Proteomic identification of the MYST domain histone acetyltransferase TIP60 (HTATIP) as a co-activator of the myeloid transcription factor C/EBP alpha

The transcription factor C/EBP alpha (CEBPA) is a key player in granulopoiesis and leukemogenesis. We have previously reported the interaction of C/EBPa with other proteins ( utilizing mass spectrometry) in transcriptional regulation. In the present study, we characterized the association of the MYST domain histone acetyltransferase Tat-interactive protein (TIP) 60 (HTA-TIP) with C/EBP alpha. We show in pull-down and co-precipitation experiments that C/EBP alpha and HTATIP interact. A chromatin immunoprecipitation (ChlP) and a confirmatory Re-ChlP assay revealed in vivo occupancy of the C/EBP alpha and GCSF-R promoter by HTATIP. Reporter gene assays showed that HTATIP is a coactivator of C/EBP alpha. The co-activator function of HTATIP is dependent on its intact histone acetyltransferase (HAT) domain and on the C/EBP alpha DNA-binding domain. The resulting balance between histone acetylation and deacetylation at the C/EBP alpha promoter might represent an important mechanism of C/EBP alpha action. We observed a lower expression of HTATIP mRNA in undifferentiated U937 cells compared to retinoic acid-induced differentiated U937 cells, and correlated expression of CEBPA and HTATIP mRNA levels were observed in leukemia samples. These findings point to a functional synergism between C/EBP alpha and HTATIP in myeloid differentiation and suggest that HTATIP might be an important player in leukemogenesis.