Pyk2 regulates multiple signaling events crucial for macrophage morphology and migration

Cooperative effects of 17β-estradiol and oocyte-derived paracrine factors on the transcriptome of mouse cumulus cells

Oocyte-derived paracrine factors (ODPFs) and estrogens are both essential for the development and function of ovarian follicles in mammals. Cooperation of these two factors was assessed in vitro using intact cumulus-oocyte complexes, cumulus cells cultured after the removal of oocytes [oocytectomized (OOX) cumulus cells], and OOX cumulus cells cocultured with denuded oocytes, all in the presence or absence of 17β-estradiol (E2). Effects on the cumulus cell transcriptome were assessed by microarray analysis. There was no significant difference between the cumulus cell transcriptomes of either OOX cumulus cells cocultured with oocytes or intact cumulus-oocyte complexes. Therefore, oocyte-mediated regulation of the cumulus cell transcriptome is mediated primarily by ODPFs and not by gap junctional communication between oocytes and cumulus cells. Gene ontology analysis revealed that both ODPFs and E2 strongly affected the biological processes associated with cell proliferation in cumulus cells. E2 had limited effects on ODPF-regulated biological processes. However, in sharp contrast, ODPFs significantly affected biological processes regulated by E2 in cumulus cells. For example, only in the presence of ODPFs did E2 significantly promote the biological processes related to phosphorylation-mediated signal transduction in cumulus cells, such as the signaling pathways of epidermal growth factor, vascular endothelial growth factor, and platelet-derived growth factor. Therefore, ODPFs and E2 cooperate to regulate the cumulus cell transcriptome and, in general, oocytes modulate the effects of estrogens on cumulus cell function.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

The transcription factor CREB enhances interleukin-17A production and inflammation in a mouse model of atherosclerosis

The enzyme 15-lipoxygenase (15-LO) plays a role in atherogenesis (also known as atherosclerosis), but the underlying mechanisms are unclear. We found that 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], the major 15-LO-dependent metabolite of arachidonic acid, stimulated the production of reactive oxygen species (ROS) by monocytes through the xanthine oxidase-mediated activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. ROS production led to the Syk-, Pyk2-, and mitogen-activated protein kinase (MAPK)-dependent production of the proinflammatory cytokine interleukin-17A (IL-17A) in a manner that required the transcription factor CREB (cyclic adenosine monophosphate response element-binding protein). In addition, this pathway was required for the 15(S)-HETE-dependent migration and adhesion of monocytes to endothelial cells. Consistent with these observations, we found that peritoneal macrophages from apolipoprotein E-deficient (ApoE-/-) mice fed a high-fat diet (a mouse model of atherosclerosis) exhibited increased xanthine oxidase and NADPH oxidase activities; ROS production; phosphorylation of Syk, Pyk2, MAPK, and CREB; and IL-17A production compared to those from similarly fed ApoE-/-:12/15-LO-/- mice. These events correlated with increased lipid deposits and numbers of monocytes and macrophages in the aortic arches of ApoE-/- mice, which resulted in atherosclerotic plaque formation. Together, these observations suggest that 15(S)-HETE exacerbates atherogenesis by enhancing CREB-dependent IL-17A production and inflammation.

The focal adhesion kinase inhibitor PF-562,271 impairs primary CD4+ T cell activation

The focal adhesion kinase inhibitor, PF-562,271, is currently in clinical development for cancer, however it is not known how PF-562,271 affects T cell function. Here, we demonstrate inhibitory effects of PF-562,271 on the activation of primary human and mouse T cells. PF-562,271 inhibits T cell receptor signaling-induced T cell adhesion to intercellular adhesion molecule-1 and T cell interactions with antigen-presenting cells. An additional focal adhesion kinase inhibitor, PF-573,228, and genetic depletion of focal adhesion kinase also impair T cell conjugation with antigen-presenting cells. PF-562,271 blocks phosphorylation of the signaling molecules zeta chain associate protein of 70 kDa, linker of activated T cells, and extracellular signal-regulated kinase, and impairs T cell proliferation. The effects observed on T cell proliferation cannot solely be attributed to focal adhesion kinase inhibition, as genetic depletion did not alter proliferation. The effect of PF-562,271 on T cell proliferation is not rescued when proximal T cell receptor signaling is bypassed by stimulation with phorbol-12-myristate-13-acetate and ionomycin. Taken together, our findings demonstrate that focal adhesion kinase regulates integrin-mediated T cell adhesion following T cell receptor activation. Moreover, our findings suggest that PF-562,271 may have immunomodulatory effects that could impact its therapeutic applications.

Intercellular adhesion molecule 1: recent findings and new concepts involved in mammalian spermatogenesis

Spermatogenesis, the process of spermatozoa production, is regulated by several endocrine factors, including testosterone, follicle stimulating hormone, luteinizing hormone and estradiol 17β. For spermatogenesis to reach completion, developing germ cells must traverse the seminiferous epithelium while remaining transiently attached to Sertoli cells. If germ cell adhesion were to be compromised for a period of time longer than usual, germ cells would slough from the seminiferous epithelium and infertility would result. Presently, Sertoli-germ cell adhesion is known to be mediated largely by classical and desmosomal cadherins. More recent studies, however, have begun to expand long-standing concepts and to examine the roles of other proteins such as intercellular adhesion molecules. In this review, we focus on the biology of intercellular adhesion molecules in the mammalian testis, hoping that this information is useful in the design of future studies.

A role for the protein tyrosine phosphatase CD45 in macrophage adhesion through the regulation of paxillin degradation

CD45 is a protein tyrosine phosphatase expressed on all cells of hematopoietic origin that is known to regulate Src family kinases. In macrophages, the absence of CD45 has been linked to defects in adhesion, however the molecular mechanisms involved remain poorly defined. In this study, we show that bone marrow derived macrophages from CD45-deficient mice exhibit abnormal cell morphology and defective motility. These defects are accompanied by substantially decreased levels of the cytoskeletal-associated protein paxillin, without affecting the levels of other proteins. Degradation of paxillin in CD45-deficient macrophages is calpain-mediated, as treatment with a calpain inhibitor restores paxillin levels in these cells and enhances cell spreading. Inhibition of the tyrosine kinases proline-rich tyrosine kinase (Pyk2) and focal adhesion kinase (FAK), kinases that are capable of mediating tyrosine phosphorylation of paxillin, also restored paxillin levels, indicating a role for these kinases in the CD45-dependent regulation of paxillin. These data demonstrate that CD45 functions to regulate Pyk2/FAK activity, likely through the activity of Src family kinases, which in turn regulates the levels of paxillin to modulate macrophage adhesion and migration.

Distinct role of Pyk2 in mediating thromboxane generation downstream of both G12/13 and integrin αIIbβ3 in platelets

Proline-rich tyrosine kinase 2 (Pyk2) is activated by various agonists in platelets. We evaluated the signaling mechanism and the functional role of Pyk2 in platelets by using pharmacological inhibitors and Pyk2-deficient platelets. We found that platelet aggregation and secretion in response to 2-methylthio-ADP (2-MeSADP) and AYPGKF were diminished in the presence of Pyk2 inhibitors or in Pyk2-deficient platelets, suggesting that Pyk2 plays a positive regulatory role in platelet functional responses. It has been shown that ADP-, but not thrombin-induced thromboxane (TxA2) generation depends on integrin signaling. Unlike ADP, thrombin activates G12/13 pathways, and G12/13 pathways can substitute for integrin signaling for TxA2 generation. We found that Pyk2 was activated downstream of both G12/13 and integrin-mediated pathways, and both 2-MeSADP- and AYPGKF-induced TxA2 generation was significantly diminished in Pyk2-deficient platelets. In addition, TxA2 generation induced by co-stimulation of Gi and Gz pathways, which is dependent on integrin signaling, was inhibited by blocking Pyk2. Furthermore, inhibition of 2-MeSADP-induced TxA2 generation by fibrinogen receptor antagonist was not rescued by co-stimulation of G12/13 pathways in the presence of Pyk2 inhibitor. We conclude that Pyk2 is a common signaling effector downstream of both G12/13 and integrin αIIbβ3 signaling, which contributes to thromboxane generation.

Retinoic acid induces adhesion and migration in NB4 cells through Pyk2 signaling

Since the introduction of all-trans-retinoic acid (ATRA) treatment for acute promyelocytic leukemia (APL) there has been increasing concern about extramedullary disease (EMD) progression despite favorable response in the bone marrow. We postulated that ATRA treatment enhances migration and adhesion abilities possibly enabling APL cells to inhabit extramedullary sites. We revealed an increase in adhesion, migration and invasion capabilities of NB4 cells following ATRA treatment. ATRA induced upregulation of Pyk2 mRNA, protein and phosphorylation levels and enhanced Pyk2 interaction with paxillin and vinculin. Pyk2 inhibition resulted in a reduction of NB4 cell adhesion and migration following ATRA treatment. These results indicate that in vitro Pyk2 might function to regulate cell adhesion and motility following ATRA treatment and its upregulated expression may contribute to EMD development in APL patients.

Protein tyrosine kinase signaling in the mouse oocyte cortex during sperm-egg interactions and anaphase resumption

Fertilization triggers activation of a series of pre-programmed signal transduction pathways in the oocyte that establish a block to polyspermy, induce meiotic resumption, and initiate zygotic development. Fusion between sperm and oocyte results in rapid changes in oocyte intracellular free-calcium levels, which in turn activate multiple protein kinase cascades in the ooplasm. The present study examined the possibility that sperm-oocyte interaction involves localized activation of oocyte protein tyrosine kinases, which could provide an alternative signaling mechanism to that triggered by the fertilizing sperm. Confocal immunofluorescence analysis with antibodies to phosphotyrosine and phosphorylated protein tyrosine kinases allowed detection of minute signaling events localized to the site of sperm-oocyte interaction that were not amenable to biochemical analysis. The results provide evidence for localized accumulation of phosphotyrosine at the site of sperm contact, binding, or fusion, which suggests active protein tyrosine kinase signaling prior to and during sperm incorporation. The PYK2 kinase was found to be concentrated and activated at the site of sperm-oocyte interaction, and likely participates in this response. Widespread activation of PYK2 and FAK kinases was subsequently observed within the oocyte cortex, indicating that sperm incorporation is followed by more global signaling via these kinases during meiotic resumption. The results demonstrate an alternate signaling pathway triggered in mammalian oocytes by sperm contact, binding, or fusion with the oocyte.

The proline-rich tyrosine kinase Pyk2 regulates platelet integrin αIIbβ3 outside-in signaling

BACKGROUND

The proline-rich tyrosine kinase Pyk2 is a focal adhesion kinase expressed in blood platelets, and is activated downstream of G-protein coupled receptors as well as integrin α2β1.

OBJECTIVE

In this study we have investigated the involvement of Pyk2 in integrin αIIbβ3 outside-in signaling in human and murine platelets.

METHODS

We analyzed the stimulation of intracellular signaling pathways in platelets from Pyk2 knockout mice adherent to immobilized fibrinogen.

RESULTS

Pyk2 was rapidly phosphorylated and activated in human and murine platelets adherent to fibrinogen through integrin αIIbβ3. Activation of Pyk2 was Src-dependent, but did not require phospholipase Cγ2 activity. Platelets from Pyk2 knockout mice showed a defective ability to adhere and spread on fibrinogen, in association with a dramatic reduction of phosphatidylinositol 3-kinase (PI3K) activation and Akt phosphorylation. Pharmacological and genetic analysis demonstrated that integrin αIIbβ3 engagement selectively stimulated the β-isoform of PI3K (PI3Kβ), and that, as for Pyk2, PI3Kβ activation required Src family kinases activity, but not phospholipase Cγ2. In fibrinogen-adherent platelets, both Pyk2 and PI3Kβ were necessary for stimulation of the small GTPase Rap1b, a regulator of cell adhesion and spreading. Integrin αIIbβ3 engagement triggered the association of the PI3Kβ regulatory subunit p85 with the adaptor protein c-Cbl, which was mediated by the p85 SH3 domain, and was independent of c-Cbl tyrosine phosphorylation. However, p85-associated c-Cbl was tyrosine phosphorylated by activated Pyk2 in fibrinogen adherent platelets.

CONCLUSIONS

These results identify a novel pathway of integrin αIIbβ3 outside-in signaling and recognize the tyrosine kinase Pyk2 as a major regulator of platelet adhesion and spreading on fibrinogen.

CaMKK2: a novel target for shaping the androgen-regulated tumor ecosystem

The androgen receptor (AR) is pivotal in the biology of sex hormone-regulated malignancies, with prostate cancer (PC) the most affected tumor. AR signals control the growth, survival, and migration of cancer cells, and they regulate the activation of macrophages, a cell type pivotal to the tumor ecosystem. Intriguingly, CaMKK2 has recently been identified as both an important AR-regulated gene in the context of PC and as a critical regulator of macrophage activation. By contrast, CaMKK2 is barely detectable in normal prostate or immune cells that mediate the response against tumorigenesis. These novel findings suggest that CaMKK2 resides at a critical molecular node that shapes the cancer ecosystem, and identifies this kinase as a novel therapeutic target for sex hormone-regulated cancers.

Monosodium urate activates Src/Pyk2/PI3 kinase and cathepsin dependent unconventional protein secretion from human primary macrophages

Monosodium urate (MSU) is an endogenous danger signal that is crystallized from uric acid released from injured cells. MSU is known to activate inflammatory response in macrophages but the molecular mechanisms involved have remained uncharacterized. Activated macrophages start to secrete proteins to activate immune response and to recruit other immune cells to the site of infection and/or tissue damage. Secretome characterization after activation of innate immune system is essential to unravel the details of early phases of defense responses. Here, we have analyzed the secretome of human primary macrophages stimulated with MSU using quantitative two-dimensional gel electrophoresis based proteomics as well as high-throughput qualitative GeLC-MS/MS approach combining protein separation by SDS-PAGE and protein identification by liquid chromatography-MS/MS. Both methods showed that MSU stimulation induced robust protein secretion from lipopolysaccharide-primed human macrophages. Bioinformatic analysis of the secretome data showed that MSU stimulation strongly activates unconventional, vesicle mediated protein secretion. The unconventionally secreted proteins included pro-inflammatory cytokines like IL-1β and IL-18, interferon-induced proteins, and danger signal proteins. Also active forms of lysosomal proteases cathepsins were secreted on MSU stimulation, and cathepsin activity was essential for MSU-induced unconventional protein secretion. Additionally, proteins associated to phosphorylation events including Src family tyrosine kinases were increased in the secretome of MSU-stimulated cells. Our functional studies demonstrated that Src, Pyk2, and PI3 kinases act upstream of cathepsins to activate the overall protein secretion from macrophages. In conclusion, we provide the first comprehensive characterization of protein secretion pathways activated by MSU in human macrophages, and reveal a novel role for cathepsins and Src, Pyk2, PI3 kinases in the activation of unconventional protein secretion.

Pyk2 cytonuclear localization: mechanisms and regulation by serine dephosphorylation

Cytonuclear signaling is essential for long-term alterations of cellular properties. Several pathways involving regulated nuclear accumulation of Ser/Thr kinases have been described but little is known about cytonuclear trafficking of tyrosine kinases. Proline-rich tyrosine kinase 2 (Pyk2) is a cytoplasmic non-receptor tyrosine kinase enriched in neurons and involved in functions ranging from synaptic plasticity to bone resorption, as well as in cancer. We previously showed the Ca(2+)-induced, calcineurin-dependent, nuclear localization of Pyk2. Here, we characterize the molecular mechanisms of Pyk2 cytonuclear localization in transfected PC12 cells. The 700-841 linker region of Pyk2 recapitulates its depolarization-induced nuclear accumulation. This region includes a nuclear export motif regulated by phosphorylation at residue S778, a substrate of cAMP-dependent protein kinase and calcineurin. Nuclear import is controlled by a previously identified sequence in the N-terminal domain and by a novel nuclear targeting signal in the linker region. Regulation of cytonuclear trafficking is independent of Pyk2 activity. The region regulating nuclear localization is absent from the non-neuronal shorter splice isoform of Pyk2. Our results elucidate the mechanisms of Ca(2+)-induced nuclear accumulation of Pyk2. They also suggest that Pyk2 nuclear accumulation is a novel type of signaling response that may contribute to specific long-term adaptations in neurons.

Intersecting roles of protein tyrosine kinase and calcium signaling during fertilization

The oocyte is a highly specialized cell that must respond to fertilization with a preprogrammed series of signal transduction events that establish a block to polyspermy, trigger resumption of the cell cycle and execution of a developmental program. The fertilization-induced calcium transient is a key signal that initiates the process of oocyte activation and studies over the last several years have examined the signaling pathways that act upstream and downstream of this calcium transient. Protein tyrosine kinase signaling was found to be an important component of the upstream pathways that stimulated calcium release at fertilization in oocytes from animals that fertilize externally, but a similar pathway has not been found in mammals which fertilize internally. The following review will examine the diversity of signaling in oocytes from marine invertebrates, amphibians, fish and mammals in an attempt to understand the basis for the observed differences. In addition to the pathways upstream of the fertilization-induced calcium transient, recent studies are beginning to unravel the role of protein tyrosine kinase signaling downstream of the calcium transient. The PYK2 kinase was found to respond to fertilization in the zebrafish system and seems to represent a novel component of the response of the oocyte to fertilization. The potential impact of impaired PTK signaling in oocyte quality will also be discussed.

Impaired thrombin-induced platelet activation and thrombus formation in mice lacking the Ca(2+)-dependent tyrosine kinase Pyk2

In the present study, we used a knockout murine model to analyze the contribution of the Ca(2+)-dependent focal adhesion kinase Pyk2 in platelet activation and thrombus formation in vivo. We found that Pyk2-knockout mice had a tail bleeding time that was slightly increased compared with their wild-type littermates. Moreover, in an in vivo model of femoral artery thrombosis, the time to arterial occlusion was significantly prolonged in mice lacking Pyk2. Pyk2-deficient mice were also significantly protected from collagen plus epinephrine-induced pulmonary thromboembolism. Ex vivo aggregation of Pyk2-deficient platelets was normal on stimulation of glycoprotein VI, but was significantly reduced in response to PAR4-activating peptide, low doses of thrombin, or U46619. Defective platelet aggregation was accompanied by impaired inside-out activation of integrin α(IIb)β(3) and fibrinogen binding. Granule secretion was only slightly reduced in the absence of Pyk2, whereas a marked inhibition of thrombin-induced thromboxane A(2) production was observed, which was found to be responsible for the defective aggregation. Moreover, we have demonstrated that Pyk2 is implicated in the signaling pathway for cPLA(2) phosphorylation through p38 MAPK. The results of the present study show the importance of the focal adhesion kinase Pyk2 downstream of G-protein-coupled receptors in supporting platelet aggregation and thrombus formation.

Regulation of Rela/p65 and endothelial cell inflammation by proline-rich tyrosine kinase 2

We investigated the role of proline-rich tyrosine kinase 2 (Pyk2) in the mechanism of NF-κB activation and endothelial cell (EC) inflammation induced by thrombin, a procoagulant serine protease released in high amounts during sepsis and other inflammatory conditions. Stimulation of ECs with thrombin resulted in a time-dependent activation of Pyk2. RNA interference knockdown of Pyk2 attenuated thrombin-induced activity of NF-κB and expression of its target genes, vascular cell adhesion molecule-1 and monocyte chemoattractant protein-1. Pyk2 knockdown impaired thrombin-induced activation of IκB kinase (IKK) and phosphorylation (Ser32 and Ser36) of IkappaBα, but, surprisingly, failed to prevent IκBα degradation. However, depletion of IKKα or IKKβ was effective in inhibiting IκBα phosphorylation/degradation, as expected. Intriguingly, Pyk2 knockdown impaired nuclear translocation and DNA binding of RelA/p65, despite the inability to prevent IκBα degradation. In addition, Pyk2 knockdown was associated with inhibition of RelA/p65 phosphorylation at Ser536, which is important for transcriptional activity of RelA/p65. Depletion of IKKα or IKKβ each impaired RelA/p65 phosphorylation. Taken together, these data identify Pyk2 as a critical regulator of EC inflammation by virtue of engaging IKK to promote the release and the transcriptional capacity of RelA/p65, and, additionally, by its ability to facilitate the nuclear translocation of the released RelA/p65. Thus, specific targeting of Pyk2 may be an effective anti-inflammatory strategy in vascular diseases associated with EC inflammation and intravascular coagulation.

Altered Toll-like receptor 9 signaling in Mycobacterium avium subsp. paratuberculosis-infected bovine monocytes reveals potential therapeutic targets

Mycobacterium avium subsp. paratuberculosis is the causative agent of Johne's disease in cattle. The complex, multifaceted interaction of M. avium subsp. paratuberculosis with its host includes dampening the ability of infected cells to respond to stimuli that promote M. avium subsp. paratuberculosis clearance. By disrupting host defenses, M. avium subsp. paratuberculosis creates an intracellular environment that favors the establishment and maintenance of infection. Toll-like receptors (TLRs) are important sensors that initiate innate immune responses to microbial challenge and are also immunotherapeutic targets. For example, TLR9 contributes to host defense against M. avium subsp. paratuberculosis, and its agonists (CpG oligodeoxynucleotides [ODNs]) are under investigation for treatment of Johne's disease and other infections. Here we demonstrate that M. avium subsp. paratuberculosis infection changes the responsiveness of bovine monocytes to TLR9 stimulation. M. avium subsp. paratuberculosis inhibits classical TLR9-mediated responses despite a 10-fold increase in TLR9 expression and maintained uptake of CpG ODNs. Other TLR9-mediated responses, such as oxidative burst, which occur through noncanonical signaling, remain functional. Kinome analysis verifies that classic TLR9 signaling is blocked by M. avium subsp. paratuberculosis infection and that signaling instead proceeds through a Pyk2-mediated mechanism. Pyk2-mediated signaling does not hinder infection, as CpG ODNs fail to promote M. avium subsp. paratuberculosis clearance. Indeed, Pyk2 signaling appears to be an important aspect of M. avium subsp. paratuberculosis infection, as Pyk2 inhibitors significantly reduce the number of intracellular M. avium subsp. paratuberculosis bacteria. The actions of M. avium subsp. paratuberculosis on TLR9 signaling may represent a strategy to generate a host environment which is better suited for infection, revealing potential new targets for therapeutic intervention.

PYK2: a calcium-sensitive protein tyrosine kinase activated in response to fertilization of the zebrafish oocyte

Fertilization begins with binding and fusion of a sperm with the oocyte, a process that triggers a high amplitude calcium transient which propagates through the oocyte and stimulates a series of preprogrammed signal transduction events critical for zygote development. Identification of the pathways downstream of this calcium transient remains an important step in understanding the basis of zygote quality. The present study demonstrates that the calcium-calmodulin sensitive protein tyrosine kinase PYK2 is a target of the fertilization-induced calcium transient in the zebrafish oocyte and that it plays an important role in actin-mediated events critical for sperm incorporation. At fertilization, PYK2 was activated initially at the site of sperm-oocyte interaction and was closely associated with actin filaments forming the fertilization cone. Later PYK2 activation was evident throughout the entire oocyte cortex, however activation was most intense over the animal hemisphere. Fertilization-induced PYK2 activation could be blocked by suppressing calcium transients in the ooplasm via injection of BAPTA as a calcium chelator. PYK2 activation could be artificially induced in unfertilized oocytes by injection of IP3 at concentrations sufficient to induce calcium release. Functionally, suppression of PYK2 activity by chemical inhibition or by injection of a dominant-negative construct encoding the N-terminal ERM domain of PKY2 inhibited formation of an organized fertilization cone and reduced the frequency of successful sperm incorporation. Together, the above findings support a model in which PYK2 responds to the fertilization-induced calcium transient by promoting reorganization of the cortical actin cytoskeleton to form the fertilization cone.

Regulation of osteoclast structure and function by FAK family kinases

Osteoclasts are highly specialized cells that resorb bone and contribute to bone remodeling. Diseases such as osteoporosis and osteolytic bone metastasis occur when osteoclast-mediated bone resorption takes place in the absence of concurrent bone synthesis. Considerable effort has been placed on identifying molecules that regulate the bone resorption activity of osteoclasts. To this end, we investigated unique and overlapping functions of members of the FAK family (FAK and Pyk2) in osteoclast functions. With the use of a conditional knockout mouse model, in which FAK is selectively targeted for deletion in osteoclast precursors (FAK(Δmyeloid)), we found that loss of FAK resulted in reduced bone resorption by osteoclasts in vitro, coincident with impaired signaling through the CSF-1R. However, bone architecture appeared normal in FAK(Δmyeloid) mice, suggesting that Pyk2 might functionally compensate for reduced FAK levels in vivo. This was supported by data showing that podosome adhesion structures, which are essential for bone degradation, were significantly more impaired in osteoclasts when FAK and Pyk2 were reduced than when either molecule was depleted individually. We conclude that FAK contributes to cytokine signaling and bone resorption in osteoclasts and partially compensates for the absence of Pyk2 to maintain proper adhesion structures in these cells.

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.

TGF-β stimulates Pyk2 expression as part of an epithelial-mesenchymal transition program required for metastatic outgrowth of breast cancer

Epithelial-mesenchymal transition (EMT) programs are essential in promoting breast cancer invasion, systemic dissemination and in arousing proliferative programs in breast cancer micrometastases, a reaction that is partially dependent on focal adhesion kinase (FAK). Many functions of FAK are shared by its homolog, protein tyrosine kinase 2 (Pyk2), raising the question as to whether Pyk2 also participates in driving the metastatic outgrowth of disseminated breast cancer cells. In addressing this question, we observed Pyk2 expression to be (i) significantly upregulated in recurrent human breast cancers; (ii) differentially expressed across clonal isolates of human MDA-MB-231 breast cancer cells in a manner predictive for metastatic outgrowth, but not for invasiveness; and (iii) dramatically elevated in ex vivo cultures of breast cancer cells isolated from metastatic lesions as compared with cells that produced the primary tumor. We further show that metastatic human and murine breast cancer cells robustly upregulate their expression of Pyk2 during EMT programs stimulated by transforming growth factor-β (TGF-β). Genetic and pharmacological inhibition of Pyk2 demonstrated that the activity of this protein tyrosine kinase was dispensable for the ability of breast cancer cells to undergo invasion in response to TGF-β, and to form orthotopic mammary tumors in mice. In stark contrast, Pyk2-deficiency prevented TGF-β from stimulating the growth of breast cancer cells in 3D-organotypic cultures that recapitulated pulmonary microenvironments, as well as inhibited the metastatic outgrowth of disseminated breast cancer cells in the lungs of mice. Mechanistically, Pyk2 expression was inversely related to that of E-cadherin, such that elevated Pyk2 levels stabilized β1 integrin expression necessary to initiate the metastatic outgrowth of breast cancer cells. Thus, we have delineated novel functions for Pyk2 in mediating distinct elements of the EMT program and metastatic cascade regulated by TGF-β, particularly the initiation of secondary tumor outgrowth by disseminated cells.

Small molecule inhibitors of the Pyk2 and FAK kinases modulate chemoattractant-induced migration, adhesion and Akt activation in follicular and marginal zone B cells

B-lymphocytes produce protective antibodies but also contribute to autoimmunity. In particular, marginal zone (MZ) B cells recognize both microbial components and self-antigens. B cell trafficking is critical for B cell activation and is controlled by chemoattactants such as CXCL13 and sphingosine 1-phosphate (S1P). The related tyrosine kinases focal adhesion kinase (FAK) and proline-rich tyrosine kinase (Pyk2) regulate cell migration and adhesion but their roles in B cells are not fully understood. Using a novel Pyk2-selective inhibitor described herein (PF-719), as well as a FAK-selective inhibitor, we show that both Pyk2 and FAK are important for CXCL13- and S1P-induced migration of B-2 cells and MZ B cells. In contrast, LFA-1-mediated adhesion required only Pyk2 whereas activation of the Akt pro-survival kinase required FAK but not Pyk2. Thus Pyk2 and FAK mediate critical processes in B cells and these inhibitors can be used to further elucidate their functions in B cells.

Safety, pharmacokinetic, and pharmacodynamic phase I dose-escalation trial of PF-00562271, an inhibitor of focal adhesion kinase, in advanced solid tumors

PURPOSE

PF-00562271 is a novel inhibitor of focal adhesion kinase (FAK). The objectives of this study were to identify the recommended phase II dose (RP2D) and assess safety and tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and antitumor activity of PF-00562271.

PATIENTS AND METHODS

Part 1 was a dose escalation without and with food. Part 2 enrolled specific tumor types in an expansion at the RP2D and also assessed the effect of PF-00562271 on single-dose midazolam PK in a subgroup of patients.

RESULTS

Ninety-nine patients (median age, 60 years; 98% with Eastern Cooperative Oncology Group performance status of 0 or 1) were treated in 12 fasting and three fed cohorts. The 125-mg twice-per-day fed dose was deemed the maximum-tolerated dose (MTD) and RP2D. Grade 3 dose-limiting toxicities included headache, nausea/vomiting, dehydration, and edema. Nausea was the most frequently observed toxicity (60% of patients, all grades 1 or 2 at RP2D). PF-00562271 exposure increased with increasing dose; serum concentration-time profiles showed characteristic nonlinear disposition. Steady-state exposures were reached within 1 week. On coadministration, geometric mean values of midazolam maximal observed serum concentration and area under the serum concentration-time curve increased by 60% and more than two-fold, respectively. Of 14 patients evaluable by [(18)F]fluorodeoxyglucose positron emission tomography in the expansion cohorts, seven metabolic responses were observed. With conventional imaging, 31 patients had stable disease at first restaging scans, and 15 of these remained stable for six or more cycles.

CONCLUSION

The MTD and RP2D of PF-00562271 is 125 mg twice per day with food. PF-00562271 displayed time- and dose-dependent nonlinear PK and is likely a potent CYP 3A inhibitor. This first-in-class study supports further investigation of FAK as a promising therapeutic target.

Macrophage Migration and Its Regulation by CSF-1

Macrophages are terminally differentiated cells of the mononuclear phagocytic lineage and develop under the stimulus of their primary growth and differentiation factor, CSF-1. Although they differentiate into heterogeneous populations, depending upon their tissue of residence, motility is an important aspect of their function. To facilitate their migration through tissues, macrophages express a unique range of adhesion and cytoskeletal proteins. Notably, macrophages do not form large, stable adhesions or actin stress fibers but rely on small, short lived point contacts, focal complexes and podosomes for traction. Thus, macrophages are built to respond rapidly to migratory stimuli. As well as triggering growth and differentiation, CSF-1 is also a chemokine that regulates macrophage migration via activation the CSF-1 receptor tyrosine kinase. CSF-1R autophosphorylation of several intracellular tyrosine residues leads to association and activation of many downstream signaling molecules. However, phosphorylation of just one residue, Y721, mediates association of PI3K with the receptor to activate the major motility signaling pathways in macrophages. Dissection of these pathways will identify drug targets for the inhibition of diseases in which macrophages contribute to adverse outcomes.

Calcium/calmodulin-dependent protein kinase kinase 2 regulates macrophage-mediated inflammatory responses

Calcium/calmodulin-dependent kinase kinase 2 (CaMKK2) plays a key role in regulating food intake and energy expenditure at least in part by its actions in hypothalamic neurons. Previously, we showed that loss of CaMKK2 protected mice from high-fat diet (HFD)-induced obesity and glucose intolerance. However, although pair feeding HFD to WT mice to match food consumption of CAMKK2-null mice slowed weight gain, it failed to protect from glucose intolerance. Here we show that relative to WT mice, HFD-fed CaMKK2-null mice are protected from inflammation in adipose and remain glucose-tolerant. Moreover, loss of CaMKK2 also protected mice from endotoxin shock and fulminant hepatitis. We explored the expression of CaMKK2 in immune cells and found it to be restricted to those of the monocyte/macrophage lineage. CaMKK2-null macrophages exhibited a remarkable deficiency to spread, phagocytose bacteria, and synthesize cytokines in response to the Toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS). Mechanistically, loss of CaMKK2 uncoupled the TLR4 cascade from activation of protein tyrosine kinase 2 (PYK2; also known as PTK2B). Our findings uncover an important function for CaMKK2 in mediating mechanisms that control the amplitude of macrophage inflammatory responses to excess nutrients or pathogen derivatives.

Strain specific transcriptional response in Mycobacterium tuberculosis infected macrophages

Background

Tuberculosis (TB), a bacterial infection caused by Mycobacterium tuberculosis (Mtb) remains a significant health problem worldwide with a third of the world population infected and nearly nine million new cases claiming 1.1 million deaths every year. The outcome following infection by Mtb is determined by a complex and dynamic host-pathogen interaction in which the phenotype of the pathogen and the immune status of the host play a role. However, the molecular mechanism by which Mtb strains induce different responses during intracellular infection of the host macrophage is not fully understood. To explore the early molecular events triggered upon Mtb infection of macrophages, we studied the transcriptional responses of murine bone marrow-derived macrophages (BMM) to infection with two clinical Mtb strains, CDC1551 and HN878. These strains have previously been shown to differ in their virulence/immunogenicity in the mouse and rabbit models of pulmonary TB.

Results

In spite of similar intracellular growth rates, we observed that compared to HN878, infection by CDC1551 of BMM was associated with an increased global transcriptome, up-regulation of a specific early (6 hours) immune response network and significantly elevated nitric oxide production. In contrast, at 24 hours post-infection of BMM by HN878, more host genes involved in lipid metabolism, including cholesterol metabolism and prostaglandin synthesis were up-regulated, compared to infection with CDC1551.

In association with the differences in the macrophage responses to infection with the 2 Mtb strains, intracellular CDC1551 expressed higher levels of stress response genes than did HN878.

Conclusions

In association with the early and more robust macrophage activation, intracellular CDC1551 cells were exposed to a higher level of stress leading to increased up-regulation of the bacterial stress response genes. In contrast, sub-optimal activation of macrophages and induction of a dysregulated host cell lipid metabolism favored a less stressful intracellular environment for HN878. Our findings suggest that the ability of CDC1551 and HN878 to differentially activate macrophages during infection probably determines their ability to either resist host cell immunity and progress to active disease or to succumb to the host protective responses and be driven into a non-replicating latent state in rabbit lungs.

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

Background

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

Methods

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

Results

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

Conclusions

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

The kinase Pyk2 is involved in renal fibrosis by means of mechanical stretch-induced growth factor expression in renal tubules

Unilateral ureteral obstruction is a well-established experimental model of progressive renal fibrosis. We tested whether mechanical stretch and subsequent renal tubular distension might lead to renal fibrosis by first studying renal tubular epithelial cells in culture. We found that mechanical stretch induced reactive oxygen species that in turn activated the cytoplasmic proline-rich tyrosine kinase-2 (Pyk2). This kinase is abundantly expressed in tubular epithelial cells where it is activated by several stimuli. Using mice with deletion of Pyk2 we found that the expression of transforming growth factor-β1 induced by mechanical stretch in renal tubular epithelial cells was significantly reduced. The expression of connective tissue growth factor was also reduced in the Pyk2(-/-) mice. We also found that expression of connective tissue growth factor was independent of transforming growth factor-β1, but dependent on the Rho-associated coiled-coil forming protein kinase pathway. Thus, Pyk2 may be an important initiating factor in renal fibrosis and might be a new therapeutic target for ameliorating renal fibrosis.

Role and regulation of phosphatidylinositol 3-kinase β in platelet integrin α2β1 signaling

Integrin α2β1-mediated adhesion of human platelets to monomeric type I collagen or to the GFOGER peptide caused a time-dependent activation of PI3K and Akt phosphorylation. This process was abrogated by pharmacologic inhibition of PI3Kβ, but not of PI3Kγ or PI3Kα. Moreover, Akt phosphorylation was undetectable in murine platelets expressing a kinase-dead mutant of PI3Kβ (PI3Kβ(KD)), but occurred normally in PI3Kγ(KD) platelets. Integrin α2β1 failed to stimulate PI3Kβ in platelets from phospholipase Cγ2 (PLCγ2)-knockout mice, and we found that intracellular Ca(2+) linked PLCγ2 to PI3Kβ activation. Integrin α2β1 also caused a time-dependent stimulation of the focal kinase Pyk2 downstream of PLCγ2 and intracellular Ca(2+). Whereas activation of Pyk2 occurred normally in PI3Kβ(KD) platelets, stimulation of PI3Kβ was strongly reduced in Pyk2-knockout mice. Neither Pyk2 nor PI3Kβ was required for α2β1-mediated adhesion and spreading. However, activation of Rap1b and inside-out stimulation of integrin αIIbβ3 were reduced after inhibition of PI3Kβ and were significantly impaired in Pyk2-deficient platelets. Finally, both PI3Kβ and Pyk2 significantly contributed to thrombus formation under flow. These results demonstrate that Pyk2 regulates PI3Kβ downstream of integrin α2β1, and document a novel role for Pyk2 and PI3Kβ in integrin α2β1 promoted inside-out activation of integrin αIIbβ3 and thrombus formation.

Role of Pyk2 in cardiac arrhythmogenesis

Proline-rich tyrosine kinase 2 (Pyk2) is a nonreceptor protein kinase regulated by intracellular Ca2+, CaMK, and PKC and can be activated by different stress signals involved in heart failure. However, Pyk2 has not been investigated in the human heart, and the functional role of Pyk2 signaling at the whole heart level has not been elucidated. We hypothesize that Ca2+-dependent activation of Pyk2 is involved in cardiac electrophysiology. We examined the expression of Pyk2 in nonfailing versus ischemic and nonischemic failing human hearts ( n = 6 hearts/group). To investigate Pyk2 function, we optically mapped perfused hearts from wild-type (WT; n = 7) and knockout (Pyk2−/−; n = 8) mice during autonomic stimulation. Experiments were done in control mice and after 1 wk of transverse aortic constriction. We used the Illumina beadarray approach for transcriptional profiling of WT and Pyk2−/− mouse ventricles. Western blot analysis revealed a doubling of Pyk2 activation in nonischemic failing versus nonfailing human hearts. In mouse hearts, we observed a much higher probability of ventricular tachyarrhythmia during ACh perfusion in Pyk2−/− versus WT mice. Parasympathetic stimulation resulted in a dose-dependent decrease of atrial action potential duration (APD) in both WT and Pyk2−/− mice, whereas in ventricles it induced APD shortening in Pyk2−/− mice but not in WT mice. Deficiency of Pyk2 abolished ACh-induced prolongation of atrioventricular delay in Pyk2−/− mouse hearts but did not affect heart rate. Lower mRNA and protein levels of sarco(endo)plasmic reticulum Ca2+-ATPase 2 and higher mRNA levels of Na+/Ca2+ exchanger 1 were detected in Pyk2−/− hearts compared with WT hearts. The transverse aortic constriction protocol did not change the phenotype. In conclusion, our results indicate a protective role of Pyk2 with respect to ventricular tachyarrhythmia during parasympathetic stimulation by regulation of gene expression related to Ca2+ handling. We hypothesize that activation of Pyk2 in the human heart during heart failure may contribute to protection against arrhythmia.

Extracellular ATP acts on P2Y2 purinergic receptors to facilitate HIV-1 infection

Extracellular adenosine triphosphate (ATP) can activate purinergic receptors of the plasma membrane and modulate multiple cellular functions. We report that ATP is released from HIV-1 target cells through pannexin-1 channels upon interaction between the HIV-1 envelope protein and specific target cell receptors. Extracellular ATP then acts on purinergic receptors, including P2Y2, to activate proline-rich tyrosine kinase 2 (Pyk2) kinase and transient plasma membrane depolarization, which in turn stimulate fusion between Env-expressing membranes and membranes containing CD4 plus appropriate chemokine co-receptors. Inhibition of any of the constituents of this cascade (pannexin-1, ATP, P2Y2, and Pyk2) impairs the replication of HIV-1 mutant viruses that are resistant to conventional antiretroviral agents. Altogether, our results reveal a novel signaling pathway involved in the early steps of HIV-1 infection that may be targeted with new therapeutic approaches.

Decreased cell adhesion promotes angiogenesis in a Pyk2-dependent manner

Angiogenesis is regulated by both soluble growth factors and cellular interactions with the extracellular matrix (ECM). While cell adhesion via integrins has been shown to be required for angiogenesis, the effects of quantitative changes in cell adhesion and spreading against the ECM remain less clear. Here, we show that angiogenic sprouting in natural and engineered three-dimensional matrices exhibited a biphasic response, with peak sprouting when adhesion to the matrix was limited to intermediate levels. Examining changes in global gene expression to determine a genetic basis for this response, we demonstrate a vascular endothelial growth factor (VEGF)-induced upregulation of genes associated with vascular invasion and remodeling when cell adhesion was limited, whereas cells on highly adhesive surfaces upregulated genes associated with proliferation. To explore a mechanistic basis for this effect, we turned to focal adhesion kinase (FAK), a central player in adhesion signaling previously implicated in angiogenesis, and its homologue, proline-rich tyrosine kinase 2 (Pyk2). While FAK signaling had some impact, our results suggested that Pyk2 can regulate both gene expression and endothelial sprouting through its enhanced activation by VEGF in limited adhesion contexts. We also demonstrate decreased sprouting of tissue explants from Pyk2-null mice as compared to wild type mice as further confirmation of the role of Pyk2 in angiogenic sprouting. These results suggest a surprising finding that limited cell adhesion can enhance endothelial responsiveness to VEGF and demonstrate a novel role for Pyk2 in the adhesive regulation of angiogenesis.

A novel role of protein tyrosine kinase2 in mediating chloride secretion in human airway epithelial cells

Ca²⁺ activated Cl⁻ channels (CaCC) are up-regulated in cystic fibrosis (CF) airway surface epithelia. The presence and functional properties of CaCC make it a possible therapeutic target to compensate for the deficiency of Cl⁻ secretion in CF epithelia. CaCC is activated by an increase in cytosolic Ca²⁺, which not only activates epithelial CaCCs, but also inhibits epithelial Na⁺ hyperabsorption, which may also be beneficial in CF. Our previous study has shown that spiperone, a known antipsychotic drug, activates CaCCs and stimulates Cl⁻ secretion in polarized human non-CF and CF airway epithelial cell monolayers in vitro, and in Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) knockout mice in vivo. Spiperone activates CaCC not by acting in its well-known role as an antagonist of either 5-HT2 or D2 receptors, but through a protein tyrosine kinase-coupled phospholipase C-dependent pathway. Moreover, spiperone independently activates CFTR through a novel mechanism. Herein, we performed a mass spectrometry analysis and identified the signaling molecule that mediates the spiperone effect in activating chloride secretion through CaCC and CFTR. Proline-rich tyrosine kinase 2 (PYK2) is a non-receptor protein tyrosine kinase, which belongs to the focal adhesion kinase family. The inhibition of PYK2 notably reduced the ability of spiperone to increase intracellular Ca²⁺ and Cl⁻ secretion. In conclusion, we have identified the tyrosine kinase, PYK2, as the modulator, which plays a crucial role in the activation of CaCC and CFTR by spiperone. The identification of this novel role of PYK2 reveals a new signaling pathway in human airway epithelial cells.

Regulation of tyrosine phosphorylation in macrophage phagocytosis and chemotaxis

Macrophages display a large variety of surface receptors that are critical for their normal cellular functions in host defense, including finding sites of infection (chemotaxis) and removing foreign particles (phagocytosis). However, inappropriate regulation of these processes can lead to human diseases. Many of these receptors utilize tyrosine phosphorylation cascades to initiate and terminate signals leading to cell migration and clearance of infection. Actin remodeling dominates these processes and many regulators have been identified. This review focuses on how tyrosine kinases and phosphatases regulate actin dynamics leading to macrophage chemotaxis and phagocytosis.

Early inflammatory reactions in atherosclerosis are induced by proline-rich tyrosine kinase/reactive oxygen species-mediated release of tumor necrosis factor-alpha and subsequent activation of the p21Cip1/Ets-1/p300 system

OBJECTIVE

Reactive oxygen species (ROS) are involved in the initial process of atherosclerosis, whereas it remains to be determined how atherogenic stimulus causes ROS-mediated proinflammatory reactions. Here, we focused on proline-rich tyrosine kinase (PYK2)-mediated ROS generation and examined how atherogenic stimulus causes early proinflammatory reactions.

METHODS AND RESULTS

PYK2-deficient (knockout [KO]) (PYK2-KO) mice were crossbred with apolipoprotein E (ApoE)-deficient (PYK2-KO/ApoE-KO) mice. PYK2-KO/ApoE-KO mice and endothelial cells (EC) were used for the study. Aortic atherogenic lesions in PYK2-KO/ApoE-KO mice were markedly decreased (55% versus ApoE-KO) after 8 weeks of a Western diet. Aortic PYK2 was activated as early as 7 days after the Western diet, when inflammatory cells were not yet activated. Addition of the proatherogenic oxidized phospholipid lysophosphatidylcholine caused activation of endothelial PYK2. Lysophosphatidylcholine-activated PYK2 induced NADPH oxidase-mediated ROS generation and ROS-mediated synthesis of tumor necrosis factor-α (TNFα), vascular cell adhesion molecule-1 (VCAM-1), monocyte chemotactic protein-1 (MCP-1), and p21Cip1/Ets-1. Neutralizing anti-TNFα antibody or knockdown of p21Cip1/Ets-1 system blocked the induction of VCAM-1 and MCP-1. PYK2 deficiency abolished these ROS-mediated proinflammatory reactions. Further analysis revealed that PYK2/ROS-mediated p21Cip1/Ets-1 activation upregulated the transcription of the MCP-1 gene in collaboration with p300 transcription coactivator.

CONCLUSIONS

PYK2 is a key tyrosine kinase activated by high cholesterol exposure, which causes ROS-mediated TNFα release and induces TNFα-dependent expression of proinflammatory molecules via the p21Cip1/Ets-1/p300 transcription system.

Src-family and Syk kinases in activating and inhibitory pathways in innate immune cells: signaling cross talk

The response of innate immune cells to growth factors, immune complexes, extracellular matrix proteins, cytokines, pathogens, cellular damage, and many other stimuli is regulated by a complex net of intracellular signal transduction pathways. The majority of these pathways are either initiated or modulated by Src-family or Syk tyrosine kinases present in innate cells. The Src-family kinases modulate the broadest range of signaling responses, including regulating immunoreceptors, C-type lectins, integrins, G-protein-coupled receptors, and many others. Src-family kinases also modulate the activity of other kinases, including the Tec-family members as well as FAK and Pyk2. Syk kinase is required for initiation of signaling involving receptors that utilize immunoreceptor tyrosine activation (ITAM) domains. This article reviews the major activating and inhibitory signaling pathways regulated by these cytoplasmic tyrosine kinases, illuminating the many examples of signaling cross talk between pathways.

Nephrocystin-4 regulates Pyk2-induced tyrosine phosphorylation of nephrocystin-1 to control targeting to monocilia

Nephronophthisis is the most common genetic cause of end-stage renal failure during childhood and adolescence. Genetic studies have identified disease-causing mutations in at least 11 different genes (NPHP1–11), but the function of the corresponding nephrocystin proteins remains poorly understood. The two evolutionarily conserved proteins nephrocystin-1 (NPHP1) and nephrocystin-4 (NPHP4) interact and localize to cilia in kidney, retina, and brain characterizing nephronophthisis and associated pathologies as result of a ciliopathy. Here we show that NPHP4, but not truncating patient mutations, negatively regulates tyrosine phosphorylation of NPHP1. NPHP4 counteracts Pyk2-mediated phosphorylation of three defined tyrosine residues of NPHP1 thereby controlling binding of NPHP1 to the trans-Golgi sorting protein PACS-1. Knockdown of NPHP4 resulted in an accumulation of NPHP1 in trans-Golgi vesicles of ciliated retinal epithelial cells. These data strongly suggest that NPHP4 acts upstream of NPHP1 in a common pathway and support the concept of a role for nephrocystin proteins in intracellular vesicular transport.

Signaling networks regulating leukocyte podosome dynamics and function

Podosomes are ventral adhesion structures prominent in cells of the myeloid lineage. A common aspect of these cells is that they are highly motile and must to traverse multiple tissue barriers in order to perform their functions. Recently podosomes have gathered attention from researchers as important cellular structures that can influence cell adhesion, motility and matrix remodeling. Adhesive and soluble ligands act via transmembrane receptors and propagate signals to the leukocyte cytoskeleton via small G proteins of the Rho family, tyrosine kinases and scaffold proteins and are able to induce podosome formation and rearrangements. Manipulation of the signals that regulate podosome formation and dynamics can therefore be a strategy to interfere with leukocyte functions in a multitude of pathological settings, such as infections, atherosclerosis and arthritis. Here, we review the major signaling molecules that act in the formation and regulation of podosomes.

Pyk2 is required for neutrophil degranulation and host defense responses to bacterial infection

The appropriate regulation of neutrophil activation is critical for maintaining host defense and limiting inflammation. Polymorphonuclear neutrophils (PMNs) express a number of cytoplasmic tyrosine kinases that regulate signaling pathways leading to activation. One of the most highly expressed, but least studied, kinases in PMNs is proline rich kinase 2 (Pyk2). By analogy to the related focal adhesion kinase, Pyk2 has been implicated in regulating PMN adhesion and migration; however, its physiologic function has yet to be described. Using pyk2(-/-) mice, we found that this kinase was required for integrin-mediated degranulation responses, but was not involved in adhesion-induced cell spreading or activation of superoxide production. Pyk2-deficient PMNs also manifested reduced migration on fibrinogen-coated surfaces. The absence of Pyk2 resulted in a severe reduction in paxillin and Vav phosphorylation following integrin ligation, which likely accounts for the poor degranulation and cell migration. Pyk2(-/-) mice were unable to efficiently clear infection with Staphylococcus aureus in a skin abscess model, owing in part to the poor release of granule contents at the site of infection. However, Pyk2-deficient PMNs responded normally to soluble agonists, demonstrating that this kinase functions mainly in the integrin pathway. These data demonstrate the unrealized physiologic role of this kinase in regulating the adhesion-mediated release of PMN granule contents.

Macrophage motility requires distinct α5β1/FAK and α4β1/paxillin signaling events

Macrophages function as key inflammatory mediators at sites of infection and tissue damage. Integrin and growth factor receptors facilitate recruitment of monocytes/macrophages to sites of inflammation in response to numerous extracellular stimuli. We have shown recently that FAK plays a role in regulating macrophage chemotaxis and invasion. As FAK is an established downstream mediator of integrin signaling, we sought to define the molecular circuitry involving FAK and the predominant β1 integrin heterodimers expressed in these cells-α4β1 and α5β1. We show that α4β1 and α5β1 integrins are required for efficient haptotactic and chemotactic invasion and that stimulation of these integrin receptors leads to the adoption of distinct morphologies associated with motility. FAK is required downstream of α5β1 for haptotaxis toward FN and chemotaxis toward M-CSF-1 and downstream of α4β1 for the adoption of a polarized phenotype. The scaffolding molecule paxillin functions independently of FAK to promote chemotaxis downstream of α4β1. These studies expand our understanding of β1 integrin signaling networks that regulate motility and invasion in macrophages and thus, provide important new insights into mechanisms by which macrophages perform their diverse functions.

Role of selective autophagy in cellular remodeling: "self-eating" into shape

The Atg1 Ser/Thr kinase, although now a well-established regulator of autophagy, was first identified genetically in C. elegans as a requirement for axonal elongation. However, possible connections between Atg1 functions in cellular morphogenesis and in autophagy were previously unaddressed. In the recent paper highlighted in this punctum, we reconciled these dual roles for Atg1, demonstrating a requirement for p62-mediated selective autophagy in the dynamic regulation of cell shape, in both fly and mammalian macrophages, with effects on immune cell functions. This work further strengthens the emerging importance of autophagy as a post-translational regulatory mechanism in diverse cell signaling contexts, including the cortical remodeling and function of immune cells.

Proline-rich tyrosine kinase 2 regulates hippocampal long-term depression

Proline-rich tyrosine kinase 2 (PYK2), also known as cell adhesion kinase beta or protein tyrosine kinase 2b, is a calcium-dependent signaling protein involved in cell migration. Phosphorylation of residue Y402 is associated with activation of PYK2 and leads to the recruitment of downstream signaling molecules. PYK2 was previously implicated in long-term potentiation (LTP); however, the role of PYK2 in long-term depression (LTD) is unknown. Here, we report that PYK2 is activated by NMDA receptor stimulation (chemical LTD) in cultured neurons. Small hairpin RNA-mediated knockdown of PYK2 blocks LTD, but not LTP, in hippocampal slice cultures. We find that the Y402 residue and, to a lesser extent, PYK2 kinase activity contribute to PYK2's role in LTD. Knockdown experiments indicate that PYK2 is required to suppress NMDA-induced extracellular signal-regulated kinase (ERK) phosphorylation. Overexpression of PYK2 depresses NMDA-induced ERK phosphorylation and inhibits LTP, but not LTD. Our data indicate that PYK2 is critical for the induction of LTD, possibly in part by antagonizing ERK signaling in hippocampal neurons.

The iNOS/Src/FAK axis is critical in Toll-like receptor-mediated cell motility in macrophages

The Toll-like receptors (TLRs) play a pivotal role in innate immunity for the detection of highly conserved, pathogen-expressed molecules. Previously, we demonstrated that lipopolysaccharide (LPS, TLR4 ligand)-increased macrophage motility required the participation of Src and FAK, which was inducible nitric oxide synthase (iNOS)-dependent. To investigate whether this iNOS/Src/FAK pathway is a general mechanism for macrophages to mobilize in response to engagement of TLRs other than TLR4, peptidoglycan (PGN, TLR2 ligand), polyinosinic-polycytidylic acid (polyI:C, TLR3 ligand) and CpG-oligodeoxynucleotides (CpG, TLR9 ligand) were used to treat macrophages in this study. Like LPS stimulation, simultaneous increase of cell motility and Src (but not Fgr, Hck, and Lyn) was detected in RAW264.7, peritoneal macrophages, and bone marrow-derived macrophages exposed to PGN, polyI:C and CpG. Attenuation of Src suppressed PGN-, polyI:C-, and CpG-elicited movement and the level of FAK Pi-Tyr861, which could be reversed by the reintroduction of siRNA-resistant Src. Besides, knockdown of FAK reduced the mobility of macrophages stimulated with anyone of these TLR ligands. Remarkably, PGN-, polyI:C-, and CpG-induced Src expression, FAK Pi-Tyr861, and cell mobility were inhibited in macrophages devoid of iNOS, indicating the importance of iNOS. These findings corroborate that iNOS/Src/FAK axis occupies a central role in macrophage locomotion in response to engagement of TLRs.

Cellular functions of FAK kinases: insight into molecular mechanisms and novel functions

Focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) are related tyrosine kinases that have important cellular functions, primarily through regulation of the cytoskeleton. Recent studies have identified multiple molecular mechanisms that regulate cytoskeletal responses, and have provided important and exciting insights into how FAK and Pyk2 control cellular processes such as cell migration. Equally exciting are reports of novel and originally unanticipated functions of these kinases, providing the groundwork for future avenues of investigation. This Commentary summarizes some of these recent discoveries that are relevant to the control of biological responses of the cell.

Proline-rich tyrosine kinase-2 is critical for CD8 T-cell short-lived effector fate

T-cell interactions with antigen-presenting cells are important for CD8 T-cell effector or memory fate determination. The integrin leukocyte function-associated antigen-1 (LFA-1) mediates T-cell adhesion but the contribution of LFA-1-induced signaling pathways to T-cell responses is poorly understood. Here we demonstrate that proline-rich tyrosine kinase-2 (PYK2) deficiency impairs CD8 T-cell activation by synergistic LFA-1 and T-cell receptor stimulation. Furthermore, PYK2 is essential for LFA-1-mediated CD8 T-cell adhesion and LFA-1 costimulation of CD8 T-cell migration. During lymphocytic choriomeningitis virus infection in vivo, PYK2 deficiency results in a specific loss of short-lived effector CD8 T cells but does not affect memory-precursor CD8 T-cell development. Similarly, lack of LFA-1 primarily impairs the generation of short-lived effector cells. Thus, PYK2 facilitates LFA-1-dependent CD8 T-cell responses and promotes CD8 T-cell short-lived effector fate, suggesting that PYK2 may be an interesting therapeutic target to suppress exacerbated CD8 T-cell responses.

Regulation of the tyrosine kinase Pyk2 by calcium is through production of reactive oxygen species in cytotoxic T lymphocytes

Pyk2 was identified as a Ca(2+)-dependent kinase, however, the regulation of Pyk2 by Ca(2+) in T cells remains controversial. We found that Ca(2+) mobilization preferentially induced Pyk2 phosphorylation in cytotoxic T lymphocytes (CTL). Furthermore, Pyk2 phosphorylation in CTL was not absolutely Ca(2+) dependent but relied on the strength of T cell receptor stimulation. Ionomycin-stimulated Pyk2 phosphorylation did not require calmodulin activity, because phosphorylation was not inhibited by the calmodulin inhibitor W7, and we detected no Ca(2+)-regulated association between Pyk2 and calmodulin. Ca(2+)-stimulated Pyk2 phosphorylation was dependent on Src-family kinase activity, even at the Pyk2 autophosphorylation site. We sought to identify a Ca(2+)-regulated pathway that could trigger Pyk2 phosphorylation in T cells and found that ionomycin stimulated the production of reactive oxygen species and an H(2)O(2) scavenger inhibited ionomycin-induced Pyk2 phosphorylation. Additionally, H(2)O(2) induced strong Erk activation and ionomycin-stimulated Pyk2 phosphorylation was Erk dependent. These data support the conclusion that Ca(2+) mobilization induces the production of reactive oxygen species, which in turn activate the Erk pathway, leading to Src-family kinase-dependent Pyk2 phosphorylation. Our data demonstrate that Pyk2 is not a Ca(2+)-dependent kinase in T cells but instead, increased intracellular Ca(2+) induces Pyk2 phosphorylation through production of reactive oxygen species. These findings are consistent with the possibility that Pyk2 acts as an early sensor of numerous extracellular signals that trigger a Ca(2+) flux and/or reactive oxygen species to amplify tyrosine phosphorylation signaling events.

The dual kinase complex FAK-Src as a promising therapeutic target in cancer

Focal adhesion kinase (FAK) and steroid receptor coactivator (Src) are intracellular (nonreceptor) tyrosine kinases that physically and functionally interact to promote a variety of cellular responses. Plenty of reports have already suggested an additional central role for this complex in cancer through its ability to promote proliferation and anoikis resistance in tumor cells. An important role for the FAK/Src complex in tumor angiogenesis has also been established. Furthermore, FAK and Src have been associated with solid tumor metastasis through their ability to promote the epithelial mesenchymal transition. In fact, a strong correlation between increased FAK/Src expression/phosphorylation and the invasive phenotype in human tumors has been found. Additionally, an association for FAK/Src with resistances to the current anticancer therapies has already been established. Currently, novel anticancer agents that target FAK or Src are under development in a broad variety of solid tumors. In this article we will review the normal cellular functions of the FAK/Src complex as an effector of integrin and/or tyrosine kinase receptor signaling. We will also collect data about their role in cancer and we will summarize the most recent data from the FAK and Src inhibitors under clinical and preclinical development. Furthermore, the association of both these proteins with chemotherapy and hormonal therapy resistances, as a rationale for new combined therapeutic approaches with these novel agents, to abrogate treatment associated resistances, will also be reviewed.