FAK mediates signal crosstalk between type II collagen and TGF-beta 1 cascades in chondrocytic cells.

The purpose of this study was to evaluate the mechanism of crosstalk between the type II collagen and TGF-beta1 signaling pathways in chondrocytic cells. Articular chondrocytes, isolated from porcine knee cartilage, and the SW1353 cell line were cultured on either type II collagen-coated or -uncoated plates in the presence or absence of TGF-beta1. Expression of pSMAD 2, pSMAD 3, pFAK(Y397) and pFAK(Y925) in articular chondrocytes and the SW1353 cell line was analyzed by immunoblotting. Cell proliferation rates and glycosaminoglycan (GAG) content was determined after treatment with type II collagen or/and TGF-beta1. For inhibition study, human FAK-specific RNA small interference (siFAK) in SW1353 cell line was performed. In this study, expression of pSMAD 2, pSMAD 3, pFAK(Y397) and pFAK(Y925) were synergistically increased by co-treatment with type II collagen and TGF-beta1 in articular chondrocytes. The proliferation of porcine articular chondrocytes and GAG secretion in SW1353 cells were synergistically increased by co-stimulation with type II collagen and TGF-beta1. Synergistically increased expression and nuclear translocation of pSMAD 2 and pSMAD 3 and GAG secretion of SW1353 cells were significantly inhibited by siFAK transfection. Therefore, we suggest that FAK-SMAD 2/3 mediates signal crosstalk between type II collagen and TGF-beta1 and regulates GAG secretion in chondrocytic cells.

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