IDENTIFICATION OF A RETINOID CHICKEN OVALBUMIN UPSTREAM PROMOTER TRANSCRIPTION FACTOR RESPONSE ELEMENT IN THE HUMAN RETINOID-X RECEPTOR GAMMA-2 GENE PROMOTER/
Pm. Barger et Dp. Kelly, IDENTIFICATION OF A RETINOID CHICKEN OVALBUMIN UPSTREAM PROMOTER TRANSCRIPTION FACTOR RESPONSE ELEMENT IN THE HUMAN RETINOID-X RECEPTOR GAMMA-2 GENE PROMOTER/, The Journal of biological chemistry, 272(5), 1997, pp. 2722-2728
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.