Zinc-induced aggregation of Abeta (10-21) potentiates its action on voltage-gated potassium channel

Zinc may play an important role in the pathogenesis of Alzheimer's disease (AD) through influencing the conformation and neurotoxicity of amyloid beta-proteins (Abeta). Zn(2+) induces rapid aggregation of synthetic or endogenous Abeta in a pH-dependent fashion. Here we show for the first time that Zn(2+)-induced aggregation of Abeta (10-21) potentiates its action on outward potassium currents in hippocampal CA1 pyramidal neurons. Using the whole-cell voltage-clamp technique, we showed that Abeta (10-21) blocked the fast-inactivating outward potassium current (I(A)) in a concentration- and aggregation-dependent manner, but with no effect on the delayed rectifier potassium current (I(K)). Both the unaggregated and aggregated forms of Abeta (10-21) significantly shifted the activation curve and the inactivation curve of I(A) to more negative potentials. But the aggregated form has more effects than the unaggregated form. These data indicated that aggregation of amyloid fragments by zinc ions is required in order to obtain full modulatory effects on potassium channel currents.     

Fluorescent phosphatidylinositol 4,5-bisphosphate derivatives with modified 6-hydroxy group as novel substrates for phospholipase C

The capacity to monitor spatiotemporal activity of phospholipase C (PLC) isozymes with a PLC-selective sensor would dramatically enhance understanding of the physiological function and disease relevance of these signaling proteins. Previous structural and biochemical studies defined critical roles for several of the functional groups of the endogenous substrate of PLC isozymes, phosphatidylinositol 4,5-bisphosphate (PIP(2)), indicating that these sites cannot be readily modified without compromising interactions with the lipase active site. However, the role of the 6-hydroxy group of PIP(2) for interaction and hydrolysis by PLC has not been explored, possibly due to challenges in synthesizing 6-hydroxy derivatives. Here, we describe an efficient route for the synthesis of novel, fluorescent PIP(2) derivatives modified at the 6-hydroxy group. Two of these derivatives were used in assays of PLC activity in which the fluorescent PIP(2) substrates were separated from their diacylglycerol products and reaction rates quantified by fluorescence. Both PIP(2) analogues effectively function as substrates of PLC-δ1, and the K(M) and V(max) values obtained with one of these are similar to those observed with native PIP(2) substrate. These results indicate that the 6-hydroxy group can be modified to develop functional substrates for PLC isozymes, thereby serving as the foundation for further development of PLC-selective sensors.     

Enhancement of Sodium Caprate on Intestine Absorption and Antidiabetic Action of Berberine

Berberine, a plant alkaloid used in traditional Chinese medicine, has a wide spectrum of pharmacological actions, but the poor bioavailability limits its clinical use. The present aim was to observe the effects of sodium caprate on the intestinal absorption and antidiabetic action of berberine. The in situ, in vitro, and in vivo models were used to observe the effect of sodium caprate on the intestinal absorption of berberine. Intestinal mucosa morphology was measured to evaluate the toxic effect of sodium caprate. Diabetic model was used to evaluate antidiabetic effect of berberine coadministrated with sodium caprate. The results showed that the absorption of berberine in the small intestine was poor and that sodium caprate could significantly improve the poor absorption of berberine in the small intestine. Sodium caprate stimulated mucosal-to-serosal transport of berberine; the enhancement ratios were 2.08, 1.49, and 3.49 in the duodenum, jejunum, and ileum, respectively. After coadministration, the area under the plasma concentration–time curve of berberine was increased 28% than that in the absence of sodium caprate. Furthermore, both berberine and coadministration with sodium caprate orally could significantly decrease fasting blood glucose and improve glucose tolerance in diabetic rats (P?P?相似文献   

Genetic Grouping of Medulloblastomas by Representative Markers in Pathologic Diagnosis

A recent analysis of the genetic features of medulloblastoma (MB) suggested classification into distinct subgroups according to gene expression profiles, including the Wingless signaling pathway-activated group (WNT group), the Sonic Hedgehog signaling pathway-activated group (SHH group), group 3, and group 4. To classify MB according to genetic features in practice, we analyzed 74 MBs using representative markers of each group. Based on immunohistochemistries (IHC), cytogenetic alterations, and a CTNNB1 mutation study, the patients were divided into the following three groups: cases showing nuclear β-catenin and/or CTNNB1 mutation and/or monosomy 6 were included in the WNT group (14/74, 18.9%); cases expressing GAB1 were included in the SHH group (15/74, 20.2%); cases that did not show positivity for markers of the WNT or SHH group were included in the non-WNT/SHH group (45/74, 60.6%). Immunoexpression of NPR3 seemed to lack sensitivity for classifying group 3, showing diffuse positivity in only two cases. KCNA1 was not specific to group 4 because it was expressed in all groups. Cases in the WNT group showed a slightly better survival than those in the SHH or non-WNT/SHH group, although additional cases are required for statistical significance. Isochromosome 17q (P = .002) and the large cell/anaplastic variant (P = .002) were demonstrated to be poor prognostic indicators in multivariate analysis. The representative IHC and cytogenetic data facilitated the division of MBs into the WNT and SHH groups; however, more specific markers should be added for the identification of group 3 and group 4 in practice.     

Expulsion of selenium/protein nanoparticles through vesicle-like structures by Saccharomyces cerevisiae under microaerophilic environment

Nano-selenium/protein is a kind of lower toxic supplement to human. Many microorganisms can reduce selenite/selenate to intracellular or extracellular selenium nanoparticles. This study examined the influence of dissolved oxygen on the expulsion of extracellular selenium/protein produced in Saccharomyces cerevisiae. More of the added selenite was reduced to extracellular selenium nanoparticles by yeast cells only under oxygen-limited condition than under aerobic or anaerobic condition. For the first time, we evidenced that selenium/protein nanoparticles synthesized in vivo were transported out of the cells by vesicle-like structures under microaerophilic environment. The characterizations of the extracellular spherical selenium/protein nanoparticles were also examined by SEM, TEM, EDX and FTIR.     

Replication-compromised cells require the mitotic checkpoint to prevent tetraploidization

Replication stress often induces chromosome instability. In this study, we explore which factors in replication-compromised cells promote abnormal chromosome ploidy. We expressed mutant forms of either polymerase α (Polα) or polymerase δ (Polδ) in normal human fibroblasts to compromise DNA replication. Cells expressing the mutant Polα-protein failed to sustain mitotic arrest and, when propagated progressively, down-regulated Mad2 and BubR1 and accumulated 4N-DNA from the 2N-DNA cells. Significantly, a population of these cells became tetraploids. The Polα mutant expressing cells also exhibited elevated cellular senescence markers, suggesting as a mechanism to limit proliferation of the tetraploids. Expression of the Polδ mutant also caused cells to accumulate 4N-DNA. In contrast to the Polα mutant expressing cells, the Polδ mutant expressing cells expressed sufficient levels of Mad2, BubR1, and cyclin B1 to sustain mitotic arrest, and these cells had normal chromosome ploidy. Together, these results suggest that replication-compromised cells depend on the mitotic checkpoint to prevent mitotic slippage that could result in tetraploidization.     

Orderly microaggregates of G-/C-rich oligonucleotides associated with spermine

Spermine-induced orderly assembling properties of G-/C-rich oligonucleotides are investigated in dilute and crowding conditions. The first time we report that the parallel G-quadruplexes is preferential to condense into anisotropic microaggregates in the presence of spermine, whereas the hybrid-type and the antiparallel G-quadruplexes have no significant interactions with spermine; and spermine can induce the condensation of i-motif C-rich oligonucleotides other than the random coiled C-rich strands. Moreover, the condensation of C-rich oligonucleotides can be reversibly regulated by pH and temperature. G-/C-rich oligonucleotides exhibit the cholesteric liquid crystalline phase at low strand concentration in the presence of spermine under crowding conditions. The results illuminate that the parallel G-quadruplex and i-motifs are probably necessity conformations for G-/C-rich oligonucleotides that involved in the regulation of chromosome organization in living cells.     

Multiple forms of SppI (secreted phosphoprotein, osteopontin) synthesized by normal and transformed rat bone cell populations: regulation by TGF-beta

Metabolic labeling has revealed that rat bone cell populations in culture synthesize several forms of the secreted phosphoprotein, SppI. Most cell populations produced two major [32PO4]-labeled forms that behaved anomolously on SDS-PAGE migrating at 60 kDa and 56 kDa on 10% gels and 55 kDa and 44 kDa on 15% gels. Minor forms of intermediate sizes were also resolved. In normal bone cells the 60 kDa form was predominant and was the only form produced by the clonal bone cell line, RCA 11, whereas the 56 kDa a form predominated in the transformed bone cell line, ROS 17/2.8. In all populations [35S]-methionine-labeling revealed SppIs at approximately 60 kDa but no 56 kDa form. Each form of SppI was specifically cleaved by thrombin which generated fragments of approximately 28 kDa. Transforming growth factor beta 1 increased SppI mRNA levels 3 to 6-fold within 24 h in the normal bone cells, but no increase occurred in the ROS 17/2.8 cells. The elevated expression of SppI was reflected in a selective increase in the synthesis of the [32PO4]-and [35S]-methionine-labeled 60 kDa SppIs.