cDNA Cloning and Chromosomal Mapping of Rat Smad2 and Smad4 and Their Expression in Cultured Rat Articular Chondrocytes

Abstract

Smad proteins are known to transduce signalling of TGF-β receptor superfamily. We report here the entire sequences of rat Smad2 and Smad4 which have not been identified yet. Entire sequences were identified by degenerated polymerase chain reaction and following phage library screening and 5' RACE. The predicted amino acid sequences of rat Smad2 and Smad4 are highly conserved among rat, human and mouse. We also mapped these Smads to chromosome 18q.12.3. Unlike endothelial cells, TGF-β1 stimulates articular chondrocyte proliferation as well as extracellular matrix production, and acts as a repairing agent against cartilage destruction. Since both Smad2 and Smad4 are essential factors for TGF-β signalling, we examined their expression and regulation in cultured articular chondrocytes. Northern blot analysis showed that TGF-β1 significantly increased the mRNA level of Smad2 but not of Smad4 in a dose- and time-dependent manner, suggesting that the augmentation of TGF-β1 action is caused by increasing the expression of the downstream signalling molecule.