Molecular mechanisms of bilirubin induced G1 cell cycle arrest and apoptosis in human breast cancer cell lines: involvement of the intrinsic pathway

Background Bilirubin, as an essential constituent of cellular signaling pathways, may have a role in cell growth and apoptosis in breast cancer, although the biochemical relevance is still unclear. The purpose of the present study is to recognize the mechanism underlying bilirubin-induced apoptosis in breast cancer cell lines. Methods and Results To detect the cell viability, MTT assay was carried out. Apoptosis was assessed by flow cytometry analysis and caspase activities were determined by colorimetric method. The expression of AhR, cyclin D1, cyclin A, p53, p27, Bcl-2, and Bax were examined using real-time PCR. The cell viability has been reduced by bilirubin in a dose-dependent manner and an intrinsic apoptotic response has been occurred that was evidenced by the elevation of caspase‐3 and − 9 activities. Bilirubin induced cell arrest in cell-cycle progression, which was associated with the induction of AhR expression, down-regulation of cyclin D1, cyclin A, and upregulation of p53 and p27 expression. Following bilirubin treatment, Bcl-2 was decreased and Bax protein was increased in both cell lines. Conclusions To discuss, bilirubin, as a naturally occurring antiproliferative molecule, mediates growth inhibition by induction of cell cycle arrest and apoptosis in MCF-7 and MDA-MB-468 breast cancer cells. It is associated with the suppression of cyclin A, D1, and Bcl-2; induction of p53, p27, and Bax together with the activation of caspase-3 and − 9.