Effects of 5-Aza-2'-deoxycytidine on the methylation state and function of the WWOX gene in the HO-8910 ovarian cancer cell line

Strategies by which WWOX-deficient metastatic cancer cells utilize to survive via dodging, compromising, and causing damage to WWOX-positive normal microenvironment

Proapoptotic tumor suppressor WWOX is upregulated in the early stage of cancer initiation, which probably provides limitation to cancer growth and progression. Later, WWOX protein is reduced to enhance cancer cell growth, migration, invasiveness and metastasis. To understand how WWOX works in controlling cancer progression, here we demonstrate that apoptotic stress mediated by ectopic WWOX stimulated cancer cells to secrete basic fibroblast growth factor (bFGF) in order to support capillary microtubule formation. This event may occur in the cancer initiation stage. Later, when WWOX loss occurs in cancer cells, hyaluronidase production is then increased in the cancer cells to facilitate metastasis. We determined that inhibition of membrane hyaluronidase Tyr216-phosphorylated Hyal-2 by antibody suppresses cancer growth in vivo. WWOX-negative (WWOX-) cells dodged WWOX+cells in the microenvironment by migrating individually backward to avoid physical contacts and yet significantly upregulating the redox activity of WWOX+parental cells or other WWOX+cell types for causing apoptosis. Upon detecting the presence of WWOX+cells from a distance, WWOX- cells exhibit activation of MIF, Hyal-2, Eph, and Wnt pathways, which converges to MEK/ERK signaling and enables WWOX- cells to evade WWOX+cells. Inhibition of each pathway by antibody or specific chemicals enables WWOX- cells to merge with WWOX+cells. In addition, exogenous TGF-β assists WWOX- cells to migrate collectively forward and merge with WWOX+cells. Metastatic WWOX- cancer cells frequently secrete high levels of TGF-β, which conceivably assists them to merge with WWOX+cells in target organs and secure a new home base in the WWOX+microenvironment. Together, loss of WWOX allows cancer cells to develop strategies to dodge, compromise and even kill WWOX-positive cells in microenvironment.

5-aza-2'-deoxycytidine, a DNA methylation inhibitor, attenuates hyperoxia-induced lung fibrosis via re-expression of P16 in neonatal rats

BackgroundP16 methylation plays an important role in the pathogenesis of hyperoxia-induced lung fibrosis. 5-aza-2'-deoxycytidine (5-aza-CdR) is a major methyltransferase-specific inhibitor. In this study, the effects of 5-aza-CdR on a hyperoxia-induced lung fibrosis in neonatal rats were investigated.MethodsRat pups were exposed to 85% O₂ for 21 days of and received intraperitoneal injections of 5-aza-CdR or normal saline (NS) once every other day. Survival rates and lung coefficients were calculated. Hematoxylin-eosin staining was performed to analyze the degree of lung fibrosis. Collagen content and TGF-β1 levels were determined. A methylation-specific polymerase chain reaction and western blotting were performed to determine P16 methylation status and P16, cyclin D1, and E2F1 protein expression.Results5-aza-CdR treatment during hyperoxia significantly improved the survival rate and weight gain, while it decreases the degree of lung fibrosis and levels of hydroxyproline and TGF-β1. Hyperoxia induced abnormal P16 methylation and 5-aza-CdR effectively reversed the hypermethylation of P16. Expression of the P16 protein in lung tissues was enhanced, while cyclin D1 and E2F1 protein were reduced by 5-aza-CdR treatment during hyperoxia.ConclusionThese data show that 5-aza-CdR attenuated lung fibrosis in neonatal rats exposed to hyperoxia by lowering hydroxyproline and TGF-β1 expression and via re-expression of P16 in neonatal rats.

5-aza-2'-deoxycytidine Inhibits the Proliferation of Lung Fibroblasts in Neonatal Rats Exposed to Hyperoxia

BACKGROUND

A persistent increase in the number of lung fibroblasts (LFs) is found in the interstitium of the lungs of infants with bronchopulmonary dysplasia (BPD), which leads to lung fibrosis. P16 methylation plays an important role in the pathogenesis of BPD. 5-aza-2'-deoxycytidine (5-aza-CdR) is a major methyltransferase-specific inhibitor. This study investigated the effects of 5-aza-CdR on LFs in vitro from a hyperoxia-induced lung fibrosis model in newborn rats.

METHODS

Methylation-specific polymerase chain reaction (PCR) and Western blotting were performed to determine P16 gene methylation status and protein expression after LFs were treated with 0 μmol/L, 0.5 μmol/L, 1.0 μmol/L, and 5.0 μmol/L 5-aza-CdR for 120 hours. Proliferation was assessed by an MTT assay after LFs were treated with 0 μmol/L, 0.5 μmol/L, 1.0 μmol/L, and 5.0 μmol/L 5-aza-CdR for 24 hours, 48 hours, 72 hours, 96 hours, and 120 hours. At the final time point, cells were also analyzed by flow cytometry to identify any change in their cell cycle profiles.

RESULTS

A methylated P16 gene promoter was detected in hyperoxia LFs. Following treatment with 5-aza-CdR, partial methylation and demethylation was detected. The expression protein's level of the P16 gene was significantly higher in the 5.0 μmol/L 5-aza-CdR-treated group compared with that in the control group (p < 0.01). The cell growth rate at each tested time point was lower in the 5-aza-CdR-treated group compared with that in the control group after 72 hours (p < 0.01). Flow cytometry revealed that the cells in the 1.0 μmol/L and 5.0 μmol/L 5-aza-CdR-treated groups were apparently arrested in the G0/G1 phase and that the number of cells in the S phase was significantly lower than the control group (p < 0.01).

CONCLUSION

5-aza-CdR inhibits the growth of the LFs in hyperoxia-induced neonatal BPD rats in vitro by demethylating the P16 gene.

Estrogen and promoter methylation in the regulation of PLA2G7 transcription

In the current study, cell lines including HEK293, SW480, HPASMC, HPCASMC and HAEC were cultured with 5-aza-2-deoxycytidine (DAC) and 17-β-estradiol to investigate whether PLA2G7 transcription was under the control of promoter methylation and 17-β-estradiol. Luciferase reporter gene assays were used to evaluate whether reporter gene activity was enhanced by PLA2G7 promoter fragment. Gene expression and methylation were detected using RT-PCR and pyrosequencing methods, respectively. Endogenous PLA2G7 transcription levels were found to be significantly lower in vascular related cell lines than in the other cell lines. Luciferase reporter gene assays indicated that gene activity was significantly enhanced by PLA2G7 promoter fragment. PLA2G7 transcription was found to be up-regulated with the treatment of DAC. The 17-β-estradiol was found to down-regulate PLA2G7 transcription in all the cell lines. However, 17-β-estradiol did not have significant effect on PLA2G7 methylation. Further chromatin immunoprecipitation assay showed that 17-β-estradiol might regulate gene transcription by affecting the acetylated histone H3 and H4 marks on PLA2G7 promoter. Our results showed that PLA2G7 gene expression was co-regulated by 17-β-estradiol and promoter methylation. Our findings might provide molecular clues for gender disparity in the contribution of PLA2G7 to vascular related diseases such as coronary heart disease.

Reduced expression of the WW domain-containing oxidoreductase in human hematopoietic malignancies

The role of the WW domain-containing oxidoreductase (WWOX) gene in multiple types of solid human cancers has been documented extensively thus far. Recently, we investigated the in vitro effects of WWOX overexpression and observed marked growth arrest in human leukemia cells; however, the clinical characterization of WWOX in leukemia remains poorly investigated. The present study evaluated the WWOX expression profiles of 182 patients with leukemia of different types and 5 leukemic cell lines, using reverse transcription-polymerase chain reaction and immunofluorescence analysis. The results found that WWOX mRNA and WWOX protein expression was significantly reduced or absent in the leukemia cases and cell lines compared with paired controls. The WWOX-positive rate was also lower in the leukemia cases compared with the rate of the normal controls. Notably, the WWOX level was reduced in newly diagnosed and relapsed cases, or in chronic myelogenous leukemia in the blastic phase, yet elevated in remission samples. Moreover, WWOX-negative cases exhibited WWOX expression restoration following induced remission. These findings suggest that WWOX may contribute to the occurrence and development of leukemia, and that it has potential to be a good biomarker or predictor for leukemia therapy.

Decreased DNA methylation in the promoter region of the WNT5A and GDNF genes may promote the osteogenicity of mesenchymal stem cells from patients with ossified spinal ligaments

Mesenchymal stem cells (MSCs) isolated from spinal ligaments with ectopic ossification have a propensity toward the osteogenic lineage. To explore epigenetic control of the osteogenic features of MSCs, we treated MSCs obtained from the spinal ligaments of ossification of yellow ligament (OYL) patients and non-OYL patients with the DNA methyltransferase inhibitor, 5-aza-2'-deoxycytidine (5AdC). We compared the non-OYL groups (untreated and treated with 5AdC) with the OYL groups (untreated and treated with 5AdC) by genome-wide microarray analysis. Next, we used methylated DNA immunoprecipitation combined with quantitative real-time PCR to assess gene methylation. Ninety-eight genes showed expression significantly increased by 5AdC treatment in MSCs from non-OYL patients but not from OYL patients. In contrast, only two genes, GDNF and WNT5A, showed significantly higher expression in OYL MSCs compared with non-OYL MSCs without 5AdC treatment. Both genes were hypermethylated in non-OYL MSCs but not in OYL MSCs. Small interfering RNA targeted to each gene decreased expression of the target gene and also several osteogenic genes. Both small interfering RNAs also suppressed the activity of alkaline phosphatase, a typical marker of osteogenesis. These results suggest that the osteogenic features of MSCs from OYL patients are promoted by unmethylated WNT5A and GDNF genes.

Ectopic expression of the WWOX gene suppresses stemness of human ovarian cancer stem cells

The present study aimed to investigate the effects of the WW domain-containing oxidoreductase (WWOX) gene on the stem cell properties of human ovarian cancer stem cells. A eukaryotic expression vector containing the WWOX gene was transfected into human ovarian cancer stem cells and Western blotting was used to assess the expression of WWOX protein in the transfected cells compared with the control cells (untransfected cells and cells transfected with the empty vector). The self-renewal abilities of these three types of stem cells was also assessed in vitro. To monitor changes in their differentiation potential, cells were cultured in medium supplemented with serum, and the expression of specific stem cell markers was determined. Drug-sensitivity tests were used to measure the sensitivity of the stem cells to cisplatin, doxorubicin, and mitoxantrone. The cells were also transplanted into non-obese diabetic (NOD)/severe combined immunodeficiency (SCID) mice to determine the changes in their tumorigenicity in vivo. Cells transfected with the WWOX-expressing plasmid stably expressed WWOX protein, while no WWOX protein was detected in control cells. Compared with the two types of control cells, WWOX-expressing stem cells manifested significantly reduced self-renewal ability. Compared with control cells, the expression levels of stem cell markers, including CD133, CD117, ATP-binding cassette sub-family G member 2, Nanog, octamer-binding transcription factor 4 and breast cancer resistance protein, were significantly lower in WWOX-expressing cells, while the level of the differentiation marker E-cadherin was significantly higher in WWOX-expressing cells. Furthermore, WWOX-expressing cells were more sensitive to treatment with cisplatin, doxorubicin and mitoxantrone. In NOD/SCID mice, the tumorigenicity of WWOX-expressing cells was significantly lower compared with that of control cells. The results indicate that the tumor suppressor WWOX suppresses stem cell properties in cancer stem cells, including self-renewal ability, differentiation potential, in vivo tumorigenic capability, high-level expression of stem cell genes and multidrug resistance.

Alteration of WWOX in human cancer: a clinical view

WWOX gene is located in FRA16D, the highly affected chromosomal fragile site. Its tumor suppressor activity has been proposed on a basis of numerous genomic alterations reported in chromosome 16q23.3-24.1 locus. WWOX is affected in many cancers, showing as high as 80% loss of heterozygosity in breast tumors. Unlike most tumor suppressors impairing of both alleles of WWOX is very rare. Despite cellular and animal models information on a WWOX role in cancer tissue is limited and sometimes confusing. This review summarizes information on WWOX in human tumors.

Epigenetic and genetic alterations affect the WWOX gene in head and neck squamous cell carcinoma

Different types of genetic and epigenetic changes are associated with HNSCC. The molecular mechanisms of HNSCC carcinogenesis are still undergoing intensive investigation. WWOX gene expression is altered in many cancers and in a recent work reduced WWOX expression has been associated with miR-134 expression in HNSCC. In this study we investigated the WWOX messenger RNA expression levels in association with the promoter methylation of the WWOX gene and miR-134 expression levels in 80 HNSCC tumor and non-cancerous tissue samples. Our results show that WWOX expression is down-regulated especially in advanced-stage tumor samples or in tumors with SCC. This down-regulation was associated with methylation of the WWOX promoter region but not with miR-134 expression. There was an inverse correlation between the expression level and promoter methylation. We also analyzed whole exons and exon/intron boundries of the WWOX gene by direct sequencing. In our study group we observed 10 different alterations in the coding sequences and 18 different alterations in the non-coding sequences of the WWOX gene in HNSCC tumor samples. These results indicate that the WWOX gene can be functionally inactivated by promoter methylation, epigenetically or by mutations affecting the sequences coding for the enzymatic domain of the gene, functionally. We conclude that inactivation of WWOX gene contributes to the progression of HNSCC.

DNMT1 and EZH2 mediated methylation silences the microRNA-200b/a/429 gene and promotes tumor progression

Aberrant expression of the microRNA-200 (miR-200) family has been linked to the occurrence and development of various types of malignant tumors, including hepatocellular carcinoma (HCC), colon cancer and breast cancer. However, little is known about the precise mechanism by which miR-200 expression is downregulated. The intricate relationship between DNA methylation and histone modifications has become a subject of increasing interest. The expression of miR-200 family members is modified by similar or complementary epigenetic mechanisms in MGC-803 and BGC-823 gastric cancer cells and U87 MG glioma cells. Chromatin immunoprecipitation assays revealed that DNA methyltransferase 1 (DNMT1) bound to miR-200b/a/429 promoter regions, indicating an interaction between DNMT1 and the miR-200b/a/429 promoter. Furthermore, Co-Immunoprecipitation (Co-IP) detection showed that DNMT1, together with the PcG protein Enhancer of Zeste homolog 2 (EZH2), a histone methyltransferase, contributed to the transcriptional repression of microRNA-200 family members. Knockdown of EZH2 not only impacted H3K27 trimethylation but also reduced DNMT1 presence on the miR-200b/a/429 promoter. EZH2 appeared to be essential for DNMT1 recruitment to the promoter region. Silencing EZH2 and DNMT1 using drugs or RNA interference dramatically reduced the levels of miR-200b/a/429 expression. Collectively, these results indicated that EZH2 and DNMT1-mediated epigenetic silencing contributed to the progression of gastric cancer and glioblastoma, and therefore represents a novel therapeutic target for malignant tumors.

Clinical importance and therapeutic implication of E-cadherin gene methylation in human ovarian cancer

E-cadherin (E-cad) is widely expressed in epithelial cells and acts as a pivotal tumor suppressor. The promoter methylation of E-cad has been reported to closely relate to its downregulation in many kinds of cancers. E-cad expression and methylation status were detected by immunohistochemistry (IHC) and methylation-specific polymerase chain reaction (MS-PCR) in 50 ovarian cancer tissues. 5-Aza-2'-deoxycytidine (5-Aza-dC) was used to demethylate E-cad in SKOV3 and ES2 ovarian cancer cell lines, of which the effect was verified by Western blot and MS-PCR. Then MTT and transwell experiments were conducted to detect the capacity of cell proliferation and migration for these cells. Downregulation of E-cad expression was observed in 60 % of ovarian cancer tissues (30/50) by IHC, whereas MS-PCR result indicated that E-cad was methylated in 64 % of (32/50) ovarian cancer specimens. And E-cad expression was significantly correlated with E-cad methylation (P = 0.004). 5-Aza-dC was used to process SKOV3 and ES2 ovarian cancer cell lines. By MTT experiment, we found that the proliferation of 5-Aza-dC-treated SKOV3 and ES2 was significantly suppressed by 28.0 % (P < 0.05) and 32.3 % (P < 0.05). By transwell experiment, the motility of SKOV3 and ES2 was found to be significantly suppressed by 38.2 and 27.4 % (P < 0.05), respectively, after treated with 5-Aza-dC. E-cad methylation is one of the main reasons for the expression reduction in ovarian cancer. 5-Aza-dC treatment could significantly restore the expression of E-cad and suppress growth and invasion of SKOV3 and ES2 cells. These results suggest E-cad methylation may be a promising target for ovarian cancer therapy.

Evaluation of the mechanism of epithelial-mesenchymal transition in human ovarian cancer stem cells transfected with a WW domain-containing oxidoreductase gene

The aim of the present study was to investigate the impact of the WW domain-containing oxidoreductase (WWOX) gene on the mechanisms underlying epithelial-mesenchymal transition (EMT) in human ovarian cancer stem cells. Western blot analysis was performed to detect the differences in the expression of the EMT markers, E-cadherin, β-catenin, N-cadherin, vimentin and fibronectin, between human ovarian cancer stem cells and the human epithelial ovarian carcinoma cell line, HO-8910. A pcDNA3.1-WWOX eukaryotic expression vector was subsequently transfected into the ovarian cancer stem cells (recombinant plasmid group) or an empty plasmid (empty plasmid group) and non-transfected ovarian cancer stem cells (blank control group) served as the controls. Following the transfection of the WWOX gene, methyl thiazolyl tetrazolium cell viability and Transwell^® invasion assays, and western blot analysis were performed to detect changes in the proliferative capability and invasive capacity of ovarian cancer stem cells, as well as the expression of EMT markers and regulatory factors, Elf5 and Snail. The expression levels of E-cadherin and β-catenin in the ovarian cancer stem cells were identified to be significantly lower than those in the HO-8910 cells, whereas the expression levels of N-cadherin, vimentin and fibronectin in the ovarian cancer stem cells were found to be significantly higher than those in the HO-8910 cells. At each time point, the cellular proliferative capacity of the recombinant plasmid group was observed to be significantly lower than that of the empty plasmid or blank control groups (P<0.05 vs. the controls). The number of penetrating cells in the recombinant plasmid, empty plasmid and the blank control groups were 105.5±3.1, 199.7±3.4 and 191.4±4.1, respectively (mean ± standard error of the mean; P<0.05 vs. the controls). In addition, the protein expression of E-cadherin, β-catenin and Elf5 in the recombinant plasmid group was found to be significantly higher than that in the other two groups, whereas the protein expression of N-cadherin, vimentin, fibronectin and Snail in the recombinant plasmid group was significantly lower than that in the other two groups. An EMT exists in ovarian cancer stem cells, and the WWOX gene inhibits the cellular proliferation of ovarian cancer stem cells and reduces their invasive capability. Therefore, the WWOX gene may reverse the EMT in ovarian cancer stem cells by regulating the expression of the EMT regulatory factors, Elf5 and Snail.