PED is overexpressed and mediates TRAIL resistance in human non-small cell lung cancer

PED (phosphoprotein enriched in diabetes) is a death-effector domain (DED) family member with a broad anti-apoptotic action. PED inhibits the assembly of the death-inducing signalling complex (DISC) of death receptors following stimulation. Recently, we reported that the expression of PED is increased in breast cancer cells and determines the refractoriness of these cells to anticancer therapy. In the present study, we focused on the role of PED in non-small cell lung cancer (NSCLC), a tumour frequently characterized by evasion of apoptosis and drug resistance. Immunohistochemical analysis of a tissue microarray, containing 160 lung cancer samples, indicated that PED was strongly expressed in different lung tumour types. Western blotting performed with specimens from NSCLC-affected patients showed that PED was strongly up-regulated (> 6 fold) in the areas of tumour compared to adjacent normal tissue. Furthermore, PED expression levels in NSCLC cell lines correlated with their resistance to tumour necrosis factor related apoptosis-inducing ligand (TRAIL)-induced cell death. The involvement of PED in the refractoriness to TRAIL-induced cell death was investigated by silencing PED expression in TRAIL-resistant NSCLC cells with small interfering (si) RNAs: transfection with PED siRNA, but not with cFLIP siRNA, sensitized cells to TRAIL-induced cell death. In conclusion, PED is specifically overexpressed in lung tumour tissue and contributes to TRAIL resistance.