Nuclear Factor-Kappa B Inhibition Can Enhance Apoptosis of Differentiated Thyroid Cancer Cells Induced by 131I

Objective: To evaluate changes of nuclear factor-kappa B (NF-kB) during radioiodine 131 ( 131 I) therapy and whether NF-kB inhibition could enhance 131 I-induced apoptosis in differentiated thyroid cancer (DTC) cells in a synergistic manner. Methods: Three human DTC cell lines were used. NF-kB inhibition was achieved by using a NF-kB inhibitor (Bay 11-7082) or by p65 siRNA transfection. Methyl-thiazolyl-tetrazolium assay was performed for cell viability assessment. DNA-binding assay, luciferase reporter assay, and Western blot were adopted to determine function and expression changes of NF-kB. Then NF-kB regulated anti-apoptotic factors XIAP, cIAP1, and Bcl-xL were measured. Apoptosis was analyzed by Western blot for caspase 3 and PARP, and by flow cytometry as well. An iodide uptake assay was performed to determine whether NF-kB inhibition could influence radioactive iodide uptake. Results: The methyl-thiazolyl-tetrazolium assay showed significant decrease of viable cells by combination therapy than by mono-therapies. The DNA-binding assay and luciferase reporter assay showed enhanced NF-kB function and reporter gene activities due to 131 I, yet significant suppression was achieved by NF-kB inhibition. Western blot proved 131 I could increase nuclear NF-kB concentration, while NF-kB inhibition reduced NF-kB concentration. Western blot also demonstrated significant up-regulation of XIAP, cIAP1, and Bcl-xL after 131 I therapy. And inhibition of NF-kB could significantly downregulate these factors. Finally, synergism induced by combined therapy was displayed by significant enhancements o