Theileria secretes proteins to subvert its host leukocyte

Upregulation of haematopoetic cell kinase (Hck) activity by a secreted parasite effector protein (Ta9) drives proliferation of Theileria annulata-transformed leukocytes

Reversible transformation of bovine leukocytes by the intracellular parasites Theileria annulata and Theileria parva is central to pathogenesis of the diseases they cause, tropical theileriosis and East Coast Fever, respectively. Parasite-dependent constitutive activation of major host transcription factors such as AP-1 (Activating Protein 1) and NF-κB (Nuclear Factor-Kappa B) sustains the transformed state. Although parasite interaction with host cell signaling pathways upstream of AP-1 have been studied, the precise contribution of Theileria encoded factors capable of modulating AP-1 transcriptional activity, and other infection-altered signaling pathways is not fully understood. We previously showed that the Ta9 protein from T. annulata (TA15705) is secreted into the host cell cytoplasm and contributes to infection-induced AP-1 transcriptional activity. The current study employed RNA-seq to investigate the ability of ectopically expressed Ta9 to modulate the gene transcription profile of a bovine macrophage cell line, BoMac. RNA-seq identified 560 (400 upregulated and 160 downregulated) differentially expressed genes. KEGG analysis predicted a high number of upregulated genes associated with carcinogenesis such as CCND1, CDKN1A, ETV4, ETV5, FLI1, FRA1, GLI2, GRO1, HCK, IL7R, MYBL1, MYCN, PIM1 and TAL1. Ta9 introduction also affected genes associated with proinflammatory processes such as cytokines, chemokines, growth factors and metalloproteinases. Enrichment analysis of differentially expressed genes revealed that Ta9 is potentially involved in activating other host cell signaling pathways in addition to those that lead to induction of AP-1. Comparing our data with data on differentially expressed BoMac genes modulated by the secreted TashAT2 factor of T. annulata identified the gene encoding the tyrosine protein kinase hematopoietic cell kinase (HCK) as common to both data sets. HCK is essential for the proliferation of T. parva-transformed B cells and herein, we demonstrate that enzymatic activity of HCK is also essential for T. annulata- and T. lestoquardi-transformed macrophage proliferation.

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 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.

Dual RNA-seq to catalogue host and parasite gene expression changes associated with virulence of T. annulata-transformed bovine leukocytes: towards identification of attenuation biomarkers

The apicomplexan parasite Theileria annulata is transmitted by Hyalomma ticks and causes an acute lymphoproliferative disease that is invariably lethal in exotic cattle breeds. The unique ability of the schizont stage of T. annulata to transform infected leukocytes to a cancer-like phenotype and the simplicity of culturing and passaging T. annulata-transformed cells in vitro have been explored for live vaccine development by attenuating the transformed cells using lengthy serial propagation in vitro. The empirical in vivo evaluation of attenuation required for each batch of long-term cultured cells is a major constraint since it is resource intensive and raises ethical issues regarding animal welfare. As yet, the molecular mechanisms underlying attenuation are not well understood. Characteristic changes in gene expression brought about by attenuation are likely to aid in the identification of novel biomarkers for attenuation. We set out to undertake a comparative transcriptome analysis of attenuated (passage 296) and virulent (passage 26) bovine leukocytes infected with a Tunisian strain of T. annulata termed Beja. RNA-seq was used to analyse gene expression profiles and the relative expression levels of selected genes were verified by real-time quantitative PCR (RT-qPCR) analysis. Among the 3538 T. annulata genes analysed, 214 were significantly differentially expressed, of which 149 genes were up-regulated and 65 down-regulated. Functional annotation of differentially expressed T. annulata genes revealed four broad categories of metabolic pathways: carbon metabolism, oxidative phosphorylation, protein processing in the endoplasmic reticulum and biosynthesis of secondary metabolites. It is interesting to note that of the top 40 genes that showed altered expression, 13 were predicted to contain a signal peptide and/or at least one transmembrane domain, suggesting possible involvement in host-parasite interaction. Of the 16,514 bovine transcripts, 284 and 277 showed up-regulated and down-regulated expression, respectively. These were assigned to functional categories relevant to cell surface, tissue morphogenesis and regulation of cell adhesion, regulation of leucocyte, lymphocyte and cell activation. The genetic alterations acquired during attenuation that we have catalogued herein, as well as the accompanying in silico functional characterization, do not only improve understanding of the attenuation process, but can also be exploited by studies aimed at identifying attenuation biomarkers across different cell lines focusing on some host and parasite genes that have been highlighted in this study, such as bovine genes (CD69, ZNF618, LPAR3, and APOL3) and parasite genes such as TA03875.

Novel secretory organelles of parasite origin - at the center of host-parasite interaction

Reorganization of cell organelle-deprived host red blood cells by the apicomplexan malaria parasite Plasmodium falciparum enables their cytoadherence to endothelial cells that line the microvasculature. This increases the time red blood cells infected with mature developmental stages remain within selected organs such as the brain to avoid the spleen passage, which can lead to severe complications and cumulate in patient death. The Maurer's clefts are a novel secretory organelle of parasite origin established by the parasite in the cytoplasm of the host red blood cell in order to facilitate the establishment of cytoadherence by conducting the trafficking of immunovariant adhesins to the host cell surface. Another important function of the organelle is the sorting of other proteins the parasite traffics into its host cell. Although the organelle is of high importance for the pathology of malaria, additional putative functions, structure, and genesis remain shrouded in mystery more than a century after its discovery. In this review, we highlight our current knowledge about the Maurer's clefts and other novel secretory organelles established within the host cell cytoplasm by human-pathogenic malaria parasites and other parasites that reside within human red blood cells.

Prevalence and Risk Factors Associated with Theileria annulata Infection in Two Bovine Portuguese Autochthonous Breeds

Tropical Bovine Theileriosis is an important tick-borne disease. This study aims to assess the occurrence of Theileria annulata infection in two indigenous Portuguese cattle breeds. A total of 843 blood samples collected from animals of Alentejana (n = 420) and Mertolenga (n = 423) breeds were analyzed. The detection of Theileria annulata was determined by amplification of a fragment of the merozoite-pyroplasm surface antigen gene with 319 base pairs (bp). The prevalence found (10.8%) is lower than that reported in previous studies (21.3%). A statistically significant difference was found for positivity between breeds (p < 0.05). There is also a higher probability of older animals being positive compared to younger ones (p < 0.05). The region where Mertolenga animals are located is shown to have a significant impact on positivity (p < 0.05). Thus, the development of sustainable T. annulata control strategies and their implementation, adapted to the epidemiological conditions of higher risk, will be extremely important.

Clinical, hematological and molecular evaluation of piroplasma and Anaplasma infections in small ruminants and tick vectors from Kurdistan province, western Iran

Tick-borne haemoparasite infections are a major challenge in small ruminant (SR) production across tropical areas. The present study evaluated the prevalence of Theileria, Babesia and Anaplasma in SRs and their tick vectors and estimated the association between pathogen prevalence with clinical hematological findings among SR populations in Kurdistan province, western Iran. In total, 250 blood samples and 250 tick species (one per animal) were collected from SR populations, along with clinical and hematological examinations. Microscopy of blood smears and molecular analysis were performed to detect potential infection with Theileria, Babesia and Anaplasma. Moreover, haemoparasites were explored in the isolated ticks using semi-nested PCR. Based on microscopy, the prevalence of Theileria, Anaplasma and Babesia infections was 91.2%, 23.2% and 2.4%, respectively. Semi-nested PCR analysis of blood samples demonstrated 86.8%, 78.8% and 14% prevalence for T. ovis, A. ovis and B. ovis, respectively. Dermacentor marginatus and Rhipicephalus turanicus were predominant isolated tick vectors from SR, while D. marginatus was the most contaminated tick in all investigated counties. There were, also, a statistically significant association between the estimated molecular prevalence rates with semi-yellow conjunctiva (A. ovis), body temperature (T. ovis and A. ovis), heart rate (T. ovis and B. ovis), mean white blood cell count (T. ovis and A. ovis), mean red blood cell count (T. ovis and B. ovis), as well as mean corpuscular volume, mean corpuscular hemoglobin and mean corpuscular hemoglobin concentration in all haemoparasite infections. Future studies are recommended to reveal the epidemiology of such infections in SRs in Iran.

Activation of telomerase activity and telomere elongation of host cells by Theileria annulata infection

Theileria annulata-transformed cells share many phenotypes with cancer cells, including uncontrolled proliferation, immortalization, and dissemination. Telomeres are DNA-protein complex at the end of eukaryotic chromosomes that function to maintain genome stability and cell replicative capacity. Telomere length maintenance is primarily dependent on telomerase activity. In up to 90% of human cancer cells, telomerase is reactivated through expression of its catalytic subunit TERT. However, the effect of T. annulata infection on telomere and telomerase activity in bovine cells has not yet been described. In the present study, we confirmed that telomere length and telomerase activity are upregulated after T. annulata infection in three types of cell lines. This change depends on the presence of parasites. After eliminating Theileria from cells with antitheilerial drug buparvaquone, telomerase activity and the expression level of bTERT were decreased. In addition, inhibition of bHSP90 by novobiocin led to decreased AKT phosphorylation levels and telomerase activity, indicating that the bHSP90-AKT complex is a potent factor modulates telomerase activity in T. annulata-infected cells.

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.

Immunopeptidomic Analysis of BoLA-I and BoLA-DR Presented Peptides from Theileria parva Infected Cells

The apicomplexan parasite Theileria parva is the causative agent of East Coast fever, usually a fatal disease for cattle, which is prevalent in large areas of eastern, central, and southern Africa. Protective immunity against T. parva is mediated by CD8+ T cells, with CD4+ T-cells thought to be important in facilitating the full maturation and development of the CD8+ T-cell response. T. parva has a large proteome, with >4000 protein-coding genes, making T-cell antigen identification using conventional screening approaches laborious and expensive. To date, only a limited number of T-cell antigens have been described. Novel approaches for identifying candidate antigens for T. parva are required to replace and/or complement those currently employed. In this study, we report on the use of immunopeptidomics to study the repertoire of T. parva peptides presented by both BoLA-I and BoLA-DR molecules on infected cells. The study reports on peptides identified from the analysis of 13 BoLA-I and 6 BoLA-DR datasets covering a range of different BoLA genotypes. This represents the most comprehensive immunopeptidomic dataset available for any eukaryotic pathogen to date. Examination of the immunopeptidome data suggested the presence of a large number of coprecipitated and non-MHC-binding peptides. As part of the work, a pipeline to curate the datasets to remove these peptides was developed and used to generate a final list of 74 BoLA-I and 15 BoLA-DR-presented peptides. Together, the data demonstrated the utility of immunopeptidomics as a method to identify novel T-cell antigens for T. parva and the importance of careful curation and the application of high-quality immunoinformatics to parse the data generated.

Genetic Resistance of Bovines to Theileriosis

Diseases caused by ticks have a high impact on the health, welfare, and productivity of livestock species. They are also an important cause of economic losses in farms worldwide. An example of such diseases is theileriosis, which can be controlled by drugs or vaccines, although these are not fully efficient. Therefore, there is a need to develop alternative and more sustainable and efficient complementary strategies. These may involve the identification and selection of animals more resistant to the disease. Several previous studies have identified significant differences in resistance between different breeds, with resistant breeds typically identified as those native to the region where they are being studied, and susceptible as those from exotic breeds. These studies have indicated that resistance traits are intrinsically related to the modulation of the immune response to infection. This review aims to systematize the general knowledge about theileriosis, emphasize resistance to this disease as a sustainable control strategy, and identify which traits of resistance to the disease are already known in cattle.

Theileria annulata histone deacetylase 1 (TaHDAC1) initiates schizont to merozoite stage conversion

A fungal metabolite, FR235222, specifically inhibits a histone deacetylase of the apicomplexan parasite Toxoplasma gondii and TgHDAC3 has emerged as a key factor regulating developmental stage transition in this species. Here, we exploited FR235222 to ask if changes in histone acetylation regulate developmental stage transition of Theileria annulata, another apicomplexan species. We found that FR235222 treatment of T. annulata-infected transformed leukocytes induced a proliferation arrest. The blockade in proliferation was due to drug-induced conversion of intracellular schizonts to merozoites that lack the ability to maintain host leukocyte cell division. Induction of merogony by FR235222 leads to an increase in expression of merozoite-marker (rhoptry) proteins. RNA-seq of FR235222-treated T. annulata-infected B cells identified deregulated expression of 468 parasite genes including a number encoding parasite ApiAP2 transcription factors. Thus, similar to T. gondii, FR235222 inhibits T. annulata HDAC (TaHDAC1) activity and places parasite histone acetylation as a major regulatory event of the transition from schizonts to merozoites.

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.