title: hnRNP K coordinates transcriptional silencing by SETDB1 in embryonic stem cells.
abstract: Retrotransposition of endogenous retroviruses (ERVs) poses a substantial threat to genome stability. Transcriptional silencing of a subset of these parasitic elements in early mouse embryonic and germ cell development is dependent upon the lysine methyltransferase SETDB1, which deposits H3K9 trimethylation (H3K9me3) and the co-repressor KAP1, which binds SETDB1 when SUMOylated. Here we identified the transcription co-factor hnRNP K as a novel binding partner of the SETDB1/KAP1 complex in mouse embryonic stem cells (mESCs) and show that hnRNP K is required for ERV silencing. RNAi-mediated knockdown of hnRNP K led to depletion of H3K9me3 at ERVs, concomitant with de-repression of proviral reporter constructs and specific ERV subfamilies, as well as a cohort of germline-specific genes directly targeted by SETDB1. While hnRNP K recruitment to ERVs is dependent upon KAP1, SETDB1 binding at these elements requires hnRNP K. Furthermore, an intact SUMO conjugation pathway is necessary for SETDB1 recruitment to proviral chromatin and depletion of hnRNP K resulted in reduced SUMOylation at ERVs. Taken together, these findings reveal a novel regulatory hierarchy governing SETDB1 recruitment and in turn, transcriptional silencing in mESCs.
authors.affiliation: Life Sciences Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Thompson
authors.affiliation: Life Sciences Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Vered
authors.initials: V
authors.lastname: Dulberg
authors.affiliation: Centre for High-Throughput Biology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Kyung-Mee
authors.initials: KM
authors.lastname: Moon
authors.affiliation: Centre for High-Throughput Biology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Leonard J
authors.initials: LJ
authors.lastname: Foster
authors.affiliation: Life Sciences Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Carol
authors.initials: C
authors.lastname: Chen
authors.affiliation: Life Sciences Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada; Biomedical Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Mohammad M
authors.initials: MM
authors.lastname: Karimi
authors.affiliation: Life Sciences Institute, Department of Medical Genetics, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Lorincz
mesh_terms: D000818:Animals; D002843:Chromatin / Q000235:genetics; D019175:DNA Methylation / Q000235:genetics*; D053595:Embryonic Stem Cells / Q000821:virology; D020077:Endogenous Retroviruses / Q000235:genetics; D020868:Gene Silencing; D005854:Germ Cells; D034641:Heterogeneous-Nuclear Ribonucleoprotein K / Q000235:genetics*; D011495:Histone-Lysine N-Methyltransferase / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D034741:RNA, Small Interfering; D018626:Retroelements; D037941:Silencer Elements, Transcriptional / Q000235:genetics; D058207:Sumoylation / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D034641:Heterogeneous-Nuclear Ribonucleoprotein K; D034741:RNA, Small Interfering; D018626:Retroelements; D011495:Histone-Lysine N-Methyltransferase; C516239:SETDB1 protein, mouse