Stress-induced Growth Research Articles

Cell growth control by stable Rbg2/Gir2 complex formation under amino acid starvation

The molecular fine-tuning mechanisms underlying adaptive responses to environmental stresses in eukaryotes remain largely unknown. Here, we report on a novel stress-induced cell growth control mechanism involving a highly conserved complex containing Rbg2 and Gir2 subunits, which are the budding yeast orthologs of human Drg2 and Dfrp2, respectively. We found that the complex is responsible for efficient cell growth under amino acid starvation. Using native PAGE analyses, we observed that, individually, Rbg2 and Gir2 were labile proteins. However, they formed a complex that stabilized each other, and this stability became significantly enhanced after amino acid starvation. We observed that the stabilization of the complex was strictly dependent on GDP or GTP binding to Rbg2. A point mutation (S77N) that inactivated nucleotide binding impaired formation of the complex and disrupted the stress-induced cell growth. Interestingly, the complex bound the translational activator Gcn1 in a dose-dependent manner according to the stress level, suggesting a dynamic association with the cellular translational machinery. We propose that the Rbg2/Gir2 complex is a modulator that maintains cellular homoeostasis, thus promoting the survival of eukaryotic organisms in stressful environments.

Overexpression of a pea DNA helicase (PDH45) in peanut (Arachis hypogaea L.) confers improvement of cellular level tolerance and productivity under drought stress.

Peanut, a major edible oil seed crop globally is predominantly grown under rainfed conditions and suffers yield losses due to drought. Development of drought-tolerant varieties through transgenic technology is a valid approach. Besides superior water relation traits like water mining, intrinsic cellular level tolerance mechanisms are important to sustain the growth under stress. To achieve this objective, the focus of this study was to pyramid drought adaptive traits by overexpressing a stress responsive helicase, PDH45 in the background of a genotype with superior water relations. PCR, Southern, and RT-PCR analyses confirmed stable integration and expression of the PDH45 gene in peanut transgenics. At the end of T₃ generation, eight transgenic events were identified as promising based on stress tolerance and improvement in productivity. Several transgenic lines showed stay-green phenotype and increased chlorophyll stability under stress and reduced chlorophyll retardation under etherel-induced simulated stress conditions. Stress-induced root growth was also substantially higher in the case of transformants. This was reflected in increased WUE (low Δ¹³C) and improved growth rates and productivity. The transgenics showed 17.2 and 26.75 % increase in yield under non-stress and stress conditions over wild type ascertaining the feasibility of trait pyramiding strategy for the development of drought-tolerant peanut.

Stress-induced growth of single-crystalline lead telluride nanowires and their thermoelectric transport properties

Uniform single-crystal lead telluride (PbTe) nanowires (NWs) were synthesized using a stress-induced method, which is an alternative technique for synthesizing PbTe NWs without a catalyst. The thermoelectrical transport measurement of a NW with a diameter of 217 nm exhibited a notable enhancement over the room-temperature thermopower of −342 μV K−1, which was approximately 95% larger than the bulk of PbTe. The power factor of 104 μW m−1 K−2 is also higher than any previously reported power factor in PbTe NWs.

Synthesis of Monolayer Graphene Having a Negligible Amount of Wrinkles by Stress Relaxation

For the chemical vapor deposition (CVD) of graphene, the grain growth of the catalyst metal and thereby surface roughening are unavoidable during the high temperature annealing for the graphene synthesis. Considering that nanoscale wrinkles and poor uniformity of synthesized graphene originate from the roughened metal surface, improving surface flatness of metal thin films is one of the key factors to synthesize high quality graphene. Here, we introduce a new method for graphene synthesis for fewer wrinkle formation on a catalyst metal. The method utilizes a reduced graphene oxide (rGO) interfacial layer between the metal film and the wafer substrate. The rGO interlayer releases the residual stress of the metal thin film and thereby suppresses stress-induced metal grain growth. This technique makes it possible to use much thinner nickel films, leading to a dramatic suppression of RMS roughness (~3 nm) of the metal surface even after high temperature annealing. It also endows excellent control of the graphene thickness due to the reduced amount of total carbon in the thin nickel film. The synthesized graphene layer having negligible amount of wrinkles exhibits excellent thickness uniformity (91% coverage of monolayer) and very high carrier mobility of ~15,000 cm(2)/V·s.

β2-AR-HIF-1α: A Novel Regulatory Axis for Stress-Induced Pancreatic Tumor Growth and Angiogenesis

The purpose of this study was to test the hypothesis that chronic stress in a negative social and psychological state plays a critical role in pancreatic cancer development and progression. In this study, we created a new stress model system to determine the effects of chronic stress on pancreatic cancer progression. Here, we show that chronic stress not only causes depression in mice, most likely attributed to an elevated level of epinephrine, but also induces pancreatic cancer progression. We provide evidence that the pancreatic cancer progression induced by chronic stress could be blocked to a significant degree by β2-AR inhibitor ICI118 551 or HIF-1α inhibitor 2-methoxyestradiol. Moreover, establishment of pancreatic cancer in mice exposed to chronic stress was accompanied by up-regulation of the expression of MMP-2, MMP-9, and VEGF, mediated by a HIF- 1α-dependent β-AR signaling pathway. Our data suggest that the β2-AR-HIF-1α axis regulates stress-induced pancreatic tumor growth and angiogenesis. This study may have a therapeutic or preventive potential for the patients with pancreatic cancer who are especially prone to psychosocial stress challenges.

Synthesis of Au microwires by selective oxidation of Au–W thin-film composition spreads

We report on the stress-induced growth of Au microwires out of a surrounding Au–W matrix by selective oxidation, in view of a possible application as ‘micro-Velcro’. The Au wires are extruded due to the high compressive stress in the tungsten oxide formed by oxidation of elemental W. The samples were fabricated as a thin-film materials library using combinatorial sputter deposition followed by thermal oxidation. Sizes and shapes of the Au microwires were investigated as a function of the W to Au ratio. The coherence length and stress state of the Au microwires were related to their shape and plastic deformation. Depending on the composition of the Au–W precursor, the oxidized samples showed regions with differently shaped Au microwires. The Au48W52 composition yielded wires with the maximum length to diameter ratio due to the high compressive stress in the tungsten oxide matrix. The values of wire length (35 μm) and diameter (2 μm) achieved at the Au48W52 composition are suitable for micro-Velcro applications.

Stress enhanced TiO 2 nanowire growth on Ti–6Al–4V particles by thermal oxidation

Abstract Titanium dioxide (TiO 2 ) nanowires were grown on Ti - 6wt% Al - 4wt% V (Ti64) particles by thermal oxidation. To investigate the effect of stress on nanowire growth, the particles were milled in a planetary ball mill prior to the thermal oxidation. Thermal oxidation of the Ti64 particles was carried out in a horizontal tube furnace in a controlled oxygen atmosphere in the temperature range of 700–900 °C. The oxygen concentration was varied from 20 ppm to 80 ppm in Ar atmosphere. Nanostructures were characterized by high resolution field emission scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. TiO 2 nanowires grew on the surface of Ti64 particles and exhibited a square/rectangular cross sectional shape with thicknesses of 20–40 nm and lengths of 2–3 μm. Residual stress was found to play a significant role in nanowire growth. This was confirmed by growing TiO 2 nanowires on Ti64 alloy sheet with an induced stress gradient along its length. An improvement in nanowire coverage was observed in regions of high residual stress. A stress-induced growth mechanism is suggested to explain the confinement of nanowire growth to one dimension during thermal oxidation.

A cortical folding model incorporating stress-dependent growth explains gyral wavelengths and stress patterns in the developing brain

In humans and many other mammals, the cortex (the outer layer of the brain) folds during development. The mechanics of folding are not well understood; leading explanations are either incomplete or at odds with physical measurements. We propose a mathematical model in which (i) folding is driven by tangential expansion of the cortex and (ii) deeper layers grow in response to the resulting stress. In this model the wavelength of cortical folds depends predictably on the rate of cortical growth relative to the rate of stress-induced growth. We show analytically and in simulations that faster cortical expansion leads to shorter gyral wavelengths; slower cortical expansion leads to long wavelengths or even smooth (lissencephalic) surfaces. No inner or outer (skull) constraint is needed to produce folding, but initial shape and mechanical heterogeneity influence the final shape. The proposed model predicts patterns of stress in the tissue that are consistent with experimental observations.

Inaccurately assembled cytochrome c oxidase can lead to oxidative stress-induced growth arrest.

To identify yeast mutants that show a strong redox dependence of the ability to respire, we systematically screened a yeast deletion library for mutants that require the presence of reductants for growth on nonfermentable carbon sources. Respirative growth of 44 yeast mutants was significantly improved by the addition of dithiothreitol or glutathione. Two mutants that were strongly stimulated by reductants lacked the proteins Cmc1 and Coa4. Both proteins belong to the family of "twin Cx(9)C" proteins present in the intermembrane space of mitochondria. Deletion of CMC1 or COA4 leads to assembly defects of cytochrome c oxidase, in particular to the lack of Cox1 and rapid degradation of Cox2 and Cox3. Interestingly, the presence of the reductants does not suppress these assembly defects and the levels of cytochrome c oxidase remain reduced. Reductants and antioxidants such as ascorbic acid rather counteract the effects of hydrogen peroxide that is produced from partially assembled cytochrome c oxidase intermediates. Here we show that oxidative stress generated by the accumulation of partially assembled respiratory chain complexes prevents growth on carbon sources that force cells to respire. Defects in the assembly of cytochrome c oxidase can lead to increased production of hydrogen peroxide, which is sensed in cells and blocks their proliferation. We propose that this redox-regulated feedback regulation specifically slows down the propagation of cells carrying respiratory chain mutations in order to select for cells of high mitochondrial fitness.

507 電析ナノ結晶ニッケルーリン合金の繰返し応力負荷による結晶粒成長(材料力学I,学術講演)

507 電析ナノ結晶ニッケルーリン合金の繰返し応力負荷による結晶粒成長(材料力学I,学術講演)

Strain-induced tissue growth laws: applications to embryonic cardiovascular development.

Hemodynamic conditions play an essential role in the cardiovascular system, with abnormal blood flow conditions leading to growth and remodeling of cardiovascular walls. During embryonic development, altered hemodynamic conditions lead to congenital heart disease, which affects about 1% of newborn babies in developed countries. However, the mechanisms by which hemodynamic conditions affect cardiovascular development have not been fully elucidated. In this paper, we propose a model of cardiac growth in response to hemodynamic conditions, in which growth is modulated by a combination of wall strains and wall shear stresses. This is in contrast to previous models that proposed stress-induced growth laws. Because during embryonic development blood pressure increases over time, and this increase in blood pressure produces an increase in wall stresses, stress-induced growth laws would require time-dependent parameters. While blood pressure increases during development, cardiovascular walls become stiffer and thicker, and thus we postulate that instead strains experienced by cells remain approximately the same during development. This assumption motivated our cardioavascular model of strain-induced growth in response to hemodynamic conditions, which we implemented using finite element methods. Model simulations show that the proposed model results in tissue growth that is physiologically reasonable. Further, our analyses demonstrate that mechanical coupling - that results from residual stresses originating from differential tissue growth - may play a more important role in the modulation of cardiovascular tissue growth and remodeling than currently acknowledged.

Interaction Between Salt Stress and Angular Leaf Spot (pseudomonas syringae pv lachrymans) in Cucumber

Summary We studied the effects of sequentially applied salt stress and Pseudomonas syringae pv lachrymans (Psl) infection in cucumber (Cucumis sativus L.). Infection development, shoot and root growth potential, the concentrations of chlorophyll and proline as well as electrolyte leakage, lipid peroxidation and H2O2 production were determined. Cucumber plants were first exposed to salt stress and irrigated for seven days with 50 or 100 mM NaCl and thereafter inoculated by Psl. Abiotic stress compromised the defence response to pathogen and disease severity was the highest in 100 mM NaCl-treated plants. The reduced performance of salinized plants under biotic stress could be related to salt stressinduced plant growth inhibition with leaf expansion being the most sensitive to salinity, decreased chlorophyll content, increased electrolyte leakage and prolonged H2O2 accumulation in leaves implying perturbations in redox homeostasis. The response of NaCl-treated and control plants to bacterial infection differed in terms of H2O2 generation and lipid peroxidation. This study confirmed that proline is an important component of local and systemic responses to salt stress and infection. The results contribute to our knowledge of the nature of plant response to a combination of abiotic and biotic stresses

A novel co-infection model withToxoplasmaandChlamydia trachomatishighlights the importance of host cell manipulation for nutrient scavenging

Toxoplasma and Chlamydia trachomatis are obligate intracellular pathogens that have evolved analogous strategies to replicate within mammalian cells. Both pathogens are known to extensively remodel the cytoskeleton, and to recruit endocytic and exocytic organelles to their respective vacuoles. However, how important these activities are for infectivity by either pathogen remains elusive. Here, we have developed a novel co-infection system to gain insights into the developmental cycles of Toxoplasma and C. trachomatis by infecting human cells with both pathogens, and examining their respective ability to replicate and scavenge nutrients. We hypothesize that the common strategies used by Toxoplasma and Chlamydia to achieve development results in direct competition of the two pathogens for the same pool of nutrients. We show that a single human cell can harbour Chlamydia and Toxoplasma. In co-infected cells, Toxoplasma is able to divert the content of host organelles, such as cholesterol. Consequently, the infectious cycle of Toxoplasma progresses unimpeded. In contrast, Chlamydia's ability to scavenge selected nutrients is diminished, and the bacterium shifts to a stress-induced persistent growth. Parasite killing engenders an ordered return to normal chlamydial development. We demonstrate that C. trachomatis enters a stress-induced persistence phenotype as a direct result from being barred from its normal nutrient supplies as addition of excess nutrients, e.g. amino acids, leads to substantial recovery of Chlamydia growth and infectivity. Co-infection of C. trachomatis with slow growing strains of Toxoplasma or a mutant impaired in nutrient acquisition does not restrict chlamydial development. Conversely, Toxoplasma growth is halted in cells infected with the highly virulent Chlamydia psittaci. This study illustrates the key role that cellular remodelling plays in the exploitation of host intracellular resources by Toxoplasma and Chlamydia. It further highlights the delicate balance between success and failure of infection by intracellular pathogens in a co-infection system at the cellular level.

Anti-Angiogenic Effect of Luteolin on Retinal Neovascularization via Blockade of Reactive Oxygen Species Production

Oxidative stress-induced vascular endothelial growth factor (VEGF) is thought to play a critical role in the pathogenesis of retinopathy of prematurity (ROP). This study was performed to investigate the anti-angiogenic effect of luteolin against reactive oxygen species (ROS)-induced retinal neovascularization. The toxicity of luteolin was evaluated through modified 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay in human retinal microvascular endothelial cells (HRMECs) as well as TUNEL staining in the retina of C57BL/6J mice. After intravitreal injection of luteolin in the mouse model of ROP, retinal neovascularization was examined by fluorescence angiography and vessel counting. Anti-angiogenic activity of luteolin was evaluated by VEGF-induced migration and tube formation assay. The effect of luteolin on tertiary-butylhydroperoxide (t-BH)-induced ROS production was measured with 2'7'-dichlorofluorescein diacetate. The effect of luteolin on t-BH-induced and hypoxia-induced VEGF transcription and expression were evaluated by RT-PCR and Western blot, respectively. Luteolin never affected the viability of HRMECs up to 10 μM, where luteolin never induced any structural change in all retinal layers. Luteolin inhibited retinal neovascularization in the mouse model of ROP. Moreover, VEGF-induced migration and tube formation were significantly decreased by cotreatment of luteolin. Luteolin attenuated VEGF transcription via blockade of t-BH-induced ROS production. Luteolin suppressed hypoxia-induced VEGF expression via attenuating hypoxia inducible factor 1 α expression. Our results suggest that luteolin could be a potent anti-angiogenic agent for retinal neovascularization, which is related to anti-oxidative activity to block ROS production and to subsequently suppress VEGF expression and the pro-angiogenic effect of VEGF.

On the crystallographic anisotropy of nanoindentation in pseudoelastic NiTi

We use a nanoindenter with a Berkovich tip to study local mechanical properties of two polycrystalline intermetallics with a B2 crystal structure, NiAl and NiTi. We use orientation imaging scanning electron microscopy to select a relevant number of grains with appropriate sizes and surface normals parallel to 〈001〉, 〈101〉 and 〈111〉. As a striking new result, we find a strong crystallographic orientation dependence for NiTi. This anisotropy is less pronounced in the case of NiAl. For NiTi, the indentation force required to impose a specific indentation depth is highest for indentation experiments performed in the 〈001〉 direction and lowest along the 〈111〉 direction. We consider transmission electron microscopy results from cross-sections below the indents and use molecular dynamics simulations and resolved shear stress calculations to discuss how this difference can be accounted for in terms of elementary deformation and transformation processes, related to dislocation plasticity (NiAl and NiTi), and in terms of the stress-induced formation and growth of martensite (NiTi). Our results show that the crystallographic anisotropy during nanoindentation of NiTi is governed by the orientation dependence of the martensitic transformation; dislocation plasticity appears to be less important.

Src Homology 2 Domain-containing Phosphatase 2 (Shp2) Is a Component of the A-kinase-anchoring Protein (AKAP)-Lbc Complex and Is Inhibited by Protein Kinase A (PKA) under Pathological Hypertrophic Conditions in the Heart

AKAP-Lbc is a scaffold protein that coordinates cardiac hypertrophic signaling. AKAP-Lbc interacts with Shp2, facilitating its regulation by PKA. AKAP-Lbc integrates PKA and Shp2 signaling in the heart. Under pathological hypertrophic conditions Shp2 is phosphorylated by PKA, and phosphatase activity is inhibited. Inhibition of Shp2 activity through AKAP-Lbc-anchored PKA is a previously unrecognized mechanism that may promote pathological cardiac hypertrophy. Pathological cardiac hypertrophy (an increase in cardiac mass resulting from stress-induced cardiac myocyte growth) is a major factor underlying heart failure. Our results identify a novel mechanism of Shp2 inhibition that may promote cardiac hypertrophy. We demonstrate that the tyrosine phosphatase, Shp2, is a component of the A-kinase-anchoring protein (AKAP)-Lbc complex. AKAP-Lbc facilitates PKA phosphorylation of Shp2, which inhibits its protein-tyrosine phosphatase activity. Given the important cardiac roles of both AKAP-Lbc and Shp2, we investigated the AKAP-Lbc-Shp2 interaction in the heart. AKAP-Lbc-tethered PKA is implicated in cardiac hypertrophic signaling; however, mechanism of PKA action is unknown. Mutations resulting in loss of Shp2 catalytic activity are also associated with cardiac hypertrophy and congenital heart defects. Our data indicate that AKAP-Lbc integrates PKA and Shp2 signaling in the heart and that AKAP-Lbc-associated Shp2 activity is reduced in hypertrophic hearts in response to chronic β-adrenergic stimulation and PKA activation. Thus, while induction of cardiac hypertrophy is a multifaceted process, inhibition of Shp2 activity through AKAP-Lbc-anchored PKA is a previously unrecognized mechanism that may promote compensatory cardiac hypertrophy.

Endoplasmic reticulum stress inhibits cell cycle progression via induction of p27 in melanoma cells

The accumulation of unfolded proteins in the endoplasmic reticulum (ER) triggers the unfolded protein response (UPR), a stress signaling pathway. The UPR coordinates the induction of ER chaperones with decreased protein synthesis and growth arrest in G1 phase of the cell cycle. However, the molecular mechanism underlying UPR-induced G1 cell cycle arrest remains largely unknown. Here we report that activation of the UPR response by tunicamycin (TM), an ER stress inducer, leads to accumulation of p27 and G1 cell cycle arrest in melanoma cells. This accumulation of p27 is due to the inhibition on its polyubiquitination and subsequent degradation upon TM treatment. Correlated with p27 stabilization, the levels of Skp2, an E3 ligase for p27, are decreased in response to TM treatment. More importantly, knockdown of p27 greatly reduces TM-induced G1 cell cycle arrest. Taken together, these data implicate p27 as a critical mediator of ER stress-induced growth arrest.

Cardiac Autophagy

Stress-induced hypertrophic growth of the myocardium is a pathogenetic milestone in the progression of heart failure. Some evidence suggests that suppression of pathological cardiac hypertrophy per se is a viable target for therapeutic intervention, and cardiomyocyte autophagy is an attractive mechanism for consideration as a means of controlling the hypertrophic response. However, although considerable insights have been gleaned in the molecular mechanisms governing cardiomyocyte autophagy, many details critical to rational targeting of the response remain unknown. Among them, mechanisms underlying the adaptive and maladaptive features of autophagy are obscure. With time and further study, it is possible that this near-ubiquitous cardiac response to stress will emerge as a target for therapeutic manipulation.

EPS Production, PHB Accumulation and Abiotic Stress Endurance of Plant Growth Promoting Methylobacterium Strains Grown in a High Carbon Concentration

In this study, we compared growth pattern, floc yield, Exo-polysaccharides (EPS) production, Poly-<TEX>${\beta}$</TEX>-hydroxybutyrate (PHB) accumulation, resistance to osmotic and acid stress in Methylobacterium strains CBMB20, CBMB27, CBMB35, and CBMB110. Modified high C:N ratio medium denoted as HCN-AMS medium was used with a C:N ratio of 30:1. The HCN-AMS medium favored increased growth in all the studied strains. All Methylobacterium strains tested positive for EPS production and showed positive fluorescence with calcoflour stain. Elevated levels of EPS production from 4.2 to 75.0% was observed in HCN-AMS medium. Accumulation of PHB in HCN-AMS medium increased by 3.8, 36.7, and 12.0% in strains CBMB27, CBMB35, and CBMB110 respectively. Among the abiotic stresses, osmotic stress-induced growth inhibition of Methylobacterium strains was found to be lowered when grown in HCN-AMS medium. Likewise, growth inhibition due to acid stress at pH 5.0 was lower for strains grown in HCN-AMS medium compared to growth in AMS medium. Enhanced survivability under stress conditions may be attributed to the high EPS and PHB production at increased carbon concentration in the growth medium.

FHY3 promotes shoot branching and stress tolerance in Arabidopsis in an AXR1‐dependent manner

The transposase-related transcription factor FAR-RED ELONGATED HYPOCOTYL3 (FHY3) promotes seedling de-etiolation in far-red light, which is perceived by phytochrome A (phyA). In this role, FHY3 indirectly mediates the nuclear import of light-activated phyA, which triggers downstream transcriptional responses. Here, we present genetic evidence for additional roles of FHY3 in plant development and growth. New fhy3 alleles were isolated as suppressors of max2-1 (more axillary branching2-1), a strigolactone-insensitive mutant characterised by highly branched shoots. Branching suppression by fhy3, in both wild-type and max2-1 backgrounds, resulted from inhibition of axillary bud outgrowth. Additional roles in axillary meristem initiation were revealed in the revoluta (rev) fhy3 double mutant, with fhy3 enhancing rev mutant defects in axillary shoot meristem formation, as well as in floral meristem maintenance. fhy3 also affected embryonic and floral patterning with low penetrance, and displayed oxidative stress-related phenotypes of retarded leaf growth and of cell death. The fhy3 phenotypes of axillary bud outgrowth suppression and of stress-induced leaf growth retardation both required the AUXIN-RESISTANT1 gene, and are independent of phyA. Consistent with the recent discovery that FHY3 regulates many Arabidopsis promoters, our results suggest much wider roles for FHY3 in growth and development, either in concert with, or beyond, light signalling.