# E3 ligase AREL1 controls perinuclear localization of lysosomes and supports Purkinje cell survival

## TL;DR

This study shows that the E3 ligase AREL1 helps position lysosomes near the nucleus in neurons, which is important for their function and for preventing cell loss in the brain.

## Contribution

The study identifies a novel mechanism involving AREL1, UBAC2, and V-ATPase that regulates lysosomal positioning and function in neurons.

## Key findings

- AREL1 interacts with V-ATPase and catalyzes ubiquitylation of V1B2, promoting perinuclear lysosome localization.
- AREL1 or UBAC2 depletion leads to peripheral lysosomes with reduced acidity and degradative capacity.
- Arel1 knockout mice show Purkinje cell loss, motor impairment, and lysosomal dysfunction.

## Abstract

Localization of lysosomes influences their properties, e.g., perinuclear lysosomes are more acidic but less mobile compared with the peripheral ones. Furthermore, the endoplasmic reticulum (ER) can actively regulate the dynamics and functions of lysosomes via membrane contact sites. In this study, we find that ER-resident apoptosis-resistant E3 ubiquitin protein ligase 1 (AREL1) establishes membrane contacts with lysosomes by directly interacting with the Voa subunit of V-ATPase. AREL1 also catalyzes K33-linked polyubiquitylation of V-ATPase V1B2 subunit, inducing its binding to UBAC2 localized in the perinuclear ER. Depletion of AREL1 or UBAC2 increases the number of peripheral lysosomes that possess partially assembled V-ATPase, elevated luminal pH, and attenuated degradative capacity. Knockdown of ZRANB1, the deubiquitylating enzyme that antagonizes AREL1-mediated V1B2 ubiquitylation, promotes perinuclear clustering of lysosomes and increases lysosomal acidity and degradation. Mice lacking Arel1 exhibit age-dependent Purkinje cell loss, an ataxic phenotype, and motor impairment. Lipofuscin accumulation in the residual Purkinje cells of Arel1−/− mice indicates lysosomal dysfunction. Orchestration of lysosomal positioning and function by the AREL1–UBAC2–V-ATPase axis underscores the physiological significance of ER-regulated perinuclear lysosomal positioning in neurons.

Lysosomal acidity is affected by their subcellular localization, with perinuclear lysosomes being more acidic than the peripheral ones. This study reveals that ER-localized proteins AREL1 and UBAC2 function in concert with V-ATPases to anchor lysosomes perinuclearly and regulate lysosomal pH.

The E3 ubiquitin ligase AREL1 interacts with the Voa subunit of V-ATPase and catalyzes K33-linked polyubiquitylation of the V1B2 subunit.The ER protein UBAC2 binds to the ubiquitylated V-ATPase subunits and constrains lysosomes at the perinuclear region.Depletion of AREL1 or UBAC2 results in more peripheral lysosomes that possess partially assembled V-ATPase, elevated luminal pH and attenuated degradative capacity.The deubiquitylating enzyme ZRANB1 antagonizes AREL1-mediated V1B2 ubiquitylation, causing dispersal of lysosomes to the cell periphery.Arel1 knockout mice display age-dependent motor impairment and Purkinje cell loss associated with lysosomal dysfunction and lipofuscin accumulation.

The E3 ubiquitin ligase AREL1 interacts with the Voa subunit of V-ATPase and catalyzes K33-linked polyubiquitylation of the V1B2 subunit.

The ER protein UBAC2 binds to the ubiquitylated V-ATPase subunits and constrains lysosomes at the perinuclear region.

Depletion of AREL1 or UBAC2 results in more peripheral lysosomes that possess partially assembled V-ATPase, elevated luminal pH and attenuated degradative capacity.

The deubiquitylating enzyme ZRANB1 antagonizes AREL1-mediated V1B2 ubiquitylation, causing dispersal of lysosomes to the cell periphery.

Arel1 knockout mice display age-dependent motor impairment and Purkinje cell loss associated with lysosomal dysfunction and lipofuscin accumulation.

AREL1-mediated polyubiquitylation of the V1B2 subunit of the lysosomal V-ATPase localizes lysosomes to the perinuclear region via an interaction with the ER protein UBAC2.