Department of Biochemistry and Molecular Pharmacology, New York University Grossman School of Medicine, New York, NY 10016, USA.
Laura and Isaac Perlmutter NYU Cancer Center, New York University Grossman School of Medicine, New York, NY 10016, USA.
Sci Adv. 2023 Oct 13;9(41):eadh1134. doi: 10.1126/sciadv.adh1134.
Intracellular degradation of proteins and organelles by the autophagy-lysosome system is essential for cellular quality control and energy homeostasis. Besides degradation, endolysosomal organelles can fuse with the plasma membrane and contribute to unconventional secretion. Here, we identify a function for mammalian SKP1 in endolysosomes that is independent of its established role as an essential component of the family of SCF/CRL1 ubiquitin ligases. We found that, under nutrient-poor conditions, SKP1 is phosphorylated on Thr, allowing its interaction with V subunits of the vacuolar ATPase (V-ATPase). This event, in turn, promotes V-ATPase assembly to acidify late endosomes and enhance endolysosomal degradation. Under nutrient-rich conditions, SUMOylation of phosphorylated SKP1 allows its binding to and dephosphorylation by the PPM1B phosphatase. Dephosphorylated SKP1 interacts with SEC22B to promote unconventional secretion of the content of less acidified hybrid endosomal/autophagic compartments. Collectively, our study implicates SKP1 phosphorylation as a switch between autophagy and unconventional secretion in a manner dependent on cellular nutrient status.
细胞自噬溶酶体系统对蛋白质和细胞器的细胞内降解对于细胞质量控制和能量稳态至关重要。除了降解作用外，内溶酶体细胞器还可以与质膜融合，有助于非常规分泌。在这里，我们发现哺乳动物 SKP1 在溶酶体中有一个独立于其作为 SCF/CRL1 泛素连接酶家族的重要组成部分的既定作用的功能。我们发现，在营养缺乏的条件下，SKP1 在 Thr 上被磷酸化，允许其与液泡 ATP 酶 (V-ATPase) 的 V 亚基相互作用。反过来，这促进了 V-ATPase 的组装，使晚期内体酸化并增强内溶酶体降解。在营养丰富的条件下，磷酸化 SKP1 的 SUMO 化允许其与 PPM1B 磷酸酶结合并去磷酸化。去磷酸化的 SKP1 与 SEC22B 相互作用，促进内容物酸化较少的混合内体/自噬隔室的非常规分泌。总的来说，我们的研究表明，SKP1 的磷酸化作为一种依赖于细胞营养状态的自噬和非常规分泌之间的转换开关。
