Markedly increased risk of postoperative bleeding complications during perioperative bridging anticoagulation in general and visceral surgery.

Background: Increasing numbers of patients receiving oral anticoagulants are undergoing elective surgery. Low molecular weight heparin (LMWH) is frequently applied as bridging therapy during perioperative interruption of anticoagulation. The aim of this study was to explore the postoperative bleeding risk of patients receiving surgery under bridging anticoagulation.

Looking back at multidrug resistance (MDR) research and ten mistakes to be avoided when writing about ABC transporters in MDR.

This paper presents a personal, selective, and sometimes critical retrospective of the history of ABC transporters in multidrug resistance (MDR) of cancer cells, overrepresenting discoveries of some early pioneers, long forgotten, and highlights of research in Amsterdam, mainly focussing on discoveries made with disruptions of ABC genes in mice (KO mice) and on the role of ABC transporters in causing drug resistance in a mouse model of mammary cancer. The history is complemented by a list of erroneous concepts often found in papers and grant applications submitted anno 2020.

A mutation in the endonuclease domain of mouse MLH3 reveals novel roles for MutLγ during crossover formation in meiotic prophase I.

During meiotic prophase I, double-strand breaks (DSBs) initiate homologous recombination leading to non-crossovers (NCOs) and crossovers (COs). In mouse, 10% of DSBs are designated to become COs, primarily through a pathway dependent on the MLH1-MLH3 heterodimer (MutLγ). Mlh3 contains an endonuclease domain that is critical for resolving COs in yeast.

PXE, a Mysterious Inborn Error Clarified.

Ever since Garrod deduced the existence of inborn errors in 1901, a vast array of metabolic diseases has been identified and characterized in molecular terms. In 2018 it is difficult to imagine that there is any uncharted backyard left in the metabolic disease landscape. Nevertheless, it took until 2013 to identify the cause of a relatively frequent inborn error, pseudoxanthoma elasticum (PXE), a disorder resulting in aberrant calcification.

Selective Loss of PARG Restores PARylation and Counteracts PARP Inhibitor-Mediated Synthetic Lethality.

Inhibitors of poly(ADP-ribose) (PAR) polymerase (PARPi) have recently entered the clinic for the treatment of homologous recombination (HR)-deficient cancers. Despite the success of this approach, drug resistance is a clinical hurdle, and we poorly understand how cancer cells escape the deadly effects of PARPi without restoring the HR pathway. By combining genetic screens with multi-omics analysis of matched PARPi-sensitive and -resistant Brca2-mutated mouse mammary tumors, we identified loss of PAR glycohydrolase (PARG) as a major resistance mechanism.

BRCA-deficient mouse mammary tumor organoids to study cancer-drug resistance.

Poly(ADP-ribose) polymerase inhibition (PARPi) is a promising new therapeutic approach for the treatment of cancers that show homologous recombination deficiency (HRD). Despite the success of PARPi in targeting HRD in tumors that lack the tumor suppressor function of BRCA1 or BRCA2, drug resistance poses a major obstacle. We developed three-dimensional cancer organoids derived from genetically engineered mouse models (GEMMs) for BRCA1- and BRCA2-deficient cancers.

Selected Alkylating Agents Can Overcome Drug Tolerance of G-like Tumor Cells and Eradicate BRCA1-Deficient Mammary Tumors in Mice.

We aimed to characterize and target drug-tolerant BRCA1-deficient tumor cells that cause residual disease and subsequent tumor relapse. We studied responses to various mono- and bifunctional alkylating agents in a genetically engineered mouse model for -mutant breast cancer. Because of the large intragenic deletion of the gene, no restoration of BRCA1 function is possible, and therefore, no BRCA1-dependent acquired resistance occurs.

Maxi-circles, glycosomes, gene transposition, expression sites, transsplicing, transferrin receptors and base J.

This is a personal story of the author of his research on trypanosomatids, covering a period of 1970-2015. Some of the highlights include the discovery of new aspects of kDNA, the mini-circle heterogeneity and the maxi-circle; the glycosome; the discovery of gene transposition as a major mechanism for antigenic variation; trans-splicing as an essential step in the synthesis of all trypanosome mRNAs; Pulsed Field Gradient gels to size-fractionate chromosome-sized DNA molecules of protozoa; the sequence of trypanosome telomeres and their growth and contraction; the first ABC-transporter of trypanosomatids, LtpgpA; the variable transferrin receptor of T. brucei and its role in Fe uptake; and base J, its structure, biosynthesis and function.

HELB Is a Feedback Inhibitor of DNA End Resection.

DNA double-strand break repair by homologous recombination is initiated by the formation of 3' single-stranded DNA (ssDNA) overhangs by a process termed end resection. Although much focus has been given to the decision to initiate resection, little is known of the mechanisms that regulate the ongoing formation of ssDNA tails. Here we report that DNA helicase B (HELB) underpins a feedback inhibition mechanism that curtails resection.

Subunit composition of VRAC channels determines substrate specificity and cellular resistance to Pt-based anti-cancer drugs.

Although platinum-based drugs are widely used chemotherapeutics for cancer treatment, the determinants of tumor cell responsiveness remain poorly understood. We show that the loss of subunits LRRC8A and LRRC8D of the heteromeric LRRC8 volume-regulated anion channels (VRACs) increased resistance to clinically relevant cisplatin/carboplatin concentrations. Under isotonic conditions, about 50% of cisplatin uptake depended on LRRC8A and LRRC8D, but neither on LRRC8C nor on LRRC8E.

ATP-binding Cassette Subfamily C Member 5 (ABCC5) Functions as an Efflux Transporter of Glutamate Conjugates and Analogs.

The ubiquitous efflux transporter ABCC5 (ATP-binding cassette subfamily C member 5) is present at high levels in the blood-brain barrier, neurons, and glia, but its in vivo substrates and function are not known. Using untargeted metabolomic screens, we show that Abcc5(-/-) mice accumulate endogenous glutamate conjugates in several tissues, but brain in particular. The abundant neurotransmitter N-acetylaspartylglutamate was 2.

N-lactoyl-amino acids are ubiquitous metabolites that originate from CNDP2-mediated reverse proteolysis of lactate and amino acids.

Despite technological advances in metabolomics, large parts of the human metabolome are still unexplored. In an untargeted metabolomics screen aiming to identify substrates of the orphan transporter ATP-binding cassette subfamily C member 5 (ABCC5), we identified a class of mammalian metabolites, N-lactoyl-amino acids. Using parallel protein fractionation in conjunction with shotgun proteomics on fractions containing N-lactoyl-Phe-forming activity, we unexpectedly found that a protease, cytosolic nonspecific dipeptidase 2 (CNDP2), catalyzes their formation.

REV7 counteracts DNA double-strand break resection and affects PARP inhibition.

Error-free repair of DNA double-strand breaks (DSBs) is achieved by homologous recombination (HR), and BRCA1 is an important factor for this repair pathway. In the absence of BRCA1-mediated HR, the administration of PARP inhibitors induces synthetic lethality of tumour cells of patients with breast or ovarian cancers. Despite the benefit of this tailored therapy, drug resistance can occur by HR restoration.

BRCA2-deficient sarcomatoid mammary tumors exhibit multidrug resistance.

Pan- or multidrug resistance is a central problem in clinical oncology. Here, we use a genetically engineered mouse model of BRCA2-associated hereditary breast cancer to study drug resistance to several types of chemotherapy and PARP inhibition. We found that multidrug resistance was strongly associated with an EMT-like sarcomatoid phenotype and high expression of the Abcb1b gene, which encodes the drug efflux transporter P-glycoprotein.

ABCC6-mediated ATP secretion by the liver is the main source of the mineralization inhibitor inorganic pyrophosphate in the systemic circulation-brief report.

Objective: Mutations in ABCC6 underlie the ectopic mineralization disorder pseudoxanthoma elasticum (PXE) and some forms of generalized arterial calcification of infancy, both of which affect the cardiovascular system. Using cultured cells, we recently showed that ATP-binding cassette subfamily C member 6 (ABCC6) mediates the cellular release of ATP, which is extracellularly rapidly converted into AMP and the mineralization inhibitor inorganic pyrophosphate (PPi). The current study was performed to determine which tissues release ATP in an ABCC6-dependent manner in vivo, where released ATP is converted into AMP and PPi, and whether human PXE ptients have low plasma PPi concentrations.

ABCC6 prevents ectopic mineralization seen in pseudoxanthoma elasticum by inducing cellular nucleotide release.

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease characterized by progressive ectopic mineralization of the skin, eyes, and arteries, for which no effective treatment exists. PXE is caused by inactivating mutations in the gene encoding ATP-binding cassette sub-family C member 6 (ABCC6), an ATP-dependent efflux transporter present mainly in the liver. Abcc6(-/-) mice have been instrumental in demonstrating that PXE is a metabolic disease caused by the absence of an unknown factor in the circulation, the presence of which depends on ABCC6 in the liver.

P-glycoprotein ABCB1: a major player in drug handling by mammals.

Mammalian P-glycoproteins are active drug efflux transporters located in the plasma membrane. In the early nineties, we generated knockouts of the three P-glycoprotein genes of mice, the Mdr1a, Mdr1b, and Mdr2 P-glycoproteins, now known as Abcb1a, Abcb1b, and Abcb4, respectively. In the JCI papers that are the subject of this Hindsight, we showed that loss of Mdr1a (Abcb1a) had a profound effect on the tissue distribution and especially the brain accumulation of a range of drugs frequently used in humans, including dexamethasone, digoxin, cyclosporin A, ondansetron, domperidone, and loperamide.

Loss of 53BP1 causes PARP inhibitor resistance in Brca1-mutated mouse mammary tumors.

Unlabelled: Inhibition of PARP is a promising therapeutic strategy for homologous recombination-deficient tumors, such as BRCA1-associated cancers. We previously reported that BRCA1-deficient mouse mammary tumors may acquire resistance to the clinical PARP inhibitor (PARPi) olaparib through activation of the P-glycoprotein drug efflux transporter. Here, we show that tumor-specific genetic inactivation of P-glycoprotein increases the long-term response of BRCA1-deficient mouse mammary tumors to olaparib, but these tumors eventually developed PARPi resistance.

EZN-2208 (PEG-SN38) overcomes ABCG2-mediated topotecan resistance in BRCA1-deficient mouse mammary tumors.

BRCA1 dysfunction in hereditary breast cancer causes defective homology-directed DNA repair and sensitivity towards DNA damaging agents like the clinically used topoisomerase I inhibitors topotecan and irinotecan. Using our conditional K14cre;Brca1(F/F);p53(F/F) mouse model, we showed previously that BRCA1;p53-deficient mammary tumors initially respond to topotecan, but frequently acquire resistance by overexpression of the efflux transporter ABCG2. Here, we tested the pegylated SN38 compound EZN-2208 as a novel approach to treat BRCA1-mutated tumors that express ABCG2.

Glucosylated hydroxymethyluracil, DNA base J, prevents transcriptional readthrough in Leishmania.

Some Ts in nuclear DNA of trypanosomes and Leishmania are hydroxylated and glucosylated to yield base J (β-D-glucosyl-hydroxymethyluracil). In Leishmania, about 99% of J is located in telomeric repeats. We show here that most of the remaining J is located at chromosome-internal RNA polymerase II termination sites.

Binding of the J-binding protein to DNA containing glucosylated hmU (base J) or 5-hmC: evidence for a rapid conformational change upon DNA binding.

Base J (β-D-glucosyl-hydroxymethyluracil) was discovered in the nuclear DNA of some pathogenic protozoa, such as trypanosomes and Leishmania, where it replaces a fraction of base T. We have found a J-Binding Protein 1 (JBP1) in these organisms, which contains a unique J-DNA binding domain (DB-JBP1) and a thymidine hydroxylase domain involved in the first step of J biosynthesis. This hydroxylase is related to the mammalian TET enzymes that hydroxylate 5-methylcytosine in DNA.