cDNA cloning and chromosomal mapping of rat Smad2 and Smad4 and their expression in cultured rat articular chondrocytes

Smad proteins are known to transduce signalling of TGF-beta receptor superf amily. We report here the entire sequences of rat Smad2 and Smad4 which hav e 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 cons erved among rat, human and mouse. We also mapped these Smads to chromosome 18q.12.3. Unlike endothelial cells, TGF-beta 1 stimulates articular chondro cyte 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-beta signalling, we examined their expressio n and regulation in cultured articular chondrocytes. Northern blot analysis showed that TGF-beta 1 significantly increased the mRNA level of Smad2 but not of Smad4 in a dose- and time-dependent manner, suggesting that the aug mentation of TGF-beta 1 action is caused by increasing the expression of th e downstream signalling molecule.