BECLIN-1 is Essential for the Maintenance of Gastrointestinal Epithelial Integrity by Regulating Endocytic Trafficking, F-actin Organization and Lysosomal Function

Abstract

Disrupted intestinal homeostasis and barrier function are key contributors to the development of various diseases, including inflammatory bowel disease (IBD). BECLIN-1, a core component of two class III phosphatidylinositol 3-kinase (PtdIns3K) complexes, has a dual role in autophagy and endocytic trafficking. Emerging evidence suggests it is involved in maintaining intestinal integrity which involves its endocytic trafficking function. To gain insights into the fatal gastrointestinal (GI) phenotype observed in BECLIN-1 knockout adult mice, organoids derived from these animals were used to investigate the role of BECLIN-1 in GI epithelial function. BECLIN-1 deletion led to disrupted localization of CADHERIN-1/E-CADHERIN to adherens junctions (AJs) and OCCLUDIN to tight junctions (TJs), resulting in the mislocalization of these critical barrier proteins. Lysosomal dysfunction was also observed, characterized by impaired cargo degradation. In addition, the filamentous actin (F-actin) cytoskeleton became disorganized though this was not associated with changes in the interaction between F-actin and CATENIN BETA-1/BETA-CATENIN nor in alterations in BETA-CATENIN localization, though BETA-CATENIN levels were reduced. These effects were all less pronounced or absent in organoids lacking the autophagy-only regulator ATG7 (autophagy related 7), further emphasizing the involvement of BECLIN-1s protein trafficking role in the maintenance of gut homeostasis and barrier function. These findings provide new insights into processes involved in epithelial dysfunction, deepening our understanding of mechanisms underlying intestinal disease.