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Bararia, Deepak (2007): Proteomic Identification of the MYST Domain Histone Acetyltransferase TIP60 as a Coactivator of the Myeloid Transcription Factor C/EBPα. Dissertation, LMU München: Faculty of Medicine
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Abstract

The transcription factor C/EBPα is a key player in granulopoiesis and leukemogenesis. In the present study, we sought to identify C/EBPα interacting proteins. A glutathione-S-transferase-C/EBPα fusion protein was used to pull down interacting proteins from U937 nuclear extracts. These proteins were analyzed by 2-D gel electrophoresis or 1-D nano LC and identified by mass spectrometry. The interaction between C/EBPand two novel interacting partners, the cell cycle regulator protein MCM5 and the MYST domain histone aceyltransferase TIP60, was confirmed by using pull-down and co-immunoprecipitation experiments. TIP60 was able to markedly enhance C/EBPα mediated transcriptional activation in reporter gene assays, suggesting that TIP60 is a co-activator of C/EBPα. This co-activator function of TIP60 was dependent on its intact histone aceyltransferase domain and on the C/EBPα DNA binding domain. TIP60 was found to be associated with the human C/EBPα promoter in vivo in a chromatin immunoprecipitation assay with a concomitant increase in histone H3 and H4 acetylation. Furthermore, we observed a lower expression of TIP60 mRNA in undifferentiated U937 CD11b- cells compared to retinoic acid induced differentiated U937 CD11b+ cells suggesting that higher TIP60 expression is associated with myeloid differentiation. Correlated expression between C/EBP and TIP60 was also observed in certain leukemia subtypes. These findings point to a functional synergism between C/EBP and TIP60 in myeloid differentiation and suggests that TIP60 might be an important player in leukemogenesis.