CONSTITUTIVE EXPRESSION OF FULL-LENGTH C-MYB TRANSFORMS AVIAN CELLS CHARACTERISTIC OF BOTH THE MONOCYTIC AND GRANULOCYTIC LINEAGES

Both viral Myb (v-Myb) and cellular Myb (c-Myb) are nuclear sequence-s pecific DNA-binding proteins that can function as transcriptional acti vators, v-Myb, encoded by avian myeloblastosis virus, induces acute mo noblastic leukemia in chickens and transforms avian myelomonocytic cel ls in culture, The normal c-Myb protein is essential for hematopoietic development. Previous reports suggested that truncation of c-Myb is r equired for oncogenic transformation of avian myelomonocytic cells in culture, In this study, we demonstrate that constitutive expression of full-length c-Myb can transform avian myelomonocytic cells isolated f rom embryonic yolk sacs by using a strategy to enhance the efficiency of infection and/or expression of c-myb-containing viruses, c-Myb-tran sformed myelomonocytic cells display a different phenotype than cells transformed by v-Myb(AMV) Or other Myb mutants, c-Myb-transformed yolk sac cells are heterogeneous populations with characteristics of both the macrophage and granulocyte lineages, Our results demonstrate that constitutive expression of full-length c-Myb is sufficient to activate its oncogenic potential, but that the target cells for c-Myb are rela tively rare and presumably quite immature.