LIGAND-INDUCIBLE RETINOID X-RECEPTOR-MEDIATED PROTEIN - DNA INTERACTIONS IN THE RETINOIC ACID RECEPTOR BETA-2 GENE PROMOTER IN-VIVO

Retinoid X receptors (RXRs) are recently characterized transcription f actors that are members of the nuclear hormone receptor superfamily. H owever, it is not known whether the endogenous RXR complex requires it s ligand for access to its hormone response element (HRE) of a target gene in vivo. Hence, dimethyl sulfate-based genomic footprinting was c arried out to examine occupancy of HREs in the retinoic acid (RA) rece ptor beta 2 (RAR beta 2) gene promoter in the murine melanoma cell lin e S91 cultured in the absence or presence of T-3, all-trans-RA (atRA), or CD2624, an RXR-selective retinoid. No footprint was observed at th e RA-response element (beta RARE) in the absence of ligands. However, a footprint was detected at the beta RARE and other cis-acting element s after a 6 h incubation with CD2624 and atRA. Interestingly, only the beta RARE was footprinted after 60 min incubation with CD2624. These results suggest that the endogenous RXR complex can interact with an H RE of a target gene in the presence of ligand, and subsequently may in itiate additional interactions between DNA and other transcription fac tors. (C) 1998 Elsevier Science Ireland Ltd.