SRC-mediated phosphorylation of focal adhesion kinase couples actin and adhesion dynamics to survival signaling

Shikonin induces apoptosis and inhibits migration of ovarian carcinoma cells by inhibiting the phosphorylation of Src and FAK

The present study identified that shikonin, a naphthoquinone extracted from the roots of Lithospermum erythrorhizon, inhibits the migration of ovarian cancer cells and induces their apoptosis by impairing the phosphorylation of two kinases, proto-oncogene tyrosine protein kinase Src (Src) and focal adhesion kinase (FAK). Ovarian carcinoma SKOV-3 cells were treated with various concentrations of shikonin and analyzed for the effects on cell migration, invasion and apoptosis via Transwell assays and flow cytometry. In addition, the effects of shikonin administration on the expression and phosphorylation of Src and FAK in the SKOV-3 cells were analyzed by western blotting. Shikonin appeared to induce apoptosis and decrease cell migration in the SKOV-3 ovarian cells. Furthermore, the present study provides evidence that shikonin may exert these effects on human ovarian carcinoma cells via the inhibition of the protein tyrosine kinases, Src and FAK. Thus, shikonin should be considered for additional investigation as a candidate agent for the prevention and treatment of human ovarian cancer.

Focal adhesion kinase (FAK) perspectives in mechanobiology: implications for cell behaviour

Mechanobiology is a scientific interface discipline emerging from engineering and biology. With regard to tissue-regenerative cell-based strategies, mechanobiological concepts, including biomechanics as a target for cell and human mesenchymal stem cell behaviour, are on the march. Based on the periodontium as a paradigm, this mini-review discusses the key role of focal-adhesion kinase (FAK) in mechanobiology, since it is involved in mediating the transformation of environmental biomechanical signals into cell behavioural responses via mechanotransducing signalling cascades. These processes enable cells to adjust quickly to environmental cues, whereas adjustment itself relies on the specific intramolecular phosphorylation of FAK tyrosine residues and the multiple interactions of FAK with distinct partners. Furthermore, interaction-triggered mechanotransducing pathways govern the dynamics of focal adhesion sites and cell behaviour. Facets of behaviour not only include cell spreading and motility, but also proliferation, differentiation and apoptosis. In translational terms, identified and characterized biomechanical parameters can be incorporated into innovative concepts of cell- and tissue-tailored clinically applied biomaterials controlling cell behaviour as desired.

EGFR-blockade with erlotinib reduces EGF and TGF-β2 expression and the actin-cytoskeleton which influences different aspects of cellular migration in lens epithelial cells

INTRODUCTION

After cataract surgery, residual lens epithelial cells migrate and proliferate within the capsular bag resulting in posterior capsule opacification (PCO). The up-regulation of TGF-β2, EGF and FGF-2 has been identified as a key factor in PCO pathogenesis leading to actin fiber assembly and alterations in the migration pattern. In this in vitro study, the influence of Erlotinib as a selective EGFR inhibitor is investigated on the cellular features indicated, which might promote a future clinical application.

METHODS

Expression of EGF, FGF-2 and TGF-β2 was measured using RT-PCR and ELISA in human lens epithelial cells (HLEC). Computational data of an in vitro time lapse microscopy assay were used for statistical analysis of single cell migration with a particular focus on cell-cell interaction; cell velocity distribution; and displacement before, during and after mitosis. The effect of Erlotinib on the actin-cytoskeleton was evaluated using Alexa Fluor 488 Phalloidin and epifluorescence microscopy.

RESULTS

EGF and TGF-β2 mRNA expression and protein levels are reduced by Erlotinib, while FGF-2 expression remained stable. Overall fluidity of cell-cell interaction is less in the presence of Erlotinib compared to the control and the velocity distribution across all cells becomes less uniform within the cell cluster. After mitosis, HLEC move significantly faster without EGFR inhibition, which can be completely blocked by Erlotinib. Furthermore, Erlotinib diminishes the amount of actin stress fibers and the stress fiber diameter.

CONCLUSION

As a novel effect of Erlotinib on HLEC, we describe the down-regulation of EGF and TGF-β2 expression, both are crucial factors for PCO development. Cellular movement displays complex alterations under EGFR inhibition, which is partly explained by actin fiber depletion. These findings further underline the role of Erlotinib in pharmacologic PCO prophylaxis.

Protein kinase C, focal adhesions and the regulation of cell migration

Cell adhesion to extracellular matrix is a complex process involving protrusive activity driven by the actin cytoskeleton, engagement of specific receptors, followed by signaling and cytoskeletal organization. Thereafter, contractile and endocytic/recycling activities may facilitate migration and adhesion turnover. Focal adhesions, or focal contacts, are widespread organelles at the cell-matrix interface. They arise as a result of receptor interactions with matrix ligands, together with clustering. Recent analysis shows that focal adhesions contain a very large number of protein components in their intracellular compartment. Among these are tyrosine kinases, which have received a great deal of attention, whereas the serine/threonine kinase protein kinase C has received much less. Here the status of protein kinase C in focal adhesions and cell migration is reviewed, together with discussion of its roles and potential substrates.

A novel synthetic oleanane triterpenoid suppresses adhesion, migration, and invasion of highly metastatic melanoma cells by modulating gelatinase signaling axis

A methyl derivative natural triterpenoid amooranin (methyl-25-hydroxy-3-oxoolean-12-en-28-oate, AMR-Me) has been found to possess antiproliferative, proapoptotic, and antiinflammatory effects against established tumor cells. Large-scale synthesis of pure AMR-Me has eliminated the need of the natural phytochemical for further development of AMR-Me as an anticancer drug. Metastatic melanoma is a fatal form of cutaneous malignancy with poor prognosis and limited therapeutic options. It was hypothesized that antitumor pharmacological effect of AMR-Me could be linked to AMR-Me-mediated suppression of the metastatic potential of B16F10 murine melanoma. AMR-Me was assessed for its antimetastatic efficacy by cell adhesion, migration, and invasion assays in B16F10 cells. The signaling crosstalk was explored by gelatin zymography, Western blot, ELISA, and immunocytochemistry. The results elicited that AMR-Me was successful in restricting the adhesion, migration, and invasion of highly metastatic cells. The antimetastatic potential of this compound may be attributed to the reduced expression of membrane type 1 metalloproteinase (MT1-MMP) and matrix metalloproteinases (MMP-2 and MMP-9). AMR-Me was found to downregulate vascular endothelial growth factor (VEGF)/phosphorylated forms of focal adhesion kinase (pFAK397 )/Jun N-terminus kinase (pJNK)/extracellular signal-regulated kinase (pERK). This, in turn, inhibited transcription factor nuclear factor-κB (NF-κB) and transactivation of MMPs. Moreover, the activation of tissue inhibitors of metalloproteinases (TIMP-1 and TIMP-2) might have influenced the downmodulation of MT1-MMP, MMP-2, and MMP-9. AMR-Me suppresses the activity of MT1-MMP, MMP-2, and MMP-9 by downregulation of VEGF/pFAK397 /pJNK/pERK/NF-κB and activation of TIMP-1 and TIMP-2 in metastatic melanoma cell line, B16F10. AMR-Me has the potential as an effective anticancer drug for metastatic melanoma which is a dismal disease.

Protein kinase C activation stimulates mesenchymal stem cell adhesion through activation of focal adhesion kinase

Emerging evidence suggests that cell therapy with mesenchymal stem cells (MSCs) has beneficial effects on the injured heart. However, the decreased survival and/or adhesion of MSCs under ischemic conditions limits the application of cell transplantation as a therapeutic modality. We investigated a potential method of increasing the adhesion ability of MSCs to improve their efficacy in the ischemic heart. Treatment of MSCs with PKC activator, phorbol 12-myristate 13-acetate (PMA), increased cell adhesion and spreading in a dose-dependent method and significantly decreased detachment. When MSCs were treated with PKC inhibitor, that is, rottlerin, adhesion of MSCs was slightly diminished, and detachment was also decreased compared to the treatment with PMA. MSCs treated with both PMA and rottlerin behaved similarly to normal controls. In 3D matrix cardio gel, treatment with PMA increased the number of MSCs compared to the control group and MSCs treated with rottlerin. Expressions of focal adhesion kinase, cytoskeleton-associated proteins, and integrin subunits were clearly demonstrated in PMA-treated MSCs by immunoblotting and/or immunocytochemistry. The effect of PKC activator treatment on MSCs was validated in vivo. Following injection into rat hearts, the PMA-treated MSCs exhibited significantly higher retention in infarcted myocardium compared to the MSC group. Infarct size, fibrosis area, and apoptotic cells were reduced, and cardiac function was improved in rat hearts injected with PMA-treated MSCs compared to sham and/or MSC-implanted group. These results indicate that PKC activator is a potential target for niche manipulation to enhance adhesion of MSCs for cardiac regeneration.

Role of ion transport in control of apoptotic cell death

Cell shrinkage is a hallmark and contributes to signaling of apoptosis. Apoptotic cell shrinkage requires ion transport across the cell membrane involving K(+) channels, Cl(-) or anion channels, Na(+)/H(+) exchange, Na(+),K(+),Cl(-) cotransport, and Na(+)/K(+)ATPase. Activation of K(+) channels fosters K(+) exit with decrease of cytosolic K(+) concentration, activation of anion channels triggers exit of Cl(-), organic osmolytes, and HCO3(-). Cellular loss of K(+) and organic osmolytes as well as cytosolic acidification favor apoptosis. Ca(2+) entry through Ca(2+)-permeable cation channels may result in apoptosis by affecting mitochondrial integrity, stimulating proteinases, inducing cell shrinkage due to activation of Ca(2+)-sensitive K(+) channels, and triggering cell-membrane scrambling. Signaling involved in the modification of cell-volume regulatory ion transport during apoptosis include mitogen-activated kinases p38, JNK, ERK1/2, MEKK1, MKK4, the small G proteins Cdc42, and/or Rac and the transcription factor p53. Osmosensing involves integrin receptors, focal adhesion kinases, and tyrosine kinase receptors. Hyperosmotic shock leads to vesicular acidification followed by activation of acid sphingomyelinase, ceramide formation, release of reactive oxygen species, activation of the tyrosine kinase Yes with subsequent stimulation of CD95 trafficking to the cell membrane. Apoptosis is counteracted by mechanisms involved in regulatory volume increase (RVI), by organic osmolytes, by focal adhesion kinase, and by heat-shock proteins. Clearly, our knowledge on the interplay between cell-volume regulatory mechanisms and suicidal cell death is still far from complete and substantial additional experimental effort is needed to elucidate the role of cell-volume regulatory mechanisms in suicidal cell death.

SRC family kinase inhibition as a novel strategy to augment melphalan-based regional chemotherapy of advanced extremity melanoma

BACKGROUND

Src kinase inhibition has been shown to augment the efficacy of chemotherapy. Dasatinib, a dual Src/Abl kinase inhibitor approved for the treatment of CML, is under investigation as monotherapy for tumors with abnormal Src signaling, such as melanoma. The goal of this study was to determine if Src kinase inhibition using dasatinib could enhance the efficacy of regionally administered melphalan in advanced extremity melanoma.

METHODS

The mutational status of c-kit and patterns of gene expression predictive of dysregulated Src kinase signaling were evaluated in a panel of 26 human melanoma cell lines. The effectiveness of dasatinib was measured by quantifying protein expression and activation of Src kinase, focal adhesion kinase, and Crk-associated substrate (p130(CAS)), in conjunction with in vitro cell viability assays using seven melanoma cell lines. Utilizing a rat model of regional chemotherapy, we evaluated the effectiveness of systemic dasatinib in conjunction with regional melphalan against the human melanoma cell line, DM443, grown as a xenograft.

RESULTS

Only the WM3211 cell line harbored a c-kit mutation. Significant correlation was observed between Src-predicted dysregulation by gene expression and sensitivity to dasatinib in vitro. Tumor doubling time for DM443 xenografts treated with systemic dasatinib in combination with regional melphalan (44.8 days) was significantly longer (p = 0.007) than either dasatinib (21.3 days) or melphalan alone (24.7 days).

CONCLUSIONS

Systemic dasatinib prior to melphalan-based regional chemotherapy markedly improves the efficacy of this alkylating agent in this melanoma xenograft model. Validation of this concept should be considered in the context of a regional therapy clinical trial.

Orientation-specific responses to sustained uniaxial stretching in focal adhesion growth and turnover

Cells are mechanosensitive to extracellular matrix (ECM) deformation, which can be caused by muscle contraction or changes in hydrostatic pressure. Focal adhesions (FAs) mediate the linkage between the cell and the ECM and initiate mechanically stimulated signaling events. We developed a stretching apparatus in which cells grown on fibronectin-coated elastic substrates can be stretched and imaged live to study how FAs dynamically respond to ECM deformation. Human bone osteosarcoma epithelial cell line U2OS was transfected with GFP-paxillin as an FA marker and subjected to sustained uniaxial stretching. Two responses at different timescales were observed: rapid FA growth within seconds after stretching, and delayed FA disassembly and loss of cell polarity that occurred over tens of minutes. Rapid FA growth occurred in all cells; however, delayed responses to stretch occurred in an orientation-specific manner, specifically in cells with their long axes perpendicular to the stretching direction, but not in cells with their long axes parallel to stretch. Pharmacological treatments demonstrated that FA kinase (FAK) promotes but Src inhibits rapid FA growth, whereas FAK, Src, and calpain 2 all contribute to delayed FA disassembly and loss of polarity in cells perpendicular to stretching. Immunostaining for phospho-FAK after stretching revealed that FAK activation was maximal at 5 s after stretching, specifically in FAs oriented perpendicular to stretch. We hypothesize that orientation-specific activation of strain/stress-sensitive proteins in FAs upstream to FAK and Src promote orientation-specific responses in FA growth and disassembly that mediate polarity rearrangement in response to sustained stretch.

Supervillin-mediated suppression of p53 protein enhances cell survival

Integrin-based adhesions promote cell survival as well as cell motility and invasion. We show here that the adhesion regulatory protein supervillin increases cell survival by decreasing levels of the tumor suppressor protein p53 and downstream target genes. RNAi-mediated knockdown of a new splice form of supervillin (isoform 4) or both isoforms 1 and 4 increases the amount of p53 and cell death, whereas p53 levels decrease after overexpression of either supervillin isoform. Cellular responses to DNA damage induced by etoposide or doxorubicin include down-regulation of endogenous supervillin coincident with increases in p53. In DNA-damaged supervillin knockdown cells, p53 knockdown or inhibition partially rescues the loss of cell metabolic activity, a measure of cell proliferation. Knockdown of the p53 deubiquitinating enzyme USP7/HAUSP also reverses the supervillin phenotype, blocking the increase in p53 levels seen after supervillin knockdown and accentuating the decrease in p53 levels triggered by supervillin overexpression. Conversely, supervillin overexpression decreases the association of USP7 and p53 and attenuates USP7-mediated p53 deubiquitination. USP7 binds directly to the supervillin N terminus and can deubiquitinate and stabilize supervillin. Supervillin also is stabilized by derivatization with the ubiquitin-like protein SUMO1. These results show that supervillin regulates cell survival through control of p53 levels and suggest that supervillin and its interaction partners at sites of cell-substrate adhesion constitute a locus for cross-talk between survival signaling and cell motility pathways.

Downregulation of Src enhances the cytotoxic effect of temozolomide through AKT in glioma

Src is an attractive target since it is overexpressed in a number of malignancies, including glioma. However, the mechanism of Src signaling as well as its silencing effect on temozolomide in glioma is not well known. We hypothesized that downregulation of Src may enhance the cytotoxic effect of temozolomide on glioma. As expected, Src was overexpressed in glioblastoma multiforme (GBM) compared with normal brain tissues. Src silencing suppressed tumor proliferation and induced apoptosis in glioma. In addition, Src silencing combined with temozolomide treatment resulted in significant inhibition of tumor growth. These effects may be mediated by AKT which is a downstream effector of Src, since downregulation of AKT exhibited a similar effect as Src siRNA when combined with temozolomide. Finally, we demonstrated that overexpression of AKT suppressed the enhanced cytotoxic effect of temozolomide mediated by Src silencing. Thus, the present study demonstrated that Src plays a biologically significant role in tumor proliferation and apoptosis and enhances the cytotoxic effect of temozolomide through AKT supression in glioma.

Natalizumab exerts direct signaling capacity and supports a pro-inflammatory phenotype in some patients with multiple sclerosis

Natalizumab is a recombinant monoclonal antibody raised against integrin alpha-4 (CD49d). It is approved for the treatment of patients with multiple sclerosis (MS), a chronic inflammatory autoimmune disease of the CNS. While having shown high therapeutic efficacy, treatment by natalizumab has been linked to progressive multifocal leukoencephalopathy (PML) as a serious adverse effect. Furthermore, drug cessation sometimes induces rebound disease activity of unknown etiology. Here we investigated whether binding of this adhesion-blocking antibody to T lymphocytes could modulate their phenotype by direct induction of intracellular signaling events. Primary CD4⁺ T lymphocytes either from healthy donors and treated with natalizumab in vitro or from MS patients receiving their very first dose of natalizumab were analyzed. Natalizumab induced a mild upregulation of IL-2, IFN-γ and IL-17 expression in activated primary human CD4⁺ T cells propagated ex vivo from healthy donors, consistent with a pro-inflammatory costimulatory effect on lymphokine expression. Along with this, natalizumab binding triggered rapid MAPK/ERK phosphorylation. Furthermore, it decreased CD49d surface expression on effector cells within a few hours. Sustained CD49d downregulation could be attributed to integrin internalization and degradation. Importantly, also CD4⁺ T cells from some MS patients receiving their very first dose of natalizumab produced more IL-2, IFN-γ and IL-17 already 24 h after infusion. Together these data indicate that in addition to its adhesion-blocking mode of action natalizumab possesses mild direct signaling capacities, which can support a pro-inflammatory phenotype of peripheral blood T lymphocytes. This might explain why a rebound of disease activity or IRIS is observed in some MS patients after natalizumab cessation.

Effects of lysophosphatidic acid on calpain-mediated proteolysis of focal adhesion kinase in human prostate cancer cells

BACKGROUND

Calcium-mediated proteolysis plays an important role in cell migration. Lysophosphatidic acid (LPA), a lipid mediator present in serum, enhances migration of carcinoma cells. The effects of LPA on calpain-mediated proteolysis were, therefore, examined in PC-3, a human prostate cancer cell line.

METHODS

Cultured PC-3 cells were used in studies utilizing pharmacologic interventions, immunoblotting, and confocal immunolocalization.

RESULTS

Focal adhesion kinase (FAK), a tyrosine kinase involved in cell adhesion, is rapidly proteolyzed in serum-starved PC-3 cells exposed to the calcium ionophore, ionomycin; Nck, p130CAS, PKCα, and Ras-GAP are also degraded. Thapsigargin, which causes more moderate increases in intracellular calcium, induces partial proteolysis of these proteins. Calpain inhibitors block the proteolytic responses to ionomycin and thapsigargin. Ionomycin does not induce proteolysis in cells maintained in serum, suggesting a protective role for growth factors contained in serum. LPA causes minor FAK proteolysis when added alone, but protects against ionomycin-induced proteolysis in a time-dependent manner. LPA also protects against the cell detachment that eventually follows ionomycin treatment. The response to LPA is blocked by an LPA receptor antagonist. A similar effect of LPA is observed in ionomycin-treated Rat-1 fibroblasts. In PC-3 cells, the protective effects of LPA and serum are correlated with phosphorylation and redistribution of paxillin, suggesting roles for phosphorylation-mediated protein-protein interactions.

CONCLUSIONS

The complex effects of LPA on calpain-mediated proteolysis of FAK and other adhesion proteins are likely to play a role in the ability of LPA to promote attachment, migration, and survival of prostate cancer cells.

Gene expression profiles of phaeochromocytomas with ERBB2 overexpression reveal a new molecular mechanism tumourigenicity

OBJECTIVE

Phaeochromocytomas (PHEO) and functional paragangliomas (PGLs) are catecholamine-secreting neuroendocrine tumours. Although most PHEO/PGLs are benign, 10-35% present as (or develop into) malignant tumours with a poor prognosis. Overexpression of ERBB2 (v-erb-b2 erythroblastic leukaemia viral oncogene homologue 2) has been reported to be associated with malignant PHEO. We used gene expression profiling of PHEO/PGLs to gain a better understanding of the tumourigenic pathways associated with ERBB2.

METHODS

We used the Affymetrix Gene Chip U133 Plus 2·0 genome-wide gene expression cDNA microarray of 18 PHEO/PGLs (12 benign and six malignant, divided into two groups depending on ERBB2 expression levels) to analyse the gene expression patterns.

RESULTS

Unsupervised hierarchical cluster analysis of transcription profiles of 18 samples identified two dominant expression clusters corresponding to samples belonging to the ERBB2+ and ERBB2- groups. According to the gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) databases, the differentially expressed genes were classified into diverse functional categories and signalling pathways. In particular, the focal adhesion signalling pathway showed significant differences between the groups; specifically, the FAK-Src-MAPK pathway was prominently activated in the ERBB2+ group.

CONCLUSIONS

In summary, ERBB2+ PHEO/PGLs have a distinct expression pattern compared with the ERBB2- group. The focal adhesion signalling pathway may participate in ERBB2-induced tumourigenesis in PHEO/PGLs.

Src-dependent autophagic degradation of Ret in FAK-signalling-defective cancer cells

We have recently described that autophagic targeting of Src maintains cancer cell viability when FAK signalling is defective. Here, we show that the Ret tyrosine kinase is also degraded by autophagy in cancer cells with altered/reduced FAK signalling, preventing its binding to FAK at integrin adhesions. Inhibition of autophagy restores Ret localization to focal adhesions. Importantly, Src kinase activity is required to target Ret to autophagosomes and enhance Ret degradation. Src is thus a general mediator of selective autophagic targeting of adhesion-linked kinases, and Ret a second FAK-binding tyrosine kinase degraded through autophagy in cancer cells under adhesion stress. Src--by controlling not only its own degradation but also that of other FAK-binding partners--allows cancer cell survival, suggesting a new therapeutic strategy.

LRP-1--CD44, a new cell surface complex regulating tumor cell adhesion

The low-density lipoprotein receptor-related protein 1 (LRP-1) is a large endocytic receptor mediating the clearance of various molecules from the extracellular matrix. In the field of cancer, LRP-1-mediated endocytosis was first associated with antitumor properties. However, recent results suggested that LRP-1 may coordinate the adhesion-deadhesion balance in malignant cells to support tumor progression. Here, we observed that LRP-1 silencing or RAP (receptor-associated protein) treatment led to accumulation of CD44 at the tumor cell surface. Moreover, we evidenced a tight interaction between CD44 and LRP-1, not exclusively localized in lipid rafts. Overexpression of LRP-1-derived minireceptors indicated that the fourth ligand-binding cluster of LRP-1 is required to bind CD44. Labeling of CD44 with EEA1 and LAMP-1 showed that internalized CD44 is routed through early endosomes toward lysosomes in a LRP-1-dependent pathway. LRP-1-mediated internalization of CD44 was highly reduced under hyperosmotic conditions but poorly affected by membrane cholesterol depletion, revealing that it proceeds mostly via clathrin-coated pits. Finally, we demonstrated that CD44 silencing abolishes RAP-induced tumor cell attachment, revealing that cell surface accumulation of CD44 under LRP-1 blockade is mainly responsible for the stimulation of tumor cell adhesion. Altogether, our data shed light on the LRP-1-mediated internalization of CD44 that appeared critical to define the adhesive properties of tumor cells.

Characteristics of, and risk factors for, infections in patients with cancer treated with dasatinib and a brief review of other complications

Dasatinib has transformed the treatment of chronic myelogenous leukemia, resulting in durable remissions and prolonged survival. The spectrum of infectious complications during and after dasatinib therapy is not known. Retrospective analysis of records among 69 patients treated with dasatinib showed that 35 (51%) developed 57 episodes of infection. Twenty-nine (51%) episodes occurred during neutropenia, and 25 (44%) were microbiologically confirmed. Compared with patients who did not develop infection with dasatinib therapy, patients with infection were significantly more likely to have acute lymphocytic leukemia (51% vs. 18%; p ≤ 0.005) and to have received high-dose corticosteroids (51% vs. 26%; p ≤ 0.05). Patients with infection were also more likely to have received dasatinib with another antineoplastic agent (57% vs. 35% without infection; p = 0.09). On multivariate analysis, treatment with three or more cycles of dasatinib increased the risk of infection (odds ratio 11.7; 95% confidence interval 2.5-54.3; p = 0.002). The presence of comorbidities tended to increase the risk of infection (odds ratio 3.9; 95% confidence interval 0.9-17.9; p = 0.07). Interestingly, viral infections, including a single case of cytomegalovirus colitis, were uncommon (7%). The rate of death in 57 patients during follow-up was non-significantly higher in patients with infection versus those without infection (35% vs. 18%; p = 0.18). Infection-associated deaths were noted in only two patients (10%) who had an infection and died. The results of our analysis suggest that antibacterial prophylaxis is important in patients who develop neutropenia during dasatinib therapy, although routine antifungal and anti-cytomegalovirus prophylaxis may not be necessary.

Autophagic targeting of Src promotes cancer cell survival following reduced FAK signalling

Here we describe a mechanism that cancer cells use to survive when flux through the Src/FAK pathway is severely perturbed. Depletion of FAK, detachment of FAK-proficient cells or expression of non-phosphorylatable FAK proteins causes sequestration of active Src away from focal adhesions into intracellular puncta that co-stain with several autophagy regulators. Inhibition of autophagy results in restoration of active Src at peripheral adhesions, and this leads to cancer cell death. Autophagic targeting of active Src is associated with a Src-LC3B complex, and is mediated by c-Cbl. However, this is independent of c-Cbl E3 ligase activity, but is mediated by an LC3-interacting region. Thus, c-Cbl-mediated autophagic targeting of active Src can occur in cancer cells to maintain viability when flux through the integrin/Src/FAK pathway is disrupted. This exposes a previously unrecognized cancer cell vulnerability that may provide a new therapeutic opportunity.

PTTG induces EMT through integrin αVβ3-focal adhesion kinase signaling in lung cancer cells

Pituitary tumor transforming gene (PTTG) is a well-studied oncogene for its role in tumorigenesis and serves as a marker of malignancy in several cancer types including lung. In the present study, we defined the role of PTTG in actin cytoskeleton remodeling, cell migration and induction of epithelial mesenchymal transition (EMT) through the regulation of integrin α(V)β(3)-FAK (focal adhesion kinase) signaling pathway. Overexpression of PTTG through an adenovirus vector resulted in a significant increase in the expression of integrins α(V) and β(3), a process that was reversed with the downregulation of PTTG expression through the use of an adenovirus expressing PTTG-specific small interfering RNA (siRNA). Western blot analysis of cells infected with adenovirus PTTG cDNA resulted in increased FAK and enhanced expression of adhesion complex molecules paxillin, metavincullin, and talin. Furthermore, downstream signaling genes Rac1, RhoA, Cdc42 and DOCK180 showed upregulation upon PTTG overexpression. This process was dependent on integrin α(V), as blockage by antagonist echistatin (RGD peptide) or α(V)-specific siRNA resulted in a decrease in FAK and subsequent adhesion molecules. Actin cytoskeleton disruption was detected as a result of integrin-FAK signaling by PTTG as well as enhanced cell motility. Taken together, our results suggest for the first time an important role of PTTG in regulation of integrins α(V) and β(3) and adhesion-complex proteins leading to induction of EMT.

SKAP2, a novel target of HSF4b, associates with NCK2/F-actin at membrane ruffles and regulates actin reorganization in lens cell

In addition to roles in stress response, heat shock factors (HSFs) play crucial roles in differentiation and development. Heat shock transcription factor 4 (HSF4) deficiency leads to defect in lens epithelial cell (LEC) differentiation and cataract formation. However, the mechanism remains obscure. Here, we identified Src kinase-associated phosphoprotein 2 (SKAP2) as a downstream target of HSF4b and it was highly expressed at the anterior tip of lens elongating fibre cells in vivo. The HSF4-deficient lenses showed reduced SKAP2 expression and defects in actin reorganization. The disassembly of stress fibres and formation of cortical actin fibres are critical for the initiation of LEC differentiation. SKAP2 localized at actin-rich ruffles in human LECs (SRA01/04 cells) and knockdown SKAP2 using RNA interference impaired the disassembly of cellular stress fibres in response to fibroblast growth factor (FGF)-b. Overexpression of SKAP2, but not the N-terminal deletion mutant of SKAP2, induced the actin remodelling. We further found that SKAP2 interacted with the SH2 domain of non-catalytic region of tyrosine kinase adaptor protein 2 (NCK2) via its N-terminus. The complex of SKAP2-NCK2-F-actin accumulated at the leading edge of the lamellipodium, where FGF receptors and focal adhesion were also recruited. These results revealed an essential role for HSF4-mediated SKAP2 expression in the regulation of actin reorganization during lens differentiation, likely through a mechanism that SKAP2 anchors the complex of NCK2/focal adhesion to FGF receptors at the lamellipodium in lens epithelial cells.

Metastasis of tumor cells is enhanced by downregulation of Bit1

Background

Resistance to anoikis, which is defined as apoptosis induced by loss of integrin-mediated cell attachment to the extracellular matrix, is a determinant of tumor progression and metastasis. We have previously identified the mitochondrial Bit1 (Bcl-2 inhibitor of transcription) protein as a novel anoikis effector whose apoptotic function is independent from caspases and is uniquely controlled by integrins. In this report, we examined the possibility that Bit1 is suppressed during tumor progression and that Bit1 downregulation may play a role in tumor metastasis.

Methodology/Principal Findings

Using a human breast tumor tissue array, we found that Bit1 expression is suppressed in a significant fraction of advanced stages of breast cancer. Targeted disruption of Bit1 via shRNA technology in lowly aggressive MCF7 cells conferred enhanced anoikis resistance, adhesive and migratory potential, which correlated with an increase in active Extracellular kinase regulated (Erk) levels and a decrease in Erk-directed phosphatase activity. These pro-metastasis phenotypes were also observed following downregulation of endogenous Bit1 in Hela and B16F1 cancer cell lines. The enhanced migratory and adhesive potential of Bit1 knockdown cells is in part dependent on their high level of Erk activation since down-regulating Erk in these cells attenuated their enhanced motility and adhesive properties. The Bit1 knockdown pools also showed a statistically highly significant increase in experimental lung metastasis, with no differences in tumor growth relative to control clones in vivo using a BALB/c nude mouse model system. Importantly, the pulmonary metastases of Bit1 knockdown cells exhibited increased phospho-Erk staining.

Conclusions/Significance

These findings indicate that downregulation of Bit1 conferred cancer cells with enhanced anoikis resistance, adhesive and migratory properties in vitro and specifically potentiated tumor metastasis in vivo. These results underscore the therapeutic importance of restoring Bit1 expression in cancer cells to circumvent metastasis at least in part through inhibition of the Erk pathway.

A deficiency of uPAR alters endothelial angiogenic function and cell morphology

The angiogenic potential of a cell requires dynamic reorganization of the cytoskeletal architecture that involves the interaction of urokinase-type plasminogen activator receptor (uPAR) with the extracellular matrix. This study focuses on the effect of uPAR deficiency (uPAR^-/-) on angiogenic function and associated cytoskeletal organization. Utilizing murine endothelial cells, it was observed that adhesion, migration, proliferation, and capillary tube formation were altered in uPAR^-/- cells compared to wild-type (WT) cells. On a vitronectin (Vn) matrix, uPAR^-/- cells acquired a "fried egg" morphology characterized by circular actin organization and lack of lamellipodia formation. The up-regulation of β1 integrin, FAK(P-Tyr925), and paxillin (P-Tyr118), and decreased Rac1 activation, suggested increased focal adhesions, but delayed focal adhesion turnover in uPAR^-/- cells. This accounted for the enhanced adhesion, but attenuated migration, on Vn. VEGF-enriched Matrigel implants from uPAR^-/- mice demonstrated a lack of mature vessel formation compared to WT mice. Collectively, these results indicate that a uPAR deficiency leads to decreased angiogenic functions of endothelial cells.

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.

Low levels of hydrogen peroxide stimulate corneal epithelial cell adhesion, migration, and wound healing

PURPOSE

Intracellular reactive oxygen species have been reported to associate with growth factor and integrin signalings in promoting cell adhesion in many cell types. This study is to explore if exogenous H(2)O(2) at low levels can be beneficial to cell adhesion, migration, and wound healing.

METHODS

Primary rabbit corneal epithelial cells treated with 0-70 μM H(2)O(2) were tested for viability by MTT assay, adhesion by centrifugation assay, focal contacts of vinculin and F-actin by immunofluorescence, activated Src(pY416), EGF receptor (pY845), vinculin(pY1065), FAK(pY397), and FAK(pY576) by immunoblotting. Cell migration was examined with 0-50 μM H(2)O(2) using the scratch wound technique. Corneal wound healing of ex vivo pig model and in vivo mouse model was examined using H(2)O(2) with and without antioxidant N-acetylcysteine (NAC).

RESULTS

Compared with the untreated control, H(2)O(2) at 10-50 μM stimulated cell viability and facilitated adhesion and migration with clear induction of vinculin-rich focal adhesions and F-actin-containing stress fibers by increasing activated Src, FAK(pY576), and vinculin(pY1065). H(2)O(2) also increased phosphorylation of EGFR(Y845) parallel to that of activated Src, but both were eliminated by NAC and PP1 (Src inhibitor). Finally, H(2)O(2) induced faster wound healing in cornea both in vitro and in vivo, but the healing was diminished by NAC.

CONCLUSIONS

These findings suggest that H(2)O(2) at low levels promotes cell adhesion, migration, and wound healing in cornea cells or tissue, and the interaction of H(2)O(2) with Src plays a major role.

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.

Minireview: steroid receptor coactivator-3: a multifarious coregulator in mammary gland metastasis

A member of the steroid receptor coactivator (SRC)/p160 family, SRC-3 acts as a coregulator for nuclear receptor (NR) and non-NR transcription factors. Such coregulator pleiotropy enables SRC-3 to influence a myriad of signaling networks that are essential for normal physiology and pathophysiology. Although SRC-3's proliferative role in primary tumor formation in the mammary gland is well established, a role for this oncogenic coregulator in tumor cell motility and invasion has only recently been elucidated. In the nucleus, SRC-3 is required for the execution of the epithelial-mesenchymal transition, a programming step which endows an immotile cancer cell with motile and invasive characteristics. Nuclear SRC-3 is also essential for proteolytic breakdown of the extracellular matrix by matrix-metalloproteinases, a process which enables primary tumor cell invasion into the surrounding stroma. At the plasma membrane, however, a truncated isoform of SRC-3 (SRC-3Δ4) serves as a signaling adaptor for the epidermal growth factor→focal adhesion kinase→c-Src signal transduction pathway, a signaling cascade that is central to growth factor-induced cell migration and invasion. Together, these studies underscore a pivotal role for SRC-3 not only as a proto-oncogene but also as a prometastatic factor during the early steps in the invasion-metastasis cascade. Beyond furnishing critical mechanistic insights into SRC-3's involvement in mammary tumor progression, these findings provide opportunities to develop new approaches for breast cancer diagnosis and intervention.

Fyn is induced by Ras/PI3K/Akt signaling and is required for enhanced invasion/migration

Src family kinases (SFKs) are frequently over-expressed and/or activated in human cancers, and play key roles in cancer cell invasion, metastasis, proliferation, survival, and angiogenesis. Allosteric activation of SFKs occurs through well-defined post-translational mechanisms, however the SFK member Fyn is over-expressed in multiple human cancers (prostate, melanoma, pancreatic, glioma, chronic myelogenous leukemia) and the mechanism of increased Fyn expression is unclear. Since activation of Ras oncogenes is a common oncogenic event leading to the activation of multiple effector pathways, we explored if Ras could induce Fyn expression. Retroviral transduction of the human keratinocyte cell line HaCaT with oncogenic H-Ras dramatically up-regulated Fyn mRNA (>100-fold, P < 0.001), protein, and kinase activity without affecting Src levels or activity. Activation of Akt, but not MAPK or EGFR, was necessary and sufficient for induction of Fyn by H-Ras. Expression of active Fyn was sufficient to increase HaCaT cell migration and invasion, and the enhanced migration and invasion induced by H-Ras could be significantly blocked (70% reduction, P < 0.01) by knockdown of Fyn with a specific siRNA or inhibition of SFKs with PP2. In addition, expression of Fyn in MDA-MB-231 breast cancer cells was dependent on PI3K activity and was involved in their invasive phenotype. Thus, the Ras/PI3K/Akt pathway can account for Fyn over-expression in cancers, and Fyn is a critical mediator of the Ras-stimulated invasive cell phenotype. These results support the development of therapeutic strategies targeting Akt/Fyn pathway to block migration and invasion of tumor cells.

Reciprocal control of cell proliferation and migration

In adult tissue the quiescent state of a single cell is maintained by the steady state conditions of its own microenvironment for what concern both cell-cell as well as cell-ECM interaction and soluble factors concentration. Physiological or pathological conditions can alter this quiescent state through an imbalance of both soluble and insoluble factors that can trigger a cellular phenotypic response. The kind of cellular response depends by many factors but one of the most important is the concentration of soluble cytokines sensed by the target cell. In addition, due to the intrinsic plasticity of many cellular types, every single cell is able, in response to the same stimulus, to rapidly switch phenotype supporting minimal changes of microenviromental cytokines concentration. Wound healing is a typical condition in which epithelial, endothelial as well as mesenchymal cells are firstly subjected to activation of their motility in order to repopulate the damaged region and then they show a strong proliferative response in order to successfully complete the wound repair process. This schema constitute the leitmotif of many other physiological or pathological conditions such as development vasculogenesis/angiogenesis as well as cancer outgrowth and metastasis.Our review focuses on the molecular mechanisms that control the starting and, eventually, the switching of cellular phenotypic outcome in response to changes in the symmetry of the extracellular environment.

Hyperphosphorylated FAK Delocalizes from Focal Adhesions to Membrane Ruffles

Cell adhesion and migration are key determinants in tumor metastasis. Adherence of tumor cell to the extracellular matrix is mediated via integrin containing focal adhesions (FAs). Binding of integrins to ECM triggers phosphorylation of two major components of FAs, focal adhesion kinase (FAK) and Src, activating downstream signaling pathway which leads to FA disassembly and cell migration. In this paper, we analyze how phosphorylation of FAK regulates its trafficking at FAs in living human astrocytoma cells. Upon pervanadate-induced FAK phosphorylation, phosphorylated FAK appeared highly expressed at newly formed membrane ruffles. This effect was abolished in presence of the specific Src inhibitor PP2. Our findings demonstrate that upon phosphorylation, FAK delocalizes from FAs to membrane ruffles.

Focal adhesion kinase can play unique and opposing roles in regulating the morphology of differentiating oligodendrocytes

During development cells of the oligodendrocyte lineage undergo significant changes in morphology when they differentiate from migratory oligodendrocyte progenitors, which are mostly bipolar, into post-migratory pre-myelinating oligodendrocytes, which extend complex and expanded process networks, and then finally into mature oligodendrocytes, which generate myelin sheaths required for efficient signal propagation within the nervous system. This extensive morphological remodeling occurs in the context of a complex extracellular environment and requires significant rearrangement of the cell's cytoskeleton. The molecular mechanisms underlying this intricate integration of signals, however, remain poorly understood. A key regulator of extracellular matrix to cytoskeleton signaling is the non-receptor tyrosine kinase FAK (focal adhesion kinase). Here, we report that FAK can regulate the morphology of differentiating post-migratory pre-myelinating oligodendrocytes in a unique and opposing fashion that is dependent on the nature of the extracellular matrix and mediated largely by FAK's catalytic activity. More specifically, FAK was found to restrict process network expansion in the presence of fibronectin but to promote morphological maturation in the presence of laminin-2. In addition, FAK's restraining role predominated for postnatal day 3-derived cells, while its maturation promoting role prevailed for postnatal day 5-derived cells. Taken together, our findings reveal a complex role of FAK in regulating the morphology of post-migratory pre-myelinating oligodendrocytes.

SRC: a century of science brought to the clinic

The SRC family kinases are the largest family of nonreceptor tyrosine kinases and one of the best-studied targets for cancer therapy. SRC, arguably the oldest oncogene, has been implicated in pathways regulating proliferation, angiogenesis, invasion and metastasis, and bone metabolism. More recently, researchers have proposed that the transforming ability of SRC is linked to its ability to activate key signaling molecules in these pathways, rather than through direct activity. It has been hypothesized that blocking SRC activation may inhibit these pathways, resulting in antitumor activity. However, successfully targeting SRC in a clinical setting remains a challenge, and SRC inhibitors have only recently begun to move through clinical development. Preclinical studies have identified specific molecular "subgroups" and histologies that may be more sensitive to SRC inhibition. In addition, other studies have demonstrated synergistic interactions between SRC inhibitors and other targeted therapies and cytotoxics. In this review, we summarize SRC biology and how it has been applied to the clinical development of SRC inhibitors. The status of SRC inhibitors, including dasatinib, saracatinib, and bosutinib, which are in phase 1, 2, and 3 trials, is highlighted.

ZF21 protein regulates cell adhesion and motility

Cell migration on an extracellular matrix (ECM) requires continuous formation and turnover of focal adhesions (FAs) along the direction of cell movement. However, our knowledge of the components of FAs and the mechanism of their regulation remains limited. Here, we identify ZF21, a member of a protein family characterized by the presence of a phosphatidylinositol 3-phosphate-binding FYVE domain, to be a new regulator of FAs and cell movement. Knockdown of ZF21 expression in cells increased the number of FAs and suppressed cell migration. Knockdown of ZF21 expression also led to a significant delay in FA disassembly following induction of synchronous disassembly of FAs by nocodazole treatment. ZF21 bound to focal adhesion kinase, localized to FAs, and was necessary for dephosphorylation of FAK at Tyr(397), which is important for disassembly of FAs. Thus, ZF21 represents a new component of FAs, mediates disassembly of FAs, and thereby regulates cell motility.

RECK is up-regulated and involved in chondrocyte cloning in human osteoarthritic cartilage

Reversion-inducing cysteine-rich protein with Kazal motifs (RECK) is a membrane-anchored matrix metalloproteinase regulator, but its functions in cartilage are not fully understood. The aim of the present study was to examine the expression and functions of RECK in human osteoarthritic (OA) cartilage. Quantitative RT-PCR indicated that the expression level of RECK is significantly higher in OA cartilage than in normal cartilage. By immunohistochemical analysis, RECK was localized to chondrocytes in OA cartilage, and the immunoreactivity directly correlated with the Mankin score and degree of chondrocyte cloning and proliferation. In cultured OA chondrocytes, RECK was expressed on the cell surface by glycosylphosphatidylinositol anchoring. The expression was stimulated by insulin-like growth factor-1 and suppressed by interleukin-1 and tumor necrosis factor-alpha. Down-regulation of RECK by small interfering RNA showed reduced spreading and smaller focal adhesions in the chondrocytes. Chondrocyte migration in a monolayer wounding assay was increased by down-regulation of RECK and inhibited by RECK overexpression in an matrix metalloproteinase activity-dependent manner. On the other hand, chondrocyte proliferation was suppressed by RECK silencing, and this was associated with reduced phosphorylation of focal adhesion kinase and extracellular signal-regulated kinase, whereas the proliferation was enhanced by RECK overexpression. These data are the first to demonstrate that RECK is up-regulated in human OA cartilage and suggest that RECK plays a role in chondrocyte cloning probably through suppression and promotion of chondrocyte migration and proliferation, respectively.

SRC-3Delta4 mediates the interaction of EGFR with FAK to promote cell migration

EGF induces signal transduction between EGFR and FAK, and FAK is required for EGF-induced cell migration. It is unknown, however, what factor mediates the interaction between EGFR and FAK and leads to EGF-induced FAK phosphorylation. Here, we identify SRC-3Delta4, a splicing isoform of the SRC-3 oncogene, as a signaling adaptor that links EGFR and FAK and promotes EGF-induced phosphorylations of FAK and c-Src. We identify three PAK1-mediated phosphorylations in SRC-3Delta4 that promote the localization of SRC-3Delta4 to the plasma membrane and mediate the interactions with EGFR and FAK. Importantly, overexpression of SRC-3Delta4 promotes MDA-MB231-induced breast tumor metastasis. Our findings identify phosphorylated SRC-3Delta4 as a missing adaptor between EGFR and its downstream signaling molecule FAK to coordinately regulate EGF-induced cell migration. Our study also reveals that a nuclear receptor coactivator can act in the periphery of a cell to directly mediate activation of an enzyme.

Src signaling in cancer invasion

Src is a non-receptor cytoplasmic tyrosine kinase which becomes activated following the stimulation of plasma membrane receptors including receptor tyrosine kinases and integrins, and is an indispensable player of multiple physiological homeostatic pathways. Once activated, Src is the starting point for several biochemical cascades that thereby propagate signals generated extracellularly along intracellular interconnected transduction pathways. Src transmits signals promoting cell survival and mitogenesis and, in addition, exerts a profound effect on the reorganization of the cytoskeleton and the adhesion systems that underpin cell migration and invasion. Because increased activity of Src is a frequent occurrence in many types of human cancer, and because there is evidence of a prominent role of Src in invasion and in other tumor progression-related events such as epithelial-mesenchymal transition (EMT) and development of metastasis, inhibitors targeting Src are being viewed as promising drugs for cancer therapy.

Regulation of adhesion dynamics by calpain-mediated proteolysis of focal adhesion kinase (FAK)

The coordinated and dynamic regulation of adhesions is required for cell migration. We demonstrated previously that limited proteolysis of talin1 by the calcium-dependent protease calpain 2 plays a critical role in adhesion disassembly in fibroblasts (Franco, S. J., Rodgers, M. A., Perrin, B. J., Han, J., Bennin, D. A., Critchley, D. R., and Huttenlocher, A. (2004) Nat. Cell Biol. 6, 977-983). However, little is known about the contribution of other calpain substrates to the regulation of adhesion dynamics. We now provide evidence that calpain 2-mediated proteolysis of focal adhesion kinase (FAK) regulates adhesion dynamics in motile cells. We mapped the preferred calpain cleavage site between the two C-terminal proline-rich regions after Ser-745, resulting in a C-terminal fragment similar in size to the FAK-related non-kinase (FRNK). We generated mutant FAK with a point mutation (V744G) that renders FAK resistant to calpain proteolysis but retains other biochemical properties of FAK. Using time-lapse microscopy, we show that the dynamics of green fluorescent protein-talin1 are impaired in FAK-deficient cells. Expression of wild-type but not calpain-resistant FAK rescues talin dynamics in FAK-deficient cells. Taken together, our findings suggest a novel role for calpain proteolysis of FAK in regulating adhesion dynamics in motile cells.

beta1 integrin/FAK/ERK signalling pathway is essential for human fetal islet cell differentiation and survival

beta1 integrin and collagen matrix interactions regulate the survival of cells by associating with focal adhesion kinase (FAK) and initiating MAPK/ERK signalling, but little is known about these signalling pathways during human fetal islet ontogeny. The purpose of this study was to investigate whether beta1 integrin/FAK activation of the MAPK/ERK pathway regulates human fetal islet cell expression of endocrine cell markers and survival. Isolated human (18-21 weeks fetal age) islet-epithelial cell clusters, cultured on collagen I, were examined using beta1 integrin blocking antibody, beta1 integrin siRNA and FAK expression vector. Perturbing beta1 integrin function in the human fetal islet-epithelial cell clusters resulted in a marked decrease in cell adhesion, in parallel with a reduction in the number of cells expressing PDX-1, insulin and glucagon (p < 0.05). beta1 integrin blockade disorganized focal adhesion contacts in the PDX-1(+) cells and decreased activation of FAK and ERK1/2 signalling in parallel with an increase in expression of cleaved caspases 9 and 3 (p < 0.01). Similar results were obtained following an siRNA knock-down of beta1 integrin expression. In contrast, over-expression of FAK not only increased phospho-ERK and the expression of PDX-1, insulin and glucagon (p < 0.05) but also abrogated the decreases in phospho-ERK and PDX-1 by beta1 integrin blockade. This study demonstrates that activation of the FAK/ERK signalling cascade by beta1 integrin is involved in the differentiation and survival of human fetal pancreatic islet cells.

Interactions with nanoscale topography: adhesion quantification and signal transduction in cells of osteogenic and multipotent lineage

Polymeric medical devices widely used in orthopedic surgery play key roles in fracture fixation and orthopedic implant design. Topographical modification and surface micro-roughness of these devices regulate cellular adhesion, a process fundamental in the initiation of osteoinduction and osteogenesis. Advances in fabrication techniques have evolved the field of surface modification; in particular, nanotechnology has allowed the development of nanoscale substrates for the investigation into cell-nanofeature interactions. In this study human osteoblasts (HOBs) were cultured on ordered nanoscale pits and random nano "craters" and "islands". Adhesion subtypes were quantified by immunofluorescent microscopy and cell-substrate interactions investigated via immuno-scanning electron microscopy. To investigate the effects of these substrates on cellular function 1.7 k microarray analysis was used to establish gene profiles of enriched STRO-1+ progenitor cell populations cultured on these nanotopographies. Nanotopographies affected the formation of adhesions on experimental substrates. Adhesion formation was prominent on planar control substrates and reduced on nanocrater and nanoisland topographies; nanopits, however, were shown to inhibit directly the formation of large adhesions. STRO-1+ progenitor cells cultured on experimental substrates revealed significant changes in genetic expression. This study implicates nanotopographical modification as a significant modulator of osteoblast adhesion and cellular function in mesenchymal populations.

The chemopreventive bioflavonoid apigenin inhibits prostate cancer cell motility through the focal adhesion kinase/Src signaling mechanism

Prostate cancer mortality is primarily attributed to metastatic rather than primary, organ-confined disease. Acquiring a motile and invasive phenotype is an important step in development of tumors and ultimately metastasis. This step involves remodeling of the extracellular matrix and of cell-matrix interactions, cell movement mediated by the actin cytoskeleton, and activation of focal adhesion kinase (FAK)/Src signaling. Epidemiologic studies suggest that the metastatic behavior of prostate cancer may be an ideal target for chemoprevention. The natural flavone apigenin is known to have chemopreventive properties against many cancers, including prostate cancer. Here, we study the effect of apigenin on motility, invasion, and its mechanism of action in metastatic prostate carcinoma cells (PC3-M). We found that apigenin inhibits PC3-M cell motility in a scratch-wound assay. Live cell imaging studies show that apigenin diminishes the speed and affects directionality of cell motion. Alterations in the cytoskeleton are consistent with impaired cell movement in apigenin-treated cells. Apigenin treatment leads to formation of "exaggerated filopodia," which show accumulation of focal adhesion proteins at their tips. Furthermore, apigenin-treated cells adhere more strongly to the extracellular matrix. Additionally, apigenin decreases activation of FAK and Src, and phosphorylation of Src substrates FAK Y576/577 and Y925. Expression of constitutively active Src blunts the effect of apigenin on cell motility and cytoskeleton remodeling. These results show that apigenin inhibits motility and invasion of prostate carcinoma cells, disrupts actin cytoskeleton organization, and inhibits FAK/Src signaling. These studies provide mechanistic insight into developing novel strategies for inhibiting prostate cancer cell motility and invasiveness.

An integrin alpha(v)beta(3)-c-Src oncogenic unit promotes anchorage-independence and tumor progression

Integrins regulate adhesion-dependent growth, survival and invasion of tumor cells. In particular, expression of integrin alpha(v)beta(3) is associated with progression of a variety of human tumors. Here we reveal a previously undescribed adhesion-independent role for integrin alpha(v)beta(3) in pancreatic cancer and other carcinomas. Specifically, alpha(v)beta(3) expressed in carcinoma cells enhanced anchorage-independent tumor growth in vitro and increased lymph node metastases in vivo. These effects required recruitment of c-Src to the beta(3) integrin cytoplasmic tail, leading to c-Src activation, Crk-associated substrate (CAS) phosphorylation and tumor cell survival that, unexpectedly, was independent of cell adhesion or focal adhesion kinase (FAK) activation. Pharmacological blockade of c-Src kinase activity or decreased expression of endogenous alpha(v)beta(3) integrin or c-Src not only inhibited anchorage-independent growth but also suppressed metastasis in vivo, yet these manipulations did not affect tumor cell migration or invasion. These data define an unexpected role for an integrin as a mediator of anchorage independence, suggesting that an alpha(v)beta(3)-c-Src signaling module may account for the aggressive behavior of integrin alpha(v)beta(3)-expressing tumors in humans.

Regulation of cross-linked actin network (CLAN) formation in human trabecular meshwork (HTM) cells by convergence of distinct beta1 and beta3 integrin pathways

PURPOSE

To determine the beta1/beta3 integrin-mediated pathways that regulate cross-linked actin network (CLAN) formation in human trabecular meshwork (HTM) cells. CLANs form in glaucomatous and steroid-treated TM cells, which may contribute to reducing outflow facility through the TM.

METHODS

Expression of CD47 (an alphavbeta3 integrin coreceptor/thrombospondin-1 receptor) and integrins alphavbeta3 and beta1 was assessed by FACS. CLANs were induced by plating cells on fibronectin (a beta1 integrin ligand) in the absence or presence of the beta3 integrin-activating mAb AP-5 and were identified by phalloidin labeling. The role of Src kinases, PI-3 kinase (PI-3K), Rac1, and CD47 was determined by incubating cells with the inhibitors PP2 and EPA (Src kinases), LY294002 (PI-3K), or NSC23766 (Rac1). Tiam1 and Trio siRNAs and dominant-negative Tiam1 were used to determine which Rac1-specific guanine nucleotide exchange factor was involved. The role of CD47 was determined using the thrombospondin-1-derived agonist peptide 4N1K and the CD47 function blocking antibody B6H12.2.

RESULTS

HTM cells expressed CD47 and integrins alphavbeta3 and beta1. beta3 Integrin or CD47 activation significantly increased CLAN formation over beta1 integrin-induced levels, whereas anti-CD47 mAb B6H12.2 inhibited this increase. PP2, NSC23766, and Trio siRNA decreased beta3-induced CLAN formation by 72%, 45%, and 67%, respectively, whereas LY294002 and dominant negative Tiam1 had no effect. LY294002 decreased beta1 integrin-mediated CLAN formation by 42%, and PP2 completely blocked it.

CONCLUSIONS

Distinct beta1 and alphavbeta3 integrin signaling pathways converge to enhance CLAN formation. beta1-Mediated CLAN formation was PI-3K dependent, whereas beta3-mediated CLAN formation was CD47 and Rac1/Trio dependent and might have been regulated by thrombospondin-1. Both integrin pathways were Src dependent.

Focal adhesion kinase: a prominent determinant in breast cancer initiation, progression and metastasis

Focal adhesion kinase (FAK) is an intracellular non-receptor tyrosine kinase. In addition to its role as a major mediator of signal transduction by integrins, FAK also participates in signaling by a wide range of extracellular stimuli including growth factors, G-protein-coupled receptor agonists, cytokines, and other inflammatory mediators. The link between FAK and breast cancers is strongly suggested by a number of reports showing that FAK gene is amplified and overexpressed in a large fraction of breast cancer specimens. In addition, increased FAK expression and activity frequently correlate with metastatic disease and poor prognosis. Since its discovery in early 1990s, numerous studies have shown a role for FAK in the regulation of cell spreading, adhesion, migration, survival, proliferation, differentiation, and angiogenesis. Many of these studies in cultured cells provided strong evidence to connect FAK expression/activation to the promotion of cancer. Recently, a prominent role of FAK in promoting mammary tumorigenesis, progression and metastasis has been unveiled by different animal models of human breast cancer, including xenograft models in immunodeficient rodents and spontaneous tumor models in transgenic mice that have specific deletion of FAK in the mammary epithelial cells during embryonic or postnatal development. These in vivo studies established FAK as a prominent determinant in mammary cancer initiation, progression and metastasis. Furthermore, a novel function of FAK in maintaining mammary cancer stem/progenitor cells in vivo has been recently reported, which may provide a novel cellular mechanism of FAK in promoting breast cancer initiation and progression. The wealth of knowledge accumulated over almost two decades of research on FAK should help to design potentially novel therapies for breast cancer.

Improving the prognosis for patients with glioblastoma: the rationale for targeting Src

Glioblastoma is the most common and aggressive form of primary brain tumor. The prognosis for patients diagnosed with glioblastoma is poor, with a median survival of 12-14 months and a 5-year survival rate of <5%. The upfront standard treatment for patients with newly diagnosed glioblastoma, consisting of surgery followed by chemotherapy combined with radiotherapy, provides only short-term survival benefits. Recurrent glioblastoma is an extremely challenging therapeutic setting because of the aggressive and resistant nature of the tumor. A set of key molecular targets in oncology is the Src family of non-receptor protein kinases. Dysregulated signaling via the Src kinases has been shown to underlie glioma-related proliferation, angiogenesis, migration, and survival. Here we review the biologic role of Src in malignant glioma and discuss key preclinical studies demonstrating the potential utility of inhibiting Src in glioma. Proof of clinical benefit is forthcoming from the first clinical studies involving the newest generation of small molecule Src inhibitors currently in clinical trials for recurrent glioblastoma. Blocking Src alone will likely not translate into a significant clinical benefit; thus, strategies for combining Src inhibitors with potential synergistic therapeutic modalities will be discussed. This review will focus on dasatinib, the most advanced Src inhibitor being tested in glioblastoma, which is currently in phase I/II trials in this setting.

How focal adhesion size depends on integrin affinity

Understanding how the thermodynamics and kinetics of integrin receptor binding and clustering impact the formation of focal adhesions is important for understanding the mechanisms cells use to sense and respond to physical cues in their environment. Cells on chemically well-defined surfaces were observed to have distributions of focal adhesions shifted toward smaller sizes when presented with higher affinity ligands (Kato, M.; Mrksich, M. Biochemistry 2004, 43, 2699). In this paper, we account for this trend with a simple model in which integrins are treated as particles on a lattice, and their stochastic dynamics are simulated with a kinetic Monte Carlo algorithm. How the trend depends on force-coupled growth, membrane fluctuations, and heterogeneity of receptor-ligand interactions is analyzed. Predictions are made for substrates in which the ligands presented can vary in either space or time, so that the model can be validated experimentally.