SB 431542

SB 431542 inhibits the activin type I receptor ALK4 and the nodal type I receptor ALK7, which are responsible for the phosphorylation of Smad2. SB 431542 has little effect on ALK1, ALK2, ALK3, and ALK6, which show phosphorylation of Smad1. SB 431542 is a selective inhibitor of endogenous activin but has no apparent effect on BMP signaling. SB 431542 could induce both Smad2/Smad4- and Smad3/Smad4-dependent transcription. ^[2] In A498 cells, SB 431542 inhibits both TGF-β1-induced collagen Iα1 and PAI-1 mRNA with IC50 of 60 nM and 50 nM, respectively. In addition, SB 431542 inhibits production of TGF-β1-induced fibronectin mRNA and protein with IC50 of 62 nM and 22 nM, respectively. ^[3] SB 431542 blocks the TGF-β-mediated growth factors, including PDGF-A, FGF-2 and HB-EGF, leading to an increase in proliferation of MG63 cells. SB 431542 also inhibits TGF-β-induced c-Myc and p21 ^WAF1/CIP1. ^[4] SB 431542 significantly suppresses TGF-β-induced G1 arrest, leading to accumulation of cells in the S phase of the cell cycle in FET, RIE, and Mv1Lu cells. SB 431542 also inhibits TGF-β-induced epithelial to mesenchymal transition (EMT) in NMuMG and PANC-1 cells. ^[5] SB 431542 significantly elevates the expression of CD86 in BM-DCs and that of CD83 within CD11c+ cells suppressed by TGF-β. SB 431542 is able to induce NK activity through functional maturation and IL-12 production of human DCs. ^[6]