Retinoic acid receptor isotype specificity in F9 teratocarcinoma stem cells results from the differential recruitment of coregulators to retinoic acid response elements

The retinoic acid receptor (RAR) alpha, beta(2), and gamma isotypes each regulate specific subsets of target genes in F9 teratocarcinoma stem cells. We used chromatin immunoprecipitation assays to monitor the association of RAR gamma, retinoic X receptor (RXR) alpha, and coregulators with the RAR beta(2), Hoxa1, and Cyp26A1 retinoic acid response elements (RAREs) in F9 wild type and RAR alpha, -beta(2), and -gamma null cells. Additionally we quantitatively monitored expression of the corresponding mRNAs. We demonstrated that the association of RAR gamma and/ or RXR alpha with a RARE was not sufficient for retinoic acid (RA)-mediated transcription of the corresponding target gene. However, the ability of RAR alpha and/ or RXR alpha to recruit pCIP (AIB1/ACTR/RAC-3/TRAM-1/SRC-3) and p300 to a RARE did correlate with RA-associated transcription of target mRNAs. Therefore, the specific functions of the RAR isotypes do not manifest at the level of their DNA binding but rather from a differential ability to recruit specific components of the transcriptional machinery. We also demonstrated that RA-mediated displacement of the polycomb group protein SUZ12 from a RARE was inhibited in the absence of RAR gamma. Thus, transcriptional components of the RAR signaling pathway are specifically required for displacement of SUZ12 from RAREs during RA-mediated differentiation of F9 cells.