FoxO3a and PU.1 in Acute Lymphoblastic Leukemia

Proto-oncogenes and tumor suppressor genes are the most important genes involved in leukemogenesis , which their alterations disrupt normal regulatory processes such as self-renewal, proliferation, differentiation and apoptosis in target cells. Among those genes FoxO3a gene and PU.1 gene.

FoxO(Fork head box ,class O) transcription factors function as a tumor suppressor gene and are important for stem cell maintenance.They are key regulators of the cellular differentiation, growth, survival, cell cycle, metabolism, and cellular stress. There are four members of the foxO transcription factors in humans : foxO1, foxO3a, foxO4, foxO6 .FoxO3a is expressed in various tissues including B - and T-lymphoid cells. Over expression of FoxO3a in B and T cell lines induces cell cycle arrest in G1 phase , so it inhibits cell proliferation . FoxO3a is an important target of PI3K/AKT signaling pathway,which is hyperactivated in various types of cancers .Hyperactivation of this pathway in leukemia leads to inactivation of foxO3a in leukemic cells and enhances tumor growth .

PU .1(Purine-rich box 1) is a member of the E26 transformation-specific (ETS) Family . Normal hematopoiesis is securely controlled by asmall number of lineage-specific transcription factors, so that the disturbed expression or function of this group may be involved in the development of leukemia . PU.1 plays an important role in hematopiotic stem cell (HSC) self renewal and in myeloid and B-lymphoid differentiation. It controls the expression of several genes involved in hematopoiesis.