RESUMO
Microglia, the resident macrophages of the mammalian central nervous system, migrate to sites of tissue damage or infection and become activated. Although the persistent secretion of inflammatory mediators by the activated cells contributes to the pathogenesis of various neurological disorders, most activated microglia eventually undergo apoptosis through the process of activation-induced cell death (AICD). The molecular mechanism of AICD, however, has remained unclear. Here, we show that Daxx and mammalian Ste20-like kinase-1 (MST1) mediate apoptosis elicited by interferon-γ (IFN-γ) in microglia. IFN-γ upregulated the expression of Daxx, which in turn mediated the homodimerization, activation, and nuclear translocation of MST1 and apoptosis in microglial cells. Depletion of Daxx or MST1 by RNA interference also attenuated IFN-γ-induced cell death in primary rat microglia. Furthermore, the extent of IFN-γ-induced death of microglia in the brain of MST1-null mice was significantly reduced compared with that apparent in wild-type mice. Our results thus highlight new functions of Daxx and MST1 that they are the key mediators of microglial cell death initiated by the proinflammatory cytokine IFN-γ.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Proteínas de Transporte/fisiologia , Fator de Crescimento de Hepatócito/fisiologia , Peptídeos e Proteínas de Sinalização Intracelular/fisiologia , Microglia/citologia , Microglia/fisiologia , Proteínas Nucleares/fisiologia , Proteínas Proto-Oncogênicas/fisiologia , Transdução de Sinais , Animais , Apoptose/genética , Células COS , Proteínas de Transporte/genética , Morte Celular/genética , Sobrevivência Celular/genética , Células Cultivadas , Chlorocebus aethiops , Proteínas Correpressoras , Fibroblastos/citologia , Fibroblastos/fisiologia , Células HEK293 , Células HeLa , Fator de Crescimento de Hepatócito/deficiência , Fator de Crescimento de Hepatócito/genética , Humanos , Mediadores da Inflamação , Interferon gama/administração & dosagem , Interferon gama/fisiologia , Peptídeos e Proteínas de Sinalização Intracelular/deficiência , Peptídeos e Proteínas de Sinalização Intracelular/genética , Camundongos , Camundongos Knockout , Chaperonas Moleculares , Proteínas Nucleares/deficiência , Proteínas Nucleares/genética , Proteínas Proto-Oncogênicas/deficiência , Proteínas Proto-Oncogênicas/genética , Ratos , Ratos Sprague-Dawley , Transdução de Sinais/genéticaRESUMO
The role and molecular mechanisms of a new Hippo signalling pathway are not fully understood in mammals. Here, we generated mice that lack WW45 and revealed a crucial role for WW45 in cell-cycle exit and epithelial terminal differentiation. Many organs in the mutant mouse embryos displayed hyperplasia accompanied by defects in terminal differentiation of epithelial progenitor cells owing to impaired proliferation arrest rather than intrinsic acceleration of proliferation during differentiation. Importantly, the MST1 signalling pathway is specifically activated in differentiating epithelial cells. Moreover, WW45 is required for MST1 activation and translocation to the nucleus for subsequent LATS1/2 activation upon differentiation signal. LATS1/2 phosphorylates YAP, which, in turn, translocates from the nucleus into the cytoplasm, resulting in cell-cycle exit and terminal differentiation of epithelial progenitor cells. Collectively, these data provide compelling evidence that WW45 is a key mediator of MST1 signalling in the coordinate coupling of proliferation arrest with terminal differentiation for proper epithelial tissue development in mammals.
Assuntos
Proteínas de Ciclo Celular/fisiologia , Epitélio/embriologia , Transdução de Sinais/fisiologia , Animais , Ciclo Celular/genética , Proteínas de Ciclo Celular/biossíntese , Proteínas de Ciclo Celular/genética , Diferenciação Celular/genética , Células Cultivadas , Epitélio/metabolismo , Epitélio/patologia , Fator de Crescimento de Hepatócito/genética , Humanos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Serina-Treonina Quinases/fisiologia , Proteínas Proto-Oncogênicas/genética , Transdução de Sinais/genéticaRESUMO
For successful mitotic entry and spindle assembly, mitosis-promoting factors are activated at the G(2)/M transition stage, followed by stimulation of the anaphase-promoting complex (APC), an E3 ubiquitin ligase, to direct the ordered destruction of several critical mitotic regulators. Given that inhibition of APC activity is important for preventing premature or improper ubiquitination and destruction of substrates, several modulators and their regulation mechanisms have been studied. Emi1, an early mitotic inhibitor, is one of these regulatory factors. Here we show, by analyzing Emi1-deficient embryos, that Emi1 is essential for precise mitotic progression during early embryogenesis. Emi1(-/-) embryos were found to be lethal due to a defect in preimplantation development. Cell proliferation appeared to be normal, but mitotic progression was severely defective during embryonic cleavage. Moreover, multipolar spindles and misaligned chromosomes were frequently observed in Emi1 mutant cells, possibly due to premature APC activation. Our results collectively suggest that the late prophase checkpoint function of Emi1 is essential for accurate mitotic progression and embryonic viability.