Molecular Mechanisms of Organellophagy in Yeast

Identification: Nakatogawa, Hitoshi



Molecular Mechanisms of Organellophagy in Yeast
Hitoshi Nakatogawa
School of Life Science and Technology, Tokyo Institute of Technology, Japan
We recently discovered that the nucleus and the endoplasmic reticulum (ER) are degraded via selective autophagy under nitrogen starvation conditions in the budding yeast Saccharomyces cerevisiae, and identified the receptors Atg39 and Atg40 responsible for these pathways (nucleophagy and ER-phagy), respectively. While double membrane vesicles derived from the nucleus are sequestered by autophagosomes in nucleophagy, fragments of the ER are loaded into autophagosomes in ER-phagy. Here, I show that fragmentation of these organelles is coupled with autophagosome formation. Atg40, which contains the reticulon-homology domain, has an ability to generate a high membrane curvature in the ER membrane, similar to reticulon-family proteins. Through its binding to Atg8 on forming autophagosomal membranes, Atg40 accumulates at ER regions that are adjacent to these membranes. We propose that these functions and dynamics of Atg40 cause the folding and fragmentation of the ER during its autophagic sequestration. Moreover, I present data suggesting that Atg40, in association with Atg39, is also involved in double membrane vesicle formation from the nucleus in nucleophagy.  
     A previous study identified Atg36 as a receptor for selective autophagy of peroxisomes (pexophagy) in S. cerevisiae, and we reported that the casein kinase 1δ homolog Hrr25 phosphorylates Atg36 to enhance its binding to Atg11, resulting in the stimulation of pexophagy initiation. In this talk, I also present our recent progress in understanding how Atg36 phosphorylation by Hrr25 is regulated.



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