Activation of protein tyrosine kinases by Coxiella burnetii: Role in actincytoskeleton reorganization and bacterial phagocytosis

Coxiella burnetii, the agent of Q fever, is an obligate intracellular micro organism that grows in monocytes/ macrophages. The internalization of virul ent organisms by monocytes is lower than that of avirulent variants and is associated with actin cytoskeleton reorganization. We studied the activatio n of protein tyrosine kinases (PTKs) by C. burnetii in THP-1 monocytes. Vir ulent organisms induced early PTK activation and the tyrosine phosphorylati on of several endogenous substrates, including Hck and Lyn, two Src related kinases. PTK activation reflects C. burnetii virulence since avirulent var iants were unable to stimulate PTK. We also investigated the role of PTK ac tivation in C. burnetii-stimulated F-actin reorganization. Tyrosine phospho rylated proteins were colocalized with F-actin inside cell protrusions indu ced by C. burnetii, and PTK activity was increased in Triton X-100-insolubl e fractions. In addition, lavendustin A, a PTK inhibitor, and PP1, a Src ki nase inhibitor, prevented C. burnetii-induced cell protrusions and F-actin reorganization, We finally assessed the role of PTK activation in bacterial phagocytosis. Pretreatment of THP-1 cells with lavendustin A and PP1 upreg ulated the uptake of virulent C. burnetii but had no effect on the phagocyt osis of avirulent organisms. Thus, it is likely that PTK activation by C. b urnetii negatively regulates bacterial uptake by interfering with cytoskele ton organization.