Blocking of NF-κB activation enhances the tumor necrosis factor α-induced apoptosis of a human gastric cancer cell line

The transcription factor NF-κB is constitutively activated in many human cancers and induces the expression of multiple genes, including those of anti-apoptotic proteins. This study investigated the mechanism by which human gastric cancer cells (MKN45) are resistant to apoptosis induced by tumor necrosis factor α (TNF-α). Confluent monolayers of MKN45 cells were either pretreated or not for 60 min with PSI, a peptide aldehyde known to specifically inhibit the chymotrypsin-like activity of 26S proteasome. Cells were subsequently stimulated with recombinant human TNF-α, and cell viabilities were determined by the WST-1 assay. Apoptosis was confirmed by fluorescence microscopy after staining with Hoechst 33342, and DNA fragmentation was determined by a DNA fragmentation detection kit. A 24-h incubation with either TNF-α or PSI alone did not affect cell viabilities; however, pretreatment with PSI significantly enhanced the level of apoptosis induced by TNF-α. Therefore, this study suggests the possibility that blocking of NF-κB activity renders gastric cancer cells susceptible to the apoptosis induced by TNF-α.