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Representing uncertainty in a spatial invasion model that incorporates human-mediated dispersal
(2013)
Most modes of human-mediated dispersal of invasive species are directional and vector-based. Classical spatial spread models usually depend on probabilistic dispersal kernels that emphasize distance over direction and have limited ability to depict rare but influential long-distance dispersal events. These aspects are problematic if such models are used to estimate invasion risk. Alternatively, a geographic network model may be better at estimating the typically low likelihoods associated with human-mediated dispersal events, but it should also provide a reasonable account of uncertainties that could affect perception of its risk estimates. We developed a network model that assesses the likelihood of dispersal of invasive forest pests in camper-transported firewood in North America. We built the model using data from the U.S. National Recreation Reservation Service, which document visitor travel between populated places and federal campgrounds across the U.S. and Canada. The study area is depicted as a set of coarse-resolution map units. Based on repeated simulations, the model estimates the probability that each unit is a possible origin and destination for firewood-facilitated forest pest invasions. We generated output maps that summarise, for each U.S. state and Canadian province, where (outside the state or province) a camper-transported forest pest likely originated. Treating these output maps as a set of baseline scenarios, we explored the sensitivity of these “origin risk” estimates to additive and multiplicative errors in the probabilities of pest transmission between locations, as well as random changes in the structure of the underlying travel network. We found the patterns of change in the origin risk estimates due to these alterations to be consistent across all states and provinces. This indicates that the network model behaves predictably in the presence of uncertainties, allowing future work to focus on closing knowledge gaps or more sophisticated treatments of the impact of uncertainty on model outputs.
Sphingosine 1-phosphate (S1P) signaling influences numerous cell biological mechanisms such as differentiation, proliferation, survival, migration, and angiogenesis. Intriguingly, our current knowledge is based solely on the role of S1P with an 18-carbon long-chain base length, S1P d18:1. Depending on the composition of the first and rate-limiting enzyme of the sphingolipid de novo metabolism, the serine palmitoyltransferase, other chain lengths have been described in vivo. While cells are also able to produce S1P d20:1, its abundance and function remains elusive so far. Our experiments are highlighting the role of S1P d20:1 in the mouse central nervous system (CNS) and human glioblastoma. We show here that S1P d20:1 and its precursors are detectable in both healthy mouse CNS-tissue and human glioblastoma. On the functional level, we focused our work on one particular, well-characterized pathway, the induction of cyclooxygenase (COX)-2 expression via the S1P receptor 2 (S1P2). Intriguingly, S1P d20:1 only fairly induces COX-2 expression and can block the S1P d18:1-induced COX-2 expression mediated via S1P2 activation in the human glioblastoma cell line LN229. This data indicates that S1P d20:1 might act as an endogenous modulator of S1P signaling via a partial agonism at the S1P2 receptor. While our findings might stimulate further research on the relevance of long-chain base lengths in sphingolipid signaling, the metabolism of S1P d20:1 has to be considered as an integral part of S1P signaling pathways in vivo.
The transporter associated with antigen processing (TAP1/2) translocates cytosolic peptides of proteasomal degradation into the endoplasmic reticulum (ER) lumen. A peptide-loading complex of tapasin, major histocompatibility complex class I, and several auxiliary factors is assembled at the transporter to optimize antigen display to cytotoxic T-lymphocytes at the cell surface. The heterodimeric TAP complex has unique N-terminal domains in addition to a 6 + 6-transmembrane segment core common to most ABC transporters. Here we provide direct evidence that this core TAP complex is sufficient for (i) ER targeting, (ii) heterodimeric assembly within the ER membrane, (iii) peptide binding, (iv) peptide transport, and (v) specific inhibition by the herpes simplex virus protein ICP47 and the human cytomegalovirus protein US6. We show for the first time that the translocation pore of the transporter is composed of the predicted TM-(5-10) of TAP1 and TM-(4-9) of TAP2. Moreover, we demonstrate that the N-terminal domains of TAP1 and TAP2 are essential for recruitment of tapasin, consequently mediating assembly of the macromolecular peptide-loading complex.
The transporter associated with antigen processing (TAP) translocates antigenic peptides from the cytosol into the endoplasmic reticular lumen for subsequent loading onto major histocompatibility complex (MHC) class I molecules. These peptide-MHC complexes are inspected at the cell surface by cytotoxic T-lymphocytes. Assembly of the functional peptide transport and loading complex depends on intra- and intermolecular packing of transmembrane helices (TMs). Here, we have examined the membrane topology of human TAP1 within an assembled and functional transport complex by cysteine-scanning mutagenesis. The accessibility of single cysteine residues facing the cytosol or endoplasmic reticular lumen was probed by a minimally invasive approach using membrane-impermeable, thiol-specific fluorophores in semipermeabilized “living” cells. TAP1 contains ten transmembrane segments, which place the N and C termini in the cytosol. The transmembrane domain consists of a translocation core of six TMs, a building block conserved among most ATP-binding cassette transporters, and a unique additional N-terminal domain of four TMs, essential for tapasin binding and assembly of the peptide-loading complex. This study provides a first map of the structural organization of the TAP machinery within the macromolecular MHCI peptide-loading complex.
Cytotoxic T lymphocytes eliminate infected cells upon surface display of antigenic peptides on major histocompatibility complex I molecules. To promote immune evasion, UL49.5 of several varicelloviruses interferes with the pathway of major histocompatibility complex I antigen processing. However, the inhibition mechanism has not been elucidated yet. Within the macromolecular peptide-loading complex we identified the transporter associated with antigen processing (TAP1 and TAP2) as the prime target of UL49.5. Moreover, we determined the active oligomeric state and crucial elements of the viral factor. Remarkably, the last two residues of the cytosolic tail of UL49.5 are essential for endoplasmic reticulum (ER)-associated proteasomal degradation of TAP. However, this process strictly requires additional signaling of an upstream regulatory element in the ER lumenal domain of UL49.5. Within this new immune evasion mechanism, we show for the first time that additive elements of a small viral factor and their signaling across the ER membrane are essential for targeted degradation of a multi-subunit membrane complex.
Brain metastases are a common finding upon initial diagnosis of otherwise locally limited non-small cell lung cancer. We present a retrospective case series describing three cases of patients with symptomatic, synchronous brain metastases and resectable lung tumors. The patients received local ablative treatment of the brain metastases followed by neoadjuvant immunochemotherapy with pemetrexed, cisplatin, and pembrolizumab. Afterwards, resection of the pulmonary lesion with curative intent was performed. One patient showed progressive disease 12 months after initial diagnosis, and passed away 31 months after initial diagnosis. Two of the patients are still alive and maintain a good quality of life with a progression-free survival and overall survival of 28 and 35 months, respectively, illustrating the potential of novel combinatorial treatment approaches.
Virus-infected cells are eliminated by cytotoxic T lymphocytes, which recognize viral epitopes displayed on major histocompatibility complex class I molecules at the cell surface. Herpesviruses have evolved sophisticated strategies to escape this immune surveillance. During the lytic phase of EBV infection, the viral factor BNLF2a interferes with antigen processing by preventing peptide loading of major histocompatibility complex class I molecules. Here we reveal details of the inhibition mechanism of this EBV protein. We demonstrate that BNLF2a acts as a tail-anchored protein, exploiting the mammalian Asna-1/WRB (Get3/Get1) machinery for posttranslational insertion into the endoplasmic reticulum membrane, where it subsequently blocks antigen translocation by the transporter associated with antigen processing (TAP). BNLF2a binds directly to the core TAP complex arresting the ATP-binding cassette transporter in a transport-incompetent conformation. The inhibition mechanism of EBV BNLF2a is distinct and mutually exclusive of other viral TAP inhibitors.
Dysregulation of blood sphingolipids is an emerging topic in clinical science. The objective of this study was to determine preanalytical biases that typically occur in clinical and translational studies and that influence measured blood sphingolipid levels. Therefore, we collected blood samples from four healthy male volunteers to investigate the effect of storage conditions (time, temperature, long-term storage, freeze–thaw cycles), blood drawing (venous or arterial sampling, prolonged venous compression), and sample preparation (centrifugation, freezing) on sphingolipid levels measured by LC-MS/MS. Our data show that sphingosine 1-phosphate (S1P) and sphinganine 1-phosphate (SA1P) were upregulated in whole blood samples in a time- and temperature-dependent manner. Increased centrifugation at higher speeds led to lower amounts of S1P and SA1P. All other preanalytical biases did not significantly alter the amounts of S1P and SA1P. Further, in almost all settings, we did not detect differences in (dihydro)ceramide levels. In summary, besides time-, temperature-, and centrifugation-dependent changes in S1P and SA1P levels, sphingolipids in blood remained stable under practically relevant preanalytical conditions.
To evade the host's immune response, herpes simplex virus employs the immediate early gene product ICP47 (IE12) to suppress antigen presentation to cytotoxic T-lymphocytes by inhibition of the ATP-binding cassette transporter associated with antigen processing (TAP). ICP47 is a membrane-associated protein adopting an alpha-helical conformation. Its active domain was mapped to residues 3-34 and shown to encode all functional properties of the full-length protein. The active domain of ICP47 was reconstituted into oriented phospholipid bilayers and studied by proton-decoupled 15N and 2H solid-state NMR spectroscopy. In phospholipid bilayers, the protein adopts a helix-loop-helix structure, where the average tilt angle of the helices relative to the membrane surface is approximately 15 degrees (+/- 7 degrees ). The alignment of both structured domains exhibits a mosaic spread of approximately 10 degrees . A flexible dynamic loop encompassing residues 17 and 18 separates the two helices. Refinement of the experimental data indicates that helix 1 inserts more deeply into the membrane. These novel insights into the structure of ICP47 represent an important step toward a molecular understanding of the immune evasion mechanism of herpes simplex virus and are instrumental for the design of new therapeutics.
Cytotoxic T-lymphocytes play an important role in the protection against viral infections, which they detect through the recognition of virus-derived peptides, presented in the context of MHC class I molecules at the surface of the infected cell. The transporter associated with antigen processing (TAP) plays an essential role in MHC class I–restricted antigen presentation, as TAP imports peptides into the ER, where peptide loading of MHC class I molecules takes place. In this study, the UL49.5 proteins of the varicelloviruses bovine herpesvirus 1 (BHV-1), pseudorabies virus (PRV), and equine herpesvirus 1 and 4 (EHV-1 and EHV-4) are characterized as members of a novel class of viral immune evasion proteins. These UL49.5 proteins interfere with MHC class I antigen presentation by blocking the supply of antigenic peptides through inhibition of TAP. BHV-1, PRV, and EHV-1 recombinant viruses lacking UL49.5 no longer interfere with peptide transport. Combined with the observation that the individually expressed UL49.5 proteins block TAP as well, these data indicate that UL49.5 is the viral factor that is both necessary and sufficient to abolish TAP function during productive infection by these viruses. The mechanisms through which the UL49.5 proteins of BHV-1, PRV, EHV-1, and EHV-4 block TAP exhibit surprising diversity. BHV-1 UL49.5 targets TAP for proteasomal degradation, whereas EHV-1 and EHV-4 UL49.5 interfere with the binding of ATP to TAP. In contrast, TAP stability and ATP recruitment are not affected by PRV UL49.5, although it has the capacity to arrest the peptide transporter in a translocation-incompetent state, a property shared with the BHV-1 and EHV-1 UL49.5. Taken together, these results classify the UL49.5 gene products of BHV-1, PRV, EHV-1, and EHV-4 as members of a novel family of viral immune evasion proteins, inhibiting TAP through a variety of mechanisms.