β-transducin repeat-containing protein (β-TrCP or FBW1A) is an F-box family protein characterized by the presence of the protein-protein mediating F-box domain first described in cyclin F. F-box proteins act as substrate adaptors that target proteins containing a specific phosphorylated sequence element, referred to as a phosphodegron, to the SCF E3 ubiquitin ligase complex for ubiquitination. β-TrCP targets many important proteins with diverse functions, such as p53, H-Ras, Smad4, IκBα, β-catenin, and the cell cycle checkpoint protein claspin, for ubiquitin-mediated degradation. Research studies have shown that inhibition of β-TrCP expression has a demonstrated benefit in the treatment of prostate cancer.