title: Depletion of luminal pyridine nucleotides in the endoplasmic reticulum activates autophagy with the involvement of mTOR pathway.
abstract: It has been recently shown that redox imbalance of luminal pyridine nucleotides in the endoplasmic reticulum (ER) together with oxidative stress results in the activation of autophagy. In the present study we demonstrated that decrease of luminal NADPH/NADP(+) ratio alone by metyrapone was sufficient to promote the mechanism of "self-eating" detected by the activation of LC3. Depletion of luminal NADPH had also significant effect on the key proteins of mTOR pathway, which got inactivated by dephosphorylation. These findings were also confirmed by silencing the proteins (glucose-6-phosphate transporter and hexose-6-phosphate dehydrogenase) responsible for NADPH generation in the ER lumen. However, silencing the key components and addition of metyrapone had different effects on downstream substrates 4EBP1 and p70S6K of mTOR. The applied treatments did not compromise the viability of the cells. Our data suggest that ER stress caused by luminal NADPH depletion activates a pro-survival autophagic mechanism firmly coupled to the activation of mTOR pathway.
authors.affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Tűzoltó utca 37-47, Budapest 1094, Hungary.
authors.forename: Orsolya
authors.initials: O
authors.lastname: Kapuy
authors.affiliation: Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Semmelweis University, Tűzoltó utca 37-47, Budapest 1094, Hungary.
authors.forename: Gábor
authors.initials: G
authors.lastname: Bánhegyi
mesh_terms: D017920:Antiporters / Q000378:metabolism; D001343:Autophagy / Q000502:physiology*; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D009711:Nucleotides / Q000378:metabolism*; D011725:Pyridines / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D017920:Antiporters; D009004:Monosaccharide Transport Proteins; D009711:Nucleotides; D011725:Pyridines; C503531:SLC37A4 protein, human; D009249:NADP; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases