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J F Leterrier

Publications and source records attributed to J F Leterrier.

At least 37 records · Page 2Linked to original sources
PubMed1992

Age-dependent changes in the ultrastructure and in the molecular composition of rat brain microtubules.

An age-dependent increase of a cathepsin D-like protease activity that preferentially degrades high molecular weight microtubule-associated proteins (MAPs) has been previously described. Microtubules (MT) purified from rat brain of different ages in the presence of several protease inhibitors retained undegraded MAPs through cycles of polymerization, and revealed several age-dependent changes in the relative amounts of MAPs and MT-associated kinases. MAP2 immunoreactivity was found significantly lower in MT preparations from aged animals in contrast with a relative increase of tau molecules. In addition, the phosphorylation of MAP2 by its associated cyclic AMP-dependent protein kinase was also altered, consecutively to the partial loss of the enzyme during polymerization cycles and an age-dependent decrease in the ability of the cyclic nucleotide to stimulate MAP2-bound kinase activity. The evidence of an unusually high packing density of sedimented MT from old rat brains further suggested the modification with aging of the physical structure of the arm-like projections of MAPs, in addition to a lower amount in high molecular weight MAPs. These results support the hypothesis of a selective alteration with aging of the mechanical and regulatory properties of brain MT, consecutive to a change in the composition and/or the structure of MAPs.

Aging↗
PubMed1992

A molecular mechanism for the induction of neurofilament bundling by aluminum ions.

A1 induces neurofibrillary tangles in the perikaryon of neurons in vivo and in culture. The effect of A1 ions complexed with maltol, a plant-derived ligand of A1, on purified neurofilament preparations was studied in vitro. The binding of A1 to the arm-like projections of the high (H)- and medium (M)-molecular-weight neurofilament subunits causes a conformational change of the molecule (intrafilamentous reaction), characterized by an altered migration on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In addition, A1 compounds strongly stimulate the interaction between neurofilaments (interfilamentous reaction). The possibility that phosphate groups of the H and M sidearms are involved in binding A1 ions is discussed with regard to the migration on SDS-PAGE of dephosphorylated neurofilaments incubated with A1 compounds and the alteration by A1 ions of neurofilament phosphorylation in vitro by the associated kinase. Immunoblotting analysis of neurofilaments in cultivated neurons intoxicated with A1 compounds revealed a similar A1-dependent alteration of the neurofilament subunit conformation. This result suggest that the mechanism of A1-induced bundling of neurofilaments derived from in vitro studies might be involved in the formation of tangles in situ.

Aluminum↗
PubMed1989

The specific binding of the microtubule-associated protein 2 (MAP2) to the outer membrane of rat brain mitochondria.

Purified mitochondria from rat brain contain microtubule-associated proteins (MAPs) bound to the outer membrane. Studies of binding in vitro performed with microtubules and with purified microtubule proteins showed that mitochondria preferentially interact with the high-molecular-mass MAPs (and not with Tau protein). Incubation of intact mitochondria with Taxol-stabilized microtubules resulted in the selective trapping of both MAPs 1 and 2 on mitochondria, indicating that an interaction between the two organelles occurred through a site on the arm-like projection of MAPs. Two MAP-binding sites were located on intact mitochondria. The lower-affinity MAP2-binding site (Kd = 2 x 10(-7) M) was preserved and enriched in the outer-membrane fraction, whereas the higher-affinity site (Kd = 1 x 10(-9) M) was destroyed after removing the outer membrane with digitonin. Detergent fractionation of mitochondrial outer membranes saturated with MAP2 bound in vitro showed that MAPs are associated with membrane fragments which contain the pore-forming protein (porin). MAP2 also partially prevents the solubilization of porin from outer membrane, indicating a MAP-induced change in the membrane environment of porin. These observations demonstrate the presence of specific MAP-binding sites on the outer membrane, suggesting an association between porin and the membrane domain involved in the cross-linkage between microtubules and mitochondria.

Animals↗
PubMed1989

Studies on the interaction between mitochondria and the cytoskeleton.

Mitochondrial movements and morphology are regulated through interactions with the cytoskeletal system, in particular the microtubules. An interaction between the microtubule-associated proteins (MAPs) and the outer surface of rat brain mitochondria has been demonstrated in vitro and in situ. One of the MAPs, MAP2, binds to specific high-affinity sites on the outer membrane. Upon binding, MAP2 is released from microtubules, and it induces a physical alteration in the outer membrane which is characterized by a tighter association of porin with the membrane. It is concluded that MAP2 either binds to porin or to a domain of the outer membrane which alters the membrane environment of porin. The possibility is raised that this domain participates in mitochondrial mobility in situ.

Animals↗
PubMed1989

Effect of a single dose of beta,beta'-iminodipropionitrile in vivo on the properties of neurofilaments in vitro: comparison with the effect of iminodipropionitrile added directly to neurofilaments in vitro.

The biochemical properties of neurofilaments isolated from control and iminodipropionitrile-treated rats were compared with regard to autophosphorylation capacity, hydrolysis of ATP, and the formation of a viscous gel between filaments. Both preparations exhibited a similar polypeptide composition, and no covalent cross-linking between neurofilament subunits was induced by iminodipropionitrile in vivo. An ATPase activity, systematically present in all preparations, was unaffected by the administration of iminodipropionitrile to the rats. Conversely, the autophosphorylation of neurofilament subunits in vitro was significantly higher in preparations from iminodipropionitrile-treated rats than from control animals, with a marked increase of the phosphorylation of a high molecular weight neurofilament-associated protein. Iminodipropionitrile provoked a higher gelation capacity of neurofilaments as measured in vitro, with a lower critical concentration for the preparation from treated animals. A similar increased interaction was obtained with millimolar concentrations of iminodipropionitrile added to bovine neurofilaments in vitro, involving likely neurofilament-associated molecules, because the effect of the drug was lost after their extraction by 0.8 M KCl. These results support the hypothesis that iminodipropionitrile interferes with the neurofilament networks through a preferential interaction with the neurofilament-associated proteins, resulting in a change in their properties and consequently in an increased capacity of interaction between the polymers.

Adenosine Triphosphatases↗
PubMed1988

Influence of the phosphorylation state of neurofilament proteins on the interactions between purified filaments in vitro.

The extensive enzymic dephosphorylation of neurofilaments determined the progressive loss of their capacity to interconnect in vitro into a reticulated network, measured by the formation of highly viscous gels in purified preparations of neurofilaments [Leterrier & Eyer (1987) Biochem. J. 245, 93-101]. Conversely, a cyclic AMP-dependent activation of the gelation process was obtained by phosphorylation of the neurofilament proteins by the cyclic-nucleotide-dependent protein kinase added to the preparation. These findings argue for a direct relationship between the high phosphorylation level of the neurofilament subunits and the cross-bridging of the polymers in vitro. However, a transient stimulation of the neurofilament viscosity kinetics was also observed during the early steps of dephosphorylation with acid phosphatase, which, moreover, disappeared with longer incubation times before the net inhibition was obtained. In the same way, the calmodulin-dependent brain phosphatase, calcineurin, induced a permanent activation of the phenomenon, correlated with a low dephosphorylation capacity of the neurofilament molecules. Taken together, these results suggest a functional heterogeneity of the numerous phosphate groups of the neurofilament subunits and raise the hypothesis of a highly controlled regulation of the neurofilament cross-bridging by selective phosphorylation-dephosphorylation mechanisms.

Acid Phosphatase↗
PubMed1987

Properties of highly viscous gels formed by neurofilaments in vitro. A possible consequence of a specific inter-filament cross-bridging.

Neurofilaments freshly isolated from bovine spinal cord form a reversible gel in vitro, consisting of nearly parallel and interlinked filaments organized in bundles. This phenomenon is obtained above a critical neurofilament concentration and is highly sensitive to denaturation. No gelation occurs with neurofilaments reconstituted from urea-solubilized subunits. The velocity of the gelation kinetics, optimum at a slightly acidic pH, is inhibited by low and high ionic strength and activated by millimolar concentrations of Mg2+ and other bivalent cations. No protein other than the purified neurofilament preparation itself (80-95% neurofilament triplet) is necessary for the formation of a gel. However, purified cytoskeletal proteins from microtubules and neurofilaments influence the viscosity of the native preparation. These observations suggest a reticulation in vitro between neurofilaments, dependent upon a fragile conformation of the polymers and possibly mediated through the high-Mr neurofilament subunits (200 kDa and 150 kDa). The significance of these results is discussed with regard to the inter-neurofilament cross-bridging in situ involving the 200 kDa subunit described by Hirokawa, Glicksman & Willard [(1984) J. Cell Biol. 98, 1523-1536].

Animals↗
PubMed1987

Subfractionation of the outer membrane of rat brain mitochondria: evidence for the existence of a domain containing the porin-hexokinase complex.

Isolated and well-characterized rat brain nonsynaptic mitochondria were subfractionated by digitonin. Antibodies to a uniquely outer membrane protein, porin, have allowed us to use this protein for the first time as an outer membrane marker in brain. Hexokinase, which binds to porin, was also measured. Based upon the sequential release of these and other marker enzymes with increasing concentrations of digitonin, three outer membrane domains have been identified. Two populations of porin were found by this treatment. The most plausible interpretation of our results is that the two porin populations exist in different membrane environments with regard to cholesterol. One of these populations binds most of the hexokinase and appears to be associated with the inner membrane. It is proposed that the porin-hexokinase complex in brain mitochondria is located in a cholesterol-free membrane domain together with inner membrane components. This domain has the features of contact points which have been visualized by electron microscopy.

Animals↗
PubMed1984

Promotion of microtubule assembly by neurofilament-associated microtubule-associated proteins.

Intact neurofilaments (NF) purified from mammalian brain and spinal cord promote the assembly of microtubules in solutions of pure phosphocellulose (PC)-purified tubulin. This assembly is temperature-dependent and is inhibited by mitotic spindle inhibitors. The ability of NF to induce microtubule formation is 20% of that of purified microtubule-associated proteins (MAPs), whereas MAPs comprise less than 5% of the protein in the NF preparations. The inducing activity of NF is rapidly lost on boiling. When intact NF are incubated with PC-tubulin and then centrifuged, tubulin is sedimented together with the filaments. This association is inhibited by colchicine and podophyllotoxin and is cold-sensitive. NF purified to homogeneity under denaturing conditions and then reassembled completely lack the ability to promote the assembly of PC-tubulin or to bind tubulin on a centrifugation assay. No MAPs are present in these preparations, though these filaments have the ability to bind exogenous MAPs. While these experiments do not rule out an intrinsic microtubule-assembly-promoting activity, they suggest that this activity is due to nontriplet proteins in the preparation, most likely filament-associated MAPs.

Animals↗
PubMed1982

Interactions between neurofilaments and microtubule-associated proteins: a possible mechanism for intraorganellar bridging.

Mammalian neurofilaments prepared from brain and spinal cord by either of two methods partially inhibit the in vitro assembly of microtubules. This inhibition is shown to be due to the association of a complex of high molecular weight microtubule-associated proteins (MAP1 and MAP2) and tubulin with the neurofilament. Further analysis of the association reveals a saturable binding of purified brain MAPs to purified neurofilaments with a Kd of 10(-7) M. Purified astroglial filaments neither inhibit microtubule assembly nor show significant binding of MAPs. It is proposed that the MAPs might function as one element in a network of intraorganellar links in the cytoplasm.

Animals↗
PubMed1981

Preferential phosphorylation of the 150,000 molecular weight component of neurofilaments by a cyclic AMP-dependent, microtubule-associated protein kinase.

Highly purified preparations of bovine brain and rabbit nerve root neurofilaments were found to be lacking in protein kinase activity when either histone FIIA or the neurofilaments themselves were used as acceptors. There was no augmentation of activity in the presence of cyclic AMP. Addition of microtubule proteins prepared by cycles of assembly and disassembly resulted in phosphorylation of histone, phosphorylation of tubulin and the microtubule-associated proteins, and phosphorylation of neurofilament subunits. The phosphorylation of neurofilaments was predominantly in the 150,000-dalton species and was completely cyclic AMP dependent.

Animals↗
PubMed1976

Phosphorylation of microtubule-associated proteins.

1. Tubulin is not an adenosine-3':5'-monophosphate-dependent (cyclic-AMP-dependent) protein kinase. Both entities have been clearly separated by sucrose gradient ultracentrifugation. With a tubulin preparation obtained by the polymerization-depolymerization technique protein kinase had a sedimentation coefficient of 8.7 S whereas tubulin sedimented with 6.4 S. After preincubation with both cyclic AMP and histone the kinase dissociated into its catalytic subunit with a sedimentation coefficient of 3.4 S. 2. Tubulin prepared by the polymerization-depolymerization technique was neither phosphorylated in vivo nor in vitro. On the contrary if this preparation was further purified by the Weisenberg's procedure (DEAE-Sephadex batch absorption) before incubation with [gamma-32 P]ATP, phosphorylation occurred. Thus, phosphorylation depended on the method used to purify tubulin i.e. was likely to an an artefact.

Brain↗