Division of Molecular Biology, School of Life Sciences, Faculty of Medicine, Tottori University, Yonago, Tottori 683-8503, Japan.
Division of Molecular Biology, School of Life Sciences, Faculty of Medicine, Tottori University, Yonago, Tottori 683-8503, Japan
Biol Open. 2020 Jun 23;9(6):bio051029. doi: 10.1242/bio.051029.
Microtubule-associated protein A1/B1-light chain 3 (LC3)-associated phagocytosis (LAP) is a type of non-canonical autophagy that regulates phagosome maturation in macrophages. However, the role and regulatory mechanism of LAP remain largely unknown. Recently, the membrane occupation and recognition nexus repeat-containing-2 (MORN2) was identified as a key component of LAP for the efficient formation of LC3-recruiting phagosomes. To characterize MORN2 and elucidate its function in LAP, we established a MORN2-overexpressing macrophage line. At a steady state, MORN2 was partially cleaved by the ubiquitin-proteasome system. MORN2 overexpression promoted not only LC3-II production but also LAP phagosome (LAPosome) acidification during uptake. Furthermore, the formation of LAPosomes containing the yeast cell wall component zymosan was enhanced in MORN2-overexpressing cells and depended on reactive oxygen species (ROS). Finally, MORN2-mediated LAP was regulated by plasma membrane-localized soluble -ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) such as SNAP-23 and syntaxin 11. Taken together, these findings demonstrate that MORN2, whose expression is downregulated via proteasomal digestion, is a limiting factor for LAP, and that membrane trafficking by SNARE proteins is involved in MORN2-mediated LAP.
微管相关蛋白 A1/B1-轻链 3（LC3）相关噬菌作用（LAP）是一种非典型的自噬作用，可调节巨噬细胞中的吞噬体成熟。然而，LAP 的作用和调节机制在很大程度上尚不清楚。最近，膜占领和识别结构域重复包含 2（MORN2）被鉴定为 LAP 的关键组成部分，可有效形成 LC3 招募的吞噬体。为了表征 MORN2 并阐明其在 LAP 中的功能，我们建立了一个 MORN2 过表达的巨噬细胞系。在稳定状态下，MORN2 部分被泛素-蛋白酶体系统切割。MORN2 的过表达不仅促进了 LC3-II 的产生，而且促进了吞噬作用期间 LAP 吞噬体（LAPosome）的酸化。此外，在 MORN2 过表达的细胞中，包含酵母细胞壁成分几丁质的 LAPosome 的形成得到增强，并且依赖于活性氧物种（ROS）。最后，MORN2 介导的 LAP 受质膜定位的可溶性 -乙基马来酰亚胺敏感因子附着蛋白受体（SNAREs）的调节，例如 SNAP-23 和 syntaxin 11。总之，这些发现表明，MORN2 的表达通过蛋白酶体消化下调，是 LAP 的限制因素，并且 SNARE 蛋白的膜运输参与了 MORN2 介导的 LAP。
