Decreased expression of RASSF6 is a novel independent prognostic marker of a worse outcome in gastric cancer patients after curative surgery

Ubiquitous mitochondrial creatine kinase promotes the progression of gastric cancer through a JNK-MAPK/JUN/HK2 axis regulated glycolysis

BACKGROUND

Ubiquitous mitochondrial creatine kinase (uMtCK) transfers high-energy phosphates from mitochondrially generated ATP to creatine to generate phosphocreatine. uMtCK overexpression has been reported in several malignant tumors, however, the clinical significance and impact of uMtCK in gastric cancer (GC) has not been comprehensively studied.

METHODS

We first examined uMtCK expression in GC by quantitative real-time PCR and western blot assays. Then the clinicopathological significance of aberrant uMtCK expression was determined by immunohistochemical staining in a GC tissue microarray. Kaplan-Meier analysis was used for survival analysis. The biological functions of uMtCK in GC cells were explored by wound-healing, transwell assays and glucose metabolism assays in vitro as well as a liver metastasis model by spleen injection in nude mice in vivo.

RESULTS

We verified that the expression of uMtCK was substantially elevated in GC tissues, significantly associating with a poorer prognosis in GC patients, especially for those with advanced stage. In univariate and multivariate analyses, uMtCK expression emerged as an independent prognostic factor for both disease-free survival and overall survival. Functionally, we demonstrated that uMtCK promoted glycolysis in GC cells and facilitated their migration, invasion and liver metastasis in vitro and in vivo. Mechanistically, uMtCK enhanced GC progression in a HK2-dependent glycolysis via acting the JNK-MAPK/JUN signaling pathway.

CONCLUSIONS

uMtCK could serve as a novel independent prognostic biomarker as well as potential therapeutic target for GC patients, particularly for GC patients with an advanced UICC stage and tumor recurrence.

DNA damage triggers the nuclear accumulation of RASSF6 tumor suppressor protein via CDK9 and BAF53 to regulate p53-target gene transcription

RASSF6, a member of the tumor suppressor Ras-association domain family (RASSF) proteins, regulates cell cycle arrest and apoptosis via p53 and plays a tumor suppressor role. We previously reported that RASSF6 blocks MDM2-mediated p53 degradation and enhances p53 expression. In this study, we demonstrated that RASSF6 has nuclear-localization and nuclear-export signals and that DNA damage triggers the nuclear accumulation of RASSF6. We found that RASSF6 directly binds to BAF53, the component of SWI/SNF complex. DNA damage induces CDK9-mediated phosphorylation of BAF53, which enhances the interaction with RASSF6 and increases the amount of RASSF6 in the nucleus. Subsequently, RASSF6 augments the interaction between BAF53 and BAF60a, another component of SWI/SNF complex, and further promotes the interaction of BAF53 and BAF60a with p53. BAF53 silencing or BAF60a silencing attenuates RASSF6-mediated p53-target gene transcription and apoptosis. Thus, RASSF6 is involved in the regulation of DNA damage-induced complex formation including CDK9, BAF53, BAF60a, and p53.

Characterization of mouse embryonic fibroblasts derived from Rassf6 knockout mice shows the implication of Rassf6 in the regulation of NF-κB signaling

RASSF6 is a member of the tumor suppressor Ras association domain family (RASSF) proteins. We have reported using human cancer cell lines that RASSF6 induces apoptosis and cell cycle arrest via p53 and plays tumor suppressive roles. In this study, we generated Rassf6 knockout mice by CRISPR/Cas technology. Contrary to our expectation, Rassf6 knockout mice were apparently healthy. However, Rassf6-null mouse embryonic fibroblasts (MEF) were resistant against ultraviolet (UV)-induced apoptosis/cell cycle arrest and senescence. UV-induced p53-target gene expression was compromised, and DNA repair was delayed in Rassf6-null MEF. More importantly, KRAS active mutant promoted the colony formation of Rassf6-null MEF but not the wild-type MEF. RNA sequencing analysis showed that NF-κB signaling was enhanced in Rassf6-null MEF. Consistently, 7,12-dimethylbenz(a)anthracene (DMBA) induced skin inflammation in Rassf6 knockout mice more remarkably than in the wild-type mice. Hence, Rassf6 deficiency not only compromises p53 function but also enhances NF-κB signaling to lead to oncogenesis.

RASSF6 Is Downregulated In Human Bladder Cancers And Regulates Doxorubicin Sensitivity And Mitochondrial Membrane Potential Via The Hippo Signaling Pathway

Background

The present study aimed to investigate the clinicopathological significance and biological roles of RASSF6 in human bladder cancers.

Materials and methods

Immunohistochemistry and Western blots were used to examine the protein expression of RASSF6 in bladder cancer tissues. Biological roles of RASSF6 were examined using MTT, colony formation assay, Matrigel invasion assay, cell cycle analysis, AnnexinV/PI staining and JC-1 staining. Western blot analysis was used to examine the potential mechanism.

Results

We found that RASSF6 was downregulated in 73 of 138 bladder cancer specimens, which correlated with advanced stages. RASSF6 overexpression decreased the cell growth rate and inhibited invasion ability in T24 cell line. Downregulation of RASSF6 using siRNA increased the cell proliferation rate and promoted invasion in 5637 cell line. Cell cycle studies showed that RASSF6 overexpression suppressed the process of cell cycle progression. RASSF6 overexpression also increased the cellular response to doxorubicin (DOX) treatment. AnnexinV/PI staining showed that RASSF6 overexpression promoted DOX-induced apoptosis with increased cytochrome c and cleavage of caspase-3 and caspase-9. We also showed that RASSF6 overexpression downregulated the mitochondrial membrane potential, while RASSF6 depletion showed the opposite effect. Western blot analysis demonstrated that RASSF6 overexpression repressed p-Rb and Bcl-xL while upregulating p21 expression. In addition, we found that RASSF6 overexpression affected the Hippo signaling pathway by downregulating YAP. Depletion of YAP downregulated Bcl-xL expression and abolished the effect of RASSF6 on Bcl-xL. Depletion of YAP also upregulated the level of apoptosis and downregulated mitochondrial membrane potential. YAP siRNA abolished the effects of RASSF6 on DOX-induced apoptosis and loss of mitochondrial membrane potential.

Conclusion

Taken together, our results showed that RASSF6 was downregulated in bladder cancers. RASSF6 inhibited cell proliferation and invasion, as well as the progression of cancer, by regulating DOX sensitivity and mitochondrial membrane potential, possibly via the Hippo signaling pathway.

The RASSF6 Tumor Suppressor Protein Regulates Apoptosis and Cell Cycle Progression via Retinoblastoma Protein

RASSF6 is a member of the tumor suppressor Ras association domain family (RASSF) proteins. RASSF6 is frequently suppressed in human cancers, and its low expression level is associated with poor prognosis. RASSF6 regulates cell cycle arrest and apoptosis and plays a tumor suppressor role. Mechanistically, RASSF6 blocks MDM2-mediated p53 degradation and enhances p53 expression. However, RASSF6 also induces cell cycle arrest and apoptosis in a p53-negative background, which implies that the tumor suppressor function of RASSF6 does not depend solely on p53. In this study, we revealed that RASSF6 mediates cell cycle arrest and apoptosis via pRb. RASSF6 enhances the interaction between pRb and protein phosphatase. RASSF6 also enhances P16INK4A and P14ARF expression by suppressing BMI1. In this way, RASSF6 increases unphosphorylated pRb and augments the interaction between pRb and E2F1. Moreover, RASSF6 induces TP73 target genes via pRb and E2F1 in a p53-negative background. Finally, we confirmed that RASSF6 depletion induces polyploid cells in p53-negative HCT116 cells. In conclusion, RASSF6 behaves as a tumor suppressor in cancers with loss of function of p53, and pRb is implicated in this function of RASSF6.

Hippo pathway affects survival of cancer patients: extensive analysis of TCGA data and review of literature

The disruption of the Hippo pathway occurs in many cancer types and is associated with cancer progression. Herein, we investigated the impact of 32 Hippo genes on overall survival (OS) of cancer patients, by both analysing data from The Cancer Genome Atlas (TCGA) and reviewing the related literature. mRNA and protein expression data of all solid tumors except pure sarcomas were downloaded from TCGA database. Thirty-two Hippo genes were considered; for each gene, patients were dichotomized based on median expression value. Survival analyses were performed to identify independent predictors, taking into account the main clinical-pathological features affecting OS. Finally, independent predictors were correlated with YAP1 oncoprotein expression. At least one of the Hippo genes is an independent prognostic factor in 12 out of 13 considered tumor datasets. mRNA levels of the independent predictors coherently correlate with YAP1 in glioma, kidney renal clear cell, head and neck, and bladder cancer. Moreover, literature data revealed the association between YAP1 levels and OS in gastric, colorectal, hepatocellular, pancreatic, and lung cancer. Herein, we identified cancers in which Hippo pathway affects OS; these cancers should be candidates for YAP1 inhibitors development and testing.

RASSF6-mediated inhibition of Mcl-1 through JNK activation improves the anti-tumor effects of sorafenib in renal cell carcinoma

Ras association domain family member 6 (RASSF6) has been shown to act as a tumor suppressor and predictor of poor prognosis in renal cell carcinoma (RCC). However, little is known about the effects of RASSF6 on sorafenib resistance or the underlying mechanism. Here, we show that RASSF6 expression positively correlates with sorafenib sensitivity in RCC cells and human samples. Stable ectopic overexpression of RASSF6 in RCC cell lines reduces resistance to sorafenib in vitro and in vivo. At a molecular level, RASSF6 activates the JNK signaling pathway, which further contributes to Mcl-1 inhibition. Suppression of the JNK pathway can partially restore Mcl-1 expression and sorafenib resistance. Together, these findings suggest that RASSF6 inhibits sorafenib resistance by repressing Mcl-1 through the JNK-dependent pathway. RASSF6 may serve as a novel regulator for sorafenib therapy in RCC.

Clinicopathologic significance and prognostic value of Ki-67 expression in patients with gastric cancer: a meta-analysis

BACKGROUND

The prognostic value and clinicopathologic significance of Ki-67 expression in gastric cancer patients was controversial. This meta-analysis was performed to clarify the prognostic value and clinicopathologic significance of Ki-67 expression in gastric cancer patients.

MATERIALS AND METHODS

Several electronic databases were searched for eligible studies. The pooled odds ratio (OR), hazard ratios (HR) and 95% confidence interval(CI) were calculated to explore the prognostic value and clinicopathologic significance of Ki-67 expression for disease free survival and overall survival.

RESULTS

Totally 5600 gastric cancer patients from 29 studies were included in this study. High Ki-67 expression was significantly related with Lauren's classification (OR = 1.70; P = 0.001; 95%CI: 1.40-2.06) and tumor size(OR = 1.54; P = 0.006; 95%CI: 1.14-2.09). However, high Ki-67 expression was not significantly associated with lymph node metastasis (OR = 1.37; P = 0.138; 95% CI: 0.90-2.08) , tumor stage (OR = 1.31; P = 0.296; 95% CI: 0.79-2.16) and tumor differentiation (OR = 1.03; P = 0.839; 95% CI: 0.78-1.35). The pooled HRs were 1.87(P = 0.001; 95% CI 1.30-2.69) for disease free survival and 1.23(P = 0.005; 95% CI 1.06-1.42) for overall survival.

CONCLUSIONS

High Ki-67 expression may serve as a predictive biomarker for poor prognosis in gastric cancer patients. Stratification by Ki-67 expression may be a consideration for selection of therapeutic regimen and integrated managements.

HOXA13 contributes to gastric carcinogenesis through DHRS2 interacting with MDM2 and confers 5-FU resistance by a p53-dependent pathway

5-FU-based chemotherapy is recently most recommended as the first-line treatment for gastric cancer (GC). However, 5-FU resistance is common for many postoperative GC patients. Homeobox A13 (HOXA13) is a member of homeobox genes highly expressed in many human tumors. Its potential roles and mechanisms of resistance to 5-FU in GC are poorly understood. In this study, we discovered that HOXA13 played an oncogenic role in vivo and in vitro. The patients with HOXA13 overexpression were closely related with poor prognosis and more prone to be resistant to 5-FU. Moreover, dehydrogenase/reductase 2 (DHRS2) was identified as a downstream gene of HOXA13. HOXA13 played a role of carcinogenesis through directly down-regulating DHRS2 to increase MDM2. Furthermore, HOXA13 conferred 5-FU resistance through MRP1 by a p53-dependent pathway. Therefore, HOXA13 might serve as a potential signature that recognized patients who were insensitive to 5-FU, and timely recommended them to other chemotherapy regimens.

Downregulation of homeobox gene Barx2 increases gastric cancer proliferation and metastasis and predicts poor patient outcomes

Barx2 is a Bar family homeodomain transcription factor shown to play a critical role in cell adhesion and cytoskeleton remodeling, key processes in carcinogenesis and metastasis. Using quantitative real-time PCR, Western blotting, and immunohistochemistry, we found that Barx2 is expressed at lower levels in human gastric cancer (GC) tissues than in adjacent normal mucosa. In a multivariate analysis, Barx2 expression emerged as an independent prognostic factor for disease-free and overall survival. Kaplan-Meier survival analysis showed a trend toward even shorter overall survival in the patient group with Barx2-negative tumors, independent of advanced UICC stage and tumor relapse. Using in vitro and in vivo assays, we demonstrated that under normal conditions Barx2 inhibited GC cell proliferation and invasiveness through inhibition of the Wnt/β-catenin signaling pathway. These findings indicate that reduction or loss of Barx2 dis-inhibits GC cell proliferation and invasion, and that reduction in Barx2 could serve as an independent prognostic biomarker for poor outcome in GC patients.

BCL-XL binds and antagonizes RASSF6 tumor suppressor to suppress p53 expression

RASSF6, a member of the tumor suppressor Ras-association domain family proteins, induces apoptosis in the caspase-dependent and caspase-independent manners. RASSF6 interacts with MDM2 and stabilizes p53. BCL-XL is a prosurvival member of BCL-2 family proteins. BCL-XL directly inhibits proapoptotic BAX and BAK. BCL-XL also traps tBID, a proapoptotic activator BH3-only protein, and sequesters p53. In addition, BCL-XL regulates the mitochondrial membrane permeability via voltage-dependent anion channel. In these manners, BCL-XL plays an antiapoptotic role. We report the interaction of BCL-XL with RASSF6. BCL-XL inhibits the interaction between RASSF6 and MDM2 and suppresses p53 expression. Consequently, BCL-XL antagonizes RASSF6-mediated apoptosis. Thus, the inhibition of RASSF6-mediated apoptosis also underlies the prosurvival role of BCL-XL.

Decreased level of RASSF6 in sporadic colorectal cancer and its anti-tumor effects both in vitro and in vivo

Ras-association domain family protein 6 (RASSF6) is a member of tumor suppressor RASSFs family with a wide range of function from RAS interaction, Hippo signaling involvement to cell cycle and apoptosis regulation. RASSF6 is reported inactivated in various types of cancer. However, whether RASSF6 is associated with colorectal cancer and the underlying mechanisms have yet to be investigated. In our previous exome sequencing study, we found a somatic loss-of-function (LoF) mutation in RASSF6 in one sporadic colorectal cancer (sCRC) patient, and two missense mutations in deep sequencing group of sCRC samples, implying the possibility that RASSF6 may be involved in the pathogenesis of sCRC. In this study, we demonstrate that RASSF6 acts as a tumor suppressor in colon cancer cells. Decreased level of RASSF6 was observed in adenocarcinoma compared to normal tissues, especially in advanced tumor cases. Further experiments showed exogenous introduction of RASSF6 into LoVo cells suppressed cell proliferation, migration, invasion, and induced apoptosis in vitro as well as tumor growth in vivo. In contrast, knockdown of RASSF6 in HT-29 cells showed the opposite effects. Taken together, our results suggest, in addition to epigenetics changes, functional somatic mutations may also contribute to the downregulation of RASSF6 and further participate in the pathogenesis of sCRC. RASSF6 may serve as a novel candidate against tumor growth for sCRC.

Meta-analysis of prognostic role of Ki-67 labeling index in gastric carcinoma

BACKGROUND

This meta-analysis aimed to elucidate the prognostic role of the Ki-67 labeling index (LI) in gastric cancer (GC).

METHODS

The current study included 3,615 GC patients in 20 eligible studies, and evaluated the prognostic role of Ki-67 LI in GC. Subgroup analysis was conducted based on depth of invasion and cutoff value for high Ki-67 LI.

RESULTS

A high Ki-67 LI correlated significantly with worse survival (hazard ratio [HR] = 1.214, 95% confidence interval [CI], 1.004-1.468). However, there was no significant correlation between high Ki-67 LI and worse survival in advanced GC (HR = 1.252, 95% CI, 0.801-1.956). The subgroup with cutoff value ≤25% showed a significant correlation with worse survival, but this was not seen in the subgroup with cutoff >25% (HR = 1.433, 95% CI, 1.094-1.876 vs. HR = 1.005, 95% CI, 0.801-1.262). In addition, in the 10% <Ki-67 LI ≤ 20% range, there was a significant correlation between high Ki-67 LI and worse overall survival (HR = 1.931, 95% CI, 1.013-3.310).

CONCLUSIONS

A high Ki-67 LI correlated significantly with a worse prognosis in GC patients. Further cumulative studies for the optimal cutoff value for high Ki-67 LI are needed before application in clinical practice.

RASSF6 downregulation promotes the epithelial-mesenchymal transition and predicts poor prognosis in colorectal cancer

Distant metastasis is the primary barrier for the successful treatment of patients with colorectal cancer, and thus, searching for new therapeutic targets by further exploring the molecular mechanisms of colorectal cancer metastasis is important. In this study, we investigated the biological and clinical significance of RASSF6 in colorectal cancer as well as the underlying molecular mechanisms. We found that low RASSF6 expression corresponds to a poor prognosis in colorectal cancer patients, and low RASSF6 expression is distinctly associated with tumour progression. Our in vitro analysis revealed that RASSF6 suppresses the proliferation and metastasis of DLD1 cells, and RASSF6 knockdown in HCT116 cells confirmed these observations. Our mechanistic investigation revealed that RASSF6 inhibits the expression of the classical target genes of Wnt signalling, as demonstrated by the reduced expression of TCF1, c-Jun, and c-Myc in RASSF6-overexpressing DLD1 stable cell lines. Furthermore, we show that RASSF6 functions as a negative regulator of the epithelial-mesenchymal transition; the expression levels of the epithelial markers ZO-1 and E-cadherin were increased, while the expression level of the mesenchymal marker Snail was decreased in a RASSF6-overexpressing DLD1 cell line. Additionally, rescue assays revealed that the activation of Wnt signalling by LiCl treatment impaired the inhibitory effect of RASSF6 on the proliferation and metastasis of colorectal cancer cells, which implies that RASSF6 suppresses the tumorigenicity of colorectal cancer cells at least in part through inhibiting Wnt signalling pathway. Collectively, these findings provide new perspectives for the future study of RASSF6 as a therapeutic target for colorectal cancer.

MALAT1 promoted invasiveness of gastric adenocarcinoma

Background

Gastric cancer is the second leading cause of cancer globally, and the mechanism of its pathogenesis is still largely unknown. Recently, non-coding RNAs have been recognized to promote metastasis in various cancers, including gastric cancer.

Methods

We found that metastasis associated lung adenocarcinoma transcript-1 (MALAT1) is upregulated in gastric cancer tissue compared to adjacent normal tissue, as determined by microarray and subsequent qRT-PCR, then investigated the impact of MALAT1 on apoptosis, cell proliferation, and the cell cycle to dissect the carcinogenesis of gastric cancer, and examined mechanisms of invasion and metastasis. Expression of MALAT1 and U6 was determined by SYBR qRT-PCR in nine-teen gastric cancer cell lines and fifty fresh samples of cancer tissue and adjacent tissues. Downregulation of MALAT1 was accomplished with two different siRNAs. Cell proliferation was determined after treatment with these siRNAs. FACS using PI/Annexin-V staining was carried out. To analyze the invasiveness, a scratch wound-healing assay and a Matrigel invasion assay were performed. Cancer related gene expression assay was done after transfection of siR- MALAT1.

Results

The expression of MALAT1 was significantly elevated in various gastric cancer cell lines and gastric cancer tissues compared to normal cell lines and tissues (p < 0.01). siR-MALAT1 significantly reduced viable AGS cell numbers and induced apoptosis (p < 0.05). Deep invasion of tumor (advanced T stages) was more common in the high MALAT1-level group (p = 0.039). siR-MALAT1 significantly decreased AGS cell invasiveness and migration. siR-MALAT1 reduced expression of snail and N-cadherin, and elevated E-cadherin. The Wnt/β-catenin related genes were significantly decreased by transfection of siRNA MALAT1. MALAT1 is involved in gastric carcinogenesis via inhibition of apoptosis and promotes invasiveness via the epithelial-to-mesenchymal transition.

Conclusions

In our study, we found that deregulation of MALAT1 could be involved in both tumorigenesis and invasiveness in gastric cancer cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2988-4) contains supplementary material, which is available to authorized users.

miR-181a-5p promotes the progression of gastric cancer via RASSF6-mediated MAPK signalling activation

We previously discovered that Ras association domain family member 6 (RASSF6) was downregulated and predicted poor prognosis in GC patients. However, the mechanisms of the down regulation of RASSF6 in GC remained unclear. Increasing evidence indicates that dysregulation of microRNAs promotes the progression of cancer through the repression of tumour suppressors. Here, we identified miR-181a-5p as a novel regulator of RASSF6 in GC. Functionally, ectopic expression or silencing of miR-181a-5p, respectively, promoted or inhibited GC cell proliferation, colony formation and cell cycle transition, as well as enhanced or prevented the invasion, metastasis of GC cells and epithelial to mesenchymal transition of GC cells in vitro and in vivo. Molecularly, miR-181a-5p functioned as an onco-miRNA by activating the RASSF6-regulated MAKP pathway. Overexpression or silencing of RASSF6 could partially reverse the effects of the overexpression or repression of miR-181a-5p on GC progress caused by activation of the MAKP pathway in vitro and in vivo. Clinically, high miR-181a-5p expression predicted poor survival in GC patients, especially combined with low RASSF6 expression. Collectively, we identified miR-181a-5p as an onco-miRNA, which acts by directly repressing RASSF6 in GC.

Overexpression of RAS-Association Domain Family 6 (RASSF6) Inhibits Proliferation and Tumorigenesis in Hepatocellular Carcinoma Cells

Ras-association domain family 6 (RASSF6), a member of the RASSF family, is frequently downregulated in various types of cancer. However, the roles of RASSF6 in human hepatocellular carcinoma (HCC) are still unclear. In this study, we investigated the biological functions and related molecular mechanisms in HCC. Our results found that RASSF6 is expressed in low amounts in HCC tissues and cell lines. Overexpression of RASSF6 obviously inhibited the proliferation, invasion, and EMT process in HCC cells. Furthermore, overexpression of RASFF6 greatly downregulated the protein levels of phosphorylated focal adhesion kinase (FAK), MMP-2, and MMP-9 in HepG2 cells. Last, overexpression of RASFF6 significantly attenuated tumor growth in Balb/c nude mice. In conclusion, the present study revealed that RASFF6 can inhibit the proliferation, invasion, and migration of HCC cells both in vivo and in vitro. These inhibitory effects are through suppressing FAK phosphorylation, leading to decreased MMP-2/9 expression. RASFF6 is therefore a potential therapeutic target for treating HCC.

Overexpression of HOXA10 promotes gastric cancer cells proliferation and HOXA10(+)/CD44(+) is potential prognostic biomarker for gastric cancer

Gastric cancer (GC) is a malignant cancer with poor prognosis. This study aims to investigate the roles of homeobox A10 (HOXA10) in GC and the correlations between HOXA10/CD44 expression and GC prognosis. Based on qRT-PCR and Western Blot analyses in 50 pairs of fresh GC samples and adjacent normal samples, it is identified that HOXA10 was significantly up-regulated in GC tissues at mRNA and protein levels. Cell proliferation, migration, and invasion were enhanced in GC cells with overexpressed HOXA10, while inhibited in cells with silenced HOXA10. Through IPA software, HOXA10 was predicted to interact with CD44 via MSN, which was preliminarily confirmed by using Western Blot. Through immunohistochemistry and tissue microarray (N=264), it is found that HOXA10 expression was significantly correlated with tumor size (P=0.011) and CD44 expression (P<0.001), while CD44 expression was significantly correlated with tumor size (P<0.001), depth of tumor invasion (P<0.001), lymph node metastasis (P<0.001), distant metastasis (P=0.001), UICC stage (P<0.001), histological differentiation (P<0.001), and HOXA10 expression (P<0.001). Additionally, the over-all survival and disease-free survival of HOXA10(+)/CD44(+) patients were dramatically decreased in comparison with that of HOXA10(+)/CD44(-), HOXA10(-)/CD44(+), or HOXA10(-)/CD44(-) patients (P<0.001), suggesting that the combinatory expression of HOXA10 and CD44 was correlated with poor GC prognosis. In conclusion, HOXA10 and CD44 might play roles in GC tumorigenesis, metastasis, and invasion. HOXA10(+)/CD44(+) expression might serve as a prognostic biomarker for GC, which needs more studies to validate.

Decreased expression and frequent promoter hypermethylation of RASSF2 and RASSF6 correlate with malignant progression and poor prognosis of gastric cardia adenocarcinoma

The RAS-association domain family (RASSF) consists of 10 members, and several members act as tumor suppressor genes and epigenetically inactivated in different tumor types. The present study investigated the role and methylation status of RASSF2, RASSF3, RASSF4, and RASSF6 in the pathogenesis and prognosis of GCA. Quantitative real-time RT-PCR, Western blot, and immunohistochemistry (IHC) methods were used respectively to detect the expression of RASSF2, RASSF3, RASSF4, and RASSF6 in 135 GCA cases and BS-MSP method was used to clarify the methylation status of these four genes. Decreased mRNA and protein expression of RASSF2, RASSF3, RASSF4, and RASSF6 were detected in GCA tumor tissues. Aberrant CpG island methylation of RASSF2, RASSF4, and RASSF6 were detected in GCA tumor tissues and were inversely correlated with the expression levels of these genes. Both of RASSF2 and RASSF6 expression and methylation were associated with TNM stage, depth of invasion, LN metastasis, distant metastasis or recurrence, and UGIC family history. GCA patients with simultaneous negative protein expression of RASSF2 and RASSF6 or with simultaneous methylation of both genes demonstrated poor patient survival. These results suggest that down-regulation of RASSF2, RASSF3, RASSF4, and RASSF6 is a tumor-specific phenomenon and the inactivation of RASSF2 and RASSF6 may be associated with tumor progression. Inactivation of RASSF2, RASSF4, and RASSF6 through CpG island methylation may play important roles in GCA carcinogenesis. A combination of RASSF2 and RASSF6 expression or hypermethylation may serve as useful prognostic biomarker for GCA. © 2015 Wiley Periodicals, Inc.

Low RASSF6 expression in pancreatic ductal adenocarcinoma is associated with poor survival

AIM: To analyze RASSF6 expression in pancreatic ductal adenocarcinoma (PDAC) and to determine whether RASSF6 has an independent prognostic value in PDAC.

METHODS: We studied RASSF6 expression in 96 histologically confirmed PDAC samples and 20 chronic pancreatitis specimens using immunohistochemistry and real-time quantitative reverse transcription-PCR. PDAC issues were then classified as RASSF6 strongly positive, weakly positive or negative. RASSF6 mRNA and protein expression in PDAC samples with strong positive staining was further evaluated using real-time PCR and Western blot analysis. Lastly, correlations between RASSF6 staining and patients’ clinicopathological variables and outcomes were assessed.

RESULTS: RASSF6 was negatively expressed in 51 (53.1%) PDAC samples, weakly positively expressed in 29 (30.2%) and strongly positively expressed in 16 (16.7%), while its expression was much higher in para-tumor tissues and chronic pancreatitis tissues. Positive relationships between RASSF6 expression and T-stage (P = 0.047) and perineural invasion (P = 0.026) were observed. The median survival time of strongly and weakly positive and negative RASSF6 staining groups was 33 mo, 15 mo and 11 mo, respectively. Cox multivariate analysis indicated that RASSF6 was an independent prognostic indicator of overall survival in patients with PDAC. A survival curve analysis revealed that increased RASSF6 expression was correlated with better overall survival (P = 0.009).

CONCLUSION: RASSF6 expression is an independent biomarker of an unfavorable prognosis in patients with PDAC.

The RASSF6 tumor suppressor protein regulates apoptosis and the cell cycle via MDM2 protein and p53 protein

Ras association domain family (RASSF) 6 is a member of the C-terminal RASSF proteins such as RASSF1A and RASSF3. RASSF6 is involved in apoptosis in various cells under miscellaneous conditions, but it remains to be clarified how RASSF6 exerts tumor-suppressive roles. We reported previously that RASSF3 facilitates the degradation of MDM2, a major E3 ligase of p53, and stabilizes p53 to function as a tumor suppressor. In this study, we demonstrate that RASSF6 overexpression induces G1/S arrest in p53-positive cells. Its depletion prevents UV- and VP-16-induced apoptosis and G1/S arrest in HCT116 and U2OS cells. RASSF6-induced apoptosis partially depends on p53. RASSF6 binds MDM2 and facilitates its ubiquitination. RASSF6 depletion blocks the increase of p53 in response to UV exposure and up-regulation of p53 target genes. RASSF6 depletion delays DNA repair in UV- and VP-16-treated cells and increases polyploid cells after VP-16 treatment. These findings indicate that RASSF6 stabilizes p53, regulates apoptosis and the cell cycle, and functions as a tumor suppressor. Together with the previous reports regarding RASSF1A and RASSF3, the stabilization of p53 may be the common function of the C-terminal RASSF proteins.

PLCɛ and the RASSF family in tumour suppression and other functions

Not all proteins implicated in direct binding to Ras appear to have a positive role in the generation and progression of tumours; examples include Phospholipase C epsilon (PLCɛ) and some members of the Ras-association domain family (RASSF). The RASSF family comprises of ten members, known as RASSF1 to RASSF10. PLCɛ and RASSF members carry a common Ras-association domain (RA) that can potentially bind Ras oncoproteins and mediate Ras-regulated functions. RASSF1 to RASSF6 also share a common SARAH domain that facilitates protein-protein interactions with other SARAH domain proteins. The majority of the family are frequently downregulated by epigenetic silencing in cancers. They are implicated in various important biological processes including apoptosis, microtubule stabilisation and cell cycle regulation. Recent studies have reinforced the tumour suppressive properties of the RASSF family, with new evidence of emerging pathways and novel functions that suggest a wider role for these proteins. This review will first describe an emerging role of PLCɛ in tumour suppression and then focus on and summarise the new findings on the RASSF family in the last five years to consolidate their well-established functions, and highlight the new regulatory roles of specific RASSF members.

Protein predictive signatures for lymph node metastasis of gastric cancer

Lymph node status remains one of most crucial indicators of gastric cancer prognosis and treatment planning. Current imaging methods have limited accuracy in predicting lymph node metastasis. We sought to identify protein markers in primary gastric cancer and to define a risk model to predict lymph node metastasis. The Protein Pathway Array (PPA) (initial selection) and Western blot (confirmation) were used to assess the protein expression in a total of 190 freshly frozen gastric cancer samples. The protein expression levels were compared between samples with lymph node metastasis (n = 73) and those without lymph node metastasis (n = 57) using PPA. There were 27 proteins differentially expressed between lymph node positive samples and lymph node negative samples. Five proteins (Factor XIII B, TFIIH p89, ADAM8, COX-2 and CUL-1) were identified as independent predictors of lymph node metastasis. Together with vascular/lymphatic invasion status, a risk score model was established to determine the risk of lymph node metastasis for each individual gastric cancer patient. The ability of this model to predict lymph node metastasis was further confirmed in a second cohort of gastric cancer patients (33 with and 27 without lymph node metastasis) using Western blot. This study indicated that some proteins differentially expressed in gastric cancer can be selected as clinically useful biomarkers. The risk score model is useful for determining patients' risk of lymph node metastasis and prognosis.

The RASSF gene family members RASSF5, RASSF6 and RASSF7 show frequent DNA methylation in neuroblastoma

Background

Hypermethylation of promotor CpG islands is a common mechanism that inactivates tumor suppressor genes in cancer. Genes belonging to the RASSF gene family have frequently been reported as epigenetically silenced by promotor methylation in human cancers. Two members of this gene family, RASSF1A and RASSF5A have been reported as methylated in neuroblastoma. Data from our previously performed genome-wide DNA methylation array analysis indicated that other members of the RASSF gene family are targeted by DNA methylation in neuroblastoma.

Results

In the current study, we found that several of the RASSF family genes (RASSF2, RASSF4, RASSF5, RASSF6, RASSF7, and RASSF10) to various degrees were methylated in neuroblastoma cell lines and primary tumors. In addition, several of the RASSF family genes showed low or absent mRNA expression in neuroblastoma cell lines. RASSF5 and RASSF6 were to various degrees methylated in a large portion of neuroblastoma tumors and RASSF7 was heavily methylated in most tumors. Further, CpG methylation sites in the CpG islands of some RASSF family members could be used to significantly discriminate between biological subgroups of neuroblastoma tumors. For example, RASSF5 methylation highly correlated to MYCN amplification and INRG stage M. Furthermore, high methylation of RASSF6 was correlated to unfavorable outcome, 1p deletion and MYCN amplification in our tumor material.

In conclusion

This study shows that several genes belonging to the RASSF gene family are methylated in neuroblastoma. The genes RASSF5, RASSF6 and RASSF7 stand out as the most promising candidate genes for further investigations in neuroblastoma.