Lipid droplet and early autophagosomal membrane targeting of Atg2A and Atg14L in human tumor cells.
Autophagy is a lysosomal bulk degradation pathway for cytoplasmic cargo, such as long-lived proteins, lipids, and organelles. Induced upon nutrient starvation, autophagic degradation is accomplished by the concerted actions of autophagy-related (ATG) proteins. Here we demonstrate that two ATGs, human Atg2A and Atg14L, colocalize at cytoplasmic lipid droplets (LDs) and are functionally involved in controlling the number and size of LDs in human tumor cell lines. We show that Atg2A is targeted to cytoplasmic ADRP-positive LDs that migrate bidirectionally along microtubules. The LD localization of Atg2A was found to be independent of the autophagic status. Further, Atg2A colocalized with Atg14L under nutrient-rich conditions when autophagy was not induced. Upon nutrient starvation and dependent on phosphatidylinositol 3-phosphate [PtdIns(3)P] generation, both Atg2A and Atg14L were also specifically targeted to endoplasmic reticulum-associated early autophagosomal membranes, marked by the PtdIns(3)P effectors double-FYVE containing protein 1 (DFCP1) and WD-repeat protein interacting with phosphoinositides 1 (WIPI-1), both of which function at the onset of autophagy. These data provide evidence for additional roles of Atg2A and Atg14L in the formation of early autophagosomal membranes and also in lipid metabolism.
Autophagy Laboratory, Department of Molecular Biology, Interfaculty Institute for Cell Biology, Eberhard Karls University Tuebingen, Tuebingen, Germany.
Simon G
SG
Pfisterer
Autophagy Laboratory, Department of Molecular Biology, Interfaculty Institute for Cell Biology, Eberhard Karls University Tuebingen, Tuebingen, Germany International Max Planck Research School 'From Molecules to Organisms', Max Planck Institute for Developmental Biology and Eberhard Karls University Tuebingen, Tuebingen, Germany.
Daniela
D
Bakula
Applied Bioinformatics Laboratory, University of Konstanz, Konstanz, Germany.
Tancred
T
Frickey
Autophagy Laboratory, Department of Molecular Biology, Interfaculty Institute for Cell Biology, Eberhard Karls University Tuebingen, Tuebingen, Germany.
Alice
A
Cezanne
Division of Experimental Pathology, Institute of Pathology, University of Bern, Bern, Switzerland.
Daniel
D
Brigger
Division of Experimental Pathology, Institute of Pathology, University of Bern, Bern, Switzerland.
Mario P
MP
Tschan
Leibniz Institute for Arteriosklerosis Research, University of Muenster, Muenster, Germany.
Horst
H
Robenek
Autophagy Laboratory, Department of Molecular Biology, Interfaculty Institute for Cell Biology, Eberhard Karls University Tuebingen, Tuebingen, Germany International Max Planck Research School 'From Molecules to Organisms', Max Planck Institute for Developmental Biology and Eberhard Karls University Tuebingen, Tuebingen, Germany.
Tassula
T
Proikas-Cezanne
D033942:Adaptor Proteins, Vesicular Transport / Q000235:genetics / Q000378:metabolism*; D000071182:Autophagosomes / Q000378:metabolism*; D000071183:Autophagy-Related Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D066292:Lipid Droplets / Q000378:metabolism*; D050356:Lipid Metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000235:genetics / Q000378:metabolism
C539000:ATG14 protein, human; D033942:Adaptor Proteins, Vesicular Transport; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D018129:Phosphatidylinositol Phosphates; C522812:WIPI1 protein, human; C426003:ZFYVE1 protein, human; C055525:phosphatidylinositol 3-phosphate
Atg14L; Atg2A; WIPI-1; autophagosome; autophagy; double-FYVE containing protein 1