ULK1 induces autophagy by phosphorylating Beclin-1 and activating VPS34 lipid kinase

Abstract

Autophagy is the primary cellular catabolic program activated in response to nutrient starvation. Initiation of autophagy, particularly by amino acid withdrawal, requires the ULK kinases. Despite its pivotal role in autophagy initiation, little is known about the mechanisms by which ULK promotes autophagy. Here we describe a molecular mechanism linking ULK to the pro-autophagic lipid kinase VPS34. Upon amino acid starvation or mTOR inhibition the activated ULK1 phosphorylates Beclin-1 on S14, thereby, enhancing the activity of the ATG14L-containing VPS34 complexes. The Beclin-1 S14 phosphorylation by ULK is required for full autophagic induction in mammals and this requirement is conserved in C. elegans. Our study reveals a molecular link from ULK1 to activation of the autophagy specific VPS34 complex and autophagy induction.

Differential regulatory functions of three classes of phosphatidylinositol and phosphoinositide 3-kinases in autophagy

“…91 More importantly, the effect of amino acid withdrawal on different PIK3C3 complexes remains unsettled: contradictory observations were reported showing the activation of general PIK3C3 116,118,120 but suppression of ATG14-interacting PIK3C3 68,120 after amino acid deprivation. It should be noted that the study by Russel et al 120 may offer a potential explanation: the opposing effects of amino acid withdrawal on class III PtdIns3K activity in PIK3C3-BECN1 and PIK3C3-ATG14 immunoprecipitates were demonstrated, and the presence of ATG14 is likely to determine the specific activation of the ATG14-containing PIK3C3 complex mediated by ULK1 phosphorylation of BECN1. Together with the evidence of differential regulation of PIK3C3 complexes by energy deprivation, 112 a hypothesis that may reconcile the contradictory roles of PIK3C3 in MTOR signaling and autophagy could be proposed: certain PIK3C3-interacting components, for instance ATG14, may specify the differential regulation of distinct PIK3C3 complexes by nutrients, or determine the spatial distribution of PIK3C3 that confers divergent biological functions.…”

“…BECN1 phosphorylation by ULK1 at Ser14 is one of the key initiating events required for autophagy induction upon starvation or MTOR inhibition, leading to activation of the ATG14-containing class III PtdIns3K complexes. 120 The aforementioned PRKA phosphorylation of BECN1 under glucose starvation also enhances the activity of ATG14-or UVRAG-containing class III PtdIns3K complexes. 112 Of note, BECN1 is an important downstream target of AKT, which inhibits autophagy, and aberrant BECN1 phosphorylation by AKT is implicated in tumorigenesis.…”

The ubiquitin system: a critical regulator of innate immunity and pathogen–host interactions

“…52,53 Following mTOR suppression, activated ULK1 boosts the kinase activity of the ATG14L-harboring VPS34 complex through the phosphorylation of Beclin-1 on Ser14. 54 Pathogen infection-triggered selective autophagy is also termed xenophagy and functions to restrict a range of pathogens, such as Mycobacterium tuberculosis (Mtb) and Salmonella enterica serovar typhimurium. The ubiquitin system is widely implicated in the initiation of the autophagic pathway as well as the subsequent coupling of autophagosomes to bacterial targets (Figure 3).…”

Molecular interactions of theSaccharomyces cerevisiaeAtg1 complex provide insights into assembly and regulatory mechanisms

“…17 The integral membrane protein Atg9 and mammalian BECN1 (the ortholog of yeast Vps30/Atg6) are direct substrates of Atg1 (or the mammalian ortholog ULK1). 18,19 Atg1-mediated phosphorylation events are essential for autophagy and, in the case of Atg9, for the Cvt pathway. [18][19][20] The C-terminal domain of Atg1 (residues 589 to 897) interacts with Atg13 and Atg17.…”

“…18,19 Atg1-mediated phosphorylation events are essential for autophagy and, in the case of Atg9, for the Cvt pathway. [18][19][20] The C-terminal domain of Atg1 (residues 589 to 897) interacts with Atg13 and Atg17. 21,22 This Atg1 domain, dubbed the EAT (early autophagy targeting) domain, appears to possess a membrane binding function with specificity for high-curvature membranes.…”