The Impact of JNK on Neuronal Migration

AP-1 controls the p11-dependent antidepressant response

Selective serotonin reuptake inhibitors (SSRIs) are the most widely prescribed drugs for mood disorders. While the mechanism of SSRI action is still unknown, SSRIs are thought to exert therapeutic effects by elevating extracellular serotonin levels in the brain, and remodel the structural and functional alterations dysregulated during depression. To determine their precise mode of action, we tested whether such neuroadaptive processes are modulated by regulation of specific gene expression programs. Here we identify a transcriptional program regulated by activator protein-1 (AP-1) complex, formed by c-Fos and c-Jun that is selectively activated prior to the onset of the chronic SSRI response. The AP-1 transcriptional program modulates the expression of key neuronal remodeling genes, including S100a10 (p11), linking neuronal plasticity to the antidepressant response. We find that AP-1 function is required for the antidepressant effect in vivo. Furthermore, we demonstrate how neurochemical pathways of BDNF and FGF2, through the MAPK, PI3K, and JNK cascades, regulate AP-1 function to mediate the beneficial effects of the antidepressant response. Here we put forth a sequential molecular network to track the antidepressant response and provide a new avenue that could be used to accelerate or potentiate antidepressant responses by triggering neuroplasticity.

The c-Jun N-terminal kinase signaling pathway in epilepsy: activation, regulation, and therapeutics

Epilepsy affects approximately 50-70 million people worldwide and 30-40% of patients do not benefit from medication. Therefore, it is necessary to identify novel targets for epileptic treatments. c-Jun N-terminal kinase (JNK) is a member of the mitogen-activated protein kinase (MAPK) family that activates diverse substrates, such as transcriptional factors, adaptor proteins, and signaling proteins, and has a wide variety of functions in both physiological and pathological conditions. The excessive activation of JNK is found not only in the acute phase of epilepsy, but also in the chronic phase, which potentiates it as a promising target in epilepsy control. In this review, we discuss the activation of the JNK pathway in epilepsy and its role in neuronal death, astrocyte activation, and mossy fiber sprouting (MFS) based on recent updates. Finally, we briefly introduce the current agents that target JNK signaling to control epilepsy.

Role of brain c-Jun N-terminal kinase 2 in the control of the insulin receptor and its relationship with cognitive performance in a high-fat diet pre-clinical model

Insulin resistance has negative consequences on the physiological functioning of the nervous system. The appearance of type 3 diabetes in the brain leads to the development of the sporadic form of Alzheimer's disease. The c-Jun N-terminal kinases (JNK), a subfamily of the Mitogen Activated Protein Kinases, are enzymes composed by three different isoforms with differential modulatory activity against the insulin receptor (IR) and its substrate. This research focused on understanding the regulatory role of JNK2 on the IR, as well as study the effect of a high-fat diet (HFD) in the brain. Our observations determined how JNK2 ablation did not induce compensatory responses in the expression of the other isoforms but led to an increase in JNKs total activity. HFD-fed animals also showed an increased activity profile of the JNKs. These animals also displayed endoplasmic reticulum stress and up-regulation of the protein tyrosine phosphatase 1B (PTP1B) and the suppressor of cytokine signalling 3 protein. Consequently, a reduction in insulin sensitivity was detected and it is correlated with a decrease on the signalling of the IR. Moreover, cognitive impairment was observed in all groups but only wild-type genotype animals fed with HFD showed neuroinflammatory responses. In conclusion, HFD and JNK2 absence cause alterations in normal cognitive activity by altering the signalling of the IR. These affectations are related to the appearance of endoplasmic reticulum stress and an increase in the levels of inhibitory proteins like PTP1B and suppressor of cytokine signalling 3 protein. Cover Image for this issue: doi: 10.1111/jnc.14502.

Neuroprotective Effects of the Absence of JNK1 or JNK3 Isoforms on Kainic Acid-Induced Temporal Lobe Epilepsy-Like Symptoms

The activation of c-Jun-N-terminal kinases (JNK) pathway has been largely associated with the pathogenesis and the neuronal death that occur in neurodegenerative diseases. Altogether, this justifies why JNKs have become a focus of screens for new therapeutic strategies. The aim of the present study was to identify the role of the different JNK isoforms (JNK1, JNK2, and JNK3) in apoptosis and inflammation after induction of brain damage. To address this aim, we induced excitotoxicity in wild-type and JNK knockout mice (jnk1 ^-/- , jnk2 ^-/- , and jnk3 ^-/- ) via an intraperitoneal injection of kainic acid, an agonist of glutamic-kainate-receptors, that induce status epilepticus.Each group of animals was divided into two treatments: a single intraperitoneal dose of saline solution, used as a control, and a single intraperitoneal dose (30 mg/kg) of kainic acid. Our results reported a significant decrease in neuronal degeneration in the hippocampus of jnk1 ^-/- and jnk3 ^-/- mice after kainic acid treatment, together with reduced or unaltered expression of several apoptotic genes compared to WT treated mice. In addition, both jnk1 ^-/- and jnk3 ^-/- mice exhibited a reduction in glial reactivity, as shown by the lower expression of inflammatory genes and a reduction of JNK phosphorylation. In addition, in jnk3 ^-/- mice, the c-Jun phosphorylation was also diminished.Collectively, these findings provide compelling evidence that the absence of JNK1 or JNK3 isoforms confers neuroprotection against neuronal damage induced by KA and evidence, for the first time, the implication of JNK1 in excitotoxicity. Accordingly, JNK1 and/or JNK3 are promising targets for the prevention of cell death and inflammation during epileptogenesis.

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.

The Ser/Thr kinase MAP4K4 drives c-Met-induced motility and invasiveness in a cell-based model of SHH medulloblastoma

Medulloblastoma (MB) comprises four molecularly and genetically distinct subgroups of embryonal brain tumors that develop in the cerebellum. MB mostly affects infants and children and is difficult to treat because of frequent dissemination of tumor cells within the leptomeningeal space. A potential promoter of cell dissemination is the c-Met proto-oncogene receptor tyrosine kinase, which is aberrantly expressed in many human tumors including MB. Database analysis showed that c-Met is highly expressed in the sonic hedgehog (SHH) subgroup and in a small subset of Group 3 and Group 4 MB tumors. Using a cell-based three-dimensional cell motility assay combined with live-cell imaging, we investigated whether the c-Met ligand HGF could drive dissemination of MB cells expressing high levels of c-Met, and determined downstream effector mechanisms of this process. We detected variable c-Met expression in different established human MB cell lines, and we found that in lines expressing high c-Met levels, HGF promoted cell dissemination and invasiveness. Specifically, HGF-induced c-Met activation enhanced the capability of the individual cells to migrate in a JNK-dependent manner. Additionally, we identified the Ser/Thr kinase MAP4K4 as a novel driver of c-Met-induced invasive cell dissemination. This increased invasive motility was due to MAP4K4 control of F-actin dynamics in structures required for migration and invasion. Thus, MAP4K4 couples growth factor signaling to actin cytoskeleton regulation in tumor cells, suggesting that MAP4K4 could present a promising novel target to be evaluated for treating growth factor-induced dissemination of MB tumors of different subgroups and of other human cancers.