OLIGONUCLEOTIDE SQUELCHING REVEALS THE MECHANISM OF ESTROGEN-RECEPTORAUTOLOGOUS DOWN-REGULATION

Antisense oligos complementary to the 5'-end, but not to the 3'-end, o f the estrogen receptor (ER) messenger RNA caused a paradox accumulati on of ER protein in MCF-7 cells, The same effect was observed after tr eatment of the cells with the corresponding sense oligos, The oligos i nterfering with ER down-regulation were demonstrated to specifically b ind the ER with affinities in the nanomolar range. It is, therefore, p roposed that the ER up-regulation induced by the oligos might be due t o squelching of the ER (or ER-inducible proteins) from their binding s ite located in the 5'-end of the ER gene. We also report that transcri ptionally inactive ER mutants can undergo down-regulation, and that in denaturing gels, the migration profile of ER-oligo and ER-estrogen-re sponsive element complexes are dissimilar. We, therefore, propose that ER can interact with DNA in different ways and at different binding s ites, These observations might have important pharmacological conseque nces, since specific drugs could be devised to induce the ER conformat ion necessary to perform only selected tasks of the ER transcriptional repertoire.