title: U7 small nuclear ribonucleoprotein represses histone gene transcription in cell cycle-arrested cells.
abstract: Histone gene expression is tightly coordinated with DNA replication, as it is activated at the onset of S phase and suppressed at the end of S phase. Replication-dependent histone gene expression is precisely controlled at both transcriptional and posttranscriptional levels. U7 small nuclear ribonucleoprotein (U7 snRNP) is involved in the 3'-end processing of nonpolyadenylated histone mRNAs, which is required for S phase-specific gene expression. The present study reports a unique function of U7 snRNP in the repression of histone gene transcription under cell cycle-arrested conditions. Elimination of U7 snRNA with an antisense oligonucleotide in HeLa cells as well as in nontransformed human lung fibroblasts resulted in elevated levels of replication-dependent H1, H2A, H2B, H3, and H4 histone mRNAs but not of replication-independent H3F3B histone mRNA. An analogous effect was observed upon depletion of Lsm10, a component of the U7 snRNP-specific Sm ring, with siRNA. Pulse-chase experiments revealed that U7 snRNP acts to repress transcription without remarkably altering mRNA stability. Mass spectrometric analysis of the captured U7 snRNP from HeLa cell extracts identified heterogeneous nuclear (hn)RNP UL1 as a U7 snRNP interaction partner. Further knockdown and overexpression experiments revealed that hnRNP UL1 is responsible for U7 snRNP-dependent transcriptional repression of replication-dependent histone genes. Chromatin immunoprecipitation confirmed that hnRNP UL1 is recruited to the histone gene locus only when U7 snRNP is present. These findings support a unique mechanism of snRNP-mediated transcriptional control that restricts histone synthesis to S phase, thereby preventing the potentially toxic effects of histone synthesis at other times in the cell cycle.
authors.affiliation: Functional RNomics Team, Biomedicinal Information Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Koutou, Tokyo 135-0064, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ideue
authors.forename: Shungo
authors.initials: S
authors.lastname: Adachi
authors.forename: Takao
authors.initials: T
authors.lastname: Naganuma
authors.forename: Akie
authors.initials: A
authors.lastname: Tanigawa
authors.forename: Tohru
authors.initials: T
authors.lastname: Natsume
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Hirose
mesh_terms: D059447:Cell Cycle Checkpoints / Q000235:genetics*; D006367:HeLa Cells; D034441:Heterogeneous-Nuclear Ribonucleoproteins / Q000378:metabolism; D006657:Histones / Q000235:genetics*; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012342:RNA, Small Nuclear / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D020885:Ribonucleoprotein, U7 Small Nuclear / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D015854:Up-Regulation / Q000235:genetics
chemical_list: C475078:HNRNPUL1 protein, human; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006657:Histones; D009687:Nuclear Proteins; D012333:RNA, Messenger; D012342:RNA, Small Nuclear; D012097:Repressor Proteins; D020885:Ribonucleoprotein, U7 Small Nuclear; D014157:Transcription Factors; C405487:U7 small nuclear RNA