Sensitization of melanoma cells to TRAIL by UVB-induced and NF-κB-mediated downregulation of xIAP

Caspase-3 cleaves XIAP in a positive feedback loop to sensitize melanoma cells to TRAIL-induced apoptosis

“…Caspase-mediated proteolytic cleavage of XIAP promotes its proteasomal degradation and sensitization of melanoma cells to TRAIL Resistance of melanoma cells to TRAIL-induced apoptosis has been shown to be independent of the tumor progression stage but to correlate with XIAPdependent inhibition of full caspase-3 processing (Thayaparasingham et al, 2009). Treating three melanoma cell lines representing the radial growth phase (RGP), the vertical growth phase (VGP) and the metastatic stage (MM) with 100 ng/ml TRAIL did not yield appreciable amounts of apoptosis, staying below 10%.…”

“…Co-exposure to a nonapoptotic UV (ultraviolet) B dose was shown to highly synergistically sensitize all melanoma cell lines to TRAIL-induced apoptosis, providing an excellent tool to study the mechanism underlying TRAIL resistance. TRAIL insensitivity was based on incomplete caspase-3 processing into the catalytic inactive p21 fragment only, while UVB-induced sensitization coincided with XIAP depletion, completion of caspase-3 activation yielding the catalytically active p17, and consequently apoptosis induction (Thayaparasingham et al, 2009). Investigating TRAIL resistance of melanoma cells and their synergistic sensitization by sub-lethal UVB, we revealed a novel mechanism involving caspase-3-induced cleavage of XIAP as a prerequisite for its proteasomal degradation.…”

“…An effective offence to malignant melanoma with the tumor selective ligand TRAIL (tumor necrosis-related apoptosis inducing ligand; Walczak et al, 1999) is curtailed by the fact that many melanoma cell lines are a priori resistant against TRAIL-induced apoptosis (Zeise et al, 2004). On investigating 18 melanoma cell lines, we could recently show that TRAIL susceptibility was completely independent of the tumor progression stage, while only the minority of cell lines responded to TRAIL at all (Thayaparasingham et al, 2009). Co-exposure to a nonapoptotic UV (ultraviolet) B dose was shown to highly synergistically sensitize all melanoma cell lines to TRAIL-induced apoptosis, providing an excellent tool to study the mechanism underlying TRAIL resistance.…”

“…In this context, caspase-3 was shown to be fully inhibited not only upon zDEVD treatment but also upon caspase-8 (zIETD) inhibition, whereas caspase-9 (zLEHD) inhibition had a minor effect on its activity as well as cleavage (Supplementary Figure S1A). As caspase-8 activity in melanoma cells is extremely low (Supplementary Figure S1B; see also Thayaparasingham et al, 2009), we rather focussed on caspase-8 processing, which was slightly reduced by caspase-3 inhibition (zDEVD) but not by caspase-9 inhibition . Primary melanocytes were treated with the same low doses or with a high TRAIL (500 ng/ml) and high UVB (400 J/m 2 ) dose.…”

Targeting inhibitor of apoptosis proteins in combination with dacarbazine or TRAIL in melanoma cells

“…There are several reports that link high expression of IAPs with increased survival of cancer cells and resisitance to therapy, 10,19,20,22 and it was therefore of interest to silence the expression of different IAPs using siRNAs and evaluate the impact on cell viability. The importance of IAP expression in therapy resistance in melanoma has been studied previously in reference 19, but concurrent evaluation of siRNAs targeting five different IAPs in the same cell lines provides new information regarding the role of the different IAPs with respect to cell viability and sensitization for therapy.…”