Recruitment of EB1, a master regulator of microtubule dynamics, to the surface of the Theileria annulata schizont

TurboID mapping reveals the exportome of secreted intrinsically disordered proteins in the transforming parasite Theileria annulata

Theileria annulata is a tick-transmitted apicomplexan parasite that gained the unique ability among parasitic eukaryotes to transform its host cell, inducing a fatal cancer-like disease in cattle. Understanding the mechanistic interplay between the host cell and malignant Theileria species that drives this transformation requires the identification of responsible parasite effector proteins. In this study, we used TurboID-based proximity labeling, which unbiasedly identified secreted parasite proteins within host cell compartments. By fusing TurboID to nuclear export or localization signals, we biotinylated proteins in the vicinity of the ligase enzyme in the nucleus or cytoplasm of infected macrophages, followed by mass spectrometry analysis. Our approach revealed with high confidence nine nuclear and four cytosolic candidate parasite proteins within the host cell compartments, eight of which had no orthologs in non-transforming T. orientalis. Strikingly, all eight of these proteins are predicted to be highly intrinsically disordered proteins. We discovered a novel tandem arrayed protein family, nuclear intrinsically disordered proteins (NIDP) 1-4, featuring diverse functions predicted by conserved protein domains. Particularly, NIDP2 exhibited a biphasic host cell-cycle-dependent localization, interacting with the EB1/CD2AP/CLASP1 parasite membrane complex at the schizont surface and the tumor suppressor stromal antigen 2 (STAG2), a cohesion complex subunit, in the host nucleus. In addition to STAG2, numerous NIDP2-associated host nuclear proteins implicated in various cancers were identified, shedding light on the potential role of the T. annulata exported protein family NIDP in host cell transformation and cancer-related pathways.IMPORTANCETurboID proximity labeling was used to identify secreted proteins of Theileria annulata, an apicomplexan parasite responsible for a fatal, proliferative disorder in cattle that represents a significant socio-economic burden in North Africa, central Asia, and India. Our investigation has provided important insights into the unique host-parasite interaction, revealing secreted parasite proteins characterized by intrinsically disordered protein structures. Remarkably, these proteins are conspicuously absent in non-transforming Theileria species, strongly suggesting their central role in the transformative processes within host cells. Our study identified a novel tandem arrayed protein family, with nuclear intrinsically disordered protein 2 emerging as a central player interacting with established tumor genes. Significantly, this work represents the first unbiased screening for exported proteins in Theileria and contributes essential insights into the molecular intricacies behind the malignant transformation of immune cells.

Theileria annulata subtelomere-encoded variable secreted protein-TA05560 interacts with bovine RNA binding motif protein 39 (RBM39)

Theileria annulata is the only eukaryotic pathogen able to transform bovine leukocytes, including B cells, macrophages and dendritic cells. T. annulata-transformed cells exhibit several cancer-like phenotypes, such as hyperproliferation, immortalization and dissemination. Although several parasite factors involved in bovine cell transformation have been explored, the roles of subtelomere-encoded variable secreted proteins (SVSPs) of the parasite in host-cell interactions are largely unknown. In the present study, the target molecule TA05560, a member of the SVSP multigene family of T. annulata, was identified at the mRNA level during different life cycles through a quantitative real-time PCR assay, and the subcellular distribution of TA05560 was examined via confocal microscopy. The results showed that the parasite molecule TA05560 was transcribed mainly in the schizont stage of T. annulata infection, and the protein was distributed in the nucleus and cytoplasm of the parasitized cells. The potential host cell proteins that interact with TA05560 were screened using the yeast two-hybrid system, and the direct interaction between TA05560 and its prey protein, Bos taurus RNA binding motif protein 39 (RBM39) was further identified in HEK293T cells by using confocal microscopy, coimmunoprecipitation and bimolecular fluorescence complementation assays. Moreover, the interaction between TA05560 and its host protein was observed in T. annulata-infected cells via confocal microscopy. Therefore, our study is the first to show that the T. annulata-secreted TA05560 protein directly binds to both the exogenous and endogenous host cell molecule RBM39, laying the foundation for exploring host-parasite interactions and understanding the transformation mechanisms induced by T. annulata and other transforming parasites.

Theileria parasites sequester host eIF5A to escape elimination by host-mediated autophagy

Intracellular pathogens develop elaborate mechanisms to survive within the hostile environments of host cells. Theileria parasites infect bovine leukocytes and cause devastating diseases in cattle in developing countries. Theileria spp. have evolved sophisticated strategies to hijack host leukocytes, inducing proliferative and invasive phenotypes characteristic of cell transformation. Intracellular Theileria parasites secrete proteins into the host cell and recruit host proteins to induce oncogenic signaling for parasite survival. It is unknown how Theileria parasites evade host cell defense mechanisms, such as autophagy, to survive within host cells. Here, we show that Theileria annulata parasites sequester the host eIF5A protein to their surface to escape elimination by autophagic processes. We identified a small-molecule compound that reduces parasite load by inducing autophagic flux in host leukocytes, thereby uncoupling Theileria parasite survival from host cell survival. We took a chemical genetics approach to show that this compound induced host autophagy mechanisms and the formation of autophagic structures via AMPK activation and the release of the host protein eIF5A which is sequestered at the parasite surface. The sequestration of host eIF5A to the parasite surface offers a strategy to escape elimination by autophagic mechanisms. These results show how intracellular pathogens can avoid host defense mechanisms and identify a new anti-Theileria drug that induces autophagy to target parasite removal.

Trifloxystrobin blocks the growth of Theileria parasites and is a promising drug to treat Buparvaquone resistance

Theileria parasites are responsible for devastating cattle diseases, causing major economic losses across Africa and Asia. Theileria spp. stand apart from other apicomplexa parasites by their ability to transform host leukocytes into immortalized, hyperproliferating, invasive cells that rapidly kill infected animals. The emergence of resistance to the theilericidal drug Buparvaquone raises the need for new anti-Theileria drugs. We developed a microscopy-based screen to reposition drugs from the open-access Medicines for Malaria Venture (MMV) Pathogen Box. We show that Trifloxystrobin (MMV688754) selectively kills lymphocytes or macrophages infected with Theileria annulata or Theileria parva parasites. Trifloxystrobin treatment reduced parasite load in vitro as effectively as Buparvaquone, with similar effects on host gene expression, cell proliferation and cell cycle. Trifloxystrobin also inhibited parasite differentiation to merozoites (merogony). Trifloxystrobin inhibition of parasite survival is independent of the parasite TaPin1 prolyl isomerase pathway. Furthermore, modeling studies predicted that Trifloxystrobin and Buparvaquone could interact distinctly with parasite Cytochrome B and we show that Trifloxystrobin was still effective against Buparvaquone-resistant cells harboring TaCytB mutations. Our study suggests that Trifloxystrobin could provide an effective alternative to Buparvaquone treatment and represents a promising candidate for future drug development against Theileria spp.

Theileria annulata SVSP455 interacts with host HSP60

Background

Theileria annulata, a transforming parasite, invades bovine B cells, dendritic cells and macrophages, promoting the uncontrolled proliferation of these cells. This protozoan evolved intricate strategies to subvert host cell signaling pathways related to antiapoptotic signaling to enable survival and proliferation within the host cells. However, the molecular mechanisms of the cell transformation induced by T. annulata remain largely unclear. Although some studies have predicted that the subtelomere-encoded variable secreted protein (SVSP) family plays roles in host-parasite interactions, the evidence for this is limited.

Methods

In the present study, the SVSP455 (TA05545) gene, a member of the SVSP gene family, was used as the target molecule. The expression pattern of SVSP455 in different life-cycle stages of T. annulata infection was explored using a quantitative real-time PCR assay, and the subcellular distribution of SVSP455 was observed using confocal microscopy. The host cell proteins interacting with SVSP455 were screened using the Y2H system, and their interactions were verified in vivo and in vitro using both bimolecular fluorescence complementation and confocal microscopy, and co-immunoprecipitation assays. The role played by SVSP455 in cell transformation was further explored by using overexpression, RNA interference and drug treatment experiments.

Results

The highest level of the SVSP455 transcript was detected in the schizont stage of T. annulata, and the protein was located both on the surface of schizonts and in the host cell cytoplasm. In addition, the interaction between SVSP455 and heat shock protein 60 was shown in vitro, and their link may regulate host cell apoptosis in T. annulata-infected cells.

Conclusion

Our findings are the first to reveal that T. annulata-secreted SVSP455 molecule directly interacts with both exogenous and endogenous bovine HSP60 protein, and that the interaction of SVSP455-HSP60 may manipulate the host cell apoptosis signaling pathway. These results provide insights into cancer-like phenotypes underlying Theilera transformation and therapeutics for protection against other pathogens.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05427-z.

CD4 T Cell Responses to Theileria parva in Immune Cattle Recognize a Diverse Set of Parasite Antigens Presented on the Surface of Infected Lymphoblasts

Parasite-specific CD8 T cell responses play a key role in mediating immunity against Theileria parva in cattle (Bos taurus), and there is evidence that efficient induction of these responses requires CD4 T cell responses. However, information on the antigenic specificity of the CD4 T cell response is lacking. The current study used a high-throughput system for Ag identification using CD4 T cells from immune animals to screen a library of ∼40,000 synthetic peptides representing 499 T. parva gene products. Use of CD4 T cells from 12 immune cattle, representing 12 MHC class II types, identified 26 Ags. Unlike CD8 T cell responses, which are focused on a few dominant Ags, multiple Ags were recognized by CD4 T cell responses of individual animals. The Ags had diverse properties, but included proteins encoded by two multimember gene families: five haloacid dehalogenases and five subtelomere-encoded variable secreted proteins. Most Ags had predicted signal peptides and/or were encoded by abundantly transcribed genes, but neither parameter on their own was reliable for predicting antigenicity. Mapping of the epitopes confirmed presentation by DR or DQ class II alleles and comparison of available T. parva genome sequences demonstrated that they included both conserved and polymorphic epitopes. Immunization of animals with vaccine vectors expressing two of the Ags demonstrated induction of CD4 T cell responses capable of recognizing parasitized cells. The results of this study provide detailed insight into the CD4 T cell responses induced by T. parva and identify Ags suitable for use in vaccine development.

The phenotypic and haemato-biochemical appraisal of tropical theileriosis in newborn calves

Tropical theileriosis is one of the major causes of newborn calves mortality. Observation of clinical manifestations is important while making the presumptive/tentative diagnosis of tropical theileriosis in newborn calves. The phenotypic and haemato-biochemical appraisals of tropical theileriosis could be of great help to make a holistic therapeutic plan for diseased newborn calves. Therefore, the present study aimed to evaluate the haemato-biochemical and phenotypic diagnostic markers of tropical theileriosis in newborn calves. A total of 43 newborn calves naturally infected with Theileria annulata and 16 age-matched healthy calves were enrolled. The percentage distribution of clinical markers was generalized lymph nodes enlargement (100%), pyrexia (97.67%), respiratory distress (95.34%), tick infestation (90.69%), anorexia (88.37%), pica (81.39%), pallor mucous membrane (67.44%), hyperlacrimation (58.13%) and exophthalmia (30.22%). Haemograms including TEC, Hb and HCT were found to be significantly (P ≤ 0.001) lowered in diseased calves. Remarkable alterations in the leukogram panels were not observed. Serum glucose, total protein, albumin and globulin concentrations of calves with theileriosis were significantly (P ≤ 0.001) lower than healthy ones, whereas triglycerides and total cholesterol levels of diseased calves were significantly (P ≤ 0.001) higher. Significantly (P ≤ 0.001) elevated activities of serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) enzymes were observed in diseased calves. An evaluation of clinical phenotypes could be helpful to initiate quick treatment of diseased calves in field conditions and save the lives of sick calves of economically poor farmers. Altered haemato-biochemical panels to be appraised by veterinary clinicians while making a therapeutic plan of tropical theileriosis.

Screening and identification of Theileria annulata subtelomere-encoded variable secreted protein-950454 (SVSP454) interacting proteins from bovine B cells

BACKGROUND

Theileria annulata is a protozoan parasite that can infect and transform bovine B cells, macrophages, and dendritic cells. The mechanism of the transformation is still not well understood, and some parasite molecules have been identified, which contribute to cell proliferation by regulating host signaling pathways. Subtelomeric variable secreted proteins (SVSPs) of Theileria might affect the host cell phenotype, but its function is still not clear. Therefore, in the present study, we explored the interactions of SVSP454 with host cell proteins to investigate the molecular mechanism of T. annulata interaction with host cells.

METHODS

The transcription level of an SVSP protein from T. annulata, SVSP454, was analyzed between different life stages and transformed cell passages using qRT-PCR. Then, SVSP454 was used as a bait to screen its interacting proteins from the bovine B cell cDNA library using a yeast two-hybrid (Y2H) system. The potential interacting proteins of host cells with SVSP454 were further identified by using a coimmunoprecipitation (Co-IP) and bimolecular fluorescence complementation (BiFC) assays.

RESULTS

SVSP454 was transcribed in all three life stages of T. annulata but had the highest transcription during the schizont stage. However, the transcription level of SVSP454 continuously decreased as the cultures passaged. Two proteins, Bos Taurus coiled-coil domain 181 (CCDC181) and Bos Taurus mitochondrial ribosomal protein L30 (MRPL30), were screened. The proteins CCDC181 and MRPL30 of the host were further identified to directly interact with SVSP454.

CONCLUSION

In the present study, SVSP454 was used as a bait plasmid, and its prey proteins CCDC181 and MRPL30 were screened out by using a Y2H system. Then, we demonstrated that SVSP454 directly interacted with both CCDC181 and MRPL30 by Co-IP and BiFC assays. Therefore, we speculate that SVSP454-CCDC181/SVSP454MRPL30 is an interacting axis that regulates the microtubule network and translation process of the host by some vital signaling molecules. Identification of the interaction of SVSP454 with CCDC181 and MRPL30 will help illustrate the transformation mechanisms induced by T. annulata.

Theileria's Strategies and Effector Mechanisms for Host Cell Transformation: From Invasion to Immortalization

One of the first events that follows invasion of leukocytes by Theileria sporozoites is the destruction of the surrounding host cell membrane and the rapid association of the intracellular parasite with host microtubules. This is essential for the parasite to establish its niche within the cytoplasm of the invaded leukocyte and sets Theileria spp. apart from other members of the apicomplexan phylum such as Toxoplasma gondii and Plasmodium spp., which reside within the confines of a host-derived parasitophorous vacuole. After establishing infection, transforming Theileria species (T. annulata, T. parva) significantly rewire the signaling pathways of their bovine host cell, causing continual proliferation and resistance to ligand-induced apoptosis, and conferring invasive properties on the parasitized cell. Having transformed its target cell, Theileria hijacks the mitotic machinery to ensure its persistence in the cytoplasm of the dividing cell. Some of the parasite and bovine proteins involved in parasite-microtubule interactions have been fairly well characterized, and the schizont expresses at least two proteins on its membrane that contain conserved microtubule binding motifs. Theileria-encoded proteins have been shown to be translocated to the host cell cytoplasm and nucleus where they have the potential to directly modify signaling pathways and host gene expression. However, little is known about their mode of action, and even less about how these proteins are secreted by the parasite and trafficked to their target location. In this review we explore the strategies employed by Theileria to transform leukocytes, from sporozoite invasion until immortalization of the host cell has been established. We discuss the recent description of nuclear pore-like complexes that accumulate on membranes close to the schizont surface. Finally, we consider putative mechanisms of protein and nutrient exchange that might occur between the parasite and the host. We focus in particular on differences and similarities with recent discoveries in T. gondii and Plasmodium species.

Theileria annulata Subtelomere-Encoded Variable Secreted Protein-TA05575 Binds to Bovine RBMX2

Tropical theileriosis is the disease caused by tick-transmitted apicomplexan parasite Theileria annulata, which has ability to transform bovine leukocytes, including B cells, macrophage cells, and dendritic cells. The T. annulata transformed cells are characterized as uncontrolled proliferation and shared some cancer-like phenotypes. The mechanism of the transformation by T. annulata is still not understood well. In previous reports, the subtelomere-encoded variable secreted proteins (SVSP) of T. parva were considered to contribute to phenotypic changes of the host cell, but the role of SVSP of T. annulata in host-pathogen relationship remains unknown. In the present study, a member of SVSP family, TA05575 of T. annulata was selected as the target molecule to analyze its expression profiles in different life cycle stages of T. annulata by qPCR and investigate its subcellular distribution of different passages of T. annulata transformed cells using confocal experiments. From the results, the transcription level of TA05575 at schizont stage was significantly higher than the other two life stages of T. annulata, and the protein of TA05575 was mainly distributed in nucleus of T. annulata infected cells. In addition, the potential proteins of host cells interacting with TA05575 were screened by Yeast-two hybrid system. The results of Co-IP experiment confirmed that TA05575 interacted with RBMX2-like protein that participated in transcription regulation of cells. In addition, a novel BiFC assay and flow cytometry were carried out, and the results further revealed that TA05575-RBMX2-like pair was directly interacted in cell context. Moreover, this interacting pair was found to distribute in intracellular compartments of HEK293T cells by using confocal microscopy. The results of the present study suggest that TA05575 may contribute for cells transformation due its distribution. According to the function of RBMX2, the interaction of TA05575 and RMMX2-like will provide a new information to further understand the mechanisms of cells transformation by T. annulata.

Theileria secretes proteins to subvert its host leukocyte

Theileria parasites are classified in the phylum Apicomplexa that includes several genera of medical and veterinary importance such as Plasmodium, Babesia, Toxoplasma and Cryptosporidium. These protozoans have evolved subtle ways to reshape their intracellular niche for their own benefit and Theileria is no exception. This tick transmitted microorganism is unique among all eukaryotes in that its intracellular schizont stage is able to transform its mammalian host leukocytes into an immortalised highly disseminating cell that phenocopies tumour cells. Here, we describe what is known about secreted Theileria-encoded host cell manipulators.

Theileria annulata surface protein (TaSP) is a target of cyclin-dependent kinase 1 phosphorylation in Theileria annulata-infected cells

Leucoproliferative Theileria parasites possess the unique capability to transform their bovine host cell, resulting in tumour-like characteristics like uncontrolled proliferation. The molecular mechanisms underlying this parasite-dependent process are only poorly understood. In the current study, bioinformatic analysis of the Theileria annulata surface protein (TaSP) from different T. annulata isolates identified a conserved CDK1 phosphorylation motif T₁₃₁ PTK within the extracellular, polymorphic domain of TaSP. Phosphorylation assays with radioactively labelled ATP as well as ELISA-based experiments using a phospho-threonine-proline (pThr-Pro) antibody revealed, that CDK1-cyclin B specifically phosphorylates T₁₃₁ , identifying TaSP as a substrate in vitro. Confocal microscopy and proximity ligation assays suggest an interaction between CDK1 and TaSP in T. annulata-infected cells. Further studies demonstrated a nearly complete co-localization of the pThr-Pro signal and TaSP only in cells in interphase, pointing towards a cell cycle-dependent event. Immunostainings of isolated, non-permeabilized schizonts confirmed the presence of the pThr-Pro epitope on the schizont's surface. Lambda phosphatase treatment abolished the pThr-Pro signal of the schizont, which was reconstituted by the addition of CDK1-cyclin B. Treatment of T. annulata-infected cells with the CDK1 inhibitor purvalanol A resulted in morphological changes characterized by tubulin-rich cell protrusions and an extension of the schizont, and a dose-dependent reduction of BrdU incorporation and Ki67 staining of T. annulata-infected cells, demonstrating a clear impact on the Theileria-dependent proliferation of the bovine host cell. Our data reveal the parasite surface protein TaSP as a target for the host cell kinase CDK1, a major player during cell division. Targeting the uncontrolled proliferation of Theileria-infected cells is a novel and reasonable approach to limit parasite load in order to facilitate a successful cellular immune response against the parasite.

Recruitment of Host Nuclear Pore Components to the Vicinity of Theileria Schizonts

Theileria schizonts are the only known eukaryotic organisms capable of transforming another eukaryotic cell; as such, probing of the interactions that occur at the host-parasite interface is likely to lead to novel insights into the cell biology underlying leukocyte proliferation and transformation. Little is known about how the parasite communicates with its host or by what route secreted parasite proteins are translocated into the host, and we propose that nuclear trafficking machinery at the parasite surface might play a role in this. The function of AL remains completely unknown, and our work provides a basis for further investigation into the contribution that these porous, cytomembranous structures might make to the survival of fast-growing transformed cells.

Parasitic protozoans of the genus Theileria are intracellular pathogens that induce the cellular transformation of leukocytes, causing uncontrolled proliferation of the infected host cell. The transforming stage of the parasite has a strictly intracellular lifestyle and ensures its distribution to both daughter cells during host cell cytokinesis by aligning itself across the metaphase plate and by binding tightly to central spindle and astral microtubules. Given the importance of the parasite surface in maintaining interactions with host microtubules, we analyzed the ultrastructure of the host-parasite interface using transmission electron microscopy combined with high-resolution fluorescence microscopy and live-cell imaging. We show that porous membranes, termed annulate lamellae (AL), closely associate with the Theileria surface in infected T cells, B cells, and macrophages and are not detectable in noninfected bovine cell lines such as BL20 or BoMACs. AL are membranous structures found in the cytoplasm of fast-proliferating cells such as cancer cells, oocytes, and embryonic cells. Although AL were first observed more than 60 years ago, the function of these organelles is still not known. Indirect immunofluorescence analysis with a pan-nuclear pore complex antibody, combined with overexpression of a panel of nuclear pore proteins, revealed that the parasite recruits nuclear pore complex components close to its surface. Importantly, we show that, in addition to structural components of the nuclear pore complex, nuclear trafficking machinery, including importin beta 1, RanGAP1, and the small GTPase Ran, also accumulated close to the parasite surface.

IMPORTANCETheileria schizonts are the only known eukaryotic organisms capable of transforming another eukaryotic cell; as such, probing of the interactions that occur at the host-parasite interface is likely to lead to novel insights into the cell biology underlying leukocyte proliferation and transformation. Little is known about how the parasite communicates with its host or by what route secreted parasite proteins are translocated into the host, and we propose that nuclear trafficking machinery at the parasite surface might play a role in this. The function of AL remains completely unknown, and our work provides a basis for further investigation into the contribution that these porous, cytomembranous structures might make to the survival of fast-growing transformed cells.

Theileria annulata transformation altered cell surface molecules expression and endocytic function of monocyte-derived dendritic cells

Theileria annulata is a protozoan parasite transmitted by ticks to cattle. The most important processes of T. annulata are the infection and transformation of host monocytes, which promote cell division and generate a neoplastic phenotype. Dendritic cells play an important role in the development of adaptive immune responses against parasites and are traditionally classified into four types. One type of dendritic cell derived from afferent lymph was successfully transformed by T. annulata in vitro in a previous report. However, whether the monocyte-derived dendritic cells could be transformed and how the endocytic function is affected by T. annulata infection were not yet known. Bovine dendritic cells (DCs) derived from blood CD14⁺ monocytes were cocultured with T. annulata sporozoites in vitro. On day 15 post infection, rounded and continuously proliferating cells were observed. The effect of this transformation on cell phenotype was studied using immunostaining and flow cytometry. After transformation, the cells maintained the expression of the DC-specific marker CD11c, but it was downregulated as were the expression of CD11b, CD14 and CD86. In contrast, CD205, CD45 and MHC class Ⅱ molecules were upregulated in transformed cells. The levels of CD172a, CD21, CD40 and CD80 expression were very low in the transformed cells (<1 %). However, the transformed cells maintained high expression levels of MHC Ⅰ (>99 %). In addition, the normal and transformed DCs were cocultured with OVA-FITC antigen to compare the differences of the endocytic functions between these two types of cells. The results revealed that the endocytic functions of MoDCs were significantly inhibited after transformation by T. annulata.

Mutations in the TaPIN1 peptidyl prolyl isomerase gene in Theileria annulata parasites isolated in Sudan

The tick-borne parasite Theileria annulata is the causative agent of tropical theileriosis or Mediterranean theileriosis. Infection of bovine leukocytes by the obligate intracellular parasites induces proliferative and invasive phenotypes associated with activated signaling pathways. The transformed phenotypes of infected cells are reversible by treatment with the theilericidal drug buparvaquone. Recent reports of resistance to buparvaquone in Africa and Asia highlight the need to investigate the mechanisms and prevalence of drug resistance. We screened 67 T. annulata isolates from Sudan to investigate mutations in the T. annulata prolyl isomerase I gene (TaPIN1). The secreted TaPin1 interacts with host proteins to induce pathways driving oncogenic transformation and metabolic reprogramming. We found an Alanine-to-Proline mutation at position 53 (A53P) in the catalytic loop that was previously found in Tunisian drug-resistant samples. This is the first study reporting independent confirmation of the A53P mutation in geographically isolated samples. We found several additional mutations in the predicted N-terminal signal peptide that might affect TaPin1 processing or targeting. We found that many parasites also share mutations in both the TaPIN1 and the cytochrome b genes, suggesting that these two genes represent important biomarkers to follow the spread of resistance in Africa, the Middle East and Asia.

Who Needs a Contractile Actomyosin Ring? The Plethora of Alternative Ways to Divide a Protozoan Parasite

Cytokinesis, or the division of the cytoplasm, following the end of mitosis or meiosis, is accomplished in animal cells, fungi, and amoebae, by the constriction of an actomyosin contractile ring, comprising filamentous actin, myosin II, and associated proteins. However, despite this being the best-studied mode of cytokinesis, it is restricted to the Opisthokonta and Amoebozoa, since members of other evolutionary supergroups lack myosin II and must, therefore, employ different mechanisms. In particular, parasitic protozoa, many of which cause significant morbidity and mortality in humans and animals as well as considerable economic losses, employ a wide diversity of mechanisms to divide, few, if any, of which involve myosin II. In some cases, cell division is not only myosin II-independent, but actin-independent too. Mechanisms employed range from primitive mechanical cell rupture (cytofission), to motility- and/or microtubule remodeling-dependent mechanisms, to budding involving the constriction of divergent contractile rings, to hijacking host cell division machinery, with some species able to utilize multiple mechanisms. Here, I review current knowledge of cytokinesis mechanisms and their molecular control in mammalian-infective parasitic protozoa from the Excavata, Alveolata, and Amoebozoa supergroups, highlighting their often-underappreciated diversity and complexity. Billions of people and animals across the world are at risk from these pathogens, for which vaccines and/or optimal treatments are often not available. Exploiting the divergent cell division machinery in these parasites may provide new avenues for the treatment of protozoal disease.

Theileria highjacks JNK2 into a complex with the macroschizont GPI (GlycosylPhosphatidylInositol)-anchored surface protein p104

Constitutive c-Jun N-terminal kinase (JNK) activity characterizes bovine T and B cells infected with Theileria parva, and B cells and macrophages infected with Theileria annulata. Here, we show that T. annulata infection of macrophages manipulates JNK activation by recruiting JNK2 and not JNK1 to the parasite surface, whereas JNK1 is found predominantly in the host cell nucleus. At the parasite's surface, JNK2 forms a complex with p104, a GPI-(GlycosylPhosphatidylInositol)-anchor T. annulata plasma membrane protein. Sequestration of JNK2 depended on Protein Kinase-A (PKA)-mediated phosphorylation of a JNK-binding motif common to T. parva and a cell penetrating peptide harbouring the conserved p104 JNK-binding motif competitively ablated binding, whereupon liberated JNK2 became ubiquitinated and degraded. Cytosolic sequestration of JNK2 suppressed small mitochondrial ARF-mediated autophagy, whereas it sustained nuclear JNK1 levels, c-Jun phosphorylation, and matrigel traversal. Therefore, T. annulata sequestration of JNK2 contributes to both survival and dissemination of Theileria-transformed macrophages.

Theileria annulata Cyclophilin1 (TaCyp1) Interacts With Host Cell MED21

Host cells infected by Theileria annulata schizonts show the character of permanent proliferation in vitro, also named transformation. To explore the molecular mechanism a T. annulata Cyp1 (TaCyp1) protein potentially involved in regulating cell transformation was used as bait to screen for its interacting proteins by yeast-two-hybrid assay. Additional GST-pull down experiments confirmed that only MED21 specifically interacted with TaCyp1. Moreover, the distribution of TaCyp1 around T. annulata schizonts facilitated interaction with host cell MED21. As a component of mediator complex, MED21 is normally involved in regulating the transcription of nearly all RNA polymerase II-dependent genes. Therefore, to explore its influence on NF-κB signaling MED21 RNA interference and parasite killing with BW720c treatment were performed. Knock down of MED21 resulted in a significant decrease in NF-κB1/2 mRNA expressions, but no significant change in P105, P52 levels, nor detectable alteration in levels of phosphorylated IκBα/β. By contrast, BW720c treatment induced an obvious decrease in the phosphorylation status of P52 and IκBα/β, but no obvious change in that of P105. This suggests that BW720c-induced parasite death had a significant negative influence on NF-κB signaling, whereas knock down of MED21 had no obvious effect on NF-κB signaling. Characterization of TaCyp1 provides information on the function of parasite cyclophilins and leads to a better understanding of the interactions between T. annulata and its host leukocytes.

Immuno-informatics Analysis to Identify Novel Vaccine Candidates and Design of a Multi-Epitope Based Vaccine Candidate Against Theileria parasites

Theileriosis poses a serious threat to ruminants in tropical and subtropical countries. It is a tick-borne disease, caused by an apicomplexan parasite, Theileria. The high disease burden in animals causes huge economic losses to marginal farmers. Further, with increasing cases of resistance to commonly used drugs, it is highly desirable to develop better and cost-effective vaccines against theileriosis. The only available vaccine, live attenuated parasite vaccine, has many drawbacks and hence is unsuitable for controlling this disease. Immuno-informatics has emerged as a useful tool in down selection of potential molecules for vaccine development. In this study, we have used an immuno-informatics driven genome-wide screening strategy to identify potential vaccine targets containing important and effective dominant immunogens against Theileria. The proteome of Theileria annulata was screened for proteins with probability of plasma membrane localization or GPI anchor. The proteins non-homologous to the host (bovine) were selected and their antigenicity was analyzed. The B-cell epitopes were identified in the selected proteins and mapped in the modeled structure of the proteins. A total of 19 linear epitopes in 12 proteins, exposed in the extracellular space and having the potential to induce protective antibodies were obtained. Additionally, CTL epitopes which are peptides with 9-mer core sequence, were also identified, modeled and docked with bovine MHC-I structures. The CTL epitopes showing high binding energy with the bovine MHC-I were further engineered in silico to design a putative multi-epitope vaccine candidate against Theileria parasites. The docking studies and molecular dynamics studies with the predicted multi-epitope vaccine candidate and modeled bovine TLR4 exhibited strong binding energy, suggesting that the complex is stable and the putative multi-epitope vaccine candidate can be a potentially good candidate for vaccine development.

Identification and characterisation of a Theileria annulata proline-rich microtubule and SH3 domain-interacting protein (TaMISHIP) that forms a complex with CLASP1, EB1, and CD2AP at the schizont surface

Theileria annulata is an apicomplexan parasite that modifies the phenotype of its host cell completely, inducing uncontrolled proliferation, resistance to apoptosis, and increased invasiveness. The infected cell thus resembles a cancer cell, and changes to various host cell signalling pathways accompany transformation. Most of the molecular mechanisms leading to Theileria-induced immortalization of leukocytes remain unknown. The parasite dissolves the surrounding host cell membrane soon after invasion and starts interacting with host proteins, ensuring its propagation by stably associating with the host cell microtubule network. By using BioID technology together with fluorescence microscopy and co-immunoprecipitation, we identified a CLASP1/CD2AP/EB1-containing protein complex that surrounds the schizont throughout the host cell cycle and integrates bovine adaptor proteins (CIN85, 14-3-3 epsilon, and ASAP1). This complex also includes the schizont membrane protein Ta-p104 together with a novel secreted T. annulata protein (encoded by TA20980), which we term microtubule and SH3 domain-interacting protein (TaMISHIP). TaMISHIP localises to the schizont surface and contains a functional EB1-binding SxIP motif, as well as functional SH3 domain-binding Px(P/A)xPR motifs that mediate its interaction with CD2AP. Upon overexpression in non-infected bovine macrophages, TaMISHIP causes binucleation, potentially indicative of a role in cytokinesis.

Cell penetrating peptides to dissect host-pathogen protein-protein interactions in Theileria-transformed leukocytes

One powerful application of cell penetrating peptides is the delivery into cells of molecules that function as specific competitors or inhibitors of protein-protein interactions. Ablating defined protein-protein interactions is a refined way to explore their contribution to a particular cellular phenotype in a given disease context. Cell-penetrating peptides can be synthetically constrained through various chemical modifications that stabilize a given structural fold with the potential to improve competitive binding to specific targets. Theileria-transformed leukocytes display high PKA activity, but PKA is an enzyme that plays key roles in multiple cellular processes; consequently genetic ablation of kinase activity gives rise to a myriad of confounding phenotypes. By contrast, ablation of a specific kinase-substrate interaction has the potential to give more refined information and we illustrate this here by describing how surgically ablating PKA interactions with BAD gives precise information on the type of glycolysis performed by Theileria-transformed leukocytes. In addition, we provide two other examples of how ablating specific protein-protein interactions in Theileria-infected leukocytes leads to precise phenotypes and argue that constrained penetrating peptides have great therapeutic potential to combat infectious diseases in general.

Isolation and purification of glycosylphosphatidylinositols (GPIs) in the schizont stage of Theileria annulata and determination of antibody response to GPI anchors in vaccinated and infected animals

BACKGROUND

Tropical theileriosis is widely distributed from North Africa to East Asia. It is a tick-borne disease caused by Theileria annulata, an obligate two-host intracellular protozoan parasite of cattle. Theileria annulata use leukocytes and red blood cells for completion of the life-cycle in mammalian hosts. The stage of Theileria annulata in monocytes and B lymphocytes of cattle is an important step in pathogenicity and diagnosis of the disease. Glycosylphosphatidylinositols (GPIs) are a distinct class of glycolipid structures found in eukaryotic cells and are implicated in several biological functions. GPIs are particularly abundant in protozoan parasites, where they are found as free glycolipids or attached to proteins in the plasma membrane.

RESULTS

In this study we first isolated and purified schizonts of Theileria annulata from infected leukocytes in Theileria annulata vaccine cell line (S15) by aerolysin-percoll technique. Then, the free GPIs of schizont stage and isolated GPI from cell membrane glycoproteins were purified by high performance liquid chromatography (HPLC) and confirmed by gas chromatography-mass spectrometry (GC-MS). Furthermore, enzyme linked immunosorbent assay (ELISA) on the serum samples obtained from naturally infected, as well as Theileria annulata-vaccinated animals, confirmed a significant (P < 0.01) high level of anti-GPI antibody in their serum.

CONCLUSIONS

The results presented in this study show, to our knowledge for the first time, the isolation of GPI from the schizont stage of Theileria annulata and demonstrate the presence of anti-GPI antibody in the serum of naturally infected as well as vaccinated animals. This finding is likely to be valuable in studies aimed at the evaluation of chemically structures of GPIs in the schizont stage of Theileria annulata and also for pathogenicity and immunogenicity studies with the aim to develop GPI-based therapies or vaccines.

Screening and identification of host proteins interacting with Theileria annulata cysteine proteinase (TaCP) by yeast-two-hybrid system

BACKGROUND

Theileria annulata can infect monocytes/macrophages and B lymphocytes and causes severe lymphoproliferative disease in ruminants. Meanwhile, infection by T. annulata leads to the permanent proliferation of cell population through regulating signaling pathways of host cells. Cysteine proteinases (CPs) are one kind of protein hydrolase and usually play critical roles in parasite virulence, host invasion, nutrition and host immune response. However, the biological function of T. annulata CP (TaCP) is still unclear. In this study, a yeast-two-hybrid assay was performed to screen host proteins interacting with TaCP, to provide information to help our understanding of the molecular mechanisms between T. annulata and host cells.

METHODS

The cDNA from purified bovine B cells was inserted into pGADT7-SfiI vector (pGADT7-SfiI-BcDNA, Prey plasmid) for constructing the yeast two-hybrid cDNA library. TaCP was cloned into the pGBKT7 vector (pGBKT7-TaCP) and was considered as bait plasmid after evaluating the expression, auto-activation and toxicity tests in the yeast strain Y2HGold. The yeast two-hybrid screening was carried out via co-transforming bait and prey plasmids into yeast strain Y2HGold. Sequences of positive preys were analyzed using BLAST, Gene Ontology, UniProt and STRING.

RESULTS

Two host proteins, CRBN (Bos taurus cereblon transcript variant X2) and Ppp4C (Bos indicus protein phosphatase 4 catalytic subunit) were identified to interact with TaCP. The results of functional analysis showed that the two proteins were involved in many cellular processes, such as ubiquitylation regulation, microtubule organization, DNA repair, cell apoptosis and maturation of spliceosomal snRNPs.

CONCLUSIONS

This study is the first to screen the host proteins of bovine B cells interacting with TaCP, and 2 proteins, CRBN and Ppp4C, were identified using yeast two-hybrid technique. The results of functional analysis suggest that the two proteins are involved in many cellular processes, such as ubiquitylation regulating, microtubule organization, DNA repair, cell apoptosis and maturation of spliceosomal snRNPs. The interaction with CRBN and Ppp4C indicate that TaCP possibly is involved in regulating signaling pathways and cell proliferation, which is helpful for understanding the interaction between T. annulata and host cells.

The Microtubule-Stabilizing Protein CLASP1 Associates with the Theileria annulata Schizont Surface via Its Kinetochore-Binding Domain

T. annulata, the only eukaryote known to be capable of transforming another eukaryote, is a widespread parasite of veterinary importance that puts 250 million cattle at risk worldwide and limits livestock development for some of the poorest people in the world. Crucial to the pathology of Theileria is its ability to interact with host microtubules and the mitotic spindle of the infected cell. This study builds on our previous work in investigating the host and parasite molecules involved in mediating this interaction. Because it is not possible to genetically manipulate Theileria schizonts, identifying protein interaction partners is critical to understanding the function of parasite proteins. By identifying two Theileria surface proteins that are involved in the interaction between CLASP1 and the parasite, we provide important insights into the molecular basis of Theileria persistence within a dividing cell.

Theileria is an apicomplexan parasite whose presence within the cytoplasm of a leukocyte induces cellular transformation and causes uncontrolled proliferation and clonal expansion of the infected cell. The intracellular schizont utilizes the host cell’s own mitotic machinery to ensure its distribution to both daughter cells by associating closely with microtubules (MTs) and incorporating itself within the central spindle. We show that CLASP1, an MT-stabilizing protein that plays important roles in regulating kinetochore-MT attachment and central spindle positioning, is sequestered at the Theileria annulata schizont surface. We used live-cell imaging and immunofluorescence in combination with MT depolymerization assays to demonstrate that CLASP1 binds to the schizont surface in an MT-independent manner throughout the cell cycle and that the recruitment of the related CLASP2 protein to the schizont is MT dependent. By transfecting Theileria-infected cells with a panel of truncation mutants, we found that the kinetochore-binding domain of CLASP1 is necessary and sufficient for parasite localization, revealing that CLASP1 interaction with the parasite occurs independently of EB1. We overexpressed the MT-binding domain of CLASP1 in parasitized cells. This exhibited a dominant negative effect on host MT stability and led to altered parasite size and morphology, emphasizing the importance of proper MT dynamics for Theileria partitioning during host cell division. Using coimmunoprecipitation, we demonstrate that CLASP1 interacts, directly or indirectly, with the schizont membrane protein p104, and we describe for the first time TA03615, a Theileria protein which localizes to the parasite surface, where it has the potential to participate in parasite-host interactions.

IMPORTANCET. annulata, the only eukaryote known to be capable of transforming another eukaryote, is a widespread parasite of veterinary importance that puts 250 million cattle at risk worldwide and limits livestock development for some of the poorest people in the world. Crucial to the pathology of Theileria is its ability to interact with host microtubules and the mitotic spindle of the infected cell. This study builds on our previous work in investigating the host and parasite molecules involved in mediating this interaction. Because it is not possible to genetically manipulate Theileria schizonts, identifying protein interaction partners is critical to understanding the function of parasite proteins. By identifying two Theileria surface proteins that are involved in the interaction between CLASP1 and the parasite, we provide important insights into the molecular basis of Theileria persistence within a dividing cell.

[What makes a parasite "transforming"? Insights into cancer from the agents of an exotic pathology, Theileria spp]

Theileria are obligate eukaryotic intracellular parasites of cattle. The diseases they cause, Tropical theileriosis and East Coast Fever, cause huge economic loss in East African, Mediterranean and central and South-East Asian countries. These apicomplexan parasites are the only intracellular eukaryotic parasites known to transform their host cell and represent a unique model to study host-parasite interactions and mechanisms of cancer onset.Here, we review how Theileria parasites induce transformation of their leukocyte host cell and discuss similarities with tumorigenesis. We describe how genomic innovation, epigenetic changes and hijacking of signal transductions enable a eukaryotic parasite to transform its host cell.

Approaches to vaccination against Theileria parva and Theileria annulata

Despite having different cell tropism, the pathogenesis and immunobiology of the diseases caused by Theileria parva and Theileria annulata are remarkably similar. Live vaccines have been available for both parasites for over 40 years, but although they provide strong protection, practical disadvantages have limited their widespread application. Efforts to develop alternative vaccines using defined parasite antigens have focused on the sporozoite and intracellular schizont stages of the parasites. Experimental vaccination studies using viral vectors expressing T. parva schizont antigens and T. parva and T. annulata sporozoite antigens incorporated in adjuvant have, in each case, demonstrated protection against parasite challenge in a proportion of vaccinated animals. Current work is investigating alternative antigen delivery systems in an attempt to improve the levels of protection. The genome architecture and protein-coding capacity of T. parva and T. annulata are remarkably similar. The major sporozoite surface antigen in both species and most of the schizont antigens are encoded by orthologous genes. The former have been shown to induce species cross-reactive neutralizing antibodies, and comparison of the schizont antigen orthologues has demonstrated that some of them display high levels of sequence conservation. Hence, advances in development of subunit vaccines against one parasite species are likely to be readily applicable to the other.

Variation in clinical markers in cattle naturally infected with bovine tropical theileriosis

124 cattle naturally infected with Theileria annulata were inspected for clinical markers. Clinical manifestations of general weakness, reduced appetite, pyrexia reaching 40-42 °C and lachrymal discharge were seen in more than 75 % of the infected animals. Presence of ticks on body, general dullness and depression, recumbency/prostration, oedema of dependent body parts, diarrhea, hypersalivation, pale mucous membranes and yellow colored urine were revealed by more than 50 % of the infected animals. Clinical manifestations of dehydration, abdominal distension/ascites, jaundice and haemoglobinuria were revealed by more than 25 % of the infected animals less than 25 % of the infected animals showed clinical manifestations of exophthalmia, constipation, melena, buccal cavity erosions, congested mucous membranes, nasal discharge and tachypnoea.

Identification of Theileria lestoquardi Antigens Recognized by CD8+ T Cells

As part of an international effort to develop vaccines for Theileria lestoquardi, we undertook a limited screen to test T. lestoquardi orthologues of antigens recognised by CD8+ T lymphocyte responses against T. annulata and T. parva in cattle. Five MHC defined sheep were immunized by live T. lestoquardi infection and their CD8+ T lymphocyte responses determined. Thirteen T. lestoquardi orthologues of T. parva and T. annulata genes, previously shown to be targets of CD8+ T lymphocyte responses of immune cattle, were expressed in autologous fibroblasts and screened for T cell recognition using an IFNγ assay. Genes encoding T. lestoquardi antigens Tl8 (putative cysteine proteinase, 349 aa) or Tl9 (hypothetical secreted protein, 293 aa) were recognise by T cells from one animal that displayed a unique MHC class I genotype. Antigenic 9-mer peptide epitopes of Tl8 and Tl9 were identified through peptide scans using CD8+ T cells from the responding animal. These experiments identify the first T. lestoquardi antigens recognised by CD8+ T cell responses linked to specific MHC class I alleles.

Identification of epitopes recognised by mucosal CD4(+) T-cell populations from cattle experimentally colonised with Escherichia coli O157:H7

Vaccines targeting enterohaemorrhagic Escherichia coli (EHEC) O157:H7 shedding in cattle are only partially protective. The correlates of protection of these vaccines are unknown, but it is probable that they reduce bacterial adherence at the mucosal surface via the induction of blocking antibodies. Recent studies have indicated a role for cellular immunity in cattle during colonisation, providing an impetus to understand the bacterial epitopes recognised during this response. This study mapped the epitopes of 16 EHEC O157:H7 proteins recognised by rectal lymph node CD4(+) T-cells from calves colonised with Shiga toxin producing EHEC O157:H7 strains. 20 CD4(+) T-cell epitopes specific to E. coli from 7 of the proteins were identified. The highly conserved N-terminal region of Intimin, including the signal peptide, was consistently recognised by mucosal CD4(+) T-cell populations from multiple animals of different major histocompatibility complex class II haplotypes. These T-cell epitopes are missing from many Intimin constructs used in published vaccine trials, but are relatively conserved across a range of EHEC serotypes, offering the potential to develop cross protective vaccines. Antibodies recognising H7 flagellin have been consistently identified in colonised calves; however CD4(+) T-cell epitopes from H7 flagellin were not identified in this study, suggesting that H7 flagellin may act as a T-cell independent antigen. This is the first time that the epitopes recognised by CD4(+) T-cells following colonisation with an attaching and effacing pathogen have been characterised in any species. The findings have implications for the design of antigens used in the next generation of EHEC O157:H7 vaccines.

EB1 regulates attachment of Ska1 with microtubules by forming extended structures on the microtubule lattice

Kinetochore couples chromosome movement to dynamic microtubules, a process that is fundamental to mitosis in all eukaryotes but poorly understood. In vertebrates, spindle-kinetochore-associated (Ska1–3) protein complex plays an important role in this process. However, the proteins that stabilize Ska-mediated kinetochore-microtubule attachment remain unknown. Here we show that microtubule plus-end tracking protein EB1 facilitates Ska localization on microtubules in vertebrate cells. EB1 depletion results in a significant reduction of Ska1 recruitment onto microtubules and defects in mitotic chromosome alignment, which is also reflected in computational modelling. Biochemical experiments reveal that EB1 interacts with Ska1, facilitates Ska1-microtubule attachment and together stabilizes microtubules. Structural studies reveal that EB1 either with Ska1 or Ska complex forms extended structures on microtubule lattice. Results indicate that EB1 promotes Ska association with K-fibres and facilitates kinetochore-microtubule attachment. They also implicate that in vertebrates, chromosome coupling to dynamic microtubules could be mediated through EB1-Ska extended structures.

Ska1 is a kinetochore-localised protein that couples kinetochore movement to microtubule (MT) depolymerisation. Here Thomas et al. show that the MT +TIP binding protein EB1 recruits Ska1 to the MT-kinetochore interface and stabilises the interaction between Ska1 and MTs.

Apicomplexans pulling the strings: manipulation of the host cell cytoskeleton dynamics

Invasive stages of apicomplexan parasites require a host cell to survive, proliferate and advance to the next life cycle stage. Once invasion is achieved, apicomplexans interact closely with the host cell cytoskeleton, but in many cases the different species have evolved distinct mechanisms and pathways to modulate the structural organization of cytoskeletal filaments. The host cell cytoskeleton is a complex network, largely, but not exclusively, composed of microtubules, actin microfilaments and intermediate filaments, all of which are modulated by associated proteins, and it is involved in diverse functions including maintenance of cell morphology and mechanical support, migration, signal transduction, nutrient uptake, membrane and organelle trafficking and cell division. The ability of apicomplexans to modulate the cytoskeleton to their own advantage is clearly beneficial. We here review different aspects of the interactions of apicomplexans with the three main cytoskeletal filament types, provide information on the currently known parasite effector proteins and respective host cell targets involved, and how these interactions modulate the host cell physiology. Some of these findings could provide novel targets that could be exploited for the development of preventive and/or therapeutic strategies.

[How does the apicomplexan parasite Theileria control host cell identity?]

Infectious agents, like bacteria or virus, are responsible for a large number of pathologies in mammals. Microbes have developed mechanisms for interacting with host cell pathways and hijacking cellular machinery to change the phenotypic state. In this review, we focus on an interesting apicomplexan parasite called Theileria. Infection by the tick-transmitted T. annulata parasite causes Tropical Theileriosis in North Africa and Asia, and the related T. parva parasite causes East Coast Fever in Sub-Saharan Africa. This parasite is the only eukaryote known to induce the transformation of its mammalian host cells. Indeed, T. annulata and T. parva infect bovine leukocytes leading to transforming phenotypes, which partially mirror human lymphoma pathologies. Theileria infection causes hyperproliferation, invasiveness and escape from apoptosis, presumably through the manipulation of host cellular pathways. Several host-signaling mechanisms have been implicated. Here we describe the mechanisms involved in parasite-induced transformation phenotypes.

A quantitative reverse-transcriptase PCR assay for the assessment of drug activities against intracellular Theileria annulata schizonts

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Quantitative RT real time PCR was used to assess metabolic impairment of Theileria schizonts.

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The method was validated with buparvaquone.

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Buparvaquone acts directly and rapidly on the parasite within 1 h of treatment.

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Electron microscopy confirmed these findings.

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A series of anti-parasitic compounds and antibiotics acted primarily on the host cells.

Intracellular schizonts of the apicomplexans Theileria annulata and Theileria parva immortalize bovine leucocytes thereby causing fatal immunoproliferative diseases. Buparvaquone, a hydroxynaphthoquinone related to parvaquone, is the only drug available against Theileria. The drug is only effective at the onset of infection and emerging resistance underlines the need for identifying alternative compounds. Current drug assays employ monitoring of proliferation of infected cells, with apoptosis of the infected host cell as a read-out, but it is often unclear whether active compounds directly impair the viability of the parasite or primarily induce host cell death. We here report on the development of a quantitative reverse transcriptase real time PCR method based on two Theileria genes, tasp and tap104, which are both expressed in schizonts. Upon in vitro treatment of T. annulata infected bovine monocytes with buparvaquone, TaSP and Tap104 mRNA expression levels significantly decreased in relation to host cell actin already within 4 h of drug exposure, while significant differences in host cell proliferation were detectable only after 48–72 h. TEM revealed marked alterations of the schizont ultrastructure already after 2 h of buparvaquone treatment, while the host cell remained unaffected. Expression of TaSP and Tap104 proteins showed a marked decrease only after 24 h. Therefore, the analysis of expression levels of mRNA coding for TaSP and Tap104 allows to directly measuring impairment of parasite viability. We subsequently applied this method using a series of compounds affecting different targets in other apicomplexan parasites, and show that monitoring of TaSP- and Tap104 mRNA levels constitutes a suitable tool for anti-theilerial drug development.

Cell cycle-dependent phosphorylation of Theileria annulata schizont surface proteins

The invasion of Theileria sporozoites into bovine leukocytes is rapidly followed by the destruction of the surrounding host cell membrane, allowing the parasite to establish its niche within the host cell cytoplasm. Theileria infection induces host cell transformation, characterised by increased host cell proliferation and invasiveness, and the activation of anti-apoptotic genes. This process is strictly dependent on the presence of a viable parasite. Several host cell kinases, including PI3-K, JNK, CK2 and Src-family kinases, are constitutively activated in Theileria-infected cells and contribute to the transformed phenotype. Although a number of host cell molecules, including IkB kinase and polo-like kinase 1 (Plk1), are recruited to the schizont surface, very little is known about the schizont molecules involved in host-parasite interactions. In this study we used immunofluorescence to detect phosphorylated threonine (p-Thr), serine (p-Ser) and threonine-proline (p-Thr-Pro) epitopes on the schizont during host cell cycle progression, revealing extensive schizont phosphorylation during host cell interphase. Furthermore, we established a quick protocol to isolate schizonts from infected macrophages following synchronisation in S-phase or mitosis, and used mass spectrometry to detect phosphorylated schizont proteins. In total, 65 phosphorylated Theileria proteins were detected, 15 of which are potentially secreted or expressed on the surface of the schizont and thus may be targets for host cell kinases. In particular, we describe the cell cycle-dependent phosphorylation of two T. annulata surface proteins, TaSP and p104, both of which are highly phosphorylated during host cell S-phase. TaSP and p104 are involved in mediating interactions between the parasite and the host cell cytoskeleton, which is crucial for the persistence of the parasite within the dividing host cell and the maintenance of the transformed state.