Regulation of Autophagy By Signaling Through the Atg1/ULK1 Complex

AbstractAutophagy is an intracellular degradation pathway highly conserved in eukaryotic species. It is characterized by selective or bulk trafficking of cytosolic structures—ranging from single proteins to cell organelles—to the vacuole or a lysosome, in which the autophagic cargo is degraded. Autophagy fulfils a large set of roles, including nutrient mobilization in starvation conditions, clearance of protein aggregates and host defence against intracellular pathogens. Not surprisingly, autophagy has been linked to several human diseases, among them neurodegenerative disorders and cancer. Autophagy is coordinated by the action of the Atg1/ULK1 kinase, which is the target of several important stress signaling cascades. In this review, we will discuss the available information on both upstream regulation and downstream effectors of Atg1/ULK1, with special focus on reported and proposed kinase substrates

LC3 and STRAP regulate actin filament assembly by JMY during autophagosome formation.

During autophagy, actin filament networks move and remodel cellular membranes to form autophagosomes that enclose and metabolize cytoplasmic contents. Two actin regulators, WHAMM and JMY, participate in autophagosome formation, but the signals linking autophagy to actin assembly are poorly understood. We show that, in nonstarved cells, cytoplasmic JMY colocalizes with STRAP, a regulator of JMY's nuclear functions, on nonmotile vesicles with no associated actin networks. Upon starvation, JMY shifts to motile, LC3-containing membranes that move on actin comet tails. LC3 enhances JMY's de novo actin nucleation activity via a cryptic actin-binding sequence near JMY's N terminus, and STRAP inhibits JMY's ability to nucleate actin and activate the Arp2/3 complex. Cytoplasmic STRAP negatively regulates autophagy. Finally, we use purified proteins to reconstitute LC3- and JMY-dependent actin network formation on membranes and inhibition of network formation by STRAP. We conclude that LC3 and STRAP regulate JMY's actin assembly activities in trans during autophagy

Sestrin2 promotes Unc‐51‐like kinase 1 mediated phosphorylation of p62/sequestosome‐1

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108630/1/febs12905.pd

Atg9 establishes Atg2-dependent contact sites between the endoplasmic reticulum and phagophores

The autophagy-related (Atg) proteins play a key role in the formation of autophagosomes, the hallmark of autophagy. The function of the cluster composed by Atg2, Atg18, and transmembrane Atg9 is completely unknown despite their importance in autophagy. In this study, we provide insights into the molecular role of these proteins by identifying and characterizing Atg2 point mutants impaired in Atg9 binding. We show that Atg2 associates to autophagosomal membranes through lipid binding and independently from Atg9. Its interaction with Atg9, however, is key for Atg2 confinement to the growing phagophore extremities and subsequent association of Atg18. Assembly of the Atg9-Atg2-Atg18 complex is important to establish phagophore-endoplasmic reticulum (ER) contact sites. In turn, disruption of the Atg2-Atg9 interaction leads to an aberrant topological distribution of both Atg2 and ER contact sites on forming phagophores, which severely impairs autophagy. Altogether, our data shed light in the interrelationship between Atg9, Atg2, and Atg18 and highlight the possible functional relevance of the phagophore-ER contact sites in phagophore expansion

mTOR independent alteration in ULK1 Ser758 phosphorylation following chronic LRRK2 kinase inhibition

Unc-51 Like Kinase 1 (ULK1) is a critical regulator of the biogenesis of autophagosomes, the central component of the catabolic macroautophagy pathway. Regulation of ULK1 activity is dependent upon several phosphorylation events acting to repress or activate the enzymatic function of this protein. Phosphorylation of Ser758 ULK1 has been linked to repression of autophagosome biogenesis and was thought to be exclusively dependent upon mTOR complex 1 kinase activity. In this study, a novel regulation of Ser758 ULK1 phosphorylation is reported following prolonged inhibition of the Parkinson's disease linked protein Leucine Rich Repeat Kinase 2 (LRRK2). Here, modulation of Ser758 ULK1 phosphorylation following LRRK2 inhibition is decoupled from the repression of autophagosome biogenesis and independent of mTOR complex 1 activity

A reversible phospho-switch mediated by ULK1 regulates the activity of autophagy protease ATG4B

Upon induction of autophagy, the ubiquitin-like protein LC3 is conjugated to phosphatidylethanolamine (PE) on the inner and outer membrane of autophagosomes to allow cargo selection and autophagosome formation. LC3 undergoes two processing steps, the proteolytic cleavage of pro-LC3 and the de-lipidation of LC3-PE from autophagosomes, both executed by the same cysteine protease ATG4. How ATG4 activity is regulated to co-ordinate these events is currently unknown. Here we find that ULK1, a protein kinase activated at the autophagosome formation site, phosphorylates human ATG4B on serine 316. Phosphorylation at this residue results in inhibition of its catalytic activity in vitro and in vivo. On the other hand, phosphatase PP2A-PP2R3B can remove this inhibitory phosphorylation. We propose that the opposing activities of ULK1-mediated phosphorylation and PP2A-mediated dephosphorylation provide a phospho-switch that regulates the cellular activity of ATG4B to control LC3 processing

Post‐translationally‐modified structures in the autophagy machinery: an integrative perspective

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113777/1/febs13356_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/113777/2/febs13356.pd

Latent variables and route choice behavior

In the last decade, a broad array of disciplines has shown a general interest in enhancing discrete choice models by considering the incorporation of psychological factors affecting decision making. This paper provides insight into the comprehension of the determinants of route choice behavior by proposing and estimating a hybrid model that integrates latent variable and route choice models. Data contain information about latent variable indicators and chosen routes of travelers driving regularly from home to work in an urban network. Choice sets include alternative routes generated with a branch and bound algorithm. A hybrid model consists of measurement equations, which relate latent variables to measurement indicators and utilities to choice indicators, and structural equations, which link travelers' observable characteristics to latent variables and explanatory variables to utilities. Estimation results illustrate that considering latent variables (i.e., memory, habit, familiarity, spatial ability, time saving skills) alongside traditional variables (e.g., travel time, distance, congestion level) enriches the comprehension of route choice behavior

Impact of integrated multimodal traveler information on auto commuter's mode switching propensity

Aim: Real-time traveler information affects auto commuter’s travel behavior. Method: An ordered probit model is used to analyze auto commuter’s mode switching propensity under influence of simulated real-time multimodal traveler information. A travel preference survey is administered to car drivers to gather individual commuter’s travel decisions under integrated multimodal traveler information. Result: It is shown that integrated multimodal traveler information can influence willingness of car drivers to switch mode of travel, while socio-economic characteristics also influence the mode choice decision