Transcriptional dysregulation during myeloid transformation in AML.

The current paradigm on leukemogenesis indicates that leukemias are propagated by leukemic stem cells. The genomic events and pathways involved in the transformation of hematopoietic precursors into leukemic stem cells are increasingly understood. This concept is based on genomic mutations or functional dysregulation of transcription factors in malignant cells of patients with acute myeloid leukemia (AML). Loss of the CCAAT/enhancer binding protein-alpha (CEBPA) function in myeloid cells in vitro and in vivo leads to a differentiation block, similar to that observed in blasts from AML patients. CEBPA alterations in specific subgroups of AML comprise genomic mutations leading to dominant-negative mutant proteins, transcriptional suppression by leukemic fusion proteins, translational inhibition by activated RNA-binding proteins, and functional inhibition by phosphorylation or increased proteasomal-dependent degradation. The PU.1 gene can be mutated or its expression or function can be blocked by leukemogenic fusion proteins in AML. Point mutations in the RUNX1/AML1 gene are also observed in specific subtypes of AML, in addition to RUNX1 being the most frequent target for chromosomal translocation in AML. These data are persuasive evidence that impaired function of particular transcription factors contributes directly to the development of human AML, and restoring their function represents a promising target for novel therapeutic strategies in AML.