Expression of 14-3-3δ, cdc2 and cyclin B proteins related to exotoxin A-induced apoptosis in HeLa S3 cells

After reports on regression of cancer in humans and animals infected with microbial pathogens date back more than 100 years, much effort has been spent over the years in developing wild type or attenuated bacterial and purified bacterial proteins for the treatment of cancer. Pseudomonas aeruginosa exotoxin A (ETA) is known to inhibit cell growth and trigger significant cell death in various cancer cells. Although ETA induces apoptosis of cancer cells, its exact mechanism of action is not yet known. Four different assays were performed in this study: morphological assessment of apoptotic cells, cell cytotoxicity, cell cycle analysis and Western blot analysis. The proliferation and survival in the cells treated with ETA was decreased. In addition, percentages of apoptotic HeLa S3 cells treated with ETA were increased. ETA-induced apoptosis rates were confirmed to have increased in a dose-dependent manner through annexin V binding assay. Flow cytometric analysis was examined to ascertain whether ETA could regulate cell cycle in HeLa S3 cells. ETA treatment demonstrated that the expression of 14-3-3δ proteins was increased, while expression of cdc and cyclin B proteins was decreased, suggesting that ETA induces cell cycle arrest and then progresses to apoptosis. Therefore, these results suggest that P. aeruginosa ETA induced apoptosis in HeLa S3 cells.