The role of NF-kappa B in TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of melanoma cells

Previous studies have shown that activation of NF-kappaB can inhibit apopto sis induced by a number of stimuli. It is also known that TNF-related apopt osis-inducing ligand (TRAIL) can activate NF-kappaB through the death recep tors TRAIL-R1 and TRAIL-R2, and decoy receptor TRAIL-R4. In view of these f indings, we have investigated the extent to which activation of NF-kappaB m ay account for the variable responses of melanoma lines to apoptosis induce d by TRAIL and other TNF family members. Pretreatment of the melanoma lines with the proteasome inhibitor N-acetyl-L-leucinyl-L-leucinyl-L-norleucinal (LLnL), which is known to inhibit activation of NF-kappaB, was shown to ma rkedly increase apoptosis in 10 of 12 melanoma lines with death receptors f or TRAIL. The specificity of results for inhibition of NF-kappaB activation was supported by an increase of TRAIL-induced apoptosis in melanoma cells transfected with a degradation-resistant I kappaB alpha. Furthermore, studi es with NF-kappaB reporter constructs revealed that the resistance of melan oma lines to TRAIL-induced apoptosis was correlated to activation of NF-kap paB in response to TRAIL. TRAIL-resistant sublines that were generated by i ntermittent exposure to TRAIL were shown to have high levels of activated N F-kappaB, and resistance to TRAIL could be reversed by LLnL and by the supe rrepressor form of I kappaB alpha. Therefore, these results suggest that ac tivation of NF-KB by TRAIL plays an important role in resistance of melanom a cells to TRAIL-induced apoptosis and further suggest that inhibitors of N F-kappaB may be useful adjuncts in clinical use of TRAIL against melanoma.