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

Abstract

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.

Theileria-transformed bovine leukocytes have cancer hallmarks

“…In contrast to both normal somatic cells and many cancer cells, T. parva-transformed lymphocytes require contact with other infected or uninfected cells to proliferate [85]. The expression levels of known regulators of contact inhibition, Merlin or liver kinase B1, are not reportedly regulated by T. annulata during infection [34,35], suggesting that Theileria-infected cells may achieve contact independence via an as-yet undiscovered mechanism.…”

“…A bTERTtargeted vaccine against Theileria infection is also an intriguing possibility because hTERT has been the target of vaccine trials for human cancers [33]. However, bTERT was not reported to be differentially expressed during infection of bovine B-lymphosarcoma cells by T. annulata [34,35], indicating that Theileria transformation may use an alternative mechanism to lengthen telomeres, or that existing telomerase may be hyperactivated.…”

“…Theileria schizonts induce anti-apoptotic proteins such as cellular FLICE-like inhibitory protein (cFLIP) and cellular inhibitor of apoptosis proteins (cIAPs) [25] by activating host IKK complexes [57] and upregulating or maintaining high c-MYC expression [34,58]. Theileria can also inhibit host pro-apoptotic signaling by sequestering host p53 [59] on their cell surface via unknown receptor(s).…”

“…T. annulata-transformed leukocytes appear to induce the latter mechanism because TGF-b signaling drives metastasis while altering transcript levels of many TGF-bregulated genes [39], whereas the core signaling components have mostly unaffected expression levels [87]. Theileria parasites are also known to induce the expression of host MYC [34,58], and sequester host p53 in the cytosol [59] to prevent host apoptosis, and these proteins may therefore also play a role in regulating host cell invasiveness.…”

“…There is evidence that Theileria infection imposes some irreversible effects on host cells. For example, an established bovine leukemia cell line infected with T. annulata and then chemically cleared of the parasite exhibits some irreversible gene expression changes and, eventually, dies from apoptosis within a couple of days [34,38]. The cytokine profiles of infected cells also vary considerably among T cell clones, even within T cell subsets [79], indicating that Theileria parasites may cause stochastic effects on their host cells.…”