GORASP2/GRASP55 collaborates with the PtdIns3K UVRAG complex to facilitate autophagosome-lysosome fusion

It has been indicated that the Golgi apparatus contributes to autophagy, but how it is involved in autophagosome formation and maturation is not well understood. Here we show that amino acid starvation causes <i>trans</i>-Golgi derived membrane fragments to colocalize with autophagosomes. Depletion of the Golgi stacking protein GORASP2/GRASP55, but not GORASP1/GRASP65, increases both MAP1LC3 (LC3)-II and SQSTM1/p62 levels. We demonstrate that GORASP2 facilitates autophagosome-lysosome fusion by physically linking autophagosomes and lysosomes through the interactions with LC3 on autophagosomes and LAMP2 on late endosomes/lysosomes. Furthermore, we provide evidence that GORASP2 interacts with BECN1 to facilitate the assembly and membrane association of the phosphatidylinositol 3-kinase (PtdIns3K) UVRAG complex. These findings indicate that GORASP2 plays an important role in autophagosome maturation during amino acid starvation.

已有研究表明高尔基体（Golgi apparatus）参与自噬过程，但其如何参与自噬体形成与成熟的机制尚未完全阐明。本研究发现，氨基酸饥饿可使反式高尔基体（trans-Golgi）衍生的膜片段与自噬体发生共定位。敲低高尔基体堆叠蛋白GORASP2/GRASP55，而非GORASP1/GRASP65，可同时提升MAP1LC3（LC3）-II与SQSTM1/p62的蛋白水平。我们证实，GORASP2可通过分别结合自噬体上的LC3以及晚期内体/溶酶体上的溶酶体相关膜蛋白2（LAMP2），实现自噬体与溶酶体的物理连接，从而促进自噬体-溶酶体融合。此外，我们还发现GORASP2可与BECN1相互作用，以促进磷脂酰肌醇3-激酶（PtdIns3K）UVRAG复合物的组装及膜定位。上述研究结果表明，GORASP2在氨基酸饥饿条件下的自噬体成熟过程中发挥重要调控作用。