Inhibition of PYK2-induced actin cytoskeleton reorganization, PYK2 autophosphorylation and focal adhesion targeting by FAK

PYK2, a hub of signaling networks in breast cancer progression

Breast cancer (BC) involves complex signaling networks characterized by extensive cross-communication and feedback loops between and within multiple signaling cascades. Many of these signaling pathways are driven by genetic alterations of oncogene and/or tumor-suppressor genes and are influenced by various environmental cues. We describe unique roles of the non-receptor tyrosine kinase (NRTK) PYK2 in signaling integration and feedback looping in BC. PYK2 functions as a signaling hub in various cascades, and its involvement in positive and negative feedback loops enhances signaling robustness, modulates signaling dynamics, and contributes to BC growth, epithelial-to-mesenchymal transition (EMT), stemness, migration, invasion, and metastasis. We also discuss the potential of PYK2 as a therapeutic target in various BC subtypes.

Role of proline-rich tyrosine kinase 2 (Pyk2) in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is the most common form of dementia in the elderly. Two major pathological hallmarks have been identified for AD: extracellular amyloid plaques and intracellular neurofibrillary tangles (NFT). Recently, proline-rich tyrosine kinase 2 (Pyk2), which belongs to the focal adhesion kinase (FAK) non-receptor tyrosine kinase family, was recognized to contribute significantly towards the pathogenesis of AD. Pyk2 can influence the formation of amyloid plaques as well as NFTs. The kinase can directly phosphorylate tau, which is a significant component of NFTs and enhances tau pathology. Several competitive inhibitors have been developed for Pyk2, tested in several cancer models, as Pyk2 is known to be overexpressed under those conditions. The current review article discusses the possible mechanistic pathways by which Pyk2 can influence the pathogenesis of AD. Besides, it describes various inhibitors for Pyk2 and their potential role as therapeutics for AD in the future.

High expression of PYK2 is associated with poor prognosis and cancer progression in early-stage cervical carcinoma

Proline-rich tyrosine kinase-2 (PYK2), also known as calcium dependent tyrosine kinase, regulates different signal transduction cascades that control cell proliferation, migration, and invasion. However, the role of PYK2 in cervical cancer remains to be elucidated. The current study retrospectively included 134 patients with cervical cancer from December 2007 to September 2014. PYK2 expression was detected in tissue microarray and cervical cancer cell lines. Statistical analysis was performed to evaluate its clinicopathological significance. Small interfering RNA (siRNA) was employed to suppress endogenous PYK2 expression in cervical cancer cells to observe the biological function. PYK2 expression was up-regulated in cervical cancer specimens compared with paired adjacent normal cervical tissue samples. Statistical analyses indicated that PYK2 expression might be an independent prognostic indicator for patients with early-stage cervical cancer. A nomogram model was constructed based on PYK2 expression and other clinicopathological risk factors, and it performed well in predicting patients survival. In cellular studies, down-regulation of PYK2 remarkably inhibited cellular proliferation, migration and invasion. PYK2 expression possessed the potential to serve as a novel prognostic marker in cervical cancer patients.

Extracellular Matrix Signals as Drivers of Mitochondrial Bioenergetics and Metabolic Plasticity of Cancer Cells During Metastasis

The role of metabolism in tumor growth and chemoresistance has received considerable attention, however, the contribution of mitochondrial bioenergetics in migration, invasion, and metastasis is recently being understood. Migrating cancer cells adapt their energy needs to fluctuating changes in the microenvironment, exhibiting high metabolic plasticity. This occurs due to dynamic changes in the contributions of metabolic pathways to promote localized ATP production in lamellipodia and control signaling mediated by mitochondrial reactive oxygen species. Recent evidence has shown that metabolic shifts toward a mitochondrial metabolism based on the reductive carboxylation, glutaminolysis, and phosphocreatine-creatine kinase pathways promote resistance to anoikis, migration, and invasion in cancer cells. The PGC1a-driven metabolic adaptations with increased electron transport chain activity and superoxide levels are essential for metastasis in several cancer models. Notably, these metabolic changes can be determined by the composition and density of the extracellular matrix (ECM). ECM stiffness, integrins, and small Rho GTPases promote mitochondrial fragmentation, mitochondrial localization in focal adhesion complexes, and metabolic plasticity, supporting enhanced migration and metastasis. Here, we discuss the role of ECM in regulating mitochondrial metabolism during migration and metastasis, highlighting the therapeutic potential of compounds affecting mitochondrial function and selectively block cancer cell migration.

CCM3 is a gatekeeper in focal adhesions regulating mechanotransduction and YAP/TAZ signalling

The YAP/TAZ transcriptional programme is not only a well-established driver of cancer progression and metastasis but also an important stimulator of tissue regeneration. Here we identified Cerebral cavernous malformations 3 (CCM3) as a regulator of mechanical cue-driven YAP/TAZ signalling, controlling both tumour progression and stem cell differentiation. We demonstrate that CCM3 localizes to focal adhesion sites in cancer-associated fibroblasts, where it regulates mechanotransduction and YAP/TAZ activation. Mechanistically, CCM3 and focal adhesion kinase (FAK) mutually compete for binding to paxillin to fine-tune FAK/Src/paxillin-driven mechanotransduction and YAP/TAZ activation. In mouse models of breast cancer, specific loss of CCM3 in cancer-associated fibroblasts leads to exacerbated tissue remodelling and force transmission to the matrix, resulting in reciprocal YAP/TAZ activation in the neighbouring tumour cells and dissemination of metastasis to distant organs. Similarly, CCM3 regulates the differentiation of mesenchymal stromal/stem cells. In conclusion, CCM3 is a gatekeeper in focal adhesions that controls mechanotransduction and YAP/TAZ signalling.

The multifactorial roles of microglia and macrophages in the maintenance and progression of glioblastoma

The functional characteristics of glial cells, in particular microglia, have attained considerable importance in several diseases, including glioblastoma, the most hostile and malignant type of intracranial tumor. Microglia performs a highly significant role in the brain's inflammatory response mechanism. They exhibit anti-tumor properties via phagocytosis and the activation of a number of different cytotoxic substances. Some tumor-derived factors, however, transform these microglial cells into immunosuppressive and tumor-supportive, facilitating survival and progression of tumorigenic cells. Glioma-associated microglia and/or macrophages (GAMs) accounts for a large proportion of glioma infiltrating cells. Once within the tumor, GAMs exhibit a distinct phenotype of initiation that subsequently supports the growth and development of tumorigenic cells, angiogenesis and stimulates the infiltration of healthy brain regions. Interventions that suppress or prohibit the induction of GAMs at the tumor site or attenuate their immunological activities accommodating anti-tumor actions are likely to exert positive impact on glioblastoma treatment. In the present paper, we aim to summarize the most recent knowledge of microglia and its physiology, as well as include a very brief description of different molecular factors involved in microglia and glioblastoma interplay. We further address some of the major signaling pathways that regulate the baseline motility of glioblastoma progression. Finally, we discussed a number of therapeutic approaches regarding glioblastoma treatment.

HIV-1 Envelope Overcomes NLRP3-Mediated Inhibition of F-Actin Polymerization for Viral Entry

Purinergic receptors and nucleotide-binding domain leucine-rich repeat containing (NLR) proteins have been shown to control viral infection. Here, we show that the NLR family member NLRP3 and the purinergic receptor P2Y2 constitutively interact and regulate susceptibility to HIV-1 infection. We found that NLRP3 acts as an inhibitory factor of viral entry that represses F-actin remodeling. The binding of the HIV-1 envelope to its host cell receptors (CD4, CXCR4, and/or CCR5) overcomes this restriction by stimulating P2Y2. Once activated, P2Y2 enhances its interaction with NLRP3 and stimulates the recruitment of the E3 ubiquitin ligase CBL to NLRP3, ultimately leading to NLRP3 degradation. NLRP3 degradation is permissive for PYK2 phosphorylation (PYK2Y402^∗) and subsequent F-actin polymerization, which is required for the entry of HIV-1 into host cells. Taken together, our results uncover a mechanism by which HIV-1 overcomes NLRP3 restriction that appears essential for the accomplishment of the early steps of HIV-1 entry.

Pyk2 downstream of G12/13 pathways regulates platelet shape change through RhoA/p160ROCK

Rho/Rho-kinase downstream of G_12/13 plays an important role in the regulation of calcium-independent platelet shape change. We have previously shown that proline-rich tyrosine kinase 2 (Pyk2) is activated downstream of G_12/13 pathways. In this study, we evaluated the role of Pyk2 in G_12/13-induced platelet shape change. We used low concentrations of YFLLRNP, a heptapeptide binding to protease-activated receptor 1 (PAR1), or PAR4-activating peptide AYPGKF in the presence of Gα_q inhibitor YM254890 to selectively stimulate G_12/13 pathways. We found that G_12/13-induced platelet shape change was completely inhibited in the presence of Pyk2 inhibitors AG17 and TAT-Pyk2-CT, suggesting an important role of Pyk2 in platelet shape change. In addition, AYPGKF-induced shape change in G_q -/- platelets was completely inhibited in the presence of AG17 or RhoA/p160^ROCK inhibitor Y27632, confirming the role of Pyk2 in RhoA-dependent shape change. Furthermore, AYPGKF-induced platelet aggregation and dense granule secretion were inhibited by blocking Pyk2 or RhoA. Finally, G_12/13-induced myosin phosphatase target subunit 1 (MYPT1) phosphorylation was inhibited by AG17, confirming that Pyk2 regulates RhoA/p160^ROCK activation in platelets. These results demonstrate that Pyk2 downstream of G_12/13 pathways regulates platelet shape change as well as platelet aggregation and dense granule secretion through the regulation of RhoA/p160^ROCK.

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.

Myristoleic acid inhibits osteoclast formation and bone resorption by suppressing the RANKL activation of Src and Pyk2

Cytoskeletal changes in osteoclasts such as formation of actin ring is required for bone-resorbing activity. The tyrosine kinase Src is a key player in massive cytoskeletal change of osteoclasts, thereby in bone destruction. In order for Src to be activated, trafficking to the inner plasma membrane via myristoylation is of importance. A previous study reported that myristoleic acid derived from myristic acid, inhibited N-myristoyl-transferase, an essential enzyme for myristoylation process. This prompted us to investigate whether myristoleic acid could affect osteoclastogenesis. Indeed, we observed that myristoleic acid inhibited RANKL-induced osteoclast formation in vitro, especially, at later stages of differentiation. Myristoleic acid attenuated the tyrosine phosphorylation of c-Src and Pyk2, which associates with Src, by RANKL. When myristoleic acid was co-administered with soluble RANKL into mice, RANKL-induced bone loss was substantially prevented. Bone dissection clearly revealed that the number of multinucleated osteoclasts was significantly diminished by myristoleic acid. On the other hand, myristoleic acid treatment had little or no influence on early osteoclast differentiation markers, such as c-Fos and NFATc1, and proteins related to cytoskeletal rearrangement, including DC-STAMP, integrin αv and integrin β3 in vitro. Taken together, our data suggest that myristoleic acid is capable of blocking the formation of large multinucleated osteoclasts and bone resorption likely through suppressing activation of Src and Pyk2.

α5-Integrin-mediated cellular signaling contributes to the myogenic response of cerebral resistance arteries

The myogenic response of resistance arterioles and small arteries involving constriction in response to intraluminal pressure elevation and dilation on pressure reduction is fundamental to local blood flow regulation in the microcirculation. Integrins have garnered considerable attention in the context of initiating the myogenic response, but evidence indicative of mechanotransduction by integrin adhesions, for example established changes in tyrosine phosphorylation of key adhesion proteins, has not been obtained to substantiate this interpretation. Here, we evaluated the role of integrin adhesions and associated cellular signaling in the rat cerebral arterial myogenic response using function-blocking antibodies against α5β1-integrins, pharmacological inhibitors of focal adhesion kinase (FAK) and Src family kinase (SFK), an ultra-high-sensitivity western blotting technique, site-specific phosphoprotein antibodies to quantify adhesion and contractile filament protein phosphorylation, and differential centrifugation to determine G-actin levels in rat cerebral arteries at varied intraluminal pressures. Pressure-dependent increases in the levels of phosphorylation of FAK (FAK-Y397, Y576/Y577), SFK (SFK-Y416; Y527 phosphorylation was reduced), vinculin-Y1065, paxillin-Y118 and phosphoinositide-specific phospholipase C-γ1 (PLCγ1)-Y783 were detected. Treatment with α5-integrin function-blocking antibodies, FAK inhibitor FI-14 or SFK inhibitor SU6656 suppressed the changes in adhesion protein phosphorylation, and prevented pressure-dependent phosphorylation of the myosin targeting subunit of myosin light chain phosphatase (MYPT1) at T855 and 20kDa myosin regulatory light chains (LC20) at S19, as well as actin polymerization that are necessary for myogenic constriction. We conclude that mechanotransduction by integrin adhesions and subsequent cellular signaling play a fundamental role in the cerebral arterial myogenic response.

OGD induced modification of FAK- and PYK2-coupled pathways in organotypic hippocampal slice cultures

Focal adhesion kinase (FAK) and proline-rich tyrosine kinase (PYK2) are two related non-receptor tyrosine kinases which are thought to play a role in transducing extracellular matrix (ECM)-derived survival signals into cells. The functions of FAK and PYK2 are linked to autophosphorylation of their specific tyrosine residues, Tyr-397 in FAK and Tyr-402 in PYK2, and then association with different signalling proteins which mediate activation of downstream targets such as ERK and JNK mitogen-activated kinase cascades. Thus, modulation of FAK as well as PYK2 autophosphorylation may affect several intracellular pathways and may participate in a variety of pathological settings. The present study provides a systematic investigation of the influence of experimental ischemia, induced by oxygen-glucose-deprivation, on the FAK- and PYK2-mediated signalling in organotypic hippocampal slice cultures. OGD induced primary down-regulation of FAK and PYK2 autophosphorylation (at Tyr 397 and Tyr 402, respectively) at 24-48 h of reoxygenation was accompanied by the diminution of phosphorylation/activation of Src and JNK. In contrast, the activity of Akt and ERK1/2 remained on the control level. It indicates that Akt kinase as well as ERK1/2 does not interfere with OGD-induced neuronal damage. The inhibition of the early step of FAK and PYK2 activation demonstrated by the decrease of tyrosine autophosphorylation may comprise an important portion of the response expressed by modulation of some coupled signal transduction pathways.

Pyk2 and Src mediate signaling to CCL18-induced breast cancer metastasis

Pyk2 and Src phosphorylation is initiated by CCL18, which promotes breast cancer metastasis via its functional G protein-coupled receptor PITPNM3. However, the function of Pyk2 and Src in CCL18-induced breast cancer metastasis is poorly understood. Quantitative reverse-transcription polymerase chain reactions (qRT-PCRs), Western blot, boyden chamber assay, and adherence assay were performed to delineate the consequences of Pyk2/Src in CCL18-induced breast cancer cells. Co-immunoprecipitation and immunofluorescence were performed to analyze the interaction of proteins. Upon the binding of CCL18 to PITPNM3, Pyk2 translocates from the cytoplasm to the plasma membrane to form a stable complex with PITPNM3, subsequently activating Src kinase. Moreover, upon stimulation with CCL18, Pyk2 and Src become essential for integrin alpha5/beta1 clustering-dependent adherence, migration, and invasion. Pyk2 and Src are important in CCL18-induced breast cancer metastasis.

Structural and mechanistic insights into the interaction between Pyk2 and paxillin LD motifs

Proline-rich tyrosine kinase 2 (Pyk2) is a member of the focal adhesion kinase (FAK) subfamily of cytoplasmic tyrosine kinases. The C-terminal Pyk2-focal adhesion targeting (FAT) domain binds to paxillin, an adhesion molecule. Paxillin has five leucine-aspartate (LD) motifs (LD1-LD5). Here, we show that the second LD motif of paxillin, LD2, interacts with Pyk2-FAT, similar to the known Pyk2-FAT/LD4 interaction. Both LD motifs can target two ligand binding sites on Pyk2-FAT. Interestingly, they also share similar binding affinity for Pyk2-FAT with preferential association to one site relative to the other. Nevertheless, the LD2-LD4 region of paxillin (paxillin(133-290)) binds to Pyk2-FAT as a 1:1 complex. However, our data suggest that the Pyk2-FAT and paxillin complex is dynamic and it appears to be a mixture of two distinct conformations of paxillin that almost equally compete for Pyk2-FAT binding. These studies provide insight into the underlying selectivity of paxillin for Pyk2 and FAK that may influence the differing behavior of these two closely related kinases in focal adhesion sites.

The role of focal adhesion complexes in fibroblast mechanotransduction during scar formation

Historically, great efforts have been made to elucidate the biochemical pathways that direct the complex process of wound healing; however only recently has there been recognition of the importance that mechanical signals play in the process of tissue repair and scar formation. The body's physiologic response to injury involves a dynamic interplay between mechanical forces and biochemical cues which directs a cascade of signals leading ultimately to the formation of fibrotic scar. Fibroblasts are a highly mechanosensitive cell type and are also largely responsible for the generation of the fibrotic matrix during scar formation and are thus a critical player in the process of mechanotransduction during tissue repair. Mechanotransduction is initiated at the interface between the cell membrane and the extracellular matrix where mechanical signals are first translated into a biochemical response. Focal adhesions are dynamic multi-protein complexes through which the extracellular matrix links to the intracellular cytoskeleton. These focal adhesion complexes play an integral role in the propagation of this initial mechanical cue into an extensive network of biochemical signals leading to widespread downstream effects including the influx of inflammatory cells, stimulation of angiogenesis, keratinocyte migration, fibroblast proliferation and collagen synthesis. Increasing evidence has demonstrated the importance of the biomechanical milieu in healing wounds and suggests that an integrated approach to the discovery of targets to decrease scar formation may prove more clinically efficacious than previous purely biochemical strategies.

Pyk2 mediates increased adrenergic contractile responses in arteries from DOCA-salt mice - VASOACTIVE PEPTIDE SYMPOSIUM

BACKGROUND

The calcium-dependent proline-rich tyrosine kinase (Pyk2), a nonreceptor protein activated by tyrosine phosphorylation, links G protein-coupled receptors to vascular responses. We tested the hypothesis that enhanced vascular reactivity in DOCA-salt hypertensive mice are due to increased activation of Pyk2.

METHODS AND RESULTS

Aorta and small mesenteric arteries from DOCA-salt and uninephrectomized (UNI) male C57Bl/6 mice were used. Systolic blood pressure (mmHg) was higher in DOCA (126+/-3) vs. UNI (100+/-4) mice. Vascular responses to phenylephrine (1nM to 100muM) were greater both in aorta and small mesenteric arteries from DOCA-salt than UNI, but treatment with Tyrphostin A-9 (0.1muM, Pyk2 inhibitor) abolished the difference among the groups. Pyk2 levels, as well as phospho-Pyk2(Tyr402), paxillin and phospho-paxillin(Tyr118) were increased in DOCA-salt aorta. Incubation of vessels with Tyrphostin A-9 restored phosphorylation of Pyk2 and paxillin.

CONCLUSION

Increased activation of Pyk2 contributes to increased vascular contractile-responses in DOCA-salt mice.

Focal adhesion kinases in adhesion structures and disease

Cell adhesion to the extracellular matrix (ECM) is essential for cell migration, proliferation, and embryonic development. Cells can contact the ECM through a wide range of matrix contact structures such as focal adhesions, podosomes, and invadopodia. Although they are different in structural design and basic function, they share common remodeling proteins such as integrins, talin, paxillin, and the tyrosine kinases FAK, Pyk2, and Src. In this paper, we compare and contrast the basic organization and role of focal adhesions, podosomes, and invadopodia in different cells. In addition, we discuss the role of the tyrosine kinases, FAK, Pyk2, and Src, which are critical for the function of the different adhesion structures. Finally, we discuss the essential role of these tyrosine kinases from the perspective of human diseases.

Striatal-enriched protein-tyrosine phosphatase (STEP) regulates Pyk2 kinase activity

Proline-rich tyrosine kinase 2 (Pyk2) is a member of the focal adhesion kinase family and is highly expressed in brain and hematopoietic cells. Pyk2 plays diverse functions in cells, including the regulation of cell adhesion, migration, and cytoskeletal reorganization. In the brain, it is involved in the induction of long term potentiation through regulation of N-methyl-d-aspartate receptor trafficking. This occurs through the phosphorylation and activation of Src family tyrosine kinase members, such as Fyn, that phosphorylate GluN2B at Tyr(1472). Phosphorylation at this site leads to exocytosis of GluN1-GluN2B receptors to synaptic membranes. Pyk2 activity is modulated by phosphorylation at several critical tyrosine sites, including Tyr(402). In this study, we report that Pyk2 is a substrate of striatal-enriched protein-tyrosine phosphatase (STEP). STEP binds to and dephosphorylates Pyk2 at Tyr(402). STEP KO mice showed enhanced phosphorylation of Pyk2 at Tyr(402) and of the Pyk2 substrates paxillin and ASAP1. Functional studies indicated that STEP opposes Pyk2 activation after KCl depolarization of cortical slices and blocks Pyk2 translocation to postsynaptic densities, a key step required for Pyk2 activation and function. This is the first study to identify Pyk2 as a substrate for STEP.

Lysophosphatidic acid 5 receptor induces activation of Na(+)/H(+) exchanger 3 via apical epidermal growth factor receptor in intestinal epithelial cells

Na(+) absorption is a vital process present in all living organisms. We have reported previously that lysophosphatidic acid (LPA) acutely stimulates Na(+) and fluid absorption in human intestinal epithelial cells and mouse intestine by stimulation of Na(+)/H(+) exchanger 3 (NHE3) via LPA(5) receptor. In the current study, we investigated the mechanism of NHE3 activation by LPA(5) in Caco-2bbe cells. LPA(5)-dependent activation of NHE3 was blocked by mitogen-activated protein kinase kinase (MEK) inhibitor PD98059 and U0126, but not by phosphatidylinositol 3-kinase inhibitor LY294002 or phospholipase C-β inhibitor U73122. We found that LPA(5) transactivated the epidermal growth factor receptor (EGFR) and that inhibition of EGFR blocked LPA(5)-dependent activation of NHE3, suggesting an obligatory role of EGFR in the NHE3 regulation. Confocal immunofluorescence and surface biotinylation analyses showed that LPA(5) was located mostly in the apical membrane. EGFR, on the other hand, showed higher expression in the basolateral membrane. However, inhibition of apical EGFR, but not basolateral EGFR, abrogated LPA-induced regulation of MEK and NHE3, indicating that LPA(5) selectively activates apical EGFR. Furthermore, transactivation of EGFR independently activated the MEK-ERK pathway and proline-rich tyrosine kinase 2 (Pyk2). Similarly to MEK inhibition, knockdown of Pyk2 blocked activation of NHE3 by LPA. Furthermore, we showed that RhoA and Rho-associated kinase (ROCK) are involved in activation of Pyk2. Interestingly, LPA(5) did not directly activate RhoA but was required for transactivation of EGFR. Together, these results unveil a pivotal role of apical EGFR in NHE3 regulation by LPA and show that the RhoA-ROCK-Pyk2 and MEK-ERK pathways converge onto NHE3.

Differential expression of FAK and Pyk2 in metastatic and non-metastatic EL4 lymphoma cell lines

The murine EL4 lymphoma cell line exists in variants that are either sensitive or resistant to phorbol 12-myristate 13-acetate (PMA). In sensitive cells, PMA causes Erk MAPK activation and Erk-mediated growth arrest. In resistant cells, PMA induces a low level of Erk activation, without growth arrest. A relatively unexplored aspect of the phenotypes is that resistant cells are more adherent to culture substrate than are sensitive cells. In this study, the roles of the protein tyrosine kinases FAK and Pyk2 in EL4 phenotype were examined, with a particular emphasis on the role of these proteins in metastasis. FAK is expressed only in PMA-resistant (or intermediate phenotype) EL4 cells, correlating with enhanced cell-substrate adherence, while Pyk2 is more highly expressed in non-adherent PMA-sensitive cells. PMA treatment causes modulation of mRNA for FAK (up-regulation) and Pyk2 (down-regulation) in PMA-sensitive but not PMA-resistant EL4 cells. The increase in Pyk2 mRNA is correlated with an increase in Pyk2 protein expression. The roles of FAK in cell phenotype were further explored using transfection and knockdown experiments. The results showed that FAK does not play a major role in modulating PMA-induced Erk activation in EL4 cells. However, the knockdown studies demonstrated that FAK expression is required for proliferation and migration of PMA-resistant cells. In an experimental metastasis model using syngeneic mice, only FAK-expressing (PMA-resistant) EL4 cells form liver tumors. Taken together, these studies suggest that FAK expression promotes metastasis of EL4 lymphoma cells.

Effects of the plasmid-encoded toxin of enteroaggregative Escherichia coli on focal adhesion complexes

Enteroaggregative Escherichia coli (EAEC) is an emerging diarrheal pathogen. Many EAEC strains produce the plasmid-encoded toxin (Pet), which exerts cytotoxic effects on human intestinal tissue. Pet-intoxicated HEp-2 cells exhibit rounding and detachment from the substratum, accompanied by loss of F-actin stress fibers and condensation of the spectrin-containing membrane cytoskeleton. Although studies suggest that Pet directly cleaves spectrin, it is not known whether this is the essential mode of action of the toxin. In addition, the effects of Pet on cytoskeletal elements other than actin and spectrin have not been reported. Here, we demonstrate by immunofluorescence that upon Pet intoxication, HEp-2 and HT29 cells lose focal adhesion complexes (FAC), a process that includes the redistribution of focal adhesion kinase (FAK), α-actinin, paxillin, vinculin, F-actin, and spectrin itself. This redistribution was coupled with the depletion of phosphotyrosine labeling at FACs. Immunoblotting and immunoprecipitation experiments revealed that FAK was tyrosine dephosphorylated, before the redistribution of FAK and spectrin. Moreover, phosphatase inhibition blocked cell retraction, suggesting that tyrosine dephosphorylation is an event that precedes FAK cleavage. Finally, we show that in vitro tyrosine-dephosphorylated FAK was susceptible to Pet cleavage. These data suggest that mechanisms other than spectrin redistribution occur during Pet intoxication.

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 influence of Pyk2 on the mechanical properties in fibroblasts

The cell surface receptor integrin is involved in signaling mechanical stresses via the focal adhesion complex (FAC) into the cell. Within FAC, the focal adhesion kinase (FAK) and Pyk2 are believed to act as important scaffolding proteins. Based on the knowledge that many signal transducing molecules are transiently immobilized within FAC connecting the cytoskeleton with integrins, we applied magnetic tweezer and atomic force microscopic measurements to determine the influence of FAK and Pyk2 in cells mechanically. Using mouse embryonic fibroblasts (MEF; FAK(+/+), FAK(-/-), and siRNA-Pyk2 treated FAK(-/-) cells) provided a unique opportunity to describe the function of FAK and Pyk2 in more detail and to define their influence on FAC and actin distribution.

Phosphoproteomic characterization of PYK2 signaling pathways involved in osteogenesis

The PYK2 tyrosine kinase is a negative regulator of bone formation, but aside from the requirement for PYK2 kinase activity there has been little progress toward understanding of the molecular mechanism involved in this function. To gain insight into the signaling pathways modulated by PYK2 we sought to identify PYK2 substrates. Challenges inherent to a quantitative phosphoproteomic analysis for non-receptor tyrosine kinases were overcome by employing an inducible PYK2 overexpression system in NIH3T3 cells in combination with a selective PYK2 inhibitor. The identification of a number of known PYK2 substrates and interacting partners validated the methodology. Results of the inducible cell system were extended to a cell model of osteogenesis, examining the effect of the PYK2 inhibitor on the phosphorylation state of targets identified in the phosphoproteomic study. Consistent with phosphoproteomic analysis, increased osteogenesis associated with a selective PYK2 inhibitor was accompanied by reduced phosphorylation of paxillin, Gab1 and p130(Cas), along with reduction of phosphorylation levels of the Met activation loop. These results further confirmed the utility of the methodology and point to a previously unknown bi-directional activation pathway between PYK2 and Met.

Chemokine-like factor 1, a novel cytokine, induces nerve cell migration through the non-extracellular Ca2+-dependent tyrosine kinases pathway

Chemokine-like factor 1 (CKLF1) is a newly cloned chemotactic cytokine. The roles of CKLF1 in the immune system and the respiratory system have been reported, but its function in the nervous system is still remaining unclear. We aimed to investigate the role of CKLF1 in the nerve cell migration and its regulatory mechanisms. By chemotaxis assays and wound-healing assays, CKLF1 stimulated the migration of SH-SY5Y cells dose-dependently. By immunofluorescence staining, CKLF1 induced actin polymerization. By western blotting, proline-rich tyrosine kinase 2 (PYK2) was phosphorylated at Tyr-402 in response to CKLF1 and this phosphorylation was apparently suppressed by phospholipase C-gamma inhibitor U73122, but not extracellular Ca(2+) chelator EGTA. Furthermore, after transfection of dominant-negative mutant PYK2 plasmid, the chemotaxis upon CKLF1 was significantly attenuated in SH-SY5Y cells. Concluding, CKLF1 stimulates the migration of SH-SY5Y cells dose-dependently by activating non-extracellular Ca(2+)-dependent tyrosine kinases pathway and inducing actin polymerization.

Imaging morphogenesis, in Xenopus with Quantum Dot nanocrystals

Mesoderm migration is a well studied morphogenetic movement that takes place during Xenopus gastrulation. The study of mesoderm migration and other morphogenetic movements has been primarily based on in vitro assays due to the inability to image deep tissue movements in the opaque embryo. We are the first to report the use of Near Infra Red Quantum Dots (NIR QD's) to image mesoderm migration in vivo with single cell resolution and provide quantitative in vivo data regarding migration rates. In addition we use QD's to address the function of the focal adhesion kinase (FAK) in this movement. Inhibition of FAK blocks mesoderm spreading and migration both in vitro and in vivo without affecting convergent extension highlighting the molecular differences between the two movements. These results provide new insights about the role of FAK and of focal adhesions during gastrulation and provide a new tool for the study of morphogenesis in vivo.

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.

Crystal structures of free and ligand-bound focal adhesion targeting domain of Pyk2

Focal adhesion targeting (FAT) domains target the non-receptor tyrosine kinases FAK and Pyk2 to cellular focal adhesion areas, where the signaling molecule paxillin is also located. Here, we report the crystal structures of the Pyk2 FAT domain alone or in complex with paxillin LD4 peptides. The overall structure of Pyk2-FAT is an antiparallel four-helix bundle with an up-down, up-down, right-handed topology. In the LD4-bound FAT complex, two paxillin LD4 peptides interact with two opposite sides of Pyk2-FAT, at the surfaces of the alpha1alpha4 and alpha2alpha3 helices of each FAT molecule. We also demonstrate that, while paxillin is phosphorylated by Pyk2, complex formation between Pyk2 and paxillin does not depend on Pyk2 tyrosine kinase activity. These experiments reveal the structural basis underlying the selectivity of paxillin LD4 binding to the Pyk2 FAT domain and provide insights about the molecular details which influence the different behavior of these two closely-related kinases.

FAK mediates the inhibition of glioma cell migration by truncated 24 kDa FGF-2

A truncated form of 24kDa FGF-2 consisting of 86 NH(2)-terminal amino acids (ATE+31) inhibits cell migration in vitro and tumor development and angiogenesis in vivo. Focal adhesion kinase (FAK) is phosphorylated on tyrosine and serine sites after cell stimulation by growth factors. This study examined the effect of ATE+31 on FAK phosphorylation in human glioma cells. FAK and Pyk phosphorylation were evaluated at serines known to be involved with cell migration. We demonstrated that ATE+31 at 3 x 10(-11)M decreases phosphorylation levels of Tyr(407)-FAK and Ser(732)-FAK in the presence of platelet-derived growth factor (PDGF), that ATE+31 in the presence of PDGF alters the distribution of FAK and other phosphotyrosine proteins in the adhesion contacts, and that ATE+31 in the presence of PDGF has no effect on the activation of Pyk2. These data suggest that the inhibition of cell migration by ATE+31 occurs via Tyr(407)-FAK and Ser(732)-FAK.

Pyk2 mediates endothelin-1 signaling via p130Cas/BCAR3 cascade and regulates human glomerular mesangial cell adhesion and spreading

Calcium-regulated non-receptor proline-rich tyrosine kinase 2 (Pyk2) is a critical mediator of endothelin-1 (ET-1) signaling in human glomerular mesangial cells (GMC). We aimed to identify which small G-protein is acting downstream of Pyk2. Dominant interfering Pyk2 construct, termed calcium regulated non kinase (CRNK) or green fluorescent protein (control) were expressed in GMC using adenovirus-mediated gene transfer. ET-1 stimulation resulted in a significant increase of Pyk2 phosphorylation accompanied by GTP-loading of Rap1 and RhoA. CRNK expression inhibited ET-1-induced autophosphorylation of endogenous Pyk2 and diminished Rap1, but not RhoA, activation. The mechanism linking Pyk2 and Rap1 included (1) increased autophosphorylation of Pyk2 associated with p130Cas, (2) augmented p130Cas Y165 and Y249 phosphorylation, and (3) enhanced p130Cas-BCAR3 complex formation. CRNK expression prevented p130Cas phosphorylation and attenuated p130Cas association with BCAR3. Downregulation of endogenous BCAR3 protein expression using an siRNA technique led to a significant decrease in Rap1 activation in response to ET-1. We observed that endogenous Pyk2 was important for GMC adhesion and spreading. Our data suggest that ET-1 stimulated the GTPase Rap1 (but neither RhoA nor Ras) by a mechanism involving Pyk2 activation and recruitment of the p130Cas/BCAR3 complex in GMC.

Focal adhesion kinase-related proline-rich tyrosine kinase 2 and focal adhesion kinase are co-overexpressed in early-stage and invasive ErbB-2-positive breast cancer and cooperate for breast cancer cell tumorigenesis and invasiveness

Early cancer cell migration and invasion of neighboring tissues are mediated by multiple events, including activation of focal adhesion signaling. Key regulators include the focal adhesion kinase (FAK) and FAK-related proline-rich tyrosine kinase 2 (Pyk2), whose distinct functions in cancer progression remain unclear. Here, we compared Pyk2 and FAK expression in breast cancer and their effects on ErbB-2-induced tumorigenesis and the potential therapeutic utility of targeting Pyk2 compared with FAK in preclinical models of breast cancer. Pyk2 is overexpressed in tissues from early and advanced breast cancers and overexpressed with both FAK and epidermal growth factor receptor-2 (ErbB-2) in a subset of breast cancer cases. Down-regulation of Pyk2 in ErbB-2-positive, FAK-proficient, and FAK-deficient cells reduced cell proliferation, which correlated with reduced mitogen-activated protein kinase (MAPK) activity. In contrast, Pyk2 silencing had little impact on cell migration and invasion. In vivo, Pyk2 down-regulation reduced primary tumor growth induced by a metastatic variant of ErbB-2-positive MDA 231 breast cancer cells but had little effect on lung metastases in contrast to FAK down-regulation. Dual reduction of Pyk2 and FAK expression resulted in strong inhibition of both primary tumor growth and lung metastases. Together, these data support the cooperative function of Pyk2 and FAK in breast cancer progression and suggest that dual inhibition of FAK and Pyk2 is an efficient therapeutic approach for targeting invasive breast cancer.

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.

Podosome-type adhesions and focal adhesions, so alike yet so different

Cell-matrix adhesions are essential for cell migration, tissue organization and differentiation, therefore playing central roles in embryonic development, remodeling and homeostasis of tissues and organs. Matrix adhesion-dependent signals cooperate with other pathways to regulate biological functions such as cell survival, cell proliferation, wound healing, and tumorigenesis. Cell migration and invasion are integrated processes requiring the continuous, coordinated assembly and disassembly of integrin-mediated adhesions. An understanding of how integrins regulate cell migration and invasiveness through the dynamic regulation of adhesions is fundamental to both physiological and pathological situations. A variety of cell-matrix adhesions has been identified, namely, focal complexes, focal adhesions, fibrillar adhesions, podosomes, and invadopodia (podosome-type adhesions). These adhesion sites contain integrin clusters able to develop specialized structures, which are different in their architecture and dynamics although they share almost the same proteins. Here we compare recent advances and developments in the elucidation of the organization and dynamics of focal adhesions and podosome-type adhesions, in order to understand how such subcellular sites - though closely related in their composition - can be structurally and functionally different. The underlying question is how their respective physiological or pathological roles are related to their distinct organization.

Calcineurin is essential for depolarization-induced nuclear translocation and tyrosine phosphorylation of PYK2 in neurons

Proline-rich tyrosine kinase 2 (PYK2) is a non-receptor tyrosine kinase expressed in many cell types and enriched in neurons. PYK2 is a cytoplasmic enzyme activated by increases in cytosolic free Ca(2+) through an unknown mechanism. We report that depolarization or electrical stimulation of hippocampal slices induced a rapid and transient nuclear accumulation of PYK2. Depolarization of cultured neurons or PC12 cells also triggered a Ca(2+)-dependent nuclear accumulation of PYK2, much more pronounced than that induced by blockade of nuclear export with leptomycin B. Src-family kinase activity, PYK2 autophosphorylation and kinase activity were not required for its nuclear translocation. Depolarization induced a slight decrease in PYK2 apparent molecular mass, compatible with a Ca(2+)-activated dephosphorylation. Pretreatment of PC12 cells with inhibitors of calcineurin (protein phosphatase 2B), cyclosporin A and FK506, prevented depolarization-induced nuclear translocation and tyrosine phosphorylation of PYK2. Transfection with dominant-negative and constitutively active calcineurin-A confirmed the role of calcineurin in the regulation of PYK2 tyrosine phosphorylation and nuclear accumulation. Our results show that depolarization independently induces nuclear translocation and tyrosine phosphorylation of PYK2, and that both responses require calcineurin activation. We suggest that PYK2 exerts some of its actions in the nucleus and that the effects of calcineurin inhibitors may involve PYK2 inhibition.

Proline-rich tyrosine kinase2 is involved in F-actin organization during in vitro maturation of rat oocyte

Microfilaments (actin filaments) regulate various dynamic events during meiotic maturation. Relatively, little is known about the regulation of microfilament organization in mammalian oocytes. Proline-rich tyrosine kinase2 (Pyk2), a protein tyrosine kinase related to focal adhesion kinase (FAK) is essential in actin filaments organization. The present study was to examine the expression and localization of Pyk2, and in particular, its function during rat oocyte maturation. For the first time, by using Western blot and confocal laser scanning microscopy, we detected the expression of Pyk2 in rat oocytes and found that Pyk2 and Try402 phospho-Pyk2 were localized uniformly at the cell cortex and surrounded the germinal vesicle (GV) or the condensed chromosomes at the GV stage or after GV breakdown. At the metaphase and the beginning of anaphase, Pyk2 distributed asymmetrically both in the ooplasm and the cortex with a marked staining associated with the chromosomes and the region overlying the meiotic spindle. At telophase, Pyk2 was observed in the cleavage furrows in addition to its cortex and cytoplasm localization. The dynamics of Pyk2 were similar to that of F-actin, and this kinase was found to co-localize with microfilaments in several developmental stages during rat oocyte maturation. Microinjection of Pyk2 antibody demolished the microfilaments assembly and also inhibited the first polar body (PB1) emission. These findings suggest an important role of Pyk2 for rat oocyte maturation by regulating the organization of actin filaments.

RAFTK/Pyk2 regulates EGF-induced PC12 cell spreading and movement

The protein tyrosine kinase RAFTK, also termed Pyk2, is a member of the focal adhesion kinase (FAK) subfamily. In this report, we show the role of RAFTK in neuroendocrine PC12 cells upon epidermal growth factor (EGF) stimulation. Following EGF treatment, we observed that RAFTK was tyrosine-phosphorylated in a time- and dose-dependent manner, while FAK was constitutively phosphorylated and primarily regulated by cell adhesion. Moreover, we found that RAFTK associated with the phosphorylated EGF receptor (EGFR) upon EGF stimulation. RAFTK phosphorylation was mediated primarily through PLCgamma-IP3-Ca(2+) signaling and partially through PI3-Kinase. Furthermore, overexpression of PRNK, a specific dominant-negative construct of RAFTK, was sufficient to block EGF-induced cell spreading and movement. Paxillin, a key modulator of the actin cytoskeleton and an RAFTK substrate, was also phosphorylated following EGF treatment. EGF induced a dynamic reorganization of RAFTK and paxillin at neuronal adhesion sites, with the specific localization of paxillin at the inner juxtaposition of RAFTK. Additionally, we observed that RAFTK associated with the scaffold protein c-Cbl and mediated its phosphorylation. Our data demonstrate that while FAK mediated cell adhesion, RAFTK was localized at the cytoplasm where it mediated inside-out signaling through intracellular Ca(2+), thus leading to cell spreading and movement upon EGF stimulation.

The role of proline-rich protein tyrosine kinase 2 in differentiation-dependent signaling in human epidermal keratinocytes

Non-receptor tyrosine kinase proline-rich protein tyrosine kinase 2 (Pyk2) functions as an integrator of multiple signaling pathways involved in the regulation of fundamental cellular processes. Pyk2 expression, regulation, and functions in skin have not been examined. Here we investigated the expression and subcellular localization of Pyk2 in human epidermis and in primary human keratinocytes, and studied the mechanisms of Pyk2 activation by differentiation-inducing stimuli, and the role of Pyk2 as a regulator of keratinocyte differentiation. We demonstrate that Pyk2 is abundantly expressed in skin keratinocytes. Notably, the endogenous Pyk2 protein is predominantly localized in keratinocyte nuclei throughout all layers of healthy human epidermis, and in cultured human keratinocytes. Pyk2 is activated by treatment with keratinocyte-differentiating agents, 12-O-tetradecanoylphorbol-13-acetate and calcium via a mechanism that requires intracellular calcium release and functional protein kinase C (PKC) and Src activities. Particularly, differentiation-promoting PKC delta and PKC eta elicit Pyk2 activation. Our data show that Pyk2 increases promoter activity and endogenous protein levels of involucrin, a marker of keratinocyte terminal differentiation. This regulation is associated with increased expression of Fra-1 and JunD, activator protein-1 transcription factors known to be required for involucrin expression. Altogether, these results provide insights into Pyk2 signaling in epidermis and reveal a novel role for Pyk2 in regulation of keratinocyte differentiation.

Thy-1, via its GPI anchor, modulates Src family kinase and focal adhesion kinase phosphorylation and subcellular localization, and fibroblast migration, in response to thrombospondin-1/hep I

Normal fibroblast subpopulations have differential surface expression of the GPI-linked raft protein Thy-1, which correlates with differences in cellular adhesion and migration in vitro. Thrombospondin-1 (TSP-1) induces an intermediate state of adhesion in fibroblasts and other cells which facilitates migration. TSP-1 and the hep I peptide derived from the amino-terminal/heparin-binding domain of TSP-1 induce disassembly of cellular focal adhesions. Our lab previously reported that the induction of focal adhesion disassembly in fibroblasts by TSP-1 or by hep I requires surface expression of Thy-1, as well as lipid raft integrity and Src family kinase (SFK) signaling. We now report that TSP-1/hep I-induced fibroblast migration requires Thy-1 expression and FAK phosphorylation, and that following TSP-1/hep I stimulation, Thy-1 associates with FAK and SFK in a lipid raft-dependent manner. Furthermore, the GPI anchor of Thy-1, which localizes the protein to specific lipid raft microdomains, is necessary for hep I-induced FAK and SFK phosphorylation, focal adhesion disassembly, and migration. This is the first report of an association between Thy-1 and FAK. Thy-1 modulates SFK and FAK phosphorylation and subcellular localization, promoting focal adhesion disassembly and migration in fibroblasts, following exposure to TSP-1/hep I.

The differential expression of Yersinia pseudotuberculosis adhesins determines the requirement for FAK and/or Pyk2 during bacterial phagocytosis by macrophages

Phagocytosis of Yersinia pseudotuberculosis by macrophages is initiated by interactions between host cell integrin receptors and the bacterial adhesins, invasin and YadA. Two non-receptor protein tyrosine kinases, FAK and Pyk2, have been implicated in this process. In this study, we investigated the mechanisms of activation and functional requirements for these kinases during phagocytosis. A panel of Yersinia strains that differentially express invasin and YadA were used to infect cells in which FAK and/or Pyk2 expression was reduced by RNA interference. Bacterial strains that simultaneously express invasin and YadA activated FAK and Pyk2 signalling pathways that perform non-redundant functions required for Yersinia internalization. In contrast, FAK activation was found to be sufficient for phagocytosis of bacteria expressing invasin alone, and Pyk2 activation was sufficient when YadA was expressed in the absence of invasin. Based on these data, we suggest that the activation states of FAK and Pyk2, as well as the subsequent signalling events that lead to phagocytosis, are differentially regulated through the unique mechanisms of integrin engagement utilized by invasin and YadA. These findings lend insight into the molecular events that control bacterial phagocytosis as well as other integrin-based processes such as cell adhesion and migration.

Selective regulation of hydrogen peroxide signaling by receptor tyrosine phosphatase-alpha

Reactive oxygen species (ROS) are constantly produced in the human body and are involved in the pathogenesis of aging, cardiovascular diseases, and cancer. Emerging evidence indicates that oxidation and inhibition of protein tyrosine phosphatases (PTPs) are critical for ROS signal transduction. However, the role of individual PTPs in ROS signaling remains unclear. Here, we demonstrated that the receptor-like PTP alpha (RPTP alpha) was an effector of H2O2, the most stable form of ROS. H2O2 at nontoxic concentration rapidly induced the association of RPTP alpha with Src family kinases, platelet-derived growth factor receptor-beta, and protein kinase D in various cultured cells, although it markedly suppressed RPTP alpha phosphorylation on Tyr-789. We further identified that RPTP alpha selectively regulated the signal transduction pathways induced by H2O2. Particularly, RPTP alpha was required for the activation of protein kinase D and for the modulation of p130Cas tyrosine phosphorylation in response to H2O2. In contrast, the H2O2-induced inactivation of Src family kinases and suppression of paxillin phosphorylation on Tyr-118 were both largely independent of RPTP alpha. Our findings indicate that H2O2 signaling pathways are selectively regulated by RPTP alpha in cells, which may provide new insights into the functional regulation of ROS signal transduction by PTPs.

RAFTK/Pyk2 mediates LPA-induced PC12 cell migration

The phospholipid lysophosphatidic acid (LPA) is a normal constituent of serum that functions as a lipid growth factor and intracellular signaling molecule. In this report, we have investigated the signaling mechanism and function of the tyrosine kinase RAFTK/Pyk2 in LPA-induced cell migration. Analysis of tyrosine phosphorylation upon LPA stimulation in neuroendocrine PC12 cells revealed 6 major tyrosine-phosphorylated proteins with estimated sizes of 180, 120, 115, 68, 44, and 42 kDa. These proteins were identified as epidermal growth factor receptor (EGFR), focal adhesion kinase, RAFTK/Pyk2, paxillin, Erk 1, and Erk 2, respectively. Using specific pharmacological inhibitors, we found that the tyrosine phosphorylation of RAFTK/Pyk2 was intracellular Ca2+-dependent, but not EGFR-dependent, during LPA stimulation of these cells. Moreover, the cytoskeletal and signal scaffolding protein, paxillin, associated with and was regulated by RAFTK/Pyk2 in a Ca2+-dependent manner. Characterization of LPA receptors showed that LPA1 (Edg2) and LPA2 (Edg4) are major receptors for LPA, while LPA3 receptor (Edg7) expression was limited. Upon using the LPA1/LPA3 receptor-specific antagonist VPC 32179, we observed that inhibition of the LPA1/LPA3 receptors had no effect on the LPA-induced phosphorylation of RAFTK, strongly suggesting that the LPA2 receptor is a key mediator of RAFTK phosphorylation. Furthermore, LPA induced PC12 cell migration, which was subsequently blocked by the dominant-negative form of FAK, FRNK. Expression of a dominant-negative form of the small GTPase Ras also blocked LPA-induced cell migration and RAFTK phosphorylation. Taken together, these results indicate that RAFTK is a key signaling molecule that mediates LPA-induced PC12 cell migration in a Ras-dependent manner.

The tyrosine kinase pyk2 promotes migration and invasion of glioma cells

Glioblastoma multiforme is extraordinarily aggressive due to the propensity of cells to migrate away from the tumor core into the surrounding normal brain. In this report, we investigated the role of proline-rich tyrosine kinase 2 (Pyk2) and FAK with regard to influencing glioma cell phenotypes. Expression of Pyk2 stimulated glioma cell migration, whereas expression of FAK inhibited glioma cell migration and stimulated cell cycle progression. Pyk2 autophosphorylation was necessary, but not sufficient, to stimulate cellular migration. The N-terminal domain of Pyk2 is required for stimulation of migration as an N-terminally deleted variant of Pyk2 failed to stimulate migration, whereas expression of an autonomous Pyk2 N-terminal domain inhibited cell migration. Substitution of the C-terminal domain of Pyk2 with the corresponding domain of FAK stimulated cell migration as effectively as wild-type Pyk2; however, substitution of the N-terminal domain of Pyk2 with that of FAK inhibited cell migration, substantiating that the N-terminal domain of Pyk2 was required to stimulate migration. Silencing of Pyk2 expression by RNA interference significantly inhibited glioma migration. Cell migration was restored on re-expression of Pyk2, but expression of FAK in Pyk2 knockdown cells failed to restore migration. We conclude that Pyk2 plays a central role in the migratory behavior of glioblastomas.

Expression and intracellular localization of Pyk2 in normal and v-src transformed chicken epiphyseal chondrocytes

The expression and localization of prolin-rich tyrosine kinase 2 (Pyk2) were studied in chick embryo epiphyseal chondrocytes. Two immunoreactive bands were detected in chondrocytes, a major band with an apparent Mr of 123 kDa and a minor band with an apparent Mr of 68 kDa. The major band appears to migrate as a doublet with apparent Mr of 116/123 kDa. Increased levels of the three forms of Pyk2 were observed in v-src transformed chondrocytes as compared to control uninfected chondrocytes. Immunofluorescent staining shows that Pyk2 is clearly visible in the cytosol and in the perinuclear region of control and v-src-chondrocytes and displays a pattern very similar to the distribution of the mitochondrial marker Mito Tracker. More, immunofluorescent staining shows that Pyk2 is nuclear in most chondrocytes. By subcellular fractionation, the p116/123 Pyk2 doublet, was found to be accumulated mainly in the cytoplasm while the p68 Pyk2 form, was found to be accumulated exclusively in the nucleus. The differential nuclear/cytoplasmic distribution of the Pyk2 forms remains unchanged after v-Src-induced transformation. The p68 Pyk2 form could no longer be detected by using a N-terminus domain-specific anti-Pyk2 antibody. Consistently, Pyk2 immunoreactivity was restricted to the cytoplasm of control and v-src transformed chondrocytes. Thus it appears that the p68 Pyk2 form that accumulates in the nucleus has a deletion in the N-terminus region.

Transient forebrain ischemia effects interaction of Src, FAK, and PYK2 with the NR2B subunit of N-methyl-d-aspartate receptor in gerbil hippocampus

Two different models of brain ischemia were used to examine the evoked changes in the tyrosine phosphorylation of NMDA receptor subunits 2A and 2B (NR2A and NR2B), as well as their interactions with non-receptor tyrosine kinases (NRTKs: FAK, PYK2 Src), and PSD-95 protein. Only short-term 5 min ischemia followed by 3 h reperfusion resulted in the elevated tyrosine phosphorylation of both investigated NMDA receptor subunits, but in contrast to previously published data, more pronounced in the case of NR2B. Concomitantly, an increased association of NR2B with FAK, PYK2, Src and PSD-95 has been observed. This sharp early reaction to brief ischemia was markedly attenuated during prolonged recovery (72 h) with almost complete return to control values. The initial recruitment of tyrosine kinases to NMDA receptor during the first 3 h of reperfusion is generally consistent with an active postischemic remodeling of PSD and may participate in the induction of the postischemic signal transduction pathway in gerbil hippocampus. In contrast, ischemia of longer duration (up to 30 min) caused an immediate decrease in the protein levels as well as tyrosine phosphorylation of both NR2A and NR2B subunits which was accompanied by the marked attenuation of the association with their investigated molecular partners--PSD-95 and NRTKs. This effect may be mimicked in vitro by Ca2+-dependent activation of endogenous calpains in purified PSD preparation suggesting irreversible deterioration of the synaptic signaling machinery during irreversible long-term ischemia.

Cardiomyocyte apoptosis triggered by RAFTK/pyk2 via Src kinase is antagonized by paxillin

Altered cellular adhesion and apoptotic signaling in cardiac remodeling requires coordinated regulation of multiple constituent proteins that comprise cytoskeletal focal adhesions. One such protein activated by cardiac remodeling is related adhesion focal tyrosine kinase (RAFTK, also known as pyk2). Adenoviral-mediated expression of RAFTK in neonatal rat cardiomyocytes involves concurrent increases in phosphorylation of Src, c-Jun N-terminal kinase, and p38 leading to characteristic apoptotic changes including cleavage of poly(ADP-ribose) polymerase, caspase-3 activation, and increased DNA laddering. DNA laddering was decreased by mutation of the Tyr(402) Src-binding site in RAFTK, suggesting a central role for Src activity in apoptotic cell death that was confirmed by adenoviral-mediated Src expression. Multiple apoptotic signaling cascades are recruited by RAFTK as demonstrated by prevention of apoptosis using caspase-3 inhibitor IV (caspase-3 specific inhibitor), PP2 (Src-specific kinase inhibitor), or Csk (cellular negative regulator for Src), as well as dominant negative constructs for p38beta or MKP-1. These RAFTK-mediated phenotypic characteristics are prevented by concurrent expression of wild-type or a phosphorylation-deficient paxillin mutated at Tyr(31) and Tyr(118). Wild-type or mutant paxillin protein accumulation in the cytoplasm has no overt effect upon cell structure, but paxillin accumulation prevents losses of myofibril organization as well as focal adhesion kinase, vinculin, and paxillin protein levels mediated by RAFTK. Apoptotic signaling cascade inhibition by paxillin indicates interruption of signaling proximal to but downstream of RAFTK activity. Chronic RAFTK activation in cardiac remodeling may represent a maladaptive reactive response that can be modulated by paxillin, opening up novel possibilities for inhibition of cardiomyocyte apoptosis and structural degeneration in heart failure.

Differential regulation of cell migration and proliferation through proline-rich tyrosine kinase 2 in endothelial cells

Proline-rich tyrosine kinase 2 (Pyk2), a member of the focal adhesion kinase family, is thought to act as a key component in vasculogenesis and angiogenesis. Therefore, we studied the effect of mutant Pyk2 expression on the migration and proliferation in endothelial cells (ECs). Two types of mutant Pyk2 were examined by adenovirus vectors AxCA-Pyk2K457A, expressing a kinase inactive mutant, and AxCA-Pyk2Y402F, expressing a tyrosine autophosphorylation site mutant, in addition to AxCA-Pyk2, expressing wild-type Pyk2. Migration of ECs infected with AxCA-Pyk2Y402F increased to a level similar to that of ECs infected with AxCA-Pyk2. The size of effect was dependent on the amount of applied adenoviruses within the range of 3-30 multiplicity of infection. In contrast, AxCA-Pyk2K457A infection did not show any significant effect on cell migration. Western blotting showed that both phosphorylation of Pyk2 Y(881) and association of p130(Cas) with Pyk2 were enhanced in ECs infected with AxCA-Pyk2Y402F as well as with AxCA-Pyk2, but not in ECs infected with AxCA-Pyk2K457A. Therefore, signaling mediated by Pyk2 Y(881) and p130(Cas) may be involved in the migration of ECs infected either with AxCA-Pyk2Y402F or with AxCA-Pyk2. In proliferation assay, AxCA-Pyk2 infection suppressed EC proliferation significantly; however, neither AxCA-Pyk2Y402F nor AxCA-Pyk2K457A showed such an inhibitory effect. Thus, the two Pyk2 mutants revealed that Pyk2 signaling differentially regulates cell migration and proliferation pathways.