SDHB reduces chemotherapy resistance in ovarian cancer cells by affecting epithelial mesenchymal transition through DNA damage repair

Abstract

Background: Ovarian carcinoma is one of the most common gynecological cancers with high mortality rates. Succinate dehydrogenase (SDH or Complex II) which is one of the important enzymes in the tricarboxylic acid (TCA) cycle plays an important role in carcinomas. Succinate dehydrogenase subunit B (SDHB) gene, which encodes one of the four subunits of SDH, has been found played as a tumor suppressor role in ovarian cancer. However, the role of SDHB in ovarian cancer chemotherapy is still unclear. Methods: Using the SDHB specific siRNA and overexpression plasmid, the expression of SDHB was silenced and conversely induced in ovarian cancer cell lines SKOV3 and A2780, respectively. The possible role of SDHB in ovarian cancer chemotherapy was investigated in vitro using CCK8 and Colony formation assays. Real-time PCR was used to exam the expression of SDH subunits in ovarian cancer tissues and normal ovarian tissues. Immunohistochemistry was used to exam the expression of SDHB in human ovarian cancer cisplatin-resistant tissues and corresponding cisplatin-sensitive tissues. To explore the mechanism, epithelial mesenchymal transition (EMT) and DNA damage repair related proteins such as E-cadherin, Vimentin, γ-H2AX and ERCC1 were examined by western blot in SKOV3 and A2780 cells. EMT related transcription factors such as Slug, Snail and Twist mRNA levels were examined by quantitative real-time reverse transcriptase PCR. Results: Succinate dehydrogenase subunits were expressed lower in ovarian cancer tissues than in normal ovarian tissues, with the SDHB subunit being expressed lower in ovarian cancer tissues. Moreover, the expression of SDHB in ovarian cancer metastatic tissues was lower than that in primary tissues, and SDHB expressed lower in human ovarian cancer cisplatin-resistant tissues than the corresponding cisplatin-sensitive tissues. In SDHB silenced ovarian cancer cells, E-cadherin was decreased, Vimentin was increased. The EMT- related transcription factors Snail and Slug were significantly increased (P<0.05), while Twist showed no significant increase (P>0.05) in SDHB-silenced cancer cells. In contrast, overexpression of SDHB increased E-cadherin expression and reduced Vimentin expression in SKOV3 cells. SDHB silencing increased drug resistance and SDHB overexpression showed the opposite results in SKOV3 and A2780 cells. In SDHB-silenced cancer cells, the level of ERCC1, which contributes to platinum drug resistance by promoting DNA repair, was increased, and γ-H2AX, which is related to cell apoptosis and drug resistance was decreased, and SDHB overexpression showed the opposite results in SKOV3 cells. Conclusions: SDHB reduced the chemotherapy resistance of ovarian cancer cells significantly, and its mechanism might be by inhibiting epithelial mesenchymal transition of ovarian cancer cells, further reducing their DNA damage repair ability and thereby reducing chemotherapy resistance, which provides a preliminary experimental and theoretical basis for the treatment of ovarian cancer.