title: WHAMM Directs the Arp2/3 Complex to the ER for Autophagosome Biogenesis through an Actin Comet Tail Mechanism.
abstract: Nucleation-promoting factors (NPFs) control the spatio-temporal activity of Arp2/3 complex in cells]. Thus, WASP and the WAVE complex direct the formation of branched actin networks at the leading edge during cell motility and endo/exocytosis, whereas the WASH complex is involved in endosomal transport. Less understood are WHAMM and JMY, two NPFs with similar domain architecture. JMY is found in the nucleus and the cytosol and is involved in transcriptional regulation, cell motility, and trans-Golgi transport. WHAMM was reported to bind microtubules and to be involved in ER to cis-Golgi transport. Here, we show that WHAMM directs the activity of Arp2/3 complex for autophagosome biogenesis through an actin-comet tail motility mechanism. Macroautophagy--the process by which cytosolic material is engulfed into autophagosomes for degradation and/or recycling--was recently shown to involve actin, but the mechanism is unknown. We found that WHAMM forms puncta that colocalize and comigrate with the autophagy markers LC3, DFCP1, and p62 through a WHAMM-dependent actin-comet tail mechanism. Under starvation, WHAMM and actin are observed at the interface between neighboring autophagosomes, whose number and size increase with WHAMM expression. Interfering with actin polymerization, inhibiting Arp2/3 complex, knocking down WHAMM, or blocking its interaction with Arp2/3 complex through mutagenesis all inhibit comet tail formation and reduce the size and number of autophagosomes. Finally, JMY shows similar localization to WHAMM and could be involved in similar processes. These results reveal a link between Arp2/3-complex-dependent actin assembly and autophagy.
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Kast
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Allison L
authors.initials: AL
authors.lastname: Zajac
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Erika L F
authors.initials: EL
authors.lastname: Holzbaur
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: E Michael
authors.initials: EM
authors.lastname: Ostap
authors.affiliation: Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA. Electronic address: droberto@mail.med.upenn.edu.
authors.forename: Roberto
authors.initials: R
authors.lastname: Dominguez
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D001343:Autophagy / Q000502:physiology; D019086:Bridged Bicyclo Compounds, Heterocyclic; D037281:Calnexin / Q000378:metabolism; D002460:Cell Line; D020552:Comet Assay; D047630:Depsipeptides; D000067493:Dynamic Light Scattering; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008164:Luminescent Proteins; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D015739:Nocodazole; D010588:Phagosomes / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D000069816:SEC Translocation Channels; D053778:Thiazolidines; D000097573:Red Fluorescent Protein
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D037281:Calnexin; D047630:Depsipeptides; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D015739:Nocodazole; D000069816:SEC Translocation Channels; D053778:Thiazolidines; D000097573:Red Fluorescent Protein; C499388:SEC61B protein, human; C578123:WHAMM protein, human; C057531:jasplakinolide; C037068:latrunculin B