Abstract
Transforming growth factor-beta (TGF-β) is critical in cancer cell invasion and metastasis. The effects of a treatment that targets TGF-β using the combination of interferon alpha (IFNα)-2b and 5-fluorouracil (5-FU) are unknown. Here, we show that the serum levels of TGF-β1 prior to the therapy correlate with increased maximum tumor diameter, which is significantly (p < 0.01) decreased after the combination therapy. 5-FU increased both the expression and secretion levels of TGF-β1 in hepatoma cells, but not in normal hepatocytes. The combination of 5-FU and IFNα-2b synergistically affected cell death. However, a TGF-β1 specific inhibitor did not affect the anti-tumor activity of 5-FU. 5-FU inhibited the phosphorylation of SMAD2 and reduced the total protein levels of SMAD2, SMAD4, and pINK4b. Conversely, 5-FU stimulated the phosphorylation of extracellular signal-regulated kinase (ERK)1/2. Accordingly, the protein levels of E-cadherin and claudin-1 were reduced in 5-FU-treated cells. The combination of 5-FU and IFNα-2b, and the inhibition of ERK1/2 by a specific inhibitor neutralized the effects of 5-FU on TGF-β-related signaling molecules and restored their protein levels to those observed in the control. Interestingly, the phosphorylated protein levels of SMAD2 and the total protein levels of E-cadherin and p15INK4b were increased in 5-FU-stimulated HuH-7 cells, but not in Hep G2 cells. Our data suggest that the higher efficacy of the 5-FU and IFNα-2b combination therapy was associated with the regulation of TGF-β expression, secretion, and the signals mediated by it.