Immunoediting role for major vault protein in apoptotic signaling induced by bacterial -acyl homoserine lactones.

The major vault protein (MVP) mediates diverse cellular responses, including cancer cell resistance to chemotherapy and protection against inflammatory responses to Here, we report the use of photoactive probes to identify MVP as a target of the -(3-oxo-dodecanoyl) homoserine lactone (C12), a quorum sensing signal of certain proteobacteria including A treatment of normal and cancer cells with C12 or other -acyl homoserine lactones (AHLs) results in rapid translocation of MVP into lipid raft (LR) membrane fractions. Like AHLs, inflammatory stimuli also induce LR-localization of MVP, but the C12 stimulation reprograms (functionalizes) bioactivity of the plasma membrane by recruiting death receptors, their apoptotic adaptors, and caspase-8 into LR. These functionalized membranes control AHL-induced signaling processes, in that MVP adjusts the protein kinase p38 pathway to attenuate programmed cell death.

NLRP3 activation and mitosis are mutually exclusive events coordinated by NEK7, a new inflammasome component.

The NLRP3 inflammasome responds to microbes and danger signals by processing and activating proinflammatory cytokines, including interleukin 1β (IL-1β) and IL-18. We found here that activation of the NLRP3 inflammasome was restricted to interphase of the cell cycle by NEK7, a serine-threonine kinase previously linked to mitosis. Activation of the NLRP3 inflammasome required NEK7, which bound to the leucine-rich repeat domain of NLRP3 in a kinase-independent manner downstream of the induction of mitochondrial reactive oxygen species (ROS).

The use of small molecule probes to study spatially separated stimulus-induced signaling pathways.

Simultaneous activation of signaling pathways requires dynamic assembly of higher-order protein complexes at the cytoplasmic domains of membrane-associated receptors in a stimulus-specific manner. Here, using the paradigm of cellular activation through cytokine and innate immune receptors, we demonstrate the proof-of-principle application of small molecule probes for the dissection of receptor-proximal signaling processes, such as activation of the transcription factor NF-κB and the protein kinase p38.

An inflammasome-independent role for epithelial-expressed Nlrp3 in renal ischemia-reperfusion injury.

Cytoplasmic innate immune receptors are important therapeutic targets for diseases associated with overproduction of proinflammatory cytokines. One cytoplasmic receptor complex, the Nlrp3 inflammasome, responds to an extensive array of molecules associated with cellular stress. Under normal conditions, Nlrp3 is autorepressed, but in the presence of its ligands, it oligomerizes, recruits apoptosis-associated speck-like protein containing a caspase recruitment domain (Asc), and triggers caspase 1 activation and the maturation of proinflammatory cytokines such as IL-1β and IL-18.

Nod1 and nod2 are expressed in human and murine renal tubular epithelial cells and participate in renal ischemia reperfusion injury.

Nucleotide-binding oligomerization domain (Nod) 1 and Nod2 are members of a family of intracellular innate sensors that participate in innate immune responses to pathogens and molecules released during the course of tissue injury, including injury induced by ischemia. Ischemic injury to the kidney is characterized by renal tubular epithelial apoptosis and inflammation. Among the best studied intracellular innate immune receptors known to contribute to apoptosis and inflammation are Nod1 and Nod2.

Modulation of gene expression via disruption of NF-kappaB signaling by a bacterial small molecule.

The control of innate immune responses through activation of the nuclear transcription factor NF-kappaB is essential for the elimination of invading microbial pathogens. We showed that the bacterial N-(3-oxo-dodecanoyl) homoserine lactone (C12) selectively impairs the regulation of NF-kappaB functions in activated mammalian cells. The consequence is specific repression of stimulus-mediated induction of NF-kappaB-responsive genes encoding inflammatory cytokines and other immune regulators.

IRAK-4 kinase activity-dependent and -independent regulation of lipopolysaccharide-inducible genes.

IRAK-4 kinase inactive (IRAK-4 KD) knock-in mice display defects in TLR- and IL-1 receptor signaling and are resistant to LPS-induced shock. In the present study we examined the LPS-induced response in IRAK-4 KD mice in more detail. We show that IRAK-4 kinase activity is required for certain aspects of TLR-mediated signaling but not for others.

Infection control by antibody disruption of bacterial quorum sensing signaling.

Quorum sensing (QS) is the process through which bacteria communicate utilizing small diffusible molecules termed autoinducers. It has been demonstrated that QS controls a plethora of microbial processes including the expression of virulence factors. Here we report an immunopharmacotherapeutic approach for the attenuation of QS in the Gram-positive human pathogen Staphylococcus aureus.

IRAK-4 kinase activity is required for interleukin-1 (IL-1) receptor- and toll-like receptor 7-mediated signaling and gene expression.

IRAK-4 is an essential component of the signal transduction complex downstream of the IL-1- and Toll-like receptors. Although regarded as the first kinase in the signaling cascade, the role of IRAK-4 kinase activity versus its scaffold function is still controversial. To investigate the role of IRAK-4 kinase function in vivo, "knock-in" mice were generated by replacing the wild type IRAK-4 gene with a mutant gene encoding kinase-deficient IRAK-4 protein (IRAK-4 KD).

Triad3A regulates ubiquitination and proteasomal degradation of RIP1 following disruption of Hsp90 binding.

Toll-like receptors (TLRs) play a crucial role in innate immunity by recognizing microbial pathogens. Triad3A is an E3 ubiquitin-protein ligase that interacts with the Toll/interleukin-1 receptor domain of TLRs and promotes their proteolytic degradation. In the present study, we further investigated its activity on signaling molecules downstream of TLRs and tumor necrosis factor (TNF) receptor 1.

N-(3-oxo-acyl)homoserine lactones signal cell activation through a mechanism distinct from the canonical pathogen-associated molecular pattern recognition receptor pathways.

Innate immune system receptors function as sensors of infection and trigger the immune responses through ligand-specific signaling pathways. These ligands are pathogen-associated products, such as components of bacterial walls and viral nuclear acids. A common response to such ligands is the activation of mitogen-activated protein kinase p38, whereas double-stranded viral RNA additionally induces the phosphorylation of eukaryotic translation initiation factor 2alpha (eIF2alpha).

Enhanced bacterial clearance and sepsis resistance in caspase-12-deficient mice.

Caspases function in both apoptosis and inflammatory cytokine processing and thereby have a role in resistance to sepsis. Here we describe a novel role for a caspase in dampening responses to bacterial infection. We show that in mice, gene-targeted deletion of caspase-12 renders animals resistant to peritonitis and septic shock.

NF-kappa B-inducing kinase regulates selected gene expression in the Nod2 signaling pathway.

The innate immune system surveys the extra- and intracellular environment for the presence of microbes. Among the intracellular sensors is a protein known as Nod2, a cytosolic protein containing a leucine-rich repeat domain. Nod2 is believed to play a role in determining host responses to invasive bacteria.

Innate immune responses during infection.

The innate immune system senses bacteria in the environment and defends against infection. Here we will discuss two types of sensor protein families. The plasma membrane receptors that comprise the Toll-like receptor (TLRs) family and the intracellular proteins termed NOD1 and NOD2.

IKKi/IKKepsilon plays a key role in integrating signals induced by pro-inflammatory stimuli.

We report that the product of the inducible gene encoding the kinase known as IKKi/IKKepsilon (IKKi) is required for expression of a group of genes up-regulated by pro-inflammatory stimuli such as bacterial endotoxin (lipopolysaccharide (LPS)). Here, using murine embryonic fibroblasts obtained from mice bearing deletions in IKK2, p65, and IKKi genes, we provide evidence to support a link between signaling through the NF-kappaB and CCAAA/enhancer-binding protein (C/EBP) pathways. This link includes an NF-kappaB-dependent regulation of C/EBPbeta and C/EBPdelta gene transcription and IKKi-mediated activation of C/EBP.

Toll-like receptor 9 mediates CpG-DNA signaling.

Among the bacterial products known to activate the innate immune '1system is bacterial DNA. This activity resides within the nonmethylated CpG motifs of the DNA and is recapitulated using appropriate synthetic CpG containing oligodeoxynucleotides (CpG-ODN). TLR9-deficient mice were shown to exhibit a nonresponsive phenotype-to-bacterial DNA and CpG-ODN.