Correlative roles of exocyst complex and septins in autophagy

Abstract

Autophagy is an evolutionarily conserved intracellular degradation process which maintains cellular homeostasis. This involves the capture and delivery of cytoplasmic contents by the hallmark organelles called autophagosomes to the vacuole/lysosome for degradation. Despite more than 50 years of investigations in the field of autophagy, the process of de novo autophagosome biogenesis is still enigmatic. The key questions regarding the origins and dynamic contribution of autophagosomal membranes for its biogenesis are poorly understood. A genetic screen performed in our lab revealed the involvement of two multisubunit protein complexes, Exocyst complex and Septins in early stages of autophagy. In depth studies on these complexes suggest their roles in autophagosome biogenesis, particularly in the trafficking of vesicles that contribute membrane to the growing autophagosome. Past studies have demonstrated a role for these complexes in exocytosis, membrane tethering and cytokinesis where they also interact with each other. As our lab has identified autophagy related roles for these complexes (exocyst and septin), my studies have explored the possibilities of these complexes interacting during autophagosome biogenesis. I started by genomically tagging exocyst and septin subunits to be used for live cell imaging. Next, I determined the colocalization between exocyst components and septin under autophagic conditions. We found that these complexes interacted during autophagic conditions also. To further understand the correlative role of exocyst-septin interaction in autophagy, I studied association of complexes individually with autophagy protein Atg9 in the absence of the other functional complex. Using live cell microscopy, colocalization experiments between these complexes and autophagy proteins have shed light on the possible rearrangement of these complexes during autophagy that may be distinct from their canonical compositions.