Transforming and nontransforming growth factors are present in medium conditioned by fetal rat calvariae

Abstract

Conditioned medium recovered from fetal rat calvarial cultures contains an autocrine factor termed bone-derived growth factor (BDGF); this factor has been purified by acid extraction, gel-permeation chromatography, and two reversed-phase HPLC steps and examined for mitogenicity on normal rat kidney fibroblasts (NRK, clone 49F). HPLC-purified BDGF caused a dose-related increase in cell number, DNA content, and [3H]thymidine incorporation into acid-insoluble material. Since highly purified BDGF appeared less mitogenic than cruder preparations, the latter were tested for additional growth factors, with particular attention to those required for anchorage-independent colony formation in soft agar. BDGF did not displace 125I-labeled epidermal growth factor (EGF) in a radioligand-receptor assay, indicating the absence of EGF and transforming growth factor alpha (TGF-alpha). Without EGF, no BDGF preparation induced NRK cells to form soft agar colonies. However, calvarial conditioned medium contained a factor which, like TGF-beta, induced large soft-agar colonies in the presence of EGF; this TGF-beta-like factor did not copurify with BDGF. Polyclonal antibodies against platelet-derived growth factor did not neutralize the effects of BDGF on NRK cells. BDGF is a potent mitogen for nonskeletal-tissue-derived fibroblasts. Although crude BDGF preparations do contain TGF-beta, BDGF is distinct from this factor and others necessary for NRK cell transformation to anchorage-independent growth.