JNK-binding Domain Research Articles

MO049FUNCTIONAL IMPORTANCE OF MAPKBP1 PROTEIN DOMAINS IN NEPHRONOPHTHISIS

Abstract Background and Aims Nephronophthisis is an autosomal-recessive kidney disease that accounts for a significant proportion of end-stage renal disease (ESRD) in childhood, adolescence and early adulthood. Biallelic pathogenic variants in MAPKBP1, encoding the c-Jun N-terminale kinase (JNK)-binding protein 1, are associated with development of Nephronophthisis and subsequent chronic kidney disease (CKD) (Macia et al, AJHG, 2017). We recently characterized MAPKBP1 as microtubule-associated protein that is able to localize to centrioles and the base of primary cilia depending on dimerization via its C-terminal coiled-coil domain (Schönauer et al, Kidney Int, 2020). However, the physiological function of its N-terminal WD40 and intermediate JNK-binding domain is still poorly understood. By in vitro comparison of artificial domain deletions with known and novel patient variants, we aim at pinpointing functional consequences of pathogenic MAPKBP1 in cilia and cell cycle control. Method N-terminally GFP-tagged MAPKBP1 constructs with either full-domain deletions or patient-derived variants were expressed in non-ciliated HeLa and ciliated H69 cells for fluorescence microscopy studies. Furthermore, RNA-seq analysis using primary patient cells was conducted to investigate differentially regulated molecular pathways compared to healthy control individuals. Results Immunofluorescence microscopy revealed inappropriate intracellular localization upon single or combined deletion of any MAPKBP1 protein domain. Compared to wild type, all deletion variants showed reduced intensity at the centrosome and ciliary base. Despite preserved dimerization ability, loss of the intermediate JNK-binding domain (JBD) most effectively abolished centrosomal or ciliary targeting, whereas loss of the N-terminal WD40-domain induced strongest mitotic aberrations. Unlike wild type, both, artificial and patient-derived truncating variants were able to enter the nucleus. RNA-seq analysis using primary patient fibroblasts with varying C-terminal truncations will allow important insights into common gene expression profiles unveiling consequences of aberrant intracellular trafficking. Conclusion In the present work, we demonstrate that all protein domains are indispensable for appropriate MAPKBP1 intracellular localization and function. Most of clinically reported patient variants exhibiting C-terminal truncation of varying lengths resulted in comparable intracellular behavior in presence of an intact N-terminal WD40 domain. Surprisingly, deletion of the JNK-binding domain alone aggravated functional disturbances hinting at a prominent regulatory role of this protein part interdepending with dimerization. Further insights into domain-specific functions will explain molecular disease mechanisms of MAPKBP1.

JLP-JNK signaling protects cancer cells from reactive oxygen species-induced cell death

Oxidative stress, which can be caused by an overproduction of reactive oxygen species (ROS), often leads to cell death. In recent years, c-Jun NH2-terminal kinase (JNK)-associated leucine zipper protein (JLP, also known as SPAG9 or JIP4), a scaffold protein for JNK mitogen-activated protein kinase (MAPK) signaling pathways, was found to serve as a novel biomarker for cancer. However, although JNK MAPK pathways are reported to be activated in response to various stimuli, including oxidative stress, whether JLP is involved in ROS signaling remains unknown. In this study, we examined the role of JLP in hydrogen peroxide (H2O2)-induced cancer cell death, and found that JLP knockdown (KD) cells exhibit a substantially enhanced cell death response, along with increased intracellular ROS levels. This is the first demonstration of a protective role for JLP in response to cell-death stimulation. We also found that the H2O2-induced JNK activation was attenuated in JLP KD cancer cells. The decreases in cell viability and JNK activation in the JLP KD cells were almost completely reversed by expressing wild-type JLP, but not a mutant JLP lacking the JNK-binding domain. These data collectively suggest that the JLP-JNK signaling pathway counteracts ROS-induced cancer cell death.

The JNK1/JNK3 interactome – Contributions by the JNK3 unique N-terminus and JNK common docking site residues

The c-Jun N-terminal Kinases (JNKs) play important roles in cell responses to stress or growth factor stimulation. The JNK1α1 isoform shares >90% identity with a predominantly neuronal JNK3α1 isoform, but JNK3α1 also includes a distinctive 38 amino acid N-terminal sequence. To address the outstanding question of the potential for these JNK isoforms to have different binding partners that mediate different biological actions, the work presented here refined the yeast two-hybrid approach to identify and categorize binding partners for JNK1α1 and JNK3α1. Specifically, site-directed mutagenesis of the JNK1α1 common docking (CD) domain that mediates typical JNK-binding domain (JBD)-dependent interactions, truncation of the distinctive JNK3 N-terminal domain (i.e. ΔN JNK3α1), and interaction evaluation in the yeast two-hybrid system defined the interacting partners as either JNK1-specific interactors (ATF7, FUS, KCNE4, PIAS1, SHANK1, TKT), typical JBD-dependent interactors shared by JNK1α1 and JNK3α1 (AKAP6, BMPR2, EEF1A1, GFAP, GRIP2, GTF2F1, HDAC2, MAP1B, MYO9B, PTPN2, RABGAP1, RUSC2, SUMO1, SYPL1, TOPBP1, ZNF668), or JNK3-specific partners (ATXN1, NNAT, PTGDS) dependent on interaction with the JNK3 N-terminal extension. The interacting partners ATF7, AKAP6, and ATXN1 were explored further as representatives of these different classes. Two potential JBDs were identified in ATF7 as important for its interaction with JNK1α1, but additionally an interaction between ATF7 and ΔN JNK3α1 was shown to be JBD-dependent, suggesting that the JNK3α1 N-terminus prevents interaction with some proteins. For the shared partner AKAP6, one of the multiple potential JBDs predicted by sequence analysis was important for the AKAP6-JNK interaction in the yeast screening system as well as in mammalian cells. Finally, the ATXN1-JNK3α1 interaction was dependent on the JNK3α1 N-terminus in a mammalian cell context. These studies therefore highlight a diversity of potential JNK-interacting partners with both JBD-dependent as well as JBD-independent modes of interaction.

JNK-Interacting Protein 3 Mediates the Retrograde Transport of Activated c-Jun N-Terminal Kinase and Lysosomes

Retrograde axonal transport requires an intricate interaction between the dynein motor and its cargo. What mediates this interaction is largely unknown. Using forward genetics and a novel in vivo imaging approach, we identified JNK-interacting protein 3 (Jip3) as a direct mediator of dynein-based retrograde transport of activated (phosphorylated) c-Jun N-terminal Kinase (JNK) and lysosomes. Zebrafish jip3 mutants (jip3nl7) displayed large axon terminal swellings that contained high levels of activated JNK and lysosomes, but not other retrograde cargos such as late endosomes and autophagosomes. Using in vivo analysis of axonal transport, we demonstrated that the terminal accumulations of activated JNK and lysosomes were due to a decreased frequency of retrograde movement of these cargos in jip3nl7, whereas anterograde transport was largely unaffected. Through rescue experiments with Jip3 engineered to lack the JNK binding domain and exogenous expression of constitutively active JNK, we further showed that loss of Jip3–JNK interaction underlies deficits in pJNK retrograde transport, which subsequently caused axon terminal swellings but not lysosome accumulation. Lysosome accumulation, rather, resulted from loss of lysosome association with dynein light intermediate chain (dynein accessory protein) in jip3nl7, as demonstrated by our co-transport analyses. Thus, our results demonstrate that Jip3 is necessary for the retrograde transport of two distinct cargos, active JNK and lysosomes. Furthermore, our data provide strong evidence that Jip3 in fact serves as an adapter protein linking these cargos to dynein.

Radiation-Induced c-Jun Activation Depends on MEK1-ERK1/2 Signaling Pathway in Microglial Cells

Radiation-induced normal brain injury is associated with acute and/or chronic inflammatory responses, and has been a major concern in radiotherapy. Recent studies suggest that microglial activation is a potential contributor to chronic inflammatory responses following irradiation; however, the molecular mechanism underlying the response of microglia to radiation is poorly understood. c-Jun, a component of AP-1 transcription factors, potentially regulates neural cell death and neuroinflammation. We observed a rapid increase in phosphorylation of N-terminal c-Jun (on serine 63 and 73) and MAPK kinases ERK1/2, but not JNKs, in irradiated murine microglial BV2 cells. Radiation-induced c-Jun phosphorylation is dependent on the canonical MEK-ERK signaling pathway and required for both ERK1 and ERK2 function. ERK1/2 directly interact with c-Jun in vitro and in cells; meanwhile, the JNK binding domain on c-Jun is not required for its interaction with ERK kinases. Radiation-induced reactive oxygen species (ROS) potentially contribute to c-Jun phosphorylation through activating the ERK pathway. Radiation stimulates c-Jun transcriptional activity and upregulates c-Jun-regulated proinflammatory genes, such as tumor necrosis factor-α, interleukin-1β, and cyclooxygenase-2. Pharmacologic blockade of the ERK signaling pathway interferes with c-Jun activity and inhibits radiation-stimulated expression of c-Jun target genes. Overall, our study reveals that the MEK-ERK1/2 signaling pathway, but not the JNK pathway, contributes to the c-Jun-dependent microglial inflammatory response following irradiation.

Docking interactions of the JNK scaffold protein WDR62

JNK (c-Jun N-terminal kinase) is part of a MAPK (mitogen-activated protein kinase) signalling cascade. Scaffold proteins simultaneously associate with various components of the MAPK signalling pathway and play a crucial role in signal transmission and MAPK regulation. WDR62 (WD repeat domain 62) is a JNK scaffold protein. Recessive mutations within WDR62 result in severe cerebral cortical malformation. In the present study we demonstrate the association of WDR62 with endogenous and overexpressed proteins of both JNK2 and the JNK2-activating kinase MKK7 (MAPK kinase 7). Association of WDR62 with JNK2 and MKK7 occurs via direct protein–protein interactions. We mapped the docking domain of WDR62 responsible for the association with JNK. WDR62 interacts with all JNK isoforms through a D domain motif located at the C-terminus. A WDR62 mutant lacking the putative JNK-binding domain fails to activate and recruit JNK to cellular granules. Furthermore, a synthetic peptide composed of the WDR62 docking domain inhibits JNK2 activity in vitro. WDR62 association with JNK2 requires both the JNK CD and ED domains, and the binding requisite is distinct from that of the previously described JNK2 association with JIP1 (JNK-interacting protein 1). Next, we characterized the association between WDR62 and MKK7. WDR62 associates directly with the MKK7β1 isoform independently of JNK binding, but fails to interact with MKK7α1. Furthermore, MKK7β1 recruits a protein phosphatase that dephosphorylates WDR62. Interestingly, a premature termination mutation in WDR62 that results in severe brain developmental defects does not abrogate WDR62 association with either JNK or MKK7. Therefore such mutations represent a loss of WDR62 function independent of JNK signalling.

GSTpi modulates JNK activity through a direct interaction with JNK substrate, ATF2

Human GSTpi, an important detoxification enzyme, has been shown to modulate the activity of JNKs by inhibiting apoptosis and by causing cell proliferation and tumor growth. In this work, we describe a detailed analysis of the interaction in vitro between GSTpi and JNK isoforms (both in their inactive and active, phosphorylated forms). The ability of active JNK1 or JNK2 to phosphorylate their substrate, ATF2, is inhibited by two naturally occurring GSTpi haplotypes (Ile105/Ala114, WT or haplotype A, and Val105/Val114, haplotype C). Haplotype C of GSTpi is a more potent inhibitor of JNK activity than haplotype A, yielding 75-80% and 25-45% inhibition, respectively. We show that GSTpi is not a substrate of JNK, as was earlier suggested by others. Through binding studies, we demonstrate that the interaction between GSTpi and phosphorylated, active JNKs is isoform specific, with JNK1 being the preferred isoform. In contrast, GSTpi does not interact with unphosphorylated, inactive JNKs unless a JNK substrate, ATF2, is present. We also demonstrate, for the first time, a direct interaction: between GSTpi and ATF2. GSTpi binds with similar affinity to active JNK + ATF2 and to ATF2 alone. Direct binding experiments between ATF2 and GSTpi, either alone or in the presence of glutathione analogs or phosphorylated ATF2, indicate that the xenobiotic portion of the GSTpi active site and the JNK binding domain of ATF2 are involved in this interaction. Competition between GSTpi and active JNK for the substrate ATF2 may be responsible for the inhibition of JNK catalysis by GSTpi.

Role of plasma membrane localization of the scaffold protein JSAP1 during differentiation of cerebellar granule cell precursors

We previously reported that the scaffold protein c-Jun NH₂-terminal kinase (JNK)/stress-activated protein kinase-associated protein 1 (JSAP1) functions in cerebellar granule cell precursors (GCPs) to promote their cell-cycle exit and differentiation. In this study, we used immunocytochemistry to examine the subcellular distribution of JSAP1 in proliferating cultured GCPs. We found that when stimulated with fibroblast growth factor-2 (FGF-2), a factor that promotes GCP differentiation through JNK and extracellular signal-regulated kinase (ERK) signaling, JSAP1 translocated to the plasma membrane and colocalized with activated JNK and ERK. In transfected cells expressing a constitutively activated FGF receptor (FGFR), JSAP1 and the activated FGFR colocalized at the plasma membrane with not only activated but also unphosphorylated and inactive JNK and ERK. These colocalizations did not occur when a mutant JSAP1 lacking the JNK-binding domain was substituted for wild-type JSAP1. Biochemical analyses of transfected cells showed that activated FGFR increased JSAP1's affinity for JNK and ERK and that JSAP1 enhanced FGFR-induced JNK and ERK activation. Collectively, these results suggest that when stimulated by FGFR, JSAP1 translocates to the plasma membrane, where it recruits JNK and ERK and facilitates their activation, leading to the differentiation of cerebellar GCPs.

Small peptide inhibitor of JNKs protects against MPTP-induced nigral dopaminergic injury via inhibiting the JNK-signaling pathway

Increasing evidence suggests that apoptosis may be the mechanism underlying cell death in selective loss of nigral dopaminergic neurons in Parkinson's disease (PD). Previous studies strongly suggested that c-Jun N-terminal kinase (JNK) signaling pathway has a critical role in the animal model with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD. In this study, we report the inhibitory effect of a peptide designated as Tat-JBD on JNKs activation. The sequence of Tat is corresponding to the cell-membrane transduction domain of human immunodeficiency virus-type 1 (HIV-1) and the sequence of an 11-amino acid peptide is corresponding to the residues of JNK-binding domain (JBD) on JNK-interacting protein-1 (JIP-1). Tat-JBD is confirmed to perturb the assembly of JIP-1-JNKs complex, inhibit the activation of JNKs induced by MPTP and consequently diminish the phosphorylation of c-Jun. It also inhibits the phosphorylation of Bcl-2 and the releasing of Bax from Bcl-2/Bax dimmers, sequentially attenuates the translocation of Bax to mitochondria, the release of cytochrome c, the activation of caspase3 and the hydrolyzation of poly-ADP-ribose-polymerase. The death of dopaminergic neurons and the loss of dopaminergic axon in the striatum were significantly suppressed by infusion of the peptide Tat-JBD in MPTP-treated mice. Our findings imply that Tat-JBD offers neuroprotection against MPTP injury via inhibiting the JNK-signaling pathway, and may provide a promising therapeutic approach for PD.

Excitotoxic Cell Death Mediated by Ca2+-Permeable Ampa Receptors is Coupled to the JNK Signalling Pathway

Event Abstract Back to Event Excitotoxic Cell Death Mediated by Ca2+-Permeable Ampa Receptors is Coupled to the JNK Signalling Pathway Marta Vieira1*, J. Fernandes1, C. B. Duarte1, 2, R. Huganir3, J. Ham4, A. L. Carvalho1, 2 and A. Santos1, 5 1 University of Coimbra, Center for Neuroscience and Cell Biology, Portugal 2 University of Coimbra, Department of Zoology, Portugal 3 Jonhs Hopkins University School of Medicine, Department of Neuroscience, Howard Hughes Medical Institute, United States 4 University College London, Institute of Child Health, United Kingdom 5 University of Coimbra, Faculty of Pharmacy, Portugal In cerebral ischemia, excitotoxic cell death is due to overactivation of glutamate receptors following an excessive glutamate release and impairement in glutamate uptake. In this work, we investigated the specific contribution of Ca2+-permeable a-amino-3-hydroxy-5-methyl-4-isoxazole propionate receptors (AMPARs) to excitotoxic cell death, using a HEK293 cell line constitutively expressing GluR4flip subunits of AMPARs (HEK- GluR4), and the excitotoxic signaling pathways induced by overactivation of this specific subtype of AMPARs. We hypothesized that c-Jun N-terminal kinase (JNK) could take part in this excitotoxic mechanism, since JNK is a mitogen-activated protein kinase (MAPK) activated in stress conditions, and was shown to be involved in several neuronal cell death paradigms. Stimulation of HEK-GluR4 cells with glutamate plus cyclothiazide for 1h decreased cell viability by 60%, as determined by MTT assay. The excitotoxic stimulation induced a biphasic JNK activation in a Ca2+-dependent manner. To determine the contribution of the JNK pathway to HEK-GluR4 excitotoxic death, cells were transduced with the JNK binding domain (JBD), which is a selective strategy to inhibit JNK signalling, or with a dominant negative form of c-Jun that inhibits the functional activity of this transcription factor. Both strategies conferred protection against Ca2+-permeable AMPAR-mediated cell death. Excitotoxic stimulation with glutamate increased c-Jun phosphorylation, and enhanced the JNK- dependent GluR4 phosphorylation. The GluR4 subunit is a newly characterized JNK substrate, which was shown to be specifically phosphorylated on T855 under physiological neuronal activity. The relevance of GluR4 T855 phosphorylation to the excitotoxic cell death mediated by Ca2+-permeable AMPARs is currently under evaluation using GluR4 subunits mutated at this site. Co-immunoprecipitation studies showed that GluR4 interacts with the JNK scaffold protein JIP-1, in HEK-GluR4 cells overexpressing this protein. Taken together, our results show that excitotoxicity mediated by Ca2+-permeable AMPARs is associated to the Ca2+-dependent activation of a cytotoxic JNK pathway. In vivo JIP-1 may be the molecular link between GluR4-containing AMPARs and the JNK signaling pathway.Supported by Biogen Idec Conference: 11th Meeting of the Portuguese Society for Neuroscience, Braga, Portugal, 4 Jun - 6 Jun, 2009. Presentation Type: Poster Presentation Topic: Neurodegenerative Disorders Citation: Vieira M, Fernandes J, Duarte CB, Huganir R, Ham J, Carvalho AL and Santos A (2009). Excitotoxic Cell Death Mediated by Ca2+-Permeable Ampa Receptors is Coupled to the JNK Signalling Pathway. Front. Neurosci. Conference Abstract: 11th Meeting of the Portuguese Society for Neuroscience. doi: 10.3389/conf.neuro.01.2009.11.081 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 07 Aug 2009; Published Online: 07 Aug 2009. * Correspondence: Marta Vieira, University of Coimbra, Center for Neuroscience and Cell Biology, Alicante, Portugal, marta.vieira@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Marta Vieira J. Fernandes C. B Duarte R. Huganir J. Ham A. L Carvalho A. Santos Google Marta Vieira J. Fernandes C. B Duarte R. Huganir J. Ham A. L Carvalho A. Santos Google Scholar Marta Vieira J. Fernandes C. B Duarte R. Huganir J. Ham A. L Carvalho A. Santos PubMed Marta Vieira J. Fernandes C. B Duarte R. Huganir J. Ham A. L Carvalho A. Santos Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The scaffold protein JSAP1 regulates proliferation and differentiation of cerebellar granule cell precursors by modulating JNK signaling

Cerebellar granule cell precursors (GCPs) proliferate in the outer part of the external granular layer (EGL). They begin their differentiation by exiting the cell cycle and migrating into the inner part of the EGL. Here we report that JSAP1, a scaffold protein for JNK signaling pathways, is expressed predominantly in the post-mitotic GCPs of the inner EGL. JSAP1 knockdown or treatment with a JNK inhibitor enhances the proliferation of cultured GCPs, but the overexpression of wild-type JSAP1 leads to increased proportions of p27 Kip1- and NeuN-positive cells, even with saturating concentrations of Sonic hedgehog (Shh), a potent GCP mitogen. However, these differentiation-promoting effects on GCPs are attenuated significantly in cells overexpressing a mutant JSAP1 that lacks the JNK-binding domain. Together, these data suggest that JSAP1 antagonizes the mitogenic effect of Shh on GCPs and promotes their exit from the cell cycle and differentiation, by modulating JNK activity.

Glucose and leptin induce apoptosis in human β‐ cells and impair glucose‐stimulated insulin secretion through activation of c‐Jun N‐terminal kinases

c-Jun N-terminal kinases (SAPK/JNKs) are activated by inflammatory cytokines, and JNK signaling is involved in insulin resistance and beta-cell secretory function and survival. Chronic high glucose concentrations and leptin induce interleukin-1beta (IL-1beta) secretion from pancreatic islets, an event that is possibly causal in promoting beta-cell dysfunction and death. The present study provides evidence that chronically elevated concentrations of leptin and glucose induce beta-cell apoptosis through activation of the JNK pathway in human islets and in insulinoma (INS 832/13) cells. JNK inhibition by the dominant inhibitor JNK-binding domain of IB1/JIP-1 (JNKi) reduced JNK activity and apoptosis induced by leptin and glucose. Exposure of human islets to leptin and high glucose concentrations leads to a decrease of glucose-induced insulin secretion, which was partly restored by JNKi. We detected an interplay between the JNK cascade and the caspase 1/IL-1beta-converting enzyme in human islets. The caspase 1 gene, which contains a potential activating protein-1 binding site, was up-regulated in pancreatic sections and in isolated islets from type 2 diabetic patients. Similarly, cultured human islets exposed to high glucose- and leptin-induced caspase 1 and JNK inhibition prevented this up-regulation. Therefore, JNK inhibition may protect beta-cells from the deleterious effects of high glucose and leptin in diabetes.

Rapid and bi-directional regulation of AMPA receptor phosphorylation and trafficking by JNK

Jun N-terminal kinases (JNKs) are implicated in various neuropathological conditions. However, physiological roles for JNKs in neurons remain largely unknown, despite the high expression level of JNKs in brain. Here, using bioinformatic and biochemical approaches, we identify the AMPA receptor GluR2L and GluR4 subunits as novel physiological JNK substrates in vitro, in heterologous cells and in neurons. Consistent with this finding, GluR2L and GluR4 associate with specific JNK signaling components in the brain. Moreover, the modulation of the novel JNK sites in GluR2L and GluR4 is dynamic and bi-directional, such that phosphorylation and de-phosphorylation are triggered within minutes following decreases and increases in neuronal activity, respectively. Using live-imaging techniques to address the functional consequence of these activity-dependent changes we demonstrate that the novel JNK site in GluR2L controls reinsertion of internalized GluR2L back to the cell surface following NMDA treatment, without affecting basal GluR2L trafficking. Taken together, our results demonstrate that JNK directly regulates AMPA-R trafficking following changes in neuronal activity in a rapid and bi-directional manner.

JNK phosphorylates synaptotagmin-4 and enhances Ca2+-evoked release

Ca2+ influx induced by membrane depolarization triggers the exocytosis of secretory vesicles in various cell types such as endocrine cells and neurons. Peptidyl growth factors enhance Ca2+-evoked release, an effect that may underlie important adaptive responses such as the long-term potentiation of synaptic transmission induced by growth factors. Here, we show that activation of the c-Jun N-terminal kinase (JNK) plays an essential role in nerve growth factor (NGF) enhancement of Ca2+-evoked release in PC12 neuroendocrine cells. Moreover, JNK associated with phosphorylated synaptotagmin-4 (Syt 4), a key mediator of NGF enhancement of Ca2+-evoked release in this system. NGF treatment led to phosphorylation of endogenous Syt 4 at Ser135 and translocation of Syt 4 from immature to mature secretory vesicles in a JNK-dependent manner. Furthermore, mutation of Ser135 abrogated enhancement of Ca2+-evoked release by Syt 4. These results provide a molecular basis for the effect of growth factors on Ca2+-mediated secretion.

Hsp70 suppresses apoptosis in sympathetic neurones by preventing the activation of c‐Jun

The anti-apoptotic effects of heat-shock protein (Hsp70) were assessed in SCG neurones following nerve growth factor (NGF) withdrawal. The results showed that the virally mediated expression of Hsp70 mirrored the effects of the c-Jun-N-terminal kinase (JNK) binding domain (JBD) of JNK interacting protein (an inhibitor of JNK and c-Jun activation) and suppressed the phosphorylation of c-Jun. Preventing c-Jun transcriptional activity subsequently led to reduced cytochrome c release and prevented caspase activation as indicated by a decrease in poly (ADP-ribose) polymerase-1 (PARP) cleavage. Together, these results show that Hsp70 is a highly effective inhibitor of apoptosis in sympathetic neurones and that it mediates this effect primarily by suppressing c-Jun transcriptional signalling.

Role of the JNK pathway in NMDA-mediated excitotoxicity of cortical neurons

Excitotoxic insults induce c-Jun N-terminal kinase (JNK) activation, which leads to neuronal death and contributes to many neurological conditions such as cerebral ischemia and neurodegenerative disorders. The action of JNK can be inhibited by the D-retro-inverso form of JNK inhibitor peptide (D-JNKI1), which totally prevents death induced by N-methyl-D-aspartate (NMDA) in vitro and strongly protects against different in vivo paradigms of excitotoxicity. To obtain optimal neuroprotection, it is imperative to elucidate the prosurvival action of D-JNKI1 and the death pathways that it inhibits. In cortical neuronal cultures, we first investigate the pathways by which NMDA induces JNK activation and show a rapid and selective phosphorylation of mitogen-activated protein kinase kinase 7 (MKK7), whereas the only other known JNK activator, mitogen-activated protein kinase kinase 4 (MKK4), was unaffected. We then analyze the action of D-JNKI1 on four JNK targets containing a JNK-binding domain: MAPK-activating death domain-containing protein/differentially expressed in normal and neoplastic cells (MADD/DENN), MKK7, MKK4 and JNK-interacting protein-1 (IB1/JIP-1).

Extracellular signal-regulated kinase is essential for interleukin-1-induced and nuclear factor κB-mediated gene expression in insulin-producing INS-1E cells

The beta cell destruction and insulin deficiency that characterises type 1 diabetes mellitus is partially mediated by cytokines, such as IL-1beta, and by nitric oxide (NO)-dependent and -independent effector mechanisms. IL-1beta activates mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase (ERK), p38 and c-Jun NH2-terminal kinase (JNK), and the nuclear factor kappa B (NFkappaB) pathway. Both pathways are required for expression of the gene encoding inducible nitric oxide synthase (iNOS) and for IL-1beta-mediated beta cell death. The molecular mechanisms by which these two pathways regulate beta cell Nos2 expression are currently unknown. Therefore, the aim of this study was to clarify the putative crosstalk between MAPK and NFkappaB activation in beta cells. The MAPKs ERK, p38 and JNK were inhibited by SB203580, PD98059 or Tat-JNK binding domain or by cells overexpressing the JNK binding domain. The effects of MAPK inhibition on IL-1beta-induced iNOS production and kappa B inhibitor protein (IkappaB) degradation were examined by western blotting. NFkappaB DNA binding was investigated by electrophoretic mobility shift assay, while NFkappaB-induced gene transcription was evaluated by gene reporter assays. Inhibition of the MAPKs did not affect IkappaB degradation or NFkappaB DNA binding. However, inhibition of ERK reduced NFkappaB-mediated Nos2 expression; serine 276 phosphorylation of the p65 unit of the NFkappaB complex seemed critical, as evaluated by amino acid mutation analysis. ERK activity is required for NFkappaB-mediated transcription of Nos2 in insulin-producing INS-1E cells, indicating that ERK regulates Nos2 expression by increasing the transactivating capacity of NFkappaB. This may involve phosphorylation of Ser276 on p65 by an as yet unidentified kinase.

JSAP1/JIP3 Cooperates with Focal Adhesion Kinase to Regulate c-Jun N-terminal Kinase and Cell Migration

c-Jun N-terminal kinase (JNK)/stress-activated protein kinase-associated protein 1 (JSAP1) (also termed JNK-interacting protein 3; JIP3) is a member of a family of scaffold factors for the mitogen-activated protein kinase (MAPK) cascades, and it also forms a complex with focal adhesion kinase (FAK). Here we demonstrate that JSAP1 serves as a cooperative scaffold for activation of JNK and regulation of cell migration in response to fibronectin (FN) stimulation. JSAP1 mediated an association between FAK and JNK, which was induced by either co-expression of Src or attachment of cells to FN. Complex formation of FAK with JSAP1 and p130 Crk-associated substrate (p130(Cas)) resulted in augmentation of FAK activity and phosphorylation of both JSAP1 and p130(Cas), which required p130(Cas) hyperphosphorylation and was abolished by inhibition of Src. JNK activation by FN was enhanced by JSAP1, which was suppressed by disrupting the FAK/p130(Cas) pathway by expression of a dominant-negative form of p130(Cas) or by inhibiting Src. We also documented the co-localization of JSAP1 with JNK and phosphorylated FAK at the leading edge and stimulation of cell migration by JSAP1 expression, which depended on its JNK binding domain and was suppressed by inhibition of JNK. The level of JSAP1 mRNA correlated with advanced malignancy in brain tumors, unlike other JIPs. We propose that the JSAP1.FAK complex functions cooperatively as a scaffold for the JNK signaling pathway and regulator of cell migration on FN, and we suggest that JSAP1 is also associated with malignancy in brain tumors.

Notch interferes with the scaffold function of JNK-interacting protein 1 to inhibit the JNK signaling pathway

The transmembrane protein Notch is cleaved by gamma-secretase to yield an active form, Notch intracellular domain (Notch-IC), in response to the binding of ligands, such as Jagged. Notch-IC contributes to the regulation of a variety of cellular events, including cell fate determination during embryonic development as well as cell growth, differentiation, and survival. We now show that Notch1-IC suppresses the scaffold activity of c-Jun N-terminal kinase (JNK)-interacting protein 1 (JIP1) in the JNK signaling pathway. Notch1-IC physically associated with the JNK binding domain of JIP1 and thereby interfered with the interaction between JIP1 and JNK. JIP1 mediated the activation of JNK1 induced by glucose deprivation in mouse embryonic fibroblasts, and ectopic expression of Notch1-IC inhibited JNK activation and apoptosis triggered by glucose deprivation. Taken together, these findings suggest that Notch1-IC negatively regulates the JNK pathway by disrupting the scaffold function of JIP1.

G protein-coupled receptor signaling through Gq and JNK negatively regulates neural progenitor cell migration

In the early development of the central nervous system, neural progenitor cells divide in an asymmetric manner and migrate along the radial glia cells. The radial migration is an important process for the proper lamination of the cerebral cortex. Recently, a new mode of the radial migration was found at the intermediate zone where the neural progenitor cells become multipolar and reduce the migration rate. However, the regulatory signals for the radial migration are unknown. Using the migration assay in vitro, we examined how neural progenitor cell migration is regulated. Neural progenitor cells derived from embryonic mouse telencephalon migrated on laminin-coated dishes. Endothelin (ET)-1 inhibited the neural progenitor cell migration. This ET-1 effect was blocked by BQ788, a specific inhibitor of the ETB receptor, and by the expression of a carboxyl-terminal peptide of Galpha q but not Galpha i. The expression of constitutively active mutant of Galpha q, Galpha qR183C, inhibited the migration of neural progenitor cells. Moreover, the inhibitory effect of ET-1 was suppressed by the c-Jun N-terminal kinase (JNK) inhibitor SP600125 and the expression of the JNK-binding domain of JNK-interacting protein-1, a specific inhibitor of the JNK pathway. Using the slice culture system of embryonic brain, we demonstrated that ET-1 and the constitutively active mutant of Galpha q caused the retention of the neural progenitor cells in the intermediate zone and JNK-binding domain of JNK-interacting protein-1 abrogated the effect of ET-1. These results indicated that G protein-coupled receptor signaling negatively regulates neural progenitor cell migration through Gq and JNK.