TRIF-GEFH1-RhoB pathway is involved in MHCII expression on dendritic cells that is critical for CD4 T-cell activation

Golgi screen identifies the RhoGEF Solo as a novel regulator of RhoB and endocytic transport

The control of intracellular membrane trafficking by Rho GTPases is central to cellular homeostasis. How specific guanine nucleotide exchange factors and GTPase-activating proteins locally balance GTPase activation in this process is nevertheless largely unclear. By performing a microscopy-based RNAi screen, we here identify the RhoGEF protein Solo as a functional counterplayer of DLC3, a RhoGAP protein with established roles in membrane trafficking. Biochemical, imaging and optogenetics assays further uncover Solo as a novel regulator of endosomal RhoB. Remarkably, we find that Solo and DLC3 control not only the activity, but also total protein levels of RhoB in an antagonistic manner. Together, the results of our study uncover the first functionally connected RhoGAP-RhoGEF pair at endomembranes, placing Solo and DLC3 at the core of endocytic trafficking.

A bacterium-like particle vaccine displaying Zika virus prM-E induces systemic immune responses in mice

The emergence of Zika virus (ZIKV) infection, which is unexpectedly associated with congenital defects, has prompted the development of safe and effective vaccines. The Gram-positive enhancer matrix-protein anchor (GEM-PA) display system has emerged as a versatile and highly effective platform for delivering target proteins in vaccines. In this study, we developed a bacterium-like particle vaccine, ZI-△-PA-GEM, based on the GEM-PA system. The fusion protein ZI-△-PA, which contains the prM-E-△TM protein of ZIKV (with a stem-transmembrane region deletion) and the protein anchor PA3, was expressed. The fusion protein was successfully displayed on the GEM surface to form ZI-△-PA-GEM. Moreover, the intramuscular immunization of BALB/c mice with ZI-△-PA-GEM combined with ISA 201 VG and poly(I:C) adjuvants induced durable ZIKV-specific IgG and protective neutralizing antibody responses. Potent B-cell/DC activation was also stimulated early after immunization. Notable, splenocyte proliferation, the secretion of multiple cytokines, T/B-cell activation and central memory T-cell responses were elicited. These data indicate that ZI-△-PA-GEM is a promising bacterium-like particle vaccine candidate for ZIKV.

Tumor necrosis factor-induced ArhGEF10 selectively activates RhoB contributing to human microvascular endothelial cell tight junction disruption

Capillary endothelial cells (ECs) maintain a semi-permeable barrier between the blood and tissue by forming inter-EC tight junctions (TJs), regulating selective transport of fluid and solutes. Overwhelming inflammation, as occurs in sepsis, disrupts these TJs, leading to leakage of fluid, proteins, and small molecules into the tissues. Mechanistically, disruption of capillary barrier function is mediated by small Rho-GTPases, such as RhoA, -B, and -C, which are activated by guanine nucleotide exchange factors (GEFs) and disrupted by GTPase-activating factors (GAPs). We previously reported that a mutation in a specific RhoB GAP (p190BRhoGAP) underlays a hereditary capillary leak syndrome. Tumor necrosis factor (TNF) treatment disrupts TJs in cultured human microvascular ECs, a model of capillary leak. This response requires new gene transcription and involves increased RhoB activation. However, the specific GEF that activates RhoB in capillary ECs remains unknown. Transcriptional profiling of cultured tight junction-forming human dermal microvascular endothelial cells (HDMECs) revealed that 17 GEFs were significantly induced by TNF. The function of each candidate GEF was assessed by short interfering RNA depletion and trans-endothelial electrical resistance screening. Knockown of ArhGEF10 reduced the TNF-induced loss of barrier which was phenocopied by RhoB or dual ArhGEF10/RhoB knockdown. ArhGEF10 knockdown also reduced the extent of TNF-induced RhoB activation and disruption at tight junctions. In a cell-free assay, immunoisolated ArhGEF10 selectively catalyzed nucleotide exchange to activate RhoB, but not RhoA or RhoC. We conclude ArhGEF10 is a TNF-induced RhoB-selective GEF that mediates TJ disruption and barrier loss in human capillary endothelial cells.

Protein-Activated Kinase 3 (PAK3)-Related Intellectual Disability Associated with Combined Immunodeficiency: A Case Report

BACKGROUND X-linked intellectual disabilities constitute a group of clinically and genetically heterogeneous disorders that are divided into syndromic and nonsyndromic forms. PAK3 mutations are associated with X-linked nonsyndromic forms of intellectual disability, with the most common clinical features being cognitive deficit, large ears, oral motor hypotonia, and neurobehavioral abnormalities. These mutations have been reported to be associated with either loss of the PAK3 protein or loss of its kinase activity. We report a case with the novel PAK3 variant c.685C>T p.(Pro229Ser), which has not been previously described. CASE REPORT We report the first case of a PAK3 mutation to present with the common clinical features along with immunodeficiency resembling common variable immune deficiency. Our patient was a 10-year-old girl who had experienced septic shock with a rapidly deteriorating course when she was 5-years-old. The initial immune work-up showed lymphopenia affecting all cell lines, but preferentially the B-cell compartment. Further work-up of this patient revealed low levels of immunoglobulin (Ig) G, undetectable IgA, reduced IgG1 and IgG2 subclasses, and poor response to the diphtheria/tetanus vaccine. Lymphocyte function, tested as the response to the mitogen phytohemagglutinin, was low and fluctuated between 9% and 22% compared with control samples. The patient experienced recurrent respiratory tract infections, and she responded well to regular intravenous Ig treatment and antibiotic prophylaxis. CONCLUSIONS The current case might provide a new insight into PAK3 gene function. Although further evidence is needed, it is worth considering that immunological abnormalities may be associated with PAK3 gene mutations.

GEF-H1 Signaling upon Microtubule Destabilization Is Required for Dendritic Cell Activation and Specific Anti-tumor Responses

Dendritic cell (DC) activation is a critical step for anti-tumor T cell responses. Certain chemotherapeutics can influence DC function. Here we demonstrate that chemotherapy capable of microtubule destabilization has direct effects on DC function; namely, it induces potent DC maturation and elicits anti-tumor immunity. Guanine nucleotide exchange factor-H1 (GEF-H1) is specifically released upon microtubule destabilization and is required for DC activation. In response to chemotherapy, GEF-H1 drives a distinct cell signaling program in DCs dominated by the c-Jun N-terminal kinase (JNK) pathway and AP-1/ATF transcriptional response for control of innate and adaptive immune responses. Microtubule destabilization, and subsequent GEF-H1 signaling, enhances cross-presentation of tumor antigens to CD8 T cells. In absence of GEF-H1, anti-tumor immunity is hampered. In cancer patients, high expression of the GEF-H1 immune gene signature is associated with prolonged survival. Our study identifies an alternate intracellular axis in DCs induced upon microtubule destabilization in which GEF-H1 promotes protective anti-tumor immunity.

Certain chemotherapeutics elicit potent anti-tumor immunity. Kashyap et al. demonstrate that microtubule-destabilizing chemotherapeutics induce maturation of dendritic cells through activation of microtubule-associated protein GEF-H1. This leads to effective priming of CD8 T cells against tumor antigens. GEF-H1 is critical for anti-tumor immunity of microtubule-targeting chemotherapy.

Vγ9Vδ2 T Cells Activation Through Phosphoantigens Can Be Impaired by a RHOB Rerouting in Lung Cancer

Vγ9Vδ2 T cells are known to be efficient anti-tumor effectors activated through phosphoantigens (PAg) that are naturally expressed by tumor cells or induced by amino bisphosphonates treatment. This PAg-activation which is TCR and butyrophilin BTN3A dependent can be modulated by NKG2D ligands, immune checkpoint ligands, adhesion molecules, and costimulatory molecules. This could explain the immune-resistance observed in certain clinical trials based on Vγ9Vδ2 T cells therapies. In NSCLC, encouraging responses were obtained with zoledronate administrations for 50% of patients. According to the in vivo results, we showed that the in vitro Vγ9Vδ2 T cell reactivity depends on the NSCLC cell line considered. If the PAg-pretreated KRAS mutated A549 is highly recognized and killed by Vγ9Vδ2 T cells, the EGFR mutated PC9 remains resistant to these killers despite a pre-treatment either with zoledronate or with exogenous BrHPP. The immune resistance of PC9 was shown not to be due to immune checkpoint ligands able to counterbalance NKG2D ligands or adhesion molecules such as ICAM-1 highly expressed by PC9. RHOB has been shown to be involved in the Vγ9Vδ2 TCR signaling against these NSCLC cell lines, in this study we therefore focused on its intracellular behavior. In comparison to a uniform distribution of RHOB in endosomes and at the plasma membrane in A549, the presence of large endosomal clusters of RHOB was visualized by a split-GFP system, suggesting that RHOB rerouting in the PC9 tumor cell could impair the reactivity of the immune response.

miR-223-3p Inhibits Antigen Endocytosis and Presentation and Promotes the Tolerogenic Potential of Dendritic Cells through Targeting Mannose Receptor Signaling and Rhob

Background

The role of miR-223-3p in dendritic cells (DCs) is unknown. This study is aimed at investigating the effect of miR-223-3p on the antigen uptake and presentation capacities of DCs and the underlying molecular mechanism.

Methods

FITC-OVA antigen uptake and cell surface markers in bone marrow-derived DCs (BMDCs) were analyzed by flow cytometry. BMDCs were transfected with the miR-223-3p mimic or inhibitor. Cytokine levels were determined by ELISA. CD4+ T cell differentiation was determined by mixed lymphocyte culture assay.

Results

OVA treatment significantly downregulated miR-223-3p in BMDCs. The miR-223-3p mimic significantly inhibited OVA-induced antigen uptake and surface expression of MHC-II on BMDCs (P < 0.01). The miR-223-3p mimic increased TGF-β1 production in OVA-treated DCs (P < 0.01). Mixed lymphocyte reaction showed that the miR-223-3p mimic significantly promoted Treg cell differentiation. In addition, the miR-223-3p mimic significantly upregulated CD103 in DCs, indicating the promotion of tolerogenic DCs. The miR-223-3p mimic downregulated Rhob protein in OVA-induced DCs. Rhob knockdown significantly suppressed the ability of FITC-OVA endocytosis (P < 0.01) and surface MHC-II molecule expression (P < 0.01) in BMDCs, promoting promoted Treg cell differentiation. Mannose receptor (MR) knockdown significantly upregulated miR-223-3p, downregulated Rhob protein in OVA-treated DCs, inhibited the FITC-OVA endocytosis and surface MHC-II expression in BMDCs, and promoted Treg cell differentiation (all P < 0.01).

Conclusion

These data suggest that miR-223-3p has an inhibitory effect on the antigen uptake and presentation capacities of BMDCs and promotes Treg cell differentiation, which is, at least partially, through targeting MR signaling and Rhob.

MicroRNA Regulation of the Small Rho GTPase Regulators-Complexities and Opportunities in Targeting Cancer Metastasis

The small Rho GTPases regulate important cellular processes that affect cancer metastasis, such as cell survival and proliferation, actin dynamics, adhesion, migration, invasion and transcriptional activation. The Rho GTPases function as molecular switches cycling between an active GTP-bound and inactive guanosine diphosphate (GDP)-bound conformation. It is known that Rho GTPase activities are mainly regulated by guanine nucleotide exchange factors (RhoGEFs), GTPase-activating proteins (RhoGAPs), GDP dissociation inhibitors (RhoGDIs) and guanine nucleotide exchange modifiers (GEMs). These Rho GTPase regulators are often dysregulated in cancer; however, the underlying mechanisms are not well understood. MicroRNAs (miRNAs), a large family of small non-coding RNAs that negatively regulate protein-coding gene expression, have been shown to play important roles in cancer metastasis. Recent studies showed that miRNAs are capable of directly targeting RhoGAPs, RhoGEFs, and RhoGDIs, and regulate the activities of Rho GTPases. This not only provides new evidence for the critical role of miRNA dysregulation in cancer metastasis, it also reveals novel mechanisms for Rho GTPase regulation. This review summarizes recent exciting findings showing that miRNAs play important roles in regulating Rho GTPase regulators (RhoGEFs, RhoGAPs, RhoGDIs), thus affecting Rho GTPase activities and cancer metastasis. The potential opportunities and challenges for targeting miRNAs and Rho GTPase regulators in treating cancer metastasis are also discussed. A comprehensive list of the currently validated miRNA-targeting of small Rho GTPase regulators is presented as a reference resource.

Transcriptome profiling of tolerogenic dendritic cells conditioned with dual mTOR kinase inhibitor, AZD8055

Dendritic cells (DCs) can initiate and regulate adaptive immunity depending on their maturation status. Many pharmacological and genetic means have been used in the generation of immature/tolerogenic DCs. However, the key factors controlling DCs tolerogenicity remain obscure. In this work, we demonstrated that AZD8055, an ATP-competitive inhibitor of mammalian target of rapamycin (mTOR), could also lead to a tolerogenic DC phenotype from several lines of evidence, such as suppression of T cell proliferation, promoting the generation of Tregs, and inducing allogeneic T cell apoptosis. Further studies using RNA-seq method identified 430, 1172 and 1436 differentially expressed genes (DEGs) between AZD-DCs vs. Control-DCs, LPS-DCs vs. Control-DCs, and AZD-DCs vs. LPS-DCs, respectively. The 5 most differentially expressed transcripts identified by RNA-seq expression profiles were validated by quantitative RT-PCR assays. NF-κB, p38MAPK, the ribosome and PPAR signaling pathways may be involved in the induction of tolerogenic DCs by AZD8055. Functional annotation showed some genes like MGL2, Cadherin-1, 4-1BB, RhoB and Pdpn, were quite different between AZD-DCs and Control-DCs/LPS-DCs, which might be related to the tolerogenic properties of AZD-DCs. Our work provided the potential underlying molecular mechanisms involved in the generation of tolerogenic DCs. Further functional characterization of individual target gene in DC tolerogenicity will help to develop novel therapeutic modalities in circumstances like transplant tolerance induction and autoimmunity.

A functional polymorphism in the promoter of RhoB is associated with susceptibility to Vibrio anguillarum in turbot (Scophthalmus maximus)

As an isoform of Rho family GTPases, RhoB plays a pivotal role in cytoskeletal organization, cell proliferation, apoptosis and immune response. However, the regulatory mechanisms of RhoB expression in aquatic animals are still unknown. In the present study, we first construct Vibrio anguillarum infection model in S. maximus, including susceptible and resistant individuals. Then the temporal expression of RhoB was detected after V. anguillarum challenge using qRT-PCR and found that RhoB transcripts were significantly induced in the liver, gill and blood despite of differential expression levels and responsive time points. In addition, the mRNA levels of RhoB in resistant individuals were significantly higher than in susceptible ones. The length of 2083 bp sequences of RhoB promoter was cloned and characterized. Moreover, DNA methylation of the RhoB promoter was measured by bisulfite sequencing (BSP) and hypo-methylated was detected in the CpG islands. Three SNPs (-1590, -1575 and -1449) and two haplotypes in the promoter region of RhoB were identified to be associated with V. anguillarum resistance in turbot by association analysis in group 17-R and 17-S. Deletion analysis indicated that these SNPs could negatively mediate the activity of RhoB promoter. Site-directed mutagenesis and qRT-PCR of individuals with different genotypes demonstrated that -1575 T/A polymorphism affected promoter activity. Further study showed that this mutation altered the binding site of the transcription factor CREB. Co-transfection of SmCREB and RhoB promoter was performed in HEK293T cells which confirmed the -1575 allelic differences on transcriptional activity, with the susceptibility allele showing reduced activity. Taken together, our findings implicate that losing of binding of CREB to SmRhoB promoter due to -1575T/A polymorphisms enhances SmRhoB expression in resistant turbot, which provide insights into the effect of SmRhoB expression in response to V. anguillarum infection.

RhoA as a Key Regulator of Innate and Adaptive Immunity

RhoA is a ubiquitously expressed cytoplasmic protein that belongs to the family of small GTPases. RhoA acts as a molecular switch that is activated in response to binding of chemokines, cytokines, and growth factors, and via mDia and the ROCK signaling cascade regulates the activation of cytoskeletal proteins, and other factors. This review aims to summarize our current knowledge on the role of RhoA as a general key regulator of immune cell differentiation and function. The contribution of RhoA for the primary functions of innate immune cell types, namely neutrophils, macrophages, and conventional dendritic cells (DC) to (i) get activated by pathogen-derived and endogenous danger signals, (ii) migrate to sites of infection and inflammation, and (iii) internalize pathogens has been fairly established. In activated DC, which constitute the most potent antigen-presenting cells of the immune system, RhoA is also important for the presentation of pathogen-derived antigen and the formation of an immunological synapse between DC and antigen-specific T cells as a prerequisite to induce adaptive T cell responses. In T cells and B cells as the effector cells of the adaptive immune system Rho signaling is pivotal for activation and migration. More recently, mutations of Rho and Rho-modulating factors have been identified to predispose for autoimmune diseases and as causative for hematopoietic malignancies.

Whole-genome resequencing from bulked-segregant analysis reveals gene set based association analyses for the Vibrio anguillarum resistance of turbot (Scophthalmus maximus)

Many achievements have been made to develop quantitative trait loci (QTLs) and gene-associated single nucleotide polymorphisms (SNPs) to facilitate practical marker-assisted selection (MAS) in aquatic animals. However, the systematic studies of SNPs associated with extreme threshold traits were poor in populations lacking of parental genomic information. Coupling next generation sequencing with bulked segregant analysis (BSA) should allow identification of numerous associated SNPs with extreme phenotypes. In the present study, using combination of SNP frequency difference and Euclidean distance, we conducted linkage analysis of SNPs located in genes involved in immune responses, and identified markers associated with Vibrio anguillarum resistance in turbot (Scophthalmus maximus). A total of 221 SNPs was found as candidate SNPs between resistant and susceptible individuals. Among these SNPs, 35 loci located in immune related genes were genotyped in verification population and 7 of them showed significant association with V. anguillarum resistance in both alleles and genotypes (P < 0.05). Among these 7 genes, PIK3CA-like, CYLD, VCAM1, RhoB and RhoGEF are involved in PI3K/Akt/mTOR pathway and NF-κB pathway, which influence the efficiency of bacteria entering the host and inflammation. SNP-SNP interaction analysis was performed by generalized multifactor dimensionality reduction (GMDR). The combination of SNP loci in RhoB, PIK3CA-like and ADCY3 showed a significant effect on V. anguillarum resistance with the verification rate in the sequencing population up to 70.8%. Taken all, our findings demonstrated the feasibility of BSA-seq approach in identifying genes responsible for the extreme phenotypes and will aid in performing MAS in turbot.

Cullin-3/KCTD10 E3 complex is essential for Rac1 activation through RhoB degradation in human epidermal growth factor receptor 2-positive breast cancer cells

Rho GTPase Rac1 is a central regulator of F‐actin organization and signal transduction to control plasma membrane dynamics and cell proliferation. Dysregulated Rac1 activity is often observed in various cancers including breast cancer and is suggested to be critical for malignancy. Here, we showed that the ubiquitin E3 ligase complex Cullin‐3 (CUL3)/KCTD10 is essential for epidermal growth factor (EGF)‐induced/human epidermal growth factor receptor 2 (HER2)‐dependent Rac1 activation in HER2‐positive breast cancer cells. EGF‐induced dorsal membrane ruffle formation and cell proliferation that depends on both Rac1 and HER2 were suppressed in CUL3‐ or KCTD10‐depleted cells. Mechanistically, CUL3/KCTD10 ubiquitinated RhoB for degradation, another Rho GTPase that inhibits Rac1 activation at the plasma membrane by suppressing endosome‐to‐plasma membrane traffic of Rac1. In HER2‐positive breast cancers, high expression of Rac1 mRNA significantly correlated with poor prognosis of the patients. This study shows that this novel molecular axis (CUL3/KCTD10/RhoB) positively regulates the activity of Rac1 in HER2‐positive breast cancers, and our findings may lead to new treatment options for HER2‐ and Rac1‐positive breast cancers.

Bmi1 Regulates IκBα Degradation via Association with the SCF Complex

Bmi1 is a polycomb group protein and regulator that stabilizes the ubiquitination complex PRC1 in the nucleus with no evidently direct link to the NF-κB pathway. In this study, we report a novel function of Bmi1: its regulation of IκBα ubiquitination in the cytoplasm. A deficiency of Bmi1 inhibited NF-κB-mediated gene expression in vitro and a NF-κB-mediated mouse model of arthritis in vivo. Mechanistic analysis showed that Bmi1 associated with the SCF ubiquitination complex via its N terminus and with phosphorylation by an IKKα/β-dependent pathway, leading to the ubiquitination of IκBα. These effects on NF-κB-related inflammation suggest Bmi1 in the SCF complex is a potential therapeutic target for various diseases and disorders, including autoimmune diseases.

Presenilin 1 Regulates NF-κB Activation via Association with Breakpoint Cluster Region and Casein Kinase II

We recently reported that NF-κB-mediated inflammation caused by breakpoint cluster region (BCR) is dependent on the α subunit of casein kinase II (CK2α) complex. In the current study, we demonstrate that presenilin 1 (Psen1), which is a catalytic component of the γ-secretase complex and the mutations of which are known to cause familial Alzheimer disease, acts as a scaffold of the BCR-CK2α-p65 complex to induce NF-κB activation. Indeed, Psen1 deficiency in mouse endothelial cells showed a significant reduction of NF-κB p65 recruitment to target gene promoters. Conversely, Psen1 overexpression enhanced reporter activation under NF-κB responsive elements and IL-6 promoter. Furthermore, the transcription of NF-κB target genes was not inhibited by a γ-secretase inhibitor, suggesting that Psen1 regulates NF-κB activation in a manner independent of γ-secretase activity. Mechanistically, Psen1 associated with the BCR-CK2α complex, which is required for phosphorylation of p65 at serine 529. Consistently, TNF-α-induced phosphorylation of p65 at serine 529 was significantly decreased in Psen1-deficient cells. The association of the BCR-CK2α-p65 complex was perturbed in the absence of Psen1. These results suggest that Psen1 functions as a scaffold of the BCR-CK2α-p65 complex and that this signaling cascade could be a novel therapeutic target for various chronic inflammation conditions, including those in Alzheimer disease.

Rbm10 regulates inflammation development via alternative splicing of Dnmt3b

RNA-binding motif 10 (Rbm10) is an RNA-binding protein that regulates alternative splicing, but its role in inflammation is not well defined. Here, we show that Rbm10 controls appropriate splicing of DNA (cytosine-5)-methyltransferase 3b (Dnmt3b), a DNA methyltransferase, to regulate the activity of NF-κB-responsive promoters and consequently inflammation development. Rbm10 deficiency suppressed NF-κB-mediated responses in vivo and in vitro. Mechanistic analysis showed that Rbm10 deficiency decreased promoter recruitment of NF-κB, with increased DNA methylation of the promoter regions in NF-κB-responsive genes. Consistently, Rbm10 deficiency increased the expression level of Dnmt3b2, which has enzyme activity, while it decreased the splicing isoform Dnmt3b3, which does not. These two isoforms associated with NF-κB efficiently, and overexpression of enzymatically active Dnmt3b2 suppressed the expression of NF-κB targets, indicating that Rbm10-mediated Dnmt3b2 regulation is important for the induction of NF-κB-mediated transcription. Therefore, Rbm10-dependent Dnmt3b regulation is a possible therapeutic target for various inflammatory diseases.

RhoB induces the production of proinflammatory cytokines in TLR-triggered macrophages

Toll-like receptors (TLRs) are the primary sensors detecting conserved molecular patterns on microorganisms, thus acting as important components of innate immunity against invading pathogens. Many positive and negative regulators of TLR-triggered signaling have been identified. The Rho GTPase RhoB plays a key role in cell migration, division and polarity; however, the function and regulatory mechanisms of RhoB in TLR ligand-triggered innate immune responses remain to be investigated. Here, we report that the expression of RhoB is induced by TLR agonists (lipopolysaccharide (LPS), CpG, poly(I:C)) in macrophages. Knockdown of RhoB expression markedly decreased TLR ligand-induced activation of mitogen activated protein kinases and nuclear factor-κB (NF-κB), and the production of tumor necrosis factor α (TNFα), interleukin (IL)-6 and IL-1β in macrophages stimulated with TLR ligands. Furthermore, we demonstrated that RhoB interacts with major histocompatibility complex class II (MHCII) α chain, but not β chain, in endosomes of macrophages. Knockdown of MHCII expression greatly reduced the interaction of RhoB with Btk, and attenuated the induction of NF-κB and interferon β activity by RhoB upon LPS stimulation. These findings suggest that RhoB is a positive physiological regulator of TLRs signaling via binding to MHCII in macrophages, and therefore RhoB may be a potential therapeutic target in inflammatory diseases.

RhoB Mediates Phosphoantigen Recognition by Vγ9Vδ2 T Cell Receptor

Human Vγ9Vδ2 T cells respond to tumor cells by sensing elevated levels of phosphorylated intermediates of the dysregulated mevalonate pathway, which is translated into activating signals by the ubiquitously expressed butyrophilin A1 (BTN3A1) through yet unknown mechanisms. Here, we developed an unbiased, genome-wide screening method that identified RhoB as a critical mediator of Vγ9Vδ2 TCR activation in tumor cells. Our results show that Vγ9Vδ2 TCR activation is modulated by the GTPase activity of RhoB and its redistribution to BTN3A1. This is associated with cytoskeletal changes that directly stabilize BTN3A1 in the membrane, and the subsequent dissociation of RhoB from BTN3A1. Furthermore, phosphoantigen accumulation induces a conformational change in BTN3A1, rendering its extracellular domains recognizable by Vγ9Vδ2 TCRs. These complementary events provide further evidence for inside-out signaling as an essential step in the recognition of tumor cells by a Vγ9Vδ2 TCR.

RASSF1A Suppresses the Invasion and Metastatic Potential of Human Non-Small Cell Lung Cancer Cells by Inhibiting YAP Activation through the GEF-H1/RhoB Pathway

Inactivation of the tumor suppressor gene RASSF1A by promoter hypermethylation represents a key event underlying the initiation and progression of lung cancer. RASSF1A inactivation is also associated with poor prognosis and may promote metastatic spread. In this study, we investigated how RASSF1A inactivation conferred invasive phenotypes to human bronchial cells. RNAi-mediated silencing of RASSF1A induced epithelial-to-mesenchymal transition (EMT), fomenting a motile and invasive cellular phenotype in vitro and increased metastatic prowess in vivo. Mechanistic investigations revealed that RASSF1A blocked tumor growth by stimulating cofilin/PP2A-mediated dephosphorylation of the guanine nucleotide exchange factor GEF-H1, thereby stimulating its ability to activate the antimetastatic small GTPase RhoB. Furthermore, RASSF1A reduced nuclear accumulation of the Hippo pathway transcriptional cofactor Yes-associated protein (YAP), which was reinforced by RhoB activation. Collectively, our results indicated that RASSF1 acts to restrict EMT and invasion by indirectly controlling YAP nuclear shuttling and activation through a RhoB-regulated cytoskeletal remodeling process, with potential implications to delay the progression of RASSF1-hypermethylated lung tumors.

Cdc42-dependent actin dynamics controls maturation and secretory activity of dendritic cells

Cdc42 control of actin dynamics keeps DCs in an immature state, and loss of Cdc42 activity facilitates secretion and rapid up-regulation of intracellular molecules to the cell surface, which shows that Cdc42 contributes to DC immunogenicity by regulating the DC actin cytoskeleton.

Cell division cycle 42 (Cdc42) is a member of the Rho guanosine triphosphatase family and has pivotal functions in actin organization, cell migration, and proliferation. To further study the molecular mechanisms of dendritic cell (DC) regulation by Cdc42, we used Cdc42-deficient DCs. Cdc42 deficiency renders DCs phenotypically mature as they up-regulate the co-stimulatory molecule CD86 from intracellular storages to the cell surface. Cdc42 knockout DCs also accumulate high amounts of invariant chain–major histocompatibility complex (MHC) class II complexes at the cell surface, which cannot efficiently present peptide antigens (Ag’s) for priming of Ag-specific CD4 T cells. Proteome analyses showed a significant reduction in lysosomal MHC class II–processing proteins, such as cathepsins, which are lost from DCs by enhanced secretion. As these effects on DCs can be mimicked by chemical actin disruption, our results propose that Cdc42 control of actin dynamics keeps DCs in an immature state, and cessation of Cdc42 activity during DC maturation facilitates secretion as well as rapid up-regulation of intracellular molecules to the cell surface.

Microtubule and Actin Interplay Drive Intracellular c-Src Trafficking

The proto-oncogene c-Src is involved in a variety of signaling processes. Therefore, c-Src spatiotemporal localization is critical for interaction with downstream targets. However, the mechanisms regulating this localization have remained elusive. Previous studies have shown that c-Src trafficking is a microtubule-dependent process that facilitates c-Src turnover in neuronal growth cones. As such, microtubule depolymerization lead to the inhibition of c-Src recycling. Alternatively, c-Src trafficking was also shown to be regulated by RhoB-dependent actin polymerization. Our results show that c-Src vesicles primarily exhibit microtubule-dependent trafficking; however, microtubule depolymerization does not inhibit vesicle movement. Instead, vesicular movement becomes both faster and less directional. This movement was associated with actin polymerization directly at c-Src vesicle membranes. Interestingly, it has been shown previously that c-Src delivery is an actin polymerization-dependent process that relies on small GTPase RhoB at c-Src vesicles. In agreement with this finding, microtubule depolymerization induced significant activation of RhoB, together with actin comet tail formation. These effects occurred downstream of GTP-exchange factor, GEF-H1, which was released from depolymerizing MTs. Accordingly, GEF-H1 activity was necessary for actin comet tail formation at the Src vesicles. Our results indicate that regulation of c-Src trafficking requires both microtubules and actin polymerization, and that GEF-H1 coordinates c-Src trafficking, acting as a molecular switch between these two mechanisms.

RhoB regulates the function of macrophages in the hypoxia-induced inflammatory response

Immune cells, particularly macrophages, play critical roles in the hypoxia-induced inflammatory response. The small GTPase RhoB is usually rapidly induced by a variety of stimuli and has been described as an important regulator of cytoskeletal organization and vesicle and membrane receptor trafficking. However, it is unknown whether RhoB is involved in the hypoxia-induced inflammatory response. Here, we investigated the effect of hypoxia on the expression of RhoB and the mechanism and significance of RhoB expression in macrophages. We found that hypoxia significantly upregulated the expression of RhoB in RAW264.7 cells, mouse peritoneal macrophages, and the spleen of rats. Hypoxia-induced expression of RhoB was significantly blocked by a specific inhibitor of hypoxia-inducible factor-1α (HIF-1α), c-Jun N-terminal kinase (JNK), or extracellular-signal regulated protein kinase (ERK), indicating that hypoxia-activated HIF-1α, JNK, and ERK are involved in the upregulation of RhoB by hypoxia. Knockdown of RhoB expression not only significantly suppressed basal production of interleukin-1 beta (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor alpha (TNF-α) in normoxia but also more markedly decreased the hypoxia-stimulated production of these cytokines. Furthermore, we showed that RhoB increased nuclear factor-kappa B (NF-κB) activity, and the inhibition of NF-κB transcriptional activity significantly decreased the RhoB-increased mRNA levels of IL-1β, IL-6, and TNF-α. Finally, we demonstrated that RhoB enhanced cell adhesion and inhibited cell migration in normoxia and hypoxia. Taken together, these results suggest that RhoB plays an important role in the hypoxia-induced activation of macrophages and the inflammatory response.Cellular & Molecular Immunology advance online publication, 21 September 2015; doi:10.1038/cmi.2015.78.

TIR Domain-Containing Adapter-Inducing Beta Interferon (TRIF) Mediates Immunological Memory against Bacterial Pathogens

Induction of adaptive immunity leads to the establishment of immunological memory; however, how innate immunity regulates memory T cell function remains obscure. Here we show a previously undefined mechanism in which innate and adaptive immunity are linked by TIR domain-containing adapter-inducing beta interferon (TRIF) during establishment and reactivation of memory T cells against Gram-negative enteropathogens. Absence of TRIF in macrophages (Mϕs) but not dendritic cells led to a predominant generation of CD4(+) central memory T cells that express IL-17 during enteric bacterial infection in mice. TRIF-dependent type I interferon (IFN) signaling in T cells was essential to Th1 lineage differentiation and reactivation of memory T cells. TRIF activated memory T cells to facilitate local neutrophil influx and enhance bacterial elimination. These results highlight the importance of TRIF as a mediator of the innate and adaptive immune interactions in achieving the protective properties of memory immunity against Gram-negative bacteria and suggest TRIF as a potential therapeutic target.

The ins and outs of MHC class II-mediated antigen processing and presentation

Antigenic peptide-loaded MHC class II molecules (peptide-MHC class II) are constitutively expressed on the surface of professional antigen-presenting cells (APCs), including dendritic cells, B cells, macrophages and thymic epithelial cells, and are presented to antigen-specific CD4(+) T cells. The mechanisms of antigen uptake, the nature of the antigen processing compartments and the lifetime of cell surface peptide-MHC class II complexes can vary depending on the type of APC. It is likely that these differences are important for the function of each distinct APC subset in the generation of effective adaptive immune responses. In this Review, we describe our current knowledge of the mechanisms of uptake and processing of antigens, the intracellular formation of peptide-MHC class II complexes, the intracellular trafficking of peptide-MHC class II complexes to the APC plasma membrane and their ultimate degradation.

Physiological roles of Rho and Rho effectors in mammals

Rho GTPase is a master regulator controlling cytoskeleton in multiple contexts such as cell migration, adhesion and cytokinesis. Of several Rho GTPases in mammals, the best characterized is the Rho subfamily including ubiquitously expressed RhoA and its homologs RhoB and RhoC. Upon binding GTP, Rho exerts its functions through downstream Rho effectors, such as ROCK, mDia, Citron, PKN, Rhophilin and Rhotekin. Until recently, our knowledge about functions of Rho and Rho effectors came mostly from in vitro studies utilizing cultured cells, and their physiological roles in vivo were largely unknown. However, gene-targeting studies of Rho and its effectors have now unraveled their tissue- and cell-specific roles and provide deeper insight into the physiological function of Rho signaling in vivo. In this article, we briefly describe previous studies of the function of Rho and its effectors in vitro and then review and discuss recent studies on knockout mice of Rho and its effectors.

The small GTPase RhoB regulates TNFα signaling in endothelial cells

The inflammatory response of endothelial cells triggered by cytokines such as TNFα and IL1β plays a pivotal role in innate immunity. Upon pro-inflammatory cytokine stimulation, endothelial cells produce chemokines and cytokines that attract and activate leukocytes, and express high levels of leukocyte adhesion molecules. This process is mediated by intracellular signaling cascades triggered by activation of e.g. the TNFα receptor (TNFR) that lead to the activation of the NFκB transcription factor and of MAP kinases, which in turn activate inflammatory gene transcription. We found that the small GTPase RhoB was strongly and rapidly upregulated in primary human endothelial cells by TNFα, IL1β and LPS. We subsequently investigated the role of RhoB in the regulation of TNFR signaling in endothelial cells by silencing RhoB expression with siRNA. We provide evidence that the TNFα-induced activation of p38 MAP kinase is strongly dependent on RhoB, but not on RhoA, while JNK activation is regulated by both RhoB and RhoA. Consistent with the important role of p38 MAP kinase in inflammation, we demonstrate that loss of RhoB impairs TNFα-induced ICAM-1 expression and reduces cell production of IL6 and IL8. In addition, we show that RhoB silencing alters the intracellular traffic of TNFα after endocytosis. Since RhoB is a known regulator of the intracellular traffic of membrane receptors, our data suggest that RhoB controls TNFα signaling through the regulation of the TNFR traffic.

Vav1 regulates MHCII expression in murine resting and activated B cells

Vav1 is a guanine nucleotide exchange factor (GEF) for Rho GTPases, which is exclusively expressed in cells of the hematopoietic system. In addition to its well-documented GEF activity, it was suggested to have other functions due to the presence of multiple domains and nuclear localization signals in its protein structure. Although GEF-dependent and GEF-independent functions of vav have been implicated in T-cell development and T-cell receptor signaling, the role of vav1 in antigen-presenting cells is poorly understood. We found that vav1 is an important regulator of MHCII expression and transport. Microarray analysis of unstimulated bone marrow-derived macrophages revealed a novel role of vav1 in transcriptional regulation of the MHCII locus, possibly by indirect means. Primary immune cells from vav1-deficient mice had a significantly lower constitutive surface expression of MHCII with the strongest impact observed on splenic and peritoneal B cells. Impaired MHCII expression resulted in a diminished capacity for T-cell activation. Using 6-thio-GTP, a specific inhibitor of the GEF function of vav1, we were able to show that the GEF activity is required for MHCII upregulation in B cells after stimulation with LPS. Furthermore, our data show that vav1 not only affects transcription of the MHCII locus but also is an important regulator of MHCII protein transport to the cell surface.

A unique host defense pathway: TRIF mediates both antiviral and antibacterial immune responses

Both anti-viral and anti-bacterial host defense mechanisms involve TRIF signaling. TRIF provides early clearance of pathogens and coordination of a local inflammatory ensemble through an interferon cascade, while it may trigger organ damage. The multipotentiality of TRIF-mediated immune machinery may direct the fate of our continuous battle with microbes.

Signal transduction pathways in chronic inflammatory autoimmune disease: small GTPases

Ras superfamily small GTPases represent a wide and diverse class of intracellular signaling proteins that are highly conserved during evolution. These enzymes serve as key checkpoints in coupling antigen receptor, growth factor, cytokine and chemokine stimulation to cellular responses. Once activated, via their ability to regulate multiple downstream signaling pathways, small GTPases amplify and diversify signaling cascades which regulate cellular proliferation, survival, cytokine expression, trafficking and retention. Small GTPases, particularly members of the Ras, Rap, and Rho family, critically coordinate the function and interplay of immune and stromal cells during inflammatory respones, and increasing evidence indicates that alterations in small GTPase signaling contribute to the pathological behavior of these cell populations in human chronic inflammatory diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). Here, we review how Ras, Rap, and Rho family GTPases contribute to the biology of cell populations relevant to human chronic inflammatory disease, highlight recent advances in understanding how alterations in these pathways contribute to pathology in RA and SLE, and discuss new therapeutic strategies that may allow specific targeting of small GTPases in the clinic.

RhoB regulates cell migration through altered focal adhesion dynamics

The Rho GTPase RhoB has been shown to affect cell migration, but how it does this is not clear. Here we show that cells depleted of RhoB by RNAi are rounded and have defects in Rac-mediated spreading and lamellipodium extension, although they have active membrane ruffling around the periphery. Depletion of the exchange factor GEF-H1 induces a similar phenotype. RhoB-depleted cells migrate faster, but less persistently in a chemotactic gradient, and frequently round up during migration. RhoB-depleted cells have similar numbers of focal adhesions to control cells during spreading and migration, but show more diffuse and patchy contact with the substratum. They have lower levels of surface β1 integrin, and β1 integrin activity is reduced in actin-rich protrusions. We propose that RhoB contributes to directional cell migration by regulating β1 integrin surface levels and activity, thereby stabilizing lamellipodial protrusions.

Neuropeptide signaling activates dendritic cell-mediated type 1 immune responses through neurokinin-2 receptor

Neurokinin A (NKA), a neurotransmitter distributed in the central and peripheral nervous system, strictly controls vital responses, such as airway contraction, by intracellular signaling through neurokinin-2 receptor (NK2R). However, the function of NKA-NK2R signaling on involvement in immune responses is less-well defined. We demonstrate that NK2R-mediated neuropeptide signaling activates dendritic cell (DC)-mediated type 1 immune responses. IFN-γ stimulation significantly induced NK2R mRNA and remarkably enhanced surface protein expression levels of bone marrow-derived DCs. In addition, the DC-mediated NKA production level was significantly elevated after IFN-γ stimulation in vivo and in vitro. We found that NKA treatment induced type 1 IFN mRNA expressions in DCs. Transduction of NK2R into DCs augmented the expression level of surface MHC class II and promoted Ag-specific IL-2 production by CD4(+) T cells after NKA stimulation. Furthermore, blockade of NK2R by an antagonist significantly suppressed IFN-γ production by both CD4(+) T and CD8(+) T cells stimulated with the Ag-loaded DCs. Finally, we confirmed that stimulation with IFN-γ or TLR3 ligand (polyinosinic-polycytidylic acid) significantly induced both NK2R mRNA and surface protein expression of human PBMC-derived DCs, as well as enhanced human TAC1 mRNA, which encodes NKA and Substance P. Thus, these findings indicate that NK2R-dependent neuropeptide signaling regulates Ag-specific T cell responses via activation of DC function, suggesting that the NKA-NK2R cascade would be a promising target in chronic inflammation caused by excessive type 1-dominant immunity.

Control of NOD2 and Rip2-dependent innate immune activation by GEF-H1

BACKGROUND

Genetic variants of nucleotide-binding oligomerization domain 2 (NOD2) lead to aberrant microbial recognition and can cause chronic inflammatory diseases in patients with Crohn's disease (CD).

METHODS

We utilized gene-specific siRNA mediated knockdown and expression of guanine nucleotide exchange factor H1 (GEF-H1) in wildtype, Rip2-, and Nod2-deficient macrophages, HCT-116 and HEK 293 cells to determine the role of GEF-H1 in NOD2 and Rip2-mediated NF-κB-dependent induction of proinflammatory cytokine expression. Confocal microscopy was used to determine subcellular distribution of GEF-H1, Rip2, and NOD2.

RESULTS

We identified GEF-H1 as an unexpected component of innate immune regulation during microbial pattern recognition by NOD2. Surprisingly, GEF-H1-mediated the activation of Rip2 during signaling by NOD2, but not in the presence of the 3020 insC variant of NOD2 associated with CD. GEF-H1 functioned downstream of NOD2 as part of Rip2-containing signaling complexes and was responsible for phosphorylation of Rip2 by Src tyrosine kinase. Rip2 variants lacking the tyrosine target of GEF-H1-mediated phosphorylation were unable to mediate NF-κB activation in Rip2-deficient macrophages and failed to transduce NOD2 signaling. GEF-H1 is required downstream of NOD2 as part of Rip2-containing signaling complexes for the activation of innate immune responses.

CONCLUSIONS

GEF-H1 connects tyrosine kinase function to NOD-like receptor signaling and is fundamental to the regulation of microbial recognition by ubiquitous innate immune mechanisms mediated by Rip2 kinase.

Transcriptional response of the bovine endometrium and embryo to endometrial polymorphonuclear neutrophil infiltration as an indicator of subclinical inflammation of the uterine environment

The aim of the present study was to analyse the effect of subclinical endometritis on endometrial and embryonic gene expression. A total of 49 cows at either Day 0 or Day 7 of the oestrous cycle (62–83 days post partum) following superovulation were classified as having subclinical endometritis (SE-0, SE-7) or a healthy endometrium (HE-0, HE-7) on the basis of endometrial cytological evaluation. Endometrial samples and associated embryos were subjected to global transcriptome analysis using the Bovine GeneChip (Affymetrix, Santa Clara, CA, USA) and aberrant transcript profiles were observed in SE-0 and SE-7 cows. At Day 0, 10 transcripts were found to be differentially expressed in endometrial samples. Specifically, the PDZK1, PXDN, DDHD2, GPLD1 and SULT1B1 genes were downregulated, whereas the PKIB, LOC534256, BT29392, LYZ and S100A14 genes were upregulated in SE-0 cows. Similarly, 11 transcripts were found to be differentially regulated on Day 7. Of these, GNPTG, BOLA-DQA5, CHD2, LOC541226, VCAM1 and ARHGEF2 were found to be downregulated, whereas PSTPIP2, BT236441 and MGC166084 were upregulated in SE-7 cows. Accordingly, endometrial health status affected the number of flushed, transferable embryos. In all, 20 genes were differentially regulated in blastocysts derived from HE-7 and SE-7 cows. Of these, GZMK, TCEAL4, MYL7, ADD3 and THEM50B were upregulated, whereas NUDCD2, MYO1E, BZW1, EHD4 and GZMB were downregulated. In conclusion, endometrial polymorphonuclear neutrophil infiltration as an indicator of subclinical endometritis is associated with changes in endometrial gene expression patterns, including genes involved in cell adhesion and immune modulation. Consequently, subclinical endometritis affects gene expression in embryos, including the expression of genes related to membrane stability, the cell cycle and apoptosis.

R-Ras is required for murine dendritic cell maturation and CD4+ T-cell priming

R-Ras is a member of the RAS superfamily of small GTP-binding proteins. The physiologic function of R-Ras has not been fully elucidated. We found that R-Ras is expressed by lymphoid and nonlymphoid tissues and drastically up-regulated when bone marrow progenitors are induced to differentiate into dendritic cells (DCs). To address the role of R-Ras in DC functions, we generated a R-Ras-deficient mouse strain. We found that tumors induced in Rras(-/-) mice formed with shorter latency and attained greater tumor volumes. This finding has prompted the investigation of a role for R-Ras in the immune system. Indeed, Rras(-/-) mice were impaired in their ability to prime allogeneic and antigen-specific T-cell responses. Rras(-/-) DCs expressed lower levels of surface MHC class II and CD86 in response to lipopolysaccharide compared with wild-type DCs. This was correlated with a reduced phosphorylation of p38 and Akt. Consistently, R-Ras-GTP level was increased within 10 minutes of lipopolysaccharide stimulation. Furthermore, Rras(-/-) DCs have attenuated capacity to spread on fibronectin and form stable immunologic synapses with T cells. Altogether, these findings provide the first demonstration of a role for R-Ras in cell-mediated immunity and further expand on the complexity of small G-protein signaling in DCs.

Contribution of a Streptococcus mutans antigen expressed by a Salmonella vector vaccine in dendritic cell activation

A Salmonella vector vaccine expressing the saliva-binding region (SBR) of the adhesin AgI/II of Streptococcus mutans has been shown to induce a mixed Th1/Th2 anti-SBR immune response in mice and to require Toll-like receptor 2 (TLR2), TLR4, and MyD88 signaling for the induction of mucosal anti-SBR antibody responses. Since dendritic cells (DC) are critical in innate and adaptive immunity, the present study assessed the role of SBR expression by the vector vaccine in DC activation. Bone marrow-derived DC from wild-type and TLR2, TLR4, and MyD88 knockout mice were stimulated with Salmonella vector BRD509, the SBR-expressing Salmonella vector vaccine BRD509(pSBRT7), or SBR protein, and the DC responses to different stimuli were compared by assessing costimulatory molecule expression, cytokine production, and signaling pathways. The DC response to both BRD509(pSBRT7) and BRD509 was dependent mainly on TLR4. BRD509(pSBRT7) and BRD509 induced upregulation of CD80, CD86, CD40, and major histocompatibility complex class II (MHC II) expression. Lower levels of interleukin-10 (IL-10) and IL-12p40 were produced by BRD509(pSBRT7)-stimulated DC than by BRD509-stimulated DC. Furthermore, BRD509(pSBRT7)-stimulated DC showed decreased p38 phosphorylation compared to that induced by DC stimulated with BRD509. However, BRD509(pSBRT7)-treated DC produced a higher level of IL-6 than BRD509-stimulated cells. The low IL-12p40 and high IL-6 cytokine profile expressed by BRD509(pSBRT7)-stimulated DC may represent a shift toward a Th2 response, as suggested by the increased expression in Jagged-1. These results provide novel evidence that a heterologous protein expressed by a Salmonella vector vaccine can differentially affect DC activation.

TLR4 signaling via MyD88 and TRIF differentially shape the CD4+ T cell response to Porphyromonas gingivalis hemagglutinin B

Recombinant hemagglutinin B (rHagB), a virulence factor of the periodontal pathogen Porphyromonas gingivalis, has been shown to induce protective immunity against bacterial infection. Furthermore, we have demonstrated that rHagB is a TLR4 agonist for dendritic cells. However, it is not known how rHagB dendritic cell stimulation affects the activation and differentiation of T cells. Therefore, we undertook the present study to examine the role of TLR4 signaling in shaping the CD4(+) T cell response following immunization of mice with rHagB. Immunization with this Ag resulted in the induction of specific CD4(+) T cells and Ab responses. In TLR4(-/-) and MyD88(-/-) but not Toll/IL-1R domain-containing adapter inducing IFN-β-deficient (TRIF(Lps2)) mice, there was an increase in the Th2 CD4(+) T cell subset, a decrease in the Th1 subset, and higher serum IgG(1)/IgG(2) levels of HagB-specific Abs compared with those in wild-type mice. These finding were accompanied by increased GATA-3 and Foxp3 expression and a decrease in the activation of CD4(+) T cells isolated from TLR4(-/-) and MyD88(-/-) mice. Interestingly, TLR4(-/-) CD4(+) T cells showed an increase in IL-2/STAT5 signaling. Whereas TRIF deficiency had minimal effects on the CD4(+) T cell response, it resulted in increased IFN-γ and IL-17 production by memory CD4(+) T cells. To our knowledge, these results demonstrate for the first time that TLR4 signaling, via the downstream MyD88 and TRIF molecules, exerts a differential regulation on the CD4(+) T cell response to HagB Ag. The gained insight from the present work will aid in designing better therapeutic strategies against P. gingivalis infection.

Induction of small G protein RhoB by non-genotoxic stress inhibits apoptosis and activates NF-κB

It has been reported by us and other groups that the expression of small GTP binding protein RhoB can be induced by genotoxic stressors and glucocorticoid (GC), a stress hormone that plays a key role in stress response. Until now stress-induced genes that confer cytoprotection under stressed conditions are largely unknown. In this study, we investigated the effects and mechanism of non-genotoxic stressors, including scalding in vivo and heat stress in vitro on the expression of RhoB. We found for the first time that both scalding, which could induce typical neuroendocrine responses of acute stress and cellular heat stress significantly increased the expression of RhoB at mRNA and protein levels. Moreover, in vitro experiments in human lung epithelial cells (A549) showed that induction of RhoB by heat stress was in a glucocorticoid receptor (GR)-independent manner and through multiple pathways including stabilization of RhoB mRNA and activation of p38 MAPK. Further experiments demonstrated that up-regulation of RhoB significantly inhibited heat stress-induced apoptosis and elevated transcriptional activity of NF-κB, but did not affect the expression of Hsp70 in A549 cells. In conclusion, we showed for the first time that RhoB was up-regulated by scalding in vivo and heat stress in vitro and played an important cytoprotective role during heat stress-induced apoptotic cell death.

What is the function of the dendritic cell side of the immunological synapse?

The adaptive immune response requires the formation of a specialized interface called the immunological synapse (IS), which is formed between a mature dendritic cell (DC) and a CD4(+) T cell in the lymph node. The IS involves organized motifs formed by cell-surface and cytoplasmic molecules at both the DC side (IS-DC) and the T cell side (IS-T) of the IS. Most studies of the functions of the IS have focused on the IS-T; however, to understand the function(s) of the entire IS, it is also necessary to gain insight into the role(s) of the IS-DC. Unlike T cells, which upon their activation leave the lymph node and return to the circulation, DCs largely become apoptotic and die in the node region. This latter observation and the known stability of the IS, which may last for hours, is consistent with the hypothesis that one of the functions of the IS-DC could be the temporal inhibition of the apoptosis of DCs, which would enable the activation of clonal T cells in the lymph nodes. Here, we discuss experimental data supporting the latter hypothesis, as well as the concept that the IS-DC is a signaling region that contributes to the functions of the IS.

TILRR, a novel IL-1RI co-receptor, potentiates MyD88 recruitment to control Ras-dependent amplification of NF-kappaB

Host defense against infection is induced by Toll-like and interleukin (IL)-1 receptors, and controlled by the transcription factor NF-κB. Our earlier studies have shown that IL-1 activation impacts cytoskeletal structure and that IL-1 receptor (IL-1RI) function is substrate-dependent. Here we identify a novel regulatory component, TILRR, which amplifies activation of IL-1RI and coordinates IL-1-induced control with mechanotransduction. We show that TILRR is a highly conserved and widely expressed enhancer of IL-1-regulated inflammatory responses and, further, that it is a membrane-bound glycosylated protein with sequence homology to members of the FRAS-1 family. We demonstrate that TILRR is recruited to the IL-1 receptor complex and magnifies signal amplification by increasing receptor expression and ligand binding. In addition, we show that the consequent potentiation of NF-κB is controlled through IL-1RI-associated signaling components in coordination with activation of the Ras GTPase. Using mutagenesis, we demonstrate that TILRR function is dependent on association with its signaling partner and, further, that formation of the TILRR-containing IL-1RI complex imparts enhanced association of the MyD88 adapter during ligand-induced activation of NF-κB. We conclude that TILRR is an IL-1RI co-receptor, which associates with the signaling receptor complex to enhance recruitment of MyD88 and control Ras-dependent amplification of NF-κB and inflammatory responses.

Toll-like receptor-induced innate immune responses in non-parenchymal liver cells are cell type-specific

Little is known of how the Toll-like receptor (TLR) system can modulate the function of non-parenchymal liver cells (NPC) as a major component of the innate and adaptive immune system of the liver. To investigate the diversification of TLR signalling pathways in NPC, we isolated Kupffer cells (KC) and liver sinusoidal endothelial cells (LSEC) from wild-type C57BL/6 mice and examined their responses to TLR1 to TLR9 agonists. The data show that KC respond to all TLR ligands by producing tumour necrosis factor-alpha (TNF-alpha) or interleukin-6 (IL-6), to TLR3 and TLR4 ligands only by producing interferon-beta (IFN-beta), to TLR1 and TLR8 ligands by significantly up-regulating major histocompatibility complex (MHC) class II and costimulatory molecules, and to TLR1, -2, -4 and -6 ligands by inducing high levels of T-cell proliferation and IFN-gamma production in the mixed lymphocyte reaction (MLR). Similarly, LSEC respond to TLR1 to -4, -6, -8 and -9 ligands by producing TNF-alpha, to TLR3 and -4 ligands by producing IL-6, and to TLR3 ligands by producing IFN-beta. Interestingly, despite significant up-regulation of MHC class II and co-stimulatory molecules in response to TLR8 ligands, LSEC stimulated by TLR1, -2 or -6 could stimulate allogeneic T cells as assessed by MLR. By contrast, myeloid dendritic cells, used as positive control for classical antigen-presenting cells, respond to TLR1, -2, -4 and -9 ligands by both up-regulation of CD40 and activation of allogeneic T cells. In conclusion, NPC display a restricted TLR-mediated activation profile when compared with 'classical' antigen-presenting cells which may, at least in part, explain their tolerogenic function in the liver.

Toll-like receptor-induced innate immune responses in non-parenchymal liver cells are cell type-specific

Little is known of how the Toll-like receptor (TLR) system can modulate the function of non-parenchymal liver cells (NPC) as a major component of the innate and adaptive immune system of the liver. To investigate the diversification of TLR signalling pathways in NPC, we isolated Kupffer cells (KC) and liver sinusoidal endothelial cells (LSEC) from wild-type C57BL/6 mice and examined their responses to TLR1 to TLR9 agonists. The data show that KC respond to all TLR ligands by producing tumour necrosis factor-alpha (TNF-alpha) or interleukin-6 (IL-6), to TLR3 and TLR4 ligands only by producing interferon-beta (IFN-beta), to TLR1 and TLR8 ligands by significantly up-regulating major histocompatibility complex (MHC) class II and costimulatory molecules, and to TLR1, -2, -4 and -6 ligands by inducing high levels of T-cell proliferation and IFN-gamma production in the mixed lymphocyte reaction (MLR). Similarly, LSEC respond to TLR1 to -4, -6, -8 and -9 ligands by producing TNF-alpha, to TLR3 and -4 ligands by producing IL-6, and to TLR3 ligands by producing IFN-beta. Interestingly, despite significant up-regulation of MHC class II and co-stimulatory molecules in response to TLR8 ligands, LSEC stimulated by TLR1, -2 or -6 could stimulate allogeneic T cells as assessed by MLR. By contrast, myeloid dendritic cells, used as positive control for classical antigen-presenting cells, respond to TLR1, -2, -4 and -9 ligands by both up-regulation of CD40 and activation of allogeneic T cells. In conclusion, NPC display a restricted TLR-mediated activation profile when compared with 'classical' antigen-presenting cells which may, at least in part, explain their tolerogenic function in the liver.

Autotaxin/lysophospholipase D-mediated lysophosphatidic acid signaling is required to form distinctive large lysosomes in the visceral endoderm cells of the mouse yolk sac

Autotaxin, a lysophospholipase D encoded by the Enpp2 gene, is an exoenzyme that produces lysophosphatidic acid in the extracellular space. Lysophosphatidic acid acts on specific G protein-coupled receptors, thereby regulating cell growth, migration, and survival. Previous studies have revealed that Enpp2(-/-) mouse embryos die at about embryonic day (E) 9.5 because of angiogenic defects in the yolk sac. However, what cellular defects occur in Enpp2(-/-) embryos and what intracellular signaling pathways are involved in the phenotype manifestation remain unknown. Here, we show that Enpp2 is required to form distinctive large lysosomes in the yolk sac visceral endoderm cells. From E7.5 to E9.5, Enpp2 mRNA is abundantly expressed in the visceral endoderm cells. In Enpp2(-/-) mouse embryos, lysosomes in the visceral endoderm cells are fragmented. By using a whole embryo culture system combined with specific pharmacological inhibitors for intracellular signaling molecules, we show that lysophosphatidic acid receptors and the Rho-Rho-associated coiled-coil containing protein kinase (ROCK)-LIM kinase pathway are required to form large lysosomes. In addition, electroporation of dominant negative forms of Rho, ROCK, or LIM kinase also leads to the size reduction of lysosomes in wild-type visceral endoderm cells. In Enpp2(-/-) visceral endoderm cells, the steady-state levels of cofilin phosphorylation and actin polymerization are reduced. In addition, perturbations of actin turnover dynamics by actin inhibitors cytochalasin B and jasplakinolide result in the defect in lysosome formation. These results suggest that constitutive activation of the Rho-ROCK-LIM kinase pathway by extracellular production of lysophosphatidic acid by the action of autotaxin is required to maintain the large size of lysosomes in visceral endoderm cells.

Locally administered T cells from mice immunized with lipopolysaccharide (LPS) accelerate LPS-induced bone resorption

T cells play important roles in bone destruction and osteoclastogenesis and are found in chronic destructive bone lesions. Lipopolysaccharide (LPS) is one of several pathological factors involved in inflammatory bone destruction. We previously described the importance of T cells in the inflammatory bone resorption that occurs after repeated LPS administration. However, whether local or systemic T cells are important for inflammatory bone resorption and whether immunization of host animals influences bone resorption remain unclear. The present study examines the effects of local extant T cells from LPS-immunized mice on LPS-induced bone resorption. T cells from LPS-immunized or non-immunized mice were injected together with LPS into the gingival tissues of mice with severe combined immunodeficiency disease that lack both T and B cells. We histomorphometrically evaluated bone resorption at sites of T cell injections and examined the influence of T cells from LPS-immunized mice on osteoclastogenesis in vitro. We found that locally administered T cells from LPS-immunized but not non-immunized mice accelerated LPS-induced bone resorption in vivo. Moreover, T cells from LPS-immunized mice increased osteoclastogenesis in vitro induced by receptor activator of NF-kappa B ligand and LPS and anti-tumor necrosis factor (TNF)-alpha antibody inhibited this increase. These results demonstrated that local extant T cells accelerate inflammatory bone resorption. Furthermore, T cells from LPS-immunized mice appear to elevate LPS-induced bone resorption using TNF-alpha.

Understanding how lipopolysaccharide impacts CD4 T-cell immunity

Lipopolysaccharide (LPS) is a natural adjuvant synthesized by gram-negative bacteria that has profound effects on CD4 T-cell responses. LPS stimulates cells through the Toll-like receptor 4 (TLR4), causing the release of inflammatory cytokines and upregulation of costimulatory molecules on antigen-presenting cells (APCs). The combination of signals from antigens, costimulation, and cytokines allows CD4 T cells to overcome suppressive barriers and accumulate in large numbers. T cells that are primed in an LPS-stimulated environment are programmed for long-term survival following clonal expansion. LPS is well-known for generating Th1 responses. However, under appropriate conditions it can also support differentiation into other T-helper lineages, demonstrating its pleiotropic nature. Although molecular analyses have provided insights into how immune responses are controlled by LPS in vivo, its powerful adjuvant activity is also associated with toxicity. Research on partial TLR4 agonists such as monophosphoryl lipid A have demonstrated that toxicity and immunogenicity are not always linked, making them useful candidates for human vaccines. In this sense, many years of LPS research have ultimately contributed to vaccine design, and the next generation may involve studying how the balance between different CD4 T-cell subsets is controlled.

SWAP-70 regulates RhoA/RhoB-dependent MHCII surface localization in dendritic cells

Stimulated dendritic cells (DCs) mature and migrate to lymphoid organs to prime naive T cells. DC maturation augments antigen-presentation capacity of DCs by increasing peptide loading, half-life, and cell surface localization of MHC molecules. Activated SWAP-70(-/-) DCs fail to properly localize MHCII molecules in the plasma membrane, are strongly impaired in T-cell activation, and are altered in F-actin rearrangement. MHCII synthesis, invariant chain removal, and MHCII internalization, however, are unaffected. MHCII surface localization is known to require RhoGTPases. Surprisingly, SWAP70, hitherto known to bind F-actin and Rac, also binds RhoA-GTP. In SWAP-70(-/-) DCs, RhoA and RhoB are stimulus-independent and constitutively active. Surface localization of MHCII molecules and T-cell activation can be restored by blocking RhoA and RhoB before but not during DC activation. Thus, contrasting positive regulation of Rac, SWAP-70 negatively regulates RhoA and-indirectly-RhoB, preventing premature RhoA/RhoB activation. Through RhoA/RhoB regulation, SWAP-70 defines a new pathway to control surface localization of MHCII, a critical element in DC-dependent immune responses.

Cellular functions of GEF-H1, a microtubule-regulated Rho-GEF: is altered GEF-H1 activity a crucial determinant of disease pathogenesis?

The Rho guanine nucleotide exchange factor GEF-H1 is uniquely regulated by microtubule binding and is crucial in coupling microtubule dynamics to Rho-GTPase activation in a variety of normal biological situations. Here, we review the roles of GEF-H1 in epithelial barrier permeability, cell motility and polarization, dendritic spine morphology, antigen presentation, leukemic cell differentiation, cell cycle regulation, and cancer. GEF-H1 might also contribute to pathophysiological signaling involved in leukemias, and in cancers associated with mutated p53 tumor suppressor gene, epithelial and endothelial cell dysfunction, infectious disease, and cardiac hypertrophy. We suggest that GEF-H1 could be a novel therapeutic target in multiple human diseases.

Signalling of toll-like receptors

Since Toll-like receptor (TLR) signaling was found crucial for the activation of innate and adaptive immunity, it has been the focus of immunological research. There are at least 13 identified mammalian TLRs, to date, that share similarities in their extracellular and intracellular domains. A vast number of ligands have been identified that are specifically recognized by different TLRs. As a response the TLRs dimerize and their signaling is initiated. The molecular basis of that signaling depends on the conserved part of their intracellular domain; namely the Toll/IL-1 receptor (TIR) domain. Upon TLR dimerization a TIR-TIR structure is formed that can recruit TIR-containing intracellular proteins that mediate their signaling. For this reason these proteins are named adapters. There are five adapters identified so far named myeloid differentiation primary response protein 88 (MyD88), MyD88-adapter like (Mal) or TIR domain-containing adapter (TIRAP), TIR domain-containing adapter inducing interferon-beta (IFN-beta) (TRIF) or TIR-containing adapter molecule-1 (TICAM-1), TRIF-related adapter molecule (TRAM) or TICAM-2, and sterile alpha and HEAT-Armadillo motifs (SARM). The first four play a fundamental role in TLR-signaling, defining which pathways will be activated, depending on which of these adapters will be recruited by each TLR. Among these adapter proteins MyD88 and TRIF are now considered as the signaling ones and hence the TLR pathways can be categorized as MyD88-dependent and TRIF-dependent.

Regulation of hepatic drug-metabolizing enzyme genes by Toll-like receptor 4 signaling is independent of Toll-interleukin 1 receptor domain-containing adaptor protein

During inflammation, drug metabolism and clearance are altered due to suppression of hepatic drug-metabolizing enzyme (DME) genes and their regulatory nuclear receptors (NRs) [pregnane X receptor, constitutive androstane receptor, and retinoid X receptor alpha (RXRalpha)]. The bacterial endotoxin, lipopolysaccharide (LPS), induces expression of proinflammatory cytokines in the liver, which contribute to altered DME expression. LPS binds to the cell-surface receptor, Toll-like receptor 4 (TLR4), which initiates a signal transduction cascade, including recruitment of the Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP). However, the role of TLR4 and TIRAP in LPS-mediated regulation of hepatic DME gene expression is not known. Wild-type (C3HeB/FeJ), TLR4-mutant (C3H/HeJ), TIRAP(+/+), and TIRAP(-/-) mice were injected i.p. with LPs. RNA levels of the major hepatic DME, Cyp3a11 and Ugt1a1, and the NRs were suppressed approximately 60 to 70% by LPS in wild-type but not in the TLR4-mutant mice. The nuclear protein levels of RXRalpha were reduced by LPS in wild-type but not in TLR4-mutant mice. Induction of hepatic cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interleukin-6), c-Jun N-terminal kinase, and nuclear factor-kappaB was blocked in TLR4-mutant mice. Surprisingly, LPS had the same effect on cytokines, kinases, NRs, and DME genes in livers of both TIRAP(+/+) and TIRAP(-/-) mice, indicating that TIRAP is not essential for TLR4-mediated suppression of NRs and DMEs in liver. However, TIRAP(-/-) mice have reduced serum cytokine expression compared with TIRAP(+/+) mice in response to LPS. This shows that although TIRAP mediates inflammatory responses induced by LPS, it is not essential in regulating LPS-mediated alterations of gene expression in liver.