Mitotic Deregulation by Survivin in ErbB2-Overexpressing Breast Cancer Cells Contributes to Taxol Resistance

Purpose: Taxol resistance remains a major obstacle to improve the benefit of breast cancer patients. Here, we studied whether overexpression of ErbB2 may lead to mitotic deregulation in breast cancer cells via up-regulation of survivin that confers Taxol resistance. Experimental Design: ErbB2-overexpressing and ErbB2-low-expressing breast cancer cell lines were used to compare their mitotic exit rate, survivin expression level, and apoptosis level in response to Taxol. Survivin was then down-regulated by antisense oligonucleotides to evaluate its contribution to mitotic exit and Taxol resistance in ErbB2-overexpressing breast cancer cells. At last, specific PI3K/Akt and Src inhibitors were used to investigate the involvement of these two pathways in ErbB2-mediated survivin up-regulation and Taxol resistance. Results: We found that Erb32-overexpressing cells expressed higher levels of survivin in multiple breast cancer cell lines and patient samples. ErbB2-overexpressing cells exited M phase faster than ErbB2-low-expressing cells, which correlated with the increased resistance to Taxol-induced apoptosis. Down-regulation of survivin by antisense oligonucleotide delayed mitotic exit of ErbB2-overexpressing cells and also sensitized ErbB2-overexpressing cells to Taxol-induced apoptosis. Moreover, ErbB2 up-regulated survivin at translational level and PI3K/Akt and Src activation are involved. In addition, combination treatment of Taxol with PI3K/Akt and Src inhibitor led to increased apoptosis in ErbB2-overexpressing breast cancer cells than single treatment. Conclusions: Survivin up-regulation by ErbB2 is a critical event in ErbB2-mediated faster mitotic exit and contributes to Taxol resistance.