Two transmembrane dimers of the bovine papillomavirus E5 oncoprotein clamp the PDGF β receptor in an active dimeric conformation

Digital droplet PCR-based detection and quantification of ovine papillomavirus DNA from the vaginal virobiota of healthy mares

There are four genotypes of ovine papillomaviruses (OaPVs): OaPV1, OaPV2, and OaPV4, which are ovine delta papillomaviruses responsible for epithelial and mesenchymal cell infections, and OaPV3, an epitheliotropic Dyokappapapillomavirus associated with cutaneous tumors in sheep, including squamous cell carcinoma. Vaginal swabs of healthy mares were evaluated for the presence of PVs to investigate whether the vaginal virobiota of asymptomatic mares harbored OaPVs. High-performance digital droplet polymerase chain reaction (ddPCR) was used to quantitatively detect OaPV types 1-4 DNA in 94 vaginal swabs collected at the National Reference Center for Veterinary and Comparative Oncology (CEROVEC), Genoa, Italy. All samples were comparatively evaluated for OaPV DNA loading using real-time quantitative PCR. ddPCR detected OaPV DNA in 25 vaginal swab samples (26.6%), whereas qPCR revealed 13 vaginal swabs (11.7%). Differences between the two molecular protocols were determined to be statistically significant using McNemar's test (p < 0.0005). The detected OaPV types were OaPV1 and OaPV3. Both methods failed to detect OaPV2 or OaPV4 DNA, which could be attributed to the limited number of samples examined. OaPV1 is the most prevalent OaPV in equine vaginal virobiota . This study is the first to provide evidence of the presence of OaPV DNA in vaginal swabs of healthy mares. This comparative detection approach underscores the superior sensitivity of ddPCR over qPCR.

Molecular findings and virological assessment of bladder papillomavirus infection in cattle

Bovine and ovine papillomaviruses (BPVs - OaPVs) are infectious agents that have an important role in bladder carcinogenesis of cattle. In an attempt to better understand territorial prevalence of papillomavirus genotypes and gain insights into their molecular pathway(s), a virological assessment of papillomavirus infection was performed on 52 bladder tumors in cattle using droplet digital polymerase chain reaction (ddPCR), an improved version of conventional PCR. ddPCR detected and quantified BPV DNA and mRNAs in all tumor samples, showing that these viruses play a determinant role in bovine bladder carcinogenesis. OaPV DNA and mRNA were detected and quantified in 45 bladder tumors. BPV14, BPV13, BPV2, OaPV2, OaPV1, and OaPV3 were the genotypes most closely related to bladder tumors. ddPCR quantified BPV1 and OaPV4 DNA and their transcripts less frequently. Western blot analysis revealed a significant overexpression of the phosphorylated platelet derived growth factor β receptor (PDGFβR) as well as the transcription factor E2F3, which modulate cell cycle progression in urothelial neoplasia. Furthermore, significant overexpression of calpain1, a Cys protease, was observed in bladder tumors related to BPVs alone and in BPV and OaPV coinfection. Calpain1 has been shown to play a role in producing free transcription factors of the E2F family, and molecular findings suggest that calpain family members work cooperatively to mutually regulate their protease activities in cattle bladder tumors. Altogether, these results showed territorial prevalence of BPV and OaPV genotypes and suggested that PDGFβR and the calpain system appeared to be molecular partners of both BPVs and OaPVs.

De novo-designed transmembrane proteins bind and regulate a cytokine receptor

Transmembrane (TM) domains as simple as a single span can perform complex biological functions using entirely lipid-embedded chemical features. Computational design has the potential to generate custom tool molecules directly targeting membrane proteins at their functional TM regions. Thus far, designed TM domain-targeting agents have been limited to mimicking the binding modes and motifs of natural TM interaction partners. Here, we demonstrate the design of de novo TM proteins targeting the erythropoietin receptor (EpoR) TM domain in a custom binding topology competitive with receptor homodimerization. The TM proteins expressed in mammalian cells complex with EpoR and inhibit erythropoietin-induced cell proliferation. In vitro, the synthetic TM domain complex outcompetes EpoR homodimerization. Structural characterization reveals that the complex involves the intended amino acids and agrees with our designed molecular model of antiparallel TM helices at 1:1 stoichiometry. Thus, membrane protein TM regions can now be targeted in custom-designed topologies.

Vertical Intrauterine Bovine and Ovine Papillomavirus Coinfection in Pregnant Cows

There is very little information available about transplacental infections by the papillomavirus in ruminants. However, recent evidence has emerged of the first report of vertical infections of bovine papillomavirus (BPV) in fetuses from naturally infected, pregnant cows. This study reports the coinfection of BPV and ovine papillomavirus (OaPV) in bovine fetuses from infected pregnant cows suffering from bladder tumors caused by simultaneous, persistent viral infections. Some molecular mechanisms involving the binary complex composed of Eras and platelet-derived growth factor β receptor (PDGFβR), by which BPVs and OaPVs contribute to reproductive disorders, have been investigated. A droplet digital polymerase chain reaction (ddPCR) was used to detect and quantify the nucleic acids of the BPVs of the Deltapapillomavirus genus (BPV1, BPV2, BPV13, and BPV14) and OaPVs belonging to the Deltapapillomavirus (OaPV1, OaPV2, and OaPV4) and Dyokappapapillomavirus (OaPV3) genera in the placenta and fetal organs (heart, lung, liver, and kidneys) of four bovine fetuses from four pregnant cows with neoplasia of the urinary bladder. A papillomaviral evaluation was also performed on the bladder tumors and peripheral blood of these pregnant cows. In all fetal and maternal samples, the genotype distribution of BPVs and OaPVs were evaluated using both their DNA and RNA. A BPV and OaPV coinfection was seen in bladder tumors, whereas only BPV infection was found in peripheral blood. The genotype distribution of both the BPVs and OaPVs detected in placentas and fetal organs indicated a stronger concordance with the viral genotypes detected in bladder tumors rather than in peripheral blood. This suggests that the viruses found in placentas and fetuses may have originated from infected bladders. Our study highlights the likelihood of vertical infections with BPVs and OaPVs and emphasizes the importance of gaining further insights into the mechanisms and consequences of this exposure. This study warrants further research as adverse pregnancy outcomes are a major source of economic losses in cattle breeding.

In silico molecular docking and dynamic simulation of anti-cholinesterase compounds from the extract of Catunaregam spinosa for possible treatment of Alzheimer's disease

Alzheimer's disease (AD), is characterized by a progressive loss of cognitive abilities as well as behavioral symptoms including disorientation, trouble solving problems, personality and mood changes. Acetylcholinesterase (AChE) is a promising target for symptomatic improvement in AD due to its consistent and early cholinergic deficit. This research has investigated the potential compounds from Catunaregam spinosa as AChE inhibitors as a treatment option for AD, aiming to enhance cholinergic neurotransmission and alleviate cognitive decline. Tacrine, the FDA's first approved treatment for AD, is no longer in use due to its hepatotoxicity. Box-Behnken design (BBD) modelling was used to optimise the ultrasonic extraction of alkaloids from the dried fruits of C. spinosa. GC-MS analysis revealed the presence of ninety phytoconstituents in the extract. Among them, eighty-nine new phytoconstituents are reported in this plant fruit for the first time. Out of ninety phytoconstituents, eight phytoconstituents showed the best binding affinity against the AChE enzyme, i.e., PDB IDs 1GQR, 1QTI and 4PQE of AD targets using iGEMDOCK. The lead hits were tested for their drug-like properties and atomistic binding mechanisms using in silico ADMET prediction, LigPlot analysis, and molecular dynamics simulation. The results suggest four compounds such as 1,4,7,10,13,16-hexaoxacyclooctadecane; butanoic acid, 3-methyl-2-[(phenylmethoxy)imino]-, trime; butane-1,2,3,4-tetraol; and D-(+)-ribonic acid.gamma-lactone as potent inhibitors of AChE for the possible treatment of AD.

Adeno-Associated Virus Type 5 Infection via PDGFRα Is Associated With Interstitial Lung Disease in Systemic Sclerosis and Generates Composite Peptides and Epitopes Recognized by the Agonistic Immunoglobulins Present in Patients With Systemic Sclerosis

OBJECTIVE

The etiopathogenesis of systemic sclerosis (SSc) is unknown. Platelet-derived growth factor receptors (PDGFRs) are overexpressed in patients with SSc. Because PDGFRα is targeted by the adeno-associated virus type 5 (AAV5), we investigated whether AAV5 forms a complex with PDGFRα exposing epitopes that may induce the immune responses to the virus-PDGFRα complex.

METHODS

The binding of monomeric human PDGFRα to the AAV5 capsid was analyzed by in silico molecular docking, surface plasmon resonance (SPR), and genome editing of the PDGFRα locus. AAV5 was detected in SSc lungs by in situ hybridization, immunohistochemistry, confocal microscopy, and molecular analysis of bronchoalveolar lavage (BAL) fluid. Immune responses to AAV5 and PDGFRα were evaluated by SPR using SSc monoclonal anti-PDGFRα antibodies and immunoaffinity-purified anti-PDGFRα antibodies from sera of patients with SSc.

RESULTS

AAV5 was detected in the BAL fluid of 41 of 66 patients with SSc with interstitial lung disease (62.1%) and in 17 of 66 controls (25.75%) (P < 0.001). In SSc lungs, AAV5 localized in type II pneumocytes and in interstitial cells. A molecular complex formed of spatially contiguous epitopes of the AAV5 capsid and of PDGFRα was identified and characterized. In silico molecular docking analysis and binding to the agonistic anti-PDGFRα antibodies identified spatially contiguous epitopes derived from PDGFRα and AAV5 that interacted with SSc agonistic antibodies to PDGFRα. These peptides were also able to bind total IgG isolated from patients with SSc, not from healthy controls.

CONCLUSION

These data link AVV5 with the immune reactivity to endogenous antigens in SSc and provide a novel element in the pathogenesis of SSc.

Molecular Detection and Quantification of Ovine Papillomavirus DNA in Equine Sarcoid

Equine sarcoids are caused by infection with bovine papillomavirus (BPV) types 1, 2, and possibly 13. However, a number of sarcoids lack BPV DNA, and new potential etiological agents for sarcoid diseases need to be considered. High-performance digital droplet polymerase chain reaction (ddPCR) was used for the quantitative detection of ovine papillomavirus (OaPV) types 1-4 DNA from 63 sarcoid DNA samples collected in Austria. All samples were comparatively evaluated for OaPV DNA loads by qPCR. Conventional PCR and amplicon sequencing were used to validate the data. Of the 63 sarcoid DNA isolates, ddPCR was able to detect 22 samples harboring OaPV DNA (34.92%), whereas only five of the OaPV-positive samples were revealed by qPCR (22.72%). The differences in detection by ddPCR and qPCR were statistically significant (p < 0.05). The detected OaPV types were OaPV1, 3, and 4. Both methods failed to detect OaPV2 DNA, which could be due to the limited number of examined samples. Importantly, ddPCR detected multiple types of OaPV DNA in seven cases, whereas the qPCR failed to detect multiple infections. This study is the first to provide evidence of the presence of OaPV types 1, 3, and 4 DNA in a subset of equine sarcoids. The comparative detection approach underscores the superior sensitivity of ddPCR compared to that of qPCR.

In Silico Exploration of Potential Phytoconstituents from the Bark Extract of Boswellia serrata for Hemorrhoidal Disease: Molecular Docking and Molecular Dynamics Analysis

Boswellia serrata Roxb. Ex Colebr is a popular medicinal plant used traditionally in herbal medicinal preparations to treat a variety of diseases. The purpose of the present investigation was to investigate the anti-hemorrhoidal property of the bark extract of B. serrata (BS). For this, the sequential Soxhlet extraction method was carried out by using different solvents such as hexane, chloroform, and methanol. After the extraction, the obtained dry extracts were tested for quantitative determinations such as total alkaloid content (TAC), total flavonoid content (TFC), total phenol content (TPC), and total tannin content (TTC) for all the extracts. Moreover, in vitro antioxidant activity was measured using 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity and scavenging activity against 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS). Methanolic bark extract showed the highest TPC (67.10±1.83), TFC (372.73±4.45), TAC (9.732±1.06), and TTC (48.932±1.82), as well as the antioxidant assays DPPH (IC50=9.88 μg/ml) and ABTS (IC50=15.09 μg/ml). In this study, both LC-MS and GC-MS were performed to identify the chemical composition of all the extracts. Consequently, 19 compounds were identified by GC-MS and 27 compounds were identified by LC-MS analysis. The identified phytoconstituent(s) that could potentially interact with the target protein cyclooxygenase-2 (COX-2) (PDB: 4RRW) using molecular dynamics simulation and in silico docking were studied. Three compounds that have passed in drug-likeness and ADME-Tox properties are having more docking score than the standard. In this study, camptothecin, justicidin B, and taxiphyllin are identified as potential lead compounds with anti-hemorrhoidal properties and may be helpful in the process of drug development and discovery of novel drugs. Hence, these results demonstrate that BS is a good source of pharmacologically active components with potential applications against hemorrhoidal disease.

Discovering immunoreceptor coupling and organization motifs

The recently determined cryo-EM structures of the T cell antigen receptor (TCR) and B cell antigen receptor (BCR) show in molecular details the interactions of the ligand-binding part with the signaling subunits but they do not reveal the signaling mechanism of these antigen receptors. Without knowing the molecular basis of antigen sensing by these receptors, a rational design of optimal vaccines is not possible. The existence of conserved amino acids (AAs) that are not involved in the subunit interaction suggests that antigen receptors form higher complexes and/or have lateral interactors that control their activity. Here, I describe evolutionary conserved leucine zipper (LZ) motifs within the transmembrane domains (TMD) of antigen and coreceptor components that are likely to be involved in the oligomerization and lateral interaction of antigen receptor complexes on T and B cells. These immunoreceptor coupling and organization motifs (ICOMs) are also found within the TMDs of other important receptor types and viral envelope proteins. This discovery suggests that antigen receptors do not function as isolated entities but rather as part of an ICOM-based interactome that controls their nanoscale organization on resting cells and their dynamic remodeling on activated lymphocytes.

On a mechanistic impact of transmembrane tetramerization in the pathological activation of RTKs

Constitutive activation of receptor tyrosine kinases (RTKs) via different mutations has a strong impact on the development of severe human disorders, including cancer. Here we propose a putative activation scenario of RTKs, whereby transmembrane (TM) mutations can also promote higher-order oligomerization of the receptors that leads to the subsequent ligand-free activation. We illustrate this scenario using a computational modelling framework comprising sequence-based structure prediction and all-atom 1 µs molecular dynamics (MD) simulations in a lipid membrane for a previously characterised oncogenic TM mutation V536E in platelet-derived growth factor receptor alpha (PDGFRA). We show that in the course of MD simulations the mutant TM tetramer retains stable and compact configuration strengthened by tight protein-protein interactions, while the wild type TM tetramer demonstrates looser packing and a tendency to dissociate. Moreover, the mutation affects the characteristic motions of mutated TM helical segments by introducing additional non-covalent crosslinks in the middle of the TM tetramer, which operate as mechanical hinges. This leads to dynamic decoupling of the C-termini from the rigidified N-terminal parts and facilitates more pronounced possible displacement between the C-termini of the mutant TM helical regions that can provide more freedom for mutual rearrangement of the kinase domains located downstream. Our results for the V536E mutation in the context of PDGFRA TM tetramer allow for the possibility that the effect of oncogenic TM mutations can go beyond alternating the structure and dynamics of TM dimeric states and might also promote the formation of higher-order oligomers directly contributing to ligand-independent signalling effectuated by PDGFRA and other RTKs.

Possible etiological association of ovine papillomaviruses with bladder tumors in cattle

INTRODUCTION

Bladder tumors of cattle are very uncommon accounting from 0.1% to 0.01% of all bovine malignancies. Bladder tumors are common in cattle grazing on bracken fern-infested pasturelands. Bovine papillomaviruses have a crucial role in tumors of bovine urinary bladder.

AIM OF THE STUDY

To investigate the potential association of ovine papillomavirus (OaPV) infection with bladder carcinogenesis of cattle.

METHODS

Droplet digital PCR was used to detect and quantify the nucleic acids of OaPVs in bladder tumors of cattle that were collected at public and private slaughterhouses.

RESULTS

OaPV DNA and RNA were detected and quantified in 10 bladder tumors of cattle that were tested negative for bovine papillomaviruses. The most prevalent genotypes were OaPV1 and OaPV2. OaPV4 was rarely observed. Furthermore, we detected a significant overexpression and hyperphosphorylation of pRb and a significant overexpression and activation of the calpain-1 as well as a significant overexpression of E2F3 and of phosphorylated (activated) PDGFβR in neoplastic bladders in comparison with healthy bladders, which suggests that E2F3 and PDGFβR may play an important role in OaPV-mediated molecular pathways that lead to bladder carcinogenesis.

CONCLUSION

In all tumors, OaPV RNA could explain the causality of the disease of the urinary bladder. Therefore, persistent infections by OaPVs could be involved in bladder carcinogenesis. Our data showed that there is a possible etiologic association of OaPVs with bladder tumors of cattle.

Designed Transmembrane Proteins Inhibit the Erythropoietin Receptor in a Custom Binding Topology

Transmembrane (TM) domains as simple as a single span can perform complex biological functions using entirely lipid-embedded chemical features. Computational design has potential to generate custom tool molecules directly targeting membrane proteins at their functional TM regions. Thus far, designed TM domain-targeting agents have been limited to mimicking binding modes and motifs of natural TM interaction partners. Here, we demonstrate the design of de novo TM proteins targeting the erythropoietin receptor (EpoR) TM domain in a custom binding topology competitive with receptor homodimerization. The TM proteins expressed in mammalian cells complex with EpoR and inhibit erythropoietin-induced cell proliferation. In vitro, the synthetic TM domain complex outcompetes EpoR homodimerization. Structural characterization reveals that the complex involves the intended amino acids and agrees with our designed molecular model of antiparallel TM helices at 1:1 stoichiometry. Thus, membrane protein TM regions can now be targeted in custom designed topologies.

Targeting the PDGF/PDGFR signaling pathway for cancer therapy: A review

Platelet-derived growth factors (PDGFs) and PDGF receptors (PDGFRs) are expressed in a variety of tumors. Activation of the PDGF/PDGFR signaling pathway is associated with cancer proliferation, metastasis, invasion, and angiogenesis through modulating multiple downstream pathways, including phosphatidylinositol 3 kinase/protein kinase B pathway and mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Therefore, targeting PDGF/PDGFR signaling pathway has been demonstrated to be an effective strategy for cancer therapy, and accordingly, some great progress has been made in this field in the past few decades. This review will focus on the PDGF isoforms and their binding with the related PDGFRs, the PDGF/PDGFR signaling and regulation, and especially present strategies and inhibitors developed for cancer therapy, and the related clinical benefits and side effects.

Metatranscriptomics Analysis Reveals Diverse Viral RNA in Cutaneous Papillomatous Lesions of Cattle

Bovine papillomavirus (BPV) is associated with bovine papillomatosis, a disease that forms benign warts in epithelial tissues, as well as malignant lesions. Previous studies have detected a co-infection between BPV and other viruses, making it likely that these co-infections could influence disease progression. Therefore, this study aimed to identify and annotate viral genes in cutaneous papillomatous lesions of cattle. Sequences were obtained from the GEO database, and an RNA-seq computational pipeline was used to analyze 3 libraries from bovine papillomatous lesions. In total, 25 viral families were identified, including Poxviridae, Retroviridae, and Herpesviridae. All libraries shared similarities in the viruses and genes found. The viral genes shared similarities with BPV genes, especially for functions as virion entry pathway, malignant progression by apoptosis suppression and immune system control. Therefore, this study presents relevant data extending the current knowledge regarding the viral microbiome in BPV lesions and how other viruses could affect this disease.

Role of BAG3 in bovine Deltapapillomavirus-mediated autophagy

Bovine Deltapapillomavirus genus (δPV), comprises four members that are highly pathogenic and are frequently associated with bladder tumors of adult cattle and water buffaloes. In particular, bovine δPV-2 and δPV-13 are commonly found in urinary bladder tumors in adult large ruminants reared fully or partially on hilly/mountain pasturelands rich in bracken fern (Pteridium spp.) as the urinary bladder of the herbivores is the specific target for bracken genotoxins such as ptaquiloside (PT). PT is a sesquiterpenoid responsible for alkylation of adenine of codon 61 of gene H-Ras, which results in Glutamine 61 substitution that is essential for guanosine triphosphate (GTP) hydrolysis. Glutamine substitution at position 61 impairs the intrinsic GTPase activity. Therefore, active GTP-bound conformations (Ras-GTP) accumulate in cells, thereby causing abnormal cell proliferation and differentiation. The aim of the present study is to stress how bovine δPVs upregulate different forms of selective autophagy, of which BAG3 is a key player. BAG3 plays a central role in autophagy and acts as a multifunctional hub for an interaction network at the cytosolic and mitochondrial level. BAG3 is a functional partner of bovine δPV E5 oncoprotein and forms a complex with molecular chaperones Hsc70/Hsp70/Hsp8B and with cochaperone CHIP. BAG3 interacts with Synpo2. It is believed that this interaction has a crucial role for autophagosome (mitophagosome) formation. Furthermore, in urothelial cells infected by bovine δPVs, BAG3 interacts with parkin and some receptors such as BNIP3/FUNDC1, which suggests that BAG3 is involved in both parkin-dependent and -independent mitophagy that appear upregulate in bladder carcinogenesis of cattle induced by bovine δPVs. Surprisingly, BAG3 interacts also with ERAS, a protein encoded by the ERas gene, a novel member of the RAS family. Unlike in humans, the ERas gene is a functional gene in the cells of adult cattle, and it appears to play a role in bovine BAG3-mediated selective autophagy, including mitophagy observed in urothelial cells spontaneously infected with bovine papillomavirus.

Pteridium spp. and Bovine Papillomavirus: Partners in Cancer

Bovine papillomavirus (BPV) are a cause for global concern due to their wide distribution and the wide range of benign and malignant diseases they are able to induce. Those lesions include cutaneous and upper digestive papillomas, multiple histological types of urinary bladder cancers—most often associated with BPV1 and BPV2—and squamous cell carcinomas of the upper digestive system, associated with BPV4. Clinical, epidemiological and experimental evidence shows that exposure to bracken fern (Pteridium spp.) and other related ferns plays an important role in allowing viral persistence and promoting the malignant transformation of early viral lesions. This carcinogenic potential has been attributed to bracken illudane glycoside compounds with immune suppressive and mutagenic properties, such as ptaquiloside. This review addresses the role of BPV in tumorigenesis and its interactions with bracken illudane glycosides. Current data indicates that inactivation of cytotoxic T lymphocytes and natural killer cells by bracken fern illudanes plays a significant role in allowing viral persistence and lesion progression, while BPV drives unchecked cell proliferation and allows the accumulation of genetic damage caused by chemical mutagens. Despite limited progress in controlling bracken infestation in pasturelands, bracken toxins remain a threat to animal health. The number of recognized BPV types has steadily increased over the years and now reaches 24 genotypes with different pathogenic properties. It remains essential to widen the available knowledge concerning BPV and its synergistic interactions with bracken chemical carcinogens, in order to achieve satisfactory control of the livestock losses they induce worldwide.

Activation of the PDGF β Receptor by a Persistent Artificial Signal Peptide

Most eukaryotic transmembrane and secreted proteins contain N-terminal signal peptides that mediate insertion of the nascent translation products into the membrane of the endoplasmic reticulum. After membrane insertion, signal peptides typically are cleaved from the mature protein and degraded. Here, we tested whether a small hydrophobic protein selected for growth promoting activity in mammalian cells retained transforming activity while also acting as a signal peptide. We replaced the signal peptide of the PDGF β receptor (PDGFβR) with a previously described 29-residue artificial transmembrane protein named 9C3 that can activate the PDGFβR in trans. We showed that a modified version of 9C3 at the N-terminus of the PDGFβR can function as a signal peptide, as assessed by its ability to support high level expression, glycosylation, and cell surface localization of the PDGFβR. The 9C3 signal peptide retains its ability to interact with the transmembrane domain of the PDGFβR and cause receptor activation and cell proliferation. Cleavage of the 9C3 signal peptide from the mature receptor is not required for these activities. However, signal peptide cleavage does occur in some molecules, and the cleaved signal peptide can persist in cells and activate a co-expressed PDGFβR in trans. Our finding that a hydrophobic sequence can display signal peptide and transforming activity suggest that some naturally occurring signal peptides may also display additional biological activities by interacting with the transmembrane domains of target proteins.

Conformational Clamping by a Membrane Ligand Activates the EphA2 Receptor

The EphA2 receptor is a promising drug target for cancer treatment, since EphA2 activation can inhibit metastasis and tumor progression. It has been recently described that the TYPE7 peptide activates EphA2 using a novel mechanism that involves binding to the single transmembrane domain of the receptor. TYPE7 is a conditional transmembrane (TM) ligand, which only inserts into membranes at neutral pH in the presence of the TM region of EphA2. However, how membrane interactions can activate EphA2 is not known. We systematically altered the sequence of TYPE7 to identify the binding motif used to activate EphA2. With the resulting six peptides, we performed biophysical and cell migration assays that identified a new potent peptide variant. We also performed a mutational screen that determined the helical interface that mediates dimerization of the TM domain of EphA2 in cells. These results, together with molecular dynamic simulations, allowed to elucidate the molecular mechanism that TYPE7 uses to activate EphA2, where the membrane peptide acts as a molecular clamp that wraps around the TM dimer of the receptor. We propose that this binding mode stabilizes the active conformation of EphA2. Our data, additionally, provide clues into the properties that TM ligands need to have in order to achieve activation of membrane receptors.

Association Between BoLA-DRB3.2 Polymorphism and Bovine Papillomavirus Infection for Bladder Tumor Risk in Podolica Cattle

Blood samples from 260 unrelated cattle (132 animals affected by papillomavirus-associated bladder tumors and 128 healthy) were genotyped using the classic polymerase chain reaction/restriction fragment length polymorphism method to screen MHC class II bovine leukocyte antigen-DRB3. 2 polymorphism. The DRB3^*22 allele was significantly (p ≤ 0.01) detected in healthy cattle, thus appearing to have a negative association (protective effect) with virus infection of the urinary bladder known to represent a bladder tumor risk for cattle living free at pasture. Considering the two sequence alleles identified in animals carrying DRB3^*22, DRB3^*011:01 allele from samples of animals harboring the unexpressed bovine papillomaviruses (BPV)-2 E5 gene was characterized by amino acid residues believed to have a protective effect against BPV infection such as arginine at position 71 (R⁷¹) in pocket 4, histidine at position 11 (H¹¹) in pocket 6, and both glutamine at position 9 (Q⁹) and serine at position 57 (S⁵⁷) in pocket 9 of the antigen-binding groove. The DRB3^*011:02v allele from affected animals was characterized by amino acids believed to be susceptibility residues such as lysine (K⁷¹), tyrosine (Y¹¹), glutamic acid (E⁹), and aspartic acid (D⁵⁷) in these pockets. These results suggest that animals harboring the DRB3^*011:01 allele may have a lower risk of BPV infection and, consequently, a reduced risk of bladder tumors.

The human papillomavirus oncoproteins: a review of the host pathways targeted on the road to transformation

Persistent infection with high-risk human papillomaviruses (HR-HPVs) is the causal factor in over 99 % of cervical cancer cases, and a significant proportion of oropharyngeal and anogenital cancers. The key drivers of HPV-mediated transformation are the oncoproteins E5, E6 and E7. Together, they act to prolong cell-cycle progression, delay differentiation and inhibit apoptosis in the host keratinocyte cell in order to generate an environment permissive for viral replication. The oncoproteins also have key roles in mediating evasion of the host immune response, enabling infection to persist. Moreover, prolonged infection within the cellular environment established by the HR-HPV oncoproteins can lead to the acquisition of host genetic mutations, eventually culminating in transformation to malignancy. In this review, we outline the many ways in which the HR-HPV oncoproteins manipulate the host cellular environment, focusing on how these activities can contribute to carcinogenesis.

Bovine Papillomavirus Type 2 Infection Associated with Papillomatosis of the Amniotic Membrane in Water Buffaloes (Bubalus bubalis)

Multiple papillomatous nodules were observed scattered over the amniotic membrane in six water buffaloes that had recently aborted. Grossly, some of the nodules had multiple villous projections while others appeared as single prominent conical or cylindrical horns. Histology revealed folded hyperplastic and hyperkeratotic epithelium supported by a narrow fibro-vascular stalk. Using PCR, sequences of the bovine Deltapapillomavirus type 2 (BPV-2) E5 gene were amplified from the amniotic papillomas. Furthermore, expression of the E5 gene was detected using reverse transcription (RT)-PCR. Western blotting revealed BPV-2 E5 oncoprotein as well as L1 protein, suggesting both abortive and productive infection. Additionally, a functional complex composed of BPV-2 E5 oncoprotein and the phosphorylated PDGFβR was detected, which is consistent with the activation of PDGFβR by the interaction with BPV-2 E5 oncoprotein. These results demonstrate that BPV-2 can infect the amnion of water buffaloes and suggest that this infection may cause proliferation of the epithelial cells of the amnion. While the precise pathogenesis in uncertain, it is possible that BPV-2 infection of stratified squamous epithelial cells within squamous metaplasia foci and/or amniotic plaques could lead to papilloma formation. Papillomavirus-associated amniotic papillomas have not previously been reported in any species, including humans.

Membrane receptor activation mechanisms and transmembrane peptide tools to elucidate them

Single-pass membrane receptors contain extracellular domains that respond to external stimuli and transmit information to intracellular domains through a single transmembrane (TM) α-helix. Because membrane receptors have various roles in homeostasis, signaling malfunctions of these receptors can cause disease. Despite their importance, there is still much to be understood mechanistically about how single-pass receptors are activated. In general, single-pass receptors respond to extracellular stimuli via alterations in their oligomeric state. The details of this process are still the focus of intense study, and several lines of evidence indicate that the TM domain (TMD) of the receptor plays a central role. We discuss three major mechanistic hypotheses for receptor activation: ligand-induced dimerization, ligand-induced rotation, and receptor clustering. Recent observations suggest that receptors can use a combination of these activation mechanisms and that technical limitations can bias interpretation. Short peptides derived from receptor TMDs, which can be identified by screening or rationally developed on the basis of the structure or sequence of their targets, have provided critical insights into receptor function. Here, we explore recent evidence that, depending on the target receptor, TMD peptides cannot only inhibit but also activate target receptors and can accommodate novel, bifunctional designs. Furthermore, we call for more sharing of negative results to inform the TMD peptide field, which is rapidly transforming into a suite of unique tools with the potential for future therapeutics.

Biologically Active Ultra-Simple Proteins Reveal Principles of Transmembrane Domain Interactions

Specific interactions between the helical membrane-spanning domains of transmembrane proteins play central roles in the proper folding and oligomerization of these proteins. However, the relationship between the hydrophobic amino acid sequences of transmembrane domains and their functional interactions is in most cases unknown. Here, we use ultra-simple artificial proteins to systematically study the sequence basis for transmembrane domain interactions. We show that most short homopolymeric polyleucine transmembrane proteins containing single amino acid substitutions can activate the platelet-derived growth factor β receptor or the erythropoietin receptor in cultured mouse cells, resulting in cell transformation or proliferation. These proteins displayed complex patterns of activity that were markedly affected by seemingly minor sequence differences in the ultra-simple protein itself or in the transmembrane domain of the target receptor, and the effects of these sequence differences are not additive. In addition, specific leucine residues along the length of these proteins are required for activity, and the positions of these required leucines differ based on the identity and position of the central substituted amino acid. Our results suggest that these ultra-simple proteins use a variety of molecular mechanisms to activate the same target and that diversification of transmembrane domain sequences over the course of evolution minimized off-target interactions.

Atomistic mechanism of the constitutive activation of PDGFRA via its transmembrane domain

Single-point mutations in the transmembrane (TM) region of receptor tyrosine kinases (RTKs) can lead to abnormal ligand-independent activation. We use a combination of computational modeling, NMR spectroscopy and cell experiments to analyze in detail the mechanism of how TM domains contribute to the activation of wild-type (WT) PDGFRA and its oncogenic V536E mutant. Using a computational framework, we scan all positions in PDGFRA TM helix for identification of potential functional mutations for the WT and the mutant and reveal the relationship between the receptor activity and TM dimerization via different interfaces. This strategy also allows us design a novel activating mutation in the WT (I537D) and a compensatory mutation in the V536E background eliminating its constitutive activity (S541G). We show both computationally and experimentally that single-point mutations in the TM region reshape the TM dimer ensemble and delineate the structural and dynamic determinants of spontaneous activation of PDGFRA via its TM domain. Our atomistic picture of the coupling between TM dimerization and PDGFRA activation corroborates the data obtained for other RTKs and provides a foundation for developing novel modulators of the pathological activity of PDGFRA.

Oral fibropapillomatosis and epidermal hyperplasia of the lip in newborn lambs associated with bovine Deltapapillomavirus

Congenital fibropapillomatosis of the gingiva and oral mucosa and epidermal hyperplasia of the lip are described, for the first time, in two newborn lambs. Expression of the E5 oncoprotein of bovine deltapapillomavirus types 2 (BPV-2) and -13 (BPV-13) was detected in both fibropapillomas and the hyperplastic epidermal cells suggesting the BPV infection was the cause of the proliferative lesions. No DNA sequences of BPV-1 and BPV-14 were detected. Both BPV-2 and BPV-13 DNA were also amplified from peripheral blood mononuclear cells (PBMCs) of the newborn lambs’ dams. The concordance between BPV genotypes detected in the blood of dam and the oral and skin pathological samples of their offspring suggests that a vertical hematogeneous transmission was most likely source of BPV infection. Immunoblotting revealed the presence of E5 dimers allowing the viral protein to be biologically active. E5 dimers bind and activate the platelet derived growth factor β receptor (PDGFβR), a major molecular mechanism contributing to disease. The detection of E5 protein within the proliferating cells therefore adds further evidence that the BPV infection was the cause of the proliferative lesions seen in these lambs. This is the first evidence of vertical transmission of BPVs in sheep resulting in a clinical disease.