title: Divergent roles of BECN1 in LC3 lipidation and autophagosomal function.
abstract: BECN1/Beclin 1 is regarded as a critical component in the class III phosphatidylinositol 3-kinase (PtdIns3K) complex to trigger autophagy in mammalian cells. Despite its significant role in a number of cellular and physiological processes, the exact function of BECN1 in autophagy remains controversial. Here we created a BECN1 knockout human cell line using the TALEN technique. Surprisingly, the complete loss of BECN1 had little effect on LC3 (MAP1LC3B/LC3B) lipidation, and LC3B puncta resembling autophagosomes by fluorescence microscopy were still evident albeit significantly smaller than those in the wild-type cells. Electron microscopy (EM) analysis revealed that BECN1 deficiency led to malformed autophagosome-like structures containing multiple layers of membranes under amino acid starvation. We further confirmed that the PtdIns3K complex activity and autophagy flux were disrupted in BECN1(-/-) cells. Our results demonstrate the essential role of BECN1 in the functional formation of autophagosomes, but not in LC3B lipidation.
authors.affiliation: a Biodynamic Optical Imaging Center (BIOPIC); Peking-Tsinghua Center for Life Sciences; State Key Laboratory of Protein and Plant Gene Research; School of Life Sciences; Peking University ; Beijing , China.
authors.forename: Ruina
authors.initials: R
authors.lastname: He
authors.forename: Jingyu
authors.initials: J
authors.lastname: Peng
authors.forename: Pengfei
authors.initials: P
authors.lastname: Yuan
authors.forename: Fang
authors.initials: F
authors.lastname: Xu
authors.forename: Wensheng
authors.initials: W
authors.lastname: Wei
mesh_terms: D051017:Apoptosis Regulatory Proteins / Q000172:deficiency / Q000378:metabolism*; D001343:Autophagy; D001483:Base Sequence; D000071186:Beclin-1; D058546:Class III Phosphatidylinositol 3-Kinases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008055:Lipids / Q000737:chemistry*; D008565:Membrane Proteins / Q000172:deficiency / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010588:Phagosomes / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D051017:Apoptosis Regulatory Proteins; C491997:BECN1 protein, human; D000071186:Beclin-1; D008055:Lipids; C477012:MAP1LC3A protein, human; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D058546:Class III Phosphatidylinositol 3-Kinases
keywords: ATG, autophagy related; BCL2L1/Bcl-xL, BCL2-like 1; BECN1; BECN1, Beclin 1, autophagy related; BECN1P1/BECN2, Beclin 1, autophagy related, pseudogene 1; BafA1, bafilomycin A1; EM, electron microscopy; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; GFP, green fluorescent protein; KO, knockout; LC3; MAP1LC3-I/LC3-I, soluble, proteolytically processed microtubule-associated protein 1 light chain 3; MAP1LC3-II/LC3-II, proteolytically processed and lipid-modified microtubule-associated protein 1 light chain 3; MAP1LC3/LC3, microtubule-associated protein 1 light chain 3; MAP1LC3B/LC3B, microtubule-associated protein 1 light chain 3 β; PIK3C3/VPS34, phosphatidylinositol 3-kinase, catalytic subunit type 3; PIK3R4/VPS15, phosphoinositide-3-kinase, regulatory subunit 4; PtdIns3K; PtdIns3K, phosphatidylinositol 3-kinase; SQSTM1/p62, sequestosome 1; TALEN, transcription activator-like effector nuclease; TUBB, tubulin, β class I; UVRAG, UV radiation resistance associated; ZFYVE1/DFCP1, zinc finger, FYVE domain containing 1.; autophagosome; autophagy