Roles moleculaires des proteines de choc thermique dans le fonctionnement des organismes a des temperatures normales et suite a des chocs thermiques; differents genes impliques

The heat-shock proteins

In the cell, as in vitro, the final conformation of a protein is determined by its amino-acid sequence. But whereas some isolated proteins can be denatured and refolded in vitro in the absence of other macromolecular cellular components, folding and assembly of polypeptides in vivo involves other proteins, many of which belong to families that have been highly conserved during evolution.

Protein folding in the cell.

Interferons play key roles in mediating antiviral and antigrowth responses and in modulating immune response. The main signaling pathways are rapid and direct. They involve tyrosine phosphorylation and activation of signal transducers and activators of transcription factors by Janus tyrosine kinases at the cell membrane, followed by release of signal transducers and activators of transcription and their migration to the nucleus, where they induce the expression of the many gene products that determine the responses. Ancillary pathways are also activated by the interferons, but their effects on cell physiology are less clear. The Janus kinases and signal transducers and activators of transcription, and many of the interferon-induced proteins, play important alternative roles in cells, raising interesting questions as to how the responses to the interferons intersect with more general aspects of cellular physiology and how the specificity of cytokine responses is maintained.

http://www3.uah.es/farmamol/Public/AnnReviews/PDF/Biochemistry/Interferons.pdf

How cells respond to interferons

The plasma membrane is the interface between cells and their harsh environment. Uptake of nutrients and all communication among cells and between cells and their environment occurs through this interface. 'Endocytosis' encompasses several diverse mechanisms by which cells internalize macromolecules and particles into transport vesicles derived from the plasma membrane. It controls entry into the cell and has a crucial role in development, the immune response, neurotransmission, intercellular communication, signal transduction, and cellular and organismal homeostasis. As the complexity of molecular interactions governing endocytosis are revealed, it has become increasingly clear that it is tightly coordinated and coupled with overall cell physiology and thus, must be viewed in a broader context than simple vesicular trafficking.

Regulated portals of entry into the cell

Engineered nanoparticles have the potential to revolutionize the diagnosis and treatment of many diseases; for example, by allowing the targeted delivery of a drug to particular subsets of cells. However, so far, such nanoparticles have not proved capable of surmounting all of the biological barriers required to achieve this goal. Nevertheless, advances in nanoparticle engineering, as well as advances in understanding the importance of nanoparticle characteristics such as size, shape and surface properties for biological interactions, are creating new opportunities for the development of nanoparticles for therapeutic applications. This Review focuses on recent progress important for the rational design of such nanoparticles and discusses the challenges to realizing the potential of nanoparticles.

Strategies in the design of nanoparticles for therapeutic applications

Since its inception, electron microscopy (EM) has revealed that cellular membranes are organized into structurally distinct subdomains, created by localized protein and lipid assemblies to perform specific complex cellular functions. Caveolae are membrane subdomains that function as signaling platforms, endocytic carriers, sensors of membrane tension, and mechanical stress, as well as in lipid homeostasis. They were first discovered almost 60 years ago by pioneering electron microscopists. While new and exciting developments in SUPER-resolution fluorescent light microscopy facilitate studies of the spatial organization of fluorescently labeled protein components, these techniques cannot reveal the underlying cellular structures. Thus, equally exciting are developments in EM: genetically encoded probes for protein localization at sub-10 nm resolution, more powerful instruments that allow imaging of larger cell volumes, and computational methods for reconstructing three-dimensional images. Used in combination, as done by Ludwig et al. in the current issue of PLOS Biology, these tools reveal high-resolution insights into the composition and organization of the caveolae coat and the formation of these specialized structures. Together, these advances are contributing to a resurgence in EM.

/pdf/integrated-electron-microscopy-super-duper-resolution-4y1v2mch17.pdf

Integrated Electron Microscopy: Super-Duper Resolution

Domain Structure and Function of Dynamin Probed by Limited Proteolysis

Whereas clathrin-mediated endocytosis (CME) exists in all eukaryotic cells, we first detect classical dynamin in Ichthyosporid, a single-cell, metazoan precursor. Based on a key functional residue in its pleckstrin homology domain, we speculate that the evolution of metazoan dynamin coincided with the specialized need for regulated CME during neurotransmission.

The evolution of dynamin to regulate clathrin-mediated endocytosis: speculations on the evolutionarily late appearance of dynamin relative to clathrin-mediated endocytosis.

Multiple mechanisms contribute to cancer cell progression and metastatic activity, including changes in endocytic trafficking and signaling of cell surface receptors downstream of gain-of-function (GOF) mutant p53. We report that dynamin-1 (Dyn1) is up-regulated at both the mRNA and protein levels in a manner dependent on expression of GOF mutant p53. Dyn1 is required for the recruitment and accumulation of the signaling scaffold, APPL1, to a spatially localized subpopulation of endosomes at the cell perimeter. We developed new tools to quantify peripherally localized early endosomes and measure the rapid recycling of integrins. We report that these perimeter APPL1 endosomes modulate Akt signaling and activate Dyn1 to create a positive feedback loop required for rapid recycling of EGFR and β1 integrins, increased focal adhesion turnover, and cell migration. Thus, Dyn1- and Akt-dependent perimeter APPL1 endosomes function as a nexus that integrates signaling and receptor trafficking, which can be co-opted and amplified in mutant p53–driven cancer cells to increase migration and invasion.

/pdf/mutant-p53-amplifies-a-dynamin-1-appl1-endosome-feedback-1mwn0xh40r.pdf

Mutant p53 amplifies a dynamin-1/APPL1 endosome feedback loop that regulates recycling and migration.

I'm a detail-oriented person, a watchmaker. I like to take things apart, put them back together, and understand exactly how they work. For most of the past 30 years, I have focused (some might say fixated) my attention on clathrin-coated vesicles (CCVs) and clathrin-mediated endocytosis (CME). CME, a major endocytic pathway, is involved in the ubiquitous uptake of nutrient–receptor complexes, membrane transporters, adhesion molecules, and signaling receptors, as well as in the recycling of synaptic vesicles—all of which play central roles in human health and disease.

The role of coated vesicles in efficient endocytosis was first proposed in 1964 based on electron micrographs of yolk protein uptake in insect oocytes (Roth and Porter, 1964 ). CME involves the assembly of clathrin coats on the plasma membrane that concentrate receptors; invaginate; pinch off to form CCVs; and finally uncoat, releasing transport vesicles that fuse and deliver their contents to the endosomal system. To understand the mechanisms underlying CME, we and others have developed and used the now “classical” techniques of cell biology. These techniques include subcellular fractionation to purify coated vesicles (Pearse, 1975 ); biochemical fractionation coupled to proteomics to identify components of the CME machinery (Blondeau et al., 2004 ; Borner et al., 2006 ); and various cell free assays to reconstitute and mechanistically probe the uncoating reaction (Rothman and Schmid, 1986 ), CME (Smythe et al., 1992 ; Carter et al., 1993 ; Miwako and Schmid, 2005 ), and dynamin-catalyzed membrane fission (Pucadyil and Schmid, 2008 ). Consequently, during the almost 50 years since its discovery, we have learned a great deal about the molecular mechanisms underlying clathrin-mediated endocytosis (Conner and Schmid, 2003 ; Doherty and McMahon, 2009 ).



Sandra L. Schmid



In 1999, Jim Keen used the then newly developed green fluorescent protein (GFP) technology to tag the clathrin light chain and, for the first time, visualized CME in real time (Gaidarov et al., 1999 ). Subsequent imaging by total internal reflection fluorescence microscopy (which selectively illuminates an ∼100-nm-deep plane in the cytosol of adherent cells, thereby increasing signal-to-noise ratios) produced spectacular live-cell movies of CME. The GFP-clathrin appeared as small points of light that grew to varying intensities and then abruptly disappeared as the nascent CCVs quickly moved deeper into the cytosol and out of the zone of illumination (Merrifield et al., 2002 ). The dynamic clathrin-coated pits (CCPs) seen in these movies (see Supplemental Movie 1) are reminiscent of stars blinking in the night's sky—and they have opened up a universe of new questions that will need to be addressed over the next 50 years. Some (those of a watchmaker) reflect the need for further understanding of the molecular basis for CME, whereas others (those of a cosmologist) seek to integrate CME with the bigger picture of organismal physiology in development, health, and disease.

Sandra L. Schmid

Papers

Integrated Electron Microscopy: Super-Duper Resolution

Domain Structure and Function of Dynamin Probed by Limited Proteolysis

The evolution of dynamin to regulate clathrin-mediated endocytosis: speculations on the evolutionarily late appearance of dynamin relative to clathrin-mediated endocytosis.

Mutant p53 amplifies a dynamin-1/APPL1 endosome feedback loop that regulates recycling and migration.

Clathrin-mediated Endocytosis: A Universe of New Questions