Signaling of de-adhesion in cellular regulation and motility

Ras-Related Protein Rab-32 and Thrombospondin 1 Confer Resistance to the EGFR Tyrosine Kinase Inhibitor Osimertinib by Activating Focal Adhesion Kinase in Non-Small Cell Lung Cancer

Simple Summary

Osimertinib is a third-generation EGFR tyrosine kinase inhibitor and the standard of care therapy for non-small cell lung cancer patients harboring EGFR-activating mutations. However, even for patients treated with osimertinib, resistance inevitably occurs leading to disease progression. Here, we utilized two osimertinib-resistant cell lines and investigated their RNA profiles. We found that Ras-related protein Rab-32 (RAB32) and thrombospondin 1 (THBS1) were upregulated and associated with resistance in osimertinib-resistant cells as well as in liquid biopsies from patients with disease progression following osimertinib treatment. Moreover, we found RAB32 and THBS1 to be mechanistically linked to activation of the focal adhesion pathway where combination of osimertinib with a FAK inhibitor resulted in a synergistic suppression of viability of osimertinib-resistant cells. Our findings propose a potential therapeutic strategy for overcoming acquired resistance to osimertinib in non-small cell lung cancer.

Abstract

Treatment with the tyrosine kinase inhibitor (TKI) osimertinib is the standard of care for non-small cell lung cancer (NSCLC) patients with activating mutations in the epidermal growth factor receptor (EGFR). Osimertinib is also used in T790M-positive NSCLC that may occur de novo or be acquired following first-line treatment with other EGFR TKIs (i.e., gefitinib, erlotinib, afatinib, or dacomitinib). However, patients treated with osimertinib have a high risk of developing resistance to the treatment. A substantial fraction of the mechanisms for resistance is unknown and may involve RNA and/or protein alterations. In this study, we investigated the full transcriptome of parental and osimertinib-resistant cell lines, revealing 131 differentially expressed genes. Knockdown screening of the genes upregulated in resistant cell lines uncovered eight genes to partly confer resistance to osimertinib. Among them, we detected the expression of Ras-related protein Rab-32 (RAB32) and thrombospondin 1 (THBS1) in plasmas sampled at baseline and at disease progression from EGFR-positive NSCLC patients treated with osimertinib. Both genes were upregulated in progression samples. Moreover, we found that knockdown of RAB32 and THBS1 reduced the expression of phosphorylated focal adhesion kinase (FAK). Combination of osimertinib with a FAK inhibitor resulted in synergistic toxicity in osimertinib-resistant cells, suggesting a potential therapeutic drug combination for overcoming resistance to osimertinib in NSCLC patients.

Thrombospondin-1 Signaling Through the Calreticulin/LDL Receptor Related Protein 1 Axis: Functions and Possible Roles in Glaucoma

Thrombospondin-1 (TSP-1) is a matricellular extracellular matrix protein. Matricellular proteins are components of the extracellular matrix (ECM) that regulate key cellular functions and impact ECM organization, but which lack direct primary structural roles in the ECM. TSP-1 expression is upregulated in response to injury, hypoxia, growth factor stimulation, inflammation, glucose, and by reactive oxygen species. Relevant to glaucoma, TSP-1 is also a mechanosensitive molecule upregulated by mechanical stretch. TSP-1 expression is increased in ocular remodeling in glaucoma in both the trabecular meshwork and in the optic nerve head. The exact roles of TSP-1 in glaucoma remain to be defined, however. It plays important roles in cell behavior and in ECM remodeling during wound healing, fibrosis, angiogenesis, and in tumorigenesis and metastasis. At the cellular level, TSP-1 can modulate cell adhesion and migration, protease activity, growth factor activity, anoikis resistance, apoptosis, and collagen secretion and matrix assembly and cross-linking. These multiple functions and macromolecular and receptor interactions have been ascribed to specific domains of the TSP-1 molecule. In this review, we will focus on the cell regulatory activities of the TSP-1 N-terminal domain (NTD) sequence that binds to cell surface calreticulin (Calr) and which regulates cell functions via signaling through Calr complexed with LDL receptor related protein 1 (LRP1). We will describe TSP-1 actions mediated through the Calr/LRP1 complex in regulating focal adhesion disassembly and cytoskeletal reorganization, cell motility, anoikis resistance, and induction of collagen secretion and matrix deposition. Finally, we will consider the relevance of these TSP-1 functions to the pathologic remodeling of the ECM in glaucoma.

Orai3 Calcium Channel Regulates Breast Cancer Cell Migration through Calcium-Dependent and -Independent Mechanisms

Orai3 calcium (Ca²⁺) channels are implicated in multiple breast cancer processes, such as proliferation and survival as well as resistance to chemotherapy. However, their involvement in the breast cancer cell migration processes remains vague. In the present study, we exploited MDA-MB-231 and MDA-MB-231 BrM2 basal-like estrogen receptor-negative (ER^-) cell lines to assess the direct role of Orai3 in cell migration. We showed that Orai3 regulates MDA-MB-231 and MDA-MB-231 BrM2 cell migration in two distinct ways. First, we showed that Orai3 remodels cell adhesive capacities by modulating the intracellular Ca²⁺ concentration. Orai3 silencing (siOrai3) decreased calpain activity, cell adhesion and migration in a Ca²⁺-dependent manner. In addition, Orai3 interacts with focal adhesion kinase (FAK) and regulates the actin cytoskeleton, in a Ca²⁺-independent way. Thus, siOrai3 modulates cell morphology by altering F-actin polymerization via a loss of interaction between Orai3 and FAK. To summarize, we demonstrated that Orai3 regulates cell migration through a Ca²⁺-dependent modulation of calpain activity and, in a Ca²⁺-independent manner, the actin cytoskeleton architecture via FAK.

The effects of aging on molecular modulators of human embryo implantation

Advancing age has a negative impact on female fertility. As implantation rates decline during the normal maternal life course, age-related, embryonic factors are altered and our inability to monitor these factors in an unbiased genome-wide manner in vivo has severely limited our understanding of early human embryo development and implantation. Our high-throughput methodology uses trophectoderm samples representing the full spectrum of maternal reproductive ages with embryo implantation potential examined in relation to trophectoderm transcriptome dynamics and reproductive maternal age. Potential embryo-endometrial interactions were tested using trophectoderm sampled from young women, with the receptive uterine environment representing the most 'fertile' environment for successful embryo implantation. Potential roles for extracellular exosomes, embryonic metabolism and regulation of apoptosis were revealed. These biomarkers are consistent with embryo-endometrial crosstalk/developmental competency, serving as a mediator for successful implantation. Our data opens the door to developing a diagnostic test for predicting implantation success in women undergoing fertility treatment.

The Tumor Microenvironment: Focus on Extracellular Matrix

The extracellular matrix (ECM) regulates the development and maintains tissue homeostasis. The ECM is composed of a complex network of molecules presenting distinct biochemical properties to regulate cell growth, survival, motility, and differentiation. Among their components, proteoglycans (PGs) are considered one of the main components of ECM. Its composition, biomechanics, and anisotropy are exquisitely tuned to reflect the physiological state of the tissue. The loss of ECM's homeostasis is seen as one of the hallmarks of cancer and, typically, defines transitional events in tumor progression and metastasis. In this chapter, we discuss the types of proteoglycans and their roles in cancer. It has been observed that the amount of some ECM components is increased, while others are decreased, depending on the type of tumor. However, both conditions corroborate with tumor progression and malignancy. Therefore, ECM components have an increasingly important role in carcinogenesis and this leads us to believe that their understanding may be a key in the discovery of new anti-tumor therapies. In this book, the main ECM components will be discussed in more detail in each chapter.

Inactivation of beta1 integrin induces proteasomal degradation of Myc oncoproteins

The MYC family oncogenes (MYC, MYCN, and MYCL) contribute to the genesis of many human cancers. Among them, amplification of the MYCN gene and over-expression of N-Myc protein are the most reliable risk factors in neuroblastoma patients. On the other hand, we previously found that a peptide derived from fibronectin, termed FNIII14, is capable of inducing functional inactivation in β1-integrins. Here, we demonstrate that inactivation of β1-integrin by FNIII14 induced proteasomal degradation in N-Myc of neuroblastoma cells with MYCN amplification. This N-Myc degradation by FNIII14 reduced the malignant properties, including the anchorage-independent proliferation and invasive migration, of neuroblastoma cells. An in vivo experiment using a mouse xenograft model showed that the administration of FNIII14 can inhibit tumor growth, and concomitantly a remarkable decrease in N-Myc levels in tumor tissues. Of note, the activation of proteasomal degradation based on β1-integrin inactivation is applicable to another Myc family oncoprotein, c-myc, which also reverses cancer-associated properties in pancreatic cancer cells. Collectively, β1-integrin inactivation could be a new chemotherapeutic strategy for cancers with highly expressed Myc. FNIII14, which is a unique pharmacological agent able to induce β1-integrin inactivation, may be a promising drug targeting Myc oncoproteins for cancer chemotherapy.

The stereotypical molecular cascade in neovascular age-related macular degeneration: the role of dynamic reciprocity

This review summarises our current understanding of the molecular basis of subretinal neovascularisation (SRNV) in age-related macular degeneration (AMD). The term neovascular AMD (NVAMD) is derived from the dominant early clinical features of haemorrhage, fluid, and lipid in the subretinal space (SRS) and the historical role of fluorescein angiography in detecting the presence of NV tissue. However, at the cellular level, SRNV resembles an aberrant but stereotypical tissue repair response that incorporates both an early inflammatory phase and a late fibrotic phase in addition to the neovascular (NV) component that dominates the early clinical presentation. This review will seek not only to highlight the important molecules involved in each of these components but to demonstrate that the development of SRNV has its origins in the earliest events in non-NV AMD pathogenesis. Current evidence suggests that this early-stage pathogenesis is characterised by complement-mediated immune dysregulation, leading to a state of chronic inflammation in the retinal pigment epithelium/Bruch's membrane/choriocapillaris complex. These initial events can be seamlessly and inextricably linked to late-stage development of SRNV in AMD by the process of dynamic reciprocity (DyR), the ongoing bidirectional communication between cells, and their surrounding matrix. Moreover, this correlation between disease onset and eventual outcome is reflected in the temporal and spatial correlation between chronic inflammation, NV, and fibrosis within the reparative microenvironment of the SRS. In summary, the downstream consequences of the earliest dysfunctional molecular events in AMD can result in the late-stage entity we recognize clinically as SRNV and is characterized by a spectrum of predictable, related, and stereotypical processes referred to as DyR.

Matricellular protein thrombospondins: influence on ocular angiogenesis, wound healing and immuneregulation

Thrombospondins are a family of large multi-domain glycoproteins described as matricelluar proteins based on their ability to interact with a broad range of receptors, matrix molecules, growth factors or proteases, and to modulate array of cellular functions including intracellular signaling, proliferation and migration. Two members of the thrombospondin family, thrombospondin 1 (TSP-1) and thrombospondin 2 (TSP-2) are studied extensively to determine their structure and function. While expressed at low levels in normal adult tissues, their increased expression is seen predominantly in response to cellular perturbations. Despite structural similarities, a notable functional difference between TSP-1 and TSP-2 includes the ability of former to activate of latent TGF-β and its competitive inhibition by the latter. Both these thrombospondins are reported to play important roles in TGF-β rich ocular environment with most reports related to TSP-1. They are expressed by many ocular cell types and detectable in the aqueous and vitreous humor. TSP-1 and TSP-2 influence many cellular interactions in the eye such as angiogenesis, cell migration, wound healing, TGF-β activation and regulation of inflammatory immune responses. Together, these processes are known to contribute to the immune privilege status of the eye. Emerging roles of TSP-1 and TSP-2 in ocular functions and pathology are reviewed here.

Triethylphosphite as a network forming agent enhances in vitro biocompatibility and corrosion protection of hybrid organic–inorganic sol–gel coatings for Ti6Al4V alloys

Introduction of phosphorous into hybrid silica sol–gel coatings on Ti6Al4V gives materials demonstrating higher levels of intermolecular condensation and fibrinogen uptake as well as improved in vitro biocompatibility and corrosion protection.

Secreted protein acidic and rich in cysteine (SPARC) is associated with nasopharyngeal carcinoma metastasis and poor prognosis

Background

The aim of the present study was to analyse the expression of Secreted protein acidic and rich in cysteine (SPARC) in nasopharyngeal carcinoma (NPC) specimens, and to evaluate its correlation with clinicopathologic features, including survival of patients with NPC

Methods

NPC tissue microarrays (TMAs) were constructed from Sun Yat-sen University Cancer Center (SYSUCC), another three centers on mainland China, Singapore and Hong Kong. Using quantitative RT-PCR and Western-blotting techniques, we detected mRNA and protein expression of SPARC in NPC cell lines and immortalized nasopharyngeal epithelial cells (NPECs) induced by Bmi-1 (NPEC2 Bmi-1). The difference of SPARC expression in the cell lines was tested using a t-test method. The relationship between the SPARC expression and clinicopathological data was assessed by chi-square. Survival analysis was estimated using the Kaplan-Meier approach with log-rank test. Univariate and multivariate analyses of clinical variables were performed using Cox proportional hazards regression models.

Results

The expression levels of SPARC mRNA and protein were markedly higher in NPC cell lines than in NPEC2 Bmi-1. Especially, the expression levels of SPARC mRNA and protein were much lower in the 6-10B than in the 5-8 F (P = 0.002, P = 0.001). SPARC immunostaining revealed cytoplasmic localization in NPC cells and no staining in the stroma and epithelium.

In addition, high level of SPARC positively correlated with the status of distant metastasis (P = 0.001) and WHO histological classification (P = 0.023). NPC patients with high SPARC expression also had a significantly poorer prognosis than patients with low SPARC expression (log-rank test, P < 0.001), especially patients with advanced stage disease (log-rank, P < 0.001). Multivariate analysis suggested that the level of SPARC expression was an independent prognostic indicator for the overall survival of patients with NPC (P < 0.001).

Conclusions

SPARC expression is common in NPC patients. Our data shows that elevated SPARC expression is a potential unfavorable prognostic factor for patients with NPC.

Thrombospondin1 in tissue repair and fibrosis: TGF-β-dependent and independent mechanisms

Thrombospondin 1 (TSP1) plays major roles in both physiologic and pathologic tissue repair. TSP1 through its type 1 repeats is a known regulator of latent TGF-β activation and plays a role in wound healing and fibrosis. Binding of the TSP N-terminal domain to cell surface calreticulin in complex with LDL-receptor related protein 1 stimulates intermediate cell adhesion, cell migration, anoikis resistance, collagen expression and matrix deposition in an in vivo model of the foreign body response. There is also emerging evidence that TSP EGF-like repeats alter endothelial cell-cell interactions and stimulate epithelial migration through transactivation of EGF receptors. The mechanisms underlying these functions of TSP1 and the implications for physiologic and pathologic wound repair and fibrosis will be discussed.

Transcriptome analysis of the effects of gomisin a on the recovery of carbon tetrachloride-induced damage in rat liver

Gomisin A possesses a hepatic function-facilitating property in liver-injured rats. Its preventive action on carbon tetrachloride-induced cholestasis is due to maintenance of the function of the bile acids-independent fraction. To investigate alterations in gene expression after gomisin A treatment on injured rat liver, DNA microarray analyses were performed on a Rat 44K 4-Plex Gene Expression platform with duplicated reactions after gomisin A treatment. We identified 255 up-regulated and 230 down-regulated genes due to the effects of gomisin A on recovery of carbon tetrachloride-induced rat liver damage. For functional characterization of these genes, Gene Ontology and Kyoto Encyclopedia of Genes and Genomes biochemical pathways analyses were performed. Many up-regulated or down-regulated genes were related to cell cycle or focal adhesion and cell death genes, respectively. Our microarray experiment indicated that the liver repair mechanism induced by gomisin A was strongly associated with increased gene expressions related to cell cycle and suppression of the gene expression related in cell death.

Molecular and structural insight into the role of key residues of thrombospondin-1 and calreticulin in thrombospondin-1-calreticulin binding

Thrombospondin-1 (TSP1) binding to calreticulin (CRT) on the cell surface signals focal adhesion disassembly, leading to the intermediate adhesive phenotype, cell migration, anoikis resistance, and collagen stimulation. Residues Lys 24 and 32 in TSP1 and amino acids 24-26 and 32-34 in CRT have been shown through biochemical and cell-based approaches to be critical for TSP1-CRT binding and signaling. This study investigated the molecular and structural basis for these key TSP1 and CRT residues in TSP1-CRT binding. On the basis of a validated TSP1-CRT complex structure, we adopted steered molecular dynamics simulations to determine the effect of mutation of these key residues on TSP1-CRT binding and validated the simulation results with experimental observations. We further performed 30 ns molecular dynamics simulations for wild-type TSP1, CRT, K24A/K32A mutant TSP1, and mutant CRT (residues 24-26 and 32-34 mutated to Ala) and studied the conformational and structural changes in TSP1 and CRT as the result of mutation of these critical residues. Results showed that mutation of residues 24 and 32 to Ala in TSP1 and of amino acids 24-26 and 32-34 to Ala in CRT results in a shortened β-strand in the binding site, decreased hydrogen bond occupancy for β-strand pairs that are located within or near the binding site, increased conformational flexibility of the binding site, a changed degree of dynamically correlated motion between the residues in the binding site and the other residues in protein, and a changed degree of overall correlated motion between the residues in the protein. These changes could directly contribute to the loss or weakened binding between TSP1 and CRT and the resultant effects on TSP1-CRT binding-induced cellular activities. Results from this study provide a molecular and structural insight into the role of these critical residues of TSP1 and CRT in TSP1-CRT binding.

Effects of RGDS sequence genetically interfused in the silk fibroin light chain protein on chondrocyte adhesion and cartilage synthesis

Initial chondrocyte-silk fibroin interactions are implicated in chondrogenesis when using fibroin as a scaffold for chondrocytes. Here, we focused on integrin-mediated cell-scaffold adhesion and prepared cell adhesive fibroin in which a tandem repeat of the Arg-Gly-Asp-Ser (RGDS) sequence was genetically interfused in the fibroin light chain (L-chain) (L-RGDSx2 fibroin). We investigated the effects of the sequence on chondrocyte adhesion and cartilage synthesis, in comparison to the effects of fibronectin. As the physicochemical surface properties (e.g., wettability and zeta potential) of the fibroin substrate were not affected by the modification, specific cell adhesion to the RGDS predominately changed the chondrocyte adhesive state. This suggestion was also supported by the competitive inhibition of chondrocyte attachment to the L-RGDSx2 fibroin substrate with soluble RGD peptides in the medium. Unlike fibronectin, the expression of RGDS in the fibroin L-chain had no effect on chondrocyte spreading area but enhanced mRNA expression levels of integrins alpha5 and beta1, and aggrecan at 12 h after seeding. Although both the sequence and fibronectin increased cell adhesive force, chondrocytes grown on the fibroin substrate exhibited a peak in the force with time in culture. These results suggested that moderate chondrocyte adhesion to fibroin induced by the RGDS sequence was able to maintain the chondrogenic phenotype and, from the histology findings, the sequence could facilitate chondrogenesis.

Dual sources of vitronectin in the human lower urinary tract: synthesis by urothelium vs. extravasation from the bloodstream

Vitronectin (VN), secreted into the bloodstream by liver hepatocytes, is known to anchor epithelial cells to basement membranes through interactions with cell surface integrin receptors. We report here that VN is also synthesized by urothelial cells of urothelium in vivo and in vitro. In situ hybridization, dideoxy sequencing, immunohistochemistry, and ELISA of urothelial cell mRNA, cDNA, tissue, and protein extracts demonstrated that the VN gene is active in vivo and in vitro. The expression of VN by urothelium is hypothesized to constitute one of several pathways that anchor basal cells to an underlying substratum and explains why urothelial cells adhere to glass and propagate under serum-free conditions. Therefore, two sources of VN in the human urinary bladder are recognized: 1) localized synthesis by urothelial cells and 2) extravasation of liver VN through fenestrated capillaries. When human plasma was fractionated by denaturing heparin affinity chromatography, VN was isolated in a biologically active form that supported rapid spreading of urothelial cells in vitro under serum-free conditions. This activity was inhibited by the matricellular protein SPARC via direct binding of VN to SPARC through a Ca(+2)-dependent mechanism. A novel form of VN, isolated from the same heparin affinity chromatography column and designated as the VN(c) chromatomer, also supported cell spreading but failed to interact with SPARC. Therefore, the steady-state balance among urothelial cells, their extracellular milieu, and matricellular proteins constitutes a principal mechanism by which urothelia are anchored to an underlying substrata in the face of constant bladder cycling.

Comparison of bone marrow stromal cell behaviors on poly(caprolactone) with or without surface modification: studies on cell adhesion, survival and proliferation

Poly(caprolactone) (PCL) is a promising biodegradable polymer for tissue engineering. However, intrinsically poor cell-adhesive properties of PCL may limit its application. In this study, the PCL film surface was modified with RGDC peptide by a chemical immobilization procedure. Furthermore, bone marrow stromal cell (BMSC) behaviors including attachment, spreading, focal adhesion formation, focal adhesion kinase (FAK) activation, apoptosis and proliferation when cultured on the modified PCL films were investigated. Our results demonstrated that PCL with RGD modification promoted initial BMSC attachment, spreading and focal adhesion formation. At a later time point (12 h), BMSC attachment on both RGD peptide-modified PCL and PCL-NH(2) films significantly increased compared to untreated PCL films. Importantly, FAK phosphorylation was significantly increased only on the films with RGD-modified films, not on the PCL-NH(2) films, demonstrating that PCL with RGD modification had an advantage in initiating the specific integrin-mediated signal transduction and might play an important role in the subsequent retardation in cell death and enhancement in cell proliferation. The present results provide more evidence that functionalizing PCL with RGD peptides may be a feasible way to improve the interaction between BMSC and PCL substrate, which is important in tissue engineering.

Cell-matrix interactions and dynamic mechanical loading influence chondrocyte gene expression and bioactivity in PEG-RGD hydrogels

The pericellular matrix (PCM) surrounding chondrocytes is thought to play an important role in transmitting biochemical and biomechanical signals to the cells, which regulates many cellular functions including tissue homeostasis. To better understand chondrocytes interactions with their PCM, three-dimensional poly(ethylene glycol) (PEG) hydrogels containing Arg-Gly-Asp (RGD), the cell-adhesion sequence found in fibronectin and which is present in the PCM of cartilage, were employed. RGD was incorporated into PEG hydrogels via tethers at 0.1, 0.4 and 0.8 mM concentrations. Bovine chondrocytes were encapsulated in the hydrogels and subjected to dynamic compressive strains (0.3 Hz, 18% amplitude strain) for 48h, and their response assessed by cell morphology, ECM gene expression, cell proliferation and matrix synthesis. Incorporation of RGD did not influence cell morphology under free swelling conditions. However, the level of cell deformation upon an applied strain was greater in the presence of RGD. In the absence of dynamic loading, RGD appears to have a negative effect on chondrocyte phenotype, as seen by a 4.7-fold decrease in collagen II/collagen I expressions in 0.8mM RGD constructs. However, RGD had little effect on early responses of chondrocytes (i.e. cell proliferation and matrix synthesis/deposition). When isolating RGD as a biomechanical cue, cellular response was very different. Chondrocyte phenotype (collagen II/collagen I ratio) and proteoglycan synthesis were enhanced with higher concentrations of RGD. Overall, our findings demonstrate that RGD ligands enhance cartilage-specific gene expression and matrix synthesis, but only when mechanically stimulated, suggesting that cell-matrix interactions mediate chondrocyte response to mechanical stimulation.

The interaction between bone marrow stromal cells and RGD-modified three-dimensional porous polycaprolactone scaffolds

We previously established a simple method to immobilize the Arg-Gly-Asp (RGD) peptide on polycaprolactone (PCL) two-dimensional film surfaces that significantly improved bone marrow stromal cell (BMSC) adhesion to these films. The current work extends this modification strategy to three-dimensional (3D) PCL scaffolds to investigate BMSC attachment, cellular distribution and cellularity, signal transduction and survival on the modified PCL scaffold compared to those on the untreated ones. The results demonstrated that treatment of 3D PCL scaffold surfaces with 1,6-hexanediamine introduced the amino functional groups onto the porous PCL scaffold homogenously as detected by a ninhydrin staining method. Followed by the cross-linking reaction, RGDC peptide was successfully immobilized on the surface of PCL scaffold. Although the static seeding method used in this study caused heterogeneous cell distribution, the RGD-modified PCL scaffold still demonstrated the improved BMSC attachment and cellular distribution in the scaffold. More importantly, the integrin-mediated signal transduction FAK-PI3K-Akt pathway was significantly up-regulated by RGD modification and a subsequent increase in cell survival and growth was found in the modified scaffold. The present study introduces an easy method to immobilize RGD peptide on the 3D porous PCL scaffold and provides further evidence that modification of 3D PCL scaffolds with RGD peptides elicits specific cellular responses and improves the final cell-biomaterial interaction.

SPARC accelerates disease progression in experimental crescentic glomerulonephritis

Podocytopenia characterizes many forms of glomerular disease, preceding the development of glomerulosclerosis. While detachment of viable podocytes from the underlying glomerular basement membrane is an important mechanism of podocyte loss, the underlying factors involved remain unclear. Secreted protein acidic and rich in cysteine (SPARC), a matricellular protein with counteradhesive properties, is normally expressed at low levels by the podocyte but is markedly increased following podocyte injury. Accordingly, we elucidate the role of SPARC in mediating experimental crescentic glomerulonephritis by inducing passive nephrotoxic nephritis in SPARC(+/+) and SPARC(-/-) mice. By days 4, 7, and 21 following disease induction, podocyte number is better preserved, glomerulosclerosis is ameliorated, and proteinuria is reduced in SPARC(-/-) mice as compared with SPARC(+/+) littermates. Moreover, the preserved podocyte number in SPARC(-/-) mice correlates with reduced urinary levels of both nephrin and podocin. To establish a causal role for SPARC in mediating detachment, cultured SPARC(+/+) and SPARC(-/-) podocytes were subjected to mechanical strain as well as trypsin digestion, and detachment assays were performed. While podocytes lacking SPARC were more resistant to stretch-induced detachment, stable re-expression of SPARC restored detachment rates to levels comparable with SPARC(+/+) podocytes. Taken together, this study proves that SPARC plays a causal role in mediating podocyte detachment and accelerating glomerulosclerosis in experimental crescentic glomerulonephritis.

SPARC is expressed by macroglia and microglia in the developing and mature nervous system

SPARC (secreted protein, acidic and rich in cysteine) is a matricellular protein that is highly expressed during development, tissue remodeling, and repair. SPARC produced by olfactory ensheathing cells (OECs) can promote axon sprouting in vitro and in vivo. Here, we show that in the developing nervous system of the mouse, SPARC is expressed by radial glia, blood vessels, and other pial-derived structures during embryogenesis and postnatal development. The rostral migratory stream contains SPARC that becomes progressively restricted to the SVZ in adulthood. In the adult CNS, SPARC is enriched in specialized radial glial derivatives (Müller and Bergmann glia), microglia, and brainstem astrocytes. The peripheral glia, Schwann cells, and OECs express SPARC throughout development and in maturity, although it appears to be down-regulated with maturation. These data suggest that SPARC may be expressed by glia in a spatiotemporal manner consistent with a role in cell migration, neurogenesis, synaptic plasticity, and angiogenesis.

Additive effect of RGD coating to functionalized titanium surfaces on human osteoprogenitor cell adhesion and spreading

Titanium-based biomaterials for endosseous implants have found widespread applications in the orthopedic, maxillofacial, and dental domains. Indeed, the surface characteristics such as their chemical modification control considerably the cellular response and, subsequently, the quality and the quantity of new-formed bone around the implant. In this study, human osteoprogenitor (HOP) cell adhesion on different titanium surfaces functionalized with hydroxyapatite (HA), type I collagen, or Arg-Gly-Asp (RGD)-containing peptides is investigated by the quartz crystal resonators and by confocal laser scanning microscopy (CLSM) for the imaging of focal contact formation. Data obtained by quartz crystal resonator technique revealed that RGD-containing peptides alone increase HOP cell adhesion in early time period of culture. Moreover, association of RGD-containing peptides with either type I collagen or with HA layers induces an additive effect on HOP cell adhesion compared to Ti-Coll or Ti-HA. CLSM shows both the area of focal contact by cell unit and the cytoskeleton network organization to differ according to the surfaces. Interestingly, association of RGD-containing peptides with HA layers induces an additive effect on focal contact formation on HOP cells compared to Ti-HA alone. These data confirm that an RGD peptide effect occurs in the early time of culture, which is beneficial for osteoblast to spreading, differentiation, and survival.

LDL receptor-related protein 1: unique tissue-specific functions revealed by selective gene knockout studies

The LDL receptor-related protein (originally called LRP, but now referred to as LRP1) is a large endocytic receptor that is widely expressed in several tissues. LRP1 is a member of the LDL receptor family that plays diverse roles in various biological processes including lipoprotein metabolism, degradation of proteases, activation of lysosomal enzymes, and cellular entry of bacterial toxins and viruses. Deletion of the LRP1 gene leads to lethality in mice, revealing a critical, but as of yet, undefined role in development. Tissue-specific gene deletion studies reveal an important contribution of LRP1 in the vasculature, central nervous system, macrophages, and adipocytes. Three important properties of LRP1 dictate its diverse role in physiology: 1) its ability to recognize more than 30 distinct ligands, 2) its ability to bind a large number of cytoplasmic adaptor proteins via determinants located on its cytoplasmic domain in a phosphorylation-specific manner, and 3) its ability to associate with and modulate the activity of other transmembrane receptors such as integrins and receptor tyrosine kinases.

ZRP-1 controls Rho GTPase-mediated actin reorganization by localizing at cell-matrix and cell-cell adhesions

Focal adhesion protein ZRP-1/TRIP6 has been implicated in actin reorganization and cell motility. The role of ZRP-1, however, remained obscure because previously reported data are often conflicting one another. In the present study, we examined roles of ZRP-1 in HeLa cells. ZRP-1 is localized to the cell-cell contact sites as well as to cell-matrix contact sites in HeLa cells. RNA-interference-mediated depletion of ZRP-1 from HeLa cells revealed that ZRP-1 is essential not only for the formation of stress fibers and assembly of mature focal adhesions, but also for the actin reorganization at cell-cell contact sites and for correct cell-cell adhesion and, thus, for collective cell migration. Impairment of focal adhesions and stress fibers caused by ZRP-1 depletion has been associated with reduced tyrosine phosphorylation of FAK. However, maturation of focal adhesions could not be recovered by expression of active FAK. Interestingly, stress fibers in ZRP-1-depleted cells were ameliorated by exogenous expression of RhoA. We also found that total Rac1 activity is elevated in ZRP-1-depleted cells, resulting in abnormal burst of actin polymerization and dynamic membrane protrusions. Taken together, we conclude that that ZRP-1 plays a crucial role in coupling the cell-matrix/cell-cell-contact signals with Rho GTPase-mediated actin remodeling by localizing at cell-matrix and cell-cell contact sites.

Trafficking of osteonectin by retinal pigment epithelial cells: Evidence for basolateral secretion

Osteonectin is a glycoprotein that modulates several aspects of cellular behaviour including proliferation and adhesion. The retinal pigment epithelium forms a continuous monolayer of polarised cells immediately bellow the neuroretina, and is integral to the homeostasis of photoreceptor cells. While osteonectin is expressed by normal retinal pigment epithelium in situ, its expression is significantly increased in retinal pigment epithelial cells associated with several common retinal diseases. This pattern of expression implies an important role for osteonectin in the biology of retinal pigment epithelial cells. However, the trafficking, processing, and eventual fate of osteonectin in these cells is not clear at present. Although the theoretical report of a leader sequence within the osteonectin open reading frame and its extracellular presence in some tissues indirectly support secretion of the protein, there is no direct experimental demonstration of the secretion route to date. As a first step towards understanding the role of osteonectin in retinal pigment epithelium, we studied the intracellular distribution and trafficking of the protein in living cells. Here, we present experimental evidence that a precursor osteonectin fusion protein is targeted to the endoplasmic reticulum/Golgi pathway, with a likely basal secretion in retinal pigment epithelial cells. In addition, we show that the precursor osteonectin protein having the leader sequence masked fails to undergo secretion leading to cell death, a phenotype which may be of relevance not only for retinal pathology, but also for other diseases such as the bone disorder known as pseudoachondroplasia that is associated with a lack of osteonectin secretion.

Leukocyte-specific protein 1 (LSP1): a regulator of leukocyte emigration in inflammation

LSP1 is an F-actin bundling cytoskeletal protein expressed in hematopoietic lineage and endothelial cells. We investigated the function of this protein by generating and analyzing an LSP1-deficient mouse strain and in this review we describe our findings together with those of other investigators. The results show a complex function of LSP1 in regulating leukocyte recruitment to inflamed sites. Based on current evidence, we propose that the levels of LSP1 on the cytoskeleton and the type of integrin involved are some of the critical elements which affect LSP1 function in modulating the threshold for transmigration.

Cyclic biaxial strain affects U937 macrophage-like morphology and enzymatic activities

As monocytes migrate to the site of a foreign body and differentiate into mature monocyte-derived macrophages (MDMs), the cells undergo a morphological transformation that involves mechanical stimulation via membrane stretch. Because the site of many cardiovascular implant devices includes substrates that are also undergoing mechanical change, it is of interest to assess the effect of such dynamic conditions on cellular-biomaterial responses. This study investigated the influence of cyclic (0.25 Hz) biaxial strain (maximum 10% amplitude) on human U937 macrophage-like cells cultured on a flexible siloxane membrane. Cell attachment was unaffected by the strain but total protein levels were significantly higher in stimulated cells. Intracellular esterase and released acid phosphatase activities were elevated by dynamic loading in addition to a strain-induced increase of monocyte-specific esterase protein as demonstrated by immunoblotting analysis. The morphology of static cells changed with cyclic strain from a round cell shape to an irregular, spread phenotype with a progressive reorganization of filamentous actin. The focal adhesion protein vinculin showed distinct reorganization in structure going from a well-defined arrangement in static cells to a diffuse staining pattern in mechano-stimulated cells. This study has demonstrated that U937 cells respond to cyclic deformation with an augmentation of select enzymatic activities that have been identified as being important in polymer biodegradation processes, as well as morphological changes, which may be characteristic of mechanical stress-induced cell activation.

Roles of osteonectin in the migration of breast cancer cells into bone

The focus of this study was to gain insight into the role(s) of osteonectin in the preferential metastasis of breast cancer cells to bone. Osteonectin was isolated from conditioned media of several cell lines including breast cancer (MDA-MB-435, MDA-MB-468), osteoblasts (hFOB1.19), non-neoplastic breast epithelial (hTERT-HME1), and vascular endothelial cells isolated from a bone biopsy (HBME-1). Chemical/physical properties of osteonectin from these five sources was analyzed to determine if unique configurations of osteonectin exist and therefore identify a chemotactic isoform. Osteonectin from all sources had a molecular weight of approximately 46 kDa, N-linked glycosylation, and undetectable phosphorylated serines, sialic acids and O-linked oligosaccharides. The cDNA for osteonectin from the breast cancer, osteoblast, and breast epithelial cell lines was identical, while the vascular endothelial cell cDNA contained point mutations that resulted in eight amino acid substitutions. Bone-derived osteonectin was then analyzed to assess its influence on breast cancer cell motility and migration. Although osteonectin increased undirected MDA-MB-231 cell motility, it did not chemoattract the same breast cancer cell line. However, the breast cancer cells did migrate toward the known chemoattractant vitronectin and to bone extracts derived from wild-type and osteonectin-null mice. Migration to vitronectin was enhanced when osteonectin was also present. We concluded that osteonectin was not a chemotactic factor. However, through its anti-adhesive properties, osteonectin induced undirected breast cancer cell motility, and may have enhanced chemoattraction to vitronectin.

Development and characterization of a high-throughput system for assessing cell-surface receptor-ligand engagement

A nonfouling interfacial interpenetrating polymer network (IPN) of poly(acrylamide-co-ethylene glycol/acrylic acid) [p(AAm-co-EG/AAc)] was grafted to polystyrene for use as a novel platform for the development of high-throughput assays for screening of specific bimolecular interactions (i.e., receptor-ligand engagement). For the development of the IPN, a water-soluble hydrogen-abstracting photoinitiator was investigated: (4-benzoylbenzyl)trimethylammonium chloride. IPN-modified polystyrene surfaces were characterized using XPS, contact angle goniometry, and protein adsorption analysis. These IPN surfaces minimized fibrinogen adsorption compared to tissue culture polystyrene (>96% reduction), prevented mammalian cell adhesion, and served as nonfouling surfaces to graft biological ligands. For bimolecular interaction studies, a model peptide ligand from bone sialoprotein (Ac-CGGNGEPRGDTYRAY-NH(2)) was grafted to p(AAm-co-EG/AAc) via a 3400 M(w) linear pEG spacer. Ligand density measurements, cell culture, and a centrifugal adhesion assay were used to study cell adhesion to peptide-modified IPNs (i.e., receptor-ligand engagement). Ligand density (Gamma) was controllable from approximately 1 to 20 pmol/cm(2) by modulating the peptide input concentration (0.02-20 microM). Cell adhesion was directly dependent on the ligand density. This technology creates a powerful high-throughput system to simultaneously probe a myriad of cell-surface receptor-ligand interactions.

Effects of Different Titanium Alloys and Nanosize Surface Patterning on Adhesion, Differentiation, and Orientation of Osteoblast-Like Cells

To test nanosize surface patterning for application as implant material, a suitable titanium composition has to be found first. Therefore we investigated the effect of surface chemistry on attachment and differentiation of osteoblast-like cells on pure titanium prepared by pulsed laser deposition (TiPLD) and different Ti alloys (Ti6Al4V, TiNb30 and TiNb13Zr13). Early attachment (30 min) and alkaline phosphatase (ALP) activity (day 5) was found to be fastest and highest, respectively, in cells grown on TiPLD and Ti6Al4V. Osteoblasts seeded on TiPLD produced most osteopontin (day 10), whereas expression of this extracellular matrix protein was an order of magnitude lower on the TiNb30 surface. In contrast, expression of the corresponding receptor, CD44, was not influenced by surface chemistry. Thus, TiPLD was used for further experiments to explore the influence of surface nanostructures on osteoblast adhesion, differentiation and orientation. By laser-induced oxidation, we produced patterns of parallel Ti oxide lines with different widths (0.2-10 microm) and distances (2-20 and 1,000 microm), but a common height of only 12 nm. These structures did not influence ALP activity (days 5-9), but had a positive effect on cell alignment. Two days after plating, the majority of the focal contacts were placed on the oxide lines. The portion of larger focal adhesions bridging two lines was inversely related to the line distance (2-20 microm). In contrast, the portion of aligned cells did not depend on the line distance. On average, 43% of the cells orientated parallel towards the lines, whereas 34% orientated vertically. In the control pattern (1,000 microm line distance), cell distribution was completely at random. Because a significant surplus of the cells preferred a parallel alignment, the nanosize difference in height between Ti surface and oxide lines may be sufficient to orientate the cells by contact guiding. However, gradients in electrostatic potential and surface charge density at the Ti/Ti oxide interface may additionally influence focal contact formation and cell guidance.

Spreading of embryologically distinct urothelial cells is inhibited by SPARC

The AON epitope of secreted protein acidic and rich in cysteine (SPARC) is a conserved motif expressed by human SPARC in a variety of human cell types. Through the use of a monoclonal antibody that recognizes this epitope, transitional epithelium was found to restrict expression of SPARC to the suprabasal and intermediate layer. Such intracellular expression was defined by immunoreactive signals that localized to the apical plasma membranes of suprabasal and intermediate cells. Polarization of SPARC to apical plasma membranes of suprabasal cells was retained in vitro by a subpopulation of cells that exhibited characteristics of suprabasal cells--cell-cycle quiescence, large cell volumes, and multiple nuclei. In contrast, the basal layer of transitional epithelium in vivo and cycling cells in vitro did not exhibit this apical staining pattern, but instead sequestered the SPARC polypeptide within urothelial cytoplasm and/or nuclei, as revealed by immunohistochemical analysis. Elution of soluble proteins and DNA from urothelial cells revealed the presence of SPARC within the nuclear matrix--and that SPARC colocalized with the nuclear matrix Ki-67 antigen. rSPARC activity was demonstrated and quantified with a rounding assay whereby the spreading of freshly plated cells was inhibited by recombinant SPARC in a concentration- and time-dependent manner. Inhibition of spreading was observed in urothelial cells derived from endoderm (bladder) and mesoderm (ureter) germ layers. Statistically significant differences were seen between urothelial cells from these two layers. Mesodermal cells recovered more slowly from the inhibitory effects of rSPARC, such that at hour 6 endodermal cells underwent significantly more spreading, as shown by a rounding index (RI). These experiments provide new insights about the matricellular trafficking of SPARC and suggest that intra- and extra-cellular localization patterns influence the development, homeostasis, and differentiation of transitional epithelium.

Thrombospondin-1 in the trabecular meshwork: localization in normal and glaucomatous eyes, and induction by TGF-beta1 and dexamethasone in vitro

Transforming growth factor-beta2 (TGF-beta2) is elevated in the aqueous humor of patients with primary open-angle glaucoma (POAG), and high levels of TGF-beta2 are thought to contribute to the pathogenesis of POAG. Most TGF-beta2 in the eye is present in a latent, inactive form and the mechanisms of its in vivo activation are unclear. Since thrombospondin-1 (TSP-1) is one of the most potent in vivo activating molecules of TGF-betas, we investigated the localization and expression of TSP-1 in the aqueous humor outflow pathways. TSP-1 immunohistochemistry was performed in the eyes of human donors (8 normal and 17 with glaucoma). In addition, the eyes of Tsp-1(-/-)-deficient mice and normal Tsp-1(+/+) mice were investigated. TSP-1 mRNA expression was assessed by reverse transcription-polymerase chain reaction and Northern blotting of RNA from fresh trabecular meshwork (TM), and human and mouse TM cells in vitro. In addition, Northern and Western blot analyses of TM cells after incubation with TGF-beta and dexamethasone were performed. In most of the eyes, TSP-1 immunolabeling was predominantly observed in extracellular areas of the juxtacanalicular (cribriform) part of the TM. Some focal staining was observed in the corneoscleral and uveal parts of the TM. In the eyes of six glaucoma patients (including one with steroid-induced glaucoma), TSP-1 immunoreactivity was considerably more intense and all regions of the TM were positively labeled. In double labeling experiments, staining for TSP-1 did not overlap with that of fibronectin or type VI collagen. mRNA for TSP-1 was detected in both fresh and cultured TM cells. Incubation of TM cells with TGF-beta1 and dexamethasone caused a marked increase in TSP-1 expression. TSP-1 in the TM might act as a potent local endogenous activator of TGF-betas in the aqueous humor and mediate any local effects of TGF-beta and/or dexamethasone on the outflow of aqueous humor.

Thrombospondin Induces RhoA Inactivation through FAK-dependent Signaling to Stimulate Focal Adhesion Disassembly

Cells utilize dynamic interactions with the extracellular matrix to adapt to changing environmental conditions. Thrombospondin 1 (TSP1) induces focal adhesion disassembly and cell migration through a sequence (hep I) in its heparin-binding domain signaling through the calreticulin-low density lipoprotein receptor-related protein receptor complex. This involves the Galphai-dependent activation of ERK and phosphoinositide (PI) 3-kinase, both of which are required for focal adhesion disassembly. Focal adhesion kinase (FAK) regulates adhesion dynamics, acting in part by modulating RhoA activity, and FAK is implicated in ERK and PI 3-kinase activation. In this work, we sought to determine the role of FAK in TSP1-induced focal adhesion disassembly. TSP1/hep I does not stimulate focal adhesion disassembly in FAK knockout fibroblasts, whereas re-expressing FAK rescues responsiveness. Inhibiting FAK signaling through FRNK or FAK Y397F expression in endothelial cells also abrogates this response. TSP1/hep I stimulates a transient increase in FAK phosphorylation that requires calreticulin and Galphai, but not ERK or PI 3-kinase. Hep I does not activate ERK or PI 3-kinase in FAK knockout fibroblasts, suggesting activation occurs downstream of FAK. TSP1/hep I stimulates RhoA inactivation with kinetics corresponding to focal adhesion disassembly in a FAK, ERK, and PI 3-kinase-dependent manner. Furthermore, hep I does not stimulate focal adhesion disassembly in cells expressing constitutively active RhoA, suggesting that RhoA inactivation is required for this response. This is the first work to illustrate a connection between FAK phosphorylation in response to a soluble factor and RhoA inactivation, as well as the first report of PI 3-kinase and ERK in FAK regulation of RhoA activity.

Importance of integrin beta1-mediated cell adhesion on biodegradable polymers under serum depletion in mesenchymal stem cells and chondrocytes

To evaluate the predominant mechanism of chondrogenic cell [mesenchymal stem cells (MSCs) and chondrocytes] adhesion under serum free conditions, we measured the surface roughness and wettability of poly(lactic acid:polyglycolic acid=75:25) (PLGA), poly(lactic acid) (PLA), and poly(-epsilon-caprolactone) (PCL)-coated glass plates. Also to evaluate the biological reactions involved in cell-polymer interactions, integrin beta1, one of the cell adhesion molecules, was blocked with monoclonal antibody. In cell attachment test, MSCs and chondrocytes adhesion to synthetic polymers in 1h were very low and ranged from 2.8% to 8.0%. In present study, the correlation between attachment rate and surface roughness, contact angle, or integrin beta1 blocking on PLGA, PLA and PCL-coated plates could not be proved. However, we found that L-arginine-coated PLA highly increased the attachment rates of MSCs (30.2%) and of chondrocytes (26%), whereas integrin beta1 blocking significantly decreased these attachment rates to 5.6% and 7.4%, respectively, suggesting that increased cell adhesion to L-arginine-coated plates is mediated by integrin beta1. In this study, we showed that polymer characteristics such as roughness and wettability did not play an important role in cell adhesion under serum free conditions, because there was no significant difference according to polymer characteristics, whereas biological interactions mediated by integrin beta1 were critical during the early period of cell adhesion. The results suggest that L-arginine could be useful for facilitating early cell adhesion to synthetic polymers in cartilage tissue engineering.

Extracellular matrix molecules regulate endothelial cell migration stimulated by lysophosphatidic acid

BACKGROUND

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) are lipids that bind G-protein coupled receptors and differentially promote transmigration of endothelial cells.

OBJECTIVE

To determine if endothelial cell transmigration stimulated by LPA, not S1P, is dependent on the extracellular matrix.

METHODS

Bovine pulmonary artery (BPAE) endothelial cell transmigration and locomotion were measured using a modified-Boyden chamber and video microscopy, respectively. Results were related to strength of adhesion and characteristics of cell adhesive contacts.

RESULTS AND CONCLUSIONS

BPAEs responded to LPA by transmigration through gelatin- or collagen-coated filters, but not through fibronectin-, vitronectin-, or fibrinogen-coated filters. Fewer cells adhered to collagen or gelatin than to fibronectin in a static cell adhesion assay or after application of a g-force to detach cells. Video microscopy revealed that S1P stimulates large lamellipodia on two-dimensional fibronectin substrate. LPA stimulated lamellipodia on fibronectin, but the trailing edge remained attached, resulting in sting ray-shaped cells in video microscopy. LPA-treated cells on gelatin released the trailing edge. To understand how the extracellular matrix may regulate endothelial cell shape during movement, we surveyed changes in focal adhesion proteins. More Hic-5, a paxillin homolog, was detected in the detergent insoluble fraction of BPAEs attached to gelatin than fibronectin. No such difference was found in paxillin. In BPAEs, Hic-5 was localized to smaller punctate structures on fibronectin and longer, thinner focal adhesions on gelatin. These results indicated that localization of Hic-5 and strength of adhesion correlate with endothelial cell transmigration stimulated by LPA, but not with transmigration stimulated by S1P.

Thy-1 regulates fibroblast focal adhesions, cytoskeletal organization and migration through modulation of p190 RhoGAP and Rho GTPase activity

The precise biological role of Thy-1, a glycophosphatidyl-inositol (GPI)-linked cell surface glycoprotein in non-caveolar lipid raft microdomains, remains enigmatic. Evidence suggests that Thy-1 affects intracellular signaling through src-family protein kinases, and modulates adhesive and migratory events, such as thymocyte adhesion and neurite extension. Primary fibroblasts sorted based on presence or absence of cell surface Thy-1 display strikingly distinct morphologies and differ with respect to production of and response to cytokines and growth factors. It is unclear the extent to which Thy-1 mediates these differences. Findings reported here indicate a novel role for Thy-1 in regulating the activity of Rho GTPase, a critical regulator of cellular adhesion and cytoskeletal organization. Endogenous or heterologous Thy-1 expression promotes focal adhesion and stress fiber formation, characteristic of increased Rho GTPase activity, and inhibits migration. Immunoblotting following transfection of RFL6 fibroblasts with Thy-1 demonstrates that Thy-1 expression inhibits src-family protein tyrosine kinase (SFK) activation, resulting in decreased phosphorylation of p190 Rho GTPase-activating protein (GAP). This results in a net increase in active Rho, and increased stress fibers and focal adhesions. We therefore conclude that Thy-1 surface expression regulates fibroblast focal adhesions, cytoskeletal organization and migration by modulating the activity of p190 RhoGAP and Rho GTPase.

Thrombospondin-1-induced focal adhesion disassembly in fibroblasts requires Thy-1 surface expression, lipid raft integrity, and Src activation

The hep I peptide of thrombospondin-1 is known to induce the disassembly of focal adhesions, a critical step in regulating cellular adhesive changes needed for cell motility. Fibroblasts that are heterogeneous with respect to the surface expression of Thy-1 differ markedly in morphology, cytoskeletal organization, and migration, suggesting differential regulation of focal adhesion dynamics. Here we demonstrate that disassembly of focal adhesions mediated by both full-length thrombospondin-1 and the hep I peptide in fibroblasts requires the expression of Thy-1, although it does not appear to function as a stable member of the hep I receptor complex. Consistent with a known function of Thy-1 in regulating lipid raft-associated signaling, intact lipid rafts are necessary for hep I-mediated focal adhesion disassembly. Furthermore, we establish Src family kinase (SFK) activation as a novel component required for hep I-induced signaling leading to focal adhesion disassembly. hep I induces transient phosphorylation of SFKs in Thy-1-expressing fibroblasts only. Therefore, we conclude that Thy-1 surface expression is required for thrombospondin-1-induced focal adhesion disassembly in fibroblasts through an SFK-dependent mechanism. This represents a novel role for Thy-1 in the regulation of fibroblast-matrix interactions critical to tissue homeostasis and remodeling.

A simple model for the study of effects of the extracellular matrix on the cell morphology in vitro

In the present work, a simple technique is proposed to study the effects of native extracellular matrix (ECM) of one cell type on the properties of other cell types. It is based on a procedure in which, after cells of one type are removed from the substrate, cells of another type are seeded on the same substrate. To obtain preparations of native ECM, cells were removed from the substrate by 0.02% EDTA only, without any proteolytic enzymes. Cells were placed on coverslips in standard Petri dishes and incubated in a culture medium for a time sufficient for adhesion and spreading, but not long enough to undergo mitosis. Up to four coverslips per Petri dish can be incubated, and various combinations of ECM and cell types can be used in one dish. It is important, therefore, that the different "ECM-cell" combinations are present in the same culture medium. For evaluation of ECM effects, the area occupied by the cell on a substrate and the perimeter of the cell were measured, and frequencies of cell distribution were calculated according to these parameters.

Expression of a naturally occurring constitutively active variant of the epidermal growth factor receptor in mouse fibroblasts increases motility

Tumor cell motility is one of the rate-limiting steps of invasion, which defines progression toward a more malignant phenotype. Elevated expression of epidermal growth factor receptor (EGFR) in many cancers is associated with progression of superficial to invasive forms of the disease. The naturally occuring type III mutant epidermal growth factor receptor (EGFRvIII) is a tumor-specific, ligand-independent, constitutively active variant of the epidermal growth factor receptor. EGFRvIII is expressed frequently by a number of human solid tumours including those of the lung, breast, prostate, brain and ovary. Our study was designed to investigate the effect of EGFRvIII expression on cell motility and compare it to that of ligand-activated EGFR using transfected fibroblasts. We show here using time-lapse video recording that expression of EGFRvIII greatly enhances the motility of fibroblasts independently of ligand stimulation. In addition, expression of EGFRvIII caused a marked increase in the number of cellular protrusions (lamellipodia) and a reduction in the number of stress fibers and focal adhesions. The EGFR tyrosine kinase inhibitor, AG1478, and the MEK inhibitor, U0126, blocked these cellular effects of EGFRvIII. Two cell lines expressing different levels of EGFR were used for comparison. The low-expressing cell line responded to EGF treatment by increasing motility in a manner very similar to the motility induced by EGFRvIII. In contrast, the high-expressing cell line responded to EGF by detachment from the extracellular matrix and decreased motility. Cellular detachment was correlated to a high phosphorylation of PLC-gamma, whereas increased motility was correlated to a high level of ERK phosphorylation. Overall these results indicate that tumor-associated EGFR mutations might be critical for tumor cell motility, invasion and thus progression of disease.

Thrombospondin signaling through the calreticulin/LDL receptor-related protein co-complex stimulates random and directed cell migration

The matricellular extracellular matrix protein thrombospondin-1 (TSP1) stimulates focal adhesion disassembly through a sequence (known as the hep I peptide) in its heparin-binding domain. This mediates signaling through a receptor co-complex involving calreticulin and low-density lipoprotein (LDL) receptor-related protein (LRP). We postulate that this transition to an intermediate adhesive state enhances cellular responses to dynamic environmental conditions. Since cell adhesion dynamics affect cell motility, we asked whether TSP1/hep I-induced intermediate adhesion alters cell migration. Using both transwell and Dunn chamber assays, we demonstrate that TSP1 and hep I gradients stimulate endothelial cell chemotaxis. Treatment with focal adhesion-labilizing concentrations of TSP1/hep I in the absence of a gradient enhances endothelial cell random migration, or chemokinesis, associated with an increase in cells migrating, migration speed, and total cellular displacement. Calreticulin-null and LRP-null fibroblasts do not migrate in response to TSP1/hep I, nor do endothelial cells treated with the LRP inhibitor receptor-associated protein (RAP). Furthermore, TSP1/hep I-induced focal adhesion disassembly is associated with reduced chemotaxis to basic fibroblast growth factor (bFGF) but enhanced chemotaxis to acidic (a)FGF, suggesting differential modulation of growth factor-induced migration. Thus, TSP1/hep I stimulation of intermediate adhesion regulates the migratory phenotype of endothelial cells and fibroblasts, suggesting a role for TSP1 in remodeling responses.

FHL3 is an actin-binding protein that regulates alpha-actinin-mediated actin bundling: FHL3 localizes to actin stress fibers and enhances cell spreading and stress fiber disassembly

Four and a half LIM domain (FHL) proteins are members of the LIM protein superfamily. Several FHL proteins function as co-activators of CREM/CREB transcription factors and the androgen receptor. FHL3 is highly expressed in skeletal muscle, but its function is unknown. FHL3 localized to the nucleus in C2C12 myoblasts and, following integrin engagement, exited the nucleus and localized to actin stress fibers and focal adhesions. In mature skeletal muscle FHL3 was found at the Z-line. Actin was identified as a potential FHL3 binding partner in yeast two-hybrid screening of a skeletal muscle library. FHL3 complexed with actin both in vitro and in vivo as shown by glutathione S-transferase pull-down assays and co-immunoprecipitation of recombinant and endogenous proteins. FHL3 promoted cell spreading and when overexpressed in spread C2C12 cells disrupted actin stress fibers. Increased FHL3 expression was detected in highly motile cells migrating into an artificial wound, compared with non-motile cells. The molecular mechanism by which FHL3 induced actin stress fiber disassembly was demonstrated by low speed actin co-sedimentation assays and electron microscopy. FHL3 inhibited alpha-actinin-mediated actin bundling. These studies reveal FHL3 as a significant regulator of actin cytoskeletal dynamics in skeletal myoblasts.

Epithelial contact guidance on well-defined micro- and nanostructured substrates

The human corneal basement membrane has a rich felt-like surface topography with feature dimensions between 20 nm and 200 nm. On the basis of these findings, we designed lithographically defined substrates to investigate whether nanotopography is a relevant stimulus for human corneal epithelial cells. We found that cells elongated and aligned along patterns of grooves and ridges with feature dimensions as small as 70 nm, whereas on smooth substrates, cells were mostly round. The percentage of aligned cells was constant on substrate tomographies with lateral dimensions ranging from the nano- to the micronscale, and increased with groove depth. The presence of serum in the culture medium resulted in a larger percentage of cells aligning along the topographic patterns than when no serum was added to the basal medium. When present, actin microfilaments and focal adhesions were aligned along the substrate topographies. The width of the focal adhesions was determined by the width of the ridges in the underlying substrate. This work documents that biologic length-scale topographic features that model features encountered in the native basement membrane can profoundly affect epithelial cell behavior.

Elevated expression and altered processing of fibulin-1 protein in human breast cancer

The extracellular matrix protein fibulin-1 suppresses the motility and invasiveness of a variety of tumour cell types in vitro as well as the growth of fibrosarcoma tumours in nude mice. In this study, fibulin-1 protein expression in breast carcinoma specimens and normal breast tissue was evaluated immunohistologically. Fibulin-1 protein expression was also semiquantitatively assessed by immunoblot analysis in a collection of normal breast tissues (n=18), benign tumours (n=5) and breast carcinomas (n=39). In normal breast tissue, fibulin-1 protein expression predominated in the ductal epithelium and underlying myoepithelium, with weaker staining evident in the loose connective surrounding the ducts. Examination of breast carcinomas revealed that the tumour cells also expressed fibulin-1 protein. The level of mature fibulin-1 polypeptide (100 kDa) was higher in the breast carcinoma specimens as compared to normal breast tissue (Mann-Whitney U-test, P=0.0005). In addition to the mature fibulin-1 polypeptide, several smaller sized polypeptides of 55, 50 and 25 kDa were detected using monoclonal antibodies reactive towards an epitope located at the N-terminus of fibulin-1. The immunoreactive 50 kDa polypeptide was detected more frequently in breast carcinoma specimens than in normal breast tissue (chi(2)=17.22, P<0.0001). Furthermore, the ratio of the 50 kDa fragment to the mature fibulin-1 polypeptide correlated with the level of oestrogen receptor alpha (Spearman correlation coefficient, rs=0.49, P<0.003, n=36) and progesterone receptor (rs=0.43, P=0.008, n=36) expression in the tumour specimens. Taken together, these findings indicate that elevated expression and altered processing of fibulin-1 is associated with human breast cancer.