Suppression of the human erythropoietin gene expression by the TR2 orphan receptor, a member of the steroid receptor superfamily

A DNA response element, TR2RE-EPO (5'-TCTGACCTCTCGACCTAC-3') has been identified in the 3'-minimal hypoxia-inducible enhancer of the human erythropoietin gene for the TR2 orphan receptor, an androgen-repressed transcription factor and a member of the steroid/thyroid hormone receptor superfamily. Electrophoretic mobility shift assay showed a specific binding with high affinity (K-d = 0.14 nM) between the TR2 orphan receptor and the TR2RE-EPO. Our data further indicated that this specific binding is not due to the homo-dimerization of the TR2 orphan receptor. In addition, reporter gene expression using chloramphenicol acetyltransferase assay demonstrated that the TR2 orphan receptor may suppress the expression of the chloramphenicol acetyltransferase activities via the TR2RE-EPO in the hypoxic/normoxic human hepatoma HepG2 cells. Finally, our in situ hybridization data also indicated that the TR2 orphan receptor and the erythropoietin transcripts can be co-expressed in mouse kidney and liver. Together, our data suggest that the human erythropoietin gene could represent the first human target gene regulated directly by the human TR2 orphan receptor.