SMAD6 and renal cell carcinoma: In vivo, the expression trends of marker proteins and mRNAs related to the TGF-β/Smad signaling pathway in mice with RCC were consistent, indicating that the mRNA and protein expression of TGF-β1, TGF-βR1, Smad2, Smad3, Smad4, and Smad9 decreased, whereas the expression of Smad6 protein increased, although its mRNA expression decreased.