3.2. Keap1 deletion-mediated Smad7 elevation is responsible for TGF-βsignaling suppression in MES-13 cellsTo elucidate the underlying molecular events in Nrf2-mediated TGFβ suppression, we determined the levels of molecules associated withthe canonical pathway of TGF-β signaling. First, among two types ofTGF-β receptors, the protein levels of TβRI were substantially diminished in shKeap1 cells as compared to the control cells (Fig. 2A). Therewas no noticeable difference in TβRI mRNA levels between shKeap1cells and the control cells (Supplementary Fig. S4). Moreover, repressedTβRI levels in shKeap1 cells were partially restored by proteasome inhibitor treatment (Supplementary Fig. S4), which suggests that TβRIreduction was done at the post-translational stage. Second, among themeasured Smad protein levels, it was notable that Smad7 levels weresignificantly high in shKeap1 cells (Fig. 2B). However, mRNA levels forSmad7 were not changed by Keap1 knockdown (Fig. 2C). The Nrf2-dependent Smad7 elevation was confirmed by the Nrf2 silencing: thetransfection of shKeap1 cells with Nrf2 siRNA abolished Smad7 elevation (Fig. 2D). These findings suggested that Smad7 elevation could beresponsible for the suppression of TGF-β signaling in Keap1 knockdownMES-13 cells. Indeed, when shKeap1 cells were transfected with siSmad7 (Supplementary Fig. S6), the expression of TβRI (which wasdiminished in shKeap1) was restored to the level of the control cells(Fig. 2E). Moreover, the levels of p-Smad2/p-Smad3 and fibrotic markers (fibronectin and α-Sma) were increased by si-Smad7 transfection(Fig. 2F). These results support the idea that activated Nrf2 is a positiveregulator of Smad7, and increased Smad7 inhibits TGF-β-induced fibrosis signaling by repressing TβRI level.