We aimed to determine whether PAX1/SOX1 methylation could be translated to clinical practice for cervical neoplasia detection when used alone and in combination with current cytology-based Pap screening. We conducted a multicenter case–control study in 11 medical centers in Taiwan from December 2009 to November 2010. Six hundred seventy-six patients were included in the analysis, including 330 in the training set and 346 in the testing set. Multiplex quantitative methylation-specific polymerase chain reaction (PCR) was performed with a TaqMan probe system using a LightCycler 480 Real-Time PCR System (Roche). The level of human papilloma virus (HPV) was analyzed using a Hybrid Capture 2 system (Digene). Receiver operating characteristic curves were generated to obtain the best cutoff values from the training data set. The sensitivities, specificities, and accuracies were validated in the testing set. The sensitivities for methylated (m) PAX1m and SOX1m and HPV testing for detecting CIN3+ lesions were 0.64, 0.71, and 0.89, and the specificities were 0.91, 0.77, and 0.68, respectively. Combined parallel testing of PAX1m/SOX1m tests with Pap smearing showed superior specificity (0.84/0.71 vs. 0.66, respectively) and similar sensitivity (0.93/0.96 vs. 0.97) to the combination of Pap smear results and HPV testing. Thus, combined parallel testing using Pap smears and PAX1 or SOX1 methylation tests may provide better performance than a combination of Pap smears with HPV testing in detection for cervical neoplasia.
Cervical cancer screening; DNA methylation; PAX1; SOX1
Spheroid formation is one property of stem cells—such as embryo-derived or neural stem cells—that has been used for the enrichment of cancer stem-like cells (CSLCs). However, it is unclear whether CSLC-derived spheroids are heterogeneous or whether they share common embryonic stemness properties. Understanding these features might lead to novel therapeutic approaches. Ovarian carcinoma is a deadly disease of women. We identified two types of spheroids (SR1 and SR2) from ovarian cancer cell lines and patients' specimens according to their morphology. Both types expressed stemness markers and could self-renew and initiate tumors when a low number of cells were used. Only SR1 could differentiate into multiple-lineage cell types under specific induction conditions. SR1 spheroids could differentiate to SR2 spheroids through epithelial–mesenchymal transition. Alkaline phosphatase (ALP) was highly expressed in SR1 spheroids, decreased in SR2 spheroids, and was absent in differentiated progenies in accordance with the loss of stemness properties. We verified that ALP can be a marker for ovarian CSLCs, and patients with greater ALP expression is related to advanced clinical stages and have a higher risk of recurrence and lower survival rate. The ALP inhibitor, levamisole, disrupted the self-renewal of ovarian CSLCs in vitro and tumor growth in vivo. In summary, this research provides a plastic ovarian cancer stem cell model and a new understanding of the cross-link between stem cells and cancers. This results show that ovarian CSLCs can be suppressed by levamisole. Our findings demonstrated that some ovarian CSLCs may restore ALP activity, and this suggests that inhibition of ALP activity may present a new opportunity for treatment of ovarian cancer.
alkaline phosphatase; cancer stem-like cells; epithelial-mesenchymal transition; epithelial ovarian cancer; levamisole; trans-lineage differentiation
Women with advanced stage ovarian cancer (OC) have a five-year survival rate of less than 25%. OC progression is associated with accumulation of epigenetic alterations and aberrant DNA methylation in gene promoters acts as an inactivating ?hit? during OC initiation and progression. Abnormal DNA methylation in OC has been used to predict disease outcome and therapy response. To globally examine DNA methylation in OC, we used next-generation sequencing technology, MethylCap-sequencing, to screen 75 malignant and 26 normal or benign ovarian tissues. Differential DNA methylation regions (DMRs) were identified, and the Kaplan?Meier method and Cox proportional hazard model were used to correlate methylation with clinical endpoints. Functional role of specific genes identified by MethylCap-sequencing was examined in in vitro assays. We identified 577 DMRs that distinguished (p < 0.001) malignant from non-malignant ovarian tissues; of these, 63 DMRs correlated (p < 0.001) with poor progression free survival (PFS). Concordant hypermethylation and corresponding gene silencing of sonic hedgehog pathway members ZIC1 and ZIC4 in OC tumors was confirmed in a panel of OC cell lines, and ZIC1 and ZIC4 repression correlated with increased proliferation, migration and invasion. ZIC1 promoter hypermethylation correlated (p < 0.01) with poor PFS. In summary, we identified functional DNA methylation biomarkers significantly associated with clinical outcome in OC and suggest our comprehensive methylome analysis has significant translational potential for guiding the design of future clinical investigations targeting the OC epigenome. Methylation of ZIC1, a putative tumor suppressor, may be a novel determinant of OC outcome.
DNA methylation; Hedgehog pathway; ZIC1; ZIC4; ovarian cancer
Resistance to TGF-β is frequently observed in ovarian cancer, and disrupted TGF-β/SMAD4 signaling results in aberrant expression of downstream target genes in the disease. Our previous study showed that ADAM19, a SMAD4 target gene, is down-regulated through epigenetic mechanisms in ovarian cancer with aberrant TGF-β/SMAD4 signaling. In this study, we investigated the mechanism of down-regulation of FBXO32, another SMAD4 target gene, and the clinical significance of loss of FBXO32 expression in ovarian cancer. Expression of FBXO32 was observed in normal ovarian surface epithelium but not in ovarian cancer cell lines. FBXO32 methylation was seen in ovarian cancer cell lines displaying constitutive TGF-β/SMAD4 signaling, and epigenetic drug treatment restored FBXO32 expression in ovarian cancer cell lines regardless of FBXO32 methylation status, suggesting that epigenetic regulation of this gene in ovarian cancer may be a common event. In advanced stage ovarian tumors, significant (29.3%; P<0.05) methylation frequency of FBXO32 was observed and the association between FBXO32 methylation and shorter progression-free survival was significant, as determined by both Kaplan-Meier analysis (P<0.05) and multivariate Cox regression analysis (hazard ratio 1.003, P<0.05). Re-expression of FBXO32 markedly reduced proliferation of a platinum-resistant ovarian cancer line both in vitro and in vivo, due to increased apoptosis of the cells, and resensitized ovarian cancer cells to cisplatin. In conclusion, the novel tumor suppressor FBXO32 is epigenetically silenced in ovarian cancer cell lines with disrupted TGF-β/SMAD4 signaling and FBXO32 methylation status predicts survival in patients with ovarian cancer.
Ovarian cancer; epigenetics; TGF-β; FBXO32
The dysregulation of transforming growth factor-β (TGF-β) signaling plays a crucial role in ovarian carcinogenesis and in maintaining cancer stem cell properties. Classified as a member of the ATP-binding cassette (ABC) family, ABCA1 was previously identified by methylated DNA immunoprecipitation microarray (mDIP-Chip) to be methylated in ovarian cancer cell lines, A2780 and CP70. By microarray, it was also found to be upregulated in immortalized ovarian surface epithelial (IOSE) cells following TGF-β treatment. Thus, we hypothesized that ABCA1 may be involved in ovarian cancer and its initiation.
We first compared the expression level of ABCA1 in IOSE cells and a panel of ovarian cancer cell lines and found that ABCA1 was expressed in HeyC2, SKOV3, MCP3, and MCP2 ovarian cancer cell lines but downregulated in A2780 and CP70 ovarian cancer cell lines. The reduced expression of ABCA1 in A2780 and CP70 cells was associated with promoter hypermethylation, as demonstrated by bisulfite pyro-sequencing. We also found that knockdown of ABCA1 increased the cholesterol level and promoted cell growth in vitro and in vivo. Further analysis of ABCA1 methylation in 76 ovarian cancer patient samples demonstrated that patients with higher ABCA1 methylation are associated with high stage (P = 0.0131) and grade (P = 0.0137). Kaplan-Meier analysis also found that patients with higher levels of methylation of ABCA1 have shorter overall survival (P = 0.019). Furthermore, tissue microarray using 55 ovarian cancer patient samples revealed that patients with a lower level of ABCA1 expression are associated with shorter progress-free survival (P = 0.038).
ABCA1 may be a tumor suppressor and is hypermethylated in a subset of ovarian cancer patients. Hypermethylation of ABCA1 is associated with poor prognosis in these patients.
Electronic supplementary material
The online version of this article (doi:10.1186/s13148-014-0036-2) contains supplementary material, which is available to authorized users.
Ovarian cancer; Epigenetics; ABCA1
Accumulating data indicate that cancer stem cells contribute to tumor chemoresistance and their persistence alters clinical outcome. Our previous study has shown that ovarian cancer may be initiated by ovarian cancer initiating cells (OCIC) characterized by surface antigen CD44 and c-KIT (CD117). It has been experimentally demonstrated that a microRNA, namely miR-193a, targets c-KIT mRNA for degradation and could play a crucial role in ovarian cancer development. How miR-193a is regulated is poorly understood and the emerging picture is complex. To unravel this complexity, we propose a mathematical model to explore how estrogen-mediated up-regulation of another target of miR-193a, namely E2F6, can attenuate the function of miR-193a in two ways, one through a competition of E2F6 and c-KIT transcripts for miR-193a, and second by binding of E2F6 protein, in association with a polycomb complex, to the promoter of miR-193a to down-regulate its transcription. Our model predicts that this bimodal control increases the expression of c-KIT and that the second mode of epigenetic regulation is required to generate a switching behavior in c-KIT and E2F6 expressions. Additional analysis of the TCGA ovarian cancer dataset demonstrates that ovarian cancer patients with low expression of EZH2, a polycomb-group family protein, show positive correlation between E2F6 and c-KIT. We conjecture that a simultaneous EZH2 inhibition and anti-estrogen therapy can constitute an effective combined therapeutic strategy against ovarian cancer.
Epigenetic regulation by promoter methylation plays a key role in tumorigenesis. Our goal was to investigate whether altered DNA methylation signatures associated with oncogenic signaling delineate biomarkers predictive of endometrial cancer recurrence.
Methyl-CpG-capture sequencing was used for global screening of aberrant DNA methylation in our endometrial cancer cohort, followed by validation in an independent The Cancer Genome Atlas (TCGA) cohort. Bioinformatics as well as functional analyses in vitro, using RNA interference (RNAi) knockdown, were performed to examine regulatory mechanisms of candidate gene expression and contribution to aggressive phenotype, such as epithelial–mesenchymal transition (EMT).
We identified 2,302 hypermethylated loci in endometrial tumors compared with control samples. Bone morphogenetic protein (BMP) family genes, including BMP1, 2, 3, 4, and 7, were among the frequently hypermethylated loci. Interestingly, BMP2, 3, 4, and 7 were less methylated in primary tumors with subsequent recurrence and in patients with shorter diseasefree interval compared with nonrecurrent tumors, which was validated and associated with poor survival in the TCGA cohort (BMP4, P = 0.009; BMP7, P = 0.007). Stimulation of endometrial cancer cells with epidermal growth factor (EGF) induced EMT and transcriptional activation of these genes, which was mediated by the epithelial cell adhesion molecule (EpCAM). EGF signaling was implicated in maintaining the promoters of candidate BMP genes in an active chromatin configuration and thus subject to transcriptional activation.
Hypomethylation signatures of candidate BMP genes associated with EpCAM-mediated expression present putative biomarkers predictive of poor survival in endometrial cancer.
DNA methylation; EGF; BMP; epithelial-mesenchymal transition; and endometrial cancer recurrence
CD164 (endolyn), a sialomucin, has been reported to play a role in the proliferation, adhesion, and differentiation of hematopoietic stem cells. The potential association of CD164 with tumorigenicity remains unclear.
The clinicopathological correlation of ovarian cancer with CD164 was assessed in a 97-patient tumor tissue microarray. Overexpression or silence CD164 was to analyze the effect of CD164 on the proliferation, colony formation and apoptosis via a mouse xenograft and western blotting analysis. The subcellular localization of CD164 was collected in the immunohistochemical and confocal analysis.
Our data demonstrated that higher expression levels of CD164 were identified in malignant ovarian cancer cell lines, such as SKOV3 and HeyA8. The clinicopathological correlation analysis showed that the upregulation of CD164 protein was significantly associated with tumor grade and metastasis. The overexpression of CD164 in human ovarian epithelial surface cells promoted cellular proliferation and colony formation and suppressed apoptosis. These tumorigenicity effects of CD164 were reconfirmed in a mouse xenograft model. We also found that the overexpression of CD164 proteins increased the amounts of CXCR4 and SDF-1α and activated the SDF-1α/CXCR4 axis, inducing colony and sphere formation. Finally, we identified the subcellular localization of CD164 in the nucleus and cytosol and found that nuclear CD164 might be involved in the regulation of the activity of the CXCR4 promoter.
Our findings suggest that the increased expression of CD164 is involved in ovarian cancer progression via the SDF-1α/CXCR4 axis, which promotes tumorigenicity. Thus, targeting CD164 may serve as a potential ovarian cancer biomarker, and targeting CD164 may serve as a therapeutic modality in the management of high-grade ovarian tumors.
Ovarian cancer; CD164; CXCR4; SDF-1α; Tumorigenesis
The primary cause of death from breast cancer is the progressive growth of tumors and resistance to conventional therapies. It is currently believed that recurrent cancer is repopulated according to a recently proposed cancer stem cell hypothesis. New therapeutic strategies that specifically target cancer stem-like cells may represent a new avenue of cancer therapy. We aimed to discover novel compounds that target breast cancer stem-like cells. We used a dye-exclusion method to isolate side population (SP) cancer cells and, subsequently, subjected these SP cells to a sphere formation assay to generate SP spheres (SPS) from breast cancer cell lines. Surface markers, stemness genes, and tumorigenicity were used to test stem properties. We performed a high-throughput drug screening using these SPS. The effects of candidate compounds were assessed in vitro and in vivo. We successfully generated breast cancer SPS with stem-like properties. These SPS were enriched for CD44high (2.8-fold) and CD24low (4-fold) cells. OCT4 and ABCG2 were overexpressed in SPS. Moreover, SPS grew tumors at a density of 103, whereas an equivalent number of parental cells did not initiate tumor formation. A clinically approved drug, niclosamide, was identified from the LOPAC chemical library of 1,258 compounds. Niclosamide downregulated stem pathways, inhibited the formation of spheroids, and induced apoptosis in breast cancer SPS. Animal studies also confirmed this therapeutic effect. The results of this proof-of-principle study may facilitate the development of new breast cancer therapies in the near future. The extension of niclosamide clinical trials is warranted.
Advances in whole genome profiling have revolutionized the cancer research field, but at the same time have raised new bioinformatics challenges. For next generation sequencing (NGS), these include data storage, computational costs, sequence processing and alignment, delineating appropriate statistical measures, and data visualization. Currently there is a lack of workflows for efficient analysis of large, MethylCap-seq datasets containing multiple sample groups.
The NGS application MethylCap-seq involves the in vitro capture of methylated DNA and subsequent analysis of enriched fragments by massively parallel sequencing. The workflow we describe performs MethylCap-seq experimental Quality Control (QC), sequence file processing and alignment, differential methylation analysis of multiple biological groups, hierarchical clustering, assessment of genome-wide methylation patterns, and preparation of files for data visualization.
Here, we present a scalable, flexible workflow for MethylCap-seq QC, secondary data analysis, tertiary analysis of multiple experimental groups, and data visualization. We demonstrate the experimental QC procedure with results from a large ovarian cancer study dataset and propose parameters which can identify problematic experiments. Promoter methylation profiling and hierarchical clustering analyses are demonstrated for four groups of acute myeloid leukemia (AML) patients. We propose a Global Methylation Indicator (GMI) function to assess genome-wide changes in methylation patterns between experimental groups. We also show how the workflow facilitates data visualization in a web browser with the application Anno-J.
This workflow and its suite of features will assist biologists in conducting methylation profiling projects and facilitate meaningful biological interpretation.
Epithelial ovarian cancer is characterized by multiple genomic alterations; most are passenger alterations which do not confer tumor growth. Like many cancers, it is a heterogeneous disease and can be broadly categorized into 4 main histotypes of clear cell, endometrioid, mucinous, and serous. To date, histotype-specific copy number alterations have been difficult to elucidate. The difficulty lies in having sufficient sample size in each histotype for statistical analyses.
To dissect the heterogeneity of ovarian cancer and identify histotype-specific alterations, we used an in silico hypothesis-driven approach on multiple datasets of epithelial ovarian cancer.
In concordance with previous studies on global copy number alterations landscape, the study showed similar alterations. However, when the landscape was de-convoluted into histotypes, distinct alterations were observed. We report here significant histotype-specific copy number alterations in ovarian cancer and showed that there is genomic diversity amongst the histotypes. 76 cancer genes were found to be significantly altered with several as potential copy number drivers, including ERBB2 in mucinous, and TPM3 in endometrioid histotypes. ERBB2 was found to have preferential alterations, where it was amplified in mucinous (28.6%) but deleted in serous tumors (15.1%). Validation of ERBB2 expression showed significant correlation with microarray data (p=0.007). There also appeared to be reciprocal relationship between KRAS mutation and copy number alterations. In mucinous tumors where KRAS mutation is common, the gene was not significantly altered. However, KRAS was significantly amplified in serous tumors where mutations are rare in high grade tumors.
The study demonstrates that the copy number landscape is specific to the histotypes and identification of these alterations can pave the way for targeted drug therapy specific to the histotypes.
Ovarian cancer; Histological biomarkers; Genomics; Copy number driver genes; ERBB2
Despite of the trend that the application of DNA methylation as a biomarker for cancer detection is promising, clinically applicable genes are few. Therefore, we looked for novel hypermethylated genes for cervical cancer screening.
Methods and Findings
At the discovery phase, we analyzed the methylation profiles of human cervical carcinomas and normal cervixes by methylated DNA immunoprecipitation coupled to promoter tiling arrays (MeDIP-on-chip). Methylation-specific PCR (MSP), quantitative MSP and bisulfite sequencing were used to verify the methylation status in cancer tissues and cervical scrapings from patients with different severities. Immunohistochemical staining of a cervical tissue microarray was used to confirm protein expression. We narrowed to three candidate genes: DBC1, PDE8B, and ZNF582; their methylation frequencies in tumors were 93%, 29%, and 100%, respectively. At the pre-validation phase, the methylation frequency of DBC1 and ZNF582 in cervical scraping correlated significantly with disease severity in an independent cohort (n = 330, both P<0.001). For the detection of cervical intraepithelial neoplasia 3 (CIN3) and worse, the area under the receiver operating characteristic curve (AUC) of ZNF582 was 0.82 (95% confidence interval = 0.76–0.87).
Our study shows ZNF582 is frequently methylated in CIN3 and worse lesions, and it is demonstrated as a potential biomarker for the molecular screening of cervical cancer.
Aberrant TGFβ signaling pathway may alter the expression of down-stream targets and promotes ovarian carcinogenesis. However, the mechanism of this impairment is not fully understood. Our previous study identified RunX1T1 as a putative SMAD4 target in an immortalized ovarian surface epithelial cell line, IOSE. In this study, we report that transcription of RunX1T1 was confirmed to be positively regulated by SMAD4 in IOSE cells and epigenetically silenced in a panel of ovarian cancer cell lines by promoter hypermethylation and histone methylation at H3 lysine 9. SMAD4 depletion increased repressive histone modifications of RunX1T1 promoter without affecting promoter methylation in IOSE cells. Epigenetic treatment can restore RunX1T1 expression by reversing its epigenetic status in MCP 3 ovarian cancer cells. When transiently treated with a demethylating agent, the expression of RunX1T1 was partially restored in MCP 3 cells, but gradual re-silencing through promoter re-methylation was observed after the treatment. Interestingly, SMAD4 knockdown accelerated this re-silencing process, suggesting that normal TGFβ signaling is essential for the maintenance of RunX1T1 expression. In vivo analysis confirmed that hypermethylation of RunX1T1 was detected in 35.7% (34/95) of ovarian tumors with high clinical stages (p = 0.035) and in 83% (5/6) of primary ovarian cancer-initiating cells. Additionally, concurrent methylation of RunX1T1 and another SMAD4 target, FBXO32 which was previously found to be hypermethylated in ovarian cancer was observed in this same sample cohort (p < 0.05). Restoration of RunX1T1 inhibited cancer cell growth. Taken together, dysregulated TGFβ/SMAD4 signaling may lead to epigenetic silencing of a putative tumor suppressor, RunX1T1, during ovarian carcinogenesis.
ovarian cancer; epigenetics; TGFβ; RunX1T1
The objective of this study was to identify and characterize a self-renewing subpopulation of human ovarian tumor cells (ovarian cancer-initiating cells, OCICs) fully capable of serial propagation of their original tumor phenotype in animals. Ovarian serous adenocarcinomas were disaggregated and subjected to growth conditions selective for self-renewing, nonadherent spheroids previously shown to derive from tissue stem cells.To affirm the existence of OCICs, xenoengraftment of as few as 100 dissociated spheroid cells allowed full recapitulation of the original tumor (grade 2/grade 3 serous adenocarcinoma), whereas >105 unselected cells remained nontumorigenic. Stemness properties of OCICs (under stem cell—selective conditions) were further established by cell proliferation assays and reverse transcription—PCR, demonstrating enhanced chemoresistance to the ovarian cancer chemotherapeutics cisplatin or paclitaxel and up-regulation of stem cell markers (Bmi-1, stem cell factor, Notch-1, Nanog, nestin, ABCG2, and Oct-4) compared with parental tumor cells or OCICs under differentiating conditions.To identify an OCIC cell surface phenotype, spheroid immunostaining showed significant up-regulation of the hyaluronate receptor CD44 and stem cell factor receptor CD117 (c-kit), a tyrosine kinase oncoprotein. Similar to sphere-forming OCICs, injection of only 100 CD44+CD117+ cells could also serially propagate their original tumors, whereas 105 CD44−]CD117− cells remained nontumorigenic. Based on these findings, we assert that epithelial ovarian cancers derive from a subpopulation of CD44+CD117+ cells, thus representing a possible therapeutic target for this devastating disease.
To evaluate a commercialized in situ hybridization (ISH) assay for detecting human papillomavirus (HPV) DNA, we compared the ability of a new ISH probe, Inform HPV III (Ventana Medical Systems, Tucson, AZ), to that of PCR assays to detect HPV DNA in cervical tissue specimens with normal cervix (20 cases), cervical intraepithelial neoplasia (CIN; CIN 1, 27 cases; CIN 2, 28 cases; and CIN 3, 33 cases), and cervical carcinoma (29 cases). General HPV DNA was detected using consensus primer-mediated PCR assays. HPV genotyping was performed by using EasyChip HPV blot (King Car Yuan Shan Institute, I-Lan, Taiwan). HPV16 integration status (E2/E6 ratio) was determined by using quantitative real-time PCR. Our findings showed that the ISH and PCR had fair to good agreements in detecting HPV DNA across all CIN categories without significant differences (Kappa coefficient, 0.34 to 0.63; P = 0.13 to 1.0). However, ISH detected significantly fewer HPV-positive cases in carcinoma than PCR did (Kappa coefficient, 0.2; P = 0.03). Eleven cases with ISH− PCR+ results had HPV types that can be detected by Inform HPV III. Five carcinoma cases with ISH− PCR+ results showed a significantly higher level of integrated HPV16 (P = 0.008) than did the ISH+ cases. As a consequence, lower copy numbers of episomal HPV16 in carcinoma might be the cause for the false-negative ISH results. Although the punctate signal pattern of HPV significantly increased with the severity of disease (P trend = 0.01), no significant difference in the HPV16 integration status was observed between the cases with a punctate signal only and the cases with mixed punctate and diffuse signals (P = 0.4). In conclusion, ISH using the Inform HPV III probe seems comparable to PCR for detecting HPV DNA in cervical tissue with CINs. False-negative ISH results appear to be associated with the lower copy numbers of the episomal HPV16 but not with the ability of the Inform HPV III probe to detect specific HPV types. In addition, signal patterns, especially a mixed punctate and diffuse pattern of HPV, cannot be reliably used to predict viral integration status.