Growth factor-deprived BALB/c 3T3 murine fibroblasts can enter the S phase after induction of c-myc gene expression.

Induction of quiescent BALB/c 3T3 murine fibroblasts by platelet-derived growth factor (PDGF) or fibroblast growth factor (FGFs) is accompanied by induction of c-myc gene expression. To study the role of c-myc in cell growth, we transfected BALB/c 3T3 cells with a plasmid construct containing a glucocorticoid-inducible c-myc gene. When these transfected cells were growth arrested in PDGF-FGF-freedefined medium, glucocorticoid treatment induced S-phase DNA synthesis. This induction of DNA synthesis was inefficient, and cell proliferation was not evident, suggesting that growth factors act through stimulation of c-myc expression together with other intracellular events.