Interaction of apoptosis signal-regulating kinase 1 with isoforms of 14-3-3 proteins

Prognostic Value of a Ferroptosis-Related Gene Signature in Patients With Head and Neck Squamous Cell Carcinoma

Background: Ferroptosis is an iron-dependent programmed cell death (PCD) form that plays a crucial role in tumorigenesis and might affect the antitumor effect of radiotherapy and immunotherapy. This study aimed to investigate distinct ferroptosis-related genes, their prognostic value and their relationship with immunotherapy in patients with head and neck squamous cell carcinoma (HNSCC). Methods: The differentially expressed ferroptosis-related genes in HNSCC were filtered based on multiple public databases. To avoid overfitting and improve clinical practicability, univariable, least absolute shrinkage and selection operator (LASSO) and multivariable Cox algorithms were performed to construct a prognostic risk model. Moreover, a nomogram was constructed to forecast individual prognosis. The differences in tumor mutational burden (TMB), immune infiltration and immune checkpoint genes in HNSCC patients with different prognoses were investigated. The correlation between drug sensitivity and the model was firstly analyzed by the Pearson method. Results: Ten genes related to ferroptosis were screened to construct the prognostic risk model. Kaplan-Meier (K-M) analysis showed that the prognosis of HNSCC patients in the high-risk group was significantly lower than that in the low-risk group (P < 0.001), and the area under the curve (AUC) of the 1-, 3- and 5-year receiver operating characteristic (ROC) curve increased year by year (0.665, 0.743, and 0.755). The internal and external validation further verified the accuracy of the model. Then, a nomogram was build based on the reliable model. The C-index of the nomogram was superior to a previous study (0.752 vs. 0.640), and the AUC (0.729 vs. 0.597 at 1 year, 0.828 vs. 0.706 at 3 years and 0.853 vs. 0.645 at 5 years), calibration plot and decision curve analysis (DCA) also shown the satisfactory predictive capacity. Furthermore, the TMB was revealed to be positively correlated with the risk score in HNSCC patients (R = 0.14; P < 0.01). The differences in immune infiltration and immune checkpoint genes were significant (P < 0.05). Pearson analysis showed that the relationship between the model and the sensitivity to antitumor drugs was significant (P < 0.05). Conclusion: Our findings identified potential novel therapeutic targets, providing further potential improvement in the individualized treatment of patients with HNSCC.

Large tumor suppressor 2, LATS2, activates JNK in a kinase-independent mechanism through ASK1

Apoptosis signal-regulating kinase 1 (ASK1) is an important mediator of the cell stress response pathways. Because of its central role in regulating cell death, the activity of ASK1 is tightly regulated by protein-protein interactions and post-translational modifications. Deregulation of ASK1 activity has been linked to human diseases, such as neurological disorders and cancer. Here we describe the identification and characterization of large tumor suppressor 2 (LATS2) as a novel binding partner for ASK1. LATS2 is a core kinase in the Hippo signaling pathway and is commonly downregulated in cancer. We found that LATS2 interacts with ASK1 and increases ASK1-mediated signaling to promote apoptosis and activate the JNK mitogen-activated protein kinase (MAPK). This change in MAPK signaling is dependent on the catalytic activity of ASK1 but does not require LATS2 kinase activity. This work identifies a novel role for LATS2 as a positive regulator of the ASK1-MKK-JNK signaling pathway and establishes a kinase-independent function of LATS2 that may be part of the intricate regulatory system for cellular response to diverse stress signals.

Proteomic response of gill microsomes of Crassostrea brasiliana exposed to diesel fuel water-accommodated fraction

Diesel fuel water-accommodated fraction (diesel-WAF) is a complex mixture of organic compounds that may cause harmful effects to marine invertebrates. Expression of microsomal proteins can be changed by oil exposure, causing functional alterations in endoplasmic reticulum (ER). The aim of this study was to investigate changes in protein expression signatures in microsomes of oysterl Crassostrea brasiliana (=C.gasar) gill after exposure to 10% diesel-WAF for 24 and 72 h. Protein expression signatures of gills of oysters exposed to diesel-WAF were compared to those of unexposed oysters using two-dimensional electrophoresis (2-DE) to identify differentially expressed proteins. A total of 458 protein spots with molecular weights between 30-75 kDa were detected by 2-DE in six replicates of exposed oyster proteomes compared to unexposed ones. Fourteen differentially expressed proteins (six up-regulated and eight down-regulated) were identified. They are: proteins related to xenobiotic biotransformation (cytochrome P450 6 A, NADPH-cytochrome P450 reductase); cytoskeleton (α-tubulin, β-tubulin, gelsolin); processing and degradation of proteins pathways (thioredoxin domain-containing protein E3 ubiquitin-protein ligase MIB2); involved in the biosynthesis of glycolipids and glycoproteins (beta-1,3-galactosyltransferase 1); associated with stress responses (glutamate receptor 4 and 14-3-3 protein zeta, corticotropin-releasing factor-binding protein); plasmalogen biosynthesis (fatty acyl-CoA reductase 1), and sodium-and chloride-dependent glycine transporter 2 and glyoxylate reductase/hydroxypyruvate reductase. Different patterns of protein responses were observed between 24 and 72 h-exposed groups. Expression pattern of microsomal proteins provided a first insight on the potential diesel-WAF effects at protein level in microsomal fraction of oyster gills and indicated new potential biomarkers of exposure and effect. The present work can be a basis for future ecotoxicological studies in oysters aiming to elucidate the molecular mechanisms behind diesel-WAF toxicity and for environmental monitoring programs.

Regulation of ASK1 signaling by scaffold and adaptor proteins

The mitogen-activated protein kinase (MAPK) signaling pathway is a three-tiered kinase cascade where mitogen-activated protein kinase kinase kinases (MAP3Ks) lead to the activation of mitogen-activated protein kinase kinases (MAP2K), and ultimately MAPK proteins. MAPK signaling can promote a diverse set of biological outcomes, ranging from cell death to proliferation. There are multiple mechanisms which govern MAPK output, such as the duration and strength of the signal, cellular localization to upstream and downstream binding partners, pathway crosstalk and the binding to scaffold and adaptor molecules. This review will focus on scaffold and adaptor proteins that bind to and regulate apoptosis signal-regulating kinase 1 (ASK1), a MAP3K protein with a critical role in mediating stress response pathways.

Reactive oxygen species induce injury of the intestinal epithelium during hyperoxia

Long-term therapeutic hyperoxia may exert serious toxic effects on intestinal epithelial cells in vitro and in vivo. The aim of the present study was to investigate the cause of this intestinal injury under conditions of hyperoxia. Caco-2 cells were treated with different concentrations of hydrogen peroxide (H2O2) and 85% hyperoxia for 24 h. higher rates of injury of Caco-2 cells were observed in the hyperoxia and H2O2 groups compared with the control group. The reactive oxygen species (ROS) level of the hyperoxia group was significantly higher compared with that of the 400 µM H2O2 group. The protein and gene levels of RelA, RelB, hypoxia‑inducible factor-1α, tumor necrosis factor-α and apoptosis signal‑regulating kinase 1 were significantly higher in the hyperoxia and H2O2 groups compared with those in the control group. In conclusion, during hyperoxia, intestinal epithelial cells were destroyed and the levels of ROS were increased. Therefore, ROS may play an important role in intestinal injury in a hyperoxic environment.

A heteromeric molecular complex regulates the migration of lung alveolar epithelial cells during wound healing

Alveolar type II epithelial cells (ATII) are instrumental in early wound healing in response to lung injury, restoring epithelial integrity through spreading and migration. We previously reported in separate studies that focal adhesion kinase-1 (FAK) and the chemokine receptor CXCR4 promote epithelial repair mechanisms. However, potential interactions between these two pathways were not previously considered. In the present study, we found that wounding of rat ATII cells promoted increased association between FAK and CXCR4. In addition, protein phosphatase-5 (PP5) increased its association with this heteromeric complex, while apoptosis signal regulating kinase-1 (ASK1) dissociated from the complex. Cell migration following wounding was decreased when PP5 expression was decreased using shRNA, but migration was increased in ATII cells isolated from ASK1 knockout mice. Interactions between FAK and CXCR4 were increased upon depletion of ASK1 using shRNA in MLE-12 cells, but unaffected when PP5 was depleted. Furthermore, we found that wounded rat ATII cells exhibited decreased ASK1 phosphorylation at Serine-966, decreased serine phosphorylation of FAK, and decreased association of phosphorylated ASK1 with FAK. These changes in phosphorylation were dependent upon expression of PP5. These results demonstrate a unique molecular complex comprising CXCR4, FAK, ASK1, and PP5 in ATII cells during wound healing.

Assembly Dynamics and Stoichiometry of the Apoptosis Signal-regulating Kinase (ASK) Signalosome in Response to Electrophile Stress

Apoptosis signal-regulating kinase 1 (ASK1) is a key sensor kinase in the mitogen-activated protein kinase pathway that transduces cellular responses to oxidants and electrophiles. ASK1 is regulated by a large, dynamic multiprotein signalosome complex, potentially including over 90 reported ASK1-interacting proteins. We employed both shotgun and targeted mass spectrometry assays to catalogue the ASK1 protein-protein interactions in HEK-293 cells treated with the prototypical lipid electrophile 4-hydroxy-2-nonenal (HNE). Using both epitope-tagged overexpression and endogenous expression cell systems, we verified most of the previously reported ASK1 protein-protein interactions and identified 14 proteins that exhibited dynamic shifts in association with ASK1 in response to HNE stress. We used precise stable isotope dilution assays to quantify protein stoichiometry in the ASK signalosome complex and identified ASK2 at a 1:1 stoichiometric ratio with ASK1 and 14-3-3 proteins (YWHAQ, YWHAB, YWHAH, and YWHAE) collectively at a 0.5:1 ratio with ASK1 as the main components. Several other proteins, including ASK3, PARK7, PRDX1, and USP9X were detected with stoichiometries of 0.1:1 or less. These data support an ASK signalosome comprising a multimeric core complex of ASK1, ASK2, and 14-3-3 proteins, which dynamically engages other binding partners needed to mediate diverse stress-response signaling events. This study further demonstrates the value of combining global and targeted MS approaches to interrogate multiprotein complex composition and dynamics.

Involvement of 14-3-3 Proteins in Regulating Tumor Progression of Hepatocellular Carcinoma

There are seven mammalian isoforms of the 14-3-3 protein, which regulate multiple cellular functions via interactions with phosphorylated partners. Increased expression of 14-3-3 proteins contributes to tumor progression of various malignancies. Several isoforms of 14-3-3 are overexpressed and associate with higher metastatic risks and poorer survival rates of hepatocellular carcinoma (HCC). 14-3-3β and 14-3-3ζ regulate HCC cell proliferation, tumor growth and chemosensitivity via modulating mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK) and p38 signal pathways. Moreover, 14-3-3ε suppresses E-cadherin and induces focal adhesion kinase (FAK) expression, thereby enhancing epithelial-mesenchymal transition (EMT) and HCC cell migration. 14-3-3ζ forms complexes with αB-crystallin, which induces EMT and is the cause of sorafenib resistance in HCC. Finally, a recent study has indicated that 14-3-3σ induces heat shock protein 70 (HSP70) expression, which increases HCC cell migration. These results suggest that selective 14-3-3 isoforms contribute to cell proliferation, EMT and cell migration of HCC by regulating distinct targets and signal pathways. Targeting 14-3-3 proteins together with specific downstream effectors therefore has potential to be therapeutic and prognostic factors of HCC. In this article, we will overview 14-3-3’s regulation of its downstream factors and contributions to HCC EMT, cell migration and proliferation.

Development of an HTS-compatible assay for the discovery of ASK1 signalosome inhibitors using alphascreen technology

Genetic target validation studies have demonstrated that the apoptosis signal-regulating kinase 1 (ASK1) represents an important target for the treatment of rheumatoid arthritis, cardiac diseases, and several neurodegenerative disorders. To identify small-molecule inhibitors of ASK1, we have developed a high-throughput screening-compatible, homogenous, biochemical assay using AlphaScreen technology. This novel assay design utilizes purified stress-activated ASK1 signalosome complex, and it monitors phosphorylation of its full-length native substrate, MKK6. The assay has been optimized in a 384-well format and validated by screening the Sigma LOPAC library. The results presented here demonstrate that the assay is sensitive and robust with a Z' factor value of 0.88±0.04 and a signal-to-background ratio of 11, indicating that this assay can be used to screen large chemical libraries to discover novel inhibitors of ASK1.

Amyloid β regulates the expression and function of AIP1

Apoptosis signal-regulating kinase 1–interacting (ASK1-interacting) protein-1 (AIP1) is a newly identified novel member of the Ras GTPase-activating protein family, which has been implicated in cell growth inhibition and cell apoptosis. However, the effects of AIP1 in Alzheimer’s disease (AD) are unknown. In the present study, we found that AIP1 was elevated in the brain of AD Tg2576 mice and Aβ1-42 treated brain cerebral microvascular endothelial cells (CECs). Aβ1-42 treatment induced the interaction of AIP1 and apoptosis signal-regulating kinase 1 (ASK1), which led to dissociation of ASK1 and its inhibitor 14-3-3. Dissociation of ASK1 from 14-3-3 leads to ASK1 activation. Indeed, Aβ1-42 dephosphorylated ASK1 at Ser-967, suggesting that Aβ1-42 increased ASK1 activity. Importantly, disassociation of ASK1 and 14-3-3 induced by Aβ1–42 could be rescued by silence of AIP1. In addition, down-regulation of AIP1 also led to attenuation of the activation of JNK, as well as p53, downstream signaling targets of ASK1. AIP1 silencing attenuated the pro-apoptotic effects of Aβ1-42 on CECs. We propose that AIP1 mediates Aβ induced ASK1 activation by facilitating dissociation of 14-3-3, suggesting a novel mechanism for Aβ-induced apoptosis in CECs.

Structural and functional analysis of novel human cytochrome C targets in apoptosis

Since the first description of apoptosis four decades ago, great efforts have been made to elucidate, both in vivo and in vitro, the molecular mechanisms involved in its regulation. Although the role of cytochrome c during apoptosis is well established, relatively little is known about its participation in signaling pathways in vivo due to its essential role during respiration. To obtain a better understanding of the role of cytochrome c in the onset of apoptosis, we used a proteomic approach based on affinity chromatography with cytochrome c as bait in this study. In this approach, novel cytochrome c interaction partners were identified whose in vivo interaction and cellular localization were facilitated through bimolecular fluorescence complementation. Modeling of the complex interface between cytochrome c and its counterparts indicated the involvement of the surface surrounding the heme crevice of cytochrome c, in agreement with the vast majority of known redox adducts of cytochrome c. However, in contrast to the high turnover rate of the mitochondrial cytochrome c redox adducts, those occurring under apoptosis led to the formation of stable nucleo-cytoplasmic ensembles, as inferred mainly from surface plasmon resonance and nuclear magnetic resonance measurements, which permitted us to corroborate the formation of such complexes in vitro. The results obtained suggest that human cytochrome c interacts with pro-survival, anti-apoptotic proteins following its release into the cytoplasm. Thus, cytochrome c may interfere with cell survival pathways and unlock apoptosis in order to prevent the spatial and temporal coexistence of antagonist signals.

14-3-3 proteins in neurodegeneration

Among the first reported functions of 14-3-3 proteins was the regulation of tyrosine hydroxylase (TH) activity suggesting a possible involvement of 14-3-3 proteins in Parkinson's disease. Since then the relevance of 14-3-3 proteins in the pathogenesis of chronic as well as acute neurodegenerative diseases, including Alzheimer's disease, polyglutamine diseases, amyotrophic lateral sclerosis and stroke has been recognized. The reported function of 14-3-3 proteins in this context are as diverse as the mechanism involved in neurodegeneration, reaching from basal cellular processes like apoptosis, over involvement in features common to many neurodegenerative diseases, like protein stabilization and aggregation, to very specific processes responsible for the selective vulnerability of cellular populations in single neurodegenerative diseases. Here, we review what is currently known of the function of 14-3-3 proteins in nervous tissue focussing on the properties of 14-3-3 proteins important in neurodegenerative disease pathogenesis.

Soybean 14-3-3 gene family: identification and molecular characterization

The 14-3-3s are a group of proteins that are ubiquitously found in eukaryotes. Plant 14-3-3 proteins are encoded by a large multigene family and are involved in signaling pathways to regulate plant development and protection from stress. Recent studies in Arabidopsis and rice have demonstrated the isoform specificity in 14-3-3s and their client protein interactions. However, detailed characterization of 14-3-3 gene family in legumes has not been reported. In this study, soybean 14-3-3 proteins were identified and their molecular characterization performed. Data mining of soybean genome and expressed sequence tag databases identified 18 14-3-3 genes, of them 16 are transcribed. All 16 SGF14s have higher expression in embryo tissues suggesting their potential role in seed development. Subcellular localization of all transcribed SGF14s demonstrated that 14-3-3 proteins in soybean have isoform specificity, however, some overlaps were also observed between closely related isoforms. A comparative analysis of SGF14s with Arabidopsis and rice 14-3-3s indicated that SGF14s also group into epsilon and non-epsilon classes. However, unlike Arabidopsis and rice 14-3-3s, SGF14s contained only one kind of gene structure belonging to each class. Overall, soybean consists of the largest family of 14-3-3 proteins characterized to date. Our results provide a solid framework for further investigations into the role of SGF14s and their involvement in legume-specific functions.

Small interfering RNA targeting 14-3-3ζ increases efficacy of chemotherapeutic agents in head and neck cancer cells

Patients diagnosed in advanced stages of head and neck squamous cell carcinoma often show limited response to chemotherapeutic agents. Recently, we reported the overexpression of 14-3-3ζ protein in head and neck premalignant and cancer tissues using liquid chromatography-tandem mass spectrometry with isotopic labeling and revealed its significance as a prognostic marker using immunohistochemical analysis. In this study, we determined the potential of 14-3-3ζ as a therapeutic target for head and neck cancer. Small interfering RNA (siRNA) targeting 14-3-3ζ was used to downregulate its expression in head and neck cancer cells in culture. Cell cycle analysis showed that head and neck cancer cells transfected with siRNA targeting 14-3-3ζ showed G(2)-M arrest. These siRNA transfectants also showed increased cell death on treatment with any one of the following chemotherapeutic agents: cisplatin, 5-fluorouracil, paclitaxel, or doxorubicin in comparison with the no transfection controls. Flow cytometric analysis using propidium iodide staining showed increased sub-G(0) fraction in siRNA-transfected cells treated with any of these chemotherapeutic agents, suggesting cell death; in addition, Annexin V staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay revealed increased apoptosis. Taken together, our results strongly showed that downregulation of 14-3-3ζ expression may serve to improve the sensitivity of head and neck cancer cells to chemotherapeutic agents.

Dual engagement of 14-3-3 proteins controls signal relay from ASK2 to the ASK1 signalosome

Faithful and efficient transmission of biological signals through mitogen-activated protein kinase (MAPK) pathways requires engagement of highly regulated cellular machinery in response to diverse environmental cues. Here, we report a novel mechanism controlling signal relay between two MAP3Ks, apoptosis signal-regulating kinase (ASK) 1 and ASK2. We show that ASK2 specifically interacts with 14-3-3 proteins through phosphorylated S964. Although a 14-3-3-binding defective mutant of ASK1 (S967A) has no effect on the ASK2/14-3-3 interaction, both overexpression of the analogous ASK2 (S964A) mutant and knockdown of ASK2 dramatically reduced the amount of ASK1 complexed with 14-3-3. These data suggest a dominant role of ASK2 in 14-3-3 control of ASK1 function. Indeed, ASK2 S964A-induced dissociation of 14-3-3 from ASK1 correlated with enhanced phosphorylation of ASK1 at T838 and increased c-Jun N-terminal kinase phosphorylation, the two biological readouts of ASK1 activation. Our results suggest a model in which upstream signals couple ASK2 S964 phosphorylation to the ASK1 signalosome through dual engagement of 14-3-3.

Responses of wheat seedlings to cadmium, mercury and trichlorobenzene stresses

The molecular response of wheat (Triticum aestivum L., cv. Yangmai 13) seedlings to heavy metal (Cd, Hg) and 1,2,4-trichlorobenzene (TCB) stresses were examined by two-dimensional gel electrophoresis, image analysis, and peptide mass fingerprinting. The results showed inhibitions of root and shoot growth by Cd, Hg, and TCB. These stresses led to water deficit and lipid phosphorylation in the seedling which also promoted protein phophorylation in the leaves. Hg stress inhibited protein synthesis while Cd and TCB stresses induced or up-regulated more proteins in the leaves. Most of these induced proteins played important roles in the biochemical reactions involved in tolerance of wheat to Cd and TCB stresses. The primary functions of Cd- and TCB-induced proteins included methionine metabolism, Rubisco modification, protein phosphorylation regulation, protein configuration protection, H+ transmembrane transportation and also the synthesis of ethylene, defense substances and cell wall compounds.

A homogenous luminescent proximity assay for 14-3-3 interactions with both phosphorylated and nonphosphorylated client peptides

The 14-3-3 proteins are a family of dimeric eukaryotic proteins that mediate both phosphorylation-dependent and -independent protein-protein interactions. Through these interactions, 14-3-3 proteins participate in the regulation of a wide range of cellular processes, including cell proliferation, cell cycle progression, and apoptosis. Because of their fundamental importance, 14-3-3 proteins have also been implicated in a variety of diseases, including cancer and neurodegenerative disorders. In order to monitor 14-3-3/client protein interactions for the discovery of small molecule 14-3-3 modulators, we have designed and optimized 14-3-3 protein binding assays based on the amplified luminescent proximity homogeneous assay (AlphaScreen) technology. Using the interaction of 14-3-3 with a phosphorylated Raf-1 peptide and a nonphosphorylated R18 peptide as model systems, we have established homogenous “add-and-measure” high-throughput screening assays. Both assays achieved robust performance with S/B ratios above 7 and Z’ factors above 0.7. Application of the known antagonistic peptides in our studies further validated the assay for screening of chemical compound libraries to identify small molecules that can modulate 14-3-3 protein-protein interactions.

Inhibition of the thioredoxin system is a basis for the antileukemic potential of 13-hydroxy-15-oxo-zoapatlin

The mammalian thioredoxin (Trx) system, composed of Trx, Trx reductase (TrxR), and NADPH, is the most important thiol system involved in the redox control of signaling and regulatory proteins in apoptosis and cell proliferation. Here we addressed the inhibition of the Trx system by 13-hydroxy-15-oxo-zoapatlin (OZ), a nor-kaurane diterpene previously shown to possess proapoptotic potential and to cause cell cycle arrest in leukemia cells. OZ was found, by both biochemical and mass spectrometry-based approaches, to target Trx1 and TrxR in a cell-free system. In particular, the formation of reversible OZ adducts to Trx1 Cys35, Cys62, and Cys73 was demonstrated. We next showed that OZ efficiently inhibited Trx and TrxR catalytic activity in Molt4 cells. The occurrence of oxidative modifications of Trx molecules was assessed by "redox Western blot" analyses. OZ-mediated Trx oxidation resulted in apoptosis signaling kinase-1 release and activation of downstream JNK and p38 pathways. By means of specific inhibitors of these two stress-activated protein kinases, we demonstrated that the JNK pathway plays a major role in determining the apoptotic fate of OZ-exposed cells, whereas p38 activation seems to be involved mainly in OZ-induced G2/M block.

Leukemia inhibitory factor induces an antiapoptotic response in oligodendrocytes through Akt-phosphorylation and up-regulation of 14-3-3

Leukemia inhibitory factor (LIF) promotes the survival of oligodendrocytes (OLG) both in vitro and in an animal model of multiple sclerosis. Here, we show that LIF protects mature rat OLG cultures selectively against the combined insult of the proinflammatory cytokines interferon-gamma and tumor necrosis factor-alpha, but it does not protect against oxidative stress nor against staurosporine induced apoptosis. We further demonstrate that LIF activates the janus kinase (JAK)/signal transducer and activator of transcription 3 (STAT3) and the phosphatidylinositol 3 kinase/Akt pathway in mature OLG. We show that LIF protection is independent of suppressors of cytokine signaling and Bcl-2 mRNA expression levels. To gain further insight into the protective mechanism, a quantitative proteomic approach (DIGE) was applied to identify differentially expressed proteins in LIF-treated OLG. Our results indicate that LIF induces a shift in the cellular machinery toward a prosurvival execution program, illustrated by an enhanced expression of isoforms of the antiapoptotic molecule 14-3-3. These data provide further insight into the mechanisms of LIF-mediated protection of mature OLGs.

Depletion of 14-3-3 zeta elicits endoplasmic reticulum stress and cell death, and increases vulnerability to kainate-induced injury in mouse hippocampal cultures

14-3-3 proteins are ubiquitous signalling molecules that regulate development and survival pathways in brain. Altered expression and cellular localization of 14-3-3 proteins has been implicated in neurodegenerative diseases and in neuronal death after acute neurological insults, including seizures. Presently, we examined expression and function of 14-3-3 isoforms in vitro using mouse organotypic hippocampal cultures. Treatment of cultures with the endoplasmic reticulum (ER) stressor tunicamycin caused an increase in levels of 14-3-3 zeta within the ER-containing microsomal fraction, along with up-regulation of Lys-Asp-Glu-Leu-containing proteins and calnexin, and the selective death of dentate granule cells. Depletion of 14-3-3 zeta levels using small interfering RNA induced both ER stress proteins and death of granule cells. Treatment of hippocampal cultures with the excitotoxin kainic acid increased levels of Lys-Asp-Glu-Leu-containing proteins and microsomal 14-3-3 zeta levels and caused cell death within the CA1, CA3 and dentate gyrus of the hippocampus. Kainic acid-induced damage was significantly increased in each hippocampal subfield of cultures treated with small interfering RNA targeting 14-3-3 zeta. The present data indicate a role for 14-3-3 zeta in survival responses following ER stress and possibly protection against seizure injury to the hippocampus.

Apoptosis Signal-Regulating Kinase 1 in Stress and Immune Response

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase (MAPK) kinase kinase of the c-Jun N-terminal kinase (JNK) and p38 MAPK pathways. ASK1 is preferentially activated by various cytotoxic stressors and plays pivotal roles in a wide variety of cellular response to them. Recent analyses of ASK1 orthologs in Caenorhabditis elegans and Drosophila melanogaster have revealed that ASK1 is an evolutionarily conserved signaling intermediate in stress responses and appears to constitute a primitive but efficient defense system against stimuli harmful to organisms. Consistent with this notion, ASK1 has been shown to be required for the innate immune response, which is essential for host defense against a wide range of pathogens. In this review, we focus on the molecular mechanisms by which ASK1 functions in stress and immune responses and discuss the possible involvement of ASK1 in human diseases.

Increases in expression of 14-3-3 eta and 14-3-3 zeta transcripts during neuroprotection induced by delta9-tetrahydrocannabinol in AF5 cells

The molecular mechanisms involved in N-methyl-D-aspartate (NMDA)-induced cell death and Delta9-tetrahydrocannabinol (THC)-induced neuroprotection were investigated in vitro with an AF5 neural progenitor cell line model. By microarray analysis, Ywhah, CK1, Hsp60, Pdcd 4, and Pdcd 7 were identified as being strongly regulated by both NMDA toxicity and THC neuroprotection. The 14-3-3 eta (14-3-3eta; gene symbol Ywhah) and 14-3-3 zeta (14-3-3zeta; gene symbol Ywhaz) transcripts were deceased by NMDA treatment and increased by THC treatment prior to NMDA, as measured by cDNA microarray analysis and quantitative real-time RT-PCR. Other 14-3-3 isoforms were unchanged. Whereas up-regulation of 14-3-3zeta expression was observed 30 min after treatment with THC plus NMDA, down-regulation by NMDA alone was not seen until 16 hr after treatment. By Western blotting, THC increased 14-3-3 protein only in cells that were also treated with NMDA. Overexpression of 14-3-3eta or 14-3-3zeta by transient plasmid transfection increased 14-3-3 protein levels and decreased NMDA-induced cell death. These data suggest that increases in 14-3-3 proteins mediate THC-induced neuroprotection under conditions of NMDA-induced cellular stress.

FTICR-MS analysis of 14-3-3 isoform substrate selection

The 14-3-3s are a ubiquitous class of eukaryotic proteins that participate in a second regulatory step in many phosphorylation-based signal transduction systems. The Arabidopsis family of 14-3-3 proteins represents a rather large 14-3-3 gene family. The biological motive for such diversity within a single protein family is not yet completely understood. The work presented here utilizes 14-3-3 micro-affinity chromatography in conjunction with Fourier transform ion cyclotron resonance mass spectrometry to survey the substrate sequence selectivity of two Arabidopsis 14-3-3 isoforms that represent the two major subclasses of this protein family. A method was developed to compare the relative binding of eight synthetic phosphopeptide sequences. The degree to which each phosphopeptide bound to either isoform was assigned a relative value, defined here as the binding ratio. The method provided a simple means for visualizing differences in substrate sequence selection among different 14-3-3 isoforms. A reproducible preference for specific phosphopeptide sequences was measured for both isoforms. This binding preference was consistent among the two classes of isoforms, suggesting that any pressure for isoform selectivity must reside outside the central core that interacts with the phosphopeptide sequence of the client.

14-3-3 sigma increases the transcriptional activity of the androgen receptor in the absence of androgens

The androgen receptor (AR) is a ligand-activated transcription factor that regulates numerous target genes, including prostate-specific antigen (PSA). We examined the ability of each member of the 14-3-3 family to modulate transcription of PSA through the AR. Despite significant homology within the 14-3-3 family we observed differences in the ability of each isoform to alter the transcriptional activity of the AR. Significantly, 14-3-3 sigma activated PSA-luciferase reporters not only at castrate levels of androgens, but also in the complete absence of androgens. 14-3-3 sigma also increased expression of the endogenous PSA gene in the absence of androgens. Knockdown of the AR by siRNA oligonucleotides abolished activation of these reporters by 14-3-3 sigma. These findings may have greatest significance in hormone refractory prostate cancer where the AR may be activated in a ligand-independent manner.

Activation of ASK1 during reperfusion of ischemic spinal cord

Apoptosis signal-regulating kinase 1 (ASK1) is a mitogen-activated protein kinase kinase kinase (MAPKKK), which plays a pivotal role in cell apoptosis. To determine the mechanism of ASK1 induction during reperfusion of ischemic spinal tissue, we used a model of rabbit spinal cord ischemia and reperfusion. To assess the role of ASK1 in spinal cord ischemia-reperfusion injuries, we examined alterations in spinal tissue morphology, protein-protein interactions, and activation of key members of the ASK1-mediated signaling pathway. Changes in spinal cord morphology were observed with hematoxylin and eosin (H&E) staining and electron microscopy. The phosphorylation levels of ASK1, JNK, and p38 were assessed by immunoblotting proteins from animals that received 30 min of ischemia followed by 1 or 24h of reperfusion. We observed increased phosphorylation of ASK1, JNK, and p38 after reperfusing ischemic spinal cords. Immunohistochemical studies were performed to determine the cellular localization of phosphorylated ASK1 (pASK1) and 14-3-3. Following reperfusion for 24h, we observed increased cytoplasmic localization of pASK1 and decreased cytoplasmic localization of 14-3-3. Immunoprecipitation analyses suggested that 14-3-3 dissociates from ASK1 during reperfusion of ischemic spinal cords. These results indicate that activation of ASK1 may play an important role in the apoptotic signaling mechanisms that occur in reperfused spinal cord injuries.

Identification of FAKTS as a novel 14-3-3-associated nuclear protein

Through bioinformatics and experimental approaches, we have assigned the first biochemical property to a predicted protein product in the human genome as a new 14-3-3 binding protein. 14-3-3 client proteins represent a diverse group of regulatory molecules that often function as signaling integrators in response to various environmental cues and include proteins such as Bad and Foxo. Using 14-3-3 as a probe in a yeast two-hybrid screen, we identified a novel 14-3-3 binding protein with unknown function, initially designated as clone 546. Confocal microscopy revealed that clone 546 localized to the nucleus of mammalian cells. Additional studies show that the gene encoding clone 546 is expressed in many human tissues, including the thymus, as well as a number of cancer cell lines. The interaction of clone 546 with 14-3-3 was confirmed in mammalian cells. Interestingly, this interaction was markedly enhanced by the expression of activated Akt/PKB, suggesting a phosphorylation dependent event. Mutational analysis was carried out to identify Ser479 as the predominant residue that mediates the clone 546/14-3-3 association. Phosphorylation of Ser479 by AKT/PKB further supports a critical role for Akt/PKB in regulation of the clone 546/14-3-3 interaction. On the basis of these findings, we named this undefined protein FAKTS: Fourteen-three-three associated AKT Substrate.

The ADP-stimulated NADPH oxidase activates the ASK-1/MKK4/JNK pathway in alveolar macrophages

The role of H2O2 as a second messenger in signal transduction pathways is well established. We show here that the NADPH oxidase-dependent production of O2*(-) and H2O2 or respiratory burst in alveolar macrophages (AM) (NR8383 cells) is required for ADP-stimulated c-Jun phosphorylation and the activation of JNK1/2, MKK4 (but not MKK7) and apoptosis signal-regulating kinase-1 (ASK1). ASK1 binds only to the reduced form of thioredoxin (Trx). ADP induced the dissociation of ASK1/Trx complex and thus resulted in ASK1 activation, as assessed by phosphorylation at Thr845, which was enhanced after treatment with aurothioglucose (ATG), an inhibitor of Trx reductase. While dissociation of the complex implies Trx oxidation, protein electrophoretic mobility shift assay detected oxidation of Trx only after bolus H2O2 but not after ADP stimulation. These results demonstrate that the ADP-stimulated respiratory burst activated the ASK1-MKK4-JNK1/c-Jun signaling pathway in AM and suggest that transient and localized oxidation of Trx by the NADPH oxidase-mediated generation of H2O2 may play a critical role in ASK1 activation and the inflammatory response.

Direct interaction and reciprocal regulation between ASK1 and calcineurin-NFAT control cardiomyocyte death and growth

The calcium-calmodulin-activated protein phosphatase calcineurin functions as a key mediator of diverse biologic processes, including differentiation, apoptosis, growth, and adaptive responses, in part through dephosphorylation and activation of nuclear factor of activated T-cell (NFAT) transcription factors. Apoptosis signal-regulating kinase 1 (ASK1) is an upstream component of the mitogen-activated protein kinases that serves as a pivotal regulator of cytokine-, oxidative-, and stress-induced cell death. Here, we performed a yeast two-hybrid screen with calcineurin B as bait, which identified ASK1 as a direct physical interacting partner. The C-terminal 218 amino acids of ASK1 were sufficient to mediate interaction with calcineurin B in yeast, as well as in mammalian cell lysates. Importantly, endogenous calcium binding B subunit (CnB) protein interacted with endogenous ASK1 protein in cardiomyocytes at baseline, suggesting that the interaction observed in yeast was of potential biologic relevance. Indeed, calcineurin directly dephosphorylated ASK1 at serine 967 using purified proteins or mammalian cell lysates. Dephosphorylation of ASK1 serine 967 by calcineurin promoted its disassociation from 14-3-3 proteins, resulting in ASK1 activation. Calcineurin and ASK1 cooperatively enhanced cardiomyocyte apoptosis, while expression of a dominant negative ASK1 blocked calcineurin-induced apoptosis. Mouse embryonic fibroblasts deficient in ask1 were also partially resistant to calcineurin- or ionomycin-induced apoptosis. Finally, ASK1 negatively regulated calcineurin-NFAT signaling indirectly through c-Jun NH2-terminal kinase (JNK)- and p38-mediated phosphorylation of NFAT, which blocked calcineurin- and agonist-dependent hypertrophic growth of cardiomyocytes. Thus, ASK1 and calcineurin-NFAT constitute a feedback regulatory circuit in which calcineurin positively regulates ASK1 through direct dephosphorylation, while ASK1 negatively regulates calcineurin-NFAT signaling through p38- and JNK-mediated NFAT phosphorylation.

Dynamic 14-3-3/client protein interactions integrate survival and apoptotic pathways

The serine/threonine binding protein, 14-3-3, possesses a diverse array of client proteins. It is involved in the regulation of apoptosis through multiple interactions with proteins of the core mitochondrial machinery, pro-apoptotic transcription factors, and their upstream signaling pathways. 14-3-3 coordinates with survival kinases to inhibit multiple pro-apoptotic molecules. One prominent mechanism for the suppression of apoptosis is through 14-3-3-mediated sequestration of pro-apoptotic client proteins. On the other hand, cellular stresses appear to signal through the inhibition of 14-3-3 function to exert their pro-apoptotic effect. Global inhibition of 14-3-3/client protein interaction induces apoptosis, and stands as an attractive intervention in diseases involving overactive survival signaling pathways. Because dysregulation of 14-3-3 has been associated with poor survival of cancer patients, targeting 14-3-3 may provide a novel therapeutic approach for the treatment of cancer.

14-3-3 proteins regulate glycogen synthase 3beta phosphorylation and inhibit cardiomyocyte hypertrophy

14-3-3 proteins are dimeric phophoserine-binding molecules that participate in important cellular processes such as cell proliferation, cell-cycle control and the stress response. In this work, we report that several isoforms of 14-3-3s are expressed in neonatal rat cardiomyocytes. To understand their function, we utilized a general 14-3-3 peptide inhibitor, R18, to disrupt 14-3-3 functions in cardiomyocytes. Cardiomyocytes infected with adenovirus-expressing YFP-R18 (AdR18) exhibited markedly increased protein synthesis and atrial natriuretic peptide production and potentiated the responses to norepinephrine stimulation. This response was blocked by the pretreatment with LY294002, a phosphoinositide 3-kinase (PI3K) inhibitor. Consistent with a role of PI3K in the R18 effect, R18 induced phosphorylation of a protein cloned from the vakt oncogene of retrovirus AKT8 (Akt - also called protein kinase B, PKB) at Ser473 and glycogen synthase 3beta (GSK3beta) at Ser9, but not extracellular signal-regulated kinase 1/2 (ERK1/2). AdR18-induced PKB and GSK3beta phosphorylation was completely blocked by LY294002. In addition, a member of the nuclear factor of activated T cells (NFAT) family, NFAT3, was converted into faster mobility forms and translocated into the nucleus upon the treatment of AdR18. These results suggest that 14-3-3s inhibits cardiomyocytes hypertrophy through regulation of the PI3K/PKB/GSK3beta and NFAT pathway.

Isoform-specific subcellular localization among 14-3-3 proteins in Arabidopsis seems to be driven by client interactions

In most higher eukaryotes, the predominantly phosphoprotein-binding 14-3-3 proteins are the products of a multigene family, with many organisms having 10 or more family members. However, current models for 14-3-3/phosphopeptide interactions suggest that there is little specificity among 14-3-3s for diverse phosphopeptide clients. Therefore, the existence of sequence diversity among 14-3-3s within a single organism begs questions regarding the in vivo specificities of the interactions between the various 14-3-3s and their clients. Chief among those questions is, Do the different 14-3-3 isoforms interact with different clients within the same cell? Although the members of the Arabidopsis 14-3-3 family of proteins typically contain highly conserved regions of sequence, they also display distinctive variability with deep evolutionary roots. In the current study, a survey of several Arabidopsis 14-3-3/GFP fusions revealed that 14-3-3s demonstrate distinct and differential patterns of subcellular distribution, by using trichomes and stomate guard cells as in vivo experimental cellular contexts. The effects of client interaction on 14-3-3 localization were further analyzed by disrupting the partnering with peptide and chemical agents. Results indicate that 14-3-3 localization is both isoform specific and highly dependent upon interaction with cellular clients.