Transcriptional Repression, a Novel Function for 3′ Untranslated Regions

Abstract

The transcription rates of the rat serine protease inhibitor 2.3 and 2.1 genes (spi 2.3 and spi 2.1), which are normally very low and high, respectively, are inversely modulated during inflammation. Two growth-hormone-response elements (GHRE-I and GHRE-II) maintain the spi 2.1 gene under the stringent control of growth hormone [Le Cam, A., Pantescu, V., Paquereau, L., Legraverend, C., Fauconnier, G. & Asins, G. (1994) J. Biol. Chem. 269, 21532-21539], whereas spi 2.3 appears to escape control by this hormone, despite the presence in its promoter of a functional GHRE-I. A major difference between these two otherwise very similar genes is the presence in spi 2.3 of a specific 348-bp extension of the 3' untranslated region (3' UTR). Inserting this 3' UTR element downstream of the polyadenylation signal or upstream of the spi 2.3 promoter in constructs containing the chloramphenicol acetyltransferase gene strongly decreases basal transcription and inhibits growth-hormone-stimulated transcription, but poorly affects transcriptional stimulation by dexamethasone or interleukin-6. The spi 2.3 3' UTR extension also inhibits, basal and growth-hormone-induced transcription from the spi 2.1 promoter. Repressor activity appears to be distributed throughout the specific extension of the 3' UTR and seems to involve interactions with two types of 5' cis-acting promoter elements. The first is the GAGA box, a key control spi promoter element, whose mutation faithfully reproduces the effects of the 3' UTR silencer on spi 2.1 and spi 2.3 promoters. The second is represented by CCAAT enhancer-binding-protein-(C/EBP)-binding sites, whose functions are severely impaired by the spi 2.3-specific 3' UTR extension. The presence of this silencer in the spi 2.3 gene very likely accounts for the lack of basal of transcription in vivo and for induction of the gene during acute inflammation.