MODULATION OF THE MOLECULAR EXPRESSION AND FUNCTION OF BCL-2 FAMILY PROTEINS BY THE ARYL HYDROCARBON RECEPTOR IN BREAST CANCER STEM CELLS OF THE MDA-MB-231

Abstract

Breast cancer (BC) is a frequently occurring neoplasm in women and is a second major cause of cancer related deaths. Despite the remarkable advancements in the understanding of BC and its treatments, the diseases still pose numerous challenges. Many BC patients develop metastasis and advanced tumor which leads to increased morbidity and mortality. There is a substantial evidence that tumor relapse in BC patients is driven by special population of cells called cancer stem cells (CSCs). Breast CSCs confer stemness to BC and survive through the maintenance of several mechanisms among which the involvement of aryl hydrocarbon receptor (AhR) has recently been evaluated. The correlation of this receptor with BCL-2 family proteins for the development of breast CSCs remains unclear. This study is conducted to evaluate the correlation between AhR and BCL-2 proteins in vitro and in patient samples. Breast CSCs were enriched through mammosphere culture and characterized by flow cytometry. BC cells and breast CSCs were exposed to DMBA, ?NF and venetoclax (VCX), respectively and the expression of different genes was evaluated through RT-PCR and Western blot analysis. Moreover, determination of cellular content and localization through immunofluorescence and functional assays through muse cell analyser were also conducted. Finally, protein expression of AhR and BCL-2 in 75 human breast tissues was determined. The constitutive expression of AhR, CYP1B1 and anti-apoptotic BCL-2 proteins were found to be significantly higher in mammospheres than differentiated cancer cells (p<0.05). Moreover, AhR induction and inhibition modulated expression of BCL-2 proteins and inhibition of BCL-2 inhibited AhR and its regulated genes. The expressions of AhR and BCL-2 were also found to be higher in tissues of BC patients compared to the non-cancerous BC tissues. These findings demonstrated crosstalk between AhR and BCL-2 for development of breast CSCs which offers a strong basis for designing therapeutic strategies to target AhR in order to overcome drug resistance in BC.