GRIP1 corepressor activity in heterologous context. (A) GRIP1 repression domain is active in the absence of GR. Parental U2OS cells were transfected with increasing amounts of pSG424 plasmid expressing Gal4DBD (Gal), Gal4DBD fused to GRIP1631–1007 (Gal:GRIP1631–1007) or to MAD repression domain (Gal:MAD), along with the 2xGal4/2xAP-1-Luc reporter and β-actin-LacZ. Total amount of DNA was equalized with empty pSG424. Reporter activity was measured in the presence of PMA, normalized to β-galactosidase activity, and expressed as the percentage of activity observed for empty pSG424. (B) Full-length GRIP1 fused to Gal4DBD is a transcriptional activator. U2OS cells were transfected with increasing amounts of Gal4DBD (Gal) or Gal:GRIP1, and the activity of 2xGal4/2xAP-1-Luc reporter was assayed with/without PMA and normalized as described in A. (C) Liganded GR blocks GRIP1-mediated transcriptional activation. U2OS.G cells were transfected with Gal:GRIP1 or empty pSG424, 2xGal4-Luc reporter, and β-actin-LacZ. Reporter activity in the presence of PMA−/+Dex, as indicated, was assayed as described in A.