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Shen XQ , Bubulya A , Zhou XF , Khazak V , Golemis EA , Shemshedini L
Ligand-free RAR can interact with the RNA polymerase II subunit hsRPB7 and repress transcription
Endocrine. 1999 Jun;10(3) :281-289
PMID: ISI:000081933200010   
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Upon binding retinoic acid (RA), the retinoic acid receptors (RARs) are able to positively and negatively regulate transcription. It has been shown that the DNA-binding domain and carboxy terminus of RARs are necessary for the 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 polymerase II, interacts with hRAR alpha, in the absence of RA and addition of RA disrupts the interaction. Truncation analysis indicates that hsRPB7 specifically interacts with the hRAR alpha DNA-binding domain. This interaction appears to compromise transcription, since overexpressed hRAR alpha, in the absence of RA, is able to repress the activity of several RNA polymerase Ii-dependent activators, including AP-1 and the glucocorticoid receptor. This repression is relieved by transfected hsRPB7, strongly suggesting that ligand-free hRAR alpha can block AP-1 activity by sequestering hsRPB7. The repression 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- free hRAR alpha repression of AP-1. These results provide evidence that nonliganded hRAR alpha can regulate transcription by directly interacting with RNA polymerase II, and thus suggest a novel pathway by which hRAR alpha can cross-talk with AP-1 and perhaps other families of transcriptional activators.
Times Cited: 1 English Article 225AR ENDOCRINE