Alternative autophagy is an autophagy-related protein 5 (Atg5)-independent type of macroautophagy. Unc51-like kinase 1 (Ulk1) is an essential initiator not only for Atg5-dependent canonical autophagy but also for alternative autophagy. However, the mechanism as to how Ulk1 differentially regulates both types of autophagy has remained unclear. In this study, we identify a phosphorylation site of Ulk1 at Ser⁷⁴⁶, which is phosphorylated during genotoxic stress-induced alternative autophagy. Phospho-Ulk1⁷⁴⁶ localizes exclusively on the Golgi and is required for alternative autophagy, but not canonical autophagy. We also identify receptor-interacting protein kinase 3 (RIPK3) as the kinase responsible for genotoxic stress-induced Ulk1⁷⁴⁶ phosphorylation, because RIPK3 interacts with and phosphorylates Ulk1 at Ser⁷⁴⁶, and loss of RIPK3 abolishes Ulk1⁷⁴⁶ phosphorylation. These findings indicate that RIPK3-dependent Ulk1⁷⁴⁶ phosphorylation on the Golgi plays a pivotal role in genotoxic stress-induced alternative autophagy.

替代性自噬是一种自噬相关蛋白5（Atg5）独立的巨自噬类型。Unc51样激酶1（Ulk1）不仅是依赖于Atg5的规范自噬的重要引发剂，也是替代自噬的重要引发剂。但是，关于Ulk1如何差异调节两种自噬的机制仍不清楚。在这项研究中，我们确定了Serk ⁷⁴⁶处Ulk1的磷酸化位点，在遗传毒性应激诱导的自噬过程中被磷酸化。Phospho-Ulk1 ^746仅定位在高尔基体上，是替代性自噬（而非规范性自噬）所必需的。我们还确定受体相互作用蛋白激酶3（RIPK3）作为负责基因毒性应激诱导的Ulk1 ⁷⁴⁶的激酶磷酸化，因为RIPK3在Ser ⁷⁴⁶处与Ulk1相互作用并使之磷酸化，而RIPK3的缺失则消除了Ulk1 ^746的磷酸化。这些发现表明，高尔基体上依赖RIPK3的Ulk1 ⁷⁴⁶磷酸化在遗传毒性应激诱导的自噬中起着关键作用。