Phenotypic and microRNA characterization of the neglected CD24⁺ cell population in MCF-7 breast cancer 3-dimensional spheroid culture

Abstract

In vitro 3-dimensional (3D) spheroid culture has been widely used as model to enrich CD44⁺CD24dim/− cancer stem cells (CSC) with high aldehyde dehydrogenase 1 (ALDH1) activity. Although CD24⁺ subpopulation was known to be present in 3D spheroids and may infuence cancer drug therapies, its characteristics and CSC properties were not well defned.In this study, CD24⁺ population from the Michigan Cancer Foundation-7 (MCF-7) spheroid was sorted and subjected to spheroid formation test, stem cell markers immunofuorescence, invasion and migration test, as well as microRNA expression profling. Sorted MCF-7 CD24⁺ cells from primary spheroids were able to reform its 3D spheroid shape after 7 days in nonadherent culture conditions. In contrast to the primary spheroids, the expression of SOX-2, CD44, CD49f, and Nanog was dim in MCF-7 CD24⁺ cells. Remarkably, MCF-7 CD24⁺ cells were found to show high expression of ALDH1 protein which may have resulted in these cells exhibiting higher resistance against doxorubicin and cisplatin when compared with that of the parental cells. Moreover, microRNA profling has shown that the absence of CSC properties was consistent with the downregulation of major CSCs-related pathways including Hedgehog, wingless-related integration site (Wnt), and microtubule associated protein kinase (MAPK) signaling pathways. However, the upregulated pathways such as adherens junctions, focal adhesion, and tight junction suggest that CD24⁺ cells were probably at an epithelial-like state of cell transition. In conclusion, neglected CD24⁺ cells in MCF-7 spheroid did not exhibit typical breast CSCs properties. The pres-ence of miRNAs and their analyzed pathways suggested that these cells could be a distinct intermediate cell state in breast CSCs.