RESUMO
Toxoplasma gondii, the causative agent of toxoplasmosis, is an obligate intracellular protozoan parasite that resides inside a parasitophorous vacuole. During infection, Toxoplasma actively remodels the transcriptome of its hosting cells with profound and coupled impact on the host immune response. We report that Toxoplasma secretes GRA24, a novel dense granule protein which traffics from the vacuole to the host cell nucleus. Once released into the host cell, GRA24 has the unique ability to trigger prolonged autophosphorylation and nuclear translocation of the host cell p38α MAP kinase. This noncanonical kinetics of p38α activation correlates with the up-regulation of the transcription factors Egr-1 and c-Fos and the correlated synthesis of key proinflammatory cytokines, including interleukin-12 and the chemokine MCP-1, both known to control early parasite replication in vivo. Remarkably, the GRA24-p38α complex is defined by peculiar structural features and uncovers a new regulatory signaling path distinct from the MAPK signaling cascade and otherwise commonly activated by stress-related stimuli or various intracellular microbes.
Assuntos
Proteínas de Protozoários/imunologia , Toxoplasma/imunologia , Toxoplasmose/imunologia , Toxoplasmose/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Linhagem Celular , Núcleo Celular/metabolismo , Quimiocinas/biossíntese , Análise por Conglomerados , Proteína 1 de Resposta de Crescimento Precoce/genética , Proteína 1 de Resposta de Crescimento Precoce/metabolismo , Ativação Enzimática , Feminino , Deleção de Genes , Perfilação da Expressão Gênica , Ordem dos Genes , Humanos , Inflamação/genética , Inflamação/imunologia , Macrófagos/imunologia , Macrófagos/metabolismo , Camundongos , Modelos Moleculares , Dados de Sequência Molecular , Fosforilação , Ligação Proteica , Conformação Proteica , Domínios e Motivos de Interação entre Proteínas , Multimerização Proteica , Transporte Proteico , Proteínas Proto-Oncogênicas c-fos/genética , Proteínas Proto-Oncogênicas c-fos/metabolismo , Proteínas de Protozoários/química , Proteínas de Protozoários/genética , Proteínas de Protozoários/metabolismo , Alinhamento de Sequência , Toxoplasma/genética , Proteínas Quinases p38 Ativadas por Mitógeno/químicaRESUMO
After invading host cells, Toxoplasma gondii multiplies within a parasitophorous vacuole (PV) that is maintained by parasite proteins secreted from organelles called dense granules. Most dense granule proteins remain within the PV, and few are known to access the host cell cytosol. We identify GRA16 as a dense granule protein that is exported through the PV membrane and reaches the host cell nucleus, where it positively modulates genes involved in cell-cycle progression and the p53 tumor suppressor pathway. GRA16 binds two host enzymes, the deubiquitinase HAUSP and PP2A phosphatase, which exert several functions, including regulation of p53 and the cell cycle. GRA16 alters p53 levels in a HAUSP-dependent manner and induces nuclear translocation of the PP2A holoenzyme. Additionally, certain GRA16-deficient strains exhibit attenuated virulence, indicating the importance of these host alterations in pathogenesis. Therefore, GRA16 represents a potentially emerging subfamily of exported dense granule proteins that modulate host function.