Collagen IV regulates Caco-2 migration and ERK activation via alpha1beta1- and alpha2beta1-integrin-dependent Src kinase activation

A defective mechanosensing pathway affects fibroblast-to-myofibroblast transition in the old male mouse heart

The cardiac fibroblast interacts with an extracellular matrix (ECM), enabling myofibroblast maturation via a process called mechanosensing. Although in the aging male heart, ECM is stiffer than in the young mouse, myofibroblast development is impaired, as demonstrated in 2-D and 3-D experiments. In old male cardiac fibroblasts, we found a decrease in actin polymerization, α-smooth muscle actin (α-SMA), and Kindlin-2 expressions, the latter an effector of the mechanosensing. When Kindlin-2 levels were manipulated via siRNA interference, young fibroblasts developed an old-like fibroblast phenotype, whereas Kindlin-2 overexpression in old fibroblasts reversed the defective phenotype. Finally, inhibition of overactivated extracellular regulated kinases 1 and 2 (ERK1/2) in the old male fibroblasts rescued actin polymerization and α-SMA expression. Pathological ERK1/2 overactivation was also attenuated by Kindlin-2 overexpression. In contrast, old female cardiac fibroblasts retained an operant mechanosensing pathway. In conclusion, we identified defective components of the Kindlin/ERK/actin/α-SMA mechanosensing axis in aged male fibroblasts.

ZINC40099027 promotes monolayer circular defect closure by a novel pathway involving cytosolic activation of focal adhesion kinase and downstream paxillin and ERK1/2

ZINC40099027 (ZN27) is a specific focal adhesion kinase (FAK) activator that promotes murine mucosal wound closure after ischemic or NSAID-induced injury. Diverse motogenic pathways involve FAK, but the direct consequences of pure FAK activation have not been studied, and how ZN27-induced FAK activation stimulates wound closure remained unclear. We investigated signaling and focal adhesion (FA) turnover after FAK activation by ZN27 in Caco-2 cells, confirming key results in CCD841 cells. ZN27 increased Caco-2 FAK-Y-397, FAK-Y-576/7, paxillin-Y-118, and ERK 1/2 phosphorylation and decreased FAK-Y-925 phosphorylation, without altering FAK-Y-861, p38, Jnk, or Akt phosphorylation. ZN27 increased FAK-paxillin interaction while decreasing FAK-Grb2 association. ZN27 increased membrane-associated FAK-Y-397 and FAK-Y-576/7 phosphorylation and paxillin-Y-118 and ERK 1/2 phosphorylation but decreased FAK-Y-925 phosphorylation without altering Src or Grb2. Moreover, ZN27 increased the fluorescence intensity of GFP-FAK and pFAK-Y397 in FAs and increased the total number of FAs but reduced their size in GFP-FAK-transfected Caco-2 cells, consistent with increased FA turnover. In contrast, FAK-Y397F transfection prevented ZN27 effects on FAK size and number and FAK and pFAK fluorescent intensity in FAs. We confirmed the proposed FAK/paxillin/ERK pathway using PP2 and U0126 to block Src and MEK1/2 in Caco-2 and CCD841 cells. These results suggest that ZN27 promotes intestinal epithelial monolayer defect closure by stimulating autophosphorylation of FAK in the cytosol, distinct from classical models of FAK activation in the FA. Phosphorylated FAK translocates to the membrane, where its downstream substrates paxillin and ERK are phosphorylated, leading to FA turnover and human intestinal epithelial cell migration.

Gut homeostasis, injury, and healing: New therapeutic targets

The integrity of the gastrointestinal mucosa plays a crucial role in gut homeostasis, which depends upon the balance between mucosal injury by destructive factors and healing via protective factors. The persistence of noxious agents such as acid, pepsin, nonsteroidal anti-inflammatory drugs, or Helicobacter pylori breaks down the mucosal barrier and injury occurs. Depending upon the size and site of the wound, it is healed by complex and overlapping processes involving membrane resealing, cell spreading, purse-string contraction, restitution, differentiation, angiogenesis, and vasculogenesis, each modulated by extracellular regulators. Unfortunately, the gut does not always heal, leading to such pathology as peptic ulcers or inflammatory bowel disease. Currently available therapeutics such as proton pump inhibitors, histamine-2 receptor antagonists, sucralfate, 5-aminosalicylate, antibiotics, corticosteroids, and immunosuppressants all attempt to minimize or reduce injury to the gastrointestinal tract. More recent studies have focused on improving mucosal defense or directly promoting mucosal repair. Many investigations have sought to enhance mucosal defense by stimulating mucus secretion, mucosal blood flow, or tight junction function. Conversely, new attempts to directly promote mucosal repair target proteins that modulate cytoskeleton dynamics such as tubulin, talin, Ehm², filamin-a, gelsolin, and flightless I or that proteins regulate focal adhesions dynamics such as focal adhesion kinase. This article summarizes the pathobiology of gastrointestinal mucosal healing and reviews potential new therapeutic targets.

Integrin β1 subunit regulates cellular and secreted MUC5AC and MUC5B production in NCI-H292 human lung epithelial cells

The surface of the human respiratory tract is covered with a mucus layer containing mucin 5AC (MUC5AC) and mucin 5B (MUC5B) as the main components. This layer contributes to biological defense by eliminating irritants, but excessive MUC5AC secretion by the airway epithelial cells exacerbates asthma. Therefore, regulating mucin production is important for asthma treatment. In this study, the effects of integrin β1 subunit on MUC5AC and MUC5B production were examined in NCI–H292 human lung cancer epithelial cells. When integrin β1 was overexpressed, cellular and secreted MUC5AC levels were decreased, whereas cellular MUC5B production was increased. Conversely, integrin β1 depletion using siRNA increased cellular and secreted MUC5AC production, but decreased cellular MUC5B production. Further, the activity of extracellular signal-regulated kinase (ERK), which promotes MUC5AC production, was decreased by integrin β1 overexpression and increased by its depletion. These results suggest that integrin β1 suppresses MUC5AC production and promotes MUC5B production by downregulating ERK.

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We studied the regulation of MUC5AC and MUC5B production by integrin β1 subunit.

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Integrin β1 overexpression reduced MUC5AC, but increased MUC5B levels.

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Integrin β1 depletion increased MUC5AC production and ROS level, but decreased MUC5B production.

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Integrin β1 overexpression decreased ERK activity in NCI–H292 airway cells.

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Integrin β1 downregulates ERK to suppress MUC5AC & promote MUC5B production.

ZINC40099027 activates human focal adhesion kinase by accelerating the enzymatic activity of the FAK kinase domain

Focal adhesion kinase (FAK) regulates gastrointestinal epithelial restitution and healing. ZINC40099027 (Zn27) activates cellular FAK and promotes intestinal epithelial wound closure in vitro and in mice. However, whether Zn27 activates FAK directly or indirectly remains unknown. We evaluated Zn27 potential modulation of the key phosphatases, PTP-PEST, PTP1B, and SHP2, that inactivate FAK, and performed in vitro kinase assays with purified FAK to assess direct Zn27-FAK interaction. In human Caco-2 cells, Zn27-stimulated FAK-Tyr-397 phosphorylation despite PTP-PEST inhibition and did not affect PTP1B-FAK interaction or SHP2 activity. Conversely, in vitro kinase assays demonstrated that Zn27 directly activates both full-length 125 kDa FAK and its 35 kDa kinase domain. The ATP-competitive FAK inhibitor PF573228 reduced basal and ZN27-stimulated FAK phosphorylation in Caco-2 cells, but Zn27 increased FAK phosphorylation even in cells treated with PF573228. Increasing PF573228 concentrations completely prevented activation of 35 kDa FAK in vitro by a normally effective Zn27 concentration. Conversely, increasing Zn27 concentrations dose-dependently activated kinase activity and overcame PF573228 inhibition of FAK, suggesting the direct interactions of Zn27 with FAK may be competitive. Zn27 increased the maximal activity (Vmax ) of FAK. The apparent Km of the substrate also increased under laboratory conditions less relevant to intracellular ATP concentrations. These results suggest that Zn27 is highly potent and enhances FAK activity via allosteric interaction with the FAK kinase domain to increase the Vmax of FAK for ATP. Understanding Zn27 enhancement of FAK activity will be important to redesign and develop a clinical drug that can promote mucosal wound healing.

Discovery of Novel Small-Molecule FAK Activators Promoting Mucosal Healing

Gastrointestinal mucosal wounds are common to patients injured by factors as diverse as drugs, inflammatory bowel disease, peptic ulcers, and necrotizing enterocolitis. However, although many drugs are used to ameliorate injurious factors, there is no drug available to actually stimulate mucosal wound healing. Focal adhesion kinase (FAK), a nonreceptor tyrosine kinase, induces epithelial sheet migration and wound healing, making FAK a potential pharmacological target in this regard. In our previous research, we found a lead compound with drug-like properties, ZINC40099027, which promotes FAK phosphorylation, inducing mucosal healing in murine models. Herein we describe the design and optimization of a small library of novel FAK activators based on ZINC40099027 and their applications toward human intestinal epithelial wound closure and mouse ulcer healing.

A method for rapid generation of model intestinal barriers in vitro

To increase the efficiency of drug development process, it is important to improve performance of preclinical experiments. A major drawback of the currently used in vitro intestinal barrier models is that it takes a significant time to obtain functional enterocyte monolayers with formed tight junctions. In this work, we have optimized various parameters such as cell density and different coatings, for a more rapid and efficient producing Caco-2 cell monolayers suitable for further experiments. In vivo microscopy and impedance spectroscopy were used to monitor cells state under various conditions. To determine possible biological mechanisms affected by exposure to various protein substrates, the transcriptomic analysis was applied. It was shown that collagen IV coating of the cell growth substrate significantly increased the rate of proliferation and migration of Caco-2 cells. This effect allows forming a functional monolayer of epithelial cells with tight junctions within 24 hours. Optimally, the initial cell density should be 90,000 to 200,000 cells/cm2. It was observed that collagen IV was poorly expressed by Caco-2 cells while the collagen IV receptor was expressed at a relatively high level in these cells. Laminin-332, another basement membrane component, was found to have no significant effect on times of formation of functional epithelial monolayers. Thus, using the optimal parameters determined in this study allows to significantly improve efficiency of using the in vitro intestinal barrier models.

Rhesus rotavirus VP6 regulates ERK-dependent calcium influx in cholangiocytes

The Rhesus rotavirus (RRV) induced murine model of biliary atresia (BA) is a useful tool in studying the pathogenesis of this neonatal biliary obstructive disease. In this model, the mitogen associated protein kinase pathway is involved in RRV infection of biliary epithelial cells (cholangiocytes). We hypothesized that extracellular signal-related kinase (ERK) phosphorylation is integral to calcium influx, allowing for viral replication within the cholangiocyte. Utilizing ERK and calcium inhibitors in immortalized cholangiocytes and BALB/c pups, we determined that ERK inhibition resulted in reduced viral yield and subsequent decreased symptomatology in mice. In vitro, the RRV VP6 protein induced ERK phosphorylation, leading to cellular calcium influx. Pre-treatment with an ERK inhibitor or Verapamil resulted in lower viral yields. We conclude that the pathogenesis of RRV-induced murine BA is dependent on the VP6 protein causing ERK phosphorylation and triggering calcium influx allowing replication in cholangiocytes.

Deguelin inhibits the migration and invasion of U-2 OS human osteosarcoma cells via the inhibition of matrix metalloproteinase-2/-9 in vitro

Osteosarcoma is the most common malignant primary bone tumor in children and young adults and lung metastasis is the main cause of death in those patients. Deguelin, a naturally occurring rotenoid, is known to be an Akt inhibitor and to exhibit cytotoxic effects, including antiproliferative and anticarcinogenic activities, in several cancers. In the present study, we determined if deguelin would inhibit migration and invasion in U-2 OS human osteosarcoma cells. Deguelin significantly inhibited migration and invasion of U-2 OS human osteosarcoma cells which was associated with a reduction of activities of matrix metalloproteinases-2 (MMP-2) and matrix metalloproteinases-9 (MMP-9). Furthermore, results from western blotting indicated that deguelin decreased the cell proliferation and cell growth-associated protein levels, such as SOS1, PKC, Ras, PI3K, p-AKT(Ser473), IRE-1α, MEKK3, iNOS, COX2, p-ERK1/2, p-JNK1/2, p-p38; the cell motility and focal adhesion-associated protein levels, such as Rho A, FAK, ROCK-1; the invasion-associated protein levels, such as TIMP1, uPA, MMP-2. MMP-9, MMP-13, MMP-1 and VEGF in U-2 OS cells. Confocal microscopy revealed that deguelin reduced NF-κB p65, Rho A and ROCK-1 protein levels in cytosol. MMP-7, MMP-9 and Rho A mRNA levels were suppressed by deguelin. These in vitro results provide evidence that deguelin may have potential as a novel anti-cancer agent for the treatment of osteosarcoma and provides the rationale for in vivo studies in animal models.

Modulation of tumor cell stiffness and migration by type IV collagen through direct activation of integrin signaling pathway

Excessive collagen deposition plays a critical role in tumor progression and metastasis. To understand how type IV collagen affects mechanical stiffness and migration, low-collagen-IV-expressing transfectants of B16F10, U118MG, and Huh7 (denoted shCol cells) were established by the lentiviral-mediated delivery of small interfering RNA against type IV-α1 collagen (Col4A1). Although having similar growth rates, shCol cells showed a flatter morphology compared to that of the corresponding controls. Notably, knocking down the Col4A1 gene conferred the cells with higher levels of elasticity and lower motility. Exposure to blocking antibodies against human β1 integrin or α2β1 integrin or the pharmacological inhibition of Src and ERK activity by PP1 and U0126, respectively, effectively reduced cell motility and raised cell stiffness. Reduced Src and ERK activities in shCol cells indicate the involvement of a collagen IV/integrin signaling pathway. The forced expression of β1 integrin significantly stimulated Src and ERK phosphorylation, reduced cell stiffness, and accelerated cell motility. In an experimental metastasis assay using C57BL/6 mice, B16F10 shCol cells formed significantly fewer and smaller lung nodules, confirming the contribution of collagen to metastasis. In summary, the integrin signaling pathway activated in a tumor environment with collagen deposition is responsible for low cell elasticity and high metastatic ability.

Focal adhesion kinase (FAK) siRNA inhibits human hypertrophic scar by suppressing integrin α, TGF-β and α-SMA

The effect of focal adhesion kinase (FAK) on suppressing scarring and the potential molecular mechanism underlying it has been investigated. Ten samples of human hypertrophic scars (HS) tissue cultured in vitro were transfected with FAK siRNA mediated by liposome. Quantitative real-time PCR was used to detect the expression of integrin α, transforming growth factor-β (TGF-β), FAK and α-smooth muscle actin (α-SMA) after transfection. MTT assay was used as a measure of fibroblast proliferation. Flow cytometry and (3)H-proincorporation technique gave measurements of the cell cycle and the quantity of collagen synthesis, respectively. Expression of FAK was effectively blocked, accompanied by decreasing expression of integrin α, TGF-β and α-SMA in hypertrophic scars fibroblast (HSFB) cells. One to 4 h after transfection with FAK siRNA, proliferation of HSFB cells was strongly inhibited (P < 0.01), reaching a maximum at 48 h. The proportion of G1 cells was higher and the proportion of the S and G2 cells lower after transfection. The amount of collagen synthesis in HSFB cells decreased when HSFB cells were transfected for 48 h. RNA interference targeting the FAK gene can block the two abnormal signal transduction pathways mediated by the integrin and TGF-β receptors that are responsible for hyperplasia and contracture of the scar, making FAK iRNA therapy a potentially effective approach in HS treatment.

Why cellular stress suppresses adipogenesis in skeletal tissue, but is ineffective in adipose tissue: control of mesenchymal cell differentiation via integrin binding sites in extracellular matrices

This Perspective addresses one of the major puzzles of adipogenesis in adipose tissue, namely its resistance to cellular stress. It introduces a concept of "density" of integrin binding sites in extracellular matrix, proposes a cellular signaling explanation for the observed effects of matrix elasticity and of cell shape on mesenchymal stem cell differentiation, and discusses how specialized integrin binding sites in collagen IV-containing matrices guard two pivotal physiological and evolutionary processes: stress-resistant adipogenesis in adipose tissues and preservation of pluripotency of mesenchymal stem-like cells in their storage niches. Finally, it proposes strategies to suppress adipogenesis in adipose tissues.

Visfatin induces stromal cell-derived factor-1 expression by β1 integrin signaling in colorectal cancer cells

Obesity has been shown to be associated with the risk of colorectal cancer (CRC). Adipokines produced by the adipose tissue are linked to some malignancies, including CRC. Visfatin is an adipokine shown to be a biomarker of CRC malignant potential. In addition, the stromal cell-derived factor-1 (SDF-1) has been reported to play a role in CRC progression. Although the relationship between visfatin and CRC has been established, the underlying mechanism has not been clarified. We investigated the molecular mechanism governing the interaction between visfatin stimulation and SDF-1 expression in human CRC cell lines. We found that visfatin stimulation led to an increase in the expression and secretion of SDF-1 in CRC DLD-1 and SW48 cells. Experiments involving specific inhibitors and small interfering RNA demonstrated that the activation of ERK and p38 mitogen-activated protein kinase (MAPK) pathways are critical for visfatin-induced SDF-1 expression. Analysis of transcription factor binding using ELISA and luciferase reporter assays revealed that visfatin increased NF-κB- and AP-1-DNA-binding activities in DLD-1 cells. Inhibition of NF-κB and AP-1 activation blocked the visfatin-induced expression and activity of the SDF-1 promoter. The effect of visfatin on DLD-1 signaling and SDF-1 expression was mediated by β1 integrin. In summary, these findings provide novel insights pertaining to the pathophysiological role of visfatin in CRC.

Chemokine stimulation promotes enterocyte migration through laminin-specific integrins

Intestinal homeostasis is regulated in part by the single cell layer of the mucosal epithelium. This physical barrier is a prominent part of the innate immune system and possesses an intrinsic ability to heal damage and limit infection. The restitutive epithelial migration phase of healing requires dynamic integrin adhesion to the extracellular matrix. Previously, we have shown that the homeostatic chemokine CXCL12 utilizes intracellular calcium to increase enterocyte migration on laminin. The aim of these studies was to investigate integrin specificity and, in turn, functional responses elicited by CXCL12 stimulation. Analysis of cellular adhesion and spreading revealed CXCL12 preferentially activated laminin-specific integrins compared with collagen IV-binding integrins. Laminin-specific cell adhesion and spreading elicited by CXCL12 was dependent on intracellular calcium. CXCL12 increased activated β1-integrins on the surface of epithelial cells compared with untreated cells. RT-PCR confirmed expression of the laminin-binding integrins-α3β1, -α6β1, and -α6β4. Interestingly, shRNA-mediated depletion of laminin-specific α3- or α6-integrin subunits revealed differential functions. α3-Integrin knockdown reduced basal as well as inducible restitution. Depletion of α6-integrin specifically abolished CXCL12-stimulated, but not TGF-β1 or basal, migration. Depletion with either shα3-integrin or shα6-integrin prevented CXCL12-evoked cell spreading. Our data indicate that CXCL12 stimulates the inside-out activation of laminin-specific integrins to promote cell migratory functions. Together, our findings support the notion that extracellular mediators within the gastrointestinal mucosa coordinate cell-matrix interactions during epithelial restitution.

Targeted intestinal epithelial deletion of the chemokine receptor CXCR4 reveals important roles for extracellular-regulated kinase-1/2 in restitution

Barrier defects and/or alterations in the ability of the gut epithelium to repair itself are critical etiological mechanisms of gastrointestinal disease. Our ongoing studies indicate that the chemokine receptor CXCR4 and its cognate ligand CXCL12 regulate intestinal-epithelial barrier maturation and restitution in cell culture models. Gene-deficient mice lacking CXCR4 expression specifically by the cells of the intestinal epithelium were used to test the hypothesis that CXCR4 regulates mucosal barrier integrity in vivo. Epithelial expression of CXCR4 was assessed by RT-PCR, Southern blot, immunoblot and immunohistochemistry. In vivo wounding assays were performed by addition of 3% dextran sodium sulfate (DSS) in drinking water for 5 days. Intestinal damage and DAI scores were assessed by histological examination. Extracellular-regulated kinase (ERK) phosphorylation was assessed in vivo by immunoblot and immunofluorescence. CXCR4 knockdown cells were established using a lentiviral approach and ERK phosphorylation was assessed. Consistent with targeted roles in restitution, epithelium from patients with inflammatory bowel disease indicated that CXCR4 and CXCL12 expression was stable throughout the human colonic epithelium. Conditional CXCR4-deficient mice developed normally, with little phenotypic differences in epithelial morphology, proliferation or migration. Re-epithelialization was absent in CXCR4 conditional knockout mice following acute DSS-induced inflammation. In contrast, heterozygous CXCR4-depleted mice displayed significant improvement in epithelial ulcer healing in acute and chronic inflammation. Mucosal injury repair was correlated with ERK1/2 activity and localization along the crypt-villus axis, with heterozygous mice characterized by increased ERK1/2 activation. Lentiviral depletion of CXCR4 in IEC-6 cells similarly altered ERK1/2 activity and prevented chemokine-stimulated migration. Taken together, these data indicate that chemokine receptors participate in epithelial barrier responses through coordination of the ERK1/2 signaling pathway.

Enteric glia promote intestinal mucosal healing via activation of focal adhesion kinase and release of proEGF

Wound healing of the gastrointestinal mucosa is essential for the maintenance of gut homeostasis and integrity. Enteric glial cells play a major role in regulating intestinal barrier function, but their role in mucosal barrier repair remains unknown. The impact of conditional ablation of enteric glia on dextran sodium sulfate (DSS)-induced mucosal damage and on healing of diclofenac-induced mucosal ulcerations was evaluated in vivo in GFAP-HSVtk transgenic mice. A mechanically induced model of intestinal wound healing was developed to study glial-induced epithelial restitution. Glial-epithelial signaling mechanisms were analyzed by using pharmacological inhibitors, neutralizing antibodies, and genetically engineered intestinal epithelial cells. Enteric glial cells were shown to be abundant in the gut mucosa, where they associate closely with intestinal epithelial cells as a distinct cell population from myofibroblasts. Conditional ablation of enteric glia worsened mucosal damage after DSS treatment and significantly delayed mucosal wound healing following diclofenac-induced small intestinal enteropathy in transgenic mice. Enteric glial cells enhanced epithelial restitution and cell spreading in vitro. These enhanced repair processes were reproduced by use of glial-conditioned media, and soluble proEGF was identified as a secreted glial mediator leading to consecutive activation of epidermal growth factor receptor and focal adhesion kinase signaling pathways in intestinal epithelial cells. Our study shows that enteric glia represent a functionally important cellular component of the intestinal epithelial barrier microenvironment and that the disruption of this cellular network attenuates the mucosal healing process.

Heterotrimeric G proteins, focal adhesion kinase, and endothelial barrier function

Ligands by binding to G protein coupled receptors (GPCRs) stimulate dissociation of heterotrimeric G proteins into Gα and Gβγ subunits. Released Gα and Gβγ subunits induce discrete signaling cues that differentially regulate focal adhesion kinase (FAK) activity and endothelial barrier function. Activation of G proteins downstream of receptors such as protease activated receptor 1 (PAR1) and histamine receptors rapidly increases endothelial permeability which reverses naturally within the following 1-2 h. However, activation of G proteins coupled to the sphingosine-1-phosphate receptor 1 (S1P1) signal cues that enhance basal barrier endothelial function and restore endothelial barrier function following the increase in endothelial permeability by edemagenic agents. Intriguingly, both PAR1 and S1P1 activation stimulates FAK activity, which associates with alteration in endothelial barrier function by these agonists. In this review, we focus on the role of the G protein subunits downstream of PAR1 and S1P1 in regulating FAK activity and endothelial barrier function.

Alpha2beta1 integrin is the major collagen-binding integrin expressed on human Th17 cells

Growing evidence indicates that collagen-binding integrins are important costimulatory molecules of effector T cells. In this study, we demonstrate that the major collagen-binding integrin expressed by human Th17 cells is alpha2beta1 (α2β1) or VLA-2, also known as the receptor for collagen I on T cells. Our results show that human naïve CD4(+) T cells cultured under Th17 polarization conditions preferentially upregulate α2β1 integrin rather than α1β1 integrin, which is the receptor for collagen IV on T cells. Double staining analysis for integrin receptors and intracellular IL-17 showed that α2 integrin but not α1 integrin is associated with Th17 cells. Cell adhesion experiments demonstrated that Th17 cells attach to collagen I and collagen II using α2β1 integrin but did not attach to collagen IV. Functional studies revealed that collagens I and II but not collagen IV costimulate the production of IL-17A, IL-17F and IFN-γ by human Th17 cells activated with anti-CD3. These results identify α2β1 integrin as the major collagen receptor expressed on human Th17 cells and suggest that it can be an important costimulatory molecule of Th17 cell responses.

Src tyrosine kinase regulates angiotensin II-induced protein kinase Czeta activation and proliferation in vascular smooth muscle cells

Protein kinase Czeta (PKCzeta) isoform plays a critical role in angiotensin II (AngII)-elicited extracellular signal-regulated kinase 1/2 (ERK1/2) activation and proliferation in vascular smooth muscle cells (VSMCs). However, the exact signal transduction mechanism by which AngII activates PKCzeta has not been clarified. In this study, we investigated the role of Src in PKCzeta activation and VSMCs proliferation induced by AngII. AngII-induced rapid activation of PKCzeta, which was associated with its phosphorylation and nuclear translocation. AngII not only induced Src activation but also promoted the physical association between Src and PKCzeta, which was abolished by Src inhibition with PP2. Src inhibition also abrogated AngII-stimulated PKCzeta activation, ERK1/2 phosphorylation and VSMCs proliferation. In conclusion, Src kinase plays an important role in AngII-elicited PKCzeta activation and the subsequent downstream signaling including ERK1/2 activation and VSMCs proliferation.

Fibrillar collagen type I stimulation of apolipoprotein B secretion in Caco-2 cells is mediated by beta1 integrin

Caco-2 cells spontaneously differentiate into enterocyte-like cells and secrete apolipoprotein B (apoB) lipoproteins. We evaluated the effect of different extracellular matrix proteins on lipoprotein secretion by these cells. Caco-2 cells grown on human amnion connective tissue (HACT) secreted twice as much apoB as control cells on Transwells, but secreted similar amounts of apoA1. Cells cultured on fibrillar collagen type I secreted increased amounts of apoB similar to the cells cultured on HACT, but cells cultured on non-fibrillar collagen type I, type IV collagen or laminin-1 did not. The increased secretion was nullified by a function inhibiting anti-integrin beta1 monoclonal antibody. Therefore, interactions between type I collagen and beta1 integrins augment apoB secretion by Caco-2 cells. Cells on HACT formed a more uniform columnar epithelium with lipid droplets polarized to the basolateral membrane. We also studied the effect of extracellular matrix proteins on transepithelial resistance (TER) of differentiated Caco-2 cells. TER in cells cultured on HACT was similar to that on Transwells, but cells on laminin-1 and collagen IV exhibited higher TER. Thus, various extracellular matrix proteins regulate apoB secretion and TER differently. This new observation that extracellular matrix proteins can enhance apoB secretion in Caco-2 cells could be useful to explore the modulation of lipid transport by these proteins.

Strain matrix-dependently dissociates gut epithelial spreading and motility

BACKGROUND

Repetitive deformation enhances intestinal epithelial migration across tissue fibronectin (tFN) via Src but inhibits migration across collagen. Since cell spreading generally precedes motility, we compared the effects of cyclic strain on Caco-2 spreading and migration on tFN, collagen-I, and plasma fibronectin (pFN), and investigated the role of Src in deformation-influenced spreading and migration.

MATERIALS AND METHODS

Human Caco-2 intestinal epithelial cells on tFN, collagen-I or pFN were subjected to an average 10% strain at 10 cycles/min for 2 h. Src was inhibited with 10muM PP2 or Src was reduced with siRNA. Parallel studies assessed deformation effects on monolayer wound closure.

RESULTS

Deformation, Src-inhibition or reduction each inhibited spreading on tFN but Src-inhibition or reduction prevented further inhibition of spreading by deformation without preventing further inhibition of motility. Deformation did not alter spreading on collagen-I or pFN, but inhibited wound closure.

CONCLUSIONS

Although cell spreading generally precedes and parallels motility, repetitive deformation regulates motility independently of spreading. Since deformation activates Src, the ability of Src blockade to mimic strain-associated inhibition of spreading on tFN suggests that this effect occurs by a separate mechanism that may also require basal Src activity. Further delineation of the mechanisms by which strain disparately modulates spreading and motility may permit acceleration of mucosal healing by targeted interventions to separately promote spreading and epithelial motility.

Collagen I matrix contributes to determination of adult human stem cell lineage via differential, structural conformation-specific elicitation of cellular stress response

Previously, we reported that the conformational transition of collagen I matrix plays, along with differentiation stimuli, a regulatory role in determination of differentiation lineage of bone marrow stromal sells via distinct signaling pathways specific for the structural state of the matrix. The present study addresses mechanisms underlying differential structural conformation-specific effects of collagen matrices on differentiation into diverse lineages. The results obtained suggest that the pivotal player in the observed matrix conformation-mediated regulation is a differential cellular stress response elicited by the exposure to native but not to denatured collagen I matrix. The stress causing such a response appears to be generated by matrix contraction and mediated by Alpha2Beta1 integrins engaged on native but not on denatured collagen I matrix. The principal facet of the observed phenomenon is not the nature of a stress but general stress response: when cells on denatured collagen I matrix are subjected to thermal stress, osteogenic pathway shifts to that seen on native collagen I matrix. Importantly, cellular stress response might be commonly involved in determination of differentiation lineage. Indeed, distinct components of cellular stress response machinery appear to regulate differentiation into diverse lineages. Thus, augmentation of Hsp90 levels enables the operation of efficient Alpha1Beta1/Alpha2Beta1 integrin-driven ERK activation pathways hence facilitating osteogenesis and suppressing adipogenesis, whereas myogenesis of satellite stem cells appears to be promoted by native collagen I matrix-elicited activation and nuclear translocation of another stress response component, Beta-catenin, shown to be essential for skeletal myogenesis, and chondrogenesis may involve stress-mediated elevation of yet another stress response constituent, Hsp70, shown to be an interactive partner of the chondrogenic transcription factor SOX9. The proposed concept of the integral role of cellular stress response in tissue generation and maintenance suggests new therapeutic approaches and indicates novel tissue engineering strategies.

Progression of human bone marrow stromal cells into both osteogenic and adipogenic lineages is differentially regulated by structural conformation of collagen I matrix via distinct signaling pathways

Adult human bone marrow stromal cells (BMSCs) containing or consisting of mesenchymal stem cells (MSCs) are an important source in tissue homeostasis and repair. Although many processes involved in their differentiation into diverse lineages have been deciphered, substantial inroads remain to be gained to synthesize a complete regulatory picture. The present study suggests that structural conformation of extracellular collagen I, the major organic matrix component in musculoskeletal tissues, plays, along with differentiation stimuli, a decisive role in the selection of differentiation lineage. It introduces a novel concept which proposes that structural transition of collagen I matrix regulates cell differentiation through distinct signaling pathways specific for the structural state of the matrix. Thus, on native collagen I matrix inefficient adipogenesis is p38-independent, whereas on its denatured counterpart, an efficient adipogenesis is primarily regulated by p38 kinase. Inversely, osteogenic differentiation occurs efficiently on native, but not on denatured collagen I matrix, with a low commencement threshold on the former and a substantially higher one on the latter. Osteogenesis on collagen I matrices in both structural conformations is fully dependent on ERK. However, whereas on native collagen I matrix osteogenic differentiation is Hsp90-dependent, on denatured collagen I matrix it is Hsp90-independent. The matrix conformation-mediated regulation appears to be one of the mechanisms determining differentiation lineage of BMSCs. It allows a novel interpretation of the bone remodeling cycle, explains the marked physiological aging-related adipogenic shift in musculoskeletal tissues, and can be a principal contributor to adipogenic shift seen in a number of clinical disorders.

DOCK5 and DOCK1 regulate Caco-2 intestinal epithelial cell spreading and migration on collagen IV

We observed previously that combined small interfering RNAs (siRNAs) targeting CrkII and CrkL, known activators of guanine nucleotide exchange factor DOCK1, strongly inhibit Caco-2 intestinal epithelial cell spreading and migration on collagen IV. DOCK1 siRNA reduced its expression >95% in Caco-2 cells but inhibited spreading much less than combined CrkII/CrkL siRNAs, suggesting that CrkII/CrkL interact with additional DOCK proteins. siRNA targeting DOCK5, a closely related DOCK1 family member, inhibited Caco-2 spreading similarly to DOCK1 siRNA, and the combined siRNAs synergistically inhibited spreading. Similar results were observed in human umbilical vein endothelial cells, and reverse transcriptase PCR demonstrated DOCK5 siRNA reduction of DOCK5 expression in both cell types. Combined DOCK1/DOCK5 siRNAs also inhibited Caco-2 migration and lamellipodial extension. Expression of DOCK5 cDNA, with silent mutations in the siRNA target region allowing expression simultaneously with DOCK5 siRNA, required CrkII/CrkL to restore cell spreading and DOCK5 coimmunoprecipitated with CrkII and CrkL. DOCK5 association with CrkII and CrkL was greatly reduced by mutations in their NH2-terminal SH3 domains. Expression of the DOCK5 COOH-terminal region (Met1738-Gln1870), containing potential Src homology 3 domain-binding proline-rich sites but lacking other functional regions, inhibited Caco-2 spreading and coimmunoprecipitated with CrkL. Coimmunoprecipitation of full-length DOCK5 with CrkL was strongly reduced by deletion of DOCK5 COOH-terminal amino acids 1832-1870. Green fluorescent protein-tagged DOCK5 localized to the membrane of Caco-2 cells spreading on collagen IV. In these studies, we describe human DOCK5 cloning and expression, our results indicating that, along with DOCK1, DOCK5 is an important mediator of CrkII/CrkL regulation of Caco-2 spreading and migration on collagen IV.

Repetitive deformation activates Src-independent FAK-dependent ERK motogenic signals in human Caco-2 intestinal epithelial cells

Repetitive deformation due to villous motility or peristalsis may support the intestinal mucosa, stimulating intestinal epithelial proliferation under normal circumstances and restitution in injured and inflamed mucosa rich in tissue fibronectin. Cyclic strain enhances Caco-2 and IEC-6 intestinal epithelial cell migration across fibronectin via ERK. However, the upstream mediators of ERK activation are unknown. We investigated whether Src and FAK mediate strain-induced ERK phosphorylation and migration in human Caco-2 intestinal epithelial cells on fibronectin. Monolayers on tissue fibronectin-precoated membranes were subjected to an average 10% repetitive deformation at 10 cycles/min. Phosphorylation of Src-Tyr 418, FAK-Tyr 397-Tyr 576-Tyr 925, and ERK were significantly increased by deformation. The stimulation of wound closure by strain was prevented by Src blockade with PP2 (10 micromol/l) or specific short interfering (si)RNA. Src inhibition also prevented strain-induced FAK phosphorylation at Tyr 397 and Tyr 576 but not FAK-Tyr 925 or ERK phosphorylation. Reducing FAK by siRNA inhibited strain-induced ERK phosphorylation. Transfection of NH2-terminal tyrosine phosphorylation-deficient FAK mutants Y397F, Y576F-Y577F, and Y397F-Y576F-Y577F did not prevent the activation of ERK2 by cyclic strain, but a FAK mutant at the COOH terminal (Y925F) prevented the strain-induced activation of ERK2. Although the Y397F-Y576F-Y577F FAK construct exhibited less basal FAK-Tyr 925 phosphorylation under static conditions, it nevertheless exhibited increased FAK-Tyr 925 phosphorylation in response to strain. These results suggest that repetitive deformation stimulates intestinal epithelial motility across fibronectin in a manner that requires both Src activation and a novel Src-independent FAK-Tyr 925-dependent pathway that activates ERK. This pathway may be an important target for interventions to promote mucosal healing in settings of intestinal ileus or fasting.

Collagen IV regulates Caco-2 cell spreading and p130Cas phosphorylation by FAK-dependent and FAK-independent pathways

We previously observed that collagen IV regulates Caco-2 intestinal epithelial cell spreading and migration via Src-dependent p130(Cas) phosphorylation and stimulates focal adhesion kinase (FAK). However, the role of FAK and the related kinase, Pyk2, in Caco-2 spreading and migration is unclear. FAK- or Pyk2-specific siRNAs reduced protein levels by 90%. However, when detached cells were replated on collagen IV neither individual nor combined FAK and Pyk2 siRNAs affected the cell spreading rate. As combined FAK and Pyk2 siRNAs increased p130(Cas) protein levels, we cotransfected cells with 1 nm p130(Cas) siRNA to partially reduce p130(Cas) protein to control levels. Although p130(Cas) Tyr(P)(249) phosphorylation was reduced by 60%, cell spreading was unaffected. Combined siRNA reduction of FAK, Pyk2 and p130(Cas) increased cell spreading by 20% compared to p130(Cas) siRNA alone, suggesting that FAK and Pyk2 negatively regulate spreading in addition to stimulating spreading via p130(Cas). FAK-binding mutant SH3 domain-deleted rat p130(Cas) was not phosphorylated after adhesion and, unlike full-length p130(Cas), did not restore spreading after human-specific p130(Cas) siRNA knockdown of endogenous p130(Cas). Together, these data suggest that FAK positively regulates Caco-2 spreading on collagen IV via p130(Cas) phosphorylation, but also suggests that FAK may negatively regulate spreading through other mechanisms and the presence of additional FAK-independent pathways regulating p130(Cas).

Interaction of transient receptor potential vanilloid 4, integrin, and SRC tyrosine kinase in mechanical hyperalgesia

Although the transient receptor potential vanilloid 4 (TRPV4) has been implicated in the process of osmomechanical transduction, it appears to make little contribution to the normal somatosensory detection of mechanical stimuli. However, evidence suggests that it may play an important role in mechanical hyperalgesia. In the present study, we examined the common requirement for TRPV4 in mechanical hyperalgesia associated with diverse pain models and investigated whether the very close association observed between TRPV4 and mechanical hyperalgesia, regardless of etiology, reflects a close functional connection of TRPV4 with other molecules implicated in mechanical transduction. In models of painful peripheral neuropathy associated with vincristine chemotherapy, alcoholism, diabetes, and human immunodeficiency virus/acquired immune deficiency syndrome therapy, mechanical hyperalgesia was markedly reduced by spinal intrathecal administration of oligodeoxynucleotides antisense to TRPV4. Similarly, mechanical hyperalgesia induced by paclitaxel, vincristine, or diabetes was strongly reduced in TRPV4 knock-out mice. We also show that alpha2beta1 integrin and Src tyrosine kinase, which have been implicated in mechanical transduction, are important for the development of mechanical hyperalgesia, and that their contribution requires TRPV4. Furthermore, we establish a direct interaction between TRPV4, alpha2 integrin, and the Src tyrosine kinase Lyn in sensory neurons. We suggest that TRPV4 plays a role in mechanotransduction, as a component of a molecular complex that functions only in the setting of inflammation or nerve injury.

Comparison of the biological activity between ultrafine and fine titanium dioxide particles in RAW 264.7 cells associated with oxidative stress

Ultrafine or fine titanium dioxide (TiO(2)) particles are widely used in the production of white pigments, for sunscreens, and in cleanup techniques. However, currently knowledge is deficient concerning cellular responses to these particles. The study evaluated and compared the biological activity of ultrafine and fine TiO(2) particles in RAW 264.7 macrophages according to an oxidative stress paradigm. In vitro exposure of macrophages to ultrafine or fine TiO(2) in the range of 0.5-200 microg/ml did not significantly alter cell viability. However, ultrafine TiO(2) enhanced intracellular generation of reactive oxygen species (ROS) to a greater extent than fine TiO(2) at each exposure concentration. Ultrafine TiO(2) induced ERK1/2 activation in a concentration-dependent manner, while the fine TiO(2)-induced changes were minimal. Phosphorylation of ERK1/2 occurred following 10 min exposure to higher concentrations of ultrafine TiO(2) (> or = 25 microg/ml). Similarly, ultrafine TiO(2) exposure significantly enhanced tumor necrosis factor (TNF)-alpha and macrophage inflammatory protein (MIP)-2 secretion in a concentration-dependent manner, and its potency was higher than fine TiO(2). These findings suggest that when exposure concentration is based upon equivalent mass, ultrafine TiO(2) exerts greater biological activity as measured by ROS generation, ERK 1/2 activation, and proinflammatory mediator secretion in RAW 264.7 macrophages than fine TiO(2).

MAPK signaling contributes to rotaviral-induced cholangiocyte injury and viral replication

BACKGROUND

Biliary atresia is a disease of newborns that results in obliteration of the biliary tree. Infection of mice with rhesus rotavirus (RRV) results in a cholangiopathy mirroring human disease. The Mitogen Associated Protein Kinase (MAPK) signaling pathway can be activated by viral binding to cell-surface receptors. We hypothesized that RRV infection of cholangiocytes results in activation of MAPK signaling.

METHODS

Extrahepatic bile ducts from BALB/c pups or immortalized cholangiocytes subjected to RRV infection or control were analyzed, using Western blots, for phosphorylated members of the MAPK family: p38, ERK 1/2, JNK 1/2, and downstream transcription factors. Inhibitors of the MAPK were used to downregulate activity. Viral replication and cytolysis in cholangiocytes were evaluated post-MAPK inhibition.

RESULTS

Phosphorylation of all MAPK increased in RRV-infected mice and cholangiocytes. Several downstream transcription factors had increased activity in vitro. Inhibition of p38 and ERK 1/2 resulted in decreased viral replication. ERK 1/2 inhibition decreased cytolysis without affecting viral entry or binding.

CONCLUSIONS

RRV infection of cholangiocytes resulted in increased MAPK signaling. Inhibition of p38 and ERK 1/2 influenced the ability of rotavirus to replicate. These novel findings provide insight into the signaling cascade involved in RRV-induced cholangiocyte injury.

Keratinocyte growth factor-transfection-stimulated adhesion of colorectal cancer cells to extracellular matrices

The keratinocyte growth factor (KGF) regulates cell growth and behavior in an autocrine or paracrine manner. In colorectal cancer tissues, KGF is expressed in tumor cells and adjacent stromal fibroblasts. We have constructed a KGF-gene-transfected cell line (HCT15-KGF) from a colorectal cancer cell line, HCT-15, that expresses the KGF receptor, and studied the effects of KGF on cell behavior, particularly growth and adhesion to extracellular matrices (ECMs). The amount of KGF secreted from HCT15-KGF was significantly higher than that from a mock-transfected cell line (HCT15-MOCK). The modes of growth of these cell lines were similar. The degree of adhesion of HCT15-KGF to ECMs, including type-IV collagen and fibronectin was higher than that of HCT15-MOCK. The expressions of integrins in both cell lines were not significantly different. However, extracellular-regulated kinase-1 and -2 (ERK1/2) phosphorylation and focal adhesion kinase (FAK) expression that regulate the adhesive functions of integrin families were enhanced in HCT15-KGF. U0126, an inhibitor of the ERK upstream regulator MEK, attenuated the adhesion and spreading of HCT15-KGF cells to type-IV collagen. These results indicate that KGF enhances the adhesion of colorectal cancer cells to type-IV collagen through ERK and FAK signaling pathways.

Alpha2beta1 integrin signalling enhances cyclooxygenase-2 expression in intestinal epithelial cells

Inflammatory bowel diseases (IBD) are linked to an increased risk of developing colon cancer, by inflammatory mediators and alterations to the extracellular matrix (ECM). The events induced by inflammatory mediators lead to dysregulated activation and induction of inflammatory genes such as cyclooxygenase-2 (COX-2). COX-2 is involved in the conversion of arachidonic acid to biologically active prostanoids and is highly upregulated in colon cancer. Since inflammation-induced changes to the extracellular matrix could affect integrin activities, we here investigated the effect of integrin signalling on the level of COX-2 expression in the non-transformed intestinal epithelial cell lines, Int 407 and IEC-6. Adhesion of these cells to a collagen I- or IV-coated surface, increased surface expression of alpha2beta1 integrin. Activation of integrins with collagen caused an increased cox-2 promoter activity, with a subsequent increase in COX-2 expression. The signalling cascade leading to this increased expression and promoter activity of cox-2, involves PKCalpha, the small GTPase Ras and NFkappaB but not Erk1/2 or Src activity. The integrin-induced increase in cellular COX-2 activity is responsible for an elevated generation of reactive oxygen species (ROS) and increased cell migration. This signalling pathway suggests a mechanism whereby inflammation-induced modulations of the ECM, can promote cancer transformation in the intestinal epithelial cells.

Inference of disease-related molecular logic from systems-based microarray analysis

Computational analysis of gene expression data from microarrays has been useful for medical diagnosis and prognosis. The ability to analyze such data at the level of biological modules, rather than individual genes, has been recognized as important for improving our understanding of disease-related pathways. It has proved difficult, however, to infer pathways from microarray data by deriving modules of multiple synergistically interrelated genes, rather than individual genes. Here we propose a systems-based approach called Entropy Minimization and Boolean Parsimony (EMBP) that identifies, directly from gene expression data, modules of genes that are jointly associated with disease. Furthermore, the technique provides insight into the underlying biomolecular logic by inferring a logic function connecting the joint expression levels in a gene module with the outcome of disease. Coupled with biological knowledge, this information can be useful for identifying disease-related pathways, suggesting potential therapeutic approaches for interfering with the functions of such pathways. We present an example providing such gene modules associated with prostate cancer from publicly available gene expression data, and we successfully validate the results on additional independently derived data. Our results indicate a link between prostate cancer and cellular damage from oxidative stress combined with inhibition of apoptotic mechanisms normally triggered by such damage.

Increased apoptosis and accelerated epithelial migration following inhibition of hedgehog signaling in adaptive small bowel postresection

The intestinal epithelium undergoes a marked adaptive response following loss of functional small bowel surface area characterized by increased crypt cell proliferation and increased enterocyte migration from crypt to villus tip, resulting in villus hyperplasia and enhanced nutrient absorption. Hedgehog (Hh) signaling plays a critical role in regulating epithelial-mesenchymal interactions during morphogenesis of the embryonic intestine. Our previous studies showed that blocking Hh signaling in neonatal mice results in increased small intestinal epithelial crypt cell proliferation and altered enterocyte fat absorption and morphology. Hh family members are also expressed in the adult intestine, but their role in the mature small bowel is unclear. With the use of a model of intestinal adaptation following partial small bowel resection, the role of Hh signaling in the adult gut was examined by determining the effects of blocking Hh signaling on the regenerative response following loss of functional surface area. Hh-inactivating monoclonal antibodies or control antibodies were administered to mice that sustained a 50% intestinal resection. mRNA analyses of the preoperative ileum by quantitative real-time PCR revealed that Indian hedgehog was the most abundant Hh family member. The Hh receptor Patched was more abundant than Patched 2. Analyses of downstream targets of Hh signaling demonstrated that Gli3 was twofold more abundant than Gli1 and Gli2 and that bone morphogenetic protein (BMP)2 was most highly expressed compared with BMP1, -4, and -7. Following intestinal resection, the expression of Hh, Patched, Gli, and most BMP genes was markedly downregulated in the remnant ileum, and, in anti-Hh antibody-treated mice, expression of Patched 2 and Gli 1 was further suppressed. In Hh antibody-treated mice following resection, the enterocyte migration rate from crypt to villus tip was increased, and by 2 wk postoperation, apoptosis was increased in the adaptive gut. However, crypt cell proliferation, villus height, and crypt depth were not augmented. These data indicate that Hh signaling plays a role in adult gut epithelial homeostasis by regulating epithelial cell migration from crypt to villus tip and by enhancing apoptosis.

Comparative study of T84 and T84SF human colon carcinoma cells: in vitro and in vivo ultrastructural and functional characterization of cell culture and metastasis

To better understand the relationship between tumor heterogeneity, differentiation, and metastasis, suitable experimental models permitting in vitro and in vivo studies are necessary. A new variant cell line (T84SF) exhibiting an altered phenotype was recently selected from a colon cancer cell line (T84) by repetitive plating on TNF-alpha treated human endothelial cells and subsequent selection for adherent cells. The matched pair of cell lines provides a useful system to investigate the extravasation step of the metastatic cascade. Since analysis of morphological differences can be instructive to the understanding of metastatic potential of tumor cells, we compared the ultrastructural and functional phenotype of T84 and T84SF cells in vitro and in vivo. The reported ultrastructural features evidence differences between the two cell lines; selected cells showed a marked pleomorphism of cell size and nuclei, shape, and greater surface complexity. These morphological differences were also coupled with biochemical data showing a distinct tyrosine phosphorylation-based signaling, an altered localization of beta-catenin, MAPK, and AKT activation, as well as an increased expression in T84SF cells of Bcl-X(L), a major regulator of apoptosis. Therefore, these cell lines represent a step forward in the development of appropriate models in vitro and in vivo to investigate colon cancer progression.

Collagen type I-mediated activation of ERK/MAP Kinase is dependent on Ras, Raf-1 and protein phosphatase 2A in Jurkat T cells

Growing evidence indicates that interactions of T cells with extracellular matrix through beta1 integrins are important for the regulation of T cell-mediated immune responses and diseases. In this regard, we have recently demonstrated that collagen I (Coll I) through alpha2beta1 integrin inhibited Fas-induced apoptosis of T cells by activating a protein phosphatase 2A (PP2A)-dependent ERK/MAP Kinase pathway. As survival of T cells is critical for their functions, we further investigated the mechanisms underlying the activation of this pathway. Inhibition studies demonstrated that Coll I activates the ERK/MAP Kinase pathway in Jurkat T cells through the activation of Ras and Raf-1. Activation of PP2A was not necessary for the binding of Coll I to Jurkat T cells, but is required for the activation of Raf-1. In accordance, activation of Ras, Raf-1 and PP2A were also required for the ability of Coll I to protect Jurkat T cells from Fas-induced apoptosis. In contrast and despite its capacity to activate Ras, fibronectin (Fbn) failed to activate PP2A and Raf-1. These results might explain, at least in part, the weak ability of Fbn to activate ERK in T cells, supporting thus the differential signaling of beta1 integrin members in these cells. This study provides novel insights into the mechanisms by which beta1 integrins activate the ERK/MAP Kinase pathway in T cells, and is the first report to provide a role for PP2A in integrin-mediated ERK/MAP Kinase activation.

Type IV collagen induces STAT5 activation in MCF7 human breast cancer cells

A rapid increase in the tyrosine phosphorylation of signal transducer and activators of transcription (STAT) proteins has been extensively documented in cells stimulated with cytokines and growth factors, but virtually nothing is known about the regulation of STAT5 activation in breast cancer cells stimulated with basement membrane (BM) components. Stimulation of MCF7 cells with type IV collagen (Col-IV) promoted a striking increase in the phosphorylation of STAT5 at Tyr-694, as revealed by site-specific antibodies that recognized the phosphorylated state of this residue. In addition, Col-IV also stimulated STAT5 nuclear translocation and an increased in STAT5 DNA binding activity. Treatment with the selective Src family inhibitor pyrazolopyrimidine PP-2 prevented STAT5 phosphorylation at Tyr-694, nuclear translocation of STAT5 and the STAT5-DNA complex formation. Our results demonstrate, for the first time, that stimulation with Col-IV induces STAT5 phosphorylation of endogenous STAT5 at Tyr-694, nuclear translocation of STAT5 and increases in STAT5 DNA binding activity via a Src-dependent pathway in MCF7 cells.

I-domain-containing integrins serve as pilus receptors for Neisseria gonorrhoeae adherence to human epithelial cells

Two pilus receptors are identified for the pathogenic Neisseria, CD46 and complement receptor 3. An intimate association between the asialoglycoprotein receptor and gonococcal lipooligosaccharide mediates invasion of primary, male urethral epithelial cells (UECs); however, studies to identify pilus receptors on these cells have not been performed. Based on our previous studies we reasoned that the I-domain-containing (IDC), alpha(1)- and alpha(2)-integrins might serve as pilus receptors on UECs and on urethral tissue. Confocal microscopy revealed colocalization of pilus with alpha(1) and alpha(2) integrins on UECs and tissue. We found that recombinant I-domain and antibodies directed against the alpha(1)- and alpha(2)-integrins inhibited gonococcal association with UECs and with immortal cell lines of variable origin. Gonococcus-integrin colocalization occurred at early time points post infection, but this interaction dissociated with extended infection. Similarly, Western Blot analyses revealed that gonococcal pilin coimmunoprecipitates with alpha(1)- and alpha(2)-integrins. However, studies performed in parallel and that were designed to capture CD46-pilus immune complexes indicated that a CD46-pilus interaction did not occur. Collectively, these data suggest that while CD46 might be able to bind gonococcal pilus, IDC integrins are preferentially used as the initial docking site for gonococci on UECs, on urethral tissue and on some immortal cell lines.

The role of the cytoskeleton in differentially regulating pressure-mediated effects on malignant colonocyte focal adhesion signaling and cell adhesion

Increased extracellular pressure stimulates colon cancer cell adhesion by activating focal adhesion kinase (FAK) and Src. We investigated the role of the cytoskeleton in pressure-induced inside-out FAK and Src phosphorylation and pressure-stimulated adhesion. We perturbed actin polymerization with phalloidin, cytochalasin D and latrunculin B, and microtubule organization with colchicine and paclitaxol. We compared the effects of these agents on pressure-induced SW620 and human primary colon cancer cell adhesion and inside-out FAK/Src activation with outside-in adhesion-dependent FAK/Src activation. Cells pretreated with cytoskeletal inhibitors were subjected to 15 mmHg increased pressure and allowed to adhere to collagen I coated plates or prevented from adhesion to pacificated plates for 30 min. Phalloidin, cytochalasin D, latrunculin B and colchicine pretreatment completely prevented pressure-stimulated and significantly inhibited basal SW620 cell adhesion. Taxol did not inhibit pressure-induced colon cancer cell adhesion, but significantly lowered basal adhesion. Cytochalasin D and colchicine had similar effects in pressure-stimulated primary human malignant colonocytes. Phalloidin, cytochalasin D, latrunculin B and colchicine prevented pressure-induced SW620 FAK phosphorylation but not Src phosphorylation. FAK phosphorylation in response to collagen I adhesion was significantly attenuated but not completely prevented by these inhibitors. Although Src phosphorylation was not increased on adhesion, the cytoskeleton disrupting agents significantly lowered basal Src phosphorylation in adherent cells. These results suggest that both cytoskeleton-dependent FAK activation and cytoskeleton-independent Src activation may be required for extracellular pressure to stimulate colon cancer cell adhesion. Furthermore, the cytoskeleton plays a different role in pressure-activated FAK and Src signaling than in FAK and Src activation in adherent cells. We, therefore, hypothesize that cytoskeletal interactions with focal adhesion signals mediate the effects of extracellular pressure on colon cancer cell adhesion.

The interplay between Src and integrins in normal and tumor biology

Src family nonreceptor protein tyrosine kinases transduce signals that control normal cellular processes such as cell proliferation, adhesion and motility. Normally, cellular Src is held in an inactive state, but in several cancer types, abnormal events lead to elevated kinase activity of the protein and cause pleiotropic cellular responses inducing transformation and metastasis. A prerequisite of the ability of a cancer cell to undergo metastasis into distant tissues is to penetrate surrounding extracellular matrices. These processes are facilitated by the integrin family of cell adhesion molecules. As is the case with Src, altered integrin activity or substrate affinity can contribute to the neoplastic phenotype. Therefore, understanding the interplay between Src and integrin function has been of intense interest over the past few years. This review focuses on the role of Src and integrin signaling in normal cells and how this is deregulated in human cancer. We will identify the key players in the integrin-mediated signaling pathways involved in cell motility and apoptosis, such as FAK, paxillin and p130(CAS), and discuss how Src signaling affects the formation of focal adhesions and the extracellular matrix.