Benzimidazolium triflate-activated synthesis of (6-4) photoproduct-containing oligonucleotides and its application.

In the solid-phase synthesis of oligonucleotides containing the pyrimidine(6-4)pyrimidone photoproduct using a dinucleotide building block, considerable amounts of by-products were found as the chain length increased. The by-products were the major product when a 49mer was synthesized on a 40 nmol scale. It was assumed that these by-products were formed by the coupling of phosphoramidites with the N3 imino function of the 5' component of the (6-4) photoproduct. We examined imidazolium triflate and benzimidazolium triflate to find an alternative activator for DNA synthesis. Imidazolium triflate prevented by-product formation to some extent, but the coupling yields were low. Benzimidazolium triflate was comparable to tetrazole in coupling efficiency and reduced by-product formation to a great extent, without modification of the synthesizer program. The obtained 49mer was used to detect proteins that recognize UV-damaged DNA in HeLa cell extracts. Two major protein-DNA complexes were found when a 49mer duplex was used as probe, while a 30mer duplex failed to detect one of them. This application showed the usefulness of long chain 'damaged' oligonucleotides in biochemical studies.     

Co-expression of soybean glycinins A1aB1b and A3B4 enhances their accumulation levels in transgenic rice seed

The soybean major storage protein glycinin is encoded by five genes, which are divided into two subfamilies. Expression of A3B4 glycinin in transgenic rice seed reached about 1.5% of total seed protein, even if expressed under the control of strong endosperm-specific promoters. In contrast, expression of A1aB1b glycinin reached about 4% of total seed protein. Co-expression of the two proteins doubled accumulation levels of both A1aB1b and A3B4 glycinins. This increase can be largely accounted for by their aggregation with rice glutelins, self-assembly and inter-glycinin interactions, resulting in the enrichment of globulin and glutelin fractions and a concomitant reduction of the prolamin fraction. Immunoelectron microscopy indicated that the synthesized A1aB1b glycinin was predominantly deposited in protein body-II (PB-II) storage vacuoles, whereas A3B4 glycinin is targeted to both PB-II and endoplasmic reticulum (ER)-derived protein body-I (PB-I) storage structures. Co-expression with A1aB1b facilitated targeting of A3B4 glycinin into PB-II by sequestration with A1aB1b, resulting in an increase in the accumulation of A3B4 glycinin.     

Acetyl-Ile-Gly-Leu protects neurons from Aβ1–42 induced toxicity in vitro and in V337M human tau-expressing mice

AimsWe previously reported that the neurotoxicity of amyloid β protein (Aβ_1–42, 10 nM) was blocked by an Aβ-derived tripeptide, Aβ_32–34 (Ile-Gly-Leu, IGL), suggesting that IGL may be a lead compound in the design of Aβ antagonists. In the present study, three stable forms of IGL peptide with acetylation of its N-terminal and/or amidation of its C-terminal (acetyl-IGL, IGL-NH₂ and acetyl-IGL-NH₂) were synthesized and examined for their effects on Aβ-induced neurotoxicity.Main methodsPhosphatidylinositol 4-kinase type II (PI4KII) activity was measured using recombinant human PI4KIIα kinase and cell viability was assessed in primary cultured hippocampal neurons. To test effects in vivo, 1.5 μl of 100 nM Aβ and/or 100 nM acetyl-IGL was injected into the hippocampal CA1 region of right hemisphere in transgenic mice expressing V337M human tau protein. Four weeks later, behavior performance in the Morris water maze was tested and after another 2 weeks, sections of brain were prepared for immunohistochemistry.Key findingsAmong the three modified tripeptides, acetyl-IGL attenuated the Aβ-induced inhibition of PI4KII activity as well as enhancement of glutamate neurotoxicity in primary cultured rat hippocampal neurons. Injection of Aβ into the hippocampus of mice impaired spatial memory and increased the number of degenerating neurons in bilateral hippocampal regions. Co-injection of acetyl-IGL prevented the learning impairment as well as the neuronal degeneration induced by Aβ.SignificanceThese results suggest that a modified tripeptide, acetyl-IGL, may be effective in the treatment of Alzheimer's disease.     

Effect of Pin1 or Microtubule Binding on Dephosphorylation of FTDP-17 Mutant Tau

Neurodegenerative tauopathies, including Alzheimer disease, are characterized by abnormal hyperphosphorylation of the microtubule-associated protein Tau. One group of tauopathies, known as frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), is directly associated with mutations of the gene tau. However, it is unknown why mutant Tau is highly phosphorylated in the patient brain. In contrast to in vivo high phosphorylation, FTDP-17 Tau is phosphorylated less than wild-type Tau in vitro. Because phosphorylation is a balance between kinase and phosphatase activities, we investigated dephosphorylation of mutant Tau proteins, P301L and R406W. Tau phosphorylated by Cdk5-p25 was dephosphorylated by protein phosphatases in rat brain extracts. Compared with wild-type Tau, R406W was dephosphorylated faster and P301L slower. The two-dimensional phosphopeptide map analysis suggested that faster dephosphorylation of R406W was due to a lack of phosphorylation at Ser-404, which is relatively resistant to dephosphorylation. We studied the effect of the peptidyl-prolyl isomerase Pin1 or microtubule binding on dephosphorylation of wild-type Tau, P301L, and R406W in vitro. Pin1 catalyzes the cis/trans isomerization of phospho-Ser/Thr-Pro sequences in a subset of proteins. Dephosphorylation of wild-type Tau was reduced in brain extracts of Pin1-knockout mice, and this reduction was not observed with P301L and R406W. On the other hand, binding to microtubules almost abolished dephosphorylation of wild-type and mutant Tau proteins. These results demonstrate that mutation of Tau and its association with microtubules may change the conformation of Tau, thereby suppressing dephosphorylation and potentially contributing to the etiology of tauopathies.One of hallmarks of Alzheimer disease (AD)³ pathology is neurofibrillary tangles, which are composed of paired helical filaments (PHFs), aggregates of the abnormally phosphorylated microtubule-associated protein Tau. Intracellular inclusions comprising Tau are also found in several other neurodegenerative diseases, including Pick disease, progressive supranuclear palsy, corticobasal degeneration, and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17), collectively called tauopathies (1–3). Identification of Tau as a causative gene of the inherited tauopathy FTDP-17 reveals that Tau mutation is sufficient to cause disease (4–6). However, the impact Tau mutations have on neurodegeneration remains unknown.Tau proteins in inclusions are hyperphosphorylated, and extensive studies have identified the phosphorylation sites; for example, more than 20 sites have been identified in PHF-Tau obtained from AD brains (7, 8). Tau can be phosphorylated by a variety of protein kinases, including glycogen synthase kinase 3β (GSK3β), cyclin-dependent kinase 5 (Cdk5), mitogen-activated protein kinase, cAMP-dependent protein kinase (PKA), microtubule affinity regulating kinase, and others (9–11). Tau is predominantly phosphorylated on the Ser or Thr residue in Ser/Thr-Pro sequences, suggesting the involvement of proline-directed protein kinases such as GSK3β and Cdk5 in hyperphosphorylation. A critical question is how mutations in Tau induce hyperphosphorylation in brain (12). Early phosphorylation experiments in vitro and in cultured cells have shown that mutant Tau is less phosphorylated than wild-type (WT) Tau (13–18). However, two later studies demonstrated higher phosphorylation of mutant Tau using brain extracts as a source of protein kinases in the presence of protein phosphatase inhibitor okadaic acid (19) or in immortalized cortical cells (20). However, it is not fully understood how mutant Tau becomes highly phosphorylated in vivo.Tau hyperphosphorylation could also be attributed to reduced dephosphorylation activity. Tau is dephosphorylated in vitro by any of the major four classes of protein phosphatases, PP1, PP2A, PP2B, and PP2C, but PP2A is thought to be the major protein phosphatase that regulates Tau phosphorylation state in brains (21–23). PP2A activity reportedly is decreased in AD brain (24–26), and highly phosphorylated Tau in PHF is relatively resistant to dephosphorylation by PP2A (27). Few studies have been done on dephosphorylation of mutant Tau, however, and thus the mechanism remains unclear. One putative factor involved in mutant Tau dephosphorylation is the peptidyl-prolyl isomerase Pin1. Pin1 catalyzes the cis/trans isomerization of phospho-Ser/Thr-Pro sequences in a subset of proteins (28, 29). Pin1 is involved in AD pathogenesis as shown by the fact that it is found in neurofibrillary tangles and that Tau is hyperphosphorylated in Pin1-deficient mouse brains (30). Pin1 is indicated to facilitate Tau dephosphorylation via PP2A by binding to the phospho-Thr-231-Pro or phospho-Thr-212-Pro site (31–33). The effect of Pin1 on the stability of mutant Tau was recently reported (34), but a detailed analysis of Pin1 action on mutant Tau has not been reported. Another possible factor affecting dephosphorylation of mutant Tau is the binding to microtubules. We previously showed that phosphorylation of Tau is stimulated upon binding to microtubules (35). We thus hypothesized that binding to microtubules may also affect the extent of Tau dephosphorylation.Here, we examined the effects of Pin1 and binding to microtubules on dephosphorylation of WT and FTDP-17 mutant (P301L and R406W) Tau proteins that had been phosphorylated by Cdk5-p25 or Cdk5-p35. P301L and R406W are two distinct types of FTDP-17 mutants that have been studied well. We show for the first time how the regulation of Tau dephosphorylation can contribute to the observed Tau hyperphosphorylation in tauopathies.     

A Novel Role for hGas7b in Microtubular Maintenance: POSSIBLE IMPLICATION IN TAU-ASSOCIATED PATHOLOGY IN ALZHEIMER DISEASE*

Here, we report a novel role for hGas7b (human growth arrest specific protein 7b) in the regulation of microtubules. Using a bioinformatic approach, we studied the actin-binding protein hGas7b with a structural similarity to the WW domain of a peptidyl prolyl cis/trans isomerase, Pin1, that facilitates microtubule assembly. Thus, we have demonstrated that hGas7b binds Tau at the WW motif and that the hGas7b/Tau protein complex interacts with the microtubules, promoting tubulin polymerization. Tau, in turn, contributes to protein stability of hGas7b. Furthermore, we observed decreased levels of hGas7b in the brains from patients with Alzheimer disease. These results suggest an important role for hGas7b in microtubular maintenance and possible implication in Alzheimer disease.     

Selective Transmission of R5 HIV-1 over X4 HIV-1 at the Dendritic Cell–T Cell Infectious Synapse Is Determined by the T Cell Activation State

Dendritic cells (DCs) are essential antigen-presenting cells for the induction of T cell immunity against HIV. On the other hand, due to the susceptibility of DCs to HIV infection, virus replication is strongly enhanced in DC–T cell interaction via an immunological synapse formed during the antigen presentation process. When HIV-1 is isolated from individuals newly infected with the mixture of R5 and X4 variants, R5 is predominant, irrespective of the route of infection. Because the early massive HIV-1 replication occurs in activated T cells and such T-cell activation is induced by antigen presentation, we postulated that the selective expansion of R5 may largely occur at the level of DC–T cell interaction. Thus, the immunological synapse serves as an infectious synapse through which the virus can be disseminated in vivo. We used fluorescent recombinant X4 and R5 HIV-1 consisting of a common HIV-1 genome structure with distinct envelopes, which allowed us to discriminate the HIV-1 transmitted from DCs infected with the two virus mixtures to antigen-specific CD4⁺ T cells by flow cytometry. We clearly show that the selective expansion of R5 over X4 HIV-1 did occur, which was determined at an early entry step by the activation status of the CD4⁺ T cells receiving virus from DCs, but not by virus entry efficiency or productivity in DCs. Our results imply a promising strategy for the efficient control of HIV infection.     

Analysis of ER stress in developing rice endosperm accumulating β‐amyloid peptide

The common neurodegenerative disorder known as Alzheimer’s disease is characterized by cerebral neuritic plaques of amyloid β (Aβ) peptide. Plaque formation is related to the highly aggregative property of this peptide, because it polymerizes to form insoluble plaques or fibrils causing neurotoxicity. Here, we expressed Aβ peptide as a new causing agent to endoplasmic reticulum (ER) stress to study ER stress occurred in plant. When the dimer of Aβ_1–42 peptide was expressed in maturing seed under the control of the 2.3‐kb glutelin GluB‐1 promoter containing its signal peptide, a maximum of about 8 μg peptide per grain accumulated and was deposited at the periphery of distorted ER‐derived PB‐I protein bodies. Synthesis of Aβ peptide in the ER lumen severely inhibited the synthesis and deposition of seed storage proteins, resulting in the generation of many small and abnormally appearing PB bodies. This ultrastructural change was accounted for by ER stress leading to the accumulation of aggregated Aβ peptide in the ER lumen and a coordinated increase in ER‐resident molecular chaperones such as BiPs and PDIs in Aβ‐expressing plants. Microarray analysis also confirmed that expression of several BiPs, PDIs and OsbZIP60 containing putative transmembrane domains was affected by the ER stress response. Aβ‐expressing transgenic rice kernels exhibited an opaque and shrunken phenotype. When grain phenotype and expression levels were compared among transgenic rice grains expressing several different recombinant peptides, such detrimental effects on grain phenotype were correlated with the expressed peptide causing ER stress rather than expression levels.     

Regulation of the expression of lysyl oxidase mRNA in cultured rabbit retinal pigment epithelium cells.

Lysyl oxidase, an extracellular amine oxidase, controls the maturation of collagen and elastin. We examined the regulation of lysyl oxidase mRNA in cultured rabbit retinal pigment epithelium (RPE) cells in relation to the changes in subretinal fluid transport and phenotype of RPE cells. The level of the mRNA in cells grown on microporous membranes was markedly increased by application of hyperosmotic mannitol solution on the apical side (191% of control), implying that RPE cells express more lysyl oxidase in the condition which may cause the accumulation of subretinal fluid. Platelet-derived growth factor increased the mRNA level in subconfluent cells in culture (137% of control) and basic fibroblast growth factor decreased it (79% of control). In addition, exposure of cells to retinoic acid alone or in combination with dibutyryl cAMP for 22 days markedly decreased the level of lysyl oxidase mRNA (52 or 35% of control) while increasing the level of mRNA of N-acetylglucosaminidase (NAG), a marker enzyme for lysosomes (162 or 142% of control). Moreover, the level of lysyl oxidase mRNA in cells grown on microporous membranes was lower than that in cells grown on plastic dishes, while the level of NAG mRNA in the former cells was higher than that in the latter. Taken together, the expression of lysyl oxidase seemed to increase during proliferation of RPE cells and decrease toward differentiation. beta-Aminopropionitrile, an inhibitor of lysyl oxidase, significantly inhibited the contraction of collagen gels by fetal calf serum, suggesting that lysyl oxidase may be involved in pathogenesis caused by RPE cells.