RESUMO
Signaling pathways are characterized by crosstalk, feedback and feedforward mechanisms giving rise to highly complex and cell-context specific signaling networks. Dissecting the underlying relations is crucial to predict the impact of targeted perturbations. However, a major challenge in identifying cell-context specific signaling networks is the enormous number of potentially possible interactions. Here, we report a novel hybrid mathematical modeling strategy to systematically unravel hepatocyte growth factor (HGF) stimulated phosphoinositide-3-kinase (PI3K) and mitogen activated protein kinase (MAPK) signaling, which critically contribute to liver regeneration. By combining time-resolved quantitative experimental data generated in primary mouse hepatocytes with interaction graph and ordinary differential equation modeling, we identify and experimentally validate a network structure that represents the experimental data best and indicates specific crosstalk mechanisms. Whereas the identified network is robust against single perturbations, combinatorial inhibition strategies are predicted that result in strong reduction of Akt and ERK activation. Thus, by capitalizing on the advantages of the two modeling approaches, we reduce the high combinatorial complexity and identify cell-context specific signaling networks.
Assuntos
Fator de Crescimento de Hepatócito/metabolismo , Hepatócitos/metabolismo , Regeneração Hepática/fisiologia , Sistema de Sinalização das MAP Quinases/fisiologia , Modelos Biológicos , Fosfatidilinositol 3-Quinases/metabolismo , Animais , Células Cultivadas , Simulação por Computador , Camundongos , Proteínas Proto-Oncogênicas c-akt/metabolismoRESUMO
The function of the oxidoreductase ERp57 in the major histocompatibility complex (MHC) class I peptide-loading complex has remained elusive. Here we show that in the absence of tapasin, the alpha2 disulfide bond in the MHC class I peptide-binding groove was rapidly reduced. Covalent sequestration of ERp57 by tapasin was needed to protect the alpha2 disulfide bond against reduction and thus to maintain the binding groove in a peptide-receptive state. Allelic variations in MHC class I tapasin dependency reflected their susceptibility to reduction of the alpha2 disulfide bond. In the absence of sequestration, ERp57 acted directly on the alpha2 disulfide bond. Our work provides insight into how the immune system customizes 'quality control' in the endoplasmic reticulum to fit the needs of antigen presentation.
Assuntos
Apresentação de Antígeno/imunologia , Antígenos de Histocompatibilidade Classe I/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Isomerases de Dissulfetos de Proteínas/metabolismo , Linhagem Celular , Eletroforese em Gel de Poliacrilamida , Retículo Endoplasmático/metabolismo , Citometria de Fluxo , Antígenos de Histocompatibilidade Classe I/química , Antígenos de Histocompatibilidade Classe I/genética , Humanos , Immunoblotting , Imunoprecipitação , Proteínas de Membrana Transportadoras/química , Proteínas de Membrana Transportadoras/imunologia , Oxirredução , Isomerases de Dissulfetos de Proteínas/química , Isomerases de Dissulfetos de Proteínas/imunologiaRESUMO
Mitochondrial respiration plays an important role in optimizing photosynthetic efficiency in plants. As yet, the mechanisms by which plant mitochondria sense and respond to changes in the environment are unclear, particularly when exposed to light. Here we describe the characterization of the Chlamydomonas reinhardtii mutant stm6, which was identified on the basis of impaired state transitions, a mechanism that regulates light harvesting in the chloroplast. The gene disrupted in stm6, termed Moc1, encodes a homologue of the human mitochondrial transcription termination factor (mTERF). MOC1 is targeted to the mitochondrion, and its expression is up-regulated in response to light. Loss of MOC1 causes a high light-sensitive phenotype and disrupts the transcription and expression profiles of the mitochondrial respiratory complexes causing, as compared with wild type, light-mediated changes in the expression levels of nuclear and mitochondrial encoded cytochrome c oxidase subunits and ubiquinone-NAD subunits. The absence of MOC1 leads to a reduction in the levels of cytochrome c oxidase and of rotenone-insensitive external NADPH dehydrogenase activities of the mitochondrial respiratory electron transfer chain. Overall, we have identified a novel mitochondrial factor that regulates the composition of the mitochondrial respiratory chain in the light so that it can act as an effective sink for reductant produced by the chloroplast.