The MKK7 gene encodes a group of c-Jun NH2-terminal kinase kinases

Pharmacological inhibition of the MAP2K7 kinase in human disease

The MAP2K7 signaling pathway activates the c-Jun NH2-terminal protein kinase (JNK) in response to stress signals, such as inflammatory cytokines, osmotic stress, or genomic damage. While there has been interest in inhibiting JNK due to its involvement in inflammatory processes and cancer, there is increasing focus on developing MAP2K7 inhibitors to enhance specificity when MAP2K7 activation is associated with disease progression. Despite some progress, further research is needed to fully comprehend the role of MAP2K7 in cancer and assess the potential use of kinase inhibitors in cancer therapy. This review examines the role of MAP2K7 in cancer and the development of small-molecule inhibitors.

Conserved gatekeeper methionine regulates the binding and access of kinase inhibitors to ATP sites of MAP2K1, 4, and 7: Clues for developing selective inhibitors

Mitogen-activated protein kinase kinases (MAP2Ks) 1, 4, and 7 are potential targets for treating various diseases. Here, we solved the crystal structures of MAP2K1 and MAP2K4 complexed with covalent inhibitor 5Z-7-oxozeaenol (5Z7O). The elucidated structures showed that 5Z7O was non-covalently bound to the ATP binding site of MAP2K4, while it covalently attached to cysteine at the DFG-1 position of the deep ATP site of MAP2K1. In contrast, we previously showed that 5Z7O covalently binds to MAP2K7 via another cysteine on the solvent-accessible edge of the ATP site. Structural analyses and molecular dynamics calculations indicated that the configuration and mobility of conserved gatekeeper methionine located at the central ATP site regulated the binding and access of 5Z7O to the ATP site of MAP2Ks. These structural features provide clues for developing highly potent and selective inhibitors against MAP2Ks. Abbreviations: ATP, adenosine triphosphate; FDA, Food and Drug Administration; MAP2Ks, mitogen-activated protein kinase kinases; MD, molecular dynamics; NSCLC, non-small cell lung cancer; 5Z7O, 5Z-7-oxozeaenol; PDB, protein data bank; RMSD, root-mean-square deviation.

Molecular Bidents with Two Electrophilic Warheads as a New Pharmacological Modality

A systematic strategy to develop dual-warhead inhibitors is introduced to circumvent the limitations of conventional covalent inhibitors such as vulnerability to mutations of the corresponding nucleophilic residue. Currently, all FDA-approved covalent small molecules feature one electrophile, leaving open a facile route to acquired resistance. We conducted a systematic analysis of human proteins in the protein data bank to reveal ∼400 unique targets amendable to dual covalent inhibitors, which we term "molecular bidents". We demonstrated this strategy by targeting two kinases: MKK7 and EGFR. The designed compounds, ZNL-8162 and ZNL-0056, are ATP-competitive inhibitors that form two covalent bonds with cysteines and retain potency against single cysteine mutants. Therefore, molecular bidents represent a new pharmacological modality with the potential for improved selectivity, potency, and drug resistance profile.

Architecture of the MKK6-p38α complex defines the basis of MAPK specificity and activation

The mitogen-activated protein kinase (MAPK) p38α is a central component of signaling in inflammation and the immune response and is, therefore, an important drug target. Little is known about the molecular mechanism of its activation by double phosphorylation from MAPK kinases (MAP2Ks), because of the challenge of trapping a transient and dynamic heterokinase complex. We applied a multidisciplinary approach to generate a structural model of p38α in complex with its MAP2K, MKK6, and to understand the activation mechanism. Integrating cryo-electron microscopy with molecular dynamics simulations, hydrogen-deuterium exchange mass spectrometry, and experiments in cells, we demonstrate a dynamic, multistep phosphorylation mechanism, identify catalytically relevant interactions, and show that MAP2K-disordered amino termini determine pathway specificity. Our work captures a fundamental step of cell signaling: a kinase phosphorylating its downstream target kinase.

Genome-wide analysis of the hard clam mitogen-activated protein kinase kinase gene family and their transcriptional profiles under abiotic stress

Mitogen-activated protein kinase kinase (MAPKK) was the hub component of the Mitogen-activated protein kinase (MAPK) signaling pathway and played an important role in the cellular response to environmental stress. In this study, we identified five MmMAPKK genes in hard clam Mercenaria mercenaria and found that all MmMAPKK genes contain a conserved protein kinase domain. The MmMAPKK genes derived from dispersed duplication were unevenly distributed in three chromosomes. Although the genome size was highly variable among different bivalve mollusks, the number of MAPKK genes was relatively stable. Phylogenetic analysis showed that bivalve MAPKK was divided into five clades, and amino acid sequences of MAPKK from the same clade consisted of similar conserved motifs. The syntenic analysis demonstrated that MmMAPKKs had the highest number of homologous gene pairs with Cyclina sinensis. MmMAPKKs were ubiquitously expressed in all examined tissues, and all MmMAPKK genes were highly expressed in the ovary. MmMAPKK genes showed stress-specific expression under envirionmental stress. MmMAPKK7 showed an upregulated in heat and heat plus hypoxia stress while MmMAPKK1 showed an upregulated in hypoxic stress groups. Dynamic changes of MmMAPKK7, MmMAPKK6 and MmMAPKK1 in hemocytes were observed in response to air exposure. MmMAPKK4 significantly downregulated after air exposure for five days. MmMAPKK7 and MmMAPKK6 might participate in adaptation to low salinity stress. Our results provided useful information about MAPKK and laid a foundation for further studies on MAPKK evolution in the bivalve.

ERK1b, a 46-kDa ERK Isoform That Is Differentially Regulated by MEK

The extracellular signal‐regulated kinases (ERK) 1 and 2 (ERK1/2) are members of the mitogen‐activated protein kinase family. Using various stimulated rodent cells and kinase activation techniques, we identified a 46‐kDa ERK. The kinetics of activation of this ERK isoform was similar to that of ERK1 and ERK2 under most but not all circumstances. We purified this isoform from rat cells followed by its cloning. The sequence of this isoform revealed that it is an alternatively spliced version of the 44‐kDa ERK1 and therefore we termed it ERK1b. Interestingly, this isoform had a 26‐amino acid insertion between residues 340 and 341 of ERK1, which results from Intron 7 insertion to the sequence. Examining the expression pattern, we found that ERK1b is detected mainly in rat and particularly in Ras‐transformed Rat1 cells. In this cell line, ERK1b was more sensitive to extracellular stimulation than ERK1 and ERK2. Moreover, unlike ERK1 and ERK2, ERK1b had a very low binding affinity to MEK1. This low interaction led to nuclear localization of this isoform when expressed together with MEK1 under conditions in which ERK1 and ERK2 are retained in the cytoplasm. In addition, ERK1b was not coimmunoprecipitated with MEK1. We identified a new, 46‐kDa ERK alternatively spliced isoform. Our results indicate that this isoform is the major one to respond to exogenous stimulation in Ras‐transformed cells, probably due to its differential regulation by MAPK/ERK kinase and by phosphatases.

Evolution of a New Testis-Specific Functional Promoter Within the Highly Conserved Map2k7 Gene of the Mouse

Map2k7 (synonym Mkk7) is a conserved regulatory kinase gene and a central component of the JNK signaling cascade with key functions during cellular differentiation. It shows complex transcription patterns, and different transcript isoforms are known in the mouse (Mus musculus). We have previously identified a newly evolved testis-specific transcript for the Map2k7 gene in the subspecies M. m. domesticus. Here, we identify the new promoter that drives this transcript and find that it codes for an open reading frame (ORF) of 50 amino acids. The new promoter was gained in the stem lineage of closely related mouse species but was secondarily lost in the subspecies M. m. musculus and M. m. castaneus. A single mutation can be correlated with its transcriptional activity in M. m. domesticus, and cell culture assays demonstrate the capability of this mutation to drive expression. A mouse knockout line in which the promoter region of the new transcript is deleted reveals a functional contribution of the newly evolved promoter to sperm motility and the spermatid transcriptome. Our data show that a new functional transcript (and possibly protein) can evolve within an otherwise highly conserved gene, supporting the notion of regulatory changes contributing to the emergence of evolutionary novelties.

Mitogen-activated protein kinase kinase 7 in inflammatory, cancer, and neurological diseases

Stress-activated mitogen-activated protein kinase kinase 7 (MKK7) is a member of the dual-specificity mitogen-activated protein kinase family. In the human body, MKK7 controls essential physiological processes, including but not limited to proliferation and differentiation in multiple tissues and organs. MKK7, along with the MKK4 pathway, has been implicated in stress-activated activities and biological events that are mediated by c-Jun N-terminal kinase (JNK) signaling. Although numerous studies have been performed to identify the role of JNK in multiple biological processes, there are limited publications that focus on dissecting the independent role of MKK7. Recent research findings have spurred testing via in vivo genetically deficient models, uncovering previously undocumented JNK-independent functions of MKK7. Here we discuss both JNK-dependent and-independent functions of MKK7 in vivo. This review summarizes the role of MKK7 in inflammation, cytokine production, cancer, and neurological diseases.

Alternative Splicing of MAPKs in the Regulation of Signaling Specificity

The mitogen-activated protein kinase (MAPK) cascades transmit signals from extracellular stimuli to a variety of distinct cellular processes. The MAPKKs in each cascade specifically phosphorylate and activate their cognate MAPKs, indicating that this step funnels various signals into a seemingly linear pathway. Still, the effects of these cascades vary significantly, depending on the identity of the extracellular signals, which gives rise to proper outcomes. Therefore, it is clear that the specificity of the signals transmitted through the cascades is tightly regulated in order to secure the desired cell fate. Indeed, many regulatory components or processes that extend the specificity of the cascades have been identified. Here, we focus on a less discussed mechanism, that is, the role of distinct components in each tier of the cascade in extending the signaling specificity. We cover the role of distinct genes, and the alternatively spliced isoforms of MAPKKs and MAPKs, in the signaling specificity. The alternatively spliced MEK1b and ERK1c, which form an independent signaling route, are used as the main example. Unlike MEK1/2 and ERK1/2, this route’s functions are limited, including mainly the regulation of mitotic Golgi fragmentation. The unique roles of the alternatively spliced isoforms indicate that these components play an essential role in determining the proper cell fate in response to distinct stimulations.

Stress-activated kinases as therapeutic targets in pancreatic cancer

Pancreatic cancer is a dismal disease with high incidence and poor survival rates. With the aim to improve overall survival of pancreatic cancer patients, new therapeutic approaches are urgently needed. Protein kinases are key regulatory players in basically all stages of development, maintaining physiologic functions but also being involved in pathogenic processes. c-Jun N-terminal kinases (JNK) and p38 kinases, representatives of the mitogen-activated protein kinases, as well as the casein kinase 1 (CK1) family of protein kinases are important mediators of adequate response to cellular stress following inflammatory and metabolic stressors, DNA damage, and others. In their physiologic roles, they are responsible for the regulation of cell cycle progression, cell proliferation and differentiation, and apoptosis. Dysregulation of the underlying pathways consequently has been identified in various cancer types, including pancreatic cancer. Pharmacological targeting of those pathways has been the field of interest for several years. While success in earlier studies was limited due to lacking specificity and off-target effects, more recent improvements in small molecule inhibitor design against stress-activated protein kinases and their use in combination therapies have shown promising in vitro results. Consequently, targeting of JNK, p38, and CK1 protein kinase family members may actually be of particular interest in the field of precision medicine in patients with highly deregulated kinase pathways related to these kinases. However, further studies are warranted, especially involving in vivo investigation and clinical trials, in order to advance inhibition of stress-activated kinases to the field of translational medicine.

AP-1 is a temporally regulated dual gatekeeper of reprogramming to pluripotency

Somatic cell transcription factors are critical to maintaining cellular identity and constitute a barrier to human somatic cell reprogramming; yet a comprehensive understanding of the mechanism of action is lacking. To gain insight, we examined epigenome remodeling at the onset of human nuclear reprogramming by profiling human fibroblasts after fusion with murine embryonic stem cells (ESCs). By assay for transposase-accessible chromatin with high-throughput sequencing (ATAC-seq) and chromatin immunoprecipitation sequencing we identified enrichment for the activator protein 1 (AP-1) transcription factor c-Jun at regions of early transient accessibility at fibroblast-specific enhancers. Expression of a dominant negative AP-1 mutant (dnAP-1) reduced accessibility and expression of fibroblast genes, overcoming the barrier to reprogramming. Remarkably, efficient reprogramming of human fibroblasts to induced pluripotent stem cells was achieved by transduction with vectors expressing SOX2, KLF4, and inducible dnAP-1, demonstrating that dnAP-1 can substitute for exogenous human OCT4. Mechanistically, we show that the AP-1 component c-Jun has two unexpected temporally distinct functions in human reprogramming: 1) to potentiate fibroblast enhancer accessibility and fibroblast-specific gene expression, and 2) to bind to and repress OCT4 as a complex with MBD3. Our findings highlight AP-1 as a previously unrecognized potent dual gatekeeper of the somatic cell state.

Structural basis for producing selective MAP2K7 inhibitors

Mitogen-activated protein kinase kinase 7 (MAP2K7) in the c-Jun N-terminal kinase signal cascade is an attractive drug target for a variety of diseases. The selectivity of MAP2K7 inhibitors against off-target kinases is a major barrier in drug development. We report a crystal structure of MAP2K7 complexed with a potent covalent inhibitor bearing an acrylamide moiety as an electrophile, which discloses a structural basis for producing selective and potent MAP2K7 inhibitors.

Phosphorylation Dynamics of JNK Signaling: Effects of Dual-Specificity Phosphatases (DUSPs) on the JNK Pathway

Protein phosphorylation affects conformational change, interaction, catalytic activity, and subcellular localization of proteins. Because the post-modification of proteins regulates diverse cellular signaling pathways, the precise control of phosphorylation states is essential for maintaining cellular homeostasis. Kinases function as phosphorylating enzymes, and phosphatases dephosphorylate their target substrates, typically in a much shorter time. The c-Jun N-terminal kinase (JNK) signaling pathway, a mitogen-activated protein kinase pathway, is regulated by a cascade of kinases and in turn regulates other physiological processes, such as cell differentiation, apoptosis, neuronal functions, and embryonic development. However, the activation of the JNK pathway is also implicated in human pathologies such as cancer, neurodegenerative diseases, and inflammatory diseases. Therefore, the proper balance between activation and inactivation of the JNK pathway needs to be tightly regulated. Dual specificity phosphatases (DUSPs) regulate the magnitude and duration of signal transduction of the JNK pathway by dephosphorylating their substrates. In this review, we will discuss the dynamics of phosphorylation/dephosphorylation, the mechanism of JNK pathway regulation by DUSPs, and the new possibilities of targeting DUSPs in JNK-related diseases elucidated in recent studies.

MKK7 transcription positively or negatively regulated by SP1 and KLF5 depends on HDAC4 activity in glioma

JNK activity has been implicated in the malignant proliferation, invasion and drug-resistance of glioma cells (GCs), but the molecular mechanisms underlying JNK activation are currently unknown. Here, we reported that MKK7, not MKK4, directly activates JNK in GCs and exerts oncogenic effects on tumor formation. Notably, MKK7 expression in glioma tissues was closely correlated with the grade of the glioma and JNK/c-Jun activation. Mechanistically, MKK7 transcription critically depends on the complexes formed by HDAC4 and the transcriptional factors SP1 and Krüppel-like factor-5 (KLF5), wherein HDAC4 directly deacetylates both SP1 and KLF5 and synergistically upregulates MKK7 transcription through two SP1 sites located on its promoter. In contrast, the increases in acetylated-SP1 and acetylated-KLF5 after HDAC4 inhibition switched to transcriptionally suppress MKK7. Selective inhibition of HDAC4 by LMK235, siRNAs or blockage of SP1 and KLF5 by the ectopic dominant-negative SP1 greatly reduced the malignant capacity of GCs. Furthermore, suppression of both MKK7 expression and JNK/c-Jun activities was involved in the tumor-growth inhibitory effects induced by LMK235 in U87-xenograft mice. Interestingly, HDAC4 is highly expressed in glioma tissues, and the rate of HDAC4 nuclear import is closely correlated with glioma grade, as well as with MKK7 expression. Collectively, these findings demonstrated that highly expressed MKK7 contributes to JNK/c-Jun signaling-mediated glioma formation. MKK7 transcription, regulated by SP1 and KLF5, critically depends on HDAC4 activity, and inhibition of HDAC4 presents a potential strategy for suppressing the oncogenic roles of MKK7/JNK/c-Jun signaling in GCs.

dl-Malic acid as a component of α-hydroxy acids: effect on 2,4-dinitrochlorobenzene-induced inflammation in atopic dermatitis-like skin lesions in vitro and in vivo

Background: dl-Malic acid (dl-M) is used widely in cosmetic formulations as a pH-adjuster or as a preservative. dl-M is used as an exfoliator in the form of α-hydroxy acids. However, the role of dl-M in skin diseases (including atopic dermatitis (AD)) has not been studied deeply. We wished to reveal the effect of dl-M on AD induced by 2,4-dinitrochlorobenzene (DNCB) in Balb/c mice.Methods: The thickness and immune-cell infiltration into the dermis and epidermis were evaluated. Moreover, serum levels of cytokines, as well as expression of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) in tissue were measured in AD mice. We also studied the effect of dl-M on inflammatory mediators in a human keratinocyte (HaCaT) cell line. Results: The dl-M (high) group improved skin condition compared with the DNCB-treated group. The dl-M (high) group inhibited phosphorylation of MAPK and NF-κB in skin tissue. dl-M reduced serum levels of interleukin-4 and IgE. Finally, dl-M decreased the expression of thymus and activation-regulated chemokine, monocyte chemoattractant protein-1 and intercellular cell adhesion molecule induced by interferon-gamma/tumor necrosis factor-α in HaCaT cells. Discussion: These results suggest that dl-M can improve the skin conditions of AD mice.

Histone deacetylase 6 promotes growth of glioblastoma through the MKK7/JNK/c-Jun signaling pathway

Histone deacetylase 6 (HDAC6) activity contributes to the malignant proliferation, invasion, and migration of glioma cells (GCs), but the molecular mechanisms underlying the processes remains elusive. Here, we reported that HDAC6 inhibition by Ricolinostat (ACY-1215) or CAY10603 led to a remarkable decrease in the phosphorylation of c-Jun N-terminal kinase (JNK) and c-Jun, which preceded its suppressive effects on glioma cell growth. Further investigation showed that these effects resulted from HDAC6 inhibitor-induced suppression of MAPK kinase 7 (MKK7), which was identified to be critical for JNK activation and exerts the oncogenic roles in GCs. Selectively silencing HDAC6 by siRNAs had the same responses, whereas transient transfections expressing HDAC6 promoted MKK7 expression. Interestingly, by performing Q-PCR, HDAC6 inhibition did not cause a down-regulation of MKK7 mRNA level, whereas the suppressive effects on MKK7 protein can be efficiently blocked by the proteasomal inhibitor MG132. As a further test, elevating MKK7-JNK activity was sufficient to rescue HDAC6 inhibitor-mediated-suppressive effects on c-Jun activation and the malignant features. The suppression of both MKK7 expression and JNK/c-Jun activities was involved in the tumor-growth inhibitory effects induced by CAY10603 in U87-xenograft mice. Collectively, our findings provide new insights into the molecular mechanism of glioma malignancy regarding HDAC6 in the selective regulation of MKK7 expression and JNK/c-Jun activity. MKK7 protein stability critically depends on HDAC6 activity, and inhibition of HDAC6 probably presents a potential strategy for suppressing the oncogenic roles of MKK7/JNK/c-Jun axis in GCs.

Subcellular Localization and Activity of the Mitogen-Activated Protein Kinase Kinase 7 (MKK7) γ Isoform are Regulated through Binding to the Phosphatase Calcineurin

Calcineurin (CaN) phosphatase signaling is regulated by targeting CaN to substrates, inhibitors, and scaffold proteins containing docking motifs with the consensus sequence of PxIxIT. Here, we identify the docking of CaN to the γ isoform of MKK7, a component of the c-Jun N-terminal kinase (JNK) pathway. Because of alternative splicing of a single exon within the N-terminal domain, MKK7γ encodes a unique PxIxIT motif (PIIVIT) that is not present in MKK7α or β We found that MKK7γ bound directly to CaN through this PIIVIT motif in vitro, immunoprecipitated with CaN from cell extracts, and exhibited fluorescence resonance energy transfer (FRET) with CaN in the cytoplasm but not in the nucleus of living cells. In contrast, MKK7α and β exhibited no direct binding or FRET with CaN and were localized more in the nucleus than the cytoplasm. Furthermore, the inhibition of CaN phosphatase activity increased the basal phosphorylation of MKK7γ but not MKK7β Deletion of the MKK7γ PIIVIT motif eliminated FRET with CaN and promoted MKK7γ redistribution to the nucleus; however, the inhibition of CaN activity did not alter MKK7γ localization, indicating that MKK7γ cytoplasmic retention by CaN is phosphatase activity independent. Finally, the inhibition of CaN phosphatase activity in vascular smooth muscle cells, which express MKK7γ mRNA, enhances JNK activation. Overall, we conclude that the MKK7γ-specific PxIxIT motif promotes high-affinity CaN binding that could promote novel cross talk between CaN and JNK signaling by limiting MKK7γ phosphorylation and restricting its localization to the cytoplasm.

Stress-activated MAPKs and CRM1 regulate the subcellular localization of Net1A to control cell motility and invasion

The neuroepithelial cell transforming gene 1A (Net1A, an isoform of Net1) is a RhoA subfamily guanine nucleotide exchange factor (GEF) that localizes to the nucleus in the absence of stimulation, preventing it from activating RhoA. Once relocalized in the cytosol, Net1A stimulates cell motility and extracellular matrix invasion. In the present work, we investigated mechanisms responsible for the cytosolic relocalization of Net1A. We demonstrate that inhibition of MAPK pathways blocks Net1A relocalization, with cells being most sensitive to JNK pathway inhibition. Moreover, activation of the JNK or p38 MAPK family pathway is sufficient to elicit Net1A cytosolic localization. Net1A relocalization stimulated by EGF or JNK activation requires nuclear export mediated by CRM1. JNK1 (also known as MAPK8) phosphorylates Net1A on serine 52, and alanine substitution at this site prevents Net1A relocalization caused by EGF or JNK activation. Glutamic acid substitution at this site is sufficient for Net1A relocalization and results in elevated RhoA signaling to stimulate myosin light chain 2 (MLC2, also known as MYL2) phosphorylation and F-actin accumulation. Net1A S52E expression stimulates cell motility, enables Matrigel invasion and promotes invadopodia formation. These data highlight a novel mechanism for controlling the subcellular localization of Net1A to regulate RhoA activation, cell motility, and invasion.

JIP3 localises to exocytic vesicles and focal adhesions in the growth cones of differentiated PC12 cells

The JNK-interacting protein 3 (JIP3) is a molecular scaffold, expressed predominantly in neurons, that serves to coordinate the activation of the c-Jun N-terminal kinase (JNK) by binding to JNK and the upstream kinases involved in its activation. The JNK pathway is involved in the regulation of many cellular processes including the control of cell survival, cell death and differentiation. JIP3 also associates with microtubule motor proteins such as kinesin and dynein and is likely an adapter protein involved in the tethering of vesicular cargoes to the motors involved in axonal transport in neurons. We have used immunofluorescence microscopy and biochemical fractionation to investigate the subcellular distribution of JIP3 in relation to JNK and to vesicular and organelle markers in rat pheochromocytoma cells (PC12) differentiating in response to nerve growth factor. In differentiated PC12 cells, JIP3 was seen to accumulate in growth cones at the tips of developing neurites where it co-localised with both JNK and the JNK substrate paxillin. Cellular fractionation of PC12 cells showed that JIP3 was associated with a subpopulation of vesicles in the microsomal fraction, distinct from synaptic vesicles, likely to be an anterograde-directed exocytic vesicle pool. In differentiated PC12 cells, JIP3 did not appear to associate with retrograde endosomal vesicles thought to be involved in signalling axonal injury. Together, these observations indicate that JIP3 may be involved in transporting vesicular cargoes to the growth cones of PC12 cells, possibly targeting JNK to its substrate paxillin, and thus facilitating neurite outgrowth.

SPATA2 regulates the activation of RIPK1 by modulating linear ubiquitination

Stimulation of cells with TNFα leads to the formation of the TNF-R1 signaling complex (TNF-RSC) to mediate downstream cellular fate decision. Activation of the TNF-RSC is modulated by different types of ubiquitination and may lead to cell death, including apoptosis and necroptosis, in both RIPK1-dependent and RIPK1-independent manners. Spata2 (spermatogenesis-associated 2) is an adaptor protein recruited into the TNF-RSC to modulate the interaction between the linear ubiquitin chain assembly complex (LUBAC) and the deubiquitinase CYLD (cylindromatosis). However, the mechanism by which Spata2 regulates the activation of RIPK1 is unclear. Here, we report that Spata2-deficient cells show resistance to RIPK1-dependent apoptosis and necroptosis and are also partially protected against RIPK1-independent apoptosis. Spata2 deficiency promotes M1 ubiquitination of RIPK1 to inhibit RIPK1 kinase activity. Furthermore, we provide biochemical evidence for the USP domain of CYLD and the PUB domain of the SPATA2 complex preferentially deubiquitinating the M1 ubiquitin chain in vitro. Spata2 deficiency also promotes the activation of MKK4 and JNK and cytokine production independently of RIPK1 kinase activity. Spata2 deficiency sensitizes mice to systemic inflammatory response syndrome (SIRS) induced by TNFα, which can be suppressed by RIPK1 inhibitor Nec-1s. Thus, Spata2 can regulate inflammatory response and cell death in both RIPK1-dependent and RIPK1-independent manners.

Inactivation of KLF4 promotes T-cell acute lymphoblastic leukemia and activates the MAP2K7 pathway

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy with a high incidence of relapse in pediatric ALL. Although most T-ALL patients exhibit activating mutations in NOTCH1, the cooperating genetic events required to accelerate the onset of leukemia and worsen disease progression are largely unknown. Here, we show that the gene encoding the transcription factor KLF4 is inactivated by DNA methylation in children with T-ALL. In mice, loss of KLF4 accelerated the development of NOTCH1-induced T-ALL by enhancing the G1-to-S transition in leukemic cells and promoting the expansion of leukemia-initiating cells. Mechanistically, KLF4 represses the gene encoding the kinase MAP2K7. Our results showed that in murine and pediatric T-ALL, loss of KLF4 leads to aberrant activation of MAP2K7 and of the downstream effectors JNK and ATF2. As a proof-of-concept for the development of a targeted therapy, administration of JNK inhibitors reduced the expansion of leukemia cells in cell-based and patient-derived xenograft models. Collectively, these data uncover a novel function for KLF4 in regulating the MAP2K7 pathway in T-ALL cells, which can be targeted to eradicate leukemia-initiating cells in T-ALL patients.

An alternative splicing program promotes adipose tissue thermogenesis

Alternative pre-mRNA splicing expands the complexity of the transcriptome and controls isoform-specific gene expression. Whether alternative splicing contributes to metabolic regulation is largely unknown. Here we investigated the contribution of alternative splicing to the development of diet-induced obesity. We found that obesity-induced changes in adipocyte gene expression include alternative pre-mRNA splicing. Bioinformatics analysis associated part of this alternative splicing program with sequence specific NOVA splicing factors. This conclusion was confirmed by studies of mice with NOVA deficiency in adipocytes. Phenotypic analysis of the NOVA-deficient mice demonstrated increased adipose tissue thermogenesis and improved glycemia. We show that NOVA proteins mediate a splicing program that suppresses adipose tissue thermogenesis. Together, these data provide quantitative analysis of gene expression at exon-level resolution in obesity and identify a novel mechanism that contributes to the regulation of adipose tissue function and the maintenance of normal glycemia.

Competition between members of the tribbles pseudokinase protein family shapes their interactions with mitogen activated protein kinase pathways

Spatio-temporal regulation of intracellular signalling networks is key to normal cellular physiology; dysregulation of which leads to disease. The family of three mammalian tribbles proteins has emerged as an important controller of signalling via regulating the activity of mitogen activated protein kinases (MAPK), the PI3-kinase induced signalling network and E3 ubiquitin ligases. However, the importance of potential redundancy in the action of tribbles and how the differences in affinities for the various binding partners may influence signalling control is currently unclear. We report that tribbles proteins can bind to an overlapping set of MAPK-kinases (MAPKK) in live cells and dictate the localisation of the complexes. Binding studies in transfected cells reveal common regulatory mechanisms and suggest that tribbles and MAPKs may interact with MAPKKs in a competitive manner. Computational modelling of the impact of tribbles on MAPK activation suggests a high sensitivity of this system to changes in tribbles levels, highlighting that these proteins are ideally placed to control the dynamics and balance of activation of concurrent signalling pathways.

Identification and characterization of MKK7 as an upstream activator of JNK in Litopenaeus vannamei

Mitogen-activated protein kinase kinase 7 (MKK7) is a key signal transduction regulator in c-Jun N-terminal kinase (JNK) signaling pathway, which is involved in a wide range of physiological and pathological processes. In this study, we described the molecular cloning of a new member of MKK7 group from Litopenaeus vannamei named as LvMKK7. The full-length cDNA of LvMKK7 was 3093 bp in length, with an open reading frame (ORF) of 1440bp encoding a putative protein of 479 amino acids. LvMKK7 contained a conserved kinase domain of 261 amino acids in which there was a characteristic S-K-A-K-T motif as a potential target site of phosphorylation by MKKK. Moreover, subcellular localization showed LvMKK7 was located in both the cytoplasm and the nucleus of Drosophila S2 cells. Real-time PCR indicated that LvMKK7 was universally expressed in all tested tissues and its expression in hepatopancreas was responsive to the challenge of LPS, Poly (I:C), Vibrio parahaemolyticus, Staphhylococcus aureus and white spot syndrome virus (WSSV). In addition, co-immunoprecipitation assay demonstrated that LvJNK was phosphorylated and activated by LvMKK7, which suggested LvMKK7 was the upper regulator of LvJNK. Furthermore, RNAi-mediated knockdown of LvMKK7 enhanced the sensitivity of shrimps to V. parahaemolyticus infection. Overall, our results suggested that LvMKK7 may play important roles in the shrimp innate immunity.

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.

Structure and dynamics of the MKK7-JNK signaling complex

Signaling specificity in the mitogen-activated protein kinase (MAPK) pathways is controlled by disordered domains of the MAPK kinases (MKKs) that specifically bind to their cognate MAPKs via linear docking motifs. MKK7 activates the c-Jun N-terminal kinase (JNK) pathway and is the only MKK containing three motifs within its regulatory domain. Here, we characterize the conformational behavior and interaction mechanism of the MKK7 regulatory domain. Using NMR spectroscopy, we develop an atomic resolution ensemble description of MKK7, revealing highly diverse intrinsic conformational propensities of the three docking sites, suggesting that prerecognition sampling of the bound-state conformation is not prerequisite for binding. Although the different sites exhibit similar affinities for JNK1, interaction kinetics differ considerably. Importantly, we determine the crystal structure of JNK1 in complex with the second docking site of MKK7, revealing two different binding modes of the docking motif correlating with observations from NMR exchange spectroscopy. Our results provide unique insight into how signaling specificity is regulated by linear motifs and, in general, into the role of conformational disorder in MAPK signaling.

Krüppel-like factor 6 interferes with cellular transformation induced by the H-ras oncogene

KLF6 is a member of the Krüppel-like factor family of transcription factors, with diverse roles in the regulation of cell physiology, including proliferation, signal transduction, and apoptosis. Mutations or down-regulation of KLF6 have been described in several human cancers. In this work, we found that KLF6-knockdown resulted in the formation of transformed foci and allowed the spontaneous conversion of NIH3T3 cells to a tumorigenic state. We further assessed the role of KLF6 in the context of oncogenic Ras. We showed that KLF6 was up-regulated by H-Ras(G12V) expression in a Jun N-terminal kinase (JNK)-dependent manner, correlated with enhanced klf6 promoter activity. We found that ectopic KLF6 expression induced a G1-phase cell cycle arrest, thereby decreasing the cell proliferation rate. In addition, constitutive KLF6 expression impaired H-Ras(G12V)-mediated loss of density-dependent growth inhibition and anchorage-independent growth. Moreover, growth of H-Ras(G12V)-driven tumors was reduced in mice challenged with cells stably expressing KLF6. KLF6 expression correlated with the up-regulation of p21, whereas neither p53 induction nor apoptotic cell death was detected. Further, p21 knockdown impaired KLF6-induced cell cycle arrest. These findings provide novel evidence highlighting KLF6 function in response to malignant transformation, suggesting the relevance of KLF6 in controlling cell proliferation and hindering tumorigenesis.

Piwil2 inhibits keratin 8 degradation through promoting p38-induced phosphorylation to resist Fas-mediated apoptosis

The piwi-like 2 (piwil2) gene is widely expressed in tumors and protects cells from apoptosis induced by a variety of stress stimuli. However, the role of Piwil2 in Fas-mediated apoptosis remains unknown. Here, we present evidence that Piwil2 inhibits Fas-mediated apoptosis. By a bacterial two-hybrid screening, we identify a new Piwil2-interacting partner, keratin 8 (K8), a major intermediate filament protein protecting the cell from Fas-mediated apoptosis. Our results show that Piwil2 binds to K8 and p38 through its PIWI domain and forms a Piwil2/K8/P38 triple protein-protein complex. Thus, Piwil2 increases the phosphorylation level of K8 Ser-73 and then inhibits ubiquitin-mediated degradation of K8. As a result, the knockdown of Piwil2 increases the Fas protein level at the membrane. In addition to our previous finding that Piwil2 inhibits the expression of p53 through the Src/STAT3 pathway, here we demonstrate that Piwil2 represses p53 phosphorylation through p38. Our present study indicates that Piwil2 plays a role in Fas-mediated apoptosis for the first time and also can affect p53 phosphorylation in tumor cells, revealing a novel mechanism of Piwil2 in apoptosis, and supports that Piwil2 plays an active role in tumorigenesis.

Network Motifs in JNK Signaling

Multiple growth factors and extracellular signals can lead to activation of the c-Jun amino N-terminal protein kinase (JNK) pathway. Activation of JNK can in turn lead to a multitude of downstream changes in phosphorylation and transcriptional activation within the cell. Mapping the upstream and downstream connectivity within the JNK network reveals an enrichment of bi-fan and feed-forward network motifs formed immediately upstream and downstream of JNK. In addition, negative feedback loops also exist through transcriptional activation of phosphatases that target the JNK pathway. The combinations of these motifs allow flexibility and tunability in signal integration and processing within the JNK network and may confer the wide range of biological responses that can be regulated by JNK activation. In this review, we highlight the pathways and motifs leading to JNK activation and its downstream signaling as well as the complexity in isoforms within this network.

MKK7 and ARF: new players in the DNA damage response scenery

Sensing, integrating, and processing of stressogenic signals must be followed by accurate differential response(s) for a cell to survive and avoid malignant transformation. The DNA damage response (DDR) pathway is vital in this process, as it deals with genotoxic/oncogenic insults, having p53 as a nodal effector that performs most of the above tasks. Accumulating data reveal that other pathways are also involved in the same or similar processes, conveying also to p53. Emerging questions are if, how, and when these additional pathways communicate with the DDR axis. Two such stress response pathways, involving the MKK7 stress-activated protein kinase (SAPK) and ARF, have been shown to be interlocked with the ATM/ATR-regulated DDR axis in a highly ordered manner. This creates a new landscape in the DDR orchestrated response to genotoxic/oncogenic insults that is currently discussed.

MKK7 mediates miR-493-dependent suppression of liver metastasis of colon cancer cells

The prognosis of advanced colon cancer patients is profoundly affected by the presence or absence of liver metastasis. miR-493 functions as a potent suppressor of liver metastasis, and low-level miR-493 expression in human primary colon cancer is associated with an elevated incidence of liver metastasis. We previously showed that IGF1R is a target gene of miR-493, and that the inhibition of IGF1R partly explains how miR-493 suppresses liver metastasis. However, major functional targets that mediate the antimetastatic activity of miR-493 remain elusive. Here, we extended our search for target genes and identified MKK7, a mitogen-activated protein kinase kinase, as a novel target of miR-493. miR-493 inhibits MKK7 expression by targeting the binding site at the 3′-UTR of the mkk7 gene. MKK7 was expressed in six out of seven colon cancer cell lines examined but not in non-transformed colon epithelial cells, and its expression was required for the activating phosphorylation of JNK. RNA interference-mediated inhibition of MKK7 resulted in marked suppression of liver metastasis of colon cancer cells. A significant decrease of metastasized cells by the MKK7 knockdown was observed, even at early stages of the metastatic settlement, in accordance with a time course of the miR-493-mediated inhibition of the metastasis. Immunohistochemical examination in human primary colon tumors revealed that the occurrence of liver metastasis is associated with elevated levels of MKK7. Thus, MKK7 is a major functional target of miR-493, and its suppression thwarts liver metastasis of colon cancer cells.

Growth cone MKK7 mRNA targeting regulates MAP1b-dependent microtubule bundling to control neurite elongation

Local mRNA translation in neurons has been mostly studied during axon guidance and synapse formation but not during initial neurite outgrowth. We performed a genome-wide screen for neurite-enriched mRNAs and identified an mRNA that encodes mitogen-activated protein kinase kinase 7 (MKK7), a MAP kinase kinase (MAPKK) for Jun kinase (JNK). We show that MKK7 mRNA localizes to the growth cone where it has the potential to be translated. MKK7 is then specifically phosphorylated in the neurite shaft, where it is part of a MAP kinase signaling module consisting of dual leucine zipper kinase (DLK), MKK7, and JNK1. This triggers Map1b phosphorylation to regulate microtubule bundling leading to neurite elongation. We propose a model in which MKK7 mRNA localization and translation in the growth cone allows for a mechanism to position JNK signaling in the neurite shaft and to specifically link it to regulation of microtubule bundling. At the same time, this uncouples activated JNK from its functions relevant to nuclear translocation and transcriptional activation.

Inhibition of MKK7-JNK by the TOR signaling pathway regulator-like protein contributes to resistance of HCC cells to TRAIL-induced apoptosis

BACKGROUND & AIMS

The TOR signaling pathway regulator-like (TIPRL) protein, the mammalian ortholog of yeast TIP41, was identified in an expression profiling screen for factors that regulate human liver carcinogenesis. We investigated the role of human TIPRL protein in hepatocellular carcinoma (HCC).

METHODS

We measured the level of TIPRL in HCC and adjacent nontumor tissues from patients. We used small interfering RNAs and zebrafish to study the function of TIPRL. We used annexin V propidium iodide staining and immunoblot analyses to measure apoptosis and activation of apoptotic signaling pathways. We used confocal microscopy, coimmunoprecipitation, and glutathione-S transferase pull-down analyses to determine interactions among mitogen-activated protein kinase kinase 7 (MKK7 or MAP2K7), TIPRL, and the protein phosphatase type 2A (PP2Ac). We studied the effects of TIPRL in tumor xenografts in mice.

RESULTS

Levels of TIPRL were higher in HCC tissues and cell lines than nontumor tissues and primary hepatocytes. Knockdown of tiprl expression in zebrafish led to large amounts of apoptosis throughout the embryos. Incubation of HCC cells, but not primary human hepatocytes, with small interfering RNA against TIPRL (siTIPRL) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) caused prolonged activation (phosphorylation) of MKK7 and c-Jun N-terminal kinase (JNK) and led to apoptosis, indicated by cleavage of procaspase-8,-3 and of poly-(adenosine diphosphate-ribose) polymerase. TIPRL bound to MKK7 and PP2Ac and promoted the interaction between MKK7 and PP2Ac. In mice, injection of HCC xenograft tumors with siTIPRL and TRAIL led to tumor apoptosis and regression.

CONCLUSIONS

TIPRL is highly up-regulated in human HCC samples and cell lines, compared with noncancerous liver tissues. TIPRL prevents prolonged activation of MKK7 and JNK and TRAIL-induced apoptosis by mediating the interaction between MKK7 and PP2Ac.

Docking interactions of the JNK scaffold protein WDR62

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

New insights into oncogenic stress

Expression of oncogenes in otherwise normal cells often leads to the activation of anti-oncogenic pathways through a poorly understood process described as 'oncogenic stress'. A new study implicates the Jnk pathway signaling in the activation of p53 in response to both K-Ras and Neu oncogene expression.

MKK7γ1 reverses nerve growth factor signals: proliferation and cell death instead of neuritogenesis and protection

c-Jun N-terminal kinases (JNKs) are the exclusive downstream substrates of mitogen-activated protein kinase kinase 7 (MKK7). Recently, we have shown that a single MKK7 splice variant, MKK7γ1, substantially changes the functions of JNKs in naïve PC12 cells. Here we provide evidence that MKK7γ1 blocks NGF-mediated differentiation and sustains proliferation by interfering with the NGF-triggered differentiation programme at several levels: (i) down-regulation of the NGF receptors TrkA and p75; (ii) attenuation of the differentiation-promoting pathways ERK1/2 and AKT; (iii) increase of JNK1 and JNK2, especially the JNK2 54kDa splice variants; (iv) repression of the cyclin-dependent kinase inhibitor p21(WAF1/CIP1), which normally supports NGF-mediated cell cycle arrest; (v) strong induction of the cell cycle promoter CyclinD1, and (vi) profound changes of p53 functions. Moreover, MKK7γ1 substantially changes the responsiveness to stress. Whereas NGF differentiation protects PC12 cells against taxol-induced apoptosis, MKK7γ1 triggers an escape from cell cycle arrest and renders transfected cells sensitive to taxol-induced death. This stress response completely differs from naïve PC12 cells, where MKK7γ1 protects against taxol-induced cell death. These novel aspects on the regulation of JNK signalling emphasise the importance of MKK7γ1 in its ability to reverse basic cellular programmes by simply using JNKs as effectors. Furthermore, our results highlight the necessity for the cells to balance the expression of JNK activators to ensure precise intracellular processes.

The MAP kinase signaling cascades: a system of hundreds of components regulates a diverse array of physiological functions

Sequential activation of kinases within the mitogen-activated protein (MAP) kinase (MAPK) cascades is a common, and evolutionary-conserved mechanism of signal transduction. Four MAPK cascades have been identified in the last 20 years and those are usually named according to the MAPK components that are the central building blocks of each of the cascades. These are the extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-Terminal kinase (JNK), p38, and ERK5 cascades. Each of these cascades consists of a core module of three tiers of protein kinases termed MAPK, MAPKK, and MAP3K, and often two additional tiers, the upstream MAP4K and the downstream MAPKAPK, which can complete five tiers of each cascade in certain cell lines or stimulations. The transmission of the signal via each cascade is mediated by sequential phosphorylation and activation of the components in the sequential tiers. These cascades cooperate in transmitting various extracellular signals and thus control a large number of distinct and even opposing cellular processes such as proliferation, differentiation, survival, development, stress response, and apoptosis. One way by which the specificity of each cascade is regulated is through the existence of several distinct components in each tier of the different cascades. About 70 genes, which are each translated to several alternatively spliced isoforms, encode the entire MAPK system, and allow the wide array of cascade's functions. These components, their regulation, as well as their involvement together with other mechanisms in the determination of signaling specificity by the MAPK cascade is described in this review. Mis-regulation of the MAPKs signals usually leads to diseases such as cancer and diabetes; therefore, studying the mechanisms of specificity-determination may lead to better understanding of these signaling-related diseases.

Defective anchoring of JNK1 in the cytoplasm by MKK7 in Jurkat cells is associated with resistance to Fas-mediated apoptosis

The c-Jun N-terminal protein kinase (JNK) plays a context-dependent role in tumorigenesis. Stress-induced redistribution of JNK from the cytoplasm to the nucleus has been demonstrated as essential for stress-induced cell death. However, accumulation of basal JNK activity in the nucleus has frequently been seen in tumor cells. Our previous report revealed aberrant nuclear entry of JNK protein in Jurkat human leukemic T-cells even without JNK hyperactivation. Because inhibition of JNK activity, especially JNK1 activity, in Jurkat cells results in augmented Fas-mediated apoptosis, it is possible that aberrant subcellular localization of JNK, especially the JNK1 isoform, contributes to the resistance to Fas-mediated apoptosis. Here we report that MKK7 works as a cytoplasmic anchoring protein for JNK1 in various types of cells, including human peripheral blood mononuclear cell (PBMC) T-cells, but exhibits aberrant nuclear entry in Jurkat cells. Ectopic expression of a JNK1 mutant defective of nuclear entry or a nuclear JNK inhibitor leads to impaired UV-induced apoptosis in both PBMC T- and Jurkat cells. The same treatment shows no effect on Fas-mediated apoptosis of PBMC T-cells but sensitizes Jurkat cells to Fas-mediated apoptosis. Taken together, our work suggests that aberrant subcellular organization of the JNK pathway might render certain tumor cells resistant to Fas-mediated apoptosis.

Withanolide D induces apoptosis in leukemia by targeting the activation of neutral sphingomyelinase-ceramide cascade mediated by synergistic activation of c-Jun N-terminal kinase and p38 mitogen-activated protein kinase

BACKGROUND

Ceramide is an important second messenger that has diverse cellular and biological effect. It is a specific and potent inducer of apoptosis and suppressor of cell growth. In leukemia, chemoresistance generally developed due to deregulated ceramide metabolism. In combinatorial treatment strategies of leukemia, few components have the capability to increases ceramide production. Manipulation in ceramide production by physiological and pharmacological modulators therefore will give additive effect in leukemia chemotherapy.

RESULTS

Here, we show that Withanolide D (C4β-C5β,C6β-epoxy-1-oxo-,20β, dihydroxy-20S,22R-witha-2,24-dienolide; WithaD), a pure herbal compound isolated from Withania somnifera could effectively induces apoptosis in a dose and time dependant manner both in myeloid (K562) and lymphoid (MOLT-4) cells being nontoxic to normal lymphocytes and control proliferative cells. WithaD potentially augment ceramide production in these cells. Downstream of ceramide, WithaD acted on MKK group of proteins and significantly increased JNK and p38MAPK phosphorylation. Pharmacological inhibition of p38MAPK and JNK proves their cooperative action on WithaD-induced cell death. Dissecting the cause of ceramide production, we found activation of neutral sphingomyelinase and showed neutral-sphingomyelinase 2 (N-SMase 2) is a critical mediator of WithaD-induced apoptosis. Knockdown of N-SMase 2 by siRNA and inhibitor of N-SMase (GW4869) significantly reduced WithaD-induced ceramide generation and phosphorylation of MKK4 and MKK3/6, whereas phosphorylation of MKK7 was moderately regulated in leukemic cells. Also, both by silencing of N-SMase 2 and/or blocking by GW4869 protects these cells from WithaD-mediated death and suppressed apoptosis, whereas Fumonisin B1, an inhibitor of ceramide synthase, did not have any effect. Additionally, WithaD effectively induced apoptosis in freshly isolated lymphoblasts from patients and the potent cell killing activity was through JNK and p38MAPK activation.

CONCLUSION

Our results demonstrate that WithaD enhance the ceramide accumulation by activating N-SMase 2, modulate phosphorylation of the JNK and p38MAPK and induced apoptosis in both myeloid and lymphoid cells along with primary cells derived from leukemia patients. Taken together, this pure herbal compound (WithaD) may consider as a potential alternative tool with additive effects in conjunction with traditional chemotherapeutic treatment, thereby accelerate the process of conventional drug development.

Specific regulation of JNK signalling by the novel rat MKK7gamma1 isoform

The c-Jun N-terminal kinases (JNKs) mediate a diversity of physiological and pathophysiological effects. Apart from isoform-specific JNK activation, upstream kinases are supposed to be the relevant regulators, which are involved in the context- and signalosome-depending functions. In the present study we report the cloning and characterization of the novel rat MKK7gamma1, a splice variant of MKK7 with an additional exon in the N-terminal region, in the neuronal pheochromocytoma cell line PC12. Transfected MKK7gamma1 increased basal JNK activity, in particular phosphorylation of JNK2. Consequently, JNK signalling was changed in mRNA-, protein- and activation-levels of JNK targets, such as transcription factors (c-Jun, p53, c-Myc), cell cycle regulators (p21, CyclinD1) and apoptotic proteins (Fas, Bim, Bcl-2, Bcl-xl). These alterations promote the sensitivity of MKK7gamma1-transfected cells towards cell death and repress cell proliferation under normal cell growth conditions. Complexes of JIP-1, MKK7 and JNK2 were the major JNK signalosomes under basal conditions. After stimulation with taxol (5muM) and tunicamycin (1.4mug/ml), MKK7gamma1- but not MKK7beta1-transfection, reduced cell death and even increased cell proliferation. Cellular stress also led to an increased phosphorylation of JNK1 and the almost complete abrogation of complexes of JIP-1, MKK7 and JNK2 in MKK7gamma1-transfected PC12 cells. Summarizing, MKK7gamma1 affects the function and activity of individual JNK isoforms and the formation of their signalosomes. This study demonstrates for the first time that one splice-variant of MKK7 tightly controls JNK signalling and effectively adapts JNK functions to the cellular context.

Filamin associates with stress signalling kinases MKK7 and MKK4 and regulates JNK activation

SAPK/JNK (stress-activated protein kinase/c-Jun N-terminal kinase) belongs to the MAPK (mitogen-activated protein kinase) family and is important in many biological contexts. JNK activation is regulated by phosphorylation of specific tyrosine and threonine residues sequentially catalysed by MKK4 and MKK7, which are both dual-specificity MAPKKs (MAPK kinases). Previously, we reported that tyrosine-phosphorylation of JNK by MKK4 precedes threonine-phosphorylation by MKK7, and that both are required for synergistic JNK activation. In the present study, we identify the actin-binding protein-280 (Filamin A) as a presumed ‘binder’ protein that can bind to MKK7, as well as to MKK4, connecting them in close proximity. We show that Filamin family members A, B and C interact with MKK4 and MKK7, but not with JNK. Filamin A binds to an N-terminal region (residues 31–60) present in the MKK7γ and MKK7β splice isoforms, but cannot bind to MKK7α which lacks these amino acids. This same N-terminal region is crucial for the intracellular co-localization of MKK7γ with actin stress fibres and Filamin A. Experiments using Filamin-A-deletion mutants revealed that the MKK7-binding region of Filamin A differs from its MKK4-binding region, and that MKK7γ (but not MKK7α) can form a complex with Filamin A and MKK4. Finally, we used Filamin-A-deficient cells to show that Filamin A enhances MKK7 activation and is important for synergistic stress-induced JNK activation in vivo. Thus Filamin A is a novel member of the group of scaffold proteins whose function is to link two MAPKKs together and promote JNK activation.

Specific phosphorylation and activation of ERK1c by MEK1b: a unique route in the ERK cascade

Extracellular signal-regulated kinases (ERKs) are key signaling molecules that regulate a large number of cellular processes, including mitosis. We showed previously that ERK1c, an alternatively spliced form of ERK1, facilitates mitotic Golgi fragmentation without the involvement of ERK1 and ERK2. Here we demonstrate that activation of ERK1c is mainly mediated by mitogen-activated protein kinase (MAPK)/ERK kinase 1b (MEK1b), which is an alternatively spliced form of MEK1 that was previously considered an inactive kinase. MEK1b phosphorylation and activity are preferentially stimulated by nocodazole, to induce its specific activity toward ERK1c. MEK1/2, on the other hand, preferentially target ERK1/2 in response to growth factors, such as EGF. As previously demonstrated for ERK1c, also MEK1b expression and activity are elevated during mitosis, and thereby enhance Golgi fragmentation and mitotic rate. MEK1 activity is also increased during mitosis, but this isoform facilitates mitotic progression without affecting the Golgi architecture. These results illustrate that the ERK cascade is divided into two routes: the classic MEK1/2-ERK1/2 and the splice-variant MEK1b-ERK1c, each of which regulates distinct cellular processes and thus extends the cascade specificity.

The Parkinson disease-associated protein kinase LRRK2 exhibits MAPKKK activity and phosphorylates MKK3/6 and MKK4/7, in vitro

Autosomal dominant mutations in the human Leucine-Rich Repeat Kinase 2 (LRRK2) gene represent the most common monogenetic cause of Parkinson disease (PD) and increased kinase activity observed in pathogenic mutants of LRRK2 is most likely causative for PD-associated neurotoxicity. The sequence of the LRRK2 kinase domain shows similarity to MAP kinase kinase kinases. Furthermore, LRRK2 shares highest sequence homology with mixed linage kinases which act upstream of canonical MAPKK and are involved in cellular stress responses. Therefore, we addressed the question if LRRK2 exhibits MAPKKK activity by systematically testing MAPKKs as candidate substrates, in vitro. We demonstrate that LRRK2 variants phosphorylate mitogen-activated protein kinase kinases (MAPKK), including MKK3 -4, -6 and -7. MKKs act upstream of the MAPK p38 and JNK mediating oxidative cell stress, neurotoxicity and apoptosis. The disease-associated LRRK2 G2019S and I2020T mutations show an increased phosphotransferase activity towards MKKs correlating with the activity shown for its autophosphorylation. Our findings present evidence of a new class of molecular targets for mutant LRRK2 that link to neurotoxicity, cellular stress, cytoskeletal dynamics and vesicular transport.