INDUCTION OF GAMMA-GLOBIN BY HISTONE DEACETYLASE INHIBITORS

The short-chain fatty acid butyrate has been shown to elevate fetal he moglobin (HbF) by inducing expression of the gamma-globin gene, Regula tion of gene expression by butyrate is thought to proceed via inhibiti on of the enzyme histone deacetylase, leading to elevated levels of co re histone acetylation which affect chromatin structure and transcript ion rates. To determine whether changes in histone acetylation are cri tical for the regulation of the gamma-globin gene, we tested three pot ent and specific inhibitors of histone deacetylase, the cyclic tetrape ptides trapoxin and Helminthsporium carbonum toxin (HC toxin), and the antifungal antibiotic trichostatin A for their ability to induce feta l hemoglobin expression in erythroid cells. These compounds induced fe tal hemoglobin in both primary erythroid cell cultures and human eryth roleukemia (K562) cells, A butyrate-responsive element spanning the du plicated CCAAT box region of the gamma-globin promoter has been identi fied in transient transfection assays using a reporter construct in K5 62 cells, and we show that the same promoter region is required for re sponse to trapoxin and trichostatin. Mutational analysis of the gamma- globin promoter indicates that the distal CCAAT box and 3' flanking se quence (CCAATAGCC) is critical for activation by butyrate, trapoxin, a nd trichostatin, whereas the proximal element (CCAATAGTC) plays a less important role, These results show that inhibition of histone deacety lase can lead to transcriptional activation of gamma-globin promoter r eporter gene constructs through proximal promoter elements, and sugges t that butyrate induces gamma-globin expression via such changes in hi stone acetylation. (C) 1997 by The American Society of Hematology.