Hasil untuk "physics.flu-dyn"

David Payne

H. Hsieh, N. Li, J. Frangos

S. Vincent, S. Vincent, T. Hökfelt et al.

J. Ando, H. Tsuboi, R. Korenaga et al.

Joji Ando, T. Komatsuda, M. Shibata et al.

K. Anderson, A. Reiner

S. Feller, Yuhong Zhang, R. Pastor

H. W. Sill, Yong S. Chang, J. Artman et al.

N. Dyn, D. Levin

Menggui Huang, Tianwen Huang, Yang Xiang et al.

S. Mohan, N. Mohan, E. Sprague

S. Sivam

The influence of the acute (single dose) or subchronic (one dose daily for 4 days) administration of cocaine to Sprague-Dawley rats on striatal enkephalin (Met5-enkephalin) and striatonigral tachykinin (substance P) and dynorphin [dynorphin A (1-8), DYN] levels was investigated. The peptide levels were determined by radioimmunoassay. The concentrations of the striatal levels of dopamine (DA), 5-hydroxytryptamine and their acid metabolites were determined by high-performance liquid chromatography with electrochemical detection. An acute administration of cocaine (20 or 30 mg/kg i.p.) did not affect the peptide levels in the striatum or in the substantia nigra. A regimen of subchronic administration of cocaine (20 mg/kg/day for 4 days) increased the striatonigral DYN levels, without altering the levels of Met5-enkephalin or substance P. The increase in DYN levels were persistent for at least 4 days after the last dose of the subchronic administration of cocaine. The DYN levels returned to control values by 12 days after the last dose. The DA levels in the striatum were increased 30 min after a single dose of cocaine. None of the other treatments elicited any changes in DA or 5-hydroxytryptamine or their metabolites. The subchronic cocaine administration to dopaminergic denervated rats with 6-hydroxydopamine failed to evoke any increase in DYN levels in the striatum or substantia nigra. The concurrent administration of the D1 DA antagonist, SCH-23390, or the D2 DA antagonist, spiperone, to the subchronic regimen of cocaine also blocked the cocaine-induced increase in DYN levels. These results indicate that cocaine selectively enhances the synthesis or decreases the release of DYN in the striatonigral neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

H. Inoguchi, Takashi Tanaka, Yoshihiko Maehara et al.

P. Cabot, L. Carter, M. Schäfer et al.

H. Segal, C. Briggs, S. Kunka et al.

Robyn M Carey, Brigitte A Balcz, I. López-Coviella et al.

BackgroundThe amyloid precursor protein (APP) is transported via the secretory pathway to the cell surface, where it may be cleaved within its ectodomain by α-secretase, or internalized within clathrin-coated vesicles. An alternative proteolytic pathway occurs within the endocytic compartment, where the sequential action of β- and γ-secretases generates the amyloid β protein (Aβ). In this study, we investigated the effects of modulators of endocytosis on APP processing.ResultsHuman embryonic kidney cells were transfected with a dominant negative mutant of dynamin I, an important mediator of clathrin-dependent endocytosis, and APP proteolysis was analyzed. Overexpression of the mutant dynamin (dyn I K44A) resulted in increased shedding of the APP ectodomain (sAPPα), accumulation of the C-terminal α-secretase product C83, and a reduction in the release of Aβ. Levels of mature APP on the cell surface were increased in cells expressing dyn I K44A, and internalization of surface-immunolabeled APP, assessed by fluorescence microscopy, was inhibited. Dynamin is a substrate for protein kinase C (PKC), and it was hypothesized that activators of PKC, which are known to stimulate α-secretase-mediated cleavage of APP, might exert their effects by inhibiting dynamin-dependent endocytosis. However, the internalization of surface-biotinylated APP was unaffected by treatment of cells with phorbol 12-myristate 13-acetate in the presence of the α-secretase inhibitor TAPI-1.ConclusionThe results indicate that APP is internalized by a dynamin-dependent process, and suggest that alterations in the activity of proteins that mediate endocytosis might lead to significant changes in Aβ production.

V. Leytin, D. Allen, S. Mykhaylov et al.

Jay H. Chyung, D. Selkoe

Sequential cleavages of the amyloid β-protein precursor (APP) by the β- and γ-secretases generate the amyloid β-protein (Aβ), which plays a central role in Alzheimer's disease. Previous work provided evidence for involvement of both the secretory and endocytic pathways in Aβ generation. Here, we used HeLa cells stably expressing a tetracycline-regulated dominant-negative dynamin I (dyn K44A), which selectively inhibits receptor-mediated endocytosis, and analyzed the effects on the processing of endogenous APP. Upon induction of dyn K44A, levels of mature APP rose at the cell surface, consistent with retention of APP on the plasma membrane. The α-secretase cleavage products of APP were increased by dyn K44A, in that α-APPs in medium and the C83 C-terminal stub in the membrane both rose. The β-secretase cleavage of APP, C99, also increased modestly. The use of specific γ-secretase inhibitors to study the accumulation of α- and β-cleavage products independent of their processing by γ-secretase confirmed that retention of APP on the plasma membrane results in increased processing by both α- and β-secretases. Unexpectedly, endogenous Aβ secretion was significantly increased by dyn K44A, as detected by three distinct methods: metabolic labeling, immunoprecipitation/Western blotting, and enzyme-linked immunosorbent assay. Levels of p3 (generated by sequential α- and γ-cleavage) also rose. We conclude that endogenous Aβ can be produced directly at the plasma membrane and that alterations in the degree of APP endocytosis may help regulate its production. Our findings are consistent with a role for the γ-secretase complex in the processing of numerous single-transmembrane receptors at the cell surface.

Chad D. Foradori, Chad D. Foradori, M. Amstalden et al.