Proprotein convertase 5/6 cleaves platelet-derived growth factor A in the human endometrium in preparation for embryo implantation

Establishment of endometrial receptivity is vital for successful embryo implantation. Proprotein convertase 5/6 (referred to as PC6) is up-regulated in the human endometrium specifically at the time of epithelial receptivity. PC6, a serine protease of the proprotein convertase family, plays an important role in converting precursor proteins into their active forms through specific proteolysis. The proform of platelet-derived growth factor A (pro-PDGFA) requires PC cleavage to convert to the active-PDGFA. We investigated the PC6-mediated activation of PDGFA in the human endometrium during the establishment of receptivity. Proteomic analysis identified that the pro-PDGFA was increased in the conditioned medium of HEC1A cells in which PC6 was stably knocked down by small interfering RNA (PC6-siRNA). Western blot analysis demonstrated an accumulation of the pro-PDGFA but a reduction in the active-PDGFA in PC6-siRNA cell lysates and medium compared with control. PC6 cleavage of pro-PDGFA was further confirmed in vitro by incubation of recombinant pro-PDGFA with PC6. Immunohistochemistry revealed cycle-stage-specific localization of the active-PDGFA in the human endometrium. During the non-receptive phase, the active-PDGFA was barely detectable. In contrast, it was localized specifically to the apical surface of the luminal and glandular epithelium in the receptive phase. Furthermore, the active-PDGFA was detected in uterine lavage with levels being significantly higher in the receptive than the non-receptive phase. We thus identified that the secreted PDGFA may serve as a biomarker for endometrial receptivity. This is also the first study demonstrating that the active-PDGFA localizes to the apical surface of the endometrium during receptivity.

The cellular redox environment alters antigen presentation

Cysteine-containing peptides represent an important class of T cell epitopes, yet their prevalence remains underestimated. We have established and interrogated a database of around 70,000 naturally processed MHC-bound peptides and demonstrate that cysteine-containing peptides are presented on the surface of cells in an MHC allomorph-dependent manner and comprise on average 5-10% of the immunopeptidome. A significant proportion of these peptides are oxidatively modified, most commonly through covalent linkage with the antioxidant glutathione. Unlike some of the previously reported cysteine-based modifications, this represents a true physiological alteration of cysteine residues. Furthermore, our results suggest that alterations in the cellular redox state induced by viral infection are communicated to the immune system through the presentation of S-glutathionylated viral peptides, resulting in altered T cell recognition. Our data provide a structural basis for how the glutathione modification alters recognition by virus-specific T cells. Collectively, these results suggest that oxidative stress represents a mechanism for modulating the virus-specific T cell response.

A mechanism for actin filament severing by malaria parasite actin depolymerizing factor 1 via a low affinity binding interface

Actin depolymerizing factor (ADF)/cofilins are essential regulators of actin turnover in eukaryotic cells. These multifunctional proteins facilitate both stabilization and severing of filamentous (F)-actin in a concentration-dependent manner. At high concentrations ADF/cofilins bind stably to F-actin longitudinally between two adjacent actin protomers forming what is called a decorative interaction. Low densities of ADF/cofilins, in contrast, result in the optimal severing of the filament. To date, how these two contrasting modalities are achieved by the same protein remains uncertain. Here, we define the proximate amino acids between the actin filament and the malaria parasite ADF/cofilin, PfADF1 from Plasmodium falciparum. PfADF1 is unique among ADF/cofilins in being able to sever F-actin but do so without stable filament binding. Using chemical cross-linking and mass spectrometry (XL-MS) combined with structure reconstruction we describe a previously overlooked binding interface on the actin filament targeted by PfADF1. This site is distinct from the known binding site that defines decoration. Furthermore, total internal reflection fluorescence (TIRF) microscopy imaging of single actin filaments confirms that this novel low affinity site is required for F-actin severing. Exploring beyond malaria parasites, selective blocking of the decoration site with human cofilin (HsCOF1) using cytochalasin D increases its severing rate. HsCOF1 may therefore also use a decoration-independent site for filament severing. Thus our data suggest that a second, low affinity actin-binding site may be universally used by ADF/cofilins for actin filament severing.

A type III effector antagonizes death receptor signalling during bacterial gut infection

Successful infection by enteric bacterial pathogens depends on the ability of the bacteria to colonize the gut, replicate in host tissues and disseminate to other hosts. Pathogens such as Salmonella, Shigella and enteropathogenic and enterohaemorrhagic (EPEC and EHEC, respectively) Escherichia coli use a type III secretion system (T3SS) to deliver virulence effector proteins into host cells during infection that promote colonization and interfere with antimicrobial host responses. Here we report that the T3SS effector NleB1 from EPEC binds to host cell death-domain-containing proteins and thereby inhibits death receptor signalling. Protein interaction studies identified FADD, TRADD and RIPK1 as binding partners of NleB1. NleB1 expressed ectopically or injected by the bacterial T3SS prevented Fas ligand or TNF-induced formation of the canonical death-inducing signalling complex (DISC) and proteolytic activation of caspase-8, an essential step in death-receptor-induced apoptosis. This inhibition depended on the N-acetylglucosamine transferase activity of NleB1, which specifically modified Arg 117 in the death domain of FADD. The importance of the death receptor apoptotic pathway to host defence was demonstrated using mice deficient in the FAS signalling pathway, which showed delayed clearance of the EPEC-like mouse pathogen Citrobacter rodentium and reversion to virulence of an nleB mutant. The activity of NleB suggests that EPEC and other attaching and effacing pathogens antagonize death-receptor-induced apoptosis of infected cells, thereby blocking a major antimicrobial host response.

High yield production of a soluble human interleukin-3 variant from E. coli with wild-type bioactivity and improved radiolabeling properties

Human interleukin-3 (hIL-3) is a polypeptide growth factor that regulates the proliferation, differentiation, survival and function of hematopoietic progenitors and many mature blood cell lineages. Although recombinant hIL-3 is a widely used laboratory reagent in hematology, standard methods for its preparation, including those employed by commercial suppliers, remain arduous owing to a reliance on refolding insoluble protein expressed in E. coli. In addition, wild-type hIL-3 is a poor substrate for radio-iodination, which has been a long-standing hindrance to its use in receptor binding assays. To overcome these problems, we developed a method for expression of hIL-3 in E. coli as a soluble protein, with typical yields of >3mg of purified hIL-3 per litre of shaking microbial culture. Additionally, we introduced a non-native tyrosine residue into our hIL-3 analog, which allowed radio-iodination to high specific activities for receptor binding studies whilst not compromising bioactivity. The method presented herein provides a cost-effective and convenient route to milligram quantities of a hIL-3 analog with wild-type bioactivity that, unlike wild-type hIL‑3, can be efficiently radio-iodinated for receptor binding studies.

Suppressor of Cytokine Signaling (SOCS) 5 utilises distinct domains for regulation of JAK1 and interaction with the adaptor protein Shc-1

Suppressor of Cytokine Signaling (SOCS)5 is thought to act as a tumour suppressor through negative regulation of JAK/STAT and epidermal growth factor (EGF) signaling. However, the mechanism/s by which SOCS5 acts on these two distinct pathways is unclear. We show for the first time that SOCS5 can interact directly with JAK via a unique, conserved region in its N-terminus, which we have termed the JAK interaction region (JIR). Co-expression of SOCS5 was able to specifically reduce JAK1 and JAK2 (but not JAK3 or TYK2) autophosphorylation and this function required both the conserved JIR and additional sequences within the long SOCS5 N-terminal region. We further demonstrate that SOCS5 can directly inhibit JAK1 kinase activity, although its mechanism of action appears distinct from that of SOCS1 and SOCS3. In addition, we identify phosphoTyr317 in Shc-1 as a high-affinity substrate for the SOCS5-SH2 domain and suggest that SOCS5 may negatively regulate EGF and growth factor-driven Shc-1 signaling by binding to this site. These findings suggest that different domains in SOCS5 contribute to two distinct mechanisms for regulation of cytokine and growth factor signaling.

Lectin switching during dengue virus infection

Dengue virus receptors are relatively poorly characterized, but there has been recent interest in 2 C-type lectin molecules, dendritic cell-specific intercellular adhesion molecule 3 (ICAM-3)-grabbing nonintegrin (DC-SIGN) and its close homologue liver/lymph node-specific ICAM-3-grabbing integrin (L-SIGN), which can both bind dengue and promote infection. In this report we have studied the interaction of dengue viruses produced in insect cells, tumor cell lines, and primary human dendritic cells (DCs) with DC-SIGN and L-SIGN. Virus produced in primary DCs is unable to interact with DC-SIGN but remains infectious for L-SIGN-expressing cells. Skin-resident DCs may thus be a site of initial infection by insect-produced virus, but DCs will likely not participate in large-scale virus replication during dengue infection. These results reveal that differential glycosylation of dengue virus envelope protein is highly dependent on cell state and suggest that studies of virus tropism using virus prepared in insect cells or tumor cell lines should be interpreted with caution.

Prevention of cytotoxic T cell escape using a heteroclitic subdominant viral T cell determinant

High affinity antigen-specific T cells play a critical role during protective immune responses. Epitope enhancement can elicit more potent T cell responses and can subsequently lead to a stronger memory pool; however, the molecular basis of such enhancement is unclear. We used the consensus peptide-binding motif for the Major Histocompatibility Complex molecule H-2K(b) to design a heteroclitic version of the mouse hepatitis virus-specific subdominant S598 determinant. We demonstrate that a single amino acid substitution at a secondary anchor residue (Q to Y at position 3) increased the stability of the engineered determinant in complex with H-2K(b). The structural basis for this enhanced stability was associated with local alterations in the pMHC conformation as a result of the Q to Y substitution. Recombinant viruses encoding this engineered determinant primed CTL responses that also reacted to the wildtype epitope with significantly higher functional avidity, and protected against selection of virus mutated at a second CTL determinant and consequent disease progression in persistently infected mice. Collectively, our findings provide a basis for the enhanced immunogenicity of an engineered determinant that will serve as a template for guiding the development of heteroclitic T cell determinants with applications in prevention of CTL escape in chronic viral infections as well as in tumor immunity.

Structural and biological basis of CTL escape in coronavirus-infected mice

Cytotoxic T lymphocyte escape occurs in many human infections, as well as mice infected with the JHM strain of mouse hepatitis virus, which exhibit CTL escape variants with mutations in a single epitope from the spike glycoprotein (S510). In all CTL epitopes prone to escape, only a subset of all potential variants is generally detected, even though many of the changes that are not selected would result in evasion of the T cell response. It is postulated that these unselected mutations significantly impair virus fitness. To define more precisely the basis for this preferential selection, we combine x-ray crystallographic studies of the MHC class I (D(b))/S510 complexes with viral reverse genetics to identify a prominent TCR contact residue (tryptophan at position 4) prone to escape mutations. The data show that a mutation that is commonly detected in chronically infected mice (tryptophan to arginine) potently disrupts the topology of the complex, explaining its selection. However, other mutations at this residue, which also abrogate the CTL response, are never selected in vivo even though they do not compromise virus fitness in acutely infected animals or induce a significant de novo CTL response. Thus, while structural analyses of the S510/D(b) complex provide a strong basis for why some CTL escape variants are selected, our results also show that factors other than effects on virus fitness limit the diversification of CD8 T cell epitopes.

T Cell Determinants Incorporating β-Amino Acid Residues Are Protease Resistant and Remain Immunogenic In Vivo

A major hurdle in designing successful epitope-based vaccines resides in the delivery, stability, and immunogenicity of the peptide immunogen. The short-lived nature of unmodified peptide-based vaccines in vivo limits their therapeutic application in the immunotherapy of cancers and chronic viral infections as well as their use in generating prophylactic immunity. The incorporation of beta-amino acids into peptides decreases proteolysis, yet its potential application in the rational design of T cell mimotopes is poorly understood. To address this, we have replaced each residue of the SIINFEKL epitope individually with the corresponding beta-amino acid and examined the resultant efficacy of these mimotopes. Some analogs displayed similar MHC binding and superior protease stability compared with the native epitope. Importantly, these analogs were able to generate cross-reactive CTLs in vivo that were capable of lysing tumor cells that expressed the unmodified epitope as a surrogate tumor Ag. Structural analysis of peptides in which anchor residues were substituted with beta-amino acids revealed the basis for enhanced MHC binding and retention of immunogenicity observed for these analogs and paves the way for future vaccine design using beta-amino acids. We conclude that the rational incorporation of beta-amino acids into T cell determinants is a powerful alternative to the traditional homologous substitution of randomly chosen naturally occurring alpha-amino acids, and these mimotopes may prove particularly useful for inclusion in epitope-based vaccines.

Lack of prominent peptide-major histocompatibility complex features limits repertoire diversity in virus-specific CD8+ T cell populations

Using both 'reverse genetics' and structural analysis, we have examined the in vivo relationship between antigenicity and T cell receptor (TCR) repertoire diversity. Influenza A virus infection of C57BL/6 mice induces profoundly different TCR repertoires specific for the nucleoprotein peptide of amino acids 366-374 (NP366) and the acid polymerase peptide of amino acids 224-233 (PA224) presented by H-2D(b). Here we show the H-2D(b)-NP366 complex with a 'featureless' structure selected a limited TCR repertoire characterized by 'public' TCR usage. In contrast, the prominent H-2D(b)-PA224 complex selected diverse, individually 'private' TCR repertoires. Substitution of the arginine at position 7 of PA224 with an alanine reduced the accessible side chains of the epitope. Infection with an engineered virus containing a mutation at the site encoding the exposed arginine at position 7 of PA224 selected a restricted TCR repertoire similar in diversity to that of the H-2D(b)-NP366-specific response. Thus, the lack of prominent features in an antigenic complex of peptide and major histocompatibility complex class I is associated with a diminished spectrum of TCR usage.

The Structure of H-2Kband Kbm8Complexed to a Herpes Simplex Virus Determinant: Evidence for a Conformational Switch That Governs T Cell Repertoire Selection and Viral Resistance

Polymorphism within the MHC not only affects peptide specificity but also has a critical influence on the T cell repertoire; for example, the CD8 T cell response toward an immunodominant HSV glycoprotein B peptide is more diverse and of higher avidity in H-2(bm8) compared with H-2(b) mice. We have examined the basis for the selection of these distinct antiviral T cell repertoires by comparing the high-resolution structures of K(b) and K(bm8), in complex with cognate peptide Ag. Although K(b) and K(bm8) differ by four residues within the Ag-binding cleft, the most striking difference in the two structures was the disparate conformation adopted by the shared residue, Arg(62). The altered dynamics of Arg(62), coupled with a small rigid-body movement in the alpha(1) helix encompassing this residue, correlated with biased Valpha usage in the B6 mice. Moreover, an analysis of all known TCR/MHC complexes reveals that Arg(62) invariably interacts with the TCR CDR1alpha loop. Accordingly, Arg(62) appears to function as a conformational switch that may govern T cell selection and protective immunity.

Functional and Structural Characteristics of NY-ESO-1-related HLA A2-restricted Epitopes and the Design of a Novel Immunogenic Analogue

NY-ESO-1, a commonly expressed tumor antigen of the cancer-testis family, is expressed by a wide range of tumors but not found in normal adult somatic tissue, making it an ideal cancer vaccine candidate. Peptides derived from NY-ESO-1 have shown preclinical and clinical trial promise; however, biochemical features of these peptides have complicated their formulation and led to heterogeneous immune responses. We have taken a rational approach to engineer an HLA A2-restricted NY-ESO-1-derived T cell epitope with improved formulation and immunogenicity to the wild type peptide. To accomplish this, we have solved the x-ray crystallographic structures of HLA A2 complexed to NY-ESO (157-165) and two analogues of this peptide in which the C-terminal cysteine residue has been substituted to alanine or serine. Substitution of cysteine by serine maintained peptide conformation yet reduced complex stability, resulting in poor cytotoxic T lymphocyte recognition. Conversely, substitution with alanine maintained complex stability and cytotoxic T lymphocyte recognition. Based on the structures of the three HLA A2 complexes, we incorporated 2-aminoisobutyric acid, an isostereomer of cysteine, into the epitope. This analogue is impervious to oxidative damage, cysteinylation, and dimerization of the peptide epitope upon formulation that is characteristic of the wild type peptide. Therefore, this approach has yielded a potential therapeutic molecule that satiates the hydrophobic F pocket of HLA A2 and exhibited superior immunogenicity relative to the wild type peptide.

Continuous measurement of caffeine and two metabolites in blood and skeletal muscle of unrestrained adult horses by semi-automated in vivo microdialysis

Concentrations of caffeine (CA) and two metabolites were measured simultaneously in venous blood and splenius muscle of adult horses using a semi-automated in vivo microdialysis sampling technique. Dialysates from muscle and jugular vein were collected continuously for 48 h and drug levels were determined by high performance liquid chromatography (HPLC). Following i.v. injection, CA (3 mg/kg) attained a peak blood level of nearly 5400 +/- 600 ng/mL and decreased with a half-life of 15.3 +/- 0.7 h. Pharmacokinetic and statistical comparisons between CA concentrations in jugular dialysates and plasma samples revealed no significant differences between these sampling techniques. However, measurements in muscle and blood revealed unexpected pharmacokinetic differences, including significantly elevated concentrations of CA in muscle for 4 h following drug administration. In contrast, the CA metabolites theophylline (TP) and theobromine (TB) exhibited delayed appearances in muscle and blood with peak concentrations of 300 +/- 60 ng/mL (TP) and 150 +/- 50 ng/mL (TB) detected in both tissues 1 day following CA administration. This study demonstrates that our novel semi-automated microdialysis procedure for continuous monitoring of drug and metabolite levels may be useful for related studies in other domesticated large animal species.

Penetration of cefaclor into the interstitial space fluid of skeletal muscle and lung tissue in rats

PURPOSE

To measure and compare the penetration of cefaclor from the plasma compartment into the interstitial space of lung and skeletal muscle in rats and to integrate the data in a pharmacokinetic model.

METHODS

Unbound interstitial concentrations in muscle and lung were measured by in vivo microdialysis following i.v. bolus doses of 50 and 75 mg/kg cefaclor. Unbound muscle concentrations were also measured after a primed, continuous i.v. infusion at an infusion rate of 0.3 mg/kg/min.

RESULTS

The cefaclor half-life in plasma, muscle and lung was approximately 1 h. Unbound cefaclor concentrations in muscle and lung were found to be virtually identical. A 2-compartment body model was fitted to the data with a tissue penetration factor (AUC(tissue(unbound)))/AUC(plasma(unbound))) of approximately 0.26 independent of dose, tissue and mode of administration.

CONCLUSIONS

Unbound concentrations of cefaclor in the interstitial space fluid of lung and skeletal muscle are of similar magnitude and lower than those in plasma. Using total plasma concentrations would overestimate the antibacterial activity of the drug and therefore its clinical efficacy. Instead, therapeutically active levels of cefaclor at the site of action should be taken into account. Microdialysis allows direct measurement of these unbound concentrations.

Intravenous pharmacokinetics of penicillin G and antipyrine in ostriches (Struthio camelus) and emus (Dromaius novaehollandiae)

Penicillin G and antipyrine, which served as model drugs to assess the relative capacities of renal and hepatic elimination pathways, respectively, were each administered intravenously to six ostriches (Struthio camelus) and to six emus (Dromaius novaehollandiae). Drug concentrations in blood samples collected over a period of 12 hr after administration were assayed, and elimination half-life, mean residence time, clearance, and steady-state volume of distribution were calculated. Mean values for elimination half-life and mean residence time of penicillin G were significantly higher in emus than in ostriches; no significant differences in antipyrine pharmacokinetics between species were demonstrated.

Effect of respiratory tract disease on pharmacokinetics of tilmicosin in rats

BACKGROUND AND PURPOSE

In rats, murine respiratory mycoplasmosis is caused by Mycoplasma pulmonis. Tilmicosin, a macrolide antibiotic, has good tissue penetration and reaches high concentration in the lungs. Therefore, a model for studying the effects of disease on pharmacokinetics of tilmicosin was developed, using LEW rats.

METHODS

Seventy-two LEW rats were assigned at random to two groups: one group was inoculated with M. pulmonis, and the other served as an uninoculated control group. On postinoculation day 31, all rats received a single dose of tilmicosin (20 mg/kg of body weight, subcutaneously).

RESULTS

Concentration of tilmicosin in the lungs of both groups of rats was significantly higher than serum tilmicosin concentration at all times. Infected rats had significantly higher lung tilmicosin concentration than did noninfected rats. No correlation was found between pH of the lungs and tilmicosin concentration in the lungs in either treatment group, nor did treatment have any effect on pH of the muscle.

CONCLUSION

Tilmicosin accumulates in the lungs, and infection/inflammation further improves its tissue penetration.

The Food Animal Residue Avoidance Databank (FARAD). Past, present and future

During the last one-and-one-half decades, FARAD has established an unparalleled compilation of residue and pharmacokinetic information for veterinary species. In order to fulfill its mission, FARAD has become as much a research project as an educational one. Pressing problems, such as disease-altered kinetics, minor-species drug use, and industrial contaminants in livestock, require the new methods of analysis FARAD is developing. The data upon which this work is based can be greatly augmented by participation by other nations. In the United States, it was the cooperation of both academic and regulatory organizations that made the success of FARAD possible. Similar international cooperation can facilitate use of the FARAD model in other countries for the economic benefit of all participants, enhancement of food safety, and promotion of animal welfare.

Pharmacokinetics and pharmacodynamics of tilmicosin in sheep and cattle

Tilmicosin is a long-acting macrolide antibiotic currently approved for treatment of bovine respiratory disease in the USA. Serum pharmacokinetics of tilmicosin were compared between cattle (major species) and sheep (minor species) after subcutaneous injection in order to evaluate a new potential application of the drug in currently nonapproved species. There were no significant differences in the elimination rates, maximum serum concentrations, half-lives (t1/2), areas under the curve (AUC), areas under the first-moment curve (AUMC), and mean residence times. Volume of distribution (Vd(area)) and clearance (Cl), when normalized by body weight, were also similar. The only significantly different parameter was time at which maximum drug concentration was reached (tmax), with sheep having the tmax of 3.9 h, compared to 0.5 h in cattle. Although macrolides are considered to be one of the safest anti-infective drugs, adverse cardiovascular effects of several macrolides have been reported. The cardiopulmonary effects of tilmicosin were monitored in healthy adult sheep after receiving a single subcutaneous (s.c.) injection of tilmicosin at the dose of 10 mg/kg, and no significant changes were found. The study indicates that tilmicosin can be used safely and effectively in sheep at the given dose, with no adverse cardiopulmonary effects.