The Role of HDAC1 Acetylation in Hematopoiesis and GATA-1 Function.

Abstract 1459

Poster Board I-482

Histone deacetylases (HDACs) play important roles in transcriptional regulation in eukaryotic cells. Several lines of evidence also link HDACs to cancer. HDAC inhibitors have shown preclinical promise when combined with other therapeutic agents in the treatments of leukemia and solid tumors. HDAC1 often presents in repressor complexes, such as Sin3, NuRD and CoREST complexes. We previously found that HDAC1 can be acetylated in vivo by acetyltransferase p300 and that acetylated HDAC1 completely loses its deacetylase activity (Qiu et al, 2006). In this study, we investigate the role of HDAC1 during erythroid differentiation. HDAC1 deacetylase activity gradually reduced upon the induction of differentiation. However, the HDAC1 protein level remains unchanged, suggesting that HDAC1 deacetylase activity, but not its protein level, is regulated. To further test the role of HDAC1 in erythroid differentiation, stable cell lines that overexpress HDAC1 and mutants mimicking acetylated or unacetylated HDAC1 were established. We also generated stable HDAC1 and HDAC2 knock down cell lines. The results showed that HDAC1 deacetylase activity is required to promote erythroid proliferation and to inhibit differentiation. Next, we studied whether HDAC1 modulates erythroid differentiation through regulating the activity of key erythroid transcription factor GATA-1. GATA-1 interacts with many other key hematopoietic transcription factors, as well as chromatin remodeling/modifying coactivators and corepressors. It is suggested that GATA-1 mediates gene activation through its association with coactivator complexes. However, recent studies indicated that GATA-1 associates with HDAC1/2 containing corepressor complexes (NuRD) throughout differentiation of erythroid cells. We investigated the deacetylase activity of the GATA-1 associated NuRD complex during erythroid differentiation. We found that the deacetylase activity of the complex decreased and further diminished at day 5 of DMSO induced MEL cells. Accordingly, the acetylated form of HDAC1 within the GATA-1 complex increased during erythroid differentiation. We further demonstrated the role of HDAC1 in GATA-1 mediated gene transcription in transient transfection assays. These studies indicate that HDAC1 plays an important role in regulating GATA-1 activity and the deacetylase activity of the GATA-1 associated NuRD complex is also regulated. This complex may play different roles in undifferentiated and differentiated erythroid cells. Thus, our results suggest a novel but rather general regulatory mechanism of histone deacetylase containing protein complexes.