Spatiotemporal Control of ULK1 Activation by NDP52 and TBK1 during Selective Autophagy

Jose Norberto S Vargas,Chunxin Wang,Eric Bunker,Ling Hao,Dragan Maric,Giampietro Schiavo,Felix Randow,Richard J Youle

doi:10.1016/j.molcel.2019.02.010

Abstract

SummarySelective autophagy recycles damaged organelles and clears intracellular pathogens to prevent their aberrant accumulation. How ULK1 kinase is targeted and activated during selective autophagic events remains to be elucidated. In this study, we used chemically inducible dimerization (CID) assays in tandem with CRISPR KO lines to systematically analyze the molecular basis of selective autophagosome biogenesis. We demonstrate that ectopic placement of NDP52 on mitochondria or peroxisomes is sufficient to initiate selective autophagy by focally localizing and activating the ULK1 complex. The capability of NDP52 to induce mitophagy is dependent on its interaction with the FIP200/ULK1 complex, which is facilitated by TBK1. Ectopically tethering ULK1 to cargo bypasses the requirement for autophagy receptors and TBK1. Focal activation of ULK1 occurs independently of AMPK and mTOR. Our findings provide a parsimonious model of selective autophagy, which highlights the coordination of ULK1 complex localization by autophagy receptors and TBK1 as principal drivers of targeted autophagosome biogenesis.

Highlights

Autophagy is critical for the bulk degradation of various intracellular components and for cellular homeostasis (Dikic and Elazar, 2018; Mizushima et al, 2011)
We previously demonstrated that CRISPR KO cell lines lacking all known sequestosome-like autophagy receptors have a defect in ULK1 complex recruitment and mitophagy (Lazarou et al, 2015), which suggests a role for autophagy receptors in initiating this first step in isolation membrane formation directly on the cargo
We find that NDP52 and TANK-Binding Kinase1 (TBK1) cooperate to recruit the ULK1 complex to ubiquitinated cargo, leading to ULK1 kinase activation, which occurs independently of energysensing pathways

Summary

Introduction

Autophagy is critical for the bulk degradation of various intracellular components and for cellular homeostasis (Dikic and Elazar, 2018; Mizushima et al, 2011). Autophagosomes can be built around specific subcellular components destined for selective degradation (Gatica et al, 2018). Selective autophagic targets, such as damaged mitochondria or invading bacteria, first become tagged by ubiquitin, which serves as an ‘‘eat me’’. The orchestrated steps of autophagosome formation, involving many ATG proteins, have been elucidated (Behrends et al, 2010; Itakura and Mizushima, 2010). There is no clear mechanism known to link cargo recognition with autophagosome biogenesis in mammals, and it is uncertain what provides the targeting mechanism to nucleate the early autophagy machinery in the vicinity of organelles destined for degradation

Results

Discussion

Conclusion