Activation of stress-activated protein kinase by MEKK1 phosphorylation of its activator SEK1

Asperulosidic Acid Restrains Hepatocellular Carcinoma Development and Enhances Chemosensitivity Through Inactivating the MEKK1/NF-κB Pathway

Asperulosidic acid (ASPA) is a plant-extracted iridoid terpenoid with tumor-suppressive and anti-inflammatory properties. At present, the antitumor function of ASPA and its related mechanisms in hepatocellular carcinoma (HCC) cells were explored. Human normal hepatocytes HL-7702 and HCC cells (Huh7 and HCCLM3) were treated with varying concentrations (0 to 200 μg/mL) of ASPA. Cell viability, proliferation, apoptosis, migration, and invasion were checked. The expression of proteins was detected by Western blot. Furthermore, the effect of ASPA (100 μg/mL) on the sensitivity of HCC cells to chemotherapeutic agents, including doxorubicin and cisplatin, was evaluated. A subcutaneous xenografted tumor model was set up in nude mice, and the antitumor effects of ASPA were evaluated. ASPA hindered HCC cells' proliferation, migration, and invasion, and amplified their apoptosis and sensitivity to chemotherapeutic agents. Additionally, ASPA inactivated the MEKK1/NF-κB pathway. Overexpression of MEKK1 increased HCC proliferation, migration, and invasion and facilitated chemoresistance. ASPA treatment alleviated the carcinogenic effect mediated by MEKK1 overexpression. MEKK1 knockdown slowed down HCC progression. However, ASPA could not exert additional antitumor effects in MEKK1 knockdown cells. In vivo results displayed that ASPA substantially curbed tumor growth and inactivated the MEKK1/NF-κB pathway in mice. All over, ASPA exerts antitumor effects in HCC by suppressing the MEKK1/NF-κB pathway.

JNK regulates ciliogenesis through the interflagellar transport complex and actin networks

The c-Jun N-terminal kinase (JNK) regulates various important physiological processes. Although the JNK pathway has been under intense investigation for over 20 yr, its complexity is still perplexing, with multiple protein partners underlying the diversity of its activity. We show that JNK is associated with the basal bodies in both primary and motile cilia. Loss of JNK disrupts basal body migration and docking and leads to severe ciliogenesis defects. JNK's involvement in ciliogenesis stems from a dual role in the regulation of the actin networks of multiciliated cells (MCCs) and the establishment of the intraflagellar transport-B core complex. JNK signaling is also critical for the maintenance of the actin networks and ciliary function in mature MCCs. JNK is implicated in the development of diabetes, neurodegeneration, and liver disease, all of which have been linked to ciliary dysfunction. Our work uncovers a novel role of JNK in ciliogenesis and ciliary function that could have important implications for JNK's role in the disease.

MKK4 Inhibitors-Recent Development Status and Therapeutic Potential

MKK4 (mitogen-activated protein kinase kinase 4; also referred to as MEK4) is a dual-specificity protein kinase that phosphorylates and regulates both JNK (c-Jun N-terminal kinase) and p38 MAPK (p38 mitogen-activated protein kinase) signaling pathways and therefore has a great impact on cell proliferation, differentiation and apoptosis. Overexpression of MKK4 has been associated with aggressive cancer types, including metastatic prostate and ovarian cancer and triple-negative breast cancer. In addition, MKK4 has been identified as a key regulator in liver regeneration. Therefore, MKK4 is a promising target both for cancer therapeutics and for the treatment of liver-associated diseases, offering an alternative to liver transplantation. The recent reports on new inhibitors, as well as the formation of a startup company investigating an inhibitor in clinical trials, show the importance and interest of MKK4 in drug discovery. In this review, we highlight the significance of MKK4 in cancer development and other diseases, as well as its unique role in liver regeneration. Furthermore, we present the most recent progress in MKK4 drug discovery and future challenges in the development of MKK4-targeting drugs.

A Multidisciplinary Approach Evaluating Soybean Meal-Induced Enteritis in Rainbow Trout Oncorhynchus mykiss

This study evaluated a diverse range of markers of feeding stress to obtain a more precise assessment of the welfare of rainbow trout in relation to inadequate husbandry conditions. A feeding stress model based on dietary soybean meal was employed to identify suitable minimally invasive “classical” stress markers, together with molecular signatures. In a 56-day feeding experiment, rainbow trout were fed diets containing different levels of soybean meal. The impact of these different soybean meal diets on rainbow trout was assessed by water quality analyses, clinical health observations, classic growth and performance parameters, gut histopathology, blood-parameter measurements and multigene-expression profiling in RNA from whole blood. Soybean meal-induced enteritis was manifested phenotypically by an inflammatory reaction in the posterior section of the intestine and by diarrhoea in some trout. These inflammatory changes were associated with decreased supranuclear vacuolation. The haematocrit values and the levels of plasma cortisol and circulating lymphocytes in the blood were increased in trout that had consumed high amounts of SBM. Notably, the increased haematocrit depended significantly on the bodyweight of the individual trout. The transcript levels of certain genes (e.g., MAP3K1, LYG, NOD1, STAT1 and HSP90AB) emerged as potentially useful indicators in the blood of rainbow trout providing valuable information about inadequate nutrition. The expression-profiling findings provide a basis for improved, minimally invasive monitoring of feeding regimens in trout farming and may stimulate the development of practical detection devices for innovative aquaculture operations.

Spectrum of MAP3K1 mutations in breast cancer is luminal subtype-predominant and related to prognosis

MAP3K1 is a MAPK family serine-threonine kinase that is frequently mutated in human cancer. The association between mutations in the MAP3K1 gene and the clinicopathological characteristics and prognosis of patients with breast cancer remain unclear in the Chinese population. Thus, the aim of the present retrospective study was to investigate the possible role and function of MAP3K1 in breast cancer. Data obtained from 412 consecutive patients with breast cancer were selected from Guangdong Provincial People's Hospital (GDPH) for analysis in the present study. Mutations were assessed using next-generation sequencing. The association between MAP3K1 mutations and clinicopathological features were analyzed and further compared with the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) cohort and data from The Cancer Genome Atlas (TCGA). In the GDPH cohort, a total of 45 mutations MAP3K1 were identified in 8.5% (n=35) of the 412 patients, compared with 9.7% (n=244) in METABRIC and 7.9% (n=88) in TCGA. The majority of the mutations identified in the in three cohorts were truncating mutations, followed by mis-sense mutations. Mutations in MAP3K1 were predominant in patients with the luminal A and B breast cancer subtypes in METABRIC datasets (P<0.001), although no significant differences were observed in the GDPH cohort (P=0.227). In the METABRIC cohort, patients with MAP3K1 mutations experienced a improved overall survival (OS) rate than patients without MAP3K1 mutations (P=0.006). In patient with hormone receptor (HR)⁺ breast cancer, a more significantly higher OS rate was observed in patients with MAP3K1 mutations (P<0.001). MAP3K1 expression was associated with OS in the HR⁺ subgroup. Moreover, the MAP3K1 methylation levels were reduced in primary breast cancer tissue, compared with normal tissue. Thus, the present findings identified MAP3K1 mutations in Chinese patients with breast cancer, and compared MAP3K1 mutations between the cohorts from Western and Eastern countries.

Exosomal miR-455-3p from BMMSCs prevents cardiac ischemia-reperfusion injury

OBJECTIVE

Bone marrow mesenchymal stem cells (BMMSCs) exert protective effects against myocardial infarction (MI). Here, we focused on the function and mechanism of miR-455-3p from BMMSCs-derived exosomes (BMMSCs-Exo) in myocardial infarction.

MATERIALS AND METHODS

BMMSCs were isolated from rat bone marrow, and the exosomes from the culture medium of BMMSCs were separated, and administered to H9C2 cells under hypoxia-reperfusion (H/R) stimulation. MTT and TUNEL staining analyzed cell viability and apoptosis, respectively. RT-qPCR determined miR-455-3p expression. Apoptosis-related proteins, autophagy-associated proteins, and the MEKK1-MKK4-JNK signaling pathway were detected. The interaction between miR-455-3p and MEKK1 was confirmed through dual luciferase activity and RIP assay. An in vivo ischemia reperfusion (I/R) model was established in rats. 2, 3, 5 triphenyltetrazolium chloride (TTC) staining, hematoxylin-eosin (H&E) staining, Masson staining, and TUNEL staining evaluated the infarct volume and histopathological changes.

RESULTS

miR-455-3p's expression was down-regulated in BMMSCs-derived exosomes, I/R myocardial tissues, and H/R myocardial cells. miR-455-3p enriched by BMMSC exosomes reduced H/R-mediated cardiomyocyte damage and death-related autophagy. miR-455-3p upregulation suppressed MEKK1-MKK4-JNK. MEKK1 overexpression notably mitigated cell apoptosis, cramped cell viability, suppressed autophagy expansion, and attenuated Exo-miR-455-3p's protection on H/R myocardial cells. In-vivo trials reflected that BMMSC exosomes enriched with miR-455-3p repressed ischemia reperfusion-induced myocardial damage and myocardial cell function.

CONCLUSION

miR-455-3p, shuttled by exosomes from MSCs, targets the MEKK1-MKK4-JNK signaling pathway to guard against myocardial ischemia-reperfusion damage.

A multiplier peroxiporin signal transduction pathway powers piscine spermatozoa

The primary task of a spermatozoon is to deliver its nuclear payload to the egg to form the next-generation zygote. With polyandry repeatedly evolving in the animal kingdom, however, sperm competition has become widespread, with the highest known intensities occurring in fish. Yet, the molecular controls regulating spermatozoon swimming performance in these organisms are largely unknown. Here, we show that the kinematic properties of postactivated piscine spermatozoa are regulated through a conserved trafficking mechanism whereby a peroxiporin ortholog of mammalian aquaporin-8 (Aqp8bb) is inserted into the inner mitochondrial membrane to facilitate H₂O₂ efflux in order to maintain ATP production. In teleosts from more ancestral lineages, such as the zebrafish (Danio rerio) and the Atlantic salmon (Salmo salar), in which spermatozoa are activated in freshwater, an intracellular Ca²⁺-signaling directly regulates this mechanism through monophosphorylation of the Aqp8bb N terminus. In contrast, in more recently evolved marine teleosts, such the gilthead seabream (Sparus aurata), in which spermatozoa activation occurs in seawater, a cross-talk between Ca²⁺- and oxidative stress-activated pathways generate a multiplier regulation of channel trafficking via dual N-terminal phosphorylation. These findings reveal that teleost spermatozoa evolved increasingly sophisticated detoxification pathways to maintain swimming performance under a high osmotic stress, and provide insight into molecular traits that are advantageous for postcopulatory sexual selection.

MEKK1-dependent activation of the CRL4 complex is important for DNA damage-induced degradation of p21 and DDB2 and cell survival

Cullin-4 ubiquitin ligase (CRL4) complexes are differentially composed and highly dynamic protein assemblies that control many biological processes including the global genome nucleotide excision repair (GG-NER) pathway. Here we identified the kinase mitogen-activated protein kinase kinase kinase 1 (MEKK1) as a novel constitutive interactor of a cytosolic CRL4 complex that disassembles after DNA damage due to the Caspase-mediated cleavage of MEKK1. The kinase activity of MEKK1 was important to trigger auto-ubiquitination of the CRL4 complex by K48- and K63-linked ubiquitin chains. MEKK1 knockdown prohibited DNA damage-induced degradation of the CRL4 component DNA-damage binding protein 2 (DDB2) and the CRL4 substrate p21 and also cell recovery and survival. A ubiquitin replacement strategy revealed a contribution of K63-branched ubiquitin chains for DNA damage-induced DDB2/p21 decay, cell cycle regulation and cell survival. These data might have also implications for cancer, as frequently occurring mutations of MEKK1 might have an impact on genome stability and the therapeutic efficacy of CRL4-dependent immunomodulatory drugs such as thalidomide-derivatives.

Phosphorylated Chitosan Hydrogels Inducing Osteogenic Differentiation of Osteoblasts via JNK and p38 Signaling Pathways

Phosphorous-containing biopolymers have been applied to expedite the regeneration of damaged bone tissue by stimulating the function of phosphorous groups in natural bones. However, the underlying mechanism of phosphorous-containing biopolymers in promoting osteogenic differentiation is unclarified. Herein, we synthesized phosphorylated chitosan hydrogels by incorporating phosphocreatine into chitosan molecular chains under mild conditions. The introduction of phosphate groups improved properties of protein adsorption and calcium deposition without affecting the morphology of hydrogels. Our results showed that phosphorylated chitosan hydrogels could not only promote alkaline phosphatase activity and mineralization but also upregulate the expression of osteogenic-related genes and proteins. Meanwhile, application of c-Jun N-terminal kinase inhibitor SP600125 and p38 mitogen-activated protein kinase inhibitor SB203580 repressed the expression of osteogenic-related markers in gene and protein levels. To the best of our knowledge, it is reported for the first time that phosphorous-containing biopolymers promote osteogenic differentiation of osteoblasts via JNK and p38 signaling pathways.

miR-196b inhibits cell migration and invasion through targeting MAP3K1 in hydatidiform mole

MicroRNAs (miRNAs) are a class of small non-coding RNAs that are closely associated with carcinogenesis. Accumulating data indicate that miR-196b participates in the development of various types of cancers. However, the role of miR-196b in the formation of hydatidiform mole (HM) is still unclear. Our previous studies have demonstrated that miR-196b levels were decreased in JAR and BeWo cells and in HM tissue samples, as demonstrated by RT-PCR analysis. Furthermore, we discovered that overexpression of miR-196b in JAR and BeWo cells inhibited cellular proliferation, migration and invasion, as shown by Cell counting kit-8 (CCK-8) and transwell assays, respectively. Subsequently, we explored the interaction of miR-196b with its target gene in human choriocarcinoma cell lines. MAP3K1 is a target gene predicted by bioinformatic analysis that was previously shown to exhibit reduced expression levels following treatment with miR-196b in JAR and BeWo cells. We demonstrated that MAP3K1 was a direct target of miR-196b using the dual-luciferase reporter assay in Hela cells. In summary, the present study demonstrated that miR-196b suppressed proliferation, migration and invasion of human choriocarcinoma cells by inhibiting its transcriptional target MAP3K1. miR-196b and MAP3K1 may be considered potential targets for the clinical treatment of HM.

Mechanistic regulation of epithelial-to-mesenchymal transition through RAS signaling pathway and therapeutic implications in human cancer

RAS effector signaling instead of being simple, unidirectional and linear cascade, is actually recognized as highly complex and dynamic signaling network. RAF-MEK-ERK cascade, being at the center of complex signaling network, links to multiple scaffold proteins through feed forward and feedback mechanisms and dynamically regulate tumor initiation and progression. Three isoforms of Ras harbor mutations in a cell and tissue specific manner. Besides mutations, their epigenetic silencing also attributes them to exhibit oncogenic activities. Recent evidences support the functions of RAS oncoproteins in the acquisition of tumor cells with Epithelial-to-mesenchymal transition (EMT) features/ epithelial plasticity, enhanced metastatic potential and poor patient survival. Google Scholar electronic databases and PubMed were searched for original papers and reviews available till date to collect information on stimulation of EMT core inducers in a Ras driven cancer and their regulation in metastatic spread. Improved understanding of the mechanistic basis of regulatory interactions of microRNAs (miRs) and EMT by reprogramming the expression of targets in Ras activated cancer, may help in designing effective anticancer therapies. Apparent lack of adverse events associated with the delivery of miRs and tissue response make 'drug target miRNA' an ideal therapeutic tool to achieve progression free clinical response.

Functional cooperation between HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR

OBJECTIVE

Hypoxia-inducible factor 1 (HIF-1) and activator protein 1 (AP-1) are important transcription factors regulating expression of genes involved in cell survival. HIF-1α and c-Jun are key components of HIF-1 and AP-1, respectively, and are regulated by epidermal growth factor receptor (EGFR)-mediated cell signaling and tumor microenvironmental cues. The roles of HIF-1α and c-Jun in development of resistance to EGFR tyrosine kinase inhibitor (TKI) in non-small cell lung cancer (NSCLC) with activating mutation of EGFR have not been explored. In this study, we investigated the roles of HIF-1α and c-Jun in mediating primary and acquired resistance to gefitinib in NSCLC cells with activating mutation of EGFR.

MATERIALS AND METHODS

Changes in HIF-1α protein and in total and phosphorylated c-Jun levels in relation to changes in total and phosphorylated EGFR levels before and after gefitinib treatment were measured using Western blot analysis in NSCLC cells sensitive or resistant to gefitinib. The impact of overexpression of a constitutively expressed HIF-1α (HIF-1α/ΔODD) or a constitutively active c-Jun upstream regulator (SEK1 S220E/T224D mutant) on cell response to gefitinib was also examined. The effect of pharmacological inhibition of SEK1-JNK-c-Jun pathway on cell response to gefitinib was evaluated.

RESULTS

Downregulation of HIF-1α and total and phosphorylated c-Jun levels correlated with cell inhibitory response to gefitinib better than decrease in phosphorylated EGFR did in NSCLC cells with intrinsic or acquired resistance to gefitinib. Overexpression of HIF-1α/ΔODD or SEK1 S220E/T224D mutant conferred resistance to gefitinib. There exists a positive feed-forward regulation loop between HIF-1 and c-Jun. The JNK inhibitor SP600125 sensitized gefitinib-resistant NSCLC cells to gefitinib.

CONCLUSIONS

HIF-1α and c-Jun functionally cooperate in development of resistance to gefitinib in NSCLC cells. The translational value of inhibiting HIF-1α/c-Jun cooperation in overcoming resistance to EGFR TKI treatment of NSCLC cells with activating mutation of EGFR deserves further investigation.

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.

pERK-dependent defective TCR-mediated activation of CD4+ T cells in end-stage renal disease patients

Background

Patients with end-stage renal disease (ESRD) have an impaired immune response with a prematurely aged T-cell system. Mitogen-activated protein kinases (MAPKs) including extracellular signal-regulated kinase (ERK) and p38, regulate diverse cellular programs by transferring extracellular signals into an intracellular response. T cell receptor (TCR)-induced phosphorylation of ERK (pERK) may show an age-associated decline, which can be reversed by inhibiting dual specific phosphatase (DUSP) 6, a cytoplasmic phosphatase with substrate specificity to dephosphorylate pERK. The aim of this study was to assess whether ESRD affects TCR-mediated signaling and explore possibilities for intervening in ESRD-associated defective T-cell mediated immunity.

Results

An age-associated decline in TCR-induced pERK-levels was observed in the different CD4⁺ (P < 0.05), but not CD8⁺, T-cell subsets from healthy individuals (HI). Interestingly, pERK-levels of CD4⁺ T-cell subsets from young ESRD patients were in between young and elderly HI. A differentiation-associated decline in TCR-induced ERK and p38 phosphorylation was observed in T cells, although TCR-induced p38 phosphorylation was not significantly affected by age and/or ESRD. Frequencies of TCR-induced CD69-expressing CD4⁺ T cells declined with age and were positively associated with pERK. In addition, an age-associated tendency of increased expression of DUSP6 was observed in CD4⁺ T cells of HI and DUSP6 expression in young ESRD patients was similar to old HI. Inhibition of DUSP6 significantly increased TCR-induced pERK-levels of CD4⁺ T cells in young and elderly ESRD patients, and elderly HI.

Conclusions

TCR-mediated phosphorylation of ERK is affected in young ESRD patients consistent with the concept of premature immunological T cell ageing. Inhibition of DUSP6 specific for pERK might be a potential intervention enhancing T-cell mediated immunity in ESRD patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12979-017-0096-1) contains supplementary material, which is available to authorized users.

Anti-proliferative Effect of C3 Exoenzyme in Fibroblasts is Mediated by c-Jun Phosphorylation

The ADP-ribosyltransferase C3 exoenzyme from C. botulinum selectively inactivates Rho and is therefore often used as an inhibitor for investigations on Rho signaling. Previous studies of our group revealed that C3 inhibited cell proliferation in HT22 cells accompanied by increased transcriptional activities of Sp1 and c-Jun and reduced levels of cyclin D1, p21 and phosphorylated p38. By use of a p38α-deficient and a p38α-expressing control cell line, the impact of p38 on C3-mediated inhibition of cell proliferation and alterations on MAPK signaling was studied by growth kinetic experiments and Western blot analyses. The cell growth of p38α-expressing cells was impaired by C3, while the p38α-deficient cells did not exhibit any C3-induced effect. The activity of the MKK3/6-p38 MAPK signaling cascade as well as the phosphorylation of c-Jun and JNK was reduced by C3 exclusively in the presence of p38α. Moreover, the activity of upstream MAPKKK TAK1 was lowered in the p38α-expressing cells. These results indicated a resistance of p38α-deficient cells to C3-mediated inhibition of cell growth. This anti-proliferative effect was highly associated with the decreased activity of c-Jun and upstream p38 and JNK MAPK signaling as a consequence of the absence of p38α in these cells.

The genome of black raspberry (Rubus occidentalis)

Black raspberry (Rubus occidentalis) is an important specialty fruit crop in the US Pacific Northwest that can hybridize with the globally commercialized red raspberry (R. idaeus). Here we report a 243 Mb draft genome of black raspberry that will serve as a useful reference for the Rosaceae and Rubus fruit crops (raspberry, blackberry, and their hybrids). The black raspberry genome is largely collinear to the diploid woodland strawberry (Fragaria vesca) with a conserved karyotype and few notable structural rearrangements. Centromeric satellite repeats are widely dispersed across the black raspberry genome, in contrast to the tight association with the centromere observed in most plants. Among the 28 005 predicted protein-coding genes, we identified 290 very recent small-scale gene duplicates enriched for sugar metabolism, fruit development, and anthocyanin related genes which may be related to key agronomic traits during black raspberry domestication. This contrasts patterns of recent duplications in the wild woodland strawberry F. vesca, which show no patterns of enrichment, suggesting gene duplications contributed to domestication traits. Expression profiles from a fruit ripening series and roots exposed to Verticillium dahliae shed insight into fruit development and disease response, respectively. The resources presented here will expedite the development of improved black and red raspberry, blackberry and other Rubus cultivars.

MAP3K1-targeting therapeutic artificial miRNA suppresses the growth and invasion of breast cancer in vivo and in vitro

Recent investigations have highlighted that therapeutic artificial microRNAs could be promising candidates for cancer therapy through the modulation of tumor promoter or suppressor. MEK kinase 1 (MEKK1) is expressed by mitogen-activated kinase kinase kinase 1 (MAP3K1), an important kinase that links Ras activation to MAPK signaling. In the present study, we showed that synthetic MAP3K1-targeting artificial miRNA may provide considerable beneficial effects in the prevention of breast cancer growth and metastasis. We showed that MEKK1 was highly expressed in human breast cancer specimens, compared with adjacent normal tissues. Using a miRNA-expressing lentivirus system, we delivered a artificial miRNA (Map3k1 amiRNA) that targets MAP3K1 into 4T1 breast cancer cells and investigated the impact of MAP3K1-targeting miRNA on the growth and invasive behavior of breast cancer in vitro and in vivo. We found that overexpression of Map3k1 amiRNA led to impaired activities of p-ERK and p-p38. In addition, Map3k1 amiRNA induced marked proliferative impairment and invasive attenuation in breast cancer cells. However, Map3k1 amiRNA did not have evident influence on the apoptotic response of 4T1 cells. Moreover, using in vivo nude mice model, we identified that Map3k1 amiRNA attenuated tumor growth and lung metastasis of breast cancer cells. Taken together, our findings explicitly indicated that MEKK1 exerted important oncogenic property in breast cancer development, and MAP3K1-targeting artificial miRNA may provide promising therapeutic effects in the treatment of breast cancer.

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

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

Identification of novel pathways and molecules able to down-regulate PHOX2B gene expression by in vitro drug screening approaches in neuroblastoma cells

PHOX2B is a transcription factor involved in the regulation of neurogenesis and in the correct differentiation of the autonomic nervous system. The pathogenetic role of PHOX2B in neuroblastoma (NB) is supported by mutations in familial, sporadic and syndromic cases of NB and overexpression of PHOX2B and its target ALK in tumor samples and NB cell lines. Starting from these observations, we have performed in vitro drug screening approaches targeting PHOX2B overexpression as a potential pharmacological means in NB. In particular, in order to identify molecules able to decrease PHOX2B expression, we have evaluated the effects of 70 compounds in IMR-32 cell line stably expressing the luciferase gene under the control of the PHOX2B promoter. Curcumin, SAHA and trichostatin A showed to down-regulate the PHOX2B promoter activity which resulted in a decrease of both protein and mRNA expressions. In addition, we have observed that curcumin acts by interfering with PBX-1/MEIS-1, NF-κB and AP-1 complexes, in this work demonstrated for the first time to regulate the transcription of the PHOX2B gene. Finally, combined drug treatments showed successful effects in down-regulating the expression of both PHOX2B and its target ALK genes, thus supporting the notion of the effectiveness of molecule combination in tumor therapy.

MAP2K1 and MAP3K1 mutations in Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is now understood to be a neoplastic disease in which over 50% of cases have somatic activating mutations of BRAF. However, the extracellular signal-related (ERK) pathway is activated in all cases including those with wild type BRAF alleles. Here, we applied a targeted massively parallel sequencing panel to 30 LCH samples to test for the presence of additional genetic alterations that might cause ERK pathway activation. In 20 BRAF wild type samples, we found 3 somatic mutations in MAP2K1 (MEK1) including C121S and C121S/G128D in the kinase domain, and 56_61QKQKVG>R, an in-frame deletion in the N-terminal regulatory domain. All three variant proteins constitutively phosphorylated ERK in in vitro kinase assays. The C121S/G128D and 56_61QKQKVG>R variants were resistant to the mitogen-activated protein kinase kinase (MEK) inhibitor trametinib in vitro. Within the entire sample set, we found 3 specimens with mutations in MAP3K1 (MEKK1), including two truncation mutants, T779fs and T1481fs; T1481fs encoded an unstable and nonfunctional protein when expressed in vitro. T779fs was present in a specimen carrying BRAF V600E. The third variant was a single nucleotide substitution, E1286V, which was fully functional and is likely a germline polymorphism. These results indicate that LCH cells can harbor additional genetic alterations in the RAS-RAF-MEK pathway which, in the case of MAP2K1, may be responsible for ERK activation in a wild type BRAF setting. The resistance of some of these variants to trametinib may also have clinical implications for the combined use of RAF and MEK inhibitors in LCH.

A RING to rule them all? Insights into the Map3k1 PHD motif provide a new mechanistic understanding into the diverse roles of Map3k1

Despite the sizable number of components that comprise Mapk cascades, Map3k1 is the only element that contains both a kinase domain and a plant homeodomain (PHD) motif, allowing Map3k1 to regulate the protein phosphorylation and ubiquitin proteasome systems. As such, Map3k1 has complex roles in the regulation of cell death, survival, migration and differentiation. Numerous mouse and human genetic analyses have demonstrated that Map3k1 is of critical importance for the immune system, cardiac tissue, testis, wound healing, tumorigenesis and cancer. Recent gene knockin of Map3k1 to mutate the E2 binding site within the Map3k1 PHD motif and high throughput ubiquitin protein array screening for Map3k1 PHD motif substrates provide critical novel insights into Map3k1 PHD motif signal transduction and bring a brand-new understanding to Map3k1 signaling in mammalian biology.

Widespread genetic epistasis among cancer genes

Quantitative genetic epistasis has been hypothesized to be an important factor in the development and progression of complex diseases. Cancers in particular are driven by the accumulation of mutations that may act epistatically during the course of the disease. However, as cancer mutations are uncovered at an unprecedented rate, determining which combinations of genetic alterations interact to produce cancer phenotypes remains a challenge. Here we show that by using combinatorial RNAi screening in cell culture, dense and often previously undetermined interactions among cancer genes were revealed by assessing gene pairs that are frequently co-altered in primary breast cancers. These interacting gene pairs are significantly associated with survival time when co-altered in patients, indicating that genetic interaction mapping may be leveraged to improve risk assessment. As many of these interacting gene pairs involve known drug targets, personalized treatment regimens may be improved by overlaying genetic interactions with mutational profiling.

Stress-induced ceramide generation and apoptosis via the phosphorylation and activation of nSMase1 by JNK signaling

Neutral sphingomyelinase (nSMase) activation in response to environmental stress or inflammatory cytokine stimuli generates the second messenger ceramide, which mediates the stress-induced apoptosis. However, the signaling pathways and activation mechanism underlying this process have yet to be elucidated. Here we show that the phosphorylation of nSMase1 (sphingomyelin phosphodiesterase 2, SMPD2) by c-Jun N-terminal kinase (JNK) signaling stimulates ceramide generation and apoptosis and provide evidence for a signaling mechanism that integrates stress- and cytokine-activated apoptosis in vertebrate cells. An nSMase1 was identified as a JNK substrate, and the phosphorylation site responsible for its effects on stress and cytokine induction was Ser-270. In zebrafish cells, the substitution of Ser-270 for alanine blocked the phosphorylation and activation of nSMase1, whereas the substitution of Ser-270 for negatively charged glutamic acid mimicked the effect of phosphorylation. The JNK inhibitor SP600125 blocked the phosphorylation and activation of nSMase1, which in turn blocked ceramide signaling and apoptosis. A variety of stress conditions, including heat shock, UV exposure, hydrogen peroxide treatment, and anti-Fas antibody stimulation, led to the phosphorylation of nSMase1, activated nSMase1, and induced ceramide generation and apoptosis in zebrafish embryonic ZE and human Jurkat T cells. In addition, the depletion of MAPK8/9 or SMPD2 by RNAi knockdown decreased ceramide generation and stress- and cytokine-induced apoptosis in Jurkat cells. Therefore the phosphorylation of nSMase1 is a pivotal step in JNK signaling, which leads to ceramide generation and apoptosis under stress conditions and in response to cytokine stimulation. nSMase1 has a common central role in ceramide signaling during the stress and cytokine responses and apoptosis.

The kinase p38 activated by the metabolic regulator AMPK and scaffold TAB1 drives the senescence of human T cells

In T lymphocytes, p38 MAP kinase (MAPK) regulates pleiotropic functions and is activated by canonical MAPK signaling or the alternative T cell receptor (TCR) activation pathway. Here we show that senescent human T cells lack the canonical and alternative pathways of p38 activation, but spontaneously engage the metabolic master regulator AMPK to trigger p38 recruitment to the scaffold TAB1 causing p38 auto-phosphorylation. Signaling via this pathway inhibits telomerase activity, T cell proliferation and expression of key components of the TCR signalosome. Our findings identify an unrecognized mode of p38 activation in T cells driven by intracellular changes such as low-nutrient and DNA-damage signaling (‘intra-sensory’ pathway). The proliferative defect of senescent T cells is reversed by blocking AMPK-TAB1-dependent p38 activation.

MAP3K1: Genomic Alterations in Cancer and Function in Promoting Cell Survival or Apoptosis

MAP3K1 is a member of the mitogen-activated protein kinase kinase kinase (MAP3K) family of serine/threonine kinases. MAP3K1 regulates JNK activation and is unique among human kinases in that it also encodes an E3 ligase domain that ubiquitylates c-Jun and ERK1/2. Full length MAP3K1 regulates cell migration and contributes to pro-survival signaling while its caspase 3-mediated cleavage generates a C-terminal kinase domain that promotes apoptosis. The critical function of MAP3K1 in cell fate decisions suggests that it may be a target for deregulation in cancer. Recent large-scale genomic studies have revealed that MAP3K1 copy number loss and somatic missense or nonsense mutations are observed in a significant number of different cancers, being most prominent in luminal breast cancer. The alteration of MAP3K1 in diverse cancer types demonstrates the importance of defining phenotypes for possible therapeutic targeting of tumor cell vulnerabilities created when MAP3K1 function is lost or gained.

When ubiquitination meets phosphorylation: a systems biology perspective of EGFR/MAPK signalling

Ubiquitination, the covalent attachment of ubiquitin to target proteins, has emerged as a ubiquitous post-translational modification (PTM) whose function extends far beyond its original role as a tag for protein degradation identified three decades ago. Although sharing parallel properties with phosphorylation, ubiquitination distinguishes itself in important ways. Nevertheless, the interplay and crosstalk between ubiquitination and phosphorylation events have become a recurrent theme in cell signalling regulation. Understanding how these two major PTMs intersect to regulate signal transduction is an important research question. In this review, we first discuss the involvement of ubiquitination in the regulation of the EGF-mediated ERK signalling pathway via the EGF receptor, highlighting the interplay between ubiquitination and phosphorylation in this cancer-implicated system and addressing open questions. The roles of ubiquitination in pathways crosstalking to EGFR/MAPK signalling will then be discussed. In the final part of the review, we demonstrate the rich and versatile dynamics of crosstalk between ubiquitination and phosphorylation by using quantitative modelling and analysis of network motifs commonly observed in cellular processes. We argue that given the overwhelming complexity arising from inter-connected PTMs, a quantitative framework based on systems biology and mathematical modelling is needed to efficiently understand their roles in cell signalling.

Ocular injury by transient formaldehyde exposure in a rabbit eye model

Formaldehyde (FA) is frequently used in sterilizing surgical instruments and materials. Exposure to FA is highly concerned for eye tissues. Rabbit corneal epithelial cells were examined for changes after FA exposure. Our results showed that cell survival decreased 7 days after transient 3 min exposure to more than 100 ppm FA by trypan blue staining while MTT assay detected significant decrease at 20 ppm at 24 hours observation. The decrease of cell survival rate was concentration (up to 600 ppm)- and observation time (1–7 day)- dependent. The cell number decreased after 100 ppm FA exposure for more than 10 min at 7-day observation. The FA treated cells showed increased apoptosis/necrosis and cell cycle accumulation at sub G1 phase as well as mitochondria clustering around nucleus. The in vivo rabbit eye exposure for tear production by Schirmer’s test revealed that the FA-induced overproduction of tear also exhibited observation time (1–10 day)- and FA concentration (20–300 ppm for 5 min exposure)-dependent. Activated extracellular signal-regulated kinase (pERK2) in cornea explants by western blotting was reduced and increased c-Jun amino - terminal kinase (JNK) activation (pJNK) in cornea and conjunctiva was evident at 2 month after exposure to 50–200 ppm FA for 5 min. In conclusion, injury to the eye with transient exposure of up to 100 ppm FA for 3 min decreased corneal cell survival while a more sensitive MTT test detected the cell decrease at 20 ppm FA exposure. Morphology changes can be observed even at 5 ppm FA exposure for 3 min at 7 days after. The FA exposure also increased apoptotic/necrotic cells and sub-G1 phase in cell cycle. Long term effect (2 months after exposure) on the eye tissues even after the removal of FA can be observed with persistent JNK activation in cornea and conjunctiva.

Branched motifs enable long-range interactions in signaling networks through retrograde propagation

Branched structures arise in the intra-cellular signaling network when a molecule is involved in multiple enzyme-substrate reaction cascades. Such branched motifs are involved in key biological processes, e.g., immune response activated by T-cell and B-cell receptors. In this paper, we demonstrate long-range communication through retrograde propagation between branches of signaling pathways whose molecules do not directly interact. Our numerical simulations and experiments on a system comprising branches with JNK and p38MAPK as terminal molecules respectively that share a common MAP3K enzyme MEKK3/4 show that perturbing an enzyme in one branch can result in a series of changes in the activity levels of molecules “upstream” to the enzyme that eventually reaches the branch-point and affects other branches. In the absence of any evidence for explicit feedback regulation between the functionally distinct JNK and p38MAPK pathways, the experimentally observed modulation of phosphorylation amplitudes in the two pathways when a terminal kinase is inhibited implies the existence of long-range coordination through retrograde information propagation previously demonstrated in single linear reaction pathways. An important aspect of retrograde propagation in branched pathways that is distinct from previous work on retroactivity focusing exclusively on single chains is that varying the type of perturbation, e.g., between pharmaceutical agent mediated inhibition of phosphorylation or suppression of protein expression, can result in opposing responses in the other branches. This can have potential significance in designing drugs targeting key molecules which regulate multiple pathways implicated in systems-level diseases such as cancer and diabetes.

Deciphering gene expression program of MAP3K1 in mouse eyelid morphogenesis

Embryonic eyelid closure involves forward movement and ultimate fusion of the upper and lower eyelids, an essential step of mammalian ocular surface development. Although its underlying mechanism of action is not fully understood, a functional mitogen-activated protein kinase kinase kinase 1 (MAP3K1) is required for eyelid closure. Here we investigate the molecular signatures of MAP3K1 in eyelid morphogenesis. At mouse gestational day E15.5, the developmental stage immediately prior to eyelid closure, MAP3K1 expression is predominant in the eyelid leading edge (LE) and the inner eyelid (IE) epithelium. We used laser capture microdissection (LCM) to obtain highly enriched LE and IE cells from wild type and MAP3K1-deficient fetuses and analyzed genome-wide expression profiles. The gene expression data led to the identification of three distinct developmental features of MAP3K1. First, MAP3K1 modulated Wnt and Sonic hedgehog signals, actin reorganization, and proliferation only in LE but not in IE epithelium, illustrating the temporal-spatial specificity of MAP3K1 in embryogenesis. Second, MAP3K1 potentiated AP-2α expression and SRF and AP-1 activity, but its target genes were enriched for binding motifs of AP-2α and SRF, and not AP-1, suggesting the existence of novel MAP3K1-AP-2α/SRF modules in gene regulation. Third, MAP3K1 displayed variable effects on expression of lineage specific genes in the LE and IE epithelium, revealing potential roles of MAP3K1 in differentiation and lineage specification. Using LCM and expression array, our studies have uncovered novel molecular signatures of MAP3K1 in embryonic eyelid closure.

Mammalian MAPK signal transduction pathways activated by stress and inflammation: a 10-year update

The mammalian stress-activated families of mitogen-activated protein kinases (MAPKs) were first elucidated in 1994, and by 2001, substantial progress had been made in identifying the architecture of the pathways upstream of these kinases as well as in cataloguing candidate substrates. This information remains largely sound. Nevertheless, an informed understanding of the physiological and pathophysiological roles of these kinases remained to be accomplished. In the past decade, there has been an explosion of new work using RNAi in cells, as well as transgenic, knockout and conditional knockout technology in mice that has provided valuable insight into the functions of stress-activated MAPK pathways. These findings have important implications in our understanding of organ development, innate and acquired immunity, and diseases such as atherosclerosis, tumorigenesis, and type 2 diabetes. These new developments bring us within striking distance of the development and validation of novel treatment strategies. Herein we first summarize the molecular components of the mammalian stress-regulated MAPK pathways and their regulation as described thus far. We then review some of the in vivo functions of these pathways.

Hepatitis C virus sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1-dependent pathway

Background

Hepatitis C virus (HCV) is the leading cause of liver fibrosis, cirrhosis and hepatocellular carcinoma. It is believed that continuous liver cell apoptosis contributes to HCV pathogenesis. Recent studies have shown that HCV infection can sensitize host cells to TNF-related apoptosis-inducing ligand (TRAIL) induced apoptosis, but the mechanism by which HCV regulates the TRAIL pathway remains unclear.

Methods and Results

Using a sub-genomic replicon and full length virus, JFH-1, we demonstrate that HCV can sensitize host cells to TRAIL-induced apoptosis by up-regulating two TRAIL receptors, death receptor 4 (DR4) and death receptor 5 (DR5). Furthermore, the HCV replicon enhanced transcription of DR5 via Sp1, and the HCV-mediated up-regulation of DR4 and DR5 required MEK1 activity. HCV infection also stimulated the activity of MEK1, and the inhibition of MEK1 activity or the knockdown of MEK1 increased the replication of HCV.

Conclusions

Our studies demonstrate that HCV replication sensitizes host cells to TRAIL-induced apoptosis by up-regulating DR4 and DR5 via a MEK1 dependent pathway. These findings may help to further understand the pathogenesis of HCV infection and provide a therapeutic target.

Lonafarnib for cancer and progeria

INTRODUCTION

Lonafarnib is a non-peptidomimetic inhibitor of farnesyl transferase, an enzyme responsible for the post-translational lipid modification of a wide variety of cellular proteins that are involved in the pathogenic pathways of various diseases including cancer and progeria. Although extensive clinical research indicates limited activity of lonafarnib in solid tumors, there is recent interest in combinations of farnesyl transferase inhibitors with imatinib or bortezomib in hematological malignancies and to investigate the role of lonafarnib in progeria.

AREAS COVERED

This review examines the in vitro and in vivo pharmacology of lonafarnib and the available clinical data for lonafarnib monotherapy and combination therapy in the treatment of solid and hematological malignancies as well as progeria, using studies identified from the PubMed database supplemented by computerized search of relevant abstracts from major cancer and hematology conferences.

EXPERT OPINION

There is no evidence to support the use of lonafarnib in solid tumors. There is ongoing interest to explore lonafarnib for progeria and to investigate other farnesyl transferase inhibitors for chronic and acute leukemias.

The bad, the good, and the ugly about oxidative stress

Alzheimer's disease (AD), Parkinson's disease (PD), and cancer (e.g., leukemia) are the most devastating disorders affecting millions of people worldwide. Except for some kind of cancers, no effective and/or definitive therapeutic treatment aimed to reduce or to retard the clinic and pathologic symptoms induced by AD and PD is presently available. Therefore, it is urgently needed to understand the molecular basis of these disorders. Since oxidative stress (OS) is an important etiologic factor of the pathologic process of AD, PD, and cancer, understanding how intracellular signaling pathways respond to OS will have a significant implication in the therapy of these diseases. Here, we propose a model of minimal completeness of cell death signaling induced by OS as a mechanistic explanation of neuronal and cancer cell demise. This mechanism might provide the basis for therapeutic design strategies. Finally, we will attempt to associate PD, cancer, and OS. This paper critically analyzes the evidence that support the “oxidative stress model” in neurodegeneration and cancer.

c-Jun, at the crossroad of the signaling network

c-Jun, the most extensively studied protein of the activator protein-1 (AP-1) complex, is involved in numerous cell activities, such as proliferation, apoptosis, survival, tumorigenesis and tissue morphogenesis. Earlier studies focused on the structure and function have led to the identification of c-Jun as a basic leucine zipper (bZIP) transcription factor that acts as homo- or heterodimer, binding to DNA and regulating gene transcription. Later on, it was shown that extracellular signals can induce post-translational modifications of c-Jun, resulting in altered transcriptional activity and target gene expression. More recent work has uncovered multiple layers of a complex regulatory scheme in which c-Jun is able to crosstalk, amplify and integrate different signals for tissue development and disease. One example of such scheme is the autocrine amplification loop, in which signal-induced AP-1 activates the c-Jun gene promoter, while increased c-Jun expression feedbacks to potentiate AP-1 activity. Another example of such scheme, based on recent characterization of gene knockout mice, is that c-Jun integrates signals of several developmental pathways, including EGFR-ERK, EGFR-RhoA-ROCK, and activin B-MAP3K1-JNK for embryonic eyelid closure. After more than two decades of extensive research, c-Jun remains at the center stage of a molecular network with mysterious functional properties, some of which are yet to be discovered. In this article, we will provide a brief historical overview of studies on c-Jun regulation and function, and use eyelid development as an example to illustrate the complexity of c-Jun crosstalking with signaling pathways.

The mechanism of MAP kinase activation under acidic condition in feline esophageal smooth muscle cells

Reflux esophagitis results from repeated exposure of the esophagus to acidic gastric juice or bile-containing duodenal contents. In Barrett's adenocarcinoma, acid increases proliferation via ERK and p38 MAPK activation. This study was focused on determination of the mechanism(s) underlying MAPKs (ERK 1/2, p38 MAPK, and JNK) activation induced by acidic medium at pH 4 in normal feline primary cultured esophageal smooth muscle cells (FESMCs). We detected ERK 1/2 and p38 MAPK phosphorylation after exposure to pH 4 or neutral media in the presence or absence of several inhibitors and quantified the MAPK levels using western blotting analysis and densitometry. Acidic medium markedly increased the phosphorylation of ERK 1/2 and p38 MAPK within 10 min. Acid-induced ERK 1/2 and p38 MAPK activation was inhibited by pertussis toxin (PTX-sensitive G(i/o) protein inhibitor), DEDA (phospholipase (PL) A(2) inhibitor), ρCMB (PLD inhibitor), GF109203X (protein kinase C (PKC) inhibitor) and D609 (phosphatidylcholine-specific PLC inhibitor). But, genistein (tyrosine kinase inhibitor), forskolin (adenylate cyclase activator) and U73122 (phosphatidylinositol-specific PLC inhibitor) had no effect on acid-induced ERK1/2 and p38 MAPK activation. These findings indicate that the activation of ERK 1/2 and p38 MAPK pathways by acidic conditions, at least in part, may be mediated by activation of the G(i/o) protein coupled receptors, PC-PLC, PLD, PLA(2), and PKC in FESMCs.

How do pleiotropic kinase hubs mediate specific signaling by TNFR superfamily members?

Tumor necrosis factor receptor (TNFR) superfamily members mediate the cellular response to a wide variety of biological inputs. The responses range from cell death, survival, differentiation, proliferation, to the regulation of immunity. All these physiological responses are regulated by a limited number of highly pleiotropic kinases. The fact that the same signaling molecules are involved in transducing signals from TNFR superfamily members that regulate different and even opposing processes raises the question of how their specificity is determined. Regulatory strategies that can contribute to signaling specificity include scaffolding to control kinase specificity, combinatorial use of several signal transducers, and temporal control of signaling. In this review, we discuss these strategies in the context of TNFR superfamily member signaling.

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.

Differentiation of mouse embryonic stem cells into endoderm without embryoid body formation

Pluripotent embryonic stem cells hold a great promise as an unlimited source of tissue for treatment of chronic diseases such as Type 1 diabetes. Herein, we describe a protocol using all-trans-retinoic acid, basic fibroblast growth factor and dibutyryl cAMP (DBcAMP) in the absence of embryoid body formation, for differentiation of murine embryonic stem cells into definitive endoderm that may serve as pancreatic precursors. The produced cells were analyzed by quantitative PCR, immunohistochemistry and static insulin release assay for markers of trilaminar embryo, and pancreas. Differentiated cells displayed increased Sox17 and Foxa2 expression consistent with definitive endoderm production. There was minimal production of Sox7, an extraembryonic endoderm marker, and Oct4, a marker of pluripotency. There was minimal mesoderm or neuroectoderm formation based on expression levels of the markers brachyury and Sox1, respectively. Various assays revealed that the cell clusters generated by this protocol express markers of the pancreatic lineage including insulin I, insulin II, C-peptide, PDX-1, carboxypeptidase E, pan-cytokeratin, amylase, glucagon, PAX6, Ngn3 and Nkx6.1. This protocol using all-trans-retinoic acid, DBcAMP, in the absence of embryoid bodies, generated cells that have features of definitive endoderm that may serve as pancreatic endocrine precursors.

Myristoylation of the dual-specificity phosphatase c-JUN N-terminal kinase (JNK) stimulatory phosphatase 1 is necessary for its activation of JNK signaling and apoptosis

Activation of the c-JUN N-terminal kinase (JNK) pathway is implicated in a number of important physiological processes, from embryonic morphogenesis to cell survival and apoptosis. JNK stimulatory phosphatase 1 (JSP1) is a member of the dual-specificity phosphatase subfamily of protein tyrosine phosphatases. In contrast to other dual-specificity phosphatases that catalyze the inactivation of mitogen-activated protein kinases, expression of JSP1 activates JNK-mediated signaling. JSP1 and its relative DUSP15 are unique among members of the protein tyrosine phosphatase family in that they contain a potential myristoylation site at the N-terminus (MGNGMXK). In this study, we investigated whether JSP1 was myristoylated and examined the functional consequences of myristoylation. Using mass spectrometry, we showed that wild-type JSP1, but not a JSP1 mutant in which Gly2 was mutated to Ala (JSP1-G2A), was myristoylated in cells. Although JSP1 maintained intrinsic phosphatase activity in the absence of myristoylation, the subcellular localization of the enzyme was altered. Compared with the wild type, the ability of nonmyristoylated JSP1 to induce JNK activation and phosphorylation of the transcription factor c-JUN was attenuated. Upon expression of wild-type JSP1, a subpopulation of cells, with the highest levels of the phosphatase, was induced to float off the dish and undergo apoptosis. In contrast, cells expressing similar levels of JSP1-G2A remained attached, further highlighting that the myristoylation mutant was functionally compromised.

MAP3K1 functionally interacts with Axin1 in the canonical Wnt signalling pathway

A central point of regulation in the Wnt/β-catenin signalling pathway is the formation of the β-catenin destruction complex. Axin1, an essential negative regulator of Wnt signalling, serves as a scaffold within this complex and is critical for rapid turnover of β-catenin. To examine the mechanism by which Wnt signalling disables the destruction complex, we used an immunoprecipitation-coupled proteomics approach to identify novel endogenous binding partners of Axin1. We found mitogen-activated protein kinase kinase kinase 1 (MAP3K1) as an Axin1 interactor in Ls174T colorectal cancer (CRC) cells. Importantly, confirmation of this interaction in HEK293T cells indicated that the Axin1-MAP3K1 interaction is induced and modulated by Wnt stimulation. siRNA depletion of MAP3K1 specifically abrogated TCF/LEF-driven transcription and Wnt3A-driven endogenous gene expression in both HEK293T as well as DLD-1 CRC. Expression of ubiquitin ligase mutants of MAP3K1 abrogated TCF/LEF transcription, whereas kinase mutants had no effect in TCF-driven activity, highlighting the essential role of the MAP3K1 E3 ubiquitin ligase activity in regulation of the Wnt/β-catenin pathway. These results suggest that MAP3K1, previously reported as an Axin1 inter-actor in c-Jun NH2-terminal kinase pathway, is also involved in the canonical Wnt signalling pathway and positively regulates expression of Wnt target genes.

Determination of ERK activity: anti-phospho-ERK antibodies and in vitro phosphorylation

The ERK signaling cascade is composed of several protein kinases that sequentially activate each other by phosphorylation. This pathway is a central component of a complex signaling network that regulates important cellular processes including proliferation, differentiation, and survival. In most of these cases, the ERK cascade is activated downstream of the small GTPase Ras that, upon activation, recruits and activates the first tier in the cascade, which contains the Raf kinases. Afterward the signal is further transmitted by MEKs, ERKs, and often RSKs in the MAPKK, MAPK, and MAPKAPKs tiers of the cascade, respectively. ERKs and RSKs can further disseminate the signal by phosphorylating and modulating the activity of a large number of regulatory proteins including transcription factors and chromatin modifying enzymes. Understanding the mechanisms of activation and the regulation of the various components of this cascade will enhance our insight into the regulation of the ERK-dependent cellular processes in normal cells or of their malfunctioning in various diseases, including cancer. In this chapter, we describe methods used to determine the activity of ERKs, which upon slight modifications can also be used for the study of other signaling kinases, either within the cascade or in other pathways. These methods have been successfully applied to study the ERK signaling cascades in a variety of tissue-cultured cell lines, homo-genized animal organs, and lower organisms. As such, the use of these methods should expand our knowledge on the regulation of many distinct systems and upon induction of various stimulations.

Silencing of the JNK pathway maintains progesterone receptor activity in decidualizing human endometrial stromal cells exposed to oxidative stress signals

Survival of the conceptus is dependent on continuous progesterone signaling in the maternal decidua but how this is achieved under conditions of oxidative stress that characterize early pregnancy is unknown. Using primary cultures, we show that modest levels of reactive oxygen species (ROS) increase sumoylation in human endometrial stromal cells (HESCs), leading to enhanced modification and transcriptional inhibition of the progesterone receptor (PR). The ability of ROS to induce a sustained hypersumoylation response, or interfere with PR activity, was lost upon differentiation of HESCs into decidual cells. Hypersumoylation in response to modest levels of ROS requires activation of the JNK pathway. Although ROS-dependent JNK signaling is disabled on decidualization, the cells continue to mount a transcriptional response, albeit distinct from that observed in undifferentiated HESCs. We further show that attenuated JNK signaling in decidual cells is a direct consequence of altered expression of key pathway modulators, including induction of MAP kinase phosphatase 1 (MKP1). Overexpression of MKP1 dampens JNK signaling, prevents hypersumoylation, and maintains PR activity in undifferentiated HESCs exposed to ROS. Thus, JNK silencing uncouples ROS signaling from the SUMO conjugation pathway and maintains progesterone responses and cellular homeostasis in decidual cells under oxidative stress conditions imposed by pregnancy.—Leitao, B., Jones, M. C., Fusi, L., Higham, J., Lee, Y. Takano, M., Goto, T., Christian, M., Lam, E. W.-F., Brosens, J. J. Silencing of the Jnk pathway maintains progesterone receptor activity in decidualizing human endometrial stromal cells exposed to oxidative stress signals.

Mixed lineage kinase phosphorylates transcription factor E47 and inhibits TrkB expression to link neuronal death and survival pathways

E47 is a basic helix-loop-helix transcription factor involved in neuronal differentiation and survival. We had previously shown that the basic helix-loop-helix protein E47 binds to E-box sequences within the promoter of the TrkB gene and activates its transcription. Proper expression of the TrkB receptor plays a key role in development and function of the vertebrate nervous system, and altered levels of TrkB have been associated with important human diseases. Here we show that E47 interacts with MLK2, a mixed lineage kinase (MLK) involved in JNK-mediated activation of programmed cell death. MLK2 enhances phosphorylation of the AD2 activation domain of E47 in vivo in a JNK-independent manner and phosphorylates in vitro defined serine and threonine residues within a loop-helix structure of AD2 that also contains a putative MLK docking site. Although these residues are essential for MLK2-mediated inactivation of E47, inhibition of MLKs by CEP11004 causes up-regulation of TrkB at a transcriptional level in cerebellar granule neurons and differentiating neuroblastoma cells. These findings allow us to propose a novel mechanism by which MLK regulates TrkB expression through phosphorylation of an activation domain of E47. This molecular link would explain why MLK inhibitors not only prevent activation of cell death processes but also enhance cell survival signaling as a key aspect of their neuroprotective potential.

Activation of JNK and PAK2 is essential for citrinin-induced apoptosis in a human osteoblast cell line

The mycotoxin citrinin (CTN), a natural contaminant in foodstuffs and animal feeds, exerts cytotoxic and genotoxic effects on various mammalian cells. CTN causes cell injury, including apoptosis. Previous studies by our group showed that CTN triggers apoptosis in mouse embryonic stem cells, as well as embryonic developmental injury. Here, we investigated the precise mechanisms governing this apoptotic effect in osteoblasts. CTN induced apoptotic biochemical changes in a human osteoblast cell line, including activation of c-Jun N-terminal kinase (JNK), loss of mitochondrial membrane potential, and caspase-3 and p21-activated protein kinase 2 (PAK2) activation. Experiments using a JNK-specific inhibitor, SP600125, and antisense oligonucleotides against JNK reduced CTN-induced activation of both JNK and caspase-3 in osteoblasts, indicating that JNK is required for caspase activation in this apoptotic pathway. Experiments using caspase-3 inhibitors and antisense oligonucleotides against PAK2 revealed that active caspase-3 is essential for PAK2 activation. Moreover, both caspase-3 and PAK2 require activation for CTN-induced apoptosis of osteoblasts. Interestingly, CTN stimulates two-stage activation of JNK in human osteoblasts. Early-stage JNK activation is solely ROS-dependent, whereas late-stage activation is dependent on ROS-mediated caspase activity, and regulated by caspase-induced activation of PAK2. On the basis of these results, we propose a signaling cascade model for CTN-induced apoptosis in human osteoblasts involving ROS, JNK, caspases, and PAK2.