At the Intersection of the Pathways for Exocytosis and Autophagy

Recent studies have suggested that there are molecular links between the two critical biological processes of exocytosis and autophagy. Exocytosis involves the transport of intracellular vesicles to the plasma membrane of the cell, where vesicular fusion results in the delivery of membrane and protein to the cell surface, and secretion of the vesicular contents. Exocytosis is utilized in, for example, hormone or antimicrobial peptide secretion, the delivery of proteoglycans to the cell surface, cell-cell communication and neurotransmission (Brennwald & Rossi, 2007; He & Guo, 2009). Autophagy is a mechanism for the recycling and degradation of cytoplasmic content, which involves surrounding an area of cytoplasm with a double membrane structure, which then interacts with degradative endosome-lysosome compartments (He & Klionsky, 2009). Autophagy has important functions in a range of cell processes including the maintenance of cellular homeostasis, starvation adaption, energy balance, organelle clearance, immunity and cell death. In human diseases, such as cancers, neurodegenerative disorders (e.g. Huntington’s disease), and chronic inflammatory diseases (e.g. Crohn’s disease), there have been reports of functional disparity in both of these important membrane-related cellular pathways. There is now increasing evidence that exocytosis and autophagy share molecular machinery and there are a number of reasons why this would be beneficial in terms of cellular function.