TGF-beta1-Dependent Regulation of miR-21 in Bovine Fetal Fibroblasts
The TGF-β/SMAD signaling pathway has been previously implicated in the induction of miR-21 expression, with studies offering conflicting data implicating transcription or expedited processing as the primary mechanism of induction. Real-time qPCR revealed significant induction of both primary-miR-21 (pri-miR-21) and mature miR-21 following TGF-β1 treatment. Luciferase reporter constructs under the control of the bovine pri-miR-21 promoter demonstrated strong TGF-β responsiveness that was lost when SMAD binding sites were ablated. To identify potential roles for the induced miR-21, we examined cellular expression of PDCD4. TGF-β1 strongly suppressed PDCD4 expression, which was, in turn, highly correlated with a significant increase in cellular viability and loss of cleaved caspase-3. Studies with miR- 21 antagonists demonstrated that these downstream effects of TGF-β1 are miR-21 dependent. Taken together, these studies show that TGF-β1 activated SMAD 2/3 proteins mediate the transcription of pri-miR-21 transcript in bovine fibroblasts in vitro which then suppress apoptosis through altered PDCD4 expression.