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

Role of epigenetic in cancer biology, in hematologic malignancies and in anticancer therapy

Major epigenetic changes are associated with carcinogenesis, including aberrant DNA methylations and post-translational modifications of histone. Indeed 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-basedclinical and experimental studies, we hypothesize that factors associated with risk for developing a hematologic malignancy (HM), such as metabolic syndrome and chronic inflammation, may trigger epigenetic mechanisms to increase the transcriptional expression of oncogenes and activate oncogenic signaling pathways. Signaling pathways associated with such risk factors include but are not limited to pro-inflammatory nuclear factor κB (NF-κB) and mitogenic, growth, and survival Janus kinase (JAK) intracellular non-receptor tyrosine kinase-triggered pathways. The latter includes 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 the biology of cancer and 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.

BCR-ABL1 Tyrosine Kinase Complex Signaling Transduction: Challenges to Overcome Resistance in Chronic Myeloid Leukemia

The constitutively active BCR-ABL1 tyrosine kinase, found in t(9;22)(q34;q11) chromosomal translocation-derived leukemia, initiates an extremely complex signaling transduction cascade that induces a strong state of resistance to chemotherapy. Targeted therapies based on tyrosine kinase inhibitors (TKIs), such as imatinib, dasatinib, nilotinib, bosutinib, and ponatinib, have revolutionized the treatment of BCR-ABL1-driven leukemia, particularly chronic myeloid leukemia (CML). However, TKIs do not cure CML patients, as some develop TKI resistance and the majority relapse upon withdrawal from treatment. Importantly, although BCR-ABL1 tyrosine kinase is necessary to initiate and establish the malignant phenotype of Ph-related leukemia, in the later advanced phase of the disease, BCR-ABL1-independent mechanisms are also in place. Here, we present an overview of the signaling pathways initiated by BCR-ABL1 and discuss the major challenges regarding immunologic/pharmacologic combined therapies.

Cancer chemoprevention through Frizzled receptors and EMT

Frizzled (FZD) transmembrane receptors are well known for their role in β-catenin signaling and development and now understanding of their role in the context of cancer is growing. FZDs are often associated with the process of epithelial to mesenchymal transition (EMT) through β-catenin, but some also influence EMT through non-canonical pathways. With ten different FZDs, there is a wide range of activity from oncogenic to tumor suppressive depending on the tissue context. Alterations in FZD signaling can occur during development of premalignant lesions, supporting their potential as targets of chemoprevention agents. Agonizing or antagonizing FZD activity may affect EMT, which is a key process in lesion progression often targeted by chemoprevention agents. Recent studies identified a specific FZD as important for activity of an EMT inhibiting chemopreventive agent and other studies have highlighted the previously unrecognized potential for targeting small molecules to FZD receptors. This work demonstrates the value of investigating FZDs in chemoprevention and here we provide a review of FZDs in cancer EMT and their potential as chemoprevention targets.

sFRP1 Expression Regulates Wnt signaling in Chronic Myeloid Leukemia K562 Cells

BACKGROUND

Wnt signaling cascades play important roles in cell fate decisions and their deregulation has been documented in many diseases, including malignant tumors and leukemia. One mechanism of aberrant Wnt signaling is the silencing of Wnt inhibitors through epigenetic mechanisms. The sFRPs are one of the most studied Wnt inhibitors; and the sFRP1 loss is known in many hematological malignancies. Therefore, we aimed to compare the expression of Wnt related genes in the presence and absence of sFRP1 in chronic myeloid leukemia (CML) cell line.

OBJECTIVE

It is important to understand how sFRP1 and sFRP1 perform on CML to design new agents and strategies for resistant and advanced forms of CML.

MATERIALS AND METHODS

We used K562 cells, which normally do not express sFRP1 and its sFRP1 expressing subclone K562s. Total RNA was isolated from K562 and K562s cell lines end converted cDNA. PCR Array experiments performed using Human Wnt Signaling Pathway Plus RT2 Profiler™ kit. Wnt signaling pathway activation was studied by western blot for downstream signaling targets.

RESULTS

The WNT3, LRP6, PRICKLE1 and BTRC expressions were significantly decreased in the presence of sFRP1; while WNT5B increased. The sFRP1 expression inhibited stabilization of total β-catenin protein and downstream effector phosphorylation of noncanonical Wnt/PCP signaling; whereas Ca2+/PKC signaling remained active.

CONCLUSION

Frizzled Receptors in Tumors, Focusing on Signaling, Roles, Modulation Mechanisms, and Targeted Therapies

Wnt molecules play crucial roles in development and adult homeostasis through their receptors Frizzled proteins (Fzds). Fzds mediate canonical β-catenin pathway and various noncanonical β-catenin-independent pathways. Aberrant Fzd signaling is involved in many diseases including cancer. Wnt/β-catenin is a well-established oncogenic pathway involved in almost every aspect of tumor development. However, Fzd-mediated noncanonical Wnt pathways function as both tumor promoters and tumor suppressors depending on cellular context. Fzd-targeted therapies have proven to be effective on cultured tumor cells, tumor cell xenografts, mouse tumor models, and patient-derived xenografts (PDX). Moreover, Fzd-targeted therapies synergize with chemotherapy in preclinical models. However, the occurrence of fragility fractures in patients treated with Fzd-targeted agents such as OMP-54F28 and OMP-18R5 limits the development of this combination. Along with new insights on signaling, roles, and modulation mechanisms of Fzds in human tumors, more Fzd-related therapeutic targets will be developed.

Methyl cap binding protein 2: a key epigenetic protein in systemic sclerosis

OBJECTIVE

SSc is an autoimmune connective tissue disease that results in skin fibrosis and currently has no effective treatment. Epigenetic modifications have been described and these may be key in initiating and driving fibroblast activation. Among these epigenetic modifications methylation may be of central importance. The aim of this study was to examine the role of methyl cap binding protein-2 (MeCP2) in SSc fibrosis.

METHODS

We used healthy and SSc dermal fibroblasts to examine the role of MeCP2, using both small interfering RNA silencing and lentiviral overexpression to determine its effects. We also examined the expression of MeCP2 in SSc fibroblasts by immunoblotting. miRNA132 was quantified by Taqman real time PCR.

RESULTS

We demonstrated that TGF-β1 induced the expression of MeCP2 in normal cells, and showed that SSc fibroblasts expressed high levels of MeCP2 under basal conditions. MeCP2 positively regulated the expression of extracellular matrix through epigenetic repression of the Wnt antagonist sFRP-1, leading to enhanced Wnt signalling. This mediated fibrosis through glycolysis, as the glycolysis inhibitor 2-deoxyglucose diminished the Wnt-mediated collagen expression. MiR132 expression was reduced in SSc fibroblasts.

CONCLUSION

The results suggest that an epigenetic loop exists mediating fibrosis. Targeting of MeCP2, as a key epigenetic regulator, may be a promising therapeutic approach, as would targeting the metabolic reprogramming that occurs through aerobic glycolysis.

Silencing microRNA-27a inhibits proliferation and invasion of human osteosarcoma cells through the SFRP1-dependent Wnt/β-catenin signaling pathway

Osteosarcoma is the most common malignant tumor of bone with a high potential for metastasis. Importantly, microRNA-27a (miR-27a) is involved in the progression of osteosarcoma. The present study aims to discuss the effects of miR-27a and its target gene secreted frizzled related protein 1 (SFRP1) on proliferation and invasion of human osteosarcoma cells via Wnt/β-catenin signaling pathway. The expression of miR-27a and SFRP1 in osteosarcoma tissues and cells was detected, followed by identification of their relations. Subsequently, miR-27a mimic, miR-27a inhibitor, or siRNA against SFRP1 were introduced into cells (HOS and U2OS) to investigate their role in cell proliferation and invasion. The expression of Wnt/β-catenin signaling pathway-related gene was analyzed to further uncover the regulatory mechanism of miR-27a. The osteosarcoma tissues and cells exhibited elevated miR-27 expression and reduced SFRP1 expression. SFRP1 was verified to be a target gene of miR-27a. Meanwhile, silenced miR-27a inhibited proliferation and invasion of human osteosarcoma cells. Finally, silencing miR-27a inhibited the activation of Wnt/β-catenin signaling pathway, evidenced by reduced β-catenin expression. Our study draws a conclusion that silencing miR-27a dampens osteosarcoma progression, which might be achieved through the inactivation of the Wnt/β-catenin signaling pathway by up-regulating SFRP1.

Secreted Wnt antagonists in leukemia: A road yet to be paved

Wnt signaling has been a topic of research for many years for its diverse and fundamental functions in physiological (such as embryogenesis, organogenesis, proliferation, tissue repair and cellular differentiation) and pathological (carcinogenesis, congenital/genetic diseases, and tissue degeneration) processes. Wnt signaling pathway aberrations are associated with both solid tumors and hematological malignancies. Unregulated Wnt signaling observed in malignancies may be due to a wide spectrum of abnormalities, from mutations in the genes of key players to epigenetic modifications of Wnt antagonists. Of these, Wnt antagonists are gaining significant attention for their potential of being targets for treatment and inhibition of Wnt signaling. In this review, we discuss and summarize the significance of Wnt signaling antagonists in the pathogenesis and treatment of hematological malignancies.

Knockdown of the Wnt receptor Frizzled-1 (FZD1) reduces MDR1/P-glycoprotein expression in multidrug resistant leukemic cells and inhibits leukemic cell proliferation

Multidrug resistance (MDR) is a major obstacle to leukemia treatment. The Frizzled-1 (FZD1) Wnt receptor is involved in MDR in some solid cancers, but has rarely been reported to act in acute myeloid leukemia (AML). We investigated whether the knockdown of FZD1 affects MDR1 expression and P-glycoprotein (P-gp) function in multidrug resistant leukemic cell lines, as well as FZD1 and MDR1/P-gp expression in leukemic cells taken from patients with AML (n = 112). FZD1 knockdown significantly reduced MDR1 expression through the Wnt/β-catenin pathway, disrupted the P-gp efflux function, induced the recovery of sensitivity to chemotherapeutic agents, and hindered cell proliferation in cell lines. FZD1 expression in leukemic cells was significantly higher in patients experiencing relapse (n = 34) than in those with no relapse (n = 44, P = .003). Leukemic cells unable to achieve complete response (CR) showed an increased expression of MDR1 and P-gp, compared to patients who achieved CR. Obtaining CR in patients with higher FZD1 expression at diagnosis is difficult. Moreover, they tend to present instances of relapse, suggesting that AML cells with increased FZD1 expression are resistant to chemotherapy. We conclude that the activated FZD1 observed in leukemic cells likely confers acquired drug resistance, whereas FZD1 silencing may be more effective in reversing MDR.

Wnt Signaling in Hematological Malignancies

Leukemia and lymphoma are a wide encompassing term for a diverse set of blood malignancies that affect people of all ages and result in approximately 23,000 deaths in the United States per year (Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016. CA Cancer J Clin. 2016;66(1):7-30.). Hematopoietic stem cells (HSCs) are tissue-specific stem cells at the apex of the hierarchy that gives rise to all of the terminally differentiated blood cells, through progressively restricted progenitor populations, a process that is known to be Wnt-responsive. In particular, the progenitor populations are subject to uncontrolled expansion during oncogenic processes, namely the common myeloid progenitor and common lymphoid progenitor, as well as the myeloblast and lymphoblast. Unregulated growth of these cell-types leads to mainly three types of blood cancers (i.e., leukemia, lymphoma, and myeloma), which frequently exhibit deregulation of the Wnt signaling pathway. Generally, leukemia is caused by the expansion of myeloid progenitors, leading to an overproduction of white blood cells; as such, patients are unable to make sufficient numbers of red blood cells and platelets. Likewise, an overproduction of lymphocytes leads to clogging of the lymph system and impairment of the immune system in lymphomas. Finally, cancer of the plasma cells in the blood is called myeloma, which also leads to immune system failure. Within each of these three types of blood cancers, there are multiple subtypes, usually characterized by their timeline of onset and their cell type of origin. Of these, 85% of leukemias are encompassed by the four most common diseases, that is, acute myeloid leukemia (AML), chronic myeloid leukemia (CML), acute lymphoblastic leukemia (ALL), and chronic lymphocytic leukemia (CLL); AML accounts for the majority of leukemia-related deaths (Siegel RL, Miller KD, Jemal A. Cancer statistics, 2016. CA Cancer J Clin. 2016;66(1):7-30.). Through understanding how HSCs are normally developed and maintained, we can understand how the normal functions of these pathways are disrupted during blood cancer progression; the Wnt pathway is important in regulation of both normal and malignant hematopoiesis. In this chapter, we will discuss the role of Wnt signaling in normal and aberrant hematopoiesis. Our understanding the relationship between Wnt and HSCs will provide novel insights into therapeutic targets.

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.

ROBO3 promotes growth and metastasis of pancreatic carcinoma

Pancreatic carcinoma is a highly lethal malignancy with an extremely poor prognosis. Recent genome-wide studies have implicated axon guidance pathways, including the SLIT/ROBO pathway, in pancreatic tumor development and progression. Here we showed that ROBO3 expression is up-regulated in pancreatic cancer tissue samples and cell lines. Over-expression of ROBO3 promotes pancreatic cancer cell growth, invasion and metastasis in vitro and in mouse xenograft tumor models. We identified miR-383 as a suppressor of ROBO3, and revealed its expression to be inversely correlated with ROBO3. Over-expression of ROBO3 activates Wnt pathway components, β-catenin and GSK-3, and the expression of markers indicating an EMT. By means of immunoprecipitation, we revealed an interaction between Wnt inhibitor SFRP and ROBO3 in pancreatic cancer cell lines. Our work suggests that ROBO3 may contribute to the progression of pancreatic cancer by sequestering Wnt inhibitor SFRP, which in turn leads to increased Wnt/β-catenin pathway activity. We also confirmed that ROBO3 increases with clinical grade and miR-383 expression is inversely correlated to that of ROBO3.

Diagnostic value of SFRP1 as a favorable predictive and prognostic biomarker in patients with prostate cancer

Growing genetic and molecular biological evidence suggests that the disruption of balance between Secreted Frizzled-Related Protein-1 (SFRP1) and β-catenin plays an important role in the initiation and development of multiple cancers. The aim of this study was to examine whether the expression of SFRP1 and β-catenin is associated with the clinical-pathologic features of patients with prostate cancer (PCa), and to evaluate their potential roles as predictive and prognostic biomarkers. In this study, a total of 61 patients with PCa and 10 patients with benign prostatic hyperplasia were included, and we showed that the expression of SFRP1 and β-catenin was correlated with the Gleason score, survival rate and response for endocrine therapy of PCa. The survival rates of PCa patients with low SFRP1 expression (P = 0.016) or high β-catenin expression (P = 0.004) were significantly poorer. A negative correlation (r = -0.275, P = 0.032) between SFRP1 and β-catenin was observed by Chi-square test. Multivariate analysis suggested that SFRP1 (hazard ratio, 0.429; 95% confidence intervals, 0.227–0.812; P = 0.009) may serve as an independent predictive and prognostic factor for PCa. We also showed that the protein and mRNA levels of SFRP1 in androgen-dependent PCa cell line LNCaP were significantly higher than those in androgen-independent PCa cell lines DU145 and PC3. However, the protein level of β-catenin in LNCaP cells was significantly lower than that in DU145 and PC3 cells, and no significant difference of β-catenin mRNA level was observed in LNCaP, DU145 and PC3 cells. Bisulfite sequencing PCR assay revealed significantly lower methylation level of SFRP1 promoter in LNCaP cells than that in DU145 and PC3 cells. Taken together, these findings suggest that SFRP1, which expression inversely correlates with that of β-catenin, is a favorable predictive and prognostic biomarker.

Downregulation of Wnt signaling by sonic hedgehog activation promotes repopulation of human tumor cell lines

Tumor repopulation after radiotherapy is a big obstacle for clinical cancer therapy. The molecular mechanisms of tumor cell repopulation after radiotherapy remain unclear. This study investigated the role of sonic hedgehog (SHH) and Wnt signaling pathways in tumor repopulation after radiotherapy in an in vitro repopulation model. In this model, irradiated dying tumor cells functioned as feeder cells, whereas luciferase-labeled living tumor cells acted as reporter cells. Proliferation of reporter cells was measured by bioluminescence imaging. Results showed that irradiated dying HT29 and Panc1 tumor cells significantly stimulated the repopulation of living cells in their respective cultures. In HT29 and Panc1 cells, radiation significantly inhibited Wnt activity. In the irradiated dying HT29 and Panc1 cells, the level of the activated nuclear β-catenin was significantly decreased. Treatment with the Wnt agonist 68166 significantly decreased, whereas treatment with Wnt antagonist significantly increased, repopulation in HT29 and Panc1 tumor cells in a dose-dependent manner. β-catenin short-hairpin RNA (shRNA) also significantly promoted tumor cell repopulation. The level of secreted frizzled related protein-1 (SFRP1), hedgehog and Gli1 were increased in irradiated cells. Our results highlight the interaction between Wnt and SHH signaling pathways in dying tumor cells and suggest that downregulation of Wnt signaling after SHH activation is negatively associated with tumor repopulation.

Myelodysplasia is in the niche: novel concepts and emerging therapies

Myelodysplastic syndromes (MDSs) represent clonal disorders mainly of the elderly that are characterized by ineffective hematopoiesis and an increased risk of transformation into acute myeloid leukemia. The pathogenesis of MDS is thought to evolve from accumulation and selection of specific genetic or epigenetic events. Emerging evidence indicates that MDS is not solely a hematopoietic disease but rather affects the entire bone marrow microenvironment, including bone metabolism. Many of these cells, in particular mesenchymal stem and progenitor cells (MSPCs) and osteoblasts, express a number of adhesion molecules and secreted factors that regulate blood regeneration throughout life by contributing to hematopoietic stem and progenitor cell (HSPC) maintenance, self-renewal and differentiation. Several endocrine factors, such as erythropoietin, parathyroid hormone and estrogens, as well as deranged iron metabolism modulate these processes. Thus, interactions between MSPC and HSPC contribute to the pathogenesis of MDS and associated pathologies. A detailed understanding of these mechanisms may help to define novel targets for diagnosis and possibly therapy. In this review, we will discuss the scientific rationale of ‘osteohematology' as an emerging research field in MDS and outline clinical implications.

Impaired proliferative potential of bone marrow mesenchymal stromal cells in patients with myelodysplastic syndromes is associated with abnormal WNT signaling pathway

It has been shown that bone marrow mesenchymal stromal cells (MSCs) from patients with myelodysplastic syndromes (MDSs) display defective proliferative potential. We have probed the impaired replicative capacity of culture-expanded MSCs in MDS patients (n=30) compared with healthy subjects (n=32) by studying senescence characteristics and gene expression associated with WNT/transforming growth factor-β1 (TGFB1) signaling pathways. We have also explored the consequences of the impaired patient MSC proliferative potential by investigating their differentiation potential and the capacity to support normal CD34(+) cell growth under coculture conditions. Patient MSCs displayed decreased gene expression of the senescence-associated cyclin-dependent kinase inhibitors CDKN1A, CDKN2A, and CDKN2B, along with PARG1, whereas the mean telomere length was upregulated in patient MSCs. MDS-derived MSCs exhibited impaired capacity to support normal CD34(+) myeloid and erythroid colony formation. No significant changes were observed between patients and controls in gene expression related to TGFB1 pathway. Patient MSCs displayed upregulated non-canonical WNT expression, combined with downregulated canonical WNT expression and upregulated canonical WNT inhibitors. MDS-derived MSCs displayed defective osteogenic and adipogenic lineage priming under non-differentiating culture conditions. Pharmacological activation of canonical WNT signaling in patient MDSs led to an increase in cell proliferation and upregulation in the expression of early osteogenesis-related genes. This study indicates abnormal WNT signaling in MSCs of MDS patients and supports the concept of a primary MSC defect that might have a contributory effect in MDS natural history.

MiR-328 promotes glioma cell invasion via SFRP1-dependent Wnt-signaling activation

Background Diffusely infiltrative growth of human astrocytic gliomas is one of the major obstacles to successful tumor therapy. Thorough insights into the molecules and pathways signaling glioma cell invasion thus appear of major relevance for the development of targeted and individualized therapies. By miRNA expression profiling of microdissected human tumor biopsy specimens we identified miR-328 as one of the main miRNAs upregulated in invading glioma cells in vivo and further investigated its role in glioma pathogenesis. Methods We employed miRNA mimics and inhibitors to functionally characterize miR-328, 3' untranslated region luciferase assays, and T-cell factor/lymphoid enhancer factor reporter assays to pinpoint miR-328 targets and signaling pathways, and analyzed miR-328 expression in a large panel of gliomas. Results First, we corroborated the invasion-promoting role of miR-328 in A172 and TP365MG glioma cells. Secreted Frizzled-related protein 1 (SFRP1), an inhibitor of Wnt signaling, was then pinpointed as a direct miR-328 target. SFRP1 expression is of prognostic relevance in gliomas with reduced expression, being associated with significantly lower overall patient survival in both the Repository of Molecular Brain Neoplasia Data (REMBRANDT) and The Cancer Genome Atlas. Of note, miR-328 regulated both SFRP1 protein expression levels and Wnt signaling pathway activity. Finally, in human glioma tissues miR-328 appeared to account for the downregulation of SFRP1 preferentially in lower-grade astrocytic gliomas and was inversely related to SFRP1 promoter hypermethylation. Conclusion Taken together, we report on a novel molecular miR-328-dependent mechanism that via SFRP1 inhibition and Wnt activation contributes to the infiltrative glioma phenotype at already early stages of glioma progression, with unfavorable prognostic implications for the final outcome of the disease.

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.

While at Rome miRNA and TRAIL do whatever BCR-ABL commands to do

It is a well-acclaimed fact that proteins expressed as a consequence of oncogenic fusions, mutations or amplifications can facilitate ectopic protein-protein interactions that re-wire signal dissemination pathways, in a manner that escalates malignancy. BCR-ABL-mediated signal transduction cascades in leukemic cells are assembled and modulated by a finely controlled network of protein-protein interactions, mediated by characteristic signaling domains and their respective binding motifs. BCR-ABL functions in a cell context-specific and cell type-specific manner to integrate signals that affect uncontrolled cellular proliferation. In this review, we draw attention to the recent progress made in outlining resistance against TRAIL-mediated apoptosis and diametrically opposed roles of miRNAs in BCR-ABL-positive leukemic cells. BCR-ABL governs carcinogenesis through well-organized web of antiapoptotic proteins and over-expressed oncomirs which target death receptors and pro-apoptotic genes. Set of oncomirs which inversely correlate with expression of TRAIL via suppression of SMAD is an important dimension which is gradually gaining attention of the researchers. Contrary to this, some current findings show a new role of BCR-ABL in nucleus with spotlight on apoptosis. It seems obvious that genetic heterogeneity of leukemias poses therapeutic challenges, and pharmacological agents that target components of the cancer promoting nano-machinery still need broad experimental validation to be considered competent as a component of the therapeutic arsenal for this group of diseases. Rapidly developing technologies are empowering us to explain the molecular "nature" of a patient and/or tumor and with this integration of personalized medicine, with maximized efficacy, cost effectiveness will hopefully improve survival chances of the patient.

Myelodysplastic syndrome hematopoietic stem cell

Myelodysplastic syndromes (MDSs) are clonal hematopoietic stem cell (HSC) malignancies that are characterized by ineffective hematopoiesis and frequent progression to acute myeloid leukemia (AML). Thus far, few treatments can actually alter the natural history of this disease. Allogeneic stem-cell transplantation for high-risk MDS is becoming the only curative therapy probably because of the improvement of bone marrow transplant procedures. The lack of other options underscores the urgent need to develop new therapy. The prevailing model suggests that genetic and/or epigenetic alterations that occur in HSCs or HSC niche compromise HSC function, resulting in MDS; therefore, MDS HSCs are likely the ideal targets for MDS treatment. Recent encouraging advances--capturing a molecular portrait of the whole genome of MDS CD34(+) cells, including identifying altered signaling pathways and altered microRNAs--have improved our understanding of MDS pathogenesis and provided novel potential clinical targets for MDS. Here, I will briefly review the characteristics of MDS HSCs and discuss the therapeutic promise of targeting MDS HSCs.

Frizzled homolog proteins, microRNAs and Wnt signaling in cancer

Wnt signaling pathways play important roles in tumorigenesis and are initiated by binding of Wnt to various receptors including frizzleds (FZDs). FZDs are one of several families of receptors comprised of FZD/LRP/ROR2/RYK in the Wnt signaling pathway. Expression of some FZD receptors are up regulated, thereby activating the Wnt signaling pathway and is correlated with cancer malignancy and patient outcomes (recurrence and survival) in many cancers. The FZD family contains ten genes in humans and their function has not been completely examined including the regulatory mechanisms of FZD genes in cancer. Knockdown of FZDs may suppress the Wnt signaling pathway resulting in decreased cell growth, invasion, motility and metastasis of cancer cells. Recently a number of microRNAs (miRNAs) have been identified and reported to be important in several cancers. MiRNAs regulate target gene expression at both the transcription and translation levels. The study of miRNA is a newly emerging field and promises to be helpful in understanding the pathogenesis of FZDs in cancer. In addition, miRNAs may be useful in regulating FZDs in cancer cells. Therefore, the aim of this review is to discuss current knowledge of the functional mechanisms of FZDs in cancer, including regulation by miRNAs and the potential for possible use of miRNAs and FZDs in future clinical applications.

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.

Effect of etafenone on total and regional myocardial blood flow

The distribution of blood flow to the subendocardial, medium and subepicardial layers of the left ventricular free wall was studied in anaesthetized dogs under normoxic (A), hypoxic (B) conditions and under pharmacologically induced (etafenone) coronary vasodilation (C). Regional myocardial blood flow was determined by means of the particle distribution method. In normoxia a transmural gradient of flow was observed, with the subendocardial layers receiving a significantly higher flow rate compared with the subepicardial layers. In hypoxia induced vasodilation this transmural gradient of flow was persistent. In contrast a marked redistribution of regional flow was observed under pharmacologically induced vasodilation. The transmural gradient decreased. In contrast to some findings these experiments demonstrate that a considerable vasodilatory capacity exists in all layers of the myocardium and can be utilized by drugs. The differences observed for the intramural distribution pattern of flow under hypoxia and drug induced vasodilation support the hypothesis that this pattern reflects corresponding gradients of regional myocardial metabolism.