title: Activation of sphingosine kinase 2 by endoplasmic reticulum stress ameliorates hepatic steatosis and insulin resistance in mice.
abstract: The endoplasmic reticulum (ER) is the principal organelle in the cell for protein folding and trafficking, lipid synthesis, and cellular calcium homeostasis. Perturbation of ER function results in activation of the unfolded protein response (UPR) and is implicated in abnormal lipid biosynthesis and development of insulin resistance. In this study, we investigated whether transcription of sphingosine kinase (Sphk)2 is regulated by ER stress-mediated UPR pathways. Sphk2, a major isotype of sphingosine kinase in the liver, was transcriptionally up-regulated by tunicamycin and lipopolysaccharides. Transcriptional regulation of Sphk2 was mediated by activation of activating transcription factor (ATF)4 as demonstrated by promoter assays, immunoblotting, and small interfering RNA analyses. In primary hepatocytes, adenoviral Sphk2 expression elevated cellular sphingosine 1 phosphate (S1P) and activated protein kinase B phosphorylation, with no alteration of insulin receptor substrate phosphorylation. Hepatic overexpression of Sphk2 in mice fed a high-fat diet (HFD) led to elevated S1P and reduced ceramide, sphingomyelin, and glucosylceramide in plasma and liver. Hepatic accumulation of lipid droplets by HFD feeding was reduced by Sphk2-mediated up-regulation of fatty acid (FA) oxidizing genes and increased FA oxidation in liver. In addition, glucose intolerance and insulin resistance were ameliorated by improved hepatic insulin signaling through Sphk2 up-regulation.
  
  
  CONCLUSIONS
  Sphk2 is transcriptionally up-regulated by acute ER stress through activation of ATF4 and improves perturbed hepatic glucose and FA metabolism.
authors: Department of Life Science, Gachon University, Sungnam, Korea.
authors: Su-Yeon
authors: SY
authors: Lee
authors: Department of Life Science, Gachon University, Sungnam, Korea.
authors: In-Kyung
authors: IK
authors: Hong
authors: Department of Life Science, Gachon University, Sungnam, Korea.
authors: Bo-Rahm
authors: BR
authors: Kim
authors: Department of Food Science and Technology, Sejong University, Seoul, Korea.
authors: Soon-Mi
authors: SM
authors: Shim
authors: Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea.
authors: Jae
authors: J
authors: Sung Lee
authors: Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea.
authors: Hui-Young
authors: HY
authors: Lee
authors: Lee Gil Ya Cancer and Diabetes Institute, Gachon University, Incheon, Korea.
authors: Cheol
authors: C
authors: Soo Choi
authors: Department of Physiology, Functional Genomics Institute, School of Medicine, Konkuk University, Seoul, Korea.
authors: Bo-Kyung
authors: BK
authors: Kim
authors: Department of Life Science, Gachon University, Sungnam, Korea.
authors: Tae-Sik
authors: TS
authors: Park
mesh_terms: D051701:Activating Transcription Factor 4 / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D059305:Diet, High-Fat; D059865:Endoplasmic Reticulum Stress; D005227:Fatty Acids / Q000378:metabolism; D005234:Fatty Liver / Q000378:metabolism*; D022781:Hepatocytes / Q000201:enzymology; D007333:Insulin Resistance; D066292:Lipid Droplets / Q000378:metabolism; D008055:Lipids / Q000097:blood; D008099:Liver / Q000201:enzymology*; D008246:Lysophospholipids / Q000378:metabolism; D008297:Male; D008810:Mice, Inbred C57BL; D010084:Oxidation-Reduction; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D056811:Unfolded Protein Response; D015854:Up-Regulation; D000099157:Sphingosine Kinase
chemical_list: D051701:Activating Transcription Factor 4; D005227:Fatty Acids; D008055:Lipids; D008246:Lysophospholipids; D017853:Phosphotransferases (Alcohol Group Acceptor); D051057:Proto-Oncogene Proteins c-akt; D013110:Sphingosine; D000099157:Sphingosine Kinase; C081452:Atf4 protein, mouse; C060506:sphingosine 1-phosphate