EXO1 protects BRCA1-deficient cells against toxic DNA lesions.

Inactivating mutations in the BRCA1 and BRCA2 genes impair DNA double-strand break (DSB) repair by homologous recombination (HR), leading to chromosomal instability and cancer. Importantly, BRCA1/2 deficiency also causes therapeutically targetable vulnerabilities. Here, we identify the dependency on the end resection factor EXO1 as a key vulnerability of BRCA1-deficient cells. EXO1 deficiency generates poly(ADP-ribose)-decorated DNA lesions during S phase that associate with unresolved DSBs and genomic instability in BRCA1-deficient but not in wild-type or BRCA2-deficient cells. Our data indicate that BRCA1/EXO1 double-deficient cells accumulate DSBs due to impaired repair by single-strand annealing (SSA) on top of their HR defect. In contrast, BRCA2-deficient cells retain SSA activity in the absence of EXO1 and hence tolerate EXO1 loss. Consistent with a dependency on EXO1-mediated SSA, we find that BRCA1-mutated tumors show elevated EXO1 expression and increased SSA-associated genomic scars compared with BRCA1-proficient tumors. Overall, our findings uncover EXO1 as a promising therapeutic target for BRCA1-deficient tumors.

Impact of post-stroke aphasia on functional communication, quality of life, perception of health and depression: A case-control study.

BACKGROUND AND PURPOSE: Post-stroke aphasia is associated with a reduced quality of life (QoL) and higher risk of depression. Few studies have addressed the effect of coping with aphasia. Our aim is to evaluate the impact of post-stroke aphasia on self-reported QoL and symptoms of depression. METHODS: This was a cross-sectional prospective case-control study. Cases involved patients with post-stroke aphasia included in the DULCINEA trial (NCT04289493). Healthy controls were recruited using snowball sampling. All subjects completed the following questionnaires: General Health Questionnaire (GHQ-12), Stroke Aphasia Quality of Life Scale (SAQOL-39), Communicative Activity Log (CAL) and Stroke Aphasic Depression Questionnaire (SADQ-10). RESULTS: Twenty-three patients (eight women; mean age 62.9 years) and 73 controls (42 women; mean age 53.7 years) were included. Cases scored lower than controls in perception of health (GHQ-12: median 3 [IQR 1; 6] vs. 0 [IQR 0; 2]) and perception of QoL (SAQOL-39: median 3.6 [IQR 3.3; 40] vs. 4.6 [IQR 4.2; 4.8]). Functional communication (CAL: median 135 [IQR 122; 148] vs. 94 [IQR 74; 103]) and SAQOL-39 communication subscale (median 2.7 [IQR 2.1; 3.2] vs. 4.8 [IQR 4.6; 5.0]) were also significantly lower in the case group. Notably, cases reported fewer depressive symptoms than controls (SADQ-10: median 11 [IQR 9; 15] vs. 13 [IQR 11; 16]; p = 0.016). A mediational analysis revealed that the relationship between post-stroke aphasia and depression was not mediated by functional communication. CONCLUSIONS: Although communication difficulties impact the QoL of patients with post-stroke aphasia, such patients report fewer depressive symptoms on the SADQ-10 scale than healthy people, with no differences in scores related to social participation.

DUbbing Language-therapy CINEma-based in Aphasia post-Stroke (DULCINEA): study protocol for a randomized crossover pilot trial.

BACKGROUND: Communication is one of the most important predictors of social reintegration after stroke. Approximately 15-42% of stroke survivors experience post-stroke aphasia. Helping people recover from aphasia is one of the research priorities after a stroke. Our aim is to develop and validate a new therapy integrating dubbing techniques to improve functional communication. METHODS: The research project is structured as three work packages (WP). WP1: development of the dubbed language cinema-based therapy: Two research assistants (a speech therapist and a dubbing actor) will select the clips, mute specific words/sentences in progressive speech difficulty, and guide patients to dub them across sessions. Words to be dubbed will be those considered to be functionally meaningful by a representative sample of aphasic patients and relatives through an online survey. WP2: a randomized, crossover, interventional pilot study with the inclusion of 54 patients with post-stroke non-fluent aphasia. Patients will be treated individually in 40-min sessions twice per week for 8 weeks. Primary outcomes will be significant pre/post differences in scores in the Communicative Activity Log (CAL) questionnaire and Boston Diagnostic Aphasia Examination (BDAE) administered by a psychologist blinded to the patients' clinical characteristics. SECONDARY OUTCOMES: General Health Questionnaire (GHQ)-12, Stroke Aphasia Quality of Life Scale (SAQOL-39), Western Aphasia Battery Revised (WAB-R), and the Stroke Aphasic Depression Questionnaire (SADQ10). WP3: educational activities and dissemination of results. WP3 includes educational activities to improve public knowledge of aphasia and dissemination of the results, with the participation of the Spanish patients' association Afasia Activa. DISCUSSION: This pilot clinical trial will explore the efficacy of a new therapeutic tool based on dubbing techniques and computer technology to improve functional communication of patients suffering from post-stroke aphasia with the use of standardized test assessment. TRIAL REGISTRATION: ClinicalTrials.gov NCT04289493 . Registered on 28 February 2020.

Harmful R-loops are prevented via different cell cycle-specific mechanisms.

Identifying how R-loops are generated is crucial to know how transcription compromises genome integrity. We show by genome-wide analysis of conditional yeast mutants that the THO transcription complex, prevents R-loop formation in G1 and S-phase, whereas the Sen1 DNA-RNA helicase prevents them only in S-phase. Interestingly, damage accumulates asymmetrically downstream of the replication fork in sen1 cells but symmetrically in the hpr1 THO mutant. Our results indicate that: R-loops form co-transcriptionally independently of DNA replication; that THO is a general and cell-cycle independent safeguard against R-loops, and that Sen1, in contrast to previously believed, is an S-phase-specific R-loop resolvase. These conclusions have important implications for the mechanism of R-loop formation and the role of other factors reported to affect on R-loop homeostasis.

ELOF1 is a transcription-coupled DNA repair factor that directs RNA polymerase II ubiquitylation.

Cells employ transcription-coupled repair (TCR) to eliminate transcription-blocking DNA lesions. DNA damage-induced binding of the TCR-specific repair factor CSB to RNA polymerase II (RNAPII) triggers RNAPII ubiquitylation of a single lysine (K1268) by the CRL4CSA ubiquitin ligase. How CRL4CSA is specifically directed towards K1268 is unknown. Here, we identify ELOF1 as the missing link that facilitates RNAPII ubiquitylation, a key signal for the assembly of downstream repair factors. This function requires its constitutive interaction with RNAPII close to K1268, revealing ELOF1 as a specificity factor that binds and positions CRL4CSA for optimal RNAPII ubiquitylation. Drug-genetic interaction screening also revealed a CSB-independent pathway in which ELOF1 prevents R-loops in active genes and protects cells against DNA replication stress. Our study offers key insights into the molecular mechanisms of TCR and provides a genetic framework of the interplay between transcriptional stress responses and DNA replication.

Untangling the crosstalk between BRCA1 and R-loops during DNA repair.

R-loops are RNA:DNA hybrids assembled during biological processes but are also linked to genetic instability when formed out of their natural context. Emerging evidence suggests that the repair of DNA double-strand breaks requires the formation of a transient R-loop, which eventually must be removed to guarantee a correct repair process. The multifaceted BRCA1 protein has been shown to be recruited at this specific break-induced R-loop, and it facilitates mechanisms in order to regulate R-loop removal. In this review, we discuss the different potential roles of BRCA1 in R-loop homeostasis during DNA repair and how these processes ensure faithful DSB repair.

Harmful DNA:RNA hybrids are formed in cis and in a Rad51-independent manner.

DNA:RNA hybrids constitute a well-known source of recombinogenic DNA damage. The current literature is in agreement with DNA:RNA hybrids being produced co-transcriptionally by the invasion of the nascent RNA molecule produced in cis with its DNA template. However, it has also been suggested that recombinogenic DNA:RNA hybrids could be facilitated by the invasion of RNA molecules produced in trans in a Rad51-mediated reaction. Here, we tested the possibility that such DNA:RNA hybrids constitute a source of recombinogenic DNA damage taking advantage of Rad51-independent single-strand annealing (SSA) assays in the yeast Saccharomyces cerevisiae. For this, we used new constructs designed to induce expression of mRNA transcripts in trans with respect to the SSA system. We show that unscheduled and recombinogenic DNA:RNA hybrids that trigger the SSA event are formed in cis during transcription and in a Rad51-independent manner. We found no evidence that such hybrids form in trans and in a Rad51-dependent manner.

Histone H3E73Q and H4E53A mutations cause recombinogenic DNA damage.

The stability and function of eukaryotic genomes is closely linked to histones and to chromatin structure. The state of the chromatin not only affects the probability of DNA to undergo damage but also DNA repair. DNA damage can result in genetic alterations and subsequent development of cancer and other genetic diseases. Here, we identified two mutations in conserved residues of histone H3 and histone H4 (H3E73Q and H4E53A) that increase recombinogenic DNA damage. Our results suggest that the accumulation of DNA damage in these histone mutants is largely independent on transcription and might arise as a consequence of problems occurring during DNA replication. This study uncovers the relevance of H3E73 and H4E53 residues in the protection of genome integrity.

The Antitumor Drugs Trabectedin and Lurbinectedin Induce Transcription-Dependent Replication Stress and Genome Instability.

R-loops are a major source of replication stress, DNA damage, and genome instability, which are major hallmarks of cancer cells. Accordingly, growing evidence suggests that R-loops may also be related to cancer. Here we show that R-loops play an important role in the cellular response to trabectedin (ET743), an anticancer drug from marine origin and its derivative lurbinectedin (PM01183). Trabectedin and lurbinectedin induced RNA-DNA hybrid-dependent DNA damage in HeLa cells, causing replication impairment and genome instability. We also show that high levels of R-loops increase cell sensitivity to trabectedin. In addition, trabectedin led to transcription-dependent FANCD2 foci accumulation, which was suppressed by RNase H1 overexpression. In yeast, trabectedin and lurbinectedin increased the presence of Rad52 foci, a marker of DNA damage, in an R-loop-dependent manner. In addition to providing new insights into the mechanisms of action of these drugs, our study reveals that R-loops could be targeted by anticancer agents. Given the increasing evidence that R-loops occur all over the genome, the ability of lurbinectedin and trabectedin to act on them may contribute to enhance their efficacy, opening the possibility that R-loops might be a feature shared by specific cancers. IMPLICATIONS: The data presented in this study provide the new concept that R-loops are important cellular factors that contribute to trabectedin and lurbinectedin anticancer activity.