An autophagy assay reveals the ESCRT-III component CHMP2A as a regulator of phagophore closure

Yoshinori Takahashi,Carson A Wills,Jennifer M Atkinson,Zhenyuan Tang,Longgui Chen,Haiyan He,Ying Liu,Megan M Young,Melat Gebru,Han Chen,Chong Chen,Hong-Gang Wang,Thomas Abraham,Tatsuya Hattori,Jacob M Serfass

doi:10.1038/s41467-018-05254-w

Abstract

The mechanism of phagophore closure remains unclear due to technical limitations in distinguishing unclosed and closed autophagosomal membranes. Here, we report the HaloTag-LC3 autophagosome completion assay that specifically detects phagophores, nascent autophagosomes, and mature autophagic structures. Using this assay, we identify the endosomal sorting complexes required for transport (ESCRT)-III component CHMP2A as a critical regulator of phagophore closure. During autophagy, CHMP2A translocates to the phagophore and regulates the separation of the inner and outer autophagosomal membranes to form double-membrane autophagosomes. Consistently, inhibition of the AAA-ATPase VPS4 activity impairs autophagosome completion. The ESCRT-mediated membrane abscission appears to be a critical step in forming functional autolysosomes by preventing mislocalization of lysosome-associated membrane glycoprotein 1 to the inner autophagosomal membrane. Collectively, our work reveals a function for the ESCRT machinery in the final step of autophagosome formation and provides a useful tool for quantitative analysis of autophagosome biogenesis and maturation.

Highlights

The mechanism of phagophore closure remains unclear due to technical limitations in distinguishing unclosed and closed autophagosomal membranes
We demonstrate that proper autophagosomal membrane closure requires the endosomal sorting complexes required for transport (ESCRT)-III component CHMP2A and the AAA-ATPase Vacuolar Protein Sorting-associated 4 (VPS4) activity and that the generation of the outer autophagosomal membrane (OAM) and inner autophagosomal membrane (IAM) by ESCRT-mediated membrane abscission prior to lysosomal recruitment is a critical step in the formation of functional autolysosomes
The Membrane-impermeable HaloTag ligand (MIL)+Membrane-permeable HaloTag ligand (MPL)− signals displayed cup- or oval-shaped structures (Fig.1d, e; arrows in h, i) in agreement with phagophore morphology[17], while MIL+MPL+ signals formed nascent autophagosome-like structures in which MIL signals (OAM-associated HT-light chain 3 (LC3)-II) surrounded MPL signals (IAM-associated HT-LC3-II) (Fig. 1f; white arrowheads in h–j) and MIL−MPL+ puncta were consistent with mature autophagosomal structures in which OAM-associated LC3-II has been delipidated (Fig. 1g; blue arrowheads in j)

Summary

Introduction

The mechanism of phagophore closure remains unclear due to technical limitations in distinguishing unclosed and closed autophagosomal membranes. We report the HaloTag-LC3 autophagosome completion assay that detects phagophores, nascent autophagosomes, and mature autophagic structures Using this assay, we identify the endosomal sorting complexes required for transport (ESCRT)-III component CHMP2A as a critical regulator of phagophore closure. How the phagophore undergoes membrane remodeling to generate the inner and outer membranes of the completed autophagosome remains far from clear[4] and has been hindered by technical challenges associated with distinguishing unclosed and closed autophagosomal membranes[5]. We demonstrate that proper autophagosomal membrane closure requires the ESCRT-III component CHMP2A and the AAA-ATPase Vacuolar Protein Sorting-associated 4 (VPS4) activity and that the generation of the OAM and IAM by ESCRT-mediated membrane abscission prior to lysosomal recruitment is a critical step in the formation of functional autolysosomes

Methods

Results

Conclusion