Addiction to the WRN helicase is a unique vulnerability of human cancers with high levels of microsatellite instability (MSI-H). However, while prolonged loss of WRN ultimately leads to cell death, little is known about how MSI-H cancers initially respond to acute loss of WRN—knowledge that would be helpful for informing clinical development of WRN targeting therapy, predicting possible resistance mechanisms, and identifying useful biomarkers of successful WRN inhibition. Here, we report the construction of an inducible ligand-mediated degradation system in which the stability of endogenous WRN protein can be rapidly and specifically tuned, enabling us to track the complete sequence of cellular events elicited by acute loss of WRN function. We found that WRN degradation leads to immediate accrual of DNA damage in a replication-dependent manner that curiously did not robustly engage checkpoint mechanisms to halt DNA synthesis. As a result, WRN-degraded MSI-H cancer cells accumulate DNA damage across multiple replicative cycles and undergo successive rounds of increasingly aberrant mitoses, ultimately triggering cell death. Of potential therapeutic importance, we found no evidence of any generalized mechanism by which MSI-H cancers could adapt to near-complete loss of WRN. However, under conditions of partial WRN degradation, addition of low-dose ATR inhibitor significantly increased their combined efficacy to levels approaching full inactivation of WRN. Overall, our results provide the first comprehensive view of molecular events linking upstream inhibition of WRN to subsequent cell death and suggest that dual targeting of WRN and ATR might be a useful strategy for treating MSI-H cancers.

中文翻译：

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微卫星不稳定癌细胞中细胞命运的全面图谱支持 WRN 和 ATR 的双重靶向

对 WRN 解旋酶的成瘾是具有高水平微卫星不稳定性 (MSI-H) 的人类癌症的独特弱点。然而，虽然 WRN 的长期缺失最终会导致细胞死亡，但人们对 MSI-H 癌症最初如何对 WRN 的急性缺失做出反应知之甚少——这些知识将有助于为 WRN 靶向治疗的临床开发提供信息、预测可能的耐药机制以及识别成功抑制 WRN 的有用生物标志物。在这里，我们报告了诱导配体介导的降解系统的构建，其中内源性 WRN 蛋白的稳定性可以快速、特异性地调节，使我们能够跟踪由 WRN 功能急性丧失引起的细胞事件的完整序列。我们发现 WRN 降解会以复制依赖性方式立即产生 DNA 损伤，奇怪的是，这种方式并没有强有力地利用检查点机制来停止 DNA 合成。结果，WRN 降解的 MSI-H 癌细胞在多个复制周期中积累 DNA 损伤，并经历连续几轮越来越异常的有丝分裂，最终引发细胞死亡。对于潜在的治疗重要性，我们没有发现任何证据表明 MSI-H 癌症可以适应 WRN 几乎完全丧失的任何普遍机制。然而，在部分 WRN 降解的条件下，添加低剂量 ATR 抑制剂可显着提高其综合功效，达到接近 WRN 完全失活的水平。总体而言，我们的结果首次全面了解了 WRN 上游抑制与随后的细胞死亡之间的分子事件，并表明 WRN 和 ATR 的双重靶向可能是治疗 MSI-H 癌症的有用策略。