Groups Of Mitogen-activated Protein Kinases Research Articles

JNK in Tumor Microenvironment: Present Findings and Challenges in Clinical Translation

Simple SummaryStress-activated c-Jun N-terminal kinases (JNKs) are members of mitogen-activated protein kinases (MAPKs). Apart from having both tumor promoting and tumor suppressing roles in cancers due to its impact on apoptosis and autophagy pathways, JNK also plays complex roles in the heterogeneous tumor microenvironment (TME) and is involved in different tumorigenesis pathways. The JNK pathway influences various stressful and chronic inflammatory conditions along with different cell populations in TME. In this review, we aim to present the current knowledge of JNK-mediated processes in TME and the challenges in clinical translation.The c-Jun N-terminal kinases (JNKs) are a group of mitogen-activated protein kinases (MAPKs). JNK is mainly activated under stressful conditions or by inflammatory cytokines and has multiple downstream targets for mediating cell proliferation, differentiation, survival, apoptosis, and immune responses. JNK has been demonstrated to have both tumor promoting and tumor suppressing roles in different cancers depending on the focused pathway in each study. JNK also plays complex roles in the heterogeneous tumor microenvironment (TME). JNK is involved in different tumorigenesis pathways. TME closely relates with tumor development and consists of various stressful and chronic inflammatory conditions along with different cell populations, in which the JNK pathway may have various mediating roles. In this review, we aim to summarize the present knowledge of JNK-mediated processes in TME, including hypoxia, reactive oxygen species, inflammation, immune responses, angiogenesis, as well as the regulation of various cell populations within TME. This review also suggests future research directions for translating JNK modulation in pre-clinical findings to clinical benefits.

Pancreas preservation in extracellular-type p38 inhibitor-containing solution improves islet yield for porcine islet isolation.

For islet transplantation, pancreas preservation and islet isolation activate p38, which is a member of the stress-activated group of mitogen-activated protein kinases (MAPKs). In this study, we evaluated an extracellular-type p38 inhibitor-containing (EP) solution with University of Wisconsin (UW) solution, the gold standard for organ preservation. The EP solution has high sodium-low potassium composition with low viscosity compared to UW solution. Moreover, EP solution contains a recently developed p38 inhibitor (11R-p38I110 ) from our laboratory. Porcine pancreata were preserved in UW, EP, or EP-P solution (EP solution without 11R-p38I110 ), and then islet isolation was performed. An optimized number (1500 IE) of isolated islets from each group were transplanted into streptozotocin-induced diabetic mice. The islet yield before and after purification was significantly higher in the EP group than in the UW group. The islet yield before and after purification was not significantly different between the EP and EP-P groups; however, the EP solution prevented a reduction in the number of islets during culture. Western blot analysis showed that p38 activation was attenuated by EP solution. For islet transplantation into streptozotocin-induced diabetic mice, pancreas preservation in EP solution improved the outcome of islet transplantation. Pancreas preservation with EP solution preserved islet function better than with UW solution. The advantages of EP solution over UW solution may include the inhibition of p38 activity as well as the composition of the solution.

An overview of mammalian p38 mitogen-activated protein kinases, central regulators of cell stress and receptor signaling.

The p38 family is a highly evolutionarily conserved group of mitogen-activated protein kinases (MAPKs) that is involved in and helps co-ordinate cellular responses to nearly all stressful stimuli. This review provides a succinct summary of multiple aspects of the biology, role, and substrates of the mammalian family of p38 kinases. Since p38 activity is implicated in inflammatory and other diseases, we also discuss the clinical implications and pharmaceutical approaches to inhibit p38.

Regulation of c-Jun NH2-Terminal Kinase for Islet Transplantation.

Islet transplantation has been demonstrated to provide superior glycemic control with reduced glucose lability and hypoglycemic events compared with standard insulin therapy. However, the insulin independence rate after islet transplantation from one donor pancreas has remained low. The low frequency of islet grafting is dependent on poor islet recovery from donors and early islet loss during the first hours following grafting. The reduction in islet mass during pancreas preservation, islet isolation, and islet transplantation leads to β-cell death by apoptosis and the prerecruitment of intracellular death signaling pathways, such as c-Jun NH2-terminal kinase (JNK), which is one of the stress groups of mitogen-activated protein kinases (MAPKs). In this review, we show some of the most recent contributions to the advancement of knowledge of the JNK pathway and several possibilities for the treatment of diabetes using JNK inhibitors.

ZPR1-Dependent Neurodegeneration Is Mediated by the JNK Signaling Pathway.

The zinc finger protein ZPR1 deficiency causes neurodegeneration and results in a mild spinal muscular atrophy (SMA)-like disease in mice with reduced Zpr1 gene dosage. Mutation of the survival motor neuron 1 (SMN1) gene causes SMA. Spinal muscular atrophy is characterized by the degeneration of the spinal cord motor neurons caused by chronic low levels of SMN protein. ZPR1 interacts with SMN and is required for nuclear accumulation of SMN. Patients with SMA express reduced levels of ZPR1. Reduced Zpr1 gene dosage increases neurodegeneration and severity of SMA disease in mice. Mechanisms underlying ZPR1-dependent neurodegeneration are largely unknown. We report that neurodegeneration caused by ZPR1 deficiency is mediated by the c-Jun NH2-terminal kinase (JNK) group of mitogen-activated protein kinases (MAPK). ZPR1-dependent neuron degeneration is mediated by central nervous system (CNS)-specific isoform JNK3. ZPR1 deficiency activates the MAPK signaling cascade, MLK3 → MKK7 → JNK3, which phosphorylates c-Jun and activates caspase-mediated neuron degeneration. Neurons from Jnk3-null mice show resistance to ZPR1-dependent neurodegeneration. Pharmacologic inhibition of JNK reduces degeneration of ZPR1-deficient neurons. These data show that ZPR1-dependent neurodegeneration is mediated by the JNK signaling pathway and suggest that ZPR1 downregulation in SMA may contribute to JNK-mediated neurodegeneration associated with SMA pathogenesis.

Charactor of JNK and P53 in Taxol-Induced Apoptotic Signaling in SKOV3 Human Ovarian Cancer Cell Proliferation

C-Jun N-terminal kinase (JNK) represents a group of mitogen-activated protein kinases (MAPKs) involved in many cellular responses including apoptosis. We have previously reported that taxol, a microtubule-interfering therapeutic agent widely used against various cancers, induces caspase-independent but apoptotic inducing factor (AIF)-dependent apoptosis in human ovarian cancer cell line SKOV3 cells. In the present study, we add to this report a detailed analysis of the taxol-induced apoptotic mechanisms in SKOV3 cells, particularly focusing on JNK and p53. In line with the previous report, we found that taxol induced caspase-independent apoptosis with concurrent activation of JNK, phosphorylation of Bcl-2, Bax translocation to the mitochondria, and AIF release from the mitochondria. Restoration of p53 functionality into SKOV3 cells, which are p53-null cells, by transfection of wild-type p53, however, induced caspase-dependent apoptosis in response to taxol treatment as evidenced by increasing PARP cleavage and the emergence of processed, active caspase-3 and -7. More to the point, treatment with a JNK inhibitor SP600125 blocked taxol-induced apoptotic cell death in both parental SKOV3 cells (p53-deficient) and p53-transfectant cells. Collectively, the aforementioned findings lend support to the view that taxol-induced apoptotic cell death in SKOV3 cells is executed by different mechanisms depending on the presence of p53 but commonly mediated by ASK1-JNK and/or -p38 axes.

Influence on mitogen-activated protein kinases as a new direction of connective tissue growth regulation

This review presents current classification, functions of main groups of mitogen-activated protein kinases (MAPK) and summarizes data on the ways of their activation and functioning, giving particular emphasis to p38 MAPK. The authors consider the influence on these signaling cascades as a promising direction for activation of connective tissue growth. This article summarizes international practices on the activation and blocking of intracellular cascades and also the authors’ own experience in this field. In particular, the article shows that p38 MAP-kinase stimulation while JNK inactivation causes accelerated formation of connective tissue in the area of postoperative surgical scar. The authors prove the opportunity to manage connective tissue growth influencing MAPK cascades – prolonged blockade of p38 МАРК reduces scar width and collagen fiber density in the area of postoperative scars and decreases intensity of adhesions in the abdominal cavity in abdominal trauma. Therefore, considering the importance and flexibility of MAP-kinase mechanisms of cell growth regulation and differentiation, studying the use of these mechanisms in biological processes (such as inflammation, apoptosis, regeneration) and the development the methods of management of these processes show promise. Using stimulators and inhibitors of MAP-kinase mechanisms is a promising new direction in treatment of the diseases with pathogeny related to the disorder of cellular differentiation, proliferation, excessive cytokine production and regulation of connective tissue growth.

Effects of statins and farnesyl transferase inhibitors on ERK phosphorylation, apoptosis and cell viability in non‐small lung cancer cells

3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) can affect post-translational processes, thus being responsible for decreased farnesylation and geranylgeranylation of intracellular small G proteins such as Ras, Rho and Rac, essential for cell survival and proliferation. In this regard, recent in vitro and in vivo studies suggest a possible role for both statins and farnesyl transferase inhibitors in the treatment of malignancies. Within such a context, the aim of our study was to investigate effects of either simvastatin (at concentrations of 1, 15, and 30μm) or the farnesyl transferase inhibitor R115777 (at concentrations of 0.1, 1, and 10μm), on two cultures of human non-small lung cancer cells, adenocarcinoma (GLC-82) and squamous (CALU-1) cell lines. In particular, we evaluated actions of these two drugs on phosphorylation of the ERK1/2 group of mitogen-activated protein kinases and on apoptosis, plus on cell numbers and morphology. Western blotting was used to detect ERK phosphorylation, and to assess apoptosis by evaluating caspase-3 activation; apoptosis was also further assessed by terminal deoxynucleotidyl-mediated dUTP nick end labelling (TUNEL) assay. Cell counting was performed after trypan blue staining. In both GLC-82 and CALU-1 cell lines, simvastatin and R115777 significantly reduced ERK phosphorylation; this effect, which reached the greatest intensity after 36h treatment, was paralleled by a concomitant induction of apoptosis, documented by significant increase in both caspase-3 activation and TUNEL-positive cells, associated with a reduction in cell numbers. Our results thus suggest that simvastatin and R115777 may exert, in susceptible lung cancer cell phenotypes, a pro-apoptotic and anti-proliferative activity, which appears to be mediated by inhibition of the Ras/Raf/MEK/ERK signalling cascade.

Intratympanic Treatment of Acute Inner Ear Disorders with AM-111: A New Cell-Permeable JNK Ligand

Background and Aim: Acute inner ear disorders like sudden deafness, acoustic trauma, tinnitus, and others are thought to initiate complex biochemical processes in the sensory hair cells that can lead to apoptosis. Apoptosis is an active process that is characterized by chromatin condensations, intracellular fragmentation, and intranucleosomal DNA fragmentation. The molecular mechanism behind it is the JNK (c-Jun N-terminal kinase) group of mitogen-activated protein kinases (MAPK), also known as stress-activated protein kinases. In different animal models, the intratympanic administration of AM-111, a cell-permeable JNK ligand also known as D-JNKI, has been shown to prevent hearing loss after acute acoustic trauma. Functional and morphological analysis of the treated ears revealed excellent otoprotective properties that could be obtained even when AM-111 was administered hours after the noise exposure. Blocking the signal pathway with D-JNKI-1 is therefore a promising way to protect the morphological integrity and physiological function of the inner ear.

Intracellular Peptides as Natural Regulators of Cell Signaling

Protein degradation by the ubiquitin proteasome system releases large amounts of oligopeptides within cells. To investigate possible functions for these intracellularly generated oligopeptides, we fused them to a cationic transactivator peptide sequence using reversible disulfide bonds, introduced them into cells, and analyzed their effect on G protein-coupled receptor (GPCR) signal transduction. A mixture containing four of these peptides (20-80 microm) significantly inhibited the increase in the extracellular acidification response triggered by angiotensin II (ang II) in CHO-S cells transfected with the ang II type 1 receptor (AT1R-CHO-S). Subsequently, either alone or in a mixture, these peptides increased luciferase gene transcription in AT1R CHO-S cells stimulated with ang II and in HEK293 cells treated with isoproterenol. These peptides without transactivator failed to affect GPCR cellular responses. All four functional peptides were shown in vitro to competitively inhibit the degradation of a synthetic substrate by thimet oligopeptidase. Overexpression of thimet oligopeptidase in both CHO-S and HEK293 cells was sufficient to reduce luciferase activation triggered by a specific GPCR agonist. Moreover, using individual peptides as baits in affinity columns, several proteins involved in GPCR signaling were identified, including alpha-adaptin A and dynamin 1. These results suggest that before their complete degradation, intracellular peptides similar to those generated by proteasomes can actively affect cell signaling, probably representing additional bioactive molecules within cells.

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

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

Deletion of the c-Jun N-terminal Kinase 3 Gene Protects Neonatal Mice against Cerebral Hypoxic—Ischaemic Injury

c-Jun N-terminal kinase 3 (JNK3) is a member of the stress-activated group of mitogen-activated protein kinases. c-Jun N-terminal kinase 3 is a potent mediator of apoptosis and the use of JNK inhibitors or jnk3 gene deletion each protect against brain injury in adults. However, little is known about the role of JNK3 or its mechanism of action in neonatal brain injury. The aim of the present study was to compare the vulnerability of neonatal JNK3 knockout (JNK3 KO) mice and wild-type (WT) mice to cerebral hypoxic-ischaemic injury (HII) using unilateral-carotid occlusion combined with transient hypoxia. The degree of neural tissue loss in JNK3 KO mice was substantially reduced compared with WT mice (JNK3 KO 27.8%+/-2.8% versus WT 48.3%+/-2.0%, P<or=0.0001) after HII. Significant attenuation of injury was observed in the cerebral cortex, hippocampus, striatum, and thalamus of JNK3 KO compared with WT mice. Hypoxic-ischaemic injury increased JNK phosphorylation and activity, with JNK3 as the major isoform. Significantly, in JNK3 KO animals there was no difference in the activation of the upstream kinases mitogen-activated protein kinase kinase (MKK4) or MKK7. Downstream of JNK3, HII lead to increased phosphorylation of the transcription factors c-Jun and adenovirus transcription factor-2 (ATF-2), which was attenuated in JNK3 KO mice. c-Jun N-terminal kinase 3 deletion also decrease caspase-3 cleavage and Bim/PUMA expression, coupled with a upregulation of AKT/FOXO3a levels, linking JNK3 to apoptosis. These findings implicate JNK3 involvement in neural cell loss resulting from cerebral HII in the developing brain.

Differential Expression of Kinase Genes in Primary Hyperparathyroidism: Adenoma Versus Normal and Hyperplastic Parathyroid Tissue

Differentiation between adenoma and hyperplasia or even normal parathyroid tissue is difficult and based mainly on the surgeon's skill. Exploration of genes that express differentially in these various tissues using microarrays and other sophisticated research tools will enable identification and perhaps development of new methods of perioperative diagnosis. To assemble a panel of kinase genes to differentiate parathyroid adenoma from normal and hyperplastic parathyroid tissue. RNA was extracted from adenoma, hyperplasia, and normal parathyroid tissue and hybridized to a microarray containing 359 human cDNAs of known kinase genes. Signals of exposure were scanned and quantified with software for digital image analysis. Semiquantitative reverse transcriptase polymerase chain reaction analysis of sample genes was performed, up-regulated or down-regulated, to validate the microarray results. The ratio values considered significant (<0.5 or >1.5) suggest that genes up-regulated in parathyroid adenoma are those responsible for blood vessel angiogenesis and genes belonging to the cyclin-dependent kinase inhibitor groups. Genes down-regulated in parathyroid adenoma are related to cellular growth and apoptosis--genes from the mitogen-activated protein kinase group and DNA-dependent protein kinase group. An interesting gene down-regulated in the parathyroid adenoma samples is related to the serine/threonine protein kinases that exert a key function in calcium handling. A panel of 5 genes was defined: p19, p21 and the gene for vascular endothelial growth factor from the up-regulated group, and the gene for protein kinase C and SGK from the down-regulated group. Reverse transcriptase polymerase chain reaction confirmed the microarray results for these genes. The kinase genes panel presented can be used to differentiate parathyroid adenoma from normal and hyperplastic parathyroid tissue in particular when histopathology fails to provide a decisive diagnosis.

Cartducin stimulates mesenchymal chondroprogenitor cell proliferation through both extracellular signal-regulated kinase and phosphatidylinositol 3-kinase/Akt pathways

Cartducin, a paralog of Acrp30/adiponectin, is a secretory protein produced by both chondrogenic precursors and proliferating chondrocytes, and belongs to a novel C1q family of proteins. We have recently shown that cartducin promotes the growth of both mesenchymal chondroprogenitor cells and chondrosarcoma-derived chondrocytic cells in vitro. However, the cartducin-signaling pathways responsible for the regulation of cell proliferation have not been documented. In this study, we examined whether cartducin exists in serum and further investigated the intracellular signaling pathways stimulated by cartducin in mesenchymal chondroprogenitor cells. Western blot analysis showed that, unlike Acrp30/adiponectin, cartducin was undetectable in mouse serum. Next, mesenchymal chondroprogenitor N1511 cells were stimulated with cartducin, and three major groups of mitogen-activated protein kinase (MAPK) pathways and the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway were examined. Cartducin activated extracellular signal-regulated kinase 1/2 (ERK1/2) and Akt, but not c-jun N-terminal kinase (JNK) nor p38 MAPK. The MEK1/2 inhibitor, U0126, blocked cartducin-stimulated ERK1/2 phosphorylation and suppressed the DNA synthesis induced by cartducin in N1511 cells. The PI3K inhibitor, LY294002, blocked cartducin-stimulated Akt phosphorylation and a decrease in cartducin-induced DNA synthesis in N1511 cells was also observed. These data suggest that cartducin is a peripheral skeletal growth factor, and that the proliferation of mesenchymal chondroprogenitor cells stimulated by cartducin is associated with activations of the ERK1/2 and PI3K/Akt signaling pathways.

Poly(ADP-ribose) Polymerase-1 Signaling to Mitochondria in Necrotic Cell Death Requires RIP1/TRAF2-mediated JNK1 Activation

Poly(ADP-ribose) polymerase-1 (PARP-1) hyperactivation-induced necrosis has been implicated in several pathophysiological conditions. Although mitochondrial dysfunction and apoptosis-inducing factor translocation from the mitochondria to the nucleus have been suggested to play very important roles in PARP-1-mediated cell death, the signaling events downstream of PARP-1 activation in initiating mitochondria dysfunction are not clear. Here we used the DNA alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine, a potent PARP-1 activator, to study PARP-1 activation-mediated cell death. We found, based on genetic knockouts and pharmacological inhibition, that c-Jun N-terminal kinase (JNK), especially JNK1, but not the other groups of mitogen-activated protein kinase, is required for PARP-1-induced mitochondrial dysfunction, apoptosis-inducing factor translocation, and subsequent cell death. We reveal that receptor-interacting protein 1 (RIP1) and tumor necrosis factor receptor-associated factor 2 (TRAF2), are upstream of JNK in PARP-1 hyperactivated cells, because PARP-1-induced JNK activation was attenuated in RIP1-/- and TRAF2-/- mouse embryonic fibroblast cells. Consistently, knockouts of RIP1 and TRAF2 caused a resistance to PARP-1-induced cell death. Therefore, our study uncovers that RIP1, TRAF2, and JNK comprise a pathway to mediate the signaling from PARP-1 overactivation to mitochondrial dysfunction.

Co-activation of ERK, NF-κB, and GADD45β in Response to Ionizing Radiation

NF-kappaB has been well documented to play a critical role in signaling cell stress reactions. The extracellular signal-regulated kinase (ERK) regulates cell proliferation and survival. GADD45beta is a primary cell cycle element responsive to NF-kappaB activation in anti-apoptotic responses. The present study provides evidence demonstrating that NK-kappaB, ERK and GADD45beta are co-activated by ionizing radiation (IR) in a pattern of mutually dependence to increase cell survival. Stress conditions generated in human breast cancer MCF-7 cells by the administration of a single exposure of 5 Gy IR resulted in the activation of ERK but not p38 or JNK, along with an enhancement of the NF-kappaB transactivation and GADD45beta expression. Overexpression of dominant negative Erk (DN-Erk) or pre-exposure to ERK inhibitor PD98059 inhibited NF-kappaB. Transfection of dominant negative mutant IkappaB that blocks NF-kappaB nuclear translocation, inhibited ERK activity and GADD45beta expression and increased cell radiosensitivity. Interaction of p65 and ERK was visualized in living MCF-7 cells by bimolecular fluorescence complementation analysis. Antisense inhibition of GADD45beta strikingly blocked IR-induced NF-kappaB and ERK but not p38 and JNK. Overall, these results demonstrate a possibility that NF-kappaB, ERK, and GADD45beta are able to coordinate in a loop-like signaling network to defend cells against the cytotoxicity induced by ionizing radiation.

Germinal center kinase is required for optimal Jun N-terminal kinase activation by Toll-like receptor agonists and is regulated by the ubiquitin proteasome system and agonist-induced, TRAF6-dependent stabilization.

Germinal center kinase (GCK), a member of the Ste20 family, selectively activates the Jun N-terminal kinase (JNK) group of mitogen-activated protein kinases. Here, we show that endogenous GCK is activated by polyinosine-polycytidine [poly(IC)] and lipopolysaccharides (LPS), lipid A, interleukin-1 (IL-1), and engagement of CD40, all agonists that require TRAF6 for JNK activation. RNA interference experiments indicate that GCK is required for the maximal activation of JNK by LPS, lipid A, poly(IC), and, to a lesser extent, IL-1 and engagement of CD40. GCK is ubiquitinated in situ and stabilized by inhibitors of the proteasome, indicating that GCK is subject to proteasomal turnover. GCK is constitutively active, and the kinase activity of GCK is required for GCK ubiquitination. Agonist activation of GCK involves the TRAF6-dependent transient stabilization of the GCK polypeptide rather than an increase in intrinsic kinase activity. Our results identify a physiologic function and unexpected mode of regulation for GCK.

MLK3 is required for mitogen activation of B-Raf, ERK and cell proliferation.

The ERK group of mitogen-activated protein kinases (MAPKs) is essential for cell proliferation stimulated by mitogens, oncogenic ras and raf (ref. 1). All MAPKs are activated by MAP3K/MEK/MAPK core pathways and the Raf proto-oncoproteins, especially B-Raf, are ERK-specific MAP3Ks (refs 1-3). Mixed lineage kinase-3 (MLK3) is a MAP3K that was thought to be a cytokine-activated, and comparatively selective, regulator of the JNK group of MAPKs (refs 1, 4-6). Here we report that silencing of mlk3 by RNAi suppressed mitogen and cytokine activation not only of JNK but of ERK and p38 as well. Silencing mlk3 also blocked mitogen-stimulated phosphorylation of B-Raf at Thr 598 and Ser 601, a step required for B-Raf activation. Furthermore, silencing mlk3 prevented serum-stimulated cell proliferation and the proliferation of tumour cells bearing either oncogenic Ki-Ras or loss-of-function neurofibromatosis-1 (NF1) or NF2 mutations. The proliferation of tumour cells containing activating B-raf or raf-1 mutations was unaffected by silencing mlk3. Our results define an unexpected role for MLK3 in mitogen regulation of B-Raf, ERK and cell proliferation.

DCX, a new mediator of the JNK pathway

Mutations in the X-linked gene DCX result in lissencephaly in males, and abnormal neuronal positioning in females, suggesting a role for this gene product during neuronal migration. In spite of several known protein interactions, the involvement of DCX in a signaling pathway is still elusive. Here we demonstrate that DCX is a substrate of JNK and interacts with both c-Jun N-terminal kinase (JNK) and JNK interacting protein (JIP). The localization of this signaling module in the developing brain suggests its functionality in migrating neurons. The localization of DCX at neurite tips is determined by its interaction with JIP and by the interaction of the latter with kinesin. DCX is phosphorylated by JNK in growth cones. DCX mutated in sites phosphorylated by JNK affected neurite outgrowth, and the velocity and relative pause time of migrating neurons. We hypothesize that during neuronal migration, there is a need to regulate molecular motors that are working in the cell in opposite directions: kinesin (a plus-end directed molecular motor) versus dynein (a minus-end directed molecular motor).

JNK initiates a cytokine cascade that causes Pax2 expression and closure of the optic fissure.

The c-Jun NH(2)-terminal kinase (JNK) group of mitogen-activated protein kinases is stimulated in response to a wide array of cellular stresses and proinflammatory cytokines. Mice lacking individual members of the Jnk family (Jnk1, Jnk2, and Jnk3) are viable and survive without overt structural abnormalities. Here we show that mice with a compound deficiency in Jnk expression can survive to birth, but fail to close the optic fissure (retinal coloboma). We demonstrate that JNK initiates a cytokine cascade of bone morphogenetic protein-4 (BMP4) and sonic hedgehog (Shh) that induces the expression of the paired-like homeobox transcription factor Pax2 and closure of the optic fissure. Interestingly, the role of JNK to regulate BMP4 expression during optic fissure closure is conserved in Drosophila during dorsal closure, a related morphogenetic process that requires JNK-regulated expression of the BMP4 ortholog Decapentaplegic (Dpp).