Aberrant methylation in the promoter region of cancer-related genes leads to gene transcriptional inactivation and plays an integral role in lung tumorigenesis. Recent studies demonstrated that promoter methylation was detected not only in lung tumors from patients with lung cancer but also in sputum of smokers without the disease, suggesting the potential for aberrant gene promoter methylation in sputum as a predictive marker for lung cancer. In the present study, we investigated promoter methylation of 4 genes frequently detected in lung tumors, including p16, MGMT, RASSF1A and DAPK genes, in sputum samples obtained from 107 individuals, including 34 never-smoking females and 73 mostly smoking males, who had no evidence of lung cancer but who were exposed to smoky coal emission in Xuan Wei County, China, where lung cancer rate is more than 6 times the Chinese national average rate. Forty nine of the individuals showed evidence of chronic bronchitis while the remaining 58 individuals showed no such a symptom. Promoter methylation of p16, MGMT, RASSF1A and DAPK was detected in 51.4% (55/107), 17.8% (19/107), 29.9% (32/107), and 15.9% (17/107) of the sputum samples from these individuals, respectively. There were no differences in promoter methylation frequencies of any of these genes according to smoking status or gender of the subjects or between individuals with chronic bronchitis and those without evidence of such a symptom. Therefore, individuals exposed to smoky coal emissions in this region harbored in their sputum frequent promoter methylation of these genes that have been previously found in lung tumors and implicated in lung cancer development.
Smoky coal emissions; Gene promoter methylation; Lung cancer
We used MethyLight assays to analyze DNA methylation status of 27 genes on 49 paired cancerous and noncancerous tissue samples from non-small cell lung cancer (NSCLC) patients who underwent surgical resection. Seven genes (RARB, BVES, CDKN2A, KCNH5, RASSF1, CDH13, and RUNX) were found to be methylated significantly more frequently in tumor tissues than in noncancerous tissues. Only methylation of CCND2 and APC was frequently detected in both cancerous and noncancerous tissues, supporting the hypothesis that the methylation of these two genes is a preneoplastic change and may be associated with tobacco smoking exposure. Methylation of any one of eight genes (RASSF1, DAPK1, BVES, CDH13, MGMT, KCNH5, RARB, or CDH1) was present in 80% of NSCLC tissues but only in 14% of noncancerous tissues. Detection of methylation of these genes in blood might have utility in monitoring and detecting tumor recurrence in early-stage NSCLC after curative surgical resection.
There is a need for new, noninvasive risk assessment tools for use in lung cancer population screening and prevention programs.
To investigate the technical feasibility of determining DNA methylation in exhaled breath condensate, we applied our previously-developed method for tag-adapted bisulfite genomic DNA sequencing (tBGS) for mapping of DNA methylation, and adapted it to exhaled breath condensate (EBC) from lung cancer cases and non-cancer controls. Promoter methylation patterns were analyzed in DAPK, RASSF1A and PAX5β promoters in EBC samples from 54 individuals, comprised of 37 controls [current- (n = 19), former- (n = 10), and never-smokers (n = 8)] and 17 lung cancer cases [current- (n = 5), former- (n = 11), and never-smokers (n = 1)].
We found: (1) Wide inter-individual variability in methylation density and spatial distribution for DAPK, PAX5β and RASSF1A. (2) Methylation patterns from paired exhaled breath condensate and mouth rinse specimens were completely divergent. (3) For smoking status, the methylation density of RASSF1A was statistically different (p = 0.0285); pair-wise comparisons showed that the former smokers had higher methylation density versus never smokers and current smokers (p = 0.019 and p = 0.031). For DAPK and PAX5β, there was no such significant smoking-related difference. Underlying lung disease did not impact on methylation density for this geneset. (4) In case-control comparisons, CpG at -63 of DAPK promoter and +52 of PAX5β promoter were significantly associated with lung cancer status (p = 0.0042 and 0.0093, respectively). After adjusting for multiple testing, both loci were of borderline significance (padj = 0.054 and 0.031). (5) The DAPK gene had a regional methylation pattern with two blocks (1)~-215~-113 and (2) -84 ~+26); while similar in block 1, there was a significant case-control difference in methylation density in block 2 (p = 0.045); (6)Tumor stage and histology did not impact on the methylation density among the cases. (7) The results of qMSP applied to EBC correlated with the corresponding tBGS sequencing map loci.
Our results show that DNA methylation in exhaled breath condensate is detectable and is likely of lung origin. Suggestive correlations with smoking and lung cancer case-control status depend on individual gene and CpG site examined.
RASSF1A and RASSF1C are two major isoforms encoded by the Ras association domain family 1 (RASSF1) gene through alternative promoter selection and mRNA splicing. RASSF1A is a well established tumor suppressor gene. Unlike RASSF1A, RASSF1C appears to have growth promoting actions in lung cancer. In this article, we report on the identification of novel RASSF1C target genes in non small cell lung cancer (NSCLC).
Over-expression and siRNA techniques were used to alter RASSF1C expression in human lung cancer cells, and Affymetrix-microarray study was conducted using NCI-H1299 cells over-expressing RASSF1C to identify RASSF1C target genes.
The microarray study intriguingly shows that RASSF1C modulates the expression of a number of genes that are involved in cancer development, cell growth and proliferation, cell death, and cell cycle. We have validated the expression of some target genes using qRT-PCR. We demonstrate that RASSF1C over-expression increases, and silencing of RASSF1C decreases, the expression of PIWIL1 gene in NSCLC cells using qRT-PCR, immunostaining, and Western blot analysis. We also show that RASSF1C over-expression induces phosphorylation of ERK1/2 in lung cancer cells, and inhibition of the MEK-ERK1/2 pathway suppresses the expression of PIWIL1 gene expression, suggesting that RASSF1C may exert its activities on some target genes such as PIWIL1 through the activation of the MEK-ERK1/2 pathway. Also, PIWIL1 expression is elevated in lung cancer cell lines compared to normal lung epithelial cells.
Taken together, our findings provide significant data to propose a model for investigating the role of RASSF1C/PIWIL1 proteins in initiation and progression of lung cancer.
RASSF1C; PIWIL1; Gene expression; RASSF1C target genes; ERK1/2
RASSF2 is a recently identified member of a class of novel tumour suppressor genes, all containing a ras association domain. We previously demonstrated that the A isoform of RASSF2, is frequently inactivated by promoter region hypermethylation in colorectal tumours and adenomas, methylation was tumour specific and that expression in methylated tumour lines could be reactivated by treatment with 5-aza-2dc. RASSF2 resides at 20p13, this region has been demonstrated to be frequently lost in human cancers. In this report we investigated methylation status of the RASSF2A promoter CpG island in a series of breast, ovarian and non-small cell lung cancers (NSCLC). RASSF2A was frequently methylated in breast tumour cell lines 65% (13/20) and in primary breast tumours 38% (15/40). RASSF2A gene expression could be switched back on in methylated breast tumour cell lines after treatment with 5-aza-2dC, whilst unmethylated lines showed no difference in level of expression before and after 5-aza-2dC treatment. RASSF2A was also frequently methylated in NSCLC tumours 44% (22/50). Methylation in breast tumours and NSCLC was tumour specific. We did not detect RASSF2A methylation in ovarian tumours (0/17). Furthermore no mutations were found in the coding region of RASSF2A in these ovarian tumours.
RASSF2A suppressed breast tumour cell growth in vitro (through colony formation and soft agar assays) and in vivo. We identified a highly conserved putative bipartite nuclear localisation signal (NLS) between amino acids 151 and 167 in the RASSF2A sequence and demonstrated that endogenous RASSF2A localised to the nucleus. Mutation of the putative nuclear localisation signal abolished the nuclear localisation so RASSF2A became predominantly cytoplasmic. Our data indicates that RASSF2A is frequently methylated in colorectal, breast and NSCLC tumours, furthermore, the methylation is tumour specific. Hence we have identified RASSF2A as a novel methylation marker for multiple malignancies and it has the potential to be developed into a valuable marker for screening several cancers in parallel using promoter hypermethylation profiles.
We also demonstrate that RASSF2 has a functional NLS signal. Furthermore this is the first report demonstrating that RASSF2 suppresses growth of cancer cells in vivo. Hence providing further evidence for its role as a tumour suppressor gene located at 20p13.
While qualitative analysis of methylation has been reviewed, the quantitative analysis of methylation has rarely been studied. We evaluated the methylation status of CDKN2A, RARβ, and RASSF1A promoter regions in non-small cell lung carcinomas (NSCLCs) by using pyrosequencing. Then, we evaluated the association between methylation at the promoter regions of these tumor suppressor genes and the clinicopathological parameters of the NSCLCs.
We collected tumor tissues from a total of 53 patients with NSCLCs and analyzed the methylation level of the CDKN2A, RARβ, and RASSF1A promoter regions by using pyrosequencing. In addition, we investigated the correlation between the hypermethylation of CDKN2A and the loss of p16INK4A immunoexpression.
Hypermethylation of CDKN2A, RARβ, and RASSF1A promoter regions were 16 (30.2%), 22 (41.5%), and 21 tumors (39.6%), respectively. The incidence of hypermethylation at the CDKN2A promoter in the tumors was higher in undifferentiated large cell carcinomas than in other subtypes (p=0.002). Hyperrmethylation of CDKN2A was significantly associated with p16INK4A immunoexpression loss (p=0.045). With regard to the clinicopathological characteristics of NSCLC, certain histopathological subtypes were found to be strongly associated with the loss of p16INK4A immunoexpression (p=0.016). Squamous cell carcinoma and undifferentiated large cell carcinoma showed p16INK4A immunoexpression loss more frequently. The Kaplan-Meier survival curves analysis showed that methylation level and patient survival were barely related to one another.
We quantitatively analyzed the promoter methylation status by using pyrosequencing. We showed a significant correlation between CDKN2A hypermethylation and p16INK4A immunoexpression loss.
DNA Methylation; Genes, p16; RASSF1 Protein, Human; Receptors, Retinoic Acid; Sequence Analysis, DNA; Carcinoma, Non-Small Cell Lung
Large tumor suppressor (LATS) 1 and 2 are tumor suppressor genes implicated in the regulation of the cell cycle. The methylation statuses of the promoter regions of these genes were studied in Japanese lung cancers. The methylation statuses of the promoter regions of LATS1 and LATS2 were investigated by methylation-specific PCR. The findings were compared to clinicopathological features of lung cancer. Methylation-specific PCR showed that the LATS1 promoter region was hypermethylated in 95 out of 119 (79.8%) lung cancers. The methylation status of LATS1 was significantly associated with squamous histology (p=0.0267) and smoking status (never smoker vs. smoker; p=0.0399). LATS1-ummethylated patients harbored more EGFR mutations (p=0.0143). The LATS2 promoter region was hypermethylated in 160 out of 203 (78.8%) lung cancers. However, the methylation status had no association with the clinicopathological characteristics of the lung cancers cases. Both the LATS1 and LATS2 methylation statuses did not correlate with survival of lung cancer patients. Thus, the EGFR methylation status of the LATS genes has limited value in Japanese lung cancers.
hypermethylation; large tumor suppressor gene; lung cancer
Epigenetic silencing of tumor suppressor genes associated with promoter methylation is considered to be a hallmark of oncogenesis. RASSF1A is a candidate tumor suppressor gene which was found to be inactivated in many human cancers. Although we have had a prelimilary cognition about the function of RASSF1A, the exact mechanisms about how RASSF1A functions in human cancers were largely unknown. Moreover, the effect of mutated K-Ras gene on the function of RASSF1A is lacking. The aim of this study was to investigate the expression profile and methylation status of RASSF1A gene, and to explore its concrete mechanisms as a tumor suppressor gene in Nasopharyngeal Carcinoma.
We examined the expression profile and methylation status of RASSF1A in two NPC cell lines, 38 primary nasopharyngeal carcinoma and 14 normal nasopharyngeal epithelia using RT-PCR and methylated specific PCR(MSP) respectively. 5-aza-dC was then added to confirm the correlation between hypermethylation status and inactivation of RASSF1A. The NPC cell line CNE-2 was transfected with exogenous pcDNA3.1(+)/RASSF1A plasmid in the presence or absence of mutated K-Ras by liposome-mediated gene transfer method. Flow cytometry was used to examine the effect of RASSF1A on cell cycle modulation and apoptosis. Meanwhile, trypan blue dye exclusion assays was used to detect the effect of RASSF1A transfection alone and the co-transfection of RASSF1A and K-Ras on cell proliferation.
Promoter methylation of RASSF1A could be detected in 71.05% (27/38) of NPC samples, but not in normal nasopharyngeal epithelia. RASSF1A expression in NPC primary tumors was lower than that in normal nasopharyngeal epithelial (p < 0.01). Expression of RASSF1A was down-regulated in two NPC cell lines. Loss of RASSF1A expression was greatly restored by the methyltransferase inhibitor 5-aza-dC in CNE-2. Ectopic expression of RASSF1A in CNE-2 could increase the percentage of G0/G1 phase cells (p < 0.01), inhibit cell proliferation and induce apoptosis (p < 0.001). Moreover, activated K-Ras could enhance the growth inhibition effect induced by RASSF1A in CNE-2 cells (p < 0.01).
Expression of RASSF1A is down-regulated in NPC due to the hypermethylation of promoter. Exogenous expression of RASSF1A is able to induce growth inhibition effect and apoptosis in tumor cell lines, and this effect could be enhanced by activated K-Ras.
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.
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.
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.
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.
In the present study, we determined the gene hypermethylation profiles of normal tissues adjacent to invasive breast carcinomas and investigated whether these are associated with the gene hypermethylation profiles of the corresponding primary breast tumors.
A quantitative methylation-specific PCR assay was used to analyze the DNA methylation status of 6 genes (DAPK, TWIST, HIN-1, RASSF1A, RARβ2 and APC) in 9 normal breast tissue samples from unaffected women and in 56 paired cancerous and normal tissue samples from breast cancer patients.
Normal tissue adjacent to breast cancer displayed statistically significant differences to unrelated normal breast tissues regarding the aberrant methylation of the RASSF1A (P = 0.03), RARβ2 (P = 0.04) and APC (P = 0.04) genes. Although methylation ratios for all genes in normal tissues from cancer patients were significantly lower than in the cancerous tissue from the same patient (P ≤ 0.01), in general, a clear correlation was observed between methylation ratios measured in both tissue types for all genes tested (P < 0.01). When analyzed as a categorical variable, there was a significant concordance between methylation changes in normal tissues and in the corresponding tumor for all genes tested but RASSF1A. Notably, in 73% of patients, at least one gene with an identical methylation change in cancerous and normal breast tissues was observed.
Histologically normal breast tissues adjacent to breast tumors frequently exhibit methylation changes in multiple genes. These methylation changes may play a role in the earliest stages of the development of breast neoplasia.
Aberrant methylation in gene promoter regions leads to transcriptional inactivation of cancer-related genes and plays an integral role in tumorigenesis. This alteration has been investigated in lung tumors primarily from smokers, whereas only a few studies involved never-smokers. Here, we applied methylation-specific polymerase chain reaction to compare the frequencies of the methylated promoter of p16 and O6-methylguanine-DNA methyltransferase (MGMT) genes in lung tumors from 122 patients with non-small cell lung cancer, including 81 smokers and 41 never-smokers. Overall, promoter methylation was detected in 52.5% (64 of 122) and 30.3% (37 of 122) of the p16 and MGMT genes, respectively. Furthermore, the frequency of promoter methylation was significantly higher among smokers, compared with never-smokers, for both the p16 [odds ratio (OR) = 3.28; 95% confidence interval (CI) = 1.28-8.39; P = .013] and MGMT (OR = 3.93; 95% CI = 1.27-12.21; P = .018) genes. The trend for a higher promoter methylation frequency of these genes was also observed among female smokers compared with female never-smokers. Our results suggest an association between tobacco smoking and an increased incidence of aberrant promoter methylation of the p16 and MGMT genes in non-small cell lung cancer.
Lung tumors; p16; MGMT; promoter methylation; never-smokers
Hypermethylation of promotor CpG islands is a common mechanism that inactivates tumor suppressor genes in cancer. Genes belonging to the RASSF gene family have frequently been reported as epigenetically silenced by promotor methylation in human cancers. Two members of this gene family, RASSF1A and RASSF5A have been reported as methylated in neuroblastoma. Data from our previously performed genome-wide DNA methylation array analysis indicated that other members of the RASSF gene family are targeted by DNA methylation in neuroblastoma.
In the current study, we found that several of the RASSF family genes (RASSF2, RASSF4, RASSF5, RASSF6, RASSF7, and RASSF10) to various degrees were methylated in neuroblastoma cell lines and primary tumors. In addition, several of the RASSF family genes showed low or absent mRNA expression in neuroblastoma cell lines. RASSF5 and RASSF6 were to various degrees methylated in a large portion of neuroblastoma tumors and RASSF7 was heavily methylated in most tumors. Further, CpG methylation sites in the CpG islands of some RASSF family members could be used to significantly discriminate between biological subgroups of neuroblastoma tumors. For example, RASSF5 methylation highly correlated to MYCN amplification and INRG stage M. Furthermore, high methylation of RASSF6 was correlated to unfavorable outcome, 1p deletion and MYCN amplification in our tumor material.
This study shows that several genes belonging to the RASSF gene family are methylated in neuroblastoma. The genes RASSF5, RASSF6 and RASSF7 stand out as the most promising candidate genes for further investigations in neuroblastoma.
The Ras association domain family (RASSF) comprises a group of tumor suppressors that are frequently epigenetically inactivated in various tumor entities and linked to apoptosis, cell cycle control and microtubule stability. In this work, we concentrated on the newly identified putative tumor suppressor RASSF10. Methylation analysis reveals RASSF10 promoter hypermethylation in lung cancer, head and neck (HN) cancer, sarcoma and pancreatic cancer. An increase in RASSF10 methylation from normal tissues, primary tumors to cancer cell lines was observed. Methylation was reversed by 5-aza-2'-deoxycytidine treatment leading to reexpression of RASSF10. We further show that overexpression of RASSF10 suppresses colony formation in cancer cell lines. In addition, RASSF10 is upregulated by cell–cell contact and regulated on promoter level as well as endogenously by forskolin, protein kinase A (PKA) and activator Protein 1 (AP-1), linking RASSF10 to the cAMP signaling pathway. Knockdown of the AP-1 member JunD interfered with contact inhibition induced RASSF10 expression. In summary, we found RASSF10 to be epigenetically inactivated by hypermethylation of its CpG island promoter in lung, HN, sarcoma and pancreatic cancer. Furthermore, our novel findings suggest that tumor suppressor RASSF10 is upregulated by PKA and JunD signaling upon contact inhibition and that RASSF10 suppresses growth of cancer cells.
epigenetics; DNA methylation; RASSF10; tumor suppressor; gene regulation
The Ras association domain family (RASSF) encodes for distinct tumor suppressors and several members are frequently silenced in human cancer. In our study, we analyzed the role of RASSF2, RASSF3, RASSF4, RASSF5A, RASSF5C and RASSF6 and the effectors MST1, MST2 and WW45 in thyroid carcinogenesis.
Frequent methylation of the RASSF2 and RASSF5A CpG island promoters in thyroid tumors was observed. RASSF2 was methylated in 88% of thyroid cancer cell lines and in 63% of primary thyroid carcinomas. RASSF2 methylation was significantly increased in primary thyroid carcinoma compared to normal thyroid, goiter and follicular adenoma (0%, 17% and 0%, respectively; p < 0.05). Patients which were older than 60 years were significantly hypermethylated for RASSF2 in their primary thyroid tumors compared to those younger than 40 years (90% vs. 38%; p < 0.05). RASSF2 promoter hypermethylation correlated with its reduced expression and treatment with a DNA methylation inhibitor reactivated RASSF2 transcription. Over-expression of RASSF2 reduced colony formation of thyroid cancer cells. Functionally our data show that RASSF2 interacts with the proapoptotic kinases MST1 and MST2 and induces apoptosis in thyroid cancer cell lines. Deletion of the MST interaction domain of RASSF2 reduced apoptosis significantly (p < 0.05).
These results suggest that RASSF2 encodes a novel epigenetically inactivated candidate tumor suppressor gene in thyroid carcinogenesis.
Epigenetic inactivation of tumor suppressor genes is a hallmark of cancer development. RASSF1A (Ras Association Domain Family 1 isoform A) tumor suppressor gene is one of the most frequently epigenetically inactivated genes in a wide range of adult and children's cancers and could be a useful molecular marker for cancer diagnosis and prognosis. RASSF1A has been shown to play a role in several biological pathways, including cell cycle control, apoptosis and microtubule dynamics. RASSF2, RASSF4, RASSF5 and RASSF6 are also epigenetically inactivated in cancer but have not been analyzed in as wide a range of malignancies as RASSF1A. Recently four new members of the RASSF family were identified these are termed N-Terminal RASSF genes (RASSF7–RASSF10). Molecular and biological analysis of these newer members has just begun. This review highlights what we currently know in respects to structural, functional and molecular properties of the N-Terminal RASSFs.
N-terminal RASSF; RAS; cancer; epigenetic; tumor suppressor
Promoter methylation of the RASSF1A and RARβ genes has been associated with susceptibility to different types of cancer. In addition, RASSF1A and RARβ methylation plays an important role in the pathogenesis of lung cancer. We investigated the aberrant promoter methylation of RASSF1A and RARβ in lung cancer patients using methylation-specific polymerase chain reaction (MSP). Aberrant promoter methylation of the RASSF1A gene was detected in 45 of 56 (80.36%) cancer patients and aberrant promoter methylation of the RARβ gene was found in 48 of 56 (85.71%) cases; promoter methylation of both genes was found in 42 of 56 (75%) lung cancer cases. None of the 52 samples from controls exhibited DNA methylation in these two target genes. Methylation was significantly associated with the lung cancer cases compared to controls for the RASSF1A gene (adjusted OR=7.50; 95% CI, 3.935–14.296; p<0.001); similar results were obtained for methylation of the RARβ gene (adjusted OR=5.727; 95% CI, 3.348–9.797; p<0.001). In addition, the association remained significant in these two target genes (adjusted OR=8.429; 95% CI, 4.205–16.896; p<0.001). Our results indicated that the high percentage of promoter methylation in the RARβ and RASSF1A genes indicate their important role in the development of lung cancer in the population studied, and that risk of lung cancer for carriers positive for both genes is higher than in single-gene positive carriers, which may serve as a useful marker for prognosis and a target for the treatment of lung cancer.
methylation; Ras association domain family 1 A gene; RARβ gene; lung cancer; methylation-specific polymerase chain reaction
Aberrant promoter hypermethylation is one of the major mechanisms in carcinogenesis and some critical growth regulatory genes have shown commonality in methylation across solid tumors. Twenty-six genes, 14 identified through methylation in colon and breast cancers, were evaluated using primary lung adenocarcinomas (n = 175) from current, former and never smokers. Tumor specificity of methylation was validated through comparison of 14 lung cancer cell lines to normal human bronchial epithelial cells derived from bronchoscopy of 20 cancer-free smokers. Twenty-five genes were methylated in 11–81% of primary tumors. Prevalence for methylation of TNFRSF10C, BHLHB5 and BOLL was significantly higher in adenocarcinomas from never smokers than smokers. The relation between methylation of individual genes was examined using pairwise comparisons. A significant association was seen between 138 (42%) of the possible 325 pairwise comparisons. Most notably, methylation of MMP2, BHLHB4 or p16 was significantly associated with methylation of 16–19 other genes, thus predicting for a widespread methylation phenotype. Kaplan–Meier log-rank test and proportional hazard models identified a significant association between methylation of SULF2 (a pro-growth, -angiogenesis and -migration gene) and better patient survival (hazard ratio = 0.23). These results demonstrate a high degree of commonality for targeted silencing of genes between lung and other solid tumors and suggest that promoter hypermethylation in cancer is a highly co-ordinated event.
Tumor suppressor gene (TSG) RASSF1A and candidate TSG BLU are two tandem head-to-tail genes located at 3p21.3. We hypothesized that there may be a concordance on their gene expression and promoter methylation status. If not, then there may be an insulator located between RASSF1A and BLU genes that provides a barrier activity.
We first identified potential transcriptionally important CpG sites using the methylation-specific oligonucleotide array in relation to mRNA expression of RASSF1A and BLU genes in primary lung tumors. We demonstrated that E2F1 bound to the potential transcriptionally important CpG sites in RASSF1A gene of a normal lung cell line expressing RASSF1A transcripts, whereas loss of E2F1 binding to RASSF1A in A549 cancer cell line was the result of DNA methylation. Both RASSF1A and BLU genes had their own potential transcriptionally important CpG regions. However, there was no correlation of methylation status between RASSF1A and BLU. Using gel shift assay and chromatin immunoprecipitation-PCR (ChIP-PCR), we found that CCCTC-binding factor (CTCF) bound to insulator sequences located between these two genes. Bisulfite sequencing and ChIP-PCR revealed distinct methylation and chromatin boundaries separated by the CTCF binding domains in normal cells, whereas such distinct epigenetic domains were not observed in cancer cells. Note that demethylation reagent and histone deacetylase inhibitor treatments led to CTCF binding and recovery of barrier effect for RASSF1A and BLU genes in cancer cells.
Our study dissects the potential transcriptionally important CpG sites for RASSF1A and BLU genes at the sequence level and demonstrates that CTCF binding to the insulator of BLU gene provides a barrier activity within separate epigenetic domains of the juxtaposed BLU and RASSF1A loci in the 3p21.3 gene cluster region.
EGFR mutations underlie the sensitivity of lung cancers to erlotinib and gefitinib and can occur in any patient with this illness. Here we examine the frequency of EGFR mutations in smokers and men.
We determined the frequency of EGFR mutations and characterized their association with cigarette smoking status and male sex.
We tested 2,142 lung adenocarcinoma specimens for the presence of EGFR exon 19 deletions and L858R. EGFR mutations were found in 15% of tumors from former smokers (181 of 1,218; 95% CI, 13% to 17%), 6% from current smokers (20 of 344; 95% CI, 4% to 9%), and 52% from never smokers (302 of 580; 95% CI, 48% to 56%; P < .001 for ever v never smokers). EGFR mutations in former or current smokers represented 40% of all those detected (201 of 503; 95% CI, 36% to 44%). EGFR mutations were found in 19% (157 of 827; 95% CI, 16% to 22%) of tumors from men and 26% (346 of 1,315; 95% CI, 24% to 29%) of tumors from women (P < .001). EGFR mutations in men represented 31% (157 of 503; 95% CI, 27% to 35%) of all those detected.
A large number of EGFR mutations are found in adenocarcinoma tumor specimens from men and people who smoked cigarettes. If only women who were never smokers were tested, 57% of all EGFR mutations would be missed. Testing for EGFR mutations should be considered for all patients with adenocarcinoma of the lung at diagnosis, regardless of clinical characteristics. This strategy can extend the use of EGFR tyrosine kinase inhibitors to the greatest number individuals with the potential for substantial benefit.
The tumour suppressor gene RASSF1A is known to be frequently silenced by promoter hypermethylation in neuroblastoma tumours. Here we explored the possible prognostic significance of aberrant promoter hypermethylation of RASSF1A in serum DNA samples of patients with neuroblastoma as a surrogate marker for circulating tumour cells. We analysed the methylation status of the RASSF1A gene in matched tumour and pretreatment serum DNA obtained from 68 neuroblastoma patients. Hypermethylation of RASSF1A in tumour samples was found in 64 patients (94%). In contrast, serum methylation of RASSF1A was observed in 17 patients (25%). Serum methylation of RASSF1A was found to be statistically associated with age ⩾12 months at diagnosis (P=0.002), stage 4 (P<0.001) and MYCN amplification (P<0.001). The influence of serum RASSF1A methylation on prognosis was found to be comparable with that of the currently most reliable marker, MYCN amplification on univariate analysis (hazard ratio, 9.2; 95% confidence interval (CI), 2.8–30.1; P<0.001). In multivariate analysis of survival, methylation of RASSF1A in serum had a hazard ratio of 2.4 (95% CI, 0.6–9.2), although this association did not reach statistical significance (P=0.194). These findings show that the methylation status of RASSF1A in the serum of patients with neuroblastoma has the potential to become a prognostic predictor of outcome.
RASSF1A; methylation; serum; DNA; neuroblastoma
The RASSF1A isoform of RASSF1 is frequently inactivated by epigenetic alterations in human cancers, but it remains unclear if and how it acts as a tumor suppressor. RASSF1A overexpression reduces in vitro colony formation and the tumorigenicity of cancer cell lines in vivo. Conversely, RASSF1A knockdown causes multiple mitotic defects that may promote genomic instability. Here, we have used a genetic approach to address the function of RASSF1A as a tumor suppressor in vivo by targeted deletion of Rassf1A in the mouse. Rassf1A null mice were viable and fertile and displayed no pathological abnormalities. Rassf1A null embryonic fibroblasts displayed an increased sensitivity to microtubule depolymerizing agents. No overtly altered cell cycle parameters or aberrations in centrosome number were detected in Rassf1A null fibroblasts. Rassf1A null fibroblasts did not show increased sensitivity to microtubule poisons or DNA-damaging agents and showed no evidence of gross genomic instability, suggesting that cellular responses to genotoxins were unaffected. Rassf1A null mice showed an increased incidence of spontaneous tumorigenesis and decreased survival rate compared with wild-type mice. Irradiated Rassf1A null mice also showed increased tumor susceptibility, particularly to tumors associated with the gastrointestinal tract, compared with wild-type mice. Thus, our results demonstrate that Rassf1A acts as a tumor suppressor gene.
The RASSF1A tumor suppressor gene is epigenetically silenced in a variety of cancers. Here we perform a genome-wide human shRNA screen and find that epigenetic silencing of RASSF1A requires the homeobox protein HOXB3. We show that HOXB3 binds to the DNA methyltransferase DNMT3B gene and increases its expression. DNMT3B, in turn, is recruited to the RASSF1A promoter, resulting in hypermethylation and silencing of RASSF1A expression. DNMT3B recruitment is facilitated through interactions with Polycomb repressor complex 2 and MYC, which is bound to the RASSF1A promoter. Mouse xenograft experiments indicate that the oncogenic activity of HOXB3 is due, at least in part, to epigenetic silencing of RASSF1A. Expression analysis in human lung adenocarcinoma samples reveals that RASSF1A silencing strongly correlates with over-expression of HOXB3 and DNMT3B. Analysis of human cancer cell lines indicates that the RASSF1A epigenetic silencing mechanism described here may be common in diverse cancer types.
Detection of lung cancer at early stages could potentially increase survival rates. One promising approach is the application of suitable lung cancer-specific biomarkers to specimens obtained by non-invasive methods. Thus far, clinically useful biomarkers that have high sensitivity have proven elusive. Certain genes, which are involved in cellular pathways such as signal transduction, apoptosis, cell to cell communication, cell cycles and cytokine signaling are down-regulated in cancers and may be considered as potential tumor suppressor genes. Aberrant promoter hypermethylation is a major mechanism for silencing tumor suppressor genes in many kinds of human cancers. Using quantitative real time PCR, we tested 11 genes (3-OST-2, RASSF1A, DcR1, DcR2, P16, DAPK, APC, ECAD, HCAD, SOCS1, SOCS3) for levels of methylation within their promoter sequences in non-small cell lung cancers (NSCLC), adjacent non-malignant lung tissues, in peripheral blood mononuclear cells (PBMC) from cancer free patients, in sputum of cancer patients and controls. Of all the 11 genes tested 3-OST-2 showed the highest levels of promoter methylation in tumors combined with lowest levels of promoter methylation in control tissues. 3-OST-2 followed by, RASSF1A showed increased levels of methylation with advanced tumor stage (P<0.05). Thus, quantitative analysis of 3-OST-2 and RASSF1A methylation appears to be a promising biomarker assay for NSCLC and should be further explored in a clinical study. Our preliminary data on the analysis of sputum DNA specimens from cancer patients further support these observations.
Real time PCR; Tumor suppressor gene; Non-small cell lung cancer
The association between promoter methylation status and survival was investigated in a large cohort of women with breast cancer, participants in the Long Island Breast Cancer Study Project. Archived tumor tissues (n=839) were collected from women diagnosed with a first primary invasive or in situ breast cancer in 1996-1997. Vital status was followed through the end of 2005 with a mean follow up time of 8 years. Promoter methylation of 8 breast cancer-related genes was assessed by MethyLight. The frequencies of methylation for HIN1, RASSF1A, DAPK1, GSTP1, CyclinD2, TWIST, CDH1 and RARβ were 62.9%, 85.2%, 14.1%, 27.8%, 19.6%, 15.3%, 5.8% and 27.6%, respectively. Since survival rates of in situ and invasive breast cancers are substantially different, survival analyses were conducted within 670 invasive cases with complete data on all genes. Age-adjusted Cox-proportional hazards models revealed that GSTP1, TWIST and RARβ methylation was significantly associated with higher breast cancer-specific mortality. Methylation of GSTP1 and RARβ were significantly associated with higher all-cause mortality. To investigate the relationship between the number of methylated genes and breast cancer-specific mortality, we included previously published MethyLight data on p16 and APC methylation status. Breast cancer-specific mortality increased in a dose-dependent manner with increasing number of methylated genes (Ptrend = 0.002), although confidence intervals were wide. Our results suggest that promoter methylation, particularly for a panel of genes, has the potential to be used as a biomarker for predicting prognosis in breast cancer.
Promoter methylation; Tumor suppressor gene; Breast cancer; Mortality
Gene silencing through promoter hypermethylation is a growing concept in the development of human cancers. In this study, we examined the contribution of aberrant methylation of promoter regions in methylation-prone tumor suppressors to the pathogenesis of vulvar cancer. Thirteen cell lines from 12 patients with squamous cell carcinoma of the vulva (SCV) were evaluated for aberrant methylation status and gene copy number alterations, concomitantly, using the methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) assay. Of the 22 tumor suppressor genes examined, aberrant methylation was observed for 9 genes: TP73, FHIT, VHL, APC, ESR1, CDKN2B, DAPK1, GSTP1 andI GSF4. The most frequently methylated genes included TP73 in 9 of 13 cell lines, and IGSF4, DAPK1 and FHIT in 3 of 13 cell lines. Methylation specific polymerase chain reaction (MSP) was performed for TP73 and FHIT to confirm aberrant methylation by MS-MLPA. In the context of gene copy number and methylation status, both copies of the TP73 gene were hypermethylated. Loss or decreased mRNA expression of TP73 and IGSF4 by RT-PCR confirmed aberrant methylation. Frequent genetic alterations of loss and gain ofgene copy number included gain of GSTP1 and MEN1, and loss of MFHAS1 and IGSF4 in over 50% of the SCV cell lines. These findings underscore the contribution of both genetic and epigenetic events to the underlying pathogenesis of squamous cell carcinoma of the vulva.
Squamous cell carcinoma of vulva (SCV); Epigenetics; Promoter hypermethylation; Methylation; specific Multiplex Ligation; dependent Probe Amplification (MS-MLPA) assay