Agata Smogorzewska

The essential kinase ataxia telangiectasia and Rad3-related (ATR) monitors the replicative (S) phase of the cell cycle to ensure faithful propagation of genetic material. While much is known about the mechanisms governing ATR activity at replication forks, how its effector checkpoint kinase 1 (CHK1) is regulated to create a localized hub of CHK1 activity at sites of replication remains poorly understood. Here, we report that replication termination factor 2 (RTF2), an essential replisome-associated protein, is necessary for maintaining CHK1 signaling at replication forks. RTF2 interacts with CHK1 and functions alongside the core replicative helicase complex-interacting protein CLASPIN to tether CHK1 to sites of DNA replication, controlling replication rates and preventing premature mitotic entry. These findings uncover how RTF2 and CLASPIN poise CHK1 at replication forks to facilitate its activation by ATR, creating fork-localized CHK1 activity that fuels unperturbed S-phase progression and promotes genome stability by maintaining the intrinsic S-G ₂ checkpoint.

Head and neck squamous cell carcinoma (HNSCC) evolves through stepwise clonal expansion within genetically altered mucosa fields, yet actionable biomarkers remain undefined. Leveraging Fanconi anemia (FA), a cancer predisposition syndrome with extreme HNSCC risk due to defective DNA interstrand crosslink repair, we profiled premalignant changes in the oral cavity using noninvasive brush biopsies. Consistent with our prior demonstration of genomic instability in FA-associated SCCs, we detected pathogenic TP53 variants in 26% and copy number alterations in 60.5% in clinically normal-appearing oral mucosa of individuals with FA. These subclinical clonal expansions define candidate biomarkers of early clonal evolution amenable to serial sampling for risk stratification and prevention studies. Since FA-associated SCCs share genomic features with sporadic HNSCC, these findings may extend to the broader population. We also identify somatic reversion of a pathogenic FANCB variant, providing evidence of genomic self-correction and suggesting a potential avenue for gene-based cancer prevention in FA. Statement of significance: Oral mucosa of individuals with Fanconi anemia contains frequent abnormal clones creating a premalignant field that increases cancer risk. The noninvasive brush sampling approach allows repeated measurements, ongoing surveillance, and assessment of prophylactic strategies that may be useful in the prevention of cancers in people with FA and in the general population. Somatic reversion of a pathogenic FANC variant may protect the oral mucosa from DNA repair deficiency and premalignant clonal evolution.

Fanconi anemia (FA) is an inherited disorder classically characterized by childhood-onset bone marrow dysfunction and lifelong cancer predisposition. FA is caused by pathogenic variants in any one of 23 genes identified so far. Of these, FANCA is the most frequently mutated and accounts for disease in two-thirds of all patients with FA. The spectrum of FANCA pathogenic variants (mutations) is broad, and genotype-phenotype correlation is often unclear. Here we describe the natural history of cytopenias associated with FANCA pathogenic variants in 139 individuals diagnosed in 1995 or later. We followed blood cell counts over time and correlated these with the classification of patient mutation subtypes. Most participants experienced age-related declines in hematologic parameters beginning in early childhood. Platelets underwent the earliest decline, reaching platelet count below 50K/μl at a median age of 8.2 years. The erythrocyte lineage was the most stable with hemoglobin below 8 g/dl identified at a median age of 10.7 years. Androgen therapy delayed the blood count decline. The presence of at least one predicted hypomorphic pathogenic variant in the FANCA gene significantly slowed the progression of the hematologic abnormalities. This study sheds light on the importance of mutation type in predicting the severity of hematological manifestations in FA. Furthermore, it serves as a historical comparative cohort for emerging therapies aimed at altering hematological disease progression in FANCA- deficient FA patients. Key Points: Thrombocytopenia and neutropenia are the earliest and most reliable indicators of hematologic decline in FANCA- deficient patients Presence of two FANCA variants with predicted complete loss of function leads to earlier onset and faster progression of disease

Fanconi anemia (FA) confers a high risk (~700-fold increase) of solid tumor formation, most often head and neck squamous cell carcinoma (HNSCC). FA germline DNA repair defects preclude administration of most chemotherapies, and prior hematopoietic stem cell transplantation limits the use of immunotherapy. Thus, surgery and judicious delivery of radiation offer the only treatment options, with most patients dying from their cancers. A paucity of preclinical models has limited the development of new treatments. Here, we report what to our knowledge are the first patient-derived xenografts (PDXs) of FA-associated HNSCC (FA-HNSCC) and highlight the efficacy of FDA-approved EGFR-targeted therapies in tumors with high EGFR and phosphorylated EGFR levels and the activity of the FDA-approved B-cell lymphoma 2 (Bcl-2) inhibitor venetoclax in a FA-HNSCC PDX overexpressing Bcl-2. These findings support the development of precision medicine approaches for FA-HNSCC.

The Fanconi anemia (FA) pathway is vital for the repair of DNA interstrand crosslinks (ICLs), which are caused by a variety of endogenous and exogenous genotoxins including reactive aldehydes. Patients with pathogenic variants in the FA pathway are predisposed to early-onset, aggressive malignancies, especially leukemia and head and neck, esophageal, and anogenital squamous cell carcinomas (SCCs). Prior studies have linked endogenous formaldehyde and acetaldehyde in hematopoietic stem cells with bone marrow failure and leukemia in FA-deficient mice. However, the genotoxic aldehydes specific to mucosal keratinocytes, precursors of FA-associated SCCs, remain to be identified. Here, to identify alcohol dehydrogenases (ADHs) and aldehyde dehydrogenases (ALDHs) necessary for protection of keratinocyte genomes from endogenous metabolites, we used a sensitized background of FA-pathway deficiency. We systematically inactivated all highly expressed ADH and ALDHs genes in FANCA -deficient keratinocyte cell lines and identified genes required for their survival. We report that loss of ADH5 or ALDH3-family enzymes in FA pathway-deficient cells has a synthetic lethal effect and induces DNA damage markers, nominating these genes as important defense mechanisms in the detoxification of endogenous aldehydes and prevention of carcinogenesis in keratinocytes. Loss of ADH5 increases formaldehyde levels, while simultaneous loss of four functionally redundant ALDH3 isozymes is predicted to cause accumulation of lipid aldehydes. FA-deficient keratinocytes are more sensitive to treatment with formaldehyde and the lipid aldehyde 4-hydroxynonenal (4HNE) compared to FA-competent cells. In addition, the thiol-rich antioxidant N-acetyl-L-cysteine (NAC) partially rescued the growth of FANCA ^−/− ADH5 ^−/− cells and lowered the level of endogenous DNA damage. This work identifies important defense mechanisms in keratinocytes and suggests cancer preventive strategies in patients with Fanconi anemia. Significance: This work shows that ADH5 and ALDH3-family enzymes function as tier 1 defense mechanisms against endogenous DNA-damaging metabolites in keratinocytes. Enhanced detoxification of endogenous aldehydes might prevent DNA damage and mutagenesis, which drive Fanconi anemia-associated head and neck and other mucosal squamous cell carcinomas.

Summary: Protein-protein interactions (PPIs) drive virtually all biological processes, yet most PPIs have not been identified and even more remain structurally unresolved. We developed a two-step computational screen for human PPIs. First, a classifier called KIRC (Knowledge-Informed Rapid Classifier), trained on biological features, was used to rank all 200 million possible protein pairs in the human proteome by their interaction likelihood. Second, the ∼1.6 million top-ranked KIRC pairs were subjected to structure prediction by AlphaFold-Multimer and ranked using SPOC (Structure Prediction and Omics Classifier), which identifies functional predictions based on biological and structural features. This pipeline revealed 16,000 high-confidence PPIs (∼90% precision), of which more than 5,000 were not previously recognized and more than 12,000 have not been structurally resolved. We use this “predictome” to formulate new hypotheses in different areas of biology, reinterpret low-resolution cryo-EM maps, and identify and validate novel PPIs that may support replication-coupled chromatin assembly. The predicted PPIs, viewable at predictomes.org , are expected to accelerate characterization of the molecular interactions that underlie vertebrate cell physiology.

Biallelic pathogenic variants in the essential DNA repair gene BRCA2 cause Fanconi anemia complementation group D1. Patients in this group are highly prone to develop embryonal tumors, most commonly medulloblastoma arising from the cerebellar granule cell progenitors (GCPs). GCPs undergo high proliferation in the postnatal cerebellum under Sonic Hedgehog (SHH) activation, but the type of DNA lesions that require the function of the BRCA2 to prevent tumorigenesis remains unknown. To identify such lesions, we assessed both GCP neurodevelopment and tumor formation using a mouse model with deletion of exons three and four of Brca2 in the central nervous system, coupled with global Trp53 loss. Brca2 ^Δex3-4 ;Trp53 ^−/− animals developed SHH subgroup medulloblastomas with complete penetrance. Whole-genome sequencing of the tumors identified structural variants with breakpoints enriched in areas overlapping putative G-quadruplexes (G4s). Brca2 -deficient GCPs exhibited decreased replication speed in the presence of the G4-stabilizer pyridostatin. Pif1 helicase, which resolves G4s during replication, was highly upregulated in tumors, and Pif1 knockout in primary medulloblastoma tumor cells resulted in increased genome instability upon pyridostatin treatment. These data suggest that G4s may represent sites prone to replication stalling in highly proliferative GCPs and without BRCA2, G4s become a source of genome instability. Tumor cells upregulate G4-resolving helicases to facilitate rapid proliferation through G4s highlighting PIF1 helicase as a potential therapeutic target for treatment of BRCA2-deficient medulloblastomas.

The Fanconi anemia (FA) DNA repair pathway is required for the repair of DNA interstrand cross-links (ICLs). ICLs are caused by genotoxins, such as chemotherapeutic agents or reactive aldehydes. Inappropriately repaired ICLs contribute to hematopoietic stem cell (HSC) failure and tumorigenesis. While endogenous acetaldehyde and formaldehyde are known to induce HSC failure and leukemia in FA patients, the effects of other toxic metabolites on FA pathogenesis have not been systematically investigated. Using a metabolism-focused CRISPR screen, we found a synthetically lethal interaction between ALDH9A1 and the deficiency of the FA pathway. Combined deficiency of ALDH9A1 and FANCD2 causes genomic instability, apoptosis, and decreased hematopoietic colony formation. Fanca−/−Aldh9a1−/− mice exhibited an increased incidence of ovarian tumors. A suppressor CRISPR screen revealed that the loss of ATP13A3, a polyamine transporter, resulted in improved survival of FANCD2−/−ALDH9A1−/− cells. These findings nominate high intracellular polyamines and the resulting 3-aminopropanal and acrolein as sources of endogenous DNA damage in patients with FA.

Fanconi anemia (FA) is a rare genetic disease characterized by loss-of-function variants in any of the 22 previously identified genes ( FANCA – FANCW ) that encode proteins participating in the repair of DNA interstrand crosslinks (ICLs). Patient phenotypes are variable but may include developmental abnormalities, early-onset pancytopenia, and a predisposition to hematologic and solid tumors. Here, we describe 2 unrelated families with multiple pregnancy losses and offspring presenting with severe developmental and hematologic abnormalities leading to death in utero or in early life. Homozygous loss-of-function variants in FAAP100 were identified in affected children of both families. The FAAP100 protein associates with FANCB and FANCL, the E3 ubiquitin ligase responsible for the monoubiquitination of FANCD2 and FANCI, which is necessary for FA pathway function. Patient-derived cells exhibited phenotypes consistent with FA. Expression of the WT FAAP100 cDNA, but not the patient-derived variants, rescued the observed cellular phenotypes. This establishes FAAP100 deficiency as a cause of FA, with FAAP100 gaining an alias as FANCX. The extensive developmental malformations of individuals with FAAP100 loss-of-function variants are among the most severe across previously described FA phenotypes, indicating that the FA pathway is essential for human development.

Biallelic pathogenic variants in the essential DNA repair gene BRCA2 causes Fanconi anemia, complementation group FA-D1. Patients in this group are highly prone to develop embryonal tumors, most commonly medulloblastoma arising from the cerebellar granule cell progenitors (GCPs). GCPs undergo high proliferation in the postnatal cerebellum under SHH activation, but the type of DNA lesions that require the function of the BRCA2 to prevent tumorigenesis remains unknown. To identify such lesions, we assessed both GCP neurodevelopment and tumor formation using a mouse model with deletion of exons three and four of Brca2 in the central nervous system, coupled with global Trp53 loss. Brca2 ^Δex3-4 ;Trp53 ^-/- animals developed SHH subgroup medulloblastomas with complete penetrance. Whole-genome sequencing of the tumors identified structural variants with breakpoints enriched in areas overlapping G-quadruplexes (G4s). Brca2 -deficient GCPs exhibited decreased replication speed in the presence of the G4-stabilizer pyridostatin. Pif1 helicase, which resolves G4s during replication, was highly upregulated in tumors, and Pif1 knockout in primary MB tumor cells resulted in increased genome instability upon pyridostatin treatment. These data suggest that G4s may represent sites prone to replication stalling in highly proliferative GCPs and without BRCA2, G4s become a source of genome instability. Tumor cells upregulate G4-resolving helicases to facilitate rapid proliferation through G4s highlighting PIF1 helicase as a potential therapeutic target for treatment of BRCA2 -deficient medulloblastomas.