Hypoxia-inducible factor-1α-induced differentiation of myeloid leukemic cells is its transcriptional activity independent

Emerging roles of MITF as a crucial regulator of immunity

Microphthalmia-associated transcription factor (MITF), a basic helix-loop-helix leucine zipper transcription factor (bHLH-Zip), has been identified as a melanocyte-specific transcription factor and plays a critical role in melanocyte survival, differentiation, function, proliferation and pigmentation. Although numerous studies have explained the roles of MITF in melanocytes and in melanoma development, the function of MITF in the hematopoietic or immune system-beyond its function in melanin-producing cells-is not yet fully understood. However, there is convincing and increasing evidence suggesting that MITF may play multiple important roles in immune-related cells. Therefore, this review is focused on recent advances in elucidating novel functions of MITF in cancer progression and immune responses to cancer. In particular, we highlight the role of MITF as a central modulator in the regulation of immune responses, as elucidated in recent studies.

MicroRNAs and JAK/STAT3 signaling: A new promising therapeutic axis in blood cancers

Blood disorders include a wide spectrum of blood-associated malignancies resulting from inherited or acquired defects. The ineffectiveness of existing therapies against blood disorders arises from different reasons, one of which is drug resistance, so different types of leukemia may show different responses to treatment. Leukemia occurs for a variety of genetic and acquired reasons, leading to uncontrolled proliferation in one or more cell lines. Regarding the genetic defects, oncogene signal transducer and activator of transcription (STAT) family transcription factor, especially STAT3, play an essential role in hematological disorders onset and progress upon mutations, dysfunction, or hyperactivity. Besides, microRNAs, as biological molecules, has been shown to play a dual role in either tumorigenesis and tumor suppression in various cancers. Besides, a strong association between STAT3 and miRNA has been reported. For example, miRNAs can regulate STAT3 via targeting its upstream mediators such as IL6, IL9, and JAKs or directly binding to the STAT3 gene. On the other hand, STAT3 can regulate miRNAs. In this review study, we aimed to determine the role of either microRNAs and STAT3 along with their effect on one another's activity and function in hematological malignancies.

Effects of hypoxia on DNA hydroxymethylase Tet methylcytosine dioxygenase 2 in a KG-1 human acute myeloid leukemia cell line and its mechanism

Hypoxia is involved in the epigenetic modification of leukemia. As an important DNA hydroxymethylase and a tumor suppressor gene, the expression regulating mechanism of Tet methylcytosine dioxygenase 2 (TET2) remains unclear. The aim of the present study was to explore whether hypoxia and hypoxia-inducible factor 1α (HIF-1α) regulate TET2 gene expression and its demethylation function in acute myeloid leukemia (AML). The human AML cell line KG-1 was used in the present study. The results demonstrated that hypoxia could increase proliferation, enhance metabolism and inhibit apoptosis in KG-1 cells, as detected by the cell counting kit-8 assay, lactate dehydrogenase assay and Annexin V-FITC/propidium iodide staining, respectively. Hypoxia reduced the genome methylation status in KG-1 cells detected using 5-methylcytosine and 5-hydroxymethylcytosine detection kits. In addition, HIF-1α overexpression increased TET2 expression, 5-hmC level and cyclin-dependent kinase inhibitor 2B [p15(INK4B)] gene demethylation compared with the HIF-1α non-overexpression group in KG-1 cells detected by reverse transcription-quantitative PCR, western blotting, 5-hydroxymethylcytosine detection kits and methylation-specific PCR, respectively. The inhibition of HIF-1α by inhibitor YC-1 reduced demethylation in KG-1 cells by decreasing TET2 expression. It was also revealed that HIF-1α could enhance TET2 transcriptional activity by binding to the hypoxia response element of the TET2 gene promoter region using chromatin immunoprecipitation and luciferase reporter gene assays. TET2 may be a potential target gene regulated by HIF-1α. Hypoxia was demonstrated to regulate the expression of TET2 by HIF-1α, which in turn affected the methylation and expression of downstream target genes and served a role in the occurrence and progression of leukemia. In the present study, the association between hypoxia metabolism and epigenetic regulation in AML was investigated and the findings provided a new idea and experimental basis for the diagnosis and treatment of hematologic malignancies.

Recent Advances in Glioma Therapy: Combining Vascular Normalization and Immune Checkpoint Blockade

Glioblastoma (GBM) accounts for more than 50% of all primary malignancies of the brain. Current standard treatment regimen for GBM includes maximal surgical resection followed by radiation and adjuvant chemotherapy. However, due to the heterogeneity of the tumor cells, tumor recurrence is often inevitable. The prognosis of patients with glioma is, thus, dismal. Glioma is a highly angiogenic tumor yet immunologically cold. As such, evolving studies have focused on designing strategies that specifically target the tyrosine kinase receptors of angiokines and encourage immune infiltration. Recent promising results from immunotherapies on other cancer types have prompted further investigations of this therapy in GBM. In this article, we reviewed the pathological angiogenesis and immune reactivity in glioma, as well as its target for drug development, and we discussed future directions in glioma therapy.

HIF in Nephrotoxicity during Cisplatin Chemotherapy: Regulation, Function and Therapeutic Potential

Simple Summary

Cisplatin is a widely used chemotherapy drug, but its use and efficacy are limited by its nephrotoxicity. HIF has protective effects against kidney injury during cisplatin chemotherapy, but it may attenuate the anti-cancer effect of cisplatin. In this review, we describe the role and regulation of HIF in cisplatin-induced nephrotoxicity and highlight the therapeutic potential of targeting HIF in chemotherapy.

Abstract

Cisplatin is a highly effective, broad-spectrum chemotherapeutic drug, yet its clinical use and efficacy are limited by its side effects. Particularly, cancer patients receiving cisplatin chemotherapy have high incidence of kidney problems. Hypoxia-inducible factor (HIF) is the “master” transcription factor that is induced under hypoxia to trans-activate various genes for adaptation to the low oxygen condition. Numerous studies have reported that HIF activation protects against AKI and promotes kidney recovery in experimental models of cisplatin-induced acute kidney injury (AKI). In contrast, little is known about the effects of HIF on chronic kidney problems following cisplatin chemotherapy. Prolyl hydroxylase (PHD) inhibitors are potent HIF inducers that recently entered clinical use. By inducing HIF, PHD inhibitors may protect kidneys during cisplatin chemotherapy. However, HIF activation by PHD inhibitors may reduce the anti-cancer effect of cisplatin in tumors. Future studies should test PHD inhibitors in tumor-bearing animal models to verify their effects in kidneys and tumors.

Isocitrate dehydrogenase variants in cancer - Cellular consequences and therapeutic opportunities

Abnormal metabolism is common in cancer cells and often correlates with mutations in genes encoding for enzymes involved in small-molecule metabolism. Isocitrate dehydrogenase 1 (IDH1) is the most frequently mutated metabolic gene in cancer. Cancer-associated substitutions in IDH1 and IDH2 impair wild-type production of 2-oxoglutarate and reduced nicotinamide adenine dinucleotide phosphate (NADPH) from isocitrate and oxidised nicotinamide adenine dinucleotide phosphate (NADP⁺ ), and substantially promote the IDH variant catalysed conversion of 2-oxoglutarate to d-2-hydroxyglutarate (d-2HG). Elevated d-2HG is a biomarker for some cancers, and inhibition of IDH1 and IDH2 variants is being pursued as a medicinal chemistry target. We provide an overview of the types of cancer-associated IDH variants, discuss some of the proposed consequences of altered metabolism as a result of elevated d-2HG, summarise therapeutic efforts targeting IDH variants and identify areas for future research.

Systemic long-term inactivation of hypoxia-inducible factor prolyl 4-hydroxylase 2 ameliorates aging-induced changes in mice without affecting their life span

Hypoxia inactivates hypoxia-inducible factor (HIF) prolyl 4-hydroxylases (HIF-P4Hs), which stabilize HIF and upregulate genes to restore tissue oxygenation. HIF-P4Hs can also be inhibited by small molecules studied in clinical trials for renal anemia. Knowledge of systemic long-term inactivation of HIF-P4Hs is limited but crucial, since HIF overexpression is associated with cancers. We aimed to determine the effects of systemic genetic inhibition of the most abundant isoenzyme HIF prolyl 4-hydroxylase-2 (HIF-P4H-2)/PHD2/EglN1 on life span and tissue homeostasis in aged mice. Our data showed no difference between wild-type and HIF-P4H-2-deficient mice in the average age reached. There were several differences, however, in the primary causes of death and comorbidities, the HIF-P4H-2-deficient mice having less inflammation, liver diseases, including cancer, and myocardial infarctions, and not developing anemia. No increased cancer incidence was observed due to HIF-P4H-2-deficiency. These data suggest that chronic inactivation of HIF-P4H-2 is not harmful but rather improves the quality of life in senescence.

Isocitrate dehydrogenase inhibitors in acute myeloid leukemia

Isocitrate dehydrogenase (IDH) is a key enzyme involved in the conversion of isocitrate to α-ketoglutarate (α-KG) in the tricarboxylic acid (TCA) cycle. IDH mutation produces a neomorphic enzyme, which can lead to the abnormal accumulation of R-2-HG and promotes leukemogenesis. IDH mutation occurs in 20% of acute myeloid leukemia (AML) patients, mainly including IDH1 R132, IDH2 R140, and IDH2 R172. Different mutant isoforms have different prognostic values. In recent years, IDH inhibitors have shown good clinical response in AML patients. Hence, enasidenib and ivosidenib, the IDH2 and IDH1 inhibitors developed by Agios Pharmaceuticals, have been approved by the Food and Drug Administration on 1 August 2017 and 20 July 2018 for the treatment of adult relapsed or refractory (R/R) AML with IDH2 and IDH1 mutations, respectively. IDH inhibitor monotherapy for R/R AML is efficacious and safe; however, there are problems, such as primary or acquired resistance. Clinical trials of IDH inhibitors combined with hypomethylating agents or standard chemotherapy for the treatment of R/R AML or newly diagnosed AML, as well as in post hematopoietic stem cell transplantation as maintenance therapy, are ongoing. This article summarizes the use of IDH inhibitors in AML with IDH mutations.

Targeting miR-193a-AML1-ETO-β-catenin axis by melatonin suppresses the self-renewal of leukaemia stem cells in leukaemia with t (8;21) translocation

AML1‐ETO, the most common fusion oncoprotein by t (8;21) in acute myeloid leukaemia (AML), enhances hematopoietic self‐renewal and leukemogenesis. However, currently no specific therapies have been reported for t (8;21) AML patients as AML1‐ETO is still intractable as a pharmacological target. For this purpose, leukaemia cells and AML1‐ETO‐induced murine leukaemia model were used to investigate the degradation of AML1‐ETO by melatonin (MLT), synthesized and secreted by the pineal gland. MLT remarkedly decreased AML1‐ETO protein in leukemic cells. Meanwhile, MLT induced apoptosis, decreased proliferation and reduced colony formation. Furthermore, MLT reduced the expansion of human leukemic cells and extended the overall survival in U937T‐AML1‐ETO‐xenografted NSG mice. Most importantly, MLT reduced the infiltration of leukaemia blasts, decreased the frequency of leukaemia stem cells (LSCs) and prolonged the overall survival in AML1‐ETO‐induced murine leukaemia. Mechanistically, MLT increased the expression of miR‐193a, which inhibited AML1‐ETO expression via targeting its putative binding sites. Furthermore, MLT decreased the expression of β‐catenin, which is required for the self‐renewal of LSC and is the downstream of AML1‐ETO. Thus, MLT presents anti‐self‐renewal of LSC through miR‐193a‐AML1‐ETO‐β‐catenin axis. In conclusion, MLT might be a potential treatment for t (8;21) leukaemia by targeting AML1‐ETO oncoprotein.

Proteomic analysis reveals diverse proline hydroxylation-mediated oxygen-sensing cellular pathways in cancer cells

Proline hydroxylation is a critical cellular mechanism regulating oxygen-response pathways in tumor initiation and progression. Yet, its substrate diversity and functions remain largely unknown. Here, we report a system-wide analysis to characterize proline hydroxylation substrates in cancer cells using an immunoaffinity-purification assisted proteomics strategy. We identified 562 sites from 272 proteins in HeLa cells. Bioinformatic analysis revealed that proline hydroxylation substrates are significantly enriched with mRNA processing and stress-response cellular pathways with canonical and diverse flanking sequence motifs. Structural analysis indicates a significant enrichment of proline hydroxylation participating in the secondary structure of substrate proteins. Our study identified and validated Brd4, a key transcription factor, as a novel proline hydroxylation substrate. Functional analysis showed that the inhibition of proline hydroxylation pathway significantly reduced the proline hydroxylation abundance on Brd4 and affected Brd4-mediated transcriptional activity as well as cell proliferation in AML leukemia cells. Taken together, our study identified a broad regulatory role of proline hydroxylation in cellular oxygen-sensing pathways and revealed potentially new targets that dynamically respond to hypoxia microenvironment in tumor cells.

The progress of angiogenic factors in the development of leukemias

Angiogenic factors have been demonstrated to play important roles in modulating angiogenesis of solid tumors. Recently, accumulating studies extensively indicated that some angiogenic factors widely exist in malignant cells of hematologic malignancy, which regulated the expression of a number of genes that were involved in abnormal proliferation, differentiation and apoptosis of these cells. With deep research of angiogenic factors, its expression, function and regulatory mechanism were gradually elucidated, and some of them were related to the development and prognosis of leukemia, or provide more possible strategies for treatment of patients with leukemia. Herein, we summarize the progress in study of some important angiogenic factors and hematological malignancies.

Hypoxia-inducible factor-1 and associated upstream and downstream proteins in the pathophysiology and management of glioblastoma

Glioblastoma multiforme (GBM) is a highly aggressive brain tumor with an exceptionally poor patient outcome despite aggressive therapy including surgery, radiation, and chemotherapy. This aggressive phenotype may be associated with intratumoral hypoxia, which probably plays a key role in GBM tumor growth, development, and angiogenesis. A key regulator of cellular response to hypoxia is the protein hypoxia-inducible factor–1 (HIF-1). An examination of upstream hypoxic and nonhypoxic regulation of HIF-1 as well as a review of the downstream HIF-1– regulated proteins may provide further insight into the role of this transcription factor in GBM pathophysiology. Recent insights into upstream regulators that intimately interact with HIF-1 could provide potential therapeutic targets for treatment of this tumor. The same is potentially true for HIF-1–mediated pathways of glycolysis-, angiogenesis-, and invasion-promoting proteins. Thus, an understanding of the relationship between HIF-1, its upstream protein regulators, and its downstream transcribed genes in GBM pathogenesis could provide future treatment options for the care of patients with these tumors.

PKM2 contributes to cancer metabolism

Reprogramming of cell metabolism is essential for tumorigenesis, and is regulated by a complex network, in which PKM2 plays a critical role. PKM2 exists as an inactive monomer, less active dimer and active tetramer. While dimeric PKM2 diverts glucose metabolism towards anabolism through aerobic glycolysis, tetrameric PKM2 promotes the flux of glucose-derived carbons for ATP production via oxidative phosphorylation. Equilibrium of the PKM2 dimers and tetramers is critical for tumorigenesis, and is controlled by multiple factors. The PKM2 dimer also promotes aerobic glycolysis by modulating transcriptional regulation. We will discuss the current understanding of PKM2 in regulating cancer metabolism.

Concise review: genetic dissection of hypoxia signaling pathways in normal and leukemic stem cells

Adult hematopoiesis depends on rare multipotent hematopoietic stem cells (HSCs) that self-renew and give rise to progenitor cells, which differentiate to all blood lineages. The strict regulation of the fine balance between self-renewal and differentiation is essential for normal hematopoiesis and suppression of leukemia development. HSCs and progenitor cells are commonly assumed to reside within the hypoxic BM microenvironment, however, there is no direct evidence supporting this notion. Nevertheless, HSCs and progenitors do exhibit a hypoxic profile and strongly express Hif-1α. Although hypoxia signaling pathways are thought to play important roles in adult HSC maintenance and leukemogenesis, the precise function of Hif-dependent signaling in HSCs remains to be uncovered. Here we discuss recent gain-of-function and loss-of-function studies that shed light on the complex roles of hypoxia-signaling pathways in HSCs and their niches in normal and malignant hematopoiesis. Importantly, we comment on the current and often contrasting interpretations of the role of Hif-dependent signaling in stem cell functions.

The driver and passenger effects of isocitrate dehydrogenase 1 and 2 mutations in oncogenesis and survival prolongation

Mutations in isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) are key events in the development of glioma, acute myeloid leukemia (AML), chondrosarcoma, intrahepatic cholangiocarcinoma (ICC), and angioimmunoblastic T-cell lymphoma. They also cause D-2-hydroxyglutaric aciduria and Ollier and Maffucci syndromes. IDH1/2 mutations are associated with prolonged survival in glioma and in ICC, but not in AML. The reason for this is unknown. In their wild-type forms, IDH1 and IDH2 convert isocitrate and NADP(+) to α-ketoglutarate (αKG) and NADPH. Missense mutations in the active sites of these enzymes induce a neo-enzymatic reaction wherein NADPH reduces αKG to D-2-hydroxyglutarate (D-2HG). The resulting D-2HG accumulation leads to hypoxia-inducible factor 1α degradation, and changes in epigenetics and extracellular matrix homeostasis. Such mutations also imply less NADPH production capacity. Each of these effects could play a role in cancer formation. Here, we provide an overview of the literature and discuss which downstream molecular effects are likely to be the drivers of the oncogenic and survival-prolonging properties of IDH1/2 mutations. We discuss interactions between mutant IDH1/2 inhibitors and conventional therapies. Understanding of the biochemical consequences of IDH1/2 mutations in oncogenesis and survival prolongation will yield valuable information for rational therapy design: it will tell us which oncogenic processes should be blocked and which "survivalogenic" effects should be retained.

Non-enzymatic chemistry enables 2-hydroxyglutarate-mediated activation of 2-oxoglutarate oxygenases

Accumulation of (R)-2-hydroxyglutarate in cells results from mutations to isocitrate dehydrogenase that correlate with cancer. A recent study reports that (R)-, but not (S)-2-hydroxyglutarate, acts as a co-substrate for the hypoxia-inducible factor prolyl hydroxylases via enzyme-catalysed oxidation to 2-oxoglutarate. Here we investigate the mechanism of 2-hydroxyglutarate-enabled activation of 2-oxoglutarate oxygenases, including prolyl hydroxylase domain 2, the most important human prolyl hydroxylase isoform. We observe that 2-hydroxyglutarate-enabled catalysis by prolyl hydroxylase domain 2 is not enantiomer-specific and is stimulated by ferrous/ferric ion and reducing agents including L-ascorbate. The results reveal that 2-hydroxyglutarate is oxidized to 2-oxoglutarate non-enzymatically, likely via iron-mediated Fenton-chemistry, at levels supporting in vitro catalysis by 2-oxoglutarate oxygenases. Succinic semialdehyde and succinate are also identified as products of 2-hydroxyglutarate oxidation. Overall, the results rationalize the reported effects of 2-hydroxyglutarate on catalysis by prolyl hydroxylases in vitro and suggest that non-enzymatic 2-hydroxyglutarate oxidation may be of biological interest.

Let-7b expression determines response to chemotherapy through the regulation of cyclin D1 in glioblastoma

Background

Glioblastoma is the most common type of primary brain tumors. Cisplatin is a commonly used chemotherapeutic agent for Glioblastoma patients. Despite a consistent rate of initial responses, cisplatin treatment often develops chemoresistance, leading to therapeutic failure. Cellular resistance to cisplatin is of great concern and understanding the molecular mechanisms is an utter need.

Methods

Glioblastoma cell line U251 cells were exposed to increasing doses of cisplatin for 6 months to establish cisplatin-resistant cell line U251R. The differential miRNA expression profiles in U251 and U251R cell lines were identified by microarray analysis and confirmed by Q-PCR. MiRNA mimics were transfected into U251R cells, and cellular response to cisplatin-induced apoptosis and cell cycle distribution were examined by FACS analysis.

Results

U251R cells showed 3.1-fold increase in cisplatin resistance compared to its parental U251 cells. Microarray analysis identified Let-7b and other miRNAs significantly down-regulated in U251R cells compared to U251 cells. Transfection of Let-7b mimics greatly re-sensitized U251R cells to cisplatin, while transfection of other miRNAs has no effect or slightly effect. Cyclin D1 is predicted as a target of Let-7b through bioinformatics analysis. Over-expression of Let-7b mimics suppressed cyclin D1 protein expression and inhibited cyclin D1-3’-UTR luciferase activity. Knockdown of cyclin D1 expression significantly increased cisplatin-induced G1 arrest and apoptosis.

Conclusions

Collectively, our results indicated that cisplatin treatment leads to Let-7b suppression, which in turn up-regulates cyclin D1 expression. Let-7b may serve as a marker of cisplatin resistance, and can enhance the therapeutic benefit of cisplatin in glioblastoma cells.

Hypoxia-inducible factor 1α mediates the down-regulation of superoxide dismutase 2 in von Hippel-Lindau deficient renal clear cell carcinoma

Hypoxia-inducible factor 1α (HIF-1α) is an oxygen-sensitive subunit of HIF-1, the master transcription factor for cellular response to hypoxia. Down-regulation of the mitochondrial enzyme superoxide dismutase 2 (SOD2) contributes to the stabilization of HIF-1α under hypoxia due to the decreased dismutation of superoxide radical. Here we report that HIF-1α could also regulate the expression of SOD2. We found that both stabilization of HIF-1α expression under nomoxia caused by pVHL deficiency and hypoxia treatment significantly reduced SOD2 expression, and shRNAs specifically against HIF-1α restored SOD2 expression in both circumstances. Further analyses with luciferase reporter assay and chromatin immunoprecipitation assay revealed that HIF-1α inhibited and directly bound to the hypoxia-responsive element in SOD2 promoter. These findings indicated the existence of a positive feedback between HIF-1α and SOD2 and provided new clues for understanding the molecular mechanisms of hypoxia adaptation.

(R)-2-hydroxyglutarate is sufficient to promote leukemogenesis and its effects are reversible

Mutations in IDH1 and IDH2, the genes coding for isocitrate dehydrogenases 1 and 2, are common in several human cancers, including leukemias, and result in overproduction of the (R)-enantiomer of 2-hydroxyglutarate [(R)-2HG]. Elucidation of the role of IDH mutations and (R)-2HG in leukemogenesis has been hampered by a lack of appropriate cell-based models. Here, we show that a canonical IDH1 mutant, IDH1 R132H, promotes cytokine independence and blocks differentiation in hematopoietic cells. These effects can be recapitulated by (R)-2HG, but not (S)-2HG, despite the fact that (S)-2HG more potently inhibits enzymes, such as the 5'-methylcytosine hydroxylase TET2, that have previously been linked to the pathogenesis of IDH mutant tumors. We provide evidence that this paradox relates to the ability of (S)-2HG, but not (R)-2HG, to inhibit the EglN prolyl hydroxylases. Additionally, we show that transformation by (R)-2HG is reversible.

PKM2, a Central Point of Regulation in Cancer Metabolism

Aerobic glycolysis is the dominant metabolic pathway utilized by cancer cells, owing to its ability to divert glucose metabolites from ATP production towards the synthesis of cellular building blocks (nucleotides, amino acids, and lipids) to meet the demands of proliferation. The M2 isoform of pyruvate kinase (PKM2) catalyzes the final and also a rate-limiting reaction in the glycolytic pathway. In the PK family, PKM2 is subjected to a complex regulation by both oncogenes and tumour suppressors, which allows for a fine-tone regulation of PKM2 activity. The less active form of PKM2 drives glucose through the route of aerobic glycolysis, while active PKM2 directs glucose towards oxidative metabolism. Additionally, PKM2 possesses protein tyrosine kinase activity and plays a role in modulating gene expression and thereby contributing to tumorigenesis. We will discuss our current understanding of PKM2's regulation and its many contributions to tumorigenesis.

Chloroquine enhances cobalt chloride-induced leukemic cell differentiation via the suppression of autophagy at the late phase

We previously reported that moderate hypoxia and hypoxia-mimetic agents including cobalt chloride (CoCl(2)) induce differentiation of human acute myeloid leukemia (AML) cells through hypoxia-inducible factor-1 α (HIF-1 α), which interacts with and enhances transcriptional activity of CCAAT-enhancer binding factor alpha and Runx1/AML1, two important transcriptional factors for hematopoietic cell differentiation. Here, we show that autophagy inhibitor chloroquine (CQ) increases HIF-1 α accumulation, thus potentiating CoCl(2)-induced growth arrest and differentiation of leukemic cells. Furthermore, the increased effect of CQ on differentiation induction is dependent of the inhibition of autophagosome maturation and degradation, since this sensitization could be mimicked by the suppression of expression of both lysosome-associated membrane proteins 1 and 2 (LAMP1 and LAMP2). These findings not only provide the evidence that CQ is a sensitizer for CoCl(2)-induced differentiation of leukemic cells but also possibly propose the new therapeutic strategy for differentiation induction of AML.

HIF-1α downregulates miR-17/20a directly targeting p21 and STAT3: a role in myeloid leukemic cell differentiation

Hypoxia-inducible factor 1 (HIF-1) is a crucial transcription factor for the cellular adaptive response to hypoxia, which contributes to multiple events in cancer biology. MicroRNAs (miRNAs) are involved in almost all cellular activities such as differentiation, proliferation, and apoptosis. In this work, we use miRNA microarrays to profile miRNA expression in acute myeloid leukemia (AML) cells with inducible HIF-1α expression, and identify 19 differentially expressed miRNAs. Our study shows that HIF-1α represses the expression of miR-17 and miR-20a by downregulating c-Myc expression. These two miRNAs alleviate hypoxia and HIF-1α-induced differentiation of AML cells. More intriguingly, miR-17 and miR-20a directly inhibit the p21 and STAT3 (signal transducer and activator of transcription 3) expression, both of which can reverse miR-17/miR-20a-mediated abrogation of HIF-1α-induced differentiation. Moreover, we show in vivo that miR-20a contributes to HIF-1α-induced differentiation of leukemic cells. Taken together, our results suggest that HIF-1α regulates the miRNA network to interfere with AML cell differentiation, representing a novel molecular mechanism for HIF-1-mediated anti-leukemic action.

The VHL/HIF axis in clear cell renal carcinoma

Inactivation of the VHL tumor suppressor protein (pVHL) is a common event in clear cell renal carcinoma, which is the most common form of kidney cancer. pVHL performs many functions, including serving as the substrate recognition module of an ubiquitin ligase complex that targets the alpha subunits of the heterodimeric HIF transcription factor for proteasomal degradation. Deregulation of HIF2α appears to be a driving force in pVHL-defective clear cell renal carcinomas. In contrast, genetic and functional studies suggest that HIF1α serves as a tumor suppressor and is a likely target of the 14q deletions that are characteristic of this tumor type. Drugs that inhibit HIF2α, or its downstream targets such as VEGF, are in various stages of clinical testing. Indeed, clear cell renal carcinomas are exquisitely sensitive to VEGF deprivation and four VEGF inhibitors have now been approved for the treatment of this disease.

Transformation by the (R)-enantiomer of 2-hydroxyglutarate linked to EGLN activation

The identification of succinate dehydrogenase (SDH), fumarate hydratase (FH) and isocitrate dehydrogenase (IDH) mutations in human cancers has rekindled the idea that altered cellular metabolism can transform cells. Inactivating SDH and FH mutations cause the accumulation of succinate and fumarate, respectively, which can inhibit 2-oxoglutarate (2-OG)-dependent enzymes, including the EGLN prolyl 4-hydroxylases that mark the hypoxia inducible factor (HIF) transcription factor for polyubiquitylation and proteasomal degradation. Inappropriate HIF activation is suspected of contributing to the pathogenesis of SDH-defective and FH-defective tumours but can suppress tumour growth in some other contexts. IDH1 and IDH2, which catalyse the interconversion of isocitrate and 2-OG, are frequently mutated in human brain tumours and leukaemias. The resulting mutants have the neomorphic ability to convert 2-OG to the (R)-enantiomer of 2-hydroxyglutarate ((R)-2HG). Here we show that (R)-2HG, but not (S)-2HG, stimulates EGLN activity, leading to diminished HIF levels, which enhances the proliferation and soft agar growth of human astrocytes. These findings define an enantiomer-specific mechanism by which the (R)-2HG that accumulates in IDH mutant brain tumours promotes transformation and provide a justification for exploring EGLN inhibition as a potential treatment strategy.

Synergistic induction of galectin-1 by CCAAT/enhancer binding protein alpha and hypoxia-inducible factor 1alpha and its role in differentiation of acute myeloid leukemic cells

Galectin-1 is a member of the galectin family and has a high affinity for galactose and N-acetylglucosamine moieties of glycoproteins. It mediates multiple signal transduction pathways to modulate cellular proliferation, survival, differentiation, and migration. However, the mechanisms for the regulation of its expression remain greatly elusive. We reported previously that galectin-1 is a direct target of the hypoxia-inducible factor 1 (HIF-1), a key heterodimeric transcriptional factor for the cellular response to hypoxia. Here we show that CCAAT/enhancer binding protein α (C/EBPα), a critical transcriptional factor for hematopoietic cell differentiation, can directly activate galectin-1 through binding to the -48 to -42 bp region of its promoter. Based on the physical interaction of C/EBPα and HIF-1α, the synergistic transcriptional activity of C/EBPα and HIF-1α on the promoter of the galectin-1 gene is also found by chromatin immunoprecipitation (ChIP), ChIP followed by ChIP (ChIP-reChIP), and luciferase assay. Moreover, knockdown or chemical inhibition of galectin-1 partially blocks the differentiation induced by HIF-1α or C/EBPα, which can be rescued by recombinant galectin-1. These discoveries would shed new insights on the mechanisms for galectin-1 expression regulation and HIF-1α- and C/EBPα-induced leukemic cell differentiation.

Apoptosis-inducing factor is a target gene of C/EBPα and participates in adipocyte differentiation

Besides the contribution in cell death, apoptosis-inducing factor (AIF) also exerts roles in other cellular activities, which are largely unknown. The CCAAT-enhancer binding protein alpha (C/EBPα) is required for differentiation of adipocytes and granulocytes. Here we report that, during 3T3-L1 adipocyte differentiation, AIF expression is robustly upregulated via transcriptional regulation by C/EBPα. The upregulated effect is also confirmed by knockdown and ectopic expression of C/EBPα in U937 and MCF-7 cells respectively with and without endogenous expression of C/EBPα protein. We also reveal that AIF knockdown attenuates 3T3-L1 adipocyte differentiation, presumably due to the mitochondrial respiratory chain deficiency. These results provide evidence for the role of AIF in adipocyte differentiation.

Oxygen tension regulates NK cells differentiation from hematopoietic stem cells in vitro

Natural killer (NK) cells are differentiated from hematopoietic stem cells (HSCs) which are located at the lowest end of an oxygen gradient within the bone marrow (BM). In this report, we investigated whether oxygen tension could affect NK cell differentiation from hematopoietic cells in vitro. We found that hypoxia led to an inhibition of differentiation in NK cells, and increased oxygen supply alleviated this inhibition and restored NK cell differentiation under hypoxic condition. Hypoxia-treated cells demonstrated reduced mRNA expression of transcription factors (TFs) that have important roles in NK cell differentiation, such as EOMES, T-bet, GATA-3 and ETS-1. Moreover, hypoxia-pretreated cells recovered mRNA expression of TFs when the oxygen tension was changed to normoxia. Our findings suggest that oxygen tension modulates in vitro differentiation of NK cells through the regulation of TF expression.

Hypoxia-inducible factor-1α protein expression is associated with poor survival in normal karyotype adult acute myeloid leukemia

We examined the predictive impact of HIF-1α protein expression on clinical outcome of 84 normal karyotype acute myeloid leukemia (NK-AML) patients (median age 66.5 years) at our institute. Thirty percent of NK-AML cells expressed cytoplasmic HIF-1α. In univariate analysis, low HIF-1α (≤ 5%, n = 66) was associated with improved event-free survival (p = 0.0453, HR = 0.22). Multivariate analysis incorporating age, complete remission, FLT3-ITD mutation, and marrow blast percentage demonstrated that HIF-1α was independently associated with poorer overall and event-free survival. HIF-1α expression correlated with VEGF-C but not VEGF-A, marrow angiogenesis, FLT3 ITD or NPM1 mutations. These results support HIF-1α as an outcome marker for NK-AML.

Induction of SENP1 in endothelial cells contributes to hypoxia-driven VEGF expression and angiogenesis

SENP1 (SUMO-specific protease 1) has been shown to be essential for the stability and activity of hypoxia-inducible factor 1 (HIF-1α) under hypoxia conditions. However, it is unknown how SENP1 activation and hypoxia signaling are coordinated in the cellular response to hypoxia. Here, we report the essential role of SENP1 in endothelial cells as a positive regulator of hypoxia-driven VEGF production and angiogenesis. SENP1 expression is increased in endothelial cells following exposure to hypoxia. Silencing of HIF-1α blocks SENP1 expression in cell response to hypoxia. Mutation of the hypoxia response element (HRE) on the Senp1 promoter abolishes its transactivation in response to hypoxia. Moreover, silencing of SENP1 expression decreases VEGF production and abrogates the angiogenic functions of endothelial cell. We also find that the elongated endothelial cells in embryonic brain section and vascular endothelial cells in embryonic renal glomeruli in Senp1(-/-) mice are markedly reduced than those in wild-type. Thus, these results show that hypoxia implies a positive feedback loop mediated by SENP1. This feedback loop is important in VEGF production, which is essential for angiogenesis in endothelial cells.

IDH1 mutations are detected in 6.6% of 1414 AML patients and are associated with intermediate risk karyotype and unfavorable prognosis in adults younger than 60 years and unmutated NPM1 status

Mutations in the IDH1 gene at position R132 coding for the enzyme cytosolic isocitrate dehydrogenase are known in glioma and have recently been detected also in acute myeloid leukemia (AML). These mutations result in an accumulation of α-ketoglutarate to R (2)-2-hydroxyglutarate (2HG). To further clarify the role of this mutation in AML, we have analyzed IDH1R132 in 1414 AML patients. We detected IDH1R132 mutations in 93 of 1414 patients (6.6%) with a clear prevalence in intermediate risk karyotype group (10.4%, P < .001). Although IDH1R132 mutations can incidentally occur together with all other molecular markers, there were strong associations with NPM1 mutations (14.2% vs 5.4% in NPM1wt, P < .001) and MLL-PTD (18.2% vs 7.0% in MLLwt, P = .020). IDH1-mutated cases more often had AML without maturation/French-American-British M1 (P < .001), an immature immunophenotype, and female sex (8.7% vs 4.7% in male, P = .003) compared with IDH1wt cases. Prognosis was adversely affected by IDH1 mutations with trend for shorter overall survival (P = .110), a shorter event-free survival (P < .003) and a higher cumulative risk for relapse (P = .001). IDH1 mutations were of independent prognostic relevance for event-free survival (P = .039) especially in the age group < 60 years (P = .028). In conclusion, these data show that IDH1R132 may significantly add information regarding characterization and prognostication in AML.

Pharicin B stabilizes retinoic acid receptor-α and presents synergistic differentiation induction with ATRA in myeloid leukemic cells

All-trans retinoic acid (ATRA), a natural ligand for the retinoic acid receptors (RARs), induces clinical remission in most acute promyelocytic leukemia (APL) patients through the induction of differentiation and/or eradication of leukemia-initiating cells. Here, we identify a novel natural ent-kaurene diterpenoid derived from Isodon pharicus leaves, called pharicin B, that can rapidly stabilize RAR-α protein in various acute myeloid leukemic (AML) cell lines and primary leukemic cells from AML patients, even in the presence of ATRA, which is known to induce the loss of RAR-α protein. Pharicin B also enhances ATRA-dependent the transcriptional activity of RAR-α protein in the promyelocytic leukemia-RARα-positive APL cell line NB4 cells. We also showed that pharicin B presents a synergistic or additive differentiation-enhancing effect when used in combination with ATRA in several AML cell lines and, especially, some primary leukemic cells from APL patients. In addition, pharicin B can overcome retinoid resistance in 2 of 3 NB4-derived ATRA-resistant subclones. These findings provide a good example for chemical biology-based investigations of pathophysiological and therapeutic significances of RAR-α and PML-RAR-α proteins. The effectiveness of the ATRA/pharicin B combination warrants further investigation on their use as a therapeutic strategy for AML patients.

Very low oxygen concentration (0.1%) reveals two FDCP-Mix cell subpopulations that differ by their cell cycling, differentiation and p27KIP1 expression

Oxygen (O(2)) concentrations in bone marrow vary from 4% in capillaries to <0.1% in subendosteum, in which hematopoietic stem cells reside in specific niches. Culture at low O(2) concentrations (3, 1 and 0.1%) influences hematopoietic stem and progenitor cells survival, proliferation and differentiation, depending on their level of differentiation. Culture of human CD34(+) cells at low O(2) concentrations (O(2) ≤3%) maintains stem cell engraftment potential better than at 20% O(2) (NOD/Scid xenograft model). In contrast, progenitors disappear from cultures at/or <1% O(2) concentrations. A very low O(2) concentration (0.1%) induces CD34(+) quiescence in G(0). The exploration of molecules and mechanisms involved in hematopoietic stem and progenitor cells' quiescence and differentiation related to low O(2) concentrations is unfeasible with primary CD34(+) cells. Therefore, we performed it using murine hematopoietic nonleukemic factor-dependent cell Paterson (FDCP)-Mix progenitor cell line. The culture of the FDCP-Mix line at 0.1% O(2) induced in parallel G(0) quiescence and granulo-monocytic differentiation of most cells, whereas a minority of undifferentiated self-renewing cells remained in active cell cycle. Hypoxia also induced hypophosphorylation of pRb and increased the expression of p27(KIP1), the two proteins that have a major role in the control of G(0) and G(1) to S-phase transition.

Hypoxia inducible factor-1 mediates expression of galectin-1: the potential role in migration/invasion of colorectal cancer cells

The expression of galectin-1, one of the most important lectins participating in the malignant tumor development, has been shown to be regulated by hypoxia, but its exact mechanism remains elusive. Here, we find that ectopically expressed hypoxia-inducible factor (HIF) 1alpha protein, an oxygen-sensitive subunit of HIF-1 that is a master factor for cellular response to hypoxia, significantly increases galectin-1 expression in both messenger RNA and protein levels in all four colorectal cancer (CRC) cell lines tested. However, hypoxia-induced galectin-1 expression cannot be seen in sentrin/SUMO-specific protease 1 homozygous-null mouse embryonic fibroblasts that fail to accumulate HIF-1alpha protein. Furthermore, silence of HIF-1alpha or HIF-1beta expression by specific short hairpin RNAs (shRNAs) antagonizes hypoxia-induced galectin-1 expression. All these results propose that galectin-1 is a direct target of transcriptional factor HIF-1. Applying luciferase reporter assay and chromatin immunoprecipitation, we identify that two hypoxia-responsive elements located at -441 to -423 bp upstream to transcriptional start site of galectin-1 gene are essential for HIF-1-mediated galectin-1 expression. Finally, the knockdown of galectin-1 by its specific shRNA can significantly reduce hypoxia-induced invasion and migration of CRC cell line, and the ectopic expression of galectin-1 can remarkably restore invasion and migration abilities of HIF-1alpha-knocked SW620 cells, proposing that galectin-1 mediates the HIF-1-induced migration and invasion of CRC cells during hypoxia. Taken together, our results shed new light for understanding mechanism for hypoxia/HIF-1-mediated migration/invasion of CRC cells.

Distinct clinical and biologic characteristics in adult acute myeloid leukemia bearing the isocitrate dehydrogenase 1 mutation

Mutations of nicotinamide adenine dinucleotide phosphate-dependent isocitrate dehydrogenase gene (IDH1) have been identified in patients with gliomas. Recent genome-wide screening also revealed IDH1 mutation as a recurrent event in acute myeloid leukemia (AML), but its clinical implications in AML are largely unknown. We analyzed 493 adult Chinese AML patients in Taiwan and found 27 patients (5.5%) harboring this mutation. IDH1 mutation was strongly associated with normal karyotype (8.4%, P = .002), isolated monosomy 8 (P = .043), NPM1 mutation (P < .001), and French-American-British M1 subtype (P < .001), but inversely associated with French-American-British M4 subtype (P = .030) and expression of HLA-DR, CD13, and CD14 (P = .002, .003, and .038, respectively). There was no impact of this mutation on patient survival. Sequential analysis of IDH1 mutation was performed in 130 patients during follow-ups. None of the 112 patients without IDH1 mutation at diagnosis acquired this mutation at relapse. In all 18 IDH1-mutated patients studied, the mutation disappeared in complete remission; the same mutation reappeared in all 11 samples obtained at relapse. We conclude that IDH1 is associated with distinct clinical and biologic characteristics and seems to be very stable during disease evolution.

Proteomics-based identification of two novel direct targets of hypoxia-inducible factor-1 and their potential roles in migration/invasion of cancer cells

Hypoxia-inducible factor-1 (HIF-1), consisting of oxygen-sensitive HIF-1alpha and constitutively expressed HIF-1beta subunits, is a master transcriptional activator for cellular response to hypoxia. To explore direct HIF-1 targets, here we used differential gel electrophoresis (DIGE) to compare the HIF-1-regulated proteins between leukemic U937T-cell line with and without conditional induction of HIF-1alpha protein by tetracycline-off system. Among the upregulated proteins identified, mRNA levels of annexin A1, macrophage-capping protein (CapG), S100 calcium-binding protein A4 (S100A4), S100A11, acyl-CoA-binding protein and calcyclin-binding protein also increased. The expressions of the annexin A1, CapG and S100A4 genes were significantly induced by hypoxia in five adherent cell lines tested besides U937 cells, while their expressions were blocked by the short hairpin RNA specifically against HIF-1alpha. Further luciferase reporter assay and chromatin immunoprecipitation showed that HIF-1alpha directly bound to three hypoxia-responsive elements located at intron 1 of S100A4 gene and hypoxia-responsive element at -350 to -346 of CapG gene, which are essential for HIF-1-induced expression. Additionally, the role of S100A4 expression in migration and invasion of cancer cells were also confirmed. These findings would provide new sights for understanding the molecular mechanisms underlying HIF-1 action.

SENP3 is responsible for HIF-1 transactivation under mild oxidative stress via p300 de-SUMOylation

The physiological function of Sentrin/SUMO-specific proteases (SENPs) remains largely unexplored, and little is known about the regulation of SENPs themselves. Here, we show that a modest increase of reactive oxygen species (ROS) regulates SENP3 stability and localization. We found that SENP3 is continuously degraded through the ubiquitin-proteasome pathway under basal condition and that ROS inhibit this degradation. Furthermore, ROS causes SENP3 to redistribute from the nucleoli to the nucleoplasm, allowing it to regulate nuclear events. The stabilization and redistribution of SENP3 correlate with an increase in the transcriptional activity of the hypoxia-inducing factor-1 (HIF-1) under mild oxidative stress. ROS-enhanced HIF-1 transactivation is blocked by SENP3 knockdown. The de-SUMOylating activity of SENP3 is required for ROS-induced increase of HIF-1 transactivation, but the true substrate of SENP3 is the co-activator of HIF-1 alpha, p300, rather than HIF-1 alpha itself. Removing SUMO2/3 from p300 enhances its binding to HIF-1 alpha. In vivo nude mouse xenografts overexpressing SENP3 are more angiogenic. Taken together, our results identify SENP3 as a redox sensor that regulates HIF-1 transcriptional activity under oxidative stress through the de-SUMOylation of p300.

Role of HIF-1alpha in the regulation ACE and ACE2 expression in hypoxic human pulmonary artery smooth muscle cells

Angiotensin-converting enzyme (ACE) enhances the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs), which contribute to the pathogenesis of hypoxic pulmonary hypertension (HPH). Previous reports have demonstrated that hypoxia upregulates ACE expression, but the underlying mechanism is unknown. Here, we found that ACE is persistently upregulated in PASMCs on the transcriptional level during hypoxia. Hypoxia-inducible factor 1alpha (HIF-1alpha), a key transcription factor activated during hypoxia, was able to upregulate ACE protein expression under normoxia, whereas knockdown of HIF-1alpha expression in PASMCs inhibited hypoxia-induced ACE upregulation. Furthermore, HIF-1alpha can bind and transactivate the ACE promoter directly. Therefore, we report that ACE is a novel target of HIF-1alpha. Recently, a homolog of ACE, ACE2, was reported to counterbalance the function of ACE. In contrast to ACE, we found that ACE2 mRNA and protein levels increased during the early stages of hypoxia and decreased to near-baseline levels at the later stages after HIF-1alpha accumulation. Thus HIF-1alpha inhibited ACE2 expression, and the accumulated ANG II catalyzed by ACE is a key mediator in the downregulation of ACE2 by HIF-1alpha. Moreover, a reduction of ACE2 expression in PASMCs by RNA interference was accompanied by significantly enhanced proliferation and migration during hypoxia. We conclude that ACE is directly regulated by HIF-1alpha, whereas ACE2 is regulated in a bidirectional way during hypoxia and may play a protective role during the development of HPH. In sum, these findings contribute to the understanding of the pathogenesis of HPH.

Hypoxia-HIF-1alpha-C/EBPalpha/Runx1 signaling in leukemic cell differentiation

Acute myeloid leukemia (AML), a class of prevalent hematopoietic malignancies, is caused by the acquisition of gene mutations that confer deregulated proliferation, impaired differentiation and a survival advantage of hematopoietic progenitors. More recently, we reported that cobalt chloride (CoCl(2))/iron chelator desferrioxamine (DFO)-mimicked hypoxia or moderate hypoxia (2% and 3% O(2)) can directly trigger differentiation of many subtypes of AML cells. Also, intermittent hypoxia significantly prolongs the survival of the transplanted leukemic mice with differentiation induction of leukemic cells. Additionally, these hypoxia-simulating agents selectively stimulate differentiation in acute promyelocytic leukemic cells induced by arsenic trioxide, an effective second-line drug for this unique type of leukemia. Based on this interesting evidence in vitro and in vivo, the ongoing investigations showed the role of hypoxia-inducible factor-1alpha (HIF-1alpha) protein through its non-transcriptional activity in myeloid cell differentiation, as evidenced by chemical interference, the conditional HIF-1alpha induction, the specific short hairpin RNAs (shRNAs) against HIF-1alpha and HIF-1beta, an essential partner for transcription activity of HIF-1. Furthermore, HIF-1alpha and two hematopoietic transcription factors CCAAT/enhancer binding protein alpha (C/EBPalpha) and Runx1/AML1 interact directly with each other. Such interactions increase the transcriptional activities of C/EBPalpha and Runx1/AML1, while C/EBPalpha competes with HIF-1beta for direct binding to HIF-1alpha protein, and significantly inhibits the DNA-binding ability of HIF-1. As a protein is rapidly responsive to all-trans retinoic acid (ATRA), a classical clinical differentiation-inducing drug for AML, HIF-1alpha also plays a role in ATRA-induced differentiation of leukemic cells.

NDRG1 contributes to retinoic acid-induced differentiation of leukemic cells

N-Myc downstream-regulated gene 1 (NDRG1) protein has been shown to be up-regulated during leukemic cell differentiation induced by some differentiation-inducing agents such as all-trans retinoic acid (ATRA). However, the potential role of up-regulated NDRG1 in the event is greatly unknown. In this work, we show that inducible NDRG1 expression can drive leukemic U937 cells to undergo differentiation, while the knock-down of NDRG1 expression by specific small interfering RNA significantly antagonizes ATRA-induced differentiation of leukemic cells, proposing the role of NDRG1 in leukemic cell differentiation. Furthermore, our work shows that CCAAT/enhancer-binding protein beta (C/EBPbeta) and PU.1, which are important hematopoiesis-related transcription factors, may act as downstream effectors of NDRG1 in leukemic cell differentiation. Taking together, this study provides direct evidence for the role of NDRG1 protein in myeloid leukemic cell differentiation.

The HIF-1 alpha-C/EBP alpha axis

The hypoxia inducible factors (HIFs) and CCAAT/enhancer binding protein alpha (C/EBP alpha) are transcription factors that mediate adaptive responses to hypoxia and control aspects of energy metabolism, respectively. New evidence suggests that when HIF-1 alpha and C/EBP alpha interact, they bring about reciprocal functional changes, so that the activity of HIF-1 alpha is decreased and that of C/EBP alpha is restricted or increased in a tissue-specific manner. This Journal Club article highlights research depicting interactions between HIF-1 alpha and C/EBP alpha and discusses conditions and tissues in which this interaction might occur.

Leukemia, an effective model for chemical biology and target therapy

The rapid rise of chemical biology aimed at studying signaling networks for basic cellular activities using specific, active small molecules as probes has greatly accelerated research on pathological mechanisms and target therapy of diseases. This research is especially important for malignant tumors such as leukemia, a heterogeneous group of hematopoietic malignancies that occurs worldwide. With the use of a chemical approach combined with genetic manipulation, great progress has been achieved over the past few decades on the biological, molecular and cytogenetic aspects of leukemia, and in its diagnosis and therapy. In particular, discoveries of the clinical effectiveness of all-trans retinoic acid and arsenic trioxide in the treatment of acute promyelocytic leukemia and the kinase inhibitors Imatinib and Dasatinib in the treatment of chronic myelogenous leukemia not only make target therapy of leukemia a reality, but also push mechanisms of leukemogenesis and leukemic cell activities forward. This review will outline advances in chemical biology that help our understanding of the molecular mechanisms of cell differentiation and apoptosis induction and target therapy of leukemia.

Physical and functional interaction of Runt-related protein 1 with hypoxia-inducible factor-1alpha

Angiogenesis and hematopoiesis are closely linked and interactive with each other, but few studies were given to identify possible links between angiogenesis-promoting proteins and hematopoiesis-related transcription factors. Here we investigated the potential relationship of oxygen-sensitive alpha-subunit of angiogenesis-related hypoxia-inducible factor-1alpha (HIF-1alpha) with Runt-related protein 1 (Runx1, also known as acute myeloid leukemia-1, AML-1), an important hematopoietic transcription factor. The results demonstrated that Runx1 and HIF-1alpha proteins directly interacted with each other to a degree, in which Runt homology domain of Runx1 was mainly involved. Leukemia-related abnormal Runx1 fusion protein AML1-ETO, which fuses the N-terminal 177 amino acid residues of the Runx1 protein in frame to ETO (eight-twenty-one) protein, also interacted with HIF-1alpha protein with greater ability than Runx1 itself. More intriguingly, Runx1 overexpression inhibited DNA-binding and transcriptional activity of HIF-1 protein with reduced expression of HIF-1-targeted genes such as vascular endothelial growth factor, while silence of Runx1 expression by specific small interfering RNA significantly increased transcriptional activity of HIF-1 protein, suggesting that Runx1 inhibited transcription-dependent function of HIF-1. Vice versa, HIF-1alpha increased DNA-binding ability and transcriptional activity of Runx1 protein. All these data would shed new insight to understanding Runx1 and HIF-1alpha-related hematopoietic cell differentiation and angiogenesis.