This review summarizes the recent research on cell fusion between mesenchymal stromal/stem cells (MSCs) and malignant cells in tumor growth and metastasis. Several studies demonstrate that MSCs can promote tumor growth and metastasis by fusing with malignant cells, while conflicting reports believe that MSCs can reduce tumorigenicity through cell fusion. The elucidation of the molecular mechanisms between MSC fusion and tumor metastasis may provide an effective strategy for tumor biotherapy.

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Background: Family with sequence similarity 96 member A and B (FAM96A and FAM96B) are two highly conserved homologous proteins belonging to MIP18 family. Many studies have shown that FAM96A and FAM96B play many different functions mainly through interacting with other different proteins. Recently, several studies show that FAM96A and FAM96B are significantly down-regulated compared in human gastrointestinal stromal tumors, colon cancer, liver cancer and gastric cancer with corresponding normal tissues. However, the molecular regulatory mechanisms of FAM96A and FAM96B in breast cancer development and metastasis are still unclear. In this work, we aimed to explore the molecular mechanisms of FAM96A and FAM96B in breast cancer progression.Methods: We used specific siRNAs to down-regulate FAM96A and FAM96B expression, and used recombinant plasmids to up-regulate FAM96A and FAM96B expression in breast cancer cells. Cell proliferation was measured using MTT and colony formation assays. Cell cycle and apoptosis were detected by flow cytometry analysis. Wound healing and transwell assays were used to examine cell migration and invasion abilities. The relationships among FAM96A/B, EMT and Wnt/β-catenin signaling pathway were determined by analyzing the expression changes of classical markers and biological functional changes after XAV-939 inhibitor treatment. Results: We found that FAM96A and FAM96B expression in breast cancer was down-regulated. FAM96A/B overexpression suppressed breast cancer cell proliferation, invasion and migration, induced cell apoptosis and led to cell cycle arrested in G0/G1 phase. Conversely, FAM96A/B knockdown exhibited the opposite effects on breast cancer cells. Moreover, our data demonstrated that FAM96A/B overexpression suppressed EMT and Wnt/β-catenin signaling pathway, while FAM96A/B knockdown showed the promoting effects on EMT and Wnt/β-catenin signaling pathway in breast cancer cells. Furthermore, a Wnt pathway inhibitor, XAV-939 treatment reversed the promoting effects of FAM96A and FAM96B knockdown on breast cancer cell proliferation, invasion and migration.Conclusions: Our findings revealed that FAM96A and FAM96B may act as tumor suppressor genes and inhibit breast cancer progression via modulating the Wnt/β-catenin pathway, which can provide the potential markers for the diagnosis and treatment of breast cancer.