Unlu, Ahmet HakanTajeri, ShahinBilgic, Huseyin BilginEren, HasanKaragenc, TulinLangsley, Gordon2025-05-102025-05-1020181932-620310.1371/journal.pone.01968752-s2.0-85046684810https://doi.org/10.1371/journal.pone.0196875https://hdl.handle.net/20.500.14720/6091Langsley, Gordon/0000-0001-6600-6286; Tajeri, Shahin/0000-0002-0482-1194; Karagenc, Tulin/0000-0002-5843-1730Theileria annulata is an obligate intracellular protozoan parasite of the phylum Apicomplexa. Theileria sporozoites invade bovine leukocytes and develop into a multinucleate syncytial macroschizont that causes uncontrolled proliferation and dissemination of infected and transformed leukocytes. Activator protein 1 (AP-1) is a transcription factor driving expression of genes involved in proliferation and dissemination and is therefore a key player in Theileria-induced leukocytes transformation. Ta9 possesses a signal peptide allowing it to be secreted into the infected leukocyte cytosol and be presented to CD8 T cells in the context of MHC class I. First, we confirmed that Ta9 is secreted into the infected leukocyte cytosol, and then we generated truncated versions of GFP-tagged Ta9 and tested their ability to activate AP-1 in non-infected HEK293T human kidney embryo cells. The ability to activate AP-1-driven transcription was found to reside in the C-terminal 100 amino acids of Ta9 distant to the N-terminally located epitopes recognised by CD8+ T cells. Secreted Ta9 has therefore, not only the ability to stimulate CD8+ T cells, but also the potential to activate AP-1-driven transcription and contribute to T. annulata-induced leukocyte transformation.eninfo:eu-repo/semantics/openAccessArticle135Q2Q129738531WOS:000431724900025