TGF-ß2, catalase activity, H2O2 output and metastatic potential of diverse types of tumour.

Theileria annulata is a protozoan parasite that infects and transforms bovine macrophages causing a myeloid-leukaemia-like disease called tropical theileriosis. TGF-ß2 is highly expressed in many cancer cells and is significantly increased in Theileria-transformed macrophages, as are levels of Reactive Oxygen Species (ROS), notably H2O2. Here, we describe the interplay between TGF-ß2 and ROS in cellular transformation. We show that TGF-ß2 drives expression of catalase to reduce the amount of H2O2 produced by T. annulata-transformed bovine macrophages, as well as by human lung (A549) and colon cancer (HT-29) cell lines. Theileria-transformed macrophages attenuated for dissemination express less catalase and produce more H2O2, but regain both virulent migratory and matrigel traversal phenotypes when stimulated either with TGF-ß2, or catalase to reduce H2O2 output. Increased H2O2 output therefore, underpins the aggressive dissemination phenotype of diverse tumour cell types, but in contrast, too much H2O2 can dampen dissemination.

HIF-1α induction, proliferation and glycolysis of Theileria-infected leukocytes.

Within 2 h of infection by Theileria annulata sporozoites, bovine macrophages display a two- to fourfold increase in transcription of hypoxia inducible factor (HIF-1α). Twenty hours post-invasion sporozoites develop into multi-nucleated macroschizonts that transform the infected macrophage into an immortalized, permanently proliferating, hyper-invasive and disease-causing leukaemia-like cell. Once immortalized Theileria-infected leukocytes can be propagated as cell lines and even though cultivated under normoxic conditions, both infected B cells and macrophages display sustained activation of HIF-1α. Attenuated macrophages used as live vaccines against tropical theileriosis also display HIF-1α activation even though they have lost their tumorigenic phenotype. Here, we review data that ascribes HIF-1α activation to the proliferation status of the infected leukocyte and discuss the possibility that Theileria may have lost its ability to render its host macrophage virulent due to continuous parasite replication in a high Reactive Oxygen Species (ROS) environment. We propose a model where uninfected macrophages have low levels of H2 O2 output, whereas virulent-infected macrophages produce high amounts of H2 O2 . Further increase in H2 O2 output leads to dampening of infected macrophage virulence, a characteristic of disease-resistant macrophages. At the same time exposure to H2 O2 sustains HIF-1α that induces the switch from mitochondrial oxidative phosphorylation to Warburg glycolysis, a metabolic shift that underpins uncontrolled infected macrophage proliferation. We propose that as macroschizonts develop into merozoites and infected macrophage proliferation arrests, HIF-1α levels will decrease and glycolysis will switch back from Warburg to oxidative glycolysis. As Theileria infection transforms its host leukocyte into an aggressive leukaemic-like cell, we propose that manipulating ROS levels, HIF-1α induction and oxidative over Warburg glycolysis could contribute to improved disease control. Finally, as excess amounts of H2 O2 drive virulent Theileria-infected macrophages towards attenuation it highlights how infection-induced pathology and redox balance are intimately linked.

The level of H2O2 type oxidative stress regulates virulence of Theileria-transformed leukocytes.

Theileria annulata infects predominantly macrophages, and to a lesser extent B cells, and causes a widespread disease of cattle called tropical theileriosis. Disease-causing infected macrophages are aggressively invasive, but this virulence trait can be attenuated by long-term culture. Attenuated macrophages are used as live vaccines against tropical theileriosis and via their characterization one gains insights into what host cell trait is altered concomitant with loss of virulence. We established that sporozoite infection of monocytes rapidly induces hif1-α transcription and that constitutive induction of HIF-1α in transformed leukocytes is parasite-dependent. In both infected macrophages and B cells induction of HIF-1α activates transcription of its target genes that drive host cells to perform Warburg-like glycolysis. We propose that Theileria-infected leukocytes maintain a HIF-1α-driven transcriptional programme typical of Warburg glycolysis in order to reduce as much as possible host cell H2 O2 type oxidative stress. However, in attenuated macrophages H2O2 production increases and HIF-1α levels consequently remained high, even though adhesion and aggressive invasiveness diminished. This indicates that Theileria infection generates a host leukocytes hypoxic response that if not properly controlled leads to loss of virulence.