Coxiella burnetii alters cyclic AMP-dependent protein kinase signaling during growth in macrophages.

Coxiella burnetii is the bacterial agent of human Q fever, an acute, flu-like illness that can present as chronic endocarditis in immunocompromised individuals. Following aerosol-mediated transmission, C. burnetii replicates in alveolar macrophages in a unique phagolysosome-like parasitophorous vacuole (PV) required for survival. The mechanisms of C. burnetii intracellular survival are poorly defined and a recent Q fever outbreak in the Netherlands emphasizes the need for better understanding this unique host-pathogen interaction. We recently demonstrated that inhibition of host cyclic AMP-dependent protein kinase (PKA) activity negatively impacts PV formation. In the current study, we confirmed PKA involvement in PV biogenesis and probed the role of PKA signaling during C. burnetii infection of macrophages. Using PKA-specific inhibitors, we found the kinase was needed for biogenesis of prototypical PV and C. burnetii replication. PKA and downstream targets were differentially phosphorylated throughout infection, suggesting prolonged regulation of the pathway. Importantly, the pathogen actively triggered PKA activation, which was also required for PV formation by virulent C. burnetii isolates during infection of primary human alveolar macrophages. A subset of PKA-specific substrates were differentially phosphorylated during C. burnetii infection, suggesting the pathogen uses PKA signaling to control distinct host cell responses. Collectively, the current results suggest a versatile role for PKA in C. burnetii infection and indicate virulent organisms usurp host kinase cascades for efficient intracellular growth.