Identification of an EGFRvIII-JNK2-HGF/c-Met-Signaling Axis Required for Intercellular Crosstalk and Glioblastoma Multiforme Cell Invasion.

Glioblastoma multiforme (GBM) is the most aggressive and common form of adult brain cancer. Current therapeutic strategies include surgical resection, followed by radiotherapy and chemotherapy. Despite such aggressive multimodal therapy, prognosis remains poor, with a median patient survival of 14 months. A proper understanding of the molecular drivers responsible for GBM progression are therefore necessary to instruct the development of novel targeted agents and enable the design of effective treatment strategies. Activation of the c-Jun N-terminal kinase isoform 2 (JNK2) is reported in primary brain cancers, where it associates with the histologic grade and amplification of the epidermal growth factor receptor (EGFR). In this manuscript, we demonstrate an important role for JNK2 in the tumor promoting an invasive capacity of EGFR variant III, a constitutively active mutant form of the receptor commonly found in GBM. Expression of EGFR variant III induces transactivation of JNK2 in GBM cells, which is required for a tumorigenic phenotype in vivo. Furthermore, JNK2 expression and activity is required to promote increased cellular invasion through stimulation of a hepatocyte growth factor-c-Met signaling circuit, whereby secretion of this extracellular ligand activates the receptor tyrosine kinase in both a cell autonomous and nonautonomous manner. Collectively, these findings demonstrate the cooperative and parallel activation of multiple RTKs in GBM and suggest that the development of selective JNK2 inhibitors could be therapeutically beneficial either as single agents or in combination with inhibitors of EGFR and/or c-Met.

Stress-induced nuclear import of apoptosis signal-regulating kinase 1 is mediated by karyopherin α2/ß1 heterodimer.

The apoptosis signal-regulating kinase 1 (ASK1) is activated in response to a wide variety of extracellular stressors. Consequently, dysregulation of ASK1 is associated with multiple pathologies. Here, we show that ASK1 translocates from the cytoplasm to the nucleus in HEK293 cells and human cardiomyocytes in response to hydrogen peroxide (H(2)O(2)) or angiotensin respectively. Immunoprecipitation and mass spectrometry experiments reveal that ASK1 physically interacts with the karyopherin α2/ß1 heterodimer in response to stress and genetic knockdown experiments confirm that this association mediates H(2)O(2)-induced ASK1 nuclear translocation. In addition, we have identified a nuclear localization signal (NLS)-like motif within the primary amino acid sequence of ASK1 composed of two clusters of basic amino acids separated by an intervening 16 amino acid spacer, KR[ACANDLLVDEFLKVSS]KKKK. Mutation of the downstream lysine cluster markedly reduces the H(2)O(2)-induced ASK1-karyopherin α2/ß1 interaction and inhibits ASK1 nuclear translocation. Furthermore, we demonstrate that nuclear ASK1 is active and participates in H(2)O(2)-induced ASK1-mediated cell death. Collectively, our findings have identified a functional interaction between ASK1 and the karyopherin α2/ß1 heterodimer and have also revealed a novel mechanism by which nuclear trafficking regulates the apoptotic function of ASK1 in response to stress.

Mechanism of oxidative stress-induced ASK1-catalyzed MKK6 phosphorylation.

Apoptosis signal-regulating kinase 1 (ASK1) is a serine/threonine kinase that responds to a plethora of stress-inducing signals. In turn, activation of ASK1 is associated with a number of human pathological conditions, including neurodegenerative disease, inflammation, and heart failure. In response to oxidative stress, ASK1 activates the cell death-associated p38 MAPK pathway by phosphorylating MKK6. Here, we investigated the regulation of oxidative stress-induced ASK1-catalyzed phosphorylation of MKK6. MKK6 phosphorylation levels increased immediately after H(2)O(2) treatment in intact cells and decreased following treatment for 30 min. When expressed in HEK293T cells, ASK1 was reproducibly purified within a high-molecular mass complex ( approximately 1500 kDa) known as the ASK1 signalosome. Measurement of the in vitro kinetic parameters revealed that the catalytic efficiency (k(cat)/K(m)) of ASK1 was 4000-fold greater in cells treated with H(2)O(2) for 3 min than in untreated cells. Interestingly, although the K(m(ATP)) values were found to be unchanged, the K(m(MKK6)) was dramatically decreased ( approximately 1000-fold). The increased affinity was specific for MKK6 and short-lived, as the K(m(MKK6)) returned to basal levels 30 min after treatment. Consistently, endogenous MKK6 was found within the ASK1 signalosome in intact cells and in addition copurified with ASK1 following treatment for 3 min. In contrast, proteins modulating ASK1 activity and degradation were found to interact with the ASK1 signalosome once MKK6 activation was completed. Taken together, these data suggest that oxidative stress rapidly increases ASK1 catalytic efficiency for MKK6 phosphorylation by increasing MKK6 binding affinity within the ASK1 signalosome prior to induction of inactivation and degradation of the complex.

Simultaneous Detection of 14 Microcystin Congeners from Tissue Samples Using UPLC- ESI-MS/MS and Two Different Deuterated Synthetic Microcystins as Internal Standards.

Cyanobacterial microcystins (MCs), potent serine/threonine-phosphatase inhibitors, pose an increasing threat to humans. Current detection methods are optimised for water matrices with only a few MC congeners simultaneously detected. However, as MC congeners are known to differ in their toxicity, methods are needed that simultaneously quantify the congeners present, thus allowing for summary hazard and risk assessment. Moreover, detection of MCs should be expanded to complex matrices, e.g., blood and tissue samples, to verify in situ MC concentrations, thus providing for improved exposure assessment and hazard interpretation. To achieve this, we applied two synthetic deuterated MC standards and optimised the tissue extraction protocol for the simultaneous detection of 14 MC congeners in a single ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) run. This procedure was validated using plasma and liver homogenates of mice (male and female) spiked with deuterated MC standards. For proof of concept, tissue and plasma samples from mice i.p. injected with MC-LR and MC-LF were analysed. While MC-LF was detected in all tissue samples of both sexes, detection of MC-LR was restricted to liver samples of male mice, suggesting different toxicokinetics in males, e.g., transport, conjugation or protein binding. Thus, deconjugation/-proteinisation steps should be employed to improve detection of bound MC.

Inhibition of TGF-beta induced lung fibroblast to myofibroblast conversion by phosphodiesterase inhibiting drugs and activators of soluble guanylyl cyclase.

Pulmonary fibroblast to myofibroblast conversion is a pathophysiological feature of idiopathic pulmonary fibrosis and COPD. This conversion is induced by transforming growth factor (TGF)-beta derived from epithelial cells as well as activated macrophages that have infiltrated the lung. Preventing this conversion might be a favourable therapeutic approach. Within this study we examined the activity of different members of the phosphodiesterase (PDE) family in primary human lung fibroblasts and various lung fibroblast cell lines both before and after TGF-beta induced differentiation to myofibroblasts as reflected by the expression of alpha-smooth muscle actin. We showed that the predominant PDE activities in lung fibroblasts are attributed to PDE5, PDE1 and to a smaller extent to PDE4. cyclic GMP (cGMP)-hydrolyzing activity declines by about half after differentiation to myofibroblasts in all pulmonary fibroblasts investigated, which is accompanied by a down-regulation of PDE5 protein. Lung fibroblast to myofibroblast differentiation is blocked by treatment with the PDE4 inhibitor piclamilast alone, depending on the TGF-beta concentration applied, and in combination with prostaglandin E(2) (PGE(2)) in a synergistic manner. Despite the high PDE5 activity the PDE5 inhibitor sildenafil by itself as well as in combination with brain natriuretic peptide or the nitric oxide-donor DETA-NONOate shows no inhibiting effects. However, combining sildenafil with the guanylyl cyclase (GC) activator BAY58-2667 and ODQ (which sensitizes GC for activation by BAY58-2667) suppressed TGF-beta induced differentiation. In summary, our data indicate that drugs interfering with the cyclic AMP (cAMP)-as well as with the NO-cGMP-pathway offer the therapeutic opportunity to prevent the differentiation of pulmonary fibroblasts to myofibroblasts in lung fibrosis.

Microcystin congener- and concentration-dependent induction of murine neuron apoptosis and neurite degeneration.

Cyanobacterial microcystins (MCs) represent a toxin group with > 100 variants, requiring active uptake into cells via organic anion-transporting polypeptides, in order to irreversibly inhibit serine/threonine-specific protein phosphatases. MCs are a human health hazard with repeated occurrences of severe poisonings. In the well-known human MC intoxication in Caruaru, Brazil (1996), patients developed signs of acute neurotoxicity, e.g., deafness, tinnitus, and intermittent blindness, as well as subsequent hepatotoxicity. The latter data, in conjunction with some animal studies, suggest that MCs are potent neurotoxins. However, there is little data to date demonstrating MC neuron-specific toxicity. MC exposure-induced cytotoxicity, caspase activity, chromatin condensation, and microtubule-associated Tau protein hyperphosphorylation (epitopes serine199/202 and serine396) were determined. Neurite degeneration was analyzed with confocal microscopy and neurite length determined using image analysis. MC-induced apoptosis was significantly increased by MC-LF and MC-LW, however, only at high concentrations (≥ 3µM), whereas significant neurite degeneration was already observed at 0.5µM MC-LF. Moreover, sustained hyperphosphorylation of Tau was observed with all MC congeners. The concentration- and congener-dependent mechanisms observed suggest that low concentrations of MC-LF and MC-LW can induce subtle neurodegenerative effects, reminiscent of Alzheimer's disease type human tauopathies, and thus should be taken more seriously with regard to potential human health effects than the apical cytotoxicity (apoptosis or necrosis) demonstrated at high MC concentrations.

Investigation of microcystin congener-dependent uptake into primary murine neurons.

BACKGROUND: Contamination of natural waters by toxic cyanobacteria is a growing problem worldwide, resulting in serious water pollution and human health hazards. Microcystins (MCs) represent a group of > 80 cyclic heptapeptides, mediating cytotoxicity via specific protein phosphatase (PP) inhibition at equimolar concentrations (comparable toxicodynamics). Because of the structure and size of MCs, active uptake into cells occurs via organic anion-transporting polypeptides (OATP/Oatp), as confirmed for liver-specific human OATP1B1 and OATP1B3, mouse Oatp1b2 (mOatp1b2), skate Oatp1d1, and the more widely distributed OATP1A2 expressed, for example, at the blood-brain barrier. Tissue-specific and cell-type-specific expression of OATP/Oatp transporters and specific transport of MC congeners (toxicokinetics) therefore appear prerequisite for the reported toxic effects in humans and other species upon MC exposure. Beyond hepatotoxicity induced by the MC-LR congener, the effects of other MC congeners, especially neuronal uptake and toxicity, are unknown. OBJECTIVES: In this study we examined the expression of mOatps and the uptake of congeners MC-LR, MC-LW, and MC-LF in primary murine neurons. METHODS: Intracellular MC accumulation was indicated indirectly via uptake inhibition experiments and directly confirmed by Western blot analysis and a PP inhibition assay. Neuronal mOatp expression was verified at the mRNA and protein level. RESULTS: MCs can cross neuronal cell membranes, with a subsequent decrease of PP activity. Of 15 mOatps, 12 were expressed at the mRNA level, but we found detectable protein levels for only two: mOatp1a5 (Slco1a5) and the known MC-LR transporter mOatp1b2 (Slco1b2). CONCLUSIONS: These data suggest mOatp-mediated uptake of MC congeners into neurons, thus corroborating earlier assumptions of the neurotoxic potential of MCs.