Impact of Hyperhomocysteinemia on Breast Cancer Initiation and Progression: Epigenetic Perspective

Our recent study showing association of hyperhomocysteinemia and hypomethioninemia in breast cancer and other studies indicating association of hyperhomocysteinemia with metastasis and development of drug resistance in breast cancer cells treated with homocysteine lead us to hypothesize that homocysteine might modulate the expression of certain tumor suppressors, i.e., RASSF1, RARβ1, CNND1, BRCA1, and p21, and might influence prognostic markers such as BNIP3 by inducing epigenetic alteration. To demonstrate this hypothesis, we have treated MCF-7 and MDA-MB-231 cells with different doses of homocysteine and observed dose-dependent inhibition of BRCA1 and RASSF1, respectively. In breast cancer tissues, we observed the following expression pattern: BNIP3 > BRCA1 > RARβ1 > CCND1 > p21 > RASSF1. Hyperhomocysteinemia was positively associated with BRAC1 hypermethylation both in breast cancer tissue and corresponding peripheral blood. Peripheral blood CpG island methylation of BRCA1 in all types of breast cancer and methylation of RASSF1 in ER/PR-negative breast cancers showed positive correlation with total plasma homocysteine. The methylation of RASSF1 and BRCA1 was associated with breast cancer initiation as well as progression, while BRCA1 methylation was associated with DNA damage. Vitamin B₁₂ showed inverse association with the methylation at both the loci. RFC1 G80A and cSHMT C1420T variants showed positive association with methylation at both the loci. Genetic variants influencing remethylation step were associated positively with BRCA1 methylation and inversely with RASSF1 methylation. GCPII C1561T variant showed inverse association with BRCA1 methylation. We found good correlation of BRAC1 (r = 0.90) and RASSF1 (0.92) methylation pattern between the breast cancer tissue and the corresponding peripheral blood. To conclude, elevated homocysteine influences methionine dependency phenotype of breast cancer cells and is associated with breast cancer progression by epigenetic modulation of RASSF1 and BRCA1 .     

Some molecular-genetic markers, defining the pathogenesis of superficial and invasive bladder cancer

We have investigated deletions of 3p14, 9p21, 9q34, 17p13 (TP53) loci, activating FGFR3 mutations in exon 9 and aberrant methylation of RASSF1, RARbeta, P16, P14, CDH1 genes with the aim of the molecular pathogenesis pathways analysis of bladder cancer. FGFR3 activating mutations and 9p21 deletions were observed significantly more frequent in the group of non-invasive bladder cancer pTa than in minimally-invasive cancers pT1 (p = 0.004 and 0.006 respectively). It was shown that groups of superficial and invasive bladder cancer are significantly differing in the frequency of 17p13 (p = 0.006) and 9q34 (p = 0.04) deletions and in aberrant methylation of the gene P16 (p = 0.02). We have revealed some differing molecular-genetic alterations in groups of superficial and invasive bladder cancers. Therefore we suppose that these two types of bladder cancer might have different pathways of development.     

Thyroid Hormone Receptors Predict Prognosis in BRCA1 Associated Breast Cancer in Opposing Ways

Since BRCA1 associated breast cancers are frequently classified as hormone receptor negative or even triple negative, the application of endocrine therapies is rather limited in these patients. Like hormone receptors that bind to estrogen or progesterone, thyroid hormone receptors (TRs) are members of the nuclear hormone receptor superfamily. TRs might be interesting biomarkers - especially in the absence of classical hormone receptors. The current study aimed to investigate whether TRs may be specifically expressed in BRCA1 associated cancer cases and whether they are of prognostic significance in these patients as compared to sporadic breast cancer cases. This study analyzed TRα and TRβ immunopositivity in BRCA1 associated (n = 38) and sporadic breast cancer (n = 86). Further, TRs were studied in MCF7 (BRCA1 wildtype) and HCC3153 (BRCA1 mutated) cells. TRβ positivity rate was significantly higher in BRCA1 associated as compared to sporadic breast cancers (p = 0.001). The latter observation remained to be significant when cases that had been matched for clinicopathological criteria were compared (p = 0.037). Regarding BRCA1 associated breast cancer cases TRβ positivity turned out to be a positive prognostic factor for five-year (p = 0.007) and overall survival (p = 0.026) while TRα positivity predicted reduced five-year survival (p = 0.030). Activation of TRβ resulted in down-modulation of CTNNB1 while TRα inhibition reduced cell viability in HCC3153. However, only BRCA1 wildtype MCF7 cells were capable of rapidly degrading TRα1 in response to T3 stimulation. Significantly, this study identified TRβ to be up-regulated in BRCA1 associated breast cancer and revealed TRs to be associated with patients’ prognosis. TRs were also found to be expressed in triple negative BRCA1 associated breast cancer. Further studies need to be done in order to evaluate whether TRs may become interesting targets of endocrine therapeutic approaches, especially when tumors are triple-negative.     

RASSF2 methylation is a strong prognostic marker in younger age patients with Ewing sarcoma

Ras-association domain family of genes consist of 10 members (RASSF1-RASSF10), all containing a Ras-association (RA) domain in either the C- or the N-terminus. Several members of this gene family are frequently methylated in common sporadic cancers; however, the role of the RASSF gene family in rare types of cancers, such as bone cancer, has remained largely uninvestigated. In this report, we investigated the methylation status of RASSF1A and RASSF2 in Ewing sarcoma (ES). Quantitative real-time methylation analysis (MethyLight) demonstrated that both genes were frequently methylated in Ewing sarcoma tumors (52.5% and 42.5%, respectively) as well as in ES cell lines and gene expression was upregulated in methylated cell lines after treatment with 5-aza-2′-deoxcytidine. Overexpression of either RASSF1A or RASSF2 reduced colony formation ability of ES cells. RASSF2 methylation correlated with poor overall survival (p = 0.028) and this association was more pronounced in patients under the age of 18 y (p = 0.002). These results suggest that both RASSF1A and RASSF2 are novel epigenetically inactivated tumor suppressor genes in Ewing sarcoma and RASSF2 methylation may have prognostic implications for ES patients.     

Methylation status and protein expression of RASSF1A in breast cancer patients

Recently genetics and epigenetics alterations have been found to be characteristic of malignancy and hence can be used as targets for detection of neoplasia. RAS association domain family protein 1A (RASSF1A) gene hypermethylation has been a subject of interest in recent researches on cancer breast patients. The aim of the present study was to evaluate whether RASSF1A methylation status and RASSF1A protein expression are associated with the major clinico-pathological parameters. One hundred and twenty breast cancer Egyptian patients and 100-control subjects diagnosed with benign lesions of the breast were enrolled in this study. We evaluated RASSF1A methylation status in tissue and serum samples using Methyl specific PCR together with RASSF1A protein expression in tissues by immunohistochemistry. Results were studied in relation to known prognostic clinicopathological features in breast cancer. Frequency of RASSF1A methylation in tissues and serum were 70 and 63.3 % respectively and RASSF1A protein expression showed frequency of 46.7 %. There was an association between RASSF1A methylation in tissues, serum and loss of protein expression in tissues with invasive carcinoma, advanced stage breast cancer, L.N. metastasis, ER/PR and HER2 negativity. RASSF1A methylation in serum showed high degree of concordance with methylation in tissues (Kappa = 0.851, P < 0.001). RASSF1A hypermethylation in tissues and serum and its protein expression may be a valid, reliable and sensitive tool for detection and follow up of breast cancer patients.     

Methylation of the promoter region of the RASSF1A gene, a candidate tumor suppressor, in primary epithelial tumors

Methylation of the promoter CpG-islands of the candidate tumor suppressor gene RASSF1A (3p21.31) was studied in primary tumors of kidney, breast and ovary (172 cases). Methylation-specific PCR (MSP) and methyl-sensitive restriction endonuclease digestion followed by PCR (MSRA) were applied. Statistically significant correlation (P < 10(-6)) was shown for the results of the MSP and MSRA, and the data of bisulfite sequencing reported earlier. The frequency of RASSF1A methylation according to MSP and MSRA was 86% (25/29) and 94% (50/53) in renal cell carcinoma (RCC) and 64% (18/28) and 78% (32/41)--in breast carcinoma (BC) samples, and 59% (17/29) and 73% (33/45) in ovarian epithelial tumors (OET), respectively. The use of several methyl-sensitive restriction enzymes (HpaII, HhaI, Bsh12361, AciI) enhanced the sensitivity of MSRA and allowed to analyze methylation status of 18 CpG-pairs in the RASSF1A CpG-island. Density of methylation of the RASSF1A CpG-island was 72% (644/900) in RCC, 63% (361/576) in BC, and 58% (346/594) in OET samples (18 CpG-pairs multiplied to the number of samples shown methylation were assumed as 100%). The RASSF1A gene methylation was also observed in samples of morphologically normal tissues adjacent to corresponding tumors (11-35%), but it was not detected in blood DNAs of healthy donors (0/15). The RASSF1A methylation frequency did not show significant correlation to tumor stage, grade and metastases (P = 0.3-1.0). The RASSF1A gene methylation was observed more frequently than other investigated aberrations--hemi- and homozygous deletions inside or around this gene. These observations are consistent with the hypothesis that the RASSF1A gene methylation is an early event in the carcinogenesis and one of the dominant ways of its inactivation.     

Promoter hypermethylation of BRCA1 correlates with absence of expression in hereditary breast cancer tumors

Germline mutations in BRCA1 account for a low proportion of hereditary cases in diverse populations. Several efforts have been made to find new genes involved in the inheritance of breast cancer with no success until today. The participation of BRCA1 in the development of breast cancer has been proposed in several studies where hypermethylation of its promoter and a decrease in expression has been reported for sporadic cases and one study on familial cases. To explore the participation of BRCA1 in hereditary carcinogenesis through a different mechanism than the inheritance of germline mutations, we studied the methylation status of its promoter in breast tumors, from patients previously screened for BRCA1/BRCA2 germline mutations. We also determined the presence of the BRCA1 protein in these tumors and correlated both events with tumor grade, hormone receptors and ERBB2 presence. Promoter hypermethylation of the BRCA1 gene was detected in 51% of our biopsies, among which 67% did not express the respective protein. This result leads us to suggest that hypermethylation could be considered as an inactivating mechanism for BRCA1 expression, either as a first or second hit. Moreover, a number of biopsies with absence of expression on BRCA1 showed negative detection of estrogen and progesterone receptors, a similar phenotype to BRCA1 mutated breast tumors.     

RASSF1A Promoter Methylation Levels Positively Correlate with Estrogen Receptor Expression in Breast Cancer Patients

The aim of this study was to investigate the relationship between the promoter methylation in five cancer-associated genes and clinicopathologic features for identification of molecular markers of tumor metastatic potential and hormone therapy response efficiency in breast cancer. The methylation levels in paraffin-embedded tumor tissues, plasma, and blood cells from 151 sporadic breast cancer patients and blood samples of 50 controls were evaluated by quantitative multiplex methylation-specific polymerase chain reaction. DNA methylation of RAS-association domain family member 1 (RASSF1A), estrogen receptor 1 (ESR1), cadherin 1, type 1, E-cadherin (CDH1), TIMP metallopeptidase inhibitor 3 (TIMP3) and spleen tyrosine kinase (SYK) genes was detected in the tumors of 124, 19, 15, 15, and 6 patients with mean levels of 48.45%, 3.81%, 2.36%, 27.55%, and 10.81%, respectively. Plasma samples exhibited methylation in the same genes in 25, 10, 15, 17, and 3 patients with levels of 22.54%, 17.20%, 22.87%, 31.93%, and 27.42%, respectively. Cumulative methylation results confirmed different spectra in tumor and plasma samples. Simultaneous methylation in tumors and plasma were shown in less than 17% of patients. RASSF1A methylation levels in tumor samples statistically differ according to tumor size (P = .029), estrogen receptor (ER) and progesterone receptor (PR) status (P = .000 and P = .004), and immunohistochemical subtype (P = .000). Moreover, the positive correlation was found between RASSF1A methylation levels and percentage of cancer cells expressing ER and PR. The direct relationship between RASSF1A promoter methylation and expression of ER could aid the prognosis of hormonal therapy response.     

Methylation of the RASSF1A gene in human cancers

Loss of genetic material from chromosome 3p21.3 is one of the most common and earliest events in the pathogenesis of lung cancer and many other solid tumors. The chromosomal area 3p21.3 is thought to harbor at least one important tumor suppressor gene, which, despite many years of investigation, has remained elusive. In our previous studies, we have identified and cloned a gene from the common homozygous deletion area at 3p21.3. The gene, named RASSF1A (Ras ASSociation domain Family 1A), has homology to a mammalian Ras effector. The RASSF1A gene is epigenetically inactivated in a large percentage of human lung cancers, in particular small cell carcinomas. A high frequency of methylation of RASSF1A is found also in breast cancers, renal cell carcinomas, ovarian, gastric and bladder cancers, and in neuroblastomas. The RASSF1A gene is a candidate for a tumor suppressor gene in 3p21.3.     

Oncosuppressor methylation: a possible key role in colon metastatic progression

K‐RAS and BRAF gene mutations are mandatory to set anti‐EGFR therapy in metastatic colorectal cancer (mCRC) patients. Due to the relationship of these mutations with tumor epigenotype, we hypothesized the potential role of oncosuppressor methylation of genes involved in K‐RAS/BRAF pathway (CDKN2A, RASSF1A, and RARbeta suppressor genes) in inhibiting EGFR signaling cascade. Primary tumor and synchronous liver metastatic tissues of 75 mCRC patients were characterized for promoter methylation by QMSP and for K‐RAS and BRAF mutations. RARbeta, RASSF1A, and CDKN2A genes were methylated in 82%, 35%, and 26% of primary tumors, respectively. RASSF1A resulted significantly more frequently methylated in liver metastasis than in primary site (P = 0.015), while RARbeta was significantly lower methylated in distant metastasis (P = 1.2 × 10^?6). As regards methylation content, RASSF1A methylation status was significantly higher in liver metastasis with respect to primary tumor (P = 0.000) underlying the role of this gene in liver metastatic progression. In our series K‐RAS and BRAF were mutated in 39% and 4% of cases, respectively. Methylation frequencies seemed to be unrelated to gene mutations; on the other hand, RASSF1A mean content methylation resulted significantly higher in liver than in primary tumor (288.78 vs. 56.23, respectively, P = 0.05) only in K‐RAS wild‐type cases sustaining a specific role of this gene in metastatic site thus supporting its function in strengthening the apoptotic role of K‐RAS. These evidences held the role of oncosuppressor methylation in both colon tumorigenesis and progression and suggested that epigenetic events should be taken into account when biological therapies in mCRC patients have to be set. J. Cell. Physiol. 226: 1934–1939, 2011. © 2010 Wiley‐Liss, Inc.     

痰液脱落细胞中p16 基因和RASSF1A 基因甲基化与周边型非小细胞 肺癌关系的研究

目的:探讨p16基因和RASSF1A基因甲基化与肺癌发生发展的关系和应用于诊断的意义。方法:采用甲基化特异性PCR(Methylation Specific PCR,MSP)检测120例周边型非小细胞肺癌患者癌组织、痰液脱落细胞和120例非肺癌人群的痰液脱落细胞中p16基因和RASSF1A基因甲基化,分析它们与临床特征的关系以及非肺癌人群与肿瘤患者之间的差异。结果:(1)120例周边型非小细胞肺癌组织中,p16基因甲基化率46.7%(56例),RASSF1A基因甲基化率53.3%(64例)。P16和RASSF1A基因甲基化与吸烟程度、肿瘤大小和临床分期正相关(P<0.05)。(2)肺癌痰液脱落细胞中有28例p16基因出现甲基化(23.3%),20例RASSF1A基因出现甲基化(16.7%),其中32例至少存在一个基因的甲基化(26.7%);66例重度吸烟者中只有4例痰液脱落细胞出现p16基因甲基化(6%),4例出现RASSF1A基因甲基化(6%);54例非重度吸烟正常人中仅有2例出现p16基因甲基化(3.7%),RASSF1A基因无甲基化。(3)液基痰细胞病理学检查与痰脱落细胞p16和RASSF1a基因甲基化检测结合起来可有效提高诊断的灵敏度(P<0.05)。结论:烟草可能具有潜在的诱导抑癌基因p16和RASSF1A发生甲基化的作用;p16和RASSF1A基因甲基化可能参与肺癌的生长过程。痰脱落细胞p16和RASSF1a基因甲基化检测结合液基痰细胞病理学诊断,可提高非小细胞肺癌诊断的灵敏度。     

Methylation of the putative tumor suppressor gene, RASSF1A, in primary cervical tumors

The methylation level of 13 CpG-dinucleotides in the promoter region of the putative tumor suppressor gene RASSF1A (3p21.31) was analyzed in HPV-positive squamous cell carcinomas of cervix using methyl-sensitive restriction endonuclease analysis followed by PCR. The methylation from 3 to 13 CpG-dinucleotides was observed in 64% (25/39) tumors, 22% (2/9) morphologically normal tissues adjacent to tumors (P = 0.0306) and in 2 from 3 leucocytes of peripheral blood of patients. The methylation of these CpG-dinucleotides was absent in DNA of healthy donor leucocytes (0/10). Methylation level of the examined fragment of the RASSF1A promoter region was significantly higher in tumors of patients with lymph node metastases in comparison to tumors of patients without metastases (P = 8.5 x 10(-12)). The methylation frequency of RASSF1A gene was in two times higher than hemi- and homozygous deletion frequency at the region of location of this gene (chromosome 3p21.31), determined earlier. These data suggest that methylation of the RASSF1A gene is one of the main ways of this gene inactivation in HPV-positive cervical squamous cell carcinomas. The methylation of the RASSF1A gene is an early event in genesis of tumor and the level of methylation increased with tumor progression.     

Knowledge, attitudes, and utilization of BRCA1/2 testing among women with early-onset breast cancer

A total of 2,400 questionnaires were mailed to members of two mid-Atlantic breast cancer awareness/support groups to investigate the association between attitudes, knowledge, and use of BRCA1/2 testing among women with early-onset breast cancer. Of the 493 (21%) questionnaires returned, 406 respondents had a diagnosis of breast cancer, of whom 248 were diagnosed prior to age 50 and included in the analyses. Eighty-three percent (206/248) of these women had heard of BRCA1/2 testing and 12.5% (31/248) had undergone BRCA1/2 testing. Among women who had heard of BRCA1/2 testing, women who had been tested were younger (p = 0.03), more likely to have a college education (p = 0.03), more likely to have a family member who had undergone BRCA1/2 testing (p = 0.005), and had greater knowledge, more positive attitudes, and fewer negative attitudes about BRCA1/2 testing (p = 0.02, p = 0.004, and p = 0.004, respectively). In this sample, knowledge regarding BRCA1/2 testing is high, but uptake of genetic testing is low. Lack of information regarding how genetic testing might alter health-care decisions and fear about the genetic testing procedure, its costs, and possible false-positive results are associated with low uptake of genetic testing. Further education regarding these specific points may enhance the use of genetic testing.     

Quantification of regional DNA methylation by liquid chromatography/tandem mass spectrometry

Promoter hypermethylation-associated tumor suppressor gene (TSG) silencing has been explored as a therapeutic target for hypomethylating agents. Promoter methylation change may serve as a pharmacodynamic endpoint for evaluation of the efficacy of these agents and predict the patient’s clinical response. Here a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay has been developed for quantitative regional DNA methylation analysis using the molar ratio of 5-methyl-2′-deoxycytidine (5mdC) to 2′-deoxycytidine (2dC) in the enzymatic hydrolysate of fully methylated bisulfite-converted polymerase chain reaction (PCR) amplicons as the methylation indicator. The assay can differentiate 5% of promoter methylation level with an intraday precision ranging from 3 to 16% using two TSGs: HIN-1 and RASSF1A. This method was applied to characterize decitabine-induced promoter DNA methylation changes of these two TSGs in a breast cancer MCF-7 cell line. Promoter methylation of these TSGs was found to decrease in a dose-dependent manner. Correspondingly, the expression of these TSGs was enhanced. The sensitivity and reproducibility of the method make it a valuable tool for specific gene methylation analysis that could aid characterization of hypomethylating activity on specific genes by hypomethylating agents in a clinical setting.     

Methylation of the Tumor Suppressor Gene <Emphasis Type="Italic">RASSF1A</Emphasis> in Human Tumors

Loss of heterozygosity of a segment at 3p21.3 is frequently observed in lung cancer and several other carcinomas. We have identified the Ras-association domain family 1A gene (RASSF1A), which is localized at 3p21.3 in a minimum deletion sequence. De novo methylation of the RASSF1A promoter is one of the most frequent epigenetic inactivation events detected in human cancer and leads to silencing of RASSF1A expression. Hypermethylation of RASSF1A was frequently found in most major types of human tumors including lung, breast, prostate, pancreas, kidney, liver, cervical, thyroid and many other cancers. The detection of RASSF1A methylation in body fluids such as serum, urine, and sputum promises to be a useful marker for early cancer detection. The functional analysis of RASSF1A reveals a potential involvement of this protein in apoptotic signaling, microtubule stabilization, and cell cycle progression.     

The tumor suppressor RASSF1A in human carcinogenesis: an update

Loss of heterozygosity of the small arm of chromosome 3 is one of the most common alterations in human cancer. Most notably, a segment in 3p21.3 is frequently lost in lung cancer and several other carcinomas. We and others have identified a novel Ras effector at this segment, which was termed Ras Association Domain family 1 (RASSF1A) gene. RASSF1 consists of two main variants (RASSF1A and RASSF1C), which are transcribed from distinct CpG island promoters. Aberrant methylation of the RASSF1A promoter region is one of the most frequent epigenetic inactivation events detected in human cancer and leads to silencing of RASSF1A. Hypermethylation of RASSF1A was commonly observed in primary tumors including lung, breast, pancreas, kidney, liver, cervix, nasopharyngeal, prostate, thyroid and other cancers. Moreover, RASSF1A methylation was frequently detected in body fluids including blood, urine, nipple aspirates, sputum and bronchial alveolar lavages. Inactivation of RASSF1A was associated with an advanced tumor stage (e.g. bladder, brain, prostate, gastric tumors) and poor prognosis (e.g. lung, sarcoma and breast cancer). Detection of aberrant RASSF1A methylation may serve as a diagnostic and prognostic marker. The functional analyses of RASSF1A reveal an involvement in apoptotic signaling, microtubule stabilization and mitotic progression. The tumor suppressor RASSF1A may act as a negative Ras effector inhibiting cell growth and inducing cell death. Thus, RASSF1A may represent an epigenetically inactivated bona fide tumor suppressor in human carcinogenesis.