title: Loss of protein targeting to glycogen sensitizes human hepatocellular carcinoma cells towards glucose deprivation mediated oxidative stress and cell death.
abstract: Protein targeting to glycogen (PTG) is a ubiquitously expressed scaffolding protein that critically regulates glycogen levels in many tissues, including the liver, muscle and brain. However, its importance in transformed cells has yet to be explored in detail. Since recent studies have demonstrated an important role for glycogen metabolism in cancer cells, we decided to assess the effect of PTG levels on the ability of human hepatocellular carcinoma (HepG2) cells to respond to metabolic stress. Although PTG expression did not significantly affect the proliferation of HepG2 cells under normal culture conditions, we determined that PTG plays an important role during glucose deprivation. Overexpression of PTG protected cells from cell death in the absence of glucose, whereas knocking down PTG further promoted cytotoxicity, as measured by the release of lactate dehydrogenase (LDH) into the media. Additionally, we demonstrated that PTG attenuates glucose deprivation induced haeme oxygenase-1 (HO-1) expression, suggesting that PTG protects against glucose deprivation-induced oxidative stress. Indeed, treating cells with the antioxidant N-acetyl cysteine (NAC) rescued cells from cytotoxicity caused by glucose deprivation. Finally, we showed that loss of PTG resulted in enhanced autophagy. In control cells, glucose deprivation suppressed autophagy as determined by the increase in the levels of p62, an autophagy substrate. However, in knockdown cells, this suppression was relieved. Blockade of autophagy also attenuated cytotoxicity from glucose deprivation in PTG knockdown cells. Taken together, our findings identify a novel role for PTG in protecting hepatocellular carcinoma cells from metabolic stress, in part by regulating oxidative stress and autophagy.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A.
authors.forename: Rongqiang
authors.initials: R
authors.lastname: Yang
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A.
authors.forename: Mei
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A.
authors.forename: Amber Renee
authors.initials: AR
authors.lastname: Gustafson
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A. Gheens Center on Aging, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A.
authors.forename: Eugenia
authors.initials: E
authors.lastname: Wang
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A.
authors.forename: Marsha Paulette
authors.initials: MP
authors.lastname: Cole
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A.
authors.forename: Christine Elizabeth Schaner
authors.initials: CE
authors.lastname: Tooley
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Louisville School of Medicine, Louisville, KY 40202, U.S.A. alan.cheng@louisville.edu.
authors.forename: Alan
authors.initials: A
authors.lastname: Cheng
mesh_terms: D001343:Autophagy; D006528:Carcinoma, Hepatocellular / Q000378:metabolism / Q000473:pathology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D016923:Cell Death / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D055785:Gene Knockdown Techniques; D005947:Glucose / Q000378:metabolism*; D006003:Glycogen / Q000378:metabolism; D006004:Glycogen Debranching Enzyme System / Q000235:genetics / Q000378:metabolism; D051547:Heme Oxygenase-1 / Q000378:metabolism; D056945:Hep G2 Cells / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008113:Liver Neoplasms / Q000378:metabolism / Q000473:pathology; D018384:Oxidative Stress; D010749:Phosphoprotein Phosphatases / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D006004:Glycogen Debranching Enzyme System; D047908:Intracellular Signaling Peptides and Proteins; C491294:PPP1R3C protein, human; C087628:TCEAL1 protein, human; D014157:Transcription Factors; D006003:Glycogen; C496541:HMOX1 protein, human; D051547:Heme Oxygenase-1; C577876:GBE1 protein, human; D010749:Phosphoprotein Phosphatases; D005947:Glucose
keywords: PTG; glycogen; hepatocellular carcinoma; oxidative stress