Retinoid X receptor alpha (RXRalpha) helix 12 plays an inhibitory role in the recruitment of the p160 co-activators by unliganded RXRalpha/retinoic acid receptor alpha heterodimers.
Retinoid X receptor (RXR)/retinoic acid receptor (RAR) heterodimers control gene expression through recruitment of co-repressors or co-activators, depending on their hormone binding status. We show that the helix 12 of RXRalpha and RARalpha is critical for recruitment of the co-regulators and transcriptional regulation by RXRalpha, RARalpha, and RXRalpha/RARalpha. LG268, an RXR-specific agonist, was able to promote co-activator association with the heterodimers, but was unable to dissociate co-repressors. Reconstitution experiments in yeast demonstrated that LG268 was capable of activating transcription by RXRalpha/RARalpha through recruitment of the co-activator. We hypothesize that the inability to release co-repressors from RXRalpha/RARalpha is responsible for the inability of LG268 to activate RXRalpha/RARalpha heterodimers in mammalian cells. Deletion of RARalpha helix 12 (RXRalpha/RARalpha Delta403) abolished both hormone-dependent dissociation from co-repressors and hormone-dependent association with co-activators. Deletion of RXRalpha helix 12 (RXRalpha Delta443/RARalpha) resulted in a higher binding affinity for co-repressors. Unexpectedly, RXRalpha Delta443/RARalpha also gained hormone-independent co-activator binding activity. Moreover, LG268 became an antagonist to RXRalpha Delta443/RARalpha heterodimers. These data suggest that the helix 12 of RXRalpha plays an inhibitory role in the recruitment of co-activators by unliganded RXRalpha/RARalpha.
Department of Biochemistry, School of Medicine, Case Western Reserve University (CWRU), the Research Institute of University Hospitals of Cleveland (UHC) and the Comprehensive Cancer Center of CWRU and UHC, Cleveland, Ohio 44106, USA.
Heng
H
Liu
Chong-Kuang
CK
Shaw
Erin L
EL
Reineke
Yu
Y
Liu
Hung-Ying
HY
Kao
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D019281:Dimerization; D017353:Gene Deletion; D005786:Gene Expression Regulation; D005982:Glutathione Transferase / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D047490:Retinoid X Receptor alpha / Q000737:chemistry* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014162:Transfection; D020798:Two-Hybrid System Techniques; D054460:rho-Associated Kinases
D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D047490:Retinoid X Receptor alpha; D005982:Glutathione Transferase; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases