Neurotrophic signalling pathway triggered by prosaposin in PC12 cells occurs through lipid rafts

Prosaposin is a neurotrophic factor that has been demonstrated to mediate trophic signalling events in different cell types; it distributes to surface membranes of neural cells and also exists as a secreted protein in different body fluids. Prosaposin was demonstrated to form tightly bound complexes with a variety of gangliosides, and a functional role has been suggested for ganglioside-prosaposin complexes. In this work, we provide evidence that exogenous prosaposin triggers a signal cascade after binding to its target molecules on lipid rafts of pheochromocytoma PC12 cell plasma membranes, as revealed by scanning confocal microscopy and linear sucrose gradient analysis. In these cells, prosaposin is able to induce extracellular signal-regulated kinase phosphorylation, sphingosine kinase activation, and consequent cell death prevention, acting through lipid rafts. These findings point to the role of lipid rafts in the prosaposin-triggered signalling pathway, thus supporting a role for this factor as a new component of the multimolecular signalling complex involved in the neurotrophic response.     

Ouabain-insensitive salt and water movements in duck red cells. II. The role of chloride in the volume response

This paper describes the effect of external chloride on the typical swelling response induced in duck red cells by hypertonicity or norepinephrine. Lowering chloride inhibits swelling and produces concomitant changes in net movements of sodium and potassium in ouabain-treated cells, which resemble the effect of lowering external sodium or potassium. Inhibition is the same whether chloride is replaced with gluconate or with an osmotic equivalent of sucrose. Since changes in external chloride also cause predictable changes in cell chloride, pH, and water, these variables were systematically investigated by varying external pH along with chloride. Lowering pH to 6.60 does not abolish the response if external chloride levels are normal, although the cells are initially swollen due to the increased acidity. Cells deliberately preswollen in hypotonic solutions with appropriate ionic composition can also respond to norepinephrine by further swelling. These results rule out initial values of cell water, chloride, and pH as significant variables affecting the response. Initial values of the chloride equilibrium potential do have marked effect on the direction and rate of net water movement. If chloride is lowered by replacement with the permeant anion, acetate, E(Cl) is unchanged and a normal response to norepinephrine, which is inhibited by furosemide, is observed. Increasing internal sodium by the nystatin technique also inhibits the response. A theory is developed which depicts that the cotransport carrier proposed in the previous paper (W.F. Schmidt and T.J. McManus. 1977b. J. Gen. Physiol. 70:81-97) moves in response to the net electrochemical potential difference driving sodium and potassium across the membrane. Predictions of this theory fit the data for both cations and anions.     

Pepstatin A alters host cell autophagic machinery and leads to a decrease in influenza A virus production

Autophagy is a survival mechanism that can take place in cells under metabolic stress and through which cells can recycle waste material. Disturbances in autophagic processes appear to be associated with a number of human pathologies, including viral infections. It has been hypothesized that viruses can subvert autophagy in order to penetrate the host cell and replicate. Because it has been suggested that autophagy is involved in influenza A virus replication, we analyzed the effects of two inhibitors of lysosomal proteases on the cellular control of influenza A virus replication. In particular, we used biochemical and morphological analyses to evaluate the modulation of influenza A/Puerto Rico/8/34 H1N1 virus production in the presence of CA074 and Pepstatin A, inhibitors of cathepsin proteases B and D, respectively. We found that Pepstatin A, but not CA074, significantly hindered influenza virus replication, probably by modulating host cell autophagic/apoptotic responses. These results are of potential interest to provide useful insights into the molecular pathways exploited by the influenza in order to replicate and to identify further cellular factors as targets for the development of innovative antiviral strategies.     

Learning impairment in honey bees caused by agricultural spray adjuvants

Background

Spray adjuvants are often applied to crops in conjunction with agricultural pesticides in order to boost the efficacy of the active ingredient(s). The adjuvants themselves are largely assumed to be biologically inert and are therefore subject to minimal scrutiny and toxicological testing by regulatory agencies. Honey bees are exposed to a wide array of pesticides as they conduct normal foraging operations, meaning that they are likely exposed to spray adjuvants as well. It was previously unknown whether these agrochemicals have any deleterious effects on honey bee behavior.

Methodology/Principal Findings

An improved, automated version of the proboscis extension reflex (PER) assay with a high degree of trial-to-trial reproducibility was used to measure the olfactory learning ability of honey bees treated orally with sublethal doses of the most widely used spray adjuvants on almonds in the Central Valley of California. Three different adjuvant classes (nonionic surfactants, crop oil concentrates, and organosilicone surfactants) were investigated in this study. Learning was impaired after ingestion of 20 µg organosilicone surfactant, indicating harmful effects on honey bees caused by agrochemicals previously believed to be innocuous. Organosilicones were more active than the nonionic adjuvants, while the crop oil concentrates were inactive. Ingestion was required for the tested adjuvant to have an effect on learning, as exposure via antennal contact only induced no level of impairment.

Conclusions/Significance

A decrease in percent conditioned response after ingestion of organosilicone surfactants has been demonstrated here for the first time. Olfactory learning is important for foraging honey bees because it allows them to exploit the most productive floral resources in an area at any given time. Impairment of this learning ability may have serious implications for foraging efficiency at the colony level, as well as potentially many social interactions. Organosilicone spray adjuvants may therefore contribute to the ongoing global decline in honey bee health.     

Do mitochondria act as "cargo boats" in the journey of GD3 to the nucleus during apoptosis?

Plasma membrane lipid rafts have been considered as a sort of "chamber", where several subcellular activities, including CD95/Fas-mediated pro-apoptotic signaling, can take place. Recently, we demonstrated that, after CD95/Fas triggering, raft-like microdomains could be detected in mitochondrial membranes. The mitochondrion appears as a dynamic and subcompartmentalized organelle in which microdomains might act as controllers of apoptosis-associated fission that results in the release of apoptogenic factors. Here, we hypothesize that some "small" mitochondria, possibly derived from their fission process, can reach the nuclear envelope and strictly interact with this. Mitochondria could act as a signaling "device" contributing to molecular trafficking of molecules, including raft-like components, during apoptosis.