a Department of Ophthalmology and Visual Sciences , Washington University School of Medicine , St. Louis , Missouri , USA.
Autophagy. 2017;13(12):2072-2085. doi: 10.1080/15548627.2017.1380124.
Macroautophagy/autophagy is an intracellular stress survival and recycling system whereas phagocytosis internalizes material from the extracellular milieu; yet, both pathways utilize lysosomes for cargo degradation. Whereas autophagy occurs in all cells, phagocytosis is performed by cell types such as macrophages and the retinal pigment epithelial (RPE) cells of the eye where it is supported by the noncanonical autophagy process termed LC3-associated phagocytosis (LAP). Autophagy and LAP are distinct pathways that use many of the same mediators and must compete for cellular resources, suggesting that cells may regulate both processes under homeostatic and stress conditions. Our data reveal that RPE cells promote LAP through the expression of RUBCN/Rubicon (RUN domain and cysteine-rich domain containing Beclin 1-interacting protein) and suppress autophagy through the activation of EGFR (epidermal growth factor receptor). In the morning when photoreceptor outer segments (POS) phagocytosis and LAP are highest, RUBCN expression is increased. At the same time, outer segment phagocytosis activates the EGFR resulting in MTOR (mechanistic target of rapamycin [serine/threonine kinase]) stimulation, the accumulation of SQSTM1/p62, and the phosphorylation of BECN1 (Beclin 1, autophagy related) on an inhibitory residue thereby suppressing autophagy. Silencing Rubcn, preventing EGFR activity or directly inducing autophagy in RPE cells by starvation inhibits phagocytic degradation of POS. Thus, RPE cells regulate lysosomal pathways during the critical period of POS phagocytosis to support retinal homeostasis.
自噬是一种细胞内应激存活和回收系统,而吞噬作用则将细胞外环境中的物质内化;然而,这两种途径都利用溶酶体进行货物降解。自噬发生在所有细胞中,而吞噬作用则由细胞类型完成,如巨噬细胞和眼睛的视网膜色素上皮 (RPE) 细胞,在这些细胞中,非典型自噬过程称为 LC3 相关吞噬作用 (LAP) 提供支持。自噬和 LAP 是不同的途径,它们使用许多相同的介质,并且必须争夺细胞资源,这表明细胞可能在稳态和应激条件下调节这两个过程。我们的数据表明,RPE 细胞通过表达 RUBCN/Rubicon(含 RUN 结构域和半胱氨酸丰富结构域的 Beclin 1 相互作用蛋白)促进 LAP,并通过激活 EGFR(表皮生长因子受体)来抑制自噬。在早晨,当光感受器外节 (POS) 吞噬作用和 LAP 最高时,RUBCN 表达增加。与此同时,外节吞噬作用激活 EGFR,导致 MTOR(雷帕霉素的作用靶点 [丝氨酸/苏氨酸激酶])刺激、SQSTM1/p62 的积累以及 BECN1(自噬相关)上抑制性残基的磷酸化,从而抑制自噬。沉默 Rubcn、阻止 EGFR 活性或通过饥饿直接诱导 RPE 细胞中的自噬可抑制 POS 的吞噬降解。因此,RPE 细胞在 POS 吞噬的关键时期调节溶酶体途径,以支持视网膜的稳态。