Phosphatidylinositol 3-kinase-dependent extracellular calcium influx is essential for CX(3)CR1-mediated activation of the mitogen-activated protein kinase cascade

Age-dependent changes on fractalkine forms and their contribution to neurodegenerative diseases

The chemokine fractalkine (FKN, CX3CL1), a member of the CX3C subfamily, contributes to neuron-glia interaction and the regulation of microglial cell activation. Fractalkine is expressed by neurons as a membrane-bound protein (mCX3CL1) that can be cleaved by extracellular proteases generating several sCX3CL1 forms. sCX3CL1, containing the chemokine domain, and mCX3CL1 have high affinity by their unique receptor (CX3CR1) which, physiologically, is only found in microglia, a resident immune cell of the CNS. The activation of CX3CR1contributes to survival and maturation of the neural network during development, glutamatergic synaptic transmission, synaptic plasticity, cognition, neuropathic pain, and inflammatory regulation in the adult brain. Indeed, the various CX3CL1 forms appear in some cases to serve an anti-inflammatory role of microglia, whereas in others, they have a pro-inflammatory role, aggravating neurological disorders. In the last decade, evidence points to the fact that sCX3CL1 and mCX3CL1 exhibit selective and differential effects on their targets. Thus, the balance in their level and activity will impact on neuron-microglia interaction. This review is focused on the description of factors determining the emergence of distinct fractalkine forms, their age-dependent changes, and how they contribute to neuroinflammation and neurodegenerative diseases. Changes in the balance among various fractalkine forms may be one of the mechanisms on which converge aging, chronic CNS inflammation, and neurodegeneration.

The CX3CL1-CX3CR1 chemokine axis can contribute to tumor immune evasion and blockade with a novel CX3CR1 monoclonal antibody enhances response to anti-PD-1 immunotherapy

CX3CL1 secreted in the tumor microenvironment serves as a chemoattractant playing a critical role in metastasis of CX3CR1 expressing cancer cells. CX3CR1 can be expressed in both cancer and immune-inhibitory myeloid cells to facilitate their migration. We generated a novel monoclonal antibody against mouse CX3CR1 that binds to CX3CR1 and blocks the CX3CL1-CX3CR1 interaction. We next explored the immune evasion strategies implemented by the CX3CL1-CX3CR1 axis and find that it initiates a resistance program in cancer cells that results in 1) facilitation of tumor cell migration, 2) secretion of soluble mediators to generate a pro-metastatic niche, 3) secretion of soluble mediators to attract myeloid populations, and 4) generation of tumor-inflammasome. The CX3CR1 monoclonal antibody reduces migration of tumor cells and decreases secretion of immune suppressive soluble mediators by tumor cells. In combination with anti-PD-1 immunotherapy, this CX3CR1 monoclonal antibody enhances survival in an immunocompetent mouse colon carcinoma model through a decrease in tumor-promoting myeloid populations. Thus, this axis is involved in the mechanisms of resistance to anti-PD-1 immunotherapy and the combination therapy can overcome a portion of the resistance mechanisms to anti-PD-1.

Potential significance of CX3CR1 dynamics in stress resilience against neuronal disorders

Recent findings have implicated inflammatory responses in the central nervous system in a variety of neuropsychiatric and neurodegenerative diseases, and the understanding and control of immunological responses could be a major factor of future therapeutic strategies for neurological disorders. Microglia, derived from myelogenous cells, respond to a number of stimuli and make immune responses, resulting in a prominent role as cells that act on inflammation in the central nervous system. Fractalkine (FKN or CX3CL1) signaling is an important factor that influences the inflammatory response of microglia. The receptor for FKN, CX3CR1, is usually expressed in microglia in the brain, and therefore the inflammatory response of microglia is modified by FKN. Reportedly, FKN often suppresses inflammatory responses in microglia and activation of its receptor may be effective in the treatment of inflammatory neurological disorders. However, it has also been suggested that inflammatory responses facilitated by FKN signaling aggravate neurological disorders. Thus, further studies are still required to resolve the conflicting interpretation of the protective or deleterious contribution of microglial FKN signaling. Yet notably, regulation of FKN signaling has recently been shown to be beneficial in the treatment of human diseases, although not neurological diseases. In addition, a CX3CR1 inhibitor has been developed and successfully tested in animal models, and it is expected to be in human clinical trials in the future. In this review, I describe the potential therapeutic consideration of microglial CX3CR1 dynamics through altered FKN signaling.

The Aryl hydrocarbon receptor mediates reproductive toxicity of polychlorinated biphenyl congener 126 in rats

Polychlorinated biphenyls (PCBs) are endocrine disrupting chemicals with documented, though mechanistically ill-defined, reproductive toxicity. The toxicity of dioxin-like PCBs, such as PCB126, is mediated via the aryl hydrocarbon receptor (AHR) in non-ovarian tissues. The goal of this study was to examine the uterine and ovarian effects of PCB126 and test the hypothesis that the AHR is required for PCB126-induced reproductive toxicity. Female Holzman-Sprague Dawley wild type (n = 14; WT) and Ahr knock out (n = 11; AHR-/-) rats received a single intraperitoneal injection of either corn oil vehicle (5 ml/kg: WT_O and AHR-/-_O) or PCB126 (1.63 mg/kg in corn oil: WT_PCB and AHR-/-_PCB) at four weeks of age. The estrous cycle was synchronized and ovary and uterus were collected 28 days after exposure. In WT rats, PCB126 exposure reduced (P < 0.05) body and ovary weight, uterine gland number, uterine area, progesterone, 17β-estradiol and anti-Müllerian hormone level, secondary and antral follicle and corpora lutea number but follicle stimulating hormone level increased (P < 0.05). In AHR-/- rats, PCB126 exposure increased (P ≤ 0.05) circulating luteinizing hormone level. Ovarian or uterine mRNA abundance of biotransformation, and inflammation genes were altered (P < 0.05) in WT rats due to PCB126 exposure. In AHR-/- rats, the transcriptional effects of PCB126 were restricted to reductions (P < 0.05) in three inflammatory genes. These findings support a functional role for AHR in the female reproductive tract, illustrate AHR's requirement in PCB126-induced reprotoxicity, and highlight the potential risk of dioxin-like compounds on female reproduction.

Role of the CX3CL1-CX3CR1 axis in renal disease

Excessive infiltration of immune cells into the kidney is a key feature of acute and chronic kidney diseases. The family of chemokines comprises key drivers of this process. Fractalkine [chemokine (C-X3-C motif) ligand 1 (CX3CL1)] is one of two unique chemokines synthesized as a transmembrane protein that undergoes proteolytic cleavage to generate a soluble species. Through interacting with its cognate receptor, chemokine (C-X3-C motif) receptor 1 (CX3CR1), CX3CL1 was originally shown to act as a conventional chemoattractant in the soluble form and as an adhesion molecule in the transmembrane form. Since then, other functions of CX3CL1 beyond leukocyte recruitment have been described, including cell survival, immunosurveillance, and cell-mediated cytotoxicity. This review summarizes diverse roles of CX3CL1 in kidney disease and potential uses as a therapeutic target and novel biomarker. As the CX3CL1-CX3CR1 axis has been shown to contribute to both detrimental and protective effects in various kidney diseases, a thorough understanding of how the expression and function of CX3CL1 are regulated is needed to unlock its therapeutic potential.

Regulation and biological functions of the CX3CL1-CX3CR1 axis and its relevance in solid cancer: A mini-review

CX3CL1 is a transmembrane protein from which a soluble form can be generated by proteolytic shedding. Membranal and soluble forms of CX3CL1 exhibit different functions, although both bind to the CX3CR1 chemokine receptor. The CX3CL1-CX3CR1 axis mediates the adhesion of leukocytes and is also involved in cell survival and recruitment of immune cell subpopulations. The function of CX3CL1 is finely tuned by cytokines and transcription factors regulating its expression and post-translational modifications. On homeostasis, the CX3CL1-CX3CR1 axis participates in the removal of damaged neurons and neurogenesis, and it is also involved on several pathological contexts. The CX3CL1-CX3CR1 axis induces several cellular responses relevant to cancer such as proliferation, migration, invasion and apoptosis resistance. In this review, we address biological aspects of this molecular axis with important therapeutic potential, emphasizing its role in cancer, one of the most prevalent chronic diseases which significantly affect the quality of life and life expectancy of patients.

The CX3CL1/CX3CR1 axis is upregulated in chronic kidney disease and contributes to angiotensin II-induced migration of vascular smooth muscle cells

BACKGROUND

The role of the chemokine axis, CX3CL1/CX3CR1, in the development of cardiovascular diseases has been widely speculated. Angiotensin II (Ang II) is a pivotal factor promoting cardiovascular complications in patients with chronic kidney disease (CKD). Whether there is a link between the two in CKD remains unclear.

METHODS

The uremic mice were treated with losartan for 8 weeks, and the expression of aortic CX3CL1/CX3CR1 was detected. Cultured mouse aortic vascular smooth muscle cells (VSMCs) were stimulated with Ang II, and then CX3CR1 expression was assessed by western blot. After the targeted disruption of CX3CR1 by transfection with siRNA, the migration of VSMCs was detected by transwell assay. Finally, both the activation of Akt pathway and the expression of IL-6 were detected by western blot.

RESULTS

Losartan treatment reduced the upregulation of aortic CX3CL1/CX3CR1 expression in uremic mice. In vitro, Ang II significantly upregulated CX3CR1 expression in VSMCs. Targeted disruption of CX3CR1 attenuated Ang II-induced migration of VSMCs. In addition, the use of CX3CR1-siRNA suppressed Akt phosphorylation and IL-6 production in VSMCs stimulated by Ang II.

CONCLUSIONS

The aortic CX3CL1/CX3CR1 is upregulated by Ang II in CKD, and it contributes to Ang II-induced migration of VSMCs in vitro.

Drug-free albumin-triggered sensitization of cancer cells to anticancer drugs

Chemosensitization strategies have been used to sensitize cancer cells to conventional drugs, but their utility is often obstructed by additional off-target toxicity, limited access to intracellular targets and heterogeneous tumor pathogenesis. To address these challenges, we rationally developed a drug-free human serum albumin (HSA)-based therapeutic (KH-1) that functions extracellularly and exhibits pleiotropic effect on multiple intracellular signaling pathways. It is a two-step touch-trigger system that consists of a pretargeting anchor on surface receptor CD20 (anti-CD20 Fab' conjugated with a morpholino oligonucleotide 1) and a CD20 clustering actuator (HSA grafted with multiple copies of complementary morpholino oligonucleotide 2). The extracellular actuation by surface CD20 crosslinking boosts robust activations of numerous intracellular responses, and promotes cancer cell susceptibility to various anticancer drugs, including docetaxel (microtubule stabilizer), gemcitabine (nucleoside analogue) and GDC-0980 (PI3K/mTOR inhibitor). The broad applicability of KH-1 is demonstrated to result from simultaneous inhibition of survival pathways and augmentation of apoptotic pathways. In addition, KH-1 covalently conjugated with anthracycline anticancer agent, epirubicin, integrates the advantages of both chemosensitization function and improved intracellular drug delivery in a single system and takes effect on the same cell. Therefore, in the present study, we have provided mechanistic demonstration that crosslinking of surface receptors can be leveraged to elicit chemosensitization.

CX3CL1/CX3CR1 Axis Contributes to Angiotensin II-Induced Vascular Smooth Muscle Cell Proliferation and Inflammatory Cytokine Production

Angiotensin II (Ang II) dysregulation has been determined in many diseases. The CX3CL1/CX3CR1 axis, which has a key role in cardiovascular diseases, is involved in the proliferation and inflammatory cytokine production of vascular smooth muscle cells (VSMCs). In this study, we aim to explore whether Ang II has a role in the expression of CX3CL1/CX3CR1, thus contributing to the proliferation and pro-inflammatory status of VSMCs. Cultured mouse aortic VSMCs were stimulated with 100 nmol/L of Ang II, and the expression of CX3CR1 was assessed by western blot. The results demonstrated that Ang II significantly up-regulated CX3CR1 expression in VSMCs and induced the production of reactive oxygen species (ROS) and the phosphorylation of p38 MAPK. Inhibitors of NADPH oxidase, ROS, and AT1 receptor significantly reduced Ang II-induced CX3CR1 expression. Targeted disruption of CX3CR1 by transfection with siRNA significantly attenuated Ang II-induced VSMC proliferation as well as down-regulated the expression of proliferating cell nuclear antigen (PCNA). Furthermore, CX3CR1-siRNA suppressed the effect of Ang II on stimulating Akt phosphorylation. Besides, the use of CX3CR1-siRNA decreased inflammatory cytokine production induced by Ang II treatment. Our results indicate that Ang II up-regulates CX3CR1 expression in VSMCs via NADPH oxidase/ROS/p38 MAPK pathway and that CX3CL1/CX3CR1 axis contributes to the proliferative and pro-inflammatory effects of Ang II in VSMCs.

The microglial fractalkine receptor is not required for activity-dependent plasticity in the mouse visual system

Microglia have recently been implicated as key regulators of activity-dependent plasticity, where they contribute to the removal of inappropriate or excess synapses. However, the molecular mechanisms that mediate this microglial function are still not well understood. Although multiple studies have implicated fractalkine signaling as a mediator of microglia-neuron communications during synaptic plasticity, it is unclear whether this is a universal signaling mechanism or whether its role is limited to specific brain regions and stages of the lifespan. Here, we examined whether fractalkine signaling mediates microglial contributions to activity-dependent plasticity in the developing and adolescent visual system. Using genetic ablation of fractalkine's cognate receptor, CX₃ CR1, and both ex vivo characterization and in vivo imaging in mice, we examined whether fractalkine signaling is required for microglial dynamics and modulation of synapses, as well as activity-dependent plasticity in the visual system. We did not find a role for fractalkine signaling in mediating microglial properties during visual plasticity. Ablation of CX₃ CR1 had no effect on microglial density, distribution, morphology, or motility, in either adolescent or young adult mice across brain regions that include the visual cortex. Ablation of CX₃ CR1 also had no effect on baseline synaptic turnover or contact dynamics between microglia and neurons. Finally, we found that fractalkine signaling is not required for either early or late forms of activity-dependent visual system plasticity. These findings suggest that fractalkine is not a universal regulator of synaptic plasticity, but rather has heterogeneous roles in specific brain regions and life stages.

Involvement of adenosine A3 receptors in the chemotactic navigation of macrophages towards apoptotic cells

The first step in the clearance of apoptotic cells is chemotactic migration of macrophages towards the apoptotic cells guided by find-me signals provided by the dying cells. Upon sensing the chemotactic signals, macrophages release ATP. ATP is then degraded to ADP, AMP and adenosine to trigger purinergic receptors concentrated at the leading edge of the cell. Previous studies have shown that in addition to the chemotactic signals, this purinergic autocrine signaling is required to amplify and translate chemotactic signals into directional motility. In the present study the involvement of adenosine A₃ receptors (A3R) was studied in the chemotactic migration of macrophages directed by apoptotic thymocyte-derived find-me signals. By taking video images in vitro, we demonstrate 1, by administering apyrase, which degrades ATP and ADP, that the purinergic autocrine signaling is required for maintaining both the velocity and the directionality of macrophage migration towards the apoptotic thymocytes; 2, by readding 5'-N-ethylcarboxamidoadenosine, an adenosine analogue, to apyrase treated cells that the adenosine receptor signaling alone is sufficient to act so; and 3, by studying migration of various adenosine receptor null or adenosine receptor antagonist-treated macrophages, that the individual loss of the A3R signaling leads to the loss of chemotactic navigation. Though loss of A3Rs does not affect the phagocytotic capacity of macrophages, intraperitoneally-injected apoptotic thymocytes were cleared with a delayed kinetics by A3R null macrophages in vivo due to the impaired chemotactic navigation. All together these data demonstrate the involvement of macrophage A3Rs in the proper chemotactic navigation and consequent in vivo clearance of apoptotic cells. Interestingly, loss of A3Rs did not affect the in vivo clearance of apoptotic thymocytes in the dexamethasone-treated thymus.

[Role of fractalkine/CX3CL1 and its receptor CX3CR1 in allergic diseases]

Allergic asthma and atopic dermatitis are diseases mainly resulting from the activation of Th2 cells, that produce cytokines favouring IgE production and eosinophilia but also of Th1 cells, that contribute to inflammation chronicity. Lymphocyte recruitment and retention of Th cells in target organs are 2 key events for asthma and atopic dermatitis pathogenesis. While lymphocyte migration is regulated by chemokines and lipid mediators such as leukotrienes and prostaglandins, factors involved in lymphocyte retention and survival within inflammatory tissues remain poorly understood. Recent works show that, in allergic diseases, there is an increased expression of fractalkine/CX3CL1 and its unique receptor CX3CR1 and that this chemokine does not act as chemoattractant. In allergic asthma, CX3CR1 expression regulates Th2 and Th1 cell survival in the inflammatory lung, while, in atopic dermatitis, it regulate Th2 and Th1 cell retention into the inflammatory site. Use of peptides blocking fractalkine binding to its receptor is currently tested in the treatment of asthma and atopic dermatitis.

The chemokine fractalkine can activate integrins without CX3CR1 through direct binding to a ligand-binding site distinct from the classical RGD-binding site

The chemokine domain of fractalkine (FKN-CD) binds to the classical RGD-binding site of αvβ3 and that the resulting ternary complex formation (integrin-FKN-CX3CR1) is critical for CX3CR1 signaling and FKN-induced integrin activation. However, only certain cell types express CX3CR1. Here we studied if FKN-CD can activate integrins in the absence of CX3CR1. We describe that WT FKN-CD activated recombinant soluble αvβ3 in cell-free conditions, but the integrin-binding defective mutant of FKN-CD (K36E/R37E) did not. This suggests that FKN-CD can activate αvβ3 in the absence of CX3CR1 through the direct binding of FKN-CD to αvβ3. WT FKN-CD activated αvβ3 on CX3CR1-negative cells (K562 and CHO) but K36E/R37E did not, suggesting that FKN-CD can activate integrin at the cellular levels in a manner similar to that in cell-free conditions. We hypothesized that FKN-CD enhances ligand binding to the classical RGD-binding site (site 1) through binding to a second binding site (site 2) that is distinct from site 1 in αvβ3. To identify the possible second FKN-CD binding site we performed docking simulation of αvβ3-FKN-CD interaction using αvβ3 with a closed inactive conformation as a target. The simulation predicted a potential FKN-CD-binding site in inactive αvβ3 (site 2), which is located at a crevice between αv and β3 on the opposite side of site 1 in the αvβ3 headpiece. We studied if FKN-CD really binds to site 2 using a peptide that is predicted to interact with FKN-CD in site 2. Notably the peptide specifically bound to FKN-CD and effectively suppressed integrin activation by FKN-CD. This suggests that FKN-CD actually binds to site 2, and this leads to integrin activation. We obtained very similar results in α4β1 and α5β1. The FKN binding to site 2 and resulting integrin activation may be a novel mechanism of integrin activation and of FKN signaling.

Microglial calcium signaling in the adult, aged and diseased brain

Microglial cells are the resident immune cells of the CNS. They mediate innate immune response of the brain to injury, inflammation and neurodegenerative diseases. Apart from their role in disease they are critically involved in the development and plasticity-driven reorganization of neuronal networks and the homeostatic maintenance of brain tissue. Accumulating in vitro evidence suggests that executive functions of microglia are coupled to the intracellular Ca(2+) signaling of these cells. So far, however, very little is known about microglial Ca(2+) signaling in situ or in vivo, both in the healthy and in the diseased brain. Here, we summarize the recent in vivo/in situ findings and compare the properties of surveillant microglia in these preparations with those of microglia in vitro. The data suggest that surveillant microglia rarely show spontaneous Ca(2+) transients, express fewer functional receptors directly coupled to changes in the intracellular free Ca(2+) concentration on their surface, but vividly respond with Ca(2+) transients to cell or tissue damage in their microenvironment. Interestingly, some of these properties microglia share with monocytes engrafting in the brain under pathological conditions.

CX3CL1 in allergic diseases: not just a chemotactic molecule

Allergic asthma and atopic dermatitis (AD) are two allergic diseases that are primarily driven by the activation of T helper (Th)2 cells. Th2 cells produce cytokines that directly contribute to the symptoms of these diseases. The recruitment and maintenance of Th2 cells into the target tissues are two key events in the pathogenesis of allergic asthma and AD. While migration is mediated by both chemokines and lipid mediators such as leukotrienes and prostaglandins, very little is known about the molecules involved in lymphocyte survival and maintenance in inflamed tissues. However, chemokines could also play a role in this phenomenon. An example of this could be illustrated by CX3CL1, also known as fractalkine. CX3CL1 is a chemokine that is upregulated in some inflammatory diseases including allergic pathologies and that was recently demonstrated to provide a survival signal upon binding to its unique receptor CX3CR1.

CX3CL1/fractalkine is a novel regulator of normal and malignant human B cell function

CX(3)CL1, or fractalkine, the unique member of the CX(3)C chemokine family, exists as a transmembrane glycoprotein, as well as in soluble form, each mediating different biological activities, and is constitutively expressed in many hematopoietic and nonhematopoietic tissues. CX(3)CR1, the CX(3)CL1 exclusive receptor, is a classical GPCR, expressed on NK cells, CD14(+) monocytes, and some subpopulation of T cells, B cells, and mast cells. A recent paper by our group has demonstrated for the first time that highly purified human B cells from tonsil and peripheral blood expressed CX(3)CR1 at mRNA and protein levels. In particular, tonsil naïve, GC, and memory B cells expressed CX(3)CR1, but only GC centrocytes were attracted by soluble CX(3)CL1, which with its receptor, are also involved in the pathogenesis of several inflammatory disorders, as well as of cancer. Previous studies have shown that CX(3)CR1 is up-regulated in different types of B cell lymphoma, as well as in B-CLL. Recently, we have demonstrated that the CX(3)CL1/CX(3)CR1 axis is involved in the interaction of B-CLL cells with their microenvironment. Taken together, our data delineate a novel role for the CX(3)CL1/CX(3)CR1 complex in the biology of normal B cells and B-CLL cells. These topics are the subject of this review article.

Elevated fractalkine in patients with obstructive sleep apnea hypopnea syndrome

BACKGROUND

Obstructive sleep apnea hypopnea syndrome (OSAHS) has been increasingly linked to cardiovascular disease. Inflammatory processes associated with OSAHS may contribute to atherosclerosis in these patients. Fractalkine is a unique chemokine which has both adhesive and chemoattractant functions. We tested the hypothesis that OSAHS patients have increased fractalkine.

METHODS AND RESULTS

We studied 20 patients (18 males and 2 females) with newly diagnosed OSAHS, who were free of other diseases, had never been treated for OSAHS, and were taking no medications. We compared fractalkine measurements in these patients to measurements obtained in 15 control subjects (14 males and 1 female) who were matched for age and body mass index, and in whom occult OSAHS was excluded. Plasma fractalkine levels were significantly higher in patients with OSAHS than in controls (463.15 ± 110.78 versus 364.67 ± 64.81 pg/mL, F = 2.58, P = 0.004). Fractalkine were associated with AHI (r = 0.756, P < 0.0001), lowest oxygen saturation (r = -0.466, P = 0.005), and mean oxygen saturation (r = -0.344, P = 0.043). Plasma fractalkine levels were significantly decreased in patients with OSAHS after four nights nCPAP (463.15 ± 110.78 versus 416.75 ± 97.67 pg/mL, P = 0.001).

CONCLUSIONS

OSAHS is associated with elevated levels of fractalkine, a marker of inflammation related to atherosclerosis. The severity of OSAHS is proportional to the fractalkine level.

Pro-oxidants ameliorate radiation-induced apoptosis through activation of the calcium-ERK1/2-Nrf2 pathway

There are no reports describing the ability of pro-oxidants to protect against radiation-induced apoptosis. Activation of the redox-sensitive transcription factor Nrf2 by low levels of ROS is known to protect against oxidative stress-induced cell death. In this study, hydrogen peroxide, diethylmaleate, and 1,4-naphthoquinone (NQ) exhibited complete protection against radiation-induced cell death in lymphocytes as estimated by propidium iodide staining. Radioprotection by NQ was demonstrated by inhibition of caspase activation, decrease in cell size, DNA fragmentation, nuclear blebbing, and clonogenic assay. Interestingly, NQ offered protection to lymphocytes even when added to cells postirradiation. NQ increased intracellular ROS levels and decreased GSH levels. NQ activated Nrf2 and increased the expression of the cytoprotective gene heme oxygenase-1 in lymphocytes. NQ increased ERK phosphorylation, which is upstream of Nrf2, and this ERK activation was through increased intracellular calcium levels. Administration of NQ to mice offered protection against whole-body irradiation (WBI)-induced apoptosis in splenic lymphocytes and loss of viability of spleen and bone marrow cells. It restored WBI-mediated changes in hematological parameters and functional responses of lymphocytes. Importantly, NQ rescued mice against WBI-induced mortality. These results demonstrated that a pro-oxidant such as NQ can protect against radiation-induced apoptosis by activation of multiple prosurvival mechanisms including activation of the calcium-ERK1/2-Nrf2 pathway.

Fractalkine/CX3CR1 and atherosclerosis

Fractalkine is a unique chemokine which has both adhesive and chemoattractant functions. With the increasing emphasis on the importance of inflammation in atherosclerosis, more attention has been focused on the role of chemokines in atherosclerosis. It has been shown that fractalkine/CX3CR1 participates in the atherosclerotic pathological process through mediating the recruitment of leukocytes and the interaction of vascular cells and leukocytes. Some signal pathways are simultaneously activated through fractalkine/CX3CR1 coupling to promote the inflammatory response in atherosclerotic vessels. Additionally, fractalkine has cytotoxic effects on endothelium as well as anti-apoptosis and proliferative effects on vascular cells which consequently changes plaque components and stability in plaque. Several studies have showed that fractalkine or CX3CR1 deficiency in atherosclerotic mice would ameliorate the severity of plaque. Population studies on CX3CR1 polymorphism have confirmed that 280M-containing haplotype is associated with reduced risk of atherosclerotic disease. Despite the apparent association with atherosclerosis, further studies on fractalkine/CX3CR1 chemokine pair are clearly warranted to more fully elucidate this relationship.

Fractalkine-induced endothelial cell migration requires MAP kinase signaling

BACKGROUND/AIMS

Angiogenesis is a well-established characteristic in the rheumatoid arthritis (RA) synovial pannus. We have previously demonstrated that fractalkine (Fkn/ CX3CL1) expression is significantly increased in the RA joint and that fractalkine induces angiogenesis. In this work we studied mechanisms through which Fkn functions as an angiogenic mediator.

METHODS

Human microvascular endothelial cells (HMVECs) and human umbilical vein endothelial cells (HUVECs) were stimulated with Fkn and analyzed by Western blotting or stained with Alexa Fluor 488 phalloidin for F-actin to characterize the time frame of cytoskeletal rearrangement. Fkn-induced HUVEC chemotaxis was performed in the presence and absence of MAP kinase inhibitors.

RESULTS

Phalloidin staining of F-actin revealed significant cytoskeletal rearrangements in HUVECs and HMVECs starting as early as 10 min after Fkn stimulation. Western blotting demonstrated that HUVEC and HMVEC stimulation with Fkn for 1-30 min resulted in phosphorylation of JNK. Fkn also induces significant phosphorylation of Erk 1/2 in HUVECs over a time course ranging from 1 to 15 min. A somewhat similar time course (5-15 min) was detected for Erk 1/2 phosphorylation in HMVECs. Inhibitors of either JNK or Erk 1/2 nearly abolish Fkn-induced HUVEC migration.

CONCLUSIONS

We demonstrate that Fkn induces significant alterations in cytoskeletal structure and specifically activates the MAP kinases, JNK and Erk 1/2, both of which appear necessary for endothelial cell migration. Our results suggest that the endogenous Fkn present in the RA joint may induce angiogenesis through activation of the JNK and Erk 1/2 pathways.

CX3CR1 is expressed by human B lymphocytes and mediates [corrected] CX3CL1 driven chemotaxis of tonsil centrocytes

Background

Fractalkine/CX₃CL1, a surface chemokine, binds to CX₃CR1 expressed by different lymphocyte subsets. Since CX₃CL1 has been detected in the germinal centres of secondary lymphoid tissue, in this study we have investigated CX₃CR1 expression and function in human naïve, germinal centre and memory B cells isolated from tonsil or peripheral blood.

Methodology/Principal Findings

We demonstrate unambiguously that highly purified human B cells from tonsil and peripheral blood expressed CX₃CR1 at mRNA and protein levels as assessed by quantitative PCR, flow cytometry and competition binding assays. In particular, naïve, germinal centre and memory B cells expressed CX₃CR1 but only germinal centre B cells were attracted by soluble CX₃CL1 in a transwell assay. CX₃CL1 signalling in germinal centre B cells involved PI3K, Erk1/2, p38, and Src phosphorylation, as assessed by Western blot experiments. CX₃CR1⁺ germinal centre B cells were devoid of centroblasts and enriched for centrocytes that migrated to soluble CX₃CL1. ELISA assay showed that soluble CX₃CL1 was secreted constitutively by follicular dendritic cells and T follicular helper cells, two cell populations homing in the germinal centre light zone as centrocytes. At variance with that observed in humans, soluble CX₃CL1 did not attract spleen B cells from wild type mice. OVA immunized CX₃CR1⁻/⁻ or CX₃CL1⁻/⁻ mice showed significantly decreased specific IgG production compared to wild type mice.

Conclusion/Significance

We propose a model whereby human follicular dendritic cells and T follicular helper cells release in the light zone of germinal centre soluble CX₃CL1 that attracts centrocytes. The functional implications of these results warrant further investigation.

Cytokine expression profiling of the myocardium reveals a role for CX3CL1 (fractalkine) in heart failure

Several lines of evidence suggest that inflammatory processes mediated by cytokines are involved in the pathogenesis of heart failure (HF). However, the regulation of cytokine expression and the role of cytokines during HF development are not well understood. To address this issue, we have examined alterations in gene expression during HF progression by microarray technology in non-infarcted left ventricular (LV) murine tissue at various time points after myocardial infarction (MI). The highest number of regulated genes was found five days after MI. In total, we identified 14 regulated genes encoding cytokines with no previous association to HF. The strongest up-regulation was found for the chemokine fractalkine (CX3CL1). In human failing hearts we detected a 3-fold increase in CX3CL1 protein production, and both cardiomyocytes and fibrous tissue revealed immunoreactivity for CX3CL1 and its specific receptor CX3CR1. We also found that the circulating level of CX3CL1 was increased in patients with chronic HF in accordance with disease severity (1.6-fold in NYHA II, 2.2-fold in NYHA III and 2.9-fold in NYHA IV). In vitro experiments demonstrated that CX3CL1 production could be induced by inflammatory cytokines known to be highly expressed in HF. CX3CL1 itself induced the expression of markers of cardiac hypertrophy and protein phosphatases in neonatal cardiomyocytes. Given the increased CX3CL1 production in both an experimental HF model and in patients with chronic HF as well as its direct effects on cardiomyocytes, we suggest a role for CX3CL1 and its receptor CX3CR1 in the pathogenesis of HF.

The neuropeptide pituitary adenylate cyclase activating polypeptide modulates Ca2+ and pro-inflammatory functions in human monocytes through the G protein-coupled receptors VPAC-1 and formyl peptide receptor-like 1

In human neutrophils, the neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) acting via the G protein-coupled receptors vasoactive intestinal peptide/PACAP receptor 1 (VPAC-1) and formyl peptide receptor-like 1 (FPRL1) modulates Ca2+ and pro-inflammatory activities. We evaluated in human monocytes the importance of the Ca2+ signal and the participation of FPRL1 in PACAP-associated signaling pathways and pro-inflammatory activities. PACAP-evoked Ca2+ transient involved both Ca2+ influx and intracytoplasmic Ca2+ mobilisation. This was pertussis toxin, protein kinase A and adenylate cyclase dependent indicating the participation of Galphai and Galphas with mobilisation of both InsP3 sensitive and insensitive stores. Intra- or extracellular Ca2+ depletion resulted in the inhibition of PACAP-induced, Akt, ERK, p38 and NF-kappaB activations as well as a decrease in PACAP-associated reactive oxygen species (ROS) production and integrin CD11b membrane upregulation. The FPRL1 antagonist, Trp-Arg-Trp-Trp-Trp (WRW4), decreased PACAP-evoked Ca2+ signal, Akt, ERK phosphorylation, ROS and CD11b upregulation without affecting p38 phosphorylation. NF-kappaB inhibitors prevented PACAP-induced Ca2+ mobilisation. Monocytes pre-treatment with fMLP but not with LPS desensitised cells to the pro-inflammatory effects of PACAP. Thus, both intra- and extracellular Ca2+ play a role in controlling pro-inflammatory functions stimulated by PACAP which acts through a VPAC-1, FPRL1/Galphai/PI3K/ERK pathway and a VPAC-1/Galphas/PKA/p38 pathway to fully activate monocytes.

CD16+ monocytes produce IL-6, CCL2, and matrix metalloproteinase-9 upon interaction with CX3CL1-expressing endothelial cells

The CD16+ subset of peripheral blood monocytes (Mo) is expanded dramatically during inflammatory conditions including sepsis, HIV-1 infection, and cancer. CD16+ express high levels of CX3CR1, which mediates arrest onto CX3CL1-expressing endothelial cells (EC) under flow conditions. In contrast, attachment of CD16- Mo onto cytokine-activated EC is independent of CX3CL1. Here, we investigate the ability of CD16+ and CD16- Mo to produce proinflammatory cytokines upon interaction with CX3CL1-expressing HUVEC. We demonstrate that CD16+ but not CD16- Mo produce high levels of IL-6, CCL2, and matrix metalloproteinase (MMP)-9 when cocultured with TNF/IFN-gamma-activated HUVEC or nonactivated HUVEC expressing CX3CL1. Furthermore, supernatants from Mo cocultured with cytokine-activated HUVEC induce neuronal death in vitro. These results suggest that membrane-bound CX3CL1 stimulates production of IL-6, CCL2, and MMP-9 by CD16+ Mo, likely via engagement of CX3CR1. Thus, expansion of CD16+ Mo and their accumulation onto CX3CL1-expressing EC may result in recruitment of Mo and T cell subsets at sites of inflammation in response to CCL2, IL-6-induced cell activation and/or differentiation, and MMP-9-mediated vascular and tissue injury.

Fractalkine is a novel chemoattractant for rheumatoid arthritis fibroblast-like synoviocyte signaling through MAP kinases and Akt

OBJECTIVE

Fibroblast-like synoviocytes (FLS) are a major constituent of the hyperplastic synovial pannus that aggressively invades cartilage and bone during the course of rheumatoid arthritis (RA). Fractalkine (FKN/CX(3)CL1) expression is up-regulated in RA synovium and RA synovial fluid. While RA FLS express the FKN receptor, CX(3)CR1, the pathophysiologic relevance of FKN stimulation of RA FLS is not understood. This study was undertaken to better characterize the relationship between FKN and the RA FLS that both produce it and express its receptor.

METHODS

RA FLS were subjected to chemotaxis and proliferation assays, Western blotting, enzyme-linked immunosorbent assays, and filamentous actin staining to characterize the relationship between FKN and RA FLS.

RESULTS

FKN secretion by RA FLS was regulated mainly by tumor necrosis factor alpha. Stimulation of RA FLS with FKN led to significant cytoskeletal rearrangement but no proliferation. Chemotaxis assays revealed that FKN was a novel chemoattractant for RA FLS. Stimulation of RA FLS with FKN resulted in activation of MAP kinases and Akt. JNK, ERK-1/2, and Akt (at both Ser-473 and Thr-308) were each up-regulated in a time-dependent manner. Inhibition of ERK-1/2-mediated signaling, but not JNK or Akt, significantly repressed FKN-induced RA FLS migration.

CONCLUSION

These findings indicate a novel role of FKN in regulating RA FLS cytoskeletal structure and migration. FKN specifically induces RA FLS phosphorylation of the MAP kinases JNK and ERK-1/2, as well as full activation of Akt.

Chemokine fractalkine/CX3CL1 negatively modulates active glutamatergic synapses in rat hippocampal neurons

We examined the effects of the chemokine fractalkine (CX3CL1) on EPSCs evoked by electrical stimulation of Schaffer collaterals in patch-clamped CA1 pyramidal neurons from rat hippocampal slices. Acute application of CX3CL1 caused a sustained reduction of EPSC amplitude, with partial recovery after washout. CX3CL1-induced EPSC depression is postsynaptic in nature, because paired-pulse ratio was maintained, amplitude distribution of spontaneous excitatory postsynaptic currents shifted to lower values, and whole-cell current responses to AMPA were reversibly inhibited. EPSC depression by CX3CL1 is mediated by CX3CL1 receptor (CX3CR1), because CX3CL1 was unable to influence EPSC amplitude in CA1 pyramidal neurons from CX3CR1 knock-out mice. CX3CL1-induced depression of both EPSC and AMPA current was not observed in the absence of afferent fiber stimulation or AMPA receptor activation, respectively, indicating the requirement of sustained receptor activity for its development. Findings obtained from hippocampal slices, cultured hippocampal neurons, and transfected human embryonic kidney cells indicate that a Ca2+-, cAMP-, and phosphatase-dependent process is likely to modulate CX3CL1 effects because of the following: (1) CX3CL1-induced depression was antagonized by intracellular BAPTA, 8Br-cAMP, phosphatase inhibitors, and pertussis toxin (PTX); (2) CX3CL1 inhibited forskolin-induced cAMP formation sensitive to PTX; and (3) CX3CL1 inhibited forskolin-induced Ser845 GluR1 phosphorylation, which was sensitive to PTX and dependent on Ca2+ and phosphatase activity. Together, these findings indicate that CX3CL1 negatively modulates AMPA receptor function at active glutamatergic synapses through cell-signaling pathways by influencing the balance between kinase and phosphatase activity.

CCL5 evokes calcium signals in microglia through a kinase-, phosphoinositide-, and nucleotide-dependent mechanism

Microglia, the resident macrophages of the CNS, are responsible for the innate immune response in the brain and participate in the pathogenesis of certain neurodegenerative disorders. Chemokines initiate activation and migration of microglia. The beta-chemokine CCL5 induces an elevation in intracellular calcium concentration ([Ca(2+)](i)) in human microglia. Here, we examined the signal transduction pathway linking activation of chemokine receptor CCR5 to an elevation in [Ca(2+)](i) in cultured microglia by using pharmacological approaches in combination with Fura-2-based digital imaging. The CCL5-induced response required Janus kinase (Jak) activity and the stimulation of an inhibitory G protein. Multiple downstream signaling pathways were involved, including phosphatidylinositol 3-kinase (PI3K), Bruton's tyrosine kinase (Btk), and phospholipase C (PLC)-mediated release of Ca(2+) from inositol 1,4,5-trisphosphate (IP(3))-sensitive stores. Activation of both the kinase and the lipase pathways was required for eliciting the Ca(2+) response. However, the majority of the [Ca(2+)](i) increase was derived from sources activated by NAD metabolites. Cyclic ADP-ribose (cADPR) evoked Ca(2+) release from intracellular stores, and ADPR evoked Ca(2+) influx via a nimodipine-sensitive channel. Thus, a multistep cascade couples CCR5 activation to Ca(2+) increases in human microglia. Because changes in [Ca(2+)](i) affect chemotaxis, secretion, and gene expression, pharmacologic modulation of this pathway may alter inflammatory and degenerative processes in the CNS.

Fractalkine stimulates angiogenesis by activating the Raf-1/MEK/ERK- and PI3K/Akt/eNOS-dependent signal pathways

Fractalkine (FKN) has been implicated in modulation of angiogenesis and vascular inflammation, but the underlying mechanism has not been elucidated. We have investigated the molecular mechanism by which FKN regulates angiogenesis. We found that recombinant FKN increases in vitro proliferation, migration, and tube formation of human umbilical vein endothelial cells and stimulates in vivo angiogenesis. FKN-induced angiogenesis was accompanied by phosphorylation of ERK, Akt, and endothelial nitric oxide (NO) synthase (eNOS), as well as an increase in NO production. These biochemical events and angiogenesis were completely inhibited by the G protein-coupled receptor inhibitor pertussis toxin. Inhibitors of Raf-1, MEK, phosphatidylinositol 3-kinase (PI3K), and eNOS or transfection with dominant-negative forms of ERK and Akt significantly suppressed the angiogenic activity of FKN. However, inhibitors of Raf-1 and MEK or a dominant-negative ERK mutant blocked FKN-induced ERK, but not Akt and eNOS, phosphorylation. The PI3K inhibitor and a dominant-negative mutant of Akt suppressed Akt and eNOS phosphorylation and NO production. Our results demonstrated that FKN stimulated angiogenesis by activating the Raf-1/MEK/ERK and PI3K/Akt/eNOS/NO signal pathways via the G protein-coupled receptor CX3CR1, indicating that two pathways are required for full angiogenic activity of FKN. This study suggests that FKN may play an important role in the pathophysiological process of inflammatory angiogenesis.

Fraktalkine produced by airway smooth muscle cells contributes to mast cell recruitment in asthma

Human airway smooth muscle cells (HASMC) secrete fractalkine (FKN), a chemokine the concentration of which is increased in asthmatic patients. HASMC also induce mast cell chemotaxis, as a component of asthma inflammation. We therefore evaluated the role of smooth muscle-derived FKN in mast cell migration. We assessed the capacity of recombinant FKN to induce human mast cell chemotaxis. This effect implicates a calcium-independent pathway involving actin reorganization and protein kinase C-delta. We found that HASMC constitutively produce FKN, the synthesis of which is reinforced upon proinflammatory stimulation. Under basal experimental conditions, FKN production by HASMC is not sufficient to induce mast cell chemotaxis. However, pretreatment of mast cells with the neuropeptide vasoactive intestinal peptide (VIP) increases FKN potency to attract mast cells. Since we observed, in asthmatic patients, an increase in both FKN and VIP expression by airway smooth muscle and a positive correlation between VIP staining and mast cell infiltration of the smooth muscle layer, we conclude that HASMC-derived FKN may contribute to mast cell recruitment in asthma.

G-protein-coupled OX1 orexin/hcrtr-1 hypocretin receptors induce caspase-dependent and -independent cell death through p38 mitogen-/stress-activated protein kinase

We have investigated the signaling of OX(1) receptors to cell death using Chinese hamster ovary cells as a model system. OX(1) receptor stimulation with orexin-A caused a delayed cell death independently of cytosolic Ca(2+) elevation. The classical mitogen-activated protein kinase (MAPK) pathways, ERK and p38, were strongly activated by orexin-A. p38 was essential for induction of cell death, whereas the ERK pathway appeared protective. A pathway often implicated in the p38-mediated cell death, activation of p53, did not mediate the cell death, as there was no stabilization of p53 or increase in p53-dependent transcriptional activity, and dominant-negative p53 constructs did not inhibit cell demise. Under basal conditions, orexin-A-induced cell death was associated with compact chromatin condensation and it required de novo gene transcription and protein synthesis, the classical hallmarks of programmed (apoptotic) cell death. However, though the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-(O-methyl)fluoromethyl ketone (Z-VAD-fmk) fully inhibited the caspase activity, it did not rescue the cells from orexin-A-induced death. In the presence of Z-VAD-fmk, orexin-A-induced cell death was still dependent on p38 and de novo protein synthesis, but it no longer required gene transcription. Thus, caspase inhibition causes activation of alternative, gene transcription-independent death pathway. In summary, the present study points out mechanisms for orexin receptor-mediated cell death and adds to our general understanding of the role of G-protein-coupled receptor signaling in cell death by suggesting a pathway from G-protein-coupled receptors to cell death via p38 mitogen-/stress-activated protein kinase independent of p53 and caspase activation.

Proline 326 in the C terminus of murine CX3CR1 prevents G-protein and phosphatidylinositol 3-kinase-dependent stimulation of Akt and extracellular signal-regulated kinase in Chinese hamster ovary cells

Naturally occurring single nucleotide polymorphisms have been identified in human CX3CR1, the chemokine receptor for fractalkine (FKN/CX3CL1). Individuals carrying the I249/M280 variant of CX3CR1 have a lower risk of cardiovascular disease compared with those homozygous for the common variant (V249/T280). The precise molecular basis for this phenotype is unclear, although differences in FKN binding, adhesive properties, and signaling efficiency between the CX3CR1 variants have been reported. FKN binding to CX3CR1 leads to an increase in intracellular calcium, actin rearrangement, and activation of the mitogen-activated protein kinase and phosphoinositide 3-kinase (PI3K) pathways. Regulation of these signaling pathways underlies the known roles for FKN in cell survival, proliferation, and migration. In the present study, we demonstrate that FKN stimulates phosphorylation of protein kinase B (Akt/PKB) in Chinese hamster ovary cells individually expressing the naturally occurring variants of human CX3CR1-, as well as rat CX3CR1-, but not in murine CX3CR1-expressing cells. Substitution of Pro326 in the C terminus of murine CX3CR1 with Ser (residue found in the analogous position of human CX3CR1) produced a mutant receptor that mimicked the human receptor in its ability to stimulate the phosphorylation of both Akt and extracellular signal-regulated kinase in a time-, PI3K-, and pertussis toxin-sensitive G-protein-dependent manner. These results identify a critical structural determinant of CX3CR1 important for activation of downstream signaling pathways.

Fractalkine reduces N-methyl-d-aspartate-induced calcium flux and apoptosis in human neurons through extracellular signal-regulated kinase activation

Our purpose was to investigate in human neurons the neuroprotective pathways induced by Fractalkine (FKN) against glutamate receptor-induced excitotoxicity. CX(3)CR1 and FKN are expressed constitutively in the tested human embryonic primary neurons and SK-N-SH, a human neuroblastoma cell line. Microfluorometry assay demonstrated that CX(3)CR1 was functional in 44% of primary neurons and in 70% of SK-N-SH. Fractalkine induced ERK1/2 phosphorylation within 1 min and Akt phosphorylation after 10 min, and both phosphorylation decreased after 20 min. No p38 and SAPK/JNK activation was observed after FKN treatment. Application of FKN triggered a 53% reduction of the NMDA-induced neuronal calcium influx, which was insensitive to pertussis toxin and LY294002 an inhibitor of Akt pathway, but abolished by PD98059, an ERK1/2 pathway inhibitor. Moreover, FKN significantly reduced neuronal NMDA-induced apoptosis, which was pertussis toxin insensitive and abolished in presence of PD98059 and LY294002. In conclusion, FKN protected human neurons from NMDA-mediated excitotoxicity in at least two ways with different kinetics: (i) an early ERK1/2 activation which reduced NMDA-mediated calcium flux; and (ii), a late Akt activation associated with the previously induced ERK1/2 activation.

Viral Macrophage Inflammatory Protein-II and Fractalkine (CX3CL1) Chimeras Identify Molecular Determinants of Affinity, Efficacy, and Selectivity at CX3CR1

Fractalkine (FKN/CX3CL1) is a cell surface-expressed chemokine involved in many aspects of leukocyte trafficking and activation. The various structural domains of FKN play distinct roles in its ability to bind and activate its receptor, CX3CR1. A human herpesvirus 8-encoded chemokine, termed viral macrophage inflammatory protein (vMIP)-II, is structurally similar to FKN; vMIP-II is a nonselective chemokine receptor antagonist (binding multiple chemokine receptors, including CX3CR1). The goal of this study was to identify FKN determinants of selectivity for its receptor and to further refine domains important in affinity and efficacy at CX3CR1. Chimeric and insertional mutagenesis was used to generate mutants of both vMIP-II and FKN, and the expressed proteins were evaluated for chemokine receptor binding affinities and efficacy at CX3CR1. Modification of the intervening amino acids between the first two conserved cysteine residues of FKN or vMIP-II indicated a role of the X3 bulge of FKN in affinity and selectivity for CX3CR1. Substitution of the vMIP-II N terminus with that of FKN created an agonist that was just as potent and efficacious as FKN for binding and stimulating CX3CR1, whereas replacement of the FKN N terminus with the cognate domain of vMIP-II disrupted the ability of FKN to bind CX3CR1. Furthermore, the entire N terminus of FKN was necessary for the high-affinity and full agonist properties of FKN at CX3CR1. These results refine the pharmacophore for chemokine binding to and activation of CX3CR1 and demonstrate the usefulness of modified virally encoded chemokines as templates for the development of selective chemokine receptor antagonists.

Prostaglandin E2 inhibits the phospholipase D pathway stimulated by formyl-methionyl-leucyl-phenylalanine in human neutrophils. Involvement of EP2 receptors and phosphatidylinositol 3-kinase gamma

Prostaglandin E(2) (PGE(2)), originally discovered as a pro-inflammatory mediator, also inhibits several chemoattractant-elicited neutrophil functions, including adhesion, secretion of cytotoxic enzymes, production of superoxide anions, and chemotaxis. In this study, we have examined the effects of PGE(2) and prostaglandin E (EP) receptor-selective agonists/antagonists on several steps of the formyl-methionyl-leucyl-phenylalanine (fMLP)-induced phospholipase D (PLD) activation pathway in human neutrophils to elucidate the PGE(2) inhibitory mechanism. PGE(2) and EP(2) receptor agonists inhibited the stimulation of the activity of PLD induced by fMLP in a concentration-dependent manner. The fMLP-stimulated translocation to membranes of protein kinase C alpha, Rho, and Arf GTPases was diminished in the presence of PGE(2) or EP(2) agonists. Moreover, PGE(2) and EP(2) agonists decreased the activation of phosphatidylinositol 3-kinase gamma (PI3Kgamma) and Tec kinases as well as the tyrosine phosphorylation of proteins stimulated by fMLP. These data provide strong evidence that 1) the inhibitory effects of PGE(2) on the fMLP-induced PLD activation pathway were mediated via EP(2) receptors and that 2) the suppression of PI3Kgamma activity was the crucial step in the EP(2)-mediated inhibition of the fMLP-induced signaling cascade.

Molecular analysis of metastasis in a polyomavirus middle T mouse model: the role of osteopontin

INTRODUCTION

In order to study metastatic disease, we employed the use of two related polyomavirus middle T transgenic mouse tumor transplant models of mammary carcinoma (termed Met and Db) that display significant differences in metastatic potential.

METHODS

Through suppression subtractive hybridization coupled to the microarray, we found osteopontin (OPN) to be a highly expressed gene in the tumors of the metastatic mouse model, and a lowly expressed gene in the tumors of the lowly metastatic mouse model. We further analyzed the role of OPN in this model by examining sense and antisense constructs using in vitro and in vivo methods.

RESULTS

With in vivo metastasis assays, the antisense Met cells showed no metastatic tumor formation to the lungs of recipient mice, while wild-type Met cells, with higher levels of OPN, showed significant amounts of metastasis. The Db cells showed a significantly reduced metastasis rate in the in vivo metastasis assay as compared with the Met cells. Db cells with enforced overexpression of OPN showed elevated levels of OPN but did not demonstrate an increase in the rate of metastasis compared with the wild-type Db cells.

CONCLUSIONS

We conclude that OPN is an essential regulator of the metastatic phenotype seen in polyomavirus middle T-induced mammary tumors. Yet OPN expression alone is not sufficient to cause metastasis. These data suggest a link between metastasis and phosphatidylinositol-3-kinase-mediated transcriptional upregulation of OPN, but additional phosphatidylinositol-3-kinase-regulated genes may be essential in precipitating the metastasis phenotype in the polyomavirus middle T model.

Phosphatidylinositide 3-kinase gamma regulates key pathologic responses to cholecystokinin in pancreatic acinar cells

BACKGROUND & AIMS

Early events in the pancreatic acinar cell critical for development of pancreatitis include activation of the transcription factor nuclear factor kappa B (NF-kappa B), abnormal Ca(2+) responses, and trypsinogen activation. Mechanisms underlying these responses, which can be studied in isolated pancreatic acini stimulated with supraphysiologic doses of cholecystokinin (CCK-8), remain poorly understood. We here report that these responses are regulated by phosphatidylinositide 3-kinase (PI3K) gamma.

METHODS

To inactivate PI3K, we used mice deficient in the catalytic PI3K gamma subunit p110 gamma as well as the PI3K inhibitors LY294002 and wortmannin. We measured Ca(2+) responses by using Fura-2, NF-kappa B-binding activity by electromobility shift assay, I kappa B degradation by Western blotting, and trypsinogen activation by fluorogenic assay.

RESULTS

CCK-induced intracellular Ca(2+) mobilization, Ca(2+) influx, trypsinogen, and NF-kappa B activation were all diminished in pancreatic acini isolated from p110 gamma(-/-) mice. Both in mouse and rat acini, these responses were inhibited by the PI3K inhibitors. The Ca(2+) signal and trypsinogen activation were similarly reduced in acini isolated from p110 gamma(-/-) and p110 gamma(+/-) mice compared with wild-type mice. By contrast, NF-kappa B activation was inhibited in p110 gamma(-/-) acini but not in p110 gamma(+/-) acini. These differences indicate that the mechanism of NF-kappa B regulation by PI3K gamma differs from those for the Ca(2+) and trypsinogen responses. CCK-induced responses in p110 gamma(-/-) acini were all further inhibited by LY294002, indicating the involvement of other PI3K isoform(s), in addition to PI3K gamma.

CONCLUSIONS

The results show that key pathologic responses of the pancreatic acinar cell are regulated by PI3K gamma and suggest an important role for this PI3K isoform in pancreatitis.

Transient phosphatidylinositol 3-kinase inhibition protects immature primary cortical neurons from oxidative toxicity via suppression of extracellular signal-regulated kinase activation

Oxidative stress has been shown to underlie a diverse range of neuropathological conditions. Glutamate-induced oxidative toxicity is a well described model of oxidative stress-induced neurodegeneration that relies upon the ability of extracellular glutamate to inhibit a glutamate/cystine antiporter, which results in a depletion of intracellular cysteine and the blockade of continued glutathione synthesis. Glutathione depletion leads to a gradual toxic accumulation of reactive oxygen species. We have previously determined that glutamate-induced oxidative toxicity is accompanied by a robust increase in activation of the mitogen-activated protein kinase (MAPK) member extracellular-signal regulated kinase (ERK) and that this activation is essential for neuronal cell death. This study demonstrates that delayed ERK activation is dependent upon the activity of phosphoinositol-3 kinase (PI3K) and that transient but not sustained PI3K inhibition leads to significant protection of neurons from oxidative stress-induced neurodegeneration. Furthermore, we show that transient PI3K inhibition prevents the delayed activation of MEK-1, a direct activator of ERK, during oxidative stress. Thus, this study is the first to demonstrate a novel level of cross-talk between the PI3K and ERK pathways in cultured immature cortical neuronal cultures that contributes to the unfolding of a cell death program. The PI3K pathway, therefore, may serve opposing roles during the progression of oxidative stress in neurons, acting at distinct kinetic phases to either promote or limit a slowly developing program of cell death.

CX3CL1 and CX3CR1 expression in human brain tissue: noninflammatory control versus multiple sclerosis

An important role for CX3CL1 in neuroinflammation and neurodegeneration has been suggested in recent publications. In this study, we compared the expression of CX3CL1 and its receptor CX3CR1 in human brain tissue derived from control patients without neurological complications and in multiple sclerosis (MS) patients. Results from this study demonstrate that CX3CL1 is constitutively expressed in human central nervous system (CNS) astrocytes in vivo and under basal conditions in human adult astrocyte cultures. CX3CR1 is expressed on astrocytes and microglial cells both in vivo and in vitro. Chemotaxis assay shows a functional response upon CX3CR1 signaling in microglial cells. Although CX3CL1 expression is upregulated in cultured astrocytes in response to proinflammatory cytokines, no evidence for expression differences of CX3CL1 between control patients and MS patients was found. Our data suggest that CX3CL1 has more general physiological functions, which occur also in the absence of proinflammatory conditions.

Calcium receptor-induced serotonin secretion by parafollicular cells: role of phosphatidylinositol 3-kinase-dependent signal transduction pathways

Elevation of extracellular Ca2+ (increase[Ca2+]e) stimulates the Ca2+ receptor (CaR) to induce secretion of 5-hydroxytryptamine (5-HT) from the calcium-sensing parafollicular (PF) cells. The CaR has been reported to couple to Galpha(q) with subsequent activation of protein kinase C-gamma (PKCgamma). We have identified a parallel transduction pathway in primary cultures of sheep PF cells by using a combinatorial approach in which we expressed adenoviral-encoded dominant-negative signaling proteins and performed in vitro kinase assays. The role of the CaR was established by expression of a dominant-negative CaR that eliminated calcium-induced 5-HT secretion but not secretion in response to KCl or phorbol esters. The calcium-induced secretion was inhibited by a dominant-negative p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3-K). PI3-K activity was also assayed using isoform-specific antibodies. The activity of p85/p110beta (PI3-Kbeta) immunocomplexes was elevated by increase[Ca2+]e and activated by Gbetagamma subunits. In addition, secretion of 5-HT was antagonized by the expression of a minigene encoding a peptide scavenger of Gbetagamma subunits (C-terminal fragment peptide of bovine beta-adrenergic receptor kinase). One target of PI3-K activity is phosphoinositide-dependent kinase-1 (PDK1), which in turn activated PKCzeta. Expression of a dominant-negative PKCzeta in PF cells reduced 5-HT secretion. Together, these observations establish that increase[Ca2+]e evokes 5-HT secretion from PF cells by stimulating both Galpha(q)- and Gbetagamma-signaling pathways downstream of the CaR. The betagamma cascade subsequently activates PI3-Kbeta-dependent signaling that is coupled to PDK1 and the downstream effector PKCzeta, and results in an increase in 5-HT release.

Alpha 2 adrenoceptor-mediated vasoconstriction in porcine palmar lateral vein: role of phosphatidylinositol 3-kinase and EGF receptor transactivation

1 Alpha(2) adrenoceptors cause vasoconstriction in the porcine palmar lateral vein through a mechanism involving the ERK signal transduction cascade, calcium influx, and a Src tyrosine kinase. The aim of the present study was to determine if phosphatidylinositol 3-kinase (PI 3-kinase) and/or epidermal growth factor (EGF) receptor transactivation are also involved. 2 alpha(2) Adrenoceptor-mediated vasoconstriction and ERK2 activation in the porcine palmar lateral vein was inhibited in the presence of either the PI 3-kinase inhibitor LY294002, or the EGF receptor tyrosine kinase inhibitor AG1478 suggesting the involvement of both PI 3-kinase and EGF receptor transactivation. 3 Akt phosphorylation was increased in segments of porcine palmar lateral vein contracted with UK14304 indicating an increase in Akt activation. This is a further indication that PI 3-kinase is involved in alpha(2) adrenoceptor-mediated vasoconstriction. Akt activation was inhibited by the Src tyrosine kinase inhibitor PP2, and removal of extracellular calcium. 4 UK14304 (10 microM) stimulated an increase in intracellular calcium in segments of palmar lateral vein. This was inhibited by removal of extracellular calcium, but not by nifedipine suggesting the rise in calcium is due to influx of calcium through non-L type calcium channels. The increase in calcium was also inhibited by LY294002 indicating that PI 3-kinase is upstream of calcium influx. 5 These data indicate that alpha(2) adrenoceptor-mediated vasoconstriction in the porcine palmar lateral vein is dependent upon stimulation of PI 3-kinase, leading to an influx of calcium. This results in activation of the EGF receptor tyrosine kinase, and finally activation of ERK-MAP kinase.

Adhesion, migration, transcriptional, interferon-inducible, and other signaling molecules newly implicated in cancer susceptibility and resistance of JB6 cells by cDNA microarray analyses

Relative expression levels of 9500 genes were determined by cDNA microarray analyses in mouse skin JB6 cells susceptible (P+) and resistant (P-) to 12-O-tetradecanoyl phorbol-13 acetate (TPA)-induced neoplastic transformation. Seventy-four genes in 6 functional classes were differentially expressed: (I) extracellular matrix (ECM) and basement membrane (BM) proteins (20 genes). P+ cells express higher levels than P- cells of several collagens and proteases, and lower levels of protease inhibitors. Multiple genes encoding adhesion molecules are expressed preferentially in P- cells, including six genes implicated in axon guidance and adhesion. (II) Cytoskeletal proteins (13 genes). These include actin isoforms and regulatory proteins, almost all preferentially expressed in P- cells. (III) Signal transduction proteins (12 genes). Among these are Ras-GTPase activating protein (Ras-GAP), the deleted in oral cancer-1 and SLIT2 tumor suppressors, and connexin 43 (Cx43) gap junctional protein, all expressed preferentially in P- cells. (IV) Interferon-inducible proteins (3 genes). These include interferon-inducible protein (IFI)-16, an Sp1 transcriptional regulator expressed preferentially in P- cells. (V) Other transcription factors (4 genes). Paired related homeobox gene 2 (Prx2)/S8 homeobox, and retinoic acid (RA)-regulated nur77 and cellular retinoic acid-binding protein II (CRABPII) transcription factors are expressed preferentially in P- cells. The RIN-ZF Sp-transcriptional suppressor exhibits preferential P+ expression. (VI) Genes of unknown functions (22 sequences). Numerous mesenchymal markers are expressed in both cell types. Data for multiple genes were confirmed by real-time PCR. Overall, 26 genes were newly implicated in cancer. Detailed analyses of the functions of the genes and their interrelationships provided converging evidence for their possible roles in implementing genetic programs mediating cancer susceptibility and resistance. These results, in conjunction with cell wounding and phalloidin staining data, indicated that concerted genetic programs were implemented that were conducive to cell adhesion and tumor suppression in P- cells and that favored matrix turnover, cell motility, and abrogation of tumor suppression in P+ cells. Such genetic programs may in part be orchestrated by Sp-, RA-, and Hox-transcriptional regulatory pathways implicated in this study.

Fractalkine (CX3CL1) and brain inflammation: Implications for HIV-1-associated dementia

Leukocyte migration and activation play an important role in immune surveillance and the pathogenesis of a variety of neurodegenerative disorders, including human immunodeficiency virus (HIV)-1-associated dementia (HAD). A novel chemokine named fractalkine (FKN, CX3CL1), which exists in both membrane-anchored and soluble isoforms, has been proposed to participate in the generation and progression of inflammatory brain disorders. Upon binding to the CX3C receptor one (CX3CR1), FKN induces adhesion, chemoattraction, and activation of leukocytes, including brain macrophages and microglia (MP). Constitutively expressed in the central nervous system (CNS), mainly by neurons, FKN is up-regulated and released in response to proinflammatory stimuli. Importantly, FKN is up-regulated in the brain tissue and cerebrospinal fluid (CSF) of HAD patients. Together, these observations suggest that FKN and its receptor have a unique role in regulating the neuroinflammatory events underlying disease. This review will examine how FKN contributes to the recruitment and activation of CX3CR1-expressing MP, which are critical events in the neuropathogenesis of HAD.