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

The Differentiation-Specific Factor CDP/Cut Represses Transcription and Replication of Human Papillomaviruses through a Conserved Silencing Element

The life cycles of human papillomaviruses (HPVs) are intimately linked to the differentiation program of infected stratified epithelia, with both viral gene expression and replication being maintained at low levels in undifferentiated basal cells and increased upon host cell differentiation. We recently identified, in HPV-16, a negative regulatory element between the epithelial-cell-specific enhancer and the E6 promoter that is capable of silencing E6 promoter activity, and we termed this element a papillomavirus silencing motif (PSM) and the unknown cellular factor that bound to it PSM binding protein (PSM-BP). Here we show that the homologous genomic segments of six other distantly related genital HPV types contain a PSM that binds PSM-BP and is capable of repressing transcription. Conservation of the PSM suggests that it is indispensable for the HPV life cycle. Purification, electrophoretic mobility shift assay experiments, and the use of specific antibodies proved that the cellular factor PSM-BP is identical to a previously described transcriptional repressor, the CCAAT displacement protein (CDP), also referred to as the human Cut protein (Cut). CDP/Cut repression of HPV-16 may stem from the modification of specifically positioned nucleosomes, as suggested by transcriptional stimulation under the influence of the histone deacetylase inhibitor trichostatin A. CDP/Cut is an important developmental regulator in several different tissues. It was recently shown that CDP/Cut is expressed in basal epithelial cells but not in differentiated primary keratinocytes. This suggests the possibility that repression by PSM couples HPV transcription to the stratification of epithelia. In each of the studied HPV types, the two CDP/Cut binding sites of PSM overlap with the known or presumed binding sites of the replication initiator protein E1. Transfection of CDP/Cut expression vectors into cells that support HPV-16 or HPV-31 replication leads to the elimination of viral episomes. Similarly, two PSM-like motifs overlapping the E1 binding site of bovine papillomavirus type 1 bind CDP/Cut, and CDP/Cut overexpression reduces the copy number of episomally replicating BPV-1 genomes in mouse fibroblasts. CDP/Cut appears to be a master regulator of HPV transcription and replication during epithelial differentiation, and PSMs are important cis -responsive targets of this repressor.

Recruitment of CREB-Binding Protein by PU.1, IFN-Regulatory Factor-1, and the IFN Consensus Sequence-Binding Protein Is Necessary for IFN-γ-Induced p67phox and gp91phox Expression

Activation of the phagocyte respiratory burst oxidase requires interaction between the oxidase components p47phox, p67phox, p22phox, and gp91phox. IFN-γ induces transcription of the genes encoding p67phox (the NCF2 gene) and gp91phox (the CYBB gene) during monocyte differentiation, and also in mature monocytes. In these studies, we identify an NCF2 cis element, necessary for IFN-γ-induced p67phox expression, and determine that this element is activated by cooperation between the transcription factors PU.1, IFN regulatory factor 1 (IRF1), and the IFN consensus-binding protein (ICSBP). Previously, we identified a CYBB cis element, necessary for IFN-γ-induced gp91phox expression, and also activated by this transcription factor combination. In these investigations, we determine that recruitment of a coactivator protein, CBP (the CREBbinding protein), to the CYBB or NCF2 promoter is the molecular mechanism of transcriptional activation by PU.1, IRF1, and ICSBP. Also, we determine that the multiprotein interaction of CBP with PU.1, IRF1, and ICSBP requires either the CYBB- or NCF2--binding site. Because IFN-γ induces simultaneous expression of p67phox and gp91phox, these investigations identify a molecular event that coordinates oxidase gene transcription during the inflammatory response. Also, these investigations identify CBP recruitment by cooperation between PU.1, IRF1, and ICSBP as a novel molecular mechanism for IFN-γ-induced activation of myeloid genes that are involved in the system of host defense.

Human cut-like repressor protein binds TGFbeta type II receptor gene promoter

Resistance to the growth inhibitory effects of transforming growth factor beta (TGFbeta) has been associated with decreased levels of the TGFbeta type II receptor (TbetaR-II) and has been correlated with tumorigenicity. Previously, we reported an A --> G mutation at position -364 in the TbetaR-II promoter in A431 tumor cells which results in reduced TbetaR-II promoter activity. In this study, we show that the CDP/Cut (CCAAT displacement protein) transcription factor, a transcriptional repressor, binds both the wild type and the mutant TbetaR-II promoter. We also demonstrate that the A --> G mutation increases CDP/Cut binding affinity, and that overexpression of CDP/Cut reduces transcription from TbetaR-II promoter reporter constructs. Increased binding of the CDP/Cut repressor protein, as a result of a mutation at position -364, represents a novel mechanism of regulation in a neoplastic cell of the promoter of a tumor suppressor gene, TbetaR-II.

Overexpression of CCAAT Displacement Protein Represses the Promiscuously Active Proximal gp91phox Promoter

CCAAT displacement protein (CDP) is a transcriptional repressor that restricts expression of the gp91phox gene to mature myeloid cells. CDP interacts with multiple sites within the −450 to +12 bp human gp91phox promoter, and down-regulation of CDP DNA-binding activity is required for induction of gp91phox transcription in mature phagocytes. Truncation of the gp91phox promoter to −102 to +12 bp removes 4 CDP-binding sites and reveals a promiscuous promoter activity that is active in some nonphagocytic cells. A cis-element at −90 bp is required for derepressed transcription and serves as a binding site for multiple transcriptional activators. We now report that this element also serves as a binding site for CDP. The affinity of CDP for this element is relatively weak compared with upstream CDP-binding sites within the promoter, consistent with the promiscuous transcriptional activity exhibited by the −102 to +12 bp gp91phox promoter fragment. Further analysis of the proximal promoter reveals an additional weak-affinity CDP-binding site centered at approximately −20 bp. Overexpression of cloned CDP represses the −102 to +12 bp gp91phox promoter, indicating that these proximal CDP-binding sites are functionally significant. The constellation of transcriptional activators and a repressor that interacts with the −90 bp cis-element is identical to that observed for a promoter element at −220 bp, reflecting the highly modular organization of the gp91phoxpromoter. These studies illustrate the complex interplay between transcriptional activators and a repressor that contribute to the myeloid-restricted expression of the gp91phox gene.

Myeloid Transcription Factor C/EBPɛ Is Involved in the Positive Regulation of Lactoferrin Gene Expression in Neutrophils

Targeted mutation of the myeloid transcription factor C/EBPɛ in mice results in gram-negative septic death at 3 to 5 months of age. This study defines the underlying molecular defects in their terminal granulocytic differentiation. The mRNA for the precursor protein of the cathelin-related antimicrobial peptides was almost completely absent in the bone marrow cells of C/EBPɛ−/− mice. This finding may help explain their susceptibility to gram-negative sepsis, because both are bacteriocidal peptides with potent activity against gram-negative bacteria. Superoxide production was found to be reduced in both granulocytes and monocytes of C/EBPɛ−/− mice. While gp91 phox protein levels were normal, p47phox protein levels were considerably reduced in C/EBPɛ −/− granulocytes/monocytes, possibly limiting the assembly of the NADPH oxidase. In addition, expression of mRNA of the secondary and tertiary granule proteins, lactoferrin and gelatinase, were not detected, and levels of neutrophil collagenase mRNA were reduced in bone marrow cells of the knock-out mice. The murine lactoferrin promoter has a putative C/EBP site close to the transcription start site. C/EBPɛ bound to this site in electromobility shift assay studies and mutation of this site abrogated binding to it. A mutation in the C/EBP site reduced the activity of the promoter by 35%. Furthermore, overexpression of C/EBPɛ in U937 cells increased the activity of the wild-type lactoferrin promoter by 3-fold. In summary, our data implicate C/EBPɛ as a critical factor of host antimicrobial defense and suggests that it has a direct role as a positive regulator of expression of lactoferrin in vivo.

Myeloid Transcription Factor C/EBPɛ Is Involved in the Positive Regulation of Lactoferrin Gene Expression in Neutrophils

Targeted mutation of the myeloid transcription factor C/EBPɛ in mice results in gram-negative septic death at 3 to 5 months of age. This study defines the underlying molecular defects in their terminal granulocytic differentiation. The mRNA for the precursor protein of the cathelin-related antimicrobial peptides was almost completely absent in the bone marrow cells of C/EBPɛ−/− mice. This finding may help explain their susceptibility to gram-negative sepsis, because both are bacteriocidal peptides with potent activity against gram-negative bacteria. Superoxide production was found to be reduced in both granulocytes and monocytes of C/EBPɛ−/− mice. While gp91 phox protein levels were normal, p47phox protein levels were considerably reduced in C/EBPɛ −/− granulocytes/monocytes, possibly limiting the assembly of the NADPH oxidase. In addition, expression of mRNA of the secondary and tertiary granule proteins, lactoferrin and gelatinase, were not detected, and levels of neutrophil collagenase mRNA were reduced in bone marrow cells of the knock-out mice. The murine lactoferrin promoter has a putative C/EBP site close to the transcription start site. C/EBPɛ bound to this site in electromobility shift assay studies and mutation of this site abrogated binding to it. A mutation in the C/EBP site reduced the activity of the promoter by 35%. Furthermore, overexpression of C/EBPɛ in U937 cells increased the activity of the wild-type lactoferrin promoter by 3-fold. In summary, our data implicate C/EBPɛ as a critical factor of host antimicrobial defense and suggests that it has a direct role as a positive regulator of expression of lactoferrin in vivo.

Overexpression of CCAAT Displacement Protein Represses the Promiscuously Active Proximal gp91phox Promoter

CCAAT displacement protein (CDP) is a transcriptional repressor that restricts expression of the gp91phox gene to mature myeloid cells. CDP interacts with multiple sites within the −450 to +12 bp human gp91phox promoter, and down-regulation of CDP DNA-binding activity is required for induction of gp91phox transcription in mature phagocytes. Truncation of the gp91phox promoter to −102 to +12 bp removes 4 CDP-binding sites and reveals a promiscuous promoter activity that is active in some nonphagocytic cells. A cis-element at −90 bp is required for derepressed transcription and serves as a binding site for multiple transcriptional activators. We now report that this element also serves as a binding site for CDP. The affinity of CDP for this element is relatively weak compared with upstream CDP-binding sites within the promoter, consistent with the promiscuous transcriptional activity exhibited by the −102 to +12 bp gp91phox promoter fragment. Further analysis of the proximal promoter reveals an additional weak-affinity CDP-binding site centered at approximately −20 bp. Overexpression of cloned CDP represses the −102 to +12 bp gp91phox promoter, indicating that these proximal CDP-binding sites are functionally significant. The constellation of transcriptional activators and a repressor that interacts with the −90 bp cis-element is identical to that observed for a promoter element at −220 bp, reflecting the highly modular organization of the gp91phoxpromoter. These studies illustrate the complex interplay between transcriptional activators and a repressor that contribute to the myeloid-restricted expression of the gp91phox gene.

YY1 binds five cis-elements and trans-activates the myeloid cell-restricted gp91(phox) promoter

Four transcriptional activating cis-elements within the gp91(phox) promoter bind a protein complex of similar mobility and binding specificity, denoted BID (binding increased during differentiation). The intensity of BID complexes increases upon myeloid cell differentiation, coincident with induction of gp91(phox) expression, and BID competes with the transcriptional repressor CDP for binding to each of these promoter elements. To determine the identity of BID, an expression library was ligand screened with the BID-binding site that surrounds the -145-base pair (bp) region of the gp91(phox) promoter. One recovered factor that exhibits the expected binding specificity is YY1, a ubiquitous multifunctional transcription factor. BID complexes that form with the four binding sites within the gp91(phox) promoter are disrupted by YY1 antiserum, and a fifth YY1-binding site was detected in the -412-bp promoter region. Overexpression of YY1 in transient co-transfection assays trans-activates a minimal promoter containing two copies of the -145-bp binding site from the gp91(phox) promoter. Neither the level of YY1 protein nor DNA binding activity increases during myeloid cell differentiation. These studies identify a target gene of YY1 function in mature myeloid cells, and demonstrate that YY1 function can be controlled during myeloid development by the modulation of a competing DNA-binding factor.

The regulation of CD4 and CD8 coreceptor gene expression during T cell development

The two major subsets of T lymphocytes in the peripheral immune system, the helper and cytotoxic T cells, are defined by their expression of either the CD4 or the CD8 glycoproteins, respectively. Expression of these molecules, which serve as coreceptors by interacting specifically with either MHC class II or class I molecules, also defines discrete stages of T cell development within the thymus. Thus, CD4+ and CD8+ single-positive (SP) thymocytes arise from common progenitor double positive (DP) cells that express both CD4 and CD8, during a process known as positive selection. The molecular mechanisms underlying the developmental choice toward the helper or cytotoxic lineage remain poorly understood. Because regulation of coreceptor gene expression appears to be coupled to the phenotypic choice of the differentiating T cell, it is likely that shared signaling pathways direct CD4 and CD8 transcription and the development of an uncommited DP thymocyte toward either the helper or cytotoxic lineage. Therefore, an understanding of how CD4 and CD8 expression is regulated will not only provide insights into transcriptional control mechanisms in T cells, but may also result in the identification of molecular factors that are involved in lineage choices during T cell development. In this review, we summarize recent progress that has been made toward an understanding of how CD4 and CD8 gene expression is regulated.

Elf-1 and PU.1 Induce Expression of gp91phox Via a Promoter Element Mutated in a Subset of Chronic Granulomatous Disease Patients

The cytochrome b heavy chain (gp91phox) is the redox center of the NADPH-oxidase and is highly expressed in mature myeloid cells. Point mutations at −57, −55, −53, and −52 bp of the gp91phox promoter have been detected in patients with chronic granulomatous disease (CGD; Newburger et al,J Clin Invest 94:1205, 1994; and Suzuki et al, Proc Natl Acad Sci USA 95:6085, 1998). We report that Elf-1 and PU.1,ets family members highly expressed in myeloid cells, bind to this promoter element. Either factor trans-activates the −102 to +12 bp gp91phox promoter when overexpressed in nonhematopoietic HeLa cells or the PLB985 myeloid cell line. However, no synergy of gp91phox promoter activation occurs when both Elf-1 and PU.1 are overexpressed. Introduction of the −57 bp or −55 bp CGD mutations into the gp91phoxpromoter significantly reduces the binding affinity of Elf-1 and PU.1 and also reduces the ability of these factors to trans-activate the promoter. These results indicate that Elf-1 and PU.1 contribute to directing the lineage-restricted expression of the gp91phox gene in phagocytes and that failure of these factors to effectively interact with this promoter results in CGD.

CCAAT displacement protein binds to and negatively regulates human papillomavirus type 6 E6, E7, and E1 promoters

Expression of human papillomavirus genes increases as the target cell, the keratinocyte, differentiates. CCAAT displacement protein (CDP) is a cellular protein which has been shown in other cell types to negatively regulate gene expression in undifferentiated cells but not in differentiated cells. We have previously shown that a 66-bp purine-thymidine-rich sequence (the 66-mer) binds CDP and negatively regulates the human papillomavirus type 6 (HPV-6) E6 promoter (S. Pattison, D. G. Skalnik, and A. Roman, J. Virol. 71:2013-2022, 1997). Cotransfection experiments with a plasmid expressing luciferase from the HPV-6 E6, E7, or E1 regulatory region and a plasmid carrying the CDP gene indicate that CDP represses transcription from all three HPV-6 promoters. Using electrophoretic mobility shift assays (EMSAs), we have shown that CDP binds HPV-6 both upstream and downstream of the E6, E7, and E1 transcription initiation start sites. Furthermore, when keratinocytes were induced to differentiate, all three promoter activities increased. Consistent with this, immunoblotting and EMSAs revealed that endogenous nucleus CDP and, correspondingly, DNA binding activity decreased when keratinocytes were induced to differentiate. The elevated promoter activities were abrogated by exogenously transfected CDP. Our data demonstrate that CDP fulfills the requirement of a differentiation-dependent negative regulator that could tie the HPV life cycle to keratinocyte differentiation.

Transcriptional repression of the cystic fibrosis transmembrane conductance regulator gene, mediated by CCAAT displacement protein/cut homolog, is associated with histone deacetylation

Human cystic fibrosis transmembrane conductance regulator gene (CFTR) transcription is tightly regulated by nucleotide sequences upstream of the initiator sequences. Our studies of human CFTR transcription focus on identifying transcription factors bound to an inverted CCAAT consensus or "Y-box element." The human homeodomain CCAAT displacement protein/cut homolog (CDP/cut) can bind to the Y-box element through a cut repeat and homeobox. Analysis of stably transfected cell lines with wild-type and mutant human CFTR-directed reporter genes demonstrates that human histone acetyltransferase GCN5 and transcription factor ATF-1 can potentiate CFTR transcription through the Y-box element. We have found 1) that human CDP/cut acts as a repressor of CFTR transcription through the Y-box element by competing for the sites of transactivators hGCN5 and ATF-1; 2) that the ability of CDP/cut to repress activities of hGCN5 and ATF-1 activity is contingent on the amount of CDP/cut expression; 3) that histone acetylation may have a role in the regulation of gene transcription by altering the accessibility of the CFTR Y-box for sequence-specific transcription factors; 4) that trichostatin A, an inhibitor of histone deacetylase activity, activates transcription of CFTR through the Y-box element; 5) that the inhibition of histone deacetylase activity leads to an alteration of local chromatin structure requiring an intact Y-box sequence in CFTR; 6) that immunocomplexes of CDP/cut possess an associated histone deacetylase activity; 7) that the carboxyl region of CDP/cut, responsible for the transcriptional repressor function, interacts with the histone deacetylase, HDAC1. We propose that CFTR transcription may be regulated through interactions with factors directing the modification of chromatin and requires the conservation of the inverted CCAAT (Y-box) element of the CFTR promoter.

Refined mapping of the region of loss of heterozygosity on the long arm of chromosome 7 in human breast cancer defines the location of a second tumor suppressor gene at 7q22 in the region of the CUTL1 gene

In breast cancer, loss of heterozygosity (LOH) has been described on the long arm of chromosome 7, at band q31, suggesting the presence of a tumor suppressor gene in this region. In this study, we have identified a second region of LOH on 7q, at band 7q22. Deletion of genetic material at 7q22 was found in all tumor types and grades and was associated with increased tumor size. The region of LOH at 7q22 in every case included one or more of three polymorphic markers that are located within the CUTL1 gene. LOH of 7q22 has also been documented in the case of human uterine leiomyomas (Zeng et al., 1997; Ishwad et al., 1997). Interestingly, in both leiomyomas and mammary tumors induced in transgenic mice expressing the Polyomavirus (PyV) large T (LT) antigen, immunocomplexes of CUTL1 and PyV LT antigen were detected (Webster et al., 1998). Altogether, genetic data in human breast cancer and biochemical analyses in breast tumors from transgenic mice suggest that CUTL1 is a candidate tumor suppressor gene.

Identification and functional characterization of the murine Rac2 gene promoter

Rac2, a member of the Rho family of GTPases, is highly expressed in myeloid cells and is a regulator of the NADPH-oxidase complex. A murine genomic clone was isolated that contains the 5' end and putative promoter region of the Rac2 gene. Ribonuclease protection experiments detected 13 transcription initiation sites scattered 50 to 130 bp upstream of the translation initiation site. Transient transfection studies revealed that -7 kb to +31 bp (relative to the strongest transcription initiation site) of the Rac2 gene 5'-flanking region exhibited strong promoter activity in both RAW 264.7 macrophage cells that express the endogenous Rac2 gene and NIH-3T3 fibroblast cells that do not express the endogenous gene. Truncated Rac2 promoter fragments containing as little as the -74 to +31 bp sequence produced full transcriptional activity. However, a -57 to +31 promoter fragment directed significantly less transcription, and a -39 to +31 promoter fragment was transcriptionally inactive. In vitro binding assays revealed sequence-specific and widely expressed DNA-binding activities that interacted within the -74 to -58 Rac2 promoter cis element. Oligonucleotide competition and antibody disruption studies indicated that these complexes contained the transcription factors Spl and Sp3. Specific ablation of the Sp1/Sp3 binding site significantly decreased Rac2 promoter activity in both RAW 264.7 and NIH-3T3 cells. Additional cis elements may be required to restrict Rac2 promoter activity to hematopoietic cells expressing the endogenous gene.

The Activity of the CCAAT-box Binding Factor NF-Y Is Modulated Through the Regulated Expression of Its A Subunit During Monocyte to Macrophage Differentiation: Regulation of Tissue-Specific Genes Through a Ubiquitous Transcription Factor

In this study, we analyzed the regulation of NF-Y expression during human monocyte to macrophage maturation. NF-Y is a ubiquitous and evolutionarily conserved transcription factor that binds specifically to the CCAAT motif present in the 5′ promoter region of a wide variety of genes. We show here that in circulating monocytes, NF-Y binding activity is not detected on the CCAAT motif present in the promoters of genes such as major histocompatibility complex (MHC) class II, gp91-phox, mig, and fibronectin, whereas during macrophage differentiation, a progressive increase in NF-Y binding activity is observed on these promoters. Analysis of NF-Y subunit expression indicates that the absence of NF-Y activity in circulating monocytes is caused by a lack of the A subunit. Furthermore, addition of the recombinant NF-YA subunit restores NF-Y binding. We show that the lack of NF-YA protein is due to posttranscriptional regulation and not to a specific proteolytic activity. In fact, NF-YA mRNA is present at the same level at all days of monocyte cultivation, whereas the protein is absent in freshly isolated monocytes but is progressively synthesized during the maturation process. We thus conclude that the NF-YA subunit plays a relevant role in activating transcription of genes highly expressed in mature monocytes. In line with this conclusion, we show that the cut/CDP protein, a transcriptional repressor that inhibits gpc91-phox gene expression by preventing NF-Y binding to the CAAT box, is absent in monocytes.

The Activity of the CCAAT-box Binding Factor NF-Y Is Modulated Through the Regulated Expression of Its A Subunit During Monocyte to Macrophage Differentiation: Regulation of Tissue-Specific Genes Through a Ubiquitous Transcription Factor

In this study, we analyzed the regulation of NF-Y expression during human monocyte to macrophage maturation. NF-Y is a ubiquitous and evolutionarily conserved transcription factor that binds specifically to the CCAAT motif present in the 5′ promoter region of a wide variety of genes. We show here that in circulating monocytes, NF-Y binding activity is not detected on the CCAAT motif present in the promoters of genes such as major histocompatibility complex (MHC) class II, gp91-phox, mig, and fibronectin, whereas during macrophage differentiation, a progressive increase in NF-Y binding activity is observed on these promoters. Analysis of NF-Y subunit expression indicates that the absence of NF-Y activity in circulating monocytes is caused by a lack of the A subunit. Furthermore, addition of the recombinant NF-YA subunit restores NF-Y binding. We show that the lack of NF-YA protein is due to posttranscriptional regulation and not to a specific proteolytic activity. In fact, NF-YA mRNA is present at the same level at all days of monocyte cultivation, whereas the protein is absent in freshly isolated monocytes but is progressively synthesized during the maturation process. We thus conclude that the NF-YA subunit plays a relevant role in activating transcription of genes highly expressed in mature monocytes. In line with this conclusion, we show that the cut/CDP protein, a transcriptional repressor that inhibits gpc91-phox gene expression by preventing NF-Y binding to the CAAT box, is absent in monocytes.

CCAAT displacement protein (CDP/cut) binds a negative regulatory element in the human tryptophan hydroxylase gene

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin, a neurotransmitter that has been implicated in many psychiatric illnesses. The mechanism of transcriptional regulation of the human TPH gene is largely unknown. We have identified a negative regulatory element located between nucleotides -310 and -220 in the human TPH (hTPH) gene. Electromobility shift analyses performed with the -310/-220 hTPH probe and nuclear extract from P815-HTR (a TPH-expressing cell line) revealed two slow migrating protein-DNA complexes, designated I and II. CCAAT displacement protein (CDP/Cut) is involved in complex I formation as shown in electromobility shift analysis, using consensus oligonucleotide competitor and antibody. Mutations in the CDP/Cut binding site not only disrupted the CDP-DNA complex but also disrupted the second complex, suggesting that the core binding sequences of the two proteins are overlapping. The functional importance of these protein-DNA interactions was assessed by transiently transfecting wild-type and mutant pTPH/luciferase reporter constructs into P815-HTR cells. Mutations in the core CDP/Cut site resulted in an approximately fourfold increase in relative luciferase activities. Because CDP/Cut has been shown to repress transcription of many target genes, we speculate that disruption of the CDP/Cut binding was responsible, at least in part, for the activation of hTPH gene.

Cux/CDP homeoprotein is a component of NF-muNR and represses the immunoglobulin heavy chain intronic enhancer by antagonizing the bright transcription activator

Nuclear matrix attachment regions (MARs) flanking the immunoglobulin heavy chain intronic enhancer (Emu) are the targets of the negative regulator, NF-muNR, found in non-B and early pre-B cells. Expression library screening with NF-muNR binding sites yielded a cDNA clone encoding an alternatively spliced form of the Cux/CDP homeodomain protein. Cux/CDP fulfills criteria required for NF-muNR identity. It is expressed in non-B and early pre-B cells but not mature B cells. It binds to NF-muNR binding sites within Emu with appropriate differential affinities. Antiserum specific for Cux/CDP recognizes a polypeptide of the predicted size in affinity-purified NF-muNR preparations and binds NF-muNR complexed with DNA. Cotransfection with Cux/CDP represses the activity of Emu via the MAR sequences in both B and non-B cells. Cux/CDP antagonizes the effects of the Bright transcription activator at both the DNA binding and functional levels. We propose that Cux/CDP regulates cell-type-restricted, differentiation stage-specific Emu enhancer activity by interfering with the function of nuclear matrix-bound transcription activators.

A nuclear matrix attachment region upstream of the T cell receptor beta gene enhancer binds Cux/CDP and SATB1 and modulates enhancer-dependent reporter gene expression but not endogenous gene expression

We have previously identified a DNase I-hypersensitive site in the T cell receptor beta locus, designated HS1, that is located 400 base pairs upstream of the transcriptional enhancer Ebeta and is induced during CD4(-)CD8(-) to CD4(+)CD8(+) thymocyte differentiation. Using electrophoretic mobility shift assays, we show that HS1 induction correlates with increased binding of two nuclear factors, Cux/CDP and SATB1, to a 170-base pair DNA sequence within HS1. Furthermore, we demonstrate that HS1 is a nuclear matrix attachment region, referred to as MARbeta. These findings demonstrate that an analogous organization of cis-regulatory elements in which a nuclear matrix attachment region is in close proximity to an enhancer is conserved in the immunoglobulin and T cell receptor loci. In addition, we show that MARbeta represses Ebeta-dependent reporter gene expression in transient transfection assays. However, the targeted deletion of MARbeta from the endogenous locus does not change T cell receptor beta gene transcription in developing T cells. These contrasting results suggest a potential pitfall of functional studies of nuclear matrix attachment regions outside of their natural chromosomal context.

Nonhomologous recombination between the cytochrome b558 heavy chain gene (CYBB) and LINE-1 causes an X-linked chronic granulomatous disease

We cloned and characterized a genomic DNA fragment including the deletion junction of a chronic granulomatous disease patient with a 25-kb deletion extending to the 5' two-thirds of CYBB. The 3' breakpoint of the deletion exists in exon 7 of CYBB. A LINE-1 element lies at 5 kb upstream of CYBB in normal persons, and the 5' breakpoint of the deletion in the patient is in the LINE-1 element. There are no significant homologies between corresponding normal 5' and 3' regions flanking the breakpoint of the patient, so a nonhomologous recombination is the most possible mechanism for this 25-kb deletion. The analysis also reveals that the patient has a novel 30-bp duplication in the 5' flanking region of the deletion point, which was transmitted by his mother with the deletion. Furthermore we suggest that the deletion occurred in his grandfather.

GATA-3 represses gp91phox gene expression in eosinophil-committed HL-60-C15 cells

To study the regulatory mechanism of gp91phox gene expression in eosinophils, we transiently transfected eosinophil-committed HL-60-C15 cells with gp91phox promoter constructs, and identified a negative element from bp -267 to -246 of the gp91phox gene, the deletion of which caused an 83% increase in promoter activity. Electrophoresis mobility shift assays demonstrated GATA-3 binds to the GATA consensus site from bp -256 to -250. An 81% increment in promoter activity was obtained when a mutation was introduced in the GATA-3 binding site of the bp -267 to +12 construct, which is comparable to that of the bp -245 to +12 construct. We therefore conclude that GATA-3 specifically binding to the GATA site negatively regulates the expression of the gene in HL-60-C15 cells.

Genetic analysis of familial myelodysplastic syndrome: absence of linkage to chromosomes 5q31 and 7q22

Myelodysplastic syndrome (MDS) is a hematological disorder that occurs primarily in the elderly as an acquired, sporadic disease. Familial cases of MDS are rare. We have identified a kindred with three affected individuals, with early age of onset, suggesting a possible inherited predisposition to this disease. Using a molecular genetic approach, we examined whether bands 5q31 or 7q22 or both, the chromosomal regions most frequently associated with sporadic MDS, are involved in familial expression of MDS in this pedigree. Linkage analysis using polymorphic microsatellite DNA markers demonstrated that neither 5q31 nor 7q22 cosegregated with MDS in this family. There was no history of common environmental or occupational exposure among family members with MDS. In addition, analysis of polymorphisms at two loci [glutathione S-transferase T1 and M1 (GSTT1 and GSTM1)] involved in carcinogen detoxification and associated with cancer susceptibility, including increased risk for MDS, showed no evidence for enhanced sensitivity to environmental carcinogens in affected family members. Taken together, our findings suggest that (1) there is an inherited predisposition to MDS in this kindred; and (2) genes at 5q31 and 7q22, the regions most commonly associated with sporadic MDS, are excluded from a causal role in this family's disease.

Hair defects and pup loss in mice with targeted deletion of the first cut repeat domain of the Cux/CDP homeoprotein gene

CDP, a ubiquitous homeoprotein homologous to Drosophila cut, is implicated as a transcriptional repressor in several developmental systems. It contains four independent DNA binding domains: three "cut repeats" plus the homeodomain. The murine Cux/CDP gene spans more than 200 kb and is composed of at least 21 exons. We designed a targeting construct to replace the first cut repeat with a neomycin resistance cassette, introducing a nonsense mutation after position 1319 of the 4.5-kb reading frame of Cux/CDP. We expected to generate a truncated product of approximately 60 kDa with this construct, but instead we obtained mice expressing a mutant form of the protein, with an internal deletion of 246 amino acids encompassing cut repeat 1, but intact in the C-terminal region. Ribonuclease protection assays and direct sequencing of mutant cDNA obtained by RT-PCR demonstrate skipping of exons 10 and 11 in the mutant. Homozygous mutant mice, designated Cux/CDPDeltaCR1, display a phenotype characterized by curly vibrissae and wavy hair. We also observed a high degree of pup loss in litters born to mutant females, most likely on a nutritional basis. The mutant protein is present at levels slightly greater than wild-type, but exhibits the same tissue distribution as wild-type protein, and has approximately normal affinity for known target sequences (though no DNA targets identified to date require the first cut repeat for binding). These results support the hypothesis that the different DNA binding domains of the ubiquitous Cux/CDP protein are responsible for regulation of different genes in diverse tissues during development.

NF-Y organizes the gamma-globin CCAAT boxes region

The CCAAT-binding activator NF-Y is formed by three evolutionary conserved subunits, two of which contain putative histone-like domains. We investigated NF-Y binding to all CCAAT boxes of globin promoters in direct binding, competition, and supershift electrophoretic mobility shift assay; we found that the alpha, zeta, and proximal gamma CCAAT boxes of human and the prosimian Galago bind avidly, and distal gamma CCAAT boxes have intermediate affinity, whereas the epsilon and beta sequences bind NF-Y very poorly. We developed an efficient in vitro transcription system from erythroid K562 cells and established that both the distal and the proximal CCAAT boxes are important for optimal gamma-globin promoter activity. Surprisingly, NF-Y binding to a mutated distal CCAAT box (a C to T at position -114) is remarkably increased upon occupancy of the high affinity proximal element, located 27 base pairs away. Shortening the distance between the two CCAAT boxes progressively prevents simultaneous CCAAT binding, indicating that NF-Y interacts in a mutually exclusive way with CCAAT boxes closer than 24 base pairs apart. A combination of circular permutation and phasing analysis proved that (i) NF-Y-induced angles of the two gamma-globin CCAAT boxes have similar amplitudes; (ii) occupancy of the two CCAAT boxes leads to compensatory distortions; (iii) the two NF-Y bends are spatially oriented with combined twisting angles of about 100 degrees. Interestingly, such distortions are reminiscent of core histone-DNA interactions. We conclude that NF-Y binding imposes a high level of functionally important coordinate organization to the gamma-globin promoter.

Mutational and functional analysis of the C-terminal region of the C3H mouse mammary tumor virus superantigen

The mouse mammary tumor virus (MMTV) encodes within the U3 region of the long terminal repeat (LTR) a protein known as the superantigen (Sag). Sag is needed for the efficient transmission of milk-borne virus from the gut to target tissue in the mammary gland. MMTV-infected B cells in the gut express Sag as a type II transmembrane protein that is recognized by the variable region of particular beta chains (Vbeta) of the T-cell receptor (TCR) on the surface of T cells. Recognition of Sag by particular TCRs results in T-cell stimulation, release of cytokines, and amplification of MMTV infection in lymphoid cells that are needed for infection of adolescent mammary tissue. Because the C-terminal 30 to 40 amino acids of Sag are variable and correlate with recognition of particular TCR Vbeta chains, we prepared a series of C-terminal Sag mutations that were introduced into a cloned infectious MMTV provirus. Virus-producing XC rat cells were used for injection of susceptible BALB/c mice, and these mice were monitored for functional Sag activity by the deletion of C3H MMTV Sag-reactive (CD4+ Vbeta14+) T cells. Injected mice also were analyzed for mutant infection and tumor formation in mammary glands as well as milk-borne transmission of MMTV to offspring. Most mutations abrogated Sag function, although one mutation (HPA242) that changed the negative charge of the extreme C terminus to a positive charge created a weaker Sag that slowed the kinetics of Sag-mediated T-cell deletion. Despite the lack of Sag activity, many of the sag mutant viruses were capable of sporadic infections of the mammary glands of injected mice but not of offspring mice, indicating that functional Sag increases the probability of milk-borne MMTV infection. Furthermore, although most viruses encoding nonfunctional Sags were unable to cause mammary tumors, tumors were induced by such viruses carrying mutations in a negative regulatory element that overlaps the sag gene within the LTR, suggesting that loss of Sag function may be compensated, at least partially, by loss of transcriptional suppression in certain tissues. Together these results confirm the importance of Sag for efficient milk-borne transmission and indicate that the entire C-terminal region is needed for complete Sag function.

X-Linked chronic granulomatous disease: mutations in the CYBB gene encoding the gp91-phox component of respiratory-burst oxidase

Chronic granulomatous disease (CGD) is a hereditary disorder of host defense due to absent or decreased activity of phagocyte NADPH oxidase. The X-linked form of the disease derives from defects in the CYBB gene, which encodes the 91-kD glycoprotein component (termed "gp91-phox") of the oxidase. We have identified the mutations in the CYBB gene responsible for X-linked CGD in 131 consecutive independent kindreds. Screening by SSCP analysis identified mutations in 124 of the kindreds, and sequencing of all exons and intron boundary regions revealed the other seven mutations. We detected 103 different specific mutations; no single mutation appeared in more than seven independent kindreds. The types of mutations included large and small deletions (11%), frameshifts (24%), nonsense mutations (23%), missense mutations (23%), splice-region mutations (17%), and regulatory-region mutations (2%). The distribution of mutations within the CYBB gene exhibited great heterogeneity, with no apparent mutational hot spots. Evaluation of 87 available mothers revealed X-linked carrier status in all but 10. The heterogeneity of mutations and the lack of any predominant genotype indicate that the disease represents many different mutational events, without a founder effect, as is expected for a disorder with a previously lethal phenotype.

PU.1, interferon regulatory factor 1, and interferon consensus sequence-binding protein cooperate to increase gp91(phox) expression

gp91(phox) is a subunit of the phagocyte respiratory burst oxidase catalytic unit. Transcription of CYBB, the gene encoding gp91(phox), is restricted to terminally differentiated phagocytic cells. An element in the proximal CYBB promoter binds a protein complex, referred to as hematopoiesis-associated factor (HAF1), that is necessary for interferon-gamma (IFNgamma)-induced gp91(phox) expression. In these investigations, we determined that HAF1 was a multiprotein complex, cross-immunoreactive with the transcription factors PU.1, interferon regulatory factor 1 (IRF-1), and interferon consensus sequence-binding protein (ICSBP). In electrophoretic mobility shift assay, the HAF1 complex was reconstituted by either in vitro translated PU.1 with IRF-1 or PU.1 with ICSBP, but not by IRF-1 with ICSBP. HAF1a, a slower mobility complex with the same binding site specificity as HAF1, was also investigated. Similar to the HAF1 complex, the HAF1a complex was cross-immunoreactive with PU. 1, IRF-1, and ICSBP. Unlike the HAF1 complex, reconstitution of the HAF1a complex required in vitro translated PU.1 with both IRF-1 and ICSBP. An artificial promoter construct containing the HAF1/HAF1a binding site was modestly activated in the myelomonocytic cell line U937 by co-transfection either with PU.1 and IRF-1 or with PU.1 and ICSBP, but it was strongly activated by co-transfection with PU.1, IRF-1, and ICSBP. This activation required serine 148-phosphorylated PU.1. These studies describe a novel mechanism for PU.1 transcriptional activation via interaction with both IRF-1 and ICSBP, a target gene for the interaction of IRF-1 with ICSBP, and a novel activation function for ICSBP as a component of a multiprotein complex.

PU.1 as an essential activator for the expression of gp91(phox) gene in human peripheral neutrophils, monocytes, and B lymphocytes

We have reported a deficiency of a 91-kDa glycoprotein component of the phagocyte NADPH oxidase (gp91(phox)) in neutrophils, monocytes, and B lymphocytes of a patient with X chromosome-linked chronic granulomatous disease. Sequence analysis of his gp91(phox) gene revealed a single-base mutation (C --> T) at position -53. Electrophoresis mobility-shift assays showed that both PU.1 and hematopoietic-associated factor 1 (HAF-1) bound to the inverted PU.1 consensus sequence centered at position -53 of the gp91(phox) promoter, and the mutation at position -53 strongly inhibited the binding of both factors. It was also indicated that a mutation at position -50 strongly inhibited PU.1 binding but hardly inhibited HAF-1 binding, and a mutation at position -56 had an opposite binding specificity for these factors. In transient expression assay using HEL cells, which express PU.1 and HAF-1, the mutations at positions -53 and -50 significantly reduced the gp91(phox) promoter activity; however, the mutation at position -56 did not affect the promoter activity. In transient cotransfection study, PU.1 dramatically activated the gp91(phox) promoter in Jurkat T cells, which originally contained HAF-1 but not PU.1. In addition, the single-base mutation (C --> T) at position -52 that was identified in a patient with chronic granulomatous disease inhibited the binding of PU.1 to the promoter. We therefore conclude that PU.1 is an essential activator for the expression of gp91(phox) gene in human neutrophils, monocytes, and B lymphocytes.

Six Arabidopsis thaliana homologues of the human respiratory burst oxidase (gp91phox)

An NADPH oxidase analogous to that in mammalian phagocytes has been hypothesized to produce reactive oxygen species (ROS) in the plant defence response. A. thaliana contains at least six gp91phox homologues, designated AtrbohA-F (A. thaliana Respiratory Burst Oxidase Homologues), which map to different positions. Transcripts of three of these genes can be detected in healthy plants by RNA gel blot analyses. The Atrboh gene products are closely related to gp91phox and the intron locations suggest a common evolutionary origin. A putative EF-hand Ca(2+)-binding motif in the extended N-terminal region of the Atrboh proteins suggests a direct regulatory effect of Ca2+ on the activity of the NADPH oxidase in plants.

Differentiation-stimulated activity binds an ETS-like, essential regulatory element in the human promyelocytic defensin-1 promoter

The human HNP-defensin-1 gene encodes a peptide antibiotic found exclusively in neutrophils and is key to elimination of microbes. Expression is a marker for the granulocytic lineage and for certain stages of differentiation and is not known to be inducible in mature cells under physiological conditions. Low level of transcription also occurs in HL-60 promyelocytic leukemia cells and is greatly activated upon drug-induced granulocytic maturation and by low doses of retinoic acid, in a strictly cell-specific manner (Herwig, S., Su, Q., Ma, Y., and Tempst, P. (1996) Blood 87, 350-364). We have analyzed a 10-kilobase pair region, upstream of the defensin-1 cap site, for the presence of control elements, and we describe a minimal promoter (position -83 to +82) required to drive transcription in HL-60 cells in a quasi cell-specific manner. Our data also suggest the presence of negative regulatory elements in the -416/-191 region that may further contribute to cell specificity in a chromosomal context. The basal promoter contains two functionally essential, ETS-like (GGAA core sequence) elements. The proximal site (-22/-19) constitutively binds the PU.1 transcription factor in vitro and could function, together perhaps with an adjacent TA-rich sequence (-32/-25), in assembly of a myeloid-restricted, basal transcription factor complex. The distal site (-62/-59) interacts in vitro with an unidentified activity, distinct from PU.1, ETS-1, PEA3, and ELK-1 (factors with definite binding site similarities), and is greatly stimulated by phosphorylation during granulocytic differentiation of HL-60 cells. Identification of this protein will be important to resolve the molecular mechanisms controlling temporal, granulocytic restricted gene expression.

Isolation and Characterization of the cDNA for Mouse Neutrophil Collagenase: Demonstration of Shared Negative Regulatory Pathways for Neutrophil Secondary Granule Protein Gene Expression

A characteristic of normal neutrophil maturation is the induction of secondary granule protein (SGP) mRNA expression. Several leukemic human cell lines mimic normal morphologic neutrophil differentiation but fail to express SGPs, such as lactoferrin (LF) and neutrophil gelatinase (NG). In contrast, two murine cell lines (32D C13 and MPRO) are able to differentiate into neutrophils and induce expression of LF and NG. Therefore, to study the normal regulation and function of these genes, the corresponding murine homologs must be isolated. Using cDNA representational difference analysis (RDA) to compare a committed myeloid progenitor cell line (EPRO) with the multipotent stem cell line from which it was derived (EML), we isolated a fragment bearing homology to human neutrophil collagenase (hNC). Here, we describe the cloning and characterization of a full-length (∼2 kb) clone that exhibits nearly 65% nucleotide and 73% amino acid identity to hNC. Ribonuclease protection analysis (RPA) of the tissues and cell lines shows that mouse NC (mNC) is expressed only in cell lines exhibiting neutrophilic characteristics, further confirming its identity as the mouse homolog of hNC. Furthermore, we have demonstrated a shared negative regulatory pathway for this and other SGP genes. We have previously shown that CCAAT displacement protein (CDP/cut) binds to a specific region of the LF promoter, and overexpression of CDP blocks G-CSF–induced upregulation of LF gene expression in 32D C13 cells. We show here that in these cells, upregulation of both NC and NG is also blocked. CDP is thus the first identified transcription factor that is a candidate for mediating the shared regulation of neutrophil SGP protein genes.

Isolation and Characterization of the cDNA for Mouse Neutrophil Collagenase: Demonstration of Shared Negative Regulatory Pathways for Neutrophil Secondary Granule Protein Gene Expression

A characteristic of normal neutrophil maturation is the induction of secondary granule protein (SGP) mRNA expression. Several leukemic human cell lines mimic normal morphologic neutrophil differentiation but fail to express SGPs, such as lactoferrin (LF) and neutrophil gelatinase (NG). In contrast, two murine cell lines (32D C13 and MPRO) are able to differentiate into neutrophils and induce expression of LF and NG. Therefore, to study the normal regulation and function of these genes, the corresponding murine homologs must be isolated. Using cDNA representational difference analysis (RDA) to compare a committed myeloid progenitor cell line (EPRO) with the multipotent stem cell line from which it was derived (EML), we isolated a fragment bearing homology to human neutrophil collagenase (hNC). Here, we describe the cloning and characterization of a full-length (∼2 kb) clone that exhibits nearly 65% nucleotide and 73% amino acid identity to hNC. Ribonuclease protection analysis (RPA) of the tissues and cell lines shows that mouse NC (mNC) is expressed only in cell lines exhibiting neutrophilic characteristics, further confirming its identity as the mouse homolog of hNC. Furthermore, we have demonstrated a shared negative regulatory pathway for this and other SGP genes. We have previously shown that CCAAT displacement protein (CDP/cut) binds to a specific region of the LF promoter, and overexpression of CDP blocks G-CSF–induced upregulation of LF gene expression in 32D C13 cells. We show here that in these cells, upregulation of both NC and NG is also blocked. CDP is thus the first identified transcription factor that is a candidate for mediating the shared regulation of neutrophil SGP protein genes.

DNA binding by cut homeodomain proteins is down-modulated by casein kinase II

The Drosophila and mammalian Cut homeodomain proteins contain, in addition to the homeodomain, three other DNA binding regions called Cut repeats. Cut-related proteins thus belong to a distinct class of homeodomain proteins with multiple DNA binding domains. Using nuclear extracts from mammalian cells, Cut-specific DNA binding was increased following phosphatase treatment, suggesting that endogenous Cut proteins are phosphorylated in vivo. Sequence analysis of Cut repeats revealed the presence of sequences that match the consensus phosphorylation site for casein kinase II (CKII). Therefore, we investigated whether CKII can modulate the activity of mammalian Cut proteins. In vitro, a purified preparation of CKII efficiently phosphorylated Cut repeats causing an inhibition of DNA binding. In vivo, overexpression of the CKII alpha and beta caused a decrease in DNA binding by Cut. The CKII phosphorylation sites within the murine Cut (mCut) protein were identified by in vitro mutagenesis as residues Ser400, Ser789, and Ser972 within Cut repeat 1, 2, and 3, respectively. Cut homeodomain proteins were previously shown to function as transcriptional repressors. Overexpression of CKII reduced transcriptional repression by mCut, whereas a mutant mCut protein containing alanine substitutions at these sites was not affected. Altogether our results indicate that the transcriptional activity of Cut proteins is modulated by CKII.

Transcriptional regulation of the steroid receptor genes

Steroid hormones, via their binding to specific receptors, are involved in the development, differentiation, and physiological response of cells to diverse stimuli. Activation by hormonal ligands induces conformational change in the receptor, enabling interaction with the target genes. The steroid receptor superfamily includes androgen, glucocorticoid, mineralocorticoid, progesterone, estrogen, thyroid, vitamin D, retinoic acid, and orphan receptors. This review will focus on the classic steroid receptors, i.e., the androgen, glucocorticoid, progesterone, and estrogen receptors, with emphasis on their transcriptional regulation. Readers are directed to several authoritative reviews for further details of steroid receptors (1-11).

Murine Macrophage Mannose Receptor Promoter Is Regulated by the Transcription Factors PU.1 and SP1

The mannose receptor (MR) is a transmembrane protein that functions primarily as a phagocytic receptor for a wide range of microorganisms. Its expression appears to be restricted to tissue macrophages and Langerhans cells. To gain an understanding of the regulation of the gene, we have isolated the 5′ flanking sequence of the murine MR gene and have analyzed a 536-bp sequence upstream of the ATG start site for transcriptional activity. This sequence lacks a TATA box but contains an initiator (Inr) consensus element overlapping the single transcriptional start site. Transcription factor binding sites contained within this sequence include PU.1, Sp1, ETS, GATA, and MYB motifs. Serial 100-bp deletions of this promoter fragment fused to a luciferase reporter gene showed various patterns of activity when transfected into different cell types. In myeloid cells, sequence elements upstream of bp −300 appeared to have a silencing effect on promoter activity. Of the four potential PU.1 binding sites contained within the fragment, one site (at −164) bound the PU.1 factor most strongly, whereas the adjacent PU.1 site (at −177 bp) bound PU.1 to a lesser degree. Mutations of these sites decreased transcriptional activity but did not abolish it. However, promoter activity was abrogated when both the −164 bp PU.1 site and the adjacent −177 bp PU.1 site were mutated. In addition, mutation of the Sp1 site also significantly reduced promoter activity. Cotransfection studies in Drosophila Schneider cells indicated that PU.1 and Sp1 may function synergistically in transactivating the murine MR. This study indicates that MR gene expression is regulated in part by the interaction between the ubiquitously expressed factor Sp1 and the lymphoid/myeloid factor PU.1 and provides a basis for studying the regulation of this gene.

The Human Antibacterial Cathelicidin, hCAP-18, Is Synthesized in Myelocytes and Metamyelocytes and Localized to Specific Granules in Neutrophils

hCAP-18 is the only human member of the antibacterial and endotoxin-binding family of proteins known as cathelicidins. The antibacterial and endotoxin binding domains reside in the C-terminal 37 amino acids of the protein (LL-37) and this is believed to be unleashed from the neutralizing N-terminus by proteases from peroxidase positive granules. In human neutrophils, peroxidase positive and peroxidase negative granules can be subdivided into granule subsets that differ in protein content and ability to be exocytosed. To determine the localization of hCAP-18, we performed high-resolution immuno-electron microscopy and subcellular fractionation on Percoll density gradients. Biosynthesis of hCAP-18 was investigated in isolated human bone marrow cells. hCAP-18 was found to colocalize and comobilize with lactoferrin, but not with gelatinase in subcellular fractions. This was confirmed by electron microscopy. hCAP-18 is synthesized at the same stage of myeloid cell maturation as lactoferrin, and is efficiently targeted to granules. Like the peroxidase negative granule's matrix metalloproteinases, collagenase and gelatinase, hCAP-18 is also stored in unprocessed form. hCAP-18 is a major protein of specific granules where it is present in equimolar ratio with lactoferrin.

The Human Antibacterial Cathelicidin, hCAP-18, Is Synthesized in Myelocytes and Metamyelocytes and Localized to Specific Granules in Neutrophils

hCAP-18 is the only human member of the antibacterial and endotoxin-binding family of proteins known as cathelicidins. The antibacterial and endotoxin binding domains reside in the C-terminal 37 amino acids of the protein (LL-37) and this is believed to be unleashed from the neutralizing N-terminus by proteases from peroxidase positive granules. In human neutrophils, peroxidase positive and peroxidase negative granules can be subdivided into granule subsets that differ in protein content and ability to be exocytosed. To determine the localization of hCAP-18, we performed high-resolution immuno-electron microscopy and subcellular fractionation on Percoll density gradients. Biosynthesis of hCAP-18 was investigated in isolated human bone marrow cells. hCAP-18 was found to colocalize and comobilize with lactoferrin, but not with gelatinase in subcellular fractions. This was confirmed by electron microscopy. hCAP-18 is synthesized at the same stage of myeloid cell maturation as lactoferrin, and is efficiently targeted to granules. Like the peroxidase negative granule's matrix metalloproteinases, collagenase and gelatinase, hCAP-18 is also stored in unprocessed form. hCAP-18 is a major protein of specific granules where it is present in equimolar ratio with lactoferrin.

CCAAT Displacement Protein (CDP/cut) Recognizes a Silencer Element Within the Lactoferrin Gene Promoter

Expression of neutrophil secondary granule protein (SGP) genes is coordinately regulated at the transcriptional level, and is disrupted in specific granule deficiency and leukemia. We analyzed the regulation of SGP gene expression by luciferase reporter gene assays using the lactoferrin (LF) promoter. Reporter plasmids were transiently transfected into non–LF-expressing hematopoietic cell lines. Luciferase activity was detected from reporter plasmids containing basepair (bp) −387 to bp −726 of the LF promoter, but not in a −916-bp plasmid. Transfection of a −916-bp plasmid into a LF-expressing cell line resulted in abrogation of the silencing effect. Sequence analysis of this region revealed three eight-bp repetitive elements, the deletion of which restored wild-type levels of luciferase activity to the −916-bp reporter plasmid. Electrophoretic mobility shift assay and UV cross-linking analysis identified a protein of approximately 180 kD that binds to this region in non–LF-expressing cells but not in LF-expressing cells. This protein was identified to be the CCAAT displacement protein (CDP/cut). CDP/cut has been shown to downregulate expression of gp91-phox, a gene expressed relatively early in the myeloid lineage. Our observations suggest that the binding of CDP/cut to the LF silencer element serves to suppress basal promoter activity of the LF gene in non–LF-expressing cells. Furthermore, overexpression of CDP/cut in cultured myeloid stem cells blocks LF expression upon granulocyte colony-stimulating factor–induced neutrophil maturation without blocking phenotypic maturation. This block in LF expression may be due, in part, to the persistence of CDP/cut binding to the LF silencer element.

CCAAT displacement protein (CDP/cut) recognizes a silencer element within the lactoferrin gene promoter

Expression of neutrophil secondary granule protein (SGP) genes is coordinately regulated at the transcriptional level, and is disrupted in specific granule deficiency and leukemia. We analyzed the regulation of SGP gene expression by luciferase reporter gene assays using the lactoferrin (LF) promoter. Reporter plasmids were transiently transfected into non-LF-expressing hematopoietic cell lines. Luciferase activity was detected from reporter plasmids containing base-pair (bp) -387 to bp -726 of the LF promoter, but not in a -916-bp plasmid. Transfection of a -916-bp plasmid into a LF-expressing cell line resulted in abrogation of the silencing effect. Sequence analysis of this region revealed three eight-bp repetitive elements, the deletion of which restored wild-type levels of luciferase activity to the -916-bp reporter plasmid. Electrophoretic mobility shift assay and UV cross-linking analysis identified a protein of approximately 180 kD that binds to this region in non-LF-expressing cells but not in LF-expressing cells. This protein was identified to be the CCAAT displacement protein (CDP/cut). CDP/cut has been shown to downregulate expression of gp91-phox, a gene expressed relatively early in the myeloid lineage. Our observations suggest that the binding of CDP/cut to the LF silencer element serves to suppress basal promoter activity of the LF gene in non-LF-expressing cells. Furthermore, overexpression of CDP/cut in cultured myeloid stem cells blocks LF expression upon granulocyte colony-stimulating factor-induced neutrophil maturation without blocking phenotypic maturation. This block in LF expression may be due, in part, to the persistence of CDP/cut binding to the LF silencer element.

CASP, a novel, highly conserved alternative-splicing product of the CDP/cut/cux gene, lacks cut-repeat and homeo DNA-binding domains, and interacts with full-length CDP in vitro

Human CDP/cut and its murine counterpart, cux1/CDP are homeodomain repressor proteins in the family of Drosophila Cut. Northern blot analysis reveals complex alternative splicing, including forms too small to encode the full 1505 amino acid protein. We have characterized a CDP/cut alternatively spliced cDNA (CASP) of 3.4 kb. Human CASP, a predicted 678 amino acid polypeptide, shares 400 amino acids with CDP, but has an alternate N terminal exon of 20 aa, and the C-terminal 258 amino acids diverge from CDP/cut entirely. As the unique C-terminus of CASP lacks the three 'cut-repeats' and homeodomain of CDP/cut, we predict it does not bind DNA. Murine CASP, 96% similar to human, shares these features. Database searches identify homologs in chicken (86% identical to human CASP) and yeast (29% identical to human). Murine CASP mRNA is ubiquitous in mouse tissues and in tissue-culture cell lines. We generated a specific antiserum against the unique C-terminus of CASP, and used this reagent to demonstrate that CASP protein is expressed as an approx. 80 kDa protein in human and murine cells. Co-translation of in vitro-translated CDP and CASP mRNA, followed by immunoprecipitation with specific anti-CASP IgG, shows that CASP polypeptide can from a complex with CDP. Studies of the intron/exon structure of the murine cux/CDP/mCASP locus (>> 100 kb) reveal that the unique 3' exons of CASP are interposed between cut-repeats 2 and 3 of the cux gene. We speculate that a primordial CASP-like gene captured a cut-repeat-homeobox gene to give rise to the eukaryotic Cut/CDP family of proteins.

Cell cycle-dependent modifications in activities of pRb-related tumor suppressors and proliferation-specific CDP/cut homeodomain factors in murine hematopoietic progenitor cells

The histone H4 gene promoter provides a paradigm for defining transcriptional control operative at the G1/S phase transition point in the cell cycle. Transcription of the cell cycle-dependent histone H4 gene is upregulated at the onset of S phase, and the cell cycle control element that mediates this activation has been functionally mapped to a proximal promoter domain designated Site II. Activity of Site II is regulated by an E2F-independent mechanism involving binding of the oncoprotein IRF2 and the multisubunit protein HiNF-D, which contains the homeodomain CDP/cut, CDC2, cyclin A, and the tumor suppressor pRb. To address mechanisms that define interactions of Site II regulatory factors with this cell cycle control element, we have investigated these determinants of transcriptional regulation at the G1/S phase transition in FDC-P1 hematopoietic progenitor cells. The representation and activities of histone gene regulatory factors were examined as a function of FDC-P1 growth stimulation. We find striking differences in expression of the pRb-related growth regulatory proteins (pRb/p105, pRb2/p130, and p107) following the onset of proliferation. pRb2/p130 is present at elevated levels in quiescent cells and declines following growth stimulation. By contrast, pRb and p107 are minimally represented in quiescent FDC-P1 cells but are upregulated at the G1/S phase transition point. We also observe a dramatic upregulation of the cellular levels of pRb2/p130-associated protein kinase activity when S phase is initiated. Selective interactions of pRb and p107 with CDP/cut are observed during the FDC-P1 cell cycle and suggest functional linkage to competency for DNA binding and/or transcriptional activity. These results are particularly significant in the context of hematopoietic differentiation where stringent control of the cell cycle program is requisite for expanding the stem cell population during development and tissue renewal.

NF-Y, a CCAAT box-binding protein, is one of the trans-acting factors necessary for the response of the murine ERp72 gene to protein traffic

The accumulation of incompletely assembled immunoglobulin mu heavy chain in transfected COS cells stimulates the cellular response to protein traffic that results in the increased transcription and elevated synthesis of several ER chaperones, including ERP72, a member of the protein disulfide isomerase family of molecular chaperones. The ERp72 promoter contains an 82 bp ER protein traffic response element (ERPTRE) that is sufficient to mediate this response. Previously, it had been shown that the alteration of a putative AP-2 site and a CCAAT and inverted CCAAT site within the ERPTRE significantly decreased the response of ERp72 promoter to mu chain accumulation. We have extended these findings by demonstrating a role for NF-Y and a potentially novel DNA-binding protein in the regulation of transcription from the ERp72 promoter. The fact that NF-Y binding to the ERPTRE is observed in extracts from both control cells and cells in which the response to protein traffic has been activated indicates that the binding of NF-Y, while necessary, is not sufficient to account for the response. Each of the two CCAAT sites in the ERPTRE can bind NF-Y independently, but both sites must be intact for full ERPTRE function. A second protein can bind to the ERPTRE independently of NF-Y and at a site overlapping or close to the 3' end of the reverse CCAAT site. It is possible that interactions between NF-Y, this protein and perhaps other factors are responsible for the regulation of the protein traffic response.

Interaction of the nuclear matrix-associated region (MAR)-binding proteins, SATB1 and CDP/Cux, with a MAR element (L2a) in an upstream regulatory region of the mouse CD8a gene

Matrix-associated regions (MARs), AT-rich DNA segments that have an affinity for the nuclear matrix, have been shown to play a role in transcriptional regulation of eukaryotic genes. The present study demonstrates that a DNA element, called L2a, which has been implicated in the transcriptional regulation of the mouse CD8a gene encoding an important T cell coreceptor, is a MAR. Moreover, the identities of two nuclear proteins, L2a-P1 and L2a-P2, previously shown to bind to the L2a element, have been determined. The L2a-P1 protein found to be present in all CD8-positive T cell lines tested is SATB1, a known MAR-binding protein. The widely expressed L2a-P2 protein is CDP/Cux, a MAR-binding protein that has been associated with repression of gene transcription. Interaction of both proteins with the L2a element was studied using the missing nucleoside approach, DNase I footprinting, and electrophoretic mobility shift assays with wild type and mutant L2a elements. The data suggest that CDP/Cux bound to the L2a element is displaced by binding of SATB1 and the accompanying conformational change in the DNA lying between the primary binding sites of SATB1 and CDP/Cux. We suggest that displacement of CDP/Cux by SATB1 favors transcription of the CD8a gene, possibly by enhancing or altering its association with the nuclear matrix.

PU.1 is essential for p47(phox) promoter activity in myeloid cells

Expression of the phagocyte cytosolic protein p47(phox), a component of NADPH oxidase, is restricted mainly to myeloid cells. To study the cis-elements and trans-acting factors responsible for its gene expression, we have cloned and characterized the p47(phox) promoter. A predominant transcriptional start site was identified 21 nucleotides upstream of the translation initiation codon. To identify the gene promoter sequences, transient transfections of HL-60 human myeloid cells were performed with a series of 5'-deletion p47(phox)-luciferase reporter constructs that extended as far upstream as -3050 bp relative to the transcriptional start site. The -224 and -86 constructs had the strongest p47(phox) promoter activity, whereas the -46 construct showed a major reduction in activity and the -36 construct a complete loss of activity. DNase I footprint analysis identified a protected region from -37 to -53. This region containing a consensus PU.1 site bound specifically both PU.1 present in nuclear extracts from myeloid cells and PU.1 synthesized in vitro. Mutations of this site eliminated PU.1 binding and abolished the ability of the p47(phox) promoter to direct expression of the reporter gene. The p47(phox) promoter was active in all myeloid cell lines tested (HL-60, THP-1, U937, PLB-985), but not in non-myeloid cells (HeLa, HEK293). Finally, PU.1 trans-activated the p47(phox)-luciferase constructs in HeLa cells. We conclude that, similar to certain other myeloid-specific genes, p47(phox) promoter activity in myeloid cells requires PU.1.

Constitutional inversion of chromosome 7 and hematologic cancers

Nonrandom aberrations of chromosome 7 have been described in various hematopoietic disorders. We describe here two unrelated families with the same constitutional inversion of chromosome 7 [inv(7)(q11.2q22)]. The probands in both families had acute leukemia and cytogenetic analysis revealed that the inversion was the sole cytogenetic abnormality in the bone marrow at diagnosis. There is a history of hematologic diseases in one of these families that included a son who is a carrier of this constitutional inversion. The distal inversion breakpoint lies within the common region of chromosome loss identified in some myeloid diseases. These observations raise the possibility that this inherited chromosome rearrangement could result in a mutation of a tumor suppressor gene and possibly represent a predisposing event for the development of leukemia in these individuals.

Phylogenetic Footprinting of Hypersensitive Site 3 of the β-Globin Locus Control Region

Hypersensitive site 3 (HS3) of the β-like globin locus control region has been implicated as an important regulator of the β-like globin genes, but the trans factors that bind HS3 have only been partially characterized. Using a five-species alignment (human, galago, rabbit, goat, and mouse) that represents 370 million years of evolution, we have identified 24 phylogenetic footprints in the HS3 core and surrounding regions. Probes corresponding to the human sequence at each footprint have been used in binding studies to identify the nuclear factors that bind within and near these conserved sequence elements. Among the high-affinity interactions observed were several binding sites for proteins with repressor activity, including YY1, CCAAT displacement protein, and G1/G2 complexes (uncharacterized putative repressors) and several binding sites for the stage selector protein. To complement this analysis, orthologous galago sequences were also used to derive probes and the pattern of proteins binding to human and galago probes was compared. Binding interactions differing between these two species could be responsible for the different expression patterns shown by the two γ genes (galago γ is embryonic; human γ is fetal). Alternatively, binding interactions that are conserved in the two species may be important in the regulation of common expression patterns (eg, repression of γ in adult life).