation status in the development of the intestinal and diffuse type of gastric carcinoma and the process of the tumorigenesis in these subtypes of gastric cancer is different from each other.

Epigenetic Mechanisms and Events in Gastric Cancer-Emerging Novel Biomarkers

Gastric cancer is one of the most common malignancy worldwide. The various genetic and epigenetic events have been found to be associated with its carcinogenesis. The epigenetic is a heritable and transient/reversible change in the gene expression that is not accompanied by modification in the DNA sequence. This event is characterized by the alteration in the promoter CpG island of the gene or histone modification. These events are associated with silencing of critical tumor suppressor gene and activation of oncogenes leading to carcinogenesis. The DNA methylation is a chemical change in the DNA sequence that most commonly occurs at cytosine moiety of CpG dinucleotide and histone, primarily on N- terminal tail that ultimately effect the interaction of DNA with chromatin modifying protein.Hypermethylation of tumor suppressor genes and global hypomethylation of oncogenes are widely studied epigenetic modifications. There are large number of publish reports regarding epigenetic events involving gastric cancer. These changes are potentially useful in identifying markers for early diagnosis and management of this lethal malignancy. Also, role of specific miRNAs and long non coding RNAs in regulation of gene expression is gaining interest and is a matter of further investigation. In this review, we aimed to summarize major epigenetic events (DNA methylation) in gastric cancer along with alteration in miRNAs and long non coding RNAs which plays an important role in pathology of this poorly understood malignancy.

Silencing of Discoidin Domain Receptor-1 (DDR1) Concurrently Inhibits Multiple Steps of Metastasis Cascade in Gastric Cancer

Accumulating evidence suggests that a unique set of receptor tyrosine kinases, known as discoidin domain receptors (DDRs), plays a role in cancer progression by interacting with the surrounding collagen matrix. In this study, we investigated the expression and role of DDR1 in human gastric cancer metastasis. Proliferation, migration, invasion, and tube formation assays were conducted in DDR1-expressing MKN74 gastric cancer cells and corresponding DDR1-silenced cells. The effects of DDR1 on tumor growth and metastasis were examined in orthotopically implanted and experimental liver metastasis models in nude mice. The expression of DDR1 in surgical specimens was analyzed by immunohistochemistry. DDR1 was expressed in human gastric cancer cell lines, and its expression in human gastric tumors was associated with poor prognosis. Among seven gastric cancer cell lines, MKN74 expressed the highest levels of DDR1. DDR1-silenced MKN74 cells showed unaltered proliferation activity. In contrast, migration, invasion, and tube formation were significantly reduced. When examined in an orthotopic nude mouse model, DDR1-silenced implanted tumors significantly reduced angiogenesis and lymphangiogenesis, thereby leading to reductions in lymph node metastasis and liver metastasis. In a model of experimental liver metastasis, DDR1-silenced cells almost completely inhibited liver colonization and metastasis. DDR1 deficiency led to reduced expression of the genes encoding vascular endothelial growth factor (VEGF)-A, VEGF-C, and platelet-derived growth factor-B. These results suggest that DDR1 is involved in gastric cancer tumor progression and that silencing of DDR1 inhibits multiple steps of the gastric cancer metastasis process.

Overexpression of denticleless E3 ubiquitin protein ligase homolog (DTL) is related to poor outcome in gastric carcinoma. Oncotarget. 2015;6:36615-36624. [PMID: 26472028 PMCID: PMC4742199 DOI: 10.18632/oncotarget.5620]

BACKGROUND

Denticleless E3 ubiquitin protein ligase homolog (DTL) has been identified in amplified region (1q32) of several cancers and has an oncogenic function. In this study, we tested whether DTL acts as a cancer-promoting gene through its activation/overexpression in gastric cancer (GC).

METHODS

We analyzed 7 GC cell lines and 100 primary tumors that were curatively resected in our hospital between 2001 and 2003.

RESULTS

Overexpression of the DTL protein was detected in GC cell lines (4/7 cell lines; 57%) and primary GC tumor samples (42/100 cases; 42%). Knockdown of DTL using several specific siRNAs inhibited the proliferation, migration and invasion in a TP53 mutation-independent manner. Overexpression of the DTL was significantly correlated with lymphatic invasion, deeper tumor depth and higher recurrence rate. Patients with DTL-overexpressing tumors had a worse survival rate than those with non-expressing tumors in overall survival (P = 0.0498, log-rank test) and disease-free survival (P = 0.0324, log-rank test). In a multivariate analysis, DTL positivity was independently associated with a worse overall survival (P = 0.0104, hazard ratio 3.7 [1.36-10.1]) and disease-free survival (P = 0.0070 (hazard ratio, 3.9 (1.45-10.46)) following radical gastrectomy.

CONCLUSIONS

These findings suggest that DTL overexpression plays a crucial role in tumor cell proliferation and highlights its usefulness as a prognosticator and potential therapeutic target in gastric cancer.

Overexpression of PBK/TOPK relates to tumour malignant potential and poor outcome of gastric carcinoma

Background:

PDZ-binding kinase/T-LAK cell-originated protein kinase (PBK/TOPK) is a serine–threonine kinase and overexpressed in various types of cancer by inhibiting the transactivation activities of p53 and PTEN. We tested whether PBK/TOPK acts as a cancer-promoting gene through its activation/overexpression in gastric cancer (GC).

Methods:

We analysed five GC cell lines and 144 primary tumours, which were curatively resected in our hospital between 2001 and 2003.

Results:

Overexpression of the PBK/TOPK protein was frequently detected in GC cell lines (4 out of 5 lines, 80.0%) was detected in primary tumour samples of GC (24 out of 144 cases, 16.6%) and was significantly correlated with venous invasion, tumour depth and recurrence rate. PDZ-binding kinase/T-LAK cell-originated protein kinase-overexpressing tumours had a worse survival rate than those with non-expressing tumours (P=0.0009, log-rank test). PDZ-binding kinase/T-LAK cell-originated protein kinase positivity was independently associated with a worse outcome in multivariate analysis (P<0.0001, hazard ratio 6.40 (2.71–14.49)). In PBK/TOPK-overexpressing GC cells, knockdown of PBK/TOPK inhibited the cell proliferation through the p53 activation in a TP53 mutation-dependent manner and inhibited the migration/invasion through the PTEN upregulation in a TP53 mutation-independent manner.

Conclusions:

These findings suggest PBK/TOPK plays a crucial role in tumour malignant potential through its overexpression and highlight its usefulness as a prognostic factor and potential therapeutic target in GC.

MicroRNA-224 aggrevates tumor growth and progression by targeting mTOR in gastric cancer

Growing evidence suggests that microRNA plays an essential role in the development and metastasis of many tumors, including gastric cancer. Aberrant miR-224 expression has been indicated in tumor growth, the mechanism of miR-224 promoting the proliferation and metastatic ability for gastric cancer remains unclear. Accumulating evidence reports that mTOR signal pathway plays an important role in the cellular process, such as apoptosis, cell growth and proliferation. The goal of the present study was to identify whether miR-224 could inhibit the growth, migration, invasion, proliferation and metastasis of gastric cancer through targeting mTOR expression. Real-time PCR (RT-PCR) was used to quantify miR-224 expression in vitro and in vivo experiments. Luciferase reporter assays were performed to confirm the activity of mTOR pathway, and immunofluorescence staining assay was conducted to observe apoptosis and cell proliferation ability. Bioinformatics as well as cell luciferase function studies distinguished the direct modulation of miR-224 on the 3'-UTR of the mTOR, which leads to the inactivation of apoptosis signaling and the activation of cell proliferation. In addition, inhibition of miR-224 significantly reduced the expression of mTOR and improved caspase-9/3 expression while decreased cyclin D1/2 levels, attenuating gastric cancer cell proliferation. Therefore, the present study revealed the mechanistic links between miR-224 and mTOR in the pathogenesis of gastric cancer through modulation of caspase-9/3 and cyclin D1/2. In addition, targeting miR-224 could serve as a novel strategy for future gastric cancer therapy.

Epigenetic alterations in gastric cancer (Review)

Gastric cancer is one of the most common types of cancer and the second most common cause of cancer-related mortality worldwide. An increasing number of recent studies have confirmed that gastric cancer is a multistage pathological state that arises from environmental factors; dietary factors in particulary are considered to play an important role in the etiology of gastric cancer. Improper dietary habits are one of the primary concerns as they influence key molecular events associated with the onset of gastric carcinogenesis. In the field of genetics, anticancer research has mainly focused on the various genetic markers and genetic molecular mechanisms responsible for the development of this of this disease. Some of this research has proven to be very fruitful, providing insight into the possible mechamisms repsonsible for this disease and into possible treatment modalities. However, the mortality rate associated with gastric cancer remains relatively high. Thus, epigenetics has become a hot topic for research, whereby genetic markers are bypassed and this research is directed towards reversible epigenetic events, such as methylation and histone modifications that play a crucial role in carcinogenesis. The present review focuses on the epigenetic events which play an important role in the development and progression of this deadly disease, gastric cancer.

Overexpression of SMYD2 contributes to malignant outcome in gastric cancer

BACKGROUND

SET and MYND domain-containing protein 2 (SMYD2) is a lysine methyltransferase for histone H3, p53 and Rb and inhibits their transactivation activities. In this study, we tested whether SMYD2 (1q42) acts as a cancer-promoting factor by being overexpressed in gastric cancer.

METHODS

We analysed 7 gastric cancer cell lines and 147 primary tumor samples of gastric cancer, which were curatively resected in our hospital.

RESULTS

SET and MYND domain-containing protein 2 was detected in these cell lines (five out of seven cell lines; 71.4%) and primary tumor samples (fifty-six out of one hundred and forty-seven cases; 38.1%). Knockdown of SMYD2 using specific small interfering RNA inhibited proliferation, migration and invasion of SMYD2-overexpressing cells in a TP53 mutation-independent manner. Overexpression of SMYD2 protein correlated with larger tumor size, more aggressive lymphatic invasion, deeper tumor invasion and higher rates of lymph node metastasis and recurrence. Patients with SMYD2-overexpressing tumours had a worse overall rate of survival than those with non-expressing tumours (P=0.0073, log-rank test) in an intensity and proportion score-dependent manner. Moreover, multivariate analysis demonstrated that SMYD2 was independently associated with worse outcome (P=0.0021, hazard ratio 4.25 (1.69-10.7)).

CONCLUSIONS

These findings suggest that SMYD2 has a crucial role in tumor cell proliferation by its overexpression and highlight its usefulness as a prognostic factor and potential therapeutic target in gastric cancer.

Role of p16 gene promoter methylation in gastric carcinogenesis: a meta-analysis

This meta-analysis was performed to evaluate the relationships between promoter DNA methylation in tumor suppressor gene p16 and gastric carcinogenesis. The PubMed, CISCOM, CINAHL, Web of Science, Google Scholar, EBSCO, Cochrane Library and CBM databases were searched for relevant articles published before November 1st, 2013 without any language restrictions. Meta-analysis was conducted using the STATA 12.0 software. Crude odds ratios (ORs) with 95% confidence intervals (95% CI) were calculated. Forty-seven clinical cohort studies that met all inclusion criteria were included in this meta-analysis. A total of 2,813 gastric cancer (GC) patients were assessed. Our meta-analysis results revealed that the frequencies of p16 promoter methylation in the GC tissues were higher than those of normal and adjacent tissues (Normal: OR = 23.04, 95% CI = 13.55-39.15, P < 0.001; Adjacent: OR = 4.42, 95% CI = 1.66-11.76, P = 0.003; respectively). Furthermore, we observed significant associations of p16 promoter methylation with TNM stage, histologic grade, invasive grade, lymph node metastasis of GC (TNM stage: OR = 3.60, 95% CI: 2.17-5.98, P < 0.001; Histologic grade: OR = 2.63, 95% CI: 1.55-4.45, P < 0.001; Invasive grade: OR = 3.44, 95% CI: 1.68-7.06, P = 0.001; Lymph node metastasis: OR = 2.68, 95% CI: 1.66-4.32, P < 0.001; respectively). However, there were no correlations of p16 promoter methylation with the TNM stage and Helicobacter pylori (HP) infection of GC (Tumor size: OR = 0.76, 95% CI: 0.14-4.07, P = 0.746; HP infection: OR = 1.31, 95% CI: 0.75-2.27, P = 0.342; respectively). Our findings provide empirical evidence that p16 promoter methylation may play an important role in gastric carcinogenesis. Thus, p16 promoter methylation may be a promising potential biomarker for the early diagnosis of GC.

CpG island methylator phenotype, Helicobacter pylori, Epstein-Barr virus, and microsatellite instability and prognosis in gastric cancer: a systematic review and meta-analysis

Background

The controversy of CpG island methylator phenotype (CIMP) in gastric cancer persists, despite the fact that many studies have been conducted on its relation with helicobacter pylori (H. pylori), Epstein-Barr virus (EBV), and microsatellite instability (MSI) and prognosis. To drive a more precise estimate of this postulated relationship, a meta-analysis was performed based on existing relevant studies.

Methods

We combined individual patient data from 12 studies which involved 1000 patients with gastric cancer, which met the criteria. We tabulated and analyzed parameters from each study, including H. pylori, EBV, MSI, and clinical information of patients.

Results

The overall OR for H. pylori infection in CIMP positive group vs. negative group revealed that significantly elevated risks of positive H. pylori infection in the former were achieved (OR 2.23 95% CI, 1.25–4.00; P = 0.007, P_{heterogeneity} = 0.05). Similarly, strong relation between EBV infection and CIMP was achieved by OR 51.27 (95% CI, 9.39–279.86; P<0.00001, P_{heterogeneity} = 0.39). The overall OR for MSI in CIMP positive group vs. negative group was 4.44 (95% CI, 1.17–16.88; P = 0.03, P_{heterogeneity} = 0.01). However, there did not appear to be any correlations with clinical parameters such as tumor site, pathological type, cell differentiation, TNM stage, distant metastasis, lymph node metastasis, and 5-year survival.

Conclusions

The meta-analysis highlights the strong relation of CIMP with H. pylori, EBV, and MSI, but CIMP can not be used as a prognostic marker for gastric cancer.

Overexpression of YWHAZ relates to tumor cell proliferation and malignant outcome of gastric carcinoma

BACKGROUND

Several studies have demonstrated that YWHAZ (14-3-3ζ), included in the 14-3-3 family of proteins, has been implicated in the initiation and progression of cancers. We tested whether YWHAZ acted as a cancer-promoting gene through its activation/overexpression in gastric cancer (GC).

METHODS

We analysed 7 GC cell lines and 141 primary tumours, which were curatively resected in our hospital between 2001 and 2003.

RESULTS

Overexpression of the YWHAZ protein was frequently detected in GC cell lines (six out of seven lines, 85.7%) and primary tumour samples of GC (72 out of 141 cases, 51%), and significantly correlated with larger tumour size, venous and lymphatic invasion, deeper tumour depth, and higher pathological stage and recurrence rate. Patients with YWHAZ-overexpressing tumours had worse overall survival rates than those with non-expressing tumours in both intensity and proportion expression-dependent manner. YWHAZ positivity was independently associated with a worse outcome in multivariate analysis (P=0.0491, hazard ratio 2.3 (1.003-5.304)). Knockdown of YWHAZ expression using several specific siRNAs inhibited the proliferation, migration, and invasion of YWHAZ-overexpressing GC cells. Higher expression of the YWHAZ protein was significantly associated with the lower expression of miR-375 in primary GC tissues (P=0.0047).

CONCLUSION

These findings suggest that YWHAZ has a pivotal role in tumour cell proliferation through its overexpression, and highlight its usefulness as a prognostic factor and potential therapeutic target in GC.

Role of DNA methylation in the development of Epstein-Barr virus-associated gastric carcinoma

The frequencies of DNA methylation of certain tumor-related genes are higher in Epstein-Barr virus (EBV)-associated gastric carcinomas than in EBV-negative gastric carcinomas. EBV-associated gastric carcinomas have distinct clinicopathological features; however, there are no case-control studies comparing methylation frequency between EBV-associated gastric carcinomas and controls that have been adjusted according to the clinicopathological features of EBV-associated gastric carcinomas. This study evaluated 25 EBV-associated gastric carcinomas that were positive for EBV-encoded small RNA 1 (EBER-1) by in situ hybridization and 50 EBV-negative gastric carcinomas that were matched with the EBV-associated gastric carcinomas by age, sex, histology, depth of tumor invasion, and stage. Methylation status of 16 loci associated with tumor-related genes was analyzed by methylation-specific polymerase chain reaction (PCR) to identify genes in which DNA methylation specifically occurred in EBV-associated gastric carcinomas. Methylation frequencies of 12 of the 16 genes were higher in EBV-associated gastric carcinomas than in EBV-negative controls, and the frequency of methylation of 6 specific loci (MINT2, MINT31, p14, p16, p73, and RUNX3) was significantly higher in EBV-associated gastric carcinomas than in EBV-negative controls. There were no significant differences in the methylation frequencies of the other genes. The mean methylation index in EBV-associated gastric carcinomas was significantly higher than that in EBV-negative controls. DNA methylation of tumor suppressor genes that regulate the cell cycle and apoptosis specifically occurred in EBV-associated gastric carcinomas. Aberrant DNA methylation might lead to the development and progression of EBV-associated gastric carcinoma.

Identification of gastric cancer risk markers that are informative in individuals with past H. pylori infection

BACKGROUND

Epigenomic damage induced by Helicobacter pylori infection is accumulated in gastric mucosae before the development of malignancy. In individuals without current H. pylori infection, DNA methylation levels of specific CpG islands (CGIs) are associated with gastric cancer risk. Because risk estimation in individuals with past infection is clinically important, we here aimed to identify the risk markers that reflect epigenomic damage induced by H. pylori infection, and that are informative in these individuals.

METHODS

Gastric mucosae were obtained from 55 gastric cancer patients (GC-Pt) (21 with current infection and 34 with past infection) and 55 healthy volunteers (HV) (7 never-infected, 21 with current infection, and 27 with past infection). Hypermethylated CGIs were searched for by methylated DNA immunoprecipitation-CGI microarray, and methylation levels were analyzed by quantitative methylation-specific polymerase chain reaction (PCR).

RESULTS

By microarray analysis of a pool of three samples from GC-Pt with past infection and another pool of samples from HV with past infection, 15 hypermethylated CGIs in the former pool were isolated. Seven of them had significantly higher methylation levels in GC-Pt with past infection (n = 10) than in HV with past infection (n = 10) (P < 0.001). In a validation cohort (21 GC-Pt with past infection and 14 HV with past infection), the seven new markers had large areas under the receiver-operating characteristic curves (0.78-0.84) and high odds ratios (12.7-36.0) compared with two currently available markers (0.60-0.65, 5.0-5.7).

CONCLUSIONS

We identified seven novel gastric cancer risk markers that are highly informative in individuals with past infection.

Overexpression of TRIM44 contributes to malignant outcome in gastric carcinoma

Recent studies have shown that some members of the tripartite motif-containing protein (TRIM) family, which is characterized by a conserved RING finger, B-box, and coiled-coil domains, function as important regulators for carcinogenesis. In this study, we tested whether TRIM44 (11p13) acts as a cancer-promoting gene through overexpression in gastric cancer. We analyzed seven gastric cancer cell lines and 112 primary tumors, which were curatively resected in our hospital between 2001 and 2003. Expression of the TRIM44 protein was detected in gastric cancer cell lines (2/7 cell lines; 29%) and primary tumor samples of gastric cancer (29/112 cases; 25%). Knockdown of TRIM44 expression using several specific siRNAs inhibited the proliferation, migration, and invasion of TRIM44-overexpressing cells. Overexpression of the TRIM44 protein was significantly correlated with an advanced type of macroscopic appearance, lymphatic invasion, and higher recurrence rate. TRIM44-overexpressing tumors had a worse overall rate of survival than those with non-expressing tumors (P = 0.0038, log-rank test) in both intensity and proportion expression-dependent manner. TRIM44 positivity was independently associated with worse outcome in multivariate analysis (P = 0.0233, hazard ratio 3.37 [1.18-9.64]). These findings suggest that TRIM44 plays a crucial role in tumor cell proliferation through its overexpression, and highlight its usefulness as a predictor and potential therapeutic target in gastric cancer.

Germline promoter hypermethylation of tumor suppressor genes in gastric cancer

AIM: To explore germline hypermethylation of the tumor suppressor genes MLH1, CDH1 and P16^INK4a in suspected cases of hereditary gastric cancer (GC).

METHODS: A group of 140 Chinese GC patients in whom the primary cancer had developed before the age of 60 or who had a familial history of cancer were screened for germline hypermethylation of the MLH1, CDH1 and P16^INK4a tumor suppressor genes. Genomic DNA was extracted from peripheral blood leukocytes and modified by sodium bisulfite. The treated DNA was then subjected to bisulfite DNA sequencing for a specific region of the MLH1 promoter. The methylation status of CDH1 or P16^INK4a was assayed using methylation-specific PCR. Clonal bisulfite allelic sequencing in positive samples was performed to obtain a comprehensive analysis of the CpG island methylation status of these promoter regions.

RESULTS: Methylation of the MLH1 gene promoter was detected in the peripheral blood DNA of only 1/140 (0.7%) of the GC patient group. However, this methylation pattern was mosaic rather than the allelic pattern which has previously been reported for MLH1 in hereditary non-polyposis colorectal cancer (HNPCC) patients. We found that 10% of the MLH1 alleles in the peripheral blood DNA of this patient were methylated, consistent with 20% of cells having one methylated allele. No germline promoter methylation of the CDH1 or P16^INK4a genes was detected.

CONCLUSION: Mosaic germline epimutation of the MLH1 gene is present in suspected hereditary GC patients in China but at a very low level. Germline epimutation of the CDH1 or P16^INK4a gene is not a frequent event.

Pathobiologic implications of methylation and expression status of Runx3 and CHFR genes in gastric cancer

Runx3 and CHFR genes were defined as tumor suppressor genes in gastric cancer (GC) recently. This paper was to investigate the roles of methylation and expression status of Runx3 and CHFR genes in GC patients. Methylation-specific polymerase chain reaction (MSP) and bisulfite DNA sequencing (BSP) were used to detect methylation status of Runx3 and CHFR genes in GC patients. The expression of Runx3 and CHFR in GC patients was analyzed by reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical analysis. The expression of the protein and mRNA decreased remarkably in the patients with aberrant promoter methylation of Runx3 and CHFR genes. The methylation status of Runx3 and CHFR were inversely related to the tumor size, tumor invasion depth and tumor differentiation in GC patients. Moreover, the protein expression of Runx3 and CHFR were significantly correlated with tumor invasion depth and tumor differentiation, respectively. Aberrant promoter methylation of Runx3 and CHFR genes may be involved in the carcinogenesis and development of GC and may provide useful clues for the prediction of the malignant behaviors of GC.

Epigenetic biomarkers

Profound changes in the epigenetic landscape of cancer cells underlie the development of human malignancies. These changes include large-scale DNA methylation changes throughout the genome as well as alterations in the compendium of post-translational chromatin modifications. Epigenetic aberrations impact multiple steps during tumorigenesis, ultimately promoting the selection of neoplastic cells with increasing pathogenicity. Identification of these alterations for use as predictive and prognostic biomarkers has been a highly sought after goal. Recent advances in the field have not only greatly expanded our knowledge of the epigenetic changes driving neoplasia but also demonstrated their significant clinical utility as cancer biomarkers. These biomarkers have proved to be useful for identifying patients whose malignancies are sensitive to specific cytotoxic chemotherapies and may hold promise for predicting which patients will benefit from newer targeted agents directed at oncogenes. The recent application of global analysis strategies has further accelerated our understanding of the epigenome and promises to enhance the identification of epigenomic programs underlying cancer progression and treatment response.

Serum olfactomedin 4 (GW112, hGC-1) in combination with Reg IV is a highly sensitive biomarker for gastric cancer patients

Gastric cancer (GC) is 1 of the most common human cancers. Early detection remains the most promising approach to improving long-term survival of patients with GC. We previously performed Serial Analysis of Gene Expression (SAGE) on 4 primary GCs and identified several GC-specific genes including Reg IV. Of these genes, olfactomedin 4 (OLFM4, also known as GW112 or hGC-1) is a candidate gene for cancer-specific expression. In this study, we examined the expression of olfactomedin 4 in human GC by immunohistochemistry. We also assessed serum olfactomedin 4 levels in GC patients by enzyme-linked immunosorbent assay. 94 (56%) of 167 GC cases were positive for olfactomedin 4 by immunostaining. Olfactomedin 4 staining was observed more frequently in stage I/II cases than in stage III/IV cases. The serum olfactomedin 4 concentration in presurgical GC patients (n = 123, mean +/- SE, 36.3 +/- 3.5 ng/mL) was significantly higher than that in healthy individuals (n = 76, 16.6 +/- 1.6 ng/mL). In patients with stage I GC, the sensitivity of serum olfactomedin 4 (25%) and Reg IV (35%) was superior to that of CA19-9 (5%) or CEA (3%). Furthermore, in patients with stage I GC, the combination of olfactomedin 4 and Reg IV elevated the diagnostic sensitivity to 52%. These results suggest that serum olfactomedin 4 is a useful marker for GC and its measurement alone or in combination with Reg IV has utility in the early detection of GC.

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.

Identification of prognostic biomarkers in gastric cancer using endoscopic biopsy samples

Endoscopic biopsy prior to chemotherapy provides an opportunity for studying biomarkers to predict the overall survival in gastric cancer patients. This prospective study was performed to identify prognostic biomarkers in patients with unresected gastric cancer. Fifty-nine cases of chemotherapy-naive metastatic gastric cancer were enrolled in this study. A microarray analysis was performed using 40 biopsy samples to identify candidate genes whose expressions might be correlated with the overall survival. After adjusting for clinical covariates based on a multivariate analysis, the identified genes were validated using real-time reverse transcription polymerase chain reaction (RT-PCR) analysis in 19 independent validation samples. Ninety-eight candidate genes whose expression levels were significantly correlated with the overall survival were identified using a microarray analysis based on a proportional hazards model (P < 0.005). Multivariate analysis was performed to assess 10 of these genes, and the results yielded a statistical significance level for DACH1 and PDCD6. We further evaluated these two genes in independent samples using real-time RT-PCR and found that lower mRNA expression levels of PDCD6 were correlated significantly with a poor overall survival. We identified PDCD6 as a prognostic biomarker in patients with unresected gastric cancer using endoscopic biopsy samples. Our PCR-based single gene prediction strategy successfully predicted the overall survival and may lead to a better understanding of this disease subgroup.

Endogastric capsule for E-cadherin gene (CDH1) promoter hypermethylation assessment in DNA from gastric juice of diffuse gastric cancer patients

BACKGROUND

We investigated whether an endogastric capsule (EC) may be a valuable tool for collecting DNA from exfoliated cells from the gastric mucosa and for carrying out an analysis of promoter methylation status of the E-cadherin (CDH1) gene in poorly differentiated, diffuse gastric cancer (DGC).

MATERIAL AND METHODS

Consecutive patients with a confirmed diagnosis of poorly differentiated DGC underwent collection of gastric juice by EC. Subjects without cancer and premalignant lesions were also accrued as controls. The samples of gastric juice were processed for DNA isolation and amplification. Then they were used for analysis of CDH1 promoter hypermethylation.

RESULTS

The procedure successfully allowed the analysis of CDH1 promoter hypermethylation in 20 patients and 14 controls. This pilot study showed feasibility of the procedure and a significantly different CDH1 promoter hypermethylation status between DGC patients and controls was detected.

CONCLUSIONS

The EC may represent an innovative and noninvasive tool for the analysis of a specific epigenetic change in DGC patients. Our findings deserve additional studies as this method may represent a cost-effective tool for early detection of sporadic as well as hereditary DGC in CDH1 germline mutations carriers.

Aberrant methylation of p16 predicts candidates for 5-fluorouracil-based adjuvant therapy in gastric cancer patients

BACKGROUND

Aberrant methylation of some cancer-related genes has been reported to correlate with sensitivity to chemotherapeutic agents. The present study was designed to determine whether DNA methylation in six cancer-related genes affects recurrence of gastric cancer in patients who received 5-fluorouracil-based adjuvant chemotherapy.

METHODS

The methylation status of six genes, MGMT, CHFR, hMLH1, p16INK4a, E-cadherin, and Runx3, was analyzed in 56 surgically resected gastric cancer tissue specimens by methylation-specific polymerase chain reaction. Of the 56 patients who underwent surgical resection, 38 received 5-fluorouracil (5-FU)-based adjuvant chemotherapy postoperatively (adjuvant group), whereas the other 18 (32%) did not (surgery group).

RESULTS

There were no significant differences between the two groups with respect to sex, cancer differentiation, depth of tumor invasion, lymph node metastasis, lymphatic invasion, vascular invasion and tumor stage. Among the genes, methylation of p16INK4a showed a significant correlation with longer survival in the 38 patients of the adjuvant group, but not in the 18 patients of the surgery group. A multivariate analysis identified p16INK4a methylation to be an independent factor predicting a longer recurrence-free period under 5-FU-based adjuvant chemotherapy.

CONCLUSIONS

The present study demonstrated for the first time that gastric cancer patients with p16INK4a methylation specifically benefit from 5-FU-based adjuvant chemotherapy.

DNA methylation of the RIZ1 gene is associated with nuclear accumulation of p53 in prostate cancer

The retinoblastoma protein-interacting zinc finger gene, RIZ1, is thought to be a tumor suppressor gene. RIZ1 is inactivated by mutation, deletion and DNA methylation in several human cancers. In the present study, the relationship between DNA methylation of RIZ1 and mutation of p53 was investigated in prostate cancer (PCa). In total, 47 cases of node-negative PCa (stages I-III) were analyzed. DNA methylation of the RIZ1 gene was detected in 20 (42.6%) of the 47 PCa tissues by methylation-specific polymerase chain reaction. DNA methylation of the RIZ1 gene was not associated with clinicopathological features. DNA methylation of RIZ1 tended to be present more frequently in PCa specimens with a high Gleason score (16/30, 53.3%) than in those with a low Gleason score (4/17, 23.5%); however, this tendency was not statistically significant (P = 0.0675). Nuclear accumulation of p53 was observed in four (8.5%) of 47 PCa specimens by immunostaining. All four PCa specimens with nuclear accumulation of p53 were stage III disease and showed DNA methylation of RIZ1. However, of the remaining 43 cancers without nuclear accumulation of p53, DNA methylation of RIZ1 was observed in only 16 (37.2%) specimens (P = 0.0272). Of the three PCa cell lines, only the PC3 cell line showed loss of RIZ1 mRNA due to DNA methylation, and this loss was rectified by treatment with a demethylating agent, 5-Aza-2'-deoxycytidine. These results suggest that transcriptional inactivation of RIZ1 by aberrant DNA methylation may contribute to prostate carcinogenesis. Genetic alterations are likely associated with epigenetic alterations in PCa.

DNA demethylation of vascular endothelial growth factor-C is associated with gene expression and its possible involvement of lymphangiogenesis in gastric cancer

Previous studies have indicated that lymphangiogenesis in solid tumors is associated with lymphatic metastasis. Overexpression of Vascular endothelial growth factor (VEGF)-C plays a major role in lymphangiogenesis in cancers. In the present study, DNA methylation and expression of the VEGF-C gene was investigated in gastric cancer (GC). Four GC cell lines (MKN-45, MKN-74, HSC-39 and HSC-43) showed no expression of VEGF-C, and the VEGF-C gene was found to be methylated in these cells. In contrast, 7 GC cell lines (MKN-1, MKN-7, MKN-28, TMK-1, KATO-III, SH101-P4 and HSC-44PE) expressed VEGF-C, and the VEGF-C gene was found to be unmethylated in these cell lines. In addition, expression of VEGF-C mRNA was retrieved by treatment with a demethylating agent, Aza-2'-deoxycytidine. In GC tissue samples, bisulfite DNA sequencing analysis revealed that VEGF-C was not methylated in 9 (29.0%) of 31 GC samples, whereas demethylation was not observed in corresponding non-neoplastic mucosa samples. Overexpression of VEGF-C mRNA was observed in 16 (51.6%) of 31 GC samples by quantitative reverse transcription-polymerase chain reaction. Of the 9 GC cases with VEGF-C demethylation, 8 (88.9%) overexpressed VEGF-C. In contrast, of the 22 GC cases without VEGF-C demethylation, 8 (36.4%) overexpressed VEGF-C (p = 0.0155). Furthermore, lymphatic vessel density determined by immunostaining of podoplanin in GC tissues was associated with overexpression of VEGF-C (p < 0.0001). These results suggest that demethylation and activation of the VEGF-C gene is likely involved in lymphangiogenesis in GC.

Expression of Wnt-5a is correlated with aggressiveness of gastric cancer by stimulating cell migration and invasion

Wnt-5a is a representative ligand that activates a beta-catenin-independent pathway in the Wnt signaling. Although abnormal activation of beta-catenin-dependent pathway is often observed in human cancer, the relationship between beta-catenin-independent pathway and tumorigenesis is not clear. We sought to clarify how Wnt-5a is involved in aggressiveness of gastric cancer. Abnormal expression of Wnt-5a was observed in 71 of 237 gastric cancer cases by means of immunohistochemistry. The positivity of Wnt-5a expression was correlated with advanced stages and poor prognosis of gastric cancer. Wnt-5a had the abilities to stimulate cell migration and invasion in gastric cancer cells. Wnt-5a activated focal adhesion kinase and small GTP-binding protein Rac, both of which are known to play a role in cell migration. Cell migration, membrane ruffling, and turnover of paxillin were suppressed in Wnt-5a knockdown cells. Furthermore, anti-Wnt-5a antibody suppressed gastric cancer cell migration. These results suggest that Wnt-5a stimulates cell migration by regulating focal adhesion complexes and that Wnt-5a is not only a prognostic factor but also a good therapeutic target for gastric cancer.

Accumulation of DNA methylation is associated with tumor stage in gastric cancer

BACKGROUND

The authors purpose in this study was to clarify the difference in terms of clinicopathologic features between gastric cancer (GC) with high numbers of DNA methylated genes and CpG island methylator phenotype (CIMP)-positive GC as originally defined.

METHODS

We analyzed DNA methylation of 12 tumor-related genes (hMLH1, MGMT, p16(INK4a), CDH1, RAR-beta, HLTF, RIZ1, TM, FLNc, LOX, HRASLS, HAND1) in 75 samples of GC from 75 patients, 25 samples of corresponding nonneoplastic mucosa from 25 patients, and 10 samples of normal gastric mucosa from 10 healthy young individuals by methylation-specific polymerase chain reaction (PCR) and bisulfite PCR. We also investigated CIMP status by examining the methylation of five MINT loci and p53 mutation status by PCR single-strand conformation polymorphism. We measured levels of expression of mRNAs for these 12 genes by quantitative reverse transcription PCR in 50 GC specimens.

RESULTS

The average number of methylated genes per tumor was 4.83. DNA methylation of each gene was correlated with low expression of the respective mRNA. High methylation (GC with 5 or more methylated genes) was detected in 39 (52.0%) of 75 GCs. Twenty-nine (37.8%) of 75 GCs were CIMP-positive. DNA methylation of each of the 12 genes was observed more frequently in the high-methylation group than in the low-methylation group. Methylation of 6 specific genes occurred more frequently in CIMP-positive GC than in CIMP-negative GC. Methylation of the remaining 6 genes was not correlated with CIMP-status. High methylation was found more frequently in Stage III/IV GC (26 of 40 cases, 65.0%) than in Stage I/II GC (13 of 35 cases, 37.1%, P = 0.029).CONCLUSIONS.These findings indicate that GCs with higher numbers of methylated genes have more distinct DNA methylation profiles than the originally defined CIMP-positive GCs. DNA methylation of tumor-related genes accumulates in conjunction with tumor progression.

Genetic, epigenetic, and clinicopathologic features of gastric carcinomas with the CpG island methylator phenotype and an association with Epstein-Barr virus

BACKGROUND

The CpG island methylator phenotype (CIMP), which is characterized by simultaneous methylation of the CpG islands of multiple genes, has been recognized as one of the important mechanisms in gastrointestinal carcinogenesis.

METHODS

Methylation of the 5 methylated-in-tumors (MINT) loci and 12 tumor-related genes in 78 primary gastric carcinomas was examined using combined bisulfite-restriction analysis. Epstein-Barr virus (EBV)-associated gastric tumors were detected using real-time polymerase chain reaction analysis followed by an evaluation of the correlations between CIMP status, EBV-association, and genetic alteration of p53 and K-ras. The authors compared the clinicopathologic features of gastric carcinomas that had high CIMP methylation (CIMP-H) with tumors that had low CIMP methylation (CIMP-L) or negative CIMP methylation (CIMP-N).

RESULTS

The methylation profiles of 12 genes showed nonrandom methylation, supporting the presence of CIMP in gastric carcinoma. No p53 mutations were detected among CIMP-H tumors, and no EBV association was detected in tumors that showed mutation of p53 and K-ras. In a multiple logistic regression model with CIMP-H as the dependent variable, proximal location (P = .011), diffuse type (P = .019), and less advanced pathologic TNM status (P = .043) contributed significantly to CIMP-H. Patients who had CIMP-N gastric tumors had a significantly worse survival than patients who had CIMP-H tumors (P = .004) or CIMP-L tumors (P = .012). EBV-associated tumors were associated strongly with CIMP-H, hypermethylation of tumor-related genes, and no p53 or K-ras mutation.

CONCLUSIONS

CIMP status appeared to be associated with distinct genetic, epigenetic, and clinicopathologic features in gastric carcinomas. The finding that gastric carcinomas arose through different molecular pathways may affect not only tumor characteristics but also patient prognosis.

CpG island hypermethylation in progression of esophageal and gastric cancer

The upper gastrointestinal (GI) cancers have various carcinogenic pathways and precursor lesions, such as dysplasia for esophageal squamous cell carcinoma, Barrett esophagus for esophageal adenocarcinoma, and intestinal metaplasia for the intestinal-type of gastric cancer. Recently, many epigenetic events in carcinogenic pathways have been revealed, along with genomic and genetic alterations. This information has provided deeper insight into an understanding of the mechanisms of upper GI carcinogenesis. Moreover, detection methods of aberrant methylation have been applied to clinical fields to stratify high-risk groups, detect early cancer, and to predict clinical outcomes. In this review, a variety of information is summarized regarding gene hypermethylation in esophageal and gastric cancer.

Down-regulation of the claudin-18 gene, identified through serial analysis of gene expression data analysis, in gastric cancer with an intestinal phenotype

Gastric cancer (GC) is one of the most common malignancies worldwide. Genes whose expression is down-regulated in GC may be tumour suppressor genes. In the present study, genes with decreased expression in GC were screened for by serial analysis of gene expression (SAGE) data analysis and reverse transcription (RT)-polymerase chain reaction (PCR), and CLDN18 (encoding claudin-18) was identified. Quantitative RT-PCR revealed that expression of CLDN18 was down-regulated in 13 (56.5%) of 23 GCs. Immunostaining showed that normal gastric mucosa and Paneth cells of the duodenum expressed claudin-18 on cell membranes. Expression of claudin-18 was reduced in several intestinal metaplasias of the stomach. Of 20 samples of gastric adenoma, 18 (90.0%) showed decreased claudin-18 expression. Down-regulation of claudin-18 was observed in 84 of 146 GCs (57.5%) and correlated with poor survival in 65 advanced GCs (p = 0.0346). In addition, expression of the gastric and intestinal phenotypes of GC was examined by immunostaining for MUC5AC, MUC6, MUC2, and CD10. Of 38 GCs showing only the intestinal phenotype, down-regulation of claudin-18 was observed in 28 (73.7%), whereas in the remaining 108 GC cases, down-regulation of claudin-18 was observed in 56 (51.9%) (p = 0.0224). These results indicate that claudin-18 is a good marker of poor survival in GC. Down-regulation of claudin-18 may be involved in GCs with an intestinal phenotype, and may be an early event in gastric carcinogenesis.

DNA methylation profiles of differentiated-type gastric carcinomas with distinct mucin phenotypes

Gastric carcinomas (GC) are classified into four phenotypes according to mucin expression. Previous studies revealed the association of distinct genetic profiles in GC with mucin phenotypic expression; however, the roles of epigenetic changes, such as DNA methylation, are poorly understood. We examined whether the phenotypic expression of GC was associated with DNA methylation of hMLH1, MGMT, p16(INK4a), RAR-beta or CDH1. Expression of HGM, M-GGMC-1, MUC2, and CD10 was analyzed immunohistochemically in 33 advanced GC with differentiated histology. HGM was expressed in 14 (42.4%) cases, M-GGMC-1 in five (15.2%) cases, MUC2 in 15 (45.5%) cases and CD10 in 18 (54.5%) cases. DNA methylation was detected in five (15.2%) cases for hMLH1, 11 (33.3%) cases for MGMT, 13 (39.4%) cases for p16(INK4a), 17 (51.5%) cases for RAR-beta and 14 (42.4%) cases for CDH1 by bisulfite-polymerase chain reaction and methylation-specific polymerase chain reaction. DNA methylation of hMLH1 occurred more frequently in MUC2-negative GC than in MUC2-positive GC (P = 0.0488, Fisher's exact test). In contrast, MGMT was more frequently methylated in MUC2-positive GC than in MUC2-negative GC (P = 0.0078, Fisher's exact test). There was no correlation between gastric or intestinal-markers and methylation of the p16(INK4a), RAR-beta and CDH1 genes. These results indicate that DNA methylation of specific genes, such as hMLH1 and MGMT, may be involved partly in the distinct phenotypic expression of GC.

Gene deregulation in gastric cancer

Despite its decreasing frequency in the Western world during recent decades, gastric cancer is still one of the leading causes of cancer-related deaths worldwide. Due to the oligosymptomatic course of early gastric cancer, most cases are diagnosed in the advanced stages of the disease. The curative potential of current standard treatment continues to be unsatisfactory, despite multimodal approaches involving surgery, chemotherapy and radiotherapy. Novel therapeutics including small molecules and monoclonal antibodies are being developed and have been partially introduced into clinical use in connection with neoplastic diseases such as chronic myeloid leukemia, non-Hodgkin's lymphoma and colorectal cancer. Thorough understanding of the changes in gene expression occurring during gastric carcinogenesis may help to develop targeted therapies and improve the treatment of this disease. Novel molecular biology techniques have generated a wealth of data on up- and down-regulation, activation and inhibition of specific pathways in gastric cancer. Here, we provide an overview of the different aspects of aberrant gene expression patterns in gastric cancer.

DNA methylation of genes linked to retinoid signaling in squamous cell carcinoma of the esophagus: DNA methylation of CRBP1 and TIG1 is associated with tumor stage

Hypermethylation of CpG islands is associated with the silencing of various tumor suppressor genes. Retinoic acid receptor-beta (RAR-beta), cellular retinol-binding protein 1 (CRBP1), and tazarotene-induced gene 1 (TIG1) have been linked to retinoic acid signaling. Little is known about the involvement of these three genes in esophageal squamous cell carcinoma (ESCC). In this study, we investigated the methylation status of these genes and analyzed the role of methylation of their DNA in ESCC. Methylation-specific polymerase chain reaction (PCR) was performed to study the methylation of CpG islands in 28 ESCC (stages I, II, and III) and 10 samples of corresponding non-neoplastic mucosa. The mRNA expression levels of the three genes were measured by quantitative reverse transcription-PCR. DNA hypermethylation of RAR-beta was found in seven (25.0%) of the 28 ESCC, of CRBP1 in five (17.9%), and of TIG1 in five (17.9%). DNA methylation of RAR-beta was identified in one of 10 samples of corresponding non-neoplastic mucosa (10.0%), whereas no DNA methylation of CRBP1 or TIG1 was detected. In total, at least one of the three genes was hypermethylated in 12 (42.9%) ESCC. Reduced expression of RAR-beta, CRBP1, and TIG1 was found in 14 (50.0%), 15 (53.6%), and 13 (46.4%) ESCC, respectively. DNA methylation of each gene was significantly associated with reduced expression of the respective mRNA. No correlation was found between the DNA methylation status of RAR-beta and clinicopathological factors such as depth of invasion, lymph node metastasis, or tumor stage. In contrast, DNA methylation of both CRBP1 and TIG1 was observed only in stage III ESCC. These results show that inactivation of the retinoic acid signaling-associated genes RAR-beta, CRBP1, and TIG1 by DNA methylation occurs frequently in ESCC.

Differential DNA hypermethylation of critical genes mediates the stage-specific tobacco smoke-induced neoplastic progression of lung cancer

Promoter DNA methylation status of six genes in samples derived from 27 bronchial epithelial cells and matching blood samples from 22 former/current smokers and five nonsmokers as well as 49 primary non-small cell lung cancer samples with corresponding blood controls was determined using methylation-specific PCR (MSP). Lung tumor tissues showed a significantly higher frequency of promoter DNA methylation in p16, MGMT, and DAPK (P < 0.05; Fisher's exact test). p16 promoter DNA methylation in tumors was observed at consistently higher levels when compared with all the other samples analyzed (P = 0.001; Fisher's exact test). ECAD and DAPK exhibited statistically insignificant differences in their levels of DNA methylation among the tumors and bronchial epithelial cells from the smokers. Interestingly, similar levels of methylation were observed in bronchial epithelial cells and corresponding blood from smokers for all four genes (ECAD, p16, MGMT, and DAPK) that showed smoking/lung cancer-associated methylation changes. In summary, our data suggest that targeted DNA methylation silencing of ECAD and DAPK occurs in the early stages and that of p16 and MGMT in the later stages of lung cancer progression. We also provide preliminary evidence that peripheral lymphocytes could potentially be used as a surrogate for bronchial epithelial cells to detect altered DNA methylation in smokers.

Loss of heterozygosity and histone hypoacetylation of the PINX1 gene are associated with reduced expression in gastric carcinoma

The expression of PINX1, a possible telomerase inhibitor and a putative tumor suppressor, has not been studied in human cancers, including gastric cancer (GC). We examined expression of PINX1 by quantitative reverse transcription (RT)-PCR in 73 cases of GC, and 45 of these cases were further studied for loss of heterozygosity (LOH) by PCR with microsatellite marker D8S277. Reduced expression (tumor vs normal ratio<0.5) of PINX1 was detected in 50 (68.5%) of 73 cases of GC. GC tissues with reduced expression of PINX1 showed significantly higher telomerase activities as measured by telomeric repeat amplification protocol than those with normal expression of PINX1 (P=0.031). LOH of PINX1 locus was detected in 15 (33.3%) of 45 cases of GC and was correlated significantly with reduced expression of PINX1 (P=0.031). Expression of PINX1 in a GC cell line, MKN-74, was induced by treatment with trichostatin A (TSA) or nicotinamide (NAM). Chromatin immunoprecipitation assay of MKN-74 cells revealed that acetylation of histone H4 in the 5' untranslated region (UTR) of PINX1 was enhanced by treatment with TSA or NAM, whereas acetylation of histone H3 was not changed by TSA or NAM. In addition, TSA or NAM treatment led to inhibition of telomerase activity in MKN-74 cells. These results indicate that LOH of PINX1 locus and hypoacetylation of histone H4 in the 5' UTR of PINX1 are associated with reduced expression of PINX1 in GC.

Histone H3 acetylation is associated with reduced p21(WAF1/CIP1) expression by gastric carcinoma

Histone acetylation appears to play an important role in transcriptional regulation. Inactivation of chromatin by histone deacetylation is involved in the transcriptional repression of several tumour suppressor genes, including p21(WAF1/CIP1). However, the in vivo status of histone acetylation in human cancers, including gastric carcinoma, is not well understood. This study shows that histone H3 in the p21(WAF1/CIP1) promoter region is hypoacetylated and that this hypoacetylation is associated with reduced p21(WAF1/CIP1) expression in gastric carcinoma specimens. Chromatin immunoprecipitation assays revealed that histone H3 was hypoacetylated in the p21(WAF1/CIP1) promoter and coding regions in 10 (34.5%) and 10 (34.5%) of 29 gastric carcinoma specimens, respectively. Hypoacetylation of histone H4 in the p21(WAF1/CIP1) promoter and coding regions was observed in 6 (20.7%) and 16 (55.2%) of 29 gastric carcinoma specimens, respectively. p21(WAF1/CIP1) mRNA levels were associated with histone H3 acetylation status in the p21(WAF1/CIP1) promoter region (p = 0.047) but not p53 mutation status (p = 0.460). In gastric carcinoma cell lines, expression of p21(WAF1/CIP1) protein was induced by trichostatin A, a histone deacetylase inhibitor. This induction was associated with hyperacetylation of histone H3 in the p21(WAF1/CIP1) promoter region. Hyperacetylation of histone H4 in the p21(WAF1/CIP1) promoter region did not appear to be associated with increased expression. Induction of p21(WAF1/CIP1) protein expression was associated with hyperacetylation of histones H3 and H4 in the p21(WAF1/CIP1) coding region. Expression of a dominant-negative mutant of p53 reduced expression of p21(WAF1/CIP1) protein. Histone H4 acetylation in both the promoter and coding regions of the p21(WAF1/CIP1) gene in cells expressing dominant-negative p53 was less than half of that in cells expressing wild-type p53, whereas histone H3 acetylation in both the promoter and coding regions was slightly reduced (by approximately 20%) in cells expressing the dominant-negative p53. These findings provide evidence that alteration of histone acetylation occurs in human cancer tissue specimens such as those from gastric carcinoma.

DNA methylation of genes linked with retinoid signaling in gastric carcinoma

BACKGROUND

Hypermethylation of CpG islands has been associated with silencing of various tumor suppressor genes, and the retinoid acid receptor beta (RARbeta), cellular retinol-binding protein 1 (CRBP1), and tazarotene-induced gene 1 (TIG1) genes have been associated with retinoic acid signaling. To the authors' knowledge, little is known regarding the involvement of these three genes in gastric carcinoma (GC). In this study, the authors investigated the methylation status of these genes and analyzed the role of their DNA methylation in GC.

METHODS

DNA methylation of 3 retinoic acid-associated genes was analyzed in 42 samples of GC from 42 patients and in 8 GC cell lines by methylation-specific polymerase chain reaction (PCR) analysis. The mRNA expression levels for these three genes were measured by quantitative reverse transcription-PCR.

RESULTS

In 7 of 8 GC cell lines, the CRBP1 gene was hypermethylated, and CRBP1 transcription was inactive. In 6 of 8 GC cell lines, the TIG1 gene was hypermethylated, and TIG1 transcription was inactive. Treatment with demethylating agent 5-aza-2'-deoxycytidine restored both CRBP1 and TIG1 transcription. DNA methylation of the RARbeta, CRBP1, and TIG1 genes was detected in 15 of 42 GC samples (36%), 14 of 42 GC samples (33%), and 4 of 42 GC samples (10%), respectively, and in 6 of 30 samples (20%), 0 of 30 samples (0%), and 1 of 30 samples (3%) of corresponding nonneoplastic mucosa. None of the 10 normal gastric mucosa samples from young, healthy individuals demonstrated hypermethylation of any of these genes. DNA methylation of each gene was associated significantly with low mRNA expression of the respective gene. Twenty-four of 42 GC samples (57%) demonstrated hypermethylation of at least 1 of the 3 genes. However, no significant, concordant hypermethylation of these genes was observed.

CONCLUSIONS

The results suggested that gastric carcinogenesis involves transcriptional inactivation by aberrant DNA methylation of genes related to retinoid signaling.

Prognostic analysis of E-cadherin gene promoter hypermethylation in patients with surgically resected, node-positive, diffuse gastric cancer

PURPOSE

Recent investigations have demonstrated that hypermethylation is a frequent mechanism for silencing tumor suppressor genes. This is a potentially reversible epigenetic change, and it is the target of a novel class of anticancer compounds with demethylating activity. Better understanding of the clinical implications of hypermethylation will allow the optimal planning of future trials with demethylating drugs. In this perspective, we investigated whether hypermethylation in the CDH1 promoter region is correlated with poor prognosis of patients with surgically resected, node-positive, diffuse gastric cancer.

EXPERIMENTAL DESIGN

Consecutive cases of diffuse gastric cancer were considered eligible for study entry. Additional inclusion criteria were radical surgery with a minimum of D1 lymphadenectomy, complete follow-up information, and availability of tumor specimens for methylation-specific PCR and immunohistochemistry analyses.

RESULTS

CDH1 promoter hypermethylation was found in 40 of 73 cases (54%), and it was significantly associated with worse prognosis. In patients with and without hypermethylation, the 5-year event-free survival rate was 30% and 62%, respectively, and the 5-year overall survival rate was 35% and 67%, respectively. CDH1 promoter hypermethylation retained its prognostic role for disease-free survival (P < 0.001) and overall survival (P < 0.001) in multivariate analysis. Immunohistochemistry showed a significant association between CDH1 methylation and E-cadherin expression (P < 0.001).

CONCLUSIONS

This study shows adverse prognostic effect of CDH1 promoter hypermethylation in patients with diffuse gastric cancer. This form of cancer, and other types with frequent hypermethylation and silencing of critical tumor suppressor genes, would make appropriate targets for the testing of novel compounds with demethylating activity.