pp60c-src and related tyrosine kinases: a role in the assembly and reorganization of matrix adhesions

Dialogue between VE-Cadherin and Sphingosine 1 Phosphate Receptor1 (S1PR1) for Protecting Endothelial Functions

The endothelial cells (EC) of established blood vessels in adults remain extraordinarily quiescent in the sense that they are not actively proliferating, but they fulfill the necessary role to control the permeability of their monolayer that lines the interior of blood vessels. The cell-cell junctions between ECs in the endothelium comprise tight junctions and adherens homotypic junctions, which are ubiquitous along the vascular tree. Adherens junctions are adhesive intercellular contacts that are crucial for the organization of the EC monolayer and its maintenance and regulation of normal microvascular function. The molecular components and underlying signaling pathways that control the association of adherens junctions have been described in the last few years. In contrast, the role that dysfunction of these adherens junctions has in contributing to human vascular disease remains an important open issue. Sphingosine-1-phosphate (S1P) is a bioactive sphingolipid mediator found at high concentrations in blood which has important roles in the control of the vascular permeability, cell recruitment, and clotting that follow inflammatory processes. This role of S1P is achieved through a signaling pathway mediated through a family of G protein-coupled receptors designated as S1PR1. This review highlights novel evidence for a direct linkage between S1PR1 signaling and the mediation of EC cohesive properties that are controlled by VE-cadherin.

Tensin3 interaction with talin drives the formation of fibronectin-associated fibrillar adhesions

The formation of healthy tissue involves continuous remodeling of the extracellular matrix (ECM). Whilst it is known that this requires integrin-associated cell-ECM adhesion sites (CMAs) and actomyosin-mediated forces, the underlying mechanisms remain unclear. Here, we examine how tensin3 contributes to the formation of fibrillar adhesions (FBs) and fibronectin fibrillogenesis. Using BioID mass spectrometry and a mitochondrial targeting assay, we establish that tensin3 associates with the mechanosensors such as talin and vinculin. We show that the talin R11 rod domain binds directly to a helical motif within the central intrinsically disordered region (IDR) of tensin3, whilst vinculin binds indirectly to tensin3 via talin. Using CRISPR knock-out cells in combination with defined tensin3 mutations, we show (i) that tensin3 is critical for the formation of α5β1-integrin FBs and for fibronectin fibrillogenesis, and (ii) the talin/tensin3 interaction drives this process, with vinculin acting to potentiate it.

CK2β Is a Gatekeeper of Focal Adhesions Regulating Cell Spreading

CK2 is a hetero-tetrameric serine/threonine protein kinase made up of two CK2α/αʹ catalytic subunits and two CK2β regulatory subunits. The free CK2α subunit and the tetrameric holoenzyme have distinct substrate specificity profiles, suggesting that the spatiotemporal organization of the individual CK2 subunits observed in living cells is crucial in the control of the many cellular processes that are governed by this pleiotropic kinase. Indeed, previous studies reported that the unbalanced expression of CK2 subunits is sufficient to drive epithelial to mesenchymal transition (EMT), a process involved in cancer invasion and metastasis. Moreover, sub-stoichiometric expression of CK2β compared to CK2α in a subset of breast cancer tumors was correlated with the induction of EMT markers and increased epithelial cell plasticity in breast carcinoma progression. Phenotypic changes of epithelial cells are often associated with the activation of phosphotyrosine signaling. Herein, using phosphotyrosine enrichment coupled with affinity capture and proteomic analysis, we show that decreased expression of CK2β in MCF10A mammary epithelial cells triggers the phosphorylation of a number of proteins on tyrosine residues and promotes the striking activation of the FAK1-Src-PAX1 signaling pathway. Moreover, morphometric analyses also reveal that CK2β loss increases the number and the spatial distribution of focal adhesion signaling complexes that coordinate the adhesive and migratory processes. Together, our findings allow positioning CK2β as a gatekeeper for cell spreading by restraining focal adhesion formation and invasion of mammary epithelial cells.

Protein tyrosine phosphatase 1B targets focal adhesion kinase and paxillin in cell-matrix adhesions

Protein tyrosine phosphatase 1B (PTP1B, also known as PTPN1) is an established regulator of cell-matrix adhesion and motility. However, the nature of substrate targets at adhesion sites remains to be validated. Here, we used bimolecular fluorescence complementation assays, in combination with a substrate trapping mutant of PTP1B, to directly examine whether relevant phosphotyrosines on paxillin and focal adhesion kinase (FAK, also known as PTK2) are substrates of the phosphatase in the context of cell-matrix adhesion sites. We found that the formation of catalytic complexes at cell-matrix adhesions requires intact tyrosine residues Y31 and Y118 on paxillin, and the localization of FAK at adhesion sites. Additionally, we found that PTP1B specifically targets Y925 on the focal adhesion targeting (FAT) domain of FAK at adhesion sites. Electrostatic analysis indicated that dephosphorylation of this residue promotes the closed conformation of the FAT 4-helix bundle and its interaction with paxillin at adhesion sites.

Circular RNA expression profiles of mouse ovaries during postnatal development and the function of circular RNA epidermal growth factor receptor in granulosa cells

PURPOSE

Circular RNAs (circRNAs) are a class of noncoding RNAs that can regulate gene expression at the post-transcriptional level. The contribution of circRNAs in the regulation of granulosa cells (GCs) functions is not yet clear. The aim of this study was to analyze circRNA expression in adult and neonate ovaries, uncover the biological roles of circ_0002861 (circEGFR) and identify the mechanism by which it modulates follicular development.

BASIC PROCEDURES

The circRNA expression profiles of adult and neonatal mouse ovaries were explored by high-throughput sequencing. The function of circEGFR was measured by RNA fluorescence in situ hybridization, overexpression, knockdown, RNA immunoprecipitation and luciferase reporter assays in GCs.

MAIN FINDINGS

Numerous differentially expressed circRNAs were identified in adult and neonatal ovaries. Through circRNAs expression patterns and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, estrogen signaling was found to be upregulated in adult ovaries compared with neonate ovaries. Further analysis revealed that the expression of circEGFR (circ_0002861, ID: mmu_circ_0002861 in circBase) was increased in adult ovaries compared with neonate ovaries. circEGFR is formed by splicing from exons 14 and 15 of the epidermal growth factor receptor (EGFR) gene to produce a covalently linked 249-nucleotide circRNA. Overexpression of circEGFR increased estradiol (E₂) production and GCs growth, whereas circEGFR knockdown enhanced progesterone production and inhibited (E₂) secretion by GCs. Bioinformatic screening identified several binding sites for miR-125a-3p in the circEGFR sequence. RNA immunoprecipitation and luciferase reporter assays demonstrated that circEGFR may act as a sponge for miR-125a-3p, thus modulating Fyn expression.

PRINCIPAL CONCLUSIONS

These findings illustrate that circEGFR may play a vital role in ovarian GCs by modulating Fyn via competitive binding with miR-125a-3p. Our results suggest potential applications of circEGFR in reproductive and steroid-related disorder therapy.

miR-125a-3p is responsible for chemosensitivity in PDAC by inhibiting epithelial-mesenchymal transition via Fyn

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers and resistance to cytotoxic chemotherapy is the major cause of mortality in PDAC patients. miR-125a-3p was found to be down-regulated in PDAC cells; however, the function of miR-125a-3p in PDAC has been elusive. Here, we explored the role of miR-125a-3p in chemosensitivity in PDAC cells.

METHODS

We used qRT-PCR to detect miR-125a-3p expression in two PDAC cell lines. And we measured cell viability and apoptosis by MTT assay and flow cytometry, respectively. Scratch wound healing assay and transwell invasion assay were used to test the effects of miR-125a-3p and Fyn on cell EMT process. In addition, we validated the interaction of miR-125a-3p and Fyn by dual luciferase reporter assay. qRT-PCR and western blot were used to detect the mRNA and protein expressions of E-cadhrein, N-cadhrein, Snail and Fyn.

RESULTS

We found that miR-125a-3p was down-regulated in a time-dependent manner following treatment with gemcitabine in PDAC cells. Meanwhile, we found that overexpression of miR-125a-3p significantly increased chemosensitivity to gemcitabine and suppressed epithelial-mesenchymal transition (EMT) of PDAC cells. Mechanistically, miR-125a-3p directly targeted Fyn and decreased the expression of Fyn that functions to promote EMT process in PDAC. Furthermore, overexpression of Fyn could partially reverse the effects of miR-125a-3p on chemosensitivity to gemcitabine.

CONCLUSION

Our study is the first to show that miR-125a-3p is responsible for chemosensitivity in PDAC and could inhibit epithelial-mesenchymal transition by directly targeting Fyn. This provides a novel potential therapeutic strategy to overcome chemoresistance in PDAC.

Hic-5 regulates fibrillar adhesion formation to control tumor extracellular matrix remodeling through interaction with tensin1

The linearization of the stromal extracellular matrix (ECM) by cancer associated fibroblasts (CAFs) facilitates tumor cell growth and metastasis. However, the mechanism by which the ECM is remodeled is not fully understood. Hic-5 (TGFβ1i1), a focal adhesion scaffold protein, has previously been reported to be crucial for stromal ECM deposition and remodeling in vivo. Herein we show that CAFs lacking Hic-5 exhibit a significant reduction in the ability to form fibrillar adhesions, a specialized form of focal adhesion that promote fibronectin fibrillogenesis. Hic-5 was found to promote fibrillar adhesion formation through a newly characterized interaction with tensin1. Furthermore, Src dependent phosphorylation of Hic-5 facilitated the interaction with tensin1 to prevent β1 integrin internalization and trafficking to the lysosome. The interaction between Hic-5 and tensin1 was mechanosensitive, promoting fibrillar adhesion formation and fibronectin fibrillogenesis in a rigidity dependent fashion. Importantly, this Src dependent mechanism was conserved in three-dimensional (3D) ECM environments. Immunohistochemistry of tensin1 showed enrichment in CAFs in vivo, which was abrogated upon deletion of Hic-5. Interestingly, elevated Hic-5 expression correlates with reduced distant metastasis free survival in patients with basal-like, HER2+ and grade 3 tumors. Thus, we have identified Hic-5 as a crucial regulator of ECM remodeling in CAFs by promoting fibrillar adhesion formation through a novel interaction with tensin1.

MiR-375 inhibits the hepatocyte growth factor-elicited migration of mesenchymal stem cells by downregulating Akt signaling

The migration of mesenchymal stem cells (MSCs) is critical for their use in cell-based therapies. Accumulating evidence suggests that microRNAs are important regulators of MSC migration. Here, we report that the expression of miR-375 was downregulated in MSCs treated with hepatocyte growth factor (HGF), which strongly stimulates the migration of these cells. Overexpression of miR-375 decreased the transfilter migration and the migration velocity of MSCs triggered by HGF. In our efforts to determine the mechanism by which miR-375 affects MSC migration, we found that miR-375 significantly inhibited the activation of Akt by downregulating its phosphorylation at T308 and S473, but had no effect on the activity of mitogen-activated protein kinases. Further, we showed that 3'phosphoinositide-dependent protein kinase-1 (PDK1), an upstream kinase necessary for full activation of Akt, was negatively regulated by miR-375 at the protein level. Moreover, miR-375 suppressed the phosphorylation of focal adhesion kinase (FAK) and paxillin, two important regulators of focal adhesion (FA) assembly and turnover, and decreased the number of FAs at cell periphery. Taken together, our results demonstrate that miR-375 inhibits HGF-elicited migration of MSCs through downregulating the expression of PDK1 and suppressing the activation of Akt, as well as influencing the tyrosine phosphorylation of FAK and paxillin and FA periphery distribution.

The ubiquitin-proteasome system regulates focal adhesions at the leading edge of migrating cells

Cell migration requires the cyclical assembly and disassembly of focal adhesions. Adhesion induces phosphorylation of focal adhesion proteins, including Cas (Crk-associated substrate/p130Cas/BCAR1). However, Cas phosphorylation stimulates adhesion turnover. This raises the question of how adhesion assembly occurs against opposition from phospho-Cas. Here we show that suppressor of cytokine signaling 6 (SOCS6) and Cullin 5, two components of the CRL5^SOCS6 ubiquitin ligase, inhibit Cas-dependent focal adhesion turnover at the front but not rear of migrating epithelial cells. The front focal adhesions contain phospho-Cas which recruits SOCS6. If SOCS6 cannot access focal adhesions, or if cullins or the proteasome are inhibited, adhesion disassembly is stimulated. This suggests that the localized targeting of phospho-Cas within adhesions by CRL5^SOCS6 and concurrent cullin and proteasome activity provide a negative feedback loop, ensuring that adhesion assembly predominates over disassembly at the leading edge. By this mechanism, ubiquitination provides a new level of spatio-temporal control over cell migration.

DOI:http://dx.doi.org/10.7554/eLife.17440.001

Animal cells can move in the body, for example to heal a wound, by protruding a leading edge forwards, attaching it to the surroundings and then pulling against these new attachments while disassembling the older ones. Mechanical forces regulate the assembly and disassembly of these attachments, known as focal adhesions, and so do signals from outside the cell that are transmitted to the adhesions via specialized proteins. However, it was not clear how the assembly and disassembly of adhesions is coordinated.

CRL5 is a ubiquitin ligase, an enzyme that can mark other proteins for destruction. Cells migrate more quickly if CRL5 is inhibited, and so Teckchandani and Cooper set out to uncover whether CRL5 affects the assembly and disassembly of focal adhesions. The experiments showed that human cells lacking a crucial component of the CRL5 complex, SOCS6, disassemble adhesions faster than normal cells, but only at their leading edge and not at the rear.

Teckchandani and Cooper also found that SOCS6 localizes to the leading edge by binding to a focal adhesion protein called Cas. Shortly after the attachments assemble, the Cas protein becomes tagged with a phosphate group and then acts to promote the adhesion to disassemble. Further experiments indicated that Cas was marked by the CRL5 complex and possibly destroyed while in or very close to the leading edge adhesions, slowing their disassembly.

Together, these findings suggest that by binding Cas, SOCS6 regulates the turnover of adhesions, specifically by inhibiting disassembly and allowing adhesions to grow at the leading edge. Since SOCS6 is not present in adhesions outside of the leading edge, this may help explain how the older adhesions are disassembled. Future studies could next focus on the exact sequence of events that occur in focal adhesions after the CRL5 complex binds to Cas as the cell migrates.

DOI:http://dx.doi.org/10.7554/eLife.17440.002

MicroRNA-203 mimics age-related aortic smooth muscle dysfunction of cytoskeletal pathways

Increased aortic stiffness is a biomarker for subsequent adverse cardiovascular events. We have previously reported that vascular smooth muscle Src-dependent cytoskeletal remodelling, which contributes to aortic plasticity, is impaired with ageing. Here, we use a multi-scale approach to determine the molecular mechanisms behind defective Src-dependent signalling in an aged C57BL/6 male mouse model. Increased aortic stiffness, as measured in vivo by pulse wave velocity, was found to have a comparable time course to that in humans. Bioinformatic analyses predicted several miRs to regulate Src-dependent cytoskeletal remodelling. qRT-PCR was used to determine the relative levels of predicted miRs in aortas and, notably, the expression of miR-203 increased almost twofold in aged aorta. Increased miR-203 expression was associated with a decrease in both mRNA and protein expression of Src, caveolin-1 and paxillin in aged aorta. Probing with phospho-specific antibodies confirmed that overexpression of miR-203 significantly attenuated Src and extracellular signal regulated kinase (ERK) signalling, which we have previously found to regulate vascular smooth muscle stiffness. In addition, transfection of miR-203 into aortic tissue from young mice increased phenylephrine-induced aortic stiffness ex vivo, mimicking the aged phenotype. Upstream of miR-203, we found that DNA methyltransferases (DNMT) 1, 3a, and 3b are also significantly decreased in the aged mouse aorta and that DNMT inhibition significantly increases miR-203 expression. Thus, the age-induced increase in miR-203 may be caused by epigenetic promoter hypomethylation in the aorta. These findings indicate that miR-203 promotes a re-programming of Src/ERK signalling pathways in vascular smooth muscle, impairing the regulation of stiffness in aged aorta.

Src family kinase expression and subcellular localization in macrophages: implications for their role in CSF-1-induced macrophage migration

A major role of colony-stimulating factor-1 is to stimulate the differentiation of mononuclear phagocytic lineage cells into adherent, motile, mature macrophages. The colony-stimulating factor-1 receptor transduces colony-stimulating factor-1 signaling, and we have shown previously that phosphatidylinositol 3-kinase p110δ is a critical mediator of colony-stimulating factor-1-stimulated motility through the colony-stimulating factor-1 receptor pY721 motif. Src family kinases are also implicated in the regulation of macrophage motility and in colony-stimulating factor-1 receptor signaling, although functional redundancy of the multiple SFKs expressed in macrophages makes it challenging to delineate their specific functions. We report a comprehensive analysis of individual Src family kinase expression in macrophage cell lines and primary macrophages and demonstrate colony-stimulating factor-1-induced changes in Src family kinase subcellular localization, which provides clues to their distinct and redundant functions in macrophages. Moreover, expression of individual Src family kinases is both species specific and dependent on colony-stimulating factor-1-induced macrophage differentiation. Hck associated with the activated colony-stimulating factor-1 receptor, whereas Lyn associated with the receptor in a constitutive manner. Consistent with this, inhibitor studies revealed that Src family kinases were important for both colony-stimulating factor-1 receptor activation and colony-stimulating factor-1-induced macrophage spreading, motility, and invasion. Distinct colony-stimulating factor-1-induced changes in the subcellular localization of individual SFKs suggest specific roles for these Src family kinases in the macrophage response to colony-stimulating factor-1.

Phosphorylation and turnover of paxillin in focal contacts is controlled by force and defines the dynamic state of the adhesion site

Micro-environmental clues are critical to cell behavior. One of the key elements of migration is the generation and response to forces. Up to now there is no definitive concept on how the generation and responses to cellular forces influence cell behavior. Here, we show that phosphorylation of paxillin is a crucial event in the response to exogenous forces. Application of force induced growth of adhesion sites and this phenomenon was accompanied by a downregulation of Src family kinase activity, which in turn led to a decrease in the phosphorylation of paxillin at the tyrosine residues Y31 and Y118. The force-dependent growth of adhesion sites is mediated by a decrease in the turnover-rate of paxillin in focal contacts. This turnover critically depended on the phosphorylation state of paxillin at Y31/118. Paxillin is an important regulator in the control of the aggregate state of the whole adhesion site since the turnover of other adhesion site proteins such as vinculin is influenced by the phosphorylation state of paxillin as well. Taken together these data suggest that SFK dependent phosphorylation of paxillin is a crucial event in the regulation of adhesion site function in response to force.

Tropomyosin Tm5NM1 spatially restricts src kinase activity through perturbation of Rab11 vesicle trafficking

In order for cells to stop moving, they must synchronously stabilize actin filaments and their associated focal adhesions. How these two structures are coordinated in time and space is not known. We show here that the actin association protein Tm5NM1, which induces stable actin filaments, concurrently suppresses the trafficking of focal-adhesion-regulatory molecules. Using combinations of fluorescent biosensors and fluorescence recovery after photobleaching (FRAP), we demonstrate that Tm5NM1 reduces the level of delivery of Src kinase to focal adhesions, resulting in reduced phosphorylation of adhesion-resident Src substrates. Live imaging of Rab11-positive recycling endosomes that carry Src to focal adhesions reveals disruption of this pathway. We propose that tropomyosin synchronizes adhesion dynamics with the cytoskeleton by regulating actin-dependent trafficking of essential focal-adhesion molecules.

Engineered kinase activation reveals unique morphodynamic phenotypes and associated trafficking for Src family isoforms

The Src kinase family comprises nine homologous members whose distinct expression patterns and cellular distributions indicate that they have unique roles. These roles have not been determined because genetic manipulation has not produced clearly distinct phenotypes, and the kinases' homology complicates generation of specific inhibitors. Through insertion of a modified FK506 binding protein (insertable FKBP12, iFKBP) into the protein kinase isoforms Fyn, Src, Lyn, and Yes, we engineered kinase analogs that can be activated within minutes in living cells (RapR analogs). Combining our RapR analogs with computational tools for quantifying and characterizing cellular dynamics, we demonstrate that Src family isoforms produce very different phenotypes, encompassing cell spreading, polarized motility, and production of long, thin cell extensions. Activation of Src and Fyn led to patterns of kinase translocation that correlated with morphological changes in temporally distinct stages. Phenotypes were dependent on N-terminal acylation, not on Src homology 3 (SH3) and Src homology 2 (SH2) domains, and correlated with movement between a perinuclear compartment, adhesions, and the plasma membrane.

Bone sialoprotein and osteopontin in bone metastasis of osteotropic cancers

The mechanisms underlying malignant cell metastasis to secondary sites such as bone are complex and no doubt multifactorial. Members of the small integrin-binding ligand N-linked glycoproteins (SIBLINGs) family, particularly bone sialoprotein (BSP) and osteopontin (OPN), exhibit multiple activities known to promote malignant cell proliferation, detachment, invasion, and metastasis of several osteotropic cancers. The expression level of BSP and OPN is elevated in a variety of human cancers, particularly those that metastasize preferentially to the skeleton. Recent studies suggest that the "osteomimicry" of malignant cells is not only conferred by transmembrane receptors bound by BSP and OPN, but includes the "switch" in gene expression repertoire typically expressed in cells of skeletal lineage. Understanding the role of BSP and OPN in tumor progression, altered pathophysiology of bone microenvironment, and tumor metastasis to bone will likely result in development of better diagnostic approaches and therapeutic regimens for osteotropic malignant diseases.

Role of hepatitis C virus induced osteopontin in epithelial to mesenchymal transition, migration and invasion of hepatocytes

Osteopontin (OPN) is a secreted phosphoprotein which has been linked to tumor progression and metastasis in a variety of cancers including hepatocellular carcinoma (HCC). Previous studies have shown that OPN is upregulated during liver injury and inflammation. However, the role of OPN in hepatitis C virus (HCV)-induced liver disease pathogenesis is not known. In this study, we determined the induction of OPN, and then investigated the effect of secreted forms of OPN in epithelial to mesenchymal transition (EMT), migration and invasion of hepatocytes. We show the induction of OPN mRNA and protein expression by HCV-infection. Our results also demonstrate the processing of precursor OPN (75 kDa) into 55 kDa, 42 kDa and 36 kDa forms of OPN in HCV-infected cells. Furthermore, we show the binding of secreted OPN to integrin αVβ3 and CD44 at the cell surface, leading to the activation of downstream cellular kinases such as focal adhesion kinase (FAK), Src, and Akt. Importantly, our results show the reduced expression of epithelial marker (E-cadherin) and induction of mesenchymal marker (N-cadherin) in HCV-infected cells. We also show the migration and invasion of HCV-infected cells using wound healing assay and matrigel coated Boyden chamber. In addition, we demonstrate the activation of above EMT markers, and the critical players involved in OPN-mediated cell signaling cascade using primary human hepatocytes infected with Japanese fulminant hepatitis (JFH)-1 HCV. Taken together, these studies suggest a potential role of OPN in inducing chronic liver disease and HCC associated with chronic HCV infection.

Role of PTPα in the destruction of periodontal connective tissues

IL-1β contributes to connective tissue destruction in part by up-regulating stromelysin-1 (MMP-3), which in fibroblasts is a focal adhesion-dependent process. Protein tyrosine phosphatase-α (PTPα) is enriched in and regulates the formation of focal adhesions, but the role of PTPα in connective tissue destruction is not defined. We first examined destruction of periodontal connective tissues in adult PTPα^+/+ and PTPα^−/− mice subjected to ligature-induced periodontitis, which increases the levels of multiple cytokines, including IL-1β. Three weeks after ligation, maxillae were processed for morphometry, micro-computed tomography and histomorphometry. Compared with unligated controls, there was ∼1.5–3 times greater bone loss as well as 3-fold reduction of the thickness of the gingival lamina propria and 20-fold reduction of the amount of collagen fibers in WT than PTPα^−/− mice. Immunohistochemical staining of periodontal tissue showed elevated expression of MMP-3 at ligated sites. Second, to examine mechanisms by which PTPα may regulate matrix degradation, human MMP arrays were used to screen conditioned media from human gingival fibroblasts treated with vehicle, IL-1β or TNFα. Although MMP-3 was upregulated by both cytokines, only IL-1β stimulated ERK activation in human gingival fibroblasts plated on fibronectin. TIRF microscopy and immunoblotting analyses of cells depleted of PTPα activity with the use of various mutated constructs or with siRNA or PTPα^KO and matched wild type fibroblasts were plated on fibronectin to enable focal adhesion formation and stimulated with IL-1β. These data showed that the catalytic and adaptor functions of PTPα were required for IL-1β-induced focal adhesion formation, ERK activation and MMP-3 release. We conclude that inflammation-induced connective tissue degradation involving fibroblasts requires functionally active PTPα and in part is mediated by IL-1β signaling through focal adhesions.

The role of integrin-linked kinase in the molecular architecture of focal adhesions

Integrin-mediated focal adhesions (FAs) are large, multi-protein complexes that link the actin cytoskeleton to the extracellular matrix and take part in adhesion-mediated signaling. These adhesions are highly complex and diverse at the molecular level; thus, assigning particular structural or signaling functions to specific components is highly challenging. Here, we combined functional, structural and biophysical approaches to assess the role of a major FA component, namely, integrin-linked kinase (ILK), in adhesion formation. We show here that ILK plays a key role in the formation of focal complexes, early forms of integrin adhesions, and confirm its involvement in the assembly of fibronectin-bound fibrillar adhesions. Examination of ILK-null fibroblasts by cryo-electron tomography pointed to major structural changes in their FAs, manifested as disarray of the associated actin filaments and an increase in the packing density of FA-related particles. Interestingly, adhesion of the mutant cells to the substrate required a higher ligand density than in control cells. These data indicate that ILK has a key role in integrin adhesion assembly and sub-structure, and in the regulation of the FA-associated cytoskeleton.

microRNA-125a-3p reduces cell proliferation and migration by targeting Fyn

Fyn, a member of the Src family kinases (SFKs), has a pivotal role in cell adhesion, proliferation, migration and survival, and its overexpression is associated with several types of cancer. MicroRNAs (miRNAs) play a major role in post-transcriptional repression of protein expression. In light of the significant functions of Fyn, together with studies demonstrating miR-125a as a tumor-suppressing miRNA that is downregulated in several cancer cell types and on our bioinformatics studies presented here, we chose to examine the post-transcription regulation of Fyn by miR-125a-3p in the HEK 293T cell line. We show that Fyn expression can be dramatically reduced by elevated levels of miR-125a-3p. Following this reduction, the activity of proteins downstream of Fyn, such as FAK, paxillin and Akt (proteins known to be overexpressed in various tumors), is also reduced. On a broader level, we show that miR-125a-3p causes an arrest of the cell cycle at the G2/M stage and decreases cell viability and migration, probably in a Fyn-directed manner. The results are reinforced by control experiments conducted using Fyn siRNA and anti-miR-125a-3p, as well as by the fact that numerous cancer cell lines show a significant downregulation of Fyn after mir-125a-3p overexpression. Collectively, we conclude that miR-125a-3p has an important role in the regulation of Fyn expression and of its signaling pathway, which implies that it has a therapeutic potential in overexpressed Fyn-related diseases.

Spatiotemporal regulation of Src and its substrates at invadosomes

In the past decade, substantial progress has been made in understanding how Src family kinases regulate the formation and function of invadosomes. Invadosomes are organized actin-rich structures that contain an F-actin core surrounded by an adhesive ring and mediate invasive migration. Src kinases orchestrate, either directly or indirectly, each phase of the invadosome life cycle including invadosome assembly, maturation and matrix degradation and disassembly. Complex arrays of Src effector proteins are involved at different stages of invadosome maturation and their spatiotemporal activity must be tightly regulated to achieve effective invasive migration. In this review, we highlight some recent progress and the challenges of understanding how Src is regulated temporally and spatially to orchestrate the dynamics of invadosomes and mediate cell invasion.

Effect of small interfering RNA transfection on FAK and DLC1 mRNA expression in OVCAR-3

RNA interference is an evolutionarily conserved cellular defense mechanism that protects cells from hostile genes and regulates the function of normal genes during growth and development. In this study, we established GFP-siFAK-DLC1 vector and transfect the vector into OVCAR-3 cells. RT-PCR and western blot analyses were performed for FAK, DLC1 mRNA, and protein expression in OVCAR-3 cells. ELISA method was used for caspase-3 and caspase-9 activities. These studies demonstrate that both recombinant pGFP-siFAK-DLC1 vector and pGFP-siCon-DLC1 vector may effectively promote DLC1 mRNA transcription and didn't affect siRNA effect. Recombinant vector (pGFP-siFAK-DLC1) may promote DLC1 gene expression, and effectively silence FAK gene expression. Silencing FAK mRNA expression and DLC1 mRNA expression may markedly enhance caspase-3 and caspase-9 activities in OVCAR-3 cells. These results showed that in ovarian cancer OVCAR-3 cell silencing FAK gene expression or / and increasing DLC-1 gene expression, could improve Caspase-3 and Caspase-9 protease activities. In the expression of DLC-1 and silence FAK expression group (double action group) effect was more significant as compared with the silence FAK gene group or expression of DLC-1 gene alone, difference was significant (p < 0.05).

Macrophage Migration and Its Regulation by CSF-1

Macrophages are terminally differentiated cells of the mononuclear phagocytic lineage and develop under the stimulus of their primary growth and differentiation factor, CSF-1. Although they differentiate into heterogeneous populations, depending upon their tissue of residence, motility is an important aspect of their function. To facilitate their migration through tissues, macrophages express a unique range of adhesion and cytoskeletal proteins. Notably, macrophages do not form large, stable adhesions or actin stress fibers but rely on small, short lived point contacts, focal complexes and podosomes for traction. Thus, macrophages are built to respond rapidly to migratory stimuli. As well as triggering growth and differentiation, CSF-1 is also a chemokine that regulates macrophage migration via activation the CSF-1 receptor tyrosine kinase. CSF-1R autophosphorylation of several intracellular tyrosine residues leads to association and activation of many downstream signaling molecules. However, phosphorylation of just one residue, Y721, mediates association of PI3K with the receptor to activate the major motility signaling pathways in macrophages. Dissection of these pathways will identify drug targets for the inhibition of diseases in which macrophages contribute to adverse outcomes.

Dissecting focal adhesions in cells differentially expressing calreticulin: a microscopy study

BACKGROUND INFORMATION

Our previous studies have shown that calreticulin, a Ca2+-binding chaperone located in the endoplasmic reticulum, affects cell-substratum adhesions via the induction of vinculin and N-cadherin. Cells overexpressing calreticulin contain more vinculin than low expressers and make abundant contacts with the substratum. However, cells that express low levels of calreticulin exhibit a weak adhesive phenotype and make few, if any, focal adhesions. To date, the identity of the types of focal adhesions made by calreticulin overexpressing and low expressing cells has not been dissected.

RESULTS

The results of the present study show that calreticulin affects fibronectin matrix assembly in L fibroblast cell lines that differentially express the protein, and that these cells also differ profoundly in focal adhesion formation. Although the calreticulin overexpressing cells generate numerous interference-reflection-microscopy-dark, vinculin- and paxillin-containing classical focal contacts, as well as some fibrillar adhesions, the cells expressing low levels of calreticulin generate only a few weak focal adhesions. The fibronectin receptor was found to be clustered in calreticulin overexpressing cells, but diffusely distributed over the cell surface in low expressing cells. Plating L fibroblasts on fibronectin-coated substrata induced extensive spreading in all cell lines tested. However, although calreticulin overexpressing cells were induced to form classical vinculin-rich focal contacts, the low calreticulin expressing cells overcame their weak adhesive phenotype by induction of many tensin-rich fibrillar adhesions, thus compensating for the low level of vinculin in these cells.

CONCLUSIONS

We propose that calreticulin affects fibronectin production and, thereby, assembly, and it indirectly influences the formation and/or stability of focal contacts and fibrillar adhesions, both of which are instrumental in matrix assembly and remodelling.

Cyclic stretch induces reorientation of cells in a Src family kinase- and p130Cas-dependent manner

Recognition of external mechanical signals by cells is an essential process for life. One important mechanical signal experienced by various cell types, e.g. around blood vessels, within the lung epithelia or around the intestine, is cyclic stretch. As a response, many cell types reorient their actin cytoskeleton and main cell axis almost perpendicular to the direction of stretch. Despite the vital necessity of cellular adaptation to cyclic stretch, the underlying mechanosensory signal cascades are far from being understood. Here we show an important function of Src-family kinase activity in cellular reorientation upon cyclic stretch. Deletion of all three family members, namely c-Src, Yes and Fyn (SYF), results in a strongly impaired cell reorientation of mouse embryonic fibroblasts with an only incomplete reorientation upon expression of c-Src. We further demonstrate that this reorientation phenotype of SYF-depleted cells is not caused by affected protein exchange dynamics within focal adhesions or altered cell force generation. Instead, Src-family kinases regulate the reorientation in a mechanotransduction-dependent manner, since knock-down and knock-out of p130Cas, a putative stretch sensor known to be phosphorylated by Src-family kinases, also reduce cellular reorientation upon cyclic stretch. This impaired reorientation is identical in intensity upon mutating stretch-sensitive tyrosines of p130Cas only. These statistically highly significant data pinpoint early events in a Src family kinase- and p130Cas-dependent mechanosensory/mechanotransduction pathway.

Trask phosphorylation defines the reverse mode of a phosphotyrosine signaling switch that underlies cell anchorage state

Phosphotyrosine signaling in anchored epithelial cells constitutes a spacially ordained signaling program that largely functions to promote integrin-linked focal adhesion complexes, serving to secure cell anchorage to matrix and as a bidirectional signaling hub that coordinates the physical state of the cell and its environment with cellular functions including proliferation and survival. Cells release their adhesions during processes such as mitosis, migration, or tumorigenesis, but the fate of signaling through tyrosine phosphorylation in unanchored cells remains poorly understood. In an examination of epithelial cells in the unanchored state, we find abundant phosphotyrosine signaling, largely recommitted to an anti-adhesive function mediated through the Src family phosphorylation of their transmembrane substrate Trask/CDCP1/gp140. Src-Trask phosphorylation inhibits integrin clustering and focal adhesion assembly and signaling, defining an active phosphotyrosine signaling program underlying the unanchored state. Src-Trask signaling and Src-focal adhesion signaling inactivate each other, constituting two opposing modes of phosphotyrosine signaling that define a switch underline cell anchorage state. Src kinases are prominent drivers of both signaling modes, identifying their position at the helm of adhesion signaling capable of specifying anchorage state through substrate selection. These experimental studies along with concurring phylogenetic evidence suggest that phosphorylation on tyrosine is a signaling function fundamentally linked with the regulation of integrins.

FAK phosphorylation at Tyr-925 regulates cross-talk between focal adhesion turnover and cell protrusion

FAK plays a key role in the regulation of cell migration. The authors show that the phosphorylation status of FAK at Tyr-925 is involved in FA turnover, formation of FAs, and increase in cell edge protrusion, together with activation of the p130^CAS/Rac1 signaling pathway.

 Cell migration is a highly complex process that requires the coordinated formation of membrane protrusion and focal adhesions (FAs). Focal adhesion kinase (FAK), a major signaling component of FAs, is involved in the disassembly process of FAs through phosphorylation and dephosphorylation of its tyrosine residues, but the role of such phosphorylations in nascent FA formation and turnover near the cell front and in cell protrusion is less well understood. In the present study, we demonstrate that, depending on the phosphorylation status of Tyr-925 residue, FAK modulates cell migration via two specific mechanisms. FAK^−/− mouse embryonic fibroblasts (MEFs) expressing nonphosphorylatable Y925F-FAK show increased interactions between FAK and unphosphorylated paxillin, which lead to FA stabilization and thus decreased FA turnover and reduced cell migration. Conversely, MEFs expressing phosphomimetic Y925E-FAK display unchanged FA disassembly rates, show increase in phosphorylated paxillin in FAs, and exhibit increased formation of nascent FAs at the cell leading edges. Moreover, Y925E-FAK cells present enhanced cell protrusion together with activation of the p130^CAS/Dock180/Rac1 signaling pathway. Together, our results demonstrate that phosphorylation of FAK at Tyr-925 is required for FAK-mediated cell migration and cell protrusion.

Phosphorylation of Trask by Src kinases inhibits integrin clustering and functions in exclusion with focal adhesion signaling

Trask is a recently described transmembrane substrate of Src kinases whose expression and phosphorylation has been correlated with the biology of some cancers. Little is known about the molecular functions of Trask, although its phosphorylation has been associated with cell adhesion. We have studied the effects of Trask phosphorylation on cell adhesion, integrin activation, clustering, and focal adhesion signaling. The small hairpin RNA (shRNA) knockdown of Trask results in increased cell adhesiveness and a failure to properly inactivate focal adhesion signaling, even in the unanchored state. On the contrary, the experimentally induced phosphorylation of Trask results in the inhibition of cell adhesion and inhibition of focal adhesion signaling. This is mediated through the inhibition of integrin clustering without affecting integrin affinity state or ligand binding activity. Furthermore, Trask signaling and focal adhesion signaling inactivate each other and signal in exclusion with each other, constituting a switch that underlies cell anchorage state. These data provide considerable insight into how Trask functions to regulate cell adhesion and reveal a novel pathway through which Src kinases can oppose integrin-mediated cell adhesion.

Mechanical integration of actin and adhesion dynamics in cell migration

Directed cell migration is a physical process that requires dramatic changes in cell shape and adhesion to the extracellular matrix. For efficient movement, these processes must be spatiotemporally coordinated. To a large degree, the morphological changes and physical forces that occur during migration are generated by a dynamic filamentous actin (F-actin) cytoskeleton. Adhesion is regulated by dynamic assemblies of structural and signaling proteins that couple the F-actin cytoskeleton to the extracellular matrix. Here, we review current knowledge of the dynamic organization of the F-actin cytoskeleton in cell migration and the regulation of focal adhesion assembly and disassembly with an emphasis on how mechanical and biochemical signaling between these two systems regulate the coordination of physical processes in cell migration.

Modulation of microvascular smooth muscle adhesion and mechanotransduction by integrin-linked kinase

OBJECTIVE

In this study, we investigated the involvement of integrin-linked kinase (ILK) in the adhesion of arteriolar vascular smooth muscle cells (VSMC) to fibronectin (FN) and in the mechano-responsiveness of VSMC focal adhesions (FA).

METHODS

ILK was visualized in VSMC by expressing EGFP-ILK and it was knocked down using ILK-shRNA constructs. Atomic force microscopy (AFM) was used to characterize VSMC interactions with FN, VSMC stiffness and to apply and measure forces at a VSMC single FA site.

RESULTS

ILK was localized to FA and silencing ILK promoted cell spreading, enhanced cell adhesion, reduced cell proliferation and reduced downstream phosphorylation of GSK-3beta and PKB/Akt. AFM studies demonstrated that silencing ILK enhanced alpha5beta1 integrin adhesion to FN and enhanced VSMC contraction in response to a pulling force applied at the level of a single FN-FA site.

CONCLUSIONS

ILK functions in arteriolar VSMC appear linked to multiple signaling pathways and processes that inhibit cell spreading, cell adhesion, FA formation, adhesion to FN and the mechano-responsiveness of FN-FA sites.

Tensin 2 modulates cell contractility in 3D collagen gels through the RhoGAP DLC1

Cytoskeletal proteins of the tensin family couple integrins to the actin cytoskeleton. They are found in both focal adhesions and the fibrillar adhesions formed between cells and the fibronectin matrix. There are four tensin genes which encode three large (approximately 200 kDa) tensin isoforms (tensin 1, 2, 3) and one short isoform (cten). However, the subcellular localization and function of the individual isoforms is poorly understood. Using human foreskin fibroblasts (HFFs), and imaging on both fixed and live cells, we show that GFP-tensin 2 is enriched in dynamic focal adhesions at the leading edge of the cell, whereas GFP-tensin 3 translocates rearward, and is enriched in fibrillar adhesions. To investigate the possible role of tensins in cell-matrix remodeling, we used siRNAs to knockdown each tensin isoform. We discovered that tensin 2 knockdown significantly reduced the ability of HFFs to contract 3D collagen gels, whilst no effect on fibronectin fibrillogenesis was observed. This inhibition of collagen gel contraction was associated with a substantial reduction in Rho activity, and it was reversed by depletion of DLC1, a RhoGAP that binds to tensin in focal adhesions. These findings suggest that focal adhesion-localized tensin 2 negatively regulates DLC1 to permit Rho-mediated actomyosin contraction and remodeling of collagen fibers.

Phosphotyrosine protein dynamics in cell membrane rafts of sphingosine-1-phosphate-stimulated human endothelium: role in barrier enhancement

Sphingosine-1-phosphate (S1P), a lipid growth factor, is critical to the maintenance and enhancement of vascular barrier function via processes highly dependent upon cell membrane raft-mediated signaling events. Anti-phosphotyrosine 2 dimensional gel electrophoresis (2-DE) immunoblots confirmed that disruption of membrane raft formation (via methyl-beta-cyclodextrin) inhibits S1P-induced protein tyrosine phosphorylation. To explore S1P-induced dynamic changes in membrane rafts, we used 2-D techniques to define proteins within detergent-resistant cell membrane rafts which are differentially expressed in S1P-challenged (1microM, 5min) human pulmonary artery endothelial cells (EC), with 57 protein spots exhibiting >3-fold change. S1P induced the recruitment of over 20 cell membrane raft proteins exhibiting increasing levels of tyrosine phosphorylation including known barrier-regulatory proteins such as focal adhesion kinase (FAK), cortactin, p85alpha phosphatidylinositol 3-kinase (p85alphaPI3K), myosin light chain kinase (nmMLCK), filamin A/C, and the non-receptor tyrosine kinase, c-Abl. Reduced expression of either FAK, MLCK, cortactin, filamin A or filamin C by siRNA transfection significantly attenuated S1P-induced EC barrier enhancement. Furthermore, S1P induced cell membrane raft components, p-caveolin-1 and glycosphingolipid (GM1), to the plasma membrane and enhanced co-localization of membrane rafts with p-caveolin-1 and p-nmMLCK. These results suggest that S1P induces both the tyrosine phosphorylation and recruitment of key actin cytoskeletal proteins to membrane rafts, resulting in enhanced human EC barrier function.

Interaction of human mesenchymal stem cells with osteopontin coated hydroxyapatite surfaces

In vitro studies of the initial attachment, spreading and motility of human bone mesenchymal stem cells have been carried out on bovine osteopontin (OPN) coated hydroxyapatite (HA) and gold (Au) model surfaces. The adsorption of OPN extracted from bovine milk was monitored by the quartz crystal microbalance with dissipation (QCM-D) and the ellipsometry techniques, and the OPN coated surfaces were further investigated by antigen-antibody interaction. It is shown that the OPN surface mass density is significantly lower and that the number of antibodies binding to the resulting OPN layers is significantly higher on the HA as compared to the Au surfaces. The initial attachment, spreading and motility of human mesenchymal stem cells show a larger cell area, a faster arrangement of vinculin in the basal cell membrane and more motile cells on the OPN coated HA surfaces as compared to the OPN coated Au surfaces and to the uncoated Au and HA surfaces. These in vitro results indicate that there may be great potential for OPN coated biomaterials, for instance as functional protein coatings or drug delivery systems on orthopaedic implants or scaffolds for tissue-engineering.

Significance of microtubule catastrophes at focal adhesion sites

Directional cell migration requires cell polarization and asymmetric distribution of cell signaling. Focal adhesions and microtubules are two systems which are essential for these. It was shown that these two systems closely interact with each other. It is known that microtubule targeting stimulates focal adhesion dissociation. Our recent study shows that focal adhesions, in turn, specifically induce microtubule catastrophe via a biochemical mechanism. We were able to track down one of the focal adhesion proteins paxillin which is involved in this process. Paxillin phosphorylation was previously shown to be the key component in the regulation of focal adhesion assembly or disassembly. Since microtubule catastrophe dynamic differs at the leading edge and cell rear, similar to paxillin phosphorylation levels, we suggest a model connecting asymmetric distribution of focal adhesions and asymmetric distribution of microtubule catastrophes at adhesion sites as a feedback loop.

Giving off mixed signals--distinct functions of alpha5beta1 and alphavbeta3 integrins in regulating cell behaviour

The formation, maturation, and dissolution of focal adhesions are basic prerequisites of cell migration and rely on the recruitment, signalling, and endocytosis of integrins. In many instances, extracellular matrix molecules are recognised by a number of integrins, and it is the sequential involvement of different integrins that allows establishment of cell polarity and migration towards a matrix stimulus. In this review, we consider both the similarities and differences between two key fibronectin receptors, alpha(v)beta(3) and alpha(5)beta(1) integrin. By considering the GTPase and kinase signalling and trafficking of two such closely-related receptors, we begin to understand how cell migration is coordinated.

Regulation of focal adhesion turnover by ErbB signalling in invasive breast cancer cells

A crucial early event by which cancer cells switch from localised to invasive phenotype is initiated by the acquisition of autonomous motile properties; a process driven by dynamic assembly and disassembly of multiple focal adhesion (FA) proteins, which mediate cell–matrix attachments, extracellular matrix degradation, and serve as traction sites for cell motility. We have reported previously that cancer cell invasion induced by overexpression of members of the ErbB tyrosine kinase receptors, including ErbB2, is dependent on FA signalling through FA kinase (FAK). Here, we show that ErbB2 receptor signalling regulates FA turnover, and cell migration and invasion through the Src–FAK pathway. Inhibition of the Src–FAK signalling in ErbB2-positive cells by Herceptin or RNA interference selectively regulates FA turnover, leading to enhanced number and size of peripherally localised adhesions and inhibition of cell invasion. Inhibition of ErbB2 signalling failed to regulate FA and cell migration and invasion in cells lacking FAK or Src but gains this activity after restoration of these proteins. Taken together, our results show a regulation of FA turnover by ErbB2 signalling.

Presenilin 1 affects focal adhesion site formation and cell force generation via c-Src transcriptional and posttranslational regulation

Presenilin 1 and 2 (PS) are critical components of the gamma-secretase complex that cleaves type I transmembrane proteins within their transmembrane domains. This process leads to release of proteolytically processed products from cellular membranes and plays an essential role in signal transduction or vital functions as cell adhesion. Here we studied the function of presenilins in cell-matrix interaction of wild-type and PS knock-out mouse embryonic fibroblasts. We found for PS1(-/-) cells an altered morphology with significantly reduced sizes of focal adhesion sites compared with wild type. Cell force analyses on micropatterned elastomer films revealed PS1(-/-) cell forces to be reduced by 50%. Pharmacological inhibition confirmed this function of gamma-secretase in adhesion site and cell force formation. On the regulatory level, PS1 deficiency was associated with strongly decreased phosphotyrosine levels of focal adhesion site-specific proteins. The reduced tyrosine phosphorylation was caused by a down-regulation of c-Src kinase activity primarily at the level of c-Src transcription. The direct regulatory connection between PS1 and c-Src could be identified with ephrinB2 as PS1 target protein. Overexpression of ephrinB2 cytoplasmic domain resulted in its nuclear translocation with increased levels of c-Src and a full complementation of the PS1(-/-) adhesion and phosphorylation phenotype. Cleavage of full-length EB2 and subsequent intracellular domain translocation depended on PS1 as these processes were only found in WT cells. Therefore, we conclude that gamma-secretase is vital for controlling cell adhesion and force formation by transcriptional regulation of c-Src via ephrinB2 cleavage.

Asymmetric focal adhesion disassembly in motile cells

Cell migration requires the integration and coordination of specific focal adhesion dynamics at the cell front, center and rear. In this review, we will present our understanding of the regulation of adhesion turnover and disassembly in various regions of the cell. Adhesion turnover involves a number of tyrosine kinases and phosphatases, most of which are engaged in FAK signaling pathways. Additionally, adhesions are regulated by tensile forces that depend on dynamic coupling with the actin cytoskeleton. The distribution of adhesion disassembly throughout a motile cell is likely coordinated by the asymmetry of the microtubule network. We present a model that suggests two stages of microtubule-driven adhesion disassembly: destabilization and detachment.

Activation of KLF8 transcription by focal adhesion kinase in human ovarian epithelial and cancer cells

KLF8 (Krüppel-like factor 8) is a transcription factor downstream of focal adhesion kinase (FAK) important in the regulation of the cell cycle and also plays a critical role in oncogenic transformation and epithelial to mesenchymal transition. Here we report the mechanisms by which FAK regulates KLF8 expression in human ovarian epithelial and cancer cells. We show that the overexpression of both KLF8 and FAK in the human ovarian cancer cells as compared with the normal human ovarian surface epithelial cells is critical for cell growth. Using promoter luciferase reporter assays, we demonstrate that exogenous FAK strongly promotes the activity of the KLF8 promoter, and knockdown of FAK inhibits it. KLF8 promoter activity and mRNA levels are induced by expression of constitutively active (CA) phosphatidylinositol 3-kinase (PI3K) or CA-Akt but are repressed by dominant negative Akt or the PI3K inhibitor LY294002. Disruption of an Sp1 binding site in the KLF8 promoter abolishes the FAK- or Sp1-mediated promoter activation. Sp1 knockdown prevents the KLF8 promoter from being activated by Sp1 or CA-Akt, and expression of CA-Akt enhances Sp1 expression in SKOV3ip1 cells. Chromatin immunoprecipitation and oligonucleotide precipitation results show that Sp1 binds to the KLF8 promoter. Taken together, our data suggest that FAK induces KLF8 expression in human ovarian cancer cells by activating the PI3K-Akt signaling pathway, leading to the activation of KLF8 promoter by Sp1.

Modeling morphogenesis and oncogenesis in three-dimensional breast epithelial cultures

Three-dimensional (3D) epithelial culture systems recreate the cardinal features of glandular epithelium in vivo and represent a valuable tool for modeling breast cancer initiation and progression in a structurally appropriate context. 3D models have emerged as a powerful method to interrogate the biological activities of cancer genes and oncogenic pathways, and recent studies have poignantly illustrated their utility in dissecting the emerging role of tensional force in regulating epithelial tissue homeostasis. We review how 3D models are being used to investigate fundamental cellular and biophysical mechanisms associated with breast cancer progression that have not been readily amenable to traditional genetic or biochemical analysis.

Differential calreticulin expression affects focal contacts via the calmodulin/CaMK II pathway

Calreticulin is an ER calcium-storage protein, which influences gene expression and cell adhesion. In this study, we analysed the differences in adhesive properties of calreticulin under- and overexpressing fibroblasts in relation to the calmodulin- and calcium/calmodulin-dependent kinase II (CaMK II)-dependent signalling pathways. Cells stably underexpressing calreticulin had elevated expression of calmodulin, activated CaMK II, activated ERK and activated c-src. Inhibition of calmodulin by W7, and CaMK II by KN-62, caused the otherwise weekly adhesive calreticulin underexpressing cells to behave like the overexpressing cells, via induction of increased cell spreading. Increased vinculin, activated paxillin, activated focal adhesion kinase and fibronectin levels were observed upon inhibition of either the calmodulin or the CaMK II signalling pathways, which was accompanied by an increase in cell spreading and focal contact formation. Both KN-62 and W7 treatment increased cell motility in underexpressing cells, but W7 treatment led to loss of directionality. Thus, both the calmodulin and CaMK II signalling pathways influence cellular spreading and motility, but subtle differences exist in their distal effects on motility effectors.

Analysis of the suitability of calreticulin inducible HEK cells for adhesion studies: microscopical and biochemical comparisons

Calreticulin is a Ca(2+)-buffering ER chaperone that also modulates cell adhesiveness. In order to study the effect of calreticulin on the expression of adhesion-related genes, we created a calreticulin inducible Human Embryonic Kidney (HEK) 293 cell line. We found that fibronectin mRNA and both intra- and extra-cellular fibronectin protein levels increased following calreticulin induction. However, despite this increase in fibronectin, HEK293 cells did not assemble an extracellular fibrillar fibronectin matrix regardless of the level of calreticulin expression. Furthermore, HEK293 cells exhibited a poorly organized actin cytoskeleton, did not have clustered fibronectin receptors at the cell surface, and did not form focal contacts. This likely accounts for the lack of fibronectin matrix deposition by these cells regardless of calreticulin expression level. Vinculin abundance did not appreciably increase upon calreticulin induction and the level of active c-Src, a regulatory kinase of focal contacts, was found to be abundant and unregulated by calreticulin induction in these cells. The inability to form stable focal contacts and to commence fibronectin fibrillogenesis due to high c-Src activity may be responsible for the poor adhesive phenotype of HEK 293 cells. Thus, we show here that HEK293 cells are not suitable for microscopical studies of cell-substratum adhesions, but are best suited for biochemical studies.

RACK1 regulates Src activity and modulates paxillin dynamics during cell migration

Receptor for Activated C Kinase, RACK1, is an adaptor protein that regulates signaling via Src and PKC-dependent pathways, and has been implicated in cell migration. In this study we demonstrate novel functions for RACK1 in regulating adhesion dynamics during cell migration. We report that cells lacking RACK1 are less motile and show reduced dynamics of paxillin and talin at focal complexes. To investigate the role of the RACK1/Src interactions in adhesion dynamics, we used RACK1 in which the putative Src binding site has been mutated (RACK Y246F). RACK1-deficient cells showed enhanced c-Src activity that was rescued by expression of wild type RACK1, but not by RACK Y246F. Expression of wild type RACK1, but not RACK Y246F, was also able to rescue the adhesion and migration defects observed in the RACK1-deficient cells. Furthermore, our findings indicate that RACK1 functions to regulate paxillin phosphorylation and that its effects on paxillin dynamics require the Src-mediated phosphorylation of tyrosine 31/118 on paxillin. Taken together, these findings support a novel role for RACK1 as a key regulator of cell migration and adhesion dynamics through the regulation of Src activity, and the modulation of paxillin phosphorylation at early adhesions.

Structure of the PTB domain of tensin1 and a model for its recruitment to fibrillar adhesions

Tensin is a cytoskeletal protein that links integrins to the actin cytoskeleton at sites of cell-matrix adhesion. Here we describe the crystal structure of the phosphotyrosine-binding (PTB) domain of tensin1, and show that it binds integrins in an NPxY-dependent fashion. Alanine mutagenesis of both the PTB domain and integrin tails supports a model of integrin binding similar to that of the PTB-like domain of talin. However, we also show that phosphorylation of the NPxY tyrosine, which disrupts talin binding, has a negligible effect on tensin binding. This suggests that tyrosine phosphorylation of integrin, which occurs during the maturation of focal adhesions, could act as a switch to promote the migration of tensin-integrin complexes into fibronectin-mediated fibrillar adhesions.