title: Lysosomal turnover of GABARAP-phospholipid conjugate is activated during differentiation of C2C12 cells to myotubes without inactivation of the mTor kinase-signaling pathway.
abstract: Although conjugation of overexpressed GABARP to phospholipid has been reported during starvation-induced autophagy, it is unclear whether endogenous GABARAP-phospholipid conjugation is also activated under starvation conditions. We observed little accumulation of GABARAP-phospholipid conjugate (GABARAP-PL) in mouse liver and kidney under starvation conditions, whereas endogenous LC3-phospholipid conjugate (LC3-II) accumulated. A small amount of endogenous GABARAP-PL was observed in the heart, independent of starvation. In rapamycin-treated HEK293 cells, there was little accumulation of endogenous GABARAP-PL, even in the presence of lysosomal protease-inhibitors, whereas there was significant accumulation of endogenous LC3-II, together with inactivation of the mTor kinase-signaling pathway. In HeLa and C2C12 cells, GABARAP-PL accumulation in the presence of lysosomal protease inhibitors was independent of starvation-induced autophagy, whereas LC3-II accumulation was significant during starvation-induced autophagy. Interestingly, we observed activation of lysosomal turnover of GABARAP-PL during the differentiation of C2C12 cells to myotubes, along with increased lysosomal turnover of LC3-II. Under these conditions, S6 ribosomal protein was still phosphorylated, suggesting that the mTor kinase-signaling pathway is active during the differentiation of C2C12 cells to myotubes, in contrast to starvation-induced autophagy. These results indicated that lysosomal turnover of GABARAP-PL was activated during the differentiation of C2C12 cells to myotubes without inactivation of the mTor kinase-signaling pathway, whereas little lysosomal turnover of GABARAP-PL was activated during starvation-induced autophagy.
authors.affiliation: Department of Biochemistry, Juntendo University School of Medicine, Tokyo, Japan.
authors.forename: Isei
authors.initials: I
authors.lastname: Tanida
authors.forename: Mika
authors.initials: M
authors.lastname: Wakabayashi
authors.forename: Takashi
authors.initials: T
authors.lastname: Kanematsu
authors.forename: Naoko
authors.initials: N
authors.lastname: Minematsu-Ikeguchi
authors.forename: Yu-shin
authors.initials: YS
authors.lastname: Sou
authors.forename: Masato
authors.initials: M
authors.lastname: Hirata
authors.forename: Takashi
authors.initials: T
authors.lastname: Ueno
authors.forename: Eiki
authors.initials: E
authors.lastname: Kominami
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000378:metabolism; D051017:Apoptosis Regulatory Proteins; D001343:Autophagy; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008247:Lysosomes / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D010743:Phospholipids / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D020123:Sirolimus / Q000378:metabolism; D013217:Starvation; D058570:TOR Serine-Threonine Kinases; D014018:Tissue Distribution
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D051017:Apoptosis Regulatory Proteins; D003598:Cytoskeletal Proteins; C116741:GABARAP protein, human; C480861:GABARAP protein, mouse; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D010743:Phospholipids; D011993:Recombinant Fusion Proteins; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus