A cytotoxic protein, TRAIL initiates apoptosis in tumor cells by binding the death-signalling receptors; DR4 and DR5. In its active conformation, TRAIL forms homotrimers. TRAIL transcripts have been shown to be constitutively expressed in a variety of human tissues. There are five known TRAIL receptors: two which transduce apoptotic signals, two which function as decoys to block TRAIL-induced apoptosis and osteoptotegrin.