부산대학교 도서관

Autophagy is an indispensable process that degrades cytoplasmic materials to maintain cellular homeostasis. During autophagy, double-membrane autophagosomes surround cytoplasmic materials and either fuse with endosomes (called amphisomes) and then lysosomes, or directly fuse with lysosomes, in both cases generating autolysosomes that degrade their contents by lysosomal hydrolases. However, it remains unclear if there are specific mechanisms and/or conditions which distinguish these alternate routes. Here, we identified PACSIN1 as a novel autophagy regulator. PACSIN1 deletion markedly decreased autophagic activity under basal nutrient-rich conditions but not starvation conditions, and led to amphisome accumulation as demonstrated by electron microscopic and co-localization analysis, indicating inhibition of lysosome fusion. PACSIN1 interacted with SNAP29, an autophagic SNARE, and was required for proper assembly of the STX17 and YKT6 complexes. Moreover, PACSIN1 was required for lysophagy, aggrephagy but not mitophagy, suggesting cargo-specific fusion mechanisms. In C. elegans, deletion of sdpn-1, a homolog of PACSINs, inhibited basal autophagy and impaired clearance of aggregated protein, implying a conserved role of PACSIN1. Taken together, our results demonstrate the amphisome-lysosome fusion process is preferentially regulated in response to nutrient state and stress, and PACSIN1 is a key to specificity during autophagy. Author summary: Autophagy is an evolutionally conserved cytoplasmic degradation system in which double membrane structure called autophagosomes sequester several cytoplasmic materials and then transport to lysosomes for degradation. Previous studies mainly based on electron microscopy indicates autophagosomes either fuse with lysosomes directly or fuse with endosomes/MVB (Multi Vesicular Body), producing amphisomes then fuse with lysosomes. However, it remains unknown how these processes are regulated and the physiological relevance of these two routes due to lack of key molecules involved in either of two routes precludes the detailed characterization. In the current study, we identified PACSIN1 as a novel regulator of autophagy, whose function is essential for amphisome-lysosome fusion process specifically. Through the analysis of PACSIN1, we revealed that PACSIN1-dependent fusion process via amphisomes is required for basal autophagy and subsets of selective autophagy, suggesting that two autophagic routes are utilized depending on the context and/or cargos. [ABSTRACT FROM AUTHOR]