ABSTRACT

The mammalian ULK kinase complex is the most upstream component in the macroautophagy/autophagy signaling pathway. ULK1 and homolog ULK2, the sole serine/threonine kinases in autophagy, transduce an array of autophagy-inducing stimuli to downstream autophagic machinery, regulating autophagy from autophagosome initiation to fusion of autophagosomes with lysosomes. ULK signaling is also implicated in a diverse array of non-canonical processes from necroptosis to ER-Golgi trafficking to stress granule clearance. However, the exact mechanisms by which ULK regulates these diverse processes remain largely unknown. Most notably, the number of validated ULK substrates is surprisingly low. Our study identifies new ULK substrates from a wide array of protein families and signaling pathways and supports an expanded range of physiological roles for the ULKs. We further characterize several new substrates, including the PIK3C3/VPS34-containing complex subunit PIK3R4/VPS15 and the AMPK component PRKAG2. Finally, by analyzing PIK3R4/VPS15-deficient models we discover novel aspects of ULK signaling with potential relevance in selective autophagy.

摘要

哺乳动物 ULK 激酶复合物是巨自噬/自噬信号通路中最上游的成分。ULK1 和同源物 ULK2，自噬中唯一的丝氨酸/苏氨酸激酶，将一系列自噬诱导刺激转导至下游自噬机制，调节从自噬体起始到自噬体与溶酶体融合的自噬。ULK 信号还涉及从坏死性凋亡到 ER-高尔基体运输到应力颗粒清除的各种非规范过程。然而，ULK 调节这些不同过程的确切机制仍然很大程度上未知。最值得注意的是，经过验证的 ULK 基板的数量非常少。我们的研究从广泛的蛋白质家族和信号通路中识别出新的 ULK 底物，并支持 ULK 的更大范围的生理作用。我们进一步表征了几种新的底物，包括含有 PIK3C3/VPS34 的复杂亚基 PIK3R4/VPS15 和 AMPK 组件 PRKAG2。最后，通过分析 PIK3R4/VPS15 缺陷模型，我们发现了与选择性自噬潜在相关的 ULK 信号传导的新方面。