Splicing regulation of DNA repair via CCAR1.

In this issue of Molecular Cell, Harada et al.1 and Karasu et al.2 identify CCAR1 as a novel regulator of the Fanconi anemia/BRCA DNA repair pathway via modulating the splicing of the mRNA encoding FANCA.

CCAR1 promotes DNA repair via alternative splicing.

DNA repair is directly performed by hundreds of core factors and indirectly regulated by thousands of others. We massively expanded a CRISPR inhibition and Cas9-editing screening system to discover factors indirectly modulating homology-directed repair (HDR) in the context of ∼18,000 individual gene knockdowns. We focused on CCAR1, a poorly understood gene that we found the depletion of reduced both HDR and interstrand crosslink repair, phenocopying the loss of the Fanconi anemia pathway. CCAR1 loss abrogated FANCA protein without substantial reduction in the level of its mRNA or that of other FA genes. We instead found that CCAR1 prevents inclusion of a poison exon in FANCA. Transcriptomic analysis revealed that the CCAR1 splicing modulatory activity is not limited to FANCA, and it instead regulates widespread changes in alternative splicing that would damage coding sequences in mouse and human cells. CCAR1 therefore has an unanticipated function as a splicing fidelity factor.

The splicing factor CCAR1 regulates the Fanconi anemia/BRCA pathway.

The twenty-three Fanconi anemia (FA) proteins cooperate in the FA/BRCA pathway to repair DNA interstrand cross-links (ICLs). The cell division cycle and apoptosis regulator 1 (CCAR1) protein is also a regulator of ICL repair, though its possible function in the FA/BRCA pathway remains unknown. Here, we demonstrate that CCAR1 plays a unique upstream role in the FA/BRCA pathway and is required for FANCA protein expression in human cells. Interestingly, CCAR1 co-immunoprecipitates with FANCA pre-mRNA and is required for FANCA mRNA processing. Loss of CCAR1 results in retention of a poison exon in the FANCA transcript, thereby leading to reduced FANCA protein expression. A unique domain of CCAR1, the EF hand domain, is required for interaction with the U2AF heterodimer of the spliceosome and for excision of the poison exon. Taken together, CCAR1 is a splicing modulator required for normal splicing of the FANCA mRNA and other mRNAs involved in various cellular pathways.

Biallelic FANCA variants detected in sisters with isolated premature ovarian insufficiency.

Premature ovarian insufficiency is a common form of female infertility affecting up to 4% of women and characterised by amenorrhea with elevated gonadotropin before the age of 40. Oocytes require controlled DNA breakage and repair for homologous recombination and the maintenance of oocyte integrity. Biallelic disruption of the DNA damage repair gene, Fanconi anemia complementation group A (FANCA), is a common cause of Fanconi anaemia, a syndrome characterised by bone marrow failure, cancer predisposition, physical anomalies and POI. There is ongoing dispute about the role of heterozygous FANCA variants in POI pathogenesis, with insufficient evidence supporting causation. Here, we have identified biallelic FANCA variants in French sisters presenting with POI, including a novel missense variant of uncertain significance and a likely pathogenic deletion that initially evaded detection. Functional studies indicated no discernible effect on DNA damage sensitivity in patient lymphoblasts. These novel FANCA variants add evidence that heterozygous loss of one allele is insufficient to cause DNA damage sensitivity and POI. We propose that intragenic deletions, that are relatively common in FANCA, may be missed without careful analysis, and could explain the presumed causation of heterozygous variants. Accurate variant curation is critical to optimise patient care and outcomes.

Reversion from basal histone H4 hypoacetylation at the replication fork increases DNA damage in FANCA deficient cells.

The FA/BRCA pathway safeguards DNA replication by repairing interstrand crosslinks (ICL) and maintaining replication fork stability. Chromatin structure, which is in part regulated by histones posttranslational modifications (PTMs), has a role in maintaining genomic integrity through stabilization of the DNA replication fork and promotion of DNA repair. An appropriate balance of PTMs, especially acetylation of histones H4 in nascent chromatin, is required to preserve a stable DNA replication fork. To evaluate the acetylation status of histone H4 at the replication fork of FANCA deficient cells, we compared histone acetylation status at the DNA replication fork of isogenic FANCA deficient and FANCA proficient cell lines by using accelerated native immunoprecipitation of nascent DNA (aniPOND) and in situ protein interactions in the replication fork (SIRF) assays. We found basal hypoacetylation of multiple residues of histone H4 in FA replication forks, together with increased levels of Histone Deacetylase 1 (HDAC1). Interestingly, high-dose short-term treatment with mitomycin C (MMC) had no effect over H4 acetylation abundance at the replication fork. However, chemical inhibition of histone deacetylases (HDAC) with Suberoylanilide hydroxamic acid (SAHA) induced acetylation of the FANCA deficient DNA replication forks to levels comparable to their isogenic control counterparts. This forced permanence of acetylation impacted FA cells homeostasis by inducing DNA damage and promoting G2 cell cycle arrest. Altogether, this caused reduced RAD51 foci formation and increased markers of replication stress, including phospho-RPA-S33. Hypoacetylation of the FANCA deficient replication fork, is part of the cellular phenotype, the perturbation of this feature by agents that prevent deacetylation, such as SAHA, have a deleterious effect over the delicate equilibrium they have reached to perdure despite a defective FA/BRCA pathway.

FANCA facilitates G1/S cell cycle advancement, proliferation, migration and invasion in gastric cancer.

The present study explores the function of FANCA gene, a pivotal member of the Fanconi anaemia (FA) pathway crucial for preserving genomic stability and preventing cancer, particularly in the context of gastric cancer (GC). Using immunohistochemistry, quantitative real-time PCR, and western blot analysis, we evaluate FANCA mRNA and protein expressions in GC cell lines. The relationship between FANCA expression and clinicopathological characteristics is also explored. Various assays, including CCK8, colony formation, wound healing, and Transwell assays, are used to assess functional changes in cells associated with FANCA. Flow cytometry is utilized to evaluate alterations in the cell cycle resulted from FANCA knockdown and overexpression. Our findings show elevated FANCA expression in GC cell lines, with levels correlated with pathologic stage and lymphatic metastasis. FANCA knockdown impedes cell proliferation, migration, and invasion and induces G1/S phase cell cycle arrest. Conversely, FANCA overexpression stimulates cell proliferation, migration, and invasion. In vivo xenograft experiments confirm the promotional role of FANCA in GC tumor progression. Moreover, FANCA overexpression is associated with the activation of cell cycle. Collectively, our results suggest that FANCA drives malignant cell behaviors in GC through the cell cycle pathway, highlighting its potential as a therapeutic target for the treatment of GC.

Fanconi Anemia Complementary Group A (FANCA) Facilitates the Occurrence and Progression of Liver Hepatocellular Carcinoma.

BACKGROUND: Liver hepatocellular carcinoma (LIHC) is a serious liver disease worldwide, and its pathogenesis is complicated. AIMS: This study investigated the potential role of FANCA in the advancement and prognosis of LIHC. METHODS: Public databases, quantitative reverse transcription polymerase chain reaction (qRT-PCR), western blot (WB) and immunohistochemistry (IHC) were employed to measure FANCA expression between tumor and normal samples. The relationship between FANCA expression and prognosis of LIHC patients were examined. Functional enrichment of FANCA-related genes was performed. Furthermore, univariate and multivariate analyses were conducted to determine the independent prognosis value of FANCA in LIHC. Finally, influence of FANCA knockout on the proliferation, migration, and invasion of HepG2 cell was validated with cloning formation, CCK8, and Transwell assays. RESULTS: Expression analysis presented that FANCA had high expression level in LIHC tissues and cells. Receiver operating characteristic (ROC) curve analysis showed that FANCA was of great diagnosis value in LIHC. Clinicopathological analysis revealed that FANCA was significantly greater expressed in the advanced stage than in the early stage of LIHC. Univariate, multivariate, and Kaplan-Meier survival analysis confirmed that high expression of FANCA was strongly associated with poor survival of LIHC patients. In addition, high level of FANCA in LIHC showed a negative association with immunoinfiltrated B cells, T cells, and stromal scores. Moreover, Knockout of FANCA significantly inhibited HepG2 cell proliferative activity, migration, and invasion ability. CONCLUSIONS: Our data revealed that high level of FANCA was closely associated with LIHC malignant progression, suggesting its potential utility as a diagnostic, predictive indicator, and therapeutic target.

FANCA c.3624C>T (p.Ser1208=) is a hypomorphic splice variant associated with delayed onset of Fanconi anemia.

ABSTRACT: Fanconi anemia (FA) is a hereditary, DNA repair deficiency disorder caused by pathogenic variants in any 1 of 22 known genes (FANCA-FANCW). Variants in FANCA account for nearly two-thirds of all patients with FA. Clinical presentation of FA can be heterogeneous and include congenital abnormalities, progressive bone marrow failure, and predisposition to cancer. Here, we describe a relatively mild disease manifestation among 6 individuals diagnosed with FA, each compound heterozygous for 1 established pathogenic FANCA variant and 1 FANCA exon 36 variant, c.3624C>T. These individuals had delayed onset of hematological abnormalities, increased survival, reduced incidence of cancer, and improved fertility. Although predicted to encode a synonymous change (p.Ser1208=), the c.3624C>T variant causes a splicing error resulting in a FANCA transcript missing the last 4 base pairs of exon 36. Deep sequencing and quantitative reverse transcription polymerase chain reaction analysis revealed that 6% to 10% of the FANCA transcripts included the canonical splice product, which generated wild-type FANCA protein. Consistently, functional analysis of cell lines from the studied individuals revealed presence of residual FANCD2 ubiquitination and FANCD2 foci formation, better cell survival, and decreased late S/G2 accumulation in response to DNA interstrand cross-linking agent, indicating presence of residual activity of the FA repair pathway. Thus, the c.3624C>T variant is a hypomorphic allele, which contributes to delayed manifestation of FA disease phenotypes in individuals with at least 1 c.3624C>T allele.

A Fanca knockout mouse model reveals novel Fancd2 function.

Fanconi anemia (FA) is a genetically and clinically heterogenous inherited disorder. Clinically, Fanca subtype patients exhibited milder phenotypes compared to Fancd2 subtypes. Increasing evidence suggests that Fancd2 perform independent functions, but the detailed mechanisms are not well characterized. In this study, we developed a Fanca KO mice model in C57BL/6 background with ATG region deletion, then performed a detailed FA phenotypes characterization and analysis with Fanca KO mice and Fancd2 KO mice in the same congenic background. We found that both the Fanca KO and Fancd2 KO cause severe FA phenotypes in mice. However, Fanca KO mice exhibited milder FA phenotypes comparing to Fancd2 KO mice. Fanca KO mice showed higher embryonic and postnatal survival rate, less congenital eye defects in early development. At adult stage, Fanca KO mice showed increased HSC number and reconstitution function. Furthermore, we did RNA-seq study and identified differential expression of Dlk1 and Dlk1 pathway genes in Fanca KO and Fancd2 KO embryonic cells and adult HSCs. Finally, we revealed that Fancd2 was expressed and physically interact with Dlk1 in Fanca KO cells. Collectively, our findings suggested that Fancd2 has distinct functions in the absence of Fanca.

Prevalencia de intento de suicidio adolescente y factores de riesgo asociados en una comuna rural de la provincia de Concepción / Suicide attempts among Chilean adolescents

Background: Suicide mortality rates are increasing among teenagers. Aim: To study the prevalence and predictive factors of suicide attempts among Chilean adolescents. Material and Methods: A random sample of 195 teenagers aged 16 ± 1 years (53% males) answered an anonymous survey about their demographic features, substance abuse, the Osaka suicidal ideation questionnaire, Smilksten familial Apgar. Beck hopelessness scale, Beck depression scale and Coppersmith self-esteem inventory. Results: Twenty five percent of respondents had attempted suicide at least in one occasion during their lives. These attempts were significantly associated with female gender, absent parents, family dysfunction, drug abuse, smoking, low self-esteem, hopelessness, depression and recent suicidal ideation. A logistic regression analysis accepted female gender, smoking and recent suicidal ideation as significant independent predictors of suicide attempt. Conclusions: Suicide attempted is common among teenagers and its predictors are female sex, smoking and previous suicidal ideation.

A Case Report of Fanconi Anemia Diagnosed by Genetic Testing Followed by Prenatal Diagnosis

Fanconi anemia (FA) is a rare genetic disorder affecting multiple body systems. Genetic testing, including prenatal testing, is a prerequisite for the diagnosis of many clinical conditions. However, genetic testing is complicated for FA because there are often many genes that are associated with its development, and large deletions, duplications, or sequence variations are frequently found in some of these genes. This study describes successful genetic testing for molecular diagnosis, and subsequent prenatal diagnosis, of FA in a patient and his family in Korea. We analyzed all exons and flanking regions of the FANCA, FANCC, and FANCG genes for mutation identification and subsequent prenatal diagnosis. Multiplex ligation-dependent probe amplification analysis was performed to detect large deletions or duplications in the FANCA gene. Molecular analysis revealed two mutations in the FANCA gene: a frameshift mutation c.2546delC and a novel splice-site mutation c.3627-1G>A. The FANCA mutations were separately inherited from each parent, c.2546delC was derived from the father, whereas c.3627-1G>A originated from the mother. The amniotic fluid cells were c.3627-1G>A heterozygotes, suggesting that the fetus was unaffected. This is the first report of genetic testing that was successfully applied to molecular diagnosis of a patient and subsequent prenatal diagnosis of FA in a family in Korea.