FIG. 6.

ERK signal strength affects AP-1 target gene expression and S-phase entry. (A) Quiescent Swiss 3T3 cells were treated with PDGF (10 or 4 ng/ml), and cyclin D1 levels in cell extracts were measured with an anti-cyclin D antibody. (B) Quiescent Swiss 3T3 cells cultured on glass coverslips were treated with PDGF, and BrdU incorporation was assayed as described in Materials and Methods. The data shown are representative of three independent experiments. DAPI, 4′,6′-diamidino-2-phenylindole. (C) Quiescent Swiss 3T3 cells were induced with PDGF for 11.75 h, treated with BrdU (20 μM) for 15 min, and then fixed. The number of BrdU-positive cells in each treatment group was quantitated by FACS analysis as described in Materials and Methods. The data shown are the mean ± standard error from triplicate determinations and are representative of three independent experiments.