Identification of new genetic pathways or molecular targets that sensitize cancer cells to chemotherapeutic drugs may improve the efficacy of current chemotherapy. Here, we report that downmodulation of UHRF1 (ubiquitin-like with PHD and RING finger domains 1) in retinoblastoma (RB) cells increases the sensitivity to histone deacetylase (HDAC) inhibitors, augmenting apoptotic cell death. We found that UHRF1 depletion downregulates two redox-responsive genes GSTA4 (glutathione S-transferase α4) and TXN2 (thioredoxin-2) in RB cells, and increases the basal level of intracellular oxidative stress. Antioxidant treatment significantly reduced both basal and HDAC inhibitor-induced DNA damage and apoptosis in UHRF1-depleted cells. Knockdown of GSTA4 or TXN2 sensitized RB cells to HDAC inhibitors, demonstrating that GSTA4 and TXN2 play key roles in redox homeostasis in RB cells and the susceptibility to HDAC inhibitor treatment upon UHRF1 depletion. In human primary RB, GSTA4 and TXN2 proteins were found to be mostly elevated along with high UHRF1 expression. In addition to augmentation of apoptosis in UHRF1-depleted RB cells, we also show that UHRF1 downmodulation derepresses the expression of photoreceptor-specific genes in RB cells in cooperation with a HDAC inhibitor MS-275 and promotes neuron-like differentiation. However, further investigation revealed that the enhanced growth-inhibitory effects of MS-275 in UHRF1-depleted cells were still mainly due to robust apoptosis induction rather than differentiation-mediated growth arrest. Consistent with our findings, UHRF1 depletion in RB cells increased the therapeutic efficacy of MS-275 in murine orthotopic xenografts. These results provide a novel basis for potential benefits of UHRF1 targeting for RB treatment.

中文翻译：

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UHRF1下调通过增加氧化应激介导的细胞凋亡，增强了视网膜母细胞瘤中组蛋白脱乙酰基酶抑制剂的抗肿瘤作用。

鉴定使癌细胞对化学治疗药物敏感的新的遗传途径或分子靶标可以改善当前化学疗法的功效。在这里，我们报道视网膜母细胞瘤（RB）细胞中的UHRF1（具有PHD和RING指域1的泛素样蛋白）的下调增加了对组蛋白脱乙酰基酶（HDAC）抑制剂的敏感性，从而增加了凋亡细胞的死亡。我们发现，UHRF1耗竭下调了RB细胞中的两个氧化还原反应基因GSTA4（谷胱甘肽S-转移酶α4）和TXN2（硫氧还蛋白2），并增加了细胞内氧化应激的基础水平。抗氧化剂治疗可显着减少基础和HDAC抑制剂诱导的UHRF1缺失细胞中的DNA损伤和细胞凋亡。击倒GSTA4或TXN2致敏的RB细胞与HDAC抑制剂，证明了GSTA4和TXN2在RB细胞的氧化还原稳态和UHRF1耗尽后对HDAC抑制剂治疗的敏感性中起关键作用。在人类原发性RB中，发现GSTA4和TXN2蛋白与高UHRF1表达一起大部分升高。除了在耗尽UHRF1的RB细胞中增加凋亡外，我们还显示UHRF1下调与HDAC抑制剂MS-275合作抑制RB细胞中光感受器特异性基因的表达，并促进神经元样分化。但是，进一步的研究表明，MS-275在UHRF1缺失的细胞中增强的生长抑制作用仍主要归因于强大的细胞凋亡诱导，而不是分化介导的生长停滞。与我们的发现一致，RB细胞中的UHRF1耗竭提高了MS-275在小鼠原位异种移植物中的治疗效果。这些结果为UHRF1靶向治疗RB的潜在益处提供了新的依据。