CCAAT displacement protein as a repressor of the myelomonocytic-specific gp91-phox gene promoter

Gene regulation in inborn errors of immunity: Implications for gene therapy design and efficacy

Inborn errors of immunity (IEI) present a unique paradigm in the realm of gene therapy, emphasizing the need for precision in therapeutic design. As gene therapy transitions from broad-spectrum gene addition to careful modification of specific genes, the enduring safety and effectiveness of these therapies in clinical settings have become crucial. This review discusses the significance of IEIs as foundational models for pioneering and refining precision medicine. We explore the capabilities of gene addition and gene correction platforms in modifying the DNA sequence of primary cells tailored for IEIs. The review uses four specific IEIs to highlight key issues in gene therapy strategies: X-linked agammaglobulinemia (XLA), X-linked chronic granulomatous disease (X-CGD), X-linked hyper IgM syndrome (XHIGM), and immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX). We detail the regulatory intricacies and therapeutic innovations for each disorder, incorporating insights from relevant clinical trials. For most IEIs, regulated expression is a vital aspect of the underlying biology, and we discuss the importance of endogenous regulation in developing gene therapy strategies.

The WNK1 kinase regulates the stability of transcription factors during wound healing of human corneal epithelial cells

Due to its superficial anatomical localization, the cornea is continuously subjected to injuries. Damages to the corneal epithelium trigger important changes in the composition of the extracellular matrix to which the basal human corneal epithelial cells (hCECs) attach. These changes are perceived by membrane-bound integrins and ultimately lead to re-epithelialization of the injured epithelium through intracellular signalin. Among the many downstream targets of the integrin-activated signaling pathways, WNK1 is the kinase whose activity is the most strongly increased during corneal wound healing. We previously demonstrated that pharmacological inhibition of WNK1 prevents proper closure of wounded human tissue-engineered cornea in vitro. In the present study, we investigated the molecular mechanisms by which WNK1 contributes to corneal wound healing. By exploiting transcription factors microarrays, electrophoretic mobility-shift assay, and gene profiling analyses, we demonstrated that the DNA binding properties and expression of numerous transcription factors (TFs), including the well-known, ubiquitous TFs specific protein 1 (Sp1) and activator protein 1 (AP1), were reduced in hCECs upon WNK1 inhibition by WNK463. This process appears to be mediated at least in part by alteration in both the ubiquitination and glycosylation status of these TFs. These changes in TFs activity and expression impacted the transcription of several genes, including that encoding the α5 integrin subunit, a well-known target of both Sp1 and AP1. Gene profiling revealed that only a moderate number of genes in hCECs had their level of expression significantly altered in response to WNK463 exposition. Interestingly, analysis of the microarray data for these deregulated genes using the ingenuity pathway analysis software predicted that hCECs would stop migrating and proliferating but differentiate more when they are grown in the presence of the WNK1 inhibitor. These results demonstrate that WNK1 plays a critical function by orienting hCECs into the appropriate biological response during the process of corneal wound healing.

CUX1 Enhances Pancreatic Cancer Formation by Synergizing with KRAS and Inducing MEK/ERK-Dependent Proliferation

Simple Summary

In pancreatic cancer, CUX1 acts as an important mediator of tumor cell proliferation and resistance to apoptosis. Using two different mouse models for the prevalent CUX1 isoforms p200 and p110, we identified p110 CUX1 as the major isoform promoting pancreatic cancer formation in the context of mutant KRAS. We could show an enhanced proliferation by activating and potentiating MEK-ERK signaling via an increased upstream activation of the ADAM17-EGFR axis. This strengthened activation in a KRAS-dependent manner, leading to a dramatically more accelerated formation of invasive PDAC in p110 CUX1 mice within 4 weeks. These results provide the first in vivo evidence for the importance of CUX1 in the development of pancreatic cancer, and highlight CUX1-dependent signaling pathways as potential therapeutic targets.

Abstract

The transcription factor CUX1 has been implicated in either tumor suppression or progression, depending on the cancer entity and the prevalent CUX1 isoform. Previously, we could show that CUX1 acts as an important mediator of tumor cell proliferation and resistance to apoptosis in pancreatic cancer cell lines. However, in vivo evidence for its impact on pancreatic carcinogenesis, isoform-specific effects and downstream signaling cascades are missing. We crossbred two different CUX1 isoform mouse models (p200 CUX1 and p110 CUX1) with KC (KrasLSL-G12D/+; Ptf1aCre/+) mice, a genetic model for pancreatic precursor lesions (PanIN). In the context of oncogenic KRASs, both mice KCCux1p200 and KCCux1p110 led to increased PanIN formation and development of invasive pancreatic ductal adenocarcinomata (PDAC). In KCCux1p110 mice, tumor development was dramatically more accelerated, leading to formation of invasive PDAC within 4 weeks. In vitro and in vivo, we could show that CUX1 enhanced proliferation by activating MEK-ERK signaling via an upstream increase of ADAM17 protein, which in turn led to an activation of EGFR. Additionally, CUX1 further enhanced MEK-ERK activation through upregulation of the serine/threonine kinase MOS, phosphorylating MEK in a KRAS-independent manner. We identified p110 CUX1 as major driver of pancreatic cancer formation in the context of mutant KRAS. These results provide the first in vivo evidence for the importance of CUX1 in the development of pancreatic cancer, and highlight the importance of CUX1-dependent signaling pathways as potential therapeutic targets.

Distinct clinical and biological implications of CUX1 in myeloid neoplasms

Somatic mutations of the CUT-like homeobox 1 (CUX1) gene (CUX1 ^MT) can be found in myeloid neoplasms (MNs), in particular, in myelodysplastic syndromes (MDSs). The CUX1 locus is also deleted in 3 of 4 MN cases with -7/del(7q). A cohort of 1480 MN patients was used to characterize clinical features and clonal hierarchy associated with CUX1 ^MT and CUX1 deletions (CUX1 ^DEL) and to analyze their functional consequences in vitro. CUX1 ^MT were present in 4% of chronic MNs. CUX1 ^DEL were preferentially found in advanced cases (6%). Most MDS and acute myeloid leukemia (AML) patients with -7/del(7q) and up to 15% of MDS patients and 5% of AML patients diploid for the CUX1 locus exhibited downmodulated CUX1 expression. In 75% of mutant cases, CUX1 ^MT were heterozygous, whereas microdeletions and homozygous and compound-heterozygous mutations were less common. CUX ^MT/DEL were associated with worse survival compared with CUX1 ^WT Within the clonal hierarchy, 1 of 3 CUX1 ^MT served as founder events often followed by secondary BCOR and ASXL1 subclonal hits, whereas TET2 was the most common ancestral lesion, followed by subclonal CUX1 ^MT Comet assay of patients' bone marrow progenitor cells and leukemic cell lines performed in various experimental conditions revealed that frameshift mutations, hemizygous deletions, or experimental CUX1 knockdown decrease the repair of oxidized bases. These functional findings may explain why samples with either CUX1 ^MT or low CUX1 expression coincided with significantly higher numbers of somatic hits by whole-exome sequencing. Our findings implicate the DNA repair dysfunction resulting from CUX1 lesions in the pathogenesis of MNs, in which they lead to a mutator phenotype.

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.

The Hap Complex in Yeasts: Structure, Assembly Mode, and Gene Regulation

The CCAAT box-harboring proteins represent a family of heterotrimeric transcription factors which is highly conserved in eukaryotes. In fungi, one of the particularly important homologs of this family is the Hap complex that separates the DNA-binding domain from the activation domain and imposes essential impacts on regulation of a wide range of cellular functions. So far, a comprehensive summary of this complex has been described in filamentous fungi but not in the yeast. In this review, we summarize a number of studies related to the structure and assembly mode of the Hap complex in a list of representative yeasts. Furthermore, we emphasize recent advances in understanding the regulatory functions of this complex, with a special focus on its role in regulating respiration, production of reactive oxygen species (ROS) and iron homeostasis.

Obesity and FTO: Changing Focus at a Complex Locus

The fat mass and obesity-associated (FTO) gene was placed center stage when common intronic variants within the gene were robustly associated with human obesity. Murine models of perturbed Fto expression have shown effects on body weight and composition. However, a clear understanding of the link between FTO intronic variants and FTO activity has remained elusive. Two recent reports now indicate that obesity-associated SNPs appear functionally connected not with FTO but with two neighboring genes: IRX3 and RPGRIP1L. Here, we review these new findings and consider the implications for future analysis of GWAS hits.

Influenza virus replication in lung epithelial cells depends on redox-sensitive pathways activated by NOX4-derived ROS

An overproduction of reactive oxygen species (ROS) mediated by NADPH oxidase 2 (NOX2) has been related to airway inflammation typical of influenza infection. Virus-induced oxidative stress may also control viral replication, but the mechanisms underlying ROS production, as well as their role in activating intracellular pathways and specific steps of viral life cycle under redox control have to be fully elucidated. In this study, we demonstrate that influenza A virus infection of lung epithelial cells causes a significant ROS increase that depends mainly on NOX4, which is upregulated at both mRNA and protein levels, while the expression of NOX2, the primary source of ROS in inflammatory cells, is downregulated. Inhibition of NOX4 activity through chemical inhibitors or RNA silencing blocks the ROS increase, prevents MAPK phosphorylation, and inhibits viral ribonucleoprotein (vRNP) nuclear export and viral release. Overall these data, obtained in cell lines and primary culture, describe a so far unrecognized role for NOX4-derived ROS in activating redox-regulated intracellular pathways during influenza virus infection and highlight their relevance in controlling specific steps of viral replication in epithelial cells. Pharmacological modulation of NOX4-mediated ROS production may open the way for new therapeutic approaches to fighting influenza by targeting cell and not the virus.

CUX1, a haploinsufficient tumour suppressor gene overexpressed in advanced cancers

CUT-like homeobox 1 (CUX1) is a homeobox gene that is implicated in both tumour suppression and progression. The accumulated evidence supports a model of haploinsufficiency whereby reduced CUX1 expression promotes tumour development. Paradoxically, increased CUX1 expression is associated with tumour progression, and ectopic CUX1 expression in transgenic mice increases tumour burden in several tissues. One CUX1 isoform functions as an ancillary factor in base excision repair and the other CUX1 isoforms act as transcriptional activators or repressors. Several transcriptional targets and cellular functions of CUX1 affect tumorigenesis; however, we have yet to develop a mechanistic framework to reconcile the opposite roles of CUX1 in cancer protection and progression.

RAS transformation requires CUX1-dependent repair of oxidative DNA damage

The base excision repair (BER) that repairs oxidative damage is upregulated as an adaptive response in maintaining tumorigenesis of RAS-transformed cancer cells.

The Cut homeobox 1 (CUX1) gene is a target of loss-of-heterozygosity in many cancers, yet elevated CUX1 expression is frequently observed and is associated with shorter disease-free survival. The dual role of CUX1 in cancer is illustrated by the fact that most cell lines with CUX1 LOH display amplification of the remaining allele, suggesting that decreased CUX1 expression facilitates tumor development while increased CUX1 expression is needed in tumorigenic cells. Indeed, CUX1 was found in a genome-wide RNAi screen to identify synthetic lethal interactions with oncogenic RAS. Here we show that CUX1 functions in base excision repair as an ancillary factor for the 8-oxoG-DNA glycosylase, OGG1. Single cell gel electrophoresis (comet assay) reveals that Cux1^+/− MEFs are haploinsufficient for the repair of oxidative DNA damage, whereas elevated CUX1 levels accelerate DNA repair. In vitro base excision repair assays with purified components demonstrate that CUX1 directly stimulates OGG1's enzymatic activity. Elevated reactive oxygen species (ROS) levels in cells with sustained RAS pathway activation can cause cellular senescence. We show that elevated expression of either CUX1 or OGG1 prevents RAS-induced senescence in primary cells, and that CUX1 knockdown is synthetic lethal with oncogenic RAS in human cancer cells. Elevated CUX1 expression in a transgenic mouse model enables the emergence of mammary tumors with spontaneous activating Kras mutations. We confirmed cooperation between Kras^G12V and CUX1 in a lung tumor model. Cancer cells can overcome the antiproliferative effects of excessive DNA damage by inactivating a DNA damage response pathway such as ATM or p53 signaling. Our findings reveal an alternate mechanism to allow sustained proliferation in RAS-transformed cells through increased DNA base excision repair capability. The heightened dependency of RAS-transformed cells on base excision repair may provide a therapeutic window that could be exploited with drugs that specifically target this pathway.

In the context of tumor development and progression, mutations are believed to accumulate owing to compromised DNA repair. Such mutations promote oncogenic growth. Yet cancer cells also need to sustain a certain level of DNA repair in order to replicate their DNA and successfully proliferate. Here we show that cancer cells that harbor an activated RAS oncogene exhibit heightened DNA repair capability, specifically in the base excision repair (BER) pathway that repairs oxidative DNA damage. RAS oncogenes alone do not transform primary cells but rather cause their senescence—that is, they stop dividing. As such, cellular senescence in this context is proposed to function as a tumor-suppressive mechanism. We show that CUX1, a protein that accelerates oxidative DNA damage repair, prevents cells from senescing and enables proliferation in the presence of a RAS oncogene. Consistent with this, RAS-induced senescence is also prevented by ectopic expression of OGG1, the DNA glycosylase that removes 8-oxoguanine, the most abundant oxidized base. Strikingly, CUX1 expression in transgenic mice enables the emergence of tumors with spontaneous activating Kras mutations. Conversely, knockdown of CUX1 is synthetic lethal for RAS-transformed cells, thereby revealing a potential Achilles' heel of these cancer cells. Overall, the work provides insight into understanding the role of DNA repair in cancer progression, showing that while DNA damage-induced mutations promote tumorigenesis, sustained RAS-dependent tumorigenesis requires suppression of DNA damage. The heightened dependency of RAS-transformed cells on base excision repair may provide a therapeutic window that could be exploited with drugs that specifically target this pathway.

The interplay between iron accumulation, mitochondrial dysfunction, and inflammation during the execution step of neurodegenerative disorders

A growing set of observations points to mitochondrial dysfunction, iron accumulation, oxidative damage and chronic inflammation as common pathognomonic signs of a number of neurodegenerative diseases that includes Alzheimer’s disease, Huntington disease, amyotrophic lateral sclerosis, Friedrich’s ataxia and Parkinson’s disease. Particularly relevant for neurodegenerative processes is the relationship between mitochondria and iron. The mitochondrion upholds the synthesis of iron–sulfur clusters and heme, the most abundant iron-containing prosthetic groups in a large variety of proteins, so a fraction of incoming iron must go through this organelle before reaching its final destination. In turn, the mitochondrial respiratory chain is the source of reactive oxygen species (ROS) derived from leaks in the electron transport chain. The co-existence of both iron and ROS in the secluded space of the mitochondrion makes this organelle particularly prone to hydroxyl radical-mediated damage. In addition, a connection between the loss of iron homeostasis and inflammation is starting to emerge; thus, inflammatory cytokines like TNF-alpha and IL-6 induce the synthesis of the divalent metal transporter 1 and promote iron accumulation in neurons and microglia. Here, we review the recent literature on mitochondrial iron homeostasis and the role of inflammation on mitochondria dysfunction and iron accumulation on the neurodegenerative process that lead to cell death in Parkinson’s disease. We also put forward the hypothesis that mitochondrial dysfunction, iron accumulation and inflammation are part of a synergistic self-feeding cycle that ends in apoptotic cell death, once the antioxidant cellular defense systems are finally overwhelmed.

Norepinephrine causes epigenetic repression of PKCε gene in rodent hearts by activating Nox1-dependent reactive oxygen species production

Heart disease is the leading cause of death in the United States. Recent studies demonstrate that fetal programming of PKCε gene repression results in ischemia-sensitive phenotype in the heart. The present study tests the hypothesis that increased norepinephrine causes epigenetic repression of PKCε gene in the heart via Nox1-dependent reactive oxygen species (ROS) production. Prolonged norepinephrine treatment increased ROS production in fetal rat hearts and embryonic ventricular myocyte H9c2 cells via a selective increase in Nox1 expression. Norepinephrine-induced ROS resulted in an increase in PKCε promoter methylation at Egr-1 and Sp-1 binding sites, leading to PKCε gene repression. N-acetylcysteine, diphenyleneiodonium, and apocynin blocked norepinephrine-induced ROS production and the promoter methylation, and also restored PKCε mRNA and protein to control levels in vivo in fetal hearts and in vitro in embryonic myocyte cells. Accordingly, norepinephrine-induced ROS production, promoter methylation, and PKCε gene repression were completely abrogated by knockdown of Nox1 in cardiomyocytes. These findings provide evidence of a novel interaction between elevated norepinephrine and epigenetic repression of PKCε gene in the heart mediated by Nox1-dependent oxidative stress and suggest new insights of molecular mechanisms linking the heightened sympathetic activity to aberrant cardioprotection and increased ischemic vulnerability in the heart.

CUX1 transcription factors: from biochemical activities and cell-based assays to mouse models and human diseases

ChIP-chip and expression analyses indicated that CUX1 transcription factors regulate a large number of genes and microRNAs involved in multiple cellular processes. Indeed, in proliferating cells CUX1 was shown to regulate several genes involved in DNA replication, progression into S phase and later, the spindle assembly checkpoint that controls progression through mitosis. siRNA-mediated knockdown established that CUX1 is required for cell motility. Moreover, higher expression of short CUX1 isoforms, as observed in many cancers, was shown to stimulate cell migration and invasion. In parallel, elevated expression particularly in higher grade tumors of breast and pancreatic cancers implicated CUX1 in tumor initiation and progression. Indeed, transgenic mouse models demonstrated a causal role of CUX1 in cancers originating from various cell types. These studies revealed that higher CUX1 expression or activity not only stimulates cell proliferation and motility, but also promotes genetic instability. CUX1 has also been implicated in the etiology of polycystic kidney diseases, both from a transgenic approach and the analysis of CUX1 activity in multiple mouse models of this disease. Studies in neurobiology have uncovered a potential implication of CUX1 in cognitive disorders, neurodegeneration and obesity. CUX1 was shown to be expressed specifically in pyramidal neurons of the neocortex upper layers where it regulates dendrite branching, spine development, and synapse formation. In addition, modulation of CUX1 expression in neurons of the hypothalamus has been associated with changes in leptin receptor trafficking in the vicinity of the primary cilium resulting in altered leptin signaling and ultimately, eating behavior. Overall, studies in various fields have allowed the development of several cell-based assays to monitor CUX1 function and have extended the range of organs in which CUX1 plays an important role in development and tissue homeostasis.

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.

High doses of TGF-β potently suppress type I collagen via the transcription factor CUX1

Uncontrolled expression of collagen often leads to tissue scarring and loss of organ function. In this study, we identify a molecular mechanism that may enable us to switch off collagen production when unnecessary (i.e., fibrosis). We conclude that CUX1, which is a CCAAT binding factor displacement protein, may serve as a therapeutic target in treating fibrosis.

Transforming growth factor-β (TGF-β) is an inducer of type I collagen, and uncontrolled collagen production leads to tissue scarring and organ failure. Here we hypothesize that uncovering a molecular mechanism that enables us to switch off type I collagen may prove beneficial in treating fibrosis. For the first time, to our knowledge, we provide evidence that CUX1 acts as a negative regulator of TGF-β and potent inhibitor of type I collagen transcription. We show that CUX1, a CCAAT displacement protein, is associated with reduced expression of type I collagen both in vivo and in vitro. We show that enhancing the expression of CUX1 results in effective suppression of type I collagen. We demonstrate that the mechanism by which CUX1 suppresses type I collagen is through interfering with gene transcription. In addition, using an in vivo murine model of aristolochic acid (AA)-induced interstitial fibrosis and human AA nephropathy, we observe that CUX1 expression was significantly reduced in fibrotic tissue when compared to control samples. Moreover, silencing of CUX1 in fibroblasts from kidneys of patients with renal fibrosis resulted in increased type I collagen expression. Furthermore, the abnormal CUX1 expression was restored by addition of TGF-β via the p38 mitogen-activated protein kinase pathway. Collectively, our study demonstrates that modifications of CUX1 expression lead to aberrant expression of type I collagen, which may provide a molecular basis for fibrogenesis.

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.

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.

The transcription factor Cux1 regulates dendritic morphology of cortical pyramidal neurons

In the murine cerebral cortex, mammalian homologues of the Cux family transcription factors, Cux1 and Cux2, have been identified as restricted molecular markers for the upper layer (II-IV) pyramidal neurons. However, their functions in cortical development are largely unknown. Here we report that increasing the intracellular level of Cux1, but not Cux2, reduced the dendritic complexity of cultured cortical pyramidal neurons. Consistently, reducing the expression of Cux1 promoted the dendritic arborization in these pyramidal neurons. This effect required the existence of the DNA-binding domains, hence the transcriptional passive repression activity of Cux1. Analysis of downstream signals suggested that Cux1 regulates dendrite development primarily through suppressing the expression of the cyclin-dependent kinase inhibitor p27^Kip1, and RhoA may mediate the regulation of dendritic complexity by Cux1 and p27. Thus, Cux1 functions as a negative regulator of dendritic complexity for cortical pyramidal neurons.

The homeodomain protein Cux1 interacts with Grg4 to repress p27 kip1 expression during kidney development

The homeodomain protein Cux1 is highly expressed in the nephrogenic zone of the developing kidney where it functions to regulate cell proliferation. Here we show that Cux1 directly interacts with the co-repressor Grg4 (Groucho 4), a known effector of Notch signaling. Promoter reporter based luciferase assays revealed enhanced repression of p27(kip1) promoter activity by Cux1 in the presence of Grg4. Chromatin immunoprecipitation (ChIP) assays demonstrated the direct interaction of Cux1 with p27(kip1) in newborn kidney tissue in vivo. ChIP assays also identified interactions of Cux1, Grg4, HDAC1, and HDAC3 with p27(kip1) at two separate sites in the p27(kip1) promoter. DNAse1 footprinting experiments revealed that Cux1 binds to the p27(kip1) promoter on the sequence containing two Sp1 sites and a CCAAT box approximately 500 bp from the transcriptional start site, and to an AT rich sequence approximately 1.5 kb from the transcriptional start site. Taken together, these results identify Grg4 as an interacting partner for Cux1 and suggest a mechanism of p27(kip1) repression by Cux1 during kidney development.

CXXC finger protein 1 contains redundant functional domains that support embryonic stem cell cytosine methylation, histone methylation, and differentiation

CXXC finger protein 1 (Cfp1) is a regulator of both cytosine methylation and histone methylation. Murine embryonic stem (ES) cells lacking Cfp1 exhibit a decreased plating efficiency, decreased cytosine methylation, elevated global levels of histone H3-Lys4 trimethylation, and a failure to differentiate in vitro. Remarkably, transfection studies reveal that expression of either the amino half of Cfp1 (amino acids 1 to 367 [Cfp1(1-367)]) or the carboxyl half of Cfp1 (Cfp1(361-656)) is sufficient to correct all of the defects observed with ES cells that lack Cfp1. However, a point mutation (C169A) that abolishes DNA-binding activity of Cfp1 ablates the rescue activity of the Cfp1(1-367) fragment, and a point mutation (C375A) that abolishes the interaction of Cfp1 with the Setd1 histone H3-Lys4 methyltransferase complexes ablates the rescue activity of the Cfp1(361-656) fragment. Introduction of both the C169A and C375A point mutations ablates the rescue activity of the full-length Cfp1 protein. These results indicate that retention of either the Cfp1 DNA-binding domain or Setd1 interaction domain is required for Cfp1 rescue activity, and they illustrate the functional complexity of this critical epigenetic regulator. A model is presented for how epigenetic cross talk may explain the finding of redundant functional domains within Cfp1.

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.

A cascade of Ca(2+)/calmodulin-dependent protein kinases regulates the differentiation and functional activation of murine neutrophils

OBJECTIVE

The function of neutrophils as primary mediators of innate immunity depends on the activity of granule proteins and critical components of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex. Expression of their cognate genes is regulated during neutrophil differentiation by a complex network of intracellular signaling pathways. In this study, we have investigated the role of two members of the calcium/calmodulin-dependent protein kinase (CaMK) signaling cascade, CaMK I-like kinase (CKLiK) and CaMKKalpha, in regulating neutrophil differentiation and functional activation.

MATERIALS AND METHODS

Mouse myeloid cell lines were used to examine the expression of a CaMK cascade in developing neutrophils and to examine the effects of constitutive activation vs inhibition of CaMKs on neutrophil maturation.

RESULTS

Expression of CaMKKalpha was shown to increase during neutrophil differentiation in multiple cell lines, whereas expression of CKLiK increased as multipotent progenitors committed to promyelocytes, but then decreased as cells differentiated into mature neutrophils. Expression of constitutively active CKLiKs did not affect morphologic maturation, but caused dramatic decreases in both respiratory burst responses and chemotaxis. This loss of neutrophil function was accompanied by reduced secondary granule and gp91(phox) gene expression. The CaMK inhibitor KN-93 attenuated cytokine-stimulated proliferative responses in promyelocytic cell lines, and inhibited the respiratory burst. Similar data were observed with the CaMKKalpha inhibitor, STO-609.

CONCLUSIONS

Overactivation of a cascade of CaMKs inhibits neutrophil maturation, suggesting that these kinases play an antagonistic role during neutrophil differentiation, but at least one CaMK is required for myeloid cell expansion and functional activation.

Regulation of Fto/Ftm gene expression in mice and humans

Two recent, large whole-genome association studies (GWAS) in European populations have associated a approximately 47-kb region that contains part of the FTO gene with high body mass index (BMI). The functions of FTO and adjacent FTM in human biology are not clear. We examined expression of these genes in organs of mice segregating for monogenic obesity mutations, exposed to underfeeding/overfeeding, and to 4 degrees C. Fto/Ftm expression was reduced in mesenteric adipose tissue of mice segregating for the Ay, Lep ob, Lepr db, Cpe fat, or tub mutations, and there was a similar trend in other tissues. These effects were not due to adiposity per se. Hypothalamic Fto and Ftm expression were decreased by fasting in lean and obese animals and by cold exposure in lean mice. The fact that responses of Fto and Ftm expression to these manipulations were almost indistinguishable suggested that the genes might be coregulated. The putative overlapping regulatory region contains at least two canonical CUTL1 binding sites. One of these nominal CUTL1 sites includes rs8050136, a SNP associated with high body mass. The A allele of rs8050136 preferentially bound CUTL1[corrected] in human fibroblast DNA. 70% knockdown of CUTL1 expression in human fibroblasts decreased FTO and FTM expression by 90 and 65%, respectively. Animals and humans with various genetic interruptions of FTO or FTM have phenotypes reminiscent of aspects of the Bardet-Biedl obesity syndrome, a confirmed "ciliopathy." FTM has recently been shown to be a ciliary basal body protein.

p110 CUX1 cooperates with E2F transcription factors in the transcriptional activation of cell cycle-regulated genes

The transcription factor p110 CUX1 was shown to stimulate cell proliferation by accelerating entry into S phase. As p110 CUX1 can function as a transcriptional repressor or activator depending on promoter context, we investigated its mechanism of transcriptional activation using the DNA polymerase alpha gene promoter as a model system. Linker-scanning analysis revealed that a low-affinity E2F binding site is required for transcriptional activation. Moreover, coexpression with a dominant-negative mutant of DP-1 suggested that endogenous E2F factors are indeed needed for p110-mediated activation. Tandem affinity purification, coimmunoprecipitation, chromatin immunoprecipitation, and reporter assays indicated that p110 CUX1 can engage in weak protein-protein interactions with E2F1 and E2F2, stimulate their recruitment to the DNA polymerase alpha gene promoter, and cooperate with these factors in transcriptional activation. On the other hand, in vitro assays suggested that the interaction between CUX1 and E2F1 either is not direct or is regulated by posttranslational modifications. Genome-wide location analysis revealed that targets common to p110 CUX1 and E2F1 included many genes involved in cell cycle, DNA replication, and DNA repair. Comparison of the degree of enrichment for various E2F factors suggested that binding of p110 CUX1 to a promoter will favor the specific recruitment of E2F1, and to a lesser extent E2F2, over E2F3 and E2F4. Reporter assays on a subset of common targets confirmed that p110 CUX1 and E2F1 cooperate in their transcriptional activation. Overall, our results show that p110 CUX1 and E2F1 cooperate in the regulation of many cell cycle genes.

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

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

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.

Understanding mechanisms of gamma-globin gene regulation to develop strategies for pharmacological fetal hemoglobin induction

The developmental regulation of gamma-globin gene expression has shaped research efforts to establish therapeutic modalities for individuals affected with sickle cell disease (SCD). Fetal hemoglobin (Hb F) synthesis is high at birth, followed by a decline to adult levels by 10 months of age. The expression of gamma-globin is controlled by a developmentally regulated transcriptional program that is recapitulated during normal erythropoiesis in the adult bone marrow. It is known that naturally occurring mutations in the gamma-gene promoters cause persistent Hb F synthesis after birth, which ameliorates symptoms in SCD by inhibiting hemoglobin S polymerization and vaso-occlusion. Several pharmacological agents have been identified over the past 2 decades that reactivate gamma-gene transcription through different cellular systems. We will review the progress made in our understanding of molecular mechanisms that control gamma-globin expression and insights gained from Hb F-inducing agents that act through signal transduction pathways.

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.

CUTL1 is phosphorylated by protein kinase A, modulating its effects on cell proliferation and motility

CUTL1, also known as CDP (CCAAT Displacement Protein), Cut, or Cux-1, is a homeodomain transcription factor known to play an essential role in development and cell cycle progression. Previously, we identified CUTL1 as modulator of cell motility and invasiveness. Here we report that protein kinase A (PKA), known to inhibit tumor progression in various tumor types, directly phosphorylates CUTL1 at serine 1215 in NIH3T3 fibroblasts. The PKA-induced phosphorylation results in decreased DNA binding affinity of CUTL1 and diminished CUTL1-mediated cell cycle progression and cell motility. Furthermore, the expression of several CUTL1 target genes involved in proliferation and migration, such as DNA polymerase A and DKK2, was modulated by PKA-induced phosphorylation. These data identify CUTL1 as a novel target of PKA through which this protein kinase can modulate tumor cell motility and tumor progression.

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.

NF-kappaB regulates phagocytic NADPH oxidase by inducing the expression of gp91phox

The superoxide-generating phagocytic NADPH oxidase is an important component of the innate immune response against microbial agents, and is involved in shaping the cellular response to a variety of physiological and pathological signals. One of the downstream targets of NADPH oxidase-derived radicals is the ubiquitous transcription factor NF-kappaB, which controls the expression of a large array of genes involved in immune function and cell survival. Here we show that NF-kappaB itself is a key factor in controlling NADPH oxidase expression and function. In monocytic and microglial cell lines, the expression of the NADPH oxidase subunit gp91(phox) was induced by lipopolysaccharide/interferon gamma treatment and was inhibited in cells constitutively expressing IkappaBalpha. Furthermore, inducible reactive oxygen species production was inhibited in IkappaBalpha overexpressing cells. gp91(phox) expression was very low in RelA(-/-) fibroblasts and could be induced by reconstituting these cells with p65/RelA. Thus, gp91(phox) expression is dependent on the presence of p65/RelA. We also found that gp91(phox) transcription is dependent on NF-kappaB and we identified two potential cis-acting elements in the murine gp91(phox) promoter that control NF-kappaB-dependent regulation. The findings raise the possibility of a positive feedback loop in which NF-kappaB activation by oxidative stress leads to further radical production via NADPH oxidase.

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.

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

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

CUTL1 is a target of TGF(beta) signaling that enhances cancer cell motility and invasiveness

CUTL1, also known as CDP, Cut, or Cux-1, is a homeodomain transcriptional regulator known to be involved in development and cell cycle progression. Here we report that CUTL1 activity is associated with increased migration and invasiveness in numerous tumor cell lines, both in vitro and in vivo. Furthermore, we identify CUTL1 as a transcriptional target of transforming growth factor beta and a mediator of its promigratory effects. CUTL1 activates a transcriptional program regulating genes involved in cell motility, invasion, and extracellular matrix composition. CUTL1 expression is significantly increased in high-grade carcinomas and is inversely correlated with survival in breast cancer. This suggests that CUTL1 plays a central role in coordinating a gene expression program associated with cell motility and tumor progression.

A functional promoter region of the CKLFSF2 gene is located in the last intron/exon region of the upstream CKLFSF1 gene

The genes for CKLFSF1 (chemokine-like factor super family member 1) and CKLFSF2 (chemokine-like factor super family member 2) are very closely linked, within 312 bp of each other. Here, we present evidence that the last intron/exon region of the CKLFSF1 gene contains a novel eukaryotic promoter capable of directing the expression of the downstream gene, CKLFSF2. We identified two segments of the upstream region of the CKLFSF2 gene, 2146 bp (-2134/+12, relative to ATG +1) and 1483 bp (-2134/-652), that were capable of efficiently driving expression of a linked reporter gene upon transient transfection into several kinds of cell lines. The 1483 bp segment exhibited more than a two-fold increase in luciferase activity relative to the 2146 bp segment. By analyzing 5'-deletion mutants of the 1483 bp segment, we identified a 195 bp segment (-846/-625) located in the last intron/exon region of the CKLFSF1 gene that was critical for promoter activity. DNA decoy experiments revealed that a 122 bp (-846/-725) fragment markedly inhibited CKLFSF2 mRNA transcription. Furthermore, we found that the putative promoter region of the CKLFSF2 gene is separated from the transcription start site by about 500 bp. Accumulating reports suggest that introns have many functions, including the modulation of regulation and structure. This work provides evidence that a eukaryotic gene promoter sequence from one gene located in an intron/exon of another.

Hepatomegaly in transgenic mice expressing the homeobox gene Cux-1

Cux-1 is a member of a family of homeobox genes structurally related to Drosophila Cut. Mammalian Cut proteins function as transcriptional repressors of genes specifying terminal differentiation in multiple cell lineages. In addition, mammalian Cut proteins serve as cell-cycle-dependent transcriptional factors in proliferating cells, where they function to repress expression of the cyclin kinase inhibitors p21 and p27. Previously we showed that transgenic mice expressing Cux-1 under control of the CMV immediate early gene promoter develop multiorgan hyperplasia. Here we show that mice constitutively expressing Cux-1 exhibit hepatomegaly correlating with an increase in cell proliferation. In addition, the increase in Cux-1 expression in transgenic livers was associated with a decrease in p21, but not p27, expression. Within transgenic livers, Cux-1 was ectopically expressed in a population of small cells, but not in mature hepatocytes, and many of these small cells expressed markers of proliferation. Transgenic livers showed an increase in alpha-smooth muscle actin, indicating activation of hepatic stellate cells, and an increase in cells expressing chromogranin-A, a marker for hepatocyte precursor cells. Morphological analysis of transgenic livers revealed inflammation, hepatocyte swelling, mixed cell foci, and biliary cell hyperplasia. These results suggest that increased expression of Cux-1 may play a role in the activation of hepatic stem cells, possibly through the repression of the cyclin kinase inhibitor p21.

HOXA9 activates transcription of the gene encoding gp91Phox during myeloid differentiation

The CYBB gene encodes gp91Phox; a component of the phagocyte respiratory burst oxidase. CYBB transcription is restricted to myeloid cells differentiated beyond the promyelocyte stage. In undifferentiated myeloid cells, the homeodomain (HD) transcription factor HoxA10 represses CYBB transcription via a cis element in the proximal promoter. During myelopoiesis, phosphorylation of conserved tyrosine residues in the HD decreases HoxA10 binding to this CYBB cis element. In the current studies, we found HoxA9 activates CYBB transcription in differentiated myeloid cells via the same cis element. We find HoxA9-mediated CYBB-transcription requires Pbx1 but is inhibited by Meis1. Additionally, phosphorylation of the conserved HD tyrosines increases HoxA9 binding to the CYBB promoter. The HOXA9 gene is involved in leukemia-associated translocations with the gene encoding Nup98, a nucleopore protein. We find expression of a Nup98-hoxA9 fusion protein blocks HoxA9-induced CYBB transcription in differentiating myeloid cells. In comparison to HoxA9, Nup98-hoxA9 has greater binding affinity for the CYBB cis element, but binding is not altered by HD tyrosine phosphorylation. Therefore, these studies identify CYBB as a common target gene repressed by HoxA10 and activated by HoxA9. These studies also suggest overexpression of Meis1 or Nup98-hoxA9 represses myeloid-specific gene transcription, thereby contributing to differentiation block in leukemogenesis.

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.

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.

CCAAT displacement protein/cut homolog recruits G9a histone lysine methyltransferase to repress transcription

CCAAT displacement protein/cut homolog (CDP/cut) is a highly conserved homeodomain protein that contains three cut repeat sequences. CDP/cut is a transcriptional factor for many diverse cellular and viral genes that are involved in most cellular processes, including differentiation, development, and proliferation. Here, we report that CDP/cut interacts with a histone lysine methyltransferase (HKMT), G9a, in vivo and in vitro. The deletion of the cut repeats within CDP/cut abrogates the interaction with G9a. The transcriptional repressor function of CDP/cut is mediated through HKMT activity of G9a associated with CDP/cut. We show that the recruitment of G9a to the human p21(waf1/cdi1) promoter is contingent on the interaction with CDP/cut, and CDP/cut is directly associated with an increase in the methylation in vivo of Lys-9 in histone H3 within the CDP/cut-regulatory region of the p21(waf1/cdi1) promoter. The endogenous level of p21(waf1/cdi1) expression is repressed through CDP/cut and mediated by HKMT activity of G9a. Furthermore, we report the identification of G9a as a component of CDP/cut complex. G9a colocalizes with CDP/cut in the nucleus. These results indicate that G9a functions as a transcriptional corepressor in association with a CDP/cut complex. These studies now reveal the interaction of G9a with a sequence-specific transcription factor that regulates gene repression through CDP/cut.

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.

NOX-2S is a new member of the NOX family of NADPH oxidases

A novel isoform of the NOX-2 subunit of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase has been identified using expressed sequence tag (EST) database mining. The novel isoform, NOX-2S, is a splice variant of NOX-2 and includes a previously unidentified exon, mapped 6.4 kb downstream of exon III, and encodes an in-frame stop codon generating a predicted truncated protein of approximately 12.7 kDa, the smallest reported member of the NOX family. Thus, NOX-2S is predicted to have only two transmembrane domains, however, the new C-terminal sequence includes two new potential protein kinase C (PKC) phosphorylation sites. Expression of NOX-2S mRNA was detected in many mouse tissues, and several human cell lines including the myeloid cell line HL-60, and the B cell line Ramos, indicating that the splice variant is conserved in mouse and man. NOX-2S is found co-expressed together with NOX-2 in all of the tissues and cells under investigation, both nonphagocytic and phagocytic. Induction of the myeloid cell line HL-60 into the neutrophil phagocytic lineage by dimethyl sulphoxide (DMSO), led to a marked increase in NOX-2S and NOX-2 expression in the myelocyte rather than promyelocyte stages of differentiation. Furthermore, in the B-cell line Ramos, differentiated with the cytokine interferon-gamma (IFN-gamma), splicing was altered to increase NOX-2S mRNA generation over NOX-2. Here we have identified NOX-2S, the first reported normally occurring splice variant of NOX-2. The sequence identity between mouse and human NOX-2S strongly implies conservation in function and possibly a role for NOX-2S in the regulation of NADPH oxidase activity.

β-Catenin regulates the gene of MMP-26, a novel matrix metalloproteinase expressed both in carcinomas and normal epithelial cells

There are several unorthodox features, which distinguish the non-redundant and unique novel matrix metalloproteinase-26 (MMP-26) (an enzyme that has recently evolved and does not exist in rodents but is present in humans) from other members of the MMP superfamily. This report describes our recent efforts to gain a better understanding of the mechanisms which restrict expression of MMP-26 to certain cell/tissue types. We examined transcriptional regulation of the human MMP-26 gene in normal and malignant cells. The AP-1 and Tcf-4 sites of the MMP-26 promoter appear most potent in regulating the expression of the MMP-26-luciferase chimera in HEK293 embryonic kidney and MCF7 breast carcinoma cells. Key regulators of the Wnt pathway (beta-catenin and lymphoid enhancer-binding factor/T-cell factor with which beta-catenin associates) enhanced the transcriptional activity of MMP-26 suggesting that the MMP-26 gene is a likely target of the Wnt pathway. Immunostaining, gene arrays and reverse-transcriptase polymerase chain reaction (RT-PCR) confirm the presence of MMP-26 in normal cells, including the apical epithelial conjunctiva cells of the human eye, as well as in malignant cells of epithelial origin. MMP-26 predominantly accumulates in its proenzyme form in the intracellular milieu of the transfected breast carcinoma MCF7 cells. This study brings us a step forward towards a better understanding of the unconventional role, regulation and functions of epithelial cell MMP-26 in physiological conditions and in neoplasms.

Molecular analysis of X-linked chronic granulomatous disease in five unrelated Korean patients

Chronic granulomatous disease (CGD) is a fatal genetic disorder in which phagocytes fail to produce antimicrobial superoxide because of NADPH oxidase deficiency. Molecular defects in CYBB gene causing X-linked CGD are responsible for about 70% of all cases. This study was done to confirm genetic defects of CYBB gene in five Korean patients who were highly suggestive of having CGD by clinical history. We performed initial screening for five unrelated Korean patients using single strand conformation polymorphism (SSCP) and then selective sequencing for the regions involving the abnormal bands. Activated NBT tests revealed that all patients were X-linked. SSCP analysis for CYBB gene showed abnormal bands in all patients. The molecular defects of five patients were as follows: c.1663insT, c.1111-1G>T, c.39_40insG, c.927delC and c.434T>C mutation. This result will help the families with prenatal diagnosis or genetic counseling.

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.

HoxA10 represses gene transcription in undifferentiated myeloid cells by interaction with histone deacetylase 2

The homeodomain proteins, HoxA10 and Pbx1a, interact with negative cis elements to repress gene transcription in undifferentiated myeloid cells. The CYBB and NCF2 genes, which encode the gp91PHOX and p67PHOX proteins, are two such HoxA10-Pbx1a target genes. In previous studies, we found that HoxA10-Pbx1a represses transcription of these genes by two mechanisms: competition for DNA binding with transcriptional activators and endogenous repression activity. In these studies, we identify a novel molecular mechanism of endogenous transcriptional repression by HoxA10-Pbx1a. Endogenous repression activity of other Hox-Pbx1a complexes requires recruitment of transcriptional co-repressor proteins by Pbx1a. In contrast, our investigations have determined that HoxA10 has Pbx1a-independent endogenous repression activity. We find that this transcriptional repression activity is abrogated by histone deacetylase inhibitors, suggesting involvement of co-repressor proteins. Consistent with this, we identify HoxA10 amino acids 224-249 as a Pbx1-independent repression domain, which interacts with histone deacetylase 2. We have determined that this HoxA10 domain is not conserved with other Abd Hox proteins, although homology exists with other transcription factors and co-repressors. Understanding the roles different Hox proteins play in myeloid differentiation is a challenging problem. Our results suggest that insight into this problem can be obtained from biochemical characterization of the various molecular mechanisms of Hox protein function.

Differentiation-dependent up-regulation of p47(phox) gene transcription is associated with changes in PU.1 phosphorylation and increased binding affinity

The p47(phox) gene encodes a cytosolic component of the phagocytic NADPH oxidase complex. Expression of p47(phox) is both tissue-specific and developmentally regulated. Stable transfection of the myeloid cell lines PLB985 and HL60, with reporter gene constructs containing as little as 58 bp of proximal promoter sequence, was capable of directing significant reporter gene activity in myeloid cells, which increased significantly on induction of myeloid differentiation. EMSA analysis of a binding site for the Ets family member, PU.1, located at positions -39 to -44 revealed that the pattern of complex formation changed significantly on induction of myeloid differentiation. All EMSA complexes were competed by a functional PU.1 binding site and could be supershifted in the presence of polyclonal anti-PU.1 antibody. Reaction of EMSA complexes with anti-phosphoserine antibody, treatment with phosphatase, or Western blotting of proteins captured on the PU.1 binding site, was used to demonstrate that the changes in PU.1 complex formation dependent on myeloid differentiation were associated with increased levels of PU.1 phosphorylation. Furthermore, the more highly phosphorylated forms of PU.1 were shown to have a greater affinity for the p47(phox) PU.1 consensus binding site. Up-regulated transcriptional activity in response to myeloid differentiation can therefore be correlated with increased levels of PU.1 phosphorylation and a greater binding affinity.