A growth inhibitory protein secreted by human diploid fibroblasts. Partial purification and characterization

We have identified and partially purified a growth inhibitor protein secreted by human diploid fibroblast cells. This protein is not secreted constitutively but only after induction with the double stranded hetero duplex polyriboinosinic:polyribocytidylic acid. The growth inhibitory activity has been purified 3,800-fold and has an estimated molecular mass of 12,000 daltons. The protein will inhibit the growth in culture of human diploid fibroblast cells, human cells derived from tumors, and mouse L cells. Although interferon-beta is secreted with the growth inhibitory protein, the partially purified growth inhibitory protein has no antiviral activity, and its activity is not neutralized by antibodies to interferon-alpha, interferon-beta, and interferon-gamma. We believe this growth inhibitory activity to reside in a newly defined protein and have named it fibroblast-derived growth inhibitor.