Theileria parasites secrete a prolyl isomerase to maintain host leukocyte transformation.

Infectious agents develop intricate mechanisms to interact with host cell pathways and hijack their genetic and epigenetic machinery to change host cell phenotypic states. Among the Apicomplexa phylum of obligate intracellular parasites, which cause veterinary and human diseases, Theileria is the only genus that transforms its mammalian host cells. Theileria infection of bovine leukocytes induces proliferative and invasive phenotypes associated with activated signalling pathways, notably JNK and AP-1 (ref. 2). The transformed phenotypes are reversed by treatment with the theilericidal drug buparvaquone. We used comparative genomics to identify a homologue of the peptidyl-prolyl isomerase PIN1 in T. annulata (TaPIN1) that is secreted into the host cell and modulates oncogenic signalling pathways. Here we show that TaPIN1 is a bona fide prolyl isomerase and that it interacts with the host ubiquitin ligase FBW7, leading to its degradation and subsequent stabilization of c-JUN, which promotes transformation. We performed in vitro and in silico analysis and in vivo zebrafish xenograft experiments to demonstrate that TaPIN1 is directly inhibited by the anti-parasite drug buparvaquone (and other known PIN1 inhibitors) and is mutated in a drug-resistant strain. Prolyl isomerization is thus a conserved mechanism that is important in cancer and is used by Theileria parasites to manipulate host oncogenic signalling.

RB regulates transcription of the p21/WAF1/CIP1 gene.

We have previously shown that RB plays an important role in the maintenance of the epithelial phenotype. p21 is also involved in several terminal differentiation systems including keratinocytes. We report here that p21 is an RB target gene in epithelial cells, but not in fibroblasts where RB is unable to transactivate p21 transcriptional expression. In epithelial cells, when RB family factors were inactivated by SV40 T antigen (LT), p21 expression was strongly repressed, whereas its expression was not affected when the cells were transformed by a mutated LT leaving RB active but inactivating p53. Moreover, retransformation by RB of LT transformed epithelial cells totally restored p21 expression. By cotransfection experiments and using deletions and point mutations of the p21 promoter, we show that the minimal region required for the RB-mediated transcriptional activation maps to a GC-rich region located between -83 and -74. This region is shown to interact specifically with the transcription factor Sp1 and Sp3. Thus for the first time, we show a positive transcriptional relationship between RB and p21 in epithelial cells. Since p21 keeps RB in a hypophosphorylated state important for its transcriptional activity during differentiation, our results imply an auto-loop of regulation between RB and p21 that may be essential for the maintenance of the differentiation state. We propose that this transcriptional relationship might be necessary of their roles in cell cycle arrest and in several differentiation pathways.

Theileria induces oxidative stress and HIF1α activation that are essential for host leukocyte transformation.

Complex links between infection and cancer suggest that we still can learn much about tumorigenesis by studying how infectious agents hijack the host cell machinery. We studied the effects of an intracellular parasite called Theileria that infects bovine leukocytes and turns them into invasive cancer-like cells. We investigated the host cells pathways that are deregulated in infected leukocytes and might link infection and lymphoproliferative disease. We show that intracellular Theileria parasites drive a Warburg-like phenotype in infected host leukocytes, characterized by increased expression of metabolic regulators, increased glucose uptake and elevated lactate production, which were lost when the parasite was eliminated. The cohabitation of the parasites within the host cells leads to disruption of the redox balance (as measured by reduced/oxidized glutathione ratio) and elevated ROS (reactive oxygen species) levels, associated with chronic stabilization of the hypoxia-inducible factor 1 alpha (HIF1α). Inhibition of HIF1α (pharmacologically or genetically), or treatment with antioxidants, led to a marked reduction in expression of aerobic glycolytic genes and inhibited the transformed phenotype. These data show that stabilization of HIF1α, following increased ROS production, modulates host glucose metabolism and is critical for parasite-induced transformation. Our study expands knowledge about the molecular strategy used by the parasite Theileria to induce the transformed phenotypes of infected cells via reprogramming of glucose metabolism and redox signaling.

The requirement for SNF5/INI1 in adipocyte differentiation highlights new features of malignant rhabdoid tumors.

ATP-dependent SWI/SNF chromatin remodeling complexes regulate cell-cycle and play critical roles in a variety of differentiation pathways. The core subunit SNF5/INI1 is a tumor suppressor that is inactivated in a highly aggressive childhood cancer of unknown cellular origin, termed malignant rhabdoid tumor (MRT). The highly undifferentiated phenotype of this tumor suggests that the loss-of-function of hSNF5/INI1 impairs specific differentiation programs of the MRT parental cell. Based on the hypothesis that these programs might be reinitialized upon hSNF5/INI1 re-expression in MRTs, we show that some MRT cell lines can differentiate toward the adipogenic lineage. We further show that the knock down of the SNF5/INI1 subunit abrogates adipocyte differentiation of murine 3T3-L1 preadipocytes and of human mesenchymal stem cells. Finally, we provide evidence that hSNF5/INI1 cooperates with C/EBPbeta and PPARgamma2 transcriptional regulators to activate the expression of adipocyte-specific genes. These data indicate that not only the ATPase subunit of the SWI/SNF complex, but also SNF5/INI1 is required for adipocyte differentiation. They further show that MRT cell lines harbor an adipogenic differentiation potential and that the tumor suppressor role of the SNF5/INI1 subunit may rely on its ability to regulate the balance between cell proliferation and differentiation.