The Sp1 transcription factor binds the CD11b promoter specifically in myeloid cells in vivo and is essential for myeloid-specific promoter activity

Inhibition of ERO1a and IDO1 improves dendritic cell infiltration into pancreatic ductal adenocarcinoma

Introduction

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal and treatment resistant cancers. Due to its desmoplastic and hypoxic nature along with an abundance of myeloid cell infiltration and scarce T cell infiltration, PDAC is considered a cold tumor.

Methods

Here we sought to investigate myeloid cell infiltration and composition in PDAC spheroids by targeting the hypoxia-associated pathways endoplasmic reticulum oxidoreductase 1 alpha (ERO1a) and indoleamine 2,3-dioxygenase 1 (IDO1). Using MiaPaCa2 spheroids with hypoxic core, we assessed the roles of ERO1a and IDO1 inhibition in modulating monocyte infiltration and differentiation, followed by characterizing immunomodulatory factors secreted using LC-MS/MS.

Results

Inhibition of ERO1a and IDO1 significantly improved monocyte infiltration and differentiation into dendritic cells. LC-MS/MS analysis of the PDAC spheroid secretome identified downregulation of hypoxia and PDAC pathways, and upregulation of antigen presentation pathways upon inhibition of ERO1a and IDO1. Furthermore, immunomodulatory factors involved in immune infiltration and migration including interleukin-8, lymphocyte cytosolic protein 1, and transgelin-2, were upregulated upon inhibition of ERO1a and IDO1.

Discussion

Collectively, our results show that inhibition of ERO1a and IDO1 modulates the tumor microenvironment associated with improved monocyte infiltration and differentiation into dendritic cells to potentially influence therapeutic responses in patients with PDAC.

Unraveling the structural aspects of the G-quadruplex in SMO promoter and elucidating its contribution in transcriptional regulation

We located a 25 nt G-rich sequence in the promoter region of SMO oncogene. We performed an array of biophysical and biochemical assays and confirmed the formation of a parallel G quadruplex (SMO1-GQ) by the identified sequence. SMO1-GQ is highly conserved in primates. For a comprehensive characterization of the SMO quadruplex structure, we have performed spectroscopic and in silico analysis with established GQ binder small molecules TMPyP4 and BRACO-19. We observed comparatively higher stable interaction of BRACO-19 with SMO1-GQ. Structure-based, rational drug design against SMO1-GQ to target SMO oncogene requires a detailed molecular anatomy of the G-quadruplex. We structurally characterised the SMO1-GQ using DMS footprinting assay and molecular modelling, docking, and MD simulation to identify the probable atomic regions that interact with either of the small molecules. We further investigated SMO1-GQ in vivo by performing chromatin immunoprecipitation (ChIP) assay. ChIP data revealed that this gene element functions as a scaffold for a number of transcription factors: specificity protein (Sp1), nucleolin (NCL), non-metastatic cell 2 (NM23-H2), cellular nucleic acid binding protein (CNBP), and heterogeneous nuclear ribonucleoprotein K (hnRNPK) which reflects the SMO1-P1 G-quadruplex to be the master regulator of SMO1 transcriptional activity. The strong binding interaction detected between SMO1-GQ and BRACO-19 contemplates the potential of the G quadruplex as a promising anti-cancer druggable target to downregulate SMO1 oncogene driven cancers.Communicated by Ramaswamy H. Sarma.

Specific innate immune cells uptake fetal antigen and display homeostatic phenotypes in the maternal circulation

Pregnancy represents a period when the mother undergoes significant immunological changes to promote tolerance of the fetal semi-allograft. Such tolerance results from the exposure of the maternal immune system to fetal antigens (Ags), a process that has been widely investigated at the maternal-fetal interface and in the adjacent draining lymph nodes. However, the peripheral mechanisms of maternal-fetal crosstalk are poorly understood. Herein, we hypothesized that specific innate immune cells interact with fetal Ags in the maternal circulation. To test this hypothesis, a mouse model was utilized in which transgenic male mice expressing the chicken ovalbumin (OVA) Ag under the beta-actin promoter were allogeneically mated with wild-type females to allow for tracking of the fetal Ag. Fetal Ag-carrying Ly6G+ and F4/80+ cells were identified in the maternal circulation, where they were more abundant in the second half of pregnancy. Such innate immune cells displayed unique phenotypes: while Ly6G+ cells expressed high levels of MHC-II and CD80 together with low levels of pro-inflammatory cytokines, F4/80+ cells up-regulated the expression of CD86 as well as the anti-inflammatory cytokines IL-10 and TGF-β. In vitro studies using allogeneic GFP+ placental particles revealed that maternal peripheral Ly6G+ and F4/80+ cells phagocytose fetal Ags in mid and late murine pregnancy. Importantly, cytotrophoblast-derived particles were also engulfed in vitro by CD15+ and CD14+ cells from women in the second and third trimester, providing translational evidence that this process also occurs in humans. Collectively, this study demonstrates novel interactions between specific maternal circulating innate immune cells and fetal Ags, thereby shedding light on the systemic mechanisms of maternal-fetal crosstalk.

Promoter G-quadruplexes and transcription factors cooperate to shape the cell type-specific transcriptome

Cell identity is maintained by activation of cell-specific gene programs, regulated by epigenetic marks, transcription factors and chromatin organization. DNA G-quadruplex (G4)-folded regions in cells were reported to be associated with either increased or decreased transcriptional activity. By G4-ChIP-seq/RNA-seq analysis on liposarcoma cells we confirmed that G4s in promoters are invariably associated with high transcription levels in open chromatin. Comparing G4 presence, location and transcript levels in liposarcoma cells to available data on keratinocytes, we showed that the same promoter sequences of the same genes in the two cell lines had different G4-folding state: high transcript levels consistently associated with G4-folding. Transcription factors AP-1 and SP1, whose binding sites were the most significantly represented in G4-folded sequences, coimmunoprecipitated with their G4-folded promoters. Thus, G4s and their associated transcription factors cooperate to determine cell-specific transcriptional programs, making G4s to strongly emerge as new epigenetic regulators of the transcription machinery.

Single-molecule imaging of transcription dynamics in somatic stem cells

Molecular noise is a natural phenomenon that is inherent to all biological systems1,2. How stochastic processes give rise to the robust outcomes that support tissue homeostasis remains unclear. Here we use single-molecule RNA fluorescent in situ hybridization (smFISH) on mouse stem cells derived from haematopoietic tissue to measure the transcription dynamics of three key genes that encode transcription factors: PU.1 (also known as Spi1), Gata1 and Gata2. We find that infrequent, stochastic bursts of transcription result in the co-expression of these antagonistic transcription factors in the majority of haematopoietic stem and progenitor cells. Moreover, by pairing smFISH with time-lapse microscopy and the analysis of pedigrees, we find that although individual stem-cell clones produce descendants that are in transcriptionally related states-akin to a transcriptional priming phenomenon-the underlying transition dynamics between states are best captured by stochastic and reversible models. As such, a stochastic process can produce cellular behaviours that may be incorrectly inferred to have arisen from deterministic dynamics. We propose a model whereby the intrinsic stochasticity of gene expression facilitates, rather than impedes, the concomitant maintenance of transcriptional plasticity and stem cell robustness.

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.

Regulation of CD11b by HIF-1α and the STAT3 signaling pathway contributes to the immunosuppressive function of B cells in inflammatory bowel disease

B cells have been reported to have a suppressive function in autoimmune diseases, which appears to require an increase of CD11b expression on B cells. However, little is known how CD11b is induced in B cells to play the function. In this study, we found that the high expression of CD11b in B cells occurred not only in the mucosal immune organs, but also in systemically immune organs such as the spleen during dextran sulfate sodium (DSS)-induced colitis. Since the inflammatory lesions in mouse models of inflammatory bowel disease (IBD) were revealed to be significantly hypoxic or even anoxic, the B cells from colitic mice Peyer's patches (PP) were investigated to express higher levels of hypoxia-inducible factor-1α (HIF-1α) than naïve B cells from wildtype (WT) mice. HIF-1α siRNA transfection or HIF-1α protein inhibition led to decreased CD11b expression at both the mRNA and protein levels in vitro. B cells with HIF-1α specific knockdown were then adoptively transferred to Rag-1^-/- mice. The result displayed that CD11b expression was decreased in B cells and an exacerbated colitis occurred. The bio-informatics promoter analysis and ChIP assay showed that HIF-1α was the critical transcription factor for CD11b and cooperatively formed a complex with the p-STAT3 homodimers to bind onto hypoxia-responsive element (HRE) regions, which was guaranteed by MEK/ERK pathway activation and IL-10 secretion. In conclusion, our study demonstrated the key function of the hypoxia-associated transcription factor HIF-1α together with p-STAT3 in driving CD11b transcription in B cells and controlling B cell's protective activity in experimental inflammatory bowel disease (IBD).

Rapid screening of anti-tumor metastasis drugs targeting integrin macrophage antigen-1 using immobilized cell capillary electrophoresis

In this research a method called immobilized cell capillary electrophoresis (ICCE) was established under approximately physiological conditions for rapid screening of anti-tumor metastasis drugs targeting integrin macrophage antigen-1 (MAC-1). In this method, separation and purification of the target receptors on cell membranes was unnecessary, thus, maintaining their natural conformation and bioactivity. MAC-1-, CD11b-, or CD18-overexpressing HEK293 cells (human embryonic kidney) were cultured and immobilized on the inner wall of capillaries as stationary phase, and their interactions with lactosyl derivative Gu-4 (positive control)/dimethylsulfoxide (DMSO; negative control) were studied using ICCE. Using this method, 29 phenylethanoid glycosides from Cistanches Herba were screened, and the binding kinetic parameters (K, ka, kd, and k') of active compounds were calculated, and the specific subunits of MAC-1 were determined. Then, molecular docking studies were performed to discover the direct interaction sites between active compounds and MAC-1, and the order of Glide-calculated Emodel value obtained from the molecular docking study is consistent with that of the binding constants obtained using ICCE. Finally, pharmaceutical efficacy assays in vitro and in vivo were carried out to show that the anti-tumor metastasis activity of the active compound had better pharmaceutical efficacy and lower toxic side effects. The method was verified to be valid and practical for further use, and it is expected that it will be transferred to capillary array electrophoresis for use in high-throughput drug screening.

A novel ASXL1-OGT axis plays roles in H3K4 methylation and tumor suppression in myeloid malignancies

ASXL1 plays key roles in epigenetic regulation of gene expression through methylation of histone H3K27, and disruption of ASXL1 drives myeloid malignancies, at least in part, via derepression of posterior HOXA loci. However, little is known about the identity of proteins that interact with ASXL1 and about the functions of ASXL1 in modulation of the active histone mark, such as H3K4 methylation. In this study, we demonstrate that ASXL1 is a part of a protein complex containing HCFC1 and OGT; OGT directly stabilizes ASXL1 by O-GlcNAcylation. Disruption of this novel axis inhibited myeloid differentiation and H3K4 methylation as well as H2B glycosylation and impaired transcription of genes involved in myeloid differentiation, splicing, and ribosomal functions; this has implications for myelodysplastic syndrome (MDS) pathogenesis, as each of these processes are perturbed in the disease. This axis is responsible for tumor suppression in the myeloid compartment, as reactivation of OGT induced myeloid differentiation and reduced leukemogenecity both in vivo and in vitro. Our data also suggest that MLL5, a known HCFC1/OGT-interacting protein, is responsible for gene activation by the ASXL1-OGT axis. These data shed light on the novel roles of the ASXL1-OGT axis in H3K4 methylation and activation of transcription.

ZNF143 protein is an important regulator of the myeloid transcription factor C/EBPα

The transcription factor C/EBPα is essential for myeloid differentiation and is frequently dysregulated in acute myeloid leukemia. Although studied extensively, the precise regulation of its gene by upstream factors has remained largely elusive. Here, we investigated its transcriptional activation during myeloid differentiation. We identified an evolutionarily conserved octameric sequence, CCCAGCAG, ∼100 bases upstream of the CEBPA transcription start site, and demonstrated through mutational analysis that this sequence is crucial for C/EBPα expression. This sequence is present in the genes encoding C/EBPα in humans, rodents, chickens, and frogs and is also present in the promoters of other C/EBP family members. We identified that ZNF143, the human homolog of the Xenopus transcriptional activator STAF, specifically binds to this 8-bp sequence to activate C/EBPα expression in myeloid cells through a mechanism that is distinct from that observed in liver cells and adipocytes. Altogether, our data suggest that ZNF143 plays an important role in the expression of C/EBPα in myeloid cells.

Estrogen Receptor-Dependent Regulation of Dendritic Cell Development and Function

Autoimmunity, infectious diseases and cancer affect women and men differently. Because they tend to develop more vigorous adaptive immune responses than men, women are less susceptible to some infectious diseases but also at higher risk of autoimmunity. The regulation of immune responses by sex-dependent factors probably involves several non-redundant mechanisms. A privileged area of study, however, concerns the role of sex steroid hormones in the biology of innate immune cells, especially dendritic cells (DCs). In recent years, our understanding of the lineage origin of DC populations has expanded, and the lineage-committing transcription factors shaping peripheral DC subsets have been identified. Both progenitor cells and mature DC subsets express estrogen receptors (ERs), which are ligand-dependent transcription factors. This suggests that estrogens may contribute to the reported sex differences in immunity by regulating DC biology. Here, we review the recent literature and highlight evidence that estrogen-dependent activation of ERα regulates the development or the functional responses of particular DC subsets. The in vitro model of GM-CSF-induced DC differentiation shows that CD11c⁺ CD11b^int Ly6c^neg cells depend on ERα activation by estrogen for their development, and for the acquisition of competence to activate naive CD4⁺ T lymphocytes and mount a robust pro-inflammatory cytokine response to CD40 stimulation. In this model, estrogen signaling in conjunction with GM-CSF is necessary to promote early interferon regulatory factor (Irf)-4 expression in macrophage-DC progenitors and their subsequent differentiation into IRF-4^hi CD11c⁺ CD11b^int Ly6c^neg cells, closely related to the cDC2 subset. The Flt3L-induced model of DC differentiation in turn shows that ERα signaling promotes the development of conventional DC (cDC) and plasmacytoid DC (pDC) with higher capability of pro-inflammatory cytokine production in response to TLR stimulation. Likewise, cell-intrinsic ER signaling positively regulates the TLR-driven production of type I interferons (IFNs) in mouse pDCs in vivo. This effect of estrogens likely contributes to the greater proficiency of women's pDCs than men's as regards the production of type I IFNs elicited by TLR7 ligands. In summary, evidence is emerging in support of the notion that estrogen signaling regulates important aspects of cDC and pDC development and/or effector functions, in both mice and humans.

Rescuing failed oral implants via Wnt activation

AIM

Implant osseointegration is not always guaranteed and once fibrous encapsulation occurs clinicians have few options other than implant removal. Our goal was to test whether a WNT protein therapeutic could rescue such failed implants.

MATERIAL AND METHODS

Titanium implants were placed in over-sized murine oral osteotomies. A lack of primary stability was verified by mechanical testing. Interfacial strains were estimated by finite element modelling and histology coupled with histomorphometry confirmed the lack of peri-implant bone. After fibrous encapsulation was established peri-implant injections of a liposomal formulation of WNT3A protein (L-WNT3A) or liposomal PBS (L-PBS) were then initiated. Quantitative assays were employed to analyse the effects of L-WNT3A treatment.

RESULTS

Implants in gap-type interfaces exhibited high interfacial strains and no primary stability. After verification of implant failure, L-WNT3A or L-PBS injections were initiated. L-WNT3A induced a rapid, significant increase in Wnt responsiveness in the peri-implant environment, cell proliferation and osteogenic protein expression. The amount of peri-implant bone and bone in contact with the implant were significantly higher in L-WNT3A cases.

CONCLUSIONS

These data demonstrate L-WNT3A can induce peri-implant bone formation even in cases where fibrous encapsulation predominates.

The heteromeric transcription factor GABP activates the ITGAM/CD11b promoter and induces myeloid differentiation

The heteromeric transcription factor GA-binding protein (GABP) consists of two subunits, the alpha subunit (GABPA) carrying the DNA-binding ETS domain, and the beta subunit (GABPB1) harbouring the transcriptional activation domain. GABP is involved in haematopoietic stem cell maintenance and differentiation of myeloid and lymphoid lineages in mice. To elucidate the molecular function of GABP in human haematopoiesis, the present study addressed effects of ectopic overexpression of GABP focussing on the myeloid compartment. Combined overexpression of GABPA and GABPB1 caused a proliferation block in cell lines and drastically reduced the colony-forming capacity of murine lineage-negative cells. Impaired proliferation resulted from perturbed cellular cycling and induction of myeloid differentiation shown by surface markers and myelomonocytic morphology of U937 cells. Depending on the dosage and functional integrity of GABP, ITGAM expression was induced. ITGAM encodes CD11b, the alpha subunit of integrin Mac-1, whose beta subunit, ITGB2/CD18, was already described to be regulated by GABP. Finally, Shield1-dependent proteotuning, luciferase reporter assays and chromatin immunoprecipitation showed that GABP activates the ITGAM/CD11b promoter via three binding sites close to the translational start site. In conclusion, the present study supports the crucial role of GABP in myeloid cell differentiation and identified ITGAM/CD11b as a novel GABP target gene.

Leukocyte β7 integrin targeted by Krüppel-like factors

Constitutive expression of Krüppel-like factor 3 (KLF3, BKLF) increases marginal zone (MZ) B cell numbers, a phenotype shared with mice lacking KLF2. Ablation of KLF3, known to interact with serum response factor (SRF), or SRF itself, results in fewer MZ B cells. It is unknown how these functional equivalences result. In this study, it is shown that KLF3 acts as transcriptional repressor for the leukocyte-specific integrin β7 (Itgb7, Ly69) by binding to the β7 promoter, as revealed by chromatin immunoprecipitation. KLF2 overexpression antagonizes this repression and also binds the β7 promoter, indicating that these factors may compete for target sequence(s). Whereas β7 is identified as direct KLF target, its repression by KLF3 is not connected to the MZ B cell increase because β7-deficient mice have a normal complement of these and the KLF3-driven increase still occurs when β7 is deleted. Despite this, KLF3 overexpression abolishes lymphocyte homing to Peyer's patches, much like β7 deficiency does. Furthermore, KLF3 expression alone overcomes the MZ B cell deficiency when SRF is absent. SRF is also dispensable for the KLF3-mediated repression of β7. Thus, despite the shared phenotype of KLF3 and SRF-deficient mice, cooperation of these factors appears neither relevant for the formation of MZ B cells nor for the regulation of β7. Finally, a potent negative regulatory feedback loop limiting KLF3 expression is shown in this study, mediated by KLF3 directly repressing its own gene promoter. In summary, KLFs use regulatory circuits to steer lymphocyte maturation and homing and directly control leukocyte integrin expression.

Curcumin Suppresses Metastasis via Sp-1, FAK Inhibition, and E-Cadherin Upregulation in Colorectal Cancer

Colorectal cancer (CRC) is a serious public health problem that results due to changes of diet and various environmental stress factors in the world. Curcumin is a traditional medicine used for treatment of a wide variety of tumors. However, antimetastasis mechanism of curcumin on CRC has not yet been completely investigated. Here, we explored the underlying molecular mechanisms of curcumin on metastasis of CRC cells in vitro and in vivo. Curcumin significantly inhibits cell migration, invasion, and colony formation in vitro and reduces tumor growth and liver metastasis in vivo. We found that curcumin suppresses Sp-1 transcriptional activity and Sp-1 regulated genes including ADEM10, calmodulin, EPHB2, HDAC4, and SEPP1 in CRC cells. Curcumin inhibits focal adhesion kinase (FAK) phosphorylation and enhances the expressions of several extracellular matrix components which play a critical role in invasion and metastasis. Curcumin reduces CD24 expression in a dose-dependent manner in CRC cells. Moreover, E-cadherin expression is upregulated by curcumin and serves as an inhibitor of EMT. These results suggest that curcumin executes its antimetastasis function through downregulation of Sp-1, FAK, and CD24 and by promoting E-cadherin expression in CRC cells.

Cell-Type Specific Determinants of NRAMP1 Expression in Professional Phagocytes

The Natural resistance-associated macrophage protein 1 (Nramp1 or Solute carrier 11 member 1, Slc11a1) transports divalent metals across the membrane of late endosomes and lysosomes in professional phagocytes. Nramp1 represents an ancient eukaryotic cell-autonomous defense whereas the gene duplication that yielded Nramp1 and Nramp2 predated the origin of Sarcopterygians (lobe-finned fishes and tetrapods). SLC11A1 genetic polymorphisms associated with human resistance to tuberculosis consist of potential regulatory variants. Herein, current knowledge of the regulation of SLC11A1 gene expression is reviewed and comprehensive analysis of ENCODE data available for hematopoietic cell-types suggests a hypothesis for the regulation of SLC11A1 expression during myeloid development and phagocyte functional polarization. SLC11A1 is part of a 34.6 kb CTCF-insulated locus scattered with predicted regulatory elements: a 3' enhancer, a large 5' enhancer domain and four elements spread around the transcription start site (TSS), including several C/EBP and PU.1 sites. SLC11A1 locus ends appear mobilized by ETS-related factors early during myelopoiesis; activation of both 5' and 3' enhancers in myelo-monocytic cells correlate with transcription factor binding at the TSS. Characterizing the corresponding cis/trans determinants functionally will establish the mechanisms involved and possibly reveal genetic variation that impacts susceptibility to infectious or immune diseases.

Epigenetic regulation of CD133/PROM1 expression in glioma stem cells by Sp1/myc and promoter methylation

Tumor stem cells, postulated to be the source cells for malignancies, have been identified in several cancers using cell-surface expression of markers including CD133, a pentaspan membrane protein. CD133+ve cells form neurospheres, exhibit self-renewal and differentiation, and are tumorigenic. However, despite its association with stem cells, a causal relationship of CD133 to tumorigenesis remains to be defined. Hypothesizing that specific epigenetic and transcription factors implicated in driving the stem cell state may concurrently regulate CD133 expression in stem cells, we analyzed the structure and regulation of CD133 promoter in glioma stem cells and glioma cell lines. Initially, a minimal promoter region was identified by analyzing the activity of CD133 promoter-driven luciferase-expressing 5'-and 3'-deletion-constructs upstream of the transcription start site. This region contained a CpG island that was hypermethylated in CD133-ve glioma stem cells (GSC) and glioma cells but unmethylated in CD133+ve ones. Of several predicted TF-binding sites in this region, the role of tandem Sp1 (-242 and -221) and two Myc (-541 and -25)-binding sites were examined. Overexpression of Sp1 or Myc increased CD133 minimal promoter-driven luciferase activity and CD133 levels in GSC and in glioma cell line. Mithramycin, a Sp1 inhibitor, decreased minimal promoter activity and downregulated CD133 levels in GSC. Gel-shift assays demonstrated direct binding of Sp1 to their predicted sites that was competitively inhibited by oligonucleotide-binding-site sequences and supershifted by anti-Sp1 confirming the interaction. Sp1 and Myc-antibody chromatin immunoprecipitation (ChIP) analysis in GSC showed enrichment of regions with Sp1 and Myc-binding sites. In CD133-ve cells, ChIP analysis showed binding of the methyl-DNA-binding proteins, MBD1, MBD2 and MeCP2 to the methylated CpG island and repression of transcription. These results demonstrate that Sp1 and Myc regulate CD133 transcription in GSC and that promoter methylation and methyl-DNA-binding proteins cause repression of CD133 by excluding transcription-factor binding.

Palmitate promotes monocyte atherogenicity via de novo ceramide synthesis

Elevated plasma free fatty acids (FAs) are associated with increased risk of cardiovascular disease. This study investigates the effects of the saturated FA palmitate and unsaturated FA oleate on monocyte phenotype and function. Incubation of human U937 and THP-1 monocytes with palmitate for 24h increased cell surface expression of integrin CD11b and scavenger receptor CD36 in a concentration-dependent manner with some decrease in mitochondrial reducing capacity at high concentration (300 μM). Monocytes incubated with palmitate, but not oleate, showed increased uptake of oxidized LDL and increased adhesion to rat aortic endothelium, particularly at bifurcations. The palmitate-induced increase in CD11b and CD36 expression was associated with increased cellular C16 ceramide and sphingomyelin, loss of reduced glutathione, and increased reactive oxygen species (ROS). Increased monocyte surface CD11b and CD36 was inhibited by fumonisin B1, an inhibitor of de novo ceramide synthesis, but not by the superoxide dismutase mimetic MnTBap. In contrast, MnTBap prevented the mitochondrial ROS increase and metabolic inhibition due to 300μM palmitate. This study demonstrates that in viable monocytes, palmitate but not oleate increases expression of surface CD11b and CD36. Palmitate increases monocyte adhesion to the aortic wall and promotes uptake of oxidized LDL and this involves de novo ceramide synthesis.

Vitamin D3-driven signals for myeloid cell differentiation--implications for differentiation therapy

Primitive myeloid leukemic cell lines can be driven to differentiate to monocyte-like cells by 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), and, therefore, 1,25(OH)(2)D(3) may be useful in differentiation therapy of myeloid leukemia and myelodysplastic syndromes (MDS). Recent studies have provided important insights into the mechanism of 1,25(OH)(2)D(3)-stimulated differentiation. For myeloid progenitors to complete monocytic differentiation a complex network of intracellular signals has to be activated and/or inactivated in a precise temporal and spatial pattern. 1,25(OH)(2)D(3) achieves this change to the 'signaling landscape' by (i) direct genomic modulation of the level of expression of key regulators of cell signaling and differentiation pathways, and (ii) activation of intracellular signaling pathways. An improved understanding of the mode of action of 1,25(OH)(2)D(3) is facilitating the development of new therapeutic regimens.

Activation of the Jak3 pathway and myeloid differentiation

Although the role of Jak3 in lymphoid development has been well-characterized, increasing evidence demonstrates that activation of the Jak3 pathway plays an important role in myeloid differentiation as well. Overexpression of Jak3 in murine myeloid 32Dcl3 cells has been shown to result in an acceleration of granulocytic differentiation induced by G-CSF. Early onset of G1 cell cycle arrest along with upregulation of the cyclin dependent kinase inhibitor p27Kip1 and downregulation of Cdk2, Cdk4, Cdk6, and Cyclin E has also been observed in Jak3-overexpressing 32Dcl3 cells. In addition, Jak3 overexpression in normal mouse bone marrow cells results in accelerated granulocytic and monocytic differentiation in response to GM-CSF, while pharmacological inhibition of Jak3 results in a block to GM-CSF-induced colony formation in normal mouse bone marrow cells. Jak3 is unique among the members of the Jak kinase family in that it is inducibly expressed and is a target for regulation at the level of transcription. Recent studies have demonstrated that upregulation of Jak3 during myeloid differentiation is achieved through the cooperative action of Sp1 and STAT3, consistent with evidence indicative of a crucial role for STAT3 in myeloid differentiation. These results suggest that cytokine-inducible activation of Jak3 plays a critical role in integrating the processes of growth arrest and differentiation of myeloid cells.

Myeloid cell differentiation in response to calcitriol for expression CD11b and CD14 is regulated by myeloid zinc finger-1 protein downstream of phosphatidylinositol 3-kinase

Immature cells of the mononuclear phagocyte series differentiate in response to calcitriol. This is accompanied by increased expression of both CD11b and CD14 and has been shown to be phosphatidylinositol 3-kinase (PI3K) dependent. The events downstream of PI3K that regulate mononuclear phagocyte gene expression, however, remain to be fully understood. In the present study, we show that incubation of THP-1 cells with calcitriol brings about activation of the myeloid zinc finger-1 (MZF-1) transcription factor dependent upon PI3K. In addition, we show that the proximal promoter regions of both CD11b and CD14 contain functional MZF-1 binding sites that are calcitriol responsive. Site-directed mutagenesis of the putative MZF-1 elements abolished MZF-1 binding to the promoters of both CD11b and CD14. Not only did calcitriol treatment increase MZF-1 DNA binding activity to these sites, but it also up-regulated cellular levels of MZF-1. Silencing of MZF-1 resulted in a markedly blunted response to calcitriol for induction of both CD11b and CD14 mRNA transcript levels. Cell surface expression of CD11b and CD14 was also reduced, but to a lesser extent. Taken together, these results show that MZF-1 is involved downstream of PI3K in a calcitriol-induced signaling pathway leading to myeloid cell differentiation and activation of CD11b and CD14.

Estrogen receptor alpha, but not beta, is required for optimal dendritic cell differentiation and [corrected] CD40-induced cytokine production

Dendritic cells (DC) are critical actors in the initiation of primary immune responses and regulation of self-tolerance. The steroid sex hormone 17beta-estradiol (E(2)) has been shown to promote the differentiation of DCs from bone marrow (BM) precursors in vitro. However, the estrogen receptor (ER) involved in this effect has not yet been characterized. Using recently generated ERalpha- or ERbeta-deficient mice, we investigated the role of ER isotypes in DC differentiation and acquisition of effector functions. We report that estrogen-dependent activation of ERalpha, but not ERbeta, is required for normal DC development from BM precursors cultured with GM-CSF. We show that reduced numbers of DCs were generated in the absence of ERalpha activation and provide evidence for a cell-autonomous function of ERalpha signaling in DC differentiation. ERalpha-deficient DCs were phenotypically and functionally distinct from wild-type DCs generated in the presence of estrogens. In response to microbial components, ERalpha-deficient DCs failed to up-regulate MHC class II and CD86 molecules, which could account for their reduced capacity to prime naive CD4(+) T lymphocytes. Although they retained the ability to express CD40 and to produce proinflammatory cytokines (e.g., IL-12, IL-6) upon TLR engagement, ERalpha-deficient DCs were defective in their ability to secrete such cytokines in response to CD40-CD40L interactions. Taken together, these results provide the first genetic evidence that ERalpha is the main receptor regulating estrogen-dependent DC differentiation in vitro and acquisition of their effector functions.

Transcriptional control of human T-BET expression: the role of Sp1

Murine T-bet (T-box expressed in T cells) is a master regulator of IFN-gamma gene expression in NK and T cells. T-bet also plays a critical role in autoimmunity, asthma and other diseases. However, cis elements or trans factors responsible for regulating T-bet expression remain largely unknown. Here, we report on our discovery of six Sp1-binding sites within the proximal human T-BET promoter that are highly conserved among mammalian species. Electrophoretic mobility shift assays demonstrate a physical association between Sp1 and the proximal T-BET promoter with a direct dose response between Sp1 expression and T-BET promoter activity. Ectopic overexpression of Sp1 also enhanced T-BET expression and cytokine-induced IFN-gamma secretion in NK cells and T cells. Mithramycin A, which blocks the binding of Sp1 to the T-BET promoter, diminished both T-BET expression and IFN-gamma protein production in monokine-stimulated primary human NK cells. Collectively, our results suggest that Sp1 is a positive transcriptional regulator of T-BET. As T-BET and IFN-gamma are critically important in inflammation, infection, and cancer, targeting Sp1, possibly with mithramycin A, may be useful for preventing and/or treating diseases associated with aberrant T-BET or IFN-gamma expression.

Identification of Pur alpha as a new hypoxia response factor responsible for coordinated induction of the beta 2 integrin family

Central to the process of inflammation are hypoxic conditions that lead to the binding of circulating leukocytes to the endothelium. We have previously shown that such binding is mediated by monocytes being able to directly sense hypoxic conditions and respond by inducing their surface expression of the beta(2) integrin family of adhesion molecules. In this study, we show that coordinated induction of the beta(2) integrins during direct hypoxia-sensing occurs through transcriptional activation of each of the genes by which they are encoded. Certain of the molecular mechanisms that mediate this activation in transcription are dependent upon hypoxia-inducible factor-1 (HIF-1), whereas others are HIF-1 independent. In search of these HIF-1-independent mechanisms, we identified Pur alpha as a new hypoxia-response factor. Binding of Pur alpha to the HIF-1-independent beta(2) integrin promoters is induced by hypoxia and mutagenesis of these Pur alpha-binding sites almost completely abolishes the ability of the promoters to respond to hypoxic conditions. Additional studies using siRNA directed against Pur alpha also revealed a loss in the hypoxic response of the beta(2) integrin promoters. Taken together, our findings demonstrate that hypoxia induces a coordinated up-regulation in beta(2) integrin expression that is dependent upon transcriptional mechanisms mediated by HIF-1 and Pur alpha.

Identifying cis-regulatory elements by statistical analysis and phylogenetic footprinting and analyzing their coexistence and related gene ontology

Discovery of cis-regulatory elements in gene promoters is a highly challenging research issue in computational molecular biology. This paper presents a novel approach to searching putative cis-regulatory elements in human promoters by first finding 8-mer sequences of high statistical significance from gene promoters of humans, mice, and Drosophila melanogaster, respectively, and then identifying the most conserved ones across the three species (phylogenetic footprinting). In this study, a conservation analysis on both closely related species (humans and mice) and distantly related species (humans/mice and Drosophila) is conducted not only to examine more candidates but also to improve the prediction accuracy. We have found 124 putative cis-regulatory elements and grouped these into 20 clusters. The investigation on the coexistence of these clusters in human gene promoters reveals that SP1, EGR, and NRF-1 are the dominant clusters appearing in the combinatorial combination of up to five clusters. Gene Ontology (GO) analysis also shows that many GO categories of transcription factors binding to these cis-regulatory elements match the GO categories of genes whose promoters contain these elements. Compared with previous research, the contribution of this study lies not only in the finding of new cis-regulatory elements, but also in its pioneering exploration on the coexistence of discovered elements and the GO relationship between transcription factors and regulated genes. This exploration verifies the putative cis-regulatory elements that have been found from this study and also gives new insight on the regulation mechanisms of gene expression.

Granulocyte colony-stimulating factor-induced upregulation of Jak3 transcription during granulocytic differentiation is mediated by the cooperative action of Sp1 and Stat3

We previously demonstrated that Jak3 is a primary response gene for G-CSF and ectopic overexpression of Jak3 can accelerate granulocytic differentiation of normal mouse bone marrow cells induced by G-CSF and GM-CSF. To gain insight into the regulation of G-CSF-induced transcription of Jak3, we constructed deletion and linker scanning mutants of the Jak3 promoter sequences and performed luciferase reporter assays in the murine myeloid cell line 32Dcl3, with and without G-CSF stimulation. These experiments showed that mutation of a -67 to -85 element, which contained a putative Sp1 binding site, or mutation of a -44 to -53 GAS element resulted in a marked reduction of Jak3 promoter activity. Electrophoretic mobility shift assays revealed that Sp1 and Stat3 present in nuclear lysates of 32Dcl3 cells stimulated with G-CSF can bind to the -67 to -85 element and -44 to -53 GAS element, respectively. In addition, cotransfection of a constitutively active mutant of Stat3 along with a Jak3 promoter/luciferase reporter resulted in enhanced Jak3 promoter activity. Together, these results demonstrate that activation of Jak3 transcription during G-CSF- induced granulocytic differentiation is mediated by the combined action of Sp1 and Stat3, a mechanism also shown to be important in IL-6-induced monocytic differentiation.

Characterization of a novel, cytokine-inducible carboxypeptidase D isoform in haematopoietic tumour cells

CPD-N is a cytokine-inducible CPD (carboxypeptidase-D) isoform identified in rat Nb2 T-lymphoma cells. The prototypic CPD (180 kDa) has three CP domains, whereas CPD-N (160 kDa) has an incomplete N-terminal domain I but intact domains II and III. CPD processes polypeptides in the TGN (trans-Golgi network) but the Nb2 CPD-N is nuclear. The present study identified a cryptic exon 1', downstream of exon 1 of the rat CPD gene, as an alternative transcription start site that encodes the N-terminus of CPD-N. Western-blot analysis showed exclusive synthesis of the 160 kDa CPD-N in rat Nb2 and Nb2-Sp lymphoma cells. Several haematopoietic cell lines including human K562 myeloma, Jurkat T-lymphoma and murine CTLL-2 cytotoxic T-cells express a 160 kDa CPD-immunoreactive protein, whereas mEL4 T-lymphoma cells express the 180 kDa CPD. The CPD-immunoreactive protein in hK562 cells is also nuclear and cytokine-inducible. In contrast, MCF-7 breast cancer cells express only the 180 kDa CPD, which is mainly in the TGN. CPD/CPD-N assays using substrate dansyl-L-alanyl-L-arginine show approx. 98% of CPD-N activity in the Nb2 nucleus, whereas MCF-7 CPD activity is enriched in the post-nuclear 10000 g pellet. The K(m) for CPD-N and CPD are 132+/-30 and 63+/-9 microM respectively. Specific activity/K(m) ratios show that dansyl-L-alanyl-L-arginine is a better substrate for CPD-N than for CPD. CPD-N has an optimal pH of 5.6 (due to domain II), whereas CPD has activity peaks at pH 5.6 (domain II) and pH 6.5-7.0 (domain I). CPD and CPD-N are inhibited non-competitively by zinc chelator 1,10-phenanthroline and competitively by peptidomimetic inhibitor DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid. The Nb2 CPD-N co-immunoprecipitated with phosphatase PP2A (protein phosphatase 2A) and alpha4 phosphoprotein. In summary, a cytokine-inducible CPD-N is selectively expressed in several haematopoietic tumour cells. Nuclear CPD-N is enzymatically active and interacts with known partners of CPD.

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)

Characterization of the mouse myeloid-associated differentiation marker (MYADM) gene: promoter analysis and protein localization

Hematopoietic differentiation is a complex process involving many genes inducing functional changes and characteristics of different cell lineages. To understand this process, it is important to identify genes involved in lineage commitment and maturation of hematopoietic progenitor cells. Recently we isolated the novel gene MYADM which is strongly up-regulated as multipotent progenitor cells differentiate towards myeloid cells. Because it is not expressed in lymphocytes, understanding the transcriptional control of MYADM could further explain differences in gene expression between myeloid and lymphoid cells. To identify regulatory elements controlling its restricted expression, we have analyzed the 5'-flanking region of the MYADM gene. The proximal promoter was found to lack both TATA and CCAAT boxes, but contained several potential binding sites for both ubiquitous and myeloid-specific transcription factors. Maximal promoter activity was contained within 800 bp from the tentative transcription initiation site, which was reduced as portions of the 5'-end were deleted, and completely abolished when the transcription initiation site was deleted. This promoter sequence had higher activity in myeloid cells compared to B cells, and activity was enhanced during myeloid differentiation, suggesting that we have identified the MYADM core promoter. Computer predictions had suggested MYADM to encode a protein with multiple transmembrane domains. By immunofluorescence and confocal microscopy we demonstrate that the protein is localized to the nuclear envelope and to intracytoplasmic membranes, indicating that MYADM constitutes an integral membrane protein.

The hematopoietic transcription factor PU.1 regulates RANK gene expression in myeloid progenitors

Osteoclasts are bone resorbing cells of hematopoietic origin. The hematopoietic transcription factor PU.1 is critical for osteoclastogenesis; however, the molecular mechanisms of PU.1-regulated osteoclastogenesis have not been explored. Here, we present evidence that the receptor activator of nuclear factor kappaB (RANK) gene that has been shown to be crucial for osteoclastogenesis is a transcriptional target of PU.1. The PU.1-/- progenitor cells failed to express the RANK gene and reconstitution of PU.1 in these cells induced RANK expression. Treatment of the PU.1 reconstituted cells with M-CSF and RANKL further augmented the RANK gene expression. To explore the regulatory mechanism of the RANK gene expression by PU.1, we have cloned the human RANK promoter. Transient transfection assays have revealed that the 2.2-kb RANK promoter was functional in a monocyte line RAW264.7, whereas co-transfection of PU.1 transactivated the RANK promoter in HeLa cells. Taken together, these results suggest that PU.1 regulates the RANK gene transcription and this may represent one of the key roles of PU.1 in osteoclast differentiation.

The Leukocyte Integrin Gene CD11d Is Repressed by Gut-enriched Kruppel-like Factor 4 in Myeloid Cells

The myeloid-specific leukocyte integrin CD11d encodes the alphaD subunit for the alphaDbeta2 receptor. A yeast one-hybrid screen showed that a longer isoform of gut-enriched Kruppel-like factor 4 (GKLF) we term GKLFa interacts with the CD11d promoter. Purified GST-GKLFa protein was shown to bind within the -61 to -44 region that overlaps a binding site for the CD11d transcriptional activators Sp1 and transforming growth factor beta-inducible early gene-1 (TIEG1). Transfection of GKLF/GKLFa in myeloid cells reduced CD11d promoter activity, whereas, down-regulation of GKLF/GKLFa with small interfering RNAs led to up-regulation of CD11d expression. Differentiation of myeloid cells with phorbol ester led to activation of the CD11d promoter and reduced occupancy of the promoter by GKLF/GKLFa but an increased occupancy by TIEG1 in vivo. Binding of GKLF/GKLFa, Sp1, and TIEG1 to the CD11d promoter in vivo is dependent on their zinc finger DNA binding domains. GKLFa physically associates with the histone deacetylases (HDAC) 1 and 2, and both HDACs are bound to the CD11d promoter in vivo but released after exposure of myeloid cells to phorbol ester suggesting that GKLF/GKLFa recruits HDACs to effect repression.

The ETS family transcription factor PU.1 is necessary for the maintenance of fetal liver hematopoietic stem cells

PU.1 is a member of the ETS family of transcription factors and is required for the development of multiple hematopoietic lineages. PU.1(-/-) mice die from hematopoietic failure at about embryonic day 18.5 (e18.5) and show a complete absence of B cells, mature T cells, and macrophages. This phenotype suggests that PU.1 may function at the level of the hematopoietic stem cell (HSC) or a multilineage progenitor. To investigate the role of PU.1 in the regulation of HSCs, PU.1(-/-) embryos were analyzed at various stages of embryonic development. The absolute number and frequency of HSCs were determined by flow cytometric analysis of c-Kit(+)Thy-1.1(lo)Lin(-)Sca-1(+) (KTLS) cells. We found that KTLS cells were absent or severely reduced in PU.1(-/-) fetal liver from e12.5 to e15.5. Progenitor cells with a c-Kit(+)Lin(-)AA4.1(+) and c-Kit(+)Lin(-)CD34(+) phenotype were also severely reduced. In addition, PU.1(-/-) fetal liver at e14.5 lacked common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) but retained megakaryocyteerythroid progenitors (MEPs). Consistent with the loss of HSC activity, a 10-fold reduction in erythroid progenitors (mature erythroid burst-forming units [BFUEs]) was observed between e14.5 and e16.5. These data suggest that PU.1 plays an important role in the maintenance or expansion of HSC number in murine fetal liver.

Leukocyte adhesion during hypoxia is mediated by HIF-1-dependent induction of beta2 integrin gene expression

Inflammatory responses are associated with significant changes in tissue metabolism. In particular, metabolic shifts during inflammation can result in significant tissue hypoxia, with resultant induction of hypoxia-responsive genes. Given this association, we hypothesized that leukocyte functional responses are influenced by hypoxia. Initial experiments revealed that exposure of the promonocytic cell line U937 to hypoxia resulted in increased adhesion to activated endothelia. Such increases were transcription-dependent and were blocked by antibodies directed against beta2, but not beta1, integrins. Analysis of beta2 integrin mRNA and protein in U937 cells revealed a 5- to 6-fold increase with hypoxia. Extension of this analysis to hypoxic human whole blood revealed prominent induction of beta2 integrin mRNA and protein ex vivo. Furthermore, murine beta2 integrin mRNA was found to be significantly induced during hypoxia in vivo. Subsequent studies identified a binding site for hypoxia-inducible factor 1 (HIF-1) in the CD18 gene. This gene encodes the subunit common to all four known types of beta2 integrin heterodimer. HIF-1 binding was demonstrated in vivo, and mutational analysis of the HIF-1 site within the CD18 promoter resulted in a loss of hypoxia inducibility. Taken together, these results demonstrate that hypoxia induces leukocyte beta2 integrin expression and function by transcriptional mechanisms dependent upon HIF-1.

The Zinc Finger Transcription Factor Transforming Growth Factor β-Inducible Early Gene-1 Confers Myeloid-specific Activation of the Leukocyte Integrin CD11d Promoter

CD11d encodes the alpha(D) subunit for a leukocyte integrin that is expressed on myeloid cells. In this study we show that the -100 to -20 region of the CD11d promoter confers myeloid-specific activation of the CD11d promoter. Transforming growth factor beta-inducible early gene-1 (TIEG1) was isolated in a yeast one-hybrid screen using the -100 to -20 region of the CD11d promoter as bait. Purified GST.TIEG1 protein was able to bind within the -61 to -45 region that overlaps a shorter binding site for Sp1. Transient overexpression of TIEG1 activated the CD11d promoter specifically in myeloid cells, whereas, down-regulation of TIEG1 with small interfering TIEG1 RNA also down-regulated expression of CD11d. In vivo, TIEG1 does not physically interact with Sp1. Cotransfection and electrophoretic mobility shift analyses of TIEG1, Sp1, and Sp3 revealed that TIEG1 competes with these Sp proteins for binding to overlapping sites in the CD11d promoter. Although TIEG1 and Sp1 are ubiquitously expressed in myeloid and non-myeloid cells, chromatin immunoprecipitation assays revealed differential occupancy of the CD11d promoter by these factors. In undifferentiated myeloid and non-myeloid cells, occupancy of the CD11d promoter by TIEG1 is similar. Upon differentiation of myeloid cells and subsequent up-regulation of CD11d expression, TIEG1 occupancy increases. In contrast, occupancy by TIEG1 remains low in non-myeloid cells exposed to phorbol ester. We propose that up-regulation of CD11d expression following differentiation of myeloid cells is mediated through increased binding of TIEG1 binding to the CD11d promoter.

Mechanisms associated with IL-6-induced up-regulation of Jak3 and its role in monocytic differentiation

We report here that Janus kinase 3 (Jak3) is a primary response gene for interleukin-6 (IL-6) in macrophage differentiation, and ectopic overexpression of Jak3 accelerates monocytic differentiation of normal mouse bone marrow cells stimulated with cytokines. Furthermore, we show that incubation of normal mouse bone marrow cells with a JAK3-specific inhibitor results in profound inhibition of myeloid colony formation in response to granulocyte-macrophage colony-stimulating factor or the combination of stem cell factor, IL-3, and IL-6. In addition, mutagenesis of the Jak3 promoter has revealed that Sp1 binding sites within a -67 to -85 element and a signal transducer and activator of transcription (Stat) binding site at position -44 to -53 are critical for activation of Jak3 transcription in murine M1 myeloid leukemia cells stimulated with IL-6. Electrophoretic mobility shift assay (EMSA) analysis has demonstrated that Sp1 can bind to the -67 to -85 element and Stat3 can bind to the -44 to -53 STAT site in IL-6-stimulated M1 cells. Additionally, ectopic overexpression of Stat3 enhanced Jak3 promoter activity in M1 cells. This mechanism of activation of the murine Jak3 promoter in myeloid cells is distinct from a recently reported mechanism of activation of the human JAK3 promoter in activated T cells.

Characterization of the murine Nramp1 promoter: requirements for transactivation by Miz-1

Murine Nramp1 encodes a divalent cation transporter that is expressed in late endosomes/lysosomes of macrophages, and the transported cations facilitate intracellular pathogen growth control. The Nramp1 promoter is TATA box-deficient, has two initiator elements, and is repressed by c-Myc, in accordance with the notion that genes that deplete the iron content of the cell cytosol antagonize cell growth. Repression via c-Myc occurs at the initiator elements, whereas a c-Myc-interacting protein (Miz-1) stimulates transcription. Here we demonstrate that a non-canonical E box (CAACTG) inhibits basal promoter activity and activation by Miz-1. A consensus Sp1-binding site or GC box is also necessary for Miz-1-dependent transactivation, but not repression. Repression occurs by c-Myc competing with p300/CBP for binding Miz-1. Our results show that an Sp1 site mutant inhibits coactivation by p300 and that the murine Nramp1 promoter is preferentially expressed within macrophages (relative to a beta-actin control) compared with non-macrophage cells. The effect of the Sp1 site mutation on promoter function shows cell-type specificity: stimulation in COS-1 and inhibition in RAW264.7 cells. Miz-1-directed RNA interference confirms a stimulatory role for Miz-1 in Nramp1 promoter function. c-Myc, Miz-1, and Sp1 were identified as binding to the Nramp1 core promoter in control cells and following acute stimulation with interferon-gamma and lipopolysaccharide. These results provide a description of sites that modulate the activity of the initiator-binding protein Miz-1 and indicate a stimulatory role for GC box-binding factors in macrophages and a inhibitory role for E box elements in proliferating cells.

Modulation of the folate receptor type beta gene by coordinate actions of retinoic acid receptors at activator Sp1/ets and repressor AP-1 sites

Folate receptor (FR) type beta is a promising target for therapeutic intervention in acute myelogenous leukemia (AML) owing particularly to its specific up-regulation in AML cells by all-trans retinoic acid (ATRA). Here we identify functional elements in the FR-beta gene and examine the molecular mechanism of transcriptional induction of FR-beta by ATRA. The basal promoter activity of FR-beta resulted from synergistic interaction between Sp1 and ets binding sites (EBSs) and repression by upstream AP-1-like elements, whose action required EBSs. A minimal promoter containing the Sp1 and ets elements was ATRA-responsive. The repressor elements bound Fos family proteins; association of the proteins with the repressor elements correlated negatively with FR-beta expression in peripheral blood neutrophils and monocytes and also in KG-1 (AML) cells grown in the absence or in the presence of ATRA. Furthermore, down-regulation of FR-beta in KG-1 cells treated with O-tetradecanoylphorbol 13-acetate (TPA) was accompanied by increased AP-1 binding to the repressor elements. From chromatin immunoprecipitation (ChIP) assays, the nuclear retinoic acid receptor alpha (RARalpha) associated with the Sp1 region, and RARs beta and gamma associated with the AP-1 and Sp1 regions; treatment of KG-1 cells with ATRA did not alter Sp1 binding but increased the association of RARalpha and decreased the association of RARs beta and gamma. ATRA also decreased RAR expression levels. The results suggest that the FR-beta gene is a target for multiple coordinate actions of nuclear receptors for ATRA directly and indirectly acting on a transcriptional complex containing activating Sp1/ets and inhibitory AP-1 proteins. The multiple mechanisms favor the prediction that ATRA will induce FR-beta expression in a broad spectrum of AML cells. Further, optimal FR-beta induction may be expected when all 3 RAR subtypes bind agonist.

Identification and characterization of a PU.1/Spi-B binding site in the bovine leukemia virus long terminal repeat

Bovine leukemia virus (BLV) is a B-lymphotropic oncogenic retrovirus whose transcriptional promoter is located in the viral 5' long terminal repeat (LTR). To date, no B-lymphocyte-specific cis-regulatory element has been identified in this region. Since ETS proteins are known to regulate transcription of numerous retroviruses, we searched for the presence in the BLV promoter region of binding sites for PU.1/Spi-1, a B-cell- and macrophage-specific ETS family member. In this report, nucleotide sequence analysis of the viral LTR identified a PUbox located at -95/-84 bp. We demonstrated by gel shift and supershift assays that PU.1 and the related Ets transcription factor Spi-B interacted specifically with this PUbox. A 2-bp mutation (GGAA-->CCAA) within this motif abrogated PU.1/Spi-B binding. This mutation caused a marked decrease in LTR-driven basal gene expression in transient transfection assays of B-lymphoid cell lines, but did not impair the responsiveness of the BLV promoter to the virus-encoded transactivator Tax(BLV). Moreover, ectopically expressed PU.1 and Spi-B proteins transactivated the BLV promoter in a PUbox-dependent manner. Taken together, our results provide the first demonstration of regulation of the BLV promoter by two B-cell-specific Ets transcription factors, PU.1 and Spi-B. The PU.1/Spi-B binding site identified here could play an important role in BLV replication and B-lymphoid tropism.

The zinc finger transcription factor ZBP-89 is a repressor of the human beta 2-integrin CD11b gene

Integrin CD11b is a differentiation marker of the myelomonocytic lineage and an important mediator of inflammation. Expression of the CD11b gene is transcriptionally induced as myeloid precursors differentiate into mature cells, then drops as monocytes further differentiate into macrophages. Previous studies have identified elements and factors involved in the transcriptional activation of the CD11b gene during myeloid differentiation, but no data exist regarding potential down-regulatory factors, especially in the later stages of differentiation. Using 2 copies of a GC-rich element (-141 to -110) in the CD11b promoter, we probed a cDNA expression library for interacting proteins. Three clones were identified among 9.1 million screened, all encoding the DNA-binding domain of the zinc finger factor ZBP-89. Overexpression of ZBP-89 in the monocyte precursor cell line U937 reduced CD11b promoter-driven luciferase activity when U937 cells were induced to differentiate into monocytelike cells using phorbol esters. To identify the differentiation stage at which ZBP-89 repression of the CD11b gene is exerted, the protein level of ZBP-89 was correlated with that of CD11b mRNA in differentiating U937 as well as in normal human monocytes undergoing in vitro differentiation into macrophages. A clear inverse relationship was observed in the latter but not the former state, suggesting that ZBP-89 represses CD11b gene expression during the further differentiation of monocytes into macrophages.

Apicidin, a histone deacetylase inhibitor, induces differentiation of HL-60 cells

The fungal metabolite apicidin (cyclo(N-O-methyl-L-tryptophanyl-L-isoleucinyl-D-pipecolinyl-L-2-amino-8-oxodecanoyl)) inhibited the growth of HL-60 cells in a concentration-dependent manner (100-1000 nM). At higher concentrations (>300 nM), cell death was induced. At 100 nM, it induced hyperacetylation of histone H4 time-dependently, while trichostatin A induced transient hyperacetylation. Apicidin (10-100 nM) increased the cells having nitroblue tetrazolium-reducing activity and expressing CD11b but not CD14 and CD15. The expression of CD11b by apicidin was long lasting, while that by trichostatin A was transient. In K562 cells, apicidin at 10-100 nM did not inhibit cell growth nor express CD11b, CD14 and CD15. Our findings indicate that apicidin inhibits proliferation and induces the early stage of differentiation of HL-60 cells.

GA-binding protein (GABP) and Sp1 are required, along with retinoid receptors, to mediate retinoic acid responsiveness of CD18 (beta 2 leukocyte integrin): a novel mechanism of transcriptional regulation in myeloid cells

CD18 (beta(2) leukocyte integrin) is transcriptionally regulated in myeloid cells, but the mechanisms that increase its expression in response to retinoic acid (RA) have not been defined. The CD18 promoter was activated by RA treatment in stably transfected U937 myeloid cells. We identified a retinoic acid response element (RARE) that lies nearly 900 nucleotides upstream of the CD18 transcriptional start site that was bound by the RA receptors, retinoic acid receptor (RAR) and retinoic X receptor (RXR). This RARE accounted for one half of the RA responsiveness of CD18. However, unexpectedly, one half of the dynamic response to RA was mediated by the 96-nucleotide CD18 minimal promoter, which lacks a recognizable RARE. Binding sites for the ets transcription factor, GA-binding protein (GABP), and Sp1 were required for full RA responsiveness of both the CD18 minimal promoter and the full-length promoter. The ets sites conferred RA responsiveness on an otherwise unresponsive heterologous promoter, and RA responsiveness was directly related to the number of ets sites. The transcriptional coactivator p300/CBP physically interacted with GABP in vivo, and p300 increased the responsiveness of the CD18 promoter to RA. These studies demonstrate a novel role for non-RAR transcription factors in mediating RA activation in myeloid cells. They support the concept that transcription factors other than RARs are required for RA-activated gene expression. We hypothesize that a multiprotein complex--an enhanceosome--that includes GABP, other transcription factors, and coactivators, dynamically regulates CD18 expression in myeloid cells.

Structural characterization of the human carboxypeptidase D gene and its promoter

Human carboxypeptidase D (CPD) is a 180-kDa type I membrane protein with three tandem active site domains. CPD is a B-type (or kininase I-type) carboxypeptidase that cleaves C-terminal basic residues from proteins and peptides, such as Arg9 from bradykinin. The human carboxypeptidase D (CPD) gene was found to encompass approximately 88.3 kb of genomic sequence, containing 21 exons ranging in size from 65 to 1813 bp, and 21 introns ranging in size from 112 bp to 35.6 kb. Although CPD and CPM belong to the same metallocarboxypeptidase subfamily, their intron/exon structures differ significantly. Multiple transcription start sites were found in the CPD gene within a GC-rich sequence lacking the typical TATA box, but containing three GC boxes. Luciferase reporter assays with various size constructs containing the promoter region upstream of the start sites showed that it was active in three different cell lines, especially in the human hepatoma cell line HepG2 and the human monocytic cell line THP-1, which have high constitutive expression of CPD.

Cooperative and antagonistic interplay between PU.1 and GATA-2 in the specification of myeloid cell fates

PU.1 and GATA transcription factors appear to antagonize each other's function in the development of distinct lineages of the hematopoietic system. In contrast, we demonstrate that PU.1, like GATA-2, is essential for the generation of mast cells. PU.1-/- hematopoietic progenitors can be propagated in IL-3 and differentiate into mast cells or macrophages upon restoration of PU.1 activity. Using these progenitors and a conditionally activatable PU.1 protein, we show that PU.1 can negatively regulate expression of the GATA-2 gene. In the absence of GATA-2, PU.1 promotes macrophage but not mast cell differentiation. Reexpression of GATA-2 in such progenitors enables the generation of mast cells. We propose a developmental model in which cooperative function or antagonistic crossregulation by PU.1 of GATA-2 promotes distinct myeloid cell fates.

Transcriptional regulation of granulocyte and monocyte development

Granulocytes and monocytes develop from a common myeloid progenitor. Early granulopoiesis requires the C/EBPalpha, PU.1, RAR, CBF, and c-Myb transcription factors, and terminal neutrophil differentiation is dependent upon C/EBPepsilon, PU.1, Sp1, CDP, and HoxA10. Monopoiesis can be induced by Maf-B, c-Jun, or Egr-1 and is dependent upon PU.1, Sp1, and ICSBP. Signals eminating from cytokine receptors modulate factor activities but do not determine cell fates. Orchestration of the myeloid developmental program is achieved via cooperative gene regulation, via synergistic and inhibitory protein-protein interactions, via promoter auto-regulation and cross-regulation, via regulation of factor levels, and via induction of cell cycle arrest: For example, c-Myb and C/EBPalpha cooperate to activate the mim-1 and NE promoters, PU.1, C/EBPalpha, and CBF, regulate the NE, MPO, and M-CSF Receptor genes. PU.1:GATA-1 interaction and C/EBP suppression of FOG transcription inhibits erythroid and megakaryocyte gene expression. c-Jun:PU.1, ICSBP:PU.1, and perhaps Maf:Jun complexes induce monocytic genes. PU.1 and C/EBPalpha activate their own promoters, C/EBPalpha rapidly induces PU.1 and C/EBPepsilon RNA expression, and RARalpha activates the C/EBPepsilon promoter. Higher levels of PU.1 are required for monopoiesis than for B-lymphopoiesis, and higher C/EBP levels may favor granulopoiesis over monopoiesis. CBF and c-Myb stimulate proliferation whereas C/EBPalpha induces a G1/S arrest; cell cycle arrest is required for terminal myelopoiesis, perhaps due to expression of p53 or hypo-phosphorylated Rb.

Macrophage-restricted and interferon gamma-inducible expression of the allograft inflammatory factor-1 gene requires Pu.1

Expression of allograft inflammatory factor-1 (Aif-1), a 17-kDa protein bearing an EF-hand Ca(2+) binding motif, increases markedly in monocytes and macrophages participating in allo- and autoimmune reactions, including the perivascular inflammation in transplanted hearts, microglial infiltrates in experimental autoimmune neuritis, and the inflamed pancreas of prediabetic BB rats. To investigate the mechanism of this regulation, we isolated the mouse aif-1 gene and determined its genomic organization. The gene has six exons distributed over 1.6 kilobases, an interferon gamma-inducible DNase I-hypersensitive site near -900, and flanking sequences on either side predicted to associate with nuclear matrix. Reporter gene analyses identified sequences between -902 and -789, including consensus Ets and interferon regulatory factor elements, required for macrophage-specific and interferon gamma-inducible transcriptional activity. Pu.1 bound to the Ets site in electromobility shift assay and forced expression of Pu.1 activated the aif-1 promoter in 3T3 fibroblasts, in which it is normally inactive. However, the transcriptional activity of a concatamer of the Ets site alone did not increase with interferon gamma treatment. Cooperation between Pu.1 and proteins binding to the interferon regulatory factor element appears to be necessary for both macrophage-specific and interferon gamma-inducible expression of the aif-1 gene.

Identification of sterol-independent regulatory elements in the human ATP-binding cassette transporter A1 promoter: role of Sp1/3, E-box binding factors, and an oncostatin M-responsive element

The ATP-binding cassette transporter A1 (ABCA1) shows a differentiation-, cAMP-, and sterol-dependent up-regulation in human monocytes. As part of an ongoing study, we investigated the proximal promoter regions that are highly conserved between the human and murine ABCA1 genes. Using reporter gene assays, we show here that a TATA box 24 bp upstream of the transcription initiation site is essential for promoter activity in RAW 264.7 and HepG2 cells, whereas further enhancement of transcriptional activity is mediated by the -175 bp promoter region. Gel shift assays revealed in vitro binding of Sp1 to a -91 GnC motif as well as binding of Sp1 and Sp3 to a -157 GnC promoter region. In co-transfection experiments using Drosophila S2 cells, we demonstrate that Sp3 competes with Sp1 for binding to the -157 GnC motif and acts as a repressor. On the other hand, overexpression of Sp1 increased ABCA1 mRNA expression in HeLa cells and enhanced cellular cholesterol and phospholipid efflux in RAW 246.7 macrophages. We also show here that the conserved E-box at position -140 binds upstream stimulatory factors 1 and 2 and hepatic nuclear factor 1alpha and that mutagenesis of the E-box enhanced constitutive ABCA1 expression in RAW 264.7 cells, implying a role for this element in silencing ABCA1 expression. Besides the functional importance for basal gene expression, we have identified that the core promoter region (-175 to +224) is also responsible for the induction of ABCA1 by the cytokine oncostatin M, resulting in a rapid increase in ABCA1 mRNA levels in HepG2 cells. Interestingly, this oncostatin M-induced expression is not dependent on the currently known sequence motifs in the ABCA1 promoter. In conclusion, a functional complex of cis-elements within the proximal human ABCA1 promoter associated with the transcription factors Sp1/3, upstream stimulatory factors 1 and 2, and hepatic nuclear factor 1alpha has been characterized, which allows a subtle tissue-specific regulation of ABCA1 gene expression.

A novel role of Sp1 and Sp3 in the interferon-gamma -mediated suppression of macrophage lipoprotein lipase gene transcription

The regulation of macrophage lipoprotein lipase by cytokines is of potentially crucial importance in the pathogenesis of atherosclerosis. We have shown previously that macrophage lipoprotein lipase expression is suppressed by interferon-gamma (IFN-gamma) at the transcriptional level. We investigated the regulatory sequence elements and the transcription factors that are involved in this response. We demonstrated that the -31/+187 sequence contains the minimal IFN-gamma-responsive elements. Electrophoretic mobility shift assays showed that the binding of proteins to two regions in the -31/+187 sequence was reduced dramatically when the cells were exposed to IFN-gamma. Both competition electrophoretic mobility shift assays and antibody supershift assays showed that the interacting proteins were composed of Sp1 and Sp3. Mutations of the Sp1/Sp3-binding sites in the minimal IFN-gamma-responsive elements abolished the IFN-gamma-mediated suppression of promoter activity, whereas multimers of the sequence were able to impart the response to a heterologous promoter. Western blot analysis showed that IFN-gamma reduced the steady state levels of Sp3 protein. In contrast, the cytokine decreased the DNA binding activity of Sp1 without affecting the protein levels. These studies therefore reveal a novel mechanism for IFN-gamma-mediated regulation of macrophage gene transcription.