RESUMO
Given the heterogeneous nature of antigens, major histocompatibility complex class I (MHC I) intracellular transport intersects with multiple degradation pathways for efficient peptide loading and presentation to cytotoxic T cells. MHC I loading with peptides in the endoplasmic reticulum (ER) is a tightly regulated process, while post-ER intracellular transport is considered to occur by default, leading to peptide-bearing MHC I delivery to the plasma membrane. We show here that MHC I traffic is submitted to a previously uncharacterized sorting step at the trans Golgi network (TGN), dependent on the ubiquitination of its cytoplasmic tail lysine residues. MHC I ubiquitination is mediated by the E3 ligase membrane-associated RING-CH 9 (MARCH9) and allows MHC I access to Syntaxin 6-positive endosomal compartments. We further show that MARCH9 can also target the human MHC I-like lipid antigen-presentation molecule CD1a. MARCH9 expression is modulated by microbial pattern exposure in dendritic cells (DCs), thus revealing the role of this ubiquitin E3 ligase in coordinating MHC I access to endosomes and DC activation for efficient antigen cross-presentation.
Assuntos
Antígenos CD1/metabolismo , Membrana Celular/metabolismo , Células Dendríticas/imunologia , Endossomos/metabolismo , Antígenos HLA/metabolismo , Antígenos de Histocompatibilidade Classe I/metabolismo , Rede trans-Golgi/metabolismo , Apresentação de Antígeno , Antígenos CD1/genética , Células Cultivadas , Retículo Endoplasmático/metabolismo , Antígenos HLA/genética , Antígenos de Histocompatibilidade Classe I/genética , Humanos , Proteínas de Membrana , Monócitos/imunologia , Domínios Proteicos/genética , Sinais Direcionadores de Proteínas/genética , Transporte Proteico , Proteínas Qa-SNARE/metabolismo , Ubiquitina-Proteína Ligases , UbiquitinaçãoAssuntos
Receptor fas/metabolismo , Proteína Reguladora de Apoptosis Semelhante a CASP8 e FADD/química , Proteína Reguladora de Apoptosis Semelhante a CASP8 e FADD/metabolismo , Caspases/metabolismo , Morte Celular , Proteínas Adaptadoras de Sinalização de Receptores de Domínio de Morte/metabolismo , Células HeLa , Humanos , NF-kappa B/metabolismo , Transdução de SinaisRESUMO
This study explores the dilemma in cellular signaling that triggering of CD95 (Fas/APO-1) in some situations results in cell death and in others leads to the activation of NF-kappaB. We established an integrated kinetic mathematical model for CD95-mediated apoptotic and NF-kappaB signaling. Systematic model reduction resulted in a surprisingly simple model well approximating experimentally observed dynamics. The model postulates a new link between c-FLIP(L) cleavage in the death-inducing signaling complex (DISC) and the NF-kappaB pathway. We validated experimentally that CD95 stimulation resulted in an interaction of p43-FLIP with the IKK complex followed by its activation. Furthermore, we showed that the apoptotic and NF-kappaB pathways diverge already at the DISC. Model and experimental analysis of DISC formation showed that a subtle balance of c-FLIP(L) and procaspase-8 determines life/death decisions in a nonlinear manner. We present an integrated model describing the complex dynamics of CD95-mediated apoptosis and NF-kappaB signaling.
Assuntos
Proteínas Adaptadoras de Sinalização de Receptores de Domínio de Morte/metabolismo , Transdução de Sinais , Receptor fas/metabolismo , Apoptose , Proteína Reguladora de Apoptosis Semelhante a CASP8 e FADD/metabolismo , Caspases/metabolismo , Morte Celular , Linhagem da Célula , Sobrevivência Celular , Ativação Enzimática , Células HeLa , Humanos , Quinase I-kappa B/metabolismo , Cinética , Modelos Biológicos , NF-kappa B/metabolismo , Ligação Proteica , Receptor fas/genéticaRESUMO
Apoptosis is a process common to all multicellular organisms. Apoptosis leads to the elimination of cells via a complex but highly defined cellular programme. Defects in the regulation of apoptosis result in serious diseases such as cancer, autoimmunity, AIDS and neurodegeneration. Recently, a substantial step forward in understanding the complex apoptotic pathways has been made by utilising systems biology approaches. Systems biology combines rigorous mathematical modelling with experimental approaches in a closed loop cycle for advancing our knowledge about complex biological processes. In this review we describe the contemporary systems biology studies devoted to apoptotic signalling and focus on the question of how systems biology helps to understand life/death decisions made in the cell and to develop new approaches to rational treatment strategies.
