Protease-Activated Receptor 2 (PAR2) Expressed in Sensory Neurons Contributes to Signs of Pain and Neuropathy in Paclitaxel Treated Mice.

Chemotherapy-induced peripheral neuropathy (CIPN) is a common, dose-limiting side effect of cancer therapy. Protease-activated receptor 2 (PAR2) is implicated in a variety of pathologies, including CIPN. In this study, we demonstrate the role of PAR2 expressed in sensory neurons in a paclitaxel (PTX)-induced model of CIPN in mice.

C781, a β-Arrestin Biased Antagonist at Protease-Activated Receptor-2 (PAR2), Displays in vivo Efficacy Against Protease-Induced Pain in Mice.

Given the limited options and often harmful side effects of current analgesics and the suffering caused by the opioid crisis, new classes of pain therapeutics are needed. Protease-activated receptors (PARs), particularly PAR2, are implicated in a variety of pathologies, including pain. Since the discovery of the role of PAR2 in pain, development of potent and specific antagonists has been slow.

β-Arrestin-biased proteinase-activated receptor-2 antagonist C781 limits allergen-induced airway hyperresponsiveness and inflammation.

Background And Purpose: Asthma is a heterogenous disease strongly associated with inflammation that has many different causes and triggers. Current asthma treatments target symptoms such as bronchoconstriction and airway inflammation. Despite recent advances in biological therapies, there remains a need for new classes of therapeutic agents with novel, upstream targets.

Alternaria alternata-induced airway epithelial signaling and inflammatory responses via protease-activated receptor-2 expression.

Inhalation of the fungus Alternaria alternata is associated with an increased risk of allergic asthma development and exacerbations. Recent work in acute exposure animal models suggests that A. alternata-induced asthma symptoms, which include inflammation, mucus overproduction and airway hyperresponsiveness, are due to A.

Proteinase-activated receptor-2 antagonist C391 inhibits Alternaria-induced airway epithelial signalling and asthma indicators in acute exposure mouse models.

Background And Purpose: Despite the availability of a variety of treatment options, many asthma patients have poorly controlled disease with frequent exacerbations. Proteinase-activated receptor-2 (PAR2) has been identified in preclinical animal models as important to asthma initiation and progression following allergen exposure. Proteinase activation of PAR2 raises intracellular Ca , inducing MAPK and β-arrestin signalling in the airway, leading to inflammatory and protective effects.

Protease-activated receptor-2 signaling through β-arrestin-2 mediates Alternaria alkaline serine protease-induced airway inflammation.

Alternaria alternata is a fungal allergen associated with severe asthma and asthma exacerbations. Similarly to other asthma-associated allergens, Alternaria secretes a serine-like trypsin protease(s) that is thought to act through the G protein-coupled receptor protease-activated receptor-2 (PAR) to induce asthma symptoms. However, specific mechanisms underlying Alternaria-induced PAR activation and signaling remain ill-defined.

The novel PAR2 ligand C391 blocks multiple PAR2 signalling pathways in vitro and in vivo.

Background And Purpose: Proteinase-activated receptor-2 (PAR2) is a GPCR linked to diverse pathologies, including acute and chronic pain. PAR2 is one of the four PARs that are activated by proteolytic cleavage of the extracellular amino terminus, resulting in an exposed, tethered peptide agonist. Several peptide and peptidomimetic agonists, with high potency and efficacy, have been developed to probe the functions of PAR2, in vitro and in vivo.

Molecular mechanisms underlying beta-arrestin-dependent chemotaxis and actin-cytoskeletal reorganization.

β-Arrestins play a crucial role in cell migration downstream of multiple G-protein-coupled receptors (GPCRs) through multiple mechanisms. There is considerable evidence that β-arrestin-dependent scaffolding of actin assembly proteins facilitates the formation of a leading edge in response to a chemotactic signal. Conversely, there is substantial support for the hypothesis that β-arrestins facilitate receptor turnover through their ability to desensitize and internalize GPCRs.

Arrestins in actin reorganization and cell migration.

Arrestins have emerged as important regulators of actin reorganization and cell migration. Both in their classical roles as mediators of receptor desensitization and internalization, and in their newer role as signaling scaffolds, β-arrestins help orchestrate the cellular response to chemotactic signals. However, there is still a considerable amount to be learned about the precise molecular mechanisms underlying these processes.

β-Arrestin-kinase scaffolds: turn them on or turn them off?

G-protein-coupled receptors (GPCRs) can signal through heterotrimeric G-proteins or through β-arrestins to elicit responses to a plethora of extracellular stimuli. While the mechanisms underlying G-protein signaling is relatively well understood, the mechanisms by which β-arrestins regulate the diverse set of proteins with which they associate remain unclear. Multi-protein complexes are a common feature of β-arrestin-dependent signaling.

β-Arrestin-2 mediates the proinflammatory effects of proteinase-activated receptor-2 in the airway.

Proteinase-Activated receptor-2 (PAR(2)), a G-protein-coupled Receptor, activated by serine proteinases, is reported to have both protective and proinflammatory effects in the airway. Given these opposing actions, both inhibitors and activators of PAR(2) have been proposed for treating asthma. PAR(2) can signal through two independent pathways: a β-arrestin-dependent one that promotes leukocyte migration, and a G-protein/Ca(2+) one that is required for prostaglandin E(2) (PGE(2)) production and bronchiolar smooth muscle relaxation.

Cofilin under control of β-arrestin-2 in NMDA-dependent dendritic spine plasticity, long-term depression (LTD), and learning.

Dendritic spines are dynamic, actin-rich structures that form the postsynaptic sites of most excitatory synapses in the brain. The F-actin severing protein cofilin has been implicated in the remodeling of dendritic spines and synapses under normal and pathological conditions, by yet unknown mechanisms. Here we report that β-arrestin-2 plays an important role in NMDA-induced remodeling of dendritic spines and synapses via translocation of active cofilin to dendritic spines.

Neutrophil elastase acts as a biased agonist for proteinase-activated receptor-2 (PAR2).

Human neutrophil proteinases (elastase, proteinase-3, and cathepsin-G) are released at sites of acute inflammation. We hypothesized that these inflammation-associated proteinases can affect cell signaling by targeting proteinase-activated receptor-2 (PAR(2)). The PAR family of G protein-coupled receptors is triggered by a unique mechanism involving the proteolytic unmasking of an N-terminal self-activating tethered ligand (TL).

Apical and basolateral pools of proteinase-activated receptor-2 direct distinct signaling events in the intestinal epithelium.

Studies suggest that there are two distinct pools of proteinase-activated receptor-2 (PAR₂) present in intestinal epithelial cells: an apical pool accessible from the lumen, and a basolateral pool accessible from the interstitial space and blood. Although introduction of PAR₂ agonists such as 2-furoyl-LIGRL-O-NH₂ (2fAP) to the intestinal lumen can activate PAR₂, the presence of accessible apical PAR₂ has not been definitively shown. Furthermore, some studies have suggested that basolateral PAR₂ responses in the intestinal epithelium are mediated indirectly by neuropeptides released from enteric nerve fibers, rather than by intestinal PAR₂ itself.

Beta-arrestins as regulators of signal termination and transduction: how do they determine what to scaffold?

Over the last decade β-arrestins have emerged as pleiotropic scaffold proteins, capable of mediating numerous diverse responses to multiple agonists. Most well characterized are the G-protein-coupled receptor (GPCR) stimulated β-arrestin signals, which are sometimes synergistic with, and sometimes independent of, heterotrimeric G-protein signals. β-arrestin signaling involves the recruitment of downstream signaling moieties to β-arrestins; in many cases specific sites of interaction between β-arrestins and the downstream target have been identified.

Beta-arrestin inhibits CAMKKbeta-dependent AMPK activation downstream of protease-activated-receptor-2.

Background: Proteinase-activated-receptor-2 (PAR2) is a seven transmembrane receptor that can activate two separate signaling arms: one through Gαq and Ca2+ mobilization, and a second through recruitment of β-arrestin scaffolds. In some cases downstream targets of the Gαq/Ca2+ signaling arm are directly inhibited by β-arrestins, while in other cases the two pathways are synergistic; thus β-arrestins act as molecular switches capable of modifying the signal generated by the receptor.

Results: Here we demonstrate that PAR2 can activate adenosine monophosphate-activated protein kinase (AMPK), a key regulator of cellular energy balance, through Ca2+-dependent Kinase Kinase β (CAMKKβ), while inhibiting AMPK through interaction with β-arrestins.

beta-Arrestins scaffold cofilin with chronophin to direct localized actin filament severing and membrane protrusions downstream of protease-activated receptor-2.

Protease-activated receptor-2 (PAR-2) mediates pro-inflammatory signals in a number of organs, including enhancing leukocyte recruitment to sites of injury and infection. At the cellular level, PAR-2 promotes activation of the actin filament-severing protein cofilin, which is crucial for the reorganization of the actin cytoskeleton and chemotaxis. These responses require the scaffolding functions of beta-arrestins; however, the mechanism by which beta-arrestins spatially regulate cofilin activity and the role of this pathway in primary cells has not been investigated.

Focal adhesion kinase acts downstream of EphB receptors to maintain mature dendritic spines by regulating cofilin activity.

Dendritic spines are the postsynaptic sites of most excitatory synapses in the brain and are highly enriched in polymerized F-actin, which drives the formation and maintenance of mature dendritic spines and synapses. We propose that suppressing the activity of the actin-severing protein cofilin plays an important role in the stabilization of mature dendritic spines, and is accomplished through an EphB receptor-focal adhesion kinase (FAK) pathway. Our studies revealed that Cre-mediated knock-out of loxP-flanked fak prompted the reversion of mature dendritic spines to an immature filopodial-like phenotype in primary hippocampal cultures.

Beta-arrestin multimers: does a crowd help or hinder function?

In this issue of the Biochemical Journal, Xu et al. describe how they use a spot peptide array to identify a unique sequence within beta-arrestin-2 that is required for both multimerization and ERK1/2 (extracellular-signal-related kinase 1/2) scaffolding. They provide evidence that dimers may serve as more than just 'storage forms' of beta-arrestins, incapable of interacting with receptors but, rather, perhaps, adding to the specificity of G-protein-coupled-receptor signalling.

Differential regulation of class IA phosphoinositide 3-kinase catalytic subunits p110 alpha and beta by protease-activated receptor 2 and beta-arrestins.

PAR-2 (protease-activated receptor 2) is a GPCR (G-protein-coupled receptor) that can elicit both G-protein-dependent and -independent signals. We have shown previously that PAR-2 simultaneously promotes Galphaq/Ca2+-dependent activation and beta-arrestin-1-dependent inhibition of class IA PI3K (phosphoinositide 3-kinase), and we sought to characterize further the role of beta-arrestins in the regulation of PI3K activity. Whereas the ability of beta-arrestin-1 to inhibit p110alpha (PI3K catalytic subunit alpha) has been demonstrated, the role of beta-arrestin-2 in PI3K regulation and possible differences in the regulation of the two catalytic subunits (p110alpha and p110beta) associated with p85alpha (PI3K regulatory subunit) have not been examined.

Beta-arrestin-dependent regulation of the cofilin pathway downstream of protease-activated receptor-2.

Beta-arrestins are pleiotropic molecules that mediate signal desensitization, G-protein-independent signaling, scaffolding of signaling molecules, and chemotaxis. Protease-activated receptor-2 (PAR-2), a Galpha(q/11)-coupled receptor, which has been proposed as a therapeutic target for inflammation and cancer, requires the scaffolding function of beta-arrestins for chemotaxis. We hypothesized that PAR-2 can trigger specific responses by differential activation of two pathways, one through classic Galpha(q)/Ca(2+) signaling and one through beta-arrestins, and we proposed that the latter involves scaffolding of proteins involved in cell migration and actin assembly.

Stop that cell! Beta-arrestin-dependent chemotaxis: a tale of localized actin assembly and receptor desensitization.

Beta-arrestins have recently emerged as key regulators of directed cell migration or chemotaxis. Given their traditional role as mediators of receptor desensitization, one theory is that beta-arrestins contribute to cell polarity during chemotaxis by quenching the signal at the trailing edge of the cell. A second theory is that they scaffold signaling molecules involved in cytoskeletal reorganization to promote localized actin assembly events leading to the formation of a leading edge.

Protease-activated receptor-2 simultaneously directs beta-arrestin-1-dependent inhibition and Galphaq-dependent activation of phosphatidylinositol 3-kinase.

Protease-activated receptor-2 (PAR-2) is a G-protein-coupled receptor (GPCR) activated upon proteolytic cleavage of its N-terminus by a number of serine proteases. We have previously reported that formation of a beta-arrestin-dependent signaling scaffold is required for PAR-2-stimulated activation of extracellular signal regulated kinases 1 and 2 and chemotaxis. beta-Arrestin-dependent pathways downstream of some GPCRs have been shown to function independently and sometimes in opposition to classic signaling through heterotrimeric G-proteins; however, this possibility has not been addressed with respect to PAR-2.