Coxiella burnetii Alters Cyclic AMP-Dependent Protein Kinase
Signaling during Growth in Macrophages
Laura J. MacDonald,aRichard C. Kurten,b,cand Daniel E. Votha
Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, USAa; Department of Physiology and Biophysics,
University of Arkansas for Medical Sciences, Little Rock, Arkansas, USAb; and Arkansas Children’s Hospital Research Institute, Little Rock, Arkansas, USAc
Coxiella burnetii is the bacterial agent of human Q fever, an acute, flu-like illness that can present as chronic endocarditis in im-
munocompromised 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
probed the role of PKA signaling during C. burnetii infection of macrophages. Using PKA-specific inhibitors, we found the ki-
nase was needed for biogenesis of prototypical PV and C. burnetii replication. PKA and downstream targets were differentially
gered PKA activation, which was also required for PV formation by virulent C. burnetii isolates during infection of primary hu-
man alveolar macrophages. A subset of PKA-specific substrates were differentially phosphorylated during C. burnetii infection,
satile role for PKA in C. burnetii infection and indicate virulent organisms usurp host kinase cascades for efficient intracellular
gen can also establish a chronic infection resulting in potentially
ing cause of noncultivatable infectious endocarditis, a condition
that is notoriously difficult to treat with current antibiotics (36).
C. burnetii is naturally spread by contaminated aerosols, and live-
stock workers are often exposed to the organism while working
with infected animals, particularly during parturition. This expo-
sure risk was recently highlighted by a major Q fever outbreak in
the Netherlands that resulted in over 4,000 cases and 11 deaths
C. burnetii has historically been difficult to study and pathogenic
determinants are not well understood.
In vivo, C. burnetii targets alveolar phagocytic cells, with mac-
ing uptake into a host cell, the pathogen is housed for 4 to 6 h in a
tight-fitting phagosome that decorates with early endosomal
early vacuole also interacts with autophagosomes (20, 37) and
fluid-phase endosomes before ultimately fusing with lysosomes
(43). Although antibacterial acid hydrolases are present in the
vacuole, lysosomal fusion triggers acid pH-dependent activation
of C. burnetii metabolism (21, 32), and the organism replicates in
tious cycle necessitates regulation of host cell survival to ensure a
intrinsic apoptosis by triggering a prosurvival transcriptional re-
vival kinases Akt and Erk1/2 to promote cell survival (44). These
events are likely controlled by the organism’s Dot/Icm type IV
oxiella burnetii is the highly infectious bacterial agent of hu-
man Q fever, a zoonotic disease that typically presents as an
secretion system that translocates effector proteins into the host
cytosol, where they regulate intracellular replication and inhibi-
tion of apoptosis (4, 10, 29). However, host signaling pathways
that regulate parasitophorous vacuole (PV) formation and main-
tenance have not been defined.
Previous studies uncovered the presence of host vacuolar fu-
sogenic proteins, such as Rab GTPases, on the PV membrane but
did not assess the role of kinase-dependent signaling cascades in
vacuole biogenesis (7, 9, 37). We recently performed a directed
for PV generation (25). This study uncovered a role for many
kinases in PV formation and suggests signaling cascades may be
intimately linked to biogenesis of pathogen replication vacuoles.
Eleven kinases were involved in PV formation, including protein
kinase C (PKC), myosin light chain kinase, calmodulin-depen-
(PKA). PKA is a versatile host protein that directs many host re-
sponses, including cell survival, cytokine production, and cyto-
skeletal organization (34). PKA target proteins are differentially
phosphorylated during C. burnetii infection, and the effects of
PKA inhibition are reversible (25), indicating the pathogen con-
tinually modulates this pathway during intracellular growth.
Received 30 January 2012 Returned for modification 1 March 2012
Accepted 13 March 2012
Published ahead of print 2 April 2012
Editor: F. C. Fang
Address correspondence to Daniel E. Voth, email@example.com.
Copyright © 2012, American Society for Microbiology. All Rights Reserved.
iai.asm.orgInfection and Immunityp. 1980–1986June 2012 Volume 80 Number 6
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