BASIC FIBROBLAST GROWTH-FACTOR DOWN-REGULATES BCL-2 AND PROMOTES APOPTOSIS IN MCF-7 HUMAN BREAST-CANCER CELLS

Basic fibroblast growth factor (bFGF) is a mitogen and a survival fact or in fibroblasts and endothelial cells. It acts as an angiogenesis fa ctor in breast cancer, but paradoxically inhibits proliferation in sev eral breast cancer cell lines. In this study, we investigated the effe cts of bFGF on the survival of MCF-7 human breast cancer cells in orde r to determine if these effects were also opposite to those in fibrobl asts. Incubation of NIH 3T3 cells with bFGF for 24 h caused an approxi mately 30% increase in day 12 +/- 2 adherent colonies while causing an approximately 50% decrease in MCF-7 colony formation, Incubation of N IH 3T3 cells with bFGF prior to etoposide or 5-fluorouracil treatment caused a proportionally smaller decrease in colony forming efficiency as a result of drug treatment, while preincubation of MCF-7 cells with bFGF caused a similar but opposite additive increase in drug-induced diminution of colony forming efficiency, These effects on MCF-7 cells were observed at variable times of incubation and doses of etoposide t o 1 mu M and 5-fluorouracil to 200 mu M and at variable times of incub ation and concentrations of bFGF to 1 ng/ml, Incubating with bFGF afte r drug exposure had similar effects on the reduction of cloning effici ency, The effects of bFGF were similar on programmed cell death, as de termined by morphologic characteristics of apoptosis on 400 cell count s and FITC-dUTP 3'-OH DNA end labeling. Basic FGF promoted apoptosis a nd increased the rate of drug-induced cell death with both etoposide a nd 5-fluorouracil. While recombinant bFGF affected Bcl-2 protein and m RNA levels in NIH 3T3 cells only marginally and variably and had no di scernible effects on Bax protein levels, it markedly downregulated Bcl -2 mRNA and]protein levels in MCF-7 cells and caused an increase in Ba x protein levels. These changes resulted in a decreased association of Bcl-2 with immunoprecipitable Bax and an increased association of Bax with immunoprecipitable Bcl-2 in MCF-7 cells treated with bFGF. These data suggest that bFGF may cause different phenotypic responses in br east cancer cells from those in surrounding cells and offer one possib le mechanism through opposite regulation of Bcl-2 and Bax. Inhibition of colony formation by bFGF was observed in several breast cancer cell s lines, demonstrating that this effect demonstrated in MCF-7 cells wa s more universal. (C) 1998 Academic Press.