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BACKGROUND Human spermatogonial stem cells (SSCs) are the basis of spermatogenesis. However, little is known about the developmental regulatory mechanisms of SSC due to sample origin and species differences. AIM To investigates the mechanisms involved in the proliferation of human SSC. METHODS The expression of mitogen-activated protein kinase kinase 7 (MKK7) in human testis was identified using immunohistochemistry and western blotting (WB). MKK7 was knocked down using small interfering RNA, and cell proliferation and apoptosis were detected by WB, EdU, cell counting kit-8 and fluorescence-activated cell sorting. After bioinformatic analysis, the interaction of MKK7 with c-Jun N-terminal kinases ( JNKs ) was verified by protein co-immunoprecipitation and WB. The phosphorylation of JNKs was inhibited by SP600125, and the phenotypic changes were detected by WB, cell counting kit-8 and fluorescence-activated cell sorting. RESULTS MKK7 is mainly expressed in human SSCs, and MKK7 knockdown inhibits SSC proliferation and promotes their apoptosis. MKK7 mediated the phosphorylation of JNKs, and after inhibiting the phosphorylation of JNKs, the phenotypic changes of the cells were similar to those after MKK7 downregulation. The expression of MKK7 was significantly downregulated in patients with abnormal spermatogenesis, suggesting that abnormal MKK7 may be associated with spermatogenesis impairment. CONCLUSION MKK7 regulates the proliferation and apoptosis of human SSC by mediating the phosphorylation of JNKs.

(1) Background: The c-Jun-NH2-terminal protein kinase (JNK) is a mitogen-activated protein kinase involved in regulating physiological processes in the central nervous system. However, the dual genetic deletion of Mkk4 and Mkk7 (upstream activators of JNK) in adult mice is not reported. The aim of this study was to induce the genetic deletion of Mkk4/Mkk7 in adult mice and analyze their effect in hippocampal neurogenesis. (2) Methods: To achieve this goal, Actin-CreERT2 (Cre+/−), Mkk4flox/flox, Mkk7flox/flox mice were created. The administration of tamoxifen in these 2-month-old mice induced the gene deletion (Actin-CreERT2 (Cre+/−), Mkk4∆/∆, Mkk7∆/∆ genotype), which was verified by PCR, Western blot, and immunohistochemistry techniques. (3) Results: The levels of MKK4/MKK7 at 7 and 14 days after tamoxifen administration were not eliminated totally in CNS, unlike what happens in the liver and heart. These data could be correlated with the high levels of these proteins in CNS. In the hippocampus, the deletion of Mkk4/Mkk7 induced a misalignment position of immature hippocampal neurons together with alterations in their dendritic architecture pattern and maturation process jointly to the diminution of JNK phosphorylation. (4) Conclusion: All these data supported that the MKK4/MKK7–JNK pathway has a role in adult neurogenic activity.

Objective To investigate the expression of phospho-c-Jun and MKK7 in gliomas and their correlation. Methods We collected and analyzed retrospectively 92 cases of gliomas, including 15 cases of diffuse astrocytoma, 5 cases of oligodendroglioma, 11 cases of anaplastic astrocytoma, 8 cases of anaplastic oligodendroglioma 53 cases of glioblastoma and 25 normal brain tissues adjacent to glioblastoma. The expression of c-Jun, phospho-c-Jun and MKK7 were detected by immunohistochemical staining. Glioma U87 cell line cultured in vitro was transfected with MKK4-siRNA, MKK7-siRNA and control siRNA for 48h, respectively. Western blot was performed to test the expression of c-Jun, phospho-c-Jun and MKK7. Results The expression of p-c-Jun and MKK7 in glioblastoma were significantly higher than those in other glioma and normal brain tissues adjacent to glioblastomas(P=0.000, P=0.000). The expression of MKK7 and phospho-c-Jun were positively correlated with WHO grading of gliomas (r＝0.494, P＝0.000; r=0.606, P=0.000). There was positive correlation between the expression of MKK7 and p-c-Jun (r=0.387, P=0.000). The knockdown of MKK7 suppressed c-Jun activities. Conclusion MKK7 promotes the development of glioblastoma by regulating the activity of c-Jun.

Mitogen-aktivierte Proteinkinase-Signalwege sind in eukaryotischen Zellen von besonderer Bedeutung, da sie einen zentralen Bestandteil der Weiterleitung von extrazellulären Signalen zum Zellkern darstellen. Beim Menschen sind insgesamt vier MAPK-Signalwege bekannt. In dieser Arbeit wurde im Speziellen der JNK-Signalweg genauer untersucht, der vor allem in Folge von physischen Stimuli wie Hitze, Strahlung und osmotischen Schock sowie Cytokine aktiviert wird. Ebenso ist der JNK-Signalweg in die Entwicklung von Organen während der Embryogenese und in der Entwicklung des Gehirns und des Nervensystems beteiligt. Dies macht den Signalweg zu einem relevanten Ziel für die Wirkstoffforschung. Es konnte bereits gezeigt werden, dass eine direkte Einwirkung auf JNK, zum Beispiel durch selektive JNK-Inhibitoren, viele Nebenwirkungen auslösen kann. Aus diesem Grund sollte in dieser Arbeit die Regulierung eine der beiden Aktivatoren von JNK, die Mitogen aktivierte Protein Kinase Kinase 7 (MKK7), genauer analysiert werden. Hierfür sollte nach Liganden gesucht werden, welche die Aktivität der Kinase innerhalb eines Organismus spezifisch modulieren können, mit dem Ziel, mit Hilfe dieser Substanz Veränderungen in der Funktionsweise des Signalweges, zum Beispiel in den Phosphorylierungsmustern der JNK Substrate, oder in der Morphologie der Zelle, zu detektieren. Dazu wurde zunächst eine Auswahl von verschiedenen biochemischen Assays hinsichtlich ihrer Eignung auf die Charakterisierung von MKK7-Liganden untersucht und mit einem, auf diese Weise identifizierten, geeignetem System eine Bibliothek niedermolekularer Substanzen durchmustert. Die gefundenen Hits wurden sowohl biochemisch als auch mit Hilfe von massenspektrometrischen Messungen validiert. Der potenteste Inhibitor (Verbindung 22) wurde anschließend in Mäusen auf seine pharmakokinetischen Eigenschaften hin untersucht, und in einem Ansatz mit DRG-Zellen auf seine spezifische Wirksamkeit hin untersucht und zeigte auch hier eine hohe Aktivität wie auch Selektivität. Zusätzlich wurde Verbindung 22 wie auch eine Reihe weiterer Inhibitoren im Komplex mit MKK7 kokristallisiert, wodurch der Bindungsmodus dieser Inhibitoren aufgeklärt werden konnte.

Peptides are emerging as an increasingly dependable class of therapeutics in the treatment of cancer and metabolic and cardiovascular diseases, which are all areas of high interest to the pharmaceutical industry. The global market for peptide therapeutics was valued at about 25 billion USD in 2018 and is estimated to reach 57.2 billion USD by the end of 2027. Here, we describe a method for the screening and deconvolution of combinatorial peptide libraries to discover compounds that target discrete signaling components of the NF-κB pathway. Recently, we used this approach to specifically disrupt the interaction between the JNK-activating kinase, MKK7, and the NF-κB-regulated antiapoptotic factor, GADD45β, in multiple myeloma (MM). We showed that the GADD45β/MKK7 complex is a functionally critical survival module downstream of NF-κB in MM cells and as such provides an attractive therapeutic target to selectively inhibit NF-κB antiapoptotic signaling in cancer cells. By integrating the library screening and deconvolution methods described here with a rational chemical optimization strategy, we developed the first-in-class GADD45β/MKK7 inhibitor, DTP3 (a D-tripeptide), which is now being trialed in MM and diffuse large B-cell lymphoma (DLBCL) patients. The same drug discovery approach may be generally applied to therapeutically target other key components of the NF-κB pathway in cancers beyond MM and DLBCL, as well as in non-malignant NF-κB-driven diseases.

GADD45&beta, /MKK7 complex is a non-redundant, cancer cell-restricted survival module downstream of the NF-kB survival pathway, and it has a pathogenically critical role in multiple myeloma, an incurable malignancy of plasma cells. The first-in-class GADD45&beta, /MKK7 inhibitor DTP3 effectively kills MM cells expressing its molecular target, both in vitro and in vivo, by inducing MKK7/JNK-dependent apoptosis with no apparent toxicity to normal cells. DTP3 combines favorable drug-like properties, with on-target-specific pharmacology, resulting in a safe and cancer-selective therapeutic effect, however, its mode of action is only partially understood. In this work, we have investigated the molecular determinants underlying the MKK7 interaction with DTP3 by combining computational, NMR, and spectroscopic methods. Data gathered by fluorescence quenching and computational approaches consistently indicate that the N-terminal region of MKK7 is the optimal binding site explored by DTP3. These findings further the understanding of the selective mode of action of GADD45&beta, /MKK7 inhibitors and inform potential mechanisms of drug resistance. Notably, upon validation of the safety and efficacy of DTP3 in human trials, our results could also facilitate the development of novel DTP3-like therapeutics with improved bioavailability or the capacity to bypass drug resistance.

c‐Jun N‐terminal kinases (JNKs) are constitutively activated in mammalian brains and are indispensable for their development and neural functions. MKK7 is an upstream activator of all JNKs. However, whether the common JNK signaling pathway regulates the brain's control of social behavior remains unclear. Here, we show that female mice in which Mkk7 is deleted specifically in mature neurons (Mkk7flox/floxSyn‐Cre mice) give birth to a normal number of pups but fail to raise them due to a defect in pup retrieval. To explore the mechanism underlying this abnormality, we performed comprehensive behavioral tests. Mkk7flox/floxSyn‐Cre mice showed normal locomotor functions and cognitive ability but exhibited depression‐like behavior. cDNA microarray analysis of mutant brain revealed an altered gene expression pattern. Quantitative RT‐PCR analysis demonstrated that mRNA expression levels of genes related to neural signaling pathways and a calcium channel were significantly different from controls. In addition, loss of neural MKK7 had unexpected regulatory effects on gene expression patterns in oligodendrocytes. These findings indicate that MKK7 has an important role in regulating the gene expression patterns responsible for promoting normal social behavior and staving off depression., c‐Jun N‐terminal kinase (JNK) signaling has well established, important roles in mammalian brain development and neural functions. However, whether the mitogen‐activated protein kinase kinase 7 (MKK7), a specific upstream activator of JNK, regulates social behavior remains unclear. In this study, we demonstrate that the MKK7‐JNK pathway in mature neurons regulates mouse mental status and plays a critical role in parental behavior.

The c-Jun N-terminal kinase (JNK)/c-Jun cascade-dependent neuronal apoptosis has been identified as a central element for early brain injury (EBI) following subarachnoid hemorrhage (SAH), but the molecular mechanisms underlying this process are still thoroughly undefined to date. In this study, we found that pan-histone deacetylase (HDAC) inhibition by TSA, SAHA, VPA, and M344 led to a remarkable decrease in the phosphorylation of JNK and c-Jun, concomitant with a significant abrogation of apoptosis caused by potassium deprivation in cultured cerebellar granule neurons (CGNs). Further investigation showed that these effects resulted from HDAC inhibition-induced transcriptional suppression of MKK7, a well-known upstream kinase of JNK. Using small interference RNAs (siRNAs) to silence the respective HDAC members, HDAC4 was screened to be required for MKK7 transcription and JNK/c-Jun activation. LMK235, a specific HDAC4 inhibitor, dose-dependently suppressed MKK7 transcription and JNK/c-Jun activity. Functionally, HDAC4 inhibition via knockdown or LMK235 significantly rescued CGN apoptosis induced by potassium deprivation. Moreover, administration of LMK235 remarkably ameliorated the EBI process in SAH rats, associated with an obvious reduction in MKK7 transcription, JNK/c-Jun activity, and neuronal apoptosis. Collectively, the findings provide new insights into the molecular mechanism of neuronal apoptosis regarding HDAC4 in the selective regulation of MKK7 transcription and JNK/c-Jun activity. HDAC4 inhibition could be a potential alternative to prevent MKK7/JNK/c-Jun axis-mediated nervous disorders, including SAH-caused EBI.

One of the mitogen-activated protein kinases (MAPKs), c-Jun NH2-terminal protein kinase (JNK) plays an important role in regulating cell fate, such as proliferation, differentiation, development, transformation, and apoptosis. Its activity is induced through the interaction of MAPK kinase kinases (MAP3Ks), MAPK kinases (MAP2Ks), and various scaffolding proteins. Because of the importance of the JNK cascade to intracellular bioactivity, many studies have been conducted to reveal its precise intracellular functions and mechanisms, but its regulatory mechanisms remain elusive. In this review, we discuss the molecular characterization, activation process, and physiological functions of mitogen-activated protein kinase kinase 7 (MKK7), the MAP2K that most specifically controls the activity of JNK. Understanding the role of MKK7/JNK signaling in physiological conditions could spark new hypotheses for targeted anticancer therapies.

Rationale Members of the c-Jun N-terminal kinase (JNK) family of mitogen-activated protein (MAP) kinases, and the upstream kinase MKK7, have all been strongly linked with synaptic plasticity and with the development of the neocortex. However, the impact of disruption of this pathway on cognitive function is unclear. Objective In the current study, we test the hypothesis that reduced MKK7 expression is sufficient to cause cognitive impairment. Methods Attentional function in mice haploinsufficient for Map2k7 (Map2k7 +/− mice) was investigated using the five-choice serial reaction time task (5-CSRTT). Results Once stable performance had been achieved, Map2k7 +/− mice showed a distinctive attentional deficit, in the form of an increased number of missed responses, accompanied by a more pronounced decrement in performance over time and elevated intra-individual reaction time variability. When performance was reassessed after administration of minocycline—a tetracycline antibiotic currently showing promise for the improvement of attentional deficits in patients with schizophrenia—signs of improvement in attentional performance were detected. Conclusions Overall, Map2k7 haploinsufficiency causes a distinctive pattern of cognitive impairment strongly suggestive of an inability to sustain attention, in accordance with those seen in psychiatric patients carrying out similar tasks. This may be important for understanding the mechanisms of cognitive dysfunction in clinical populations and highlights the possibility of treating some of these deficits with minocycline. Electronic supplementary material The online version of this article (doi:10.1007/s00213-016-4463-y) contains supplementary material, which is available to authorized users.

Reprogramming of somatic cells to the phenotypic state termed “induced pluripotency” is thought to occur through three consecutive stages: initiation, maturation, and stabilisation. The initiation phase is stochastic but nevertheless very important as it sets the gene expression pattern that permits completion of reprogramming; hence a better understanding of this phase and how this is regulated may provide the molecular cues for improving the reprogramming process. c‐Jun N‐terminal kinase (JNK)/stress‐activated protein kinase (SAPKs) are stress activated MAPK kinases that play an essential role in several processes known to be important for successful completion of the initiation phase such as cellular proliferation, mesenchymal to epithelial transition (MET) and cell cycle regulation. In view of this, we postulated that manipulation of this pathway would have significant impacts on reprogramming of human fibroblasts to induced pluripotent stem cells. Accordingly, we found that key components of the JNK/SAPK signaling pathway increase expression as early as day 3 of the reprogramming process and continue to rise in reprogrammed cells throughout the initiation and maturation stages. Using both chemical inhibitors and RNA interference of MKK4, MKK7 and JNK1, we tested the role of JNK/SAPK signaling during the initiation stage of neonatal and adult fibroblast reprogramming. These resulted in complete abrogation of fully reprogrammed colonies and the emergence of partially reprogrammed colonies which disaggregated and were lost from culture during the maturation stage. Inhibition of JNK/SAPK signaling resulted in reduced cell proliferation, disruption of MET and loss of the pluripotent phenotype, which either singly or in combination prevented establishment of pluripotent colonies. Together these data provide new evidence for an indispensable role for JNK/SAPK signaling to overcome the well‐established molecular barriers in human somatic cell induced reprogramming. Stem Cells 2016;34:1198–1212

Background/Aims: The hepatitis B virus X protein (HBx) contributes to HBV-induced injury of renal tubular cells and induces apoptosis via Fas/FasL up-regulation. However, the mechanism of Fas/FasL activation is unknown. Recent studies indicated that HBx induction of apoptosis in hepatic cells depends on activating the MLK3-MKK7-JNKs signaling module, which then up-regulates FasL expression. In this study, we used NRK-52E cells transfected an HBx expression vector to examine the role of the MLK3-MKK7-JNKs signaling pathway on HBx-induced renal tubular cell injury. Methods: NRK-52E cells were transfected with pc-DNA3.1(+)-HBx to establish an HBx over-expression model, and with pc-DNA3.1(+)-HBx and pSilencer3.1-shHBx to establish an HBx low expression model. One control group was not transfected and another control group was transfected with an empty plasmid. Cell proliferation was determined by the formazan dye method (Cell Counting Kit-8) and apoptosis was measured by flow cytometry and fluorescence microscopy. Western blotting was used to measure the expression of Fas, FasL, and MLK3-MKK7-JNKs signaling pathway-related proteins. The activity of caspase-8 was measured by spectrophotometry. Results: Transfection of NRK-52E cells with pc-DNA3.1(+)-HBx inhibited cell proliferation and increased apoptosis and caspase-8 activity. The expression of Fas, FasL, and MLK3-MKK7-JNKs signaling pathway-related proteins were also greater in the pc-DNA3.1(+)-HBx group, but lower in RNAi group. Furthermore, the activity of MLK3-MKK7-JNKs signaling pathway, expression of Fas/FasL, and apoptosis were significantly lower in the pc-DNA3.1(+)-HBx group when treated with K252a, a known inhibitor of MLK3. Conclusions: Our results show that HBx induces apoptosis in NRK-52E cells and activates Fas/FasL via the MLK3-MKK7-JNK3-c-Jun signaling pathway.

Activator protein 1 (AP-1) is a transcriptional factor composed of the dimeric members of bZIP proteins, which are frequently deregulated in human cancer cells. In this study, we aimed to identify an oncogenic AP-1 dimer critical for the proliferation of neuroblastoma cells and to investigate whether histone deacetylase inhibitors (HDACIs), a new generation of anticancer agents, could target the AP-1 dimer. We report here that HDACIs including trichostatin A, suberoylanilidehydroxamic acid, valproic acid and M344 can transcriptionally suppress both c-Jun and Fra-1, preceding their inhibition of cell growth. c-Jun preferentially interacting with Fra-1 as a heterodimer is responsible for AP-1 activity and critical for cell growth. Mechanistically, HDACIs suppress Fra-1 expression through transcriptionally downregulating Raf1 and subsequently decreasing MEK1/2-ERK1/2 activity. Unexpectedly, HDACI treatment caused MKK7 downregulation at both the protein and mRNA levels. Deletion analysis of the 5'-flanking sequence of the MKK7 gene revealed that a major element responsible for the downregulation by HDACI is located at -149 to -3 relative to the transcriptional start site. Knockdown of MKK7 but not MKK4 remarkably decreased JNK/c-Jun activity and proliferation, whereas ectopic MKK7-JNK1 reversed HDACI-induced c-Jun suppression. Furthermore, suppression of both MKK-7/c-Jun and Raf-1/Fra-1 activities was involved in the tumor growth inhibitory effects induced by SAHA in SH-SY5Y xenograft mice. Collectively, these findings demonstrated that c-Jun/Fra-1 dimer is critical for neuroblastoma cell growth and that HDACIs act as effective suppressors of the two oncogenes through transcriptionally downregulating MKK7 and Raf1.

c-Jun-N-terminal kinase (JNK) activity plays a critical role in modulating cell death, which depends on the level and duration of JNK activation. The kinase cascade from MAPkinase kinase kinase (MAP3K) to MAPkinase kinase (MAP2K) to MAPKinase (MAPK) can be regulated by a number of direct and indirect post-transcriptional modifications, including acetylation, ubiquitination, phosphorylation, and their reversals. Recently, a JNK-mitochondrial SH3-domain binding protein 5 (SH3BP5/SAB)-ROS activation loop has been elucidated, which is required to sustain JNK activity. Importantly, the level of SAB expression in the outer membrane of mitochondria is a major determinant of the set-point for sustained JNK activation. SAB is a docking protein and substrate for JNK, leading to an intramitochondrial signal transduction pathway, which impairs electron transport and promotes reactive oxygen species (ROS) release to sustain the MAPK cascade.

Background/aims Lipoxin A4 (LXA4), an anti-inflammatory lipid mediator, regulates leukocyte cellular activity and activates gene transcription. The therapeutic effect of LXA4 on liver fibrosis and its mechanism on the immune system are largely unknown. Because the regenerative capacity of hepatocytes in acute and chronic liver failure models of mouse increases by silencing MKK4, we aimed to investigate the effect of parenteral administration of LXA4 on the genes responsible for regeneration of liver, namely MKK4, MKK7, and ATF2, and visualize the therapeutic effects in an experimental model. Materials and methods Fibrosis was induced in mice by administration of thioacetamide (TAA). LXA4 was administered during the last two weeks of fibrosis induction. The fibrosis level was measured by Knodell scoring. The liver function was measured by analyzing serum ALT, AST, and AP levels. Expression levels of genes responsible for liver fibrosis (TGF-α) and cell regeneration (MKK4, MKK7, and ATF2) have been measured by RT-PCR analysis. Inflammatory and anti-inflammatory cytokine levels were measured in serum samples and liver homogenates by Enzyme Linked Immunosorbent Assay (ELISA). Ultrathin sections were examined using a transmission electron microscope and analyzed. Results We observed significant healing in liver of the LXA4-treated group, histologically. This finding was in parallel with reduction of serum ALT, AST, but not AP levels. TGF-α and MKK4 expressions were significantly reduced in the LXA4-treated group. Administration of LXA4 caused significant elevation of IL-10 in systemic circulation; however, that elevation was not detected in liver homogenates. Nevertheless, significant reductions in TNF-α and IL-17 have been observed. Conclusion The anti-inflammatory effect of LXA4 maintains the regenerative capacity of liver during fibrosis in an experimental liver fibrosis model. LXA4 may be therapeutically beneficial in liver fibrosis.

GADD45β is selectively and constitutively expressed in Multiple Myeloma cells, and this expression correlates with an unfavourable clinical outcome. GADD45β physically interacts with the JNK kinase, MKK7, inhibiting its activity to enable the survival of cancer cells. DTP3 is a small peptide inhibitor of the GADD45β/MKK7 complex and is able to restore MKK7/JNK activation, thereby promoting selective cell death of GADD45β-overexpressing cancer cells. Enzymatic MS foot-printing and diazirine-based chemical cross-linking MS (CX-MS) strategies were applied to study the interactions between GADD45β and MKK7 kinase domain (MKK7_KD) and between DTP3 and MKK7_KD. Our data show that the binding between GADD45β and MKK7 largely occurs between GADD45β loop 2 (region 103-117) and the kinase enzymatic pocket. We also show that DTP3 interferes with this GADD45β/MKK7 interaction by contacting the MKK7 peptides, 113-136 and 259-274. Accordingly, an MKK7_KD Δ(101-136) variant lacking Trp135 did not produce a fluorescence quenching effect upon the binding of DTP3. The assessment of the interaction between GADD45β and MKK7 and the elucidation of the recognition surfaces between DTP3 and MKK7 significantly advance the understanding of the mechanism underlying the inhibition of the GADD45β/MKK7 interaction by DTP3 and pave the way to the design of small-molecule DTP3 analogues. GADD45β is selectively and constitutively expressed in Multiple Myeloma cells, and this expression correlates with an unfavourable clinical outcome. GADD45β physically interacts with the JNK kinase, MKK7, inhibiting its activity to enable the survival of cancer cells. DTP3 is a small peptide inhibitor of the GADD45β/MKK7 complex and is able to restore MKK7/JNK activation, thereby promoting selective cell death of GADD45β-overexpressing cancer cells. Enzymatic MS foot-printing and diazirine-based chemical cross-linking MS (CX-MS) strategies were applied to study the interactions between GADD45β and MKK7 kinase domain (MKK7_KD) and between DTP3 and MKK7_KD. Our data show that the binding between GADD45β and MKK7 largely occurs between GADD45β loop 2 (region 103–117) and the kinase enzymatic pocket. We also show that DTP3 interferes with this GADD45β/MKK7 interaction by contacting the MKK7 peptides, 113–136 and 259–274. Accordingly, an MKK7_KD Δ(101–136) variant lacking Trp135 did not produce a fluorescence quenching effect upon the binding of DTP3. The assessment of the interaction between GADD45β and MKK7 and the elucidation of the recognition surfaces between DTP3 and MKK7 significantly advance the understanding of the mechanism underlying the inhibition of the GADD45β/MKK7 interaction by DTP3 and pave the way to the design of small-molecule DTP3 analogues.

金沢大学医薬保健研究域保健学系, Growth arrest and DNA damage-inducible 45 (GADD45) family genes encode related proteins, including GADD45α, GADD45β, and GADD45γ. In HeLa cells, expression of GADD45 members is differentially regulated under a variety of environmental conditions, but thermal and genotoxic stresses induce the expression of all genes. The heat shock response of GADD45β is mediated by the heat shock transcription factor 1 (HSF1), and GADD45β is necessary for heat stress survival. Heat and genotoxic stress-induced activation of c-Jun N-terminal kinase (JNK) is suppressed by the expression of GADD45 proteins. GADD45 proteins bind the JNK kinase mitogen-activated protein kinase kinase 7 (MKK7) and inhibit its activity, even under normal physiological conditions. Our findings indicate that GADD45 essentially suppresses the MKK7-JNK pathway and suggest that differentially expressed GADD45 family members fine-tune stress-inducible JNK activity. © 2017 Elsevier Inc., Embargo Period 12 months

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.

CELF2 is an RNA binding protein that has been implicated in developmental and signal-dependent splicing in the heart, brain and T cells. In the heart, CELF2 expression decreases during development, while in T cells CELF2 expression increases both during development and in response to antigen-induced signaling events. Although hundreds of CELF2-responsive splicing events have been identified in both heart and T cells, the way in which CELF2 functions has not been broadly investigated. Here we use CLIP-Seq to identified physical targets of CELF2 in a cultured human T cell line. By comparing the results with known functional targets of CELF2 splicing regulation from the same cell line we demonstrate a generalizable position-dependence of CELF2 activity that is consistent with previous mechanistic studies of individual CELF2 target genes in heart and brain. Strikingly, this general position-dependence is sufficient to explain the bi-directional activity of CELF2 on 2 T cell targets recently reported. Therefore, we propose that the location of CELF2 binding around an exon is a primary predictor of CELF2 function in a broad range of cellular contexts.

Alpinetin is a type of novel plant flavonoid derived from Alpinia katsumadai Hayata, found to possess strong anti-hepatoma effects. However, the detailed antitumor mechanism of alpinetin remains unclear. Mitogen-activated protein kinase kinase-7 (MKK7) can regulate cellular growth, differentiation and apoptosis. The aim of this study was to investigate the role of MKK7 in the anti-hepatoma effect mediated by alpinetin. HepG2 cells were treated with alpinetin at various doses and for different times, and the levels of phosphorylated MKK7 (p-MKK7) and total MKK7 were tested by RT-PCR and western blotting. Following transient transfection with RNA interference, cell viability and cell cycle stage were determined using methyl thiazolyl tetrazolium assay and flow cytometry, in order to assess the antitumor action of alpinetin. In addition, chemosensitization to cis-diammined dichloridoplatium (CDDP) by alpinetin was assessed by cell counting array and the cell growth inhibitory rate was calculated. The results showed that alpinetin suppressed HepG2 cell proliferation and arrested cells in the G0/G1 phase by up-regulating the expression levels of p-MKK7. On the contrary, inhibiting the expression of MKK7 reversed the antitumor effect of alpinetin. Moreover, alpinetin enhanced the sensitivity of HepG2 hepatoma cells to the chemotherapeutic agent CDDP. Taken together, our studies indicate that activation of MKK7 mediates the anti-hepatoma effect of alpinetin. MKK7 may be a putative target for molecular therapy against hepatoma and alpinetin could serve as a potential agent for the development of hepatoma therapy.

Different scaffold proteins play distinct roles in various signaling pathways by recruiting different downstream molecules. Here, using MKK4−/− and MKK4−/−/7−/− murine embryonic fibroblast cells, we examined differential employment of MKK4 and MKK7 by scaffold proteins Axin, Dvl, and Epstein–Barr virus latent membrane protein-1 (LMP-1) in mediating JNK activation. We present evidence that Axin depends mainly on MKK7 for activation of JNK, while Dvl depends almost equally on MKK4 and MKK7 for JNK activation, In contrast, LMP-1-induced JNK activation is primarily dependent on MKK4. Our results demonstrate that Axin, Dvl, and LMP-1 differentially utilize MKK4 and MKK7 for JNK activation.

The dual specificity kinases mitogen-activated protein kinase (MAPK) kinase (MKK)7 and MKK4 are the only molecules known to directly activate the stress kinases stress-activated protein kinases (SAPKs)/c-Jun N-terminal kinases (JNKs) in response to environmental or mitogenic stimuli. To examine the physiological role of MKK7 in hematopoietic cells, we used a gene targeting strategy to mutate MKK7 in murine T and B cells and non-lymphoid mast cells. Loss of MKK7 in thymocytes and mature B cells results in hyperproliferation in response to growth factor and antigen receptor stimulation and increased thymic cellularity. Mutation of mkk7 in mast cells resulted in hyperproliferation in response to the cytokines interleukin (IL)-3 and stem cell factor (SCF). SAPK/JNK activation was completely abolished in the absence of MKK7, even though expression of MKK4 was strongly upregulated in mkk7−/− mast cell lines, and phosphorylation of MKK4 occurred normally in response to multiple stress stimuli. Loss of MKK7 did not affect activation of extracellular signal–regulated kinase (ERK)1/2 or p38 MAPK. mkk7−/− mast cells display reduced expression of JunB and the cell cycle inhibitor p16INK4a and upregulation of cyclinD1. Reexpression of p16INK4a in mkk7−/− mast cells abrogates the hyperproliferative response. Apoptotic responses to a variety of stimuli were not affected. Thus, MKK7 is an essential and specific regulator of stress-induced SAPK/JNK activation in mast cells and MKK7 negatively regulates growth factor and antigen receptor–driven proliferation in hematopoietic cells. These results indicate that the MKK7-regulated stress signaling pathway can function as negative regulator of cell growth in multiple hematopoietic lineages.

The Liver X Receptor (LXR) and Pregnane X Receptor (PXR) are members of the nuclear receptor superfamily. Previously, they have been classified as important regulators of lipid homeostasis. However, recent studies have shown that they may be implicated in anti-inflammatory responses as well. This study shows that Tumour Necrosis Factor-α (TNF-α) treatment reduces both LXR-α and PXR mRNA expression. However, pre-treatment with rapamycin, an mTOR inhibitor, followed by TNF-α stimulation, significantly induces LXR-α and PXR mRNA expression to ~17- and ~2-fold, respectively. This suggests that mTORC1, a multi-molecular complex of which mTOR is a member, may act as a negative regulator that inhibits the induction of LXR-α and PXR as anti-inflammatory genes. It is also shown here that inhibition of JNK1 via the mTOR/Akt pathway coincides with the up-regulation of LXR-α and PXR mRNA, after TNF-α treatment. Together, these observations suggest that JNK1 possibly act downstream of mTORC1 as an LXR-α and PXR inhibitor. From the results gleaned in this study, rapamycin (and its analogues) may be used to reduce acute inflammation by promoting the induction of LXR-α and PXR as anti-inflammatory genes.

The Liver X Receptor (LXR) and Pregnane X Receptor (PXR) are members of the nuclear receptor superfamily. Previously, they have been classified as important regulators of lipid homeostasis. However, recent studies have shown that they may be implicated in anti-inflammatory responses as well. This study shows that Tumour Necrosis Factor-α (TNF-α) treatment reduces both LXR-α and PXR mRNA expression. However, pre-treatment with rapamycin, an mTOR inhibitor, followed by TNF-α stimulation, significantly induces LXR-α and PXR mRNA expression to ~17- and ~2-fold, respectively. This suggests that mTORC1, a multi-molecular complex of which mTOR is a member, may act as a negative regulator that inhibits the induction of LXR-α and PXR as anti-inflammatory genes. It is also shown here that inhibition of JNK1 via the mTOR/Akt pathway coincides with the up-regulation of LXR-α and PXR mRNA, after TNF-α treatment. Together, these observations suggest that JNK1 possibly act downstream of mTORC1 as an LXR-α and PXR inhibitor. From the results gleaned in this study, rapamycin (and its analogues) may be used to reduce acute inflammation by promoting the induction of LXR-α and PXR as anti-inflammatory genes.

Die molekularbiologische Untersuchung der Wechselwirkungen zwischen Pathogenen und ihren Wirtszellen ist ein wertvoller Ansatz zur Erschließung bakterieller Pathogenitätsmechanismen und hilft, unser ständig wachsendes Wissen über fundamentale Prozesse in eukaryotischen Zellen zu erweitern. Das Gram-negative Bakterium Salmonella Typhimurium ist ein gängiger Modellorganismus, um den intrazellulären Lebensstil bakterieller Pathogene und deren Einfluss auf Wirtszellprozesse zu erforschen. In der vorliegenden Arbeit wurde ein FACS-basierter Hochdurchsatz RNA Interferenz Screen etabliert und durchgeführt, um Wirtszellfaktoren zu entschlüsseln, welche in die intrazelluläre Replikation von Salmonella Typhimurium in humanen Epithelzellen involviert sind. Ein Salmonellen-Stamm, der zwei fluoreszierende Reporterproteine exprimiert, wurde konstruiert, um die bakterielle Replikation und die metabolische Aktivität in infizierten Wirtszellen zu detektieren. Der Einsatz einer humanen Kinase-Bibliothek lieferte 48 potentielle Kandidatengene, von denen 15 in einer anschließenden Validierung als relevante Faktoren identifiziert werden konnten. Die Mitogen-aktivierte Protein Kinase MKK7, deren Depletion eine verminderte bakterielle Replikation zur Folge hatte, wurde für eine weitergehende funktionelle Charakterisierung ausgewählt. Es zeigte sich, dass reduzierte MKK7 Proteinmengen eine Verringerung des Proteins zytosolische Phospholipase A2 (cPLA2) durch eine transkriptionelle Regulation zur Folge hatten. Die Bedeutung von cPLA2 für die bakterielle Infektion wurde durch die Salmonellen-induzierte, dauerhafte Phosphorylierung des Faktors deutlich und konnte durch Replikationsvergleiche in cPLA2-depletierten und nicht-depletierten Zellen bestätigt werden. Mikroskopische Ergebnisse deuteten darauf hin, dass die Phospholipase für den fehlerfreien Aufbau von Salmonellen-induzierten Filamenten notwendig ist, welche unerlässlich für die Salmonellenreplikation in Epithelzellen sind., The study of pathogen-host cell interactions on the molecular level is a valuable tool to reveal bacterial pathogenicity mechanisms and, moreover, contributes to our increasing knowledge of fundamental cellular processes of eukaryotic cells. The Gram negative bacterium Salmonella Typhimurium is a well established model organism to investigate the intracellular lifestyle of bacterial pathogens and their modulation of host cell processes. In this work, a FACS-based high-throughput RNA interference screen was established and performed to elucidate host cell factors involved in the intracellular replication of Salmonella Typhimurium. A Salmonella strain expressing two fluorescent reporter constructs was generated which allowed for monitoring the bacterial replication and metabolic activity within infected cells. A human kinome-wide siRNA library was screened and 48 candidates were chosen for further validation. Among these, 15 host cell genes were identified to influence Salmonella intracellular replication. The mitogen activated protein kinase MKK7, whose depletion caused a decrease in bacterial replication, was selected for a more profound functional characterization. It could be demonstrated that the knock down of MKK7 caused a decrease in phospholipase A2 (cPLA2) protein levels due to a transcriptional regulation. A role for cPLA2 during the bacterial intracellular lifestyle was implicated by the finding that Salmonella induced a permanent phosphorylation of the phospholipase. The necessity of cPLA2 was confirmed with replication assays in cPLA2 depleted cells using siRNA and shRNA mediated knock down strategies. Microscopic experiments indicated that the phospholipase A2 is involved in the accurate generation of Salmonella-induced filaments, structures that were reported to be indispensable for replication.

The mitogen-activated protein kinase (MAPK) pathways are ubiquitious and highly expressed in all eukaryotic cells. Diverse stimuli activate MAPKs, whose intracellular network translates and integrates those signals into complex cytoplasmatic and nuclear processes which lead to organized cellular responses, like proliferation, differentiation or apoptosis. The c-Jun N- terminale kinases (JNKs), one subfamily of MAPKs, are considered as essential signalling molecules for the differentiation, regeneration and programmed cell death of neurons. Apart from those physiological functions, JNKs mediate neurodegeneration and are involved in a number of pathologies such as Alzheimer’s or Parkinson’s disease. In answering the question, how JNKs regulate this functional dichotomy, their upstream activators, mitogen-activated protein kinase kinase (MKK) 4 and MKK7 are largely underestimated. The aim of this thesis was to use stable overexpression of MKK4 and MKK7 to investigate their effects on JNK functions in the rat adrenal pheochromocytoma cell line PC12. During cloning of both known JNK activators in the rat, MKK4 and MKK7β1, two so far unknown splice variants, MKK4∆ and MKK7γ1, were identified. Overexpression of MKK7γ1 in PC12 cells mediated distinct changes in activation and protein levels of JNK isoforms. Consequently, JNK signalling was changed at mRNA, protein and phosphorylation levels of JNK targets, such as transcription factors (c-Jun, p53, c-Myc), cell cycle regulators (p21WAF-1/CIP-1, CyclinD1) and apoptotic proteins (Fas, Bim, Bcl-2, Bcl-xl). Additionally, the assembly of JNK signalosomes was affected. These alterations promoted the sensitivity of PC12 cells towards cell death and repressed proliferation under normal cell growth conditions. After stimulation with taxol and tunicamycin, MKK7γ1 but not MKK7β1 transfection, reduced cell death and even increased cell proliferation. Furthermore, MKK7γ1 partially blocked nerve growth factor (NGF)-induced differentiation of PC12 cells via additional down-regulation of the NGF receptors TrkA and p75 as well as of the differentiation-promoting extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol-3-kinase (PI3K) pathways. These MKK7γ1-triggered effects induced an escape from cell cycle arrest and rendered PC12 cells sensitive to taxol- mediated cell death. Overexpression of MKK4 and MKK4∆ caused opposite effects in PC12 cells. MKK4 decreased the viability of cells under basal conditions and enhanced cell survival following taxol stimulation. In contrast, MKK4∆ increased the number of viable cells under basal conditions, but reduced the viability of taxol-treated cells. Thus, single MKK4 and MKK7 splice variants are powerful inductors of distinct and contrasting JNK actions depending on the cellular context and are at least partially responsible for the dichotomy of JNK signalling. Die Mitogen-aktivierten Proteinkinasen (MAPK) sind zentrale Elemente der Signaltransduktion bei allen Eukaryoten. MAPK werden von einer Vielzahl verschiedenster Stimuli aktiviert. In der Zelle bilden sie ein Enzymnetzwerk, dass die Signale aufnimmt und in zytoplasmatische und nukleäre Vorgänge übersetzt, die schließlich zu organisierten zellulären Reaktionen, wie Proliferation, Differenzierung oder Apoptose führen. Eine wichtige Unterfamilie der MAPK sind die c-Jun N-terminalen Kinasen (JNK), die eine entscheidende Rolle bei der Differenzierung, Regeneration und beim programmierten Zelltod von Neuronen spielen. Abgesehen von diesen physiologischen Funktionen, vermitteln JNK auch Neurodegeneration und sind an einer Vielzahl von Krankheitsbildern wie Morbus Alzheimer oder Morbus Parkinson beteiligt. Bei der Beantwortung der Frage, wie JNK diese funktionelle Dichotomie bewirken, hat man der Bedeutung ihrer Aktivatoren, der Mitogen- aktivierten Proteinkinasekinase (MKK) 4 und MKK7, bisher zu wenig Aufmerksamkeit geschenkt. Das Ziel dieser Arbeit war es, den Effekt von MKK4 und MKK7 auf JNK- vermittelte Funktionen zu untersuchen. Dazu wurden sie in Phäochromozytom (PC12)-Zellen aus der Ratte stabil überexprimiert. Bei der Klonierung der beiden JNK-Aktivatoren, MKK4 und MKK7β1, wurden zwei bisher unbekannte Spleißvarianten, MKK4∆ und MKK7γ1, in PC12 Zellen identifiziert. Überexpression von MKK7γ1 in PC12-Zellen veränderte die Phosphorylierung und die Proteinmenge von JNK-Isoformen. Infolgedessen war die Wirkung der JNK auf ihre Substrate verändert. Effekte konnten auf mRNA-, Protein- und Aktivitätsebene von Transkriptionsfaktoren (c-Jun, p53, c-Myc), Zellzyklusregulatoren (p21WAF1/CIP1, CyclinD1) und Regulatoren der Apoptose (Fas, Bim, Bcl-2 und Bcl-xl) beobachtet werden. Zusätzlich war die Zusammensetzung von JNK-Signalosomen verändert. All diese Veränderungen erhöhten die basale Apoptoserate der Zellen und verringerten ihre Proliferation unter normalen Wachstumsbedingungen. Nach Stimulation der Zellen mit Taxol oder Tunicamycin, verringerte MKK7γ1, aber nicht MKK7β1, den Zelltod und verstärkte gleichzeitig die Proliferation. Des Weiteren wurde die durch den Nervenwachstumsfaktor (nerve growth factor, NGF) eingeleitete Differenzierung von PC12-Zellen durch MKK7γ1 blockiert. Überexpression von MKK7γ1 verringerte die Proteinmengen und Phosphorylierung der NGF- Rezeptoren (TrkA und p75) und einzelner Komponenten differenzierungsfördernder Signaltransduktionswege, wie den Extrazellulären Signal-regulierten Kinase 1/2 (ERK1/2)und Phosphatidyl-Inositol-3-Kinase (PI3K). Außerdem verhinderte MKK7γ1 den Zelllzyklusarrest und machte die Zellen so anfällig gegenüber Taxol. Die Überexpression von MKK4 und MKK4∆ in PC12-Zellen bewirkte gegensätzliche Effekte. MKK4 verringerte die Viabilität der Zellen unter basalen Bedingungen und erhöhte die Überlebensrate der Zellen nach Taxol-Stimulation. Im Gegensatz dazu, erhöhte MKK4∆ die Anzahl lebender Zellen unter basalen Bedingungen, verstärkte jedoch den Taxol- induzierten Zelltod. Somit sind einzelne MKK4 und MKK7 Spleißvarianten entscheidende Regulatoren von unterschiedlichen, teils auch gegensätzlichen JNK-Wirkungen in Abhängigkeit von der zellulären Umgebung.

Gadd45 alpha, beta, and gamma proteins, also known as growth arrest and DNA damage-inducible factors, have a number of cellular functions, including cell-cycle regulation and propagation of signals produced by a variety of cellular stimuli, maintaining genomic stability and apoptosis. Furthermore, Gadd45 beta has been indicated as a major player in the endogenous NF-kappa B-mediated resistance to apoptosis in a variety of cell lines. In fibroblasts this mechanism involves the inactivation of MKK7, the upstream activator of JNK, by direct binding within the kinase ATP pocket. On the basis of a number of experimental data, the structures of Gadd45 beta and the Gadd45 beta-MKK7 complex have been predicted recently and data show that interactions are mediated by acidic loops 1 and 2, and helices 3 and 4 of Gadd45 beta. Here, we provide further evidence that Gadd45 beta is a prevailingly alpha-helical protein and that in solution it is able to form non covalent dimers but not higher-order oligomers, in contrast to what has been reported for the homologous Gadd45 alpha. We show that the contact region between the two monomers is comprised of the predicted helix 1 (residues Q17-Q33) and helix 5 (residues K131-R146) of the protein, which appear to be antiparallel and to form a large dimerisation surface not involved in MKK7 recognition. The results suggest the occurrence of a large complex containing at least an MKK7-Gadd45 beta:Gadd45 beta -MKK7 tetrameric unit whose complexity could be further increased by the dimeric nature of the isolated MKK7

NF-kappaB/Rel factors control programmed cell death (PCD), and this control is crucial to oncogenesis, cancer chemoresistance, and antagonism of tumor necrosis factor (TNF) alpha-induced killing. With TNFalpha, NF-kappaB-mediated protection involves suppression of the c-Jun-N-terminal kinase (JNK) cascade, and we have identified Gadd45beta, a member of the Gadd45 family, as a pivotal effector of this activity of NF-kappaB. Inhibition of TNFalpha-induced JNK signaling by Gadd45beta depends on direct targeting of the JNK kinase, MKK7/JNKK2. The mechanism by which Gadd45beta blunts MKK7, however, is unknown. Here we show that Gadd45beta is a structured protein with a predicted four-stranded beta-sheet core, five alpha-helices, and two acidic loops. Association of Gadd45beta with MKK7 involves a network of interactions mediated by its putative helices alpha3 and alpha4 and loops 1 and 2. Whereas alpha3 appears to primarily mediate docking to MKK7, loop 1 and alpha4-loop 2 seemingly afford kinase inactivation by engaging the ATP-binding site and causing conformational changes that impede catalytic function. These data provide a basis for Gadd45beta-mediated blockade of MKK7, and ultimately, TNFalpha-induced PCD. They also have important implications for treatment of widespread diseases.

NF-kappa B/Rel transcription factors control apoptosis, also known as programmed cell death. This control is crucial for oncogenesis, cancer chemo-resistance and for antagonizing tumour necrosis factor alpha (TNFalpha)-induced killing. With regard to TNFalpha, the anti-apoptotic activity of NF-kappa B involves suppression of the c-Jun N-terminal kinase (JNK) cascade. Using an unbiased screen, we have previously identified Gadd45 beta/Myd118, a member of the Gadd45 family of inducible factors, as a pivotal mediator of this suppressive activity of NF-kappa B. However, the mechanisms by which Gadd45 beta inhibits JNK signalling are not understood. Here, we identify MKK7/JNKK2--a specific and essential activator of JNK--as a target of Gadd45 beta, and in fact, of NF-kappa B itself. Gadd45 beta binds to MKK7 directly and blocks its catalytic activity, thereby providing a molecular link between the NF-kappa B and JNK pathways. Importantly, Gadd45 beta is required to antagonize TNFalpha-induced cytotoxicity, and peptides disrupting the Gadd45 beta/MKK7 interaction hinder the ability of Gadd45 beta, as well as of NF-kappa B, to suppress this cytotoxicity. These findings establish a basis for the NF-kappa B control of JNK activation and identify MKK7 as a potential target for anti-inflammatory and anti-cancer therapy.

c-Jun NH2-terminal protein kinase (JNK) is a mitogen-activated protein kinase (MAPK) involved in the regulation of numerous physiological processes during development and in response to stress. Its activity is increased upon phosphorylation by the MAPK kinases, MKK4 and MKK7. Similar to the early embryonic death of mice caused by the targeted deletion of the jnk genes, mice lacking mkk4 or mkk7 die before birth. The inability of MKK4 and MKK7 to compensate for each other's functions in vivo is consistent with their synergistic effect in mediating JNK activation. However, the phenotypic analysis of the mutant mouse embryos indicates that MKK4 and MKK7 have specific roles that may be due to their selective regulation by extracellular stimuli and their distinct tissue distribution. MKK4 and MKK7 also have different biochemical properties. For example, whereas MKK4 can activate p38 MAPK, MKK7 functions as a specific activator of JNK. Here we summarize the studies that have shed light on the mechanism of activation of MKK4 and MKK7 and on their physiological functions.