Choriocarcinoma is sensitive to chemotherapy. However, drug resistance has become one of the major problems in recent years. Previous studies have shown that many tumors contained a small fraction of cells that exhibited enhanced tumor initiating potential and stem cell-like properties. It is hypothesized that cancer stem cells (CSCs) are organized in a cellular hierarchy. They also have the qualities of selfrenewal, chemoresistance, and so on. The identification of CSCs in choriocarcinoma and the mechanism contributing to their qualities remain largely unknown. This study focused on the role of AhR, a transcription factor abundantly expressed in many different types of cancer, in the regulation of the expansion of choriocarcinoma CSCs and the exact molecular mechanisms. Spheroid cells isolated from choriocarcinoma in serum-free conditions have stem cell-like characteristics. The expression and nuclear translocation of AhR were markedly elevated in spheroid cells. Activation of AhR by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) significantly increased the spheroid-forming efficiency, chemotherapy resistance, and ability to form tumor xenografts of the cells, whereas AhR knockdown, using short hairpin RNA (shRNA), dramatically reduced stem cell properties. Mechanistically, activating the β-catenin pathway might be an essential biological function of AhR during the regulation of the CSC characteristics. This study also identified ABCG2, which plays an important role in CSCs, as a direct target of AhR. Together, these results strongly suggested the participation of AhR in choriocarcinoma carcinogenesis. Targeting AhR may provide a novel therapeutic opportunity for choriocarcinoma. ARTICLE HISTORY

Choriocarcinoma (CC) is a trophoblast tumor prone to early distant organ metastases. At present, the main treatment for CC is chemotherapy, but chemotherapy resistance readily occurs and leads to treatment failure. H19 is a long noncoding RNA, and its abnormal expression has been found in various tumors, including CC. H19 is also considered to be related to the drug resistance mechanism of the same cancers. To investigate the role of H19 in drug‐resistant CC cells, the following experiments were designed. We used human CC cell line JEG‐3 to establish cell lines resistant to methotrexate and 5‐fluorouracil (JEG‐3/MTX and JEG‐3/5‐FU) and detected the expression of H19 in JEG‐3, JEG‐3/MTX, JEG‐3/5‐FU cells, JEG‐3 with MTX, and JEG‐3 with 5‐FU. We found that the expression of H19 in the JEG‐3/MTX and JEG‐3/5‐FU cells were significantly higher than that in JEG‐3 cells. JEG‐3 cells were treated with MTX or 5‐FU for and quantitative real‐time polymerase chain reaction assay revealed that H19 messenger RNA expression increased. Furthermore, after H19 was knocked out, the drug resistance index of the JEG‐3/MTX and JEG‐3/5‐FU cells decreased; the proliferation, migration, and invasion ability diminished significantly; and apoptosis increased significantly. Finally, we detected the total and phosphorylation protein expression of phosphatidylinositol‐3‐kinase (PI3K), protein kinase B (AKT), and mammalian target of rapamycin (mTOR) in the JEG‐3/MTX and JEG‐3/5‐FU cells. The total protein of PI3K, AKT, and mTOR in the H19 knockout resistant cells showed no significant change relative to those in the H19 non‐knockout resistant cells, whereas the phosphorylated proteins of PI3K, AKT, and mTOR were significantly decreased. Phosphorylated proteins of PI3K, AKT, and mTOR in the JEG‐3/MTX and JEG‐3/5‐FU cells were significantly higher than that in JEG‐3 cells. After using inhibition of phosphorylated PI3K/AKT/mTOR, the proliferation, migration, and invasion ability of the JEG‐3/MTX and JEG‐3/5‐FU cells diminished significantly; and apoptosis increased significantly. On the basis of the above experiments, we concluded that H19 is related to the drug resistance of CC, and the knockout of H19 can reduce the drug resistance of resistant CC cells; and decrease the proliferative, migratory, and invasive ability; and increase the apoptosis. PI3K/AKT/mTOR pathway might be involved in H19‐mediated effects. H19 is expected to be a therapeutic target for the treatment of drug‐resistant chorionic carcinoma.

No abstract

No abstract