Mutation of TRIM28-Lys304 to Gln Attenuates its Interaction with KRAB-ZNFs and Promotes Differentiation of Erythroleukemic K562 Cells

Abstract BackgroundTRIM28/KAP1/TIF1β is a key epigenetic modifier. Genetic ablation of trim28 is embryonic lethal although RNAi-mediated knockdown in somatic cells yields viable cells. Reduction in TRIM28 abundance at the cellular or organismal level results in polyphenism. Posttranslational modifications such as phosphorylation and sumoylation have been shown to regulate TRIM28 activity. Moreover, the methylation of DNA, RNA and histones and acetylation of histones are key epigenetic modifications that regulate gene expression. A number of lysine residues of TRIM28 are subject to acetylation, but how acetylation of TRIM28 affects its functions remains poorly understood. ResultsHere we report that, compared with wild-type TRIM28, the acetylation-mimic mutant TRIM28-K304Q has an altered interaction with Krüppel-associated box zinc-finger proteins (KRAB-ZNFs), with consequent effects on the phenotype of the erythroleukemic cell line K562. TRIM28-K304Q was comparable with its wild-type counterpart with respect to intracellular level, homodimerization, phosphorylation at S473 and S824, and interactions with heterochromatin-binding protein HP1. The expression of embryonic-related and fetal globin genes was activated in TRIM28-K304Q mutant cells. Transcriptome analysis revealed that TRIM28-K304Q and TRIM28 knockout K562 cells had similar global gene expression profiles, yet the profiles differed considerably from that of wild-type K562 cells. The gene expression ensemble of mutant K562 cells indicated a general induction of differentiation-promoting genes and attenuation of proliferation-promoting genes. ConclusionsThese results suggest that acetylation/deacetylation of K304 in TRIM28 or TRIM28-K304Q constitutes a switch for regulating its interaction with KRAB-ZNFs and alters the gene regulation of this key epigenetic modifier as demonstrated by the acetylation mimic TRIM28-K304Q.