| Fas-associated death domain (FADD or Mort 1) functions as an important adaptor in coupling death signaling from membrane receptors, such as the Fas ligand and TNF family (DR3, DR4 and DR5), to caspase-8 (1,2). FADD has a carboxy-terminal death domain, which interacts with the cytoplasmic tail of the membrane receptor, and an amino-terminal death effector domain, which interacts with caspase-8. Clustering of the receptors upon stimulation brings about FADD and caspase-8 oligomerization, activating the caspase signaling pathway. Human FADD is phosphorylated mainly at Ser194, while mouse FADD is phosphorylated at Ser191. In both cases, the phosphorylation is cell cycle-dependent (3) and may be related to its regulatory role in embryonic development and cell cycle progression (4,5). |
