Localization of agonist- and antagonist-binding domains of human corticotropin-releasing factor receptors

The CRF receptors, CRFR1 and CRFR2, are members of the G protein-coupled receptor superfamily. Despite their considerable sequence similarity, CRFR1 and CRFR2 have quite different affinities for the peptide ligand rat/human CRF. Previous studies using chimeric receptors between human CRFR1 and CRFR2 have identified three potentially important regions in the second and third extracellular domains of CRF receptor for the binding of rat/human CRF. The present report further demonstrates that these same three regions also affect the binding of urocortin and sauvagine, two other members of the CRF peptide family, albeit to different extents. We also show that a fourth region in the third extracellular domain, Asp254, has been identified to be important for sauvagine but not CRF or urocortin binding. Thus, the three peptide ligands not only interact with a different set of regions on CRFR1 and CRFR2 but also differentially interact with some of the same regions. These data could, at least in part, account for the much higher affinity of CRFR2 for urocortin and sauvagine compared with rat/human CRF. We have also identified two amino acid residues, His199 in the third transmembrane domain and Met276 in the fifth transmembrane domain, that are important for binding the non-peptide high-affinity CRFR1 antagonist NBI 27914. Mutations of His199 and Met276 to the corresponding amino acids in CRFR2 each decreased the binding affinity of NBI 27914 for CRFR1 by 40- and 200-fold, respectively. This suggests that the transmembrane regions are critically important in forming the binding pocket for the nonpeptide antagonist.

Methylation of an ETS site in the intron enhancer of the keratin 18 gene participates in tissue-specific repression

The activities of ETS transcription factors are modulated by posttranscriptional modifications and cooperation with other proteins. Another factor which could alter the regulation of genes by ETS transcription factors is DNA methylation of their cognate binding sites. The optimal activity of the keratin 18 (K18) gene is dependent upon an ETS binding site within an enhancer region located in the first intron. The methylation of the ETS binding site was correlated with the repression of the K18 gene in normal human tissues and in K18 transgenic mouse tissues. Neither recombinant ETS2 nor endogenous spleen ETS binding activities bound the methylated site effectively. Increased expression of the K18 gene in spleens of transgenic mice by use of an alternative, cryptic promoter 700 bp upstream of the enhancer resulted in modestly decreased methylation of the K18 ETS site and increased RNA expression. Expression in transgenic mice of a mutant K18 gene, which was still capable of activation by ETS factors but was no longer a substrate for DNA methylation of the ETS site, was fivefold higher in spleen and heart. However, expression in other organs such as liver and intestine was similar to that of the wild-type gene. This result suggests that DNA methylation of the K18 ETS site may be functionally important in the tissue-specific repression of the K18 gene. Epigenetic modification of the binding sites for some ETS transcription factors may result in a refractory transcriptional response even in the presence of necessary trans-acting activities.

Expression and characterization of a putative high affinity human soluble leptin receptor

Leptin, a circulating 16-kDa protein secreted by adipocytes, decreases body weight by reducing food intake and enhancing energy utilization. Leptin receptors that share homology to the glycoprotein gp130 have been recently cloned. In addition, differentially spliced leptin receptor messenger RNAs have been identified. Functional mutations in either the leptin or leptin receptor gene cause obesity. In the present study, expression of the full length human leptin receptor complementary DNA encoding the long cytoplasmic domain of leptin receptor in COS7 cells resulted in high affinity membrane binding of 125I-leptin (Ki approximately 200 pM); no detectable binding was present in the medium. In addition, we expressed the extracellular domain of human leptin receptor in COS7 cells and identified a soluble leptin receptor in the conditioned medium that binds human and mouse leptin with high affinity comparable with the full length membrane receptor. Transfected COS7 cells expressing the soluble leptin receptor also demonstrated modest specific 125I-leptin binding in whole cells, presumably due to association of the soluble leptin receptor to cell membrane proteins. Data from cross-linking studies identified two specific bands in the 125I-leptin/soluble leptin receptor complex with molecular masses of approximately 130-150 kDa and 300 kDa. The 130-150 kDa molecular mass was confirmed in Western blot analysis and Coomassie staining of the purified soluble receptor and probably represents the glycosylated form of the receptor. The 300-kDa band most likely represents a homodimer of the soluble leptin receptor complex because HPLC gel filtration analysis of the 125I-leptin/soluble leptin receptor complex identified a single peak corresponding to a molecular mass of approximately 340 kDa. The soluble leptin receptor antagonized 125I-leptin binding to the membrane receptor, suggesting its potential utility as a functional tool for determining the role of endogenous leptin.

Localization of ligand-binding domains of human corticotropin-releasing factor receptor: a chimeric receptor approach

Two CRF receptors, CRFR1 and CRFR2, have recently been cloned and characterized. CRFR1 shares 70% sequence identity with CRFR2, yet has much higher affinity for rat/human CRF (r/hCRF) than CRFR2. As a first step toward understanding the interactions between rat/human CRF and its receptor, the regions that are involved in receptor-ligand binding and/or receptor activation were determined by using chimeric receptor constructs of the two human CRFR subtypes, CRFR1 and CRFR2, followed by generating point mutations of the receptor. The EC50 values in stimulation of intracellular cAMP of the chimeric and mutant receptors for the peptide ligand were determined using a cAMP-dependent reporter system. Three regions of the receptor were found to be important for optimal binding of r/hCRF and/or receptor activation. The first region was mapped to the junction of the third extracellular domain and the fifth transmembrane domain; substitution of three amino acids of CRFR1 in this region (Val266, Tyr267, and Thr268) by the corresponding CRFR2 amino acids (Asp266, Leu267, and Val268) increased the EC50 value by approximately 10-fold. The other two regions were localized to the second extracellular domain of the CRFR1 involving amino acids 175-178 and His189 residue. Substitutions in these two regions each increased the EC50 value for r/hCRF by approximately 7- to 8-fold only in the presence of the amino acid 266-268 mutation involving the first region, suggesting that their roles in peptide ligand binding might be secondary.

Stimulation of macrophages by lipopolysaccharide alters the phosphorylation state, conformation, and function of PU.1 via activation of casein kinase II

We previously reported that LPS stimulation of the RAW264.7 murine macrophage cell line rapidly induced a structural change within the N terminus of the transcriptional regulatory factor PU.1. PU.1 is required for the expression of a variety of cytokine, cytokine receptor, and integrin genes. Western blot analysis of nuclear extracts prepared from LPS-stimulated macrophages revealed increased phosphorylation of PU.1 at serine residues relative to that in unstimulated controls. PU.1-DNA complexes prepared using nuclear extracts from LPS-stimulated macrophages were less sensitive to protease digestion compared with PU.1-DNA complexes generated using nuclear extracts prepared from unstimulated cells. This altered protease sensitivity probably reflects a conformational change within PU.1 resulting from LPS-induced phosphorylation. This possibility was supported by the finding that in vitro-phosphorylated PU.1 was similarly resistant to protease digestion. Transient transfection studies suggest that LPS-induced phosphorylation of PU.1 at serine 148, located within a casein kinase II (CKII) consensus motif, increases the transactivation function of PU.1. Other serine/CKII sites located at positions 41, 45, 132, and 133 do not appear to be required for LPS-induced PU.1 function. Lastly, we found that LPS also increased the enzymatic activity of CKII in these cells. To our knowledge, these are the first studies to demonstrate that LPS can stimulate CKII activity, induce PU.1 phosphorylation, and enhance the capacity of PU.1 to activate transcription in macrophages.

Stimulation of macrophages by lipopolysaccharide alters the phosphorylation state, conformation, and function of PU.1 via activation of casein kinase II

We previously reported that LPS stimulation of the RAW264.7 murine macrophage cell line rapidly induced a structural change within the N terminus of the transcriptional regulatory factor PU.1. PU.1 is required for the expression of a variety of cytokine, cytokine receptor, and integrin genes. Western blot analysis of nuclear extracts prepared from LPS-stimulated macrophages revealed increased phosphorylation of PU.1 at serine residues relative to that in unstimulated controls. PU.1-DNA complexes prepared using nuclear extracts from LPS-stimulated macrophages were less sensitive to protease digestion compared with PU.1-DNA complexes generated using nuclear extracts prepared from unstimulated cells. This altered protease sensitivity probably reflects a conformational change within PU.1 resulting from LPS-induced phosphorylation. This possibility was supported by the finding that in vitro-phosphorylated PU.1 was similarly resistant to protease digestion. Transient transfection studies suggest that LPS-induced phosphorylation of PU.1 at serine 148, located within a casein kinase II (CKII) consensus motif, increases the transactivation function of PU.1. Other serine/CKII sites located at positions 41, 45, 132, and 133 do not appear to be required for LPS-induced PU.1 function. Lastly, we found that LPS also increased the enzymatic activity of CKII in these cells. To our knowledge, these are the first studies to demonstrate that LPS can stimulate CKII activity, induce PU.1 phosphorylation, and enhance the capacity of PU.1 to activate transcription in macrophages.

Cloning of a cDNA encoding a novel interleukin-1 receptor related protein (IL 1R-rp2)

We have identified and isolated both the rat and human cDNAs for a novel putative receptor related to the interleukin-1 type 1 receptor. We have named this protein interleukin 1 receptor related protein two (IL 1R-rp2). The rat cDNA for IL1R-rp2 was first identified using oligonucleotides of degenerate sequence in a polymerase chain reaction (PCR) paradigm with rat brain mRNA as the template. The protein encoded by both of these cDNAs are 561 amino acids long and exhibit 42% and 26% overall identity with the interleukin-1 type 1 and type 2 receptors, respectively. RNase protection assays from rat tissues revealed a predominant expression for IL 1R-rp2 in the lung and epididymis with lower levels detected in the testis and cerebral cortex. By in situ hybridization we were able to determine that the expression in rat brain appeared to be non-neuronal and associated with the cerebral vasculature. When expressed transiently in COS-7 cells the receptor was incapable of high affinity binding to either [125I]-recombinant human IL 1 alpha or [125I]-recombinant human IL 1 beta. Together, these data demonstrate the existence of a novel protein that is related to the interleukin-1 receptor but does not bind IL-1 by itself.

PU.1 but not ets-2 is essential for macrophage development from embryonic stem cells

Transcription factors play an important role choreographing lineage commitment and expansion of blood cells. Nuclear factors that are expressed primarily or exclusively in hematopoietic cells are likely candidates for regulating blood cell development. The transcription factor PU.1 is found only in hematopoietic cells, whereas ets-2, a related family member, is ubiquitously expressed. To compare the role of these two transcription factors in macrophage development, embryonic stem (ES) cells with a homozygous disruption of either the PU.1 or the ets-2 gene were generated. The ability of both knockout ES cells to differentiate to macrophages was tested. Normal development of macrophages, as determined by histochemical and immunohistochemical analysis, from PU.1 knockout ES cells was significantly blocked. Furthermore, the expression of known markers associated with macrophages, such as c-fms, CD11b, CD18 and granulocyte-macrophage colony-stimulating factor receptor, were not detected by reverse transcriptase-polymerase chain reaction. In contrast to the PU.1 knockout ES cells, macrophages, development from the ets-2 knockout ES cells was normal. Although both PU.1 and ets-2 are found in macrophages, these data show a distinct role for the lineage-restricted PU.1 transcription factor in macrophage development.

Targeted disruption of the PU.1 gene results in multiple hematopoietic abnormalities

PU.1 is a member of the ets family of transcription factors and is expressed exclusively in cells of the hematopoietic lineage. Mice homozygous for a disruption in the PU.1 DNA binding domain are born alive but die of severe septicemia within 48 h. The analysis of these neonates revealed a lack of mature macrophages, neutrophils, B cells and T cells, although erythrocytes and megakaryocytes were present. The absence of lymphoid commitment and development in null mice was not absolute, since mice maintained on antibiotics began to develop normal appearing T cells 3-5 days after birth. In contrast, mature B cells remained undetectable in these older mice. Within the myeloid lineage, despite a lack of macrophages in the older antibiotic-treated animals, a few cells with the characteristics of neutrophils began to appear by day 3. While the PU.1 protein appears not to be essential for myeloid and lymphoid lineage commitment, it is absolutely required for the normal differentiation of B cells and macrophages.

New insights on DNA recognition by ets proteins from the crystal structure of the PU.1 ETS domain-DNA complex

Transcription factors belonging to the ets family regulate gene expression and share a conserved ETS DNA-binding domain that binds to the core sequence 5'-(C/A)GGA(A/T)-3'. The domain is similar to alpha+beta ("winged") helix-turn-helix DNA-binding proteins. The crystal structure of the PU.1 ETS domain complexed to a 16-base pair oligonucleotide revealed a pattern for DNA recognition from a novel loop-helix-loop architecture (Kodandapani, R., Pio, F., Ni. C.-Z., Piccialli, G., Klemsz, M., McKercher, S., Maki, R. A., and Ely, K. R. (1996) Nature 380, 456-460). Correlation of this model with mutational analyses and chemical shift data on other ets proteins confirms this complex as a paradigm for ets DNA recognition. The second helix in the helix-turn-helix motif lies deep in the major groove with specific contacts with bases in both strands in the core sequence made by conserved residues in alpha3. On either side of this helix, two loops contact the phosphate backbone. The DNA is bent (8 degrees) but uniformly curved without distinct kinks. ETS domains bind DNA as a monomer yet make extensive DNA contacts over 30 A. DNA bending likely results from phosphate neutralization of the phosphate backbone in the minor groove by both loops in the loop-helix-loop motif. Contacts from these loops stabilize DNA bending and may mediate specific base interactions by inducing a bend toward the protein.

Cloning and characterization of an alternatively processed human type II interleukin-1 receptor mRNA

Two types of interleukin (IL)-1 receptors with three extracellular immunoglobulin-like domains, limited homology (28%), and different pharmacological characteristics termed type I and type II have been cloned from mouse and human cell lines. Both receptors exist in transmembrane and soluble forms; the soluble IL-1 receptor is thought to be post-translationally derived from cleavage of the extracellular portion of the membrane receptors. In preliminary cross-linking studies with radiolabeled IL-1, we found that monkey kidney COS1 cells express a soluble receptor with molecular mass of approximately 55-60 kDa, which is different from previously reported soluble IL-1 receptors. This soluble IL-1 receptor protein from COS1 cells was purified to homogeneity by affinity chromatography using recombinant IL-1beta as the ligand and shown to have an affinity for human 125I-IL-1beta (KD approximately 2-3 nM) comparable to the human type II IL-1 receptor (IL-1RII). The purified protein was microsequenced, and the sequence information was used to design primers to clone the COS1 IL-1RII using reverse transcription-coupled polymerase chain reaction; the DNA comparison with monkey COS1 and human IL-1RII indicate that they are 95% identical at the nucleic acid and amino acid levels. In addition, another cDNA, which represents an alternatively processed mRNA of the IL-1RII gene, was also cloned both from monkey COS1 and human Raji cells and was shown to have approximately 95% sequence identity between these species. While the cDNA of the novel alternatively processed gene has a 5' end identical to the IL-1RII, the 200 base pairs at the 3' end are different and the sequence predicts a soluble IL-1 receptor protein of 296 amino acids. Radioligand binding studies of the alternatively processed IL-1RII mRNA demonstrated kinetic and pharmacological characteristics similar to the known type II IL-1 receptor. COS7 cells (which lack IL-1 receptor) transfected with the transmembrane form of the human IL-1RII cDNA showed 125I-IL-1beta binding in both the membrane fractions and supernatant. In contrast, COS7 cells transfected with the alternatively processed human IL-1RII cDNA showed high affinity 125I-IL-1beta binding (Ki approximately 1.2 nM) predominantly in the supernatant; a very small amount of detectable membrane IL-1 binding activity was also observed presumably due to association of the soluble IL-1 receptor and membrane-integrated proteins. In cross-linking and ligand blot studies, the alternatively processed human IL-1RII cDNA-transfected COS7 cells expressed a soluble IL-1 receptor with molecular masses ranging from 60 to 160 kDa, further indicating the association between this soluble IL-1 receptor and other soluble proteins. In summary, we report the purification and characterization of a soluble IL-1 receptor expressed by COS1 cells and the cloning of an alternatively processed type II IL-1 receptor mRNA from both human and COS1 cells. The alternative splicing of a primary transcript leading to a secreted protein provides a potentially important mechanism by which soluble IL-1RII can be produced.

Identification of the transcription factors NF-YA and NF-YB as factors A and B that bound to the promoter of the major histocompatibility complex class II gene I-A beta

The Y box is a conserved sequence in the promoter of major histocompatibility complex (MHC) class II genes, which contains a CCAAT sequence (CCAAT box). Previously, we partially purified the DNA-binding protein that recognizes the Y box of the I-A beta gene and showed that it consisted of two components (factors A and B) both of which were necessary for optimal DNA binding. The genes for the heteromeric protein NF-Y (NF-YA and NF-YB), which binds to the I-E alpha Y box have been cloned. We subsequently isolated the genes for NF-YA and NF-YB using oligonucleotides designed from the published sequences. NF-YA and NF-YB were tested for binding to the I-A beta and I-E alpha Y boxes. While neither NF-YA or NF-YB alone bound to the Y box, when the components were mixed the complex bound to the I-A beta Y box with high affinity. Moreover, NF-YA and NF-YB could be complemented for binding to DNA by factor B or factor A, respectively. These results suggest that the active binding protein is NF-YA in factor A extracts and NF-YB in factor B extracts. Finally, antibodies against NF-YA and NF-YB were shown to induce a supershift when nuclear extracts were added to the double-stranded oligodeoxynucleotide covering the Y box of the I-A beta gene. Antisense expression constructs of both NF-YA and NF-YB were made and their effect on expression from the I-A beta promoter was tested. Either antisense construction, when transfected into cells, lowered the expression of a reporter gene linked to the I-A beta promoter. This study provides direct evidence of the identification of NF-YA and NF-YB as the previously described factors A and B. Moreover, these results strongly implicate NF-Y in the expression of the MHC class II gene I-A beta.

Rat p67 GBP is induced by interferon-gamma and isoprenoid-modified in macrophages

The guanylate binding proteins, GBPs, are a family of interferon-induced GTP-binding proteins that include the rat p67. We report here that rat p67, for which interferon regulation had not previously been demonstrated, is induced by IFN-gamma and also by LPS in both cultured bone marrow-derived macrophages and microglia. The basal level of rat p67 in macrophages is low but increases dramatically between 2 and 4 hours after treating cells with either IFN-gamma or LPS. It then remains elevated over the next 24 hours. Rat p67 is isoprenoid modified. The isoprenoid modification was detected in p67 isolated both from primary IFN-gamma-activated macrophages and when the gene for p67 was transfected into COS cells. This is the first demonstration of in vivo prenylation of a GBP. The interferon regulation and prenylation of rat p67 point toward this protein being significant in the functions of both activated macrophages and microglia.

The transcription factor PU.1 is involved in macrophage proliferation

PU.1 is a tissue-specific transcription factor that is expressed in cells of the hematopoietic lineage including macrophages, granulocytes, and B lymphocytes. Bone marrow-derived macrophages transfected with an antisense PU.1 expression construct or treated with antisense oligonucleotides showed a decrease in proliferation compared with controls. In contrast, bone marrow macrophages transfected with a sense PU.1 expression construct displayed enhanced macrophage colony-stimulating factor (M-CSF)-dependent proliferation. Interestingly, there was no effect of sense or antisense constructs of PU.1 on the proliferation of the M-CSF-independent cell line, suggesting that the response was M-CSF dependent. This was further supported by the finding that macrophages transfected with a sense or an antisense PU.1 construct showed, respectively, an increased or a reduced level of surface expression of receptors for M-CSF. The enhancement of proliferation seems to be selective for PU.1, since transfections with several other members of the ets family, including ets-2 and fli-1, had no effect. Various mutants of PU.1 were also tested for their ability to affect macrophage proliferation. A reduction in macrophage proliferation was found when cells were transfected with a construct in which the DNA-binding domain of PU.1 was expressed. The PEST (proline-, glutamic acid-, serine-, and threonine-rich region) sequence of the PU.1 protein, which is an important domain for protein-protein interactions in B cells, was found to have no influence on PU.1-enhanced macrophage proliferation when an expression construct containing PU.1 minus the PEST domain was transfected into bone marrow-derived macrophages. In vivo, PU.1 is phosphorylated on several serine residues. The transfection of plasmids containing PU.1 with mutations at each of five serines showed that only positions 41 and 45 are critical for enhanced macrophage proliferation. We conclude that PU.1 is necessary for the M-CSF-dependent proliferation of macrophages. One of the proliferation-relevant targets of this transcription factor could be the M-CSF receptor.

A new pattern for helix-turn-helix recognition revealed by the PU.1 ETS-domain-DNA complex

The Ets family of transcription factors, of which there are now about 35 members regulate gene expression during growth and development. They share a conserved domain of around 85 amino acids which binds as a monomer to the DNA sequence 5'-C/AGGAA/T-3'. We have determined the crystal structure of an ETS domain complexed with DNA, at 2.3-A resolution. The domain is similar to alpha + beta (winged) 'helix-turn-helix' proteins and interacts with a ten-base-pair region of duplex DNA which takes up a uniform curve of 8 degrees. The domain contacts the DNA by a novel loop-helix-loop architecture. Four of amino acids that directly interact with the DNA are highly conserved: two arginines from the recognition helix lying in the major groove, one lysine from the 'wing' that binds upstream of the core GGAA sequence, and another lysine, from the 'turn' of the 'helix-turn-helix' motif, which binds downstream and on the opposite strand.

Identification of a transcription factor that binds to the S box of the I-A beta gene of the major histocompatibility complex

Class II genes of the MHC show a striking homology upstream of the transcription start site that is composed of three conserved sequences (S, X and Y boxes, each separated by 15-20 bp). The presence of the S-box sequence in the mouse MHC class II gene I-A Beta was examined for its influence on the expression of this gene. Deletion or mutation of the S box decreased the induction of chloramphenicol acetyltransferase (CAT) activity in B lymphocytes by 32%. In macrophages, deletion or mutation of the S box abolished interferon-gamma (IFN-gamma) inducibility of CAT activity. Using a gel-retardation assay, we have identified a nuclear factor whose binding site overlaps the 7-mer conserved sequence of the S box. This factor is present in lymphocytes, macrophages, mastocytes and fibroblasts. Surprisingly, binding of this nuclear factor to DNA was induced by IFN-gamma in bone-marrow-derived macrophages, but not in macrophage-like cell lines. The binding site for this factor was defined by DNase I footprinting and partially purified by using an affinity column containing double-stranded oligonucleotides containing a sequence of the S box. A prominent protein of 43 kDa was found that bound specifically to the S-box sequence.

Ras-mediated phosphorylation of a conserved threonine residue enhances the transactivation activities of c-Ets1 and c-Ets2

The Ras oncogene products regulate the expression of genes in transformed cells, and members of the Ets family of transcription factors have been implicated in this process. To determine which Ets factors are the targets of Ras signaling pathways, the abilities of several Ets factors to activate Ras-responsive enhancer (RRE) reporters in the presence of oncogenic Ras were examined. In transient transfection assay, reporters containing RREs composed of Ets-AP-1 binding sites could be activated 30-fold in NIH 3T3 fibroblasts and 80-fold in the macrophage-like line RAW264 by the combination of Ets1 or Ets2 and Ras but not by several other Ets factors that were tested in the assay. Ets2 and Ras also superactivated an RRE composed of Ets-Ets binding sites, but the Ets-responsive promoter of the c-fms gene was not superactivated. Mutation of a threonine residue to alanine in the conserved amino-terminal regions of Ets1 and Ets2 (threonine 38 and threonine 72, respectively) abrogated the ability of each of these proteins to superactivate reporter gene expression. Phosphoamino acid analysis of radiolabeled Ets2 revealed that Ras induced normally absent threonine-specific phosphorylation of the protein. The Ras-dependent increase in threonine phosphorylation was not observed in Ets2 proteins that had the conserved threonine 72 residue mutated to alanine or serine. These data indicate that Ets1 and Ets2 are specific nuclear targets of Ras signaling events and that phosphorylation of a conserved threonine residue is a necessary molecular component of Ras-mediated activation of these transcription factors.

Activation of transcription by PU.1 requires both acidic and glutamine domains

The B-lymphocyte- and macrophage-specific transcription factor PU.1 is a member of the ets family of proteins. To understand how PU.1 functions as a transcription factor, we initiated a series of experiments to define its activation domain. Using deletion analysis, we showed that the activation domain of PU.1 is located in the amino-terminal half of the protein. Within this region, we identified three acidic subdomains and one glutamine-rich subdomain. The deletion of any of these subdomains resulted in a significant loss in the ability of PU.1 to transactivate in cotransfection studies. Amino acid substitution analysis showed that the activation of transcription by PU.1 requires acidic residues between amino acids 7 and 74 and a group of glutamine residues between amino acids 75 and 84. These data show that PU.1 contains two types of known activation domains and that both are required for maximal transactivation.

Induction of a prenylated 65-kd protein in macrophages by interferon or lipopolysaccharide

Treatment of murine bone marrow-derived macrophages with interferon-gamma (IFN-gamma) and/or lipopolysaccharide (LPS) resulted in changes in the abundance of a number of prenylated proteins. The most significant change involved a protein of 65 kd (p65) that became one of the most abundant prenylated proteins following treatment. The 65-kd protein was induced by agents that stimulate macrophage activation (IFNs or LPS) but not by cytokines that promote macrophage proliferation, such as granulocyte-macrophage colony-stimulating factor (GM-CSF), M-CSF, or interleukin-3. The majority of p65 was localized to subcellular fractions containing internal and plasma membranes but was not detected in nuclear membranes. The farnesyltransferase inhibitor BZA-5B caused a dramatic decrease in p65 prenylation, suggesting that this protein may be modified by the C15 isoprenoid farnesyl. These observations provide the first direct evidence that interferons and LPS cause changes in the abundance of specific isoprenoid-modified proteins in macrophages.

Co-crystallization of an ETS domain (PU.1) in complex with DNA. Engineering the length of both protein and oligonucleotide

The PU.1 transcription factor is a member of the ets gene family of regulatory proteins. These molecules play a role in normal development and also have been implicated in malignant processes such as the development of erythroid leukemia. The Ets proteins share a conserved DNA-binding domain (the ETS domain) that recognizes a purine-rich sequence with the core sequence: 5'-C/AGGAA/T-3'. This domain binds to DNA as a monomer, unlike many other DNA-binding proteins. The ETS domain of the PU.1 transcription factor has been crystallized in complex with a 16-base pair oligonucleotide that contains the recognition sequence. The crystals formed in the space group C2 with a = 89.1, b = 101.9, c = 55.6 A, and beta = 111.2 degrees and diffract to at least 2.3 A. There are two complexes in the asymmetric unit. Production of large usable crystals was dependent on the length of both protein and DNA components, the use of oligonucleotides with unpaired A and T bases at the termini, and the presence of polyethylene glycol and zinc acetate in the crystallization solutions. This is the first ETS domain to be crystallized, and the strategy used to crystallize this complex may be useful for other members of the ets family.

Repression of I-A beta gene expression by the transcription factor PU.1

The PU.1 protein is an ets-related transcription factor that is expressed in macrophages and B lymphocytes. We present evidence that PU.1 binds to the promoter of the I-A beta gene, i.e. a PU box located next to the Y box. Transfection of PU.1 in B lymphocytes or in interferon-gamma-treated macrophages represses I-A beta gene expression. The inhibitory effect of PU.1 was obtained with the DNA binding domain of the protein, but not with the activation domain. Using the gel shift retardation assay we found that in vitro transcribed/translated NF-YA and NF-YB bind to the Y box of the I-A beta promoter. When PU.1 was added to the assay, a supershifted DNA band was found, indicating that PU.1 and NFY proteins bind to the same DNA molecule. We conclude that I-A beta gene expression is repressed by PU.1 binding to the PU box domain.

Repression of major histocompatibility complex I-A beta gene expression by dbpA and dbpB (mYB-1) proteins

The induction of major histocompatibility complex class II gene expression is mediated by three DNA elements in the promoters of these genes (W, X, and Y boxes). The Y box contains an inverted CCAAT box sequence, and the binding activity to the CAAT box is mediated by factor NF-Y, which is composed of subunits NF-YA and NF-YB. We have found that transfection of either dbpA or dbpB (mYB-1) or both inhibits I-A beta gene expression. Although the genes for some members of the Y-box family of binding proteins have been isolated by screening an expression library using the Y-box sequence, under our conditions no binding of dbpA or dbpB to the Y box of the I-A beta or I-E alpha promoter was detected. This suggested that repression of I-A beta gene expression by dbpA and dbpB was not due to competition for binding to the Y-box sequence. The results suggest two other mechanisms by which dbpA and dbpB can inhibit transcription from the I-A beta promoter. When dbpA was added, the binding of NF-YA to DNA increased, which could be explained by interaction between these two proteins whose purpose is to increase the binding affinity of NF-YA for DNA. However, this complex was unable to stimulate transcription from the I-A beta promoter. Thus, dbpA competed for the interaction between NF-YA and NF-YB by binding to NF-YA. When dbpB factor was added together with NF-YA and NF-YB, the binding of the NF-YA--NF-YB complex was reduced. This suggested that dbpB may complete with NF-YB for interaction with NF-YA. These results provide an example of how dbpA and dbpB may regulate transcription of promoters that utilize NF-Y as a transcription factor.

Binding of an ETS-related protein within the DNase I hypersensitive site of the HER2/neu promoter in human breast cancer cells

Promoter elements accounting for HER2 (c-erbB-2/neu) overexpression were searched for in several human breast cancer cell lines (MDA-453, BT-474, ZR-75-1, MCF-7) known to express constitutively a 30-fold range in HER2 transcripts per gene copy. HER2 overexpressing cells showed a single prominent DNase I hypersensitive site near a conserved and hitherto unrecognized ets response element (GAGGAA), located 38 bases down-stream from the CAAT box and directly 5' of the TATA box in the human HER2 promoter. Transient transfection of HER2 promoter constructs (0.125, 0.5, and 2.0 kilobase pairs (kb)) demonstrated that the most proximal promoter region (0.125 kb) was capable of conferring up to 30-fold enhanced activity in HER2-overexpressing cell lines relative to low HER2-expressing control lines. Site-directed mutagenesis of the ets response element (GAGGAA-->GAGAGA) caused a > or = 60% reduction in promoter activity affecting at least 0.5 kb of upstream HER2 regulatory sequence. Gel-shift assays with nuclear extracts and oligonucleotide sequences spanning the 0.125-kb promoter region detected an ETS-immunoreactive complex, present most abundantly in cells overexpressing HER2, whose high-affinity binding depended on the GAGGAA response element. Methylation interference confirmed the ETS-specific pattern of protein binding by this complex to guanine bases in the ets response element. UV cross-linking and immunoprecipitation implicate a approximately 60-kDa ETS protein, and candidate ETS genes expressed in these breast cancer cells include GABP alpha, elk-1, elf-1, and PEA3.