Inhibition of ligand induced promoter occupancy in vivo by a dominant negative RXR.
BACKGROUND
Retinoid X receptors (RXRs) heterodimerize with other nuclear hormone receptors and control ligand mediated transcription. To address how RXRs function as heterodimers, we investigated activities of truncated RXR alpha and RXR beta that lack approximately 20 conserved C-terminal amino acids.


RESULTS
The truncated RXRs formed heterodimers and bound to respective DNA elements in vitro. By transient reporter assays we found that these RXRs act as dominant negative receptors and inhibit ligand dependent transcription by the retinoic acid receptor (RAR) and vitamin D receptor. P19 embryonal carcinoma cells stably expressing the truncated RXR beta (termed delta C2) were deficient in activating the endogenous RAR beta gene and an RA responsive reporter. To study the dominant negative activity of delta C2 further, genomic footprinting analysis was performed for the RAR beta2 promoter. In control P19 clones, the RA responsive element (RARE) and other elements in the promoter were protected after RA treatment. However, in delta C2 clones RA-induced protection was markedly inhibited at all elements.


CONCLUSIONS
These results indicate that the C-terminal region of RXR is required for full RARE occupancy in vivo, a RA dependent process that leads to the recruitment of other factors to the promoter and the subsequent transcriptional activation. Thus, RXRs play an integral role in ligand dependent transcription.
Blanco
J C
JC
Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Dey
A
A
Leid
M
M
Minucci
S
S
Park
B K
BK
Jurutka
P W
PW
Haussler
M R
MR
Ozato
K
K
D000818:Animals; D018983:DNA Footprinting; D019175:DNA Methylation; D004268:DNA-Binding Proteins / Q000235:genetics*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D008024:Ligands; D051379:Mice; D008957:Models, Genetic; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid / Q000235:genetics*; D047488:Retinoid X Receptors; D017384:Sequence Deletion; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D014212:Tretinoin / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014807:Vitamin D / Q000378:metabolism
D004268:DNA-Binding Proteins; D008024:Ligands; D018167:Receptors, Calcitriol; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D014807:Vitamin D; D014212:Tretinoin