¹Department of Dermatology and Allergy, Skin Cancer Center, Charité – Universitätsmedizin Berlin, Berlin, Germany

Correspondence: Dr J Eberle, Department of Dermatology and Allergy, Skin Cancer Center, Charité – Universitätsmedizin Berlin, Hindenburgdamm 30, 12203 Berlin, Germany. E-mail: juergen.eberle@charite.de

Received 25 April 2006; Revised 25 August 2006; Accepted 13 October 2006; Published online 11 December 2006.

Abstract

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted considerable attention as a novel anticancer agent. However, its efficiency may be diminished by occurring resistance in cancer cells. The mechanisms of TRAIL resistance in melanoma are still unsolved. Here we show for the first time that TRAIL-induced activation of NF-B occurs in apoptosis-sensitive melanoma cell lines through TRAIL receptor 1/death receptor 4 (TRAIL-R1/DR4), whereas TRAIL failed to activate nuclear factor kappa B (NF-B) in melanoma cells positive only for TRAIL receptor 2/death receptor 5 (TRAIL-R2/DR5). However, activation of NF-B by TRAIL was not associated with enhanced expression of antiapoptotic factors: cellular FLICE-inhibitory protein (c-FLIP), Bcl-x_L, X-linked inhibitor of apoptosis protein (XIAP), Survivin, Livin. Rather in one of the cell lines, TRAIL induced the downregulation of DR4. In an established cell culture model for TRAIL resistance and regained TRAIL sensitivity, resistance was neither associated with increased NF-B activity by TRAIL nor by an increased expression of antiapoptotic proteins. However, significant downregulation of caspase-8, caspase-10 and of DR4 was characteristic for TRAIL-resistant, DR4-positive melanoma cells, and regained TRAIL sensitivity coincided with re-expression of these factors. Sensitivity was also largely retained after their exogenous overexpression. Thus, initiator caspases and DR4 rather than NF-B may control melanoma cell sensitivity to TRAIL, and strategies, which result in their upregulation, may be useful for enhancement of TRAIL sensitivity.