Fig. 3. Effects of neuregulins and PG-J₂ on the growth properties of human MCF-7 cells. (A) Effects of NRG1, NRG2, and PG-J₂ treatment on proliferation of MCF-7 cells. MCF-7 cells were treated with 30 nM of NRG1 or NRG2 in the presence or absence of PG-J₂, and the incorporation of [³H]thymidine into DNA was determined. Results are the mean of three determinations from three different experiments. **P0.01; ***P0.001. (B) Effects of PG-J₂ and kinase inhibitors on NRG-1 and NRG-2 effects on cell cycle progression. Cells were grown for 24 hours in the presence or absence of NRG1 or NRG2 preincubated or not for 10 hours with PG-J₂, and analyzed by PI staining and FACS analysis. Inhibitors of MEK1 and 2 (40 µM PD98059) or PI 3-K (4 µM LY294002) were added 1 hour before treatment with neuregulins. Curves modeling the G0/G1, S, and G2/M compartments, derived by using the ModFit program, are shown. Cell number is plotted on the y axes, and DNA content is plotted on the x axes.