Discussion
Many studies have shown that miRNAs have an important role in the development of human cancers. For example, miRNAs can regulate cancer metastasis by affecting cancer cell migration, invasion, angiogenesis and proliferation.18 MiRNAs also regulate macrophages, a crucial component in the innate immune system, to control cell differentiation, phagocytosis and apoptosis, implying a promising therapy target to fight against cancers.19 At present, miRNAs have been used as diagnostic and prognostic biomarkers in different cancers, including colorectal cancer, digestive tract cancers, hepatic cancer stem cells and oesophageal cancer.20 In hypopharyngeal cancer , there has been some studies reporting roles of miRNAs. Fukumoto et al. discovered that miR-451a was significantly inhibited in hypopharyngeal cancer.21 Kikkawa et al. showed that miR-489 could suppress tumor development by targeting PTPN11 in hypopharyngeal cancer.22 The role of miR-21 has not yet been revealed in hypopharyngeal cancer although abnormal increase of miRNA-21 expression level has been detected in a variety of tumor specimens and cell lines, including breast cancer, cervical cancer, lung cancer, pancreatic cancer, prostate cancer, colorectal cancer and glioma. Here, we demonstrated that the expression of miR-21 significantly increased in human hypopharyngeal cancer tissues, and this increase was closely related to the transition of hBMSCs to CAFs.
We firstly found that miR-21 was up-regulated in hypopharyngeal cancer tissue and FaDu cells. Further understanding of this novel biomarker miR-21 and its associated function could potentially provide new insights into future applications to the prevention of the hypopharyngeal cancer. Our continued studies found that exosomes from FaDu cells could mediate induction of CAF-like features in hBMSCs after co-culture of FaDu cell exosomes and hBMSCs. In this experiment, we detected high expression level of CAF-related markers, includingα-SMA and FAP, and increased number of CAF-like cells. Flow cytometry results showed that the cell proportion of G1 phase in FaDu-exo+BMSC group was significantly decreased, while the cell proportion of G2 phase was significantly increased compared to the control.
Our findings further confirmed that it’s miR-21 that mediated induction of CAF-like features in hBMSCs. We co-cultured BMSCs and exosomes in which miR-21 was knocked out and found that expression level of α-SMA and FAP decreased and the number of CAF-like cells was significantly decreased. Flow cytometry results showed that the cell proportion of G1 phase in miR-21 inhibitor-treated group was significantly increased, while the cell proportion of G2 phase was significantly decreased compared to the control.