JNK2 is a positive regulator of the cJun transcription factor

Mitonuclear Communication in Stem Cell Function

Mitochondria perform multiple functions within the cell, including the production of ATP and a great deal of metabolic intermediates, while also contributing to the cellular stress response. The majority of mitochondrial proteins are encoded by nuclear genomes, highlighting the importance of mitonuclear communication for sustaining mitochondrial homeostasis and functional. As a crucial part of the intracellular signalling network, mitochondria can impact stem cell fate determinations. Considering the essential function of stem cells in tissue maintenance, regeneration and aging, it is important to understand how mitochondria influence stem cell fate. This review explores the significant roles of mitonuclear communication and mitochondrial proteostasis, highlighting their influence on stem cells. We also examine how mitonuclear interactions contribute to cellular homeostasis, stem cell therapies, and the potential for extending lifespan.

Quantitative phosphoproteomics reveals that nestin is a downstream target of dual leucine zipper kinase during retinoic acid-induced neuronal differentiation of Neuro-2a cells

BACKGROUND

Dual leucine zipper kinase (DLK) is critical for neurite outgrowth in the developing nervous system and during nerve regeneration, but the underlying mechanisms remain largely unknown. To address this issue, we generated stable shRNA-mediated DLK-depleted Neuro-2a cell lines and analyzed their phosphoproteome after induction of neuronal differentiation by retinoic acid (RA).

RESULTS

Here, we report the identification of 32 phosphopeptides that exhibited significant differences in relative abundance between control and DLK-depleted cells. Two of the most downregulated phosphopeptides identified after DLK depletion were derived from nestin, a type VI intermediate filament (IF) protein typically expressed in neural progenitor cells. The reduced abundance of these phosphopeptides in response to DLK knockdown was validated using parallel reaction monitoring (PRM)-based quantitative proteomics and paired with a concomitant reduction in nestin mRNA and protein expression, indicating that the decrease in nestin phosphorylation was due to a decrease in total nestin in DLK-depleted cells compared to control cells. This DLK-mediated regulation of nestin expression had no apparent effect on neurite formation because nestin knockdown alone was not sufficient to impair RA-induced neurite extension in parental Neuro-2a cells, and nestin overexpression failed to rescue the neurite outgrowth defect observed in DLK-depleted Neuro-2a cells.

CONCLUSIONS

Together, these results demonstrate that nestin is a novel downstream target of DLK signaling but not a mediator of its ability to promote neurite outgrowth during neuronal differentiation.

Protective role of triiodothyronine in sepsis‑induced cardiomyopathy through phospholamban downregulation

Sepsis is often a cause of mortality in patients admitted to the intensive care unit. Notably, the heart is the organ most susceptible to the impact of sepsis and this condition is referred to as sepsis‑induced cardiomyopathy (SIC). Low triiodothyronine (T3) syndrome frequently occurs in patients with sepsis, and the heart is one of the most important target organs for the action of T3. Phospholamban (PLN) is a key protein associated with Ca2+‑pump‑mediated cardiac diastolic function in the myocardium of mice with SIC, and PLN is negatively regulated by T3. The present study aimed to explore whether T3 can protect cardiac function during sepsis and to investigate the specific molecular mechanism underlying the regulation of PLN by T3. C57BL/6J mice and H9C2 cells were used to establish in vivo and in vitro models, respectively. Myocardial damage was detected via pathological tissue sections, a Cell Counting Kit-8 assay, an apoptosis assay and crystal violet staining. Intracellular calcium levels and reactive oxygen species were detected by Fluo‑4AM and DHE fluorescence. The protein and mRNA expression levels of JNK and c‑Jun were measured by western blotting and reverse transcription‑quantitative PCR to investigate the molecular mechanisms involved. Subsequently, 100 clinical patients were recruited to verify the clinical application value of PLN in SIC. The results revealed a significant negative correlation between PLN and T3 in the animal disease model. Furthermore, the expression levels of genes and proteins in the JNK/c‑Jun signaling pathway and PLN expression levels were decreased, whereas the expression levels of sarcoplasmic reticulum calcium ATPase were increased after T3 treatment. These results indicated that T3 alleviated myocardial injury in SIC by inhibiting PLN expression and its phosphorylation, which may be related to the JNK/c‑Jun signaling pathway. Accordingly, PLN may have clinical diagnostic value in patients with SIC.

JNK signaling and its impact on neural cell maturation and differentiation

C-Jun-N-terminal-kinases (JNKs), members of the mitogen-activated-protein-kinase family, are significantly linked with neurological and neurodegenerative pathologies and cancer progression. However, JNKs serve key roles under physiological conditions, particularly within the central-nervous-system (CNS), where they are critical in governing neural proliferation and differentiation during both embryogenesis and adult stages. These processes control the development of CNS, avoiding neurodevelopment disorders. JNK are key to maintain the proper activity of neural-stem-cells (NSC) and neural-progenitors (NPC) that exist in adults, which keep the convenient brain plasticity and homeostasis. This review underscores how the interaction of JNK with upstream and downstream molecules acts as a regulatory mechanism to manage the self-renewal capacity and differentiation of NSC/NPC during CNS development and in adult neurogenic niches. Evidence suggests that JNK is reliant on non-canonical Wnt components, Fbw7-ubiquitin-ligase, and WDR62-scaffold-protein, regulating substrates such as transcription factors and cytoskeletal proteins. Therefore, understanding which pathways and molecules interact with JNK will bring knowledge on how JNK activation orchestrates neuronal processes that occur in CNS development and brain disorders.

Crosstalk between phytochemicals and inflammatory signaling pathways

Novel bioactive constituents from natural sources are actively being investigated. The phytochemicals in these phenolic compounds are believed to have a variety of beneficial effects on human health. Several phenolic compounds have been found in plants. The antioxidant potential of phenols has been discussed in numerous studies along with their anti-inflammatory effects on pro-inflammatory cytokine, inducible cyclooxygenase-2, and nitric oxide synthase. Through current study, an attempt is made to outline and highlight a wide variety of inflammation-associated signaling pathways that have been modified by several natural compounds. These signaling pathways include nuclear factor-kappa B (NF-кB), activator protein (AP)-1, protein tyrosine kinases (PTKs), mitogen-activated protein kinases (MAPKs), nuclear factor erythroid 2-related factor 2 (Nrf2) transcription factors, tyrosine phosphatidylinositol 3-kinase (PI3K)/AKT, and the ubiquitin-proteasome system. In light of the influence of natural substances on signaling pathways, their impact on the production of inflammatory mediator is highlighted in this review.

Early construction of the thalamocortical axon pathway requires c-Jun N-terminal kinase signaling within the ventral forebrain

BACKGROUND

Thalamocortical connectivity is essential for normal brain function. This important pathway is established during development, when thalamic axons extend a long distance through the forebrain before reaching the cerebral cortex. In this study, we identify a novel role for the c-Jun N-terminal kinase (JNK) signaling pathway in guiding thalamocortical axons through intermediate target territories.

RESULTS

Complete genetic removal of JNK signaling from the Distal-less 5/6 (Dlx5/6) domain in mice prevents thalamocortical axons from crossing the diencephalon-telencephalon boundary (DTB) and the internal capsule fails to form. Ventral telencephalic cells critical for thalamocortical axon extensions including corridor and guidepost neurons are also disrupted. In addition, corticothalamic, striatonigral, and nigrostriatal axons fail to cross the DTB. Analyses of different JNK mutants demonstrate that thalamocortical axon pathfinding has a non-autonomous requirement for JNK signaling.

CONCLUSIONS

We conclude that JNK signaling within the Dlx5/6 territory enables the construction of major axonal pathways in the developing forebrain. Further exploration of this intermediate axon guidance territory is needed to uncover mechanisms of axonal pathfinding during normal brain development and to elucidate how this vital process may be compromised in neurodevelopmental disorders.

Exercise alters the mitochondrial proteostasis and induces the mitonuclear imbalance and UPRmt in the hypothalamus of mice

The maintenance of mitochondrial activity in hypothalamic neurons is determinant to the control of energy homeostasis in mammals. Disturbs in the mitochondrial proteostasis can trigger the mitonuclear imbalance and mitochondrial unfolded protein response (UPR^mt) to guarantee the mitochondrial integrity and function. However, the role of mitonuclear imbalance and UPR^mt in hypothalamic cells are unclear. Combining the transcriptomic analyses from BXD mice database and in vivo experiments, we demonstrated that physical training alters the mitochondrial proteostasis in the hypothalamus of C57BL/6J mice. This physical training elicited the mitonuclear protein imbalance, increasing the mtCO-1/Atp5a ratio, which was accompanied by high levels of UPR^mt markers in the hypothalamus. Also, physical training increased the maximum mitochondrial respiratory capacity in the brain. Interestingly, the transcriptomic analysis across several strains of the isogenic BXD mice revealed that hypothalamic mitochondrial DNA-encoded genes were negatively correlated with body weight and several genes related to the orexigenic response. As expected, physical training reduced body weight and food intake. Interestingly, we found an abundance of mt-CO1, a mitochondrial DNA-encoded protein, in NPY-producing neurons in the lateral hypothalamus nucleus of exercised mice. Collectively, our data demonstrated that physical training altered the mitochondrial proteostasis and induced the mitonuclear protein imbalance and UPR^mt in hypothalamic cells.

JNK3 as Therapeutic Target and Biomarker in Neurodegenerative and Neurodevelopmental Brain Diseases

The c-Jun N-terminal kinase 3 (JNK3) is the JNK isoform mainly expressed in the brain. It is the most responsive to many stress stimuli in the central nervous system from ischemia to Aβ oligomers toxicity. JNK3 activity is spatial and temporal organized by its scaffold protein, in particular JIP-1 and β-arrestin-2, which play a crucial role in regulating different cellular functions in different cellular districts. Extensive evidence has highlighted the possibility of exploiting these adaptors to interfere with JNK3 signaling in order to block its action. JNK plays a key role in the first neurodegenerative event, the perturbation of physiological synapse structure and function, known as synaptic dysfunction. Importantly, this is a common mechanism in many different brain pathologies. Synaptic dysfunction and spine loss have been reported to be pharmacologically reversible, opening new therapeutic directions in brain diseases. Being JNK3-detectable at the peripheral level, it could be used as a disease biomarker with the ultimate aim of allowing an early diagnosis of neurodegenerative and neurodevelopment diseases in a still prodromal phase.

Mitochondrial Protein Quality Control Mechanisms

Mitochondria serve as a hub for many cellular processes, including bioenergetics, metabolism, cellular signaling, redox balance, calcium homeostasis, and cell death. The mitochondrial proteome includes over a thousand proteins, encoded by both the mitochondrial and nuclear genomes. The majority (~99%) of proteins are nuclear encoded that are synthesized in the cytosol and subsequently imported into the mitochondria. Within the mitochondria, polypeptides fold and assemble into their native functional form. Mitochondria health and integrity depend on correct protein import, folding, and regulated turnover termed as mitochondrial protein quality control (MPQC). Failure to maintain these processes can cause mitochondrial dysfunction that leads to various pathophysiological outcomes and the commencement of diseases. Here, we summarize the current knowledge about the role of different MPQC regulatory systems such as mitochondrial chaperones, proteases, the ubiquitin-proteasome system, mitochondrial unfolded protein response, mitophagy, and mitochondria-derived vesicles in the maintenance of mitochondrial proteome and health. The proper understanding of mitochondrial protein quality control mechanisms will provide relevant insights to treat multiple human diseases.

Alternative splicing of jnk1a in zebrafish determines first heart field ventricular cardiomyocyte numbers through modulation of hand2 expression

The planar cell polarity pathway is required for heart development and whilst the functions of most pathway members are known, the roles of the jnk genes in cardiac morphogenesis remain unknown as mouse mutants exhibit functional redundancy, with early embryonic lethality of compound mutants. In this study zebrafish were used to overcome early embryonic lethality in mouse models and establish the requirement for Jnk in heart development. Whole mount in-situ hybridisation and RT-PCR demonstrated that evolutionarily conserved alternative spliced jnk1a and jnk1b transcripts were expressed in the early developing heart. Maternal zygotic null mutant zebrafish lines for jnk1a and jnk1b, generated using CRISPR-Cas9, revealed a requirement for jnk1a in formation of the proximal, first heart field (FHF)-derived portion of the cardiac ventricular chamber. Rescue of the jnk1a mutant cardiac phenotype was only possible by injection of the jnk1a EX7 Lg alternatively spliced transcript. Analysis of mutants indicated that there was a reduction in the size of the hand2 expression field in jnk1a mutants which led to a specific reduction in FHF ventricular cardiomyocytes within the anterior lateral plate mesoderm. Moreover, the jnk1a mutant ventricular defect could be rescued by injection of hand2 mRNA. This study reveals a novel and critical requirement for Jnk1 in heart development and highlights the importance of alternative splicing in vertebrate cardiac morphogenesis. Genetic pathways functioning through jnk1 may be important in human heart malformations with left ventricular hypoplasia.

Chemogenetic interactions in human cancer cells

Chemogenetic profiling enables the identification of genes that enhance or suppress the phenotypic effect of chemical compounds. Using this approach in cancer therapies could improve our ability to predict the response of specific tumor genotypes to chemotherapeutic agents, thus accelerating the development of personalized drug therapy. In the not so distant past, this strategy was only applied in model organisms because there was no feasible technology to thoroughly exploit desired genetic mutations and their impact on drug efficacy in human cells. Today, with the advent of CRISPR gene-editing technology and its application to pooled library screens in mammalian cells, chemogenetic screens are performed directly in human cell lines with high sensitivity and specificity. Chemogenetic profiling provides insights into drug mechanism-of-action, genetic vulnerabilities, and resistance mechanisms, all of which will help to accurately deliver the right drug to the right target in the right patient while minimizing side effects.

Role of Signaling Molecules in Mitochondrial Stress Response

Mitochondria are established essential regulators of cellular function and metabolism. Mitochondria regulate redox homeostasis, maintain energy (ATP) production through oxidative phosphorylation, buffer calcium levels, and control cell death through apoptosis. In addition to these critical cell functions, recent evidence supports a signaling role for mitochondria. For example, studies over the past few years have established that peptides released from the mitochondria mediate stress responses such as the mitochondrial unfolded protein response (UPR^MT) through signaling to the nucleus. Mitochondrial damage or danger associated molecular patterns (DAMPs) provide a link between mitochondria, inflammation and inflammatory disease processes. Additionally, a new class of peptides generated by the mitochondria affords protection against age-related diseases in mammals. In this short review, we highlight the role of mitochondrial signaling and regulation of cellular activities through the mitochondrial UPR^MT that signals to the nucleus to affect homeostatic responses, DAMPs, and mitochondrial derived peptides.

JNK2 silencing and caspase-9 activation by hyperosmotic polymer inhibits tumor progression

c-Jun N-terminal kinase 2 (JNK2) is primarily responsible for the oncogenic transformation of the transcription factor c-Jun. Expression of the proto-oncogene c-Jun progresses the cell cycle from G1 to S phase, but when its expression becomes awry it leads to uncontrolled proliferation and angiogenesis. Delivering a JNK2 siRNA (siJNK2) in tumor tissue was anticipated to reverse the condition with subsequent onset of apoptosis which predominantly requires an efficient delivering system capable of penetrating through the compact tumor mass. In the present study, it was demonstrated that polymannitol-based vector (PMGT) with inherent hyperosmotic properties was able to penetrate through and deliver the siJNK2 in the subcutaneous tumor of xenograft mice. Hyperosmotic activity of polymannitol was shown to account for the enhanced therapeutic delivery both in vitro and in vivo because of the induction of cyclooxygenase-2 (COX-2) which stimulates caveolin-1 for caveolae-mediated endocytosis of the polyplexes. Further suppression of JNK2 and hence c-Jun expression led to the activation of caspase-9 to induce apoptosis and inhibition of tumor growth in xenograft mice model. The study exemplifies PMGT as an efficient vector for delivering therapeutic molecules in compact tumor tissue and suppression of JNK2 introduces a strategy to inhibit tumor progression.

IL-17RC is critically required to maintain baseline A20 production to repress JNK isoform-dependent tumor-specific proliferation

The IL-17/IL-17R axis has controversial roles in cancer, which may be explained by tumor-specific results. Here, we describe a novel molecular mechanism underlying IL-17RC-controlled tumor-specific proliferation. Triggered by IL-17RC knockdown (KD), B16 melanoma and 4T1 carcinoma cells inversely altered homeostatic tumor proliferation and tumor growth in vitro and in vivo. In contrast to the existing dogma that IL-17RC-dependent signaling activates the JNK pathway, IL-17RC KD in both tumor cell lines caused aberrant expression and activation of different JNK isoforms along with markedly diminished levels of the ubiquitin-editing enzyme A20. We demonstrated that differential up-regulation of JNK1 and JNK2 in the two tumor cell lines was responsible for the reciprocal regulation of c-Jun activity and tumor-specific proliferation. Furthermore, we showed that A20 reconstitution of IL-17RCKD clones with expression of full-length A20, but not a truncation-mutant, reversed aberrant JNK1/JNK2 activities and tumor-specific proliferation. Collectively, our study reveals a critical role of IL-17RC in maintaining baseline A20 production and a novel role of the IL-17RC-A20 axis in controlling JNK isoform-dependent tumor-specific homeostatic proliferation.

The STAT3 Target Mettl8 Regulates Mouse ESC Differentiation via Inhibiting the JNK Pathway

The capacity of embryonic stem cells (ESCs) to differentiate into all lineages of mature organism is precisely regulated by cellular signaling factors. STAT3 is a crucial transcription factor that plays a central role in maintaining ESC identity. However, the underlying mechanism by which STAT3 directs differentiation is still not completely understood. Here, we show that STAT3 positively regulates gene expression of methyltransferase-like protein 8 (Mettl8) in mouse ESCs. We found that METTL8 is dispensable for pluripotency but affects ESC differentiation. Subsequently, we discovered that METTL8 interacts with Mapkbp1's mRNA, which is an intermediate factor in c-Jun N-terminal kinase (JNK) signaling, and inhibits the translation of the mRNA. Thereby, METTL8 prohibits the activation of JNK signaling and enhances the differentiation of mouse ESCs. Collectively, our study uncovers a STAT3 target, Mettl8, which regulates mouse ESC differentiation via JNK signaling.

Ataxia-Telangiectasia Mutated (ATM) Kinase Regulates eNOS Expression and Modulates Radiosensitivity in Endothelial Cells Exposed to Ionizing Radiation

Endothelial nitric oxide synthase (eNOS), a constitutive enzyme expressed in vascular endothelial cells, is the main source of nitric oxide (NO), which plays key roles in diverse biological functions, including regulation of vascular tone. Exposure to radiation has been known to generate nitric oxide from eNOS; however, the precise mechanism of its generation and function is not known. The goal of this study was to determine the involvement of radiation-induced DNA damage response (DDR) on eNOS transcription and its effect on cell survival after irradiation. Irradiated bovine aortic endothelial cells showed increased eNOS transcription and NO generation through upregulation of ataxia-telangiectasia mutated (ATM) kinase. Radiation exposure induced NO inhibited cell death, as well as induced cellular senescence postirradiation. This study established that radiation-induced DDR uses ATM kinase to upregulate eNOS transcription and NO generation, leading to cellular senescence, which may play a critical role in radiation-mediated cardiovascular injury.

Vangl2 is essential for myocardial remodeling activated by Wnt/JNK signaling

The Wnt/JNK pathway, responsible for tissue polarity in cardiogenesis in vertebrates, has been shown to play numerous roles during differentiation and development of cardiac myocytes. Van Gogh-like-2 (Vangl2) is a core component that regulates the induction of polarized cellular and tissue morphology during animal development. However, little is known about Wnt/JNK signaling pathway in the process of myocardial remodeling. In present study, we found that activation of Wnt/JNK signaling by Wnt5a stimulates enlargement of cardiomyocyte surface area. The hypertrophic features were inhibited in Vangl2 depleted cells. Meanwhile, Wnt/JNK activation induced cytoskeleton rearrangement but failed to activate these effects in cells lacking Vangl2. Moreover, Wnt/JNK activation significantly increased the cell apoptosis by mediating the mitochondrial permeability transition pore (mPTP) dysfunction, whereas knockdown of Vangl2 partly reversed these effects. These results suggest that activation of Wnt/JNK signaling stimulates myocardial remodeling (cell morphological changes, apoptosis and mitochondrial dysfunction), in which Vangl2 may play an essential role.

Abnormal expression of TFIIIB subunits and RNA Pol III genes is associated with hepatocellular carcinoma

The levels of the products of RNA polymerase III-dependent genes (Pol III genes), including tRNAs and 5S rRNA, are elevated in transformed and tumor cells, which potentiate tumorigenesis. TFIIB-related factor 1 (Brf1) is a key transcription factor and specifically regulates the transcription of Pol III genes. In vivo and in vitro studies have demonstrated that a decrease in Brf1 reduces Pol III gene transcription and is sufficient for inhibiting cell transformation and tumor formation. Emerging evidence indicates that dysregulation of Brf1 and Pol III genes is linked to the development of hepatocellular carcinoma (HCC) in humans and animals. We have reported that Brf1 is overexpressed in human liver cancer patients and that those with high Brf1 levels have shorter survivals. This review summarizes the effects of dysregulation of these genes on HCC and their regulation by signaling pathways and epigenetics. These novel data should help us determine the molecular mechanisms of HCC from a different perspective and guide the development of therapeutic approaches for HCC patients.

Unacylated ghrelin normalizes skeletal muscle oxidative stress and prevents muscle catabolism by enhancing tissue mitophagy in experimental chronic kidney disease

Unacylated ghrelin (UnAG) may lower skeletal muscle oxidative stress, inflammation, and insulin resistance in lean and obese rodents. UnAG-induced autophagy activation may contribute to these effects, likely involving removal of dysfunctional mitochondria (mitophagy) and redox state maintenance. In chronic kidney disease (CKD) oxidative stress, inflammation and insulin resistance may negatively influence patient outcome by worsening nutritional state through muscle mass loss. Here we show in a 5/6 nephrectomy (Nx) CKD rat model that 4 d s.c. UnAG administration (200 µg twice a day) normalizes CKD-induced loss of gastrocnemius muscle mass and a cluster of high tissue mitochondrial reactive oxygen species generation, high proinflammatory cytokines, and low insulin signaling activation. Consistent with these results, human uremic serum enhanced mitochondrial reactive oxygen species generation and lowered insulin signaling activation in C2C12 myotubes while concomitant UnAG incubation completely prevented these effects. Importantly, UnAG enhanced muscle mitophagy in vivo and silencing RNA-mediated autophagy protein 5 silencing blocked UnAG activities in myotubes. UnAG therefore normalizes CKD-induced skeletal muscle oxidative stress, inflammation, and low insulin signaling as well as muscle loss. UnAG effects are mediated by autophagy activation at the mitochondrial level. UnAG administration and mitophagy activation are novel potential therapeutic strategies for skeletal muscle metabolic abnormalities and their negative clinical impact in CKD.-Gortan Cappellari, G., Semolic, A., Ruozi, G., Vinci, P., Guarnieri, G., Bortolotti, F., Barbetta, D., Zanetti, M., Giacca, M., Barazzoni, R. Unacylated ghrelin normalizes skeletal muscle oxidative stress and prevents muscle catabolism by enhancing tissue mitophagy in experimental chronic kidney disease.

Alternative promotion and suppression of metastasis by JNK2 governed by its phosphorylation

Fos-related antigen 1 (Fra1) has been proposed as a gatekeeper of the mesenchymal-epithelial transition to epithelial-mesenchymal transition. Here, we showed that de-phosphorylated JNK2 increased the expression of Fra1 by promoting the expression of c-Jun and Jun-B. Conversely, phosphorylated JNK2 suppressed its expression via enhancing the ubiquitination of c-Jun and Jun-B. These data provided insights into the regulatory mechanism of JNK2 on the expression of Fra1. Our study thus demonstrated that the conversion of JNK2 from its phosphorylation to de-phosphorylation status promoted the switch of breast cancer cells from mesenchymal-epithelial transition to epithelial-mesenchymal transition.

JNKs function as CDK4-activating kinases by phosphorylating CDK4 and p21

Cyclin D-CDK4/6 are the first cyclin-dependent kinase (CDK) complexes to be activated by mitogenic/oncogenic pathways. They have a central role in the cell multiplication decision and in its deregulation in cancer cells. We identified T172 phosphorylation of CDK4 rather than cyclin D accumulation as the distinctly regulated step determining CDK4 activation. This finding challenges the view that the only identified metazoan CDK-activating kinase, cyclin H-CDK7-Mat1 (CAK), which is constitutively active, is responsible for the activating phosphorylation of all cell cycle CDKs. We previously showed that T172 phosphorylation of CDK4 is conditioned by an adjacent proline (P173), which is not present in CDK6 and CDK1/2. Although CDK7 activity was recently shown to be required for CDK4 activation, we proposed that proline-directed kinases might specifically initiate the activation of CDK4. Here, we report that JNKs, but not ERK1/2 or CAK, can be direct CDK4-activating kinases for cyclin D-CDK4 complexes that are inactivated by p21-mediated stabilization. JNKs and ERK1/2 also phosphorylated p21 at S130 and T57, which might facilitate CDK7-dependent activation of p21-bound CDK4, however, mutation of these sites did not impair the phosphorylation of CDK4 by JNKs. In two selected tumor cells, two different JNK inhibitors inhibited the phosphorylation and activation of cyclin D1-CDK4-p21 but not the activation of cyclin D3-CDK4 that is mainly associated to p27. Specific inhibition by chemical genetics in MEFs confirmed the involvement of JNK2 in cyclin D1-CDK4 activation. Therefore, JNKs could be activating kinases for cyclin D1-CDK4 bound to p21, by independently phosphorylating both CDK4 and p21.

JNK Signaling: Regulation and Functions Based on Complex Protein-Protein Partnerships

The c-Jun N-terminal kinases (JNKs), as members of the mitogen-activated protein kinase (MAPK) family, mediate eukaryotic cell responses to a wide range of abiotic and biotic stress insults. JNKs also regulate important physiological processes, including neuronal functions, immunological actions, and embryonic development, via their impact on gene expression, cytoskeletal protein dynamics, and cell death/survival pathways. Although the JNK pathway has been under study for >20 years, its complexity is still perplexing, with multiple protein partners of JNKs underlying the diversity of actions. Here we review the current knowledge of JNK structure and isoforms as well as the partnerships of JNKs with a range of intracellular proteins. Many of these proteins are direct substrates of the JNKs. We analyzed almost 100 of these target proteins in detail within a framework of their classification based on their regulation by JNKs. Examples of these JNK substrates include a diverse assortment of nuclear transcription factors (Jun, ATF2, Myc, Elk1), cytoplasmic proteins involved in cytoskeleton regulation (DCX, Tau, WDR62) or vesicular transport (JIP1, JIP3), cell membrane receptors (BMPR2), and mitochondrial proteins (Mcl1, Bim). In addition, because upstream signaling components impact JNK activity, we critically assessed the involvement of signaling scaffolds and the roles of feedback mechanisms in the JNK pathway. Despite a clarification of many regulatory events in JNK-dependent signaling during the past decade, many other structural and mechanistic insights are just beginning to be revealed. These advances open new opportunities to understand the role of JNK signaling in diverse physiological and pathophysiological states.

Redundancy in the World of MAP Kinases: All for One

The protein kinases ERK1 and ERK2 are the effector components of the prototypical ERK1/2 mitogen-activated protein (MAP) kinase pathway. This signaling pathway regulates cell proliferation, differentiation and survival, and is essential for embryonic development and cellular homeostasis. ERK1 and ERK2 homologs share similar biochemical properties but whether they exert specific physiological functions or act redundantly has been a matter of controversy. However, recent studies now provide compelling evidence in support of functionally redundant roles of ERK1 and ERK2 in embryonic development and physiology. In this review, we present a critical assessment of the evidence for the functional specificity or redundancy of MAP kinase isoforms. We focus on the ERK1/ERK2 pathway but also discuss the case of JNK and p38 isoforms.

JNK1 Inhibition Attenuates Hypoxia-Induced Autophagy and Sensitizes to Chemotherapy

Inhibition of hypoxia-induced stress signaling through JNK potentiates the effects of oxaliplatin. The JNK pathway plays a role in both autophagy and apoptosis; therefore, it was determined how much of the effect of JNK inhibition on oxaliplatin sensitivity is dependent on its effect on autophagy. We studied the impact of JNK isoform downregulation in the HT29 colon adenocarcinoma cell line on hypoxia- and oxaliplatin-induced responses. Electron microscopic analyses demonstrated that both oxaliplatin- and hypoxia-induced formations of autophagosomes were reduced significantly in HT29 cells treated with the JNK inhibitor SP600125. The role of specific JNK isoforms was defined using HT29-derived cell lines stably expressing dominant-negative constructs for JNK1 and JNK2 (HTJ1.3 and HTJ2.2, respectively). These cell lines demonstrated that functional JNK1 is required for hypoxia-induced autophagy and that JNK2 does not substitute for it. Inhibition of autophagy in HTJ1.3 cells also coincided with enhancement of intrinsic apoptosis. Analysis of Bcl2-family proteins revealed hyperphosphorylation of Bcl-XL in the HTJ1.3 cell line, but this did not lead to the expected dissociation from Beclin 1. Consistent with this, knockdown of Bcl-XL in HT29 cells did not significantly affect the induction of autophagy, but abrogated hypoxic resistance to oxaliplatin due to the faster and more robust activation of apoptosis.

IMPLICATIONS

These data suggest that balance between autophagy and apoptosis is shifted toward apoptosis by downregulation of JNK1, contributing to oxaliplatin sensitization. These findings further support the investigation of JNK inhibition in colorectal cancer treatment. Mol Cancer Res; 14(8); 753-63. ©2016 AACR.

Molecular clone and characterization of c-Jun N-terminal kinases 2 from orange-spotted grouper, Epinephelus coioides

c-Jun N-terminal kinase 2 (JNK2) is a multifunctional mitogen-activated protein kinases involving in cell differentiation and proliferation, apoptosis, immune response and inflammatory conditions. In this study, we reported a new JNK2 (Ec-JNK2) derived from orange-spotted grouper, Epinephelus coioides. The full-length cDNA of Ec-JNK2 was 1920 bp in size, containing a 174 bp 5'-untranslated region (UTR), 483 bp 3'-UTR, and a 1263 bp open reading frame (ORF), which encoded a putative protein of 420 amino acids. The deduced protein sequence of Ec-JNK2 contained a conserved Thr-Pro-Tyr (TPY) motif in the domain of serine/threonine protein kinase (S-TKc). Ec-JNK2 has been found to involve in the immune response to pathogen challenges in vivo, and the infection of Singapore grouper iridovirus (SGIV) in vitro. Immunofluorescence staining showed that Ec-JNK2 was localized in the cytoplasm of grouper spleen (GS) cells, and moved to the nucleus after infecting with SGIV. Ec-JNK2 distributed in all immune-related tissues examined. After challenging with lipopolysaccharide (LPS), SGIV and polyriboinosinic polyribocytidylic acid (poly I:C), the mRNA expression of Ec-JNK2 was significantly (P < 0.01) up-regulated in juvenile orange-spotted grouper. Over-expressing Ec-JNK2 in fathead minnow (FHM) cells increased the SGIV infection and replication, while over-expressing the dominant-negative Ec-JNK2Δ181-183 mutant decreased it. These results indicated that Ec-JNK2 could be an important molecule in the successful infection and evasion of SGIV.

Transplant-induced reactivation of murine cytomegalovirus immediate early gene expression is associated with recruitment of NF-κB and AP-1 to the major immediate early promoter

Reactivation of latent human cytomegalovirus is a significant infectious complication of organ transplantation and current therapies target viral replication once reactivation of latent virus has already occurred. The specific molecular pathways that activate viral gene expression in response to transplantation are not well understood. Our studies aim to identify these factors, with the goal of developing novel therapies that prevent transcriptional reactivation in transplant recipients. Murine cytomegalovirus (MCMV) is a valuable model for studying latency and reactivation of CMV in vivo. We previously demonstrated that transplantation of MCMV-latently infected kidneys into allogeneic recipients induces reactivation of immediate early (IE) gene expression and epigenetic reprogramming of the major immediate early promoter (MIEP) within 48 h. We hypothesize that these events are mediated by activation of signalling pathways that lead to binding of transcription factors to the MIEP, including AP-1 and NF-κB. Here we show that transplantation induces rapid activation of several members of the AP-1 and NF-κB transcription factor family and we demonstrate that canonical NF-κB (p65/p50), the junD component of AP-1, and nucleosome remodelling complexes are recruited to the MIEP following transplantation. Proteomic analysis of recipient plasma and transcriptome analysis of kidney RNA identified five extracellular ligands, including TNF, IL-1β, IL-18, CD40L and IL-6, and three intracellular signalling pathways associated with reactivation of IE gene expression. Identification of the factors that mediate activation of these signalling pathways may eventually lead to new therapies to prevent reactivation of CMV and its sequelae.

Tumor cell survival pathways activated by photodynamic therapy: a molecular basis for pharmacological inhibition strategies

Photodynamic therapy (PDT) has emerged as a promising alternative to conventional cancer therapies such as surgery, chemotherapy, and radiotherapy. PDT comprises the administration of a photosensitizer, its accumulation in tumor tissue, and subsequent irradiation of the photosensitizer-loaded tumor, leading to the localized photoproduction of reactive oxygen species (ROS). The resulting oxidative damage ultimately culminates in tumor cell death, vascular shutdown, induction of an antitumor immune response, and the consequent destruction of the tumor. However, the ROS produced by PDT also triggers a stress response that, as part of a cell survival mechanism, helps cancer cells to cope with the PDT-induced oxidative stress and cell damage. These survival pathways are mediated by the transcription factors activator protein 1 (AP-1), nuclear factor E2-related factor 2 (NRF2), hypoxia-inducible factor 1 (HIF-1), nuclear factor κB (NF-κB), and those that mediate the proteotoxic stress response. The survival pathways are believed to render some types of cancer recalcitrant to PDT and alter the tumor microenvironment in favor of tumor survival. In this review, the molecular mechanisms are elucidated that occur post-PDT to mediate cancer cell survival, on the basis of which pharmacological interventions are proposed. Specifically, pharmaceutical inhibitors of the molecular regulators of each survival pathway are addressed. The ultimate aim is to facilitate the development of adjuvant intervention strategies to improve PDT efficacy in recalcitrant solid tumors.

The activation of p38 MAPK limits the abnormal proliferation of vascular smooth muscle cells induced by high sodium concentrations

The aim of the present study was to ascertain whether high sodium levels can directly promote the proliferation of vascular smooth muscle cells (VSMCs) and to elucidate the underlying mechanisms. Additional sodium chloride (NaCl) was added to the routine culture medium. Cell proliferation was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and 5-ethynyl-2′-deoxyuridine (EdU) incorporation assay. The mRNA expression level of proliferating cell nuclear antigen (PCNA) was measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The protein expression levels of PCNA and phosphorylated c-Jun amino N-terminal kinase (p-JNK), phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) and phosphorylated p38 mitogen-activated protein kinase (p-p38 MAPK) were measured by western blot analysis. Cell proliferation assay revealed that Na⁺ rather than Cl⁻ or osmotic pressure promoted the proliferation of the VSMCs. The high sodium level upregulated the expression of PCNA and the phosphorylation levels of JNK, ERK1/2 and p38 MAPK. The inhibition of JNK and ERK1/2 decreased PCNA expression. Of note, the inhibition of p38 MAPK using the inhibitor, SB203580, increased PCNA expression. However, when p38 MAPK was activated by anisomycin, PCNA expression was decreased. On the whole, our findings demonstrate that a relatively high sodium level per se directly promotes the proliferation of VSMCs through the JNK/ERK1/2/PCNA pathway. At the same time, this induction of the proliferation of VSMCs due to high sodium levels can be maintained at a low level via the activation of p38 MAPK.

CSN6 positively regulates c-Jun in a MEKK1-dependent manner

c-Jun is a proto-oncoprotein that is commonly overexpressed in many types of cancer and is believed to regulate cell proliferation, the cell cycle, and apoptosis by controlling AP-1 activity. Understanding the c-Jun regulation is important to develop treatment strategy for cancer. The COP9 signalosome subunit 6 (CSN6) plays a critical role in ubiquitin-mediated protein degradation. MEKK1 is a serine/threonine kinase and E3 ligase containing PHD/RING domain involved in c-Jun ubiquitination. Here, we show that CSN6 associates with MEKK1 and reduces MEKK1 expression level by facilitating the ubiquitin-mediated degradation of MEKK1. Also we show that CSN6 overexpression diminishes MEKK1-mediated c-Jun ubiquitination, which is manifested in mitigating osmotic stress-mediated c-Jun downregulation. Thus, CSN6 is involved in positively regulating the stability of c-Jun. Overexpression of CSN6 correlates with the upregulation of c-Jun target gene expression in cancer. These findings provide new insight into CSN6-MEKK1-c-Jun axis in tumorigenesis.

The Potential of Vitamin D-Regulated Intracellular Signaling Pathways as Targets for Myeloid Leukemia Therapy

The current standard regimens for the treatment of acute myeloid leukemia (AML) are curative in less than half of patients; therefore, there is a great need for innovative new approaches to this problem. One approach is to target new treatments to the pathways that are instrumental to cell growth and survival with drugs that are less harmful to normal cells than to neoplastic cells. In this review, we focus on the MAPK family of signaling pathways and those that are known to, or potentially can, interact with MAPKs, such as PI3K/AKT/FOXO and JAK/STAT. We exemplify the recent studies in this field with specific relevance to vitamin D and its derivatives, since they have featured prominently in recent scientific literature as having anti-cancer properties. Since microRNAs also are known to be regulated by activated vitamin D, this is also briefly discussed here, as are the implications of the emerging acquisition of transcriptosome data and potentiation of the biological effects of vitamin D by other compounds. While there are ongoing clinical trials of various compounds that affect signaling pathways, more studies are needed to establish the clinical utility of vitamin D in the treatment of cancer.

Generation and characterization of ATP analog-specific protein kinase Cδ

To better study the role of PKCδ in normal function and disease, we developed an ATP analog-specific (AS) PKCδ that is sensitive to specific kinase inhibitors and can be used to identify PKCδ substrates. AS PKCδ showed nearly 200 times higher affinity (Km) and 150 times higher efficiency (kcat/Km) than wild type (WT) PKCδ toward N(6)-(benzyl)-ATP. AS PKCδ was uniquely inhibited by 1-(tert-butyl)-3-(1-naphthyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine (1NA-PP1) and 1-(tert-butyl)-3-(2-methylbenzyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine (2MB-PP1) but not by other 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP1) analogs tested, whereas WT PKCδ was insensitive to all PP1 analogs. To understand the mechanisms for specificity and affinity of these analogs, we created in silico WT and AS PKCδ homology models based on the crystal structure of PKCι. N(6)-(Benzyl)-ATP and ATP showed similar positioning within the purine binding pocket of AS PKCδ, whereas N(6)-(benzyl)-ATP was displaced from the pocket of WT PKCδ and was unable to interact with the glycine-rich loop that is required for phosphoryl transfer. The adenine rings of 1NA-PP1 and 2MB-PP1 matched the adenine ring of ATP when docked in AS PKCδ, and this interaction prevented the potential interaction of ATP with Lys-378, Glu-428, Leu-430, and Phe-633 residues. 1NA-PP1 failed to effectively dock within WT PKCδ. Other PP1 analogs failed to interact with either AS PKCδ or WT PKCδ. These results provide a structural basis for the ability of AS PKCδ to efficiently and specifically utilize N(6)-(benzyl)-ATP as a phosphate donor and for its selective inhibition by 1NA-PP1 and 2MB-PP1. Such homology modeling could prove useful in designing molecules to target PKCδ and other kinases to understand their function in cell signaling and to identify unique substrates.

JNK signalling in cancer: in need of new, smarter therapeutic targets

The JNKs are master protein kinases that regulate many physiological processes, including inflammatory responses, morphogenesis, cell proliferation, differentiation, survival and death. It is increasingly apparent that persistent activation of JNKs is involved in cancer development and progression. Therefore, JNKs represent attractive targets for therapeutic intervention with small molecule kinase inhibitors. However, evidence supportive of a tumour suppressor role for the JNK proteins has also been documented. Recent studies showed that the two major JNK proteins, JNK1 and JNK2, have distinct or even opposing functions in different types of cancer. As such, close consideration of which JNK proteins are beneficial targets and, more importantly, what effect small molecule inhibitors of JNKs have on physiological processes, are essential. A number of ATP-competitive and ATP-non-competitive JNK inhibitors have been developed, but have several limitations such as a lack of specificity and cellular toxicity. In this review, we summarize the accumulating evidence supporting a role for the JNK proteins in the pathogenesis of different solid and haematological malignancies, and discuss many challenges and scientific opportunities in the targeting of JNKs in cancer.

Mitochondrial stress signaling in longevity: a new role for mitochondrial function in aging

Mitochondria are principal regulators of cellular function and metabolism through production of ATP for energy homeostasis, maintenance of calcium homeostasis, regulation of apoptosis and fatty acid oxidation to provide acetyl CoA for fueling the electron transport chain. In addition, mitochondria play a key role in cell signaling through production of reactive oxygen species that modulate redox signaling. Recent findings support an additional mechanism for control of cellular and tissue function by mitochondria through complex mitochondrial-nuclear communication mechanisms and potentially through extracellular release of mitochondrial components that can act as signaling molecules. The activation of stress responses including mitophagy, mitochondrial number, fission and fusion events, and the mitochondrial unfolded protein response (UPR(MT)) requires mitochondrial-nuclear communication for the transcriptional activation of nuclear genes involved in mitochondrial quality control and metabolism. The induction of these signaling pathways is a shared feature in long-lived organisms spanning from yeast to mice. As a result, the role of mitochondrial stress signaling in longevity has been expansively studied. Current and exciting studies provide evidence that mitochondria can also signal among tissues to up-regulate cytoprotective activities to promote healthy aging. Alternatively, mitochondria release signals to modulate innate immunity and systemic inflammatory responses and could consequently promote inflammation during aging. In this review, established and emerging models of mitochondrial stress response pathways and their potential role in modulating longevity are discussed.

Inhibition of GTPase Rac1 in endothelium by 6-mercaptopurine results in immunosuppression in nonimmune cells: new target for an old drug

Azathioprine and its metabolite 6-mercaptopurine (6-MP) are well established immunosuppressive drugs. Common understanding of their immunosuppressive properties is largely limited to immune cells. However, in this study, the mechanism underlying the protective role of 6-MP in endothelial cell activation is investigated. Because 6-MP and its derivative 6-thioguanosine-5'-triphosphate (6-T-GTP) were shown to block activation of GTPase Rac1 in T lymphocytes, we focused on Rac1-mediated processes in endothelial cells. Indeed, 6-MP and 6-T-GTP decreased Rac1 activation in endothelial cells. As a result, the compounds inhibited TNF-α-induced downstream signaling via JNK and reduced activation of transcription factors c-Jun, activating transcription factor-2 and, in addition, NF κ-light-chain-enhancer of activated B cells (NF-κB), which led to decreased transcription of proinflammatory cytokines. Moreover, 6-MP and 6-T-GTP selectively decreased TNF-α-induced VCAM-1 but not ICAM-1 protein levels. Rac1-mediated generation of cell membrane protrusions, which form docking structures to capture leukocytes, also was reduced by 6-MP/6-T-GTP. Consequently, leukocyte transmigration was inhibited after 6-MP/6-T-GTP treatment. These data underscore the anti-inflammatory effect of 6-MP and 6-T-GTP on endothelial cells by blocking Rac1 activation. Our data provide mechanistic insight that supports development of novel Rac1-specific therapeutic approaches against chronic inflammatory diseases.

Potential role of proteasome on c-jun related signaling in hypercholesterolemia induced atherosclerosis

Atherosclerosis and its complications are major causes of death all over the world. One of the major risks of atherosclerosis is hypercholesterolemia. During atherosclerosis, oxidized low density lipoprotein (oxLDL) regulates CD36-mediated activation of c-jun amino terminal kinase-1 (JNK1) and modulates matrix metalloproteinase (MMP) induction which stimulates inflammation with an invasion of monocytes. Additionally, inhibition of proteasome leads to an accumulation of c-jun and phosphorylated c-jun and activation of activator protein-1 (AP-1) related increase of MMP expression. We have previously reported a significant increase in cluster of differentiation 36 (CD36) mRNA levels in hypercholesterolemic rabbits and shown that vitamin E treatment prevented the cholesterol induced increase in CD36 mRNA expression. In the present study, our aim is to identify the signaling molecules/transcription factors involved in the progression of atherosclerosis following CD36 activation in an in vivo model of hypercholesterolemic (induced by 2% cholesterol containing diet) rabbits. In this direction, proteasomal activities by fluorometry and c-jun, phospo c-jun, JNK1, MMP-9 expressions by quantitative RT-PCR and immunoblotting were tested in aortic tissues. The effects of vitamin E on these changes were also investigated in this model. As a result, c-jun was phosphorylated following decreased proteasomal degradation in hypercholesterolemic group. MMP-9 expression was also increased in cholesterol group rabbits contributing to the development of atherosclerosis. In addition, vitamin E showed its effect by decreasing MMP-9 levels and phosphorylation of c-jun.

Convergent regulation of the lysosomal two-pore channel-2 by Mg²⁺, NAADP, PI(3,5)P₂ and multiple protein kinases

Lysosomal Ca(2+) homeostasis is implicated in disease and controls many lysosomal functions. A key in understanding lysosomal Ca(2+) signaling was the discovery of the two-pore channels (TPCs) and their potential activation by NAADP. Recent work concluded that the TPCs function as a PI(3,5)P2 activated channels regulated by mTORC1, but not by NAADP. Here, we identified Mg(2+) and the MAPKs, JNK and P38 as novel regulators of TPC2. Cytoplasmic Mg(2+) specifically inhibited TPC2 outward current, whereas lysosomal Mg(2+) partially inhibited both outward and inward currents in a lysosomal lumen pH-dependent manner. Under controlled Mg(2+), TPC2 is readily activated by NAADP with channel properties identical to those in response to PI(3,5)P2. Moreover, TPC2 is robustly regulated by P38 and JNK. Notably, NAADP-mediated Ca(2+) release in intact cells is regulated by Mg(2+), PI(3,5)P2, and P38/JNK kinases, thus paralleling regulation of TPC2 currents. Our data affirm a key role for TPC2 in NAADP-mediated Ca(2+) signaling and link this pathway to Mg(2+) homeostasis and MAP kinases, pointing to roles for lysosomal Ca(2+) in cell growth, inflammation and cancer.

The role of mitogen- and stress-activated protein kinase pathways in melanoma

Recent discoveries have increased our comprehension of the molecular signaling events critical for melanoma development and progression. Many oncogenes driving melanoma have been identified, and most of them exert their oncogenic effects through the activation of the RAF/MEK/ERK mitogen-activated protein kinase (MAPK) pathway. The c-Jun N-terminal kinase (JNK) and p38 MAPK pathways are also important in melanoma, but their precise role is not clear yet. This review summarizes our current knowledge on the role of the three main MAPK pathways, extracellular regulated kinase (ERK), JNK, and p38, and their impact on melanoma biology. Although the results obtained with BRAF inhibitors in melanoma patients are impressive, several mechanisms of acquired resistance have emerged. To overcome this obstacle constitutes the new challenge in melanoma therapy. Given the major role that MAPKs play in melanoma, understanding their functions and the interconnection among them and with other signaling pathways represents a step forward toward this goal.

The mitochondrial unfolded protein response, a conserved stress response pathway with implications in health and disease

The ability to respond to various intracellular and/or extracellular stresses allows the organism to adapt to changing environmental conditions and drives evolution. It is now well accepted that a progressive decline of the efficiency of stress response pathways occurs with aging. In this context, a correct proteostasis is essential for the functionality of the cell, and its dysfunction has been associated with protein aggregation and age-related degenerative diseases. Complex response mechanisms have evolved to deal with unfolded protein stress in different subcellular compartments and their moderate activation translates into positive effects on health. In this review, we focus on the mitochondrial unfolded protein response (UPR(mt)), a response to proteotoxic stress specifically in mitochondria, an organelle with a wide array of fundamental functions, most notably the harvesting of energy from food and the control of cell death. We compare UPR(mt) with the extensively characterized cytosolic heat shock response (HSR) and the unfolded protein response in endoplasmic reticulum (UPR(ER)), and discuss the current knowledge about UPR(mt) signaling pathways as well as their potential involvement in physiology.

JNK1 and JNK2 regulate α-SMA in hepatic stellate cells during CCl4 -induced fibrosis in the rat liver

Following liver injuries, hepatic stellate cells (HSCs) express α-SMA. Mitogen activated protein kinase (MAPK) signaling pathways mediate α-SMA expression in distinct cell types. However, the regulation of α-SMA expression by MAPKs in HSCs has been rarely studied. We aimed to study the role of MAPKs in the activation of HSCs during liver fibrosis. Liver fibrosis of rats was induced by carbon tetrachloride. HSC-T6 cells, murine embryonic fibroblasts, JNK1(-/-) and JNK2(-/-) cells were used for in vitro studies. Immunohistochemistry and immunoblot analysis were used. We have found that the expression of JNK and α-SMA co-localized in HSCs during liver fibrosis, but ERK and p38 expressed in macrophages. The expression of α-SMA was up-regulated by JNK1 and JNK2 in non-stress condition. Under TGF-β stimulation, however, the level α-SMA expression was increased by only JNK1, but not significantly changed by JNK2. We suggest that JNKs are responsible for α-SMA regulation, and especially JNK1 has a major role in up-regulation of α-SMA expression in HSCs under stress condition induced by TGF-β during liver fibrosis.

Porphyromonas gingivalis promotes invasion of oral squamous cell carcinoma through induction of proMMP9 and its activation

Recent epidemiological studies have revealed a significant association between periodontitis and oral squamous cell carcinoma (OSCC). Furthermore, matrix metalloproteinase 9 (MMP9) is implicated in the invasion and metastasis of tumour cells. We examined the involvement of Porphyromonas gingivalis, a periodontal pathogen, in OSCC invasion through induced expression of proMMP and its activation. proMMP9 was continuously secreted from carcinoma SAS cells, while P. gingivalis infection increased proenzyme expression and subsequently processed it to active MMP9 in culture supernatant, which enhanced cellular invasion. In contrast, Fusobacterium nucleatum, another periodontal organism, failed to demonstrate such activities. The effects of P. gingivalis were observed with highly invasive cells, but not with the low invasivetype. P. gingivalis also stimulated proteinase-activated receptor 2 (PAR2) and enhanced proMMP9 expression, which promoted cellular invasion. P. gingivalis mutants deficient in gingipain proteases failed to activate MMP9. Infected SAS cells exhibited activation of ERK1/2, p38, and NF-kB, and their inhibitors diminished both proMMP9-overexpression and cellular invasion. Together, our results show that P. gingivalis activates the ERK1/2-Ets1, p38/HSP27, and PAR2/NF-kB pathways to induce proMMP9 expression, after which the proenzyme is activated by gingipains to promote cellular invasion of OSCC cell lines. These findings suggest a novel mechanism of progression and metastasis of OSCC associated with periodontitis.

Differential regulation of c-Jun protein plays an instrumental role in chemoresistance of cancer cells

The chemotherapeutic drug cisplatin (cis-diamminedichloroplatinum(II) (CDDP)) is widely used in the treatment of human cancers. However, the mechanism underlying intrinsic tumor resistance to CDDP remains elusive. Here, we demonstrate that treatment with CDDP resulted in down-regulation of c-Jun expression via caspase-9-dependent cleavage of c-Jun at Asp-65 and MEKK1-mediated ubiquitylation and degradation of c-Jun in CDDP-sensitive cancer cells. In contrast, activation of JNK2 (but not JNK1) phosphorylated and up-regulated the expression of c-Jun in CDDP-resistant cells. Activated c-Jun bound to the promoter regions of the MDR1 gene and promoted the expression of MDR1. Expression of a cleavage-resistant c-Jun mutant (D65A) suppressed CDDP-induced apoptosis of CDDP-sensitive cells, whereas depletion of JNK2, c-Jun, or MDR1 in CDDP-resistant cancer cells promoted apoptosis upon CDDP treatment. In addition, mammary gland tumors induced by polyomavirus middle T antigen in JNK2(-/-) mice were more sensitive to CDDP compared with those in JNK2(+/+) mice. These findings highlight the instrumental role of c-Jun in the resistance of tumors to treatment with CDDP and indicate that c-Jun is a molecular target for improving cancer therapy.

Luteolin suppresses UVB-induced photoageing by targeting JNK1 and p90 RSK2

Multiple lines of evidence suggest that natural compounds can prevent skin ageing induced by ultraviolet light. Luteolin, a bioactive compound found in chilli, onion, broccoli, celery and carrot, has been reported to exhibit anti-photoageing effects in vitro. However, the molecular targets and mechanisms of luteolin are still poorly understood. In this study, we sought to investigate the effects of luteolin on UVB-induced photoageing and the molecular mechanisms involved, using HaCaT human keratinocytes and SKH-1 hairless mice. Luteolin was found to inhibit UVB-induced MMP-1 expression in HaCaT cells, as well as UVB-induced activation of AP-1, a well-known transcription factor targeting the MMP-1 promoter region, as well as c-Fos and c-Jun, which comprise the AP-1 complex. In contrast, Western blot data showed that UVB-induced phosphorylation of JNK, ERK and p90RSK was not inhibited by luteolin. In vitro kinase assay data revealed that luteolin significantly suppressed JNK1 and p90RSK activity, but not that of JNK2 and ERK2. Pull-down assays showed that luteolin binds JNK1 in an ATP-competitive manner and p90RSK2 in an ATP-independent manner. Luteolin also inhibited UVB-induced wrinkle formation and MMP-13 expression, a rodent interstitial collagenase in mouse skin, in vivo. Taken together, our observations suggest that luteolin exhibits anti-photoageing effects in vitro and in vivo and may have potential as a treatment for the prevention of skin ageing.

Skeletal muscle-specific overproduction of constitutively activated c-Jun N-terminal kinase (JNK) induces insulin resistance in mice

AIMS/HYPOTHESIS

Although skeletal muscle insulin resistance has been associated with activation of c-Jun N-terminal kinase (JNK), whether increased JNK activity causes insulin resistance in this organ is not clear. In this study we examined the metabolic consequences of isolated JNK phosphorylation in muscle tissue.

METHODS

Plasmids containing genes encoding a wild-type JNK1 (WT-JNK) or a JNK1/JNKK2 fusion protein (rendering JNK constitutively active; CA-Jnk) were electroporated into one tibialis anterior (TA) muscle of C57Bl/6 mice, with the contralateral TA injected with an empty vector (CON) to serve as a within-animal control.

RESULTS

Overproduction of WT-JNK resulted in a modest (~25%) increase in phosphorylation (Thr(183)/Tyr(185)) of JNK, but no differences were observed in Ser(307) phosphorylation of insulin receptor substrate 1 (IRS-1) or total IRS-1 protein, nor in insulin-stimulated glucose clearance into the TA muscle when comparing WT-JNK with CON. By contrast, overexpression of CA-Jnk, which markedly increased the phosphorylation of CA-JNK, also increased serine phosphorylation of IRS-1, markedly decreased total IRS-1 protein, and decreased insulin-stimulated phosphorylation of the insulin receptor (Tyr(1361)) and phosphorylation of Akt at (Ser(473) and Thr(308)) compared with CON. Moreover, overexpression of CA-Jnk decreased insulin-stimulated glucose clearance into the TA muscle compared with CON and these effects were observed without changes in intramuscular lipid species.

CONCLUSIONS/INTERPRETATION

Constitutive activation of JNK in skeletal muscle impairs insulin signalling at the level of IRS-1 and Akt, a process which results in the disruption of normal glucose clearance into the muscle.

Mechanism for the induction of cell death in ONS-76 medulloblastoma cells by Zhangfei/CREB-ZF

Cells from medulloblastoma lines do not contain detectable amounts of the basic leucine-zipper protein Zhangfei. However, we have previously shown that expression of this protein in cells of the ONS-76 and UW228 medulloblastoma lines causes the cells to stop growing and develop processes that resemble neurites. Our objective was to determine the molecular mechanisms by which Zhangfei influences ONS-76 cells. We infected ONS-76 cells with adenovirus vectors expressing either Zhangfei or the control protein LacZ and then compared the following parameters in Zhangfei and LacZ-expressing cells: (a) markers of apoptosis, autophagy and macropinocytosis, (b) transcripts for genes involved in neurogenesis and apoptosis, (c) phosphorylation of peptide targets of selected cellular protein kinases, and (d) activation of transcription factors. Zhangfei-expressing cells appeared to succumb to apoptosis. Increased staining for autophagic vesicles and upregulated expression of autophagy response genes in these cells indicated that they were undergoing autophagy, possibly associated with apoptosis. Within our analysis, patterns of gene expression and phosphorylation-mediated signal transduction activity in Zhangfei-expressing cells indicated that the mitogen-activated protein kinase (MAPK) pathway was active. In addition, we found that the transcription factor Brn3a as well as factors implicated in differentiation were also active in Zhangfei-expressing cells. We tested the hypothesis that Zhangfei enhances the expression of Brn3a, a known inducer of TrkA, the high-affinity receptor for nerve growth factor (NGF). TrkA then engages NGF in an autocrine manner triggering the MAPK pathway and leading to differentiation of ONS-76 cells into neuron and glia-like cells-a process that eventually brings about cell death. We showed that: (a) Zhangfei could enhance transcription from the isolated Brn3a promoter, (b) ONS-76 cells produced NGF and (c) antibodies against NGF and inhibitors of TrkA and selected components of the MAPK pathway could partially restore the growth of Zhangfei-expressing ONS-76 cells.

Molecular mechanisms of liver injury and hepatocarcinogenesis: focusing on the role of stress-activated MAPK

Hepatocellular carcinoma (HCC) is the third most common cause of cancer mortality. Short-term prognosis of patients with HCC has improved recently due to advances in early diagnosis and treatment, but long-term prognosis is still unsatisfactory. Therefore, obtaining a further understanding of the molecular carcinogenic mechanisms and the unique pathogenic biology of HCC is important. The most characteristic process in hepatocarcinogenesis is underlying chronic liver injury, which leads to repeated cycles of hepatocyte death, inflammation, and compensatory proliferation and subsequently provides a mitogenic and mutagenic environment leading to the development of HCC. Recent in vivo studies have shown that the stress-activated mitogen-activated protein kinase (MAPK) cascade converging on c-Jun NH(2)-terminal kinase (JNK) and p38 plays a central role in these processes, and it has attracted considerable attention as a therapeutic target. However, JNK and p38 have complex functions and a wide range of cellular effects. In addition, crosstalk with each other and the nuclear factor-kappaB pathway further complicate these functions. A full understanding is essential to bring these observations into clinical settings. In this paper, we discuss the latest findings regarding the mechanisms of liver injury and hepatocarcinogenesis focusing on the role of the stress-activated MAPK pathway.

Activation of JNK triggers release of Brd4 from mitotic chromosomes and mediates protection from drug-induced mitotic stress

Some anti-cancer drugs, including those that alter microtubule dynamics target mitotic cells and induce apoptosis in some cell types. However, such drugs elicit protective responses in other cell types allowing cells to escape from drug-induced mitotic inhibition. Cells with a faulty protective mechanism undergo defective mitosis, leading to genome instability. Brd4 is a double bromodomain protein that remains on chromosomes during mitosis. However, Brd4 is released from mitotic chromosomes when cells are exposed to anti-mitotic drugs including nocodazole. Neither the mechanisms, nor the biological significance of drug-induced Brd4 release has been fully understood. We found that deletion of the internal C-terminal region abolished nocodazole induced Brd4 release from mouse P19 cells. Furthermore, cells expressing truncated Brd4, unable to dissociate from chromosomes were blocked from mitotic progression and failed to complete cell division. We also found that pharmacological and peptide inhibitors of the c-jun-N-terminal kinases (JNK) pathway, but not inhibitors of other MAP kinases, prevented release of Brd4 from chromosomes. The JNK inhibitor that blocked Brd4 release also blocked mitotic progression. Further supporting the role of JNK in Brd4 release, JNK2-/- embryonic fibroblasts were defective in Brd4 release and sustained greater inhibition of cell growth after nocodazole treatment. In sum, activation of JNK pathway triggers release of Brd4 from chromosomes upon nocodazole treatment, which mediates a protective response designed to minimize drug-induced mitotic stress.