Formation of cristae and crista junctions in mitochondria depends on antagonism between Fcj1 and Su e/g

Crista junctions (CJs) are important for mitochondrial organization and function, but the molecular basis of their formation and architecture is obscure. We have identified and characterized a mitochondrial membrane protein in yeast, Fcj1 (formation of CJ protein 1), which is specifically enriched in CJs. Cells lacking Fcj1 lack CJs, exhibit concentric stacks of inner membrane in the mitochondrial matrix, and show increased levels of F1FO–ATP synthase (F1FO) supercomplexes. Overexpression of Fcj1 leads to increased CJ formation, branching of cristae, enlargement of CJ diameter, and reduced levels of F1FO supercomplexes. Impairment of F1FO oligomer formation by deletion of its subunits e/g (Su e/g) causes CJ diameter enlargement and reduction of cristae tip numbers and promotes cristae branching. Fcj1 and Su e/g genetically interact. We propose a model in which the antagonism between Fcj1 and Su e/g locally modulates the F1FO oligomeric state, thereby controlling membrane curvature of cristae to generate CJs and cristae tips

NF-κB Signalling in Glioblastoma

Nuclear factor-κB (NF-κB) is a transcription factor regulating a wide array of genes mediating numerous cellular processes such as proliferation, differentiation, motility and survival, to name a few. Aberrant activation of NF-κB is a frequent event in numerous cancers, including glioblastoma, the most common and lethal form of brain tumours of glial cell origin (collectively termed gliomas). Glioblastoma is characterized by high cellular heterogeneity, resistance to therapy and almost inevitable recurrence after surgery and treatment. NF-κB is aberrantly activated in response to a variety of stimuli in glioblastoma, where its activity has been implicated in processes ranging from maintenance of cancer stem-like cells, stimulation of cancer cell invasion, promotion of mesenchymal identity, and resistance to radiotherapy. This review examines the mechanisms of NF-κB activation in glioblastoma, the involvement of NF-κB in several mechanisms underlying glioblastoma propagation, and discusses some of the important questions of future research into the roles of NF-κB in glioblastoma

La sous-unité 4 dans le second pied de la F1F0-ATP synthase de la levure Saccharomyces cerevisiae (Etude topologique de cette sous-unité et son implication dans le processus de dimérisation / oligomérisation de l'enzyme)

La F1-Fo-ATP synthase est un complexe protéique mitochondrial composé d'au moins vingt sous-unités chez la levure Saccharomyces cerevsiae. Cette enzyme présente des organisations supra-moleculaires correspondant à des formes dimériques. La sous-unité 4(b) est la composante essentielle du second pied de la F1Fo-ATP synthase qui relie le domaine catalytique F1 au domaine protonophorique membranaire Fo. Afin de décrire l'organisation du second pied de l'ATP synthase, l'environnement protéique de la sous-unité 4 a été exploré grâce à des pontages chimiques utilisant un agent pontant hétéro-bifonctionnel. Cette étude topologique a mis en évidence différents rapports de voisinage avec d'autres sous-unités : l'extrémité N-terminale de la sous-unité 4 est à proximité de la sous-unité g, tandis que la région C-terminale est au voisinage des sous-unités h, d, b, et OSCP. Le voisinage entre le résidu C-terminal de la sous-unité 4 et la sous-unité OSCP laissait envisager que l'extrémité C-terminale dela sous-unité 4 constituait une zone d'interaction avec la sous-unité OSCP. Les dix derniers résidus de la sous-unité 4 sont essentiels à l'assemblage entre les secteurs F1 et Fo. Aussi l'environnement protéique de ces dix derniers résidus de la sous-unité 4 a été étudié grâce à des pontages chimiques utilisant des agents pontant homo-et hétéro-bifonctionnels. Cette étude topologique a permis de préciser que cette zone de xconnexion entre les secteurs F1 et Fo serait composée au moins des sous-unités 4, OSCP, h et a. Enfin, nous avons cherché à établir le rôle que pouvait jouer le premier segment transmembranaire des sous-unités 4 (b) mitochondriales qui est absent dans les sous-unités b procaryotiques et chloroplastiques. Nos études ont montré que cette région N-terminale additionnelle n'est pas indispensable auu fonctionnement de la F1Fo ATP synthase et que sa perte n'altère pas non plus les phosphorylations oxydatives. Par contre, la perte du premier segment transmembranaire de la sous-unité 4 aboutit à la perte d'assemblage de la sous-unité g. La sous-unité g étant indispensable à la dimérisation/oligomérisation de l'enzyme, l'ATP synthase n'est alors plus capable de se dimériser ni de s'oligomériser. L'altération de la morphologie des crêtes mitochondriales est une autre conséquence de la perte d'assemblage de la sous-unité g, l'oligomérisation de l'ATP synthase étant essentielle à la formation des crêtes. Ces observations suggèrent que le premier segment transmembranaire de la sous-unité 4 constitue une zone d'interaction avec le segment transmembranaire de la sous-unité g.BORDEAUX2-BU Santé (330632101) / SudocSudocFranceF

Positioning mitochondrial plasticity within cellular signaling cascades

AbstractMitochondria evolved from alpha-proteobacteria captured within a host between two and three billion years ago. This origin resulted in the formation of a double-layered organelle resulting in four distinct sub-compartments: the outer membrane, the intermembrane space, the inner membrane and the matrix. The inner membrane is organized in cristae, harboring the respiratory chain and ATP synthase complexes responsible of the oxidative phosphorylation, the main energy-generating system of the cell. It is generally considered that the ultrastructure of the inner membrane provides a large variety of morphologies that facilitate metabolic output. This classical view of mitochondria as bean-shaped organelles was static until in the last decade when new imaging studies and genetic screens provided a more accurate description of a dynamic mitochondrial reticulum that fuse and divide continuously. Since then significant findings have been made in the study of machineries responsible for fusion, fission and motility, however the mechanisms and signals that regulate mitochondrial dynamics are only beginning to emerge. A growing body of evidence indicates that metabolic and cellular signals influence mitochondrial dynamics, leading to a new understanding of how changes in mitochondrial shape can have a profound impact on the functional output of the organelle. The mechanisms that regulate mitochondrial morphology are incompletely understood, but evidence to date suggests that the morphology machinery is modulated through the use of post-translational modifications, including nucleotide-binding proteins, phosphorylation, ubiquitination, SUMOylation, and changes in the lipid environment. This review focuses on the molecular switches that control mitochondrial dynamics and the integration of mitochondrial morphology within cellular signaling cascades

HBpF-proBDNF: A New Tool for the Analysis of Pro-Brain Derived Neurotrophic Factor Receptor Signaling and Cell Biology.

Neurotrophins activate intracellular signaling pathways necessary for neuronal survival, growth and apoptosis. The most abundant neurotrophin in the adult brain, brain-derived neurotrophic factor (BDNF), is first synthesized as a proBDNF precursor and recent studies have demonstrated that proBDNF can be secreted and that it functions as a ligand for a receptor complex containing p75NTR and sortilin. Activation of proBDNF receptors mediates growth cone collapse, reduces synaptic activity, and facilitates developmental apoptosis of motoneurons but the precise signaling cascades have been difficult to discern. To address this, we have engineered, expressed and purified HBpF-proBDNF, an expression construct containing a 6X-HIS tag, a biotin acceptor peptide (BAP) sequence, a PreScission™ Protease cleavage site and a FLAG-tag attached to the N-terminal part of murine proBDNF. Intact HBpF-proBDNF has activities indistinguishable from its wild-type counterpart and can be used to purify proBDNF signaling complexes or to monitor proBDNF endocytosis and retrograde transport. HBpF-proBDNF will be useful for characterizing proBDNF signaling complexes and for deciphering the role of proBDNF in neuronal development, synapse function and neurodegenerative disease

Reconstitution of Mitochondria Derived Vesicle Formation Demonstrates Selective Enrichment of Oxidized Cargo

<div><p>The mechanisms that ensure the removal of damaged mitochondrial proteins and lipids are critical for the health of the cell, and errors in these pathways are implicated in numerous degenerative diseases. We recently uncovered a new pathway for the selective removal of proteins mediated by mitochondrial derived vesicular carriers (MDVs) that transit to the lysosome. However, it was not determined whether these vesicles were selectively enriched for oxidized, or damaged proteins, and the extent to which the complexes of the electron transport chain and the mtDNA-containing nucloids may have been incorporated. In this study, we have developed a cell-free mitochondrial budding reaction <em>in vitro</em> in order to better dissect the pathway. Our data confirm that MDVs are stimulated upon various forms of mitochondrial stress, and the vesicles incorporated quantitative amounts of cargo, whose identity depended upon the nature of the stress. Under the conditions examined, MDVs did not incorporate complexes I and V, nor were any nucleoids present, demonstrating the specificity of cargo incorporation. Stress-induced MDVs are selectively enriched for oxidized proteins, suggesting that conformational changes induced by oxidation may initiate their incorporation into the vesicles. Ultrastructural analyses of MDVs isolated on sucrose flotation gradients revealed the formation of both single and double membranes vesicles of unique densities and uniform diameter. This work provides a framework for a reductionist approach towards a detailed examination of the mechanisms of MDV formation and cargo incorporation, and supports the emerging concept that MDVs are critical contributors to mitochondrial quality control.</p> </div

The Nogo Receptor Ligand LGI1 Regulates Synapse Number and Synaptic Activity in Hippocampal and Cortical Neurons

International audienceLeucine-rich glioma-inactivated protein 1 (LGI1) is a secreted neuronal protein and a Nogo receptor 1 (NgR1) ligand. Mutations in LGI1 in humans causes autosomal dominant lateral temporal lobe epilepsy and homozygous deletion of LGI1 in mice results in severe epileptic seizures that cause early postnatal death. NgR1 plays an important role in the development of CNS synapses and circuitry by limiting plasticity in the adult cortex via the activation of RhoA. These relationships and functions prompted us to examine the effect of LGI1 on synapse formation in vitro and in vivo. We report that application of LGI1 increases synaptic density in neuronal culture and that LGI1 null hippocampus has fewer dendritic mushroom spines than in wild-type (WT) littermates. Further, our electrophysiological investigations demonstrate that LGI1 null hippocampal neurons possess fewer and weaker synapses. RhoA activity is significantly increased in cortical cultures derived from LGI1 null mice and using a reconstituted system; we show directly that LGI1 antagonizes NgR1-tumor necrosis factor receptor orphan Y (TROY) signaling. Our data suggests that LGI1 enhances synapse formation in cortical and hippocampal neurons by reducing NgR1 signaling