TRAIL-β and TRAIL-γ: two novel splice variants of the human TNF-related apoptosis-inducing ligand (TRAIL) without apoptotic potential

Abstract

Tumour necrosis factor (TNF) related apoptosis-inducing ligand (TRAIL/APO2L) is a recently identified member of the TNF family, which induces programmed cell death in a variety of neoplastic cell types, but not in most nonneoplastic cells. In this study, we report on the identification of two novel alternative splice variants of TRAIL in neoplastic and non-neoplastic human cells lacking either exon 3 (TRAIL-b) or exons 2 and 3 (TRAIL-g). In both splice variants, loss of exon 3 resulted in a frame shift generating a stop codon with consecutive extensive truncation in the extracellular domain. Ectopic expression revealed a loss of proapoptotic potential for both alternative splice variants. In contrast to the predominantly cytoplasmatic localisation of GFP-tagged TRAIL-a and TRAIL-b, TRAIL-g showed an additional association with the cell surface and nuclear membrane. In conclusion, alternative splicing might be involved in fine tuning of TRAIL-induced apoptosis and underlines the complexity of the TRAIL system.

Novel transcript variants of TRAIL show different activities in activation of NF-κB and apoptosis

“…Loss of apoptotic activities in all our truncated TRAIL proteins is in accordance with previous observations that the other two preciously reported TRAIL β and γ isoform have also shown loss of apoptosis inducing potential (Krieg et al, 2003;Woods et al, 2008). It seems that certain region responsible for apoptosis is missing in the truncated TRAIL isoforms.…”

“…All the splice sites in these variants display the typical GT-AG sequences. AK (65 aa) and DA (98 aa) contain a novel exon, whereas DA lacks exon 3 and therefore it encodes a protein product identical to the previously reported TRAIL β (Krieg et al, 2003). E2 (88 aa), E3 (123 aa), and E4 (145 aa) are transcribed from exons 1-2, 1-3, and 1-4, respectively, with an extended sequence at the end of their last exon.…”

“…Up to date, in addition to the full-length TRAIL protein or TRAIL α, three other TRAIL transcript variants have been reported: TRAIL β lacking exon 3, TRAIL γ lacking both exons 2 and 3, and TRAIL δ lacking both exons 3 and 4 (Krieg et al, 2003;Woods et al, 2008). These truncated variants seem to have no apoptotic potential, and are speculated to play a passive regulatory role in TRAIL actions through neutralizing the biological activities of wild type TRAIL (Krieg et al, 2003). However, other functional studies on these truncated TRAIL variants such as their NF-κB inducing activities have not been performed.…”

Major apoptotic mechanisms and genes involved in apoptosis

“…Exon 5 also encodes for the C-terminal amino acids along with containing the 3′-untranslated region (3′-UTR) and poly-A tail [112]. There are various variants of TRAIL; however, only one specific isoform of TRAIL (TRAILα) is responsible for its cancer-selective apoptosis induction potential [113].…”

Proteomics of tissue factor silencing in cardiomyocytic cells reveals a new role for this coagulation factor in splicing machinery control

“…The inability to detect, in our experimental system, the pro-apoptotic splice variant of Survivin, 447 Survivin 2B, and the two alternative TRAIL-splice variants, TRAIL-β and TRAIL-γ, which are 448 characterised by the loss of their pro-apoptotic properties [22], does not allow us to establish a 449 clear relationship between TF-mediated deregulation of splicing factors and these proteins 450 involved in the apoptotic process. 451…”