ABSTRACT
WNT signalling is important for development in all metazoans and is associated with various human diseases. The ubiquitin-proteasome system (UPS) and regulatory endoplasmic reticulum-associated degradation (ERAD) have been implicated in the production of WNT proteins. Here, we investigated how the WNT secretory factor EVI (also known as WLS) is ubiquitylated, recognised by ERAD components and subsequently removed from the secretory pathway. We performed a focused immunoblot-based RNAi screen for factors that influence EVI/WLS protein stability. We identified the VCP-binding proteins FAF2 and UBXN4 as novel interaction partners of EVI/WLS and showed that ERLIN2 links EVI/WLS to the ubiquitylation machinery. Interestingly, we also found that EVI/WLS is ubiquitylated and degraded in cells irrespective of their level of WNT production. This K11, K48 and K63-linked ubiquitylation is mediated by the E2 ubiquitin-conjugating enzymes UBE2J2, UBE2K and UBE2N, but is independent of the E3 ubiquitin ligases HRD1 (also known as SYVN1) and GP78 (also known as AMFR). Taken together, our study identifies factors that link the UPS to the WNT secretory pathway and provides mechanistic details of the fate of an endogenous substrate of regulatory ERAD in mammalian cells. This article has an associated First Person interview with the first author of the paper.
Subject(s)
Endoplasmic Reticulum-Associated Degradation , Endoplasmic Reticulum , Animals , Endoplasmic Reticulum/genetics , Endoplasmic Reticulum/metabolism , Humans , Membrane Proteins/metabolism , Ubiquitin/metabolism , Ubiquitin-Conjugating Enzymes/genetics , Ubiquitin-Conjugating Enzymes/metabolism , Ubiquitin-Protein Ligases/genetics , Ubiquitin-Protein Ligases/metabolism , UbiquitinationABSTRACT
Ferroptosis has emerged as an attractive strategy in cancer therapy. Understanding the operational networks regulating ferroptosis may unravel vulnerabilities that could be harnessed for therapeutic benefit. Using CRISPR-activation screens in ferroptosis hypersensitive cells, we identify the selenoprotein P (SELENOP) receptor, LRP8, as a key determinant protecting MYCN-amplified neuroblastoma cells from ferroptosis. Genetic deletion of LRP8 leads to ferroptosis as a result of an insufficient supply of selenocysteine, which is required for the translation of the antiferroptotic selenoprotein GPX4. This dependency is caused by low expression of alternative selenium uptake pathways such as system Xc- . The identification of LRP8 as a specific vulnerability of MYCN-amplified neuroblastoma cells was confirmed in constitutive and inducible LRP8 knockout orthotopic xenografts. These findings disclose a yet-unaccounted mechanism of selective ferroptosis induction that might be explored as a therapeutic strategy for high-risk neuroblastoma and potentially other MYCN-amplified entities.