AnnexinA6 is recruited into lipid rafts of Niemann-Pick type C disease fibroblasts in a Ca2+ -dependent manner

International audienc

A novel retinoid binding property of human annexin A6

AbstractVitamin A (all-trans retinol) and all-trans retinoid acid (ATRA) interacted with human annexin A6 (AnxA6) as evidenced by AnxA6-induced blue shift of retinoid absorption maxima, by AnxA6-Trp fluorescence quenching and by a fluorescence resonance energy transfer from a Trp residue of AnxA6 to retinol. In addition, both retinoids stimulated the calcium-dependent binding of AnxA6 to liposomes, accompanied by oligomerization of AnxA6. Up to our knowledge, it is a first report supporting the hypothesis of a direct implication of AnxA6 in vitamin A-dependent tissue mineralization

Ankylosing spondylitis, late osteoarthritis, vascular calcification, chondrocalcinosis and pseudo gout: toward a possible drug therapy.

International audienceIn this review we consider diseases associated with pathological mineralization/ossification, namely, ankylosing spondylitis (AS), osteoarthritis (OA), generalized artery calcification of infancy (GACI), vascular calcification as well as chondrocalcinosis (CC) and pseudo gout. Deciphering the key enzymes implicated in the calcification process is an objective of prime importance and the ultimate goal is to synthesize inhibitors of these enzymes in order to provide efficient alternate therapeutic strategies that will slow down the pathologic mineralization and complement the arsenal of anti-inflammatory drugs. One of the difficulties in the definition of diseases associated with pathologic mineralization/ossification lies in the controversial relationship between the type of calcification and the nature of the disease. Here, we propose to clarify this relationship by making a distinction between diseases associated with hydroxyapatite (HA) and calcium pyrophosphate dihydrate (CPPD) deposits. AS, OA, GACI and vascular calcification are usually characterized by mineralization/ossification associated with HA deposits, while CC and pseudo gout are mostly characterized by CPPD deposits. Although both HA and CPPD deposits may occur concomitantly, as in chronic pyrophosphate arthritis or in OA with CPPD, they are formed as a result of two antagonistic processes indicating that treatment of distinct diseases can be only achieved by disease-specific drug therapies. The hydrolysis of PPi, an inhibitor of HA formation, is mostly controlled by tissue non-specific alkaline phosphatase TNAP, while PPi production in the extracellular medium is controlled by ANK, a PPi transporter, and/or NPP1 which generates PPi from nucleotide triphosphates. Low PPi concentration may lead to a preferential deposition of HA while high PPi concentration will favor the formation of CPPD deposits. Thus, HA and CCPD deposition cannot occur concomitantly because they are determined by the Pi/PPi ratio which, in turn, depends on the relative activities of antagonistic enzymes, TNAP hydrolyzing PPi or ANK and NPP1 producing PPi. TNAP inhibitors could prevent HA formation in AS, in late OA, in GACI, as well as in vascular calcifications, while ANK or NPP1 inhibitors could slow down CCPD deposition in CC and pseudo gout

Ankylosing spondylitis, late osteoarthritis, vascular calcification, chondrocalcinosis and pseudo gout: toward a possible drug therapy.

International audienceIn this review we consider diseases associated with pathological mineralization/ossification, namely, ankylosing spondylitis (AS), osteoarthritis (OA), generalized artery calcification of infancy (GACI), vascular calcification as well as chondrocalcinosis (CC) and pseudo gout. Deciphering the key enzymes implicated in the calcification process is an objective of prime importance and the ultimate goal is to synthesize inhibitors of these enzymes in order to provide efficient alternate therapeutic strategies that will slow down the pathologic mineralization and complement the arsenal of anti-inflammatory drugs. One of the difficulties in the definition of diseases associated with pathologic mineralization/ossification lies in the controversial relationship between the type of calcification and the nature of the disease. Here, we propose to clarify this relationship by making a distinction between diseases associated with hydroxyapatite (HA) and calcium pyrophosphate dihydrate (CPPD) deposits. AS, OA, GACI and vascular calcification are usually characterized by mineralization/ossification associated with HA deposits, while CC and pseudo gout are mostly characterized by CPPD deposits. Although both HA and CPPD deposits may occur concomitantly, as in chronic pyrophosphate arthritis or in OA with CPPD, they are formed as a result of two antagonistic processes indicating that treatment of distinct diseases can be only achieved by disease-specific drug therapies. The hydrolysis of PPi, an inhibitor of HA formation, is mostly controlled by tissue non-specific alkaline phosphatase TNAP, while PPi production in the extracellular medium is controlled by ANK, a PPi transporter, and/or NPP1 which generates PPi from nucleotide triphosphates. Low PPi concentration may lead to a preferential deposition of HA while high PPi concentration will favor the formation of CPPD deposits. Thus, HA and CCPD deposition cannot occur concomitantly because they are determined by the Pi/PPi ratio which, in turn, depends on the relative activities of antagonistic enzymes, TNAP hydrolyzing PPi or ANK and NPP1 producing PPi. TNAP inhibitors could prevent HA formation in AS, in late OA, in GACI, as well as in vascular calcifications, while ANK or NPP1 inhibitors could slow down CCPD deposition in CC and pseudo gout

Interaction of annexin A6 with cholesterol rich membranes is pH-dependent and mediated by the sterol OH

International audienc

Two-Step Membrane Binding of NDPK‑B Induces Membrane Fluidity Decrease and Changes in Lipid Lateral Organization and Protein Cluster Formation

Nucleoside diphosphate kinases (NDPKs) are crucial elements in a wide array of cellular physiological or pathophysiological processes such as apoptosis, proliferation, or metastasis formation. Among the NDPK isoenzymes, NDPK-B, a cytoplasmic protein, was reported to be associated with several biological membranes such as plasma or endoplasmic reticulum membranes. Using several membrane models (liposomes, lipid monolayers, and supported lipid bilayers) associated with biophysical approaches, we show that lipid membrane binding occurs in a two-step process: first, initiation by a strong electrostatic adsorption process and followed by shallow penetration of the protein within the membrane. The NDPK-B binding leads to a decrease in membrane fluidity and formation of protein patches. The ability of NDPK-B to form microdomains at the membrane level may be related to protein–protein interactions triggered by its association with anionic phospholipids. Such accumulation of NDPK-B would amplify its effects in functional platform formation and protein recruitment at the membrane

Apoptosis-like, reversible changes in plasma membrane asymmetry and permeability, and transient modifications in mitochondrial membrane potential induced by curcumin in rat thymocytes

Curcumin (diferuoylmethane) is a natural compound with anticarcinogenic activities which is able to exert either proapoptotic or antiapoptotic effects in different cell types, This paper focuses on the sequence and extent of primary events induced by curcumin, in comparison with those occurring during dexamethasone-induced apoptosis in rat thymocytes, It also presents annexin VI-FITC as a new probe for studying membrane asymmetry. Curcumin readily penetrates into the cytoplasm, and is able to accumulate in membranous structures such as plasma membrane, endoplasmic reticulum and nuclear envelope. Curcumin-treated cells exhibit typical features of apoptotic cell death, including shrinkage, transient phosphatidylserine exposure, increased membrane permeability and decrease in mitochondrial membrane potential. However, nuclei morphology, DNA fragmentation, the extent and time-course of membrane changes are different from those observed during dexamethasone-induced apoptosis, suggesting that, despite many similarities, the mode of action and the events triggered by curcumin are different from those occurring during typical apoptosis, (C) 1998 Federation of European Biochemical Societies

Localization of annexin A6 in matrix vesicles during physiological mineralization

Annexin A6 (AnxA6) is the largest member of the annexin family of proteins present in matrix vesicles (MVs). MVs are a special class of extracellular vesicles that serve as a nucleation site during cartilage, bone, and mantle dentin mineralization. In this study, we assessed the localization of AnxA6 in the MV membrane bilayer using native MVs and MV biomimetics. Biochemical analyses revealed that AnxA6 in MVs can be divided into three distinct groups. The first group corresponds to Ca2+-bound AnxA6 interacting with the inner leaflet of the MV membrane. The second group corresponds to AnxA6 localized on the surface of the outer leaflet. The third group corresponds to AnxA6 inserted in the membrane's hydrophobic bilayer and co-localized with cholesterol (Chol). Using monolayers and proteoliposomes composed of either dipalmitoylphosphatidylcholine (DPPC) to mimic the outer leaflet of the MV membrane bilayer or a 9:1 DPPC:dipalmitoylphosphatidylserine (DPPS) mixture to mimic the inner leaflet, with and without Ca2+, we confirmed that, in agreement with the biochemical data, AnxA6 interacted differently with the MV membrane. Thermodynamic analyses based on the measurement of surface pressure exclusion (πexc), enthalpy (ΔH), and phase transition cooperativity (Δt1/2) showed that AnxA6 interacted with DPPC and 9:1 DPPC:DPPS systems and that this interaction increased in the presence of Chol. The selective recruitment of AnxA6 by Chol was observed in MVs as probed by the addition of methyl-β-cyclodextrin (MβCD). AnxA6-lipid interaction was also Ca2+-dependent, as evidenced by the increase in πexc in negatively charged 9:1 DPPC:DPPS monolayers and the decrease in ΔH in 9:1 DPPC:DPPS proteoliposomes caused by the addition of AnxA6 in the presence of Ca2+ compared to DPPC zwitterionic bilayers. The interaction of AnxA6 with DPPC and 9:1 DPPC:DPPS systems was distinct even in the absence of Ca2+ as observed by the larger change in Δt1/2 in 9:1 DPPC:DPPS vesicles as compared to DPPC vesicles. Protrusions on the surface of DPPC proteoliposomes observed by atomic force microscopy suggested that oligomeric AnxA6 interacted with the vesicle membrane. Further work is needed to delineate possible functions of AnxA6 at its different localizations and ways of interaction with lipids