The mechanism of apoptosis induced by a novel thioredoxin reductase inhibitor in A549 cells: possible involvement of nuclear factor-kappaB-dependent pathway.

1,2-[bis(1,2-benzisoselenazolone-3(2H)-ketone)]ethane (BBSKE, PCT: CN02/00412), a novel thioredoxin reductase inhibitor previously synthesized in our lab, has been demonstrated to inhibit the growth of a variety of human cancer cells and to induce apoptosis. Here we report on the potential molecular mechanism of apoptosis induced by BBSKE in A549 cells. The treatment of BBSKE reduced the protein levels of Bcl-2, Bcl-xL, procaspase-9 and procaspase-3, and caused the release of cytochrome C from the mitochondria to the cytosol in a dose-dependent manner, suggesting the onset of mitochondria-dependent apoptosis. Through electrophoretic mobility shift assay (EMSA), the DNA-binding activity of nuclear factor-kappaB (NF-kappaB) was found to be attenuated after BBSKE treatment, accompanied by the diminution of the immunoprecipitated complex of thioredoxin and NF-kappaB in co-immunoprecipitation experiments. Meanwhile, the ratio of pIkappaB-alpha to IkappaB-alpha and the subcellular localization of p65 between cytoplasm and nucleus were not significantly altered by BBSKE treatment, as demonstrated in western analysis and immunocytochemistry assay. Furthermore, the mRNA levels of the NF-kappaB regulated anti-apoptosis genes Bcl-2, Bcl-xL, cIAP-2 and XIAP were decreased in a dose-dependent manner after BBSKE treatment. All the above observations suggest that BBSKE induce mitochondria-dependent apoptosis in A549 cells probably through suppressing the thioredoxin reductase-thioredoxin-NF-kappaB pathway.