IL-1 receptor-associated kinase and low molecular weight GTPase RhoA signal molecules are required for bacterial lipopolysaccharide-induced cytokine gene transcription

RhoA balances microglial reactivity and survival during neuroinflammation

Microglia are the largest myeloid cell population in the brain. During injury, disease, or inflammation, microglia adopt different functional states primarily involved in restoring brain homeostasis. However, sustained or exacerbated microglia inflammatory reactivity can lead to brain damage. Dynamic cytoskeleton reorganization correlates with alterations of microglial reactivity driven by external cues, and proteins controlling cytoskeletal reorganization, such as the Rho GTPase RhoA, are well positioned to refine or adjust the functional state of the microglia during injury, disease, or inflammation. Here, we use multi-biosensor-based live-cell imaging approaches and tissue-specific conditional gene ablation in mice to understand the role of RhoA in microglial response to inflammation. We found that a decrease in RhoA activity is an absolute requirement for microglial metabolic reprogramming and reactivity to inflammation. However, without RhoA, inflammation disrupts Ca2+ and pH homeostasis, dampening mitochondrial function, worsening microglial necrosis, and triggering microglial apoptosis. Our results suggest that a minimum level of RhoA activity is obligatory to concatenate microglia inflammatory reactivity and survival during neuroinflammation.

Pattern recognition receptor mediated innate immune response requires a Rif-dependent pathway

Small GTPases play critical roles in cell morphology, movement, and adhesion by dynamic regulation of actin cytoskeleton. The small Rho GTPase Rif/RhoF (Rho in filopodia) regulates the formation of filopodia and stress fibers in cells. Rif is highly expressed in a number of cell types in the immune system; however, it's role in immune system function is unclear. In this research, we found that Rif expression is necessary for NF-κB activation in primary immune cells, and mature dendritic cell (mature DCs) induced from Bone Marrow-Derived Dendritic Cells (BMDCs) isolated from Rif knock out (Rif KO) mice displayed impaired degradation of I-κBα, as well as reduced TNF-α secretion and p38 MAPK phosphorylation under LPS stimulation. Interestingly, we revealed that TLR agonists, such as LPS and poly (I:C), as well as bacterial virulence factor SopE could induce a transient increase in Rif activation in monocytes THP-1 cells. Furthermore, Rif was found to be an integral part of the TLR4, TLR3 and nodosome signaling complex. We further identified Src tyrosine kinases as upstream activator of Rif in both bacterial and viral induced immune responses. Moreover, activated Rif induces activation of transcription factors, such as NF-κB, AP-1 and IRF-3, and mediates inflammation through secretion of IL-6, IL-8 or TNFα. Rif activation by PRRs contributes in a variety of ways to protective host responses against invading microbes. Taken together, this study reveals that Rif is indispensable for both extracellular and intracellular pattern-recognition receptor-mediated innate immune responses. Rif possess broad anti-pathogenic effect and understanding of the molecular mechanisms by which this small Rho GTPase interferes with innate immune system will be beneficial to develop therapies against infectious agents.

Role of Ezrin in Asthma-Related Airway Inflammation and Remodeling

Ezrin is an actin binding protein connecting the cell membrane and the cytoskeleton, which is crucial to maintaining cell morphology, intercellular adhesion, and cytoskeleton remodeling. Asthma involves dysfunction of inflammatory cells, cytokines, and airway structural cells. Recent studies have shown that ezrin, whose function is affected by extensive phosphorylation and protein interactions, is closely associated with asthma, may be a therapeutic target for asthma treatment. In this review, we summarize studies on ezrin and discuss its role in asthma-related airway inflammation and remodeling.

The ROCK-ezrin signaling pathway mediates LPS-induced cytokine production in pulmonary alveolar epithelial cells

BACKGROUND

Ezrin/radixin/moesin (ERM) proteins are members of the protein 4.1 superfamily and function as linkers that connect the actin cytoskeleton to the plasma membrane of cells. ERM also play critical role in the Lipopolysaccharide (LPS)-induced inflammatory response. However, the signaling mechanisms involved in this process remain unclear. In this study, we aimed to investigate the potential role of the rho-associated coiled-coil containing protein kinase (ROCK) pathway in LPS-induced ezrin phosphorylation and cytokine production in pulmonary alveolar epithelial cells.

METHODS

Cultured A549 and HPAEpiC cells were treated with LPS. The expression and localization of ezrin in A549 and HPAEpiC cells were then analyzed by western blotting and immunoflurescence. Activation of RhoA/ROCK was assessed by western blotting and RhoA activity assays. The interaction of ezrin with Syk and myeloid differentiation factor 88 (MyD88)/IL-1R-associated kinase 1 (IRAK-1) was investigated by co-immunoprecipitation. The activation of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) was measured with electrophoretic mobility shift assays and by western blotting. ELISA and western blotting were performed to detect the levels of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and high mobility group box 1 protein (HMGB1) release into the culture supernatant, and cellular HMGB1 levels.

RESULTS

LPS induced ezrin phosphorylation in a concentration- and time-dependent manner. The blockade of RhoA/ROCK inhibited LPS-induced ezrin phosphorylation and its translocation from the cytoplasm to the cell membrane. Co-immunoprecipitation assays further revealed that ezrin associated with Syk constitutively, but only associated with MyD88/IRAK-1 upon LPS challenge. Moreover, LPS-induced p38 and nuclear NF-κB activation was found to be ezrin dependent. The suppression of ezrin by siRNA or the blockade of ROCK activation with Y-27632 reduced the production of TNF-α, IL-1β, and HMGB1 in response to LPS.

CONCLUSIONS

Our findings reveal a novel regulatory mechanism involving ezrin in the LPS-induced production of pro-inflammatory cytokines, and highlight the importance of the RhoA/ROCK-ezrin/Syk-MyD88/IRAK1 axis. Data presented in this manuscript provide novel insights into the signaling pathways activated in pulmonary alveolar epithelial cells by LPS. Video Abstract.

Exploring the therapeutic promise of targeting Rho kinase in rheumatoid arthritis

Rheumatoid arthritis (RA) is a prevalent systemic autoimmune disease caused by dysregulated inflammatory reactions, T lymphocyte invasion into the joints, and articular thickening. Immune cells, primarily tumor necrosis factor-alpha (TNF-α) and chemokines (interleukin or IL-1), which are predominantly generated by activated macrophages cells, have also been involved with the pathogenesis of rheumatoid arthritis. Rho GTPases are integral factors of biochemical cascades utilized by antigens, and also by cellular receptors, cytokines, and chemokines, to modulate inflammatory reactions, according to growing data. The Rho family is a group of G proteins that govern a variety of biological and physiological activities such as mobility, actin stress fiber production, growth, and polarity. Research suggests that the Rho A and Rho-associated coiled-coil kinase (ROCK) regulatory cascade could be essential in several autoimmune conditions, including RA. ROCK is activated in the synovial of rheumatoid arthritis patients, while the blocking of ROCK with fasudil could also decrease IL-6, TNF-α, and IL-1. This review covers current developments in understanding the overactivation of Rho enzyme activity in RA suppressed by ROCK inhibitors which can be utilized for the treatment of autoimmune disease. We offer an outline of the function of ROCK inhibitors in immune cells and discuss findings which emphasize the rising participation of this category of kinases within the pathological process of autoimmune disorders. Assuming the potential ability of ROCK as a therapeutic, we define approaches that might be used to inhibit Rho kinase activity in rheumatoid disorders.

Spatiotemporal proteomic profiling of the pro-inflammatory response to lipopolysaccharide in the THP-1 human leukaemia cell line

Protein localisation and translocation between intracellular compartments underlie almost all physiological processes. The hyperLOPIT proteomics platform combines mass spectrometry with state-of-the-art machine learning to map the subcellular location of thousands of proteins simultaneously. We combine global proteome analysis with hyperLOPIT in a fully Bayesian framework to elucidate spatiotemporal proteomic changes during a lipopolysaccharide (LPS)-induced inflammatory response. We report a highly dynamic proteome in terms of both protein abundance and subcellular localisation, with alterations in the interferon response, endo-lysosomal system, plasma membrane reorganisation and cell migration. Proteins not previously associated with an LPS response were found to relocalise upon stimulation, the functional consequences of which are still unclear. By quantifying proteome-wide uncertainty through Bayesian modelling, a necessary role for protein relocalisation and the importance of taking a holistic overview of the LPS-driven immune response has been revealed. The data are showcased as an interactive application freely available for the scientific community.

MicroRNA‑502‑3p promotes Mycobacterium tuberculosis survival in macrophages by modulating the inflammatory response by targeting ROCK1

Tuberculosis (TB) is caused by Mycobacterium tuberculosis (M. tuberculosis) infection and has the highest mortality rate of any single infectious disease worldwide. The aim of the present study was to investigate the function of microRNA (miR)-502-3p in M. tuberculosis-infected macrophages. The Gene Expression Omnibus database was used to analyze miR-502-3p expression in patients with TB and healthy individuals. THP-1 and RAW 264.7 cells were transfected with miR-502-3p mimic, miR-502-3p inhibitor, pcDNA3.1-ROCK1 or their negative controls. The expression levels of miR-502-3p and inflammatory cytokines were evaluated using reverse transcription-quantitative PCR. The colony-forming unit assay was performed to assess the survival of M. tuberculosis in macrophages, and Toll-like receptor (TLR)4/NF-κB signaling pathway-associated protein expression levels were detected by western blotting. The nuclear translocation of NF-κB p65 was detected via immunocytochemistry. TargetScan was used to predict the binding sites between miR-502-3p and ROCK1. The interaction between miR-502-3p and Rho-associated coiled-coil-forming protein kinase 1 (ROCK1) was confirmed using a dual-luciferase reporter assay; ROCK1 was demonstrated to be a direct target gene of miR-502-3p. Results from the present study demonstrated that miR-502-3p expression was significantly increased during M. tuberculosis infection in macrophages. Upregulation of miR-502-3p expression levels significantly enhanced the survival of intracellular M. tuberculosis. IL-6, TNF-α, and IL-1β mRNA expression levels were significantly upregulated during M. tuberculosis infection but were downregulated by miR-502-3p overexpression. Moreover, miR-502-3p mimics transfection significantly downregulated TLR4/NF-κB signaling pathway-associated protein expression and significantly reduced nuclear transcription of NF-κB in M. tuberculosis-infected macrophages. ROCK1 overexpression reversed the miR-502-3p inhibitory effect on cytokine production in M. tuberculosis-infected macrophages. In conclusion, miR-502-3p/ROCK1 may serve an anti-inflammatory role and may improve the survival of M. tuberculosis within macrophages, which may provide a promising therapeutic target for TB.

Enhanced autophagy suppresses inflammation-mediated bone loss through ROCK1 signaling in bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells (BMSCs) have strong proliferative ability and multi-directional differentiation potential. Osteoarthritis is a degenerative joint disease that is closely related to the loss of osteogenic differentiation function of BMSCs. Autophagy, plays a crucial role in the maintenance of cellular functions, but its regulatory mechanism during the osteogenic differentiation of BMSCs remains unclear. In this study, we analyzed the differential gene networks and pathways during BMSC osteogenesis using bioinformatics, and further validated the regulatory roles of autophagy during the osteogenic differentiation of BMSCs in inflammatory condition in vitro. We found that Tumor necrosis factor alpha (TNF-α) treatment led to actin cytoskeleton rearrangements and inhibited osteogenic differentiation in BMSCs. In addition, TNF-α enhanced Rho-associated protein kinase 1 (ROCK1) expression and decreased autophagy activation. ROCK1 knockdown reduced Endoplasmic Reticulum stress (ER stress) and promoted autophagy, resulting reversion of osteogenic differentiation in BMSCs under inflammatory condition. Rapamycin reversed the TNF-α-induced decrease in osteogenesis of BMSCs, assessed by alkaline phosphatase (ALP) activity and Alizarin staining. Autophagy treated with inhibitor 3-Methyladenine (3-MA) further increased TNF-α-induced osteogenesis inhibition of BMSCs. Collectively, these results indicate that ER stress and dysfunction of autophagy promote inflammation-induced bone loss through the activation of ROCK1 signaling in BMSCs.

Functional and Therapeutic Relevance of Rho GTPases in Innate Immune Cell Migration and Function during Inflammation: An In Silico Perspective

Systematic regulation of leukocyte migration to the site of infection is a vital step during immunological responses. Improper migration and localization of immune cells could be associated with disease pathology as seen in systemic inflammation. Rho GTPases act as molecular switches during inflammatory cell migration by cycling between Rho-GDP (inactive) to Rho-GTP (active) forms and play an essential role in the precise regulation of actin cytoskeletal dynamics as well as other immunological functions of leukocytes. Available reports suggest that the dysregulation of Rho GTPase signaling is associated with various inflammatory diseases ranging from mild to life-threatening conditions. Therefore, it is crucial to understand the step-by-step activation and inactivation of GTPases and the functioning of different Guanine Nucleotide Exchange Factors (GEFs) and GTPase-Activating Proteins (GAPs) that regulate the conversion of GDP to GTP and GTP to GDP exchange reactions, respectively. Here, we describe the molecular organization and activation of various domains of crucial elements associated with the activation of Rho GTPases using solved PDB structures. We will also present the latest evidence available on the relevance of Rho GTPases in the migration and function of innate immune cells during inflammation. This knowledge will help scientists design promising drug candidates against the Rho-GTPase-centric regulatory molecules regulating inflammatory cell migration.

Long Non-coding RNAs (lncRNAs), A New Target in Stroke

Stroke has become the most disabling and the second most fatal disease in the world. It has been a top priority to reveal the pathophysiology of stroke at cellular and molecular levels. A large number of long non-coding RNAs (lncRNAs) are identified to be abnormally expressed after stroke. Here, we summarize 35 lncRNAs associated with stroke, and clarify their functions on the prognosis through signal transduction and predictive values as biomarkers. Changes in the expression of these lncRNAs mediate a wide range of pathological processes in stroke, including apoptosis, inflammation, angiogenesis, and autophagy. Based on the exploration of the functions and mechanisms of lncRNAs in stroke, more timely, accurate predictions and more effective, safer treatments for stroke could be developed.

LncRNA SNHG14 promotes inflammatory response induced by cerebral ischemia/reperfusion injury through regulating miR-136-5p /ROCK1

Recently, long non-coding RNAs (lncRNAs) are considered as critical regulators in pathogenesis progression of cerebral ischemia. In present study, lncRNA-small nucleolar RNA host gene 14 (SNHG14) was found upregulated in middle cerebral artery occlusion/reperfusion (MCAO/R) treated brain tissues and oxygen-glucose deprivation and reoxygenation (OGD/R) treated PC-12 cells. Interference of SNHG14 by shRNA vector enhanced neuron survival and suppressed inflammation in response to OGD/R insult. SNHG14 positively regulated the expression of Rho-associated coiled-coil-containing protein kinase 1 (ROCK1) via acting as a sponge of microRNA (miR)-136–5p. SNHG14 promoted neurological impairment and inflammatory response through elevating the expression of ROCK1 while decreasing miR-136–5p level in OGD/R induced damage. Collectively, we illustrated that SNHG14 could be a novel strategy for treatment ischemia stoke.

Rho Kinase Type 1 (ROCK1) Promotes Lipopolysaccharide-induced Inflammation in Corneal Epithelial Cells by Activating Toll-Like Receptor 4 (TLR4)-Mediated Signaling

Background

Rho kinases (ROCKs) are the typical downstream effectors of RhoA, which can regulate corneal epithelial wound healing. In this study, the role of ROCK1 in lipopolysaccharide (LPS)-induced cornea inflammation was investigated.

Material/Methods

The expression of ROCK1 in human corneal epithelial cells (HCECs) was bilaterally modulated with ROCK1 expression vector and ROCK1 inhibitor Y-27632. The effects of ROCK1 modulation on the inflammatory response, cell viability, cell apoptosis, and cell cycle distribution were detected by ELISA assay, MTT assay, and flow cytometry, respectively. The pathways involved in the effect of ROCK1 in HCECs was preliminarily explained by detecting changes of TLR4-mediated NF-κB and ERK signaling using western blotting and electrophoretic mobility shift assays.

Results

Overexpression of ROCK1 promoted LPS-induced production of IL-6, IL-8, IL-1β, and TNF-α, and the apoptotic process in HCECs. Augmented inflammation and apoptosis were associated with stronger activation of TLR4-mediated signal transduction; the phosphorylation of IκBα, JNK, ERK1/2, and p38, and nuclear translocation of NF-κB p65 induced by LPS were further increased by overexpression of ROCK1. Inhibition of ROCK1 function by Y-27632 blocked the effect of LPS on HCECs; both LPS-induced inflammation and apoptosis was alleviated by Y-27632, which was associated with suppression of TLR4-mediated NF-κB and ERK signaling.

Conclusions

LPS-induced inflammation and apoptosis in HCECs depended on the function of ROCK1, inhibition of which would attenuate impairments on cornea cells due to LPS.

Myeloid Notch1 deficiency activates the RhoA/ROCK pathway and aggravates hepatocellular damage in mouse ischemic livers

Notch signaling plays an emerging role in the regulation of immune cell development and function during inflammatory response. Activation of the ras homolog gene family member A/Rho-associated protein kinase (ROCK) pathway promotes leukocyte accumulation in tissue injury. However, it remains unknown whether Notch signaling regulates ras homolog gene family member A/ROCK-mediated immune responses in liver ischemia and reperfusion (IR) injury. This study investigated intracellular signaling pathways regulated by Notch receptors in the IR-stressed liver and in vitro. In a mouse model of IR-induced liver inflammatory injury, we found that mice with myeloid-specific Notch1 knockout showed aggravated hepatocellular damage, with increased serum alanine aminotransferase levels, hepatocellular apoptosis, macrophage/neutrophil trafficking, and proinflammatory mediators compared to Notch1-proficient controls. Unlike in the controls, myeloid Notch1 ablation diminished hairy and enhancer of split-1 (Hes1) and augmented c-Jun N-terminal kinase (JNK)/stress-activated protein kinase-associated protein 1 (JSAP1), JNK, ROCK1, and phosphatase and tensin homolog (PTEN) activation in ischemic livers. Disruption of JSAP1 in myeloid-specific Notch1 knockout livers improved hepatocellular function and reduced JNK, ROCK1, PTEN, and toll-like receptor 4 activation. Moreover, ROCK1 knockdown inhibited PTEN and promoted Akt, leading to depressed toll-like receptor 4. In parallel in vitro studies, transfection of lentivirus-expressing Notch1 intracellular domain promoted Hes1 and inhibited JSAP1 in lipopolysaccharide-stimulated bone marrow-derived macrophages. Hes1 deletion enhanced JSAP1/JNK activation, whereas clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9-mediated JSAP1 knockout diminished ROCK1/PTEN and toll-like receptor 4 signaling.

CONCLUSION

Myeloid Notch1 deficiency activates the ras homolog gene family member A/ROCK pathway and exacerbates hepatocellular injury by inhibiting transcriptional repressor Hes1 and inducing scaffold protein JSAP1 in IR-triggered liver inflammation; our findings underscore the crucial role of the Notch-Hes1 axis as a novel regulator of innate immunity-mediated inflammation and imply the therapeutic potential for the management of organ IR injury in transplant recipients. (Hepatology 2018;67:1041-1055).

Effect of Rho-kinase Inhibitor, Y27632, on Porcine Corneal Endothelial Cell Culture, Inflammation and Immune Regulation

PURPOSE

To investigate the effect of the Rho-kinase inhibitor, Y27632, on pig corneal endothelial cell (pCEC) culture, and on inflammation and immune regulation of the responses of human cells to pCECs.

METHODS

pCECs were cultured with/without Y27632 to assess cell proliferation and in vitro wound healing assay. The level of MCP-1 and VEGF in pCECs stimulated with human TNF-α were measured. Proliferation of human PBMCs stimulated with pCECs, and cytokine production in human T cells, and monocyte migration after stimulation were investigated.

RESULTS

Y27632 promoted pCEC proliferation, prevented pCEC death, and enhanced in vitro wound healing. After stimulation, there were significantly lower levels of MCP-1 and VEGF measured in pCECs cultured with Y27632, and significantly reduced human PBMC proliferation, cytokine production, and monocyte migration.

CONCLUSIONS

The application of the Rho-kinase inhibitor will be beneficial when culturing pCECs, and may provide a novel therapy to reduce inflammation after corneal xenotransplantation.

Toll-like receptor 2 mediates vascular contraction and activates RhoA signaling in vascular smooth muscle cells from STZ-induced type 1 diabetic rats

Increased vascular smooth muscle cell (VSMC) contraction is an early and critical contributor to the pathogenesis of vascular dysfunction in diabetes; however, knowledge regarding the underlying mechanisms is scarce. Toll-like receptor 2 (TLR2), a well-known component of the innate immunity, is expressed in VSMC and recently has been identified to be systemically activated in diabetes. Whether TLR2 is locally activated in the diabetic blood vessels and have effect on contraction is not known. In the current study, we examined the role of TLR2 in increased vascular contraction in diabetes. Utilizing rat model of type 1 diabetes (induced by streptozotocin (STZ)), we demonstrated that aortas from STZ-diabetic rats exhibit increased expression of TLR2 and its adaptor protein, myeloid differentiation primary response 88 (MyD88), as well as enhanced protein-protein interaction between TLR2 and MyD88, suggesting a TLR2 signaling activation. Blockade of TLR2 in intact aortas using anti-TLR2 antibody attenuated increased vascular contraction in STZ-diabetic rat as assessed by wire myograph. Activation of TLR2 by specific ligand in primary aortic VSMC cultures triggered activation of RhoA which was exacerbated in cells from STZ-diabetic rats than control rats. Activation of RhoA was accompanied by phosphorylation and therefore activation of its downstream targets myosin phosphatase target subunit I and myosin light chain (markers of VSMC contraction). Taken together, these results provide evidence for the role of TLR2 in increased contraction in diabetic blood vessels that involves RhoA signaling. Thus, targeting vascular TLR2 offers a promising drug target to treat vascular dysfunction in diabetes.

Simvastatin inhibits transforming growth factor-β1-induced expression of type I collagen, CTGF, and α-SMA in keloid fibroblasts

Simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme-A reductase inhibitor, is used to reduce cholesterol levels. Accumulating evidence has revealed the immunomodulatory and anti-inflammatory effects of simvastatin that prevent cardiovascular diseases. In addition, the beneficial effects of statins on fibrosis of various organs have been reported. However, the functional effect of statins on dermal fibrosis of keloids has not yet been explored. The objective of this study was to determine whether simvastatin could affect dermal fibrosis associated with keloids. We examined the effect of simvastatin on transforming growth factor (TGF)-β1-induced production of type I collagen, connective tissue growth factor (CTGF or CCN2), and α-smooth muscle actin (α-SMA). Keloid fibroblasts were cultured and exposed to different concentrations of simvastatin in the presence of TGF-β1, and the effects of simvastatin on TGF-β1-induced collagen and CTGF production in keloid fibroblasts were determined. The type I collagen, CTGF, and α-SMA expression levels and the Smad2 and Smad3 phosphorylation levels were assessed by Western blotting. The effect of simvastatin on cell viability was evaluated by assessing the colorimetric conversion of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide. Simvastatin suppressed TGF-β1-induced type I collagen, CTGF, and α-SMA production in a concentration-dependent manner. The TGF-β1-induced Smad2 and Smad3 phosphorylation levels were abrogated by simvastatin pretreatment. The inhibition of type I collagen, CTGF, and α-SMA expression by simvastatin was reversed by geranylgeranyl pyrophosphate, suggesting that the simvastatin-induced cellular responses were due to inhibition of small GTPase Rho involvement. A RhoA activation assay showed that preincubation with simvastatin significantly blocked TGF-β1-induced RhoA activation. The Rho-associated coiled kinase inhibitor Y27632 abrogated TGF-β1-induced production of type I collagen, CTGF, and α-SMA. However, Y27632 had no significant effect on TGF-β1-induced phosphorylation of Smad2 and Smad3. In conclusion, the present study suggests that simvastatin is an effective inhibitor of TGF-β1-induced type I collagen, CTGF, and α-SMA production in keloid fibroblasts.

RhoA activity and post-ischemic inflammation in an experimental model of adult rodent anterior ischemic optic neuropathy

Activation of inflammatory cells and the RhoA signaling pathway may contribute to optic nerve damage following non-arteritic anterior ischemic optic neuropathy (NAION). We induced an optic nerve infarct with a photothrombotic mechanism in a rat model of AION (rAION). Immunohistochemistry and Western blot were performed to detect activation of RhoA signaling and inflammation. The extent of Rho activity, inflammation, retinal ganglion cell (RGC) loss and extent of axon regeneration were determined at 8 and 14 days after infarct. Eight days after stroke, we observed significant inflammation and RhoA activity at the site of infarction as well as loss of cells in the RGC layer. RhoA activity had decreased and inflammation had decreased at day 14 compared with day 8; however, loss of RGCs was greater at 14 days than at 8 days. Stroked eyes showed minor axon regeneration around the optic nerve lesion site at both 8 and 14 days. These results demonstrate that inflammation and RhoA activation occur in rAION at the site of infarction.

Induction of olfaction and cancer-related genes in mice fed a high-fat diet as assessed through the mode-of-action by network identification analysis

The pathophysiological mechanisms underlying the development of obesity and metabolic diseases are not well understood. To gain more insight into the genetic mediators associated with the onset and progression of diet-induced obesity and metabolic diseases, we studied the molecular changes in response to a high-fat diet (HFD) by using a mode-of-action by network identification (MNI) analysis. Oligo DNA microarray analysis was performed on visceral and subcutaneous adipose tissues and muscles of male C57BL/6N mice fed a normal diet or HFD for 2, 4, 8, and 12 weeks. Each of these data was queried against the MNI algorithm, and the lists of top 5 highly ranked genes and gene ontology (GO)-annotated pathways that were significantly overrepresented among the 100 highest ranked genes at each time point in the 3 different tissues of mice fed the HFD were considered in the present study. The 40 highest ranked genes identified by MNI analysis at each time point in the different tissues of mice with diet-induced obesity were subjected to clustering based on their temporal patterns. On the basis of the above-mentioned results, we investigated the sequential induction of distinct olfactory receptors and the stimulation of cancer-related genes during the development of obesity in both adipose tissues and muscles. The top 5 genes recognized using the MNI analysis at each time point and gene cluster identified based on their temporal patterns in the peripheral tissues of mice provided novel and often surprising insights into the potential genetic mediators for obesity progression.

Guanine-nucleotide exchange factor H1 mediates lipopolysaccharide-induced interleukin 6 and tumor necrosis factor α expression in endothelial cells via activation of nuclear factor κB

The development of sepsis is multifactorial. Tissue damage and organ dysfunction may be caused not only by the microorganisms but also by the inflammatory mediators released in response to the infection. Interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) levels in serum are well known to be upregulated in humans with sepsis and can be used to predict outcome. Using human umbilical vein endothelial cells, we analyzed the role of guanine-nucleotide exchange factor H1 (GEF-H1) on lipopolysaccharide (LPS)-dependent IL-6/TNF-α expression in endothelial cells. Lipopolysaccharide upregulated IL-6 secretion in a dose- and time-dependent manner. Specific inactivation of RhoA/Cdc42/Rac1 by Clostridium difficile toxin B-10463 (TcdB-10463) reduced LPS-induced nuclear factor κB (NF-κB) p65 phosphorylation, IL-6/TNF-α messenger RNA (mRNA), and IL-6/TNF-α protein productions. Guanine-nucleotide exchange factor H1 protein expression remained on a high level among 1 to 9 h in response to LPS challenge of endothelial cells. Inhibition of GEF-H1 by specific small interfering RNA or inactivation of Rho-associated kinase with Y-27632 not only significantly reduced LPS-induced p38 and extracellular signal-regulated kinase 1/2 (ERK1/2) activities but also blocked LPS-induced NF-κB translocation and activation, thereby inhibiting IL-6/TNF-α mRNA and protein productions. Furthermore, SB203580 (p38 inhibitor) but not PD98059 (ERK1/2 inhibitor) blocked LPS-induced NF-κB activation; however, both inhibitors significantly suppressed IL-6/TNF-α mRNA and protein expression. In summary, our data suggest that LPS rapidly upregulates GEF-H1 expression. Activated Rho-associated kinase by GEF-H1 subsequently activates p38 and ERK1/2, thereby increasing IL-6/TNF-α expression in endothelial cells. P38 and ERK1/2 regulate LPS-induced IL-6/TNF-α expression through an NF-κB-dependent manner and an NF-κB-independent manner, respectively.

Protein kinase C and toll-like receptor signaling

Protein kinase C (PKC) is a family of kinases that are implicated in a plethora of diseases, including cancer and cardiovascular disease. PKC isoforms can have different, and sometimes opposing, effects in these disease states. Toll-like receptors (TLRs) are a family of pattern recognition receptors that bind pathogens and stimulate the secretion of cytokines. It has long been known that PKC inhibitors reduce LPS-stimulated cytokine secretion by macrophages, linking PKC activation to TLR signaling. Recent studies have shown that PKC-α, -δ, -ε, and -ζ are directly involved in multiple steps in TLR pathways. They associate with the TLR or proximal components of the receptor complex. These isoforms are also involved in the downstream activation of MAPK, RhoA, TAK1, and NF-κB. Thus, PKC activation is intimately involved in TLR signaling and the innate immune response.

Bacterial LPS up-regulated TLR3 expression is critical for antiviral response in human monocytes: evidence for negative regulation by CYLD

In the host immune system, the leukocytes are often exposed to multiple pathogens including bacteria and viruses. The principal challenge for the host is to efficiently detect the invading pathogen and mount a rapid defensive response. Leukocytes recognize invading pathogens by directly interacting with pathogen-associated molecular patterns via Toll-like receptors (TLRs) expressed on the leukocyte surfaces. In this study, we provide direct evidence that bacterial LPS enhances the host antiviral response by up-regulating TLR3 expression in human peripheral blood monocytes and monocytic cell lines, THP1 cells. Moreover, LPS induces TLR3 expression via a TLR4-MyD88-IRAK-TRAF6-NF-κB-dependent signaling pathway. Interestingly, CYLD, an important deubiquitinase, acts as a negative regulator of TLR3 induction by LPS. Our study thus provides new insights into a novel role for bacterial infection in enhancing host antiviral response; furthermore, it identifies CYLD for the first time as a critical negative regulator of bacterial LPS-induced response.

Toll-like receptor signaling in cell proliferation and survival

Toll-like receptors (TLRs) are important sensors of foreign microbial components as well as products of damaged or inflamed self tissues. Upon sensing these molecules, TLRs initiate a series of downstream signaling events that drive cellular responses including the production of cytokines, chemokines, and other inflammatory mediators. This outcome results from the intracellular assembly of protein complexes that drive phosphorylation and other signaling cascades ultimately leading to chromatin remodeling and transcription factor activation. In addition to driving inflammatory responses, TLRs also regulate cell proliferation and survival which serves to expand useful immune cells and integrate inflammatory responses and tissue repair processes. In this context, central TLR signaling molecules, such as the mitogen-activated protein kinases (MAPK) and phosphoinositide 3-kinase (PI3K), play key roles. In addition, four major groups of transcription factors which are targets of TLR activation also control cell fate. This review focuses on the role of TLR signaling as it relates to cell proliferation and survival. This topic not only has important implications for understanding host defense and tissue repair, but also cancer which is often associated with conditions of chronic inflammation.

Lipopolysaccharide-driven Th2 cytokine production in macrophages is regulated by both MyD88 and TRAM

Gram-negative bacterial lipopolysaccharide (LPS) activates macrophages by interacting with Toll-like receptor 4 (TLR4) and triggers the production of various pro-inflammatory Th1 type (type 1) cytokines such as IFNgamma, TNFalpha, and IL8. Though some recent studies cited macrophages as potential sources for Th2 type (type 2) cytokines, little however is known about the intracellular events that lead to LPS-induced type 2 cytokines in macrophages. To understand the mechanisms by which LPS induces type 2 cytokine gene expression, macrophages were stimulated with LPS, and the expression of IL-4 and IL-5 genes were examined. LPS, acting through TLR4, activates both type 1 and type 2 cytokine production both in vitro and in vivo by using macrophages from C3H/HeJ or C3H/HeOuJ mice. Although the baseline level of both TNFalpha and IL-4 protein was very low, TNFalpha was released rapidly after stimulation (within 4 h); however, IL-4 was released after 48 h LPS stimulation in secreted form. Silencing of myeloid differentiation protein (MyD88) and TRIF-related adaptor molecule (TRAM), using small interfering RNA abolished IL-4 induction induced by LPS whereas silencing of TRAM has no effect on TNFalpha induction, thereby indicating that LPS-induced TNFalpha is MyD88-dependent but IL-4 is required both MyD88 and TRAM. These findings suggest a novel function of LPS and the signaling pathways in the induction of IL-4 gene expression.

Rho proteins are negative regulators of TLR2, TLR3, and TLR4 signaling in astrocytes

The family of Toll-like receptors (TLRs) expressed by innate immune cells recognizes a spectrum of microbial components as well as molecules released from injured tissues. TLR ligation activates intracellular signaling cascades that culminate in the up-regulation of proinflammatory genes. We have recently demonstrated that the up-regulation of inflammatory cytokines mediated by TLR4 in astrocytes is negatively controlled by the monomeric GTPases of Rho subfamily. The present study was undertaken to examine further the involvement of Rho proteins in the inflammatory response of astrocytes elicited by the ligation of three TLRs that use divergent signaling pathways. Astrocyte cultures established from newborn rat brains were challenged with ligands of TLR2, TLR3, and TLR4. The expression of genes encoding interleukin (IL)-1beta, IL-6, tumor necrosis factor-alpha (TNFalpha), interferon-beta (IFNbeta), and inducible nitric oxide synthase (NOS2) was up-regulated 24 hr after the challenge as determined by real-time RT-PCR. Pretreatment of the cells with toxin B, which specifically inactivates Rho proteins, enhanced the up-regulation of gene expression. The extent of this enhancement was both receptor and gene dependent. The enhancing effect of Rho protein inactivation was also evident at the protein level of IL-6 and NOS2 as revealed by ELISA and immunoblot analyses, respectively. These results suggest that Rho proteins control TLR-mediated up-regulation of inflammatory genes in astrocytes by interfering with multiple events along the signaling pathways.

RhoA GTPase activation by TLR2 and TLR3 ligands: connecting via Src to NF-kappa B

Rho GTPases are essential regulators of signaling networks emanating from many receptors involved in innate or adaptive immunity. The Rho family member RhoA controls cytoskeletal processes as well as the activity of transcription factors such as NF-kappaB, C/EBP, and serum response factor. The multifaceted host cell activation triggered by TLRs in response to soluble and particulate microbial structures includes rapid stimulation of RhoA activity. RhoA acts downstream of TLR2 in HEK-TLR2 and monocytic THP-1 cells, but the signaling pathway connecting TLR2 and RhoA is still unknown. It is also not clear if RhoA activation is dependent on a certain TLR adapter. Using lung epithelial cells, we demonstrate TLR2- and TLR3-triggered recruitment and activation of RhoA at receptor-proximal cellular compartments. RhoA activity was dependent on TLR-mediated stimulation of Src family kinases. Both Src family kinases and RhoA were required for NF-kappaB activation, whereas RhoA was dispensable for type I IFN generation. These results suggest that RhoA plays a role downstream of MyD88-dependent and -independent TLR signaling and acts as a molecular switch downstream of TLR-Src-initiated pathways.

Synergistic induction of inflammation by bacterial products lipopolysaccharide and fMLP: an important microbial pathogenic mechanism

A wide variety of stimuli have been shown to induce inflammation, but bacteria products/components are considered the major inducers during bacterial infections. We previously demonstrated that bacterial products/components such as LPS, a glycolipid component of the bacterial outer membrane, and formylated peptides (fMLP), a bacterial-derived peptide, induced proinflammatory cytokine gene expression in human peripheral blood monocytes. We now present evidence that mixtures of bacterial products/components LPS and fMLP behave synergistically in the induction of inflammation in vitro and in vivo. Furthermore, our results indicate that the TLR4 and the IKKbeta-IkappaBalpha signaling pathways are involved in the synergistic induction of inflammatory cytokines. The mechanism of synergistic activation of NF-kappaB is depended on nuclear translocation of p65 and phosphorylation of p65 at both Ser536 and Ser276 sites. These results demonstrate an important role for bacterial products/components from lysed bacteria in the pathogenesis of infectious diseases. We believe that this synergistic induction of inflammation by bacterial products LPS and fMLP represents an important pathogenic mechanism during bacterial infection, which may suggest novel therapeutic strategies or targets to minimize host injury following bacterial infection.

Antiinflammatory effect of Rho kinase blockade via inhibition of NF-kappaB activation in rheumatoid arthritis

OBJECTIVE

There is increasing evidence that the RhoA signaling pathway may play a critical role in the inflammatory response. This study was undertaken to examine the effects of RhoA and its downstream effector Rho kinase (ROK) in synovial inflammation in rheumatoid arthritis (RA).

METHODS

RhoA activity was assessed by pull-down assay. Fasudil and Y27632, both specific inhibitors of ROK, were used to examine the role of ROK in inflammatory responses in vivo and in vitro. Nuclear translocation of NF-kappaB was measured by confocal fluorescence microscopy, and DNA binding activity was assessed with a sensitive multiwell colorimetric assay. Enzyme-linked immunosorbent assay was used to detect cytokine production.

RESULTS

Increased activation of RhoA was found in inflamed synovial membrane cells isolated from patients with RA and from rats with collagen-induced arthritis (CIA). Intraperitoneal administration of fasudil in rats with CIA significantly reduced synovial inflammation and ROK activity. In vitro, treatment with fasudil or Y27632 decreased production of tumor necrosis factor alpha (TNFalpha), interleukin-1beta (IL-1beta), and IL-6 by synovial membrane cells, peripheral blood mononuclear cells, and fibroblast-like synoviocytes from patients with active RA. Inhibition of ROK by specific inhibitors or ROK small interfering RNA suppressed lipopolysaccharide- or TNFalpha-induced NF-kappaB nuclear translocation, DNA binding activity, luciferase reporter gene expression, and IkappaBalpha degradation.

CONCLUSION

The results of this study provide new evidence that blockade of ROK inhibits activation of NF-kappaB and production of proinflammatory cytokines, suggesting a critical role of ROK in the synovial inflammation of RA. Specific inhibition of ROK may be a novel therapeutic approach in RA.

Regulation of TLR4-mediated signaling by IBP/Def6, a novel activator of Rho GTPases

TLRs play a fundamental role in innate immune responses. Although Rho GTPases have been implicated in TLR-mediated signaling pathways, the molecules that control their activation in response to TLR engagement are largely unknown. IFN regulatory factor-4-binding protein (IBP; which is encoded by the gene Def6) is a unique type of activator for Rac that plays a crucial role in TCR-mediated signaling and adaptive immune responses. Here, we demonstrate that IBP/Def6 also controls innate immune responses by modulating TLR-induced signaling events. Mice deficient in IBP/Def6 are protected from LPS-induced septic shock. This protection is associated with a decrease in the production of proinflammatory cytokines and is accompanied by diminished activation of MAPKs and NF-kappaB. Our results thus identify IBP/Def6 as a novel component of the TLR4-induced signaling cascade that controls the production of proinflammatory cytokines.

GEF-H1 mediated control of NOD1 dependent NF-kappaB activation by Shigella effectors

Shigella flexneri has evolved the ability to modify host cell function with intracellular active effectors to overcome the intestinal barrier. The detection of these microbial effectors and the initiation of innate immune responses are critical for rapid mucosal defense activation. The guanine nucleotide exchange factor H1 (GEF-H1) mediates RhoA activation required for cell invasion by the enteroinvasive pathogen Shigella flexneri. Surprisingly, GEF-H1 is requisite for NF-κB activation in response to Shigella infection. GEF-H1 interacts with NOD1 and is required for RIP2 dependent NF-κB activation by H-Ala-D-γGlu-DAP (γTriDAP). GEF-H1 is essential for NF-κB activation by the Shigella effectors IpgB2 and OspB, which were found to signal in a NOD1 and RhoA Kinase (ROCK) dependent manner. Our results demonstrate that GEF-H1 is a critical component of cellular defenses forming an intracellular sensing system with NOD1 for the detection of microbial effectors during cell invasion by pathogens.

Shigella is a bacterium that causes food poisoning and serious intestinal infections with diarrheal illness. Pathogens like Shigella utilize intracellular active effectors to overcome the intestinal barrier and invade the host. We demonstrate that intestinal epithelial cells can sense the disturbance of the tight junctional seal, which normally prevents access of microbes to the circulation. A signaling molecule, which is required for cell invasion by Shigella, also activates messengers that activate immune defenses. This pathway of intestinal pathogen detection is activated by Shigella products, which are injected into host cells by the pathogen and depends on intracellular microbial recognition receptors. The detection of altered cellular function by bacterial effectors may be important for the ability to rapidly respond to barrier disruption in the intestine with the attraction and activation of immune cells to defend against the intruders.

Rho GTPase-activating bacterial toxins: from bacterial virulence regulation to eukaryotic cell biology

Studies on the interactions of bacterial pathogens with their host have provided an invaluable source of information on the major functions of eukaryotic and prokaryotic cell biology. In addition, this expanding field of research, known as cellular microbiology, has revealed fascinating examples of trans-kingdom functional interplay. Bacterial factors actually exploit eukaryotic cell machineries using refined molecular strategies to promote invasion and proliferation within their host. Here, we review a family of bacterial toxins that modulate their activity in eukaryotic cells by activating Rho GTPases and exploiting the ubiquitin/proteasome machineries. This family, found in human and animal pathogenic Gram-negative bacteria, encompasses the cytotoxic necrotizing factors (CNFs) from Escherichia coli and Yersinia species as well as dermonecrotic toxins from Bordetella species. We survey the genetics, biochemistry, molecular and cellular biology of these bacterial factors from the standpoint of the CNF1 toxin, the paradigm of Rho GTPase-activating toxins produced by urinary tract infections causing pathogenic Escherichia coli. Because it reveals important connections between bacterial invasion and the host inflammatory response, the mode of action of CNF1 and its related Rho GTPase-targetting toxins addresses major issues of basic and medical research and constitutes a privileged experimental model for host-pathogen interaction.

C3 exoenzymes, novel insights into structure and action of Rho-ADP-ribosylating toxins

The family of C3-like exoenzymes comprises seven bacterial ADP-ribosyltransferases of different origin. The common hallmark of these exoenzymes is the selective N-ADP-ribosylation of the low molecular mass GTP-binding proteins RhoA, B, and C and inhibition of signal pathways controlled by Rho GTPases. Therefore, C3-like exoenzymes were applied as pharmacological tools for analyses of cellular functions of Rho protein in numerous studies. Recent structural and functional analyses of C3-like exoenzymes provide detailed information on the molecular mechanisms and functional consequences of ADP-ribosylation catalyzed by these toxins. More recently additional non-enzymatic actions of C3-like ADP-ribosyltransferases have been identified showing that C3 transferases from Clostridium botulinum and Clostridium limosum form a GDI-like complex with the Ras-like low molecular mass GTPase Ral without ADP-ribosylation. These results add novel information on the molecular mode of action(s) of C3-like exoenzymes and are discussed in this review.

Dual role for RhoA in suppression and induction of cytokines in the human neutrophil

Production of tumor necrosis factor-alpha (TNFalpha) by the neutrophil (PMN) is a pivotal event in innate immunity, but the signals regulating TNFalpha induction in this primary cell are poorly understood. Herein, we use protein transduction to identify novel, opposing anti- and pro-cytokine-inducing roles for RhoA in the resting and lipopolysaccharide (LPS)-stimulated human PMN, respectively. In the resting cell, RhoA suppresses Cdc42 activation, IkappaBalpha degradation, nuclear factor-kappaB (NF-kappaB) activation, and induction of TNFalpha and NF-kappaB-dependent chemokines. Suppression of TNFalpha induction by RhoA is Rho kinase alpha (ROCKalpha) independent, but Cdc42 dependent, because TNFalpha induction by C3 transferase is attenuated by inhibition of Cdc42, and constitutively active Cdc42 suffices to activate NF-kappaB and induce TNFalpha. By contrast, we also place RhoA downstream of p38 mitogen-activated protein kinase and Cdc42 in a novel LPS-activated pathway in which p38, Cdc42, and ROCKalpha all promote TNFalpha protein expression. The p65 subunit of NF-kappaB coprecipitates with RhoA in a manner sensitive to the RhoA activation state. Our findings suggest a new, 2-faced role for RhoA as a checkpoint in innate immunity.

New players in TLR-mediated innate immunity: PI3K and small Rho GTPases

Toll-like receptors (TLRs) play a crucial role in the innate immune system as a first line of defense against pathogens. TLR activation in phagocytes produces pro-inflammatory cytokines and chemokines that contribute directly to elimination of infectious agents and activation of adaptive immune responses. However, a sustained inflammatory response can result in tissue damage and generalized sepsis. This review summarizes the complex and sometimes conflicting links of TLR signaling with two important regulators of immune cells functions: phosphoinositide 3-kinases (PI3Ks) and small GTPases of the Rho family. A unified model of hierarchical organization of these signaling participants is still premature, given that the tools for delineating how control of TLRmediated pathways is achieved are just emerging. Critical progress in our understanding of spatial-temporal propagation of TLR signaling will certainly be provided in the near future by pharmacological targeting of PI3Ks using recently characterized, second-generation PI3K inhibitors in combination with gene-targeting strategies for PI3K subunits and Rho GTPases targeted to the murine myeloid compartment.

Protective effect of fasudil, a Rho-kinase inhibitor, on chemokine expression, leukocyte recruitment, and hepatocellular apoptosis in septic liver injury

Rho-kinase signaling regulates important features of inflammatory reactions. Herein, we investigated the effect and mechanisms of action of the Rho-kinase inhibitor fasudil in endotoxemic liver injury. C57/BL/6 mice were challenged with lipopolysaccharide (LPS) and D-galactosamine, with or without pretreatment with the Rho-kinase inhibitor fasudil. Six hours after endotoxin challenge, leukocyte-endothelium interactions in the hepatic microvasculature were studied by use of intravital fluorescence microscopy and tumor necrosis factor alpha (TNF-alpha); CXC chemokines as well as liver enzymes and apoptosis were determined. Administration of fasudil reduced LPS-induced leukocyte adhesion in postsinusoidal venules and sequestration in sinusoids. Moreover, we found that fasudil abolished extravascular infiltration of leukocytes as well as production of TNF-alpha and CXC chemokines in the liver of endotoxemic mice. Liver enzymes and hepatocellular apoptosis were markedly reduced, and sinusoidal perfusion was improved significantly in endotoxemic mice pretreated with fasudil. Our novel data document that fasudil is a potent inhibitor of endotoxin-induced expression of TNF-alpha and CXC chemokines as well as leukocyte infiltration and hepatocellular apoptosis in the liver. Based on the present findings, it is suggested that inhibition of the Rho-kinase signaling pathway may be a useful target in the treatment of septic liver injury.

A comprehensive map of the toll-like receptor signaling network

Recognition of pathogen-associated molecular signatures is critically important in proper activation of the immune system. The toll-like receptor (TLR) signaling network is responsible for innate immune response. In mammalians, there are 11 TLRs that recognize a variety of ligands from pathogens to trigger immunological responses. In this paper, we present a comprehensive map of TLRs and interleukin 1 receptor signaling networks based on papers published so far. The map illustrates the possible existence of a main network subsystem that has a bow-tie structure in which myeloid differentiation primary response gene 88 (MyD88) is a nonredundant core element, two collateral subsystems with small GTPase and phosphatidylinositol signaling, and MyD88-independent pathway. There is extensive crosstalk between the main bow-tie network and subsystems, as well as feedback and feedforward controls. One obvious feature of this network is the fragility against removal of the nonredundant core element, which is MyD88, and involvement of collateral subsystems for generating different reactions and gene expressions for different stimuli.

Rho GTPases as therapeutic targets for the treatment of inflammatory diseases

Diseases related to inflammation are a major cause of morbidity and mortality throughout the world and affect the functions of several tissues. The pathophysiology of these diseases involves release of many pro-inflammatory cytokines, such as TNF and IL-1, in addition to anti-inflammatory molecules. Recent studies have demonstrated that neuroimmune interactions are important in the initiation and progress of inflammatory processes. TNF, IL-1 and neuropeptides such as substance P and neurotensin stimulate the release of chemokines, in particular IL-8, a potent neutrophil chemoattractant. Expression of IL-8 is regulated mainly by the transcription factors NF-kappaB, activating protein-1 and CCAAT/enhancer-binding proteins. Recent exciting results indicate that the Rho family of small GTP-binding proteins plays an important role in the expression of NF-kappaB-dependent genes and migration of leukocytes. These results suggest that these proteins may represent a potential therapeutic target to treat several inflammatory states.

Reactivation of antigen-induced arthritis in mice by oral administration of lipopolysaccharide

We examined whether oral administration of lipopolysaccharide (LPS) from Escherichia coli reactivated antigen-induced arthritis (AIA) in mice that is one of models of human rheumatoid arthritis. To induce AIA, mice were immunized by subcutaneous injection of ovalbumin (OVA) emulsified with complete Freund's adjuvant into the base of the tail (day 0) followed by intraarticular injection of OVA on day 21. To investigate the ability of LPS to reactivate AIA, varying doses of LPS were p.o. administered 48 h after the challenge injection. The results showed that administration of LPS was followed by reactivation of AIA in a dose-related fashion. The reactivation of AIA by LPS was associated with increases in interferon-gamma, interleukin-1beta and tumour necrosis factor-alpha. Polymyxin B sulfate given immediately before administration of LPS suppressed the reactivation of AIA. These findings suggest that LPS from intestinal bacteria may play a role in the reactivation of joint inflammation in which immune responses to pathogenic antigens are involved.

A novel protein kinase C (PKCepsilon) is required for fMet-Leu-Phe-induced activation of NF-kappaB in human peripheral blood monocytes

We have reported that the chemoattractant, fMet-Leu-Phe (fMLP), induces the activation of NF-kappaB in human peripheral blood monocytes and that this requires the activity of small GTPase, RhoA (Huang, S., Chen, L.-Y., Zuraw, B. L., Ye, R. D., and Pan, Z. K. (2001) J. Biol. Chem. 276, 40977-40981). Here we showed that the novel protein kinase C isozyme, PKCepsilon, associates functionally with RhoA in fMLP-stimulated monocytes and that PKCepsilon acted as a signaling component downstream of the GTPase RhoA during fMLP-induced activation of NF-kappaB. Stimulation of monocytes with fMLP resulted in activation of both PKCepsilon and NF-kappaB. This latter activation was largely blocked by specific inhibitors of PKCepsilon by transient expression of a dominant-negative form of PKCepsilon and by PKCepsilon-specific short interfering RNA. These findings demonstrate, for the first time, that fMLP-induced activation of NF-kappaB utilizes a signaling pathway, which requires activity of PKCepsilon, and that PKCepsilon acts as a signaling component downstream of RhoA in cytokine gene transcription stimulated by a chemoattractant. The specificity of this response suggests an important role for the Rho GTPase-PKCepsilon-NF-kappaB pathway in host defense and represents a novel and potentially important mechanism through which fMLP not only attracts leukocytes but may also contribute directly to inflammation.

Regulation of innate immunity by Rho GTPases

Leukocytes are key cellular components of innate immunity. These phagocytic cells respond to bacteria at sites of infection through chemotactic sensing and directed motility regulated by Rho GTPases. The development of sensitive probes of Rho GTPase dynamics has provided insights into the temporal and spatial aspects of GTPase regulation during chemotaxis and subsequent microbial phagocytosis. The resulting destruction of ingested bacteria by means of reactive oxygen species (ROS) depends on a Rac-regulated "molecular switch" that is modulated by antagonistic crosstalk involving Cdc42. Recent studies of leukocytes derived from Rac1- and Rac2-knockout mice have shown that these highly homologous GTPases have unique biological roles. An understanding of the biochemical basis for such distinct activities should provide novel insights into the molecular details of Rho GTPase function and regulation in innate immunity.

Rho-modifying C3-like ADP-ribosyltransferases

C3-like exoenzymes comprise a family of seven bacterial ADP-ribosyltransferases, which selectively modify RhoA, B, and C at asparagine-41. Crystal structures of C3 exoenzymes are available, allowing novel insights into the structure-function relationships of these exoenzymes. Because ADP-ribosylation specifically inhibits the biological functions of the low-molecular mass GTPases, C3 exoenzymes are established pharmacological tools to study the cellular functions of Rho GTPases. Recent studies, however, indicate that the functional consequences of C3-induced ADP-ribosylation are more complex than previously suggested. In the present review the basic properties of C3 exoenzymes are briefly summarized and new findings are reviewed.

The low molecular weight GTPase RhoA and atypical protein kinase Czeta are required for TLR2-mediated gene transcription

The Rho GTPases are molecular switches that regulate many essential cellular processes, including actin dynamics, gene transcription, cell cycle progression, cell adhesion, and motility. In this study, we report that stimulation of TLR2 in human epithelial and monocytic cells leads to rapid and transient activation of RhoA. RhoA cooperated with the canonical I-kappaB kinase-mediated pathway that induces the release of NF-kappaB, in regulating the trans activation of the NF-kappaB subunit p65/RelA by affecting Ser(311) phosphorylation, and subsequent cytokine production. Another consequence of TLR2 stimulation by bacterial derived products was the activation of atypical protein kinase C (PKC) zeta and association of this protein kinase with RhoA. Inhibition of PKCzeta decreased NF-kappaB activation and p65/RelA trans activation without affecting I-kappaBalpha degradation. The observation of a transient, stimulus-dependent association of RhoA with PKCzeta suggests that RhoA mediates at least partially its effect on gene transcription through atypical PKC. In contrast to previous studies, identifying Rac1-PI3K as an upstream element in TLR2-initiated response to NF-kappaB, PI3K signaling was not required for RhoA or PKCzeta activity. These results indicate that multiple GTPase-regulated pathways emerge from stimulated Toll receptors, controlling different aspects of NF-kappaB-mediated gene transcription.

Activation of Raf/MEK/ERK/cPLA2 Signaling Pathway Is Essential for Chlamydial Acquisition of Host Glycerophospholipids

Chlamydiae, a diverse group of obligate intracellular pathogens replicating within cytoplasmic vacuoles of eukaryotic cells, are able to acquire lipids from host cells. Here we report that activation of the host Raf-MEK-ERK-cPLA2 signaling cascade is required for the chlamydial uptake of host glycerophospholipids. Both the MAP kinase pathway (Ras/Raf/MEK/ERK) and Ca(2+)-dependent cytosolic phospholipase A2 (cPLA2) were activated in chlamydia-infected cells. The inhibition of cPLA2 activity resulted in the blockade of the chlamydial uptake of host glycerophospholipids and impairment in chlamydial growth. Blocking either c-Raf-1 or MEK1/2 activity prevented the chlamydial activation of ERK1/2, leading to the suppression of both chlamydial activation of the host cPLA2 and uptake of glycerophospholipids from the host cells. The chlamydia-induced phosphorylation of cPLA2 was also blocked by a dominant negative ERK2. Furthermore, activation of both ERK1/2 and cPLA2 was dependent on chlamydial growth and restricted within chlamydia-infected cells, suggesting an active manipulation of the host ERK-cPLA2 signaling pathway by chlamydiae.