CD254, also known as RANKL, TNFSF11, TRANCE, OPGL and ODF, is a type II membrane protein of the tumor necrosis factor (TNF) superfamily, and affects the immune system and control bone regeneration and remodeling. RANKL is the ligand of nuclear factor (NF)-κB (RANK). When RANKL binds to RANK, it will undergo trimerization and then bind to an adaptor molecule TNF receptor-associated factor 6 (TRAF6). This results in the activation of several downstream signaling cascades, including the NFκB, mitogen-activated protein kinases (MAPK), activating protein 1 (AP-1), and nuclear factor of activated T cells (NFATc1), resulting in the formation of multinucleated bone-resorbing osteoclasts. RANKL is widely expressed in skeletal muscle, thymus, liver, colon, small intestine, adrenal gland, osteoblast, mammary gland epithelial cells, prostate and pancreas.