The Ras effectors NORE1A and RASSF1A are frequently inactivated in pheochromocytoma and abdominal paraganglioma

Genetic and epigenetic differences of benign and malignant pheochromocytomas and paragangliomas (PPGLs)

Pheochromocytomas and paragangliomas (PPGLs) are tumors arising from the adrenal medulla and sympathetic/parasympathetic paraganglia, respectively. According to Th e Cancer Genome Atlas (TCGA), approximately 40% of PPGLs are due to germ line mutations in one of 16 susceptibility genes, and a further 30% are due to somatic alterations in at least seven main genes (VHL, EPAS1, CSDE1, MAX, HRAS, NF1, RET, and possibly KIF1B). Th e diagnosis of malignant PPGL was straight forward in most cases as it was defined as presence of PPGL in non-chromaffin tissues. Accordingly, there is an extreme need for new diagnostic marker(s) to identify tumors with malignant prospective. Th e aim of this study was to review all suggested genetic and epigenetic alterations that are remarkably different between benign and malignant PPGLs. It seems that more than two genetic mutation clusters in PPGLs and other genetic and methylation biomarkers could be targeted for malignancy discrimination in different studies.

Epigenetics of pheochromocytoma and paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) are neuroendocrine tumors arising in the medullae of the adrenal glands or in paraganglia. The knowledge of the tumor biology of these lesions has increased dramatically during the past two decades and more than a dozen recurrently mutated genes have been identified. Different clusters have been described that share epigenetic signatures. Mutations in the succinate dehydrogenase complex subunit genes play a pivotal role in reprogramming the epigenetic state of these tumors by inhibiting epigenetic regulators such as TET enzymes and histone demethylases. Another subgroup of tumors carries hypomethylated genomes, and overexpression of several micro-RNAs has been described. While much remains to be investigated regarding the epigenetics of PPGLs, it is clear that it plays an important role in PPGL biology.

Global DNA Methylation Analysis Identifies Two Discrete clusters of Pheochromocytoma with Distinct Genomic and Genetic Alterations

Pheochromocytomas and paragangliomas (PPGLs) are rare and frequently heritable neural-crest derived tumours arising from the adrenal medulla or extra-adrenal chromaffin cells respectively. The majority of PPGL tumours are benign and do not recur with distant metastases. However, a sizeable fraction of these tumours secrete vasoactive catecholamines into the circulation causing a variety of symptoms including hypertension, palpitations and diaphoresis. The genetic landscape of PPGL has been well characterized and more than a dozen genes have been described as recurrently mutated. Recent studies of DNA-methylation have revealed distinct clusters of PPGL that share DNA methylation patterns and driver mutations, as well as identified potential biomarkers for malignancy. However, these findings have not been adequately validated in independent cohorts. In this study we use an array-based genome-wide approach to study the methylome of 39 PPGL and 4 normal adrenal medullae. We identified two distinct clusters of tumours characterized by different methylation patterns and different driver mutations. Moreover, we identify genes that are differentially methylated between tumour subcategories, and between tumours and normal tissue.

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

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

Promoter methylation status of Ras-association domain family members in pheochromocytoma

Pheochromocytomas (PCCs) are rare neuroendocrine tumors that arise from the medulla of the adrenal gland or the sympathetic ganglia and are characterized by the secretion of catecholamines. In 30-40% of patients, PCCs are genetically determined by susceptibility genes as various as RET, VHL, and NF1. We have analyzed the Ras-association domain family members (RASSFs) in PCCs regarding their inactivating promoter hypermethylation status. Previously, we reported a promoter methylation in PCC for the first family member RASSF1A. Promoter hypermethylation of CpG islands leads to the silencing of the according transcript and is a common mechanism for inactivation of tumor suppressors. In this study, we observed inactivating DNA modifications for the RASSF members RASSF2, RASSF5A, RASSF9, and RASSF10, but not for the members RASSF3, RASSF4, RASSF5C, RASSF6, RASSF7, and RASSF8. The degree of promoter methylation was 19% for RASSF2, 67% for RASSF5A, 18% for RASSF9, and 74% for RASSF10. Interestingly, the degree of hypermethylation for RASSF10 in hereditary PCCs was 89 vs. 60% in sporadic PCCs. A similar but less dramatic effect was observed in RASSF5A and RASSF9. Including all RASSF members, we found that of 25 PCCs, 92% show promoter methylation in at least in one RASSF member. In 75% of the hereditary PCC samples, we found two or more methylated RASSF promoters, whereas in sporadic PCCs only 46% were observed. In summary, we could show that in PCC several RASSF members are strongly hypermethylated in their promoter regions and methylation of more than one RASSF member occurs in the majority of PCCs. This adds the inactivation of genes of the RASSF tumor suppressor family to the already known deregulated genes of PCC.

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

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

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

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

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

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

Epigenetic silencing of RASSF1A deregulates cytoskeleton and promotes malignant behavior of adrenocortical carcinoma

Background

Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with high mutational heterogeneity and a generally poor clinical outcome. Despite implicated roles of deregulated TP53, IGF-2 and Wnt signaling pathways, a clear genetic association or unique mutational link to the disease is still missing. Recent studies suggest a crucial role for epigenetic modifications in the genesis and/or progression of ACC. This study specifically evaluates the potential role of epigenetic silencing of RASSF1A, the most commonly silenced tumor suppressor gene, in adrenocortical malignancy.

Results

Using adrenocortical tumor and normal tissue specimens, we show a significant reduction in expression of RASSF1A mRNA and protein in ACC. Methylation-sensitive and -dependent restriction enzyme based PCR assays revealed significant DNA hypermethylation of the RASSF1A promoter, suggesting an epigenetic mechanism for RASSF1A silencing in ACC. Conversely, the RASSF1A promoter methylation profile in benign adrenocortical adenomas (ACAs) was found to be very similar to that found in normal adrenal cortex. Enforced expression of ectopic RASSF1A in the SW-13 ACC cell line reduced the overall malignant behavior of the cells, which included impairment of invasion through the basement membrane, cell motility, and solitary cell survival and growth. On the other hand, expression of RASSF1A/A133S, a loss-of-function mutant form of RASSF1A, failed to elicit similar malignancy-suppressing responses in ACC cells. Moreover, association of RASSF1A with the cytoskeleton in RASSF1A-expressing ACC cells and normal adrenal cortex suggests a role for RASSF1A in modulating microtubule dynamics in the adrenal cortex, and thereby potentially blocking malignant progression.

Conclusions

Downregulation of RASSF1A via promoter hypermethylation may play a role in the malignant progression of adrenocortical carcinoma possibly by abrogating differentiation-promoting RASSF1A- microtubule interactions.

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.

Acquired hypermethylation of the P16INK4A promoter in abdominal paraganglioma: relation to adverse tumor phenotype and predisposing mutation

Recurrent alterations in promoter methylation of tumor suppressor genes (TSGs) and LINE1 (L1RE1) repeat elements were previously reported in pheochromocytoma and abdominal paraganglioma. This study was undertaken to explore CpG methylation abnormalities in an extended tumor panel and assess possible relationships between metastatic disease and mutation status. CpG methylation was quantified by bisulfite pyrosequencing for selected TSG promoters and LINE1 repeats. Methylation indices above normal reference were observed for DCR2 (TNFRSF10D), CDH1, P16 (CDKN2A), RARB, and RASSF1A. Z-scores for overall TSG, and individual TSG methylation levels, but not LINE1, were significantly correlated with metastatic disease, paraganglioma, disease predisposition, or outcome. Most strikingly, P16 hypermethylation was strongly associated with SDHB mutation as opposed to RET/MEN2, VHL/VHL, or NF1-related disease. Parallel analyses of constitutional, tumor, and metastasis DNA implicate an order of events where constitutional SDHB mutations are followed by TSG hypermethylation and 1p loss in primary tumors, later transferred to metastatic tissue. In the combined material, P16 hypermethylation was prevalent in SDHB-mutated samples and was associated with short disease-related survival. The findings verify the previously reported importance of P16 and other TSG hypermethylation in an independent tumor series. Furthermore, a constitutional SDHB mutation is proposed to predispose for an epigenetic tumor phenotype occurring before the emanation of clinically recognized malignancy.

Impact of DNA methylation on trophoblast function

The influence of epigenetics is evident in many fields of medicine today. This is also true in placentology, where versatile epigenetic mechanisms that regulate expression of genes have shown to have important influence on trophoblast implantation and placentation. Such gene regulation can be established in different ways and on different molecular levels, the most common being the DNA methylation. DNA methylation has been shown today as an important predictive component in assessing clinical prognosis of certain malignant tumors; in addition, it opens up new possibilities for non-invasive prenatal diagnosis utilizing cell-free fetal DNA methods. By using a well known demethylating agent 5-azacytidine in pregnant rat model, we have been able to change gene expression and, consequently, the processes of trophoblast differentiation and placental development. In this review, we describe how changes in gene methylation effect trophoblast development and placentation and offer our perspective on use of trophoblast epigenetic research for better understanding of not only placenta development but cancer cell growth and invasion as well.

Methylation-associated down-regulation of RASSF1A and up-regulation of RASSF1C in pancreatic endocrine tumors

Background

RASSF1A gene silencing by DNA methylation has been suggested as a major event in pancreatic endocrine tumor (PET) but RASSF1A expression has never been studied. The RASSF1 locus contains two CpG islands (A and C) and generates seven transcripts (RASSF1A-RASSF1G) by differential promoter usage and alternative splicing.

Methods

We studied 20 primary PETs, their matched normal pancreas and three PET cell lines for the (i) methylation status of the RASSF1 CpG islands using methylation-specific PCR and pyrosequencing and (ii) expression of RASSF1 isoforms by quantitative RT-PCR in 13 cases. CpG island A methylation was evaluated by methylation-specific PCR (MSP) and by quantitative methylation-specific PCR (qMSP); pyrosequencing was applied to quantify the methylation of 51 CpGs also encompassing those explored by MSP and qMSP approaches.

Results

MSP detected methylation in 16/20 (80%) PETs and 13/20 (65%) normal pancreas. At qMSP, 11/20 PETs (55%) and 9/20 (45%) normals were methylated in at least 20% of RASSF1A alleles.

Pyrosequencing showed variable distribution and levels of methylation within and among samples, with PETs having average methylation higher than normals in 15/20 (75%) cases (P = 0.01). The evaluation of mRNA expression of RASSF1 variants showed that: i) RASSF1A was always expressed in PET and normal tissues, but it was, on average, expressed 6.8 times less in PET (P = 0.003); ii) RASSF1A methylation inversely correlated with its expression; iii) RASSF1 isoforms were rarely found, except for RASSF1B that was always expressed and RASSF1C whose expression was 11.4 times higher in PET than in normal tissue (P = 0.001). A correlation between RASSF1A expression and gene methylation was found in two of the three PET cell lines, which also showed a significant increase in RASSF1A expression upon demethylating treatment.

Conclusions

RASSF1A gene methylation in PET is higher than normal pancreas in no more than 75% of cases and as such it cannot be considered a marker for this neoplasm. RASSF1A is always expressed in PET and normal pancreas and its levels are inversely correlated with gene methylation. Isoform RASSF1C is overexpressed in PET and the recent demonstration of its involvement in the regulation of the Wnt pathway points to a potential pathogenetic role in tumor development.

Integrative epigenomic and genomic analysis of malignant pheochromocytoma

Epigenomic and genomic changes affect gene expression and contribute to tumor development. The histone modifications trimethylated histone H3 lysine 4 (H3K4me3) and lysine 27 (H3K27me3) are epigenetic regulators associated to active and silenced genes, respectively and alterations of these modifications have been observed in cancer. Furthermore, genomic aberrations such as DNA copy number changes are common events in tumors. Pheochromocytoma is a rare endocrine tumor of the adrenal gland that mostly occurs sporadic with unknown epigenetic/genetic cause. The majority of cases are benign. Here we aimed to combine the genome-wide profiling of H3K4me3 and H3K27me3, obtained by the ChIP-chip methodology, and DNA copy number data with global gene expression examination in a malignant pheochromocytoma sample. The integrated analysis of the tumor expression levels, in relation to normal adrenal medulla, indicated that either histone modifications or chromosomal alterations, or both, have great impact on the expression of a substantial fraction of the genes in the investigated sample. Candidate tumor suppressor genes identified with decreased expression, a H3K27me3 mark and/or in regions of deletion were for instance TGIF1, DSC3, TNFRSF10B, RASSF2, HOXA9, PTPRE and CDH11. More genes were found with increased expression, a H3K4me3 mark, and/or in regions of gain. Potential oncogenes detected among those were GNAS, INSM1, DOK5, ETV1, RET, NTRK1, IGF2, and the H3K27 trimethylase gene EZH2. Our approach to associate histone methylations and DNA copy number changes to gene expression revealed apparent impact on global gene transcription, and enabled the identification of candidate tumor genes for further exploration.

Epigenetic inactivation of the NORE1 gene correlates with malignant progression of colorectal tumors

Background

NORE1 (RASSF5) is a newly described member of the RASSF family with Ras effector function. NORE1 expression is frequently inactivated by aberrant promoter hypermethylation in many human cancers, suggesting that NORE1 might be a putative tumor suppressor. However, expression and mutation status of NORE1 and its implication in colorectal tumorigenesis has not been evaluated.

Methods

Expression, mutation, and methylation status of NORE1A and NORE1B in 10 cancer cell lines and 80 primary tumors were characterized by quantitative PCR, SSCP, and bisulfite DNA sequencing analyses. Effect of NORE1A and NORE1B expression on tumor cell growth was evaluated using cell number counting, flow cytometry, and colony formation assays.

Results

Expression of NORE1A and NORE1B transcript was easily detectable in all normal colonic epithelial tissues, but substantially decreased in 7 (70%) and 4 (40%) of 10 cancer cell lines and 31 (38.8%) and 25 (31.3%) of 80 primary carcinoma tissues, respectively. Moreover, 46 (57.6%) and 38 (47.5%) of 80 matched tissue sets exhibited tumor-specific reduction of NORE1A and NORE1B, respectively. Abnormal reduction of NORE1 was more commonly observed in advanced stage and high grade tumors compared to early and low grade tumors. While somatic mutations of the gene were not identified, its expression was re-activated in all low expressor cells after treatment with the demethylating agent 5-aza-dC. Bisulfite DNA sequencing analysis of 31 CpG sites within the promoter region demonstrated that abnormal reduction of NORE1A is tightly associated with promoter CpG sites hypermethylation. Moreover, transient expression and siRNA-mediated knockdown assays revealed that both NORE1A and NORE1B decrease cellular growth and colony forming ability of tumor cells and enhance tumor cell response to apoptotic stress.

Conclusion

Our data indicate that epigenetic inactivation of NORE1 due to aberrant promoter hypermethylation is a frequent event in colorectal tumorigenesis and might be implicated in the malignant progression of colorectal tumors.

Frequent promoter hypermethylation of the APC and RASSF1A tumour suppressors in parathyroid tumours

Background

Parathyroid adenomas constitute the most common entity in primary hyperparathyroidism, and although recent advances have been made regarding the underlying genetic cause of these lesions, very little data on epigenetic alterations in this tumour type exists. In this study, we have determined the levels of promoter methylation regarding the four tumour suppressor genes APC, RASSF1A, p16^INK4A and RAR-β in parathyroid adenomas. In addition, the levels of global methylation were assessed by analyzing LINE-1 repeats.

Methodology/Principal Findings

The sample collection consisted of 55 parathyroid tumours with known HRPT2 and/or MEN1 genotypes. Using Pyrosequencing analysis, we demonstrate APC promoter 1A and RASSF1A promoter hypermethylation in the majority of parathyroid tumours (71% and 98%, respectively). Using TaqMan qRT-PCR, all tumours analyzed displayed lower RASSF1A mRNA expression and higher levels of total APC mRNA than normal parathyroid, the latter of which was largely conferred by augmented APC 1B transcription levels. Hypermethylation of p16^INK4A was demonstrated in a single adenoma, whereas RAR-β hypermethylation was not observed in any sample. Moreover, based on LINE-1 analyses, parathyroid tumours exhibited global methylation levels within the range of non-neoplastic parathyroid tissues.

Conclusions/Significance

The results demonstrate that APC and RASSF1A promoter hypermethylation are common events in parathyroid tumours. While RASSF1A mRNA levels were found downregulated in all tumours investigated, APC gene expression was retained through APC 1B mRNA levels. These findings suggest the involvement of the Ras signaling pathway in parathyroid tumorigenesis. Additionally, in contrast to most other human cancers, parathyroid tumours were not characterized by global hypomethylation, as parathyroid tumours exhibited LINE-1 methylation levels similar to that of normal parathyroid tissues.

Investigating the targets of MIR-15a and MIR-16-1 in patients with chronic lymphocytic leukemia (CLL)

Background

MicroRNAs (miRNAs) are short, noncoding RNAs that regulate the expression of multiple target genes. Deregulation of miRNAs is common in human tumorigenesis. The miRNAs, MIR-15a/16-1, at chromosome band 13q14 are down-regulated in the majority of patients with chronic lymphocytic leukaemia (CLL).

Methodology/Principal Findings

We have measured the expression of MIR-15a/16-1, and 92 computationally-predicted MIR-15a/16-1 target genes in CLL patients and in normal controls. We identified 35 genes that are deregulated in CLL patients, 5 of which appear to be specific targets of the MIR-15a/16-1 cluster. These targets included 2 genes (BAZ2A and RNF41) that were significantly up-regulated (p<0.05) and 3 genes (RASSF5, MKK3 and LRIG1) that were significantly down-regulated (p<0.05) in CLL patients with down-regulated MIR-15a/16-1 expression.

Significance

The genes identified here as being subject to MIR-15a/16-1 regulation could represent direct or indirect targets of these miRNAs. Many of these are good biological candidates for involvement in tumorigenesis and as such, may be important in the aetiology of CLL.

The Ras-association domain family (RASSF) members and their role in human tumourigenesis

Ras proteins play a direct causal role in human cancer with activating mutations in Ras occurring in approximately 30% of tumours. Ras effectors also contribute to cancer, as mutations occur in Ras effectors, notably B-Raf and PI3-K, and drugs blocking elements of these pathways are in clinical development. In 2000, a new Ras effector was identified, RAS-association domain family 1 (RASSF1), and expression of the RASSF1A isoform of this gene is silenced in tumours by methylation of its promoter. Since methylation is reversible and demethylating agents are currently being used in clinical trials, detection of RASSF1A silencing by promoter hypermethylation has potential clinical uses in cancer diagnosis, prognosis and treatment. RASSF1A belongs to a new family of RAS effectors, of which there are currently 8 members (RASSF1-8). RASSF1-6 each contain a variable N-terminal segment followed by a Ras-association (RA) domain of the Ral-GDS/AF6 type, and a specialised coiled-coil structure known as a SARAH domain extending to the C-terminus. RASSF7-8 contain an N-terminal RA domain and a variable C-terminus. Members of the RASSF family are thought to function as tumour suppressors by regulating the cell cycle and apoptosis. This review will summarise our current knowledge of each member of the RASSF family and in particular what role they play in tumourigenesis, with a special focus on RASSF1A, whose promoter methylation is one of the most frequent alterations found in human tumours.