Vasodilator-Stimulated Phosphoprotein Activity Is Required for Coxiella burnetii Growth in Human Macrophages.

Coxiella burnetii is an intracellular bacterial pathogen that causes human Q fever, an acute flu-like illness that can progress to chronic endocarditis and liver and bone infections. Humans are typically infected by aerosol-mediated transmission, and C. burnetii initially targets alveolar macrophages wherein the pathogen replicates in a phagolysosome-like niche known as the parasitophorous vacuole (PV). C. burnetii manipulates host cAMP-dependent protein kinase (PKA) signaling to promote PV formation, cell survival, and bacterial replication. In this study, we identified the actin regulatory protein vasodilator-stimulated phosphoprotein (VASP) as a PKA substrate that is increasingly phosphorylated at S157 and S239 during C. burnetii infection. Avirulent and virulent C. burnetii triggered increased levels of phosphorylated VASP in macrophage-like THP-1 cells and primary human alveolar macrophages, and this event required the Cα subunit of PKA. VASP phosphorylation also required bacterial protein synthesis and secretion of effector proteins via a type IV secretion system, indicating the pathogen actively triggers prolonged VASP phosphorylation. Optimal PV formation and intracellular bacterial replication required VASP activity, as siRNA-mediated depletion of VASP reduced PV size and bacterial growth. Interestingly, ectopic expression of a phospho-mimetic VASP (S239E) mutant protein prevented optimal PV formation, whereas VASP (S157E) mutant expression had no effect. VASP (S239E) expression also prevented trafficking of bead-containing phagosomes to the PV, indicating proper VASP activity is critical for heterotypic fusion events that control PV expansion in macrophages. Finally, expression of dominant negative VASP (S157A) in C. burnetii-infected cells impaired PV formation, confirming importance of the protein for proper infection. This study provides the first evidence of VASP manipulation by an intravacuolar bacterial pathogen via activation of PKA in human macrophages.

Coxiella burnetii exploits host cAMP-dependent protein kinase signalling to promote macrophage survival.

Intracellular bacterial pathogens often subvert apoptosis signalling to regulate survival of their host cell, allowing propagation of the bacterial population. Coxiella burnetii, the intracellular agent of human Q fever, inhibits host cell apoptosis through several mechanisms, including prevention of mitochondrial cytochrome c release, triggering of an anti-apoptotic transcriptional programme, and activation of pro-survival kinases. To control host cell survival, C. burnetii delivers effector proteins to the eukaryotic cytosol using a specialized Dot/Icm type IV secretion system (T4SS). Effectors are predicted to regulate activity of pro-survival host signalling proteins, such as Akt and cAMP-dependent protein kinase (PKA), to control infection. Here, we show that host PKA activity is required for C. burnetii inhibition of macrophage apoptosis. PKA is activated during infection and inhibits activity of the pro-apoptotic protein Bad via phosphorylation. Bad is also phosphorylated at an Akt-specific residue, indicating C. burnetii uses two kinases to fully inactivate Bad. Additionally, Bad and the tethering protein 14-3-3ß colocalize at the C. burnetii parasitophorous vacuole (PV) membrane during infection, an event predicted to alter Bad promotion of apoptosis. Inhibiting PKA activity prevents Bad recruitment to the PV, but the protein is retained at the membrane during induction of apoptosis. Finally, PKA regulatory subunit I (RI) traffics to the PV membrane in a T4SS-dependent manner, suggesting a C. burnetii effector(s) regulates PKA-dependent activities. This study is the first to demonstrate subversion of host PKA activity by an intracellular bacterial pathogen to prevent apoptosis and survive within macrophages.

Virulent Coxiella burnetii pathotypes productively infect primary human alveolar macrophages.

The intracellular bacterial pathogen Coxiella burnetii is a category B select agent that causes human Q fever. In vivo, C. burnetii targets alveolar macrophages wherein the pathogen replicates in a lysosome-like parasitophorous vacuole (PV). In vitro, C. burnetii infects a variety of cultured cell lines that have collectively been used to model the pathogen's infectious cycle. However, differences in the cellular response to infection have been observed, and virulent C. burnetii isolate infection of host cells has not been well defined. Because alveolar macrophages are routinely implicated in disease, we established primary human alveolar macrophages (hAMs) as an in vitro model of C. burnetii-host cell interactions. C. burnetii pathotypes, including acute disease and endocarditis isolates, replicated in hAMs, albeit with unique PV properties. Each isolate replicated in large, typical PV and small, non-fused vacuoles, and lipid droplets were present in avirulent C. burnetii PV. Interestingly, a subset of small vacuoles harboured single organisms undergoing degradation. Prototypical PV formation and bacterial growth in hAMs required a functional type IV secretion system, indicating C. burnetii secretes effector proteins that control macrophage functions. Avirulent C. burnetii promoted sustained activation of Akt and Erk1/2 pro-survival kinases and short-termphosphorylation of stress-related p38. Avirulent organisms also triggered a robust, early pro-inflammatory response characterized by increased secretion of TNF-α and IL-6, while virulent isolates elicited substantially reduced secretion of these cytokines. A corresponding increase in pro- and mature IL-1ß occurred in hAMs infected with avirulent C. burnetii, while little accumulation was observed following infection with virulent isolates. Finally, treatment of hAMs with IFN-γ controlled intracellular replication, supporting a role for this antibacterial insult in the host response to C. burnetii. Collectively, the current results demonstrate the hAM model is a human disease-relevant platform for defining novel innate immune responses to C. burnetii.

Modulation of p38 MAPK signaling enhances dendritic cell activation of human CD4+ Th17 responses to ovarian tumor antigen.

The recent finding that Th17 infiltration of ovarian tumors positively predicts patient outcomes suggests that Th17 responses play a protective role in ovarian tumor immunity. This observation has led to the question of whether Th17 cells could be induced or expanded to therapeutic advantage by tumor vaccination. In this study, we show that treatment of ovarian tumor antigen-loaded, cytokine-matured human dendritic cells (DC) with a combination of IL-15 and a p38 MAP kinase inhibitor offers potent synergy in antagonism of CD4(+) Treg induction and redirection toward CD4(+) Th17 responses that correlate with strong CD8(+) cytotoxic T lymphocyte (CTL) activation. Ovarian tumor antigen-specific CD4(+) T cells secrete high levels of IL-17 and show reduced expression of CTLA-4, PD-1, and Foxp3 following activation with IL-15/p38 inhibitor-treated DC. We further show that modulation of p38 MAPK signaling in DC is associated with reduced expression of B7-H1 (PD-L1), loss of indoleamine 2,3-dioxygenase activity, and increased phosphorylation of ERK 1/2 MAPK. These observations may allow the development of innovative DC vaccination strategies to boost Th17 immunity in ovarian cancer patients.

Relatedness communicated in lemur scent.

Lemurs are the most olfactory-oriented of primates, yet there is still only a basic level of understanding of what their scent marks communicate. We analyzed scent secretions from Milne-Edwards' sifakas (Propithecus edwardsi) collected in their natural habitat of Ranomafana National Park, Madagascar. We sought to test whether the scent mark could signal genetic relatedness in addition to species, sex, season, and individuality. We not only found correlations (r (2) = 0.38, P = 0.017) between the total olfactory fingerprint and genetic relatedness but also between relatedness and specific components of the odor, despite the complex environmental signals from differences in diet and behavior in a natural setting. To the best of our knowledge, this is the first demonstration of an association between genetic relatedness and chemical communication in a wild primate population. Furthermore, we found a variety of compounds that were specific to each sex and each sampling period. This research shows that scent marks could act as a remote signal to avoid inbreeding, optimize mating opportunities, and potentially aid kin selection.

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.