CCAAT displacement protein competes with multiple transcriptional activators for binding to four sites in the proximal gp91phox promoter

CUT homeobox genes: transcriptional regulation of neuronal specification and beyond

CUT homeobox genes represent a captivating gene class fulfilling critical functions in the development and maintenance of multiple cell types across a wide range of organisms. They belong to the larger group of homeobox genes, which encode transcription factors responsible for regulating gene expression patterns during development. CUT homeobox genes exhibit two distinct and conserved DNA binding domains, a homeodomain accompanied by one or more CUT domains. Numerous studies have shown the involvement of CUT homeobox genes in diverse developmental processes such as body axis formation, organogenesis, tissue patterning and neuronal specification. They govern these processes by exerting control over gene expression through their transcriptional regulatory activities, which they accomplish by a combination of classic and unconventional interactions with the DNA. Intriguingly, apart from their roles as transcriptional regulators, they also serve as accessory factors in DNA repair pathways through protein-protein interactions. They are highly conserved across species, highlighting their fundamental importance in developmental biology. Remarkably, evolutionary analysis has revealed that CUT homeobox genes have experienced an extraordinary degree of rearrangements and diversification compared to other classes of homeobox genes, including the emergence of a novel gene family in vertebrates. Investigating the functions and regulatory networks of CUT homeobox genes provides significant understanding into the molecular mechanisms underlying embryonic development and tissue homeostasis. Furthermore, aberrant expression or mutations in CUT homeobox genes have been associated with various human diseases, highlighting their relevance beyond developmental processes. This review will overview the well known roles of CUT homeobox genes in nervous system development, as well as their functions in other tissues across phylogeny.

CUX1, A Controversial Player in Tumor Development

CUX1 belongs to the homeodomain transcription factor family and is evolutionarily and functionally conserved from Drosophila to humans. In addition to the involvement in various physiological events including tissue development, cell proliferation, differentiation and migration, and DNA damage response, CUX1 has been implicated in tumorigenesis. Interestingly, CUX1 has been recently recognized as a haploinsufficient tumor suppressor, which is paradoxically overexpressed in tumor cells. While loss of heterozygosity and/or mutations of CUX1 have been frequently detected in many types of cancers, genomic amplification, and overexpression of CUX1 have also been reported in cancer tissues and are correlated with higher tumor grade and poor prognosis. Therefore, deciphering the roles of different CUX1 isoforms and in different tumor stages is required to establish a CUX1-based therapeutic strategy for cancer treatment.

Recruitment of Histone Methyltransferase Ehmt1 to Foxp3 TSDR Counteracts Differentiation of Induced Regulatory T Cells

Differentiation toward CD4⁺ regulatory T (Treg) cells is essentially dependent on an epigenetic program at Treg signature genes, which involves remodeling of the Treg-specific demethylated regions (TSDRs). In particular, the epigenetic status of the conserved non-coding sequence 2 of Foxp3 (Foxp3 TSDR) determines expression stability of the master transcription factor and thus Treg lineage identity. However, the molecular mechanisms controlling the epigenetic remodeling at TSDRs in Treg and conventional T cells are largely unknown. Using a combined approach of DNA pull-down and mass spectrometric analysis, we report a novel regulatory mechanism in which transcription factor Wiz recruits the histone methyltransferase Ehmt1 to Foxp3 TSDR. We show that both Wiz and Ehmt1 are crucial for shaping the region with the repressive histone modification H3K9me2 in conventional T cells. Consistently, knocking out either Ehmt1 or Wiz by CRISPR/Cas resulted in the loss of H3K9me2 and enhanced Foxp3 expression during iTreg differentiation. Moreover, the essential role of the Wiz-Ehmt1 interaction as observed at several TSDRs indicates a global function of Ehmt1 in the Treg differentiation program.

Tetramerization of SATB1 is essential for regulating of gene expression

Special AT-rich sequence-binding protein 1 (SATB1) functions as a 'genome organizer' in tumorigenesis. Our previous report showed that SATB1 forms a tetramer through its N-terminal ubiquitin like domain rather than the proposed PDZ domain. In the present study, we aim to illustrate whether this oligomerization is critical to its function as a global repressor of gene expression in vivo. Luciferase and GST pull-down assays demonstrated that disrupting SATB1's tetramerization not only affects the activities of promoters but also influences the recruitment of interaction partners. Furthermore, we developed stable cell lines that overexpressed either the SATB1 tetramer or STAB1 dimer (KWN-AAA) and monitored global gene expression. Gene expression profiling revealed that over 1000 genes were significantly upregulated or downregulated upon the overexpression of SATB1 or the SATB1 (KWN-AAA) mutant. These data implied that SATB1 might regulate gene expression through its different oligomerization state. In conclusion, we inferred that the oligomerization of SATB1 is pivotal to its function of different biological processes.

Ultraviolet irradiation represses TGF-β type II receptor transcription through a 38-bp sequence in the proximal promoter in human skin fibroblasts

Transforming growth factor-β (TGF-β) is a major regulator of collagen gene expression in human skin fibroblasts. Cellular responses to TGF-β are mediated primarily through its cell surface type I (TβRI) and type II (TβRII) receptors. Ultraviolet (UV) irradiation impairs TGF-β signalling largely due to reduced TβRII gene expression, thereby decreasing type I procollagen synthesis, in human skin fibroblasts. UV irradiation does not alter either TβRII mRNA or protein stability, indicating that UV reduction in TβRII expression likely results from transcriptional or translational repression. To understand how UV irradiation regulates TβRII transcription, we used a series of TβRII promoter-luciferase 5'-deletion constructs (covering 2 kb of the TβRII proximal promoter) to determine transcriptional rate in response to UV irradiation. We identified a 137-bp region upstream of the transcriptional start site that exhibited high promoter activity and was repressed 60% by UV irradiation, whereas all other TβRII promoter reporter constructs exhibited either low promoter activities or no regulation by UV irradiation. Mutation of potential transcription factor binding sites within the promoter region revealed that an inverted CCAAT box (-81 bp from transcription start site) is required for promoter activity. Mutation of the CCAAT box completely abolished UV irradiation regulation of the TβRII promoter. Protein-binding assay, as determined by electrophoretic mobility-shift assays (EMSAs) using the inverted CCAAT box as probe (-100/-62), demonstrated significantly enhanced protein binding in response to UV irradiation. Super shift experiments indicated that nuclear factor Y (NFY) is able to binding to this sequence, but NFY binding was not altered in response to UV irradiation, indicating additional protein(s) are capable of binding this sequence in response to UV irradiation. Taken together, these data indicate that UV irradiation reduces TβRII expression, at least partially, through transcriptional repression. This repression is mediated by a 38-bp sequence in TβRII promoter, in human skin fibroblasts.

Lessons from Anaplasma phagocytophilum: chromatin remodeling by bacterial effectors

Bacterial pathogens can alter global host gene expression via histone modifications and chromatin remodeling in order to subvert host responses, including those involved with innate immunity, allowing for bacterial survival. Shigella flexneri, Listeria monocytogenes, Chlamydia trachomatis, and Anaplasma phagocytophilum express effector proteins that modify host histones and chromatin structure. A. phagocytophilum modulates granulocyte respiratory burst in part by dampening transcription of several key phagocyte oxidase genes. The A. phagocytophilum protein AnkA localizes to the myeloid cell nucleus where it binds AT-rich regions in the CYBB promoter and decreases its transcription. AT-rich regions of DNA are characteristic of matrix attachment regions (MARs) which are critical for chromatin structure and transcription. MAR-binding proteins, such as SATB1, interact with histone modifying enzymes resulting in altered gene expression. With A. phagocytophilum infection, histone deacetylase 1 (HDAC1) expression is increased and histone H3 acetylation is decreased at the CYBB promoter, suggesting a role for AnkA in altering host epigenetics and modulating gene transcription, at this, and perhaps other loci. This review will focus on how bacterial pathogens alter host epigenetics, by specifically examining A. phagocytophilum AnkA cis-regulation of CYBB transcription and epigenetic changes associated with infection.

Physiological roles of NOX/NADPH oxidase, the superoxide-generating enzyme

NADPH oxidase is a superoxide (O₂^•−)-generating enzyme first identified in phagocytes, essential for their bactericidal activities. Later, in non-phagocytes, production of O₂^•− was also demonstrated in an NADPH-dependent manner. In the last decade, several non-phagocyte-type NADPH oxidases have been identified. The catalytic subunit of these oxidases, NOX, constitutes the NOX family. There are five homologs in the family, NOX1 to NOX5, and two related enzymes, DUOX1 and DUOX2. Transgenic or gene-disrupted mice of the NOX family have also been established. NOX/DUOX proteins possess distinct features in the dependency on other components for their enzymatic activities, tissue distributions, and physiological functions. This review summarized the characteristics of the NOX family proteins, especially focused on their functions clarified through studies using gene-modified mice.

GCN5 regulates the superoxide-generating system in leukocytes via controlling gp91-phox gene expression

The superoxide anion (O(2)(-))-generating system is an important mechanism of innate immune response against microbial infection in phagocytes and is involved in signal transduction mediated by various physiological and pathological signals in phagocytes and other cells, including B lymphocytes. The O(2)(-)-generating system is composed of five specific proteins: p22-phox, gp91-phox, p40-phox, p47-phox, p67-phox, and a small G protein, Rac. Little is known regarding epigenetic regulation of the genes constituting the O(2)(-)-generating system. In this study, by analyzing the GCN5 (one of most important histone acetyltransferases)-deficient DT40 cell line, we show that GCN5 deficiency causes loss of the O(2)(-)-generating activity. Interestingly, transcription of the gp91-phox gene was drastically downregulated (to ∼4%) in GCN5-deficient cells. To further study the involvement of GCN5 in transcriptional regulation of gp91-phox, we used in vitro differentiation system of U937 cells. When human monoblastic U937 cells were cultured in the presence of IFN-γ, transcription of gp91-phox was remarkably upregulated, and the cells were differentiated to macrophage-like cells that can produce O(2)(-). Chromatin immunoprecipitation assay using the U937 cells during cultivation with IFN-γ revealed not only that association of GCN5 with the gp91-phox gene promoter was significantly accelerated, but also that GCN5 preferentially elevated acetylation levels of H2BK16 and H3K9 surrounding the promoter. These results suggested that GCN5 regulates the O(2)(-)-generating system in leukocytes via controlling the gp91-phox gene expression as a supervisor. Our findings obtained in this study should be useful in understanding the molecular mechanisms involved in epigenetic regulation of the O(2)(-)-generating system in leukocytes.

Cux1 transcription factor is induced in inflammatory bowel disease and protects against experimental colitis

BACKGROUND

Cux1 is a ubiquitous transcriptional factor that has been associated with cell proliferation, migration, invasion, and differentiation. Cux1 is an effector of the transforming growth factor beta (TGFβ) pathway, PAR(2) receptor signaling, and cellular migration, mechanisms intimately related to inflammatory bowel diseases (IBD).

METHODS

CD1 mice treated with dextran sulfate sodium (DSS) in drinking water and cultured intestinal epithelial cells were used to determine Cux1 expression under inflammatory conditions. A commercial cDNA library was used to monitor CUX1 expression in IBD patients. The Cux1(ΔHD/ΔHD) hypomorphic mouse model (Cux1ΔHD) treated with DSS in drinking water was used and the disease severity assessed.

RESULTS

Cux1 expression increased in cultured intestinal epithelial cells stimulated with tumor necrosis factor alpha (TNFα), in the mouse intestinal epithelium during experimental colitis and in human IBD patient samples. DSS-induced colitis in Cux1ΔHD mice was more severe according to clinical observations such as weight loss, colon length, and rectal bleeding. Histological observations confirmed an increase of IBD-related morphological changes including ulceration and mucosal infiltration of leukocytes in Cux1ΔHD mice. An increased number of pSer(276)-RelA-positive cells and higher expression levels of proinflammatory cytokines were also measured in the colon of Cux1ΔHD diseased animals. Elevated levels of Cxcl1 were measured before and after DSS-treatment and a greater neutrophilic infiltration was quantified in DSS-treated Cux1ΔHD mice. Finally, mucosal healing was significantly impaired in Cux1ΔHD mice during recovery from DSS treatment.

CONCLUSIONS

CUX1 is increased in response to inflammatory stress and its nuclear expression is crucial to protect against DSS-induced colitis and subsequent mucosal healing.

NOX/NADPH oxidase, the superoxide-generating enzyme: its transcriptional regulation and physiological roles

NADPH oxidase is a superoxide (O(2)(-))-generating enzyme first identified in phagocytes that shows bactericidal activities. It has been reported that O(2)(-) is also produced in an NADPH-dependent manner in non-phagocytes. In the last decade, non-phagocyte-type NADPH oxidases have been identified, and the catalytic subunit NOX family has been found to be composed of five homologs, NOX1 to NOX5, and two related enzymes, DUOX1 and DUOX2. These NOX proteins have distinct features in dependency on other components for maximal enzymatic activity, tissue distribution, expressional regulation, and physiological functions. This review summarized the distinct characteristics of NOX family proteins, especially focusing on their functions and mechanisms of their expressional regulation.

Cut mutant Drosophila auditory organs differentiate abnormally and degenerate

The Drosophila antenna is a sophisticated structure that functions in both olfaction and audition. Previous studies have identified Homothorax, Extradenticle, and Distal-less, three homeodomain transcription factors, as required for specification of antennal identity. Antennal expression of cut is activated by Homothorax and Extradenticle, and repressed by Distal-less. cut encodes the Drosophila homolog of human CAAT-displacement protein, a cell cycle-regulated homeodomain transcription factor. Cut is required for normal development of external mechanosensory structures and Malphigian tubules (kidney analogs). The role of cut in the Drosophila auditory organ, Johnston's organ, has not been characterized. We have employed the FLP/FRT system to generate cut null clones in developing Johnston's organ. In cut mutants, the scolopidial subunits that constitute Johnston's organ differentiate abnormally and subsequently degenerate. Electrophysiological experiments confirm that adult Drosophila with cut null antennae are deaf. We find that cut acts in parallel to atonal, spalt-major, and spalt-related, which encode other transcription factors required for Johnston's organ differentiation. We speculate that Cut functions in conjunction with these factors to regulate transcription of as yet unidentified targets.

Receptor activator of nuclear factor-kappaB ligand-induced mouse osteoclast differentiation is associated with switching between NADPH oxidase homologues

Reactive oxygen species (ROS) have been suggested to regulate receptor activator of nuclear factor-kappaB ligand (RANKL)-stimulated osteoclast differentiation. Stimulation of wild-type mouse bone marrow monocyte/macrophage lineage (BMM) cells by RANKL down-regulated NADPH oxidase 2 (Nox2) mRNA expression by half. RANKL reciprocally increased Nox1 mRNA levels and newly induced Nox4 transcript expression. BMM cells from Nox1 knockout (Nox1(-/-)) as well as Nox2(-/-) mice generated ROS in response to RANKL and differentiated into osteoclasts in the same way as wild-type BMM cells, which was assessed by the appearance of tartrate-resistant acid phosphatase-positive, multinucleated cells having the ability to form resorption pits and by the expression of osteoclast marker genes. A small interfering RNA (siRNA) targeting Nox1 or Nox2 failed to inhibit the RANKL-stimulated ROS generation and osteoclast formation in wild-type cells, whereas Nox1 and Nox2 siRNAs significantly suppressed the ROS generation and osteoclast formation in Nox2(-/-) and Nox1(-/-) cells, respectively. We also confirmed that Nox4 siRNA did not affect the RANKL-dependent events in Nox2(-/-) cells, whereas p22(phox) siRNA suppressed the events in both wild-type and Nox1(-/-) cells. Collectively, our results suggest that there may be a flexible compensatory mechanism between Nox1 and Nox2 for RANKL-stimulated ROS generation to facilitate osteoclast differentiation.

The Torso signaling pathway modulates a dual transcriptional switch to regulate tailless expression

The Torso (Tor) signaling pathway activates tailless (tll) expression by relieving tll repression. None of the repressors identified so far, such as Capicuo, Groucho and Tramtrack69 (Ttk69), bind to the tor response element (tor-RE) or fully elucidate tll repression. In this study, an expanded tll expression pattern was shown in embryos with reduced heat shock factor (hsf) and Trithorax-like (Trl) activities. The GAGA factor, GAF encoded by Trl, bound weakly to the tor-RE, and this binding was enhanced by both Hsf and Ttk69. A similar extent of expansion of tll expression was observed in embryos with simultaneous knockdown of hsf, Trl and ttk69 activities, and in embryos with constitutively active Tor. Hsf is a substrate of mitogen-activated protein kinase and S378 is the major phosphorylation site. Phosphorylation converts Hsf from a repressor to an activator that works with GAF to activate tll expression. In conclusion, the GAF/Hsf/Ttk69 complex binding to the tor-RE remodels local chromatin structure to repress tll expression and the Tor signaling pathway activate tll expression by modulating a dual transcriptional switch.

Transcription factors Sp1 and C/EBP regulate NRAMP1 gene expression

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

Repression of human cytomegalovirus major immediate early gene expression by the cellular transcription factor CCAAT displacement protein

Initiation of human cytomegalovirus (HCMV) productive infection is dependent on the major immediate early (MIE) genes ie1 and ie2. Several putative binding sites for CCAAT displacement protein (CDP or CUX1) were identified within the MIE promoter/regulatory region. Binding assays demonstrated binding of CUX1 to MIE-region oligonucleotides containing the CUX1 core binding sequence ATCGAT and mutagenesis of this sequence abrogated CUX1 binding. Furthermore, CUX1 repressed expression of a luciferase reporter construct controlled by the MIE promoter, and mutation of CUX1 binding sites within the promoter diminished this repressive function of CUX1. In the context of virus infection of HEK293 cells transfected with the CUX1 expression vector, CUX1 showed evidence of association with the HCMV MIE regulatory region and inhibited the capacity of the virus to express ie1 and ie2 transcripts, suggesting that this cellular factor regulates MIE gene expression following virus entry. These data identify a role for CUX1 in repressing HCMV gene expression essential for initiation of the replicative cycle.

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

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

The NOX family of ROS-generating NADPH oxidases: physiology and pathophysiology

For a long time, superoxide generation by an NADPH oxidase was considered as an oddity only found in professional phagocytes. Over the last years, six homologs of the cytochrome subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the phagocyte NADPH oxidase itself (NOX2/gp91(phox)), the homologs are now referred to as the NOX family of NADPH oxidases. These enzymes share the capacity to transport electrons across the plasma membrane and to generate superoxide and other downstream reactive oxygen species (ROS). Activation mechanisms and tissue distribution of the different members of the family are markedly different. The physiological functions of NOX family enzymes include host defense, posttranlational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. NOX enzymes also contribute to a wide range of pathological processes. NOX deficiency may lead to immunosuppresion, lack of otoconogenesis, or hypothyroidism. Increased NOX activity also contributes to a large number or pathologies, in particular cardiovascular diseases and neurodegeneration. This review summarizes the current state of knowledge of the functions of NOX enzymes in physiology and pathology.

Human papillomavirus type 16 P670 promoter is negatively regulated by CCAAT displacement protein

HPV16 late gene transcription from P670 is suppressed in undifferentiated keratinocytes. To identify DNA sites involved in the negative regulation, we examined the effect of a series of substitutions in the P670 promoter region (nucleotide (nt) 106-855) on the transcription, using an expression plasmid having the promoter fragment placed to drive the firefly-luciferase gene. Twenty-base pair-long segments covering the entire promoter region were replaced with a sequence lacking any so far known factor-binding motifs to produce 38 mutants. These plasmids were introduced by transfecton into undifferentiated or partially differentiated human HaCaT and HeLa cells, and transient expression of the reporter was examined with the cell extracts. The reporter expression from the wild-type promoter region was lower, half to one-third, in the undifferentiated cells than in the partially differentiated cells, which expressed hSkn-1a, a keratinocyte specific transcription factor that activates P670, and CCAAT displacement protein (CDP), a transcriptional repressor involved in cell differentiation. Two mutants with substitutions including the putative CDP-binding sites, one from nt 562 to 567 and the other from nt 673 to 678, induced markedly enhanced reporter expression particularly in the partially differentiated cells. Electrophoretic mobility shift analysis demonstrated that bacterially produced GST-CDP bound to the two sites in a sequence-specific manner. The data strongly suggest that CDP acts as a major suppressor for P670 transcription by binding to the promoter region in the undifferentiated cells and even in the partially differentiated cells that express the activator hSkn-1a.

A novel proteolytically processed CDP/Cux isoform of 90 kDa is generated by cathepsin L

The Cut-like genes code for multiple isoforms of the CDP/Cux transcription factor. The full-length protein contains four DNA-binding domains: Cut repeats 1, 2 and 3 (CR1, CR2 and CR3) and the Cut homeodomain (HD). The p75 isoform is expressed from an mRNA that is initiated within intron 20 and contains only CR3 and HD. The p110 isoform is generated by proteolytic processing by cathepsin L and contains CR2, CR3 and HD. In the present study, we show that an additional isoform of 90 kDa is expressed in many cell lines of epithelial origin. Mapping experiments with deletion mutants indicated that the N-terminus of p90 is located upstream of CR2, between amino acids 918 and 938. Indeed, p90 and p110 displayed similar DNA-binding and transcriptional activities. The p90 isoform, like p110, was found to be generated by proteolytic processing. The steady-state level of both p90 and p110 correlated with the level of cathepsin L activity. Importantly, co-expression with a cathepsin L mutant that is initiated at downstream AUG sites also stimulated the generation of p90 and p110. These results strongly suggest that p90, like p110, is generated by cathepsin L isoforms that are devoid of a signal peptide.

NADPH oxidases in the gastrointestinal tract: a potential role of Nox1 in innate immune response and carcinogenesis

The gastrointestinal epithelium functions as physical and innate immune barriers against commensal or pathogenic microbes. NADPH oxidase 1 (Nox1) and dual oxidase 2 (Duox2), highly expressed in the colon, are suggested to play a potential role in host defense. Guinea-pig gastric pit cells and human colonic epithelial cells (T84 cells) express Nox1. With regard to activation of Nox1, the gastric epithelial cells are primed with Helicobacter pylori lipopolysaccharide, whereas T84 cells preferentially use the Toll-like receptor (TLR) 5, rather than TLR4, against Salmonella enteritidis infection. Thus, gastric and colonic epithelial cells may use different TLR members to discern pathogenicities among bacteria, depending on their environments and to activate Nox1 appropriately for host defense. Nox1-derived reactive oxygen species (ROS) have been implicated in the pathogenesis of inflammation-associated tumor development. The human stomach does not express Nox1. Helicobacter pylori infection alone does not induce it, whereas Nox1 is specifically expressed in gastric adenocarcinomas. In the human colon, Nox1 is differentiation-dependently expressed, and its expression is upregulated in adenomas and well-differentiated adenocarcinomas. Although Nox1 expression may not be directly linked to mitogenic activity, Nox1-derived ROS may exert a cancer-promoting effect by increasing resistance to programmed cell death of tumor cells.

NADPH oxidases in cardiovascular health and disease

Increased oxidative stress plays an important role in the pathophysiology of cardiovascular diseases such as hypertension, atherosclerosis, diabetes, cardiac hypertrophy, heart failure, and ischemia-reperfusion. Although several sources of reactive oxygen species (ROS) may be involved, a family of NADPH oxidases appears to be especially important for redox signaling and may be amenable to specific therapeutic targeting. These include the prototypic Nox2 isoform-based NADPH oxidase, which was first characterized in neutrophils, as well as other NADPH oxidases such as Nox1 and Nox4. These Nox isoforms are expressed in a cell- and tissue-specific fashion, are subject to independent activation and regulation, and may subserve distinct functions. This article reviews the potential roles of NADPH oxidases in both cardiovascular physiological processes (such as the regulation of vascular tone and oxygen sensing) and pathophysiological processes such as endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, angiogenesis, and vascular and cardiac remodeling. The complexity of regulation of NADPH oxidases in these conditions may provide the possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the disease process.

Interactions of the cellular CCAAT displacement protein and human papillomavirus E2 protein with the viral origin of replication can regulate DNA replication

Previously, we and others have shown that CCAAT displacement protein (CDP) negatively regulates the papillomavirus promoters. Overexpression of CDP has been shown to inhibit high-risk human papillomavirus virus (HPV) and bovine papillomavirus DNA replication in vivo presumably through reduction in expression of viral replication proteins, E1 and E2. Sequence analysis of the HPV origin indicates several potential CDP-binding sites with one site overlapping the E1-binding site. Therefore, CDP could also negatively regulate papillomavirus replication directly by preventing the loading of the initiation complex. We show here that purified CDP inhibits in vitro HPV DNA replication. Footprint analysis demonstrated that CDP binds the E1-binding site and the TATA box, and that the binding of purified CDP to the E1-binding site is decreased by the addition of purified E2 protein. Consistent with this, E2-independent in vitro HPV replication is inhibited by CDP to a greater extent than E2-dependent replication. These results suggest that binding of E2 at the E2-binding site may play an important role in overcoming the inhibition of E1 initiation complex formation caused by the binding of negative regulators like CDP to the origin of replication.

The p110 isoform of the CDP/Cux transcription factor accelerates entry into S phase

The CDP/Cux transcription factor was previously found to acquire distinct DNA binding and transcriptional properties following a proteolytic processing event that takes place at the G1/S transition of the cell cycle. In the present study, we have investigated the role of the CDP/Cux processed isoform, p110, in cell cycle progression. Populations of cells stably expressing p110 CDP/Cux displayed a faster division rate and reached higher saturation density than control cells carrying the empty vector. p110 CDP/Cux cells reached the next S phase faster than control cells under various experimental conditions: following cell synchronization in G0 by growth factor deprivation, synchronization in S phase by double thymidine block treatment, or enrichment in G2 by centrifugal elutriation. In each case, duration of the G1 phase was shortened by 2 to 4 h. Gene inactivation confirmed the role of CDP/Cux as an accelerator of cell cycle progression, since mouse embryo fibroblasts obtained from Cutl1z/z mutant mice displayed a longer G1 phase and proliferated more slowly than their wild-type counterparts. The delay to enter S phase persisted following immortalization by the 3T3 protocol and transformation with H-RasV12. Moreover, CDP/Cux inactivation hindered both the formation of foci on a monolayer and tumor growth in mice. At the molecular level, expression of both cyclin E2 and A2 was increased in the presence of p110 CDP/Cux and decreased in its absence. Overall, these results establish that p110 CDP/Cux functions as a cell cycle regulator that accelerates entry into S phase.

Interferon-gamma activates transcription of NADPH oxidase 1 gene and upregulates production of superoxide anion by human large intestinal epithelial cells

NADPH oxidase 1 (Nox1), a homolog of gp91(phox), is dominantly expressed in large intestinal epithelium, and reactive oxygen species derived from Nox1 are suggested to serve a role in host defense. We report that interferon (IFN)-gamma, a crucial transactivator of the gp91(phox) gene, also stimulates expression of Nox1 mRNA and protein in large intestinal epithelium (T84 cells), leading to fourfold upregulation of superoxide anion (O(2)(-)) generation. Introduction of small interfering Nox1 RNA completely blocked this priming. We cloned the region from -4,831 to +195 bp of the human Nox1 gene. To reveal IFN-gamma-responsive cis elements, we performed transient expression assays using a reporter gene driven by serially truncated Nox1 promoters in T84 cells. IFN-gamma-responsive elements were located between -4.3 and -2.6 kb, and one gamma-activated sequence (GAS) element present at -3,818 to -3,810 bp exhibited this IFN-gamma-dependent promoter activity. IFN-gamma caused tyrosine phosphorylation of signal transducer and activator of transcription 1 (STAT1) and produced a protein-GAS complex that was recognized by anti-STAT1 antibody. The introduction of three-point mutation of GAS, which did not interact with STAT1, completely canceled the IFN-gamma-dependent promoter activity of the region from -4,831 to +195 bp. A Janus protein tyrosine kinase 2 inhibitor (AG490) blocked the IFN-gamma-stimulated tyrosine phosphorylation of STAT1, promoter activity of the -4,831 to +195 bp region, Nox1 mRNA expression, and O(2)(-) production, also suggesting a crucial role of STAT1 and GAS in the IFN-gamma-stimulated transcription of the Nox1 gene. Our results support a potential contribution of Nox1 to mucosal host defense and inflammation in the colon.

Differential regulation of CDP/Cux p110 by cyclin A/Cdk2 and cyclin A/Cdk1

Previous experiments with peptide fusion proteins suggested that cyclin A/Cdk1 and Cdk2 might exhibit similar yet distinct phosphorylation specificities. Using a physiological substrate, CDP/Cux, our study confirms this notion. Proteolytic processing of CDP/Cux by cathepsin L generates the CDP/Cux p110 isoform at the beginning of S phase. CDP/Cux p110 makes stable interactions with DNA during S phase but is inhibited in G2 following the phosphorylation of serine 1237 by cyclin A/Cdk1. In this study, we propose that differential phosphorylation by cyclin A/Cdk1 and cyclin A/Cdk2 enables CDP/Cux p110 to exert its function as a transcriptional regulator specifically during S phase. We found that like cyclin A/Cdk1, cyclin A/Cdk2 interacted efficiently with recombinant CDP/Cux proteins that contain the Cut homeodomain and an adjacent cyclin-binding motif (Cy). In contrast to cyclin A/Cdk1, however, cyclin A/Cdk2 did not efficiently phosphorylate CDP/Cux p110 on serine 1237 and did not inhibit its DNA binding activity in vitro. Accordingly, co-expression with cyclin A/Cdk2 in cells did not inhibit the DNA binding and transcriptional activities of CDP/Cux p110. To confirm that the sequence surrounding serine 1237 was responsible for the differential regulation by Cdk1 and Cdk2, we replaced 4 amino acids flanking the phosphorylation site to mimic a known Cdk2 phosphorylation site present in the Cdc6 protein. Both cyclin A/Cdk2 and Cdk1 efficiently phosphorylated the CDP/Cux(Cdc6) mutant and inhibited its DNA binding activity. Altogether our results help explain why the DNA binding activity of CDP/Cux p110 is maximal during S phase and decreases in G2 phase.

Anaplasma phagocytophilum modulates gp91phox gene expression through altered interferon regulatory factor 1 and PU.1 levels and binding of CCAAT displacement protein

Infection of neutrophil precursors with Anaplasma phagocytophilum, the causative agent of human granulocytic ehrlichiosis, results in downregulation of the gp91(phox) gene, a key component of NADPH oxidase. We now show that repression of gp91(phox) gene transcription is associated with reduced expression of interferon regulatory factor 1 (IRF-1) and PU.1 in nuclear extracts of A. phagocytophilum-infected cells. Loss of PU.1 and IRF-1 correlated with increased binding of the repressor, CCAAT displacement protein (CDP), to the promoter of the gp91(phox) gene. Reduced protein expression of IRF-1 was observed with or without gamma interferon (IFN-gamma) stimulation, and the defect in IFN-gamma signaling was associated with diminished binding of phosphorylated Stat1 to the Stat1 binding element of the IRF-1 promoter. The diminished levels of activator proteins and enhanced binding of CDP account for the transcriptional inhibition of the gp91(phox) gene during A. phagocytophilum infection, providing evidence of the first molecular mechanism that a pathogen uses to alter the regulation of genes that contribute to an effective respiratory burst.

Biochemical characterization of the mammalian Cux2 protein

The CCAAT displacement protein (CDP) and cux (Cut homeobox) genes were originally identified as the human and mouse orthologs of Drosophila melanogaster cut. More recently, vertebrates were found to possess a second cut orthologs that was generated by gene duplication: Cux2. We report the initial biochemical characterization of the Cux2 protein in tissue culture and in vitro. We generated four polyclonal antibodies that were able to recognize the human and mouse Cux2 protein but displayed little or no cross-reactivity towards CDP1 and Cux1. The expression of the Cux2 protein was convincingly detected in only one among 19 neuronal cell lines: the SH-SY5Y human neuroblastoma cell line. CDP/Cux proteins contain four DNA binding domains, three Cut repeat (CR1, CR2 and CR3) and one Cut homeodomain (HD). Purified fusion proteins containing either CR1CR2, CR2CR3HD or CR3HD exhibited similar DNA binding specificities as the corresponding domains of Cux1, but their DNA binding kinetics were much more rapid. Similarly, the full-length Cux2 protein made rapid but transient interactions with DNA. We did not observe an N-terminally processed Cux2 isoform equivalent to the Cux1 p110 isoform. Whereas Cux1 can function as a repressor or activator in a promoter-specific manner, Cux2 functioned exclusively as a transcriptional repressor in NIH3T3 cells. Overall, our results suggest that the Cux1 and Cux2 proteins carry distinct biochemical functions. Cux2 is able, like Cux1, to perform the CCAAT-displacement activity. However, Cux2 is unlikely to execute transcriptional regulatory functions that require stable interaction with DNA.

The N-terminal Region of the CCAAT Displacement Protein (CDP)/Cux Transcription Factor Functions as an Autoinhibitory Domain that Modulates DNA Binding

The CCAAT displacement protein/Cut homeobox (CDP/Cux) transcription factor is expressed as multiple isoforms that may contain up to four DNA-binding domains: Cut repeats 1, 2, and 3 (CR1, CR2, CR3) and the Cut homeodomain (HD). The full-length protein, which contains all four DNA-binding domains, is surprisingly less efficient than the shorter isoforms in DNA binding. Using a panel of recombinant proteins expressed in mammalian or bacterial cells, we have identified a domain at the extreme N terminus of the protein that can inhibit DNA binding. This domain was able to inhibit the activity of full-length CDP/Cux and of proteins containing various combinations of DNA-binding domains: CR1CR2, CR3HD, or CR2CR3HD. Since inhibition of DNA binding was also observed with purified proteins obtained from bacteria, we conclude that autoinhibition does not require post-translational modification or interaction with an interacting protein but instead functions through an intramolecular mechanism. Antibodies directed against the N-terminal region were able to partially relieve inhibition. In vivo, the transition between the inactive and active states for DNA binding is likely to be governed by posttranslational modifications and/or interaction with one or more protein partners. In addition, we show that the relief of autoinhibition can be accomplished via the proteolytic processing of CDP/Cux. Altogether, these results reveal a novel mode of regulation that serves to modulate the DNA binding activity of CDP/Cux.

IFN-gamma induces gp91phox expression in human monocytes via protein kinase C-dependent phosphorylation of PU.1

We previously reported that the stimulation of human blood monocytes with IFN-gamma induces the binding of PU.1 to the gp91(phox) promoter and the consequent expression of gp91(phox). In this study, we show that the effect of IFN-gamma is reproduced by the serine phosphatase inhibitor, okadaic acid, and this suggests that serine kinases could be involved in gp91(phox) expression. We also show that IFN-gamma induces the serine/threonine phosphorylation of PU.1 in cultured monocytes. This phosphorylation, as well as the IFN-gamma-induced PU.1 binding and gp91(phox) protein synthesis, is slightly affected by the casein kinase II inhibitor, daidzein, but is abrogated by the protein kinase C (PKC) -alpha and -beta inhibitor, Go6976, and by synthetic peptides with sequences based on the endogenous pseudosubstrate region of the classical PKC alpha and beta isoforms. In contrast, peptides reproducing the pseudosubstrate region of PKC epsilon were without effect. Moreover, we found that the treatment of monocytes with IFN-gamma induces the nuclear translocation and the activation of PKC alpha and beta I, but not of PKC beta II, and that the IFN-gamma-induced phosphorylation of PU.1 was greatly reduced by LY333531, a selective inhibitor of PKC beta isoforms. Finally, nuclear run-on assays demonstrated that while the PKC inhibitors, Go6976 and LY333531, decrease the IFN-gamma-induced gp91(phox) transcription, the serine phosphatase inhibitor, okadaic acid, enhances the gp91(phox) gene transcription. Our results indicate that in cultured monocytes, IFN-gamma induces the binding of PU.1 to the gp91(phox) promoter and the expression of gp91(phox) by phosphorylation of PU.1 via activation of PKC alpha and/or beta I.

Structure and regulation of the neutrophil respiratory burst oxidase: comparison with nonphagocyte oxidases

Neutrophils play an essential role in the body's innate defense against pathogens and are one of the primary mediators of the inflammatory response. To defend the host, neutrophils use a wide range of microbicidal products, such as oxidants, microbicidal peptides, and lytic enzymes. The generation of microbicidal oxidants by neutrophils results from the activation of a multiprotein enzyme complex known as the reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, which is responsible for transferring electrons from NADPH to O2, resulting in the formation of superoxide anion. During oxidase activation, cytosolic oxidase proteins translocate to the phagosome or plasma membrane, where they assemble around a central membrane-bound component known as flavocytochrome b. This process is highly regulated, involving phosphorylation, translocation, and multiple conformational changes. Originally, it was thought that the NADPH oxidase was restricted to phagocytes and used solely in host defense. However, recent studies indicate that similar NADPH oxidase systems are present in a wide variety of nonphagocytic cells. Although the nature of these nonphagocyte NADPH oxidases is still being defined, it is clear that they are functionally distinct from the phagocyte oxidases. It should be noted, however, that structural features of many nonphagocyte oxidase proteins do seem to be similar to those of their phagocyte counterparts. In this review, key structural and functional features of the neutrophil NADPH oxidase and its protein components are described, including a consideration of transcriptional and post-translational regulatory features. Furthermore, relevant details about structural and functional features of various nonphagocyte oxidase proteins will be included for comparison.

Activation of the growth-differentiation factor 11 gene by the histone deacetylase (HDAC) inhibitor trichostatin A and repression by HDAC3

Histone deacetylase (HDAC) inhibitors inhibit the proliferation of transformed cells in vitro, restrain tumor growth in animals, and are currently being actively exploited as potential anticancer agents. To identify gene targets of the HDAC inhibitor trichostatin A (TSA), we compared the gene expression profiles of BALB/c-3T3 cells treated with or without TSA. Our results show that TSA up-regulates the expression of the gene encoding growth-differentiation factor 11 (Gdf11), a transforming growth factor beta family member that inhibits cell proliferation. Detailed analyses indicated that TSA activates the gdf11 promoter through a conserved CCAAT box element. A comprehensive survey of human HDACs revealed that HDAC3 is necessary and sufficient for the repression of gdf11 promoter activity. Chromatin immunoprecipitation assays showed that treatment of cells with TSA or silencing of HDAC3 expression by small interfering RNA causes the hyperacetylation of Lys-9 in histone H3 on the gdf11 promoter. Together, our results provide a new model in which HDAC inhibitors reverse abnormal cell growth by inactivation of HDAC3, which in turn leads to the derepression of gdf11 expression.

SATB1 makes a complex with p300 and represses gp91(phox) promoter activity

The expression of gp91(phox), the key component of the phagocyte NADPH oxidase, is regulated by various factors binding to its proximal promoter. Two nuclear matrix attachment region (MAR)-binding proteins, special AT-rich binding protein 1 (SATB1) and CCAAT displacement protein (CDP), have been reported as rare examples of gp91(phox) gene repressors. However, their individual roles and interactions with other factors in the promoter have not been elucidated in detail. We have focused on these two repressive proteins recognizing the bp -115 to bp -106 segment of the gene and obtained the following results: 1. SATB1 makes a complex, mainly with p300, regardless of the presence of DNA. 2. SATB1/p300 complex binding to the 5' upstream AT-rich region in the bp -115 to bp -106 segment represses the gp91(phox) promoter activity, and the repressed activity is partially released by CDP binding to the CCAAT element directly downstream of the AT-rich region. Our findings imply a novel role for p300 in SATB1-associated global transcription regulation.

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

In vitro models of granulopoiesis involving the inducible expression of either CCAAT enhancer binding protein alpha (C/EBP alpha) or C/EBP epsilon in myeloid cells have been shown to lead to the induction of a granulocytic maturation program accompanied by the expression of myeloid-specific genes. Since members of the C/EBP family of transcription factors recognize and bind to similar DNA-binding motifs, it has been difficult to elucidate the specific role of each of the C/EBP family members in eliciting myeloid gene expression. In order to address this issue, we focused on the expression of the lactoferrin (LF) gene. LF expression is transcriptionally regulated in a C/EBP-dependent manner in myeloid cells. Using chromatin immunoprecipitation (ChIP) analysis we demonstrate that C/EBP alpha binds to the LF promoter in nonexpressing cells. Upon induction of maturation, C/EBP epsilon binds to the LF promoter, which correlates with LF expression. Lack of LF expression in the acute promyelocytic leukemia cell line NB4, which harbors the t(15;17) translocation, cannot be correlated with aberrant binding at the C/EBP site in the LF promoter. It is, however, associated with the persistent binding of the silencer CCAAT displacement protein (CDP/cut) to the LF promoter in these cells. We conclude that C/EBP alpha, C/EBP epsilon, and CDP/cut all play definitive roles in regulating late gene expression during normal myeloid development.

CDP/Cux stimulates transcription from the DNA polymerase alpha gene promoter

CDP/Cux (CCAAT-displacement protein/cut homeobox) contains four DNA binding domains, namely, three Cut repeats (CR1, CR2, and CR3) and a Cut homeodomain. CCAAT-displacement activity involves rapid but transient interaction with DNA. More stable DNA binding activity is up-regulated at the G(1)/S transition and was previously shown to involve an N-terminally truncated isoform, CDP/Cux p110, that is generated by proteolytic processing. CDP/Cux has been previously characterized as a transcriptional repressor. However, here we show that expression of reporter plasmids containing promoter sequences from the human DNA polymerase alpha (pol alpha), CAD, and cyclin A genes is stimulated in cotransfections with N-terminally truncated CDP/Cux proteins but not with full-length CDP/Cux. Moreover, expression of the endogenous DNA pol alpha gene was stimulated following the infection of cells with a retrovirus expressing a truncated CDP/Cux protein. Chromatin immunoprecipitation (ChIP) assays revealed that CDP/Cux was associated with the DNA pol alpha gene promoter specifically in the S phase. Using linker scanning analyses, in vitro DNA binding, and ChIP assays, we established a correlation between binding of CDP/Cux to the DNA pol alpha promoter and the stimulation of gene expression. Although we cannot exclude the possibility that stimulation of gene expression by CDP/Cux involved the repression of a repressor, our data support the notion that CDP/Cux participates in transcriptional activation. Notwithstanding its mechanism of action, these results establish CDP/Cux as an important transcriptional regulator in the S phase.

Identification of the human HEX1/hExo1 gene promoter and characterization of elements responsible for promoter activity

HEX1/hExo1 is a Class III nuclease of the RAD2 family with 5' to 3' exonuclease and flap structure-specific endonuclease activities. HEX1/hExo1 is expressed at low levels in a wide variety of tissues, but at higher levels in fetal liver and adult bone marrow, suggesting HEX1/hExo1 is important for hematopoietic stem cell development. A putative HEX1/hExo1 promoter fragment extending from -6240 to +1600bp exhibits cell-type specific activity in transient transfection assays. This fragment directs high luciferase reporter gene expression in the hematopoietic cell line K562, chronic myelogenous leukemia cells, but low luciferase expression in the non-hematopoietic cell line HeLa, human cervical carcinoma cells. Deletion studies identified a fragment spanning -688 to +1600bp that exhibits full transcriptional activity while a slightly shorter fragment from -658 to +1600bp exhibits significantly decreased promoter activity. In vitro binding assays revealed DNA-binding activities that interact with -687 to -681bp and -665 to -658bp elements. Oligonucleotide competition and antibody disruption studies determined that the transcription factor CREB-1 recognizes the -687 to -681bp element, while transcription factors Sp1 and Sp3 recognize the -665 to -658bp element. Mutation of either the CREB-1 or Sp1/Sp3 binding sites dramatically reduces HEX1/hExo1 promoter activity and elimination of both elements abolishes promoter activity.

Repression of rac2 mRNA expression by Anaplasma phagocytophila is essential to the inhibition of superoxide production and bacterial proliferation

Anaplasma phagocytophila, the etiologic agent of human granulocytic ehrlichiosis, is an emerging bacterial pathogen that invades neutrophils and can be cultivated in HL-60 cells. Infected neutrophils and HL-60 cells fail to produce superoxide anion (O(2)(-)), which is partially attributable to the fact that A. phagocytophila inhibits transcription of gp91(phox), an integral component of NADPH oxidase. cDNA microarray and RT-PCR analyses demonstrated that transcription of the gene encoding Rac2, a key component in NADPH oxidase activation, was down-regulated in infected HL-60 cells. Quantitative RT-PCR demonstrated that rac2 mRNA expression was reduced 7-fold in retinoic acid-differentiated HL-60 cells and 50-fold in neutrophils following A. phagocytophila infection. Rac2 protein expression was absent in infected HL-60 cells. Rac1 and Rac2 are interchangeable in their abilities to activate NADPH oxidase. HL-60 cells transfected to express myc-tagged rac1 and gp91(phox) from the CMV immediate early promoter maintained the ability to generate O(2)(-) 120 h postinfection. A. phagocytophila proliferation was severely inhibited in these cells. These results directly attribute the inhibition of rac2 and gp91(phox) transcription to the loss of NADPH oxidase activity in A. phagocytophila-infected cells and demonstrate its importance to bacterial intracellular survival.

GM-CSF induces expression of gp91phox and stimulates retinoic acid-induced p47phox expression in human myeloblastic leukemia cells

All-trans retinoic acid (ATRA) combined with granulocyte macrophage colony-stimulating factor (GM-CSF) synergistically increases superoxide-generating activity in human myeloblastic leukemia ML-1 cells. ATRA is known to increase the expression of some NADPH components; however, little is known about the effect of GM-CSF on the expression of these components. We examined the expression of NADPH oxidase components in ML-1 cells treated with ATRA, GM-CSF, or a combination of ATRA and GM-CSF. Expression of p47phox and gp91phox proteins increased markedly after treatment with both reagents. p47phox expression was increased by ATRA alone, and the expression was increased synergistically by the combination of ATRA with GM-CSF. gp91phox was increased by ATRA or GM-CSF alone. The expression of p47phox and gp91phox mRNA underwent similar changes to those seen in protein level. These results indicate that GM-CSF induces expression of gp91phox and enhances ATRA-induced p47phox expression. We speculate that the remarkable induction of gp91phox and p47phox protein is associated with an increase in superoxide-generating activity due to the synergistic effect of ATRA plus GM-CSF.

Transcriptional regulation of myelopoiesis

A common myeloid progenitor gives rise to both granulocytes and monocytes. The early stages of granulopoiesis are mediated by the C/EBPalpha, PU.1, RAR, CBF, and c-Myb transcription factors, and the later stages require C/EBPepsilon, PU.1, and CDP. Monocyte development requires PU.1 and interferon consensus sequence binding protein and can be induced by Maf-B, c-Jun, or Egr-1. Cytokine receptor signals modulate transcription factor activities but do not determine cell fates. Several mechanisms orchestrate the myeloid developmental program, including cooperative gene regulation, protein:protein interactions, regulation of factor levels, and induction of cell cycle arrest.

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.

Cooperation of STAT-1 and IRF-1 in interferon-gamma-induced transcription of the gp91(phox) gene

Interferon (IFN)-gamma induces the expression of the gp91(phox) gene both during myeloid differentiation and also in mature phagocytes through several cis-elements and their binding proteins. To find new cis-elements for this induction, transient expression assays were performed using a reporter gene driven by serially truncated gp91(phox) promoters in U937 cells. The results suggest that a critical cis-element for induction exists in the region from bp -115 to -96 of the promoter. Site-directed mutagenesis showed that a gamma-activated sequence (GAS) element at bp -100 (-100GAS) of the gp91(phox) promoter plays a pivotal role for the IFN-gamma-dependent activity of the bp -115 to +12 region of the gp91(phox) promoter. Electrophoretic mobility shift assays using several GAS competitors and specific antibodies indicated that phosphorylated STAT-1alpha specifically binds to the -100GAS. Site-directed mutagenesis showed that an interferon-stimulated response element (ISRE) at bp -88 (-88ISRE) mediates the induction of the gene by IFN-gamma in cooperation with -100GAS. Electrophoretic mobility shift assay showed that IRF-1 dominantly binds to -88ISRE in an IFN-gamma-dependent fashion. These results demonstrate a new mechanism for IFN-gamma-induced transcription of the gp91(phox) gene by the cooperation of STAT-1alpha and IRF-1 binding to -100GAS and -88ISRE, respectively.

CDP binding to multiple sites in the mouse mammary tumor virus long terminal repeat suppresses basal and glucocorticoid-induced transcription

Mouse mammary tumor virus (MMTV) is transcribed at high levels in the lactating mammary gland to ensure transmission of virus from the milk of infected female mice to susceptible offspring. We previously have shown that the transcription factor CCAAT displacement protein (CDP) is expressed in high amounts in virgin mammary gland, yet DNA-binding activity for the MMTV long terminal repeat (LTR) disappears as mammary tissue differentiates during lactation. CDP is a repressor of MMTV expression and, therefore, MMTV expression is suppressed during early mammary gland development. In this study, we have shown using DNase I footprinting and electrophoretic mobility shift assays that there are at least five CDP-binding sites in the MMTV LTR upstream of those previously described in the promoter-proximal negative regulatory element (NRE). Single mutations in two of these upstream sites (+691 or +692 and +735 relative to the first base of the LTR) reduced CDP binding to the cognate sites and elevated reporter gene expression from the full-length MMTV LTR. Combination of a mutation in the promoter-distal NRE with a mutation in the proximal NRE gave approximately additive increases in LTR-reporter gene activity, suggesting that these binding sites act independently. Mutations in several different CDP-binding sites allowed elevation of reporter gene activity from the MMTV promoter in the absence and presence of glucocorticoids, hormones that contribute to high levels of MMTV transcription during lactation by activation of hormone receptor binding to the LTR. In addition, overexpression of CDP in transient-transfection assays suppressed both basal and glucocorticoid-induced LTR-mediated transcription in a dose-dependent manner. These data suggest that multiple CDP-binding sites contribute independently to regulate binding of positive factors, including glucocorticoid receptor, to the MMTV LTR during mammary gland development.

Transcriptional mechanisms regulating myeloid-specific genes

Myeloid blood cells comprise an important component of the immune system. Proper control of both lineage- and stage-specific gene expression is required for normal myeloid cell development and function. In recent years, a relatively small number of critical transcriptional regulators have been identified that serve important roles both in myeloid cell development and regulation of lineage-restricted gene expression in mature myeloid cells. This review summarizes our current understanding of the regulation of lineage- and stage-restricted transcription during myeloid cell differentiation, how critical transcriptional regulators control myeloid cell development, and how perturbations in transcription factor function results in the development of leukemia.

Lymphoid apoptosis and myeloid hyperplasia in CCAAT displacement protein mutant mice

CCAAT displacement protein (cux/CDP) is an atypical homeodomain protein that represses expression of several developmentally regulated lymphoid and myeloid genes in vitro, including gp91-phox, immunoglobulin heavy chain, the T-cell receptor beta and gamma chains, and CD8. To determine how this activity affects cell development in vivo, a hypomorphic allele of cux/CDP was created by gene targeting. Homozygous mutant mice (cux/CDP(Delta HD/Delta HD)) demonstrated a partial neonatal lethality phenotype. Surviving animals suffered from a wasting disease, which usually resulted in death between 2 and 3 weeks of age. Analysis of T lymphopoiesis demonstrated that cux/CDP(Delta HD/Delta HD) mice had dramatically reduced thymic cellularity due to enhanced apoptosis, with a preferential loss of CD4(+)CD8(+) thymocytes. Ectopic CD25 expression was also observed in maturing thymocytes. B lymphopoiesis was also perturbed, with a 2- to 3-fold reduction in total bone marrow B-lineage cells and a preferential loss of cells in transition from pro-B/pre-BI to pre-BII stages due to enhanced apoptosis. These lymphoid abnormalities were independent of effects related to antigen receptor rearrangement. In contrast to the lymphoid demise, cux/CDP(Delta HD/Delta HD) mice demonstrated myeloid hyperplasia. Bone marrow reconstitution experiments identified that many of the hematopoietic defects were linked to microenvironmental effects, suggesting that underexpression of survival factors or overexpression of death-inducing factors accounted for the phenotypes observed. Tumor necrosis factor (TNF) levels were elevated in several tissues, especially thymus, suggesting that TNF may be a target gene for cux/CDP-mediated repression. These data suggest that cux/CDP regulates normal hematopoiesis, in part, by modulating the levels of survival and/or apoptosis factors expressed by the microenvironment.

Phosphorylation of the CCAAT displacement protein (CDP)/Cux transcription factor by cyclin A-Cdk1 modulates its DNA binding activity in G(2)

Stable DNA binding by the mammalian CCAAT displacement protein (CDP)/Cux transcription factor was previously found to be up-regulated at the G(1)/S transition as the result of two events, dephosphorylation by the Cdc25A phosphatase and proteolytic processing, to generate an amino-truncated isoform of 110 kDa. In S phase, CDP/Cux was shown to interact with and repress the core promoter of the p21(WAF1) gene. Here we demonstrate that DNA binding by p110 CDP/Cux is down-modulated as cells progress into G(2). Accordingly, cyclin A-Cdk1 was found to bind to CDP/Cux and modulate its DNA binding activity in vitro and in vivo. Interaction with CDP/Cux required the presence of both cyclin A and a cyclin-dependent kinase (Cdk)-activating kinase-activated Cdk1 and involved the Cut homeodomain and a downstream Cy motif. Phosphorylation of serines 1237 and 1270 caused inhibition of DNA binding in vitro. In cotransfection studies, cyclin A-Cdk1 inhibited CDP/Cux stable DNA binding and prevented repression of the p21(WAF1) reporter. In contrast, mutant CDP/Cux proteins in which serines 1237 and 1270 were replaced with alanines were not affected by cyclin A-Cdk1. In summary, our results suggest that the phosphorylation of CDP/Cux by cyclin A-Cdk1 contributes to down-modulate CDP/Cux activity as cells progress into the G(2) phase of the cell cycle.

The matrix attachment region-binding protein SATB1 interacts with multiple elements within the gp91phox promoter and is down-regulated during myeloid differentiation

The gp91(phox) gene encodes a component of the respiratory burst NADPH oxidase complex and is highly expressed in mature myeloid cells. The transcriptional repressor CCAAT displacement protein binds to at least five sites within the proximal gp91(phox) promoter and represses expression prior to terminal phagocyte differentiation. The DNA binding activity of CCAAT displacement protein decreases during terminal phagocyte differentiation, thus permitting the binding of transcriptional activators and induction of gp91(phox) expression. We report here that the matrix attachment region-binding protein SATB1 interacts with at least seven sites within the -1542 to +12-base pair gp91(phox) promoter. Four additional binding sites for CCAAT displacement protein were also identified. Furthermore, the most proximal SATB1-binding site within the gp91(phox) promoter binds specifically to the nuclear matrix fraction in vitro. SATB1 expression is down-regulated during terminal myeloid cell differentiation, coincident with induction of gp91(phox) expression. Transient transfection assays demonstrate that a SATB1-binding site derived from the gp91(phox) promoter represses promoter activity in cells expressing SATB1. These findings underscore the importance of transcriptional repression in the regulation of gp91(phox) expression and reveal a candidate myeloid cell target gene for SATB1, a factor previously found to be essential for T cell development.

Transcriptional regulation of the p67phox gene: role of AP-1 in concert with myeloid-specific transcription factors

We have investigated the myeloid-specific transcriptional regulation of p67(phox), an essential component of phagocyte respiratory burst NADPH oxidase. Analysis was carried out on the p67(phox) 5'-flanking region from -3669 to -4 (relative to ATG), including the first exon and intron and part of the second exon. The construct extending from -985 to -4 produced the highest luciferase activity in myeloid HL-60 cells but was not active in HeLa or Jurkat cells, indicating myeloid-specific expression. Four active elements were identified: Sp1/Sp3 at -694, PU.1 at -289, AP-1 at -210, and PU.1/HAF1 at -182, the latter three being in the first intron. These cis elements bound their cognate transacting factors both in vitro and in vivo. Mutation of the Sp1, PU.1, or PU.1/HAF1 site each decreased promoter activity by 35-50%. Mutations in all three sites reduced promoter activity by 90%. However, mutation of the AP-1 site alone nearly abolished promoter activity. The AP-1 site bound Jun and Fos proteins from HL-60 cell nuclear extract. Co-expression with Jun B in AP-1-deficient cells increased promoter activity by 3-fold. These data show that full p67(phox) promoter activity requires cooperation between myeloid-specific and nonmyeloid transcription factors, with AP-1 being the most critical for function.

Transcriptional regulation of hemopoiesis

The regulation of blood cell formation, or hemopoiesis, is central to the replenishment of mature effector cells of innate and acquired immune responses. These cells fulfil specific roles in the host defense against invading pathogens, and in the maintenance of homeostasis. The development of hemopoietic cells is under stringent control from extracellular and intracellular stimuli that result in the activation of specific downstream signaling cascades. Ultimately, all signal transduction pathways converge at the level of gene expression where positive and negative modulators of transcription interact to delineate the pattern of gene expression and the overall cellular hemopoietic response. Transcription factors, therefore, represent a nodal point of hemopoietic control through the integration of the various signaling pathways and subsequent modulation of the transcriptional machinery. Transcription factors can act both positively and negatively to regulate the expression of a wide range of hemopoiesis-relevant genes including growth factors and their receptors, other transcription factors, as well as various molecules important for the function of developing cells. The expression of these genes is dependent on the complex interactions between transcription factors, co-regulatory molecules, and specific binding sequences on the DNA. Recent advances in various vertebrate and invertebrate systems emphasize the importance of transcription factors for hemopoiesis control and the evolutionary conservation of several of such mechanisms. In this review we outline some of the key issues frequently identified in studies of the transcriptional regulation of hemopoietic gene expression. In teleosts, we expect that the characterization of several of these transcription factors and their regulatory mechanisms will complement recent advances in a number of fish systems where identification of cytokine and other hemopoiesis-relevant factors are currently under investigation.