The role of Yin and Yang 1 (YY1) transcription factor in acute myeloid leukemia (AML)

“The role of Yin and Yang 1 (YY1) transcription factor in Acute Myeloid Leukemia (AML)” Introduction: Acute Myeloid Leukemia is an heterogeneous disease with different molecular signatures, therapeutic responses, and survival rates. Recent studies suggest that the transcription factor YY1 is overexpressed in AML patients and it may have a role in the onset of AML differentiation block. Our aim was to investigate the role and the effect of YY1 downregulation in granulocytic differentiation. Methods: We used molecular and cellular biology methods such as plasmid constructions and lentiviral infection, qRT-PCR, Western Blot, Immonophenotypes, Morphological analysis and Apoptotic assays. Results: Our results confirm a higher level of YY1 gene expression in AML patients compared to CD34+ hematopoietic progenitors and CD34- mature cells. When YY1 is downregulated, by short hairpin interference in HL60 myeloid cell line, we observed a significant increase in the expression of factors relevant to myeloid differentiation and in particular to granulocytic maturation, such as GMCSFr, GCSFr, CEBPε and CEBPδ and a significant decrease of the MPO gene expression. We also measured an increase in the staining of the CD11b surface antigene. Importantly, YY1 downregulation reinforced the prodifferentiative effects of all trans retinoic acid (RA) treatment compared to RA treated HL60 cells expressing YY1, including an increase in CEBPα gene expression and morphological changes compatible with granulocytic maturation. YY1 knockdown determined a significant increase of RARα expression that is crucial to mediate the intracellular effects of RA. In addition, YY1 knockdown also promoted a terminal apoptosis in RA HL60 treated cells, as shown by the activation of caspasis, increased expression of BAX gene and increased Annexin V and Propidium Iodide stainings. Conclusions: We identified YY1 as an important player in the onset of the differentiation block in AML HL60 cell line. Indeed, in these cells YY1 downregulation remove the differentiation block and restore a myeloid differentiation gene expression program, mainly toward granulocytic lineage. Moreover, YY1 downregulation reinforces the therapeutic effect of RA treatment.