The major findings of this study were as follows: (i) Poly(I:C) decreased the expression of mitochondrial dynamics-related proteins and DAP3 in human lung adenocarcinoma cells; (ii) DAP3 was involved in the resistance of lung adenocarcinoma cells to IR-induced cell death, whereas mitochondrial dynamics were not; (iii) a more-than-additive effect of cotreatment with Poly(I:C) and IR on increasing cell death was diluted by DAP3-knockdown because of an increase in cell death induced by IR alone. Here, DAP3 is linked to lung adenocarcinoma.