Exosomal miR-331-3p derived from chemoresistant osteosarcoma cells induces chemoresistance through autophagy

BACKGROUND

Osteosarcoma is a common malignant bone tumor, and chemotherapy can effectively improve the prognosis. MicroRNA-331 (MiR-331) is associated with poor cancer outcomes. However, the role of miR-331 in osteosarcoma remains to be explored.

METHODS

Drug-resistant osteosarcoma cells were cultured, and their exosomes were purified. The secretion and uptake of exosomes by drug-resistant osteosarcoma and osteosarcoma cells were confirmed using a fluorescence tracking assay and Transwell experiments. The effects of drug-resistant exosomes on cell proliferation were determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. siRNA-Drosha and neutral sphingomyelinase inhibitor GW4869 were used to determine the transfer of miRNAs. qRT-PCR and western blotting were used to detect the role of autophagy in the regulation of drug-resistant cell-derived exosomal miR-331-3p.

RESULTS

Exosomal miR-331-3p levels in drug-resistant cells were higher than in exosomes from osteosarcoma cells. The exosomes secreted by the drug-resistant osteosarcoma cells could be absorbed by osteosarcoma cells, leading to acquired drug resistance in previously non-resistance cells. Inhibition of miRNAs resulted in reduced transmission of drug resistance transmission by exosomes. Exosomes from drug-resistant osteosarcoma cells transfected with siRNA-Drosha or treated by GW4869 could not enhance the proliferation of MG63 and HOS cells. Finally, miR-331-3p in the exosomes secreted by drug-resistant osteosarcoma cells could induce autophagy of osteosarcoma cells, allowing them to acquire drug resistance. The inhibition of miR-331-3p decreased drug resistance of osteosarcoma cells.

CONCLUSION

Exosomes secreted from chemoresistant osteosarcoma cells promote drug resistance through miR-331-3p and autophagy. Inhibition of miR-331-3p could be used to alleviate drug resistance in osteosarcoma.

A comprehensive clinicopathological evaluation of the differential expression of microRNA-331 in breast tumors and its diagnostic significance

OBJECTIVE

MicroRNA-331 (miR-331) has shown regulatory activity against several genes whose expression has been claimed to be deregulated in breast tumors, including that of epidermal growth factor receptor 2 (HER2). Herein, the clinical value of miR-331 expression was investigated by analyzing its levels in breast benign and malignant tumors.

METHODS

The expression levels of miR-331 were quantified via real-time PCR in 130 malignant and 66 benign breast tissue specimens collected after surgical resection of primary tumors. The generated data were analyzed by applying several statistical tests in order to examine the relationship of miR-331 expression with various established clinicopathological features and survival data of patients.

RESULTS

Our data showed that miR-331 was overexpressed in malignant breast tumors compared to their benign counterparts both overall (P = 0.026) and individually when the subgroups of fibroadenoma and invasive ductal carcinoma were analyzed with each other (P = 0.001). ROC curve analysis confirmed the diagnostic value of these variations, providing an AUC value equal to 0.597 (P = 0.026) and 0.663 (P = 0.001), respectively. Furthermore, miR-331 levels were elevated (P = 0.026) in ductal cancerous specimens compared to the lobular ones but failed to correlate with other clinicopathological features or survival data of the breast cancer patients.

CONCLUSIONS

Our results provide evidence that miR-331 levels might provide valuable information regarding the differential diagnosis of benign and malignant breast tumors but present no prognostic value for breast cancer.