Microvesicles secreted by macrophages shuttle invasion-potentiating microRNAs into breast cancer cells.

Tumor-associated macrophages (TAMs) are alternatively activated cells induced by interleukin-4 (IL-4)-releasing CD4+ T cells. TAMs promote breast cancer invasion and metastasis; however, the mechanisms underlying these interactions between macrophages and tumor cells that lead to cancer metastasis remain elusive. Previous studies have found microRNAs (miRNAs) circulating in the peripheral blood and have identified microvesicles, or exosomes, as mediators of cell-cell communication. Therefore, one alternative mechanism for the promotion of breast cancer cell invasion by TAMs may be through macrophage-secreted exosomes, which would deliver invasion-potentiating miRNAs to breast cancer cells. We utilized a co-culture system with IL-4-activated macrophages and breast cancer cells to verify that miRNAs are transported from macrophages to breast cancer cells. The shuttling of fluorescently-labeled exogenous miRNAs from IL-4-activated macrophages to co-cultivated breast cancer cells without direct cell-cell contact was observed. miR-223, a miRNA specific for IL-4-activated macrophages, was detected within the exosomes released by macrophages and was significantly elevated in the co-cultivated SKBR3 and MDA-MB-231 cells. The invasiveness of the co-cultivated breast cancer cells decreased when the IL-4-activated macrophages were treated with a miR-223 antisense oligonucleotide (ASO) that would inhibit miR-223 expression. Furthermore, results from a functional assay revealed that miR-223 promoted the invasion of breast cancer cells via the Mef2c-β-catenin pathway. We conclude that macrophages regulate the invasiveness of breast cancer cells through exosome-mediated delivery of oncogenic miRNAs. Our data provide insight into the mechanisms underlying the metastasis-promoting interactions between macrophages and breast cancer cells.

肿瘤相关巨噬细胞（TAMs）是由释放白细胞介素 - 4（IL - 4）的CD4 + T细胞诱导的另一种活化细胞。TAMs促进乳腺癌的侵袭和转移；然而，巨噬细胞与肿瘤细胞之间导致癌症转移的这些相互作用的潜在机制仍然不清楚。先前的研究已经发现外周血中循环的微小RNA（miRNAs），并确定微泡或外泌体是细胞间通讯的介质。因此，TAMs促进乳腺癌细胞侵袭的一种替代机制可能是通过巨噬细胞分泌的外泌体，其将增强侵袭的miRNAs递送至乳腺癌细胞。 我们利用白细胞介素 - 4激活的巨噬细胞和乳腺癌细胞的共培养系统来验证miRNAs从巨噬细胞转运至乳腺癌细胞。观察到荧光标记的外源性miRNAs从白细胞介素 - 4激活的巨噬细胞转运至无直接细胞 - 细胞接触的共培养乳腺癌细胞。miR - 223是白细胞介素 - 4激活的巨噬细胞特有的一种miRNA，在巨噬细胞释放的外泌体中被检测到，并且在共培养的SKBR3和MDA - MB - 231细胞中显著升高。当用抑制miR - 223表达的miR - 223反义寡核苷酸（ASO）处理白细胞介素 - 4激活的巨噬细胞时，共培养的乳腺癌细胞的侵袭性降低。此外，功能测定的结果显示miR - 223通过Mef2c - β - 连环蛋白途径促进乳腺癌细胞的侵袭。 我们得出结论，巨噬细胞通过外泌体介导的致癌miRNAs的传递来调节乳腺癌细胞的侵袭性。我们的数据为巨噬细胞与乳腺癌细胞之间促进转移的相互作用的潜在机制提供了见解。