Micro-RNA-21 regulates TGF-β-induced myofibroblast differentiation by targeting PDCD4 in tumor-stroma interaction

Transforming growth factor-β1 (TGF-β1) induces stromal fibroblast-to-myofibroblast transdifferentiation in the tumor-stroma interactive microenvironment via modulation of multiple phenotypic and functional genes, which plays a critical role in tumor progression. Up to now, the involvement of micro-RNAs (miRNAs) and their roles in TGF-β1-induced myofibroblast differentiation in tumor-stroma interaction are unclear. Using quantitative real-time RT-PCR, we demonstrated that the expression of micro-RNA-21 (miR-21) was upregulated in activated fibroblasts after treatment with TGF-β1 or conditioned medium from cancer cells. To determine the potential roles of miR-21 in TGF-β1-mediated gene regulation during myofibroblast conversion, we showed that miR-21 expression was downregulated by miR-21 inhibitor and upregulated by miR-21 mimic. Interestingly, downregulation of miR-21 with the inhibitor effectively inhibited TGF-β1-induced myofibroblast differentiation while upregulation of miR-21 with a mimic significantly promoted myofibroblast differentiation. We further demonstrated that MiR-21 directly targeted and downregulated programmed cell death 4 (PDCD4) gene, which in turn acted as a negative regulator of several phenotypic and functional genes of myofibroblasts. Taken together, these results suggested that miR-21 participated in TGF-β1-induced myofibroblast transdifferentiation in cancer stroma by targeting PDCD4.