Format

Send to

Choose Destination
Nucleic Acids Res. 2019 Jun 11. pii: gkz518. doi: 10.1093/nar/gkz518. [Epub ahead of print]

Double-strand breaks in ribosomal RNA genes activate a distinct signaling and chromatin response to facilitate nucleolar restructuring and repair.

Korsholm LM1,2, Gál Z1,2, Lin L3,4, Quevedo O1,2, Ahmad DA1,2, Dulina E1,2, Luo Y3,4,5, Bartek J2,6, Larsen DH1,2.

Author information

1
Nucleolar Stress and Disease Group, Danish Cancer Society Research Center, Danish Cancer Society, Strandboulevarden 49, DK-2100 Copenhagen, Denmark.
2
Genome Integrity Unit, Danish Cancer Society Research Center, Danish Cancer Society, Strandboulevarden 49, DK-2100 Copenhagen, Denmark.
3
Department of Biomedicine, Aarhus University, 8000 Aarhus, Denmark.
4
China National GeneBank, BGI-Shenzhen, 518083 Shenzhen, China.
5
Lars Bolund Institute of Regenerative Medicine, BGI-Qingdao, 266555 Qingdao, China.
6
Department of Medical Biochemistry and Biophysics, Science for Life Laboratory, Division of Genome Biology, Karolinska Institutet, SE-171 65 Solna, Sweden.

Abstract

The nucleolus is a nuclear sub-domain containing the most highly transcribed genes in the genome. Hundreds of human ribosomal RNA (rRNA) genes, located in the nucleolus, rely on constant maintenance. DNA double-strand breaks (DSBs) in rRNA genes activate the ATM kinase, repress rRNA transcription and induce nucleolar cap formation. Yet how ribosomal-DNA (rDNA) lesions are detected and processed remains elusive. Here, we use CRISPR/Cas9-mediated induction of DSBs and report a chromatin response unique to rDNA depending on ATM-phosphorylation of the nucleolar protein TCOF1 and recruitment of the MRE11-RAD50-NBS1 (MRN) complex via the NBS1-subunit. NBS1- and MRE11-depleted cells fail to suppress rRNA transcription and to translocate rDNA into nucleolar caps. Furthermore, the DNA damage response (DDR) kinase ATR operates downstream of the ATM-TCOF1-MRN interplay and is required to fully suppress rRNA transcription and complete DSB-induced nucleolar restructuring. Unexpectedly, we find that DSBs in rDNA neither activate checkpoint kinases CHK1/CHK2 nor halt cell-cycle progression, yet the nucleolar-DDR protects against genomic aberrations and cell death. Our data highlight the concept of a specialized nucleolar DNA damage response (n-DDR) with a distinct protein composition, spatial organization and checkpoint communication. The n-DDR maintains integrity of ribosomal RNA genes, with implications for cell physiology and disease.

PMID:
31184714
DOI:
10.1093/nar/gkz518

Supplemental Content

Full text links

Icon for Silverchair Information Systems
Loading ...
Support Center