Effect of IGF1 on IGF1R promoter activity in IGF1R KD and INSR KD cells. MCF7-derived IGF1R KD, INSR KD and control cells were transiently transfected with a proximal IGF1R promoter luciferase reporter construct [p(−476/+640)LUC]. After 24 h, cells were treated with IGF1 (50 ng/mL) (dotted bars), or left untreated, for control purposes (solid bars) for an additional 24 h, after which cells were harvested and luciferase levels were measured. Promoter activities are expressed as luciferase values normalized to total protein. A value of 100% was given to the promoter activity generated by the reporter plasmid in control MCF7 cells. Bars represent mean ± SEM of three independent experiments in duplicate wells. *, p < 0.05 versus control cells.