IP3 3-kinase opposes NGF driven neurite outgrowth.

The inositol (1,4,5) trisphosphate 3-kinases comprise a family of enzymes (A, B, and C) that phosphorylate the calcium mobilising molecule inositol (1,4,5) trisphosphate (IP(3)) to generate inositol (1,3,4,5) tetrakisphosphate. This molecule can function as a second messenger, but its roles are not completely understood. The A isoform of inositol (1,4,5) trisphosphate 3-kinase localises to filamentous actin within dendritic spines in the hippocampus and is implicated in the regulation of spine morphology and long term potentiation, however the mechanisms through which it signals in neuronal cells are not completely understood. We have used NGF driven neurite outgrowth from PC12 cells as a platform to examine the impact of signaling via inositol (1,4,5) trisphosphate 3-kinase activity in a neuronal cell. We have found that the catalytic activity of the enzyme opposes neurite outgrowth, whilst pharmacological inhibition of inositol (1,4,5) trisphosphate 3-kinase leads to a significant increase in neurite outgrowth, and we show that the reduction in neurite outgrowth in response to inositol (1,4,5) trisphosphate 3-kinase activity correlates with reduced ERK activity as determined by western blotting using phosphorylation-specific antibodies. Our findings suggest a novel neuronal signaling pathway linking metabolism of IP(3) to signaling via ERK

Expression of HIV-1 Vpu Leads to Loss of the Viral Restriction Factor CD317/Tetherin from Lipid Rafts and Its Enhanced Lysosomal Degradation

CD317/tetherin (aka BST2 or HM1.24 antigen) is an interferon inducible membrane protein present in regions of the lipid bilayer enriched in sphingolipids and cholesterol (often termed lipid rafts). It has been implicated in an eclectic mix of cellular processes including, most notably, the retention of fully formed viral particles at the surface of cells infected with HIV and other enveloped viruses. Expression of the HIV viral accessory protein Vpu has been shown to lead to intracellular sequestration and degradation of tetherin, thereby counteracting the inhibition of viral release. There is evidence that tetherin interacts directly with Vpu, but it remains unclear where in the cell this interaction occurs or if Vpu expression affects the lipid raft localisation of tetherin. We have addressed these points using biochemical and cell imaging approaches focused on endogenous rather than ectopically over-expressed tetherin. We find i) no evidence for an interaction between Vpu and endogenous tetherin at the cell surface, ii) the vast majority of endogenous tetherin that is at the cell surface in control cells is in lipid rafts, iii) internalised tetherin is present in non-raft fractions, iv) expression of Vpu in cells expressing endogenous tetherin leads to the loss of tetherin from lipid rafts, v) internalised tetherin enters early endosomes, and late endosomes, in both control cells and cells expressing Vpu, but the proportion of tetherin molecules destined for degradation rather than recycling is increased in cells expressing Vpu vi) lysosomes are the primary site for degradation of endogenous tetherin in cells expressing Vpu. Our studies underlie the importance of studying endogenous tetherin and let us propose a model in which Vpu intercepts newly internalised tetherin and diverts it for lysosomal destruction rather than recycling to the cell surface

Studying Your Own Country. Social Scientific Knowledge For Our Times and Places; Presidential Address to the Canadian Political Science Association, St Catharines, May 28, 2014

Political science is both a generalizing and an anchored, nationally defined, discipline. Too often, the first perspective tends to crowd out the latter, because it appears more prestigious, objective, or scientific. Behind the international/national dichotomy, there are indeed rival conceptions of social science, and important ontological, epistemological and methodological assumptions. This article discusses these assumptions and stresses the critical contribution of idiographic, single-outcome studies, the importance of producing relevant, usable knowledge, and the distinctive implications of studying one’s own country, where a scholar is also a citizen, involved in more encompassing national conversations. The aim is not to reject the generalizing, international perspective, or even the comparative approach, but rather to reaffirm the importance of maintaining as well, and in fact celebrating, the production of social scientific knowledge directly relevant for our own times and places.La science politique est une discipline qui aspire à la fois à la généralisation et à la production de connaissances ancrées localement, sur le plan national. Trop souvent, la première perspective domine la seconde, parce qu’elle apparait plus prestigieuse, objective ou scientifique. La dichotomie international/national recouvre en effet des postulats fort différents en ce qui concerne les fondements ontologiques, épistémologiques et méthodologiques de la discipline. Cet article discute ces postulats et souligne la contribution déterminante des études idiographiques, centrées sur des évènements uniques, l’importance de produire des connaissances pertinentes et utilisables, et le caractère distinctif de l’étude de son propre pays, qui fait aussi du chercheur un citoyen impliqué dans de plus larges conversations. Le but n’est pas de rejeter la généralisation ou même l’approche comparative, mais plutôt de réaffirmer l’importance de maintenir également, et même de célébrer, la production de connaissances directement pertinentes pour nos propres temps et milieux de vie

A CD317/tetherin–RICH2 complex plays a critical role in the organization of the subapical actin cytoskeleton in polarized epithelial cells

CD317/tetherin is a lipid raft–associated integral membrane protein with a novel topology. It has a short N-terminal cytosolic domain, a conventional transmembrane domain, and a C-terminal glycosyl-phosphatidylinositol anchor. We now show that CD317 is expressed at the apical surface of polarized epithelial cells, where it interacts indirectly with the underlying actin cytoskeleton. CD317 is linked to the apical actin network via the proteins RICH2, EBP50, and ezrin. Knocking down expression of either CD317 or RICH2 gives rise to the same phenotype: a loss of the apical actin network with concomitant loss of apical microvilli, an increase in actin bundles at the basal surface, and a reduction in cell height without any loss of tight junctions, transepithelial resistance, or the polarized targeting of apical and basolateral membrane proteins. Thus, CD317 provides a physical link between lipid rafts and the apical actin network in polarized epithelial cells and is crucial for the maintenance of microvilli in such cells