Preferential Release of microRNAs via Extracellular Vesicles is Associated with Ductal Carcinoma In Situ to Invasive Breast Cancer Progression

Ductal carcinoma in situ (DCIS) is a benign “pre-cancer” that increases the risk of invasive breast cancer (IBC). Not all DCIS progress to IBC, and the primary factors driving progression remain unclear. Small extracellular vesicles (sEVs) or exosomes are known to play a role in advanced cancers, but their involvement in DCIS is poorly understood. This study examined the role of sEVs and their RNA content in DCIS progression. Rab27A, which regulates exosome release, is elevated in DCIS and IBC tissues compared with normal breast tissues. Inhibition of sEV release via Rab27A knockdown alters pro-invasive pathways and reduces invasion in a DCIS mouse model. Using the isogenic MCF10 breast cancer progression series, we found a significant increase in microRNAs (miRNAs) in sEVs from normal to malignant states, with the highest number of differentially expressed miRNAs in IBC sEVs compared with DCIS sEVs. In vivo, DCIS invasive progression elevated circulating sEV miRNA levels, which decreased upon Rab27A knockdown. Re-expression of miR-205, preferentially loaded into IBC sEVs, reduced proliferation, invasion, and EMT marker expression in DCIS cells. Combined Rab27A knockdown and miR-205 expression repressed TGF-β signaling, activated p38, and induced cell cycle arrest and cell death. These findings illustrate that sEVs and their miRNAs promote DCIS progression, and the reintroduction of miR-205 in DCIS cells can inhibit invasive progression.