p130cas but not paxillin is essential for Caco-2 intestinal epithelial cell spreading and migration on collagen IV

Focal Adhesion Kinase and Colony Stimulating Factors: Intestinal Homeostasis and Innate Immunity Crosstalk

Thousands struggle with acute and chronic intestinal injury due to various causes. Epithelial intestinal healing is dependent on phenotypic transitions to a mobile phenotype. Focal adhesion kinase (FAK) is a ubiquitous protein that is essential for cell mobility. This phenotype change is mediated by FAK activation and proves to be a promising target for pharmaceutical intervention. While FAK is crucial for intestinal healing, new evidence connects FAK with innate immunity and the importance it plays in macrophage/monocyte chemotaxis, as well as other intracellular signaling cascades. These cascades play a part in macrophage/monocyte polarization, maturation, and inflammation that is associated with intestinal injury. Colony stimulating factors (CSFs) such as macrophage colony stimulating factor (M-CSF/CSF-1) and granulocyte macrophage colony stimulating factor (GM-CSF/CSF-2) play a critical role in maintaining homeostasis within intestinal mucosa by crosstalk capabilities between macrophages and epithelial cells. The communication between these cells is imperative in orchestrating healing upon injury. Diving deeper into these connections may allow us a greater insight into the role that our immune system plays in healing, as well as a better comprehension of inflammatory diseases of the gut.

Cas phosphorylation regulates focal adhesion assembly

Integrin-mediated cell attachment rapidly induces tyrosine kinase signaling. Despite years of research, the role of this signaling in integrin activation and focal adhesion assembly is unclear. We provide evidence that the Src-family kinase (SFK) substrate Cas (Crk-associated substrate, p130Cas, BCAR1) is phosphorylated and associated with its Crk/CrkL effectors in clusters that are precursors of focal adhesions. The initial phospho-Cas clusters contain integrin β1 in its inactive, bent closed, conformation. Later, phospho-Cas and total Cas levels decrease as integrin β1 is activated and core focal adhesion proteins including vinculin, talin, kindlin, and paxillin are recruited. Cas is required for cell spreading and focal adhesion assembly in epithelial and fibroblast cells on collagen and fibronectin. Cas cluster formation requires Cas, Crk/CrkL, SFKs, and Rac1 but not vinculin. Rac1 provides positive feedback onto Cas through reactive oxygen, opposed by negative feedback from the ubiquitin proteasome system. The results suggest a two-step model for focal adhesion assembly in which clusters of phospho-Cas, effectors and inactive integrin β1 grow through positive feedback prior to integrin activation and recruitment of core focal adhesion proteins.

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

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

Gut homeostasis, injury, and healing: New therapeutic targets

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

Endothelial p130cas confers resistance to anti-angiogenesis therapy

Anti-angiogenic therapies, such as anti-VEGF antibodies (AVAs), have shown promise in clinical settings. However, adaptive resistance to such therapies occurs frequently. We use orthotopic ovarian cancer models with AVA-adaptive resistance to investigate the underlying mechanisms. Genomic profiling of AVA-resistant tumors guides us to endothelial p130cas. We find that bevacizumab induces cleavage of VEGFR2 in endothelial cells by caspase-10 and that VEGFR2 fragments internalize into the nucleus and autophagosomes. Nuclear VEGFR2 and p130cas fragments, together with TNKS1BP1 (tankyrase-1-binding protein), initiate endothelial cell death. Blockade of autophagy in AVA-resistant endothelial cells retains VEGFR2 at the membrane with bevacizumab treatment. Targeting host p130cas with RGD (Arg-Gly-Asp)-tagged nanoparticles or genomic ablation of vascular p130cas in p130casflox/floxTie2Cre mice significantly extends the survival of mice with AVA-resistant ovarian tumors. Higher vascular p130cas is associated with shorter survival of individuals with ovarian cancer. Our findings identify opportunities for new strategies to overcome adaptive resistance to AVA therapy.

A Cas-BCAR3 co-regulatory circuit controls lamellipodia dynamics

Integrin adhesion complexes regulate cytoskeletal dynamics during cell migration. Adhesion activates phosphorylation of integrin-associated signaling proteins, including Cas (p130Cas, BCAR1), by Src-family kinases. Cas regulates leading-edge protrusion and migration in cooperation with its binding partner, BCAR3. However, it has been unclear how Cas and BCAR3 cooperate. Here, using normal epithelial cells, we find that BCAR3 localization to integrin adhesions requires Cas. In return, Cas phosphorylation, as well as lamellipodia dynamics and cell migration, requires BCAR3. These functions require the BCAR3 SH2 domain and a specific phosphorylation site, Tyr 117, that is also required for BCAR3 downregulation by the ubiquitin-proteasome system. These findings place BCAR3 in a co-regulatory positive-feedback circuit with Cas, with BCAR3 requiring Cas for localization and Cas requiring BCAR3 for activation and downstream signaling. The use of a single phosphorylation site in BCAR3 for activation and degradation ensures reliable negative feedback by the ubiquitin-proteasome system.

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

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

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

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

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

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

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

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

Tyrosine phosphatase SHP2 increases cell motility in triple-negative breast cancer through the activation of SRC-family kinases

Tumor cell migration has a fundamental role in early steps of metastasis, the fatal hallmark of cancer. In the present study, we investigated the effects of the tyrosine phosphatase, SRC-homology 2 domain-containing phosphatase 2 (SHP2), on cell migration in metastatic triple-negative breast cancer (TNBC), an aggressive disease associated with a poor prognosis for which a targeted therapy is not yet available. Using mouse models and multiphoton intravital imaging, we have identified a crucial effect of SHP2 on TNBC cell motility in vivo. Further, analysis of TNBC cells revealed that SHP2 also influences cell migration, chemotaxis and invasion in vitro. Unbiased phosphoproteomics and biochemical analysis showed that SHP2 activates several SRC-family kinases and downstream targets, most of which are inducers of migration and invasion. In particular, direct interaction between SHP2 and c-SRC was revealed by a fluorescence resonance energy transfer assay. These results suggest that SHP2 is a crucial factor during early steps of TNBC migration to distant organs.

N-WASP-directed actin polymerization activates Cas phosphorylation and lamellipodium spreading

Tyrosine phosphorylation of the substrate domain of Cas (CasSD) correlates with increased cell migration in healthy and diseased cells. Here, we address the mechanism leading to the phosphorylation of CasSD in the context of fibronectin-induced early spreading of fibroblasts. We have previously demonstrated that mechanical stretching of CasSD exposes phosphorylation sites for Src family kinases (SFKs). Surprisingly, phosphorylation of CasSD was independent of myosin contractile activity but dependent on actin polymerization. Furthermore, we found that CasSD phosphorylation in the early stages of cell spreading required: (1) integrin anchorage and integrin-mediated activation of SFKs, (2) association of Cas with focal adhesion kinase (FAK), and (3) N-WASP-driven actin-assembly activity. These findings, and analyses of the interactions of the Cas domains, indicate that the N-terminus of Cas associates with the FAK-N-WASP complex at the protrusive edge of the cell and that the C-terminus of Cas associates with the immobilized integrin-SFK cluster. Thus, extension of the leading edge mediated by actin polymerization could stretch Cas during early cell spreading, priming it for phosphorylation.

Netrin-1 attracts axons through FAK-dependent mechanotransduction

The mechanism by which extracellular cues influence intracellular biochemical cascades that guide axons is important, yet poorly understood. Because of the mechanical nature of axon extension, we explored whether the physical interactions of growth cones with their guidance cues might be involved. In the context of mouse spinal commissural neuron axon attraction to netrin-1, we found that mechanical attachment of netrin-1 to the substrate was required for axon outgrowth, growth cone expansion, axon attraction and phosphorylation of focal adhesion kinase (FAK) and Crk-associated substrate (CAS). Myosin II activity was necessary for traction forces >30 pN on netrin-1. Interestingly, while these myosin II-dependent forces on netrin-1 substrates or beads were needed to increase the kinase activity and phosphorylation of FAK, they were not necessary for netrin-1 to increase CAS phosphorylation. When FAK kinase activity was inhibited, the growth cone's ability to recruit additional adhesions and to generate forces >60 pN on netrin-1 was disrupted. Together, these findings demonstrate an important role for mechanotransduction during chemoattraction to netrin-1 and that mechanical activation of FAK reinforces interactions with netrin-1 allowing greater forces to be exerted.

Paxillin mediates sensing of physical cues and regulates directional cell motility by controlling lamellipodia positioning

Physical interactions between cells and the extracellular matrix (ECM) guide directional migration by spatially controlling where cells form focal adhesions (FAs), which in turn regulate the extension of motile processes. Here we show that physical control of directional migration requires the FA scaffold protein paxillin. Using single-cell sized ECM islands to constrain cell shape, we found that fibroblasts cultured on square islands preferentially activated Rac and extended lamellipodia from corner, rather than side regions after 30 min stimulation with PDGF, but that cells lacking paxillin failed to restrict Rac activity to corners and formed small lamellipodia along their entire peripheries. This spatial preference was preceded by non-spatially constrained formation of both dorsal and lateral membrane ruffles from 5-10 min. Expression of paxillin N-terminal (paxN) or C-terminal (paxC) truncation mutants produced opposite, but complementary, effects on lamellipodia formation. Surprisingly, pax-/- and paxN cells also formed more circular dorsal ruffles (CDRs) than pax+ cells, while paxC cells formed fewer CDRs and extended larger lamellipodia even in the absence of PDGF. In a two-dimensional (2D) wound assay, pax-/- cells migrated at similar speeds to controls but lost directional persistence. Directional motility was rescued by expressing full-length paxillin or the N-terminus alone, but paxN cells migrated more slowly. In contrast, pax-/- and paxN cells exhibited increased migration in a three-dimensional (3D) invasion assay, with paxN cells invading Matrigel even in the absence of PDGF. These studies indicate that paxillin integrates physical and chemical motility signals by spatially constraining where cells will form motile processes, and thereby regulates directional migration both in 2D and 3D. These findings also suggest that CDRs may correspond to invasive protrusions that drive cell migration through 3D extracellular matrices.

Protein-tyrosine kinase 6 promotes peripheral adhesion complex formation and cell migration by phosphorylating p130 CRK-associated substrate

Protein-tyrosine kinase 6 (PTK6) is a non-myristoylated intracellular tyrosine kinase evolutionarily related to Src kinases. Aberrant PTK6 expression and intracellular localization have been detected in human prostate tumors. In the PC3 prostate cancer cell line, the pool of endogenous activated PTK6, which is phosphorylated on tyrosine residue 342, is localized at the membrane. Expression of ectopic membrane-targeted PTK6 led to dramatic morphology changes and formation of peripheral adhesion complexes in PC3 cells. Peripheral adhesion complex formation was dependent upon PTK6 kinase activity. We demonstrated that p130 CRK-associated substrate (p130CAS) is a novel direct substrate of PTK6, and it works as a crucial adapter protein in inducing peripheral adhesion complexes. Activation of ERK5 downstream of p130CAS was indispensable for this process. Knockdown of endogenous PTK6 led to reduced cell migration and p130CAS phosphorylation, whereas knockdown of p130CAS attenuated oncogenic signaling induced by membrane-targeted PTK6, including ERK5 and AKT activation. Expression of membrane-targeted PTK6 promoted cell migration, which could be impaired by knockdown of p130CAS or ERK5. Our study reveals a novel function for PTK6 at the plasma membrane and suggests that the PTK6-p130CAS-ERK5 signaling cascade plays an important role in cancer cell migration and invasion.

Silencing of p130cas in ovarian carcinoma: a novel mechanism for tumor cell death

BACKGROUND

We investigated the clinical and biological significance of p130cas, an important cell signaling molecule, in ovarian carcinoma.

METHODS

Expression of p130cas in ovarian tumors, as assessed by immunohistochemistry, was associated with tumor characteristics and patient survival. The effects of p130cas gene silencing with small interfering RNAs incorporated into neutral nanoliposomes (siRNA-DOPC), alone and in combination with docetaxel, on in vivo tumor growth and on tumor cell proliferation (proliferating cell nuclear antigen) and apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling) were examined in mice bearing orthotopic taxane-sensitive (HeyA8 and SKOV3ip1) or taxane-resistant (HeyA8-MDR) ovarian tumors (n = 10 per group). To determine the specific mechanisms by which p130cas gene silencing abrogates tumor growth, we measured cell viability (MTT assay), apoptosis (fluorescence-activated cell sorting), autophagy (immunoblotting, fluorescence, and transmission electron microscopy), and cell signaling (immunoblotting) in vitro. All statistical tests were two-sided.

RESULTS

Of 91 ovarian cancer specimens, 70 (76%) had high p130cas expression; and 21 (24%) had low p130cas expression. High p130cas expression was associated with advanced tumor stage (P < .001) and higher residual disease (>1 cm) following primary cytoreduction surgery (P = .007) and inversely associated with overall survival and progression-free survival (median overall survival: high p130cas expression vs low expression, 2.14 vs 9.1 years, difference = 6.96 years, 95% confidence interval = 1.69 to 9.48 years, P < .001; median progression-free survival: high p130cas expression vs low expression, 1.04 vs 2.13 years, difference = 1.09 years, 95% confidence interval = 0.47 to 2.60 years, P = .01). In mice bearing orthotopically implanted HeyA8 or SKOV3ip1 ovarian tumors, treatment with p130cas siRNA-DOPC in combination with docetaxel chemotherapy resulted in the greatest reduction in tumor growth compared with control siRNA therapy (92%-95% reduction in tumor growth; P < .001 for all). Compared with control siRNA therapy, p130cas siRNA-DOPC reduced SKOV3ip1 cell proliferation (31% reduction, P < .001) and increased apoptosis (143% increase, P < .001) in vivo. Increased tumor cell apoptosis may have persisted despite pan-caspase inhibition by the induction of autophagy and related signaling pathways.

CONCLUSIONS

Increased p130cas expression is associated with poor clinical outcome in human ovarian carcinoma, and p130cas gene silencing decreases tumor growth through stimulation of apoptotic and autophagic cell death.

Leupaxin is similar to paxillin in focal adhesion targeting and tyrosine phosphorylation but has distinct roles in cell adhesion and spreading

Focal adhesion (FA) formation is induced by extracellular matrix-stimulated integrin clustering and activation of receptors for diffusible factors. Leupaxin (LPXN) is a member of the paxillin family of FA proteins expressed in many cancer cell lines. We found activation of gastrin-releasing peptide receptor (GRPr) by bombesin (BN) stimulated LPXN translocation from cytoplasm to FAs. Using mutagenesis, we identified LIM3 as the primary FA targeting domain for LPXN and showed BN-induced LPXN tyrosine phosphorylation on residues 22, 62 and 72. A LIM3 point mutant of LPXN failed to target to FAs and had no BN-stimulated tyrosine phosphorylation. Conversely, a non-phosphorylatable mutant (Y22/62/72F) translocated to FAs after BN addition. Stimulation of FA formation using vinblastine also induced LPXN translocation and tyrosine phosphorylation. Therefore, dynamic LPXN tyrosine phosphorylation requires translocation to FAs. LPXN and paxillin had opposite roles in adhesion to collagen I (CNI) in MDA-MB-231 breast cancer cells. LPXN siRNA stimulated whereas paxillin siRNA inhibited cell adhesion. Knockdown of both LPXN and paxillin behaved similarly to paxillin knockdown alone, suggesting LPXN’s function in adhesion might depend on paxillin. Additionally, LPXN regulated cell spreading on CNI but not on fibronectin whereas paxillin knockdown suppressed spreading on both substrates. These results demonstrate that although LPXN and paxillin’s FA targeting and tyrosine phosphorylation are similar, each protein has distinct functions.

β2 integrin induces TCRζ-Syk-phospholipase C-γ phosphorylation and paxillin-dependent granule polarization in human NK cells

Cytotoxic lymphocytes kill target cells through polarized release of the content of lytic granules at the immunological synapse. In human NK cells, signals for granule polarization and for degranulation can be uncoupled: Binding of β(2) integrin LFA-1 to ICAM is sufficient to induce polarization but not degranulation, whereas CD16 binding to IgG triggers unpolarized degranulation. In this study, we investigated the basis for this difference. IL-2-expanded human NK cells were stimulated by incubation with plate-bound ligands of LFA-1 (ICAM-1) and CD16 (human IgG). Surprisingly, LFA-1 elicited signals similar to those induced by CD16, including tyrosine phosphorylation of the TCR ζ-chain, tyrosine kinase Syk, and phospholipase C-γ. Whereas CD16 activated Ca(2+) mobilization and LAT phosphorylation, LFA-1 did not, but induced strong Pyk2 and paxillin phosphorylation. LFA-1-dependent granule polarization was blocked by inhibition of Syk, phospholipase C-γ, and protein kinase C, as well as by paxillin knockdown. Therefore, common signals triggered by CD16 and LFA-1 bifurcate to provide independent control of Ca(2+)-dependent degranulation and paxillin-dependent granule polarization.

CAS proteins in normal and pathological cell growth control

Proteins of the CAS (Crk-associated substrate) family (BCAR1/p130Cas, NEDD9/HEF1/Cas-L, EFS/SIN and CASS4/HEPL) are integral players in normal and pathological cell biology. CAS proteins act as scaffolds to regulate protein complexes controlling migration and chemotaxis, apoptosis, cell cycle, and differentiation, and have more recently been linked to a role in progenitor cell function. Reflecting these complex functions, over-expression of CAS proteins has now been strongly linked to poor prognosis and increased metastasis in cancer, as well as resistance to first-line chemotherapeutics in multiple tumor types including breast and lung cancers, glioblastoma, and melanoma. Further, CAS proteins have also been linked to additional pathological conditions including inflammatory disorders, Alzheimer's and Parkinson's disease, as well as developmental defects. This review will explore the roles of the CAS proteins in normal and pathological states in the context of the many mechanistic insights into CAS protein function that have emerged in the past decade.

p130Cas substrate domain signaling promotes migration, invasion, and survival of estrogen receptor-negative breast cancer cells

Elevated Src tyrosine kinase activity is commonly observed in breast cancer and likely contributes to neoplasia and malignancy. p130Cas ("Crk-associated substrate") is a major Src substrate found at the sites where integrins mediate cell adhesion to the extracellular matrix. Src phosphorylates multiple tyrosines in the p130Cas "substrate domain" (SD) and this signaling event has been implicated in the promotion of cell motility, primarily from studies on fibroblasts. In breast cancer, studies on p130Cas have focused on its role in conferring antiestrogen resistance to cells that express the estrogen receptor (ER+). However, little is known regarding the role of p130Cas in the more aggressive estrogen receptor negative (ER-) breast cancers for which there is a need for development of effective targeted therapies. We found high levels of p130Cas SD tyrosine phosphorylation to be a common characteristic of ER- breast cancer cell lines, with particularly high levels observed for the BT-549 cell line. Using RNA interference to knock down p130Cas expression in BT-549 cells, combined with rescue by WT p130Cas versus a signaling-deficient control, we provide evidence that p130Cas SD tyrosine phosphorylation is an important signaling event in the migration, invasion, proliferation, and survival of this ER-breast cancer cell line.

Breast carcinoma cells in primary tumors and effusions have different gene array profiles

The detection of breast carcinoma cells in effusions is associated with rapidly fatal outcome, but these cells are poorly characterized at the molecular level. This study compared the gene array signatures of breast carcinoma cells in primary carcinomas and effusions. The genetic signature of 10 primary tumors and 10 effusions was analyzed using the Array-Ready Oligo set for the Human Genome platform. Results for selected genes were validated using PCR, Western blotting, and immunohistochemistry. Array analysis identified 255 significantly downregulated and 96 upregulated genes in the effusion samples. The majority of differentially expressed genes were part of pathways involved in focal adhesion, extracellular matrix-cell interaction, and the regulation of the actin cytoskeleton. Genes that were upregulated in effusions included KRT8, BCAR1, CLDN4, VIL2, while DCN, CLDN19, ITGA7, and ITGA5 were downregulated at this anatomic site. PCR, Western blotting, and immunohistochemistry confirmed the array findings for BCAR1, CLDN4, VIL2, and DCN. Our data show that breast carcinoma cells in primary carcinomas and effusions have different gene expression signatures, and differentially express a large number of molecules related to adhesion, motility, and metastasis. These differences may have a critical role in designing therapy and in prognostication for patients with metastatic disease localized to the serosal cavities.

Propofol inhibits pressure-stimulated macrophage phagocytosis via the GABAA receptor and dysregulation of p130cas phosphorylation

Surgical stress and anesthesia result in systemic immunosuppression. Propofol, a commonly used anesthetic agent, alters immune cell functions. Previously, we demonstrated that extracellular pressure increases macrophage phagocytosis. We hypothesized that propofol might influence pressure-induced macrophage phagocytosis in monocytes from patients undergoing surgery. Pressure (20 mmHg above ambient pressure) augmented phagocytosis in monocytes from non-propofol-anesthetized patients but reduced phagocytosis in monocytes from propofol-anesthetized patients. In vitro, propofol stimulated phagocytosis but reversed pressure-induced phagocytosis in THP-1 macrophages and monocytes from healthy volunteers. The GABA(A) receptor antagonists picrotoxin and SR-95531 did not affect basal THP-1 phagocytosis or prevent pressure-stimulated phagocytosis. However, picrotoxin and SR-95531 negated the inhibitory effect of pressure in propofol-treated cells without altering propofol-induced phagocytosis. Phosphorylation of the adaptor protein p130cas was inversely related to phagocytosis: it was inhibited by pressure or propofol but increased by pressure + propofol compared with propofol alone. Reduction of p130cas by small interfering RNA in THP-1 macrophages increased basal phagocytosis and prevented pressure and propofol effects. In conclusion, propofol may alter macrophage responses to pressure via the GABA(A) receptor and p130cas, whereas pressure also acts via p130cas but independently of GABA(A) receptors. p130cas may be an important target for modulation of macrophage function in anesthetized patients.

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

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

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

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

Differential involvement of destrin and cofilin-1 in the control of invasive properties of Isreco1 human colon cancer cells

Actin depolymerizing factor (ADF)/cofilin family proteins are key regulators of actin filament turnover and cytoskeleton reorganization. The role of cofilin-1 in cell motility has been demonstrated in several cell types but remained poorly documented in the case of colon cancer. In addition, the putative function of destrin (also known as ADF) had not been explored in this context despite the fact that it is expressed in all colon cancer cell lines examined. We were therefore prompted to evaluate the respective contributions of these proteins to the invasive properties of the human colon cancer Isreco1 cell line, which expresses a comparatively high destrin/cofilin ratio. Reduction of cofilin-1 or destrin expression in Isreco1 cells using RNA interference led to an increase of the number of multinucleated cells and altered polarized lamellipodium protrusion and distribution of paxillin-containing adhesions. Both cofilin-1 and destrin silencing enhanced cell adhesion to extracellular matrix components. However, only destrin appeared to be required for cell migration on collagen I and for cell invasion through Matrigel in response to the proinvasive neuroendocrine peptide bombesin. This differential functional involvement was supported by a destrin-dependent, cofilin-independent phosphorylation of p130Crk-associated substrate (p130Cas) upon cell adhesion to collagen I or Matrigel. Taken together, our results suggest that destrin is a significant regulator of various processes important for invasive phenotype of human colon cancer Isreco1 cells whereas cofilin-1 may be involved in only a subset of them.

Alpha-actinin-1 phosphorylation modulates pressure-induced colon cancer cell adhesion through regulation of focal adhesion kinase-Src interaction

Physical forces including pressure, strain, and shear can be converted into intracellular signals that regulate diverse aspects of cell biology. Exposure to increased extracellular pressure stimulates colon cancer cell adhesion by a beta(1)-integrin-dependent mechanism that requires an intact cytoskeleton and activation of focal adhesion kinase (FAK) and Src. alpha-Actinin facilitates focal adhesion formation and physically links integrin-associated focal adhesion complexes with the cytoskeleton. We therefore hypothesized that alpha-actinin may be necessary for the mechanical response pathway that mediates pressure-stimulated cell adhesion. We reduced alpha-actinin-1 and alpha-actinin-4 expression with isoform-specific small interfering (si)RNA. Silencing of alpha-actinin-1, but not alpha-actinin-4, blocked pressure-stimulated cell adhesion in human SW620, HT-29, and Caco-2 colon cancer cell lines. Cell exposure to increased extracellular pressure stimulated alpha-actinin-1 tyrosine phosphorylation and alpha-actinin-1 interaction with FAK and/or Src, and enhanced FAK phosphorylation at residues Y397 and Y576. The requirement for alpha-actinin-1 phosphorylation in the pressure response was investigated by expressing the alpha-actinin-1 tyrosine phosphorylation mutant Y12F in the colon cancer cells. Expression of Y12F blocked pressure-mediated adhesion and inhibited the pressure-induced association of alpha-actinin-1 with FAK and Src, as well as FAK activation. Furthermore, siRNA-mediated reduction of alpha-actinin-1 eliminated the pressure-induced association of alpha-actinin-1 and Src with beta(1)-integrin receptor, as well as FAK-Src complex formation. These results suggest that alpha-actinin-1 phosphorylation at Y12 plays a crucial role in pressure-activated cell adhesion and mechanotransduction by facilitating Src recruitment to beta(1)-integrin, and consequently the association of FAK with Src, to enhance FAK phosphorylation.

Identification of functional domains in AKT responsible for distinct roles of AKT isoforms in pressure-stimulated cancer cell adhesion

Cell adhesion is a critical step in cancer metastasis, activated by extracellular forces such as pressure and shear. Reducing AKT1, but not AKT2, ablates the increase in cancer cell adhesion associated with 15 mm Hg increased extracellular pressure. To identify the determinants of this AKT isoform specificity, we exchanged the pleckstrin homology (PH) domains and/or hinge regions of AKT1 and AKT2. Wild type isoforms or these chimeras were overexpressed in Caco-2 cells in the absence or presence of isoform-specific siRNA to suppress endogenous AKT1. Pressure-induced AKT translocation and phosphorylation to the membrane were compared, along with the stimulation of cell adhesion by pressure. Pressure stimulated translocation of AKT1, but not AKT2 to the plasma membrane. Among our chimeras, only the chimeric AKT2 (chimera2), in which both the AKT2 PH domain and hinge region had been replaced by those of AKT1, translocated to the membrane in response to pressure. Similarly, only chimera2 rescued the function of AKT1 in mediating pressure-stimulated adhesion after endogenous AKT1 had been reduced. Pressure also promoted phosphorylation of AKT1 but not AKT2, and expression of a nonphosphorylatable double point mutant prevented pressure-stimulated adhesion. Among the chimeras, pressure promoted only chimera2 phosphorylation. These results identify the AKT1 PH domain and hinge region as functional domains which jointly permit AKT1 translocation and phosphorylation in response to extracellular pressure and distinguish determine the specificity of AKT1 in mediating the effects of extracellular pressure on cancer cell adhesion. These may be useful targets for interventions to inhibit metastasis.

Invasion of host cells by Salmonella typhimurium requires focal adhesion kinase and p130Cas

Salmonella typhimurium colonizes the intestinal epithelium by injecting an array of effector proteins into host cells that induces phagocytic uptake of attached bacteria. However, the host molecules targeted by these effectors remain poorly defined. Here, we demonstrate that S. typhimurium induces formation of focal adhesion-like complexes at sites of bacterial attachment and that both focal adhesion kinase (FAK) and the scaffolding protein p130Cas are required for Salmonella uptake. Entry of Salmonella into FAK(-/-) cells is dramatically impaired and can be restored to control levels by expression of wild-type FAK. Surprisingly, reconstitution of bacterial internalization requires neither the kinase domain of FAK nor activation of c-Src, but does require a C-terminal PXXP motif through which FAK interacts with Cas. Infection of Cas(-/-) cells is also impaired, and reconstitution of invasiveness requires the central Cas YXXP repeat domain. The invasion defect in Cas(-/-) cells can be suppressed by overexpression of FAK, suggesting a functional link between FAK and Cas in the regulation of Salmonella invasion. Together, these findings reveal a novel role for focal adhesion proteins in the invasion of host cells by Salmonella.

SRC uses Cas to suppress Fhl1 in order to promote nonanchored growth and migration of tumor cells

Anchorage independence and motility are hallmarks of tumor cell growth. Tumor cell growth and morphology can be normalized by contact with nontransformed cells. The Src tyrosine kinase phosphorylates specific sites on the focal adhesion adaptor protein Crk-associated substrate (Cas) to promote nonanchored cell growth and migration. We studied the effects of Src and Cas on the expression of >14,000 genes to identify molecular events that underlie these activities. Gene expression in tumor cells that were normalized by neighboring nontransformed cells was used as an additional filter to identify genes that control metastatic cell growth. This process enabled the identification of genes that play roles in anchorage-independent cell growth and migration. One candidate, four and a half LIM domains 1 (Fhl1), acts as a transcriptional regulator that can associate with cell junctions as well as with the nucleus. We show here that Src phosphorylates Cas to block Fhl1 expression. In addition, suppression of Fhl1 is required for Src to promote tumor cell growth. These data show that Fhl1 is a tumor suppressor gene that acts downstream of Src and Cas to specifically block anchorage-independent cell growth and migration. Moreover, Fhl1 was suppressed in tumors from several human tissues. Thus, identification of how Fhl1 controls fundamental aspects of tumor cell growth and metastasis may lead to the development of novel markers that can be used to diagnose human clinical specimens as well as open innovative avenues of investigations aimed at developing reagents that target cancer cells while minimizing damage to normal cells.