Cell Biology: Watching the First Steps of Podosome Formation

SummaryPodosomes and invadopodia are actin-rich structures that have come under intense scrutiny over the past several years due to their critical roles in cell migration and invasion. Examination of the initial stages of podosome formation has revealed an important role for the phosphoinositide PI(3,4)P2 in anchoring the scaffold protein Tks5 to the plasma membrane

Rac and Rho driving tumor invasion: who's at the wheel?

Interplay between Rho and Rac controls the invasive behavior of melanoma cells

Les facteurs qui favorisent l’implication des médecins généralistes belges dans la gestion des abus de substances. Une étude qualitative basée sur le I-Change Model

Objectifs Les médecins généralistes (MG) jouent un rôle majeur dans la détection et la gestion des abus de substances. L’étude présentée ici investiguait les facteurs qui influencent leur implication concernant la gestion des abus d’alcool, des drogues illégales, des hypnotiques et des anxiolytiques dans la population belge des 18-65 ans. Méthodes 20 MG ont été interrogés par entretiens semi-directifs dans les régions de Liège et d’Anvers. Le I-Change Model de de Vries a été utilisé pour construire le guide d’entretien et analyser les données récoltées. Résultats Parmi les principaux résultats de l’étude, il ressortait que les MG étaient fortement influencés dans leur approche par leurs propres représentations de l’abus, qui oscillait leurs responsabilités professionnelles envers ces patients et la responsabilité de ces derniers quant à la gestion de leur santé, avec l’idée de faute morale en substrat. En ce sens, l’abus de substance était perçu sur un continuum entre l’abus comme forme de maladie chronique d’une part, et la faute morale d’autre part. L’alcool et le cannabis étaient néanmoins mieux acceptés socialement que les autres substances. Les propres expériences personnelles des MG concernant les abus avaient aussi une incidence sur leur volonté de s’investir avec ces patients. Pour autant, les pratiques multidisciplinaires (notamment au forfait) et l’expérience étaient évoqués comme des facteurs importants quant à l’engagement dans la gestion. Les contraintes temporelles et l’investissement demandé étaient, en revanche, considérés comme des barrières. Conclusion Les facteurs motivationnels apparaissaient centraux dans la décision de s’investir dans la gestion des abus de substances, bien davantage que les connaissances théoriques et les formations qui semblaient plus secondaires. La peur du burn-out s’exprimait donc en substrat. La formation des MG devrait tenir compte de ce souhait de se protéger, afin de favoriser simultanément une approche centrée sur le patient

Transforming Potential of Dbl Family Proteins Correlates with Transcription from the Cyclin D1 Promoter but Not with Activation of Jun NH 2 -terminal Kinase, p38/Mpk2, Serum Response Factor, or c-Jun

The dbl family of oncogenes encodes a large, structurally related, family of growth-regulatory molecules that possess guanine nucleotide exchange factor activity for specific members of the Rho family of Ras-related GTPases. We have evaluated matched sets of weakly and strongly transforming versions of five Dbl family proteins (Lfc, Lsc, Ect2, Dbl, and Dbs) to determine their ability to stimulate signaling pathways that are activated by Rho family proteins. We found that the transforming potential of this panel did not correlate directly with their ability to activate Jun NH2-terminal kinase, p38/Mpk2, serum response factor, or c-Jun. In contrast, transient stimulation of transcription from the cyclin D1 promoter provided a strong correlation with transforming potential, and we found constitutive up-regulation of cyclin D1 protein in Dbl family protein-transformed cells. In addition, we observed that at least two Dbl family members (Lfc and Ect2) induced changes in the actin cytoskeleton and exhibited nuclear signaling profiles that are consistent with a broader range of in vivo substrate utilization than is predicted from their in vitro exchange specificities. In summary, although Dbl family proteins exhibit signaling profiles that are consistent with their in vivo activation of Rho proteins, stimulation of cyclin D1 transcription is the only activity that correlates with transforming potential, thus suggesting that deregulated cell cycle progression may be important for Dbl family protein transformation

RhoA/ROCK-mediated switching between Cdc42- and Rac1-dependent protrusion in MTLn3 carcinoma cells

Rho GTPases are versatile regulators of cell shape that act on the actin cytoskeleton. Studies using Rho GTPase mutants have shown that, in some cells, Rac1 and Cdc42 regulate the formation of lamellipodia and filopodia, respectively at the leading edge, whereas RhoA mediates contraction at the rear of moving cells. However, recent reports have described a zone of RhoA/ROCK activation at the front of cells undergoing motility. In this study, we use a FRET-based RhoA biosensor to show that RhoA activation localizes to the leading edge of EGF-stimulated cells. Inhibition of Rho or ROCK enhanced protrusion, yet markedly inhibited cell motility; these changes correlated with a marked activation of Rac-1 at the cell edge. Surprisingly, whereas EGF-stimulated protrusion in control MTLn3 cells is Rac-independent and Cdc42-dependent, the opposite pattern is observed in MTLn3 cells after inhibition of ROCK. Thus, Rho and ROCK suppress Rac-1 activation at the leading edge, and inhibition of ROCK causes a switch between Cdc42 and Rac-1 as the dominant Rho GTPase driving protrusion in carcinoma cells. These data describe a novel role for Rho in coordinating signaling by Rac and Cdc42

Childhood brain tumors: A review of strategies to translate CNS drug delivery to clinical trials

Brain tumors account for over 20% of childhood cancers and are the biggest cancer killer in children and young adults. Several initiatives over the past 40 years have tried to identify more effective drug treatments, but with very limited success. This is largely due to the bloodâ brain barrier, which restricts the entry of many drugs into the brain. In this review, we describe the main techniques that are being developed to enhance brain tumor drug delivery and explore the preclinical brain tumor models that are essential for translational development of these techniques. We also identify existing approved drugs that, if coupled with an efficient delivery method, could have potential as brain tumor treatments. Bringing this information together is part of a funded initiative to highlight drug delivery as a research strategy to overcome the current challenges for children diagnosed with brain tumors

Impact of the 2002 Canadian Forest Fires on Particulate Matter Air Quality in Baltimore City

With increasing evidence of adverse health effects associated with particulate matter (PM), the exposure impact of natural sources, such as forest fires, has substantial public health relevance. In addition to the threat to nearby communities, pollutants released from forest fires can travel thousands of kilometers to heavily populated urban areas. There was a dramatic increase in forest fire activity in the province of Quebec, Canada, during July 2002. The transport of PM released from these forest fires was examined using a combination of a moderateresolution imaging spectroradiometer satellite image, backtrajectories using a hybrid single-particle Lagrangian integrated trajectory, and local light detection and ranging measurements. Time- and size-resolved PM was evaluated at three ambient and four indoor measurement sites using a combination of direct reading instruments (laser, timeof- flight aerosol spectrometer, nephelometer, and an oscillating microbalance). The transport and monitoring results consistently identified a forest fire relatedPMepisode in Baltimore that occurred the first weekend of July 2002 and resulted in as much as a 30-fold increase in ambient fine PM. On the basis of tapered element oscillating microbalance measurements, the 24 h PM2.5 concentration reached 86 μg/m3 on July 7, 2002, exceeding the 24 h national ambient air quality standard. The episode was primarily comprised of particles less than 2.5 μm in aerodynamic diameter, highlighting the preferential transport of the fraction of PM that is of greatest health concern. Penetration of the ambient episode indoors was efficient (median indoor-to-outdoor ratio 0.91) such that the high ambient levels were similarly experienced indoors. These results are significant in demonstrating the impact of a natural source thousands of kilometers away on ambient levels of and potential exposures to air pollution within an urban center. This research highlights the significance of transboundary air pollution and the need for studies that assess the public health impacts associated with such sources and transport processes

The regulation of RhoA at focal adhesions by StarD13 is important for astrocytoma cell motility

Malignant astrocytomas are highly invasive into adjacent and distant regions of the normal brain. Rho GTPases are small monomeric G proteins that play important roles in cytoskeleton rearrangement, cell motility, and tumor invasion. In the present study, we show that the knock down of StarD13, a GTPase activating protein (GAP) for RhoA and Cdc42, inhibits astrocytoma cell migration through modulating focal adhesion dynamics and cell adhesion. This effect is mediated by the resulting constitutive activation of RhoA and the subsequent indirect inhibition of Rac. Using Total Internal Reflection Fluorescence (TIRF)-based Förster Resonance Energy Transfer (FRET), we show that RhoA activity localizes with focal adhesions at the basal surface of astrocytoma cells. Moreover, the knock down of StarD13 inhibits the cycling of RhoA activation at the rear edge of cells, which makes them defective in retracting their tail. This study highlights the importance of the regulation of RhoA activity in focal adhesions of astrocytoma cells and establishes StarD13 as a GAP playing a major role in this process