c-Jun N-terminal kinase binding domain-dependent phosphorylation of mitogen-activated protein kinase kinase 4 and mitogen-activated protein kinase kinase 7 and balancing cross-talk between c-Jun N-terminal kinase and extracellular signal-regulated kinase pathways in cortical neurons

The Role of the Dysregulated JNK Signaling Pathway in the Pathogenesis of Human Diseases and Its Potential Therapeutic Strategies: A Comprehensive Review

JNK is named after c-Jun N-terminal kinase, as it is responsible for phosphorylating c-Jun. As a member of the mitogen-activated protein kinase (MAPK) family, JNK is also known as stress-activated kinase (SAPK) because it can be activated by extracellular stresses including growth factor, UV irradiation, and virus infection. Functionally, JNK regulates various cell behaviors such as cell differentiation, proliferation, survival, and metabolic reprogramming. Dysregulated JNK signaling contributes to several types of human diseases. Although the role of the JNK pathway in a single disease has been summarized in several previous publications, a comprehensive review of its role in multiple kinds of human diseases is missing. In this review, we begin by introducing the landmark discoveries, structures, tissue expression, and activation mechanisms of the JNK pathway. Next, we come to the focus of this work: a comprehensive summary of the role of the deregulated JNK pathway in multiple kinds of diseases. Beyond that, we also discuss the current strategies for targeting the JNK pathway for therapeutic intervention and summarize the application of JNK inhibitors as well as several challenges now faced. We expect that this review can provide a more comprehensive insight into the critical role of the JNK pathway in the pathogenesis of human diseases and hope that it also provides important clues for ameliorating disease conditions.

Dose-dependent neuroprotective effect of the JNK inhibitor Brimapitide in 5xFAD transgenic mice

Alzheimer's disease (AD) is a neurodegenerative disease mainly affecting old people. According to the "amyloid cascade hypothesis", the accumulation of Aβ oligomers could lead to kinase activation and Tau phosphorylation. Activated kinases include c-Jun N-terminal kinase (JNK) and previous studies highlighted the beneficial effects of the JNK-specific inhibitor Brimapitide (10 mg/kg) in 5xFAD transgenic mice. Our aim was to evaluate the effects of decreasing doses of Brimapitide on cognition and neurodegeneration in early treated 5xFAD mice. Three month-old 5xFAD were intravenously treated for 6 months with either Brimapitide (3 mg/kg or 0.3 mg/kg) or Nacl. Cognition and amyloid burden, neuronal and synaptic impairments were evaluated. Low doses of Brimapitide (0.3 mg/kg) reduced neuronal degeneration and improved cognition in treated mice compared to non-treated mice. Amyloid burden and synaptic degeneration only decreased with the 3 mg/kg dose. This JNK inhibitor can afford neuroprotection but with a differential effect on amyloid deposition in 5xFAD mice. Brimapitide might partially prevent ongoing neurodegeneration in 5xFAD mice.

Retinoic acid-induced survival effects in SH-SY5Y neuroblastoma cells

Neuroblastoma is a malignant childhood cancer arising from the embryonic sympathoadrenal lineage of the neural crest. Retinoic acid (RA) is included in the multimodal therapy of patients with high-risk neuroblastoma to eliminate minimal residual disease. However, the formation of RA-resistant cells substantially lowers 5-year overall survival rates. To examine mechanisms that lead to treatment failure, we chose human SH-SY5Y cells, which are known to tolerate incubation with RA by activating the survival kinases Akt and extracellular signal-regulated kinase 1/2. Characterization of downstream pathways showed that both kinases increased the phosphorylation of the ubiquitin ligase mouse double minute homolog 2 (Mdm2) and thereby enhanced p53 degradation. When p53 signaling was sustained by blocking complex formation with Mdm2 or enhancing c-Jun N-terminal kinase (JNK) activation, cell viability was significantly reduced. In addition, Akt-mediated phosphorylation of the cell-cycle regulator p21 stimulated complex formation with caspase-3, which also contributed to cell protection. Thus, treatment with RA augmented survival signaling and attenuated basal apoptotic pathways in SH-SY5Y cells, which increased cell viability.

An Internal Standard for Assessing Phosphopeptide Recovery from Metal Ion/Oxide Enrichment Strategies

Phosphorylation-mediated signaling pathways have major implications in cellular regulation and disease. However, proteins with roles in these pathways are frequently less abundant and phosphorylation is often sub-stoichiometric. As such, the efficient enrichment, and subsequent recovery of phosphorylated peptides, is vital. Mass spectrometry-based proteomics is a well-established approach for quantifying thousands of phosphorylation events in a single experiment. We designed a peptide internal standard-based assay directed toward sample preparation strategies for mass spectrometry analysis to understand better phosphopeptide recovery from enrichment strategies. We coupled mass-differential tandem mass tag (mTMT) reagents (specifically, TMTzero and TMTsuper-heavy), nine mass spectrometry-amenable phosphopeptides (phos9), and peak area measurements from extracted ion chromatograms to determine phosphopeptide recovery. We showcase this mTMT/phos9 recovery assay by evaluating three phosphopeptide enrichment workflows. Our assay provides data on the recovery of phosphopeptides, which complement other metrics, namely the number of identified phosphopeptides and enrichment specificity. Our mTMT/phos9 assay is applicable to any enrichment protocol in a typical experimental workflow irrespective of sample origin or labeling strategy. Graphical Abstract ᅟ.

MS3-IDQ: Utilizing MS3 Spectra beyond Quantification Yields Increased Coverage of the Phosphoproteome in Isobaric Tag Experiments

Protein phosphorylation is critically important for many cellular processes, including progression through the cell cycle, cellular metabolism, and differentiation. Isobaric labeling, for example, tandem mass tags (TMT), in phosphoproteomics workflows enables both relative and absolute quantitation of these phosphorylation events. Traditional TMT workflows identify peptides using fragment ions at the MS2 level and quantify reporter ions at the MS3 level. However, in addition to the TMT reporter ions, MS3 spectra also include fragment ions that can be used to identify peptides. Here we describe using MS3 spectra for both phosphopeptide identification and quantification, a process that we term MS3-IDQ. To maximize quantified phosphopeptides, we optimize several instrument parameters, including the modality of mass analyzer (i.e., ion trap or Orbitrap), MS2 automatic gain control (AGC), and MS3 normalized collision energy (NCE), to achieve the best balance of identified and quantified peptides. Our optimized MS3-IDQ method included the following parameters for the MS3 scan: NCE = 37.5 and AGC target = 1.5 × 10⁵, and scan range = 100-2000. Data from the MS3 scan were complementary to those of the MS2 scan, and the combination of these scans can increase phosphoproteome coverage by >50%, thereby yielding a greater number of quantified and accurately localized phosphopeptides.

Dual Kinase Inhibition Affords Extended in vitro Neuroprotection in Amyloid-β Toxicity

In Alzheimer's disease (AD), the amyloid cascade hypothesis proposes that amyloid-beta (Aβ) neurotoxicity leads to neuroinflammation, synaptic loss, and neuronal degeneration. In AD patients, anti-amyloid immunotherapies did not succeed because they were possibly administered late in AD progression. Modulating new targets associated with Aβ toxicity, such as PKR (double-stranded RNA dependent kinase), and JNK (c-Jun N-terminal kinase) is a major goal for neuroprotection. These two pro-apoptotic kinases are activated in AD brains and involved in Aβ production, tau phosphorylation, neuroinflammation, and neuronal death. In HEK cells transfected with siRNA directed against PKR, and in PKR knockout (PKR-/-) mice neurons, we showed that PKR triggers JNK activation. Aβ-induced neuronal apoptosis, measured by cleaved PARP (Poly ADP-ribose polymerase) and cleaved caspase 3 levels, was reduced in PKR-/- neurons. Two selective JNK inhibitory peptides also produced a striking reduction of Aβ toxicity. Finally, the dual inhibition of PKR and JNK nearly abolished Aβ toxicity in primary cultured neurons. These results reveal that dual kinase inhibition can afford neuroprotection and this approach is worth being tested in in vivo AD and oxidative stress models.

Inhibition of plasma kallikrein-kinin system to alleviate renal injury and arthritis symptoms in rats with adjuvant-induced arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease. Impairment of kidney functions in RA was observed. However, the mechanism of kidney injury of RA has not been clear. Plasma kallikrein-kinin system (KKS) was involved in inflammatory processes in kidney disease.

AIM

This study aimed to explore the role of plasma KKS in immune reactions and kidney injury of RA.

RESULTS

The paw of AA rats appeared to be swelling and redness, the arthritis index was significantly increased on the 18, 21 and 24 d after injection and secondary inflammation in multi-sites was observed. Kidney dysfunction accompanied with inflammatory cell infiltration, tubular epithelial cell mitochondrial swelling and vacuolar degeneration, renal glomerular foot process fusions and glomerular basement membrane thickening were observed in AA rats. The expressions of neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (Kim-1) in kidney of AA rats were increased. In addition, expressions of BK, PK, B1R and B2R in the renal tissue of AA rats were up-regulated. Pro-inflammatory cytokines IL-2, IFN-γ and TNF-α were increased and anti-inflammatory cytokines IL-4 and IL-10 were low in kidney. Plasma kallikrein (PK) inhibitor PKSI-527 attenuated arthritis signs and renal damage, and inhibited BK, PK, B1R and B2R expressions. The protein expressions of P38, p-P38 and p-JNK and IFN-γ and TNF-α were inhibited by PKSI-527.

CONCLUSIONS

These findings demonstrate that plasma KKS activation contributed to the renal injury of AA rats through MAPK signaling pathway. Plasma KKS might be a potential target for RA therapy.

Inhibition of Vascular c-Jun N-Terminal Kinase 2 Improves Obesity-Induced Endothelial Dysfunction After Roux-en-Y Gastric Bypass

Background

Roux‐en‐Y gastric bypass (RYGB) reduces obesity‐associated comorbidities and cardiovascular mortality. RYGB improves endothelial dysfunction, reducing c‐Jun N‐terminal kinase (JNK) vascular phosphorylation. JNK activation links obesity with insulin resistance and endothelial dysfunction. Herein, we examined whether JNK1 or JNK2 mediates obesity‐induced endothelial dysfunction and if pharmacological JNK inhibition can mimic RYGB vascular benefits.

Methods and Results

After 7 weeks of a high‐fat high‐cholesterol diet, obese rats underwent RYGB or sham surgery; sham–operated ad libitum–fed rats received, for 8 days, either the control peptide D‐TAT or the JNK peptide inhibitor D‐JNKi‐1 (20 mg/kg per day subcutaneous). JNK peptide inhibitor D‐JNKi‐1 treatment improved endothelial vasorelaxation in response to insulin and glucagon‐like peptide‐1, as observed after RYGB. Obesity increased aortic phosphorylation of JNK2, but not of JNK1. RYGB and JNK peptide inhibitor D‐JNKi‐1 treatment blunted aortic JNK2 phosphorylation via activation of glucagon‐like peptide‐1–mediated signaling. The inhibitory phosphorylation of insulin receptor substrate‐1 was reduced, whereas the protein kinase B/endothelial NO synthase pathway was increased and oxidative stress was decreased, resulting in improved vascular NO bioavailability.

Conclusions

Decreased aortic JNK2 phosphorylation after RYGB rapidly improves obesity‐induced endothelial dysfunction. Pharmacological JNK inhibition mimics the endothelial protective effects of RYGB. These findings highlight the therapeutic potential of novel strategies targeting vascular JNK2 against the severe cardiovascular disease associated with obesity.

Exploring the role of MKK7 in excitotoxicity and cerebral ischemia: a novel pharmacological strategy against brain injury

Excitotoxicity following cerebral ischemia elicits a molecular cascade, which leads to neuronal death. c-Jun-N-terminal kinase (JNK) has a key role in excitotoxic cell death. We have previously shown that JNK inhibition by a specific cell-permeable peptide significantly reduces infarct size and neuronal death in an in vivo model of cerebral ischemia. However, systemic inhibition of JNK may have detrimental side effects, owing to blockade of its physiological function. Here we designed a new inhibitor peptide (growth arrest and DNA damage-inducible 45β (GADD45β-I)) targeting mitogen-activated protein kinase kinase 7 (MKK7), an upstream activator of JNK, which exclusively mediates JNK's pathological activation. GADD45β-I was engineered by optimizing the domain of the GADD45β, able to bind to MKK7, and by linking it to the TAT peptide sequence, to allow penetration of biological membranes. Our data clearly indicate that GADD45β-I significantly reduces neuronal death in excitotoxicity induced by either N-methyl-D-aspartate exposure or by oxygen–glucose deprivation in vitro. Moreover, GADD45β-I exerted neuroprotection in vivo in two models of ischemia, obtained by electrocoagulation and by thromboembolic occlusion of the middle cerebral artery (MCAo). Indeed, GADD45β-I reduced the infarct size when injected 30 min before the lesion in both models. The peptide was also effective when administrated 6 h after lesion, as demonstrated in the electrocoagulation model. The neuroprotective effect of GADD45β-I is long lasting; in fact, 1 week after MCAo the infarct volume was still reduced by 49%. Targeting MKK7 could represent a new therapeutic strategy for the treatment of ischemia and other pathologies involving MKK7/JNK activation. Moreover, this new inhibitor can be useful to further dissect the physiological and pathological role of the JNK pathway in the brain.

PTPN21 exerts pro-neuronal survival and neuritic elongation via ErbB4/NRG3 signaling

Although expression quantitative trait locus, eQTL, serves as an explicit indicator of gene-gene associations, challenges remain to disentangle the mechanisms by which genetic variations alter gene expression. Here we combined eQTL and molecular analyses to identify an association between two seemingly non-associated genes in brain expression data from BXD inbred mice, namely Ptpn21 and Nrg3. Using biotinylated receptor tracking and immunoprecipitation analyses, we determined that PTPN21 de-phosphorylates the upstream receptor tyrosine kinase ErbB4 leading to the up-regulation of its downstream signaling. Conversely, kinase-dead ErbB4 (K751R) or phosphatase-dead PTPN21 (C1108S) mutants impede PTPN21-dependent signaling. Furthermore, PTPN21 also induced Elk-1 activation in embryonic cortical neurons and a novel Elk-1 binding motif was identified in a region located 1919bp upstream of the NRG3 initiation codon. This enables PTPN21 to promote NRG3 expression through Elk-1, which provides a biochemical mechanism for the PTPN21-NRG3 association identified by eQTL. Biologically, PTPN21 positively influences cortical neuronal survival and, similar to Elk-1, it also enhances neuritic length. Our combined approaches show for the first time, a link between NRG3 and PTPN21 within a signaling cascade. This may explain why these two seemingly unrelated genes have previously been identified as risk genes for schizophrenia.

Regulatory role of the JNK-STAT1/3 signaling in neuronal differentiation of cultured mouse embryonic stem cells

Stem cell transplantation therapy has provided promising hope for the treatment of a variety of neurodegenerative disorders. Among challenges in developing disease-specific stem cell therapies, identification of key regulatory signals for neuronal differentiation is an essential and critical issue that remains to be resolved. Several lines of evidence suggest that JNK, also known as SAPK, is involved in neuronal differentiation and neural plasticity. It may also play a role in neurite outgrowth during neuronal development. In cultured mouse embryonic stem (ES) cells, we test the hypothesis that the JNK pathway is required for neuronal differentiation. After neural induction, the cells were plated and underwent differentiation for up to 5 days. Western blot analysis showed a dramatic increase in phosphorylated JNKs at 1-5 days after plating. The phosphorylation of JNK subsequently induced activation of STAT1 and STAT3 that lead to expressions of GAP-43, neurofilament, βIII-tubulin, and synaptophysin. NeuN-colabelled with DCX, a marker for neuroblast, was enhanced by JNK signaling. Neuronal differentiation of ES cells was attenuated by treatment with SP600125, which inhibited the JNK activation and decreased the activation of STAT1 and STAT3, and consequently suppressed the expressions of GAP-43, neurofilament, βIII-tubulin, and the secretion of VEGF. Data from immunocytochemistry indicated that the nuclear translocation of STAT3 was reduced, and neurites of ES-derived neurons were shorter after treatment with SP600125 compared with control cells. These results suggest that the JNK-STAT3 pathway is a key regulator required for early neuronal differentiation of mouse ES cells. Further investigation on expression of JNK isoforms showed that JNK-3 was significantly upregulated during the differentiation stage, while JNK-1 and JNK-2 levels decreased. Our study provided interesting information on JNK functions during ES cell neuronal differentiation.

Determination of tissue levels of a neuroprotectant drug: the cell permeable JNK inhibitor peptide

INTRODUCTION

Cell permeable peptides (CPPs) represent a novel tool for the delivery of bioactive molecules into scarcely accessible organs, such as the brain. CPPs have been successfully used in pre-clinical studies for a variety of diseases, ranging from cancer to neurological disorders. However, the mechanisms by which CPPs cross biological membranes, as well as their pharmacokinetic properties, have been poorly explored due to the lack of specific and sensitive analytical methods.

METHODS

In this paper we describe a protocol to quantitatively determine the amount of CPPs in in vitro and in vivo experimental models. To this end we selected the peptide D-JNKI1 that was shown to prevent neurodegeneration in both acute and chronic degenerative disorders. This method allows an accurate quantitative analysis of D-JNKI1 in both neuronal lysates and tissue homogenates using mass spectrometry and stable isotope dilution approach.

RESULTS

We found that D-JNKI1 crosses cellular membranes with fast kinetics, through an active and passive mechanism. After acute intraperitoneal (ip) administration of D-JNKI1 in mice, the peptide was found in the main organs with particular regard to the liver and kidney. Interestingly, D-JNKI1 crosses the blood brain barrier (BBB) and reaches the brain, where it remains for one week.

DISCUSSION

The challenge lies in developing the clinical application of therapeutic cell permeable peptides. Discerning pharmacokinetic properties is a high priority to produce a powerful therapeutic strategy. Overall, our data shed light on the pharmacokinetic properties of D-JNKI1 and supports its powerful neuroprotective effect.

PI3 k/akt inhibition induces apoptosis through p38 activation in neurons

Accumulating evidence suggests that the PI3K/AKT pathway is a pro-survival signalling system in neurons. Therefore, the inhibition of this pathway may be implicated in the degeneration of neurons in Parkinson's disease (PD), Alzheimer's disease (AD), and other neurological disorders. Here we study the participation of the mitogen-activated protein kinase (MAPK) pathway on apoptosis induced by PI3K/AKT inhibition in cultured cerebellar granule cells (CGCs). LY294002, a specific PI3K/AKT inhibitor, selectively activated the p38 MAPK kinase pathway and enhanced c-Jun phosphorylation, but did not activate JNK. The pharmacological inhibitors SB203580 (p38 inhibitor) and SP600125 (a JNK inhibitor) protected primary cultures of rat CGCs from LY294002-induced apoptosis. Furthermore, both compounds decreased the phosphorylation of c-Jun and lowered mRNA levels of the pro-apoptotic gene dp5, a direct target of c-Jun. Taken together, our data demonstrate that PI3K/AKT inhibition induces neuronal apoptosis, a process that is mediated by the activation of p38 MAPK/c-Jun/dp5.

Mitochondrial JNK phosphorylation as a novel therapeutic target to inhibit neuroinflammation and apoptosis after neonatal ischemic brain damage

Neonatal encephalopathy is associated with high mortality and life-long developmental consequences. Therapeutic options are very limited. We assessed the effects of D-JNKi, a small peptide c-Jun N-terminal kinase (JNK) MAP kinase inhibitor, on neuroinflammation, mitochondrial integrity and neuronal damage in a neonatal rat model of ischemic brain damage. Hypoxic-ischemic (HI) brain injury was induced in postnatal-day 7 rats by unilateral carotid artery occlusion and hypoxia, and was followed by intraperitoneal D-JNKi treatment. We demonstrate here for the first time that a single intraperitoneal injection with D-JNKi directly after HI strongly reduces neonatal brain damage by >85% with a therapeutic window of at least 6h. D-JNKi treatment also restored cognitive and motor function as analyzed at 9weeks post-insult. Neuroprotective D-JNKi treatment inhibited phosphorylation of nuclear c-Jun (P-c-Jun), and consequently reduced activity of the AP-1 transcription factor and production of cerebral cytokines/chemokines as determined at 3 and 24h post-HI. Inhibition of P-c-Jun by D-JNKi is thought to be mediated via inhibition of the upstream phosphorylation of cytosolic and nuclear JNK and/or by preventing the direct interaction of phosphorylated (P-)JNK with c-Jun. Surprisingly, however, HI did not induce a detectable increase in P-JNK in cytosol or nucleus. Notably, we show here for the first time that HI induces P-JNK only in the mitochondrial fraction, which was completely prevented by D-JNKi treatment. The hypothesis that mitochondrial JNK activation is key to HI brain injury was supported by data showing that treatment of rat pups with SabKIM1 peptide, a specific mitochondrial JNK inhibitor, is also neuroprotective. Inhibition of HI-induced mitochondrial JNK activation was associated with preservation of mitochondrial integrity as evidenced by prevention of ATP loss and inhibition of lipid peroxidation. The HI-induced increase in apoptotic markers (cytochrome c release and caspase 3 activation) as analyzed at 24h post-HI were also strongly reduced by D-JNKi and the mitochondrial anti-apoptotic proteins Bcl-2 and Bcl-xL were upregulated. Neuroprotection was lost after repeated 0+3h D-JNKi treatment which was associated with complete inhibition of the second peak of AP-1 activity and disability to upregulate mitochondrial Bcl-2 and Bcl-xL. We show here for the first time that D-JNKi treatment efficiently protects the neonatal brain against ischemic brain damage and subsequent cognitive and motor impairment. We propose that inhibition of phosphorylation of mitochondrial JNK is a pivotal step in preventing early loss of mitochondrial integrity leading to reduced neuroinflammation and inhibition of apoptotic neuronal loss. Moreover we show the crucial role of upregulation of mitochondrial anti-apoptotic proteins to maintain neuroprotection.

Manipulating JNK signaling with (--)-zuonin A

Recently, in a virtual screening strategy to identify new compounds targeting the D-recruitment site (DRS) of the c-Jun N-terminal kinases (JNKs), we identified the natural product (-)-zuonin A. Here we report the asymmetric synthesis of (-)-zuonin A and its enantiomer (+)-zuonin A. A kinetic analysis for the inhibition of c-Jun phosphorylation by (-)-zuonin A revealed a mechanism of partial competitive inhibition. Its binding is proposed to weaken the interaction of c-Jun to JNK by approximately 5-fold, without affecting the efficiency of phosphorylation within the complex. (-)-Zuonin A inhibits the ability of both MKK4 and MKK7 to phosphorylate and activate JNK. The binding site of (-)-zuonin A is predicted by docking and molecular dynamics simulation to be located in the DRS of JNK. (+)-Zuonin A also binds JNK but barely impedes the binding of c-Jun. (-)-Zuonin A inhibits the activation of JNK, as well as the phosphorylation of c-Jun in anisomycin-treated HEK293 cells, with the inhibition of JNK activation being more pronounced. (-)-Zuonin A also inhibits events associated with constitutive JNK2 activity, including c-Jun phosphorylation, basal Akt activation, and MDA-MB-231 cell migration. Mutations in the predicted binding site for (-)-zuonin A can render it significantly more or less sensitive to inhibition than wild type JNK2, allowing for the design of potential chemical genetic experiments. These studies suggest that the biological activity reported for other lignans, such as saucerneol F and zuonin B, may be the result of their ability to impede protein-protein interactions within MAPK cascades.

From in Silico Discovery to intra-Cellular Activity: Targeting JNK-Protein Interactions with Small Molecules

The JNK-JIP1 interaction represents an attractive target for the selective inhibition of JNK-mediated signaling. We report a virtual screening (VS) workflow, based on a combination of three-dimensional shape and electrostatic similarity to discover novel scaffolds for the development of non-ATP competitive inhibitors of JNK targeting the JNK-JIP interaction. Of 352 (0.13%) compounds selected from the NCI diversity set more than 22% registered as hits in a biochemical kinase assay. Several compounds discovered to inhibit JNK activity under standard kinase assay conditions also impeded JNK activity in HEK293 cells. These studies led to the discovery that the lignan (-)-zuonin A inhibits JNK-protein interactions with a selectivity of 100-fold over ERK2 and p38 MAPKα. These results demonstrate the utility of a virtual screening protocol to identify novel scaffolds for highly selective, cell-permeable inhibitors of JNK-protein interactions.

ETS-1 protein regulates vascular endothelial growth factor-induced matrix metalloproteinase-9 and matrix metalloproteinase-13 expression in human ovarian carcinoma cell line SKOV-3

Matrix metalloproteinase-mediated degradation of extracellular matrix is a crucial event for invasion and metastasis of malignant cells. The expressions of matrix metalloproteinases (MMPs) are regulated by different cytokines and growth factors. VEGF, a potent angiogenic cytokine, induces invasion of ovarian cancer cells through activation of MMPs. Here, we demonstrate that invasion and scattering in SKOV-3 cells were induced by VEGF through the activation of p38 MAPK and PI3K/AKT pathways. VEGF induced the expression of MMP-2, MMP-9, and MMP-13 and hence regulated the metastasis of SKOV-3 ovarian cancer cells, and the activities of these MMPs were reduced after inhibition of PI3K/AKT and p38 MAPK pathways. Interestingly, VEGF induced expression of ETS-1 factor, an important trans-regulator of different MMP genes. ETS-1 bound to both MMP-9 and MMP-13 promoters. Furthermore, VEGF acted through its receptor to perform the said functions. In addition, VEGF-induced MMP-9 and MMP-13 expression and in vitro cell invasion were significantly reduced after knockdown of ETS-1 gene. Again, VEGF-induced MMP-9 and MMP-13 promoter activities were down-regulated in ETS-1 siRNA-transfected cells. VEGF enriched ETS-1 in the nuclear fraction in a dose-dependent manner. VEGF-induced expression of ETS-1 and its nuclear localization were blocked by specific inhibitors of the PI3K and p38 MAPK pathways. Therefore, based on these observations, it is hypothesized that the activation of PI3K/AKT and p38 MAPK by VEGF results in ETS-1 gene expression, which activates MMP-9 and MMP-13, leading to the invasion and scattering of SKOV-3 cells. The study provides a mechanistic insight into the prometastatic functions of VEGF-induced expression of relevant MMPs.

c-Jun N-terminal kinase regulates soluble Aβ oligomers and cognitive impairment in AD mouse model

Alzheimer disease (AD) is characterized by cognitive impairment that starts with memory loss to end in dementia. Loss of synapses and synaptic dysfunction are closely associated with cognitive impairment in AD patients. Biochemical and pathological evidence suggests that soluble Aβ oligomers correlate with cognitive impairment. Here, we used the TgCRND8 AD mouse model to investigate the role of JNK in long term memory deficits. TgCRND8 mice were chronically treated with the cell-penetrating c-Jun N-terminal kinase inhibitor peptide (D-JNKI1). D-JNKI1, preventing JNK action, completely rescued memory impairments (behavioral studies) as well as the long term potentiation deficits of TgCRND8 mice. Moreover, D-JNKI1 inhibited APP phosphorylation in Thr-668 and reduced the amyloidogenic cleavage of APP and Aβ oligomers in brain parenchyma of treated mice. In conclusion, by regulating key pathogenic mechanisms of AD, JNK might hold promise as innovative therapeutic target.

The JNK inhibitor D-JNKI-1 blocks apoptotic JNK signaling in brain mitochondria

Kainic acid (KA) induced seizures provokes an extensive neuronal degeneration initiated by c-Jun N-terminal kinases (JNK) as central mediators of excitotoxicity. However, the actions of their individual isoforms in cellular organelles including mitochondria remain to be elucidated. Here, we have studied the activation of JNK1, JNK2 and JNK3 and their activators, mitogen-activated protein kinase kinase (MKK) 4/7, in brain mitochondria, cytosolic and nuclear fractions after KA seizures. In the mitochondrial fraction, KA significantly increased the presence of JNK1, JNK3 and MKK4 and stimulated their phosphorylation i.e. activation. The pro-apoptotic proteins, Bim and Bax were induced and, consequently, the ratio Bcl-2-Bax decreased. These changes were paralleled by the release of cytochrome c and cleavage of poly(ADP-ribose)-polymerase (PARP). The JNK peptide inhibitor, D-JNKI-1 (XG-102) reversed these pathological events in the mitochondria and almost completely abolished cytochrome c release and PARP cleavage. Importantly, JNK3, but not JNK1 or JNK2, was associated with Bim in mitochondria and D-JNKI-1 prevented the formation of this apoptotic complex. Apart from of the attenuation of c-Jun phosphorylation in the nucleus, D-JNKI-1 did not affect the level of JNK3 isoform in the nuclear and cytosolic fractions. These findings provide novel insights into the mode of action of individual JNK isoforms in cell organelles and points to the JNK3 pool in mitochondria as a target of the JNK inhibitor D-JNKI-1 to confer neuroprotection.

Crosstalk between JNK and SUMO signaling pathways: deSUMOylation is protective against H2O2-induced cell injury

BACKGROUND

Oxidative stress is a key feature in the pathogenesis of several neurological disorders. Following oxidative stress stimuli a wide range of pathways are activated and contribute to cellular death. The mechanism that couples c-Jun N-terminal kinase (JNK) signaling, a key pathway in stress conditions, to the small ubiquitin-related modifier (SUMO), an emerging protein in the field, is largely unknown.

METHODOLOGY/PRINCIPAL FINDINGS

With this study we investigated if SUMOylation participates in the regulation of JNK activation as well as cellular death in a model of H(2)O(2) induced-oxidative stress. Our data show that H(2)O(2) modulates JNK activation and induces cellular death in neuroblastoma SH-SY5Y cells. Inhibition of JNK's action with the D-JNKI1 peptide rescued cells from death. Following H(2)O(2), SUMO-1 over-expression increased phosphorylation of JNK and exacerbated cell death, although only in conditions of mild oxidative stress. Furthermore inhibition of SUMOylation, following transfection with SENP1, interfered with JNK activation and rescued cells from H(2)O(2) induced death. Importantly, in our model, direct interaction between these proteins can occur.

CONCLUSIONS/SIGNIFICANCE

Taken together our results show that SUMOylation may significantly contribute to modulation of JNK activation and contribute to cell death in oxidative stress conditions.

Development of JNK2-selective peptide inhibitors that inhibit breast cancer cell migration

Despite their lack of selectivity toward c-Jun N-terminal kinase (JNK) isoforms, peptides derived from the JIP (JNK Interacting Protein) scaffolds linked to the cell-penetrating peptide TAT are widely used to investigate JNK-mediated signaling events. To engineer an isoform-selective peptide inhibitor, several JIP-based peptide sequences were designed and tested. A JIP sequence connected through a flexible linker to either the N-terminus of an inverted TAT sequence (JIP(10)-Δ-TAT(i)) or to a poly arginine sequence (JIP(10)-Δ-R(9)) enabled the potent inhibition of JNK2 (IC(50) ≈ 90 nM) and exhibited 10-fold selectivity for JNK2 over JNK1 and JNK3. Examination of both peptides in HEK293 cells revealed a potent ability to inhibit the induction of both JNK activation and c-Jun phosphorylation in cells treated with anisomycin. Notably, Western blot analysis indicates that only a fraction of total JNK must be activated to elicit robust c-Jun phosphorylation. To examine the potential of each peptide to selectively modulate JNK2 signaling in vivo, their ability to inhibit the migration of Polyoma Middle-T Antigen Mammary Tumor (PyVMT) cells was assessed. PyVMTjnk2-/- cells exhibit a lower migration potential compared to PyVMTjnk2+/+ cells, and this migration potential is restored through the overexpression of GFP-JNK2α. Both JIP(10)-Δ-TAT(i) and JIP(10)-Δ-R(9) inhibit the migration of PyVMTjnk2+/+ cells and PyVMTjnk2-/- cells expressing GFP-JNK2α. However, neither peptide inhibits the migration of PyVMTjnk2-/- cells. A control form of JIP(10)-Δ-TAT(i) containing a single leucine to arginine mutation lacks ability to inhibit JNK2 in vitro cell-free and cell-based assays and does not inhibit the migration of PyVMTjnk2+/+ cells. Together, these data suggest that JIP(10)-Δ-TAT(i) and JIP(10)-Δ-R(9) inhibit the migration of PyVMT cells through the selective inhibition of JNK2. Finally, the mechanism of inhibition of a D-retro-inverso JIP peptide, previously reported to inhibit JNK, was examined and found to inhibit p38MAPKα in an in vitro cell-free assay with little propensity to inhibit JNK isoforms.

c-Jun N-terminal kinases in memory and synaptic plasticity

The c-Jun N-terminal kinases (JNK) belong to the subfamily of mitogen-activated protein kinases (MAPK). JNK is an important signaling enzyme that is involved in many facets of cellular regulation including gene expression, cell proliferation and programmed cell death. Activation of JNK isoforms (JNK1, 2, and 3) is regarded as a molecular switch in stress signal transduction. The activation of JNK pathways is also critical for pathological death associated with neurodegenerative diseases. Considering that a variety of stressors activate JNK, it is surprising that the role of hippocampal JNK in memory and synaptic plasticity has not yet been systematically investigated. Here we summarize the emerging evidence for the functions of hippocampal JNK in memory and synaptic plasticity, including our recent demon­stration that JNK isoforms play critical roles in regulation of contextual fear conditioning under stressful and baseline conditions. We postulate that sustained activation of the hippocampal JNK2 and JNK3 pathways is involved in the initial stress response that ultimately leads to deficits in memory and long-term potentiation, whereas transient JNK1 activation regulates baseline contextual fear conditioning. Results obtained within the framework of our recent findings will be used for future work, which will differentiate mechanisms underlying beneficial short-term JNK action from prolonged JNK activation that may lead to memory deficits and neurodegeneration.

A new fluorogenic peptide determines proteasome activity in single cells

The ubiquitin-proteasome system plays a critical role in many diseases, making it an attractive biomarker and therapeutic target. However, the impact of results obtained in vitro using purified proteasome particles or whole cell extracts is limited by the lack of efficient methods to assess proteasome activity in living cells. We have engineered an internally quenched fluorogenic peptide with a proteasome-specific cleavage motif fused to TAT and linked to the fluorophores DABCYL and EDANS. This peptide penetrates cell membranes and is rapidly cleaved by the proteasomal chymotrypsin-like activity, generating a quantitative fluorescent reporter of in vivo proteasome activity as assessed by time-lapse or flow cytometry fluorescence analysis. This reporter is an innovative tool for monitoring proteasomal proteolytic activities in physiological and pathological conditions.

Hippocampal c-Jun-N-terminal kinases serve as negative regulators of associative learning

In the adult mouse, signaling through c-Jun N-terminal kinases (JNKs) links exposure to acute stress to various physiological responses. Inflammatory cytokines, brain injury and ischemic insult, or exposure to psychological acute stressors induce activation of hippocampal JNKs. Here we report that exposure to acute stress caused activation of JNKs in the hippocampal CA1 and CA3 subfields, and impaired contextual fear conditioning. Conversely, intrahippocampal injection of JNKs inhibitors sp600125 (30 μm) or D-JNKI1 (8 μm) reduced activity of hippocampal JNKs and rescued stress-induced deficits in contextual fear. In addition, intrahippocampal administration of anisomycin (100 μg/μl), a potent JNKs activator, mimicked memory-impairing effects of stress on contextual fear. This anisomycin-induced amnesia was abolished after cotreatment with JNKs selective inhibitor sp600125 without affecting anisomycin's ability to effectively inhibit protein synthesis as measured by c-Fos immunoreactivity. We also demonstrated milder and transient activation of the JNKs pathway in the CA1 subfield of the hippocampus during contextual fear conditioning and an enhancement of contextual fear after pharmacological inhibition of JNKs under baseline conditions. Finally, using combined biochemical and transgenic approaches with mutant mice lacking different members of the JNK family (Jnk1, Jnk2, and Jnk3), we provided evidence that JNK2 and JNK3 are critically involved in stress-induced deficit of contextual fear, while JNK1 mainly regulates baseline learning in this behavioral task. Together, these results support the possibility that hippocampal JNKs serve as a critical molecular regulator in the formation of contextual fear.

Cell Permeable Peptides: A Promising Tool to Deliver Neuroprotective Agents in the Brain

The inability of most drugs to cross the blood-brain barrier and/or plasma membrane limits their use for biomedical applications in the brain. Cell Permeable Peptides (CPPs) overcome this problem and are effective in vivo, crossing the plasma membrane and the blood-brain barrier. CPPs deliver a wide variety of compounds intracellularly in an active form. In fact, many bioactive cargoes have neuroprotective properties, and due to their ability to block protein-protein interactions, offer exciting perspectives in the clinical setting. In this review we give an overview of the Cell Permeable Peptides strategy to deliver neuroprotectants against neurodegeneration in the CNS.

Neuroprotective effects of bone morphogenetic protein 7 (BMP7) treatment after spinal cord injury

Bone morphogenetic protein 7 (BMP7) has been shown to ameliorate reduced dendritic growth induced by glutamate excitotoxicity in neuronal tissue cultures and/or provide an enhancement of functional recovery in central nervous system (CNS) injury. BMP7 expression is modulated by spinal cord injury (SCI), but the molecular mechanisms involved in neuroprotection have not been clearly defined. Here, we show that BMP7 treatment of rats subjected to mild cervical SCI significantly increased the pro-survival mitogen-activated protein kinase-38 (MAPK-38) pathway and levels of N-methyl-D-aspartate receptor 1 (NMDAR-1) resulting in a significant increase in neuronal sparing in the ventral horn of the spinal cord. Moreover, BMP7 was neuroprotective against glutamate-mediated excitotoxicity in cultured cortical neurons. These studies show that BMP7 administration may be used as a therapeutic strategy to reduce the damaging excitotoxic effects following SCI.