Critical role of the FERM domain in Pyk2 stimulated glioma cell migration

Activated PyK2 and Its Associated Molecules Transduce Cellular Signaling from the Cancerous Milieu for Cancer Metastasis

PyK2 is a member of the proline-rich tyrosine kinase and focal adhesion kinase families and is ubiquitously expressed. PyK2 is mainly activated by stimuli, such as activated Src kinases and intracellular acidic pH. The mechanism of PyK2 activation in cancer cells has been addressed extensively. The up-regulation of PyK2 through overexpression and enhanced phosphorylation is a key feature of tumorigenesis and cancer migration. In this review, we summarized the cancer milieu, including acidification and cancer-associated molecules, such as chemical reagents, interactive proteins, chemokine-related molecules, calcium channels/transporters, and oxidative molecules that affect the fate of PyK2. The inhibition of PyK2 leads to a beneficial strategy to attenuate cancer cell development, including metastasis. Thus, we highlighted the effect of PyK2 on various cancer cell types and the distribution of molecules that affect PyK2 activation. In particular, we underlined the relationship between PyK2 and cancer metastasis and its potential to treat cancer cells.

Small Molecular Inhibitors Reverse Cancer Metastasis by Blockading Oncogenic PITPNM3

Most cancer-related deaths are a result of metastasis. The development of small molecular inhibitors reversing cancer metastasis represents a promising therapeutic opportunity for cancer patients. This pan-cancer analysis identifies oncogenic roles of membrane-associated phosphatidylinositol transfer protein 3 (PITPNM3), which is crucial for cancer metastasis. Small molecules targeting PITPNM3 must be explored further. Here, PITPNM3-selective small molecular inhibitors are reported. These compounds exhibit target-specific inhibition of PITPNM3 signaling, thereby reducing metastasis of breast cancer cells. Besides, by using nanoparticle-based delivery systems, these PITPNM3-selective compounds loaded nanoparticles significantly repress metastasis of breast cancer in mouse xenograft models and organoid models. Notably, the results establish an important metastatic-promoting role for PITPNM3 and offer PITPNM3 inhibition as a therapeutic strategy in metastatic breast cancer.

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.

Endogenous Control Mechanisms of FAK and PYK2 and Their Relevance to Cancer Development

Focal adhesion kinase (FAK) and its close paralogue, proline-rich tyrosine kinase 2 (PYK2), are key regulators of aggressive spreading and metastasis of cancer cells. While targeted small-molecule inhibitors of FAK and PYK2 have been found to have promising antitumor activity, their clinical long-term efficacy may be undermined by the strong capacity of cancer cells to evade anti-kinase drugs. In healthy cells, the expression and/or function of FAK and PYK2 is tightly controlled via modulation of gene expression, competing alternatively spliced forms, non-coding RNAs, and proteins that directly or indirectly affect kinase activation or protein stability. The molecular factors involved in this control are frequently deregulated in cancer cells. Here, we review the endogenous mechanisms controlling FAK and PYK2, and with particular focus on how these mechanisms could inspire or improve anticancer therapies.

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.

The nonreceptor protein tyrosine kinase Pyk2 promotes the turnover of monocytes at steady state

Monocytes are short-lived myeloid cells that perform functions essential for tissue homeostasis and disease resolution. However, the cellular mechanisms controlling the maintenance and turnover of monocyte populations are largely undefined. Proline-rich tyrosine kinase 2 (Pyk2) is a nonreceptor tyrosine kinase that regulates numerous immune cell functions, but its role in monocytes is currently unknown. In this study, we sought to characterize the expression and function of Pyk2 in lineage-committed monocyte populations. Here, we report that Pyk2 protein expression is increased in the Ly6C^- monocyte population. Using a Pyk2 knockout mouse model (Pyk2^-/-), we show that Pyk2 regulates the relative proportion of monocyte subsets normally represented in the bone marrow (BM) at steady state. In support of this conclusion, a similar phenotype was observed in the peripheral blood and spleen. Data from reciprocal BM chimera experiments indicate that the alterations in monocyte populations exhibited by Pyk2^-/- mice are due to factors intrinsic to the monocytes. Lineage-tracing of monocyte populations suggests that Pyk2 promotes apoptosis in BM monocytes, thereby acting as an important homeostatic regulator of turnover in these short-lived, innate immune cells.

Novel Role of Src in Priming Pyk2 Phosphorylation

Proline-rich tyrosine kinase 2 (Pyk2) is a member of the focal adhesion kinase (FAK) family of non-receptor tyrosine kinases and plays an important role in diverse cellular events downstream of the integrin-family of receptors, including cell migration, proliferation and survival. Here, we have identified a novel role for Src kinase in priming Pyk2 phosphorylation and subsequent activation upon cell attachment on the integrin-ligand fibronectin. By using complementary methods, we show that Src activity is indispensable for the initial Pyk2 phosphorylation on the Y402 site observed in response to cell attachment. In contrast, the initial fibronectin-induced autophosphorylation of FAK in the homologous Y397 site occurs in a Src-independent manner. We demonstrate that the SH2-domain of Src is required for Src binding to Pyk2 and for Pyk2 phosphorylation at sites Y402 and Y579. Moreover, Y402 phosphorylation is a prerequisite for the subsequent Y579 phosphorylation. While this initial phosphorylation of Pyk2 by Src is independent of Pyk2 kinase activity, subsequent autophosphorylation of Pyk2 in trans is required for full Pyk2 phosphorylation and activation. Collectively, our studies reveal a novel function of Src in priming Pyk2 (but not FAK) phosphorylation and subsequent activation downstream of integrins, and shed light on the signaling events that regulate the function of Pyk2.

Store-operated Ca(2+) entry regulates glioma cell migration and invasion via modulation of Pyk2 phosphorylation

BACKGROUND

The ubiquitous second messenger Ca(2+) has been demonstrated to play an important role in cancer progression. Store-operated Ca(2+) entry (SOCE) is the main Ca(2+) entry pathway regulating intracellular Ca(2+) concentration in a variety of cancer types. The present study aimed to explore the specific mechanisms of SOCE in the processes of glioma migration and invasion.

METHODS

The expression of Orai1, a key component of SOCE, was examined in glioma samples and glioma cell lines by immunohistochemistry and western blot analysis. Both pharmacological intervention and RNA interference were employed to investigate the role of SOCE in glioma cell migration and invasion in vitro. The intracellular Ca(2+) was certified through Fluo-4/AM based Ca(2+) measurement. The effect of SOCE on cell viability, migration, and invasion was explored by methyl thiazolyl tetrazolium (MTT) assay, wound healing assay, transwell invasion assay. Western blot analysis and immunofluorescence assay were used to observe the changes of downstream related protein and cell morpholog.

RESULTS

Orai1 expression was elevated in glioma tissues and several glioma cell lines compared with non-neoplastic brain tissues. Either inhibition of SOCE by a pharmacological inhibitor or Orai1 downregulation suppressed glioma cell migration and invasion. However, re-expression of Orai1 could rescue glioma cell motility. Furthermore, phosphorylation of proline-rich tyrosine kinase 2 (Pyk2) participated in the mechanisms by which SOCE regulated focal adhesion turnover and epithelial-to-mesenchymal (-like) transition in glioma cells, both of which are considered to be critical for tumor progression.

CONCLUSIONS

The SOCE-Pyk2 pathway is essential for glioma migration and invasion. The study indicates the potential value of Orai1 as a molecular target for anti-invasion therapy.

Store-operated Ca(2+) entry regulates glioma cell migration and invasion via modulation of Pyk2 phosphorylation

Background

The ubiquitous second messenger Ca²⁺ has been demonstrated to play an important role in cancer progression. Store-operated Ca²⁺ entry (SOCE) is the main Ca²⁺ entry pathway regulating intracellular Ca²⁺ concentration in a variety of cancer types. The present study aimed to explore the specific mechanisms of SOCE in the processes of glioma migration and invasion.

Methods

The expression of Orai1, a key component of SOCE, was examined in glioma samples and glioma cell lines by immunohistochemistry and western blot analysis. Both pharmacological intervention and RNA interference were employed to investigate the role of SOCE in glioma cell migration and invasion in vitro. The intracellular Ca²⁺ was certified through Fluo-4/AM based Ca²⁺ measurement. The effect of SOCE on cell viability, migration, and invasion was explored by methyl thiazolyl tetrazolium (MTT) assay, wound healing assay, transwell invasion assay. Western blot analysis and immunofluorescence assay were used to observe the changes of downstream related protein and cell morpholog.

Results

Orai1 expression was elevated in glioma tissues and several glioma cell lines compared with non-neoplastic brain tissues. Either inhibition of SOCE by a pharmacological inhibitor or Orai1 downregulation suppressed glioma cell migration and invasion. However, re-expression of Orai1 could rescue glioma cell motility. Furthermore, phosphorylation of proline-rich tyrosine kinase 2 (Pyk2) participated in the mechanisms by which SOCE regulated focal adhesion turnover and epithelial-to-mesenchymal (−like) transition in glioma cells, both of which are considered to be critical for tumor progression.

Conclusions

The SOCE-Pyk2 pathway is essential for glioma migration and invasion. The study indicates the potential value of Orai1 as a molecular target for anti-invasion therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-014-0098-1) contains supplementary material, which is available to authorized users.

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.

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.

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.

The FERM domain: organizing the structure and function of FAK

Focal adhesion kinase (FAK) is a scaffold and tyrosine kinase protein that binds to itself and cellular partners through its four-point-one, ezrin, radixin, moesin (FERM) domain. Recent structural work reveals that regulatory protein partners convert auto-inhibited FAK into its active state by binding to its FERM domain. Further, the identity of FAK FERM domain-interacting proteins yields clues as to how FAK coordinates diverse cellular responses, including cell adhesion, polarization, migration, survival and death, and suggests that FERM domains might mediate information transfer between the cell cortex and nucleus. Importantly, the FAK FERM domain might act as a paradigm for the actions of other FERM domain-containing proteins.

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.

The T cell receptor-mediated phosphorylation of Pyk2 tyrosines 402 and 580 occurs via a distinct mechanism than other receptor systems

The tyrosine kinase Pyk2 is vital for integrating receptor-mediated signals controlling adhesion and motility in neuronal, epithelial, and hematopoietic cell types. In T cells, the stimulation of the TCR and costimulatory, chemokine, cytokine, and integrin receptors leads to the phosphorylation of Pyk2 and the induction of its catalytic activity. However, our understanding of the mechanism of the TCR-induced, site-specific phosphorylation of this kinase is incomplete and contradictory. To address this issue, the role of individual signaling pathways in the phosphorylation of Pyk2 tyrosines 402 and 580 upon TCR activation was assessed in human T cells. In contrast to other receptor systems, the TCR-induced phosphorylation of Pyk2 tyrosines 402 and 580 was dependent on the Src family kinases, Fyn or Lck. Interestingly, the TCR-mediated phosphorylation of Pyk2 tyrosines 402 and 580 did not require Ca(2+) influx, ZAP-70 activation, actin cytoskeleton rearrangement, or PI3K function. These observations are different than other receptor systems, which require the induction of one or more of these pathways. Together, these data have defined more fully the mechanism for the TCR-induced phosphorylation of specific sites on Pyk2, suggesting that the TCR has a distinct pathway for the activation of Pyk2 compared with other receptor systems.

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.

The Pyk2 FERM domain as a target to inhibit glioma migration

The invasion of malignant glioma cells into the surrounding normal brain precludes effective clinical treatment. In this report, we investigated the role of the NH(2)-terminal FERM domain in the regulation of the promigratory function of Pyk2. We report that the substitution of residues that constitute a small cleft on the surface of the F3 module of the FERM domain do not significantly alter Pyk2 expression but result in the loss of Pyk2 phosphorylation. A monoclonal antibody, designated 12A10, specifically targeting the Pyk2 FERM domain was generated and recognizes an epitope located on the beta5C-alpha1C surface of the F3 module of the FERM domain. Amino acid substitutions in the F3 module that resulted in the loss of Pyk2 phosphorylation also inhibited the binding of 12A10, suggesting that the 12A10 epitope overlaps a site that plays a role in Pyk2 activity. Conjugation of 12A10 to a membrane transport peptide led to intracellular accumulation and inhibition of glioma cell migration in a concentration-dependent manner. A single chain Fv fragment of 12A10 was stable when expressed in the intracellular environment, interacted directly with Pyk2, reduced Pyk2 phosphorylation, and inhibited glioma cell migration in vitro. Stable intracellular expression of the 12A10 scFv significantly extended survival in a glioma xenograft model. Together, these data substantiate a central role for the FERM domain in regulation of Pyk2 activity and identify the F3 module as a novel target to inhibit Pyk2 activity and inhibit glioma progression.

Differential effects of Pyk2 and FAK on the hypertrophic response of cardiac myocytes

The related cytoplasmic non-receptor tyrosine kinases Pyk2 (proline-rich tyrosine kinase 2) and FAK (focal adhesion kinase) have been implicated in phenylephrine-induced G-protein-coupled receptor-mediated signaling mechanisms leading to cardiomyocyte hypertrophy. We report that, in phenylephrine-stimulated neonatal rat ventricular myocytes (NRVM), Pyk2 augments expression of the hypertrophic marker atrial natriuretic factor (ANF) but reduces cytoskeletal organization and cell spreading. In contrast, FAK attenuates ANF production but does not alter cytoskeletal organization and cell spreading. Pyk2 and FAK exhibit differential localization in both unstimulated and phenylephrine-stimulated myocytes. Pyk2 catalytic activity is required for Pyk2 to augment ANF secretion but is not necessary to reduce cell spreading. Pyk2 autophosphorylation is required but not sufficient for Pyk2 to augment ANF secretion. Expression of the Pyk2 FERM domain as an autonomous fragment inhibits phenylephrine-mediated ANF secretion and reduces cell spreading. In addition, expression of the Pyk2 FERM domain inhibits the ability of Pyk2 to augment ANF secretion; this is correlated with reduced Pyk2 autophosphorylation. These data indicate that Pyk2 and FAK have different roles and occupy different positions in signaling pathways leading to the development of cardiomyocyte hypertrophy.

Extended survival of Pyk2 or FAK deficient orthotopic glioma xenografts

Disease progression of glioblastoma involves a complex interplay between tumor cells and the peri-tumor microenvironment. The propensity of malignant glioma cells to disperse throughout the brain typifies the disease and portends a poor response to surgical resection, radiotherapy, and current chemotherapeutics. The focal adhesion kinases FAK and Pyk2 function as important signaling effectors in glioma through stimulation of pro-migratory and proliferative signaling pathways. In the current study, we examined the importance of Pyk2 and FAK in the pathobiology of malignant glioma in an intracranial xenograft model. We show that mice with xenografts established with glioma cells with specific knockdown of Pyk2 or FAK expression by RNA interference had significantly increased survival compared to control mice. Furthermore, the effect of inhibition of Pyk2 activity in xenografts was compared to the effect of knockdown of Pyk2 expression. Inhibition of Pyk2 activity by stable expression an autonomous FERM domain in glioma cells slowed disease progression in the intracranial xenograft model. In contrast, expression of a variant FERM domain that does not inhibit Pyk2 activity did not alter survival. These results substantiate the disease relevance of both Pyk2 and FAK in glioma and suggest a novel approach to target Pyk2 for therapeutic benefit.

Up-regulation of proline-rich tyrosine kinase 2 in non-small cell lung cancer

Proline-rich tyrosine kinase 2 (PYK2) is a non-receptor tyrosine kinase, plays different roles in intracellular signaling pathways, that regulates a number of biological processes, such as cell proliferation, differentiation, adhesion and migration, which have been shown to correlate with tumor development and aggression. However, the involvement of PYK2 in human non-small cell lung cancer (NSCLC) has not yet been determined. In the present study, 90 patients with NSCLC (represented by adenocarcinoma and squamous cell carcinoma) were included retrospectively. NSCLC tissues were detected for the expression of PYK2 by immunohistochemistry. Correlation between the expression of PYK2 with the clinicopathological characteristics was analyzed. There were 64% (58 out of 90) of NSCLC patients with higher level of PYK2. Higher expression of PYK2 was significantly correlated with lymph node metastasis (node positive versus node negative, p=0.007). Patients with higher expression of PYK2 had advanced stage of NSCLCs (I+II versus III+IV, p=0.012). Protein level of PYK2 was also examined in 30 of these tumorous samples and matched non-tumorous counterparts by western blotting. PYK2 was apparently up-regulated in NSCLC tissues (tumor versus non-tumor, p=0.000). In the cell studies, extensive expression and activation of PYK2 were both found in higher metastatic BE1 cells. The activity of ERK1/2 in BE1 cells appeared extremely high as well. In conclusion, our results demonstrated that PYK2 is up-regulated in NSCLCs, and the higher expression and activation of PYK2 may play a role in modulating the activity of ERK1/2, and lead to the progression of NSCLC.

Protein-tyrosine kinase CAKbeta/PYK2 is activated by binding Ca2+/calmodulin to FERM F2 alpha2 helix and thus forming its dimer

CAKbeta (cell adhesion kinase beta)/PYK2 (proline-rich tyrosine kinase 2) is the second protein-tyrosine kinase of the FAK (focal adhesion kinase) subfamily. It is different from FAK in that it is activated following an increase in cytoplasmic free Ca2+. In the present study we have investigated how Ca2+ activates CAKbeta/PYK2. Calmodulin-agarose bound CAKbeta/PYK2, but not FAK, in the presence of CaCl2. An alpha-helix (F2-alpha2) present in the FERM (band four-point-one, ezrin, radixin, moesin homology) F2 subdomain of CAKbeta/PYK2 was the binding site of Ca2+/calmodulin; a mutant of this region, L176A/Q177A (LQ/AA) CAKbeta/PYK2, bound to Ca2+/calmodulin much less than the wild-type. CAKbeta/PYK2 is known to be prominently tyrosine phosphorylated when overexpressed from cDNA. The enhanced tyrosine phosphorylation was inhibited by W7, an inhibitor of calmodulin, and by a cell-permeable Ca2+ chelator and was almost defective in the LQ/AA-mutant CAKbeta/PYK2. CAKbeta/PYK2 formed a homodimer on binding of Ca2+/calmodulin, which might then induce a conformational change of the kinase, resulting in transphosphorylation within the dimer. The dimer was formed at a free-Ca2+ concentration of 8-12 muM and was stable at 500 nM Ca2+, but dissociated to a monomer in a Ca2+-free buffer. The dimer formation of CAKbeta/PYK2 FERM domain was partially defective in the LQ/AA-mutant FERM domain and was blocked by W7 and by a synthetic peptide with amino acids 168-188 of CAKbeta/PYK2, but not by a peptide with its LQ/AA-mutant sequence. It is known that the F2-alpha2 helix is found immediately adjacent to a hydrophobic pocket in the FERM F2 lobe, which locks, in the autoinhibited FAK, the C-lobe of the kinase domain. Our results indicate that Ca2+/calmodulin binding to the FERM F2-alpha2 helix of CAKbeta/PYK2 releases its kinase domain from autoinhibition by forming a dimer.

Calcium-dependent Pyk2 activation: a role for calmodulin?

Pyk2 (proline-rich tyrosine kinase 2) and FAK (focal adhesion kinase) are highly related tyrosine kinases. One distinguishing feature is the differential regulation of the two enzymes in response to elevation of cytoplasmic calcium. In the latest issue of the Biochemical Journal, Sasaki and co-workers have provided insight into the calcium-dependent regulation of Pyk2. The findings suggest that calmodulin may bind the FERM (4.1/ezrin/radixin/moesin) domain to promote Pyk2 activation in response to calcium signals triggered by vasopressin. While the molecular details of the protein-protein interaction and mechanism of activation remain to be firmly established, this study is the first to provide mechanistic insight into the regulation of Pyk2 by calcium.

Interaction of Membrane Skeletal Protein, Protein 4.1B and p55, and Sodium Bicarbonate Cotransporter1 in Mouse Renal S1-S2 Proximal Tubules

Our recent studies demonstrated the localization of protein 4.1B, a member of the 4.1 skeletal membrane proteins, to the basolateral membranes of the S1-S2 renal proximal tubules. In the present studies, we investigated the presence of binding partners that could form a molecular complex with the 4.1B protein. Immunohistochemistry revealed the localization of p55, a membrane-associated guanylate kinase, and the sodium bicarbonate cotransporter1 (NBC1), to the basolateral membrane domain of S1-S2 in mouse renal proximal tubules. Using immunoprecipitation of kidney lysates with anti-p55 antibody, a positive band was blotted with anti-4.1B antibody. GST fusion proteins including the NBC1 and 4.1B regions were confirmed to bind with each other by electrophoresis after mixing. Both NBC1- and 4.1B-specific bands were detected in renal protein mixtures immunoprecipated by either anti-4.1B- or NBC1-specific antibodies. It is likely that NBC1, 4.1B, and p55 form a molecular complex in the basolateral membrane of the kidney S1-S2 proximal tubules. We propose that the 4.1B-containing membrane skeleton may play a role in regulating the Na+ and HCO3- reabsorption in S1-S2 proximal tubules.