Regulation of polymerase exchange between Poleta and Poldelta by monoubiquitination of PCNA and the movement of DNA polymerase holoenzyme

To ensure efficient and timely replication of genomic DNA, organisms in all three kingdoms of life possess specialized translesion DNA synthesis (TLS) polymerases (Pols) that tolerate various types of DNA lesions. It has been proposed that an exchange between the replicative DNA Pol and the TLS Pol at the site of DNA damage enables lesion bypass to occur. However, to date the molecular mechanism underlying this process is not fully understood. In this study, we demonstrated in a reconstituted system that the exchange of Saccharomyces cerevisiae Poldelta with Poleta requires both the stalling of the holoenzyme and the monoubiquitination of proliferating cell nuclear antigen (PCNA). A moving Poldelta holoenzyme is refractory to the incoming Poleta. Furthermore, we showed that the Poleta C-terminal PCNA-interacting protein motif is required for the exchange process. We also demonstrated that the second exchange step to bring back Poldelta is prohibited when Lys-164 of PCNA is monoubiquitinated. Thus the removal of the ubiquitin moiety from PCNA is likely required for the reverse exchange step after the lesion bypass synthesis by Poleta.     

Nrf2/Bach1竞争调控抗氧化酶与支气管哮喘

氧化/抗氧化失衡是支气管哮喘的重要发病机制之一.抗氧化酶的基因表达均通过抗氧化反应元件(ARE)介导,核因子相关因子-2(Nrf2)能上调ARE介导抗氧化酶的基因表达,而转录因子BTBCNC异体同源体(Bach1)下调ARE介导抗氧化酶的基因表达,Nrt2/Baeh1在核内竞争调控抗氧化酶的基因表达.     

Dynamics of the heart rate variability and oxygen saturation response to acute normobaric hypoxia within the first 10 min of exposure

Although the heart rate variability (HRV) response to hypoxia has been studied, little is known about the dynamics of HRV after hypoxia exposure. The purpose of this study was to assess the HRV and oxygen saturation (SpO₂) responses to normobaric hypoxia (FiO₂ = 9·6%) comparing 1 min segments to baseline (normoxia). Electrocardiogram and SpO₂ were recorded during a 10‐min hypoxia exposure in 29 healthy male subjects aged 26·0 ± 4·9 years. Baseline HRV values were obtained from a 5‐min recording period prior to hypoxia. The hypoxia period was split into 10 non‐overlapping 1‐min segments and time domain HRV indexes (RMSSD and SDNN) were calculated for each segment. Differences (Δ) from baseline values were calculated and transformed using natural logarithm (Ln). This study revealed that the decrease in ΔSpO₂ became significant (P<0·001) in the first minute of hypoxia, the decrease in ΔLn RMSSD became significant (P = 0·002) in the second minute, and the decrease in ΔLn SDNN became significant (P = 0·001) in the third minute. Between the second and fifth minute of hypoxia, ΔSpO₂ correlated with ΔLn RMSSD (r = 0·57, P<0·001) and ΔLn SDNN (r = 0·44, P<0·001). Five min after the onset of hypoxia, ΔSpO₂ was significantly (P = 0·002) decreased but changes in ΔLn RMSSD (P = 0·344) and ΔLn SDNN (P = 0·558) were not significant. In conclusion, the decrease in HRV was proportional to desaturation but only during the first 5 min of hypoxia.     

Clinical Implications of Clonal Hematopoiesis

Clonal hematopoiesis (CH)—an expansion of blood cells derived from a single hematopoietic stem cell—is a defining feature of hematologic cancers, but recently CH was also found to be a frequent consequence of aging. When aging-associated CH results from acquisition of a somatic mutation in a driver gene associated with leukemia, and this mutation is present at a variant allele frequency of at least 0.02 (2%) yet the patient does not meet World Health Organization diagnostic criteria for a hematologic neoplasm, this state is termed clonal hematopoiesis of indeterminate potential (CHIP). CHIP is present in approximately 10% to 15% of people older than 70 years and more than 30% by age 85 years and represents a precursor state for neoplasia akin to monoclonal gammopathy of undetermined significance. Recently, CHIP was unexpectedly found to be an important risk factor for cardiovascular events, with accumulating evidence supporting a mechanism of accelerated atherogenesis as a result of vascular inflammation driven by clonally derived monocytes/macrophages. Risk factors for CHIP include aging, male sex, cigarette smoking, and a common germline variant in the telomere-associated gene TERT. Clonal hematopoiesis can also occur after cytotoxic chemotherapy or radiotherapy for a solid tumor, after hematopoietic stem cell transplant, in the context of aplastic anemia, or after induction chemotherapy for acute leukemia; in each setting, CH has distinct clinical implications. This review summarizes recent studies of CH and CHIP and outlines challenges in clinical management of affected patients.     

Phylogeny of the Vitamin K 2,3-Epoxide Reductase (VKOR) Family and Evolutionary Relationship to the Disulfide Bond Formation Protein B (DsbB) Family

In humans and other vertebrate animals, vitamin K 2,3-epoxide reductase (VKOR) family enzymes are the gatekeepers between nutritionally acquired K vitamins and the vitamin K cycle responsible for posttranslational modifications that confer biological activity upon vitamin K-dependent proteins with crucial roles in hemostasis, bone development and homeostasis, hormonal carbohydrate regulation and fertility. We report a phylogenetic analysis of the VKOR family that identifies five major clades. Combined phylogenetic and site-specific conservation analyses point to clade-specific similarities and differences in structure and function. We discovered a single-site determinant uniquely identifying VKOR homologs belonging to human pathogenic, obligate intracellular prokaryotes and protists. Building on previous work by Sevier et al. (Protein Science 14:1630), we analyzed structural data from both VKOR and prokaryotic disulfide bond formation protein B (DsbB) families and hypothesize an ancient evolutionary relationship between the two families where one family arose from the other through a gene duplication/deletion event. This has resulted in circular permutation of primary sequence threading through the four-helical bundle protein folds of both families. This is the first report of circular permutation relating distant α-helical membrane protein sequences and folds. In conclusion, we suggest a chronology for the evolution of the five extant VKOR clades.     

UBXN2A regulates nicotinic receptor degradation by modulating the E3 ligase activity of CHIP

Neuronal nicotinic acetylcholine receptors (nAChRs) containing the α3 subunit are known for their prominent role in normal ganglionic transmission while their involvement in the mechanisms underlying nicotine addiction and smoking-related disease has been emerging only in recent years. The amount of information available on the maturation and trafficking of α3-containing nAChRs is limited. We previously showed that UBXN2A is a p97 adaptor protein that facilitates the maturation and trafficking of α3-containing nAChRs. Further investigation of the mechanisms of UBXN2A actions revealed that the protein interacts with CHIP (carboxyl terminus of Hsc70 interacting protein), whose ubiquitin E3 ligase activity regulates the degradation of several disease-related proteins. We show that CHIP displays E3 ligase activity toward the α3 nAChR subunit and contributes to its ubiquitination and subsequent degradation. UBXN2A interferes with CHIP-mediated ubiquitination of α3 and protects the nicotinic receptor subunit from endoplasmic reticulum associated degradation (ERAD). UBXN2A also cross-talks with VCP/p97 and HSC70/HSP70 proteins in a complex where α3 is likely to be targeted by CHIP. Overall,we identify CHIP as an E3 ligase for α3 and UBXN2A as a protein that may efficiently regulate the stability of CHIP’s client substrates.     

Hazard identification of cis/trans-zearalenone through the looking-glass

Among the food-related health issues, the presence of contaminants has a prominent role, due to the wide range of exogenous compounds that can occur in food commodities and to their large differences in structure and biological activity. A comprehensive assessment of the related risk is thus actually demanding in terms of time and facilities involved. In this context, the use of computational strategies can be an effective choice for supporting the hazard identification procedure at the early stage. In this work, we focused on the food contaminant zearalenone by comparing the trans and cis isomers, respectively the well-known mycoestrogen and its still largely understudied isomer. We estimated the possible effects exerted by human metabolism on the xenoestrogenicity of cis-ZEN by using a validated in silico strategy based on docking simulations and rescoring procedures. Similarly, the exploitation of the most promising enzymatic detoxifying routes designed for trans-ZEN – which relies on the enzyme lactono hydrolase from Clonostachys rosea – has been assessed for the cis-isomer as well. Our results showed that both isomers can act as functional analogues with respect to xenoestrogenic activity, and several cis-ZEN metabolites with high biological potential have been identified. On the contrary, in spite of the high degree of structural analogy, the cis isomer showed a pattern of interaction with the degrading enzyme in stark contrast with that observed for trans-ZEN. For these reasons, the outcomes presented herein strongly support the inclusion of cis-ZEN in further studies of occurrence, metabolism and bioactivity assessment, and suggest the need for a dedicated handling for the cis isomer in risk assessment studies.     

医院环境中物体表面碳青霉烯耐药鲍曼不动杆菌污染及同源性分析

目的调查某院重点部门物体表面碳青霉烯耐药鲍曼不动杆菌污染情况及其同源性。方法对该院重症监护室(ICU)、急诊重症监护室(EICU)、血液透析室、手术室进行环境卫生学监测,采用肠杆菌科基因间重复序列聚合酶链反应(ERIC-PCR),对ICU、EICU环境中污染的条件致病菌鲍曼不动杆菌进行扩增分型。结果除EICU医务人员手卫生结果达标外,ICU及EICU各检测项目细菌计数均不达标;血液透析室及手术室采样标本均合格。ICU、EICU物体表面共采集标本53份,检出鲍曼不动杆菌7株,检出率为13.21%;此7株菌均为碳青霉烯耐药鲍曼不动杆菌,其中6株基因型相同,与患者痰中分离的鲍曼不动杆菌基因型相同。结论该院重点部门环境中物体表面分离的碳青霉烯耐药鲍曼不动杆菌具有同源性,应加强其环境物体表面清洁与消毒,降低医院感染的发生。