RFG (ARA70, ELE1) interacts with the human androgen receptor in a ligand-dependent fashion, but functions only weakly as a coactivator in cotransfection assays.

Abnormalities of the human androgen receptor (hAR) cause a range of clinical defects in male development. A large proportion of these mutations are single amino acid substitutions in the hormone-binding domain (HBD) that alter AR function by interfering with the capacity of the AR to bind androgen or to form stable hormone-receptor complexes. Prior studies have suggested that the formation of such stable, active hormone-receptor complexes is a crucial step in the modulation of genes by the AR. It is presumed that these hormone-receptor complexes interact with other proteins to participate in the formation of active transcription complexes at the initiation sites of androgen-responsive genes. Using a yeast two-hybrid screening method, we isolated a partial cDNA encoding the carboxy terminus of a protein that interacts with the hAR-HBD (amino acid residues 623-917) in a ligand-dependent fashion in a yeast two-hybrid assay. Sequence analysis of this clone revealed that it encoded a portion of a protein that had been previously characterized as RFG (RET Fused Gene). Using glutathione-S-transferase (GST) fusions of the hAR HBD and immunoprecipitation of the in vitro translated proteins, we have demonstrated that this interaction can be reproduced in vitro. To determine the capacity of this protein to modulate the activity of the AR in transfection assays, we expressed full-length RFG in the CV1 and DU145 cell lines, in combination with an AR expression vector and model androgen-responsive genes [mouse mammary tumor virus (MMTV) and PRE2-tk luciferase]. Our results demonstrate that RFG alters the induction of these reporter genes very weakly (no greater than 2-fold compared with transfections without the RFG expression plasmid). Thus, while our findings are in agreement with published reports which indicate that RFG interacts with AR-HBD in a ligand-dependent fashion, in our assays RFG does not exert major effects on the activity of the hAR in response to androgen or to other steroid hormones.