Characterization of the novel focal adhesion kinase RAFTK in hematopoietic cells

Functions of the FAK family kinases in T cells: beyond actin cytoskeletal rearrangement

T cells control the focus and extent of adaptive immunity in infectious and pathological diseases. The activation of T cells occurs when the T cell antigen receptor (TCR) and costimulatory and/or adhesion receptors are engaged by their ligands. This process drives signaling that promotes cytoskeletal rearrangement and transcription factor activation, both of which regulate the quality and magnitude of the T cell response. However, it is not fully understood how different receptor-induced signals combine to alter T cell activation. The related non-receptor tyrosine kinases focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) are phosphorylated downstream of the TCR and several costimulatory and adhesion receptors. FAK family proteins integrate receptor-mediated signals that influence actin cytoskeletal rearrangement and effector T cell responses. In this review, we summarize the receptor-specific roles that FAK and Pyk2 control to influence T cell development and activation.

Hematopoietic Pyk2 regulates migration of differentiated HL-60 cells

Background

Pyk2 is a non-receptor cytoplasmic tyrosine kinase that belongs to the focal adhesion kinase family and has been implicated in neutrophil spreading and respiratory burst activity caused by TNF-α. However, the role of Pyk2 in neutrophil migration is incompletely defined. In this study, we tested the hypothesis that Pyk2 regulates the migration of neutrophil-like differentiated HL-60 cells subsequent to β2-integrin mediated cell adhesion.

Methods

HL-60 cells were induced to differentiate into neutrophil-like cells (dHL60) by incubation in medium containing 1.25% DMSO for up to 4 days. Pyk2 expression and tyrosine phosphorylation was measured by Western blot analysis. Adhesion of dHL60 cells to plated fibrinogen was measured by residual myeloperoxidase activity. dHL60 cell migration was evaluated using a 96-well chemoTx chamber.

Results

Western blot analysis demonstrated that hematopoietic Pyk2 was predominantly expressed after HL60 cell differentiation. Pyk2 was tyrosine phosphorylated upon adhesion of dHL60 cells to plated fibrinogen in the presence of fMLP. By contrast, tyrosine phosphorylation of Pyk2 was insignificant in dHL60 cells treated in suspension with fMLP. Antibodies against CD18 blocked both phosphorylation of Pyk2 and adhesion of dHL60 cells to fibrinogen, demonstrating that phosphorylation of Pyk2 was β₂-integrin dependent. TAT-Pyk2-CT, a dominant negative fusion protein in which the TAT protein transduction domain was fused to the c-terminal Pyk2, attenuated fMLP-stimulated spreading, migration and phosphorylation of endogenous Pyk2 without blocking adhesion of dHL-60 cells to fibrinogen. Similarly, silencing of Pyk2 expression by siRNA in dHL60 cells also attenuated dHL60 cell migration caused by fMLP. Phospho-Pyk2 was evenly distributed around cell membrane circumferentially in unstimulated dHL-60 cells adherent to plated fibrinogen. In dHL60 cells treated with fMLP to cause cell spreading and polarization, Pyk2 was concentrated at the leading edge of pseudopods or at the trailing edge of uropods during migration of neutrophilic dHL-60 cells.

Conclusions

We conclude that Pyk2 is activated by β2-integrin adhesion. The activated concentration of Pyk2 and colocalization with F-actin in pseudopodia suggests that Pyk2 may regulate cell spreading and migration in dHL60 cells.

Inhibition of Pyk2 blocks airway inflammation and hyperresponsiveness in a mouse model of asthma

The objective of this investigation was to determine the role of Pyk2, an intracellular nonreceptor protein tyrosine kinase for postadhesive inflammatory cell migration, on airway inflammation and hyperresponsiveness in immune-sensitized mice. Blockade of Pyk2 was effected by intraperitoneal administration of dominant-negative C-terminal Pyk2 fused to a TAT protein transduction domain (TAT-Pyk2-CT). Ovalbumin challenge elicited infiltration of both eosinophils and lymphocytes into airways, increased mucus-containing epithelial cells, and caused increased airway hyperresponsiveness to methacholine in immune-sensitized mice. Pretreatment with 10 mg/kg TAT-Pyk2-CT intraperitoneally blocked all of these effects and further decreased secretion of Th2 cytokine IL-4, IL-5, and IL-13 into the bronchoalveolar lavage fluid. Intranasal administration of IL-5 caused eosinophil migration into the airway lumen, which was attenuated by systemic pretreatment with TAT-Pyk2-CT. In each paradigm, treatment with control protein TAT-GFP had no blocking effect. We conclude that Pyk2, which is essential for inflammatory cell migration in vitro, regulates airway inflammation, Th2 cytokine secretion, and airway hyperresponsiveness in the ovalbumin-sensitized mice during antigen challenge in vivo.

Chondromodulin-1 directly suppresses growth of human cancer cells

Background

Chondromodulin-1 (ChM1), an endogenous anti-angiogenic factor expressed in cartilage, has been suggested to inhibit invasion of endothelial cells into cartilage. In addition, the ectopic administration of ChM1 has been reported to suppress tumorigenesis in vivo. However, it is unclear whether the anti-tumor effect is due to not only the anti-vascularization effect of ChM1, but also its direct action against oncocytes. In the present study, we sought to determine whether ChM1 has a direct action on tumor cells.

Methods

BrdU incorporation assay was performed on human umbilical vein endothelial cells (HUVECs), normal human dermal fibroblasts (NHDFs), HepG2 cells and HeLa cells in the presence or absence of recombinant human ChM1 (rhChM1). An adenovirus that expresses ChM1, Ad-ChM1, was established and applied to the tumor xenografted in vivo, and to in vitro tumor cells cultured on plates or in soft agar. Cell cycle-related proteins and the phosphorylation of Erk, Akt, and GSK3β, the downstream molecules of the extracellular matrix-integrin signaling pathways, in HepG2 cells treated with or without Ad-ChM1 were detected by western blot analysis. Luciferase reporter assays of STAT, GAS, and ISRE, which participate in another cytokine signaling pathway, ware performed in HepG2, HeLa, and HUVEC cells.

Results

ChM1 suppressed BrdU incorporation in HUVECs and in HepG2 cells dose-dependently, but did not suppress BrdU incorporation in NHDFs and HeLa cells cultured on plates. In soft agar, however, ChM1 suppressed the growth of HeLa cells, as well as HepG2 cells. Western blot analyses demonstrated that ChM1 decreased the levels of cyclin D1, cyclin D3, and cdk6 and increased those of p21^cip1 without affecting the phosphorylation levels of Erk, Akt, and GSK3β in HepG2 cells. The luciferase reporter assay demonstrated that ChM1 suppressed the transcriptional activities of STAT and GAS but not of ISRE.

Conclusion

ChM1 directly suppressed the proliferation of tumor cells in an anchorage-independent manner. However, ChM1 did not alter the phosphorylation of downstream molecules, at which the signaling pathways through growth factor and cytokine receptors converge with the anchorage-dependent pathway. Our results show that ChM1 has a direct anti-tumor effect; moreover, this effect occurs by inhibiting the STAT signaling pathway.

Expression of focal adhesion kinase in acute myeloid leukemia is associated with enhanced blast migration, increased cellularity, and poor prognosis

Focal adhesion kinase (FAK) is a nonreceptor tyrosine kinase playing an important role in cell motility and survival. However, very little is known about FAK in normal and leukemic myeloid cells. In this study, FAK protein expression and mRNA were detected in 25 of 60 cases (42%) of acute myeloid leukemia (AML). Whereas FAK was expressed in 46% of CD34+ AML cells, it was not detected in normal purified CD34+ cells. Conversely, the FAK homologue proline-rich tyrosine kinase 2 (PYK2) was found to be expressed both in normal and leukemic myeloid cells. When expressed, FAK displayed phosphorylation on Tyr-397, an important step for its activation. Moreover, FAK expression was correlated with the phosphorylation of PYK2 on Tyr-881, a critical site for the PYK2 function in cell migration. FAK+ AML cells displayed significantly higher migration capacities and resistance to daunorubicin, compared with FAK- cells. The implication of FAK in both cell motility and drug resistance was demonstrated by small interfering RNA experiments with the FAK-positive KG1 cell line. However, adhesion on fibronectin efficiently protected FAK- AML cells from daunorubicin-mediated killing, suggesting that cellular adhesion mediated-drug resistance is not mediated by FAK. Finally, in a retrospective cohort of 60 AML patients, FAK expression was significantly correlated with high blast cell count, early death, and shorter survival rate. Altogether, this study shows that FAK is aberrantly expressed and activated in about half of the cases of AML and suggests that FAK may contribute to the regulation of AML cell transit from the marrow to blood compartment and that it may influence clinical outcome.

Characterization of the MM.1 human multiple myeloma (MM) cell lines: a model system to elucidate the characteristics, behavior, and signaling of steroid-sensitive and -resistant MM cells

Multiple myeloma (MM) is a clonal B-lymphocyte malignancy, which is characterized by the accumulation of terminally differentiated antibody-producing cells in the bone marrow. Because current treatments offer only a median survival of 3 years, investigators continue to search for novel therapeutic strategies to combat the disease. Rational drug design is enhanced by understanding MM cell proliferation and key signaling pathways employed. In addition, a model system for preclinical evaluation of novel therapeutics is critical. Our laboratory has developed MM cell lines to study drug action and resistance, cell proliferation, and apoptosis. These cell lines are widely used in MM research. From a single MM patient, three separate cell lines were established that parallel the progression of the disease. These three cell lines, designated MM1.S, MM1.R(E), and MM1.R(L), can be distinguished on the basis of their sensitivity to steroid hormones such as glucocorticoids (GCs). Utilization of these cell lines to study the etiology of MM, effects of chemotherapeutic agents, and development of clinical resistance, will provide us with vital information for the evolution of new and more efficacious therapeutics. The aim of this review is to summarize the morphological, biochemical, and growth characteristics of these cells, and to review the results from investigations of the MM.1 signaling pathways. This information will enhance the study, treatment, and eventual eradication of MM.

Involvement of Hic-5 in platelet activation: integrin alphaIIbbeta3-dependent tyrosine phosphorylation and association with proline-rich tyrosine kinase 2

Hic-5 and paxillin, members of the LIM protein family, have been shown to be localized in focal adhesion and to have a role in integrin-mediated signalling. In the present study we examined the involvement of Hic-5 in human platelet activation: platelets express Hic-5 but not paxillin, whereas human umbilical-vein vascular endothelial cells and MEG-01 cells express mainly paxillin. When platelets were stimulated with thrombin, collagen or the stable thromboxane A(2) analogue U46619, Hic-5 was markedly tyrosine-phosphorylated, in a manner dependent on integrin alphaIIbbeta3-mediated aggregation. In addition, direct activation of protein kinase C with PMA resulted in tyrosine phosphorylation of Hic-5 only when platelets were fully aggregated with the exogenous addition of fibrinogen. Furthermore, PMA-induced Hic-5 tyrosine phosphorylation was also observed when platelets adhered to immobilized fibrinogen. In studies on immunoprecipitation and immunodepletion, Hic-5 seemed to associate with proline-rich tyrosine kinase 2 (Pyk2) but only marginally with focal adhesion kinase. When platelets were stimulated with thrombin, both Hic-5 and Pyk2 translocated to the cytoskeleton from the cytosol and membrane fractions in a manner dependent on alphaIIbbeta3-mediated aggregation. Finally, on stimulation with PMA, Hic-5, as well as Pyk2, translocated to the cell periphery, where a meshwork of actin filaments assembled after adhesion to immobilized fibrinogen. Our results suggest that Hic-5 might be important in platelet aggregation and adhesion, in a manner dependent on alphaIIbbeta3-mediated outside-in signalling, through association with Pyk2.

Focal adhesion kinases: interest in immunoendocrinology, developmental biology, and cancer

The research field on focal adhesion-related kinases started a decade ago, but the term focal adhesion was introduced for the first time nearly 20 yr before. Since its identification, many studies have enlightened the role of the first intermediate of focal adhesion-related signals in a large number of biologic and physiologic processes. In this review, we try to integrate the most recent data about the known focal adhesion-related kinases, and we focus on three topics in which they deserve great interest: neuroendocrine-immune interactions, developmental biology, and proliferative diseases.

RAFTK/Pyk2-mediated cellular signalling

Intracellular signal transduction following extracellular ligation by a wide variety of surface molecules involves the activation and tyrosine phosphorylation of protein tyrosine kinases (PTKs). Tyrosine phosphorylation, controlled by the coordinated actions of protein tyrosine phosphatases (PTPs) and tyrosine kinases, is a critical regulatory mechanism for various physiological processes, including cell growth, differentiation, metabolism, cell cycle regulation and cytoskeleton function. The focal adhesion PTK family consists of the focal adhesion kinase (FAK) and the RAFTK/Pyk2 kinase (also known as CAK-beta and CADTK). RAFTK/Pyk2 can be activated by a variety of extracellular signals that elevate intracellular calcium concentration, and by stress signals. RAFTK/Pyk2 is expressed mainly in the central nervous system and in cells derived from hematopoietic lineages, while FAK is widely expressed in various tissues and links transmembrane integrin receptors to intracellular pathways. This review describes the role of RAFTK/Pyk2 in various signalling cascades and details the differential signalling by FAK and RAFTK/Pyk2.

Opposing effects of engagement of integrins and stimulation of cytokine receptors on cell cycle progression of normal human hematopoietic progenitors

We evaluated the effect of β1-integrin receptor engagement on the expression and activity of cell cycle regulatory proteins in CD34+ cells under conditions that mimic the steady-state marrow microenvironment and in the presence of supraphysiological concentrations of interleukin-3 (IL3) and stem cell factor (SCF). Adhesion of CD34+ progenitors to fibronectin (FN) was similar whether IL3 or SCF was present or absent. Engagement of β1-integrins blocked S-phase entry of CD34+ cells in the absence of IL3 or SCF, whereas addition of 10 ng/mL IL3 or SCF prevented such a block in S-phase entry. In the absence of IL3 or SCF, cyclin-E levels were significantly lower and p27KIP1 levels significantly higher in FN-adherent than in FN-nonadherent cells, or than in poly-L-lysine (PLL)–adherent or (PLL)–nonadherent cells. Cyclin-dependent-kinase (cdk)-2 activity was decreased and levels of cyclin-E–cdk2 complexes were lower in FN-adherent than in PLL-adherent cells. In contrast, cyclin-E and p27KIP1 protein levels and cdk2 activity in cells adherent to FN in the presence of IL3 or SCF were similar to those in PLL-adherent and FN-nonadherent or PLL-nonadherent cells. In conclusion, under physiological cytokine conditions, integrin engagement prevents S-phase entrance of CD34+ cells, which is associated with elevated levels of the contact-dependent cyclin kinase inhibitor p27KIP1. Supraphysiological concentrations of IL3 or SCF prevent p27KIP1 elevation and override the integrin-mediated inhibition of entry into S phase.

RAFTK/PYK2-dependent and -independent apoptosis in multiple myeloma cells

Related Adhesion Focal Tyrosine Kinase (RAFTK; also known as Pyk2), is a member of the Focal Adhesion Kinase (FAK) subfamily and is activated by TNF alpha, UV light and increases in intracellular calcium levels. However, the function of RAFTK remains largely unknown. Our previous studies demonstrated that treatment with dexamethasone (Dex), ionizing radiation (IR), and anti-Fas mAb induces apoptosis in multiple myeloma (MM) cells. In the present study, we examined the potential role of RAFTK during induction of apoptosis in human MM cells triggered by these three stimuli. Dex-induced apoptosis, in contrast to apoptosis triggered by anti-Fas mAb or IR, is associated with activation of RAFTK. Transient overexpression of RAFTK wild type (RAFTK WT) induces apoptosis, whereas transient overexpression of Kinase inactive RAFTK (RAFTK K-M) blocks Dex-induced apoptosis. In contrast, transient overexpression of RAFTK K-M has no effect on apoptosis triggered by IR or Fas. In Dex-resistant cells, Dex does not trigger either RAFTK activation or apoptosis. Finally, interleukin-6 (IL-6), a known survival factor for MM cells, inhibits both activation of RAFTK and apoptosis of MM.1S cells triggered by Dex. Our studies therefore demonstrate Dex-induced RAFTK-dependent, and IR or Fas induced RAFTK-independent apoptotic signaling cascades in MM cells.

Activation of several MAP kinases upon stimulation of rat alveolar macrophages: role of the NADPH oxidase

Zymosan-activated serum (ZAS), a source of C5a, stimulates the rat alveolar macrophages (AM) to release superoxide anion. Here we show that treatment of rat AM with ZAS induced a time-dependent increase in the tyrosine phosphorylation of several proteins (116, 105-110, 82-78, 66-72, 62, 45, 42, and 38 kDa). This increase was sensitive to genistein, a tyrosine kinase inhibitor. ZAS stimulated the tyrosine phosphorylation and activation of three members of a family of serine/threonine kinases known as the mitogen-activated protein kinases (MAPK), i.e., ERK1 and ERK2, as assessed by immunoblotting, immunoprecipitation, and phosphotransferase activity, and p38 MAPK, as determined by immunoblotting with phospho-specific antibodies. In addition, ZAS induced the tyrosine phosphorylation of the SHC proteins and their association with GRB2, suggesting a role for this complex in the activation of the ERK pathway. Addition of extracellular catalase during ZAS stimulation significantly reduced the tyrosine phosphorylation response and the activation of ERK1 and ERK2 and their activator MEK1/2 while it did not affect that of p38 MAPK and MKK3/MKK6. Superoxide dismutase marginally increased the response to ZAS, supporting a role for hydrogen peroxide. In contrast to the results with AM, stimulation of human neutrophils with ZAS in the presence of catalase minimally altered the activation of ERK1 and ERK2. These data show that, in ZAS-stimulated rat AM, activation of the respiratory burst and production of hydrogen peroxide via superoxide dismutation are largely responsible for the activation of the ERK pathway through an upstream target.

Regulation of actin cytoskeleton in lymphocytes: PKC-delta disrupts IL-3-induced membrane ruffles downstream of Rac1

In the murine pre-B lymphoid cell line Baf3, the presence of IL-3 is required for the formation of membrane ruffles that intensely stain for actin and are responsible for the elongated cell phenotype. Withdrawal of IL-3 dissolves ruffled protrusions and converts the cell phenotype to round. Flow cytometric analysis of the cell shape showed that an inactive analog of Rac1 but not inactive RhoA or inactive cdc42 rounds the cells in the presence of IL-3. Constitutively activated Rac1 restores the elongated cell phenotype to IL-3-starved cells. We conclude that the activity of Rac1 is necessary and sufficient for the IL-3-induced assembly of membrane ruffles. Similar to the IL-3 withdrawal, phorbol 12-myristate 13-acetate (PMA) dissolves actin-formed membrane ruffles and rounds the cells in the presence of IL-3. Flow cytometric analysis of the cell shape demonstrated that in the presence of IL-3 the PMA-induced cell rounding cannot be abolished by constitutively active Rac1 but can be imitated by inactive Rac1. These data indicate that PMA disrupts the IL-3 pathway downstream of Rac1. Cells rounded by PMA return to the elongated phenotype concomitantly with PKC depletion. PMA-induced cell rounding can be reversed by the PKC-specific inhibitor GF109203X. Experiments with overexpression in Baf3 of individual PKC isoforms and a dominant negative PKC-delta indicate that activation of PKC-delta but not other PKC isoforms is responsible for disruption of membrane ruffles.

Cytoskeleton and integrin-mediated adhesion signaling in human CD34+ hemopoietic progenitor cells

Significant progress has been made recently in the understanding of cell adhesion signaling. Many components of focal adhesion complexes have been identified in fibroblasts and endothelial cells, showing considerable overlap and complementarity between growth signaling mediated by growth factor receptors and adhesive signaling mediated by cell adhesion receptors such as integrins. These studies showed that the cytoskeleton is essential for the correct intracellular localization of large signaling complexes that regulate the cellular machinery. Although adhesive interactions are essential to maintain steady-state hemopoiesis, the study of the function and role of adhesive interactions in hemopoietic progenitor and stem cells is less advanced. As in fibroblasts, functional overlap between hemopoietic growth factor receptors and cell adhesion receptors has been demonstrated, with the cytoskeleton likely playing a critical role in integrating information provided by soluble factors and cell adhesion molecules constituting the hemopoietic microenvironment. The intention of this article is to give a critical review of the current knowledge about the cytoskeleton and integrin-mediated signaling in hemopoietic progenitor cells.

Leukocyte polarization in cell migration and immune interactions

Cell migration plays a key role in a wide variety of biological phenomena. This process is particularly important for leukocyte function and the inflammatory response. Prior to migration leukocytes undergo polarization, with the formation of a lamellipodium at the leading edge and a uropod at the trailing edge. This cell shape allows them to convert cytoskeletal forces into net cell-body displacement. Leukocyte chemoattractants, including chemokines, provide directional cues for leukocyte motility, and concomitantly induce polarization. Chemoattractant receptors, integrins and other adhesion molecules, cytoskeletal proteins and intracellular regulatory molecules change their cellular localization during cell polarization. A complex system of signal transduction molecules, including tyrosine kinases, lipid kinases, second messengers and members of the Rho family of small GTPases is thought to regulate the cytoskeletal rearrangements underlying leukocyte polarization and migration. The elucidation of the mechanisms and signals that control this complex reorganization will lead to a better understanding of critical questions in cell biology of leukocyte migration and polarity.

Involvement of PYK2 in angiotensin II signaling of vascular smooth muscle cells

-PYK2, a recently identified Ca2+-sensitive tyrosine kinase, has been implicated in extracellular signal-regulated kinase (ERK) activation via several G protein-coupled receptors. We have reported that angiotensin II (Ang II) induces Ca2+-dependent transactivation of the epidermal growth factor receptor (EGFR) which serves as a scaffold for preactivated c-Src and downstream adaptors (Shc/Grb2), leading to ERK activation in cultured rat vascular smooth muscle cells (VSMC). Herein we demonstrate the involvement of PYK2 in this cascade. Ang II rapidly induced tyrosine phosphorylation of PYK2, whose effect was completely inhibited by an AT1 receptor antagonist and an intracellular Ca2+ chelator. A Ca2+ ionophore also induced PYK2 tyrosine phosphorylation to a level comparable with that by Ang II, whereas phorbol ester-induced phosphorylation was less than that by Ang II. Moreover, PYK2 formed a complex coprecipitable with catalytically active c-Src after Ang II stimulation. Although a selective EGFR kinase inhibitor completely abolished Ang II-induced recruitment of Grb2 to EGFR and markedly attenuated Ang II-induced ERK activation, it had no effect on Ang II-induced PYK2 tyrosine phosphorylation or its association with c-Src and Grb2. These data suggest that the AT1 receptor uses Ca2+-dependent PYK2 to activate c-Src, thereby leading to EGFR transactivation, which preponderantly recruits Grb2 in rat VSMC.