Transactivation of the epidermal growth factor receptor by heat shock protein 90 via Toll-like receptor 4 contributes to the migration of glioblastoma cells

Extracellular heat shock protein HSP90α was reported to participate in tumor cell growth, invasion, and metastasis formation through poorly understood signaling pathways. Herein, we show that extracellular HSP90α favors cell migration of glioblastoma U87 cells. More specifically, externally applied HSP90α rapidly induced endocytosis of EGFR. This response was accompanied by a transient increase in cytosolic Ca(2+) appearing after 1-3 min of treatment. In the presence of EGF, U87 cells showed HSP90α-induced Ca(2+) oscillations, which were reduced by the ATP/ADPase, apyrase, and inhibited by the purinergic P(2) inhibitor, suramin, suggesting that ATP release is requested. Disruption of lipid rafts with methyl β-cyclodextrin impaired the Ca(2+) rise induced by extracellular HSP90α combined with EGF. Specific inhibition of TLR4 expression by blocking antibodies suppressed extracellular HSP90α-induced Ca(2+) signaling and the associated cell migration. HSPs are known to bind lipopolysaccharides (LPSs). Preincubating cells with Polymyxin B, a potent LPS inhibitor, partially abrogated the effects of HSP90α without affecting Ca(2+) oscillations observed with EGF. Extracellular HSP90α induced EGFR phosphorylation at Tyr-1068, and this event was prevented by both the protein kinase Cδ inhibitor, rottlerin, and the c-Src inhibitor, PP2. Altogether, our results suggest that extracellular HSP90α transactivates EGFR/ErbB1 through TLR4 and a PKCδ/c-Src pathway, which induces ATP release and cytosolic Ca(2+) increase and finally favors cell migration. This mechanism could account for the deleterious effects of HSPs on high grade glioma when released into the tumor cell microenvironment.     

Release Factor eRF3 Mediates Premature Translation Termination on Polylysine-Stalled Ribosomes in Saccharomyces cerevisiae

Ribosome stalling is an important incident enabling the cellular quality control machinery to detect aberrant mRNA. Saccharomyces cerevisiae Hbs1-Dom34 and Ski7 are homologs of the canonical release factor eRF3-eRF1, which recognize stalled ribosomes, promote ribosome release, and induce the decay of aberrant mRNA. Polyadenylated nonstop mRNA encodes aberrant proteins containing C-terminal polylysine segments which cause ribosome stalling due to electrostatic interaction with the ribosomal exit tunnel. Here we describe a novel mechanism, termed premature translation termination, which releases C-terminally truncated translation products from ribosomes stalled on polylysine segments. Premature termination during polylysine synthesis was abolished when ribosome stalling was prevented due to the absence of the ribosomal protein Asc1. In contrast, premature termination was enhanced, when the general rate of translation elongation was lowered. The unconventional termination event was independent of Hbs1-Dom34 and Ski7, but it was dependent on eRF3. Moreover, premature termination during polylysine synthesis was strongly increased in the absence of the ribosome-bound chaperones ribosome-associated complex (RAC) and Ssb (Ssb1 and Ssb2). On the basis of the data, we suggest a model in which eRF3-eRF1 can catalyze the release of nascent polypeptides even though the ribosomal A-site contains a sense codon when the rate of translation is abnormally low.     

Barogali et l’Oued Doure. Deux gisements représentatifs du Paléolithique ancien en République de Djibouti

In the Republic of Djibouti, surveys and excavations, carried out from 1985 to 1992, confirmed the presence of the pre-Acheulean (Oldowan) and Acheulean sites in the country. Three seasons of excavations (1985-1987 in the Gobaad Basin, have unearthed in a hardened compact clay strata of an ancient marshland dating to the Lower Pleistocene, the fossilized skeletal remains of an Elephas recki ileretensis. Numerous stone tools have been gathered with the bones. The E.S.R. dating the elephant’s lower third molar gave a date between 1,.6 and 1,.3 MY that would confirm its paleontological grouping and the membership of this butchery site to the Oldowan period. The animal appeared to have been lying on its left side. The cranial roof had been separated from the calvarium, perhaps to get at the brain; but the skull remains in anatomic connection with the tusks. The jaw (mandible) seems to have been broken to extract the tongue. Hominids, perhaps Homo ergaster, knapped tools from a nearly outcrop of poor quality lava. The tools were specifically adapted to their needs, such as scraping, chopping and scattering the bones. The site has yielded 569 artifacts: utilized material and hammerstones (121); pebble tools (32); cores (14); “debitage” products (366); retouched flakes (36). Artifacts are rarely retouched and often broken. Five different types of choppers have been classified. The polyedrons and one bola make up 22% of the pebble tools. The cores are divided into unipolar, centripetal and polyhedrical types. In another site, Haïdalo, an almost complete skeleton of an Elephas recki recki in anatomical connection and without any sign of predation, has been found at eight kilometers from Barogali. During surveys in the Ali Sabîh region (1990-1992) seven sectors have been discovered and prospected in the Oued Doure Basin. On the surface area and also in situ into some little pits, 345 rhiolitic Acheulean artifacts have been found, near rhyolitic outcrop. These artifacts are generally large. The choppers (18) can be dividended into 2 sets : side choppers (55%) and end choppers (27%), often with a bifacial cutting edge. There is only one polyedron, but we have found eight heavy scrapers. The Acheulean group is important (43 tools). The bifaces are varied and there are also a few cleavers and picks. Cores are numerous (92) and Levallois cores are preponderant (45%). We find also centripetal cores (27%) and so unipolar, bipolar and polyhedral cores. Tools made of flakes (118) are numerous: scrapers are typologically diversified. Some of them have a double utilization. Notch tools, denticulate tools are presents but also end scrapers, burin, borer, back knifes and scantily retouched flakes. The characters of this lithic material, large cores and big flakes, large bifaces of various types, cleavers and retouched flakes, indicates that they are Acheulean products. So, the Doure Site can be placed in the Middle / Upper Acheulean transition.     

Disentangling invasion processes in a dynamic shipping-boating network

The relative importance of multiple vectors to the initial establishment, spread and population dynamics of invasive species remains poorly understood. This study used molecular methods to clarify the roles of commercial shipping and recreational boating in the invasion by the cosmopolitan tunicate, Botryllus schlosseri. We evaluated (i) single vs. multiple introduction scenarios, (ii) the relative importance of shipping and boating to primary introductions, (iii) the interaction between these vectors for spread (i.e. the presence of a shipping-boating network) and (iv) the role of boating in determining population similarity. Tunicates were sampled from 26 populations along the Nova Scotia, Canada, coast that were exposed to either shipping (i.e. ports) or boating (i.e. marinas) activities. A total of 874 individuals (c. 30 per population) from five ports and 21 marinas was collected and analysed using both mitochondrial cytochrome c oxidase subunit I gene (COI) and 10 nuclear microsatellite markers. The geographical location of multiple hotspot populations indicates that multiple invasions have occurred in Nova Scotia. A loss of genetic diversity from port to marina populations suggests a stronger influence of ships than recreational boats on primary coastal introductions. Population genetic similarity analysis reveals a dependence of marina populations on those that had been previously established in ports. Empirical data on marina connectivity because of boating better explains patterns in population similarities than does natural spread. We conclude that frequent primary introductions arise by ships and that secondary spread occurs gradually thereafter around individual ports, facilitated by recreational boating.     

Studies of ribosomal proteins of yeast species and their hybrids gel electrophoresis and immunochemical cross-reactions

Summary The cytoplasmic ribosomal proteins (r-proteins) of seventeen yeast species of the genera Saccharomyces and Kluyveromyces were analyzed by one-dimensional gradient polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The electrophoretic patterns of cytoplasmic r-proteins from different species display extensive differences in both the 40S and the 60S subunit. Relatedness of species suggested by r-protein patterns correlates well with that based on DNA/DNA homology (Bicknell and Douglas 1970). Immunochemical cross-reactions and antibiotic susceptibility tests were also used to compare different species.Analyses of r-proteins from two different interspecific hybrids showed that their ribosomes were hybrid, containing r-proteins from both parents. These findings are discussed in relation to the evolution of yeast species and the regulation of expression of r-proteins in cucaryotes.     

Activation of Xenopus Eggs by the Kinase Inhibitor 6-DMAP Suggests a Differential Regulation of Cyclin B and p39 Proteolysis

In Xenopus eggs, metaphase II arrest is due to the cytostatic factor that maintains a high level of MPF activity. Kinases are important in this phenomenon since p39^mos and MAPK play a part in the cytostatic activity whereas p34^cdc2 is the catalytic subunit of MPF. Fertilization induces a rise in intracellular calcium leading to egg activation that can be mimicked by calcium-increasing agents such as calcium ionophore. We have performed on Xenopus eggs a biochemical comparison of the effects of the kinase inhibitor 6-DMAP and the calcium ionophore. Both drugs were able to induce pronucleus formation but the underlying molecular events were different. The inactivation of MAPK occurred earlier in eggs exposed to 6-DMAP. Cyclins B1 and B2 were stable and p39^mos was proteolysed in 6-DMAP-treated eggs while the three proteins underwent degradation in A23187-treated ones. These results suggest a differential regulation of ubiquitin-dependent proteolysis of cyclin B and p39^mos.