Induction of autophagic flux by amino acid deprivation is distinct from nitrogen starvation-induced macroautophagy.
A number of signaling mechanisms have been implicated in the regulation of autophagic trafficking. TOR kinase activity, cAMP levels, and the GAAC pathway have all been suggested to be involved. Here, we closely analyzed the stimuli that underlie induction of autophagic trafficking in Saccharomyces cerevisiae. We find evidence for the existence of a novel aspect of the autophagic pathway that is regulated by intracellular amino acids, uncoupled from extracellular nutrient levels, and is absolutely dependent on Gcn2 and Gcn4. This requirement for Gcn2 and Gcn4 distinguishes amino-acid starvation induced autophagy from classic macroautophagy: Macroautophagic flux in response to nitrogen starvation is only partly diminished in gcn2Δ and gcn4Δ cells. However this maintenance of autophagic flux in gcn mutants during nitrogen starvation reflects the formation of larger numbers of smaller autophagosomes. We report that gcn2Δ and gcn4Δ cells are defective in the induction of Atg8 and Atg4 upon starvation, and this defect results, during total nitrogen starvation, in the formation of abnormally small autophagosomes, although overall autophagic flux remains close to normal due to a compensatory increase in the overall number of autophagosomes.
Ecker
Nitai
N
Institute of Biochemistry, Food Science and Nutrition, Robert H. Smith Faculty of Agriculture, Food, and Environment, Hebrew University of Jerusalem, Rehovot, Israel.
Mor
Angelica
A
Journo
Dikla
D
Abeliovich
Hagai
H
D000596:Amino Acids / Q000378:metabolism*; D001343:Autophagy / Q000502:physiology*; D000071190:Autophagy-Related Protein 8 Family; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010588:Phagosomes / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000502:physiology; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D013217:Starvation / Q000378:metabolism*
C113757:ATG8 protein, S cerevisiae; D000596:Amino Acids; D000071190:Autophagy-Related Protein 8 Family; D050976:Basic-Leucine Zipper Transcription Factors; C501391:GCN4 protein, S cerevisiae; D008869:Microtubule-Associated Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; C512912:GCN2 protein, S cerevisiae; D017346:Protein Serine-Threonine Kinases; D009584:Nitrogen