Abstract
The objective of this investigation was to clarify how the integrin pathway modulates downstream effectors of the TGF-β1 pathway in chondrocytic cell signaling. The levels of Smad2 and Smad3 phosphorylation upon TGF-β1 or α2β1 integrin (Type II collagen) stimulation were analyzed by Western blotting techniques. Cellular response was determined by quantitation of procollagen gene expression.
Stimulation of cells with TGF-β1 and Type II collagen led to rapid phosphorylation of Smad2 and 3 with phosphorylation peaking between 15 min and 1 h. Combined stimulation led to a synergistic increase in the phosphorylation of Smad2 and Smad3. Type II collagen gene expression paralleled Smad phosphorylation.
Type II collagen modulates the TGF signaling cascade involving Smad2 and Smad3 leading to an increase in Type II collagen transcription. Therefore, we conclude that TGF-β1 and integrin stimuli interact prior to Smad2 and 3 phosphorylation in the cytoplasm of chondrocytic cells and regulates the expression of ECM components in chondrocytes.
