NF-kappaB elements contribute to junB inducibility by lipopolysaccharide in the murine macrophage cell line RAW264.7

JunB: a paradigm for Jun family in immune response and cancer

Jun B proto-oncogene (JunB) is a crucial member of dimeric activator protein-1 (AP-1) complex, which plays a significant role in various physiological processes, such as placental formation, cardiovascular development, myelopoiesis, angiogenesis, endochondral ossification and epidermis tissue homeostasis. Additionally, it has been reported that JunB has great regulatory functions in innate and adaptive immune responses by regulating the differentiation and cytokine secretion of immune cells including T cells, dendritic cells and macrophages, while also facilitating the effector of neutrophils and natural killer cells. Furthermore, a growing body of studies have shown that JunB is involved in tumorigenesis through regulating cell proliferation, differentiation, senescence and metastasis, particularly affecting the tumor microenvironment through transcriptional promotion or suppression of oncogenes in tumor cells or immune cells. This review summarizes the physiological function of JunB, its immune regulatory function, and its contribution to tumorigenesis, especially focusing on its regulatory mechanisms within tumor-associated immune processes.

Fisetin Ameliorates the Inflammation and Oxidative Stress in Lipopolysaccharide-Induced Endometritis

Purpose

Fisetin is a natural flavone of polyphenol, which widely exists in many fruits and vegetables and has many pharmacological activities. However, the mechanism involved remains largely unknown. Here, we investigate the mechanisms of fisetin on the inflammatory response and oxidative stress in LPS-induced endometritis model and bovine endometrial epithelial cell line (BEND).

Methods

The function of fisetin was analyzed by network pharmacology. Effects of increasing doses of fisetin on inflammation and oxidative stress are studied in BALB/c mice with LPS-induced endometritis. The underlying mechanisms of antioxidant activity of fisetin were further explored in LPS-stimulated BEND cells.

Results

The results showed that fisetin significantly alleviated LPS-induced inflammatory injury and oxidative stress both in vivo and in vitro. Further studies found that fisetin greatly inhibited the LPS stimulated TLR4 expression and nuclear translocation of nuclear factor-κB (NF-κB), thus reducing the pro-inflammatory mediators secretion. Silencing TLR4 reduced LPS-induced inflammatory responses. Moreover, we observed that fisetin evidently decreased ROS production but activated Nrf2/HO-1 pathway in LPS-stimulated BEND cells. To further explore the role of Nrf2 in fisetin-induced HO-1 protein expression, the specific siRNA was used to silence Nrf2 expression. Silencing Nrf2 abrogated the inhibitory effects of fisetin on LPS-induced pro-inflammatory cytokines TNF-α, IL-1β secretion, NADPH oxidase-4 (Nox4) and ROS production.

Conclusion

In conclusion, fisetin effectively protected against LPS-induced oxidative stress and inflammatory responses which may be closely correlated to inhibition of TLR4-mediated ROS/NF-κB and activation of the Nrf2/HO-1 pathway.

Protective effects of total alkaloids from Dendrobium crepidatum against LPS-induced acute lung injury in mice and its chemical components

Dendrobium crepidatum was one of the sources of Herba Dendrobii, a famous and precious traditional Chinese medicine. Indolizine-type alkaloids are the main characteristic ingredients of D. crepidatum, which possesses a variety of changeable skeletons. In the present study, we found that the total alkaloids of D. crepidatum (TAD) can inhibit the production of nitric oxide (NO) in lipopolysaccharide (LPS)-activated macrophages and showed protective effects against LPS-induced acute lung injury (ALI) in mice through downregulating the TLR4-mediated MyD88/MAPK signaling pathway. Further phytochemical study showed that six previously undescribed indolizine-type compounds, including a racemic mixture (dendrocrepidine A-E) were isolated from TAD. Meanwhile, dendrocrepidine F was separated into a pair of enantiomers by a chiral chromatography, and their absolute configurations were assigned by single-crystal X-ray diffraction analysis. The isomer (-)-dendrocrepidine F showed higher anti-inflammatory effects by inhibiting NO production in LPS-treated macrophages with an IC₅₀ value of 13.3 μM. Taken together, indolizine-type alkaloids are the active components of D. crepidatum through downregulating the TLR4-mediated pathway, indicating some kind of therapy of TAD for ALI treatment.

The Anti-Inflammatory Effects of Interferon Tau by Suppressing NF-κB/MMP9 in Macrophages Stimulated with Staphylococcus aureus

Previous studies have reported that interferon tau (IFNT) significantly mitigates tissue inflammation. However, this effect and its regulating pathways have not been reported for Staphylococcus aureus-induced inflammation. In this study, RAW 264.7 cells stimulated with S. aureus were used to identify the anti-inflammatory effects and mechanism of IFNT. First, IFNT was found to be noncytotoxic to macrophages treated with the high dose of 200 ng/mL IFNT. ELISA and qPCR revealed that IFNT decreased the expression of proinflammatory cytokines such as TNF-α, IL-1β, and IL-6. TLR2, which is involved in the immune response during S. aureus infection, directly affected NF-κB pathway activation and was also downregulated by IFNT. Subsequent Western blotting showed that the phosphorylation of IκBα and NF-κB p65 was inhibited by IFNT. Therefore, although the MMP9 levels were significantly downregulated in a dose-dependent manner by IFNT, little change in MMP2 was observed in S. aureus-stimulated RAW 264.7 cells. Furthermore, PDTC, an inhibitor of NF-κB, also significantly decreased MMP9 levels by inhibiting NF-κB p65 activation. All of these findings strongly suggested that IFNT suppresses the NF-κB/MMP9 signal transduction pathway and subsequently exerts its anti-inflammatory effects in S. aureus-stimulated RAW 264.7 cells.

DJ-1 contributes to adipogenesis and obesity-induced inflammation

Adipose tissue functions as an endocrine organ, and the development of systemic inflammation in adipose tissue is closely associated with metabolic diseases, such as obesity and insulin resistance. Accordingly, the fine regulation of the inflammatory response caused by obesity has therapeutic potential for the treatment of metabolic syndrome. In this study, we analyzed the role of DJ-1 (PARK7) in adipogenesis and inflammation related to obesity in vitro and in vivo. Many intracellular functions of DJ-1, including oxidative stress regulation, are known. However, the possibility of DJ-1 involvement in metabolic disease is largely unknown. Our results suggest that DJ-1 deficiency results in reduced adipogenesis and the down-regulation of pro-inflammatory cytokines in vitro. Furthermore, DJ-1-deficient mice show a low-level inflammatory response in the high-fat diet-induced obesity model. These results indicate previously unknown functions of DJ-1 in metabolism and therefore suggest that precise regulation of DJ-1 in adipose tissue might have a therapeutic advantage for metabolic disease treatment.

The natural chemopreventive agent sulforaphane inhibits STAT5 activity

Signal transducer and activator of transcription STAT5 is an essential mediator of cytokine, growth factor and hormone signaling. While its activity is tightly regulated in normal cells, its constitutive activation directly contributes to oncogenesis and is associated to a number of hematological and solid tumor cancers. We previously showed that deacetylase inhibitors can inhibit STAT5 transcriptional activity. We now investigated whether the dietary chemopreventive agent sulforaphane, known for its activity as deacetylase inhibitor, might also inhibit STAT5 activity and thus could act as a chemopreventive agent in STAT5-associated cancers. We describe here sulforaphane (SFN) as a novel STAT5 inhibitor. We showed that SFN, like the deacetylase inhibitor trichostatin A (TSA), can inhibit expression of STAT5 target genes in the B cell line Ba/F3, as well as in its transformed counterpart Ba/F3-1*6 and in the human leukemic cell line K562 both of which express a constitutively active form of STAT5. Similarly to TSA, SFN does not alter STAT5 initial activation by phosphorylation or binding to the promoter of specific target genes, in favor of a downstream transcriptional inhibitory effect. Chromatin immunoprecipitation assays revealed that, in contrast to TSA however, SFN only partially impaired the recruitment of RNA polymerase II at STAT5 target genes and did not alter histone H3 and H4 acetylation, suggesting an inhibitory mechanism distinct from that of TSA. Altogether, our data revealed that the natural compound sulforaphane can inhibit STAT5 downstream activity, and as such represents an attractive cancer chemoprotective agent targeting the STAT5 signaling pathway.

Chromatin loop organization of the junb locus in mouse dendritic cells

The junb gene behaves as an immediate early gene in bacterial lipopolysaccharide (LPS)-stimulated dendritic cells (DCs), where its transient transcriptional activation is necessary for the induction of inflammatory cytokines. junb is a short gene and its transcriptional activation by LPS depends on the binding of NF-κB to an enhancer located just downstream of its 3′ UTR. Here, we have addressed the mechanisms underlying the transcriptional hyper-reactivity of junb. Using transfection and pharmacological assays to complement chromatin immunoprecipitation analyses addressing the localization of histones, polymerase II, negative elongation factor (NELF)-, DRB sensitivity-inducing factor (DSIF)- and Positive Transcription Factor b complexes, we demonstrate that junb is a RNA Pol II-paused gene where Pol II is loaded in the transcription start site domain but poorly active. Moreover, High salt-Recovered Sequence, chromosome conformation capture (3C)- and gene transfer experiments show that (i) junb is organized in a nuclear chromatin loop bringing into close spatial proximity the upstream promoter region and the downstream enhancer and (ii) this configuration permits immediate Pol II release on the junb body on binding of LPS-activated NF-κB to the enhancer. Thus, our work unveils a novel topological framework underlying fast junb transcriptional response in DCs. Moreover, it also points to a novel layer of complexity in the modes of action of NF-κB.

DSIF restricts NF-κB signaling by coordinating elongation with mRNA processing of negative feedback genes

NF-κB is central for immune response and cell survival, and its deregulation is linked to chronic inflammation and cancer through poorly defined mechanisms. IκBα and A20 are NF-κB target genes and negative feedback regulators. Upon their activation by NF-κB, DSIF is recruited, P-TEFb is released, and their elongating polymerase II (Pol II) C-terminal domain (CTD) remains hypophosphorylated. We show that upon DSIF knockdown, mRNA levels of a subset of NF-κB targets are not diminished; yet much less IκBα and A20 protein are synthesized, and NF-κB activation is abnormally prolonged. Further analysis of IκBα and A20 mRNA revealed that a significant portion is uncapped, unspliced, and retained in the nucleus. Interestingly, the Spt5 C-terminal repeat (CTR) domain involved in elongation stimulation through P-TEFb is dispensable for IκBα and A20 regulation. These findings assign a function for DSIF in cotranscriptional mRNA processing when elongating Pol II is hypophosphorylated and define DSIF as part of the negative feedback regulation of NF-κB.

Ets-1 activates overexpression of JunB and CD30 in Hodgkin's lymphoma and anaplastic large-cell lymphoma

Overexpression of CD30 and JunB is a hallmark of tumor cells in Hodgkin's lymphoma (HL) and anaplastic large-cell lymphoma (ALCL). We reported that CD30-extracellular signal-regulated kinase (ERK)1/2 mitogen-activated protein kinase (MAPK) signaling induces JunB, which maintains constitutive activation of the CD30 promoter. Herein, we localize a cis-acting enhancer in the JunB promoter that is regulated by Ets-1. We show that E26 transformation-specific-1 (Ets-1) (-146 to -137) enhances JunB promoter activation in a manner that is dependent on CD30 or the nucleophosmin-anaplastic lymphoma kinase (NPM-ALK)-ERK1/2 MAPK pathway. Ets-1 knockdown reduces the expression of both JunB and CD30, and CD30 knockdown significantly reduces JunB expression in HL and ALCL cell lines. NPM-ALK knockdown also reduces JunB expression in ALCL cell lines expressing NPM-ALK. Collectively, these results indicate that CD30 and NPM-ALK cooperate to activate the ERK1/2 MAPK-Ets-1 pathway. Ets-1, constitutively activated by ERK1/2-MAPK, plays a central role in the overexpression of JunB and CD30, which are both involved in the pathogenesis of HL and ALCL.

An NF-kappaB-dependent role for JunB in the induction of proinflammatory cytokines in LPS-activated bone marrow-derived dendritic cells

Background

Dendritic cells (DCs) play a key role in the induction of adaptive and memory immune responses. Upon encounter with pathogens, they undergo a complex maturation process and migrate toward lymphoid organs where they stimulate immune effector cells. This process is associated with dramatic transcriptome changes, pointing to a paramount role for transcription factors in DC activation and function. The regulation and the role of these transcription factors are however ill-defined and require characterization. Among those, AP-1 is a family of dimeric transcription complexes with an acknowledged role in the control of immunity. However, it has not been studied in detail in DCs yet.

Methodology/Principal Findings

Here, we have investigated the regulation and function of one of its essential components, JunB, in primary bone marrow–derived DCs induced to maturate upon stimulation by Escherichia coli lipopolysaccharide (LPS). Our data show fast and transient NF-κB–dependent transcriptional induction of the junb gene correlating with the induction of the TNFα, IL-6, and IL-12 proinflammatory cytokines. Inhibition of JunB protein induction by RNA interference hampered the transcriptional activation of the TNF-α, IL-6, and IL-12p40 genes. Consistently, chromatin immunoprecipitation experiments showed LPS-inducible binding of JunB at AP-1–responsive sites found in promoter regions of these genes. Concomitant LPS-inducible NF-κB/p65 binding to these promoters was also observed.

Conclusions/Significance

We identified a novel role for JunB—that is, induction of proinflammatory cytokines in LPS-activated primary DCs with NF-κB acting not only as an inducer of JunB, but also as its transcriptional partner.

JunB Induced by Constitutive CD30–Extracellular Signal-Regulated Kinase 1/2 Mitogen-Activated Protein Kinase Signaling Activates the CD30 Promoter in Anaplastic Large Cell Lymphoma and Reed-Sternberg Cells of Hodgkin Lymphoma

High expression of CD30 and JunB is characteristic of tumor cells in anaplastic large cell lymphoma (ALCL) and Hodgkin lymphoma (HL). Possible interactions of CD30 and JunB were examined in this study. We found that the CD30 promoter in tumor cells of both nucleophosmin (NPM)-anaplastic lymphoma kinase (ALK)-positive and NPM-ALK-negative ALCL and HL is regulated by a constitutively active CD30-extracellular signal-regulated kinase (ERK) 1/2 mitogen-activated protein kinase (MAPK). Phosphorylation of ERK1/2 MAPK was confirmed in nuclei of tumor cells in both ALCL and HL. CD30-ERK1/2 MAPK signals induce JunB expression, which maintains high activity of the CD30 promoter. JunB induction seems to be largely independent of nuclear factor kappaB in ALCL and HL. These results show a common mechanism of CD30 overexpression in ALCL and HL, although the outcome of CD30 signaling differs between NPM-ALK-positive ALCL and NPM-ALK-negative ALCL, cutaneous ALCL, and HL as we recently reported.

DNA microarray analysis of gene expression in iris and ciliary body of rat eyes with endotoxin-induced uveitis

The purposes of this study are to determine the genes that are up- or down-regulated in eyes with endotoxin-induced uveitis (EIU) by an oligonucleotide microarray system, and to determine the temporal and spatial changes in expression of selected genes that show strong up-regulation. EIU was induced by a footpad injection of lipopolysaccharide (LPS) in male Lewis rats. The expression of genes in the iris-ciliary body (ICB) at 2, 6, 12, and 24 hr after LPS injection was determined by oligonucleotide microarray analyses and compared to that in control rats. The microarray displayed 9911 genes and expressed sequence tags (ESTs). Cluster analysis was performed for highly up-regulated genes. Selected genes for cytokines (interleukin (IL)-1 beta and IL-6), chemokines (RANTES), and immediate early genes (Jun B, c-Fos, and c-Jun) were also studied by real-time polymerase chain reaction (PCR). Immunohistochemical studies were performed to localize the protein expression of some immediate early gene products. After LPS injection, the expression of 1930 genes were increased or decreased over 2-folds compared with normal controls by 24 hr. One hundred and seventeen genes were up-regulated over 10-fold, and these were classified into five clusters with similar expression pattern. The immediate early genes and transcription factors genes were included in one cluster of up-regulated genes peaking at 2 hr after the LPS injection. The expressions of cytokines, chemokines, and adhesion molecules were highly up-regulated. Real-time PCR analyses for selected genes showed similar expression changes as detected by the microarray analyses. Jun B immunoreactivity was found in the ICB cells at 3 and 6 hr after LPS injection. Gene expression changes after LPS injection were profiled by using an oligonucleotide microarray system. Our data suggest that the immediate early genes, such as Jun B, play an important role in inducing the inflammatory-related genes in the ICB.

Identification of endogenous glucocorticoid repressed genes differentially regulated by a glucocorticoid receptor mutant able to separate between nuclear factor-kappaB and activator protein-1 repression

Glucocorticoids are commonly used in the clinic, but long-term treatment is often associated with severe side effects. One way to reduce unwanted effects is to restrict glucocorticoid receptor (GR) signaling through defined pathways. In this study, we examine endogenous target genes regulated by a GR mutant that in contrast to the wild-type GR is unable to repress stimulated nuclear factor-kappaB (NF-kappaB) activity, whereas repression of activator protein-1 (AP-1) activity is maintained. This GR mutant (GRR488Q) harbors a point mutation in the second zinc finger of the DNA binding domain. Its ability to distinguish between NF-kappaB and AP-1 repression is defined using reporter genes regulated by both simple and natural promoters. The inability of GRR488Q to repress NF-kappaB was not related to its inability to activate target genes through a glucocorticoid response element. Furthermore, the discriminating property was observed in three different cell lines, suggesting that this is not a cell-specific effect. These results show that different receptor surfaces or mechanisms are involved in repression of NF-kappaB and AP-1, respectively. It is interesting that the GRR488Q still interacted physically with NF-kappaB. Gene expression profiling of human embryonic kidney 293 cells, which express the wild-type GR and the GRR488Q mutant allowed identification of endogenous genes preferentially repressed by GR interference with NF-kappaB activity. The genes differentially regulated by GRR488Q mutant versus the wild-type GR after 2 h of treatment seem mainly to be involved in control of transcription and cell growth. At 8 h, no such distinction could be seen.

Transcriptional regulation of the MAIL gene in LPS-stimulated RAW264 mouse macrophages

IkappaB inhibits nuclear factor kappa B (NF-kappaB), which is known to regulate the expression of various genes, including genes involved in inflammation. Recently, a novel IkappaB family protein, 'molecule possessing ankyrin repeats induced by lipopolysaccharide' (MAIL), was identified. MAIL is a nuclear-acting, inducible protein, unlike typical IkappaB proteins. However, the mechanism of its induction by lipopolysaccharide (LPS) is unclear. Using the LPS-reactive region located upstream from the MAIL gene, we investigated the mechanism of MAIL induction. MAIL expression was strongly regulated by NF-kappaB and partly regulated by CREB. Furthermore, deletion, point mutation and binding analyses revealed that the NF-kappaB binding site located at -229 to -220 bp is an essential target of MAIL expression. Overexpression of MAIL protein suppressed the LPS-induced promoter activity of the MAIL gene. These data indicate that MAIL expression is strongly upregulated by NF-kappaB, and it is controlled, at least in part, by an autoregulation mechanism.

The IkappaB kinase complex and NF-kappaB act as master regulators of lipopolysaccharide-induced gene expression and control subordinate activation of AP-1

Toll-like receptors (TLRs) recognize conserved products of microbial pathogens to initiate the innate immune response. TLR4 signaling is triggered upon binding of lipopolysaccharides (LPS) from gram-negative bacteria. Using comparative gene expression profiling, we demonstrate a master regulatory role of IkappaB kinase (IKK)/NF-kappaB signaling for immediate-early gene induction after LPS engagement in precursor B cells. IKK/NF-kappaB signaling controls a large panel of gene products associated with signaling and transcriptional activation and repression. Intriguingly, the induction of AP-1 activity by LPS in precursor B cells and primary dendritic cells fully depends on the IKK/NF-kappaB pathway, which promotes expression of several AP-1 family members, including JunB, JunD, and B-ATF. In pre-B cells, AP-1 augments induction of a subset of primary NF-kappaB targets, as shown for chemokine receptor 7 (CCR7) and immunoglobulin kappa light chain. Thus, our data illustrate that NF-kappaB orchestrates immediate-early effects of LPS signaling and controls secondary AP-1 activation to mount an appropriate biological response.

Molecular mechanisms of macrophage activation and deactivation by lipopolysaccharide: roles of the receptor complex

Bacterial lipopolysaccharide (LPS), the major structural component of the outer wall of Gram-negative bacteria, is a potent activator of macrophages. Activated macrophages produce a variety of inflammatory cytokines. Excessive production of cytokines in response to LPS is regarded as the cause of septic shock. On the other hand, macrophages exposed to suboptimal doses of LPS are rendered tolerant to subsequent exposure to LPS and manifest a profoundly altered response to LPS. Increasing evidence suggests that monocytic cells from patients with sepsis and septic shock survivors have characteristics of LPS tolerance. Thus, an understanding of the molecular mechanisms underlying activation and deactivation of macrophages in response to LPS is important for the development of therapeutics for septic shock and the treatment of septic shock survivors. Over the past several years, significant progress has been made in identifying and characterizing several key molecules and signal pathways involved in the regulation of macrophage functions by LPS. In this paper, we summarize the current findings of the functions of the LPS receptor complex, which is composed of CD14, Toll-like receptor 4 (TLR4), and myeloid differentiation protein-2 (MD-2), and the signal pathways of this LPS receptor complex with regard to both activation and deactivation of macrophages by LPS. In addition, recent therapeutic approaches for septic shock targeting the LPS receptor complex are described.

Generation of stably transfected Mammalian cell lines as fluorescent screening assay for NF-kappaB activation-dependent gene expression

Cellular stress protection responses lead to increased transcription of several genes via modulation of transcription factors. Activation of the Nuclear Factor kappaB (NF-kappaB) pathway as a possible antiapoptotic route represents one important cellular stress response. To identify conditions that are capable of modifying this pathway, a screening assay for detection of NF-kappaB-dependent gene activation using the reporter protein Enhanced Green Fluorescent Protein (EGFP) and its destabilized variant (d2EGFP) was developed. Human Embryonic Kidney (HEK/293) cells were stably transfected with a vector carrying EGFP or d2EGFP under control of a synthetic promoter containing 4 copies of the NF-kappaB response element. Treatment with tumor necrosis factor alpha (TNF-alpha) gave rise to substantial EGFP/d2EGFP expression in up to 90% of the cells and was therefore used to screen different stably transfected clones for induction of NF-kappaB-dependent gene expression. The time course of NF-kappaB activation leading to d2EGFP expression was measured in an oligonucleotide-based NF-kappaB-ELISA. NF-kappaB binding in-creased after 15-min incubation with TNF-alpha. In parallel, d2EGFP increased after 3 h and reached its maximum at 24 h. These results show (1) the time lag between NF-kappaB activation and d2EGFP transcription, translation, and protein folding and (2) the increased reporter gene expression after treatment with TNF-alpha to be caused by the activation of NF-kappaB. The detection of d2EGFP expression required FACS analysis or fluorescence microscopy, while EGFP could also be measured in the microplate reader, rendering the assay useful for high-throughput screening.

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

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