Crosstalk between aryl hydrocarbon receptor (AhR) and BCL-2 pathways suggests the use of AhR antagonist to maintain normal differentiation state of mammary epithelial cells during BCL-2 inhibition therapy.

[Display omitted] • Activation of the AhR/CYP1A1 increased EpCAMHigh/CD49fLow CD61+ luminal progenitor-like cells in vivo mice model. • Activation of the AhR/CYP1A1 pathway increased BCL-2 expression and activity in vitro and in vivo. • Activation of BCL-2 increased the expression of the pluripotency factors in vitro and in vivo , while its inhibition by venetoclax prevented CSC expansion and chemoresistance. • Venetoclx treatment alone increased EpCAMHigh/CD49fLow CD61+ luminal progenitor-like cells causing inhibition of epithelial lineage markers and disruption of mammary gland branching. • Combined treatment of VCX with AhR antagonist in mice corrected the abnormal differentiation in mammary epithelial cells and protected mammary gland branching and cell identity. Activating the aryl hydrocarbon receptor upon exposure to environmental pollutants promotes development of breast cancer stem cell (CSCs). BCL-2 family proteins protect cancer cells from the apoptotic effects of chemotherapeutic drugs. However, the crosstalk between AhR and the BCL-2 family in CSC development remains uninvestigated. This study explored the interaction mechanisms between AhR and BCL-2 in CSC development and chemoresistance. A quantitative proteomic analysis study was performed as a tool for comparative expression analysis of breast cancer cells treated by AhR agonist. The basal and inducible levels of BCL-2, AhR, and CYP1A1 in vitro breast cancer and epithelial cell lines and in vivo mice animal models were determined by RT-PCR, Western blot analysis, immunofluorescence, flow cytometry, silencing of the target, and immunohistochemistry. In addition, an in silico toxicity study was conducted using DEREK software. Activation of the AhR/CYP1A1 pathway in mice increased EpCAMHigh/CD49fLow CD61+ luminal progenitor-like cells in early tumor formation but not in advanced tumors. In parallel, a chemoproteomic study on breast cancer MCF-7 cells revealed that the BCL-2 protein expression was the most upregulated upon AhR activation. The crosstalk between the AhR and BCL-2 pathways in vitro and in vivo modulated the CSCs features and chemoresistance. Interestingly, inhibition of BCL-2 in mice by venetoclax (VCX) increased EpCAMHigh/CD49fLow CD61+ luminal progenitor-like cells, causing inhibition of epithelial lineage markers, disruption of mammary gland branching and induced the epithelial-mesenchymal transition in mammary epithelial cells (MECs). The combined treatment of VCX and AhR antagonists in mice corrected the abnormal differentiation in MECs and protected mammary gland branching and cell identity. This is the first study to report crosstalk between AhR and BCL-2 in breast CSCs and provides the rationale for using a combined treatment of BCL-2 inhibitor and AhR antagonist for more effective cancer prevention and treatment. [ABSTRACT FROM AUTHOR]