title: KAP1/TRIM28: an inhibitor of IRF5 function in inflammatory macrophages.
abstract: IRF5 plays a key role in the induction of pro-inflammatory cytokines, contributing to the plasticity and polarisation of macrophages to an M1 phenotype and initiation of a potent T(H)1-T(H)17 response. To better understand the means of IRF5 transcriptional action, we conducted a screen for IRF5-interacting partners by affinity purification coupled to mass spectrometry and identified KAP1/TRIM28 as a novel protein-protein interaction partner of IRF5. KAP1 acts as a transcriptional co-repressor, chiefly via recruitment of complexes involved in chromatin silencing, such as histone deacetylases and methyltransferases. We mapped the N-terminus of IRF5, encompassing its DNA-binding domain together with a highly intrinsically disordered region, as crucial for the IRF5-KAP1 interaction interface, and demonstrated that IRF5 can also form complexes with the methyltransferase SETDB1. Knockdown of KAP1 (TRIM28) gene expression in human M1 macrophages potentiated IRF5-mediated expression of TNF and other M1 macrophage markers. This effect may be linked to methyltransferase activity of SETDB1, such as trimethylation of lysine 9 of histone 3 (H3K9me3), deposition of which was decreased at the human TNF locus upon KAP1 knockdown. Our study furthers an understanding of the complex molecular interactions between the TRIM and IRF protein families, and highlights a role of the inhibitory properties of KAP1 in association with IRF5-mediated gene expression.
authors.affiliation: Kennedy Institute of Rheumatology, Imperial College, 65 Aspenlea Road, London W6 8LH, United Kingdom. h.eames09@imperial.ac.uk
authors.forename: H L
authors.initials: HL
authors.lastname: Eames
authors.forename: D G
authors.initials: DG
authors.lastname: Saliba
authors.forename: T
authors.initials: T
authors.lastname: Krausgruber
authors.forename: A
authors.initials: A
authors.lastname: Lanfrancotti
authors.forename: G
authors.initials: G
authors.lastname: Ryzhakov
authors.forename: I A
authors.initials: IA
authors.lastname: Udalova
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D056970:Co-Repressor Proteins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020868:Gene Silencing; D057809:HEK293 Cells; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D011495:Histone-Lysine N-Methyltransferase; D006801:Humans; D007249:Inflammation / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D050835:Interferon Regulatory Factors / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism* / Q000473:pathology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D054730:Protein Interaction Domains and Motifs; D011496:Protein Methyltransferases / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D000076183:Tripartite Motif-Containing Protein 28; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002843:Chromatin; D056970:Co-Repressor Proteins; D004268:DNA-Binding Proteins; C431713:IRF5 protein, human; D050835:Interferon Regulatory Factors; C498178:Irf5 protein, mouse; D008565:Membrane Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; C439524:TNF protein, human; C114030:TRAT1 protein, human; D014409:Tumor Necrosis Factor-alpha; D011496:Protein Methyltransferases; D011495:Histone-Lysine N-Methyltransferase; C454062:SETDB1 protein, human; C101116:TRIM28 protein, human; C103190:Trim28 protein, mouse; D000076183:Tripartite Motif-Containing Protein 28; D006655:Histone Deacetylases