Focal adhesion kinase: at the crossroads of signal transduction

Disintegrins: integrin selective ligands which activate integrin-coupled signaling and modulate leukocyte functions

Extracellular matrix proteins and cell adhesion receptors (integrins) play essential roles in the regulation of cell adhesion and migration. Interactions of integrins with the extracellular matrix proteins lead to phosphorylation of several intracellular proteins such as focal adhesion kinase, activating different signaling pathways responsible for the regulation of a variety of cell functions, including cytoskeleton mobilization. Once leukocytes are guided to sites of infection, inflammation, or antigen presentation, integrins can participate in the initiation, maintenance, or termination of the immune and inflammatory responses. The modulation of neutrophil activation through integrin-mediated pathways is important in the homeostatic control of the resolution of inflammatory states. In addition, during recirculation, T lymphocyte movement through distinct microenvironments is mediated by integrins, which are critical for cell cycle, differentiation and gene expression. Disintegrins are a family of low-molecular weight, cysteine-rich peptides first identified in snake venom, usually containing an RGD (Arg-Gly-Asp) motif, which confers the ability to selectively bind to integrins, inhibiting integrin-related functions in different cell systems. In this review we show that, depending on the cell type and the microenvironment, disintegrins are able to antagonize the effects of integrins or to act agonistically by activating integrin-mediated signaling. Disintegrins have proven useful as tools to improve the understanding of the molecular events regulated by integrin signaling in leukocytes and prototypes in order to design therapies able to interfere with integrin-mediated effects.

A truncated FAK lacking the FERM domain displays high catalytic activity but retains responsiveness to adhesion-mediated signals

In order to determine the role of the FERM domain in the regulation of FAK phosphorylation at Tyr-397, the major autophosphorylation site, we generated a truncated FAK lacking a region of the N-terminus corresponding to amino acids 1-384 (FAKDelta384). FAKDelta384 showed a striking increase in phosphorylation, as compared with wild type FAK, in lysates of either HEK 293 or FAK-/- cells. Interestingly, the truncated form of FAK lacking the N-terminal domain retains responsiveness to integrin-mediated signals, as judged by its dephosphorylation by holding cells in suspension and by the recovery of the phosphorylation when replating the cells on fibronectin. We propose a model in which removal of FERM-mediated auto-inhibition is important to increase FAK catalytic activity but the translocation and clustering of this enzyme at the focal adhesions is required for maximal phosphorylation at Tyr-397.

Myotubularin phosphoinositide phosphatases, protein phosphatases, and kinases: their roles in junction dynamics and spermatogenesis

Spermatogenesis in the seminiferous epithelium of the mammalian testis is a dynamic cellular event. It involves extensive restructuring at the Sertoli-germ cell interface, permitting germ cells to traverse the epithelium from basal to adluminal compartment. As such, Sertoli-germ cell actin-based adherens junctions (AJ), such as ectoplasmic specializations (ES), must disassemble and reassemble to facilitate this event. Recent studies have shown that AJ dynamics are regulated by intricate interactions between AJ integral membrane proteins (e.g., cadherins, alpha6beta1 integrins and nectins), phosphatases, kinases, adaptors, and the underlying cytoskeleton network. For instance, the myotubularin (MTM) phosphoinositide (PI) phosphatases, such as MTM related protein 2 (MTMR2), can form a functional complex with c-Src (a non-receptor protein tyrosine kinase). In turn, this phosphatase/kinase complex associates with beta-catenin, a constituent of the N-cadherin/beta-catenin functional unit at the AJ site. This MTMR2-c-Src-beta-catenin complex apparently regulates the phosphorylation status of beta-catenin, which determines cell adhesive function conferred by the cadherin-catenin protein complex in the seminiferous epithelium. In this review, we discuss the current status of research on selected phosphatases and kinases, and how these proteins potentially interact with adaptors at AJ in the seminiferous epithelium to regulate cell adhesion in the testis. Specific research areas that are open for further investigation are also highlighted.

Neonatal cerebral hypoxia-ischemia: involvement of FAK-dependent pathway

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase thought to play a major role in transducing extracellular matrix (ECM)-derived survival signals into cells. Thus, modulation of FAK activity may affect the linkage between ECM and signaling cascade to which it is connected and may participate in a variety of pathological settings. In the present study, we investigated the effect of neonatal cerebral hypoxia-ischemia (HI) on levels and tyrosine phosphorylation of focal adhesion kinase and the interaction of this enzyme with Src protein tyrosine kinase and adapter protein p130Cas, involved in FAK-mediated signaling pathway. The total amount of focal adhesion kinase as well as its phosphorylated form declined substantially to about 50% of the control between 24 and 48 h after the insult. Concomitantly a decreased association of FAK with its investigated molecular partners, Src kinase and p130Cas protein has been observed. This early response to brain hypoxia-ischemia was attenuated during prolonged recovery with almost complete return to control values at 7 days. These data are indicative of an involvement of FAK-dependent signaling pathway in the evolution of HI-induced neuronal degeneration.

Transient forebrain ischemia effects interaction of Src, FAK, and PYK2 with the NR2B subunit of N-methyl-d-aspartate receptor in gerbil hippocampus

Two different models of brain ischemia were used to examine the evoked changes in the tyrosine phosphorylation of NMDA receptor subunits 2A and 2B (NR2A and NR2B), as well as their interactions with non-receptor tyrosine kinases (NRTKs: FAK, PYK2 Src), and PSD-95 protein. Only short-term 5 min ischemia followed by 3 h reperfusion resulted in the elevated tyrosine phosphorylation of both investigated NMDA receptor subunits, but in contrast to previously published data, more pronounced in the case of NR2B. Concomitantly, an increased association of NR2B with FAK, PYK2, Src and PSD-95 has been observed. This sharp early reaction to brief ischemia was markedly attenuated during prolonged recovery (72 h) with almost complete return to control values. The initial recruitment of tyrosine kinases to NMDA receptor during the first 3 h of reperfusion is generally consistent with an active postischemic remodeling of PSD and may participate in the induction of the postischemic signal transduction pathway in gerbil hippocampus. In contrast, ischemia of longer duration (up to 30 min) caused an immediate decrease in the protein levels as well as tyrosine phosphorylation of both NR2A and NR2B subunits which was accompanied by the marked attenuation of the association with their investigated molecular partners--PSD-95 and NRTKs. This effect may be mimicked in vitro by Ca2+-dependent activation of endogenous calpains in purified PSD preparation suggesting irreversible deterioration of the synaptic signaling machinery during irreversible long-term ischemia.

G protein-coupled receptor activation rapidly stimulates focal adhesion kinase phosphorylation at Ser-843. Mediation by Ca2+, calmodulin, and Ca2+/calmodulin-dependent kinase II

A rapid increase in the tyrosine phosphorylation of focal adhesion kinase (FAK) has been extensively documented in cells stimulated by multiple signaling molecules, but little is known about the regulation of FAK phosphorylation at serine residues. Stimulation of Swiss 3T3 cells with the G protein-coupled receptor agonists bombesin, vasopressin, or bradykinin induced an extremely rapid (within 5 s) increase in FAK phosphorylation at Ser-843. The phosphorylation of this residue preceded FAK phosphorylation at Tyr-397, the major autophosphorylation site, and FAK phosphorylation at Ser-910. Treatment of intact cells with ionomycin stimulated a rapid increase in FAK phosphorylation at Ser-843, indicating that an increase in intracellular Ca2+ concentration ([Ca2+]i) is a potential pathway leading to FAK-Ser-843 phosphorylation. Indeed, treatment with agents that prevent an agonist-induced increase in [Ca2+]i (e.g. thapsigargin or BAPTA (1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid)), interfere with calmodulin function (e.g. trifluoperazine, W13, and W7), or block Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation (KN93) or expression (small interfering RNA) abrogated the rapid FAK phosphorylation at Ser-843 induced by bombesin, bradykinin, or vasopressin. Furthermore, activated CaMKII directly phosphorylated the recombinant COOH-terminal region of FAK at a residue equivalent to Ser-843. Thus, our results demonstrate that G protein-coupled receptor activation induces rapid FAK phosphorylation at Ser-843 through Ca2+, calmodulin, and CaMKII.

Cyclic mechanical strain inhibits skeletal myogenesis through activation of focal adhesion kinase, Rac-1 GTPase, and NF-kappaB transcription factor

Myogenesis is a multistep developmental program that generates and regenerates skeletal muscles. Several extracellular factors have been identified that participate in the regulation of myogenesis. Although skeletal muscles are always subjected to mechanical stress in vivo, the role of mechanical forces in the regulation of myogenesis remains unknown. We have investigated the molecular mechanisms by which cyclic mechanical strain modulates myogenesis. Application of cyclic mechanical strain using the computer-controlled Flexcell Strain Unit increased the proliferation of C2C12 cells and inhibited their differentiation into myotubes. Cyclic strain increased the activity of cyclin-dependent kinase 2 (cdk2) and the cellular level of cyclin A, and inhibited the expression of myosin heavy chain and formation of myotubes in C2C12 cultures. The activity of nuclear factor-kappa B (NF-kappaB) transcription factor and the expression of NF-kappaB-regulated genes, cyclin D1 and IL-6, were augmented in response to mechanical strain. Cyclic strain also increased the activity of Rho GTPases, especially Rac-1. The inhibition of Rho GTPases activity, by overexpression of Rho GDP dissociation inhibitor (Rho-GDI), inhibited the strain-induced activation of NF-kappaB in C2C12 cells. Overexpression of either NF-kappaB inhibitory protein IkappaBalphaDeltaN (a degradation resistant mutant IkappaBalpha) or Rho-GDI blocked the strain-induced proliferation of C2C12 cells. Furthermore, overexpression of FRNK, a dominant negative mutant of focal adhesion kinase (FAK), inhibited the strain-induced proliferation of C2C12 cells. Our study demonstrates that cyclic mechanical strain inhibits myogenesis through the activation of FAK, Rac-1, and NF-kappaB.

Specific deletion of focal adhesion kinase suppresses tumor formation and blocks malignant progression

We have generated mice with a floxed fak allele under the control of keratin-14-driven Cre fused to a modified estrogen receptor (CreER(T2)). 4-Hydroxy-tamoxifen treatment induced fak deletion in the epidermis, and suppressed chemically induced skin tumor formation. Loss of fak induced once benign tumors had formed inhibited malignant progression. Although fak deletion was associated with reduced migration of keratinocytes in vitro, we found no effect on wound re-epithelialization in vivo. However, increased keratinocyte cell death was observed after fak deletion in vitro and in vivo. Our work provides the first experimental proof implicating FAK in tumorigenesis, and this is associated with enhanced apoptosis.

Loss of Rb-E2F Repression Results in Caspase-8-mediated Apoptosis through Inactivation of Focal Adhesion Kinase

Molecular hardwiring of the cell cycle to the apoptotic machinery is a critical tumor suppressor mechanism for eliminating hyperproliferative cells. Deregulation of the Rb-E2F repressor complex by genetic deletion or functional inhibition of Rb triggers apoptosis through both the intrinsic (caspase-9 mediated) and extrinsic (caspase-8 mediated) death pathways. Induction of the intrinsic pathway has been studied extensively and involves release of free E2F and direct transcriptional activation of E2F-responsive apoptotic genes such as ARF, APAF1, and CASP9. In contrast, the mechanisms leading to activation of the extrinsic pathway are less well understood. There is growing evidence that Rb-E2F perturbation induces the extrinsic pathway, at least in part, through derepression (as opposed to transactivation) of apoptotic genes. Here, we explore this possibility using cells in which Rb-E2F complexes are displaced from promoters without stimulating E2F transactivation. This derepression of Rb-E2F-regulated genes leads to apoptosis through inactivation of focal adhesion kinase and activation of caspase-8. These findings reveal a new mechanistic link between Rb-E2F and the extrinsic (caspase 8-mediated) apoptotic pathway.

Residues within the First Subdomain of the FERM-like Domain in Focal Adhesion Kinase Are Important in Its Regulation

We have previously described regulation of focal adhesion kinase (FAK) by its amino-terminal FERM-like domain through an autoinhibitory interaction with its kinase domain (Cooper, L. A., Shen, T. L., and Guan, J. L. (2003) Mol. Cell. Biol. 23, 8030-8041). Here we show that the first two subdomains of the FERM-like domain are independently capable of inhibiting phosphorylation of FAK in trans. We characterized several point mutations within the first subdomain of the FERM-like domain and find that mutation of Lys-38 to alanine results in a FAK mutant that is strongly hyperphosphorylated when expressed in mammalian cells, and promotes increased phosphorylation of the FAK substrate paxillin. A second mutation of Lys-78 to alanine results in a FAK mutant that is underphosphorylated, but can be activated by extracellular matrix stimuli. Like deletion of the amino terminus itself the K38A mutation is phosphorylated in suspension. The Delta375 truncation mutant of FAK is strongly phosphorylated both when Tyr-397 is mutated to phenylalanine, and in the presence of the Src inhibitor, PP2, suggesting that removal of the amino terminus can render FAK Src independent. This is in contrast to the K38A mutant that is not phosphorylated in the Y397F background, and which shows decreased phosphorylation in the presence of the Src inhibitor PP2, suggesting that regulation of FAK by Src is a secondary step in its activation. The K38A mutation weakens the interaction between the amino terminus of FAK and its own kinase domain, and disrupts the ability of the amino terminus to inhibit the phosphorylation of FAK in trans. The K38A mutation of FAK also increases the ability of FAK to promote cell cycle progression and cell migration, suggesting that hyperphosphorylation of this mutant can positively affect FAK function in cells. Together, these data strongly suggest a role for the first FAK subdomain of the FERM domain in its normal regulation and function in the cell.

Stimulation of proliferation and migration of a colorectal cancer cell line by amidated and glycine-extended gastrin-releasing peptide via the same receptor

Although amidated forms of gastrin-releasing peptide (GRP) have been identified as autocrine growth factors in small cell lung cancer, their role in the development and progression of colorectal carcinoma is less clear. In addition, the biological activity of non-amidated gastrin-releasing peptide has not been investigated in colorectal carcinoma cells. We therefore investigated the effect of bombesin (a homologue of gastrin-releasing peptide) on proliferation, migration and inositol phosphate production in the human colorectal carcinoma cell line DLD-1, and determined the ability of gastrin-releasing peptide receptor antagonists to inhibit these effects. We also compared the biological activities of amidated and non-amidated GRP in the same assays. Treatment with either bombesin, or amidated or non-amidated GRP resulted in significant increase in proliferation, and in migration in a wound-healing assay. Both the mitogenic and migratory effects of amidated and non-amidated forms were inhibited by the GRP receptor antagonist [D-Phe(6), Leu-NHet(13), des-Met(14)]-bombesin(6-13). The presence of GRP receptor mRNA and GRP binding sites in three colorectal carcinoma cell lines was demonstrated by RT-PCR and by binding of radiolabelled bombesin, respectively. Transfection of DLD-1 cells with a dominant negative phosphatidylinositol 3-kinase did not affect bombesin-stimulated cell proliferation, but inhibited bombesin-stimulated cell migration. Bombesin and GRPgly activated phospholipase C, mitogen-activated protein kinase and focal adhesion kinase. We conclude that both amidated and non-amidated forms of gastrin-releasing peptide accelerate proliferation and migration of DLD-1 human colorectal carcinoma cells via the gastrin-releasing peptide receptor, but that phosphatidylinositol 3-kinase is only involved in the cell migration signalling pathway. Our results suggest a potential role for gastrin-releasing peptide receptor antagonists in the management of colorectal carcinoma.

Entamoeba histolytica: focal adhesion kinase and Erk phosphorylation are altered in the cytoskeleton mutant BG-3

The Entamoeba histolytica mutant BG-3 has several altered cytoskeletal properties, including the distribution of actin and certain surface characteristics such as osmolarity and electrophoretic mobility. By Western blot analysis and assays for cell adhesion to collagen, we demonstrate that mutant BG-3 shows an increase in the phosphorylation levels of protein kinases that participate in proliferation, adhesion and migration, such as focal adhesion kinase and MAP kinase (Erk2), and that it has also altered its capacity of binding to collagen type I. These results indicate that E. histolytica cytoskeleton integrity plays an important role in adhesion and thus invasion of the host.

TIMP-1 inhibits microvascular endothelial cell migration by MMP-dependent and MMP-independent mechanisms

It was reported over a decade ago that tissue inhibitor of metalloproteinases-1 (TIMP-1) suppresses angiogenesis in experimental models but the mechanism is still incompletely understood. This in vitro study focused on the molecular basis of TIMP-1-mediated inhibition of endothelial cell (EC) migration, a key step in the angiogenic process. Both recombinant human TIMP-1 and the synthetic MMP inhibitors, GM6001 and MMP-2-MMP-9 Inhibitor III, suppressed migration of human dermal microvascular endothelial cells (HDMVEC) in a dose-dependent fashion. The MMP-dependent inhibition of migration was associated with increased expression of the junctional adhesion proteins, VE-cadherin and PECAM-1, and VE-cadherin accumulation at cell-cell junctions. TIMP-1 also caused MMP-independent dephosphorylation of focal adhesion kinase (FAK) (pY397) and paxillin, which was associated with reduced number of F-actin stress fibers and focal adhesions. Moreover, TIMP-1 stimulated expression of PTEN that has been shown to reduce phosphorylation of FAK and inhibit cell migration. Our data suggest that TIMP-1 inhibits HDMVEC migration through MMP-dependent stimulation of VE-cadherin and MMP-independent stimulation of PTEN with subsequent dephosphorylation of FAK and cytoskeletal remodeling.

Effect of cigarette smoke extract on the proliferation of human airway epithelial cells and expression and activation of FAK

The effect of cigarette smoke extract (CSE) on the proliferation of human airway epithelial cells and the possible mechanism was studied. After airway epithelial cells were treated with different concentrations of CSE for 24 h, the cell proliferation was measured by MTT and the distribution of different cell cycles by flow cytometry. The FAK expression level was detected by Western blot and the degree of tyrosine phosphorylation by immunoprecipitation. The results showed that CSE could inhibit the proliferation of human airway epithelial cells, arrest the epithelial cells in G1 phase of cell cycle, dramatically decrease the number of epithelial cells in S and G2 phases; Meanwhile CSE could decrease the expression level of FAK and the degree of its tyrosine phosphorylation. The above effects of CSE were concentration-dependent. The expression of FAK and the degree of its phosphorylation was positively correlated to the increased number of epithelial cells in G1 phase, and negatively to the number of epithelial cells in S and G2 phases. It was concluded that the mechanism by which CSE could inhibit the proliferation of human epithelial cells was contributed to the increased expression and activation of FAK.

Characterization of an actin-binding site within the talin FERM domain

Talin is a large cytoskeletal protein that couples integrins to F-actin. Three actin-binding sites (ABS1-3) have been reported: one in the N-terminal head, and two in the C-terminal rod domain. Although the C-terminal ABS3 has been partially characterized, the presence and properties of ABS1 within the talin head are less well defined. We show here that the talin head binds F-actin in vitro and in vivo at a specific site within the actin filament. Thus, purified talin head liberated from gizzard talin by calpain cleavage cosediments with F-actin in a low salt buffer at pH 6.4 (conditions that are optimal for binding intact talin), and using recombinant polypeptides, we have mapped ABS1 to the FERM domain within the talin head. Both the F2 and F3 FERM subdomains contribute to binding, and EGFP-tagged FERM subdomains colocalize with actin stress fibers when expressed in COS cells. High-resolution electron microscopy of actin filaments decorated with F2F3 localizes binding to a site that is distinct from that recognized by members of the calponin-homology superfamily. Finally, we show that the FERM domain can couple F-actin to PIPkin, and by inference to integrins, since they bind to the same pocket in the F3 subdomain. This suggests that the talin FERM domain functions as a linker between PIPkin or integrins and F-actin at sites of cell-matrix adhesions.

Assembly of exogenous fibronectin by fibronectin-null cells is dependent on the adhesive substrate

The role of endogenously synthesized fibronectin (FN) in assembly was studied with cells lacking or expressing FN. Cells were cultured as homogeneous or mixed populations on surfaces coated with different matrix proteins. Compared with FN-expressing cells, FN-null cells poorly assembled exogenous plasma FN (pFN) when adhered to vitronectin or the recombinant cell-binding domain (III(7-10)) of FN. Vitronectin had a suppressive effect that was overcome by co-adsorbed pFN or laminin-1 but not by soluble FN. In co-cultures of FN-expressing cells and FN-null cells, endogenous FN was preferentially assembled around FN-expressing cells regardless of the adhesive ligand. If the adhesive ligand was vitronectin, exogenous pFN assembled preferentially around cells expressing cellular FN or recombinant EDa- or EDa+ FN. In co-cultures on vitronectin of FN-null cells and beta(1) integrin subunit-null cells, fibrils of cellular FN and pFN were preferentially deposited by FN-null (beta(1)-expressing) cells immediately adjacent to (FN-secreting) beta(1)-null cells. In co-cultures on vitronectin of FN-null cells and beta(1)-null cells expressing a chimera with the extracellular domain of beta(1) and the cytoplasmic domain of beta(3), preferential assembly was by the chimera-expressing cells. These results indicate that the adhesive ligand is a determinant of FN assembly by cells not secreting endogenous FN (suppressive if vitronectin, non-suppressive but non-supportive if III(7-10), supportive if pFN or laminin-1) and suggest that efficient interaction of freshly secreted cellular FN with a beta(1) integrin, presumably alpha(5)beta(1), substitutes for integrin-mediated adherence to a preformed matrix of laminin-1 or pFN to support assembly of FN.

Phosphorylation of hepatocyte growth factor receptor and epidermal growth factor receptor of human hepatocytes can be maintained in a (3D) collagen sandwich culture system

In vitro culture models that employ human liver cells could be potent tools for predictive studies on drug toxicity and metabolism in the pharmaceutical industry. However, an adequate receptor responsiveness is necessary to allow intracellular signalling and metabolic activity. We tested the ability of three-dimensionally arranged human hepatocytes to respond to the growth factors hepatocyte growth factor (HGF) or epidermal growth factor (EGF). Isolated adult human hepatocytes were cultivated within a three-dimensional collagen gel (sandwich) or on a two-dimensional collagen matrix. Cells were treated with HGF or EGF and expression and phosphorylative activity of HGF receptors (HGFr, c-met) or EGF receptors (EGFr) were measured by flow cytometry and Western blot. Increasing HGFr and EGFr levels were detected in hepatocytes growing two-dimensionally. However, both receptors were not activated in presence of growth factors. In contrast, when hepatocytes were plated within a three-dimensional matrix, HGFr and EGFr levels remained constantly low. However, both receptors became strongly phosphorylated by soluble HGF or EGF. We conclude that cultivation of human hepatocytes in a three-dimensionally arranged in vitro system allows the maintenance of specific functional activities. The necessity of cell dimensionality for HGFr and EGFr function should be considered when an adequate in vitro system has to be introduced for drug testing.

Activation of a vinculin-binding site in the talin rod involves rearrangement of a five-helix bundle

The interaction between the cytoskeletal proteins talin and vinculin plays a key role in integrin-mediated cell adhesion and migration. We have determined the crystal structures of two domains from the talin rod spanning residues 482-789. Talin 482-655, which contains a vinculin-binding site (VBS), folds into a five-helix bundle whereas talin 656-789 is a four-helix bundle. We show that the VBS is composed of a hydrophobic surface spanning five turns of helix 4. All the key side chains from the VBS are buried and contribute to the hydrophobic core of the talin 482-655 fold. We demonstrate that the talin 482-655 five-helix bundle represents an inactive conformation, and mutations that disrupt the hydrophobic core or deletion of helix 5 are required to induce an active conformation in which the VBS is exposed. We also report the crystal structure of the N-terminal vinculin head domain in complex with an activated form of talin. Activation of the VBS in talin and the recruitment of vinculin may support the maturation of small integrin/talin complexes into more stable adhesions.

Distraction Osteogenesis of the Craniofacial Skeleton

LEARNING OBJECTIVES:: After studying this article, the participant should be able to: 1. Review the biomechanical principles and pertinent cellular and molecular biology of distraction osteogenesis of the craniofacial skeleton. 2. Describe the clinical indications and applications of distraction osteogenesis of the craniofacial skeleton. 3. Describe maxillary, mandibular, midface, and calvarial procedures in distraction osteogenesis. 4. Discuss the clinical outcomes and complications of distraction osteogenesis of the craniofacial skeleton.The year 2002 marked the end of the first decade in clinical distraction osteogenesis of the craniofacial skeleton. In this short period, its application has increased exponentially. More than 3000 cases have been performed according to a recent survey, and more than 700 articles have been written on this subject in the MEDLINE database since 1996. It is a powerful surgical tool and enables surgeons to achieve results not previously attainable. Despite all this, distraction osteogenesis is practiced by only a small number of plastic surgeons. This article reviews the biomechanical principles; the pertinent cellular and molecular biology; and the clinical indications, applications, controversies, and complications of distraction osteogenesis of the craniofacial skeleton.

Transinactivation of the epidermal growth factor receptor tyrosine kinase and focal adhesion kinase phosphorylation by dietary flavonoids: effect on invasive potential of human carcinoma cells

Focal adhesion kinase (FAK), a member of a growing family of structurally distinct protein tyrosine kinases (PTK), has been linked to specific phosphorylation events, and the elevation of FAK activity in human carcinoma cells correlated with increased invasive potential. Transactivation of the epidermal growth factor receptor (EGFR) tyrosine kinase activity is proposed to stimulate cell migration and the subsequent activation of downstream signaling pathways. Quercetin (Qu) and luteolin (Lu), are potent PTK inhibitors as well as putative chemopreventive agents. The present work, we demonstrate that Qu and Lu at concentration of 20 microM transinactivated EGFR tyrosine kinase activity with marked reduction in phosphotyrosyl level of 170, 125, 65, 60 and 42 kDa cellular proteins, and induced apoptosis in MiaPaCa-2 cells. The 125 kDa protein was further identified as a FAK by immunoprecipitation and immunoblotting analyses. Tumor cells treated with Lu or Qu dampened the phosphorylation of FAK. In addition, our data clearly demonstrated that tumor cells responded to Qu and Lu by parallel reductions in the levels of phosphorylated FAK and the secreted matrix metalloproteinase (MMP) that may lead to the suppression of invasive potential and cell migration in vitro. While the molecular mechanism of FAK regulation of MMP secretion in tumor cells remains unclear, our results suggested that blockade of the EGFR-signaling pathway may contributed to the net effect. As suggested in the current study, targeting EGFR and FAK with the objective of modulating their regulatory pathways could offer prospects for the treatment of EGFR-responsive cancers in the future.

Rewiring cell adhesion

The adhesion of cells is mediated by the binding of several cell-surface receptors to ligands found in the extracellular matrix. These receptors often have overlapping specificities for the peptide ligands, making it difficult to understand the roles for discrete receptors in cell adhesion, migration, and differentiation as well as to direct the selective adhesion of cell types in tissue-engineering applications. To overcome these limitations, we developed a strategy to rewire the receptor-ligand interactions between a cell and substrate to ensure that adhesion is mediated by a single receptor with unique specificity. The strategy combines a genetic approach to engineer the cell surface with a chimeric integrin receptor having a unique ligand binding domain with a surface chemistry approach to prepare substrates that present ligands that are bound by the new binding domain. We show that Chinese hamster ovary cells that are engineered with a chimeric beta1 integrin adhere, signal, and even migrate on a synthetic matrix.

Extracellular matrix: recent advances on its role in junction dynamics in the seminiferous epithelium during spermatogenesis

Spermatogenesis takes place in the seminiferous epithelium of the mammalian testis in which one type A1 spermatogonium (diploid, 2n) gives rise to 256 spermatids (haploid, 1n). To accomplish this, developing germ cells, such as preleptotene and leptotene spermatocytes, residing in the basal compartment of the seminiferous epithelium must traverse the blood-testis barrier (BTB) entering into the adluminal compartment for further development into round, elongating, and elongate spermatids. Recent studies have shown that the basement membrane in the testis (a modified form of extracellular matrix, ECM) is important to the event of germ cell movement across the BTB because proteins in the ECM were shown to regulate BTB dynamics via the interactions between collagens, proteases, and protease inhibitors, possibly under the regulation of cytokines. While these findings are intriguing, they are not entirely unexpected. For one, the basement membrane in the testis is intimately associated with the BTB, which represents the basolateral region of Sertoli cells. Also, Sertoli cell tight junctions (TJs) that constitute the BTB are present side-by-side with cell-cell actin-based adherens junctions (AJ, such as basal ectoplasmic specialization [ES]) and intermediate filament-based desmosome-like junctions. As such, the relative morphological layout between TJs, AJs, and desmosome-like junctions in the seminiferous epithelium is in sharp contrast to other epithelia where TJs are located at the apical portion of an epithelium or endothelium, furthest away from ECM, to be followed by AJs and desmosomes, which in turn constitute the junctional complex. For another, anchoring junctions between a cell epithelium and ECM found in multiple tissues, also known as focal contacts (or focal adhesion complex, FAC, an actin-based cell-matrix anchoring junction type), are the most efficient junction type that permits rapid junction restructuring to accommodate cell movement. It is therefore physiologically plausible, and perhaps essential, that the testis is using some components of the focal contacts to regulate rapid restructuring of AJs between Sertoli and germ cells when germ cells traverse the seminiferous epithelium. Indeed, recent findings have shown that the apical ES, a testis-specific AJ type in the seminiferous epithelium, is equipped with proteins of FAC to regulate its restructuring. In this review, we provide a timely update on this exciting yet rapidly developing field regarding how the homeostasis of basement membrane in the tunica propria regulates BTB dynamics and spermatogenesis in the testis, as well as a critical review on the molecular architecture and the regulation of ES in the seminiferous epithelium.

The effect of elevated extracellular glucose on adherens junction proteins in cultured rat heart endothelial cells

Vascular permeability is a proof of vascular endothelial cell dysfunction induced by diabetes. Vascular permeability is directly related to the width of intercellular endothelial cells junctions, which may become permeable to macromolecules as a result of a change in endothelial cell shape. To determine the role of hyperglycemia in endothelial cell shape, the study examined the effect of high concentrations of glucose on the shape of cultured rat heart endothelial cells. This result indicated that the high-glucose-induced changes in the morphology of endothelial cells, via the glucose-mediated reorganization of F-actin. In endothelial cells, the actin cytoskeleton is tethered to the zonula adherens and focal adhesions, which mediate cell-cell and cell-matrix interactions respectively. The present study demonstrated that the high-glucose-induced changes in the actin-binding protein such as filamin, zonula adherens proteins such as alpha-, beta-, and gamma-catenin, focal adhesions proteins such as focal adhesion kinase, paxillin, and tyrosine phosphorylation of paxillin. It appears that differences in expression of adherens junctions molecules on rat heart endothelial cells in response to high glucose reflect endothelial glucose toxicity, which may also induce endothelial dysfunction in diabetes.

The expression and tyrosine phosphorylation of E-cadherin/catenin adhesion complex, and focal adhesion kinase in invasive cervical carcinomas

The present study aimed to confirm the hypothesis that the expression and phosphorylation status of the E-cadherin/catenin adhesion complex is related to cervical carcinogenesis and cervical cancer invasion, and to investigate the expression and the tyrosine phosphorylation of focal adhesion kinase (FAK) and its relation with E-cadherin/catenin adhesion complex. The expression of E-cadherin, alpha- and beta-catenin, and FAK were studied by a western blot analysis with 26 cervical carcinomas, nine normal cervices, and five carcinomas in situ of cervix. The tyrosine phosphorylation of alpha- and beta-catenin and FAK were examined by an immunoprecipitation. The expressions of alpha- and beta-catenin and E-cadherin were reduced in cervical carcinoma, and the tyrosine phosphorylation of alpha- and beta-catenin in cervical carcinoma was higher than in normal cervix and carcinoma in situ of cervix. Tyrosine phosphorylation of FAK was elevated in cervical carcinoma although the expression of FAK was not significantly different. Moreover, alpha- and beta-catenin were coimmunoprecipitated with FAK. We conclude that the loss of E-cadherin/catenin proteins and the tyrosine phosphorylation of E-cadherin/catenin are involved in cervical carcinogenesis and cancer invasion. Tyrosine phosphorylation of focal adhesion kinase is also related to the cervical cancer invasion. The E-cadherin/catenin complex and FAK may be related functionally and structurally.

PDGF and FGF induce focal adhesion kinase (FAK) phosphorylation at Ser-910: Dissociation from Tyr-397 phosphorylation and requirement for ERK activation

A rapid increase in the tyrosine phosphorylation of focal adhesion kinase (FAK) has been extensively documented in cells stimulated by multiple signaling molecules, but very little is known about the regulation of FAK phosphorylation at serine residues. Stimulation of Swiss 3T3 cells with platelet-derived growth factor (PDGF) promoted a striking increase in the phosphorylation of FAK at Ser-910, as revealed by site-specific antibodies that recognized the phosphorylated state of this residue. FAK phosphorylation at Ser-910 could be distinguished from that at Tyr-397 in terms of dose-response relationships and kinetics. Furthermore, the selective phosphoinositide 3-kinase (PI 3-kinase) inhibitors wortmannin and LY 294002 abrogated FAK phosphorylation at Tyr-397 but did not interfere with PDGF-induced FAK phosphorylation at Ser-910. Conversely, treatment with U0126, a potent inhibitor of MEK-mediated ERK activation, prevented FAK phosphorylation at Ser-910 induced by PDGF but did not interfere with PDGF-induced FAK phosphorylation at Tyr-397. These results were extended using growth factors that either stimulate, fibroblast growth factor (FGF), or do not stimulate (insulin) the ERK pathway activation in Swiss 3T3 cells. FGF but not insulin promoted a striking ERK-dependent phosphorylation of FAK at Ser-910. Our results indicate that FAK phosphorylation at Tyr-397 and FAK phosphorylation at Ser-910 are induced in response to PDGF stimulation through different signaling pathways, namely PI 3-kinase and ERK, respectively.

Regulation of focal adhesion kinase by its amino-terminal domain through an autoinhibitory interaction

We have investigated a role for the amino-terminal FERM-like domain of the focal adhesion kinase (FAK) as a negative regulator of its own activity and phosphorylation state. Deletion of the first 375 amino acids from the amino terminus of FAK increases its catalytic activity in vitro, its phosphorylation when expressed in mammalian cells, and the phosphorylation of a FAK substrate, paxillin. Deletion mutants are phosphorylated in suspension, suggesting that they are no longer regulated by adhesion. The amino terminus of FAK can interact with the kinase domain of FAK in vitro and in vivo, suggesting that it might act as an autoinhibitor of FAK activity. The amino terminus of FAK can act in trans to inhibit FAK phosphorylation when expressed in mammalian cells or to directly inhibit FAK activity in vitro. Expression of the amino terminus of FAK inhibits cell cycle progression in CHO cells, consistent with its inhibition of FAK phosphorylation and function in trans. A glutathione S-transferase fusion protein containing the cytoplasmic tail of the beta1 integrin stimulates FAK activity in vitro, suggesting that FAK could be regulated by molecular interactions with the amino terminus. Based on these and previous data, we propose a working model for activation of FAK in cell adhesion.

The C-terminal domain of focal adhesion kinase reduces the tumor cell invasiveness in chondrosarcoma cell lines

Human chondrosarcoma is a malignancy that has no effective systemic therapy, making the interruption of the metastatic cascade critical to enhance patient survival. The processes of local invasion and metastases share similar mechanisms at a cellular level. Focal adhesion kinase (FAK) has been implicated in local invasion of malignant tumor cells. In the current manuscript we examine the effect of FAK inhibition on cell attachment to extracellular matrix (ECM) and in vitro invasion. Bovine articular chondrocytes and two human chondrosarcoma cell lines were utilized to examine FAK activity in tumor cell invasiveness. Endogenous FAK activity was inhibited by adenoviral transfection with the C-terminal domain of FAK. This inhibition resulted from decreased FAK phosphorylation, while FAK expression remained unchanged. Inhibition of FAK phosphorylation and hence its activity lead to decreased cell adhesion to Type II collagen and decreased cell invasiveness. These effects were not due to changes in integrin expression, indicating that the inhibition was the result of disruption of outside: in signaling. There are three important aspects to these results. The first is that interruption of transmembrane signaling can affect cell attachment. The second is that in chondrosarcoma, cell differentiation correlates with FAK expression and metastatic potential. Thirdly, that cell invasiveness correlates with FAK activity and implies a mechanistic role for this molecular complex in local invasion and metastasis.

A cyclo peptide activates signaling events and promotes growth and the production of the bone matrix

The interaction of bone cells and their underlying extracellular matrix impacts biological processes such as maintenance of tissue integrity. The biological recognition of the extracellular matrix by attached cells is mediated by the activity of integrins that recognize adhesive-specific domains. The most widely recognized adhesive motif is the RGD sequence, common to many of the adhesive matrix molecules. Here, we show that cyclo DFKRG which was previously selected to increase cell adhesion of human bone marrow stromal cells (HBMSC), increases both cell differentiation and mineralization through activation of tyrosine kinases, focal adhesion kinase (p(125)FAK) and Mitogen Activated Protein (MAP) kinases.

Tumor necrosis factor-induced nuclear factor kappaB activation is impaired in focal adhesion kinase-deficient fibroblasts

Focal adhesion kinase (FAK) is widely involved in important cellular functions such as proliferation, migration, and survival, although its roles in immune and inflammatory responses have yet to be explored. We demonstrate a critical role for FAK in the tumor necrosis factor (TNF)-induced activation of nuclear factor (NF)-kappaB, using FAK-deficient (FAK-/-) embryonic fibroblasts. Interestingly, TNF-induced interleukin (IL)-6 production was nearly abolished in FAK-/- fibroblasts, whereas a normal level of production was obtained in FAK+/- or FAK+/+ fibroblasts. FAK deficiency did not affect the three types of mitogen-activated protein kinases, ERK, JNK, and p38. Similarly, TNF-induced activation of activator protein 1 or NF-IL-6 was not impaired in FAK-/- cells. Of note, TNF-induced NF-kappaB DNA binding activity and activation of IkappaB kinases (IKKs) were markedly impaired in FAK-/- cells, whereas the expression of TNF receptor I or other signaling molecules such as receptor-interacting protein (RIP), tumor necrosis factor receptor-associated factor 2 (TRAF2), IKKalpha, IKKbeta, and IKKgamma was unchanged. Also, TNF-induced association of FAK with RIP and subsequent association of RIP with TRAF2 were not observed, resulting in a failure of RIP to recruit the IKK complex in FAK-/- cells. The reintroduction of wild type FAK into FAK-/- cells restored the interaction of RIP with TRAF2 and the IKK complex and allowed recovery of NF-kappaB activation and subsequent IL-6 production. Thus, we propose a novel role for FAK in the NF-kappaB activation pathway leading to the production of cytokines.

Arg-Gly-Asp-Ser (RGDS) peptide stimulates transforming growth factor beta1 transcription and secretion through integrin activation

Extracellular matrix (ECM) components, through specific peptide motifs such as Arg-Gly-Asp (RGD), interact with integrins and can modify the behavior of cells. Transforming growth factor-beta1 (TGF-beta1) is the main cytokine involved in the synthesis of ECM proteins. We analyzed the effect of a RGD-containing peptide, as Arg-Gly-Asp-Ser (RGDS), on the regulation of TGF-beta1 secretion in cultured human mesangial cells. We found that RGDS increased mRNA expression and secretion of TGF-beta1 by stimulating the TGF-beta1 gene promoter. This effect was dependent on the interaction of RGDS with integrins. We evaluated the signaling pathways implicated in TGF-beta1 production by analyzing the effect of RGDS on kinase-related integrins. RGDS stimulated tyrosine phosphorylation as well as integrin-linked kinase (ILK) activity. However, tyrosine kinase inhibitors did not prevent the RGDS effect. In contrast, the inhibition of ILK by cell transfection with a kinase dead-ILK completely abolished the increased TGF-beta1 secretion and promoter activity in the presence of RGDS. Thus RGDS modulates the secretion of TGF-beta1, probably through increased synthesis by interacting with integrins and activating ILK. This supports a role for ECM components in the regulation of their own secretion.

Endothelin receptor blockade inhibits molecular effectors of Kaposi's sarcoma cell invasion and tumor growth in vivo

Endothelin-1 (ET-1) and its receptors are overexpressed in human Kaposi's sarcoma lesions. Here we show that in human KS IMM cell line ET-1 increased secretion and activation of matrix-metalloproteinase-2 (MMP-2), -3, -7, -9 and -13, as well as of membrane-type 1-MMP (MT1-MMP). ET-1 and ET-3 also enhanced the expression of tissue inhibitor of MMP-2, essential for MT1-MMP-mediated MMP-2 activation. Combined addition of both ET(B) receptor (ET(B)R) and ET(A)R antagonists completely blocked the ET-1-induced MMP activity. By immunohistochemistry, we observed that ET-1 increased MMP-2 and MT1-MMP expression and their localization at the cell surface. Treatment with both antagonists resulted also in the suppression of ET-1-induced phosphorylation of focal adhesion proteins, FAK and paxillin, which are essentials for cell motility. ET-1 induced a dose-dependent enhancement in KS IMM cell migration and MMP-dependent invasiveness that were inhibited by ET-1 receptor antagonists. The small molecule, A-182086, an orally bioavailable ET(A/B)R antagonist, completely inhibited cell proliferation and tumor growth in KS IMM xenografts. These findings demonstrate that ET-1-driven autocrine loop is crucial for enhanced invasiveness of KS IMM cells and promote tumor growth in vivo. Such activities can be blocked by the ET(A/B)R antagonists, which may be effective anti-angiogenic and anti-tumor molecules for the treatment of Kaposi's sarcoma.

ERK 1/2- and JNKs-dependent synthesis of interleukins 6 and 8 by fibroblast-like synoviocytes stimulated with protein I/II, a modulin from oral streptococci, requires focal adhesion kinase

Protein I/II, a pathogen-associated molecular pattern from oral streptococci, is a potent inducer of interleukin-6 (IL-6) and IL-8 synthesis and release from fibroblast-like synoviocytes (FLSs), cells that are critically involved in joint inflammation. This synthesis implicates ERK 1/2 and JNKs as well as AP-1-binding activity and nuclear translocation of NF-kappaB. The mechanisms by which protein I/II activates MAPKs remain, however, elusive. Because focal adhesion kinase (FAK) was proposed to play a role in signaling to MAPKs, we examined its ability to contribute to the MAPKs-dependent synthesis of IL-6 and IL-8 in response to protein I/II. We used FAK-/- fibroblasts as well as FAK+/+ fibroblasts and FLSs transfected with FRNK, a dominant negative form of FAK. The results demonstrate that IL-6 and IL-8 release in response to protein I/II was strongly inhibited in both protein I/II-stimulated FAK-/- and FRNK-transfected cells. Cytochalasin D, which inhibits protein I/II-induced phosphorylation of FAK (Tyr-397), had no effect either on activation of ERK 1/2 and JNKs or on IL-6 and IL-8 release. Taken together, these results indicate that IL-6 and IL-8 release by protein I/II-activated FLSs is regulated by FAK independently of Tyr-397 phosphorylation.

Transient forebrain ischemia modulates signal transduction from extracellular matrix in gerbil hippocampus

Cell adhesion to the extracellular matrix (ECM) functions as a survival factor and disruption of cell-ECM interaction can lead to cell death. Our previous study has demonstrated ischemia-induced enhancement of activity of extracellular metalloproteinases, which might result in the alteration of adhesive contact with ECM and affect the intracellular signaling pathway. The enzyme thought to play a major role in conveying survival signals from ECM to the cell interior is focal adhesion kinase (pp125(FAK)). In the present study, the temporal relation between activation of extracellular metalloproteinases (MMP-2 and MMP-9), degradation of extracellular matrix protein laminin and the expression of pp125(FAK) after 5 min of global ischemia in gerbil hippocampus were investigated. While significant activation of both investigated metalloproteinases occurred in the course of reperfusion, only changes in MMP-9 activity were correlated with degradation of laminin. These ischemia-induced extracellular events coincide temporarily with proteolytic modification of FAK protein and diminished level of its phosphorylated form, to about 50% of the initial value. These results are indicative of an involvement of ECM-pp125(FAK) signaling pathway in ischemia-induced neuronal degeneration.

Bombesin, lysophosphatidic acid, and epidermal growth factor rapidly stimulate focal adhesion kinase phosphorylation at Ser-910: requirement for ERK activation

A rapid increase in the tyrosine phosphorylation of focal adhesion kinase (FAK) has been extensively documented in cells stimulated by multiple signaling molecules, but virtually nothing is known about the regulation of FAK phosphorylation at serine residues. Stimulation of Swiss 3T3 cells with bombesin promoted a striking increase ( approximately 13-fold) in the phosphorylation of FAK at Ser-910, as revealed by site-specific antibodies that recognized the phosphorylated state of this residue. Lysophosphatidic acid and epidermal growth factor (EGF) also stimulated FAK phosphorylation at Ser-910. Direct activation of protein kinase C isoforms with phorbol-12,13-dibutyrate (PDB) also promoted striking phosphorylation of FAK at Ser-910. Treatment with the protein kinase C inhibitor GF I or Ro 31-8220 or chronic exposure to PDB prevented the increase in FAK phosphorylation at Ser-910 induced by bombesin or PDB but not by EGF. Treatment with the ERK inhibitors U0126 and PD98059 prevented FAK phosphorylation at Ser-910 in response to all of the stimuli tested. Furthermore, incubation of activated ERK2 with FAK immunocomplexes leads to FAK phosphorylation at Ser-910 in vitro. Our results demonstrate, for the first time, that stimulation with bombesin, lysophosphatidic acid, PDB, or EGF induces phosphorylation of endogenous FAK at Ser-910 via an ERK-dependent pathway in Swiss 3T3 cells.

FAK induces expression of Prx1 to promote tenascin-C-dependent fibroblast migration

Fibroblast migration depends, in part, on activation of FAK and cellular interactions with tenascin-C (TN-C). Consistent with the idea that FAK regulates TN-C, migration-defective FAK-null cells expressed reduced levels of TN-C. Furthermore, expression of FAK in FAK-null fibroblasts induced TN-C, whereas inhibition of FAK activity in FAK-wild-type cells had the opposite effect. Paired-related homeobox 1 (Prx1) encodes a homeobox transcription factor that induces TN-C by interacting with a binding site within the TN-C promoter, and it also promotes fibroblast migration. Therefore, we hypothesized that FAK regulates TN-C by controlling the DNA-binding activity of Prx1 and/or by inducing Prx1 expression. Prx1-homeodomain binding site complex formation observed with FAK-wild-type fibroblasts failed to occur in FAK-null fibroblasts, yet expression of Prx1 in these cells induced TN-C promoter activity. Thus, FAK is not essential for Prx1 DNA-binding activity. However, activated FAK was essential for Prx1 expression. Functionally, Prx1 expression in FAK-null fibroblasts restored their ability to migrate toward fibronectin, in a manner that depends on TN-C. These results appear to be relevant in vivo because Prx1 and TN-C expression levels were reduced in FAK-null embryos. This paper suggests a model whereby FAK induces Prx1, and subsequently the formation of a TN-C-enriched ECM that contributes to fibroblast migration.

Molecular mechanisms of lung cell activation induced by cyclic stretch

OBJECTIVE

To review molecular mechanisms of lung cell activation by stretch.

DATA SOURCES

Published original and review articles.

DATA SUMMARY

Positive-pressure mechanical ventilation is associated with both beneficial and harmful effects. Data indicate that mechanical ventilation can induce, or increase, lung inflammation. This effect is clearly linked to the degree of lung cell stretching. By modeling cyclic stretch in cultured cells, it has been possible to investigate the cellular pathways activated by this mechanical strain. Integrin receptors, proteins of the focal adhesion plaque, and the cytoskeleton itself participate in the multiple molecular complex that senses cyclic stretch, transforming a mechanical signal into a biological response. Several intracellular signaling pathways then are activated and eventually result in increased transcription of genes harboring "stretch-response elements" in their promoters. Among these pathways, the mitogen-activated protein kinase signaling cascade appears to be central in mediating the effects of cell stretching. Other posttranscriptional mechanisms, such as messenger RNA stabilization and the secretion of preformed mediators, also may account for the secretion of inflammatory mediators after cyclic stretch.

CONCLUSION

Identification of the relevant molecular mechanisms will help in the development of novel ventilatory and pharmacologic therapeutic strategies aimed at preventing the deleterious effects of mechanical ventilation.

IL-8-induced migratory responses through CXCR1 and CXCR2: association with phosphorylation and cellular redistribution of focal adhesion kinase

CXCR1 and CXCR2 mediate migratory activities in response to IL-8 and other ELR+-CXC chemokines (e.g., GCP-2 and NAP-2). In vitro, activation of migration is induced by low IL-8 concentrations (10-50 ng/mL), whereas migratory shut-off is induced by high IL-8 concentrations (1000 ng/mL). The stimulation of CXCR1 and CXCR2 by IL-8 concentrations that result in migratory activation induced focal adhesion kinase (FAK) phosphorylation in a G(alpha)i-dependent manner. The expression of FRNK, a dominant negative mutant of FAK, perturbed migratory responses to the activating dose of 50 ng/mL IL-8. The migration-activating concentrations of 50 ng/mL GCP-2 and NAP-2 induced less potent migratory responses and FAK phosphorylation in CXCR2-expressing cells as compared with IL-8. These results indicate that FAK is phosphorylated, and required, for the chemotactic response under conditions of migratory activation by ELR+-CXC chemokines. In addition, FAK phosphorylation was determined following exposure to migration-attenuating concentrations of IL-8. In CXCR1-RBL cells this treatment resulted in FAK phosphorylation, in similar levels to those induced by activating concentrations of IL-8. In contrast, in CXCR2-RBL cells the migration-attenuating concentrations of IL-8 induced promoted levels of FAK phosphorylation and different patterns of FAK phosphorylation on its six potential tyrosine phosphorylation sites, as compared to activating concentrations of the chemokine. Exposure to IL-8 resulted not only in FAK phosphorylation but also in its cellular redistribution, indicated by the formation of defined contact regions with the substratum, enriched in phosphorylated FAK and vinculin. Overall, FAK phosphorylation was associated with, and found to be differently regulated upon, ELR+-CXC chemokine-induced migration.

Effects of monocrotaline pyrrole and thrombin on pulmonary endothelial cell junction and matrix adhesion proteins

Previous work in our laboratory has shown that monocrotaline pyrrole (MCTP) interacts with actin and potentiates thrombin-mediated endothelial barrier permeability through increasing the overall surface area of intercellular gaps. To better characterize endothelial barrier leak in this model, we examined the effects of MCTP and thrombin on the localization and structure of three adhesion associated proteins that directly or indirectly interact with actin in regulating barrier function: cell-cell occludens junction molecule (ZO-1), the cell-cell adherens junction linker, ss-catenin, and the cell-matrix intermediary signaling protein, focal adhesion kinase (FAK). Immunohistochemistry demonstrated that thrombin treatment resulted in radial reorganization of focal adhesions and broader distribution of adherens and occludins junctions at the cell border suggestive of membrane stretching in contracture. MCTP pretreatment resulted in fewer and more disorganized focal adhesions and marked thinning of occludins and adherens junctions. MCTP pretreatment also interfered with thrombin stimulated junctional reorganization. Western blot analysis showed thrombin stimulated catalysis of ZO-1 and FAK while MCTP pretreatment resulted in FAK fragmentation similar to previous reports for apoptosis. We conclude that both MCTP and thrombin alter critical endothelial cell adhesion molecules and this may be an underlying mechanism for the potentiating effect MCTP has on thrombin induced vascular permeability in vitro.

Dissociation of focal adhesion kinase and paxillin tyrosine phosphorylation induced by bombesin and lysophosphatidic acid from epidermal growth factor receptor transactivation in Swiss 3T3 cells

Tyrosine phosphorylation of the nonreceptor tyrosine kinase p125 focal adhesion kinase (FAK) and the adapter protein paxillin is rapidly increased by multiple agonists, including bombesin (BOM) and lysophosphatidic acid (LPA), through heptahelical G protein-coupled receptors (GPCRs). The pathways involved remain incompletely understood. The experiments presented here were designed to test the role of epidermal growth factor receptor (EGFR) transactivation in the rapid increase of tyrosine phosphorylation of FAK and paxillin induced by GPCR agonists. Our results show that treatment with the selective EGFR tyrosine kinase inhibitor AG 1478, at concentrations that completely blocked the increase in tyrosine phosphorylation of these proteins induced by EGF, did not affect the stimulation of tyrosine phosphorylation of either FAK or paxillin induced by multiple GPCR agonists including LPA, BOM, vasopressin, bradykinin, and endothelin. Similar results were obtained when Swiss 3T3 cells were treated with another highly specific inhibitor of the EGF receptor kinase activity, PD-158780. Collectively, our results clearly dissociate EGFR transactivation from the tyrosine phosphorylation of FAK and paxillin induced by multiple GPCR agonists.

Chemical anoxia of tubular cells induces activation of c-Src and its translocation to the zonula adherens

Cyanide (CN)-induced chemical anoxia of cultured mouse proximal tubular (MPT) cells increased the kinase activity of c-Src by approximately threefold. 4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2), a specific inhibitor of c-Src, prevented Src activation. CN also increased the permeability of MPT cell monolayers, an event ameliorated by PP2. During CN treatment, the proteins of the zonula adherens (ZA; E-cadherin and the catenins) disappeared from their normal location at cell-cell borders and appeared within the cytosol. CN also resulted in the appearance of c-Src at cell-cell borders. PP2 prevented these CN-induced alterations in the distribution of ZA proteins and c-Src. CN also increased the association of c-Src with beta-catenin and p120 and induced a substantial increase in tyrosine phosphorylation of both catenins. PP2 prevented the CN-induced phosphorylation of these catenins. In summary, we show that CN-induced chemical anoxia activates c-Src and induces its translocation to cell-cell junctions where it binds to and phosphorylates beta-catenin and p120. Our findings suggest that these events contribute to the loss of the epithelial barrier function associated with chemical anoxia.

Reelin activates SRC family tyrosine kinases in neurons

BACKGROUND

Reelin is a large signaling molecule that regulates the positioning of neurons in the mammalian brain. Transmission of the Reelin signal to migrating embryonic neurons requires binding to the very-low-density lipoprotein receptor (VLDLR) and the apolipoprotein E receptor-2 (apoER2). This induces tyrosine phosphorylation of the adaptor protein Disabled-1 (Dab1), which interacts with a shared sequence motif in the cytoplasmic tails of both receptors. However, the kinases that mediate Dab1 tyrosine phosphorylation and the intracellular pathways that are triggered by this event remain unknown.

RESULTS

We show that Reelin activates members of the Src family of non-receptor tyrosine kinases (SFKs) and that this activation is dependent on the Reelin receptors apoER2 and VLDLR and the adaptor protein Dab1. Dab1 is tyrosine phosphorylated by SFKs, and the kinases themselves can be further activated by phosphorylated Dab1. Increased Dab1 protein expression in fyn-deficient mice implies a response to impaired Reelin signaling that is also observed in mice lacking Reelin or its receptors. However, fyn deficiency alone does not compound the neuronal positioning defect of vldlr- or apoer2-deficient mice, and this finding suggests functional compensation by other SFKs.

CONCLUSIONS

Our results show that Dab1 is a physiological substrate as well as an activator of SFKs in neurons. Based on genetic evidence gained from multiple strains of mutant mice with defects in Reelin signaling, we conclude that activation of SFKs is a normal part of the cellular Reelin response.

Cell adhesion aside from integrin system can abrogate anoikis in rat liver cells by down-regulation of FasL expression, not by activation of PI-3K/Akt and ERK signaling pathway

Epithelial cells require contact with extracellular matrix (ECM) to inhibit detachment-induced apoptosis (anoikis). The ERK and PI-3K/Akt signaling pathways have been identified to inhibit anoikis. We present here a different story. An adult rat liver cell line, ARLJ301-3, underwent apoptosis within 4h under suspension conditions even with active forms of Akt and ERK1/2. Once ARLJ301-3 cells are plated on tissue culture plates coated with synthetic polymer, such as poly-(N-p-vinyl benzyl-O-beta-D-galactopyranosyl-D-gluconamide) (PVLA), poly-L-lysine or polystyrene, instead of functional ECM such as fibronectin, they could survive and proliferate without activation of Akt and ERK1/2. The expression of Fas receptor ligand (FasL) is specifically detected in cells under suspension conditions or treated with cytochalasin-D. We present here the first report that FasL expression is up-regulated by the cytoskeletal disruption directed by cytochalasin-D treatment or cell detachment from ECM.

Tuberin, the tuberous sclerosis complex 2 tumor suppressor gene product, regulates Rho activation, cell adhesion and migration

Tuberous sclerosis complex (TSC) is a tumor suppressor gene syndrome characterized by seizures, mental retardation, autism, and tumors of the brain, kidney, heart, retina, and skin. TSC is caused by mutations in either TSC1 or TSC2, both of which are tumor suppressor genes. Hamartin, the protein product of TSC1, was found to interact with the ezrin-radixin-moesin family of cytoskeletal proteins and to activate the small GTPase Rho. To determine whether tuberin, the TSC2 product, can also activate Rho, we stably expressed full-length human tuberin in two cell types: MDCK cells and ELT3 cells. ELT3 cells lack endogenous tuberin expression. We found that expression of human tuberin in both MDCK and ELT3 cells was associated with an increase in the amount of Rho-GTP, but not in Rac1-GTP or cdc42-GTP. Tuberin expression increased cell adhesion in both cell types, and decreased chemotactic cell migration in ELT3 cells. In MDCK cells, there was a decrease in the amount of total Focal Adhesion Kinase (FAK) and an increase in the fraction of phosphorylated FAK. These findings demonstrate for the first time that tuberin activates Rho and regulates cell adhesion and migration. Pathways involving Rho activation may have relevance to the clinical manifestations of TSC, including pulmonary lymphangioleiomyomatosis.

Platelet-derived growth factor-BB and lysophosphatidic acid distinctly regulate hepatic myofibroblast migration through focal adhesion kinase

Although hepatic myofibroblast (HMF) migration contributes to the development of fibrosis, the mechanisms coordinating this movement are uncertain. We determined the effects of lysophosphatidic acid (LPA) and platelet-derived growth factor-BB (PDGF) on actin polymerization, FAK tyrosine phosphorylation, and migration of cultured human HMFs. LPA (0.4-100 microM) stimulated migration, FAK tyrosine phosphorylation, and stress fiber assembly with a sigmoidal dose response. PDGF (1-250 ng/ml) stimulated migration, FAK tyrosine phosphorylation, and actin polymerization with a bell-shape dose-response characterized by a maximum at 10-25 ng/ml. Concentrations of cytochalasin D, which abolished FAK tyrosine phosphorylation, also blocked LPA- and PDGF-induced migration. A dose of 1-10 ng/ml PDGF acted synergistically with LPA (10 microM) to stimulate FAK tyrosine phosphorylation and migration, whereas higher concentrations of PDGF (100-250 ng/ml) inhibited FAK tyrosine phosphorylation and migration in response to LPA (10 microM). These data indicate that PDGF and LPA coordinately govern the migration of HMFs by differentially regulating FAK and suggest a novel model in which PDGF, acting as an amplifier/attenuator of LPA-induced signaling, facilitates HMF accumulation within injured areas of the liver.

DAP-kinase induces apoptosis by suppressing integrin activity and disrupting matrix survival signals

Death-associated protein kinase (DAP-kinase) is a calcium/calmodulin-dependent serine/threonine kinase, and participates in various apoptosis systems. However, its apoptosis-promoting mechanism is poorly understood. Here, we demonstrate that DAP-kinase suppresses integrin-mediated cell adhesion and signal transduction, whereas dominant-negative interference of this kinase promotes adhesion. This effect of DAP-kinase is neither a consequence of apoptosis nor a result of decreased expression of integrins. Rather, DAP-kinase downregulates integrin activity through an inside-out mechanism. We present evidence indicating that this adhesion-inhibitory effect accounts for a major mechanism of the apoptosis induced by DAP-kinase. First, in growth-arrested fibroblasts, DAP-kinase triggers apoptosis in cells plated on fibronectin, but does not affect the death of cells on poly-l-lysine. Second, in epithelial cells, DAP-kinase induces apoptosis in the anoikis-sensitive MCF10A cells, but not in the anoikis-resistant BT474 cells. Most importantly, the apoptosis-promoting effect of DAP-kinase is completely abolished by enforced activation of integrin-mediated signaling pathways from either integrin itself or its downstream effector, FAK. Finally, we show that integrin or FAK activation blocks the ability of DAP-kinase to upregulate p53. Our results indicate that DAP-kinase exerts apoptotic effects by suppressing integrin functions and integrin-mediated survival signals, thereby activating a p53-dependent apoptotic pathway.

Dual inhibition of focal adhesion kinase and epidermal growth factor receptor pathways cooperatively induces death receptor-mediated apoptosis in human breast cancer cells

The focal adhesion kinase (FAK) and epidermal growth factor receptor (EGFR) are protein-tyrosine kinases that are overexpressed and activated in human breast cancer. To determine the role of EGFR and FAK survival signaling in breast cancer, EGFR was stably overexpressed in BT474 breast cancer cells, and each signaling pathway was specifically targeted for inhibition. FAK and EGFR constitutively co-immunoprecipitated in EGFR-overexpressing BT474 cells. In low EGFR-expressing BT474-pcDNA3 vector control cells, inhibition of FAK by the FAK C-terminal domain caused detachment and apoptosis via pathways involving activation of caspase-3 and -8, cleavage of poly(ADP-ribose) polymerase, and caspase-3-dependent degradation of AKT. This apoptosis could be rescued by the dominant-negative Fas-associated death domain, indicating involvement of the death receptor pathway. EGFR overexpression did not inhibit detachment induced by the FAK C-terminal domain, but did suppress apoptosis, activating AKT and ERK1/2 survival pathways and inhibiting cleavage of FAK, caspase-3 and -8, and poly(ADP-ribose) polymerase. Furthermore, this protective effect of EGFR signaling was reversed by EGFR kinase inhibition with AG1478. In addition, inhibition of FAK and EGFR in another breast cancer cell line (BT20) endogenously overexpressing these kinases also induced apoptosis via the same mechanism as in the EGFR-overexpressing BT474 cells. The results of this study indicate that dual inhibition of FAK and EGFR signaling pathways can cooperatively enhance apoptosis in breast cancers.

Association of the Ste20-like kinase (SLK) with the microtubule. Role in Rac1-mediated regulation of actin dynamics during cell adhesion and spreading

Cytoskeletal remodeling events are tightly regulated by signal transduction systems that impinge on adhesion components and modulators of cellular architecture. We have previously shown that the Ste20-like kinase (SLK) can induce apoptosis through the induction of actin disassembly and cellular retraction (Sabourin, L. A., Tamai, K., Seale, P., Wagner, J., and Rudnicki, M. A. (2000) Mol. Cell. Biol. 20, 684-696). Using immunofluorescence studies, we report that SLK is redistributed with adhesion components at large podosome-like adhesion sites in fibronectin-stimulated fibroblasts. However, in vitro kinase assays demonstrate that its activity is not modulated following fibronectin stimulation. Double immunofluorescence studies in exponentially growing or spreading fibroblasts show that SLK is associated with the microtubule network and can be coprecipitated with alpha-tubulin. Furthermore, the stimulation of adhesion site formation by microtubule-disrupting agents induces the relocalization of SLK with unpolymerized alpha-tubulin to large vinculin-containing adhesion complexes. Using microinjection studies, we show that ectopic expression of activated SLK induces the disassembly of actin stress fibers, a process that can be inhibited by dominant negative Rac1. Significantly, endogenous SLK can be colocalized with Rac1 in spreading cells on FN. Finally, the overexpression of SLK by adenoviral infection inhibits cell spreading on fibronectin. These results suggest that SLK is part of a microtubule-associated complex that is targeted to adhesion sites and implicated in the regulation of cytoskeletal dynamics.

Association of Grb7 with phosphoinositides and its role in the regulation of cell migration

Grb7 is the prototype of a family of adaptor molecules that also include Grb10 and Grb14 that share a conserved molecular architecture including Src homology 2 (SH2) and pleckstrin homology (PH) domains. Grb7 has been implicated as a downstream mediator of integrin-FAK signal pathways in the regulation of cell migration, although the molecular mechanisms are still not well understood. In this paper, we investigated the potential role and mechanisms of PH domain in Grb7 in the regulation of cell migration. We found that the PH domain mediated Grb7 binding to phospholipids both in vitro and in intact cells. Furthermore, both Grb7 and its PH domain preferentially interacted with phosphatidylinositol phosphates showing strongest affinity to the D3- and D5-phosphoinositides. The PH domain interaction with phosphoinositides was shown to play a role in the stimulation of cell migration by Grb7. It was also shown to be necessary for Grb7 phosphorylation by FAK, although it was not required for Grb7 interaction with FAK or recruitment to the focal contacts. Last, we found that PI 3-kinase activity played a role in both Grb7 association with phosphoinositides and its stimulation of cell migration. In addition, both FAK binding to PI 3-kinase via its autophosphorylated Tyr(397) and integrin-mediated cell adhesion increased Grb7 association with phosphoinositides. Together, these results identified the Grb7 PH domain interaction with phosphoinositides and suggested a potential mechanism by which several signaling molecules including Grb7, FAK, and PI 3-kinase and their interactions cooperate to mediate signal transduction pathways in integrin-mediated cell migration.

TGFbeta1 -mediated epithelial to mesenchymal transition is accompanied by invasion in the SiHa cell line

It has recently been suggested by several investigators that the epithelial-mesenchymal transition-inducing capacity of TGFbetas contributes to invasive transition of tumors at later stages of carcinogenesis. In the present study, we examined the possibility of TGFbeta1-stimulated epithelial-mesenchymal transition in SiHa cell line, detailed molecular events in the process, and its possible contribution to the invasive transition of tumors. TGFbeta1-induced epithelial-mesenchymal transition of SiHa cells was based on morphological and biochemical criteria; actin stress fiber formation, focal translocalization of integrin alphav, talin, and vinculin, fibronectin-based matrix assembly at the cell periphery, and translocalization and down-regulation of E-cadherin. TGFbeta1 also stimulated surface expression of integrin alphavbeta3 and FAK activation. Focal translocalization of integrin alphav preceded actin reorganization and fibronectin matrix assembly, and functional blocking of the integrin suppressed actin stress fiber formation. Furthermore, induction of actin reorganization and fibronectin matrix assembly by TGFbeta1 were shown to be mutually independent events. These changes were irreversible because 5 minutes pulse exposure to TGFbeta1 was sufficient to stimulate progress of actin reorganization and fibronectin matrix assembly. In further studies with raft culture, TGFbeta1 was found to stimulate invasion of SiHa cells into a type I collagen gel matrix. In conclusion, TGFbeta1 stimulated epithelial-mesenchymal transition of SiHa cells, indicating a positive role in the invasive transition of tumors.