title: Protein kinase B/Akt1 inhibits autophagy by down-regulating UVRAG expression.
abstract: Autophagy, or autophagocytosis, is a selective intracellular degradative process involving the cell's own lysosomal apparatus. An essential component in cell development, homeostasis, repair and resistance to stress, autophagy may result in either cell death or survival. The targeted region of the cell is sequestered within a membrane structure, the autophagosome, for regulation of the catabolic process. A key factor in both autophagosome formation and autophagosome maturation is a protein encoded by the ultraviolet irradiation resistance-associated gene (UVRAG). Conversely, the serine/threonine-specific protein kinase B (PKB, also known as Akt), which regulates survival in various cancers, inhibits autophagy through mTOR activation. We found that Akt1 may also directly inhibit autophagy by down-regulating UVRAG both in a 293T transient transfection system and breast cancer cells stably expressing Akt1. The UVRAG with mutations at putative Akt1-phosphorylation sites were still inhibited by Akt1, and dominant-negative Akt1 also inhibited UVRAG expression, suggesting that Akt1 down-regulates UVRAG by a kinase activity-independent mechanism. We showed that Akt1 overexpression in MDA-MB-231 breast cancer cells down-regulated UVRAG transcription. Cells over-expressing Akt1 were more resistant than control cells to ultraviolet light-induced autophagy and exhibited the associated reduction in cell viability. Levels of the autophagosome indicator protein LC3B-II and mRFP-GFP-LC3 were reduced in cells that over-expressing Akt1. Inhibiting Akt1 by siRNA or reintroducing UVRAG gene rescued the level of LC3B-II in UV-irradiation. Altogether, these data suggest that Akt1 may inhibit autophagy by decreasing UVRAG expression, which also sensitizes cancer cells to UV irradiation.
authors.affiliation: Department of Life Science, College of Natural Science, Hanyang University, Seoul, Republic of Korea.
authors.forename: Wonseok
authors.initials: W
authors.lastname: Yang
authors.forename: Ji-hyun
authors.initials: JH
authors.lastname: Ju
authors.forename: Kyung-min
authors.initials: KM
authors.lastname: Lee
authors.forename: KeeSoo
authors.initials: K
authors.lastname: Nam
authors.forename: Sunhwa
authors.initials: S
authors.lastname: Oh
authors.forename: Incheol
authors.initials: I
authors.lastname: Shin
mesh_terms: D001343:Autophagy / Q000187:drug effects / Q000235:genetics* / Q000502:physiology / Q000528:radiation effects; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000528:radiation effects; D006801:Humans; D009369:Neoplasms / Q000235:genetics / Q000473:pathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; D025521:Tumor Suppressor Proteins; C408122:UVRAG protein, human; C494918:AKT1 protein, human; D051057:Proto-Oncogene Proteins c-akt