Basic fibroblast growth factor confers a less malignant phenotype in MDA-MB-231 human breast cancer cells

Basic fibroblast growth factor (FGF-2) expression is associated with a more differentiated phenotype, earlier stage of disease, and a better prognosis in breast cancer patients. To determine whether expression of FGF-2 can ca use a less malignant phenotype, we engineered MDA-MB-231 cells, a highly de differentiated, invasive breast cancer cell line, to express different isof orms of FGF-2. Cells expressed either cytoplasmic, nuclear, or a combinatio n of both FGF-2 isoforms. Western blots of 2 M NaCl washes and of condition ed medium demonstrated that these cells did not export FGF-2. Cells express ing FGF-2 had levels of fibroblast growth factor receptors equivalent with those of control cells. Transformation was assayed by anchorage-independent colony formation and tumor formation in athymic mice, All of the construct s expressing various FGF-2 isoforms had a 60-70% reduction in colony format ion in soft agar, but only cells expressing the M-r 18,000 FGF-2 isoform fo rmed fewer and smaller tumors in mice. To determine potential mechanisms re sponsible for a less malignant phenotype, experiments measuring invasion in Matrigel, the secretion of matrix metalloprotease activity and migration i n a modified Boyden chamber and in a patch wound motility assay were carrie d out. Cells expressing the M-r 18,000 cytoplasmic FGF-2 moiety had a 45% d ecrease in invasion in Matrigel compared to vector-transfected controls. Ce lls expressing M-r 18,000 FGF-2 had an increase in M-r 97,000 and M-r 38,00 0:collagenase, demonstrating that the decreased invasive potential was not due to a down-regulation of gelatinolytic or caseinolytic matrix metallopro teinases. However, motility was decreased in both assays, primarily in cell s expressing M-r 18,000 FGF-2, whereas exogenous recombinant human FGF-2 ha d no effect. These studies demonstrate for the first time that FGF-2 expres sion can cause a less malignant phenotype in breast cancer:cells, possibly as a result of decreased motility and invasion.