Cycloheximide, an inhibitor of protein synthesis, prevents gamma-interferon-induced expression of class II mRNA in a macrophage cell line

Large-scale chromatin organization of the major histocompatibility complex and other regions of human chromosome 6 and its response to interferon in interphase nuclei

The large-scale chromatin organization of the major histocompatibility complex and other regions of chromosome 6 was studied by three-dimensional image analysis in human cell types with major differences in transcriptional activity. Entire gene clusters were visualized by fluorescence in situ hybridization with multiple locus-specific probes. Individual genomic regions showed distinct configurations in relation to the chromosome 6 terrritory. Large chromatin loops containing several megabases of DNA were observed extending outwards from the surface of the domain defined by the specific chromosome 6 paint. The frequency with which a genomic region was observed on an external chromatin loop was cell type dependent and appeared to be related to the number of active genes in that region. Transcriptional up-regulation of genes in the major histocompatibility complex by interferon-gamma led to an increase in the frequency with which this large gene cluster was found on an external chromatin loop. Our data are consistent with an association between large-scale chromatin organization of specific genomic regions and their transcriptional status.

Glutarimide: a carrier transporting drug through cell membranes

It is suggested that glutarimide moiety (2,6-piperidinedione) with the intact imide group (OC-NH-CO) and substituted at alpha or beta position in the ring, is acting as the carrier molecule (vector), which transports biologically active substituents (functional groups) through cell membranes. The results obtained from quantum chemical calculations and experimental studies indicate that structural features and physicochemical properties of glutarimide moiety are remarkably similar with those of uracil derivatives. Therefore, glutarimide drug may interact with specific receptors involved in transport of uracil and thymine nucleosides and it may easily cross biological membranes. (c) 2000 Harcourt Publishers Ltd.

HLA-DMB expression by thyrocytes: indication of the antigen-processing and possible presenting capability of thyroid cells

Expression of HLA class II molecules on thyrocytes is a characteristic feature of autoimmune thyroid disease and may lead the thyroid cells to present autoantigens to CD4+ T lymphocytes. Since HLA-DM is a critical molecule in class II-restricted antigen processing and presentation, we assessed the expression of HLA-DMB, -invariant chain (Ii), class II transactivator (CIITA) and DRA in an untransformed, pure thyrocyte strain HTV-59A. Here we report that both HLA-DMB mRNA and the protein are expressed in thyrocytes and that CIITA expression is enhanced by interferon-gamma (IFN-gamma) treatment and occurs before DMB, Ii and DRA up-regulation, suggesting CIITA expression is a requirement for antigen processing in thyrocytes. These results indicate that thyrocytes are capable of antigen processing and possibly antigen presentation to T cells.

The cytokine-adhesion molecule cascade in ischemia/reperfusion injury of the rat kidney. Inhibition by a soluble P-selectin ligand

Ischemia/reperfusion (I/R) injury associated with renal transplantation may influence both early graft function and late changes. The initial (</= 7 d) events of warm and in situ perfused cold ischemia of native kidneys in uninephrectomized rats were examined. mRNA expression of the early adhesion molecule, E-selectin, peaked within 6 h; PMNs infiltrated in parallel. T cells and macrophages entered the injured kidney by 2-5 d; the associated upregulation of MHC class II antigen expression suggested increased immunogenicity of the organ. Th1 products (IL-2, TNFalpha, IFNgamma) and macrophage-associated products (IL-1, IL-6, TGFbeta) remained highly expressed after 2 d. To examine directly the effects of selectins in I/R injury, a soluble P-selectin glycoprotein ligand (sPSGL) was used. Ischemic kidneys were perfused in situ with 5 microg of sPSGL in UW solution; 50 microg was administered intravenously 3 h after reperfusion. E-selectin mRNA remained at baseline, leukocytes did not infiltrate the injured organs throughout the 7-d period, and their associated products were markedly inhibited. Class II expression did not increase. No renal dysfunction secondary to I/R occurred. The early changes of I/R injury may be prevented by treatment with soluble P- and E-selectin ligand. This may reduce subsequent host inflammatory responses after transplantation.

Molecular analysis of G1B and G3A IFN gamma mutants reveals that defects in CIITA or RFX result in defective class II MHC and Ii gene induction

Class II major histocompatibility complex (MHC) genes and the invariant (Ii) gene are inducible by interferon-gamma (IFN gamma) but not by interferon-alpha and interferon-beta. The promoter regions of these genes contain three regulatory elements that mediate constitutive and IFN gamma-induced expressions; however, none of the DNA-binding proteins that interact with these elements are regulated by IFN gamma. Recently, a gene coding for a transactivator (CIITA) of class II MHC genes that complements a HLA-DR-negative immunodeficiency has been isolated. Using one IFN gamma mutant cell line (G3A) that is selectively defective in HLA-DR and Ii induction, four lines of evidence are presented to show that CIITA mediates the IFN gamma induction of HLA-DR and Ii genes. Analysis of another mutant line, G1B, indicates that the lack of DRA and Ii gene induction by IFN gamma is correlated with the lack of RFX DNA binding activity, thus providing the link between RFX and an IFN gamma response.

Class II transactivator (CIITA) is sufficient for the inducible expression of major histocompatibility complex class II genes

The class II transactivator (CIITA) has been shown to be required for major histocompatibility complex (MHC) class II gene expression in B cells and its deficiency is responsible for a hereditary MHC class II deficiency. Here we show that CIITA is also involved in the inducible expression of class II genes upon interferon gamma (IFN-gamma) treatment. The expression of CIITA is also inducible with IFN-gamma before the induction of MHC class II mRNA. In addition, CIITA mRNA expression does not require new protein synthesis, although new protein synthesis is necessary for the transcription of class II. This suggests that synthesis of new CIITA protein may be essential to induce class II gene expression. We also showed that the JAK1 protein tyrosine kinase activity is required to induce the expression of CIITA upon IFN-gamma stimulation. This finding indicates that CIITA is part of the signaling cascade from the IFN-gamma receptor to the activation of class II genes. In addition, the expression of CIITA is sufficient to activate class II genes in the absence of IFN-gamma stimulation suggesting that CIITA is the major regulatory factor for the inducible expression of class II genes. Together, these data suggest that CIITA is the IFN-inducible cycloheximide sensitive factor previously shown to be required for the induction of MHC class II gene expression.

Two cis-DNA elements involved in myeloid-cell-specific expression and gamma interferon (IFN-gamma) activation of the human high-affinity Fc gamma receptor gene: a novel IFN regulatory mechanism

The human high-affinity receptor for the constant region of immunoglobulin G (human Fc gamma R1) is encoded by two mRNAs induced selectively by gamma interferon (IFN-gamma) and expressed in cells of myeloid lineage. The cis-DNA element (GRR) previously found to confer IFN-gamma responsiveness to this gene acts as an inducible enhancer and is the target of an IFN-gamma-activated factor(s) (GIRE-BP) in cells of different origins. Although the GRR motif is not related to the DNA elements involved in the regulation of other IFN-stimulated genes, GIRE-BP binding depends on the IFN-gamma-dependent activation of the 91-kDa protein known to be one of the factors of a transcriptional complex activated by IFN-alpha. Deletions of the Fc gamma R1 promoter allowed us to identify a 25-bp element, downstream from the GRR motif, conferring cell-type-specific expression. This element, called MATE (myeloid activating transcription element), is the DNA target for constitutive factors forming two complexes, MATE-BP1 and MATE-BP2. In accordance with the functional analysis, MATE-BP binding activities were detected in extracts prepared from myeloid cell lines such as THP-1, HL-60, and U-937 but not in HeLa cell extracts. The MATE motif is present not only in the promoter of other Fc receptor genes but also in several promoters of genes whose expression is restricted to monocytic cells. Our results suggest that human Fc gamma R1 gene expression in myeloid cells is initiated by the interaction of IFN-gamma-activated factors with cell-type-specific factors through their binding to the GRR and MATE motifs.

Two cis-DNA elements involved in myeloid-cell-specific expression and gamma interferon (IFN-gamma) activation of the human high-affinity Fc gamma receptor gene: a novel IFN regulatory mechanism

The human high-affinity receptor for the constant region of immunoglobulin G (human Fc gamma R1) is encoded by two mRNAs induced selectively by gamma interferon (IFN-gamma) and expressed in cells of myeloid lineage. The cis-DNA element (GRR) previously found to confer IFN-gamma responsiveness to this gene acts as an inducible enhancer and is the target of an IFN-gamma-activated factor(s) (GIRE-BP) in cells of different origins. Although the GRR motif is not related to the DNA elements involved in the regulation of other IFN-stimulated genes, GIRE-BP binding depends on the IFN-gamma-dependent activation of the 91-kDa protein known to be one of the factors of a transcriptional complex activated by IFN-alpha. Deletions of the Fc gamma R1 promoter allowed us to identify a 25-bp element, downstream from the GRR motif, conferring cell-type-specific expression. This element, called MATE (myeloid activating transcription element), is the DNA target for constitutive factors forming two complexes, MATE-BP1 and MATE-BP2. In accordance with the functional analysis, MATE-BP binding activities were detected in extracts prepared from myeloid cell lines such as THP-1, HL-60, and U-937 but not in HeLa cell extracts. The MATE motif is present not only in the promoter of other Fc receptor genes but also in several promoters of genes whose expression is restricted to monocytic cells. Our results suggest that human Fc gamma R1 gene expression in myeloid cells is initiated by the interaction of IFN-gamma-activated factors with cell-type-specific factors through their binding to the GRR and MATE motifs.

Interferon-γ response region in the promoter of the class II MHC gene, DPA

The class II MHC gene DPA is inducible by interferon-gamma (IFN-gamma), whereas the DQB gene is not inducible in most cell types. To investigate the DNA region specifically responsible for inducibility or its lack that may be required (in addition to the elements required for constitutive expression of class II genes), hybrid promoters were constructed between the proximal 5' regions of the DPA promoter up to -148 bp, which is IFN-gamma inducible, and of the DQB promoter up to -160 bp, which is not inducible. As a result of these and previous studies [9, 10], the region of the DPA gene required for its IFN-gamma inducibility was localized to 27 bp between -55 and -81, including the Y-box element and its flanking nucleotides.

Depletion of tryptophan is not involved in expression of tryptophanyl-tRNA synthetase mediated by interferon

Gamma interferon (IFN-gamma) affects tryptophan metabolism by mediating the expression of indoleamine 2,3-dioxygenase and tryptophanyl-tRNA synthetase. In the present study, we investigated the role of indoleamine 2,3-dioxygenase-mediated tryptophan depletion in the induction of tryptophanyl-tRNA synthetase by IFN-gamma. The addition of excess tryptophan to the culture medium did not affect the induction of tryptophanyl-tRNA synthetase by IFN-gamma, indicating that tryptophan degradation is not directly involved in the IFN-gamma-mediated expression of tryptophanyl-tRNA synthetase.

Interferon-γ regulates expression of a novel keratin classe I gene

Interferon (IFN)-gamma has been implicated in the pathogenesis of several autoimmune disorders and inflammatory skin diseases. To identify novel mediators involved in the IFN-gamma response we have used differential hybridization of a cDNA library prepared from IFN-gamma-treated HeLa cells to isolate a gene that is induced following treatment with IFN-gamma. We report here the molecular cloning and characterization of a cDNA detecting a 1.6-kb mRNA that accumulated in response to IFN-gamma but not in response to IFN-alpha or IFN-beta. The gene is regulated by IFN-gamma in human cell lines of epithelial origin. The mRNA encodes a predicted protein of 432 amino acids and the primary structure of the protein demonstrates that it is a novel member of developmentally regulated keratin class I genes.

Molecular cloning and characterization of an interferon induced human cDNA with sequence homology to a mammalian peptide chain release factor

Here we report the molecular cloning of several related human cDNAs from which a full-length sequence can be determined. The cDNAs encode a 2.8 kb mRNA that is strongly induced by interferon (IFN) gamma and the expression of which is not cell-restricted but observed in fibroblasts, macrophages and epithelial cells. The deduced amino acid sequence predicts a protein of 471 amino acids with high sequence similarity to a previously identified rabbit peptide chain release factor. Functional studies to demonstrate release factor activity showed that the protein encoded by this cDNA inhibited the readthrough activity of a yeast UGA suppressor tRNA in an in vitro translation system. The identification of this novel cDNA implies that translational control by IFN induced proteins may not be restricted to the initial steps of protein synthesis but may also act by regulation of peptide chain termination.

An HLA-DR alpha promoter DNA-binding protein is expressed ubiquitously and maps to human chromosomes 22 and 5

The class II major histocompatibility complex antigens are a family of integral membrane proteins whose expression is tissue-specific and developmentally regulated. Three consensus sequences, X1, X2, and Y, separated by an interspace element, is found upstream from all class II genes. Deletion of each of these sequences eliminates expression of class II genes in vitro or in transgenic mice. Here we further characterize the expression of a cDNA encoding a DNA binding protein (human X-box binding protein, hXBP-1) which, like the proteins in whole nuclear extract, recognizes both the X2 promoter element of the human DR alpha and DP beta and mouse A alpha genes. The hXBP-1 cDNA hybridizes to human RNA species of approximately 2.2 kilobases (kb) and 1.6 kb, which are expressed in class II negative as well as class II positive cells. hXBP-1 transcripts are present in several class II deficient mutant B cell lines, although in one such line, 6.1.6, levels were somewhat reduced. Chromosome mapping studies demonstrate that hXBP-1 arises from a small gene family, two of whose members map to human chromosomes 5 and 22. Taken together, these data suggest a high degree of complexity in the transcriptional control of the class II gene family.

Stimulated kidney tubular epithelial cells express membrane associated and secreted TNF alpha

Tumor necrosis factor-alpha (TNF alpha) is a pleiotropic, pro-inflammatory peptide cytokine which promotes immune renal injury, and participates in T cell activation. It is produced by macrophages, T cells, and some non-hematopoietic cells, and is cytotoxic in picogram quantities. As renal tubular epithelial cells (TEC) bearing MHC class II (Ia) antigens and adhesion molecules (ICAM-1) can act as immune accessory cells, the ability of TEC to produce costimulatory cytokines could augment TEC accessory capacity in vivo. We report that transformed TEC express low levels of TNF alpha in response to LPS or IL-1 alpha as a secreted product and as a cytotoxic membrane associated molecule displayed on the cell surface. Surface labelling and immunoprecipitation studies of TEC detect a number of bands including a prominent 26 kD protein, which is the predicted size of TNF alpha precursor. TNF alpha mRNA transcripts were also detected by in situ hybridization in cortical tubules of C3H/FeJ mice injected with LPS, demonstrating the capacity of normal tubular epithelial cells to express TNF alpha in vivo. This report demonstrates for the first time the ability of kidney tubular cells to express TNF alpha protein and that membrane associated TNF alpha is not limited to hematopoietic cells. The function of small amounts of TNF displayed on the surface of tubular cells may be amplified by the abundance of these cells within the renal cortex, and may allow TEC to modulate immune responses within the kidney during inflammation.

Induction and regulation of class II major histocompatibility complex mRNA expression in astrocytes by interferon-gamma and tumor necrosis factor-alpha

Astrocytes can function as antigen-presenting cells (APC) upon expression of class II major histocompatibility complex (MHC) antigens, which are induced by interferon-gamma (IFN-gamma). Previous data from this laboratory had shown that the cytokine tumor necrosis factor-alpha (TNF-alpha) enhances IFN-gamma-mediated class II antigen expression on astrocytes. We have now investigated the effect of IFN-gamma and TNF-alpha on class II MHC mRNA expression in astrocytes using Northern blot analysis. Astrocytes do not constitutively express mRNA for class II MHC. Kinetic analysis of class II MHC mRNA expression in IFN-gamma-treated cells demonstrated an 8 h time lag, which was followed by an increase over the next 16 h. Optimal expression of class II mRNA was detected after a 24 h incubation with IFN-gamma. This level of expression was further enhanced by the simultaneous addition of IFN-gamma and TNF-alpha to the astrocytes, while TNF-alpha alone had no effect on class II mRNA expression. TNF-alpha does not act by increasing the stability of IFN-gamma-induced class II mRNA, indicating its action is not at that specific level of post-transcriptional control. Furthermore, astrocyte class II mRNA expression was inhibited when cycloheximide (CHX) was added together with IFN-gamma or IFN-gamma/TNF-alpha, and when CHX was added up to 4 h after treatment with IFN-gamma or IFN-gamma/TNF-alpha. These results indicate that astrocyte class II mRNA expression is mediated by newly synthesized proteins induced by IFN-gamma and/or IFN-gamma/TNF-alpha. The expression of class II antigens on astrocytes, and cytokine modulation of their expression, may be important in the initiation and perpetuation of intracerebral immune responses.

Interferon gamma regulates binding of two nuclear protein complexes in a macrophage cell line

Interferon gamma (IFN-gamma) is a potent inducer of major histocompatibility complex (MHC) antigens during normal immune responses and in abnormal responses in autoimmune disease. In this report we identify two nuclear factors whose binding to the murine E beta class II MHC beta-chain gene is regulated by this cytokine. IFN-gamma stimulation of murine macrophages results in the appearance of increased binding of one protein complex, complex A, and decreased binding of a second, faster migrating protein complex, complex B. Although the contact residues for both of these proteins lie within the highly conserved Y-box transcriptional element, their binding specificity differs. The protein in complex B is a CCAAT-box-binding protein that may be similar or identical to NF-Y or YB1, previously identified class II Y-box-binding proteins. The DNA sequence requirements for the binding of the slower migrating complex, complex A, are not limited to CCAAT-box sequences but include sequences upstream of the Y box. These upstream sequences are required both for IFN-gamma-induced gene transcription and for IFN-gamma-induced modulation of binding activity. These data suggest a model in which upstream sequences contribute to formation of a lymphokine-regulated complex downstream. The IFN-gamma-induced binding protein described as complex A in this report differs from the IFN-gamma, -alpha, or -beta-induced nuclear factors previously identified.

MHC class II, antigen presentation and tumor necrosis factor in renal tubular epithelial cells

Proximal tubular (PT) epithelial cells express MHC class II (Ia) antigens in immunologically-mediated renal injury. To study the role of PT as accessory cells, we generated several murine PT-like epithelial cell lines by transformation with origin-defective SV40 DNA. These transformed cell lines display typical alkaline phosphatase and gamma-glutamyl-transpeptidase enzyme activity, proliferation to epidermal growth factor (EGF) and sodium-dependent glucose uptake. Clonal lines of transformed tubular cells from both normal C3H/FeJ and autoimmune MRL-lpr mice do not constitutively express Ia antigens or mRNA for class II. However, stimulation with recombinant interferon-gamma(rIFN-gamma) induces Ia mRNA and surface product in the cell lines. These Ia-positive cells can process and present hen egg-white lysozyme (HEL) to antigen-specific Iak-restricted T cell hybrids. Unstimulated tubular cells do not express detectable IL-1 alpha, IL-1 beta, TNA-alpha, or IL-6 mRNA. However, stimulation with IL-1 alpha or LPS induces TNF-alpha transcripts. We conclude that these cell lines have characteristics most consistent with a proximal tubular origin. They also bear characteristics of accessory cells such as processing and presentation of antigen and TNF-alpha gene expression. We speculate that PT have the capacity to participate in the pathogenesis of immune renal injury.

Interferon-gamma activates multiple pathways to regulate the expression of the genes for major histocompatibility class II I-A beta, tumor necrosis factor and complement component C3 in mouse macrophages

The purpose of this study was to obtain additional information on the mechanism by which interferon-gamma (IFN-gamma) is able to regulate gene expression in macrophages. The expression of the genes for class II histocompatibility I-A beta, tumor necrosis factor (TNF) and complement component C3 was assayed after treating bone marrow macrophages with IFN-gamma. Each gene displayed a characteristic pattern of regulation. First, the increase in the level of RNA for each gene followed different kinetics. The level of TNF RNA increased within 15 min after IFN-gamma treatment and reached a plateau after 4 h. In contrast, there was a lag of about 4 h before the level of I-A beta RNA began to rise and a plateau was not reached until 48 h after the IFN-gamma treatment began. C3 gene expression followed an intermediate time course between that for TNF and I-A beta. Second, the expression of I-A beta was inhibited when cells were treated with both IFN-gamma and cycloheximide, while the expression of TNF and C3 was not. Interestingly, the sensitivity to cycloheximide only lasted 30 min following the addition of IFN-gamma, after which cycloheximide had no effect on the expression of I-A beta. Third, lipopolysaccharide abolished the IFN-gamma-induced expression of I-A beta, but enhanced the expression of TNF. Based on these observations, we conclude that IFN-gamma must activate multiple pathways to regulate gene expression in macrophages.