Actin filaments are involved in the regulation of trafficking of two closely related chemokine receptors, CXCR1 and CXCR2

Pseudonormal Morphology of Salivary Gland Adenoid Cystic Carcinoma Cells Subverts the Antitumor Reactivity of Immune Cells: A Tumour-Cell-Based Initiation of Immune Evasion

INTRODUCTION

Salivary gland adenoid cystic carcinoma (ACC), mucoepidermoid carcinoma (MEC) and oral squamous cell carcinoma (OSCC) occurs within the head and neck region. So far immune check point inhibitors failed in ACC. Gipie (CCDC88B) is a microtubule linker protein that activates immune cells. Gipie expressions found in head and neck cancer cells. We hypothesised that the presence of Gipie diminishes anti-tumour reactivity of immune cells towards head and neck cancer.

METHOD

To determine the effect of Gipie in oral and salivary gland cancer cells, Gipie was silenced in cancer cells in cancer-immune cells co-culture models and we performed 3D Z series confocal imaging, annexin V and immune activation flow cytometry, proteome profiler and discovery phase proteomics.

RESULTS

ACC cells morphed into pseudonormal morphology in immune co-culture models. Silencing Gipie in ACC cells showed significant increase of apoptotic cells and activated natural killer cells, and lowering of regulatory T cells. Other salivary and oral cancer cells showed negligible effect of Gipie. Proteome profiler and proteomics assay confirmed Gipie affecting proliferation mechanism and immune activated proteins in ACC immune co-culture models.

CONCLUSION

Overall, we conclude that the presence of Gipie has a confounding role during the ACC-immune cell interaction.

Autoantibodies against chemokines post-SARS-CoV-2 infection correlate with disease course

Infection with severe acute respiratory syndrome coronavirus 2 associates with diverse symptoms, which can persist for months. While antiviral antibodies are protective, those targeting interferons and other immune factors are associated with adverse coronavirus disease 2019 (COVID-19) outcomes. Here we discovered that antibodies against specific chemokines were omnipresent post-COVID-19, were associated with favorable disease outcome and negatively correlated with the development of long COVID at 1 yr post-infection. Chemokine antibodies were also present in HIV-1 infection and autoimmune disorders, but they targeted different chemokines compared with COVID-19. Monoclonal antibodies derived from COVID-19 convalescents that bound to the chemokine N-loop impaired cell migration. Given the role of chemokines in orchestrating immune cell trafficking, naturally arising chemokine antibodies may modulate the inflammatory response and thus bear therapeutic potential.

Actin dynamics in protein homeostasis

Cell homeostasis is maintained in all organisms by the constant adjustment of cell constituents and organisation to account for environmental context. Fine-tuning of the optimal balance of proteins for the conditions, or protein homeostasis, is critical to maintaining cell homeostasis. Actin, a major constituent of the cytoskeleton, forms many different structures which are acutely sensitive to the cell environment. Furthermore, actin structures interact with and are critically important for the function and regulation of multiple factors involved with mRNA and protein production and degradation, and protein regulation. Altogether, actin is a key, if often overlooked, regulator of protein homeostasis across eukaryotes. In this review, we highlight these roles and how they are altered following cell stress, from mRNA transcription to protein degradation.

Chemokines in Type 1 Diabetes Mellitus

BACKGROUND

Previous studies suggested that chemokines may play an important role in the formation and mediation of immune microenvironments of patients affected by Type 1 Diabetes Mellitus (T1DM). The aim of this study was to summarise available evidence on the associations of different chemokines with T1DM.

METHODS

Following PRISMA guidelines, we systematically searched in PubMed, Web of Science, Embase and Cochrane Library databases for studies on the associations of different chemokines with T1DM. The effect size of the associations were the standardized mean differences (SMDs) with corresponding 95% confidence intervals (CIs) of the chemokines concentrations, calculated as group differences between the T1DM patients and the controls. These were summarized using network meta-analysis, which was also used to rank the chemokines by surface under cumulative ranking curve (SUCRA) probabilities.

RESULTS

A total of 32 original studies on the association of different chemokines with T1DM were identified. Fifteen different chemokine nodes were compared between 15,683 T1DM patients and 15,128 controls, and 6 different chemokine receptor nodes were compared between 463 T1DM patients and 460 controls. Circulating samples (blood, serum, and plasma) showed that concentrations of CCL5 and CXCL1 were significantly higher in the T1DM patients than in the controls (SMD of 3.13 and 1.50, respectively). On the other hand, no significant difference in chemokine receptors between T1DM and controls was observed. SUCRA probabilities showed that circulating CCL5 had the highest rank in T1DM among all the chemokines investigated.

CONCLUSION

The results suggest that circulating CCL5 and CXCL1 may be promising novel biomarkers of T1DM. Future research should attempt to replicate these findings in longitudinal studies and explore potential mechanisms underlying this association.

CXCL1 activates TRPV1 via Gi/o protein and actin filaments

AIMS

CXCL1 is a chemokine with pleiotropic effects, including pain and itch. Itch, an unpleasant sensation that elicits the desire or reflex to scratch, it is evoked mainly from the skin and implicates activation of a specific subset of IB4+, C-type primary afferents. In previous studies we showed that acute application of CXCL1 induced a Ca²⁺ influx of low amplitude and slow kinetics in a subpopulation of transient receptor potential vanilloid type 1 (TRPV1)+/isolectin B4 (IB4)+dorsal root ganglia neurons which also responded to other itch-inducing agents. In this study we explored the mechanism behind the Ca²⁺ influx to better understand how CXCL1 acts on primary sensitive neurons to induce itch.

MATERIALS AND METHODS

Intracellular Ca²⁺ imaging and patch-clamp recordings on dorsal root ganglia neurons primary cultures and HEK293T cell transiently transfected with TRPV1 and CXCR2 plasmids were used to investigate the acute effect (12min application) of 4nM CXCL1. In primary cultures, the focus was on TRPV1+/IB4+ cells to which the itch-sensitive neurons belong.

KEY FINDINGS

The results showed that the Ca²⁺ influx induced by the acute application of CXCL1 is mediated mainly by TRPV1 receptors and depends on extracellular Ca²⁺ not on intracellular stores. TRPV1 was activated, not sensitized by CXCL1, in a CXCR2 receptors- and actin filaments-dependent manner, since specific blockers and actin depolymerizing agents disrupted the CXCL1 effect.

SIGNIFICANCE

This study brings additional data about the itch inducing mechanism of CXCL1 chemokine and about a new mechanism of TRPV1 activation via actin filaments.

The CXCR1/2 Pathway: Involvement in Diabetes Pathophysiology and Potential Target for T1D Interventions

Although numerous chemokine/chemokine receptor pathways have been described to be implicated in the pathogenesis of type 1 diabetes (T1D), the CXCR1/2 axis has recently been proved to be crucial for leucocyte recruitment involved in insulitis and β cell damage. Multiple strategies blocking the CXCR1/2 pathway are available such as neutralizing antibodies, small molecules and peptide-derived inhibitors. They were firstly and widely used in cancer thanks to their anti-tumorigenic activity and only recently they were tested as a new interventional approach for T1D. As well, CXCR1/2 inhibition has been demonstrated to prevent inflammation- and autoimmunity-mediated damage of the pancreatic islets through inhibiting the migration of CXCR1/2-expressing cells. Among them, neutrophils, macrophages, and, although to a smaller extent, lymphoid cells are the main CXCR1/2-expressing cells. These results supported the active role of the innate immunity in the autoimmune process and opened new interventional approaches for the management of T1D.

Regulation of CXCR2 expression and function by a disintegrin and metalloprotease-17 (ADAM17)

The chemokine receptor CXCR2 is expressed at high levels on circulating neutrophils and is critical for directing their migration to sites of inflammation. CXCR2 surface levels are rapidly modulated by 2 mechanisms-cell internalization and recycling upon ligand binding-and by a metalloprotease activity following overt neutrophil activation by nonligand stimuli. The latter process has only been described in human neutrophils, and essentially, nothing is known about its functional relevance and the specific protease involved. We show that targeting ADAM17 in mouse and human neutrophils blocks CXCR2 down-regulation induced by nonligand stimuli but not by chemokine ligands. This was determined by use of a selective ADAM17 inhibitor, an ADAM17 function-blocking antibody, and ADAM17 gene-targeted mice. CXCR2 is known to undergo a marked down-regulation during various inflammatory disorders, and this is associated with impaired neutrophil recruitment. We show that blocking ADAM17 activity reduced CXCR2 down-regulation on circulating neutrophils and enhanced their recruitment during acute inflammation, which was reversed by a CXCR2 inhibitor. Taken together, our findings demonstrate that unlike CXCR2 internalization, ADAM17 induction down-regulates the receptor in an irreversible manner and may serve as a master switch in controlling CXCR2 function, but may also contribute to neutrophil dysfunction during excessive inflammation.

The histamine H4 receptor is a potent inhibitor of adhesion-dependent degranulation in human neutrophils

The histamine H4 receptor regulates the inflammatory response. However, it is not known whether this receptor has a functional role in human neutrophils. We found that fMLP (1 μM), but not histamine (0.1-1 μM), induced Mac-1-dependent adhesion, polarization, and degranulation (release of lactoferrin). A pretreatment of neutrophils with histamine (0.001-1 μM) or JNJ 28610244 (0.1-10 μM), a specific H4 receptor agonist, led to inhibition of degranulation. Total inhibition of degranulation was obtained with 0.1 μM histamine and 10 μM JNJ 28610244. Furthermore, such inhibition by histamine of degranulation was reversed by JNJ 7777120 and JNJ 28307474, two selective H4 receptor antagonists. However, neither histamine nor the H4 receptor agonist JNJ 28610244 prevented fMLP-induced, Mac-1-dependent adhesion, indicating that the H4 receptor may block signals emanating from Mac-1-controlling degranulation. Likewise, engagement of the H4 receptor by the selective agonist JNJ 28610244 blocked Mac-1-dependent activation of p38 MAPK, the kinase that controls neutrophil degranulation. We also show expression of the H4 receptor at the mRNA level in ultrapure human neutrophils and myeloid leukemia PLB-985 cells. We concluded that engagement of this receptor by selective H4 receptor agonists may represent a good, therapeutic approach to accelerate resolution of inflammation.

Epithelial Cells Secrete Interleukin-8 in Response to Adhesion and Invasion of Diffusely AdheringEscherichia coliLacking Afa/Dr Genes

Escherichia coli that sparsely adhere to human epithelial cells are known as diffusely adherent E. coli (DAEC), and the role of the Afa/Dr family of adhesins is now understood. Strains that do not possess Afa/Dr, however, comprise another group of DAEC, of which the pathogenicity remains unknown. The ability to induce interleukin-8 (IL-8) secretion from intestinal epithelial cells might be a feature of enterovirulent bacteria. We previously found that some Afa/Dr DAEC strains induce IL-8 by stimulating epithelial cells with flagella. The present study examines whether non-Afa/Dr DAEC can induce IL-8 in epithelial cells (HEp-2, INT407, and T84). Among 21 strains, 11 (52%; 11/21) induced as much IL-8 as high inducer strains of Afa/Dr DAEC. Adhesion did not significantly differ between high and low inducers; therefore diffuse adhesion alone is probably insufficient to induce IL-8. It was shown that IL-8 induction and the number of intracellular bacteria directly correlated. Wortmannin, an inhibitor of the phosphatidylinositol-3-phosphate kinase, reduced both intracellular bacteria and IL-8 secretion. Motile strains were significantly more prevalent among high (10/11) than low (4/10) inducers. However, 4 low invasive strains hardly induced IL-8 despite their motility. In conclusion, some non-Afa/Dr DAEC invoke the induction of high levels of inflammatory cytokines. Unlike Afa/Dr DAEC, however, non-Afa/Dr strains may require invasion to cause strong induction. These non-Afa/Dr high inducers can be enteropathogenic for the cytokine-inducing properties.

Rationale and Means to Target Pro-Inflammatory Interleukin-8 (CXCL8) Signaling in Cancer

It is well established that chronic inflammation underpins the development of a number of human cancers, with pro-inflammatory signaling within the tumor microenvironment contributing to tumor progression and metastasis. CXCL8 is an ELR⁺ pro-inflammatory CXC-chemokine which mediates its effects via signaling through two G protein-coupled receptors, CXCR1 and CXCR2. Elevated CXCL8-CXCR1/2 signaling within the tumor microenvironment of numerous cancers is known to enhance tumor progression via activation of signaling pathways promoting proliferation, angiogenesis, migration, invasion and cell survival. This review provides an overview of established roles of CXCL8-CXCR1/2 signaling in cancer and subsequently, discusses the possible strategies of targeting CXCL8-CXCR1/2 signaling in cancer, covering indirect strategies (e.g., anti-inflammatories, NFκB inhibitors) and direct CXCL8 or CXCR1/2 inhibition (e.g., neutralizing antibodies, small molecule receptor antagonists, pepducin inhibitors and siRNA strategies). Reports of pre-clinical cancer studies and clinical trials using CXCL8-CXCR1/2-targeting strategies for the treatment of inflammatory diseases will be discussed. The future translational opportunities for use of such agents in oncology will be discussed, with emphasis on exploitation in stratified populations.

Inhibitory effects of cytoskeleton disrupting drugs and GDP-locked Rab mutants on bradykinin B₂ receptor cycling

The bradykinin (BK) B₂ receptor (B₂R) is G protein coupled and phosphorylated upon agonist stimulation; its endocytosis and recycling are documented. We assessed the effect of drugs that affect the cytoskeleton on B2R cycling. These drugs were targeted to tubulin (paclitaxel, or the novel combretastatin A-4 mimetic 3,4,5-trimethoxyphenyl-4-(2-oxoimidazolidin-1-yl)benzenesulfonate [IMZ-602]) and actin (cytochalasin D). Tubulin ligands did not alter agonist-induced receptor endocytosis, as shown using antibodies reactive with myc-tagged B₂Rs (microscopy, cytofluorometry), but rather reduced the progression of the ligand-receptor-β-arrestin complex from the cell periphery to the interior. The 3 fluorescent probes of this complex (B2R-green fluorescent protein [B2R-GFP], the fluorescent agonist fluorescein-5-thiocarbamoyl-D-Arg-[Hyp³, Igl⁵, Oic⁷, Igl⁸]-BK and β-arrestin2-GFP) were condensed in punctuate structures that remained close to the cell surface in the presence of IMZ-602. Cytochalasin D selectively inhibited the recycling of endocytosed B₂R-GFP (B₂R-GFP imaging, [³H]BK binding). Dominant negative (GDP-locked)-Rab5 and -Rab11 reproduced the effects of inhibitors of tubulin and actin, respectively, on the cycling of B₂R-GFP. GDP-locked-Rab4 also inhibited B₂R-GFP recycling to the cell surface. Consistent with the displacement of cargo along specific cytoskeletal elements, Rab5-associated progression of the endocytosed BK B₂R follows microtubules toward their (-) end, while its recycling progresses along actin fibers to the cell surface. However, tubulin ligands do not suppress the tested desensitization or resensitization mechanisms of the B₂R.

Interleukin-8 (IL-8) over-production and autocrine cell activation are key factors in monomethylarsonous acid [MMA(III)]-induced malignant transformation of urothelial cells

The association between chronic human exposure to arsenicals and bladder cancer development is well recognized; however, the underlying molecular mechanisms have not been fully determined. We propose that inflammatory responses can play a pathogenic role in arsenic-related bladder carcinogenesis. In previous studies, it was demonstrated that chronic exposure to 50 nM monomethylarsenous acid [MMA(III)] leads to malignant transformation of an immortalized model of urothelial cells (UROtsa), with only 3 mo of exposure necessary to trigger the transformation-related changes. In the three-month window of exposure, the cells over-expressed pro-inflammatory cytokines (IL-1β, IL-6 and IL-8), consistent with the sustained activation of NFKβ and AP1/c-jun, ERK2, and STAT3. IL-8 was over-expressed within hours after exposure to MMA(III), and sustained over-expression was observed during chronic exposure. In this study, we profiled IL-8 expression in UROtsa cells exposed to 50 nM MMA(III) for 1 to 5 mo. IL-8 expression was increased mainly in cells after 3 mo MMA(III) exposure, and its production was also found increased in tumors derived from these cells after heterotransplantation in SCID mice. UROtsa cells do express both receptors, CXCR1 and CXCR2, suggesting that autocrine cell activation could be important in cell transformation. Supporting this observation and consistent with IL-8 over-expression, CXCR1 internalization was significantly increased after three months of exposure to MMA(III). The expression of MMP-9, cyclin D1, bcl-2, and VGEF was significantly increased in cells exposed to MMA(III) for 3 mo, but these mitogen-activated kinases were significantly decreased after IL-8 gene silencing, together with a decrease in cell proliferation rate and in anchorage-independent colony formation. These results suggest a relevant role of IL-8 in MMA(III)-induced UROtsa cell transformation.

Myeloperoxidase attracts neutrophils by physical forces

Recruitment of polymorphonuclear neutrophils (PMNs) remains a paramount prerequisite in innate immune defense and a critical cofounder in inflammatory vascular disease. Neutrophil recruitment comprises a cascade of concerted events allowing for capture, adhesion and extravasation of the leukocyte. Whereas PMN rolling, binding, and diapedesis are well characterized, receptor-mediated processes, mechanisms attenuating the electrostatic repulsion between the negatively charged glycocalyx of leukocyte and endothelium remain poorly understood. We provide evidence for myeloperoxidase (MPO), an abundant PMN-derived heme protein, facilitating PMN recruitment by its positive surface charge. In vitro, MPO evoked highly directed PMN motility, which was solely dependent on electrostatic interactions with the leukocyte's surface. In vivo, PMN recruitment was shown to be MPO-dependent in a model of hepatic ischemia and reperfusion, upon intraportal delivery of MPO and in the cremaster muscle exposed to local inflammation or to intraarterial MPO application. Given MPO's affinity to both the endothelial and the leukocyte's surface, MPO evolves as a mediator of PMN recruitment because of its positive surface charge. This electrostatic MPO effect not only displays a so far unrecognized, catalysis-independent function of the enzyme, but also highlights a principal mechanism of PMN attraction driven by physical forces.

LRP6 is internalized by Dkk1 to suppress its phosphorylation in the lipid raft and is recycled for reuse

Beta-catenin-mediated Wnt signaling is crucial in animal development and tumor progression. The phosphorylation of low-density lipoprotein receptor-related protein 6 (LRP6), a single-span transmembrane Wnt receptor, plays a vital role in this signaling. Dickkopf1 (Dkk1) has been shown to inhibit the Wnt-beta-catenin pathway, but the mechanism is not yet clear. Here, evidence is presented that Wnt3a-dependent phosphorylation of LRP6 occurs in the lipid raft and that Dkk1 inhibits the formation of a complex between LRP6 and casein kinase 1gamma (CK1gamma) by removing LRP6 from the lipid raft. Dkk1 internalized LRP6 in a Rab5-dependent mechanism to prevent phosphorylation mediated by CK1gamma. The internalized LRP6 was recycled back in a Rab11-dependent mechanism to the cell-surface membrane, and the recycled LRP6 again responded to Wnt3a and Dkk1. Internalized Dkk1 was trafficked in a Rab7-mediated route and degraded in the lysosome. These results suggest that Dkk1 induces the internalization of LRP6 to suppress its phosphorylation in the lipid raft and allows subsequent recycling of LRP6 so that it can be reused for signaling.

Evidence that cathelicidin peptide LL-37 may act as a functional ligand for CXCR2 on human neutrophils

LL-37, derived from human cathelicidin, stimulates immune responses in neutrophils. Although FPR2 and P2X7 were proposed as LL-37 receptors, we have shown that among 21 neutrophil receptors only CXCR2 was down-regulated by LL-37. LL-37 functions similarly to CXCR2-specific chemokines CXCL1 and CXCL7 in terms of receptor down-regulation and intracellular calcium mobilization on freshly isolated neutrophils. Neutrophils pretreated with CXCL8, a chemokine that binds both CXCR1/2, completely blocked the calcium mobilization in response to LL-37, while LL-37 also partially inhibited (125)I-CXCL8 binding to neutrophils. SB225002, a selective CXCR2 antagonist, blocked LL-37-induced calcium mobilization and migration of neutrophils. LL-37 stimulates calcium mobilization in CXCR2-transfected HEK293 cells, CXCR2(+) THP-1 cells and monocytes, but not in CXCR1-transfected HEK293 cells. WKYMVm peptide (ligand for FPR2) does not block LL-37-stimulated calcium flux in either THP-1 (FPR2(-)) or monocytes (FPR2(high)), further confirming the specificity of LL-37 for CXCR2 and not FPR2. Among all ligands tested (ATP, BzATP, WKYMVm, CXCL1, and LL-37), only LL-37 stimulated migration of monocytes (CXCR2(+) and FPR2(+)) and migration was inhibited by the CXCR2 inhibitor SB225002. Moreover, CXCR2 but not CXCR1 was internalized in LL-37-treated neutrophils. Thus, our data provide evidence that LL-37 may act as a functional ligand for CXCR2 on human neutrophils.

The functional significance behind expressing two IL-8 receptor types on PMN

PMN are critical to innate immunity and are fundamental to antibacterial defense. To localize to sites of infection, PMN possess receptors that detect chemoattractant stimuli elicited at the site, such as chemokines, complement split products, or bioactive lipids. Signaling through these receptors stimulates chemotaxis toward the site of infection but also activates a number of biochemical processes, with the result that PMN kill invading bacteria. PMN possess two receptors, CXCR1 and CXCR2, for the N-terminal ELR motif-containing CXC chemokines, although only two chemokine members bind both receptors and the remainder binding only CXCR2. This peculiar pattern in receptor specificity has drawn considerable interest and investigation into whether signaling through each receptor might impart unique properties on the PMN. Indeed, at first glance, CXCR1 and CXCR2 appear to be functionally redundant; however, there are differences. Considering these proinflammatory activities of activating PMN through chemokine receptors, there has been great interest in the possibility that blocking CXCR1 and CXCR2 on PMN will provide a therapeutic benefit. The literature examining CXCR1 and CXCR2 in PMN function during human and modeled diseases will be reviewed, asking whether the functional differences can be perceived based on alterations in the role PMN play in these processes.

Rapid recycling of beta-adrenergic receptors is dependent on the actin cytoskeleton and myosin Vb

For the beta(2)-adrenergic receptor (beta(2)AR), published evidence suggests that an intact actin cytoskeleton is required for the endocytosis of receptors and their proper sorting to the rapid recycling pathway. We have characterized the role of the actin cytoskeleton in the regulation of beta(2)AR trafficking in human embryonic kidney 293 (HEK293) cells using two distinct actin filament disrupting compounds, cytochalasin D and latrunculin B (LB). In cells pretreated with either drug, beta(2)AR internalization into transferrin-positive vesicles was not altered but both agents significantly decreased the rate at which beta(2)ARs recycled to the cell surface. In LB-treated cells, nonrecycled beta(2)ARs were localized to early embryonic antigen 1-positive endosomes and also accumulated in the recycling endosome (RE), but only a small fraction of receptors localized to LAMP-positive late endosomes and lysosomes. Treatment with LB also markedly enhanced the inhibitory effect of rab11 overexpression on receptor recycling. Dissociating receptors from actin by expression of the myosin Vb tail fragment resulted in missorting of beta(2)ARs to the RE, while the expression of various CART fragments or the depletion of actinin-4 had no detectable effect on beta(2)AR sorting. These results indicate that the actin cytoskeleton is required for the efficient recycling of beta(2)ARs, a process that likely is dependent on myosin Vb.

Glucagon receptor recycling: role of carboxyl terminus, beta-arrestins, and cytoskeleton

Glucagon receptor (GR) activity and expression are altered in several diseases, including Type 2 diabetes. Previously, we investigated the mechanism of GR desensitization and internalization. The present study focused on the fate of internalized GR. Using both hamster hepatocytes and human embryonic kidney (HEK)-293 cells, we showed that internalized GR recycled to the plasma membrane within 30-60 min following stimulation of the cells with 100 nM glucagon. In HEK-293 cells and during recycling, GR colocalized with Rab4, Rab11, beta-arrestin1, beta-arrestin2, and actin filaments, in the cytosolic and/or perinuclear domains. Glucagon treatment triggered redistribution of actin filaments from the plasma membrane to the cytosol. GR coimmunoprecipitated with beta-actin in both hepatocytes and HEK-293 cells. Downregulation of beta-arrestin1 and beta-arrestin2 or disruption of the cytoskeleton inhibited recycling, but not internalization of GR. Deletion of the GR carboxyl-terminal 70 amino acids abolished internalization of GR in response to glucagon while deletion of the last 40 amino acids only did not affect GR internalization and recycling. After exposure of the cells to either high concentrations or prolonged duration of glucagon, GR colocalized with lysosomes. GR degradation was inhibited by lysosomal, but not proteosomal, inhibitors. In conclusion, GR recycles through Rab4- and Rab11- positive vesicles. The actin cytoskeleton, beta-arrestin1, beta-arrestin2, and the receptor's carboxyl terminus are involved in recycling. Prolonged stimulation with glucagon targets GR for degradation in lysosomes. Therefore, the present study provides a better understanding of the GR recycling mechanism, which could become useful in the treatment of certain diseases, including diabetes.

Human B cells express the orphan chemokine receptor CRAM-A/B in a maturation-stage-dependent and CCL5-modulated manner

Chemokines orchestrate the organization of leucocyte recruitment during inflammation and homeostasis. Despite growing knowledge of chemokine receptors, some orphan chemokine receptors are still not characterized. The gene CCRL2 encodes such a receptor that exists in two splice variants, CRAM-A and CRAM-B. Here, we report that CRAM is expressed by human peripheral blood and bone marrow B cells, and by different B-cell lines dependent on the B-cell maturation stage. Intriguingly, CRAM surface expression on the pre-B-cell lines Nalm6 and G2 is specifically upregulated in response to the inflammatory chemokine CCL5 (RANTES), a chemokine that is well known to play an important role in modulating immune responses. Although Nalm6 cells do not express any of the known CCL5 binding receptors, extracellular signal-regulated kinases 1 and 2 (ERK1/2) are phosphorylated upon CCL5 stimulation, suggesting a direct effect of CCL5 through the CRAM receptor. However, no calcium mobilization or migratory responses upon CCL5 stimulation are induced in B-cell lines or in transfected cells. Also, ERK1/2 phosphorylation cannot be inhibited by pertussis toxin, suggesting that CRAM does not couple to Gi proteins. Our results describe the expression of a novel, non-classical chemokine receptor on B cells that is potentially involved in immunomodulatory functions together with CCL5.

A comparison of random vs. chemotaxis-driven contacts of T cells with dendritic cells during repertoire scanning

Generating adaptive immunity after infection or immunization requires physical interactions within a lymph node (LN) T-zone between antigen-bearing dendritic cells (DCs) that arrive from peripheral tissues and rare cognate T cells entering via high endothelial venules (HEVs). This interaction results in activation of cognate T cells, expansion of that T cell lineage and their exit from the LN T-zone via efferent lymphatics (ELs). How antigen-specific T cells locate DCs within this complex environment is controversial, and both random T cell migration and chemotaxis have been proposed. We developed an agent-based computational model of a LN that captures many features of T cell and DC dynamics observed by two-photon microscopy. Our simulations matched in vivo two-photon microscopy data regarding T cell speed, short-term directional persistence of motion and cell motility. We also obtained in vivo data regarding density of T cells and DCs within a LN and matched our model environment to measurements of the distance from HEVs to ELs. We used our model to compare chemotaxis with random motion and showed that chemotaxis increased total number of T cell DC contacts, but decreased unique contacts, producing fewer activated T cells. Our results suggest that, within a LN T-zone, a random search strategy is optimal for a rare cognate T cell to find its DC match and maximize production of activated T cells.

Intracellular cross-talk between the GPCR CXCR1 and CXCR2: role of carboxyl terminus phosphorylation sites

In the present study, we used the human chemokine receptors CXCR1 and CXCR2 as a model system for the study of intracellular cross-talk between two closely related G protein-coupled receptors (GPCR). In cells expressing either CXCR1 or CXCR2, exposure to the CXCL8 ligand resulted in prominent reduction in cell surface expression of the receptors. We have shown previously that the reduction in cell surface expression of CXCR1 and CXCR2, to be termed herein "down-regulation", is significantly lower in cells expressing both receptors together. Now we show that reduced receptor down-regulation was specific to the CXCR1+CXCR2 pair. Also, CXCR2 carboxyl terminus phosphorylation sites were required for inducing inhibition of CXCR1 down-regulation, and vice versa. Accordingly, phosphorylation of CXCR2 carboxyl terminus domain was intact when expressed together with CXCR1. Moreover, specific carboxyl terminus phosphorylation sites on each of the wild type receptors protected them from more severe inhibition of down-regulation, induced by joint expression with the other receptor. When concomitantly expressed, CXCR1 and CXCR2 were impaired in recycling to the plasma membrane, despite their undergoing intact dephosphorylation. Overall, we show that cross-talk between two GPCR is manifested by impairment of their intracellular trafficking, primarily of ligand-induced down-regulation, via carboxyl terminus phosphorylation sites.

RhoB plays an essential role in CXCR2 sorting decisions

The CXCR2 chemokine receptor is a G-protein-coupled receptor that undergoes clathrin-mediated endocytosis upon ligand binding. The trafficking of CXCR2 is crucial for cells to maintain a proper chemotactic response. The mechanisms that regulate the recycling/degradation sorting decision are unknown. In this study, we used dominant-negative (T19N) and GTPase-deficient activated (Q63L) RhoB mutants, as well as RhoB small interfering RNA (siRNA) to investigate the role of RhoB in CXCR2 trafficking. Expression of either of the RhoB mutants or transfection of RhoB siRNA impaired CXCR2-mediated chemotaxis. Expression of RhoB T19N and transfection of RhoB siRNA impaired sorting of CXCR2 to the lysosome after 3 hours of CXCL8 stimulation and impaired CXCL8-induced CXCR2 degradation. In cells expressing the RhoB Q63L mutant, CXCR2 recycling through the Rab11a recycling compartment was impaired after 30 minutes of CXCL8 stimulation as was CXCL8-induced CXCR2 degradation. For cells expressing activated RhoB, CXCR2 colocalized with Rab4, a marker for the rapid recycling pathway, and with the mannose-6-phosphate receptor, which traffics between the trans-Golgi network and endosomes. These data suggest that CXCR2 recycles through alternative pathways. We conclude that oscillation of RhoB GTPase activity is essential for appropriate sorting decisions, and for directing CXCR2 degradation and recycling--events that are required for optimal chemotaxis.

Actin disruption inhibits endosomal traffic of P-glycoprotein-EGFP and resistance to daunorubicin accumulation

Intracellular traffic of human P-glycoprotein (P-gp), a membrane transporter responsible for multidrug resistance in cancer chemotherapy, was investigated using a P-gp and enhanced green fluorescent fusion protein (P-gp-EGFP) in human breast cancer MCF-7 cells. The stably expressed P-gp-EGFP from a clonal cell population was functional as a drug efflux pump, as demonstrated by the inhibition of daunorubicin accumulation and the conferring of resistance of the cells to colchicine and daunorubicin. Colocalization experiments demonstrated that a small fraction of the total P-gp-EGFP expressed was localized intracellularly and was present in early endosome and lysosome compartments. P-gp-EGFP traffic was shown to occur via early endosome transport to the plasma membrane. Subsequent movement of P-gp-EGFP away from the plasma membrane occurred by endocytosis to the early endosome and lysosome. The component of the cytoskeleton responsible for P-gp-EGFP traffic was demonstrated to be actin rather than microtubules. In functional studies it was shown that in parallel with the interruption of the traffic of P-gp-EGFP, cellular accumulation of the P-gp substrate daunorubicin was increased after cells were treated with actin inhibitors, and cell proliferation was inhibited to a greater extent than in the presence of daunorubicin alone. The actin dependence of P-gp traffic and the parallel changes in cytotoxic drug accumulation demonstrated in this study delineates the pathways of P-gp traffic and may provide a new approach to overcoming multidrug resistance in cancer chemotherapy.

RSV-infected airway epithelial cells cause biphasic up-regulation of CCR1 expression on human monocytes

Respiratory syncytial virus (RSV) infection can cause extensive airway inflammation, which is orchestrated by chemokines and their receptors. RSV-infected epithelial cells secrete many cytokines and chemokines, but little is known about regulation of chemokine receptors on target cells. We investigated the effects of conditioned media (CM) from RSV-infected epithelial cells on monocyte CCR1, CCR2, and CCR5 expression. RSV-CM but not control-CM stimulated a biphasic increase in cell-surface CCR1, and levels peaked at 36 h and 96 h poststimulation. Similar CCR1 up-regulation occurred on monocyte-derived macrophages. Cytochlasin D and colchicine blocked both peaks of expression, demonstrating requirement of a functional cytoskeleton. Intracellular staining revealed little internal sequestration of CCR1 protein, and CCR1 up-regulation was inhibited by actinomycin D and cycloheximide, indicating that both waves of RSV-CM-induced surface CCR1 expression were dependent on de novo transcription and protein synthesis. Cytokine-neutralizing experiments showed that the effects of RSV-CM were decreased by blocking TNF-alpha (percent inhibition=51+/-2.3% at 36 h peak and 42+/-7.7% at 96 h peak) and to a lesser extent, IL-1 (percent inhibition=32+/-7.2% at 36 h and 23+/-2.9% at 96 h). In summary, RSV-CM causes a biphasic up-regulation of surface CCR1 on monocytes, which is dependent on an intact cytoskeleton, requires new gene transcription and protein synthesis, and is mediated in part by the proinflammatory cytokines TNF-alpha and IL-1.

Role of CXCR3 carboxyl terminus and third intracellular loop in receptor-mediated migration, adhesion and internalization in response to CXCL11

The chemokine receptor CXCR3 is predominantly expressed on activated T and natural killer (NK) cells. CXCR3 and its ligands, CXCL11, CXCL10, and CXCL9, play a major role in T-helper 1 (Th1)-dependent inflammatory responses. CXCL11 is the most dominant physiological inducer of adhesion, migration, and internalization of CXCR3. To study the role of CXCR3 carboxyl-terminus and the third intracellular (3i) loop in chemokine-mediated migration, adhesion, and CXCR3 internalization, we generated CXCR3 receptors mutated in their distal (Ser-Thr domain) or proximal (trileucine domain) membrane carboxyl terminus, and/or the third intracellular loop. We found that migration of CXCR3-expressing HEK 293 cells toward CXCL11 was pertussis toxin-dependent and required the membrane proximal carboxyl terminus of CXCR3. Internalization induced by CXCL11 and protein kinase C (PKC) activation was also regulated by the membrane proximal carboxyl terminus; however, only CXCL11-induced internalization required the LLL motif of this region. Internalization and Ca(2+) flux induced by CXCL11 were independent of the 3i loop S245, whereas migration at high CXCL11 concentrations, integrin-dependent adhesion, and actin polymerization were S245 dependent. Our findings indicate that CXCL11-dependent CXCR3 internalization and cell migration are regulated by the CXCR3 membrane proximal carboxyl terminus, whereas adhesion is regulated by the 3i loop S245. Thus, distinct conformational changes induced by a given CXCR3 ligand trigger different downstream effectors of adhesion, motility, and CXCR3 desensitization.

Chemokine receptor internalization and intracellular trafficking

The internalization and intracellular trafficking of chemokine receptors have important implications for the cellular responses elicited by chemokine receptors. The major pathway by which chemokine receptors internalize is the clathrin-mediated pathway, but some receptors may utilize lipid rafts/caveolae-dependent internalization routes. This review discusses the current knowledge and controversies regarding these two different routes of endocytosis. The functional consequences of internalization and the regulation of chemokine receptor recycling will also be addressed. Modifications of chemokine receptors, such as palmitoylation, ubiquitination, glycosylation, and sulfation, may also impact trafficking, chemotaxis and signaling. Finally, this review will cover the internalization and trafficking of viral and decoy chemokine receptors.

Involvement of Actin in Agonist-induced Endocytosis of the G Protein-coupled Receptor for Thromboxane A2

The role of actin in endocytosis of G protein-coupled receptors is poorly defined. In the present study, we demonstrate that agents that depolymerize (latrunculin B and cytochalasin D) or stabilize (jasplakinolide) the actin cytoskeleton blocked agonist-induced endocytosis of the beta isoform of the thromboxane A(2) receptor (TPbeta) in HEK293 cells. This suggests that endocytosis of TPbeta requires active remodeling of the actin cytoskeleton. On the other hand, disruption of microtubules with colchicine did not affect endocytosis of the receptor. Expression of wild-type and mutant forms of the small GTPases RhoA and Cdc42 potently inhibited endocytosis of TPbeta, further indicating a role for the dynamic regulation of the actin cytoskeleton in this pathway. Agonist treatment of TPbeta in HEK293 cells resulted in the formation of actin stress fibers through Galpha(q/11) signaling. Because we previously showed that endocytosis of TPbeta is dependent on arrestins, we decided to explore the relation between arrestin-2 and -3 and actin in endocytosis of this receptor. Interestingly, we show that the inhibition of TPbeta endocytosis by the actin toxins in HEK293 cells was overcome by the overexpression of arrestin-3, but not of arrestin-2. These results indicate that the actin cytoskeleton is not essential in arrestin-3-mediated endocytosis of TPbeta. However, arrestin-3 could not promote endocytosis of the TPbetaY339A and TPbetaI343A carboxyl-terminal mutants when the actin cytoskeleton was disrupted. Our data provide new evidence that the actin cytoskeleton plays an essential role in TPbeta endocytosis. Furthermore, our work suggests the existence of actin-dependent and -independent arrestin-mediated pathways of endocytosis.

CART: an Hrs/actinin-4/BERP/myosin V protein complex required for efficient receptor recycling

Altering the number of surface receptors can rapidly modulate cellular responses to extracellular signals. Some receptors, like the transferrin receptor (TfR), are constitutively internalized and recycled to the plasma membrane. Other receptors, like the epidermal growth factor receptor (EGFR), are internalized after ligand binding and then ultimately degraded in the lysosome. Routing internalized receptors to different destinations suggests that distinct molecular mechanisms may direct their movement. Here, we report that the endosome-associated protein hrs is a subunit of a protein complex containing actinin-4, BERP, and myosin V that is necessary for efficient TfR recycling but not for EGFR degradation. The hrs/actinin-4/BERP/myosin V (CART [cytoskeleton-associated recycling or transport]) complex assembles in a linear manner and interrupting binding of any member to its neighbor produces an inhibition of transferrin recycling rate. Disrupting the CART complex results in shunting receptors to a slower recycling pathway that involves the recycling endosome. The novel CART complex may provide a molecular mechanism for the actin-dependence of rapid recycling of constitutively recycled plasma membrane receptors.

The epithelial-mesenchymal transition of colon carcinoma involves expression of IL-8 and CXCR-1-mediated chemotaxis

The epithelial-mesenchymal transition (EMT) is an essential component of embryonic development, tissue remodeling, and wound repair. In addition, many epithelial tumors, including colorectal carcinomas, appear to undergo this transition that may facilitate their invasion. Using a novel model of EMT in colon carcinoma in which the inflammatory cytokine TNF-alpha accelerates this TGF-beta directed process, we report that TNF-alpha stimulation upregulates expression of the chemokine IL-8, and that this upregulation is dependent on the transcription factor NF-kappaB. Significantly, this effect is not merely an inflammatory response by these colon carcinoma cells because IL-8 expression is induced in cells undergoing a TGF-beta-driven EMT in the absence of exogenous TNF-alpha. During the EMT, a concomitant increase in the chemokine receptor CXCR-1, but not CXCR-2, also occurs. Moreover, both IL-8 and CXCR-1 function in the chemokinetic and chemotactic migration of colon carcinoma cells as assessed by antibody inhibition studies. These studies establish that the regulated expression of a specific chemokine and its receptor are linked to the EMT and they provide a biochemical framework for understanding the mechanisms by which the EMT promotes migration.

Alpha C protein of group B Streptococcus binds host cell surface glycosaminoglycan and enters cells by an actin-dependent mechanism

Group B Streptococcus (GBS) colonizes mucosal surfaces of the human gastrointestinal and gynecological tracts and causes disease in a wide range of patients. Invasive illness occurs after organisms traverse an epithelial boundary and enter deeper tissues. Previously we have reported that the alpha C protein (ACP) on the surface of GBS mediates GBS entry into ME180 cervical epithelial cells and GBS translocation across layers of these cells. We now demonstrate that ACP interacts with host cell glycosaminoglycan (GAG); the interaction of ACP with ME180 cells is inhibited if cells are pretreated with sodium chlorate, an inhibitor of sulfate incorporation, or with heparitinases. The interaction is also inhibited in the presence of soluble heparin or heparan sulfate or host cell-derived GAG. In addition, ACP binds soluble heparin specifically in inhibition and dot blot assays. After interaction with host GAG, soluble ACP enters ME180 cells and fractionates to the eukaryotic cell cytosol. These events are inhibited in cells pretreated with cytochalasin D or with Clostridium difficile toxin B. These data indicate that full-length ACP interacts with ME180 cell GAG and enters the eukaryotic cell cytosol by a mechanism that involves Rho GTPase-dependent actin rearrangements. We suggest that these molecular interactions drive ACP-mediated translocation of GBS across epithelial barriers, thereby facilitating invasive GBS infection.

A critical 'threshold' of beta 2-integrin engagement regulates augmentation of cytokine-mediated superoxide anion release

1. Neutrophil adhesion regulates a number of processes involved in the pathogenesis of inflammatory diseases including rheumatoid arthritis. Neutrophil destructive potential can be modulated by adhesion, allowing alteration of inflammatory cell behaviour while preserving antimicrobial defences. beta(2)-Integrin-mediated neutrophil adhesion to albumin-coated latex beads (ACLB) allows modulation of integrin clustering and ligation and analysis of the effects of adhesion on neutrophil responses. Tumour necrosis factor-alpha (TNF alpha) enhanced neutrophil binding of different diameter ACLB equally, by almost four-fold, and independently of bead size. Adhesion of neutrophils to ACLB caused a size-dependent generation and release of O(2)(-) and also potentiated TNF alpha-induced O(2)(-) release. 2. Binding of ACLB was not affected by disruption of cytoskeletal integrity with nocodazole or cytochalasin D or following blockade of tyrosine kinase activity. In contrast, tyrosine phosphorylation and an intact cytoskeleton were essential for adhesion- and cytokine-induced O(2)(-) release from neutrophils. Inhibition of adhesion- and cytokine-induced O(2)(-) release by 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazol[3,4-d]pyrimidine (PP2) indicated that a Src-family tyrosine kinase was the principal regulatory pathway mediating this response in neutrophils, a distal role for p38 MAPK was revealed by use of SB203580. 3. Tyrosine phosphorylation of c-Fgr, a Src-family tyrosine kinase, occurred following ACLB adhesion and exposure to TNF alpha, and was susceptible to inhibition by PP2. We suggest that activation of the key regulatory enzyme c-Fgr is achieved following ligation of a critical threshold of integrins following binding of large (>3 microM) ACLB.

Rab11-family interacting protein 2 and myosin Vb are required for CXCR2 recycling and receptor-mediated chemotaxis

Agonist-stimulated internalization followed by recycling to the cell membrane play an important role in fine-tuning the activity of chemokine receptors. Because the recycling of chemokine receptors is critical for the reestablishment of the cellular responsiveness to ligand, it is crucial to understand the mechanisms underlying the receptor recycling and resensitization. In the present study, we have demonstrated that the chemokine receptor CXCR2 associated with myosin Vb and Rab11-family interacting protein 2 (FIP2) in a ligand-dependent manner. Truncation of the C-terminal domain of the receptor did not affect the association, suggesting that the interactions occur upstream of the C terminus of CXCR2. After ligand stimulation, the internalized CXCR2 colocalized with myosin Vb and Rab11-FIP2 in Rab11a-positive vesicles. The colocalization lasted for approximately 2 h, and little colocalization was observed after 4 h of ligand stimulation. CXCR2 also colocalized with myosin Vb tail or Rab11-FIP2 (129-512), the N-terminal-truncated mutants of myosin Vb and Rab11-FIP2, respectively, but in a highly condensed manner. Expression of the enhanced green fluorescent protein-tagged myosin Vb tail significantly retarded the recycling and resensitization of CXCR2. CXCR2 recycling was also reduced by the expression Rab11-FIP2 (129-512). Moreover, expression of the myosin Vb tail reduced CXCR2- and CXCR4-mediated chemotaxis. These data indicate that Rab11-FIP2 and myosin Vb regulate CXCR2 recycling and receptor-mediated chemotaxis and that passage of internalized CXCR2 through Rab11a-positive recycling system is critical for physiological response to a chemokine.

Mechanisms of internalization and recycling of the chemokine receptor, CCR5

CCR5 is a G protein-coupled receptor that binds several natural chemokines but it is also a coreceptor for the entry of M tropic strains of HIV-1 into cells. Levels of CCR5 on the cell surface are important for the rate of HIV-1 infection and are determined by a number of factors including the rates of CCR5 internalization and recycling. Here we investigated the involvement of the actin cytoskeleton in the control of ligand-induced internalization and recycling of CCR5. Cytochalasin D, an actin depolymerizing agent, inhibited chemokine-induced internalization of CCR5 and recycling of the receptor in stably transfected CHO cells and in the monocytic cell line, THP-1. CCR5 internalization and recycling were inhibited by Toxin B and C(3) exoenzyme treatment in CHO and THP-1 cells, confirming activation of members of the RhoGTPase family by CCR5. The specific Rho kinase inhibitor Y27632, however, had no effect on CCR5 internalization or recycling. Ligand-induced activation of CCR5 leads to Rho kinase-dependent formation of focal adhesion complexes. These data indicate that CCR5 internalization and recycling are regulated by actin polymerization and activation of small G proteins in a Rho-dependent manner.

Predominant Intracellular Expression of CXCR4 and CCR5 in Purified Primary Trophoblast Cells from First Trimester and Term Human Placentae

PROBLEM

The aim of the present study was to define the expression of CXCR4 and CCR5 on non-cultured non-stimulated primary human trophoblast cells (TCs) immediately after their immunopurification.

METHOD OF STUDY

We have evaluated by flow cytometric analysis and immunofluorescence, highly purified primary TCs prepared from first trimester (8.2 +/- 0.3 weeks, n = 15) and term (Caesarean section, n = 10) placentae for the cell surface and intracellular expression of CXCR4 and CCR5.

RESULTS

There was a high level of individual variability for CXCR4 and CCR5 expression between trophoblast batches. In first trimester and term placentae TCs, we found a greater number of TCs preparations expressing intracellular CXCR4 than CCR5 (P < 0.05). Both receptors were predominantly localized in the intracellular compartment of TCs, whatever if isolated from first trimester or term placentae.

CONCLUSIONS

The functional consequences of the predominance of CXCR4 expression and of cellular addressing are briefly discussed.

IL-8-induced migratory responses through CXCR1 and CXCR2: association with phosphorylation and cellular redistribution of focal adhesion kinase

CXCR1 and CXCR2 mediate migratory activities in response to IL-8 and other ELR+-CXC chemokines (e.g., GCP-2 and NAP-2). In vitro, activation of migration is induced by low IL-8 concentrations (10-50 ng/mL), whereas migratory shut-off is induced by high IL-8 concentrations (1000 ng/mL). The stimulation of CXCR1 and CXCR2 by IL-8 concentrations that result in migratory activation induced focal adhesion kinase (FAK) phosphorylation in a G(alpha)i-dependent manner. The expression of FRNK, a dominant negative mutant of FAK, perturbed migratory responses to the activating dose of 50 ng/mL IL-8. The migration-activating concentrations of 50 ng/mL GCP-2 and NAP-2 induced less potent migratory responses and FAK phosphorylation in CXCR2-expressing cells as compared with IL-8. These results indicate that FAK is phosphorylated, and required, for the chemotactic response under conditions of migratory activation by ELR+-CXC chemokines. In addition, FAK phosphorylation was determined following exposure to migration-attenuating concentrations of IL-8. In CXCR1-RBL cells this treatment resulted in FAK phosphorylation, in similar levels to those induced by activating concentrations of IL-8. In contrast, in CXCR2-RBL cells the migration-attenuating concentrations of IL-8 induced promoted levels of FAK phosphorylation and different patterns of FAK phosphorylation on its six potential tyrosine phosphorylation sites, as compared to activating concentrations of the chemokine. Exposure to IL-8 resulted not only in FAK phosphorylation but also in its cellular redistribution, indicated by the formation of defined contact regions with the substratum, enriched in phosphorylated FAK and vinculin. Overall, FAK phosphorylation was associated with, and found to be differently regulated upon, ELR+-CXC chemokine-induced migration.

Altered tropomyosin expression in essential hypertension

Abnormal erythrocyte sodium-lithium countertransport is common in a subgroup of patients with essential hypertension and a strong family history of hypertension and cardiovascular disease. We have previously shown that the abnormality in sodium-lithium countertransport is associated with tropomyosin, a cytoskeletal protein required to stabilize actin filament formation. Leukocyte trafficking events, which depend on cytoskeletal reorganization, are also altered in patients with essential hypertension with abnormal sodium-lithium countertransport. The aim of this study was to determine whether there is an abnormality in isoforms of tropomyosin that are common to erythrocytes and leukocytes. Analysis of reticulocyte RNA by reverse transcription (RT) and polymerase chain reaction (PCR) showed expression of TPMN and TPM5b isoforms of tropomyosin. No other isoforms were expressed. These isoforms were also detected in RNA from leukocytes. In patients with essential hypertension with abnormal erythrocyte sodium-lithium countertransport compared with normal control subjects, there was a higher TPMN/TPM5b ratio of protein in erythrocytes (median 3.8 [range 1.8 to 6.6] versus 2.9 [1.9 to 4.0], P<0.001) and of RNA in leukocytes (3.7 [1.7 to 8.2] versus 2.6 [1.2 to 4.3], P<0.01). Furthermore, the protein ratio of TPMN/TPM5b in erythrocytes showed significant correlation with the V(max)/K(m) ratio of sodium-lithium countertransport across the patient groups (r=-0.42; P<0.01). Therefore, altered tropomyosin expression may be the underlying abnormality associated with blood cell membrane changes in essential hypertension and implicates the cytoskeleton in the pathogenesis of the disease in a major subgroup of patients.

Role of the intracellular domains of CXCR4 in SDF-1-mediated signaling

The CXCR4 chemokine receptor is a G(i) protein-coupled receptor that triggers multiple intracellular signals in response to stromal cell-derived factor 1 (SDF-1), including calcium mobilization and p44/42 extracellular signal-regulated kinases (ERK1/2). Transduced signals lead to cell chemotaxis and are terminated through receptor internalization depending on phosphorylation of the C terminus part of CXCR4. Receptor endocytosis is also required for some receptors to stimulate ERK1/2 and to migrate through a chemokine gradient. In this study, we explored the role played by the 3 intracellular loops (ICL1-3) and the C terminus domain of CXCR4 in SDF-1-mediated signaling by using human embryonic kidney (HEK)-293 cells stably expressing wild-type or mutated forms of CXCR4. ICL3 of CXCR4 is specifically involved in G(i)-dependent signals such as calcium mobilization and ERK activation, but does not trigger CXCR4 internalization after SDF-1 binding, indicating that ERK phosphorylation is independent of CXCR4 endocytosis. Surprisingly, ICL2, with or without the aspartic acid, arginine, and tyrosine (DRY) motif, is dispensable for G(i) signaling. However, ICL2 and ICL3, as well as the C terminus part of CXCR4, are needed to transduce SDF-1-mediated chemotaxis, suggesting that this event involves multiple activation pathways and/or cooperation of several cytoplasmic domains of CXCR4.

Expression of AMPA-type glutamate receptors in HEK cells and cerebellar granule neurons impairs CXCL2-mediated chemotaxis

We find that cerebellar granule neurons (CGN) obtained from newborn rats (p3) migrate in response to both CXC chemokine ligand-2 (CXCL2) and -12 (CXCL12), while CGN from p7 rats are unresponsive to CXCL2. The expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type glutamate receptor 1 (GluR1) greatly impairs the chemotaxis induced by CXCL2 in CXCR2-expressing HEK cells. By immunoprecipitation, we show that CXCR2 is associated with AMPA receptors (AMPARs) in p7 CGN, and with GluR1 co-expressed in HEK cells. Taken together, these results suggest that the association between CXCR2 and AMPARs results in the inhibition of CXCL2-dependent chemotaxis, and may represent a molecular mechanism underlying the modulation of nerve cell migration.

Intracellular trafficking of human CXCR1 and CXCR2: regulation by receptor domains and actin-related kinases

In this study we investigated the regulation of CXCR1 and CXCR2 intracellular trafficking. First, we produced a chimeric CXCR2 receptor that contained the internalization motifs of both CXCR2 and CXCR1 (CXCR2: LLKIL sequence; CXCR1: C-terminal phosphorylation sites). Elevated levels of internalization were induced by different ELR-expressing CXC chemokines on the chimeric receptor, as compared to wild-type CXCR2. Analysis of inter-relationships between CXCR1 and CXCR2 during internalization indicated that the exposure of cells that expressed both CXCR1 and CXCR2 to CXCL8 or CXCL6 resulted in decreased levels of CXCR1 internalization as compared to those in cells that expressed only CXCR1. To characterize the role of actin-related components in CXCR1 and CXCR2 trafficking, wortmannin, a potent inhibitor of phosphatidylinositol kinases, was used. The presence of wortmannin during receptor recycling inhibited CXCR1 and CXCR2 re-expression following CXCL8-induced internalization, and resulted in a marked disruption of the proper organization of actin filaments. The kinase-dependent recycling process required CXCR2 C-terminal phosphorylation sites. Our results suggest that actin-related kinases are required for the proper functionality of actin filaments, which are the instrumental factors needed for receptor recycling. In all, CXCR1 and CXCR2 internalization and recycling are tightly regulated by receptor domains and by actin-related kinases.

Inhibition of G protein-coupled receptor trafficking in neuroblastoma cells by MAP 4 decoration of microtubules

One mechanism for the reappearance of G protein-coupled receptors after agonist activation is microtubule-based transport. In pressure-overload cardiac hypertrophy, there is downregulation of G protein-coupled receptors and the appearance of a densified microtubule network extensively decorated by a microtubule-associated protein, MAP 4. Our hypothesis is that overdecoration of a dense microtubule network with this structural protein, as in hypertrophied myocardium, would impede receptor recovery. We tested this hypothesis by studying muscarinic acetylcholine receptor (mAChR) internalization and recovery after agonist stimulation in neuroblastoma cells. Exposure of cells to carbachol, a muscarinic receptor agonist, decreased membrane receptor binding activity. After carbachol withdrawal, receptor binding recovered toward the initial value. When microtubules were depolymerized before carbachol withdrawal, mAChR recovery was only 44% of that in intact cells. Cells were then infected with an adenovirus containing MAP 4 cDNA. MAP 4 protein decorated the microtubules extensively, and receptor recovery upon carbachol withdrawal was reduced to 54% of control. Thus muscarinic receptor recovery after agonist exposure is microtubule dependent, and MAP 4 decoration of microtubules inhibits receptor recovery.

Substantial changes in gene expression level due to the storage temperature and storage duration of human whole blood

Blood is a valuable clinical sample for high-throughput analysis of gene expression and is likely to become more popular as a diagnostic tool and as a predictive measure of disease progression and drug responsiveness. Gene expression data from blood that has been stored at ambient temperature for greater than 1 h vs. blood samples that have been lysed immediately post-collection shows dramatic changes in relative gene expression for a number of cytokines, chemokines, and transcription factors. Results indicate significant changes in the relative expression of several genes, many of which were either up-regulated or down-regulated, because of storage at ambient temperature: (1) In only 4 h of storage at ambient temperature, greater than 10-fold increases in relative gene expression were observed for interleukin-8 (IL-8), c-myc, and c-fos; (2) Up-regulation of IL-8, a chemokine that mediates inflammatory cell migration, took place only 1-h after collection and increased nearly 100-fold by 4 h; (3) Down-regulation of several anti-inflammatory genes was observed for blood stored at ambient temperature; and (4) A general trend toward selective enhancement of inflammatory responses was observed, mediated by possible mRNA transcription and turnover. These results validate the need for the rapid lysis of whole blood after removal from the source.

Phagocytosing neutrophils down-regulate the expression of chemokine receptors CXCR1 and CXCR2

CXC chemokines play a central role in regulation of neutrophil activation and chemotaxis. Because the chemotactic responses of neutrophils are impaired after phagocytosis, we explored the effect of phagocytic stimuli on the expression of interleukin-8 (IL-8) receptors, CXCR1 and CXCR2, in human neutrophils. After phagocytosis of opsonized yeast, the expression of CXCR1 and CXCR2 was substantially down-regulated and was accompanied by reduced Ca(++) responses to corresponding ligands, IL-8 and neutrophil-activating peptide-2 (NAP-2). The levels of CXCR1 and CXCR2 mRNA were constant during phagocytic stimulation of neutrophils. Confocal microscopy revealed that CXCR reduction was not via internalization. Metalloproteinase inhibitor, 1,10-phenantroline, prevented the reduction of CXCRs induced by phagocytosis, indicating that proteolytic degradation may be responsible for down-regulation. These observations suggest that down-regulation of CXCR expression may substantially reduce the responsiveness of phagocytosing neutrophils to CXC chemokines.

A possible role for CXCR4 and its ligand, the CXC chemokine stromal cell-derived factor-1, in the development of bone marrow metastases in neuroblastoma

The homing of hemopoietic stem cells to the bone marrow is mediated by specific interactions occurring between CXCR4, which is expressed on hemopoietic stem cells, and its ligand, stromal cell-derived factor-1 (SDF-1), a CXC chemokine secreted by bone marrow stromal cells. In the present study we evaluated the possibility that neuroblastoma cells use a mechanism similar to that used by hemopoietic stem cells to home to the bone marrow and adhere to bone marrow stromal cells. Our study suggests that CXCR4 expression may be a general characteristic of neuroblastoma cells. SH-SY5Y neuroblastoma cells express not only CXCR4, but also its ligand, SDF-1. CXCR4 expression on SH-SY5Y neuroblastoma cells is tightly regulated by tumor cell-derived SDF-1, as demonstrated by the ability of neutralizing Abs against human SDF-1alpha to up-regulate CXCR4 expression on the tumor cells. The reduction in CXCR4 expression following short term exposure to recombinant human SDF-1alpha can be recovered as a result of de novo receptor synthesis. Recombinant human SDF-1alpha induces the migration of CXCR4-expressing SH-SY5Y neuroblastoma cells in CXCR4- and heterotrimeric G protein-dependent manners. Furthermore, SH-SY5Y cells interact at multiple levels with bone marrow components, as evidenced by the fact that bone marrow-derived constituents promote SH-SY5Y cell migration, adhesion to bone marrow stromal cells, and proliferation. These results suggest that SH-SY5Y neuroblastoma cells are equipped with adequate machinery to support their homing to the bone marrow. Therefore, the ability of neuroblastoma tumors to preferentially form metastases in the bone marrow may be influenced by a set of complex CXCR4-SDF-1 interactions.