Ligand-free RAR can interact with the RNA polymerase II subunit hsRPB7 andrepress transcription

Upon binding retinoic acid (RA), the retinoic acid receptors (RARs) are abl e to positively and negatively regulate transcription. It has been shown th at the DNA-binding domain and carboxy terminus of RARs are necessary for th e ligand-dependent ability of the receptor to repress AP-1 transcriptional activity. A fusion of these two regions, shown to constitutively inhibit AP -1 activity, was used in a yeast two-hybrid screen to identify a novel hRAR alpha-interacting protein. This protein, hsRPB7, a subunit of RNA polymera se II, interacts with hRAR alpha, in the absence of RA and addition of RA d isrupts the interaction. Truncation analysis indicates that hsRPB7 specific ally interacts with the hRAR alpha DNA-binding domain. This interaction app ears to compromise transcription, since overexpressed hRAR alpha, in the ab sence of RA, is able to repress the activity of several RNA polymerase Ii-d ependent activators, including AP-1 and the glucocorticoid receptor. This r epression is relieved by transfected hsRPB7, strongly suggesting that ligan d-free hRAR alpha can block AP-1 activity by sequestering hsRPB7. The repre ssion is dependent on the integrity of the hRAR alpha DBD, since a mutation within the DBD blocks both the hRAR alpha-hsRPB7 interaction and ligand-fr ee hRAR alpha repression of AP-1. These results provide evidence that nonli ganded hRAR alpha can regulate transcription by directly interacting with R NA polymerase II, and thus suggest a novel pathway by which hRAR alpha can cross-talk with AP-1 and perhaps other families of transcriptional activato rs.