Notch is constitutively active in Theileria-transformed B cells and can be further stimulated by the filarial nematode-secreted product, ES-62

Changes in TFG gene expression in bovine leucocytes transformed by Theileria annulata

Theileria annulata schizont-infected host cells in culture in vitro show unlimited proliferation similar to tumor cells; thus far, T. annulata and T. parva are the only eukaryotes that have been found to transform mammalian cells (immortalized). The transformation of these cells is reversible; when the parasite is eliminated in transformed cells by buparvaquone (BW720c), the host cells show normal growth and apoptosis. TFG is a tropomyosin-receptor kinase fused gene that is conserved among many species and is an important proto-oncogene. In this study, the bovine TFG gene was amplified by PCR from the cDNA of T. annulata schizont-transformed cells, cloned into the pGEX-4T-1 vector and expressed in Escherichia coli BL21 (DE3). After purification, the fusion protein was injected into rabbits to produce polyclonal antibodies. Using T. annulata-transformed cells together with BW720c treatment to kill the parasite, we aimed to identify changes in TFG gene expression by real-time PCR and Western blotting. The results showed that the bovine TFG gene was ~582 bp in size; SDS-PAGE analysis showed that the fusion protein was expressed in BL21 (DE3) cells with a molecular mass of 48 kD, and Western blotting indicated that the polyclonal antibodies could react with bovine TFG proteins from T. annulata-transformed cells and showed high specificity. Compared with that in the control group, the transcription level of the host TFG gene decreased significantly in the BW720c test group, and the expression of host tumor-related TFG protein decreased sharply after 72 h of drug treatment, suggesting that the TFG protein expression in transformed cells was directly related to T. annulata. This finding laid a foundation for further study on the interaction between T. annulata and host cells.

Interaction between transforming Theileria parasites and their host bovine leukocytes

Theileria are tick-transmitted parasites that cause often fatal leuko-proliferative diseases in cattle called tropical theileriosis (T. annulata) and East Coast fever (T. parva). However, upon treatment with anti-theilerial drug-transformed leukocytes die of apoptosis indicating that Theileria-induced transformation is reversible making infected leukocytes a powerful example of how intracellular parasites interact with their hosts. Theileria-transformed leukocytes disseminate throughout infected cattle causing a cancer-like disease and here, we discuss how cytokines, noncoding RNAs and oncometabolites can contribute to the transformed phenotype and disease pathology.

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.

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 protozoan parasite Theileria annulata alters the differentiation state of the infected macrophage and suppresses musculoaponeurotic fibrosarcoma oncogene (MAF) transcription factors

The tick-borne protozoan parasite Theileria annulata causes a debilitating disease of cattle called Tropical Theileriosis. The parasite predominantly invades bovine macrophages (m phi) and induces host cell transformation by a mechanism that has not been fully elucidated. Infection is associated with loss of characteristic m phi functions and phenotypic markers, indicative of host cell de-differentiation. We have investigated the effect of T. annulata infection on the expression of the m phi differentiation marker c-maf. The up-regulation of c-maf mRNA levels observed during bovine monocyte differentiation to m phi was suppressed by T. annulata infection. Furthermore, mRNA levels for c-maf and the closely related transcription factor mafB were significantly lower in established T. annulata-infected cell-lines than in bovine monocyte-derived m phi. Treatment of T. annulata-infected cells with the theileriacidal drug buparvaquone induced up-regulation of c-maf and mafB, which correlated with altered expression of down-stream target genes, e.g. up-regulation of integrin B7 and down-regulation of IL12A. Furthermore, T. annulata infection is associated with the suppression of the transcription factors, Pu.1 and RUNX1, and colony stimulating factor 1 receptor (CSF1R) which are also involved in the regulation of monocyte/m phi differentiation. We believe these results provide the first direct evidence that T. annulata modulates the host m phi differentiation state, which may diminish the defence capabilities of the infected cell and/or promote cell proliferation. Musculoaponeurotic fibrosarcoma oncogene (MAF) transcription factors play an important role in cell proliferation, differentiation and survival; therefore, regulation of these genes may be a major mechanism employed by T. annulata to survive within the infected m phi.

Intracellular survival of apicomplexan parasites and host cell modification

The intracellular stages of apicomplexan parasites are known to extensively modify their host cells to ensure their own survival. Recently, considerable progress has been made in understanding the molecular details of these parasite-dependent effects for Plasmodium-, Toxoplasma- and Theileria-infected cells. We have begun to understand how Plasmodium liver stage parasites protect their host hepatocytes from apoptosis during parasite development and how they induce an ordered cell death at the end of the liver stage. Toxoplasma parasites are also known to regulate host cell survival pathways and it has been convincingly demonstrated that they block host cell major histocompatibility complex (MHC)-dependent antigen presentation of parasite epitopes to avoid cell-mediated immune responses. Theileria parasites are the masters of host cell modulation because their presence immortalises the infected cell. It is now accepted that multiple pathways are activated to induce Theileria-dependent host cell transformation. Although it is now known that similar host cell pathways are affected by the different parasites, the outcome for the infected cell varies considerably. Improved imaging techniques and new methods to control expression of parasite and host cell proteins will help us to analyse the molecular details of parasite-dependent host cell modifications.

Resistance and susceptibility to a protozoan parasite of cattle—Gene expression differences in macrophages from different breeds of cattle

Cattle infected with the tick-borne protozoan, Theileria annulata, usually undergo severe morbidity, and mortality ensues in a high proportion of animals. However, we have shown that a Bos indicus breed, the Sahiwal, which originates in a T. annulata endemic area, is more resistant to the parasite. Although Sahiwals become infected, the breed exhibits fewer clinical signs and recovers from a dose of parasite which is fatal in the Holstein B. taurus breed. The Sahiwals have a significantly lower fever response, and lower levels of parasite than the Holsteins. One unusual feature of this disease is the production of acute phase proteins (APP), indicating that the parasite induces high systemic levels of pro-inflammatory cytokines. In the Holsteins there is prolonged production of the APP, alpha1-glycoprotein, which, in contrast, is only slightly elevated in the Sahiwals. As the parasite infects macrophages (mphi), our hypothesis is that the Sahiwals can control the excessive production of pro-inflammatory cytokines in response to infection, and that this control is expressed at the level of the mphi. We thus reasoned that the genes underlying the observed difference in resistance to tropical theileriosis, might be identified by investigating gene expression differences in mphi from both breeds. It is possible that relevant polymorphisms might in themselves result in gene expression differences, so initially we targeted likely candidates. However, we detected no differences in expression of the pro-inflammatory cytokines, tumour necrosis factor-alpha (TNFalpha), interleukin-1beta (IL-1beta) or IL-6, in infected mphi. As it is more likely that polymorphisms in candidate genes influence the expression of other genes involved in interrelated pathways, we undertook a more global approach. We designed a bovine mphi specific cDNA microarray, which contains representatives of 5000 different genes expressed in mphi, and investigated the transcriptional responses of mphi from both breeds in response to a variety of stimuli, including infection with T. annulata. Our results indicate that there are fundamental differences in gene expression in mphi from both breeds in the way they respond to infection, and even in their pre-infection resting state.