| Delivery of granule contents to epithelial surfaces by secretory cells is a critical physiologic process. In the intestine, goblet cells secrete mucus that is required for homeostasis. Autophagy proteins have been implicated in regulating secretion in a variety of cell types, however, the mechanism and cell biological basis for this requirement remains unknown. We found that in colonic goblet cells, proteins involved in initiation and elongation of autophagosomes were required for efficient mucus secretion.;The autophagy protein LC3 localized to amphisomes, multi-vesicular vacuoles that were consistent with a fusion of autophagosomes and endosomes. These vacuoles were distinct from mucin granules, which were negative for LC3. Using cultured intestinal epithelial cells, we found that NADPH oxidases localized to and enhanced the formation of amphisomes. Both autophagy proteins and endosome formation were required for maximal production of reactive oxygen species (ROS) derived from NADPH oxidases. Importantly, generation of ROS was critical to control mucin granule accumulation in colonic goblet cells. Thus, autophagy proteins regulate secretory function through ROS, which is in part generated by amphisome-associated NADPH oxidases.;Overall, these findings provide a novel mechanism by which autophagy proteins can control secretion. We uncovered an intermediate autophagy organelle, the amphisome, which may act as a signaling platform to control cellular function in a variety of cell types. |
