The leucine zipper region of Myb oncoprotein regulates the commitment of hematopoietic progenitors.

The development of blood cells proceeds from pluripotent stem cells through multipotent progenitors into mature elements belonging to at least 8 different lineages. The lineage choice process during which stem cells and progenitors commit to a particular lineage is regulated by a coordinated action of extracellular signals and transcription factors. Molecular mechanisms controlling commitment are largely unknown. Here, the transcription factor v-Myb and its leucine zipper region (LZR) are identified as regulators of the commitment of a common myeloid progenitor and progenitors restricted to the myeloid lineage. It is demonstrated that wild-type v-Myb with the intact LZR directs development of progenitors into the macrophage lineage. Mutations in this region compromise commitment toward myeloid cells and cause v-Myb to also support the development of erythroid cells, thrombocytes, and granulocytes, similar to the c-Myb protein. In agreement with that, the wild-type v-Myb induces high expression of myeloid factors C/EBP beta, PU.1, and Egr-1 in its target cells, whereas SCL, GATA-1, and c-Myb are more abundant in cells expressing the v-Myb LZR mutant. It is proposed that Myb LZR can function as a molecular switch, affecting expression of lineage-specifying transcription factors and directing the development of hematopoietic progenitors into either myeloid or erythroid lineages.