FKBP4 and prostate cancer: Given that ID4 is undetectable or weakly expressed in prostate cancer DU145 cells, they provide an ID4‐negative background as compared to the LNCaP cells wherein ID4 is endogenously expressed (Sharma et al., 2012), further confirming the domain‐specific interaction between ID4, FKBP52, and AR–protein complexes.