Down-regulation of the major histocompatibility complex class I enhancer in adenovirus type 12-transformed cells is accompanied by an increase in factor binding.
In transformed cells, the E1A gene of adenovirus type 12 (Ad12) represses transcription of class I genes of the major histocompatibility complex. The tumorigenic potential of Ad12-transformed cells correlates with this diminished class I expression. In contrast, the E1A gene of the nontumorigenic Ad5 does not affect class I expression. We show here that a transfected reporter chloramphenicol acetyltransferase plasmid driven by an H-2K promoter (-1049 bp) was expressed at much lower levels in Ad12- than in Ad5-transformed mouse cells. Analysis of mutant constructs revealed that only 83 bp of H-2 DNA, consisting of the enhancer juxtaposed to the basal promoter, was sufficient for this differential expression. Whereas the H-2 basal promoter alone was somewhat less active in Ad12-transformed cells, the H-2 TATA box itself did not appear to be important. The H-2 enhancer proved to be the principal element in Ad12 E1A-mediated repression, since (i) substitution of the H-2 enhancer by simian virus 40 enhancers overcame the repression, and (ii) when juxtaposed to either its native or heterologous basal promoters, the H-2 enhancer was functional in Ad5- but not Ad12-transformed cells. Mobility shift assays showed that there is a DNA-binding activity to the 5' site (R2 element) of the enhancer that is significantly higher in Ad12- than in Ad5-transformed cells. These results suggest that decreased class I enhancer activity in Ad12-transformed cells may, at least in part, be due to the higher levels of an enhancer-specific factor, possibly acting as a repressor.
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Wistar Institute of Anatomy and Biology, Philadelphia, Pennsylvania 19104.
Kralli
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Weinmann
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Ricciardi
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D017500:Adenovirus E1A Proteins / Q000235:genetics*; D000260:Adenoviruses, Human / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D002461:Cell Line, Transformed; D002471:Cell Transformation, Neoplastic; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D015967:Gene Expression Regulation, Viral; D005805:Genes, MHC Class I; D005814:Genes, Viral; D006183:H-2 Antigens / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009838:Oligodeoxyribonucleotides; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins / Q000378:metabolism; D016385:TATA Box; D014158:Transcription, Genetic
D017500:Adenovirus E1A Proteins; D006183:H-2 Antigens; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D015500:Chloramphenicol O-Acetyltransferase