IDENTIFICATION OF A RETINOID CHICKEN OVALBUMIN UPSTREAM PROMOTER TRANSCRIPTION FACTOR RESPONSE ELEMENT IN THE HUMAN RETINOID-X RECEPTOR GAMMA-2 GENE PROMOTER/

To investigate the mechanisms involved in the transcriptional control of retinoid X receptor (RXR) gene expression, the 5'-flanking region o f the human RXR gamma 2 isoform was characterized. An imperfect hexame r repeat (gamma retinoid X response element; gamma RXRE) with a single nucleotide spacer (GGTTGAaAGGTCA) was identified immediately upstream of the RXR gamma 2 gene transcription start site. Cotransfection stud ies in CV-1 cells with expression vectors for the retinoid receptors R XR alpha and retinoic acid receptor beta (RAR beta) demonstrated that the gamma RXRE confers retinoid-mediated transcriptional activation wi th preferential activation by RXR in the presence of its cognate ligan d, 9-cis-retinoic acid (RA). Electrophoretic mobility shift assays dem onstrated that RXR homodimer binding to gamma RXRE is markedly enhance d by 9-cis-RA, whereas RAR . RXR heterodimer binding is ligand-indepen dent. DNA binding studies and cell cotransfection experiments also dem onstrated that the nuclear receptor, chicken ovalbumin upstream promot er transcription factor (COUP-TF), repressed transcription via the gam ma RXRE. Cotransfection experiments revealed that COUP-TF and RXR alph a compete at the gamma RXRE to modulate transcription bidirectionally over a wide range. These results demonstrate that the human RXR gamma 2 gene promoter contains a novel imperfect repeat element capable of m ediating RXR-dependent transcriptional autoactivation and COUP-TF-depe ndent repression.