Previously, we discovered that deletion of c-Rel in the Eµ-Myc mouse model of lymphoma results in earlier onset of disease, a finding that contrasted with the expected function of this NF-κB subunit in B-cell malignancies. Here we report that Eµ-Myc/cRel−/− cells have an unexpected and major defect in the CHK1 pathway. Total and phospho proteomic analysis revealed that Eµ-Myc/cRel−/− lymphomas highly resemble wild-type (WT) Eµ-Myc lymphomas treated with an acute dose of the CHK1 inhibitor (CHK1i) CCT244747. Further analysis demonstrated that this is a consequence of Eµ-Myc/cRel−/− lymphomas having lost expression of CHK1 protein itself, an effect that also results in resistance to CCT244747 treatment in vivo. Similar down-regulation of CHK1 protein levels was also seen in CHK1i resistant U2OS osteosarcoma and Huh7 hepatocellular carcinoma cells. Further investigation revealed that the deubiquitinase USP1 regulates CHK1 proteolytic degradation and that its down-regulation in our model systems is responsible, at least in part, for these effects. We demonstrate that treating WT Eµ-Myc lymphoma cells with the USP1 inhibitor ML323 was highly effective at reducing tumour burden in vivo. Targeting USP1 activity may thus be an alternative therapeutic strategy in MYC-driven tumours.

中文翻译：

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通过 c-Rel 和 USP1 依赖途径调节 CHK1 抑制剂耐药性

以前，我们发现在 Eµ-Myc 小鼠淋巴瘤模型中删除 c-Rel 会导致疾病提前发作，这一发现与该 NF-κB 亚基在 B 细胞恶性肿瘤中的预期功能形成对比。在这里，我们报告 Eµ-Myc/cRel−/− 细胞在 CHK1 通路中有一个意想不到的重大缺陷。总蛋白质组学和磷酸化蛋白质组学分析表明，Eµ-Myc/cRel-/- 淋巴瘤与用急性剂量的 CHK1 抑制剂 (CHK1i) CCT244747 治疗的野生型 (WT) Eµ-Myc 淋巴瘤高度相似。进一步分析表明，这是 Eµ-Myc/cRel-/- 淋巴瘤失去 CHK1 蛋白表达的结果，这种效应也会导致体内对 CCT244747 治疗产生耐药性。在 CHK1i 抗性 U2OS 骨肉瘤和 Huh7 肝细胞癌细胞中也观察到类似的 CHK1 蛋白水平下调。进一步的调查表明，去泛素化酶 USP1 调节 CHK1 蛋白水解降解，并且它在我们的模型系统中的下调至少部分是造成这些影响的原因。我们证明用 USP1 抑制剂 ML323 治疗 WT Eµ-Myc 淋巴瘤细胞在减少体内肿瘤负荷方面非常有效。因此，靶向 USP1 活性可能是 MYC 驱动肿瘤的另一种治疗策略。