15 research outputs found

    The marine n-3 PUFA DHA evokes cytoprotection against oxidative stress and protein misfolding by inducing autophagy and NFE2L2 in human retinal pigment epithelial cells

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    <p>Accumulation and aggregation of misfolded proteins is a hallmark of several diseases collectively known as proteinopathies. Autophagy has a cytoprotective role in diseases associated with protein aggregates. Age-related macular degeneration (AMD) is the most common neurodegenerative eye disease that evokes blindness in elderly. AMD is characterized by degeneration of retinal pigment epithelial (RPE) cells and leads to loss of photoreceptor cells and central vision. The initial phase associates with accumulation of intracellular lipofuscin and extracellular deposits called drusen. Epidemiological studies have suggested an inverse correlation between dietary intake of marine n-3 polyunsaturated fatty acids (PUFAs) and the risk of developing neurodegenerative diseases, including AMD. However, the disease-preventive mechanism(s) mobilized by n-3 PUFAs is not completely understood. In human retinal pigment epithelial cells we find that physiologically relevant doses of the n-3 PUFA docosahexaenoic acid (DHA) induce a transient increase in cellular reactive oxygen species (ROS) levels that activates the oxidative stress response regulator NFE2L2/NRF2 (nuclear factor, erythroid derived 2, like 2). Simultaneously, there is a transient increase in intracellular protein aggregates containing SQSTM1/p62 (sequestosome 1) and an increase in autophagy. Pretreatment with DHA rescues the cells from cell cycle arrest induced by misfolded proteins or oxidative stress. Cells with a downregulated oxidative stress response, or autophagy, respond with reduced cell growth and survival after DHA supplementation. These results suggest that DHA both induces endogenous antioxidants and mobilizes selective autophagy of misfolded proteins. Both mechanisms could be relevant to reduce the risk of developing aggregate-associate diseases such as AMD.</p

    SIK1 inhibits migration in AGS-G<sub>R</sub> cells via suppression of MMP-9.

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    <p><b>A–B:</b> AGS-G<sub>R</sub> cells (<b>A</b>) and MKN45 cells (<b>B</b>) were treated with gastrin, and phospho-LKB1 (Ser-428) protein levels determined by Western blot. The phospho-LKB1 bands from a representative experiment are shown. <b>C–D:</b> AGS-G<sub>R</sub> cells (<b>C</b>) and MKN45 (<b>D</b>) were treated with gastrin, and phospho-SIK1 (Thr-182) protein levels determined by Western blot. The phospho-SIK1 bands from a representative experiment are shown. <b>E:</b> AGS-G<sub>R</sub> cells transfected with siSIK1 or siCtr and real-time cell migration monitored (0–24 h). Results show one representative of three independent experiments (mean ±SD of three technical replicates). <b>F:</b> MMP-9 mRNA expression in cells transfected with pSIK1 and treated with gastrin. Results show one representative of three independent experiments, (mean ± SD).</p

    ICER represses the level of <i>SIK1</i> mRNA and protein.

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    <p><b>A:</b> AGS-G<sub>R</sub> cells were treated with gastrin and mRNA levels of ICER measured by qRT-PCR. Results shown are mean ± SEM of three independent biological experiments. <b>B:</b> AGS-G<sub>R</sub> cells were transfected with ICER I, ICER IIγ or control expression plasmids, treated with gastrin (1 h) and mRNA levels of SIK1 measured by qRT-PCR. Results show one representative of three independent experiments; mean ± SD of three technical replicates. <b>C:</b> AGS-G<sub>R</sub> cells were transfected with siRNAs, treated with gastrin and mRNA levels measured by qRT-PCR. Results show one representative of three independent experiments; mean ± SD of three technical replicates. <b>D:</b> SIK1 Western blot in cells transfected with siICER. A representative image is shown and quantified.</p

    Gastrin-induced activation of SIK1.

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    <p><b>A:</b> AR42J cells were treated with gastrin and mRNA levels measured by qRT-PCR. Mean expression level relative to untreated cells is shown. Results show one representative of three independent biological experiments; mean ± SD of three technical replicates. <b>B:</b> SIK1 Western blot of gastrin treated AR42J cells. A representative image is shown and quantified <b>C:</b> AGS-G<sub>R</sub> cells were treated with gastrin and mRNA levels measured by qRT-PCR. Mean ± SEM of three independent biological experiments is shown. <b>D:</b> SIK1 Western blot of gastrin treated AGS-G<sub>R</sub> cells. A representative image is shown and the SIK1 bands from two independent experiments were quantified; results shown are mean intensities ±SD. <b>E:</b> SIK1 Western blot of gastrin treated MKN45 cells. The SIK1 bands from a representative experiment were quantified. <b>F:</b> Intracellular localization of endogenous CRTC2 protein (Red; CRTC2, blue; Draq-5-stained DNA). G: Intracellular localization of SIK1 protein. AGS-G<sub>R</sub> cells transfected with pEGFP-SIK1.</p

    The role of SIK1 in gastrin responsive cells.

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    <p>Gastrin binds to the CCK2 receptor (CCK2R) and activates the LKB1–SIK1 signalling pathway in adenocarcinoma cells. SIK1 mediated phosphorylation of HDAC leads to cytosolic translocation and activation of transcription. In the gastric adenocarcinoma cell line AGS-G<sub>R</sub> ectopic SIK1 inhibits migration.</p

    APIM and PIP-box peptides have overlapping binding site on PCNA.

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    <p>(A) Protein sequence and structural model of PCNA (PDB entry 1vym) with M40 highlighted in red and the center loop (CL) in yellow (upper panel). Live cell (HeLa) confocal fluorescence images of CFP-PCNA wild type (WT) and CFP-PCNA M40 mutants. Bar, 5 µm (lower panel). (B) Normalized FRET (N<sub>FRET</sub>) measurements between WT and mutated CFP-PCNA M40/APIM-YFP (light grey diamonds, PCNA WT−/PCNA M40A−/PCNA M40N−/PCNA M40R−/PCNA M40S- APIM) and WT and mutated CFP-PCNA M40/PIP-YFP (dark grey diamonds, PCNA WT−/PCNA M40A−/PCNA M40N−/PCNA M40R/PCNA M40S- PIP). CFP/YFP (vectors only) was used as background control (open diamonds). Data is from three independent experiments (mean ± SEM, n = 72–214). P-values were calculated by the unpaired Student’s t-test.</p

    ATX-101 induces apoptosis in the MM cell line JJN-3.

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    <p>(A–C) Flow cytometric measurement of the apoptotic cell population by annexin V-Pacific Blue labeling. (A) JJN-3 cells treated with 6 µM ATX-101 and 0.5 µM melphalan alone or combined were incubated for 1, 2, and 3 days. Control cells were left unexposed. (B and C) JJN-3 cells treated with 6 and 10 µM ATX-101 were incubated for 1, 2, and 4 h. In addition to annexin V labeling, cells were stained with DRAQ5 for DNA profile. (C) The histograms show the cell cycle distribution of live (blue) and apoptotic (pink) cells after 1 h of ATX-101 treatments. (A–C) show data from representative experiments out of three. (D) Flow cytometric measurement of caspase 8, 9, and 3/7 activity by Fluorescent Labeled Inhibitor of Caspases (FLICA) assay. JJN-3 cells were left unexposed and exposed to 8 µM ATX-101 for 2 and 4 h before the FLICA probe was added for staining. The FLICA probe binds irreversible only to the activated caspase and labels apoptotic cells. Data is from four independent experiments for caspase 8 activity and three independent experiments for caspase 9 and 3/7 activity (mean ± SD, ** P < 0.01, Student’s t-test).</p

    NR4A2 suppresses gastrin-induced migration and invasion.

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    <p><b>A</b>: Real-time cell migration monitored (0-24 h) in AGS-G<sub>R</sub> cells transfected with siNR4A2 or siCtr, with or without gastrin treatment (10 nM). Results show one representative of three biological replicas; mean ±SD of three technical replicas. <b>B</b>: Invasion assay with AGS-G<sub>R</sub> cells transfected with pCMX-NR4A2 or pCMX (control) was performed in 24-well plates containing 8-µm pore Matrigel-coated inserts (with or without 0.3 nM gastrin). Cells invading the lower surface of the membrane were stained with Reastain Quick-Diff reagents and total numbers of cells in 5 fields per membrane were counted. The mean of three independent experiments is shown.</p

    Negative regulation of gastrin-induced NR4A2 expression.

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    <p><b>A</b>: AGS-G<sub>R</sub> cells transfected with NR4A2-luc and ICER expression plasmids or empty vector. Cells were treated with gastrin for 6 h prior to measurement of NR4A2 activity. Data shown represent mean ± SEM of five biological replicas (** p<0.03, * p = 0.06). <b>B</b>: AGS-G<sub>R</sub> cells transfected with NBRE-luc and ICER expression plasmid or empty vector and treated with gastrin for 4 h prior to measurement of NBRE activity. Data shown represent mean ± SEM of four biological replicas (** p<0.03). <b>C</b>: AGS-G<sub>R</sub> cells were transfected with pZfp36l1 expression plasmid or empty vector and treated with gastrin (5 nM) NR4A2 mRNA expression was measured by qRT-PCR. Data shown represent one of three biological replicas; mean ± SD of three technical replicas is shown. <b>D</b>: Cyclin L1 represents one of three control genes examined.</p

    ATX-101, a cell-penetrating APIM-peptide, targets PCNA.

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    <p>(A) Confocal fluorescence image of live HeLa cells 2 minutes after addition of fluorescently tagged ATX-101. Bar, 5 µm. (B) Cell growth measured by MTT assay of HeLa cells stably expressing YFP and APIM-(hABH2 <sub>1–7</sub> F4W)-YFP unexposed (♦ and×, respectively) and after continuous exposure to 0.5 µM cisplatin (▴ and •, respectively) (left panel) and parental HeLa cells unexposed (♦) and after continuous exposure to 8 µM ATX-101 (×), 0.5 µM cisplatin (▴), and combination of ATX-101 and cisplatin (•) (right panel). Data is from one representative experiment out of at least three. (C) Normalized FRET (N<sub>FRET</sub>) measurements in HeLa cells between CFP-PCNA and APIM-YFP without and in the presence of ATX-101. The cells were treated with 8 µM ATX-101 8 h after transient transfection and incubated for 16 h before the N<sub>FRET</sub> measurements. CFP/YFP (vectors only) was used as background control. Data is from three independent experiments (mean ± SEM, n = 36–40). P-value was calculated by the unpaired Student’s t-test. (D) Cell growth measured by MTT assay of HeLa cells unexposed (♦) and after continuous exposure to 8 µM ATX-A (—), 8 µM ATX-101 (×), 0.5 µM cisplatin (▴), and combination of ATX-A or ATX-101 and cisplatin (▪ and •, respectively). The confocal image shows fluorescently tagged ATX-A in HeLa cells as in (A). Bar, 5 µm. Data is from one representative experiment out of three.</p
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