Regulation of chromatin remodeling during thymocyte differentiation (88.5)

Abstract

Abstract The Ikaros gene encodes a DNA-binding protein that functions as a master regulator of lymphoid development. Ikaros protein interacts with histone deacetylation complex and represses transcription of its target genes via chromatin remodeling. We have previously reported that Ikaros’ activity and protein stability is regulated by CK2 kinase (Popescu et al. J Biol Chem 2009 284:13869). We studied the effect of CK2-mediated phosphorylation on Ikaros function in primary thymocytes. Ikaros proteins with phosphomimetic mutations at CK2 phosphorylation sites 1) lose the ability to associate with Sin3a, a component of the NuRD histone deacetylase, as indicated by co-immunoprecipitation assays and 2) fail to repress genes involved in thymocyte differentiation as indicated by luciferase reporter assay. The introduction of phosphoresistant mutations at five N-terminal CK2 phosphorylation sites on the Ikaros protein restored Ikaros’ association with Sin3a, as well as wild-type levels of repressor activity. The treatment of primary thymocytes with CK2 kinase inhibitors resulted in increased levels of Ikaros protein and increased Ikaros’ DNA-binding affinity to the promoter regions of its target genes, as measured by quantitative chromatin immunoprecipitation. These results demonstrate that CK2 kinase regulates thymocyte differentiation by controlling Ikaros’ association with chromatin remodeling complexes and its ability to repress the transcription of developmentally regulated genes.