BBA - Molecular Cell Research (v.1793, #5)

β-hydroxy-β-methylbutyrate (HMB) stimulates myogenic cell proliferation, differentiation and survival via the MAPK/ERK and PI3K/Akt pathways by Reut Kornasio; Ingo Riederer; Gillian Butler-Browne; Vincent Mouly; Zehava Uni; Orna Halevy (755-763).
β-hydroxy-β-methylbutyrate (HMB), a leucine catabolite, has been shown to prevent exercise-induced protein degradation and muscle damage. We hypothesized that HMB would directly regulate muscle-cell proliferation and differentiation and would attenuate apoptosis, the latter presumably underlying satellite-cell depletion during muscle degradation or atrophy. Adding various concentrations of HMB to serum-starved myoblasts induced cell proliferation and MyoD expression as well as the phosphorylation of MAPK/ERK. HMB induced differentiation-specific markers, increased IGF-I mRNA levels and accelerated cell fusion. Its inhibition of serum-starvation- or staurosporine-induced apoptosis was reflected by less apoptotic cells, reduced BAX expression and increased levels of Bcl-2 and Bcl-X. Annexin V staining and flow cytometry analysis showed reduced staurosporine-induced apoptosis in human myoblasts in response to HMB. HMB enhanced the association of the p85 subunit of PI3K with tyrosine-phosphorylated proteins. HMB elevated Akt phosphorylation on Thr308 and Ser473 and this was inhibited by Wortmannin, suggesting that HMB acts via Class I PI3K. Blocking of the PI3K/Akt pathway with specific inhibitors revealed its requirement in mediating the promotive effects of HMB on muscle cell differentiation and fusion. These direct effects of HMB on myoblast differentiation and survival resembling those of IGF-I, at least in culture, suggest its positive influence in preventing muscle wasting.
Keywords: HMB; Myoblast; Akt; Apoptosis; Proliferation; Differentiation; Skeletal muscle;

Dexamethasone (DX) induces apoptosis resistance in most solid malignant tumors during co-treatment with chemotherapy agents, such as camptothecin (CAM). In this study, we investigated the mechanism by which DX reduces chemotherapy efficiency in C6-glioma. DX reduced CAM-increased DNA fragmentation and caspase-3 activation. The DX's protection was negated by RU486, an antagonist of glucocorticoid receptor (GR). DX itself increased anti-apoptotic gene, Bcl-xL expression, and its transcription factor, signaling transducer and activator of transcription 5 (Stat5), DNA binding activity and phospho-Stat5 expression. DX blocked the CAM-decreased Bcl-xL and phospho-Stat5 expression, and Stat5 binding activity. RU486 negated DX's actions. To determine whether Stat5 regulates Bcl-xL expression in CAM-induced cell death, C6-glioma was infected with an adenovirus containing a constitutively activated Stat5-GFP (Ad-Stat5ca). Overexpression of Stat5ca increased Bcl-xL and decreased CAM-induced cell death compared to control adenovirus infected cells; whereas Stat5 siRNA decreased DX-induced Bcl-xL and increased cell death. Phospho-Stat5 expression was observed in the nuclear extract by co-immunoprecipitation with an anti-GR antibody, indicating that Stat5 and GR were interactive and formed a complex in the nuclei. These results suggest that DX's prevention from CAM-induced apoptosis and RU486's antagonism of DX's protection may be through Stat5/Bcl-xL signal pathway regulated by a GR.
Keywords: Apoptosis; Bcl-xL; Camptothecin; C6-glioma; Dexamethasone; Stat5;

A designed angiopoietin-2 variant, pentameric COMP-Ang2, strongly activates Tie2 receptor and stimulates angiogenesis by Hak-Zoo Kim; Keehoon Jung; Ho Min Kim; Yifan Cheng; Gou Young Koh (772-780).
Despite that angiopoietin-2 (Ang2) produces more versatile and dynamic functions than angiopoietin-1 (Ang1) in angiogenesis and inflammation, the molecular mechanism that underlies this difference is still unknown. To define the role of oligomerization of Ang2 in activation of its receptor, Tie2, we designed and generated different oligomeric forms of Ang2 by replacement of the amino-terminal domains of Ang2 with dimeric, tetrameric, and pentameric short coiled-coil domains derived from GCN4, matrillin-1, and COMP. COMP-Ang2 strongly binds and activates Tie2, whereas GCN4-Ang2 and MAT-Ang2 weakly to moderately bind and activate Tie2. Although native Ang2 strongly binds to Tie2, it does not activate Tie2. Accordingly, COMP-Ang2 strongly promotes endothelial cell survival, migration, and tube formation in a Tie2-dependent manner, and the potency of COMP-Ang2 is almost identical to that of COMP-Ang1. Furthermore, the potency of COMP-Ang2-induced enhanced angiogenesis in the wound healing region is almost identical to the potency of COMP-Ang1-induced enhanced angiogenesis. Overall, there is no obvious difference between COMP-Ang2 and COMP-Ang1 in in vitro and in vivo angiogenesis. Our results provide compelling evidence that proper oligomerization of Ang2 is a critical determinant of its binding and activation of Tie2.
Keywords: Angiopoietin-2; Oligomerization; Tie2; COMP-Ang1; COMP-Ang2;

Specific tyrosine phosphorylation of focal adhesion kinase mediated by Fer tyrosine kinase in suspended hepatocytes by Min-A Oh; Suyong Choi; Mi Ji Lee; Moon-Chang Choi; Sin-Ae Lee; Wonil Ko; William G. Cance; Eok-Soo Oh; Laszlo Buday; Sung-Hoon Kim; Jung Weon Lee (781-791).
Cell adhesion to the extracellular matrix (ECM) can activate signaling via focal adhesion kinase (FAK) leading to dynamic regulation of cellular morphology. Mechanistic basis for the lack of effective intracellular signaling by non-attached epithelial cells is poorly understood. To examine whether signaling in suspended cells is regulated by Fer cytoplasmic tyrosine kinase, we investigated the effect of ectopic Fer expression on signaling in suspended or adherent hepatocytes. We found that ectopic Fer expression in Huh7 hepatocytes in suspension or on non-permissive poly-lysine caused significant phosphorylation of FAK Tyr577, Tyr861, or Tyr925, but not Tyr397 or Tyr576. Fer-mediated FAK phosphorylation in suspended cells was independent of c-Src activity or growth factor stimulation, but dependent of cortactin expression. Consistent with these results, complex formation between FAK, Fer, and cortactin was observed in suspended cells. The Fer-mediated effect correlated with multiple membrane protrusions, even on poly-lysine. Together, these observations suggest that Fer may allow a bypass of anchorage-dependency for intracellular signal transduction in hepatocytes.
Keywords: Cell adhesion; Focal adhesion kinase; Fer; Cortactin; Protein–protein interaction;

Role of the intracellular localization of HIF-prolyl hydroxylases by Ken-ichi Yasumoto; Yusuke Kowata; Atsushi Yoshida; Satoru Torii; Kazuhiro Sogawa (792-797).
Hypoxia-inducible factor-1 (HIF-1) is a major transcription factor regulating the response of tumor cells to hypoxia and is comprised of HIF-1α and Arnt (HIF-1β). In mammalian cells, HIF-1 protein levels are regulated by three HIF-prolyl hydroxylases, termed PHD1, PHD2 and PHD3. To assess whether intracellular localization of PHD1 and PHD2 affects the hypoxic response via HIF-1, we investigated the localization signal of PHDs. PHD1 possessed at least one nuclear localization signal (NLS), and PHD2 contained a region as essential for nuclear export in their N-terminal region. Treatment of cells with leptomycin B revealed that PHD2 was able to shuttle between the cytoplasm and the nucleus. Reporter assay indicated that differences in the intracellular distribution of PHD1 did not influence on HIF-1α activity. However, a PHD2 mutant lacking the region for nuclear export exhibited significantly reduced effect to HIF-1α activity compared to wild-type PHD2, suggesting that the regulation of the intracellular distribution of PHD2 is an effective pathway for the control of the hypoxic response.
Keywords: Hypoxia; Prolyl hydroxylase; HIF-1;

FXa-induced intracellular signaling links coagulation to neoangiogenesis: Potential implications for fibrosis by Keren Borensztajn; Hella Aberson; Maikel P. Peppelenbosch; C. Arnold Spek (798-805).
Fibrosis represents the end-stage of a broad range of disorders affecting organ function. These disorders are often associated with aberrant angiogenesis, but whether vascular abnormalities during fibrosis are characterized by excessive or diminished neo-vascularization remains questionable. Strikingly, activation of the coagulation cascade is frequently observed in association with the progression of fibroproliferative disorders. As we recently showed that coagulation factor (F)Xa induced fibrotic responses in fibroblasts, we hypothesized that FXa might indirectly induce angiogenesis by triggering fibroblasts to secrete proangiogenic factors. In the present study, we show that although FXa induces p42/44 MAP Kinase phosphorylation in endothelial cells, it has no direct effect on endothelial cell proliferation, protein synthesis and tube formation. In contrast, conditioned medium of fibroblasts stimulated with FXa enhanced endothelial cell proliferation, extra cellular matrix synthesis, wound healing and endothelial tube formation. FXa induced VEGF production by fibroblasts and a VEGF neutralizing antibody blocked the indirect effect of FXa on proliferation and realignment of endothelial cells identifying VEGF as a crucial player in angiogenesis during coagulation factor-induced fibrosis. Overall, our results establish a link between the coagulation cascade and angiogenesis during fibrosis.
Keywords: Fibrosis; Angiogenesis; Coagulation; Factor Xa; VEGF;

ARHGAP21 modulates FAK activity and impairs glioblastoma cell migration by Carolina Louzão Bigarella; Luciene Borges; Fernando Ferreira Costa; Sara Terezinha Olalla Saad (806-816).
Glioblastoma multiforme is highly aggressive and is the most common glial tumor type. Although there have been advances in treatment, the average survival expectancy is 12–15 months. Several genes have been shown to influence glioblastoma progression. In the present work, we demonstrate that the RhoGTPase Activating Protein 21 (ARHGAP21) is expressed in the nuclear and perinuclear regions of several cell lines. In T98G and U138MG, glioblastoma derived cell lines, ARHGAP21 interacts with the C-terminal region of Focal Adhesion Kinase (FAK). ARHGAP21 depletion by shRNAi in T98G cells alters cellular morphology and increases: FAK phosphorylation states and activation of downstream signaling; the activity state of Cdc42; the production of metalloproteinase 2 (MMP-2) and cell migration rates. These modifications were found to be mainly due to the loss of ARHGAP21 action on FAK and, consequently, the activation of downstream effectors. These results suggest not only that ARHGAP21 might act as a tumor suppressor gene, but also indicate that ARHGAP21 might be a master regulator of migration having a crucial role in controlling the progression of different tumor types.
Keywords: ARHGAP21; Glioblastoma multiforme (GBM); FAK; Migration;

We have created and analyzed the properties of a yeast model of the human mitochondrial DNA T8993C mutation that has been associated with maternally-inherited Leigh syndrome and/or with neurogenic muscle weakness, ataxia and retinitis pigmentosa. This mutation changes a highly conserved leucine to proline in the Atp6p subunit of the ATP synthase, at position 156 in the human protein, position 183 in yeast. In vitro the yeast T8993C mitochondria showed a 40–50% decrease in the rate of ATP synthesis. The ATP-driven translocation of protons across the inner mitochondrial membrane was normal in the mutant and fully sensitive to oligomycin, an inhibitor of the ATP synthase proton channel. However under conditions of maximal ATP hydrolytic activity, using non-osmotically protected mitochondria, the mutant ATPase activity was poorly inhibited by oligomycin (by 40% versus 85% in wild type cells). These anomalies were attributed by BN-PAGE and mitochondrial protein synthesis analyses to a less efficient incorporation of Atp6p within the ATP synthase. Interestingly, the cytochrome c oxidase content was selectively decreased by 40–50% in T8993C yeast, apparently due to a reduced synthesis of its mitochondrially encoded Cox1p subunit. This observation further supports the existence of a control of cytochrome c oxidase expression by the ATP synthase in yeast mitochondria. Despite the ATPase deficiency, growth of the atp6-L183P mutant on respiratory substrates and the efficiency of oxidative phosphorylation were similar to that of wild type, indicating that the mutation did not affect the proton permeability of the mitochondrial inner membrane.
Keywords: ATP6; F1F0 ATP synthase, NARP/MILS disease; Mitochondrial DNA; Yeast;

Las17p–Vrp1p but not Las17p–Arp2/3 interaction is important for actin patch polarization in yeast by Rajamuthiah Rajmohan; Ming Hwa Wong; Lei Meng; Alan L. Munn; Thirumaran Thanabalu (825-835).
The actin cytoskeleton plays a central role in many important cellular processes such as cell polarization, cell division and endocytosis. The dynamic changes to the actin cytoskeleton that accompany these processes are regulated by actin-associated proteins Wiskott–Aldrich Syndrome Protein (WASP) (known as Las17p in yeast) and WASP-Interacting Protein (WIP) (known as Vrp1p in yeast). Both yeast and human WASP bind to and stimulate the Arp2/3 complex which in turn nucleates assembly of actin monomers into filaments at polarized sites at the cortex. WASP–WIP interaction in yeast and humans are important for Arp2/3 complex stimulation in vitro. It has been proposed that these interactions are also important for polarized actin assembly in vivo. However, the redundancy of actin-associated proteins has made it difficult to test this hypothesis. We have identified two point mutations (L80T and H94L) in yeast WASP that in combination abolish WASP–WIP interaction in yeast. We also identify an N-terminal fragment of Las17p (N-Las17p1–368) able to interact with Vrp1p but not Arp2/3. Using these mutant and truncated forms of yeast WASP we provide novel evidence that WASP interaction with WIP is more important than interaction with Arp2/3 for polarized actin assembly and endocytosis in yeast.
Keywords: Actin filament; Cortical actin patch; Membrane traffic; Proline-rich motif; SH3 domain; Type I myosin;

Growth plate cartilage is responsible for long bone growth in children and adolescents and is regulated by vitamin D metabolites in a cell zone-specific manner. Resting zone chondrocytes (RC cells) are regulated by 24,25-dihydroxyvitamin D3 via a phospholipase D-dependent pathway, suggesting downstream phospholipid metabolites are involved. In this study, we showed that 24R,25(OH)2D3 stimulates rat costochondral RC chondrocytes to release lysophosphatidic acid (LPA) and, therefore sought to determine the role of LPA signaling in these cells. RC cells expressed the G-protein coupled receptors LPA1–5 and peroxisome proliferator-activated receptor gamma (PPAR-γ). LPA and the LPA1/3 selective agonist OMPT increased proliferation and two maturation markers, alkaline phosphatase activity and [35S]-sulfate incorporation. LPA and 24R,25(OH)2D3's effects were inhibited by the LPA1/3 selective antagonist VPC32183(S). Furthermore, apoptosis induced by either inorganic phosphate or chelerythrine was attenuated by LPA, based on DNA fragmentation, TUNEL staining, caspase-3 activity, and Bcl-2:Bax protein ratio. LPA prevented apoptotic signaling by decreasing the abundance, nuclear localization, and transcriptional activity of the tumor-suppressor p53. LPA treatment also regulated the expression of the p53-target genes Bcl-2 and Bax to enhance cell survival. Collectively, these data suggest that LPA promotes differentiation and survival in RC chondrocytes, demonstrating a novel physiological function of LPA-signaling.
Keywords: Lysophosphatidic acid; LPA receptor; Growth plate cartilage; Chondrocyte maturation and apoptosis;

Extraordinary pleiotropy of protein kinase CK2 revealed by weblogo phosphoproteome analysis by Mauro Salvi; Stefania Sarno; Luca Cesaro; Hideji Nakamura; Lorenzo A. Pinna (847-859).
A weblogo has been generated from the sequences surrounding 433 Ser/Thr protein residues whose phosphorylation by protein kinase CK2 had been previously validated (“bona fide” CK2 phosphosites). This has been compared to the weblogo extracted from 2275 putative CK2 phosphosites displaying the motif pS/pT-x1-x2-D/E/pS (where x1  ≠ P) present in the human phosphoElm database including 10 899 naturally occurring phosphosites. The two weblogos are strikingly similar supporting the notion that indeed the 2275 putative sites (accounting for 20.9% of the whole phosphoproteome they belong to), or at least the great majority of these are generated by CK2. This conclusion has been corroborated by the random validation of 8 of such putative CK2 sites (belonging to 5 different proteins) as real targets of CK2 in vitro and/or in cells, leading to the inclusion into the repertoire of bona fide CK2 targets of 5 new entries, namely: oxidative stress-responsive kinase-1, anthrax toxin receptor 1, hepatoma derived growth factor, EpsinR and BCL2/adenovirus E1B 19 kDa protein-interacting protein 3-like.
Keywords: Protein kinase CK2; OSR1; ANTXR1; HDGF; EpsinR; Bnip3L;

In vitro import of peroxisome-targeting signal type 2 (PTS2) receptor Pex7p into peroxisomes by Non Miyata; Ken-ichiro Hosoi; Satoru Mukai; Yukio Fujiki (860-870).
Pex7p, the peroxisome-targeting signal type 2 (PTS2) receptor, transports PTS2 proteins to peroxisomes from the cytosol. We here established a cell-free Pex7p translocation system. In assays using post-nuclear supernatant fractions each from wild-type CHO-K1 and pex7 ZPG207 cells, 35S-labeled Pex7p was imported into peroxisomes. 35S-Pex7p import was also evident using rat liver peroxisomes. 35S-Pex7p was not imported into peroxisomal remnants from a pex5 ZPG231 defective in PTS2 import and pex2 Z65. When the import of 35S-Pex5pL was inhibited with an excess amount of recombinant Pex5pS, 35S-Pex7p import was concomitantly abrogated, suggesting that Pex5pL was a transporter for Pex7p, unlike a yeast cochaperone, Pex18p. 35S-Pex7p as well as 35S-Pex5p was imported in an ATP-independent manner, whilst the import of PTS1 and PTS2 cargo-proteins was ATP-dependent. Thereby, ATP-independent import of Pex7p implicated that Pex5p export requiring ATP hydrolysis is not a limiting step for its cargo recruitment to peroxisomes. PTS1 protein import was indeed insensitive to N-ethylmaleimide, whereas Pex5p export was N-ethylmaleimide-sensitive. Taken together, the cargo-protein translocation through peroxisomal membrane more likely involves another ATP-requiring step in addition to the Pex5p export. Moreover, upon concurrent import into peroxisomes, 35S-Pex5pL and 35S-Pex7p were detected at mutually distinct ratios in the immunoprecipitates each of the import machinery peroxins including Pex14p, Pex13p, and Pex2p, hence suggesting that Pex7p as well as Pex5p translocated from the initial docking complex to RING complex on peroxisomes.
Keywords: Peroxisome; Protein import; PTS2 receptor; In vitro import assay;

Muscle fructose 1,6-bisphosphatase (FBPase), a well-known regulatory enzyme of glyconeogenic pathway has recently been found inside nuclei of several cell types (cardiomyocytes, smooth muscle cells, myogenic progenitor cells). This surprising finding raised a question concerning the role of FBPase in this compartment of the cell, and of the extracellular signals regulating nuclear transport of the enzyme. In the present paper we show that, in HL-1 cardiomyocyte cell line, the activity of adenylyl cyclase and cAMP-dependent protein kinase A is essential to nuclear import of FBPase. The import is also stimulated by isoproterenol (a nonselective β-adrenergic receptors agonist) and inhibited by metoprolol (a selective β1 antagonist), strongly suggesting that nucleo-cytoplasmic shuttling of FBPase is under the control of β1-adrenergic receptor-dependent Gs protein signaling cascade.
Keywords: Muscle FBPase; HL-1 cell; Norepinephrine; Protein kinase A; Phosphoinositide 3-kinase;

Selective localization of PCBP2 to cytoplasmic processing bodies by Ken Fujimura; Jun Katahira; Fumi Kano; Yoshihiro Yoneda; Masayuki Murata (878-887).
Processing bodies (P-bodies) are cytoplasmic domains that have been implicated in critical steps of the regulation of gene expression, including mRNA decay and post-transcriptional gene silencing. Previously, we reported that PCBP2 (Poly-(rC) Binding Protein 2), a facilitator of IRES-mediated translation, is a novel P-body component. Interestingly, PCBP2 is recruited to only a subset of Dcp1a-positive P-bodies, which may reflect functional diversity among these structures. In this study, we examined the selective P-body localization of PCBP2 in detail. Co-localization studies between Dcp1a and PCBP2 revealed that PCBP2 is present in ∼ 40% of P-bodies. While PCBP2 was more likely to reside in larger P-bodies, P-body size did not seem to be the sole determinant, and puromycin-induced enlargement of P-bodies only modestly increased the percentage of PCBP2-positive P-bodies. Photobleaching experiments demonstrated that the accumulation of PCBP2 to specific P-bodies is a dynamic process, which does not involve the protein's transcription-dependent nucleo-cytoplasmic shuttling activity. Finally, we found that PCBP1, a close relative of PCBP2, localizes to P-bodies in a similar manner to PCBP2. Taken together, these results establish the compositional diversity among P-bodies, and that PCBP2, probably in complex with other mRNP factors, may dynamically recognize such differences and accumulate to specific P-bodies.
Keywords: Processing body; PCBP2; FRAP; Post-transcriptional regulation;

The regulation of tenascin expression by tissue microenvironments by Richard P. Tucker; Ruth Chiquet-Ehrismann (888-892).
Tenascins are a family of four extracellular matrix proteins: tenascin-C, X, R and W. The four members of the family have strikingly diverse patterns of expression during development and in the adult organism indicating independent mechanisms of regulation. In this review we illustrate that there are two types of tenascins, those that are significantly regulated by the tissue microenvironment (tenascin-C and tenascin-W), and those that have stabile, restricted expression patterns (tenascin-R and tenascin-X). We summarize what is known about the regulation of tenascin expression by transforming growth factor betas, fibroblast growth factors, platelet derived growth factors, as well as pro- and anti-inflammatory cytokines or hormones that either induce or inhibit expression of tenascins.
Keywords: Extracellular matrix; Growth factor; Transforming growth factor beta; Development; Tumor stroma; Fibroblast growth factor;

Cell response to matrix mechanics: Focus on collagen by Anne L. Plant; Kiran Bhadriraju; Tighe A. Spurlin; John T. Elliott (893-902).
Many model systems and measurement tools have been engineered for observing and quantifying the effect of mechanics on cellular response. These have contributed greatly to our current knowledge of the molecular events by which mechanical cues affect cell biology. Cell responses to the mechanical properties of type 1 collagen gels are discussed, followed by a description of a model system of very thin, mechanically tunable collagen films that evoke similar responses from cells as do gel systems, but have additional advantages. Cell responses to thin films of collagen suggest that at least some of the mechanical cues that cells can respond to in their environment occur at the sub-micron scale. Mechanical properties of thin films of collagen can be tuned without altering integrin engagement, and in some cases without altering topology, making them useful in addressing questions regarding the roles of specific integrins in transducing or mitigating responses to mechanical cues. The temporal response of cells to differences in ECM may provide insight into mechanisms of signal transduction.
Keywords: Extracellular matrix; Collagen; Type 1 collagen; Collagen gel; Collagen thin film; Collagen fibril; Vascular smooth muscle cell; Integrin; Mechanical cue; Myosin light chain; Cell spreading; Actin cytoskeleton; Proliferation;

Geometric control of tissue morphogenesis by Celeste M. Nelson (903-910).
Morphogenesis is the dynamic and regulated change in tissue form that leads to creation of the body plan and development of mature organs. Research over the past several decades has uncovered a multitude of genetic factors required for morphogenesis in animals. The behaviors of individual cells within a developing tissue are determined by combining these genetic signals with information from the surrounding microenvironment. At any point in time, the local microenvironment is influenced by macroscale tissue geometry, which sculpts long range signals by affecting gradients of morphogens and mechanical stresses. The geometry of a tissue thus acts as both a template and instructive cue for further morphogenesis.
Keywords: Emergence; Pattern formation; Mechanotransduction; Multicellular form;

From mechanotransduction to extracellular matrix gene expression in fibroblasts by Matthias Chiquet; Laurent Gelman; Roman Lutz; Silke Maier (911-920).
Tissue mechanics provide an important context for tissue growth, maintenance and function. On the level of organs, external mechanical forces largely influence the control of tissue homeostasis by endo- and paracrine factors. On the cellular level, it is well known that most normal cell types depend on physical interactions with their extracellular matrix in order to respond efficiently to growth factors. Fibroblasts and other adherent cells sense changes in physical parameters in their extracellular matrix environment, transduce mechanical into chemical information, and integrate these signals with growth factor derived stimuli to achieve specific changes in gene expression. For connective tissue cells, production of the extracellular matrix is a prominent response to changes in mechanical load. We will review the evidence that integrin-containing cell–matrix adhesion contacts are essential for force transmission from the extracellular matrix to the cytoskeleton, and describe novel experiments indicating that mechanotransduction in fibroblasts depends on focal adhesion adaptor proteins that might function as molecular springs. We will stress the importance of the contractile actin cytoskeleton in balancing external with internal forces, and describe new results linking force-controlled actin dynamics directly to the expression of specific genes, among them the extracellular matrix protein tenascin-C. As assembly lines for diverse signaling pathways, matrix adhesion contacts are now recognized as the major sites of crosstalk between mechanical and chemical stimuli, with important consequences for cell growth and differentiation.
Keywords: Mechanotransduction; Fibroblast; Focal adhesion; Extracellular matrix; Cytoskeleton; RhoA; Integrin linked kinase; p130Cas; Megakaryocytic leukemia protein; Tenascin-C;

Getting a grip on Thy-1 signaling by Thomas H. Barker; James S. Hagood (921-923).
A recent study by Hermosilla et al. [T. Hermosilla, D. Munoz, R. Herrera-Molina, A. Valdivia, N. Munoz, S.U. Nham, P. Schneider, K. Burridge, A.F. Quest, L. Leyton, Direct Thy-1/alphaVbeta3 integrin interaction mediates neuron to astrocyte communication, Biochim Biophys Acta 1783 (2008) 1111–1120] demonstrates that Thy-1 on neurons binds to αvβ3 integrin on astrocytes via a conserved RLD motif, triggering the formation of focal adhesions and stress fibers via tyrosine phosphorylation and RhoA activation. This study adds to growing evidence regarding the signaling mechanisms and biological roles of Thy-1, an important regulator of context-dependent signaling. As knowledge of Thy-1 approaches its fiftieth year, it is critical to begin to synthesize insights from different fields to determine how this heretofore enigmatic molecule modulates cell behavior in both cis and trans.
Keywords: Thy-1; Integrin; Neuron; Astrocyte; Context-dependent signaling;

Soft materials to treat central nervous system injuries: Evaluation of the suitability of non-mammalian fibrin gels by Raivo Uibo; Ivo Laidmäe; Evelyn S. Sawyer; Lisa A. Flanagan; Penelope C. Georges; Jessamine P. Winer; Paul A. Janmey (924-930).
Polymeric scaffolds formed from synthetic or natural materials have many applications in tissue engineering and medicine, and multiple material properties need to be optimized for specific applications. Recent studies have emphasized the importance of the scaffolds' mechanical properties to support specific cellular responses in addition to considerations of biochemical interactions, material transport, immunogenicity, and other factors that determine biocompatibility. Fibrin gels formed from purified fibrinogen and thrombin, the final two reactants in the blood coagulation cascade, have long been shown to be effective in wound healing and supporting the growth of cells in vitro and in vivo. Fibrin, even without additional growth factors or other components has potential for use in neuronal wound healing in part because of its mechanical compliance that supports the growth of neurons without activation of glial proliferation. This review summarizes issues related to the use of fibrin gels in neuronal cell contexts, with an emphasis on issues of immunogenicity, and considers the potential advantages and disadvantages of fibrin prepared from non-mammalian sources.
Keywords: Fibrin; Tissue engineering; Immunogenic; Wound healing; Stiffness;