The cortical endoplasmic reticulum (ER) undergoes autophagic degradation in response to the accumulation of aggregated proteins within its lumen or in response to starvation. Our studies in yeast have shown that the cortical ER is remodeled by an actin-dependent mechanism so as to bring elements of ER carrying the selective autophagy receptor Atg40 into the vicinity of the autophagy machinery near the vacuole. The segment of ER destined for degradation must be severed from the remainder of the ER network, engulfed by an autophagosome and delivered to the vacuole for degradation. To identify the components involved in each step we have conducted a systematic screen for mutants specifically defective in autophagy of the cortical ER. Here we focus on two key aspects: The first concerns actin-dependent ER-remodeling. Several lines of evidence suggest that the cortical ER is tethered to endocytic pits on the plasma membrane as they are internalized by actin polymerization. We will explore the spatial and temporal relationship between the endocytic pit and the cortical ER during internalization as well as the role of a putative bridge connecting the two membranes. We will test the role of the ARP2/3 complex in remodeling the cortical ER as well as the role of a GTPase activating protein, its substrate and various effectors. The second focus concerns the role of a putative tether in autophagy of the cortical ER. This tether is a large protein found at inter-organelle contact sites that is thought to mediate phospholipid transfer. We will determine which stage of the ER autophagy pathway is affected by its loss. We will establish which contact sites are involved in autophagy of the cortical ER and will identify the adaptor that links it to these contact sites. Humans express several isoforms and each is associated with a different disease. We will determine which isoform is involved in ER autophagy.
The cortical endoplasmic reticulum (ER) undergoes autophagic degradation in response to the accumulation of aggregated proteins within its lumen or in response to starvation. A systematic screen for mutants defective in autophagy of the cortical ER has led us to focus on two areas: 1) the role of the cytoskeleton in a remodeling process that brings elements of the cortical ER into the vicinity of the autophagy machinery; 2) the role of a large inter-organelle tether in a subsequent event leading to engulfment of ER fragments by autophagosomes. Many human diseases result in the accumulation of aggregated proteins in the ER, therefore it is important to understand how these impaired regions of the ER are cleared by autophagy.
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