Routing Misfolded Proteins through the Multivesicular Body (MVB) Pathway Protects against Proteotoxicity

Songyu Wang,Guillaume Thibault,Davis T.W Ng

doi:10.1074/jbc.m111.233346

Songyu Wang, Guillaume Thibault + Show 1 more

Open Access

https://doi.org/10.1074/jbc.m111.233346

Copy DOI

Abstract

The secretory pathway maintains multiple quality control checkpoints. Initially, endoplasmic reticulum-associated degradation pathways monitor protein folding to retain and eliminate aberrant products. Despite its broad client range, some molecules escape detection and traffic to Golgi membranes. There, a poorly understood mechanism termed Golgi quality control routes aberrant proteins for lysosomal/vacuolar degradation. To better understand Golgi quality control, we examined the processing of the obligate substrate Wsc1p. Misfolded Wsc1p does not use routes of typical vacuolar membrane proteins. Instead, it partitions into intralumenal vesicles of the multivesicular body (MVB) pathway, mediated by the E3 ubiquitin ligase Rsp5p. Its subsequent transport to the vacuolar lumen is essential for complete molecule breakdown. Surprisingly, the transport mode plays a second crucial function in neutralizing potential substrate toxicity. Eliminating the MVB sorting signal diverted molecules to the vacuolar limiting membrane, resulting in the generation of toxic by-products. These data demonstrate a new role of the MVB pathway in protein quality control.

Highlights

Dent substrates revealed post-ER quality control mechanisms that efficiently capture the wayward molecules
We previously reported that a plasma membrane protein, Wsc1p, is an endogenous, obligate substrate of post-ER quality control [26]
We show that Golgi quality control (GQC) and peripheral quality control pathways converge at the multivesicular body (MVB) endosomal sorting compartment

Summary

Introduction

Dent substrates revealed post-ER quality control mechanisms that efficiently capture the wayward molecules. Among four well characterized endosomal sorting complexes required for transport (ESCRT) involved in cargo clustering (ESCRT-0), membrane budding (ESCRT-I and ESCRT-II), and membrane scission (ESCRT-III) (for review, see Ref. 43), most mutants caused the accumulation of Wsc1*GFP in class E compartments (seen prominently in the micrographs as a strongly staining structure juxtaposed to the vacuolar membrane) and the vacuolar limiting membrane (supplemental Fig. S2B). The absence of signal in the vacuolar lumen of ⌬pep4⌬vps27 cells suggests that Wsc1* molecules use the MVB pathway for its primary vacuolar transport (Fig. 2, A (m–p) and B).

Results

Conclusion