The aim of this project is to isolate and characterize a protein from adult rat liver that produces a reversible inhibition of the proliferation of liver-derived epithelial cells. An improved analytical-scale purification procedure has been developed that produces a preparation with a specific activity about 1000-fold greater than previously reported. The inhibitory activity was labile at low pH, at temperatures over 50 degrees C, in the presence of sulphydryl reducing agents, and it could be completely abolished by trypsin under mild denaturing conditions. Its isoelectric point was determined to be 5.5 by chromatofocusing. The growth inhibitory activity, which could be eluted from SDS-PAGE at 17-19 kD, was compared to that of TGF-beta. The ID-50 of the liver-derived inhibitor was similar to that of TGF-beta in rat liver epithelial cells and also in primary hepatocyte cultures. In contrast to TGF-beta the activity of the liver-derived growth inhibitor was unaltered in the presence of a neutralizing antibody raised against TGF-beta. In addition the liver-derived inhibitor did not stimulate the growth of NRK cells in soft agar. Current efforts are focused on the large-scale purification of the liver-derived inhibitor such that antibody production and amino acid sequence analysis can be performed.
