STRUCTURAL DETERMINANTS FOR TRANSCRIPTIONAL ACTIVATION BY CAMP-RESPONSIVE DNA ELEMENTS

  • 5 December 1988
    • journal article
    • research article
    • Vol. 263  (34) , 18466-18472
Abstract
A transcriptional cAMP-responsive enhancer element (CRE) consisting of the 8-base pair (bp) palindrome, 5'' TGACGTCA 3'', is found in several eukaryotic genes. We analyzed the effects on gene transcriptional of point mutations within the CRE, the influence of the bases surrounding the CRE, and the requirements for transcriptional synergism of tandemly repeated CREs. When inserted as an oligonucleotide with restriction enzyme linker sites, the 8-bp CRE itself is as active in conferring cAMP responsivity on an enhancerless chloramphenicol acetyltransferase reporter plasmid as is a single copy of the choriogonadotropin .alpha. (CG.alpha.), twice repeated 18-bp sequence containing the CRE. Point mutations in the first (T to A), fourth (C to G), or eight (A to T) positions of the CRE, when contained within the CG.alpha. 18-bp sequence, each inhibited transcriptional activity greater than 90%. However, the identical eigth position A to T mutation occurs in the cAMP-responsive sequence of the vasoactive intestinal peptide (VIP) gene, and that mutant sequence in the context of the adjacent bases of the native VIP sequence is maximally cAMP responsive when inserted in the reporter plasmid. The substantially reduced activity of the core 8-bp CRE when synthesized as a cassette including the adjacent bases of the rat glucagon or bovine parathyroid hormone gene further emphasizes the restrictive influence of particular surrounding sequences. Active oligonucleotides containing the 8-bp palindrome and different but equally permissive contexts have comparable properties in transfected reporter genes and gel mobility-shift assays. The pair of tandemly repeated 18-bp elements containing the CRE in the CG.alpha. gene synergistically stimulate transcription either with paired native CREs or when one native CRE is paried with one mutant CRE, suggesting the presence of cooperative interactions. Tandem insertion of more than two 18-bp sequences, or insertion of additional sequences between the two CREs, inhibits transcription. These observations indicate that the contexts of the bases adjacent to CREs exert profound influences on the transcriptional activities mediated by the cAMP-responsive elements.