Characterization of the IGF axis in a rat liver-derived epithelial cell line

We have used the techniques of chemical cross-linking, Western blotting and immunoprecipitation-ligand blotting to demonstrate that insulin-like growt h factor binding protein-2 (IGFBP-2) is associated with plasma membranes of an epithelial cell line derived from rat liver as well as being secreted i nto the medium by these cells. We demonstrate that these cells secrete IGF- I, but not IGF-II into serum free medium. Evidence from signalling, cell pr oliferation and cross-linking experiments indicate that these cells also ex press cell surface IGF-I receptors. Dose-response experiments indicate an e nhanced biological activity of the IGF-I analogue des (1-3) IGF-I compared to wild-type IGF-I in both acute signalling experiments and longer-term (24 h) mitogenic assays. As this IGF-I analogue has lower affinity for IGFBPs, we believe that in this cell culture system, activity of IGF-I may be atte nuated in the long and short term by the accumulation of IGFBP-2 in conditi oned medium and by the presence of IGFBP-2 associated with the cell membran e and/or ECM. (C) 1999 Harcourt Publishers Ltd.