Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.3.1.28 (chloramphenicol acetyltransferase)
 5,100 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The cytokine tumor necrosis factor alpha (TNF-alpha) alone does not induce class II major histocompatibility complex (MHC) expression in most primary cells but can regulate ongoing class II expression in either a positive or negative fashion. The mechanism(s) by which TNF-alpha enhances interferon gamma (IFN-gamma)-induced class II expression was examined in a primary cell type, the astrocyte, by transient transfection of the HLA-DRA promoter linked to a chloramphenicol acetyltransferase reporter gene (DRA-CAT). We show that TNF-alpha, while having no effect on its own, can synergize with IFN-gamma to increase the level of promoter activity of a DRA-CAT construct. Three known sequences--W, X, and Y--are required for TNF-alpha enhancement of IFN-gamma-induced promoter activity. The corollary effect of TNF-alpha on DNA-binding proteins specific for these elements was examined. A previous report described a DNA-binding protein, IFN-gamma-enhanced factor X (IFNEX), which is upregulated by IFN-gamma in astrocytes and is specific for the X box of the DRA promoter. In this study, we found that TNF-alpha alone did not induce any nuclear proteins; however, combined treatment of astrocytes with both IFN-gamma and TNF-alpha induced a DNA-protein complex of slower electrophoretic mobility than IFNEX. The TNF-alpha-induced complex (TIC-X) has specificity for the X element of the DRA promoter. These results suggest a mechanism by which TNF-alpha enhances IFN-gamma-induced class II MHC expression via the formation of TIC-X.
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PMID:Tumor necrosis factor alpha response elements in the HLA-DRA promoter: identification of a tumor necrosis factor alpha-induced DNA-protein complex in astrocytes. 145 41

The B lymphoblastoid cell line clone 13 (a subclone of the mutant cell line P3JHR-1) has been found to express high levels of HLA-DQ; by contrast, HLA-DR and -DP antigens are not expressed and cannot be induced by interferon gamma. Northern blot analysis using gene-specific probes indicated that the lack of surface expression of the DR and DP antigens is due to a marked decrease in the levels of steady-state RNA for both the alpha and beta chains. Southern blots demonstrated that none of the transcriptionally repressed genes are grossly deleted. Preparations of interspecific transient heterokaryons between clone 13 and the class II antigen-positive murine B cell lymphoma, A20, resulted in reactivation of the DRA gene and surface expression of both the DR and DP molecules. The efficiency of the DRA promoter relative to the DQB promoter is markedly and specifically diminished in clone 13 (P3JHR-1) as compared with the parental cell line, Jijoye, as assayed both by transient expression of appropriate chloramphenicol acetyltransferase gene (CAT) constructs and by in vitro transcription analysis. These data clearly demonstrate the existence of an isotype-specific trans-acting factor, and provide direct evidence that the highly homologous class II genes have distinct regulatory mechanisms.
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PMID:An isotype-specific trans-acting factor is defective in a mutant B cell line that expresses HLA-DQ, but not -DR or -DP. 199 50

We examined the signal transduction mechanism responsible for the IFN-gamma-induced HLA class II molecule expressions on glioblastoma cell lines, T98G and A172. A series of experiments demonstrated that the activation of protein kinase C (PKC) is involved in the DR and DP molecule expressions on T98G cells. In addition to the activation of PKC, calcium influx appeared to be involved in the DR and DP molecule expressions on T98G. Northern blot analyses with actinomycin D or cycloheximide revealed that these second messengers induce the transcription of DRA and B and DPA and B genes without de novo protein synthesis. Furthermore, we examined the region of the DPB gene that is responsible for IFN-gamma-induced gene transcription by gene transfer of a series of 5' and 3' deletion mutants in which the upstream region of the DPB was linked to a reporter gene, chloramphenicol acetyltransferase. By using these deletion mutants, it appeared that the region between -152 and -126 bp contains a critical IFN-gamma-responsive element. Taken together, these results suggest that IFN-gamma activates PKC and stimulates calcium influx, resulting in the induction of transcription of DRA and B and DPA and B genes without de novo protein synthesis. In DPB gene, we speculate that preexiting protein(s) phosphorylated by PKC in the presence of Ca2+ might directly bind or indirectly interact with the region between -152 and -126 bp of the upstream sequence, leading to the induction of the transcription (possibly in concert with other nuclear protein(s) bound to the promoter sequences).
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PMID:Regulation of HLA class II molecule expressions by IFN-gamma. The signal transduction mechanism in glioblastoma cell lines. 221 76

The molecular mechanism(s) by which three cytokines (IFN-gamma, TNF-alpha, TGF-beta) affect class II MHC gene expression in primary rat microglia was examined. IFN-gamma is a potent inducer of the class II gene, and this induction is unaffected by treatment with either TNF-alpha or TGF-beta. Transient transfection of primary rat microglia with an HLA-DRA promoter linked to the chloramphenicol acetyltransferase reporter gene (DRA-CAT) demonstrated that IFN-gamma acts at the transcriptional level to induce class II MHC gene expression, and that TNF-alpha and TGF-beta have no influence on IFN-gamma-induced promoter activity. Experiments using a series of DRA substitution mutants that individually affect the W, X1, X2, or Y elements, as well as a double mutation in both X1 and X2, indicate that all four of these elements are required for responsiveness of the DRA promoter to IFN-gamma. The effect of IFN-gamma and TNF-alpha on DNA binding proteins by microglia was examined. A constitutive complex with specificity for the X2 box was detected in extracts from unstimulated microglia. IFN-gamma treatment changed this complex to migrate with slower mobility, and TNF-alpha had no effect on either the constitutive or IFN-gamma-induced complexes. These studies provide information on the molecular regulation of the class II MHC gene in microglia, a cell type critically involved in immune regulation within the central nervous system.
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PMID:Class II MHC gene expression in microglia. Regulation by the cytokines IFN-gamma, TNF-alpha, and TGF-beta. 787 54