Downregulation of c-Jun expression by transcription factor C/EBPalpha is critical for granulocytic lineage commitment

Insight into the mechanism of AML del(9q) progression: hnRNP K targets the myeloid master regulators CEBPA (C/EBPα) and SPI1 (PU.1)

Deletions on the long arm of chromosome 9 (del(9q)) are recurrent abnormalities in about 2 % of acute myeloid leukemia cases, which usually involve HNRNPK and are frequently associated with other known aberrations. Based on an Hnrnpk haploinsufficient mouse model, a recent study demonstrated a function of hnRNP K in pathogenesis of myeloid malignancies via the regulation of cellular proliferation and myeloid differentiation programs. Here, we provide evidence that reduced hnRNP K expression results in the dysregulated expression of C/EBPα and additional transcription factors. CyTOF analysis revealed monocytic skewing with increased levels of mature myeloid cells. To explore the role of hnRNP K during normal and pathological myeloid differentiation in humans, we characterized hnRNP K-interacting RNAs in human AML cell lines. Notably, RNA-sequencing revealed several mRNAs encoding key transcription factors involved in the regulation of myeloid differentiation as targets of hnRNP K. We showed that specific sequence motifs confer the interaction of SPI1 and CEBPA 5' and 3'UTRs with hnRNP K. The siRNA mediated reduction of hnRNP K in human AML cells resulted in an increase of PU.1 and C/EBPα that is most pronounced for the p30 isoform. The combinatorial treatment with the inducer of myeloid differentiation valproic acid resulted in increased C/EBPα expression and myeloid differentiation. Together, our results indicate that hnRNP K post-transcriptionally regulates the expression of myeloid master transcription factors. These novel findings can inaugurate novel options for targeted treatment of AML del(9q) by modulation of hnRNP K function.

The Role of DNMT1 and C/EBPα in the Regulation of CYP11A1 Expression During Syncytialization of Human Placental Trophoblasts

Progesterone synthesized in the placenta is essential for pregnancy maintenance. CYP11A1 is a key enzyme in progesterone synthesis, and its expression increases greatly during trophoblast syncytialization. However, the underlying mechanism remains elusive. Here, we demonstrated that passive demethylation of CYP11A1 promoter accounted for the upregulation of CYP11A1 expression during syncytialization with the participation of the transcription factor C/EBPα. We found that the methylation rate of a CpG locus in the CYP11A1 promoter was significantly reduced along with decreased DNA methyltransferase 1 (DNMT1) expression and its enrichment at the CYP11A1 promoter during syncytialization. DNMT1 overexpression not only increased the methylation of this CpG locus in the CYP11A1 promoter, but also decreased CYP11A1 expression and progesterone production. In silico analysis disclosed multiple C/EBPα binding sites in both CYP11A1 and DNMT1 promoters. C/EBPα expression and its enrichments at both the DNMT1 and CYP11A1 promoters were significantly increased during syncytialization. Knocking-down C/EBPα expression increased DNMT1 while it decreased CYP11A1 expression during syncytialization. Conclusively, C/EBPα plays a dual role in the regulation of CYP11A1 during syncytialization. C/EBPα not only drives CYP11A1 expression directly, but also indirectly through downregulation of DNMT1, which leads to decreased methylation in the CpG locus of the CYP11A1 promoter, resulting in increased progesterone production during syncytialization.

Identification and interrogation of the gene regulatory network of CEBPA-double mutant acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous hematological malignancy caused by mutations in genes encoding transcriptional and epigenetic regulators together with signaling genes. It is characterized by a disturbance of differentiation and abnormal proliferation of hematopoietic progenitors. We have previously shown that each AML subtype establishes its own core gene regulatory network (GRN), consisting of transcription factors binding to their target genes and imposing a specific gene expression pattern that is required for AML maintenance. In this study, we integrate gene expression, open chromatin and ChIP data with promoter-capture Hi-C data to define a refined core GRN common to all patients with CEBPA-double mutant (CEBPAN/C) AML. These mutations disrupt the structure of a major regulator of myelopoiesis. We identify the binding sites of mutated C/EBPα proteins in primary cells, we show that C/EBPα, AP-1 factors and RUNX1 colocalize and are required for AML maintenance, and we employ single cell experiments to link important network nodes to the specific differentiation trajectory from leukemic stem to blast cells. Taken together, our study provides an important resource which predicts the specific therapeutic vulnerabilities of this AML subtype in human cells.

The AML-associated K313 mutation enhances C/EBPα activity by leading to C/EBPα overexpression

Mutations in the transcription factor C/EBPα are found in ~10% of all acute myeloid leukaemia (AML) cases but the contribution of these mutations to leukemogenesis is incompletely understood. We here use a mouse model of granulocyte progenitors expressing conditionally active HoxB8 to assess the cell biological and molecular activity of C/EBPα-mutations associated with human AML. Both N-terminal truncation and C-terminal AML-associated mutations of C/EBPα substantially altered differentiation of progenitors into mature neutrophils in cell culture. Closer analysis of the C/EBPα-K313-duplication showed expansion and prolonged survival of mutant C/EBPα-expressing granulocytes following adoptive transfer into mice. C/EBPα-protein containing the K313-mutation further showed strongly enhanced transcriptional activity compared with the wild-type protein at certain promoters. Analysis of differentially regulated genes in cells overexpressing C/EBPα-K313 indicates a strong correlation with genes regulated by C/EBPα. Analysis of transcription factor enrichment in the differentially regulated genes indicated a strong reliance of SPI1/PU.1, suggesting that despite reduced DNA binding, C/EBPα-K313 is active in regulating target gene expression and acts largely through a network of other transcription factors. Strikingly, the K313 mutation caused strongly elevated expression of C/EBPα-protein, which could also be seen in primary K313 mutated AML blasts, explaining the enhanced C/EBPα activity in K313-expressing cells.

Mesenchymal Stem Cell-Mediated Delivery of an Oncolytic Adenovirus Enhances Antitumor Efficacy in Hepatocellular Carcinoma

Oncolytic virotherapy is a promising alternative to conventional treatment, yet systemic delivery of these viruses to tumors remains a major challenge. In this regard, mesenchymal stem cells (MSC) with well-established tumor-homing property could serve as a promising systemic delivery tool. We showed that MSCs could be effectively infected by hepatocellular carcinoma (HCC)-targeted oncolytic adenovirus (HCC-oAd) through modification of the virus' fiber domain and that the virus replicated efficiently in the cell carrier. HCC-targeting oAd loaded in MSCs (HCC-oAd/MSC) effectively lysed HCC cells in vitro under both normoxic and hypoxic conditions as a result of the hypoxia responsiveness of HCC-oAd. Importantly, systemically administered HCC-oAd/MSC, which were initially infected with a low viral dose, homed to HCC tumors and resulted in a high level of virion accumulation in the tumors, ultimately leading to potent tumor growth inhibition. Furthermore, viral dose reduction and tumor localization of HCC-oAd/MSC prevented the induction of hepatotoxicity by attenuating HCC-oAd hepatic accumulation. Taken together, these results demonstrate that MSC-mediated systemic delivery of oAd is a promising strategy for achieving synergistic antitumor efficacy with improved safety profiles. SIGNIFICANCE: Mesenchymal stem cells enable delivery of an oncolytic adenovirus specifically to the tumor without posing any risk associated with systemic administration of naked virions to the host.

Regulatory networks upon neurogenesis induction in PC12 cell line by small molecules

Alteration in the normal regulatory pathway of differentiation can lead to the induction of programmed cell death. Accordingly, some chemicals like staurosporine, nerve growth factor, pituitary adenylate cyclase activating peptide, and trimethyltin are shown to be able to induce differentiation in vitro, via different mechanisms in the PC12 cell line. Hence, understanding the details of the molecular mechanisms of differentiation induction by these small molecules are important for further application of these molecules in neurogenesis. Therefore, we sought to determine these signaling pathways, using gene regulatory networks analysis. Then, we have conducted a comparative analysis of the alterations in the gene expression pattern of the PC12 cell lines in response to these chemicals at the early stages. Based on the comparative analysis and previous knowledge, we have proposed the affected pathways during differentiation and apoptosis. Our findings could be useful in the development of protocols to reprogramming of neurons by such small molecules with high efficiency.

C/EBPα deregulation as a paradigm for leukemogenesis

Myeloid master regulator CCAAT enhancer-binding protein alpha (C/EBPα) is deregulated by multiple mechanisms in leukemia. Inhibition of C/EBPα function plays pivotal roles in leukemogenesis. While much is known about how C/EBPα orchestrates granulopoiesis, our understanding of molecular transformation events, the role(s) of cooperating mutations and clonal evolution during C/EBPα deregulation in leukemia remains elusive. In this review, we will summarize the latest research addressing these topics with special emphasis on CEBPA mutations. We conclude by describing emerging therapeutic strategies to restore C/EBPα function.

Expression and regulation of C/EBPα in normal myelopoiesis and in malignant transformation

One of the most studied transcription factors in hematopoiesis is the leucine zipper CCAAT-enhancer binding protein α (C/EBPα), which is mainly involved in cell fate decisions for myeloid differentiation. Its involvement in acute myeloid leukemia (AML) is diverse, with patients frequently exhibiting mutations, deregulation of gene expression, or alterations in the function of C/EBPα. In this review, we emphasize the importance of C/EBPα for neutrophil maturation, its role in myeloid priming of hematopoietic stem and progenitor cells, and its indispensable requirement for AML development. We discuss that mutations in the open reading frame of CEBPA lead to an altered C/EBPα function, affecting the expression of downstream genes and consequently deregulating myelopoiesis. The emerging transcriptional mechanisms of CEBPA are discussed based on recent studies. Novel insights on how these mechanisms may be deregulated by oncoproteins or mutations/variants in CEBPA enhancers are suggested in principal to reveal novel mechanisms of how CEBPA is deregulated at the transcriptional level.

C/EBPα in normal and malignant myelopoiesis

CCAAT/enhancer binding protein α (C/EBPα) dimerizes via its leucine zipper (LZ) domain to bind DNA via its basic region and activate transcription via N-terminal trans-activation domains. The activity of C/EBPα is modulated by several serine/threonine kinases and via sumoylation, its gene is activated by RUNX1 and additional transcription factors, its mRNA stability is modified by miRNAs, and its mRNA is subject to translation control that affects AUG selection. In addition to inducing differentiation, C/EBPα inhibits cell cycle progression and apoptosis. Within hematopoiesis, C/EBPα levels increase as long-term stem cells progress to granulocyte-monocyte progenitors (GMP). Absence of C/EBPα prevents GMP formation, and higher levels are required for granulopoiesis compared to monopoiesis. C/EBPα interacts with AP-1 proteins to bind hybrid DNA elements during monopoiesis, and induction of Gfi-1, C/EBPε, KLF5, and miR-223 by C/EBPα enables granulopoiesis. The CEBPA ORF is mutated in approximately 10 % of acute myeloid leukemias (AML), leading to expression of N-terminally truncated C/EBPαp30 and C-terminal, in-frame C/EBPαLZ variants, which inhibit C/EBPα activities but also play additional roles during myeloid transformation. RUNX1 mutation, CEBPA promoter methylation, Trib1 or Trib2-mediated C/EBPαp42 degradation, and signaling pathways leading to C/EBPα serine 21 phosphorylation reduce C/EBPα expression or activity in additional AML cases.

Monocytic cell differentiation from band-stage neutrophils under inflammatory conditions via MKK6 activation

During inflammation, neutrophils are rapidly mobilized from the bone marrow storage pool into peripheral blood (PB) to enter lesional sites, where most rapidly undergo apoptosis. Monocytes constitute a second wave of inflammatory immigrates, giving rise to long-lived macrophages and dendritic cell subsets. According to descriptive immunophenotypic and cell culture studies, neutrophils may directly "transdifferentiate" into monocytes/macrophages. We provide mechanistic data in human and murine models supporting the existence of this cellular pathway. First, the inflammatory signal-induced MKK6-p38MAPK cascade activates a monocyte differentiation program in human granulocyte colony-stimulating factor-dependent neutrophils. Second, adoptively transferred neutrophils isolated from G-CSF-pretreated mice rapidly acquired monocyte characteristics in response to inflammatory signals in vivo. Consistently, inflammatory signals led to the recruitment of osteoclast progenitor cell potential from ex vivo-isolated G-CSF-mobilized human blood neutrophils. Monocytic cell differentiation potential was retained in left-shifted band-stage neutrophils but lost in neutrophils from steady-state PB. MKK6-p38MAPK signaling in HL60 model cells led to diminishment of the transcription factor C/EBPα, which enabled the induction of a monocytic cell differentiation program. Gene profiling confirmed lineage conversion from band-stage neutrophils to monocytic cells. Therefore, inflammatory signals relayed by the MKK6-p38MAPK cascade induce monocytic cell differentiation from band-stage neutrophils.

Interleukin (IL)-32β-mediated CCAAT/enhancer-binding protein α (C/EBPα) phosphorylation by protein kinase Cδ (PKCδ) abrogates the inhibitory effect of C/EBPα on IL-10 production

We previously reported that IL-32β promotes IL-10 production in myeloid cells. However, the underlying mechanism remains elusive. In this study, we demonstrated that IL-32β abrogated the inhibitory effect of CCAAT/enhancer-binding protein α (C/EBPα) on IL-10 expression in U937 cells. We observed that the phosphorylation of C/EBPα Ser-21 was inhibited by a PKCδ-specific inhibitor, rottlerin, or IL-32β knockdown by siRNA and that IL-32β shifted to the membrane from the cytosol upon phorbol 12-myristate 13-acetate treatment. We revealed that IL-32β suppressed the binding of C/EBPα to IL-10 promoter by using ChIP assay. These data suggest that PKCδ and IL-32β may modulate the effect of C/EBPα on IL-10 expression. We next demonstrated by immunoprecipitation that IL-32β interacted with PKCδ and C/EBPα, thereby mediating C/EBPα Ser-21 phosphorylation by PKCδ. We showed that IL-32β suppressed the inhibitory effect of C/EBPα on IL-10 promoter activity. However, the IL-10 promoter activity was reduced to the basal level by rottlerin treatment. When C/EBPα serine 21 was mutated to glycine (S21G), the inhibitory effect of C/EBPα S21G on IL-10 promoter activity was not modulated by IL-32β. Taken together, our results show that IL-32β-mediated C/EBPα Ser-21 phosphorylation by PKCδ suppressed C/EBPα binding to IL-10 promoter, which promoted IL-10 production in U937 cells.

Phorbol esters from Jatropha meal triggered apoptosis, activated PKC-δ, caspase-3 proteins and down-regulated the proto-oncogenes in MCF-7 and HeLa cancer cell lines

Jatropha meal produced from the kernel of Jatropha curcas Linn. grown in Malaysia contains phorbol esters (PEs). The potential benefits of PEs present in the meal as anticancer agent are still not well understood. Hence, this study was conducted to evaluate the cytotoxic effects and mode of actions of PEs isolated from Jatropha meal against breast (MCF-7) and cervical (HeLa) cancer cell lines. Isolated PEs inhibited cells proliferation in a dose-dependent manner of both MCF-7 and HeLa cell lines with the IC₅₀ of 128.6 ± 2.51 and 133.0 ± 1.96 µg PMA equivalents/mL respectively, while the values for the phorbol 12-myristate 13-acetate (PMA) as positive control were 114.7 ± 1.73 and 119.6 ± 3.73 µg/mL, respectively. Microscopic examination showed significant morphological changes that resemble apoptosis in both cell lines when treated with PEs and PMA at IC₅₀ concentration after 24 h. Flow cytometry analysis and DNA fragmentation results confirmed the apoptosis induction of PEs and PMA in both cell lines. The PEs isolated from Jatropha meal activated the PKC-δ and down-regulated the proto-oncogenes (c-Myc, c-Fos and c-Jun). These changes probably led to the activation of Caspase-3 protein and apoptosis cell death occurred in MCF-7 and HeLa cell lines upon 24 h treatment with PEs and PMA. Phorbol esters of Jatropha meal were found to be promising as an alternative to replace the chemotherapeutic drugs for cancer therapy.

A general model for binary cell fate decision gene circuits with degeneracy: indeterminacy and switch behavior in the absence of cooperativity

Background

The gene regulatory circuit motif in which two opposing fate-determining transcription factors inhibit each other but activate themselves has been used in mathematical models of binary cell fate decisions in multipotent stem or progenitor cells. This simple circuit can generate multistability and explains the symmetric “poised” precursor state in which both factors are present in the cell at equal amounts as well as the resolution of this indeterminate state as the cell commits to either cell fate characterized by an asymmetric expression pattern of the two factors. This establishes the two alternative stable attractors that represent the two fate options. It has been debated whether cooperativity of molecular interactions is necessary to produce such multistability.

Principal Findings

Here we take a general modeling approach and argue that this question is not relevant. We show that non-linearity can arise in two distinct models in which no explicit interaction between the two factors is assumed and that distinct chemical reaction kinetic formalisms can lead to the same (generic) dynamical system form. Moreover, we describe a novel type of bifurcation that produces a degenerate steady state that can explain the metastable state of indeterminacy prior to cell fate decision-making and is consistent with biological observations.

Conclusion

The general model presented here thus offers a novel principle for linking regulatory circuits with the state of indeterminacy characteristic of multipotent (stem) cells.

AP-1 protein induction during monopoiesis favors C/EBP: AP-1 heterodimers over C/EBP homodimerization and stimulates FosB transcription

AP-1 proteins heterodimerize via their LZ domains to bind TGACGTCA or TGACTCA, whereas C/EBPs dimerize to bind ATTGCGCAAT. We demonstrate that intact C/EBPα also heterodimerizes with c-Jun or c-Fos to bind a hybrid DNA element, TGACGCAA, or more weakly to TGATGCAA. A 2:1 ratio of c-Jun:C/EBPα or c-Fos:C/EBPα was sufficient for preferential binding. Semiquantitative Western blot analysis indicates that the summation of c-Jun, JunB, and c-Fos levels in differentiating myeloid cells is similar to or exceeds the entirety of C/EBPα and C/EBPβ, indicating the feasibility of heterodimer formation. Induction of AP-1 proteins during monocytic differentiation favored formation of C/EBP:AP-1 heterodimers, with C/EBPα homodimers more evident during granulopoiesis. Approximately 350 human and 300 murine genes contain the TGACGCAA motif between -2 kb and +1 kb of their transcription start sites. We focused on the murine Fosb promoter, which contains a C/EBP:AP-1 cis element at -56 and -253, with the hFOSB gene containing an identical site at -253 and a 1-bp mismatch at -56. C/EBPα:AP-1 heterodimers bound either site preferentially in a gel-shift assay, C/EBPα:c-Fos ER fusion proteins induced endogenous Fosb mRNA but not in the presence of CHX, C/EBP and AP-1 proteins bound the endogenous Fosb promoter, mutation of the -56 cis element reduced reporter activity fivefold, and endogenous FosB protein was expressed preferentially during monopoiesis versus granulopoiesis. Increased expression of Jun/Fos proteins elevates C/EBP:AP-1 heterodimer formation to potentially activate novel sets of genes during monopoiesis and potentially during other biologic processes.

Dual roles for MEF2A and MEF2D during human macrophage terminal differentiation and c-Jun expression

Recent reports have evidenced a role for MEF2C (myocyte enhancer factor 2C) in myelopoiesis, although the precise functions of this transcription factor are still unclear. We show in the present study that MEF2A and MEF2D, two other MEF2 family members, are expressed in human primary monocytes and in higher amounts in monocyte-derived macrophages. High levels of MEF2A-MEF2D heterodimers are found in macrophage-differentiated HL60 cells. Chromatin immunoprecipitations demonstrate that MEF2A is present on the c-Jun promoter, both in undifferentiated and in macrophage-differentiated cells. Moreover, c-Jun expression is derepressed in undifferentiated cells in the presence of HDAC (histone deacetylase) inhibitor, indicating the importance of chromatin acetylation in this process. We show that MEF2A/D dimers strongly interact with HDAC1, and to a lesser extent with HDAC7 in macrophages, whereas low levels of MEF2A/D-HDAC1 complexes are found in undifferentiated cells or in monocytes. Since trichostatin A does not disrupt MEF2A/D-HDAC1 complexes, we analysed the potential interaction of MEF2A with p300 histone acetyltransferase, whose expression is up-regulated in macrophages. Interestingly, endogenous p300 only associates with MEF2A in differentiated macrophages, indicating that MEF2A/D could activate c-Jun expression in macrophages through a MEF2A/D-p300 activator complex. The targets of MEF2A/D-HDAC1-HDAC7 multimers remain to be identified. Nevertheless, these data highlight for the first time the possible dual roles of MEF2A and MEF2D in human macrophages, as activators or as repressors of gene transcription.

Proteomics of AML1/ETO Target Proteins: AML1–ETO Targets a C/EBP–NM23 Pathway

Introduction

The rational design of targeted therapies for acute myeloid leukemia (AML) requires the discovery of novel protein pathways in the systems biology of a specific AML subtype. We have shown that in the AML subtype with translocation t(8;21), the leukemic fusion protein AML1–ETO inhibits the function of transcription factors PU.1 and C/EBPα via direct protein–protein interaction. In addition, recently using proteomics, we have also shown that the AML subtypes differ in their proteome, interactome, and post-translational modifications.

Methods

We, therefore, hypothesized that the systematic identification of target proteins of AML1–ETO on a global proteome-wide level will lead to novel insights into the systems biology of t(8;21) AML on a post-genomic functional level. Thus, 6 h after inducible expression of AML1–ETO, protein expression changes were identified by two-dimensional gel electrophoresis and subsequent mass spectrometry analysis.

Results

Twenty-eight target proteins of AML1–ETO including prohibitin, NM23, HSP27, and Annexin1 were identified by MALDI-TOF mass spectrometry. AML1–ETO upregulated the differentiation inhibitory factor NM23 protein expression after 6 h, and the NM23 mRNA expression was also elevated in t(8;21) AML patient samples in comparison with normal bone marrow. AML1–ETO inhibited the ability of C/EBP transcription factors to downregulate the NM23 promoter. These data suggest a model in which AML1–ETO inhibits the C/EBP-induced downregulation of the NM23 promoter and thereby increases the protein level of differentiation inhibitory factor NM23.

Conclusions

Proteomic pathway discovery can identify novel functional pathways in AML, such as the AML1–ETO–C/EBP–NM23 pathway, as the main step towards a systems biology and therapy of AML.

Elevated PIN1 expression by C/EBPalpha-p30 blocks C/EBPalpha-induced granulocytic differentiation through c-Jun in AML

The transcription factor CCAAT enhancer-binding protein alpha (C/EBPalpha) has an important role in granulopoiesis. The tumor suppressor function of C/EBPalpha is shown by the findings that loss of expression or function of C/EBPalpha in leukemic blasts contributes to a block in myeloid cell differentiation and to leukemia. C/EBPalpha mutations are found in around 9% of acute myeloid leukemia (AML) patients. The mechanism by which the mutant form of C/EBPalpha (C/EBPalpha-p30) exerts a differentiation block is not well understood. By using a proteomic screen, we have recently reported PIN1 as a target of C/EBPalpha-p30 in AML. In the present study, we show that C/EBPalpha-p30 induces PIN1 expression. We observed elevated PIN1 expression in leukemic patient samples. Induction of C/EBPalpha-p30 results in recruitment of E2F1 in the PIN1 promoter. We show that the inhibition of PIN1 leads to myeloid differentiation in primary AML blasts with C/EBPalpha mutations. Overexpression of PIN1 in myeloid cells leads to block of granulocyte differentiation. We also show that PIN1 increases the stability of the c-Jun protein by inhibiting c-Jun ubiquitination, and c-Jun blocks granulocyte differentiation mediated by C/EBPalpha. Our data suggest that the inhibition of PIN1 could be a potential strategy of treating AML patients with C/EBPalpha mutation.

Regulation of HIV-1 transcription in cells of the monocyte-macrophage lineage

Human immunodeficiency virus type 1 (HIV-1) has been shown to replicate productively in cells of the monocyte-macrophage lineage, although replication occurs to a lesser extent than in infected T cells. As cells of the monocyte-macrophage lineage become differentiated and activated and subsequently travel to a variety of end organs, they become a source of infectious virus and secreted viral proteins and cellular products that likely initiate pathological consequences in a number of organ systems. During this process, alterations in a number of signaling pathways, including the level and functional properties of many cellular transcription factors, alter the course of HIV-1 long terminal repeat (LTR)-directed gene expression. This process ultimately results in events that contribute to the pathogenesis of HIV-1 infection. First, increased transcription leads to the upregulation of infectious virus production, and the increased production of viral proteins (gp120, Tat, Nef, and Vpr), which have additional activities as extracellular proteins. Increased viral production and the presence of toxic proteins lead to enhanced deregulation of cellular functions increasing the production of toxic cellular proteins and metabolites and the resulting organ-specific pathologic consequences such as neuroAIDS. This article reviews the structural and functional features of the cis-acting elements upstream and downstream of the transcriptional start site in the retroviral LTR. It also includes a discussion of the regulation of the retroviral LTR in the monocyte-macrophage lineage during virus infection of the bone marrow, the peripheral blood, the lymphoid tissues, and end organs such as the brain. The impact of genetic variation on LTR-directed transcription during the course of retrovirus disease is also reviewed.

BCR-ABL promotes neutrophil differentiation in the chronic phase of chronic myeloid leukemia by downregulating c-Jun expression

The mechanism that is responsible for mature neutrophil overproduction in the chronic phase (CP) of chronic myeloid leukemia (CML), a neoplastic disease of hematopoietic stem cells carrying a constitutively active tyrosine kinase BCR-ABL, remains obscure. In this study, microarray analysis revealed that c-Jun, a monopoiesis-promoting transcription factor, was downregulated in CML neutrophils. BCR-ABL directly inhibited c-Jun expression, as c-Jun downregulation in primary CML neutrophils and in the CML blast cell lines, KCL22 and K562, was reversed by the tyrosine kinase inhibitor imatinib. We established a myeloid differentiation model in KCL22 cells using zinc-inducible CCAAT/enhancer-binding protein (C/EBP)alpha (KCL22/alpha). Myeloid differentiation was observed in C/EBP-induced KCL22/alpha cells. Imatinib-induced c-Jun upregulation promoted the monocytic differentiation of KCL22/alpha cells. c-Jun knockdown in KCL22/alpha cells by a short interfering RNA redirected their differentiation from the monocytic to the neutrophilic lineage, even after imatinib treatment. A blockade of PI3K-Akt signaling with an Akt inhibitor upregulated c-Jun and induced the monocytic differentiation of KCL22, K562, and C/EBP-induced KCL22/alpha cells. Thus, BCR-ABL downregulates c-Jun expression by activating the PI3K-Akt pathway during CML-CP, thereby allowing C/EBPs to promote neutrophil differentiation.

In prostate cancer C/EBPalpha promotes cell growth by the loss of interactions with CDK2, CDK4, and E2F and by activation of AKT

BACKGROUND

The CCAAT/Enhancer binding protein alpha (C/EBPalpha) is an important transcription factor for granulopoiesis and adipogenesis. While decreased expression and mutation of C/EBPalpha has been found in several types of tumors, the role of C/EBPalpha in prostate cancer has not been well characterized.

METHODS

We quantitatively analyzed the immunochemical staining of prostate cancer tissue and examined the growth properties of prostate cancer cells stably expressing C/EBPalpha by measure growth curve, cell cycle, and anchorage independent colony formation, investigated the association of C/EBPalpha with E2Fs and CDKs by co-immunoprecipitation and examined the expression of CDKs and activation of AKT by Western blot analysis.

RESULTS

The ratio of C/EBPalpha expression between cancer cells close to the pseudolumen of glands and those nearer the basal cell layer was more than threefold greater than that seen in the normal prostate epithelium. Further, this ratio increased with increased Gleason score of the prostate cancer. Forced expression of C/EBPalpha in prostate cancer cell lines accelerated cell growth, stimulated cells into the S and G2 phases of cell cycle, and enhanced anchorage-independent colony formation. Simultaneously, forced expression of C/EBPalpha increased expression of CDK2/CDK4 and nuclear PP2A, and activated AKT. In addition, C/EBPalpha was no longer found associated with E2F1/E2F4 and CDK2/CDK4. AKT and PPA2 inhibitors restored both the anti-proliferation function of C/EBPalpha and the interaction between C/EBPalpha and E2F1/E2F4.

CONCLUSION

In prostate cancer cells C/EBPalpha cannot function as a tumor suppressor.

PU.1 and partners: regulation of haematopoietic stem cell fate in normal and malignant haematopoiesis

During normal haematopoiesis, cell development and differentiation programs are accomplished by switching ‘on’ and ‘off’ specific set of genes. Specificity of gene expression is primarily achieved by combinatorial control, i.e. through physical and functional interactions among several transcription factors that form sequence-specific multiprotein complexes on regulatory regions (gene promoters and enhancers). Such combinatorial gene switches permit flexibility of regulation and allow numerous developmental decisions to be taken with a limited number of regulators. The haematopoietic-specific Ets family transcription factor PU.1 regulates many lymphoid- and myeloid-specific gene promoters and enhancers by interacting with multiple proteins during haematopoietic development. Such protein–protein interactions regulate DNA binding, subcellular localization, target gene selection and transcriptional activity of PU.1 itself in response to diverse signals including cytokines, growth factors, antigen and cellular stresses. Specific domains of PU.1 interact with many protein motifs such as bHLH, bZipper, zinc fingers and paired domain for regulating its activity. This review focuses on important protein–protein interactions of PU.1 that play a crucial role in regulation of normal as well as malignant haematopoiesis. Precise delineation of PU.1 protein-partner interacting interface may provide an improved insight of the molecular mechanisms underlying haematopoietic stem cell fate regulation. Its interactions with some proteins could be targeted to modulate the aberrant signalling pathways for reversing the malignant phenotype and to control the generation of specific haematopoietic progeny for treatment of haematopoietic disorders.

Multiple ways of C/EBPalpha inhibition in myeloid leukaemia

Transcription factors play a crucial role in myeloid differentiation and lineage determination. Tumour suppressor protein C/EBPalpha is a key regulator of granulocytic differentiation whose functional inactivation has become a pathophysiological signature of myeloid leukaemia. In this review we describe various mechanisms such as antagonistic protein-protein interaction, mutation and posttranslational modifications of C/EBPalpha which lead to its transcriptional inhibition and render C/EBPalpha inactive in its functions.

The MADS transcription factor Mef2c is a pivotal modulator of myeloid cell fate

Mef2c is a MADS (MCM1-agamous–deficient serum response factor) transcription factor best known for its role in muscle and cardiovascular development. A causal role of up-regulated MEF2C expression in myelomonocytic acute myeloid leukemia (AML) has recently been demonstrated. Due to the pronounced monocytic component observed in Mef2c-induced AML, this study was designed to assess the importance of Mef2c in normal myeloid differentiation. Analysis of bone marrow (BM) cells manipulated to constitutively express Mef2c demonstrated increased monopoiesis at the expense of granulopoiesis, whereas BM isolated from Mef2cΔ/− mice showed reduced levels of monocytic differentiation in response to cytokines. Mechanistic studies showed that loss of Mef2c expression correlated with reduced levels of transcripts encoding c-Jun, but not PU.1, C/EBPα, or JunB transcription factors. Inhibiting Jun expression by short-interfering RNA impaired Mef2c-mediated inhibition of granulocyte development. Moreover, retroviral expression of c-Jun in BM cells promoted monocytic differentiation. The ability of Mef2c to modulate cell-fate decisions between monocyte and granulocyte differentiation, coupled with its functional sensitivity to extracellular stimuli, demonstrate an important role in immunity—and, consistent with findings of other myeloid transcription factors, a target of oncogenic lesions in AML.

C/EBP alpha:AP-1 leucine zipper heterodimers bind novel DNA elements, activate the PU.1 promoter and direct monocyte lineage commitment more potently than C/EBP alpha homodimers or AP-1

The basic-region leucine zipper (BR-LZ or bZIP) transcription factors dimerize via their LZ domains to position the adjacent BRs for DNA binding. Members of the C/EBP, AP-1 and CREB/ATF bZIP subfamilies form homodimeric or heterodimeric complexes with other members of the same subset and bind-specific DNA motifs. Here we demonstrate that C/EBPalpha also zippers with AP-1 proteins and that this interaction allows contact with novel DNA elements and induction of monocyte lineage commitment in myeloid progenitors. A leucine zipper swap:gel shift assay demonstrates that C/EBPalpha zippers with c-Jun, JunB or c-Fos, but not with c-Maf or MafB. To evaluate activities of specific homodimers or heterodimers we utilized LZs with acid (LZE) or basic (LZK) residues in their salt bridge positions. C/EBPalphaLZE:C/EBPalphaLZK preferentially binds a C/EBP site, c-JunLZE:c-FosLZK an AP-1 site and C/EBPalphaLZE:c-JunLZK a hybrid element identified as TTGCGTCAT by oligonucleotide selection. In murine myeloid progenitors, C/EBPalpha:c-Jun or C/EBPalpha:c-Fos LZE:LZK heterodimers induce monocyte lineage commitment with markedly increased potency compared with C/EBPalpha or c-Jun homodimers or c-Jun:c-Fos heterodimers, demonstrating a positive functional consequence of C/EBP:AP-1 bZIP subfamily interaction. C/EBPalpha:cJun binds and activates the endogenous PU.1 promoter, providing one mechanism for induction of monopoiesis by this complex.

Comparative analysis of the acute response of the trout, O. mykiss, head kidney to in vivo challenge with virulent and attenuated infectious hematopoietic necrosis virus and LPS-induced inflammation

BACKGROUND

The response of the trout, O. mykiss, head kidney to bacterial lipopolysaccharide (LPS) or active and attenuated infectious hematopoietic necrosis virus (IHNV and attINHV respectively) intraperitoneal challenge, 24 and 72 hours post-injection, was investigated using a salmonid-specific cDNA microarray.

RESULTS

The head kidney response to i.p. LPS-induced inflammation in the first instance displays an initial stress reaction involving suppression of major cellular processes, including immune function, followed by a proliferative hematopoietic-type/biogenesis response 3 days after administration. The viral response at the early stage of infection highlights a suppression of hematopoietic and protein biosynthetic function and a stimulation of immune response. In fish infected with IHNV a loss of cellular function including signal transduction, cell cycle and transcriptional activity 72 hours after infection reflects the tissue-specific pathology of IHNV infection. attIHNV treatment on the other hand shows a similar pattern to native IHNV infection at 24 hours however at 72 hours a divergence from the viral response is seen and replace with a recovery response more similar to that observed for LPS is observed.

CONCLUSION

In conclusion we have been able to identify and characterise by transcriptomic analysis two different types of responses to two distinct immune agents, a virus, IHNV and a bacterial cell wall component, LPS and a 'mixed' response to an attenuated IHNV. This type of analysis will lead to a greater understanding of the physiological response and the development of effective immune responses in salmonid fish to different pathogenic and pro-inflammatory agents.

miR-21 Gene expression triggered by AP-1 is sustained through a double-negative feedback mechanism

miR-21 has been reported to be highly expressed in various cancers and to be inducible in a human promyelocytic cell line, HL-60, after phorbol 12-myristate 13-acetate (PMA) treatment. To examine molecular mechanisms involved in miR-21 expression, we analyzed the structure of the miR-21 gene by determining its promoter and primary transcripts. We show that activation protein 1 (AP-1) activates the miR-21 transcription in conjugation with the SWI/SNF complex, after PMA stimulation, through the conserved AP-1 and PU.1 binding sites in the promoter identified here. The previous findings of enhanced miR-21 expression in several cancers may therefore reflect the elevated AP-1 activity in these carcinomas. A single precursor RNA containing miR-21 was transcribed just downstream from the TATA box in this promoter, which is located in an intron of a coding gene, TMEM49. More important, expression of this overlapping gene is completely PMA-independent and all its transcripts are polyadenylated before reaching the miR-21 hairpin embedding region, indicating that miRNAs could have their own promoter even if overlapped with other genes. By available algorithms that predict miRNA target using a conservation of sequence complementary to the miRNA seed sequence, we next predicted and confirmed that the NFIB mRNA is a target of miR-21. NFIB protein usually binds the miR-21 promoter in HL-60 cells as a negative regulator and is swept off from the miR-21 promoter during PMA-induced macrophage differentiation of HL-60. The translational repression of NFIB mRNA by miR-21 accelerates clearance of NFIB in parallel with the simultaneous miR-21-independent transcriptional repression of NFIB after PMA stimulation. Since exogenous miR-21 expression moderately induced endogenous miR-21, an evolutionarily conserved double-negative feedback regulation would be operating as a mechanism to sustain miR-21 expression.

Proteomic identification of the MYST domain histone acetyltransferase TIP60 (HTATIP) as a co-activator of the myeloid transcription factor C/EBPalpha

The transcription factor C/EBPalpha (CEBPA) is a key player in granulopoiesis and leukemogenesis. We have previously reported the interaction of C/EBPalpha with other proteins (utilizing mass spectrometry) in transcriptional regulation. In the present study, we characterized the association of the MYST domain histone acetyltransferase Tat-interactive protein (TIP) 60 (HTATIP) with C/EBPalpha. We show in pull-down and co-precipitation experiments that C/EBPalpha and HTATIP interact. A chromatin immunoprecipitation (ChIP) and a confirmatory Re-ChIP assay revealed in vivo occupancy of the C/EBPalpha and GCSF-R promoter by HTATIP. Reporter gene assays showed that HTATIP is a co-activator of C/EBPalpha. The co-activator function of HTATIP is dependent on its intact histone acetyltransferase (HAT) domain and on the C/EBPalpha DNA-binding domain. The resulting balance between histone acetylation and deacetylation at the C/EBPalpha promoter might represent an important mechanism of C/EBPalpha action. We observed a lower expression of HTATIP mRNA in undifferentiated U937 cells compared to retinoic acid-induced differentiated U937 cells, and correlated expression of CEBPA and HTATIP mRNA levels were observed in leukemia samples. These findings point to a functional synergism between C/EBPalpha and HTATIP in myeloid differentiation and suggest that HTATIP might be an important player in leukemogenesis.

C/EBPalpha induces PU.1 and interacts with AP-1 and NF-kappaB to regulate myeloid development

C/EBPalpha and PU.1 are key regulators of early myeloid development. Mice lacking C/EBPalpha or PU.1 have reduced granulocytes and monocytes. Consistent with a model in which induction of PU.1 by C/EBPalpha contributes to monocyte lineage specification, mice with reduced PU.1 have diminished monocytes but retain granulocytes, C/EBPalpha directly activates PU.1 gene transcription, and exogenous C/EBPalpha increases monocytic lineage commitment from bipotential myeloid progenitors. In addition to C/EBPalpha, AP-1 proteins also have the capacity to induce monocytic maturation. C/EBPalpha:c-Jun or C/EBPalpha:c-Fos leucine zipper heterodimers induce monopoiesis more potently than C/EBPalpha or c-Jun homodimers or c-Fos:c-Jun heterodimers. C/EBPs and NF-kappaB cooperatively regulate numerous genes during the inflammatory response. The C/EBPalpha basic region interacts with NF-kappaB p50, but not p65, to induce bcl-2, and this interaction may be relevant to myeloid cell survival and development.

The transcriptional repressor GFI-1 antagonizes PU.1 activity through protein-protein interaction

Mice lacking the zinc finger transcriptional repressor protein GFI-1 are neutropenic. These mice generate abnormal immature myeloid cells exhibiting characteristics of both macrophages and granulocytes. Furthermore, Gfi-1(-/-) mice are highly susceptible to bacterial infection. Interestingly, Gfi-1(-/-) myeloid cells overexpress target genes of the PU.1 transcription factor such as the macrophage colony-stimulating factor receptor and PU.1 itself. We therefore determined whether GFI-1 modulates the transcriptional activity of PU.1. Our data demonstrate that GFI-1 physically interacts with PU.1, repressing PU.1-dependent transcription. This repression is functionally significant, as GFI-1 blocked PU.1-induced macrophage differentiation of a multipotential hematopoietic progenitor cell line. Retroviral expression of GFI-1 in primary murine hematopoietic progenitors increased granulocyte differentiation at the expense of macrophage differentiation. We interbred Gfi-1(+/-) and PU.1(+/-) mice and observed that heterozygosity at the PU.1 locus partially rescued the Gfi-1(-/-) mixed myeloid lineage phenotype, but failed to restore granulocyte differentiation. Our data demonstrate that GFI-1 represses PU.1 activity and that lack of this repression in Gfi-1(-/-) myeloid cells contributes to the observed mixed lineage phenotype.

Ets-2 and C/EBP-beta are important mediators of ovine trophoblast Kunitz domain protein-1 gene expression in trophoblast

Background

The trophoblast Kunitz domain proteins (TKDPs) constitute a highly expressed, placenta-specific, multigene family restricted to ruminant ungulates and characterized by a C-terminal "Kunitz" domain, preceded by one or more unique N-terminal domains. TKDP-1 shares an almost identical expression pattern with interferon-tau, the "maternal recognition of pregnancy protein" in ruminants. Our goal here has been to determine whether the ovine (ov) Tkdp-1 and IFNT genes possess a similar transcriptional code.

Results

The ovTkdp-1 promoter has been cloned and characterized. As with the IFNT promoter, the Tkdp-1 promoter is responsive to Ets-2, and promoter-driven reporter activity can be increased over 700-fold in response to over-expression of Ets-2 and a constitutively active form of protein Kinase A (PKA). Unexpectedly, the promoter element of Tkdp-1 responsible for this up-regulation, unlike that of the IFNT, does not bind Ets-2. However, mutation of a CCAAT/enhancer binding element within this control region not only reduced basal transcriptional activity, but prevented Ets-2 as well as cyclic adenosine 5'-monophosphate (cAMP)/PKA and Ras/mitogen-activated protein kinase (MAPK) responsiveness. In vitro binding experiments and in vivo protein-protein interaction assays implicated CCAAT/enhancer binding protein-beta (C/EBP-β) as involved in up-regulating the Tkdp-1 promoter activity. A combination of Ets-2 and C/EBP-β can up-regulate expression of the minimal Tkdp-1 promoter as much as 930-fold in presence of a cAMP analog. An AP-1-like element adjacent to the CCAAT enhancer, which binds Jun family members, is required for basal and cAMP/ C/EBP-β-dependent activation of the gene, but not for Ets-2-dependent activity.

Conclusion

This paper demonstrates how Ets-2, a key transcription factor for trophoblast differentiation and function, can control expression of two genes (Tkdp-1 and IFNT) having similar spatial and temporal expression patterns via very different mechanisms.

Proteomic discovery of Max as a novel interacting partner of C/EBPalpha: a Myc/Max/Mad link

The transcription factor CCAAT/enhancer binding protein a (C/EBPalpha) is important in the regulation of granulopoiesis and is disrupted in human acute myeloid leukemia. In the present study, we sought to identify novel C/EBPalpha interacting proteins in vivo through immunoprecipitation using mass spectrometry-based proteomic techniques. We identified Max, a heterodimeric partner of Myc, as one of the interacting proteins of C/EBPalpha in our screen. We confirmed the in vivo interaction of C/EBPalpha with Max and showed that this interaction involves the basic region of C/EBPalpha. Endogenous C/EBPalpha and Max, but not Myc and Max, colocalize in intranuclear structures during granulocytic differentiation of myeloid U937 cells. Max enhanced the transactivation capacity of C/EBPalpha on a minimal promoter. A chromatin immunoprecipitation assay revealed occupancy of the human C/EBPalpha promoter in vivo by Max and Myc under cellular settings and by C/EBPalpha and Max under retinoic acid induced granulocytic differentiation. Interestingly, enforced expression of Max and C/EBPalpha results in granulocytic differentiation of the human hematopoietic CD34(+) cells, as evidenced by CD11b, CD15 and granulocyte colony-stimulating factor receptor expression. Silencing of Max by short hairpin RNA in CD34(+) and U937 cells strongly reduced the differentiation-inducing potential of C/EBPalpha, indicating the importance of C/EBPalpha-Max in myeloid progenitor differentiation. Taken together, our data reveal Max as a novel co-activator of C/EBPalpha functions, thereby suggesting a possible link between C/EBPalpha and Myc-Max-Mad network.

Proteomic identification of C/EBP-DBD multiprotein complex: JNK1 activates stem cell regulator C/EBPalpha by inhibiting its ubiquitination

Functional inactivation of transcription factors in hematopoietic stem cell development is involved in the pathogenesis of acute myeloid leukemia (AML). Stem cell regulator C/enhancer binding protein (EBP)alpha is among such transcription factors known to be inactive in AML. This is either due to mutations or inhibition by protein-protein interactions. Here, we applied a mass spectrometry-based proteomic approach to systematically identify putative co-activator proteins interacting with the DNA-binding domain (DBD) of C/EBP transcription factors. In our proteomic screen, we identified c-Jun N-terminal kinase (JNK) 1 among others such as PAK6, MADP-1, calmodulin-like skin proteins and ZNF45 as proteins interacting with DBD of C/EBPs from nuclear extract of myelomonocytic U937 cells. We show that kinase JNK1 physically interacts with DBD of C/EBPalpha in vitro and in vivo. Furthermore, we show that active JNK1 inhibits ubiquitination of C/EBPalpha possibly by phosphorylating in its DBD. Consequently, JNK1 prolongs C/EBPalpha protein half-life leading to its enhanced transactivation and DNA-binding capacity. In certain AML patients, however, the JNK1 mRNA expression and its kinase activity is decreased which suggests a possible reason for C/EBPalpha inactivation in AML. Thus, we report the first proteomic screen of C/EBP-interacting proteins, which identifies JNK1 as positive regulator of C/EBPalpha.

C/EBPalpha directs monocytic commitment of primary myeloid progenitors

C/EBPalpha is required for generation of granulocyte-monocyte progenitors, but the subsequent role of C/EBPalpha in myeloid lineage commitment remains uncertain. We transduced murine marrow cells with C/EBPalpha-estradiol receptor (ER) or empty vector and subjected these to lineage depletion just prior to culture in estradiol with myeloid cytokines. This protocol limits biases due to lineage-specific effects on developmental kinetics, proliferation, and apoptosis. Also, lowering the dose of estradiol reduced activated C/EBPalpha-ER to near the physiologic range. C/EBPalpha-ER increased Mac1(+)/Gr1(-)/MPO(-)/low monocytes 1.9-fold while reducing Mac1(+)/Gr1(+)/MPO(hi) granulocytes 2.5-fold at 48 hours, even in 0.01 microM estradiol. This pattern was confirmed morphologically and by quantitative polymerase chain reaction (PCR) assay of lineage markers. To directly assess effects on immature progenitors, transduced cells were cultured for 1 day with and then in methylcellulose without estradiol. A 2-fold increase in monocytic compared with granulocytic colonies was observed in IL-3/IL-6/SCF or GM-CSF, but not G-CSF, even in 0.01 microM estradiol. C/EBPalpha-ER induced PU.1 mRNA, and PU.1-ER stimulated monocytic development, suggesting that transcriptional induction of PU.1 by C/EBPalpha contributes to monopoiesis. A C/EBPalpha variant incapable of zippering with c-Jun did not induce monopoiesis, and a variant unable to bind NF-kappaB p50 stimulated granulopoiesis, suggesting their cooperation with C/EBPalpha during monocytic commitment.

Transcriptional analysis of LPS-stimulated activation of trout (Oncorhynchus mykiss) monocyte/macrophage cells in primary culture treated with cortisol

Primary immune responses to pathogen invasion are mediated by the innate immune system in which tissue macrophages play a key role. During infectious processes glucocorticoids generally may function to dampen inflammatory responses. In this study, the ability of cortisol to directly modulate the transcriptional response of rainbow trout macrophages to the cellular activator lipopolysaccharide (LPS) was investigated. The results indicate that cortisol significantly inhibits the well-described LPS-dependent induction of the expression of TNF-alpha2, a pro-inflammatory cytokine. In order to further characterize the molecular effects of LPS and the immunomodulatory role of cortisol, the in vitro macrophage response to LPS in the absence or presence of 12-h cortisol exposure was analyzed utilizing a salmonid-specific microarray platform. Genes that were stimulated or inhibited with LPS plus cortisol fell into several major functional groups. The first, a general "response" group comprising genes within ontology classes including the response to external stimuli, stress, humoral immunity and apoptosis, exhibited a significant increase after LPS stimulation, whereas suppression of this response was observed in the presence of cortisol. LPS stimulated other genes in a second group involved in cell signalling and also genes in a third group involved in the activation of transcription. Categories activated with cortisol were mainly related to various aspects of metabolism (including protein biosynthesis, binding and transport of ions) and structural proteins (mainly cytoskeleton and microtubules). The immunomodulatory action of cortisol on LPS-stimulated macrophages therefore appears more complex than simply the antagonism of LPS-induced transcriptional responses.

Genome-wide monocytic mRNA expression in polytrauma patients for identification of clinical outcome

Immune activation in multiple trauma is closely linked to the development of multiple organ dysfunction and failure, and consequently, has a profound influence on patient outcome. Although peripheral blood monocytes play a critical role in this immune response, the biological significance of changes in genome-wide expression immediately after traumatic injury have not been explored previously. Thirteen patients presenting with multiple blunt trauma were studied. Peripheral blood monocytes were obtained within 90 min and at 6, 12, 24, 48, and 72 h after trauma. Apparent genome-wide expression was determined with Affymetrix U133A microarrays. Supervised analysis identified 698 probe sets that were differentially expressed in the 13 trauma subjects (P < 0.001) over the 72-h study period. An additional 763 probe sets were differentially expressed in patients who died (n = 3) compared with those who survived (n = 10). The ability of these probe sets to function as a classifier of survival was significantly demonstrated with six prediction models. Using pathway analysis, a network of proinflammatory genes and intracellular signaling pathways leading to c-JUN activation were consistently overexpressed in patients who died. Genome-wide mRNA expression patterns in circulating peripheral blood monocytes from multiple-injured patients can discriminate clinical outcome. The pattern of gene expression in patients who died suggests that in these individuals, there is a reprioritization of gene expression consistent with an early activation of selected genes involved in the initiation and propagation of a proinflammatory response.

Dietary PUFA modulate the expression of proliferation and differentiation markers in Morris 3924A hepatoma cells

The effect of dietary polyunsaturated fatty acids on the expression of differentiation and proliferation markers in Morris 3924A hepatoma cells was investigated. ACT/I rats were conditioned 10 days with diets enriched with linoleic acid or alpha-linolenic acid before subcutaneous hepatoma cell transplantation. After 19 days from the inoculum, the mRNA levels of liver-enriched transcription factors and of their target genes were quantified. Both linoleic acid- and linolenic acid-enriched diets induced a decrease of beta-actin, AFP, PCNA, c-myc and of hepatocyte nuclear factors HNF-1alpha and HNF-4alpha mRNA levels in tumor tissue whereas HNF-3beta expression was induced by both dietary treatments. Only the alpha-linolenic acid-enriched diet was effective in reducing c-jun and increasing albumin mRNA levels. Since albumin is a C/EBPalpha target gene, C/EBPalpha gene transcription was evaluated at both protein and mRNA levels. It was found that alpha-linolenic acid-enriched diet did not enhance the C/EBPalpha mRNA content in hepatoma tissue while inducing C/EBPalpha protein expression with an isoform pattern similar to the hepatic phenotype. This evidence implies that alpha-linolenic acid or one of its metabolic products induce albumin synthesis in hepatoma cells by modulating C/EBPalpha gene expression at post-transcriptional level.

Towards a pathogenesis-oriented therapy of acute myeloid leukemia

Genetic and molecular techniques have provided increasing insights into the biology of acute myeloid leukemia (AML). These investigations showed that AML is not a homogeneous disease but a heterogeneous group of biologically different subentities. These subentities are currently primarily defined by cytogenetics by which three main subgroups can be discriminated: AML with balanced translocations, AML with unbalanced aberrations and AML without cytogenetically detectable aberrations. Within the latter group molecular alterations are identified in more than half of cases such as NPM mutations, FLT3 mutations, MLL duplications and mutations of CEBP-alpha. The clinical meaning of these findings is illustrated by substantial differences in response to therapy and long-term outcome. As demonstrated by the recent multicenter trial of the German AML Cooperative Group (AMLCG) and other studies intensification of induction therapy may improve the results in distinct subtypes but fails to do so in others. Therefore, new strategies need to be explored which incorporate the knowledge about the biology of AML to develop biology adapted treatment strategies. This process has just begun and is predominantly determined by the availability of new agents and their evaluation in clinical phase I and II studies. A variety of targets are currently explored and some trials have yielded promising results already. The step towards a biology adapted treatment of AML is long and requires the combined efforts of researchers, clinicians and the pharmaceutical industry. The first steps towards this goal have been taken and give rise to the hope for more effective and more specific therapies of AML.

C/EBPα functionally and physically interacts with GABP to activate the human myeloid IgA Fc receptor (FcαR, CD89) gene promoter

Human Fcα receptor (FcαR; CD89), the receptor for the crystallizable fragment (Fc) of immunoglobulin A (IgA), is expressed exclusively in myeloid cells, including granulocytes and monocytes/macrophages, and is considered to define a crucial role of these cells in immune and inflammatory responses. A 259-base pair fragment of the FCAR promoter is sufficient to direct myeloid expression of a reporter gene and contains functionally important binding sites for CCAAT/enhancer-binding protein α (C/EBPα) (CE1, CE2, and CE3) and an unidentified Ets-like nuclear protein. Here, we show that the Ets-binding site is bound by a heterodimer composed of GA-binding protein α (GABPα), an Ets-related factor, and GABPβ, a Notch-related protein. Cotransfection of GABP increased FCAR promoter activity 3.7-fold through the Ets-binding site. GABP and C/EBPα synergistically activated the FCAR promoter 280-fold. Consistent with these observations, in vitro binding analyses revealed a physical interaction between the GABPα subunit and C/EBPα. This is the first report demonstrating both physical and functional interactions between GABP and C/EBPα and will provide new insights into the molecular basis of myeloid gene expression. (Blood. 2005;106:2534-2542)

Combination of retinoic acid and tumor necrosis factor overcomes the maturation block in a variety of retinoic acid-resistant acute promyelocytic leukemia cells

Retinoic acid (RA) overcomes the maturation block in t(15:17) acute promyelocytic leukemia (APL), leading to granulocytic differentiation. Patients receiving RA alone invariably develop RA resistance. RA-resistant cells can serve as useful models for the development of treatments for both APL and other leukemias. Previously, we showed that RA and tumor necrosis factor (TNF) promote monocytic differentiation of the APL cell line NB4 and U937 monoblastic cells. Here, we report that combining TNF with RA leads to maturation of several RA-resistant APL cells along a monocytic pathway, whereas UF-1, a patient-derived RA-resistant cell line, showed characteristics of granulocytic differentiation. We found distinct differences in gene regulation between UF-1 cells and cells showing monocytic differentiation. Although IRF-7 was up-regulated by TNF and RA in all cells tested, expression of c-jun and PU.1 correlated with monocytic differentiation. Furthermore, synergistic induction of PU.1 DNA binding and macrophage colony-stimulating factor receptor (m-CSF-1R) mRNA was observed only in cells differentiating into monocytes. Using neutralizing antibodies against m-CSF-1R or its ligand, we found that inhibiting this pathway strongly reduced CD14 expression in response to RA and TNF, suggesting that this pathway is essential for their synergy in RA-resistant leukemia cells. (Blood. 2004;104:3335-3342)

MEIS 1 expression is downregulated through promoter hypermethylation in AML1-ETO acute myeloid leukemias

Retroviral insertional mutagenesis in BXH2 mice commonly induces myeloid leukemias. One of the most frequently involved genes in experimental studies is Meis 1. In contrast to other genes in murine models, Meis 1 has not been affected by recurrent chromosomal translocations or point mutations in human leukemias. We found a constant downregulation of the Meis 1 gene mRNA in AML1-ETO acute myeloid leukemias and in those cases harboring in frame mutations in the bZIP domain of CEBPalpha. The absence of the Meis 1 mRNA was not caused by inactivating point mutations in the coding sequence. Promoter hypermethylation was present in more than half of the cases (9/14), including samples obtained from the widely employed Kasumi-1 cell line. Double treatment with 5-Aza-2'-deoxycytidine and trichostatin A of the Kasumi-1 cell line partially reverses Meis 1 inhibition. HoxA9 levels were also low. In a cell line model (U937 Tet AML1-ETO), AML1-ETO expression was not associated with Meis 1 suppression at 72 h. Nevertheless, Meis 1 repression is dependent on the AML1-ETO transcript levels in treated leukemic patients. Chimeric products that arise from chromosomal translocations may be associated with locus-specific epigenetic inactivation. It remains to be investigated when this methylation process is acquired and which are the basic mechanisms underlying these molecular events in AML1-ETO and CEBPalpha-mutated AML.

A dominant-negative mutant of C/EBPα, associated with acute myeloid leukemias, inhibits differentiation of myeloid and erythroid progenitors of man but not mouse

The CCAAT/enhancer binding protein alpha (C/EBPα) is an essential transcription factor for granulocytic differentiation. C/EBPα mutations are found in approximately 8% of acute myeloid leukemia (AML) patients. Most of these mutations occur in the N-terminal coding region, resulting in a frame shift and the enhanced translation of a dominant-negative 30-kDa protein, which may be responsible for the differentiation block observed in AML. To test this hypothesis, we introduced a cDNA encoding an N-terminal mutated C/EBPα (mut10) into primary hematopoietic progenitors using a retroviral vector. Expression of mut10 in human CD34+ cord blood cells dramatically inhibited differentiation of both myeloid and erythroid lineages. Immunohistochemical analysis demonstrated coexpression of both myeloid and erythroid markers in the immature transformed cells. Surprisingly, mut10 did not block myelocytic differentiation in murine progenitors but did alter their differentiation kinetics and clonogenicity. Experiments were performed to confirm that the differential effect of mut10 on murine and human progenitors was not due to species-specific differences in C/EBPα protein sequences, expression levels, or inefficient targeting of relevant cells. Taken together, our results underline the intrinsic differences between hematopoietic controls in mouse and human and support the hypothesis that mutations in CEBPA are critical events in the disruption of myeloid differentiation in AMLs. (Blood. 2004;103:2744-2752)

C/EBPalphap30, a myeloid leukemia oncoprotein, limits G-CSF receptor expression but not terminal granulopoiesis via site-selective inhibition of C/EBP DNA binding

Heterozygous mutations of the CEBPA gene are present in 5% of acute myeloid leukemia (AML) cases and often lead to the expression of an N-terminally truncated, 30 kDa isoform, C/EBPalphap30, from an internal translation start site. We have assessed the effect of C/EBPalphap30 on granulopoiesis utilizing C/EBPalphap30-ER, containing the estradiol receptor ligand-binding domain. In contrast to C/EBPalpha-ER, C/EBPalphap30-ER did not induce 32Dcl3 myeloid cell differentiation in IL-3. However, both isoforms, when expressed at high levels, were capable of inhibiting E2F activity in 32Dcl3 cells and of slowing their G1 to S progression. C/EBPalphap30 repressed expression of the endogenous G-CSF receptor several-fold. To facilitate investigation of the effect of C/EBPalphap30-ER on granulopoiesis downstream of G-CSF signalling, we coexpressed exogenous G-CSF receptor. C/EBPalphap30-ER/GR cells expressed several granulocytic markers in G-CSF and demonstrated nuclear maturation. Rat C/EBPalpha-ER and C/EBPalphap30-ER, expressed in 293T cells, bound the C/EBP site from the NE gene with similar affinity, as did human C/EBPalpha and C/EBPalphap30. In contrast, C/EBPalphap30 bound the C/EBP sites in the PU.1 or GR gene with 3-6-fold reduced affinity. Thus, the selective inhibition of GR expression by C/EBPalphap30-ER is due in part to its variable affinity for C/EBP sites. Variation in affinity for selected cis elements among isoforms may affect the biology of basic region-leucine zipper (bZIP) proteins.

The fusion protein AML1-ETO in acute myeloid leukemia with translocation t(8;21) induces c-jun protein expression via the proximal AP-1 site of the c-jun promoter in an indirect, JNK-dependent manner

Overexpression of proto-oncogene c-jun and constitutive activation of the Jun N-terminal kinase (JNK) signaling pathway have been implicated in the leukemic transformation process. However, c-jun expression and the role of the JNK signaling pathway have not been investigated in primary acute myeloid leukemia (AML) cells with frequently observed balanced rearrangements such as t(8;21). In the present study, we report elevated c-jun mRNA expression in AML patient bone marrow cells with t(8;21), t(15;17) or inv(16), and a high correlation in mRNA expression levels of AML1-ETO and c-jun within t(8;21)-positive AML patient cells. In myeloid U937 cells, c-jun mRNA and protein expression increase upon inducible expression of AML1-ETO. AML1-ETO transactivates the human c-jun promoter through the proximal activator protein (AP-1) site by activating the JNK pathway. Overexpression of JNK-inhibitor JIP-1 and chemical JNK inhibitors reduce the transactivation capacity of AML1-ETO on the c-jun promoter and the proapoptotic function of AML1-ETO in U937 cells. An autocrine mechanism involving granulocyte-colony stimulating factor (G-CSF) and G-CSF receptor (G-CSF-R) might participate in AML1-ETO mediated JNK-signaling, because AML1-ETO induces G-CSF and G-CSF-R expression, and G-CSF-R-neutralizing antibodies reduce AML1-ETO-induced JNK phosphorylation. These data suggest a model in which AML1-ETO induces proto-oncogene c-jun expression via the proximal AP-1 site of the c-jun promoter in a JNK-dependent manner.

Elevated c-Jun expression in acute myeloid leukemias inhibits C/EBPalpha DNA binding via leucine zipper domain interaction

Transcription factor C/EBPalpha induces normal myeloid differentiation, inactivation of C/EBPalpha leads to a differentiation block in acute myeloid leukemias (AML), and overexpression of C/EBPalpha results in AML growth arrest and differentiation. Recent reports suggest that C/EBPalpha is activated or inactivated via protein-protein interactions. We previously reported that C/EBPalpha needs to inactivate the proto-oncogene c-Jun via leucine zipper domain interaction in order to induce granulocytic differentiation. We, therefore, hypothesized that c-Jun expression might be elevated in AML and subsequently inactivate C/EBPalpha. In fact, compared to normal bone marrow mononuclear cells, c-Jun expression is increased in AML patient samples (Affymetrix expression microarray analysis, n=166). c-Jun binds to C/EBPalpha via the leucine zipper domains and prevents C/EBPalpha from DNA binding. Inactivation of C/EBPalpha by c-Jun is necessary for c-Jun to induce proliferation because c-Jun-induced proliferation can be prevented by ectopic overexpression of C/EBPalpha. The dominant-negative 30-kDa C/EBPalpha protein, found in AML, fails to downregulate c-Jun mRNA expression in AML patient samples. Thus, our data suggest a model for AML in which c-Jun promotes proliferation and prevents differentiation by inhibiting C/EBPalpha DNA binding via leucine zipper domain interaction. It might depend on the expression levels of C/EBPalpha and c-Jun, if inhibition of C/EBPalpha by c-Jun or if inhibition of c-Jun by C/EBPalpha is more predominant: proliferation versus differentiation; AML versus normal myeloid development.

Reciprocal effects of C/EBPalpha and PKCdelta on JunB expression and monocytic differentiation depend upon the C/EBPalpha basic region

Monocytic differentiation of 32DPKCdelta cells in response to activation of protein kinase C delta (PKCdelta) by phorbol 12-myristate 13-acetate (PMA) was inhibited by exogenous CCAAT/enhancer binding protein alpha-estradiol receptor (C/EBPalpha-ER), which impeded morphologic maturation and induction of macrosialin mRNA. Inhibition of monopoiesis was also evident in 32DPKCdelta subclones expressing C/EBPalphaLeu12Val-ER, which cannot dimerize or bind DNA because of mutation of the leucine zipper, C/EBPalphaGZ-ER, in which the leucine zipper has been replaced by the GCN4 zipper, or C/EBPalphaDelta3-8-ER, lacking the C/EBPalpha transactivation domains. In contrast, C/EBPalphaBR3-ER, containing a mutant basic region, did not inhibit monocytic differentiation. C/EBPalpha-ER strongly inhibited endogenous AP-1 DNA-binding. Supershift analysis revealed that the major AP-1 complex contains JunB. Activation of C/EBPalpha-ER specifically reduced endogenous JunB RNA and protein and exogenous JunB levels without affecting endogenous or exogenous c-Jun. The stability of PMA-induced JunB was not affected. Thus, C/EBPalpha-ER suppresses both JunB transcription and posttranscriptional protein generation or induction. PU.1 levels and activity were increased. The Leu12Val, GZ, and Delta3-8 mutants also inhibited JunB expression, whereas the BR3 mutant was ineffective, indicating that inhibition of JunB expression and monocytic differentiation by C/EBPalpha-ER depends upon an interaction mediated by its basic region. Exogenous JunB restored AP-1 DNA-binding but did not prevent inhibition of macrosialin expression by C/EBPalpha-ER, indicating that JunB is not the only target relevant to inhibition of monopoiesis by C/EBPalpha.

Downregulation of c-Jun expression and cell cycle regulatory molecules in acute myeloid leukemia cells upon CD44 ligation

In the present study, we investigated the mechanism of CD44 ligation with the anti-CD44 monoclonal antibody A3D8 to inhibit the proliferation of human acute myeloid leukemia (AML) cells. The effects of A3D8 on myeloid cells were associated with specific disruption of cell cycle events and induction of G0/G1 arrest. Induction of G0/G1 arrest was accompanied by an increase in the expression of p21, attenuation of pRb phosphorylation and associated with decreased Cdk2 and Cdk4 kinase activities. Since c-Jun is an important regulator of proliferation and cell cycle progression, we analysed its role in A3D8-mediated growth arrest. We observed that A3D8 treatment of AML patient blasts and HL60/U937 cells led to the downregulation of c-Jun expression at mRNA and protein level. Transient transfection studies showed the inhibition of c-jun promoter activity by A3D8, involving both AP-1 sites. Furthermore, A3D8 treatment caused a decrease in JNK protein expression and a decrease in the level of phosphorylated c-Jun. Ectopic overexpression of c-Jun in HL60 cells was able to induce proliferation and prevent the antiproliferative effects of A3D8. In summary, these data identify an important functional role of c-Jun in the induction of cell cycle arrest and proliferation arrest of myeloid leukemia cells because of the ligation of the cell surface adhesion receptor CD44 by anti-CD44 antibody. Moreover, targeting of G1 regulatory proteins and the resulting induction of G1 arrest by A3D8 may provide new insights into antiproliferative and differentiation therapy of AML.