ALS‐linked mutations impair UBQLN2 stress‐induced biomolecular condensate assembly in cells

Autor: Julia F. Riley, Heidi Hehnly, Amber K. Rusnock, Peter J. Fioramonti, Carlos A. Castañeda
Rok vydání: 2021
Předmět:
Zdroj: J Neurochem
ISSN: 1471-4159
0022-3042
DOI: 10.1111/jnc.15453
Popis: Mutations in Ubiquilin-2 (UBQLN2), a ubiquitin-binding shuttle protein involved in several protein quality control processes, can lead to amyotrophic lateral sclerosis (ALS). We previously found that wild-type UBQLN2 forms dynamic, membraneless biomolecular condensates upon cellular stress, and undergoes liquid-liquid phase separation in vitro. However, the impact of ALS-linked mutations on UBQLN2 condensate formation in cells is unknown. Here, we overexpress five patient-derived ALS-linked mutations in mCherry-fused UBQLN2 and employ live-cell imaging and photokinetic analysis to investigate how these mutations impact stress-induced UBQLN2 condensate assembly and condensate material properties. Unlike endogenous UBQLN2, exogenously introduced UBQLN2 forms condensates distinct from stress granules. Both wild-type and mutant UBQLN2 condensates are generally cytoplasmic and liquid-like. However, cells overexpressing mutant UBQLN2 contain fewer stress-induced UBQLN2 condensates than those with wild-type UBQLN2. Exogenously expressed P506T UBQLN2 forms the lowest number of stress-induced condensates of all UBQLN2 mutants, and these condensates are significantly smaller than those of wild-type UBQLN2. Fluorescence recovery after photobleaching (FRAP) analysis of UBQLN2 condensates revealed higher immobile fractions for UBQLN2 mutants, especially P506T. P497S and P497H mutations differentially impact condensate properties, demonstrating that the effects of ALS-linked mutations are both position- and amino acid-dependent. Collectively, our data show that disease mutations hinder assembly and alter viscoelastic properties of stress-induced UBQLN2 condensates, potentially leading to aggregates commonly observed in ALS. An essential next step is to study how mutants expressed at endogenous levels and localize to stress granules affect the assembly, disassembly, and material properties of stress granules.
Databáze: OpenAIRE
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