Induction of gamma-globin by histone deacetylase inhibitors

The short-chain fatty acid butyrate has been shown to elevate fetal hemoglobin (HbF) by inducing expression of the gamma-globin gene. Regulation of gene expression by butyrate is thought to proceed via inhibition of the enzyme histone deacetylase, leading to elevated levels of core histone acetylation which affect chromatin structure and transcription rates. To determine whether changes in histone acetylation are critical for the regulation of the gamma-globin gene, we tested three potent and specific inhibitors of histone deacetylase, the cyclic tetrapeptides trapoxin and Helminthsporium carbonum toxin (HC toxin), and the antifungal antibiotic trichostatin A for their ability to induce fetal hemoglobin expression in erythroid cells. These compounds induced fetal hemoglobin in both primary erythroid cell cultures and human erythroleukemia (K562) cells. A butyrate-responsive element spanning the duplicated CCAAT box region of the gamma-globin promoter has been identified in transient transfection assays using a reporter construct in K562 cells, and we show that the same promoter region is required for response to trapoxin and trichostatin. Mutational analysis of the gamma-globin promoter indicates that the distal CCAAT box and 3' flanking sequence (CCAATAGCC) is critical for activation by butyrate, trapoxin, and trichostatin, whereas the proximal element (CCAATAGTC) plays a less important role. These results show that inhibition of histone deacetylase can lead to transcriptional activation of gamma-globin promoter reporter gene constructs through proximal promoter elements, and suggest that butyrate induces gamma-globin expression via such changes in histone acetylation.