Proteinase-activated receptor-1 and -2 induce the release of chemokine GRO/CINC-1 from rat astrocytes via differential activation of JNK isoforms, evoking multiple protective pathways in brain

Physiological JNK3 Concentrations Are Higher in Motor-related and Disease-implicated Brain Regions of C57BL6/J Mice

The c-Jun N-terminal kinase 3 (JNK3) is a stress-responsive protein kinase primarily expressed in the central nervous system (CNS). JNK3 exhibits nuanced neurological activities, such as roles in behavior, circadian rhythms, and neurotransmission, but JNK3 is also implicated in cell death and neurodegeneration. Despite the critical role of JNK3 in neurophysiology and pathology, its localization in the brain is not fully understood due to a paucity of tools to distinguish JNK3 from other isoforms. While previous functional and histological studies suggest locales for JNK3 in the CNS, a comprehensive and higher resolution of JNK3 distribution and abundance remained elusive. Here, we sought to define the anatomical and cellular distribution of JNK3 in adult mouse brains. Data reveal the highest levels of JNK3 and pJNK3 were found in the cortex and the hippocampus. JNK3 possessed neuron-type selectivity as JNK3 was present in GABAergic, cholinergic, and dopaminergic neurons, but was not detectable in VGLUT-1-positive glutamatergic neurons and astrocytes in vivo . Intriguingly, higher JNK3 signals were found in motor neurons and relevant nuclei in the cortex, basal ganglia, brainstem, and spinal cord. While JNK3 was primarily observed in the cytosol of neurons in the cortex and the hippocampus, JNK3 appeared commonly within the nucleus in the brainstem. These distinctions suggest the potential for significant differences between JNK3 actions in distinct brain regions and cell types. Our results provide a significant improvement over previous reports of JNK3 spatial organization in the adult CNS and support continued investigation of JNK3's role in neurophysiology and pathophysiology.

Genetic deletion of c-Jun amino-terminal kinase 3 (JNK3) modestly increases disease severity in a mouse model of multiple sclerosis

The c-Jun amino terminal kinases (JNKs) regulate transcription, and studies suggest they contribute to neuropathology in the EAE model of MS. To examine the role of the JNK3 isoform, we compared EAE in JNK3 null mice to wild type (WT) littermates. Although disease severity was similar in female mice, in male JNK3 null mice the day of onset and time to reach 100% incidence occurred sooner, and disease severity was increased. While glial activation in spinal cord was similar, white matter lesions were increased in JNK3 null mice. These results suggest JNK3 normally limits EAE disease in a sex-dependent manner.

MAPK10 Expression as a Prognostic Marker of the Immunosuppressive Tumor Microenvironment in Human Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) remains a devastating malignancy worldwide due to lack of effective therapy. The immune-rich contexture of HCC tumor microenvironment (TME) makes this tumor an appealing target for immune-based therapies; however, the immunosuppressive TME is still a major challenge for more efficient immunotherapy in HCC. Using bioinformatics analysis based on the TCGA database, here we found that MAPK10 is frequently down-regulated in HCC tumors and significantly correlates with poor survival of HCC patients. HCC patients with low MAPK10 expression have lower expression scores of tumor infiltration lymphocytes (TILs) and stromal cells in the TME and increased scores of tumor cells than those with high MAPK10 expression. Further transcriptomic analyses revealed that the immune activity in the TME of HCC was markedly reduced in the low-MAPK10 group of HCC patients compared to the high-MAPK10 group. Additionally, we identified 495 differentially expressed immune-associated genes (DIGs), with 482 genes down-regulated and 13 genes up-regulated in parallel with the decrease of MAPK10 expression. GO enrichment and KEGG pathway analyses indicated that the biological functions of these DIGs included cell chemotaxis, leukocyte migration and positive regulation of the response to cytokine–cytokine receptor interaction, T cell receptor activation and MAPK signaling pathway. Protein–protein interaction (PPI) analyses of the 495 DIGs revealed five potential downstream hub genes of MAPK10, including SYK, CBL, VAV1, LCK, and CD3G. Several hub genes such as SYK, LCK, and VAV1 could respond to the immunological costimulatory signaling mediated by the transmembrane protein ICAM1, which was identified as a down-regulated DIG associated with low-MAPK10 expression. Moreover, ectopic overexpression or knock-down of MAPK10 could up-regulate or down-regulate ICAM1 expression via phosphorylation of c-jun at Ser63 in HCC cell lines, respectively. Collectively, our results demonstrated that MAPK10 down-regulation likely contributes to the immunosuppressive TME of HCC, and this gene might serve as a potential immunotherapeutic target and a prognostic factor for HCC patients.

Single intratracheal administration of cross-linked water-soluble acrylic acid polymer causes acute alveolo-interstitial inflammation and the subsequent fibrotic formation possibly via the TGF-β1 pathway in the lung of rats

In a Japanese chemical factory, a lung disease like pneumoconiosis appeared at a high rate among workers handling cross-linked water-soluble acrylic acid polymer (CWAAP). To our knowledge, no such case was known in the world until very recently. The present study was designed to elucidate the effect of single intratracheal CWAAP instillation on the lung of rats. The CWAAP group had a significant increase in relative lung weight accompanied by a significant elevation in the number of total cells, total protein concentrations, and myeloperoxidase concentrations in bronchoalveolar lavage fluid when compared to the control group. The histopathological study revealed acute lung inflammation with the destruction of alveoli. The factors promoting fibrosis, macrophages, TGF-β1, collagen and fibronectin vs. the factors suppressing fibrosis, matrix metalloproteinases were more powerfully driven in the CWAAP group, resultantly leading to fibrotic formation. In turn, we examined if acute lung inflammation and the subsequent fibrotic formation seen in the CWAAP group appeared in the other water-soluble polymer groups. Their histopathological findings were observed only in the polyacrylic acid sodium (PAAS), a monomer of CWAAP, group. The degree of inflammation and fibrogenesis was stronger in the CWAAP group than in the PAAS group. In conclusion, the present study demonstrated the induction of acute lung inflammation and the subsequent fibrotic formation by single intratracheal CWAAP instillation. The structural features of CWAAP that contains many carboxyl groups and cross-linked chains may be responsible for enhanced inflammation and fibrogenesis in the lung.

Biological Properties of JNK3 and Its Function in Neurons, Astrocytes, Pancreatic β-Cells and Cardiovascular Cells

JNK is a protein kinase, which induces transactivation of c-jun. The three isoforms of JNK, JNK1, JNK2, and JNK3, are encoded by three distinct genes. JNK1 and JNK2 are expressed ubiquitously throughout the body. By contrast, the expression of JNK3 is limited and observed mainly in the brain, heart, and testes. Concerning the biological properties of JNKs, the contribution of upstream regulators and scaffold proteins plays an important role in the activation of JNKs. Since JNK signaling has been described as a form of stress-response signaling, the contribution of JNK3 to pathophysiological events, such as stress response or cell death including apoptosis, has been well studied. However, JNK3 also regulates the physiological functions of neurons and non-neuronal cells, such as development, regeneration, and differentiation/reprogramming. In this review, we shed light on the physiological functions of JNK3. In addition, we summarize recent advances in the knowledge regarding interactions between JNK3 and cellular reprogramming.

The Need for SMN-Independent Treatments of Spinal Muscular Atrophy (SMA) to Complement SMN-Enhancing Drugs

Spinal Muscular Atrophy (SMA) is monogenic motoneuron disease caused by low levels of the Survival of Motoneuron protein (SMN). Recently, two different drugs were approved for the treatment of the disease. The antisense oligonucleotide Nusinersen/Spinraza® and the gene replacement therapy Onasemnogene Abeparvovec/Zolgensma® both enhance SMN levels. These treatments result in impressive benefits for the patients. However, there is a significant number of non-responders and an intervention delay has a strong negative impact on the efficacy. Obviously, later stages of motoneuron degeneration cannot be reversed by SMN-restoration. Therefore, complementary, SMN-independent strategies are needed which are able to address such SMN-irreversible degenerative processes. Those are defined as pathological alterations which are not reversed by SMN-restoration for a given dose and intervention delay. It is crucial to tailor SMN-independent approaches to the novel clinical situation with SMN-restoring treatments. On the molecular level, such SMN-irreversible changes become manifest in altered signaling modules as described by molecular systems biology. Based on our current knowledge about altered signaling, we introduce a network approach for an informed decision for the most potent SMN-independent treatment targets. Finally, we present recommendations for the identification of novel treatments which can be combined with SMN-restoring drugs.

Genetic targeting of protease activated receptor 2 reduces inflammatory astrogliosis and improves recovery of function after spinal cord injury

Inflammatory-astrogliosis exacerbates damage in the injured spinal cord and limits repair. Here we identify Protease Activated Receptor 2 (PAR2) as an essential regulator of these events with mice lacking the PAR2 gene showing greater improvements in motor coordination and strength after compression-spinal cord injury (SCI) compared to wild type littermates. Molecular profiling of the injury epicenter, and spinal segments above and below, demonstrated that mice lacking PAR2 had significantly attenuated elevations in key hallmarks of astrogliosis (glial fibrillary acidic protein (GFAP), vimentin and neurocan) and in expression of pro-inflammatory cytokines (interleukin-6 (IL-6), tumor necrosis factor (TNF) and interleukin-1 beta (IL-1β)). SCI in PAR2-/- mice was also accompanied by improved preservation of protein kinase C gamma (PKCγ)-immunopositive corticospinal axons and reductions in GFAP-immunoreactivity, expression of the pro-apoptotic marker BCL2-interacting mediator of cell death (BIM), and in signal transducer and activator of transcription 3 (STAT3). The potential mechanistic link between PAR2, STAT3 and astrogliosis was further investigated in primary astrocytes to reveal that the SCI-related serine protease, neurosin (kallikrein 6) promotes IL-6 secretion in a PAR2 and STAT3-dependent manner. Data point to a signaling circuit in primary astrocytes in which neurosin signaling at PAR2 promotes IL-6 secretion and canonical STAT3 signaling. IL-6 promotes expression of GFAP, vimentin, additional IL-6 and robust increases in both neurosin and PAR2, thereby driving the PAR2-signaling circuit forward. Given the significant reductions in astrogliosis and inflammation as well as superior neuromotor recovery observed in PAR2 knockout mice after SCI, we suggest that this receptor and its agonists represent new drug targets to foster neuromotor recovery.

JNK inhibition of VMAT2 contributes to rotenone-induced oxidative stress and dopamine neuron death

Treatment with rotenone, both in vitro and in vivo, is widely used to model dopamine neuron death in Parkinson's disease upon exposure to environmental neurotoxicants and pesticides. Mechanisms underlying rotenone neurotoxicity are still being defined. Our recent studies suggest that rotenone-induced dopamine neuron death involves microtubule destabilization, which leads to accumulation of cytosolic dopamine and consequently reactive oxygen species (ROS). Furthermore, the c-Jun N-terminal protein kinase (JNK) is required for rotenone-induced dopamine neuron death. Here we report that the neural specific JNK3 isoform of the JNKs, but not JNK1 or JNK2, is responsible for this neuron death in primary cultured dopamine neurons. Treatment with taxol, a microtubule stabilizing agent, attenuates rotenone-induced phosphorylation and presumably activation of JNK. This suggests that JNK is activated by microtubule destabilization upon rotenone exposure. Moreover, rotenone inhibits VMAT2 activity but not VMAT2 protein levels. Significantly, treatment with SP600125, a pharmacological inhibitor of JNKs, attenuates rotenone inhibition of VMAT2. Furthermore, decreased VMAT2 activity following in vitro incubation of recombinant JNK3 protein with purified mesencephalic synaptic vesicles suggests that JNK3 can inhibit VMAT2 activity. Together with our previous findings, these results suggest that rotenone induces dopamine neuron death through a series of sequential events including microtubule destabilization, JNK3 activation, VMAT2 inhibition, accumulation of cytosolic dopamine, and generation of ROS. Our data identify JNK3 as a novel regulator of VMAT2 activity.

c-Jun N-terminal kinase 1/c-Jun activation of the p53/microRNA 34a/sirtuin 1 pathway contributes to apoptosis induced by deoxycholic acid in rat liver

MicroRNAs (miRs) are increasingly associated with metabolic liver diseases. We have shown that ursodeoxycholic acid, a hydrophilic bile acid, counteracts the miR-34a/sirtuin 1 (SIRT1)/p53 pathway, activated in the liver of nonalcoholic steatohepatitis (NASH) patients. In contrast, hydrophobic bile acids, particularly deoxycholic acid (DCA), activate apoptosis and are increased in NASH. We evaluated whether DCA-induced apoptosis of rat hepatocytes occurs via miR-34a-dependent pathways and whether they connect with c-Jun N-terminal kinase (JNK) induction. DCA enhanced miR-34a/SIRT1/p53 proapoptotic signaling in a dose- and time-dependent manner. In turn, miR-34a inhibition and SIRT1 overexpression significantly rescued targeting of the miR-34a pathway and apoptosis by DCA. In addition, p53 overexpression activated the miR-34a/SIRT1/p53 pathway, further induced by DCA. DCA increased p53 expression as well as p53 transcriptional activation of PUMA and miR-34a itself, providing a functional mechanism for miR-34a activation. JNK1 and c-Jun were shown to be major targets of DCA, upstream of p53, in engaging the miR-34a pathway and apoptosis. Finally, activation of this JNK1/miR-34a proapoptotic circuit was also shown to occur in vivo in the rat liver. These results suggest that the JNK1/p53/miR-34a/SIRT1 pathway may represent an attractive pharmacological target for the development of new drugs to arrest metabolism- and apoptosis-related liver pathologies.

Endogenous protease nexin-1 protects against cerebral ischemia

The serine protease thrombin plays a role in signalling ischemic neuronal death in the brain. Paradoxically, endogenous neuroprotective mechanisms can be triggered by preconditioning with thrombin (thrombin preconditioning, TPC), leading to tolerance to cerebral ischemia. Here we studied the role of thrombin’s endogenous potent inhibitor, protease nexin-1 (PN-1), in ischemia and in tolerance to cerebral ischemia induced by TPC. Cerebral ischemia was modelled in vitro in organotypic hippocampal slice cultures from rats or genetically engineered mice lacking PN-1 or with the reporter gene lacZ knocked into the PN-1 locus PN-1HAPN-1-lacZ/HAPN-1-lacZ (PN-1 KI) exposed to oxygen and glucose deprivation (OGD). We observed increased thrombin enzyme activity in culture homogenates 24 h after OGD. Lack of PN-1 increased neuronal death in the CA1, suggesting that endogenous PN-1 inhibits thrombin-induced neuronal damage after ischemia. OGD enhanced β-galactosidase activity, reflecting PN-1 expression, at one and 24 h, most strikingly in the stratum radiatum, a glial cell layer adjacent to the CA1 layer of ischemia sensitive neurons. TPC, 24 h before OGD, additionally increased PN-1 expression 1 h after OGD, compared to OGD alone. TPC failed to induce tolerance in cultures from PN-1^−/− mice confirming PN-1 as an important TPC target. PN-1 upregulation after TPC was blocked by the c-Jun N-terminal kinase (JNK) inhibitor, L-JNKI1, known to block TPC. This work suggests that PN-1 is an endogenous neuroprotectant in cerebral ischemia and a potential target for neuroprotection.

Activation of protease-activated receptor 2-mediated signaling by mast cell tryptase modulates cytokine production in primary cultured astrocytes

Protease-activated receptor 2 (PAR-2), which is abundantly expressed in astrocytes, is known to play major roles in brain inflammation. However, the influence of the natural agonist of PAR-2, tryptase, on proinflammatory mediator releasedfrom astrocytes remains uninvestigated. In the present study, we found that tryptase at lower concentrations modestly reduced intracellular ROS production but significantly increased IL-6 and TNF-α secretion at higher concentrations without affecting astrocytic viability and proliferation. The actions of tryptase were alleviated by specific PAR-2 antagonist FSLLRY-NH2 (FS), indicating that the actions of tryptase were via PAR-2. PI3K/AKT inhibitor LY294002 reversed the effect of tryptase on IL-6 production, whereas inhibitors specific for p38, JNK, and ERK1/2 abolished the effect of tryptase on TNF-α production, suggesting that different signaling pathways are involved. Moreover, tryptase-induced activation of MAPKs and AKT was eliminated by FS, implicating that PAR-2 is responsible for transmitting tryptase biosignals to MAPKs and AKT. Tryptase provoked also expression of TGF-β and CNTF in astrocytes. The present findings suggest for the first time that tryptase can regulate the release of cytokines from astrocytes via PAR-2-MAPKs or PAR-2-PI3K/AKT signaling pathways, which reveals PAR-2 as a new target actively participating in the regulation of astrocytic functions.

Neuroprotective effect of protease-activated receptor-2 in the hypoxia-induced apoptosis of rat RGC-5 cells

Hypoxia-induced apoptosis of retinal ganglion cells (RGCs) is regarded as a pivotal pathological process in various ocular diseases. Protease-activated receptor-2 (PAR-2) is involved in the regulation of cell inflammation, differentiation, and apoptosis in many cell types and tissues, but the role of PAR-2 in RGCs under pathological conditions remains unknown. The purpose of this study was to investigate the role of PAR-2 in the apoptosis of RGCs under hypoxic stress. An immortalized rat RGC line (RGC-5) was exposed to hypoxia (5 % O₂). The expression and location of PAR-2 in RGC-5 cells under hypoxia stress were investigated using real-time PCR, western blotting and immunocytochemistry. Cell viability was determined using the Cell Counting Kit-8 assay. Apoptosis was detected using Hoechst 33342 staining and AnnexinV-FITC/PI assays. The role of Bcl-2, Bax, and the active subunit of caspase-3 was also investigated. The results showed that PAR-2 was functionally expressed in RGC-5 cells and up-regulated at both mRNA and protein levels under hypoxic stress. The PAR-2 selective agonist, SLIGRL, rescued RGC-5 cells from hypoxia-induced apoptosis through up-regulation of the Bcl-2/Bax ratio and down-regulation of caspase-3 activation. This study provides the first evidence that PAR-2 has a protective effect against the hypoxia-induced apoptosis of RGC-5 cells.

Kallikrein 6 is a novel molecular trigger of reactive astrogliosis

Kallikrein-related peptidase 6 (KLK6) is a trypsin-like serine protease upregulated at sites of central nervous system (CNS) injury, including de novo expression by reactive astrocytes, yet its physiological actions are largely undefined. Taken with recent evidence that KLK6 activates G-protein-coupled protease-activated receptors (PARs), we hypothesized that injury-induced elevations in KLK6 contribute to the development of astrogliosis and that this occurs in a PAR-dependent fashion. Using primary murine astrocytes and the Neu7 astrocyte cell line, we show that KLK6 causes astrocytes to transform from an epitheliod to a stellate morphology and to secrete interleukin 6 (IL-6). By contrast, KLK6 reduced expression of glial fibrillary acidic protein (GFAP). The stellation-promoting activities of KLK6 were shown to be dependent on activation of the thrombin receptor, PAR1, as a PAR1-specific inhibitor, SCH79797, blocked KLK6-induced morphological changes. The ability of KLK6 to promote astrocyte stellation was also shown to be linked to activation of protein kinase C (PKC). These studies indicate that KLK6 is positioned to serve as a molecular trigger of select physiological processes involved in the development of astrogliosis and that this is likely to occur at least in part by activation of the G-protein-coupled receptor, PAR1.

Where Do AQP4 Antibodies Fit in the Pathogenesis of NMO?

Recent advances in the field of neuromyelitis optica (NMO) research provided convincing evidence that anti-AQP4 antibody (AQP4-Ab) not only serves as a highly specific disease marker, but also plays an essential role in the pathogenesis of the disease. Although it is now widely recognized that AQP4-Ab induces astrocytic necrosis in a complement-dependent manner, additional triggers are also suspected as a prerequisite for the development of the disease. Unraveling these unresolved aspects of the disease will provide substantial insight into still controversial issues in the pathogenesis of NMO.

Specific phosphorylation of αA-crystallin is required for the αA-crystallin-induced protection of astrocytes against staurosporine and C2-ceramide toxicity

We previously reported that αA-crystallin and protease-activated receptor are involved in protection of astrocytes against C2-ceramide- and staurosporine-induced cell death (Li et al., 2009). Here, we investigated the molecular mechanism of αA-crystallin-mediated cytoprotection. We found that the expression of mutants mimicking specific phosphorylation of αA-crystallin increases the protection of astrocytes. However, the expression of mutants mimicking unphosphorylation of αA-crystallin results in loss of protection. These data revealed that the phosphorylation of αA-crystallin at Ser122 and Ser148 is required for protection. Furthermore, we explored the mechanism of cytoprotection of astrocytes by αA-crystallin. Application of specific inhibitors of p38 and ERK abrogates the protection of astrocytes by over-expression of αA-crystallin. Thus, p38 and ERK contribute to protective processes by αA-crystallin. This is comparable to our previous results which demonstrated that p38 and ERK regulated protease-activated receptor-2 (PAR-2)/αB-crystallin-mediated cytoprotection. Furthermore, we found that PAR-2 activation increases the expression of αA-crystallin. Thus, endogenous αA-crystallin protects astrocytes via mechanisms, which regulate the expression and/or phosphorylation status of αA-crystallin.

Expression of protease-activated receptor (PAR)-2, but not other PARs, is regulated by inflammatory cytokines in rat astrocytes

Protease-activated receptors (PARs) are widely expressed in the central nervous system (CNS) and are believed to play an important role in normal brain functioning as well as in development of various inflammatory and neurodegenerative disorders. Pathological conditions cause altered expression of PARs in brain cells and therefore altered responsiveness to PAR activation. The exact mechanisms of regulation of PAR expression are not well studied. Here, we evaluated in rat astrocytes the influence of LPS, pro-inflammatory cytokines TNFα and IL-1β and continuous PAR activation by PAR agonists on the expression levels of PARs. These stimuli are important in inflammatory and neurological disorders, where their levels are increased. We report that LPS as well as cytokines TNFα and IL-1β affected only the PAR-2 level, but their effects were opposite. LPS and TNFα increased the functional expression of PAR-2, whereas IL-1β down-regulated the functional response of PAR-2. Agonists of PAR-1 specifically increased mRNA level of PAR-2, but not protein level. Transcript levels of other PARs were not changed after PAR-1 activation. Stimulation of the cells with PAR-2 or PAR-4 agonists did not alter PAR levels. We found that up-regulation of PAR-2 is dependent on PKC activity, mostly via its Ca²⁺-sensitive isoforms. Two transcription factors, NFκB and AP-1, are involved in up-regulation of PAR-2. These findings provide new information about the regulation of expression of PAR subtypes in brain cells. This is of importance for targeting PARs, especially PAR-2, for the treatment of CNS disorders.

The phosphorylation status of extracellular-regulated kinase 1/2 in astrocytes and neurons from rat hippocampus determines the thrombin-induced calcium release and ROS generation

Challenge of protease-activated receptors induces cytosolic Ca(2+) concentration ([Ca(2+) ](c)) increase, mitogen-activated protein kinase activation and reactive oxygen species (ROS) formation with a bandwidth of responses in individual cells. We detected in this study in situ the thrombin-induced [Ca(2+) ](c) rise and ROS formation in dissociated hippocampal astrocytes and neurons in a mixed culture. In identified cells, single cell responses were correlated with extracellular-regulated kinase (ERK)1/2 phosphorylation level. On average, in astrocytes, thrombin induced a transient [Ca(2+) ](c) rise with concentration-dependent increase in amplitude and extrusion rate and high ERK1/2 phosphorylation level. Correlation analysis of [Ca(2+) ](c) response characteristics of single astrocytes reveals that astrocytes with nuclear phosphoERK1/2 localization have a smaller Ca(2+) amplitude and extrusion rate compared with cells with a cytosolic phosphoERK1/2 localization. In naive neurons, without thrombin challenge, variable ERK1/2 phosphorylation patterns are observed. ROS were detected by hydroethidine. Only in neurons with increased ERK1/2 phosphorylation level, we see sustained intracellular rise in fluorescence of the dye lasting over several minutes. ROS formation was abolished by pre-incubation with the NADPH oxidase inhibitor apocynin. Additionally, thrombin induced an immediate, transient hydroethidine fluorescence increase. This was interpreted as NADPH oxidase-mediated O(2) (•-) -release into the extracellular milieu, because it was decreased by pre-incubation with apocynin, and could be eluted by superfusion. In conclusion, the phosphorylation status of ERK1/2 determines the thrombin-dependent [Ca(2+) ](c) increase and ROS formation and, thus, influences the capacity of thrombin to regulate neuroprotection or neurodegeneration.

Anatomical localization of protease-activated receptor-1 and protease-mediated neuroglial crosstalk on peri-synaptic astrocytic endfeet

We studied the localization, activation and function of protease-activated receptor 1 (PAR-1) at the CNS synapse utilizing rat brain synaptosomes and slices. Confocal immunofluoresence and transmission electron microscopy in brain slices with pre-embedding diaminobenzidine (DAB) immunostaining found PAR-1 predominantly localized to the peri-synaptic astrocytic endfeet. Structural confocal immunofluorescence microscopy studies of isolated synaptosomes revealed spherical structures stained with anti-PAR-1 antibody which co-stained mainly for glial-filament acidic protein compared with the neuronal markers synaptophysin and PSD-95. Immunoblot studies of synaptosomes demonstrated an appropriate major band corresponding to PAR-1 and activation of the receptor by a specific agonist peptide (SFLLRN) significantly modulated phosphorylated extracellular signal-regulated kinase. A significant membrane potential depolarization was produced by thrombin (1 U/mL) and the PAR-1 agonist (100 μM) and depolarization by high K(+) elevated extracellular thrombin-like activity in the synaptosomes preparation. The results indicate PAR-1 localized to the peri-synaptic astrocytic endfeet is most likely activated by synaptic proteases and induces cellular signaling and modulation of synaptic electrophysiology. A protease mediated neuron-glia pathway may be important in both physiological and pathological regulation of the synapse.

Expression of plasminogen activator inhibitor-1 by olfactory ensheathing glia promotes axonal regeneration

Olfactory ensheathing glia (OEG) cells are known to facilitate repair following axotomy of adult neurons, although the molecular mechanisms involved are not fully understood. We previously identified plasminogen activator inhibitor-1 (PAI-1), proteinase-activated receptor-1 (PAR-1), and thrombomodulin (TM) as candidates to regulate rat OEG-dependent axonal regeneration. In this study, we have validated the involvement of these proteins in promoting axonal regeneration by immortalized human OEGs. We studied the effect of silencing these proteins in OEGs on their capacity to promote the regeneration of severed adult retinal ganglion cells (RGCs) axons. Our results support the role of glial PAI-1 as a downstream effector of PAR-1 in promoting axon regeneration. In contrast, we found that TM inhibits OEG induced-axonal regeneration. We also assessed the signaling pathways downstream of PAR-1 that might modulate PAI-1 expression, observing that specifically inhibiting Gα(i), Rho kinase, or PLC and PKC downregulated the expression of PAI-1 in OEGs, with a concomitant reduction in OEG-dependent axon regeneration in adult RGCs. Our findings support an important role for the thrombin system in regulating adult axonal regeneration by OEGs.

Chemokine transcripts as targets of the RNA-binding protein HuR in human airway epithelium

HuR is a regulator of mRNA turnover or translation of inflammatory genes through binding to adenylate-uridylate-rich elements and related motifs present in the 3'untranslated region (UTR) of mRNAs. We postulate that HuR critically regulates the epithelial response by associating with multiple ARE-bearing, functionally related inflammatory transcripts. We aimed to identify HuR targets in the human airway epithelial cell line BEAS-2B challenged with TNF-α plus IFN-γ, a strong stimulus for inflammatory epithelial responses. Ribonucleoprotein complexes from resting and cytokine-treated cells were immunoprecipitated using anti-HuR and isotype-control Ab, and eluted mRNAs were reverse-transcribed and hybridized to an inflammatory-focused gene array. The chemokines CCL2, CCL8, CXCL1, and CXCL2 ranked highest among 27 signaling and inflammatory genes significantly enriched in the HuR RNP-IP from stimulated cells over the control immunoprecipitation. Among these, 20 displayed published HuR binding motifs. Association of HuR with the four endogenous chemokine mRNAs was validated by single-gene ribonucleoprotein-immunoprecipitation and shown to be 3'UTR-dependent by biotin pull-down assay. Cytokine treatment increased mRNA stability only for CCL2 and CCL8, and transient silencing and overexpression of HuR affected only CCL2 and CCL8 expression in primary and transformed epithelial cells. Cytokine-induced CCL2 mRNA was predominantly cytoplasmic. Conversely, CXCL1 mRNA remained mostly nuclear and unaffected, as CXCL2, by changes in HuR levels. Increase in cytoplasmic HuR and HuR target expression partially relied on the inhibition of AMP-dependent kinase, a negative regulator of HuR nucleocytoplasmic shuttling. HuR-mediated regulation in airway epithelium appears broader than previously appreciated, coordinating numerous inflammatory genes through multiple posttranscriptional mechanisms.

JNK3-mediated apoptotic cell death in primary dopaminergic neurons

Investigation of mechanisms responsible for dopaminergic neuron death is critical for understanding the pathogenesis of Parkinson's disease, yet this is often quite challenging technically. Here, we describe detailed methods for culturing primary mesencephalic dopaminergic neurons and examining the activation of c-Jun N-terminal protein Kinase (JNK) in these cultures. We utilized immunocytochemistry and computerized analysis to quantify the number of surviving dopaminergic neurons and JNK activation in dopaminergic neurons. TUNEL staining was used to quantify apoptotic cell death. siRNA was used to specifically inhibit JNK3, the neural specific isoform of JNK. Our data implicate the activation of JNK3 in rotenone-induced dopaminergic neuron apoptosis.

Thrombin stimulates RPE cell motility by PKC-zeta- and NF-kappaB-dependent gene expression of MCP-1 and CINC-1/GRO chemokines

Retinal pigment epithelial cells (RPE) are the major cell type involved in the pathogenesis of proliferative vitreoretinopathy (PVR), which involves the epithelial-mesenchymal transition, proliferation, and directional migration of transformed RPE cells to the vitreous upon RPE exposure to serum components, thrombin among them. Although the aqueous humor and vitreous of PVR patients contain high levels of chemokines, their possible involvement in PVR development has not been explored. We here analyzed the effect of thrombin on chemokine gene expression and its correlation with RPE cell migration using rat RPE cells in culture as a model system. We demonstrated that thrombin induces RPE cell migration through the dose-dependent stimulation of MCP1 and GRO expression/release, and the autocrine activation of CXCR-2 and CCR-2 chemokine receptors. Whereas inhibition of CXCR2 by Sb-225002 and of CCR2 by Rs-504393 partially prevented hirudin-sensitive cell migration, the joint inhibition of these receptors abolished thrombin effect, suggesting the contribution of distinct but coincident mechanisms. Thrombin effects were not modified by Ro-32-0432 inhibition of conventional/novel PKC isoenzymes or by the MAPkinase pathway inhibitor U0126. MCP1 and GRO expression/secretion, and cell migration were completely prevented by the inhibitory PKC-zeta pseudosubstrate and by the nuclear factor-kappa B (NF-kappaB) inhibitor BAY11-7082, but not by wortmannin inhibition of PI3K. Results show that signaling pathways leading to RPE cell migration differ from the MEK-ERK-PI3K-mediated promotion RPE of cell proliferation, both of which concur at the activation of PKC-zeta.

Role of protease-activated receptor-2 on cell death and DNA fragmentation in Helicobacter pylori-infected gastric epithelial cells

Background

Helicobacter pylori (H. pylori) infection is associated with chronic gastritis, peptic ulceration and gastric carcinoma. Protease-activated receptor-2 (PAR-2), which is activated by trypsin, induced the activation of mitogen-activated protein kinases (MAPK), cell proliferation and apoptosis in several cells. Previously, we found that H. pylori induces the expression of PAR-2, which mediates the expression of adhesion molecules integrins in gastric epithelial cells. In the present study, the role of PAR-2 on H. pylori-induced cell death was investigated by determining cell viability, DNA fragmentation, and the activation of MAPK in gastric epithelial AGS cells.

Methods

AGS cells were cultured in the presence of H. pylori transfected with PAR-2 antisense (AS) oligonucleotide (ODN) or treated with a soybean trypsin inhibitor (SBTI). Viable cells and DNA fragmentation were determined by trypan blue exclusion assay and the amount of oligonucleosome-bound DNA, respectively. The activation of MAPK such as extracellular signal-regulated kinases (ERK), p38, and c-Jun N-terminal kinases (JNK), was assessed by Western blotting for phospho-specific forms of MAPK.

Results

H. pylori-induced cell death and DNA fragmentation augmented in the cells transfected with PAR-2 AS ODN or treated with SBTI. The activation of MAPK, induced by H. pylori, were suppressed by transfection with PAR-2 AS ODN or treatment with SBTI.

Conclusion

PAR-2, whose expression is induced by H. pylori, may prevent cell death and DNA fragmentation with the activation of MAPK in gastric epithelial cells.

JNK3 mediates paraquat- and rotenone-induced dopaminergic neuron death

Mechanistic studies underlying dopaminergic neuron death may identify new drug targets for the treatment of Parkinson disease. Epidemiological studies have linked pesticide exposure to increased risk for sporadic Parkinson disease. Here, we investigated the role of c-Jun-N-terminal kinase 3 (JNK3), a neural-specific JNK isoform, in dopaminergic neuron death induced by the pesticides rotenone and paraquat. The role of JNK3 was evaluated using RNA silencing and gene deletion to block JNK3 signaling. Using an antibody that recognizes all isoforms of activated JNKs, we found that paraquat and rotenone stimulate JNK phosphorylation in primary cultured dopaminergic neurons. In cultured neurons transfected with Jnk3-specific siRNA and in neurons from Jnk3 mice, JNK phosphorylation was nearly abolished, suggesting that JNK3 is the main JNK isoform activated in dopaminergic neurons by these pesticides. Paraquat- and rotenone-induced death of dopaminergic neurons was also significantly reduced by Jnk3 siRNA or Jnk3 gene deletion, and deletion of the Jnk3 gene completely attenuated paraquat-induced dopaminergic neuron death and motor deficits in vivo. Our data identify JNK3 as a common and critical mediator of dopaminergic neuron death induced by paraquat and rotenone, suggesting that it is a potential drug target for Parkinson disease treatment.

Astrocytic activation and an inhibition of MAP kinases are required for proteinase-activated receptor-2-mediated protection from neurotoxicity

Proteinase-activated receptor-2 (PAR-2) expression levels are altered in several CNS disorders with these changes being proposed to either exacerbate or diminish the disease state depending on the cell type in which this occurs. Here we present data investigating the consequence of PAR-2 activation on kainate (KA)-induced neurotoxicity in organotypic hippocampal slices cultures (OHSC). Exposure of OHSC to the PAR-2 activators trypsin or Ser-Leu-Ile-Gly-Arg-Leu (SLIGRL) induced no neurotoxicity when applied alone but was neuroprotective against KA-induced neurotoxicity. SLIGRL-mediated neuroprotection involved astrocytic activation as the neuroprotective effect was abolished following OHSC pre-treatment with fluoroacetate. Moreover, co-application of either reparixin or LY341495, antagonists of the CXCR2 chemokine receptor and metabotropic glutamate receptors respectively, inhibited the SLIGRL-mediated neuroprotection. SLIGRL application inhibited both p38 MAPK and ERK activity in OHSC, but not the JNK 1/2 signalling pathway. Accordingly, the co-application of the p38 MAPK and ERK inhibitors SB203580 and UO126 reduced KA-induced cell death, mimicking PAR-2-mediated neuroprotection. These data indicate that PAR-2 activation is neuroprotective and involves astrocytic activation, gliotransmitter release, and the subsequent inhibition of MAPK signalling cascades, providing further evidence for PAR-2 as an interesting therapeutic target in certain CNS disorders.

Close association of p38 and JNK with plasminogen-dependent upregulation of PAI-1 in rat astrocytes in vitro

As reported previously, stimulation of astrocytes with plasminogen (PLGn) remarkably enhances their production/release of plasminogen activator inhibitor-1 (PAI-1). In addition, both p38 mitogen-activated protein kinase (p38MAPK) and c-Jun N-terminal kinase (JNK) are activated in these astrocytes. However, it remains to be determined whether the MAPK activation is associated with the PAI-1 induction in PLGn-stimulated astrocytes. In the present study, we investigated the relationship between MAPK activity and PAI-1 induction in PLGn-stimulated astrocytes. PLGn stimulation led to definitive phosphorylation of three MAPKs: external signal regulated kinase (ERK), JNK and p38. These results suggest that all of these MAPKs, either alone or in combination, are involved in PAI-1 induction. To verify this association, an inhibition experiment was carried out by using inhibitors specific for each MAPK. The results of the immunoblotting analysis indicated that 20 microM SB203580 (the p38 inhibitor) or SP600125 (the JNK inhibitor) suppressed approximately 85% or 40% of PLGn-inducible PAI-1, respectively. Only 20% inhibition was achieved by pretreatment of astrocytes with 20 microM PD98059 (the inhibitor of MEK1/2, an upstream kinase of ERK). In conclusion, p38 and JNK were shown to be the major MAPKs involved in the signaling cascade leading to PAI-1 induction in astrocytes stimulated with PLGn.

JNK3 is abundant in insulin-secreting cells and protects against cytokine-induced apoptosis

AIMS/HYPOTHESIS

In insulin-secreting cells, activation of the c-Jun NH(2)-terminal kinase (JNK) pathway triggers apoptosis. Whereas JNK1 and JNK2 are ubiquitously produced, JNK3 has been described exclusively in neurons. This report aims to characterise the expression and role in apoptosis of the three JNK isoforms in insulin-secreting cells exposed to cytokines.

METHODS

Sections of human and mouse pancreases were used for immunohistochemistry studies with isoform-specific anti-JNK antibodies. Human, pig, mouse and rat pancreatic islets were isolated by enzymatic digestion and RNA or protein extracts were prepared. RNA and protein levels were determined by quantitative RT-PCR and western blotting respectively, using JNK-isoform-specific primers and isoform-specific antibodies; activities of the three JNK isoforms were determined by kinase assays following quantitative immunoprecipitation/depletion of JNK3. JNK silencing was performed with small interfering RNAs and apoptotic rates were determined in INS-1E cells by scoring cells displaying pycnotic nuclei.

RESULTS

JNK3 and JNK2 mRNAs are the predominant isoforms expressed in human pancreatic islets. JNK3 is nuclear while JNK2 is also cytoplasmic. In INS-1E cells, JNK3 knockdown increases c-Jun levels and caspase-3 cleavage and sensitises cells to cytokine-induced apoptosis; in contrast, JNK1 or JNK2 knockdown is protective.

CONCLUSIONS/INTERPRETATION

In insulin-secreting cells, JNK3 plays an active role in preserving pancreatic beta cell mass from cytokine attacks. The specific localisation of JNK3 in the nucleus, its recruitment by cytokines, and its effects on key transcription factors such as c-Jun, indicate that JNK3 is certainly an important player in the transcriptional control of genes expressed in insulin-secreting cells.

Coagulation factor Xa activates thrombin in ischemic neural tissue

Thrombin is involved in mediating neuronal death in cerebral ischemia. We investigated its so far unknown mode of activation in ischemic neural tissue. We used an in vitro approach to distinguish the role of circulating coagulation factors from endogenous cerebral mechanisms. We modeled ischemic stroke by subjecting rat organotypic hippocampal slice cultures to 30-min oxygen (5%) and glucose (1 mmol/L) deprivation (OGD). Perinuclear activated factor X (FXa) immunoreactivity was observed in CA1 neurons after OGD. Selective FXa inhibition by fondaparinux during and after OGD significantly reduced neuronal death in the CA1 after 48 h. Thrombin enzyme activity was increased in the medium 24 h after OGD and this increase was prevented by fondaparinux suggesting that FXa catalyzes the conversion of prothrombin to thrombin in neural tissue after ischemia in vitro. Treatment with SCH79797, a selective antagonist of the thrombin receptor protease-activated receptor-1 (PAR-1), significantly decreased neuronal cell death indicating that thrombin signals ischemic damage via PAR-1. The c-Jun N-terminal kinase (JNK) pathway plays an important role in excitotoxicity and cerebral ischemia and we observed activation of the JNK substrate, c-Jun in our model. Both the FXa inhibitor, fondaparinux and the PAR-1 antagonist SCH79797, decreased the level of phospho-c-Jun Ser73. These results indicate that FXa activates thrombin in cerebral ischemia, which leads via PAR-1 to the activation of the JNK pathway resulting in neuronal death.

Alpha A-crystallin and alpha B-crystallin, newly identified interaction proteins of protease-activated receptor-2, rescue astrocytes from C2-ceramide- and staurosporine-induced cell death

Protease-activated receptor-2 (PAR-2) is a G protein-coupled receptor activated by trypsin and other trypsin-like serine proteases. The widely expressed PAR-2 is involved in inflammation response but the physiological/pathological roles of PAR-2 in the nervous system are still uncertain. In the present study, we report novel PAR-2 interaction proteins, alphaA-crystallin and alphaB-crystallin. These 20 kDa proteins have been implicated in neurodegenerative diseases like Alexander's disease, Creutzfeldt-Jacob disease, Alzheimer's disease, and Parkinson's disease. Results from yeast two-hybrid assay using the cytoplasmic C-tail of PAR-2 as bait suggested that alphaA-crystallin interacts with PAR-2. We further demonstrate the in vitro and cellular in vivo interaction of C-tail of PAR-2 as well as of full-length PAR-2 with alphaA(alphaB)-crystallins. We use pull-down, co-immunoprecipitation, and co-localization assays. Analysis of alphaA-crystallin deletion mutants showed that amino acids 120-130 and 136-154 of alphaA-crystallin are required for the interaction with PAR-2. Co-immunoprecipitation experiments ruled out an interaction of alphaA(alphaB)-crystallins with PAR-1, PAR-3, and PAR-4. This demonstrates that alphaA(alphaB)-crystallins are PAR-2-specific interaction proteins. Moreover, we investigated the functional role of PAR-2 and alpha-crystallins in astrocytes. Evidence is presented to show that PAR-2 activation and increased expression of alpha-crystallins reduced C2-ceramide- and staurosporine-induced cell death in astrocytes. Thus, both PAR-2 and alpha-crystallins are involved in cytoprotection in astrocytes.

Calpain activation is not required for AIF translocation in PARP-1-dependent cell death (parthanatos)

Apoptosis-inducing factor (AIF) is critical for poly(ADP-ribose) polymerase-1 (PARP-1)-dependent cell death (parthanatos). The molecular mechanism of mitochondrial AIF release to the nucleus remains obscure, although a possible role of calpain I has been suggested. Here we show that calpain is not required for mitochondrial AIF release in parthanatos. Although calpain I cleaved recombinant AIF in a cell-free system in intact cells under conditions where endogenous calpain was activated by either NMDA or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) administration, AIF was not cleaved, and it was released from mitochondria to the nucleus in its 62-kDa uncleaved form. Moreover, NMDA administration under conditions that failed to activate calpain still robustly induced AIF nuclear translocation. Inhibition of calpain with calpastatin or genetic knockout of the regulatory subunit of calpain failed to prevent NMDA- or MNNG-induced AIF nuclear translocation and subsequent cell death, respectively, which was markedly prevented by the PARP-1 inhibitor, 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-iso-quinolinone. Our study clearly shows that calpain activation is not required for AIF release during parthanatos, suggesting that other mechanisms rather than calpain are involved in mitochondrial AIF release in parthanatos.

Protease-activated receptor dependent and independent signaling by kallikreins 1 and 6 in CNS neuron and astroglial cell lines

While protease-activated receptors (PARs) are known to mediate signaling events in CNS, contributing both to normal function and pathogenesis, the endogenous activators of CNS PARs are poorly characterized. In this study, we test the hypothesis that kallikreins (KLKs) represent an important pool of endogenous activators of CNS PARs. Specifically, KLK1 and KLK6 were examined for their ability to evoke intracellular Ca(2+) flux in a PAR-dependent fashion in NSC34 neurons and Neu7 astrocytes. Both KLKs were also examined for their ability to activate mitogen-activated protein kinases (extracellular signal-regulated kinases, C-Jun N-terminal kinases, and p38) and protein kinase B (AKT) intracellular signaling cascades. Cumulatively, these studies show that KLK6, but not KLK1, signals through PARs. KLK6 evoked intracellular Ca(2+) flux was mediated by PAR1 in neurons and both PAR1 and PAR2 in astrocytes. Importantly, both KLK1 and KLK6 altered the activation state of mitogen-activated protein kinases and AKT, suggestive of important roles for each in CNS neuron and glial differentiation, and survival. The cellular specificity of CNS-KLK activity was underscored by observations that both proteases promoted AKT activation in astrocytes, but inhibited such signaling in neurons. PAR1 and bradykinin receptor inhibitors were used to demonstrate that KLK1-mediated activation of extracellular signal-regulated kinases in neurons occurred in a non-PAR, bradykinin 2 (B2) receptor-dependent fashion, while similar signaling by KLK6 was mediated by the combined activation of PAR1 and B2. Cumulatively results indicate KLK6, but not KLK1 is an activator of CNS PARs, and that both KLKs are poised to signal in a B2 receptor-dependent fashion to regulate multiple signal transduction pathways relevant to CNS physiologic function and dysfunction.

Activation of protease-activated receptors in astrocytes evokes a novel neuroprotective pathway through release of chemokines of the growth-regulated oncogene/cytokine-induced neutrophil chemoattractant family

Activation of protease-activated receptors (PARs) is known to exert neuroprotection when low concentrations of the agonist protease thrombin are applied. However, the mechanism of protection is still unclear. Here, we showed that activation of multiple PARs, including PAR-1, PAR-2 and PAR-4, was able to elevate the release of the chemokine cytokine-induced neutrophil chemoattractant (CINC)-3 from rat astrocytes, in addition to evoking CINC-1 secretion. Different molecular mechanisms were identified as being involved in the secretion of CINC-1 and CINC-3, upon activation of different PARs. Importantly, we found that both CINC-1 and CINC-3 could signal to rat cortical neurons. Both chemokines acted via CXCR2 to prevent C2-ceramide-induced cytochrome c release from mitochondria. Consequently CINC-1 and CINC-3 protected neurons from apoptosis. We further revealed that conditioned media obtained from PAR-activated astrocytes similarly protected cortical neurons against C2-ceramide-induced cell death. The neuroprotection was considerably suppressed by a CXCR2 antagonist. CXCR2 is the cognate receptor for CINC. Therefore, our findings demonstrate that PAR-activated astrocytes are able to protect neurons against neurodegeneration and cell death via regulation of the secretion of chemokines CINC-1 and CINC-3. These data indicate a previously unknown mechanism for astrocyte-mediated neuroprotection achieved by PAR activation.

Protease-activated receptors in the brain: receptor expression, activation, and functions in neurodegeneration and neuroprotection

Protease-activated receptors (PARs) are G protein-coupled receptors that regulate the cellular response to extracellular serine proteases, like thrombin, trypsin, and tryptase. The PAR family consists of four members: PAR-1, -3, and -4 as thrombin receptors and PAR-2 as the trypsin/tryptase receptor, which are abundantly expressed in the brain throughout development. Recent evidence has supported the direct involvement of PARs in brain development and function. The expression of PARs in the brain is differentially upregulated or downregulated under pathological conditions in neurodegenerative disorders, like Parkinson's disease, Alzheimer's disease, multiple sclerosis, stroke, and human immunodeficiency virus-associated dementia. Activation of PARs mediates cell death or cell survival in the brain, depending on the amplitude and the duration of agonist stimulation. Interference or potentiation of PAR activation is beneficial in animal models of neurodegenerative diseases. Therefore, PARs mediate either neurodegeneration or neuroprotection in neurodegenerative diseases and represent attractive therapeutic targets for treatment of brain injuries. Here, we review the abnormal expression of PARs in the brain under pathological conditions, the functions of PARs in neurodegenerative disorders, and the molecular mechanisms involved.

Signal transduction for formation/release of interleukin-8 caused by a PAR2-activating peptide in human lung epithelial cells

Proteinase-activated receptor-2 (PAR2) plays a dual role in the respiratory system, being pro- and anti-inflammatory. In human lung epithelial cells (A549), PAR2 activation causes release of interleukin-8 (IL-8) in addition to prostaglandin E(2) (PGE(2)). In the present study, we thus investigated PAR2-triggered signal transduction pathways causing IL-8 formation in A549 cells. SLIGRL-NH(2), a PAR2-activating peptide, but not LSIGRL-NH(2), a scrambled peptide, elicited release of IL-8 from A549 cells for 18 h, as measured by the ELISA method, an effect being suppressed by inhibitors of MEK, JNK, EGF receptor-tyrosine kinase (EGFR-TK), Src, pan-tyrosine kinases and protein kinase C, but not p38 MAP kinase or cyclooxygenase. SLIGRL-NH(2) also up-regulated IL-8 at protein and mRNA levels, as determined by Western blotting and RT-PCR, respectively. The PAR2-triggered up-regulation of IL-8 protein and mRNA was blocked by an inhibitor of MEK, but not clearly by inhibitors of JNK and EGFR-TK. SLIGRL-NH(2) actually phosphorylated JNK as well as ERK, the JNK activation being resistant to inhibitors of Src, pan-tyrosine kinases, protein kinase C and EGFR-TK. Our data suggest that PAR2-triggered IL-8 formation involves transcriptional up-regulation of IL-8 via the MEK-ERK pathway, while the JNK and EGF receptor pathways might rather contribute to a post-transcriptional process for the release of IL-8.

p24A, a type I transmembrane protein, controls ARF1-dependent resensitization of protease-activated receptor-2 by influence on receptor trafficking

Protease-activated receptor-2 (PAR-2), the second member of the G protein-coupled PAR family, is irreversibly activated by trypsin or tryptase and then targeted to lysosomes for degradation. Intracellular presynthesized receptors stored at the Golgi apparatus repopulate the cell surface after trypsin stimulation, thereby leading to rapid resensitization to trypsin signaling. However, the molecular mechanisms of the exocytic trafficking of PAR-2 from the Golgi apparatus to the plasma membrane remain largely unclear. Here we show that p24A, a type I transmembrane protein, which is a crucial constituent of the Golgi apparatus, associates with PAR-2 at the Golgi apparatus. The protein interaction occurs between the N-terminal region of p24A (residues 1-105; p24A-GL (GOLD domain with a small linker)) and the second extracellular loop of PAR-2. After receptor activation, PAR-2 dissociates from p24A. Importantly, we found that ADP-ribosylation factor 1 regulated the dissociation process and initiated PAR-2 trafficking to the plasma membrane. Conversely, overexpression of the fragment p24A-GL, but not other mutants containing the functional coiled-coil domain of p24A, arrested PAR-2 at the Golgi apparatus and inhibited receptor trafficking to the plasma membrane, which consequently prevented resensitization of PAR-2. These findings identify a new function of p24A as a regulator of signal-dependent trafficking that regulates the life cycle of PAR-2, Thus, we reveal a new molecular mechanism underlying resensitization of PAR-2.

The role of calcium in protease-activated receptor-induced secretion of chemokine GRO/CINC-1 in rat brain astrocytes

Our recent data showed that activation of protease-activated receptor (PAR)-1 and PAR-2 in rat astrocytes not only evokes calcium signaling, but also regulates the release of the chemokine growth-regulated oncogene/cytokine-induced neutrophil chemoattractant-1 (GRO/CINC-1), a counterpart of the human GRO. This chemokine provides a feedback to protect astrocytes from toxic insults. Activated PAR-1 and PAR-2 were strong stimuli to induce the release of GRO/CINC-1. The effect was comparable to that induced by TNF-alpha. However, the role of calcium in the PAR-induced GRO/CINC-1 secretion remains unknown. Here, we found that the pharmacological blockade of either calcium release from the intracellular stores, or influx from the extracellular space, increased PAR-1- and PAR-2-induced GRO/CINC-1 secretion. Under calcium-free conditions, the basal mRNA level of GRO/CINC-1 was clearly increased. Further studies revealed that the intracellular GRO/CINC-1 protein level was slightly increased by treatment with thrombin or TRag in calcium-free conditions. However, the amount of protein synthesized was largely reduced in the absence of extracellular calcium as compared to that under normal calcium conditions. Importantly, we found that the intracellularly formed GRO/CINC-1 was not secreted into the cell culture supernatant under calcium-free conditions. These data suggest a dual role of calcium. On the one side, an increase in cytosolic calcium negatively regulates PAR-induced GRO/CINC-1 gene expression in rat astrocytes, but on the other side, the basal level of calcium is the pre-requisite for GRO/CINC-1 protein synthesis and secretion.

Protease-activated receptor signaling: new roles and regulatory mechanisms

PURPOSE OF REVIEW

Protease-activated receptors are G-protein-coupled receptors that transmit cellular responses to coagulant proteases in a variety of cell types in the vasculature and other tissues. Several other proteases can activate protease-activated receptors in vitro and may affect their function in vivo. While a role for these receptors in hemostasis and thrombosis has been established, their functions in inflammatory and other responses have yet to be fully elucidated. In addition, the mechanisms responsible for protease and cell type-specific signaling mediated by these receptors are largely undefined. Here, we highlight recent advances in understanding the roles and regulation of protease-activated receptor signaling.

RECENT FINDINGS

Recent studies have increased our knowledge of the function of protease-activated receptor signaling in platelets and its contribution to thrombosis. In other cell types, recent work has revealed new connections between these receptors and signaling effectors important for vascular development and inflammatory responses. Other studies have advanced our understanding of protease and cell type-specific responses as well as novel regulatory mechanisms for control of protease-activated receptor signaling.

SUMMARY

Thus, elucidating the signaling and regulatory mechanisms of protease-activated receptors in various tissues and cell types is important for understanding their biological function as well as for designing therapeutic strategies to control their function.

The emergence of proteinase-activated receptor-2 as a novel target for the treatment of inflammation-related CNS disorders

The signalling molecules that are involved in inflammatory pathways are now thought to play a part in many disorders of the central nervous system (CNS). In common with peripheral chronic inflammatory diseases such a rheumatoid arthritis and ulcerative colitis, evidence now exists for the involvement of inflammatory cytokines, for example tumour necrosis factor (TNF) and interleukins (IL), in neurological disorders. A common factor observed with the up-regulation of these cytokines in peripheral inflammatory diseases, is the increased expression of the proteinase-activated receptor (PAR) subtype PAR-2. Indeed, recent evidence suggests that targeting PAR-2 helps reduce joint swelling observed in animal models of arthritis. So could targeting this receptor prove to be useful in treating those CNS disorders where inflammatory processes are thought to play an intrinsic role? The aim of this review is to summarize the emerging data regarding the role of PAR-2 in neuroinflammation and ischaemic injury and discuss its potential as an exciting new target for the prevention and/or treatment of CNS disorders.