title: Suppressed translation and ULK1 degradation as potential mechanisms of autophagy limitation under prolonged starvation.
abstract: Macroautophagy/autophagy is a well-organized process of intracellular degradation, which is rapidly activated under starvation conditions. Recent data demonstrate a transcriptional upregulation of several autophagy genes as a mechanism that controls autophagy in response to starvation. Here we report that despite the significant upregulation of mRNA of the essential autophagy initiation gene ULK1, its protein level is rapidly reduced under starvation. Although both autophagic and proteasomal systems contribute to the degradation of ULK1, under prolonged nitrogen deprivation, its level was still reduced in ATG7 knockout cells, and only initially stabilized in cells treated with the lysosomal or proteasomal inhibitors. We demonstrate that under starvation, protein translation is rapidly diminished and, similar to treatments with the proteosynthesis inhibitors cycloheximide or anisomycin, is associated with a significant reduction of ULK1. Furthermore, it was found that inhibition of the mitochondrial respiratory complexes or the mitochondrial ATP synthase function that could also take place in the absence of substrates, promote upregulation of ULK1 mRNA and protein expression in an AMPK-dependent manner in U1810 lung cancer cells growing in complete culture medium. These inhibitors could also drastically increase the ULK1 protein in U1810 cells with knockout of ATG13, where the ULK1 expression is significantly diminished. However, such upregulation of ULK1 protein is negligible under starvation conditions, further signifying the contribution of translation and suggesting that transcriptional upregulation of ULK1 protein will be diminished under such conditions. Thus, we propose a model where inhibition of protein translation, together with the degradation systems, limit autophagy during starvation.
authors.affiliation: a Institute of Environmental Medicine , Division of Toxicology, Karolinska Institutet , Stockholm , Sweden.|b Department of Molecular and Developmental Medicine , University of Siena , Siena , Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Allavena
authors.affiliation: a Institute of Environmental Medicine , Division of Toxicology, Karolinska Institutet , Stockholm , Sweden.
authors.forename: Caroline
authors.initials: C
authors.lastname: Boyd
authors.affiliation: a Institute of Environmental Medicine , Division of Toxicology, Karolinska Institutet , Stockholm , Sweden.
authors.forename: Kyaw Soe
authors.initials: KS
authors.lastname: Oo
authors.affiliation: b Department of Molecular and Developmental Medicine , University of Siena , Siena , Italy.
authors.forename: Emilia
authors.initials: E
authors.lastname: Maellaro
authors.affiliation: a Institute of Environmental Medicine , Division of Toxicology, Karolinska Institutet , Stockholm , Sweden.|c Faculty of Basic Medicine , MV Lomonosov Moscow State University , Moscow , Russia.
authors.forename: Boris
authors.initials: B
authors.lastname: Zhivotovsky
authors.affiliation: a Institute of Environmental Medicine , Division of Toxicology, Karolinska Institutet , Stockholm , Sweden.
authors.forename: Vitaliy O
authors.initials: VO
authors.lastname: Kaminskyy
mesh_terms: D001343:Autophagy; D000071189:Autophagy-Related Protein-1 Homolog / Q000378:metabolism*; D045744:Cell Line, Tumor; D019069:Cell Respiration; D015536:Down-Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D025261:Mitochondrial Proton-Translocating ATPases / Q000378:metabolism; D008954:Models, Biological; D009584:Nitrogen / Q000172:deficiency*; D014176:Protein Biosynthesis; D059748:Proteolysis; D015854:Up-Regulation
chemical_list: D047908:Intracellular Signaling Peptides and Proteins; D000071189:Autophagy-Related Protein-1 Homolog; C484754:ULK1 protein, human; D025261:Mitochondrial Proton-Translocating ATPases; D009584:Nitrogen
keywords: AMPK; ATG13 knockout; ATG7 knockout; ULK complex; ULK1; autophagy; lung cancer; protein translation; starvation