title: The Unfolded Protein Response Plays a Predominant Homeostatic Role in Response to Mitochondrial Stress in Pancreatic Stellate Cells.
abstract: Activated pancreatic stellate cells (PaSC) are key participants in the stroma of pancreatic cancer, secreting extracellular matrix proteins and inflammatory mediators. Tumors are poorly vascularized, creating metabolic stress conditions in cancer and stromal cells that necessitate adaptive homeostatic cellular programs. Activation of autophagy and the endoplasmic reticulum unfolded protein response (UPR) have been described in hepatic stellate cells, but the role of these processes in PaSC responses to metabolic stress is unknown. We reported that the PI3K/mTOR pathway, which AMPK can regulate through multiple inputs, modulates PaSC activation and fibrogenic potential. Here, using primary and immortalized mouse PaSC, we assess the relative contributions of AMPK/mTOR signaling, autophagy and the UPR to cell fate responses during metabolic stress induced by mitochondrial dysfunction. The mitochondrial uncoupler rottlerin at low doses (0.5-2.5 μM) was added to cells cultured in 10% FBS complete media. Mitochondria rapidly depolarized, followed by altered mitochondrial dynamics and decreased cellular ATP levels. This mitochondrial dysfunction elicited rapid, sustained AMPK activation, mTOR pathway inhibition, and blockade of autophagic flux. Rottlerin treatment also induced rapid, sustained PERK/CHOP UPR signaling. Subsequently, high doses (>5 μM) induced loss of cell viability and cell death. Interestingly, AMPK knock-down using siRNA did not prevent rottlerin-induced mTOR inhibition, autophagy, or CHOP upregulation, suggesting that AMPK is dispensable for these responses. Moreover, CHOP genetic deletion, but not AMPK knock-down, prevented rottlerin-induced apoptosis and supported cell survival, suggesting that UPR signaling is a major modulator of cell fate in PaSC during metabolic stress. Further, short-term rottlerin treatment reduced both PaSC fibrogenic potential and IL-6 mRNA expression. In contrast, expression levels of the angiogenic factors HGF and VEGFα were unaffected, and the immune modulator IL-4 was markedly upregulated. These data imply that metabolic stress-induced PaSC reprogramming differentially modulates neighboring cells in the tumor microenvironment.
authors: Pancreatic Research Group, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, United States of America.
authors: Hsin-Yuan
authors: HY
authors: Su
authors: Pancreatic Research Group, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, United States of America.|Department of Medicine, David Geffen School of Medicine, UCLA/VA Greater Los Angeles Health Sciences Center, Los Angeles, California, United States of America.
authors: Richard T
authors: RT
authors: Waldron
authors: Pancreatic Research Group, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, United States of America.
authors: Raymond
authors: R
authors: Gong
authors: Department of Medicine, David Geffen School of Medicine, UCLA/VA Greater Los Angeles Health Sciences Center, Los Angeles, California, United States of America.|Metabolic Photonics Laboratory, Departments of Surgery and Biomedical Sciences, Cedars-Sinai Medical center, Los Angeles, California, United States of America.
authors: V Krishnan
authors: VK
authors: Ramanujan
authors: Pancreatic Research Group, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, United States of America.|Department of Medicine, David Geffen School of Medicine, UCLA/VA Greater Los Angeles Health Sciences Center, Los Angeles, California, United States of America.
authors: Stephen J
authors: SJ
authors: Pandol
authors: Pancreatic Research Group, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, California, United States of America.|Department of Medicine, David Geffen School of Medicine, UCLA/VA Greater Los Angeles Health Sciences Center, Los Angeles, California, United States of America.
authors: Aurelia
authors: A
authors: Lugea
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001343:Autophagy; D004789:Enzyme Activation / Q000235:genetics; D015847:Interleukin-4 / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism* / Q000473:pathology; D010190:Pancreatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D059016:Tumor Microenvironment; D056811:Unfolded Protein Response; D015854:Up-Regulation / Q000235:genetics; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism
chemical_list: D055372:AMP-Activated Protein Kinases; D015847:Interleukin-4; D009363:Neoplasm Proteins; D019869:Phosphatidylinositol 3-Kinases; D058570:TOR Serine-Threonine Kinases; D051742:Transcription Factor CHOP; D019892:eIF-2 Kinase; C497250:Ddit3 protein, mouse; C546843:mTOR protein, mouse