The deubiquitinating enzyme USP36 controls selective autophagy activation by ubiquitinated proteins

Abstract

Initially described as a nonspecific degradation process induced upon starvation, autophagy is now known also to be involved in the degradation of specific ubiquitinated substrates such as mitochondria, bacteria and aggregated proteins, ensuring crucial functions in cell physiology and immunity. We report here that the deubiquitinating enzyme USP36 controls selective autophagy activation in Drosophila and in human cells. We show that dUsp36 loss of function autonomously inhibits cell growth while activating autophagy. Despite the phenotypic similarity, dUSP36 is not part of the TOR signaling pathway. Autophagy induced by dUsp36 loss of function depends on p62/SQSTM1, an adaptor for delivering cargo marked by polyubiquitin to autophagosomes. Consistent with p62 requirement, dUsp36 mutant cells display nuclear aggregates of ubiquitinated proteins, including Histone H2B, and cytoplasmic ubiquitinated proteins; the latter are eliminated by autophagy. Importantly, USP36 function in p62-dependent selective autophagy is conserved in human cells. Our work identifies a novel, crucial role for a deubiquitinating enzyme in selective autophagy.

Keywords: :

• autophagy
• DUB
• cell growth
• deubiquitinase
• deubiquitinating enzyme
• p62
• ubiquitin

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Acknowledgments

We thank J. Jackson and D. Schneider for critical reading of the manuscript. We are grateful to R. Delanoue, S. Gaumer, P. Leopold, T. Neufeld and H. Stenmark for providing mutant and transgenic flies. We also thank S. Gaumer and D. Contamine for the Ref(2)P antibody, D. Grunwald and O. Azocar for help with confocal microscopy, E. Engel and P.E. Joubert for testing and validating siUSP36, and C. Bama and I. Maréchal for fly food preparation. The Bloomington Drosophila Stock Center and Vienna Drosophila RNAi Center contributed to this work by providing mutant and transgenic fly strains. This work was supported by grant from Cluster 10 Infectiologie, Région Rhône Alpes and ANR-08-JCJC-0064-01.