Activation of Raf-1, but not H-Ras or MEK, induces κ chain expression in the pre-B-cell lines. (A) BKO84 cells were cultured for 2 days with PMA, FTI-277, PD98059, and U0126, alone or in combination, or solvent alone (-), as indicated, and analyzed for the expression of κ chain by flow cytometry. The number in each histogram indicates the percentage of total live cells. (B) BKO84 cells 4 days after infection with the indicated retroviral vectors were analyzed for the expression of κ chain by flow cytometry. The bar graph indicates the frequency of κ-positive cells among GFP-positive (▪) or GFP-negative (□) cells. (C) BKO84 cells 2 days after infection (as in panel B) were sorted for GFP-positive cells. The whole-cell lysates of the sorted GFP-positive cells or the cells treated with PMA (100 ng/mL) for 5 minutes as a positive control were subjected to Western blot analysis using antiphospho-ERK2 (top lane) or anti-ERK2 (bottom lane).