SYNTHESIS AND SECRETION OF TRANSFORMING GROWTH-FACTOR-BETA ISOFORMS BY PRIMARY CULTURES OF HUMAN BREAST-TUMOR FIBROBLASTS IN-VITRO AND THEIR MODULATION BY TAMOXIFEN

Tamoxifen may mediate its effect in early breast cancer in part via an oestrogen receptor (ER)-independent pathway by directly stimulating f ibroblasts to produce the negative paracrine growth factor transformin g growth Factor (TGF)-beta. We have previously shown that secretion of this factor is induced 3- to 30-fold in human fetal fibroblasts in vi tro, and by stromal fibroblasts in vivo following tamoxifen treatment of ER-positive and ER-negative breast cancer patients. Primary culture s of breast tumour fibroblasts have been exposed to tamoxifen for 48 h , and rates of secretion of TGF-beta(1) and TGF-beta(2) measured using a quantitative immunoassay. Fibroblast strains derived from malignant and benign tumours produced and secreted similar amounts of TGF-beta( 1), but benign breast tumour fibroblasts secreted significantly higher levels of TGF-beta(2) compared with fibroblasts of malignant origin. Tamoxifen did not induce any consistent increase in TGF-beta secretion into the conditioned medium, but immunofluorescence analysis for the intracellular form of TGF-beta(1) revealed evidence of increased immun oreactive protein in tamoxifen-treated fibroblasts, which is localised to the nucleus. Therefore synthesis of TGF-beta(1) appears to be stim ulated by tamoxifen, but increased secretion may be abrogated in vitro . Furthermore, using immunocytochemistry and transient transfection wi th an ER-responsive reporter construct, no ER was demonstrable in thes e fibroblasts supporting the proposed ER-independent paracrine pathway .