Burkholderia pseudomallei invasion and activation of epithelial cells requires activation of p38 mitogen-activated protein kinase

Burkholderia pseudomallei is a causative agent of melioidosis. This gram-negative bacterium is able to survive inside the macrophages and also able to invade non-phagocytic cells including epithelial cells. Interaction of pathogenic bacteria to the host cells is frequently associated with activation of mitogen-activated protein (MAP) kinases signaling activity. In this study, we demonstrated that B. pseudomallei stimulated p38 MAP kinase of human alveolar lung epithelial cell line (A549). Phosphorylation of p38 was observed after 15 min, attained a maximal level at 60 min after the infection. A specific inhibitor of p38 phosphorylation, SB 203580, was able to inhibit invasion of this bacterium into the cells suggesting that invasion of B. pseudomallei required activation of p38. In contrast, wortmannin which is a specific inhibitor of phosphoinositide 3-kinase (PI3-kinase) failed to inhibit the invasion. Moreover, SB 203580 can also interfere with IκBα degradation and IL-8 mRNA expression, indicating that the phosphorylation of p38 occurred upstream of NF-κB activation. Cytochalasin D, an inhibitor of actin polymerization needed for internalisation of bacteria, did not have any effect on the phosphorylation of p38. These results indicate that B. pseudomallei stimulate phosphorylation of p38 making by initial contact with the cell surface components and do not require internalisation and interaction with intracellular cytoplasmic components of the cells.