The promoter of the CD11b gene directs myeloid-specific and developmentally regulated expression

Impact of Depletion of Microglia/Macrophages on Regeneration after Spinal Cord Injury

Microglia/macrophages play important functional roles in regeneration after central nervous system injury. Infiltration of circulating macrophages and proliferation of resident microglia occur within minutes following spinal cord injury. Activated microglia/macrophages clear tissue debris, but activation over time may hamper repair. To study the role of these cells in regeneration after spinal cord injury we used CD11b-herpes simplex virus thymidine kinase (HSVTK) (TK) transgenic mice, in which viral thymidine kinase activates ganciclovir toxicity in CD11b-expressing myeloid cells, including macrophages and microglia. A severe reduction in number of these cells was seen in TK versus wild-type littermate mice at 1 week and 5 weeks after injury, and numbers of Mac-2 expressing activated microglia/macrophages were almost completely reduced at these time points. One week after injury TK mice showed better locomotor recovery, but recovery was similar to wild-type mice as measured weekly up to 5 weeks thereafter. At 5 weeks after injury, numbers of axons at the lesion site and neurons in the lumbar spinal cord did not differ between groups. Also, catecholaminergic innervation of spinal motoneurons was similar. However, cholinergic innervation was lower and glial scarring was increased in TK mice compared to wild-type mice. We conclude that reducing numbers of CD11b-expressing cells improves locomotor recovery in the early phase after spinal cord injury, but does not affect recovery in the following 4 weeks. These observations point to differences in outcomes of astrocytic response and cholinergic innervation under CD11b cell ablation, which are, however, not reflected in the locomotor parameters analyzed at 5 weeks after injury.

Regulation of CD11b by HIF-1α and the STAT3 signaling pathway contributes to the immunosuppressive function of B cells in inflammatory bowel disease

B cells have been reported to have a suppressive function in autoimmune diseases, which appears to require an increase of CD11b expression on B cells. However, little is known how CD11b is induced in B cells to play the function. In this study, we found that the high expression of CD11b in B cells occurred not only in the mucosal immune organs, but also in systemically immune organs such as the spleen during dextran sulfate sodium (DSS)-induced colitis. Since the inflammatory lesions in mouse models of inflammatory bowel disease (IBD) were revealed to be significantly hypoxic or even anoxic, the B cells from colitic mice Peyer's patches (PP) were investigated to express higher levels of hypoxia-inducible factor-1α (HIF-1α) than naïve B cells from wildtype (WT) mice. HIF-1α siRNA transfection or HIF-1α protein inhibition led to decreased CD11b expression at both the mRNA and protein levels in vitro. B cells with HIF-1α specific knockdown were then adoptively transferred to Rag-1^-/- mice. The result displayed that CD11b expression was decreased in B cells and an exacerbated colitis occurred. The bio-informatics promoter analysis and ChIP assay showed that HIF-1α was the critical transcription factor for CD11b and cooperatively formed a complex with the p-STAT3 homodimers to bind onto hypoxia-responsive element (HRE) regions, which was guaranteed by MEK/ERK pathway activation and IL-10 secretion. In conclusion, our study demonstrated the key function of the hypoxia-associated transcription factor HIF-1α together with p-STAT3 in driving CD11b transcription in B cells and controlling B cell's protective activity in experimental inflammatory bowel disease (IBD).

Hypoxia: The Force that Drives Chronic Kidney Disease

In the United States the prevalence of end-stage renal disease (ESRD) reached epidemic proportions in 2012 with over 600,000 patients being treated. The rates of ESRD among the elderly are disproportionally high. Consequently, as life expectancy increases and the baby-boom generation reaches retirement age, the already heavy burden imposed by ESRD on the US health care system is set to increase dramatically. ESRD represents the terminal stage of chronic kidney disease (CKD). A large body of evidence indicating that CKD is driven by renal tissue hypoxia has led to the development of therapeutic strategies that increase kidney oxygenation and the contention that chronic hypoxia is the final common pathway to end-stage renal failure. Numerous studies have demonstrated that one of the most potent means by which hypoxic conditions within the kidney produce CKD is by inducing a sustained inflammatory attack by infiltrating leukocytes. Indispensable to this attack is the acquisition by leukocytes of an adhesive phenotype. It was thought that this process resulted exclusively from leukocytes responding to cytokines released from ischemic renal endothelium. However, recently it has been demonstrated that leukocytes also become activated independent of the hypoxic response of endothelial cells. It was found that this endothelium-independent mechanism involves leukocytes directly sensing hypoxia and responding by transcriptional induction of the genes that encode the β2-integrin family of adhesion molecules. This induction likely maintains the long-term inflammation by which hypoxia drives the pathogenesis of CKD. Consequently, targeting these transcriptional mechanisms would appear to represent a promising new therapeutic strategy.

Gene therapy of canine leukocyte adhesion deficiency using lentiviral vectors with human CD11b and CD18 promoters driving canine CD18 expression

To identify cellular promoters in a self-inactivating (SIN) lentiviral vector that might be beneficial in treating children with leukocyte adhesion deficiency type 1 (LAD-1), we tested lentiviral vectors with human CD11 and CD18 leukocyte integrin proximal promoter elements directing expression of canine CD18 in animals with canine LAD (CLAD). Lentiviral vectors with either the human CD11b (637 bp) proximal promoter or the human CD18 (1,060 bp) proximal promoter resulted in the highest percentages of CD18(+) CLAD CD34(+) cells in vitro. Subsequently, two CLAD dogs were infused with autologous CD34(+) cells transduced with the hCD11b (637 bp)-cCD18 vector, and two CLAD dogs were infused with autologous CD34(+) cells transduced with the hCD18 (1,060 bp)-cCD18 vector. Each dog received a nonmyeloablative dose of 200 cGy total body irradiation (TBI) before the infusion of transduced cells. The two CLAD dogs treated with the hCD18 (1,060 bp)-cCD18 vector, and one of the two dogs treated with the hCD11b (637 bp)-cCD18 vector, had reversal of the CLAD phenotype. These studies using endogenous leukocyte integrin proximal promoters represent an important step in the development of gene therapy for children with LAD-1.

Junctional adhesion molecule C mediates leukocyte adhesion to rheumatoid arthritis synovium

OBJECTIVE

Leukocyte infiltration into the rheumatoid arthritis (RA) synovium is a multistep process in which leukocytes leave the bloodstream and invade the synovial tissue (ST). Leukocyte transendothelial migration and adhesion to RA ST requires adhesion molecules on the surface of endothelial cells and RA ST fibroblasts. This study was undertaken to investigate the role of junctional adhesion molecule C (JAM-C) in mediating leukocyte recruitment and retention in the RA joint.

METHODS

Immunohistologic analysis was performed on RA, osteoarthritis (OA), and normal ST samples to quantify JAM-C expression. Fibroblast JAM-C expression was also analyzed using Western blotting, cell surface enzyme-linked immunosorbent assay, and immunofluorescence. To determine the role of JAM-C in leukocyte retention in the RA synovium, in vitro and in situ adhesion assays and RA ST fibroblast transmigration assays were performed.

RESULTS

JAM-C was highly expressed by RA ST lining cells, and its expression was increased in OA ST and RA ST endothelial cells compared with normal ST endothelial cells. JAM-C was also expressed on the surface of OA ST and RA ST fibroblasts. Furthermore, we demonstrated that myeloid U937 cell adhesion to both OA ST and RA ST fibroblasts and to RA ST was dependent on JAM-C. U937 cell migration through an RA ST fibroblast monolayer was enhanced in the presence of neutralizing antibodies against JAM-C.

CONCLUSION

Our results highlight the novel role of JAM-C in recruiting and retaining leukocytes in the RA synovium and suggest that targeting JAM-C may be important in combating inflammatory diseases such as RA.

Uptake and presentation of exogenous antigen and presentation of endogenously produced antigen by skin dendritic cells represent equivalent pathways for the priming of cellular immune responses following biolistic DNA immunization

Gene gun-mediated biolistic DNA vaccination with beta-galactosidase (betaGal)-encoding plasmid vectors efficiently modulated antigen-induced immune responses in an animal model of type I allergy, including the inhibition of immunoglobulin E (IgE) production. Here we show that CD4(+) as well as CD8(+) T cells from mice biolistically transfected with a plasmid encoding betaGal under the control of the fascin promoter (pFascin-betaGal) are capable of inhibiting betaGal-specific IgE production after adoptive transfer into naïve recipients. Moreover, suppression of IgE production was dependent on interferon (IFN)-gamma. To analyse the modalities of activation of CD4(+) and CD8(+) T cells regarding the localization of antigen synthesis following gene gun-mediated DNA immunization, we used the fascin promoter and the keratin 5 promoter (pK5-betaGal) to direct betaGal production mainly to dendritic cells (DCs) and to keratinocytes, respectively. Gene gun-mediated DNA immunization with each vector induced considerable activation of betaGal-specific CD8(+) cytotoxic T cells. Cytokine production by re-stimulated CD4(+) T cells in draining lymph nodes and immunoglobulin isotype profiles in sera of immunized mice indicated that immunization with pFascin-betaGal induced a T helper type 1 (Th1)-biased immune response, whereas immunization with pK5-betaGal generated a mixed Th1/Th2 immune response. Nevertheless, DNA vaccination with pFascin-betaGal and pK5-betaGal, respectively, efficiently inhibited specific IgE production in the mouse model of type I allergy. In conclusion, our data show that uptake of exogenous antigen produced by keratinocytes and its presentation by untransfected DCs as well as the presentation of antigen synthesized endogenously in DCs represent equivalent pathways for efficient priming of cellular immune responses.

Identification of Pur alpha as a new hypoxia response factor responsible for coordinated induction of the beta 2 integrin family

Central to the process of inflammation are hypoxic conditions that lead to the binding of circulating leukocytes to the endothelium. We have previously shown that such binding is mediated by monocytes being able to directly sense hypoxic conditions and respond by inducing their surface expression of the beta(2) integrin family of adhesion molecules. In this study, we show that coordinated induction of the beta(2) integrins during direct hypoxia-sensing occurs through transcriptional activation of each of the genes by which they are encoded. Certain of the molecular mechanisms that mediate this activation in transcription are dependent upon hypoxia-inducible factor-1 (HIF-1), whereas others are HIF-1 independent. In search of these HIF-1-independent mechanisms, we identified Pur alpha as a new hypoxia-response factor. Binding of Pur alpha to the HIF-1-independent beta(2) integrin promoters is induced by hypoxia and mutagenesis of these Pur alpha-binding sites almost completely abolishes the ability of the promoters to respond to hypoxic conditions. Additional studies using siRNA directed against Pur alpha also revealed a loss in the hypoxic response of the beta(2) integrin promoters. Taken together, our findings demonstrate that hypoxia induces a coordinated up-regulation in beta(2) integrin expression that is dependent upon transcriptional mechanisms mediated by HIF-1 and Pur alpha.

Se-methylselenocysteine enhances PMA-mediated CD11c expression via phospholipase D1 activation in U937 cells

CD11c/CD18 is expressed primarily on myeloid cells, where its expression is regulated both during differentiation and during monocyte maturation into tissue macrophages, and is also a receptor for fibrinogen and lipopolysaccharide (LPS). We focused on the molecular mechanisms leading to the activation of CD11c expression in differentiating U937 cells. During phorbol myristate acetate (PMA)-induced differentiation of U937 cells, we found that the mRNA expression of CD11c was increased. Se-methylselenocysteine (Se-MSC) potentiated up-regulation of CD11c expression and its promoter activity and increased PLD1 activity without affecting the level of PLD1 protein in PMA-treated cells. To examine the regulation mechanism of PMA and Se-MSC on CD11c gene expression through the activation of PLD1, we analyzed changes in the CD11c mRNA level and the promoter activity following treatment of a selective PLD inhibitor n-butanol. The combinatory effect of PMA and Se-MSC on CD11c gene expression was abolished by n-butanol in a dose-dependent manner. Further, introduction of PLD1 gene into U937 cells increased CD11c mRNA expression and activated CD11c promoter activity in a dose-dependent manner. These results showed that Se-MSC increased PMA-induced CD11c expression through the activation of PLD1 signaling pathway. To our knowledge, this is the first report that expression of the CD11c gene is regulated by PLD1 and is enhanced by Se-MSC during PMA-induced U937 differentiation.

Leukocyte adhesion during hypoxia is mediated by HIF-1-dependent induction of beta2 integrin gene expression

Inflammatory responses are associated with significant changes in tissue metabolism. In particular, metabolic shifts during inflammation can result in significant tissue hypoxia, with resultant induction of hypoxia-responsive genes. Given this association, we hypothesized that leukocyte functional responses are influenced by hypoxia. Initial experiments revealed that exposure of the promonocytic cell line U937 to hypoxia resulted in increased adhesion to activated endothelia. Such increases were transcription-dependent and were blocked by antibodies directed against beta2, but not beta1, integrins. Analysis of beta2 integrin mRNA and protein in U937 cells revealed a 5- to 6-fold increase with hypoxia. Extension of this analysis to hypoxic human whole blood revealed prominent induction of beta2 integrin mRNA and protein ex vivo. Furthermore, murine beta2 integrin mRNA was found to be significantly induced during hypoxia in vivo. Subsequent studies identified a binding site for hypoxia-inducible factor 1 (HIF-1) in the CD18 gene. This gene encodes the subunit common to all four known types of beta2 integrin heterodimer. HIF-1 binding was demonstrated in vivo, and mutational analysis of the HIF-1 site within the CD18 promoter resulted in a loss of hypoxia inducibility. Taken together, these results demonstrate that hypoxia induces leukocyte beta2 integrin expression and function by transcriptional mechanisms dependent upon HIF-1.

CD11c gene expression in hairy cell leukemia is dependent upon activation of the proto-oncogenes ras and junD

Hairy cell leukemia (HCL) is a chronic lymphoproliferative disease, the cause of which is unknown. Diagnostic of HCL is abnormal expression of the gene that encodes the beta2 integrin CD11c. In order to determine the cause of CD11c gene expression in HCL the CD11c gene promoter was characterized. Transfection of the CD11c promoter linked to a luciferase reporter gene indicated that it is sufficient to direct expression in hairy cells. Mutation analysis demonstrated that of predominant importance to the activity of the CD11c promoter is its interaction with the activator protein-1 (AP-1) family of transcription factors. Comparison of nuclear extracts prepared from hairy cells with those prepared from other cell types indicated that hairy cells exhibit abnormal constitutive expression of an AP-1 complex containing JunD. Functional inhibition of AP-1 expressed by hairy cells reduced CD11c promoter activity by 80%. Inhibition of Ras, which represents an upstream activator of AP-1, also significantly inhibited the CD11c promoter. Furthermore, in the hairy cell line EH, inhibition of Ras signaling through mitogen-activated protein kinase/extracellular signal-regulated kinase kinases 1 and 2 (MEK1/2) reduced not only CD11c promoter activity but also reduced both CD11c surface expression and proliferation. Expression in nonhairy cells of a dominant-positive Ras mutant activated the CD11c promoter to levels equivalent to those in hairy cells. Together, these data indicate that the abnormal expression of the CD11c gene characteristic of HCL is dependent upon activation of the proto-oncogenes ras and junD.

The zinc finger transcription factor ZBP-89 is a repressor of the human beta 2-integrin CD11b gene

Integrin CD11b is a differentiation marker of the myelomonocytic lineage and an important mediator of inflammation. Expression of the CD11b gene is transcriptionally induced as myeloid precursors differentiate into mature cells, then drops as monocytes further differentiate into macrophages. Previous studies have identified elements and factors involved in the transcriptional activation of the CD11b gene during myeloid differentiation, but no data exist regarding potential down-regulatory factors, especially in the later stages of differentiation. Using 2 copies of a GC-rich element (-141 to -110) in the CD11b promoter, we probed a cDNA expression library for interacting proteins. Three clones were identified among 9.1 million screened, all encoding the DNA-binding domain of the zinc finger factor ZBP-89. Overexpression of ZBP-89 in the monocyte precursor cell line U937 reduced CD11b promoter-driven luciferase activity when U937 cells were induced to differentiate into monocytelike cells using phorbol esters. To identify the differentiation stage at which ZBP-89 repression of the CD11b gene is exerted, the protein level of ZBP-89 was correlated with that of CD11b mRNA in differentiating U937 as well as in normal human monocytes undergoing in vitro differentiation into macrophages. A clear inverse relationship was observed in the latter but not the former state, suggesting that ZBP-89 represses CD11b gene expression during the further differentiation of monocytes into macrophages.

hnRNP-K and Pur(alpha) act together to repress the transcriptional activity of the CD43 gene promoter

CD43 is an abundant, heavily glycosylated molecule expressed specifically on the surface of leukocytes and platelets. When leukocytes are at rest, CD43 acts to prevent both homotypic and heterotypic interactions. However, during leukocyte activation CD43 expression is repressed, facilitating the intercellular contact required for chemotaxis, phagocytosis, aggregation, adhesion to endothelium, and transendothelial migration. Consequently, CD43 repression plays a vital role both in innate and acquired immunity. Here we report that a dramatic down-regulation of CD43 mRNA levels occurs during activation of the leukocytic cell line K562. This repression coincides with repression of the transcriptional activity of the CD43 gene promoter. We have determined that heterogeneous nuclear ribonucleoprotein K (hnRNP-K) and Pur(alpha) act together to mediate repression of the CD43 promoter during K562 activation. The hnRNP-K molecule and Pur(alpha) bind single-stranded DNA. Therefore, exposure of single-stranded structures within the CD43 promoter probably plays a major role in effecting CD43 repression.

Characterization of the promoter for the mouse alpha 3 integrin gene

The alpha 3 beta 1 integrin is an adhesion receptor for extracellular matrix proteins including isoforms of laminin, and the changes of its expression level in various cancer cells are thought to cause their malignant phenotypes. We have cloned an approximately 4 kb DNA fragment of the 5'-flanking region of the murine alpha 3 integrin gene and analyzed its promoter activity. Transfection of MKN1 gastric carcinoma cells with serially truncated segments of the 5'-flanking region linked to a luciferase gene indicated that a 537-bp SalI/SacI fragment upstream of exon 1 was sufficient to promote high level gene expression. By 5'-rapid amplification of cDNA ends (5'-RACE) using a cap site-labeled cDNA library, we determined one major and one minor transcription start sites in this region. The murine alpha 3 integrin gene was found to contain a CCAAT box, but to lack a TATA box. Luciferase assay following transfection with a series of deletion constructs of the SalI/SacI fragment revealed that the sequence between positions -260 and -119 bp (relative to the major transcription start site) is required for efficient transcription in gastric carcinoma cells. The sequence analysis of this segment showed the presence of several consensus sequences for transcription factors including Ets, GATA and MyoD/E-box binding factors. The introduction of mutation in one of the Ets-binding sequences greatly decreased its promoter activity, suggesting that the transcription of the alpha 3 integrin gene in these cells is regulated by the Ets-family of transcription factors.

During differentiation of the monocytic cell line U937, Pur alpha mediates induction of the CD11c beta 2 integrin gene promoter

CD11c is a member of the beta(2) integrin family of adhesion molecules that, together with CD18, forms a heterodimeric receptor on the surface of myeloid, NK, dendritic, and certain leukemic, lymphoma, and activated lymphoid cells. Monocytic differentiation is associated with an induction of both CD11c and CD18 gene expression. The resulting CD11c/CD18 receptor mediates firm adhesion to the vascular endothelium, transendothelial migration, chemotaxis, and phagocytosis. Monocytic differentiation can be mimicked in vitro by treatment of the promonocytic cell line U937 with PMA. Recently, we reported that in U937 cells, expression of the CD11c gene is controlled by an unidentified transcription factor that binds ssDNA. This finding suggested that DNA secondary structure plays an important role in controlling the CD11c gene and prompted us to search for additional ssDNA-binding activities with which this gene interacts. In this study, we report that in U937 cells, expression of the CD11c gene is mediated by the ssDNA-binding protein Puralpha. During PMA-induced differentiation, the ability of Puralpha to activate the CD11c promoter in U937 cells increases, as does that of Sp1. Together, these increases in the functional activity of both Puralpha and Sp1 combine to induce CD11c expression.

During U937 monocytic differentiation repression of the CD43 gene promoter is mediated by the single-stranded DNA binding protein Pur alpha

Human CD43 is an abundant, heavily glycosylated molecule expressed exclusively on the surface of leucocytes. When leucocytes are at rest, CD43 acts to prevent intercellular interaction but during leucocyte differentiation such cell-cell interaction is facilitated by CD43. This change in the function of CD43 is mediated in part by a reduction in its level of expression. Previous studies have implicated proteolytic cleavage events at the cell surface in causing such reduction. Here, we report that, in an in vitro model of leucocyte differentiation, CD43 mRNA levels were also subject to reduction. Specifically, we demonstrated that within 48 h of the cell line U937 being induced to differentiate along the monocytic pathway, CD43 mRNA levels were reduced by 69%. This decline coincided with a decrease in the activity of the CD43 gene promoter mediated by the single-stranded DNA binding protein Pur alpha. Previously, we have demonstrated that Pur alpha mediates induction of the CD11c beta 2 integrin promoter during U937 differentiation. Consequently, Pur alpha represents a potential means by which the induction of pro-adhesive molecules and the repression of anti-adhesive molecules is co-ordinated during leucocyte differentiation.

Effects of deregulated Raf activation on integrin, cytokine-receptor expression and the induction of apoptosis in hematopoietic cells

The effects of deregulated Raf activation on the growth and differentiation of hematopoietic cells were investigated. The cytokine-dependent murine myeloid FDC-P1 and human erythroleukemic TF-1 cell lines were transformed to grow in response to deregulated Raf expression in the absence of exogenous cytokines. The conditionally active Raf proteins were regulated by beta-estradiol as cDNAs containing the Raf catalytic, but lacking negative-regulatory domains, were ligated to the hormone binding domain of the estrogen receptor (deltaRaf:ER). Continuous deltaRaf expression prevented apoptosis in the absence of exogenous cytokines and altered the morphology of the FD/deltaRaf:ER cells as they grew in large aggregated masses (>100 cells) whereas the parental cytokine-dependent FDC-P1 cells grew in smaller grape-like clusters (< 10 cells). FD/deltaRaf-1:ER cells growing in response to Raf activation displayed decreased levels of the Mac-2 and Mac-3 molecules on their cell surface. In contrast, when these cells were cultured in IL-3, higher levels of these adhesion molecules were detected. Expression of activated Raf oncoproteins also abrogated cytokine dependency and prevented apoptosis of TF-1 cells. Moreover, the differentiation status of these Raf-responsive cells was more immature upon Raf activation as culture with the differentiation-inducing agent phorbol 12 myristate 13-acetate (PMA) and beta-estradiol resulted in decreased levels of the CD11b and CD18 integrin molecules on the cell surface. In contrast when the Raf-responsive cells were induced to differentiate with PMA and GM-CSF, in the absence of deltaRaf:ER activation, increased levels of the CD11b and CD18 molecules were detected. Retinoic acid (RA) inhibited 3H-thymidine incorporation in response to GM-CSF. Interestingly, Raf activation counterbalanced the inhibition of DNA synthesis caused by RA but not PMA. Thus deregulated Raf expression can alter cytokine dependency, integrin expression and the stage of differentiation. These Raf-responsive cell lines will be useful in elucidating the roles of the MAP kinase cascade on hematopoietic cell differentiation and malignant transformation.

CD43 gene expression is mediated by a nuclear factor which binds pyrimidine-rich single-stranded DNA

CD43 is a leukocyte-specific surface molecule which plays an important role both in adhesion and signal transduction. We have identified a site spanning nucleotides +18 to +39 within the human CD43 gene promoter which in vitro is hypersensitive to cleavage by nuclease S1. Repeats of this region are sufficient to activate expression of a heterologous promoter in CD43-positive cell lines. Two nuclear factors, PyRo1 and PyRo2, interact with the hypersensitive site. PyRo1 is a single-stranded DNA-binding protein which binds the pyrimidine-rich sense strand. Mutation analysis demonstrates that the motif TCCCCT is critical for PyRo1 interaction. Replacement of this motif with the sequence CATATA abolishes PyRo1 binding and reduces expression of the CD43 promoter by 35% in Jurkat T lymphocytic cells and by 52% in the pre-erythroid/pre-megakaryocytic cell line K562. However, this same replacement failed to affect expression in U937 monocytic cells or in CEM T lymphocytic cells. PyRo1, therefore, exhibits cell-specific differences in its functional activity. Further analysis demonstrated that PyRo1 not only interacts with the CD43 gene promoter but also motifs present within the promoters of the CD11a, CD11b, CD11c and CD11d genes. These genes encode the alpha subunits of the beta2 integrin family of leukocyte adhesion receptors. Deletion of the PyRo1 binding site within the CD11c gene reduced promoter activity in T lymphocytic cells by 47%. However, consistent with our analysis of the CD43 gene, the effect of this same deletion within U937 monocytic cells was less severe. That PyRo1 binds preferentially to single-stranded DNA and sequences within the CD43 and CD11 gene promoters suggests that expression of these genes is influenced by DNA secondary structure.

Human NM23/nucleoside diphosphate kinase regulates gene expression through DNA binding to nuclease-hypersensitive transcriptional elements

NM23-H2/NDP kinase B has been identified as a sequence-specific DNA-binding protein with affinity for a nuclease-hypersensitive element of the c-MYC gene promoter (Postel et al., 1993). The ability of Nm23-H2 to activate c-MYC transcription in vitro and in vivo via the same element demonstrates the biological significance of this interaction. Mutational analyses have identified Arg34, Asn69 and Lys135 as critical for DNA binding, but not required for the NDP kinase reaction. However, the catalytically important His118 residue is dispensible for sequence-specific DNA binding, suggesting that sequence-specific DNA recognition and phosphoryl transfer are independent properties. Nm23-H2 also has an activity that cleaves DNA site-specifically, involving a covalent protein-DNA complex. In a DNA sequence-dependent manner, Nm23-H2 recognizes additional target genes for activation, including myeloperoxidase, CD11b, and CCR5, all involved in myeloid-specific differentiation. Moreover, both NM23-H1 and Nm23-H2 bind to nuclease hypersensitive elements in the platelet-derived growth factor PDGF-A gene promoter sequence-specifically, correlating with either positive or negative transcriptional regulation. These data support a model in which NM23/NDP kinase modulates gene expression through DNA binding and subsequent structural transactions.

Differential effect on U937 cell differentiation by targeting transcriptional factors implicated in tissue- or stage-specific induced integrin expression

The inhibition of transcription factor functions was used to define their role in phorbol ester-induced cellular differentiation of a monocytic cell line, U937. We demonstrate a differential effect on cell adhesion and differentiation: antisense or competitive binding with double-stranded oligonucleotides antagonized the functions of AP-1, NF-kappaB, and PU.1 transcriptional factors. In the presence of phorbol 12-myristate 13-acetate (PMA), U937 cells attached to the plastic surface and cells were characterized by marked expression of beta2-integrin molecules on the cell surface. We show that the in vivo differentiation of U937 cells appears to occur normally in the absence of AP-1 activity. In contrast, the addition to the cell culture of phosphorothioate oligonucleotides that contained the NF-kappaB or PU.1 binding sites significantly inhibited U937 differentiation. The absence of NF-kappaB led to pleiotropic effects with a clear reduction in the expression of integrin and other lineage-specific myeloid antigens on the cell surface. In contrast, the absence of PU.1 had a more restricted effect on integrin expresion on the cell surface, probably as a result of blockage of CD18 gene expression.

Transcription of alpha2 integrin gene in osteosarcoma cells is enhanced by tumor promoters

Integrin alpha2beta1 is a heterodimeric transmembrane receptor for collagens. In osteogenic cells the expression of alpha2beta1 integrin is induced by both Kirsten sarcoma virus and chemical transformation. The association of alpha2 integrin with transformed cell phenotype was studied further by testing the effects of two tumor promoters, 12-O-tetradecanoylphorbol 13-acetate (TPA) and okadaic acid (OA), on human MG-63 osteosarcoma cells. TPA, an activator of protein kinase C, increased the cell surface expression of alpha2 integrin and the corresponding mRNA levels. Nuclear run-on assays indicated that TPA activated the transcription of alpha2 integrin gene. TPA also slightly increased the expression of alpha3 integrin but had no effect on the transcription of alpha5, alphav, or beta1 integrin subunits. OA, an inhibitor of serine/threonine phosphatases, increased alpha2 integrin gene transcription and mRNA levels, but in contrast to TPA, OA decreased alpha3 integrin expression. The increased expression of alpha2 integrin on TPA-treated MG-63 cells led to faster cell spreading on type I collagen. Our results link the enhanced transcription of alpha2 integrin gene to tumor progression and show the independent regulation of alpha2 integrin compared to other integrin genes.

Characterization of the Human Platelet/Endothelial Cell Adhesion Molecule-1 Promoter: Identification of a GATA-2 Binding Element Required for Optimal Transcriptional Activity

Platelet/endothelial cell adhesion molecule-1 (PECAM-1) is a 130-kD member of the Ig gene superfamily that is expressed on platelets, endothelial cells, and certain leukocyte subsets. To examine the factors controlling vascular-specific expression of PECAM-1, we cloned the 5′-flanking region of the PECAM-1 gene and analyzed its transcriptional activity. 5′-Rapid amplification of cDNA ends (5′-RACE) analysis showed that transcription initiation occurred at several closely spaced nearby sites originating approximately 204 bp upstream from the translation start site. Analysis of the sequence immediately upstream from the transcription initiation site (TIS) showed no canonical TATA or CAAT elements, however an initiator element commonly found in TATA-less promoters encompassed the TIS. 5′-serially truncated PECAM-1 promoter segments cloned in front of a luciferase reporter drove transcription in both a lineage- and orientation-specific manner. Putative cis-acting control elements present within a 300-bp core promoter included two ets sites, an Sp1 site, tandem E-box domains, two GATA-associated sites (CACCC), an AP-2 binding site, and a GATA element at −24. Mutational analysis showed that optimal transcriptional activity required the GATA sequence at position −24, and gel-shift assays further showed that the GATA-2 transcription factor, but not GATA-1, bound to this region of the PECAM-1 promoter. Understanding the cis- and trans-acting factors that regulate the tissue-specific expression of PECAM-1 should increase our understanding of the mechanisms by which vascular-specific gene expression is achieved.

Transgenic expression of PML/RARalpha impairs myelopoiesis

The translocation found in acute promyelocytic leukemia rearranges the promyelocytic leukemia gene (PML) on chromosome 15 with the retinoic acid receptor alpha (RARalpha) on chromosome 17. This yields a fusion transcript, PML/RARalpha, a transcription factor with reported dominant negative functions in the absence of hormone. Clinical remissions induced with all-trans retinoic acid (RA) treatment in acute promyelocytic leukemia are linked to PML/RARalpha expression in leukemic cells. To evaluate the PML/RARalpha role in myelopoiesis, transgenic mice expressing PML/RARalpha were engineered. A full-length PML/RARalpha cDNA driven by the CD11b promoter was expressed in transgenic mice. Expression was confirmed in the bone marrow with a reverse transcription PCR assay. Basal total white blood cell and granulocyte counts did not appreciably differ between PML/RARalpha transgenic and control mice. Cell sorter analysis of CD11b+ bone marrow cells revealed similar CD11b+ populations in transgenic and control mice. However, in vitro clonal growth assays performed on peripheral blood from transgenic versus control mice revealed a marked reduction of myeloid progenitors, especially in those responding to granulocyte/ macrophage colony-stimulating factor. Granulocyte/macrophage colony-stimulating factor and kit ligand cotreatment did not overcome this inhibition. Impaired myelopoiesis in vivo was shown by stressing these mice with sublethal irradiation. Following irradiation, PML/RARalpha transgenic mice, as compared with controls, more rapidly depressed peripheral white blood cell and granulocyte counts. As expected, nearly all control mice (94.4%) survived irradiation, yet this irradiation was lethal to 45.8% of PML/RARalpha transgenic mice. Lethality was associated with more severe leukopenia in transgenic versus control mice. Retinoic acid treatment of irradiated PML/RARalpha mice enhanced granulocyte recovery. These data suggest that abnormal myelopoiesis due to PML/RARalpha expression is an early event in oncogenic transformation.

Cell type specific and inducible promoters for vectors in gene therapy as an approach for cell targeting

Gene therapy is used to correct genetic defects or to deliver new therapeutic functions to the target cells. Viral vectors are employed mainly as a gene delivery system. A great variety of viral expression systems have been developed and assessed for their ability to transfer genes into somatic cells. In particular, retroviral and adenoviral mediated gene transfer have been extensively studied and improved. Preclinical and clinical studies covering a large range of genetic disorders are currently underway to solve basic issues dealing with gene transfer efficiencies, regulation of gene expression, and potential risks of the use of viral vectors. The majority of clinical gene therapy trials that employ viral vectors perform exvivo gene transfer into target cells. The main issue in potential clinical application of gene therapy is the need for increased gene transfer efficiency and target specificity associated with regulated gene expression at therapeutically relevant levels in vivo. Gene regulatory elements, such as promoters and enhancers, possess cell type specific activities and can be activated by certain induction factors (e.g., hormones, growth factors, cytokines, cytostatics, irradiation, heat shock) via responsive elements. A controlled and restricted expression of these genes can be achieved using such regulatory elements as internal promoters to drive the expression of therapeutic genes in viral vector constructs. In addition to high level and efficient gene expression, minimizing or excluding inappropriate gene expression in surrounding nontarget cells is of great importance for numerous gene therapeutic approaches. This contribution furnishes insight into the field of cell type specific promoter and enhancer systems which have been used for targeted and inducible expression of therapeutic genes in certain genetic disorders, viral infections, and malignancies. We also discuss promoters that represent attractive candidates for the construction of viral vectors.

Identification of Sp1-binding sites in the CD11c (p150,95 alpha) and CD11a (LFA-1 alpha) integrin subunit promoters and their involvement in the tissue-specific expression of CD11c

The leukocyte integrins LFA-1 (CD11a/CD18) and p150,95 (CD11c/CD18) mediate cell-cell and cell-extracellular matrix interactions during inflammatory responses and signal transduction into the cytoplasm. While the CD11a integrin subunit is expressed on all leukocytes, CD11c is almost exclusively expressed on cells of the myeloid lineage and on activated B lymphocytes. Its expression is regulated during cell activation and differentiation by transcriptional mechanisms. We have previously demonstrated that the proximal region of the CD11c promoter directs tissue-restricted and developmentally-regulated expression of reporter genes. Structural studies by electrophoretic mobility shift assays have demonstrated the presence of two Sp1-binding sites at -70 (Sp1-70) and -120 (Sp1-120) which mediate the Sp1 transactivation of the CD11c promoter in Sp1-defective SL2 cells, and which are involved in cell lineage-specific DNA-protein interactions, as demonstrated by footprinting in vivo. More importantly, mutation of either Sp1 site inhibited the activity of the CD11c promoter both in myeloid U937 cells and the CD11c-expressing B lymphoblastoid JY cell line, while the opposite effect was observed in the CD11c-negative epithelial HeLa cell line, demonstrating the involvement of both Sp1-binding sites in the basal and the tissue-restricted expression of the CD11c integrin subunit gene. Interestingly, the analysis of the CD11a proximal promoter also revealed the existence of an Sp1-binding site at -70, indicating a common role for these cis-acting elements in the transcription of the leukocyte integrin alpha subunit genes. The binding of Sp1 to the regulatory regions of the leukocyte integrin genes raises the possibility that the retinoblastoma susceptibility gene product is implicated in integrin expression through its functional interaction with Sp1, thus establishing a link between integrin-dependent leukocyte adhesiveness and the state of cellular differentiation/proliferation.

Regulation of expression of the LFA-1 and p150,95 leukocyte integrins: involvement of the CD11a and CD11c gene promoters

Human Lymphocyte Associated Antigen-1 (LFA-1, CD11a/CD18, alpha L/beta 2) and p150,95 (CD11c/CD18, alpha X/beta 2) are cell surface alpha/beta heterodimers that, together with Mac-1 (CD11b/CD18, alpha M/beta 2) comprise the leukocyte-restricted beta 2 subfamily of integrins. LFA-1 is the only integrin expressed on all leukocyte lineages while p150,95 is exclusively expressed on cells of the myeloid lineage and on activated B lymphocytes and natural killer cells. The expression of the leukocyte integrins is regulated during cell activation and differentiation by transcriptional mechanisms. To dissect the molecular basis for the tissue-restricted and developmentally regulated expression of LFA-1 and p150,95, the promoter regions of their corresponding alpha subunits (CD11a and CD11c) were isolated and functionally characterized. Both promoters lack TATA and CAAT boxes, but exhibit initiator-like sequences at their major transcriptional start sites. Transient expression of CD11a- and CD11c-based reporter gene constructs have demonstrated the involvement of both promoters in the tissue-specific expression of LFA-1 and p150,95. Furthermore, a combination of DNAse I protection experiments and mobility band shift assays have revealed the existence of numerous DNA-protein interactions at the proximal region of both promoters, some of which overlap with consensus binding sequences for known transcription factors and correlate with the pattern of expression of both integrins.

Multiple regulatory elements control the basal promoter activity of the human alpha 4 integrin gene

It has been suggested that expression of the genes encoding the alpha 4/beta 1 integrin increases during wound healing of the cornea. As a first step in understanding the mechanisms required to stimulate alpha 4 gene expression during this process, we defined the minimal upstream sequence required to direct basal promoter activity for this gene. Using deletion analyses of the alpha 4 gene upstream sequence, we identified two functionally important negative regulatory elements. Dimethylsulfate (DMS) methylation interference assays provided evidence for the binding of a single nuclear protein to tandemly repeated homologous cis-acting elements (designated alpha 4.1 and alpha 4.2) from the alpha 4 basal promoter that share the core sequence 5'-GTGGGT-3'. The formation of a protection only at alpha 4.1 in DNase I footprinting suggested that it is the primary target element for the binding of nuclear proteins. Three distinct nuclear proteins bound a double-stranded oligonucleotide bearing the DNA sequence of alpha 4.1 to produce specific DNA-protein complexes (R1 to R3) in gel-shift assays, from which that producing R3 was identified as the protein yielding DNase I protection at alpha 4.1. Detailed mutational analysis of alpha 4.1 and alpha 4.2 indicated that both elements positively regulate gene expression in primary cultures of corneal epithelial cells and Jurkat tissue culture cells, which is consistent with the deletion analysis. However, when transiently transfected into pituitary GH4C1, the alpha 4.2 mutants yielded increased chloramphenicol acetyl transferase activity therefore demonstrating that these elements have the ability to function either as positive or negative regulators of gene transcription in a manner that is dependent on the type of cell transfected.

Cloning and characterization of the promoter region of the murine alpha-4 integrin subunit

To study the differential expression of the murine VLA-4 (alpha 4 beta 1) integrin, the 5'-flanking region of the gene for the alpha subunit (alpha 4m) was isolated and a cDNA for alpha 4m was obtained with reverse transcriptase polymerase chain reaction (RT-PCR). The cDNA sequence contained a difference in the signal peptide region compared to the previously described cDNA (Neuhaus et al., 1991). As a consequence, another start codon is predicted, resulting in a decrease in size of the signal peptide. This was confirmed by genomic sequencing. The promoter region was delimited by ribonuclease protection assay (RPA) and transfection experiments fusing 5'-upstream fragments to the luciferase gene. A fragment extending from -936 to +221 was capable of controlling the expected cell-type-specific expression. Sequence comparison of the mouse alpha 4m promoter region with the human alpha 4h promoter revealed little homology. Like most integrin subunits, alpha 4m lacks TATA anc CCAAT boxes. Putative recognition sites for DNA-binding nuclear factors (AP1, AP2, Sp1, and PU1) were identified. The characterization of the promoter region and further identification of the transcription regulatory elements should provide insight in the regulation of alpha 4m integrin gene expression.

Expression from leukocyte integrin promoters in retroviral vectors

Human gene therapy for diseases involving leukocytes would be facilitated by the identification of specific promoter/enhancer sequences capable of directing high levels of tissue and stage-specific expression of the requisite cDNA when used in a retroviral vector. We tested the promoter sequences from the leukocyte integrin CD11a (LFA-1), CD11b (Mac-1), and CD18 subunits in retroviral vectors to express a reporter gene, adenosine deaminase, in the human leukocyte cell lines K562 and HL-60. The leukocyte integrins are expressed in leukocytes, and they are inducible in HL-60 cells, a model system for myeloid differentiation. Although the leukocyte integrin promoter/enhancer sequences direct the expression of reporter genes in myeloid lineage cell lines in transient transfection assays, in these studies, the leukocyte integrin promoters direct low levels of reporter gene expression following retroviral-mediated transduction in K562 and HL-60 cells and selection of stable integrants. Treatment of HL-60 cells transduced with retroviral vectors containing the leukocyte integrin promoters with retinoic acid or phorbol myristate acetate results in less than a two-fold increase in reporter gene expression. These studies indicate that: (i) expression from the leukocyte integrin promoters from stable integrants in retroviral vectors does not parallel the results observed in transient transfection assays, and (ii) additional promoter/enhancer sequences will likely be required for these promoters to direct high levels of tissue and stage-specific expression in retroviral vectors.

The Krüppel-associated box-A (KRAB-A) domain of zinc finger proteins mediates transcriptional repression

We have previously reported the cloning, sequencing, and partial characterization of Kid-1, a zinc finger-encoding cDNA from the rat kidney. The Kid-1 protein and approximately one-third of all other zinc finger proteins contain a highly conserved region of approximately 75 amino acids at their NH2 terminus named Krüppel-associated box (KRAB), which is subdivided into A and B domains. The evolutionary conservation, wide distribution, and genomic organization of the KRAB domains suggest an important role of this region in the transcriptional regulatory function of zinc finger proteins. The functional significance of the KRAB domain was evaluated by studying transcriptional activities of yeast GAL4-rat Kid-1 fusion proteins containing various regions of the non-zinc-finger domain of Kid-1. Transcriptional repressor activity of GAL4-Kid-1 fusion proteins maps to the KRAB-A domain. The KRAB-A domain of another zinc finger protein, ZNF2, also has repressor activity. Site-directed mutagenesis of conserved amino acids in this motif results in decreased repressor activity. Thus, we have established a functional significance for the KRAB-A domain, a consensus sequence common in zinc finger proteins.

The human beta 2 integrin CD18 promoter consists of two inverted Ets cis elements

To define the minimal promoter responsible for expression of CD18 in myeloid and lymphoid cells, we generated 5' and 3' deletion constructs of a segment extending 785 bp upstream and 19 bp downstream of a major transcription start site and determined their effects on driving expression of the luciferase reporter gene in transfected hematopoietic cell lines. A region extending from nucleotides (nt) -302 to +19 was sufficient for cell-restricted and phorbol ester-inducible expression. DNase I footprinting of this region revealed two adjacent protected segments extending from nt -81 to -68 (box A) and -55 to -41 (box B). When a construct of 47 nt in length containing box A and box B and lacking other 3' or 5' elements was cloned into a promoterless vector, it conferred tissue-specific and phorbol ester-inducible expression. Gel retardation revealed that the protein components of two major protein-DNA complexes that form on both box A and box B and are required for transcriptional activation are members of the Ets oncoprotein family; one is related to the GA-binding protein (GABP), and the other is related to PU.1/Spi-1. The minimal CD18 promoter, lacking TATA, CAAT, and initiator elements and consisting primarily of Ets repeats, may exemplify an emerging class of promoters with which the concerted binding of Ets factors is necessary and sufficient to mediate transcriptional activation through direct recruitment of the basal transcription machinery.

The human beta 2 integrin CD18 promoter consists of two inverted Ets cis elements

To define the minimal promoter responsible for expression of CD18 in myeloid and lymphoid cells, we generated 5' and 3' deletion constructs of a segment extending 785 bp upstream and 19 bp downstream of a major transcription start site and determined their effects on driving expression of the luciferase reporter gene in transfected hematopoietic cell lines. A region extending from nucleotides (nt) -302 to +19 was sufficient for cell-restricted and phorbol ester-inducible expression. DNase I footprinting of this region revealed two adjacent protected segments extending from nt -81 to -68 (box A) and -55 to -41 (box B). When a construct of 47 nt in length containing box A and box B and lacking other 3' or 5' elements was cloned into a promoterless vector, it conferred tissue-specific and phorbol ester-inducible expression. Gel retardation revealed that the protein components of two major protein-DNA complexes that form on both box A and box B and are required for transcriptional activation are members of the Ets oncoprotein family; one is related to the GA-binding protein (GABP), and the other is related to PU.1/Spi-1. The minimal CD18 promoter, lacking TATA, CAAT, and initiator elements and consisting primarily of Ets repeats, may exemplify an emerging class of promoters with which the concerted binding of Ets factors is necessary and sufficient to mediate transcriptional activation through direct recruitment of the basal transcription machinery.

Regulated expression of p150,95 (CD11c/CD18; alpha X/beta 2) and VLA-4 (CD49d/CD29; alpha 4/beta 1) integrins during myeloid cell differentiation

Integrins are a family of cell surface heterodimers which mediate both cell-cell and cell-extracellular matrix interactions and affect cellular differentiation through their signal transduction capacity. Integrin expression is regulated during differentiation as well as by numerous growth factors and cytokines. We have analyzed the changes in p150,95 (CD11c/CD18 or alpha X/beta 2) and VLA-4 (CD49d/CD29 or alpha 4/beta 1) integrin subunits mRNA levels that take place during the myeloid differentiation of HL60 and U937 cells, and compared them to other integrins with similar functional activities. Northern blot analysis revealed that the monocytic differentiation of U937 and HL60 cells alters the alpha X and alpha 4 mRNA steady-state levels: alpha X mRNA is induced de novo whereas alpha 4 mRNA decreases to undetectable levels. Both changes were dependent on the activity of protein kinase C and were also observed upon granulocytic differentiation of HL60 cells. Parallel analysis of other integrin subunits mRNA (beta 1, alpha 5, beta 7) demonstrated that the mRNA levels for the alpha subunits of the fibronectin receptors alpha 4/beta 1 (VLA-4) and alpha 5/beta 1 (VLA-5) are differentially regulated during the monocytic differentiation of myeloid cell lines, and suggested that myeloid cells express a heterodimer formed by the association of beta 7 with an integrin alpha subunit distinct from alpha 4. Nuclear transcription assays and functional analysis of the alpha X and alpha 4 promoter regions demonstrated that the transcription rate of the alpha X gene is considerably elevated after phorbol 12-myristate 13-acetate treatment of U937 cells, while that of alpha 4 is almost unaffected, suggesting that post-transcriptional mechanisms are causing the extremely low alpha 4 mRNA levels observed in differentiated U937 cells.

Identification of cell-specific and developmentally regulated nuclear factors that direct myeloid and lymphoid expression of the CD11a gene

Human CD11a/CD18 is a noncovalently associated heterodimeric receptor expressed exclusively on the surface of lymphocytes and myeloid cells. To begin to understand the mechanisms that direct the expression of the genes encoding this receptor, we have cloned and characterized the promoter region of the CD11a gene and localized cis-acting elements involved in its expression in lymphoid and myeloid cells. One such element is the "LYM" box, which interacts with two sets of DNA-binding activities, one primarily expressed in lymphocytes and preerythroid cells and the other expressed predominantly in myeloid cells. A second element required for expression of the CD11a gene contains the "GAGA" sequence RRRGAGGAAG (R indicates a purine), which interacts with the DNA-binding activities MS-1 and MS-2. MS-1 is expressed exclusively in myeloid cells and probably represents a member of the Ets family of transcription activators. MS-2 is present in epithelial, preerythroid, and lymphoid cells but is only detected in myeloid cells after differentiation. MS-2 also binds to a second element within the CD11a promoter and homologous elements present in the promoter regions of the CD11b and CD43 genes. Since MS-2 interacts with a number of different gene promoters and is developmentally regulated in myeloid cells, it may play a major role in regulating myeloid gene expression.

The murine myeloperoxidase promoter contains several functional elements, one of which binds a cell type-restricted transcription factor, myeloid nuclear factor 1 (MyNF1)

The myeloperoxidase (MPO) gene is expressed specifically in myeloid cells. There is significant homology between the murine and human MPO genes in the 1.6-kb region located upstream of the murine MPO transcription initiation sites. 5',3', and internal deletions of this DNA segment localized several cis-acting DNA elements in the murine MPO promoter which are functional in 32D cl3 cells, a murine myeloblast cell line which expresses MPO. These DNA elements did not function well in mouse L-cell fibroblasts. Additional mutagenesis of the most active promoter region allowed the delimitation of a functional 20-bp segment. Mutation of the enhancer core motif within this segment was functionally deleterious, and an oligonucleotide containing these base pairs increased the activity of a minimal promoter. This same oligonucleotide, but not a mutant variant, could bind a set of nuclear proteins, myeloid nuclear factors 1 alpha and 1 beta (MyNF1 alpha and -1 beta), present in 32D cl3 cells but absent from L cells, murine erythroleukemia cells, and SP2 lymphoid cells.

Kid-1, a putative renal transcription factor: regulation during ontogeny and in response to ischemia and toxic injury

We have identified a new putative transcription factor from the rat kidney, termed Kid-1 (for kidney, ischemia and developmentally regulated gene 1). Kid-1 belongs to the C2H2 class of zinc finger genes. Its mRNA accumulates with age in postnatal renal development and is detected predominantly in the kidney. Kid-1 mRNA levels decline after renal injury secondary to ischemia or folic acid administration, two insults which result in epithelial cell dedifferentiation, followed by regenerative hyperplasia and differentiation. The low expression of Kid-1 early in postnatal development, and when renal tissue is recovering after injury, suggests that the gene product is involved in establishment of a differentiated phenotype and/or regulation of the proliferative response. The deduced protein contains 13 C2H2 zinc fingers at the COOH end in groups of 4 and 9 separated by a 32-amino-acid spacer. There are consensus sites for phosphorylation in the NH2 terminus non-zinc finger region as well as in the spacer region between zinc fingers 4 and 5. A region of the deduced protein shares extensive homology with a catalytic region of Raf kinases, a feature shared only with TFIIE among transcription factors. To determine whether Kid-1 can modulate transcription, a chimeric construct encoding the Kid-1 non-zinc finger region (sense or antisense) and the DNA-binding region of GAL4 was transfected into COS and LLC-PK1 cells together with a chloramphenicol acetyltransferase (CAT) reporter plasmid containing GAL4 binding sites, driven by either a minimal promoter or a simian virus 40 enhancer. CAT activity was markedly inhibited in cells transfected with the sense construct compared with the activity in cells transfected with the antisense construct. To our knowledge, this pattern of developmental regulation, kidney expression, and regulation of transcription is unique among the C2H2 class of zinc finger-containing DNA-binding proteins.

The murine myeloperoxidase promoter contains several functional elements, one of which binds a cell type-restricted transcription factor, myeloid nuclear factor 1 (MyNF1)

The myeloperoxidase (MPO) gene is expressed specifically in myeloid cells. There is significant homology between the murine and human MPO genes in the 1.6-kb region located upstream of the murine MPO transcription initiation sites. 5',3', and internal deletions of this DNA segment localized several cis-acting DNA elements in the murine MPO promoter which are functional in 32D cl3 cells, a murine myeloblast cell line which expresses MPO. These DNA elements did not function well in mouse L-cell fibroblasts. Additional mutagenesis of the most active promoter region allowed the delimitation of a functional 20-bp segment. Mutation of the enhancer core motif within this segment was functionally deleterious, and an oligonucleotide containing these base pairs increased the activity of a minimal promoter. This same oligonucleotide, but not a mutant variant, could bind a set of nuclear proteins, myeloid nuclear factors 1 alpha and 1 beta (MyNF1 alpha and -1 beta), present in 32D cl3 cells but absent from L cells, murine erythroleukemia cells, and SP2 lymphoid cells.

Kid-1, a putative renal transcription factor: regulation during ontogeny and in response to ischemia and toxic injury

We have identified a new putative transcription factor from the rat kidney, termed Kid-1 (for kidney, ischemia and developmentally regulated gene 1). Kid-1 belongs to the C2H2 class of zinc finger genes. Its mRNA accumulates with age in postnatal renal development and is detected predominantly in the kidney. Kid-1 mRNA levels decline after renal injury secondary to ischemia or folic acid administration, two insults which result in epithelial cell dedifferentiation, followed by regenerative hyperplasia and differentiation. The low expression of Kid-1 early in postnatal development, and when renal tissue is recovering after injury, suggests that the gene product is involved in establishment of a differentiated phenotype and/or regulation of the proliferative response. The deduced protein contains 13 C2H2 zinc fingers at the COOH end in groups of 4 and 9 separated by a 32-amino-acid spacer. There are consensus sites for phosphorylation in the NH2 terminus non-zinc finger region as well as in the spacer region between zinc fingers 4 and 5. A region of the deduced protein shares extensive homology with a catalytic region of Raf kinases, a feature shared only with TFIIE among transcription factors. To determine whether Kid-1 can modulate transcription, a chimeric construct encoding the Kid-1 non-zinc finger region (sense or antisense) and the DNA-binding region of GAL4 was transfected into COS and LLC-PK1 cells together with a chloramphenicol acetyltransferase (CAT) reporter plasmid containing GAL4 binding sites, driven by either a minimal promoter or a simian virus 40 enhancer. CAT activity was markedly inhibited in cells transfected with the sense construct compared with the activity in cells transfected with the antisense construct. To our knowledge, this pattern of developmental regulation, kidney expression, and regulation of transcription is unique among the C2H2 class of zinc finger-containing DNA-binding proteins.