RAF-1 IS A NECESSARY COMPONENT OF THE MITOGENIC RESPONSE OF THE HUMANMEGAKARYOBLASTIC LEUKEMIA-CELL LINE MO7 TO HUMAN STEM-CELL FACTOR, GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR, INTERLEUKIN-3, AND INTERLEUKIN-9

We have examined the role of Raf-1 in the mitogenic response of the fa ctor-deprived human megakaryoblastic leukemia cell line MO7 to recombi nant human granulocyte-macrophage colony-stimulating factor, interleuk in 3, interleukin 9, and stem cell factor by using c-raf antisense oli godeoxyribonucleotides. Uptake of oligodeoxyribonucleotides by MO7 cel ls was maximal at 5-10 h in culture, and oligomers remained stable in these cells for at least 24 h. Treatment of MO7 cells with the antisen se oligomer resulted in intracellular oligomer/mRNA duplex formation f ollowed by efficient translation blockade of c-raf-1. In contrast, sen se and non-sense oligodeoxyribonucleotides failed to form intracellula r duplexes and did not interfere with translation of c-raf-1, suggesti ng specific elimination of c-raf-1 by the antisense oligodeoxyribonucl eotide. Furthermore, exposure of MO7 cells to c-raf-1 antisense preven ted factor-induced nuclear translocation of Raf-1. Most importantly, p roliferation of MO7 cells ([H-3]thymidine incorporation) enabled by th ese growth factors was significantly reduced when the c-raf-1 antisens e oligodeoxyribonucleotide was added to cultures, whereas the mitogeni c response to these factors remained almost unaffected in the presence of sense and non-sense oligodeoxyribonucleotides.