Predominant interaction of both Ikaros and Helios with the NuRD complex in immature thymocytes.
Ikaros is the founding member of a small family of C2H2 zinc-finger DNA-binding proteins that carry out critical functions during lymphocyte development. Although interactions between Ikaros and various proteins have been reported, Ikaros-containing complexes have not been purified to determine their composition and identify the predominant interacting partners. In this study, a tandem affinity purification-mass spectrometry strategy was developed for the isolation of complexes formed by Ikaros and by Helios, a T-cell-restricted member of the Ikaros family that remains largely uncharacterized. This strategy, which appears to be well suited for general use in mammalian cells, relies on an N-terminal polypeptide containing a double FLAG epitope, followed by a tobacco etch virus protease cleavage site and calmodulin binding peptide. In extracts from a murine thymocyte line, Ikaros and Helios associated under moderate stringency conditions only with other members of the Ikaros family. However, under low stringency conditions, both tagged proteins assembled into higher molecular weight complexes. Mass spectrometry revealed that both proteins associated predominantly with subunits of NuRD, an ATP-dependent nucleosome remodeling complex implicated in transcriptional repression and activation and previously reported to associate with Ikaros. Further analysis of the affinity-purified Ikaros revealed that several serines and threonines are phosphorylated in the thymocyte line, with apparent changes upon thymocyte maturation. These results support the hypothesis that the NuRD complex makes major contributions to the functions of both Ikaros and Helios and that the activities of these proteins may be regulated in part by changes in phosphorylation.
Howard Hughes Medical Institute and Department of Microbiology, Immunology, and Molecular Genetics, UCLA, Los Angeles, California 90095, USA.
Rupa
R
Sridharan
Stephen T
ST
Smale
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006655:Histone Deacetylases / Q000378:metabolism*; D006801:Humans; D051740:Ikaros Transcription Factor / Q000378:metabolism*; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex; D051379:Mice; D018613:Microscopy, Confocal; D008954:Models, Biological; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011485:Protein Binding; D013950:Thymus Gland / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; C497239:IKZF1 protein, human; C111431:IKZF2 protein, human; D014157:Transcription Factors; C497238:Zfpn1a1 protein, mouse; C491746:Zfpn1a2 protein, mouse; D051740:Ikaros Transcription Factor; D006655:Histone Deacetylases; D056245:Mi-2 Nucleosome Remodeling and Deacetylase Complex