Modulation of apoptotic cell death by extracellular matrix proteins and a fibronectin-derived antiadhesive peptide

Into the Tissues: Extracellular Matrix and Its Artificial Substitutes: Cell Signalling Mechanisms

The existence of orderly structures, such as tissues and organs is made possible by cell adhesion, i.e., the process by which cells attach to neighbouring cells and a supporting substance in the form of the extracellular matrix. The extracellular matrix is a three-dimensional structure composed of collagens, elastin, and various proteoglycans and glycoproteins. It is a storehouse for multiple signalling factors. Cells are informed of their correct connection to the matrix via receptors. Tissue disruption often prevents the natural reconstitution of the matrix. The use of appropriate implants is then required. This review is a compilation of crucial information on the structural and functional features of the extracellular matrix and the complex mechanisms of cell-cell connectivity. The possibilities of regenerating damaged tissues using an artificial matrix substitute are described, detailing the host response to the implant. An important issue is the surface properties of such an implant and the possibilities of their modification.

Inhibition of fibronectin accumulation suppresses tumor growth

Understanding how the extracellular matrix affects cancer development constitutes an emerging research field. Fibronectin and collagen are two intriguing matrix components found in cancer. Large concentrations of fibronectin or collagen type I have been implicated in poor prognosis in patients. In a mouse model, we had shown that genetically decreasing circulating fibronectin resulted in smaller tumors. We therefore aimed to manipulate fibronectin pharmacologically and determine how cancer development is affected. Deletion of fibronectin in human breast cancer cells (MDA-MB-231) using shRNA (knockdown: Kd) improved survival and diminished tumor burden in a model of metastatic lesions and in a model of local growth. Based on these findings, it seemed reasonable to attempt to prevent fibronectin accumulation using a bacterial derived peptide called pUR4. Treatment with this peptide for 10 days in the breast cancer local growth model or for 5 days in a melanoma skin cancer model (B16) was associated with a significant suppression of cancer growth. Treatment aimed at inhibiting collagen type I accumulation without interfering with fibronectin could not affect any changes in vivo. In the absence of fibronectin, diminished cancer progression was due to inhibition of proliferation, even though changes in blood vessels were also detected. Decreased proliferation could be attributed to decreased ERK phosphorylation and diminished YAP expression. In summary, manipulating fibronectin diminishes cancer progression, mostly by suppressing cell proliferation. This suggests that matrix modulation could be used as an adjuvant to conventional therapy as long as a decrease in fibronectin is obtained.

Coadministration of the FNIII14 Peptide Synergistically Augments the Anti-Cancer Activity of Chemotherapeutic Drugs by Activating Pro-Apoptotic Bim

The acquisition of drug resistance mediated by the interaction of tumor cells with the extracellular matrix (ECM), commonly referred to as cell adhesion-mediated drug resistance (CAM-DR), has been observed not only in hematopoietic tumor cells but also in solid tumor cells. We have previously demonstrated that a 22-mer peptide derived from fibronectin, FNIII14, can inhibit cell adhesion through the inactivation of β1 integrin; when coadministered with cytarabine, FNIII14 completely eradicates acute myelogenous leukemia by suppressing CAM-DR. In this study, we show that our FNIII14 peptide also enhances chemotherapy efficacy in solid tumors. Coadministration of FNIII14 synergistically enhances the cytotoxicity of doxorubicin and aclarubicin in mammary tumor and melanoma cells, respectively. The solid tumor cell chemosensitization induced by FNIII14 is dependent upon the upregulation and activation of the pro-apoptotic protein, Bim. Furthermore, the metastasis of tumor cells derived from ventrally transplanted mammary tumor grafts is suppressed by the coadministration of FNIII14 and doxorubicin. These results suggest that the coadministration of our FNIII14 peptide with chemotherapy could achieve efficient solid tumor eradication by increasing chemosensitivity and decreasing metastasis. The major causes of tumor recurrence are the existence of chemotherapy-resistant primary tumor cells and the establishment of secondary metastatic lesions. As such, coadministering FNIII14 with anti-cancer drugs could provide a promising new approach to improve the prognosis of patients with solid tumors.

Human platelet lysate improves human cord blood derived ECFC survival and vasculogenesis in three dimensional (3D) collagen matrices

Human cord blood (CB) is enriched in circulating endothelial colony forming cells (ECFCs) that display high proliferative potential and in vivo vessel forming ability. Since diminished ECFC survival is known to dampen the vasculogenic response in vivo, we tested how long implanted ECFC survive and generate vessels in three-dimensional (3D) type I collagen matrices in vitro and in vivo. We hypothesized that human platelet lysate (HPL) would promote cell survival and enhance vasculogenesis in the 3D collagen matrices. We report that the percentage of ECFC co-cultured with HPL that were alive was significantly enhanced on days 1 and 3 post-matrix formation, compared to ECFC alone containing matrices. Also, co-culture of ECFC with HPL displayed significantly more vasculogenic activity compared to ECFC alone and expressed significantly more pro-survival molecules (pAkt, p-Bad and Bcl-xL) in the 3D collagen matrices in vitro. Treatment with Akt1 inhibitor (A-674563), Akt2 inhibitor (CCT128930) and Bcl-xL inhibitor (ABT-263/Navitoclax) significantly decreased the cell survival and vasculogenesis of ECFC co-cultured with or without HPL and implicated activation of the Akt1 pathway as the critical mediator of the HPL effect on ECFC in vitro. A significantly greater average vessel number and total vascular area of human CD31(+) vessels were present in implants containing ECFC and HPL, compared to the ECFC alone implants in vivo. We conclude that implantation of ECFC with HPL in vivo promotes vasculogenesis and augments blood vessel formation via diminishing apoptosis of the implanted ECFC.

Notch ligand Delta-like 1 promotes in vivo vasculogenesis in human cord blood-derived endothelial colony forming cells

BACKGROUND AIMS

Human cord blood (CB) is enriched in circulating endothelial colony forming cells (ECFCs) that display high proliferative potential and in vivo vessel forming ability. Because Notch signaling is critical for embryonic blood vessel formation in utero, we hypothesized that Notch pathway activation may enhance cultured ECFC vasculogenic properties in vivo.

METHODS

In vitro ECFC stimulation with an immobilized chimeric Notch ligand (Delta-like1(ext-IgG)) led to significant increases in the mRNA and protein levels of Notch regulated Hey2 and EphrinB2 that were blocked by treatment with γ-secretase inhibitor addition. However, Notch stimulated preconditioning in vitro failed to enhance ECFC vasculogenesis in vivo. In contrast, in vivo co-implantation of ECFCs with OP9-Delta-like 1 stromal cells that constitutively expressed the Notch ligand delta-like 1 resulted in enhanced Notch activated ECFC-derived increased vessel density and enlarged vessel area in vivo, an effect not induced by OP9 control stromal implantation.

RESULTS

This Notch activation was associated with diminished apoptosis in the exposed ECFC.

CONCLUSIONS

We conclude that Notch pathway activation in ECFC in vivo via co-implanted stromal cells expressing delta-like 1 promotes vasculogenesis and augments blood vessel formation via diminishing apoptosis of the implanted ECFC.

Biologic scaffold for CNS repair

Injury to the CNS typically results in significant morbidity and endogenous repair mechanisms are limited in their ability to restore fully functional CNS tissue. Biologic scaffolds composed of individual purified components have been shown to facilitate functional tissue reconstruction following CNS injury. Extracellular matrix scaffolds derived from mammalian tissues retain a number of bioactive molecules and their ability for CNS repair has recently been recognized. In addition, novel biomaterials for dural mater repairs are of clinical interest as the dura provides barrier function and maintains homeostasis to CNS. The present article describes the application of regenerative medicine principles to the CNS tissues and dural mater repair. While many approaches have been exploring the use of cells and/or therapeutic molecules, the strategies described herein focus upon the use of extracellular matrix scaffolds derived from mammalian tissues that are free of cells and exogenous factors.

Cell death induced on cell cultures and nude mouse skin by non-thermal, nanosecond-pulsed generated plasma

Non-thermal plasmas are gaseous mixtures of molecules, radicals, and excited species with a small proportion of ions and energetic electrons. Non-thermal plasmas can be generated with any high electro-magnetic field. We studied here the pathological effects, and in particular cell death, induced by nanosecond-pulsed high voltage generated plasmas homogeneously applied on cell cultures and nude mouse skin. In vitro, Jurkat cells and HMEC exhibited apoptosis and necrosis, in dose-dependent manner. In vivo, on nude mouse skin, cell death occurred for doses above 113 J/cm² for the epidermis, 281 J/cm² for the dermis, and 394 J/cm² for the hypodermis. Using electron microscopy, we characterized apoptosis for low doses and necrosis for high doses. We demonstrated that these effects were not related to thermal, photonic or pH variations, and were due to the production of free radicals. The ability of cold plasmas to generate apoptosis on cells in suspension and, without any sensitizer, on precise skin areas, opens new fields of application in dermatology for extracorporeal blood cell treatment and the eradication of superficial skin lesions.

Cell cycle arrest or survival signaling through αv integrins, activation of PKC and ERK1/2 lead to anoikis resistance of ovarian cancer spheroids

Ovarian cancer is the most lethal gynecologic cancer mainly due to spheroids organization of cancer cells that disseminate within the peritoneal cavity. We have investigated the molecular mechanisms by which ovarian cancer spheroids resist anoikis, choosing as models the 2 well-characterized human ovarian cancer cell lines IGROV1 and SKOV3. These cell lines have the propensity to float as clusters, and were isolated from tumor tissue and ascites, respectively. To form spheroids, IGROV1 and SKOV3 ovarian adenocarcinoma cells were maintained under anchorage-independent culture conditions, in which both lines survive at least a week. A short apoptotic period prior to a survival signaling commitment was observed for IGROV1 cells whereas SKOV3 cells entered G0/G1 phase of the cell cycle. This difference in behavior was due to different signals. With regard to SKOV3 cells, activation of p38 and an increase in p130/Rb occurred once anchorage-independent culture was established. Analyses of the survival signaling pathway switched on by IGROV1 cells showed that activation of ERK1/2 was required to evade apoptosis, an effect partly dependent on PKC activation and αv integrins. αv-integrin expression is essential for survival through activation of ERK1/2 phosphorylation. The above data indicate that ovarian cancer cells can resist anoikis in the spheroid state by arrest in the cell cycle or through activation of αv-integrin-ERK-mediated survival signals. Such signaling might result in the selection of resistant cells within disseminating spheroids, favoring further relapse in ovarian cancers.

Multifunctional materials through modular protein engineering

The diversity of potential applications for protein-engineered materials has undergone profound recent expansion through a rapid increase in the library of domains that have been utilized in these materials. Historically, protein-engineered biomaterials have been generated from a handful of peptides that were selected and exploited for their naturally evolved functionalities. In recent years, the scope of the field has drastically expanded to include peptide domains that were designed through computational modeling, identified through high-throughput screening, or repurposed from wild type domains to perform functions distinct from their primary native applications. The strategy of exploiting a diverse library of peptide domains to design modular block copolymers enables the synthesis of multifunctional protein-engineered materials with a range of customizable properties and activities. As the diversity of peptide domains utilized in modular protein engineering continues to expand, a tremendous and ever-growing combinatorial expanse of material functionalities will result.

Eukaryotic translation elongation factor 1A induces anoikis by triggering cell detachment

Anoikis, apoptosis because of loss of cell anchorage, is crucial for tissue homeostasis. Fibronectin not only provides a scaffold for cell anchorage but also harbors a cryptic antiadhesive site capable of inducing β1-integrin inactivation. In this study, this cryptic antiadhesive site is implicated in spontaneous induction of anoikis. Nontransformed fibroblasts (NIH3T3) adhering to a fibronectin substratum underwent anoikis during serum starvation culture. This anoikis was caused by proteolytic exposure of the cryptic antiadhesive site in fibronectin by matrix metalloproteinase. Eukaryotic elongation factor 1A (eEF1A) was identified as a membrane receptor for the exposed antiadhesive site. Serum starvation raised the membrane residence of eEF1A, and siRNA-based disruption of this increase rendered cells anoikis-resistant. By contrast, cells became more susceptible to anoikis in parallel with increased membrane residence of eEF1A by enforced expression. These results demonstrate that eEF1A acts as a membrane receptor for the cryptic antiadhesive site of fibronectin, which contributes to cell regulation, including anoikis, through negative regulation of cell anchorage.

Liver fibrosis protects mice from acute hepatocellular injury

BACKGROUND & AIMS

Development of fibrosis is part of the pathophysiologic process of chronic liver disease. Although it is considered deleterious, it also represents a form of tissue repair. Deposition of extracellular matrix changes the cellular environment of the liver; we investigated whether it increases resistance to noxious stimuli and the role of changes in intracellular signaling to hepatocytes in mediating this effect.

METHODS

Primary cultures of mouse hepatocytes were exposed to type I collagen (COL1); cell injury was assessed by morphologic and biochemical criteria. The expression of Bcl-2 family members was evaluated by immunoblot analyses. Activation of extracellular signal-regulated kinase (ERK) was assessed using phospho-specific antibodies. Liver fibrosis was induced by repeated administration of thioacetamide or carbon tetrachloride to mice; mice were then exposed to Fas antibodies.

RESULTS

Hepatocytes exposed to COL1 were more resistant to a variety of hepatotoxins, in a dose-dependent manner, and had lower levels of Bad, Bid, and Bax proapoptotic proteins compared with control hepatocytes. Activation of ERK1/2 was stronger and quicker in hepatocytes exposed to COL1. The MEK1/2 inhibitors U0126 and PD98059 reversed the protective effects of COL1 and the decrease in proapoptotic proteins. Hepatocytes isolated from ERK1(-/-) mice were insensitive to the protective effect of COL1. Fibrotic livers from wild-type mice had high levels of phospho-ERK1 and were resistant to Fas-induced cell death. ERK1(-/-) mice lost this effect.

CONCLUSIONS

Production of COL1 during liver fibrosis induces a hepatoprotective response that is mediated by activation of ERK1 signaling.

Fibronectin coating of collagen modules increases in vivo HUVEC survival and vessel formation in SCID mice

Modular tissue engineering is a novel approach to creating scalable, self-assembling, three-dimensional tissue constructs with inherent vascularization. Under initial methods, the subcutaneous implantation of human umbilical vein endothelial cell (HUVEC)-covered collagen modules in immunocompromised mice resulted in significant host inflammation and limited HUVEC survival. A minimally invasive injection technique was used to minimize surgery-related inflammation, and cell death was attributed to extensive apoptosis within 72 h of implantation. Coating collagen modules with fibronectin (Fn) was shown in vivo to reduce short-term HUVEC TUNEL staining by nearly 40%, while increasing long-term HUVEC survival by 30-45%, relative to collagen modules without fibronectin. Consequently, a ∼100% increase in the number of HUVEC-lined vessels was observed with Fn-coated modules, as compared to collagen-only modules, at 7 and 14 days post-implantation. Furthermore, vessels appeared to be perfused with host erythrocytes by day 7, and vessel maturation and stabilization was evident by day 14.

Endothelial cell behaviour within a microfluidic mimic of the flow channels of a modular tissue engineered construct

To study the effect of disturbed flow patterns on endothelial cells, the channels found within a modular tissue engineering construct were reproduced in a microfluidic chip and lined with endothelial cells whose resulting phenotype under flow was assessed using confocal microscopy. Modular tissue engineered constructs formed by the random packing of sub-millimetre, cylindrically shaped, endothelial cell-covered modules into a larger container creates interconnected channels that permit the flow of fluids such as blood. Due to the random packing, the flow path is tortuous and has the potential to create disturbed flow, resulting in an activated endothelium. At an average shear stress of 2.8 dyn cm⁻², endothelial cells within channels of varying geometries showed higher amounts of activation, as evidenced by an increase in ICAM-1 and VCAM-1 levels with respect to static controls. VE-cadherin expression also increased, however, it appeared discontinuous around the perimeter of the cells. An increase in flow (15.6 dyn cm⁻²) was sufficient to reduce ICAM-1 and VCAM-1 expression to a level below that of static controls for many disturbed flow-prone channels that contained branches, curves, expansions and contractions. VE-cadherin expression was also reduced and became discontinuous in all channels, possibly due to paracrine signaling. Other than showing a mild correlation to VE-cadherin, which may be linked through a cAMP-initiated pathway, KLF2 was found to be largely independent of shear stress for this system. To gauge the adhesiveness of the endothelium to leukocytes, THP-1 cells were introduced into flow-conditioned channels and their attachment measured. Relative to static controls, THP-1 adhesion was reduced in straight and bifurcating channels. However, even in the presence of flow, areas where multiple channels converged were found to be the most prone to THP-1 attachment. The microfluidic system enabled a full analysis of the effect of the tortuous flow expected in a modular construct on endothelial cell phenotype.

N-terminal and C-terminal heparin-binding domain polypeptides derived from fibronectin reduce adhesion and invasion of liver cancer cells

Background

Fibronectin (FN) is known to be a large multifunction glycoprotein with binding sites for many substances, including N-terminal and C-terminal heparin-binding domains. We investigated the effects of highly purified rhFNHN29 and rhFNHC36 polypeptides originally cloned from the two heparin-binding domains on the adhesion and invasion of highly metastatic human hepatocellular carcinoma cells (MHCC97H) and analyzed the underlying mechanism involved.

Methods

The MHCC97H cells that adhered to FN in the presence of various concentrations of rhFNHN29 and rhFNHC36 polypeptides were stained with crystal violet and measured, and the effects of rhFNHN29 and rhFNHC36 on the invasion of the MHCC97H cells were then detected using the Matrigel invasion assay as well as a lung-metastasis mouse model. The expression level of integrins and focal adhesion kinase (FAK) phosphotyrosyl protein was examined by Western blot, and the activity of matrix metalloproteinases (MMPs) and activator protein 1 (AP-1) was analyzed by gelatin zymography and the electrophoretic mobility band-shift assay (EMSA), respectively.

Results

Both of the polypeptides rhFNHN29 and rhFNHC36 inhibited adhesion and invasion of MHCC97H cells; however, rhFNHC36 exhibited inhibition at a lower dose than rhFNHN29. These inhibitory effects were mediated by integrin αvβ3 and reversed by a protein tyrosine phosphatase inhibitor. Polypeptides rhFNHN29 and rhFNHC36 abrogated the tyrosine phosphorylation of focal adhesion kinase (p-FAK) and activation of activator protein 1 (AP-1), resulting in the decrease of integrin αv, β3 and β1 expression as well as the reduction of MMP-9 activity.

Conclusions

Polypeptides rhFNHN29 and rhFNHC36 could potentially be applicable to human liver cancer as anti-adhesive and anti-invasive agents.

Single-cell hydrogel encapsulation for enhanced survival of human marrow stromal cells

Inadequate extracellular matrix cues and subsequent apoptotic cell death are among crucial factors currently limiting cell viability and organ retention in cell-based therapeutic strategies for vascular regeneration. Here we describe the use of a single-cell hydrogel capsule to provide enhanced cell survival of adherent cells in transient suspension culture. Human marrow stromal cells (hMSCs) were singularly encapsulated in agarose capsules containing the immobilized matrix molecules, fibronectin and fibrinogen to ameliorate cell-matrix survival signals. MSCs in the enriched capsules demonstrated increased viability, greater metabolic activity and enhanced cell-cytoskeletal patterning. Increased cell viability resulted from the re-induction of cell-matrix interactions likely via integrin clustering and subsequent activation of the extracellular signal regulated MAPK (ERK)/mitogen activated protein kinase (MAPK) signaling cascade. Proof of principle in-vivo studies, investigating autologous MSC delivery into Fisher 344 rat hindlimb, depicted a significant increase in the number of engrafted cells using the single-cell encapsulation system. Incorporation of immobilized adhesion molecules compensates, at least in part, for the missing cell-matrix cues, thereby attenuating the initial anoikis stimuli and providing protection from subsequent apoptosis. Thus, this single-cell encapsulation strategy may markedly enhance therapeutic cell survival in targeted tissues.

Mast Cell Chymase Induces Conjunctival Epithelial Cell Apoptosis by a Mechanism Involving Degradation of Fibronectin

PURPOSE

To determine the mechanism of conjunctival epithelial injury in vernal keratoconjunctivitis, we investigated the effects of human chymase on conjunctival epithelial cells in vitro.

METHODS

Human conjunctival epithelial cells were incubated with human chymase for 24 or 48 hr at levels of activity that were likely to exist in the tear fluid of patients with vernal keratoconjunctivitis. Morphologic changes of the cells were observed by phase contrast microscopy. To determine the number of detached cells, we used an automated cell counter, while apoptotic cells were quantitated by flow cytometry. The level of soluble fibronectin in conditioned medium was measured by ELISA.

RESULTS

Most of the cells in the incubation with chymase were detached by 24 hr. However, chymase-mediated apoptosis was a slower process and was only detected after incubation of cells with chymase for 36 to 48 hr. Both cell detachment and apoptosis were blocked when cells were incubated in fibronectin-coated plates. The increase of soluble fibronectin was dependent on the amount of chymase added and the exposure time. A caspase inhibitor (antiapoptotic agent) rescued cells from apoptosis but did not prevent cell detachment. These results indicate that chymase-induced apoptosis of conjunctival epithelial cells represents anoikis, which is a slowly occurring apoptotic process induced by lack of adhesion to an extracellular matrix.

CONCLUSIONS

Human mast cell chymase caused conjunctival epithelial cell detachment by degrading fibronectin, and this led to secondary apoptosis.

Cell survival, activation and apoptosis of hepatic stellate cells: modulation by extracellular matrix proteins

AIM

Cytokines and growth factors released by various hepatic cells exert both paracrine and autocrine effects on hepatic stellate cell (HSC) activation during liver injury. The aim of the present study was to examine whether the surrounding extracellular matrix (ECM) influences the activation, transdifferentiation and survival of HSCs.

METHODS

An in vitro model system of isolated HSCs maintained in culture on different matrix protein substrata was employed.

RESULTS

The rate of loss of HSC-specific retinol uptake activity and gain of myofibroblast-like activity such as (35)[S] proteoglycan synthesis varied in cells maintained on different matrix proteins and was in the order collagen I > collagen IV >/= laminin. (3)[H]-thymidine incorporation by HSCs maintained on different matrix proteins varied and was in the order collagen I > collagen IV > laminin. MTT assay revealed that the growth inhibition in response to curcumin was significantly low in cells maintained on collagen I. Apoptotic marker activities such as DNA fragmentation, 4',6'-diamidino-2-phenylindole dihydrochloride (DAPI) staining, annexin staining and caspase-3 activities showed that cells maintained on collagen I showed minimal apoptosis than those maintained on collagen IV, laminin and polylysine, showing the influence of ECM on HSC apoptosis. Experiments using blocking antibodies showed that the collagen I effect was mediated through alpha(2)beta(1) integrin.

CONCLUSIONS

These results indicate that ECM influences activation, transdifferentiation and survival of HSCs, and suggest that apart from diffusible factors, the surrounding ECM also influences HSC behavior critical in both the progression of the fibrosis and the restitution of the liver during recovery after hepatic injury.

Roscovitine synergizes with conventional chemo-therapeutic drugs to induce efficient apoptosis of human colorectal cancer cells

AIM: To examine the ability of cyclin-dependent kinase inhibitor (CDKI) roscovitine (Rosco) to enhance the antitumor effects of conventional chemotherapeutic agents acting by different mechanisms against human colorectal cancer.

METHODS: Human colorectal cancer cells were treated, individually and in combination, with Rosco, taxol, 5-Fluorouracil (5-FU), doxorubicin or vinblastine. The antiproliferative effects and the type of interaction of Rosco with tested chemotherapeutic drugs were determined. Cell cycle alterations were investigated by fluorescence-activated cell sorter FACS analysis. Apoptosis was determined by DNA fragmentation assay.

RESULTS: Rosco inhibited the proliferation of tumor cells in a time- and dose-dependent manner. The efficacies of all tested chemotherapeutic drugs were markedly enhanced 3.0-8.42 × 10³ and 130-5.28 × 10³ fold in combination with 5 and 10 μg/mL Rosco, respectively. The combination of Rosco and chemotherapeutic drugs inhibited the growth of human colorectal cancer cells in an additive or synergistic fashion, and in a time and dose dependent manner. Rosco induced apoptosis and synergized with tested chemotherapeutic drugs to induce efficient apoptosis in human colorectal cancer cells. Sequential, inverted sequential and simultaneous treatment of cancer cells with combinations of chemotherapeutic drugs and Rosco arrested the growth of human colorectal cancer cells at various phases of the cell cycle as follows: Taxol/Rosco (G₂/M- and S-phases), 5-FU/Rosco (S-phase), Dox/Rosco (S-phase) and Vinb/Rosco (G₂/M- and S-phases).

CONCLUSION: Since the efficacy of many anticancer drugs depends on their ability to induce apoptotic cell death, modulation of this parameter by cell cycle inhibitors may provide a novel chemo-preventive and chemotherapeutic strategy for human colorectal cancer.

Attenuation of retinal endothelial cell migration and capillary morphogenesis in the absence of bcl-2

Apoptosis plays a critical role during development and in the maintenance of the vascular system. B-cell leukemia lymphoma 2 (bcl-2) protects endothelial cells (EC) from apoptosis in response to a variety of stimuli. Previous work from this laboratory demonstrated attenuation of postnatal retinal vascular development and retinal neovascularization during oxygen-induced ischemic retinopathy in bcl-2-deficient (bcl-2-/-) mice. To gain further insight into the function of bcl-2 in the endothelium, we isolated retinal EC from bcl-2+/+ and bcl-2-/- mice. Retinal EC lacking bcl-2 demonstrated reduced cell migration, tenascin-C expression, and adhesion to vitronectin and fibronectin. The bcl-2-/- retinal EC also failed to undergo capillary morphogenesis in Matrigel. In addition, using an ex vivo angiogenesis assay, we observed reduced sprouting from aortic rings grown in culture from bcl-2-/- mice compared with bcl-2+/+ mice. Furthermore, reexpression of bcl-2 was sufficient to restore migration and capillary morphogenesis defects observed in bcl-2-/- retinal EC. Mechanistically, bcl-2-/- cells expressed significantly less endothelial nitric oxide synthase, an important downstream effecter of proangiogenic signaling. This may be attributed to increased oxidative stress in the absence of bcl-2. In fact, incubation of retinal EC or aortic rings from bcl-2-/- mice with the antioxidant N-acetylcysteine rescued their capillary morphogenesis and sprouting defects. Thus, bcl-2-mediated cellular functions play important roles not only in survival but also in proangiogenic phenotype of EC with a significant impact on vascular development and angiogenesis.

Activated mast cells induce endothelial cell apoptosis by a combined action of chymase and tumor necrosis factor-alpha

OBJECTIVE

Activated mast cells (MCs) induce endothelial cell (EC) apoptosis in vitro and are present at sites of plaque erosions in vivo. To further elucidate the role of MCs in endothelial apoptosis and consequently in plaque erosion, we have studied the molecular mechanisms involved in MC-induced EC apoptosis.

METHODS AND RESULTS

Primary cultures of rat cardiac microvascular ECs (RCMECs) and human coronary artery ECs (HCAECs) were treated either with rat MC releasate (ie, mediators released on MC activation), rat chymase and tumor necrosis factor-alpha (TNF-alpha), or with human chymase and TNF-alpha, respectively. MC releasate induced RCMEC apoptosis by inactivating the focal adhesion kinase (FAK) and Akt-dependent survival signaling pathway, and apoptosis was partially inhibited by chymase and TNF-alpha inhibitors. Chymase avidly degraded both vitronectin (VN) and fibronectin (FN) produced by the cultured RCMECs. In addition, MC releasate inhibited the activation of NF-kappaB (p65) and activated caspase-8 and -9. Moreover, in HCAECs, human chymase and TNF-alpha induced additive levels of apoptosis.

CONCLUSIONS

Activated MCs induce EC apoptosis by multiple mechanisms: chymase inactivates the FAK-mediated cell survival signaling, and TNF-alpha triggers apoptosis. Thus, by inducing EC apoptosis, MCs may contribute to plaque erosion and complications of atherosclerosis.

A peptide derived from tenascin-C induces beta1 integrin activation through syndecan-4

Tenascin-C (TN-C) is unique for its cell adhesion modulatory function. We have shown that TNIIIA2, a synthetic 22-mer peptide derived from TN-C, stimulated beta1 integrin-mediated cell adhesion of nonadherent and adherent cell types, by inducing activation of beta1 integrin. The active site of TNIIIA2 appeared cryptic in the TN-C molecule but was exposed by MMP-2 processing of TN-C. The following results suggest that cell surface heparan sulfate (HS) proteoglycan (HSPG), including syndecan-4, participated in TNIIIA2-induced beta1 integrin activation: 1) TNIIIA2 bound to cell surface HSPG via its HS chains, as examined by photoaffinity labeling; 2) heparitinase I treatment of cells abrogated beta1 integrin activation induced by TNIIIA2; 3) syndecan-4 was isolated by affinity chromatography using TNIIIA2-immobilized beads; 4) small interfering RNA-based down-regulation of syndecan-4 expression reduced TNIIIA2-induced beta1 integrin activation, and consequent cell adhesion to fibronectin; 5) overexpression of syndecan-4 core protein enhanced TNIIIA2-induced activation of beta1 integrin. However, treatments that targeted the cytoplasmic region of syndecan-4, including ectopic expression of its mutant truncated with the cytoplasmic domains and treatment with protein kinase Calpha inhibitor Gö6976, did not influence the TNIIIA2 activity. These results suggest that a TNIIIA2-related matricryptic site of the TN-C molecule, exposed by MMP-2 processing, may have bound to syndecan-4 via its HS chains and then induced conformational change in beta1 integrin necessary for its functional activation. A lateral interaction of beta1 integrin with the extracellular region of the syndecan-4 molecule may be involved in this conformation change.

Head and neck squamous cell carcinoma cell lines: established models and rationale for selection

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) cell lines are important preclinical models in the search for novel and targeted therapies to treat head and neck cancer. Unlike many other cancer types, a wide variety of primary and metastatic HNSCC cell lines are available. An easily accessible guide that organizes important characteristics of HNSCC cell lines would be valuable for the selection of appropriate HNSCC cell lines for in vitro or in vivo studies.

METHODS

A literature search was performed.

RESULTS

Cell growth and culture parameters from HNSCC cell lines were catalogued into tables or lists of selected characteristics. Methods for establishing cancer cell lines and basic cell culture maintenance techniques were reviewed.

CONCLUSIONS

A compendium of HNSCC cell line characteristics is useful for organizing the accumulating information regarding cell line characteristics to assist investigators with the development of appropriate preclinical models.

Induction of Anoikis following myoblast transplantation into SCID mouse muscles requires the Bit1 and FADD pathways

Seventy-five percent of the myoblasts transplanted in the mouse muscle die during the first 4 days following transplantation. The purpose of this study was to determine if anoikis plays a role in this phenomenon. Survival and proliferation of myoblasts in vitro were determined by Hoescht-PI labeling and cell counts respectively. In vivo cell survival and proliferation were quantified by injecting human male myoblasts labeled with (14)C-thymidine in SCID mouse muscles. Survival and proliferation of the transplanted myoblasts were evaluated by scintigraphy and quantitative PCR of human Y chromosomal DNA. Inclusion of the extracellular matrix protein fibronectin enhanced transplanted myoblast survival by 1.7-fold while vitronectin improved their proliferation by 1.8-fold. Reductions in FADD and Bit1 expression reduced anoikis in vitro and improved the injected myoblast survival in vivo. Ectopic expression of the anti-apoptotic protein Bcl-2 completely abolished myoblast anoikis in vitro and enhanced cell survival by 3.1-fold in vivo. Cell death following transplantation appears to me mediated in part by anoikis. Inclusion of extracellular matrix proteins enhanced both survival and proliferation. Reduced expression of the proapoptotic proteins Bit1 and FADD or overexpression of Bcl-2 improved myoblast survival.

Short peptides enhance single cell adhesion and viability on microarrays

Single cell patterning holds important implications for biology, biochemistry, biotechnology, medicine, and bioinformatics. The challenge for single cell patterning is to produce small islands hosting only single cells and retaining their viability for a prolonged period of time. This study demonstrated a surface engineering approach that uses a covalently bound short peptide as a mediator to pattern cells with improved single cell adhesion and prolonged cellular viability on gold patterned SiO2 substrates. The underlying hypothesis is that cell adhesion is regulated by the type, availability, and stability of effective cell adhesion peptides, and thus covalently bound short peptides would promote cell spreading and, thus, single cell adhesion and viability. The effectiveness of this approach and the underlying mechanism for the increased probability of single cell adhesion and prolonged cell viability by short peptides were studied by comparing cellular behavior of human umbilical cord vein endothelial cells on three model surfaces whose gold electrodes were immobilized with fibronectin, physically adsorbed Arg-Glu-Asp-Val-Tyr, and covalently bound Lys-Arg-Glu-Asp-Val-Tyr, respectively. The surface chemistry and binding properties were characterized by reflectance Fourier transform infrared spectroscopy. Both short peptides were superior to fibronectin in producing adhesion of only single cells, whereas the covalently bound peptide also reduced apoptosis and necrosis of adhered cells. Controlling cell spreading by peptide binding domains to regulate apoptosis and viability represents a fundamental mechanism in cell-materials interaction and provides an effective strategy in engineering arrays of single cells.

Inhibition of endothelial cell proliferation, in vitro angiogenesis, and the down-regulation of cell adhesion-related genes by genistein. Combined with a cDNA microarray analysis

Antiangiogenesis is presently one of the powerful strategies for treating cancer, and endothelial cells play a pivotal role in the process of angiogenesis. Genistein, a tyrosine kinase inhibitor, a major isoflavone plentiful in soybeans, is known to inhibit both tumor growth and angiogenesis. However, the precise molecular mechanism(s) by which genistein affects endothelial cells has yet to be elucidated. In the present study, a cDNA microarray was performed to investigate the targeted genes of human umbilical vein endothelial cells (HUVECs) affected by 10 microM genistein. As a result, a total of 256 genes showed an altered expression of more than twofold. Among them were the genes related to cell proliferation, adhesion, transcription, translation, metabolism, cytoskeleton, apoptosis, kinases, and functionally unknown. The down-regulation of mRNA or the protein expression of cell adhesion-related genes, including VE-cadherin, gap junction protein alpha 1 (connexin 43), integrin alpha V, and multimerin, were confirmed by reverse transcriptase-polymerase chain reaction (RT-PCR) or by immunofluorescence staining. The impaired cell-cell adhesion by genistein was also observed by electron microscopy. In addition, the antiangiogenesis role of genistein was confirmed on Matrigel using inverted microscopy and electron microscopy. In conclusion, genistein affects endothelial cells as a negative mediator of proliferation and angiogenesis in vitro, partially by down-regulating cell adhesion-related genes and impairing cell adhesions.

Antiadhesive Sites Present in the Fibronectin Type III-Like Repeats of Human Plasma Fibronectin

We have found that fibronectin (FN) has a functional cryptic site opposing cell adhesion to extracellular matrix (ECM): a synthetic FN peptide derived from the 14th FN type III-like (FN-III) repeat, termed peptide FNIII14, inhibits cell adhesion to the FN without binding to beta1 integrins. This antiadhesive activity of peptide FNIII14 depends on its C-terminal amino acid sequence YTIYVIAL. A 50-kDa membrane protein (p50) has been detected as a specific binding protein of peptide FNIII14. Here we showed that antiadhesive activity of peptide FNIII14 was depedent upon the presence of p50 on cell surfaces. Furthermore, we found that there exists a sequence, analogous to the YTIYVIAL, in the 10th FN-III repeat of the FN molecule and that a FN peptide containing this analogous sequence, termed peptide FNIII10, inhibited cell adhesion to the FN. Peptide FNIII10 appeared to share p50 with peptide FNIII14 in expressing the antiadhesive activity. As a physiological consequence of decreased adhesion, peptides FNIII10 and FNIII14 accelerated the anoikis-like apoptosis of normal fibroblasts by down-regulating Bcl-2 expression through blocking the FAK/PI3K/Akt signaling pathway. Thus, the YTIYVIAL-related sequences of the FN molecule may be involved in cell regulation by modulating negatively cell adhesion to the ECM, in which p50 probably serves as a membrane receptor.

Fibronectin and Laminin Increase in the Mouse Brain after Controlled Cortical Impact Injury

The complex environment of the traumatically injured brain exhibits aspects of inhibition and ongoing cell death together with attempts at repair and regeneration. Elucidating these events and exploiting those factors involved in endogenous repair and regeneration may aid in developing more effective treatments for traumatic brain injury. Two extracellular matrix proteins critical to neural development--fibronectin and laminin--may also play a protective or reparative role in the injury response. While both of these proteins have been found to increase following human brain injury,the presence of these proteins has not been studied in a clinically-relevant animal model of blunt head trauma. In this study, we examined the spatiotemporal profile of both fibronectin and laminin in the mouse brain following controlled cortical impact injury. Fibronectin and laminin reactivity was localized to the injury penumbra up to 14 days post-injury and was significantly higher than uninjured controls at 3 days post-injury. Upon examining the spatial relationship of fibronectin and laminin to support cells, we found macrophages/activated microglia prominently present in the fibronectin-rich tissue, consistent with a role for fibronectin in facilitating debris clearing. Furthermore, reactive astrocyte processes were found sheathing laminin positive vasculature, suggesting that laminin may play a role in repairing the blood-brain barrier. These and other hypothesized reparative roles for fibronectin and laminin after traumatic brain injury are discussed.

Perlecan proteolysis induces an alpha2beta1 integrin- and Src family kinase-dependent anti-apoptotic pathway in fibroblasts in the absence of focal adhesion kinase activation

Dysregulation of apoptosis in endothelial cells (EC) and fibroblasts contributes to fibrosis. We have shown previously that apoptosis of EC triggers the proteolysis of extracellular matrix components and the release of a C-terminal fragment of perlecan, which in turn inhibits apoptosis of fibroblasts. Here we have defined the receptors and pathways implicated in this anti-apoptotic response in fibroblasts. Neutralizing alpha2beta1 integrin activity in fibroblasts exposed to either medium conditioned by apoptotic EC (SSC) or a recombinant perlecan C-terminal fragment (LG3) prevented resistance to apoptosis and is associated with decreased levels of Akt phosphorylation. Co-incubation of fibroblasts for 24 h with SSC or LG3 in the presence of PP2 (AG1879), a biochemical inhibitor of Src family kinases (SFKs) and focal adhesion kinase, showed a significantly decreased anti-apoptotic response. However, focal adhesion kinase gene silencing with RNA interference did not inhibit the anti-apoptotic response in fibroblasts. Src phosphorylation was increased in fibroblasts exposed to SSC, and transfection of fibroblasts with constitutively active Src mutants induced an anti-apoptotic response that was not further increased by SSC. Also, Src(-/-)Fyn(-/-) fibroblasts failed to mount an anti-apoptotic response in presence of SSC for 24 h but developed a complete anti-apoptotic response when exposed to SSC for 7 days. These results suggest that extracellular matrix fragments produced by apoptotic EC initiate a state of resistance to apoptosis in fibroblasts via an alpha2beta1 integrin/SFK (Src and Fyn)/phosphatidylinositol 3-kinase (PI3K)-dependent pathway. In the long term, additional SFK members are recruited for sustaining the anti-apoptotic response, which could play crucial roles in abnormal fibrogenic healing.

Modulation of response to tumor therapies by the extracellular matrix

The composition of the extracellular matrix in tumors is vastly different from that found in the normal tissue counterparts. As the extracellular matrix can signal to cells via integrin binding and activation, which is known to modulate cell proliferation, survival and migration, it may influence the response of both tumor and endothelial cells to anticancer therapies. Certain tumor-associated extracellular matrix proteins have been shown to confer resistance to chemotherapeutic drugs, radiation and anti-angiogenic factors. The current literature regarding this phenomenon and the potential therapeutic modalities to overcome extracellular matrix-induced resistance will be discussed.

The inhibitory effects of endostatin on endothelial cells are modulated by extracellular matrix

We investigated the ability of extracellular matrix (ECM) proteins to modulate the response of endothelial cells to both promoters and inhibitors of angiogenesis. Using human dermal microvascular endothelial cells (HDMEC), we found that cells demonstrated different adhesive properties and proliferative responses to the growth factor VEGF depending upon which ECM protein with which they were in contact, with fibronectin having the most impact on VEGF-induced HDMEC proliferation and survival. More importantly, we observed that ECM could modulate the ability of the angiogenic inhibitor endostatin to prevent endothelial cell proliferation, survival and migration. We observed that growth on vitronectin or fibronectin impaired the ability of endostatin to inhibit VEGF-induced HDMEC proliferation to the greatest extent as determined by BrdU incorporation. We found that, following growth on collagen I or collagen IV, endostatin only inhibited VEGF-induced HDMEC proliferation at the highest dose tested (2500 ng/ml). In a similar manner, we observed that growth on ECM proteins modulated the ability of endostatin to induce endothelial cell apoptosis, with growth on collagen I, fibronectin and collagen IV impairing endostatin-induced apoptosis. Interestingly, endostatin inhibited VEGF-induced HDMEC migration following culture on collagen I, collagen IV and laminin, while migration was not inhibited by endostatin following HDMEC culture on other matrices including vitronectin, fibronectin and tenascin-C. These results suggest that different matrix proteins may affect different mechanisms of endostatin inhibition of angiogenesis. Taken together, our results suggest that the ECM may have a profound impact on the ability of angiostatic molecules such as endostatin to inhibit angiogenesis and thus may have impact on the clinical efficacy of such inhibitors.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

Engagement of integrin alpha4beta1 enhances thrombopoietin-induced megakaryopoiesis

OBJECTIVE

Studies in numerous adherent cell systems have indicated that engagement of integrins is required for cell survival and proliferation. Although not classically thought of as an adherent cell type, megakaryocytes in the marrow develop in juxtaposition to endothelial cells which display a number of integrin counter-receptors. Moreover, a number of other hematopoietic cell types, including stem cells and erythroid progenitors, have been shown to engage and be affected by integrin ligands.

METHODS

The role of beta1 integrins in thrombopoietin-mediated megakaryopoiesis was studied using both gain-of-function and loss-of-function strategies.

RESULTS

We found that pan-blockade of integrins with a relatively nonspecific disintegrin blocked TPO-induced MK growth, but that an alpha5beta1 disintegrin, and a function-blocking monoclonal antibody, failed to affect megakaryopoiesis in vitro. In contrast, a neutralizing alpha4beta1 monoclonal antibody blocked TPO-induced MK growth, and an integrin alpha4beta1 ligand, the H296 fragment of fibronectin, enhanced MK growth at all concentrations of TPO.

CONCLUSIONS

These findings have important implications for thrombopoiesis in general, and potentially for the enhanced platelet production found in states of systemic inflammation and following the use of therapeutic strategies designed to block alpha4beta1 integrin engagement in states of chronic inflammation and autoimmunity.

Anastellin, a Fragment of the First Type III Repeat of Fibronectin, Inhibits Extracellular Signal-Regulated Kinase and Causes G1 Arrest in Human Microvessel Endothelial Cells

The formation of a microvascular endothelium plays a critical role in the growth and metastasis of established tumors. The ability of a fragment from the first type III repeat of fibronectin (III1C), anastellin, to suppress tumor growth and metastasis in vivo has been reported to be related to its antiangiogenic properties, however, the mechanism of action of anastellin remains unknown. Utilizing cultures of human dermal microvascular endothelial cells, we provide evidence that anastellin inhibits signaling pathways which regulate the extracellular signal-regulated (ERK) mitogen-activated protein kinase pathway and subsequent expression of cell cycle regulatory proteins. Addition of anastellin to primary microvascular endothelial cells resulted in a complete inhibition of serum-dependent proliferation. Growth inhibition correlated with a decrease in serum-dependent expression of cyclin D1, cyclin A and the cyclin-dependent kinase, cdk4, key regulators of cell cycle progression through G1 phase. Consistent with a block in G1-S transition, anastellin inhibited serum-dependent incorporation of [3H]-thymidine into S-phase nuclei. Addition of anastellin to serum-starved microvessel cells resulted in a time-dependent and dose-dependent decrease in basal levels of phosphorylated MEK/ERK and blocked serum-dependent activation of ERK. Adenoviral infection with Ad.ΔB-Raf:ER, an inducible estrogen receptor-B-Raf fusion protein, restored levels of active ERK in anastellin-treated cells, rescued levels of cyclin D1, cyclin A, and cdk4, and rescued [3H]-thymidine incorporation. These data suggest that the antiangiogenic properties of anastellin observed in mouse models of human cancer may be due to its ability to block endothelial cell proliferation by modulating ERK signaling pathways and down-regulating cell cycle regulatory gene expression required for G1-S phase progression.

Squamous cell carcinoma cell aggregates escape suspension-induced, p53-mediated anoikis: fibronectin and integrin alphav mediate survival signals through focal adhesion kinase

Resistance to anoikis, or apoptosis triggered by detachment from the extracellular matrix (ECM), lengthens the survival of malignant cells, facilitating reattachment and colonization of secondary sites. To examine the molecular mechanisms underlying resistance to anoikis in human oral squamous cell carcinoma (SCC) cells, we cultured human squamous carcinoma (HSC-3) cells in suspension on plates coated with poly-2-hydroxyethyl methacrylate, which blocks access to the ECM. Cells in suspension that formed multicellular aggregates had significantly lower levels of apoptosis than single cells. Aggregates, but not single cells, had high levels of fibronectin. Preincubation with a cyclic arginine-glycine-aspartic acid peptide or fibronectin-blocking antibody significantly increased anoikis. Single cells had markedly lower expression of the integrin alpha(v) receptor than aggregates. Blocking alpha(v) function with a blocking antibody or by transfection with an antisense oligonucleotide increased apoptosis and inhibited aggregation. In single cells but not aggregates, phosphorylation of the integrin-associated focal adhesion kinase (FAK) at tyrosine 397 was reduced, and p53 levels were increased. Apoptosis was increased by blocking FAK with an antisense oligonucleotide and reduced by blocking p53. These findings show that SCC cells escape suspension-induced anoikis by forming multicellular aggregates that avail themselves of fibronectin survival signals mediated by integrin alpha(v). Single cells in suspension that do not form aggregates undergo anoikis because of decreased FAK phosphorylation and increased p53 levels. Thus, SCC cells appear to use neighboring cells and the ECM molecule FN to promote the metastatic phenotype.

Integrin signaling in inflammatory and neuropathic pain in the rat

Many painful conditions are associated with alterations in the extracellular matrix (ECM) of affected tissues. While several integrins, the receptors for ECM proteins, are present on sensory neurons that mediate pain, the possible role of these cell adhesion molecules in inflammatory or neuropathic pain has not been explored. We found that the intradermal injection of peptide fragments of domains of laminin and fibronectin important for adhesive signaling selectively inhibited the hyperalgesia caused by prostaglandin E2 (PGE2) and epinephrine (EPI), respectively. The block of EPI hyperalgesia was mimicked by other peptides containing the RGD integrin-binding sequence. Monoclonal antibodies (mAbs) against the alpha1 or alpha3 integrin subunits, which participate in laminin binding, selectively blocked PGE2 hyperalgesia, while a mAb against the alpha5 subunit, which participates in fibronectin binding, blocked only EPI-induced hyperalgesia. A mAb against the beta1 integrin subunit, common to receptors for both laminin and fibronectin, inhibited hyperalgesia caused by both agents, as did the knockdown of beta1 integrin expression by intrathecal injection of antisense oligodeoxynucleotides. The laminin peptide, but not the fibronectin peptides, also reversibly abolished the longer lasting inflammatory hyperalgesia induced by carrageenan. Finally, the neuropathic hyperalgesia caused by systemic administration of the cancer chemotherapy agent taxol was reversibly inhibited by antisense knockdown of beta1 integrin. These results strongly implicate specific integrins in the maintenance of inflammatory and neuropathic hyperalgesia.

The cellular responses of articular cartilage to sharp and blunt trauma

OBJECTIVE

To determine the response of immature articular cartilage to both sharp and blunt trauma in terms of cell death, cell proliferation and matrix synthesis.

DESIGN

Blunt wounds were made with a trephine in full depth immature bovine articular cartilage explants which were cut in half through the center of the trephine wound with a sharp scalpel to produce blunt and sharp trauma on the same explant. Explants were maintained in culture for up to 10 days. Prior to fixation at days 2, 5 and 10, medium was supplemented with 10 microCi ml-1 35S-sulphate, [3H]-proline or [3H]-thymidine for 24h to assess matrix synthesis and cell proliferation. Cell death was assessed using a Live/Dead label.

RESULTS

In the case of blunt wounds, a band of cell death was observed adjacent to the lesion edge. Microautoradiography demonstrated little radiolabel incorporation and, therefore, no new matrix synthesis or cell proliferation within this region. In contrast, wounds made with a sharp scalpel showed restricted cell death, with radiolabel incorporation adjacent to the lesion edge at all time points. This demonstrated not only chondrocyte proliferation and new matrix synthesis at the wound margin, but also an up-regulation of matrix synthesis adjacent to the lesion edge.

CONCLUSIONS

In terms of clinical relevance, the use of sharp precise instruments during the surgical management of cartilage defects may be necessary to reduce cell death and promote matrix elaboration at the lesion edge in order to facilitate successful integration.

Extracellular Matrix Protein-dependent Apoptosis of T Cells in Women with a History of Recurrent Spontaneous Abortion

PROBLEM

The purpose of the study was to determine the role of T-cell apoptosis in extracellular matrix (ECM) environment in pregnancy maintenance in women with a history of recurrent spontaneous abortion (RSA).

METHOD OF STUDY

Thirty-nine non-pregnant women with the history of RSA (anatomic, genetic, endocrine and microbiologic causes were excluded) and 22 healthy women with the previous successful pregnancy outcome were studied. In addition, 21 women with the history of RSA were also studied at the beginning of their next pregnancy. We studied apoptosis of peripheral blood T cells after culture with monoclonal antibody (mAb) OKT-3 alone or with mAb OKT-3 following ECM proteins: collagen IV (C-IV) or fibronectin (Fn). We used Cell Death Detection ELISA for studying cell death in cell population. In addition, apoptotic peripheral blood T cells were identified by annexin V-PE staining protocol using flow cytometry. CD29+ and CD95+ T-cell surface receptors were also analyzed by flow cytometry.

RESULTS

The significantly higher values of enrichment factor: mU of the sample (dying/dead cells) per mU of the corresponding control (viable cells) were observed after peripheral blood T-cell culture with C-IV (P = 0.0002) or Fn (P = 0.004) in samples of non-pregnant women with the history of RSA when compared with control women. The significantly higher values of enrichment factor were observed after peripheral blood T-cell culture with C-IV in samples of pregnant women with the history of RSA with successful pregnancy outcome when compared with pregnant women with the history of RSA with failed pregnancy outcome (P = 0.01). However, the percentage of apoptotic T cells stained by annexin V was significantly lower in non-pregnant RSA women compared with control (P = 0.0001). CD95 expression was significantly lower in non-pregnant RSA women compared with control (P = 0.01).

CONCLUSIONS

Apoptosis of T cells might be an interesting possible explanation of successful pregnancy outcome in women with the history of RSA.

Rapid tyrosine phosphorylation of focal adhesion kinase, paxillin, and p130Cas by gastrin in human colon cancer cells

Although the expression of CCK(2) receptors is widely reported in human colorectal cancers, little is known on its role in mediating the proliferative effects of mature amidated gastrin (G17 amide) on colorectal cancers. The purpose of the present study was to determine the effects of G17 amide on tyrosine phosphorylation of focal adhesion kinase (FAK), paxillin, and p130 Crk-associated substrate (p130(Cas)) in Colo 320 cells, a human colorectal cancer cell line which expresses CCK(2) receptors. By immunoprecipitation and immunoblotting, an increase in tyrosine phosphorylation of FAK (tyrosine-397), paxillin (tyrosine-31), and p130(Cas) was detected in a time- and dose-dependent manner. Overexpression of CCK(2) receptors in Colo 320 cells (Colo 320 WT) by stable transfection with the human CCK(2) receptor cDNA resulted in an increased tyrosine phosphorylation of FAK, paxillin, and p130(Cas). After incubation with 1 microM L-365,260, a specific CCK(2) receptor antagonist, this increase was completely inhibited. Our results demonstrate that in human colon cancer cells, gastrin caused a rapid tyrosine phosphorylation of FAK, paxillin, and p130(Cas) by activation of CCK(2) receptor. The phosphorylation of these proteins might be important in mediating gastrin effects on proliferation, apoptosis, and metastasis.

Anoikis in the cardiovascular system: known and unknown extracellular mediators

Anoïkis is defined as programmed cell death induced by the loss of cell/matrix interactions. Adhesion to structural glycoproteins of the extracellular matrix is necessary for survival of the differentiated adherent cells in the cardiovascular system, including endothelial cells, smooth muscle cells, fibroblasts, and cardiac myocytes. Adhesion is also a key factor for the differentiation of mesenchymal stem cells. In particular, fibronectin is considered a factor of survival and differentiation for many adherent cells. Adhesion generates cell tensional integrity (tensegrity) and repression of apoptotic signals, whereas detachment has the opposite effect. Anoïkis plays a physiological role by regulating cell homeostasis in tissues. However, anoïkis can also be involved in pathological processes, as illustrated by the resistance to anoïkis in cancer and its enhancement in degenerative tissue remodeling. Extracellular mediators of anoïkis include matrix retraction, leading to loss of tensegrity in fibroblasts, pharmacological disengagement of integrins by RGD-like peptides and fragments of fibronectin, and focal adhesion disassembly by fragments of thrombospondin, plasminogen activator-1, and high-molecular-weight kininogen. In addition to binding of the RGD peptide by integrins, the engagement of the heparin binding sites of adhesive glycoproteins with glycosaminoglycans on the cell surface is also involved in the prevention of cell detachment-induced apoptosis. Proteases able to degrade adhesive glycoproteins, such as fibronectin, induce anoïkis of vascular adherent cells. Active proteases can either be secreted directly by inflammatory cells, as elastase and cathepsin G by polymorphonuclear leukocytes, chymase and tryptase by mast cells, and granzymes by lymphocytes, or generated from circulating zymogens by activation in close contact with the cells. This is the case for the pericellular conversion of plasminogen to plasmin, which degrades fibronectin and induces anoïkis of smooth muscle cells. Involvement of proteases has also been proposed in the apoptotic response of cultured adherent cells to serum starvation. Anoïkis is probably involved in pathological remodeling of cardiovascular tissues, including cardiac myocyte detachment in heart failure, deendothelialization and plaque rupture in atherosclerosis, and smooth muscle cell disappearance in aneurysms and varicose veins. The absence of cell adhesion and growth resulting from cleavage of adhesive proteins also represents a major impediment to cellular healing, including the absence of cell recolonization of proteolytically injured tissue and the low efficacy of cell transplantation. However, the exact role of anoïkis in cardiovascular pathologies remains to be further defined.

Induction of apoptosis in vascular cells by plasminogen activator inhibitor-1 and high molecular weight kininogen correlates with their anti-adhesive properties

Plasminogen activator inhibitor-1 (PAI-1) and two-chain high molecular weight kininogen (HKa) exert anti-adhesive properties in vitronectin-dependent cell adhesion. Here, the hypothesis was tested that these anti-adhesive components promote apoptosis in vascular cells. PAI-1 or HKa induced a 2- to 3-fold increase in apoptosis of human umbilical-vein endothelial cells (HUVEC) and vascular smooth muscle cells (VSMC) adherent to vitronectin, as determined by annexin V-FACS assay, similar to alphav-integrin inhibitor cyclo-(Arg-Gly-Asp-D-Phe-Val)-peptide (cRGDfV). Apoptosis occurred after 12 h incubation and was attributable to caspase 3 activation that in turn induced DNA fragmentation. Induction of apoptosis strongly correlated with the anti-adhesive effect of PAI-1 and HKa on these cells. In contrast, PAI-1 and HKa did not affect fibronectin-dependent adhesion or cell survival. uPA did not influence apoptosis in vitronectin- or fibronectin-adherent cells. In atherosclerotic vessel sections, congruent distribution of vitronectin, PAI-1, HK, and of components of the urokinase plasminogen activator/receptor system with apoptotic cells lining foam cell lesions was demonstrated by immunostaining. These results indicate that inhibition of vitronectin-dependent cell adhesion through PAI-1 and HKa correlates with apoptosis induction in vascular cells mediated through the caspase 3 pathway. Co-distribution of apoptosis with plasminogen activation system components in atherosclerosis exemplifies the significance of anti-adhesive mechanisms and apoptosis for tissue remodeling, such as in neointima development.

Mast cell chymase induces smooth muscle cell apoptosis by a mechanism involving fibronectin degradation and disruption of focal adhesions

OBJECTIVE

Chymase released from activated mast cells has been shown to induce apoptosis of vascular smooth muscle cells (SMCs) in vitro. The proteolytic activity of chymase is essential for the proapoptotic effect, but the mechanism of chymase-induced apoptosis has remained unknown.

METHODS AND RESULTS

Here we show by means of FACS analysis, immunohistochemistry, and Western blotting that mast cell-derived chymase induces SMC apoptosis by a mechanism involving degradation of an extracellular matrix component, fibronectin (FN), with subsequent disruption of focal adhesions. The FN degradation products induced SMC apoptosis of similar magnitude and with similar changes in outside-in signaling, as did chymase. Sodium orthovanadate, an inhibitor of tyrosine phosphatases, inhibited the chymase-induced SMC apoptosis. Focal adhesion kinase (FAK), one of the key mediators of integrin-extracellular matrix interactions and cell survival, was rapidly degraded in the presence of chymase or FN degradation products. Loss of phosphorylated FAK (p-FAK) resulted in a rapid dephosphorylation of the p-FAK-dependent downstream mediator Akt.

CONCLUSIONS

The results suggest that chymase-secreting mast cells can mediate apoptosis of neighboring SMCs through a mechanism involving degradation of pericellular FN and disruption of the p-FAK-dependent cell-survival signaling cascade.

Novel cartilage-specific splice variants of fibronectin

OBJECTIVE

To determine the nature of alternatively spliced isoforms of fibronectin expressed in healthy bovine articular cartilage and cartilage derived from human osteoporotic and osteoarthritic joints.

DESIGN

Our study focused on a single alternatively spliced region of the fibronectin gene, the variable region. Bovine cartilage samples were obtained within 12h of slaughter and human cartilage samples were obtained within 8h of the time of joint replacement surgery. RNA was extracted and alternatively spliced isoforms of fibronectin were amplified using RT-PCR.

RESULTS

Two novel alternatively spliced forms of fibronectin designated (V+I-10)(-) and (V+III-15)(-) were identified in bovine articular cartilage. Fibronectin is composed of multiple repeats of three types of homologous units and these two novel isoforms specifically splice out single individual repeating units. Expression of all these isoforms was dependent upon the presence of an extracellular matrix. In the human samples the expression profiles obtained with osteoporotic hip and osteoarthritic knee cartilage was not uniform. The (V+C)(-) isoform was present in all samples and the (V+I-10)(-) isoform was distributed between both osteoporotic and osteoarthritic cartilage. However, the (V+III-15)(-) isoform was shown to be associated with osteoarthritic cartilage with statistical significance (P< 0.015 ). In addition a third novel splice variant was identified and designated as III-15X. Translation of the III-15X isoform results in a truncated form of fibronectin lacking a significant portion of the C-terminus. Further RT-PCR analysis of several other tissue types suggests that these variants are cartilage specific.

CONCLUSION

Our results demonstrate the existence of three new cartilage specific isoforms of fibronectin and indicate that expression of one or more may be associated with osteoarthritis. Published by Elsevier Science Ltd. All rights reserved.

Insulin-like growth factor 2 and potential regulators of hemangioma growth and involution identified by large-scale expression analysis

Hemangiomas are benign tumors of the vascular endothelium and are the most common tumors of infancy. These tumors are characterized by an initial phase of rapid proliferation, which is followed, in most cases, by spontaneous involution. Although most lesions resolve without complication, there are some cases in which hemangiomas can be life threatening when occurring near a vital structure. Treatment for these aggressive tumors represents an unmet clinical need. In addition, this characteristic progression of hemangiomas through distinct phases provides a unique opportunity for studying endothelial cell biology and angiogenesis. Using DNA microarrays representing approximately 10,000 human genes, we identified insulin-like growth factor 2 (IGF-2) as a potentially important regulator of hemangioma growth. IGF-2 was highly expressed during the proliferative phase and substantially decreased during involution. This finding was confirmed at the message level by quantitative reverse transcription-PCR and at the protein level by immunohistochemistry. IGF-2 protein was localized primarily to tumor vessels or vascular channels. Using a human hemangioma explant model, we show that IGF-2 promotes sprouting from intact hemangioma tissue. In addition, several angiogenesis-related factors, including integrins alpha(v)beta3 and alpha5beta1, are present in proliferating hemangiomas. During the involuting phase, an increase in several IFN-induced genes was observed. These studies identify potential regulators of hemangioma growth and involution and provide a foundation on which to build further mechanistic investigations into angiogenesis, using hemangiomas as a model.