Overexpression of basic fibroblast growth factor (FGF-2) downregulates Bcl-2 and promotes apoptosis in MCF-7 human breast cancer cells

Basic fibroblast growth factor (bFGF, FGF-2), a classical transforming fact or, mitogen, and survival factor in multiple cell types, and has a paradoxi c role in mammary epithelial cell transformation and proliferation. We have also demonstrated that recombinant FGF-2 uncharacteristically promotes cel l death in MCF-7 human breast cancer cells. In this study, we investigated the effects of FGF-2 overexpression on survival in the same MCF-7 cells. In eight breast cancer cell lines and two nontransformed mammary epithelial c ell lines, we demonstrated that high levels of Bcl-2 are only expressed in cells with undetectable levels of FGF-2 on western blot. In retrovirally tr ansduced MCF-7 cells expressing both cytoplasm- and nucleus-localizing FGF- 2 species and ones expressing only cytoplasm-localizing FGF-2 species, Bcl- 2 levels were strongly decreased at both the mRNA and protein levels. Immun oprecipitation of Bax demonstrated a decreased association of Bax with Bcl- 2 in these cells. Levels of Bax did not correlate with expression of FGF-2 in the 10 cell lines or in MCF-7 cells. The clonogenic potential of MCF-7 c ells in tissue culture was decreased by the expression of FGF-2 and was add itively suppressed by the chemotherapeutic agents etoposide and 5-fluoroura cil in a dose and time dependent manner. MCF-7 cells overexpressing FGF-2 h ad a greater rate of programmed cell death at baseline and in response to e toposide and 5-fluorouracil in a TUNEL assay by immunofluorescent microphot ography and by flow cytometric quantitation. The pro-apoptotic effect of FG F-2 overexpression on the chemosensitivity of these cells was confirmed by quantitative morphologic determination. These data demonstrate that the exp ression of FGF-2 downregulates Bcl-2 and promotes programmed cell death in MCF-7 human breast cancer cells.