An ikaros-containing chromatin-remodeling complex in adult-type erythroid cells.
We have previously described a SWI/SNF-related protein complex (PYR complex) that is restricted to definitive (adult-type) hematopoietic cells and that specifically binds DNA sequences containing long stretches of pyrimidines. Deletion of an intergenic DNA-binding site for this complex from a human beta-globin locus construct results in delayed human gamma- to beta-globin switching in transgenic mice, suggesting that the PYR complex acts to facilitate the switch. We now show that PYR complex DNA-binding activity also copurifies with subunits of a second type of chromatin-remodeling complex, nucleosome-remodeling deacetylase (NuRD), that has been shown to have both nucleosome-remodeling and histone deacetylase activities. Gel supershift assays using antibodies to the ATPase-helicase subunit of the NuRD complex, Mi-2 (CHD4), confirm that Mi-2 is a component of the PYR complex. In addition, we show that the hematopoietic cell-restricted zinc finger protein Ikaros copurifies with PYR complex DNA-binding activity and that antibodies to Ikaros also supershift the complex. We also show that NuRD and SWI/SNF components coimmunopurify with each other as well as with Ikaros. Competition gel shift experiments using partially purified PYR complex and recombinant Ikaros protein indicate that Ikaros functions as a DNA-binding subunit of the PYR complex. Our results suggest that Ikaros targets two types of chromatin-remodeling factors-activators (SWI/SNF) and repressors (NuRD)-in a single complex (PYR complex) to the beta-globin locus in adult erythroid cells. At the time of the switch from fetal to adult globin production, the PYR complex is assembled and may function to repress gamma-globin gene expression and facilitate gamma- to beta-globin switching.
Pubmed ID: 11003653 RIS Download
Adenosine Triphosphatases | Aging | Animals | Autoantigens | Chromatin | DNA | DNA Helicases | DNA-Binding Proteins | Gene Expression Regulation | Globins | Histone Deacetylases | Histones | Humans | Ikaros Transcription Factor | Leukemia, Erythroblastic, Acute | Macromolecular Substances | Mi-2 Nucleosome Remodeling and Deacetylase Complex | Mice | Mice, Transgenic | Nuclear Proteins | Precipitin Tests | Protein Binding | Sin3 Histone Deacetylase and Corepressor Complex | Substrate Specificity | Transcription Factors | Tumor Cells, Cultured | Zinc Fingers