Suspension state affects the stemness of breast cancer cells by regulating the glycogen synthase kinase-3β.

Circulating tumor cells (CTCs) are considered an important factor involved in tumor metastasis and can overcome mechanical interactions to gain the ability to distant metastasis. The previous study had shown that the suspension state could regulate the stemness of breast cancer cells (BCCs). However, the specific molecular mechanisms involved have not yet been explored clearly. In this study, MCF-7 and MDA-MBA-231 BCCs were cultured in suspension and adherent. The effect of suspension state on BCCs was further elucidated by observing suspension cell clusters, sorting CD44/CD24 cell subpopulation and detecting self-renewal ability. Furthermore, it was found that glycogen synthase kinase-3β (GSK-3β) was significantly down-regulated in MCF-7 suspension cells along with the activation of the Wnt/β-catenin signaling, but the converse was true for MDA-MB-231 cells. Subsequently, GSK-3β was differentially expressed in MCF-7 suspension cells. The activation of the Wnt/β-catenin signaling, epithelial-mesenchymal transition (EMT) and stemness were all inhibited when GSK-3 was overexpressed in suspension MCF-7 cells. While GSK-3β was down-regulated, it further promoted the Wnt/β-catenin signaling, mesenchymal characteristic and stemness of MCF-7 cells. This study demonstrated that suspension state could activate the Wnt/β-catenin signaling by inhibiting GSK-3β to promote the stemness of epithelial BCCs, providing a therapeutic strategy for targeted CTCs.