While ultraviolet (UV) radiation damages DNA, eliciting the DNA damage response (DDR), it also damages RNA, triggering transcriptome-wide ribosomal collisions and eliciting a ribotoxic stress response (RSR). However, the relative contributions, timing, and regulation of these pathways in determining cell fate is unclear. Here we use time-resolved phosphoproteomic, chemical-genetic, single-cell imaging, and biochemical approaches to create a chronological atlas of signaling events activated in cells responding to UV damage. We discover that UV-induced apoptosis is mediated by the RSR kinase ZAK and not through the DDR. We identify two negative-feedback modules that regulate ZAK-mediated apoptosis: (1) GCN2 activation limits ribosomal collisions and attenuates ZAK-mediated RSR and (2) ZAK activity leads to phosphodegron autophosphorylation and its subsequent degradation. These events tune ZAK's activity to collision levels to establish regimes of homeostasis, tolerance, and death, revealing its key role as the cellular sentinel for nucleic acid damage.

虽然紫外线 (UV) 辐射会损伤 DNA，引发 DNA 损伤反应 (DDR)，但它也会损伤 RNA，引发转录组范围内的核糖体碰撞并引发核糖毒性应激反应 (RSR)。然而，这些途径在决定细胞命运方面的相对贡献、时间和调节尚不清楚。在这里，我们使用时间分辨磷酸化蛋白质组学、化学遗传学、单细胞成像和生化方法来创建细胞响应紫外线损伤时激活的信号事件的时间顺序图谱。我们发现紫外线诱导的细胞凋亡是由 RSR 激酶 ZAK 介导的，而不是通过 DDR 介导的。我们确定了调节 ZAK 介导的细胞凋亡的两个负反馈模块：（1）GCN2 激活限制核糖体碰撞并减弱 ZAK 介导的 RSR；（2）ZAK 活性导致磷酸化蛋白自磷酸化及其随后的降解。这些事件将 ZAK 的活性调整至碰撞水平，以建立稳态、耐受性和死亡机制，揭示了其作为核酸损伤的细胞哨兵的关键作用。