Theileria annulata promotes Src kinase-dependent host cell polarization by manipulating actin dynamics in podosomes and lamellipodia Martin Baumgartner* Division Molecular Pathobiology, Department of Clinical Research and Veterinary Public Health, Vetsuisse Faculty, University of Bern, Länggassstrasse 122, CH-3012 Bern, Switzerland. Summary Theileria annulata is an intracellular protozoan parasite that infects B cells and macrophages of ruminants. Macrophages infected with T. annulata are de-differentiated and display tumour cell prop- erties and a metastatic behaviour. How parasitized cells adapt their morphology, motility and invasive behaviour has not yet been addressed in detail. In this study, I investigated the regulation of host cell actin dynamics in T. annulata-transformed mac- rophages and how this affects host cell morphol- ogy and motility. T. annulata was found to promote the formation of filamentous-actin-rich podosome- type adhesions (PTAs) and lamellipodia, and to establish a polarized morphology of the infected cell. Characteristic for parasite-dependent host cell polarization is that infected cells display a single, persistent lamellipodium. Src kinases – in particular Hck – are required for the polar exten- sion of this lamellipodium. Hck does so by pro- moting the clustered assembly of PTAs and accumulation of proteins of the Ezrin, Radixin, Moesin (ERM) family in lamellipodia. Polar accu- mulation of PTAs and ERM proteins correlates with focal matrix degradation underneath lamellipodia. These findings suggest that T. annulata equips its host cell with properties to adhere and invade. These properties are likely to promote the motile behaviour required for dissemination of infected cells in vivo. Introduction Theileria annulata is an intracellular, apicomplexan para- site that causes the lympho- and myeloproliferative disor- der tropical theileriosis in ruminants. Tropical theileriosis is prevalent in Southern Europe, Northern Africa, the Middle East, the Indian subcontinent and China, where its tick vector is endemic. Mortality rates in infected animals from non-endemic areas are 40–90%, which is the conse- quence of the unique ability of T. parva to transform T cells and B cells and of T. annulata to transform monocytes/ macrophages and B cells (reviewed in Dessauge et al., 2005; Dobbelaere and Baumgartner, 2009). Mortality is associated with anaemia and with the acquired capability of infected cells to spread in the lymphoid and to non- lymphoid organs (Hooshmand-Rad, 1976; Forsyth et al., 1999). This propensity of infected cells to spread from the site of the tick bite in natural infections or from the site of inoculation in experimentally infected ruminants or mice resembles the behaviour of metastasizing tumour cells (Irvin et al., 1975; Somerville et al., 1998; Forsyth et al., 1999; Lizundia et al., 2006). T. annulata-infected leuco- cytes display increased production and activities of metallo proteinases including MMP-9, which were reduced in experimentally attenuated cells (Baylis et al., 1992; Adamson and Hall, 1997). Synthetic inhibitors of matrix metalloproteinases inhibit dissemination of infected cells in mice (Somerville et al., 1998), indicating that parasite- dependent metastasis in vivo requires proteolytic activity. Constitutive activation of the c-Jun NH2-terminal kinase 1 (JNK1) and c-jun induction in infected cells (Galley et al., 1997; Chaussepied et al., 1998) was suggested to control the expression of metalloproteinases and to increase inva- siveness of infected B cells in vivo (Lizundia et al., 2006). Overall, the phenotype of Theileria-transformed cells is reminiscent of that of de-differentiated, metastasizing human tumour cells. In contrast to tumour cells, however, the transforming agent – the intracellular parasite Theileria – can be eliminated by treating infected cells with the theilericidal drug buparvaquone (McHardy et al., 1985). Elimination of T. annulata from macrophages leads to re-differentiation and the re-acquisition, at last in part, of monocyte/macrophage markers and features (Sager et al., 1997; Jensen et al., 2009) and thereby allows the Received 27 August, 2010; revised 3 November, 2010; accepted 16 November, 2010. *For correspondence. E-mail martin.baumgartner@ mopa.unibe.ch; Tel. (+41) 31 631 2408; Fax (+41) 31 631 2658. Cellular Microbiology (2011) 13(4), 538–553 doi:10.1111/j.1462-5822.2010.01553.x First published online 19 December 2010 © 2010 Blackwell Publishing Ltd cellular microbiology