Dysregulated BARD1 Contributes to Paclitaxel Resistance in Ovarian Cancer via Up-regulating CYP2C8

Ovarian cancer remains one of the most lethal gynaecological malignancies, with paclitaxel resistance being a major therapeutic challenge that limits treatment efficacy and patient survival. We found that although the BARD1 level was not signi-ficantly altered in patients with ovarian cancer (OC), patients with higher BARD1 levels had increased survival time, suggesting that the down-regulation of BARD1 may be related to the paclitaxel sensitivity. Through examining the expression of BARD1 in tumour samples from paclitaxel responders and non-responders, we observed that the BARD1 level was significantly reduced in non-responders. CYP2C8 was up-regulated in non-responders. Also, the BARD1 level was negatively correlated with the level of CYP2C8. BARD1 over-expression in OC cells could repress the CYP2C8 expression, while knockdown of BARD1 could up-regulate CYP2C8 expression, which could be rescued by H2A-Ub. Results from gain and loss of functional experiments indicated that BARD1 functions as a tumour suppressor during paclitaxel treatment, and BARD1 down-regulation increased the IC50 of paclitaxel from 2.46 nM to 5.33 nM in SK-OV-3 cells and from 3.11 nM to 7.51 nM in CaoV-3 cells. We are the first to demonstrate that the down-regulation of BARD1 contributes to paclitaxel resistance via up-regulating CYP2C8 in patients with OC, which provides a potent target for clinical OC treatment.