Regulated recruitment of HP1 to a euchromatic gene induces mitotically heritable, epigenetic gene silencing: a mammalian cell culture model of gene variegation.
Heterochromatin protein 1 (HP1) is a key component of constitutive heterochromatin in Drosophila and is required for stable epigenetic gene silencing classically observed as position effect variegation. Less is known of the family of mammalian HP1 proteins, which may be euchromatic, targeted to expressed loci by repressor-corepressor complexes, and retained there by Lys 9-methylated histone H3 (H3-MeK9). To characterize the physical properties of euchromatic loci bound by HP1, we developed a strategy for regulated recruitment of HP1 to an expressed transgene in mammalian cells by using a synthetic, hormone-regulated KRAB repression domain. We show that its obligate corepressor, KAP1, can coordinate all the machinery required for stable gene silencing. In the presence of hormone, the transgene is rapidly silenced, spatially recruited to HP1-rich nuclear regions, assumes a compact chromatin structure, and is physically associated with KAP1, HP1, and the H3 Lys 9-specific methyltransferase, SETDB1, over a highly localized region centered around the promoter. Remarkably, silencing established by a short pulse of hormone is stably maintained for >50 population doublings in the absence of hormone in clonal-cell populations, and the silent transgenes in these clones show promoter hypermethylation. Thus, like variegation in Drosophila, recruitment of mammalian HP1 to a euchromatic promoter can establish a silenced state that is epigenetically heritable.
Ayyanathan
Kasirajan
K
The Wistar Institute, Philadelphia, Pennsylvania 19104-4268, USA.
Lechner
Mark S
MS
Bell
Peter
P
Maul
Gerd G
GG
Schultz
David C
DC
Yamada
Yoshihiko
Y
Tanaka
Kazuhiro
K
Torigoe
Kiyoyuki
K
Rauscher
Frank J
FJ
D016475:3T3 Cells; D020816:Amino Acid Motifs; D000818:Animals; D018929:Cell Culture Techniques; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism; D000090266:Chromobox Protein Homolog 5; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D019175:DNA Methylation; D004720:Endonucleases / Q000378:metabolism; D020868:Gene Silencing; D017930:Genes, Reporter; D006657:Histones / Q000378:metabolism; D006915:Hydroxytestosterones / Q000494:pharmacology; D017404:In Situ Hybridization, Fluorescence; D008156:Luciferases / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008938:Mitosis; D008957:Models, Genetic; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014162:Transfection; D019076:Transgenes; D016335:Zinc Fingers
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D006657:Histones; D006915:Hydroxytestosterones; D012333:RNA, Messenger; D000090266:Chromobox Protein Homolog 5; C032278:4,17 beta-dihydroxy-4-androstene-3-one; D008156:Luciferases; D004720:Endonucleases; D008239:Lysine