Let-7a suppresses Ewing sarcoma CSCs’ malignant phenotype via forming a positive feedback circuit with STAT3 and lin28

Abstract Background：Cancer stem cells (CSCs) have been documented to be closely related with tumor metastasis and recurrence, and the same important role were identified in Ewing Sarcoma (ES). In our previous study, we found that let-7a was repressed in ES. Herein, we further identified its putative effects in the CSCs of ES. Methods：Side population (SP) cells were isolated from ES cell lines A673 and SK-ES-1 via fluorescence-activated cell sorting (FACS) Assays and then identified. The expression of let-7a, signal Transducer and Activator of Transcription 3 (STAT3) and lin28 were detected by Real-time qPCR and western blotting. Cell colony formation assay and cell invasion assays were performed to detected the effect of let-7a on the malignant phenotype of ES SP cells. Finally, we injected the let-7a or scramble mimic into the xenograft tumors in nude mice to evaluated its effects on the growth of ES SP cells in vivo.Results：The expression of let-7a was consistently suppressed in the separated ES SP cells, which were identified to contain the characteristics of the stem cells. The ability of colony formation or invasion of ES SP cells was suppressed in vitro when we restored the expression of let-7a. The same results were found in the tumor growth of ES SP cells’ xenograft mice in vivo. Furthermore, we found STAT3 and lin28 were involved in the suppressive effects.Conclusion：Let-7a, STAT3 and lin28 might form a positive circuit to regulate the malignant phenotype of ES CSCs.