Infection of bovine cells by the protozoan parasite Theileria annulata modulates expression of the ISGylation system.

The apicomplexan parasite, Theileria annulata, dedifferentiates and induces continuous division of infected bovine myeloid cells. Re-expression of differentiation markers and a loss of proliferation occur upon treatment with buparvaquone, implying that parasite factors actively maintain the altered status of the infected cell. The factors that induce this unique transformation event have not been identified. However, parasite polypeptides (TashAT family) that are located in the infected leucocyte nucleus have been postulated to function as modulators of host cell phenotype. In this study differential RNA display and proteomic analysis were used to identify altered mRNA and polypeptide expression profiles in a bovine macrophage cell line (BoMac) transfected with TashAT2. One of the genes identified by differential display was found to encode an ubiquitin-like protease (bUBP43) belonging to the UBP43 family. The bUBP43 gene and the gene encoding its ubiquitin-like substrate, bISG15, were expressed at a low level in T. annulata-infected cells. However, infected cells were refractory to induction of elevated bISG15 expression by lipopolysaccharide or type 1 interferons while TashAT2-transfected cells showed no induction when treated with camptothecin. Modulation of the ISGylation system may be of relevance to the establishment of the transformed infected host cell, as ISGylation is associated with resistance to intracellular infection by pathogens, stimulation of the immune response and terminal differentiation of leukaemic cells.

TashHN, a Theileria annulata encoded protein transported to the host nucleus displays an association with attenuation of parasite differentiation.

The intracellular apicomplexan parasite, Theileria annulata, manipulates its bovine host cell by over-riding the cells natural apoptotic response and inducing proliferation of the infected leukocyte. We have recently identified a T. annulata encoded family of polypeptides (TashATs) with characteristics that indicate that they are involved in control of host cell gene expression. Here we present data on another member of this family, TashHN, showing that it is located to the parasite and host cell nucleus. Immunoblot analysis demonstrated that, unlike TashAT2 and 3, TashHN displays three forms, the largest of which is enriched in the host nuclear fraction and appears to be phosphorylated. Northern and 5 prime race analyses identified multiple TashHN RNA species in infected cells that have retained the ability to differentiate. These transcripts showed subtly different kinetics, but all decreased during differentiation to the merozite, and two showed reduced levels prior to down-regulation of the other TashATs. In addition, analyses of multiple cell lines that have become severely attenuated in their potential to differentiate, indicated a substantial increase in TashHN expression, with host nuclear reactivity particularly enhanced.