London Research Institute, Cancer Research UK, 44 Lincolns Inn Fields, London WC2A 3LY, UK.
Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada.
Mol Cell. 2014 Jul 17;55(2):238-52. doi: 10.1016/j.molcel.2014.05.021. Epub 2014 Jun 19.
Mammalian cell homeostasis during starvation depends on initiation of autophagy by endoplasmic reticulum-localized phosphatidylinositol 3-phosphate (PtdIns(3)P) synthesis. Formation of double-membrane autophagosomes that engulf cytosolic components requires the LC3-conjugating Atg12-5-16L1 complex. The molecular mechanisms of Atg12-5-16L1 recruitment and significance of PtdIns(3)P synthesis at autophagosome formation sites are unknown. By identifying interacting partners of WIPIs, WD-repeat PtdIns(3)P effector proteins, we found that Atg16L1 directly binds WIPI2b. Mutation experiments and ectopic localization of WIPI2b to plasma membrane show that WIPI2b is a PtdIns(3)P effector upstream of Atg16L1 and is required for LC3 conjugation and starvation-induced autophagy through recruitment of the Atg12-5-16L1 complex. Atg16L1 mutants, which do not bind WIPI2b but bind FIP200, cannot rescue starvation-induced autophagy in Atg16L1-deficient MEFs. WIPI2b is also required for autophagic clearance of pathogenic bacteria. WIPI2b binds the membrane surrounding Salmonella and recruits the Atg12-5-16L1 complex, initiating LC3 conjugation, autophagosomal membrane formation, and engulfment of Salmonella.
哺乳动物细胞在饥饿时的内稳态依赖于内质网定位的磷脂酰肌醇 3-磷酸（PtdIns(3)P）合成引发自噬。形成吞噬细胞质成分的双层自噬体需要 LC3 连接的 Atg12-5-16L1 复合物。Atg12-5-16L1 募集的分子机制和 PtdIns(3)P 合成在自噬体形成部位的意义尚不清楚。通过鉴定 WD 重复 PtdIns(3)P 效应蛋白 WIPI 的相互作用伙伴，我们发现 Atg16L1 直接结合 WIPI2b。突变实验和 WIPI2b 质膜异位定位表明，WIPI2b 是 Atg16L1 的 PtdIns(3)P 效应物，是通过募集 Atg12-5-16L1 复合物来促进 LC3 连接和饥饿诱导的自噬所必需的。不能结合 WIPI2b 但能结合 FIP200 的 Atg16L1 突变体不能拯救 Atg16L1 缺陷 MEF 中饥饿诱导的自噬。WIPI2b 对于致病性细菌的自噬清除也是必需的。WIPI2b 结合围绕沙门氏菌的膜并募集 Atg12-5-16L1 复合物，启动 LC3 连接、自噬体膜形成和沙门氏菌的吞噬。
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