Apoptosis, or programmed cell death, is a normal component of cellular differentiation and the development of multicellular organisms. Receptor activator of NF-kB (RANK) lacks significant homology with the other family members of the tumor necrosis factor receptor (TNFR) superfamily. The cytoplasmic domain of RANK interacts with the tumor necrosis factor receptor associated factors, adaptor proteins such as TRAF2, TRAF5 and TRAF6.