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

Esculetin releases maturation arrest and induces terminal differentiation in leukemic blast cells by altering the Wnt signaling axes

BACKGROUND

The "Differentiation therapy" has been emerging as a promising and more effective strategy against acute leukemia relapses.

OBJECTIVE

In extension to the revolutionising therapeutic outcomes of All Trans Retinoic Acid (ATRA) to induce terminal differentiation of Acute Promyelocytic Leukemic (APL) blast cells, we decipher the potential effect of a natural compound "Esculetin" to serve as a differentiating agent in Acute Myeloid Leukemia (AML). Underlaying role of Wnt signaling pathways in esculetin mediated blast cell differentiation was also evaluated.

METHODS

Human acute myeloid leukemic cells (Kasumi-1) with t(8;21/AML-ETO) translocation were used as a model system. Growth inhibitory and cytotoxic activity of esculetin were analysed using growth kinetics and MTT assay. Morphological alterations, cell scatter characteristics, NBT reduction assay and cell surface marker expression patterns were analysed to detect terminally differentiated phenotypes. We employed RT²profiler PCR array system for the analysis of transcriptome profile of Wnt signaling components. Calcium inhibitors (TMB8 and Amlodipine) and Transforming growth factor beta (TGF-β) were used to modulate the Wnt signaling axes.

RESULTS

We illustrate cytotoxic as well as blast cell differentiation potential of esculetin on Kasumi-1 cells. Morphological alterations akin to neutrophilic differentiation as well as the corresponding acquisition of myeloid lineage markers indicate terminal differentiation potential of esculetin in leukemic blast cells. Exposure to esculetin also resulted in downregulation of canonical Wnt axis while upto ~ 21 fold upregulation of non-canonical axis associated genes.

CONCLUSIONS

Our study highlights the importance of selective use of calcium pools as well as "axis shift" of the canonical to non-canonical Wnt signaling upon esculetin treatment which might abrogate the inherent proliferation to release maturation arrest and induce the differentiation in leukemic blast cells. The current findings provide further therapeutic interventions to consider esculetin as a potent differentiating agent to counteract AML relapses.

"Losing the Brakes"-Suppressed Inhibitors Triggering Uncontrolled Wnt/ß-Catenin Signaling May Provide a Potential Therapeutic Target in Elderly Acute Myeloid Leukemia

Dysregulated Wnt/β-catenin signal transduction is implicated in initiation, propagation, and poor prognosis in AML. Epigenetic inactivation is central to Wnt/β-catenin hyperactivity, and Wnt/β-catenin inhibitors are being investigated as targeted therapy. Dysregulated Wnt/β-catenin signaling has also been linked to accelerated aging. Since AML is a disease of old age (>60 yrs), we hypothesized age-related differential activity of Wnt/β-catenin signaling in AML patients. We probed Wnt/β-catenin expression in a series of AML in the elderly (>60 yrs) and compared it to a cohort of pediatric AML (<18 yrs). RNA from diagnostic bone marrow biopsies (n = 101) were evaluated for key Wnt/β-catenin molecule expression utilizing the NanoString platform. Differential expression of significance was defined as >2.5-fold difference (p < 0.01). A total of 36 pediatric AML (<18 yrs) and 36 elderly AML (>60 yrs) were identified in this cohort. Normal bone marrows (n = 10) were employed as controls. Wnt/β-catenin target genes (MYC, MYB, and RUNX1) showed upregulation, while Wnt/β-catenin inhibitors (CXXR, DKK1-4, SFRP1-4, SOST, and WIFI) were suppressed in elderly AML compared to pediatric AML and controls. Our data denote that suppressed inhibitor expression (through mutation or hypermethylation) is an additional contributing factor in Wnt/β-catenin hyperactivity in elderly AML, thus supporting Wnt/β-catenin inhibitors as potential targeted therapy.

A Systematic Review of the Role of Runt-Related Transcription Factor 1 (RUNX1) in the Pathogenesis of Hematological Malignancies in Patients With Inherited Bone Marrow Failure Syndromes

Somatic runt-related transcription factor 1 (RUNX1) mutations are the most common mutations in various hematological malignancies, such as myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML). Mono-allelic RUNX1 mutations in germline cells may cause familial platelet disorder (FPD), an inherited bone marrow failure syndrome (IBMFS) associated with an increased lifetime risk of AML. It is suspected that additional RUNX1 mutations may play a role in the pathogenesis of hematological malignancies in IBMFS. This review aims to study the role of RUNX1 mutations in the pathogenesis of hematological malignancies in patients with IBMFS. A PubMed database search was conducted using the following medical subject heading (MeSH) terms: "inherited bone marrow failure syndromes," "hematological neoplasms," "gene expression regulation, leukemic," "RUNX1 protein, human," "RUNX1 protein, mouse," and "Neutropenia, Severe Congenital, Autosomal recessive." Three studies published in 2020 were identified as meeting our inclusion and exclusion criteria. Leukemic progression in severe congenital neutropenia was used as a disease model to evaluate the clinical, molecular, and mechanistic basis of RUNX1 mutations identified in hematological malignancies. Studies in mice and genetically reprogrammed or induced pluripotent stem cells (iPSCs) have shown that isolated RUNX1 mutations are weakly leukemogenic and only initiate hyperproduction of immature hematopoietic cells when in combination with granulocyte colony-stimulating factor 3 receptor (GCSF3R) mutations. Despite this, whole-exome sequencing (WES) performed on leukemogenic transformed cells revealed that all AML cells had an additional mutation in the CXXC finger protein 4 (CXXC4) gene that caused hyperproduction of the ten-eleven translocation (TET2) protein. This protein causes inflammation in cells with RUNX1 mutations. This process is thought to be critical for clonal myeloid malignant transformation (CMMT) of leukemogenic cells. In conclusion, the combinations of GCSF3R and RUNX1 mutations have a prominent effect on myeloid differentiation resulting in the hyperproduction of myeloblasts. In other studies, it has been noted that the mutations in GCSF3R and RUNX1 genes are not sufficient for the full transformation of leukemogenic cells to AML, and an additional clonal mutation in the CXXC4 gene is essential for full transformation to occur. These data have implicitly demonstrated that RUNX1 mutations are critical in the pathogenesis of various hematological malignancies, and further investigations into the role of RUNX1 are paramount for the development of new cancer treatments.

Targeting β-catenin in acute myeloid leukaemia: past, present, and future perspectives

Acute myeloid leukaemia (AML) is an aggressive disease of the bone marrow with a poor prognosis. Evidence suggests long established chemotherapeutic regimens used to treat AML are reaching the limits of their efficacy, necessitating the urgent development of novel targeted therapies. Canonical Wnt signalling is an evolutionary conserved cascade heavily implicated in normal developmental and disease processes in humans. For over 15 years its been known that the central mediator of this pathway, β-catenin, is dysregulated in AML promoting the emergence, maintenance, and drug resistance of leukaemia stem cells. Yet, despite this knowledge, and subsequent studies demonstrating the therapeutic potential of targeting Wnt activity in haematological cancers, β-catenin inhibitors have not yet reached the clinic. The aim of this review is to summarise the current understanding regarding the role and mechanistic dysregulation of β-catenin in AML, and assess the therapeutic merit of pharmacologically targeting this molecule, drawing on lessons from other disease contexts.

Canonical Wnt: a safeguard and threat for erythropoiesis

Myeloid dysplastic syndrome (MDS) reflects a preleukemic bone marrow (BM) disorder with limited treatment options and poor disease survival. As only a minority of MDS patients are eligible for curative hematopoietic stem cell transplantation, there is an urgent need to develop alternative treatment options. Chronic activation of Wnt/β-catenin has been implicated to underlie MDS formation and recently assigned to drive MDS transformation to acute myeloid leukemia. Wnt/β-catenin signaling therefore may harbor a pharmaceutical target to treat MDS and/or prevent leukemia formation. However, targeting the Wnt/β-catenin pathway will also affect healthy hematopoiesis in MDS patients. The control of Wnt/β-catenin in healthy hematopoiesis is poorly understood. Whereas Wnt/β-catenin is dispensable for steady-state erythropoiesis, its activity is essential for stress erythropoiesis in response to BM injury and anemia. Manipulation of Wnt/β-catenin signaling in MDS may therefore deregulate stress erythropoiesis and even increase anemia severity. Here, we provide a comprehensive overview of the most recent and established insights in the field to acquire more insight into the control of Wnt/β-catenin signaling in healthy and inefficient erythropoiesis as seen in MDS.

Deciphering the role of Wnt signaling in acute myeloid leukemia prognosis: how alterations in DNA methylation come into play in patients' prognosis

Acute myeloid leukemia (AML) is a malignant clonal disorder affecting myeloid differentiation through mechanisms that include epigenetic dysregulation. Abnormal changes in DNA methylation and gene expression profiles of pathways involved in hematopoietic development, such as Wnt/β-catenin, contribute to the transformation, development, and maintenance of leukemic cells. This review summarizes the alterations of Wnt signaling-related genes at the epigenetic and transcriptional level and their implications for AML prognosis. Among the implications of epigenetic alterations in AML, methylation of Wnt antagonists is related to poor prognosis, whereas their upregulation has been associated with a better clinical outcome. Furthermore, Wnt target genes c-Myc and LEF-1 present distinct implications. LEF-1 expression positively influences the patient overall survival. c-Myc upregulation has been associated with treatment resistance in AML, although c-Myc expression is not exclusively dependent of Wnt signaling. Understanding the signaling abnormalities could help us to further understand leukemogenesis, improve the current risk stratification for AML patients, and even serve to propose novel therapeutic targets.

The Clinical, Molecular, and Mechanistic Basis of RUNX1 Mutations Identified in Hematological Malignancies

RUNX1 plays an important role in the regulation of normal hematopoiesis. RUNX1 mutations are frequently found and have been intensively studied in hematological malignancies. Germline mutations in RUNX1 cause familial platelet disorder with predisposition to acute myeloid leukemia (FPD/AML). Somatic mutations of RUNX1 are observed in various types of hematological malignancies, such as AML, acute lymphoblastic leukemia (ALL), myelodysplastic syndromes (MDS), myeloproliferative neoplasm (MPN), chronic myelomonocytic leukemia (CMML), and congenital bone marrow failure (CBMF). Here, we systematically review the clinical and molecular characteristics of RUNX1 mutations, the mechanisms of pathogenesis caused by RUNX1 mutations, and potential therapeutic strategies to target RUNX1-mutated cases of hematological malignancies.

Native Oligodendrocytes in Astrocytomas Might Inhibit Tumor Proliferation by WIF1 Expression

Malignant astrocytoma remains incurable and rapidly fatal despite multimodal therapy. In particular, accelerated tumor cell heterogeneity often overcomes therapeutic effects of molecular protein targeting. This study aimed at identifying a gene with therapeutic potential that was consistently downregulated with astrocytoma progression. Analysis of the "Rembrandt" gene expression data revealed Wnt inhibitory factor 1 (WIF1) gene as the most promising candidate with tumor suppressor function. Consequently, 288 randomly selected tissue regions of astrocytoma specimens were investigated immunohistochemically with the aid of image analysis. This in situ approach identified tumor areas with numerous single cells strongly expressing Wif-1. In diffuse and anaplastic astrocytoma, the proliferation index was independent of the generally weak Wif-1 expression in tumor cells but was significantly correlated with the density of Wif-1-expressing single cells, subsequently characterized as native and non-neoplastic oligodendrocytes. Because these cells may contribute to inhibition of tumor cell proliferation by paracrine signaling, the endogenous protein Wif-1 may represent a promising therapeutic agent with expected minimal side effects. Moreover, we suggest that immunohistochemistry for Wif might be useful for discriminating between astrocytic tumors and reactive changes.

Dnmt3a-mediated inhibition of Wnt in cardiac progenitor cells improves differentiation and remote remodeling after infarction

Adult cardiac progenitor cells (CPCs) display a low capacity to differentiate into cardiomyocytes in injured hearts, strongly limiting the regenerative capacity of the mammalian myocardium. To identify new mechanisms regulating CPC differentiation, we used primary and clonally expanded Sca-1+ CPCs from murine adult hearts in homotypic culture or coculture with cardiomyocytes. Expression kinetics analysis during homotypic culture differentiation showed downregulation of Wnt target genes concomitant with increased expression of the Wnt antagonist, Wnt inhibitory factor 1 (Wif1), which is necessary to stimulate CPC differentiation. We show that the expression of the Wif1 gene is repressed by DNA methylation and regulated by the de novo DNA methyltransferase Dnmt3a. In addition, miR-29a is upregulated early during CPC differentiation and downregulates Dnmt3a expression, thereby decreasing Wif1 gene methylation and increasing the efficiency of differentiation of Sca-1+ CPCs in vitro. Extending these findings in vivo, transient silencing of Dnmt3a in CPCs subsequently injected in the border zone of infarcted mouse hearts improved CPC differentiation in situ and remote cardiac remodeling. In conclusion, miR-29a and Dnmt3a epigenetically regulate CPC differentiation through Wnt inhibition. Remote effects on cardiac remodeling support paracrine signaling beyond the local injection site, with potential therapeutic interest for cardiac repair.

[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.

[Promoter methylation status of SFRP genes and induced apoptosis by demethylation in Jurkat cells]

目的

探讨人T淋巴细胞白血病（T-ALL）细胞株Jurkat细胞分泌性卷曲相关蛋白（SFRP）基因甲基化及去甲基化诱导细胞凋亡对Wnt/β-catenin信号通路的影响。

方法

以不同浓度（1.0、2.0、4.0 µmol/L）5-杂氮-2′-脱氧胞苷（5-Aza-CdR）对Jurkat细胞进行去甲基化处理，采用MTT法观察5-Aza-CdR对Jurkat细胞增殖的抑制作用，流式细胞术检测细胞凋亡率，甲基化特异性PCR(MSP)法检测药物处理前后SFRP基因的甲基化状态，实时荧光定量PCR检测SFRP基因以及RT-PCR检测survivin、c-myc和cyclin D1基因mRNA的表达改变，Western blot鉴定处理前后β-catenin的蛋白表达。

结果

1.0、2.0、4.0 µmol/L 5-Aza-CdR对Jurkat细胞的增殖有明显抑制作用，呈时间-剂量依赖性（P<0.05）；流式细胞术检测显示5-Aza-CdR作用Jurkat细胞48 h后，不同浓度5-Aza-CdR处理组与对照组比较细胞早期凋亡率明显升高（P<0.05）；SFRP1、SFRP2、SFRP4、SFRP5基因甲基化水平随5-Aza-CdR浓度升高而下降，呈剂量依赖性（P<0.05），同时mRNA表达水平较对照组明显上调（P<0.05）；Jurkat细胞总蛋白中β-catenin的蛋白表达随5-Aza-CdR浓度的升高而逐渐下降，呈剂量依赖性（P<0.05）；凋亡相关基因survivin、c-myc和cyclin D1的mRNA表达随5-Aza-CdR浓度的增高而降低，呈剂量依赖性（P<0.05）。

结论

逆转Jurkat细胞SFRP基因的甲基化，可以恢复SFRP基因转录表达，通过阻断β-catenin蛋白抑制Wnt/β-catenin信号通路的激活而诱导细胞凋亡。

Targeting the canonical Wnt/β-catenin pathway in hematological malignancies

The canonical Wnt/β-catenin pathway plays an important role in different developmental processes through the regulation of stem cell functions. In the activation of the canonical Wnt/β-catenin pathway, β-catenin protein is imported into the nucleus and activates transcription of target genes including cyclin D1 and c-myc. Aberrant activation of the Wnt/β-catenin pathway contributes to carcinogenesis and malignant behaviors, and Wnt signaling is essential for the maintenance of cancer stem cells. The canonical Wnt/β-catenin pathway has been investigated extensively as a target in cancer treatment and several specific inhibitors of this signaling pathway have been identified through high-throughput screening. In this review, the significance of the canonical Wnt/β-catenin pathway in hematological carcinogenesis and screening methods for specific inhibitors are discussed.

An integrated approach of gene expression and DNA-methylation profiles of WNT signaling genes uncovers novel prognostic markers in acute myeloid leukemia

Background

The wingless-Int (WNT) pathway has an essential role in cell regulation of hematopoietic stem cells (HSC). For Acute Myeloid Leukemia (AML), the malignant counterpart of HSC, currently only a selective number of genes of the WNT pathway are analyzed by using either gene expression or DNA-methylation profiles for the identification of prognostic markers and potential candidate targets for drug therapy. It is known that mRNA expression is controlled by DNA-methylation and that specific patterns can infer the ability to differentiate biological differences, thus a combined analysis using all WNT annotated genes could provide more insight in the WNT signaling.

Approach

We created a computational approach that integrates gene expression and DNA promoter methylation profiles. The approach represents the continuous gene expression and promoter methylation profiles with nine discrete mutually exclusive scenarios. The scenario representation allows for a refinement of patient groups by a more powerful statistical analysis, and the construction of a co-expression network. We focused on 268 WNT annotated signaling genes that are derived from the molecular signature database.

Results

Using the scenarios we identified seven prognostic markers for overall survival and event-free survival. Three genes are novel prognostic markers; two with favorable outcome (PSMD2, PPARD) and one with unfavorable outcome (XPNPEP). The remaining four genes (LEF1, SFRP2, RUNX1, and AXIN2) were previously identified but we could refine the patient groups. Three AML risk groups were further analyzed and the co-expression network showed that only the good risk group harbors frequent promoter hypermethylation and significantly correlated interactions with proteasome family members.

Conclusion

Our results provide novel insights in WNT signaling in AML, we discovered new and previously identified prognostic markers and a refinement of the patient groups.

Study of SFRP1 and SFRP2 methylation status in patients with de novo Acute Myeloblastic Leukemia

INTODUCTION

Acute myeloid leukemia (AML) is a heterogeneous group of hematologic malignancies with abundant changeability in the pathogenesis. DNA methylation of CpG islands within the promoters of specific genes may play roles in tumor initiation and progression. Secreted frizzled-related proteins (SFRPs) are negative regulator of the Wnt signaling pathway. In the present study, we examined the methylation status of SFRP1 and SFRP2 genes in patients with AML.

METHODS

Isolated DNA from peripheral blood of 43 AML patients and 25 healthy subjects as a control group was treated with sodium bisulfite was treated with sodium bisulfite and analyzed by methylation-specific polymerase chain reaction (MSP) with primers specific for methylated and unmethylated promoter sequences of the SFRP1 & -2 genes. We used Mann-Whitney u-tests to investigate the correlation between SFRP1 and SFRP2 genes hypermethylation and clinical parameters.

RESULTS

The frequency of aberrant hypermethylation of SFRP1 and SFRP2 genes in patients with AML was determined 30.2% (13/43) and 20.9% (9/43), respectively. In addition, for all subjects in control group, methylation of SFRP1 and SFRP2 genes were negative. Patients with M0 subtype of FAB-AML had the highest incidence of hypermethylation of SFRP1 (P = 0.028) and SFRP2 (P = 0.004).

CONCLUSION

The present study showed that, like many solid tumors, methylation of SFRP genes also occurs in AML. Therefore, the methylation of these genes may play a role in the initiation of leukmogenesis.

Wnt signaling is involved in 6-benzylthioinosine-induced AML cell differentiation

Background

We previously demonstrated that 6-benzylthioinosine (6-BT) could induce the differentiation of a subset of acute myeloid leukemia (AML) cell lines and primary AML cells regardless of their cytogenetics. In this study we investigated whether Wnt signaling pathways played roles in 6-BT-induced differentiation of AML cells.

Methods

We induced differentiation of HL-60 leukemic cells and primary AML cells in vitro using 6-BT. Real-time PCR (qPCR), western blot, and luciferase assays were used to examine the molecules’ expression and biological activity in canonical and noncanonical Wnt signaling pathways. AML cell differentiation was measured by the Nitroblue tetrozolium (NBT) reduction assay.

Results

6-BT regulated the expression of both canonical and non-canonical Wnt signaling molecules in HL-60 cells. Both 6-BT and all-trans-retinoic-acid (ATRA) reduced canonical Wnt signaling and activated noncanonical Wnt/Ca²⁺ signaling in HL-60 cells. Pre-treatment of HL-60 cells with an inhibitor of glycogen synthase kinase-3β (GSK-3β), which activated canonical Wnt signaling, partly abolished the differentiation of HL-60 cells induced by 6-BT. Pre-treatment of HL-60 cells with an inhibitor of protein kinase C (PKC), resulting in inactivation of non-canonical Wnt/Ca²⁺ signaling, abolished 6-BT-induced differentiation of HL-60 cells. Several molecules in the non-canonical Wnt/Ca²⁺ pathway were detected in bone marrow samples from AML patients, and the expression of FZD4, FZD5, Wnt5a and RHOU were significantly reduced in newly diagnosed AML samples compared with normal controls.

Conclusions

Both canonical and non-canonical Wnt signaling were involved in 6-BT-induced differentiation of HL-60 cells, and played opposite roles in this process. Wnt signaling could be involved in the pathogenesis of AML not only by regulating self-renewal of hematopoietic stem cells, but also by playing a role in the differentiation of AML cells.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-886) contains supplementary material, which is available to authorized users.

Regulation of hematopoiesis by activators and inhibitors of Wnt signaling from the niche

Hematopoietic stem cells (HSCs) are a rare population of somatic stem cells that have the ability to regenerate the entire mature blood system in a hierarchical way for the duration of an adult life. Adult HSCs reside in the bone marrow niche. Different niche cell types and molecules regulate the balance of HSC dormancy and activation as well as HSC behavior in both normal and malignant hematopoiesis. Here, we describe the interplay of HSCs and their niche, in particular the involvement of the Wnt signaling pathway. Although the prevailing notion has been that malignant transformation of HSCs is the main cause of leukemia, evidence is mounting that disruption of niche regulation by transformed hematopoietic cells, which may overexpress Wnt signaling or intrinsic stromal defects in gene expression, is at least a collaborative factor in leukemogenesis. Thus, insights into the normal and altered functions of niche components will help to obtain a better understanding of normal and malignant hematopoiesis and how environmental factors affect these processes.

Downregulation of sFRP-2 by epigenetic silencing activates the β-catenin/Wnt signaling pathway in esophageal basaloid squamous cell carcinoma

Basaloid squamous cell carcinoma (BSCC) of the esophagus is a rare variant of typical squamous cell carcinoma (SCC) associated with poor survival. A characteristic feature is nuclear accumulation of β-catenin, without a mutation of the gene. We studied the methylation status of Wnt antagonist genes, such as secreted frizzled-related protein (sFRP) gene family members, Wnt inhibitory factor-1 (WIF-1), Dickkopf-1 (Dkk-1), and human Dapper protein-1 (HDPR-1), and alterations of the APC, Axin1, and Axin2 genes in 30 cases of esophageal BSCC. β-catenin and sFRP (sFRP-1, sFRP-2, sFRP-4, sFRP-5) protein expression was examined by immunohistochemistry. APC, Axin1, and Axin2 gene mutations were detected in 3, 2, and 2 cases, respectively, and 6 cases (20 %) harbored at least 1 alteration in these genes. Methylation of the sFRP-2 promoter region was observed in all cases, and methylation was frequent in sFRP-1 and sFRP-5, but infrequent in Dkk-1, WIF-1, sFRP-4, and HDPR-1. sFRP-2 expression was almost completely absent in 25 cases (83 %), consistent with the methylation status. Nuclear accumulation of β-catenin was observed in all cases. sFRP-5 expression was associated with a low nuclear β-catenin labeling index. These results show that sFRP-2 is a target gene of hypermethylation in esophageal BSCC and suggest that sFRP-2 might contribute to BSCC tumorigenesis through the Wnt/β-catenin signaling pathway.

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.

Syndecan-4 inhibits Wnt/β-catenin signaling through regulation of low-density-lipoprotein receptor-related protein (LRP6) and R-spondin 3

Regulation of Wnt signaling is crucial for embryonic development and adult homeostasis. Here we study the role of Syndecan-4 (SDC4), a cell-surface heparan sulphate proteoglycan, and Fibronectin (FN), in Wnt/β-catenin signaling. Gain- and loss-of-function experiments in mammalian cell lines and Xenopus embryos demonstrate that SDC4 and FN inhibit Wnt/β-catenin signaling. Epistatic and biochemical experiments show that this inhibition occurs at the cell membrane level through regulation of LRP6. R-spondin 3, a ligand that promotes canonical and non-canonical Wnt signaling, is more prone to potentiate Wnt/β-catenin signaling when SDC4 levels are reduced, suggesting a model whereby SDC4 tunes the ability of R-spondin to modulate the different Wnt signaling pathways. Since SDC4 has been previously related to non-canonical Wnt signaling, our results also suggest that this proteoglycan can be a key component in the regulation of Wnt signaling.

Wnt signaling in liver fibrosis: progress, challenges and potential directions

Liver fibrosis is a common wound-healing response to chronic liver injuries, including alcoholic or drug toxicity, persistent viral infection, and genetic factors. Myofibroblastic transdifferentiation (MTD) is the pivotal event during liver fibrogenesis, and research in the past few years has identified key mediators and molecular mechanisms responsible for MTD of hepatic stellate cells (HSCs). HSCs are undifferentiated cells which play an important role in liver regeneration. Recent evidence demonstrates that HSCs derive from mesoderm and at least in part via septum transversum and mesothelium, and HSCs express markers for different cell types which derive from multipotent mesenchymal progenitors. There is a regulatory commonality between differentiation of adipocytes and that of HSC, and the shift from adipogenic to myogenic or neuronal phenotype characterizes HSC MTD. Central of this shift is a loss of expression of the master adipogenic regulator peroxisome proliferator activated receptor γ (PPARγ). Restored expression of PPARγ and/or other adipogenic transcription genes can reverse myofibroblastic HSCs to differentiated cells. Vertebrate Wnt and Drosophila wingless are homologous genes, and their translated proteins have been shown to participate in the regulation of cell proliferation, cell polarity, cell differentiation, and other biological roles. More recently, Wnt signaling is implicated in human fibrosing diseases, such as pulmonary fibrosis, renal fibrosis, and liver fibrosis. Blocking the canonical Wnt signal pathway with the co-receptor antagonist Dickkopf-1 (DKK1) abrogates these epigenetic repressions and restores the gene PPARγ expression and HSC differentiation. The identified morphogen mediated epigenetic regulation of PPARγ and HSC differentiation also serves as novel therapeutic targets for liver fibrosis and liver regeneration. In conclusion, the Wnt signaling promotes liver fibrosis by enhancing HSC activation and survival, and we herein discuss what we currently know and what we expect will come in this field in the next future.

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.

Secreted frizzled-related protein 5 suppresses adipocyte mitochondrial metabolism through WNT inhibition

Preadipocytes secrete several WNT family proteins that act through autocrine/paracrine mechanisms to inhibit adipogenesis. The activity of WNT ligands is often decreased by secreted frizzled-related proteins (SFRPs). Sfrp5 is strongly induced during adipocyte differentiation and increases in adipocytes during obesity, presumably to counteract WNT signaling. We tested the hypothesis that obesity-induced Sfrp5 expression promotes the development of new adipocytes by inhibiting endogenous suppressors of adipogenesis. As predicted, mice that lack functional SFRP5 were resistant to diet-induced obesity. However, counter to our hypothesis, we found that adipose tissue of SFRP5-deficient mice had similar numbers of adipocytes, but a reduction in large adipocytes. Transplantation of adipose tissue from SFRP5-deficient mice into leptin receptor-deficient mice indicated that the effects of SFRP5 deficiency are tissue-autonomous. Mitochondrial gene expression was increased in adipose tissue and cultured adipocytes from SFRP5-deficient mice. In adipocytes, lack of SFRP5 stimulated oxidative capacity through increased mitochondrial activity, which was mediated in part by PGC1α and mitochondrial transcription factor A. WNT3a also increased oxygen consumption and the expression of mitochondrial genes. Thus, our findings support a model of adipogenesis in which SFRP5 inhibits WNT signaling to suppress oxidative metabolism and stimulate adipocyte growth during obesity.