Epigenetic inactivation of secreted Frizzled-related proteins in acute myeloid leukaemia

Differential DNA methylation associated with multiple sclerosis and disease modifying treatments in an underrepresented minority population

Black and Hispanic American patients frequently develop earlier onset of multiple sclerosis (MS) and a more severe disease course that can be resistant to disease modifying treatments. The objectives were to identify differential methylation of genomic DNA (gDNA) associated with disease susceptibility and treatment responses in a cohort of MS patients from underrepresented minority populations. Patients with MS and controls with non-inflammatory neurologic conditions were consented and enrolled under an IRB-approved protocol. Approximately 64% of donors identified as Black or African American and 30% as White, Hispanic-Latino. Infinium MethylationEPIC bead arrays were utilized to measure epigenome-wide gDNA methylation of whole blood. Data were analyzed in the presence and absence of adjustments for unknown covariates in the dataset, some of which corresponded to disease modifying treatments. Global patterns of differential methylation associated with MS were strongest for those probes that showed relative demethylation of loci with lower M values. Pathway analysis revealed unexpected associations with shigellosis and amoebiasis. Enrichment analysis revealed an over-representation of probes in enhancer regions and an under-representation in promoters. In the presence of adjustments for covariates that included disease modifying treatments, analysis revealed 10 differentially methylated regions (DMR's) with an FDR <1E-77. Five of these genes (ARID5B, BAZ2B, RABGAP1, SFRP2, WBP1L) are associated with cancer risk and cellular differentiation and have not been previously identified in MS studies. Hierarchical cluster and multi-dimensional scaling analysis of differential DNA methylation at 147 loci within those DMR's was sufficient to differentiate MS donors from controls. In the absence of corrections for disease modifying treatments, differential methylation in patients treated with dimethyl fumarate was associated with immune regulatory pathways that regulate cytokine and chemokine signaling, axon guidance, and adherens junctions. These results demonstrate possible associations of gastrointestinal pathogens and regulation of cellular differentiation with MS susceptibility in our patient cohort. This work further suggests that analyses can be performed in the presence and absence of corrections for immune therapies. Because of their high representation in our patient cohort, these results may be of specific relevance in the regulation of disease susceptibility and treatment responses in Black and Hispanic Americans.

Osteoprogenitor SFRP1 prevents exhaustion of hematopoietic stem cells via PP2A-PR72/130-mediated regulation of p300

Remodeling of the bone marrow microenvironment in chronic inflammation and in aging reduces hematopoietic stem cell (HSC) function. To assess the mechanisms of this functional decline of HSC and find strategies to counteract it, we established a model in which the Sfrp1 gene was deleted in Osterix+ osteolineage cells (OS1Δ/Δ mice). HSC from these mice showed severely diminished repopulating activity with associated DNA damage, enriched expression of the reactive oxygen species pathway and reduced single-cell proliferation. Interestingly, not only was the protein level of Catenin beta-1 (bcatenin) elevated, but so was its association with the phosphorylated co-activator p300 in the nucleus. Since these two proteins play a key role in promotion of differentiation and senescence, we inhibited in vivo phosphorylation of p300 through PP2A-PR72/130 by administration of IQ-1 in OS1Δ/Δ mice. This treatment not only reduced the b-catenin/phosphop300 association, but also decreased nuclear p300. More importantly, in vivo IQ-1 treatment fully restored HSC repopulating activity of the OS1Δ/Δ mice. Our findings show that the osteoprogenitor Sfrp1 is essential for maintaining HSC function. Furthermore, pharmacological downregulation of the nuclear b-catenin/phospho-p300 association is a new strategy to restore poor HSC function.

The Role of Notch and Wnt Signaling in MSC Communication in Normal and Leukemic Bone Marrow Niche

Notch and Wnt signaling are highly conserved intercellular communication pathways involved in developmental processes, such as hematopoiesis. Even though data from literature support a role for these two pathways in both physiological hematopoiesis and leukemia, there are still many controversies concerning the nature of their contribution. Early studies, strengthened by findings from T-cell acute lymphoblastic leukemia (T-ALL), have focused their investigation on the mutations in genes encoding for components of the pathways, with limited results except for B-cell chronic lymphocytic leukemia (CLL); in because in other leukemia the two pathways could be hyper-expressed without genetic abnormalities. As normal and malignant hematopoiesis require close and complex interactions between hematopoietic cells and specialized bone marrow (BM) niche cells, recent studies have focused on the role of Notch and Wnt signaling in the context of normal crosstalk between hematopoietic/leukemia cells and stromal components. Amongst the latter, mesenchymal stromal/stem cells (MSCs) play a pivotal role as multipotent non-hematopoietic cells capable of giving rise to most of the BM niche stromal cells, including fibroblasts, adipocytes, and osteocytes. Indeed, MSCs express and secrete a broad pattern of bioactive molecules, including Notch and Wnt molecules, that support all the phases of the hematopoiesis, including self-renewal, proliferation and differentiation. Herein, we provide an overview on recent advances on the contribution of MSC-derived Notch and Wnt signaling to hematopoiesis and leukemia development.

WNT Signaling in Hematological Malignancies

The role of the WNT signaling pathway in key cellular processes, such as cell proliferation, differentiation and migration is well documented. WNT signaling cascade is initiated by the interaction of WNT ligands with receptors belonging to the Frizzled family, and/or the ROR1/ROR2 and RYK families. The downstream signaling cascade results in the activation of the canonical β-catenin dependent pathway, ultimately leading to transcriptional control of cell proliferation, or the non-canonical pathway, mainly acting on cell migration and cell polarity. The high level of expression of both WNT ligands and WNT receptors in cancer cells and in the surrounding microenvironment suggests that WNT may represent a central conduit of interactions between tumor cells and microenviroment. In this review we will focus on WNT pathways deregulation in hematological cancers, both at the ligand and receptor levels. We will review available literature regarding both the classical β-catenin dependent pathway as well as the non-canonical pathway, with particular emphasis on the possible exploitation of WNT aberrant activation as a therapeutic target, a notion supported by preclinical data.

Use of DNA methylation profiling in translational oncology

DNA methylation is a highly regulated process that has a critical role in human development and homeostatic control of the cell. The number of genes affected by anomalous DNA methylation in cancer-associated pathways is swiftly accelerating and with the advancement of molecular technologies, new layers of complexity are opening up and refining our strategies to combat cancer. DNA methylation profiling is an essential facet to understanding malignant transformation and is becoming an increasingly important tool for cancer diagnosis, prognosis and therapy monitoring. In this review, the role of DNA methylation in normal cellular function is discussed, as well as how epigenetic aberrations override normal cellular cues that lead to tumor initiation and propagation. The review also focuses on the latest advancements in DNA methylation profiling as a biomarker for early cancer detection, predicting patient clinical outcomes and responses to treatment and provides new insights into epigenetic-based therapy in clinical oncology.

Alterations in WNT Signaling in Leukemias

The WNT/β-catenin signaling pathway plays an important role in the differentiation and proliferation of hematopoietic cells. In recent years, special attention has been paid to the role of impairments in the WNT signaling pathway in pathogenesis of malignant neoplasms of the hematopoietic system. Disorders in the WNT/β-catenin signaling in leukemias identified to date include hypersensitivity to the WNT ligands, epigenetic repression of WNT antagonists, overexpression of WNT ligands, impaired β-catenin degradation in the cytoplasm, and changes in the activity of the TCF/Lef transcription factors. At the molecular level, these impairments involve overexpression of the FZD protein, hypermethylation of the SFRP, DKK, WiF, Sox, and CXXC gene promoters, overexpression of Lef1 and plakoglobin, mutations in GSK3β, and β-catenin phosphorylation by the BCR-ABL kinase. This review is devoted to the systematization of these data.

WNT Signaling in Cancer Immunosurveillance

Deregulated WNT signaling has been shown to favor malignant transformation, tumor progression, and resistance to conventional cancer therapy in a variety of preclinical and clinical settings. Accumulating evidence suggests that aberrant WNT signaling may also subvert cancer immunosurveillance, hence promoting immunoevasion and resistance to multiple immunotherapeutics, including immune checkpoint blockers. Here, we discuss the molecular and cellular mechanisms through which WNT signaling influences cancer immunosurveillance and present potential therapeutic avenues to harness currently available WNT modulators for cancer immunotherapy.

Identification of DNA methylation prognostic signature of acute myelocytic leukemia

BACKGROUND

The aim of this study is to find the potential survival related DNA methylation signature capable of predicting survival time for acute myelocytic leukemia (AML) patients.

METHODS

DNA methylation data were downloaded. DNA methylation signature was identified in the training group, and subsequently validated in an independent validation group. The overall survival of DNA methylation signature was performed. Functional analysis was used to explore the function of corresponding genes of DNA methylation signature. Differentially methylated sites and CpG islands were also identified in poor-risk group.

RESULTS

A DNA methylation signature involving 8 DNA methylation sites and 6 genes were identified. Functional analysis showed that protein binding and cytoplasm were the only two enriched Gene Ontology terms. A total of 70 differentially methylated sites and 6 differentially methylated CpG islands were identified in poor-risk group.

CONCLUSIONS

The identified survival related DNA methylation signature adds to the prognostic value of AML.

Epigenetic reprogramming converts human Wharton's jelly mesenchymal stem cells into functional cardiomyocytes by differential regulation of Wnt mediators

Background

Lineage commitment of mesenchymal stem cells (MSCs) to cardiac differentiation is controlled by transcription factors that are regulated by epigenetic events, mainly histone deacetylation and promoter DNA methylation. Here, we studied the differentiation of human Wharton’s jelly MSCs (WJMSCs) into the cardiomyocyte lineage via epigenetic manipulations.

Methods

We introduced these changes using inhibitors of DNA methyl transferase and histone deacetylase, DC301, DC302, and DC303, in various combinations. We characterized for cardiogenic differentiation by assessing the expression of cardiac-specific markers by immunolocalization, quantitative RT-PCR, and flow cytometry. Cardiac functional studies were performed by FURA2AM staining and Greiss assay. The role of Wnt signaling during cardiac differentiation was analyzed by quantitative RT-PCR. In-vivo studies were performed in a doxorubicin-induced cardiotoxic mouse model by injecting cardiac progenitor cells. Promoter methylation status of the cardiac transcription factor Nkx2.5 and the Wnt antagonist, secreted frizzled-related protein 4 (sFRP4), after cardiac differentiation was studied by bisulfite sequencing.

Results

By induction with DC301 and DC302, WJMSCs differentiated into cardiomyocyte-like structures with an upregulation of Wnt antagonists, sFRP3 and sFRP4, and Dickkopf (Dkk)1 and Dkk3. The cardiac function enhancer, vinculin, and DDX20, a DEAD-box RNA helicase, were also upregulated in differentiated cardiomyocytes. Additionally, bisulfite sequencing revealed, for the first time in cardiogenesis, that sFRP4 is activated by promoter CpG island demethylation. In vivo, these MSC-derived cardiac progenitors could not only successfully engraft to the site of cardiac injury in mice with doxorubicin-induced cardiac injury, but also form functional cardiomyocytes and restore cardiac function.

Conclusion

The present study unveils a link between Wnt inhibition and epigenetic modification to initiate cardiac differentiation, which could enhance the efficacy of stem cell therapy for ischemic heart disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-017-0638-7) contains supplementary material, which is available to authorized users.

Hypermethylation of secreted frizzled-related proteins predicts poor prognosis in non-M3 acute myeloid leukemia

Objective

Secreted frizzled-related proteins (SFRPs) as Wnt signaling antagonists have been found to be dysregulated by promoter hypermethylation in several cancers including acute myeloid leukemia (AML). This study aimed to investigate the methylated status of SFRPs promoter region and its clinical relevance in Chinese non-M3 AML patients.

Methods

SFRPs methylation in 139 primary non-M3 AML patients was determined using methylation-specific real-time quantitative polymerase chain reaction.

Results

The frequency of aberrant methylation was as follows: 30.2% for SFRP1, 27.3% for SFRP2, 5.0% for SFRP4, and 1.4% for SFRP5. Hypermethylation of at least one SFRP gene occurred in 51.8% (72/139) of non-M3 AML patient samples, which was significantly higher compared to normal control (0/21) (P<0.001). Hypermethylation of SFRP1 was potentially associated with N/K-RAS mutations (P=0.043), and the frequency of SFRPs methylation was higher in patients ≥50 years compared to those <50 years, especially for SFRP2 (P<0.05). Furthermore, both whole cohort and cytogenetically normal (CN) patients with high SFRPs-methylated group showed a shorter overall survival (OS) compared to those with low group (P=0.036 and P=0.035, respectively). Moreover, Cox regression multivariate analysis revealed that SFRPs hypermethylation acts as an independent prognostic biomarker among both whole cohort (hazard ratio =1.804, P=0.026) and CN (hazard ratio =2.477, P=0.023) patients. In leukemic cell line HL60 treated with 5-aza-2′-deoxycytidine, the alteration of SFRP1/2 expression inversely correlated with change in SFRP1/2 methylation (r=−0.975, P=0.005 and r=−0.975, P=0.005, respectively). A tendency of negative correlation was observed between SFRP1 expression and its promoter methylation in AML patients (r=−0.334, P=0.038).

Conclusion

These findings suggested that hypermethylation of SFRP1/2 was a frequent event and silenced SFRP1/2 expression in AML. Moreover, hypermethylation of SFRPs promoter was an adverse risk factor for OS in Chinese non-M3 AML patients.

[Aberrant methylation of the promoter regions of the SOX7 and p15INK4b genes and Wnt signaling pathway antagonists in patients with acute myeloid leukemias]

AIM

to investigate the methylation status of the SOX7 and p15NK4b genes and Wnt signaling pathway antagonists in patients with acute myeloid leukemia (AML) in order to assess the association of the rate of aberrant methylation (AM) with the morphological variant and pattern of chromosomal aberrations, as well as the impact of the methylation status on survival.

SUBJECTS AND METHODS

The data of 57 AML patients aged 20 to 79 years were analyzed. The methylation status of the genes was studied by methylation-specific polymerase chain reaction.

RESULTS

The signs of the AM of ≥1 gene were detected in 52 (91.2%) of the 57 patients. The most common finding was AM of simultaneously 2 or 3 genes: in 29.8 and 21.1% of the patients, respectively. Concurrent methylation of 3-5 genes proved to be a more frequent finding in AML patients with myelodysplasia: in 7 (70%) of 10 patients. The proportion of patients with methylation of 5 genes was considerably higher in a group of patients with a complex karyotype: 50% versus 8.3% among other patients (odds ratio: 11.0; 95% confidence interval 2.0 to 61.6; p=0.01). There were no differences in the median overall and relapse-free survival rates in patients with a normal karyotype and without FLT3 and NPM mutations, who received induction therapy, in relation to the number of genes with AM.

CONCLUSION

AM of the p15NK4b and SOX7 genes and Wnt signaling pathway antagonists is detected in the majority of patients with AML, which allows hypomethylating agents to be recommended for the treatment of patients who cannot use intensive cytostatic therapy for different reasons. The detection of a large number of genes with the aberrant methylation status in most AML patients with myelodysplasia or a complex karyotype serves as the basis for initiating trials to evaluate the efficiency of a combination of 5-azacytidine and cytostatics.

Loss of Sfrp2 in the Niche Amplifies Stress-Induced Cellular Responses, and Impairs the In Vivo Regeneration of the Hematopoietic Stem Cell Pool

Sfrp2 is overexpressed in stromal cells which maintain hematopoietic stem cells (HSCs) during in vitro culture. We here showed, that coculture of hematopoetic cells with stromal cells with reduced expression of Sfrp2 increases the number lineage-negative Kit(+) Sca-1(+) (LSK) and progenitor cells in vitro. The LSK cells from these cocultures showed activation of canonical Wnt signaling, higher levels of Ki-67, BrdU incorporation, and the number of γH2A.X positive foci. Total repopulating activity of these cultures was, however, diminished, indicating loss of HSC. To extend these in vitro data, we modelled stress in vivo, i.e., by aging, or 5-FU treatment in Sfrp2(-) (/) (-) mice, or replicative stress in regeneration of HSCs in Sfrp2(-) (/) (-) recipients. In all three in vivo stress situations, we noted an increase of LSK cells, characterized by increased levels of β-catenin and cyclin D1. In the transplantation experiments, the increase in LSK cells in primary recipients was subsequently associated with a progressive loss of HSCs in serial transplantations. Similar to the in vitro coculture stress, in vivo genotoxic stress in 5-FU-treated Sfrp2(-) (/) (-) mice increased cell cycle activity of LSK cells with higher levels of BrdU incorporation, increased expression of Ki-67, and canonical Wnt signaling. Importantly, as noted in vitro, increased cycling of LSKs in vivo was accompanied by a defective γH2A.X-dependent DNA damage response and depolarized localization of acetylated H4K16. Our experiments support the view that Sfrp2 expression in the niche is required to maintain the HSC pool by limiting stress-induced DNA damage and attenuating canonical Wnt-mediated HSC activation. Stem Cells 2016;34:2381-2392.

Wnt/β-catenin signaling in bone marrow niche

The bone marrow (BM) niche is a specific physiological environment for hematopoietic and non-hematopoietic stem cells (HSCs). Several signaling pathways (including Wnt/β-catenin) regulate various aspects of stem cell growth, function and death in the BM niche. In addition, the canonical Wnt pathway is crucial for directing self-renewal and differentiation as important mechanisms in many types of stem cells. We review the role of the Wnt/β-catenin pathway in the BM niche and its importance in stem cells. Relevant literature was identified by a PubMed search (1997-2014) of English-language literature by using the following keywords: BM niche, Wnt/β-catenin signaling, osteoblast, osteoclast and bone disease. The Wnt/β-catenin pathway regulates the stability of the β-catenin proto-oncogene. The stabilized β-catenin then translocates to the nucleus, forming a β-catenin-TCF/LEF complex regulating the transcription of specific target genes. Stem cells require β-catenin to mediate their response to Wnt signaling for maintenance and transition from the pluripotent state during embryogenesis. In adult stem cells, Wnt signaling functions at various hierarchical levels to contribute to the specification of the diverse tissues. Aberrant Wnt/β-catenin signaling and its downstream transcriptional regulators are observed in several malignant stem cells and human cancers. Because Wnt signaling can maintain stem cells and cancer cells, the ability to modulate the Wnt pathway either positively or negatively may be of therapeutic relevance. The controlled activation of Wnt signaling might allow us to enhance stem and progenitor cell activity when regeneration is needed.

Wnt signaling in leukemias and myeloma: T-cell factors are in control

Aberrant activation of the Wnt pathway has been implicated in the pathogenesis of many malignancies, especially solid tumors. During the past decade it also became clear that in hematological malignancies abnormal regulation of the Wnt pathway can either be causative or enhance disease progression, which will be discussed in detail in this review.

Secreted frizzled related proteins: Implications in cancers

The Wnt (wingless-type) signaling pathway plays an important role in embryonic development, tissue homeostasis, and tumor progression becaluse of its effect on cell proliferation, migration, and differentiation. Secreted frizzled-related proteins (SFRPs) are extracellular inhibitors of Wnt signaling that act by binding directly to Wnt ligands or to Frizzled receptors. In recent years, aberrant expression of SFRPs has been reported to be associated with numerous cancers. As gene expression of SFRP members is often lost through promoter hypermethylation, inhibition of methylation through the use of epigenetic modifying agents could renew the expression of SFRP members and further antagonize deleterious Wnt signaling. Several reports have described epigenetic silencing of these Wnt signaling antagonists in various human cancers, suggesting their possible role as tumor suppressors. SFRP family members thus come across as potential tools in combating Wnt-driven tumorigenesis. However, little is known about SFRP family members and their role in different cancers. This review comprehensively covers all the available information on the role of SFRP molecules in various human cancers.

Importance of epigenetic changes in cancer etiology, pathogenesis, clinical profiling, and treatment: what can be learned from hematologic malignancies?

Epigenetic alterations represent a key cancer hallmark, even in hematologic malignancies (HMs) or blood cancers, whose clinical features display a high inter-individual variability. Evidence accumulated in recent years indicates that inactivating DNA hypermethylation preferentially targets the subset of polycomb group (PcG) genes that are regulators of developmental processes. Conversely, activating DNA hypomethylation targets oncogenic signaling pathway genes, but outcomes of both events lead in the overexpression of oncogenic signaling pathways that contribute to the stem-like state of cancer cells. On the basis of recent evidence from population-based, clinical and experimental studies, we hypothesize that factors associated with risk for developing a HM, such as metabolic syndrome and chronic inflammation, trigger epigenetic mechanisms to increase the transcriptional expression of oncogenes and activate oncogenic signaling pathways. Among others, signaling pathways associated with such risk factors include pro-inflammatory nuclear factor κB (NF-κB), and mitogenic, growth, and survival Janus kinase (JAK) intracellular non-receptor tyrosine kinase-triggered pathways, which include signaling pathways such as transducer and activator of transcription (STAT), Ras GTPases/mitogen-activated protein kinases (MAPKs)/extracellular signal-related kinases (ERKs), phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR), and β-catenin pathways. Recent findings on epigenetic mechanisms at work in HMs and their importance in the etiology and pathogenesis of these diseases are herein summarized and discussed. Furthermore, the role of epigenetic processes in the determination of biological identity, the consequences for interindividual variability in disease clinical profile, and the potential of epigenetic drugs in HMs are also considered.

Normal hematopoiesis and hematologic malignancies: role of canonical Wnt signaling pathway and stromal microenvironment

Wnts are a family of evolutionary-conserved secreted signaling molecules critically involved in a variety of developmental processes and in cell fate determination. A growing body of evidence suggests that Wnt signaling plays a crucial role in the influence of bone marrow stromal microenvironment on the balance between hematopoietic stem cell self-renewal and differentiation. Emerging clinical and experimental evidence also indicates Wnt signaling involvement in the disruption of the latter balance in hematologic malignancies, where the stromal microenvironment favors the homing of cancer cells to the bone marrow, as well as leukemia stem cell development and chemoresistance. In the present review, we summarize and discuss the role of the canonical Wnt signaling pathway in normal hematopoiesis and hematologic malignancies, with regard to recent findings on the stromal microenvironment involvement in these process and diseases.

B-lineage transcription factors and cooperating gene lesions required for leukemia development

Differentiation of hematopoietic stem cells into B lymphocytes requires the concerted action of specific transcription factors, such as RUNX1, IKZF1, E2A, EBF1 and PAX5. As key determinants of normal B-cell development, B-lineage transcription factors are frequently deregulated in hematological malignancies, such as B-cell precursor acute lymphoblastic leukemia (BCP-ALL), and affected by either chromosomal translocations, gene deletions or point mutations. However, genetic aberrations in this developmental pathway are generally insufficient to induce BCP-ALL, and often complemented by genetic defects in cytokine receptors and tyrosine kinases (IL-7Rα, CRLF2, JAK2 and c-ABL1), transcriptional cofactors (TBL1XR1, CBP and BTG1), as well as the regulatory pathways that mediate cell-cycle control (pRB and INK4A/B). Here we provide a detailed overview of the genetic pathways that interact with these B-lineage specification factors, and describe how mutations affecting these master regulators together with cooperating lesions drive leukemia development.

Epigenetic dysregulation of secreted frizzled-related proteins in myeloproliferative neoplasms complements the JAK2V617F-mutation

Background

Secreted frizzled-related proteins (SFRPs) are antagonists of the Wnt signaling pathway, which plays a central role in stem cell maintenance and differentiation of stem cells and hematopoietic progenitors. Epigenetic downregulation of SFRPs by promoter hypermethylation has been described to be involved in the pathogenesis of hematopoietic malignancies. There is an association between aberrant Wnt signaling and the established cancer stem cell concept. In contrast to BCR-ABL1-positive chronic myeloid leukemia CML, BCR-ABL1-negative myeloproliferative neoplasms (Ph^-MPN) are characterized by the frequent occurrence of an autoactivating mutation in the JAK2 tyrosine kinase (JAK2V617F) or other mutations in the JAK-STAT pathway. However, pathogenetic mechanisms of JAK2 mutated or unmutated Ph^-MPN remain not completely understood. We determined the promoter methylation status of SFRP-1, -2, -4, and -5 in 57 MPN patient samples by methylation-specific polymerase chain reaction (PCR) (MSP). JAK2V617F was assessed by allele-specific PCR.

Results

Aberrant methylation among primary MPN samples was 4% for SFRP-1, 25% for SFRP-2, 2% for SFRP-4, and 0% for SFRP-5. Hypermethylation of SFRP-2, which was the most frequently hypermethylated gene in our study, could not be correlated to any specific MPN subtype. However, we detected a significant correlation between SFRP-2 methylation and presence of a JAK2V617F mutation (P = 0.008). None of the 10 CML samples showed any SFRP-methylation.

Conclusions

Our data indicate that epigenetic dysregulation of the Wnt signaling pathway is a common event in MPN with aberrant methylation of at least one SFRP being detected in 25% of the primary patient samples and in 30% if only accounting for Ph^-MPN. A significant correlation between SFRP-2 methylation and presence of JAK2V617F in our data supports the hypothesis that epigenetic dysregulation may be a complementary mechanism to genetic aberrations. Aberrant methylation of crucial stem cell maintenance genes seems to contribute to disease pathogenesis in Ph^-MPN.

A systematic comparison of quantitative high-resolution DNA methylation analysis and methylation-specific PCR

Assessment of DNA methylation has become a critical factor for the identification, development and application of methylation based biomarkers. Here we describe a systematic comparison of a quantitative high-resolution mass spectrometry-based approach (MassARRAY), pyrosequencing and the broadly used methylation-specific PCR (MSP) technique analyzing clinically relevant epigenetically silenced genes in acute myeloid leukemia (AML). By MassARRAY and pyrosequencing, we identified significant DNA methylation differences at the ID4 gene promoter and in the 5' region of members of the SFRP gene family in 62 AML patients compared with healthy controls. We found a good correlation between data obtained by MassARRAY and pyrosequencing (correlation coefficient R(2) = 0.88). MSP-based assessment of the identical samples showed less pronounced differences between AML patients and controls. By direct comparison of MSP-derived and MassARRAY-based methylation data as well as pyrosequencing, we could determine overestimation of DNA methylation data by MSP. We found sequence-context dependent highly variable cut-off values of quantitative DNA methylation values serving as discriminator for the two MSP methylation categories. Moreover, good agreements between quantitative methods and MSP could not be achieved for all investigated loci. Significant correlation of the quantitative assessment but not of MSP-derived methylation data with clinically important characteristics in our patient cohort demonstrated clinical relevance of quantitative DNA methylation assessment. Taken together, while MSP is still the most commonly applied technique for DNA methylation assessment, our data highlight advantages of quantitative approaches for precise characterization and reliable biomarker use of aberrant DNA methylation in primary patient samples, particularly.

Cancer stem cells and epithelial-mesenchymal transition: concepts and molecular links

The epithelial-mesenchymal transition (EMT) confers mesenchymal properties on epithelial cells and has been closely associated with the acquisition of aggressive traits by carcinoma cells. EMT programs are orchestrated by a set of pleiotropically acting transcription factors (TFs). The actions of these EMT-TFs enable the early steps of metastasis: local invasion and subsequent dissemination of carcinoma cells to distant sites. However, in most malignancies, the subsequent outgrowth of micrometastatic deposits into macroscopic metastases has the greatest impact on clinical progression. Such metastatic "colonization" reflects the ability of disseminated tumor cells to adapt to a foreign tissue microenvironment. The outgrowth of a metastasis is also thought to be associated with self-renewal, the defining cellular trait of cancer stem cells (CSCs), also termed tumor-initiating cells. Importantly, molecular links between EMT-TFs and self-renewal have emerged, suggesting that EMT programs play critical roles both early and late in the metastatic cascade. The genetic and epigenetic mechanisms that regulate the activation of EMT-TFs and the traits they induce are areas under intensive investigation. Such studies may provide new opportunities for therapeutic intervention and help to overcome tumor heterogeneity and therapeutic resistance.

Clinical applications of epigenetic markers and epigenetic profiling in myeloid malignancies

Aberrant DNA methylation is frequent in the myeloid malignancies, particularly myelodysplastic syndrome (MDS) and acute myelogenous leukemia (AML). Promoter CpG methylation is correlated with silencing of tumor-suppressor genes (TSGs) in specific pathways that are also targets of mutation or other mechanisms of inactivation, and is thought to contribute to disease progression and poor prognosis. Epigenetic contributions to myeloid pathogenesis are more complex. Examples include TSG inactivation and oncogenic activation associated with formation of altered chromatin separate from CpG methylation. Epigenetic dysregulation occurs at multiple disease stages and at non-CpG island genomic sites, and also includes genomic hypomethylation and small RNA mechanisms of epigenetic regulation. Identification of recurrent mutations in potential epigenetic regulators, including TET2, IDH1, IDH2, DNMT3A, UTX, and ASXL1, were recently described. Accordingly, therapeutics directed towards epigenetic mechanisms including methylation inhibitors and histone deacetylase (HDAC) inhibitors have had some clinical success when applied to MDS and AML. However, identification of the underlying mechanisms associated with clinical responses and drug resistance remain enigmatic. Remarkably, in spite of significant molecular and translational progress, there are currently no epigenetic biomarkers in widespread clinical use. In this review, we explore the potential applications of epigenetic biomarker discovery, including epigenetic profiling for myeloid malignancy pathogenesis understanding, diagnostic classification, and development of effective treatment paradigms for these generally considered poor prognosis disorders.

SFRP1 promoter methylation and expression in human trabecular meshwork cells

Glaucoma is a leading cause of blindness worldwide. In primary open angle glaucoma (POAG) patients, impaired trabecular meshwork (TM) function results in elevated intraocular pressure (IOP), which is the primary risk factor of developing optic neuropathy. Our previous studies showed that Wnt signaling pathway components are expressed in the human TM (HTM), and the Wnt inhibitor, secreted frizzled-related protein 1 (SFRP1) is elevated in the glaucomatous TM (GTM). Elevated SFRP1 increased IOP in mice eyes and in perfusion cultured anterior segments of the human eye. However, the cause of elevated SFRP1 in the GTM remains unknown. Promoter methylation plays a key role in regulating SFRP1 expression in certain cancer cells. In light of this, we studied whether promoter methylation is also involved in SFRP1 differential expression in the TM. Two normal TM (NTM) and two GTM cell strains were cultured for an additional 7 days after they were confluent. RNA and genomic DNA (gDNA) were isolated simultaneously to compare SFRP1 expression levels by quantitative PCR (qPCR) and to determine SFRP1 promoter methylation status by bisulfite conversion and methylation-sensitive high resolution melting analysis (MS-HRM). To study whether DNA methylation inhibitors affect SFRP1 expression in TM cells, the four TM cell strains were treated with or without 2 μM 5-aza-2'-deoxycytidine (AZA-dC) for 4 days. RNA was isolated to compare SFRP1 expression by qPCR. In addition, a human cancer cell line, NCI-H460, was used as a positive control. We found that the two GTM cell strains had significantly higher expression levels of SFRP1 than the two NTM cell strains. However, the SFRP1 promoter of all four TM cell strains was unmethylated. In addition, AZA-dC treatment did not affect SFRP1 expression in any of the TM cell strains (n = 3, p > 0.05). In contrast, the hypermethylated SFRP1 promoter of NCI-H460 cells was partially demethylated by the same treatment. AZA-dC treatment also elevated SFRP1 expression by approximately two fold in NCI-H460 cells (n = 3, p < 0.01). Our data suggest that the differential expression of SFRP1 in HTM cells is not due to differential promoter methylation.

Wnt signaling strength regulates normal hematopoiesis and its deregulation is involved in leukemia development

A strict balance between self-renewal and differentiation of hematopoietic stem cells (HSCs) is required in order to maintain homeostasis, as well as to efficiently respond to injury and infections. Numbers and fate decisions made by progenitors derived from HSC must also be carefully regulated to sustain large-scale production of blood cells. The complex Wnt family of molecules generally is thought to be important to these processes, delivering critical signals to HSC and progenitors as they reside in specialized niches. Wnt proteins have also been extensively studied in connection with malignancies and are causatively involved in the development of several types of leukemias. However, studies with experimental animal models have produced contradictory findings regarding the importance of Wnt signals for normal hematopoiesis and lymphopoiesis. Here, we will argue that dose dependency of signaling via particular Wnt pathways accounts for much, if not all of this controversy. We conclude that there seems little doubt that Wnt proteins are required to sustain normal hematopoiesis, but are likely to be presented in carefully controlled gradients in a tissue-specific manner.

Distinct association between aberrant methylation of Wnt inhibitors and genetic alterations in acute myeloid leukaemia

Background:

Aberrant activation of Wnt signalling through hypermethylation of Wnt inhibitor genes is involved in several human malignancies, including acute myeloid leukaemia (AML). It remains unclear whether hypermethylation of Wnt inhibitors is associated with molecular gene mutations in the development of AML.

Methods:

We investigated the association of the promoter hypermethylation of six Wnt inhibitors (Wif-1, SFRP1, SFRR2, SFRP4, SFRP5, and DKK1) with gene aberrations in the leukaemogenesis of 269 AML patients.

Results:

In total, 166 patients (61.7%) had hypermethylation of at least one Wnt inhibitor. The majority (68.5%) of patients with Wnt inhibitor hypermethylation had concurrent Class II gene mutations that affect transcription factors or cofactors. There was a close association of Wif-1 hypermethylation with t(15;17) (P=0.0005) and CEBPA mutation (P<0.0001), DKK1 hypermethylation with t(8;21) (P<0.0001) and ASXL1 mutation (P=0.0078), SFRP-1 hypermethylation with t(8;21) (P<0.0001), SFRP-2 hypermethylation with AML1/RUNX1 mutation (P=0.0012), and SFRP-5 hypermethylation with MLL/PTD (P=0.0505). On the other side, hypermethylation of Wnt inhibitors was always negatively associated with NPM1 mutation and FLT3/ITD.

Conclusion:

There was distinct association between hypermethylation of individual Wnt inhibitors and specific gene aberrations, especially Class II mutations. The Wnt inhibitor hypermethylation might interact with genetic alterations in the leukaemogenesis.

Secreted-frizzled related protein 1 is a transcriptional repression target of the t(8;21) fusion protein in acute myeloid leukemia

Secreted-frizzled related proteins (SFRPs) are modulators of the Wnt signaling pathway that is closely involved in normal and malignant hematopoiesis. Epigenetic deregulation of Wnt modulators leading to aberrant signaling has been reported in adult patients with acute myeloid leukemia (AML), but its occurrence in childhood patients with AML and the role of individual modulators are unclear. In this study, we examined SFRP1, SFRP2, SFRP4, and SFRP5 promoter methylation in 83 patients with AML (59 children and 24 adults) and found preferential SFRP1 methylation and mRNA down-regulation in the prognostically favorable subgroup of AML with t(8;21) translocation. Among the 4 genes, SFRP1 methylation independently predicted prolonged event-free and relapse-free survivals in childhood patients with nonacute promyelocytic leukemia with nonadverse cytogenetics. Mechanistically, we further demonstrated that RUNX1-ETO, the t(8;21) fusion product, specifically bound the SFRP1 promoter and repressed its transcription via a consensus RUNX binding site. In t(8;21)-leukemia cells, SFRP1 selectively inhibited canonical Wnt signaling and cellular proliferation that were associated with concomitant down-regulation of Wnt/β-catenin target genes, including CCND1 and MYC. Taken together, we identified SFRP1 as a transcriptional repression target of the t(8;21) fusion protein and demonstrated a novel mechanism of Wnt activation in a specific subtype of AML.

Array-based DNA methylation profiling in acute myeloid leukaemia

Methylation in the promoter region of many genes is involved in regulating gene expression patterns. Using the Illumina GoldenGate© methylation assay, we examined the methylation status of 1505 CpG-sites from 807 genes in 32 samples from patients with acute myeloid leukaemia (AML) at diagnosis, nine at relapse and 15 normal controls and performed additional pyrosequencing and semiquantitative methylation specific polymerase chain reaction (MSP) of the GNMT promoter in 113 diagnostic AML samples. We found a gain of overall methylation in AML samples with a further increase at relapse. Regional hypermethylation as assessed by array analysis could be confirmed by both MSP and pyrosequencing. Additionally, large-scale methylation analysis identified interesting candidate genes. Cluster analysis indicated that cytogenetic subgroups seemed to be characterized by additional distinct epigenetic modifications and that basic DNA methylation patterns remain at relapse. Therefore, promoter hypermethylation is a frequent event in AML and is accentuated at relapse. Array-based methylation analysis determined distinct methylation profiles for non-malignant controls and AML samples with specific chromosomal aberrations and can identify target genes for further evaluation.

Promoter methylation of Wnt antagonists DKK1 and SFRP1 is associated with opposing tumor subtypes in two large populations of colorectal cancer patients

Aberrant activation of canonical Wnt signaling is a hallmark event in colorectal carcinogenesis. The Dickkopf-1 (DKK1) and Secreted Frizzled Related Protein 1 (SFRP1) genes encode extracellular inhibitors of Wnt signaling that are frequently silenced by promoter hypermethylation in colorectal cancer (CRC). These methylation events have been identified as prognostic markers of patient outcome and tumor subtype in several cancers but similar roles in CRC have not been comprehensively examined. In CRC, the microsatellite instability (MSI) subtype associates with favorable disease outcome but the molecular events that are responsible remain poorly understood. Consequently, we quantified promoter methylation status of the Wnt antagonist genes DKK1 and SFRP1 in a large population-based cohort of CRCs from Ontario (n = 549) and Newfoundland (n = 696) stratified by MSI status. We examined the association between methylation status and clinicopathological features including tumor MSI status and patient survival. DKK1 and SFRP1 were methylated in 13 and 95% of CRCs, respectively. In Ontario, DKK1 methylation was strongly associated with MSI tumors after adjustment for age, sex and tumor location [odds ratio (OR) = 13.7, 95% confidence interval (CI) = 7.8-24.2, P < 0.001]. Conversely, SFRP1 methylation was inversely associated with MSI tumors after these adjustments (OR = 0.3, 95% CI = 0.1-0.9, P = 0.009). Similar results were obtained in Newfoundland. There were no independent associations with recurrence-free survival. This is the first large study to identify associations between Wnt antagonist promoter hypermethylation and CRC MSI subtype. These events provide insight into subtype-specific epigenetic mediation of Wnt signaling in CRC.

Resistance or sensitivity of Wilms' tumor to anti-FZD7 antibody highlights the Wnt pathway as a possible therapeutic target

Wilms' tumor (WT), the most frequent renal solid tumor in children, has been linked to aberrant Wnt signaling. Herein, we demonstrate that different WTs can be grouped according to either sensitivity or resistance to an antibody (Ab) specific to frizzled7 (FZD7), a Wnt receptor. In the FZD7-sensitive WT phenotype, the Ab induced cell death of the FZD7(+) fraction, which in turn depleted primary WT cultures of their clonogenic and sphere-forming cells and decreased in vivo proliferation and survival on xenografting to the chick chorio-allantoic-membrane. In contrast, FZD7-resistant WT in which no cell death was induced showed a different intra-cellular route of the Ab-FZD7 complex compared with sensitive tumors and accumulation of β-catenin. This coincided with a low sFRP1 and DKK1 (Wnt inhibitors) expression pattern, restored epigenetically with de-methylating agents, and lack of β-catenin or WTX mutations. The addition of exogenous DKK1 and sFRP1 to the tumor cells enabled the sensitization of FZD7-resistant WT to the FZD7 Ab. Finally, although extremely difficult to achieve because of dynamic cellular localization of FZD7, sorting of FZD7(+) cells from resistant WT, showed them to be highly clonogenic/proliferative, overexpressing WT 'stemness' genes, emphasizing the importance of targeting this fraction. FZD7 Ab therapy alone or in combination with Wnt pathway antagonists may have a significant role in the treatment of WT via targeting of a tumor progenitor population.

Acute myeloid leukemia is characterized by Wnt pathway inhibitor promoter hypermethylation

Nuclear localization of non-phosphorylated, active beta-catenin is a measure of Wnt pathway activation and is associated with adverse outcome in patients with acute myeloid leukemia (AML). While genetic alterations of the Wnt pathway are infrequent in AML, inhibitors of this pathway are silenced by promoter methylation in other malignanices. Leukemia cell lines were examined for Wnt pathway inhibitor methylation and total beta-catenin levels, and had frequent methylation of Wnt inhibitors and upregulated beta-catenin by Western blot and immunofluorescence. One hundred sixty-nine AML samples were examined for methylation of Wnt inhibitor genes. Diagnostic samples from 72 patients with normal cytogenetics who received standard high-dose induction chemotherapy were evaluated for associations between methylation and event-free or overall survival. Extensive methylation of Wnt pathway inhibitor genes was observed in cell lines, and 89% of primary AML samples had at least one methylated gene: DKK1 (16%), DKK3 (8%), RUNX3 (27%), sFRP1 (34%), sFRP2 (66%), sFRP4 (9%), sFRP5 (54%), SOX17 (29%), and WIF1 (32%). In contrast to epithelial tumors, methylation of APC (2%) and RASSF1A (0%) was rare. In patients with AML with normal cytogenetics, sFRP2 and sFRP5 methylation at the time of diagnosis was associated with an increased risk of relapse, and sFRP2 methylation was associated with an increased risk for death. In patients with AML: (a) there is a high frequency of Wnt pathway inhibitor methylation; (b) Wnt pathway inhibitor methylation is distinct from that observed in epithelial malignancies; and (c) methylation of sFRP2 and sFRP5 may predict adverse clinical outcome in patients with normal karyotype AML.

Proliferation and bone marrow engraftment of AML blasts is dependent on β-catenin signalling

B-catenin is the central effector molecule of the canonical Wnt signalling pathway, which controls self-renewal of haematopoietic stem cells. Deregulation of this pathway occurs in various malignancies including myeloid leukaemias. The present study examined the functional outcome of stable β-catenin down-regulation through lentivirus-mediated expression of short hairpin RNA (shRNA). Reduction of the β-catenin levels in acute myeloid leukaemia (AML) cell lines and patient samples decelerated their in vitro proliferation ability without affecting cell viability. Transplantation of leukaemic cells with control or reduced levels of β-catenin in non-obese diabetic severe combined immunodeficient animals indicated that, while the immediate homing of the cells was unaffected, the bone marrow engraftment was directly dependent on β-catenin levels. Subsequent examination of bone sections revealed that β-catenin was implicated in the localization of AML to the endosteum. Examination of adhesion molecule expression before and after transplantation, revealed down-regulation of CD44 expression, accompanied by reduced in vitro adhesion. Gene expression analysis disclosed the presence of an autocrine compensatory mechanism, which responds to the reduced β-catenin levels by altering the expression of positive and negative pathway regulators. In conclusion, our study showed that β-catenin comprises an integral part of AML cell proliferation, cell cycle progression, and adhesion, and influences disease establishment in vivo.

Role of Wnt canonical pathway in hematological malignancies

Wnt canonical signaling pathway plays a diverse role in embryonic development and maintenance of organs and tissues in adults. It has been observed that Wnt/β-catenin signaling pathway is involved in the pathogenesis of many carcinomas. Moreover, Wnt/β-catenin pathway has been revealed to be associated with angiogenesis. Wnt canonical pathway signaling has great potential as a therapeutic target. It has been disclosed that some hematological malignancies, such as chronic lymphocytic leukemia, mantle cell lymphoma, may occur partly due to the constitutive activation of Wnt canonical signaling pathway. This review will summarize the latest development in Wnt canonical signaling pathway and its roles in tumorigenesis and angiogenesis.

The advantages and disadvantages of sfrp1 and sfrp2 expression in pathological events

Secreted Frizzled Related Proteins (Sfrps) are a family of secreted proteins that can bind both to Wnt ligands and Frizzled receptors, thereby modulating the Wnt signalling cascades. Recent studies have shown that Sfrps can also interact with Wnt unrelated molecules such as RANKL, a member of the tumor necrosis factor family, Tolloid metalloproteinases or integrin-fibronectin complexes. Alterations in the levels of Sfrp expression have been recently associated with different pathological conditions, including tumor formation and bone and myocardial disorders. Here, we summarise the evidence that relates Sfrps with these diseases and discuss how the proposed multiple Sfrp interactions with Wnt related and unrelated pathways may explain their implication in such diverse pathologies.

Transcriptional down-regulation of the Wnt antagonist SFRP1 in haematopoietic cells of patients with different risk types of MDS

Secreted frizzled related protein 1 (SFRP1) is an extracellular antagonist of the Wnt signalling pathway that plays an important role in the pathogenesis of solid tumours and haematopoietic malignancies. SFRP1 has been observed to be transcriptionally down-regulated due to hypermethylation in acute and chronic leukaemia, but so far not in myelodysplastic syndrome (MDS). Moreover, it has been shown that the epigenetic inactivation of SFRP1 correlates with an overexpression of the Wnt receptor Frizzled 3 (Fzd3) in acute leukaemia. Using real-time quantitative reverse transcription polymerase chain reaction (RT-PCR) we examined mRNA expression of SFRP1 and Fzd3 in bone marrow cells derived from 121 patients with different risk types of MDS, acute myeloid leukaemia (AML) and acute lymphoblastic leukaemia (ALL). We employed pyrosequencing to quantify promoter DNA methylation in MDS and acute leukaemia. We detected significant lower mRNA transcription of SFRP1 in MDS compared to healthy individuals. However, DNA sequence mutations or frequent elevated DNA methylation levels of the SFRP1 promoter could not be observed in MDS but in AML and ALL as previously reported. The expression levels of Fzd3 were up-regulated in both acute leukaemia and MDS. Our data show a significant transcriptional down-regulation of SFRP1 as a common event in AML, ALL and - as demonstrated for the first time - in MDS. An inactivation of SFRP1 and the transcriptional up-regulation of Fzd3 seem to be associated with an activation of the Wnt signalling pathway in these haematopoietic diseases.

Epigenetic regulation of the non-canonical Wnt pathway in acute myeloid leukemia

Wnt5a is a member of the Wnt family of proteins that signals through the non-canonical Wnt/Ca(2+)pathway to suppress cyclin D1. Deregulation of this pathway has been found in animal models suggesting that it acts as tumour suppressor in acute myeloid leukemia (AML). Although DNA methylation is the main mechanism of regulation of the canonical Wnt pathway in AML, the role of WNT5A abnormalities has never been evaluated in this clinical setting. The methylation status of WNT5A promoter-exon 1 was analyzed by methylation-specific PCR and sequencing in eleven AML-derived cell lines and 252 AML patients. We observed WNT5A hypermethylation in seven cell lines and in 43% (107/252) of AML patients. WNT5A methylation was associated with decreased WNT5A expression (P < 0.001) that was restored after exposure to 5-Aza-2'-deoxycytidine. Moreover, WNT5A hypermethylation correlated with upregulation of CYCLIN D1 expression (P < 0.001). Relapse (15%vs 37%, P < 0.001) and mortality (61%vs 79%, P = 0.004) rates were lower for patients in the non-methylated group. Disease-free survival and overall survival at 6 and 7 years, respectively, were 60% and 27% for unmethylated patients and 20% and 0% for hypermethylated patients (P = 0.0001 and P = 0.04, respectively). Interestingly, significant differences were also observed when the analysis was carried out according to cytogenetic risk groups. We demonstrate that WNT5A, a putative tumor suppressor gene in AML, is silenced by methylation in this disease and that this epigenetic event is associated with upregulation of CYCLIN D1 expression and confers poor prognosis in patients with AML.

CpG island methylation patterns in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most common leukemia in Western countries. In CLL, a large number of genes affecting cancer-related pathways may be dysregulated by epigenetic silencing. We analysed by methylation-specific polymerase chain reaction the CpG island methylation status of 15 well-characterised cancer-related genes in 32 patients with CLL. Aberrant methylation in the sample of patients with CLL was shown for secreted frizzled-related protein 1 (68.8%), secreted frizzled-related protein 2 (65.6%), death-associated protein kinase 1 (50.0%), E-cadherin (21.9%), secreted frizzled-related protein 4 (15.6%), p15 (9.4%), p16 (6.3%), retinoic acid receptor beta2 (3.1%), secreted frizzled-related protein 5 (3.1%) and tissue inhibitor of matrix metalloproteinases 3 (3.1%). For human Mut-L homolog 1, O(6)-methylguanine DNA methyltransferase, p73, suppressor of cytokine signalling 1 and tissue inhibitor of matrix metalloproteinases 2 no hypermethylation was detected. Hypermethylation of at least one gene was observed in 87.5% of the samples. Our results show that aberrant CpG island methylation affecting cancer-related pathways such as Wnt signalling, regulation of apoptosis, cell cycle control and tissue invasion is a common phenomenon in CLL. Epigenetic disturbances may be involved in the pathogenesis of CLL and thus may provide a molecular rationale for therapeutic approaches.

Wnt signaling pathway is epigenetically regulated by methylation of Wnt antagonists in acute myeloid leukemia

Activation of the Wnt signaling pathway has been implicated recently in the pathogenesis of leukemia. We studied the function of epigenetic regulation of the Wnt pathway and its prognostic relevance in acute myelogenous leukemia (AML). We used a methylation-specific polymerase chain reaction approach to analyze the promoter methylation status of a panel of Wnt antagonists including sFRP1, sFRP2, sFRP4, sFRP5, DKK1 and DKK3. Aberrant methylation of Wnt antagonists was detected in four AML cell lines and in up to 64% of AML marrow samples. Treatment of the cell lines with 5-aza-2'-deoxycytidine induced reexpression of methylated Wnt antagonists and inactivation of the Wnt pathway by downregulating the Wnt pathway genes cyclin D1, TCF1 and LEF1 and reducing nuclear localization of beta-catenin. In a subgroup of patients 60 years and younger with newly diagnosed AML and intermediate-risk cytogenetics, abnormal methylation of Wnt antagonists was associated with decreased 4-year relapse-free survival (28 vs 61%, respectively, P=0.03). Our results indicate a function of the epigenetic regulation of the Wnt pathway in predicting relapse in a subgroup of AML patients.

Epigenetic dysregulation of secreted Frizzled-related proteins in multiple myeloma

We analysed the clinical impact of epigenetic dysregulation of the Wnt pathway in malignant plasma cell disorders. In multiple myeloma (MM) cell lines, aberrant promoter hypermethylation of the secreted Frizzled-related protein (SFRP) genes was a common event, and hypermethylation of SFRP1,-2 and -5 was associated with transcriptional silencing. Among 76 primary patient samples, the frequency of aberrant methylation was 35.5% for SFRP1, 52.6% for SFRP2, 1.3% for SFRP4 and 6.9% for SFRP5. Hypermethylation of SFRP1 and -2 genes was detected in monoclonal gammopathy of undetermined significance and all MM stages including plasma cell leukaemia (PCL), while SFRP5 methylation was restricted to advanced MM stages and PCL. Our data indicate that epigenetic silencing of Wnt antagonists is an early event in MM pathogenesis and that SFRP5 hypermethylation may play a role in disease progression.

Small molecule inhibitors of WNT signaling effectively induce apoptosis in acute myeloid leukemia cells

In a significant proportion of acute myeloid leukemia (AML) cases the canonical WNT pathway is upregulated and targeting the WNT/LEF1 signaling cascade in AML may be a promising approach to develop new treatments for this entity. Recently two compounds (CGP049090 and PFK115-584) have been identified, which specifically inhibit complexation of beta-catenin (CTNNB1) and lymphoid enhancer-binding factor 1 (LEF1) leading to transcriptional inactivation of LEF1 in colon carcinoma cell lines. To evaluate the effect of WNT inhibition utilizing theses compounds with regard to their effectivity in AML we treated the AML cell lines Kasumi-1 and HL-60, primary AML blasts and healthy peripheral blood mononuclear cells (PBMCs) with varying concentrations of both substances. Treatment with both compounds for 24 h resulted in a significant killing of AML cell lines and primary AML blasts with 50% effective concentration doses (EC(50)) within the submicromolar range. PBMCs were not significantly affected as indicated by EC(50)-values 100-fold higher than for AML cells. Cell kill was mediated by apoptosis as indicated by induction of caspases 3 and 7 and cleavage of poly(ADP-ribose) polymerase (PARP) upon treatment. Furthermore, we could show that both compounds substantially decrease expression of CTNNB1/LEF1 target genes c-myc, cyclin D1 and survivin, proofing the specificity of the substances. This was shown in both, AML cell lines and most of the tested primary samples. Our data demonstrate that targeting this pathway seems to be an innovative approach in the treatment of AML.

Advances in molecular genetics and treatment of core-binding factor acute myeloid leukemia

PURPOSE OF REVIEW

Core-binding factor (CBF) acute myeloid leukemia (AML) is among the most common cytogenetic subtypes of AML, being detected in approximately 13% of adults with primary disease. Although CBF-AML is associated with a relatively favorable prognosis, only one-half of the patients are cured. Herein we review recent discoveries of genetic and epigenetic alterations in CBF-AML that may represent novel prognostic markers and therapeutic targets and lead to improvement of the still disappointing clinical outcome of these patients.

RECENT FINDINGS

Several acquired gene mutations and gene-expression and microRNA-expression changes that occur in addition to t(8;21)(q22;q22) and inv(16)(p13q22)/t(16;16)(p13;q22), the cytogenetic hallmarks of CBF-AML, have been recently reported. Alterations that may represent cooperative events in CBF-AML leukemogenesis include mutations in the KIT, FLT3, JAK2 and RAS genes, haploinsufficiency of the putative tumor suppressor genes TLE1 and TLE4 in t(8;21)-positive patients with del(9q), MN1 overexpression in inv(16) patients, and epigenetic and posttranscriptional silencing of CEBPA. Genome-wide gene-expression and microRNA-expression profiling identifying subgroups of CBF-AML patients with distinct molecular signatures, different clinical outcomes, or both, have also been reported.

SUMMARY

Progress has been made in delineating the genetic basis of CBF-AML that will likely result in improved prognostication and development of novel, risk-adapted therapeutic approaches.