The long non-coding RNA GAS5 regulates transforming growth factor (TGF-)-induced smooth muscle cell differentiation via RNA Smad-binding elements

Smooth muscle cell (SMC) differentiation is essential for vascular development, and TGF- signaling plays a critical role in this process. Although long non-coding RNAs (lncRNAs) regulate various cellular events, their functions in SMC differentiation remain largely unknown. Here, we demonstrate that the lncRNA growth arrest-specific 5 (GAS5) suppresses TGF-/Smad3 signaling in smooth muscle cell differentiation of mesenchymal progenitor cells. We found that forced expression of GAS5 blocked, but knockdown of GAS5 increased, the expression of SMC contractile proteins. Mechanistically, GAS5 competitively bound Smad3 protein via multiple RNA Smad-binding elements (rSBEs), which prevented Smad3 from binding to SBE DNA in TGF--responsive SMC gene promoters, resulting in suppression of SMC marker gene transcription and, consequently, in inhibition of TGF-/Smad3-mediated SMC differentiation. Importantly, other lncRNAs or artificially synthesized RNA molecules that contained rSBEs also effectively inhibited TGF-/Smad3 signaling, suggesting that lncRNA-rSBE may be a general mechanism used by cells to fine-tune Smad3 activity in both basal and TGF--stimulated states. Taken together, our results have uncovered an lncRNA-based mechanism that modulates TGF-/Smad3 signaling during SMC differentiation.