Timeless couples G-quadruplex detection with processing by DDX11 helicase during DNA replication

Regions of the genome with the potential to form secondary DNA structures pose a frequent and significant impediment to DNA replication and must be actively managed in order to preserve genetic and epigenetic integrity. How the replisome detects and responds to secondary structures is poorly understood. Here, we show that a core component of the fork protection complex in the eukaryotic replisome, Timeless, harbours in its C-terminal region a previously unappreciated DNA-binding domain that exhibits specific binding to G-quadruplex (G4) DNA structures. We show that this domain contributes to maintaining processive replication through G4-forming sequences, and exhibits partial redundancy with an adjacent PARP-binding domain. Further, this function of Timeless requires interaction with and activity of the helicase DDX11. Loss of both Timeless and DDX11 causes epigenetic instability at G4-forming sequences and DNA damage. Our findings indicate that Timeless contributes to the ability of the replisome to sense replication-hindering G4 formation and ensures the prompt resolution of these structures by DDX11 to maintain processive DNA synthesis.

Structural Basis for Inhibition of Human Primase by Arabinofuranosyl Nucleoside Analogues Fludarabine and Vidarabine

Nucleoside analogues are widely used in clinical practice as chemotherapy drugs. Arabinose nucleoside derivatives such as fludarabine are effective in the treatment of patients with acute and chronic leukemias and non-Hodgkin's lymphomas. Although nucleoside analogues are generally known to function by inhibiting DNA synthesis in rapidly proliferating cells, the identity of their in vivo targets and mechanism of action are often not known in molecular detail. Here we provide a structural basis for arabinose nucleotide-mediated inhibition of human primase, the DNA-dependent RNA polymerase responsible for initiation of DNA synthesis in DNA replication. Our data suggest ways in which the chemical structure of fludarabine could be modified to improve its specificity and affinity toward primase, possibly leading to less toxic and more effective therapeutic agents.

The human CTF4-orthologue AND-1 interacts with DNA polymerase α/primase via its unique C-terminal HMG box

A dynamic multi-protein assembly known as the replisome is responsible for DNA synthesis in eukaryotic cells. In yeast, the hub protein Ctf4 bridges DNA helicase and DNA polymerase and recruits factors with roles in metabolic processes coupled to DNA replication. An important question in DNA replication is the extent to which the molecular architecture of the replisome is conserved between yeast and higher eukaryotes. Here, we describe the biochemical basis for the interaction of the human CTF4-orthologue AND-1 with DNA polymerase α (Pol α)/primase, the replicative polymerase that initiates DNA synthesis. AND-1 has maintained the trimeric structure of yeast Ctf4, driven by its conserved SepB domain. However, the primary interaction of AND-1 with Pol α/primase is mediated by its C-terminal HMG box, unique to mammalian AND-1, which binds the B subunit, at the same site targeted by the SV40 T-antigen for viral replication. In addition, we report a novel DNA-binding activity in AND-1, which might promote the correct positioning of Pol α/primase on the lagging-strand template at the replication fork. Our findings provide a biochemical basis for the specific interaction between two critical components of the human replisome, and indicate that important principles of replisome architecture have changed significantly in evolution.

Crystal structure of the N-terminal domain of human Timeless and its interaction with Tipin

Human Timeless is involved in replication fork stabilization, S-phase checkpoint activation and establishment of sister chromatid cohesion. In the cell, Timeless forms a constitutive heterodimeric complex with Tipin. Here we present the 1.85 Å crystal structure of a large N-terminal segment of human Timeless, spanning amino acids 1-463, and we show that this region of human Timeless harbours a partial binding site for Tipin. Furthermore, we identify minimal regions of the two proteins that are required for the formation of a stable Timeless-Tipin complex and provide evidence that the Timeless-Tipin interaction is based on a composite binding interface comprising different domains of Timeless.

Methylphenidate challenge followed by therapeutic drug monitoring in adults with attention deficit/hyperactivity disorder: Clinical effects and its predictors

Introduction

Attention deficit/hyperactivity disorder (ADHD) affects 5–6% of adults. Methylphenidate challenge is used to test functions such as concentration. Therapeutic drug monitoring (TDM) identifies optimal drug ranges in plasma.

Objectives/Aims

We aimed to: assess the clinical impact of the drug challenge in adults with ADHD; analyze the relationship with the drug plasma levels after the challenge; identify predictors of the challenge's clinical impact.

Methods

In 2015–2016, we recruited 45 consecutive adult DSM-5 ADHD outpatients (mean age ± SD = 35.3 ± 2.1 years; females = 64.4%) at the Bolzano hospital department of psychiatry. Before and after administration of methylphenidate 10 mg, we measured concentration, impulsivity, tension, and general well-being with a VAS and an interview. After two hours, TDM was performed. Deltas were calculated for pre-/post-challenge measures. Correlations were measured with Pearson's r/point-biserial coefficient. A generalized linear mixed model estimated the size of association between tension/general well-being improvement and patient characteristics.

Results

After the challenge, the mean improvement ± SD was 24 ± 22 for concentration, 17 ± 23 for impulsivity, 21 ± 28 for tension, 16 ± 24 for general well-being. The mean TDM ± SD was 4.6 ± 0.5 ng/mL. A negative correlation between TDM, tension (P = 0.009), and general well-being (P = 0.028) after the challenge emerged: higher drug plasma levels relate to less tension and greater general well-being. At the GLMM the main predictor for tension/general well-being improvement was psychopharmacological treatment (P = 0.011/P = 0.05, respectively). Older age and difficult tasks prevented improvement.

Conclusions

Methylphenidate challenge had a positive effect on all patients’ performance. TDM values were lower than literature ones, although the latter are usually obtained after the administration of methylphenidate 20 mg.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Crystal structure of the yeast ribosomal protein rpS3 in complex with its chaperone Yar1

Eukaryotic ribosome assembly involves a plethora of factors, which ensure that a correctly folded ribosome contains all ribosomal protein components. Among these assembly factors, Yar1 has recently emerged as a molecular chaperone for ribosomal protein rpS3 of the small ribosomal subunit (40S) in yeast. In complex with its chaperone, rpS3 is imported into the nucleus and protected from aggregation. How rpS3 and other ribosomal proteins are initially sequestered and subsequently integrated into pre-ribosomal particles is currently poorly understood. Here, we present the crystal structure of yeast rpS3 in complex with its chaperone Yar1 at 2.8Å resolution. The crystal structure rationalizes how Yar1 can protect rpS3 from aggregation while facilitating nuclear import and suggests a mechanism for a stepwise exchange of molecular partners that ribosomal proteins interact with during ribosome assembly.

Hospitalization and total medical costs for privately insured persons with schizophrenia

This study used data from the 1991-1993 MarketScan files, a large database of private sector inpatient, outpatient, and prescription drug medical claims, to identify a sample of 665 patients with schizophrenia. Descriptive and multivariate analyses were conducted on the subsamples with hospitalizations (N = 185) and without hospitalizations (N = 480) in the 1-year period following the initial diagnosis for schizophrenia observed in the 1991-1993 time period. After controlling for patient demographic characteristics, medical co-morbidities, and other factors, the cost of hospitalization itself was found to be $15,805.

Analysis of medical-decision making and the use of standards of care in oncology

Guidelines in medicine have been proposed as a way to assist physicians in the clinical decision-making process. Increasingly, they form the basis for assessing accountability in the delivery of healthcare services. However, experiences with their evaluation, as the most important step in the continuous guidelines process, are rare. Patient Care Evaluation Studies have been developed by the Commission on Cancer in the United States. As they reflect the "real-world" medical practice they are helpful in evaluating the quality of diagnosis, therapy and follow-up of tumor diseases in hospitals and cancer center and the compliance with current standards of care. In this context, they can provide an infrastructure for the analysis of the decision-making process.

Low glutamine concentrations induce phenotypical and functional differentiation of U937 myelomonocytic cells

L-Glutamine is the most abundant free amino acid of the human body and is essential for the culture of many cell types. Clinically, reduction of glutamine by administration of glutaminase or the use of glutamine analogs is a common therapy for patients with acute lymphocytic leukemia. In the current study, we investigated the influence of glutamine concentrations on the human myelomonocytic cell line U937. Decreasing the glutamine concentration evoked a reduction in DNA synthesis (R2 = 0.9885, P < 0.0001), increased cell volume (P < 0.01) and the cytoplasm/nuclear ratio, and enhanced the development of vacuoles but did not influence cell viability. Culturing cells in reduced concentrations of glutamine augmented the percentage of cells expressing CD64 (Fc receptor for IgG/FcgammaRI, P < 0.01), CD11b (complement receptor type 3/CR3, P < 0.001) and CD71 (transferrin receptor, P < 0.05). The percentage of U937 cells expressing CD23 (low affinity receptor for IgE/FcepsilonRII) was increased at low concentrations of glutamine at both the protein (P < 0.01) and mRNA levels. The percentage of U937 cells phagocytizing opsonized E. coli (P < 0.001) or latex particles (P < 0.001) was enhanced by lowering the glutamine concentration. In conclusion, reducing glutamine concentration causes differentiation of the cell line U937 along the monocytic pathway. These effects may indicate a mechanistic basis for prior published evidence that glutaminase and glutamine antagonists are effective anti-tumor agents.

A clinical monitoring system for centrifugal blood pumps

In clinical application of rotary blood pumps, flow obstruction as a result of suction of the inflow cannula, kinking of tubing, or thrombus formation occurs quite frequently. Early detection of such problems is essential to avoid hemolysis, tissue degradation, or release of thrombi to the patient. A program was developed for automatic observation of pump performance, tubing resistance, and suction effects, which requires only the measurement of already available parameters (i.e., pump speed, pump flow, aortic pressure). The software is based on Visual-C and provides a user surface formatted in Windows. Pump flow, its time derivate, and the relationship between the pulsatile component and the mean graft flow are observed to detect suction in the left atrium. Furthermore, the generated pressure head is predicted from pump speed, graft flow, and the resistance of tubing/cannula and compared with the actually measured aortic pressure. An alarm sounds if a given limit between prediction and measurement is exceeded. In a mock circulation, suction events were detected in more than 95% with a mean deviation of actual aortic pressure from its predicted value of less than 5%. For in vivo application, even incomplete suction could be detected reliably in more than 90% of events. This system improves and standardizes monitoring of pump performance; it should therefore lead to greater safety during application of such devices.