Synaptotagmin VII as a plasma membrane Ca(2+) sensor in exocytosis

Synaptotagmins I and II are Ca(2+) binding proteins of synaptic vesicles essential for fast Ca(2+)-triggered neurotransmitter release. However, central synapses and neuroendocrine cells lacking these synaptotagmins still exhibit Ca(2+)-evoked exocytosis. We now propose that synaptotagmin VII functions as a plasma membrane Ca(2+) sensor in synaptic exocytosis complementary to vesicular synaptotagmins. We show that alternatively spliced forms of synaptotagmin VII are expressed in a developmentally regulated pattern in brain and are concentrated in presynaptic active zones of central synapses. In neuroendocrine PC12 cells, the C(2)A and C(2)B domains of synaptotagmin VII are potent inhibitors of Ca(2+)-dependent exocytosis, but only when they bind Ca(2+). Our data suggest that in synaptic vesicle exocytosis, distinct synaptotagmins function as independent Ca(2+) sensors on the two fusion partners, the plasma membrane (synaptotagmin VII) versus synaptic vesicles (synaptotagmins I and II).

Role of protein-protein interactions in the function of replication protein A (RPA): RPA modulates the activity of DNA polymerase alpha by multiple mechanisms

Replication Protein A (RPA) from human cells is a stable complex of 70-, 32-, and 14-kDa subunits that is required for multiple processes in DNA metabolism. RPA binds with high affinity to single-stranded DNA and interacts with multiple proteins, including proteins required for the initiation of SV40 DNA replication, DNA polymerase alpha and SV40 large T antigen. We have used a series of mutant derivatives of RPA to map the regions of RPA required for specific protein-protein interactions and have examined the roles of these interactions in DNA replication. T antigen, DNA polymerase alpha and the activation domain of VP16 all have overlapping sites of interaction in the N-terminal half (residues 1-327) of the 70-kDa subunit of RPA. In addition, the interaction site for DNA polymerase alpha is composed of two functionally distinct regions, one (residues 1- approximately 170) which stimulates polymerase activity and a second (residues approximately 170-327) which increases polymerase processivity. In the latter, both the direct protein-protein interaction and ssDNA-binding activities of RPA were needed for RPA to modulate polymerase processivity. We also found that SV40 T antigen inhibited the ability of RPA to increase processivity of DNA polymerase alpha, suggesting that this activity of RPA may be important for elongation but not during the initiation of DNA replication. DNA polymerase alpha, but not T antigen also interacted with the 32- and/or 14-kDa subunits of RPA, but these interactions did not seem to effect polymerase activity.

The C2B domain of synaptotagmin I is a Ca2+-binding module

Synaptotagmin I is a synaptic vesicle protein that contains two C(2) domains and acts as a Ca(2+) sensor in neurotransmitter release. The Ca(2+)-binding properties of the synaptotagmin I C(2)A domain have been well characterized, but those of the C(2)B domain are unclear. The C(2)B domain was previously found to pull down synaptotagmin I from brain homogenates in a Ca(2+)-dependent manner, leading to an attractive model whereby Ca(2+)-dependent multimerization of synaptotagmin I via the C(2)B domain participates in fusion pore formation. However, contradictory results have been described in studies of Ca(2+)-dependent C(2)B domain dimerization, as well as in analyses of other C(2)B domain interactions. To shed light on these issues, the C(2)B domain has now been studied using biophysical techniques. The recombinant C(2)B domain expressed as a GST fusion protein and isolated by affinity chromatography contains tightly bound bacterial contaminants despite being electrophoretically pure. The contaminants bind to a polybasic sequence that has been previously implicated in several C(2)B domain interactions, including Ca(2+)-dependent dimerization. NMR experiments show that the pure recombinant C(2)B domain binds Ca(2+) directly but does not dimerize upon Ca(2+) binding. In contrast, a cytoplasmic fragment of native synaptotagmin I from brain homogenates, which includes the C(2)A and C(2)B domains, participates in a high molecular weight complex as a function of Ca(2+). These results show that the recombinant C(2)B domain of synaptotagmin I is a monomeric, autonomously folded Ca(2+)-binding module and suggest that a potential function of synaptotagmin I multimerization in fusion pore formation does not involve a direct interaction between C(2)B domains or requires a posttranslational modification.

Replication protein A interactions with DNA. 2. Characterization of double-stranded DNA-binding/helix-destabilization activities and the role of the zinc-finger domain in DNA interactions

Human replication protein A (RPA) is a heterotrimeric single-stranded DNA-binding protein that is composed of subunits of 70, 32, and 14 kDa. RPA is required for multiple processes in cellular DNA metabolism. RPA has been reported to (1) bind with high affinity to single-stranded DNA (ssDNA), (2) bind specifically to certain double-stranded DNA (dsDNA) sequences, and (3) have DNA helix-destabilizing ("unwinding") activity. We have characterized both dsDNA binding and helix destabilization. The affinity of RPA for dsDNA was lower than that of ssDNA and precisely correlated with the melting temperature of the DNA fragment. The rates of helix destabilization and dsDNA binding were similar, and both were slow relative to the rate of binding ssDNA. We have previously mapped the regions required for ssDNA binding [Walther et al. (1999) Biochemistry 38, 3963-3973]. Here, we show that both helix-destabilization and dsDNA-binding activities map to the central DNA-binding domain of the 70-kDa subunit and that other domains of RPA are needed for optimal activity. We conclude that all types of RPA binding are manifestations of RPA ssDNA-binding activity and that dsDNA binding occurs when RPA destabilizes a region of dsDNA and binds to the resulting ssDNA. The 70-kDa subunit of all RPA homologues contains a highly conserved putative (C-X2-C-X13-C-X2-C) zinc finger. This motif directly interacts with DNA and contributes to dsDNA-binding/unwinding activity. Evidence is presented that a metal ion is required for the function of the zinc-finger motif.

Replication protein A interactions with DNA. III. Molecular basis of recognition of damaged DNA

Human replication protein A (RPA) is a heterotrimeric single-stranded DNA-binding protein (subunits of 70, 32, and 14 kDa) that is required for cellular DNA metabolism. RPA has been reported to interact specifically with damaged double-stranded DNA and to participate in multiple steps of nucleotide excision repair (NER) including the damage recognition step. We have examined the mechanism of RPA binding to both single-stranded and double-stranded DNA (ssDNA and dsDNA, respectively) containing damage. We show that the affinity of RPA for damaged dsDNA correlated with disruption of the double helix by the damaged bases and required RPAs ssDNA-binding activity. We conclude that RPA is recognizing single-stranded character caused by the damaged nucleotides. We also show that RPA binds specifically to damaged ssDNA. The specificity of binding varies with the type of damage with RPA having up to a 60-fold preference for a pyrimidine(6-4)pyrimidone photoproduct. We show that this specific binding was absolutely dependent on the zinc-finger domain in the C-terminus of the 70-kDa subunit. The affinity of RPA for damaged ssDNA was 5 orders of magnitude higher than that of the damage recognition protein XPA (xeroderma pigmentosum group A protein). These findings suggest that RPA probably binds to both damaged and undamaged strands in the NER excision complex. RPA binding may be important for efficient excision of damaged DNA in NER.

Replication protein A interactions with DNA. 1. Functions of the DNA-binding and zinc-finger domains of the 70-kDa subunit

Human replication protein A (RPA) is a multiple subunit single-stranded DNA-binding protein that is required for multiple processes in cellular DNA metabolism. This complex, composed of subunits of 70, 32, and 14 kDa, binds to single-stranded DNA (ssDNA) with high affinity and participates in multiple protein-protein interactions. The 70-kDa subunit of RPA is known to be composed of multiple domains: an N-terminal domain that participates in protein interactions, a central DNA-binding domain (composed of two copies of a ssDNA-binding motif), a putative (C-X2-C-X13-C-X2-C) zinc finger, and a C-terminal intersubunit interaction domain. A series of mutant forms of RPA were used to elucidate the roles of these domains in RPA function. The central DNA-binding domain was necessary and sufficient for interactions with ssDNA; however, adjacent sequences, including the zinc-finger domain and part of the N-terminal domain, were needed for optimal ssDNA-binding activity. The role of aromatic residues in RPA-DNA interactions was examined. Mutation of any one of the four aromatic residues shown to interact with ssDNA had minimal effects on RPA activity, indicating that individually these residues are not critical for RPA activity. Mutation of the zinc-finger domain altered the structure of the RPA complex, reduced ssDNA-binding activity, and eliminated activity in DNA replication.

Vancomycin levels are frequently subtherapeutic in critically ill patients: a prospective observational study

Background

Appropriate utilization of vancomycin is important to attain therapeutic targets while avoiding clinical failure and the development of antimicrobial resistance. Our aim was to observe the use of vancomycin in an intensive care population, with the main focus on achievement of therapeutic serum concentrations (15–20 mg/l) and to evaluate how this was influenced by dose regimens, use of guidelines and therapeutic drug monitoring.

Methods

A prospective observational study was carried out in the intensive care units at two tertiary hospitals in Norway. Data were collected from 83 patients who received vancomycin therapy, half of these received continuous renal replacement therapy. Patients were followed for 72 h after initiation of therapy. Blood samples were drawn for analysis of trough serum concentrations. Urine was collected for calculations of creatinine clearance. Information was gathered from medical records and electronic health records.

Results

Less than 40% of the patients attained therapeutic trough serum concentrations during the first 3 days of therapy. Patients with augmented renal clearance had lower serum trough concentrations despite receiving higher maintenance doses and more loading doses. When trough serum concentrations were outside of therapeutic range, dose adjustments in accordance to therapeutic drug monitoring were made to less than half.

Conclusion

The present study reveals significant challenges in the utilization of vancomycin in critically ill patients. There is a need for clearer guidelines regarding dosing and therapeutic drug monitoring of vancomycin for patient subgroups.

MicroRNA-20a-mediated loss of autophagy contributes to breast tumorigenesis by promoting genomic damage and instability

Gene expression analysis of The Cancer Genome Atlas (TCGA) breast cancer data set show that miR-20a is upregulated in human breast cancer, especially in triple-negative subtype. Gene Set Enrichment Analysis suggests that miR-20a expression negatively correlates with the autophagy/lysosome pathway. We report here that miR-20a inhibits the basal and nutrient starvation-induced autophagic flux and lysosomal proteolytic activity, increases intracellular reactive oxygen species levels and DNA damage response by targeting several key regulators of autophagy, including BECN1, ATG16L1 and SQSTM1. Re-introduction of exogenous BECN1, ATG16L1 or SQSTM1 reverses the inhibitory effect of miR-20a on autophagy and decreases DNA damage. A negative correlation between miR-20a and its target genes is observed in breast cancer tissues. Lower levels of BECN1, ATG16L1 and SQSTM1 are more common in triple-negative cancers than in other subtypes. High levels of miR-20a also associate with higher frequency of copy-number alterations and DNA mutations in breast cancer patients. Further studies in a xenograft mouse model show that miR-20a promotes tumor initiation and tumor growth. Collectively, these findings suggest that miR-20a-mediated autophagy defect might be a new mechanism underlying the oncogenic function of miRNA during breast tumorigenesis.

Guttiferone K impedes cell cycle re-entry of quiescent prostate cancer cells via stabilization of FBXW7 and subsequent c-MYC degradation

Cell cycle re-entry by quiescent cancer cells is an important mechanism for cancer progression. While high levels of c-MYC expression are sufficient for cell cycle re-entry, the modality to block c-MYC expression, and subsequent cell cycle re-entry, is limited. Using reversible quiescence rendered by serum withdrawal or contact inhibition in PTEN(null)/p53(WT) (LNCaP) or PTEN(null)/p53(mut) (PC-3) prostate cancer cells, we have identified a compound that is able to impede cell cycle re-entry through c-MYC. Guttiferone K (GUTK) blocked resumption of DNA synthesis and preserved the cell cycle phase characteristics of quiescent cells after release from the quiescence. In vehicle-treated cells, there was a rapid increase in c-MYC protein levels upon release from the quiescence. However, this increase was inhibited in the presence of GUTK with an associated acceleration in c-MYC protein degradation. The inhibitory effect of GUTK on cell cycle re-entry was significantly reduced in cells overexpressing c-MYC. The protein level of FBXW7, a subunit of E3 ubiquitin ligase responsible for degradation of c-MYC, was reduced upon the release from the quiescence. In contrast, GUTK stabilized FBXW7 protein levels during release from the quiescence. The critical role of FBXW7 was confirmed using siRNA knockdown, which impaired the inhibitory effect of GUTK on c-MYC protein levels and cell cycle re-entry. Administration of GUTK, either in vitro prior to transplantation or in vivo, suppressed the growth of quiescent prostate cancer cell xenografts. Furthermore, elevation of FBXW7 protein levels and reduction of c-MYC protein levels were found in the xenografts of GUTK-treated compared with vehicle-treated mice. Hence, we have identified a compound that is capable of impeding cell cycle re-entry by quiescent PTEN(null)/p53(WT) and PTEN(null)/p53(mut) prostate cancer cells likely by promoting c-MYC protein degradation through stabilization of FBXW7. Its usage as a clinical modality to prevent prostate cancer progression should be further evaluated.

Cdk-mediated phosphorylation of Chk1 is required for efficient activation and full checkpoint proficiency in response to DNA damage

Here, we show that activation of the checkpoint effector kinase Chk1 in response to irradiation-induced DNA damage is minimal in G1, maximal during S-phase and diminishes as cells enter G2. In addition, formation of irradiation-induced replication protein A (RPA)-coated single-stranded DNA (RPA-ssDNA), a structure required for ATM and Rad3-related (ATR)-Chk1 activation, occurs in a broadly similar pattern. Cyclin-dependent kinase (Cdk) activity is thought to promote RPA-ssDNA formation by stimulating DNA strand resection at double-strand breaks (DSBs), providing one possible mechanism of imposing cell cycle dependence on DNA damage signaling. However, it has recently been shown that Chk1 itself is also subject to Cdk-mediated phosphorylation at serines 286 and 301 (S286 and 301). We show that Chk1 S301 phosphorylation increases as cells progress through S and G2 and that both Cdk1 and Cdk2 are likely to contribute to this modification in vivo. We also find that substitution of S286 and S301 with non-phosphorylatable alanine residues strongly attenuates DNA damage-induced Chk1 activation and G2 checkpoint proficiency, but does not eliminate the underlying cell cycle dependence of Chk1 regulation. Taken together, these data indicate that Cdk activity regulates multiple steps in the DNA damage response pathway including full activation of Chk1 and checkpoint proficiency.

Upregulation of DNMT1 mediated by HBx suppresses RASSF1A expression independent of DNA methylation

The hepatitis B virus (HBV) X protein (HBx) plays a key role in the molecular pathogenesis of HBV-related hepatocellular carcinoma (HCC). However, its critical gene targets remain largely unknown. RASSF1A gene (Ras-association domain family 1A, RASSF1A), a tumor-suppressor gene, is frequently found to be hypermethylated and downregulated in HCC. In the present study, we investigated whether HBx is involved in the hypermethylation and downregulation of RASSF1A and we examined the potential regulation mechanisms. RT-PCR analysis was used to determine RASSF1A and HBx expression in 9 liver cell lines and the results showed that RASSF1A expression was relatively low in HBx-positive cells. Notably, RASSF1A was downregulated in HepG2.2.15 cells, as compared to HepG2 cells. Further analysis revealed that HBx transfection suppressed RASSF1A expression and HBx knockdown induced its expression. Enforced HBx suppressed RASSF1A and meanwhile induced DNMT1 and DNMT3B expression. In addition, RASSF1A is negatively regulated by DNMT1. ChIP analysis using an antibody against DNMT1 revealed that HBx enhanced the binding of DNMT1 to the RASSF1A promoter but the inhibition of RASSF1A by HBx is DNA methylation-independent as detected by methylation-specific PCR (MSP). Further studies using MSP and bisulfite genomic sequencing (BGS) revealed that no significant methylation changes were observed for regional methylation levels of RASSF1A in DNMT1 knockdown cells, although methylation levels of specific CpG sites at the predicted binding sites for the Sp1 and USF transcription factors were reduced. Additionally, RASSF1A was downregulated in HBV-associated HCC (HBV-HCC) as detected by RT-PCR and immunohistochemistry suggesting RASSF1A expression may be related to HBx in HCC and the clinical relevance of our observations. Collectively, our data showed that HBx suppressed RASSF1A expression via DNMT1 and offered a new mechanism of RASSF1A inactive in HCC in addition to the widely known DNA methylation, enriching the epigenetic mechanism by which HBx contributes to the pathogenesis of HBV-HCC.

Is metformin still the most efficacious first-line oral hypoglycaemic drug in treating type 2 diabetes? A network meta-analysis of randomized controlled trials

OBJECTIVES

The objective of the study is to compare the efficacy of hypoglycaemic drugs for type 2 diabetes mellitus (T2DM) by network meta-analysis of randomized controlled trials (RCTs).

METHODS

We compared 11 major oral hypoglycaemic drugs under five categories evaluated by RCTs as drug monotherapy for the patients with T2DM, measuring glycosylated haemoglobin (%) or fasting plasma glucose (mmol L-1 ) as outcomes. RCT quality was assessed with the Cochrane risk of bias tool. Network meta-analysis estimated the mean differences and 95% credible intervals. Subgroup and sensitivity analyses were performed to determine the results robustness. The Grading of Recommendation, Assessment, Development, and Evaluation evidence strength was assessed.

RESULTS

Seventy-five RCTs including 33,830 patients were identified. Their study quality was high. Regarding glycosylated haemoglobin, top three anti-diabetics were repaglinide (mean differences -1.39 [95% credible intervals -1.75 to -1.03]), gliclazide (-1.37 [-2.04 to -0.71]) and metformin (-1.13 [-1.37 to -0.90]), against placebo. Regarding fasting plasma glucose, top three anti-diabetics were repaglinide (-2.01 [-2.75 to -0.97]), metformin (-1.72 [-2.16 to -1.27]) and glipizide (-1.57 [-2.44 to -0.64]), against placebo. There was no difference between metformin and repaglinide. Subgroup and sensitivity analyses found the results to be robust. The evidence strength was moderate to high.

CONCLUSION

This meta-analysis showed that repaglinide and metformin would be the most efficacious oral drugs for first-line monotherapy of T2DM.

HBx represses RIZ1 expression by DNA methyltransferase 1 involvement in decreased miR-152 in hepatocellular carcinoma

Hepatitis B virus (HBV) is mainly suspected to promote hepatocellular carcinoma (HCC) development by epigenetic alteration. The HBV X protein (HBx) plays a key role in the molecular pathogenesis of HBV-related HCC. However, the mechanism of HBx-mediated hepatocarcinogenesis remains to be elucidated. RIZ1 gene, a candidate HCC suppressor gene, is frequently found to be hypermethylated and downregulated in HCC. In the present study, we show that the expression of RIZ1 was downregulated in 65% HCC tissues. Decreased expression of RIZ1 was restored by 5'-Aza in MHCC-97H HCC cell lines. HBx recombinant transfection increased DNMT1 expression level and suppressed RIZ1 expression. Moreover, knockdown of DNMT1 by siRNA restored RIZ1 expression in HCC cell SMMC-7721 and reduced methylated CpG sites of RIZ1. ChIP results showed that DNMT1 protein could bind to RIZ1 promoter, and this interaction was further enhanced with the transfected HBX recombinant. Moreover, miR-152 was decreased and involved in upregulation of DNMT1 in HBx transfected cells, at least partly, contributed to the epigenetic inactivation of RIZ1. Taken together, our data found that HBx repressed RIZ1 expression via DNMT1, which offered a new mechanism of RIZ1 inactivation in HCC, except for the widely known DNA methylation. These results enriched the epigenetic mechanism by which HBx contributes to pathogenesis of HBV-HCC.

Effects of feeding lutein on production performance, antioxidative status, and milk quality of high-yielding dairy cows

This experiment was conducted to determine the influences of supplementing different levels of an additive containing lutein in the diet of Chinese Holstein lactating cows on production performance, antioxidative plasma metabolites, and milk quality. This study was performed on 60 multiparous Holstein dairy cows in peak lactation. The cows were randomly allocated to 1 of 4 homogeneous treatments, with lutein preparation (extracted from marigolds; effective lutein content was 2%) added at levels of 0, 100, 150, and 200 g/d per head, with the actual available amounts being 0, 2, 3, and 4 g of lutein/d per head, respectively. The experiment lasted for 13 wk, with the first week for adaptation. Milk yield and milk compositions were recorded weekly, and milk concentrations of lutein, dry matter intake, and antioxidative blood index were analyzed in the first, fourth, seventh, and thirteenth week of the study. The results showed that adding lutein in the diet had no effect on dry matter intake compared with the control group; however, it slowed down the trend of decline in milk yield, and had a linear incremental effect on milk yield with increasing concentration of lutein. Dietary lutein tended to quadratically increase the percentage of milk fat, and linearly increased milk lactose concentration, with the highest value when treated at 200 g of lutein preparation/d per head, and decreased somatic cell count, with the lowest values when treated with 150 and 200 g of lutein preparation/d per head. The concentration of lutein in milk linearly increased with the incorporation of the additive, with a value of 0.59, 0.70, 1.20, and 1.50 μg/100mL when treated with 0, 100, 150, and 200 g/d, respectively. Total plasma antioxidant capacity tended to linearly increase in cows fed lutein preparation, whereas plasma superoxide dismutase and glutathione peroxidase activities did not differ significantly. In conclusion, addition of lutein in the diet could improve the production performance and health status of dairy cows.

Promoter polymorphisms of DNA methyltransferase 3B and risk of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most common solid tumors worldwide. Epigenetic changes in gene expression, including DNA methylation and histone modifications, may contribute to the development of HCC. Polymorphisms of the DNA methyltransferase 3B (DNMT3B) gene may affect the activity of this enzyme and increase the susceptibility to several types of cancer, including HCC. To confirm this hypothesis, we investigated the association between single-nucleotide polymorphisms-149C>T (rs2424913) and -579G>T (rs1569686) in the promoter region of DNMT3B and the risk of HCC. DNMT single-nucleotide polymorphisms (SNPs) were genotyped by polymerase chain reaction-restriction fragment length polymorphism in 108 HCC patients and 240 healthy controls matched for age, gender and ethnicity. The DNMT3B-149 TT genotype was not significantly associated with an increased risk of HCC. The frequency of DNMT3B-149C was 0.46% in HCC patients and 1.39% in healthy individuals, whereas the frequency of DNMT3B-579G was 8.33% in HCC patients and 10.42% in healthy individuals. No significant differences were observed in the genotype or allelic distribution between HCC patients and controls. In conclusion, DNMT3B-149C>T and -579G>T polymorphisms are not significantly associated with an increased risk of HCC. These results demonstrated that these particular SNPs may not be used as biomarkers to predict susceptibility to HCC.

Ventricular shape and relative position abnormalities in preterm neonates

Recent neuroimaging findings have highlighted the impact of premature birth on subcortical development and morphological changes in the deep grey nuclei and ventricular system. To help characterize subcortical microstructural changes in preterm neonates, we recently implemented a multivariate tensor-based method (mTBM). This method allows to precisely measure local surface deformation of brain structures in infants. Here, we investigated ventricular abnormalities and their spatial relationships with surrounding subcortical structures in preterm neonates. We performed regional group comparisons on the surface morphometry and relative position of the lateral ventricles between 19 full-term and 17 preterm born neonates at term-equivalent age. Furthermore, a relative pose analysis was used to detect individual differences in translation, rotation, and scale of a given brain structure with respect to an average. Our mTBM results revealed broad areas of alterations on the frontal horn and body of the left ventricle, and narrower areas of differences on the temporal horn of the right ventricle. A significant shift in the rotation of the left ventricle was also found in preterm neonates. Furthermore, we located significant correlations between morphology and pose parameters of the lateral ventricles and that of the putamen and thalamus. These results show that regional abnormalities on the surface and pose of the ventricles are also associated with alterations on the putamen and thalamus. The complementarity of the information provided by the surface and pose analysis may help to identify abnormal white and grey matter growth, hinting toward a pattern of neural and cellular dysmaturation.

The DNMT3B -579 G>T promoter polymorphism and risk of lung cancer

The present study aimed to investigate the association of the -579 G>T polymorphism in the DNMT3B promoter with susceptibility to lung cancer. A total of 174 lung cancer patients and 135 healthy controls from the northern part of China were enrolled, and were matched for gender and age. All subjects were genotyped by polymerase chain reaction-restriction-fragment length polymorphism analysis and confirmed by DNA sequencing. Stratification analyses were used to study the subgroups of subjects by age and gender, and evaluate the association between the -579 G>T polymorphism and the genetic susceptibility to lung cancer. The results revealed that individuals with the DNMT3B -579 GT genotype had a significantly decreased risk of lung cancer [odds ratio (OR), 0.517; 95% confidence interval (CI), 0.273-0.981] compared with those with a -579 TT genotype in the studied population. However, the deviation was significant (OR, 0.138, 95% CI, 0.034-0.549) between the risk of lung cancer and the GT and GG genotype, when the smoking factor was considered. The data from this study indicate that the DNMT3B genetic polymorphism varies among various races, ethnic groups and geographical areas. The DNMT3B -579 G>T polymorphism may contribute to the genetic susceptibility to lung cancer.

Delayed onset of hyperglycaemia in a mouse model with impaired glucagon secretion demonstrates that dysregulated glucagon secretion promotes hyperglycaemia and type 2 diabetes

AIMS/HYPOTHESIS

Type 2 diabetes is caused by relative deficiency of insulin secretion and is associated with dysregulation of glucagon secretion during the late stage of diabetes development. Like insulin secretion from beta cells, glucagon secretion is dependent on calcium signals and a calcium sensing protein, synaptotagmin-7. In this study, we tested the relative contribution of dysregulated glucagon secretion and reduced insulin release in the development of hyperglycaemia and type 2 diabetes by using synaptotagmin-7 knockout (KO) mice, which exhibit glucose intolerance, reduced insulin secretion and nearly abolished Ca(2+)-stimulated glucagon secretion.

METHODS

We fed the synaptotagmin-7 KO and control mice with a high-fat diet (HFD) for 14 weeks, and compared their body weight, glucose levels, glucose and insulin tolerance, and insulin and glucagon secretion.

RESULTS

On the HFD, synaptotagmin-7 KO mice showed progressive impairment of glucose tolerance and insulin secretion, along with continued maintenance of a low glucagon level. The control mice were less affected in terms of glucose intolerance, and showed enhanced insulin secretion with a concurrent increase in glucagon levels. Unexpectedly, after 14 weeks of HFD feeding, only the control mice displayed resting hyperglycaemia, whereas in synaptotagmin-7 KO mice defective insulin secretion and reduced insulin sensitivity were not sufficient to cause hyperglycaemia in the absence of enhanced glucagon secretion.

CONCLUSIONS/INTERPRETATION

Our data uncover a previously overlooked role of dysregulated glucagon secretion in promoting hyperglycaemia and the ensuing diabetes, and strongly suggest maintenance of adequate regulation of glucagon secretion as an important therapeutic target in addition to the preservation of beta cell function and mass in the prevention and treatment of diabetes.

How well can we quantify dust deposition to the ocean?

Deposition of continental mineral aerosols (dust) in the Eastern Tropical North Atlantic Ocean, between the coast of Africa and the Mid-Atlantic Ridge, was estimated using several strategies based on the measurement of aerosols, trace metals dissolved in seawater, particulate material filtered from the water column, particles collected by sediment traps and sediments. Most of the data used in this synthesis involve samples collected during US GEOTRACES expeditions in 2010 and 2011, although some results from the literature are also used. Dust deposition generated by a global model serves as a reference against which the results from each observational strategy are compared. Observation-based dust fluxes disagree with one another by as much as two orders of magnitude, although most of the methods produce results that are consistent with the reference model to within a factor of 5. The large range of estimates indicates that further work is needed to reduce uncertainties associated with each method before it can be applied routinely to map dust deposition to the ocean. Calculated dust deposition using observational strategies thought to have the smallest uncertainties is lower than the reference model by a factor of 2-5, suggesting that the model may overestimate dust deposition in our study area.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

How well can we quantify dust deposition to the ocean?

Deposition of continental mineral aerosols (dust) in the Eastern Tropical North Atlantic Ocean, between the coast of Africa and the Mid-Atlantic Ridge, was estimated using several strategies based on the measurement of aerosols, trace metals dissolved in seawater, particulate material filtered from the water column, particles collected by sediment traps and sediments. Most of the data used in this synthesis involve samples collected during US GEOTRACES expeditions in 2010 and 2011, although some results from the literature are also used. Dust deposition generated by a global model serves as a reference against which the results from each observational strategy are compared. Observation-based dust fluxes disagree with one another by as much as two orders of magnitude, although most of the methods produce results that are consistent with the reference model to within a factor of 5. The large range of estimates indicates that further work is needed to reduce uncertainties associated with each method before it can be applied routinely to map dust deposition to the ocean. Calculated dust deposition using observational strategies thought to have the smallest uncertainties is lower than the reference model by a factor of 2-5, suggesting that the model may overestimate dust deposition in our study area.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

195 EFFECTS OF GSK3 INHIBITOR ON THE PLURIPOTENCY MAINTENANCE OF BUFFALO EMBRYONIC STEM-CELL-LIKE CELLS

In this study, to explore the effects and mechanism of Wnt/β-catenin signalling pathway on the maintenance of pluripotency of buffalo embryonic stem-cell-like cells (buffalo ESC-like cells), the GSK3 inhibitors BIO and CHIR99021 were added throughout the experiment – i.e. from buffalo inner cell mass (ICM) culture to ESC-like line generation. The buffalo ICM were respectively cultured in the medium containing 0.5 μg mL–1 BIO and 5 mmol L–1 CHIR99021. The percentage of ICMs attachment and primary colony formation were observed, and found that there was no significant difference in the ICMs attachment rate among of the BIO, CHIR99021, and the control groups (91.18% and 92.98% v. 94.59%; P > 0.05). Treating ICMs with CHIR99021 resulted in more primary colony formation rate compared with the control group (77.71% v. 55.41%; P < 0.05). The proliferation rate of primary colonies of buffalo ESC-like cells was detected by bromodeoxyuridine immunofluorescence techniques. The results show that the proliferation rate of primary colonies in the group of buffalo ESC-like cells treated with CHIR99021 was significantly higher than that of the control group on Day 1, Day 3, Day 4, and Day 5 (P < 0.05), and it was also evidently higher than that of control group only on Day 1 (P < 0.05) in the group of BIO, but there was no significant difference in other days (P > 0.05). The mRNA expression level of proliferation marker PCNA of ESC-like cells was significantly up-regulated in both CHIR99021 and BIO treatment groups (P < 0.05), however, treating buffalo ESC-like cells with CHIR99021 significantly up-regulated the expression of pluripotent gene Oct4 and Sox2 (P < 0.05), but had no effect on pluripotent gene Nanog expression (P > 0.05). Oct4 expression was significantly increased (P < 0.05), and the expression of Sox2 and Nanog were significantly decreased (P < 0.05) in the group of BIO treatment. Furthermore, the relative protein level of β-catenin (the downstream effector of Wnt/β-catenin signalling pathway) and the mRNA expression level of c-Myc (the downstream target gene of Wnt/β-catenin signalling pathway) were significantly increased when buffalo ESC-like cells respectively treated with CHIR99021 and BIO (P < 0.05). In conclusion, treating buffalo ESC-like cells with GSK3 inhibitors CHIR99021 can promote proliferation of buffalo ESC-like cells, maintain their undifferentiated state, and up-regulate the expression levels of β-Catenin and c-Myc in buffalo ESC-like cells. These results indicate that Wnt/β-catenin signalling pathway plays an important role in regulation of self-renewal of buffalo ESC-like cells. This work was funded by the China High Technology Development Program (2011AA100607), China Natural Science Foundation (31072033), and Guangxi Science Foundation (2012GXNSFFA060004).