ESR1 and breast cancer: To determine that decreased MLK3 transcription in ER+ breast cancer cell is mediated via E2-ER axis, and diminished mRNA expression ultimately leads to decreased MLK3 protein expression, we treated three ER+ breast cancer cell lines (MCF7, T47D and ZR75.1) with physiological dose of E2 (10 nM) for different periods of time (1–5 days).