Sal B depressed CK-18 expression induced by TGF-β1 in HK-2 cells. HK-2 cells were cultured in complete medium containing 5% FBS for 18 h. Thereafter, the cells were kept in serum-free medium or treated with (1) 2.5 ng/ml TGF-β1, (2) 2.5 ng/ml TGF-β1 plus 1 μM of Sal B, (3) 2.5 ng/ml TGF-β1 plus 10 μM of Sal B, (4) 2.5 ng/ml TGF-β1 plus 10 μM of SB-431542 for 24 h. (a) Immunofluorescence staining (×200) showed decreased immunolabeling intensity of CK-18 after TGF-β1 treatment. This effect was depressed by 1 μM and 10 μM of Sal B as well as SB-431542 treatments. The blue-colored stain is nuclear counterstaining with Hoechst 33258. (B) Western blot analysis for CK-18. CK-18 expression was decreased when cells were exposed to TGF-β1, whereas 1 μM and 10 μM of Sal B and SB-431542 significantly attenuated the TGF-β1-induced up-regulation of α-SMA. (C) Graphic presentation of the relative expression of CK-18. The values are represented as 100% vs. control. **P < 0.01 vs. control; #P < 0.05 vs. TGF-β1, # #P < 0.01 vs. TGF-β1.