Estrogen receptor-dependent regulation of CYP2B6 in human breast cancer cells

Estrogen receptor α (ERα) mediates the biological actions of estrogens and also contributes to the development and progression of breast cancer. To gain a more comprehensive understanding of ERα-mediated transcription, we used chromatin immunoprecipitation and promoter focused microarrays (ChIP-chip) to identify ERα binding sites in T-47D human breast cancer cells. Transcription factor binding site analysis revealed that the estrogen response element (ERE) was significantly over-represented and was found in 50% of the 243 ERα-bound regions identified. Interestingly, multiple ERα-bound regions were detected in the upstream regulatory sequences of the CYP2B gene cluster. Because ERα has been reported to regulate the expression of other cytochrome P450 enzymes and CYP2B6 is highly expressed in ERα-positive breast tumors, we focused on characterizing the ERα-dependent regulation of CYP2B6. Reporter gene assays revealed that ERα and ERβ increased CYP2B6-regulated gene expression through a functional ERE located at −1669 to −1657 in the upstream regulatory region of CYP2B6. E2 increased ERα and nuclear receptor coactivator 3 (NCoA3) recruitment to the 5′-flanking region of CYP2B6, and increased CYP2B6 mRNA levels in T-47D but not in MCF-7 human breast cancer cells. RNAi-mediated knockdown of ERα in the T-47D cells resulted in a significant decrease in CYP2B6 mRNA levels. Taken together, our study provides evidence for cell-type specific transcriptional regulation of the CYP2B6 gene by ERs.