beta-Arrestin 2: a Negative Regulator of Inflammatory Responses in Polymorphonuclear Leukocytes.

Heterotrimeric Gi proteins have been previously implicated in signaling leading to inflammatory mediator production induced by bacterial lipopolysaccharide (LPS). beta-arrestins are ubiquitously expressed proteins that alter G-protein-coupled receptors signaling. beta-arrestin 2 plays a multifaceted role as a scaffold protein in regulating cellular inflammatory responses.

Lysophosphatidic acid inhibits bacterial endotoxin-induced pro-inflammatory response: potential anti-inflammatory signaling pathways.

Previous studies have demonstrated that heterotrimeric guanine nucleotide-binding regulatory (Gi) protein-deficient mice exhibit augmented inflammatory responses to lipopolysaccharide (LPS). These findings suggest that Gi protein agonists will suppress LPS-induced inflammatory gene expression. Lysophosphatidic acid (LPA) activates G protein-coupled receptors leading to Gi protein activation.

Differential regulation of lipopolysaccharide and Gram-positive bacteria induced cytokine and chemokine production in macrophages by Galpha(i) proteins.

Heterotrimeric G(i) proteins play a role in signalling activated by lipopolysaccharide (LPS), Staphylococcus aureus (SA) and group B streptococci (GBS), leading to production of inflammatory mediators. We hypothesized that genetic deletion of G(i) proteins would alter cytokine and chemokine production induced by LPS, SA and GBS stimulation. LPS-induced, heat-killed SA-induced and heat-killed GBS-induced cytokine and chemokine production in peritoneal macrophages from wild-type (WT), Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice were investigated.

Beta-arrestins 1 and 2 differentially regulate LPS-induced signaling and pro-inflammatory gene expression.

Toll like receptors, the critical receptor family in innate immunity, have been shown to signal via both ERK 1/2 and transcription factor NFkappaB. beta-Arrestins 1 and 2 have recently been implicated in modulation of NFkappaB signaling and ERK 1/2 activation. Using a number of approaches: mouse embryonic fibroblasts (MEF) from wild-type (WT), beta-arrestins knockouts (KO), beta-arrestins 1 and 2 double KO, and MEFs with reconstituted WT beta-arrestins in the double KO cells, RNA interference (siRNA) specific knockdown of beta-arrestins, and overexpression of WT beta-arrestins, it was demonstrated that beta-arrestin 2 positively regulates LPS-induced ERK 1/2 activation and both beta-arrestins 1 and 2 negatively regulate LPS-induced NFkappaB activation.

Differential regulation of lipopolysaccharide and Gram-positive bacteria induced cytokine and chemokine production in splenocytes by Galphai proteins.

Heterotrimeric Gi proteins play a role in lipopolysaccharide (LPS) and Staphylococcus aureus (SA) activated signaling leading to inflammatory mediator production. We hypothesized that genetic deletion of Gi proteins would alter cytokine and chemokine production induced by LPS and SA. LPS- and heat killed SA-induced cytokine and chemokine production in splenocytes from wild type (WT), Galpha(i2) (-/-) or Galpha(i1/3) (-/-) mice were investigated.

The phosphatidylinositol 3 kinase pathway regulates tolerance to lipopolysaccharide and priming responses to Staphylococcus aureus and lipopolysaccharide.

Our previous studies have demonstrated that although LPS and Staphylococcus aureus induce homologous tolerance, they induce priming to each other instead of cross-tolerance. The phosphatidylinositol 3 (PI3) kinase pathway has been implicated in microbial signaling and inflammatory gene expression regulation. We hypothesized that LPS or S.

Gi proteins regulate lipopolysaccharide and Staphylococcus aureus induced cytokine production but not (1--> 3)-beta-D-glucan induced cytokine suppression.

Previous studies have demonstrated that bacterial lipopolysaccharide (LPS) and heat killed Staphylococcus aureus (SA) activation of inflammatory cells depended in part upon activation of heterotrimeric Gi proteins. It has also been shown that (1 --> 3) beta-D-glucan can suppress inflammatory cell activation by microbial products although the cellular mechanism of the glucan effect remains to be clearly defined. We hypothesized that Gi proteins function as a common convergent signaling pathway for both LPS and SA leading to monocyte mediator production.

Lipopolysaccharide- and gram-positive bacteria-induced cellular inflammatory responses: role of heterotrimeric Galpha(i) proteins.

Heterotrimeric G(i) proteins may play a role in lipopolysaccharide (LPS)-activated signaling through Toll-like receptor 4 (TLR4), leading to inflammatory mediator production. Although LPS is a TLR4 ligand, the gram-positive bacterium Staphylococcus aureus (SA) is a TLR2 ligand, and group B streptococci (GBS) are neither TLR2 nor TLR4 ligands but are MyD88 dependent. We hypothesized that genetic deletion of G(i) proteins would alter mediator production induced by LPS and gram-positive bacterial stimulation.

Toll-like receptor 4 coupled GI protein signaling pathways regulate extracellular signal-regulated kinase phosphorylation and AP-1 activation independent of NFkappaB activation.

Previous studies have implicated heterotrimeric Gi proteins in signaling leading to inflammatory mediator production induced by lipopolysaccharide (LPS). TLR4 has recently been shown to play a central role in response to LPS activation. We hypothesized that Gi proteins are coupled to TLR4 activation of signaling pathways.

Differential regulation of cytokine and chemokine production in lipopolysaccharide-induced tolerance and priming.

LPS pretreatment of human pro-monocytic THP-1 cells induces tolerance to secondary LPS stimulation with reduced TNFalpha production. However, secondary stimulation with heat-killed Staphylococcus aureus (HKSa) induces priming as evidenced by augmented TNFalpha production. The pro-inflammatory cytokine, IFNgamma, also abolishes suppression of TNFalpha in LPS tolerance.

Staphylococcus aureus and lipopolysaccharide induce homologous tolerance but heterologous priming: role of interferon-gamma.

Lipopolysaccharide (LPS), the gram-negative bacterial cell wall component, induces tolerance to a secondary challenge of LPS in macrophages (Mphi) as evidenced by reduced inflammatory mediator production. However, it is uncertain if heat-killed (HK) gram-positive bacteria Staphylococcus aureus (Sa) can induce a similar tolerance and alter responses to LPS. We hypothesized that HKSa induces homologous tolerance and cross tolerance to LPS stimulation in human promonocytic THP-1 cells.

Involvement of G(i) proteins and Src tyrosine kinase in TNFalpha production induced by lipopolysaccharide, group B Streptococci and Staphylococcus aureus.

Previous studies have suggested that heterotrimeric G(i) proteins, Src tyrosine kinase and phosphatidylinositol-3 kinase (PI3 Kinase) are involved in signaling events induced by lipopolysaccharide (LPS) leading to pro-inflammatory cytokines gene expression. To investigate the involvement of these mediators in Gram-positive bacteria induced pro-inflammatory cytokine expression, LPS (10 ng/ml), heat killed group B Streptococci (GBS 1 microg/ml) and Staphylococcus aureus (SA 10 microg/ml) were used to induce TNFalpha production in the murine J774A.1 macrophage (MØ) cell line and human promonocytic THP-1 cell line.

Peroxisome proliferator-activated receptor-gamma agonists modulate macrophage activation by gram-negative and gram-positive bacterial stimuli.

Bacterial products, such as lipopolysaccharide (LPS) or heat-killed Escherichia coli (EC), and heat-killed Staphylococcus aureus (SA) are potent activators of macrophages (MØ). When stimulated by these bacterial components, MØ produce inflammatory mediators, such as nitric oxide (NO) and thromboxane (Tx) B(2). Bacterial mediator production is preceded by the activation of various signal transduction pathways.