Causes and consequences of microsatellite instability in gastric carcinogenesis

Loss of ARID1A Expression in Gastric Cancer: Correlation with Mismatch Repair Deficiency and Clinicopathologic Features

Purpose

The AT-rich interactive domain 1A (ARID1A) gene encodes BRG1-associated factor 250a, a component of the SWItch/Sucrose NonFermentable chromatin remodeling complex, which is considered a tumor suppressor in many tumors. We aimed to investigate the prognostic significance of ARID1A expression in gastric cancers and explore its relationship with clinicopathologic parameters such as mismatch repair protein expression.

Materials and Methods

Four tissue microarrays were constructed from 191 resected specimens obtained at Soonchunhyang University Cheonan Hospital from 2006 to 2008. Nuclear expression of ARID1A was semiquantitatively assessed and binarized into retained and lost expression.

Results

Loss of ARID1A expression was observed in 62 cases (32.5%). This was associated with more frequent vascular invasion (P=0.019) and location in the upper third of the stomach (P=0.001), and trended toward more poorly differentiated subtypes (P=0.054). ARID1A loss was significantly associated with the mismatch repair-deficient phenotype (P=0.003). ARID1A loss showed a statistically significant correlation with loss of MLH1 (P=0.001) but not MSH2 expression (P=1.000). Kaplan-Meier survival analysis showed no statistically significant difference in overall survival; however, patients with retained ARID1A expression tended to have better overall survival than those with loss of ARID1A expression (P=0.053). In both mismatch repair-deficient and mismatch repair-proficient groups, survival analysis showed no differences related to ARID1A expression status.

Conclusions

Our results demonstrated that loss of ARID1A expression is closely associated with the mismatch repair-deficient phenotype, especially in sporadic microsatellite instability-high gastric cancers.

Epigenetic regulation of DNA repair machinery in Helicobacter pylori-induced gastric carcinogenesis

Although thousands of DNA damaging events occur in each cell every day, efficient DNA repair pathways have evolved to counteract them. The DNA repair machinery plays a key role in maintaining genomic stability by avoiding the maintenance of mutations. The DNA repair enzymes continuously monitor the chromosomes to correct any damage that is caused by exogenous and endogenous mutagens. If DNA damage in proliferating cells is not repaired because of an inadequate expression of DNA repair genes, it might increase the risk of cancer. In addition to mutations, which can be either inherited or somatically acquired, epigenetic silencing of DNA repair genes has been associated with carcinogenesis. Gastric cancer represents the second highest cause of cancer mortality worldwide. The disease develops from the accumulation of several genetic and epigenetic changes during the lifetime. Among the risk factors, Helicobacter pylori (H. pylori) infection is considered the main driving factor to gastric cancer development. Thus, in this review, we summarize the current knowledge of the role of H. pylori infection on the epigenetic regulation of DNA repair machinery in gastric carcinogenesis.

The involvement of survivin in insulin-like growth factor 1-induced epithelial-mesenchymal transition in gastric cancer

It has been identified that insulin-like growth factor 1 (IGF-1) activated various pathways of the epithelial-mesenchymal transition (EMT) in a couple of tumors. At the same time, survivin is implicated in EMT of gastric cancer (GC). To date, the impact of survivin on IGF-1-mediated EMT of GC has not been featured. In this work, we used the immunohistochemistry and molecular and cellular experiments to investigate the existence and significance of IGF-1 and survivin. Our findings revealed that survivin protein can be observed in majority of samples in all GC samples. Importantly, survivin expression has an obvious association with GC stage, and metastasis. In vitro, GC cell line BGC823 was treated with different concentrations of IGF-1, resulting in the activation of p-ERK, p-AKT, survivin, and the expression of EMT biomarkers, including N-cadherin, MMP2, and Snail. However, the silencing of survivin eradicated the expression IGF-1-induced EMT biomarkers and affected the migration and invasion of BGC823 cells. In conclusion, IGF-1 signaling activated survivin expression and controlled the expression of EMT biomarkers in the development of GC. This study lays a new stage for the molecular therapy of GC patients in the clinical treatment.

Recognition of and recent issues in hereditary diffuse gastric cancer

In East Asian countries, gastric cancer incidence is high, but detection rates for germline CDH1 mutations that cause hereditary diffuse gastric cancers (HDGCs) are low. Consequently, screens and genetic testing for HDGC are often considered unimportant. Since the first germline truncating CDH1 mutations in Japanese patients were reported, some HDGC cases have been reported, and some of these involve large germline rearrangements and de novo mutation of CDH1. New methods for mutation detection--such as multiplex ligation-dependent probe amplification, array comparative genomic hybridization, and exome sequencing--have become available, as have new experimental models, including novel gene-knockout mice and gastric organoids. Because of these advances, searches for candidate genes (e.g., CTNNA1, MAP3K6) and our understanding of HDGC pathogenesis have improved in recent years; moreover, there have been substantial changes in the field since the current HDGC consensus guidelines were released. This review focuses on recent issues and advances in the study of HDGC. For example, lobular breast cancer cases and de novo occurrences of DGC are unlikely to meet the existing criteria for genetic testing, but current evidence indicates that some such cases may be good candidates for genetic testing. It is important to recognize that HDGC is a syndrome and that lobular breast cancer can be the first manifestation of this syndrome. CDH1 testing, including analyses of large genomic rearrangements, should be recommended even in countries where few HDGC cases have been reported.

CrkL meditates CCL20/CCR6-induced EMT in gastric cancer

BACKGROUND

In recent years, Crk-like adapter protein (CrkL) has been identified as a key regulator in the epithelial-to-mesenchymal transition (EMT). However, the molecular mechanisms underlying the CC chemokine receptor 6 (CCR6) and chemokine (C-C motif) ligand 20 (CCL20)-induced EMT in gastric cancer are still unclear.

METHODS

We conducted the immunohistochemistry and immunoblotting to detect the expression of CCR6 and CrkL in 90 cases of gastric cancer tissues and five kinds of cell lines. And then, gastric cancer cells were subjected to small interfering RNA (siRNA) treatment and in vitro assay.

RESULTS

Both CCR6 and CrkL were aberrantly expressed in gastric cancer specimens and closely correlated with differentiation of cell lines. The expression of CCR6 and CrkL was also significantly associated with metastasis, stage, and poor prognosis of gastric cancer. In addition, we validated CCL20 activated the expression of p-CrkL, p-Erk1/2, p-Akt, vimentin, N-cadherin and MMP2 in MGC803 cells in a dose-dependent manner. However, si-CrkL abrogated the CCL20-induced p-Erk1/2, vimentin, N-cadherin and MMP2 expression. Most importantly, the knockdown of CrkL decreased migration and invasion of MGC803 cells.

CONCLUSIONS

CrkL mediates CCL20/CCR6-induced EMT via Akt pathway, instead of Erk1/2 pathway in development of gastric cancer, which indicated CCL20/CCR6-CrkL-Erk1/2-EMT pathway may be targeted to antagonize the progression of gastric cancer.

C23 protein meditates bone morphogenetic protein-2-mediated EMT via up-regulation of Erk1/2 and Akt in gastric cancer

In our previous study, the epithelial-to-mesenchymal transition (EMT) has been identified to be involved in gastric cancer progression. Notably, nuclear protein C23 and bone morphogenetic protein-2 (BMP2) have been linked into EMT. However, the specific mechanisms underlying BMP2 pathway-mediated EMT are not still unraveled. In this study, we adopted immunohistochemistry and immunoblotting to determine the expression of C23 and BMP2 receptor II (BMPR-II) in 90 gastric cancer samples and cell lines. Subsequently, relevant cell lines were selected to be treated with si-C23 or si-BMPRII and the detection of in vitro assay. Our results revealed that both C23 and BMPRII were aberrantly and constitutively expressed in gastric cancer specimens and cell lines, whose expression was positively associated with metastasis, stage and differentiation, and portended poor survival outcome of gastric cancer patients. In vitro assay validated the increased expression of p-Erk1/2, p-Akt, vimentin, N-cadherin, and MMP2 in BMP2-stimulated MGC803 cells, which was in a dose-dependent manner. By contrast, si-C23 treatment attenuated the BMP2-stimulated expression of p-Erk1/2, p-Akt, vimentin, N-cadherin, and MMP2. Also, the treatment of either si-C23 or si-BMPRII decreased the ability of migration and invasion of MGC803 cells. In conclusion, C23 mediates BMP2-induced EMT progression via the up-regulation of Erk1/2 and Akt signaling pathway in gastric cancer, which indicated both C23 and BMPRII pathway could be recommended as prospective targets or biomarkers to antagonize the progression of gastric cancer.

CCR7 pathway induces epithelial-mesenchymal transition through up-regulation of Snail signaling in gastric cancer

The chemokine receptor 7 (CCR7) and Snail signaling have been linked to various types of cancers. The associations between these signalings and the epithelial-mesenchymal transition (EMT) are not clear in gastric cancer. Here, the expression of CCR7 and Snail was detected in gastric cancer by immunohistochemistry and Western blot. Meanwhile, gastric cancer cells were subjected to CCL19, si-control, and si-Snail treatment. Cell cycle, migration, and invasion were also analyzed. The expression patterns of CCR7 and Snail were similar in either gastric cancer tissues or cells. The increased expression of CCR7 was closely associated with the increased Snail expression, which both were closely correlated with metastasis, stage and differentiation, and poor prognosis. The increased p-ERK, p-AKT, Snail, and MMP9 expression and the decreased E-cadherin were confirmed in MGC803 cells in a dose-dependent manner in response to CCL19 treatment. However, the blockade of Snail abrogated the up-regulation of MMP9 and down-regulation of E-cadherin. CCR7-induced ERK and PI3K pathway regulated Snail signaling. Besides si-Snail treatment led to MGC803 cell cycle arrest and affected the migration and invasion. In conclusion, our study suggested that CCR7 promotes Snail expression to induce the EMT, resulting in cell cycle progression, migration, and invasion in gastric cancer. CCR7-Snail pathway provided more potential regimens for cancer therapy.