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

The transcription factor C/EBPα (CEBPA) is a key player in granulopoiesis and leukemogenesis. We have previously reported the interaction of C/EBPα 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 (HTATIP) with C/EBPα. We show in pull-down and co-precipitation experiments that C/EBPα and HTATIP interact. A chromatin immunoprecipitation (ChIP) and a confirmatory Re-ChIP assay revealed in vivo occupancy of the C/EBPα and GCSF-R promoter by HTATIP. Reporter gene assays showed that HTATIP is a co-activator of C/EBPα. The co-activator function of HTATIP is dependent on its intact histone acetyltransferase (HAT) domain and on the C/EBPα DNA-binding domain. The resulting balance between histone acetylation and deacetylation at the C/EBPα promoter might represent an important mechanism of C/EBPα 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/EBPα and HTATIP in myeloid differentiation and suggest that HTATIP might be an important player in leukemogenesis.