ID2 down-regulates basal and USF-induced Fshr promoter activity. A, MSC-1 cells were transfected with FSHR(−220/+123)Luc and empty vector (EV) or plasmids expressing USF1, USF2, or ID2 in the absence of forskolin or with forskolin stimulation for 8 h. Relative luciferase activities are expressed relative to the activity resulting from the overexpression of USF1 + USF2 (=1). B, MSC-1 cells were cotransfected with the κBLUC reporter plasmid and either 2 μg of empty expression vector (EV) or ID2 expression vector. Relative luciferase activities were expressed relative to the activity resulting from the cotransfection of EV (=1). C, MSC-1 cells were transfected with FSHR(−220/+123)Luc and expression vectors for USF1 or USF2 (1 μg), empty vector and/or varying levels of ID2 as indicated. Appropriate amounts of empty vector were added to maintain equal total levels (3 μg) of expression vector for each transfection. Relative luciferase activities are expressed relative to that in which USF1 is overexpressed alone (=1). For A–C, the results represent the mean (±se) luciferase activity for four (A and B) and three (C) independent experiments using two replicates. Values with different lower-case letters differ significantly (P < 0.05).