Cytosolic PTEN-induced Putative Kinase 1 Is Stabilized by the NF-κB Pathway and Promotes Non-selective Mitophagy

Grace G.Y Lim,Doreen S.K Chua,Adeline H Basil,Hui-Ying Chan,Chou Chai,Thiruma Arumugam,Kah-Leong Lim

doi:10.1074/jbc.m114.622399

Abstract

The potential cellular function of the 53-kDa cytosolic form of PINK1 (PINK1-53) is often overlooked because of its rapid degradation by the proteasome upon its production. Although a number of recent studies have suggested various roles for PINK1-53, how this labile PINK1 species attains an adequate expression level to fulfil these roles remains unclear. Here we demonstrated that PINK1-53 is stabilized in the presence of enhanced Lys-63-linked ubiquitination and identified TRAF6-related NF-κB activation as a novel pathway involved in this. We further showed that a mimetic of PINK1-53 promotes mitophagy but, curiously, in apparently healthy mitochondria. We speculate that this "non-selective" form of mitophagy may potentially help to counteract the build-up of reactive oxygen species in cells undergoing oxidative stress and, as such, represent a cytoprotective response.

Highlights

Full-length PTEN-induced putative kinase 1 (PINK1) is an important regulator of mitophagy, but the function of its highly labile cytosolic counterpart is often overlooked
Given that the stability of a protein may be enhanced by Lys63-linked ubiquitination, we wondered whether this form of ubiquitin modification that is typically uncoupled from the proteasome could influence the stability of the otherwise shortlived PINK1-53 protein, which is presumably normally ubiquitinated via linkages associated with proteasomal degradation
Consistent with the proteasome-independent role of Lys-63-linked ubiquitination, we found that the level of PINK1-53 is increased in the presence of Lys-63 HA-ubiquitin coexpression and, to a comparable extent, to that found in MG132-treated PINK1-transfected cells (Fig. 1B)

Summary

Introduction

Full-length PTEN-induced putative kinase 1 (PINK1) is an important regulator of mitophagy, but the function of its highly labile cytosolic counterpart is often overlooked. Results: Cytosolic PINK1 is stabilized by TRAF6/NF-␬B activation via Lys-63-linked ubiquitination and promotes the removal of apparently healthy mitochondria. We demonstrated that PINK1-53 is stabilized in the presence of enhanced Lys-63-linked ubiquitination and identified TRAF6related NF-␬B activation as a novel pathway involved in this. We further showed that a mimetic of PINK1-53 promotes mitophagy but, curiously, in apparently healthy mitochondria. We speculate that this “non-selective” form of mitophagy may potentially help to counteract the build-up of reactive oxygen species in cells undergoing oxidative stress and, as such, represent a cytoprotective response

Methods

Results

Conclusion