RNA interference-mediated knockdown of DNMT1 and DNMT3B induces CXCL12 expression in MCF-7 breast cancer and AsPC1 pancreatic carcinoma cell lines

Physiology of chemokines in the cancer microenvironment

Chemokines are chemotactic cytokines whose canonical functions govern movement of receptor-expressing cells along chemical gradients. Chemokines are a physiological system that is finely tuned by ligand and receptor expression, ligand or receptor oligomerization, redundancy, expression of atypical receptors, and non-GPCR binding partners that cumulatively influence discrete pharmacological signaling responses and cellular functions. In cancer, chemokines play paradoxical roles in both the directed emigration of metastatic, receptor-expressing cancer cells out of the tumor as well as immigration of tumor-infiltrating immune cells that culminate in a tumor-unique immune microenvironment. In the age of precision oncology, strategies to effectively harness the power of immunotherapy requires consideration of chemokine gradients within the unique spatial topography and temporal influences with heterogeneous tumors. In this article, we review current literature on the diversity of chemokine ligands and their cellular receptors that detect and process chemotactic gradients and illustrate how differences between ligand recognition and receptor activation influence the signaling machinery that drives cellular movement into and out of the tumor microenvironment. Facets of chemokine physiology across discrete cancer immune phenotypes are contrasted to existing chemokine-centered therapies in cancer.

The role of lncRNA H19 in tumorigenesis and drug resistance of human Cancers

Systemic therapy is one of the most significant cancer treatments. However, drug resistance often appears and has become the primary cause of cancer therapy failure. Regulation of drug target, drug metabolism and drug efflux, cell death escape (apoptosis, autophagy, et al.), epigenetic changes, and many other variables are complicatedly involved in the mechanisms of drug resistance. In various types of cancers, long non-coding RNA H19 (lncRNA H19) has been shown to play critical roles in tumor development, proliferation, metastasis, and multiple drug resistance as well. The efficacy of chemotherapy, endocrine therapy, and targeted therapy are all influenced by the expression of H19, especially in breast cancer, liver cancer, lung cancer and colorectal cancer. Here, we summarize the relationship between lncRNA H19 and tumorigenesis, and illustrate the drug resistance mechanisms caused by lncRNA H19 as well. This review may provide more therapeutic potential targets for future cancer treatments.

DNMT3A and DNMT3B in Breast Tumorigenesis and Potential Therapy

Breast cancer has become a leading cause of cancer-related deaths in women worldwide. DNA methylation has been revealed to play an enormously important role in the development and progression of breast cancer. DNA methylation is regulated by DNA methyltransferases (DNMTs), including DNMT1, DNMT2, and DNMT3. DNMT3 family has three members: DNMT3A, DNMT3B, and DNMT3L. The roles and functions of DNMT1 in breast cancer have been well reviewed. In this article, the roles of DNMT3A and DNMT3B in breast tumorigenesis and development are reviewed. We also discuss the SNP and mutations of DNMT3A and DNMT3B in breast cancer. In addition, we summarize how DNMT3A and DNMT3B are regulated by non-coding RNAs and signaling pathways in breast cancer, and targeting the expression levels of DNMT3A and DNMT3B may be a promising therapeutic approach for breast cancer. This review will provide reference for further studies on the biological functions and molecular mechanisms of DNMT3A and DNMT3B in breast cancer.

DNMT3B silencing suppresses migration and invasion by epigenetically promoting miR-34a in bladder cancer

The role of DNA methyltransferase 3B (DNMT3B) in tumorigenesis and development has been widely recognized; however, the mechanism underlying its action remains unclear. Considering its function in de novo methylation, we aimed to investigate whether DNMT3B plays its role via microRNA (miR)-34a promoter methylation in bladder cancer. We found that DNMT3B expression was low in 10 bladder cancer tissues and high in 20 bladder cancer tissues. miR-34a expression was higher in bladder cancer tissues with low expression of DNMT3B than that in bladder cancer tissues with high expression of DNMT3B. The level of miR-34a was negatively correlated with the level of DNMT3B. The methylation ratio of the miR-34a promoter was positively correlated with the level of DNMT3B and negatively correlated with the level of miR-34a. DNMT3B knockdown increased the expression of miR-34a and the transcriptional activity of the miR-34a promoter, while decreasing miR-34a promoter methylation. DNMT3B knockdown inhibited migration and invasion, while decreasing the protein levels of hepatocyte nuclear factor 4 gamma and Notch1 which are downstream targets of miR-34a. These inhibitory effects of DNMT3B were mitigated by the miR-34a inhibitor. In conclusion, DNMT3B silencing suppresses migration and invasion by epigenetically promoting miR-34a in bladder cancer.

The long noncoding RNA H19 promotes tamoxifen resistance in breast cancer via autophagy

Background

Tamoxifen resistance remains a clinical challenge for hormone receptor-positive breast cancer. Recently, dysregulations in autophagy have been suggested as a potential mechanism for tamoxifen resistance. Although the long noncoding RNA H19 is involved in various stages of tumorigenesis, its role in tamoxifen resistance remains unknown. Here, we assessed the role of H19 in the development of tamoxifen-resistant breast cancer.

Methods

Quantitative real-time PCR analyzed expression of H19 in tamoxifen-resistant breast cancer tissues. Knockdown of H19 was used to assess the sensitivity to tamoxifen in vitro and in vivo. Both knockdown and overexpression of H19 were used to analyze the status of autophagy. Real-time quantitative methylation-specific polymerase chain reaction, chromatin immunoprecipitation, immunofluorescence, and Western blot were used to explore the tamoxifen resistance mechanism of H19.

Results

In this study, we observed that the expression of H19 was substantially upregulated in tamoxifen-resistant breast cancer cell line and tumor tissues, and knockdown of H19 enhanced the sensitivity to tamoxifen both in vitro and in vivo. Furthermore, knockdown of H19 significantly inhibited autophagy in MCF7 tamoxifen-resistant (MCF7/TAMR) cells. Conversely, overexpression of H19 promoted autophagy. Interestingly, overexpression of H19 in MCF7 tamoxifen-sensitive cells could recapitulate tamoxifen resistance. Moreover, an increase in methylation in the promoter region of Beclin1 was observed in MCF7/TAMR-shH19 cells. In the double knockdown groups, both shH19+shSAHH and shH19+shDNMT3B rescued the Beclin1 promoter region methylation levels and reactivated autophagy functions. A chromatin immunoprecipitation assay further validated that DNMT3B binds to the Beclin1 promoter region and the knockdown of H19 increases this binding.

Conclusions

Our findings demonstrate that H19 induces autophagy activation via the H19/SAHH/DNMT3B axis, which could contribute to tamoxifen resistance in breast cancer.

Electronic supplementary material

The online version of this article (10.1186/s13045-019-0747-0) contains supplementary material, which is available to authorized users.

Methyl Donor Micronutrients that Modify DNA Methylation and Cancer Outcome

DNA methylation is an epigenetic mechanism that is essential for regulating gene transcription. However, aberrant DNA methylation, which is a nearly universal finding in cancer, can result in disturbed gene expression. DNA methylation is modified by environmental factors such as diet that may modify cancer risk and tumor behavior. Abnormal DNA methylation has been observed in several cancers such as colon, stomach, cervical, prostate, and breast cancers. These alterations in DNA methylation may play a critical role in cancer development and progression. Dietary nutrient intake and bioactive food components are essential environmental factors that may influence DNA methylation either by directly inhibiting enzymes that catalyze DNA methylation or by changing the availability of substrates required for those enzymatic reactions such as the availability and utilization of methyl groups. In this review, we focused on nutrients that act as methyl donors or methylation co-factors and presented intriguing evidence for the role of these bioactive food components in altering DNA methylation patterns in cancer. Such a role is likely to have a mechanistic impact on the process of carcinogenesis and offer possible therapeutic potentials.

DNMT1 regulates human endometrial carcinoma cell proliferation

Endometrial carcinoma (EC) is the most common gynecologic malignancy, but the molecular events involved in the development and progression of EC remain unclear. This study aimed to investigate the role of DNA methyltransferase 1 (DNMT1), a member of DNA methyltransferases, in EC. AN3CA cells were transfected with DNMT1 siRNA. The proliferation, cell cycle, and apoptosis of AN3CA cells were evaluated by Cell Counting Kit-8 (CCK-8) assay and flow cytometry. The expression of related genes was detected by polymerase chain reaction and Western blot analysis. Knockdown of DNMT1 inhibited the proliferation, induced apoptosis, and G0/G1 phase arrest of AN3CA cells. Furthermore, knockdown of DNMT1 upregulated the expression of nuclear factor kappa-B-inhibitor alpha (NF-κBIA) and Bax and downregulated the expression of Bcl-2 and CCND1/2 in AN3CA cells. In conclusion, this study provides the first evidence that knockdown of DNMT1 affects the expression of cell cycle- and apoptosis-associated proteins in EC cells, suggesting the potential of DNMT1 in EC therapy.

Tackling breast cancer chemoresistance with nano-formulated siRNA

Breast cancer is the leading cancer diagnosed in women and the second leading cause of cancer-related deaths in women. Current limitations to standard chemotherapy in the clinic are extensively researched, including problems arising from repeated treatments with the same drugs. The phenomenon that cancer cells become resistant toward certain chemo drugs is called chemotherapy resistance. In this review, we are focusing on nanoformulation of siRNA for the fight against breast cancer chemoresistance.

Tobacco carcinogen NNK-induced lung cancer animal models and associated carcinogenic mechanisms

Tobacco usage is a major risk factor in the development, progression, and outcomes for lung cancer. Of the carcinogens associated with lung cancer, tobacco-specific nitrosamines 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is among the most potent ones. The oncogenic mechanisms of NNK are not entirely understood, hindering the development of effective strategies for preventing and treating smoking-associated lung cancers. Here, we introduce the NNK-induced lung cancer animal models in different species and its potential mechanisms. Finally, we summarize several chemopreventive agents developed from these animal models.

Genetic variants of DNMT3A and systemic lupus erythematosus susceptibility

OBJECTIVES

A significant increase in DNA methyltransferase 3A (DNMT3A) transcript levels has recently been demonstrated in peripheral blood mononuclear cells from systemic lupus erythematosus (SLE) patients as compared to healthy individuals.

METHODS

Employing high resolution melting curve analysis (HRM) and PCR-restriction fragment length polymorphism analysis, we assessed the frequency of five single nucleotide polymorphisms (SNPs) of this gene: rs2289195, rs7590760, rs13401241, rs749131 and rs1550117, situated in different linkage disequilibrium blocks of the DNMT3A gene in two hundred and fifty seven women with SLE and six hundred and twenty five controls.

RESULTS

The lowest p values of the trend test were observed for the DNMT3A -448A> G (rs1550117) SNP (ptrend = 0.0111). We also found that, in a dominant inheritance model, the DNMT3A -448A> G SNP may protect from SLE development [odds ratio (OR) = 0.494 (0.294-0.830), p = 0.0068, pcorr = 0.034]. Furthermore, we observed that the DNMT3A -448A > G SNP in dominant inheritance models may protect from immunologic manifestations of SLE [OR = 0.1753 (95% CI = 0.04976-0.6176, p = 0.0026, pcorr = 0.0468).

CONCLUSIONS

Our study demonstrates that the DNMT3A -448A> G SNP might protect from SLE and its immunologic manifestations in a sample from the Polish population.

DNMT1, DNMT3A and DNMT3B gene variants in relation to ovarian cancer risk in the Polish population

Studies have demonstrated that changes in DNA methylation of cancer related genes can be an elementary process accounting for ovarian tumorigenesis. Therefore, we evaluated the possible association of single nucleotide polymorphisms (SNPs) of DNA methyltransferases (DNMTs) genes, including DNMT1, DNMT3B, and DNMT3A, with ovarian cancer development in the Polish population. Using PCR-RFLP and HRM analyses, we studied the prevalence of the DNMT1 rs8101626, rs2228611 and rs759920, DNMT3A rs2289195, 7590760, rs13401241, rs749131 and rs1550117, and DNMT3B rs1569686, rs2424913 and rs2424932 SNPs in patients with ovarian cancer (n=159) and controls (n=180). The lowest p values of the trend test were observed for the DNMT1 rs2228611 and rs759920 SNPs in patients with ovarian cancer (p trend=0.0118 and p trend=0.0173, respectively). Moreover, we observed, in the recessive inheritance model, that the DNMT1 rs2228611 and rs759920 SNPs are associated with an increased risk of ovarian cancer development [OR 1.836 (1.143-2.949), p=0.0114, p corr=0.0342, and OR 1.932 (1.185-3.152), p=0.0078, p cor=0.0234, respectively]. However, none of other nine studied SNPs displayed significant contribution to the development of ovarian cancer. Furthermore, haplotype and multifactor dimensionality reduction analysis of the studied DNMT1, DNMT3B, and DNMT3A polymorphisms did not reveal either SNP combinations or gene interactions to be associated with the risk of ovarian cancer development. Our results may suggest that DNMT1 variants may be risk factors of ovarian cancer.

HBP1-mediated transcriptional regulation of DNA methyltransferase 1 and its impact on cell senescence

The activity of DNA methyltransferase 1 (DNMT1) is associated with diverse biological activities, including cell proliferation, senescence, and cancer development. In this study, we demonstrated that the HMG box-containing protein 1 (HBP1) transcription factor is a new repressor of DNMT1 in a complex mechanism during senescence. The DNMT1 gene contains an HBP1-binding site at bp -115 to -134 from the transcriptional start site. HBP1 repressed the endogenous DNMT1 gene through sequence-specific binding, resulting in both gene-specific (e.g., p16(INK4)) and global DNA hypomethylation changes. The HBP1-mediated repression by DNMT1 contributed to replicative and premature senescence, the latter of which could be induced by Ras and HBP1 itself. A detailed investigation unexpectedly revealed that HBP1 has dual and complex transcriptional functions, both of which contribute to premature senescence. HBP1 both repressed the DNMT1 gene and activated the p16 gene in premature senescence. The opposite transcriptional functions proceeded through different DNA sequences and differential protein acetylation. While intricate, the reciprocal partnership between HBP1 and DNMT1 has exceptional importance, since its abrogation compromises senescence and promotes tumorigenesis. Together, our results suggest that the HBP1 transcription factor orchestrates a complex regulation of key genes during cellular senescence, with an impact on overall DNA methylation state.

Polymorphic variants of DNMT3A and the risk of endometriosis

OBJECTIVE

Overexpression of DNA methyltransferase 3A (DNMT3A) and aberrant methylation of various genes in eutopic endometrium have been demonstrated in women with endometriosis. We aimed to study whether DNMT3A polymorphisms could be a genetic risk factor for endometriosis and endometriosis-related infertility.

STUDY DESIGN

We studied 5 SNPs (rs2289195, rs7590760, rs13401241, rs749131 and rs1550117) located in the DNMT3A gene in 357 women with endometriosis and 640 controls.

RESULTS

We did not observe significant differences between genotype and allele frequencies of rs2289195, rs7590760, rs13401241, rs749131 and rs1550117 SNPs in women with endometriosis, endometriosis-related infertility, and controls. The lowest p values of the trend test were observed for DNMT3A rs1550117 in endometriosis and endometriosis-related infertility (p(trend)=0.049 and p(trend)=0.055, respectively).

CONCLUSIONS

Our results did not supply evidence for the contribution of SNPs located in DNMT3A to either endometriosis or endometriosis-related infertility.

DNA methylation inhibitors in cancer: recent and future approaches

This review presents the different human DNA methyltransferases (DNMTs), their biological roles, their mechanisms of action and their role in cancer. The description of assays for detecting DNMT inhibitors (DNMTi) follows. The different known DNMTi are reported along with their advantages, drawbacks and clinical trials. A discussion on the features of the future DNMT inhibitors will conclude this review.

ATRA inhibits the proliferation of DU145 prostate cancer cells through reducing the methylation level of HOXB13 gene

All-trans retinoic acid (ATRA) has been widely investigated for treatments of many cancers including prostate cancer. HOXB13, silenced in androgen receptor-negative (AR(-)) prostate cancer cells, plays a role in AR(-) prostate cancer cell growth arrest. In this study we intended to elucidate the mechanisms that are involved in the proliferation inhibition of AR(-) prostate cancer cells triggered by ATRA. We discovered that ATRA was able to induce the growth arrest and to increase HOXB13 expression in AR(-) prostate cancer cells. Both EZH2 and DNMT3b participated in the repression of HOXB13 expression through an epigenetic mechanism involving DNA and histone methylation modifications. Specifically, EZH2 recruited DNMT3b to HOXB13 promoter to form a repression complex. Moreover, ATRA could upregulate HOXB13 through decreasing EZH2 and DNMT3b expressions and reducing their interactions with the HOXB13 promoter. Concurrently, the methylation level of the HOXB13 promoter was reduced upon the treatment of ATRA. Results from this study implicated a novel effect of ATRA in inhibition of the growth of AR(-) resistant human prostate cancer cells through alteration of HOXB13 expression as a result of epigenetic modifications.

De novo DNA methyltransferases: oncogenes, tumor suppressors, or both?

Aberrant promoter DNA hypermethylation of tumor suppressor genes is a hallmark of cancer. This alteration is largely dependent on the action of de novo DNA methyltransferases (DNMTs) early during tumor progression, which supports the oncogenic role for these enzymes. However, recent research has identified several inactivating mutations of de novo DNMTs in various types of tumor. In addition, it has been shown that loss of de novo DNA methylation activity at advanced tumor stages leads to the promoter DNA demethylation-dependent expression of specific oncogenes. These new data support the notion that de novo DNMTs also have an important role in the maintenance of DNA methylation and suggest that, in addition to acting as oncogenes, they also behave as tumor suppressors. This potential dual role might have clinical implications, as DNMTs are currently considered bona fide targets in cancer therapy.

Enhancement of chemotherapeutic efficacy in hypermethylator breast cancer cells through targeted and pharmacologic inhibition of DNMT3b

A subset of primary breast cancers and breast cancer cell lines express a hypermethylation defect (characterized by DNMT hyperactivity and DNMT3b overexpression) which contributes to chemotherapy resistance and provides a target for development of new treatment strategies. The objective of the current study was to determine if targeting the epigenome enhances the sensitivity of breast cancer cells to cytotoxic chemotherapy. Hypermethylator breast cancer cell lines (MDA-MB-453, BT549, and Hs578T) were treated with 250 or 500 nM 5-aza-2'-deoxycytidine (5-aza) and/or were subjected to RNAi-mediated DNMT3b knockdown (KD), and then tested for sensitivity to doxorubicin hydrochloride (DOX), paclitaxel (PAX), and 5-fluorouracil (5-FU). In MDA-MB-453 cells, DNMT3b KD reduces the IC(50) for DOX from 0.086 to 0.048 μM (44% reduction), for PAX from 0.497 to 0.376 nM (24%), and for 5-FU from 0.817 to 0.145 mM (82%). Treatment with 250 nM 5-aza for 7 days did not increase the efficacy of DOX, PAX, or 5-FU, but 7-day treatment with 500 nM 5-aza sensitized cells, reducing the IC(50) for DOX to 0.035 μM (60%), PAX to 0.311 nM (37%), and 5-FU to 0.065 mM (92%). 5-aza treatment of DNMT3b KD cells reduced the IC(50) for DOX to 0.036 μM (59%), for PAX to 0.313 nM (37%) and for 5-FU to 0.067 (92%). Similar trends of enhancement of cell kill were seen in BT549 (13-60%) and Hs578T (29-70%) cells after RNAi-mediated DNMT3b KD and/or treatment with 5-aza. The effectiveness of DOX, PAX, and 5-FU is enhanced through targeted and/or pharmacological inhibition of DNMT3b, strongly suggesting that combined epigenetic and cytotoxic treatment will improve the efficacy of breast cancer chemotherapy.

Role of DNMT3B in the regulation of early neural and neural crest specifiers

The de novo DNA methyltransferase DNMT3B functions in establishing DNA methylation patterns during development. DNMT3B missense mutations cause immunodeficiency, centromere instability and facial anomalies (ICF) syndrome. The restriction of Dnmt3b expression to neural progenitor cells, as well as the mild cognitive defects observed in ICF patients, suggests that DNMT3B may play an important role in early neurogenesis. We performed RNAi knockdown of DNMT3B in human embryonic stem cells (hESCs) in order to investigate the mechanistic contribution of DNMT3B to DNA methylation and early neuronal differentiation. While DNMT3B was not required for early neuroepithelium specification, DNMT3B deficient neuroepithelium exhibited accelerated maturation with earlier expression, relative to normal hESCs, of mature neuronal markers (such as NEUROD1) and of early neuronal regional specifiers (such as those for the neural crest). Genome-wide analyses of DNA methylation by MethylC-seq identified novel regions of hypomethylation in the DNMT3B knockdowns along the X chromosome as well as pericentromeric regions, rather than changes to promoters of specific dysregulated genes. We observed a loss of H3K27me3 and the polycomb complex protein EZH2 at the promoters of early neural and neural crest specifier genes during differentiation of DNMT3B knockdown but not normal hESCs. Our results indicate that DNMT3B mediates large-scale methylation patterns in hESCs and that DNMT3B deficiency in the cells alters the timing of their neuronal differentiation and maturation.

Role of PTEN promoter methylation in tamoxifen-resistant breast cancer cells

Tamoxifen (TAM) resistance is a serious clinical problem in the treatment of breast cancer. Here, we found that S-adenosylmethionine (SAM) and DNA methyltransferase1 (DNMT1) expression are up-regulated in TAM-resistant breast cancer (TAMR-MCF-7) cells. We further focused on whether increased SAM with DNMT1 overexpression in TAMR-MCF-7 cells lead to aberrant methylation of the PTEN gene promoter and its therapeutic potential. Methylation-specific PCR analyses revealed that two sites within the PTEN promoters were methylated in TAMR-MCF-7 cells, which resulted in down-regulation of PTEN expression and increase in Akt phosphorylation. Both the loss of PTEN expression and the increased Akt phosphorylation in TAMR-MCF-7 cells were completely reversed by 5-aza-2'-deoxycytidine (5-Aza), a DNMT inhibitor. 5-Aza inhibited the basal cell proliferation rate of TAMR-MCF-7 cells and intraperitoneal injection of 5-Aza significantly suppressed TAMR-MCF-7 tumor growth in a xenograft study. Immunohistochemistry showed that PTEN expression in TAM-resistant human breast cancer tissues was lower than in TAM-responsive cases. These results suggest that methylation of the PTEN promoter related to both SAM increase and DNMT1 activation contributes to persistent Akt activation and are potential therapeutic targets for reversing TAM resistance in breast cancer.

Effects of DNMT1 silencing on malignant phenotype and methylated gene expression in cervical cancer cells

Background

DNA methylation has been widely used in classification, early diagnosis, therapy and prediction of metastasis as well as recurrence of cervical cancer. DNMT methyltransferase 1 (DNMT1), which plays a significant role in maintaining DNA methylation status and regulating the expression of tumor suppressor genes. The aim of this research was to investigate the relationship between DNMT1 and abnormal methylation of tumor suppressor genes and malignant phenotype in cervical cancer.

Methods

Levels of DNMT1 mRNA and protein were detected using qPCR and Western blot, respectively. Cell proliferation was analyzed by MTT and apoptosis was performed by Annexin V-FITC/PI double staining flow cytometry, respectively. MeDIP-qPCR and qPCR were performed to measure demethylation status and mRNA re-expression level of 7 tumor-suppressor genes (CCNA1, CHFR, FHIT, PAX1, PTEN, SFRP4, TSLC1) in Hela and Siha cells after silencing DNMT1.

Results

The average expression levels of DNMT1 mRNA and protein in Hela and Siha cells were decreased significantly compared with control group. The flow cytometry and MTT results showed that Hela and Siha cells apoptosis rates and cell viabilities were 19.4 ± 2.90%, 25.7 ± 3.92% as well as 86.7 ± 3.12%, 84.16 ± 2.67% respectively 48 h after transfection (P < 0.01). Furthermore, the promoter methylation of five tumor suppressor genes was decreased with the increased mRNA expression after silencing DNMT1, whereas there were no significant changes in PTEN and FHIT genes in Hela cells, and CHFR and FHIT genes in Siha cells.

Conclusions

Our experimental results demonstrate that methylation status of DNMT1 can influence several important tumor suppressor genes activity in cervical tumorigenesis and may have the potential to become an effective target for treatment of cervical cancer.

Impact of the DNA methyltransferases expression on the methylation status of apoptosis-associated genes in glioblastoma multiforme

Disruption of apoptosis is considered as an important factor aiding tumorigenesis, and aberrant DNA methylation of apoptosis-associated genes could be an important and significant mechanism through which tumor cells avoid apoptosis. However, little is known about (1) the impact of methylation status of apoptosis-associated genes on the presence of apoptosis evasion phenotype in glioma; and (2) the molecular mechanism governing the aberrant methylation of apoptosis-associated genes in glioma. By analyzing human glioma biopsies, we first show that low level of apoptosis in tumor is correlated with aberrant methylation of the bcl-2, bax and XAF-1 genes, but not with the aberrant methylation of the bcl-w, survivin, TMS1, caspase-8 and HRK genes. Our work also indicates that the expression levels of DNA methyltransferase 1 (Dnmt1), Dnmt3b and Dnmt1/Dnmt3a coregulate the methylation status of survivin, TMS1 and caspase-8, whereas no correlation was observed between the expression level of Dnmts and the methylation status of the bcl-w, bcl-2, bax, XAF-1 and HRK genes. Thus, these results indicate that the epigenetic regulation of some apoptosis-regulated genes could dictate whether glioma harbors the apoptosis evasion phenotype, and provide some bases to the identification of the methylation machineries of apoptosis-associated genes for which the Dnmt expression acts as a limiting factor.

CXCL12 (SDF1alpha)-CXCR4/CXCR7 pathway inhibition: an emerging sensitizer for anticancer therapies?

Addition of multiple molecularly targeted agents to the existing armamentarium of chemotherapeutics and radiotherapies represents a significant advance in the management of several advanced cancers. In certain tumor types with no efficacious therapy options, these agents have become the first line of therapy, for example, sorafenib in advanced hepatocellular carcinoma or bevacizumab in recurrent glioblastoma. Unfortunately, in many cases, the survival benefits are modest, lasting only weeks to a few months. Moreover, they may not show benefit in patients with localized disease (i.e., in the adjuvant setting). Recent studies have provided increasing evidence that activation of the chemokine CXCL12 (SDF1α) pathway is a potential mechanism of tumor resistance to both conventional therapies and biological agents via multiple complementary actions: (i) by directly promoting cancer cell survival, invasion, and the cancer stem and/or tumor-initiating cell phenotype; (ii) by recruiting "distal stroma" (i.e., myeloid bone marrow-derived cells) to indirectly facilitate tumor recurrence and metastasis; and (iii) by promoting angiogenesis directly or in a paracrine manner. Here, we discuss recent preclinical and clinical data that support the potential use of anti-CXCL12 agents (e.g., AMD3100, NOX-A12, or CCX2066) as sensitizers to currently available therapies by targeting the CXCL12/CXCR4 and CXCL12/CXCR7 pathways.

Depletion of DNMT3A suppressed cell proliferation and restored PTEN in hepatocellular carcinoma cell

Promoter hypermethylation mediated by DNA methyltransferases (DNMTs) is the main reason for epigenetic inactivation of tumor suppressor genes (TSGs). Previous studies showed that DNMT1 and DNMT3B play an important role in CpG island methylation in tumorigenesis. Little is known about the role of DNMT3A in this process, especially in hepatocellular carcinoma (HCC). In the present study, increased DNMT3A expression in 3 out of 6 HCC cell lines and 16/25 (64%) HCC tissues implied that DNMT3A is involved in hepatocellular carcinogenesis. Depletion of DNMT3A in HCC cell line SMMC-7721 inhibited cell proliferation and decreased the colony formation (about 65%). Microarray data revealed that 153 genes were upregulated in DNMT3A knockdown cells and that almost 71% (109/153) of them contain CpG islands in their 5′ region. 13 of them including PTEN, a crucial tumor suppressor gene in HCC, are genes involved in cell cycle and cell proliferation. Demethylation of PTEN promoter was observed in DNMT3A-depleted cells implying that DNMT3A silenced PTEN via DNA methylation. These results provide insights into the mechanisms of DNMT3A to regulate TSGs by an epigenetic approach in HCC.

Increased CXCR4 expression in AsPC1 pancreatic carcinoma cells with RNA interference-mediated knockdown of DNMT1 and DNMT3B

The effect of DNA methylation on CXCR4 expression has been demonstrated in pancreatic cancer and melanoma cells, but little is known about the effect of DNA methyltransferases 1 and 3 (DNMT1 and DNMT3B) on CXCR4 expression. Employing lentiviral vectors, we created stable RNA interference-mediated knockdown of DNMT1 and DNMT3B in AsPC1 pancreatic cancer cells. Using reverse transcription real-time quantitative PCR and flow cytometric analysis, we evaluated the increase in the expression of CXCR4 transcript and protein levels in these cells. Bisulfite sequencing analysis showed that the level of promoter demethylation appeared more effective in cells with knockdown of DNMT1 than in those with DNMT3B knockdown. Furthermore, the combined RNA interference knockdown of both DNMT1 and DNMT3B increased promoter demethylation, leading to a slight increase in CXCR4 expression. However, the demethylating agent 5-Aza-2'-deoxycytidine exhibited the strongest effect on promoter demethylation, which correlated with the highest production of CXCR4 transcript and protein in AsPC1 cells. Our results indicate that DNMT1 plays the main role in maintenance of methylation of CXCR4 promoter, while DNMT3B may function as an accessory DNA methyltransferase to modulate CXCR4 expression in AsPC1 cells.

c-myb activates CXCL12 transcription in T47D and MCF7 breast cancer cells

Chemokine C-X-C motif ligand 12 (CXCL12) is a potent chemotactic and angiogenic factor that has been proposed to play a role in organ-specific metastasis and angiogenic activity in several malignancies. In this study, we found that the overexpression of c-myb could elevate CXCL12 mRNA level and CXCL12 promoter activity in human T47D and MCF-7 breast cancer cells. Chromatin immunoprecipitation assay demonstrated that c-myb could bind to the CXCL12 promoter in the cells transfected with cmyb expression vector. c-myb siRNA attenuated CXCL12 promoter activity and the binding of c-myb to the CXCL12 promoter in T47D and MCF-7 cells. These results indicated that c-myb could activate CXCL12 promoter transcription.

Tamoxifen epigenetically modulates CXCL12 expression in MCF-7 breast cancer cells

The CXCL12 chemokine binds to the CXCR4 receptor and contributes to survival, proliferation, and migration of malignant cells. Recent reports indicate that breast cancer cells lacking expression of CXCL12 but exhibiting CXCR4 can metastasize to target organs that secrete CXCL12. We observed that Tamoxifen (Tam), similarly to 5-dAzaC, results in significantly increased levels of CXCL12 transcript and protein in MCF-7 breast cancer cells. Bisulfite sequencing suggests that Tam, similarly to 5-dAzaC, may increase CXCL12 expression via reduction in methylation of cytosine in the cytosine-guanosine (CpG) dinucleotide island of the CXCL12 promoter of MCF-7 cells. Our results, together with findings of other researches, may suggest that Tam epigenetically activates CXCL12 expression in breast cancer cells and can make these cells less susceptible to attraction by exogenous CXCL12 to metastasis sites.

Down-regulation of CXCL12 mRNA expression by promoter hypermethylation and its association with metastatic progression in human breast carcinomas

PURPOSE

Not only is the expression of CXCR4 on breast cancers a key determinant of tumor metastasis, CXCL12 exhibiting peak levels of constitutive expression in organs representing the first destinations of cancer metastasis, but is proposed to be also essential for the organ-specific metastatic process.

METHODS

In this study, the expressions of CXCR4 and CXCL12 were investigated using quantitative RT-PCR and immunohistochemistry in samples of 63 primary breast carcinomas and 20 normal breast tissues. Using methylation-specific PCR, we also analyzed the methylation status of CXCL12.

RESULTS

Both up-regulation of CXCR4 and down-regulation of CXCL12 were observed in primary breast carcinomas. Over-expression of CXCR4 mRNA was significantly related to lymph node metastasis status and strong Her-2 expression, while decreased expression of CXCL12 mRNA was significantly associated with positive lymph node metastasis and estrogen receptor negativity. Methylation-specific PCR showed that 52.4% of breast tumors were hypermethylated in the CXCL12 promoter region. The expression levels of DNA methyltransferase (DNMT) 1 and DNMT3B were significantly higher in the CXCL12-methylated breast carcinomas than in the CXCL12-unmethylated ones.

CONCLUSIONS

In summary, DNA hypermethylation of CXCL12 plays an important role in the down-regulation of CXCL12 expression in breast carcinomas. Cancer cells lacking expression of CXCL12, but maintaining over-expression of CXCR4, can selectively spread to target organs in which the ligand is highly secreted.

The critical role of SDF-1/CXCR4 axis in cancer and cancer stem cells metastasis

Chemokines exert their multifunctional role in several physiologic and pathologic processes through interaction with their specific receptors. Much evidence have revealed that metastatic spread tumor cells may use chemokine-mediated mechanisms. In particular, an involvement of stromal cell-derived factor-1 (SDF-1) in growth of primary tumors and in metastatic process has been demonstrated. Indeed, it has been suggested that CXCR4 expression by tumor cells, plays a critical role in cell metastasis by a chemotactic gradient to organs expressing the ligand SDF-1. Moreover, CXCR4 overexpression correlated with poor prognosis in many types of cancer. In physiologic condition, SDF-1 also plays an essential role modulating stem cell proliferation, survival, and homing through its canonical receptor CXCR4. Recently, several studies have demonstrated the existence of a small subset of cancer cells which share many characteristics with stem cells and named cancer stem cells (CSC). They constitute a reservoir of self-sustaining cells with the ability to maintain the tumor growth. In particular, most of them express CXCR4 receptor and respond to a chemotactic gradient of its specific ligand SDF-1, suggesting that CSC probably represent a subpopulation capable of initiating metastasis. This review focuses on the role of SDF-1/CXCR4 axis in cancer and in the metastatic progression by tumoral cells, as well as the role of CSC in tumor pathogenesis and in metastatic process. A better understanding of migratory mechanism involving cancer cells and CSC provides a powerful tool for developing novel therapies reducing both local and distant recurrences.