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Several polymorphic loci linked to lactase persistence (LP) have been described, all located in a small mutational hotspot region far upstream (approximate to 14kb) of the lactase (LCT) gene. One is typically found in Europeans, LCT -13910C>T, several others are found in East Africans and Arabs, e.g. LCT -13907C>G and LCT -13915T>G. The possibility of similar loci, specific to populations in South and Central America, has not received much attention so far. To identify possible novel polymorphisms in the mutational hotspot region, we sampled 158 subjects from a rural area in South-Central Mexico. DNA was isolated from serum, and Sanger sequencing of a 501bp region spanning the LCT -13910C>T hotspot was successfully performed in 150 samples. The frequency of the European-type LCT -13910T-allele was q=0.202, and 35% of the population was thus lactase-persistent (CT or TT). Sixteen novel genetic variants were found amongst 11 of the subjects, all were heterozygotes: seven of the subjects were also carriers of at least one LCT -13910T-allele. Thus, the mutational hotspot region is also a hotspot in the rural Mexican population: 11/150 subjects carried a total of 16 previously unknown private mutations but no novel polymorphism was found. The relationship between such novel genetic variants in Mexicans and lactase persistence is worthy of more investigation.

Acquired cisplatin resistance is a common feature of tumours following cancer treatment with cisplatin and also of non-small cell lung cancer (H1299) and mesothelioma (P31) cell lines exposed to cisplatin. To elucidate the cellular basis of acquired cisplatin resistance, a comprehensive bioenergetic analysis was undertaken. We demonstrate that cellular oxygen consumption was significantly decreased in cisplatin resistant cells and that the reduction was primarily due to reduced mitochondrial activity as a result of reduced mitochondrial abundance. The differential mitochondrial abundance was supported by data showing reduced sirtuin 1 (SIRT1), peroxisome-proliferator activator receptor-gamma co-activator 1-alpha (PGC1 alpha), sirtuin 3 (SIRT3) and mitochondrial transcription factor A (TFAM) protein expression in resistant cells. Consistent with these data we observed increased reactive oxygen species (ROS) production and increased hypoxia inducible factor 1-alpha (HIF1 alpha) stabilization in cisplatin resistant cells when compared to cisplatin sensitive controls. We also observed an increase in AMP kinase subunit alpha 2 (AMPK alpha 2) transcripts and protein expression in resistant H1299 cells. mRNA expression was also reduced for cisplatin resistant H1299 cells in these genes, however the pattern was not consistent in resistant P31 cells. There was very little change in DNA methylation of these genes, suggesting that the cells are not stably reprogrammed epigenetically. Taken together, our data demonstrate reduced oxidative metabolism, reduced mitochondrial abundance, potential for increased glycolytic flux and increased ROS production in acquired cisplatin resistant cells. This suggests that the metabolic changes are a result of reduced SIRT3 expression and increased HIF-1 alpha stabilization.

The absolute and relative concentrations of the four dNTPs are key determinants of DNA replication fidelity, yet the consequences of altered dNTP pools on replication fidelity have not previously been investigated on a genome-wide scale. Here, we use deep sequencing to determine the types, rates and locations of uncorrected replication errors that accumulate in the nuclear genome of a mismatch repair-deficient diploid yeast strain with elevated dCTP and dTTP concentrations. These imbalanced dNTP pools promote replication errors in specific DNA sequence motifs suggesting increased misinsertion and increased mismatch extension at the expense of proofreading. Interestingly, substitution rates are similar for leading and lagging strand replication, but are higher in regions replicated late in S phase. Remarkably, the rate of single base deletions is preferentially increased in coding sequences and in short rather than long mononucleotides runs. Based on DNA sequence motifs, we propose two distinct mechanisms for generating single base deletions in vivo. Collectively, the results indicate that elevated dCTP and dTTP pools increase mismatch formation and decrease error correction across the nuclear genome, and most strongly increases mutation rates in coding and late replicating sequences., Originally published in manuscript form with the title Genome-wide analysis of the specificity and mechanisms of replication infidelity driven by a mutation in ribnucleotide reductase that imbalances dNTP pools.

The fidelity of DNA replication requires an appropriate balance of dNTPs, yet the nascent leading and lagging strands of the nuclear genome are primarily synthesized by replicases that differ in subunit composition, protein partnerships and biochemical properties, including fidelity. These facts pose the question of whether imbalanced dNTP pools differentially influence leading and lagging strand replication fidelity. Here we test this possibility by examining strand-specific replication infidelity driven by a mutation in yeast ribonucleotide reductase, rnr1-Y285A, that leads to elevated dTTP and dCTP concentrations. The results for the CAN1 mutational reporter gene present in opposite orientations in the genome reveal that the rates, and surprisingly even the sequence contexts, of replication errors are remarkably similar for leading and lagging strand synthesis. Moreover, while many mismatches driven by the dNTP pool imbalance are efficiently corrected by mismatch repair, others are repaired less efficiently, especially those in sequence contexts suggesting reduced proofreading due to increased mismatch extension driven by the high dTTP and dCTP concentrations. Thus the two DNA strands of the nuclear genome are at similar risk of mutations resulting from this dNTP pool imbalance, and this risk is not completely suppressed even when both major replication error correction mechanisms are genetically intact.

The thienopyridine P2Y12 receptor antagonists clopidogrel and prasugrel prevent arterial thrombosis and are routinely used following percutaneous coronary intervention. However, the optimal level of P2Y12 blockade to effectively inhibit platelet function is unknown. These studies utilised the active metabolite of prasugrel (R-138727) to achieve a range of P2Y12 blockade in vitro and assessed several aspects of platelet function. Blood from healthy volunteers was incubated with R-138727 (0-10 microM). P2Y12 receptor number was assessed using a 33P-2MeSADP binding assay. Platelet aggregation (PA) was measured by optical aggregometry with ADP 2-20 microM. VASP phosphorylation, annexin V binding, microparticle formation and P-selectin expression were assessed by flow cytometry. Increasing numbers of unblocked receptors were required for a sustained aggregation response with decreasing concentrations of ADP. A P2Y12 receptor blockade of 60-80% resulted in strong inhibition of final PA response, P-selectin expression, microparticle formation and vasodilator-stimulated phosphoprotein (VASP). PA induced by ADP 2 microM and P-selectin expression were particularly sensitive to low levels of receptor blockade whereas the VASP phosphorylation assay was relatively insensitive, requiring 60% receptor blockade to achieve substantial inhibition. Different assays varied in their ability to discriminate particular ranges of P2Y12 blockade and 80% or greater P2Y12 receptor blockade is required for consistently strong inhibition of several aspects of platelet function. These data guide the interpretation of results from different assays used to monitor the effects of P2Y12 receptor antagonists.

The aim of these studies was to investigate the extent of platelet P2Y(12) receptor inhibition by the thienopyridine active metabolite of prasugrel, R-138727. Blood was taken from healthy volunteers and pre-incubated with R-138727 or cangrelor (AR-C66931MX). Platelet aggregation was assessed in platelet rich plasma (PRP) and whole blood (WB). Vasodilator stimulated phosphoprotein (VASP) phosphorylation, platelet procoagulant activity (annexin V binding and microparticle formation) and calcium mobilisation were measured by flow cytometry. Platelet-leukocyte co-aggregate formation and sCD40L release, both pro-inflammatory responses of platelets, were measured by flow cytometry and ELISA, respectively. P2Y(12) receptor antagonism was determined using a radioligand binding assay ((33)P 2-MeSADP) in resting and stimulated platelets and the effects of clopidogrel administration were also assessed. R-138727 yielded concentration-dependent inhibition of platelet aggregation, VASP phosphorylation inhibition, procoagulant activity and pro-inflammatory responses. In the presence of R-138727 or cangrelor there was increased calcium reuptake following agonist stimulation. R-138727 30 micromol/L and cangrelor 1 micromol/L completely inhibited (33)P 2-MeSADP binding, compared to partial inhibition following clopidogrel administration. Platelet activation and granule secretion did not expose an additional pool of P2Y(12) receptors. Prasugrel's active metabolite effectively blocks the P2Y(12) receptor with the highest concentrations tested yielding complete inhibition of P2Y(12)-mediated amplification of several important platelet responses.

Glycoprotein IIb/IIIa (GPIIb/IIIa) antagonists, including abciximab and tirofiban, are administered concurrently with clopidogrel, a P2Y12 antagonist, and aspirin in some patients undergoing percutaneous coronary intervention. We studied the effects of, and interactions between, abciximab, tirofiban, aspirin and the P2Y12 antagonist cangrelor on platelet aggregation, alpha and dense granule secretion and procoagulant responses in vitro. Blood was obtained from healthy volunteers. Platelet aggregation, dense granule secretion, alpha granule secretion (PAI-1 and soluble CD40 ligand levels) and procoagulant responses (annexin-V and microparticle formation) were assessed using collagen and thrombin receptor activating peptide (TRAP) as agonists. All the antagonists used singularly inhibited collagen-induced responses. Combinations of abciximab or tirofiban with aspirin and/or cangrelor gave additive inhibition with the greatest effect seen when abciximab or tirofiban was combined with both aspirin and cangrelor. Cangrelor inhibited TRAP-induced responses and, again, there was additive inhibition of these parameters when abciximab or tirofiban were combined with cangrelor. The GPIIb/IIIa receptor plays an important role in amplification of platelet activation such that there are important interactions between GPIIb/IIIa antagonists and inhibitors of both P2Y12 receptor activation and, to a lesser extent, thromboxane A2 generation. These interactions are likely to have important influences on the safety and efficacy of combination anti-platelet therapies.