Key roles of histone methyltransferase and demethylase in leukemogenesis

Histone Demethylase Modulation: Epigenetic Strategy to Combat Cancer Progression

Epigenetic modifications are heritable, reversible changes in histones or the DNA that control gene functions, being exogenous to the genomic sequence itself. Human diseases, particularly cancer, are frequently connected to epigenetic dysregulations. One of them is histone methylation, which is a dynamically reversible and synchronously regulated process that orchestrates the three-dimensional epigenome, nuclear processes of transcription, DNA repair, cell cycle, and epigenetic functions, by adding or removing methylation groups to histones. Over the past few years, reversible histone methylation has become recognized as a crucial regulatory mechanism for the epigenome. With the development of numerous medications that target epigenetic regulators, epigenome-targeted therapy has been used in the treatment of malignancies and has shown meaningful therapeutic potential in preclinical and clinical trials. The present review focuses on the recent advances in our knowledge on the role of histone demethylases in tumor development and modulation, in emphasizing molecular mechanisms that control cancer cell progression. Finally, we emphasize current developments in the advent of new molecular inhibitors that target histone demethylases to regulate cancer progression.

KDM3B suppresses APL progression by restricting chromatin accessibility and facilitating the ATRA-mediated degradation of PML/RARα

Background

A hallmark of acute promyelocytic leukemia (APL) is the expression of PML/RARα fusion protein. Treatment with all-trans retinoic acid (ATRA) results in the terminal differentiation of neutrophil granulocytes. However, the underlying mechanisms remain largely unknown. Here, we identify and elucidate a novel differentiation-suppressive model of APL involving the histone demethylase KDM3B, which has been identified as a suppressor of the tumor genes involved in hematopoietic malignancies.

Methods

First, we established a KDM3B knockdown NB4 cell model to determine the functional characteristics of KDM3B by cell proliferation assay and flow cytometry. Then, we performed ChIP-seq and ATAC-seq to search for potential relationships among KDM3B, histone modification (H3K9me1/me2) and the chromatin state. Finally, molecular biological techniques and a multi-omics analysis were used to explore the role of KDM3B in differentiation of the leukemia cells after ATRA treatment.

Results

We found that knocking down KDM3B contributed to the growth of NB4 APL cells via the promotion of cell-cycle progression and blocked granulocytic differentiation. Through global and molecular approaches, we provided futher evidence that knocking down KDM3B altered the global distribution of H3K9me1/me2 and increased the chromatin accessibility. Moreover, knocking down KDM3B inhibited the ATRA-induced degradation of the PML/RARα oncoprotein.

Conclusion

Our study suggested that KDM3B was able to inhibit APL progression by maintaining chromatin in a compact state and facilitating the ATRA-mediated degradation of PML/RARα. Taken together, the results show that KDM3B may be an alternative target for the treatment regimens and the targeted therapy for APL by sustaining the function of PML/RARα fusion protein.

JmjC domain-containing protein 8 (JMJD8) represses Ku70/Ku80 expression via attenuating AKT/NF-κB/COX-2 signaling

Jumonji C (JmjC) domain-containing proteins have been shown to regulate cellular processes by hydroxylating or demethylating histone and non-histone targets. JMJD8 is a Jumonji C domain-containing protein localized in the lumen of the endoplasmic reticulum and was recently shown to be involved in endothelial differentiation and cellular inflammation response. However, other physiological functions of JMJD8 remain to be elucidated. In this research, we found that knockdown of JMJD8 in cancer cells significantly increased cell proliferation, and attenuated ionizing irradiation or etoposide treatment-induced DNA double-strand breaks (DSBs) level through enhancing the expression of Ku70 and Ku80 which are key participants in the non-homologous end-joining repair of DSBs. We also provided evidence to show that knockdown of JMJD8 up-regulated cyclooxygenase-2 (COX-2) expression which contributed to the enhanced expression of Ku70/Ku80 as shown by the results that pre-treatment of JMJD8 knockdown cells with COX-2 selective inhibitor NS-398 inhibited the induction of Ku70/Ku80. Furthermore, we identified that the up-regulation of COX-2 in JMJD8 knockdown cells was partially due to the increased activation of AKT/NF-κB signaling, and LY294002 (an inhibitor of the PI3K/AKT signaling pathway) repressed the induction of COX-2 and Ku70/Ku80. In conclusion, our research provided data to establish the role of JMJD8 in regulating tumor cell proliferation and their sensitivity to ionizing irradiation or chemo-therapy drug, and the AKT/NF-κB/COX-2 signaling mediated expression of Ku70/Ku80 was involved. The results of this research indicated that JMJD8 is a potential target for enhancing the efficacy of tumor radio- and chemo-therapies.

Epigenetic modifications in chronic myeloid leukemia cells through ruxolitinib treatment

Chronic myeloid leukemia is a clonal malignancy of hematopoietic stem cell that is characterized by the occurrence of t(9;22)(q34;q11.2) translocation, named Philadelphia chromosome. Ruxolitinib is a powerful Janus tyrosine kinase 1 and 2 inhibitor that is used for myelofibrosis treatment. DNA-histone connection mediates a wide range of genes that code methylation, demethylation, acetylation, deacetylation, ubiquitination, and phosphorylation enzymes. Epigenetic modifications regulate chromatin compactness, which plays pivotal roles in critical biological processes including the transcriptional activity and cell proliferation as well as various pathological mechanisms, including CML. This study is aimed to determine the alterations of the expression levels of epigenetic modification-related genes after ruxolitinib treatment. Total RNA was isolated from K-562 cells treated with the IC₅₀ value of ruxolitinib and untreated K-562 control cells. A reverse transcription procedure was performed for complementary DNA synthesis, and gene expressions were detected by real-time polymerase chain reaction compared with the untreated cells. Ruxolitinib treatment caused a significant alteration in the expression levels of epigenetic regulation-related genes in K-562 cells. Our novel results suggested that ruxolitinib has inhibitor effects on epigenetic modification-regulator genes.

Epigenetic therapy in gastrointestinal cancer: the right combination

Epigenetics is a relatively recent field of molecular biology that has arisen over the past 25 years. Cancer is now understood to be a disease of widespread epigenetic dysregulation that interacts extensively with underlying genetic mutations. The development of drugs targeting these processes has rapidly progressed; with several drugs already FDA approved as first-line therapy in hematological malignancies. Gastrointestinal (GI) cancers possess high degrees of epigenetic dysregulation, exemplified by subtypes such as CpG island methylator phenotype (CIMP), and the potential benefit of epigenetic therapy in these cancers is evident. The application of epigenetic drugs in solid tumors, including GI cancers, is just emerging, with increased understanding of the cancer epigenome. In this review, we provide a brief overview of cancer epigenetics and the epigenetic targets of therapy including deoxyribonucleic acid (DNA) methylation, histone modifications, and chromatin remodeling. We discuss the epigenetic drugs currently in use, with a focus on DNA methyltransferase (DNMT) and histone deacetylase (HDAC) inhibitors, and explain the pharmacokinetic and mechanistic challenges in their application. We present the strategies employed in incorporating these drugs into the treatment of GI cancers, and explain the concept of the cancer stem cell in epigenetic reprogramming and reversal of chemo resistance. We discuss the most promising combination strategies in GI cancers including: (1) epigenetic sensitization to radiotherapy, (2) epigenetic sensitization to cytotoxic chemotherapy, and (3) epigenetic immune modulation and priming for immune therapy. Finally, we present preclinical and clinical trial data employing these strategies thus far in various GI cancers including colorectal, esophageal, gastric, and pancreatic cancer.

Inhibition of H3K9me2 Reduces Hair Cell Regeneration after Hair Cell Loss in the Zebrafish Lateral Line by Down-Regulating the Wnt and Fgf Signaling Pathways

The activation of neuromast (NM) supporting cell (SC) proliferation leads to hair cell (HC) regeneration in the zebrafish lateral line. Epigenetic mechanisms have been reported that regulate HC regeneration in the zebrafish lateral line, but the role of H3K9me2 in HC regeneration after HC loss remains poorly understood. In this study, we focused on the role of H3K9me2 in HC regeneration following neomycin-induced HC loss. To investigate the effects of H3K9me2 in HC regeneration, we took advantage of the G9a/GLP-specific inhibitor BIX01294 that significantly reduces the dimethylation of H3K9. We found that BIX01294 significantly reduced HC regeneration after neomycin-induced HC loss in the zebrafish lateral line. BIX01294 also significantly reduced the proliferation of NM cells and led to fewer SCs in the lateral line. In situ hybridization showed that BIX01294 significantly down-regulated the Wnt and Fgf signaling pathways, which resulted in reduced SC proliferation and HC regeneration in the NMs of the lateral line. Altogether, our results suggest that down-regulation of H3K9me2 significantly decreases HC regeneration after neomycin-induced HC loss through inactivation of the Wnt/β-catenin and Fgf signaling pathways. Thus H3K9me2 plays a critical role in HC regeneration.

Transcriptional repression of ANGPT1 by histone H3K9 demethylase KDM3B

Here we report that the H3K9 demethylase KDM3B represses transcription of the angiogenesis regulatory gene, ANGPT1. Negative regulation of ANGPT1 by KDM3B is independent of its Jumonji (JmjC) domain-mediated H3K9 demethylase activity. We demonstrate that KDM3B downregulates ANGPT1 via interaction with SMRT, and suggest that the repressor complex is formed at the promoter area of ANGPT1. Using MTT and wound healing assays, depletion of KDM3B was found to increase cell proliferation and cell motility, indicating that KDM3B has a role in angiogenesis. [BMB Reports 2015; 48(7): 401-406]

Defining and Treating Older Adults with Acute Myeloid Leukemia Who Are Ineligible for Intensive Therapies

Although acute myeloid leukemia (AML) is primarily a disease of older adults (age ≥60 years), the optimal treatment for older adults remains largely undefined. Intensive chemotherapy is rarely beneficial for frail older adults or those with poor-risk disease, but criteria that define fitness and/or appropriateness for intensive chemotherapy remain to be standardized. Evaluation of disease-related and patient-specific factors in the context of clinical decision making has therefore been largely subjective. A uniform approach to identify those patients most likely to benefit from intensive therapies is needed. Here, we review currently available objective measures to define older adults with AML who are ineligible for intensive chemotherapy, and discuss promising investigational approaches.

LSD1 is Required for Hair Cell Regeneration in Zebrafish

Lysine-specific demethylase 1 (LSD1/KDM1A) plays an important role in complex cellular processes such as differentiation, proliferation, apoptosis, and cell cycle progression. It has recently been demonstrated that during development, downregulation of LSD1 inhibits cell proliferation, modulates the expression of cell cycle regulators, and reduces hair cell formation in the zebrafish lateral line, which suggests that LSD1-mediated epigenetic regulation plays a key role in the development of hair cells. However, the role of LSD1 in hair cell regeneration after hair cell loss remains poorly understood. Here, we demonstrate the effect of LSD1 on hair cell regeneration following neomycin-induced hair cell loss. We show that the LSD1 inhibitor trans-2-phenylcyclopropylamine (2-PCPA) significantly decreases the regeneration of hair cells in zebrafish after neomycin damage. In addition, immunofluorescent staining demonstrates that 2-PCPA administration suppresses supporting cell proliferation and alters cell cycle progression. Finally, in situ hybridization shows that 2-PCPA significantly downregulates the expression of genes related to Wnt/β-catenin and Fgf activation. Altogether, our data suggest that downregulation of LSD1 significantly decreases hair cell regeneration after neomycin-induced hair cell loss through inactivation of the Wnt/β-catenin and Fgf signaling pathways. Thus, LSD1 plays a critical role in hair cell regeneration and might represent a novel biomarker and potential therapeutic approach for the treatment of hearing loss.

Chromatin dynamics: H3K4 methylation and H3 variant replacement during development and in cancer

The dynamic nature of chromatin and its myriad modifications play a crucial role in gene regulation (expression and repression) during development, cellular survival, homeostasis, ageing, and apoptosis/death. Histone 3 lysine 4 methylation (H3K4 methylation) catalyzed by H3K4 specific histone methyltransferases is one of the more critical chromatin modifications that is generally associated with gene activation. Additionally, the deposition of H3 variant(s) in conjunction with H3K4 methylation generates an intricately reliable epigenetic regulatory circuit that guides transcriptional activity in normal development and homeostasis. Consequently, alterations in this epigenetic circuit may trigger disease development. The mechanistic relationship between H3 variant deposition and H3K4 methylation during normal development has remained foggy. However, recent investigations in the field of chromatin dynamics in various model organisms, tumors, cancer tissues, and cell lines cultured without and with therapeutic agents, as well as from model reconstituted chromatins reveal that there may be different subsets of chromatin assemblage with specific patterns of histone replacement executing similar functions. In this light, we attempt to explain the intricate control system that maintains chromatin structure and dynamics during normal development as well as during tumor development and cancer progression in this review. Our focus is to highlight the contribution of H3K4 methylation-histone variant crosstalk in regulating chromatin architecture and subsequently its function.

Reversible LSD1 inhibition interferes with global EWS/ETS transcriptional activity and impedes Ewing sarcoma tumor growth

PURPOSE

Ewing sarcoma is a pediatric bone tumor that absolutely relies on the transcriptional activity of the EWS/ETS family of fusion oncoproteins. While the most common fusion, EWS/FLI, utilizes lysine-specific demethylase 1 (LSD1) to repress critical tumor suppressors, small-molecule blockade of LSD1 has not yet been thoroughly explored as a therapeutic approach for Ewing sarcoma. We therefore evaluated the translational potential of potent and specific LSD1 inhibition with HCI2509 on the transcriptional program of both EWS/FLI and EWS/ERG as well as the downstream oncogenic phenotypes driven by EWS/ETS fusions in both in vitro and in vivo models of Ewing sarcoma.

EXPERIMENTAL DESIGN

RNA-seq was used to compare the transcriptional profiles of EWS/FLI, EWS/ERG, and treatment with HCI2509 in both EWS/FLI- and EWS/ERG-containing cell lines. We then evaluated morphologic phenotypes of treated cells with immunofluorescence. The induction of apoptosis was evaluated using caspase-3/7 activation and TUNEL staining. Colony forming assays were used to test oncogenic transformation and xenograft studies with patient-derived cell lines were used to evaluate the effects of HCI2509 on tumorigenesis.

RESULTS

HCI2509 caused a dramatic reversal of both the up- and downregulated transcriptional profiles of EWS/FLI and EWS/ERG accompanied by the induction of apoptosis and disruption of morphologic and oncogenic phenotypes modulated by EWS/FLI. Importantly, HCI2509 displayed single-agent efficacy in multiple xenograft models.

CONCLUSIONS

These data support epigenetic modulation with HCI2509 as a therapeutic strategy for Ewing sarcoma, and highlight a critical dual role for LSD1 in the oncogenic transcriptional activity of EWS/ETS proteins.

Inhibition of histone methyltransferase EZH2 depletes leukemia stem cell of mixed lineage leukemia fusion leukemia through upregulation of p16

Leukemia stem cells (LSC) are resistant to conventional chemotherapy and persistent LSC after chemotherapy are supposed to be a major cause of relapse. However, information on genetic or epigenetic regulation of stem cell properties is still limited and LSC-targeted drugs have scarcely been identified. Epigenetic regulators are associated with many cellular processes including maintenance of stem cells. Of note are polycomb group proteins, because they potentially control stemness, and can be pharmacologically targeted by a selective inhibitor (DZNep). Therefore, we investigated the therapeutic potential of EZH2 inhibition in mixed lineage leukemia (MLL) fusion leukemia. Intriguingly, EZH2 inhibition by DZNep or shRNA not only suppressed MLL fusion leukemia proliferation but also reduced leukemia initiating cells (LIC) frequency. Expression analysis suggested that p16 upregulation was responsible for LICs reduction. Knockdown of p16 canceled the survival advantage of mice treated with DZNep. Chromatin immunoprecipitation assays demonstrated that EZH2 was highly enriched around the transcription-start-site of p16, together with H3K27 methylation marks in MLL/ENL and Hoxa9/Meis1 transduced cells but not in E2A/HLF transduced cells. Although high expression of Hoxa9 in MLL fusion leukemia is supposed to be responsible for the recruitment of EZH2, our data also suggest that there may be some other mechanisms independent of Hoxa9 activation to suppress p16 expression, because expression levels of Hoxa9 and p16 were not inversely related between MLL/ENL and Hoxa9/Meis1 transduced cells. In summary, our findings show that EZH2 is a potential therapeutic target of MLL fusion leukemia stem cells.

SMYD2 is highly expressed in pediatric acute lymphoblastic leukemia and constitutes a bad prognostic factor

Acute lymphoblastic leukemia (ALL) is the most common childhood malignancy. Although several clinical characteristics can be associated with worse prognosis, more robust biological markers still remains uncovered. SMYD2, a member of SMYD protein family, regulates the activity of several proteins through methylation. In this study, we performed quantitative real time PCR to compare the expression of SMYD2 in 83 pediatric ALL patients and non-neoplastic bone marrow samples (BMS). The study revealed that SMYD2 expression is altered in ALL BMS and its high expression was correlated with a bad prognosis. Moreover, we also revealed that SMYD2 expression level significantly decreases in patients that respond to chemotherapy treatment.

Histone lysine-specific methyltransferases and demethylases in carcinogenesis: new targets for cancer therapy and prevention

Aberrant histone lysine methylation that is controlled by histone lysine methyltransferases (KMTs) and demethylases (KDMs) plays significant roles in carcinogenesis. Infections by tumor viruses or parasites and exposures to chemical carcinogens can modify the process of histone lysine methylation. Many KMTs and KDMs contribute to malignant transformation by regulating the expression of human telomerase reverse transcriptase (hTERT), forming a fused gene, interacting with proto-oncogenes or being up-regulated in cancer cells. In addition, histone lysine methylation participates in tumor suppressor gene inactivation during the early stages of carcinogenesis by regulating DNA methylation and/or by other DNA methylation independent mechanisms. Furthermore, recent genetic discoveries of many mutations in KMTs and KDMs in various types of cancers highlight their numerous roles in carcinogenesis and provide rare opportunities for selective and tumor-specific targeting of these enzymes. The study on global histone lysine methylation levels may also offer specific biomarkers for cancer detection, diagnosis and prognosis, as well as for genotoxic and non-genotoxic carcinogenic exposures and risk assessment. This review summarizes the role of histone lysine methylation in the process of cellular transformation and carcinogenesis, genetic alterations of KMTs and KDMs in different cancers and recent progress in discovery of small molecule inhibitors of these enzymes.

Gene amplification of the histone methyltransferase SETDB1 contributes to human lung tumorigenesis

Disruption of the histone modification patterns is one of the most common features of human tumors. However, few genetic alterations in the histone modifier genes have been described in tumorigenesis. Herein we show that the histone methyltransferase SETDB1 undergoes gene amplification in non-small and small lung cancer cell lines and primary tumors. The existence of additional copies of the SETDB1 gene in these transformed cells is associated with higher levels of the corresponding mRNA and protein. From a functional standpoint, the depletion of SETDB1 expression in amplified cells reduces cancer growth in cell culture and nude mice models, whereas its overexpression increases the tumor invasiveness. The increased gene dosage of SETDB1 is also associated with enhanced sensitivity to the growth inhibitory effect mediated by the SETDB1-interfering drug mithramycin. Overall, the findings identify SETDB1 as a bona fide oncogene undergoing gene amplification-associated activation in lung cancer and suggest its potential for new therapeutic strategies.

Nitric oxide modifies global histone methylation by inhibiting Jumonji C domain-containing demethylases

Methylation of lysine residues on histone tails is an important epigenetic modification that is dynamically regulated through the combined effects of methyltransferases and demethylases. The Jumonji C domain Fe(II) α-ketoglutarate family of proteins performs the majority of histone demethylation. We demonstrate that nitric oxide ((•)NO) directly inhibits the activity of the demethylase KDM3A by forming a nitrosyliron complex in the catalytic pocket. Exposing cells to either chemical or cellular sources of (•)NO resulted in a significant increase in dimethyl Lys-9 on histone 3 (H3K9me2), the preferred substrate for KDM3A. G9a, the primary methyltransferase acting on H3K9me2, was down-regulated in response to (•)NO, and changes in methylation state could not be accounted for by methylation in general. Furthermore, cellular iron sequestration via dinitrosyliron complex formation correlated with increased methylation. The mRNA of several histone demethylases and methyltransferases was also differentially regulated in response to (•)NO. Taken together, these data reveal three novel and distinct mechanisms whereby (•)NO can affect histone methylation as follows: direct inhibition of Jumonji C demethylase activity, reduction in iron cofactor availability, and regulation of expression of methyl-modifying enzymes. This model of (•)NO as an epigenetic modulator provides a novel explanation for nonclassical gene regulation by (•)NO.

Small changes, big effects: chromatin goes aging

Aging is a complex trait and is influenced by multiple factors that are both intrinsic and extrinsic to the organism (Kirkwood et al. 2000; Knight 2000). Efforts to understanding the mechanisms that extend or shorten lifespan have been made since the early twentieth century. Aging is characteristically associated with a progressive decline in the overall fitness of the organism. Several studies have provided valuable information about the molecular events that accompany this process and include accumulation of nuclear and mitochondrial mutations, shortened and dysfunctional telomeres, oxidative damage of protein/DNA, senescence and apoptosis (Muller 2009). Clinical studies and work on model organisms have shown that there is an increased susceptibility to conditions such as neurological disorders, diabetes, cardiovascular diseases, degenerative syndromes and even cancers, with age (Arvanitakis et al. 2006; Lee and Kim 2006; Rodriguez and Fraga 2010).

Citosol (thiamylal sodium) triggers apoptosis and affects gene expressions of murine leukemia RAW 264.7 cells

Citosol (thiamylal sodium) is one of generally used anesthetic–sedative agents for clinical patients, and it has not been reported to show induction of cytotoxic effects in cancer cells, especially in mice leukemia RAW 264.7 cells in vitro. In the present study, we investigated the cytotoxic effects of citosol on mice leukemic RAW 264.7 cells, including the effects on protein and gene expression levels which are determined by Western blotting and DNA microarray methods, respectively. Results indicated that citosol induced cell morphological changes, cytotoxic effect, and induction of apoptosis in RAW 264.7 cells. Western blotting analysis demonstrated that citosol promoted the levels of Fas, cytochrome c, caspase 9 and 3 active form and Bax levels, but it suppressed Bcl-xl protein level that may lead to apoptotic death in RAW 264.7 cells. Furthermore, DNA microarray assay indicated that citosol significantly promoted the expression of 5 genes (Gm4884, Gm10883, Lce1c, Lrg1, and LOC100045878) and significantly inhibited the expression of 24 genes (Gm10679, Zfp617, LOC621831, Gm5929, Snord116, Gm3994, LOC380994, Gm5592, LOC380994, LOC280487, Gm4638, Tex24, A530064D06Rik, BC094916, EG668725, Gm189, Hist2h3c2, Gm8020, Snord115, Gm3079, Olfr198, Tdh, Snord115, and Olfr1249). Based on these observations, citosol induced cell apoptosis and influenced gene expression in mice leukemia RAW 264.7 cells in vitro.

The role of histone demethylases in cancer therapy

Reversible histone methylation has emerged in the last few years as an important mechanism of epigenetic regulation. Histone methyltransferases and demethylases have been identified as contributing factors in the development of several diseases, especially cancer. Therefore, they have been postulated to be new drug targets with high therapeutic potential. Here, we review histone demethylases with a special focus on their potential role in oncology drug discovery. We present an overview over the different classes of enzymes, their biochemistry, selected data on their role in physiology and already available inhibitors.

Molecular mechanisms and potential functions of histone demethylases

Histone modifications are thought to regulate chromatin structure, transcription and other nuclear processes. Histone methylation was originally believed to be an irreversible modification that could only be removed by histone eviction or by dilution during DNA replication. However, the isolation of two families of enzymes that can demethylate histones has changed this notion. The biochemical activities of these histone demethylases towards specific Lys residues on histones, and in some cases non-histone substrates, have highlighted their importance in developmental control, cell-fate decisions and disease. Their ability to be regulated through protein-targeting complexes and post-translational modifications is also beginning to shed light on how they provide dynamic control during transcription.

Epigenetic-based therapies in cancer: progress to date

Epigenetic gene silencing is a hallmark of cancer cells. Two important types of epigenetic changes are DNA methylation and histone modification. These modifications are catalysed by DNA methyltransferases (DNMTs) and histone deacetylases (HDACs), resulting in chromatin structure changes and gene inactivation. Interestingly, inhibition of these enzymes is known to induce differentiation or apoptosis of cancer cells. Therefore, DNMTs and HDACs have become attractive therapeutic targets. In recent years, many different DNMT and HDAC inhibitors have been developed, and multiple molecular mechanisms through which these agents exert anti-cancer effects have been identified. While a large number of clinical trials are ongoing, hypomethylating agents and HDAC inhibitors seem to be promising for treating several types of cancer. Moreover, developing effective strategies of combining epigenetic therapy with conventional chemotherapy will be one of the major challenges in the future. We briefly review current advances in epigenetic therapies with a focus on recently reported clinical trials.

Evi1 forms a bridge between the epigenetic machinery and signaling pathways

Recent studies have demonstrated the significance of the leukemia oncogene Evi1 as the regulator of hematopoietic stem cells and marker of poor clinical outcomes in myeloid malignancies. Evi1-mediated leukemogenic activities include a wide array of functions such as the induction of epigenetic modifications, transcriptional control, and regulation of signaling pathways. We have recently succeeded in comprehensively elucidating the oncogenic function of Evi1 in a model of the polycomb-Evi1-PTEN/AKT/mTOR axis. These results may provide us with novel therapeutic approaches to conquer the poor prognosis associated with Evi1-activated leukemia or other solid tumors with high Evi1 expression. Here, we review the current understanding of the role of Evi1 in controlling the development of leukemia and highlight potential modalities for targeting factors involved in Evi1-regulated signaling.

Cancer and altered metabolism: potential importance of hypoxia-inducible factor and 2-oxoglutarate-dependent dioxygenases

Hypoxia-inducible factor (HIF) deregulation contributes to the Warburg effect. HIF consists of an unstable α subunit and a stable β subunit. In the presence of oxygen, HIFα becomes prolyl hydroxylated by members of the EglN (also called PHD) family, leading to its proteasomal degradation. Under hypoxic conditions, EglN activity is diminished and HIF levels rise. EglN1 is the primary HIF prolyl hydroxylase with EglN2 and EglN3 playing compensatory roles under certain conditions. EglN2 and EglN3 also appear to play HIF-independent roles in regulating cell proliferation and apoptosis, respectively. The EglNs belong to a large family of 2-oxoglutarate-dependent dioxygenases that includes the TET DNA hydroxymethylases and JmjC-containing histone demethylases. Members of this superfamily can be inhibited by endogenous metabolites, including fumarate and succinate, which accumulate in tumors that have fumarate hydratase (FH) or succinate dehydrogenase (SDH) mutations, respectively, as well as by the 2-hydroxyglutarate detected in isocitrate dehydrogenase (IDH) mutant tumors. 2-Oxoglutarate-dependent dioxygenases therefore provide a link between altered metabolism and cancer.