Activation of ULK Kinase and Autophagy by GABARAP Trafficking from the Centrosome Is Regulated by WAC and GM130

Abstract

SummaryStarvation-induced autophagy requires activation of the ULK complex at the phagophore. Two Golgi proteins, WAC and GM130, regulate autophagy, however their mechanism of regulation is unknown. In search of novel interaction partners of WAC, we found that GM130 directly interacts with WAC, and this interaction is required for autophagy. WAC is bound to the Golgi by GM130. WAC and GM130 interact with the Atg8 homolog GABARAP and regulate its subcellular localization. GABARAP is on the pericentriolar matrix, and this dynamic pool contributes to autophagosome formation. Tethering of GABARAP to the Golgi by GM130 inhibits autophagy, demonstrating an unexpected role for a golgin. WAC suppresses GM130 binding to GABARAP, regulating starvation-induced centrosomal GABARAP delivery to the phagophore. GABARAP, unlipidated and lipidated, but not LC3B, GABARAPL1, and GATE-16, specifically promotes ULK kinase activation dependent on the ULK1 LIR motif, elucidating a unique non-hierarchical role for GABARAP in starvation-induced activation of autophagy.

Dedicated SNARE s and specialized TRIM cargo receptors mediate secretory autophagy

“…Both the conventional autophagosomal membranes earmarked for fusion with the lysosomes and those that are destined for secretion may be derived from a subset of ERGIC‐derived autophagosomal precursors (Ge et al , ). Other contributing sources of autophagic membrane may modulate this (Hamasaki et al , ; Puri et al , ; Joachim et al , ; Lamb et al , ). The sorting step between LC3 + Sec22b + IL‐1β secretory carriers and ERGIC‐derived (Ge et al , ) autophagosomal membranes destined for degradative autophagosomes could involve differential syntaxin 17 insertion (Itakura et al , ; Tsuboyama et al , ) or alternatively its regulation, if syntaxin 17 is present at all on IL‐1β secretory carriers, which has not been excluded in our study (Itakura et al , ; Hamasaki et al , ; Takats et al , ; Diao et al , ).…”

“…The initiation of autophagosome formation depends on upstream Ser/Thr protein kinases, including AMPK (Kim et al , , ), mTOR (Egan et al , ; Kim et al , ; Settembre et al , ), and ULK1 (Russell et al , ), and lipid kinases centered upon phosphatidylinositol 3‐kinase VPS34 complex containing Beclin 1 (Liang et al , ) and ATG14L (Sun et al , ), to generate phosphatidylinositol 3‐phosphate (PI3P) on autophagic membranes. These membranes likely originate from the endoplasmic reticulum (ER) (Axe et al , ), with ER‐to‐Golgi intermediate compartment (ERGIC) playing a key role in LC3 lipidation and formation of autophagosomal membranes (Ge et al , ), whereas contributions of the ER–mitochondrial contact sites (Hamasaki et al , ), endocytic membranes (Puri et al , ; Lamb et al , ), and potentially other intracellular compartments (Joachim et al , ) play additional roles in redirecting net membrane flow to autophagosomes. The production of PI3P by VPS34 is recognized by WIPI2, which in turn binds to ATG16L (Dooley et al , ) of the ATG5‐ATG12/ATG16L1 complex, thus localizing LC3 lipidation (Fujita et al , ).…”

Canonical and noncanonical functions of ULK/Atg1

“…Similarly, ULK1 interacts with GATE-16, an essential factor for intra-Golgi transport [63], and GABARAP [64], the γ2 subunit of GABA-A receptor–associated protein, which regulates receptor trafficking [65–67]. Both proteins are mammalian homologs of Atg8 and are involved in autophagy [68,69]. In yeast, the interaction between Atg8 and Atg1 targets Atg1 to autophagosomes, and also triggers vacuolar degradation of the Atg1-Atg13 complex [70].…”

Control of GABARAP‐mediated autophagy by the Golgi complex, centrosome and centriolar satellites

“…Examples include the plasma membrane, Golgi, endoplasmic reticulum-Golgi intermediate compartment, recycling endosomes, endoplasmic reticulum, mitochondria, lipid droplets and the primary cilium [Lamb et al, 2013;Pampliega et al, 2013;Tang et al, 2013;Fullgrabe et al, 2014]. Furthermore, microtubules and the (non-ciliated) centrosome also regulate autophagy [Mackeh et al, 2013;Joachim et al, 2015] and we have now discovered a role for centriolar satellites in the regulation of autophagy [Joachim et al, 2017]. In this regard, GABARAP that is normally found in the cytosol and on the phagophores in starved cells, is also found in fed cells on the Golgi, the pericentriolar material and centriolar satellites.…”