Nuclear signaling in human neutrophils. Stimulation of RNA synthesis is a response to a limited number of proinflammatory agonists

In Vitro Effects of Certain Membrane-acting Agents on Superoxide and Hydrogen Peroxide Production, Protein Synthesis and Membrane ATPase Activity in Buffalo PMN Cells

Polymorphonuclear (PMN) cells play a key role in innate immunity, due to their ability to produce reactive oxidants such as superoxide (O2–) and hydrogen peroxide (H2O2), and to release antimicrobial proteins and peptides stored in their lysosomal granules. In the present study, the effects of the activation of buffalo PMN cells with various membrane-acting agents were evaluated in terms of O2– and H2O2 production, the activities of membrane ATPases, and protein synthesis. Studies involving the incorporation of 35S-methionine revealed significant protein-synthesising ability in resting PMN cells and in cells treated with lipopolysaccharide (LPS), as well as with opsonised zymosan (OZ). Protein synthesis, as judged by fluorography of the cytosolic fraction, showed more than 12 bands, whilst the cytoskeletal fraction showed 2–3 bands. PMN activation with concanavalin A (ConA), digitonin and sodium nitroprusside (SNP) resulted in increased O2– and H2O2 production. However, in the presence of anti-inflammatory agents such as indomethacin and cortisol, the production of O2– and H2O2 by these cells was found to decline. Studies pertaining to membrane ATPases revealed that verapamil hydrochloride (VpHCl) significantly increased total ATPase and Na+K+ATPase activity. ConA treatment yielded only a moderate level of activity. Similarly, digitonin up to 24μM also caused a significant increase in ATPase activity. Our observations indicate that these membrane-acting agents influenced oxygen-dependent and oxygen-independent microbicidal mechanisms in buffalo PMN cells.

Transcription of liver X receptor is down-regulated by 15-deoxy-Δ(12,14)-prostaglandin J(2) through oxidative stress in human neutrophils

Liver X receptors (LXRs) are ligand-activated transcription factors of the nuclear receptor superfamily. They play important roles in controlling cholesterol homeostasis and as regulators of inflammatory gene expression and innate immunity, by blunting the induction of classical pro-inflammatory genes. However, opposite data have also been reported on the consequences of LXR activation by oxysterols, resulting in the specific production of potent pro-inflammatory cytokines and reactive oxygen species (ROS). The effect of the inflammatory state on the expression of LXRs has not been studied in human cells, and constitutes the main aim of the present work. Our data show that when human neutrophils are triggered with synthetic ligands, the synthesis of LXRα mRNA became activated together with transcription of the LXR target genes ABCA1, ABCG1 and SREBP1c. An inflammatory mediator, 15-deoxy-Δ^12,14-prostaglandin J₂ (15dPGJ₂), hindered T0901317-promoted induction of LXRα mRNA expression together with transcription of its target genes in both neutrophils and human macrophages. This down-regulatory effect was dependent on the release of reactive oxygen species elicited by 15dPGJ₂, since it was enhanced by pro-oxidant treatment and reversed by antioxidants, and was also mediated by ERK1/2 activation. Present data also support that the 15dPGJ₂-induced serine phosphorylation of the LXRα molecule is mediated by ERK1/2. These results allow to postulate that down-regulation of LXR cellular levels by pro-inflammatory stimuli might be involved in the development of different vascular diseases, such as atherosclerosis.

Expression profiling of human immune cell subsets identifies miRNA-mRNA regulatory relationships correlated with cell type specific expression

Blood consists of different cell populations with distinct functions and correspondingly, distinct gene expression profiles. In this study, global miRNA expression profiling was performed across a panel of nine human immune cell subsets (neutrophils, eosinophils, monocytes, B cells, NK cells, CD4 T cells, CD8 T cells, mDCs and pDCs) to identify cell-type specific miRNAs. mRNA expression profiling was performed on the same samples to determine if miRNAs specific to certain cell types down-regulated expression levels of their target genes. Six cell-type specific miRNAs (miR-143; neutrophil specific, miR-125; T cells and neutrophil specific, miR-500; monocyte and pDC specific, miR-150; lymphoid cell specific, miR-652 and miR-223; both myeloid cell specific) were negatively correlated with expression of their predicted target genes. These results were further validated using an independent cohort where similar immune cell subsets were isolated and profiled for both miRNA and mRNA expression. miRNAs which negatively correlated with target gene expression in both cohorts were identified as candidates for miRNA/mRNA regulatory pairs and were used to construct a cell-type specific regulatory network. miRNA/mRNA pairs formed two distinct clusters in the network corresponding to myeloid (nine miRNAs) and lymphoid lineages (two miRNAs). Several myeloid specific miRNAs targeted common genes including ABL2, EIF4A2, EPC1 and INO80D; these common targets were enriched for genes involved in the regulation of gene expression (p<9.0E-7). Those miRNA might therefore have significant further effect on gene expression by repressing the expression of genes involved in transcriptional regulation. The miRNA and mRNA expression profiles reported in this study form a comprehensive transcriptome database of various human blood cells and serve as a valuable resource for elucidating the role of miRNA mediated regulation in the establishment of immune cell identity.

Proteinase-activated receptor-2 up-regulation by Fcgamma-receptor activation in human neutrophils

We shed new light on the expression and function of the proteinase-activated receptor (PAR) family, associated with inflammation and hyperalgesia, in human granulocytes. Resting cells expressed constitutive levels of PAR-2 and PAR-3 mRNA but not PAR-1 or PAR-4. Based on flow cytometry, stimulation with opsonized bacteria (Bop) specifically up-regulated cell surface expression of PAR-2 in a concentration-dependent and time-dependent manner, independent of transcription or de novo protein synthesis. Primary granules were identified as a source of preformed PAR-2 that can readily be mobilized at the surface on fusion with the plasma membrane. Cellular response to PAR-2 activation, measured as changes in intracellular calcium concentration, was enhanced in PAR-2 up-regulated cells. Increase of cell-surface PAR-2 and of cell responsiveness were dependent specifically on the engagement of immunoglobulin (Ig)-binding receptors. Together, our results reveal that mobilization of intracellular granules, in response to Ig-receptor activation, up-regulates PAR-2 surface expression and makes neutrophils more responsive to proteinase activity. This enhanced response to PAR-2 activation indicates that molecular communication between pain and inflammation may be more important than previously believed.

Reorganization of nuclear factors during myeloid differentiation

Differentiation in several stem cell systems is associated with major morphological changes in global nuclear shape. We studied the fate of inner-nuclear structures, splicing factor-rich foci and Cajal (coiled) bodies in differentiating hemopoietic, testis and skin tissues. Using antibodies to the splicing factors PSF, U2AF(65) and snRNPs we find that these proteins localize in foci throughout the nuclei of immature bone marrow cells. Yet, when granulocytic cells differentiate and their nuclei condense and become segmented, the staining localizes in a unique compact and thread-like structure. The splicing factor-rich foci concentrate in the interior of these nuclei while the nuclear periphery and areas of highly compact chromatin remain devoid of these molecules. Differentiated myeloid cells do not stain for p80 coilin, the marker for Cajal bodies. Immature myeloid cells contain Cajal bodies although these usually do not coloclaize with PSF-rich foci. Following complete inhibition of transcription in myeloid cells, the threaded PSF pattern becomes localized in several foci in the different lobes of mature granulocytes while in human HL-60 immature myeloid leukemia cells PSF is found in the perinucleolar compartment. Studies of other differentiating stem cell systems show that PSF staining disappears completely in differentiated, transcriptionally inactive sperm cells, is scarce as cells migrate from the inner skin layers outward and is lost as cells of the hair follicle mature. We conclude that the formation and distribution of splicing factor-rich foci in the nucleus during differentiation of various cell lineages is dependent on the levels of chromatin condensation and the differentiation status of the cell.

Lipid mediator class switching during acute inflammation: signals in resolution

Leukotrienes (LTs) and prostaglandins (PGs) amplify acute inflammation, whereas lipoxins (LXs) have unique anti-inflammatory actions. Temporal analyses of these eicosanoids in clinical and experimental exudates showed early coordinate appearance of LT and PG with polymorphonuclear neutrophil (PMN) recruitment. This was followed by LX biosynthesis, which was concurrent with spontaneous resolution. Human peripheral blood PMNs exposed to PGE2 (as in exudates) switched eicosanoid biosynthesis from predominantly LTB4 and 5-lipoxygenase (5-LO)-initiated pathways to LXA4, a 15-LO product that "stopped" PMN infiltration. These results indicate that first-phase eicosanoids promote a shift to anti-inflammatory lipids: functionally distinct lipid-mediator profiles switch during acute exudate formation to "reprogram" the exudate PMNs to promote resolution.

Human neutrophil gelatinase-associated lipocalin and homologous proteins in rat and mouse

Neutrophil gelatinase-associated lipocalin (NGAL) is a 25-kDa lipocalin originally purified from human neutrophils. It exists in monomeric and homo- and heterodimeric forms, the latter as a dimer with human neutrophil gelatinase. It is secreted from specific granules of activated human neutrophils. Homologous proteins have been identified in mouse (24p3/uterocalin) and rat (alpha(2)-microglobulin-related protein/neu-related lipocalin). Structural data have confirmed a typical lipocalin fold of NGAL with an eight-stranded beta-barrel, but with an unusually large cavity lined with more polar and positively charged amino acid residues than normally seen in lipocalins. Chemotactic formyl-peptides from bacteria have been proposed as ligands of NGAL, but binding experiments and the structure of NGAL do not support this hypothesis. Besides neutrophils, NGAL is expressed in most tissues normally exposed to microorganisms, and its synthesis is induced in epithelial cells during inflammation. This may indicate either a microbicidal activity of NGAL or a role in regulation of inflammation or cellular growth, putative functions yet to be demonstrated.

Alteration in the responsiveness to tumour necrosis factor-alpha is crucial for maximal expression of monocyte chemoattractant protein-1 in human neutrophils

We previously reported delayed expression of monocyte chemoattractant protein-1 (MCP-1) in human neutrophils cultured with a cytokine-rich crude supernatant of phytohaemagglutinin-stimulated peripheral blood mononuclear cells (PHA-sup). Tumour necrosis factor-alpha (TNF-alpha) contained in the PHA-sup played a key role in this event, but there appeared to be another factor(s) in the same supernatant that co-operated with TNF-alpha for maximal MCP-1 expression. In the present study, we reduced TNF-alpha concentrations in the PHA-sup to minimal levels using anti-TNF-alpha affinity columns (TNF-depleted-sup) and investigated the co-operation between TNF-alpha and TNF-depleted-sup. Nine hours of preincubation with TNF-depleted-sup altered the responsiveness of neutrophils to TNF-alpha and enabled TNF-alpha to increase the level of MCP-1 expression to a maximal level within 4 hr. The priming effect was not due to the increased expression of cell-surface TNF receptors. However, the activation of primed cells by TNF-alpha was clearly through TNF receptor-p55. Finally, the activity in the TNF-depleted-sup that co-operated with TNF-alpha was eluted at 60 000 MW on high-performance liquid chromatography-gel filtration. Thus, delayed neutrophil expression of MCP-1 is regulated by a cytokine-dependent mechanism that induces neutrophils to enter a 'mature' stage.

Corticotropin-Releasing Factor Receptor 1 in Mouse Spleen: Expression After Immune Stimulation and Identification of Receptor-Bearing Cells

A specific polyclonal Ab against the N-terminal domain of corticotropin-releasing factor (CRF) receptor, type 1 (CRF-R1), was employed to an immunohistochemical analysis of the spleen from naive mice and mice exposed to an immune challenge. Cell types stained with anti-CRF-R1 Ab were identified by their nuclear shapes and colocalization with the cell type-specific markers ER-MP58, ER-MP20, Moma-1, Moma 2, anti-CD3e mAbs, and anti-Ig Ab. Only a few clusters of CRF-R1+ cells were found in spleen sections of naive mice at sites typical for granulopoietic islands. However, a 17-fold increase in the mean number of CRF-R1+ cells was noted within hours following a challenge of acute systemic inflammation induced by i.p. administration of LPS. The majority of these cells were identified as mature neutrophils. CRF-R1 was shown to mediate suppression of the IL-1β secretion by these cells. However, at later time points a large number of granulocyte-macrophage precursors was strongly labeled with anti-CRF-R1 Ab. Western blot analysis of splenic membranes from animals treated with LPS revealed a m.w. of approximately 70,000 for CRF-R1. Subcellular staining patterns were suggestive for the predominant localization of CRF-R1 on granule membranes. CRF-R1 mRNA was detected in spleen but not in bone marrow and peripheral blood leukocytes from naive mice. Thus, it was indicated that CRF-R1 was not produced constitutively by mature or immature neutrophils. Its production was rather triggered by inflammatory stimuli.

MENT, a heterochromatin protein that mediates higher order chromatin folding, is a new serpin family member

Terminal cell differentiation is correlated with the extensive sequestering of previously active genes into compact transcriptionally inert heterochromatin. In vertebrate blood cells, these changes can be traced to the accumulation of a developmentally regulated heterochromatin protein, MENT. Cryoelectron microscopy of chicken granulocyte chromatin, which is highly enriched with MENT, reveals exceptionally compact polynucleosomes, which maintain a level of higher order folding above that imposed by linker histones. The amino acid sequence of MENT reveals a close structural relationship with serpins, a large family of proteins known for their ability to undergo dramatic conformational transitions. Conservation of the "hinge region" consensus in MENT indicates that this ability is retained by the protein. MENT is distinguished from the other serpins by being a basic protein, containing several positively charged surface clusters, which are likely to be involved in ionic interactions with DNA. One of the positively charged domains bears a significant similarity to the chromatin binding region of nuclear lamina proteins and with the A.T-rich DNA-binding motif, which may account for the targeting of MENT to peripheral heterochromatin. MENT ectopically expressed in a mammalian cell line is transported into nuclei and is associated with intranuclear foci of condensed chromatin.

Treatment with Anti-Granulocyte Antibodies Inhibits the Effector Phase of Experimental Autoimmune Encephalomyelitis

Emerging data suggest that polymorphonuclear leukocytes (PMNLs) can play an important role in Ag-dependent immune responses. Therefore, we have assessed the involvement of these cells in the development of an organ-specific autoimmune disease, experimental autoimmune encephalomyelitis (EAE), in the mouse. Depletion of peripheral blood PMNLs beginning day 8 after immunization significantly delayed and in some cases totally prevented the development of clinical EAE in mice. Depletion of PMNLs beginning 1 day before sensitization and continuing until day 7 postimmunization had no effect on the subsequent development of EAE, suggesting that depletion alters the efferent but not the afferent arm of the immune response. In vitro studies showed that lymphoid cells from mice protected from EAE by PMNL depletion beginning on day 8 postsensitization proliferated in response to specific Ag to a level equal to cells from sensitized animals treated with control serum, again indicating that treatment was not affecting the afferent limb of the immune response. Further evidence that PMNL may be necessary in initiating the pathology of EAE was seen in passive transfer experiments where PMNL-depleted recipients of MBP-specific lymphoid effector cells developed EAE much less effectively than did animals treated with control Ab. Taken together, these data indicate that PMNLs play a critical role in the effector phase of the development of the clinicopathologic expression of EAE in mice.

Regulation of Chemokine Gene Expression in Human Peripheral Blood Neutrophils Phagocytosing Microbial Pathogens

Production of chemokines (chemotactic cytokines) by neutrophils is likely to be important in the regulation of inflammation and the control of infection. In this study we show that exposure of human neutrophils to various microbial pathogens leads to the production of both macrophage inflammatory protein 1α (MIP-1α) and IL-8. The bacterial microbes, Salmonella typhimurium and Pseudomonas aeruginosa, and Staphylococcus aureus all strongly induced both IL-8 and MIP-1α secretion, whereas Streptococcus pneumoniae, Staphylococcus epidermidis, and the opportunistic yeast Candida albicans were less potent. Saccharomyces cerevisiae and zymosan both induced IL-8 secretion but failed to stimulate that of MIP-1α. Coincubation of neutrophils with the proinflammatory cytokine TNF-α and the micro-organisms also led to differential expression of MIP-1α and IL-8. Significant enhancement of the induction of both MIP-1α and IL-8 by S. typhimurium, P. aeruginosa, and S. pneumoniae as well as by C. albicans was observed. In contrast, while IL-8 production in response to S. cerevisiae and zymosan was enhanced in the presence of TNF-α, no MIP-1α was produced. These combined results indicate that while neutrophils exposed to some micro-organisms alone or in the presence of inflammatory cytokines such as TNF-α will produce both MIP-1α and IL-8, resulting in generation of signals for the recruitment of mononuclear leukocytes and neutrophils, respectively, certain types of micro-organisms can skew this response toward synthesis of IL-8.

The N-formyl peptide receptor: a model for the study of chemoattractant receptor structure and function

N-formyl peptides, such as fMet-Leu-Phe, are one of the most potent chemoattractants for phagocytic leukocytes. The interaction of N-formyl peptides with their specific cell surface receptors has been studied extensively and used as a model system for the characterization of G-protein-coupled signal transduction in phagocytes. The cloning of the N-formyl peptide receptor cDNA from several species and the identification of homologous genes have allowed detailed studies of structural and functional aspects of the receptor. Recent findings that the receptor is expressed in nonhematopoietic cells and that nonformylated peptides can activate the receptor suggest potentially novel functions and the existence of additional ligands for this receptor.

Absence of the IL-7 receptor component CDw127 indicates that gamma(c) expression alone is insufficient for IL-7 to modulate human neutrophil responses

It has been proposed that neutrophils are targets for interleukin-7 (IL-7) because this cytokine was found to increase the number of murine immature neutrophils in vivo. In addition, some nonhuman myeloid cell lines were shown to express the IL-7 receptor (IL-7R). Moreover, it was recently discovered that human neutrophils constitutively express the common gamma chain (gamma(c)), known to be a component of not only IL-7R, but also IL-2R, IL-4R, IL-9R, and IL-15R. Among these, we have recently observed that IL-4 and IL-15 are neutrophil agonists. All of the above observations prompted us to study IL-7-human neutrophil interactions. In this study, we investigated potential effects of IL-7 on a range of neutrophil responses. Although we were able to confirm the presence of the gamma(c) component on human neutrophils, we report, for the first time, that these cells lack the CDw127 component of IL-7R. When studying potential modulatory effects of IL-7 on human neutrophils, we found that IL-7 does not induce respiratory burst, phagocytosis, or cytoskeletal functions and does not alter gene expression. Positive controls were included in each assay and the expected results were obtained. In addition, in contrast to IL-4 and IL-15, we found that neutrophil apoptosis is not modulated by IL-7, while granulocyte-macrophage colony-stimulating factor, used here as control, strongly delayed this process as expected. We conclude that the sole expression of gamma(c) on human neutrophils is insufficient to modulate neutrophil responses with respect to the studied functions. Therefore, it cannot be proposed, based on studies performed with nonhuman cells or cell lines, that human neutrophils are targets for IL-7.

Induction of NGAL synthesis in epithelial cells of human colorectal neoplasia and inflammatory bowel diseases

In inflammatory and neoplastic disorders of the colon a defect barrier function of the mucosa may result in absorption of bacterial products from the intestinal lumen. These products may further recruit inflammatory cells and thus augment the inflammatory response. A novel lipocalin in neutrophils, neutrophil gelatinase associated lipocalin (NGAL), with the ability to bind bacterial formylpeptides, has been described and therefore it is of interest to investigate the expression of this protein in diseases of the colon. Expression of NGAL was investigated by immunohistochemistry and by mRNA in situ hybridisation in normal colon and in neoplastic and inflammatory colorectal diseases. A very high expression of NGAL was seen in colonic epithelium in areas of inflammation, both in non-malignant epithelium (diverticulitis, inflammatory bowel disease, and appendicitis) as well as in premalignant and malignant neoplastic lesions of the colon. In adenocarcinoma, the NGAL expression was especially abundant in the transitional mucosa and in the superficial ulcerated area. On the other hand, no NGAL expression could be detected in lymph node metastases from these adenocarcinomas. A weak expression of NGAL in some epithelial cells was only occasionally seen in normal colon. In conclusion, NGAL synthesis is induced in epithelial cells in inflammatory and neoplastic, colorectal diseases. NGAL may serve an important anti-inflammatory function as a scavenger of bacterial products.

Inhibition by FK506 of formyl peptide-induced neutrophil activation and associated protein synthesis

The macrolide FK506 inhibited, by up to 50%, neutrophil migration and the production of the superoxide radical in response to the formyl peptide, formyl-methionyl-leucyl-phenylalanine (FMLP). The production of the superoxide radical in response to phorbol 12-myristate 13-acetate (PMA) was unaffected by FK506. The inhibition of neutrophil functions was accompanied by a partial reversal of FMLP-induced synthesis of cellular proteins, despite a rise in intracellular Ca2+. Neutrophils treated with FK506 demonstrated a small (average 23%) though significant decrease in formyl-peptide receptor numbers but receptor binding affinity was unaffected. The effects of FK506 on neutrophil activation appear to be analogous to those in T-lymphocytes. The incomplete inhibition, by FK506, of neutrophil responses suggests further that activation by FMLP is mediated via distinct multiple signalling pathways, including protein kinase activation and protein synthesis. The inability of FK506 to reduce FMLP-induced rises in cellular Ca2+ or PMA-induced activation of neutrophils suggests that its action is distal to Ca2+ mobilization and distinct from pathways relying on PKC activation. Thus the immunosuppressive effects of FK506 in vivo might be mediated through the inhibition of inflammatory cells other than lymphocytes and the drug therefore has therapeutic potential in a variety of inflammatory conditions. The drug also has potential in vitro for the characterization of signalling pathways from the plasma membrane to the nucleus.

Programmed cell death of the normal human neutrophil: an in vitro model of senescence

The present study provides experimental data which indicate that the neutrophil is ideal for studying programmed cell death or apoptosis in vitro. Neutrophils can be obtained from human peripheral blood in large numbers with minimal experimental manipulation and are easily separated from other leukocytes, providing nearly pure cell suspensions. The neutrophil life span in vitro is sufficiently short to allow observations to be made within eight hours after experimental manipulation. Neutrophils can also be easily maintained in serum-free, chemically defined media which can be systematically altered, thereby defining specific variables that influence the apoptotic process. Since the neutrophils do not need an exogenous trigger to undergo programmed cell death, it is also an excellent model to study senescence. It was determined from this study that neutrophils undergo apoptosis most efficiently at 37 degrees C, a temperature requirement for physiologic cell death. Neutrophils undergo apoptosis at a slightly faster rate and maintain membrane integrity better when incubated in a tissue culture medium (e.g., RPMI 1640) compared with a balanced salt solution (e.g., HBBB). Cycloheximide, an inhibitor of protein synthesis, was shown to accelerate apoptosis in a dose-dependent manner. The presence of Zn++ significantly decreased the rate of apoptosis, whereas the presence of Ca++ and Mg++ had no apparent effect. These studies indicate that the process of senescence, culminating in cell death, is subject to modulation by a variety of agents and experimental conditions. In addition, the ultrastructural features of neutrophils undergoing programmed cell death in vitro were compared in detail to those occurring in vivo and were found to be comparable.

Differential expression of two major cytokines produced by neutrophils, interleukin-8 and the interleukin-1 receptor antagonist, in neutrophils isolated from the synovial fluid and peripheral blood of patients with rheumatoid arthritis

OBJECTIVE

Neutrophils have been shown to produce interleukin-8 (IL-8) and interleukin-1 receptor antagonist (IL-1ra) in large amounts compared with other cytokines. Since IL-8 has a proinflammatory action whereas IL-1ra is antiinflammatory, our objective was to examine the relative levels of production of these cytokines by synovial fluid (SF) neutrophils isolated from patients with rheumatoid arthritis (RA).

METHODS

We measured cytokine production using an enzyme-linked immunosorbent assay and analyzed messenger RNA accumulation in cells by Northern blot.

RESULTS

SF neutrophils produced significantly more IL-8 and IL-1 beta, but significantly less IL-1ra, than peripheral blood neutrophils.

CONCLUSION

These observations provide new information on the production of pro- and antiinflammatory molecules by neutrophils in the SF environment, and their possible role in RA.

Human chemotaxis receptor genes cluster at 19q13.3-13.4. Characterization of the human C5a receptor gene

The human C5a anaphylatoxin and formyl peptide receptor genes, as well as two genes with high sequence identity to the formyl peptide receptor, FPRH1 and FPRH2, have been mapped to chromosome 19 (Lu et al., 1992). Further analysis reveals that these genes are present in the 19q13.3 band adjacent to the 13.3-13.4 interface. MRNAs for the C5a and formyl peptide receptors, as well as for FPRH1, are expressed in cAMP differentiated U937 cells and human eosinophils, while all four transcripts are expressed in human lung. This observation opens the possibility for coordinate regulation of these genes. In order to initiate the mapping of fine structure at this locus, genomic clones have been analyzed. All four of the genes have a similar structure, with the receptor protein encoded in a single exon. Detailed characterization of the C5a receptor gene reveals a two exon structure, with the 5' untranslated sequence and initiating methionine located in the first exon. An intron of approximately 9 kb separates exon 1 from the receptor-encoding exon 2. The region of genomic DNA flanking the 5' untranslated sequence possesses promoter activity when transfected into the myeloid-derived rat basophilic leukemia RBL-1 cells, but the same region is inactive when transfected into nonmyeloid cells. Deletional analyses indicate that C5a receptor 5' flanking region contains both cell-specific suppressor and promoter regions.

Involvement of a disulfide bond in the binding of flunitrazepam to the benzodiazepine receptor from bovine cerebral cortex

The effects of chemical modification of a disulfide bond(s) (-SS-) or sulfhydryl group(s) (-SH) on the [3H]-flunitrazepam ([3H]FNZ) binding to membrane-bound or immunoprecipitated benzodiazepine (BZD) receptors (BZD-R) from bovine cerebral cortex were examined. Reduction of -SS- with dithiothreitol (DTT) brought about a reversible, time- and dose-dependent inhibition of [3H]FNZ binding to the membrane-bound BZD-R. Alkylation of the membranes with the -SH-modifying reagent iodoacetamide (IAA) or 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) produced a slight inhibition of [3H]FNZ binding in a dose-dependent manner. Scatchard analysis of saturation curves of [3H]FNZ binding in the presence and absence of 5 mM DTT revealed changes in affinity without modification in the maximal binding capacity, thus indicating a competitive mode of interaction. DTT pretreatment of both the membrane-bound and the immunoprecipitated BZD-R led to [3H]FNZ binding inhibition. Consistent with the modification of a binding site is the observation that reduction of -SS- does not bear on the binding affinity, but rather reduces the number of sites. Complete protection from DTT inhibition of [3H]FNZ binding by FNZ (an agonist) or by Ro 15-1788 (an antagonist) suggests the presence of -SS- at, or very close to, the BZD recognition binding site. No protection against IAA or DTNB inhibition was provided by FNZ. Photoaffinity labeling experiments with [3H]FNZ revealed a clear-cut band of 50 kDa in native and alkylated membranes but an extremely weak label in 5 mM DTT/IAA-treated membranes. The present results provide evidence for the participation of a disulfide bond in the recognition binding site of the bovine cerebral cortex BZD-R.

Interleukin-1 receptor antagonist

IL-1ra is the first described naturally occurring receptor antagonist of any cytokine or hormone-like molecule. IL-1ra is a member of the IL-1 family by three criteria: amino acid sequence homology of 26 to 30% to IL-1 beta and 19% to IL-1 alpha; similarities in gene structure; and common gene localization to human chromosome 2q14. Two structural variants of IL-1ra exist: sIL-1ra, a secretory molecule produced by monocytes, macrophages, neutrophils, fibroblasts, and other cells; and icIL-1ra, an intracellular molecule produced by keratinocytes and other epithelial cells, macrophages, and fibroblasts. IL-1ra production by monocytes, macrophages, and neutrophils may be regulated in a differential fashion with IL-1 beta. Human IL-1ra binds to both human IL-1RIs and IL-1RIIs on cell surfaces, although with 100-fold greater avidity to IL-1RIs. IL-1ra may bind preferentially to soluble IL-1RIs and not at all to soluble IL-1RIIs. IL-1ra competitively inhibits binding of both IL-1 alpha and IL-1 beta to cell surface receptors without inducing any discernible intracellular responses. All three forms of IL-1 may bind to IL-1 receptors in a similar fashion but IL-1ra may lack the secondary interactions necessary to trigger cell responses. A 100-fold or greater excess of IL-1ra over IL-1 may be necessary to inhibit biological responses to IL-1 both in vitro and in vivo. The roles of sIL-1ra and icIL-1ra in normal physiology or in host defense mechanisms remain unclear. The administration of IL-1ra blocks the effects of IL-1 in some animal models of septic shock, inflammatory arthritis, graft-versus-host disease, and inflammatory bowel disease. The preliminary results of clinical trials in humans indicate possible efficacy of IL-1ra in sepsis syndrome, rheumatoid arthritis, and GVHD.