Structure of the Catalytic Domain of EZH2 Reveals Conformational Plasticity in Cofactor and Substrate Binding Sites and Explains Oncogenic Mutations

Polycomb repressive complex 2 (PRC2) is an important regulator of cellular differentiation and cell type identity. Overexpression or activating mutations of EZH2, the catalytic component of the PRC2 complex, are linked to hyper-trimethylation of lysine 27 of histone H3 (H3K27me3) in many cancers. Potent EZH2 inhibitors that reduce levels of H3K27me3 kill mutant lymphoma cells and are efficacious in a mouse xenograft model of malignant rhabdoid tumors. Unlike most SET domain methyltransferases, EZH2 requires PRC2 components, SUZ12 and EED, for activity, but the mechanism by which catalysis is promoted in the PRC2 complex is unknown. We solved the 2.0 Å crystal structure of the EZH2 methyltransferase domain revealing that most of the canonical structural features of SET domain methyltransferase structures are conserved. The site of methyl transfer is in a catalytically competent state, and the structure clarifies the structural mechanism underlying oncogenic hyper-trimethylation of H3K27 in tumors harboring mutations at Y641 or A677. On the other hand, the I-SET and post-SET domains occupy atypical positions relative to the core SET domain resulting in incomplete formation of the cofactor binding site and occlusion of the substrate binding groove. A novel CXC domain N-terminal to the SET domain may contribute to the apparent inactive conformation. We propose that protein interactions within the PRC2 complex modulate the trajectory of the post-SET and I-SET domains of EZH2 in favor of a catalytically competent conformation.     

Ginsenoside Rg-1 Protects Retinal Pigment Epithelium (RPE) Cells from Cobalt Chloride (CoCl2) and Hypoxia Assaults

Severe retinal ischemia causes persistent visual impairments in eye diseases. Retinal pigment epithelium (RPE) cells are located near the choroidal capillaries, and are easily affected by ischemic or hypoxia. Ginsenoside Rg-1 has shown significant neuroprotective effects. This study was performed to test the cytoprotective effect of ginsenoside Rg-1 in RPE cells against hypoxia and cobalt chloride (CoCl₂) assaults, and to understand the underlying mechanisms. We found that Rg-1 pre-administration significantly inhibited CoCl₂- and hypoxia-induced RPE cell death and apoptosis. Reactive oxygen specisis (ROS)-dependent p38 and c-Jun NH(2)-terminal kinases (JNK) MAPK activation was required for CoCl₂-induced RPE cell death, and Rg-1 pre-treatment significantly inhibited ROS production and following p38/JNK activation. Further, CoCl₂ suppressed pro-survival mTOR complex 1 (mTORC1) activation in RPE cells through activating of AMP-activated protein kinase (AMPK), while Rg-1 restored mTORC1 activity through inhibiting AMPK activation. CoCl₂-induced AMPK activation was also dependent on ROS production, and anti-oxidant N-acetylcysteine (NAC) prevented AMPK activation and RPE cell death by CoCl₂. Our results indicated that Rg-1 could be further investigated as a novel cell-protective agent for retinal ischemia.     

A Functional Variant rs1820453 in YAP1 and Breast Cancer Risk in Chinese Population

Background

To investigate the association between rs1820453 which located in the promoter region of yes-associated protein 1 (YAP1) gene and breast cancer (BC) risk.

Method and Findings

We conducted a hospital-based case-control study including a total of 480 BC cases and 545 cancer-free controls in Chinese population. Then the expression quantitative trait locus (e-QTL) analysis was performed to explore the possible function of rs1820453 to the YAP1 gene expression. The association between rs1820453 and BC risk was significantly identified with the odds ratio (OR) was 1.27 (95 % confidence interval (CI) =1.03-1.57) under allelic model when adjusted by age and menopausal status. In addition, the correlation analysis of rs1820453 and YAP1 expression level found that this variant was significantly associated with the gene expression in Chinese population. When compared with level of mRNA expression of the AA genotype (6.011±0.046), the mRNA expression level in CC genotype (5.903±0.026) was statistically lower (P=0.024).

Conclusion

The results from this study suggested that rs1820453 A>C change may affect the gene expression and contribute to the risk of developing BC in Chinese population though larger sample-size studies along with functional experiments were anticipated to warrant the results.     

Prevalence and Trends of the Abdominal Aortic Aneurysms Epidemic in General Population - A Meta-Analysis

Objective

To conduct a meta-analysis assessing the prevalence and trends of the abdominal aortic aneurysms (AAA) epidemic in general population.

Method

Studies that reported prevalence rates of AAA from the general population were identified through MEDLINE, EMBASE, Web of Science, and reference lists for the period between 1988 and 2013. Studies were included if they reported prevalence rates of AAA in general population from the community. In stratified analyses possible sources of bias, including areas difference, age, gender and diameter of aneurysms were examined. Publication bias was assessed with Egger''s test method.

Results

56 studies were identified. The overall pooled prevalence of AAA was 4.8% (4.3%, 5.3%). Stratified analyses showed the following results, areas difference: America 2.2% (2.2%, 2.2%), Europe 2.5% (2.4%, 2.5%), Australia 6.7% (6.5%, 7.0%), Asia 0.5% (0.3%, 0.7%); gender difference: male 6.0% (5.3%, 6.7%), female 1.6% (1.2%, 1.9%); age difference: 55–64years 1.3% (1.2%, 1.5%), 65–74 years 2.8% (2.7%, 2.9%), 75–84 years1.2%(1.1%, 1.3%), ≥85years0.6% (0.4%, 0.7%); aortic diameters difference: 30–39 mm, 3.3% (2.8%, 3.9%), 40–49 mm,0.7% (0.4%,1.0%), ≥50 mm, 0.4% (0.3%, 0.5%). The prevalence of AAA has decreased in Europe from 1988 to 2013. Hypertension, smoking, coronary artery disease, dyslipidemia, respiratory disease, cerebrovascular disease, claudication and renal insufficiency were risk factors for AAA in Europe.

Conclusion

AAA is common in general population. The prevalence of AAA is higher in Australia than America and Europe. The pooled prevalence in western countries is higher than the Asia. Future research requires a larger database on the epidemiology of AAA in general population.     

Investigation of the binding network of IGF-I on the cavity surface of IGFBP4

Insulin-like growth factor-binding proteins (IGFBPs) control bioactivity and distribution of insulin-like growth factors (IGFs) through high-affinity complex of IGFBP and IGF. To get more insight into the binding interaction of IGF system, the site-directed mutagenesis and force-driving desorption methods were employed to study the interaction mechanism of IGFBP4 and IGF-I by molecular dynamics (MD) simulation. In IGF-I, residues Gly7 to Asp12 were found to be the hot spots and they mainly anchored on the N-domain of IGFBP4. The contact area, the shape and size of protein, the surroundings of the binding site, the hydrophobic and electrostatic interaction between the two proteins worked as a complex network to regulate the protein-protein interaction. It was also found that the unfolding of the helix was not inevitable in the mutant, and it could be regulated by careful selection of the substituted amino acid.

The tumourigenicity of iPS cells and their differentiated derivates

Induced pluripotent stem cell (iPSC) provides a promising seeding cell for regenerative medicine. However, iPSC has the potential to form teratomas after transplantation. Therefore, it is necessary to evaluate the tumorigenic risks of iPSC and all its differentiated derivates prior to use in a clinical setting. Here, murine iPSCs were transduced with dual reporter gene consisting of monomeric red fluorescent protein (mRFP) and firefly luciferase (Fluc). Undifferentiated iPSCs, iPSC derivates from induced differentiation (iPSC‐derivates), iPSC‐derivated cardiomyocyte (iPSC‐CMs) were subcutaneously injected into the back of nude mice. Non‐invasive bioluminescence imaging (BLI) was longitudinally performed at day 1, 7, 14 and 28 after transplantation to track the survival and proliferation of transplanted cells. At day 28, mice were killed and grafts were explanted to detect teratoma formation. The results demonstrated that transplanted iPSCs, iPSC‐derivates and iPSC‐CMs survived in receipts. Both iPSCs and iPSC‐derivates proliferated dramatically after transplantation, while only slight increase in BLI signals was observed in iPSC‐CM transplanted mice. At day 28, teratomas were detected in both iPSCs and iPSC‐derivates transplanted mice, but not in iPSC‐CM transplanted ones. In vitro study showed the long‐term existence of pluripotent cells during iPSC differentiation. Furthermore, when these cells were passaged in feeder layers as undifferentiated iPSCs, they would recover iPSC‐like colonies, indicating the cause for differentiated iPSC's tumourigenicity. Our study indicates that exclusion of tumorigenic cells by screening in addition to lineage‐specific differentiation is necessary prior to therapeutic use of iPSCs.     

Occult Hepatitis B Virus Infection in Anti-HBs-Positive Infants Born to HBsAg-Positive Mothers in China

Objective

To investigate the prevalence of occult HBV infection (OBI) among children and to characterize virology of occult HBV, we conducted an epidemiological survey.

Methods

186 HB-vaccinated infants born to HBsAg-positive mothers were included in the study. Serological tests for HBV markers were performed using commercial ELISA kits. Real-time quantitative PCR and nested PCR were used to detect HBV DNA. PCR products of the C and pre-S/S regions were sequenced and analyzed.

Results

1.61% (3/186) infants were HBsAg positive, and 4.92% (9/183) infants were considered as occult infection. The viral load of mothers was associated with occult infection (P = 0.020). Incomplete three-dose injections of HB vaccine was associated with HBV infection (P = 0.022). Six OBI infants were positive for anti-HBs, but their titers were not greater than 100 mIU/mL. Seven isolated HBV pre-S/S sequences were obtained from nine OBI infants. Three of the sequences were genotype C, and four of the sequences were genotype C/D. Escape mutation S143L was found in the four sequences of genotype C/D. All seven sequences lacked G145R and other escape mutation in S region.

Conclusions

Occult HBV infection was detected in anti-HBs positive infants born to HBsAg-positive mothers in China. Occult infection was associated with absent anti-HBs or with low anti-HBs level, high maternal viral loads and escape mutations in the S gene.     

Identification and Candidate Gene Analysis of a Novel Phytophthora Resistance Gene Rps10 in a Chinese Soybean Cultivar

Resistance to Phytophthora sojae isolate PsMC1 was evaluated in 102 F_2∶3 families derived from a cross between the resistant soybean cultivar Wandou 15 and the susceptible cultivar Williams and genotyped using simple sequence repeat (SSR) markers. The segregation ratio of resistant, segregating, and susceptible phenotypes in the population suggested that the resistance in Wandou 15 was dominant and monogenic. Twenty-six polymorphic SSR markers were identified on soybean chromosome 17 (Molecular linkage group D2; MLG D2), which were linked to the resistance gene based on bulked segregation analysis (BSA). Markers Sattwd15-24/25 and Sattwd15-47 flanked the resistance gene at a distance of 0.5 cM and 0.8 cM, respectively. Two cosegregating markers, Sattwd15-28 and Sattwd15-32, were also screened in this region. This is the first Rps resistance gene mapped on chromosome 17, which is designated as Rps10. Eight putative genes were found in the mapped region between markers Sattwd15-24/25 and Sattwd15-47. Among them, two candidate genes encoding serine/threonine (Ser/Thr) protein kinases in Wandou 15 and Williams were identified and sequenced. And the differences in genomic sequence and the putative amino acid sequence, respectively, were identified within each candidate gene between Wandou 15 and Williams. This novel gene Rps10 and the linked markers should be useful in developing soybean cultivars with durable resistance to P. sojae.