TR4 Orphan Receptor Represses the Human Steroid 21-Hydroxylase Gene Expression through the Monomeric AGGTCA Motif

Abstract

The human TR4 orphan receptor (TR4) is a member of the nuclear receptor superfamily. It functions as a transcriptional factor which regulates and controls many important physiological functions. It has been documented that TR4 may bind as a homodimer to a DNA response element containing two direct repeats of the AGGTCA consensus motif. Surprisingly, our data reveal that the expression of the human steroid 21-hydroxylase (21-OHase) gene could be repressed by TR4 via the monomeric AGGTCA motif (−228TR4RE) at its 5′ flanking region (nucleotide numbers 1431–1444, 5′-GGAAAAAGGTCAGG-3′). Electrophoretic mobility shift assay showed specific binding with a dissociation constant of 0.4 nM between TR4 and the monomeric −288TR4RE motif. However, TR4 does not form heterodimers with either retinoid X receptor alpha or SHP (short heterodimer partner) orphan receptor. Additionally, both dual-luciferase and chloramphenicol acetyltransferase assays demonstrated that TR4 can function as a repressor via the −228TR4RE of the 21-OHase gene. In conclusion, our data suggest that TR4 may bind to a monomeric DNA response element and play an important role in the suppression of the 21-OHase gene expression.