Effect of spindle checkpoint on Akt2-mediated paclitaxel-resistance in A2780 ovarian cancer cells

Integrative microRNA and gene expression analysis identifies new epigenetically regulated microRNAs mediating taxane resistance in ovarian cancer

Taxane is a family of front-line chemotherapeutic agents against ovarian cancer (OC). The therapeutic efficacy is frequently counteracted by the development of chemoresistance, leading to high rates of relapse in OC patients. The role(s) of microRNAs (miRNAs) in cancer chemoresistance had been supported by many evidences Epigenetic regulation by miRNAs has been reported to influence cancer development and response to therapeutics, however, their role in OC resistance to paclitaxel (PTX) is unclear. Here, we conducted miRNA profiling in the responsive and PTX-resistant OC cell lines before and after treatment with epigenetic modulators. We reveal 157 miRNAs to be downregulated in the PTX-resistant cells compared to parental controls. The expression of five miRNAs (miRNA-7-5p, -204-3p, -501-5p, -3652 and -4286) was restored after epigenetic modulation, which was further confirmed by qPCR. In silico analysis of the signaling pathways targeted by the selected miRNAs identified the PI3K-AKT pathway as the primary target. Subsequent cDNA array analysis confirmed multiple PI3K-AKT pathway members such as AKT2, PIK3R3, CDKN1A, CCND2 and FGF2 to be upregulated in PTX-resistant cells. STRING analysis showed the deregulated genes in PTX-resistant cells to be primarily involved in cell cycle progression and survival. Thus, high throughput miRNA and cDNA profiling coupled with pathway analysis and data mining provide evidence for epigenetically regulated miRNAs-induced modulation of signaling pathways in PTX resistant OC cells. It paves the way to more in-depth mechanistic studies and new therapeutic strategies to combat chemoresistance.

Mitotic checkpoint defects: en route to cancer and drug resistance

Loss of mitosis regulation is a common feature of malignant cells that leads to aberrant cell division with inaccurate chromosome segregation. The mitotic checkpoint is responsible for faithful transmission of genetic material to the progeny. Defects in this checkpoint, such as mutations and changes in gene expression, lead to abnormal chromosome content or aneuploidy that may facilitate cancer development. Furthermore, a defective checkpoint response is indicated in the development of drug resistance to microtubule poisons that are used in treatment of various blood and solid cancers for several decades. Mitotic slippage and senescence are important cell fates that occur even with an active mitotic checkpoint and are held responsible for the resistance. However, contradictory findings in both the scenarios of carcinogenesis and drug resistance have aroused questions on whether mitotic checkpoint defects are truly responsible for these dismal outcomes. Here, we discuss the possible contribution of the faulty checkpoint signaling in cancer development and drug resistance, followed by the latest research on this pathway for better outcomes in cancer treatment.

Effect of Mad2 on paclitaxel-induced cell death in ovarian cancer cells

In this article, the status of spindle assembly checkpoint and the alteration of its major component, Mad2 protein level were examined in A2780 and SKOV3 ovarian cancer cell lines. Recombinant eukaryotic expression plasmid pEGFP-Mad2 was transfected into paclitaxel-resistant SKOV3 cells and Mad2 protein was knocked down by Mad2-specific siRNA in paclitaxel-sensitive A2780 cells. Then the expression level of Mad2 gene was detected by Western blotting. Flow cytometry revealed that SKOV3 cells were not fully arrested in G(2)/M phase in contrast to A2780 cells in the presence of paclitaxel. However, paclitaxel sensitivity assay showed that sensitivity to paclitaxel was reversed after the transfection in both cell lines in terms of number of cells arrested at G(2)/M phase and the expression of Bcl-2 was significantly changed. These results suggest that weakened spindle checkpoint with reduced expression of Mad2 is associated with resistance to paclitaxel in ovarian cells and Bcl-2 may be involved in this process.