Evidence for localisation of a Theileria parasite AT hook DNA-binding protein to the nucleus of immortalised bovine host cells

Immortalisation of bovine leukocytes by the macroschizont stage of the tick transmitted protozoan parasite, Theileria annulata, results in the clonal expansion of infected cells and dissemination throughout the bovine host. T he parasite-encoded factors which induce this unique transformation event h ave not been defined to date. In this study, a gene family (TashAT) has bee n characterised that encodes polypeptides with homology to known DNA-bindin g proteins. Expression of TashAT genes occurs at the intracellular macrosch izont stage of the parasite life cycle and during differentiation to the me rozoite, negative regulation of TashAT genes is detected early relative to other macroschizont genes. Interestingly, the early reduction in TashAT exp ression coincides with the initial decrease in host cell proliferation. One member of the family, TashAT2, was characterised in detail and the predict ed polypeptide sequence was found to harbor three AT hook DNA-binding domai ns. Antisera generated against two distinct regions of TashAT2 both located the antigen to the host cell nucleus and, combined with protein translatio n inhibition and immunoprecipitation studies, provide evidence that this po lypeptide could be transported from the parasite to this location. Further evidence for this postulation was provided by transfection studies which de monstrated that TashAT2 does encode the structural information required for localisation to the nucleus of a mammalian cell. Thus, TaskAT2 is a potent ial candidate for a parasite-encoded factor that modulates host cell gene e xpression and may be involved in the control of host cell proliferation. (C ) 1999 Elsevier Science B.V. All rights reserved.