The locus-specific enhancer activity of the class I major histocompatibility complex interferon-responsive element is associated with a gamma-interferon (IFN)-inducible factor distinct from STAT1alpha, p48, and IFN regulatory factor-1.
Recent analyses of the upstream regulatory regions of the class I major histocompatibility complex genes in higher primates provided a generalized structural basis for the differential expression of A- and B-locus gene products in response to specific physiological stimulus. Among the regulatory sequences that differ between the loci is the interferon-responsive element (IRE). While the B-IRE is conserved, the A-IREs have species-specific sequence variation. We previously demonstrated that the B-IRE was an interferon (IFN)-inducible enhancer, whereas none of the A-IREs were functional. In the present study, we examined the biochemical basis for the enhancer activity of the conserved B-IRE and found that this may be attributed to a novel gamma-IFN-inducible factor. This factor accumulated in nuclei of cells within minutes of exposure to gamma-IFN. Its appearance was independent of de novo protein synthesis. However, it was not detected in nuclei of cells treated with herbimycin A, suggesting that its appearance depends on a protein kinase activation pathway. Supershift assays indicated that it was distinct from STAT1alpha, IFN regulatory factor-1, and p48, transcription factors known to bind IRE-like sequences found in regulatory regions of many non-major histocompatibility complex gamma-IFN-responsive genes. Competition assays show that this novel factor bound B-IRE with relatively high affinity, about 100-fold more than that for the A-IRE sequence. This factor was also present in STAT1alpha and p48 somatic mutants that also exhibited B-IRE enhancer activity in reporter gene bioassays in a manner similar to those seen with wild type cells. These observations indicate the existence of a novel gamma-IFN-dependent transcriptional activation pathway that correlates with the differential enhancer activity of the HLA-B IRE.
Vallejo
A N
AN
Department of Immunology, Mayo Clinic-Foundation, Rochester, Minnesota 55905, USA.
Pease
L R
LR
D016227:Benzoquinones; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D006367:HeLa Cells; D006801:Humans; D050856:Interferon Regulatory Factor-1; D007371:Interferon-gamma / Q000378:metabolism*; D047029:Lactams, Macrocyclic; D008285:Major Histocompatibility Complex / Q000235:genetics*; D009154:Mutation; D010750:Phosphoproteins / Q000378:metabolism; D011809:Quinones / Q000494:pharmacology; D017828:Rifabutin / Q000031:analogs & derivatives; D050794:STAT1 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
D016227:Benzoquinones; D004268:DNA-Binding Proteins; C494257:IRF1 protein, human; D050856:Interferon Regulatory Factor-1; D047029:Lactams, Macrocyclic; D010750:Phosphoproteins; D011809:Quinones; D050794:STAT1 Transcription Factor; C494079:STAT1 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D017828:Rifabutin; C020754:herbimycin; D007371:Interferon-gamma; D003513:Cycloheximide