title: KRAB-zinc finger proteins and KAP1 can mediate long-range transcriptional repression through heterochromatin spreading.
abstract: Krüppel-associated box domain-zinc finger proteins (KRAB-ZFPs) are tetrapod-specific transcriptional repressors encoded in the hundreds by the human genome. In order to explore their as yet ill-defined impact on gene expression, we developed an ectopic repressor assay, allowing the study of KRAB-mediated transcriptional regulation at hundreds of different transcriptional units. By targeting a drug-controllable KRAB-containing repressor to gene-trapping lentiviral vectors, we demonstrate that KRAB and its corepressor KAP1 can silence promoters located several tens of kilobases (kb) away from their DNA binding sites, with an efficiency which is generally higher for promoters located within 15 kb or less. Silenced promoters exhibit a loss of histone H3-acetylation, an increase in H3 lysine 9 trimethylation (H3K9me3), and a drop in RNA Pol II recruitment, consistent with a block of transcriptional initiation following the establishment of silencing marks. Furthermore, we reveal that KRAB-mediated repression is established by the long-range spreading of H3K9me3 and heterochromatin protein 1 beta (HP1beta) between the repressor binding site and the promoter. We confirm the biological relevance of this phenomenon by documenting KAP1-dependent transcriptional repression at an endogenous KRAB-ZFP gene cluster, where KAP1 binds to the 3' end of genes and mediates propagation of H3K9me3 and HP1beta towards their 5' end. Together, our data support a model in which KRAB/KAP1 recruitment induces long-range repression through the spread of heterochromatin. This finding not only suggests auto-regulatory mechanisms in the control of KRAB-ZFP gene clusters, but also provides important cues for interpreting future genome-wide DNA binding data of KRAB-ZFPs and KAP1.
authors.affiliation: School of Life Sciences, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.
authors.forename: Anna C
authors.initials: AC
authors.lastname: Groner
authors.forename: Sylvain
authors.initials: S
authors.lastname: Meylan
authors.forename: Angela
authors.initials: A
authors.lastname: Ciuffi
authors.forename: Nadine
authors.initials: N
authors.lastname: Zangger
authors.forename: Giovanna
authors.initials: G
authors.lastname: Ambrosini
authors.forename: Nicolas
authors.initials: N
authors.lastname: Dénervaud
authors.forename: Philipp
authors.initials: P
authors.lastname: Bucher
authors.forename: Didier
authors.initials: D
authors.lastname: Trono
mesh_terms: D000107:Acetylation; D020029:Base Pairing; D001665:Binding Sites; D002460:Cell Line; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism; D020868:Gene Silencing; D006570:Heterochromatin / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D006801:Humans; D008745:Methylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D012319:RNA Polymerase II / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D014158:Transcription, Genetic; D000076183:Tripartite Motif-Containing Protein 28; D016335:Zinc Fingers
chemical_list: C000715593:CBX1 protein, human; D002868:Chromosomal Proteins, Non-Histone; D006570:Heterochromatin; D006657:Histones; D012097:Repressor Proteins; C422407:ZNF350 protein, human; D000090266:Chromobox Protein Homolog 5; C101116:TRIM28 protein, human; D000076183:Tripartite Motif-Containing Protein 28; D012319:RNA Polymerase II