Cobalt chloride and low oxygen tension trigger differentiation of acute myeloid leukemic cells: possible mediation of hypoxia-inducible factor-1alpha

Recombinant canstatin inhibits angiopoietin-1-induced angiogenesis and lymphangiogenesis

We describe the effect of recombinant canstatin, the NC1 domain of the α2 chain of Type IV collagen, on suppression of angiogenesis and lymphangiogenesis both in vitro and in vivo. Recombinant canstatin produced from stably transformed Drosophila S2 cells reduced the expression of angiopoietin-1 in hypoxia mimetic agent, CoCl(2) -treated CT-26 cells. Recombinant canstatin inhibited proliferation, tube formation and migration of human angiopoietin-1 (rhAngpt-1)-treated human umbilical vein endothelial cells (HUVEC) and lymphatic endothelial cells (LEC). Recombinant canstatin suppressed the expression of Tie-2 and vascular endothelial growth factor-3 (VEGFR-3) transcripts in rhAngpt-1-treated HUVEC and LEC, respectively. The inhibitory effect of recombinant canstatin on tumor growth was also investigated using a heterotopic CT-26 colon carcinoma animal (BALB/c mice) model. Recombinant canstatin reduced the final volume and weight of tumors, and blood and lymphatic vessel densities of tumors, which were evaluated by CD-31 and LYVE-1 immunostaining. Immunohistochemical analysis showed that recombinant canstatin dramatically reduced the expression of angiopoietin-1 in CT-26 colon carcinoma-induced tumor, but not the expression of VEGF-C. Tie-2 and VEGFR-3 expressions were also reduced in recombinant canstatin-treated tumors. These results indicate that recombinant canstatin has anti-tumoral activities against CT-26 colon carcinoma cells. Recombinant canstatin reduces the expression of angiopoietin-1 in hypoxia-induced CT-26 cells and inhibits the angiogenic and lymphangiogenic signaling induced by angiopoietin-1. Recombinant canstatin probably inhibits angiogenesis and lymphangiogenesis via suppression of the integrin-dependent FAK signaling induced by angiopoietin-1/Tie-2 and/or VEGFR-3.

A Cullin3-KLHL20 Ubiquitin ligase-dependent pathway targets PML to potentiate HIF-1 signaling and prostate cancer progression

Tumor hypoxia is associated with disease progression and treatment failure, but the hypoxia signaling mechanism is not fully understood. Here, we show that KLHL20, a Cullin3 (Cul3) substrate adaptor induced by HIF-1, coordinates with the actions of CDK1/2 and Pin1 to mediate hypoxia-induced PML proteasomal degradation. Furthermore, this PML destruction pathway participates in a feedback mechanism to maximize HIF-1α induction, thereby potentiating multiple tumor hypoxia responses, including metabolic reprogramming, epithelial-mesenchymal transition, migration, tumor growth, angiogenesis, and chemoresistance. In human prostate cancer, overexpression of HIF-1α, KLHL20, and Pin1 correlates with PML down-regulation, and hyperactivation of the PML destruction pathway is associated with disease progression. Our study indicates that the KLHL20-mediated PML degradation and HIF-1α autoregulation play key roles in tumor progression.

Hypoxia-mimetic agents inhibit proliferation and alter the morphology of human umbilical cord-derived mesenchymal stem cells

BACKGROUND

The therapeutic efficacy of human mesenchymal stem cells (hMSCs) for the treatment of hypoxic-ischemic diseases is closely related to level of hypoxia in the damaged tissues. To elucidate the potential therapeutic applications and limitations of hMSCs derived from human umbilical cords, the effects of hypoxia on the morphology and proliferation of hMSCs were analyzed.

RESULTS

After treatment with DFO and CoCl₂, hMSCs were elongated, and adjacent cells were no longer in close contact. In addition, vacuole-like structures were observed within the cytoplasm; the rough endoplasmic reticulum expanded, and expanded ridges were observed in mitochondria. In addition, DFO and CoCl₂ treatments for 48 h significantly inhibited hMSCs proliferation in a concentration-dependent manner (P < 0.05). This treatment also increased the number of cells in G0/G1 phase and decreased those in G2/S/M phase.

CONCLUSIONS

The hypoxia-mimetic agents, DFO and CoCl₂, alter umbilical cord-derived hMSCs morphology and inhibit their proliferation through influencing the cell cycle.

Regulation of hypoxia adaptation: an overlooked virulence attribute of pathogenic fungi?

Over the past two decades, the incidence of fungal infections has dramatically increased. This is primarily due to increases in the population of immunocompromised individuals attributed to the HIV/AIDS pandemic and immunosuppression therapies associated with organ transplantation, cancer, and other diseases where new immunomodulatory therapies are utilized. Significant advances have been made in understanding how fungi cause disease, but clearly much remains to be learned about the pathophysiology of these often lethal infections. Fungal pathogens face numerous environmental challenges as they colonize and infect mammalian hosts. Regardless of a pathogen's complexity, its ability to adapt to environmental changes is critical for its survival and ability to cause disease. For example, at sites of fungal infections, the significant influx of immune effector cells and the necrosis of tissue by the invading pathogen generate hypoxic microenvironments to which both the pathogen and host cells must adapt in order to survive. However, our current knowledge of how pathogenic fungi adapt to and survive in hypoxic conditions during fungal pathogenesis is limited. Recent studies have begun to observe that the ability to adapt to various levels of hypoxia is an important component of the virulence arsenal of pathogenic fungi. In this review, we focus on known oxygen sensing mechanisms that non-pathogenic and pathogenic fungi utilize to adapt to hypoxic microenvironments and their possible relation to fungal virulence.

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.

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.

NSC606985 induces apoptosis, exerts synergistic effects with cisplatin, and inhibits hypoxia-stabilized HIF-1alpha protein in human ovarian cancer cells

The camptothecins, which target the intranuclear enzyme topoisomerase I, have advanced to the forefront of several areas of developmental chemotherapy of cancers. In the present study, we investigated the potential anti-human ovarian cancer effects of NSC606985, a novel and rarely studied camptothecin analog, and its combination with cisplatin (CDDP). Human ovarian cancer cell line COC1 cells were treated with different nanomolar of NSC606985 with or without CDDP, and cell growth and apoptosis were evaluated, respectively, by MTT assay and annexin-V assay on flow cytometry. Chou-Talalay analysis was used to evaluate combined effect of NSC606985 and CDDP. Western blot was used to detect protein kinase Cdelta (PKCdelta), caspase-3 and hypoxia-inducible factor-1alpha (HIF-1alpha) proteins. Our results showed that NSC606985 at nanomolar concentration induced apoptosis with the activation of PKCdelta in COC1 cells. Especially, NSC606985 presented the significant combined effects on COC1 cells in terms of growth inhibition and apoptosis induction. In addition, NSC606985 significantly antagonized the accumulation of HIF-1alpha stabilized by hypoxia or hypoxia-mimetic agent. These results suggest that NSC606985 and its combination with CDDP present the therapeutic potential on ovarian cancer, and deserve further preclinical and clinical studies.

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.

Effect of curcumin on hypoxia-inducible factor-1 alpha expression in hepatocellular carcinoma cells HepG2 under hypoxia and its possible mechanism

AIM: To study the effect of curcumin on hypoxia-inducible factor-1 alpha (HIF-1α) expression in HepG2 hepatocellular carcinoma cells under hypoxic conditions as well as the possible mechanism.

METHODS: HepG2 cells were treated with different concentrations (0, 1, 2, 5, 10 μmol/L) of curcumin under hypoxic conditions for 6 h. The protein and mRNA levels of HIF-1α were detected by Western blot and reverse transcription-polymerase chain reation (RT-PCR) respectively. Then HepG2 cells were treated with 0, 10 μmol/L curcumin, or 10 μmol/L curcumin plus 10 μmol/L MG-132 under hypoxic conditions for 6 h. The protein levels of HIF-1α and vascular endothelial growth factor (VEGF) were detected by Western blot.

RESULTS: After HepG2 cells were co-incubated with curcumin (1-10 μmol/L) for 6 h, the protein level of HIF-1α decreased significantly as compared with that in the control cells (0 μmol/L curcumin treatment ), in a dose-dependent manner (F = 79.81, P < 0.01), but the mRNA level of HIF-1α was not affected by curcumin. In the presence of MG-132, a proteasome inhibitor, the HIF-1α and VEGF protein levels decreased by curcunmin was restored to the level of control cells (F = 68.47, 83.79, both P < 0.01).

CONCLUSION: Curcumin suppresses HIF-1α expression at post-transcriptional level in HepG2 cells under hypoxia, probably via proteasome-dependent pathway.

Effect of curcumin on vascular endothelial growth factor expression in HepG2 hepatocellular carcinoma cells under hypoxic conditions

AIM: To investigate the effect of curcumin on the expression of vascular endothelial growth factor (VEGF) in hepatocellular carcinoma cell line HepG2 under hypoxic conditions.

METHODS: Hepatocellular carcinoma HepG2 cells were treated with different concentrations (0, 1, 2, 5, 10 μmol/L) of curcumin under hypoxic conditions for 6 h. Cellular viability was detected by MTT assay.The level of VEGF expression was detected at protein and mRNA level by Western blot technique and reverse transcription-poly chain reaction respectively.

RESULTS: The levels of VEGF protein and mRNA decreased significantly in the cells co-incubated with curcumin at 1, 2, 5, and 10 μmol/L for 6 h in a dose-dependent manner as compared with those in the control cells (0 μmol/L curcumin treatment) (VEGF protein: 2.12 ± 0.23, 1.59 ± 0.13, 0.82 ± 0.11, 0.33 ± 0.05 vs 2.85 ± 0.37, P < 0.05 or P < 0.01; VEGF mRNA: 0.60 ± 0.05, 0.54 ± 0.04, 0.16 ± 0.02, 0.06 ± 0.01 vs 0.81 ± 0.07, all P < 0.01).

CONCLUSION: Curcumin can decrease the expression of VEGF in hepatocellular carcinoma HepG2 cells.

CCAAT/enhancer-binding protein alpha antagonizes transcriptional activity of hypoxia-inducible factor 1 alpha with direct protein-protein interaction

Hypoxia-inducible factor 1 (HIF-1), a master heterodimeric transcriptional regulator consisting of HIF-1alpha and HIF-1beta subunits for cellular response to hypoxia, plays an important role in carcinogenesis, while CCAAT/enhancer-binding protein alpha (C/EBPalpha) is proposed to act as a tumor suppressor in C/EBPalpha-expressing tissues. Previously, we reported that ectopically expressed HIF-1alpha protein interacts with and enhances transcriptional activity of C/EBPalpha, which favors leukemic cell differentiation. Here we further showed that such an interaction also occurred in their endogenously expressing state of leukemic U937 cells. Glutathione S-transferase pull-down assay proposed that the protein-protein interaction was direct, and transactivation domains of C/EBPalpha and the basic helix-loop-helix domain of HIF-1alpha were essential for such an interaction. More intriguingly, we provided the first demonstration that C/EBPalpha competed with HIF-1beta for direct binding to HIF-1alpha protein. Correspondingly, C/EBPalpha overexpression significantly inhibited the DNA-binding ability of HIF-1 and expressions of hypoxia-responsive element-driven luciferase and HIF-1-targeted genes vascular endothelial growth factor, glucose transporter-1 and phosphoglycerate kinase 1. In parallel, suppression of C/EBPalpha expression by specific small hairpin RNA increased DNA-binding ability of HIF-1 and expression of these HIF-1-targeted genes in leukemic U937 cells. These results would provide new insights for antitumor potential of C/EBPalpha protein.

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.

Cobalt chloride, a hypoxia-mimicking agent, targets sterol synthesis in the pathogenic fungus Cryptococcus neoformans

We investigated the effects of the hypoxia-mimetic CoCl2 in the pathogenic fungus Cryptococcus neoformans and demonstrated that CoCl2 leads to defects in several enzymatic steps in ergosterol biosynthesis. Sterol defects were amplified in cells lacking components of the Sre1p-mediated oxygen-sensing pathway. Consequently, Sre1p and its binding partner Scp1p were essential for growth in the presence of CoCl2. Interestingly, high copies of a single gene involved in ergosterol biosynthesis, ERG25, rescued this growth defect. We show that the inhibitory effect of CoCl2 on scp1Delta and sre1Delta cells likely resulted from either an accumulation of non-viable methylated sterols or a decrease in the amount of ergosterol. Similar findings were also observed in the ascomycetous yeast, Schizosaccharomyces pombe, suggesting that the effects of CoCl2 on the Sre1p-mediated response are conserved in fungi. In addition, gene expression analysis revealed limited overlap between Sre1p-dependant gene activation in the presence of CoCl2 and low oxygen. The majority of genes similarly affected by both CoCl2 and low oxygen were involved in ergosterol synthesis and in iron/copper transport. This article identifies the Sre1p pathway as a common mechanism by which yeast cells sense and adapt to changes in both CoCl2 concentrations and oxygen levels.

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

Hypoxia or hypoxia mimetic has been shown to induce differentiation together with the accumulation of hypoxia-inducible factor-1alpha (HIF-1alpha) protein of myeloid leukemic cells and normal hematopoietic progenitors. To provide direct evidence for the role of HIF-1alpha in acute myeloid leukemia (AML) cell differentiation and its mechanisms, we generated myeloid leukemic U937T transformants, in which HIF-1alpha was tightly induced by tetracycline withdrawal. The results showed that the conditional HIF-1alpha induction triggered granulocytic differentiation of these transformants, while the suppression of HIF-1alpha expression by specific short hairpin RNAs (shRNAs) effectively inhibited hypoxia-induced differentiation of U937 cells, as evidenced by morphology, maturation-related antigens as well as expressions of myeloid differentiation signatures and hematopoietic cells-specific cytokine receptors. The specific shRNAs-inhibited expression of HIF-1beta, an essential partner for transcription activity of HIF-1, failed, while the inhibition of hematopoietic differentiation-critical CCAAT/enhancer-binding protein-alpha (C/EBPalpha) significantly eliminated HIF-1alpha-mediated myeloid leukemic cell differentiation. Collectively, this work provided several lines of direct evidence for the role of HIF-1alpha protein through its nontranscriptional activity in myeloid cell differentiation, in which C/EBPalpha elicits a role as an effector downstream to HIF-1alpha. These discoveries would shed new insights for understanding mechanisms underlying leukemogenesis and designing the new therapeutic strategy for differentiation induction of AML.

Hypoxia-mimetic agents desferrioxamine and cobalt chloride induce leukemic cell apoptosis through different hypoxia-inducible factor-1alpha independent mechanisms

Hypoxia presents pro-apoptotic and anti-apoptotic biphasic effects that appear to be dependent upon cell types and conditions around cells. The substantial reports demonstrated that commonly used hypoxia-mimetic agents cobalt chloride (CoCl(2)) and desferrioxamine (DFO) could also induce apoptosis in many different kinds of cells, but the mechanism was poorly understood. In this work, we compare the apoptosis-inducing effects of these two hypoxia-mimetic agents with acute myeloid leukemic cell lines NB4 and U937 as in vitro models. The results show that both of them induce these leukemic cells to undergo apoptosis with a loss of mitochondrial transmembrane potentials (DeltaPsi m), the activation of caspase-3/8 and the cleavage of anti-apoptotic protein Mcl-1, together with the accumulation of hypoxia-inducible factor-1 alpha (HIF-1alpha) protein, a critical regulator for the cellular response to hypoxia. Metavanadate and sodium nitroprusside significantly abrogate DFO rather than CoCl(2)-induced mitochondrial Delta Psi m collapse, caspase-3/8 activation, Mcl-1 cleavage and apoptosis, but they fail to influence DFO and CoCl(2)-induced HIF-1alpha protein accumulation. Moreover, inducible expression of HIF-1alpha gene dose not alter DFO and CoCl(2)-induced apoptosis in U937 cells. In conclusion, these results propose that although both DFO and CoCl(2)-induced leukemic cell apoptosis by mitochondrial pathway-dependent and HIF-1alpha-independent mechanisms, DFO and CoCl(2)-induced apoptosis involves different initiating signal pathways that remain to be investigated.

Effects of YC-1 on hypoxia-inducible factor 1-driven transcription activity, cell proliferative vitality, and apoptosis in hypoxic human pancreatic cancer cells

OBJECTIVES

To investigate the effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole (YC-1) on HIF-1-driven transcription activity, cell proliferative vitality, and apoptosis in hypoxic human pancreatic cancer cells.

METHODS

Human pancreatic cancer PC-3 cells were incubated under normoxic or hypoxic conditions. YC-1 was added to the media with different concentrations. The HIF-1alpha protein expression was detected by means of immunocytochemical staining and Western blotting. Semiquantitative reverse transcriptase polymerase chain reaction was used to determine the mRNA expression of HIF-1alpha, vascular endothelial growth factor (VEGF), and glucose phosphate isomerase (GPI). A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and flow cytometry were used to detect the cells' proliferative vitality and apoptosis.

RESULTS

Hypoxic PC-3 cells expressed a higher level of HIF-alpha protein in nucleus compared with the normoxic controls. When the dose of YC-1 was at 100 micromol/L, the expression location of HIF-alpha shifted from nucleus to cytoplasm. Western blotting revealed that YC-1 reduced the level of HIF-1alpha protein expression, and the inhibitory effect was dose dependent. Moreover, YC-1 dose dependently inhibited mRNA expression levels of VEGF and GPI in hypoxic cells. YC-1 inhibited proliferative vitality and induced apoptosis of hypoxic PC-3 cells in a dose-dependent manner.

CONCLUSIONS

YC-1 inhibits HIF-1alpha expression in hypoxic pancreatic cancer cells, which is accompanied by the translocation of HIF-1alpha from nucleus to cytoplasm, decreased mRNA expression of VEGF and GPI, reduced cell proliferative vitality, and increased apoptosis. These results suggest that HIF-1 is a potential therapeutic target for pancreatic cancer.

Commonly dysregulated genes in murine APL cells

To identify genes that are commonly dysregulated in a murine model of acute promyelocytic leukemia (APL), we first defined gene expression patterns during normal murine myeloid development; serial gene expression profiling studies were performed with primary murine hematopoietic progenitors that were induced to undergo myeloid maturation in vitro with G-CSF. Many genes were reproducibly expressed in restricted developmental "windows," suggesting a structured hierarchy of expression that is relevant for the induction of developmental fates and/or differentiated cell functions. We compared the normal myeloid developmental transcriptome with that of APL cells derived from mice expressing PML-RARalpha under control of the murine cathepsin G locus. While many promyelocyte-specific genes were highly expressed in all APL samples, 116 genes were reproducibly dysregulated in many independent APL samples, including Fos, Jun, Egr1, Tnf, and Vcam1. However, this set of commonly dysregulated genes was expressed normally in preleukemic, early myeloid cells from the same mouse model, suggesting that dysregulation occurs as a "downstream" event during disease progression. These studies suggest that the genetic events that lead to APL progression may converge on common pathways that are important for leukemia pathogenesis.

Comparative proteomic analysis of hypoxia-treated and untreated human leukemic U937 cells

We reported recently that moderate hypoxia and hypoxia-mimetic agents could induce growth arrest and differentiation of leukemic cells via the mediation of hypoxia-inducible factor 1 alpha (HIF-1alpha), but the exact molecular mechanisms remain largely unknown. In this study, human acute promonocytic leukemic U937 cells were incubated under 2% O2 or in 50 microM of the hypoxia mimetic agent cobalt chloride (CoCl2) and normal oxygen for 24 h, and their protein expression profiles were compared by 2-DE coupled with MALDI-TOF/TOF MS/MS. We identified 62 and 16 proteins that were significantly deregulated by hypoxia and CoCl2 treatment, respectively. These proteins were mainly involved in metabolism, gene expression regulation, signal transduction, cell proliferation, differentiation and apoptosis. As an example, N-myc downstream regulated gene 1 (NDRG1), a putative differentiation-related gene, was up-regulated in both 2% O2- and CoCl2-treated U937 cells. Moreover, enforced HIF-1alpha expression also elevated NDRG1 mRNA and protein in U937 cells. These data will provide some clues for understanding mechanisms by which leukemic cells response to hypoxia.

Synergistic effects of CoCl(2) and ROCK inhibition on mesenchymal stem cell differentiation into neuron-like cells

Bone-marrow-derived mesenchymal stem cells (MSCs) constitute an interesting cellular source to promote brain regeneration after neurodegenerative diseases. Recently, several studies suggested that oxygen-dependent gene expression is of crucial importance in governing the essential steps of neurogenesis such as cell proliferation, survival and differentiation. In this context, we analysed the effect of the HIF-1 (hypoxia inducible factor-1) activation-mimicking agent CoCl(2) on MSCs. CoCl(2) treatment increased the expression of the anti-proliferative gene BTG2/PC3 and decreased cyclin D1 expression. Expression of HIF-1alpha and its target genes EPO, VEGF and p21 was also upregulated. These changes were followed by inhibition of cell proliferation and morphological changes resulting in neuron-like cells, which had increased neuronal marker expression and responded to neurotransmitters. Echinomycin, a molecule inhibiting HIF-1 DNA-binding activity, blocked the CoCl(2) effect on MSCs. Additionally, by using Y-27632, we demonstrated that Rho kinase (ROCK) inhibition potentiated CoCl(2)-induced MSC differentiation in particular into dopaminergic neuron-like cells as attested by its effect on tyrosine hydroxylase expression. Altogether, these results support the ability of MSCs to differentiate into neuron-like cells in response to CoCl(2), an effect that might act, in part, through HIF-1 activation and cell-cycle arrest, and which is potentiated by inhibition of ROCK.

Proliferation and differentiation of bone marrow stromal cells under hypoxic conditions

Low oxygen tension is a potent differentiation inducer of numerous cell types and an effective stimulus of many gene expressions. Here, we described that under 8% O(2), bone marrow stromal cells (MSCs) exhibited proliferative and morphologic changes. The level of differentiated antigen H-2Dd and the number of G(2)/S/M phase cells increased evidently under 8% O(2) condition. Also, the proportion of wide, flattened, and epithelial-like cells (which were alkaline phosphatase staining positive) in MSCs increased significantly. When cultured in adipogenic medium, there was a 5- to 6-fold increase in the number of lipid droplets under hypoxic conditions compared with that in normoxic culture. We also demonstrated the existence of MSC differentiation under hypoxic conditions by electron microscopy. Expression of Oct4 was inhibited under 8% O(2) condition, but after adipocyte differentiation in normoxic culture and hypoxia-mimicking agents cobalt chloride (CoCl(2)) and deferoxamine mesylate (DFX) treatments, Oct4 was still expressed in MSCs. These results indicate hypoxia accelerates MSC differentiation and hypoxia and hypoxia-mimicking agents exert different effects on MSC differentiation.

Effects of Tiron, 4,5-dihydroxy-1,3-benzene disulfonic acid, on human promyelotic HL-60 leukemia cell differentiation and death

Tiron, 4,5-dihydroxy-1,3-benzene disulfonic acid, has been known to be a widely used antioxidant to rescue ROS-evoked cell death and a non-toxic chelator to alleviate an acute metal overload. In this study, we showed that Tiron is a potent inducer of cell differentiation and apoptotic cell death in human promyelotic HL-60 leukemia cell. At a low level of concentration (<0.5mM), Tiron caused HL-60 cells to induce differentiation-related alterations such as the increase of CD11b and CD14 expression or chromatin condensation. Hypoxia inducible factor-1alpha (HIF-1alpha) was also increased at mRNA and protein level, and thus the CCAAT/enhancer-binding protein alpha, which is a downstream target of HIF-1alpha and acts as a critical factor for granulocytic differentiation was increased. High dose of Tiron (>0.5mM) induced severe DNA damage in HL-60 cells, as measured by the cytokinesis-block micronucleus test and the comet assay. Consequently, high dose of Tiron led to apoptotic cell death, which showed the DNA fragmentation, the caspase activation and the unbalance between antiapoptotic (Bcl-2) and proapoptotic proteins (Bax). However, an exogenous supplement of iron (FeCl(3)) reversed all of these effects, the cell differentiation and the apoptotic cell death. Therefore, these results suggest that Tiron-mediated differentiation and cell death result from the disturbance of iron metabolism.

Induction of tumor arrest and differentiation with prolonged survival by intermittent hypoxia in a mouse model of acute myeloid leukemia

We showed previously that mild real hypoxia and hypoxia-mimetic agents induced in vitro cell differentiation of acute myeloid leukemia (AML). We here investigate the in vivo effects of intermittent hypoxia on syngenic grafts of leukemic blasts in a PML-RARalpha transgenic mouse model of AML. For intermittent hypoxia, leukemic mice were housed in a hypoxia chamber equivalent to an altitude of 6000 m for 18 hours every consecutive day. The results show that intermittent hypoxia significantly prolongs the survival of the leukemic mice that received transplants, although it fails to cure the disease. By histologic and cytologic analyses, intermittent hypoxia is shown to inhibit the infiltration of leukemic blasts in peripheral blood, bone marrow, spleen, and liver without apoptosis induction. More intriguingly, intermittent hypoxia also induces leukemic cells to undergo differentiation with progressive increase of hypoxia-inducible factor-1alpha protein, as evidenced by morphologic criteria of maturating myeloid cells and increased expression of mouse myeloid cell differentiation-related antigens Gr-1 and Mac-1. Taken together, this study represents the first attempt to characterize the in vivo effects of hypoxia on an AML mouse model. Additional investigations may uncover ways to mimic the differentiative effects of hypoxia in a manner that will benefit human patients with AML.

Desferrioxamine induces leukemic cell differentiation potentially by hypoxia-inducible factor-1 alpha that augments transcriptional activity of CCAAT/enhancer-binding protein-alpha

We reported recently that cobalt chloride-simulated hypoxia and mild hypoxia modified the differentiation of human acute myeloid leukemic (AML) cells, probably acting via a hypoxia-inducible factor-1 alpha (HIF-1 alpha)-dependent mechanism. In this study, we investigated the effect of desferrioxamine (DFO), an iron chelator with 'hypoxia-mimetic' activity, on the differentiation of AML cells. The results showed that DFO at nontoxic concentrations induced the differentiation of AML cell lines NB4 and U937, as assessed by morphological criteria and differentiation-associated antigens. DFO-induced differentiation parallel to the rapid accumulation of HIF-1 alpha protein in these two cell lines. Of importance, the transient transfection of HIF-1 alpha cDNA induced U937 cells to develop the differentiation-related alterations such as growth arrest and increased CD11b expression. Furthermore, the inducible expression of chromosome translocation t(8;21)-generated leukemogenic AML1-ETO fusion gene attenuated DFO-induced differentiation of U937 cells with the decrease of CCAAT/enhancer-binding protein alpha (C/EBP alpha), a critical factor for granulocytic differentiation. Using immunoprecipitation and luciferase reporter assay, HIF-1 alpha was also shown to interact physically with and to increase the transcriptional activity of C/EBP alpha. Taken together, these results provided novel evidence for a role of HIF-1 alpha in AML cell differentiation, and suggested that C/EBP alpha might be a downstream effector for HIF-1 alpha-mediated differentiation.

Metavanadate suppresses desferrioxamine-induced leukemic cell differentiation with reduced hypoxia-inducible factor-1α protein

We recently showed that moderate hypoxia and hypoxia-mimetic agents CoCl(2) and desferrioxamine (DFO) induce differentiation of acute myeloid leukemic cells via hypoxia-inducible factor-1alpha (HIF-1alpha) that interacts with and increases the transcriptional activity of CCAAT/enhancer-binding protein alpha (C/EBPalpha), a critical factor for granulocytic differentiation. Here, we show that metavanadate antagonizes DFO-induced growth arrest and differentiation with the inhibition of HIF-1alpha protein accumulation in leukemic cells. Furthermore, DFO also increased C/EBPalpha expression rapidly but transiently, which was inhibited by metavanadate. Taken together, these findings provide further evidence for the role of HIF-1alpha and C/EBPalpha in DFO-induced leukemic cell differentiation.

Angiotensin II induces hypoxia-inducible factor-1 alpha in PC 12 cells through a posttranscriptional mechanism: role of AT2 receptors

BACKGROUND

Angiotensin II (ANG II) inhibits proliferation and induces differentiation in PC 12 cells via AT(2) receptor activation. Using differential display analysis, we previously isolated SM-20/PHD3 as a key factor, which is downregulated by ANG II treatment. Subsequently, it turned out that SM-20/PHD3 is a rat homologue of PHD3, a key prolyl hydroxylase involved in the initial steps fostering the degradation of hypoxia-inducible factor (HIF). The present study was undertaken to investigate whether the ANG-II-mediated suppression of SM-20/PHD3/PHD3 may be associated with an increase in HIF-1 alpha.

METHODS

HIF-1 alpha protein expression was assessed by Western blots. mRNA levels for HIF-1 alpha were measured by real-time PCR and for SM-20/PHD3 by Northern blots. Binding of HIF-1 alpha to consensus oligonucleotides in vitro was determined with gel shift analysis. SM-20/PHD3 was transiently overexpressed in PC 12 cells using an inducible expression system.

RESULTS

ANG II stimulated HIF-1alpha protein expression. This effect was already detected after 30 min and peaked at 6 h, but was not detectable anymore after 24- 48 h of stimulation. PD 123177, but not losartan, antagonized this effect, indicating transduction through AT(2) receptors. Real-time PCR failed to show a significant increase in HIF-1 alpha transcripts after ANG II challenge at any time point. Gel shift analysis revealed that ANG-II-induced nuclear HIF-1 alpha protein binds to consensus sites. A reduction in SM-20/PHD3 mRNA expression paralleled the increase in HIF-1 alpha. Overexpression of SM-20/PHD3 transiently resulted in a decrease in HIF-1 alpha protein concentrations under basal conditions as well as after stimulation with ANG II.

CONCLUSION

ANG II stimulates HIF-1 alpha expression by a posttranscriptional mechanism via AT(2) receptors. This increase is likely caused by a downregulation of SM-20/PHD3. The ANG-II-mediated increase in HIF-1 alpha expression could be potentially involved in physiological as well as pathophysiological processes such as differentiation, growth inhibition, and remodeling.