title: TERRA and hnRNPA1 orchestrate an RPA-to-POT1 switch on telomeric single-stranded DNA.
abstract: Maintenance of telomeres requires both DNA replication and telomere 'capping' by shelterin. These two processes use two single-stranded DNA (ssDNA)-binding proteins, replication protein A (RPA) and protection of telomeres 1 (POT1). Although RPA and POT1 each have a critical role at telomeres, how they function in concert is not clear. POT1 ablation leads to activation of the ataxia telangiectasia and Rad3-related (ATR) checkpoint kinase at telomeres, suggesting that POT1 antagonizes RPA binding to telomeric ssDNA. Unexpectedly, we found that purified POT1 and its functional partner TPP1 are unable to prevent RPA binding to telomeric ssDNA efficiently. In cell extracts, we identified a novel activity that specifically displaces RPA, but not POT1, from telomeric ssDNA. Using purified protein, here we show that the heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) recapitulates the RPA displacing activity. The RPA displacing activity is inhibited by the telomeric repeat-containing RNA (TERRA) in early S phase, but is then unleashed in late S phase when TERRA levels decline at telomeres. Interestingly, TERRA also promotes POT1 binding to telomeric ssDNA by removing hnRNPA1, suggesting that the re-accumulation of TERRA after S phase helps to complete the RPA-to-POT1 switch on telomeric ssDNA. Together, our data suggest that hnRNPA1, TERRA and POT1 act in concert to displace RPA from telomeric ssDNA after DNA replication, and promote telomere capping to preserve genomic integrity.
authors.affiliation: Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, Massachusetts 02129, USA.
authors.forename: Rachel Litman
authors.initials: RL
authors.lastname: Flynn
authors.forename: Richard C
authors.initials: RC
authors.lastname: Centore
authors.forename: Roderick J
authors.initials: RJ
authors.lastname: O'Sullivan
authors.forename: Rekha
authors.initials: R
authors.lastname: Rai
authors.forename: Alice
authors.initials: A
authors.lastname: Tse
authors.forename: Zhou
authors.initials: Z
authors.lastname: Songyang
authors.forename: Sandy
authors.initials: S
authors.lastname: Chang
authors.forename: Jan
authors.initials: J
authors.lastname: Karlseder
authors.forename: Lee
authors.initials: L
authors.lastname: Zou
mesh_terms: D064007:Ataxia Telangiectasia Mutated Proteins; D001667:Binding, Competitive; D018797:Cell Cycle Proteins / Q000378:metabolism; D002457:Cell Extracts; D004261:DNA Replication; D004277:DNA, Single-Stranded / Q000378:metabolism*; D006367:HeLa Cells; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B / Q000378:metabolism*; D006801:Humans; D011485:Protein Binding; D012313:RNA / Q000235:genetics / Q000378:metabolism*; D051716:Replication Protein A / Q000378:metabolism*; D016196:S Phase; D000089804:Shelterin Complex; D016615:Telomere / Q000235:genetics* / Q000378:metabolism*; D034501:Telomere-Binding Proteins / Q000378:metabolism*
chemical_list: C495876:ACD protein, human; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D004277:DNA, Single-Stranded; D000076245:Heterogeneous Nuclear Ribonucleoprotein A1; D034481:Heterogeneous-Nuclear Ribonucleoprotein Group A-B; C440849:POT1 protein, human; D051716:Replication Protein A; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; C000619656:hnRNPA1 protein, human; D012313:RNA; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins