RETINOID-INDUCED CHROMATIN STRUCTURE ALTERATIONS IN THE RETINOIC ACIDRECEPTOR BETA-2 PROMOTER

Transcription of the retinoic acid receptor beta 2 (RAR beta 2) gene i s induced by retinoic acid (RA) in mouse P19 embryonal carcinoma (EC) cells. Here we studied RA-induced chromatin structure alterations in t he endogenous RAR beta 2 promoter and in an integrated, multicopy RAR beta 2 promoter in EC cells, RA markedly increased restriction site ac cessibility within the promoter, including a site near the RA responsi ve element (RARE) to which the nuclear receptor retinoid X receptor (R XR)-RAR heterodimer binds, These changes coincided with RA-induced alt erations in the DNase I hypersensitivity pattern in and around the pro moter. These changes became undetectable upon removal of RA, which coi ncided with the extinction of transcription, Analyses with receptor-se lective ligands and an antagonist showed that increase in restriction site accessibility correlates with transcriptional activation, which p arallels the RA-induced in vivo footprint of the promoter. Despite the se changes, the micrococcal nuclease digestion profile of this promote r was not altered by RA, These results indicate that concurrent with t he binding of the RXR-RAR heterodimer to the RARE, the local chromatin structure undergoes dynamic, reversible changes in and around the pro moter without globally affecting the nucleosomal organization.