Fig. 2. Bax overexpression accelerates the onset of EGF-induced apoptosis. A431/ErbB2 cells were transfected with a construct encoding a Bax*GFP fusion protein and stable cell lines were selected. The addition of EGF (20 ng/ml) to the parental A431/ErbB2 cells resulted in the majority of cells dying in 3-5 days (A, upper row). Expression of the Bax*GFP fusion protein dramatically accelerates the rate of apoptosis in an EGF-dependent fashion, as nearly all cells died during the first 14-18 hours of incubation with EGF (A, lower row). (B) Quantitative differences in viability of A431/ErbB2 and A431/ErbB2/Bax cells after incubation with EGF for the indicated times.