ESR1 and breast cancer: Our results showed that cyclin D1 expressions were downregulated upon IKKε knockdown in both estrogen receptor-positive (MCF-7) and estrogen receptor-negative (SK-BR-3) breast cancer cells (Figure 9c, d), and the reduced cyclin D1 expressions in both breast cancer cell lines were correlated with a cell cycle arrest in G0/G1 (Figure 6a, b).