Focal adhesion kinase regulates pathogen-killing capability and life span of neutrophils via mediating both adhesion-dependent and -independent cellular signals

Comprehensive pan-cancer analysis of 33 human cancers reveals immunotherapeutic value of focal adhesion tyrosine kinase

The immune environment in tumors is the key factor affecting the survival and immunotherapeutic response of patients. This research aimed to explore the underlying association between focal adhesion tyrosine kinase (FAK/PTK2) and cancer immunotherapy in 33 human cancers. Gene expression data and clinical features of 33 cancers were retrieved from the Cancer Genome Atlas Database. The immunotherapy cohorts included GSE67501, GSE78220, and IMVIGOR210, which were derived from the comprehensive gene expression database or from previous studies. Clinical parameters including patient age, gender, survival rate, and tumor stage were analyzed to evaluate the prognostic value of FAK/PTK2. FAK/PTK2 activity was detected by single-sample gene set enrichment analysis and used to compare the difference between FAK/PTK2 transcriptome and protein expression levels. To better understand the role of FAK/PTK2 in cancer immunotherapy, we analyzed its correlations with tumor microenvironment and with immune processes/elements (e.g., immune cell infiltration, immunosuppressants, and stimulants) and major histocompatible complexes. Potential pathways associated with FAK/PTK2 signaling in cancers were also explored. Correlations between FAK/PTK2 and 2 immunotherapeutic biomarkers (tumor mutation load and microsatellite instability) were studied. Finally, the 3 independent immunotherapy cohorts were used to study the relationship between FAK/PTK2 and immunotherapeutic response. Although FAK/PTK2 is not closely associated with age (13/33), gender (5/33), or tumor stage (5/33) in any of the studied human cancers, it has potential prognostic value for predicting patient survival. Consistency between FAK/PTK2 activity and expression exists in some cancers (3/33). Generally, FAK/PTK2 is robustly correlated with immune cell infiltration, immune modulators, and immunotherapeutic markers. Moreover, high FAK/PTK2 expression is significantly related to immune-relevant pathways. However, FAK/PTK2 is not significantly correlated with the immunotherapeutic response. Research on the immunotherapeutic value of FAK/PTK2 in 33 human cancers provides evidence regarding the function of FAK/PTK2 and its role in clinical treatment. However, given the use of a bioinformatics approach, our results are preliminary and require further validation.

Myeloid Poldip2 Contributes to the Development of Pulmonary Inflammation by Regulating Neutrophil Adhesion in a Murine Model of Acute Respiratory Distress Syndrome

Background Lung injury, a severe adverse outcome of lipopolysaccharide-induced acute respiratory distress syndrome, is attributed to excessive neutrophil recruitment and effector response. Poldip2 (polymerase δ-interacting protein 2) plays a critical role in regulating endothelial permeability and leukocyte recruitment in acute inflammation. Thus, we hypothesized that myeloid Poldip2 is involved in neutrophil recruitment to inflamed lungs. Methods and Results After characterizing myeloid-specific Poldip2 knockout mice, we showed that at 18 hours post-lipopolysaccharide injection, bronchoalveolar lavage from myeloid Poldip2-deficient mice contained fewer inflammatory cells (8 [4-16] versus 29 [12-57]×10⁴/mL in wild-type mice) and a smaller percentage of neutrophils (30% [28%-34%] versus 38% [33%-41%] in wild-type mice), while the main chemoattractants for neutrophils remained unaffected. In vitro, Poldip2-deficient neutrophils responded as well as wild-type neutrophils to inflammatory stimuli with respect to neutrophil extracellular trap formation, reactive oxygen species production, and induction of cytokines. However, neutrophil adherence to a tumor necrosis factor-α stimulated endothelial monolayer was inhibited by Poldip2 depletion (225 [115-272] wild-type [myePoldip2^+/+] versus 133 [62-178] myeloid-specific Poldip2 knockout [myePoldip2^-/-] neutrophils) as was transmigration (1.7 [1.3-2.1] versus 1.1 [1.0-1.4] relative to baseline transmigration). To determine the underlying mechanism, we examined the surface expression of β2-integrin, its binding to soluble intercellular adhesion molecule 1, and Pyk2 phosphorylation. Surface expression of β2-integrins was not affected by Poldip2 deletion, whereas β2-integrins and Pyk2 were less activated in Poldip2-deficient neutrophils. Conclusions These results suggest that myeloid Poldip2 is involved in β2-integrin activation during the inflammatory response, which in turn mediates neutrophil-to-endothelium adhesion in lipopolysaccharide-induced acute respiratory distress syndrome.

Mycobacterium tuberculosis Exploits Focal Adhesion Kinase to Induce Necrotic Cell Death and Inhibit Reactive Oxygen Species Production

Tuberculosis is a deadly, contagious respiratory disease that is caused by the pathogenic bacterium Mycobacterium tuberculosis (Mtb). Mtb is adept at manipulating and evading host immunity by hijacking alveolar macrophages, the first line of defense against inhaled pathogens, by regulating the mode and timing of host cell death. It is established that Mtb infection actively blocks apoptosis and instead induces necrotic-like modes of cell death to promote disease progression. This survival strategy shields the bacteria from destruction by the immune system and antibiotics while allowing for the spread of bacteria at opportunistic times. As such, it is critical to understand how Mtb interacts with host macrophages to manipulate the mode of cell death. Herein, we demonstrate that Mtb infection triggers a time-dependent reduction in the expression of focal adhesion kinase (FAK) in human macrophages. Using pharmacological perturbations, we show that inhibition of FAK (FAKi) triggers an increase in a necrotic form of cell death during Mtb infection. In contrast, genetic overexpression of FAK (FAK⁺) completely blocked macrophage cell death during Mtb infection. Using specific inhibitors of necrotic cell death, we show that FAK-mediated cell death during Mtb infection occurs in a RIPK1-depedent, and to a lesser extent, RIPK3-MLKL-dependent mechanism. Consistent with these findings, FAKi results in uncontrolled replication of Mtb, whereas FAK⁺ reduces the intracellular survival of Mtb in macrophages. In addition, we demonstrate that enhanced control of intracellular Mtb replication by FAK⁺ macrophages is a result of increased production of antibacterial reactive oxygen species (ROS) as inhibitors of ROS production restored Mtb burden in FAK⁺ macrophages to same levels as in wild-type cells. Collectively, our data establishes FAK as an important host protective response during Mtb infection to block necrotic cell death and induce ROS production, which are required to restrict the survival of Mtb.

Mirage or long-awaited oasis: reinvigorating T-cell responses in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is plagued by a dismal 5-year survival rate, early onset of metastasis and limited efficacy of systemic therapies. This scenario highlights the need to fervently pursue novel therapeutic strategies to treat this disease. Recent research has uncovered complicated dynamics within the tumor microenvironment (TME) of PDAC. An abundant stroma provides a framework for interactions between cancer-associated fibroblasts, suppressive myeloid cells and regulatory lymphocytes, which together create an inhospitable environment for adaptive immune responses. This accounts for the poor infiltration and exhausted phenotypes of effector T cells within pancreatic tumors. Innovative studies in genetically engineered mouse models have established that with appropriate pharmacological modulation of suppressive elements in the TME, T cells can be prompted to regress pancreatic tumors. In light of this knowledge, innovative combinatorial strategies involving immunotherapy and targeted therapies working in concert are rapidly emerging. This review will highlight recent advances in the field related to immune suppression in PDAC, emerging preclinical data and rationale for ongoing immunotherapy clinical trials. In particular, we draw attention to foundational findings involving T-cell activity in PDAC and encourage development of novel therapeutics to improve T-cell responses in this challenging disease.

β2 Integrin Signaling Cascade in Neutrophils: More Than a Single Function

Neutrophils are the most prevalent leukocytes in the human body. They have a pivotal role in the innate immune response against invading bacterial and fungal pathogens, while recent emerging evidence also demonstrates their role in cancer progression and anti-tumor responses. The efficient execution of many neutrophil effector responses requires the presence of β2 integrins, in particular CD11a/CD18 or CD11b/CD18 heterodimers. Although extensively studied at the molecular level, the exact signaling cascades downstream of β2 integrins still remain to be fully elucidated. In this review, we focus mainly on inside-out and outside-in signaling of these two β2 integrin members expressed on neutrophils and describe differences between various neutrophil stimuli with respect to integrin activation, integrin ligand binding, and the pertinent differences between mouse and human studies. Last, we discuss how integrin signaling studies could be used to explore the therapeutic potential of targeting β2 integrins and the intracellular signaling cascade in neutrophils in several, among other, inflammatory conditions in which neutrophil activity should be dampened to mitigate disease.

The Adhesome Network: Key Components Shaping the Tumour Stroma

Beyond the conventional perception of solid tumours as mere masses of cancer cells, advanced cancer research focuses on the complex contributions of tumour-associated host cells that are known as "tumour microenvironment" (TME). It has been long appreciated that the tumour stroma, composed mainly of blood vessels, cancer-associated fibroblasts and immune cells, together with the extracellular matrix (ECM), define the tumour architecture and influence cancer cell properties. Besides soluble cues, that mediate the crosstalk between tumour and stroma cells, cell adhesion to ECM arises as a crucial determinant in cancer progression. In this review, we discuss how adhesome, the intracellular protein network formed at cell adhesions, regulate the TME and control malignancy. The role of adhesome extends beyond the physical attachment of cells to ECM and the regulation of cytoskeletal remodelling and acts as a signalling and mechanosensing hub, orchestrating cellular responses that shape the tumour milieu.

The proline-rich tyrosine kinase Pyk2 modulates integrin-mediated neutrophil adhesion and reactive oxygen species generation

Neutrophils are first responders in infection and inflammation. They are able to roll, adhere and transmigrate through the endothelium to reach the site of infection, where they fight pathogens through secretion of granule contents, production of reactive oxygen species, extrusion of neutrophil extracellular traps, and phagocytosis. In this study we explored the role of the non-receptor focal adhesion kinase Pyk2 in neutrophil adhesion and activation. Using a specific Pyk2 pharmacological inhibitor, PF-4594755, as well as Pyk2-deficient murine neutrophils, we found that Pyk2 is activated upon integrin αMβ2-mediated neutrophil adhesion to fibrinogen. This process is triggered by Src family kinases-mediated phosphorylation and supported by Pyk2 autophosphorylation on Y402. In neutrophil adherent to fibrinogen, Pyk2 activates PI3K-dependent pathways promoting the phosphorylation of Akt and of its downstream effector GSK3. Pyk2 also dynamically regulates MAP kinases in fibrinogen-adherent neutrophils, as it stimulates p38MAPK but negatively regulates ERK1/2. Pharmacological inhibition of Pyk2 significantly prevented adhesion of human neutrophils to fibrinogen, and neutrophils from Pyk2-knockout mice showed a reduced ability to adhere compared to wildtype cells. Accordingly, neutrophil adhesion to fibrinogen was reduced upon inhibition of p38MAPK but potentiated by ERK1/2 inhibition. Neutrophil adherent to fibrinogen, but not to polylysine, were able to produce ROS upon lipopolysaccharide challenge and ROS production was completely suppressed upon inhibition of Pyk2. By contrast PMA-induced ROS production by neutrophil adherent to either fibrinogen or polylysine was independent from Pyk2. Altogether these results demonstrate that Pyk2 is an important effector in the coordinated puzzle regulating neutrophil adhesion and activation.

F-actin flashes on phagosomes mechanically deform contents for efficient digestion in macrophages

The mechanism and role of transient F-actin recruitment, or F-actin 'flashes', on phagosomes remains enigmatic. Here we provide a comprehensive characterization of F-actin flashing dynamics on phagosomes, including receptor and signaling involvement. F-actin flashes predominate during the integrin-driven complement receptor (CR)-mediated phagocytosis. F-actin flashes begin shortly after internalization and persist on phagosomes for approximately 3 minutes before disassembling and reassembling several times within the first hour. Strikingly, the appearance of F-actin flashes on phagosomes coincides with morphological deformation, lysis and occasional fission of internalized red blood cells. The cadence of flashes depends on particle stiffness, and the F-actin networks on phagosomes are enriched in mechanosensitive components including focal adhesion proteins, RhoA and actomyosin. Inhibiting Arp2/3 and myosin IIA activity significantly reduces the frequency at which phagosome cargo becomes deformed during transient F-actin accumulation. At later time points, post-F-actin flashing, enhanced degradation of phagosome contents is observed, compared with non-flashing phagosomes. Taken together, these data suggest that actomyosin-driven phagosome contractions serve to disrupt malleable particles physically, a process akin to mastication, to enhance later enzymatic digestion.

Mechanical strength determines Ca2+ transients triggered by the engagement of β2 integrins to their ligands

Lymphocyte function-associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1) are key adhesion receptors to mediate neutrophil (PMN) recruitment and intracellular calcium (Ca²⁺) signaling. Binding of LFA-1 and Mac-1 to their ligands is essential in triggering Ca²⁺ transients and activating Ca²⁺-dependent kinases involved in cytoskeletal remodeling and migratory function. While mechanical forces are critical in regulating integrin-mediated Ca²⁺ transients, it is still unclear how the bond strength of β₂-integrin-ligand pair affects Ca²⁺ responses. Here three typical ligands with known mechanical features with LFA-1 and Mac-1 in our previous work were adopted to quantify their capabilities in inducing Ca²⁺ transients in adherent PMNs under shear flow. Data indicated that LFA-1 dominates Ca²⁺ transients in PMNs on intercellular adhesive molecule 1 (ICAM-1) and junctional adhesion molecule-A (JAM-A), while Mac-1 mediates Ca²⁺ transients induced by receptor for advanced glycation end products (RAGE), consistent with their corresponding bond strengths. These results link β₂ integrin-ligand bond strength with Ca²⁺ transients in PMNs, suggesting high bond strength gives rise to strong Ca²⁺ response especially under physiological-like shear flow. The outcomes provide a new insight in understanding the mechanical regulatory mechanisms of PMN recruitment.

Phosphoproteomic Analyses Provide Insight into Molecular Mechanisms Underlying NETosis

NETosis, a novel cell death mechanism which leads to neutrophil extracellular trap (NET) formation, is involved in both infectious and noninfectious diseases. However, its underlying mechanisms remain unclear. To explore the mechanisms and common factors associated with NADPH oxidase (NOX)-dependent and NOX-independent NETosis, global proteomics and phosphoproteomics analyses are conducted in neutrophils treated with phorbol 12-myristate 13-acetate (PMA), ionomycin, and monosodium urate (MSU). Global proteomic analyses identify 64, 97, and 141 proteins differentially regulated in the PMA, ionomycin, and MSU groups compared with the control group, respectively. Phosphoproteomic analysis identifies 931, 565, and 201 phosphorylation sites differentially regulated in the PMA, ionomycin, and MSU groups, compared with the control, respectively. Overlap analysis of the three comparisons identifies nine proteins and 49 phosphorylation sites derived from 41 phosphoproteins. Among the 41 differentially regulated phosphoproteins, 23 are associated with nuclear function, five with chromatin binding, and 13 with poly(A) RNA binding activities based on GO annotation. Among these, DEK, methyl-CpG-binding protein 2 (MECP2), and structure-specific recognition protein 1 (SSRP1) are involved in both chromatin and poly(A) RNA binding. In conclusion, this study provides insight into molecular mechanisms of NETosis and a useful dataset for the guidance of future studies.

Intracellular β2 integrin (CD11/CD18) interacting partners in neutrophil trafficking

BACKGROUND

Neutrophil recruitment during acute inflammation critically depends on the spatial and temporal regulation of β₂ integrins (CD11/CD18). This regulation occurs by inside-out and outside-in signalling via interaction of cytoplasmic proteins with the intracellular domains of the integrin α- and β-subunits. The underlying molecular mechanisms regulating β₂ integrins in neutrophils are still incompletely understood.

AIM

This review provides a comprehensive overview of our current knowledge on proteins interacting with the cytoplasmic tail of CD18, the conserved β-subunit of β₂ integrins, their regulation and their functional importance for neutrophil trafficking during acute inflammation.

RESULTS

A total of 22 proteins including Talin, Kindlin 3 and Coronin 1A have been reported to interact with the CD18 cytoplasmic tail. Here, proteins binding to the cytoplasmic domain of CD18 in experiments using purified, recombinant proteins or peptides in, for example, pull-down assays, are defined as direct interactors. Proteins that have been shown to interact with the cytoplasmic domain of CD18 using whole cell lysates in, for example, pull-down experiments are claimed as interacting proteins without evidence for direct interaction. In summary, β₂ integrin activation and signalling depend on a specific subset of proteins interacting with CD18 and their precise regulation. If disturbed, profound defects of neutrophil recruitment and activation become evident compromising the innate immune response.

CONCLUSIONS

The knowledge of proteins interacting with β₂ integrins and their regulation during neutrophil trafficking does not only improve our basic understanding of innate immunity but may pave the way to novel therapeutic strategies in the treatment of inflammatory diseases.

Gasdermin D Exerts Anti-inflammatory Effects by Promoting Neutrophil Death

Gasdermin D (GSDMD) is considered a proinflammatory factor that mediates pyroptosis in macrophages to protect hosts from intracellular bacteria. Here, we reveal that GSDMD deficiency paradoxically augmented host responses to extracellular Escherichia coli, mainly by delaying neutrophil death, which established GSDMD as a negative regulator of innate immunity. In contrast to its activation in macrophages, in which activated inflammatory caspases cleave GSDMD to produce an N-terminal fragment (GSDMD-cNT) to trigger pyroptosis, GSDMD cleavage and activation in neutrophils was caspase independent. It was mediated by a neutrophil-specific serine protease, neutrophil elastase (ELANE), released from cytoplasmic granules into the cytosol in aging neutrophils. ELANE-mediated GSDMD cleavage was upstream of the caspase cleavage site and produced a fully active ELANE-derived NT fragment (GSDMD-eNT) that induced lytic cell death as efficiently as GSDMD-cNT. Thus, GSDMD is pleiotropic, exerting both pro- and anti-inflammatory effects that make it a potential target for antibacterial and anti-inflammatory therapies.

Neutrophil microparticle production and inflammasome activation by hyperglycemia due to cytoskeletal instability

Microparticles are lipid bilayer-enclosed vesicles produced by cells under oxidative stress. MP production is elevated in patients with diabetes, but the underlying cellular mechanisms are poorly understood. We hypothesized that raising glucose above the physiological level of 5.5 mm would stimulate leukocytes to produce MPs and activate the nucleotide-binding domain, leucine-rich repeat pyrin domain-containing 3 (NLRP3) inflammasome. We found that when incubated in buffer with up to 20 mm glucose, human and murine neutrophils, but not monocytes, generate progressively more MPs with high interleukin (IL)-1β content. Enhanced MP production required generation of reactive chemical species by mitochondria, NADPH oxidase, and type 2 nitric-oxide synthase (NOS-2) and resulted in S-nitrosylation of actin. Depleting cells of capon (C-terminal PDZ ligand of neuronal nitric-oxide synthase protein), apoptosis-associated speck-like protein containing C-terminal caspase recruitment domain (ASC), or pro-IL-1β prevented the hyperglycemia-induced enhancement of reactive species production, MP generation, and IL-1β synthesis. Additional components required for these responses included inositol 1,3,5-triphosphate receptors, PKC, and enhancement of filamentous-actin turnover. Numerous proteins become localized to short filamentous actin in response to S-nitrosylation, including vasodilator-stimulated phosphoprotein, focal adhesion kinase, the membrane phospholipid translocation enzymes flippase and floppase, capon, NLRP3, and ASC. We conclude that an interdependent oxidative stress response to hyperglycemia perturbs neutrophil cytoskeletal stability leading to MP production and IL-1β synthesis.

Multiple Phenotypic Changes Define Neutrophil Priming

Exposure to pro-inflammatory cytokines, chemokines, mitochondrial contents, and bacterial and viral products induces neutrophils to transition from a basal state into a primed one, which is currently defined as an enhanced response to activating stimuli. Although, typically associated with enhanced generation of reactive oxygen species (ROS) by the NADPH oxidase, primed neutrophils show enhanced responsiveness of exocytosis, NET formation, and chemotaxis. Phenotypic changes associated with priming also include activation of a subset of functions, including adhesion, transcription, metabolism, and rate of apoptosis. This review summarizes the breadth of phenotypic changes associated with priming and reviews current knowledge of the molecular mechanisms behind those changes. We conclude that the current definition of priming is too restrictive. Priming represents a combination of enhanced responsiveness and activated functions that regulate both adaptive and innate immune responses.

Increased carbon dioxide levels stimulate neutrophils to produce microparticles and activate the nucleotide-binding domain-like receptor 3 inflammasome

We hypothesized that elevations of carbon dioxide (CO₂) commonly found in modern buildings will stimulate leukocytes to produce microparticles (MPs) and activate the nucleotide-binding domain-like receptor 3 (NLRP3) inflammasome due to mitochondrial oxidative stress. Human and murine neutrophils generate MPs with high interleukin-1β (IL-1β) content when incubated ex vivo in buffer equilibrated with 0.1-0.4% additional CO₂. Enhanced MPs production requires mitochondrial reactive oxygen species production, which is mediated by activities of pyruvate carboxylase and phosphoenolpyruvate carboxykinase. Subsequent events leading to MPs generation include perturbation of inositol 1,3,5-triphosphate receptors, a transient elevation of intracellular calcium, activation of protein kinase C and NADPH oxidase (Nox). Concomitant activation of type-2 nitric oxide synthase yields secondary oxidants resulting in actin S-nitrosylation and enhanced filamentous actin turnover. Numerous proteins are linked to short filamentous actin including vasodilator-stimulated phosphoprotein, focal adhesion kinase, the membrane phospholipid translocation enzymes flippase and floppase, and the critical inflammasome protein ASC (Apoptosis-associated Speck protein with CARD domain). Elevations of CO₂ cause oligomerization of the inflammasome components ASC, NLRP3, caspase 1, thioredoxin interacting protein, and calreticulin - a protein from endoplasmic reticulum, leading to IL-1β synthesis. An increased production rate of MPs containing elevated amounts of IL-1β persists for hours after short-term exposures to elevated CO₂.

Microparticle formation by platelets exposed to high gas pressures - An oxidative stress response

This investigation explored the mechanism for microparticles (MPs) production by human and murine platelets exposed to high pressures of inert gases. Results demonstrate that MPs production occurs via an oxidative stress response in a dose-dependent manner and follows the potency series N₂>Ar>He. Gases with higher van der Waals volumes or polarizability such as SF₆ and N₂O, or hydrostatic pressure, do not cause MPs production. Singlet O₂ is generated by N₂, Ar and He, which is linked to NADPH oxidase (NOX) activity. Progression of oxidative stress involves activation of nitric oxide synthase (NOS) leading to S-nitrosylation of cytosolic actin. Exposure to gases enhances actin filament turnover and associations between short actin filaments, NOS, vasodilator-stimulated phosphoprotein (VASP), focal adhesion kinase (FAK) and Rac1. Inhibition of NOS or NOX by chemical inhibitors or using platelets from mice lacking NOS2 or the gp91phox component of NOX diminish generation of reactive species, enhanced actin polymerization and MP generation by high pressure gases. We conclude that by initiating a sequence of progressive oxidative stress responses high pressure gases cause platelets to generate MPs.

Molecular Pathways: Endothelial Cell FAK-A Target for Cancer Treatment

The nonreceptor protein tyrosine kinase, focal adhesion kinase (FAK, also known as PTK2), is a key mediator of signal transduction downstream of integrins and growth factor receptors in a variety of cells, including endothelial cells. FAK is upregulated in several advanced-stage solid tumors and has been described to promote tumor progression and metastasis through effects on both tumor cells and stromal cells. This observation has led to the development of several FAK inhibitors, some of which have entered clinical trials (GSK2256098, VS-4718, VS-6062, VS-6063, and BI853520). Resistance to chemotherapy is a serious limitation of cancer treatment and, until recently, most studies were restricted to tumor cells, excluding the possible roles performed by the tumor microenvironment. A recent report identified endothelial cell FAK (EC-FAK) as a major regulator of chemosensitivity. By dysregulating endothelial cell-derived paracrine (also known as angiocrine) signals, loss of FAK solely in the endothelial cell compartment is able to induce chemosensitization to DNA-damaging therapies in the malignant cell compartment and thereby reduce tumor growth. Herein, we summarize the roles of EC-FAK in cancer and development and review the status of FAK-targeting anticancer strategies. Clin Cancer Res; 22(15); 3718-24. ©2016 AACR.

Alleviation of skin inflammation after Lin(-) cell transplantation correlates with their differentiation into myeloid-derived suppressor cells

To understand the cellular mechanism underlying the therapeutic effects exerted by hematopoietic stem cell transplantation in the repair of tissue damage, we investigated the in vivo dynamics of bone marrow (BM) lineage-negative (Lin⁻) cells transplanted into mice with hyper sensitivity dermatitis. Longitudinal in vivo imaging and flow cytometry analyses revealed that Lin⁻ cells home directly to inflamed skin within 6 h, where they undergo extensive expansion with the peak on day 14 post-transplantation, and preferential differentiation into CD11b⁺Ly6G^intLy6C⁺ cells by day 7. Cells with phenotypic profiles of neutrophils, macrophages, and DCs appeared in inflamed skin on day 14. Progenies of transplanted Lin⁻ cells showed similar kinetics of expansion and myeloid differentiation in BM. However, differentiation into CD11b⁺Ly6G^intLy6C⁺ cells in the inflamed skin on day 7 was more skewed toward CD115⁺ cells (≥60%) with immune suppressive function and higher expression levels of iNOS, arginase, and IL-10, compared with those in the BM. Transplantation of Lin⁻ cells reduced the levels of Cd3 transcript and CD4⁺/CD8⁺ cells in inflamed skin. These results demonstrate differentiation of transplanted Lin⁻ cells into myeloid-derived suppressor cells in inflamed skin to be the basis of the alleviation of skin inflammation after Lin⁻ cell transplantation.

Cell type-specific differences in β-glucan recognition and signalling in porcine innate immune cells

β-glucans exert receptor-mediated immunomodulating activities, including oxidative burst activity and cytokine secretion. The role of the β-glucan receptors dectin-1 and complement receptor 3 (CR3) in the response of immune cells towards β-glucans is still unresolved. Dectin-1 is considered as the main β-glucan receptor in mice, while recent studies in man show that CR3 is more important in β-glucan-mediated responses. This incited us to elucidate which receptor contributes to the response of innate immune cells towards particulate β-glucans in pigs as the latter might serve as a better model for man. Our results show an important role of CR3 in β-glucan recognition, as blocking this receptor strongly reduced the phagocytosis of β-glucans and the β-glucan-induced ROS production by porcine neutrophils. Conversely, dectin-1 does not seem to play a major role in β-glucan recognition in neutrophils. However, recognition of β-glucans appeared cell type-specific as both dectin-1 and CR3 are involved in the β-glucan-mediated responses in pig macrophages. Moreover, CR3 signalling through focal adhesion kinase (FAK) was indispensable for β-glucan-mediated ROS production and cytokine production in neutrophils and macrophages, while the Syk-dependent pathway was only partly involved in these responses. We may conclude that CR3 plays a cardinal role in β-glucan signalling in porcine neutrophils, while macrophages use a more diverse receptor array to detect and respond towards β-glucans. Nonetheless, FAK acts as a master switch that regulates β-glucan-mediated responses in neutrophils as well as macrophages.

Focal adhesion kinase is required for synovial fibroblast invasion, but not murine inflammatory arthritis

INTRODUCTION

Synovial fibroblasts invade cartilage and bone, leading to joint destruction in rheumatoid arthritis. However, the mechanisms that regulate synovial fibroblast invasion are not well understood. Focal adhesion kinase (FAK) has been implicated in cellular invasion in several cell types, and FAK inhibitors are in clinical trials for cancer treatment. Little is known about the role of FAK in inflammatory arthritis, but, given its expression in synovial tissue, its known role in invasion in other cells and the potential clinical availability of FAK inhibitors, it is important to determine if FAK contributes to synovial fibroblast invasion and inflammatory arthritis.

METHODS

After treatment with FAK inhibitors, invasiveness of human rheumatoid synovial fibroblasts was determined with Matrigel invasion chambers. Migration and focal matrix degradation, two components of cellular invasion, were assessed in FAK-inhibited rheumatoid synovial fibroblasts by transwell assay and microscopic examination of fluorescent gelatin degradation, respectively. Using mice with tumor necrosis factor α (TNFα)-induced arthritis in which fak could be inducibly deleted, invasion and migration by FAK-deficient murine arthritic synovial fibroblasts were determined as described above and arthritis was clinically and pathologically scored in FAK-deficient mice.

RESULTS

Inhibition of FAK in human rheumatoid synovial fibroblasts impaired cellular invasion and migration. Focal matrix degradation occurred both centrally and at focal adhesions, the latter being a novel site for matrix degradation in synovial fibroblasts, but degradation was unaltered with FAK inhibitors. Loss of FAK reduced invasion in murine arthritic synovial fibroblasts, but not migration or TNFα-induced arthritis severity and joint erosions.

CONCLUSIONS

FAK inhibitors reduce synovial fibroblast invasion and migration, but synovial fibroblast migration and TNFα-induced arthritis do not rely on FAK itself. Thus, inhibition of FAK alone is unlikely to be sufficient to treat inflammatory arthritis, but current drugs that inhibit FAK may inhibit multiple factors, which could increase their efficacy in rheumatoid arthritis.

FAK in cancer: mechanistic findings and clinical applications

Focal adhesion kinase (FAK) is a cytoplasmic protein tyrosine kinase that is overexpressed and activated in several advanced-stage solid cancers. FAK promotes tumour progression and metastasis through effects on cancer cells, as well as stromal cells of the tumour microenvironment. The kinase-dependent and kinase-independent functions of FAK control cell movement, invasion, survival, gene expression and cancer stem cell self-renewal. Small molecule FAK inhibitors decrease tumour growth and metastasis in several preclinical models and have initial clinical activity in patients with limited adverse events. In this Review, we discuss FAK signalling effects on both tumour and stromal cell biology that provide rationale and support for future therapeutic opportunities.

Neutrophils generate microparticles during exposure to inert gases due to cytoskeletal oxidative stress

This investigation was to elucidate the mechanism for microparticle (MP) formation triggered by exposures to high pressure inert gases. Human neutrophils generate MPs at a threshold of ∼186 kilopascals with exposures of 30 min or more. Murine cells are similar, but MP production occurs at a slower rate and continues for ∼4 h, whether or not cells remain under pressure. Neutrophils exposed to elevated gas but not hydrostatic pressure produce MPs according to the potency series: argon ≃ nitrogen > helium. Following a similar pattern, gases activate type-2 nitric-oxide synthase (NOS-2) and NADPH oxidase (NOX). MP production does not occur with neutrophils exposed to a NOX inhibitor (Nox2ds) or a NOS-2 inhibitor (1400W) or with cells from mice lacking NOS-2. Reactive species cause S-nitrosylation of cytosolic actin that enhances actin polymerization. Protein cross-linking and immunoprecipitation studies indicate that increased polymerization occurs because of associations involving vasodilator-stimulated phosphoprotein, focal adhesion kinase, the H(+)/K(+) ATPase β (flippase), the hematopoietic cell multidrug resistance protein ABC transporter (floppase), and protein-disulfide isomerase in proximity to short actin filaments. Using chemical inhibitors or reducing cell concentrations of any of these proteins with small inhibitory RNA abrogates NOS-2 activation, reactive species generation, actin polymerization, and MP production. These effects were also inhibited in cells exposed to UV light, which photoreverses S-nitrosylated cysteine residues and by co-incubations with the antioxidant ebselen or cytochalasin D. The autocatalytic cycle of protein activation is initiated by inert gas-mediated singlet O2 production.

Focal adhesion kinase negatively regulates Lck function downstream of the T cell antigen receptor

Focal adhesion kinase (FAK) is a critical regulator of signal transduction in multiple cell types. Although this protein is activated upon TCR engagement, the cellular function that FAK plays in mature human T cells is unknown. By suppressing the function of FAK, we revealed that FAK inhibits TCR-mediated signaling by recruiting C-terminal Src kinase to the membrane and/or receptor complex following TCR activation. Thus, in the absence of FAK, the inhibitory phosphorylation of Lck and/or Fyn is impaired. Together, these data highlight a novel role for FAK as a negative regulator TCR function in human T cells. These results also suggest that changes in FAK expression could modulate sensitivity to TCR stimulation and contribute to the progression of T cell malignancies and autoimmune diseases.

Focal adhesion kinase regulates the localization and retention of pro-B cells in bone marrow microenvironments

Progenitor B cells reside in complex bone marrow (BM) microenvironments where they receive signals for growth and maturation. We reported previously that the CXCL12-focal adhesion kinase (FAK)-VLA4 pathway plays an important role in progenitor B cell adhesion and migration. In this study, we have conditionally targeted in B cells FAK, and found that the numbers of progenitor pro-B, pre-B, and immature B cells are reduced by 30-40% in B cell-specific FAK knockout mice. When cultured in methylcellulose with IL-7 ± CXCL12, Fak-deleted pro-B cells yield significantly fewer cells and colonies. Using in situ quantitative imaging cytometry, we establish that in longitudinal femoral BM sections, pro-B cells are preferentially localized in close proximity to the endosteum of the metaphyses and the diaphysis. Fak deletion disrupts the nonrandom distribution of pro-B cells and induces the mobilization of pro-B cells to the periphery in vivo. These effects of Fak deletion on pro-B cell mobilization and localization in BM are amplified under inflammatory stress, that is, after immunization with nitrophenol-conjugated chicken γ-globulin in alum. Collectively, these studies suggest the importance of FAK in regulating pro-B cell homeostasis and maintenance of their spatial distribution in BM niches.

Reactive oxygen species-induced actin glutathionylation controls actin dynamics in neutrophils

The regulation of actin dynamics is pivotal for cellular processes such as cell adhesion, migration, and phagocytosis and thus is crucial for neutrophils to fulfill their roles in innate immunity. Many factors have been implicated in signal-induced actin polymerization, but the essential nature of the potential negative modulators are still poorly understood. Here we report that NADPH oxidase-dependent physiologically generated reactive oxygen species (ROS) negatively regulate actin polymerization in stimulated neutrophils via driving reversible actin glutathionylation. Disruption of glutaredoxin 1 (Grx1), an enzyme that catalyzes actin deglutathionylation, increased actin glutathionylation, attenuated actin polymerization, and consequently impaired neutrophil polarization, chemotaxis, adhesion, and phagocytosis. Consistently, Grx1-deficient murine neutrophils showed impaired in vivo recruitment to sites of inflammation and reduced bactericidal capability. Together, these results present a physiological role for glutaredoxin and ROS- induced reversible actin glutathionylation in regulation of actin dynamics in neutrophils.

Focal adhesion kinase signaling mediates acute renal injury induced by ischemia/reperfusion

Renal ischemia/reperfusion (I/R) injury is associated with cell matrix and focal adhesion remodeling. Focal adhesion kinase (FAK) is a nonreceptor protein tyrosine kinase that localizes at focal adhesions and regulates their turnover. Here, we investigated the role of FAK in renal I/R injury, using a novel conditional proximal tubule-specific fak-deletion mouse model. Tamoxifen treatment of FAK(loxP/loxP)//γGT-Cre-ER(T2) mice caused renal-specific fak recombination (FAK(ΔloxP/ΔloxP)) and reduction of FAK expression in proximal tubules. In FAK(ΔloxP/ΔloxP) mice compared with FAK(loxP/loxP) controls, unilateral renal ischemia followed by reperfusion resulted in less tubular damage with reduced tubular cell proliferation and lower expression of kidney injury molecule-1, which was independent from the postischemic inflammatory response. Oxidative stress is involved in the pathophysiology of I/R injury. Primary cultured mouse renal cells were used to study the role of FAK deficiency for oxidative stress in vitro. The conditional fak deletion did not affect cell survival after hydrogen peroxide-induced cellular stress, whereas it impaired the recovery of focal adhesions that were disrupted by hydrogen peroxide. This was associated with reduced c-Jun N-terminal kinase-dependent phosphorylation of paxillin at serine 178 in FAK-deficient cells, which is required for focal adhesion turnover. Our findings support a role for FAK as a novel factor in the initiation of c-Jun N-terminal kinase-mediated cellular stress response during renal I/R injury and suggest FAK as a target in renal injury protection.

Intracellular HMGB1 negatively regulates efferocytosis

High mobility group box 1 (HMGB1) is a highly conserved protein with multiple intracellular and extracellular functions, including transcriptional regulation, as well as modulation of inflammation, cell migration, and ingestion of apoptotic cells. In these experiments, we examined a potential role for intracellular HMGB1 in modulating phagocytosis. We found that phagocytosis of apoptotic cells resulted in translocation of HMGB1 into the cytoplasm and extracellular space. Transient or stable inhibition of HMGB1 expression in bone marrow-derived macrophages or fibroblasts resulted in increased phagocytosis of apoptotic thymocytes and apoptotic neutrophils. Knockdown of HMGB1 was associated with enhanced activation of Rac-1 and cytoskeletal rearrangement. Intracellular events involved in phagocytosis and upstream of Rac-1 activation, such as phosphorylation of ERK and focal adhesion kinase (FAK), were increased after knockdown of HMGB1. Inhibition of Src kinase activity prevented the increase in phosphorylation of FAK and ERK present during phagocytosis in HMGB1 knockdown cells, and also abrogated the enhancement in phagocytosis associated with HMGB1 knockdown. Interaction between Src and FAK in the cytoplasm of HMGB1 knockdown fibroblasts was enhanced compared with that present in control fibroblasts. Under in vitro conditions, the presence of HMGB1 diminished interactions between purified FAK and Src. These studies demonstrate a novel role for HMGB1 in the regulation of phagocytosis. In particular, these experiments show that intracellular HMGB1, through associating with Src kinase and inhibiting interactions between Src and FAK, diminishes the phagocytic ability of macrophages and other cell populations.

Neutrophil transmigration, focal adhesion kinase and endothelial barrier function

Neutrophil activation is an essential component of innate immune defense against infection and injury. In response to inflammatory stimulation, circulating neutrophils undergo a series of dynamic and metabolic changes characterized by β2-intergrin mediated adhesion to microvascular endothelium and subsequent transendothelial migration. During this process, neutrophils release granular contents containing digestive enzymes and produce cytotoxic agents such as reactive oxygen species and cytokines. These products target endothelial barriers inducing phosphorylation-triggered junction dissociation, actin stress fiber formation, and actomyosin contraction, manifest as paracellular hyperpermeability. Endothelial cell-matrix focal adhesions play an integral role in this process by providing structural support for endothelial conformational changes that facilitate neutrophil transmigration, as well as by recruiting intracellular molecules that constitute the hyperpermeability signaling cascades. As a central connector of the complex signaling network, focal adhesion kinase (FAK) is activated following neutrophil adhesion, and further mediates the reorganization of endothelial integrin-matrix attachments in a pattern coordinating with cytoskeleton contraction and junction opening. In this review, we present recent experimental evidence supporting the importance of FAK in neutrophil-dependent regulation of endothelial permeability. The discussion focuses on the mechanisms by which neutrophils activate FAK and its downstream effects on endothelial barriers.

Reactive oxygen species as signaling molecules in neutrophil chemotaxis

Neutrophil chemotaxis is a critical component in innate immunity. Recently, using a small-molecule functional screening, we identified NADPHoxidase- dependent Reactive Oxygen Species (ROS) as key regulators of neutrophil chemotactic migration. Neutrophils depleted of ROS form more frequent multiple pseudopodia and lost their directionality as they migrate up a chemoattractant concentration gradient. Here, we further studied the role of ROS in neutrophil chemotaxis and found that multiple pseudopodia formation induced by NADPH inhibitor diphenyleneiodonium chloride (DPI) was more prominent in relatively shallow chemoattractant gradient. It was reported that, in shallow chemoattractant gradients, new pseudopods are usually generated when existing ones bifurcate. Directional sensing is mediated by maintaining the most accurate existing pseudopod, and destroying pseudopods facing the wrong direction by actin depolymerization. We propose that NADPH-mediated ROS production may be critical for disruption of misoriented pseudopods in chemotaxing neutrophils. Thus, inhibition of ROS production will lead to formation of multiple pseudopodia.

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.

Essential role for focal adhesion kinase in regulating stress hematopoiesis

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that has been extensively studied in fibroblasts; however its function in hematopoiesis remains an enigma. FAK is thought to be expressed in myeloid and erythroid progenitors, and its expression is enhanced in response to cytokines such as granu-locyte macrophage colony-stimulating factor. Furthermore, bone marrow cells cultured in granulocyte macrophage colony-stimulating factor show active migration and chemoattractant-induced polarization, which correlates with FAK induction. While loss of FAK in mice results in embryonic lethality, we have deleted FAK in the adult bone marrow. We show an essential role for FAK in regulating hemolytic, myelotoxic, as well as acute inflammatory stress responses in vivo. In vitro, loss of FAK in erythroid and myeloid progenitor's results in impaired cytokine induced growth and survival, as well as defects in the activation and expression of antiapoptotic proteins caspase 3 and Bcl-x(L). Additionally, reduced migration and adhesion of myeloid cells on extracellular matrix proteins, as well as impaired activation of Rac GTPase is also observed in the absence of FAK. Our studies reveal an essential role for FAK in integrating growth/survival and adhesion based functions in myeloid and erythroid cells predominantly under conditions of stress.

Nanotopographical modification: a regulator of cellular function through focal adhesions

As materials technology and the field of biomedical engineering advances, the role of cellular mechanisms, in particular adhesive interactions with implantable devices, becomes more relevant in both research and clinical practice. A key tenet of medical device design has evolved from the exquisite ability of biological systems to respond to topographical features or chemical stimuli, a process that has led to the development of next-generation biomaterials for a wide variety of clinical disorders. In vitro studies have identified nanoscale features as potent modulators of cellular behavior through the onset of focal adhesion formation. The focus of this review is on the recent developments concerning the role of nanoscale structures on integrin-mediated adhesion and cellular function with an emphasis on the generation of medical constructs with regenerative applications.

FROM THE CLINICAL EDITOR

In this review, recent developments related to the role of nanoscale structures on integrin-mediated adhesion and cellular function is discussed, with an emphasis on regenerative applications.

Characterization of a novel focal adhesion kinase inhibitor in human platelets

Focal adhesion kinase (FAK) is activated in human platelets downstream of integrins, e.g. α_IIbβ₃, and other adhesion receptors e.g. GPVI. Mice in which platelets lack FAK have been shown to exhibit extended bleeding times and their platelets have been shown to display decreased spreading on fibrinogen-coated surfaces. Recently, a novel FAK inhibitor (PF-573,228) has become available, its selectivity for FAK shown in vitro and in cell lines. We determined the effect of this inhibitor on platelet function and signaling pathways. Like murine platelets lacking FAK, we found that PF-573,228 was effective at blocking human platelet spreading on fibrinogen-coated surfaces but did not affect the initial adhesion. We also found a reduced spreading on CRP-coated surfaces. Further analysis of the morphology of platelets adhered to these surfaces showed the defect in spreading occurred at the transition from filopodia to lamellipodia. Similar to that seen with murine neutrophils lacking FAK, we also observed an unexpected defect in intracellular calcium release in human platelets pre-treated with PF-573,228 which correlated with impaired dense granule secretion and aggregation. The aggregation defect could be partially rescued by addition of ADP, normally secreted from dense granules, suggesting that PF-573,228 has effects on FAK downstream of α_IIbβ₃ and elsewhere. Our data show that PF-573,228 is a useful tool for analysis of FAK function in cells and reveal that in human platelets FAK may regulate a rise in cell calcium and platelet spreading.