Effects of Brefeldin A on disassembly of the Golgi body in MDCK cells subjected to a Ca2+ shift at low temperature

Golgi bypass: skirting around the heart of classical secretion

Classical secretion consists of the delivery of transmembrane and soluble proteins to the plasma membrane and the extracellular medium, respectively, and is mediated by the organelles of the secretory pathway, the Endoplasmic Reticulum (ER), the ER exit sites, and the Golgi, as described by the Nobel Prize winner George Palade (Palade 1975). At the center of this transport route, the Golgi stack has a major role in modifying, processing, sorting, and dispatching newly synthesized proteins to their final destinations. More recently, however, it has become clear that an increasing number of transmembrane proteins reach the plasma membrane unconventionally, either by exiting the ER in non-COPII vesicles or by bypassing the Golgi. Here, we discuss the evidence for Golgi bypass and the possible physiological benefits of it. Intriguingly, at least during Drosophila development, Golgi bypass seems to be mediated by a Golgi protein, dGRASP, which is found ectopically localized to the plasma membrane.

Thiamine-dependent processes and treatment strategies in neurodegeneration

Reductions in brain glucose metabolism and increased oxidative stress invariably occur in Alzheimer's disease (AD) and thiamine (vitamin B1) deficiency. Both conditions cause irreversible cognitive impairment; their behavioral consequences overlap but are not identical. Thiamine-dependent processes are critical in glucose metabolism, and recent studies implicate thiamine in oxidative stress, protein processing, peroxisomal function, and gene expression. The activities of thiamine-dependent enzymes are characteristically diminished in AD, and the reductions in autopsy AD brain correlate highly with the extent of dementia in the preagonal state. Abnormalities in thiamine-dependent processes can be plausibly linked to the pathology of AD. Seemingly paradoxical properties of thiamine-dependent processes may underlie their relation to the pathophysiology of AD: Reduction of thiamine-dependent processes increase oxidative stress. Thiamine can act as a free radical scavenger. Thiamine-dependent mitochondrial dehydrogenase complexes produce oxygen free radicals and are sensitive to oxidative stress. Genetic disorders of thiamine metabolism that lead to neurological disease can be treated with large doses of thiamine. Although thiamine itself has not shown dramatic benefits in AD patients, the available data is scanty. Adding thiamine or more absorbable forms of thiamine to tested treatments for the abnormality in glucose metabolism in AD may increase their efficacy.

BFA-sensitive and insensitive exocytic pathways in Entamoeba histolytica trophozoites: their relationship to pathogenesis

Entamoeba histolytica manifests its pathogenicity through several cellular processes triggered by external stimuli that activate signal transduction pathways. The intense secretory activity resulting from stimulation is not correlated with a typical endoplasmic reticulum (ER) or Golgi organization, and little is known in this parasite about endocytic/exocytic pathways. The interactions of trophozoites with fibronectin (FN) and cultured mammalian cells, which elicit secretory activities, were chosen to study mechanisms that regulate cytoplamic traffic. Results showed that Brefeldin A (BFA) induced redistribution of the vesicular network recognized by antibodies against amoebic proteins PDI and ERD2. Furthermore, BFA diminished traffic to the plasma membrane of the beta1 integrin-like FN receptor and the heavy subunit of the Gal/GalNAc lectin, required for adhesion to FN and target cells, respectively. However, BFA did not prevent thiol-proteinase secretion or inhibit the traffic of de novo synthesized proteinases. These data suggest that two distinct transport systems occur in E. histolytica, one similar to classical membrane protein transport and another independent of BFA and inducible by external stimuli. Actin-myosin contractility of the cortical cytoskeleton seems necessary for the final release of exported proteinases and the proper function of the surface proteins involved in adhesion.