Su Benyu, Lim David, Tian Zhujun, Liu Guochao, Ding Chenxia, Cai Zuchao, Chen Chen, Zhang Fengmei, Feng Zhihui
Department of Occupational and Environmental Health, School of Public Health, Cheeloo College of Medicine, Shandong University, Jinan, China.
School of Health Sciences, Western Sydney University, Campbelltown, NSW, Australia.
Front Oncol. 2021 Aug 27;11:681278. doi: 10.3389/fonc.2021.681278. eCollection 2021.
Breast cancer is the primary problem threatening women's health. The combined application of valproic acid (VPA) and hydroxyurea (HU) has a synergistic effect on killing breast cancer cells, but the molecular mechanism remains elusive. Replication protein A2 phosphorylation (pRPA2), is essential for homologous recombination (HR) repair and cell cycle. Here we showed that in response to HU, the VPA significantly decreased the tumor cells survival, and promoted S-phase slippage, which was associated with the decrease of pCHK1 and WEE1/pCDK1-mediated checkpoint kinases phosphorylation pathway and inhibited pRPA2/Rad51-mediated HR repair pathway; the mutation of pRPA2 significantly diminished the above effect, indicating that VPA-caused HU sensitization was pRPA2 dependent. It was further found that VPA and HU combination treatment also resulted in the decrease of endonuclease MUS81. After MUS81 elimination, not only the level of pRPA2 was abolished in response to HU treatment, but also VPA-caused HU sensitization was significantly down-regulated through pRPA2-mediated checkpoint kinases phosphorylation and HR repair pathways. In addition, the VPA altered the tumor microenvironment and reduced tumor burden by recruiting macrophages to tumor sites; the Kaplan-Meier analysis showed that patients with high pRPA2 expression had significantly worse survival. Overall, our findings demonstrated that VPA influences HR repair and cell cycle through down-regulating MUS81-pRPA2 pathway in response to HU treatment.
乳腺癌是威胁女性健康的首要问题。丙戊酸（VPA）与羟基脲（HU）联合应用对杀伤乳腺癌细胞具有协同作用，但其分子机制仍不清楚。复制蛋白A2磷酸化（pRPA2）对同源重组（HR）修复和细胞周期至关重要。在此我们发现，在HU作用下，VPA显著降低肿瘤细胞存活率，并促进S期滑脱，这与pCHK1和WEE1/pCDK1介导的检查点激酶磷酸化途径的降低相关，并抑制pRPA2/Rad51介导的HR修复途径；pRPA2的突变显著减弱了上述作用，表明VPA导致的HU敏感性是pRPA2依赖性的。进一步发现，VPA与HU联合治疗还导致核酸内切酶MUS81水平降低。消除MUS81后，不仅HU处理后pRPA2水平消失，而且VPA导致的HU敏感性通过pRPA2介导的检查点激酶磷酸化和HR修复途径显著下调。此外，VPA通过将巨噬细胞募集到肿瘤部位改变肿瘤微环境并减轻肿瘤负担；Kaplan-Meier分析显示，pRPA2高表达患者的生存率显著较差。总体而言，我们的研究结果表明，VPA通过在HU处理后下调MUS81-pRPA2途径影响HR修复和细胞周期。
