Characterization of autophagy regulating genes kibra and aPKC in drosophila melanogaster

Abstract

Autophagy is a bulk degradation system that functions in response to cellular stresses such as metabolic stress, endoplasmic reticulum stress, oxidative stress, and developmental processes. During autophagy, cytoplasmic components are captured in double-membrane vesicles called autophagosomes. The autophagosome fuses with the lysosome, producing a vacuole known as an autolysosome. The cellular components are degraded by lysosomal proteases and recycled. Autophagy is important for maintaining cellular homeostasis, and the process is evolutionarily conserved. According to recent studies, autophagy regulates cancer, immune response and neurodegenerative disease. In this study, we performed RNAi screening using Drosophila S2 cells and larvae, we found that Kibra acts as a novel autophagy regulator. Kibra is an upstream regulator of the hippo signaling pathway, which controls organ size by affecting cell growth, proliferation, and apoptosis. In mammals, Kibra is mostly expressed in the kidney and brain, and it is known to regulate learning and memory, cell migration, and membrane trafficking. Kibra is mainly localized in the apical membrane domain of epithelial cells and acts as a scaffold protein. We found that Kibra is required for autophagy to function properly. The absence of Kibra caused defects in the formation of autophagic vesicles and autophagic degradation during starvation. We also found that the well-known cell polarity protein aPKC interacts with Kibra, and its activity affects autophagy upstream of Kibra. Constitutively active aPKC decreased autophagic vesicle formation and autophagic degradation during starvation. We confirmed the interaction between aPKC and Kibra in S2 cells and Drosophila larvae. In our study, overexpression of Kibra rescued autophagy defects in constitutively active aPKC expression. Taken together, our data suggests that Kibra and aPKC are essential for regulating starvation-induced autophagy.