RASSF1A Gene Expression Research Articles

Extracellular Superoxide Dismutase (EC-SOD) Regulates Gene Methylation and Cardiac Fibrosis During Chronic Hypoxic Stress.

Chronic hypoxic stress induces epigenetic modifications mainly DNA methylation in cardiac fibroblasts, inactivating tumor suppressor genes (RASSF1A) and activating kinases (ERK1/2) leading to fibroblast proliferation and cardiac fibrosis. The Ras/ERK signaling pathway is an intracellular signal transduction critically involved in fibroblast proliferation. RASSF1A functions through its effect on downstream ERK1/2. The antioxidant enzyme, extracellular superoxide dismutase (EC-SOD), decreases oxidative stress from chronic hypoxia, but its effects on these epigenetic changes have not been fully explored. To test our hypothesis, we used an in-vitro model: wild-type C57B6 male mice (WT) and transgenic males with an extra copy of human hEC-SOD (TG). The studied animals were housed in hypoxia (10% O2) for 21 days. The right ventricular tissue was studied for cardiac fibrosis markers using RT-PCR and Western blot analyses. Primary C57BL6 mouse cardiac fibroblast tissue culture was used to study the in-vitro model, the downstream effects of RASSF-1 expression and methylation, and its relation to ERK1/2. Our findings showed a significant increase in cardiac fibrosis markers: Collagen 1, alpha smooth muscle actin (ASMA), and SNAIL, in the WT hypoxic animals as compared to the TG hypoxic group (p < 0.05). The expression of DNA methylation enzymes (DNMT 1&3b) was significantly increased in the WT hypoxic mice as compared to the hypoxic TG mice (p < 0.001). RASSF1A expression was significantly lower and ERK1/2 was significantly higher in hypoxia WT compared to the hypoxic TG group (p < 0.05). Use of SiRNA to block RASSF1A gene expression in murine cardiac fibroblast tissue culture led to increased fibroblast proliferation (p < 0.05). Methylation of the RASSF1A promoter region was significantly reduced in the TG hypoxic group compared to the WT hypoxic group (0.59 vs. 0.75, respectively). Based on our findings, we can speculate that EC-SOD significantly attenuates RASSF1A gene methylation and can alleviate cardiac fibrosis induced by hypoxia.

Multidrug resistance affects the prognosis of primary epithelial ovarian cancer.

Multidrug-resistant tumor cells can tolerate different structures, functions and antidrug action mechanisms, therefore, allowing these cells to respond to various structurally unrelated mechanisms of different chemotherapy drugs and to exhibit cross-resistance. The present study aimed to investigate the role of Multi-drug resistance gene (MDR1), Placental glutathione S-transferase-P1 (GSTP1), Lung resistance protein (LRP) and Ras association domain family member 1 (RASSF1A) in primary epithelial ovarian cancer (PEOC). The mRNA (protein) expression levels of MDR1, product P glycoprotein, LRP and GSTP1 were evaluated with reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis in all tissue samples, ovarian cancer cell line A2780 and A2780/DDP. Methylation-specific PCR (MSP) was used to detect RASSF1A gene methylation in all tissue samples. The resistance genes/proteins were either poorly or not expressed in A2780, however were highly expressed in A2780/DDP cell line. The expression of resistance genes/proteins decreased following different concentrations of zebularine-stimulated A2780/DDP. Hypermethylation and low expression of RASSF1A gene were detected in PEOC and A2780/DDP. Subsequent to being exposed to different concentrations of zebularine-stimulated A2780/DDP, the RASSF1A methylation level was decreased, while the unmethylation level was increased. The expression of RASSF1A gene/protein was gradually restored, and the gene/protein expression was enhanced with the increase in drug concentration. Multivariate logistic regression indicated that the expression level of gene LRP and GSTP1 was a risk factor for PEOC prognosis. Furthermore, the expression of LRP and GSTP1 in the negative-group survival curves was higher compared with the positive group. High expression of resistance genes may serve an important role in cancer primary resistance. Low expression caused by hyper-methylation of RASSF1A gene may serve an important role in cancer-acquired resistance in PEOC. The present study suggested that resistant gene expression may be a potential prognostic biomarker.

RASSF-1A modulates proliferation-mediated oral squamous cell carcinoma progression

BackgroundTo investigate the expression of RASSF-1A in oral squamous cell carcinoma (OSCC) and adjacent tissues, and to explore its mechanism of action in the development of OSCC.MethodsRASSF-1A and proliferation-related protein expression in clinical and OSCC mouse models were detected by qPCR and western blot. In vitro experiments were used siRNA knockdown of RASSF-1A gene in SCC9 cells to detect cell proliferation, migration and apoptosis. In vivo experiments were performed using adenovirus overexpressing RASSF-1A gene in mice and observing tumor growth.ResultsThe results of qPCR and western blot showed that the expression of RASSF-1A gene was decreased in OSCC, and the expression of CyclinD1 protein was increased. The results of co-immunoprecipitation showed that the two proteins were significantly combined in the oral cancer cell line. Knocking down the RASSF-1A gene in SCC9 cells promotes cell migration and proliferation, while reducing apoptosis and increasing CyclinD1 protein expression. Overexpression of RASSF-1A gene in mice reduces tumor volume and inhibits CyclinD1 protein expression.ConclusionsLow expression of RASSF-1A gene in OSCC promotes the expression of CyclinD1 protein and tumor growth.

CpG island promoter hypermethylation of Ras association domain family 1A gene contributes to gastric carcinogenesis

Methylation rates of the Ras association domain family 1A gene (RASSF1A) have been variously reported as between 7.5 and 66.7% in gastric carcinoma tissues. The role of this gene in gastric cancer also remains to be fully elucidated. The present study aimed to investigate whether promoter hypermethylation of RASSF1A occurs in gastric adenocarcinoma tissues and gastric cancer cell lines, and to determine the effects of RASSF1A in gastric carcinoma cell lines. The results showed a methylation‑specific band only in SNU‑719, MKN28 and AGS human gastric cancer cells (indicating full methylation), none of which exhibited RASSF1A expression. By contrast, SNU‑16, MKN‑45 and KATO‑III human gastric carcinoma cells exhibited methylation as well as unmethylation‑specific bands (indicating partial methylation), and all displayed positive or weakly positive expression of RASSF1A. Bisulfite sequencing in AGS and SNU‑719 cells revealed that virtually all CpG sites were densely methylated. When SNU‑719, MKN‑28 and AGS cells were treated with the demethylating agent 5‑aza‑2'‑deoxycytidine, RASSF1A gene expression was restored and the methylation‑specific polymerase chain reaction pattern was altered in all three cell lines. Transfection of a plasmid expressing RASSF1A into AGS and SNU‑719 cells significantly inhibited cell proliferation. Exogenous RASSF1A also reduced the expression of cyclin D1 and phospho‑retinoblastoma protein, and increased that of p27 as demonstrated by western blot analysis. Furthermore, RASSF1A expression was significantly reduced (P=0.048) and the methylation rate was elevated in gastric adenocarcinoma tissues, compared with those in adjacent healthy intestinal metaplasia (34.6 vs. 66.7%, P=0.029). The present study indicated that epigenetic silencing of RASSF1A is frequently caused by promoter hypermethylation in gastric cancer cell lines as well as in gastric adenocarcinoma tissues, which may contribute to gastric carcinogenesis.

No Relationship between the Amount of DNA Damage and the Level of hMLH1 and RASSF1A Gene Expression in Bladder Cancer Cells Treated with Cisplatin and Gemcitabine

Tumor response to antineoplastic drugs is not always predictable. This is also true for bladder carcinoma, a highly recurrent neoplasia. Currently, the combination of cisplatin and gemcitabine is well accepted as a standard protocol for treating bladder carcinoma. However, in some cases, this treatment protocol causes harmful side effects. Therefore, we investigated the roles of the genes TP53, RASSF1A (a tumor suppressor gene) and hMLH1 (a gene involved in the mismatch repair pathway) in cell susceptibility to cisplatin/gemcitabine treatment. Two bladder transitional carcinoma cell (TCC) lines, RT4 (wild-type TP53) and 5637 (mutated TP53), were used in this study. First, we evaluated whether the genotoxic potential of cisplatin/gemcitabine was dependent on TP53 status. Then, we evaluated whether the two antineoplastic drugs modulated RASSF1A and hMLH1 expression in the two cell lines. Increased DNA damage was observed in both cell lines after treatment with cisplatin or gemcitabine and with the two drugs simultaneously, as depicted by the comet assay. A lack of RASSF1A expression and hypermethylation of its promoter were observed before and after treatment in both cell lines. On the other hand, hMLH1 downregulation, unrelated to methylation status, was observed in RT4 cells after treatment with cisplatin or with cisplatin and gemcitabine simultaneously (wild-type TP53); in 5637 cells, hMLH1 was upregulated only after treatment with gemcitabine. In conclusion, the three treatment protocols were genotoxic, independent of TP53 status. However, cisplatin was the most effective, causing the highest level of DNA damage in both wild-type and mutated TP53 cells. Gemcitabine was the least genotoxic agent in both cell lines. Furthermore, no relationship was observed between the amount of DNA damage and the level of hMLH1 and RASSF1A expression. Therefore, other alternative pathways might be involved in cisplatin and gemcitabine genotoxicity in these two bladder cancer cell lines.

DNA methylation and histone modification relate to RASSF1A gene deletion in laryngeal carcinoma tissues

To investigate the relationship between RASSF1A gene expression and DNA methylation or histone modification in laryngeal carcinoma tissues. Chromatin immunoprecipitation (ChIP), methylation specific polymerase chain reaction (MSP) and realtime quantitative reverse transcription polymerase chain reaction (realtime RT-PCR) were used to analyze RASSF1A gene promoter region histone H3 lysine 9 methylation, H3 lysine 4 methylation, H3 lysine 9 acetylation, DNA methylation, and RASSF1A gene expression in laryngeal carcinoma tissue of 50 cases. DNA methylation rate of gene RASSF1A was 62% in 50 cases of laryngeal carcinoma, but no DNA methylation was found in normal control group, with a significant difference (χ(2) = 15.381, P < 0.05). DNA methylation had no correlation with age, gender, differentiation degree, T stage, pathological type and lymph node metastasis (P > 0.05). The affection of DNA methylation group was more than unmethylation group to expression of gene RASSF1A (t = -3.108, P < 0.01). There was positive correlation between RASSF1A deletion and gene hypermethylation or between H3 lysine 9 methylation of RASSF1A gene promoter and DNA methylation in laryngeal carcinoma tissue(r = 0.816, P < 0.05), but there was negative correlation between H3 lysine 4 methylation of RASSF1A gene promoter and DNA methylation (r = -0.837, P < 0.05) and no correlation between H3 lysine 9 acetylation and DNA methylation (r = -0.383, P > 0.05). Laryngeal tumor suppressor gene RASSF1A promoter methylation is a key factor down-regulating the gene expression, and histone modifications also plays an important role in tumor development.

Expression of RASSF1A gene in human lung carcinoma and its clinical significance

Objective To investigate the expression of RASSF1A gene in human lung carcinoma.Methods The samples were obtained from 56 cases of lung carcinoma. By using reverse transcription-polymerase chain reaction (RT-PCR), the expression of RASSF1A mRNA was detected in 56 samples and adjacent non-cancerous tissues. Results RASSF1A mRNA was detected in 67. 85% of human lung carcinomas and 32. 14% of adjacent cancerous tissues ( P ＜ 0. 05 ). Conclusion In advance lung carcinoma, the expression of RASSF1A might be inactivated. RASSF1 A gene inactivation can be used as a potential marker in the early diagnosis and prognosis of lung carcinoma. Key words: Lung carcinoma; RASSF1A; Gene expression

Effects of 5-Aza-2'-deoxycytidine on biological behaviors and the RASSF1A gene expression of human lung carcinoma cell lines H460

Objective To investigate the effects of demethylating agent 5-Aza-2'-deoxycytidine (5-Aza-CdR) on the biological behaviors and the expression of RASSF1A of lung carcinoma cells H460. Methods Lung carcinoma cell line H460 were treated with 5-Aza-CdR. Cell proliferation was determined by MTT assay and colony forming test. The methylation status of RASSF1A gene was detected by PCR. The expression of RASSF1A protein was measured by Western blotting, and the cell cycle was analyzed by flow cytometry. Results With 5-Aza-CdR treatment, the proliferation speed of H460 lung carcinoma cells was slowed down and the colony formation rate of H460 cells was decreased significantly compared with control group (38.5 %, 27.5 % and 60.5 % in 5-Aza-CdR 5 and 10 μmol/L groups and control group, respectively, P <0.05). The methylation degree in the promoter of RASSF1A gene was decreased and the expression of RASSF1A protein was detected after 5-Aza-CdR treatment. 5-Aza-CdR induced G1 phase arrest of the H460 cells. Conclusion The hypermethylation of CpG island in the promoter of RASSF1A gene results in the loss of RASSF1A protein expression in human Lung carcinoma cell line. The demethylating agent 5-Aza-CdR could restore RASSF1A gene expression.These findings provide theoretic evidence for clinical treatment of human lung carcinoma with demethylation agent 5-Aza-CdR. Key words: Lung neoplasms; DNA methylation; Deoxycytidine

Abstract 4925: Promoter methylation of RASSF1A Tumor Suppressor Gene Modulates the Effect of Microtubule-Targeting Agent, docetaxl, in Breast Cancer

Abstract RASSF1A has been previously demonstrated to be inactivated by CpG island methylation in breast cancer cell lines and primary tumor tissues. There have been evidences suggesting that methylation of this gene have a significant impact on biological characteristics of breast tumors and have a relationship with prognosis in breast cancer. The tumor suppressive effect of RASSF1A has been reported to be mediated by its 2 important roles in other cells; induction of cell cycle arrest and apoptosis. Therefore, it is possible that expression status of RASSF1A by promoter methylation may alter patient's sensitivity to chemotherapeutic agents affecting cell cycle. However, there is few data regarding the relationship between the methylation status of RASSF1A gene and clinical response to chemotherapeutic agents in breast cancer patients. In this current study, we show that RASSF1A gene expression was suppressed in the human breast cancer cell lines (MCF-7, MDA-MB-231, and ZR75-1) by the mechanism of promoter methylation using methylation -specific PCR. It was confirmed by the results that treatment with the DNA demethylating agent, 5-aza-2′-deoxycytidine, reactivated the expression of RASSF1A at the level of mRNA and protein. Re-expression of RASSF1A gene in breast cancer cell lines could decrease the cell growth and proliferation by both decreasing cyclin D1 expression and inducing cyclin A and B1 accumulation, then resulting in cell cycle arrest at G2/M phase. In addition, re-introduction of RASSF1A further increased docetaxel-induced cell death in breast cancer cells. We next questioned whether the methylation status of RASSF1A gene is associated with clinical response to taxane-based chemotherapy in breast cancer patients. Fresh frozen primary breast cancer tissues were ananlyzed for methylation status of RASSF1A gene using MS-PCR. Thirty three out of 39 patients (84.6%) showed RASSF1A methylation and 6 had un-methylated gene. Patients who had unmethylated or partially methylated RASSF1A gene showed some mRNA in RT-PCR analysis. And, the clinical response to taxane-based chemotherapy was significantly better in the un-, or partially-methylated patient group (100% vs 62.5%). These results suggest that hypermethylation of the CpG island promoter of RASSF1A may play an important role in breast cancer pathogenesis and is a modulating factor for docetaxel activity in breast cancer patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4925.

Abstract 4090: RASSF1A gene specific methylation by overexpression of miR-200c in lung cancer

Abstract DNA methylation, which is an important epigenetic mechanism of gene regulation during cellular differentiation, is mediated by enzymatic actions of DNA methyl transferase family (DNMT). In pathologic conditions, however, certain critical genes such as tumor suppressor genes of various human cancers are aberrantly methylated resulting in inactivation of the genes regardless of DNMT amount. In this process, what induces aberrant methylation of a specific gene is currently unknown. We focused actions of microRNA because of their natural function of sequence recognition. As a model, we selected miR-200c and RASSF1A since those are frequently overexpressed and hypermethylated in lung cancer, respectively, and have partial sequence homology between miR-200c and promoter region of RASSF1A. In this study, we tested expression of miR-17, 21, 200c and 205 by quantitative real-time PCR and methylation status of RASSF1A, CDH13, p16ink4a, DAPK1, and APC1 by pyrosequencing assay in 3 lung cancer cell lines and 10 fresh frozen normal and tumor lung tissues. Fluorescent In Situ Hybridization (FISH) using anti-miR-200c probe labeled with Cy-3 dye was performed to confirm expression and localization of mature miR-200c. Interestingly, we found A549 and H460 cells were completely hypermethylated in RASSF1A promoter region and showed high level of miR-200c expression. In contrast, Calu6 cells showed opposite results. In vitro inhibition of miR-200c by transfection of anti-miR-200c oligonucleotide induced gradual decrease in methylation level of RASSF1A in A549 and H460 cells without change in expression of DNMT. Decrease of CpG methylation by anti-miR-200c transfection was associated with increase of RASSF1A gene expression in A549 and H460 cells. Calu6 cell showed no change in methylation level of RASSF1A. This effect was not seen in anti-miR-17 transfected cells. Transfection of anti-miR-200c did not affect methylation level of other frequently hypermethylated genes including CDH13, p16ink4a, DAPK1, and APC1. The results suggest that overexpression of miR-200c induces sequence specific methylation of RASSF1A and provide a clue to gene specific reactivation of epigenetically silenced genes. (This work was supported by the Korea Research Foundation Grant funded by the Korean Government. [KRF-2008-357-E00006], This study was supported by a grant of the Korea Health 21 R&amp;D Project, Ministry of Health &amp; Welfare, Republic of Korea. (A062254)) Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4090.

Study of 5-Aza-CdR on Transcription Regulation of RASSF1A Gene in the BIU87 Cell Line

Objectives: To investigate the effect of 5-Aza-CdR on methylation and expression of RASSF1A gene in the human bladder cancer BIU87 cell line. Methods: Cultured BIU87 cells were treated with increasing concentrations (0.1, 0.5, 1.0, 5.0 μmol/l) of 5-Aza-CdR. MTT was used to detect the proliferation of BIU87 cells. The methylation status and expression level of RASSF1A gene in BIU87 cells were analyzed by methylation-specific polymerase chain reaction and RT-PCR before and after treatment with 5-Aza-CdR. Meanwhile, Western blot was used to detect the changes of RASSF1A protein. Results: In this study we found that the growth velocity of the BIU87 cell line was suppressed to various degrees after having been treated with different concentrations of 5-Aza-CdR, and the survival rate decreased with increasing 5- Aza-CdR concentrations. Besides, the methylation status of RASSF1A was obviously reversed and mRNA was re-expressed after treatment with 5-Aza-CdR. Expression of RASSF1A protein increased with increasing 5-Aza-CdR concentrations. Conclusions: Our results suggest that the tumor-suppressive effect of 5-Aza-CdR may result from reactivation of silenced RASSF1A through a demethylation function.

5-Aza-CdR regulates the expression of RASSF1A gene in human gastric cancer cell line and inhibits the growth of cells

To investigate the effect of demethylating agent 5-Aza-CdR (5-aza-2'- deoxycytidine) on demethylation and transcription-regulating of RASSF1A gene in gastric cancer cell SGC7901 in vitro, as well as on the growth inhibition of cells. After SGC7901 cells were treated with 5-Aza-CdR, MTT assay, flow cytometry, and Annexin V-FITC staining were performed to analyze the cell proliferation, cell cycle and apoptotic rate respectively. Methylation- specific PCP (MSP), RT-PCR and Western blotting were used to detect methylation state, expression of mRNA and protein of RASSF1A gene. After SGC7901 cells were treated with different concentrations of 5-Aza-CdR, the cell growth was inhibited(P<0.05), the cell cycle was blocked at G(1) phase, and the apoptotic rate increased significantly(P<0.05). Hypermethylation was detected in the promoter region of RASSF1A gene in SGC7901 cells, and no expression of RASSF1A mRNA and protein was found. After treated with 5-Aza-CdR, demethylation occurred in RASSF1A gene,which subsequently induced re-expression of this gene at both mRNA and protein level. Demethylating agent 5-Aza-CdR can regulate demethylation and re-expression of RASSF1A gene in gastric cancer cell SGC7901,and inhibit its growth.

Critical role of ΔDNMT3B4/2 in regulating RASSF1A promoterspecific DNA methylation in non-small cell lung cancer

DeltaDNMT3B (a new DNMT3B subfamily) expression is initiated through a novel promoter. We identified at least 7 transcription variants of deltaDNMT3B as a result of alternative pre-mRNA processing. The aim of this study was to detect the expression pattern of deltaDNMT3B variants in non-small cell lung cancer (NSCLC) and to explore the role of deltaDNMT3B variants in regulating the promoter-specific DNA methylation. Specific polymerase chain reaction (PCR) primer sets were designed to distinguish individual deltaDNMT3B variants according to their splicing patterns. The expressions of seven deltaDNMT3B variants were measured in 13 cell lines, 109 NSCLC patients, and the corresponding normal lung tissues using reverse transcription-PCR (RT-PCR). The status of the p16 and RASSF1A promoter methylations in the tumors was detected using a methylation specific PCR (MSP). The relationships of the expression patterns of the deltaDNMT3B variants were analyzed by observing the status of p16 and RASSF1A promoter methylations in the tumors. The siRNA and the anti-sense oligo-dioxynucleotide specifically targeting the junction of exon 5 and 7 of deltaDNMT3B were designed and transfected by lipofectmane 2000 into H1299 and H358 cell lines. RASSF1A promoter methylation from cells treated by siRNA-deltaDNMT3B4/2 was detected using MSP and Bisulfite sequencing, and Western blotting was used to detect the protein expression of DNMT3B and ADNMT3B. Cell growth and cell cycle distribution were measured by applying real-time cell growth analysis and flowcytometry, respectively. ADNMT3B variants, not DNMT3B, were the predominant transcripts in both NSCLC cell lines and primary tumors. The expression of deltaDNMT3B4 strongly correlated to the promoter methylation status of RASSF1A in a primary NSCLC. The knockdown of deltaDNMT3B4/2 by RNA-interference or anti-sense approaches resulted in a complete demethylation of RASSF1A promoter with the reactivation of a RASSF1A gene expression in less than 12 hours, but no effect resulted from the p16(INK4a) promoter in the NSCLC cell lines. These results demonstrate an important role of deltaDNMT3B4/2 in the maintenance of promoter-specific DNA methylation in a cell type specific manner and provide a novel cell model for the study of the regulation of replication-independent DNA methylation.

Expression and promoter methylation of the RASSF1A gene in sporadic breast cancers in Chinese women

The novel tumor suppressor RASSF1A is frequently inactivated during human tumorigenesis by promoter methylation. In this study, we detected the RASSF1A promoter methylation by methylated-specific PCR and investigated RASSF1A gene expression by semi-quantitative RT-PCR and immunohistochemical staining in 36 cases of breast cancer and their adjacent normal tissues in Chinese women. The promoter methylation of the RASSF1A gene was found to be a frequent event in the breast cancers (61.1%). RASSF1A methylation was not found in the matched adjacent normal tissues. The loss frequency of RASSF1A mRNA was 33.3% and that of the RASSF1A protein was 44.4% in breast cancers. RASSF1A mRNA and protein were all expressed in adjacent normal tissues. The mRNA and protein expression level of RASSF1A was significantly lower in breast cancer than in adjacent normal tissue. However, the promoter methylation of the RASSF1A gene in breast cancers were not correlated with clinical parameters, such as ages, histological types, TNM stages and lymph node metastases. Thus, the promoter methylation of RASSF1A was one reason for the low level of RASSF1A mRNA and protein expression and was a frequent event in primary sporadic breast tumorigenesis in Chinese women.

Regulation of demethylation and re-expression of RASSF1A gene in gastric cancer cell lines by combined treatment of 5-Aza-CdR and NaB

To investigate the changes of methylation state and expression of RASSF1A gene in human gastric cancer cell lines SGC7901 and BGC823 which were treated in vitro with demethlylating agent 5-Aza-CdR in combination with histone deacetylase inhibitor NaB. After SGC7901 and BGC823 cells were treated with 5-Aza-CdR and/or NaB, the methylation state of RASSF1A gene was detected by methylation-specific PCR, and the changes in expression of mRNA and protein level of RASSF1A gene were observed by RT-PCR and Western-blotting before and after drug treatment. Hypermethylation was detected in the promoter region of RASSF1A gene in both SGC7901 and BGC823 cells, and there was no expression of this gene at both mRNA and protein level. After treatment with 5-Aza-CdR, demethylation occurred in the promoter region of RASSF1A gene, which subsequently induced re-expression of this gene. The treatment with NaB alone showed no effect on the methylation state and expression of RASSF1A gene. The combined treatment of 5-Aza-CdR and NaB induced complete demethylation of RASSF1A gene, leading to a significantly higher re-expression of the mRNA and protein of RASSF1A than those treated with 5-Aza-CdR alone (P<0.05). Hypermethylation in the promoter region is related to inactivation of RASSF1A gene in human gastric cancer cell lines SGC7901 and BGC823, while demethlylating agent 5-Aza-CdR can reverse the methylation state of RASSF1A gene and induce its re-expression. Histone deacetylase inhibitor NaB had a synergistic effect with 5-Aza-CdR in both demethylation and gene transcriptional regulation.

Expression and inactivation of RASSF1A gene in liver cancer

最新研究进展揭示,抑癌基因功能的抑制或失活,除了与基因片段的丢失,DNA序列的错位、缺失、重组、变换、点突变等机制相关外,还与DNA序列中CpG岛(CpG island)中胞嘧啶(C)碱基环上发生的甲基化(mCpG)有极其重要的相关性。

Frequent epigenetic inactivation of RASSF1A and BLU genes located within the critical 3p21.3 region in gliomas.

RASSF1A is a major tumor suppressor gene located at 3p21.3. We investigated the role of aberrant promoter region hypermethylation of RASSF1A in a large series of adult gliomas. RASSF1A was frequently methylated in both primary tumors (36/63; 57%) and tumor cell lines (7/7; 100%). Hypermethylation of RASSF1A in glioma cell lines correlated with loss of expression and treatment with a demethylating agent-reactivated RASSF1A gene expression. Furthermore, re-expression of RASSF1A suppressed the growth of glioma cell line H4 in vitro. Next, we investigated whether other members of the RASSF gene family were also inactivated by methylation. NORE1B and RASSF3 were not methylated in gliomas, while NORE1A and RASSF5/AD037 demonstrated methylation in glioma cell lines but not in primary tumors. We then investigated the methylation status of three other candidate 3p21.3 tumor suppressor genes. CACNA2D2 and SEMA3B were not frequently methylated, but the BLU gene located just centromeric to RASSF1 was frequently methylated in glioma cell lines (7/7) and in 80% (35/44) of glioma tumors. In these tumor cell lines, BLU expression was restored after treatment with a demethylating agent. Loss of BLU gene expression in glioma tumors correlated with BLU methylation. There was no association between RASSF1A and BLU methylation. RASSF1A methylation increased with tumor grade, while BLU methylation was seen at similar frequencies in all grades. Our data implicate RASSF1A and BLU promoter methylation in the pathogenesis of adult gliomas, while other RASSF family members and CACNA2D2 and SEMA3B appear to have only minor roles. In addition, RASSF1A and BLU methylation appear to be independent and specific events and not due to region-wide changes in DNA methylation.

RASSF1A gene inactivation in non-small cell lung cancer and its clinical implication.

Methylation-associated inactivation of RASSF1, a putative tumor suppressor identified at 3p21.3, is reported in several cancers. We examined RASSF1 in non-small lung cancer (NSCLC) to search for clinical implications. RT-PCR analysis showed no expression of RASSF1A in 12 of 20 lung cancer cell lines. Loss of expression correlated well with promoter methylation status of these lines. Sequence analysis revealed 2 polymorphisms (codons 21 and 133) in RASSF1A transcripts, but not in RASSF1C transcripts. No somatic mutations were found. Of 7 cell lines with K-ras mutations at codon 12 or 61, 2 lost expression of RASSF1A, whereas in 13 cell lines with wild-type K-ras gene, 10 lost RASSF1A gene expression (p = 0.0521). We investigated methylation status of this putative tumor suppressor gene in 100 primary NSCLCs to determine whether there is a clinical significance. Forty-two of primary NSCLCs demonstrated methylated allele. There is no correlation between promoter methylation of RASSF1A and clinicopathological findings, including histological type or grade, tumor staging, p53 and K-ras mutational status, or patients' survival. In the cases of Stage I and II disease, however, RASSF1A methylation was associated with earlier recurrence (p = 0.0247). Epigenetic silencing of RASSF1A is a frequent event in non-small lung cancer and will provide novel opportunities to develop diagnosis and therapy of NSCLC.