Transforming growth factor–β (TGF-β) signaling is a critical driver of epithelial-to-mesenchymal transition (EMT) and cancer progression. In SMAD-dependent TGF-β signaling, activation of the TGF-β... Show moreTransforming growth factor–β (TGF-β) signaling is a critical driver of epithelial-to-mesenchymal transition (EMT) and cancer progression. In SMAD-dependent TGF-β signaling, activation of the TGF-β receptor complex stimulates the phosphorylation of the intracellular receptor-associated SMADs (SMAD2 and SMAD3), which translocate to the nucleus to promote target gene expression. SMAD7 inhibits signaling through the pathway by promoting the polyubiquitination of the TGF-β type I receptor (TβRI). We identified an unannotated nuclear long noncoding RNA (lncRNA) that we designated LETS1 (lncRNA enforcing TGF-β signaling 1) that was not only increased but also perpetuated by TGF-β signaling. Loss of LETS1 attenuated TGF-β–induced EMT and migration in breast and lung cancer cells in vitro and extravasation of the cells in a zebrafish xenograft model. LETS1 potentiated TGF-β–SMAD signaling by stabilizing cell surface TβRI, thereby forming a positive feedback loop. Specifically, LETS1 inhibited TβRI polyubiquitination by binding to nuclear factor of activated T cells (NFAT5) and inducing the expression of the gene encoding the orphan nuclear receptor 4A1 (NR4A1), a component of a destruction complex for SMAD7. Overall, our findings characterize LETS1 as an EMT-promoting lncRNA that potentiates signaling through TGF-β receptor complexes. Show less
Endothelial-to-mesenchymal transition (EndoMT) is an instrumental step in the development of valves in the embryonic heart. This process is driven by activation of transforming growth factor-β (TGF... Show moreEndothelial-to-mesenchymal transition (EndoMT) is an instrumental step in the development of valves in the embryonic heart. This process is driven by activation of transforming growth factor-β (TGF-β) signaling and is characterized by the loss of endothelial and gain of mesenchymal phenotype, and by delamination of cells from the surface into the underlying endocardial cushion matrix. The endothelial cells (ECs) overlying the cushions are typically exposed to high blood flow and concomitant shear stress and do not have a primary cilium. Here, we show that shear stress activates TGF-β-Alk5 signaling in ECs, which is necessary for EndoMT in the cushions. Moreover, we show that the absence of a primary cilium is critically important for this transition process. Show less
