Non-redundant role of Shc in Erk activation by cytoskeletal reorganization

We have shown previously that cytoskeletal reorganization (CSR) induced by pharmacological reagents such as colchicine or cytochalasins can up-regulate the urokinase-type plasminogen activator (uPA) gene via the Ras/Erk signaling pathway. In this present study using the small interfering RNA technique, we have found that ShcA adapter proteins play a rather active role in CSR-induced Erk activation, contrary to their mostly redundant role in other signaling pathways, e.g. growth factor-induced Erk activation, where Grb2 can bind directly to the receptor tyrosine kinase and activate Erk in the absence of ShcA. ShcA knockdown abolished CSR-induced activation of both Erk and the uPA promoter. Expression of small interfering RNA-escaping silent mutants of p52 or p46 but not p66 ShcA isoform efficiently rescued CSR-induced Erk activation. Moreover, we have shown that phosphorylation of either Tyr-239/Tyr-240 or Tyr-313 in p52(ShcA) can mediate CSR-induced Erk activation equally well. In a quest for molecules upstream of ShcA in this signaling, we found that CSR-induced ShcA tyrosine phosphorylation, its association with Grb2, Erk activation, and uPA gene expression were all dependent on Rho kinase, p38 mitogen-activated protein kinase, and Src. In summary, we have found a novel, non-redundant role for ShcA in contrast to its redundant role in many other signaling pathways.     

Proteolytic shedding of the extracellular domain of photoreceptor cadherin. Implications for outer segment assembly

Photoreceptor cadherin (prCAD) is a distinctive cadherin family member that is concentrated at the base of rod and cone outer segments and is required for their structural integrity. During retinal development, prCAD localizes to the site of the future outer segment before rhodopsin or other phototransduction proteins. In vivo, prCAD undergoes a single proteolytic cleavage that releases the ectodomain as a soluble fragment. The C-terminal fragment containing the transmembrane and cytosolic domains remains associated with the outer segment. In rds(-/-) retinas, in which outer segment assembly is severely disrupted because of the absence of retinal degeneration slow (RDS)/peripherin, an essential outer segment structural protein, the level of prCAD is increased, whereas the levels of other outer segment proteins are decreased relative to wild type retinas. Additionally, the ratio of intact:cleaved prCAD polypeptides is increased in rds(-/-) retinas. These data imply that prCAD ectodomain cleavage is an integral part of the outer segment assembly process, and they further suggest that outer segment assembly might be driven, at least in part, by the near irreversibility of proteolysis.     

Enhancement of Cry19Aa mosquitocidal activity against Aedes aegypti by mutations in the putative loop regions of domain II

Improvements in the mosquitocidal activity of Bacillus thuringiensis Cry19Aa were achieved by protein engineering of putative surface loop residues in domain II through rational design. The improvement of Aedes toxicity in Cry19Aa was 42,000-fold and did not affect its toxicity against Anopheles or Culex.     

Make love to forget: two cases of transient global amnesia triggered by sexual intercourse

Transient global amnesia (TGA) is characterized by a sudden onset and by a typical resolution within several hours. Several precipitating events have been proposed: physical exertion, emotional experiences, etc. The aim of this paper was to present two cases of TGA triggered by sexual intercourse and to suggest a possible mechanism for the development of TGA. In both patients, clinical examination revealed elevated blood pressure. Laboratory examinations and brain CTs were normal. EEG demonstrated diffuse dysrhythmia and slow spike-waves, respectively. SPECT revealed hypoperfusion in the left frontal and right medial temporal regions. Various explanations of the mechanism of TGA are discussed. Based on the observed hypoperfusion in the medial temporal regions, a new hypothesis is advanced, suggesting the possibility that TGA occurs due to a pathologically changed or less adaptable anterior chorioid artery, initially constricted by hypotension following a blood shift from the center towards periphery.     

Role of caveolae in ouabain-induced proliferation of cultured vascular smooth muscle cells of the synthetic phenotype

We have shown earlier that low concentrations of ouabain that do not perturb the ionic milieu can initiate proliferation of vascular smooth muscle cells (VSMCs) in the synthetic phenotype from three different species: canine, rodent, and human. This effect occurs by activation of Src and the epidermal growth factor receptor (EGFR), and thus supports the concept of an additional, nonionic, transducing function of the Na pump. The present study presents data suggesting that such activation occurs through specific Na pump sites localized to the caveolae, and subsequent interactions with selected signaling proteins resident within the same membrane microdomain. Our data show that at rest, 30% of the total number of Na pumps are concentrated within the caveolae. When the various VSMCs were treated with proliferating concentrations of ouabain, the key protein content in isolated caveolae was increased. However, the recruited proteins were different between the different tissues. Thus ouabain activated the recruitment of both the Na pump alpha1-subunit and EGFR in the caveolae from rat A7r5 cells, whereas in both human and canine cells, ouabain activated the recruitment of Src, with the caveolar content of the other proteins remaining constant. These data demonstrate that ouabain interacts with the alpha1-subunit of the Na pump that resides within the caveolar domain, and such interaction selectively recruits signal transducing proteins to this microdomain resulting in their activation, which is necessary for the initiation of the proliferative cascade.     

Modulation of the vascular response to injury by autologous blood-derived outgrowth endothelial cells

Delivery of a heterogeneous population of cells with endothelial phenotype derived from peripheral blood has been shown to improve vascular responses after balloon arterial injury in an endothelium-dependent manner. Refinement of culture techniques has enabled the generation of outgrowth endothelial cells (OECs), a homogeneous population of distinctly endothelial cells expanded from circulating progenitor cells. The present study tested the hypothesis that OEC delivery would confer vascular protection after balloon arterial injury in a rabbit model. Rabbit peripheral blood mononuclear cells (PBMCs) were cultured in endothelial growth medium for 4-5 wk, yielding proliferative OECs with distinct endothelial phenotype (morphology, incorporation of acetylated LDL, and expression of endothelial nitric oxide synthase and caveolin-1 but not CD14). Animals underwent balloon carotid injury immediately followed by local delivery of autologous OECs for 20 min. Fluorescent-labeled OECs were detected in all layers at 4 wk, with immunostaining revealing maintenance of endothelial phenotype (von Willebrand factor-positive and RAM-11-negative) by luminal and nonluminal cells. To evaluate functional effects, additional animals received autologous OECs, saline, or freshly harvested PBMCs as noncultured cell controls by local dwell after balloon injury. Local OEC delivery improved endothelium-dependent vasoreactivity (P < 0.05 vs. saline and PBMC) and similarly reduced neointimal formation (P < 0.05 vs. saline and PBMC). These data suggest that OECs can be detected in injured arterial segments at 4 wk. Moreover, delivery of OECs confers greater vascular protection than PBMCs or saline controls and may thus offer a novel, autologous strategy to limit the response to mechanical injury.     

Fast collapse but slow formation of secondary structure elements in the refolding transition of E. coli adenylate kinase

The various models proposed for protein folding transition differ in their order of appearance of the basic steps during this process. In this study, steady state and time-resolved dynamic non-radiative excitation energy transfer (FRET and trFRET) combined with site specific labeling experiments were applied in order to characterize the initial transient ensemble of Escherichia coli adenylate kinase (AK) molecules upon shifting conditions from those favoring denaturation to refolding and from folding to denaturing. Three sets of labeled AK mutants were prepared, which were designed to probe the equilibrium and transient distributions of intramolecular segmental end-to-end distances. A 176 residue section (residues 28-203), which spans most of the 214 residue molecule, and two short secondary structure chain segments including an alpha-helix (residues 169-188) and a predominantly beta-strand region (residues 188-203), were labeled. Upon fast change of conditions from denaturing to folding, the end-to-end distance of the 176 residue chain section showed an immediate collapse to a mean value of 26 A. Under the same conditions, the two short secondary structure elements did not respond to this shift within the first ten milliseconds, and retained the characteristics of a fully unfolded state. Within the first 10 ms after changes of the solvent from folding to denaturing, only minor changes were observed at the local environments of residues 203 and 169. The response of these same local environments to the shift of conditions from denaturing to folding occurred within the dead time of the mixing device. Thus, the response of the CORE domain of AK to fast transfer from folding to unfolding conditions is slow at all three conformational levels that were probed, and for at least a few milliseconds the ensemble of folded molecules is maintained under unfolding conditions. A different order of the changes was observed upon initiation of refolding. The AK molecules undergo fast collapse to an ensemble of compact structures where the local environment of surface probes seems to be native-like but the two labeled secondary structure elements remain unfolded.     

Directed evolution of proteins for heterologous expression and stability

Recent developments have been made in the application of directed evolution to achieve the efficient heterologous expression of proteins in Escherichia coli and yeast by increasing the stability and solubility of the protein in the host environment. One interesting conclusion that emerges is that the evolutionary process often improves the stability and solubility of an intermediate (apoprotein, proprotein or folding intermediate) that otherwise constitutes a bottleneck to functional expression, rather than altering the protein's final state.