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J Avila

Publications and source records attributed to J Avila.

At least 127 records · Page 7Linked to original sources
PubMed1996

Polymerization of tau into filaments in the presence of heparin: the minimal sequence required for tau-tau interaction.

Paired helical filaments isolated from the brains of patients with Alzheimer's disease are composed of a major protein component, the microtubule-associated protein termed tau, together with other nonprotein components, including heparan, a glycosaminoglycan, the more extensively sulfated form of which is heparin. As some of these nonprotein components may modulate the assembly of tau into filamentous structures, we have analyzed the ability of the whole tau protein or some of its fragments to self-assemble in the presence of heparin. Different tau fragments, all of them containing some sequences of the tubulin-binding motif, can assemble in vitro into filaments. We have also found formation of polymers with the 18-residue-long peptide corresponding to the third tubulin-binding motif of tau. This suggests that the ability of tau for self-assembly could be localized in a short sequence of amino acids present in the tubulin-binding repeats of the tau molecule.

Actin Cytoskeleton↗
PubMed1996

The role of the Maillard reaction in other pathologies: Alzheimer's disease.

Many approaches have and are being undertaken to treat Alzheimer's disease but, as yet, no therapy is available with any established efficacy. Given the heterogeneity of the aetiological factors involved in Alzheimer's disease and the difficulties encountered in the clinical diagnosis, the lack of pharmacological success is not surprising. Furthermore, the lack of an adequate animal model of Alzheimer's disease has delayed the development of novel therapeutic strategies. At present, and with the exception of the rarer forms of familial Alzheimer's disease, the need remains to treat the symptoms rather than the causes of the disease, primarily because the pathogenesis of Alzheimer's disease is still unknown. The evidence for the role of glycation and advanced glycation end-products (AGEs) in the formation of neurofibrillary tangles and neuritic plaques, the characteristic histopathological lesions of Alzheimer's disease, is briefly reviewed. While the role of glycation in the pathogenesis of Alzheimer's disease is not yet unequivocally proven, it is the only single protein modification that would explain the formation of both the characteristic histopathological lesions first described by Alois Alzheimer in 1907. With our improved understanding of the molecular basis for the clinical symptoms of dementia, it is hoped that the aetiological causes will afford more suitable targets for therapeutic intervention. In this respect it is interesting to note that the anti-inflammatory compounds indomethacin and acetylsalicylic acid, both inhibitors of the Maillard reaction, have been reported to have therapeutic potential and the nootropic agent tenilsetam inhibits protein cross-linking by AGEs.

Alzheimer Disease↗
PubMed1996

Involvement of gamma and beta actin isoforms in mouse neuroblastoma differentiation.

Two actin isoforms, gamma and beta, are contained within neuroblastoma cells. However, the relative amount and distribution of both isoforms within the cells are differentially regulated during neurite extension. The proportion of gamma-actin isoform became about four times greater than that of beta actin during neuroblastoma cell differentiation. Additionally, whereas beta actin appears to be concentrated in the cell cortex, gamma actin is also present throughout the cell body. Upon differentiation, neuroblastoma cells reorganize their actin cytoskeleton and gamma actin is induced to polymerize whereas beta actin polymers are partially disassembled. Moreover, both actin isoforms are differentially distributed within differentiated cells. Thus, gamma actin polymers are located both in the soma and proximal regions of extended neurites, whereas beta actin is enriched in the terminal tip of the neurites. Our results strongly suggest that both actin isoforms are involved in a different way in neuroblastoma cell differentiation.

Actins↗
PubMed1996

Tubulin folding is altered by mutations in a putative GTP binding motif.

Tubulins contain a glycine-rich loop, that has been implicated in microtubule dynamics by means of an intramolecular interaction with the carboxy-terminal region. As a further extension of the analysis of the role of the carboxy-terminal region in tubulin folding we have mutated the glycine-rich loop of tubulin subunits. An alpha-tubulin point mutant with a T150-->G substitution (the corresponding residue present in beta-tubulin) was able to incorporate into dimers and microtubules. On the other hand, four beta-tubulin point mutants, including the G148-->T substitution, did not incorporate into dimers, did not release monomers, but were able to form C900 and C300 complexes (intermediates in the process of tubulin folding). Three other mutants within this region (which approximately encompasses residues 137-152) were incapable of forming dimers and C300 complexes but gave rise to the formation of C900 complexes. These results suggest that tubulin goes through two sequential folding states during the folding process, first in association with TCP1-complexes (C900) prior to the transfer to C300 complexes. It is this second step that implies binding/hydrolysis of GTP, reinforcing our previous proposed model for tubulin folding and assembly.

Amino Acid Sequence↗
PubMed1996

[Relation of spondylarthropathies and HLA-B27 antigen in patients from the state of Zulia, Venezuela].

HLA-B27 and associate antigens incidence were studied in 620 cases of seronegative spondiloarthropathies (SNS) and 262 controls of a Venezuelan mestizo population from Zulla state between 1985 and 1995. The incidence of HLA-B27 was 20.96% of all cases of SNS. It was increased in patients with ankilosing spondylitis (AS) 33.33% and Relter's syndrome (RS) 30%, but not in uveitis (Uv) 20% an psoriatic arthropathy (PsA) 0%. The incidence in the control group was 4.2%. This results are lower than the previous description in Venezuelan mestizo and caucasic population but are close to the incidence described in population of West Africa with important contribution to admixture of the occidental part of Venezuela.

Adolescent↗
PubMed1995

Characterization of microtubule-associated protein phosphoisoforms present in isolated growth cones.

The presence of microtubule-associated proteins (MAPs) in growth cones has been analyzed by isolation of these structures and characterization of their proteins by immunofluorescence studies. Two major MAPs, MAP1B and tau, were present in growth cones of cerebellum neurons isolated from 5-day-old rats. Both MAPs could be modified by proline-dependent protein kinases (PDPK) with opposite effects. PDPK-modified MAP1B isoforms are present at the growth cones whereas PDPK-modified tau isoforms are absent. This result suggests a different role for each phosphoMAP. To look for a possible PDPK involved in the modification of MAP1B at the growth cone, the localization of MAP and cdc2 kinases was studied. Our results indicate that the distribution in neuronal cells of MAP kinase is compatible with a possible role of this protein in modifying MAP1B.

Animals↗
PubMed1995

Glycogen synthase kinase 3 phosphorylates recombinant human tau protein at serine-262 in the presence of heparin (or tubulin).

Tau protein, the major component of the aberrant structures termed paired helical filaments (PHFs) present in the brain of Alzheimer's disease patients, is pathologically phosphorylated in sites in and around the tubulin-binding sites. A single protein kinase, glycogen synthase kinase 3 (GSK 3), is able to phosphorylate tau at the flanking regions and, additionally, at the tubulin-binding motifs if heparin or tubulin is present. Serines-262 and -324 have been found to be modified at the tubulin-binding region of tau protein by GSK 3 in the presence of heparin or tubulin.

Amino Acid Sequence↗
PubMed1995

The role of tau phosphorylation in transfected COS-1 cells.

Tau cDNAs from each of the six human isoforms were transfected into COS-1 cells and, in every case, more than one peptide was observed. The diversity of expressed isoforms was due to different levels of tau phosphorylation. Tau phosphorylation results in a decrease of the protein electrophoretic mobility. The major contribution to this mobility shift is due to the phosphorylation at the at the C-terminus of the molecule, as inferred from the expression of tau fragments. Phosphorylation takes place in some of the sites modified in neural cells and in the basis of AD patients. Copolymerization studies indicate that the level of phosphorylation, as well as the localization of the modified residues, may affect the binding of the protein to microtubules. These results indicate that phosphorylation regulates tau function inside the cell.

Actins↗
PubMed1995

Cloning and disruption of the YNR1 gene encoding the nitrate reductase apoenzyme of the yeast Hansenula polymorpha.

The nitrate reductase gene (YNR1) from the yeast H. polymorpha was isolated from a lambda EMBL3 genomic DNA library. As probe a 350 bp DNA fragment synthesized by PCR from H. polymorpha cDNA was used. By DNA sequencing an ORF of 2,577 bp was found. The predicted protein has 859 amino acids and presents high identity with nitrate reductases from other organisms. Chromosomal disruption of YNR1 causes inability to grow in nitrate. Northern blot analysis showed that YNR1 expression is induced by nitrate and repressed by ammonium.

Amino Acid Sequence↗
PubMed1995

Dual DNA binding specificity of a petal epidermis-specific MYB transcription factor (MYB.Ph3) from Petunia hybrida.

The MYB.Ph3 protein recognized two DNA sequences that resemble the two known types of MYB DNA binding site: consensus I (MBSI), aaaAaaC(G/C)-GTTA, and consensus II (MBSII), aaaAGTTAGTTA. Optimal MBSI was recognized by animal c-MYB and not by Am305 from Antirrhinum, whereas MBSII showed the reverse behaviour. Different constraints on MYB.Ph3 binding to the two classes of sequences were demonstrated. DNA binding studies with mutated MBSI and MBSII and hydroxyl radical footprinting analysis, pointed to the N-terminal MYB repeat (R2) as the most involved in determining the dual DNA binding specificity of MYB.Ph3 and supported the idea that binding to MBSI and MBSII does not involve alternative orientations of the two repeats of MYB.Ph3. Minimal promoters containing either MBSI and MBSII were activated to the same extent by MYB.Ph3 in yeast, indicating that both types of binding site can be functionally equivalent. MYB.Ph3 binding sites are present in the promoter of flavonoid biosynthetic genes, such as the Petunia chsJ gene, which was transcriptionally activated by MYB.Ph3 in tobacco protoplasts. MYB.Ph3 was immunolocalized in the epidermal cell layer of petals, where flavonoid biosynthetic genes are actively expressed. This strongly suggests a role for MYB.Ph3 in the regulation of flavonoid biosynthesis.

Acyltransferases↗
PubMed1995

A 205 kDa protein from non-neuronal cells in culture contains tubulin binding epitopes.

Microtubule-associated proteins (MAPs) interact with tubulin in vitro and in vivo. Despite that there is a large amount of information on the roles of these proteins in neurons, the data on non-neuronal MAPs or MAPs-related proteins is scarce. There is an increasing number of microtubule-interacting proteins that have been identified in different cultured cell lines, and some of them share common functional epitopes with the most well-known MAPs, MAP-2 and tau. In a search for tubulin-interacting proteins in non-neuronal cells we identified a 205 kDa protein in the monkey kidney Vero cells in culture, on the basis of immunological studies and affinity chromatography. This protein interacts with the C-terminal moiety of beta-tubulin and cosediments with taxol assembled microtubules, but it was not recovered after successive cycles of assembly and disassembly. The presence of neuronal MAPs such as MAP-1, MAP-2 and tau was not detected in these cells. Interestingly, the studies showed that the 205 kDa protein contained a tubulin binding motif which was recognized by site-directed antibodies that also tag tubulin binding epitopes on MAP-2 and tau. This characteristic led us to designate this protein as MBD-205, a component that shares binding domains with these MAPs, rather than as a marker of the MAPs family. On the other hand, immunofluorescence experiments using site-specific antibodies, i.e. MAP-reacting monoclonal anti-idiotypic reagent MTB6.22 and a polyclonal antibody to the second tau repeat, revealed a MBD-205 co-localization with membrane structures and microtubule-organizing centers in Vero cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Beta-tubulin folding is modulated by the isotype-specific carboxy-terminal domain.

To investigate the contribution of the carboxy-terminal domain in the process of tubulin folding and dimer formation, we constructed a beta 1-beta 3 tubulin chimaera and two truncated carboxy-terminal beta 3-tubulins. The capacity of these altered polypeptides to incorporate into dimers and into microtubules was tested by non-denaturing electrophoresis and co-assembly experiments. The chimaera and the truncated protein with a deletion encompassing the last 12 amino acid residues (beta 3 delta C12) were incorporated into dimers and microtubules, though the level of incorporation was diminished compared to wild-type beta 3-tubulin. However, the level of incorporation of beta 3 delta C12 into subtilisin-digested dimers was similar to the incorporation of wild-type beta 3-tubulin. Since subtilisin deletes the carboxy-terminal region, these results suggest a regulatory role of the carboxy-terminal region in the folding process itself and not in the formation of the dimer.

Animals↗
PubMed1995

Variations in in vivo phosphorylation at the proline-rich domain of the microtubule-associated protein 2 (MAP2) during rat brain development.

Microtubule-associated protein 2 (MAP2) is an in vitro substrate for MAP kinase. Part of the phosphorylation occurs at the C-terminal microtubule-binding domain of the molecule which contains a cluster of putative consensus sites for MAP kinase on a proline-rich region. A peptide with the sequence RTPGTPG-TPSY, located at this region of the molecule, is efficiently phosphorylated by MAP kinase in vitro. An antibody (972) raised against this non-phosphorylated peptide has been used to test for in vivo phosphorylation at the proline-rich domain of the MAP2 molecule. The reaction of purified MAP2 with antibody 972 diminishes after in vitro phosphorylation by MAP kinase and is enhanced after in vitro dephosphorylation by alkaline phosphatase. A fraction of brain MAP2 isolated by iron-chelation affinity chromatography appears to be phosphorylated in vivo at the site recognized by antibody 972. There is some variation in the phosphorylation of MAP2 at the proline-rich region throughout rat brain development. MAP2C is more highly phosphorylated in the developing rat brain, whereas high-molecular-mass MAP2 is more extensively phosphorylated in the adult rat brain.

Alkaline Phosphatase↗
PubMed1995

An increase in phosphorylation of microtubule-associated protein 2 accompanies dendrite extension during the differentiation of cultured hippocampal neurones.

Hippocampal neurones, from embryonic rats, were cultured for different times and the extension of dendrite-like processes was analysed morphologically and by immunofluorescence, using microtubule-associated protein 2 (MAP2) as a marker. Simultaneously, the changes in phosphorylation in MAP2 were analyzed and a correlation between dendrite sprouting and an increase in MAP2 phosphorylation was found. Phospho-MAP2 was cleaved by Staphylococcus aureus V8 protease limited proteolysis and its phosphopeptide pattern was compared to that obtained with two protein kinases (calcium/calmodulin-dependent kinase and protein kinase C) in vitro. An involvement of calcium/calmodulin-dependent protein kinase in the phosphorylation of MAP2, occurring simultaneously with dendrite extension during neuronal differentiation in vitro, is suggested.

Animals↗
PubMed1995

Tau protein from Alzheimer's disease patients is glycated at its tubulin-binding domain.

Glycated residues of tau protein from paired helical filaments isolated from the brains of Alzheimer's disease patients were localized by doing a proteolytic cleavage of the protein, fractionation of the resulting peptides, and identification of those peptides using specific antibodies. The most suitable residues for glycation, lysines, present at the tubulin-binding motif of tau protein, seem to be preferentially modified compared with those lysines present at other regions. Among these modified lysines, those located in the sequence comprising residues 318-336 (in the largest human tau isoform) were found to be glycated, as determined by the reaction with an antibody that recognizes a glycated peptide containing this sequence. Because those lysines are present in a tubulin binding motif of tau protein, its modification could result in a decrease in the interaction of tau with tubulin.

Alzheimer Disease↗
PubMed1994

Tissue-type plasminogen activator (tPA) is the main plasminogen activator associated with isolated rat nerve growth cones.

Different studies in tissue culture have shown the involvement of plasminogen activators (PAs) in nerve growth-cone migration. We have studied PA activity associated with isolated rat brain growth cones. Fibrin-agarose zymographies show that tissue-type PA (tPA) is the main PA associated with these structures. After fractionation of growth cones, a slightly higher tPA activity was found associated with the particulate fraction. The present findings support the requirement of this protease for neurite growth.

Animals↗