MiR-203a-3p regulates TGF-β1-induced epithelial–mesenchymal transition (EMT) in asthma by regulating Smad3 pathway through SIX1

Asthma is a common chronic airway disease with increasing prevalence. MicroRNAs act as vital regulators in cell progressions and have been identified to play crucial roles in asthma. The objective of the present study is to clarify the molecular mechanism of miR-203a-3p in the development of asthma. The expression of miR-203a-3p and Sine oculis homeobox homolog 1 (SIX1) were detected by quantitative real-time polymerase chain reaction (qRT-PCR). The protein levels of SIX1, fibronectin, E-cadherin, vimentin, phosphorylated-drosophila mothers against decapentaplegic 3 (p-Smad3) and Smad3 were measured by Western blot. The interaction between miR-203a-3p and SIX1 was confirmed by dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay. MiR-203a-3p was down-regulated and SIX1 was up-regulated in asthma serums, respectively. Transforming growth factor-β1 (TGF-β1) treatment induced the reduction of miR-203a-3p and the enhancement of SIX1 in BEAS-2B and 16HBE cells in a time-dependent manner. Subsequently, functional experiments showed the promotion of epithelial–mesenchymal transition (EMT) induced by TGF-β1 treatment could be reversed by miR-203a-3p re-expression or SIX1 deletion in BEAS-2B and 16HBE cells. SIX1 was identified as a target of miR-203a-3p and negatively regulated by miR-203a-3p. Then rescue assay indicated that overexpressed miR-203a-3p ameliorated TGF-β1 induced EMT by regulating SIX1 in BEAS-2B and 16HBE cells. Moreover, miR-203a-3p/SIX1 axis regulated TGF-β1 mediated EMT process in bronchial epithelial cells through phosphorylating Smad3. These results demonstrated that MiR-203a-3p modulated TGF-β1-induced EMT in asthma by regulating Smad3 pathway through targeting SIX1.