Aup1p, a Yeast Mitochondrial Protein Phosphatase Homolog, Is Required for Efficient Stationary Phase Mitophagy and Cell Survival

Nitai Ecker,Daniel J Klionsky,Hagai Abeliovich,Gal Winter,Ruth Tal

doi:10.1074/jbc.m605940200

Nitai Ecker, Daniel J Klionsky + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m605940200

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Abstract

Autophagy is a catabolic membrane-trafficking process that occurs in all eukaryotic cells and leads to the hydrolytic degradation of cytosolic material in the vacuolar or lysosomal lumen. Mitophagy, a selective form of autophagy targeting mitochondria, is poorly understood at present. Several recent reports suggest that mitophagy is a selective process that targets damaged mitochondria, whereas other studies imply a role for mitophagy in cell death processes. In a screen for protein phosphatase homologs that functionally interact with the autophagy-dedicated protein kinase Atg1p in yeast, we have identified Aup1p, encoded by Saccharomyces cerevisiae reading frame YCR079w. Aup1p is highly similar to a family of protein phosphatase homologs in animal cells that are predicted to localize to mitochondria based on sequence analysis. Interestingly, we found that Aup1p localizes to the mitochondrial intermembrane space and is required for efficient mitophagy in stationary phase cells. Viability studies demonstrate that Aup1p is required for efficient survival of cells in prolonged stationary phase cultures, implying a pro-survival role for mitophagy under our working conditions. Our data suggest that Aup1p may be part of a signal transduction mechanism that marks mitochondria for sequestration into autophagosomes.

Highlights

Underlie many age-related metabolic diseases and late-onset genetic disorders [1, 2]
Whereas most of the protein factors required for Cvt trafficking and for macroautophagy are identical, there exist Cvt pathway-specific factors that are dispensable for macroautophagy, and autophagy-specific factors that are not required in the Cvt pathway [3]
To identify protein phosphatases that potentially interact with the Atg1 protein kinase, we screened for mutants that, in the genetic background of the atg1⌬880 allele, would cause a synthetic phenotype such that autophagic trafficking of prApe1 would be abolished

Summary

The abbreviations used are

Cytoplasm to vacuole targeting; HA, influenza virus hemagglutinin; GFP, green fluorescent protein; RFP, red fluorescent protein; SLM, synthetic lactate medium; PP2C, protein phosphatase 2C; PP1K, protein phosphatase 1K; PAS, preautophagosomal structure. Atg1p is a protein kinase required for both classical, starvation-induced macroautophagy as well as for the selective variants of autophagy such as the Cvt pathway and pexophagy. Aup1p is a highly conserved protein that localizes to the mitochondrial intermembrane space While it is not absolutely required for classical starvation-induced macroautophagy, we find that it is required for effective mitophagy in stationary phase yeast cells. These data suggest that AUP1 may be part of a signal transduction mechanism that marks mitochondria for selective degradation through mitophagy

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION