Recombinant insulin-like growth factor-I (IGF-I) production in Super-CHO results in the expression of IGF-I receptor and IGF binding protein 3

Previously, we described the genetic construction Super-CHO, a cell line ca pable of autocrine growth under fully defined protein-free conditions. Supe r-CHO cells constitutively express insulin growth factor-I (IGF-I) and tran sferrin in sufficient amounts to support long-term, stable growth without t he addition of exogenous growth factors, thus making it an ideal host for t he production of recombinant biopharmaceuticals. although IGF-I has been su ccessfully expressed in Chinese Hamster Ovary (CHO) cells, the long term ef fects of recombinant IGF-I expression have not been explored. In particular , the expression of the endogenous IGF-I receptor in response to IGF-I prod uction has not been reported. We report here the transcriptional induction of the type I IGF receptor gene in Surer-CHO. In addition, we examined the conditioned medium for the presence of IGF-I binding proteins. Ligand blot analysis reveals the presence of IGF binding proteins present in the medium conditioned by Super-CHO cells as well as CHO cells incubated in the prese nce of IGF-I. Furthermore, immunoaffinity reveals that Super-CHO expresses IGF binding protein-3 in response to IGF-I production. These results sugges t the autocrine growth of Super-CHO involves a complex interaction of cell type specific factors which regulate its utility of IGF-I.