A Dibromotyrosine Derivative from Pseudoceratina sp. Suppresses TGF-β Responsiveness by Inhibiting TGF-β type I Receptor Kinase Activity

For clinical application, there is a great need for small molecule inhibitors (SMIs) that could control pathogenic effects of transforming growth factor (TGF-β) and/or modulate effects of TGF-β in normal responses. Selective SMIs of the TGF-β signaling pathway developed for therapeutics will also be powerful tools in experimentally dissecting this complex pathway, especially its cross-talk with other signaling pathways. In this study, we characterized (1′R,5′S,6′S)-2-(3′,5′-dibromo-1′, 6′-dihydroxy-4′-oxocyclohex-2′-enyl) acetonitrile (DT), a member of a new class of small molecule inhibitors related to bromotyrosine derivate from Pseudoceratina sp, which inhibits the TGF-β type I receptor serine/threonine kinase known as activin receptor-like kinase (ALK) 5. The inhibitory effects of DT on TGF-β-induced Smad signaling and epithelial-to-mesenchymal transition (EMT) were investigated in epithelial cells using in vitro kinase assay, luciferase reporter assays, immunoblotting, confocal microscopy, and wound healing assays. The novel ALK5 inhibitor, DT, inhibited the TGF-β-stimulated transcriptional activations of 3TP-Lux. In addition, DT decreased phosphorylated Smad2 levels and the nuclear translocation of Smad2 increased by TGF-β. In addition, DT inhibited TGF-β-induced EMT and wound healing of A549 cells. Our results suggest that DT is a potential therapeutic approach for fibrotic disease and cancer treatment.