Regulation of rat insulin 1 gene expression: evidence for negative regulation in nonpancreatic cells.
Two cis-acting elements, the enhancer and the promoter, independently contribute to the cell-specific expression of the rat insulin 1 gene. The activities of these elements are presumably mediated by trans-acting factors. We have performed intracellular competition experiments that suggest the presence of a negative factor(s) that represses the enhancer activity in cells that do not express the insulin gene. In these experiments fibroblast cells (COS-7) were transfected with two plasmids: a test plasmid containing the gene for chloramphenicol acetyltransferase under the control of the thymidine kinase promoter and the insulin enhancer; and a competitor plasmid containing insulin enhancer sequences and the simian virus 40 origin of replication to permit its replication in the recipient cells. The presence of the competitor plasmid led to a 5- to 6-fold increase in chloramphenicol acetyltransferase activity as compared with the activity detected when insulin enhancer was absent from either the competitor or the test plasmid. A 5-fold increase in chloramphenicol acetyltransferase activity was also seen when the rat amylase enhancer was present on the competitor plasmid; in contrast the simian virus 40 enhancer exerted no effect. Efficient derepression required additional sequences downstream from those essential for enhancer activity. We propose that the activity of the rat insulin 1 enhancer is modulated by a negative trans-acting factor(s) that is active in cells not expressing insulin but is overridden by the dominant positive trans-acting factor(s) present in insulin-producing cells.
D000818:Animals; D003001:Cloning, Molecular; D004261:DNA Replication; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D005809:Genes, Regulator; D007328:Insulin / Q000235:genetics*; D007515:Islets of Langerhans / Q000502:physiology; D051381:Rats; D014018:Tissue Distribution; D014157:Transcription Factors / Q000502:physiology; D014158:Transcription, Genetic; D014162:Transfection
D007328:Insulin; D014157:Transcription Factors