The genus beta human papillomaviruses (beta HPVs) cause cutaneous lesions and are thought to be involved in the initiation of some nonmelanoma skin cancers (NMSCs), particularly in patients with the genetic disorder epidermodysplasia verruciformis (EV). We have previously reported that at least two of the genus beta HPV E6 proteins bind to and/or increase the steady-state levels of p53 in squamous epithelial cells. This is in contrast to a well-characterized ability of the E6 proteins of cancer-associated HPVs of genus alpha HPV, which inactivate p53 by targeting its ubiquitin-mediated proteolysis. In this study, we have investigated the ability of genus beta E6 proteins from eight different HPV types to block the transactivation of p53 target genes following DNA damage. We find that the E6 proteins from diverse beta HPV species and types vary in their capacity to block the induction of MDM2, p21, and proapoptotic genes after genotoxic stress. We conclude that some genus beta HPV E6 proteins inhibit at least some p53 target genes, although perhaps not by the same mechanism or to the same degree as the high-risk genus alpha HPV E6 proteins.
IMPORTANCE This study addresses the ability of various human papillomavirus E6 proteins to block the activation of p53-responsive cellular genes following DNA damage in human keratinocytes, the normal host cell for HPVs. The E6 proteins encoded by the high-risk, cancer-associated HPV types of genus alpha HPV have a well-established activity to target p53 degradation and thereby inhibit the response to DNA damage. In this study, we have investigated the ability of genus beta HPV E6 proteins from eight different HPV types to block the ability of p53 to transactivate downstream genes following DNA damage. We find that some, but not all, genus beta HPV E6 proteins can block the transactivation of some p53 target genes. This differential response to DNA damage furthers the understanding of cutaneous HPV biology and may help to explain the potential connection between some beta HPVs and cancer.
Drug resistance mutations archived in resting memory CD4+ cells may persist despite suppression of HIV RNA to <50 copies/ml. We sequenced pol gene from proviral DNA among viremic and suppressed patients to identify drug resistance mutations.
The Peninsula AIDS Research Cohort study enrolled and followed over 2 years 120 HIV infected patients from San Mateo and San Francisco Counties. HIV-1 pol genotyping by bulk sequencing was performed on 38 DNA and RNA from viremic patients and DNA only among 82 suppressed patients at baseline. Antiretroviral susceptibility was predicted by HIVDB.stanford.edu.
Among 120 subjects, 81% were on antiretroviral therapy and had been treated for a median time of 7 years. Thirty-two viremic patients showed concordant RNA and DNA genotypes (84%); the discordant profiles were mainly observed in patients with low-level viremia. Among suppressed patients, 21 had drug resistance mutations in proviral DNA (26%) with potential resistance to one, two or three ARV classes in 16, 4 and 1 samples respectively.
The high level of genotype concordance between DNA and RNA in viremic patients suggested that DNA genotyping might be used to assess drug resistance in resource-limited settings, and further investigation of extracted DNA from dried blood spots is needed. Drug resistance mutations in proviral DNA in 26% of subjects with less than 50 copies/ml pose a risk for the transmission of drug resistant virus with virologic failure, treatment interruption or decreased adherence.
Several recent studies have converged upon the innate immune DNA cytosine deaminase APOBEC3B (A3B) as a significant source of genomic uracil lesions and mutagenesis in multiple human cancers, including those of the breast, head/neck, cervix, bladder, lung, ovary, and other tissues. A3B is upregulated in these tumor types relative to normal tissues, but the mechanism is unclear. Because A3B also has antiviral activity in multiple systems and is a member of the broader innate immune response, we tested the hypothesis that human papillomavirus (HPV) infection causes A3B upregulation. We found that A3B mRNA expression and enzymatic activity were upregulated following transfection of a high-risk HPV genome and that this effect was abrogated by inactivation of E6. Transduction experiments showed that the E6 oncoprotein alone was sufficient to cause A3B upregulation, and a panel of high-risk E6 proteins triggered higher A3B levels than did a panel of low-risk or noncancer E6 proteins. Knockdown experiments in HPV-positive cell lines showed that endogenous E6 is required for A3B upregulation. Analyses of publicly available head/neck cancer data further support this relationship, as A3B levels are higher in HPV-positive cancers than in HPV-negative cancers. Taken together with the established role for high-risk E6 in functional inactivation of TP53 and published positive correlations in breast cancer between A3B upregulation and genetic inactivation of TP53, our studies suggest a model in which high-risk HPV E6, possibly through functional inactivation of TP53, causes derepression of A3B gene transcription. This would lead to a mutator phenotype that explains the observed cytosine mutation biases in HPV-positive head/neck and cervical cancers.
The innate immune DNA cytosine deaminase APOBEC3B (A3B) accounts for a large proportion of somatic mutations in cervical and head/neck cancers, but nothing is known about the mechanism responsible for its upregulation in these tumor types. Almost all cervical carcinomas and large proportions of head/neck tumors are caused by human papillomavirus (HPV) infection. Here, we establish a mechanistic link between HPV infection and A3B upregulation. The E6 oncoprotein of high-risk, but not low-risk, HPV types triggers A3B upregulation, supporting a model in which TP53 inactivation causes a derepression of A3B gene transcription and elevated A3B enzyme levels. This virus-induced mutator phenotype provides a mechanistic explanation for A3B signature mutations observed in HPV-positive head/neck and cervical carcinomas and may also help to account for the preferential cancer predisposition caused by high-risk HPV isolates.
AUF1 is a family of four proteins generated by alternative pre-mRNA splicing that form high affinity complexes with AU-rich, mRNA-destabilizing sequences located within the 3′ untranslated regions of many labile mRNAs. While AUF1 binding is most frequently associated with accelerated mRNA decay, emerging examples have demonstrated roles as a mRNA stabilizer or even translational regulator for specific transcripts. In this review, we summarize recent advances in our understanding of mRNA recognition by AUF1 and the biochemical and functional consequences of these interactions. In addition, unique properties of individual AUF1 isoforms and the roles of these proteins in modulating expression of genes associated with inflammatory, neoplastic, and cardiac diseases are discussed. Finally, we describe mechanisms that regulate AUF1 expression in cells, and current knowledge of regulatory switches that modulate the cellular levels and/or activities of AUF1 isoforms through distinct protein post-translational modifications. This article is part of a Special Issue entitled: RNA Decay mechanisms.
AU-rich element; RNA-binding protein; mRNA turnover; Gene regulation; Alternative splicing; RNA structure
The identification of interactions between viral and host cellular proteins has provided major insights into papillomavirus research, and these interactions are especially relevant to the role of papillomaviruses in the cancers with which they are associated. Recent advances in mass spectrometry technology and data processing now allow the systematic identification of such interactions. This has led to an improved understanding of the different pathologies associated with the many papillomavirus types, and the diverse nature of these viruses is reflected in the spectrum of interactions with host proteins. Here we review a history of proteomic approaches, particularly as applied to the papillomaviruses, and summarize current techniques. Current proteomic studies on the papillomaviruses use yeast-two-hybrid or affinity purification-mass spectrometry approaches. We detail the advantages and disadvantages of each and describe current examples of papillomavirus proteomic studies, with a particular focus on the HPV E6 and E7 oncoproteins.
papillomavirus; proteomics; interaction; HPV; mass spectrometry; yeast two hybrid
Advances in genomic sequencing technologies in the past decade have revolutionized the field of genomics, resulting in faster and less expensive sequencing. Holding back the potential for innovation, however, is a widespread lack of understanding of genomics and sequencing by the general public. In an attempt to remedy this problem, this paper presents an introduction to the fields of genomics, bioinformatics, and proteomics using the blueberry genome as a model case study of the plant genomics field. The blueberry (Vaccinium sect. Cyanococcus) is often cited as a “super food” in the media due to its nutritional benefits and global economic importance. There have been a number of related genomic publications in the past 20 years; however, a completed genome and a full analysis into the health-related pathways are still needed. As exemplified by this blueberry case study, there are opportunities for future genomic research into numerous beneficial plant species. The solid background presented in this paper provides future researchers the foundation to explore these uncharted areas.
blueberry; sequencing; assembly; mapping; annotation; pathway elucidation; genomics
SR-BI deficient mice that are also hypomorphic for apolipoprotein E expression develop diet induced occlusive coronary artery atherosclerosis, myocardial infarction and early death. To test the role of SR-BI in bone marrow derived cells, we used bone marrow transplantation to generate SR-BI-null; apoE-hypomorphic mice in which SR-BI expression was restored solely in bone marrow derived cells. SR-BI-null; apoE-hypomorphic mice were transplanted with SR-BI+/+apoE-hypomorphic, or control, autologous SR-BI-null; apoE-hypomorphic bone marrow. Four weeks later, mice were fed a high-fat, high-cholesterol, cholate-containing diet to induce coronary artery atherosclerosis. Mice transplanted with autologous bone marrow developed extensive aortic atherosclerosis and severe occlusive coronary artery atherosclerosis after 4 weeks of feeding. This was accompanied by myocardial fibrosis and increased heart weights. In contrast, restoration of SR-BI expression in bone marrow derived-cells reduced diet induced aortic and coronary artery atherosclerosis, myocardial fibrosis and the increase in heart weights in SR-BI-null; apoE-hypomorphic mice. Restoration of SR-BI in bone marrow derived cells did not, however, affect steady state lipoprotein cholesterol levels, but did reduce plasma levels of IL-6. Monocytes from SR-BI-null mice exhibited a greater capacity to bind to VCAM-1 and ICAM-1 than those from SR-BI+/+ mice. Furthermore, restoration of SR-BI expression in bone marrow derived cells attenuated monocyte recruitment into atherosclerotic plaques in mice fed high fat, high cholesterol cholate containing diet. These data demonstrate directly that SR-BI in bone marrow-derived cells protects against both aortic and CA atherosclerosis.
We have begun to define the human papillomavirus (HPV)-associated proteome for a subset of the more than 120 HPV types that have been identified to date. Our approach uses a mass spectrometry-based platform for the systematic identification of interactions between human papillomavirus and host cellular proteins, and here we report a proteomic analysis of the E6 proteins from 16 different HPV types. The viruses included represent high-risk, low-risk, and non-cancer-associated types from genus alpha as well as viruses from four different species in genus beta. The E6 interaction data set consists of 153 cellular proteins, including several previously reported HPV E6 interactors such as p53, E6AP, MAML1, and p300/CBP and proteins containing PDZ domains. We report the genus-specific binding of E6s to either E6AP or MAML1, define the specific HPV E6s that bind to p300, and demonstrate several new features of interactions involving beta HPV E6s. In particular, we report that several beta HPV E6s bind to proteins containing PDZ domains and that at least two beta HPV E6s bind to p53. Finally, we report the newly discovered interaction of proteins of E6 of beta genus, species 2, with the Ccr4-Not complex, the first report of a viral protein binding to this complex. This data set represents a comprehensive survey of E6 binding partners that provides a resource for the HPV field and will allow continued studies on the diverse biology of the human papillomaviruses.
Children build up knowledge about the world and also remember individual episodes. How individual episodes during which children learn new things become integrated with one another to form general knowledge is only beginning to be explored. Integration between separate episodes is called on in educational contexts and in everyday life as a major means of extending knowledge and organizing information. Bauer and San Souci (2010) provided an initial demonstration that 6-year-olds extend their knowledge by integrating between separate but related episodes; the episodes shared a high level of surface similarity. Experiments 1A and 1B of the current research were tests of integration under low and high levels of surface similarity, respectively. In Experiment 1A, when surface similarity of the episodes was low, 6-year-olds integrated between passages of text, yet their performance was not as robust as observed previously. In Experiment 1B, when surface similarity of the episodes was high, a replication of Bauer and San Souci’s results was observed. In Experiment 2, we tested whether a “hint” to consult the information learned in the passages improved performance even when surface level similarity was low. The hint had a strong facilitating effect. Possible mechanisms of integration between separate yet related episodes are discussed.
Episodic memory; Facilitating factors; Integration; Learning; Semantic memory; Surface similarity
Drug resistance mutations (DRM) in viral RNA are important in defining to provide effective antiretroviral therapy (ART) in HIV-1 infected patients. Detection of DRM in peripheral blood mononuclear cell (PBMC) DNA is another source of information, although the clinical significance of DRMs in proviral DNA is less clear.
Materials and Methods
From 25 patients receiving ART at a center in Zimbabwe, 32 blood samples were collected. Dideoxy-sequencing of gag-pol identified subtype and resistance mutations from plasma viral RNA and proviral DNA. Drug resistance was estimated using the calibrated population resistance tool on www.hivdb.stanford.edu database. Numerical resistance scores were calculated for all antiretroviral drugs and for the subjects’ reported regimen. Phylogenetic analysis as maximum likelihood was performed to determine the evolutionary distance between sequences.
Of the 25 patients, 4 patients (2 of which had given 2 blood samples) were not known to be on ART (NA) and had exclusively wild-type virus, 17 had received Protease inhibitors (PI), 18, non-nucleoside reverse transcriptase inhibitors (NNRTI) and 19, two or more nucleoside reverse transcriptase inhibitors (NRTI). Of the 17 with history of PI, 10 had PI mutations, 5 had minor differences between mutations in RNA and DNA. Eighteen samples had NNRTI mutations, six of which demonstrated some discordance between DNA and RNA mutations. Although NRTI resistance mutations were frequently different between analyses, mutations resulted in very similar estimated phenotypes as measured by resistance scores. The numerical resistance scores from RNA and DNA for PIs differed between 2/10, for NNRTIs between 8/18, and for NRTIs between 17/32 pairs. When calculated resistance scores were collapsed, 3 pairs showed discordance between RNA and DNA for at least one PI, 6 were discordant for at least one NNRTI and 11 for at least one NRTI. Regarding phylogenetic evolutionary analysis, all RNA and DNA sequence pairs clustered closely in a maximum likelihood tree.
PBMC DNA could be useful for testing drug resistance in conjunction with plasma RNA where the results of each yielded complementary information about drug resistance. Identification of DRM, archived in proviral DNA, could be used to provide for sustainable public health surveillance among subtype C infected patients.
AIDS; Peripheral blood mononuclear cell; Viral RNA; pol sequence; HIV-1 subtype C; Antiretroviral therapy
During the course of HIV infection, some HIV-1 viruses switch from using the CCR5 (R5) coreceptor to using CXCR4 (X4). Here, we describe two subtype C isolates from a Zimbabwean patient that switched from using R5 to using both R5 and X4 with an accompanying addition of five amino acids to the V3 loop region of envelope. The insert appears to be derived from the human genome rather than a duplication within HIV-1.
The serine/threonine kinase Pim-1 directs selected signaling events that promote cell growth and survival and is overexpressed in diverse human cancers. Pim-1 expression is tightly controlled through multiple mechanisms, including regulation of mRNA turnover. In several cultured cell models, mitogenic stimulation rapidly induced and stabilized PIM1 mRNA, however, vigorous destabilization 4–6 hours later helped restore basal expression levels. Acceleration of PIM1 mRNA turnover coincided with accumulation of tristetraprolin (TTP), an mRNA-destabilizing protein that targets transcripts containing AU-rich elements. TTP binds PIM1 mRNA in cells, and suppresses its expression by accelerating mRNA decay. Reporter mRNA decay assays localized the TTP-regulated mRNA decay element to a discrete AU-rich sequence in the distal 3′-untranslated region that binds TTP. These data suggest that coordinated stimulation of TTP and PIM1 expression limits the magnitude and duration of PIM1 mRNA accumulation by accelerating its degradation as TTP protein levels increase. Consistent with this model, PIM1 and TTP mRNA levels were well correlated across selected human tissue panels, and PIM1 mRNA was induced to significantly higher levels in mitogen-stimulated fibroblasts from TTP-deficient mice. Together, these data support a model whereby induction of TTP mediates a negative feedback circuit to limit expression of selected mitogen-activated genes.
Niemann-Pick Disease, type C (NPC) is a fatal, neurodegenerative, lysosomal storage disorder. It is a rare disease with broad phenotypic spectrum and variable age of onset. These issues make it difficult to develop a universally accepted clinical outcome measure to assess urgently needed therapies. To this end, clinical investigators have defined emerging, disease severity scales. The average time from initial symptom to diagnosis is approximately 4 years. Further, some patients may not travel to specialized clinical centers even after diagnosis. We were therefore interested in investigating whether appropriately trained, community-based assessment of patient records could assist in defining disease progression using clinical severity scores. In this study we evolved a secure, step wise process to show that pre-existing medical records may be correctly assessed by non-clinical practitioners trained to quantify disease progression. Sixty-four undergraduate students at the University of Notre Dame were expertly trained in clinical disease assessment and recognition of major and minor symptoms of NPC. Seven clinical records, randomly selected from a total of thirty seven used to establish a leading clinical severity scale, were correctly assessed to show expected characteristics of linear disease progression. Student assessment of two new records donated by NPC families to our study also revealed linear progression of disease, but both showed accelerated disease progression, relative to the current severity scale, especially at the later stages. Together, these data suggest that college students may be trained in assessment of patient records, and thus provide insight into the natural history of a disease.
The three human LIG genes encode polypeptides that catalyze phosphodiester bond formation during DNA replication, recombination and repair. While numerous studies have identified protein partners of the human DNA ligases (hLigs), there has been little characterization of the catalytic properties of these enzymes. In this study, we developed and optimized a fluorescence-based DNA ligation assay to characterize the activities of purified hLigs. Although hLigI joins DNA nicks, it has no detectable activity on linear duplex DNA substrates with short, cohesive single-strand ends. By contrast, hLigIIIβ and the hLigIIIα/XRCC1 and hLigIV/XRCC4 complexes are active on both nicked and linear duplex DNA substrates. Surprisingly, hLigIV/XRCC4, which is a key component of the major non-homologous end joining (NHEJ) pathway, is significantly less active than hLigIII on a linear duplex DNA substrate. Notably, hLigIV/XRCC4 molecules only catalyze a single ligation event in the absence or presence of ATP. The failure to catalyze subsequent ligation events reflects a defect in the enzyme-adenylation step of the next ligation reaction and suggests that, unless there is an in vivo mechanism to reactivate DNA ligase IV/XRCC4 following phosphodiester bond formation, the cellular NHEJ capacity will be determined by the number of adenylated DNA ligaseIV/XRCC4 molecules.
Proteomic identification of human papillomavirus type 16 (HPV16) E6-interacting proteins revealed several proteins involved in ubiquitin-mediated proteolysis. In addition to the well-characterized E6AP ubiquitin-protein ligase, a second HECT domain protein (HERC2) and a deubiquitylating enzyme (USP15) were identified by tandem affinity purification of HPV16 E6-associated proteins. This study focuses on the functional consequences of the interaction of E6 with USP15. Overexpression of USP15 resulted in increased levels of the E6 protein, and the small interfering RNA-mediated knockdown of USP15 decreased E6 protein levels. These results implicate USP15 directly in the regulation of E6 protein stability and suggest that ubiquitylated E6 could be a substrate for USP15 ubiquitin peptidase activity. It remains possible that E6 could affect the activity of USP15 on specific cellular substrates, a hypothesis that can be tested as more is learned about the substrates and pathways controlled by USP15.
Infection with Aspergillus terreus is more likely to result in invasive, disseminated disease when compared to other Aspergillus species; importantly this species appears to be less susceptible to the antifungal drug amphotericin B. Unique to this species is the ability to produce specialized structures denoted as accessory conidia (AC) directly on hyphae both in vitro and in vivo. With the hypothesis that production of AC by A. terreus may enhance virulence of this organism, we analyzed the phenotype, structure and metabolic potential of these conidia. Comparison of A. terreus phialidic conidia (conidia that arise from conidiophores, PC) and AC architecture by electron microscopy revealed distinct morphological differences between the two conidial forms; AC have a smoother, thicker outer cell surface with no apparent pigment-like layer. Further, AC germinated rapidly, had enhanced adherence to microspheres, and were metabolically more active compared to PC. Additionally, AC contained less cell membrane ergosterol, which correlated with decreased susceptibility to AMB as determined using a flow cytometry based analysis. Furthermore, AC exhibited surface patches of β1-3 glucan, suggestive of attachment scarring. Collectively, the findings of this study suggest a possible role for AC in A. terreus pathogenesis.
The major immediate-early (IE) region of human cytomegalovirus encodes two IE proteins, IE1 72 and IE2 86, that are translated from alternatively spliced transcripts that differ in their 3′ ends. Two other proteins that correspond to the C-terminal region of IE2 86, IE2 60 and IE2 40, are expressed at late times. In this study, we used IE2 mutant viruses to examine the mechanism by which IE2 86, IE2 60, and IE2 40 affect the expression of a viral DNA replication factor, UL84. Deletion of amino acids (aa) 136 to 290 of IE2 86 results in a significant decrease in UL84 protein during the infection. This loss of UL84 is both proteasome and calpain independent, and the stability of the protein in the context of infection with the mutant remains unaffected. The RNA for UL84 is expressed to normal levels in the mutant virus-infected cells, as are the RNAs for two other proteins encoded by this region, UL85 and UL86. Moreover, nuclear-to-cytoplasmic transport and the distribution of the UL84 mRNA on polysomes are unaffected. A region between aa 290 and 369 of IE2 86 contributes to the UL84-IE2 86 interaction in vivo and in vitro. IE2 86, IE2 60, and IE2 40 are each able to interact with UL84 in the mutant-infected cells, suggesting that these interactions may be important for the roles of UL84 and the IE2 proteins. Thus, these data have defined the contribution of IE2 86, IE2 60, and IE2 40 to the efficient expression of UL84 throughout the infection.
The ubiquitous RNA-binding protein AUF1 promotes the degradation of some target mRNAs, but increases the stability and translation of other targets. Here, we isolated AUF1-associated mRNAs by immunoprecipitation of (AUF1–RNA) ribonucleoprotein (RNP) complexes from HeLa cells, identified them using microarrays, and used them to elucidate a signature motif shared among AUF1 target transcripts. The predicted AUF1 motif (29–39 nucleotides) contained 79% As and Us, consistent with the AU-rich sequences of reported AUF1 targets. Importantly, 10 out of 15 previously reported AUF1 target mRNAs contained the AUF1 motif. The predicted interactions between AUF1 and target mRNAs were recapitulated in vitro using biotinylated RNAs. Interestingly, further validation of predicted AUF1 target transcripts revealed that AUF1 associates with both the pre-mRNA and the mature mRNA forms. The consequences of AUF1 binding to 10 predicted target mRNAs were tested by silencing AUF1, which elevated the steady-state levels of only four mRNAs, and by overexpressing AUF1, which also lowered the levels of only four mRNAs. In total, we have identified a signature motif in AUF1 target mRNAs, have found that AUF1 also associates with the corresponding pre-mRNAs, and have discovered that altering AUF1 levels alone only modifies the levels of subsets of target mRNAs.
Reliable information extraction applications have been a long sought goal of the biomedical text mining community, a goal that if reached would provide valuable tools to benchside biologists in their increasingly difficult task of assimilating the knowledge contained in the biomedical literature. We present an integrated approach to concept recognition in biomedical text. Concept recognition provides key information that has been largely missing from previous biomedical information extraction efforts, namely direct links to well defined knowledge resources that explicitly cement the concept's semantics. The BioCreative II tasks discussed in this special issue have provided a unique opportunity to demonstrate the effectiveness of concept recognition in the field of biomedical language processing.
Through the modular construction of a protein interaction relation extraction system, we present several use cases of concept recognition in biomedical text, and relate these use cases to potential uses by the benchside biologist.
Current information extraction technologies are approaching performance standards at which concept recognition can begin to deliver high quality data to the benchside biologist. Our system is available as part of the BioCreative Meta-Server project and on the internet .
The fluorescent base analogue 2-aminopurine (2-AP) is commonly used to study specific conformational and protein-binding events involving nucleic acids. Here, combinations of steady-state and time-resolved fluorescence spectroscopy of 2-AP were employed to monitor conformational transitions within a model hairpin RNA from diverse structural perspectives. RNA substrates adopting stable, unambiguous secondary structures were labeled with 2-AP at an unpaired base, within the loop, or inside the base-paired stem. Steady-state fluorescence was monitored as the RNA hairpins were transitioned between folded and unfolded conformations using thermal denaturation, urea titration, and cation-mediated folding. Unstructured control RNA substrates permitted the effects of higher-order RNA structures on 2-AP fluorescence to be distinguished from stimulus-dependent changes in intrinsic 2-AP photophysics and/or interactions with adjacent residues. Thermodynamic parameters describing local conformational changes were thus resolved from multiple perspectives within the model RNA hairpin. These data provided energetic bases for construction of folding mechanisms, which varied among different folding/unfolding stimuli. Time-resolved fluorescence studies further revealed that 2-AP exhibits characteristic signatures of component fluorescence lifetimes and respective fractional contributions in different RNA structural contexts. Together, these studies demonstrate localized conformational events contributing to RNA folding and unfolding that could not be observed by approaches monitoring only global structural transitions.
To assess the accuracy of kV cone-beam CT (CBCT) based setup corrections as compared to orthogonal MV portal image-based corrections for patients undergoing external-beam radiotherapy of the prostate.
Method and Materials
Daily cone-beam CT volumetric images were acquired after setup for patients with three intra-prostatic fiducial markers. The estimated couch shifts were compared retrospectively to patient adjustments based on two orthogonal MV portal images (the current clinical standard of care in our institution). The CBCT soft-tissue based shifts were also estimated by digitally removing the gold markers in each projection to suppress the artifacts in the reconstructed volumes. A total of 256 volumetric images for 15 patients were analyzed.
The Pearson coefficient of correlation for the patient position shifts using fiducial markers in MV vs kV was (R2 = 0.95, 0.84, 0.81) in the L/R, A/P and S/I directions respectively. The correlation using soft-tissue matching was ((R2 = 0.90, 0.49, 0.51) in the L/R, A/P and S/I directions. A Bland-Altman analysis showed no significant trends in the data. The percentage of shifts within a +/−3mm tolerance (the clinical action level) was (99.7, 95.5, 91.3) for fiducial marker matching and (99.5, 70.3, 78.4) for soft-tissue matching.
Cone-beam CT is an accurate and precise tool for image-guidance. It provides an equivalent means of patient setup correction for prostate patients with implanted gold fiducial markers. Use of the additional information provided by the visualization of soft-tissue structures is an active area of research.
cone-beam CT; image-guided; prostate radiotherapy; fiducial markers; surrogates
The RNA-binding factor HuR is a ubiquitously expressed member of the Hu protein family that binds and stabilizes mRNAs containing AU-rich elements (AREs). Hu proteins share a common domain organization of two tandemly arrayed RNA Recognition Motifs (RRMs) near the N-terminus followed by a basic hinge domain and a third RRM near the C-terminus. In this study we have engineered recombinant wild type and mutant HuR proteins lacking affinity tags to characterize their ARE-binding properties. Using combinations of electrophoretic mobility shift and fluorescence anisotropy-based binding assays, we show that HuR can bind ARE substrates as small as 13 nucleotides with low nanomolar affinity, but forms cooperative, oligomeric protein complexes on ARE substrates of at least 18 nucleotides in length. Analyses of deletion mutant proteins indicate that RRM3 does not contribute to high affinity recognition of ARE substrates, but is required for cooperative assembly of HuR oligomers on RNA. Finally, the hinge domain between RRMs 2 and 3 contributes significant binding energy to HuR:ARE complex formation in an ARE length-dependent manner. The hinge does not enhance RNA-binding activity by increased ion pair formation despite extensive positive charge within this region, nor does it thermodynamically stabilize protein folding. Together, these studies define distinct roles for the HuR hinge and RRM3 domains in formation of cooperative HuR:ARE complexes in solution.
Association of tristetraprolin (TTP) with mRNAs containing selected AU-rich mRNA-destabilizing elements (AREs) initiates rapid cytoplasmic degradation of these transcripts. The RNA-binding activity of TTP is mediated by an internal tandem zinc finger domain that preferentially recognizes U-rich RNA ligands containing adjacent UUAU half-sites, and is accompanied by conformational changes within the peptide. Here, we have used analogues of the TTP RNA-binding domain containing specific tryptophan substitutions to probe the Zn2+- and RNA substrate-dependence of conformational events within individual zinc fingers. Fluorescence methods demonstrate that the N-terminal, but not C-terminal zinc finger domain adopts a stably folded conformation in the presence of Zn2+. Denaturant titrations suggest that both the N- and C-terminal zinc fingers exhibit limited structural heterogeneity in the absence of RNA substrates, although this is more pronounced for the C-terminal finger. Binding to a cognate ARE substrate induced significant conformational changes within each zinc finger, which also included increased resistance to chemical denaturation. Studies with mutant ARE ligands revealed that a single UUAU half-site was sufficient to induce structural modulation of the N-terminal finger. However, RNA-dependent folding of the C-terminal zinc finger was only observed in the presence of tandem UUAU half-sites, suggesting that the conformation of this domain is linked not only to RNA substrate recognition, but also to the ligand occupancy and/or conformational status of the N-terminal finger. Coupled with previous structural and thermodynamic analyses, these data provide a mechanistic framework for discrimination of RNA substrates involving ligand-dependent conformational adaptation of both zinc fingers within the TTP RNA-binding domain.
Although multiple studies have documented the expression of over 70 novel virus-encoded microRNAs (miRNAs), the targets and functions of most of these regulatory RNA species are unknown. In this study a comparative bioinformatics approach was employed to identify potential human cytomegalovirus (HCMV) mRNA targets of the virus-encoded miRNA miR-UL112-1. Bioinformatics analysis of the known HCMV mRNA 3′ untranslated regions (UTRs) revealed 14 potential viral transcripts that were predicted to contain functional target sites for miR-UL112-1. The potential target sites were screened using luciferase reporters that contain the HCMV 3′UTRs in co-transfection assays with miR-UL112-1. Three of the 14 HCMV miRNA targets were validated, including the major immediate early gene encoding IE72 (UL123, IE1), UL112/113, and UL120/121. Further analysis of IE72 regulation by miR-UL112-1 with clones encoding the complete major immediate early region revealed that the IE72 3′UTR target site is necessary and sufficient to direct miR-UL112-1-specific inhibition of expression in transfected cells. In addition, miR-UL112-1 regulation is mediated through translational inhibition rather than RNA degradation. Premature expression of miR-UL112-1 during HCMV infection resulted in a significant decrease in genomic viral DNA levels, suggesting a functional role for miR-UL112-1 in regulating the expression of genes involved in viral replication. This study demonstrates the ability of a viral miRNA to regulate multiple viral genes.
Our ability to understand the biology of viruses depends not only on functional analysis of genes they encoded but also on specific regulation of those genes during viral infection. In herpesviruses, viral gene regulation is highly complex and plays a significant role in determining the viral life cycle during acute, latent, or persistent infection. The discovery that many herpesviruses express small regulatory RNAs, known as microRNAs, has opened up a whole new area of research in regulation of gene expression. In this paper we demonstrate that a microRNA expressed by human cytomegalovirus is able to regulate multiple viral genes, including one gene thought to be crucial for both acute and latent stages of viral infection in the host. Expression of this microRNA results in a significant reduction in viral replication. This work therefore demonstrates that viral microRNAs can regulate multiple viral genes and can have significant effects on the replication of a virus.