Overexpression of Smad7 inhibits TGF-β-induced Smad2 mRNA and protein expression in peritoneal mesothelial cells

AIM: To investigate the role of Smad7 in the Smad2 expression induced by transforming growth factor-β₁ (TGF-β₁) in rat peritoneal mesothelial cells (PMCs).METHODS: Rat PMCs were cultured at different doses of TGF-β₁ (0，1.25，2.5，10 μg/L) for different time (0，5，15，30，60，120 min).PCDNA3-Smad7 was then transfected into cultured rat PMCs by lipofectamine, and the cells were stimulated like the above.Endogenous Smad2 and Smad7 expression was evaluated by RT-PCR and Western blotting.RESULTS: TGF-β₁ induced increase in Smad2 mRNA and protein expression at 5 min, peaked at 30 min, and declined to baseline levels at 120 min, which was in a time-dependent manner.TGF-β₁ also induced Smad7 mRNA expression at 5 min, and then declined, down to the lowest at 30 min, but at 60 min it increased again.Smad2, Smad7 mRNA and protein expression induced by TGF-β₁ were also dose-dependent.After transfection, overexpressions of Smad7 mRNA and protein in rat PMCs were observed, which did not decline with time.The expression of Smad2 mRNA significantly decreased by 33%, 56%, 67%, 71%, 63% and 57% (P<0.05), the expression of Smad2 protein declined by 78%，89%，89%，88% and 76% (P<0.05) respectively at 0, 5, 15, 30, 60 and 120 min.CONCLUSION: Overexpression of Smad7 inhibits Smad2 gene and protein expression in peritoneal mesothelial cells.Smad7 may be a negative regulator of TGF-β₁ signaling.