Modulation of activation-associated host cell gene expression by the apicomplexan parasite Theileria annulata

A parasite DNA binding protein with potential to influence disease susceptibility acts as an analogue of mammalian HMGA transcription factors

Intracellular pathogens construct their environmental niche, and influence disease susceptibility, by deploying factors that manipulate infected host cell gene expression. Theileria annulata is an important tick-borne parasite of cattle that causes tropical theileriosis. Excellent candidates for modulating host cell gene expression are DNA binding proteins bearing AT-hook motifs encoded within the TashAT gene cluster of the parasite genome. In this study, TashAT2 was transfected into bovine BoMac cells to generate three expressing and three non-expressing (opposite orientation) cell lines. RNA-Seq was conducted and differentially expressed (DE) genes identified. The resulting dataset was compared with genes differentially expressed between infected cells and non-infected cells, and DE genes between infected cell lines from susceptible Holstein vs tolerant Sahiwal cattle. Over 800 bovine genes displayed differential expression associated with TashAT2, 209 of which were also modulated by parasite infection. Network analysis showed enrichment of DE genes in pathways associated with cellular adhesion, oncogenesis and developmental regulation by mammalian AT-hook bearing high mobility group A (HMGA) proteins. Overlap of TashAT2 DE genes with Sahiwal vs Holstein DE genes revealed that a significant number of shared genes were associated with disease susceptibility. Altered protein levels encoded by one of these genes (GULP1) was strongly linked to expression of TashAT2 in BoMac cells and was demonstrated to be higher in infected Holstein leucocytes compared to Sahiwal. We conclude that TashAT2 operates as an HMGA analogue to differentially mould the epigenome of the infected cell and influence disease susceptibility.

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.

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.

Susceptibility to disease (tropical theileriosis) is associated with differential expression of host genes that possess motifs recognised by a pathogen DNA binding protein

Background

Knowledge of factors that influence the outcome of infection are crucial for determining the risk of severe disease and requires the characterisation of pathogen-host interactions that have evolved to confer variable susceptibility to infection. Cattle infected by Theileria annulata show a wide range in disease severity. Native (Bos indicus) Sahiwal cattle are tolerant to infection, whereas exotic (Bos taurus) Holstein cattle are susceptible to acute disease.

Methodology/Principal findings

We used RNA-seq to assess whether Theileria infected cell lines from Sahiwal cattle display a different transcriptome profile compared to Holstein and screened for altered expression of parasite factors that could generate differences in host cell gene expression.

Significant differences (<0.1 FDR) in the expression level of a large number (2211) of bovine genes were identified, with enrichment of genes associated with Type I IFN, cholesterol biosynthesis, oncogenesis and parasite infection. A screen for parasite factors found limited evidence for differential expression. However, the number and location of DNA motifs bound by the TashAT2 factor (TA20095) were found to differ between the genomes of B. indicus vs. B. taurus, and divergent motif patterns were identified in infection-associated genes differentially expressed between Sahiwal and Holstein infected cells.

Conclusions/Significance

We conclude that divergent pathogen-host molecular interactions that influence chromatin architecture of the infected cell are a major determinant in the generation of gene expression differences linked to disease susceptibility.

Characterization of the Rhipicephalus (Boophilus) microplus Sialotranscriptome Profile in Response to Theileria equi Infection

This study intends to characterize the sialotranscriptome profile of Rhipicephalus (Boophilus) microplus in response to Theileria equi and identify genes of interest with differential genomic expression, indicating relevant targets in the tick–protozoan interactions. The experimental design consisted of RNA sequencing from uninfected and T. equi-infected R. microplus salivary glands (SGs) to obtain transcriptomic profiles for characterization and comparison. A total of 288,952 transcripts were obtained from both tick profiles, 3456 transcripts (p < 0.05) differentially expressed in response to T. equi infection. The uninfected SGs’ registered 231,179 transcripts, of which 155,359 were annotated. The most transcribed sequences were female-specific histamine binding protein and lipocalins. Regarding the T. equi-infected SGs, from the 238,964 assembled transcripts, 163,564 were annotated. The most transcribed sequences were histone demethylase JARID1 and Y-box-binding protein. Five transcripts (cystatin, arginase, nuclear factor κB kinase inhibitor subunit β (IκB), IκB delta, lysosomal-trafficking regulator, and reeler protein) presented the gene ontology (GO) category “response to protozoan” and were exclusively displayed in the T. equi-infected profile. The transcriptome of T. equi was also analyzed, registering 4728 hits. The study’s genetic and molecular information would be of great value for future studies and biotechnological applications envisaging disease control.

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.

Establishment and Expression of Cytokines in a Theileria annulata-Infected Bovine B Cell Line

This study aimed to establish a pure single-cell Theileria annulata-infected B cell line for the assessment of cytokine production in transformed and lipopolysaccharide (LPS)-stimulated cells. Several studies have aimed to identify cell surface markers in T. annulata-transformed cells; however, no information on cytokine production in these cells is available. To investigate the potential of the transformed cells to produce cytokines and their potential responses to antigen-stimulation, we purified mature B cells (CD21) from the whole blood of cattle experimentally infected with the T. annulata Kashi strain by magnetic separation. The purity and specificity of the established cell line was assessed by the identification of specific cell surface markers (CD21, IgM, and WC4) by flow cytometry analysis. The transcript levels of the cytokines IL1A, IL1B, IL2, IL4, IL6, IL8, IL10, IL16, LTA, TGFB1, TNFA, IFNA, and IFNB in transformed, buparvaquone (BW720c)-treated cells, and antigen-stimulated cells were analyzed by quantitative polymerase chain reaction (qPCR) using cDNA from these cells. A T. annulata-infected bovine B cell line was successfully established with a purity of ~98.8% (CD21). IL4 and IL12A were significantly (p < 0.01) upregulated in the transformed cells. In BW720c-treated transformed cells, IL12B, TGFB1, and IFNB were significantly (p < 0.01) upregulated. Notably, no significant (p > 0.05) upregulation of cytokines was observed in LPS-stimulated transformed cells. Moreover, IL1A, IL1B, IL8, and IL16 were significantly (p < 0.01) upregulated in LPS-stimulated B cells. Our data signify the potential use of this cell line for cytokine production, observance of immunoglobulins, and production of an attenuated vaccine against tropical theileriosis.

Characterisation of infection associated microRNA and protein cargo in extracellular vesicles of Theileria annulata infected leukocytes

The protozoan parasites Theileria annulata and Theileria parva are unique amongst intracellular eukaryotic pathogens as they induce a transformation-like phenotype in their bovine host cell. T. annulata causes tropical theileriosis, which is frequently fatal, with infected leukocytes becoming metastatic and forming foci in multiple organs resulting in destruction of the lymphoid system. Exosomes, a subset of extracellular vesicles (EV), are critical in metastatic progression in many cancers. Here, we characterised the cargo of EV from a control bovine lymphosarcoma cell line (BL20) and BL20 infected with T. annulata (TBL20) by comparative mass spectrometry and microRNA (miRNA) profiling (data available via ProteomeXchange, identifier PXD010713 and NCBI GEO, accession number GSE118456, respectively). Ingenuity pathway analysis that many infection-associated proteins essential to migration and extracellular matrix digestion were upregulated in EV from TBL20 cells compared with BL20 controls. An altered repertoire of host miRNA, many with known roles in tumour and/or infection biology, was also observed. Focusing on the tumour suppressor miRNA, bta-miR-181a and bta-miR-181b, we identified putative messenger RNA targets and confirmed the interaction of bta-miR181a with ICAM-1. We propose that EV and their miRNA cargo play an important role in the manipulation of the host cell phenotype and the pathobiology of Theileria infection.

Potential Sabotage of Host Cell Physiology by Apicomplexan Parasites for Their Survival Benefits

Plasmodium, Toxoplasma, Cryptosporidium, Babesia, and Theileria are the major apicomplexan parasites affecting humans or animals worldwide. These pathogens represent an excellent example of host manipulators who can overturn host signaling pathways for their survival. They infect different types of host cells and take charge of the host machinery to gain nutrients and prevent itself from host attack. The mechanisms by which these pathogens modulate the host signaling pathways are well studied for Plasmodium, Toxoplasma, Cryptosporidium, and Theileria, except for limited studies on Babesia. Theileria is a unique pathogen taking into account the way it modulates host cell transformation, resulting in its clonal expansion. These parasites majorly modulate similar host signaling pathways, however, the disease outcome and effect is different among them. In this review, we discuss the approaches of these apicomplexan to manipulate the host–parasite clearance pathways during infection, invasion, survival, and egress.

Subverting Host Cell P21-Activated Kinase: A Case of Convergent Evolution across Pathogens

Intracellular pathogens have evolved a wide range of strategies to not only escape from the immune systems of their hosts, but also to directly exploit a variety of host factors to facilitate the infection process. One such strategy is to subvert host cell signalling pathways to the advantage of the pathogen. Recent research has highlighted that the human serine/threonine kinase PAK, or p21-activated kinase, is a central component of host-pathogen interactions in many infection systems involving viruses, bacteria, and eukaryotic pathogens. PAK paralogues are found in most mammalian tissues, where they play vital roles in a wide range of functions. The role of PAKs in cell proliferation and survival, and their involvement in a number of cancers, is of great interest in the context of drug discovery. In this review we discuss the latest insights into the surprisingly central role human PAK1 plays for the infection by such different infectious disease agents as viruses, bacteria, and parasitic protists. It is our intention to open serious discussion on the applicability of PAK inhibitors for the treatment, not only of neoplastic diseases, which is currently the primary objective of drug discovery research targeting these enzymes, but also of a wide range of infectious diseases.

HK2 Recruitment to Phospho-BAD Prevents Its Degradation, Promoting Warburg Glycolysis by Theileria-Transformed Leukocytes

Theileria annulata infects bovine leukocytes, transforming them into invasive, cancer-like cells that cause the widespread disease called tropical theileriosis. We report that in Theileria-transformed leukocytes hexokinase-2 (HK2) binds to B cell lymphoma-2-associated death promoter (BAD) only when serine (S) 155 in BAD is phosphorylated. We show that HK2 recruitment to BAD is abolished by a cell-penetrating peptide that acts as a nonphosphorylatable BAD substrate that inhibits endogenous S155 phosphorylation, leading to complex dissociation and ubiquitination and degradation of HK2 by the proteasome. As HK2 is a critical enzyme involved in Warburg glycolysis, its loss forces Theileria-transformed macrophages to switch back to HK1-dependent oxidative glycolysis that down-regulates macrophage proliferation only when they are growing on glucose. When growing on galactose, degradation of HK2 has no effect on Theileria-infected leukocyte proliferation, because metabolism of this sugar is independent of hexokinases. Thus, targeted disruption of the phosphorylation-dependent HK2/BAD complex may represent a novel approach to control Theileria-transformed leukocyte proliferation.

Global gene expression profile of peripheral blood mononuclear cells challenged with Theileria annulata in crossbred and indigenous cattle

Bovine tropical theileriosis is an important haemoprotozoan disease associated with high rates of morbidity and mortality particularly in exotic and crossbred cattle. It is one of the major constraints of the livestock development programmes in India and Southeast Asia. Indigenous cattle (Bos indicus) are reported to be comparatively less affected than exotic and crossbred cattle. However, genetic basis of resistance to tropical theileriosis in indigenous cattle is not well documented. Recent studies incited an idea that differentially expressed genes in exotic and indigenous cattle play significant role in breed specific resistance to tropical theileriosis. The present study was designed to determine the global gene expression profile in peripheral blood mononuclear cells derived from indigenous (Tharparkar) and cross-bred cattle following in vitro infection of T. annulata (Parbhani strain). Two separate microarray experiments were carried out each for cross-bred and Tharparkar cattle. The cross-bred cattle showed 1082 differentially expressed genes (DEGs). Out of total DEGs, 597 genes were down-regulated and 485 were up-regulated. Their fold change varied from 2283.93 to -4816.02. Tharparkar cattle showed 875 differentially expressed genes including 451 down-regulated and 424 up-regulated. The fold change varied from 94.93 to -19.20. A subset of genes was validated by qRT-PCR and results were correlated well with microarray data indicating that microarray results provided an accurate report of transcript level. Functional annotation study of DEGs confirmed their involvement in various pathways including response to oxidative stress, immune system regulation, cell proliferation, cytoskeletal changes, kinases activity and apoptosis. Gene network analysis of these DEGs plays an important role to understand the interaction among genes. It is therefore, hypothesized that the different susceptibility to tropical theileriosis exhibited by indigenous and crossbred cattle is due to breed-specific differences in the dealing of infected cells with other immune cells, which ultimately influence the immune response responded against T. annulata infection.

Pathogens hijack the epigenome: a new twist on host-pathogen interactions

Pathogens have evolved strategies to promote their survival by dramatically modifying the transcriptional profile and protein content of the host cells they infect. Modifications of the host transcriptome and proteome are mediated by pathogen-encoded effector molecules that modulate host cells through a variety of different mechanisms. Recent studies highlight the importance of the host chromatin and other epigenetic regulators as targets of pathogens. Host gene regulatory mechanisms may be targeted through cytoplasmic signaling, directly by pathogen effector proteins, and possibly by pathogen RNA. Although many of these changes are short-lived and persist only during the course of infection, several studies indicate that pathogens are able to induce long-term, heritable changes that are essential to pathogenesis of infectious diseases and persistence of pathogens within their hosts. In this review, we discuss how pathogens modulate the epigenome of host cells, a new and flourishing avenue of host-pathogen interaction studies.

A Bovine Lymphosarcoma Cell Line Infected with Theileria annulata Exhibits an Irreversible Reconfiguration of Host Cell Gene Expression

Theileria annulata, an intracellular parasite of bovine lymphoid cells, induces substantial phenotypic alterations to its host cell including continuous proliferation, cytoskeletal changes and resistance to apoptosis. While parasite induced modulation of host cell signal transduction pathways and NFκB activation are established, there remains considerable speculation on the complexities of the parasite directed control mechanisms that govern these radical changes to the host cell. Our objectives in this study were to provide a comprehensive analysis of the global changes to host cell gene expression with emphasis on those that result from direct intervention by the parasite. By using comparative microarray analysis of an uninfected bovine cell line and its Theileria infected counterpart, in conjunction with use of the specific parasitacidal agent, buparvaquone, we have identified a large number of host cell gene expression changes that result from parasite infection. Our results indicate that the viable parasite can irreversibly modify the transformed phenotype of a bovine cell line. Fifty percent of genes with altered expression failed to show a reversible response to parasite death, a possible contributing factor to initiation of host cell apoptosis. The genes that did show an early predicted response to loss of parasite viability highlighted a sub-group of genes that are likely to be under direct control by parasite infection. Network and pathway analysis demonstrated that this sub-group is significantly enriched for genes involved in regulation of chromatin modification and gene expression. The results provide evidence that the Theileria parasite has the regulatory capacity to generate widespread change to host cell gene expression in a complex and largely irreversible manner.

Regulation of Trypanosoma brucei Total and Polysomal mRNA during Development within Its Mammalian Host

The gene expression of Trypanosoma brucei has been examined extensively in the blood of mammalian hosts and in forms found in the midgut of its arthropod vector, the tsetse fly. However, trypanosomes also undergo development within the mammalian bloodstream as they progress from morphologically ‘slender forms’ to transmissible ‘stumpy forms’ through morphological intermediates. This transition is temporally progressive within the first wave of parasitaemia such that gene expression can be monitored in relatively pure slender and stumpy populations as well as during the progression between these extremes. The development also represents the progression of cells from translationally active forms adapted for proliferation in the host to translationally quiescent forms, adapted for transmission. We have used metabolic labelling to quantitate translational activity in slender forms, stumpy forms and in forms undergoing early differentiation to procyclic forms in vitro. Thereafter we have examined the cohort of total mRNAs that are enriched throughout development in the mammalian bloodstream (slender, intermediate and stumpy forms), irrespective of strain, revealing those that exhibit consistent developmental regulation rather than sample specific changes. Transcripts that cosediment with polysomes in stumpy forms and slender forms have also been enriched to identify transcripts that escape translational repression prior to transmission. Combined, the expression and polysomal association of transcripts as trypanosomes undergo development in the mammalian bloodstream have been defined, providing a resource for trypanosome researchers. This facilitates the identification of those that undergo developmental regulation in the bloodstream and therefore those likely to have a role in the survival and capacity for transmission of stumpy forms.

Proteomic analysis of the Theileria annulata schizont

The apicomplexan parasite, Theileria annulata, is the causative agent of tropical theileriosis, a devastating lymphoproliferative disease of cattle. The schizont stage transforms bovine leukocytes and provides an intriguing model to study host/pathogen interactions. The genome of T. annulata has been sequenced and transcriptomic data are rapidly accumulating. In contrast, little is known about the proteome of the schizont, the pathogenic, transforming life cycle stage of the parasite. Using one-dimensional (1-D) gel LC-MS/MS, a proteomic analysis of purified T. annulata schizonts was carried out. In whole parasite lysates, 645 proteins were identified. Proteins with transmembrane domains (TMDs) were under-represented and no proteins with more than four TMDs could be detected. To tackle this problem, Triton X-114 treatment was applied, which facilitates the extraction of membrane proteins, followed by 1-D gel LC-MS/MS. This resulted in the identification of an additional 153 proteins. Half of those had one or more TMD and 30 proteins with more than four TMDs were identified. This demonstrates that Triton X-114 treatment can provide a valuable additional tool for the identification of new membrane proteins in proteomic studies. With two exceptions, all proteins involved in glycolysis and the citric acid cycle were identified. For at least 29% of identified proteins, the corresponding transcripts were not present in the existing expressed sequence tag databases. The proteomics data were integrated into the publicly accessible database resource at EuPathDB (www.eupathdb.org) so that mass spectrometry-based protein expression evidence for T. annulata can be queried alongside transcriptional and other genomics data available for these parasites.