Proteomic analysis of AML1/RUNX1 mutant complexes

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Myelodysplastic syndrome(MDS) is a clonal disorder of hematopoietic stem cells characterized by ineffective and inadequate hematopoiesis. MDS in a subset of patients arise after previous chemotherapy or radiation exposure for other malignancies. As MDS is a heterogeneous disorder, specific gene abnormalities playing a role in the myelodysplastic process have been difficult to identify. In this study, we analyzed the somatic mutations in the AML1/RUNX1 gene, which is a critical regulator of definitive hematopoiesis and the most frequent targets for translocation of acute myeloid leukemia (AML), in patients with MDS. We detected AML1 point mutations in 26 of 110(23.6%) patients with refractory anemia with excess blasts (RAEB), RAEB in transformation (RAEBt) and AML following MDS (defined these categories as MDS/AML). Among 22 patients with radiation-related (including 14 atomic bomb survivors) and/or therapy-related MDS/AML, 11(50%) patients had the AML1 mutations mostly in N-terminal re … More gion. In contrast, 15 of 88(17%) patients with sporadic MDS/AML showed the AML1 mutations equally in both N-terminal and C-terminal region. The MDS/AML patients with AML1 mutations had a significantly worse prognosis than those without AML1 mutations. Most of AML1 mutants lost trans-activation potential, regardless of their DNA binding potential. These data suggested that AML1 point mutation is one of the major driving forces of MDS/AML, and these mutations may represent a distinct clinicopathologic-genetic entity.To clarify mechanisms of the AML1 dysfunctions, we established cell lines stably expressing FLAG-tagged wild-type or mutant AML1 proteins. A complex of transcriptional factors including these AML1 proteins were purified by immunoprecipitation with an anti-FLAG antibody, and then were analyzed by MALDI-TOF/TOF analyzer. We identified CBFβ,ets-1,p300,C/EBPα and GATA-1 in the complex with wild-type AML1 as well as previous studies using different methods. However, other proteins were identified in the complex with mutated-AML1. We have been analyzing the direct binding ability of AML1 to these proteins. Less