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-β_1(TGF-β_1) in rat peritoneal mesothelial cells(PMCs).METHODS: Rat PMCs were cultured at different doses of TGF-β_1 (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-β_1 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-β_1 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-β_1 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%(P0.05),the expression of Smad2 protein declined by 78%,89%,89%,88% and 76%(P0.05) 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-β_1 signaling.