Assessing ATP binding and hydrolysis by NLR proteins

The balance between nuclear import and export of NLRC5 regulates MHC class I transactivation

Major histocompatibility complex (MHC) class I molecules play an essential role in regulating the adaptive immune system by presenting antigens to CD8 T cells. CITA (MHC class I transactivator), also known as NLRC5 (NLR family, CARD domain-containing 5), regulates the expression of MHC class I and essential components involved in the MHC class I antigen presentation pathway. While the critical role of the nuclear distribution of NLRC5 in its transactivation activity has been known, the regulatory mechanism to determine the nuclear localization of NLRC5 remains poorly understood. In this study, a comprehensive analysis of all domains in NLRC5 revealed that the regulatory mechanisms for nuclear import and export of NLRC5 coexist and counterbalance each other. Moreover, GCN5 (general control non-repressed 5 protein), a member of HATs (histone acetyltransferases), was found to be a key player to retain NLRC5 in the nucleus, thereby contributing to the expression of MHC class I. Therefore, the balance between import and export of NLRC5 has emerged as an additional regulatory mechanism for MHC class I transactivation, which would be a potential therapeutic target for the treatment of cancer and virus-infected diseases.

Characterization and expression analysis of mitochondrial localization molecule: NOD-like receptor X1 (Nlrx1) in mucosal tissues of turbot (Scophthalmus maximus) following bacterial challenge

The NOD-like receptor X1 (NLRX1) is a member of highly conserved nucleotide-binding domain (NBD)- and leucine-rich-repeat (LRR)-containing family (known as NLR), that localizes to the mitochondrial outer membrane and regulate the innate immunity by interacting with mitochondrial antiviral-signaling protein (MAVS). As one of cytoplasmic PRRs, NLRX1 plays key roles for pathogen recognition, autophagy and regulating of subsequent immune signaling pathways. In this study, we identified the nlrx1 in turbot as well as its expression profiles in mucosal surfaces following bacterial infection. In our results, the full-length nlrx1 transcript consists of an open reading frame (ORF) of 4,886 bp encoding the putative peptide of 966 amino acids. The phylogenetic analysis revealed the SmNlrx1 showed the closest relationship to Cynoglossus semilaevis. In addition, the Nlrx1 mRNA expression could be detected in all the examined tissues, with the most abundant expression level in head kidney, and the lowest expression level in liver. Moreover, Nlrx1 showed similar expression patterns following Vibrio anguillarum and Streptococcus iniae infection, that were both significantly up-regulated following challenge, especially post S. iniae challenge. Finally, fluorescence microscopy unveiled that the SmNlrx1 localized to mitochondria in HEK293T by N-terminal mitochondrial targeting sequence. Characterization of Nlrx1 might have an important implication in bioenergetic adaptation during metabolic stress, oncogenic transformation and innate immunity and will probably contribute to the development of novel intervention strategies for farming turbot.

Dynamics of the DEAD-box ATPase Prp5 RecA-like domains provide a conformational switch during spliceosome assembly

The DEAD-box family of proteins are ATP-dependent, RNA-binding proteins implicated in many aspects of RNA metabolism. Pre-mRNA splicing in eukaryotes requires three DEAD-box ATPases (Prp5, Prp28 and Sub2), the molecular mechanisms of which are poorly understood. Here, we use single molecule FRET (smFRET) to study the conformational dynamics of yeast Prp5. Prp5 is essential for stable association of the U2 snRNP with the intron branch site (BS) sequence during spliceosome assembly. Our data show that the Prp5 RecA-like domains undergo a large conformational rearrangement only in response to binding of both ATP and RNA. Mutations in Prp5 impact the fidelity of BS recognition and change the conformational dynamics of the RecA-like domains. We propose that BS recognition during spliceosome assembly involves a set of coordinated conformational switches among U2 snRNP components. Spontaneous toggling of Prp5 into a stable, open conformation may be important for its release from U2 and to prevent competition between Prp5 re-binding and subsequent steps in spliceosome assembly.

Functional characterization of NLRX1 in rabbit during enterohemorrhagic Escherichia coli infection

Nucleotide oligomerization domain (NOD) like receptor X1 (NLRX1) is a member of pattern recognition receptor, which has been linked to viral response, cancer, and inflammatory diseases. In this study, rabbit NLRX1 (rNLRX1) was firstly cloned from RK-13 cells, which protein contained a NACHT domain and seven LRRs. rNLRX1 was widely expressed in tissues of rabbits, and highly increased in liver, spleen, kidney, and colon after infected with enterohemorrhagic Escherichia coli (EHEC). Overexpression of rNLRX1 negatively regulated NF-κB signaling, and impaired the expression of pro-inflammatory cytokines and defensins. Moreover, deficient of rNLRX1 in RK-13 cells was performed to investigate the possible roles of rNLRX1. Upon EHEC stimulation, knockdown of rNLRX1 markedly enhanced NF-κB activation and downstream responsive cytokines (IL1β and TNFα) and β-defensins (DEFB114, DEFB124, and DEFB125). Furthermore, overexpression of rNLRX1 promoted the proliferation of EHEC, whereas knockdown of rNLRX1 inhibited its growth. Our study identified that rNLRX1 acts as a negative regulatory in anti-microbial responses after EHEC infection.

Parallel Colorimetric Quantification of Choline and Phosphocholine as a Method for Studying Choline Kinase Activity in Complex Mixtures

Choline kinase (Chok) is an enzyme found in eukaryotes and Gram-positive bacteria. Chok catalyzes the production of phosphocholine from choline and ATP. This enzyme has been validated as a drug target in Streptococcus pneumonia, but the role Chok enzymatic activity plays in bacterial cell growth and division is not well understood. Phosphocholine production by Chok and its attenuation by inhibitors in the context of complex samples such as cell extracts can currently be quantified by several methods. These include choline depletion measurements, radioactive methods, mass-spectrometry, and nuclear magnetic resonance. The first does not measure phosphocholine directly, the second requires elaborate safety procedures, and the third and fourth require significant capital investments and technical expertise. For these reasons, a less expensive, higher throughput, more easily accessible assay is needed to facilitate further study in Gram-positive Choks. Here, we present the development of a triiodide/activated charcoal/molybdenum blue system for detecting and quantifying choline and phosphocholine in parallel. We demonstrate that this system can reliably quantify changes in choline and phosphocholine concentrations over time in Chok enzymatic assays using cell extracts as the source of the enzyme. This is an easily accessible, convenient, robust, and economical method for studying Chok activity in complex samples. The triiodide/activated charcoal/molybdenum blue system opens new doors into the study choline kinase in Gram-positive pathogens.

14-3-3γ Regulates Lipopolysaccharide-Induced Inflammatory Responses and Lactation in Dairy Cow Mammary Epithelial Cells by Inhibiting NF-κB and MAPKs and Up-Regulating mTOR Signaling

As a protective factor for lipopolysaccharide (LPS)-induced injury, 14-3-3γ has been the subject of recent research. Nevertheless, whether 14-3-3γ can regulate lactation in dairy cow mammary epithelial cells (DCMECs) induced by LPS remains unknown. Here, the anti-inflammatory effect and lactation regulating ability of 14-3-3γ in LPS-induced DCMECs are investigated for the first time, and the molecular mechanisms responsible for their effects are explored. The results of qRT-PCR showed that 14-3-3γ overexpression significantly inhibited the mRNA expression of tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β) and inducible nitric oxide synthase (iNOS). Enzyme-linked immunosorbent assay (ELISA) analysis revealed that 14-3-3γ overexpression also suppressed the production of TNF-α and IL-6 in cell culture supernatants. Meanwhile, CASY-TT Analyser System showed that 14-3-3γ overexpression clearly increased the viability and proliferation of cells. The results of kit methods and western blot analysis showed that 14-3-3γ overexpression promoted the secretion of triglycerides and lactose and the synthesis of β-casein. Furthermore, the expression of genes relevant to nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPKs) and lactation-associated proteins were assessed by western blot, and the results suggested that 14-3-3γ overexpression inactivated the NF-κB and MAPK signaling pathways by down-regulating extracellular signal regulated protein kinase (ERK), p38 mitogen-activated protein kinase (p38MAPK) and inhibitor of NF-κB (IκB) phosphorylation levels, as well as by inhibiting NF-κB translocation. Meanwhile, 14-3-3γ overexpression enhanced the expression levels of β-casein, mammalian target of rapamycin (mTOR), ribosomal protein S6 kinase 1 (S6K1), serine/threonine protein kinase Akt 1 (AKT1), sterol regulatory element binding protein 1 (SREBP1) and peroxisome proliferator-activated receptor gamma (PPARγ). These results suggest that 14-3-3γ was able to attenuate the LPS-induced inflammatory responses and promote proliferation and lactation in LPS-induced DCMECs by inhibiting the activation of the NF-κB and MAPK signaling pathways and up-regulating mTOR signaling pathways to protect against LPS-induced injury.

IL-21 modulates release of proinflammatory cytokines in LPS-stimulated macrophages through distinct signaling pathways

The aim of this study was to investigate the anti-inflammatory effect of IL-21 on LPS-induced mouse peritoneal macrophages. The results showed that IL-21 significantly inhibited LPS-induced mRNA expression of IL-1β, TNF-α, and IL-6 in macrophages, but not of IFN-γ, IL-10, CCL5, or CXCL2. ELISA analysis showed that IL-21 also suppressed LPS-induced production of TNF-α and IL-6 in culture supernatants. Western blot analysis showed that IL-21 clearly inhibited ERK and IκBα phosphorylation and NF-κB translocation in LPS-stimulated macrophages, but it increased STAT3 phosphorylation. Flow cytometric and Western blot analysis showed that IL-21 decreased M1 macrophages surface markers expression of CD86, iNOS, and TLR4 in LPS-stimulated cells. All results suggested that IL-21 decreases IL-6 and TNF-α production via inhibiting the phosphorylation of ERK and translocation of NF-κB and promotes a shift from the M1 to M2 macrophage phenotype by decreasing the expression of CD86, iNOS, and TLR4 and by increasing STAT3 phosphorylation in LPS-stimulated cells.