liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
DNA-PK and the TRF2 iDDR inhibit MRN-initiated resection at leading-end telomeres
Rockefeller Univ, NY 10021 USA.
Linköping University, Department of Biomedical and Clinical Sciences, Division of Molecular Medicine and Virology. Linköping University, Faculty of Medicine and Health Sciences.ORCID iD: 0000-0003-0451-1839
Univ Texas, TX USA.
Rockefeller Univ, NY 10021 USA.
Show others and affiliations
2023 (English)In: Nature Structural & Molecular Biology, ISSN 1545-9993, E-ISSN 1545-9985, Vol. 30, no 9, p. 1346-+Article in journal (Refereed) Published
Abstract [en]

Telomeres replicated by leading-strand synthesis lack the 3 overhang required for telomere protection. Surprisingly, resection of these blunt telomeres is initiated by the telomere-specific 5 exonuclease Apollo rather than the Mre11-Rad50-Nbs1 (MRN) complex, the nuclease that acts at DNA breaks. Without Apollo, leading-end telomeres undergo fusion, which, as demonstrated here, is mediated by alternative end joining. Here, we show that DNA-PK and TRF2 coordinate the repression of MRN at blunt mouse telomeres. DNA-PK represses an MRN-dependent long-range resection, while the endonuclease activity of MRN-CtIP, which could cleave DNA-PK off of blunt telomere ends, is inhibited in vitro and in vivo by the iDDR of TRF2. AlphaFold-Multimer predicts a conserved association of the iDDR with Rad50, potentially interfering with CtIP binding and MRN endonuclease activation. We propose that repression of MRN-mediated resection is a conserved aspect of telomere maintenance and represents an ancient feature of DNA-PK and the iDDR.

Place, publisher, year, edition, pages
NATURE PORTFOLIO , 2023. Vol. 30, no 9, p. 1346-+
National Category
Biochemistry Molecular Biology
Identifiers
URN: urn:nbn:se:liu:diva-199141DOI: 10.1038/s41594-023-01072-xISI: 001085159500020PubMedID: 37653239OAI: oai:DiVA.org:liu-199141DiVA, id: diva2:1811776
Note

Funding Agencies|Cancerfonden [CAN 2018/493]; Vetenskapsradet [AR-MH 2018-03215]; NIH [R01GM138548, R35 CA210036, AG016642]; Knut and Alice Wallenberg Foundation; Lions forskningsfond [LiU-2022-01245]

Available from: 2023-11-14 Created: 2023-11-14 Last updated: 2025-02-20
In thesis
1. Molecular characterization of the interplay between DNA-PK and TRF2 in telomere protection
Open this publication in new window or tab >>Molecular characterization of the interplay between DNA-PK and TRF2 in telomere protection
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The genetic material of mammalian cells is organized as linear chromosomes inside their nucleus. In order to preserve genomic stability, mammalian cells have developed several mechanisms to detect and repair DNA lesions that can occasionally occur in the genome. Nevertheless, in certain circumstances, these pathways can promote aberrant repair that can result in genomic instability and tumorigenesis. One such case are the ends of linear chromosomes, which are particularly susceptible since they can be mistakenly recognized as DNA lesions by the DNA repair machinery, which seeks to repair the damage by joining the two DNA ends together and thus causing rearrangements and genome instability. Therefore, the linear ends of chromosomes need to be protected from being sensed as sites of damage, and this is promoted by the presence of specialized structures known as telomeres, with the aim of preventing determinantal consequences of having exposed DNA ends. Telomeres are formed by a repetitive DNA sequence that is bound by a protein complex named shelterin, which forms a protective structure at the end of chromosomes. Among the shelterin subunits, TRF2 plays a crucial role. Other factors that have been found essential for the protection of telomeres are Apollo and DNA-PK proteins which, strikingly, are also involved in DNA repair mechanisms.

Understanding the underlying mechanism of telomere protection and the interplay between factors involved is of relevance since defects in telomere protection activate aberrant repair, which is associated with genome instability, a prime mechanism shaping cancer.

In Paper I, we focused on how Apollo and the catalytic subunit of DNA-PK (DNA-PKcs) cooperate in preserving telomere homeostasis, and we shed light on the mechanistic function of DNA-PKcs in granting access to Apollo to the telomeric ends. We found that this function requires the kinase activity of DNA-PKcs to promote autophosphorylation, and the binding of Apollo to DNA-PKcs for optimal positioning at the DNA ends. This study shows an analogous mechanism of function of DNA-PK at sites of DNA lesions and at telomeres.

In Paper II, we found that the localization of DNA-PK at telomeres post-replication is essential to block the nucleolytic erosion of the telomeric ends by any other nuclease than Apollo. This protective function is also independently fulfilled by the iDDR domain of TRF2, which specifically inhibits the endonucleolytic activity of MRN protein complex. This study reveals the high pressure for cells to keep tight control of resection at telomeres.

In Paper III, we expanded our studies by investigating the role of Apollo and DNA-PKcs in ALT cancerous cells, which utilize a recombination-mediated mechanism to elongate telomeres. Here, we show that DNA-PKcs and Apollo have a conserved role in promoting G-overhang formation, but in the absence of Apollo and/or DNA-PKcs kinase activity, telomeres are insensitive to fusion. Moreover, we found that Apollo promotes telomere recombination events at ALT telomeres. This study opens the possibility for different mechanisms of telomere maintenance in ALT cells.

Abstract [sv]

Det genetiska materialet i däggdjursceller är organiserat som linjära kromosomer inuti cellernas kärna. För att bevara genomisk stabilitet har däggdjursceller utvecklat flera mekanismer för att upptäcka och reparera DNA-skador som ibland kan uppstå i genomet. Under vissa omständigheter, kan dessa vägar leder till avvikande reparation som i sin tur kan resultera i genomisk instabilitet och tumörbildning. Ett sådant fall är ändarna i linjära kromosomer då de är särskilt känsliga eftersom det kan av misstag igenkännas som DNA-skador av DNA-reparationsmaskineriet, som försöker reparera skadan genom att förena de två DNA-ändarna, och därmed orsaka omlagring och genominstabilitet. Därför måste de linjära ändarna av kromosomerna skyddas från att uppfattas som skador och detta främjas av närvaron av specialiserade strukturer som kallas telomerer i syfte att förhindra konsekvenserna av att ha exponerade DNA-ändar. Telomerer består av en repetitiv DNA-sekvens som är bunden av ett proteinkomplex, nämligen shelterin, som bildar en skyddande struktur bland vilka TRF2 spelar avgörande roller. Andra faktorer som har visat sig spela en skyddande roll vid telomerer är Apollo- och DNA-PK-proteiner som, slående nog, också är involverade i DNA-reparation.

Att förstå den underliggande mekanismen för telomerskydd och samspelet mellan inblandade faktorer är av relevans eftersom defekter i telomerskyddet aktiverar avvikande reparationer som associeras med genominstabilitet vilket är en betydande mekanism för cancerformation.

I Artikel I belyser vi den mekanistiska funktionen hos den katalytiska subenheten av DNA-PK (DNA-PKcs) för att ge tillgång åt Apollo till telomerändarna. Denna funktion kräver att kinasaktiviteten hos DNA-PK genomgår autofosforylering och bindningen av Apollo till DNA-PK för optimal positionering till DNA-ändarna. Denna studie visar på en analog funktion för DNA-PK vid DNA-skador och vid telomerer.

I Artikel II fann vi att lokaliseringen av DNA-PK vid telomerer efter replikering är väsentlig för att blockera den nukleolytiska erosionen av de telomera ändarna av något annat nukleas än Apollo. Denna skyddande funktion uppfylls också oberoende av iDDR-domänen av TRF2, som specifikt hämmar den endonukleolytiska aktiviteten av MRN proteinkomplex. Denna studie avslöjar det höga trycket för celler att hålla en tät kontroll av resektion vid telomerer.

I Artikel III undersökte vi rollen av Apollo och DNA-PK i ALT-cancerceller, som använder en rekombinationsmedierad mekanism för att förlänga telomerer. Här visar vi att DNA-PKcs och Apollo har en konserverad roll för att leder till G-överhängsbildning, men i frånvaro av Apollo- och/eller DNA-PKcs-kinasaktivitet är telomerer okänsliga för fusion. Dessutom fann vi att Apollo leder till telomer rekombinationshändelser vid ALT-telomerer. Denna studie öppnar möjligheten för olika mekanismer för telomerunderhåll i ALT-celler.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2024. p. 112
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1894
National Category
Medical Biotechnology (with a focus on Cell Biology (including Stem Cell Biology), Molecular Biology, Microbiology, Biochemistry or Biopharmacy)
Identifiers
urn:nbn:se:liu:diva-201296 (URN)9789180755108 (ISBN)9789180755115 (ISBN)
Public defence
2024-04-03, Belladonna, Building 511, Campus US, Linköping, 09:00 (English)
Opponent
Supervisors
Available from: 2024-03-04 Created: 2024-03-04 Last updated: 2024-03-04Bibliographically approved

Open Access in DiVA

fulltext(17431 kB)36 downloads
File information
File name FULLTEXT01.pdfFile size 17431 kBChecksum SHA-512
9b157d92f1828b45c60d698d2649417d6f68b801570a32105afcfe7822e5994205029d3a45faa764b8198a2c95bebb89f6c95ca18f2e9863ea398055dafbfd88
Type fulltextMimetype application/pdf

Other links

Publisher's full textPubMed

Search in DiVA

By author/editor
Toia, BeatriceMatei, Andreea M.Lottersberger, Francisca
By organisation
Division of Molecular Medicine and VirologyFaculty of Medicine and Health SciencesDepartment of Biomedical and Clinical Sciences
In the same journal
Nature Structural & Molecular Biology
BiochemistryMolecular Biology

Search outside of DiVA

GoogleGoogle Scholar
Total: 36 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

doi
pubmed
urn-nbn

Altmetric score

doi
pubmed
urn-nbn
Total: 92 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf