Summary 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 harbored 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 term phosphorylation 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-1β 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.

Key Points• Autophagy, an essential degradation pathway, is constitutively active in resting platelets and is induced upon platelet activation.• Platelet autophagy is indispensable for hemostasis and thrombus formation.Autophagy is important for maintaining cellular homeostasis, and thus its deficiency is implicated in a broad spectrum of human diseases. Its role in platelet function has only recently been examined. Our biochemical and imaging studies demonstrate that the core autophagy machinery exists in platelets, and that autophagy is constitutively active in resting platelets. Moreover, autophagy is induced upon platelet activation, as indicated by agonist-induced loss of the autophagy marker LC3II. Additional experiments, using inhibitors of platelet activation, proteases, and lysosomal acidification, as well as platelets from knockout mouse strains, show that agonist-induced LC3II loss is a consequence of platelet signaling cascades and requires proteases, acidic compartments, and membrane fusion. To assess the physiological role of platelet autophagy, we generated a mouse strain with a megakaryocyte-and platelet-specific deletion of Atg7, an enzyme required for LC3II production. Ex vivo analysis of platelets from these mice shows modest defects in aggregation and granule cargo packaging. Although these mice have normal platelet numbers and size distributions, they exhibit a robust bleeding diathesis in the tail-bleeding assay and a prolonged occlusion time in the FeCl 3 -induced carotid injury model. Our results demonstrate that autophagy occurs in platelets and is important for hemostasis and thrombosis. (Blood. 2015;126(10):1224-1233 Introduction Autophagy, one of the major degradation pathways in eukaryotes, is important for cellular homeostasis and is implicated in a broad spectrum of human diseases including cancer, neurodegeneration, and cardiovascular diseases.1 There are 3 main types: chaperone-mediated autophagy, 2 microautophagy, 3,4 and the primary form, macroautophagy (referred to hereafter as autophagy).5 Autophagy involves de novo synthesis of double-membraned organelles called autophagosomes that contain cytosolic constituents including damaged organelles (eg, mitochondria) and protein aggregates. Autophagosomes fuse with multivesicular bodies, late endosomes, and lysosomes to form autolysosomes, 6 in which waste elimination, energy production, and recycling of cellular components take place.Autophagosome biogenesis and maturation use several protein complexes. [7][8][9][10] In mammals, cellular signals (eg, starvation) activate the Ulk1 complex (Ulk1, FIP200, Atg13, and Atg101), 11-14 which together with syntaxin 17, 15 localizes Atg14/Atg14L [16][17][18][19] to the endoplasmic reticulum. 15,20 This recruits the Beclin 1-Vps34 core complex (Beclin 1, Vps34, and Vps15) to autophagosome initiation sites and promotes phosphatidylinositol 3-phosphate production for recruitment of additional autophagy pathway components.20,21 Two ubiquitin-like conjugation systems are also important for autoph...

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.

Summary Conventional microscopy techniques, namely the confocal microscope or deconvolution processes, are resolution limited, ~250 nm, by the diffraction properties of light as developed by Ernst Abbe in 1873. This diffraction limit is appreciably above the size of most multi-protein complexes, which are typically 20–50 nm in diameter. In the mid 2000s, biophysicists moved beyond the diffraction barrier by structuring the illumination pattern and then applying mathematical principles and algorithms to allow a resolution of approximately 100 nm, sufficient to address protein subcellular colocalization questions. This “breaking” of the diffraction barrier, affording resolution beyond 200 nm is termed super resolution microscopy. More recent approaches include single molecule localization (such as PhotoActivated Localization Microscopy (PALM)/STochastic Optical Reconstruction Microscopy (STORM)) and point spread function engineering (such as STimulated Emission Depletion (STED) microscopy). In this review, we explain basic principles behind currently commercialized super resolution setups and address advantages and considerations in applying these techniques to protein colocalization in biological systems.

Summary Intracellular bacterial pathogens often subvert apoptosis signaling 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 program, 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 signaling 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 14-3-3β co-localize 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.

ABSTRACTCoxiella burnetiiis 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. burnetiireplicates in alveolar macrophages in a unique phagolysosome-like parasitophorous vacuole (PV) required for survival. The mechanisms ofC. burnetiiintracellular 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 duringC. burnetiiinfection of macrophages. Using PKA-specific inhibitors, we found the kinase was needed for biogenesis of prototypical PV andC. burnetiireplication. 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 virulentC. burnetiiisolates during infection of primary human alveolar macrophages. A subset of PKA-specific substrates were differentially phosphorylated duringC. burnetiiinfection, suggesting the pathogen uses PKA signaling to control distinct host cell responses. Collectively, the current results suggest a versatile role for PKA inC. burnetiiinfection and indicate virulent organisms usurp host kinase cascades for efficient intracellular growth.

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.

bearing nitrilotriacetic acid substituents at the end of a poly(ethylene glycol)grafted surface that promotes specific capture of protein targets for single particle reconstruction analysis. The utilization of these grids for specific adsorption of the targeted protein onto the grid surface results in wellcontrolled surface concentration enhancements and a days-to-minutes reduction in time required for the preparation of a purified sample for cryoEM analysis from an E. coli expression system. The selective and reversible capture of his-tag T7 bacteriophage and GroEL from crude lysates, as well as purified nanodisc-solubilized his-malFGK2, on these NTA-modified grids with an exceptionally low level of adsorption by non-target proteins has been observed. Our data illustrates the utility of these grids for selective capture from complex mixtures, detergent-solubilized membrane protein isolates, and expression systems yielding low copy numbers of the desired target in a manner that is well-suited for single particle reconstruction analysis.