title: Integrated stress response is critical for gemcitabine resistance in pancreatic ductal adenocarcinoma.
abstract: Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with marked chemoresistance and a 5-year survival rate of 7%. The integrated stress response (ISR) is a cytoprotective pathway initiated in response to exposure to various environmental stimuli. We used pancreatic cancer cells (PCCs) that are highly resistant to gemcitabine (Gem) and an orthotopic mouse model to investigate the role of the ISR in Gem chemoresistance. Gem induced eIF2 phosphorylation and downstream transcription factors ATF4 and CHOP in PCCs, and these effects occurred in an eIF2α-S51 phosphorylation-dependent manner as determined using PANC-1 cells, and wild type and S51 mutant mouse embryo fibroblasts. Blocking the ISR pathway in PCCs with the ISR inhibitor ISRIB or siRNA-mediated depletion of ATF4 resulted in enhanced Gem-mediated apoptosis. Polyribosomal profiling revealed that Gem caused repression of global translation and this effect was reversed by ISRIB or by expressing GADD34 to facilitate eIF2 dephosphorylation. Moreover, Gem promoted preferential mRNA translation as determined in a TK-ATF4 5'UTR-Luciferase reporter assay, and this effect was also reversed by ISRIB. RNA-seq analysis revealed that Gem upregulated eIF2 and Nrf2 pathways, and that ISRIB significantly inhibited these pathways. Gem also induced the expression of the antiapoptotic factors Nupr1, BEX2, and Bcl2a1, whereas ISRIB reduced their expression. In an orthotopic tumor model using PANC-1 cells, ISRIB facilitated Gem-mediated increases in PARP cleavage, which occurred in conjunction with decreased tumor size. These findings indicate that Gem chemoresistance is enhanced by activating multiple ISR-dependent pathways, including eIF2, Nrf2, Nupr1, BEX2, and Bcl2A1. It is suggested that targeting the ISR pathway may be an efficient mechanism for enhancing therapeutic responsiveness to Gem in PDAC.
authors.affiliation: Departments of Medicine, Biochemistry and Molecular Biology, Indiana University School of Medicine, The Melvin and Bren Simon Cancer Center and The Center for Pancreatic Cancer Research, Indianapolis, IN, USA.
authors.forename: L R
authors.initials: LR
authors.lastname: Palam
authors.affiliation: Departments of Medicine, Biochemistry and Molecular Biology, Indiana University School of Medicine, The Melvin and Bren Simon Cancer Center and The Center for Pancreatic Cancer Research, Indianapolis, IN, USA.
authors.forename: J
authors.initials: J
authors.lastname: Gore
authors.affiliation: Departments of Medicine, Biochemistry and Molecular Biology, Indiana University School of Medicine, The Melvin and Bren Simon Cancer Center and The Center for Pancreatic Cancer Research, Indianapolis, IN, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Craven
authors.affiliation: Departments of Medicine, Biochemistry and Molecular Biology, Indiana University School of Medicine, The Melvin and Bren Simon Cancer Center and The Center for Pancreatic Cancer Research, Indianapolis, IN, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Wilson
authors.affiliation: Departments of Medicine, Biochemistry and Molecular Biology, Indiana University School of Medicine, The Melvin and Bren Simon Cancer Center and The Center for Pancreatic Cancer Research, Indianapolis, IN, USA.
authors.forename: M
authors.initials: M
authors.lastname: Korc
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D051701:Activating Transcription Factor 4 / Q000235:genetics / Q000378:metabolism; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D021441:Carcinoma, Pancreatic Ductal / Q000188:drug therapy* / Q000378:metabolism; D045744:Cell Line, Tumor; D003514:Cyclohexylamines / Q000494:pharmacology; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D015870:Gene Expression; D006801:Humans; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress; D010190:Pancreatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D014176:Protein Biosynthesis; D054645:Protein Phosphatase 1 / Q000378:metabolism; D015398:Signal Transduction; D059467:Transcriptome; D023041:Xenograft Model Antitumor Assays; D000093542:Gemcitabine
chemical_list: D000081:Acetamides; D051701:Activating Transcription Factor 4; D000964:Antimetabolites, Antineoplastic; D051792:Basic Helix-Loop-Helix Proteins; D003514:Cyclohexylamines; D003841:Deoxycytidine; D009363:Neoplasm Proteins; D054645:Protein Phosphatase 1; D000093542:Gemcitabine; C000599093:2-(4-chlorophenoxy)-N-(4-(2-(4-chlorophenoxy)acetamido)cyclohexyl)acetamide; C497109:ATF4 protein, human; C491643:NUPR1 protein, human; C087519:PPP1R15A protein, human