title: Inhibition of palmitate-induced GADD34 expression augments apoptosis in mouse insulinoma cells (MIN6).
abstract: Saturated fatty acids like palmitate induce endoplasmic reticulum (ER) stress in pancreatic beta-cells, an event linked to apoptotic loss of β-cells in type 2 diabetes. Sustained activation of the ER stress response leads to expression of growth arrest and DNA damage-inducible protein 34 (GADD34), a regulatory subunit of protein phosphatase 1. In the present study, we have used small interfering RNA in order to knockdown GADD34 expression in insulin-producing MIN6 cells prior to induction of ER stress by palmitate and evaluated its consequences on RNA-activated protein kinase-like ER-localized eIF2alpha kinase (PERK) signalling and apoptosis. Salubrinal, a specific inhibitor of eukaryotic initiation factor 2α (eIF2α) dephosphorylation, was used as a comparison. Salubrinal treatment augmented palmitate-induced ER stress and increased GADD34 levels. Both GADD34 knockdown and salubrinal treatment potentiated the cytotoxic effects of palmitate as evidenced by increased DNA fragmentation and activation of caspase 3, with the fundamental difference that the former did not involve enhanced levels of GADD34. The data from this study suggest that sustained activation of PERK signalling and eIF2α phosphorylation sensitizes insulin-producing MIN6 cells to lipoapoptosis independently of GADD34 expression levels.
authors.affiliation: Department of Clinical Science and Education, Södersjukhuset, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Liselotte
authors.initials: L
authors.lastname: Fransson
authors.forename: Ake
authors.initials: A
authors.lastname: Sjöholm
authors.forename: Henrik
authors.initials: H
authors.lastname: Ortsäter
mesh_terms: D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D053938:DNA Fragmentation / Q000187:drug effects; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D007340:Insulinoma / Q000378:metabolism / Q000473:pathology; D051379:Mice; D010168:Palmitates / Q000633:toxicity*; D010766:Phosphorylation / Q000187:drug effects; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: D051701:Activating Transcription Factor 4; D053148:Caspase 3; D015852:Eukaryotic Initiation Factor-2; D010168:Palmitates; D054645:Protein Phosphatase 1; D034741:RNA, Small Interfering; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C081452:Atf4 protein, mouse; C497250:Ddit3 protein, mouse; C513256:Ppp1r15a protein, mouse
keywords: GADD34; beta-cell; diabetes; endoplasmic reticulum stress; islet; palmitate; salubrinal