CCNE1 and breast cancer: Moreover, re-expression of both Bcl-2 and Cyclin E1 almost fully restored tamoxifen-resistance (Figure 2E–2G) when miR-15a/16 mimics were co-transfected, suggesting Bcl-2 and Cyclin E1 work synergistically to confer tamoxifen resistance in breast cancer cells, but not being redundant to each other.