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

Double-strand breaks in ribosomal RNA genes activate a distinct signaling and chromatin response to facilitate nucleolar restructuring and repair. Nucleic Acids Res. 2019 Jun 11;: Authors: Korsholm LM, Gál Z, Lin L, Quevedo O, Ahmad DA, Dulina E, Luo Y, Bartek J, Larsen DH 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 d...
Source: Cell Research - Category: Cytology Authors: Tags: Nucleic Acids Res Source Type: research