Chromatin immunoprecipitation (ChIP) studies indicate a role for CCAAT enhancer binding proteins alpha and epsilon (C/EBP alpha and C/EBP epsilon ) and CDP/cut in myeloid maturation-induced lactoferrin gene expression

Molecular cloning, characterisation, and expression patterns of pigeon CCAAT/enhancer binding protein-α and -β genes

1. CCAAT/enhancer binding proteins (C/EBPs), as a family of transcription factors, consists of six functionally and structurally related proteins which share a conserved basic leucine zipper (bZIP) DNA-binding domain. The aim of this study was to clone the full-length coding sequences (CDS) of C/EBP-α and -β genes, and determine the abundance of these two genes in various tissues of white king pigeon (C. livia). 2. The complete cDNA sequences of C/EBP-α and -β genes were cloned from pigeons by using PCR combined with rapid amplification of cDNA ends (RACE). The sequences were bioinformatically analysed, and the tissue distribution determined by quantitative real-time RT-PCR (qRT-PCR). 3. The results showed that the full-length cDNA sequences of pigeon C/EBP-α and -β genes were 2,807bp and 1,778bp, respectively. The open reading frames of C/EBP-α (978 bp) and -β (987bp) encoded 325 amino acids and 328 amino acids, respectively. The pigeon C/EBP-α and C/EBP-β proteins were predicted to have a conserved basic leucine zipper (bZIP) domain, which is a common structure feature of the C/EBP family. Multiple sequence alignments indicated that pigeon C/EBP-α and -β shared more than 90% amino-acid identity with their corresponding homologues in other avian species. Phylogenetic analysis revealed that these two proteins were highly conserved across different species and evolutionary processes. QRT-PCR results indicated that the pigeon C/EBP-α and -β mRNA transcripts were expressed in all investigated organs. The mRNA expression levels of pigeon C/EBP-α in descending order, were in spleen, heart, liver, lung, kidney and muscle. The pigeon C/EBP-β gene had the most abundant expression in lung, followed by the kidney, with minimal expression detected in muscle. 4. This study investigated the full-length cDNA sequences, genetic characteristics and tissue distribution of pigeon C/EBP-α and -β genes and found that they may have functions in various tissues of pigeon. This provides a foundation for further study for regulatory mechanisms of these two genes in birds.

Strategies to generate functionally normal neutrophils to reduce infection and infection-related mortality in cancer chemotherapy

Neutrophils form an essential part of innate immunity against infection. Cancer chemotherapy-induced neutropenia (CCIN) is a condition in which the number of neutrophils in a patient's bloodstream is decreased, leading to increased susceptibility to infection. Granulocyte colony-stimulating factor (GCSF) has been the only approved treatment for CCIN over two decades. To date, CCIN-related infection and mortality remain a significant concern, as neutrophils generated in response to administered GCSF are functionally immature and cannot effectively fight infection. This review summarizes the molecular regulatory mechanisms of neutrophil granulocytic differentiation and innate immunity development, dissects the biology of GCSF in myeloid expansion, highlights the shortcomings of GCSF in CCIN treatment, updates the recent advance of a selective retinoid agonist that promotes neutrophil granulocytic differentiation, and evaluates the benefits of developing GCSF biosimilars to increase access to GCSF biologics versus seeking a new mode to fundamentally advance GCSF therapy for treatment of CCIN.

CARD10, a CEBPE target involved in granulocytic differentiation

Maturation of granulocytes is dependent on controlled gene expression by myeloid lineage restricted transcription factors. CEBPE is one of the essential transcription factors required for granulocytic differentiation. Identification of downstream targets of CEBPE is vital to understand better its role in terminal granulopoiesis. In this study, we have identified Card10 as a novel target of CEBPE. We show that CEBPE binds to regulatory elements upstream of the murine Card10 locus, and expression of CARD10 is significantly reduced in Cebpe knock-out mice. Silencing Card10 in a human cell line and in murine primary cells impaired granulopoiesis, affecting expression of genes involved in myeloid cell development and function. Taken together, our data demonstrate for the first time that Card10 is expressed in granulocytes and is a direct target of CEBPE with functions extending to myeloid differentiation.

Armed for destruction: formation, function and trafficking of neutrophil granules

Neutrophils respond nearly instantly to infection, rapidly deploying a potent enzymatic and chemical arsenal immediately upon entering an infected site. This capacity for rapid and potent responses is endowed by stores of antimicrobial proteins contained in readily mobilizable granules. These granules contain the proteins necessary to mediate the recruitment, chemotaxis, antimicrobial function and NET formation of neutrophils. Four granule types exist, and are sequentially deployed as neutrophils enter infected sites. Secretory vesicles are released first, enabling recruitment of neutrophils out of the blood. Next, specific and gelatinase granules are released to enable neutrophil migration and begin the formation of an antimicrobial environment. Finally, azurophilic granules release potent antimicrobial proteins at the site of infection and into phagosomes. The step-wise mobilization of these granules is regulated by calcium signaling, while specific trafficking regulators and membrane fusion complexes ensure the delivery of granules to the correct subcellular site. In this review, we describe neutrophil granules from their formation through to their deployment at the site of infection, focusing on recent developments in our understanding of the signaling pathways and vesicular trafficking mechanisms which mediate neutrophil degranulation.

Epigenetic regulation of cellular and cytomegalovirus genes during myeloid cell development

Myeloid cells are important cell types that carry human cytomegalovirus. Latent viral DNA is present in CD34+ progenitor cells and their derived monocytes. However, differentiation of latently infected monocytes to mature macrophages or dendritic cells causes reactivation of latent viruses. During hematopoietic development, pluripotent genes are repressed, and lineage specific genes are activated in a step-wise manner. This process is governed by cell-type specific chromatin states. Enhancers in the hematopoietic system are highly dynamic and established by pioneer (first tier) transcription factors (TFs), which set the stage for second and third tier TF binding. In this review, we examine the epigenetic mechanisms that regulate myeloid cell development, cell identity, and activation with a special focus on factors that regulate viral gene expression and the status of viral infection in myeloid cells.

Belinostat, a potent HDACi, exerts antileukaemic effect in human acute promyelocytic leukaemia cells via chromatin remodelling

Epigenetic changes play a significant role in leukaemia pathogenesis, therefore histone deacetylases (HDACis) are widely accepted as an attractive strategy for acute promyelocytic leukaemia (APL) treatment. Belinostat (Bel, PXD101), a hydroxamate-type HDACi, has proved to be a promising cure in clinical trials for solid tumours and haematological malignancies. However, insight into molecular effects of Bel on APL, is still lacking. In this study, we investigated the effect of Bel alone and in combination with differentiation inducer retinoic acid (RA) on human promyelocytic leukaemia NB4 and HL-60 cells. We found that treatment with Bel, depending on the dosage used, inhibits cell proliferation, whereas in combination with RA enhances and accelerates granulocytic leukaemia cell differentiation. We also evaluated the effect of used treatments with Bel and RA on certain epigenetic modifiers (HDAC1, HDAC2, PCAF) as well as cell cycle regulators (p27) gene expression and protein level modulation. We showed that Bel in combination with RA up-regulates basal histone H4 hyperacetylation level more strongly compared to Bel or RA alone. Furthermore, chromatin immunoprecipitation assay indicated that Bel induces the accumulation of hyperacetylated histone H4 at the p27 promoter region. Mass spectrometry analysis revealed that in control NB4 cells, hyperacetylated histone H4 is mainly found in association with proteins involved in DNA replication and transcription, whereas after Bel treatment it is found with proteins implicated in pro-apoptotic processes, in defence against oxidative stress and tumour suppression. Summarizing, our study provides some novel insights into the molecular mechanisms of HDACi Bel action on APL cells.

ProHNPs are specific markers of normal myelopoiesis

Pro human neutrophil peptides (proHNP)s are proforms of α-defensins produced by precursors of human neutrophils. They are secreted to bone marrow plasma in large amounts by myelocytes. We hypothesized that the plasma concentration of proHNPs might serve as a specific marker of myelopoietic activity, heralding the onset of normal myelopoiesis before reappearance of neutrophils, in the setting of bone marrow regeneration. To investigate this, plasma levels of proHNPs were measured by enzyme-linked immunosorbent assay in blood samples collected from patients undergoing allogeneic (n=11) or autologous (n=16) stem cell transplantations (SCTs) and patients receiving chemotherapy for acute leukemia (n=14). To compare proHNPs with previously suggested myeloid markers, myeloperoxidase (MPO), lysozyme and neutrophil gelatinase-associated lipocalin (NGAL) were also assayed. In all but one patient, chemotherapy led to the complete disappearance of ProHNPs from plasma. It reappeared in plasma on average 6.3 days before reappearance of neutrophils in the allogeneic setting, whereas this was reduced to an average of 2.8 days in the autologous SCT patients who received granulocyte colony-stimulating factor. Patients with acute myeloid leukemia (n=19) had significantly lower levels of plasma proHNPs than healthy controls, indicating that proHNPs are not produced by leukemic blasts. We conclude that plasma concentration of proHNPs is a clinically useful marker of normal myelopoiesis.

Human α-defensin expression is not dependent on CCAAT/enhancer binding protein-ε in a murine model

Specific granule deficiency (SGD) is a rare congenital disorder characterized by recurrent infections. The disease is caused by inactivating mutations of the CCAAT/enhancer binding protein-ε (C/EBP-ε) gene. As a consequence, specific and gelatinase granules lack most matrix proteins. Furthermore, azurophil granules contain diminished amounts of their most abundant proteins, α-defensins, also known as human neutrophil peptides (HNPs). In accordance with this, in vitro models have demonstrated induction of HNPs by C/EBP-ε. Since mice do not express myeloid defensins, they cannot per se be used to characterize the role of C/EBP-ε in controlling HNP expression in vivo. We therefore crossed a transgenic HNP-1-expressing mouse with the Cebpe^-/- mouse to study the in vivo significance of C/EBP-ε for HNP-1 transcription and expression. Surprisingly, neither expression nor processing of HNP-1 was affected by lack of C/EBP-ε in these mice. Transduction of C/EBP-ε into primary bone marrow cells from HNP-1 mice induced some HNP-1 expression, but not to levels comparable to expression human cells. Taken together, our data infer that the HNP-1 of the transgenic mouse does not show an expression pattern equivalent to endogenous secondary granule proteins. This limits the use of these transgenic mice as a model for human conditions.

RARα-PLZF oncogene inhibits C/EBPα function in myeloid cells

In acute promyelocytic leukemia, granulocytic differentiation is arrested at the promyelocyte stage. The variant t(11;17) translocation produces two fusion proteins, promyelocytic leukemia zinc finger-retinoic acid receptor α (PLZF-RARα) and RARα-PLZF, both of which participate in leukemia development. Here we provide evidence that the activity of CCAAT/enhancer binding protein α (C/EBPα), a master regulator of granulocytic differentiation, is severely impaired in leukemic promyelocytes with the t(11;17) translocation compared with those associated with the t(15;17) translocation. We show that RARα-PLZF inhibits myeloid cell differentiation through interactions with C/EBPα tethered to DNA, using ChIP and DNA capture assays. Furthermore, RARα-PLZF recruits HDAC1 and causes histone H3 deacetylation at C/EBPα target loci, thereby decreasing the expression of C/EBPα target genes. In line with these results, HDAC inhibitors restore in part C/EBPα target gene expression. These findings provide molecular evidence for a mechanism through which RARα-PLZF acts as a modifier oncogene that subverts differentiation in the granulocytic lineage by associating with C/EBPα and inhibiting its activity.

CEBP factors regulate telomerase reverse transcriptase promoter activity in whey acidic protein-T mice during mammary carcinogenesis

Telomerase is activated in the majority of invasive breast cancers, but the time point of telomerase activation during mammary carcinogenesis is not clear. We have recently presented a transgenic mouse model to study human telomerase reverse transcriptase (TERT) gene expression in vivo (hTERTp-lacZ). In the present study, hTERTp-lacZxWAP-T bitransgenic mice were generated to analyze the mechanisms responsible for human and mouse TERT upregulation during tumor progression in vivo. We found that telomerase activity and TERT expression were consistently upregulated in SV40-induced invasive mammary tumors compared to normal and hyperplastic tissues and ductal carcinoma in situ (DCIS). Human and mouse TERT genes are regulated similarly in the breast tissue, involving the CEBP transcription factors. Loss of CEBP-α and induction of CEBP-β expression correlated well with the activation of TERT expression in mouse mammary tumors. Transfection of CEBP-α into human or murine cells resulted in TERT repression, whereas knockdown of CEBP-α in primary human mammary epithelial cells resulted in reactivation of endogenous TERT expression and telomerase activity. Conversely, ectopic expression of CEBP-β activated endogenous TERT gene expression. Moreover, ChIP and EMSA experiments revealed binding of CEBP-α and CEBP-β to human TERT-promoter. This is the first evidence indicating that CEBP-α and CEBP-β are involved in TERT gene regulation during carcinogenesis.

C/EBPα and DEK coordinately regulate myeloid differentiation

The transcription factor C/EBPα is a critical mediator of myeloid differentiation and is often functionally impaired in acute myeloid leukemia. Recent studies have suggested that oncogenic FLT3 activity disrupts wild-type C/EBPα function via phosphorylation on serine 21 (S21). Despite the apparent role of pS21 as a negative regulator of C/EBPα transcription activity, the mechanism by which phosphorylation tips the balance between transcriptionally competent and inhibited forms remains unresolved. In the present study, we used immuno-affinity purification combined with quantitative mass spectrometry to delineate the proteins associated with C/EBPα on chromatin. We identified DEK, a protein with genetic links to leukemia, as a member of the C/EBPα complexes, and demonstrate that this association is disrupted by S21 phosphorylation. We confirmed that DEK is recruited specifically to chromatin with C/EBPα to enhance GCSFR3 promoter activation. In addition, we demonstrated that genetic depletion of DEK reduces the ability of C/EBPα to drive the expression of granulocytic target genes in vitro and disrupts G-CSF-mediated granulocytic differentiation of fresh human BM-derived CD34(+) cells. Our data suggest that C/EBPα and DEK coordinately activate myeloid gene expression and that S21 phosphorylation on wild-type C/EBPα mediates protein interactions that regulate the differentiation capacity of hematopoietic progenitors.

Ongoing Trials in Low-Grade Lymphoma

There are many therapies available for the management of low-grade lymphoma. With follicular lymphoma, for example, combination of chemotherapy and rituximab (immuno-chemotherapy) and consecutive maintenance therapy for 2 years is the current standard of care. To date, the most widely used regimen seems to be rituximab combined with cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP). Substitution of liposomal doxorubicin in place of conventional doxorubicin may improve outcomes in this indication, although evidence for its use in low-grade lymphoma is not as relevant as in aggressive lymphoma. Bendamustine, in combination with rituximab, has shown very good efficacy and tolerability in several lymphoma types, particularly follicular lymphoma and other low-grade lymphomas. Other combinations, such as those including bortezomib and lenalidomide, are under investigation in low-grade lymphoma, and the duration of rituximab maintenance therapy following bendamustine-rituximab-containing induction is being researched by the German Study Group for Indolent Lymphoma (StiL).

Differential effects of sumoylation on the activities of CCAAT enhancer binding protein alpha (C/EBPα) p42 versus p30 may contribute in part, to aberrant C/EBPα activity in acute leukemias

In this study, we have examined the role of post-translational modification of the myeloid master regulator C/EBPα by small ubiquitin-related modifier (SUMO). We have used transient transfection analysis, oligonucleotide pulldown assays and chromatin immuno-precititation in all-trans retinoic acid (ATRA)-inducible promyelocytic cell lines MPRO and NB4. We demonstrate that sumoylated wild-type p42-C/EBPα is associated with negative regulation of the myeloid specific lactoferrin (LF) gene in early myeloid cells and that a reduction in p42-C/EBPα sumoylation coincides with expression of the LF gene in maturing myeloid cells. In the acute promyelocytic leukemia cell line NB4 however, sumoylated p42 remains persistently bound to the LF promoter following ATRA-induction. This correlates with lack of lactoferrin expression in these cells. Changes in sumoylation status of C/EBPα thus appear to contribute to a switch that regulates transcriptional activity of this master regulator during normal neutrophil development. We also demonstrate that sumoylation of the AML associated dominant negative p30-C/EBPα isoform does not alter transactivation activity of the LF promoter. This may be because the p30 C/EBPα isoform binds to the LF promoter much less efficiently than its full length counterpart. Our data suggest that the activity of p42-C/EBPα in the developing neutrophil is more sensitive to changes in sumoylation than the p30 isoform. This difference may contribute to the leukemogenic potential of p30-C/EBPα.

Inhibitory mechanisms of the transcriptional activity of androgen receptor by resveratrol: Implication of DNA binding and acetylation of the receptor

Androgen receptor (AR) is a ligand-dependent transcription factor and plays a key role in the development of prostate cancer. Resveratrol, a polyphenolic compound, inhibits AR function and reduces the level of prostate-specific antigen (PSA), a notable target gene of AR. Here, we investigated the mechanisms by which resveratrol inhibits AR function. Although the protein levels of AR were decreased by resveratrol treatment for 24h, the decrease could not fully account for the suppression of AR function. The total and the nuclear AR levels were not affected after incubation with 10μM resveratrol for 3h, whereas resveratrol inhibited the binding of AR to the enhancer region of PSA and decreased the acetylation of AR even at this early phase. Inhibition of transcription by resveratrol was weaker in the AR acetylation site mutant than in the wild-type. In later phase (24h) after incubation with resveratrol, the ligand-induced nuclear accumulation of AR was markedly decreased by resveratrol. These data show that resveratrol inhibits DNA binding of AR, presumably by decreasing its level of acetylation and suggest that acetylation of AR is involved in its accumulation in the nucleus.

Cut-like homeobox 1 (CUX1) regulates expression of the fat mass and obesity-associated and retinitis pigmentosa GTPase regulator-interacting protein-1-like (RPGRIP1L) genes and coordinates leptin receptor signaling

The first intron of FTO contains common single nucleotide polymorphisms associated with body weight and adiposity in humans. In an effort to identify the molecular basis for this association, we discovered that FTO and RPGRIP1L (a ciliary gene located in close proximity to the transcriptional start site of FTO) are regulated by isoforms P200 and P110 of the transcription factor, CUX1. This regulation occurs via a single AATAAATA regulatory site (conserved in the mouse) within the FTO intronic region associated with adiposity in humans. Single nucleotide polymorphism rs8050136 (located in this regulatory site) affects binding affinities of P200 and P110. Promoter-probe analysis revealed that binding of P200 to this site represses FTO, whereas binding of P110 increases transcriptional activity from the FTO as well as RPGRIP1L minimal promoters. Reduced expression of Fto or Rpgrip1l affects leptin receptor isoform b trafficking and leptin signaling in N41 mouse hypothalamic or N2a neuroblastoma cells in vitro. Leptin receptor clusters in the vicinity of the cilium of arcuate hypothalamic neurons in C57BL/6J mice treated with leptin, but not in fasted mice, suggesting a potentially important role of the cilium in leptin signaling that is, in part, regulated by FTO and RPGRIP1L. Decreased Fto/Rpgrip1l expression in the arcuate hypothalamus coincides with decreased nuclear enzymatic activity of a protease (cathepsin L) that has been shown to cleave full-length CUX1 (P200) to P110. P200 disrupts (whereas P110 promotes) leptin receptor isoform b clustering in the vicinity of the cilium in vitro. Clustering of the receptor coincides with increased leptin signaling as reflected in protein levels of phosphorylated Stat3 (p-Stat3). Association of the FTO locus with adiposity in humans may reflect functional consequences of A/C alleles at rs8050136. The obesity-risk (A) allele shows reduced affinity for the FTO and RPGRIP1L transcriptional activator P110, leading to the following: 1) decreased FTO and RPGRIP1L mRNA levels; 2) reduced LEPR trafficking to the cilium; and, as a consequence, 3) a diminished cellular response to leptin.

C/EBPepsilon directs granulocytic-vs-monocytic lineage determination and confers chemotactic function via Hlx

OBJECTIVE

Mutations in the CCAAT enhancer binding protein epsilon (C/EBPepsilon) gene have been identified in the cells of patients with neutrophil specific granule deficiency, a rare congenital disorder marked by recurrent bacterial infections. Their neutrophils, in addition to lacking specific granules required for normal respiratory burst activity, also lack normal phagocytosis and chemotaxis. Although the specific granule deficiency phenotype has been replicated in C/EBPepsilon(-/-) (knockout [KO]) mice, the mechanisms by which C/EBPepsilon mutations act to decrease neutrophil function are not entirely clear.

MATERIALS AND METHODS

In order to determine the role of C/EBPepsilon in neutrophil differentiation and migration, we generated immortalized progenitor cell lines from C/EBPepsilon KO and wild-type mice and performed expression and flow cytometric analysis and functional studies.

RESULTS

Expression of lineage-specific cell surface antigens on our in vitro differentiated cell lines revealed persistent expression of monocytic markers on KO granulocytes. We verified this in primary murine peripheral blood and bone marrow cells. In addition, KO bone marrow had an increase in immature myeloid precursors at the common myeloid progenitor and granulocyte/monocyte progenitor levels, suggesting a critical role for C/EBPepsilon not only in granulocyte maturation beyond the promyelocyte stage, but also in the monocyte/granulocyte lineage decision. We found that restoration of Hlx (H2.0-like homeo box 1) expression, which was decreased in C/EBPepsilon KO cells, rescued chemotaxis, but not the other defects of C/EBPepsilon KO neutrophils.

CONCLUSIONS

We show two new regulatory functions of C/EBPepsilon in myelopoiesis: in the absence of C/EBPepsilon, there is not only incomplete differentiation of granulocytes, but myelopoiesis is disrupted with the appearance of an intermediate cell type with monocyte and granulocyte features, and the neutrophils have abnormal chemotaxis. Restoration of expression of Hlx provides partial recovery of function; it has no effect on neutrophil maturation, but can completely ameliorate the chemotaxis defect in C/EBPepsilon KO cells.

Transcription factors Sp1 and C/EBP regulate NRAMP1 gene expression

The natural resistance-associated macrophage protein 1 (Nramp1), which belongs to a conserved family of membrane metal transporters, contributes to phagocyte-autonomous antimicrobial defense mechanisms. Genetic polymorphisms in the human NRAMP1 gene predispose to susceptibility to infectious or inflammatory diseases. To characterize the transcriptional mechanisms controlling NRAMP1 expression, we previously showed that a 263 bp region upstream of the ATG drives basal promoter activity, and that a 325 bp region further upstream confers myeloid specificity and activation during differentiation of HL-60 cells induced by vitamin D. Herein, the major transcription start site was mapped in the basal region by S1 protection assay, and two cis-acting elements essential for myeloid transactivation were characterized by in vitro DNase footprinting, electrophoretic mobility shift experiments, in vivo transfection assays using linker-mutated constructs, and chromatin immunoprecipitation assays in differentiated monocytic cells. One distal cis element binds Sp1 and is required for NRAMP1 myeloid regulation. Another site in the proximal region binds CCAAT enhancer binding proteins alpha or beta and is crucial for transcription. This study implicates Sp1 and C/EBP factors in regulating the expression of the NRAMP1 gene in myeloid cells.

Anaplasma phagocytophilum increases cathepsin L activity, thereby globally influencing neutrophil function

Anaplasma phagocytophilum, the agent of human granulocytic anaplasmosis, is an unusual obligate intracellular pathogen that persists in neutrophils. A. phagocytophilum increases the binding of a repressor, CCAAT displacement protein (CDP), to the gp91(phox) promoter, thereby diminishing the host oxidative burst. We now show that A. phagocytophilum infection also enhances the binding of CDP to the promoters of human neutrophil peptide 1 and C/EBPepsilon--molecules important for neutrophil defense and maturation--suggesting that this is a general strategy used by this pathogen to alter polymorphonuclear leukocyte function. To explore the mechanism by which A. phagocytophilum increases CDP activity, we assessed the effects of this microbe on cathepsin L, a protease that cleaves CDP into a form with increased DNA binding ability. A. phagocytophilum infection resulted in elevated cathepsin L activity and the proteolysis of CDP. Blocking the action of cathepsin L with a chemical inhibitor or small interfering RNA targeting of this molecule caused a marked reduction in the degree of A. phagocytophilum infection. These data demonstrate that increasing cathepsin L activity is a strategy used by A. phagocytophilum to alter CDP activity and thereby globally influence neutrophil function. As therapeutic options for A. phagocytophilum and related organisms are limited, these results also identify a cellular pathway that may be targeted for the treatment of A. phagocytophilum infection.

The multiple roles of CUX1: insights from mouse models and cell-based assays

Cux (Cut homeobox) genes are present in all metazoans. Early reports described many phenotypes caused by cut mutations in Drosophila melanogaster. In vertebrates, CUX1 was originally characterized as the CCAAT-displacement protein (CDP). Another line of investigation revealed the presence of CUX1 within a multi-protein complex called the histone nuclear factor D (HiNF-D). Recent studies led to the identification of several CUX1 isoforms with distinct DNA binding and transcriptional properties. While the CCAAT-displacement activity was implicated in the transcriptional repression of several genes, some CUX1 isoforms were found to participate in the transcriptional activation of some genes. The expression and activity of CUX1 was shown to be regulated through the cell cycle and to be a target of TGF-beta signaling. Mechanisms of regulation include alternative transcription initiation, proteolytic processing, phosphorylation and acetylation. Cell-based assays have established a role for CUX1 in the control of cell cycle progression, cell motility and invasion. In the mouse, gene inactivation as well as over-expression in transgenic mice has revealed phenotypes in multiple organs and cell types. While some phenotypes could be explained by the presumed functions of CUX1 in the affected cells, other phenotypes invoked non-cell-autonomous effects that suggest regulatory functions with an impact on cell-cell interactions. The implication of CUX1 in cancer was suggested first from its over-expression in primary tumors and cancer cell lines and was later confirmed in mouse models.

Transgenic mice expressing the p75 CCAAT-displacement protein/Cut homeobox isoform develop a myeloproliferative disease-like myeloid leukemia

The p75 CCAAT-displacement protein/Cut homeobox (CDP/Cux) isoform was previously reported to be overexpressed in human breast cancers. To investigate its oncogenic potential, we engineered two transgenic mouse lines expressing p75 CDP/Cux under the control of the mouse mammary tumor virus-long terminal repeat. The FVB strain of mouse is generally used in the generation of mouse models for breast cancer. The transgene was introduced into the hprt locus of 129/Ola embryonic stem cells and, following germ line passage, was backcrossed onto the FVB and C57BL/6 mouse strains. Here, we describe the phenotype of p75 CDP/Cux transgenic virgin female mice of the first backcross generations. We report that after a long latency period, approximately 33% of mice from two independent transgenic lines and from backcrosses into either the FVB or the C57BL/6 strains succumbed to a similar disease characterized by splenomegaly, hepatomegaly, and frequent infiltration of leukocytes into nonhematopoietic organs like the kidneys and lungs. Although an excess of B or T cells was observed in three diseased mice, in 17 other cases, histologic and flow cytometry analyses revealed the expansion of a population of neutrophils in the blood, spleen, and bone marrow. The increase in neutrophils correlated with signs of anemia and thrombocytopenia, whereas there was no indication of a reactive process. Therefore, p75 CDP/Cux transgenic mice displayed heightened susceptibility to a disease defined as a myeloproliferative disease-like myeloid leukemia. These results indicate that the overexpression of p75 CDP/Cux could alter homeostasis in the hematopoietic compartment.

ATF4 differentially regulates transcriptional activation of myeloid-specific genes by C/EBPepsilon and C/EBPalpha

Dimerization between different basic region leucine zipper (ZIP) transcription factors is regarded as an important mechanism for integrating various extracellular signals to control specific patterns of gene expression in cells. The activating transcription factor 4 (ATF4) protein was identified as a principal partner for the myeloid-specific transcriptional factor C/EBPepsilon. Dimerization required the ZIP motif of each protein and redirected DNA binding of C/EBPepsilon and ATF4 from their respective symmetric consensus sites to asymmetric C/EBP and cAMP response element sites. The C/EBPepsilon:ATF4 heterodimer bound to the C/EBP sites in the promoters of the myeloid-specific genes encoding neutrophil elastase (NE) and the G-CSF receptor (G-CSFR). Also, the heterodimer bound a previously uncharacterized site in the promoter of the mim-1 gene at nucleotide -174. Coexpression of ATF4 and C/EBPepsilon in the presence of c-Myb synergistically activated the mim-1 and NE promoters compared with C/EBPepsilon plus c-Myb alone. Synergistic activation was not observed for the G-CSFR promoter and only occurred in the presence of c-myb with the NE or mim-1 promoters. In contrast, ATF4:C/EBPalpha dimers bound to the C/EBP sites in the G-CSFR and NE promoters, but transcriptional activation was inhibited by 30-80% in the presence or absence of c-Myb. We propose that ATF4 may regulate myeloid gene expression differentially by potentiating C/EBPepsilon but inhibiting C/EBPalpha-mediated transcriptional activation.

Modulation of DNA binding properties of CCAAT/enhancer binding protein epsilon by heterodimer formation and interactions with NFkappaB pathway

C/EBP epsilon is a transcription factor involved in myeloid cell differentiation. Along with C/EBP-alpha, -beta, -gamma, -delta, and -zeta, C/EBP-epsilon belongs to the family of CCAAT/enhancer binding proteins that are implicated in control of growth and differentiation of several cell lineages in inflammation and stress response. We have previously shown that C/EBP-epsilon preferentially binds DNA as a heterodimer with other C/EBP family members such as C/EBP-delta, CHOP (C/EBP-zeta), and the b-zip family protein ATF4. In this study, we define the consensus binding sites for C/EBP-epsilon dimers and C/EBP-epsilon-ATF4 heterodimers. We show that the activated NFkappaB pathway promotes interaction of the C/EBP-epsilon subunit with its cognate DNA binding site via interaction with RelA. RelA-C/EBP interaction is enhanced by phosphorylation of threonine at amino acid 75 and results in increased DNA binding compared with the wild-type nonphosphorylated C/EBP both in vitro and in vivo. We suggest that interaction of the activated NFkappaB pathway and C/EBP-epsilon may be important in selective activation of a subset of C/EBP-epsilon-responsive genes.

Growth factor independence-1 (Gfi-1) plays a role in mediating specific granule deficiency (SGD) in a patient lacking a gene-inactivating mutation in the C/EBPepsilon gene

Neutrophil-specific granule deficiency (SGD) is a rare congenital disorder marked by recurrent bacterial infections. Neutrophils from SGD patients lack secondary and tertiary granules and their content proteins and lack normal neutrophil functions. Gene-inactivating mutations in the C/EBPepsilon gene have been identified in 2 SGD patients. Our studies on a third SGD patient revealed a heterozygous mutation in the C/EBPepsilon gene. However, we demonstrate elevated levels of C/EBPepsilon and PU.1 proteins in the patient's peripheral blood neutrophils. The expression of the transcription factor growth factor independence-1 (Gfi-1), however, was found to be markedly reduced in our SGD patient despite the absence of an obvious mutation in this gene. This may explain the elevated levels of both C/EBPepsilon and PU.1, which are targets of Gfi-1 transcriptional repression. We have generated a growth factor-dependent EML cell line from the bone marrow of Gfi-1(+/-) and Gfi-1(+/+) mice as a model for Gfi-1-deficient SGD, and demonstrate that lower levels of Gfi-1 expression in the Gfi-1(+/-) EML cells is associated with reduced levels of secondary granule protein (SGP) gene expression. Furthermore, we demonstrate a positive role for Gfi-1 in SGP expression, in that Gfi-1 binds to and up-regulates the promoter of neutrophil collagenase (an SGP gene), in cooperation with wild-type but not with mutant C/EBPepsilon. We hypothesize that decreased Gfi-1 levels in our SGD patient, together with the mutant C/EBPepsilon, block SGP expression, thereby contributing to the underlying etiology of the disease in our patient.

Expression of CCL9/MIP-1gamma is repressed by BCR/ABL and its restoration suppresses in vivo leukemogenesis of 32D-BCR/ABL cells

Transformation of hematopoietic cells by the BCR/ABL oncogene is caused by perturbation of signal transduction pathways leading to altered patterns of gene expression and activity. By oligonucleotide microarray hybridization of polysomal RNA of untreated and STI571-treated 32D-BCR/ABL cells, we identified the beta-chemokine CCL9 as a gene regulated by BCR/ABL in a tyrosine kinase-dependent manner. BCR/ABL repressed CCL9 expression at the transcriptional level by mechanisms involving suppression of p38 MAP kinase, and modulation of the activity of CDP/cut and C/EBPalpha, two transcription regulators of myeloid differentiation. However, repression of C/EBP-dependent transcription did not prevent the induction of CCL9 expression by STI571, suggesting that C/EBPalpha is involved in maintaining rather than in inducing CCL9 expression. Restoration of CCL9 expression in 32D-BCR/ABL cells had no effect on the in vitro proliferation of these cells, but reduced their leukemogenic potential in vivo, possibly by recruitment of CD3-positive immune cells. Together, these findings suggest that downregulation of chemokine expression may be involved in BCR/ABL-dependent leukemogenesis by altering the relationship between transformed cells and the microenvironment.

Induction of lactoferrin gene expression in myeloid or mammary gland cells by human T-cell leukemia virus type 1 (HTLV-1) tax: implications for milk-borne transmission of HTLV-1

Human T-cell leukemia virus type 1 (HTLV-1), the causative agent of adult T-cell leukemia, is transmitted vertically via breastfeeding. We have previously demonstrated that lactoferrin, a major milk protein, enhances HTLV-1 replication, at least in part by upregulating the HTLV-1 long terminal repeat promoter. We now report that HTLV-1 infection can induce lactoferrin gene expression. Coculture with HTLV-1-infected MT-2 cells increased the levels of lactoferrin mRNA in myeloid-differentiated HL-60 cells, as well as MCF-7 cells, models of two probable sources (neutrophils and mammary epithelium) of lactoferrin in breast milk. MT-2 cell coculture could be replaced with cell-free culture supernatants of MT-2 cells to exert the same effect. Furthermore, extracellularly administered Tax protein also induced lactoferrin gene expression at physiologically relevant concentrations. In transient-expression assays, Tax transactivated the lactoferrin gene promoter in HL-60 or MCF-7 cells. Experiments with Tax mutants, as well as site-directed mutants of the lactoferrin promoter reporters, indicated that the NF-kappaB transactivation pathway is critical for Tax induction of the lactoferrin gene promoter activity in myeloid-differentiated HL-60 cells, but not in MCF-7 cells. These results suggest that HTLV-1 infection may be able to induce expression of lactoferrin in a paracrine manner in the lactic compartment. Our findings, in conjunction with our previous study, implicate that mutual interaction between HTLV-1 and lactoferrin would benefit milk-borne transmission of this virus.

Derangement of transcription factor profiles during in vitro differentiation of HL60 and NB4 cells

Sequential up- and down-regulation of a handful of critical transcription factors is required for proper neutrophil differentiation. Malfunction of transcription factors may lead to diseases such as acute myeloid leukemia (AML) and specific granule deficiency. In order to understand the molecular background for normal and malignant granulopoiesis, a good model system is required that faithfully mimics the in vivo transcription factor expression profiles. The two human leukemic cell lines HL60 and NB4 have been widely used as model cell lines for these purposes. Differentiation of HL60 and NB4 cells resulted in asynchronous differentiation to morphologically mature neutrophils over a period of 5-7 days. To obtain cell populations of more even maturity, cells at different stages of in vitro differentiation were purified by immunomagnetic isolation. This resulted in three cell populations that could be classified as promyelocytes, myelocytes/metamyelocytes, and mature neutrophils, respectively. Comparison of transcription factor mRNA profiles from these cell populations with those previously seen in normal human bone marrow, demonstrated that although all of the 14 transcription factors described in vivo, could be detected during in vitro differentiation, vast differences in their expression profiles was observed. These data illustrate the limitations of cell lines as models for normal granulopoiesis.

Norepinephrine stimulates calprotectin expression in human monocytic cells

BACKGROUND AND OBJECTIVE

Calprotectin is composed of two proteins, S100A8 and S100A9, which are S100 family members, and is detected in gingival crevicular fluid and gingival tissue with inflammation. The release and production of calprotectin are regulated by lipopolysaccharides of periodontopathic bacteria and cytokines. Emotional or psychological stress, a risk factor of periodontal disease, is transmitted by stress modulators including norepinephrine and cortisol. The aim of the present study was to investigate the effect of stress on calprotectin expression using norepinephrine and cortisol.

METHODS

U-937 cells, a human monocytic cell line, were incubated with norepinephrine in the presence or absence of beta- or alpha-adrenergic receptor antagonists, or with cortisol. The expression of S100A8/S100A9 mRNAs was examined by northern blotting and the amount of calprotectin was measured by enzyme-linked immunosorbent assay (ELISA). The DNA binding activity of C/EBPalpha (CCAAT enhancing binding protein), a transcription factor, was examined by electrophoretic mobility shift assay.

RESULTS

Norepinephrine stimulated the expression of S100A8/S100A9 mRNAs via beta-adrenergic receptors in U-937 cells and significantly increased calprotectin production to about 3.6-fold that of the control. However, cortisol had no effect on calprotectin expression at the mRNA and protein levels. Norepinephrine elevated C/EBPalpha DNA binding activity, but cortisol did not increase the activity.

CONCLUSION

Norepinephrine, a stress modulator, stimulated calprotectin expression in human monocytic cells. Calprotectin expression may be regulated by stress in addition to inflammatory factors.

Factors regulating lactoferrin gene expressionThis paper is one of a selection of papers published in this Special Issue, entitled 7th International Conference on Lactoferrin: Structure, Function, and Applications, and has undergone the Journal's usual peer review process

Regulation of gene expression by nuclear receptors and transcription factors involves the concerted action of multiple proteins. The process of transcriptional activation involves chromatin modification, nuclear receptor or transcription factor binding to the response element of the promoter, and coregulator recruitment. Despite advances in knowledge pertaining to the molecular mechanisms of gene regulation overall, there is very limited information available on the molecular mechanism of lactoferrin gene regulation. This review will outline novel information relating to general gene regulation and will discuss the current understanding of the regulation of lactoferrin gene expression by nuclear receptors and transcription factors.

p120 nucleolar-proliferating antigen is a direct target of G-CSF signaling during myeloid differentiation

Granulocyte-colony stimulating factor (G-CSF) is an essential cytokine, which contributes to proliferation and differentiation of granulocyte precursor cells in the bone marrow. Despite recent progress in understanding G-CSF signaling events, the mechanisms that underlie the distinct spectrum of biological functions attributed to G-CSF-mediated gene expression remain unclear. Previous studies have identified a number of genes, which are up-regulated in G-CSF-stimulated myeloid precursor cells. In this study, we sought to identify additional target genes of G-CSF-mediated proliferation and/or differentiation. cDNA representational difference analysis was used with the 32Dcl3 cell line as a model system to isolate genes, which are up-regulated in an immediate-early manner upon G-CSF stimualtion. We isolated p120 nucleolar-proliferation antigen (NOL1), a highly conserved, nucleolar-specific, RNA-binding protein of unknown function, and confirmed its expression by Northern blot analysis in 4-h, G-CSF-induced 32Dcl3 cells. Isolation of a mouse p120 genomic clone revealed the presence of a signal tranducer and activator of transcription (STAT)-binding site in the first intron of the gene. We demonstrate the importance of STAT3 and STAT5 in mediating the G-CSF response with respect to p120 expression by transient transfection analysis, oligonucleotide pull-down assays, and the loss of p120 expression in the bone marrow of mice lacking normal STAT3 signaling. In addition, overexpression of p120 in G-CSF-induced 32D cells revealed normal, morphologic maturation and growth characteristics but loss of lactoferrin expression, a marker of normal neutrophil maturation, suggesting that inappropriate expression of the p120 gene can result in aberrant neutrophil maturation.

A minicircuitry comprised of microRNA-223 and transcription factors NFI-A and C/EBPalpha regulates human granulopoiesis

MicroRNAs play important roles in cell differentiation by acting as translational inhibitors of specific target genes. Here we show that human granulocytic differentiation is controlled by a regulatory circuitry involving miR-223 and two transcriptional factors, NFI-A and C/EBPalpha. The two factors compete for binding to the miR-223 promoter: NFI-A maintains miR-223 at low levels, whereas its replacement by C/EBPalpha, following retinoic acid (RA)-induced differentiation, upregulates miR-223 expression. The competition by C/EBPalpha and the granulocytic differentiation are favored by a negative-feedback loop in which miR-223 represses NFI-A translation. In line with this, both RNAi against NFI-A and ectopic expression of miR-223 in acute promyelocytic leukemia (APL) cells enhance differentiation, whereas miR-223 knockdown inhibits the differentiation response to RA. Altogether, our data indicate that miR-223 plays a crucial role during granulopoiesis and point to the NFI-A repression as an important molecular pathway mediating gene reprogramming in this cell lineage.

Transcription profiling of C/EBP targets identifies Per2 as a gene implicated in myeloid leukemia

CCAAT/enhancer-binding proteins (C/EBPs) are a family of transcription factors that regulate cell growth and differentiation in numerous cell types. To identify novel C/EBP-target genes, we performed transcriptional profiling using inducible NIH 3T3 cell lines expressing 1 of 4 members of the C/EBP family. Functional analysis revealed a previously unknown link between C/EBP proteins and circadian clock genes. Our microarray data showed that the expression levels of 2 core components of the circadian network, Per2 and Rev-Erbalpha, were significantly altered by C/EBPs. Recent studies suggested that Per2 behaves as a tumor suppressor gene in mice. Therefore, we focused our additional studies on Per2. We showed that Per2 expression is up-regulated by C/EBPalpha and C/EBPepsilon. Per2 levels were reduced in lymphoma cell lines and in acute myeloid leukemia (AML) patient samples. In addition, we generated stable K562 cells that expressed an inducible Per2 gene. Induction of Per2 expression resulted in growth inhibition, cell cycle arrest, apoptosis, and loss of clonogenic ability. These results suggest that Per2 is a downstream C/EBPalpha-target gene involved in AML, and its disruption might be involved in initiation and/or progression of AML.

Aberrant expression of neutrophil and macrophage-related genes in a murine model for human neutrophil-specific granule deficiency

Neutrophil-specific granule deficiency involves inheritance of germline mutations in the CCAAT/enhancer-binding protein epsilon (C/EBPE) gene. Humans and mice lacking active C/EBPepsilon suffer frequent bacterial infections as a result of functionally defective neutrophils and macrophages. We hypothesized that these defects reflected dysregulation of important immune response genes. To test this, gene expression differences of peritoneally derived neutrophils and macrophages from C/EBPepsilon-/- and wild-type mice were determined with DNA microarrays. Of 283 genes, 146 known genes and 21 expressed sequence tags (ESTs) were down-regulated, and 85 known genes and 31 ESTs were up-regulated in the C/EBP-/- mice. These included genes involved in cell adhesion/chemotaxis, cytoskeletal organization, signal transduction, and immune/inflammatory responses. The cytokines CC chemokine ligand 4, CXC chemokine ligand 2, and interleukin (IL)-6, as well as cytokine receptors IL-8RB and granulocyte-colony stimulating factor, were down-regulated. Chromatin immunoprecipitation analysis identified binding of C/EBPepsilon to their promoter regions. Increased expression for lipid metabolism genes apolipoprotein E (APOE), scavenger receptor class B-1, sorting protein-related receptor containing low-density lipoprotein receptor class A repeat 1, and APOC2 in the C/EBPepsilon-/- mice correlated with reduced total cholesterol levels in these mice before and after maintenance on a high-fat diet. Also, C/EBPepsilon-deficient macrophages showed a reduced capacity to accumulate lipids. In summary, dysregulation of numerous, novel C/EBPepsilon target genes impairs innate immune response and possibly other important biological processes mediated by neutrophils and macrophages.

Regulation of RANKL promoter activity is associated with histone remodeling in murine bone stromal cells

Receptor activator of NFkappa-B ligand (RANKL) is essential for osteoclast formation, function, and survival. Although RANKL mRNA and protein levels are modulated by 1,25(OH)2D3 and other osteoactive factors, regulatory mechanisms remain unclear. In this study, we show that 2 kb or 2 kb plus exon 1 of a RANKL promoter sequence conferred neither 1,25(OH)2D3 response nor tissue specificity. The histone deacetylase inhibitors trichostatin A (TSA) and sodium butyrate (SB), however, strongly increased RANKL promoter activity. A series of 5'-deleted RANKL promoter constructs from 2,020 to 110 bp showed fourfold increased activity after TSA treatment. TSA also dose dependently enhanced endogenous RANKL mRNA expression with 50 microM of TSA treatment causing equivalent RANKL expression to that seen with 1 nM 1,25(OH)2D3. Using a chromatin immunoprecipitation (ChIP) assay we showed that TSA significantly enhanced association of both acetylated histone H3 and H4 on the RANKL promoter, with H4 > H3. A similar increase in acetylated histone H4 on the RANKL gene locus was seen after 1,25(OH)2D3 treatment, but ChIP assay did not reveal localization of VDR/RXR heterodimers on the putative VDRE of the RANKL promoter. To explore the role of H4 acetylation of 1,25(OH)2D3 stimulated RANKL, we added both TSA and 1,25(OH)2D3 together. While the combination further increased acetylation of H4 on the RANKL locus, surprisingly, TSA inhibited 1,25(OH)2D3-induced RANKL mRNA expression by 70% at all doses of 1 ,25(OH)2D3 studied. These results suggest that TSA increases of endogenous expression of RANKL involve enhanced acetylation of histones on the proximal RANKL promoter. Preventing deacetylation, however, blocks 1,25(OH)2D3 action on this gene. Chromatin remodeling is therefore involved in RANKL expression.

Identification of genetic loci that interact with cut during Drosophila wing-margin development

The Drosophila selector gene cut is a hierarchal regulator of external sensory organ identity and is required to pattern the sensory and nonsensory cells of the wing margin. Cut performs the latter function, in part, by maintaining expression of the secreted morphogen encoded by wingless (wg). We find that Cut is required for wing-margin sensory organ specification in addition to and independently of Wg maintenance. In addition, we performed a genetic modifier screen to identify other genes that interact with cut in the regulation of wing-margin patterning. In total, 45 genetic loci (35 gain-of-function and 10 loss-of-function loci) were identified by virtue of their ability to suppress the wing-margin defects resulting from gypsy retrotransposon-mediated insulation of the cut wing-margin enhancer. Further genetic characterization identified several subgroups of candidate cut interacting loci. One group consists of putative regulators of gypsy insulator activity. A second group is potentially required for the regulation of Cut expression and/or activity and includes longitudinals lacking, a gene that encodes a family of BTB-domain zinc-finger transcription factors. A third group, which includes a component of the Brahma chromatin remodeling complex encoded by moira, affects the level of Cut expression in two opposing ways by suppressing the gypsy-mediated ct(K) phenotype and enhancing the non-gypsy ct(53d) phenotype. This suggests that the Brahma complex modulates both enhancer-controlled transcription and gypsy-mediated gene insulation of the cut locus.

Human neutrophil collagenase expression is C/EBP-dependent during myeloid development

OBJECTIVE

Human neutrophil collagenase (HNC) is one of several secondary granule proteins (SGP) expressed late in the myeloid maturation pathway. SGPs are encoded by unlinked and functionally diverse genes that are hypothesized to be coordinately regulated at the transcriptional level and demonstrate uniform dysregulation in leukemic cells. In support of the hypothesis that tissue and stage-specific expression of SGP genes is regulated by shared factor(s), we sought to identify factors responsible for positive regulation of the SGP genes.

METHODS

Using 5' deletion analysis, we identified a minimal HNC promoter located within the first 193 bp upstream of the transcription start site. Three CCAAT enhancer binding protein (C/EBP) sites were identified within this region and their functional importance was confirmed by mutational analysis, gel retardation, and oligonucleotide pulldown assays. Using chromatin immunoprecipitation (ChIP), we demonstrated that C/EBPalpha binds to the SGP gene promoters lactoferrin and HNC in nonexpressing cells. Upon induction of maturation, C/EBPalpha binds to these promoters and this binding correlates with the expression of both SGP genes.

CONCLUSION

We conclude that in the later stages of myeloid development, SGP genes are coordinately upregulated, and that members of the C/EBP family of transcription factors, in particular C/EBPalpha and C/EBPepsilon, play specific and unique roles in upregulating their expression.

Interleukin-6 and mevastatin regulate plasminogen activator inhibitor-1 through CCAAT/enhancer-binding protein-delta

OBJECTIVE

We sought to determine the etiologic mechanism of proinflammatory cytokine, interleukin-6 (IL-6), and statin as regulators of synthesis of plasminogen activator inhibitor-1 (PAI-1), the physiological fibrinolysis inhibitor and an acute-phase reactant.

METHODS AND RESULTS

Transient transfection and luciferase assay in HepG2 human hepatoma-derived cells demonstrated that IL-6 increased PAI-1 promoter activity and mevastatin decreased IL-6-inducible response. Systematic deletion assay of the promoter demonstrated that the region (-239 to -210 bp) containing a putative CCAAT/enhancer-binding protein (C/EBP) binding site was necessary. Point mutation in this site abolished the IL-6-inducible response. Electrophoretic mobility shift assay and chromatin immunoprecipitation assay demonstrated that C/EBPalpha, C/EBPbeta, and C/EBPdelta were involved in protein-DNA complex formation in intact cells. Deoxyribonuclease (DNase) I footprinting analysis revealed that 5' flanking region (-232 to -210 bp) is acute-phase response protein-binding site. C/EBPdelta binding activity was increased by IL-6 and attenuated by mevastatin. Mevastatin attenuated IL-6-mediated increase of C/EBPdelta protein in the nuclear extracts. IL-6 also increased PAI-1 and C/EBPdelta mRNA in mouse primary hepatocytes.

CONCLUSIONS

IL-6 increases hepatic PAI-1 expression mediated by the -232- to -210-bp region of the promoter containing a C/EBPdelta binding site. Vascular protection by statins may be partly mediated through regulation of CEBPdelta and consequent modulation of PAI-1 expression.

Repression and coactivation of CCAAT/enhancer-binding protein epsilon by sumoylation and protein inhibitor of activated STATx proteins

CCAAT/enhancer-binding protein epsilon (C/EBPepsilon) is a neutrophil-specific transcription factor whose activity is controlled by juxtaposed activating and regulatory domains. We previously determined that the function of the major regulatory domain (RD1) in C/EBPepsilon was dependent on the integrity of a five-amino acid motif that was identical to the recognition site for members of the small ubiquitin-like modifier (SUMO) family of ubiquitin-related proteins. We show here that the SUMO attachment site (the regulatory domain motif) is necessary and sufficient both for the intrinsic inhibitory function of RD1 and for coactivation by PIASxalpha and PIASxbeta, two members of the protein inhibitor of activated STAT (PIAS) family of SUMO E3 ligases. PIASxbeta was a more potent coactivator than PIASxalpha of both full-length C/EBPepsilon and fusion proteins containing the N-terminal portion of C/EBPepsilon, whereas PIASxalpha was more active on fusion proteins containing a heterologous activation domain. Two modes of coactivation were observed, one that was dependent on the integrity of the RING finger (RF) domain and was shared by both PIASxalpha and PIASxbeta and a second mode that was independent of the RF and was only observed with PIASxbeta. Sumoylation of C/EBPepsilon was enhanced by coexpression of PIASxalpha, suggesting that this modification is associated with the enhanced activity of the target protein. These results suggest that a complex interplay of accessory factors, including SUMO and PIAS proteins, modulates the activity of C/EBPepsilon.

The homeodomain protein CDP regulates mammary-specific gene transcription and tumorigenesis

The CCAAT-displacement protein (CDP) has been implicated in developmental and cell-type-specific regulation of many cellular and viral genes. We previously have shown that CDP represses mouse mammary tumor virus (MMTV) transcription in tissue culture cells. Since CDP-binding activity for the MMTV long terminal repeat declines during mammary development, we tested whether binding mutations could alter viral expression. Infection of mice with MMTV proviruses containing CDP binding site mutations elevated viral RNA levels in virgin mammary glands and shortened mammary tumor latency. To determine if CDP has direct effects on MMTV transcription rather than viral spread, virgin mammary glands of homozygous CDP-mutant mice lacking one of three Cut repeat DNA-binding domains (DeltaCR1) were examined by reverse transcription-PCR. RNA levels of endogenous MMTV as well as alpha-lactalbumin and whey acidic protein (WAP) were elevated. Heterozygous mice with a different CDP mutation that eliminated the entire C terminus and the homeodomain (DeltaC mice) showed increased levels of MMTV, beta-casein, WAP, and alpha-lactalbumin RNA in virgin mammary glands compared to those from wild-type animals. No differences in amounts of WDNM1, epsilon-casein, or glyceraldehyde-3-phosphate dehydrogenase RNA were observed between the undifferentiated mammary tissues from wild-type and mutant mice, indicating the specificity of this effect. These data show independent contributions of different CDP domains to negative regulation of differentiation-specific genes in the mammary gland.

Role of p38α Map Kinase in Type I Interferon Signaling

Multiple signaling pathways are activated during engagement of the Type I interferon (IFN) receptor to mediate biological responses, including the Jak-Stat and Rac1/p38 Map kinase signaling cascades. In the present study we sought to determine the functional relevance of the p38alpha isoform in IFN signaling, using cells from mouse embryos with targeted disruption of the p38alpha gene. Our data demonstrate that p38alpha activation is essential for Type I IFN-dependent transcriptional regulation via ISRE or GAS elements. On the other hand, the function of p38alpha is not required for IFN-dependent Ser727 or Tyr701 phosphorylation of Stat1 and does not impact on the formation of ISGF3 or SIF nuclear binding complexes. In efforts to identify downstream effectors of p38 that may mediate IFN-dependent transcriptional responses, we found that IFNalpha activates the kinase Msk1, a known regulator of histone phosphorylation and chromatin remodeling. In other studies, we demonstrate that Type I IFN-dependent activation of the kinases MapKapK-2 and MapKapK-3 is defective in the absence of p38alpha, while Type I IFN-dependent antiviral properties are decreased in cells with targeted disruption of the MapKapK-2 gene. Altogether, our data establish that the p38alpha Map kinase pathway regulates activation of downstream effectors that participate in the induction of IFN-dependent gene transcription, to mediate IFN-responses.

A panorama of lineage-specific transcription in hematopoiesis

The hematopoietic system consists of more than ten differentiated cell types, all of which are derived from a single type of hematopoietic stem cell. The accessibility and interest of this system have made it a model for understanding normal and abnormal differentiation of mammalian cells. Newer techniques have generated a mass of data that requires integrative approaches for analysis and interpretation. The traditional view of the differentiation program holds that a small number of regulators are involved in each stage of cell specification. However, this may not be the case. Recent analyses have shown that almost all substantial subsets of genes, including the set of broadly expressed transcription factors, are expressed in patterns that are unique for each lineage. Further, much of this difference between lineages can be captured in two-dimensional graphs. Understanding the biologic significance, mechanisms and constraints underlying these differences is a challenge for experimentalists and computational biologists alike.

G-CSF signaling can differentiate promyelocytes expressing a defective retinoic acid receptor: evidence for divergent pathways regulating neutrophil differentiation

Several lines of investigation suggest that granulocyte colony-stimulating factor (G-CSF) augments all-trans retinoic acid (ATRA)-induced neutrophil differentiation in acute promyelocytic leukemia (APL). We sought to characterize the relationship between G-CSF- and ATRA-mediated neutrophil differentiation. We established a G-CSF receptor-transduced promyelocytic cell line, EPRO-Gr, derived from the granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent EPRO cell line harboring a dominant-negative retinoic acid receptor alpha (RARalpha). In EPRO-Gr, neutrophil differentiation occurs either in GM-CSF upon addition of ATRA or upon induction with G-CSF alone. Transient transfection of EPRO-Gr cells with a RARE-containing reporter plasmid demonstrates increased activity in the presence of ATRA, but not G-CSF, while STAT3 phosphorylation occurs only in response to G-CSF. This suggests that ATRA-mediated differentiation of EPRO-Gr cells occurs via a RARE-dependent, STAT3-independent pathway, while G-CSF-mediated differentiation occurs via a RARE-independent, STAT3-dependent pathway. ATRA and G-CSF thus regulate differentiation by divergent pathways. We characterized these pathways in the APL cell line, NB4. ATRA induction of NB4 cells resulted in morphologic differentiation and up-regulation of C/EBPepsilon and G-CSFR, but not in STAT3 phosphorylation. The addition of G-CSF with ATRA during NB4 induction resulted in STAT3 phosphorylation but did not enhance differentiation. These results may elucidate how G-CSF and ATRA affect the differentiation of primary and ATRA-resistant APL cells.

Activation of protein kinase C delta by all-trans-retinoic acid

All-trans-retinoic acid (RA) is a potent inhibitor of leukemia cell proliferation and induces differentiation of acute promyelocytic leukemia cells in vitro and in vivo. For RA to induce its biological effects in target cells, binding to specific retinoic acid nuclear receptors is required. The resulting complexes bind to RA-responsive elements (RAREs) in the promoters of RA-inducible genes to initiate gene transcription and to generate protein products that mediate the biological effects of RA. In this report, we provide evidence that a member of the protein kinase C (PKC) family of proteins, PKC delta, is activated during RA treatment of the NB-4 and HL-60 acute myeloid leukemia cell lines as well as the MCF-7 breast cancer cell line. Such RA-dependent phosphorylation was also observed in primary acute promyelocytic leukemia cells and resulted in activation of the kinase domain of PKC delta. In studies aimed at understanding the functional relevance of PKC delta in the induction of RA responses, we found that pharmacological inhibition of PKC delta (but not of other PKC isoforms) diminished RA-dependent gene transcription via RAREs. On the other hand, overexpression of a constitutively active form of the kinase strongly enhanced RA-dependent gene transcription via RAREs. Gel shift assays and chromatin immunoprecipitation studies demonstrated that PKC delta associated with retinoic acid receptor-alpha and was present in an RA-inducible protein complex that bound to RAREs. Pharmacological inhibition of PKC delta activity abrogated the induction of cell differentiation and growth inhibition of NB-4 blast cells, demonstrating that its function is required for such effects. Altogether, our data provide strong evidence that PKC delta is activated in an RA-dependent manner and plays a critical role in the generation of the biological effects of RA in malignant cells.