Quantifying the Pressure-dependence of Work of Adhesion in Silicon-Diamond Contacts

Continuum mechanics models for contacting surfaces assume a constant interfacial energy, or work of adhesion, between materials. Recent studies have challenged this assumption, instead demonstrating that stress-dependent chemical reactions across the interface modify the work of adhesion. Here, we perform 77 adhesion tests on diamond-silicon contacts using in situ TEM and atomistic simulations to quantify how the adhesion changes as a function of applied pressure. The results show a 7-fold increase in work of adhesion (from approximately 1 to 7 J/m2) with an increase in mean applied pressure from 0 to 11 GPa, where the most significant increase occurs above 5 GPa. We rule out alternative explanations for the changing work of adhesion, such as electron-beam artifacts, bulk shape change by inelastic deformation, and time-dependent processes such as creep. Therefore, these results confirm the presence of stress-driven chemical reactions in the contact and quantify the resulting change in adhesion of these materials with applied pressure

The CT20 peptide causes detachment and death of metastatic breast cancer cells by promoting mitochondrial aggregation and cytoskeletal disruption

Metastasis accounts for most deaths from breast cancer, driving the need for new therapeutics that can impede disease progression. Rationally designed peptides that take advantage of cancer-specific differences in cellular physiology are an emerging technology that offer promise as a treatment for metastatic breast cancer. We developed CT20p, a hydrophobic peptide based on the C terminus of Bax that exhibits similarities with antimicrobial peptides, and previously reported that CT20p has unique cytotoxic actions independent of full-length Bax. In this study, we identified the intracellular actions of CT20p which precede cancer cell-specific detachment and death. Previously, we found that CT20p migrated in the heavy membrane fractions of cancer cell lysates. Here, using MDA-MB-231 breast cancer cells, we demonstrated that CT20p localizes to the mitochondria, leading to fusion-like aggregation and mitochondrial membrane hyperpolarization. As a result, the distribution and movement of mitochondria in CT20p-treated MDA-MB-231 cells was markedly impaired, particularly in cell protrusions. In contrast, CT20p did not associate with the mitochondria of normal breast epithelial MCF-10A cells, causing little change in the mitochondrial membrane potential, morphology or localization. In MDA-MB-231 cells, CT20p triggered cell detachment that was preceded by decreased levels of alpha 5 beta 1 integrins and reduced F-actin polymerization. Using folate-targeted nanoparticles to encapsulate and deliver CT20p to murine tumors, we achieved significant tumor regression within days of peptide treatment. These results suggest that CT20p has application in the treatment of metastatic disease as a cancer-specific therapeutic peptide that perturbs mitochondrial morphology and movement ultimately culminating in disruption of the actin cytoskeleton, cell detachment, and loss of cell viability

Matching atomistic simulations and in situ experiments to investigate the mechanics of nanoscale contact

Many emerging devices and technologies rely on contacts between nanoscale bodies. Recent analytical theories, experiments, and simulations of nanocontacts have made conflicting predictions about the mechanical response as these contacts are loaded and separated. The present investigation combined in situ transmission electron microscopy (TEM) and molecular dynamics (MD) simulation to study the contact between a flat diamond indenter and a nanoscale silicon tip. The TEM was used to pre-characterize the materials, such that an atomistic model tip could be created with identically matched materials, geometry, crystallographic orientation, loading conditions, and degree of amorphization. A large work of adhesion was measured in the experiment and attributed to unpassivated surfaces and a large compressive stress applied before separation, resulting in covalent bonding across the interface. The simulations modeled atomic interactions across the interface using a Buckingham potential in order to reproduce the experimental work of adhesion without explicitly modeling covalent bonds, thereby enabling larger time- and length-scale simulations than would be achievable with a reactive potential. Then, the experimental and simulation tips were loaded under similar conditions with real-time measurement of contact area and deformation, yielding three primary findings. First, the results demonstrated that significant variation in the value of contact area can be obtained from simulations, depending on the technique used to determine it. Therefore, care is required in comparing measured values of contact area between simulations and experiments. Second, the contact area and deformation demonstrated significant hysteresis, with larger values measured upon unloading as compared to loading. Therefore, continuum predictions, in the form of a Maugis-Dugdale contact model, could not be fit to full loading/unloading curves. Third, the load-dependent contact area could be accurately fit by allowing the work of adhesion in the continuum model to increase with applied force from 1.3 to 4.3 J/m^2. The most common mechanisms for hysteretic behavior—which are viscoelasticity, capillary interactions, and plasticity—can be ruled out using the TEM and atomistic characterization. Stress-dependent formation of covalent bonds is suggested as a physical mechanism to describe these findings, which is qualitatively consistent with trends in the areal density of in-contact atoms as measured in the simulation. The implications of these results for real-world nanoscale contacts are that significant hysteresis may cause significant and unexpected deviations in contact size, even for nominally elastic contact

β-Adrenergic Inhibition of Contractility in L6 Skeletal Muscle Cells

The β-adrenoceptors (β-ARs) control many cellular processes. Here, we show that β-ARs inhibit calcium depletion-induced cell contractility and subsequent cell detachment of L6 skeletal muscle cells. The mechanism underlying the cell detachment inhibition was studied by using a quantitative cell detachment assay. We demonstrate that cell detachment induced by depletion of extracellular calcium is due to myosin- and ROCK-dependent contractility. The β-AR inhibition of L6 skeletal muscle cell detachment was shown to be mediated by the β2-AR and increased cAMP but was surprisingly not dependent on the classical downstream effectors PKA or Epac, nor was it dependent on PKG, PI3K or PKC. However, inhibition of potassium channels blocks the β2-AR mediated effects. Furthermore, activation of potassium channels fully mimicked the results of β2-AR activation. In conclusion, we present a novel finding that β2-AR signaling inhibits contractility and thus cell detachment in L6 skeletal muscle cells by a cAMP and potassium channel dependent mechanism

Hypoxia-Induced Invadopodia Formation Involves Activation of NHE-1 by the p90 Ribosomal S6 Kinase (p90RSK)

The hypoxic and acidic microenvironments in tumors are strongly associated with malignant progression and metastasis, and have thus become a central issue in tumor physiology and cancer treatment. Despite this, the molecular links between acidic pH- and hypoxia-mediated cell invasion/metastasis remain mostly unresolved. One of the mechanisms that tumor cells use for tissue invasion is the generation of invadopodia, which are actin-rich invasive plasma membrane protrusions that degrade the extracellular matrix. Here, we show that hypoxia stimulates the formation of invadopodia as well as the invasive ability of cancer cells. Inhibition or shRNA-based depletion of the Na+/H+ exchanger NHE-1, along with intracellular pH monitoring by live-cell imaging, revealed that invadopodia formation is associated with alterations in cellular pH homeostasis, an event that involves activation of the Na+/H+ exchange rate by NHE-1. Further characterization indicates that hypoxia triggered the activation of the p90 ribosomal S6 kinase (p90 RSK), which resulted in invadopodia formation and site-specific phosphorylation and activation of NHE-1. This study reveals an unsuspected role of p90RSK in tumor cell invasion and establishes p90RS kinase as a link between hypoxia and the acidic microenvironment of tumors

Transcriptome Dataset

Transcriptome data in pancreatic tissues with Chronic Pancreatitis (CP; n=3) , Pancreatic ductal adenocarcinoma with a background of CP (PDAC-CP; n=4) and Pancreatic ductal adenocarcinoma (PDAC; n=2) and controls (Con; n=3) were generated to understand and identify markers that have a role in the early neoplastic transformation of chronic pancreatitisTHIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

The Use Of Therapeutic Peptides To Target And To Kill Cancer Cells

Peptide therapeutics is a promising field for emerging anti-cancer agents. Benefits include the ease and rapid synthesis of peptides and capacity for modifications. An existing and vast knowledge base of protein structure and function can be exploited for novel peptide design. Current research focuses on developing peptides that can (1) serve as tumor targeting moieties and (2) permeabilize membranes with cytotoxic consequences. A survey of recent findings reveals significant trends. Amphiphilic peptides with clusters of hydrophobic and cationic residues are features of anti-microbial peptides that confer the ability to eradicate microbes and show considerable anti-cancer toxicity. Peptides that assemble and form pores can disrupt cell or organelle membranes and cause apoptotic or necrotic death. Cell permeable and tumor-homing peptides can carry biologically active cargo to tumors or tumor vasculature. The challenge lies in developing the clinical application of therapeutic peptides. Improving delivery to tumors, minimizing non-specific toxic effects and discerning pharmacokinetic properties are high among the needs to produce a powerful therapeutic peptide for cancer treatment. © 2012 Bentham Science Publishers