title: NLRC5 exclusively transactivates MHC class I and related genes through a distinctive SXY module.
abstract: MHC class II (MHCII) genes are transactivated by the NOD-like receptor (NLR) family member CIITA, which is recruited to SXY enhancers of MHCII promoters via a DNA-binding "enhanceosome" complex. NLRC5, another NLR protein, was recently found to control transcription of MHC class I (MHCI) genes. However, detailed understanding of NLRC5's target gene specificity and mechanism of action remained lacking. We performed ChIP-sequencing experiments to gain comprehensive information on NLRC5-regulated genes. In addition to classical MHCI genes, we exclusively identified novel targets encoding non-classical MHCI molecules having important functions in immunity and tolerance. ChIP-sequencing performed with Rfx5(-/-) cells, which lack the pivotal enhanceosome factor RFX5, demonstrated its strict requirement for NLRC5 recruitment. Accordingly, Rfx5-knockout mice phenocopy Nlrc5 deficiency with respect to defective MHCI expression. Analysis of B cell lines lacking RFX5, RFXAP, or RFXANK further corroborated the importance of the enhanceosome for MHCI expression. Although recruited by common DNA-binding factors, CIITA and NLRC5 exhibit non-redundant functions, shown here using double-deficient Nlrc5(-/-)CIIta(-/-) mice. These paradoxical findings were resolved by using a "de novo" motif-discovery approach showing that the SXY consensus sequence occupied by NLRC5 in vivo diverges significantly from that occupied by CIITA. These sequence differences were sufficient to determine preferential occupation and transactivation by NLRC5 or CIITA, respectively, and the S box was found to be the essential feature conferring NLRC5 specificity. These results broaden our knowledge on the transcriptional activities of NLRC5 and CIITA, revealing their dependence on shared enhanceosome factors but their recruitment to distinct enhancer motifs in vivo. Furthermore, we demonstrated selectivity of NLRC5 for genes encoding MHCI or related proteins, rendering it an attractive target for therapeutic intervention. NLRC5 and CIITA thus emerge as paradigms for a novel class of transcriptional regulators dedicated for transactivating extremely few, phylogenetically related genes.
authors: Department of Biochemistry, University of Lausanne, Epalinges, Switzerland.
authors: Kristina
authors: K
authors: Ludigs
authors: Department of Pathology and Immunology, University of Geneva Medical School, Geneva, Switzerland.
authors: Queralt
authors: Q
authors: Seguín-Estévez
authors: Department of Pathology and Immunology, University of Geneva Medical School, Geneva, Switzerland.
authors: Sylvain
authors: S
authors: Lemeille
authors: Ludwig Center for Cancer Research of the University of Lausanne, Epalinges, Switzerland.
authors: Isabel
authors: I
authors: Ferrero
authors: Department of Biochemistry, University of Lausanne, Epalinges, Switzerland.
authors: Giorgia
authors: G
authors: Rota
authors: Department of Biochemistry, University of Lausanne, Epalinges, Switzerland.
authors: Sonia
authors: S
authors: Chelbi
authors: Department of Biochemistry, University of Lausanne, Epalinges, Switzerland.
authors: Chantal
authors: C
authors: Mattmann
authors: Ludwig Center for Cancer Research of the University of Lausanne, Epalinges, Switzerland.
authors: H Robson
authors: HR
authors: MacDonald
authors: Department of Pathology and Immunology, University of Geneva Medical School, Geneva, Switzerland.
authors: Walter
authors: W
authors: Reith
authors: Department of Biochemistry, University of Lausanne, Epalinges, Switzerland.
authors: Greta
authors: G
authors: Guarda
mesh_terms: D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D005805:Genes, MHC Class I; D005802:Genes, MHC Class II; D016678:Genome; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D051379:Mice; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000276:immunology; D011401:Promoter Regions, Genetic; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D015534:Trans-Activators / Q000096:biosynthesis / Q000235:genetics* / Q000276:immunology; D015533:Transcriptional Activation / Q000235:genetics* / Q000276:immunology
chemical_list: D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; C083728:MHC class II transactivator protein; C549161:NLRC5 protein, mouse; D009687:Nuclear Proteins; D015534:Trans-Activators