I17 Chromatin exchange in interferon induced transcription

• Published in: Cytokine (Philadelphia, Pa.) Vol. 59; no. 3; p. 494
• Main Author: Ozato, K.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2012
• Subjects: Chromatin; epigenetics; Histones; Interferon; Recruitment; Transcription
• ISSN: 1043-4666; 1096-0023
• DOI: 10.1016/j.cyto.2012.06.307

Type I interferons (IFNs) activate the JAK/STAT pathway and stimulate transcription from many IFNstimulated genes (ISGs). This process likely involves destabilization and reorganization of chromatin. However,chromatin events associated with ISG induction is poorly understood. To gain insight into a link between transcription andchromatin regulation, we studied whether IFN stimulation causes exchange of histones relevant to epigenetic regulation.Because the histone H3.3 is implicated in transcription coupled chromatin change, we constructed NIH3T3cells expressing GFP- H3.3 and examined H3.3 incorporation into ISGs by ChIP in parallel with ISG transcription andtranscription factor recruitment.
IFN stimulation led to rapid recruitment of RNA polymerase II and BRD4, an acetyl-histone binding factor to theISG. This was followed by recruitment of the elongation factor P-TEFb, the pausing complex NELF/DSIF and SPT6.Along with these events, IFN stimulation caused rapid H3.3 accumulation in the ISGs. H3.3 accumulation was greater inthe coding region and the gene end than in the promoter region where virtually no H3.3 incorporation was detected.Analysis with a BRD4 specific inhibitorJQ1 showed that H3.3 incorporation depended on BRD4 recruitment and ISGelongation. However, H3.3 incorporation into ISGs continued past ISG elongation, leaving the H3.3 mark on ISGs for atleast two cycles of cell division. The mutant GFP-H3.3K36R was not incorporated into ISGs, indicating that methylation ofK36 is requreid for H3.3 incorporation. Finally, H3.3 incorporation was also observed in another activation model,indicating the generality of transcription-induced histone exchange.
We show that IFN stimulation triggers rapid and extensive H3.3 incorporation into ISGs, which ispresumably associated with expulsion of the preexisting H3 (H3.1/H3.2). This event required active ISG elongation,suggesting that passage of RNA polymerase II through the ISG gene body destabilizes the architecture of the RNA-DNAnucleosome,necessitating reconstruction of nucleosomes composed of H3.3. Based on the remarkable persistence ofthe H3.3 mark left on the ISGs long after transcription, we suggest that transcription-induced H3.3 deposition representsan epigenetic mark linked to transcriptional memory.