Mild replication stress causes aneuploidy by deregulating microtubule dynamics in mitosis

Chromosomal instability (CIN) causes structural and numerical chromosome aberrations and represents a hallmark of cancer. Replication stress (RS) has emerged as a driver for structural chromosome aberrations while mitotic defects can cause whole chromosome missegregation and aneuploidy. Recently, first evidence indicated that RS can also influence chromosome segregation in cancer cells exhibiting CIN, but the underlying mechanisms remain unknown. Here, we show that chromosomally unstable cancer cells suffer from very mild RS, which allows efficient proliferation and which can be mimicked by treatment with very low concentrations of aphidicolin. Both, endogenous RS and aphidicolin-induced very mild RS cause chromosome missegregation during mitosis leading to the induction of aneuploidy. Moreover, RS triggers an increase in microtubule plus end growth rates in mitosis, an abnormality previously identified to cause chromosome missegregation in cancer cells. In fact, RS-induced chromosome missegregation is mediated by increased mitotic microtubule growth rates and is suppressed after restoration of proper microtubule growth rates and upon rescue of replication stress. Hence, very mild and cancer-relevant RS triggers aneuploidy by deregulating microtubule dynamics in mitosis.染色体不稳定性（CIN）可引发染色体结构与数目畸变，是癌症的标志性特征之一。复制应激（RS）已被证实是染色体结构畸变的驱动因素，而有丝分裂缺陷则会导致整条染色体分离错误与非整倍体的产生。近期已有初步证据表明，复制应激亦可对存在染色体不稳定性的癌细胞的染色体分离过程产生影响，但其背后的潜在分子机制仍未明确。本研究证实，染色体不稳定的癌细胞会受到极轻度复制应激的影响：这类应激既能够维持癌细胞的高效增殖，也可通过极低浓度的阿非迪霉素（aphidicolin）处理得以模拟。无论是内源性复制应激，还是阿非迪霉素诱导的极轻度复制应激，都会在有丝分裂过程中引发染色体分离错误，进而诱导非整倍体的产生。此外，复制应激会提高有丝分裂期微管正端的生长速率——这一异常此前已被证实会导致癌细胞出现染色体分离错误。事实上，复制应激诱导的染色体分离错误是由有丝分裂微管生长速率升高所介导的，而恢复正常的微管生长速率或缓解复制应激后，该现象会受到抑制。综上，与癌症相关的极轻度复制应激，可通过扰乱有丝分裂期的微管动力学，进而诱导非整倍体的产生。