The Pyk2 FERM domain as a target to inhibit glioma migration

EGFRvIII Confers Sensitivity to Saracatinib in a STAT5-Dependent Manner in Glioblastoma

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults, with few effective treatments. EGFR alterations, including expression of the truncated variant EGFRvIII, are among the most frequent genomic changes in these tumors. EGFRvIII is known to preferentially signal through STAT5 for oncogenic activation in GBM, yet targeting EGFRvIII has yielded limited clinical success to date. In this study, we employed patient-derived xenograft (PDX) models expressing EGFRvIII to determine the key points of therapeutic vulnerability within the EGFRvIII-STAT5 signaling axis in GBM. Our findings reveal that exogenous expression of paralogs STAT5A and STAT5B augments cell proliferation and that inhibition of STAT5 phosphorylation in vivo improves overall survival in combination with temozolomide (TMZ). STAT5 phosphorylation is independent of JAK1 and JAK2 signaling, instead requiring Src family kinase (SFK) activity. Saracatinib, an SFK inhibitor, attenuates phosphorylation of STAT5 and preferentially sensitizes EGFRvIII+ GBM cells to undergo apoptotic cell death relative to wild-type EGFR. Constitutively active STAT5A or STAT5B mitigates saracatinib sensitivity in EGFRvIII+ cells. In vivo, saracatinib treatment decreased survival in mice bearing EGFR WT tumors compared to the control, yet in EGFRvIII+ tumors, treatment with saracatinib in combination with TMZ preferentially improves survival.

Pyk2/FAK Signaling Is Upregulated in Recurrent Glioblastoma Tumors in a C57BL/6/GL261 Glioma Implantation Model

The majority of glioblastomas (GBMs) recur shortly after tumor resection and recurrent tumors differ significantly from newly diagnosed GBMs, phenotypically and genetically. In this study, using a Gl261-C57Bl/6 mouse glioma implantation model, we identified significant upregulation of proline-rich tyrosine kinase Pyk2 and focal adhesion kinase (FAK) phosphorylation levels-pPyk2 (579/580) and pFAK (925)-without significant modifications in total Pyk2 and FAK protein expression in tumors regrown after surgical resection, compared with primary implanted tumors. Previously, we demonstrated that Pyk2 and FAK are involved in the regulation of tumor cell invasion and proliferation and are associated with reduced overall survival. We hypothesized that the use of inhibitors of Pyk2/FAK in the postsurgical period may reduce the growth of recurrent tumors. Using Western blot analysis and confocal immunofluorescence approaches, we demonstrated upregulation of Cyclin D1 and the Ki67 proliferation index in tumors regrown after resection, compared with primary implanted tumors. Treatment with Pyk2/FAK inhibitor PF-562271, administered through oral gavage at 50 mg/kg daily for two weeks beginning 2 days before tumor resection, reversed Pyk2/FAK signaling upregulation in recurrent tumors, reduced tumor volume, and increased animal survival. In conclusion, the use of Pyk2/FAK inhibitors can contribute to a delay in GBM tumor regrowth after surgical resection.

Microglial Cytokines Induce Invasiveness and Proliferation of Human Glioblastoma through Pyk2 and FAK Activation

Simple Summary

Microglia infiltrate most gliomas and have been demonstrated to promote tumor growth, invasion, and treatment resistance. To develop improved treatment methods, that take into consideration the supporting role of microglia in tumor progression, the functional and mechanistic pathways of glioma–microglia interactions need to be identified and experimentally dissected. Our recent studies and literature reports revealed the overexpression of Pyk2 and FAK in glioblastomas. Pyk2 and FAK signaling pathways have been shown to regulate migration and proliferation in glioma cells, including microglia-promoted glioma cell migration. However, the specific factors released by microglia that modulate Pyk2 and FAK to promote glioma invasiveness and proliferation are poorly understood. The aim of this study was to identify key microglia-derived signaling molecules that induce the activation of Pyk2- and FAK-dependent glioma cell proliferation and invasiveness.

Abstract

Glioblastoma is the most aggressive brain tumor in adults. Multiple lines of evidence suggest that microglia create a microenvironment favoring glioma invasion and proliferation. Our previous studies and literature reports indicated the involvement of focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) in glioma cell proliferation and invasion, stimulated by tumor-infiltrating microglia. However, the specific microglia-released factors that modulate Pyk2 and FAK signaling in glioma cells are unknown. In this study, 20 human glioblastoma specimens were evaluated with the use of RT-PCR and western blotting. A Pierson correlation test demonstrated a correlation (0.6–1.0) between the gene expression levels for platelet-derived growth factor β(PDGFβ), stromal-derived factor 1α (SDF-1α), IL-6, IL-8, and epidermal growth factor (EGF) in tumor-purified microglia and levels of p-Pyk2 (Y579/Y580) and p-FAK(Y925) in glioma cells. siRNA knockdown against Pyk2 or FAK in three primary glioblastoma cell lines, developed from the investigated specimens, in combination with the cytokine receptor inhibitors gefitinib (1 μM), DMPQ (200 nM), and burixafor (1 μM) identified EGF, PDGFβ, and SDF-1α as key extracellular factors in the Pyk2- and FAK-dependent activation of invadopodia formation and the migration of glioma cells. EGF and IL-6 were identified as regulators of the Pyk2- and FAK-dependent activation of cell viability and mitosis.

TROY signals through JAK1-STAT3 to promote glioblastoma cell migration and resistance

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and carries a discouraging prognosis. Its aggressive and highly infiltrative nature renders the current standard treatment of maximal surgical resection, radiation, and chemotherapy relatively ineffective. Identifying the signaling pathways that regulate GBM migration/invasion and resistance is required to develop more effective therapeutic regimens to treat GBM. Expression of TROY, an orphan receptor of the TNF receptor superfamily, increases with glial tumor grade, inversely correlates with patient overall survival, stimulates GBM cell invasion in vitro and in vivo, and increases resistance to temozolomide and radiation therapy. Conversely, silencing TROY expression inhibits GBM cell invasion, increases sensitivity to temozolomide, and prolongs survival in a preclinical intracranial xenograft model. Here, we have identified for the first time that TROY interacts with JAK1. Increased TROY expression increases JAK1 phosphorylation. In addition, increased TROY expression promotes STAT3 phosphorylation and STAT3 transcriptional activity that is dependent upon JAK1. TROY-mediated activation of STAT3 is independent of its ability to stimulate activity of NF-κB. Inhibition of JAK1 activity by ruxolitinib or knockdown of JAK1 expression by siRNA significantly inhibits TROY-induced STAT3 activation, GBM cell migration, and decreases resistance to temozolomide. Taken together, our data indicate that the TROY signaling complex may represent a potential therapeutic target with the distinctive capacity to exert effects on multiple pathways mediating GBM cell invasion and resistance.

EGFR signaling pathway occupies an important position in cancer-related downstream signaling pathways of Pyk2

Proline-rich tyrosine kinase 2 (Pyk2) is a member of focal adhesion kinase (FAK) non-receptor tyrosine kinase family and has been found to promote cancer cell survival, proliferation, migration, invasion, and metastasis. Pyk2 takes part in different carcinogenic signaling pathways to promote cancer progression, including epidermal growth factor receptor (EGFR) signaling pathway. EGFR signaling pathway is a traditional carcinogenic signaling pathway, which plays a critical role in tumorigenesis and tumor progression. FAK inhibitors have been reported to fail to get the ideal anti-cancer outcomes because of activation of EGFR signaling pathway. Better understanding of Pyk2 downstream targets and interconnectivity between Pyk2 and carcinogenic EGFR signaling pathway will help finding more effective targets for clinical anti-cancer combination therapies. Thus, the interconnectivity between Pyk2 and EGFR signaling pathway, which regulates tumor development and metastasis, needs to be elucidated. In this review, we summarized the downstream targets of Pyk2 in cancers, focused on the connection between Pyk2 and EGFR signaling pathway in different cancer types, and provided a new overview of the roles of Pyk2 in EGFR signaling pathway and cancer development.

Role of Pyk2 in Human Cancers

Proline-rich tyrosine kinase 2 (Pyk2) plays essential roles in tumorigenesis and tumor progression. Pyk2 serves as a non-receptor tyrosine kinase regulating tumor cell survival, proliferation, migration, invasion, metastasis, and chemo-resistance, and is associated with poor prognosis and shortened survival in various cancer types. Thus, Pyk2 has been traditionally regarded as an oncogene and potential therapeutic target for cancers. However, a few studies have also demonstrated that Pyk2 exerts tumor-suppressive effects in some cancers, and anti-cancer treatment of Pyk2 inhibitors may only achieve marginal benefits in these cancers. Therefore, more detailed knowledge of the contradictory functions of Pyk2 is needed. In this review, we summarized the tissue distribution, expression, interactive molecules of Pyk2 in the signaling pathway, and roles of Pyk2 in cancers, and focused on regulation of the interconnectivity between Pyk2 and its downstream targets. The potential use of inhibitors of Pyk2 and its related pathways in cancer therapy is also discussed.

Proline-Rich Protein Tyrosine Kinase 2 in Inflammation and Cancer

Focal adhesion kinase (FAK) and its homologous FAK-related proline-rich tyrosine kinase 2 (Pyk2) contain the same domain, exhibit high sequence homology and are defined as a distinct family of non-receptor tyrosine kinases. This group of kinases plays critical roles in cytoskeletal dynamics and cell adhesion by regulating survival and growth signaling. This review summarizes the physiological and pathological functions of Pyk2 in inflammation and cancers. In particular, overexpression of Pyk2 in cancerous tissues is correlated with poor outcomes. Pyk2 stimulates multiple oncogenic signaling pathways, such as Wnt/β-catenin, PI3K/Akt, MAPK/ERK, and TGF-β/EGFR/VEGF, and facilitates carcinogenesis, migration, invasion, epithelial⁻mesenchymal transition and metastasis. Therefore, Pyk2 is a high-value therapeutic target and has clinical significance.

A Novel Signaling Complex between TROY and EGFR Mediates Glioblastoma Cell Invasion

Glioblastoma is the most frequent primary brain tumor in adults and a highly lethal malignancy with a median survival of about 15 months. The aggressive invasion of the surrounding normal brain makes complete surgical resection impossible, increases the resistance to radiation and chemotherapy, and assures tumor recurrence. Thus, there is an urgent need to develop innovative therapeutics to target the invasive tumor cells for improved treatment outcomes of this disease. Expression of TROY (TNFRSF19), a member of the tumor necrosis factor (TNF) receptor family, increases with increasing glial tumor grade and inversely correlates with patient survival. Increased expression of TROY stimulates glioblastoma cell invasion in vitro and in vivo and increases resistance to temozolomide and radiation therapy. Conversely, silencing TROY expression inhibits glioblastoma cell invasion, increases temozolomide sensitivity, and prolongs survival in an intracranial xenograft model. Here, a novel complex is identified between TROY and EGFR, which is mediated predominantly by the cysteine-rich CRD3 domain of TROY. Glioblastoma tumors with elevated TROY expression have a statistically positive correlation with increased EGFR expression. TROY expression significantly increases the capacity of EGF to stimulate glioblastoma cell invasion, whereas depletion of TROY expression blocks EGF stimulation of glioblastoma cell invasion. Mechanistically, TROY expression modulates EGFR signaling by facilitating EGFR activation and delaying EGFR receptor internalization. Moreover, the association of EGFR with TROY increases TROY-induced NF-κB activation. These findings substantiate a critical role for the TROY-EGFR complex in regulation of glioblastoma cell invasion.Implications: The TROY-EGFR signaling complex emerges as a potential therapeutic target to inhibit glioblastoma cell invasion. Mol Cancer Res; 16(2); 322-32. ©2017 AACR.

A Cell Internalizing Antibody Targeting Capsid Protein (p24) Inhibits the Replication of HIV-1 in T Cells Lines and PBMCs: A Proof of Concept Study

There remains a need for newer therapeutic approaches to combat HIV/AIDS. Viral capsid protein p24 plays important roles in HIV pathogenesis. Peptides and small molecule inhibitors targeting p24 have shown to inhibit virus replication in treated cell. High specificity and biological stability of monoclonal antibodies (mAbs) make them an attractive contender for in vivo treatments. However, mAbs do not enter into cells, thus are restricted to target surface molecules. This also makes targeting intracellular HIV-1 p24 a challenge. A mAb specific to p24 that can internalize into the HIV-infected cells is hypothesized to inhibit the virus replication. We selected a mAb that has previously shown to inhibit p24 polymerization in an in vitro assay and chemically conjugated it with cell penetrating peptides (CPP) to generate cell internalizing anti-p24 mAbs. Out of 8 CPPs tested, κFGF-MTS -conjugated mAbs internalized T cells most efficiently. At nontoxic concentration, the κFGF-MTS-anti-p24-mAbs reduced the HIV-1 replication up to 73 and 49% in T-lymphocyte and PBMCs respectively. Marked inhibition of HIV-1 replication in relevant cells by κFGF-MTS-anti-p24-mAbs represents a viable strategy to target HIV proteins present inside the cells.

Microglia Activate Migration of Glioma Cells through a Pyk2 Intracellular Pathway

Glioblastoma is one of the most aggressive and fatal brain cancers due to the highly invasive nature of glioma cells. Microglia infiltrate most glioma tumors and, therefore, make up an important component of the glioma microenvironment. In the tumor environment, microglia release factors that lead to the degradation of the extracellular matrix and stimulate signaling pathways to promote glioma cell invasion. In the present study, we demonstrated that microglia can promote glioma migration through a mechanism independent of extracellular matrix degradation. Using western blot analysis, we found upregulation of proline rich tyrosine kinase 2 (Pyk2) protein phosphorylated at Tyr579/580 in glioma cells treated with microglia conditioned medium. This upregulation occurred in rodent C6 and GL261 as well as in human glioma cell lines with varying levels of invasiveness (U-87MG, A172, and HS683). siRNA knock-down of Pyk2 protein and pharmacological blockade by the Pyk2/focal-adhesion kinase (FAK) inhibitor PF-562,271 reversed the stimulatory effect of microglia on glioma migration in all cell lines. A lower concentration of PF-562,271 that selectively inhibits FAK, but not Pyk2, did not have any effect on glioma cell migration. Moreover, with the use of the CD11b-HSVTK microglia ablation mouse model we demonstrated that elimination of microglia in the implanted tumors (GL261 glioma cells were used for brain implantation) by the local in-tumor administration of Ganciclovir, significantly reduced the phosphorylation of Pyk2 at Tyr579/580 in implanted tumor cells. Taken together, these data indicate that microglial cells activate glioma cell migration/dispersal through the pro-migratory Pyk2 signaling pathway in glioma cells.

How to awaken your nanomachines: Site-specific activation of focal adhesion kinases through ligand interactions

The focal adhesion kinase (FAK) and the related protein-tyrosine kinase 2-beta (Pyk2) are highly versatile multidomain scaffolds central to cell adhesion, migration, and survival. Due to their key role in cancer metastasis, understanding and inhibiting their functions are important for the development of targeted therapy. Because FAK and Pyk2 are involved in many different cellular functions, designing drugs with partial and function-specific inhibitory effects would be desirable. Here, we summarise recent progress in understanding the structural mechanism of how the tug-of-war between intramolecular and intermolecular interactions allows these protein 'nanomachines' to become activated in a site-specific manner.

Proliferation and migration of tumor cells in tapered channels

Tumor cells depict two deviant tendencies; over-proliferation and vigorous migration. A tapered channel device is designed and fabricated for in vitro studies. We report inhibited proliferation and migration of human glioblastoma (hGBM) cells when exposed to an aptamer that is known to bind epidermal growth factor receptors (EGFR). The device is integrated with controlled ambient and microscope for providing real-time and quantitative characterization of the tumor cell behavior. The results show that hGBM cells loose proliferation and motility when exposed to the anti-EGFR aptamer. The aptamer directly inhibits and blocks EGF-induced EGFR phosphorylation. This also reduces the ability of cells to remodel their internal structure for invasion through narrow constrictions. This provides a framework for possible studies on efficacy of other inhibiting molecules.

A Novel Interaction between Pyk2 and MAP4K4 Is Integrated with Glioma Cell Migration

Glioma cell migration correlates with Pyk2 activity, but the intrinsic mechanism that regulates the activity of Pyk2 is not fully understood. Previous studies have supported a role for the N-terminal FERM domain in the regulation of Pyk2 activity as mutations in the FERM domain inhibit Pyk2 phosphorylation. To search for novel protein-protein interactions mediated by the Pyk2 FERM domain, we utilized a yeast two-hybrid genetic selection to identify the mammalian Ste20 homolog MAP4K4 as a binding partner for the Pyk2 FERM domain. MAP4K4 coimmunoprecipitated with Pyk2 and was a substrate for Pyk2 but did not coimmunoprecipitate with the closely related focal adhesion kinase FAK. Knockdown of MAP4K4 expression inhibited glioma cell migration and effectively blocked Pyk2 stimulation of glioma cell. Increased expression of MAP4K4 stimulated glioma cell migration; however, this stimulation was blocked by knockdown of Pyk2 expression. These data support that the interaction of MAP4K4 and Pyk2 is integrated with glioma cell migration and suggest that inhibition of this interaction may represent a potential therapeutic strategy to limit glioblastoma tumor dispersion.

Reciprocal activation of transcription factors underlies the dichotomy between proliferation and invasion of glioma cells

Histology of malignant glioma depicts dense proliferative areas rich in angiogenesis as well as dissemination of neoplastic cells into adjacent brain tissue. Although the mechanisms that trigger transition from proliferative to invasive phenotypes are complex, the dichotomy of cell proliferation and migration, the “Go or Grow” hypothesis, argues for specific and coordinated regulation of these phenotypes. We investigated transcriptional elements that accompany the phenotypes of migration and proliferation, and consider the therapeutic significance of the “Go or Grow” hypothesis. Interrogation of matched core and rim regions from human glioblastoma biopsy specimens in situ (n = 44) revealed higher proliferation (Ki67 labeling index) in cells residing at the core compared to the rim. Profiling activated transcription factors in a panel of migration-activated versus migration-restricted GBM cells portrayed strong NF-κB activity in the migratory cell population. In contrast, increased c-Myc activity was found in migration-restricted proliferative cells. Validation of transcriptional activity by NF-κB- or c-Myc-driven GFP or RFP, respectively, showed an increased NF-κB activity in the active migrating cells, whereas the proliferative, migration restricted cells displayed increased c-Myc activity. Immunohistochemistry on clinical specimens validated a robust phosphorylated c-Myc staining in tumor cells at the core, whereas increased phosphorylated NF-κB staining was detected in the invasive tumor cells at the rim. Functional genomics revealed that depletion of c-Myc expression by siRNA oligonucleotides reduced cell proliferation in vitro, but surprisingly, cell migration was enhanced significantly. Conversely, inhibition of NF-κB by pharmacological inhibitors, SN50 or BAY-11, decreased both cell migration in vitro and invasion ex vivo. Notably, inhibition of NF-κB was found to have no effect on the proliferation rate of glioma cells. These findings suggest that the reciprocal and coordinated suppression/activation of transcription factors, such as c-Myc and NF-κB may underlie the shift of glioma cells from a “growing-to-going” phenotype.

TROY (TNFRSF19) promotes glioblastoma survival signaling and therapeutic resistance

Of the features that characterize glioblastoma, arguably none is more clinically relevant than the propensity of malignant glioma cells to aggressively invade into the surrounding normal brain tissue. These invasive cells render complete resection impossible, confer significant resistance to chemo- and radiation-therapy, and virtually assure tumor recurrence. Expression of TROY (TNFRSF19), a member of the TNF receptor superfamily, inversely correlates with patient survival and stimulates glioblastoma cell migration and invasion in vitro. In this study, we report that TROY is overexpressed in glioblastoma tumor specimens and TROY mRNA expression is increased in the invasive cell population in vivo. In addition, inappropriate expression of TROY in mouse astrocytes in vivo using glial-specific gene transfer in transgenic mice induces astrocyte migration within the brain, validating the importance of the TROY signaling cascade in glioblastoma cell migration and invasion. Knockdown of TROY expression in primary glioblastoma xenografts significantly prolonged survival in vivo. Moreover, TROY expression significantly increased resistance of glioblastoma cells to both IR- and TMZ-induced apoptosis via activation of Akt and NF-κB. Inhibition of either Akt or NF-κB activity suppressed the survival benefits of TROY signaling in response to TMZ treatment. These findings position aberrant expression and/or signaling by TROY as a contributor to the dispersion of glioblastoma cells and therapeutic resistance.

IMPLICATIONS

Targeting of TROY may increase tumor vulnerability and improve therapeutic response in glioblastoma. Mol Cancer Res; 11(8); 865-74. ©2013 AACR.

Dynamin and PTP-PEST cooperatively regulate Pyk2 dephosphorylation in osteoclasts

Bone loss is caused by the dysregulated activity of osteoclasts which degrade the extracellular bone matrix. The tyrosine kinase Pyk2 is highly expressed in osteoclasts, and mice lacking Pyk2 exhibit an increase in bone mass, in part due to impairment of osteoclast function. Pyk2 is activated by phosphorylation at Y402 following integrin activation, but the mechanisms leading to Pyk2 dephosphorylation are poorly understood. In the current study, we examined the mechanism of action of the dynamin GTPase on Pyk2 dephosphorylation. Our studies reveal a novel mechanism for the interaction of Pyk2 with dynamin, which involves the binding of Pyk2's FERM domain with dynamin's plextrin homology domain. In addition, we demonstrate that the dephosphorylation of Pyk2 requires dynamin's GTPase activity and is mediated by the tyrosine phosphatase PTP-PEST. The dephosphorylation of Pyk2 by dynamin and PTP-PEST may be critical for terminating outside-in integrin signaling, and for stabilizing cytoskeletal reorganization during osteoclast bone resorption.

Inhibition of Pyk2 blocks lung inflammation and injury in a mouse model of acute lung injury

Background

Proline-rich tyrosine kinase 2 (Pyk2) is essential in neutrophil degranulation and chemotaxis in vitro. However, its effect on the process of lung inflammation and edema formation during LPS induced acute lung injury (ALI) remains unknown. The goal of the present study was to determine the effect of inhibiting Pyk2 on LPS-induced acute lung inflammation and injury in vivo.

Methods

C57BL6 mice were given either 10 mg/kg LPS or saline intratracheally. Inhibition of Pyk2 was effected by intraperitoneal administration TAT-Pyk2-CT 1 h before challenge. Bronchoalveolar lavage analysis of cell counts, lung histology and protein concentration in BAL were analyzed at 18 h after LPS treatment. KC and MIP-2 concentrations in BAL were measured by a mouse cytokine multiplex kit. The static lung compliance was determined by pressure-volume curve using a computer-controlled small animal ventilator. The extravasated Evans blue concentration in lung homogenate was determined spectrophotometrically.

Results

Intratracheal instillation of LPS induced significant neutrophil infiltration into the lung interstitium and alveolar space, which was attenuated by pre-treatment with TAT-Pyk2-CT. TAT-Pyk2-CT pretreatment also attenuated 1) myeloperoxidase content in lung tissues, 2) vascular leakage as measured by Evans blue dye extravasation in the lungs and the increase in protein concentration in bronchoalveolar lavage, and 3) the decrease in lung compliance. In each paradigm, treatment with control protein TAT-GFP had no blocking effect. By contrast, production of neutrophil chemokines MIP-2 and keratinocyte-derived chemokine in the bronchoalveolar lavage was not reduced by TAT-Pyk2-CT. Western blot analysis confirmed that tyrosine phosphorylation of Pyk2 in LPS-challenged lungs was reduced to control levels by TAT-Pyk2-CT pretreatment.

Conclusions

These results suggest that Pyk2 plays an important role in the development of acute lung injury in mice and that pharmacological inhibition of Pyk2 might provide a potential therapeutic strategy in the pretreatment for patients at imminent risk of developing acute lung injury.

Extracellular ATP stimulates epithelial cell motility through Pyk2-mediated activation of the EGF receptor

Wounding usually causes considerable cell damage, and released ATP promotes migration of nearby epithelium. ATP binds to purinergic receptors on the cell surface and induces transactivation of the EGF receptor through signaling by the Src family kinases (SFKs). Here we tested whether ATP activates these kinases through Pyk2, a member of the focal adhesion kinase family. Pyk2 was rapidly and potently activated by treating corneal epithelial cells with ATP, and physical interaction of Pyk2 with the SFKs was enhanced. Disruption of Pyk2 signaling either by siRNA or by expression of a dominant-negative mutant led to inhibition of ATP-induced activation of the SFKs and the EGF receptor. Inhibiting Pyk2 activity also blocked ATP stimulation of healing of wounds in epithelial cell sheets. These data suggest that ATP stimulates sequential activation of Pyk2, SFKs, and the EGF receptor to induce cell migration.

HCMV pUS28 initiates pro-migratory signaling via activation of Pyk2 kinase

Background

Human Cytomegalovirus (HCMV) has been implicated in the acceleration of vascular disease and chronic allograft rejection. Recently, the virus has been associated with glioblastoma and other tumors. We have previously shown that the HCMV-encoded chemokine receptor pUS28 mediates smooth muscle cell (SMC) and macrophage motility and this activity has been implicated in the acceleration of vascular disease. pUS28 induced SMC migration involves the activation of the protein tyrosine kinases (PTKs) Src and Focal adhesion kinase as well as the small GTPase RhoA. The PTK Pyk2 has been shown to play a role in cellular migration and formation of cancer, especially glioblastoma. The role of Pyk2 in pUS28 signaling and migration are unknown.

Methods

In the current study, we examined the involvement of the PTK Pyk2 in pUS28-induced cellular motility. We utilized in vitro migration of SMC to determine the requirements for Pyk2 in pUS28 pro-migratory signaling. We performed biochemical analysis of Pyk2 signaling in response to pUS28 activation to determine the mechanisms involved in pUS28 migration. We performed mass spectrometric analysis of Pyk2 complexes to identify novel Pyk2 binding partners.

Results

Expression of a mutant form of Pyk2 lacking the autophosphorylation site (Tyr-402) blocks pUS28-mediated SMC migration in response to CCL5, while the kinase-inactive Pyk2 mutant failed to elicit the same negative effect on migration. pUS28 stimulation with CCL5 results in ligand-dependent and calcium-dependent phosphorylation of Pyk2 Tyr-402 and induced the formation of an active Pyk2 kinase complex containing several novel Pyk2 binding proteins. Expression of the autophosphorylation null mutant Pyk2 F402Y did not abrogate the formation of an active Pyk2 kinase complex, but instead prevented pUS28-mediated activation of RhoA. Additionally, pUS28 activated RhoA via Pyk2 in the U373 glioblastoma cells. Interestingly, the Pyk2 kinase complex in U373 contained several proteins known to participate in glioma tumorigenesis.

Conclusions

These findings represent the first demonstration that pUS28 signals through Pyk2 and that this PTK participates in pUS28-mediated cellular motility via activation of RhoA. Furthermore, these results provide a potential mechanistic link between HCMV-pUS28 and glioblastoma cell activation.

TROY (TNFRSF19) is overexpressed in advanced glial tumors and promotes glioblastoma cell invasion via Pyk2-Rac1 signaling

A critical problem in the treatment of malignant gliomas is the extensive infiltration of individual tumor cells into adjacent brain tissues. This invasive phenotype severely limits all current therapies, and to date, no treatment is available to control the spread of this disease. Members of the tumor necrosis factor (TNF) ligand superfamily and their cognate receptors regulate various cellular responses including proliferation, migration, differentiation, and apoptosis. Specifically, the TNFRSF19/TROY gene encodes a type I cell surface receptor that is expressed on migrating or proliferating progenitor cells of the hippocampus, thalamus, and cerebral cortex. Here, we show that levels of TROY mRNA expression directly correlate with increasing glial tumor grade. Among malignant gliomas, TROY expression correlates inversely with overall patient survival. In addition, we show that TROY overexpression in glioma cells activates Rac1 signaling in a Pyk2-dependent manner to drive glioma cell invasion and migration. Pyk2 coimmunoprecipitates with the TROY receptor, and depletion of Pyk2 expression by short hairpin RNA interference oligonucleotides inhibits TROY-induced Rac1 activation and subsequent cellular migration. These findings position aberrant expression and/or signaling by TROY as a contributor, and possibly as a driver, of the malignant dispersion of glioma cells.

The Pyk2 FERM regulates Pyk2 complex formation and phosphorylation

The focal adhesion kinase Pyk2 integrates signals from cell adhesion receptors, growth factor receptors, and G-protein-coupled receptors leading to the activation of intracellular signaling pathways that regulate cellular phenotypes. The intrinsic mechanism for the activation of Pyk2 activity remains to be fully defined. Previously, we reported that mutations in the N-terminal FERM domain result in loss of Pyk2 activity and expression of the FERM domain as an autonomous fragment inhibits Pyk2 activity. In the present study, we sought to determine the mechanism that underlies these effects. Utilizing differentially epitope-tagged Pyk2 constructs, we observed that Pyk2 forms oligomeric complexes in cells and that complex formation correlates positively with tyrosine phosphorylation. Similarly, when expressed as an autonomous fragment, the Pyk2 FERM domain formed a complex with other Pyk2 FERM domains but not the FAK FERM domain. When co-expressed with full-length Pyk2, the autonomously expressed Pyk2 FERM domain formed a complex with full-length Pyk2 preventing the formation of Pyk2 oligomers and resulting in reduced Pyk2 phosphorylation. Deletion of the FERM domain from Pyk2 enhanced Pyk2 complex formation and phosphorylation. Together, these data indicate that the Pyk2 FERM domain is involved in the regulation of Pyk2 activity by acting to regulate the formation of Pyk2 oligomers that are critical for Pyk2 activity.

Structural conservation in band 4.1, ezrin, radixin, moesin (FERM) domains as a guide to identify inhibitors of the proline-rich tyrosine kinase 2

The nonreceptor focal adhesion kinases FAK and Pyk2 play a central role in the regulation of glioma cell proliferation and migration, making them attractive targets to improve clinical outcome. Noncatalytic targeting represents a novel approach to regulate the activity of these tyrosine kinases. A combination of site directed mutagenesis and molecular modeling was used to identify compounds that target the F3 module of the Pyk2 FERM domain. A protein pharmacophore model for the Pyk2 FERM/F3 module, generated utilizing the structural conservation of ligand-bound FERM domains with known 3D structures, was used to search the LeadQuest compound library. Compounds compliant with the model were tested for their ability to inhibit the binding of a monoclonal antibody that maps to a functional site on the F3 module. The highest scoring compound bound directly to the Pyk2 FERM domain, inhibited Pyk2 stimulated glioma migration, and provides the framework for the development of novel therapeutic agents to target the activity of the focal adhesion kinases.

Targeting Pyk2 for therapeutic intervention

IMPORTANCE OF THE FIELD

The focal adhesion tyrosine kinases FAK and Pyk2 are uniquely situated to act as critical mediators for the activation of signaling pathways that regulate cell migration, proliferation and survival. By coordinating adhesion and cytoskeletal dynamics with survival and growth signaling, FAK and Pyk2 represent molecular therapeutic targets in cancer as malignant cells often exhibit defects in these processes.

AREAS COVERED IN THIS REVIEW

This review examines the structure and function of the focal adhesion kinase Pyk2 and intends to provide a rationale for the employment of modulating strategies that include both catalytic and extra-catalytic approaches that have been developed in the last 3 - 5 years.

WHAT THE READER WILL GAIN

Targeting tyrosine kinases in oncology has focused on the ATP binding pocket as means to inhibit catalytic activity and downregulate pathways involved in tumor invasion. This review discusses the available catalytic inhibitors and compares them to the alternative approach of targeting protein-protein interactions that regulate kinase activity.

TAKE HOME MESSAGE

Development of specific catalytic inhibitors of the focal adhesion kinases has improved but significant challenges remain. Thus, approaches that inhibit the effector function of Pyk2 by targeting regulatory modules can increase specificity and will be a welcome asset to the therapeutic arena.

Pyk2 inhibition of p53 as an adaptive and intrinsic mechanism facilitating cell proliferation and survival

Pyk2 is a cytoplasmic tyrosine kinase related to focal adhesion kinase (FAK). Compensatory Pyk2 expression occurs upon FAK loss in mice. However, the impact of Pyk2 up-regulation remains unclear. Previous studies showed that nuclear-localized FAK promotes cell proliferation and survival through FAK FERM domain-enhanced p53 tumor suppressor degradation (Lim, S. T., Chen, X. L., Lim, Y., Hanson, D. A., Vo, T. T., Howerton, K., Larocque, N., Fisher, S. J., Schlaepfer, D. D., and Ilic, D. (2008) Mol. Cell 29, 9-22). Here, we show that FAK knockdown triggered p53 activation and G(1) cell cycle arrest in human umbilical vein endothelial cells after 4 days. However, by 7 days elevated Pyk2 expression occurred with a reduction in p53 levels and the release of the G(1) block under conditions of continued FAK knockdown. To determine whether Pyk2 regulates p53, experiments were performed in FAK(-/-)p21(-/-) mouse embryo fibroblasts expressing endogenous Pyk2 and in ID8 ovarian carcinoma cells expressing both Pyk2 and FAK. In both cell lines, Pyk2 knockdown increased p53 levels and inhibited cell proliferation associated with G(1) cell cycle arrest. Pyk2 FERM domain re-expression was sufficient to reduce p53 levels and promote increased BrdUrd incorporation. Pyk2 FERM promoted Mdm2-dependent p53 ubiquitination. Pyk2 FERM effects on p53 were blocked by proteasomal inhibition or mutational-inactivation of Pyk2 FERM nuclear localization. Staurosporine stress of ID8 cells promoted endogenous Pyk2 nuclear accumulation and enhanced Pyk2 binding to p53. Pyk2 knockdown potentiated ID8 cell death upon staurosporine addition. Moreover, Pyk2 FERM expression in human fibroblasts upon FAK knockdown prevented cisplatin-mediated apoptosis. Our studies demonstrate that nuclear Pyk2 functions to limit p53 levels, thus facilitating cell growth and survival in a kinase-independent manner.