ESR1 and breast cancer: Furthermore, our series of transcriptional regulation analyses in the MCF7 ER-positive breast cancer cell line has demonstrated that PPARGC1B expression can be induced by estrogen treatment, and this transcriptional response of PPARGC1B is probably mediated by five functional ER binding sites around PPARGC1B that are all engaged in interlocking chromatin loops highly indicative of an ER regulated gene [35].