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Inhibition of Stearoyl-CoA Desaturase 1 Expression Induces CHOP-Dependent Cell Death in Human Cancer Cells

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      Abstract

      BackgroundCancer cells present a sustained de novo fatty acid synthesis with an increase of saturated and monounsaturated fatty acid (MUFA) production. This change in fatty acid metabolism is associated with overexpression of stearoyl-CoA desaturase 1 (Scd1), which catalyses the transformation of saturated fatty acids into monounsaturated fatty acids (e.g., oleic acid). Several reports demonstrated that inhibition of Scd1 led to the blocking of proliferation and induction of apoptosis in cancer cells. Nevertheless, mechanisms of cell death activation remain to be better understood.Principal FindingsIn this study, we demonstrated that Scd1 extinction by siRNA triggered abolition of de novo MUFA synthesis in cancer and non-cancer cells. Scd1 inhibition-activated cell death was only observed in cancer cells with induction of caspase 3 activity and PARP-cleavage. Exogenous supplementation with oleic acid did not reverse the Scd1 ablation-mediated cell death. In addition, Scd1 depletion induced unfolded protein response (UPR) hallmarks such as Xbp1 mRNA splicing, phosphorylation of eIF2α and increase of CHOP expression. However, the chaperone GRP78 expression, another UPR hallmark, was not affected by Scd1 knockdown in these cancer cells indicating a peculiar UPR activation. Finally, we showed that CHOP induction participated to cell death activation by Scd1 extinction. Indeed, overexpression of dominant negative CHOP construct and extinction of CHOP partially restored viability in Scd1-depleted cancer cells.ConclusionThese results suggest that inhibition of de novo MUFA synthesis by Scd1 extinction could be a promising anti-cancer target by inducing cell death through UPR and CHOP activation.

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      Most cited references 63

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      Signal integration in the endoplasmic reticulum unfolded protein response.

      The endoplasmic reticulum (ER) responds to the accumulation of unfolded proteins in its lumen (ER stress) by activating intracellular signal transduction pathways - cumulatively called the unfolded protein response (UPR). Together, at least three mechanistically distinct arms of the UPR regulate the expression of numerous genes that function within the secretory pathway but also affect broad aspects of cell fate and the metabolism of proteins, amino acids and lipids. The arms of the UPR are integrated to provide a response that remodels the secretory apparatus and aligns cellular physiology to the demands imposed by ER stress.
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        Regulated translation initiation controls stress-induced gene expression in mammalian cells.

         H Zeng,  R Wek,  Isabel Novoa (2000)
        Protein kinases that phosphorylate the alpha subunit of eukaryotic initiation factor 2 (eIF2alpha) are activated in stressed cells and negatively regulate protein synthesis. Phenotypic analysis of targeted mutations in murine cells reveals a novel role for eIF2alpha kinases in regulating gene expression in the unfolded protein response (UPR) and in amino acid starved cells. When activated by their cognate upstream stress signals, the mammalian eIF2 kinases PERK and GCN2 repress translation of most mRNAs but selectively increase translation of Activating Transcription Factor 4 (ATF4), resulting in the induction of the downstream gene CHOP (GADD153). This is the first example of a mammalian signaling pathway homologous to the well studied yeast general control response in which eIF2alpha phosphorylation activates genes involved in amino acid biosynthesis. Mammalian cells thus utilize an ancient pathway to regulate gene expression in response to diverse stress signals.
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          XBP1 mRNA is induced by ATF6 and spliced by IRE1 in response to ER stress to produce a highly active transcription factor.

          In yeast, the transmembrane protein kinase/endoribonuclease Ire1p activated by endoplasmic reticulum stress cleaves HAC1 mRNA, leading to production of the transcription factor Hac1p that activates the unfolded protein response (UPR). In mammals, no Hac1p counterpart has yet been discovered despite the presence of Ire1p homologs in the endoplasmic reticulum. Instead, the transcription factor ATF6 specific to the mammalian UPR is regulated by intramembrane proteolysis. Here, we identified the transcription factor XBP1, a target of ATF6, as a mammalian substrate of such an unconventional mRNA splicing system and showed that only the spliced form of XBP1 can activate the UPR efficiently. Our results reveal features of the UPR conserved during evolution and clarify the relationship between IRE1- and ATF6-dependent pathways.
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            Author and article information

            Affiliations
            Université de Bourgogne, Centre de Recherche INSERM «Lipides, Nutrition, Cancer» UMR866, Dijon, France
            Texas A&M University, United States of America
            Author notes

            Conceived and designed the experiments: MMW ASP MN MR. Performed the experiments: MMW ASP LP CF MR. Analyzed the data: MMW ASP JB MN MR. Contributed reagents/materials/analysis tools: LP SB CF JB CT MR. Wrote the paper: MMW ASP LP MN MR.

            Contributors
            Role: Editor
            Journal
            PLoS One
            plos
            plosone
            PLoS ONE
            Public Library of Science (San Francisco, USA )
            1932-6203
            2010
            16 December 2010
            : 5
            : 12
            3002938
            21179554
            10-PONE-RA-21538R1
            10.1371/journal.pone.0014363
            (Editor)
            Minville-Walz et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
            Counts
            Pages: 13
            Categories
            Research Article
            Oncology
            Cell Biology/Cell Signaling
            Cell Biology/Cellular Death and Stress Responses

            Uncategorized

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