Apoptosis and cell cycle regulatory effects of adenosine by modulation of GLI-1 and ERK1/2 pathways in CD44(+) and CD24(-) breast cancer stem cells

Abstract

Objectives: Breast cancer stem cells (CSCs) are a small population of tumour cells with the ability of self-renewal and resistance to chemotherapy. Targeting CSCs is a promising strategy for treatment of cancer. A recent study demonstrated that adenosine receptor agonists inhibit glioblastoma CSCs proliferation. At present, the effect of adenosine on breast CSCs has not been reported. Therefore, this study was designed to evaluate the effect of adenosine and its signalling pathways in breast CSCs. Materials and methods: Anti-proliferative effect of adenosine on breast CSCs was evaluated by mammosphere formation and MTS assay. The effect of adenosine on cell cycle progression was examined using flow cytometry. Detection of apoptosis was conducted by Annexin V-FITC. The expression levels of cell cycle and apoptosis regulatory proteins as well as ERK1/2, and GLI-1 were measured by Western blot. Results: Adenosine reduced CSCs population and mammosphere formation in breast CSCs. Adenosine induced G1 cell cycle arrest in breast CSCs in conjunction with a marked down-regulation of cyclin D1 and CDK4. Adenosine also induced apoptosis by regulation of Bax/Bcl-2 ratio, mitochondrial membrane potential depletion and activation of caspase-6. Moreover, adenosine inhibited ERK1/2 phosphorylation and GLI-1 protein expression. Conclusions: These findings indicated that adenosine induces cell cycle arrest and apoptosis through inhibition of GLI-1 and ERK1/2 pathways in breast CSCs.