DNA double-strand breaks (DSBs) are highly toxic lesions that can drive genetic instability. These lesions also contribute to the efficacy of radiotherapy and many cancer chemotherapeutics. DNA repair efficiency is regulated by both intracellular and extracellular chemical signals. However, it is largely unknown whether this process is regulated by physical stimuli such as extracellular mechanical signals. Here, we report that DSB repair is regulated by extracellular mechanical signals. Low extracellular matrix (ECM) stiffness impairs DSB repair and renders cells sensitive to genotoxic agents. Mechanistically, we found that the MAP4K4/6/7 kinases are activated and phosphorylate ubiquitin in cells at low stiffness. Phosphorylated ubiquitin impairs RNF8-mediated ubiquitin signaling at DSB sites, leading to DSB repair deficiency. Our results thus demonstrate that ECM stiffness regulates DSB repair efficiency and genotoxic sensitivity through MAP4K4/6/7 kinase–mediated ubiquitin phosphorylation, providing a previously unidentified regulation in DSB-induced ubiquitin signaling.

DNA 双链断裂 (DSB) 是剧毒损伤，可导致遗传不稳定。这些病变也有助于放射疗法和许多癌症化学疗法的功效。DNA 修复效率受细胞内和细胞外化学信号的调节。然而，这个过程是否受到物理刺激（如细胞外机械信号）的调节在很大程度上是未知的。在这里，我们报告 DSB 修复受细胞外机械信号的调节。细胞外基质 (ECM) 硬度低会损害 DSB 修复并使细胞对基因毒剂敏感。从机制上讲，我们发现 MAP4K4/6/7 激酶在低刚度的细胞中被激活并磷酸化泛素。磷酸化泛素在 DSB 位点损害 RNF8 介导的泛素信号传导，导致 DSB 修复缺陷。