Histone acetylation contributes to chromatin looping between the locus control region and globin gene by influencing hypersensitive site formation

Chromatin loops are formed between enhancers and promoters and between insulators to regulate gene transcription in the eukaryotic genome. These transcription regulatory elements forming loops have highly acetylated histones. To understand the correlation between histone acetylation and chromatin loop formation, we inhibited the expression of histone acetyltransferase CBP and p300 in elythroid K562 cells and analyzed the chromatin structure of the beta-globin locus. The proximity between the locus control region (LCR) and the active (G)gamma-globin gene was decreased in the beta-globin locus when histones were hypoacetylated by the double knockdown of CBP and p300. Sensitivity to DNase I and binding of erythroid specific activators were reduced in the hypoacetylated LCR hypersensitive sites (HSs) and gene promoter. Interestingly, the chromatin loop between HS5 and 3'HS1 was formed regardless of the hypoacetylation of the beta-globin locus. CTCF binding was maintained at HS5 and 3'HS1 in the hypoacetylated locus. Thus, these results indicate that histone acetylation contributes to chromatin looping through the formation of HSs in the LCR and gene promoter. However, looping between insulators appears to be independent from histone acetylation. (c) 2013 Elsevier B.V. All rights reserved.