Alcohol-derived DNA crosslinks are repaired by two distinct mechanisms.

Acetaldehyde is a highly reactive, DNA-damaging metabolite that is produced upon alcohol consumption1. Impaired detoxification of acetaldehyde is common in the Asian population, and is associated with alcohol-related cancers1,2. Cells are protected against acetaldehyde-induced damage by DNA crosslink repair, which when impaired causes Fanconi anaemia (FA), a disease resulting in failure to produce blood cells and a predisposition to cancer3,4. The combined inactivation of acetaldehyde detoxification and the FA pathway induces mutation, accelerates malignancies and causes the rapid attrition of blood stem cells5-7. However, the nature of the DNA damage induced by acetaldehyde and how this is repaired remains a key question. Here we generate acetaldehyde-induced DNA interstrand crosslinks and determine their repair mechanism in Xenopus egg extracts. We find that two replication-coupled pathways repair these lesions. The first is the FA pathway, which operates using excision-analogous to the mechanism used to repair the interstrand crosslinks caused by the chemotherapeutic agent cisplatin. However, the repair of acetaldehyde-induced crosslinks results in increased mutation frequency and an altered mutational spectrum compared with the repair of cisplatin-induced crosslinks. The second repair mechanism requires replication fork convergence, but does not involve DNA incisions-instead the acetaldehyde crosslink itself is broken. The Y-family DNA polymerase REV1 completes repair of the crosslink, culminating in a distinct mutational spectrum. These results define the repair pathways of DNA interstrand crosslinks caused by an endogenous and alcohol-derived metabolite, and identify an excision-independent mechanism.

Histone Methylation by SETD1A Protects Nascent DNA through the Nucleosome Chaperone Activity of FANCD2.

Components of the Fanconi anemia and homologous recombination pathways play a vital role in protecting newly replicated DNA from uncontrolled nucleolytic degradation, safeguarding genome stability. Here we report that histone methylation by the lysine methyltransferase SETD1A is crucial for protecting stalled replication forks from deleterious resection. Depletion of SETD1A sensitizes cells to replication stress and leads to uncontrolled DNA2-dependent resection of damaged replication forks. The ability of SETD1A to prevent degradation of these structures is mediated by its ability to catalyze methylation on Lys4 of histone H3 (H3K4) at replication forks, which enhances FANCD2-dependent histone chaperone activity. Suppressing H3K4 methylation or expression of a chaperone-defective FANCD2 mutant leads to loss of RAD51 nucleofilament stability and severe nucleolytic degradation of replication forks. Our work identifies epigenetic modification and histone mobility as critical regulatory mechanisms in maintaining genome stability by restraining nucleases from irreparably damaging stalled replication forks.

PP2A inhibitor SET promotes mTORC1 and Bmi1 signaling through Akt activation and maintains the colony-formation ability of cancer cells.

Protein phosphatase 2A (PP2A) is an essential tumor suppressor, with its activity often hindered in cancer cells by endogenous PP2A inhibitory proteins like SE translocation (SET). SET/PP2A axis plays a pivotal role in the colony-formation ability of cancer cells and the stabilization of c-Myc and E2F1 proteins implicated in this process. However, in osteosarcoma cell line HOS, SET knock-down (KD) suppresses the colony-formation ability without affecting c-Myc and E2F1. This study aimed to unravel the molecular mechanism through which SET enhances the colony-formation ability of HOS cells and determine if it is generalized to other cancer cells. Transcriptome analysis unveiled that SET KD suppressed mTORC1 signaling. SET KD inhibited Akt phosphorylation, an upstream kinase for mTORC1. PP2A inhibitor blocked SET KD-mediated decrease in phosphorylation of Akt and a mTORC1 substrate p70S6K. A constitutively active Akt restored decreased colony-formation ability by SET KD, indicating the SET/PP2A/Akt/mTORC1 axis. Additionally, enrichment analysis highlighted that Bmi-1, a polycomb group protein, is affected by SET KD. SET KD decreased Bmi-1 protein by Akt inhibition but not by mTORC1 inhibition, and exogenous Bmi-1 expression rescued the reduced colony formation by SET KD. Four out of eight cancer cell lines exhibited decreased Bmi-1 by SET KD. Further analysis of these cell lines revealed that Myc activity plays a role in SET KD-mediated Bmi-1 degradation. These findings provide new insights into the molecular mechanism of SET-regulated colony-formation ability, which involved Akt-mediated activation of mTORC1/p70S6K and Bmi-1 signaling.

The luciferase-based in vivo protein-protein interaction assay revealed that CHK1 promotes PP2A and PME-1 interaction.

Protein phosphatase 2A (PP2A) is an essential serine/threonine protein phosphatase, and its dysfunction is involved in the onset of cancer and neurodegenerative disorders. PP2A functions as a trimeric holoenzyme whose composition is regulated by the methyl-esterification (methylation) of the PP2A catalytic subunit (PP2Ac). Protein phosphatase methylesterase-1 (PME-1) is the sole PP2Ac methylesterase, and the higher PME-1 expression is observed in various cancer and neurodegenerative diseases. Apart from serving as a methylesterase, PME-1 acts as a PP2A inhibitory protein, binding directly to PP2Ac and suppressing its activity. The intricate function of PME-1 hinders drug development by targeting the PME-1/PP2Ac axis. This study applied the NanoBiT system, a bioluminescence-based protein interaction assay, to elucidate the molecular mechanism that modulates unknown PME-1/PP2Ac protein-protein interaction (PPI). Compound screening identified that the CHK1 inhibitors inhibited PME-1/PP2Ac association without affecting PP2Ac methylation levels. CHK1 directly phosphorylates PP2Ac to promote PME-1 association. Phospho-mass spectrometry identified multiple phospho-sites on PP2Ac, including the Thr219, that affect PME-1 interaction. An anti-phospho-Thr219 PP2Ac antibody was generated and showed that CHK1 regulates the phosphorylation levels of this site in cells. On the contrary, in vitro phosphatase assay showed that CHK1 is the substrate of PP2A, and PME-1 hindered PP2A-mediated dephosphorylation of CHK1. Our data provides novel insights into the molecular mechanisms governing the PME-1/PP2Ac PPI and the triad relationship between PP2A, PME-1, and CHK1.

RFWD3-Mediated Ubiquitination Promotes Timely Removal of Both RPA and RAD51 from DNA Damage Sites to Facilitate Homologous Recombination.

RFWD3 is a recently identified Fanconi anemia protein FANCW whose E3 ligase activity toward RPA is essential in homologous recombination (HR) repair. However, how RPA ubiquitination promotes HR remained unknown. Here, we identified RAD51, the central HR protein, as another target of RFWD3. We show that RFWD3 polyubiquitinates both RPA and RAD51 in vitro and in vivo. Phosphorylation by ATR and ATM kinases is required for this activity in vivo. RFWD3 inhibits persistent mitomycin C (MMC)-induced RAD51 and RPA foci by promoting VCP/p97-mediated protein dynamics and subsequent degradation. Furthermore, MMC-induced chromatin loading of MCM8 and RAD54 is defective in cells with inactivated RFWD3 or expressing a ubiquitination-deficient mutant RAD51. Collectively, our data reveal a mechanism that facilitates timely removal of RPA and RAD51 from DNA damage sites, which is crucial for progression to the late-phase HR and suppression of the FA phenotype.

CAF-1 deposits newly synthesized histones during DNA replication using distinct mechanisms on the leading and lagging strands.

During every cell cycle, both the genome and the associated chromatin must be accurately replicated. Chromatin Assembly Factor-1 (CAF-1) is a key regulator of chromatin replication, but how CAF-1 functions in relation to the DNA replication machinery is unknown. Here, we reveal that this crosstalk differs between the leading and lagging strand at replication forks. Using biochemical reconstitutions, we show that DNA and histones promote CAF-1 recruitment to its binding partner PCNA and reveal that two CAF-1 complexes are required for efficient nucleosome assembly under these conditions. Remarkably, in the context of the replisome, CAF-1 competes with the leading strand DNA polymerase epsilon (Polϵ) for PCNA binding. However, CAF-1 does not affect the activity of the lagging strand DNA polymerase Delta (Polδ). Yet, in cells, CAF-1 deposits newly synthesized histones equally on both daughter strands. Thus, on the leading strand, chromatin assembly by CAF-1 cannot occur simultaneously to DNA synthesis, while on the lagging strand these processes may be coupled. We propose that these differences may facilitate distinct parental histone recycling mechanisms and accommodate the inherent asymmetry of DNA replication.

Protein phosphatase 6 promotes stemness of colorectal cancer cells.

Colorectal cancer (CRC) remains a significant global health concern, demanding a more profound comprehension of its molecular foundations for the development of improved therapeutic strategies. This study aimed to elucidate the role of protein phosphatase 6 (PP6), a member of the type 2A protein phosphatase family, in CRC. Protein phosphatase 6 functions as a heterotrimer with a catalytic subunit (PP6c), regulatory subunits (PP6Rs; PP6R1, PP6R2, and PP6R3), and scaffold subunits (ANKRD28, ANKRD44, and ANKRD52). Elevated PP6c expression has been identified in CRC tissues compared to normal mucosa, aligning with its potential involvement in CRC pathogenesis. PP6c knockdown resulted in decreased colony-forming ability and in vivo proliferation of various CRC cell lines. Transcriptome analysis revealed that PP6c knockdown resulted in altered expression of genes associated with cancer stemness. Notably, the PP6c-PP6R3 complex is a key player in regulating cancer stem cell (CSC) markers. Additionally, increased PP6c expression was observed in CSC-like cells induced by sphere formation, implicating the role of PP6c in CSC maintenance. This study highlights the role of PP6c in CRC and suggests that it is a potential therapeutic target disrupting a pathway critical for CRC progression and stem cell maintenance.

Transcriptome analysis revealed that PME-1 suppresses inflammatory signaling, activates PI3K/Akt signaling, and promotes epithelial-mesenchymal transition.

Protein phosphatase 2A (PP2A) is an essential serine/threonine protein phosphatase that belongs to the type2A protein phosphatase family with PP4 and PP6. PP2A functions as a trimeric holoenzyme, and the composition of the trimer is regulated by the methyl-esterification (methylation) of PP2A. Demethylation of PP2A is catalyzed by protein phosphatase methyl-esterase-1 (PME-1). Despite the physiological and pathophysiological importance of PME-1, the impact of changes in PME-1 expression on the transcriptome has not been reported. This study provides transcriptome data to gain a comprehensive understanding of the effects of PME-1 knockout on intracellular signaling of mouse embryonic fibroblasts. Our data showed that PME-1 suppresses inflammatory signaling, activates PI3K/Akt signaling, and promotes epithelial-mesenchymal transition.

Myocardin-related transcription factor contributes to renal fibrosis through the regulation of extracellular microenvironment surrounding fibroblasts.

Fibroblast accumulation and extracellular matrix (ECM) deposition are common critical steps for the progression of organ fibrosis, but the precise molecular mechanisms remain to be fully investigated. We have previously demonstrated that lysophosphatidic acid contributes to organ fibrosis through the production of connective tissue growth factor (CTGF) via actin cytoskeleton-dependent signaling, myocardin-related transcription factor family (MRTF) consisting of MRTF-A and MRTF-B-serum response factor (SRF) pathway. In this study, we investigated the role of the MRTF-SRF pathway in the development of renal fibrosis, focusing on the regulation of ECM-focal adhesions (FA) in renal fibroblasts. Here we showed that both MRTF-A and -B were required for the expressions of ECM-related molecules such as lysyl oxidase family members, type I procollagen and fibronectin in response to transforming growth factor (TGF)-ß1 . TGF-ß1 -MRTF-SRF pathway induced the expressions of various components of FA such as integrin α subunits (αv , α2 , α11 ) and ß subunits (ß1 , ß3 , ß5 ) as well as integrin-linked kinase (ILK). On the other hand, the blockade of ILK suppressed TGF-ß1 -induced MRTF-SRF transcriptional activity, indicating a mutual relationship between MRTF-SRF and FA. Myofibroblast differentiation along with CTGF expression was also dependent on MRTF-SRF and FA components. Finally, global MRTF-A deficient and inducible fibroblast-specific MRTF-B deficient mice (MRTF-AKO BiFBKO mice) are protected from renal fibrosis with adenine administration. Renal expressions of ECM-FA components and CTGF as well as myofibroblast accumulation were suppressed in MRTF-AKO BiFBKO mice. These results suggest that the MRTF-SRF pathway might be a therapeutic target for renal fibrosis through the regulation of components forming ECM-FA in fibroblasts.

Kif26b contributes to the progression of interstitial fibrosis via migration and myofibroblast differentiation in renal fibroblast.

Kinesin family member 26b (Kif26b) is essential for kidney development, and its deletion in mice leads to kidney agenesis. However, the roles of this gene in adult settings remain elusive. Thus, this study aims to investigate the role of Kif26b in the progression of renal fibrosis. A renal fibrosis model with adenine administration using Kif26b heterozygous mice and wild-type mice was established. Renal fibrosis and the underlying mechanism were investigated. The underlying pathways and functions of Kif26b were evaluated in an in vitro model using primary renal fibroblasts. Kif26b heterozygous mice were protected from renal fibrosis with adenine administration. Renal expressions of connective tissue growth factor (CTGF) and myofibroblast accumulation were reduced in Kif26b heterozygous mice. The expression of nonmuscle myosin heavy chain II (NMHCII), which binds to the C-terminus of Kif26b protein, was also suppressed in Kif26b heterozygous mice. The in vitro study revealed reduced expressions of CTGF, α-smooth muscle actin, and myosin heavy chain 9 (Myh9) via transfection with siRNAs targeting Kif26b in renal fibroblasts (RFB). RFBs, which were transfected by the expression vector of Kif26b, demonstrated higher expressions of these genes than non-transfected cells. Finally, Kif26b suppression and NMHCII blockage led to reduced abilities of migration and collagen gel contraction in renal fibroblasts. Taken together, Kif26b contributes to the progression of interstitial fibrosis via migration and myofibroblast differentiation through Myh9 in the renal fibrosis model. Blockage of this pathway at appropriate timing might be a therapeutic approach for renal fibrosis.

Intestinal Bacterial Translocation Contributes to Diabetic Kidney Disease.

BACKGROUND: In recent years, many studies have focused on the intestinal environment to elucidate pathogenesis of various diseases, including kidney diseases. Impairment of the intestinal barrier function, the "leaky gut," reportedly contributes to pathologic processes in some disorders. Mitochondrial antiviral signaling protein (MAVS), a component of innate immunity, maintains intestinal integrity. The effects of disrupted intestinal homeostasis associated with MAVS signaling in diabetic kidney disease remains unclear. METHODS: To evaluate the contribution of intestinal barrier impairment to kidney injury under diabetic conditions, we induced diabetic kidney disease in wild-type and MAVS knockout mice through unilateral nephrectomy and streptozotocin treatment. We then assessed effects on the kidney, intestinal injuries, and bacterial translocation. RESULTS: MAVS knockout diabetic mice showed more severe glomerular and tubular injuries compared with wild-type diabetic mice. Owing to impaired intestinal integrity, the presence of intestine-derived Klebsiella oxytoca and elevated IL-17 were detected in the circulation and kidneys of diabetic mice, especially in diabetic MAVS knockout mice. Stimulation of tubular epithelial cells with K. oxytoca activated MAVS pathways and the phosphorylation of Stat3 and ERK1/2, leading to the production of kidney injury molecule-1 (KIM-1). Nevertheless, MAVS inhibition induced inflammation in the intestinal epithelial cells and KIM-1 production in tubular epithelial cells under K. oxytoca supernatant or IL-17 stimulation. Treatment with neutralizing anti-IL-17 antibody treatment had renoprotective effects. In contrast, LPS administration accelerated kidney injury in the murine diabetic kidney disease model. CONCLUSIONS: Impaired MAVS signaling both in the kidney and intestine contributes to the disrupted homeostasis, leading to diabetic kidney disease progression. Controlling intestinal homeostasis may offer a novel therapeutic approach for this condition.

Protective effect of d-alanine against acute kidney injury.

Recent studies have revealed the connection between amino acid chirality and diseases. We have previously reported that the gut microbiota produces various d-amino acids in a murine acute kidney injury (AKI) model. Here, we further explored the pathophysiological role of d-alanine (d-Ala) in AKI. Levels of d-Ala were evaluated in a murine AKI model. We analyzed transcripts of the N-methyl-d-aspartate (NMDA) receptor, a receptor for d-Ala, in tubular epithelial cells (TECs). The therapeutic effect of d-Ala was then assessed in vivo and in vitro. Finally, the plasma level of d-Ala was evaluated in patients with AKI. The Grin genes encoding NMDA receptor subtypes were expressed in TECs. Hypoxic conditions change the gene expression of Grin1, Grin2A, and Grin2B. d-Ala protected TECs from hypoxia-related cell injury and induced proliferation after hypoxia. These protective effects are associated with the chirality of d-Ala. d-Ala inhibits reactive oxygen species (ROS) production and improves mitochondrial membrane potential, through NMDA receptor signaling. The ratio of d-Ala to l-Ala was increased in feces, plasma, and urine after the induction of ischemia-reperfusion (I/R). Moreover, Enterobacteriaceae, such as Escherichia coli and Klebsiella oxytoca, produce d-Ala. Oral administration of d-Ala ameliorated kidney injury after the induction of I/R in mice. Deficiency of NMDA subunit NR1 in tubular cells worsened kidney damage in AKI. In addition, the plasma level of d-Ala was increased and reflected the level of renal function in patients with AKI. In conclusion, d-Ala has protective effects on I/R-induced kidney injury. Moreover, the plasma level of d-Ala reflects the estimated glomerular filtration rate in patients with AKI. d-Ala could be a promising therapeutic target and potential biomarker for AKI.NEW & NOTEWORTHY d-Alanine has protective effects on I/R-induced kidney injury. d-Ala inhibits ROS production and improves mitochondrial membrane potential, resulting in reduced TEC necrosis by hypoxic stimulation. The administration of d-Ala protects the tubules from I/R injury in mice. Moreover, the plasma level of d-Ala is conversely associated with eGFR in patients with AKI. Our data suggest that d-Ala is an appealing therapeutic target and a potential biomarker for AKI.

Ethylenediaminetetraacetic acid (EDTA) enhances cAMP production in human TDAG8-expressing cells.

Ethylenediaminetetraacetic acid (EDTA) is a chelating agent that binds tightly to metal ions. We found that cAMP response element (CRE)-driven promoter activity by protons was enhanced by EDTA in human T-cell death-associated gene 8 (TDAG8)-overexpressed HEK293T cells. The enhancing action by EDTA was also detected by proton-induced cAMP production that is located upstream from the CRE-driven promoter activity even at physiological proton concentration pH7.4. The proton-induced CRE-driven promoter activity was not enhanced by other chelating agents, ethylene glycol tetraacetic acid (EGTA) and sodium citrate. The enhanced CRE-driven promoter activity by EDTA was not attenuated by increasing the extracellular calcium ion concentration. These results indicate that the EDTA-enhancing action may not be due to its chelating action but might rather be another EDTA-specific effect. Enhanced cAMP production by EDTA was also detected in a human leukemia cell line HL-60, in which TDAG8 and OGR1 (ovarian cancer G-protein-coupled receptor 1) were endogenously expressed, suggesting that the medical use of EDTA would influence the physiological and pathophysiological functions of hematopoietic cells.

Pre-treatment serum protein levels predict survival of non-small cell lung cancer patients without durable clinical benefit by PD-1/L1 inhibitors.

While PD-1/L1 inhibitors are characterized by durable tumor control, they also prolong survival without prolongation of progression-free survival (PFS) in part of patients. However, little is known about the factors and mechanisms involved in this. Between December 2015 and September 2018, 106 patients with advanced non-small cell lung cancer treated with ICI monotherapy were enrolled in a prospective-observational study. Sixty-nine of whom progressed or died within 6 months after ICI initiation were defined as patients without durable clinical benefit (NDBs). Clinical factors and 39 serum proteins before ICI initiation and at the time of progressive disease (PD) were explored for an association with overall survival (OS) and OS after PD (OS-PD). As a result, median PFS, OS, and OS-PD were 44 days [95% confidence interval (CI): 39-56), 211 days (95% CI: 158-425), and 193 days (95% CI: 118-349), respectively. By multivariate analysis for OS, CRP (> 1.44 mg/dl) [HR 2.59 (95% CI:1.33-5.04), P = 0.005] and follistatin (> 685 pg/ml) [HR 2.29 (95% CI:1.12-4.69), P = 0.023] before ICI initiation were significantly predictive. Notably, no serum protein at the time of PD was predictive for OS-PD. There were also no serum predictive factors of OS in the 33 patients with durable clinical benefit. In conclusion, serum levels of CRP and follistatin before ICI initiation, not at the time of PD, are predictive for OS in NDBs, suggesting long-term survivor in NDBs are predetermined by the immune status before ICI initiation.

Prenatal stress enhances atherosclerosis and telomere shortening in ApoE knockout mouse offspring.

Children born to women who experience stress during pregnancy have an increased risk of atherosclerosis in later life, but few animal models have explored mechanisms. To study this phenomenon, timed-bred ApoE knockout mice were determined pregnant with ultrasound and randomly assigned on gestation day 8.5 to either a control (no stress) or prenatal stress (PS) group using 2 h of restraint for five consecutive days. PS significantly increased plasma corticosterone levels in pregnant mice. The litters from PS mice showed increased neonatal mortality within the first week of life. Body weights (at euthanasia) of adult offspring at 25 wk from the PS group were significantly increased compared with weights of controls. Adult offspring from these pregnancies were serially imaged with ultrasound to measure plaque thickness and were compared with plaque macroscopic and microscopic pathology. PS groups had increased plaque thickness determined by ultrasound, gross, histological evaluation and increased aortic root and valve macrophage infiltration at 25 wk. Five-week-old mice from PS group had significant decrease in mean arterial pressure, yet blood pressure normalized by 10 wk. As prenatal stress induced increased atherosclerosis, and telomeres are susceptible to stress, aortas from 10-wk-old mice were compared for telomere lengths and were found to be significantly shorter in PS mice compared with control mice. These studies support future investigation of how stress impacts telomere shortening in animal models and human aortas. This model could be further used to investigate the role of prenatal stress, telomere biology, and atherosclerosis pathogenesis in adults.

Differential properties of KRAS transversion and transition mutations in non-small cell lung cancer: associations with environmental factors and clinical outcomes.

BACKGROUND: KRAS-mutated non-small cell lung cancer (NSCLC) accounts for 23-35% and 13-20% of all NSCLCs in white patients and East Asians, respectively, and is therefore regarded as a major therapeutic target. However, its epidemiology and clinical characteristics have not been fully elucidated because of its wide variety of mutational subtypes. Here, we focused on two distinct base substitution types: transversion mutations and transition mutations, as well as their association with environmental factors and clinical outcome. METHODS: Dataset from the Japan Molecular Epidemiology Study, which is a prospective, multicenter, and molecular study epidemiology cohort study involving 957 NSCLC patients who underwent surgery, was used for this study. Questionnaire-based detailed information on clinical background and lifestyles was also used to assess their association with mutational subtypes. Somatic mutations in 72 cancer-related genes were analyzed by next-generation sequencing, and KRAS mutations were classified into three categories: transversions (G > C or G > T; G12A, G12C, G12R, G12V), transitions (G > A; G12D, G12S, G13D), and wild-type (WT). Clinical correlations between these subtypes have been investigated, and recurrence-free survival (RFS) and overall survival (OS) were evaluated. RESULTS: Of the 957 patients, KRAS mutations were detected in 80 (8.4%). Of these, 61 were transversions and 19 were transitions mutations. Both pack-years of smoking and smoking duration had significant positive correlation with the occurrence of transversion mutations (p = 0.03 and < 0.01, respectively). Notably, transitions showed an inverse correlation with vegetable intake (p = 0.01). Patients with KRAS transitions had the shortest RFS and OS compared to KRAS transversions and WT. Multivariate analysis revealed that KRAS transitions, along with age and stage, were significant predictors of shorter RFS and OS (HR 2.15, p = 0.01; and HR 2.84, p < 0.01, respectively). CONCLUSIONS: Smoking exposure positively correlated with transversions occurrence in a dose-dependent manner. However, vegetable intake negatively correlated with transitions. Overall, KRAS transition mutations are significantly poor prognostic factors among resected NSCLC patients.

Unique left pulmonary vein isolation in straight common trunk based on longitudinal conduction of left lateral ridge.

BACKGROUND: A left common pulmonary vein (LCPV) is the most common anatomical variation in the pulmonary vein (PV) and often influences strategies of PV isolation for atrial fibrillation (AF). Our objective was to elucidate the electrical properties of the specific shape of LCPV and to apply it to an ablation procedure. METHODS AND RESULTS: We investigated consecutive 12 out of 204 paroxysmal AF patients who had the shape of a straight common trunk in LCPV defined by the formation of a single conduit with parallel cranial and caudal walls after the coalescence of superior and inferior PVs on the distal side. The distance between the top of the bifurcation of LPVs and the level coinciding with the middle of the anterior wall of LCPV (left lateral ridge: LLR) was more than 10 mm in all the patients. The activation pattern of the LLR showed longitudinal conduction without outside connections. All the LCPV except one were successfully isolated without ablating the LLR (C-shape ablation). Only one patient had AF recurrence during the follow-up period. CONCLUSION: The LLR in LCPV with a straight common trunk has longitudinal conduction without outside connections, which permits the isolation of LCPV without ablating LLR.

Rare toxin A-negative and toxin B-positive strain of Clostridioides difficile from Japan lacking a complete tcdA gene.

INTRODUCTION: Clostridioides difficile (C. difficile) produces three kinds of toxins: toxin A (enterotoxin), toxin B (cytotoxin), and C. difficile transferase (CDT), a binary toxin. Some strains show positivity only for toxin B. These strains reportedly possess a gene for toxin A, tcdA. However, toxin A production is inhibited due to a mutated stop codon and/or deletion within the tcdA gene. Here for the first case in Japan, we describe toxin genomes and proteins of a strain possessing only toxin B and lacking a complete tcdA gene, along with clinical manifestations. METHODS: C. difficile was isolated from the bloody stool of a 60-year-old female patient treated with meropenem. Although a rapid detection kit of toxins (C. DIFF QUIK CHEK COMPLETE®, TechLab, Blacksburg, VA, USA) showed positivity, Western blotting detected no toxins. Therefore, we explored the strain's toxin genes and their sequences to determine whether the strain possessed a toxin. RESULTS: Polymerase chain reaction did not identify toxin genes. Whole-genome sequencing analysis showed that a gene for toxin A, tcdA, was completely deleted in the strain. Moreover, 701 mutations and some deletions/insertions were identified on the tcdB gene. CONCLUSIONS: We isolated a rare strain of C. difficile producing only toxin B and lacking a complete tcdA gene herein Japan. The possibility of a false negative needs to be considered with a genetic method for a diagnose of C. difficile infection.

HSF2BP negatively regulates homologous recombination in DNA interstrand crosslink repair.

The tumor suppressor BRCA2 is essential for homologous recombination (HR), replication fork stability and DNA interstrand crosslink (ICL) repair in vertebrates. We show that ectopic production of HSF2BP, a BRCA2-interacting protein required for meiotic HR during mouse spermatogenesis, in non-germline human cells acutely sensitize them to ICL-inducing agents (mitomycin C and cisplatin) and PARP inhibitors, resulting in a phenotype characteristic of cells from Fanconi anemia (FA) patients. We biochemically recapitulate the suppression of ICL repair and establish that excess HSF2BP compromises HR by triggering the removal of BRCA2 from the ICL site and thereby preventing the loading of RAD51. This establishes ectopic expression of a wild-type meiotic protein in the absence of any other protein-coding mutations as a new mechanism that can lead to an FA-like cellular phenotype. Naturally occurring elevated production of HSF2BP in tumors may be a source of cancer-promoting genomic instability and also a targetable vulnerability.