Assessment of NORE1A as a putative tumor suppressor in human neuroblastoma

RASSF5A, a candidate tumor suppressor, is epigenetically inactivated in esophageal squamous cell carcinoma

As a result of alternative splicing and differential promoter usage, RASSF5 exists in at least three isoforms (RASSF5A-RASSF5C), which may play different roles in tumorigenesis. The present study was to detect the role of RASSF5A, B and C in esophageal squamous cell carcinoma (ESCC) and clarify the critical CpG sites of RASSF5A, in order to clarify more information on the role of RASSF5 with regard to the pathogenesis of ESCC. Frequent silencing of RASSF5A but not RASSF5B and RASSF5C were found in esophageal cancer cell lines and the silencing of RASSF5A may be reversed by 5-Aza-dC or TSA treatment. The aberrant CpG island 1 methylation of RASSF5A induces silencing of its expression in TE13 cell line. Decreased mRNA and protein expression of RASSF5A was observed in ESCC tumor tissues and was associated with RASSF5A CpG island 1 methylation status. Unlike RASSF5A, expression variation of RASSF5B and RASSF5C was not found in ESCC tissues. Aberrant promoter methylation of RASSF5C was also not found in ESCC. RASSF5A methylation and protein expression were independently associated with ESCC patients' survival. These data indicated that the inactivation of RASSF5A through CpG island 1 methylation may play an important role in ESCC carcinogenesis, RASSF5A may be a functional tumor suppressor and may serve as a prognostic biomarker for ESCC.

Decreased expression and aberrant methylation of RASSF5A correlates with malignant progression of gastric cardia adenocarcinoma

Due to alternative splicing and differential promoter usage, RASSF5 exists in at least three isoforms, RASSF5A, RASSF5B, and RASSF5C. Expression and epigenetic inactivation of different transcripts of RASSF5 in gastric cardia adenocarcinoma (GCA) progression have not been evaluated. Quantitative real-time RT-PCR and immunohistochemistry (IHC) methods were used respectively to detect the role of RASSF5A, RASSF5B, and RASSF5C in 132 GCA cases and BS-MSP method was used to clarify the critical CpG sites of RASSF5A. Expression of RASSF5A and RASSF5C transcripts were easily detectable in all normal gastric cardia epithelial tissues; however, expression of RASSF5B was rare detected in normal gastric cardia epithelial tissues and tumor tissues. Both RASSF5A and RASSF5C expression were frequently downregulated in GCA tumor tissues and RASSF5A was more commonly down-regulated compared to RASSF5C. Abnormal reduction of RASSF5A was more commonly observed in advanced stage and poor differentiated tumors. The methylation frequency of CpG island 1 region of RASSF5A in GCA tumor tissues was significantly higher than that in corresponding normal tissues and was inversely correlated with RASSF5A expression. Aberrant promoter methylation of RASSF5C was not found in GCA. RASSF5A methylation and protein expression were independently associated with GCA patients' survival. These results indicate that down-regulation of RASSF5A and RASSF5C expression is a tumor-specific phenomenon and RASSF5A may be a more common target for inactivation in GCA. Inactivation of RASSF5A through CpG island 1 methylation may play an important role in GCA carcinogenesis and may serve as a prognostic biomarker for GCA.

RASSF5 inhibits growth and invasion and induces apoptosis in osteosarcoma cells through activation of MST1/LATS1 signaling

Ras association (RalGDS/AF-6) domain family member RASSF5 has been implicated in a variety of key biological processes, including cell proliferation, cell cycle regulation and apoptosis. It is believed to play an important role in tumorigenesis as a tumor suppressor in a number of malignancies. Yet, little is known concerning the function and underlying mechanisms of RASSF5 in human osteosarcoma (OS). The expression of RASSF5 was examined by immunohistochemical assay using a tissue microarray in 45 cases of OS tissues. A gain-of-function approach was used to observe the effects of lentiviral vector-mediated overexpression of RASSF5 (Lv-RASSF5) on cell growth, invasion and apoptosis, respectively, as indicated by MTT, Transwell and flow cytometry assays, and the expression levels of mammalian sterile 20-like (MST1) kinase, large tumor suppressor 1 (LATS1), proliferating cell nuclear antigen (PCNA), matrix metallopeptidase-9 (MMP-9) and p53 were detected by real-time PCR and western blot assays in OS cells (MG-63 and U-2 OS). The results indicated that the expression of RASSF5 protein was significantly downregulated in OS tissues compared to that in adjacent non-cancerous tissues (ANCT) (40.0 vs. 73.3%, P=0.002), and had a negative correlation with distant metastasis of the tumor (P=0.01). Overexpression of RASSF5 markedly suppressed cell proliferation and invasion, and induced cell apoptosis in the OS cell lines with increased expression of MST1, LATS1 and p53 and decreased expression of PCNA and MMP-9. Taken together, our findings demonstrate that RASSF5 expression is negatively correlated with distant metastasis of OS, and RASSF5 may function as a tumor suppressor in OS cells through activation of the MST1/LATS1 pathway.

Genetic and epigenetic mutations of tumor suppressive genes in sporadic pituitary adenoma

Human pituitary adenomas are the most common intracranial neoplasms. Approximately 5% of them are familial adenomas. Patients with familial tumors carry germline mutations in predisposition genes, including AIP, MEN1 and PRKAR1A. These mutations are extremely rare in sporadic pituitary adenomas, which therefore are caused by different mechanisms. Multiple tumor suppressive genes linked to sporadic tumors have been identified. Their inactivation is caused by epigenetic mechanisms, mainly promoter hypermethylation, and can be placed into two groups based on their functional interaction with tumor suppressors RB or p53. The RB group includes CDKN2A, CDKN2B, CDKN2C, RB1, BMP4, CDH1, CDH13, GADD45B and GADD45G; AIP and MEN1 genes also belong to this group. The p53 group includes MEG3, MGMT, PLAGL1, RASSF1, RASSF3 and SOCS1. We propose that the tumor suppression function of these genes is mainly mediated by the RB and p53 pathways. We also discuss possible tumor suppression mechanisms for individual genes.

The E3 ubiquitin ligase Itch regulates tumor suppressor protein RASSF5/NORE1 stability in an acetylation-dependent manner

Ras association (RalGDS/AF-6) domain family member RASSF5 is a non-enzymatic RAS effector super family protein, known to be involved in cell growth regulation. Expression of RASSF5 is found to be extinguished by promoter hypermethylation in different human cancers, and its ectopic expression suppresses cell proliferation and tumorigenicity. Interestingly, this role in tumorigenesis has been confounded by the fact that regulation at molecular level remains unclear and many transformed cells actually display elevated RASSF5 expression. Here, we demonstrate that E3 ubiquitin ligase Itch is a unique binding partner of RASSF5. Itch can interact with PPxY motif in RASSF5 both in vivo and in vitro through its WW domains. Importantly, the overexpression of Itch induces RASSF5 degradation by poly-ubiquitination via 26S proteasome pathway. In addition, our results indicate that the elevated levels of RASSF5 found in tumor cells due to acetylation, which restricts its binding to Itch and results in a more stable inert protein. Inhibition of RASSF5 acetylation permits its interaction with Itch and provokes proteasomal degradation. These data suggest that apart from promoter methylation, hyperacetylation could also be downregulating RASSF5 function in different human cancer. Finally, results from functional assays suggest that the overexpression of wild type, not the ligase activity defective Itch negatively regulate RASSF5-mediated G1 phase transition of cell cycle as well as apoptosis, suggesting that Itch alone is sufficient to alter RASSF5 function. Collectively, the present investigation identifies a HECT class E3 ubiquitin ligase Itch as a unique negative regulator of RASSF5, and suggests the possibility that acetylation as a potential therapeutic target for human cancer.

Quantitative global and gene-specific promoter methylation in relation to biological properties of neuroblastomas

BACKGROUND

In this study we aimed to quantify tumor suppressor gene (TSG) promoter methylation densities levels in primary neuroblastoma tumors and cell lines. A subset of these TSGs is associated with a CpG island methylator phenotype (CIMP) in other tumor types.

METHODS

The study panel consisted of 38 primary tumors, 7 established cell lines and 4 healthy references. Promoter methylation was determined by bisulphate Pyrosequencing for 14 TSGs; and LINE-1 repeat element methylation was used as an indicator of global methylation levels.

RESULTS

Overall mean TSG Z-scores were significantly increased in cases with adverse outcome, but were unrelated to global LINE-1 methylation. CIMP with hypermethylation of three or more gene promoters was observed in 6/38 tumors and 7/7 cell lines. Hypermethylation of one or more TSG (comprising TSGs BLU, CASP8, DCR2, CDH1, RASSF1A and RASSF2) was evident in 30/38 tumors. By contrast only very low levels of promoter methylation were recorded for APC, DAPK1, NORE1A, P14, P16, TP73, PTEN and RARB. Similar involvements of methylation instability were revealed between cell line models and neuroblastoma tumors. Separate analysis of two proposed CASP8 regulatory regions revealed frequent and significant involvement of CpG sites between exon 4 and 5, but modest involvement of the exon 1 region.

CONCLUSIONS/SIGNIFICANCE

The results highlight the involvement of TSG methylation instability in neuroblastoma tumors and cell lines using quantitative methods, support the use of DNA methylation analyses as a prognostic tool for this tumor type, and underscore the relevance of developing demethylating therapies for its treatment.

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.

Combined RASSF1A and RASSF2A Promoter Methylation Analysis as Diagnostic Biomarker for Bladder Cancer

Promoter hypermethylation, a widely studied epigenetic event known to influence gene expression levels, has been proposed as a potential biomarker in multiple types of cancer. Clinical diagnostic biomarkers are needed for reliable prediction of bladder cancer recurrence. In this paper, DNA promoter methylation of five C-terminal Ras-association family members (RASSF1A, RASSF2A, RASSF4, RASSF5, and RASSF6) was studied in 64 formalin-fixed paraffin-embedded (FFPE) bladder cancer and normal adjacent tissues using methylation-specific high-resolution melting (MS-HRM) analysis. Results showed that 73% (30/41) of transitional cell carcinoma, 100% (3/3) of squamous cell carcinoma, and 100% (4/4) of small cell carcinoma demonstrated promoter methylation of the RASSF1A or RASSF2A gene, but only 6% (1/16) of normal tissues had promoter methylation of RASSF genes. Testing positive for hypermethylation of RASSF1A or RASSF2A promoter provided 77% sensitivity and 94% specificity for identification of cancer tissues with an area under the curve of 0.854, suggesting that promoter methylation analysis of RASSF1A and RASSF2A genes has potential for use as a recurrence biomarker for bladder cancer patients.

Methylation associated inactivation of RASSF1A and its synergistic effect with activated K-Ras in nasopharyngeal carcinoma

Background

Epigenetic silencing of tumor suppressor genes associated with promoter methylation is considered to be a hallmark of oncogenesis. RASSF1A is a candidate tumor suppressor gene which was found to be inactivated in many human cancers. Although we have had a prelimilary cognition about the function of RASSF1A, the exact mechanisms about how RASSF1A functions in human cancers were largely unknown. Moreover, the effect of mutated K-Ras gene on the function of RASSF1A is lacking. The aim of this study was to investigate the expression profile and methylation status of RASSF1A gene, and to explore its concrete mechanisms as a tumor suppressor gene in Nasopharyngeal Carcinoma.

Methods

We examined the expression profile and methylation status of RASSF1A in two NPC cell lines, 38 primary nasopharyngeal carcinoma and 14 normal nasopharyngeal epithelia using RT-PCR and methylated specific PCR(MSP) respectively. 5-aza-dC was then added to confirm the correlation between hypermethylation status and inactivation of RASSF1A. The NPC cell line CNE-2 was transfected with exogenous pcDNA3.1(+)/RASSF1A plasmid in the presence or absence of mutated K-Ras by liposome-mediated gene transfer method. Flow cytometry was used to examine the effect of RASSF1A on cell cycle modulation and apoptosis. Meanwhile, trypan blue dye exclusion assays was used to detect the effect of RASSF1A transfection alone and the co-transfection of RASSF1A and K-Ras on cell proliferation.

Results

Promoter methylation of RASSF1A could be detected in 71.05% (27/38) of NPC samples, but not in normal nasopharyngeal epithelia. RASSF1A expression in NPC primary tumors was lower than that in normal nasopharyngeal epithelial (p < 0.01). Expression of RASSF1A was down-regulated in two NPC cell lines. Loss of RASSF1A expression was greatly restored by the methyltransferase inhibitor 5-aza-dC in CNE-2. Ectopic expression of RASSF1A in CNE-2 could increase the percentage of G0/G1 phase cells (p < 0.01), inhibit cell proliferation and induce apoptosis (p < 0.001). Moreover, activated K-Ras could enhance the growth inhibition effect induced by RASSF1A in CNE-2 cells (p < 0.01).

Conclusion

Expression of RASSF1A is down-regulated in NPC due to the hypermethylation of promoter. Exogenous expression of RASSF1A is able to induce growth inhibition effect and apoptosis in tumor cell lines, and this effect could be enhanced by activated K-Ras.