The macrophage and B cell-specific transcription factor PU.1 is related to the ets oncogene

The natural resistance-associated macrophage protein 1 Slc11a1 (formerly Nramp1) and iron metabolism in macrophages

Slc11a1 (solute carrier family 11 member 1) (formerly Nramp1) modulation of iron metabolism in macrophages plays an important role in early phase macrophage activation, and therefore host innate immunity. This review focuses on the role of Nramp1 in intramacrophage iron metabolism, with emphasis on the two prevailing mechanisms of Nramp1 modulation of iron metabolism in macrophages.

High-dose chemoradiotherapy (HDC) in the Ewing family of tumors (EFT)

EFT is defined by the expression of ews/ets fusion genes. The type of the fusion transcript impacts on the clinical biology. EFT requires risk adapted treatment. A risk-adapted treatment is determined by tumor localisation, tumor stage and volume. For metastatic and relapsed disease the pattern of spread and the time of relapse are the determinants of risk stratification. Staging of Ewing tumors has been considerably improved by magnetic resonance imaging and modern isotope scanning techniques. However, the determination of the extent of the metastatic spread in particular number of involved bones remains an unresolved issue. The prognosis for high-risk Ewing tumors has been improved by multimodal and high-dose radio/chemotherapy (HDC). The concepts for high-dose therapy in Ewing tumors are based on dose response and dose intensity relationships. In single agent HDC most experience exists with Melphalan. Several chemotherapeutic agents have been used in combination HDC with or without TBI such as Adriamycin, BCNU, Busulphan, Carboplatin, Cyclophosphamide, Etoposide, Melphalan, Thiotepa Procarbazin and Vincristine. To date, superiority of any high-dose chemotherapy regimen has not been established. However, the clinical biology, the pattern of spread and the time of relapse determine the prognosis of patient who are eligible for HDC. In particular, patients with multifocal bone or bone marrow metastases have a poorer prognosis than patients with lung metastases. In addition, patients with a relapse within 24 months have a poorer prognosis than patients with a relapse later than 24 months after diagnosis. This review will analyze the results of single- and multi-agent chemotherapy with respect to agent combination, dose and risk stratum of patient population. Future therapeutic modalities for the treatment of EFT might encompass immunotherapeutic and genetic strategies including allogeneic stem cell transplantation.

PU.1 is involved in the regulation of B lineage-associated and developmental stage-dependent expression of the germinal center-associated DNA primase GANP

Germinal center-associated DNA primase (GANP) associated with MCM3 of the DNA replication complex is up-regulated selectively in germinal center B cells. We studied promoter activity of the 5' region involved in the developmental stage-dependent expression in B lineage cells by luciferase reporter assay. Selective regulation of ganp expression was observed in the -737-bp promoter region in B and plasma cell lines but was significantly low in pre-B and T cell lines. The deletion constructs displayed a gap decrease after shortening the region from -134 to -108 bp. Further narrowing suggested the involvement of the PU.1 consensus sequence at -126 bp by electrophoretic mobility shift assay. The protein component PU.1 complex is not inhibited with mutated probes at the consensus site but is inhibited with the known PU.1 probe of CD72 and with anti-PU.1 antibody. Moreover, introduction of PU.1 cDNA enhanced the reporter gene activity in a dose-dependent manner in B cells, whereas the reporter construct with the mutated PU.1 site did not respond. Anti-CD40 stimulation induced the reporter activity with a 100% increase, which is not observed with the PU.1-mutated reporter construct. These results demonstrate that the germinal center-associated DNA primase expression is partly regulated by the transcription factor PU.1 expressed in B lineage cells.

The pattern of gene expression in human CD34(+) stem/progenitor cells

We have analyzed the pattern of gene expression in human primary CD34(+) stem/progenitor cells. We identified 42,399 unique serial analysis of gene expression (SAGE) tags among 106,021 SAGE tags collected from 2.5 x 10(6) CD34(+) cells purified from bone marrow. Of these unique SAGE tags, 21,546 matched known expressed sequences, including 3,687 known genes, and 20,854 were novel without a match. The SAGE tags that matched known sequences tended to be at higher levels, whereas the novel SAGE tags tended to be at lower levels. By using the generation of longer sequences from SAGE tags for gene identification (GLGI) method, we identified the correct gene for 385 of 440 high-copy SAGE tags that matched multiple genes and we generated 198 novel 3' expressed sequence tags from 138 high-copy novel SAGE tags. We observed that many different SAGE tags were derived from the same genes, reflecting the high heterogeneity of the 3' untranslated region in the expressed genes. We compared the quantitative relationship for genes known to be important in hematopoiesis. The qualitative identification and quantitative measure for each known gene, expressed sequence tag, and novel SAGE tag provide a base for studying normal gene expression in hematopoietic stem/progenitor cells and for studying abnormal gene expression in hematopoietic diseases.

Regulation of the PU.1 gene by distal elements

The transcription factor PU.1 (also known as Spi-1) plays a critical role in the development of the myeloid lineages, and myeloid cells derived from PU.1(-/-) animals are blocked at the earliest stage of myeloid differentiation. Expression of the PU.1 gene is tightly regulated during normal hematopoietic development, and dysregulation of PU.1 expression can lead to erythroleukemia. However, relatively little is known about how the PU.1 gene is regulated in vivo. Here it is shown that myeloid cell type-specific expression of PU.1 in stable cell lines and transgenic animals is conferred by a 91-kilobase (kb) murine genomic DNA fragment that consists of the entire PU.1 gene (20 kb) plus approximately 35 kb of upstream and downstream sequences, respectively. To further map the important transcriptional regulatory elements, deoxyribonuclease I hypersensitive site mapping studies revealed at least 3 clusters in the PU.1 gene. A 3.5-kb fragment containing one of these deoxyribonuclease I hypersensitive sites, located -14 kb 5' of the transcriptional start site, conferred myeloid cell type-specific expression in stably transfected cell lines, suggesting that within this region is an element important for myeloid specific expression of PU.1. Further analysis of this myeloid-specific regulatory element will provide insight into the regulation of this key transcriptional regulator and may be useful as a tool for targeting expression to the myeloid lineage.

Loss of PU.1 expression following inhibition of histone deacetylases

Altering chromatin structure by blocking histone deacetylase activity with specific inhibitors such as trichostatin A can result in an up-regulation of gene expression. In this report, however, we show that expression of the ETS domain transcription factor PU.1 is down-regulated in cells following the addition of trichostatin A. The loss of PU.1 is seen at both the mRNA and protein levels in multiple cell lines and is reversible following removal of the drug. More importantly, we show that the loss of PU.1 results in a loss of PU.1 target gene expression, including CD11b, c-fms, Toll-like receptor 4, and scavenger receptor. Chromatin immunoprecipitation analysis of cells treated with trichostatin A showed a significant increase in the acetylation of histone H4, but not histone H3, across approximately 650 bp of the PU.1 promoter region. Our data suggest that the consequences of using drugs that inhibit histone deacetylase activity may be a loss of blood cell development and/or function due to a block in PU.1 gene expression.

Unique function for carboxyl-terminal domain of Oct-2 in Ig-secreting cells

The activity of Ig gene promoters and enhancers is regulated by two related transcription factors, Oct-1 (ubiquitous) and Oct-2 (B lineage specific), which bind the octamer motif (ATTTGCAT) present in these elements. As Ig promoter-binding factors, Oct-1 and Oct-2 each work together with a B lymphocyte-specific cofactor OCA-B/OBF-1/Bob-1 that interacts with them through their POU (DNA-binding) domains. Because both can mediate Ig promoter activity in B cells, there has been some question as to whether these two octamer-binding factors serve distinct functions in lymphocytes. We have shown previously that the silencing of B lymphocyte-specific genes in plasmacytoma x T lymphoma hybrids can be prevented by preserving Oct-2 expression. The pronounced effect of this transcription factor on the phenotype of plasmacytoma x T lymphoma hybrids established a critical role for Oct-2 not only in maintaining Ig gene expression, but in maintaining the overall genetic program of Ig-secreting cells. In the present study, we have explored the functional differences between Oct-1 and Oct-2 using chimeric Oct-1/Oct-2 proteins in cell fusion assays. Our results provide further evidence for an essential role for Oct-2 in Ig-secreting cells and identify the C-terminal domain of Oct-2 as responsible for its unique function in these cells.

SHP1 protein-tyrosine phosphatase inhibits gp91PHOX and p67PHOX expression by inhibiting interaction of PU.1, IRF1, interferon consensus sequence-binding protein, and CREB-binding protein with homologous Cis elements in the CYBB and NCF2 genes

The CYBB and NCF2 genes encode the phagocyte respiratory burst oxidase proteins, gp91PHOX and p67PHOX. Previously, we identified homologous CYBB and NCF2 cis elements that are necessary for lineage-specific transcription during late myeloid differentiation. We determined that these homologous cis elements are activated by PU.1, IRF1, interferon consensus sequence-binding protein (ICSBP), and the CREB-binding protein (CBP). Since expression of PU.1 and ICSBP is lineage-restricted, our investigations identified a mechanism of lineage-specific CYBB and NCF2 transcription. Since PU.1, IRF1, ICSBP, and CBP are expressed in undifferentiated myeloid cells, our investigations did not determine the mechanism of differentiation stage-specific CYBB and NCF2 transcription. In the current investigations, we determine that SHP1 protein-tyrosine phosphatase (SHP1-PTP) inhibits gp91PHOX and p67PHOX expression, in undifferentiated myeloid cell lines, by decreasing interaction of PU.1, IRF1, ICSBP, and CBP with the CYBB and NCF2 genes. We also determine that IRF1 and ICSBP are tyrosine-phosphorylated during interferon gamma differentiation of myeloid cell lines, and we identify IRF1 and ICSBP tyrosine residues that are necessary for CYBB and NCF2 transcription. Therefore, these investigations identify a novel mechanism by which SHP1-PTP antagonizes myeloid differentiation and determine that tyrosine phosphorylation of IRF1 and ICSPB mediates stage-specific transcriptional activation in differentiating myeloid cells.

PU.1/Spi-B regulation of c-rel is essential for mature B cell survival

PU.1(+/-)Spi-B(-/-) mice exhibit reduced numbers of immature and mature B lymphocytes, which exhibit severe defects in response to BCR-mediated stimulation and poor survival. We found that expression of c-rel, a member of the Rel/NF-kappa B family, is dramatically reduced in PU.1(+/-)Spi-B(-/-) splenic B cells. Analysis of the murine c-rel promoter identified three PU.1/Spi-B binding sites critical for c-rel promoter activity. Furthermore, reintroduction of Rel protein restored wild-type B cell numbers to mice reconstituted with PU.1(+/-)Spi-B(-/-) bone marrow. These findings are the first to demonstrate that a member of the Rel/NF-kappa B family is directly regulated by Ets proteins and dissect the molecular basis for the function of two Ets factors, PU.1 and Spi-B, in promoting B lymphocyte survival.

GM-CSF regulates alveolar macrophage differentiation and innate immunity in the lung through PU.1

GM-CSF gene targeted (GM(-/-)) mice are susceptible to respiratory infections and develop alveolar proteinosis due to defects in innate immune function and surfactant catabolism in alveolar macrophages (AMs), respectively. Reduced cell adhesion, phagocytosis, pathogen killing, mannose- and Toll-like receptor expression, and LPS- or peptidoglycan-stimulated TNFalpha release were observed in AMs from GM(-/-) mice. The transcription factor PU.1 was markedly reduced in AMs of GM(-/-) mice in vivo and was restored by selective expression of GM-CSF in the lungs of SPC-GM/GM(-/-) transgenic mice. Retrovirus-mediated expression of PU.1 in AMs from GM(-/-) mice rescued host defense functions and surfactant catabolism by AMs. We conclude that PU.1 mediates GM-CSF-dependent effects on terminal differentiation of AMs regulating innate immune functions and surfactant catabolism by AMs.

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.

In vivo complex formation of PU.1 with HDAC1 associated with PU.1-mediated transcriptional repression

We previously reported that overexpression of PU.1, a member of the Ets family of transcription factors, induces differentiation inhibition and apoptosis associated with c-Myc down-regulation in murine erythroleukemia (MEL) cells. To understand the molecular mechanism by which c-Myc is down-regulated due to overexpression of PU.1, we performed luciferase reporter assays using the mouse c-myc promoter. PU.1 repressed the activities of not only the c-myc promoter but also several other promoters. Experiments with deletion mutants of PU.1 revealed that the C-terminal region spanning amino acids (aa) 123-272 including the PEST and ETS domains but not the activation domain was sufficient for this transcriptional repression. It was unlikely that the repression was due to sequestration of a limited amount of CBP/p300 nor pCAF, because overexpression of these co-activators did not relieve PU.1-mediated transcriptional repression. Instead, it was found that the C-terminal aa 101-272 of PU.1 formed a complex with mSin3A and HDAC1 in vivo, which was speculated to be associated with the repression. The C-terminal region of PU.1 also formed a complex with the basic transcription factor TBP in vitro and in vivo. Our results suggest that overexpression of PU.1 induces transcriptional repression in several gene promoters including the c-myc promoter which may be mediated by its complex formation with HDACs.

Allelic loss on chromosome 4 (Lyr2/TLSR5) is associated with myeloid, B-lympho-myeloid, and lymphoid (B and T) mouse radiation-induced leukemias

The CBA/H mouse model of radiation-induced acute myeloid leukemia (AML) was re-examined using molecular approaches. In addition to the typical promyelocytic AMLs, 34% were reclassified as early pre-B lympho-myeloid leukemias (L-ML) based on leukemic blood cell morphology, immunoglobulin heavy-chain gene re-arrangements (IgH(R)), or expression of both lymphoid (Vpre-B1 and Rag1) and myeloid (myeloperoxidase and lysozyme M) genes. Allelic loss on chromosome 4 was frequently detected in AMLs (53%) and L-MLs (more than 95%), and the preferential loss of the maternally transmitted allele suggests the locus may be imprinted. A minimally deleted region (MDR) maps to a 3.4-cM interval, which is frequently deleted in radiation-induced thymic lymphomas (TLSR5) and contains a recessive, maternally transmitted genetic locus (Lyr2) that confers resistance to spontaneous and radiation-induced pre-B and T cell lymphomas, suggesting they are one and the same. Thus, the Lyr2/TLSR5 locus is frequently implicated in myeloid, lymphoid (B and T), and mixed-lineage mouse leukemias and lymphomas. Epigenetic inactivation of one Lyr2/TLSR5 allele during normal mouse development suggests that only a single hit is required for its inactivation during leukemogenesis, and this may be a significant contributing factor to the efficiency of the leukemogenic process in the mouse.

B cell development pathways

B cell development is a highly regulated process whereby functional peripheral subsets are produced from hematopoietic stem cells, in the fetal liver before birth and in the bone marrow afterward. Here we review progress in understanding some aspects of this process in the mouse bone marrow, focusing on delineation of the earliest stages of commitment, on pre-B cell receptor selection, and B cell tolerance during the immature-to-mature B cell transition. Then we note some of the distinctions in hematopoiesis and pre-B selection between fetal liver and adult bone marrow, drawing a connection from fetal development to B-1/CD5(+) B cells. Finally, focusing on CD5(+) cells, we consider the forces that influence the generation and maintenance of this distinctive peripheral B cell population, enriched for natural autoreactive specificities that are encoded by particular germline V(H)-V(L) combinations.

Characterization of the human Fc gamma RIIB gene promoter: human zinc-finger proteins (ZNF140 and ZNF91) that bind to different regions function as transcription repressors

Expression of the human low-affinity Fc receptors for IgG (human Fc gamma RII) is differentially regulated. We report here the characterization of the promoter structure of the human Fc gamma RIIB gene and the isolation of the promoter region-binding proteins by a yeast one-hybrid assay. The minimal 154-bp region upstream from the transcription start site of the human Fc gamma RIIB gene was shown to possess promoter activity in a variety of cells. An electrophoretic mobility shift assay indicated that multiple nuclear factors in cell extracts bind to the two regions [F2-3 (-110 to -93) and F4-3 (-47 to -31)] of the human Fc gamma RIIB gene promoter. Mutation analysis indicated that GGGAGGAGC (-105 to -97) and AATTTGTTTGCC (-47 to -36) sequences are responsible for binding to nuclear factors respectively. By using GGGAGGAGC and AATTTGTTTGCC as bait sequences, we cloned two zinc-finger proteins (ZNF140 and ZNF91) that bind to the F2-3 and F4-3 regions within the promoter of the human Fc gamma RIIB gene respectively. When the ZNF140 and ZNF91 were transfected with reporter plasmid, both showed repressor activity with additive effects. Thus, these results indicate that these cloned ZNF140 and ZNF91 proteins function as repressors for the human Fc gamma RIIB transcription.

Dendritic cell potentials of early lymphoid and myeloid progenitors

It has been proposed that there are at least 2 classes of dendritic cells (DCs), CD8alpha(+) DCs derived from the lymphoid lineage and CD8alpha(-) DCs derived from the myeloid lineage. Here, the abilities of lymphoid- and myeloid-restricted progenitors to generate DCs are compared, and their overall contributions to the DC compartment are evaluated. It has previously been shown that primitive myeloid-committed progenitors (common myeloid progenitors [CMPs]) are efficient precursors of both CD8alpha(+) and CD8alpha(-) DCs in vivo. Here it is shown that the earliest lymphoid-committed progenitors (common lymphoid progenitors [CLPs]) and CMPs and their progeny granulocyte-macrophage progenitors (GMPs) can give rise to functional DCs in vitro and in vivo. CLPs are more efficient in generating DCs than their T-lineage descendants, the early thymocyte progenitors and pro-T cells, and CMPs are more efficient DC precursors than the descendant GMPs, whereas pro-B cells and megakaryocyte-erythrocyte progenitors are incapable of generating DCs. Thus, DC developmental potential is preserved during T- but not B-lymphoid differentiation from CLP and during granulocyte-macrophage but not megakaryocyte-erythrocyte development from CMP. In vivo reconstitution experiments show that CLPs and CMPs can reconstitute CD8alpha(+) and CD8alpha(-) DCs with similar efficiency on a per cell basis. However, CMPs are 10-fold more numerous than CLPs, suggesting that at steady state, CLPs provide only a minority of splenic DCs and approximately half the DCs in thymus, whereas most DCs, including CD8alpha(+) and CD8alpha(-) subtypes, are of myeloid origin. (Blood. 2001;97:3333-3341)

c-Myc is a critical target for c/EBPalpha in granulopoiesis

CCAAT/enhancer binding protein alpha (C/EBPalpha) is an integral factor in the granulocytic developmental pathway, as myeloblasts from C/EBPalpha-null mice exhibit an early block in differentiation. Since mice deficient for known C/EBPalpha target genes do not exhibit the same block in granulocyte maturation, we sought to identify additional C/EBPalpha target genes essential for myeloid cell development. To identify such genes, we used both representational difference analysis and oligonucleotide array analysis with RNA derived from a C/EBPalpha-inducible myeloid cell line. From each of these independent screens, we identified c-Myc as a C/EBPalpha negatively regulated gene. We mapped an E2F binding site in the c-Myc promoter as the cis-acting element critical for C/EBPalpha negative regulation. The identification of c-Myc as a C/EBPalpha target gene is intriguing, as it has been previously shown that down-regulation of c-Myc can induce myeloid differentiation. Here we show that stable expression of c-Myc from an exogenous promoter not responsive to C/EBPalpha-mediated down-regulation forces myeloblasts to remain in an undifferentiated state. Therefore, C/EBPalpha negative regulation of c-Myc is critical for allowing early myeloid precursors to enter a differentiation pathway. This is the first report to demonstrate that C/EBPalpha directly affects the level of c-Myc expression and, thus, the decision of myeloid blasts to enter into the granulocytic differentiation pathway.

The regulation of CD5 expression in murine T cells

BACKGROUND

CD5 is a pan-T cell surface marker that is also present on a subset of B cells, B-1a cells. Functional and developmental subsets of T cells express characteristic CD5 levels that vary over roughly a 30-fold range. Previous investigators have cloned a 1.7 Kb fragment containing the CD5 promoter and showed that it can confer similar lymphocyte-specific expression pattern as observed for endogenous CD5 expression.

RESULTS

We further characterize the CD5 promoter and identify minimal and regulatory regions on the CD5 promoter. Using a luciferase reporter system, we show that a 43 bp region on the CD5 promoter regulates CD5 expression in resting mouse thymoma EL4 T cells and that an Ets binding site within the 43 bp region mediates the CD5 expression. In addition, we show that Ets-1, a member of the Ets family of transcription factors, recognizes the Ets binding site in the electrophoretic mobility shift assay (EMSA). This Ets binding site is directly responsible for the increase in reporter activity when co-transfected with increasing amounts of Ets-1 expression plasmid.We also identify two additional evolutionarily-conserved regions in the CD5 promoter (CD5X and CD5Y) and demonstrate the respective roles of the each region in the regulation of CD5 transcription.

CONCLUSION

Our studies define a minimal and regulatory promoter for CD5 and show that the CD5 expression level in T cells is at least partially dependent on the level of Ets-1 protein. Based on the findings in this report, we propose a model of CD5 transcriptional regulation in T cells.

PU.1 exhibits partial functional redundancy with Spi-B, but not with Ets-1 or Elf-1

Previously it was shown that the Ets proteins, PU.1 and Spi-B, exhibit functional redundancy in B lymphocytes. To investigate the possibility that PU.1 or Spi-B or both share overlapping roles with Ets-1 or Elf-1, PU.1(+/-)Ets-1(-/-), PU.1(+/-)Elf-1(-/-), and Spi-B(-/-)Ets-1(-/-) animals were generated. No blood cell defects were observed in these animals except those previously reported for Ets-1(-/-) mice. Therefore, no genetic overlap was detected between PU.1 or Spi-B with Ets-1 or Elf-1. In contrast, the results confirmed functional redundancy for PU.1 and Spi-B in that PU.1(+/-)Spi-B(-/-) bone marrow progenitors yielded smaller colonies in methylcellulose cultures than did wild-type, PU.1(+/-) or Spi-B(-/-) progenitors. In addition, PU.1(+/-)Spi-B(+/+), PU.1(+/-)Spi-B(+/-), and PU.1(+/-) Spi-B(-/-) mice displayed extramedullary splenic hematopoiesis. In summary, PU.1 and Spi-B regulate common target genes required for proliferation of hematopoietic progenitors or their committed descendants, whereas Ets-1 or Elf-1 do not appear to regulate shared target genes with PU.1 or Spi-B.

Stable transfection of the bovine NRAMP1 gene into murine RAW264.7 cells: effect on Brucella abortus survival

Genetically based natural resistance to brucellosis in cattle provides for novel strategies to control zoonotic diseases. Bovine NRAMP1, the homologue of a murine gene (Bcg), has been identified as a major candidate for controlling the in vivo resistant phenotype. We developed an in vitro model for expression of resistance- and susceptibility-associated alleles of bovine NRAMP1 as stable transgenes under the regulatory control of the bovine NRAMP1 promoter in the murine RAW264.7 macrophage cell line (Bcg(s)) to analyze the regulation of the NRAMP1 gene and its role in macrophage function. We demonstrated that the 5'-flanking region of bovine NRAMP1, despite the lack of TATA and CAAT boxes, has a functional promoter capable of driving the expression of a transgene in murine macrophages. A polymorphism within a microsatellite in the 3' untranslated region critically affects the expression of bovine NRAMP1 and the control of in vitro replication of Brucella abortus but not Salmonella enterica serovar Dublin. We did not observe any differences in the production of NO by resting or gamma interferon (IFN-gamma)- and IFN-gamma-lipopolysaccharide (LPS)-treated transfected cell lines, yet the resistant transfected cell lines produced significantly less NO than other cell lines, following stimulation with LPS at 24 and 48 h.

Myeloblastin is an Myb target gene: mechanisms of regulation in myeloid leukemia cells growth-arrested by retinoic acid

A pivotal role has been assigned to Myb in the control of myeloid cell growth. Although Myb is a target of retinoic acid, little is known about the mechanisms by which it may contribute to induced growth arrest in leukemia cells. Indeed, few Myb target genes are known to be linked to proliferation. Myeloblastin is involved in the control of proliferation in myeloid leukemia cells. It is expressed early during hematopoiesis and is a granulocyte colony-stimulating factor-responsive gene. Myeloblastin can confer factor-independent growth to hematopoietic cells, an early step in leukemia transformation. The myeloblastin promoter contains PU.1, C/EBP, and Myb binding sites, each of which are critical for constitutive expression in myeloid cells. Inhibition of myeloblastin expression in leukemia cells growth-arrested by retinoic acid is demonstrated to depend on Myb down-regulation. Myb is shown to induce myeloblastin expression and abolish its down-regulation by retinoic acid. Altogether, the data offer a clue as to how a myeloid-specific transcriptional machinery can be accessible to regulation by retinoic acid and point to myeloblastin as a novel target of Myb. This link between Myb and myeloblastin suggests a previously nonidentified Myb pathway through which growth arrest is induced by retinoic acid in myeloid leukemia cells.

Lineage switch induced by overexpression of Ets family transcription factor PU.1 in murine erythroleukemia cells

PU.1 is an Ets family transcription factor essential for myelomonocyte and B-cell development. We previously showed that overexpression of PU.1 in murine erythroleukemia (MEL) cells inhibits growth and erythroid differentiation and induces apoptosis of the cells. In an effort to identify target genes of PU.1 concerning these phenomena by using a messenger RNA differential display strategy, we found that some myeloid-specific and lymphoid-specific genes, such as the osteopontin gene, are transcriptionally up-regulated in MEL cells after overexpression of PU.1. We then found that expression of several myelomonocyte-specific genes, including the CAAT-enhancer-binding protein-alpha and granulocyte-macrophage colony-stimulating factor receptor genes, was induced in MEL cells after overexpression of PU.1. B-cell-specific genes were also examined, and expression of the CD19 gene was found to be induced. Expression of the myelomonocyte-specific proteins CD11b and F4/80 antigen but not the B-cell-specific proteins B220 and CD19 was also induced. After overexpression of PU.1, MEL cells became adherent and phagocytic and showed enhanced nitroblue tetrazolium reduction activity. Expression of myelomonocyte-specific and B-cell-specific genes was not induced when a mutant PU.1 with part of the activation domain deleted (a change found to inhibit erythroid differentiation of MEL cells) was expressed. These results indicate that PU.1 induces a lineage switch in MEL cells toward myelomonocytic cells and that its activation domain is essential for this effect. The results also suggest that the pathway of the lineage switch is distinct from that of inhibition of erythroid differentiation in MEL cells.

Transcription factor regulation of B lineage commitment

The past year has provided insight into the mechanisms by which multipotent progenitors commit to differentiation through the B lymphocyte lineage. Mice lacking the Pax5 gene develop pro-B lymphocytes but these cells are not uniquely committed to the B lineage as they can give rise to all hematopoietic cell types if cultured under appropriate conditions. Regulators of lymphocyte proliferation and survival have also been identified that may allow lymphocytes to respond to information provided by the external environment.

MLL and CREB bind cooperatively to the nuclear coactivator CREB-binding protein

A fragment of the mixed-lineage leukemia (MLL) gene (Mll, HRX, ALL-1) was identified in a yeast genetic screen designed to isolate proteins that interact with the CREB-CREB-binding protein (CBP) complex. When tested for binding to CREB or CBP individually, this MLL fragment interacted directly with CBP, but not with CREB. In vitro binding experiments refined the minimal region of interaction to amino acids 2829 to 2883 of MLL, a potent transcriptional activation domain, and amino acids 581 to 687 of CBP (the CREB-binding or KIX domain). The transactivation activity of MLL was dependent on CBP, as either adenovirus E1A expression, which inhibits CBP activity, or alteration of MLL residues important for CBP interaction proved effective at inhibiting MLL-mediated transactivation. Single amino acid substitutions within the MLL activation domain revealed that five hydrophobic residues, potentially forming a hydrophobic face of an amphipathic helix, were critical for the interaction of MLL with CBP. Using purified components, we found that the MLL activation domain facilitated the binding of CBP to phosphorylated CREB. In contrast with paradigms in which factors compete for limiting quantities of CBP, these results reveal that two distinct transcription factor activation domains can cooperatively target the same motif on CBP.

Suppression of Il-12 transcription in macrophages following Fc gamma receptor ligation

Ligating Fc gamma R on macrophages results in suppression of IL-12 production. We show that Fc gamma R ligation selectively down-regulates IL-12 p40 and p35 gene expression at the level of transcription. The region responsive to this inhibition maps to the Ets site of the p40 promoter. PU.1, IFN consensus sequence binding protein, and c-REL: form a complex on this element upon macrophage activation. Receptor ligation abolishes the binding of this PU.1-containing activation complex, and abrogates p40 transcription. A dominant-negative construct of PU.1 diminishes IL-12 p40 promoter activity and endogenous IL-12 p40 protein secretion. Thus, the specificity of IL-12 down-regulation following receptor ligation lies in the inhibition of binding of a PU.1-containing complex to the Ets site of the IL-12 promoter. These findings provide evidence demonstrating for the first time the importance of PU.1 in the transcriptional regulation of IL-12 gene expression.

PU.1-mediated transcription is enhanced by HMG-I(Y)-dependent structural mechanisms

The ets transcription factor PU.1 is an important regulator of the immunoglobulin heavy chain gene intronic enhancer, or mu enhancer. However, PU.1 is only one component of the large multiprotein complex required for B cell-specific enhancer activation. The transcriptional coactivator HMG-I(Y), a protein demonstrated to physically interact with PU.1, increases PU.1 affinity for the mu enhancer muB element, indicating that HMG-I(Y) may play a role in the transcriptionally active mu enhanceosome. Increased PU.1 affinity is not mediated by HMG-I(Y)-induced changes in DNA structure. Investigation of alternative mechanisms to explain the HMG-I(Y)-mediated increase in PU.1/mu enhancer binding demonstrated, by trypsin and chymotrypsin mapping, that interaction between PU.1 and HMG-I(Y) in solution induces a structural change in PU.1. In the presence of HMG-I(Y) and wild-type mu enhancer DNA, PU.1 becomes more chymotrypsin resistant, suggesting an additional change in PU.1 structure upon HMG-I(Y)-induced PU.1/DNA binding. From these results, we suggest that increased DNA affinity under limiting PU.1 concentrations is mediated by an HMG-I(Y)-induced structural change in PU.1. In functional assays, HMG-I(Y) further augments transcriptional synergy between PU.1 and another member of the ets family, Ets-1, indicating that HMG-I(Y) is a functional component of the active enhancer complex. These studies suggest a new mechanism for HMG-I(Y)-mediated coactivation; HMG-I(Y) forms protein-protein interactions with a transcription factor, which alters the three-dimensional structure of the factor, resulting in enhanced DNA binding and transcriptional activation. This mechanism may be important for transcriptional activation under conditions of limiting transcription factor concentration, such as at the low levels of PU.1 expressed in B cells.

AKT induces transcriptional activity of PU.1 through phosphorylation-mediated modifications within its transactivation domain

Signal transduction by the antigen receptor complexes is critical for developmental progression of B-lymphocytes, which are defined by assembly and sequential expression of immunoglobulin genes, which in turn are regulated by the enhancer elements. Although proximal antigen-receptor signal transduction pathways are well defined, the precise nuclear factors targeted by these signals remained unknown. Previous studies have demonstrated that tissue-restricted transcription factors including PU.1 and PU.1 interaction partner (PIP) function synergistically with c-Fos plus c-Jun to stimulate the kappaE3'-enhancer in 3T3 cells. In this study, we demonstrate that the functional synergy between these factors is enhanced in response to mitogen-activated protein kinase kinase kinase, in 3T3 cells, where the enhancer is inactive. However in S194 plasmacytoma cells, mitogen-activated protein kinase kinase kinase was able to stimulate the activity of PU.1 but unable to induce the kappaE3'-enhancer activity. We have found that Ras-phosphoinositide 3-kinase-dependent externally regulated kinase, AKT, induces kappaE3'-enhancer activity in both pre-B and plasmacytoma cells. AKT stimulation of the kappaE3'-enhancer is primarily due to PU.1 induction and is independent of PU.1 interaction with PIP. Activation of AKT had no effect on the expression levels of PU.1 or its protein-protein interaction with PIP. Using a series of deletion constructs, we have determined that the PU.1 acid-rich (amino acids 33-74) transactivation domain is necessary for AKT-mediated induction. Substitution analyses within this region indicate that phosphorylation of Ser(41) is necessary to respond to AKT. Consistent with these studies, ligation of antigen receptors in A20 B cells mimics AKT activation of PU.1. Taken together, these results provide evidence that PU.1 is induced by AKT signal in a phosphoinositide 3-kinase-dependent manner, leading to inducible or constitutive activation of its target genes.

PU.1 is a lineage-specific regulator of tyrosine phosphatase CD45

The hematopoietic cell-specific ets family transcription factor PU.1 regulates many lymphoid and myeloid genes. We have determined that PU.1 is critical for lineage-specific expression of the tyrosine phosphatase CD45. CD45 is expressed exclusively in hematopoietic cells at all stages of development, except for mature red cells and platelets. Although CD45 is normally expressed in all leukocyte lineages, it is critically regulated by PU.1 only in myeloid cells. Whereas myeloid cells from PU.1 null mice failed to express CD45, lymphoid cells were CD45(+) by flow cytometry. Additionally, mRNA for CD45 was absent from PU.1-deficient myeloid cells. To understand the molecular basis for these observations, we characterized a transcriptional regulatory region of the murine CD45 gene containing exons 1a, 1b, and 2. Distinct transcriptional initiation sites for CD45 were demonstrated in T and B cells versus myeloid cells. A transcriptional initiation site in exon 1b (P1b) was principally utilized by myeloid cells. A PU.1 binding site was identified upstream of exon 1b by sequence analysis and DNA binding assays. Using this region of the CD45 locus we demonstrated that PU.1 directly transactivated reporter gene expression. Finally, retrovirus-mediated restoration of PU.1 expression to PU.1-deficient myeloid cells resulted in expression of cell surface CD45 and restored phosphatase activity, confirming the role of PU.1 in the positive regulation of this well known signaling molecule. We conclude that CD45 is regulated differentially in myeloid and lymphoid cells and that sequences critical to direct myeloid expression include a PU.1 binding site upstream of the P1b transcriptional initiation site.

Functional pleiotropy of an intramolecular triplex-forming fragment from the 3'-UTR of the rat Pigr gene

A microsatellite-containing 359-bp restriction fragment, isolated from the rat Pigr gene (murine polymeric immunoglobulin receptor gene) 3'-untranslated region (3'-UTR) and inserted into 3'-UTR or 3' flanking positions in transcription units of supercoiled plasmids, attenuates luciferase reporter gene expression in orientation- and position-dependent ways following transient transfection of human 293 cells. The same fragment stimulates orientation-dependent gene expression in a 5' flanking position. Plasmid linearization abrogates both orientation- and position-dependent responses. Cell-free translation reveals that 5' and 3' flanking expression responses are proportional to increased and decreased luciferase mRNA levels, whereas 3'-UTR expression is associated with control mRNA levels. Hypersensitivity to nucleases S1 and P1, gel mobility differences between supercoiled plasmids carrying opposing microsatellite orientations, and anomalous melting profiles of this fragment are also observed. These results suggest that functional pleiotropy of this fragment depends on the DNA context of its purine-rich microsatellite strand and on DNA supercoiling. Intramolecular triplexes stabilized by supercoiling and secondary structures of purine repeat-rich mRNAs may also confer regulatory properties to similar genomic elements.

Mechanisms of expression of NADPH oxidase components in human cultured monocytes: role of cytokines and transcriptional regulators involved

Human blood monocytes lose their capability to produce microbicidal oxidants during culture. We report that this process is associated with decreased gp91phox, p22phox and p47phox expression, release of PU.1 and CP-1 from gp91phox promoter, and PU.1 from p47phox promoter. However, in presence of IFN-gamma or TNF-alpha, the superoxide anion (O(2)(-)) production, the p47phox, gp91phox and p22phox expression, and the binding of PU.1 and CP-1 to DNA are maintained at the high levels observed in blood monocytes. To clarify the role of PU.1 in the expression of NADPH oxidase components, oligonucleotides competing for PU.1-DNA binding were added to cultured monocytes. These oligonucleotides abrogated the maintenance of gp91phox and p22phox expression by IFN-gamma and TNF-alpha, but did not inhibit the effect of these cytokines on p47phox expression and O(2)(-) production. Our results indicate that in monocytes the IFN-gamma- and TNF-alpha-induced expression of gp91phox and p22phox, but not p47phox, requires the binding of PU.1 to gp91phox promoter. However, the preservation of O(2)(-) production by IFN-gamma and TNF-alpha is unrelated to their effect on gp91phox and p22phox expression.

Transcription factors and translocations in lymphoid and myeloid leukemia

Chromosomal translocations involving transcription factors and aberrant expression of transcription factors are frequently associated with leukemogenesis. Transcription factors are essential in maintaining the regulation of cell growth, development, and differentiation in the hematopoietic system. Alterations in the mechanisms that normally control these functions can lead to hematological malignancies. Further characterization of the molecular biology of leukemia will enhance our ability to develop disease-specific treatment strategies, and to develop effective methods of diagnosis and prognosis.

Derivation of dendritic cells from myeloid and lymphoid precursors

The antigen presenting dendritic cells (DC) found in mouse and human lymphoid tissues are heterogeneous. Several subsets of mature DC have been described and these may correspond to distinct lineages. In this review, we present evidence obtained from a series of studies on the lineage origin of DC. This evidence points to the existence of at least three pathways for DC development, namely one from myeloid progenitors, a second from lymphoid progenitors and the third for Langerhans cells from precursors whose relationship to myeloid or lymphoid cell types is not yet clearly defined.

The PEA3 subfamily of Ets transcription factors synergizes with beta-catenin-LEF-1 to activate matrilysin transcription in intestinal tumors

The matrix metalloproteinase matrilysin (MMP-7) is expressed in the tumor cells of a majority of mouse intestinal and human colonic adenomas. We showed previously that matrilysin is a target gene of beta-catenin-Tcf, the transcription factor complex whose activity is thought to play a crucial role in the initiation of intestinal tumorigenesis. Here we report that overexpression of a stable mutant form of beta-catenin alone was not sufficient to effect expression of luciferase from a matrilysin promoter-luciferase reporter plasmid. However, cotransfection of the reporter with an expression vector encoding the PEA3 Ets transcription factor, or its close relatives ER81 and ERM, increased luciferase expression and rendered the promoter responsive to beta-catenin-LEF-1 as well as to the AP-1 protein c-Jun. Other Ets proteins could not substitute for the PEA3 subfamily. Luciferase activity was induced up to 250-fold when PEA3, c-Jun, beta-catenin, and LEF-1 were coexpressed. This combination of transcription factors was also sufficient to induce expression of the endogenous matrilysin gene. Furthermore, all matrilysin-expressing benign intestinal tumors of the Min mouse expressed a member of the PEA3 subfamily, as did all human colon tumor cell lines examined. These data suggest that the expression of members of the PEA3 subfamily, in conjunction with the accumulation of beta-catenin in these tumors, leads to coordinate upregulation of matrilysin gene transcription, contributing to gastrointestinal tumorigenesis.

Evolution of hematopoiesis: Three members of the PU.1 transcription factor family in a cartilaginous fish, Raja eglanteria

T lymphocytes and B lymphocytes are present in jawed vertebrates, including cartilaginous fishes, but not in jawless vertebrates or invertebrates. The origins of these lineages may be understood in terms of evolutionary changes in the structure and regulation of transcription factors that control lymphocyte development, such as PU.1. The identification and characterization of three members of the PU.1 family of transcription factors in a cartilaginous fish, Raja eglanteria, are described here. Two of these genes are orthologs of mammalian PU.1 and Spi-C, respectively, whereas the third gene, Spi-D, is a different family member. In addition, a PU.1-like gene has been identified in a jawless vertebrate, Petromyzon marinus (sea lamprey). Both DNA-binding and transactivation domains are highly conserved between mammalian and skate PU.1, in marked contrast to lamprey Spi, in which similarity is evident only in the DNA-binding domain. Phylogenetic analysis of sequence data suggests that the appearance of Spi-C may predate the divergence of the jawed and jawless vertebrates and that Spi-D arose before the divergence of the cartilaginous fish from the lineage leading to the mammals. The tissue-specific expression patterns of skate PU.1 and Spi-C suggest that these genes share regulatory as well as structural properties with their mammalian orthologs.

Evolution of hematopoiesis: Three members of the PU.1 transcription factor family in a cartilaginous fish, Raja eglanteria

T lymphocytes and B lymphocytes are present in jawed vertebrates, including cartilaginous fishes, but not in jawless vertebrates or invertebrates. The origins of these lineages may be understood in terms of evolutionary changes in the structure and regulation of transcription factors that control lymphocyte development, such as PU.1. The identification and characterization of three members of the PU.1 family of transcription factors in a cartilaginous fish, Raja eglanteria, are described here. Two of these genes are orthologs of mammalian PU.1 and Spi-C, respectively, whereas the third gene, Spi-D, is a different family member. In addition, a PU.1-like gene has been identified in a jawless vertebrate, Petromyzon marinus (sea lamprey). Both DNA-binding and transactivation domains are highly conserved between mammalian and skate PU.1, in marked contrast to lamprey Spi, in which similarity is evident only in the DNA-binding domain. Phylogenetic analysis of sequence data suggests that the appearance of Spi-C may predate the divergence of the jawed and jawless vertebrates and that Spi-D arose before the divergence of the cartilaginous fish from the lineage leading to the mammals. The tissue-specific expression patterns of skate PU.1 and Spi-C suggest that these genes share regulatory as well as structural properties with their mammalian orthologs.

The Ets-transcription factor family in embryonic development: lessons from the amphibian and bird

This chapter reviews the expression and role of Ets-genes during embryogenesis of amphibians and birds. In addition to overlapping expression domains, some of them exhibit cell type-specific expression. Many of them are expressed in migratory cells: neural crest, endothelial, and pronephric duct cells for instance. They are also transcribed in embryonic areas affected by epithelio-mesenchymal transitions. Both processes involve modifications of cellular adhesion. Ets-family genes appear to coordinate changes in the expression of adhesion molecules and degradation of the extracellular matrix upon regulation of matrix metalloproteinases and their specific inhibitors. These functions are essential for physiological processes like tissue remodelling during embryogenesis or wound healing. Unfortunately they also play a harmful role in metastasis. Recent studies in the nervous system showed that Ets-genes contribute to the establishment of a cellular identity. This identity could rely on definite cell-surface determinants, among which cadherins could play an important role. In addition to cell-type specific expression, other factors contribute to the specificity of function of Ets-genes. These genes have a broad specificity of recognition of target sequences in gene promoters, insufficient for accurate control of gene expression. A fine tuning could arise from combinatorial interactions with other Ets- or accessory proteins.

Ets and retroviruses - transduction and activation of members of the Ets oncogene family in viral oncogenesis

Studies of retroviral-induced oncogenesis in animal systems led to the initial discovery of viral oncogenes and their cellular homologs, and provided critical insights into their role in the neoplastic process. V-ets, the founding member of the ETS oncogene family, was originally identified as part of the fusion oncogene encoded by the avian acute leukemia virus E26 and subsequent analysis of virus induced leukemias led to the initial isolation of two other members of the ETS gene family. PU.1 was identified as a target of insertional activation in the majority of tumors induced by the murine Spleen Focus Forming virus (SFFV), while fli-1 proved to be the target of Friend murine leukemia virus (F-MuLV) in F-MuLV induced erythroleukemia, as well as that of the 10A1 and Graffi viruses. The common features of the erythroid and myeloid diseases induced by these viruses provided the initial demonstration that these and other members of the ETS family play important roles in hematopoietic development as well as disease. This review provides an overview of the role of ETS genes in retrovirally induced neoplasia, their possible mechanisms of action, and how these viral studies relate to current knowledge of the functions of these genes in hematopoiesis.

Expression and function of Ets transcription factors in mammalian development: a regulatory network

The Ets transcription factor family is involved in a variety of mammalian developmental processes at the cellular, tissue and organ levels. They are implicated in cellular proliferation, differentiation, migration, apoptosis and cell - cell interactions. This article reviews recent studies that demonstrate the integral importance of Ets in the dosage dependent regulation of development. The expression of many Ets genes is associated with mesenchymal - epithelial interactions and changes in extracellular matrix proteins. These inductive processes contribute to tissue remodeling and integrity, particularly during embryonic development. Overlapping as well as unique patterns of Ets expression are evident in developing tissues, including development of the lymphoid and myeloid lineages, brain and central nervous system, bone and mammary gland. Integration of these data will allow the development of predictive models for the regulation of complex developmental processes.

Molecular organization, expression and chromosomal localization of the mouse pronapsin gene

Napsins have been identified only very recently as new aspartic proteinases of the pepsin family. Isolation, sequencing and functional analysis of the mouse genomic locus indicates that the organization of the pronapsin gene into nine exons is identical to that of other mammalian aspartic proteinase precursors, including pepsinogen. However, the additional C-terminal residues, which are a distinguishing feature of napsins, are encoded within exon 9 and not within an additional exon. Quantitation of pronapsin mRNA using RT-PCR indicates that the gene is transcribed in lung, kidney and spleen but not in heart. Regulation of gene expression was not influenced by the extent of CpG methylation but depended on the recognition of potential binding motifs in the promoter region by specific transcription factors such as YY-1. The single copy of the mouse pronapsin gene was located on chromosome 7. In humans, there are two pronapsin genes and, based on the mouse information, preliminary structures were deduced for these from sequences in the human genome databases. They appear to be located together on chromosome 19.

Characterization of the promoter of human leukocyte-specific transcript 1. A small gene with a complex pattern of alternative transcripts

The gene for the human leukocyte-specific transcript 1 (LST1) encodes a small protein that modulates immune responses and cellular morphogenesis. The LST1 transcripts are expressed at high levels in dendritic cells. Because of the complex splicing pattern, use of alternative 5'-untranslated exons, and a biologically interesting pattern of expression of LST1 mRNA, we studied the human LST1 gene promoter and regulatory elements. We identified an additional upstream 5'-untranslated exon in U937 monocytic cells. Transient transfection studies demonstrated that the combination of regions from -1363 to -621 with -112 to -54, relative to the translation start codon, produced the highest level of transcripts from among the various constructs tested, but the pattern of transcripts produced was only a subset of those produced from the endogenous gene. DNase I footprinting analysis and electrophoretic mobility shift assays showed that oligonucleotide probes corresponding to three regions, -1171 to -1142 (BI), -1136 to -1111 (BII), and -783 to -751 (BIV), bound proteins in U937 nuclear extracts. Competition and supershift electrophoretic mobility shift assay did not identify any known transcription factors responsible for BII probe binding. These studies suggest that a novel DNA-binding site and interaction of multiple regulatory elements may be involved in mediating the expression of the various forms of LST1 mRNA.

Homeobox gene Hex is essential for onset of mouse embryonic liver development and differentiation of the monocyte lineage

Disruption of the mouse Hex gene resulted in embryonic lethality around embryonic age (E) 10.5, due to no substantial liver formation. Expression of albumin was detectable in heterozygous (Hex(+/-)) but not in homozygous (Hex(-/-)) [corrected] embryos at E8.5. Instead of liver bud formation at E9.5, a liver-like capsule structure was observed in Hex(-/-) [corrected] embryos. In Hex(-/-) [corrected] mutant liver, we found no hepatocytes but no signs of apoptotic cell death in the area. Expression of transcription factors involved in hepatocyte differentiation, hepatocyte nuclear factor (Hnf)3beta, Hnf6, Hnf4alpha and Hnf1alpha, were restricted to the capsule and internal matrix-like structure in the mutant liver and expression of a subset of these factors were reduced. Hematopoiesis of monocytes was impaired in mutant embryos while erythroid lineage was unaffected. These results indicate that Hex plays an essential role in progenitor cells which commit to the hepatic endoderm and in the hematopoietic differentiation of the monocyte lineage.

Synergistic induction of the Tap-1 gene by IFN-gamma and lipopolysaccharide in macrophages is regulated by STAT1

Proper regulation of the Tap-1 gene is critical for the initiation and continuation of a cellular immune response. Analysis of the Tap-1/low molecular mass polypeptide 2 bidirectional promoter showed that the IFN-gamma activation site element is critical for the rapid induction of the promoter by IFN-gamma following transfection into the human macrophage cell line THP-1. Furthermore, activation of STAT1 binding to this site was important for the synergistic response seen following the stimulation with both IFN-gamma and LPS. Mutation of an IFN-stimulated regulatory element that binds IFN regulatory factor 1 appeared to enhance the response to IFN-gamma and LPS. These data show that STAT1 is necessary for the activation of Tap-1 gene expression in APCs and initiation of cellular immune responses. Furthermore, our data suggest that bacterial products such as LPS may enhance cellular immune responses through augmenting the ability of STAT1 to regulate IFN-gamma-inducible genes.

Involvement of STAT-1 and ets family members in interferon-gamma induction of CD40 transcription in microglia/macrophages

Cluster of differentiation (CD)-40 is a cell surface receptor belonging to the tumor necrosis factor receptor family that plays a critical role in the regulation of immune responses. We have previously shown that the cytokine interferon (IFN)-gamma induces CD40 expression in microglia. Herein, we have elucidated the molecular mechanisms underlying IFN-gamma induction of CD40 gene expression in microglia/macrophages. IFN-gamma up-regulates CD40 expression at the transcriptional level, and this regulation involves the STAT-1alpha transcription factor. Microglia from STAT-1alpha-deficient mice were refractive to IFN-gamma induction of CD40 expression, illustrating the importance of STAT-1alpha in this response. Functional analysis of the CD40 promoter indicates that two gamma activated sequence elements as well as two Ets elements are involved in IFN-gamma induction of CD40 promoter activity. STAT-1alpha binds to the gamma activated sequence elements, whereas PU.1 and/or Spi-B bind to the Ets elements. The expression of PU.1 and Spi-B, in conjuction with STAT-1alpha activation, correlates with IFN-gamma inducibility of CD40 expression. Collectively, our data demonstrate the involvement of STAT-1alpha, PU.1, and Spi-B in IFN-gamma induction of CD40 gene expression in cells of the macrophage lineage.

Role of hypoxia-inducible factor-1 in transcriptional activation of ceruloplasmin by iron deficiency

A role of the copper protein ceruloplasmin (Cp) in iron metabolism is suggested by its ferroxidase activity and by the tissue iron overload in hereditary Cp deficiency patients. In addition, plasma Cp increases markedly in several conditions of anemia, e.g. iron deficiency, hemorrhage, renal failure, sickle cell disease, pregnancy, and inflammation. However, little is known about the cellular and molecular mechanism(s) involved. We have reported that iron chelators increase Cp mRNA expression and protein synthesis in human hepatocarcinoma HepG2 cells. Furthermore, we have shown that the increase in Cp mRNA is due to increased rate of transcription. We here report the results of new studies designed to elucidate the molecular mechanism underlying transcriptional activation of Cp by iron deficiency. The 5'-flanking region of the Cp gene was cloned from a human genomic library. A 4774-base pair segment of the Cp promoter/enhancer driving a luciferase reporter was transfected into HepG2 or Hep3B cells. Iron deficiency or hypoxia increased luciferase activity by 5-10-fold compared with untreated cells. Examination of the sequence showed three pairs of consensus hypoxia-responsive elements (HREs). Deletion and mutation analysis showed that a single HRE was necessary and sufficient for gene activation. The involvement of hypoxia-inducible factor-1 (HIF-1) was shown by gel-shift and supershift experiments that showed HIF-1alpha and HIF-1beta binding to a radiolabeled oligonucleotide containing the Cp promoter HRE. Furthermore, iron deficiency (and hypoxia) did not activate Cp gene expression in Hepa c4 hepatoma cells deficient in HIF-1beta, as shown functionally by the inactivity of a transfected Cp promoter-luciferase construct and by the failure of HIF-1 to bind the Cp HRE in nuclear extracts from these cells. These results are consistent with in vivo findings that iron deficiency increases plasma Cp and provides a molecular mechanism that may help to understand these observations.

Detection of protein binding to a glucocorticoid response element-like sequence in a chicken major histocompatibility complex class II promoter

The glucocorticoid response element in gene promoters mediates regulation of gene expression by glucocorticoids. The major histocompatibility (MHC) class II genes, crucial for immunoresponsiveness, are among those modulated by glucocorticoids. A GRE-like sequence has been located in the promoter of a chicken MHC class II promoter. DNase footprinting revealed protein binding by the GRE-like sequence when nuclear extract from chicken T or B cell lines were used. Gel shift assays detected multiple binding activities in the lymphocyte cell lines, but little binding in the macrophage cell line. Relative band intensity differed among the lymphocyte cell lines. By using a mutant GRE oligonucleotide, most of the binding activities were demonstrated to be specific to the GRE. This study suggests a role of the GRE-like sequence in regulating chicken MHC class II genes and provides further evidence for the previously reported influence of glucocorticoids on chicken MHC class II expression which may be the molecular basis of glucocorticoid immunomodulation.

Do lampreys have lymphocytes? The Spi evidence

It is generally accepted that living jawless vertebrates (lampreys and hagfishes) lack the capability of mounting an adaptive immune response. At the same time, however, there are reports describing histological evidence for the presence in agnathan tissues of lymphocytes, the key players in adaptive immunity. The question therefore arises whether the cells identified morphologically as lymphocytes are true lymphocytes in terms of their genetic developmental program. In this study, evidence is provided that the lampreys express a member of the purine box 1 (PU.1)/spleen focus-forming virus integration B (Spi-B) gene family known to be critically and specifically involved in the differentiation of lymphocytes in jawed vertebrates. The lamprey gene is expressed in the lymphocyte-like cells of the digestive tract and inexplicably also in the ovary.

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.