MiR-21/Smad 7 signaling determines TGF-β1-induced CAF formation

TLDR: It is demonstrated that miR-21 and Smad7 are critical regulators of TGF-β1 signaling during the induction of CAF formation.

Abstract: How TGF-β1-mediated signaling pathways are finely tuned to orchestrate the generation of carcinoma-associated fibroblasts (CAFs) is poorly understood Here, we demonstrate that miR-21 and the signaling of its target Smad 7 determine TGF-β1-induced CAF formation In primary cultured fibroblasts, mature miR-21 increases after TGF-β1 treatment, whereas the Smad 7 protein level decreases MiR-21 binds to the 3′ UTR of Smad7 mRNA and inhibits its translation, rather than causing its degradation Most importantly, Smad 7 is bound to Smad 2 and 3, which are thought to competitively bind to TGFBR1 and prevents their activation upon TGF-β1 stimulation The depletion of miR-21 or the overexpression of Smad 7 blocks TGF-β1-induced CAF formation, whereas the overexpression of miR-21 or the depletion of Smad 7 promotes CAF formation, even without TGF-β1 stimulation Collectively, these findings clearly demonstrate that miR-21 and Smad7 are critical regulators of TGF-β1 signaling during the induction of CAF formation