title: Withdrawal of essential amino acids increases autophagy by a pathway involving Ca2+/calmodulin-dependent kinase kinase-β (CaMKK-β).
abstract: Autophagy is the main lysosomal catabolic process that becomes activated under stress conditions, such as amino acid starvation and cytosolic Ca(2+) upload. However, the molecular details on how both conditions control autophagy are still not fully understood. Here we link essential amino acid starvation and Ca(2+) in a signaling pathway to activate autophagy. We show that withdrawal of essential amino acids leads to an increase in cytosolic Ca(2+), arising from both extracellular medium and intracellular stores, which induces the activation of adenosine monophosphate-activated protein kinase (AMPK) via Ca(2+)/calmodulin-dependent kinase kinase-β (CaMKK-β). Furthermore, we show that autophagy induced by amino acid starvation requires AMPK, as this induction is attenuated in its absence. Subsequently, AMPK activates UNC-51-like kinase (ULK1), a mammalian autophagy-initiating kinase, through phosphorylation at Ser-555 in a process that requires CaMKK-β. Finally, the mammalian target of rapamycin complex C1 (mTORC1), a negative regulator of autophagy downstream of AMPK, is inhibited by amino acid starvation in a Ca(2+)-sensitive manner, and CaMKK-β appears to be important for mTORC1 inactivation, especially in the absence of extracellular Ca(2+). All these results highlight that amino acid starvation regulates autophagy in part through an increase in cellular Ca(2+) that activates a CaMKK-β-AMPK pathway and inhibits mTORC1, which results in ULK1 stimulation.
authors.affiliation: Laboratorio de Biología Celular, Centro de Investigación Príncipe Felipe and CIBERER, C/Eduardo Primo Yúfera 3, 46012 Valencia, Spain.
authors.forename: Ghita
authors.initials: G
authors.lastname: Ghislat
authors.forename: Maria
authors.initials: M
authors.lastname: Patron
authors.forename: Rosario
authors.initials: R
authors.lastname: Rizzuto
authors.forename: Erwin
authors.initials: E
authors.lastname: Knecht
mesh_terms: D016475:3T3 Cells; D000601:Amino Acids, Essential / Q000737:chemistry; D000818:Animals; D001343:Autophagy; D000071189:Autophagy-Related Protein-1 Homolog; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034622:RNA Interference; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D000601:Amino Acids, Essential; D007328:Insulin; D046912:Multiprotein Complexes; D000071189:Autophagy-Related Protein-1 Homolog; D000076222:Mechanistic Target of Rapamycin Complex 1; D017346:Protein Serine-Threonine Kinases; D058570:TOR Serine-Threonine Kinases; C112444:Ulk1 protein, mouse; D054737:Calcium-Calmodulin-Dependent Protein Kinase Kinase