The TGFβ2‐Snail1‐miRNATGFβ2 Circuitry is Critical for the Development of Aggressive Functions in Breast Cancer

Abstract There have been contradictory reports on the biological role of transforming growth factor‐βs (TGFβs) in breast cancer (BC), especially with regard to their ability to promote epithelial‐mesenchymal transition (EMT). Here, we show that TGFβ2 is preferentially expressed in mesenchymal‐like BCs and maintains the EMT phenotype, correlating with cancer stem cell‐like characteristics, growth, metastasis and chemo‐resistance and predicting worse clinical outcomes. However, this is only true in ERα − BC. In ERα + luminal‐type BC, estrogen receptor interacts with p‐Smads to block TGFβ signalling. Furthermore, we also identify a microRNAs (miRNAs) signature (miRNAs TGFβ2 ) that is weakened in TGFβ2‐overexpressing BC cells. We discover that TGFβ2‐Snail1 recruits enhancer of zeste homolog‐2 to convert miRNAsTGFβ2 promoters from an active to repressive chromatin configuration and then repress miRNAs TGFβ2 transcription, forming a negative feedback loop. On the other hand, miRNAs TGFβ2 overexpression reverses the mesenchymal‐like traits in agreement with the inhibition of TGFβ2‐Snail1 signalling in BC cells. These findings clarify the roles of TGFβ2 in BC and suggest novel therapeutic strategies based on the TGFβ2‐Snail1‐miRNAs TGFβ2 loop for a subset type of human BCs.