Altered redox state of luminal pyridine nucleotides facilitates the sensitivity towards oxidative injury and leads to endoplasmic reticulum stress dependent autophagy in HepG2 cells.
Maintenance of the reduced state of luminal pyridine nucleotides in the endoplasmic reticulum - an important pro-survival factor in the cell - is ensured by the concerted action of glucose-6-phosphate transporter and hexose-6-phosphate dehydrogenase. The mechanism by which the redox imbalance leads to cell death was investigated in HepG2 cells. The chemical inhibition of the glucose-6-phosphate transporter, the silencing of hexose-6-phosphate dehydrogenase and/or the glucose-6-phosphate transporter, or the oxidation of luminal NADPH by themselves did not cause a significant loss of cell viability. However, these treatments caused ER calcium store depletion. If these treatments were supplemented with the administration of a subliminal dose of the oxidizing agent menadione, endoplasmic reticulum vacuolization and a loss of viability were observed. Combined treatments resulted in the activation of ATF6 and procaspase-4, and in the induction of Grp78 and CHOP. In spite of the presence of UPR markers and proapoptotic signaling the effector caspases - caspase-3 and caspase-7 - were not active. On the other hand, an elevation of the autophagy marker LC3B was observed. Immunohistochemistry revealed a punctuated distribution of LC3B II, coinciding with the vacuolization of the endoplasmic reticulum. The results suggest that altered redox state of endoplasmic reticulum luminal pyridine nucleotides sensitizes the cell to autophagy.
Száraz
Péter
P
Dipartimento di Fisiopatologia, Medicina Sperimentale e Sanità Pubblica, Università di Siena, Via Aldo Moro, 53100 Siena, Italy.
Bánhegyi
Gábor
G
Benedetti
Angelo
A
D017920:Antiporters / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects; D015415:Biomarkers / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002237:Carbohydrate Dehydrogenases / Q000378:metabolism; D053471:Caspases, Initiator / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000473:pathology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation / Q000187:drug effects; D020868:Gene Silencing; D056945:Hep G2 Cells; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009249:NADP / Q000172:deficiency; D009711:Nucleotides / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects; D011725:Pyridines / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000378:metabolism; D024483:Vitamin K 3 / Q000494:pharmacology
D017920:Antiporters; D015415:Biomarkers; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D009004:Monosaccharide Transport Proteins; D009711:Nucleotides; D011725:Pyridines; D013438:Sulfhydryl Compounds; C111261:glucose 6-phosphate(transporter); D009249:NADP; D024483:Vitamin K 3; D002237:Carbohydrate Dehydrogenases; C020552:galactose-6-phosphate dehydrogenase; C093516:CASP4 protein, human; D053471:Caspases, Initiator; C023666:pyridine; D002118:Calcium