Hemoglobin synthesis in murine virus-induced leukemic cells in vitro: stimulation of erythroid differentiation by dimethyl sulfoxide

Erythroid-specific transcriptional changes in PBMCs from pulmonary hypertension patients

Background

Gene expression profiling of peripheral blood mononuclear cells (PBMCs) is a powerful tool for the identification of surrogate markers involved in disease processes. The hypothesis tested in this study was that chronic exposure of PBMCs to a hypertensive environment in remodeled pulmonary vessels would be reflected by specific transcriptional changes in these cells.

Methodology/Principal Findings

The transcript profiles of PBMCs from 30 idiopathic pulmonary arterial hypertension patients (IPAH), 19 patients with systemic sclerosis without pulmonary hypertension (SSc), 42 scleroderma-associated pulmonary arterial hypertensio patients (SSc-PAH), and 8 patients with SSc complicated by interstitial lung disease and pulmonary hypertension (SSc-PH-ILD) were compared to the gene expression profiles of PBMCs from 41 healthy individuals. Multiple gene expression signatures were identified which could distinguish various disease groups from controls. One of these signatures, specific for erythrocyte maturation, is enriched specifically in patients with PH. This association was validated in multiple published datasets. The erythropoiesis signature was strongly correlated with hemodynamic measures of increasing disease severity in IPAH patients. No significant correlation of the same type was noted for SSc-PAH patients, this despite a clear signature enrichment within this group overall. These findings suggest an association of the erythropoiesis signature in PBMCs from patients with PH with a variable presentation among different subtypes of disease.

Conclusions/Significance

In PH, the expansion of immature red blood cell precursors may constitute a response to the increasingly hypoxic conditions prevalent in this syndrome. A correlation of this erythrocyte signature with more severe hypertension cases may provide an important biomarker of disease progression.

NDRG2 Promotes GATA-1 Expression through Regulation of the JAK2/STAT Pathway in PMA-stimulated U937 Cells

BACKGROUND

N-myc downstream-regulated gene 2 (NDRG2), a member of a newly described family of differentiation-related genes, has been characterized as a regulator of dendritic cells. However, the role of NDRG2 on the expression and activation of transcription factors in blood cells remains poorly understood. In this study, we investigated the effects of NDRG2 overexpression on GATA-1 expression in PMA-stimulated U937 cells.

METHODS

We generated NDRG2-overexpressing U937 cell line (U937-NDRG2) and treated the cells with PMA to investigate the role of NDRG2 on GATA-1 expression.

RESULTS

NDRG2 overexpression in U937 cells significantly induced GATA-1 expression in response to PMA stimulation. Interestingly, JAK2/STAT and BMP-4/Smad pathways associated with the induction of GATA-1 were activated in PMA-stimulated U937-NDRG2 cells. We found that the inhibition of JAK2 activation, but not of BMP-4/Smad signaling, can elicit a decrease of PMA-induced GATA-1 expression in U937-NDRG2 cells.

CONCLUSION

The results reveal that NDRG2 promotes the expression of GATA-1 through activation of the JAK2/STAT pathway, but not through the regulation of the BMP-4/Smad pathway in U937 cells. Our findings further suggest that NDRG2 may play a role as a regulator of erythrocyte and megakaryocyte differentiation during hematopoiesis.

Cholesterol esterification during differentiation of mouse erythroleukemia (Friend) cells

Cholesterol is an essential constituent of all mammalian cell membranes and its availability is therefore a prerequisite for cellular growth and other functions. Several lines of evidence are now indicating an association between alterations of cholesterol homeostasis and cell cycle progression. However, the role of cholesterol in cell differentiation is still largely unknown. To begin to address this issue, in this study we examined changes in cholesterol metabolism and in the mRNA levels of proteins involved in cholesterol import and esterification (multi-drug resistance, MDR-3) and acylCoA: cholesterol acyltransferase (ACAT) and cholesterol export (caveolin-1) in Friend virus-induced erythroleukemia cells (MELC), in the absence or in the presence of the chemical inducer of differentiation, hexamethylene bisacetamide (HMBA). FBS-stimulated growth of MELC was accompanied by an immediate elevation of cholesterol synthesis and cholesterol esterification, and by an increase in the levels of MDR-3 and ACAT mRNAs. A decrease in caveolin-1 expression was also observed. However, when MELC were treated with HMBA, the inhibition of DNA synthesis caused by HMBA treatment, was associated with a decrease in cholesterol esterification and in ACAT and MDR-3 mRNA levels and an increase in caveolin-1 mRNA. Detection of cytoplasmic neutral lipids by staining MELC with oil red O, a dye able to evidence CE but not FC, revealed that HMBA-treatment also reduced growth-stimulated accumulation of cholesterol ester to approximately the same extent as the ACAT inhibitor, SaH. Overall, these results indicate for the first time a role of cholesterol esterification and of some related genes in differentiation of erythroid cells.

For disease in need, a Friend indeed

It has been 40 years since Charlotte Friend demonstrated the unbelievable for the second time.

Specific differentiation of mesenchymal stem cells by small molecules

Mesenchymal stem cells (MSCs) are multipotent, self-renewing cells harboring multi-lineage differentiation potential and immunosuppressive properties that make them an attractive candidate for biological cell-based regenerative medicine. In addition to its undoubted clinical interest, controlling the fate and behaviors of MSCs is a crucial prerequisite for their therapeutic applications in regenerative medicine. Stem cell differentiation and modulation of functional activities are generally controlled by "cocktails" of growth factors, signaling molecules, and/or genetic manipulations. However, these approaches have several limiting factors, such as undefined conditions leading to heterogeneous populations of cells and unexpected risks of virus-mediated genetic modifications. Small molecules targeting specific signaling pathways have been shown to be key modulators in controlling stem cells' fate and function. Small molecules are also important tools for understanding mechanistic and developmental processes. Furthermore, the precise mode of action of small molecules for controlling MSCs fate is still under study. However, Wnt, GSK, and other protein kinases signaling pathways are likely to be involved. These target-based manipulations of stem cells fate by small molecules provide new insights into stem cell biology, and facilitate the development of regenerative medicine using stem cells. Here, we review the recent progress in controlling MSCs fate and functional activities by small molecules.

Therapeutic strategies to enhance the anticancer efficacy of histone deacetylase inhibitors

Histone acetylation is a posttranslational modification that plays a role in regulating gene expression. More recently, other nonhistone proteins have been identified to be acetylated which can regulate their function, stability, localization, or interaction with other molecules. Modulating acetylation with histone deacetylase inhibitors (HDACi) has been validated to have anticancer effects in preclinical and clinical cancer models. This has led to development and approval of the first HDACi, vorinostat, for the treatment of cutaneous T cell lymphoma. However, to date, targeting acetylation with HDACi as a monotherapy has shown modest activity against other cancers. To improve their efficacy, HDACi have been paired with other antitumor agents. Here, we discuss several combination therapies, highlighting various epigenetic drugs, ROS-generating agents, proteasome inhibitors, and DNA-damaging compounds that together may provide a therapeutic advantage over single-agent strategies.

Cohesin mediates chromatin interactions that regulate mammalian β-globin expression

The β-globin locus undergoes dynamic chromatin interaction changes in differentiating erythroid cells that are thought to be important for proper globin gene expression. However, the underlying mechanisms are unclear. The CCCTC-binding factor, CTCF, binds to the insulator elements at the 5' and 3' boundaries of the locus, but these sites were shown to be dispensable for globin gene activation. We found that, upon induction of differentiation, cohesin and the cohesin loading factor Nipped-B-like (Nipbl) bind to the locus control region (LCR) at the CTCF insulator and distal enhancer regions as well as at the specific target globin gene that undergoes activation upon differentiation. Nipbl-dependent cohesin binding is critical for long-range chromatin interactions, both between the CTCF insulator elements and between the LCR distal enhancer and the target gene. We show that the latter interaction is important for globin gene expression in vivo and in vitro. Furthermore, the results indicate that such cohesin-mediated chromatin interactions associated with gene regulation are sensitive to the partial reduction of Nipbl caused by heterozygous mutation. This provides the first direct evidence that Nipbl haploinsufficiency affects cohesin-mediated chromatin interactions and gene expression. Our results reveal that dynamic Nipbl/cohesin binding is critical for developmental chromatin organization and the gene activation function of the LCR in mammalian cells.

Single domain intracellular antibodies from diverse libraries: emphasizing dual functions of LMO2 protein interactions using a single VH domain

Interfering intracellular antibodies are valuable for biological studies as drug surrogates and as potential macromolecular drugs per se. Their application is still limited because of the difficulty of acquisition of functional intracellular antibodies. We describe the use of the new intracellular antibody capture procedure (IAC(3)) to facilitate direct isolation of functional single domain antibody fragments using four independent target molecules (LMO2, TP53, CRAF1, and Hoxa9) from a set of diverse libraries. Initially, these have variability in only one of the three antigen-binding CDR regions of VH or VL and first round single domains are affinity matured by iterative randomization of the two other CDRs and reselection. We highlight the approach using a single domain binding to LMO2 protein. Our results show that interfering with LMO2 protein function demonstrates a role specifically in erythroid differentiation, confirm a necessary and sufficient function for LMO2 as a cancer therapy target in T-cell neoplasia and allowed for the first time production of soluble recombinant LMO2 protein by co-expression with intracellular domain antibodies. Co-crystallization of LMO2 and the anti-LMO2 VH protein was successful. These results demonstrate that this third generation IAC(3) offers a robust toolbox for various biomedical applications and consolidates functional features of the LMO2 protein complex, which includes the importance of Lmo2-Ldb1 protein interaction.

Antagonistic roles of the ERK and p38 MAPK signalling pathways in globin expression, haem biosynthesis and iron uptake

Late-stage erythroid cells synthesize large quantities of haemoglobin, a process requiring the co-ordinated regulation of globin and haem synthesis as well as iron uptake. In the present study, we investigated the role of the ERK (extracellular-signal-regulated kinase) and p38 MAPK (mitogen-activated protein kinase) signalling pathways in MEL (mouse erythroleukaemia) cell differentiation. We found that treatment of HMBA (hexamethylene bisacetamide)-induced MEL cells with the ERK pathway inhibitor UO126 results in an increase in intracellular haem and haemoglobin levels. The transcript levels of the genes coding for β(major)-globin, the haem biosynthesis enzyme 5-aminolevulinate synthase 2 and the mitochondrial iron transporter mitoferrin 1 are up-regulated. We also showed enhanced expression of globin and transferrin receptor 1 proteins upon UO126 treatment. With respect to iron uptake, we found that ERK inhibitor treatment led to an increase in both haem-bound and total iron. In contrast, treatment of MEL cells with the p38 MAPK pathway inhibitor SB202190 had the opposite effect, resulting in decreased globin expression, haem synthesis and iron uptake. Reporter assays showed that globin promoter and HS2 enhancer-mediated transcription was under the control of MAPKs, as inhibition of the ERK and p38 MAPK pathways led to increased and decreased gene activity respectively. Our present results suggest that the ERK1/2 and p38α/β MAPKs play antagonistic roles in HMBA-induced globin gene expression and erythroid differentiation. These results provide a novel link between MAPK signalling and the regulation of haem biosynthesis and iron uptake in erythroid cells.

Is there a role for differentiating therapy in non-APL AML?

Differentiation therapy with all-trans retinoic acid has been a very successful therapeutic strategy in acute promyelocytic leukemia (APL), but the value of differentiation therapy in acute myeloid leukemia (AML) remains to be determined. A number of current treatments, such as tyrosine kinase inhibitors, cytokines, and epigenetic agents, induce differentiation of leukemic cells to some extent, but differentiation is not the main goal of these treatments. Forcing expression of certain transcription factors, such as C/EBP, has also been useful in inducing differentiation in cell lines and in murine models, but an effective way to force expression of these genes in humans is yet to be discovered.

Friend Spleen Focus-Forming Virus Activates the Tyrosine Kinase sf-Stk and the Transcription Factor PU.1 to Cause a Multi-Stage Erythroleukemia in Mice

Hematological malignancies in humans typically involve two types of genetic changes: those that promote hematopoietic cell proliferation and survival (often the result of activation of tyrosine kinases) and those that impair hematopoietic cell differentiation (often the result of changes in transcription factors). The multi-stage erythroleukemia induced in mice by Friend spleen focus-forming virus (SFFV) is an excellent animal model for studying the molecular basis for both of these changes. Significant progress has been made in understanding the molecular basis for the multi-stage erythroleukemia induced by Friend SFFV. In the first stage of leukemia, the envelope protein encoded by SFFV interacts with and activates the erythropoietin (Epo) receptor and the receptor tyrosine kinase sf-Stk in erythroid cells, causing their Epo-independent proliferation, differentiation and survival. In the second stage, SFFV integration into the Sfpi1 locus activates the myeloid transcription factor PU.1, blocking erythroid cell differentiation, and in conjunction with the loss of p53 tumor suppressor activity, results in the outgrowth of malignant cells. In this review, we discuss the current level of understanding of how SFFV alters the growth and differentiation of erythroid cells and results in the development of erythroleukemia. Our knowledge of how SFFV causes erythroleukemia in mice may give us clues as to how the highly related human retrovirus XMRV causes malignancies in humans.

Recent advances in histone deacetylase targeted cancer therapy

Epigenetic regulators such as histone acetyltransferases (HATs) and histone deacetylases (HDACs) are known to play an important role in gene expression. Of these enzymes, HDACs have been shown to be commonly associated with many types of cancers and to affect cancer development. Consequently, HDACs have been considered as promising targets for cancer therapy. In addition, the inhibition of HDACs by histone deacetylase inhibitors (HDACIs) shifts the balance between the deacetylating activity of HDACs and the acetylating activity of HATs in the regulation of gene expression. Therefore, HDACIs are an exciting new addition in cancer therapies. Numerous HDACIs have been identified and some have recently been used in clinical trials for cancer treatment, although the mechanisms underlying the anticancer effects of HDACIs remain unclear. In this review, we examine the most recent developments in HDACIs and various aspects of HDAC-targeted cancer treatment.

High-content screening of small compounds on human embryonic stem cells

Human ES (embryonic stem) cells and iPS (induced pluripotent stem) cells have been heralded as a source of differentiated cells that could be used in the treatment of degenerative diseases, such as Parkinson's disease or diabetes. Despite the great potential for their use in regenerative therapy, the challenge remains to understand the basic biology of these remarkable cells, in order to differentiate them into any functional cell type. Given the scale of the task, high-throughput screening of agents and culture conditions offers one way to accelerate these studies. The screening of small-compound libraries is particularly amenable to such high-throughput methods. Coupled with high-content screening technology that enables simultaneous assessment of multiple cellular features in an automated and quantitative way, this approach is proving powerful in identifying both small molecules as tools for manipulating stem cell fates and novel mechanisms of differentiation not previously associated with stem cell biology. Such screens performed on human ES cells also demonstrate the usefulness of human ES/iPS cells as cellular models for pharmacological testing of drug efficacy and toxicity, possibly a more imminent use of these cells than in regenerative medicine.

Protein acetylation in the cardiorenal axis: the promise of histone deacetylase inhibitors

Acetylation of histone and nonhistone proteins provides a key mechanism for controlling signaling and gene expression in heart and kidney. Pharmacological inhibition of protein deacetylation with histone deacetylase (HDAC) inhibitors has shown promise in preclinical models of cardiovascular and renal disease. Efficacy of HDAC inhibitors appears to be governed by pleiotropic salutary actions on a variety of cell types and pathophysiological processes, including myocyte hypertrophy, fibrosis, inflammation and epithelial-to-mesenchymal transition, and occurs at compound concentrations below the threshold required to elicit toxic side effects. We review the roles of acetylation/deacetylation in the heart and kidney and provide rationale for extending HDAC inhibitors into clinical testing for indications involving these organs.

The saving switch

The epigenome consists of a system of chemical tags that attach to our DNA and its associated molecules, switching genes on and off. But the system is not without glitches-and scientists think that the misplacement of these tags can cause disease. This idea has led to new drugs that aim to correct gene activity (and obliterate disease) by altering the proteins around which DNA winds. Cassandra Willyard examines whether this approach will unlock the long-awaited promise of epigenetic therapy.

The main product of specialized tissues regulates cell life and may cause neoplastic transformation

Many tissues and cells in vertebrates are highly specialized and devoted to a single function through the action of a single molecule, that we call the "main product" (MP) of the cell. The hypothesis here proposed is that these MPs control all aspects of the cell life, namely activity, division, differentiation and apoptosis. Evidences supporting this hypothesis are reported for the immune system, pancreatic beta-cells, melanocytes, connective tissues, thyroid cells, skin and erythroid cells. In all cases cell division and differentiation is promoted by a normal activity of the MP, while hyperactivity leads to cell apoptosis. Evidences are also provided that alterations of the activity of the MP may elicit pathological disorders; in particular mutations altering the structure of the MP may elicit tumoural transformation.

Erythropoiesis: model systems, molecular regulators, and developmental programs

Human erythropoiesis is a complex multistep developmental process that begins at the level of pluripotent hematopoietic stem cells (HSCs) at bone marrow microenvironment (HSCs niche) and terminates with the production of erythrocytes (RBCs). This review covers the basic and contemporary aspects of erythropoiesis. These include the: (a) cell-lineage restricted pathways of differentiation originated from HSCs and going downward toward the blood cell development; (b) model systems employed to study erythropoiesis in culture (erythroleukemia cell lines and embryonic stem cells) and in vivo (knockout animals: avian, mice, zebrafish, and xenopus); (c) key regulators of erythropoiesis (iron, hypoxia, stress, and growth factors); (d) signaling pathways operating at hematopoietic stem cell niche for homeostatic regulation of self renewal (SCF/c-kit receptor, Wnt, Notch, and Hox) and for erythroid differentiation (HIF and EpoR). Furthermore, this review presents the mechanisms through which transcriptional factors (GATA-1, FOG-1, TAL-1/SCL/MO2/Ldb1/E2A, EKLF, Gfi-1b, and BCL11A) and miRNAs regulate gene pattern expression during erythroid differentiation. New insights regarding the transcriptional regulation of alpha- and beta-globin gene clusters were also presented. Emphasis was also given on (i) the developmental program of erythropoiesis, which consists of commitment to terminal erythroid maturation and hemoglobin production, (two closely coordinated events of erythropoieis) and (ii) the capacity of human embryonic and umbilical cord blood (UCB) stem cells to differentiate and produce RBCs in culture with highly selective media. These most recent developments will eventually permit customized red blood cell production needed for transfusion.

Dual role for the methyltransferase G9a in the maintenance of beta-globin gene transcription in adult erythroid cells

Using a proteomics screen, we have identified the methyltransferase G9a as an interacting partner of the hematopoietic activator NF-E2. We show that G9a is recruited to the beta-globin locus in a NF-E2-dependent manner and spreads over the entire locus. While G9a is often regarded as a corepressor, knocking down this protein in differentiating adult erythroid cells leads to repression of the adult beta(maj) globin gene and aberrant reactivation of the embryonic beta-like globin gene E(y). While in adult cells G9a maintains E(y) in a repressed state via dimethylation of histone H3 at lysines 9 and 27, it activates beta(maj) transcription in a methyltransferase-independent manner. Interestingly, the demethylase UTX is recruited to the beta(maj) (but not the E(y)) promoter where it antagonizes G9a-dependent H3K27 dimethylation. Collectively, these results reveal a dual role for G9a in maintaining proper expression (both repression and activation) of the beta-globin genes in differentiating adult erythroid cells.

The possible evolutionary role of tumors in the origin of new cell types

The ability of tumor cells to differentiate in combination with their ability to express genes that are not expressed in normal tissues, may result in the emergence of new cell types in evolution. Tumors may play an evolutionary role by providing conditions (space and resources) for the expression of newly evolving genes. Genetically or epigenetically predetermined tumors at the early stages of progression, benign tumors, and some tumor-like processes in invertebrates and plants, all of which are modes of excess cell growth which provide evolving multicellular organisms with extra cell masses, are considered as potentially evolutionarily meaningful. Malignant tumors at the late stages of progression, however, are not. The preexisting cell types of multicellular organisms had restricted potential for the expression of newly evolving genes. Because of regulation and gene competition, some of the newly evolving genes may stay silent. Multicellular organisms would need excess cell masses for the expression of newly evolving genes. The preexisting cell types cannot provide such excess cell masses because of limitations imposed on the number of possible cell divisions. Tumors could provide the evolving multicellular organisms with the excess cell masses for the expression of newly evolving genes. We suggest that tumors could be a sort of proving ground (or reservoir) for the expression of newly evolving genes that originate in the course of genome evolution in the DNA of germ cells (i.e., not in tumor cells themselves). The case in which the expression of a newly evolving gene in tumors results in the origin of a new function would be associated with the origin of new feedback and regulatory circuits, as in root nodules in legumes and macromelanophores in Xiphophorus fishes. Tumor cells would differentiate, resulting in a new cell type for the given multicellular species. This cell type would be inherited because of epigenomic mechanisms similar to those in preexisting cell types. Populations of tumor-bearing organisms with genetically or epigenetically programmed tumors could represent the transition between established species of organisms at different stages of progressive evolution. Experimental confirmation of the prediction of the hypothesis of evolution by tumor cells differentiation concerning the expression of evolutionarily new genes and/or silent (neutrally evolving) sequences in tumor cells is presented.

Tumour virology--history, status and future challenges

Viruses enter host cells in order to complete their life cycles and have evolved to exploit host cell structures, regulatory factors and mechanisms. The virus and host cell interactions have consequences at multiple levels, spanning from evolution through disease to models and tools for scientific discovery and treatment. Virus-induced human cancers arise after a long duration of time and are monoclonal or oligoclonal in origin. Cancer is therefore a side effect rather than an essential part of viral infections in humans. Still, 15-20% of all human cancers are caused by viruses. A review of tumour virology shows its close integration in cancer research. Viral tools and experimental models have been indispensible for the progress of molecular biology. In particular, retroviruses and DNA tumour viruses have played major roles in our present understanding of the molecular biology of both viruses and the host. Recently, additional complex relationships due to virus and host co-evolution have appeared and may lead to a further understanding of the overall regulation of gene expression programmes in cancer.

Indian hedgehog supports definitive erythropoiesis

Indian hedgehog (Ihh) has been reported to stimulate haematopoiesis ex vivo. In this study we studied the consequences of loss of function of Ihh for murine haematopoietic development. Ihh has no essential role in primitive erythropoiesis, but it is required in a non cell autonomous fashion for definitive erythropoieisis. Many components of the hedgehog signaling pathway are present in the fetal liver, with Ihh and Gli1 being most highly expressed in the stroma and Ptc1 being most highly expressed in haematopoietic stem and progenitor cells. Ihh knockout HSC and progenitor cell populations are produced in normal numbers in vivo and respond normally to haematopoietic cytokines in vitro, but terminal erythroid differentiation is defective leading to fatal anemia in mid gestation in many Ihh knockout embryos. These loss-of-function studies are consistent with previous gain-of-function studies which show Ihh can induce blood from ectoderm or expand HSCs in stroma-dependent culture.

Differentiation therapy of leukemia: 3 decades of development

A characteristic feature of leukemia cells is a blockade of differentiation at a distinct stage in cellular maturation. In the 1970s and 1980s, studies demonstrating the capabilities of certain chemicals to induce differentiation of hematopoietic cell lines fostered the concept of treating leukemia by forcing malignant cells to undergo terminal differentiation instead of killing them through cytotoxicity. The first promising reports on this notion prompted a review article on this subject by us 25 years ago. In this review, we revisit this interesting field of study and report the progress achieved in the course of nearly 3 decades. The best proof of principle for differentiation therapy has been the treatment of acute promyelocytic leukemia with all-trans retinoic acid. Attempts to emulate this success with other nuclear hormone ligands such as vitamin D compounds and PPARgamma agonists or different classes of substances such as hematopoietic cytokines or compounds affecting the epigenetic landscape have not been successful on a broad scale. However, a multitude of studies demonstrating partial progress and improvements and, finally, the new powerful possibilities of forward and reverse engineering of differentiation pathways by manipulation of transcription factors support the continued enthusiasm for differentiation therapy of leukemia in the future.

Hexamethylene bisacetamide can convert nonpermissive human cells to a permissive state for expressing the major immediate-early genes of human cytomegalovirus by up-regulating NF-kappaB activity

Expression of the major immediate-early (MIE) genes of human cytomegalovirus (HCMV) in the human thyroid papillary carcinoma cell line TPC-1 is repressed at the transcriptional level. However, treatment of these cells with hexamethylene bisacetamide (HMBA), a chemical inducer of differentiation, for 12 to 24 h before infection enabled the cells to support IE1 and IE2 gene expression and consequently HCMV replication. In HMBA-treated cells the transcription factor NF-kappaB was induced and the MIE promoter (MIEP) was activated. The presence of a NF-kappaB inhibitory peptide SN-50 or expression of a dominant negative IkappaBalpha protein during the HMBA pretreatment period efficiently prevented the HMBA-induced MIEP activation and MIE protein synthesis. Moreover, introduction of mutations into the NF-kappaB binding sites in the MIEP in a plasmid expressing the IE1 protein diminished its ability to express the protein in HMBA-treated cells. Therefore, the NF-kappaB activity previously induced in HMBA-treated cells and the NF-kappaB sites in the MIEP were shown to be essential for HCMV to respond to HMBA action and to express the MIE genes. Investigation of the mechanisms by which HMBA activates NF-kappaB revealed that degradation of IkappaBalpha and translocation of the phosphorylated NF-kappaB p65 subunit to the nucleus, both of which are known to be critical steps in NF-kappaB activation, are stimulated in the HMBA-treated cells. These results indicate that treatment of nonpermissive TPC-1 cells with HMBA induces MIE gene permissiveness by up-regulating NF-kappaB activity.

Magnetic resonance imaging assays for dimethyl sulfoxide effect on cancer vasculature

OBJECTIVES

To evaluate the potential of quantitative assays of vascular characteristics based on dynamic contrast-enhanced magnetic resonance imaging (MRI) using a macromolecular contrast medium (MMCM) to search for and measure effects of dimethyl sulfoxide (DMSO) on cancer vasculature with microscopic correlations.

MATERIAL AND METHODS

Saline-treated control (n = 8) and DMSO-treated (n = 7) human breast cancer xenografts (MDA-MB-435) in rats were imaged dynamically by MMCM-enhanced MRI using albumin-(Gd-DTPA)27-(biotin)11 (molecular weight approximately 90 kDa), before and after a 1-week, 3-dose treatment course. After the posttreatment MRI examinations, tumors were perfused with lectin and fixative and subsequently stained with RECA-1 and streptavidin for quantitative fluorescent microscopy. Quantitative MRI estimates of cancer microvessel permeability (KPS; microL/min.100 cm3) and fractional plasma volume (fPV; %) were based on a 2-compartment kinetic model. Fluorescent microscopy yielded estimates of MMCM extravasation and vascular density that were compared to the MRI results.

RESULTS

DMSO decreased cancer vascular endothelial permeability significantly (P < 0.05) from tumor KPSday0 = 19.3 +/- 8.8 microL/min.100 cm3 to KPSday7 = 0 microL/min.100 cm3). K values in the saline-treated tumors did not change significantly. The amount of extravasated albumin-Gd-(DTPA)27-(biotin)11, as assayed by a fluorescently labeled streptavidin stain that strongly binds to the biotin tag on the MMCM, was significantly (P < 0.05) lower in the DMSO-treated cancers than in the control cancers (57.7% +/- 5.5% vs. 34.2% +/- 4.9%). Tumor vascular richness as reflected by the MRI-assayed fPV and by the RECA-1 and lectin-stained microscopy did not change significantly with DMSO or saline treatment.

CONCLUSION

Reductions in cancer microvascular leakiness induced by a 7-day course of DMSO could be detected and measured by dynamic MMCM-enhanced MRI and were confirmed by microscopic measurements of the leaked macromolecular agents in the same cancers. Results support the robustness of an MMCM-enhanced MRI approach to the characterization of cancers and providing first evidence for an in vivo effect of DMSO on cancer blood vessels.

Acute promyelocytic leukemia: from highly fatal to highly curable

Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia. Morphologically, it is identified as the M3 subtype of acute myeloid leukemia by the French-American-British classification and cytogenetically is characterized by a balanced reciprocal translocation between chromosomes 15 and 17, which results in the fusion between promyelocytic leukemia (PML) gene and retinoic acid receptor alpha (RARalpha). It seems that the disease is the most malignant form of acute leukemia with a severe bleeding tendency and a fatal course of only weeks. Chemotherapy (CT; daunorubicin, idarubicin and cytosine arabinoside) was the front-line treatment of APL with a complete remission (CR) rate of 75% to 80% in newly diagnosed patients. Despite all these progresses, the median duration of remission ranged from 11 to 25 months and only 35% to 45% of the patients could be cured by CT. Since the introduction of all-trans retinoic acid (ATRA) in the treatment and optimization of the ATRA-based regimens, the CR rate was raised up to 90% to 95% and 5-year disease free survival (DFS) to 74%. The use of arsenic trioxide (ATO) since early 1990s further improved the clinical outcome of refractory or relapsed as well as newly diagnosed APL. In this article, we review the history of introduction of ATRA and ATO into clinical use and the mechanistic studies in understanding this model of cancer targeted therapy.

1-Methylnicotinamide stimulates cell growth and inhibits hemoglobin synthesis in differentiating murine erythroleukemia cells

Exposure of murine erythroleukemia cells (MELCs) to nicotinamide (NA) or its synthetic analog N'-methylnicotinamide (N'-MN) reduces cell growth and induces terminal differentiation, marked by increased heme and globin accumulation. On the contrary, 1-methylnicotinamide (1-MN), the primary metabolite of excess NA, was found to stimulate cell growth and reduce spontaneous differentiation of cultured MELCs. Log phase MELCs exhibited up to 50% higher cell density above untreated cells when cultured for up to 96 h with 2.5 mM 1-MN. When combined with NA or several chemically-unrelated inducers of hemoglobin synthesis in cultured MELCs, 1-MN reduced the globin mRNA levels and heme accumulation by 40-80%. 1-MN was able to inhibit heme production if present during only the first 24-48 h after NA exposure. Pre-treatment with 1-MN could not confer resistance of cells to effects of NA, suggesting the inhibition is reversible. Commitment to differentiate in semisolid medium by the most potent inducer, 5mM N'-MN, was inhibited up to 95% by 2.5mM concentrations of 1-MN. It appears that 1-MN has opposing effects on growth and induction of differentiation than those seen in MELC cultures exposed to NA or N'-MN.

Proteomic analysis of erythroid differentiation induced by hexamethylene bisacetamide in murine erythroleukemia cells

OBJECTIVE

Murine erythroleukemia (MEL) cells are transformed erythroid precursors that are arrested in an immature and proliferating state. These leukemic cells can be grown in cell cultures and induced to terminal erythroid differentiation by a treatment with a specific chemical inducer such as N,N'-hexamethylene bisacetamide. MEL cells then re-enter their original erythroid program and differentiate along the erythroid pathway into non-dividing hemoglobin-rich cells resembling orthochromatophilic normoblasts. To deepen our understanding of the molecular mechanisms underlying and erythroid differentiation and leukemia we monitored changes in protein expression in differentiating MEL cells.

METHODS

In our effort to find new candidate proteins involved in the differentiation of MEL cells, we embraced a proteomic approach. Employing two-dimensional (2D) electrophoresis combined with mass spectrometry, we compared protein expression in non-induced MEL cells with MEL cells exposed to N,N'-hexamethylene bisacetamide for 48 h.

RESULTS

From 700 proteins spots observed, 31 proteins were differentially expressed. We successfully identified 27 of the differentially expressed molecules by mass spectrometry (MALDI-MS).

CONCLUSION

In addition to proteins involved in heme biosynthesis, protein metabolism, stress defense and cytoskeletal organization, we identified 3 proteins engaged in regulation of cellular trafficking and 7 proteins important for regulation of gene expression and cell cycle progression including 3 components of chromatin remodeling complexes. Many of the identified molecules are associated with erythroid differentiation or leukemia for the first time. To our knowledge, this is the first study applying a modern proteomic approach to the direct analysis of erythroid differentiation of leukemic cells.

Differential gene expression during terminal erythroid differentiation

Terminal erythroid differentiation in mammals is the process whereby nucleated precursor cells accumulate erythroid-specific proteins such as hemoglobin, undergo extensive cellular and nuclear remodeling, and ultimately shed their nuclei to form reticulocytes, which then become mature erythrocytes in the circulation. Little is known about the mechanisms that enable erythroblasts to undergo such a transformation. We hypothesized that genes involved in these mechanisms were likely expressed at restricted times during the differentiation process and used differential display reverse transcriptase polymerase chain reaction as a first step in identifying such genes. We identified three differentially expressed cDNAs that we termed late erythroblast (LEB) 1-3. None of these cDNAs were previously identified as being expressed in erythroblasts and their patterns of expression indicated they are likely to be involved in the differentiation process. LEB-1 cDNA was derived from the gene A330102K04Rik (approved gene symbol Apoll1), and shares homology with members of the apolipoprotein L family in humans. LEB-3 cDNA was derived from the novel gene D930015E06Rik, that has no known function. LEB-2 cDNA was derived from the gene ranBP16 (approved gene symbol Xpo7), a nuclear exportin. D930015E06Rik mRNA is also strongly expressed in the testis and was localized to a region of the seminiferous tubule where secondary spermatocytes and early spermatids are found, suggesting a role for D930015E06Rik in spermatogenesis as well as terminal erythroid differentiation. We have thus identified three genes not previously described as being expressed in erythroblasts that could be relevant in elucidating mechanisms involved in terminal erythroid differentiation.

Lymphoid neoplasia and the control of haemopoietic differentiation

Our broad aims are to delineate oncogenic events in lymphoid neoplasia and to search for genes that control haemopoietic differentiation. To explore lymphoid neoplasia, we have constructed transgenic mice bearing different oncogenes coupled to the immunoglobulin heavy chain enhancer (E mu), to force expression within lymphocytes. The prototype E mu-myc mice are highly prone to lymphomagenesis, generating pre-B and B cell lymphomas. In their pre-neoplastic phase, E mu-myc expression perturbs B cell development, accelerating the accumulation of pre-B cells. Lymphomagenesis requires additional oncogenic events, such as ras activation, and can be reconstructed in vitro. Transgenic mice bearing the N-myc, N-ras, v-abl and bcr-v-abl oncogenes are also prone to tumours. A striking demonstration that oncogenes can perturb lineage commitment has emerged. Introduction of the v-raf gene into cloned E mu-myc transgenic B cells frequently led to a switch in haemopoietic lineage: the cells became macrophages. Two clues to this remarkable metamorphosis are that the macrophage lines produce a myeloid growth factor and most bear marked karyotypic alterations, perhaps indicating that the balance between a few critical lineage control genes has been disturbed. To explore the hypothesis that genes encoding the DNA-binding homeo box domain participate in haemopoiesis, cDNA libraries from haemopoietic sources were screened, and several distinct homeo box cDNAs were isolated. They revealed a complex pattern of expression among haemopoietic cell lines. These genes are attractive candidates for regulators of haemopoietic differentiation.

Induction of acute lymphocytic leukemia differentiation by maintenance therapy

Despite extensive study in many malignancies, maintenance therapy has clinically benefited only two diseases: acute lymphocytic leukemia (ALL) and acute promyelocytic leukemia (APL). ALL maintenance therapy utilizes low-dose 6-mercaptopurine (6MP) and methotrexate (MTX), while maintenance in APL primarily consists of all-trans-retinoic acid (ATRA). 6MP and MTX as used in ALL are also now usually added to maintenance ATRA for APL, based on data suggesting an improved disease-free survival. Although the mechanism of action of MTX and 6MP as maintenance is unknown, low-dose cytotoxic agents are potent inducers of differentiation in vitro. Thus, we studied whether maintenance therapy in ALL, like ATRA in APL, may be inducing terminal differentiation of ALL progenitors. The APL cell line NB4, the ALL cell lines REH and RS4;11, and patients' ALL blasts were incubated with ATRA, 6MP, and MTX in vitro. All three drugs inhibited the clonogenic growth of the APL and ALL cell lines without inducing immediate apoptosis, but associated with induction of phenotypic differentiation. The three drugs similarly upregulated lymphoid antigen expression, while decreasing CD34 expression, on patients' ALL blasts. These data suggest that induction of leukemia progenitor differentiation plays an important role in the mechanism of action of maintenance therapy in ALL.

Discovery and development of SAHA as an anticancer agent

The path to the discovery of suberoylanilide hydroxamic acid (SAHA, vorinostat) began over three decades ago with our studies designed to understand why dimethylsulfoxide causes terminal differentiation of the virus-transformed cells, murine erythroleukemia cells. SAHA can cause growth arrest and death of a broad variety of transformed cells both in vitro and in vivo at concentrations that have little or no toxic effects on normal cells. It was discovered that SAHA inhibits the activity of histone deacetylases (HDACs), including all 11 known human class I and class II HDACs. HDACs have many protein targets whose structure and function are altered by acetylation including histones and non-histone proteins component of transcription factors controlling gene expression and proteins that regulate cell proliferation, migration and death. SAHA is in clinical trials and has significant anticancer activity against both hematologic and solid tumors at doses well tolerated by patients. A new drug application has been approved for SAHA (vorinostat) treatment of cutaneous T-cell lymphoma.

Dimethyl sulfoxide to vorinostat: development of this histone deacetylase inhibitor as an anticancer drug

In our quest to understand why dimethyl sulfoxide (DMSO) can cause growth arrest and terminal differentiation of transformed cells, we followed a path that led us to discover suberoylanilide hydroxamic acid (SAHA; vorinostat (Zolinza)), which is a histone deacetylase inhibitor. SAHA reacts with and blocks the catalytic site of these enzymes. Extensive structure-activity studies were done along the path from DMSO to SAHA. SAHA can cause growth arrest and death of a broad variety of transformed cells both in vitro and in tumor-bearing animals at concentrations not toxic to normal cells. SAHA has many protein targets whose structure and function are altered by acetylation, including chromatin-associated histones, nonhistone gene transcription factors and proteins involved in regulation of cell proliferation, migration and death. In clinical trials, SAHA has shown significant anticancer activity against both hematologic and solid tumors at doses well tolerated by patients. A new drug application was approved by the US Food and Drug Administration for vorinostat for treatment of cutaneous T-cell lymphoma. More potent analogs of SAHA have shown unacceptable toxicity.

First among equals: the cancer cell hierarchy

Primary cancer cells exhibit heterogeneity in their proliferative ability. The cancer stem cell (CSC) model accounts for this heterogeneity by proposing that each cancer consists of a small population of CSCs that are capable of unlimited growth and self-renewal and a much larger population of cells, descendants of the CSCs, that have lost self-renewal capacity. The CSC model has important implications for cancer therapy. Eradication of CSCs, the cells responsible for maintenance of the neoplasm, would be necessary and sufficient to achieve cure. By extension, both the frequency of stem cells in a tumor and their propensity to undergo self-renewal (Psr) would have a direct impact on the curability of that tumor. The Psr is a critical biological characteristic of CSCs-small differences in Psr have enormous impact on the probability of success in cancer therapy. Differentiation therapy, defined as treatment that reduces the Psr of CSCs, is one approach to targeting CSCs.

Cytokines in the differentiation therapy of leukemia: from laboratory investigations to clinical applications

Differentiation therapy of leukemia is the treatment of leukemia cells with biological or chemical agents that induce the terminal differentiation of the cancer cells. It is regarded as a novel and targeted approach to leukemia treatment, based on our better understanding of the hematopoietic process and the mechanisms of its deregulation during leukemogenesis. Clinically, differentiation therapy has been most successful in acute promyelocytic leukemia using all-trans-retinoic acid as the inducer, either alone or in combination with chemotherapy. This review presents evidence that a number of hematopoietic cytokines play important roles in both normal and aberrant hematopoietic processes. In vitro laboratory investigations in the past two decades using well-characterized myeloid leukemic cell lines and primary blast cells from leukemia patients have revealed that many hematopoietic cytokines can trigger lineage-specific differentiation of leukemia cells, which may have important implications in the clinical setting. Moreover, our current understanding of cytokine interactions and the molecular mechanisms of cytokine-induced leukemic cell differentiation will be discussed in the light of recent findings. Finally, ways in which laboratory research on cytokines in the differentiation therapy of leukemia can lead to the improved design of protocols for future clinical applications to leukemia therapy will also be addressed.

The carbonic anhydrase I locus contains a c-Myb target promoter and modulates differentiation of murine erythroleukemia cells

The Myb proto-oncogene encodes a transcription factor (c-Myb) that is essential for normal hematopoiesis and is thought to regulate hematopoietic cell proliferation and differentiation by regulating expression of specific target genes. We identify the mouse erythroid-specific carbonic anhydrase I promoter (CAIe) as a target of c-Myb activity and demonstrate that Myb activity is critical for carbonic anhydrase I (CAI) expression in C19 MEL cells. CAI expression is downregulated when MEL cells differentiate in response to MEnT or treatment with N, N-hexamethylene bisacetamide (HMBA). Coexpression of GATA-1 with c-Myb results in synergistic activation of transcription from the CAIe promoter and both transcription factors interact with the CAIe promoter in vivo. We identify a novel 20 bp sequence in the CAIe promoter that is sufficient to mediate synergistic activation of the CAIe promoter by c-Myb and GATA-1. c-Myb and GATA-1 interact with this DNA sequence suggesting that c-Myb and GATA-1 may be contained in a complex that interacts with this region of the CAIe promoter. Forced expression of CAI delayed HMBA-induced differentiation of MEL cells and maintained them in a proliferating state. These data strongly suggest that CAI is a c-Myb target and is involved in regulating MEL cell proliferation and differentiation.

C/EBPalpha determines hematopoietic cell fate in multipotential progenitor cells by inhibiting erythroid differentiation and inducing myeloid differentiation

C/EBPalpha is an essential transcription factor required for myeloid differentiation. While C/EBPalpha can act as a cell fate switch to promote granulocyte differentiation in bipotential granulocyte-macrophage progenitors (GMPs), its role in regulating cell fate decisions in more primitive progenitors is not known. We found increased numbers of erythroid progenitors and erythroid cells in C/EBPalpha(-/-) fetal liver (FL). Also, enforced expression of C/EBPalpha in hematopoietic stem cells resulted in a loss of erythroid progenitors and an increase in myeloid cells by inhibition of erythroid development and inducing myeloid differentiation. Conditional expression of C/EBPalpha in murine erythroleukemia (MEL) cells induced myeloid-specific genes, while inhibiting erythroid-specific gene expression including erythropoietin receptor (EpoR), which suggests a novel mechanism to determine hematopoietic cell fate. Thus, C/EBPalpha functions in hematopoietic cell fate decisions by the dual actions of inhibiting erythroid and inducing myeloid gene expression in multipotential progenitors.

Role of O6-alkylguanine-DNA alkyltransferase in the cytotoxic activity of cloretazine

Cloretazine (VNP40101M; 101M; 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)-2-[(methylamino)carbonyl]hydrazine) is a sulfonylhydrazine prodrug that generates both chloroethylating and carbamoylating species on activation. To explore the molecular mechanisms underlying the broad anticancer activity observed in preclinical studies, cloretazine and chloroethylating-only [i.e., 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine] and carbamoylating-only (i.e., 1,2-bis(methylsulfonyl)-1-[(methylamino)carbonyl]hydrazine) analogues were evaluated in five murine hematopoietic cell lines. These cell lines were separable into two groups by virtue of their sensitivity to 1,2-bis(methylsulfonyl)-1-(2-chloroethyl)hydrazine; the sensitive group included L1210, P388, and F-MEL leukemias (IC50s, 6-8 micromol/L) and the resistant group consisted of Ba/F3 bone marrow and WEHI-3B leukemia cells (IC50s, 50-70 micromol/L). Resistant cells expressed O6-alkylguanine-DNA alkyltransferase (AGT), whereas sensitive cells did not. A correlation existed between AGT expression and the functional status of p53; AGT- cells possessed defective p53, whereas AGT+ cells contained wild-type p53. Based on recent findings on regulation of AGT gene expression by others, we suspect that silencing of the AGT gene by promoter hypermethylation frequently occurs during tumor progression involving p53 inactivation. O6-Chloroethylguanine is the initial DNA lesion that progresses to lethal interstrand DNA cross-links. Cloretazine exhibited a much higher preference toward the O6-chloroethylation of guanine, as measured by the difference in IC50s to wild-type and AGT-transfected L1210 cells, than 1,3-bis(2-chloroethyl)-1-nitrosourea, which targets the same site in DNA. Preferential toxicity of cloretazine against AGT- tumor cells coupled with decreased toxicity to AGT+ cells in host tissues constitute the therapeutic basis for cloretazine.