Methylation of the Tumor Suppressor Gene RASSF1A in Human Tumors

Wakefield M. The role of aberrant DNA methylation in cancer initiation and clinical impacts

Epigenetic alterations, including aberrant DNA methylation, are now recognized as bone fide hallmarks of cancer, which can contribute to cancer initiation, progression, therapy responses and therapy resistance. Methylation of gene promoters can have a range of impacts on cancer risk, clinical stratification and therapeutic outcomes. We provide several important examples of genes, which can be silenced or activated by promoter methylation and highlight their clinical implications. These include the mismatch DNA repair genes MLH1 and MSH2, homologous recombination DNA repair genes BRCA1 and RAD51C, the TERT oncogene and genes within the P15/P16/RB1/E2F tumour suppressor axis. We also discuss how these methylation changes might occur in the first place - whether in the context of the CpG island methylator phenotype or constitutional DNA methylation. The choice of assay used to measure methylation can have a significant impact on interpretation of methylation states, and some examples where this can influence clinical decision-making are presented. Aberrant DNA methylation patterns in circulating tumour DNA (ctDNA) are also showing great promise in the context of non-invasive cancer detection and monitoring using liquid biopsies; however, caution must be taken in interpreting these results in cases where constitutional methylation may be present. Thus, this review aims to provide researchers and clinicians with a comprehensive summary of this broad, but important subject, illustrating the potentials and pitfalls of assessing aberrant DNA methylation in cancer.

Analytical and therapeutic profiles of DNA methylation alterations in cancer; an overview of changes in chromatin arrangement and alterations in histone surfaces

DNA methylation is the most important epigenetic element that activates the inhibition of gene transcription and is included in the pathogenesis of all types of malignancies. Remarkably, the effectors of DNA methylation are DNMTs (DNA methyltransferases) that catalyze de novo or keep methylation of hemimethylated DNA after the DNA replication process. DNA methylation structures in cancer are altered, with three procedures by which DNA methylation helps cancer development which are including direct mutagenesis, hypomethylation of the cancer genome, and also focal hypermethylation of the promoters of TSGs (tumor suppressor genes). Conspicuously, DNA methylation, nucleosome remodeling, RNA-mediated targeting, and histone modification balance modulate many biological activities that are essential and indispensable to the genesis of cancer and also can impact many epigenetic changes including DNA methylation and histone modifications as well as adjusting of non-coding miRNAs expression in prevention and treatment of many cancers. Epigenetics points to heritable modifications in gene expression that do not comprise alterations in the DNA sequence. The nucleosome is the basic unit of chromatin, consisting of 147 base pairs (bp) of DNA bound around a histone octamer comprised of one H3/H4 tetramer and two H2A/H2B dimers. DNA methylation is preferentially distributed over nucleosome regions and is less increased over flanking nucleosome-depleted DNA, implying a connection between nucleosome positioning and DNA methylation. In carcinogenesis, aberrations in the epigenome may also include in the progression of drug resistance. In this report, we report the rudimentary notes behind these epigenetic signaling pathways and emphasize the proofs recommending that their misregulation can conclude in cancer. These findings in conjunction with the promising preclinical and clinical consequences observed with epigenetic drugs against chromatin regulators, confirm the important role of epigenetics in cancer therapy.

Clinical potential of the Hippo-YAP pathway in bladder cancer

Bladder cancer (BC) is one of the world’s most frequent cancers. Surgery coupled with adjuvant platinum-based chemotherapy is the current standard of therapy for BC. However, a high proportion of patients progressed to chemotherapy-resistant or even neoplasm recurrence. Hence, identifying novel treatment targets is critical for clinical treatment. Current studies indicated that the Hippo-YAP pathway plays a crucial in regulating the survival of cancer stem cells (CSCs), which is related to the progression and reoccurrence of a variety of cancers. In this review, we summarize the evidence that Hippo-YAP mediates the occurrence, progression and chemotherapy resistance in BC, as well as the role of the Hippo-YAP pathway in regulating bladder cancer stem-like cells (BCSCs). Finally, the clinical potential of Hippo-YAP in the treatment of BC was prospected.

Correlations between histological characterizations and methylation statuses of tumour suppressor genes in Wilms' tumours

Wilms' tumour is a solid tumour that frequently occurs in children. Genetic changes in WT1 and epigenetic aberrations that affect imprinted control region 1 in WT2 loci are implicated in its aetiology. Moreover, tumour suppressor genes are frequently silenced by methylation in this tumour. In the present study, we analysed the methylation statuses of promoter regions of 24 tumour suppressor genes using a methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA)-based approach in 6 Wilms' tumours. Methylation of RASSF1 was specific to all 6 Wilms' tumours and was not observed in normal tissues. Moreover, methylated HIC1 was identified in stromal-type Wilms' tumours and methylated BRCA1 was identified in epithelial-type Wilms' tumours. Unmethylated CASP8, RARB, MLH1_167, APC and CDKN2A were found only in blastemal predominant-type Wilms' tumour. Our results indicated that methylation of RASSF1 may be a vital event in the tumorigenesis of Wilms' tumour, which informs its clinical and therapeutic management. In addition, mixed-type Wilms' tumours may be classified according to epithelial, stromal and blastemal components via MS-MLPA-based approach.

Mechanisms of Fritillariae Thunbergii Flos in lung cancer treatment from a systems pharmacology perspective

ETHNOPHARMACOLOGICAL RELEVANCE

Fritillariae Thunbergii Flos (FTF) included in the Chinese Pharmacopoeia (1977 Edition) is a Chinese medicinal herb traditionally used to treat bronchitis. In recent years, it has been applied in the treatment of lung cancer. However, the molecular mechanism remains largely unknown.

METHODS

The screening of bioactive compounds, acquisition of drug targets, network construction, and experimental validation in vivo were combined to explored the mechanism of FTF in the treatment of lung carcinoma with regards to systems pharmacology.

RESULTS

The network Lung Cancer Pathway consisted of 114 nodes (44 compounds and 70 potential targets) and 361 edges, as well as modules that included inflammatory response, angiogenesis, negative regulation of the apoptotic process, and positive regulation of cell proliferation and migration. It was examined by conducting experiments that involved the administration of ethanol-based extracts of FTF in Lewis lung carcinoma mice. The extracts exerted excellent anti-lung cancer effects in vivo by significantly inhibiting tumor proliferation, thereby extending the survival period of tumor-bearing mice. Moreover, FTF induced the downregulation of PIK3CG, Bcl-2, eNOS, VEGF, p-STAT3, and STAT3 genes in tumor-bearing mice.

CONCLUSIONS

The findings of the present study verify the therapeutic effects and mechanism of FTF on lung cancer and provide a theoretical basis to support the comprehensive utilization of FTF resources.

Association of RASSF1A, DCR2, and CASP8 Methylation with Survival in Neuroblastoma: A Pooled Analysis Using Reconstructed Individual Patient Data

Neuroblastoma (NB) is a heterogeneous tumor affecting children. It shows a wide spectrum of clinical outcomes; therefore, development of risk stratification is critical to provide optimum treatment. Since epigenetic alterations such as DNA methylation have emerged as an important feature of both development and progression in NB, in this study, we aimed to quantify the effect of methylation of three distinct genes (RASSF1A, DCR2, and CASP8) on overall survival in NB patients. We performed a systematic review using PubMed, Embase, and Cochrane libraries. Individual patient data was retrieved from extracted Kaplan–Meier curves. Data from studies was then merged, and analysis was done on the full data set. Seven studies met the inclusion criteria. Methylation of the three genes had worse overall survival than the unmethylated arms. Five-year survival for the methylated arm of RASSF1A, DCR2, and CASP8 was 63.19% (95% CI 56.55-70.60), 57.78% (95% CI 47.63-70.08), and 56.39% (95% CI 49.53-64.19), respectively, while for the unmethylated arm, it was 93.10% (95% CI 87.40–99.1), 84.84% (95% CI 80.04-89.92), and 83.68% (95% CI 80.28-87.22), respectively. In conclusion, our results indicate that in NB patients, RASSF1A, DCR2, and CASP8 methylation is associated with poor prognosis. Large prospective studies will be necessary to confirm definitive correlation between methylation of these genes and survival taking into account all other known risk factors. (PROSPERO registration number CRD42017082264).

RASSF1A Regulates Spindle Organization by Modulating Tubulin Acetylation via SIRT2 and HDAC6 in Mouse Oocytes

Dynamic changes in microtubules during cell cycle progression are essential for spindle organization to ensure proper segregation of chromosomes. There is growing evidence that post translational modifications of tubulins are the key factors that contribute to microtubule dynamics. However, how dynamic properties of microtubules are regulated in mouse oocytes is unclear. Here, we show that tumor suppressor RASSF1A is required for tubulin acetylation by regulating SIRT2 and HDAC6 during meiotic maturation in mouse oocytes. We found that RASSF1A was localized at the spindle microtubules in mouse oocytes. Knockdown of RASSF1A perturbed meiotic progression by impairing spindle organization and chromosome alignment. Moreover, RASSF1A knockdown disrupted kinetochore-microtubule (kMT) attachment, which activated spindle assembly checkpoint and increased the incidence of aneuploidy. In addition, RASSF1A knockdown decreased tubulin acetylation by increasing SIRT2 and HDAC6 levels. Notably, defects in spindle organization and chromosome alignment after RASSF1A knockdown were rescued not only by inhibiting SIRT2 or HDAC6 activity, but also by overexpressing acetylation mimicking K40Q tubulin. Therefore, our results demonstrated that RASSF1A regulates SIRT2- and HDAC6-mediated tubulin acetylation for proper spindle organization during oocyte meiotic maturation.

Significant decrease of a master regulator of genes (REST/NRSF) in high-grade squamous intraepithelial lesion and cervical cancer

Background

Methods

Results

Conclusion

RASSF1A-Hippo pathway link in patients with urothelial carcinoma of bladder: plausible therapeutic target

RASSF1A is a tumor suppressor gene, and its hypermethylation has been observed in cancers. RASSF1A acts as an upstream regulator of Hippo pathway and modulates its function. The aim of this study was to analyze expression of RASSF1A, Hippo pathway molecules (YAP, MST) and downstream targets (CTGF, Cyr61 and AREG) in bladder cancer patients. Later, the link between RASSF1A and Hippo pathway and a potential therapeutic scope of this link in UBC were also studied. MSPCR was performed to study methylation of RASSF1A promoter. Expression of molecules was studied using qPCR, Western blot and IHC. The link between RASSF1A and Hippo pathway was studied using Spearman's correlation in patients and validated by overexpressing RASSF1A in HT1376 cells and its effect on Hippo pathway was observed using qPCR and Western blot. Further therapeutic potential of this link was studied using MTT and PI assays. The expression of RASSF1A was lower, whereas the expression of YAP, CTGF and CYR61 was higher. The expression of RASSF1A protein gradually decreased, while the expression of YAP, CTGF and CYR61 increased with severity of disease. Based on Spearman's correlation, RASSF1A showed a negative correlation with YAP, CTGF and CYR61. YAP showed a positive correlation with CTGF and CYR61. To validate this link, RASSF1A was overexpressed in HT1376 cells. Overexpressed RASSF1A activated Hippo pathway, followed by a decrease in CTGF and CYR61 at mRNA, and enhanced cytotoxicity to chemotherapeutic drugs. This study finds a previously unrecognized role of RASSF1A in the regulation of CTGF and CYR61 through mediation of Hippo pathway in UBC and supports the significance of this link as a potential therapeutic target for UBC.

The long non-coding RNA ANRASSF1 in the regulation of alternative protein-coding transcripts RASSF1A and RASSF1C in human breast cancer cells: implications to epigenetic therapy

Alternative protein-coding transcripts of the RASSF1 gene have been associated with dual functions in human cancer: while RASSF1C isoform has oncogenic properties, RASSF1A is a tumour suppressor frequently silenced by hypermethylation. Recently, the antisense long non-coding RNA RASSF1 (ANRASSF1) was implicated in a locus-specific mechanism for the RASSF1A epigenetic repression mediated by PRC2 (Polycomb Repressive Complex 2). Here, we evaluated the methylation patterns of the promoter regions of RASSF1A and RASSF1C and the expression levels of these RASSF1 transcripts in breast cancer and breast cancer cell lines. As expected, RASSF1C remained unmethylated and RASSF1A was hypermethylated at high frequencies in 75 primary breast cancers, and also in a panel of three mammary epithelial cells (MEC) and 10 breast cancer cell lines (BCC). Although RASSF1C was expressed in all cell lines, only two of them expressed the transcript RASSF1A. ANRASSF1 expression levels were increased in six BCCs. In vitro induced demethylation with 5-Aza-2'-deoxicytydine (5-Aza-dC) resulted in up-regulation of RASSF1A and an inverse correlation with ANRASSF1 relative abundance in BCCs. However, increased levels of both transcripts were observed in two MECs (184A1 and MCF10A) after treatment with 5-Aza-dC. Overall, these findings indicate that ANRASSF1 is differentially expressed in MECs and BCCs. The lncRNA ANRASSF1 provides new perspectives as a therapeutic target for locus-specific regulation of RASSF1A.

Prognostic value of RASSF1A methylation status in non-small cell lung cancer (NSCLC) patients: A meta-analysis of prospective studies

Objective: Ras association domain family 1 A (RASSF1A) has been regarded as a biomarker predicting the prognosis of non-small cell lung cancer (NSCLC), but previous findings are inconsistent. This meta-analysis of prospective studies aimed to assess the value of RASSF1A methylation in predicting the prognosis of NSCLC patients. Methods: Studies were searched in PubMed and Web of Science. The estimates of the effects and the corresponding 95% confidence intervals (95% CIs) were used for the analyses. The overall effects of RASSF1A methylation on overall survival (OS) were estimated, after which subgroup analysis based on regions was conducted. Sensitivity analyses were conducted to restrict the studies with certain features. Results: A total of 16 studies with 2210 participants were included in this meta-analysis. The overall analysis result indicated that RASSF1A methylation had no statistically significant effects on OS of NSCLC patients (HR = 1.28; 95% CI 0.86-1.70), which were confirmed by the subgroup analysis. However, the sensitivity analysis indicated that RASSF1A methylation from lung cancer tissues was significantly associated with lower OS (HR = 1.24; 95% CI 1.04-1.45). Conclusion: RASSF1A methylation in lung cancer tissue can serve as a prognostic factor of NSCLC. More studies are needed to uncover the underlying mechanisms.

Gestational oral low-dose estradiol-17β induces altered DNA methylation of CDKN2D and PSAT1 in embryos and adult offspring

Endocrine disrupting chemicals (EDC) interfere with the natural hormone balance and may induce epigenetic changes through exposure during sensitive periods of development. In this study, the effects of short-term estradiol-17β (E2) exposure on various tissues of pregnant sows (F₀) and on day 10 blastocysts (F₁) were assessed. Intergenerational effects were investigated in the liver of 1-year old female offspring (F₁). During gestation, sows were orally exposed to two low doses and a high dose of E2 (0.05, 10, and 1000 µg/kg body weight/day). In F₀, perturbed tissue specific mRNA expression of cell cycle regulation and tumour suppressor genes was found at low and high dose exposure, being most pronounced in the endometrium and corpus luteum. The liver showed the most significant DNA hypomethylation in three target genes; CDKN2D, PSAT1, and RASSF1. For CDKN2D and PSAT1, differential methylation in blastocysts was similar as observed in the F₀ liver. Whereas blastocysts showed hypomethylation, the liver of 1-year old offspring showed subtle, but significant hypermethylation. We show that the level of effect of estrogenic EDC, with the periconceptual period as a sensitive time window, is at much lower concentration than currently presumed and propose epigenetics as a sensitive novel risk assessment parameter.

Gene methylation as a powerful biomarker for detection and screening of non-small cell lung cancer in blood

DNA methylation has been reported to become a potential powerful tool for cancer detection and diagnosis. However, the possibilities for the application of blood-based gene methylation as a biomarker for non-small cell lung cancer (NSCLC) detection and screening remain unclear. Hence, we performed this meta-analysis to evaluate the value of gene methylation detected in blood samples as a noninvasive biomarker in NSCLC. A total of 28 genes were analyzed from 37 case-control studies. In the genes with more than three studies, we found that the methylation of P16, RASSF1A, APC, RARβ, DAPK, CDH13, and MGMT was significantly associated with risks of NSCLC. The methylation statuses of P16, RASSF1A, APC, RARβ, DAPK, CDH13, and MGMT were not linked to age, gender, smoking behavior, and tumor stage and histology in NSCLC. Therefore, the use of the methylation status of P16, RASSF1A, APC, RARβ, DAPK, CDH13, and MGMT could become a promising and powerful biomarker for the detection and screening of NSCLC in blood in clinical settings. Further large-scale studies with large sample sizes are necessary to confirm our findings in the future.

Evaluation of Promoter Methylation of RASSF1A and ATM in Peripheral Blood of Breast Cancer Patients and Healthy Control Individuals

Breast cancer (BC) is the most common cancer among women and has high mortality rates. Early detection is supposed to be critical for the patient’s prognosis. In recent years, several studies have investigated global DNA methylation profiles and gene-specific DNA methylation in blood-based DNA to develop putative screening markers for cancer. However, most of the studies have not yet been validated. In our study, we analyzed the promoter methylation of RASSF1A and ATM in peripheral blood DNA of 229 sporadic patients and 151 healthy controls by the MassARRAY EpiTYPER assay. There were no significant differences in DNA methylation levels of RASSF1A and ATM between the sporadic BC cases and the healthy controls. Furthermore, we performed the Infinium HumanMethylation450 BeadChip (450K) array analysis using 48 sporadic BC cases and 48 healthy controls (cases and controls are the same from those of the MassARRAY EpiTYPER assay) and made a comparison with the published data. No significant differences were presented in DNA methylation levels of RASSF1A and ATM between the sporadic BC cases and the healthy controls. So far, the evidence for powerful blood-based methylation markers is still limited and the identified markers need to be further validated.

Epigenetic activation of LY6K predicts the presence of metastasis and poor prognosis in breast carcinoma

The role of lymphocyte antigen 6 complex, locus K (LY6K) in breast cancer has been studied, whereas the epigenetic control of LY6K transcription is not fully understood. Here, we report that breast cancer patients with increased LY6K expression had shorter disease-free and overall survival than the patients with low levels of LY6K by multivariate analysis. LY6K also was upregulated in breast cancer patients with distant metastases than those without distant metastases, downregulating E-cadherin expression. Furthermore, xenograft tumor volumes from LY6K knockdown nude mice were reduced than those of mice treated with control lentivirus. Interestingly, LY6K has a CpG island (CGI) around the transcription start site and non-CGI in its promoter, called a CGI shore. LY6K expression was inversely correlated with methylation in not only CGI but CGI shore, which are associated with histone modifications. Additionally, LY6K methylation was increased by the PAX3 transcription factor due to the SNP242 mutation in LY6K CGI shore. Taken together, breast cancer risk and metastasis were significantly associated with not only LY6K expression, but also methylation of CGI shore which induced by SNP242 mutation. Our results suggest that an understanding epigenetic mechanism of the LY6K gene may be useful to diagnose carcinogenic risk and predict outcomes of patients with metastatic breast cancer.

RASSF1A promoter methylation was associated with the development, progression and metastasis of cervical carcinoma: a meta-analysis with trial sequential analysis

BACKGROUND

RASSF1A promoter methylation has been reported in cervical cancer. However, clinical effect of RASSF1A promoter methylation in cervical cancer remains unclear. This meta-analysis was conducted to assess the correlation between RASSF1A promoter methylation and cervical cancer and the association of RASSF1A promoter methylation with clinicopathological features.

METHODS

Electronic databases were searched to identify eligible publications. The pooled odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Trial sequential analysis (TSA) was performed to assess the required study population information.

RESULTS

Twenty-six papers published from 2001 to 2017 were analyzed in the meta-analysis, including a total of 1820 patients with cervical cancer, 507 patients with cervical intraepithelial neoplasia (CIN) lesions and 894 nonmalignant controls. RASSF1A promoter methylation was significantly increased in cervical cancer than in CIN lesions and nonmalignant tissue samples. In addition, RASSF1A promoter methylation was correlated with cervical cancer among two studies of blood and cytology samples (cancer vs nonmalignant controls). No correlation was found between RASSF1A promoter methylation and age factor, human papillomavirus (HPV) subtypes or clinical stage. RASSF1A promoter methylation was associated with tumor grade (grade 3-4 vs 1-2: OR 2.31, 95% CI 1.12-4.77, P = 0.023), lymph node metastasis (yes vs no: OR 2.97, 95% CI 1.60-5.52, P = 0.001), tumor histology (squamous cell carcinoma vs adenocarcinoma: OR 0.49, 95% CI 0.22-1.08, P = 0.076), and HPV infection (positive vs negative: OR 0.45, 95% CI 0.28-0.73, P = 0.001). TSA showed that the cumulative Z-curve did not cross the trial sequential monitoring boundary for significant results.

CONCLUSIONS

RASSF1A promoter methylation may be associated with cervical cancer development, progression and metastasis. Methylated RASSF1A may be a noninvasive blood or cytology biomarker. Based on TSA, more studies are essential in the future.

Promoter Methylation of RASSF1A indicates Prognosis for Patients with Stage II and III Colorectal Cancer Treated with Oxaliplatin-Based Chemotherapy

Background

The purpose of this study was to investigate the prognostic significance of methylation of RAS association domain family protein 1 (RASSF1A) in the promoter region for patients with stage II and III colorectal cancer (CRC) receiving oxaliplatin-based chemotherapy.

Material/Methods

There were 108 eligible CRC patients and 78 healthy controls included in this study. Methylation-specific polymerase chain reaction (MSP) was applied to detect the methylation status of RASSF1A in patients before and after chemotherapy. The effects of RASSF1A methylation on chemotherapy-sensitivity and prognosis for patients were also evaluated in the present study.

Results

The frequency of RASSF1A methylation was higher in CRC patients than in the healthy controls (48.44% versus 5.13%, p<0.001). After two cycles of chemotherapy, methylation ratio was significantly decreased (21.30%, p<0.001). Promoter methylation of RASSF1A was significantly correlated with tumor stage and pathological differentiation (p=0.008 and p=0.007, respectively). Patients without methylation had a favorable objective response (OR), compared with those with methylation (53.33% versus 25%, p=0.014). Methylation status of RASSF1A could influence progression-free survival and overall survival (log rank test, p<0.05). Cox regression analysis indicated that RASSF1A methylation (HR=2.471, 95% CI=1.125–5.428, p=0.024) and OR (HR=2.678, 95% CI=1.085–6.610, p 0.033) were independently correlated with prognosis for patients treated with oxaliplatin-based chemotherapy.

Conclusions

Promoter methylation of RASSF1A can influence sensitivity to oxaliplatin-based chemotherapy, which can be used to predict outcomes for patients with stage II and III CRC. In addition, the aberrant methylation may be a promising target for improving chemotherapy efficacy.

Distinct DNA methylation alterations are associated with cribriform architecture and intraductal carcinoma in Gleason pattern 4 prostate tumors

The aim of the present study was to explore DNA methylation aberrations in association with cribriform architecture and intraductal carcinoma (IDC) of the prostate, as there is robust evidence that these morphological features are associated with aggressive disease and have significant clinical implications. Herein, the associations of a panel of seven known prognostic DNA methylation biomarkers with cribriform and IDC features were examined in a series of 91 Gleason pattern (GP) 4 tumors derived from Gleason score 7 radical prostatectomies. Gene specific DNA methylation was compared between cribriform and/or IDC positive vs. negative cases, and in association with clinicopathological features, using Chi square and Mann-Whitney U tests. DNA methylation of the adenomatous polyposis coli, Ras association domain family member 1 and T-box 15 genes was significantly elevated in GP4 tumors with cribriform and/or IDC features compared with negative cases (P=0.045, P=0.007 and P=0.013, respectively). To the best of our knowledge, this provides the first evidence for an association between cribriform and/or IDC and methylation biomarkers, and warrants further investigation of additional DNA methylation events in association with various architectural patterns in prostate cancer.

HPV16 oncogenes E6 or/and E7 may influence the methylation status of RASSFIA gene promoter region in cervical cancer cell line HT-3

Both human papillomavirus (HPV) infection and the aberrant Ras associated domain family gene 1A (RASSF1A) promoter methylation status participate in the pathogenesis of cervical cancer. Some studies suggest that E6, and E7 are involved in the pathogenetic mechanisms of RASSF1A. We mainly explored a possible involvement of HPV16 oncogenes E6 or/and E7 in RASSF1A promoter methylation status and possible roles of RASSF1A gene methylation in cervical cancer. Bisulfite genomic sequencing (BGS) PCR combined with TA clone, methylation-specific PCR (MSP) were used to analyze methylation status of the RASSF1A gene promoter in HPV16/18-positive and HPV-negative cervical cancer cell lines; ectopically expressed HPV16 E6, E7 and E6/E7 cervical cancer cell lines; normal cervical and cervical cancer tissues. The mRNA and protein expression of RASSF1A was detected by RT-PCR and western blotting. Re-expression and downregulated promoter methylation status were detected in the ectopically expressed HPV16 E6 and E7 cervical cancer cell line HT-3. The methylation status and expression of RASSF1A could be downregulated or reactivated by 5-Aza-dc in HT-3 and C33A cells. Additionally, statistics showed significant hypermethylation of RASSF1A in cervical cancer samples compared to that in normal cervical samples (P<0.05). The false negative rate (FNR) was 6.25% by HC2 method, when reconfirmed by HPV detection combining the MY09/11, GP5+/6+ and SPF1/2 methods. The ectopic expression of HPV16 E6 and/or E7 may be involved in aberrant methylation and expression of the RASSF1A gene. RASSF1A gene expression could be regulated by its promoter methylation status. Additionally, the false negativity of the HPV detection may contribute to the uncertain relationship between HPV infection and aberrant RASSF1A promoter methylation.

Quantitative assessment of the relationship between RASSF1A gene promoter methylation and bladder cancer (PRISMA)

BACKGROUND

Methylation of the Ras-association domain family 1 isoform A (RASSF1A) gene promoter region is thought to participate in the initiation and development of many different cancers. However, in bladder cancer the role of RASSF1A methylation was unclear. To evaluate the relationship between RASSF1A methylation and bladder cancer, a quantitative assessment of an independent meta-analysis was performed. In addition, a DNA methylation microarray database from the cancer genome atlas (TCGA) project was used to validate the results of the meta-analysis.

METHODS

We searched published articles from computerized databases, and DNA methylation data were extracted from TCGA project. All data were analyzed by R software.

RESULTS

The results of the meta-analysis indicated that the frequency of RASSF1A gene methylation in bladder cancer patients is significantly higher than in healthy controls. The hazard ratio (HR) was 2.24 (95% CI = [1.45; 3.48], P = 0.0003) for overall survival (OS), and the RASSF1A gene promoter methylation status was strongly associated with the TNM stage and differentiation grade of the tumor. The similar results were also found by the data from TCGA project.

CONCLUSION

There was a significant relationship between the methylation of the RASSF1A gene promoter and bladder cancer. Therefore, RASSF1A gene promoter methylation will be a potential biomarker for the clinical diagnosis of bladder cancer.

Association between Ras association domain family 1A promoter methylation and esophageal squamous cell carcinoma: a meta-analysis

RASSF1A has been reported to be a candidate tumor suppressor in esophageal squamous cell carcinoma (ESCC). However, the association between RASSF1A promoter methylation and ESCC remains unclear. Eligible studies were identified through searching PubMed, Medline, Web of Science, and the China National Knowledge Infrastucture database. Studies were pooled and odds ratios (ORs) with corresponding confidence intervals (CIs) were calculated. Funnel plots were also performed to evaluate publication bias. Twelve studies involving 859 cases and 675 controls were included in this meta-analysis. A significant association was observed between RASSF1A methylation and ESCC overall (OR = 11.7, 95% CI: 6.59-20.9, z=8.36, P<0.00001). Subgroup analysis showed that the OR for heterogeneous tissues was 5.35 (95% CI = 2.95-9.71) while for autologous tissues it was 16.0 (8.31-30.96). For patient sample size, the OR for the <50 subgroup was 9.92 (95% CI = 2.88-34.2) and for the 50 case group was 13.1 (95% CI = 6.59-25.91). The OR for a relationship between RASSF1A methylation and TNM stages was 0.27 (95% CI=0.10-0.77), whereas there were no significant differences in RASSF1A methylation in relation to gender and differentiation among ESCC cases. This meta-analysis suggests a significant association between RASSF1A methylation and ESCC.

Asialoglycoprotein receptor-magnetic dual targeting nanoparticles for delivery of RASSF1A to hepatocellular carcinoma

We developed a nanovector with double targeting properties for efficiently delivering the tumor suppressor gene RASSF1A specifically into hepatocellular carcinoma (HCC) cells by preparing galactosylated-carboxymethyl chitosan-magnetic iron oxide nanoparticles (Gal-CMCS-Fe₃O₄-NPs). After conjugating galactose and CMCS to the surface of Fe₃O₄-NPs, we observed that Gal-CMCS-Fe₃O₄-NPs were round with a relatively stable zeta potential of +6.5 mV and an mean hydrodynamic size of 40.1 ± 5.3 nm. Gal-CMCS-Fe₃O₄-NPs had strong DNA condensing power in pH 7 solution and were largely nontoxic. In vitro experiments demonstrated that Gal-CMCS-Fe₃O₄-NPs were highly selective for HCC cells and liver cells. In vivo experiments showed the specific accumulation of Gal-CMCS-Fe₃O₄-NPs in HCC tissue, especially with the aid of an external magnetic field. Nude mice with orthotopically transplanted HCC received an intravenous injection of the Gal-CMCS-Fe₃O₄-NPs/pcDNA3.1(+)RASSF1A compound and intraperitoneal injection of mitomycin and had an external magnetic field applied to the tumor area. These mice had the smallest tumors, largest percentage of TUNEL-positive cells, and highest caspase-3 expression levels in tumor tissue compared to other groups of treated mice. These results suggest the potential application of Gal-CMCS-Fe₃O₄-NPs for RASSF1A gene delivery for the treatment of HCC.

The tumor suppressive role of RASSF1A in osteosarcoma through the Wnt signaling pathway

Ras-association domain family 1 isoform A (RASSF1A) is a tumor suppressor gene and its expression is lost in numerous types of cancer cells, including primary osteosarcoma cells. However, its functional significance in osteosarcoma has not been well defined. The messenger RNA (mRNA) expression of RASSF1A in osteosarcoma tissues and corresponding non-tumoral tissues was measured by real-time PCR. Overexpression of RASSF1A was established by an adenoviral vector expressing RASSF1A. Cell migration and invasion were analyzed in transwells. Apoptosis and cell cycle were analyzed using flow cytometry. Wnt/β-catenin activity was measured by TCF reporter dual-luciferase assay. Cell viability was measured by MTT assay. Protein expression was detected by Western blot. RASSF1A mRNA expression was significantly lower in osteosarcoma tissues than that in the corresponding non-tumoral tissues. The lowered RASSF1A expression correlated with the clinical severity of osteosarcoma. rAd-RASSF1A injection significantly inhibited the growth of xenograft MNNG/HOS tumors in mice. Overexpression of RASSF1A resulted in significant inhibition of the proliferation, migration, and invasion; induced apoptosis; and arrested cell cycle at G0/G1 phase in both the MNNG/HOS and SaOS2 cells. Overexpression of RASSF1A inhibited the Wnt/β-catenin activity, decreased phosphorylation of Akt/glycogen synthase kinase-3-β (GSK3-β), and increased phosphorylation of mammalian sterile 20-like kinase 1 (MST1). Overexpression of RASSF1A downregulated the cyclin D1, c-Myc, and matrix metalloproteinase-7 (MMP-7) protein levels. RASSF1A functions as a tumor suppressor in osteosarcoma and exerts anti-cancer roles through regulating Akt/GSK-3-Wnt/β-catenin signaling.

Molecular genetic approaches in the diagnosis of lung cancer

It is an acute problem for the 21st century to find effective and inexpensive methods for early detection of lung cancer. Patients, suspected of having a malignant disease of lungs, generally undergo clinical studies such as CT scans of the chest and bronchoscopy. The latter is mainly used to confirm the diagnosis. However, even when the signs, symptoms and radiological findings indicate that clinical diagnosis of malignant lung disease is evident, additional invasive procedures for obtaining the biological material suitable for the final confirmation of the presence of malignant cells are required. Currently, there is a clear understanding of the need to find biomarkers able to detect pre-clinical stage of cancer cells using minimally invasive procedures.

DNA hypermethylation analysis in sputum for the diagnosis of lung cancer: training validation set approach

Background:

Lung cancer has the highest mortality of all cancers. The aim of this study was to examine DNA hypermethylation in sputum and validate its diagnostic accuracy for lung cancer.

Methods:

DNA hypermethylation of RASSF1A, APC, cytoglobin, 3OST2, PRDM14, FAM19A4 and PHACTR3 was analysed in sputum samples from symptomatic lung cancer patients and controls (learning set: 73 cases, 86 controls; validation set: 159 cases, 154 controls) by quantitative methylation-specific PCR. Three statistical models were used: (i) cutoff based on Youden's J index, (ii) cutoff based on fixed specificity per marker of 96% and (iii) risk classification of post-test probabilities.

Results:

In the learning set, approach (i) showed that RASSF1A was best able to distinguish cases from controls (sensitivity 42.5%, specificity 96.5%). RASSF1A, 3OST2 and PRDM14 combined demonstrated a sensitivity of 82.2% with a specificity of 66.3%. Approach (ii) yielded a combination rule of RASSF1A, 3OST2 and PHACTR3 (sensitivity 67.1%, specificity 89.5%). The risk model (approach iii) distributed the cases over all risk categories. All methods displayed similar and consistent results in the validation set.

Conclusions:

Our findings underscore the impact of DNA methylation markers in symptomatic lung cancer diagnosis. RASSF1A is validated as diagnostic marker in lung cancer.

Epigenetic modifications in human thyroid cancer

Thyroid carcinoma is the most common endocrine malignancy of the endocrine organs, and its incidence rate has steadily increased over the last decade. Over 95% of thyroid carcinoma is derived from follicular cells that have a spectrum of differentiation to the most invasive malignancy. The molecular pathogenesis of thyroid cancer remains to be clarified, although activating the RET, RAS and BRAF oncogenes have been well characterized. Increasing evidence from previous studies demonstrates that acquired epigenetic abnormalities participating with genetic alteration results in altered patterns of gene expression/function. Aberrant DNA methylation has been established in the CpG regions and microRNAs (miRNAs) expression profile recognized in cancer development. In the present review, a literature review was performed using MEDLINE and PubMed with the terms 'epigenetic patterns in thyroid cancer [or papillary thyroid carcinoma (PTC), follicular thyroid carcinoma (FTC), medullary thyroid cancer (MTC), anaplastic thyroid cancer (ATC)]', 'DNA methylation in thyroid cancer (or PTC, FTC, MTC, ATC)', 'miRNA expression in thyroid cancer (or PTC, FTC, MTC, ATC)', 'epigenetic patterns in cancer' and the current understanding of epigenetic patterns in thyroid cancer was discussed.

Methylated RASSF1A in malignant peripheral nerve sheath tumors identifies neurofibromatosis type 1 patients with inferior prognosis

Background

Malignant peripheral nerve sheath tumor (MPNST) is a rare and highly aggressive disease with no evidence of effect from adjuvant therapy. It is further associated with the hereditary syndrome neurofibromatosis type 1 (NF1). Silencing of the tumor suppressor gene RASSF1A through DNA promoter hypermethylation is known to be involved in cancer development, but its impact in MPNSTs remains unsettled.

Methods

The RASSF1A promoter was analyzed by methylation-specific PCR in 113 specimens, including 44 NF1-associated MPNSTs, 47 sporadic MPNSTs, 21 benign neurofibromas, and 1 nonneoplastic nerve sheath control.

Results

RASSF1A methylation was found only in the malignant samples (60%) and identified a subgroup among patients with NF1-associated MPNST with a poor prognosis. These patients had a mean 5-year disease-specific survival of 27.3 months (95% CI: 17.2–37.4) versus 47.4 months (95% CI: 37.5–57.2) for NF1 patients with unmethylated promoters, P = 0.014. In multivariate Cox regression analysis, methylated RASSF1A remained an adverse prognostic factor independent of clinical risk factors, P = .013 (hazard ratio: 5.2; 95% CI: 1.4–19.4).

Conclusion

A considerable number of MPNST samples display hypermethylation of the RASSF1A gene promoter, and for these tumors, this is the first molecular marker that if validated can characterize a subgroup of patients with inferior prognosis, restricted to individuals with NF1.

New insights into the diagnosis of nodular goiter

Preoperative diagnostic investigations of nodular goiter are based on two main examinations: ultrasonography of the thyroid gland and ultrasound-guided fine-needle aspiration biopsy. So far, FNAB has been the best method for the differentiation of nodules, but in some cases it fails to produce a conclusive diagnosis. Some of the biopsies do not provide enough material to establish the diagnosis, in some other biopsies cytological picture is inconclusive.

Determining the eligibility of thyroid focal lesions for surgery has been more and more often done with molecular methods. The most common genetic changes leading to the development of thyroid cancer include mutations, translocations and amplifications of genes, disturbances in gene methylation and dysregulation of microRNA. The mutations of Ras proto-oncogenes and BRAF gene as well as disturbances of DNA methylation in promoter regions of genes regulating cell cycle (e.g. hypermethylation of RASSF1A gene and TIMP-3 gene) play an important role in the process of neoplastic transformation of thyreocyte. The advances in molecular biology made it possible to investigate these genetic disturbances in DNA and/or RNA from peripheral blood, postoperative thyroid tissue material and cytology specimens obtained through fine-needle aspiration biopsy of focal lesions in the thyroid gland.

As it became possible to analyze the mutations and methylation of genes from cell material obtained through fine-needle aspiration biopsy, it would be beneficial to introduce the techniques of molecular biology in the pre-operative diagnosis of nodular goiter as a valuable method, complementary to ultrasonography and FNAB. The knowledge obtained from molecular studies might help to determine the frequency of follow-up investigations in patients with nodular goiter and to select patients potentially at risk of developing thyroid cancer, which would facilitate their qualification for earlier strumectomy.

APC alterations are frequently involved in the pathogenesis of acinar cell carcinoma of the pancreas, mainly through gene loss and promoter hypermethylation

Genetic and epigenetic alterations involved in the pathogenesis of pancreatic acinar cell carcinomas (ACCs) are poorly characterized, including the frequency and role of gene-specific hypermethylation, chromosome aberrations, and copy number alterations (CNAs). A subset of ACCs is known to show alterations in the APC/β-catenin pathway which includes mutations of APC gene. However, it is not known whether, in addition to mutation, loss of APC gene function can occur through alternative genetic and epigenetic mechanisms such as gene loss or promoter methylation. We investigated the global methylation profile of 34 tumor suppressor genes, CNAs of 52 chromosomal regions, and APC gene alterations (mutation, methylation, and loss) together with APC mRNA level in 45 ACCs and related peritumoral pancreatic tissues using methylation-specific multiplex ligation probe amplification (MS-MLPA), fluorescence in situ hybridization (FISH), mutation analysis, and reverse transcription-droplet digital PCR. ACCs did not show an extensive global gene hypermethylation profile. RASSF1 and APC were the only two genes frequently methylated. APC mutations were found in only 7 % of cases, while APC loss and methylation were more frequently observed (48 and 56 % of ACCs, respectively). APC mRNA low levels were found in 58 % of cases and correlated with CNAs. In conclusion, ACCs do not show extensive global gene hypermethylation. APC alterations are frequently involved in the pathogenesis of ACCs mainly through gene loss and promoter hypermethylation, along with reduction of APC mRNA levels.

β-D-glucan inhibits endocrine-resistant breast cancer cell proliferation and alters gene expression

Endocrine therapies have been successfully used for breast cancer patients with estrogen receptor α (ERα) positive tumors, but ∼40% of patients relapse due to endocrine resistance. β-glucans are components of plant cell walls that have immunomodulatory and anticancer activity. The objective of this study was to examine the activity of β-D-glucan, purified from barley, in endocrine-sensitive MCF-7 versus endocrine-resistant LCC9 and LY2 breast cancer cells. β-D-glucan dissolved in DMSO but not water inhibited MCF-7 cell proliferation in a concentration-dependent manner as measured by BrdU incorporation with an IC₅₀ of ∼164±12 μg/ml. β-D-glucan dissolved in DMSO inhibited tamoxifen/endocrine-resistant LCC9 and LY2 cell proliferation with IC₅₀ values of 4.6±0.3 and 24.2±1.4 μg/ml, respectively. MCF-10A normal breast epithelial cells showed a higher IC₅₀ ∼464 μg/ml and the proliferation of MDA-MB-231 triple negative breast cancer cells was not inhibited by β-D-glucan. Concentration-dependent increases in the BAX/BCL2 ratio and cell death with β-D-glucan were observed in MCF-7 and LCC9 cells. PCR array analysis revealed changes in gene expression in response to 24-h treatment with 10 or 50 μg/ml β-D-glucan that were different between MCF-7 and LCC9 cells as well as differences in basal gene expression between the two cell lines. Select results were confirmed by quantitative real-time PCR demonstrating that β-D-glucan increased RASSF1 expression in MCF-7 cells and IGFBP3, CTNNB1 and ERβ transcript expression in LCC9 cells. Our data indicate that β-D-glucan regulates breast cancer-relevant gene expression and may be useful for inhibiting endocrine-resistant breast cancer cell proliferation.

The association between RASSF1A promoter methylation and prostate cancer: evidence from 19 published studies

Ras-associated domain family 1A (RASSF1A) is a putative tumor suppressor gene located at 3p21.3, and the epigenetic inactivation of RASSF1A by hypermethylation of CpG islands within the promoter region has been observed in various cancer types, including prostate cancer (PCa). However, results from published studies on the association between RASSF1A promoter methylation and PCa risk are conflicting and inconclusive. Hence, we conducted a meta-analysis of 19 eligible studies with odds ratio (OR) and its corresponding 95% confidence intervals (95% CI) in order to investigate the strength of relationship of RASSF1A promoter methylation with PCa risk and its clinicopathological variables. Overall, the RASSF1A promoter methylation was significantly associated with PCa risk (OR = 9.58, 95% CI 5.64-16.88, P heterogeneity <0.001) and Gleason score (GS) (OR = 2.58, 95% CI 1.64-4.04, P(heterogeneity) = 0.019). In addition, subgroup analysis by testing material demonstrated the significant association between RASSF1A methylation and GS (OR = 3.09, 95% CI 1.92-4.97, P heterogeneity =0.042), PSA level (OR = 2.75, 95% CI 1.67-4.52, P(heterogeneity) = 0.639), and tumor stage (OR = 1.74, 95% CI 1.05-2.87, P(heterogeneity) = 0.026) in tissue rather than urine samples. In conclusion, this meta-analysis suggested that RASSF1A promoter methylation was significantly associated with an increased risk for PCa; furthermore, the RASSF1A methylation status in tissue rather than urine was positively correlated with GS, serum PSA level, and tumor stage, which can be utilized for the early detection and prognosis prediction of PCa.

Association between RASSF1A promoter methylation and ovarian cancer: a meta-analysis

Background

The RAS association domain family protein 1a gene (RASSF1A) is one of the tumor suppressor genes (TSG). Inactivation of RASSF1A is critical to the pathogenesis of cancer. Aberrant TSG methylation was considered an important epigenetic silencing mechanism in the progression of ovarian cancer. A number of studies have discussed association between RASSF1A promoter methylation and ovarian cancer. However, they were mostly based on a small number of samples and showed inconsist results, Therefore, we conducted a meta-analysis to better identify the association.

Methods

Eligible studies were identified by searching the PubMed, EMBASE, Web of Science, and CNKI databases using a systematic searching strategy. We pooled the odds ratio (ORs) from individual studies using a fixed-effects model. We performed heterogeneity and publication bias analysis simultaneously.

Results

Thirteen studies, with 763 ovarian cancer patients and 438 controls were included in the meta-analysis. The frequencies of RASSF1A promoter methylation ranged from 30% to 58% (median is 48%) in the cancer group and 0 to 21% (median is 0) in the control group. The frequencies of RASSF1A promoter methylation in the cancer group were significantly higher than those in the control group. The pooled odds ratio was 11.17 (95% CI = 7.51–16.61) in the cancer group versus the corresponding control group under the fixed-effects model.

Conclusion

The results suggested that RASSF1A promoter methylation had a strong association with ovarian cancer.

Effect of DNA methylation inhibitor on RASSF1A genes expression in non-small cell lung cancer cell line A549 and A549DDP

Background

Ras association domain family 1A gene (RASSFlA) is a candidate suppressor gene, Lack of RASSF1A expression was found in lung cancer. High DNA methylation at the promoter region is the main reason for inactivating RASSF1A transcription.

Methods

In this study, we examined RASSF1A’s methylation status and its mRNA expression level between non-small cell lung cancer cell line A549 and anti-Cisplatin cell strain A549DDP, Furthermore, methylation of A549DDP was reversed by treatment of 5-Aza-2′ - deoxycytidine (5-Aza-cdR),a DNA methyltransferase inhibitor.

Results

We found that RASSF1A’s methylation status and its mRNA expression were obvious differences between A549 and A549DDP. 5-Aza-CdR treatment remarkablly reduced cell vability of A549DDP. Moreover, 5-Aza-CdR treatment induced A549DDP cell apoptosis in a dose dependent manner with declining cell percentage in S and G2/M stage, and increasing proportion in G0/G1 stage. Cell motility was blocked in G0/G1 stage. All of A549DDP cells showed unmethylated expression, its high methylation status was reversed in a dose-dependent manner within a certain range.

Conclusions

The abnormal gene methylation status of RASSF1A is a molecular biomarker in lung cancer diagnosis, treatment and prognosis.

DNA methylation and apoptosis resistance in cancer cells

Apoptosis is a cell death programme primordial to cellular homeostasis efficiency. This normal cell suicide program is the result of the activation of a cascade of events in response to death stimuli. Apoptosis occurs in normal cells to maintain a balance between cell proliferation and cell death. A deregulation of this balance due to modifications in the apoptosic pathway leads to different human diseases including cancers. Apoptosis resistance is one of the most important hallmarks of cancer and some new therapeutical strategies focus on inducing cell death in cancer cells. Nevertheless, cancer cells are resistant to treatment inducing cell death because of different mechanisms, such as DNA mutations in gene coding for pro-apoptotic proteins, increased expression of anti-apoptotic proteins and/or pro-survival signals, or pro-apoptic gene silencing mediated by DNA hypermethylation. In this context, aberrant DNA methylation patterns, hypermethylation and hypomethylation of gene coding for proteins implicated in apoptotic pathways are possible causes of cancer cell resistance. This review highlights the role of DNA methylation of apoptosis-related genes in cancer cell resistance.

RASSF1A Suppresses Cell Migration through Inactivation of HDAC6 and Increase of Acetylated α-Tubulin

Purpose

The RAS association domain family protein 1 (RASSF1) has been implicated in a tumor-suppressive function through the induction of acetylated α-tubulin and modulation of cell migration. However, the mechanisms of how RASSF1A is associated with acetylation of α-tubulin for controlling cell migration have not yet been elucidated. In this study, we found that RASSF1A regulated cell migration through the regulation of histon deacetylase 6 (HDAC6), which functions as a tubulin deacetylase.

Materials and Methods

The cell migration was assessed using wound-healing and transwell assays. The role of RASSF1A on cell migration was examined by immunofluorescence staining, HDAC activity assay and western blot analysis.

Results

Cell migration was inhibited and cell morphology was changed in RASSF1A-transfected H1299 cells, compared with controls, whereas HDAC6 protein expression was not changed by RASSF1A transfection in these cells. However, RASSF1A inhibited deacetylating activity of HDAC6 protein and induced acetylated α-tubulin expression. Furthermore, acetylated α-tubulin and HDAC6 protein were co-localized in the cytoplasm in RASSF1A-transfected H1299 cells. Conversely, when the endogenous RASSF1A expression in HeLa cells was blocked with RASSF1A siRNA treatment, acetylated α-tubulin was co-localized with HDAC6 protein throughout the whole cells, including the nucleus, compared with scramble siRNA-treated HeLa cells. The restoration of RASSF1A by 5-Aza-dC treatment also induced acetylated α-tubulin through inhibition of HDAC6 activity that finally resulted in suppressing cell migration in H1299 cells. To further confirm the role of HDAC6 in RASSF1A-mediated cell migration, the HDAC6 expression in H1299 cells was suppressed by using HDAC6 siRNA, and cell motility was found to be decreased through enhanced acetylated α-tubulin.

Conclusion

The results of this study suggest that the inactivation of HDAC6 by RASSF1A regulates cell migration through increased acetylated α-tubulin protein.

Loss of RASSF1A expression in colorectal cancer and its association with K-ras status

BACKGROUND

The RAS-association domain family 1 A (RASSF1A) is a classical member of RAS effectors regulating cell proliferation and apoptosis. Loss of RASSF1A expression may shift the balance towards a growth-promoting effect without the necessity of activating K-ras mutations. Its potential association with K-ras mutations in colorectal cancer (CRC) is unclear.

METHODS

RASSF1A expression was examined in normal mucosa, adenoma, and tumor tissues of colon and rectum, respectively. We examined the association of RASSF1A expression, mutations of K-ras, and EGFR status in 76 primary CRCs. The relationship between clinicopathological characteristics and RASSF1A expression was also analyzed.

RESULTS

RASSF1A expression level decreased progressively in normal mucosa, adenoma and, tumor tissues, and the loss of RASSF1A expression occurred more frequently in tumor tissues. Of 76 primary CRCs, loss of RASSF1A expression and/or K-ras mutations were detected in 77% cases. Loss of RASSF1A expression was more frequent in K-ras wild-type than in mutation cases (63% versus 32%, P = 0.011).

CONCLUSIONS

Our study indicates that loss of RASSF1A may be involved in pathogenesis of CRC, its expression was found predominantly in K-ras wild-type CRCs, suggesting that it may be another way of affecting RAS signaling, in addition to K-ras mutations.

Epigenetic regulation and role of metastasis suppressor genes in pancreatic ductal adenocarcinoma

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is distinguished by rapid dissemination. Thus, genetic and/or epigenetic deregulation of metastasis suppressor genes (MSG) is a likely event during early pancreatic carcinogenesis and a potential diagnostic marker for the disease. We investigated 9 known MSGs for their role in the dissemination of PDAC and examined their promoters for methylation and its use in PDAC detection.

METHODS

MRNA expression of 9 MSGs was determined in 18 PDAC cell lines by quantitative RT-PCR and promoter methylation was analyzed by Methylation Specific PCR and validated by Bisulfite Sequencing PCR. These data were compared to the cell lines' in vivo metastatic and invasive potential that had been previously established. Statistical analysis was performed with SPSS 20 using 2-tailed Spearman's correlation with P < 0.05 being considered significant.

RESULTS

Complete downregulation of MSG-mRNA expression in PDAC cell lines vs. normal pancreatic RNA occurred in only 1 of 9 investigated genes. 3 MSGs (CDH1, TIMP3 and KiSS-1) were significantly methylated. Methylation only correlated to loss of mRNA expression in CDH1 (P < 0.05). Bisulfite Sequencing PCR showed distinct methylation patterns, termed constant and variable methylation, which could distinguish methylation-regulated from non methylation-regulated genes. Higher MSG mRNA-expression did not correlate to less aggressive PDAC-phenotypes (P > 0.14).

CONCLUSIONS

Genes with metastasis suppressing functions in other tumor entities did not show evidence of assuming the same role in PDAC. Inactivation of MSGs by promoter methylation was an infrequent event and unsuitable as a diagnostic marker of PDAC. A distinct methylation pattern was identified, that resulted in reduced mRNA expression in all cases. Thus, constant methylation patterns could predict regulatory significance of a promoter's methylation prior to expression analysis and hence present an additional tool during target gene selection.

Comparative analysis of interactions of RASSF1-10

Members of the RASSF family (RASSF1-10) have been identified as candidate tumour suppressors that are frequently downregulated by promoter hypermethylation in cancers. These proteins carry a common Ras-association (RA) and SARAH domain (RASSF1-6) that can potentially bind Ras oncoproteins and mediate protein-protein interactions with other SARAH domain proteins. However, there is a notable lack of comparative characterisation of the RASSF family, as well as molecular and structural information that facilitate their tumour suppressive functions. As part of our comparative analysis, we modelled the RA and SARAH domains of the RASSF members based on existing structures and predicted their potential interactions. These in silico predictions were compared to in vitro interaction studies with Ras and MST kinase (a SARAH domain-containing protein). Our data shows a diversity of interaction within the RASSF family RA domain, whereas the SARAH domain-mediated interactions for RASSF1-6 are consistent with the predictions. This suggests that different members, despite shared general architecture, could have distinct functional properties. Additionally, we identify a new interacting partner for MST kinase in the form of RASSF7. Current data supports an interaction model where RASSF serves as an adaptor for the assembly of multiple protein complexes and further functional interactions, involving MST kinases and other SARAH domain proteins, which could be regulated by Ras.

RASSF1A-mediated regulation of AREG via the Hippo pathway in hepatocellular carcinoma

Ras association domain family 1 isoform A (RASSF1A) is a tumor suppressor that is methylated in many human cancers, including hepatocellular carcinoma (HCC). RASSF1A has been shown to suppress tumors via activation of the Hippo tumor suppressor pathway, including mammalian STE20-like kinase (MST). Amphiregulin (AREG), a target gene for Yes-associated protein (YAP), is a known oncogenic component of the Hippo pathway; however, the tumor-suppressive effect of RASSF1A on AREG in regard to regulation of the Hippo pathway remains unclear in HCC. Overexpression of RASSF1A in HCC cells, which lack functional RASSF1A, significantly inhibited cell proliferation and induced apoptosis by activating the Hippo pathway. Consequently, overexpression of RASSF1A inhibited the oncogenic functions of YAP, leading to a significant reduction in AREG secretion via regulation of the Hippo pathway. In human specimens, greater expression of RASSF1A was observed in chronic hepatitis/cirrhosis than in HCC, whereas expression of YAP and AREG was higher in 81% and 86% of HCC than in corresponding chronic hepatitis/cirrhosis, respectively. Furthermore, RASSF1A protein gradually decreased as multistep hepatocarcinogenesis progressed from chronic hepatitis/cirrhosis dysplastic nodules toward HCC, whereas the protein expression of YAP and AREG gradually increased. These findings provide mechanistic insight into the regulation of YAP and AREG by RASSF1A in human multistep hepatocarcinogenesis.

MicroRNAs in malignant melanoma

Melanoma is the most aggressive form of skin cancer, and the incidence of melanoma has been increasing faster than that of most other cancers. While the survival rate following surgical resection of early-stage primary tumors is nearly 100%, the survival of patients with metastasized tumors is strongly reduced, likely due to resistance to conventional therapies. Therefore, it is important to use new molecular approaches to develop new biomarkers to better prevent and diagnose melanoma. MicroRNAs (miRNAs) are short non-coding RNAs that post-transcriptionally regulate gene expression via repression of translation or direct degradation of their complementary mRNA. In this review, we summarize our current understanding of the involvement of miRNAs and their corresponding targets in melanomagenesis as well as the potential use of miRNAs as biomarkers.

Aberrant promoter methylation of the RASSF1A and APC genes in epithelial ovarian carcinoma development

PURPOSE

Tumor suppressor gene (TSG) silencing through promoter hypermethylation plays an important role in cancer development. The aim of this study was to assess the extent of methylation of the RASSF1A and APC TSG promoters in ovarian epithelial adenomas, low malignant potential tumours and carcinomas in order to reveal a role for epigenetic TSG silencing in the development of these ovarian malignancies.

METHOD

The promoter methylation status of the RASSF1A and APC genes was assessed in 19 benign cystadenomas, 14 low malignant potential (LMP) tumours, and 86 carcinomas using methylation specific PCR (MSP).

RESULTS

The methylation frequencies of the RASSF1A and APC gene promoters in benign cystadenomas were found to be 37 % and 16 %, respectively. The LMP tumours exhibited RASSF1A and APC gene promoter methylation frequencies of 50 % and 28 %, respectively, whereas the carcinomas exhibited methylation frequencies of 58 % and 29 %, respectively. Methylation of either the RASSF1A or the APC gene promoter was encountered in 58 % of the invasive carcinomas.

CONCLUSION

The observed aberrant methylation frequencies of the RASSF1A and APC gene promoters indicate that an accumulation of epigenetic events at these specific TSG promoters may be associated with the malignant transformation of benign cystadenomas and LMP tumours to carcinomas.

Epigenetic and epigenomic mechanisms shape sarcoma and other mesenchymal tumor pathogenesis

Sarcomas comprise a large number of rare, histogenetically heterogeneous, mesenchymal tumors. Cancers such as Ewing's sarcoma, liposarcoma, rhabdomyosarcoma and synovial sarcoma can be generated by the transduction of mesenchymal stem cell progenitors with sarcoma-pathognomonic oncogenic fusions, a neoplastic transformation process accompanied by profound locus-specific and pangenomic epigenetic alterations. The epigenetic activities of histone-modifying and chromatin-remodeling enzymes such as SUV39H1/KMT1A, EZH2/KMT6A and BMI1 are central to epigenetic-regulated transformation, a property we coin oncoepigenic. Sarcoma-specific oncoepigenic aberrations modulate critical signaling pathways that control cell growth and differentiation including several miRNAs, Wnt, PI3K/AKT, Sav-RASSF1-Hpo and regulators of the G1 and G2/M checkpoints of the cell cycle. Herein an overview of the current knowledge of this rapidly evolving field that will undoubtedly uncover additional oncoepigenic mechanisms and yield druggable targets in the near future is discussed.

Silencing of tumor suppressor genes RASSF1A, SLIT2, and WIF1 by promoter hypermethylation in hereditary breast cancer

Promoter hypermethylation is gaining strength as one of the main mechanisms through which tumor suppressor genes are silenced during tumor progression. Three tumor suppressor genes are frequently found methylated in their promoter, in concordance with absence of expression, RASSF1A, SLIT2, and WIF1. In addition, a previous array-CGH analysis from our group showed that these genes are found in deleted genomic regions observed in hereditary breast cancer tumors. In the present work we analyzed the methylation status of these three tumor suppressor gene promoters in 47 hereditary breast cancer tumors. Promoter methylation status analysis of hereditary breast tumors revealed high methylation frequencies for the three genes (67% RASSF1A, 80% SLIT2, and 72% WIF1). Additionally, the presence of methylated PCR products was associated with absence of protein expression for the three genes and statistically significant for RASSF1A and WIF1. Interestingly, methylation of all the three genes was found in 4 out of 6 grade I invasive ductal carcinoma tumors. Association between RASSF1A methylation and DCIS tumors was found. These results suggest that silencing of these tumor suppressor genes is an early event in hereditary breast cancer, and could be a marker for pre-malignant phenotypes.