La P-glycoprotéine (analyse des différents sites de liaison de ses substrats et de sa fonction de transport)

Résumé françaisRésumé anglaisORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

L' endocytose (une fonction cellulaire qui est stimulée par les champs électromagnétiques et qui joue un rôle dans l'internalisation de la bléomycine)

La bléomycine (BLM) est une drogue utilisée en chimiothérapie, caractérisée par une faible incorporation cellulaire et un très fort pouvoir cytotoxique une fois qu'elle a atteint le cytosol d'où elle peut interagir avec sa cible (l'ADN). Nous avons montré sur différentes lignées cellulaires en culture que la cytotoxicité de la BLM nécessite sa liaison sur une protéine membranaire spécifique (récepteur), et qu'elle est corrélée à la vitesse d'endocytose. Cette cytotoxicité dépend de la surface de membrane incorporée mais pas du volume contenu dans les vésicules d'endocytose. Ces résultats permettent de conclure que les molécules de BLM exercent leur toxicité grâce à leur internalisation suivant un mécanisme de type endocytose médiée par récepteur. Nous avons aussi montré que l'endocytose en phase fluide, que est un processus cellulaire fondamental, est stimulée aussi bien par l'application des champs électromagnétiques de type GSM que par les champs électriques pulsés de basse fréquence qui leur correspndent...PARIS5-BU Saints-Pères (751062109) / SudocSudocFranceF

Lipid rafts: dream or reality for cholesterol transporters?

The original publication is available at www.springerlink.comInternational audienceAs a key constituent of the cell membranes, cholesterol is an endogenous component of mammalian cells of primary importance, and is thus subjected to highly regulated homeostasis at the cellular level as well as at the level of the whole body. This regulation requires adapted mechanisms favoring the handling of cholesterol in aqueous compartments, as well as its transfer into or out of membranes, involving membrane proteins. A membrane exhibits functional properties largely depending on its lipid composition and on its structural organization, which very often involves cholesterol-rich microdomains. Then there is the appealing possibility that cholesterol may regulate its own transmembrane transport at a purely functional level, independently of any transcriptional regulation based on cholesterol-sensitive nuclear factors controling the expression level of lipid transport proteins. Indeed, the main cholesterol "transporters" presently believed to mediate for instance the intestinal absorption of cholesterol, that are SR-BI, NPC1L1, ABCA1, ABCG1, ABCG5/G8 and even P-glycoprotein, all present privileged functional relationships with membrane cholesterol-containing microdomains. In particular, they all more or less clearly induce membrane disorganization, supposed to facilitate cholesterol exchanges with the close aqueous medium. The actual lipid substrates handled by these transporters are not yet unambiguously determined, but they likely concern the components of membrane microdomains. Conversely, raft alterations may provide specific modulations of the transporter activities, as well as they can induce indirect effects via local perturbations of the membrane. Finally, these cholesterol transporters undergo regulated intracellular trafficking, with presumably some relationships to rafts which remain to be clarified

Coronaviruses, cholesterol and statins: Involvement and application for Covid-19

International audienceThe infectious power of coronaviruses is dependent on cholesterol present in the membranes of their target cells. Indeed, the virus enters the infected cell either by fusion or by endocytosis, in both cases involving cholesterol-enriched membrane microdomains. These membrane domains can be disorganized in-vitro by various cholesterol-altering agents, including statins that inhibit cell cholesterol biosynthesis. As a consequence, numerous cell physiology processes, such as signaling cascades, can be compromised. Also, some examples of anti-bacterial and anti-viral effects of statins have been observed for infectious agents known to be cholesterol dependent. In-vivo, besides their widely-reported hypocholesterolemic effect, statins display various pleiotropic effects mediated, at least partially, by perturbation of membrane microdomains as a consequence of the alteration of endogenous cholesterol synthesis. It should thus be worth considering a high, but clinically well-tolerated, dose of statin to treat Covid-19 patients, in the early phase of infection, to inhibit virus entry into the target cells, in order to control the viral charge and hence avoid severe clinical complications. Based on its efficacy and favorable biodisposition, an option would be considering Atorvastatin, but randomized controlled clinical trials are required to test this hypothesis. This new therapeutic proposal takes benefit from being a drug repurposing, applied to a widely-used drug presenting a high efficiency-to-toxicity ratio. Additionally, this therapeutic strategy avoids any risk of drug resistance by viral mutation since it is host-targeted. Noteworthy, the same pharmacological approach could also be proposed to address different animal coronavirus endemic infections that are responsible for heavy economic losses

Ectopic Neo-Formed Intracellular Membranes in Escherichia coli: A Response to Membrane Protein-Induced Stress Involving Membrane Curvature and Domains

Bacterial cytoplasmic membrane stress induced by the overexpression of membrane proteins at high levels can lead to formation of ectopic intracellular membranes. In this review, we report the various observations of such membranes in Escherichia coli, compare their morphological and biochemical characterizations, and we analyze the underlying molecular processes leading to their formation. Actually, these membranes display either vesicular or tubular structures, are separated or connected to the cytoplasmic membrane, present mono- or polydispersed sizes and shapes, and possess ordered or disordered arrangements. Moreover, their composition differs from that of the cytoplasmic membrane, with high amounts of the overexpressed membrane protein and altered lipid-to-protein ratio and cardiolipin content. These data reveal the importance of membrane domains, based on local specific lipid–protein and protein–protein interactions, with both being crucial for local membrane curvature generation, and they highlight the strong influence of protein structure. Indeed, whether the cylindrically or spherically curvature-active proteins are actively curvogenic or passively curvophilic, the underlying molecular scenarios are different and can be correlated with the morphological features of the neo-formed internal membranes. Delineating these molecular mechanisms is highly desirable for a better understanding of protein–lipid interactions within membrane domains, and for optimization of high-level membrane protein production in E. coli