title: Autophagic removal of micronuclei.
abstract: Macroautophagy is known to participate in the quality control and turnover of cytoplasmic organelles, yet there is little evidence that macroautophagy targets nuclei in mammalian cells. Here, we investigated whether autophagy may target micronuclei, which arise as a result of deficient bipolar chromosome segregation in cells exposed to cell cycle perturbations. After removal of several distinct cell cycle blockers (nocodazole, cytochalasin D, hydroxyurea or SP600125), cells manifested an increase in the frequency of micronuclei (positive for histone H2B-RFP) as well as an increase in autophagic puncta (positive for GFP-LC3) over several days. A small but significant percentage of micronuclei co-localized with GFP-LC3 in autophagy-competent cells and this co-localization was lost after knockdown of ATG5 or ATG7. Electron microscopy analyses confirmed autophagic sequestration of micronuclei. "Autophagic micronuclei" (GFP-LC3⁺) were also decorated with p62/SQSTM1, while non-autophagic (GFP-LC3⁻) micronuclei where p62/SQSTM1 negative. In addition, GFP-LC3⁺ micronuclei exhibited signs of envelope degradation and γH2AX⁺ DNA damage foci, yet stained less intensively for chromatin markers, whereas GFP-LC3⁻ micronuclei were surrounded by an intact envelope and rarely exhibited markers or DNA damage. These results indicate that micronuclei can be subjected to autophagic degradation. Moreover, it can be speculated that removal of micronuclei may contribute to the genome-stabilizing effects of autophagy.
authors.affiliation: INSERM, U848, Orsay, Paris, France.
authors.forename: Santiago
authors.initials: S
authors.lastname: Rello-Varona
authors.forename: Delphine
authors.initials: D
authors.lastname: Lissa
authors.forename: Shensi
authors.initials: S
authors.lastname: Shen
authors.forename: Mireia
authors.initials: M
authors.lastname: Niso-Santano
authors.forename: Laura
authors.initials: L
authors.lastname: Senovilla
authors.forename: Guillermo
authors.initials: G
authors.lastname: Mariño
authors.forename: Ilio
authors.initials: I
authors.lastname: Vitale
authors.forename: Mohamed
authors.initials: M
authors.lastname: Jemaá
authors.forename: Francis
authors.initials: F
authors.lastname: Harper
authors.forename: Gérard
authors.initials: G
authors.lastname: Pierron
authors.forename: Maria
authors.initials: M
authors.lastname: Castedo
authors.forename: Guido
authors.initials: G
authors.lastname: Kroemer
mesh_terms: D001343:Autophagy; D000071187:Autophagy-Related Protein 5; D000071193:Autophagy-Related Protein 7; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D004249:DNA Damage; D006657:Histones / Q000378:metabolism; D006801:Humans; D048629:Micronuclei, Chromosome-Defective; D008869:Microtubule-Associated Proteins / Q000032:analysis / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009685:Nuclear Envelope / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism
chemical_list: C502778:ATG5 protein, human; D000071187:Autophagy-Related Protein 5; C468783:H2AX protein, human; D006657:Histones; C477012:MAP1LC3A protein, human; D008869:Microtubule-Associated Proteins; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; C509349:ATG7 protein, human; D000071193:Autophagy-Related Protein 7; D044764:Ubiquitin-Activating Enzymes