RESUMEN
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.
Asunto(s)
Neoplasias Colorrectales/genética , Proteínas de Unión al ADN/biosíntesis , Genes Supresores de Tumor , MicroARNs/biosíntesis , Anciano , Animales , Apoptosis/efectos de los fármacos , Apoptosis/genética , Neoplasias Colorrectales/tratamiento farmacológico , Neoplasias Colorrectales/patología , Daño del ADN/genética , Reparación del ADN/efectos de los fármacos , Reparación del ADN/genética , Proteínas de Unión al ADN/genética , Resistencia a Antineoplásicos/genética , Fluorouracilo/administración & dosificación , Regulación Neoplásica de la Expresión Génica , Humanos , Estimación de Kaplan-Meier , Ratones , MicroARNs/genética , Persona de Mediana Edad , Ubiquitina-Proteína Ligasas , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
Hepatocellular carcinoma (HCC) is the fifth most common cancer type worldwide and the third leading cause of cancer-associated mortality. To date, its pathogenesis has remained poorly understood. Previous studies have demonstrated that deregulated microRNA (miR) participates in hepatocarcinogenesis. In the present study, miR-218 and miR-520a were observed to be downregulated in human HCC cells relative to normal hepatic cells. Overexpression of miR-218 or miR-520a inhibited cell proliferation and induced cell cycle arrest at the G0/G1 phase checkpoint. Furthermore, a dual-luciferase reporter assay identified that E2F2 was a novel direct target of miR-218 but not miR-520a in HCC. In addition, miR-218 and miR-520a were observed to negatively regulate E2F2 mRNA and protein levels. This suggested that miR-218 regulated the expression of E2F2 via directly binding to its 3'-untranslated region, whereas miR-520a affected E2F2 expression indirectly. In conclusion, these results indicated that miR-218 and miR-520a are crucial in the development of HCC via the inhibition of cell proliferation and cycle progression by downregulating E2F2.
