Subcellular Translocation Research Articles

Human mesenchymal factors induce rat hippocampal- and human neural stem cell dependent oligodendrogenesis.

The generation of new oligodendrocytes is essential for adult brain repair in diseases such as multiple sclerosis. We previously identified the multifunctional p57kip2 protein as a negative regulator of myelinating glial cell differentiation and as an intrinsic switch of glial fate decision in adult neural stem cells (aNSCs). In oligodendroglial precursor cells (OPCs), p57kip2 protein nuclear exclusion was recently found to be rate limiting for differentiation to proceed. Furthermore, stimulation with mesenchymal stem cell (MSC)-derived factors enhanced oligodendrogenesis by yet unknown mechanisms. To elucidate this instructive interaction, we investigated to what degree MSC secreted factors are species dependent, whether hippocampal aNSCs respond equally well to such stimuli, whether apart from oligodendroglial differentiation also tissue integration and axonal wrapping can be promoted and whether the oligodendrogenic effect involved subcellular translocation of p57kip2. We found that CC1 positive oligodendrocytes within the hilus express nuclear p57kip2 protein and that MSC dependent stimulation of cultured hippocampal aNSCs was not accompanied by nuclear p57kip2 exclusion as observed for parenchymal OPCs after spontaneous differentiation. Stimulation with human MSC factors was observed to equally promote rat stem cell oligodendrogenesis, axonal wrapping and tissue integration. As forced nuclear shuttling of p57kip2 led to decreased CNPase- but elevated GFAP expression levels, this indicates heterogenic oligodendroglial mechanisms occurring between OPCs and aNSCs. We also show for the first time that dominant pro-oligodendroglial factors derived from human fetal MSCs can instruct human induced pluripotent stem cell-derived NSCs to differentiate into O4 positive oligodendrocytes.

Effect of Subcellular Translocation of Protein Disulfide Isomerase on Tetrachlorobenzoquinone-Induced Signaling Shift from Endoplasmic Reticulum Stress to Apoptosis.

Our previous studies illustrated tetrachlorobenzoquinone (TCBQ)-caused toxicities in neuron-like cells which imply its association with neurodegenerative disorders. Although it is known that TCBQ induces oxidative damage that in turn results in endoplasmic reticulum (ER) stress and apoptosis, it is unclear how TCBQ triggers the signaling switch from pro-survival (to restore cellular homeostasis) to pro-death (trigger apoptosis). Protein disulfide isomerase family proteins (PDIs) regulate the progress of various neurodegenerative disorders, including Parkinson's disease and Alzheimer's disease. We tested the hypothesis that subcellular translocation of PDIs implicates the survival/death signaling switch by inducing mitochondrial outer membrane permeabilization (MOMP). The rat pheochromocytoma PC12 cells were exposed to TCBQ, and the concentration-dependent ER stress was observed upon TCBQ treatment, as indicated by the increase in inositol-requiring kinase/endonuclease 1α (IRE1α) phosphorylation, C/EBP homologous protein (CHOP) expression, X-box-binding protein 1 (XBP1) splicing, and caspase 12 activation. Interestingly, pharmacological (or siRNA) abrogation of PDIA1/PDIA3 aggravated the loss of cell viability induced by the relatively low concentration (10 μM) of TCBQ. However, inhibition of PDIA1/PDIA3 rescued the high concentration (20 μM) of TCBQ-induced cell death. Further mechanistic study illustrated that PDIs initially acted to restore cellular homeostasis to pro-survival but that the constant ER stress promoted the signaling switch to pro-apoptotis by the release of PDIA1/PDIA3 from the ER lumen to induce Bak-dependent MOMP. Our findings suggested that subcellular translocation of PDIs determined the "life or death" fate of PC12 cells to TCBQ-induced oxidative insult.

Phospholipase Dδ negatively regulates plant thermotolerance by destabilizing cortical microtubules in Arabidopsis.

The pattern of cortical microtubule arrays plays an important role in plant growth and adaptation in response to hormonal and environmental changes. Cortical microtubules are connected with the plasma membrane (PM); however, how the membrane affects cortical microtubule organization is not well understood. Here, we showed that phospholipase Dδ (PLDδ) was associated with the PM and co-localized with microtubules in cells. In vitro analysis revealed that PLDδ bound to microtubules, resulting in microtubule disorganization. Site-specific mutations that decreased PLDδ enzymatic activity impaired its effects on destabilizing microtubule organization. Heat shock transiently activated PLDδ, without any change of its PM localization, triggering microtubule dissociation from PM and depolymerization and seedling death in Arabidopsis, but these effects were alleviated in pldδ knockout mutants. Complementation of pldδ with wild-type PLDδ, but not mutated PLDδ, restored the phenotypes of microtubules and seedling survival to those of wild-type Arabidopsis. Thus, we conclude that the PM-associated PLDδ negatively regulates plant thermotolerance via destabilizing cortical microtubules, in an activity-dependent manner, rather than its subcellular translocation.

ROS-dependent activation of RhoA/Rho-kinase in pulmonary artery: Role of Src-family kinases and ARHGEF1

The role of reactive oxygen species (ROS) in smooth muscle contraction is poorly understood. We hypothesised that G-protein coupled receptor (GPCR) activation and hypoxia induce Rho-kinase activity and contraction in rat intra-pulmonary artery (IPA) via stimulation of ROS production and subsequent Src-family kinase (SrcFK) activation.The T-type prostanoid receptor agonist U46619 induced ROS production in pulmonary artery smooth muscle cells (PASMC). U46619 also induced c-Src cysteine oxidation, SrcFK auto-phosphorylation, MYPT-1 and MLC20 phosphorylation and contraction in IPA, and all these responses were inhibited by antioxidants (ebselen, Tempol). Contraction and SrcFK/MYPT-1/MLC20 phosphorylations were also inhibited by combined superoxide dismutase and catalase, or by the SrcFK antagonist PP2, while contraction and MYPT-1/MLC20 phosphorylations were inhibited by the Rho guanine nucleotide exchange factor (RhoGEF) inhibitor Y16. H2O2 and the superoxide-generating quinoledione LY83583 both induced c-Src oxidation, SrcFK auto-phosphorylation and contraction in IPA. LY83583 and H2O2-induced contractions were inhibited by PP2, while LY83583-induced contraction was also inhibited by antioxidants and Y16. SrcFK auto-phosphorylation and MYPT-1/MLC20 phosphorylation was also induced by hypoxia in IPA and this was blocked by mitochondrial inhibitors rotenone and myxothiazol. In live PASMC, sub-cellular translocation of RhoA and the RhoGEF ARHGEF1 was triggered by both U46619 and LY83583 and this translocation was blocked by antioxidants and PP2. RhoA translocation was also inhibited by an ARHGEF1 siRNA. U46619 enhanced ROS-dependent co-immunoprecipitation of ARHGEF1 with c-Src.Our results demonstrate a link between GPCR-induced cytosolic ROS or hypoxia-induced mitochondrial ROS and SrcFK activity, Rho-kinase activity and contraction. ROS and SrcFK activate RhoA via ARHGEF1.

Amylin Enhances Amyloid-β Peptide Brain to Blood Efflux Across the Blood-Brain Barrier.

Findings from Alzheimer's disease (AD) mouse models showed that amylin treatment improved AD pathology and enhanced amyloid-β (Aβ) brain to blood clearance; however, the mechanism was not investigated. Using the Tg2576 AD mouse model, a single intraperitoneal injection of amylin significantly increased Aβ serum levels, and the effect was abolished by AC253, an amylin receptor antagonist, suggesting that amylin effect could be mediated by its receptor. Subsequent mechanistic studies showed amylin enhanced Aβ transport across a cell-based model of the blood-brain barrier (BBB), an effect that was abolished when the amylin receptor was inhibited by two amylin antagonists and by siRNA knockdown of amylin receptor Ramp3. To explain this finding, amylin effect on Aβ transport proteins expressed at the BBB was evaluated. Findings indicated that cells treated with amylin induced LRP1 expression, a major receptor involved in brain Aβ efflux, in plasma membrane fraction, suggesting intracellular translocation of LRP1 from the cytoplasmic pool. Increased LRP1 in membrane fraction could explain, at least in part, the enhanced uptake and transport of Aβ across the BBB. Collectively, our findings indicated that amylin induced Aβ brain to blood clearance through amylin receptor by inducing LRP1 subcellular translocation to the plasma membrane of the BBB endothelium.

Abstract TP84: Comparative Analysis of Genetic and Pharmacological Inhibition of Sirt3 in Post Ischemic Injury

Background: Sirtuin3 (Sirt3), NAD+-dependent deacetylase, regulates several key proteins in both mitochondria and nucleus. The majority of early studies have shown neuroprotective effects of Sirt3 activation in various models of CNS injury. Recently, it was found that genetic loss of Sirt3 is beneficial in ischemia/reperfusion (I/R) injury. Therefore, this study was designed to explore the effects of both genetic and pharmacological inhibition of Sirt3 in a middle cerebral artery occlusion (MCAo) model of stroke. Methods: Focal cerebral ischemia was induced by transient right MCAo for 60min followed by 0, 6, 24 and 72 hrs of reperfusion. A 72hrs post ischemic injury time point was chosen to measure infarction in various treatment groups. The Sirt3 inhibitor AGK7 (sc- 204281 Santa cruz,) that selectively inhibits Sirt3 over Sirt1 and Sirt2, was given as single intraperitoneal injection (0.15, 0.5 and 1.5mg/kg) 3hrs after stroke onset. Activity or expression of Sirt3, was examined with Sirt3 activity kit or western blot using anti-Sirt3, anti-acetylated lysine antibodies. Results: Sirt3 knockout mice showed a significant reduction in hemispheric infarct volume compared to WT littermate controls (37.72±5.21 vs 52.8±6.76, p<0.05). In the pharmacological study, a dose of 0.5 mg/kg i.p of inhibitor showed significant reduction in Sirt3 activity and but had no neuroprotective effect. Furthermore, a much higher dose (1.5mg/kg i.p) did not show any additional inhibitory effect on sirt3 activity but unexpectedly increased infarct volume (51.8±6.87 vs. 62.56± 7.89, P<0.05) and hemorrhagic transformation. Expression studies showed no overall change in Sirt3 expression in whole cell lysates at 0, 6, 24 or 72 hrs after reperfusion; however the expression pattern and activity varied with time in different subcellular compartments. Summary and Conclusions: Changes in subcellular translocation and activity of Sirt3 after I/R stress suggests it important role in target protein deacetylation in stroke pathophysiology. Surprisingly, genetic deletion but not pharmacological inhibition led to neuroprotection, indicating the need to carefully examine target protein by both genetic and pharmacological approaches.

Translocation of an Intracellular Protein via Peptide-Directed Ligation.

Ligand-directed reactions allow chemical transformations at very low reactant concentrations and can thus provide access to efficient approaches for the post-translational modification of proteins. The development of these proximity-induced reactions is hampered by the number of appropriate ligands and the lack of design principles. Addressing these limitations, we report a proximity-induced labeling system which applies a moderate affinity peptide ligand. The design process was structure-guided and supported by molecular dynamics simulations. We show that selective protein labeling can be performed inside living cells enabling the subcellular translocation of a protein via ligand-directed chemistry for the first time.

Protein disulfide isomerases: Redox connections in and out of the endoplasmic reticulum

Protein disulfide isomerases are thiol oxidoreductase chaperones from thioredoxin superfamily. As redox folding catalysts from the endoplasmic reticulum (ER), their roles in ER-related redox homeostasis and signaling are well-studied. PDIA1 exerts thiol oxidation/reduction and isomerization, plus chaperone effects. Also, substantial evidence indicates that PDIs regulate thiol-disulfide switches in other cell locations such as cell surface and possibly cytosol. Subcellular PDI translocation routes remain unclear and seem Golgi-independent. The list of signaling and structural proteins reportedly regulated by PDIs keeps growing, via thiol switches involving oxidation, reduction and isomerization, S-(de)nytrosylation, (de)glutathyonylation and protein oligomerization. PDIA1 is required for agonist-triggered Nox NADPH oxidase activation and cell migration in vascular cells and macrophages, while PDIA1-dependent cytoskeletal regulation appears a converging pathway. Extracellularly, PDIs crucially regulate thiol redox signaling of thrombosis/platelet activation, e.g., integrins, and PDIA1 supports expansive caliber remodeling during injury repair via matrix/cytoskeletal organization. Some proteins display regulatory PDI-like motifs. PDI effects are orchestrated by expression levels or post-translational modifications. PDI is redox-sensitive, although probably not a mass-effect redox sensor due to kinetic constraints. Rather, the “all-in-one” organization of its peculiar redox/chaperone properties likely provide PDIs with precision and versatility in redox signaling, making them promising therapeutic targets.

Designed inhibitor for nuclear localization signal of polo-like kinase 1 induces mitotic arrest.

Polo-like kinase 1 (Plk1), a member of polo-like kinase family, regulates multiple essential steps of the cell cycle progression. Plk1 is overexpressed in multiple cancer cell lines and considered to be a prime anticancer target. Plk1 accumulates in the nucleus during S and G2 phases by its bipartite nuclear localization signal (NLS) sequence, which is crucial for Plk1 regulation during normal cell cycle progression. Here, through combined computational and experimental studies, we identified compound D110, which inhibits Plk1 kinase activity with an IC50 of 85nm and blocks the nuclear localization of Plk1 during S and G2 phases. D110-treated cancer cells were arrested at mitosis with monopolar spindle, indicating the inhibition of the Plk1 kinase activity in cell. As D110 interacts with both the ATP site and the NLS in Plk1, it demonstrates good selectivity toward Plk2 and Plk3. The strategy of simultaneously inhibiting kinase activity and its subcellular translocations offers a novel approach for selective kinase inhibitor design.

MiR-222 promotes drug-resistance of breast cancer cells to adriamycin via modulation of PTEN/Akt/FOXO1 pathway

Background and purposeAcquisition of resistance to adriamycin (ADR) is one of the most important clinical obstacles in the treatment of breast cancer, but the molecular mechanisms underlying sensitivity to ADR remain elusive. In our previous study, through miRNA microarray and experiments, we have emphasized that miR-222 could promote the ADR-resistance in breast cancer cells. The aim of this study was to explore the possible mechanism by which miR-222 affects sensitivity to ADR. MethodsThrough pathway enrichment analyses for miR-222, we found that PTEN/Akt/FOXO1 signaling pathway may be of importance. RT-qPCR analyses and western blot assays confirmed the relationship between miR-222 expression and target genes. Immunofluorescence further visually displayed the location of FOXO1. When blocking PTEN/Akt/FOXO1 signaling pathway, we demonstrated the effects of miR-222-mediated ADR resistance by MTT and apoptosis assays. ResultsRT-qPCR and Western blot results showed that miR-222 expression was negatively correlated with FOXO1 expression. In addition, the subcellular translocation of FOXO1 due to the altered expression of miR-222 was observed from immunofluorescence. Moreover, upregulation of miR-222 expression in MCF-7/S cells is associated with decreased PTEN expression levels and increased phospho-Akt (p-Akt) expression. Conversely in MCF-7/ADR cells, inhibition of miR-222 resulted in increased PTEN expression and decreased p-Akt expression. For further validation, results of the present study also demonstrated that PTEN/Akt/FOXO1 signaling was responsible for the ADR-resistance of breast cancer cells since LY294002, an inhibitor of Akt signaling, partially increased the sensitivity of MCF-7/S cells to ADR. More importantly, we postulated that high expression of miR-222 is closely related to poor overall survival by TCGA database validation. ConclusionsTaken together, these data elucidated that miR-222 mediated ADR-resistance of breast cancer cells partly through regulation of PTEN/Akt/FOXO1 signaling pathway and inhibition of miR-222 may improve the prognosis of breast cancer patients.

Activation of STING requires palmitoylation at the Golgi.

Stimulator of interferon genes (STING) is essential for the type I interferon response against DNA pathogens. In response to the presence of DNA and/or cyclic dinucleotides, STING translocates from the endoplasmic reticulum to perinuclear compartments. However, the role of this subcellular translocation remains poorly defined. Here we show that palmitoylation of STING at the Golgi is essential for activation of STING. Treatment with palmitoylation inhibitor 2-bromopalmitate (2-BP) suppresses palmitoylation of STING and abolishes the type I interferon response. Mutation of two membrane-proximal Cys residues (Cys88/91) suppresses palmitoylation, and this STING mutant cannot induce STING-dependent host defense genes. STING variants that constitutively induce the type I interferon response were found in patients with autoimmune diseases. The response elicited by these STING variants is effectively inhibited by 2-BP or an introduction of Cys88/91Ser mutation. Our results may lead to new treatments for cytosolic DNA-triggered autoinflammatory diseases.

Leptin receptor overlapping transcript (LepROT) gene participates in insulin pathway through FoxO

Leptin receptor overlapping transcript (LepROT) is co-transcribed with the leptin receptor (LepR). However, the function and mechanism of LepROT in insulin pathway is unclear. In this study, we report the function of LepROT in maintaining consistent FoxO transcription. LepROT is constitutively expressed during larval development. 20-Hydroxyecdysone, methoprene, and insulin have no effect on the transcription of LepROT. However, the knockdown of LepROT by dsRNA injection in larvae causes delay of the development of Helicoverpa armigera. Knockdown of LepROT results in the upregulation of FoxO and downregulation of PI3K. The knockdown of LepROT also results in the subcellular translocation of FoxO from cytoplasm to nuclei. By contrast, overexpression of LepROT in the HaEpi cell line inhibits FoxO expression. Results suggest that LepROT participates in insulin signaling.

IL-6 induced proliferation and cytotoxic activity of CD8(+) T cells is elevated by SUMO2 overexpression.

T cells play an important role in adaptive immune responses that destroy pathogens or infected cells. Therefore, regulation of T cell activity is important in various diseases, such as autoimmune diseases, hypersensitivity, and cancer. The conjugation of small ubiquitin-related modifier (SUMO) is a post-translational protein modification that regulates activity, stability, and subcellular translocation of target proteins. In this study, CD8(+) T cells overexpressing SUMO2 showed greater proliferation and cytotoxic activity against tumor cells in the presence of IL-6 than wild-type CD8(+) T cells in vitro. These CD8(+) T cell functions were suppressed during treatment with MEK1 or PI3K-specific inhibitors. Therefore, our findings suggest that IL-6-derived signaling pathways, including the MEK1 and PI3K pathways, are upregulated by SUMO2 overexpression. However, transgenic expression of SUMO2 in T cells did not modulate Th1/2 balance. Collectively, our results showed that SUMO2-Tg promotes cytotoxic activity against tumor cells by increasing the proliferation and cytotoxicity of CD8(+) T cells.

The Exon Junction Complex proteins are non‐AMP kinase dependent sensors of energetic stress and regulate contractility and sarcomere structure in cardiac myocytes

The heart is known to undergo significant alterations in gene expression during stress and sometimes this adaptation can lead to heart failure. The mechanism by which cells select specific mRNAs for translation is not fully understood, but the Exon Junction Complex (EJC) plays a major role in this process in eukaryotes. The EJC selects the mRNA isoforms to be exported to the cytoplasm and determines whether they are then translated into protein. In this study we hypothesised that the EJC is involved in the regulation of gene expression during the stress response in cardiac myocytes. Using cultured rat neonatal myocytes and subcellular fractionation we examined the cellular distribution of two major components of the EJC in response to metabolic stress. In cardiac myocytes we found that there was a significant relocalisation of eIF4A3 and mago from the nucleus to cytoplasm following 18 hours of hypoxia. To examine the effect of metabolic stress on the EJC in more detail we treated cardiac myocytes with 50mM NaN3 for 4 hours to mimic the metabolic stress induced by hypoxia. Following NaN3 treatment there was a significant relocalisation of eIF4A3 and mago to the cytoplasm and this was associated with the formation of cytoplasmic stress granules. However, immunocytochemical staining with the stress granule marker PABP1 showed that cytoplasmic mago did not colocalise with stress granules. To examine whether the effects of metabolic stress on the EJC proteins was dependent on the metabolic sensor AMP kinase (AMPK), we treated myocytes with 1μM dorsomorphin in combination with NaN3. Dorsomorphin augmented the translocation of mago and eIF4A3 from the nucleus to the cytoplasm. This indicates that the EJC proteins respond to metabolic stress independently of AMPK activity. Moreover, the inhibition of AMPK was associated with increased metabolic cellular stress resulting in the augmented subcellular translocation of EJC proteins. Constructs of eIF4A3 tagged with green fluorescence protein on the N terminus resulted in a predominantly cytosolic protein distribution that did not relocalise in response to NaN3 treatment. This suggests that the N‐terminus of eIF4A3 is necessary for subcellular localisation. Finally, to determine the function of eIF4A3 in cardiac myocytes we knocked down the protein with siRNA. Protein knockdown of eIF4A3 resulted in cessation of cell contractility 96 hours post treatment. There was also a significant reduction in the number of intact sarcomeres suggesting that the contractile filaments were degrading in response to reduced eIF4A3. Taken together, these data suggest that eIF4A3 and other EJC members play an important role in the myocyte stress response, cell contractility and morphology.Support or Funding InformationThis work was supported by the British Heart Foundation project grant PG/10/64/28520 and PG/10/97/28666

Definitive localization of intracellular proteins: Novel approach using CRISPR-Cas9 genome editing, with glucose 6-phosphate dehydrogenase as a model

Studies to determine subcellular localization and translocation of proteins are important because subcellular localization of proteins affects every aspect of cellular function. Such studies frequently utilize mutagenesis to alter amino acid sequences hypothesized to constitute subcellular localization signals. These studies often utilize fluorescent protein tags to facilitate live cell imaging. These methods are excellent for studies of monomeric proteins, but for multimeric proteins, they are unable to rule out artifacts from native protein subunits already present in the cells. That is, native monomers might direct the localization of fluorescent proteins with their localization signals obliterated. We have developed a method for ruling out such artifacts, and we use glucose 6-phosphate dehydrogenase (G6PD) as a model to demonstrate the method's utility. Because G6PD is capable of homodimerization, we employed a novel approach to remove interference from native G6PD. We produced a G6PD knockout somatic (hepatic) cell line using CRISPR-Cas9 mediated genome engineering. Transfection of G6PD knockout cells with G6PD fluorescent mutant proteins demonstrated that the major subcellular localization sequences of G6PD are within the N-terminal portion of the protein. This approach sets a new gold standard for similar studies of subcellular localization signals in all homodimerization-capable proteins.

Heterogeneous nuclear ribonucleoprotein A1 post-transcriptionally regulates Drp1 expression in neuroblastoma cells

Excessive mitochondrial fission is associated with the pathogenesis of neurodegenerative diseases. Dynamin-related protein 1 (Drp1) possesses specific fission activity in the mitochondria and peroxisomes. Various post-translational modifications of Drp1 are known to modulate complex mitochondrial dynamics. However, the post-transcriptional regulation of Drp1 remains poorly understood. Here, we show that the heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1) regulates Drp1 expression at the post-transcriptional level. hnRNP A1 directly interacts with Drp1 mRNA at its 3′UTR region, and enhances translation potential without affecting mRNA stability. Down-regulation of hnRNP A1 induces mitochondrial elongation by reducing Drp1 expression. Moreover, depletion of hnRNP A1 suppresses 3-NP-mediated mitochondrial fission and dysfunction. In contrast, over-expression of hnRNP A1 promotes mitochondrial fragmentation by increasing Drp1 expression. Additionally, hnRNP A1 significantly exacerbates 3-NP-induced mitochondrial dysfunction and cell death in neuroblastoma cells. Interestingly, treatment with 3-NP induces subcellular translocation of hnRNP A1 from the nucleus to the cytoplasm, which accelerates the increase in Drp1 expression in hnRNP A1 over-expressing cells. Collectively, our findings suggest that hnRNP A1 controls mitochondrial dynamics by post-transcriptional regulation of Drp1.

Contra-directional Coupling of Nur77 and Nurr1 in Neurodegeneration: A Novel Mechanism for Memantine-Induced Anti-inflammation and Anti-mitochondrial Impairment.

Recent evidence suggests that nerve growth factor IB (Nur77) and nuclear receptor related1 (Nurr1) are differentially involved in dopaminergic neurodegeneration. Since memantine has shown clinically relevant efficacy in Parkinson's disease (PD) and displayed a potent protective effect on dopaminergic neurons in experimental PD models, we asked if it exerts its neuroprotection by regulating Nur77 and Nurr1 signaling. We adopted a well-established in vitro PD model, 6-hydroxydopamine (OHDA)-lesioned PC12 cells, to test our hypothesis. Different concentrations of memantine were incubated with 6-OHDA-lesioned PC12 cells, and Nur77/Nurr1 and their related signaling molecules were examined by Western blot and immunocytochemistry. Nur77-deficient PC12 cells were used to verify the influences of Nur77 on neurodegeneration and memantine-mediated neuroprotection. We found that memantine reversed Nur77 upregulation and restored Nurr1 downregulation in 6-OHDA-lesioned PC12 cells. 6-OHDA incubation caused Nur77 translocation from the nucleus to cytosol and induced co-localization of Cyt c/HSP60/Nur77 in the cytosol. Memantine strongly reduced the sub-cellular translocations of Nur77/Cyt c/HSP60 under 6-OHDA-induced oxidative condition. Knockdown of Nur77 enhanced the viability of PC12 cells exposed to 6-OHDA, while memantine-induced neuroprotection was much less in the cells with Nur77 knockdown than in those without it. We conclude that Nur77 plays a crucial role in modulating mitochondrial impairment and contributes to neurodegeneration under the experimental PD condition. Memantine effectively suppresses such Nur77-mediated neurodegeneration and promotes survival signaling through post-translational modification of Nurr1. Nur77 and Nurr1 present a contra-directionally coupling interaction in memantine-mediated neuroprotection.

Protein kinase Cδ regulates nuclear export of FOXO1 through phosphorylation of the chaperone 14-3-3ζ.

Forkhead box protein O1 (FOXO1) is a transcription factor essential for beta cell fate. Protein kinase B-dependent phosphorylation of FOXO1 at S256 (P-FOXO1) enables its binding to 14-3-3 dimers and nuclear export. Dephosphorylated FOXO1 enters nuclei and activates pro-apoptotic genes. Since our previous observations suggest that protein kinase C delta (PKCδ) induces nuclear accumulation of FOXO1, the underlying mechanism was examined. In human islets, genetically modified mice and INS-1E cells apoptosis was assessed by TUNEL staining. Subcellular translocation of proteins was examined by confocal microscopy and signalling pathways were analysed by western blotting and overlay assay. In PKCδ-overexpressing (PKCδ-tg) mouse islet cells and INS-1E cells FOXO1 accumulated in nuclei, surprisingly, as P-FOXO1. PKCδ-tg decelerated IGF-1-dependent stimulation of nuclear export, indicating that changes in export caused nuclear retention of P-FOXO1. Nuclear accumulation of P-FOXO1 was accompanied by increased phosphorylation of 14-3-3ζ at S58 and reduced dimerisation of 14-3-3ζ. Palmitic acid further augmented phosphorylation of 14-3-3ζ and triggered nuclear accumulation of FOXO1 in both INS-1E and human islet cells. Furthermore, the overexpression of a phosphomimicking mutant of 14-3-3ζ (S58D) enhanced nuclear FOXO1. In accordance with the nuclear accumulation of P-FOXO1, PKCδ overexpression alone did not increase apoptotic cell death. Additionally, insulin secretion and glucose homeostasis in PKCδ-overexpressing mice remained unaffected. These results suggest that PKCδ-mediated phosphorylation of 14-3-3ζ contributes to the nuclear retention of FOXO1, even when FOXO1 is phosphorylated as under non-stress conditions. P-FOXO1 does not induce pro-apoptotic genes, but may rather exert beneficial effects on beta cells.

Abstract 4082: PDLIM2 : A cytoskeleton to nuclear courier protein for the IGF-1, Wnt and TGF beta signalling pathways in Epithelial to Mesenchymal Transition

Abstract PDLIM2 is a PDZ-LIM domain protein that regulates the stability and activity of transcription factor families (including NFκB, STATs and beta catenin). PDLIM2 expression is repressed in certain cancers but it is also highly expressed in Triple Negative Basal Breast cancers that are characterized by poor survival. Suppression of PDLIM2 reverses the EMT phenotype, inhibits polarized cell migration, and disrupts formation of polarized epithelial acini in 3D cell cultures. PDLIM2 shuttles from the cytoskeleton to the nucleus, but what mediates this nuclear translocation or activity in transcription factor regulation is unknown. The aim of this study was to identify the mechanisms governing PDLIM2 subcellular localization and nuclear translocation. We found that IGF-1or TGF-β promotes PDLIM2 accumulation in the nucleus. Similarly, WNT3a stimulation enhances PDLIM2 accumulation in the nucleus while inhibition of WNT activity results in PDLIM2 stabilization in the cytoplasm. Cytoplasmic to nuclear translocation is associated with reduced phosphorylation on several serine residues in PDLIM2. The de-phosphorylation and subsequent nuclear translocation of PDLIM2 can be prevented by inhibiting the protein phosphatase PP1. In contrast, PDLIM2 phosphorylation can be enhanced by activation of protein kinase C, which is dependent on the presence of the focal adhesion scaffolding protein RACK1 in a complex with PDLIM2. Overall, the data indicate that PDLIM2 cytoplasmic to nuclear translocation in response to IGF-1, WNT or TGF beta signalling is mediated by serine phosphorylation and de-phosphorylation by cytoskeleton-associated kinases and phosphatases. Thus PDLIM2 acts as a “cytoskeleton to nucleus” courier protein for these signalling pathways to promote cancer cell migration and EMT. Citation Format: Milan Bustamante Garrido, Orla T. Cox, Ciara O'Flanagan, Deirdre A. Buckley, Patrick A. Kiely, Rosemary O'Connor. PDLIM2 : A cytoskeleton to nuclear courier protein for the IGF-1, Wnt and TGF beta signalling pathways in Epithelial to Mesenchymal Transition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4082. doi:10.1158/1538-7445.AM2015-4082

Abstract 1137: Mitochondrial targeting of EGFR-VIII in temozolomide resistant glioblastoma models

Abstract Epidermal growth factor receptor (EGFR) over-expression is the most frequent genetic alteration associated with glioblastoma and has emerged as a highly attractive therapeutic target based on its high frequency of gene amplification and mutation as well as its deregulated cell signaling cascades that drive GBM pathophysiology. The genetic aberration of wtEGFR is often accompanied by the overexpression of a mutant EGFR known as EGFR variant III (EGFRvIII), which is expressed in 30% of GBM tumors. Despite recent innovations, may it be neurosurgical techniques, chemotherapeutics or molecular targeted therapies only few treatments showed promise. Temozolomide (TMZ) is one such and has shown improved survival in GBM when administered with concomitant radiotherapy. However, acquired TMZ chemoresistance occurs in more than 90% of recurrent GBMs. To delineate the mechanisms in the context of TMZ resistance, we generated an aggressive TMZ resistant model by continual exposure of U373 cells constitutively expressing EGFRvIII (U373vIII) to 150uM TMZ for 6 months (U373vIIIR). Our preliminary data showed that dichloroacetic acid (DCA) induced apoptosis and demonstrated reduced cell survival in the context of TMZ resistance. DCA treatment also demonstrated reduced EGFRvIII mitochondrial translocation in U373vIIIR cells. Micro array studies conducted on U373vIII or U373vIIR and their subsequent treatment with DCA revealed that PDK1 is the sole target in TMZ resistant tumors expressing EGFRvIII. Since EGFRvIII expression displays an aggressive phenotype yet remains tumor specific, we propose studying DCA alone or in combination with dasatinib, an inhibitor of EGFR subcellular translocation, in U373vIII and U373vIII-TMZ-R cell lines. By more accurately depicting the status of GBM at the time of recurrence after standard of care chemotherapy treatment, the investigation of DCA will augment and possibly redefine our current understanding of resistance mechanisms and establish novel methods of circumventing this pervasive phenomena. Note: This abstract was not presented at the meeting. Citation Format: Kiran Kumar Velpula, Swapna Asuthkar, Sarah E. Martin, Justin D. Lathia, Andrew J. Tsung. Mitochondrial targeting of EGFR-VIII in temozolomide resistant glioblastoma models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1137. doi:10.1158/1538-7445.AM2015-1137