Visualization of PR homodimers and heterodimers have been reported as showing increased FRET signal upon progestin ORG2058 treatment in human osteosarcoma cell line U-2 OS cells transfected with CFP-PRA, YFP-PRA, CFP-PRB, and YFP-PRB, respectively (Arnett-Mansfield et al. 2007). Here, RB1 is linked to osteosarcoma.