Correlation of the size of type II transforming growth factor β (TGF-β) receptor with TGF-β responses of isolated bovine articular chondrocytes

Abstract

Objectives: Transforming growth factor β (TGF-β) is a multipotent regulator of cell proliferation and extracellular matrix production. The effect of TGF-β on chondrocyte matrix production was studied in relation to the expression of TGF-β binding proteins. The effect of TGF-β on proteoglycan synthesis of isolated articular chondrocytes depended on the culture period. Proteoglycan synthesis of chondrocytes which were cultured for one day was inhibited by TGF-β whereas proteoglycan synthesis of chondrocytes cultured in monolayer for seven days or longer was stimulated hy TGF-β. To investigate if this differential response is related to a distinct expression of TGF-β receptors, this parameter was studied by affinity labelling. Methods: Chondrocytes were incubated with 100 pM TGF-β labelled with iodine-125. Crosslinking was performed using 0.25 mM disuccinimidyl suberate. Membrane proteins were extracted and analysed by denaturating sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and autoradiography. Results: Freshly isolated and cultured chondrocytes expressed types I, II, and III TGF-β receptors. The type II TGF-β receptor of cultured chondrocytes appeared to be about 15 kilodaltons smaller than the type II TGF-β receptor expressed on freshly isolated chondrocytes, however. Conclusions: As the type II TGF-β receptor appears to be involved in signal transduction, this change in size of the type II TGF-β receptor might be related to the differential effect of TGF-β on proteoglycan synthesis of freshly isolated and cultured bovine articular chondrocytes.