Fer-mediated cortactin phosphorylation is associated with efficient fibroblast migration and is dependent on reactive oxygen species generation during integrin-mediated cell adhesion

Integrins and cadherins join forces to form adhesive networks

Cell-cell and cell-extracellular-matrix (cell-ECM) adhesions have much in common, including shared cytoskeletal linkages, signaling molecules and adaptor proteins that serve to regulate multiple cellular functions. The term 'adhesive crosstalk' is widely used to indicate the presumed functional communication between distinct adhesive specializations in the cell. However, this distinction is largely a simplification on the basis of the non-overlapping subcellular distribution of molecules that are involved in adhesion and adhesion-dependent signaling at points of cell-cell and cell-substrate contact. The purpose of this Commentary is to highlight data that demonstrate the coordination and interdependence of cadherin and integrin adhesions. We describe the convergence of adhesive inputs on cell signaling pathways and cytoskeletal assemblies involved in regulating cell polarity, migration, proliferation and survival, differentiation and morphogenesis. Cell-cell and cell-ECM adhesions represent highly integrated networks of protein interactions that are crucial for tissue homeostasis and the responses of individual cells to their adhesive environments. We argue that the machinery of adhesion in multicellular tissues comprises an interdependent network of cell-cell and cell-ECM interactions and signaling responses, and not merely crosstalk between spatially and functionally distinct adhesive specializations within cells.

The Fer tyrosine kinase regulates interactions of Rho GDP-Dissociation Inhibitor α with the small GTPase Rac

Background

RhoGDI proteins are important regulators of the small GTPase Rac, because they shuttle Rac from the cytoplasm to membranes and also protect Rac from activation, deactivation and degradation. How the binding and release of Rac from RhoGDI is regulated is not precisely understood.

Results

We report that the non-receptor tyrosine kinase Fer is able to phosphorylate RhoGDIα and form a direct protein complex with it. This interaction is mediated by the C-terminal end of RhoGDIα. Activation of Fer by reactive oxygen species caused increased phosphorylation of RhoGDIα and pervanadate treatment further augmented this. Tyrosine phosphorylation of RhoGDIα by Fer prevented subsequent binding of Rac to RhoGDIα, but once a RhoGDIα-Rac complex was formed, the Fer kinase was not able to cause Rac release through tyrosine phosphorylation of preformed RhoGDIα-Rac complexes.

Conclusions

These results identify tyrosine phosphorylation of RhoGDIα by Fer as a mechanism to regulate binding of RhoGDIα to Rac.

Transducer of Cdc42-dependent actin assembly promotes epidermal growth factor-induced cell motility and invasiveness

Toca-1 (transducer of Cdc42-dependent actin assembly) interacts with the Cdc42·N-WASP and Abi1·Rac·WAVE F-actin branching pathways that function in lamellipodia formation and cell motility. However, the potential role of Toca-1 in these processes has not been reported. Here, we show that epidermal growth factor (EGF) induces Toca-1 localization to lamellipodia, where it co-localizes with F-actin and Arp2/3 complex in A431 epidermoid carcinoma cells. EGF also induces tyrosine phosphorylation of Toca-1 and interactions with N-WASP and Abi1. Stable knockdown of Toca-1 expression by RNA interference has no effect on cell growth, EGF receptor expression, or internalization. However, Toca-1 knockdown cells display defects in EGF-induced filopodia and lamellipodial protrusions compared with control cells. Further analyses reveal a role for Toca-1 in localization of Arp2/3 and Abi1 to lamellipodia. Toca-1 knockdown cells also display a significant defect in EGF-induced motility and invasiveness. Taken together, these results implicate Toca-1 in coordinating actin assembly within filopodia and lamellipodia to promote EGF-induced cell migration and invasion.

The tyrosine kinase Fer is a downstream target of the PLD-PA pathway that regulates cell migration

Phosphatidic acid (PA), which can be produced by phospholipase D (PLD), is involved in various signaling events, such as cell proliferation, survival, and migration. However, the molecular mechanisms that link PA to cell migration are largely unknown. Here, we show that PA binds to the tyrosine kinase Fer and enhances its ability to phosphorylate cortactin, a protein that promotes actin polymerization. We found that a previously unknown lipid-binding module in Fer adjacent to the F-BAR [Fes-Cdc42-interacting protein 4 (CIP4) homology (FCH) and bin-amphiphysin-Rvs] domain mediated PA binding. We refer to this lipid-binding domain as the FX (F-BAR extension) domain. Overexpression of Fer enhanced lamellipodia formation and cell migration in a manner dependent on PLD activity and the PA-FX interaction. Thus, the PLD-PA pathway promotes cell migration through Fer-induced enhancement of actin polymerization.

fps/fes knockout mice display a lactation defect and the fps/fes tyrosine kinase is a component of E-cadherin-based adherens junctions in breast epithelial cells during lactation

The fps/fes proto-oncogene encodes a cytoplasmic protein-tyrosine kinase implicated in vesicular trafficking and cytokine and growth factor signaling in hematopoietic, neuronal, vascular endothelial and epithelial lineages. Genetic evidence has suggested a tumor suppressor role for Fps/Fes in breast and colon. Here we used fps/fes knockout mice to investigate potential roles for this kinase in development and function of the mammary gland. Fps/Fes expression was induced during pregnancy and lactation, and its kinase activity was dramatically enhanced. Milk protein and fat composition from nursing fps/fes-null mothers was normal; however, pups reared by them gained weight more slowly than pups reared by wild-type mothers. Fps/Fes displayed a predominantly dispersed punctate intracellular distribution which was consistent with vesicles within the luminal epithelial cells of lactating breast, while a small fraction co-localized with beta-catenin and E-cadherin on their basolateral surfaces. Fps/Fes was found to be a component of the E-cadherin adherens junction (AJ) complex; however, the phosphotyrosine status of beta-catenin and core AJ components in fps/fes-null breast tissue was unaltered, and epithelial cell AJs and gland morphology were intact. We conclude that Fps/Fes is not essential for the maintenance of epithelial cell AJs in the lactating breast but may instead play important roles in vesicular trafficking and milk secretion.

NADPH oxidases and angiotensin II receptor signaling

Over the last decade many studies have demonstrated the importance of reactive oxygen species (ROS) production by NADPH oxidases in angiotensin II (Ang II) signaling, as well as a role for ROS in the development of different diseases in which Ang II is a central component. In this review, we summarize the mechanism of activation of NADPH oxidases by Ang II and describe the molecular targets of ROS in Ang II signaling in the vasculature, kidney and brain. We also discuss the effects of genetic manipulation of NADPH oxidase function on the physiology and pathophysiology of the renin-angiotensin system.

Specific tyrosine phosphorylation of focal adhesion kinase mediated by Fer tyrosine kinase in suspended hepatocytes

Cell adhesion to the extracellular matrix (ECM) can activate signaling via focal adhesion kinase (FAK) leading to dynamic regulation of cellular morphology. Mechanistic basis for the lack of effective intracellular signaling by non-attached epithelial cells is poorly understood. To examine whether signaling in suspended cells is regulated by Fer cytoplasmic tyrosine kinase, we investigated the effect of ectopic Fer expression on signaling in suspended or adherent hepatocytes. We found that ectopic Fer expression in Huh7 hepatocytes in suspension or on non-permissive poly-lysine caused significant phosphorylation of FAK Tyr577, Tyr861, or Tyr925, but not Tyr397 or Tyr576. Fer-mediated FAK phosphorylation in suspended cells was independent of c-Src activity or growth factor stimulation, but dependent of cortactin expression. Consistent with these results, complex formation between FAK, Fer, and cortactin was observed in suspended cells. The Fer-mediated effect correlated with multiple membrane protrusions, even on poly-lysine. Together, these observations suggest that Fer may allow a bypass of anchorage-dependency for intracellular signal transduction in hepatocytes.

Hsp90 and a tyrosine embedded in the Hsp90 recognition loop are required for the Fer tyrosine kinase activity

Hsp90 is a key regulator of tyrosine kinases activity and is therefore considered as a promising target for intervention with deregulated signaling pathways in malignant cells. Here we describe a novel Hsp90 client - the intracellular tyrosine kinase, Fer, which is subjected to a unique regulatory regime by this chaperone. Inhibition of Hsp90 activity led to proteasomal degradation of the Fer enzyme. However, circumventing the dependence of Fer accumulation on Hsp90, revealed the dependence of the Fer kinase activity and its ability to phosphorylate Stat3 on the chaperone, expressing the necessity of Hsp90 for its function. Mutation analysis unveiled a tyrosine (Tyr(616)) embedded in the Hsp90 recognition loop, which is required for the kinase activity of Fer. Replacement of this tyrosine by phenylalanine (Y616F) disabled the auto-phosphorylation activity of Fer and abolished its ability to phosphorylate Stat3. Notably, surrounding the replaced Y616F with subtle mutations restored the auto and trans-phosphorylation activities of Fer suggesting that Y(616) is not itself an essential auto-phosphorylation site of the kinase. Taken together, our results portray Hsp90 and its recognition loop as novel positive regulators of the Fer tyrosine kinase stability and activity.

Contributions of F-BAR and SH2 domains of Fes protein tyrosine kinase for coupling to the FcepsilonRI pathway in mast cells

This study investigates the roles of Fer-CIP4 homology (FCH)-Bin/amphiphysin/Rvs (F-BAR) and SH2 domains of Fes protein tyrosine kinase in regulating its activation and signaling downstream of the high-affinity immunoglobulin G (IgE) receptor (FcepsilonRI) in mast cells. Homology modeling of the Fes F-BAR domain revealed conservation of some basic residues implicated in phosphoinositide binding (R113/K114). The Fes F-BAR can bind phosphoinositides and induce tubulation of liposomes in vitro. Mutation of R113/K114 to uncharged residues (RK/QQ) caused a significant reduction in phosphoinositide binding in vitro and a more diffuse cytoplasmic localization in transfected COS-7 cells. RBL-2H3 mast cells expressing full-length Fes carrying the RK/QQ mutation show defects in FcepsilonRI-induced Fes tyrosine phosphorylation and degranulation compared to cells expressing wild-type Fes. This correlated with reduced localization to Lyn kinase-containing membrane fractions for the RK/QQ mutant compared to wild-type Fes in mast cells. The Fes SH2 domain also contributes to Fes signaling in mast cells, via interactions with the phosphorylated FcepsilonRI beta chain and the actin regulatory protein HS1. We show that Fes phosphorylates C-terminal tyrosine residues in HS1 implicated in actin stabilization. Thus, coordinated actions of the F-BAR and SH2 domains of Fes allow for coupling to FcepsilonRI signaling and potential regulation the actin reorganization in mast cells.

Structural coupling of SH2-kinase domains links Fes and Abl substrate recognition and kinase activation

The SH2 domain of cytoplasmic tyrosine kinases can enhance catalytic activity and substrate recognition, but the molecular mechanisms by which this is achieved are poorly understood. We have solved the structure of the prototypic SH2-kinase unit of the human Fes tyrosine kinase, which appears specialized for positive signaling. In its active conformation, the SH2 domain tightly interacts with the kinase N-terminal lobe and positions the kinase αC helix in an active configuration through essential packing and electrostatic interactions. This interaction is stabilized by ligand binding to the SH2 domain. Our data indicate that Fes kinase activation is closely coupled to substrate recognition through cooperative SH2-kinase-substrate interactions. Similarly, we find that the SH2 domain of the active Abl kinase stimulates catalytic activity and substrate phosphorylation through a distinct SH2-kinase interface. Thus, the SH2 and catalytic domains of active Fes and Abl pro-oncogenic kinases form integrated structures essential for effective tyrosine kinase signaling.

CD44-epidermal growth factor receptor interaction mediates hyaluronic acid-promoted cell motility by activating protein kinase C signaling involving Akt, Rac1, Phox, reactive oxygen species, focal adhesion kinase, and MMP-2

Hyaluronic acid (HA) is known to play an important role in motility of tumor cells. However, the molecular mechanisms associated with HA-promoted melanoma cell motility are not fully understood. Treatment of cells with HA was shown to increase the production of reactive oxygen species (ROS) in a CD44-dependent manner. Antioxidants, such as N-acetyl-l-cysteine and seleno-l-methionine, prevented HA from enhancing cell motility. Protein kinase C (PKC)-alpha and PKCdelta were responsible for increased Rac1 activity, production of ROS, and mediated HA-promoted cell motility. HA increased Rac1 activity via CD44, PKCalpha, and PKCdelta. Transfection with dominant negative and constitutive active Rac1 mutants demonstrated that Rac1 was responsible for the increased production of ROS and cell motility by HA. Inhibition of NADPH oxidase by diphenylene iodonium and down-regulation of p47Phox and p67Phox decreased the ROS level, suggesting that NADPH oxidase is the main source of ROS production. Rac1 increased phosphorylation of FAK. FAK functions downstream of and is necessary for HA-promoted cell motility. Secretion and expression of MMP-2 were increased by treatment with HA via the action of PKCalpha, PKCdelta, and Rac1 and the production of ROS and FAK. Ilomastat, an inhibitor of MMP-2, exerted a negative effect on HA-promoted cell motility. HA increased interaction between CD44 and epidermal growth factor receptor (EGFR). AG1478, an inhibitor of EGFR, decreased phosphorylation of PKCalpha, PKCdelta, and Rac1 activity and suppressed induction of p47Phox and p67Phox. These results suggest that CD44-EGFR interaction is necessary for HA-promoted cell motility by regulating PKC signaling. EGFR-Akt interaction promoted by HA was responsible for the increased production of ROS and HA-promoted cell motility. In summary, HA promotes CD44-EGFR interaction, which in turn activates PKC signaling, involving Akt, Rac1, Phox, and the production of ROS, FAK, and MMP-2, to enhance melanoma cell motility.

NOX enzymes as novel targets for drug development

The members of the NOX/DUOX family of NADPH oxidases mediate such physiologic functions as host defense, cell signaling, and thyroid hormone biosynthesis through the generation of reactive oxygen species (ROS), including superoxide anion and hydrogen peroxide. Moreover, ROS are involved in a broad range of fundamental biochemical and cellular processes, and data accumulated in recent years indicate that the NOX enzymes comprise one of the most important biological sources of ROS. Given the high biochemical reactivity of ROS, it is not surprising that they have been implicated in a wide variety of pathologies and diseases. Prominent among the settings that feature ROS-mediated tissue injury are disorders associated with inflammation, aging, and progressive degenerative changes in cells and organ systems, and it appears that essentially no organ system is exempt. Among the disorders currently believed to be mediated at least in part by NOX-derived ROS are hypertension, aortic aneurysm, myocardial infarction (and other ischemia-reperfusion disorders), pulmonary fibrosis and hypertension, amyotropic lateral sclerosis, Alzheimer's disease, Parkinson's disease, ischemic stroke, diabetic nephropathy, and renal cell carcinoma. Several small-molecule and peptide inhibitors of the NOX enzymes have been useful in experimental studies, but issues of specificity, potency, and toxicity militate against any of the existing published compounds as candidates for drug development. Given the broad array of disease targets documented in recent work, the time is here for vigorous efforts to develop clinically useful inhibitors of the NOX enzymes. As most (though not all) NOX-related diseases appear to be mediated by a single member of the NOX family, agents with isoform specificity will be preferred, although broadly active NOX inhibitors may prove to be useful in some settings.

From anchorage dependent proliferation to survival: lessons from redox signalling

Anchorage to extracellular matrix (ECM) is essential for the execution of the mitotic program of nontransformed cells as they need simultaneous signals starting from mitogenic molecules, as growth factors (GFs), and adhesive agents belonging to ECM. Reactive oxygen species play a key function during both GF and integrin receptor signalling and are therefore recognised to have a synergistic function with several others transducers for anchorage-dependent growth (ADG). Indeed, redox-regulated proteins include protein tyrosine phosphatases, protein tyrosine kinases, small GTPases, cytoskeleton proteins, as well as several transcription factors. In this review, we focus on the role of reactive oxygen species (ROS) as key second messengers granting a proper executed mitosis for anchorage-dependent cells through redox regulation of several downstream targets. Besides, redox signals elicited by ECM contact assure a protection from anoikis, a specific apoptosis induced by lack of anchorage. Cancer cells frequently show a deregulation of ROS production and a constitutive oxidative stress has been associated to the achievement of an invasive phenotype. Hence, in cancer cells, the constitutive deregulation of both mitogenic and survival pathways, likely mimicking autocrine/adhesive signals, helps to guide the transformed cells to escape the innate apoptotic response to abolish the signals started by cell/ECM contact, thus sustaining the spreading of anchorage-independent cancer cells and the metastases growth.

Cortactin in tumor invasiveness

Cortactin is a cytoskeletal protein and src kinase substrate that is frequently overexpressed in cancer. Animal studies suggest that cortactin overexpression increases tumor aggressiveness, possibly through promotion of tumor invasion and metastasis. Recently, many studies have documented a role for cortactin in promoting cell motility and invasion, including a critical role in invadopodia, actin rich-subcellular protrusions associated with degradation of the extracellular matrix by cancer cells. Here, I review the evidence and potential mechanisms for cortactin as a critical mediator of tumor cell invasion.

Cortactin adopts a globular conformation and bundles actin into sheets

Cortactin is a filamentous actin-binding protein that plays a pivotal role in translating environmental signals into coordinated rearrangement of the cytoskeleton. The dynamic reorganization of actin in the cytoskeleton drives processes including changes in cell morphology, cell migration, and phagocytosis. In general, structural proteins of the cytoskeleton bind in the N-terminal region of cortactin and regulatory proteins in the C-terminal region. Previous structural studies have reported an extended conformation for cortactin. It is therefore unclear how cortactin facilitates cross-talk between structural proteins and their regulators. In the study presented here, circular dichroism, chemical cross-linking, and small angle x-ray scattering are used to demonstrate that cortactin adopts a globular conformation, thereby bringing distant parts of the molecule into close proximity. In addition, the actin bundling activity of cortactin is characterized, showing that fully polymerized actin filaments are bundled into sheet-like structures. We present a low resolution structure that suggests how the various domains of cortactin interact to coordinate its array of binding partners at sites of actin branching.

Roles of F-BAR/PCH proteins in the regulation of membrane dynamics and actin reorganization

The Pombe Cdc15 Homology (PCH) proteins have emerged in many species as important coordinators of signaling pathways that regulate actomyosin assembly and membrane dynamics. The hallmark of the PCH proteins is the presence of a Fes/CIP4 homology-Bin/Amphiphysin/Rvsp (F-BAR) domain; therefore they are commonly referred to as F-BAR proteins. The prototype F-BAR protein, Cdc15p of Schizosaccharomyces pombe, has a role in the formation of the contractile actomyosin ring during cytokinesis. Vertebrate F-BAR proteins have an established role in binding phospholipids and they participate in membrane deformations, for instance, during the internalization of transmembrane receptors. This way the F-BAR proteins will function as linkers between the actin polymerization apparatus and the machinery regulating membrane dynamics. Interestingly, some members of the F-BAR proteins are implicated in inflammatory or neurodegenerative disorders and the observations can be expected to have clinical implications for the treatment of the diseases.

The role of reactive oxygen species in integrin and matrix metalloproteinase expression and function

Cell adhesion and migration is largely dependent on integrin binding to extracellular matrix, and several signalling pathways involved in these processes have been shown to be modified by reactive oxygen species (ROS). In fact, integrin activation is linked to increased ROS production by NADPH-oxidases, 5-lipoxygenase, and release from mitochondria. Cell migration is intimately linked to degradation of the extracellular matrix, and activated matrix metalloproteinases (MMPs) are a prerequisite for cancer cell invasion and metastasis. In this minireview, we focus on the interplay between integrin-mediated ROS production and MMP expression as well as its biological and pathobiological significance.

The Fer tyrosine kinase regulates an axon retraction response to Semaphorin 3A in dorsal root ganglion neurons

Background

Fps/Fes and Fer are the only two members of a distinct subclass of cytoplasmic protein tyrosine kinases. Fps/Fes was previously implicated in Semaphorin 3A (Sema3A)-induced growth cone collapse signaling in neurons from the dorsal root ganglion (DRG) through interaction with and phosphorylation of the Sema3A receptor component PlexinA1, and members of the collapsin response mediator protein (CRMP) family of microtubule regulators. However, the potential role of the closely related Fer kinase has not been examined.

Results

Here we provide novel biochemical and genetic evidence that Fer plays a prominent role in microtubule regulation in DRG neurons in response to Sema3A. Although Fps/Fes and Fer were both expressed in neonatal brains and isolated DRGs, Fer was expressed at higher levels; and Fer, but not Fps/Fes kinase activity was detected in vivo. Fer also showed higher in vitro kinase activity toward tubulin, as an exogenous substrate; and this activity was higher when the kinases were isolated from perinatal relative to adult brain stages. CRMP2 was a substrate for both kinases in vitro, but both CRMP2 and PlexinA1 inhibited their autophosphorylation activities. Cultured mouse DRG neurons retracted their axons upon exposure to Sema3A, and this response was significantly diminished in Fer-deficient, but only slightly attenuated in Fps/Fes-deficient DRG neurons.

Conclusion

Fps/Fes and Fer are both capable of phosphorylating tubulin and the microtubule regulator CRMP2 in vitro; and their in vitro kinase activities were both inhibited by CRMP2 or PlexinA1, suggesting a possible regulatory interaction. Furthermore, Fer plays a more prominent role than Fps/Fes in regulating the axon retraction response to Sema3A in DRG neurons. Therefore, Fps/Fes and Fer may play important roles in developmental or regenerative axon pathfinding through signaling from Sema3A to the microtubule cytoskeleton.