LOW-LEVEL EXPRESSION OF BASIC FGF UP-REGULATES BCL-2 AND DELAYS APOPTOSIS, BUT HIGH INTRACELLULAR LEVELS ARE REQUIRED TO INDUCE TRANSFORMATION IN NIH 3T3 CELLS

We investigated the roles of basic fibroblast growth factor (bFGF) in the transformation and survival of NIH 3T3 cells. We constructed NIH 3 T3-derived cell lines expressing human bFGF using retroviral gene tran sfer with an N2-based vector. Clonally derived cell lines containing a single copy of the vector overexpress bFGF mRNA and produce more immu noreactive protein (0.407 +/- 0.010-3.028 +/- 0.087 ng bFGF/10(6) cell s) which is biologically active than nontransduced (0.151 +/- 0.013 ng bFGF/10(6) cells) or N2-transduced (0.211 +/- 0.029 ng bFGF/10(6) cel ls) NIH 3T3 cells. All cells producing excess amounts of bFGF achieve greater density at confluence, show delayed apoptosis and increased su rvival and have elevated intracellular levels of Bcl-2. However, only cells expressing from 8-15 times background levels of bFGF are phenoty pically transformed. The transformed cells form dense foci at confluen ce, have decreased adherence to tissue culture plates and grow colonie s in soft agar. Exogenous bFGF induces higher Bcl-2 levels in a dose d ependent manner and recapitulates the antiapoptotic effects of the ove rexpressed species but fails to induce changes associated with the tra nsformed phenotype. In this study, we demonstrate a dissociation betwe en phenotypic transformation secondary to bFGF overexpression and upre gulation of cellular Bcl-2 that correlates with a delay in programmed cell death. Although low level expression of bFGF or exogenous bFGF is sufficient to upregulate Bcl-2 and delay apoptosis, high intracellula r levels are required for cellular transformation. These data suggest that overexpression of bFGF modulates cellular transformation and Bcl- 2-mediated inhibition of apoptosis through alternate molecular mechani sms.