Activation of RARα-mediated transcription in cells expressing the core. (A) COS-7 cells were transfected with 25 ng of pRARE-Luc, pCMV-core at the doses indicated, and the empty vector for a total amount of 400 ng of plasmids. Cells were then treated with (solid bars) or without (open bars) 1 μM ATRA. At 24 h posttransfection, luciferase activities of whole-cell lysates were measured. Data are means of the relative luciferase activities in three independent experiments. Error bars, standard deviations. (B) MCF-7-core 6, MCF-7-core 21, and MCF-7-vec cells were transfected with 25 ng of the pRARE-Luc reporter plasmid. (C) Identification of the region within the core essential for activation of RARα-mediated transcription. COS-7 cells were transfected with 25 ng of pRARE-Luc and 350 ng of a series of truncated core expression plasmids [core full, pCMV-core; coreΔ(101-191), pCMV-coreΔ(101-191); coreΔ(1-20 + 81-191), pCMV-coreΔ(1-20 + 81-191); coreΔ(21-80)-p7, pCMV-coreΔ(21-80)-p7] or control plasmids (control, pKS+/CMV; p7, pCMV-p7). Experimental conditions and presentation of data for panels B and C were the same as those described for panel A.