CXCL1/CXCR2 and CCL5/CCR1/CCR5 Promote Radiation-Induced Reprogramming of Breast Non-cancer Stem Cells into Cancer Stem Cells and Predict Patient Clinical Outcome

Abstract

Cancer stem cell (CSC) has paved the way to many fundamental and translational studies. Recent studies have highlighted differentiated breast cancer cells (non-CSCs) switching phenotype to CSCs in response to various stimuli, depicting the existence of cancer stem cell plasticity. Although strategies to reduce the phenotypic plasticity of non-CSCs into CSCs are likely to prevent treatment-resilient cancer cells driving recurrence, most phenotypic plasticity mechanisms involve Notch, Wnt or MAPK signaling pathways. In this study, breast cancer cells were irradiated to identify soluble reprogramming factors. Using conditioned medias, protein arrays analyses, flow cytometry and in cellulo/in vivo functional assays, we demonstrated, for the first time, that radiation-induced chemokine expression, especially CXCL1 and CCL5 and their receptors CXCR2, CCR1 and CCR5, stimulates reprogramming of breast non-CSCs into CSCs. Treatment of non-CSCs with recombinant CXCL1 and CCL5 is sufficient to induce cell reprogramming, while their inhibition can be used to prevent reprogramming and sensitize tumor to radiation. Moreover, analysis of gene expression profiles from 38 public merged databases demonstrated that combined over-expression of CXCL1/CXCR2, CCL5/CCR1 or CCL5/CCR5 has a poorer prognosis in patients treated with radiotherapy, suggesting a promising way for patient stratification, where individuals with elevated cytokine levels could benefit from radiotherapy in conjunction with cytokine inhibitors. Taken together, our findings provide a rationale to consider these axes as potential targets and predictive biomarkers in breast cancer patients.