Liu Rui-Lei, Dong Ye, Deng Yan-Zhen, Wang Wen-Jun, Li Wei-Dong
Department of the First Medicine, Cancer Hospital of Guangzhou Medical College, Guangzhou, 510095, China.
Tumour Biol. 2015 Jul;36(7):5011-9. doi: 10.1007/s13277-015-3152-5. Epub 2015 Apr 27.
Colorectal cancer (CRC) is one of the most common cancers worldwide. Although chemotherapy is used as a palliative treatment, ultimately, nearly all patients develop drug resistance. Therefore, the cell-inherent DNA repair pathway must reverse the DNA-damaging effect of cytotoxic drugs that mediates therapeutic resistance to chemotherapy. RAD18, a DNA damage-activated E3 ubiquitin ligase, is known to play a critical role in DNA damage repair in cancer cells. Here, we show that RAD18 is highly expressed in human 5-fluorouracil (5-FU)-resistant cancer cells after 5-FU treatment. In addition, RAD18 increases in CRC cells could induce DNA damage repair, suggesting that RAD18 might be a possible target for overcoming drug resistance. Moreover, the expression of tumor suppressor microRNA-145 (miR-145) was negatively correlated with RAD18 expression in CRC tissues of 140 patients. Using luciferase reporters carrying the 3'-untranslated region of RAD18 combined with Western blotting, we identified RAD18 as a direct target of miR-145. Also of interest, suppression of RAD18 by miR-145 enhanced DNA damage in CRC cells after 5-FU treatment. Finally, the 5-FU-resistant cancer cells could be selectively ablated by treatment with miR-145. Taken together, these results suggest that miR-145 can act as an RAD18 inhibitor and contribute as an important factor in reversing drug resistance after chemotherapy.
结直肠癌（CRC）是全球最常见的癌症之一。尽管化疗被用作姑息治疗，但最终几乎所有患者都会产生耐药性。因此，细胞内在的DNA修复途径必须逆转细胞毒性药物的DNA损伤效应，而这种效应介导了对化疗的治疗抗性。RAD18是一种DNA损伤激活的E3泛素连接酶，已知在癌细胞的DNA损伤修复中起关键作用。在此，我们表明RAD18在5-氟尿嘧啶（5-FU）处理后的人5-FU耐药癌细胞中高度表达。此外，CRC细胞中RAD18的增加可诱导DNA损伤修复，这表明RAD18可能是克服耐药性的一个潜在靶点。此外，在140例患者的CRC组织中，肿瘤抑制性微小RNA-145（miR-145）的表达与RAD18的表达呈负相关。通过使用携带RAD18 3'-非翻译区的荧光素酶报告基因并结合蛋白质免疫印迹，我们确定RAD18是miR-145的直接靶点。同样有趣的是，miR-145对RAD18的抑制增强了5-FU处理后CRC细胞中的DNA损伤。最后，用miR-145处理可选择性地消除5-FU耐药癌细胞。综上所述，这些结果表明miR-145可作为RAD18抑制剂，并作为化疗后逆转耐药性的重要因素发挥作用。
