Starvation Triggers the Delivery of the Endoplasmic Reticulum to the Vacuole via Autophagy in Yeast

Abstract

Autophagy is a survival mechanism necessary for eukaryotic cells to overcome nutritionally challenged environments. When autophagy is triggered, cells degrade nonselectively engulfed cytosolic proteins and free ribosomes that are evenly distributed throughout the cytoplasm. The resulting pool of free amino acids is used to sustain processes crucial for survival. Here we characterize an autophagic degradation of the endoplasmic reticulum (ER) under starvation conditions in addition to cytosolic protein degradation. Golgi membrane protein was not engulfed by the autophagosome under the same conditions, indicating that the uptake of ER by autophagosome was the specific event. Although the ER exists in a network structure that is mutually connected and resides predominantly around the nucleus and beneath the plasma membrane, most of autophagosome engulfed ER. The extent of the ER uptake by autophagy was nearly identical to that of the soluble cytosolic proteins. This phenomenon was explained by the appearance of fragmented ER membrane structures in almost all autophagosomes. Furthermore, ER dynamism is required for this process: ER uptake by autophagosomes occurs in an actin-dependent manner.