Topoisomerase 2a (Topo2a)-dependent G2 arrest engenders faithful segregation of sister chromatids, yet in certain tumor cell lines where this arrest is dysfunctional, a PKCε-dependent failsafe pathway can be triggered. Here we elaborate on recent advances in understanding the underlying mechanisms associated with this G2 arrest by determining that p53–p21 signaling is essential for efficient arrest in cell lines, in patient-derived cells, and in colorectal cancer organoids. Regulation of this p53 axis required the SMC5/6 complex, which is distinct from the p53 pathways observed in the DNA damage response. Topo2a inhibition specifically during S phase did not trigger G2 arrest despite affecting completion of DNA replication. Moreover, in cancer cells reliant upon the alternative lengthening of telomeres (ALT) mechanism, a distinct form of Topo2a-dependent, p53-independent G2 arrest was found to be mediated by BLM and Chk1. Importantly, the previously described PKCε-dependent mitotic failsafe was engaged in hTERT-positive cells when Topo2a-dependent G2 arrest was dysfunctional and where p53 was absent, but not in cells dependent on the ALT mechanism. In PKCε knockout mice, p53 deletion elicited tumors were less aggressive than in PKCε-replete animals and exhibited a distinct pattern of chromosomal rearrangements. This evidence suggests the potential of exploiting synthetic lethality in arrest-defective hTERT-positive tumors through PKCε-directed therapeutic intervention. Significance: The identification of a requirement for p53 in stringent Topo2a-dependent G2 arrest and engagement of PKCε failsafe pathways in arrest-defective hTERT-positive cells provides a therapeutic opportunity to induce selective synthetic lethality.

中文翻译：

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hTERT 阳性癌细胞中基因组保护性拓扑异构酶 2a 依赖性 G2 阻滞需要 p53

拓扑异构酶 2a (Topo2a) 依赖性 G2 停滞会导致姐妹染色单体的忠实分离，但在这种停滞功能失调的某些肿瘤细胞系中，可能会触发 PKCε 依赖性故障保护途径。在这里，我们通过确定 p53-p21 信号传导对于细胞系、患者来源的细胞和结直肠癌类器官的有效停滞至关重要，详细阐述了理解与 G2 停滞相关的潜在机制的最新进展。p53 轴的调节需要 SMC5/6 复合物，该复合物与 DNA 损伤反应中观察到的 p53 途径不同。尽管影响 DNA 复制的完成，但特别是在 S 期期间抑制 Topo2a 不会引发 G2 停滞。此外，在依赖端粒选择性延长（ALT）机制的癌细胞中，发现一种独特形式的 Topo2a 依赖性、p53 独立性 G2 停滞是由 BLM 和 Chk1 介导的。重要的是，当 Topo2a 依赖性 G2 停滞功能失调且 p53 缺失时，先前描述的 PKCε 依赖性有丝分裂故障保护在 hTERT 阳性细胞中起作用，但在依赖 ALT 机制的细胞中则不然。在 PKCε 敲除小鼠中，p53 缺失引起的肿瘤比 PKCε 充足的动物的侵袭性要低，并且表现出独特的染色体重排模式。这一证据表明，通过 PKCε 导向的治疗干预，有可能在逮捕缺陷型 hTERT 阳性肿瘤中发挥合成致死作用。意义：