EMBRYONIC SKIN FIBROBLASTS RELEASE TGF-ALPHA AND TGF-BETA ABLE TO INFLUENCE SYNTHESIS AND SECRETION OF GAG

Conditioned medium (CM), collected from 7 and 14 days-old chick embryo skin fibroblasts and added to the same cells, increases glycosaminogl ycans (GAG) intra- and extracellular accumulation. The factors respons ible for GAG enhancement are TGFalpha and TGFbeta because they are try psin and dithiothreitol sensitive, stable or enhanced by heat and tran sient acidification. Moreover, Sephadex G-75 fractions of CM active on GAG synthesis contain, when analysed on SDS-polyacrylamide gel electr ophoresis, two bands that comigrate with TGFalpha and TGFbeta and indu ce NRK cells clone 49F to form large colonies of mean size >8.000 mum2 in soft agar. Since both the factors must be present to induce the fo rmation of large colonies we come to the conclusion that CM contains T GFalpha and TGFbeta. The two growth factors have different effects on the accumulation of individual classes of GAG in the ECM. In particula r, TGFbeta stimulates a marked increase of CS and DS, TGFalpha of HA a nd DS in the medium. The contemporaneous addition of TGFalpha and TGFb eta to 7 days-old fibroblasts produces a pattern of GAG response simil ar to CM. These embryonic fibroblasts may control their own GAG synthe sis and secretion through autocrine TGFalpha and beta activity.