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

Abstract

The tick-borne protozoan parasite Theileria annulata causes a debilitating disease of cattle called Tropical Theileriosis. The parasite predominantly invades bovine macrophages (mϕ) and induces host cell transformation by a mechanism that has not been fully elucidated. Infection is associated with loss of characteristic mϕ functions and phenotypic markers, indicative of host cell de-differentiation. We have investigated the effect of T. annulata infection on the expression of the mϕ differentiation marker c-maf. The up-regulation of c-maf mRNA levels observed during bovine monocyte differentiation to mϕ 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 mϕ. 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/mϕ differentiation. We believe these results provide the first direct evidence that T. annulata modulates the host mϕ 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 mϕ.

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

“…A similar profile has been described in other studies and was associated with repression of high level expression of genes induced by cellular activation, macrophage differentiation or the inflammatory response, that may be detrimental to the parasite infected cell [15], [17]. Taken together, the data indicated that only approximately 6% of differentially expressed genes in TBL20 cells show a sustained trend associated with reversion to the BL20 phenotype although >30% show evidence of immediate susceptibility to parasite death.…”

“…These results imply that parasite infection may target regulators of the host cell gene expression network as a primary mechanism to alter host cell phenotype. Altered expression of factors (HOX, LMO2, RUNX and SMAD) and networks (MYB) involved in regulation of haematopoetic cell fate decisions [75] is clearly evident, supporting previous work indicating that parasite-mediated transformation is associated with a de-differentiated myeloid type cell [17]. It is accepted that transcription factors and modulation of chromatin status operate to produce stable changes to cellular phenotype [54], [75].…”

“…This latter property has been utilised in several studies including those by [18], [33] and [17] to predict whether individual host genes/pathways are under direct influence of the viable macroschizont. BW720c, a hydroxynaphthoquinone, most probably acts as a ubiquinone analogue [34], [35] to specifically block parasite electron transport and exposure of infected cells to the drug leads to rapid arrest and death of the parasite, followed by cessation of host cell proliferation and apoptosis within a few days [4].…”

“…Evidence from ectopic expression studies has shown that at least two TashAT factors which bind to AT-rich DNA [14] can modify a bovine cell phenotype [15], [16], pointing to a role for these proteins in modulation of the infected cell transcriptome. These studies together with the extensive data on manipulation of cell signalling pathways and leukocyte differentiation status [17], [18] suggest that Theileria parasites orchestrate a major reorganisation of leukocyte gene expression networks and illustrate the complexity of parasite governance over the host cell, reviewed in [1], [19].…”

Theileria-transformed bovine leukocytes have cancer hallmarks

“…31,No. 7 molecules, including nitric oxide and TNF-a [69]. They also upregulate several cytokines that are known to play a crucial role in immune responses against parasites [70,71].…”