c-Jun homodimers can function as a context-specific coactivator

Reactive Bergmann glia play a central role in spinocerebellar ataxia inflammation via the JNK pathway

The spinocerebellar ataxias (SCAs) are devastating neurological diseases characterized by progressive cerebellar incoordination. While neurons bear the brunt of the pathology, a growing body of evidence suggests that glial cells are also affected. It has, however, been difficult to understand the role of glia, given the diversity of subtypes, each with their individual contributions to neuronal health. Using human SCA autopsy samples we have discovered that Bergmann glia-the radial glia of the cerebellum, which form intimate functional connections with cerebellar Purkinje neurons-display inflammatory JNK-dependent c-Jun phosphorylation. This phosphorylation defines a signaling pathway not observed in other activated glial populations, providing an opportunity to isolate the role of Bergmann glia in SCA inflammation. Turning to an SCA1 mouse model as a paradigmatic SCA, we demonstrate that inhibiting the JNK pathway reduces Bergmann glia inflammation accompanied by improvements in the SCA1 phenotype both behaviorally and pathologically. These findings demonstrate the causal role for Bergmann glia inflammation in SCA1 and point to a novel therapeutic strategy that could span several ataxic syndromes where Bergmann glia inflammation is a major feature.

Airborne particulate matter (PM10) induces cell invasion through Aryl Hydrocarbon Receptor and Activator Protein 1 (AP-1) pathway deregulation in A549 lung epithelial cells

BACKGROUND

Particulate matter with an aerodynamic size ≤ 10 μm (PM₁₀) is a risk factor for lung cancer development, mainly because some components are highly toxic. Polycyclic aromatic hydrocarbons (PAHs) are present in PM₁₀, such as benzo[a]pyrene (BaP), which is a well-known genotoxic and carcinogenic compound to humans, capable of activating AP-1 transcription factor family genes through the Aryl Hydrocarbon Receptor (AhR). Because effects of BaP include metalloprotease 9 (MMP-9) activation, cell invasion, and other pathways related to carcinogenesis, we aimed to demonstrate that PM₁₀ (10 µg/cm²) exposure induces the activation of AP-1 family members as well as cell invasion in lung epithelial cells, through AhR pathway.

METHODS AND RESULTS

The role of the AhR gene in cells exposed to PM₁₀ (10 µg/cm²) and BaP (1µM) for 48 h was evaluated using AhR-targeted interference siRNA. Then, the AP-1 family members (c-Jun, Jun B, Jun D, Fos B, C-Fos, and Fra-1), the levels/activity of MMP-9, and cell invasion were analyzed. We found that PM₁₀ increased AhR levels and promoted its nuclear localization in A549 treated cells. Also, PM₁₀ and BaP deregulated the activity of AP-1 family members. Moreover, PM₁₀ upregulated the secretion and activity of MMP-9 through AhR, while BaP had no effect. Finally, we found that cell invasion in A549 cells exposed to PM₁₀ and BaP is modulated by AhR.

CONCLUSION

Our results demonstrated that PM₁₀ exposure induces upregulation of the c-Jun, Jun B, and Fra-1 activity, the expression/activity of MMP-9, and the cell invasion in lung epithelial cells, effects mediated through the AhR. Also, the Fos B and C-Fos activity were downregulated. In addition, the effects induced by PM₁₀ exposure were like those induced by BaP, which highlights the potentially toxic effects of the PM₁₀ mixture in lung epithelial cells.

PU.1-c-Jun interaction is crucial for PU.1 function in myeloid development

The Ets transcription factor PU.1 is essential for inducing the differentiation of monocytes, macrophages, and B cells in fetal liver and adult bone marrow. PU.1 controls hematopoietic differentiation through physical interactions with other transcription factors, such as C/EBPα and the AP-1 family member c-Jun. We found that PU.1 recruits c-Jun to promoters without the AP-1 binding sites. To address the functional importance of this interaction, we generated PU.1 point mutants that do not bind c-Jun while maintaining normal DNA binding affinity. These mutants lost the ability to transactivate a target reporter that requires a physical PU.1-c-Jun interaction, and did not induce monocyte/macrophage differentiation of PU.1-deficient cells. Knock-in mice carrying these point mutations displayed an almost complete block in hematopoiesis and perinatal lethality. While the PU.1 mutants were expressed in hematopoietic stem and early progenitor cells, myeloid differentiation was severely blocked, leading to an almost complete loss of mature hematopoietic cells. Differentiation into mature macrophages could be restored by expressing PU.1 mutant fused to c-Jun, demonstrating that a physical PU.1-c-Jun interaction is crucial for the transactivation of PU.1 target genes required for myeloid commitment and normal PU.1 function in vivo during macrophage differentiation.

In vitro single molecule and bulk phase studies reveal the AP-1 transcription factor cFos binds to DNA without its partner cJun

The AP-1 transcription factor family crucially regulates progression of the cell cycle, as well as playing roles in proliferation, differentiation, and the stress response. The two best described AP-1 family members, cFos and cJun, are known to dimerize to form a functional AP-1 heterodimer that binds to a consensus response element sequence. Although cJun can also homodimerize and bind to DNA, the canonical view is that cFos cannot bind DNA without heterodimerizing with cJun. Here, we show that cFos can actually bind to DNA in the absence of cJun in vitro. Using dual color single molecule imaging of cFos alone, we directly visualize binding to and movement on DNA. Of all these DNA-bound proteins, detailed analysis suggested 30 to 46% were homodimers. Furthermore, we constructed fluorescent protein fusions of cFos and cJun for Förster resonance energy transfer experiments. These constructs indicated complete dimerization of cJun, but although cFos could dimerize, its extent was reduced. Finally, to provide orthogonal confirmation of cFos binding to DNA, we performed bulk-phase circular dichroism experiments that showed clear structural changes in DNA; these were found to be specific to the AP-1 consensus sequence. Taken together, our results clearly show cFos can interact with DNA both as monomers and dimers independently of its archetypal partner, cJun.

Contribution of the Transcription Factors Sp1/Sp3 and AP-1 to Clusterin Gene Expression during Corneal Wound Healing of Tissue-Engineered Human Corneas

In order to reduce the need for donor corneas, understanding of corneal wound healing and development of an entirely tissue-engineered human cornea (hTECs) is of prime importance. In this study, we exploited the hTEC to determine how deep wound healing affects the transcriptional pattern of corneal epithelial cells through microarray analyses. We demonstrated that the gene encoding clusterin (CLU) has its expression dramatically repressed during closure of hTEC wounds. Western blot analyses confirmed a strong reduction in the expression of the clusterin isoforms after corneal damage and suggest that repression of CLU gene expression might be a prerequisite to hTEC wound closure. Transfection with segments from the human CLU gene promoter revealed the presence of three regulatory regions: a basal promoter and two more distal negative regulatory regions. The basal promoter bears DNA binding sites for very potent transcription factors (TFs): Activator Protein-1 (AP-1) and Specificity protein-1 and 3 (Sp1/Sp3). By exploiting electrophoretic mobility shift assays (EMSA), we demonstrated that AP-1 and Sp1/Sp3 have their DNA binding site overlapping with one another in the basal promoter of the CLU gene in hCECs. Interestingly, expression of both these TFs is reduced (at the protein level) during hTEC wound healing, thereby contributing to the extinction of CLU gene expression during that process. The results of this study contribute to a better understanding of the molecular mechanisms accounting for the repression of CLU gene expression during corneal wound healing.

Mutational synergy during leukemia induction remodels chromatin accessibility, histone modifications and three-dimensional DNA topology to alter gene expression

Altered transcription is a cardinal feature of acute myeloid leukemia (AML); however, exactly how mutations synergize to remodel the epigenetic landscape and rewire three-dimensional DNA topology is unknown. Here, we apply an integrated genomic approach to a murine allelic series that models the two most common mutations in AML: Flt3-ITD and Npm1c. We then deconvolute the contribution of each mutation to alterations of the epigenetic landscape and genome organization, and infer how mutations synergize in the induction of AML. Our studies demonstrate that Flt3-ITD signals to chromatin to alter the epigenetic environment and synergizes with mutations in Npm1c to alter gene expression and drive leukemia induction. These analyses also allow the identification of long-range cis-regulatory circuits, including a previously unknown superenhancer of Hoxa locus, as well as larger and more detailed gene-regulatory networks, driven by transcription factors including PU.1 and IRF8, whose importance we demonstrate through perturbation of network members.

JunB can enhance the transcription of IL-8 in oral squamous cell carcinoma

Proteasome inhibitor MG132 was shown to enhance the secretion of interleukin 8 (IL-8) by various cells. The enhancement is regulated by the transcription factor activator protein-1 (AP-1) at the transcriptional level. AP-1 is a dimer formed by AP-1 family proteins. The purpose of the present study was to explore the combinations of the AP-1 family proteins that contribute to MG132-driven IL-8 secretion. Oral squamous cell carcinoma-derived cell lines, Ca9-22 and HSC3, were used to demonstrate their response to MG132. IL-8 secretion was augmented by MG132 in both cell lines. c-Jun expression was detected in both the cell lines, whereas c-Fos expression was detected only in the HSC3. The influence of MG132 stimulation on c-Jun and c-Fos expression was further examined by western blot analysis. c-Jun expression was increased by MG132 stimulation, whereas c-Fos expression was not detected even after MG132 stimulation. As JunB is reported to inhibit the transcriptional activity of the AP-1 complex, we speculated that the c-Jun homodimer should contribute to IL-8 enhancement. Expression vectors encoding wild type and c-Jun mutants, M17 and M22-23, respectively, were constructed and transfected into the Ca9-22 cells. In contrast to our expectations, MG132-induced IL-8 secretion was significantly reduced in all the transfectants suggesting that other c-Jun members might form homodimers with c-Jun and contribute to IL-8 enhancement. Transfection of the cells with c-Jun or JunB small hairpin RNA (shRNA) reduced IL-8 secretion up to 50% and 65% of the control shRNA transfectant. Furthermore, cotransfection of both shRNA almost completely inhibited the IL-8 secretion. These results indicate that JunB not only inhibits but also enhances the transcription of c-Jun targets in combination with c-Jun.

Bone Marrow Monocytes and Derived Dendritic Cells from Myelodysplastic Patients Have Functional Abnormalities Associated with Defective Response to Bacterial Infection

Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell diseases characterized by dysplasia of one or more hematologic lineages and a high risk of developing into acute myeloid leukemia. MDS patients have recurrent bacterial infections and abnormal expression of CD56 by monocytes. We investigated MDS patients' bone marrow CD56⁺/CD56^- monocytes and their in vitro-derived dendritic cell populations in comparison with cells obtained from disease-free subjects. We found that monocytes from MDS patients, irrespective of CD56 expression, have reduced phagocytosis activity and low expression of genes involved in triggering immune responses, regulation of immune and inflammatory response signaling pathways, and in the response to LPS. Dendritic cells derived in vitro from MDS monocytes failed to develop dendritic projections and had reduced expression of HLA-DR and CD86, suggesting that Ag processing and T cell activation capabilities are impaired. In conclusion, we identified, in both CD56⁺ and CD56^- monocytes from MDS patients, several abnormalities that may be related to the increased susceptibility to infections observed in these patients.

The Role of Activator Protein-1 (AP-1) Family Members in CD30-Positive Lymphomas

The Activator Protein-1 (AP-1) transcription factor (TF) family, composed of a variety of members including c-JUN, c-FOS and ATF, is involved in mediating many biological processes such as proliferation, differentiation and cell death. Since their discovery, the role of AP-1 TFs in cancer development has been extensively analysed. Multiple in vitro and in vivo studies have highlighted the complexity of these TFs, mainly due to their cell-type specific homo- or hetero-dimerization resulting in diverse transcriptional response profiles. However, as a result of the increasing knowledge of the role of AP-1 TFs in disease, these TFs are being recognized as promising therapeutic targets for various malignancies. In this review, we focus on the impact of deregulated expression of AP-1 TFs in CD30-positive lymphomas including Classical Hodgkin Lymphoma and Anaplastic Large Cell Lymphoma.

Macrophage-Associated Lipin-1 Enzymatic Activity Contributes to Modified Low-Density Lipoprotein-Induced Proinflammatory Signaling and Atherosclerosis

OBJECTIVE

Macrophage proinflammatory responses induced by modified low-density lipoproteins (modLDL) contribute to atherosclerotic progression. How modLDL causes macrophages to become proinflammatory is still enigmatic. Macrophage foam cell formation induced by modLDL requires glycerolipid synthesis. Lipin-1, a key enzyme in the glycerolipid synthesis pathway, contributes to modLDL-elicited macrophage proinflammatory responses in vitro. The objective of this study was to determine whether macrophage-associated lipin-1 contributes to atherogenesis and to assess its role in modLDL-mediated signaling in macrophages.

APPROACH AND RESULTS

We developed mice lacking lipin-1 in myeloid-derived cells and used adeno-associated viral vector 8 expressing the gain-of-function mutation of mouse proprotein convertase subtilisin/kexin type 9 (adeno-associated viral vector 8-proprotein convertase subtilisin/kexin type 9) to induce hypercholesterolemia and plaque formation. Mice lacking myeloid-associated lipin-1 had reduced atherosclerotic burden compared with control mice despite similar plasma lipid levels. Stimulation of bone marrow-derived macrophages with modLDL activated a persistent protein kinase Cα/βII-extracellular receptor kinase1/2-jun proto-oncogene signaling cascade that contributed to macrophage proinflammatory responses that was dependent on lipin-1 enzymatic activity.

CONCLUSIONS

Our data demonstrate that macrophage-associated lipin-1 is atherogenic, likely through persistent activation of a protein kinase Cα/βII-extracellular receptor kinase1/2-jun proto-oncogene signaling cascade that contributes to foam cell proinflammatory responses. Taken together, these results suggest that modLDL-induced foam cell formation and modLDL-induced macrophage proinflammatory responses are not independent consequences of modLDL stimulation but rather are both directly influenced by enhanced lipid synthesis.

A feed-forward regulation of endothelin receptors by c-Jun in human non-pigmented ciliary epithelial cells and retinal ganglion cells

c-Jun, c-Jun N-terminal kinase(JNK) and endothelin B (ET_B) receptor have been shown to contribute to the pathogenesis of glaucoma. Previously, we reported that an increase of c-Jun and CCAAT/enhancer binding protein β (C/EBPβ) immunohistostaining is associated with upregulation of the ET_B receptor within the ganglion cell layer of rats with elevated intraocular pressure (IOP). In addition, both transcription factors regulate the expression of the ET_B receptor in human non-pigmented ciliary epithelial cells (HNPE). The current study addressed the mechanisms by which ET-1 produced upregulation of ET receptors in primary rat retinal ganglion cells (RGCs) and HNPE cells. Treatment of ET-1 and ET-3 increased the immunocytochemical staining of c-Jun and C/EBPβ in primary rat RGCs and co-localization of both transcription factors was observed. A marked increase in DNA binding activity of AP-1 and C/EBPβ as well as elevated protein levels of c-Jun and c-Jun-N-terminal kinase (JNK) were detected following ET-1 treatment in HNPE cells. Overexpression of ET_A or ET_B receptor promoted the upregulation of c-Jun and also elevated its promoter activity. In addition, upregulation of C/EBPβ augmented DNA binding and mRNA expression of c-Jun, and furthermore, the interaction of c-Jun and C/EBPβ was confirmed using co-immunoprecipitation. Apoptosis of HNPE cells was identified following ET-1 treatment, and overexpression of the ET_A or ET_B receptor produced enhanced apoptosis. ET-1 mediated upregulation of c-Jun and C/EBPβ and their interaction may represent a novel mechanism contributing to the regulation of endothelin receptor expression. Reciprocally, c-Jun was also found to regulate the ET receptors and C/EBPβ appeared to play a regulatory role in promoting expression of c-Jun. Taken together, the data suggests that ET-1 triggers the upregulation of c-Jun through both ET_A and ET_B receptors, and conversely c-Jun also upregulates endothelin receptor expression, thereby generating a positive feed-forward loop of endothelin receptor activation and expression. This feed-forward regulation may contribute to RGC death and astrocyte proliferation following ET-1 treatment.

JunD/AP-1 Antagonizes the Induction of DAPK1 To Promote the Survival of v-Src-Transformed Cells

The increase in AP-1 activity is a hallmark of cell transformation by tyrosine kinases. Previously, we reported that blocking AP-1 using the c-Jun dominant negative mutant TAM67 induced senescence, adipogenesis, or apoptosis in v-Src-transformed chicken embryo fibroblasts (CEFs) whereas inhibition of JunD by short hairpin RNA (shRNA) specifically induced apoptosis. To investigate the role of AP-1 in Src-mediated transformation, we undertook a gene profiling study to characterize the transcriptomes of v-Src-transformed CEFs expressing either TAM67 or the JunD shRNA. Our study revealed a cluster of 18 probe sets upregulated exclusively in response to AP-1/JunD impairment and v-Src transformation. Four of these probe sets correspond to genes involved in the interferon pathway. One gene in particular, death-associated protein kinase 1 (DAPK1), is a C/EBPβ-regulated mediator of apoptosis in gamma interferon (IFN-γ)-induced cell death. Here, we show that inhibition of DAPK1 abrogates cell death in v-Src-transformed cells expressing the JunD shRNA. Chromatin immunoprecipitation data indicated that C/EBPβ was recruited to the DAPK1 promoter while the expression of a dominant negative mutant of C/EBPβ abrogated the induction of DAPK1 in response to the inhibition of AP-1. In contrast, as determined by chromatin immunoprecipitation (ChIP) assays, JunD was not detected on the DAPK1 promoter under any conditions, suggesting that JunD promotes survival by indirectly antagonizing the expression of DAPK1 in v-Src transformed cells.

IMPORTANCE

Transformation by the v-Src oncoprotein causes extensive changes in gene expression in primary cells such as chicken embryo fibroblasts. These changes, determining the properties of transformed cells, are controlled in part at the transcriptional level. Much attention has been devoted to transcription factors such as AP-1 and NF-κB and the control of genes associated with a more aggressive phenotype. In this report, we describe a novel mechanism of action determined by the JunD component of AP-1, a factor enhancing cell survival in v-Src-transformed cells. We show that the loss of JunD results in the aberrant activation of a genetic program leading to cell death. This program requires the activation of the tumor suppressor death-associated protein kinase 1 (DAPK1). Since DAPK1 is phosphorylated and inhibited by v-Src, these results highlight the importance of this kinase and the multiple mechanisms controlled by v-Src to antagonize the tumor suppressor function of DAPK1.

An Elk transcription factor is required for Runx-dependent survival signaling in the sea urchin embryo

Elk proteins are Ets family transcription factors that regulate cell proliferation, survival, and differentiation in response to ERK (extracellular-signal regulated kinase)-mediated phosphorylation. Here we report the embryonic expression and function of Sp-Elk, the single Elk gene of the sea urchin Strongylocentrotus purpuratus. Sp-Elk is zygotically expressed throughout the embryo beginning at late cleavage stage, with peak expression occurring at blastula stage. Morpholino antisense-mediated knockdown of Sp-Elk causes blastula-stage developmental arrest and embryo disintegration due to apoptosis, a phenotype that is rescued by wild-type Elk mRNA. Development is also rescued by Elk mRNA encoding a serine to aspartic acid substitution (S402D) that mimics ERK-mediated phosphorylation of a conserved site that enhances DNA binding, but not by Elk mRNA encoding an alanine substitution at the same site (S402A). This demonstrates both that the apoptotic phenotype of the morphants is specifically caused by Elk depletion, and that phosphorylation of serine 402 of Sp-Elk is critical for its anti-apoptotic function. Knockdown of Sp-Elk results in under-expression of several regulatory genes involved in cell fate specification, cell cycle control, and survival signaling, including the transcriptional regulator Sp-Runt-1 and its target Sp-PKC1, both of which were shown previously to be required for cell survival during embryogenesis. Both Sp-Runt-1 and Sp-PKC1 have sequences upstream of their transcription start sites that specifically bind Sp-Elk. These results indicate that Sp-Elk is the signal-dependent activator of a feed-forward gene regulatory circuit, consisting also of Sp-Runt-1 and Sp-PKC1, which actively suppresses apoptosis in the early embryo.

Differential Expression of the Activator Protein 1 Transcription Factor Regulates Interleukin-1ß Induction of Interleukin 6 in the Developing Enterocyte

The innate immune response is characterized by activation of transcription factors, nuclear factor kappa B and activator protein-1 and their downstream targets, the pro-inflammatory cytokines including interleukin 1β and interleukin 6. Normal development of this response in the intestine is critical to survival of the human neonate and delays can cause the onset of devastating inflammatory diseases such as necrotizing enterocolitis. Previous studies have addressed the role of nuclear factor kappa B in the development of the innate immune response in the enterocyte, however despite its central role in the control of multiple pro-inflammatory cytokine genes, little is known on the role of Activator Protein 1 in this response in the enterocyte. Here we show that the canonical Activator Protein 1 members, cJun and cFos and their upstream kinases JNK and p38 play an essential role in the regulation of interleukin 6 in the immature enterocyte. Our data supports a model whereby the cFos/cJun heterodimer and the more potent cJun homodimer downstream of JNK are replaced by less efficient JunD containing dimers, contributing to the decreased responsiveness to interleukin 1β and decreased interleukin 6 secretion observed in the mature enterocyte. The tissue specific expression of JunB in colonocytes and colon derived tissues together with its ability to repress Interleukin-1β induction of an Interleukin-6 gene reporter in the NCM-460 colonocyte suggests that induction of JunB containing dimers may offer an attractive therapeutic strategy for the control of IL-6 secretion during inflammatory episodes in this area of the intestine

The LMO2 oncogene regulates DNA replication in hematopoietic cells

Oncogenic transcription factors are commonly activated in acute leukemias and subvert normal gene expression networks to reprogram hematopoietic progenitors into preleukemic stem cells, as exemplified by LIM-only 2 (LMO2) in T-cell acute lymphoblastic leukemia (T-ALL). Whether or not these oncoproteins interfere with other DNA-dependent processes is largely unexplored. Here, we show that LMO2 is recruited to DNA replication origins by interaction with three essential replication enzymes: DNA polymerase delta (POLD1), DNA primase (PRIM1), and minichromosome 6 (MCM6). Furthermore, tethering LMO2 to synthetic DNA sequences is sufficient to transform these sequences into origins of replication. We next addressed the importance of LMO2 in erythroid and thymocyte development, two lineages in which cell cycle and differentiation are tightly coordinated. Lowering LMO2 levels in erythroid progenitors delays G1-S progression and arrests erythropoietin-dependent cell growth while favoring terminal differentiation. Conversely, ectopic expression in thymocytes induces DNA replication and drives these cells into cell cycle, causing differentiation blockade. Our results define a novel role for LMO2 in directly promoting DNA synthesis and G1-S progression.

The MacBlue binary transgene (csf1r-gal4VP16/UAS-ECFP) provides a novel marker for visualisation of subsets of monocytes, macrophages and dendritic cells and responsiveness to CSF1 administration

The MacBlue transgenic mouse uses the Csf1r promoter and first intron to drive expression of gal4-VP16, which in turn drives a cointegrated gal4-responsive UAS-ECFP cassette. The Csf1r promoter region used contains a deletion of a 150 bp conserved region covering trophoblast and osteoclast-specific transcription start sites. In this study, we examined expression of the transgene in embryos and adult mice. In embryos, ECFP was expressed in the large majority of macrophages derived from the yolk sac, and as the liver became a major site of monocytopoiesis. In adults, ECFP was detected at high levels in both Ly6C+ and Ly6C- monocytes and distinguished them from Ly6C+, F4/80+, CSF1R+ immature myeloid cells in peripheral blood. ECFP was also detected in the large majority of microglia and Langerhans cells. However, expression was lost from the majority of tissue macrophages, including Kupffer cells in the liver and F4/80+ macrophages of the lung, kidney, spleen and intestine. The small numbers of positive cells isolated from the liver resembled blood monocytes. In the gut, ECFP+ cells were identified primarily as classical dendritic cells or blood monocytes in disaggregated cell preparations. Immunohistochemistry showed large numbers of ECFP+ cells in the Peyer's patch and isolated lymphoid follicles. The MacBlue transgene was used to investigate the effect of treatment with CSF1-Fc, a form of the growth factor with longer half-life and efficacy. CSF1-Fc massively expanded both the immature myeloid cell (ECFP-) and Ly6C+ monocyte populations, but had a smaller effect on Ly6C- monocytes. There were proportional increases in ECFP+ cells detected in lung and liver, consistent with monocyte infiltration, but no generation of ECFP+ Kupffer cells. In the gut, there was selective infiltration of large numbers of cells into the lamina propria and Peyer's patches. We discuss the use of the MacBlue transgene as a marker of monocyte/macrophage/dendritic cell differentiation.

Selection and characterization of a DNA aptamer that can discriminate between cJun/cJun and cJun/cFos

The AP-1 family of transcriptional activators plays pivotal roles in regulating a wide range of biological processes from the immune response to tumorigenesis. Determining the roles of specific AP-1 dimers in cells, however, has remained challenging because common molecular biology techniques are unable to distinguish between the role of, for example, cJun/cJun homodimers versus cJun/cFos heterodimers. Here we used SELEX (systematic evolution of ligands by exponential enrichment) to identify and characterize DNA aptamers that are >100-fold more specific for binding cJun/cJun compared to cJun/cFos, setting the foundation to investigate the biological functions of different AP-1 dimer compositions.

Involvement of AP-1 and C/EBPβ in upregulation of endothelin B (ETB) receptor expression in a rodent model of glaucoma

Previous studies showed that the endothelin B receptor (ET_B) expression was upregulated and played a key role in neurodegeneration in rodent models of glaucoma. However, the mechanisms underlying upregulation of ET_B receptor expression remain largely unknown. Using promoter-reporter assays, the 1258 bp upstream the human ET_B promoter region was found to be essential for constitutive expression of ET_B receptor gene in human non-pigmented ciliary epithelial cells (HNPE). The −300 to −1 bp and −1258 to −600 bp upstream promoter regions of the ET_B receptor appeared to be the key binding regions for transcription factors. In addition, the crucial AP-1 binding site located at −615 to −624 bp upstream promoter was confirmed by luciferase assays and CHIP assays which were performed following overexpression of c-Jun in HNPE cells. Overexpression of either c-Jun or C/EBPβ enhanced the ET_B receptor promoter activity, which was reflected in increased mRNA and protein levels of ET_B receptor. Furthermore, knock-down of either c-Jun or C/EBPβ in HNPE cells was significantly correlated to decreased mRNA levels of both ET_B and ET_A receptor. These observations suggest that c-Jun and C/EBPβ are important for regulated expression of the ET_B receptor in HNPE cells. In separate experiments, intraocular pressure (IOP) was elevated in one eye of Brown Norway rats while the corresponding contralateral eye served as control. Two weeks of IOP elevation produced increased expression of c-Jun and C/EBPβ in the retinal ganglion cell (RGC) layer from IOP-elevated eyes. The mRNA levels of c-Jun, ET_A and ET_B receptor were upregulated by 2.2-, 3.1- and 4.4-fold in RGC layers obtained by laser capture microdissection from retinas of eyes with elevated IOP, compared to those from contralateral eyes. Taken together, these data suggest that transcription factor AP-1 plays a key role in elevation of ET_B receptor in a rodent model of ocular hypertension.

Distinct mechanisms for induction and tolerance regulate the immediate early genes encoding interleukin 1β and tumor necrosis factor α

Interleukin-1β and Tumor Necrosis Factor α play related, but distinct, roles in immunity and disease. Our study revealed major mechanistic distinctions in the Toll-like receptor (TLR) signaling-dependent induction for the rapidly expressed genes (IL1B and TNF) coding for these two cytokines. Prior to induction, TNF exhibited pre-bound TATA Binding Protein (TBP) and paused RNA Polymerase II (Pol II), hallmarks of poised immediate-early (IE) genes. In contrast, unstimulated IL1B displayed very low levels of both TBP and paused Pol II, requiring the lineage-specific Spi-1/PU.1 (Spi1) transcription factor as an anchor for induction-dependent interaction with two TLR-activated transcription factors, C/EBPβ and NF-κB. Activation and DNA binding of these two pre-expressed factors resulted in de novo recruitment of TBP and Pol II to IL1B in concert with a permissive state for elongation mediated by the recruitment of elongation factor P-TEFb. This Spi1-dependent mechanism for IL1B transcription, which is unique for a rapidly-induced/poised IE gene, was more dependent upon P-TEFb than was the case for the TNF gene. Furthermore, the dependence on phosphoinositide 3-kinase for P-TEFb recruitment to IL1B paralleled a greater sensitivity to the metabolic state of the cell and a lower sensitivity to the phenomenon of endotoxin tolerance than was evident for TNF. Such differences in induction mechanisms argue against the prevailing paradigm that all IE genes possess paused Pol II and may further delineate the specific roles played by each of these rapidly expressed immune modulators.

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.

NFATc2 recruits cJun homodimers to an NFAT site to synergistically activate interleukin-2 transcription

Transcription of interleukin-2 (IL-2), a pivotal cytokine in the mammalian immune response, is induced by NFAT and AP-1 transcriptional activators in stimulated T cells. NFATc2 and cJun drive high levels of synergistic human IL-2 transcription, which requires a unique interaction between the C-terminal activation domain of NFATc2 and cJun homodimers. Here we studied the mechanism by which this interaction contributes to synergistic activation of IL-2 transcription. We found that NFATc2 can recruit cJun homodimers to the -45 NFAT element, which lacks a neighboring AP-1 site. The bZip domain of cJun is sufficient to interact with the C-terminal activation domain of NFATc2 in the absence of DNA and this interaction is inhibited by AP-1 DNA. When the -45 NFAT site was replaced by either an NFAT/AP-1 composite site or a single AP-1 site the specificity for cJun homodimers in synergistically activating IL-2 transcription was lost, and cJun/cFos heterodimers strongly activated transcription. These studies support a model in which IL-2 transcriptional synergy is mediated by the unique recruitment of a cJun homodimer to the -45 NFAT site by NFATc2, where it acts as a co-activator for IL-2 transcription.

Elevated cJUN expression and an ATF/CRE site within the ATF3 promoter contribute to activation of ATF3 transcription by the amino acid response

Mammalian cells respond to amino acid deprivation through multiple signaling pathways referred to as the amino acid response (AAR). Transcription factors mediate the AAR after their activation by several mechanisms; examples include translational control (activating transcription factor 4, ATF4), phosphorylation (p-cJUN), and transcriptional control (ATF3). ATF4 induces ATF3 transcription through a promoter-localized C/EBP-ATF response element (CARE). The present report characterizes an ATF/CRE site upstream of the CARE that also contributes to AAR-induced ATF3 transcription. ATF4 binds to the ATF/CRE and CARE sequences and both are required for a maximal response to ATF4 induction. ATF3, which antagonizes ATF4 and represses its own gene, also exhibited binding activity to the ATF/CRE and CARE sequences. The AAR resulted in elevated total cJUN and p-cJUN protein levels and both forms exhibited binding activity to the ATF/CRE and CARE ATF3 sequences. Knockdown of AAR-enhanced cJUN expression blocked induction of the ATF3 gene and mutation of either the ATF/CRE or the CARE site prevented the cJUN-dependent increase in ATF3-driven luciferase activity. The results indicate that both increased cJUN and the cis-acting ATF/CRE sequence within the ATF3 promoter contribute to the transcriptional activation of the gene during the AAR.

Activation of IL-1β and TNFα genes is mediated by the establishment of permissive chromatin structures during monopoiesis

IL-1β and TNFα participate in a wide range of immunoregulatory activities. The overproduction of these cytokines can result in inflammatory and autoimmune diseases. Monocytes are the main producers of both cytokines. In contrast, studies with highly purified polymorphonuclear leukocytes (PMN) showed their inability to synthesize IL-1β and TNFα. Mature monocytes and PMN are derived from the same precursors. However, the reason for the differential IL-1β and TNFα expression is not elucidated. Our study investigates the epigenetic mechanisms that may explain this apparent discrepancy. The expression and promoter accessibilities of IL-1β and TNFα genes of primary and in vitro differentiated monocytes and PMN and their common precursors were compared. The effects of histone deacetylase (HDAC)-inhibition by trichostatin A (TSA) on IL-1β and TNFα expression and their promoter structures were measured in promyeloid HL-60 cells. Cytokine expression was assessed by real-time PCR and ELISA. Chromatin structures were analyzed using chromatin accessibility by real-time PCR (CHART) assay. The proximal IL-1β promoter was remodeled into an open conformation during monopoiesis, but not granulopoiesis. Although stimulation-dependent, remodeling of the TNFα promoter was again only observed in monocytes. TSA activated IL-1β and TNFα expression and supported chromatin remodeling of their promoters in HL-60 cells. The ability to express IL-1β and TNFα is linked to a cell type specific promoter structure, which is established during monocytic but not granulocytic differentiation. The participation of acetylation in IL-1β and TNFα promoter activation shed new light on the regulation of IL-1β or TNFα expression. These data may have implications for understanding the progression from normal to disease conditions.

Auto-activation of c-JUN gene by amino acid deprivation of hepatocellular carcinoma cells reveals a novel c-JUN-mediated signaling pathway

Mammalian cells respond to protein or amino acid (AA) limitation by activating a number of signaling pathways, collectively referred to as the AA response (AAR), that modulate a range of cellular functions, including transcriptional induction of target genes. This study demonstrates that in hepatocellular carcinoma cells, expression of c-JUN, JUN-B, c-FOS, and FOS-B was induced by the AAR, whereas JUN-D, FRA-1, and FRA-2 were not. Of the four activated FOS/JUN members, c-JUN made the largest contribution to the induction of several known AAR target genes. For several human liver, prostate, and ovarian cell lines, the AAR-induced increase in c-JUN expression was greater in transformed cells compared with nontransformed counterparts, an effect independent of cell growth rate. Thus far, the best characterized AA-responsive genes are all transcriptionally activated by ATF4, but the AAR-dependent induction of c-JUN transcription was ATF4-independent. The increased expression of c-JUN was dependent on ATF2 and on activation of the MEK-ERK and JNK arms of the MAPK signaling pathways. Formation of c-JUN-ATF2-activated heterodimers was increased after AA limitation, and c-JUN or ATF2 knockdown suppressed the induction of c-JUN and other AAR target genes. AA deprivation triggers a feed-forward process that involves phosphorylation of existing c-JUN protein by JNK and subsequent auto-activation of the c-JUN gene by recruitment of c-JUN and ATF2 to two AP-1 sites within the proximal promoter. The results document the novel observation that AP-1 sequences within the c-JUN gene can function as transcriptional amino acid-response elements.

Eicosapentaenoic acid demethylates a single CpG that mediates expression of tumor suppressor CCAAT/enhancer-binding protein delta in U937 leukemia cells

Polyunsaturated fatty acids (PUFAs) inhibit proliferation and induce differentiation in leukemia cells. To investigate the molecular mechanisms whereby fatty acids affect these processes, U937 leukemia cells were conditioned with stearic, oleic, linolenic, α-linolenic, arachidonic, eicosapentaenoic, and docosahexaenoic acids. PUFAs affected proliferation; eicosapentaenoic acid (EPA) was the most potent on cell cycle progression. EPA enhanced the expression of the myeloid lineage-specific transcription factors CCAAT/enhancer-binding proteins (C/EBPβ and C/EBPδ), PU.1, and c-Jun, resulting in increased expression of the monocyte lineage-specific target gene, the macrophage colony-stimulating factor receptor. Indeed, it is known that PU.1 and C/EBPs interact with their consensus sequences on a small DNA fragment of macrophage colony-stimulating factor receptor promoter, which is a determinant for expression. We demonstrated that C/EBPβ and C/EBPδ bind the same response element as a heterodimer. We focused on the enhanced expression of C/EBPδ, which has been reported to be a tumor suppressor gene silenced by promoter hypermethylation in U937 cells. After U937 conditioning with EPA and bisulfite sequencing of the -370/-20 CpG island on the C/EBPδ promoter region, we found a site-specific CpG demethylation that was a determinant for the binding activity of Sp1, an essential factor for C/EBPδ gene basal expression. Our results provide evidence for a new role of PUFAs in the regulation of gene expression. Moreover, we demonstrated for the first time that re-expression of the tumor suppressor C/EBPδ is controlled by the methylation state of a site-specific CpG dinucleotide.

Pleiotropic action of AP-1 in v-Src-transformed cells

The activation of AP-1 is a hallmark of cell transformation by tyrosine kinases. In this study, we characterize the role of AP-1 proteins in the transformation of chicken embryo fibroblasts (CEF) by v-Src. In normal CEF, the expression of a dominant negative mutant of c-Jun (TAM67) induced senescence. In contrast, three distinct phenotypes were observed when TAM67 was expressed in v-Src-transformed CEF. While senescent cells were also present, the inhibition of AP-1 caused apoptosis in a fraction of the v-Src-transformed cells. In addition, cells containing lipid-rich vesicles accumulated, suggesting that a subpopulation of the v-Src-transformed cells underwent differentiation in response to the inhibition of AP-1. JunD and Fra-2 were the main components of this factor, while c-Jun accounted for a minor fraction of AP-1 in v-Src-transformed CEF. The downregulation of c-Jun expression by short hairpin RNA (shRNA) induced senescence in normal and v-Src-transformed cells. In contrast, a high incidence of apoptosis was caused by the downregulation of JunD, suggesting that it is required for the survival of v-Src-transformed CEF. Levels of the p53 tumor suppressor were elevated under conditions of JunD inhibition. Repression of p53 by shRNA enhanced the survival and anchorage-independent proliferation of v-Src-transformed CEF with JunD/AP-1 inhibition. The inhibition of Fra-2 had no visible phenotype in normal CEF but caused the appearance of lipid-rich vesicles in v-Src-transformed CEF. Therefore, AP-1 facilitated transformation by acting as a survival factor, by inhibiting premature entry into senescence, and by blocking the differentiation of v-Src-transformed CEF.

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

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

Changes in chromatin structure and methylation of the human interleukin-1beta gene during monopoiesis

SUMMARY

Interleukin-1beta (IL-1beta) induces the expression of a variety of proteins responsible for acute inflammation and chronic inflammatory diseases. However, the molecular regulation of IL-1beta expression in myeloid differentiation has not been elucidated. In this study the chromatin structure of the IL-1beta promoter and the impact of methylation on IL-1beta expression in monocytic development were examined. The results revealed that the IL-1beta promoter was inaccessible in undifferentiated promyeloid HL-60 cells but highly accessible in differentiated monocytic cells which additionally acquired the ability to produce IL-1beta. Accessibilities of differentiated cells were comparable to those of primary monocytes. Lipopolysaccharide (LPS) stimulation did not affect promoter accessibility in promyeloid and monocytic HL-60 cells, demonstrating that the chromatin remodelling of the IL-1beta promoter depends on differentiation and not on the transcriptional status of the cell. Demethylation via 5-aza-2'-deoxycytodine led to the induction of IL-1beta expression in undifferentiated and differentiated cells, which could be increased after LPS stimulation. Our data indicate that the IL-1beta promoter is reorganized into an open poised conformation during monopoiesis being a privilege of mature monocytes but not of the entire myeloid lineage. As a second mechanism, IL-1beta expression is regulated by methylation acting independently of the developmental stage of myeloid cells.

TLR cross-talk specifically regulates cytokine production by B cells from chronic inflammatory disease patients

Chronic systemic inflammation links periodontal disease and diabetes to increased incidence of serious comorbidities. Activation of TLRs, particularly TLR2 and TLR4, promotes chronic systemic inflammation. Human B cells have been generally thought to lack these TLRs. However, recent work showed that an increased percentage of circulating B cells from inflammatory disease patients express TLR2 and TLR4, and that TLR engagement on B cells resulted in unexpected changes in gene expression. New data show that B cells from inflammatory disease patients secrete multiple cytokines in response to different classes of TLR ligands. Furthermore, the B cell response to combinations of TLR ligands is cytokine- and ligand-specific. Some cytokines (IL-1beta and IL-10) are predominantly regulated by TLR4, but others (IL-8 and TNF-alpha) are predominantly regulated by TLR2, due in part to TLR-dictated changes in transcription factor/promoter association. TLR2 and TLR9 also regulate B cell TLR4 expression, demonstrating that TLR cross-talk controls B cell responses at multiple levels. Parallel examination of B cells from periodontal disease and diabetes patients suggested that outcomes of TLR cross-talk are influenced by disease pathology. We conclude that disease-associated alteration of B cell TLR responses specifically regulates cytokine production and may influence chronic inflammation.

Defining the chromatin signature of inducible genes in T cells

Inducible genes in T cells show the chromatin characteristics of active genes, suggesting they are primed for transcription.

Background

Specific chromatin characteristics, especially the modification status of the core histone proteins, are associated with active and inactive genes. There is growing evidence that genes that respond to environmental or developmental signals may possess distinct chromatin marks. Using a T cell model and both genome-wide and gene-focused approaches, we examined the chromatin characteristics of genes that respond to T cell activation.

Results

To facilitate comparison of genes with similar basal expression levels, we used expression-profiling data to bin genes according to their basal expression levels. We found that inducible genes in the lower basal expression bins, especially rapidly induced primary response genes, were more likely than their non-responsive counterparts to display the histone modifications of active genes, have RNA polymerase II (Pol II) at their promoters and show evidence of ongoing basal elongation. There was little or no evidence for the presence of active chromatin marks in the absence of promoter Pol II on these inducible genes. In addition, we identified a subgroup of genes with active promoter chromatin marks and promoter Pol II but no evidence of elongation. Following T cell activation, we find little evidence for a major shift in the active chromatin signature around inducible gene promoters but many genes recruit more Pol II and show increased evidence of elongation.

Conclusions

These results suggest that the majority of inducible genes are primed for activation by having an active chromatin signature and promoter Pol II with or without ongoing elongation.

c-Jun Protects Hypoxia-Inducible Factor-1α from Degradation via Its Oxygen-Dependent Degradation Domain in a Nontranscriptional Manner

Although hypoxia-inducible factor-1α (HIF-1α) has long been intensively investigated as a drug target by interfering with its expression or transcriptional function, the regulatory mechanisms of HIF-1α remain to be further clarified. We report here that c-Jun associates with HIF-1α via its oxygen-dependent degradation domain, masks the sites for ubiquitination, and thus protects HIF-1α from proteasome-executing degradation. All of these together resulted in the stabilization and accumulation of HIF-1α, consequently promoting the transcription of its target gene and driving angiogenesis-related events. The stabilization of HIF-1α was dependent on the domains of c-Jun for DNA binding and heterodimerization but independent of the Ser63/73 phosphorylation that is critical for transcriptional function. These findings highlight a previously unrecognized nontranscriptional function of c-Jun on the one hand and a distinct regulatory mechanism of HIF-1α activity on the other, consequently offering profound mechanistic insights into multiple events simultaneously involving both c-Jun and HIF-1α in tumor progression. [Cancer Res 2009;69(19):7704–12]

Cooperation between PU.1 and CAAT/enhancer-binding protein beta is necessary to induce the expression of the MD-2 gene

Myeloid differentiation factor 2 (MD-2) binds Gram-negative bacterial lipopolysaccharide with high affinity and is essential for Toll-like receptor 4-dependent signal transduction. MD-2 has recently been recognized as a type II acute phase protein. Plasma concentrations of the soluble form of MD-2 increase markedly during the course of severe infections. Its production is regulated in hepatocytes and myeloid cells by interleukin-6 (IL-6) but not IL-1beta. In the present work we show that two transcription factors (TF), PU.1 and CAAT/enhancer-binding protein beta (C/EBPbeta), participate in the activation of the human MD-2 gene in hepatocytic cells after stimulation with IL-6. PU.1 TF and proximal PU.1 binding sites in the MD-2 promoter were shown to be critical for the basal activity of the promoter as well as for IL-6-induced soluble MD-2 production. Deletions of proximal portions of the MD-2 promoter containing PU.1 and/or NF-IL-6 consensus binding sites as well as site-directed mutagenesis of these binding sites abrogated IL-6-dependent MD-2 gene activation. We show that the cooperation between C/EBPbeta and PU.1 is critical for the transcriptional activation of the MD-2 gene by IL-6. PU.1 was essentially known as a TF involved in the differentiation of myeloid precursor cells and the expression of surface receptors of the innate immunity. Herein, we show that it also participates in the regulation of an acute phase protein, MD-2, in nonmyeloid cells cooperatively with C/EBPbeta, a classical IL-6-inducible TF.

Identification of a minimal cis-element and cognate trans-factor(s) required for induction of Rac2 gene expression during K562 cell differentiation

Rac2 is a Rho family GTPase that is widely expressed in hematopoietic cells and plays a critical role in host defense. This study investigates the mechanisms responsible for increased Rac2 gene expression during myeloid cell differentiation. Treatment of K562 chronic myelogenous leukemia cells with phorbol-12-myristate-13-acetate (PMA) induces megakaryocytic differentiation and Rac2 gene transcription following a lag of 6-12 h. Promoter/luciferase reporter gene assays reveal that a 135 bp cis-element located between -4223 and -4008 bp upstream of the Rac2 transcription start site is necessary and sufficient for PMA-induced gene expression. The AP1 transcription factor binds to three cis-elements within the 135 bp Rac2 gene regulatory region both in vitro and in vivo following PMA treatment, and mutagenesis of the AP1 binding sites ablates the PMA responsiveness of the 135 bp Rac2 gene regulatory region. Over-expression of AP1 is sufficient to induce expression of a transiently transfected Rac2 promoter/luciferase plasmid, but not the endogenous Rac2 gene. Induction of AP1 in vitro DNA-binding activity is apparent within 1 h of PMA stimulation. However, AP1 binding to the endogenous Rac2 promoter exhibits a lag of 5-9 h, which correlates with reduced histone H3-Lys9 methylation, increased histone H3 acetylation, and increased nuclease accessibility within the 135 bp Rac2 gene regulatory region. These results demonstrate that PMA induction of Rac2 expression during terminal myeloid differentiation requires the coordinate induction of transcription factors and remodeling of Rac2 gene chromatin structure.

Increased c-Jun expression and reduced GATA2 expression promote aberrant monocytic differentiation induced by activating PTPN11 mutants

Juvenile myelomonocytic leukemia (JMML) is characterized by myelomonocytic cell overproduction and commonly bears activating mutations in PTPN11. Murine hematopoietic progenitors expressing activating Shp2 undergo myelomonocytic differentiation, despite being subjected to conditions that normally support only mast cells. Evaluation of hematopoietic-specific transcription factor expression indicates reduced GATA2 and elevated c-Jun in mutant Shp2-expressing progenitors. We hypothesized that mutant Shp2-induced Ras hyperactivation promotes c-Jun phosphorylation and constitutive c-Jun expression, permitting, as a coactivator of PU.1, excessive monocytic differentiation and reduced GATA2. Hematopoietic progenitors expressing activating Shp2 demonstrate enhanced macrophage CFU (CFU-M) compared to that of wild-type Shp2-expressing cells. Treatment with the JNK inhibitor SP600125 or cotransduction with GATA2 normalizes activating Shp2-generated CFU-M. However, cotransduction of DeltaGATA2 (lacking the C-terminal zinc finger, needed to bind PU.1) fails to normalize CFU-M. NIH 3T3 cells expressing Shp2E76K produce higher levels of luciferase expression directed by the macrophage colony-stimulating factor receptor (MCSFR) promoter, which utilizes c-Jun as a coactivator of PU.1. Coimmunoprecipitation demonstrates increased c-Jun-PU.1 complexes in mutant Shp2-expressing hematopoietic progenitors, while chromatin immunoprecipitation demonstrates increased c-Jun binding to the c-Jun promoter and an increased c-Jun-PU.1 complex at the Mcsfr promoter. Furthermore, JMML progenitors express higher levels of c-JUN than healthy controls, substantiating the disease relevance of these mechanistic findings.

EVI1 Impairs myelopoiesis by deregulation of PU.1 function

EVI1 is an oncogene inappropriately expressed in the bone marrow (BM) of approximately 10% of myelodysplastic syndrome (MDS) patients. This disease is characterized by severe anemia and multilineage myeloid dysplasia that are thought to be a major cause of mortality in MDS patients. We earlier reported on a mouse model that constitutive expression of EVI1 in the BM led to fatal anemia and myeloid dysplasia, as observed in MDS patients, and we subsequently showed that EVI1 interaction with GATA1 blocks proper erythropoiesis. Whereas this interaction could provide the basis for the erythroid defects in EVI1-positive MDS, it does not explain the alteration of myeloid differentiation. Here, we have examined the expression of several genes activated during terminal myelopoiesis in BM cells and identified a group of them that are altered by EVI1. A common feature of these genes is their regulation by the transcription factor PU.1. We report here that EVI1 interacts with PU.1 and represses the PU.1-dependent activation of a myeloid promoter. EVI1 does not seem to inhibit PU.1 binding to DNA, but rather to block its association with the coactivator c-Jun. After mapping the PU.1-EVI1 interaction sites, we show that an EVI1 point mutant, unable to bind PU.1, restores the activation of PU.1-regulated genes and allows a normal differentiation of BM progenitors in vitro.

B cells from periodontal disease patients express surface Toll-like receptor 4

Chronic systemic inflammation links periodontal disease (PD) to increased incidence of cardiovascular disease. Activation of TLRs, particularly TLR4, promotes chronic inflammation in PD by stimulating myeloid cells. B cells from healthy individuals are generally refractory to TLR4 agonists as a result of low surface TLR4 expression. Unexpectedly, a significantly increased percentage of gingival and peripheral blood B cells from patients with PD expressed surface TLR4. Surface expression correlated with an active TLR4 promoter that mimicked the TLR4 promoter in neutrophils. B cells from PD patients were surface myeloid differentiation protein 2-positive and also packaged the enhancer of a proinflammatory cytokine, IL-1 beta, into an active structure, demonstrating that these cells harbor key characteristics of proinflammatory cell types. Furthermore, B cells lacked activating signatures of a natural IL-1 beta inhibitor, IL-1 receptor antagonist. Surprisingly, despite multiple signatures of proinflammatory cells, freshly isolated B cells from PD patients had decreased expression of TLR pathway genes compared with B cells from healthy individuals. Decreases in inflammatory gene expression were even more dramatic in B cells stimulated with a TLR4 ligand from a periodontal pathogen, Porphyromonas gingivalis LPS 1690. In contrast, B cell TLR4 was not activated by the prototypic TLR4 ligand Escherichia coli LPS. These findings raise the unexpected possibility that TLR4 engagement modulates B cell activation in PD patients.

Dynamic protein associations define two phases of IL-1beta transcriptional activation

IL-1beta is a key proinflammatory cytokine with roles in multiple diseases. Monocytes package the IL-1beta promoter into a "poised architecture" characterized by a histone-free transcription start site and constitutive transcription factor associations. Upon LPS stimulation, multiple proteins inducibly associate with the IL-1beta gene. To understand how the complex combination of constitutive and inducible transcription factors activate the IL-1beta gene from a poised structure, we measured temporal changes in NF-kappaB and IFN regulatory factor (IRF) association with IL-1beta regulatory elements. Association of the p65 subunit of NF-kappaB peaks 30-60 min post-monocyte stimulation, and it shortly precedes IRF-4 recruitment to the IL-1beta enhancer and maximal mRNA production. In contrast, IRF-8/enhancer association decreases poststimulation. To test the importance of delayed IRF-4/enhancer association, we introduced a mutated PU.1 protein shown to prevent PU.1-mediated IRF-4 recruitment to the enhancer sequence. Mutated PU.1 initially increased IL-1beta mRNA followed by decreased mRNA levels 2-3 h poststimulation. Taken together, these data support a dynamic model of IL-1beta transcriptional activation in which a combination of IRF-8 and p65 drives the initial phase of IL-1beta transcription, while PU.1-mediated IRF-4 recruitment to the enhancer is important for the second phase. We further demonstrate that activation of both NF-kappaB and IRF-4 depends on CK2 kinase activity. Because IRF-4/enhancer association requires CK2 but not p65 activation, we conclude that CK2 triggers the IRF-4 and p65 pathways independently to serve as a master regulator of IL-1beta transcription.

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

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