ORCID Profile
0000-0002-1826-953X
Current Organisation
University of Oxford
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Publisher: Elsevier BV
Date: 04-2000
Publisher: Elsevier BV
Date: 1994
DOI: 10.1016/0166-2236(94)90179-1
Abstract: In nerve terminals, neurotransmitters are packaged in synaptic vesicles, and released by exocytosis. Empty synaptic vesicles are rapidly recycled for reuse by endocytosis. Much progress has been made in identifying the proteins involved in synaptic-vesicle trafficking, but the mechanism and regulation of endocytosis have largely remained an enigma. One approach to defining regulatory proteins that might be involved is to study stimulus-dependent phosphorylation events in nerve terminals. This has led to the identification of dephosphin, which is quantitatively dephosphorylated by nerve-terminal depolarization. Sequencing reveals that dephosphin is identical with dynamin I, a GTP-binding protein that functions in endocytosis. Phosphorylation and dephosphorylation of nerve-terminal dynamin I/dephosphin regulates its intrinsic GTPase activity in parallel with the regulation of synaptic-vesicle recycling. Therefore, phosphorylation and dephosphorylation of dynamin I might provide a Ca(2+)-dependent switch for endocytosis in the synaptic-vesicle pathway.
Publisher: Elsevier BV
Date: 02-2001
DOI: 10.1016/S0167-4889(00)00130-0
Abstract: Phosphatidylinositol 3-kinase (PI 3-kinase) plays a role in late stages of endocytosis as well as in cellular proliferation and transformation. The SH3 domain of its regulatory p85 subunit stimulates the GTPase activity of dynamin in vitro. Dynamin is a GTPase enzyme required for endocytosis of activated growth factor receptors. An interaction between these proteins has not been demonstrated in vivo. Here, we report that dynamin associates with PI 3-kinase in hematopoietic cells. We detected both p85 and PI 3-kinase activity in dynamin immune complexes from IL-3-dependent BaF3 cells. However, this association was significantly reduced in BaF3 cells transformed with the BCR/abl oncogene. After transformation only a 4-fold increase in PI 3-kinase activity was detected in dynamin immune complexes, whereas grb2 associated activity was elevated 20-fold. Furthermore, dynamin inhibited the activity of both purified recombinant and immunoprecipitated PI 3-kinase. In BaF3 cells expressing a temperature-sensitive mutant of BCR/abl, a significant decrease in p85 and dynamin association was observed 4 h after the induction of BCR/abl activity. In contrast, in IL-3-stimulated parental BaF3 cells, this association was increased. Our results demonstrate an in vivo association of PI 3-kinase with dynamin and this interaction regulates the activity of PI 3-kinase.
Publisher: Elsevier BV
Date: 02-1995
DOI: 10.1016/0306-4522(94)00337-5
Abstract: Dephosphin/dynamin is a 94,000/96,000 mol. wt protein kinase C substrate from rat brain that is phosphorylated in nerve terminals and dephosphorylated upon stimulation of exocytosis and synaptic vesicle recycling. Phosphorylation activates an intrinsic GTPase activity and dephosphin may play a role in endocytosis [Robinson P. J. et al. (1993) Nature 365, 163-166]. In this study a specific polyclonal antiserum to dephosphin was used to investigate its distribution in rat brain by immunoblotting and immunocytochemistry. Immunoblots of various organs of the rat showed that dephosphin was detectable only in the whole brain and not in the testes, lung, kidney, adrenals, heart, liver or skeletal muscle. Immunoblotting of various regions of the brain revealed high levels of dephosphin, particularly in the hippoc us, cerebellum and cerebral cortex, but its absence from the anterior pituitary. Synaptosomes were prepared from these three regions and labelled with 32Pi for 60 min, followed by incubation in control or 41 mM K+ depolarizing buffer. Dephosphin was present in each region and was stoichiometrically dephosphorylated by depolarization, indicating the presence and regulation of dephosphin in intact cerebellar nerve terminals. The cerebellum was selected for detailed study, using conventional light and confocal microscopy, owing to its ordered and well-characterized structure. Immunostaining was abundant within the cerebellar cortex and deep cerebellar nuclei, but almost entirely absent from the medulla. In the cortex many neuronal cells contained dephosphin-like immunoreactivity which was also evident in perikarya, axons, and nerve terminals. Dephosphin-like immunoreactivity was not detected in the radial Bergman glial cells. The greatest concentrations were observed in synaptic terminals, particularly in granular layer glomeruli and basket cell terminals surrounding Purkinje cell bodies and dendrites. Dephosphin therefore appears to be exclusive to neuronal tissue, but is distributed widely throughout the brain. It is located in many neuronal cell types of the cerebellum and may be particularly enriched in synaptic terminals, where it is regulated by phosphorylation and dephosphorylation. This distribution suggests a role for dephosphin in synaptic vesicle cycling in nerve terminals.
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Kate Powell.