Unraveling the distinct distributions of VE- and N-cadherins in endothelial cells: A key role for p120-catenin

Endothelial cells express two different classical cadherins, vascular endothelial (VE) cadherin and neural (N) cadherin, having distinct functions in the vascular system. VE-cadherin is specific to endothelial adherens junctions and is strictly necessary for vascular morphogenesis. On the contrary, N-cadherin shows diffuse localization on the cell surface and interacts with mural cells for vessel stabilization. In this study, we sought to clarify the cellular mechanisms leading to the distinct cellular locations and functions of the two cadherins in the endothelium. VE-cadherin has been shown to be responsible for the junctional exclusion of N-cadherin. Using several endothelial models, we demonstrate that this property is dependent on VE-cadherin binding to p120 catenin (p120^ctn). Moreover, although in the absence of VE-cadherin N-cadherin can localize to cell contacts, angiogenesis remains impaired, demonstrating that endothelial junction formation is not sufficient for normal vessel development. Interestingly, we show that VE-cadherin, but not N-cadherin, is partially associated with cholesterol-enriched microdomains. Lipid raft-associated-VE-cadherin is characterized by a very high level of p120^ctn association, and this association is necessary for VE-cadherin recruitment into lipid rafts. Altogether, our results indicate a critical role for p120^ctn in regulating the membrane distribution of endothelial cadherins with functional consequences in terms of cadherin stabilization and intracellular signaling.     

Protein tyrosine phosphatase-1B and T-cell protein tyrosine phosphatase regulate IGF-2-induced MCF-7 cell migration

The protein tyrosine phosphatase-1B (PTP1B) and the T-cell protein tyrosine phosphatase (TC-PTP) have been implicated in down-regulation of tyrosine kinase receptors, conferring anti-oncogenic functions to these PTPases. However, recent work has shown that PTP1B is positively implicated in oncogenic properties of breast cancer cells by regulating the ERK pathway. Here, we studied the function of PTP1B and TC-PTP in IGF-2-induced growth, survival and migration of MCF-7 breast cancer cells. Using siRNA, we showed that reduction in the expression of these PTPases decreased cell growth and ERK phosphorylation. Reduction in the expression of these PTPases did not impair IGF-2 effects on cell survival to acute treatment with 4-OH Tamoxifen. In contrast, IGF-2-induced MCF-7 cell migration was markedly impaired by reduction of PTP1B or TC-PTP expression, independently of the ERK pathway. This novel finding reinforces the potential role of these PTPases as therapeutic targets for treatment of breast cancer.     

Bias‐Corrected Diagonal Discriminant Rules for High‐Dimensional Classification

Summary Diagonal discriminant rules have been successfully used for high‐dimensional classification problems, but suffer from the serious drawback of biased discriminant scores. In this article, we propose improved diagonal discriminant rules with bias‐corrected discriminant scores for high‐dimensional classification. We show that the proposed discriminant scores dominate the standard ones under the quadratic loss function. Analytical results on why the bias‐corrected rules can potentially improve the predication accuracy are also provided. Finally, we demonstrate the improvement of the proposed rules over the original ones through extensive simulation studies and real case studies.     

Chloride intracellular channel 1 (CLIC1): Sensor and effector during oxidative stress

Oxidative stress, characterized by overproduction of reactive oxygen species (ROS), is a major feature of several pathological states. Indeed, many cancers and neurodegenerative diseases are accompanied by altered redox balance, which results from dysregulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In this review, we consider the role of the intracellular chloride channel 1 (CLIC1) in microglial cells during oxidative stress. Following microglial activation, CLIC1 translocates from the cytosol to the plasma membrane where it promotes a chloride conductance. The resultant anionic current balances the excess charge extruded by the active NADPH oxidase, supporting the generation of superoxide by the enzyme. In this scenario, CLIC1 could be considered to act as both a second messenger and an executor.     

Methods to Reduce Avian Bycatch in Small Mammal Studies Using Snap Traps

ABSTRACT Avian bycatch, a common and undesired occurrence in small mammal studies, should be minimized by researchers. We examined effects of trap covering, treadle color (copper or yellow plastic), trap size (mouse or rat), and trap weathering (traps <1 yr or ≥ 1 yr old) on avian bycatch during 3 years. We found that covered traps caught 81% fewer birds and 70% fewer small mammals than did uncovered traps, that mouse traps caught 30% more birds and 38% more small mammals than did rat traps, and no capture differences for treadle color or trap weathering. Covered traps effectively reduced avian bycatch and should be used when reduced small-mammal capture rates are acceptable.     

Structure of the Small Outer Capsid Protein, Soc: A Clamp for Stabilizing Capsids of T4-like Phages

Many viruses need to stabilize their capsid structure against DNA pressure and for survival in hostile environments. The 9-kDa outer capsid protein (Soc) of bacteriophage T4, which stabilizes the virus, attaches to the capsid during the final stage of maturation. There are 870 Soc molecules that act as a “glue” between neighboring hexameric capsomers, forming a “cage” that stabilizes the T4 capsid against extremes of pH and temperature. Here we report a 1.9 Å resolution crystal structure of Soc from the bacteriophage RB69, a close relative of T4. The RB69 crystal structure and a homology model of T4 Soc were fitted into the cryoelectron microscopy reconstruction of the T4 capsid. This established the region of Soc that interacts with the major capsid protein and suggested a mechanism, verified by extensive mutational and biochemical studies, for stabilization of the capsid in which the Soc trimers act as clamps between neighboring capsomers. The results demonstrate the factors involved in stabilizing not only the capsids of T4-like bacteriophages but also many other virus capsids.     

At the foot of the shrew: manus morphology distinguishes closely‐related Cryptotis goodwini and Cryptotis griseoventris (Mammalia: Soricidae) in Central America

Small‐eared shrews (Mammalia, Soricidae) of the New World genus Cryptotis are distributed from eastern North America to the northern Andes of South America. One well‐defined clade in this genus is the Central American Cryptotis mexicana group, whose members are set off from other species in the genus by their variably broader fore feet and more elongate and broadened fore claws. Two species in the C. mexicana group, Cryptotis goodwini Jackson and Cryptotis griseoventris Jackson, inhabit highlands in Guatemala and southern Mexico and are presumed to be sister species whose primary distinguishing feature is the larger body size of C. goodwini. To better characterize these species and confirm the identification of recently‐collected specimens, we obtained digital X‐ray images of the manus from large series of dried skins of both species. Measurements of the metacarpals and phalanges successfully separated most specimens of C. goodwini and C. griseoventris. These measurements also show that the fore feet of C. griseoventris from Chiapas, Mexico, are morphologically distinct from those of members of the species inhabiting Guatemala. Univariate, bivariate, and multivariate analyses indicate that fore foot characters are more conservative within species of the C. mexicana group than are cranio‐mandibular characters. Patterns of evolution of fore foot characters that superficially appear to be linear gradations are actually more complex, illustrating individual evolutionary trajectories. No claim to original US government works. Journal compilation © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 118–134.     

Genetic analysis of Ras signalling pathways in cell proliferation,migration and survival

We have used mouse embryonic fibroblasts (MEFs) devoid of Ras proteins to illustrate that they are essential for proliferation and migration, but not for survival, at least in these cells. These properties are unique to the Ras subfamily of proteins because ectopic expression of other Ras‐like small GTPases, even when constitutively active, could not compensate for the absence of Ras proteins. Only constitutive activation of components of the Raf/Mek/Erk pathway was sufficient to sustain normal proliferation and migration of MEFs devoid of Ras proteins. Activation of the phosphatidylinositol 3‐kinase (PI3K)/PTEN/Akt and Ral guanine exchange factor (RalGEF)/Ral pathways, either alone or in combination, failed to induce proliferation or migration of Rasless cells, although they cooperated with Raf/Mek/Erk signalling to reproduce the full response mediated by Ras signalling. In contrast to current hypotheses, Ras signalling did not induce proliferation by inducing expression of D‐type Cyclins. Rasless MEFs had normal levels of Cyclin D1/Cdk4 and Cyclin E/Cdk2. However, these complexes were inactive. Inactivation of the pocket proteins or knock down of pRb relieved MEFs from their dependence on Ras signalling to proliferate.     

Newly formed E‐cadherin contacts do not activate Cdc42 or induce filopodia protrusion in human keratinocytes1

Background information. The appropriate regulation of cell–cell adhesion is an important event in the homoeostasis of different cell types. In epithelial cells, tight adhesion mediated by E‐cadherin receptors is essential for the differentiation and functionality of epithelial sheets. Upon assembly of cadherin‐mediated cell–cell contacts, it is well established that the small GTPases Rho and Rac are activated and are necessary for junction stability. However, the role of the small GTPase Cdc42 in cadherin adhesion is less clear. Cdc42 can be activated by E‐cadherin in a breast tumour cell line, but the requirement for Cdc42 function for new junction assembly or maintenance has been contradictory. Cdc42 participation in cell–cell contacts has been inferred from the presence of filopodia, the typical F‐actin structure induced by Cdc42 activation, as cells approach each other to establish cell–cell contacts. Yet, under these conditions, the contribution of migration to filopodia protrusion cannot be excluded and the results are difficult to interpret. Results. In the present study, we set out to address (a) whether Cdc42 is activated by new E‐cadherin cell–cell contacts when junction assembly occurs without prior migration and (b) whether Cdc42 function is necessary for cadherin stability. We found that junction formation in confluent keratinocytes or upon E‐cadherin clustering decreased Cdc42‐GTP levels. In the absence of serum‐ and migration‐induced Cdc42 activation, we demonstrated that cell–cell contacts do not induce filopodia or require Cdc42 function to assemble. Conclusion. We conclude that Cdc42 does not participate in the early events that initiate stable cadherin adhesion in keratinocytes. Yet, it is feasible that Cdc42 may be activated at later time points or by other receptors. Cdc42 can then participate in additional functions during polarization, such as Golgi re‐positioning or basolateral trafficking.