Design, synthesis, and biological evaluation of 4-(2-fluorophenoxy)-7-methoxyquinazoline derivatives as dual EGFR/c-Met inhibitors for the treatment of NSCLC

In non-small cell lung cancer (NSCLC) treatment, aberrant expression of c-mesenchymal-epithelial transition factor (c-Met) has been identified as a driving factor in epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) resistance. Unfortunately, none of the EGFR/c-Met dual-target inhibitors have successfully passed clinical trials. Hence, based on molecular docking analysis and combination principles of EGFR and c-Met inhibitors, three series of 4-(2-fluorophenoxy)-7-methoxyquinazoline derivatives as new EGFR/c-Met inhibitors were designed, synthesized, and evaluated for their biological activities. Among these compounds, TS-41 displayed the best inhibitory activity against EGFRL858R and c-Met kinases, with an IC50 value of 68.1 nM and 0.26 nM respectively. Moreover, it also showed excellent inhibitory activity on three NSCLC cell lines A549-P, H1975 and PC-9 with IC50 values ranging from 1.48 to 2.76 μM. Flow cytometry assays demonstrated that TS-41 induced apoptosis and cell cycle arrest of A549-P cells in a concentration-dependent manner, corresponding to JC-1 staining assay results. Western blot analysis revealed that TS-41 significantly downregulated the phosphorylation of EGFR, c-Met, and downstream AKT at molecular level. Importantly, TS-41 exhibited potent in vivo anticancer efficacy in an A549-P-bearing allograft nude mouse model at a dose of 60 mg/kg with a tumor growth inhibition rate of 55.3 % compared with Afatinib (46.4 %), as well as low hemolytic toxicity and organ toxicity. Molecular docking results showed that TS-41 was well embedded into the cavity of EGFR (PDB: 5GMP) and c-Met (PDB: 3LQ8) proteins, respectively. In summary, TS-41 is a high-efficiency and low-toxicity EGFR/c-Met inhibitor for the treatment of NSCLC and is worthy of further exploration.

Novel quinazoline-based dual EGFR/c-Met inhibitors overcoming drug resistance for the treatment of NSCLC: Design, synthesis and anti-tumor activity

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR TKIs) have demonstrated the ability to impede tumor cell proliferation by suppressing EGFR expression. Nonetheless, patients undergoing treatment may acquire resistance, which may occur through an EGFR-dependent (such as T790M mutation) or an EGFR-independent (such as c-Met amplification) manner. Therefore, developing dual-target inhibitors might present a potential avenue for addressing treatment-acquired resistance in patients. Herein, we designed, synthesized, and screened several novel 4-phenoxyquinazoline derivatives, aiming to identify a potent dual EGFR/c-Met inhibitor for the treatment of NSCLC, among which H-22 emerged as the most promising candidate exhibiting significant antitumor properties. Moreover, we assessed the in vitro inhibitory effect of H-22 on EGFR kinase and c-Met kinase in five cancer cell lines. In addition, a series of functional experiments (cell cycle, apoptosis assays, in vitro/in vivo animal model, etc.) were conducted to further investigate the anti-tumor mechanisms of H-22. The present study revealed that H-22 exhibited strong antitumor activity both in vitro and in vivo. Interestingly, H-22 exhibited anti-proliferative activity (2.27-3.35 μM) similar to Afatinib against all five cancer cells, with inhibitory functions against EGFRWT, EGFRL858R/T790M, and c-Met kinases at a concentration of 64.8, 305.4 and 137.4 nM, respectively. Cell cycle analysis indicated that the antiproliferative activity of H-22 was associated with its ability to cause G2/M arrest. Furthermore, in vivo data showed that H-22 could inhibit tumor growth in our xenograft models and induce apoptosis. Collectively, our findings uncovered that H-22 is a novel dual EGFR and c-Met inhibitor and a prospective anti-tumor therapeutic drug.

Depth profiles of microplastics in sediments from inland water to coast and their influential factors

Microplastics, plastic particles with a size smaller than 5 mm, are widely observed in the global environments and pose a growing threat as they accumulate and affect the environments in numerous ways. These particles can be transported from inland water to coast and disperse from surface water to deep sediments, especially the latter, while knowledge of the hidden microplastics in sediment layers is still lacking. Understanding the characteristics and behavior of microplastics in deep sediments from inland water to coast is crucial for estimating the present and future global plastic budget from land to seas. Herein, present knowledge of microplastic sedimentation from inland water to coast is reviewed, with a focus on the physical characteristics of microplastics and environmental factors that affect sedimentation. The abundance, shape, composition, and timeline of microplastics in sediment layers in rivers, floodplains, lakes, estuaries and coastal wetlands are presented. The abundance of microplastics in sediment layers varies across sites and may exhibit opposite trends along depth, and generally the proportion of relatively small microplastics increases with depth, while less is known about the vertical trends in the shape and composition of microplastics. Timeline of microplastics is generally linked to the sedimentation rate, which varies from millimeters to centimeters per year in the reviewed studies. The spatiotemporal characteristics of microplastic sedimentation depend on the settling and erosion of microplastics, which are determined by two aspects, microplastic characteristics and environmental factors. The former aspect includes size, shape and density influenced by aggregation and biofouling, and the latter includes dynamic forces, topographic features, bioturbation and human activities. The comprehensive review of these factors highlights the needs to further quantify the characteristics of microplastic sedimentation and explore the role of these factors in microplastic sedimentation on various spatiotemporal scales.

XS-2, a novel potent dual PI3K/mTOR inhibitor, exhibits high in vitro and in vivo anti-breast cancer activity and low toxicity with the potential to inhibit the invasion and migration of triple-negative breast cancer

Breast cancer has become the most commonly diagnosed cancer, surpassing lung cancer, with 2.26 million new breast cancers worldwide in 2020. Hence, there is an urgent need to develop effective molecularly targeted therapeutic drugs to treat breast cancer. In this paper, we designed, synthesized and screened a novel thiophene-triazine derivative, XS-2, as a potent dual PI3K/mTOR inhibitor for the treatment of breast cancer. Also, XS-2 was found to be potentially effective against triple-negative breast cancer (TNBC) in vitro during the investigation. We evaluated the in vitro inhibitory effect of XS-2 on 10 cancer cell lines by MTT and 6 kinases to investigated its in vivo antitumor activity in MCF-7 xenograft tumor-bearing BALB/c nude mice. In addition, the in vitro/in vivo toxicity to mice was also assessed by hemolytic toxicity, H&E staining and blood biochemical analysis. In order to investigate the antitumor mechanism of XS-2, a series of experiments were carried out in vitro/in vivo animal model and molecular biological levels such as the cell cycle and the apoptosis assay, real-time PCR, western blot, docking and molecular simulations analysis, etc. What's more, wound healing assay, Transwell and Western Blot were applied to explore the ability of XS-2 to inhibit the cell invasion and migration. The results showed that XS-2 exhibited strong antitumor activity both in vitro and in vivo. The inhibitory activities of XS-2 on ten cancer cell lines were ranging from 1.07 ± 0.11 to 0.002 ± 0.001 μM, which were 1565 times better than that of the lead compound GDC-0941, inhibitory activities against PI3Kα and mTOR kinases were 291.0 and 60.8 nM, respectively. Notably, XS-2 not only showed significant in vivo antitumor activity and low toxicity, with the tumor inhibition rate of 57.0 %, but also exhibited strong inhibitory in the expression of related proteins of PI3K pathway in tumor tissues. In addition, XS-2 significantly inhibited breast cancer MCF-7 and MDA-MB-231 cells in a concentration- and time-dependent manner, and inhibited the migration and invasion ability of MDA-MB-231 and MCF-7 cells. More than that, XS-2 could inhibit the increase of the expression levels of N-cadherin and vimentin upregulated by EGF and reversed the E-cadherin expression down regulated by EGF, resulting in inhibiting EMT in MCF-7 and MDA-MB-231 cells. The results showed that XS-2 was expected to be successfully developed as a high-efficiency and low-toxicity breast cancer therapeutic drug with the potential to inhibit the invasion and migration of TNBC. This provides a new research idea for the treatment of TNBC, which is of great significance.

New insights into thiamphenicol biodegradation mechanism by Sphingomonas sp. CL5.1 deciphered through metabolic and proteomic analysis

Biological treatment is an efficient and economical process to remove thiamphenicol (TAP) residues from the environment. The discovery of TAP-degrading bacteria and the decryption of its biodegradation mechanism will be beneficial to enhance the biological removal of TAP. In this study, Sphingomonas sp. CL5.1 was found to be capable of catabolizing TAP as the sole carbon, nitrogen, and energy source. This strain could degrade 93.9% of 25 mg/L TAP in 36 h, and remove about 11.9% of the total organic carbon of TAP. A novel metabolism pathway of TAP was constructed, and the enzymes involved in TAP metabolism in strain CL5.1 were predicted via proteomic and metabolic analysis. TAP was proposed to be transformed to O-TAP via oxidation of C₃-OH and DD-TAP via dehydration of C₃-OH and dehydrogenation of C₁-OH. A novel glucose-methanol-choline (GMC) family oxidoreductase CapO was predicted to be involved in the oxidation of C₃-OH. O-TAP was supposed to be further cleaved into DCA, glycine, and PMB. Glycine might be a pivotal direct nitrogen source for strain CL5.1, and it could be involved in nitrogen metabolism through the glycine cleavage system or directly participate in the biosynthetic processes.

Chloramphenicol biodegradation by enriched bacterial consortia and isolated strain Sphingomonas sp. CL5.1: The reconstruction of a novel biodegradation pathway

Figuring out the comprehensive metabolic mechanism of chloramphenicol (CAP) is critical to improving CAP removal in the bioremediation process. In this study, CAP biodegradation by six consortia and isolated Sphingomonas sp. CL5.1 were systematically investigated using the combination of high-performance liquid chromatography-quadrupole time-of-flight mass spectrometry, second-generation, and third-generation sequencing technologies. The CAP-degrading capability of six consortia was enhanced while CAP mineralization rate declined after long-term enrichment. The microbial community structures of six consortia were all simplified with 69%-82% decline in species richness after continuous passages for one year. The core genera of consortia CL and CH included Sphingomonas, Cupriavidus, Burkholderia, Chryseobacterium, and Pigmentiphaga, which accounted for over 98% of the total population. Sphingomonas was discovered as a new CAP degrader that could subsist on CAP as the sole carbon, nitrogen, and energy sources. Sphingomonas sp. CL5.1 was able to completely remove 120 mg/L CAP within 48 hours with a mineralization rate of 50.4%. The presence of acetate or nitrite could inhibit CAP metabolization by strain CL5.1. Four CAP metabolic pathways were constructed, including modification of the C₃ hydroxyl group of CAP via acetylation, oxidization, dehydration and the bond cleavage between C₁ and C₂. C₃ hydroxyl group dehydration and C₁-C₂ bond-cleavage were first reported regarding to CAP biotransformation. Strain CL5.1 played a core role in the consortia and was responsible for C3 hydroxyl oxidation, C3 dehydration, and C1-C2 bond cleavage. Genomic information of strain CL5.1 revealed the further mineralization pathways of downstream product p-nitrobenzoic acid via ortho- and meta-cleavage.

Small RNA sequencing reveals miRNAs important for hypoxic adaptation in the Tibetan chicken

1. The Tibetan chicken, which is an indigenous breed living on the Tibetan Plateau, exhibits hypoxic adaptations to its high-altitude environment. However, the molecular mechanism behind this hypoxic adaptation is still unclear. This study aimed to investigate differentially expressed miRNAs involved in hypoxic adaptation through high-throughput RNA sequencing. 2. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to verify the differentially expressed miRNAs and their target genes in chicken embryonic heart tissues and fibroblasts. Luciferase reporter assays were performed to confirm the relationship between miRNAs and target genes. 3. The study identified 37 differentially expressed miRNAs in Tibetan chicken embryonic heart tissues, including 20 up- and 17 down-regulated miRNAs, compared to those found in lowland chickens. Differentially expressed miRNAs were mainly involved in biological processes, such as cell cycle arrest, toll-like receptor signalling pathways, and I-kappa B kinase/NF-kappa B signalling. The data showed that gga-miR-34 c-5p was significantly upregulated in Tibetan chicken tissues and hypoxic fibroblasts, while EHHADH, a target gene of gga-miR-34 c-5p, was downregulated. Moreover, gga-miR-34 c-5p dramatically decreased the luciferase activity of the wild EHHADH, whereas no effect on the mutational EHHADH was found. 4. This study identified miRNA expression profiles in the Tibetan chicken and suggested that miR-34 c-5p acts as a novel miRNA associated with hypoxic adaptation. This facilitates the understanding of molecular mechanisms that underlie long-term exposure to hypoxia.

Discovery of Triazolo-pyridazine/-pyrimidine Derivatives Bearing Aromatic (Heterocycle)-Coupled Azole Units as Class II c-Met Inhibitors

Two series of novel triazolo-pyridazine/-pyrimidine derivatives were designed, synthesized, and evaluated for their inhibitory activity against c-Met kinase, as well as three c-Met overexpressed cancer cell lines (A549, MCF-7, and HeLa) and one normal human hepatocytes cell line LO2 in vitro. The pharmacological data indicated that most of the tested compounds showed moderate cytotoxicity, and the most promising compound 12e exhibited significant cytotoxicity against A549, MCF-7, and HeLa cell lines with IC₅₀ values of 1.06 ± 0.16, 1.23 ± 0.18, and 2.73 ± 0.33 μM, respectively. Moreover, the inhibitory activity of compound 12e against c-Met kinase (IC₅₀ = 0.090 μM) was equal to that of Foretinib (IC₅₀ = 0.019 μM). The result of the acridine orange (AO) single staining test demonstrated that compound 12e could remarkably induce apoptosis of A549 cells. The results of apoptosis and cycle distribution of cells showed that compound 12e could induce late apoptosis of A549 cells and stimulate A549 cells arresting in the G0/G1 phase. Structure-activity relationships (SARs), pharmacological results, and docking studies indicated that the introduction of 5-methylthiazole fragment to the five-atom moiety was beneficial for the activity. So far, the existing data indicated that compound 12e may become a potential class II c-Met inhibitor.

Exploration of reaction rates of chlorine dioxide with tryptophan residue in oligopeptides and proteins

Chlorine dioxide (ClO₂), an alternative disinfectant to chlorine, has a superior ability to inactivate microorganisms, in which protein damage has been considered as the main inactivation mechanism. However, the reactivity of ClO₂ with amino acid residues in oligopeptides and proteins remains poorly investigated. In this research, we studied the reaction rate constants of ClO₂ with tryptophan residues in five heptapeptides and four proteins using stopped-flow or competition kinetic method. Each heptapeptide and protein contain only one tryptophan residue and the reactivity of tryptophan residue with ClO₂ was lower than that of free tryptophan (3.88 × 10⁴ (mol/L)^-1sec^-1 at pH 7.0). The neighboring amino acid residues affected the reaction rates through promoting inter-peptide aggregation, changing electron density, shifting pK_a values or inducing electron transfer via redox reactions. A single amino acid residue difference in oligopeptides can make the reaction rate constants differ by over 60% (e.g. 3.01 × 10⁴ (mol/L)^-1sec^-1 for DDDWNDD and 1.85 × 10⁴ (mol/L)^-1sec^-1 for DDDWDDD at pH 7.0 (D: aspartic acid, W: tryptophan, N: asparagine)). The reaction rates of tryptophan-containing oligopeptides were also highly pH-dependent with higher reactivity for deprotonated tryptophan than the neutral specie. Tryptophan residues in proteins spanned a 4-fold range reactivity toward ClO₂ (i.e. 0.84 × 10⁴ (mol/L)^-1sec^-1 for ribonuclease T1 and 3.21 × 10⁴ (mol/L)^-1sec^-1 for melittin at pH 7.0) with accessibility to the oxidant as the determinating factor. The local environment surrounding the tryptophan residue in proteins can also accelerate the reaction rates by increasing the electron density of the indole ring of tryptophan or inhibit the reaction rates by inducing electron transfer reactions. The results are of significance in advancing understanding of ClO₂ oxidative reactions with proteins and microbial inactivation mechanisms.

P6231Iron status and risk of cardio-metabolic diseases in European adults: a Mendelian randomization study

Background

Observational studies have reported conflicting results about the associations of iron status with risk of cardio-metabolic diseases but such studies are constrained by confounding and reverse causality.

Purpose

To assess the causal relevance of iron status biomarkers (transferrin, serum iron, and ferritin) for risk of coronary artery diseases (CAD), ischaemic stroke (IS), and type 2 diabetes (T2D), using Mendelian randomization (MR).

Methods

Effect size estimates for genetic variants associated with iron status biomarkers were obtained from the Genetics of Iron Status consortium (transferrin saturation, serum iron, and ferritin: n=48,972). The corresponding effects of these variants on the risk of CAD, IS and T2D were obtained from a meta-analysis of unrelated participants of European ancestry in the UK Biobank (UKB), together with previously recruited participants in CARDIOGRAMplusC4D (total n=90,377 CAD cases), MEGASTROKE (total n=43,381 IS cases) and DIAGRAM (total n=74,124 T2D cases), respectively. The main analysis used a two-sample inverse-variance weighted MR, while the sensitivity analyses used weighted-median, weighted-mode, MR-PRESSO, and MR-Egger approaches.

Results

MR analysis demonstrated significant inverse association of each of the three genetically-instrumented iron status biomarker with risk of CAD (transferrin saturation OR=0.96 [95% CI: 0.92–0.99], p=0.02; serum iron OR=0.93 [0.89–0.97], p=0.001; and ferritin OR=0.86 (0.79–0.94), p=0.001, per 1 SD higher level). In contrast, these iron status biomarkers showed positive associations with risk of T2D (transferrin saturation OR=1.06 [1.01–1.11], p=0.01; serum iron OR=1.06 [0.99–1.13], p=0.07; and ferritin OR=1.12 [0.99–1.26], p=0.06, per 1 SD higher level). There was positive, but non-significant, association of IS with each of the iron status biomarker analysed. Sensitivity analyses using several different MR approaches yielded concordant results.

Conclusions

Among European adults, iron status appeared to have causal associations, but in opposite directions, with the risk of CHD and T2D. Our findings highlight the need for caution about strategies for advocating iron supplementation in individuals with normal haemoglobin levels for prevention of CAD.

Acknowledgement/Funding

British Heart Found, Medical Research Council, Wellcome Trust, NIHR Biomedical Research Centre, Oxford

Disinfection byproducts and their toxicity in wastewater effluents treated by the mixing oxidant of ClO2/Cl2

Mixing oxidant of chlorine dioxide (ClO₂) and chlorine (Cl₂) often applied in water disinfection. Two secondary wastewater effluents at different ammonium-N levels (0.1 and 1.6 mg N L^-1) were treated with the mixing oxidant (ClO₂/Cl2) to evaluate the formation of disinfection byproducts (DBPs) and the associated cytotoxicity of treated wastewaters. The total chlorine concentrations of ClO₂ and Cl₂ were maintained at 10 mg L^-1 as Cl₂ with varied mixing ratios of ClO₂ to Cl₂. The formation of 37 halogenated DBPs, including nitrogenous, brominated and iodinated analogues, and 2 inorganic DBPs (chlorite and chlorate) was examined. The sum concentrations of the halogenated DBPs were reduced remarkably with decreasing Cl₂ percentages, but each individual DBP group had distinct features. The regulated trihalomethanes reduced the most when ClO₂ was present in chlorination, but decreasing Cl₂ percentage from 70% to 30% was not quite effective to reduce the formation of iodinated trihalomethanes, haloacetic acids and haloacetontriles in low ammonium-N wastewater. The bromine and iodine substitution factors tend to increase with decreasing Cl₂ percentages, indicating that destruction of DBP precursors by ClO₂ favored bromine and iodine incorporation. Additionally, decreasing Cl₂ percentages in the mixing oxidant (ClO₂/Cl₂) was often accompanied with lower chlorate formation but higher chlorite formation. The toxicity of treated wastewaters was evaluated through two approaches: the calculated cytotoxicity based on the concentrations of detected DBPs and the experimental cytotoxicity using the Chinese hamster ovary (CHO) cells. The calculated cytotoxicity decreased with decreasing Cl₂ percentages, with haloacetonitriles and haloacetaldehydes as predominate contributors. However, the experimental cytotoxicity tests showed that treatment of high ammonium-N wastewater with ClO₂/Cl₂ exhibited considerable higher (> 3 times) cytotoxicity potency than using single disinfectant.

Chlorite formation during ClO2 oxidation of model compounds having various functional groups and humic substances

Chlorine dioxide (ClO₂) has been used as an alternative to chlorine in water purification to reduce the formation of halogenated by-products and give superior inactivation of microorganisms. However, the formation of chlorite (ClO₂^-) is a major consideration in the application of ClO₂. In order to improve understanding in ClO₂^- formation kinetics and mechanisms, this study investigated the reactions of ClO₂ with 30 model compounds, 10 humic substances and 2 surface waters. ClO₂^- yields were found to be dependent on the distribution of functional groups. ClO₂ oxidation of amines, di- and tri-hydroxybenzenes at pH 7.0 had ClO₂^- yields >50%, while oxidation of olefins, thiols and benzoquinones had ClO₂^- yields <50%. ClO₂^- yields from humic substances depended on the ClO₂ dose, pH and varied with different reaction intervals, which mirrored the behavior of the model compounds. Phenolic moieties served as dominant fast-reacting precursors (during the first 5 min of disinfection). Aromatic precursors (e.g., non-phenolic lignins or benzoquinones) contributed to ClO₂^- formation over longer reaction time (up to 24  h). The total antioxidant capacity (indication of the amount of electron-donating moieties) determined by the Folin-Ciocalteu method was a good indicator of ClO₂-reactive precursors in waters, which correlated with the ClO₂ demand of waters. Waters bearing high total antioxidant capacity tended to generate more ClO₂^- at equivalent ClO₂ exposure, but the prediction in natural water should be conservative.

ClO2 pre-oxidation changes the yields and formation pathways of chloroform and chloral hydrate from phenolic precursors during chlorination

Phenolic moieties in natural organic matter (NOM) are important precursors of disinfection by-products (DBPs). In this study, the formation of chloral hydrate from chlorination of seventeen phenolic compounds, including mono-, di- and tri-hydroxybenzenes, were evaluated and the role of chlorine dioxide (ClO₂) pre-oxidation on its formation pathways was explored. Chloroform, was also evaluated for comparison. Chlorination of resorcinol exhibited the highest chloral hydrate yield (2.83 ± 0.13%) followed by chlorination of 2,4,6-trichlorophenol (0.61 ± 0.03%). The median of chloral hydrate yields from the tested phenolic compounds was 0.22%. ClO₂ pre-oxidation reduced the yields of chloroform from phenol derivatives by 37-97%, except 4-methoxyphenol, catechol and 2,3-dihydroxyphenol. On the contrary, ClO₂ pre-oxidation of di- and tri-hydroxybenzenes tended to increase chloral hydrate yields in post-chlorination. Mixed results (both increases and decreases) were observed in chloral hydrate formation from chlorination of mono-hydroxybenzenes after ClO₂ pre-oxidation. The changes of their formation were dependent on ClO₂ pre-oxidation time and dosages. Identification of transformation products suggested that phenolic compounds were mainly converted to unsaturated carbonyl structures by ClO₂. Chlorine substituted benzoquinones and cyclopent-4-ene-1,3-diones were important transformation products after a series of ring open, decarboxylation, hydrolysis and chlorine substitution reactions. The changes in the formation yields of chloral hydrate and chloroform were governed by the difference in initial phenolic precursors and the transformation products after ClO₂ pre-oxidation. ClO₂ pre-oxidation in water treatment can effectively reduce chloroform formation but may have a risk of increasing chloral hydrate formation.

Differential UV-vis absorbance can characterize the reaction of organic matter with ClO2

UV-vis differential spectroscopy was applied to characterize and quantify the spectral changes after ClO₂ oxidation of ten humic substances, seven aromatic model compounds and four surface waters. The differential spectra of ten humic substances after ClO₂ oxidation all exhibited a peak near 230 nm and a broad absorbance band with a maximum at around 316 nm. The differential spectra after ClO₂ oxidation were distinguished from the one after chlorination, which was indicative of their different oxidation mechanisms. The differential spectra after ClO₂ treatment were well fitted by seven Gaussian bands with maxima at about 200, 225, 240, 276, 316, 385 and 457 nm. Differential absorbance at 316 nm and 400 nm (denoted as DA₃₁₆ and DA₄₀₀, respectively) were found to best quantify the degradation of organic matters during ClO₂ oxidation with negligible interferences from water matrixes. Oxidation of substituted functional groups on aromatic structures, rather than destruction of aromatic rings, was more responsible for chlorite formation. Spectral parameters-DA₃₁₆ and DA₄₀₀ showed strong correlations with ClO₂ consumption and chlorite formation during ClO₂ oxidation of humic substances and surface water samples. The results demonstrate that DA₃₁₆ and DA₄₀₀ can serve as promising indicators of chlorite formation and ClO₂ consumption, which provide a practical approach for online water quality monitoring during ClO₂ water purification.

Cannabis use and risk of schizophrenia: a Mendelian randomization study

Cannabis use is observationally associated with an increased risk of schizophrenia, but whether the relationship is causal is not known. Using a genetic approach, we took 10 independent genetic variants previously identified to associate with cannabis use in 32 330 individuals to determine the nature of the association between cannabis use and risk of schizophrenia. Genetic variants were employed as instruments to recapitulate a randomized controlled trial involving two groups (cannabis users vs nonusers) to estimate the causal effect of cannabis use on risk of schizophrenia in 34 241 cases and 45 604 controls from predominantly European descent. Genetically-derived estimates were compared with a meta-analysis of observational studies reporting ever use of cannabis and risk of schizophrenia or related disorders. Based on the genetic approach, use of cannabis was associated with increased risk of schizophrenia (odds ratio (OR) of schizophrenia for users vs nonusers of cannabis: 1.37; 95% confidence interval (CI), 1.09-1.67; P-value=0.007). The corresponding estimate from observational analysis was 1.43 (95% CI, 1.19-1.67; P-value for heterogeneity =0.76). The genetic markers did not show evidence of pleiotropic effects and accounting for tobacco exposure did not alter the association (OR of schizophrenia for users vs nonusers of cannabis, adjusted for ever vs never smoker: 1.41; 95% CI, 1.09-1.83). This adds to the substantial evidence base that has previously identified cannabis use to associate with increased risk of schizophrenia, by suggesting that the relationship is causal. Such robust evidence may inform public health messages about cannabis use, especially regarding its potential mental health consequences.

Size exclusion chromatography with online ICP-MS enables molecular weight fractionation of dissolved phosphorus species in water samples

Phosphorus (P) is an important and often limiting element in terrestrial and aquatic ecosystem. A lack of understanding of its distribution and structures in the environment limits the design of effective P mitigation and recovery approaches. Here we developed a robust method employing size exclusion chromatography (SEC) coupled to an ICP-MS to determine the molecular weight (MW) distribution of P in environmental samples. The most abundant fraction of P varied widely in different environmental samples: (i) orthophosphate was the dominant fraction (93-100%) in one lake, two aerosols and DOC isolate samples, (ii) species of 400-600 Da range were abundant (74-100%) in two surface waters, and (iii) species of 150-350 Da range were abundant in wastewater effluents. SEC-DOC of the aqueous samples using a similar SEC column showed overlapping peaks for the 400-600 Da species in two surface waters, and for >20 kDa species in the effluents, suggesting that these fractions are likely associated with organic matter. The MW resolution and performance of SEC-ICP-MS agreed well with the time integrated results obtained using conventional ultrafiltration method. Results show that SEC in combination with ICP-MS and DOC has the potential to be a powerful and easy-to-use method in identifying unknown fractions of P in the environment.

Occurrence of nitrogenous and carbonaceous disinfection byproducts in drinking water distributed in Shenzhen, China

A 12-month sampling program was conducted throughout a drinking water distribution system in Shenzhen and the data from 251 samples provide a comprehensive picture of the spatial and seasonal variability of 17 species disinfection by-products (DBPs) in a city with subtropical monsoon climate. The carbonaceous disinfection by-product (C-DBPs) included four trihalomethanes (THMs), three trihaloacetaldehydes (THAs) and two haloketones (HKs). Their median concentrations over the entire period were 19.9 μg/L, 3.4 μg/L and 1.4 μg/L, respectively. The nitrogenous DBPs (N-DBPs) monitored were four haloacetonitriles (HANs) and four haloacetamides (HAcAms). Their median levels were 2.0 μg/L and 1.5 μg/L, respectively. Low levels of brominated DBP species (bromine substitution factors ≤ 0.5) were observed. The BSF of each DBP class followed the trend: THMs ≈ DHAcAms > DHANs > THAs. All the DBP concentrations showed clear seasonal variations with the highest average concentrations in spring. Correlation analyses showed that the THMs and CH levels in Shenzhen drinking water could be used as statistical indicators of the levels of unregulated N-DBPs (0.4 < r < 0.7, p < 0.5). The results supplement the database of DBP occurrence in drinking water in China, and provide an important reference data set for DBP occurrence in cities with a subtropical monsoon climate around the world.

PPCP degradation by UV/chlorine treatment and its impact on DBP formation potential in real waters

The ultraviolet/chlorine (UV/chlorine) water purification process was evaluated for its ability to degrade the residues of pharmaceuticals and personal care products (PPCPs) commonly found in drinking water sources. The disinfection byproducts (DBPs) formed after post-chlorination were documented. The performance of the UV/chlorine process was compared with that of the UV/hydrogen peroxide (UV/H2O2) process in treating three types of sand-filtered natural water. Except caffeine and carbamazepine residues, the UV/chlorine process was found to be 59-99% effective for feed water with a high level of dissolved organic carbon and alkalinity, and 27-92% effective for water with a high ammonia content. Both chlorine radicals and hydroxyl radicals were found to contribute to the observed PPCP degradation. The removal efficiencies of chlorine- and UV-resistant PPCPs such as carbamazepine and caffeine were 2-3 times greater than in the UV/H2O2 process in waters not enriched with ammonia. UV/chlorine treatment slightly enhanced the formation chloral hydrate (CH), haloketone (HK) and trichloronitromethane (TCNM). It reduced haloacetonitrile (HAN) formation during the post-chlorination in comparison with the UV/H2O2 process. In waters with high concentrations of ammonia, the UV/chlorine process was only 5-7% more effective than the UV/H2O2 process, and it formed slightly more THMs, HKs and TCNM along with reduced formation of CH and HAN. The UV/chlorine process is thus recommended as a good alternative to UV/H2O2 treatment for its superior PPCP removal without significantly enhancing DBP formation.

Role of Chlorine Dioxide in N-Nitrosodimethylamine Formation from Oxidation of Model Amines

N-Nitrosodimethylamine (NDMA) is an emerging disinfection byproduct, and we show that use of chlorine dioxide (ClO2) has the potential to increase NDMA formation in waters containing precursors with hydrazine moieties. NDMA formation was measured after oxidation of 13 amines by monochloramine and ClO2 and pretreatment with ClO2 followed by postmonochloramination. Daminozide, a plant growth regulator, was found to yield 5.01 ± 0.96% NDMA upon reaction with ClO2, although no NDMA was recorded during chloramination. The reaction rate was estimated to be ∼0.0085 s(-1), and on the basis of our identification by mass spectrometry of the intermediates, the reaction likely proceeds via the hydrolytic release of unsymmetrical dimethylhydrazine (UDMH), with the hydrazine structure a key intermediate in NDMA formation. The presence of UDMH was confirmed by gas chromatography-mass spectrometry analysis. For 10 of the 13 compounds, ClO2 preoxidation reduced NDMA yields compared with monochloramination alone, which is explained by our measured release of dimethylamine. This work shows potential preoxidation strategies to control NDMA formation may not impact all organic precursors uniformly, so differences might be source specific depending upon the occurrence of different precursors in source waters. For example, daminozide is a plant regulator, so drinking water that is heavily influenced by upstream agricultural runoff could be at risk.

Investigation of disinfection byproducts formation in ferrate(VI) pre-oxidation of NOM and its model compounds followed by chlorination

This study investigated the effect of disinfection by-products (DBPs) formation in pre-oxidation with ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) and relationship between subsequent chlorination of Suwannee river natural organic matter (SRNOM) and eight model compounds containing moieties of alcohol, aldehyde, amines, amino acids, and phenol. The DBPs studied were trihalomethanes (THMs), chloral hydrate (CH), haloacetonitriles (HANs), and trichloronitromethane (TCNM). When the interaction of Fe(VI) and SRNOM was independently examined at pH 7.0, a decrease was seen in dissolved organic carbon and in the hydrophobic and hydrophilic fractions of NOM. With the model compounds, the results showed that Fe(VI) pre-oxidation and subsequent chlorination decreased the formation of THMs with most of the compounds except amines and glycine. The effect of Fe(VI) preoxidation on CH and HANs formation from model compounds varied and was dependent on ferrate doses. Fe(VI) pre-oxidation significantly enhanced TCNM formation, compared to without pre-oxidation, from subsequent chlorination of methylamine, dimethylamine and glycine and the formation increased with increasing doses of ferrate. Correlations of DBPs formation between SRNOM and model compounds were sought to identify the moieties involved in influencing the formation of DBPs. The generation of DBPs is described using the parent molecules and the kinetics and reaction products of Fe(VI)/chlorine oxidation.

Association between FTO polymorphism in exon 3 with carcass and meat quality traits in crossbred ducks

The fat mass and obesity-associated gene (FTO) is an excellent candidate gene that affects energy metabolism. Single nucleotide polymorphisms (SNPs) in FTO are associated with carcass and meat quality traits in pigs, cattle, and rabbits. The aim of this study was to investigate the association between novel SNPs in the FTO coding region and carcass and meat quality traits in 95 crossbred ducks, using DNA sequencing. We found two transitions G/A (SNP 387 and 473) within exon 3. SNP 387 was a synonymous mutation, whereas SNP 473 was a missense mutation. Association analysis suggested that SNP g.387G>A was significantly associated with all of the carcass traits measured, the intramuscular fat content (IMF), cooking yield (CY), pH values 45 min after slaughter (pH45m), drip losses from the breast muscle, and the leg muscle (P < 0.05). For SNP g.473G>A, the genotype AA exhibited greater leg muscle weight than the genotypes GG or AG (P < 0.05). The D value suggested that the two SNPs exhibited strong linkage disequilibrium. Three haplotypes (G1G2, G1A2, and A1A2) were significantly associated with IMF, CY, the a* value, and all of the carcass traits measured (P < 0.05). The results suggest that FTO is a candidate locus that affects carcass and meat quality traits in ducks.

Lowered Nudix type 5 expression leads to cellular senescence in IMR-90 fibroblast cells

The molecule 8-oxo-7,8-dihydroguanine (8-oxoGua), an oxidized form of guanine, can pair with adenine or cytosine during nucleic acid synthesis. RNA sequences that contain 8-oxoGua cause translational errors that lead to the synthesis of abnormal proteins. Human Nudix type 5 (NUDT5), a MutT-related protein, catalyzes the hydrolysis of 8-oxoGDP to 8-oxoGMP, thereby preventing the misincorporation of 8-oxoGua into RNA. To investigate the biological roles of NUDT5 in human fibroblast cells, we established cell lines with decreased levels of NUDT5 expression. In NUDT5 knockdown cells, the RNA oxidation levels were significantly higher, the rates of cellular senescence and cell apoptosis were significantly increased, and the cell viability was significantly decreased in comparison with control cells. These results suggested that the NUDT5 protein could play significant roles in the prevention of RNA oxidation and survival in human fibroblast cells.

The occurrence of disinfection by-products in municipal drinking water in China's Pearl River Delta and a multipathway cancer risk assessment

Disinfection byproducts were measured in the finished drinking water from ten water treatment plants in three Chinese cities - Guangzhou, Foshan and Zhuhai. A total of 155 water samples were collected in 2011 and 2012. The median (range) of trihalomethane (THM) and haloacetic acid (HAA) levels were 17.7 (0.7-62.7) μg/L and 8.6 (0.3-81.3) μg/L, respectively. Chloroform, dichloroacetic acid and trichloroacetic acid were the dominant species observed in Guangzhou and Foshan water, while brominated THMs predominated in water from Zhuhai. Haloacetonitriles, haloketones, chloral hydrate and trichloronitromethane were usually detected at levels ranging from unquantifiable (<0.2μg/L) to 12.2μg/L (choral hydrate). THMs and HAAs showed clear seasonal variations with the total concentrations higher in winter than in summer. Correlations among DBP levels varied, with the strongest linear correlation observed between chloroform and chloral hydrate levels (R(2)=0.77). The risk of cancer from ingestion, inhalation and dermal contact exposure to THMs was estimated. CHCl2Br contributed the highest percentage of the cancer risk from ingestion pathway and CHCl3 contributed the highest of cancer risk from inhalation pathway.

Apolipoprotein E isoform-specific regulation of dendritic spine morphology in apolipoprotein E transgenic mice and Alzheimer's disease patients

Dendritic spines are postsynaptic sites of excitatory input in the mammalian nervous system. Apolipoprotein (apo) E participates in the transport of plasma lipids and in the redistribution of lipids among cells. A role for apoE is implicated in regeneration of synaptic circuitry after neural injury. The apoE4 allele is a major risk factor for late-onset familial and sporadic Alzheimer's disease (AD) and is associated with a poor outcome after brain injury. ApoE isoforms are suggested to have differential effects on neuronal repair mechanisms. In vitro studies have demonstrated the neurotrophic properties of apoE3 on neurite outgrowth. We have investigated the influence of apoE genotype on neuronal cell dendritic spine density in mice and in human postmortem tissue. In order to compare the morphology of neurons developing under different apoE conditions, gene gun labeling studies of dendritic spines of dentate gyrus (DG) granule cells of the hippocampus were carried out in wild-type (WT), human apoE3, human apoE4 expressing transgenic mice and apoE knockout (KO) mice; the same dendritic spine parameters were also assessed in human postmortem DG from individuals with and without the apoE4 gene. Quantitative analysis of dendritic spine length, morphology, and number was carried out on these mice at 3 weeks, 1 and 2 years of age. Human apoE3 and WT mice had a higher density of dendritic spines than human E4 and apoE KO mice in the 1 and 2 year age groups (P<0.0001), while at 3 weeks there were no differences between the groups. These age dependent differences in the effects of apoE isoforms on neuronal integrity may relate to the increased risk of dementia in aged individuals with the apoE4 allele. Significantly in human brain, apoE4 dose correlated inversely with dendritic spine density of DG neurons cell in the hippocampus of both AD (P=0.0008) and aged normal controls (P=0.0015). Our findings provide one potential explanation for the increased cognitive decline seen in aged and AD patients expressing apoE4.

[Evaluation on the effect of cardiovascular prevention program in Fangshan, Beijing]

OBJECTIVE

To evaluate the effect of cardiovascular prevention program in Fangshan, Beijing (BFCP) from 1991-1999.

METHODS

BFCP was a comprehensive community trial covering 120,000 residents in five communities, including three as intervention communities (IC), and two as control communities (CC), in Fangshan, suburb of Beijing. The program was implemented under both population and high risk individual strategies, focusing on health education and hypertension control. The main intervention measures were as follows: (1) network setup; (2) health education and promotion; (3) health professional training; (4) detection and management of hypertensive patients.

RESULTS

Baseline, midterm and final cross-sectional surveys were conducted in the year 1991, 1995 and 1999, respectively. After 9-year intervention, improvement was found in population of IC versus CC (P < 0.01 or P < 0.05) for knowledge, attitude and behavior of CVD prevention, awareness on hypertension, treatment and control rates, as well as the quantity of dietary intake of protein, potassium and calcium. Risk factors such as systolic blood pressure, diastolic blood pressure, rates of smoking and alcohol drinking declined in the population in IC versus CC (P < 0.01). The average morbidity and mortality of stroke were 18.7% (u = 2.81, P < 0.01) and 17.7% (u = 2.91, P < 0.01), significantly lower in the IC versus CC. No significant difference was identified on the morbidity and mortality of coronary heart diseases between IC and CC.

CONCLUSION

The comprehensive community prevention approach was feasible and effective in the prevention and control of cardiovascular diseases in rural populations in China.

The sequence of the human genome

A 2.91-billion base pair (bp) consensus sequence of the euchromatic portion of the human genome was generated by the whole-genome shotgun sequencing method. The 14.8-billion bp DNA sequence was generated over 9 months from 27,271,853 high-quality sequence reads (5.11-fold coverage of the genome) from both ends of plasmid clones made from the DNA of five individuals. Two assembly strategies-a whole-genome assembly and a regional chromosome assembly-were used, each combining sequence data from Celera and the publicly funded genome effort. The public data were shredded into 550-bp segments to create a 2.9-fold coverage of those genome regions that had been sequenced, without including biases inherent in the cloning and assembly procedure used by the publicly funded group. This brought the effective coverage in the assemblies to eightfold, reducing the number and size of gaps in the final assembly over what would be obtained with 5.11-fold coverage. The two assembly strategies yielded very similar results that largely agree with independent mapping data. The assemblies effectively cover the euchromatic regions of the human chromosomes. More than 90% of the genome is in scaffold assemblies of 100,000 bp or more, and 25% of the genome is in scaffolds of 10 million bp or larger. Analysis of the genome sequence revealed 26,588 protein-encoding transcripts for which there was strong corroborating evidence and an additional approximately 12,000 computationally derived genes with mouse matches or other weak supporting evidence. Although gene-dense clusters are obvious, almost half the genes are dispersed in low G+C sequence separated by large tracts of apparently noncoding sequence. Only 1.1% of the genome is spanned by exons, whereas 24% is in introns, with 75% of the genome being intergenic DNA. Duplications of segmental blocks, ranging in size up to chromosomal lengths, are abundant throughout the genome and reveal a complex evolutionary history. Comparative genomic analysis indicates vertebrate expansions of genes associated with neuronal function, with tissue-specific developmental regulation, and with the hemostasis and immune systems. DNA sequence comparisons between the consensus sequence and publicly funded genome data provided locations of 2.1 million single-nucleotide polymorphisms (SNPs). A random pair of human haploid genomes differed at a rate of 1 bp per 1250 on average, but there was marked heterogeneity in the level of polymorphism across the genome. Less than 1% of all SNPs resulted in variation in proteins, but the task of determining which SNPs have functional consequences remains an open challenge.

[An epidemiological study on pesticide poisoning with mixed preparation]

OBJECTIVE

To investigate the incidence of pesticide poisoning with mixed preparation and risk factors contributing to it.

METHODS

Twenty-five administrative villages were studied in three townships of Jiangsu and Shandong Provinces with cluster sampling. The sampled villages were divided into study group (12 villages) and control group (13 villages) with approximately equal number of people each. Pesticide sprayers in the study group applied mixed preparation containing organophosphorous and dimethrin and those in the control group applied single organophosphorous preparation. All the sprayers in sampled villages were interviewed with a same questionnaire about their situation of pesticide spraying during the observation period. Cases of pesticide poisoning were ascertained by seniors physicians in occupational diseases after group discussion.

RESULTS

Incidence of pesticide poisoning was higher in 2 179 sprayers of the study group (10.10 %) than that in 2 615 of the control group (2.29%), with a highly statistically difference (chi(2) = 12.46, P < 0.01) and an risk ratio (RR) of 4.45 (95% CI = 1.94 approximately 10.05) adjusted for other risk factors by logistic regression. Other risk factors for pesticide poisoning with mixed preparation were smoking or taking food during spraying, leaking or breakdown of sprayers, without washing their whole body as soon as possible after spraying, poor personal protection, spraying for a long time, spraying by women and spraying pesticide on cotton.

CONCLUSIONS

If toxicity of mixed preparation of single pesticide showed a synergistic or additional effect, risk of poisoning by spraying mixed preparation increased. Health education and technical training should be strengthened for pesticide sprayers.

The human gene for gammaS-crystallin: alternative transcripts and expressed sequences from the first intron

PURPOSE

gammaS-crystallins are major components of adult vertebrate lenses. Here we examine the population of gammaS transcripts in adult human lens and the structure of the human CRYGS genes.

METHODS

Adult lens human transcripts were obtained from NEIBANK, an Expressed Sequence Tag (EST) analysis of human eye tissues. The human CRYGS gene was isolated as a PAC clone and sequenced by direct and PCR-based methods.

RESULTS

As judged by EST frequency, gammaS is one of the most abundant transcripts in the adult human lens, ranking just behind betaB2-, alphaB- and alphaA-crystallins. EST analysis reveals two transcript sizes resulting from alternative AATAAA and ATTAAA polyadenylation signals. In addition, one cDNA clone was found to contain a novel insert sequence that disrupted the open reading frame. Gene sequencing confirmed that this insert comes from intron 1 and is part of a sequence corresponding to a cluster of unidentified human transcripts in dbEST. Human and mouse gammaS gene proximal promoter sequences were compared and showed a high degree of evolutionary conservation, including consensus binding sites for transcription factors of the maf and SOX families.

CONCLUSIONS

The human CRYGS gene can give rise to at least two transcripts through alternative polyadenylation. A minor transcript results from alternative splicing into sequences in intron 1. These sequences form part of a transcription unit (Mys) expressed in several non-lens tissues. The identity and function Mys of is not yet known, however, the cryptic splicing of CRYGS could produce a defective protein product, with potentially deleterious results for the adult human lens.

Cloning, modeling, and chromosomal localization for a small leucine-rich repeat proteoglycan (SLRP) family member expressed in human eye

PURPOSE

To examine a highly abundant novel transcript from human iris.

METHODS

Expressed sequence tag (EST) analysis of an adult human iris cDNA library revealed an abundant (>0.7%) transcript for a novel member of the small leucine-rich proteoglycan (SLRP) family. Other 3' ESTs from retina were also detected in dbEST. The structure of the leucine-rich repeat (LRR) domain was investigated by molecular modeling. Antisera were raised against a specific peptide and used in western blots of human and rat eye tissues.

RESULTS

From its prevalence in the eye and its superfamily relationships, this SLRP protein has been given the names oculoglycan or opticin (Optc). Sequence analysis suggests that Optc has a signal peptide and two structural domains, the larger of which is the LRR domain. Modeling of the LRR domain reveals structural variability in the repeat motifs, forming potential interaction sites for binding partners. Antiserum to a specific peptide detected a protein of approximately 48 kDa, in human iris, ciliary body and retina while the major protein detected in rat ocular tissues was 37 kDa in size. This may reflect a species difference in post-translational modification. Radiation hybrid mapping shows that the gene for OPTC is located on chromosome 1q31, close to the inherited eye diseases ARMD1 and AXPC1.

CONCLUSIONS

Optc is a newly identified SLRP family member, which appears to have eye-preferred expression. Molecular modeling reveals local deviations from the familiar LRR structure, which are candidates for specific interaction sites. Western blotting with a specific peptide antibody detects Optc in iris, ciliary body and retina in the human eye and suggests that the protein is post-translationally modified. In rat, the antibody detects Optc in several eye tissues and in brain but the protein appears to have undergone much less modification, suggesting that this is not essential for all aspects of function. Considering its eye-preferred expression, the OPTC gene has the potential for involvement in inherited eye disease. Indeed, it maps close to at least two disease loci for which no gene has so far been identified.

[Determination of cadmium in soil slurry samples by GFAAS using ammonium oxalate as disperstant]

A method for the determination of trace cadmium in soil slurry samples by GFAAS was optimized. The factors that influence the performances of cadmium at different chemical modifier were investigated. The effect of background has also been studied. It is found that the slurry of soil samples was most stable with ammonium oxalate as disperstant. The results show that the determination of trace cadmium in soil slurry samples could performed.

Protein synthesis initiation factor 4G

eIF4G is a member of the class of translational initiation factors involved in mRNA recruitment to the 43S initiation complex. The proteins from yeast to mammals are present in multiple isoforms of 82-176 kDa. Mammalian eIF4G-1 is synthesized by internal initiation of translation and is specifically degraded by viral and host proteases activated by stress conditions. The role of eIF4G in protein synthesis is inferred from the presence of binding sites for other initiation factors that serve to co-localize the 5'- and 3'-termini of mRNA with RNA-helicase activity and the 40S ribosomal subunit. Growth-regulated mRNAs are preferentially translated under conditions of accentuated eIF4E-eIF4G interaction. Proteolysis of eIF4G or expression of competitor proteins interferes with its binding to either the 5'- or 3'-termini, changing the spectrum of mRNAs translated. Elevated eIF4G levels correlate with malignant cell transformation and diminished eIF4G levels, with nutritional deprivation and anoxia.

[Analysis of chiral compounds by micelle electrokinetic capillary chromatography]

An overview on applications of micelle electrokinetic capillary chromatography (MECC) in chiral compounds analysis is presented. Ionic chiral surfactants such as bile salts, long-alkyl-chain surfactants and high-molecular-weight surfactants, which can migrate with electroosmosis and its electrophoretic mobility, and interact with the solutes, are employed as chiral selectors. Addition of electrically neutral chiral selectors such as cyclodextrins is also successful in MECC separation. Theory of MECC enantiomer separation is briefly described.

Functional characterization of the internal ribosome entry site of eIF4G mRNA

The eIF4 group initiation factors are required for cap-dependent translation initiation. Infection of mammalian cells by picornaviruses results in proteolytic cleavage of one of these factors, eIF4G, which severely restricts cap-dependent initiation but permits cap-independent initiation to proceed from an internal ribosome entry site (IRES) in picornaviral RNAs. The first 357 nucleotides (nt) of the 5'-untranslated region of eIF4G mRNA also contains an IRES. Using bicistronic constructs for expression in K562 cells, we have now shown that progressive deletions of the 5'-untranslated region can have either stimulatory or inhibitory effects. Furthermore, a 101-nt segment exhibits full IRES activity, and an 81-nt segment exhibits detectable IRES activity. A polypyrimidine tract (PPT) at the 3' terminus is essential for internal initiation, a property which is characteristic of picornaviral IRESs but not the other host cellular IRESs studied to date. IRES activity does not require sequences beyond 357 nt. Out-of-frame AUGs have no effect on IRES-driven luciferase expression when introduced upstream of the PPT but markedly decrease expression when introduced at sites between the PPT and the authentic initiation codon at nt 369. These results suggest that the ribosomal subunit enters at or near the PPT and then scans downstream for the initiation codon.