GROWTH-HORMONE AND INSULIN-LIKE GROWTH FACTOR-I REGULATE COLLAGEN GENE-EXPRESSION AND EXTRACELLULAR COLLAGEN IN CULTURES OF AVIAN SKIN FIBROBLASTS

Avian skin fibroblasts were isolated, cultured and incubated with [H-3]proline for 24 h. The cells exported radiolabeled collagenase-digestible (CDP) and non-collagenase-digestible (NCDP) proteins into the medium. Human, bovine and avian growth hormone (GH) as well as insulin-like growth factor I (IGF-I) attenuated the appearance of [H-3]CDP in the medium without affecting [H-3]NCDP. The appearance of [H-3]CDP was not affected by prolactin. The effects of GH and IGF-I were enhanced by increasing concentrations of fetal calf serum (FCS). A synergism was observed between GH and IGF-I in their effect on CDP. Each peptide, at an ineffective concentration, increased the sensitivity of the cells to the other peptide. Collagenase activity in the medium was enhanced by IGF-I, but not modified by GH, FCS, or by their interaction with IGF-I. GH and IGF-I inhibition of type I procollagen gene expression was demonstrated with the aid of probes containing sequences corresponding to the mRNAs for avian alpha-I and alpha-II chains. The results suggest that GH and IGF-I cooperate in regulating collagen synthesis, but collagen degradation is affected by IGF-I and not by GH.