FGF2 AS AN AUTOCRINE GROWTH-FACTOR FOR IMMORTAL HUMAN BREAST EPITHELIAL-CELLS

HBL100 is a human breast epithelial cell line which has been immortali zed by the defective genome of SV40 but which is not tumorigenic in nu de mice. Growth experiments in defined serum-free and protein-free med ia revealed its ability to grow without exogenous supply of serum grow th factors. Addition of heparin to the serum-free medium increased its growth rate, suggesting the release of heparin-binding autocrine grow th factor(s) in the culture medium. HBL100-conditioned medium was mito genic for HEMG (human embryonic mammary gland) and CCL39 fibroblasts. Western blot analysis of growth factors revealed the presence of the M (r) 18,000, 22,000 and 24,000 forms of basic fibroblast growth factor (bFGF or FGF2) both in HBL100 cell extracts partially purified on hepa rin-Sepharose beads and in concentrated conditioned medium. Northern b lot analysis of HBL100 RNA demonstrated the synthesis of 7-, 3.7-, and 1.8-kilobase (kb) FGF2-specific mRNAs by these cells. Anti-FGF2 neutr alizing IgG inhibited HBL100 growth in serum-free medium in a dose-dep endent manner. Affinity crosslinking of I-125-FGF2 to the HBL100 cell surface revealed an FGF receptor of 130 kDa. Taken together, these res ults suggest that FGF2 may be implicated as an autocrine growth factor in the early events leading to neoplastic transformation of human bre ast epithelial cells.