Deregulation of Proteasome Function Induces Abl-mediated Cell Death by Uncoupling p130CAS and c-CrkII

Natural Killer Cells: Tumor Surveillance and Signaling

Natural killer (NK) cells play a pivotal role in cancer immunotherapy due to their innate ability to detect and kill tumorigenic cells. The decision to kill is determined by the expression of a myriad of activating and inhibitory receptors on the NK cell surface. Cell-to-cell engagement results in either self-tolerance or a cytotoxic response, governed by a fine balance between the signaling cascades downstream of the activating and inhibitory receptors. To evade a cytotoxic immune response, tumor cells can modulate the surface expression of receptor ligands and additionally, alter the conditions in the tumor microenvironment (TME), tilting the scales toward a suppressed cytotoxic NK response. To fully harness the killing power of NK cells for clinical benefit, we need to understand what defines the threshold for activation and what is required to break tolerance. This review will focus on the intracellular signaling pathways activated or suppressed in NK cells and the roles signaling intermediates play during an NK cytotoxic response.

The Abl-1 Kinase is Dispensable for NK Cell Inhibitory Signalling and is not Involved in Murine NK Cell Education

Natural killer (NK) cell responsiveness in the mouse is determined in an education process guided by inhibitory Ly49 and NKG2A receptors binding to MHC class I molecules. It has been proposed that inhibitory signalling in human NK cells involves Abl-1 (c-Abl)-mediated phosphorylation of Crk, lowering NK cell function via disruption of a signalling complex including C3G and c-Cbl, suggesting that NK cell education might involve c-Abl. Mice deficient in c-Abl expression specifically in murine NK cells displayed normal inhibitory and activating receptor repertoires. Furthermore, c-Abl-deficient NK cells fluxed Ca²⁺ normally after triggering of ITAM receptors, killed YAC-1 tumour cells efficiently and showed normal, or even slightly elevated, capacity to produce IFN-γ after activating receptor stimulation. Consistent with these results, c-Abl deficiency in NK cells did not affect NK cell inhibition via the receptors Ly49G2, Ly49A and NKG2A. We conclude that signalling downstream of murine inhibitory receptors does not involve c-Abl and that c-Abl plays no major role in NK cell education in the mouse.

Neuroprotective efficacy of a new brain-penetrating C-Abl inhibitor in a murine Parkinson's disease model

Experimental evidence suggests that oxidative and nitrative mechanisms account for much of the dopaminergic neuronal injury in Parkinson’s disease (PD). The ubiquitously expressed non-receptor tyrosine kinase c-Abl is activated by oxidative stress and thus, may play a role in redox-mediated neurodegeneration. Recently, we reported that c-Abl is activated in PD and that a c-Abl inhibitor mitigated neuronal damage in a PD animal model, suggesting a novel neuroprotective therapeutic approach. In the studies presented here, we evaluated the efficacy of a potent and clinically relevant second-generation irreversible Abl kinase inhibitor, INNO-406, as a therapeutic agent for PD. Our studies reveal that INNO-406 is capable of preventing the progression of dopaminergic neuronal damage in a toxin-induced C57 mouse model of PD. Using bovine brain microvessel endothelium as an in vitro blood-brain barrier (BBB) model, we detected rapid and significant transfer of INNO-406. Additionally, pharmacokinetic analyses demonstrated significant nanomolar concentrations of INNO-406 in brain in the presence or absence of MPTP administration, however, INNO-406 did not alter the brain levels of MPP+ in MPTP-treated mice. Finally, we showed that 10 mg/kg of INNO-406 given to C57 mice for one week before MPTP treatment (4×20 mg/kg i.p., every 2 h) and then for one week after MPTP treatment decreased the loss of dopamine in the striatum by 45% and the loss of TH+ neurons in substantia nigra pars compacts by 40%. This treatment regimen also abrogated activation of c-Abl, tyrosine phosphorylation of the Abl substrate and E3-ubiquitin ligase parkin, and accumulation of the toxic parkin substrate AIMP2. We propose that compounds of the INNO-406 class of Abl inhibitors will be useful new neuroprotective drugs for the treatment of PD-like pathology in preclinical systems that should be easily translated to the clinic.

Dynamic phosphorylation of tyrosine 665 in pseudopodium-enriched atypical kinase 1 (PEAK1) is essential for the regulation of cell migration and focal adhesion turnover

Pseudopodium-enriched atypical kinase 1 (PEAK1) is a recently described tyrosine kinase that associates with the actin cytoskeleton and focal adhesion (FA) in migrating cells. PEAK1 is known to promote cell migration, but the responsible mechanisms remain unclear. Here, we show that PEAK1 controls FA assembly and disassembly in a dynamic pathway controlled by PEAK1 phosphorylation at Tyr-665. Knockdown of endogenous PEAK1 inhibits random cell migration. In PEAK1-deficient cells, FA lifetimes are decreased, FA assembly times are shortened, and FA disassembly times are extended. Phosphorylation of Tyr-665 in PEAK1 is essential for normal PEAK1 localization and its function in the regulation of FAs; however, constitutive phosphorylation of PEAK1 Tyr-665 is also disruptive of its function, indicating a requirement for precise spatiotemporal regulation of PEAK1. Src family kinases are required for normal PEAK1 localization and function. Finally, we provide evidence that PEAK1 promotes cancer cell invasion through Matrigel by a mechanism that requires dynamic regulation of Tyr-665 phosphorylation.

A critical role for p130Cas in the progression of pulmonary hypertension in humans and rodents

RATIONALE

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease characterized by pulmonary arterial muscularization due to excessive pulmonary vascular cell proliferation and migration, a phenotype dependent upon growth factors and activation of receptor tyrosine kinases (RTKs). p130(Cas) is an adaptor protein involved in several cellular signaling pathways that control cell migration, proliferation, and survival.

OBJECTIVES

We hypothesized that in experimental and human PAH p130(Cas) signaling is overactivated, thereby facilitating the intracellular transmission of signal induced by fibroblast growth factor (FGF)2, epidermal growth factor (EGF), and platelet-derived growth factor (PDGF).

MEASUREMENTS AND MAIN RESULTS

In patients with PAH, levels of p130(Cas) protein and/or activity are higher in the serum, in the walls of distal pulmonary arteries, in cultured smooth muscle cells (PA-SMCs), and in pulmonary endothelial cells (P-ECs) than in control subjects. These abnormalities in the p130(Cas) signaling were also found in the chronically hypoxic mice and monocrotaline-injected rats as models of human PAH. We obtained evidence for the convergence and amplification of the growth-stimulating effect of the EGF-, FGF2-, and PDGF-signaling pathways via the p130(Cas) signaling pathway. We found that daily treatment with the EGF-R inhibitor gefitinib, the FGF-R inhibitor dovitinib, and the PDGF-R inhibitor imatinib started 2 weeks after a subcutaneous monocrotaline injection substantially attenuated the abnormal increase in p130(Cas) and ERK1/2 activation and regressed established pulmonary hypertension.

CONCLUSIONS

Our findings demonstrate that p130(Cas) signaling plays a critical role in experimental and idiopathic PAH by modulating pulmonary vascular cell migration and proliferation and by acting as an amplifier of RTK downstream signals.

Src, p130Cas, and Mechanotransduction in Cancer Cells

Anchorage-independent growth is the most significant hallmark of cell transformation, which has an intimate relevance to cancer. Anchorage or adhesion physically links cells to the extracellular matrix and allows the transmission of external mechanical cues to intracellular signaling machineries. Transformation involves acquiring the ability to proliferate without requiring mechanically initiated signal transduction, known as mechanotransduction. A number of signaling and cytoskeletal molecules are located at focal adhesions. Src and its related proteins, including p130Cas, localize to adhesion sites, where their functions can be mechanically regulated. In addition, the aberrant activation and expression of Src and p130Cas are linked to transformation and malignancy both in vitro and in vivo. These findings shed light on the importance of mechanotransduction in tumorigenesis and the regulation of cancer progression and also provide insights into the mechanical aspects of cancer signaling.

The docking protein p130Cas regulates cell sensitivity to proteasome inhibition

BACKGROUND

The focal adhesion protein p130Cas (Cas) activates multiple intracellular signaling pathways upon integrin or growth factor receptor ligation. Full-length Cas frequently promotes cell survival and migration, while its C-terminal fragment (Cas-CT) produced upon intracellular proteolysis is known to induce apoptosis in some circumstances. Here, we have studied the putative role of Cas in regulating cell survival and death pathways upon proteasome inhibition.

RESULTS

We found that Cas-/- mouse embryonic fibroblasts (MEFs), as well as empty vector-transfected Cas-/- MEFs (Cas-/- (EV)) are significantly resistant to cell death induced by proteasome inhibitors, such as MG132 and Bortezomib. As expected, wild-type MEFs (WT) and Cas-/- MEFs reconstituted with full-length Cas (Cas-FL) were sensitive to MG132- and Bortezomib-induced apoptosis that involved activation of a caspase-cascade, including Caspase-8. Cas-CT generation was not required for MG132-induced cell death, since expression of cleavage-resistant Cas mutants effectively increased sensitivity of Cas-/- MEFs to MG132. At the present time, the domains in Cas and the downstream pathways that are required for mediating cell death induced by proteasome inhibitors remain unknown. Interestingly, however, MG132 or Bortezomib treatment resulted in activation of autophagy in cells that lacked Cas, but not in cells that expressed Cas. Furthermore, autophagy was found to play a protective role in Cas-deficient cells, as inhibition of autophagy either by chemical or genetic means enhanced MG132-induced apoptosis in Cas-/- (EV) cells, but not in Cas-FL cells. Lack of Cas also contributed to resistance to the DNA-damaging agent Doxorubicin, which coincided with Doxorubicin-induced autophagy in Cas-/- (EV) cells. Thus, Cas may have a regulatory role in cell death signaling in response to multiple different stimuli. The mechanisms by which Cas inhibits induction of autophagy and affects cell death pathways are currently being investigated.

CONCLUSION

Our study demonstrates that Cas is required for apoptosis that is induced by proteasome inhibition, and potentially by other death stimuli. We additionally show that Cas may promote such apoptosis, at least partially, by inhibiting autophagy. This is the first demonstration of Cas being involved in the regulation of autophagy, adding to the previous findings by others linking focal adhesion components to the process of autophagy.

Proteasome inhibition, the pursuit of new cancer therapeutics, and the adaptor molecule p130Cas

Current interest in proteasome inhibitors for cancer therapy has stimulated considerable research efforts to identify the molecular pathway to their cytotoxicity with a view to identifying the mechanisms of sensitivity and resistance as well as informing the development of new drugs. Zhao and Vuori describe this month in BMC Biology experiments indicating a novel role of the adaptor protein p130Cas in sensitivity to apoptosis induced not only by proteasome inhibitors but also by the unrelated drug doxorubicin.

See research article: http:// http://www.biomedcentral.com/1741-7007/9/73

Integrin signalling adaptors: not only figurants in the cancer story

Current evidence highlights the ability of adaptor (or scaffold) proteins to create signalling platforms that drive cellular transformation upon integrin-dependent adhesion and growth factor receptor activation. The understanding of the biological effects that are regulated by these adaptors in tumours might be crucial for the identification of new targets and the development of innovative therapeutic strategies for human cancer. In this Review we discuss the relevance of adaptor proteins in signalling that originates from integrin-mediated cell-extracellular matrix (ECM) adhesion and growth factor stimulation in the context of cell transformation and tumour progression. We specifically underline the contribution of p130 Crk-associated substrate (p130CAS; also known as BCAR1), neural precursor cell expressed, developmentally down-regulated 9 (NEDD9; also known as HEF1), CRK and the integrin-linked kinase (ILK)-pinch-parvin (IPP) complex to cancer, along with the more recently identified p140 Cas-associated protein (p140CAP; also known as SRCIN1).

F-actin-binding domain of c-Abl regulates localized phosphorylation of C3G: role of C3G in c-Abl-mediated cell death

The c-Abl tyrosine kinase maintains cellular homeostasis through its ability to regulate apoptosis and actin dynamics. In vivo, c-Abl activity is stringently regulated and mechanisms involved are not fully understood. Here, we identified the Rap1 guanine nucleotide exchange factor, C3G (RapGEF1), as a substrate and an effector of c-Abl-mediated functions. Ectopic expression of c-Abl in mammalian cell lines, known to induce apoptosis, resulted in phosphorylation of endogenous C3G on Y504 coincident with cell detachment and chromatin condensation. Phosphorylation of C3G coincided with restricted c-Abl activation in regions rich in actin, and was dependent on cellular F-actin dynamics. Unlike C3G or c-Abl, p-C3G was resistant to detergent extraction, suggesting its enhanced affinity for the cytoskeleton. Localized C3G phosphorylation and coincidence with cells undergoing cell death was dependent on F-actin-binding domain (FABD) of c-Abl. Activation of endogenous c-Abl by oxidative stress was associated with phosphorylation of cellular C3G on Y504. Inhibition of C3G expression and function using RNAi or dominant-negative approaches inhibited c-Abl-mediated cell death. These findings identify C3G as a novel target of c-Abl and also show that FABD of c-Abl is essential for regulation of its restricted activation to induce apoptosis.

Pseudopodium-enriched atypical kinase 1 regulates the cytoskeleton and cancer progression [corrected]

Regulation of the actin-myosin cytoskeleton plays a central role in cell migration and cancer progression. Here, we report the discovery of a cytoskeleton-associated kinase, pseudopodium-enriched atypical kinase 1 (PEAK1). PEAK1 is a 190-kDa nonreceptor tyrosine kinase that localizes to actin filaments and focal adhesions. PEAK1 undergoes Src-induced tyrosine phosphorylation, regulates the p130Cas-Crk-paxillin and Erk signaling pathways, and operates downstream of integrin and epidermal growth factor receptors (EGFR) to control cell spreading, migration, and proliferation. Perturbation of PEAK1 levels in cancer cells alters anchorage-independent growth and tumor progression in mice. Notably, primary and metastatic samples from colon cancer patients display amplified PEAK1 levels in 81% of the cases. Our findings indicate that PEAK1 is an important cytoskeletal regulatory kinase and possible target for anticancer therapy.

c-Abl mediates endothelial apoptosis induced by inhibition of integrins alphavbeta3 and alphavbeta5 and by disruption of actin

Inhibition of integrins alphavbeta3 and alphavbeta5 in human brain microvascular endothelial cells (HBMECs) by the function-blocking peptide RGDfV induces loss of spreading on vitronectin, cell detachment, and apoptosis. We demonstrate that cell detachment is not required for apoptosis because plating on bovine serum albumin-blocked poly-L-lysine (allows attachment, but not integrin ligation and cell spreading) also induced apoptosis. Latrunculin B (LatB), which inhibits F-actin polymerization, induced transient loss of HBMEC spreading on vitronectin, but not their detachment, and induced apoptosis despite recovery of cell spreading. However, LatB did not cause apoptosis in 5 tumor cell lines. In HBMECs, both LatB and RGDfV induced transient Y412 and Y245 phosphorylation of endogenous c-Abl, a nonreceptor tyrosine kinase that reciprocally regulates F-actin. LatB also induced nuclear translocation of c-Abl in HBMECs. STI-571 (imatinib), a targeted therapy for BCR-ABL1(+) leukemias and inhibitor of c-Abl, platelet-derived growth factor receptor, and c-Kit, decreased endothelial apoptosis. LatB-induced HBMEC apoptosis, and its inhibition by STI-571 also occurred in a 3-dimensional collagen model, supporting physiologic relevance. Last, siRNA to c-Abl (but not nonspecific siRNA) also inhibited RGDfV- and LatB-induced apoptosis. Thus, endogenous c-Abl mediates endothelial apoptosis induced by inhibition of integrins alphavbeta3/alphavbeta5 or by LatB-induced disruption of F-actin.

Induction of cell retraction by the combined actions of Abl-CrkII and Rho-ROCK1 signaling

Dynamic modulation of cell adhesion is integral to a wide range of biological processes. The small guanosine triphosphatase (GTPase) Rap1 is an important regulator of cell–cell and cell–matrix adhesions. We show here that induced expression of activated Abl tyrosine kinase reduces Rap1-GTP levels through phosphorylation of Tyr221 of CrkII, which disrupts interaction of CrkII with C3G, a guanine nucleotide exchange factor for Rap1. Abl-dependent down-regulation of Rap1-GTP causes cell rounding and detachment only when the Rho–ROCK1 pathway is also activated, for example, by lysophosphatidic acid (LPA). During ephrin-A1–induced retraction of PC3 prostate cancer cells, we show that endogenous Abl is activated and disrupts the CrkII–C3G complex to reduce Rap1-GTP. Interestingly, ephrin-A1–induced PC3 cell retraction also requires LPA, which stimulates Rho to a much higher level than that is activated by ephrin-A1. Our results establish Rap1 as another downstream target of the Abl–CrkII signaling module and show that Abl–CrkII collaborates with Rho–ROCK1 to stimulate cell retraction.

Inhibitory receptor signaling via tyrosine phosphorylation of the adaptor Crk

Many cellular responses, such as autoimmunity and cytotoxicity, are controlled by receptors with cytoplasmic immunoreceptor tyrosine-based inhibition motifs (ITIMs). Here, we showed that binding of inhibitory natural killer (NK) cell receptors to human leukocyte antigen (HLA) class I on target cells induced tyrosine phosphorylation of the adaptor Crk, concomitant with dephosphorylation of the guanine exchange factor Vav1. Furthermore, Crk dissociated from the guanine exchange factor C3G and bound to the tyrosine kinase c-Abl during inhibition. Membrane targeting of a tyrosine-mutated form of Crk could overcome inhibition of NK cell cytotoxicity, providing functional evidence that Crk phosphorylation contributes to inhibition. The specific phosphorylation of Crk and its dissociation from a signaling complex, observed here with two types of inhibitory receptors, expands the signaling potential of the large ITIM-receptor family and reveals an unsuspected component of the inhibitory mechanism.

Targeting N-cadherin enhances antitumor activity of cytotoxic therapies in melanoma treatment

Malignant transformation in melanoma is characterized by a phenotype "switch" from E- to N-cadherin, which is associated with increased motility and invasiveness of the tumor and altered signaling, leading to decreased apoptosis. We hypothesized that the novel pentapeptide (ADH-1), which disrupts N-cadherin adhesion, could sensitize melanoma tumors to the cytotoxic effects of chemotherapy. N-cadherin-expressing human melanoma-derived cell lines were used to generate xenografts in animal models to study isolated limb infusion with melphalan and systemic chemotherapy with temozolomide. We report here that melphalan in combination with ADH-1 significantly reduced tumor growth up to 30-fold over melphalan alone. ADH-1 enhancement of response to melphalan was associated with increased formation of DNA adducts, increased apoptosis, and intracellular signaling changes associated with focal adhesions and fibroblast growth factor receptors. Targeted therapy using an N-cadherin antagonist can dramatically augment the antitumor effects of chemotherapy and is a novel approach to optimizing treatment for melanoma.

Proapoptotic function of the nuclear Crk II adaptor protein

Crk II and Crk L have both cytosolic and nuclear functions. While Crk L is a bona fide nuclear signaling protein because of its ability to bind tyrosine-phosphorylated STAT5 and act as a transcriptional coactivator, the function of nuclear Crk II is less well understood. The present study was undertaken to investigate whether Crk II is in the nucleus, how Crk II translocates into the nucleus, whether it possesses a functional NES, and to determine if nuclear Crk II affects cell cycle checkpoints and promotes apoptosis. Toward this goal, we used several independent techniques to show that a significant percentage of the total endogenous Crk II partitions in the nucleus in mammalian cells, where it forms distinct complexes with DOCK180, Wee1, and Abl. We found no evidence that Crk II bound to Crm1 nor that the localization of GFP-Crk II was sensitive to LMB, an inhibitor of Crm1. To better define the significance of nuclear Crk II localization, we generated a GFP-Crk II protein (GFP-Crk-nuc) fused to three tandem nuclear localization signals derived from the SV40 large T-antigen. GFP-Crk-nuc exhibited exclusive nuclear localization, and in contrast to wild-type Crk, GFP-Crk-nuc expressing cells could not be propagated upon selection in G418-containing media, suggesting nuclear accumulation of Crk II caused either growth arrest or apoptosis. When transiently transfected cells were FACS sorted, GFP-expressing cells showed defective cell adhesion on tissue culture surfaces and showed an increased level of apoptosis assessed by pycnotic nuclei, annexin V staining, and PARP cleavage. Although we found that Crk II bound to the cell cycle protein Wee1, expression of GFP-Crk-nuc did not induce a G2/M cell cycle block or cause increased Cdc2 Tyr15 phosphorylation. Finally, upon UV stimulation, we found that endogenous Crk II translocated to the nucleus and potentiated the extent of UV-inducible apoptosis after 4 h. These data suggest that nuclear compartmentalization of Crk II antagonizes its cytoskeletal functions and assign a proapoptotic role to the nuclear pool of Crk II.

Relation of a hypoxia metagene derived from head and neck cancer to prognosis of multiple cancers

Affymetrix U133plus2 GeneChips were used to profile 59 head and neck squamous cell cancers. A hypoxia metagene was obtained by analysis of genes whose in vivo expression clustered with the expression of 10 well-known hypoxia-regulated genes (e.g., CA9, GLUT1, and VEGF). To minimize random aggregation, strongly correlated up-regulated genes appearing in >50% of clusters defined a signature comprising 99 genes, of which 27% were previously known to be hypoxia associated. The median RNA expression of the 99 genes in the signature was an independent prognostic factor for recurrence-free survival in a publicly available head and neck cancer data set, outdoing the original intrinsic classifier. In a published breast cancer series, the hypoxia signature was a significant prognostic factor for overall survival independent of clinicopathologic risk factors and a trained profile. The work highlights the validity and potential of using data from analysis of in vitro stress pathways for deriving a biological metagene/gene signature in vivo.

C3G is required for c-Abl-induced filopodia and its overexpression promotes filopodia formation

The Rap1 guanine nucleotide exchange factor, C3G (also known as Rap1GEF-1) is involved in signaling from growth factors, cytokines and integrins and plays a role in cell adhesion and migration, but the mechanism by which C3G regulates various cellular functions is poorly understood. We, therefore, investigated the ability of C3G to affect actin cytoskeleton-dependent morphological changes in cells. Using RNA interference, we provide evidence that C3G is required for c-Abl-induced filopodia during cell spreading on fibronectin. C3G expression induces actin cytoskeletal reorganization and promotes filopodia formation independent of its catalytic activity. It showed enrichment at filopodia tips characteristic of molecules involved in filopodia dynamics. C3G-induced filopodia were not inhibited by dominant negative mutants of Rho, Rac and Cdc42, but required Abl catalytic activity. Coexpression of N-Wasp-Crib inhibited C3G induced as well as c-Abl-induced filopodia and wiskostatin, a pharmacological inhibitor of N-Wasp attenuates C3G-induced filopodia. Cellular C3G interacts with c-Abl and C3G expression results in enhanced localization of endogenous c-Abl in the cytoplasm. We suggest that C3G and c-Abl function in an interdependent manner, in linking external signals to remodeling the cytoskeleton to induce filopodia.

Up-regulation of c-Jun inhibits proliferation and induces apoptosis via caspase-triggered c-Abl cleavage in human multiple myeloma

Here we show the antimyeloma cytotoxicity of adaphostin and carried out expression profiling of adaphostin-treated multiple myeloma (MM) cells to identify its molecular targets. Surprisingly, c-Jun was the most up-regulated gene even at the earliest point of analysis (2 h). We also observed adaphostin-induced c-Abl cleavage in immunoblot analysis. Proteasome inhibitor bortezomib, but not melphalan or dexamethasone, induced similar effects, indicating unique agent-dependent mechanisms. Using caspase inhibitors, as well as caspase-resistant mutants of c-Abl (TM-c-Abl and D565A-Abl), we then showed that c-Abl cleavage in MM cells requires caspase activity. Importantly, both overexpression of the c-Abl fragment or c-Jun and knockdown of c-Abl and c-Jun expression by small interfering RNA confirmed that adaphostin-induced c-Jun up-regulation triggers downstream caspase-mediated c-Abl cleavage, inhibition of MM cell growth, and induction of apoptosis. Finally, our data suggest that this mechanism may not only be restricted to MM but may also be important in a broad range of malignancies including erythroleukemia and solid tumors.

Integrin-regulated FAK-Src signaling in normal and cancer cells

Integrins can alter cellular behavior through the recruitment and activation of signaling proteins such as non-receptor tyrosine kinases including focal adhesion kinase (FAK) and c-Src that form a dual kinase complex. The FAK-Src complex binds to and can phosphorylate various adaptor proteins such as p130Cas and paxillin. In normal cells, multiple integrin-regulated linkages exist to activate FAK or Src. Activated FAK-Src functions to promote cell motility, cell cycle progression and cell survival. Recent studies have found that the FAK-Src complex is activated in many tumor cells and generates signals leading to tumor growth and metastasis. As both FAK and Src catalytic activities are important in promoting VEGF-associated tumor angiogenesis and protease-associated tumor metastasis, support is growing that FAK and Src may be therapeutically relevant targets in the inhibition of tumor progression.