ESR1 and breast cancer: Interestingly, estrogen treatment significantly upregulates the RNF115 mRNA in a dose-dependent manner in ER-positive T47D and MCF7 breast cancer cells as well as in ER-negative MDA-MB-231 cells stably transfected with ER (28, 31), whereas knockdown of ER substantially impairs the RNF115 mRNA levels (31).