Involvement of the p38 mitogen activated protein kinase signal pathway in Staphylococcus aureus-induced apoptosis of human monocyte U937 cells

To establish a apoptotic model of human monocyte U937 cells induced by Staphylococcus aureus used to investigate the role of the p38 mitogen activated protein kinase (MAPK) signal pathway in this apoptotic process, the U937 cell line was pre-treated with different concentrations of SB203580(an inhibitor of p38 MAPK pathway) and the apoptotic rate of U937 cells was determined using Annexin V-FITC and propidium iodide(PI) double staining and flow cytometry (FCM) 30 minutes after infection with S.aureus. The level of phosphorylation on p38 MAPK was tested by Western blotting. It was found that S.aureus could induce apoptosis of the cultured U937 cells in a time-dependent manner, in which the phosphorylation of p38 protein was found in 15 minutes ,the maximal phosphorylation occurred in 30 minutes and began to decline 60 minutes after infection. In contrast, the level of the total p38 protein was not changed in the whole course of experiment. When the p38 MAPK signal pathway was inhibited by SB203580, the rate of the inhibitor concentration-dependent apoptosis of U937 cells was reduced. These results indicate that S.aureus can induce apoptosis of the cultured U937 cells in a time-dependent manner, and the activation of the p38 MAPK signal pathway by S.aureus appears to be the main way to mediate apoptosis.