Structure and function analysis of the human myeloid cell nuclear differentiation antigen promoter: evidence for the role of Sp1 and not of c-Myb or PU.1 in myelomonocytic lineage-specific expression

Altered recruitment of Sp isoforms to HIV-1 long terminal repeat between differentiated monoblastic cell lines and primary monocyte-derived macrophages

Human immunodeficiency virus type 1 (HIV-1) transcription in cells of the monocyte-macrophage lineage is regulated by interactions between the HIV-1 long terminal repeat (LTR) and a variety of host cell and viral proteins. Binding of the Sp family of transcription factors (TFs) to the G/C box array of the LTR governs both basal as well as activated LTR-directed transcriptional activity. The effect of monocytic differentiation on Sp factor binding and transactivation was examined with respect to the HIV-1 LTR. The binding of Sp1, full-length Sp3 and truncated Sp3 to a high affinity HIV-1 Sp element was specifically investigated and results showed that Sp1 binding increased relative to the binding of the sum of full-length and truncated Sp3 binding following chemically-induced monocytic differentiation in monoblastic (U-937, THP-1) and myelomonocytic (HL-60) cells. In addition, Sp binding ratios from PMA-induced cell lines were shown to more closely approximate those derived from primary monocyte-derived macrophages (MDMs) than did ratios derived from uninduced cell lines. The altered Sp binding phenotype associated with changes in the transcriptional activation mediated by the HIV-1 G/C box array. Additionally, analysis of post-translational modifications on Sp1 and Sp3 revealed a loss of phosphorylation on serine and threonine residues with chemically-induced differentiation indicating that the activity of Sp factors is additionally regulated at the level of post-translational modifications (PTMs).

Transcription factors Sp1 and C/EBP regulate NRAMP1 gene expression

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

Antisense targeting of CXXC finger protein 1 inhibits genomic cytosine methylation and primitive hematopoiesis in zebrafish

CXXC finger protein 1 (CFP1) binds to unmethylated CpG dinucleotides and is a component of the Set1 histone methyltransferase complex. Mice lacking CFP1 suffer a peri-implantation lethal phenotype, and CFP1-deficient embryonic stem cells are viable but unable to differentiate and exhibit a 60-80% decrease in genomic cytosine methylation. A zebrafish homolog of CFP1 has been identified, is approximately 70% similar to murine CFP1, and is widely expressed during development. Zebrafish embryos treated with a zCFP1 antisense morpholino oligonucleotide had little or no circulating red blood cells and exhibited abnormal yolk sac morphology at 48 h post-fertilization. Many of the antisense-treated zebrafish also exhibited cardiac edema, and 14% were dead at 24 h post-fertilization. Morphant zebrafish also exhibited elevated levels of apoptosis, particularly in the intermediate cell mass, the site of primitive erythropoiesis, as well as aberrations in vascular development. Genomic DNA isolated from morphant embryos exhibited a 60% reduction of global genomic cytosine methylation. A similar phenotype was observed with an independent zCFP1 antisense morpholino oligonucleotide, but not following injection of an unrelated control oligonucleotide. The morphant phenotype was rescued when mRNA encoding murine CFP1 was co-injected with the antisense oligonucleotide. Genomic data base analysis reveals the presence of a second version of zebrafish CFP1 (zCFP1b). However, the morphant phenotype observed following specific depletion of zCFP1 indicates that these related genes have nonredundant functions controlling normal zebrafish hematopoiesis and epigenetic regulation. These findings establish the importance of CFP1 during postgastrulation development.

Granulocyte colony-stimulating factor-induced upregulation of Jak3 transcription during granulocytic differentiation is mediated by the cooperative action of Sp1 and Stat3

We previously demonstrated that Jak3 is a primary response gene for G-CSF and ectopic overexpression of Jak3 can accelerate granulocytic differentiation of normal mouse bone marrow cells induced by G-CSF and GM-CSF. To gain insight into the regulation of G-CSF-induced transcription of Jak3, we constructed deletion and linker scanning mutants of the Jak3 promoter sequences and performed luciferase reporter assays in the murine myeloid cell line 32Dcl3, with and without G-CSF stimulation. These experiments showed that mutation of a -67 to -85 element, which contained a putative Sp1 binding site, or mutation of a -44 to -53 GAS element resulted in a marked reduction of Jak3 promoter activity. Electrophoretic mobility shift assays revealed that Sp1 and Stat3 present in nuclear lysates of 32Dcl3 cells stimulated with G-CSF can bind to the -67 to -85 element and -44 to -53 GAS element, respectively. In addition, cotransfection of a constitutively active mutant of Stat3 along with a Jak3 promoter/luciferase reporter resulted in enhanced Jak3 promoter activity. Together, these results demonstrate that activation of Jak3 transcription during G-CSF- induced granulocytic differentiation is mediated by the combined action of Sp1 and Stat3, a mechanism also shown to be important in IL-6-induced monocytic differentiation.

The GRIMs: a new interface between cell death regulation and interferon/retinoid induced growth suppression

Cytokines and vitamins play a central role in controlling neoplastic cell growth. The interferon (IFN) family of cytokines regulates antiviral, anti-tumor, antimicrobial, differentiation, and immune responses in mammals. Significant advances have been made with respect to IFN-induced signal transduction pathways and antiviral responses. However, the IFN-induced anti-tumor actions are poorly defined. Although IFNs themselves inhibit tumor growth, combination of IFNs with retinoids (a class of Vitamin A related compounds) strongly potentiates the IFN-regulated anti-tumor action in a number of cell types. To define the molecular mechanisms involved in IFN/retinoid (RA)-induced apoptosis we have employed a genetic approach and identified several critical genes. In this review, I provide the current picture of IFN- RA- and IFN/RA-regulated growth suppressive pathways. In particular, I focus on a novel set of genes, the genes-associated with retinoid-interferon induced mortality (GRIM). GRIMs may be novel types of tumor suppressors, useful as biological response markers and potentially novel targets for drug development.

Latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus up-regulates transcription of human telomerase reverse transcriptase promoter through interaction with transcription factor Sp1

Telomerase is required for the maintenance of telomere length and is an important determinant for cell immortalization. In human cells, telomerase activity is due to the expression of its enzymatic subunit, human telomerase reverse transcriptase (hTERT). The expression of hTERT is not typically detectable in healthy somatic human cells but is present in cancerous tissues and immortalized cells. We have previously shown that hTERT promoter activity is up-regulated by the Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded latency-associated nuclear antigen (LANA). LANA is expressed in all forms of human malignancies associated with KSHV. The hTERT promoter sequence located at positions -130 to +5 contains several Sp1 binding motifs and was shown be important for up-regulation by LANA. In this report, we demonstrate that hTERT promoter activity is due to the direct interaction of LANA with Sp1. The interaction of LANA with Sp1 was demonstrated through in vitro binding experiments and coimmunoprecipitation and is supported by the colocalization of these two molecules in the nuclei of KSHV-infected cells. Moreover, LANA modulates Sp1-mediated transcription in transient GAL4 fusion reporter assays. Mapping of the regions involved in binding and transcriptional activation showed that the amino terminus of LANA is the major site for interaction and up-regulation but that it can cooperate with the carboxy terminus to enhance these functions. An analysis of Sp1 binding to its cognate sequence corroborated the binding data. Together, our results suggest that the interaction of LANA with Sp1 up-regulates the telomerase promoter, potentially contributing to the immortalization of KSHV-infected cells.

Mechanisms associated with IL-6-induced up-regulation of Jak3 and its role in monocytic differentiation

We report here that Janus kinase 3 (Jak3) is a primary response gene for interleukin-6 (IL-6) in macrophage differentiation, and ectopic overexpression of Jak3 accelerates monocytic differentiation of normal mouse bone marrow cells stimulated with cytokines. Furthermore, we show that incubation of normal mouse bone marrow cells with a JAK3-specific inhibitor results in profound inhibition of myeloid colony formation in response to granulocyte-macrophage colony-stimulating factor or the combination of stem cell factor, IL-3, and IL-6. In addition, mutagenesis of the Jak3 promoter has revealed that Sp1 binding sites within a -67 to -85 element and a signal transducer and activator of transcription (Stat) binding site at position -44 to -53 are critical for activation of Jak3 transcription in murine M1 myeloid leukemia cells stimulated with IL-6. Electrophoretic mobility shift assay (EMSA) analysis has demonstrated that Sp1 can bind to the -67 to -85 element and Stat3 can bind to the -44 to -53 STAT site in IL-6-stimulated M1 cells. Additionally, ectopic overexpression of Stat3 enhanced Jak3 promoter activity in M1 cells. This mechanism of activation of the murine Jak3 promoter in myeloid cells is distinct from a recently reported mechanism of activation of the human JAK3 promoter in activated T cells.

Identification of a novel SP3 binding site in the promoter of human IGFBP4 gene: role of SP3 and AP-1 in regulating promoter activity in CaCo2 cells

Insulin-like growth factor binding protein 4 (IGFBP4/BP4) gene expression plays an important role in the transition from proliferation to differentiation of a human colon cancer cell line, CaCo2. We recently cloned and identified multiple cis elements (including putative binding sites for activator protein 1 (AP-1) and specificity proteins (Sps) ) in the promoter of human BP4 gene, and measured a significant upregulation of the promoter activity in response to c-Jun. We therefore examined the role of the single AP-1 site (-869/-863) and other cis elements, in regulating the expression of hBP4 gene, in the current studies. Deletion of a 25 bp sequence from -872 to -848, which contains the AP-1 site, significantly reduced BP4 promoter activity by approximately 50%. Surprisingly, mutation of the AP-1 site did not produce significant alteration in the activity of the BP4 promoter. However, mutation of 7 bp (5'-TGCTGCA) at the 3' end of the AP-1 site resulted in significantly decreasing the promoter activity by >50%. Proteins bound to the 25 bp probe (-872/-848) could be supershifted by antibodies specific for JunD and Sp3 in an EMSA. JunD binding was abolished on mutation of the AP-1 site and Sp3 binding was abolished on mutation of the 7 bp at -861/-855; binding of the purified Sp3 protein to the 25 bp probe was similarly abolished on mutation of the newly discovered Sp3 binding site (TGCTGCA). BP4 promoter activity was upregulated in insect cells in response to Sp3 expression, confirming a functional importance of the novel Sp3 binding site. These studies suggest that the Sp3 binding site, rather than the AP-1 site, may be playing a significant role in regulating the expression of IGFBP4 gene in CaCo2 cells.

The mouse Ifi200 gene cluster: genomic sequence, analysis, and comparison with the human HIN-200 gene cluster

The interferon-activatable Ifi200 gene cluster is located on mouse Chromosome 1q21-q23. We report here our analysis of two genomic regions encoding at least 10 closely related 200 family genes (Ifi201, Ifi202a, Ifi202b, Ifi202c, Ifi203a, Ifi203b, Ifi203c, Ifi203', Ifi204, and Ifi204') in 129/SvJ mice. Through a BAC-based sequencing approach, the exact structure and organization of these highly similar Ifi200 genes were obtained. A high degree of conservation (99% identity) was observed between Ifi202a and b and between Ifi203a and b. The presence of an additional transcribed region in intron 4 of Ifi203a and b suggests the possibility of alternative splicing, and a spliced variant of the Ifi204' mRNA exhibits 91% sequence identity with a related but unmapped D3 mRNA. Comparative analysis of the mouse and human clusters indicates an absence of significant sequence conservation in noncoding sequences, suggesting that the 200 family emerged prior to human-mouse speciation and subsequently diverged after gene duplication.

Sp1 and C/EBP are necessary to activate the lactoferrin gene promoter during myeloid differentiation

In this study, we sought to identify factors responsible for the positive modulation of lactoferrin (LF), a neutrophil-specific, secondary-granule protein gene. Initial reporter gene transfection assays indicated that the first 89 base pairs of the LF promoter are capable of directing myeloid-specific LF gene expression. The presence of a C/EBP site flanked by 2 Sp1 sites within this segment of the LF promoter prompted us to investigate the possible role of these sites in LF expression. Cotransfection studies of LF-89luc plasmid with increasing concentrations of a C/EBP expression vector in myeloid cells resulted in a linear transactivation of luciferase reporter activity. Electrophoretic mobility shift assays found that the C/EBP site is recognized by C/EBP and that both LF Sp1 binding sites bind the Sp1 transcription factor specifically in myeloid cells. Mutation of either Sp1 site markedly reduced activity of the LF-89luc plasmid in myeloid cells, and neither Sp1 mutant plasmid was transactivated by a C/EBP expression plasmid to the same extent as wild-type LF-89luc. We also transfected LF-89luc into Drosophila Schneider cells, which do not express endogenous Sp1, and demonstrated up-regulation of luciferase activity in response to a cotransfected Sp1 expression plasmid, as well as to a C/EBP expression plasmid. Furthermore, cotransfection of LF-89luc plasmid simultaneously with C/EBP and Sp1 expression plasmids resulted in an increase in luciferase activity greater than that induced by either factor alone. Taken together, these observations indicate a functional interaction between C/EBP and Sp1 in mediating LF expression.

Sp1 and C/EBP are necessary to activate the lactoferrin gene promoter during myeloid differentiation

In this study, we sought to identify factors responsible for the positive modulation of lactoferrin (LF), a neutrophil-specific, secondary-granule protein gene. Initial reporter gene transfection assays indicated that the first 89 base pairs of the LF promoter are capable of directing myeloid-specific LF gene expression. The presence of a C/EBP site flanked by 2 Sp1 sites within this segment of the LF promoter prompted us to investigate the possible role of these sites in LF expression. Cotransfection studies of LF-89luc plasmid with increasing concentrations of a C/EBP expression vector in myeloid cells resulted in a linear transactivation of luciferase reporter activity. Electrophoretic mobility shift assays found that the C/EBP site is recognized by C/EBP and that both LF Sp1 binding sites bind the Sp1 transcription factor specifically in myeloid cells. Mutation of either Sp1 site markedly reduced activity of the LF-89luc plasmid in myeloid cells, and neither Sp1 mutant plasmid was transactivated by a C/EBP expression plasmid to the same extent as wild-type LF-89luc. We also transfected LF-89luc into Drosophila Schneider cells, which do not express endogenous Sp1, and demonstrated up-regulation of luciferase activity in response to a cotransfected Sp1 expression plasmid, as well as to a C/EBP expression plasmid. Furthermore, cotransfection of LF-89luc plasmid simultaneously with C/EBP and Sp1 expression plasmids resulted in an increase in luciferase activity greater than that induced by either factor alone. Taken together, these observations indicate a functional interaction between C/EBP and Sp1 in mediating LF expression.

Immunocytochemical analysis of MNDA in tissue sections and sorted normal bone marrow cells documents expression only in maturing normal and neoplastic myelomonocytic cells and a subset of normal and neoplastic B lymphocytes

The human myeloid cell nuclear differentiation antigen (MNDA) is a nuclear antigen known to be expressed in mature myelomonocytic cell lines. An extensive immunocytochemical evaluation of fixed tissues confirmed MNDA expression in normal maturing granulocytes and monocytes and in acute nonlymphocytic leukemias and chronic myelogenous leukemia. MNDA was not detected in normal tissue histiocytes but was found in activated macrophages and foreign body giant cells associated with inflammation. Flow cytometric cell sorting of normal bone marrow established that MNDA is initially expressed in myeloid blast cells. Examination of lymphoid tissues showed a low level of expression in a population of normal mande B lymphocytes but not in germinal center cells or plasma cells. A subset of B cell neoplasms expressing MNDA included hairy cell leukemia, parafollicular (monocytoid) B cell lymphoma, mantle cell lymphoma, and small lymphocytic lymphoma. Cell sorting of normal bone marrow showed MNDA expression in CD20+/CD10-/CD5- B cells. MNDA was not detected in other normal bone marrow or all other nonhematopoietic cells. The hematopoietic cell-specific pattern of MNDA expression was elucidated through a comprehensive analysis of normal and neoplastic tissues, and the results provide further evidence of the coexpression of B- and myeloid cell markers in neoplastic B cells and identify a normal B cell population that might be related to the cell of origin of a subset of B cell neoplasms.

Role of antimetabolites of purine and pyrimidine nucleotide metabolism in tumor cell differentiation

Transformed cells are characterized by imbalances in metabolic routes. In particular, different key enzymes of nucleotide metabolism and DNA biosynthesis, such as CTP synthetase, thymidylate synthase, dihydrofolate reductase, IMP dehydrogenase, ribonucleotide reductase, DNA polymerase, and DNA methyltransferase, are markedly up-regulated in certain tumor cells. Together with the concomitant down-modulation of the purine and pyrimidine degradation enzymes, the increased anabolic propensity supports the excessive proliferation of transformed cells. However, many types of cancer cells have maintained the ability to differentiate terminally into mature, non-proliferating cells not only in response to physiological receptor ligands, such as retinoic acid, vitamin D metabolites, and cytokines, but also following exposure to a wide variety of non-physiological agents such as antimetabolites. Interestingly, induction of tumor cell differentiation is often associated with reversal of the transformation-related enzyme deregulations. An important class of differentiating compounds comprises the antimetabolites of purine and pyrimidine nucleotide metabolism and nucleic acid synthesis, the majority being structural analogs of natural nucleosides. The CTP synthetase inhibitors cyclopentenylcytosine and 3-deazauridine, the thymidylate synthase inhibitor 5-fluoro-2'-deoxyuridine, the dihydrofolate reductase inhibitor methotrexate, the IMP dehydrogenase inhibitors tiazofurin, ribavirin, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and mycophenolic acid, the ribonucleotide reductase inhibitors hydroxyurea and deferoxamine, and the DNA polymerase inhibitors ara-C, 9-(2-phosphonylmethoxyethyl)adenine (PMEA), and aphidicolin, as well as several nucleoside analogs perturbing the DNA methylation pattern, have been found to induce tumor cell differentiation through impairment of DNA synthesis and/or function. Thus, by selectively targeting those anabolic enzymes that contribute to the neoplastic behavior of cancer cells, the normal cellular differentiation program may be reactivated and the malignant phenotype suppressed.

The Ifi 200 genes: an emerging family of IFN-inducible genes

The biological activities of interferons (IFNs) are mediated by IFN-induced proteins. One family is encoded by several structurally related genes located on murine chromosome 1 (Ifi 200 cluster) and three homologous genes (MNDA, IFI 16 and AIM2) located on human chromosome 1 as well, within a linkage group highly conserved between mouse and human. All the proteins of this family contain at least one copy of a conserved 200 amino acid domain, in addition to other regions that are different or missing among the various family members. Conservation of the 200 amino acid segment, therefore, may be responsible for a common function, while individually expressed domains may afford other tissue- or cell-specific functions. The data available demonstrate that at least two members of the Ifi 200 protein family, p202 and p204, inhibit cell proliferation in vitro. Moreover, high constitutive levels of p204 expression impair normal embryo development in transgenic animals. Here, we will review the principal features of murine and human proteins belonging to this family and their function in the cell growth-regulatory activities mediated by IFNs.