M2 Macrophage-Derived Exosomes Regulate miR-199a-3p Promoter Methylation Through the LINC00470-Mediated myc/DNMT3a Axis to Promote Breast Cancer Development.

Breast cancer (BC) is the most common invasive cancer in women. M2 macrophage exosomes promote cancer development and play multiple roles in the tumor microenvironment, but the mechanism of action by which M2 macrophage exosomes promote BC remains unclear. Therefore, the purpose of this study was to investigate the mechanism by which M2 macrophage-derived exosomes promote the development of breast cancer. We collected BC tissues and determined the expression of LINC00470, followed by the establishment of M2 macrophages in culture and the isolation and identification of M2 macrophage exosomes. Next, we investigated the effects of M2 macrophage exosomes on BC cell proliferation, invasion, miR-199a-3p promoter methylation, and the expression of LINC00470, myc, DNMT3A, and miR-199a-3p. Finally, LINC00470 expression was inhibited in M2 macrophage exosomes, while miR-199a-3p expression was inhibited in BC cells, and changes in BC cell proliferation, invasion, miR-199a-3p promoter methylation, and the expression of LINC00470, myc, DNMT3A, and miR-199a-3p were analyzed. We demonstrated that LINC00470 was highly expressed in BC tissues, M2-type macrophages were successfully induced in vitro, and Dil-labeled M2 macrophage exosomes could successfully enter MDA-MB-231 and MCF-7 cells. Coculture of M2 macrophage exosomes with MDA-MB-231 and MCF-7 cells significantly enhanced the proliferation and invasion of MDA-MB-231 and MCF-7 cells, upregulated the expression of LINC00470, myc, and DNMT3A and downregulated the expression of miR-199a-3p. Moreover, the inhibition of LINC00470 expression in M2 macrophage exosomes significantly downregulated the expression of LINC00470, myc, and DNMT3A in MDA-MB-231 and MCF-7 cells, upregulated the expression of miR-199a-3p, and hypomethylated the promoter of the miR-199a-3p locus. Moreover, inhibition of LINC00470 expression in M2 macrophage-derived exosomes significantly attenuated the proliferation and invasive ability of MDA-MB-231 and MCF-7 cells, while miR-199a-3p inhibitor transfection reversed this effect. Collectively, these findings indicated that M2-type macrophage-derived exosomes promote BC proliferation and migration by regulating miR-199a-3p promoter methylation through the LINC00470-mediated myc/DNMT3a axis.

lncRNA HEIH, an indicator of high malignancy and poor prognosis, functions as an oncogene in breast cancer.

Long non­coding RNA high expression in hepatocellular carcinoma (lncRNA HEIH) acts as an oncogene in multiple tumors, including hepatocellular carcinoma, colorectal cancer, melanoma and non­small cell lung cancer. However, the role of HEIH in breast cancer remains unknown. The present study focused on the clinical significance and biological function of HEIH in breast cancer. Specifically, the expression levels of HEIH in breast cancer tissues and breast cancer cell lines were investigated. The results indicated high expression levels of HEIH in human breast cancer tissues, and its expression was positively associated with malignancy status and poor disease prognosis. High expression levels of HEIH were detected in the breast cancer cell lines, including MCF­7, SK­BR­3, MDA­MB­231 and MDA­MB­468. These data were consistent with those derived from the in vivo study. Therefore, small interfering RNA was used to knockdown HEIH expression in order to explore whether HEIH exhibits an oncogenic function in breast cancer. Following HEIH knockdown, the proliferative and metastatic activity of MDA­MB­231 cells was decreased, whereas the induction of cell apoptosis was increased. These results suggested the oncogenic role of HEIH in breast cancer and the potential application of HEIH as an index of malignancy and poor prognosis in breast cancer.