Association Of Focal Adhesion Kinase Research Articles

ORP2 couples LDL‐cholesterol transport to FAK activation by endosomal cholesterol/PI(4,5)P2 exchange

Low‐density lipoprotein (LDL)‐cholesterol delivery from late endosomes to the plasma membrane regulates focal adhesion dynamics and cell migration, but the mechanisms controlling it are poorly characterized. Here, we employed auxin‐inducible rapid degradation of oxysterol‐binding protein‐related protein 2 (ORP2/OSBPL2) to show that endogenous ORP2 mediates the transfer of LDL‐derived cholesterol from late endosomes to focal adhesion kinase (FAK)‐/integrin‐positive recycling endosomes in human cells. In vitro, cholesterol enhances membrane association of FAK to PI(4,5)P2‐containing lipid bilayers. In cells, ORP2 stimulates FAK activation and PI(4,5)P2 generation in endomembranes, enhancing cell adhesion. Moreover, ORP2 increases PI(4,5)P2 in NPC1‐containing late endosomes in a FAK‐dependent manner, controlling their tubulovesicular trafficking. Together, these results provide evidence that ORP2 controls FAK activation and LDL‐cholesterol plasma membrane delivery by promoting bidirectional cholesterol/PI(4,5)P2 exchange between late and recycling endosomes.

Atezolizumab potentiates Tcell-mediated cytotoxicity and coordinates with FAK to suppress cell invasion and motility in PD-L1+ triple negative breast cancer cells

ABSTRACTImmune check point inhibitors targeting programmed cell death protein-1 (PD-1) and its ligand (PD-L1) have shown clinical success in treatment of human malignancies. Triple negative breast cancer (TNBC), which is primarily characterized by high heterogeneity and presence of tumor infiltrating lymphocytes, remains therapeutic challenge due to unavailability of approved targeted therapy. Therapeutic potential of immune check point inhibitors for TNBC patients is under active clinical investigation. In this study, we show that FDA-approved anti-PD-L1 antibody, atezolizumab (ATE), potentiates T cell-mediated cytotoxicity and apoptosis of TNBC cells that express higher levels of PD-L1, but does not have significant effect on TNBC cells expressing low levels of PD-L1. PD-L1 knockdown further confirmed that ability of ATE to promote T cell-induced cytotoxicity is PD-L1 expression dependent. Combination of ATE with PD-L1 upregulating agents, such as HDAC, proteasomal, and lysosomal inhibitors, further augmented cytotoxic activity of T cells toward TNBC cells. Based on analysis of breast cancer tissue samples deposited in The Cancer Genome Atlas (TCGA), we found a positive correlation between PD-L1 and focal adhesion kinase (FAK) mRNA expression in PD-L1-positive (PD-L1+) TNBC, suggesting a functional association of FAK and immune checkpoints. We further demonstrate that ATE dramatically downregulates phosphorylation status of FAK, an important regulator of cell invasion and migration, and significantly enhances FAK inhibitor mediated inhibition of cell motility and invasion of PD-L1+ TNBC cells independent of T cells. Taken together, our data suggest that ATE shows promising anti-tumor activity in PD-L1+ TNBC via both T cell-dependent and -independent mechanisms.

Quercetin Prevents Escherichia coli O157:H7 Adhesion to Epithelial Cells via Suppressing Focal Adhesions.

The attachment of Escherichia coli O157:H7 to intestinal epithelial cells is indispensable for its pathogenesis. Besides translocated-intimin receptor (Tir), E. coli O157:H7 interacts with host cell surface receptors to promote intimate adhesion. This study showed that integrin β1 was increased in Caco-2 cells upon E. coli O157:H7 infection, while Caco-2 cells subjected to integrin β1 antibody blocking or CRISPR/Cas9 knockout had reduced bacterial attachment. Infection of E. coli O157:H7 inactivated focal adhesion kinase (FAK) and paxillin, increased focal adhesion (FA) and actin polymerization, and decreased cell migration in Caco-2 cells, which were rescued by integrin β1 antibody blocking or knockout. Pre-treatment with quercetin, known for its anti-oxidant and anti-inflammatory activity, reduced bacterial infection to Caco-2 cells, which might be partially via interfering integrin β1 and FAK association augmented by E. coli O157:H7. In addition, quercetin decreased FA formation induced by bacterial infection and recovered host cell motility. Taken together, data showed that E. coli O157:H7 interacts with integrin β1 to facilitate its adhesion to host cells. Quercetin inhibits bacterial infection possibly by blocking the interaction between E. coli O157:H7 and integrin β1. Collectively, these data indicate that quercetin provides an alternative antimicrobial to mitigate and control E. coli O157:H7 intestinal infection, and suggest potential broad benefits of quercetin and related polyphenols in fighting other enteric pathogen infections.

FAK activity protects nucleostemin in facilitating breast cancer spheroid and tumor growth

IntroductionFocal adhesion kinase (FAK) controls cell growth and survival downstream of integrin-matrix receptors. Upon adhesion loss or FAK inhibition, FAK can translocate to the nucleus. The nucleolus is a non-membrane nuclear structure that regulates ribosome biogenesis and cell proliferation. Nucleostemin (NS), a nucleolar-localized protein, modulates cell cycle progression, stemness, and three-dimensional tumor spheroid formation. The signaling pathways that regulate NS levels in tumors remain undefined.MethodsHuman breast carcinoma cells were evaluated for growth in culture (adherent and anchorage-independent spheroid) and as orthotopic tumors. FAK signaling was evaluated by pharmacological FAK inhibitor addition (PF-271, IC50 ~ 0.1 μM) and by small hairpin RNA (shRNA) knockdown followed by re-expression of FAK wildtype (WT) or a kinase-dead (KD, K454R) FAK point mutant. Immunoblotting was used to evaluate FAK, NS, nucleolar phosphoprotein B23, and nucleolin levels. Total and phosphospecific antibody imunoblotting were used to detect changes in FAK, Akt kinase (Akt also known as protein kinase B), and 4E-binding protein 1 (4E-BP1) phosphorylation, a translation repressor protein and target of the mammalian target of rapamycin (mTOR) complex. Immunohistochemical, co-immunoprecipitation, and cellular fractionation analyses were used to evaluate FAK association with nucleoli.ResultsPharmacological (0.1 μM PF-271) or genetic inhibition of FAK activity prevents MDA-MB-231 and 4T1L breast carcinoma growth as spheroids and as orthotopic tumors. FAK inhibition triggers proteasome-mediated decreased NS levels but no changes in other nucleolar proteins such as B23 (nucleophosmin) or nucleolin. Active FAK was associated with purified nucleoli of anchorage-independent cells and present within nucleoli of human invasive ductal carcinoma tumor samples. FAK co-immunoprecipitated with B23 that binds NS and a complex between FAK, NS, Akt, and mTOR was detected. Constitutively-active Akt kinase promoted tumor spheroid growth, stabilized NS levels, and promoted pS65 4E-BP1 phosphorylation in the presence of inhibited FAK. Rapamycin lowered NS levels and inhibited pS65 4E-BP1 phosphorylation in cells with activated Akt-mTOR signaling.ConclusionsFAK signaling occurs in the nucleolus, active FAK protects NS, and Akt-mTOR pathway regulates NS protein stability needed for breast carcinoma spheroid and tumor growth.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-015-0551-x) contains supplementary material, which is available to authorized users.

Focal adhesion kinase induces matrix metalloproteinase-2 by involving α5β1-mediated signaling in breast cancer cell, MCF-7

Introduction: Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that plays a pivotal role in cell invasion. Matrix metalloproteinases (MMPs) are implicated as the key players in cancer cell invasion. Hence, the role of FAK in MMP regulation is very important in understanding tumor progression. Materials and Methods: Here, we studied the role of FAK, its association with other signaling kinases and involvement in the α5β1 integrin receptor-mediated regulation of MMP-2 activity and expression in human breast cancer cell line MCF-7. Results: Immuno blot analysis revealed that FN treatment causes phosphorylation of FAK and FAK gets localized at the cell attachment focal point of MCF-7 cells. FN treatment did not change the mRNA status of FAK but enhanced mRNA level of MMP-2 and MT1-MMP, also caused downregulation of TIMP-2. Co-imunoprecipitation and inhibitor studies revealed the association of FAK with α5β1, Paxillin, PI3K and ERK. siRNA studies revealed that FAK is critical in regulation of activity and expression of MMP-2 and downstream signaling kinases. Conclusion: The interaction of α5β1 integrin with FN initiates a signaling cascade with FAK as its central player. FAK gets phosphorylated and in turn associates with tyrosine kinases like PI3K and ERK. FAK also activates PI3K and ERK that serve as very crucial mediators of the signaling pathway leading to induction of MMP-2 activity and resulting invasion of breast cancer cell, MCF-7.

Proteomic Profiling of Endothelial Invasion Revealed Receptor for Activated C Kinase 1 (RACK1) Complexed with Vimentin to Regulate Focal Adhesion Kinase (FAK)

Angiogenesis is critical for many physiological and pathological processes. To identify molecules relevant to angiogenesis, we performed a proteomic screen comparing invading versus non-invading endothelial cells in three-dimensional collagen matrices. We found up-regulated levels of receptor for activated C kinase 1 (RACK1) and the intermediate filament protein vimentin that correlated with increased endothelial cell invasion. Because both RACK1 and vimentin have been linked to focal adhesion kinase (FAK), we investigated whether this pathway regulated invasion. RACK1 depletion reduced invasion responses, and this was associated with attenuated activation of FAK. Knockdown of vimentin significantly decreased levels of phosphorylated and total FAK. Treatment with a pharmacological inhibitor of FAK dose-dependently reduced invasion, indicating a crucial role for FAK activity during invasion. Because RACK1 and vimentin were both up-regulated with sphingosine 1-phosphate treatment, required for invasion, and regulated FAK, we tested whether they complexed together. RACK1 complexed with vimentin, and growth factors enhanced this interaction. In addition, RACK1, vimentin, and FAK formed an intermolecular complex in invading endothelial cultures in three dimensions in response to stimulation by sphingosine 1-phosphate and growth factors. Moreover, depletion of RACK1 decreased the association of vimentin and FAK, suggesting that RACK1 was required for stabilizing vimentin-FAK interactions during sprouting. Silencing of vimentin and RACK1 decreased cell adhesion and focal contact formation. Taken together, these results demonstrate that proangiogenic signals converge to enhance expression and association of RACK1 and vimentin, which regulated FAK, resulting in successful endothelial sprout formation in three-dimensional collagen matrices.

Stiff Collagen Matrices Increase Tumorigenic Prolactin Signaling in Breast Cancer Cells

Clinically, circulating prolactin levels and density of the extracellular matrix (ECM) are individual risk factors for breast cancer. As tumors develop, the surrounding stroma responds with increased deposition and cross-linking of the collagen matrix (desmoplasia). In mouse models, prolactin promotes mammary carcinomas that resemble luminal breast cancers in women, and increased collagen density promotes tumor metastasis and progression. Although the contributions of the ECM to the physiologic actions of prolactin are increasingly understood, little is known about the functional relationship between the ECM and prolactin signaling in breast cancer. Here, we examined consequences of increased ECM stiffness on prolactin signals to luminal breast cancer cells in three-dimensional collagen I matrices in vitro. We showed that matrix stiffness potently regulates a switch in prolactin signals from physiologic to protumorigenic outcomes. Compliant matrices promoted physiological prolactin actions and activation of STAT5, whereas stiff matrices promoted protumorigenic outcomes, including increased matrix metalloproteinase-dependent invasion and collagen scaffold realignment. In stiff matrices, prolactin increased SRC family kinase-dependent phosphorylation of focal adhesion kinase (FAK) at tyrosine 925, FAK association with the mitogen-activated protein kinase mediator GRB2, and pERK1/2. Stiff matrices also increased co-localization of prolactin receptors and integrin-activated FAK, implicating altered spatial relationships. Together, these results demonstrate that ECM stiffness is a powerful regulator of the spectrum of prolactin signals and that stiff matrices and prolactin interact in a feed-forward loop in breast cancer progression. Our study is the first reported evidence of altered ECM-prolactin interactions in breast cancer, suggesting the potential for new therapeutic approaches.

The CB1 Cannabinoid Receptor Stimulates Cooperative Signaling Between Integrin Receptors and Flk‐1 Vascular Endothelial Growth Factor Receptors to Regulate FAK Tyrosine Phosphorylation in Neuronal Cells

This study investigated the signaling pathways utilized by CB1 cannabinoid receptors (CB1R) to regulate neuronal Focal Adhesion Kinase (FAK) tyrosine phosphorylation (Tyr‐P) in murine N18TG2 cells. Immunoblotting experiments revealed the CB1R agonist WIN55212‐2 (WIN, 10 nM), produces three distinct phases of FAK Tyr‐P: Phase I (0–5 min) involves maximal Tyr‐P, Phase II (5–20 min) involves a decline in Tyr‐P, and Phase III (> 20 min) involves a plateau in Tyr‐P at submaximal levels. Phase I was blocked by the CB1R antagonist SR141716A and pertussis toxin which suggests maximal FAK Tyr‐P is mediated by CB1Rs and Gi/o proteins. The Src kinase inhibitor PP2 abolished Phase I which indicates Src is an absolute requirement for CB1R‐mediated maximal FAK Tyr‐P. Phase I also involved CB1R‐mediated transactivation of the Flk‐1 vascular endothelial growth factor receptor (Flk‐1 VEGFR). WIN induced Flk‐1 VEGFR Tyr‐P during Phase I, while Phase I was inhibited by the Flk‐1 VEGFR antagonist SU5416. The integrin receptor antagonist RGDS peptide also inhibited Phase I FAK Tyr‐P, while Cytochalasin D abolished Phase I FAK Tyr‐P which indicates dependence on an intact actin cytoskeleton and focal adhesions. WIN induced FAK association with β‐actin and the p85 subunit of phosphatidylinositol 3‐kinase during Phase I, as well as Protein Kinase B/Akt phosphorylation at Serine 473. These studies have identified a novel signaling pathway that mediates CB1R‐stimulated FAK Tyr‐P in neurons. Supported by NIDA grants R01DA003690 (ACH) and F32DA026295 (GDD).

Studies on Focal Adhesion Kinase in human breast cancer cell MDA-MB-231

AIM: 1) To study the participation of Focal Adhesion Kinase (FAK) in regulation of Breast Cancer cell migration in relation with MMP-9 and other signaling proteins. 2) To study the effect of some natural products on FAK. METHODS: Cell culture, Western Blot, Immunoprecipitation, Immunocytochemistry, Zymography, SiRNA transfection, RT-PCR, Real-Time PCR. RESULTS: For our study on FAK, we selected invasive Breast Cancer cell line MDA-MB-231 and treated the cells with Fibronectin (FN). Treatment of FN was found to increase FAK expression, phosphorylation (Tyr 397). FAK was found to be involved in re- gulation of breast cancer cell migration and MMP-9 expression, activity. Fi-bronectin increases association of FAK with integrin α5β1, Paxillin, Actin, ERK, PI3K and localization at Focal Adhesion sites. FAK was found to be involved in modulation of ERK and PI3K phosphorylation. Moreover, FAK signal was found to be transduced through ERK and PI3K, which modulate MMP-9 and thereby cell migration. CONCLUSION: FAK expression, phosphorylation and processing are induced in response to Cell-ECM interactions. Integrin α5β1 is involved in FN induced FAK phosphorylation. FAK is a potent regulator of MMP-9 expression and activity. FAK is involved in regulation of ERK and PI3K phosphorylation. ERK and PI3K are involved in FAK regulated MMP-9 expression & activity. FAK regulates MMP-9 expression and activity and thereby migration of human breast cancer cell. By the regulation of FAK, cell attachment and migration may be regulated by Curcumin, ATRA or EGCG treatment. It may be concluded that invasive potential of breast cancer cells may be modulated by regulation of FAK.

A role for focal adhesion kinase in cardiac mitochondrial biogenesis induced by mechanical stress

We studied the implication of focal adhesion kinase (FAK) in cardiac mitochondrial biogenesis induced by mechanical stress. Prolonged stretching (2-12 h) of neonatal rat ventricular myocytes (NRVM) upregulated the main components of mitochondrial transcription cascade [peroxisome proliferator-activated receptor coactivator-1 (PGC-1α), nuclear respiratory factor (NRF-1), and mitochondrial transcription factor A]. Concomitantly, prolonged stretching enhanced mitochondrial biogenesis [copy number of mitochondrial DNA (mtDNA), content of the subunit IV of cytochrome oxidase, and mitochondrial staining-green fluorescence intensity of Mitotracker green] and induced the hypertrophic growth (cell size and atrial natriuretic peptide transcripts) of NRVM. Furthermore, the stretching of NRVM enhanced phosphorylation, nuclear localization, and association of FAK with PGC-1α. Recombinant FAK COOH-terminal, but not the NH(2)-terminal or kinase domain, precipitated PGC-1α from nuclear extracts of NRVM. Depletion of FAK by RNA interference suppressed the upregulation of PGC-1α and NRF-1 and markedly attenuated the enhanced mitochondrial biogenesis and hypertrophic growth of stretched NRVM. In the context of energy metabolism, FAK depletion became manifest by a reduction of ATP levels in stretched NRVM. Complementary studies in adult mice left ventricle demonstrated that pressure overload upregulated PGC-1α, NRF-1, and mtDNA. In vivo FAK silencing transiently attenuated the upregulation of PGC-1α, NRF-1, and mtDNA, as well as the left ventricular hypertrophy induced by pressure overload. In conclusion, activation of FAK signaling seems to be important for conferring enhanced mitochondrial biogenesis coupled to the hypertrophic growth of cardiomyocytes in response to mechanical stress, via control of mitochondrial transcription cascade.

Anoikis mediators in oral squamous cell carcinoma

Anoikis - apoptotic cell death triggered by loss of extracellular matrix (ECM) contacts - is dysregulated in many chronic debilitating and fatal diseases. Mechanisms rendering tumor cells resistant to anoikis, although not completely understood, possess significant therapeutic promise. In death receptor-mediated anoikis mechanisms, focal adhesion kinase (FAK) and receptor-interacting protein (RIP) dissociate, leading to association of RIP with Fas, formation of the death-inducing signaling complex (DISC), activation of caspase-3, and propagation of anoikis. In contrast, anoikis resistance is accomplished through constitutive activation of survival pathways that include integrin-dependent activation of FAK and extracellular-signal-regulated kinase (ERK). In addition, FAK and RIP association confers anoikis resistance by inhibiting the association of RIP with Fas and formation of the death signaling complex, which allows cells to escape anoikis. Up-regulation of CD44 also contributes to survival signals and promotes anoikis resistance. This review will focus on the roles of death receptors, prosurvival pathways, and the molecular players involved in anoikis escalation and resistance in oral squamous cell carcinoma.

Leukotriene B 4 mediates vascular smooth muscle cell migration through αvβ3 integrin transactivation

Vascular injury leads to a local inflammatory response, characterized by endothelial damage, extracellular matrix exposition and aggregation/adhesion of platelets and circulating leukocytes. The release of inflammatory mediators amplifies the process, and can induce vascular smooth muscle cells (SMC) migration and proliferation. Released by leukocytes, leukotriene B 4 (LTB 4) induces reactive oxygen species production and SMC chemotaxis. This study was conducted to elucidate the molecular mechanisms involved in the effect of LTB 4 on SMC migration, and a rat linage of vascular SMC (A7r5) were used throughout. The chemotactic effect of LTB 4 was dependent on the concentration used, being comparable to AngII at 100 nM. Migration induced by LTB 4 was inhibited in the presence of pertussis toxin, CP-105696, a BLT1 receptor antagonist, and by LY294002 or PD98059, two inhibitors of PI3K and MEK1/2, respectively. Stimulation of SMC with LTB 4 triggered integrin-associated signaling pathways, inducing focal adhesion kinase (FAK) phosphorylation, mobilization of actin cytoskeleton, association of FAK to PI3K, ERK-2 phosphorylation and nuclear translocation, and also NFκB pathway activation. Pretreatment of SMC with a selective ligand of αvβ3 integrin, kistrin, inhibited LTB 4-induced chemotaxis, FAK phosphorylation, FAK-PI3K association, and also inhibited ERK-2 and NFκB pathways activation. Taken together, the data demonstrated, for the first time, that the effect of LTB 4 on SMC migration is modulated by integrin signaling activation, suggesting that these adhesion molecules might be important target for therapeutic intervention in cardiovascular diseases.

Oscillatory Flow-induced Proliferation of Osteoblast-like Cells Is Mediated by αvβ3 and β1 Integrins through Synergistic Interactions of Focal Adhesion Kinase and Shc with Phosphatidylinositol 3-Kinase and the Akt/mTOR/p70S6K Pathway

Interstitial flow in and around bone tissue is oscillatory in nature and affects the mechanical microenvironment for bone cell growth and formation. We investigated the role of oscillatory shear stress (OSS) in modulating the proliferation of human osteoblast-like MG63 cells and its underlying mechanisms. Application of OSS (0.5 +/- 4 dynes/cm(2)) to MG63 cells induced sustained activation of phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR/p70S6K (p70S6 kinase) signaling cascades and hence cell proliferation, which was accompanied by increased expression of cyclins A and D1, cyclin-dependent protein kinases-2, -4, and -6, and bone formation-related genes (c-fos, Egr-1, and Cox-2) and decreased expression of p21(CIP1) and p27(KIP1). OSS-induced activation of PI3K/Akt/mTOR/p70S6K and cell proliferation were inhibited by specific antibodies or small interference RNAs of alpha(v)beta(3) and beta(1) integrins and by dominant-negative mutants of Shc (Shc-SH2) and focal adhesion kinase (FAK) (FAK(F397Y)). Co-immunoprecipitation assay showed that OSS induces sustained increases in association of Shc and FAK with alpha(v)beta(3) and beta(1) integrins and PI3K subunit p85, which were abolished by transfecting the cells with FAK(F397Y) or Shc-SH2. OSS also induced sustained activation of ERK, which was inhibited by the specific PI3K inhibitor LY294002 and was required for OSS-induced activation of mTOR/p70S6K and proliferation in MG63 cells. Our findings provide insights into the mechanisms by which OSS induces osteoblast-like cell proliferation through activation of alpha(v)beta(3) and beta(1) integrins and synergistic interactions of FAK and Shc with PI3K, leading to the modulation of downstream ERK and Akt/mTOR/p70S6K pathways.

Phosphorylation of RACK1 on Tyrosine 52 by c-Abl Is Required for Insulin-like Growth Factor I-mediated Regulation of Focal Adhesion Kinase

Focal Adhesion Kinase (FAK) activity is controlled by growth factors and adhesion signals in tumor cells. The scaffolding protein RACK1 (receptor for activated C kinases) integrates insulin-like growth factor I (IGF-I) and integrin signaling, but whether RACK1 is required for FAK function is unknown. Here we show that association of FAK with RACK1 is required for both FAK phosphorylation and dephosphorylation in response to IGF-I. Suppression of RACK1 by small interfering RNA ablates FAK phosphorylation and reduces cell adhesion, cell spreading, and clonogenic growth. Peptide array and mutagenesis studies localize the FAK binding interface to blades I-III of the RACK1 beta-propeller and specifically identify a set of basic and hydrophobic amino acids (Arg-47, Tyr-52, Arg-57, Arg-60, Phe-65, Lys-127, and Lys-130) as key determinants for association with FAK. Mutation of tyrosine 52 alone is sufficient to disrupt interaction of RACK1 with FAK in cells where endogenous RACK1 is suppressed by small interfering RNA. Cells expressing a Y52F mutant RACK1 are impaired in adhesion, growth, and foci formation. Comparative analyses of homology models and crystal structures for RACK1 orthologues suggest a role for Tyr-52 as a site for phosphorylation that induces conformational change in RACK1, switching the protein into a FAK binding state. Tyrosine 52 is further shown to be phosphorylated by c-Abl kinase, and the c-Abl inhibitor STI571 disrupts FAK interaction with RACK1. We conclude that FAK association with RACK1 is regulated by phosphorylation of Tyr-52. Our data reveal a novel mechanism whereby IGF-I and c-Abl control RACK1 association with FAK to facilitate adhesion signaling.

Role of Formation of an ERK-FAK-Paxillin Complex in Migration of Human Corneal Epithelial Cells during Wound Closure In Vitro

Migration of corneal epithelial cells is an important step in the corneal wound healing. The role of extracellular signal regulated kinase (ERK) for the regulation of cell migration during wound closure was examined. Scratch wounds were introduced into human corneal epithelial cells in the absence or presence of PD98059, an ERK signaling inhibitor. The phosphorylation and localization of ERK during wound closure were examined by immunoblot and immunofluorescence analyses. The tyrosine phosphorylation of focal adhesion kinase (FAK) and paxillin, as well as the association of FAK with paxillin and ERK, were evaluated by immunoprecipitation and immunoblot analysis. The effect of a mutant form of MEK1 on cell migration and proliferation was determined by transfection. PD98059 inhibited cell migration in a concentration- and time-dependent manner. Wounding increased the phosphorylation of ERK as well as the tyrosine phosphorylation of FAK and paxillin in a manner sensitive to PD98059. Furthermore, wounding induced the formation of an ERK-FAK-paxillin complex and this effect as well as the wounding-induced formation of focal adhesions, membrane ruffles, and bundles of F-actin, were inhibited by PD98059. Phosphorylated ERK localized at the wound margin, and such localization was not observed in the presence of PD98059. Expression of dominant negative mutant form of MEK1 inhibited cell migration during wound closure without the effect of cell proliferation. ERK regulates cell migration during wound healing in vitro by modulating the phosphorylation of FAK and paxillin and the consequent formation of focal adhesions. An ERK-FAK-paxillin signaling pathway may play an important role in corneal epithelial wound healing in vivo.

A FAK-p120RasGAP-p190RhoGAP complex regulates polarity in migrating cells

Directional motility is a complex process requiring the spatiotemporal integration of signals that regulate cytoskeletal changes, and the establishment of an anteroposterior or polarized cell axis. Focal adhesion kinase (FAK) promotes cell migration, but a molecular role for FAK in promoting cell polarity remains undefined. Here, using wound healing and Golgi-reorientation analyses, we show that fibroblast, endothelial and carcinoma polarity during cell migration requires FAK and is associated with a complex between FAK, p120RasGAP and p190RhoGAP (p190A), leading to p190A tyrosine phosphorylation. Fibronectin-integrin-mediated FAK activation and phosphorylation promote SH2-mediated binding of p120RasGAP to FAK and FAK-mediated p190A tyrosine phosphorylation. The association of p120RasGAP with FAK facilitates the formation of a FAK-p120RasGAP-p190A complex targeted to leading-edge focal adhesions by FAK. Knockdown of p120RasGAP, mutation of FAK Y397 or inhibition of FAK activity prevent the association of FAK with p190A and subsequent tyrosine phosphorylation of p190A, and result in the loss of cell polarity. Because reconstitution of FAK-null fibroblasts with FAK or a Pyk2-FAK chimera restore the normal decrease in RhoA GTP binding upon cell spreading on fibronectin, our studies support a model whereby FAK activity facilitates the recruitment and stabilization of a p120RasGAP-p190A complex at leading-edge focal adhesions connected to the transient inhibition of RhoA activity and the regulation of cell polarity.

Focal Adhesion Kinase as a RhoA-activable Signaling Scaffold Mediating Akt Activation and Cardiomyocyte Protection

RhoA a small G-protein that has an established role in cell growth and in regulation of the actin cytoskeleton. Far less is known about whether RhoA can modulate cell fate. We previously reported that sustained RhoA activation induces cardiomyocyte apoptosis (Del Re, D. P., Miyamoto, S., and Brown, J. H. (2007) J. Biol. Chem. 282, 8069-8078). Here we demonstrate that less chronic RhoA activation affords a survival advantage, protecting cardiomyocytes from apoptotic insult induced by either hydrogen peroxide treatment or glucose deprivation. Under conditions where RhoA is protective, we observe Rho kinase-dependent cytoskeletal rearrangement and activation of focal adhesion kinase (FAK). Activation of endogenous cardiomyocyte FAK leads to its increased association with the p85 regulatory subunit of phosphatidylinositol-3-kinase (PI3K) and to concomitant activation of Akt. Treatment of isolated perfused hearts with sphingosine 1-phosphate recapitulates this response. The pathway by which RhoA mediates cardiomyocyte Akt activation is demonstrated to require Rho kinase, FAK and PI3K, but not Src, based on studies with pharmacological inhibitors (Y-27632, LY294002, PF271 and PP2) and inhibitory protein expression (FAK-related nonkinase). Inhibition of RhoA-mediated Akt activation at any of these steps, including inhibition of FAK, prevents RhoA from protecting cardiomyocytes against apoptotic insult. We further demonstrate that stretch of cardiomyocytes, which activates endogenous RhoA, induces the aforementioned signaling pathway, providing a physiologic context in which RhoA-mediated FAK phosphorylation can activate PI3K and Akt. We suggest that RhoA-mediated effects on the cardiomyocyte cytoskeleton provide a novel mechanism for protection from apoptosis.

Endothelin-1 promotes migration of endothelial cells through the activation of ARF6 and the regulation of FAK activity

Several proteins act in concert to promote remodeling of the actin cytoskeleton during migration. This process is highly regulated by small GTP-binding proteins of the ADP-ribosylation factor (ARF) family of proteins. Here, we show that endothelin-1 (ET-1) can promote the activation of ARF6 and migration of endothelial cells through the activation of ETB receptors. Inhibition of ARF6 expression using RNA interference markedly impairs basal and ET-1 stimulated cell migration. In contrast, depletion of ARF1 has no significant effect. In order to delineate the underlying mechanism, we examined the signaling events activated in endothelial cells following ET-1 stimulation. Here, we show that this hormone promotes the phosphorylation of focal adhesion kinase (FAK), Erk1/2, and the association of FAK to Src, as well as of FAK to GIT1. These have been shown to be important for the formation and turnover of focal adhesions. In non-stimulated cells, depletion of ARF6 leads to increased FAK and Erk1/2 phosphorylation, similar to what is observed in ET-1 treated cells. In these conditions, FAK is found constitutively associated with the soluble tyrosine kinase, Src. In contrast, depletion of ARF6 impairs the ability of GIT1 to form an agonist promoted complex with FAK, thereby preventing disassembly of focal adhesions. As a consequence, ARF6 depleted endothelial cells are impaired in their ability to form capillary tubes. Taken together, our data suggest that ARF6 is central in regulating focal adhesion turnover in endothelial cells. Our study provides a molecular mechanism by which, this small GTPase regulates cell motility, and ultimately angiogenesis.

Shp2 Negatively Regulates Growth in Cardiomyocytes by Controlling Focal Adhesion Kinase/Src and mTOR Pathways

The aim of this study was to investigate whether Shp2 (Src homology region 2, phosphatase 2) controls focal adhesion kinase (FAK) activity and its trophic actions in cardiomyocytes. We show that low phosphorylation levels of FAK in nonstretched neonatal rat ventricular myocytes (NRVMs) coincided with a relatively high basal association of FAK with Shp2 and Shp2 phosphatase activity. Cyclic stretch (15% above initial length) enhanced FAK phosphorylation at Tyr397 and reduced FAK/Shp2 association and phosphatase activity in anti-Shp2 precipitates. Recombinant Shp2 C-terminal protein tyrosine phosphatase domain (Shp2-PTP) interacted with nonphosphorylated recombinant FAK and dephosphorylated FAK immunoprecipitated from NRVMs. Depletion of Shp2 by specific small interfering RNA increased the phosphorylation of FAK Tyr397, Src Tyr418, AKT Ser473, TSC2 Thr1462, and S6 kinase Thr389 and induced hypertrophy of nonstretched NRVMs. Inhibition of FAK/Src activity by PP2 {4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine} abolished the phosphorylation of AKT, TSC2, and S6 kinase, as well as the hypertrophy of NRVMs induced by Shp2 depletion. Inhibition of mTOR (mammalian target of rapamycin) with rapamycin blunted the hypertrophy in NRVMs depleted of Shp2. NRVMs treated with PP2 or depleted of FAK by specific small interfering RNA were defective in FAK, Src, extracellular signal-regulated kinase, AKT, TSC2, and S6 kinase phosphorylation, as well as in the hypertrophic response to prolonged stretch. The stretch-induced hypertrophy of NRVMs was also prevented by rapamycin. These findings demonstrate that basal Shp2 tyrosine phosphatase activity controls the size of cardiomyocytes by downregulating a pathway that involves FAK/Src and mTOR signaling pathways.

Mutation of Y925F in focal adhesion kinase (FAK) suppresses melanoma cell proliferation and metastasis

This study focused on the role of focal adhesion kinase (FAK), a cytoplasmic tyrosine kinase important for many cellular processes, in the proliferation, adhesion, and invasion of melanoma cells in vitro and in vivo. We found that the Y925F-mutation of FAK in B16F10 melanoma cells suppressed metastasis in an experimental model, which correlated well with decreased extracellular matrix dependent proliferative capability, adhesive, migrational, and invasive capabilities. Transduction of the mutation Y925F resulted in a down-regulation of the phosphorylation of Erk, the expression of VEGF, and the association of FAK with paxillin. The results provide clear evidence that 925Y of FAK is critical for melanoma metastasis and this phosphorylation site will be an anti-metastatic target.