Extracellular vesicles released by hypoxia‐induced tumor‐associated fibroblasts impart chemoresistance to breast cancer cells via long noncoding RNA H19 delivery

Abstract Recently, extracellular vesicles (EVs) have been emphasized in regulating the hypoxic tumor microenvironment of breast cancer (BC), where tumor‐associated fibroblasts (TAFs) play a significant role. In this study, we describe possible molecular mechanisms behind the pro‐tumoral effects of EVs, secreted by hypoxia (HP)‐induced TAFs, on BC cell growth, metastasis, and chemoresistance. These mechanisms are based on long noncoding RNA H19 (H19) identified by microarray analysis. We employed an in silico approach to identify differentially expressed lncRNAs that were associated with BC. Subsequently, we explored possible downstream regulatory mechanisms. We isolated EVs from TAFs that were exposed to HP, and these EVs were denoted as HP‐TAF‐EVs henceforth. MTT, transwell, flow cytometry, and TUNEL assays were performed to assess the malignant phenotypes of BC cells. A paclitaxel (TAX)‐resistant BC cell line was constructed, and xenograft tumor and lung metastasis models were established in nude mice for in vivo verification. Our observation revealed that lncRNA H19 was significantly overexpressed, whereas miR‐497 was notably downregulated in BC. HP induced activation of TAFs and stimulated the secretion of EVs. Coculture of HP‐TAF‐EVs and BC cells led to an increase in TAX resistance of the latter. HP‐TAF‐EVs upregulated methylation of miR‐497 by delivering lncRNA H19, which recruited DNMT1, thus lowering the expression of miR‐497. In addition, lncRNA H19‐containing HP‐TAF‐EVs hindered miR‐497 expression, enhancing tumorigenesis and TAX resistance of BC cells in vivo. Our study presents evidence for the contribution of lncRNA H19‐containing HP‐TAF‐EVs in the reduction of miR‐497 expression through the recruitment of DNMT1, which in turn promotes the growth, metastasis, and chemoresistance of BC cells.