Intercellular adhesion molecule-1 dimerization and its consequences for adhesion mediated by lymphocyte function associated-1

Computational prediction of protein interactions in single cells by proximity sequencing

Proximity sequencing (Prox-seq) simultaneously measures gene expression, protein expression and protein complexes on single cells. Using information from dual-antibody binding events, Prox-seq infers surface protein dimers at the single-cell level. Prox-seq provides multi-dimensional phenotyping of single cells in high throughput, and was recently used to track the formation of receptor complexes during cell signaling and discovered a novel interaction between CD9 and CD8 in naïve T cells. The distribution of protein abundance can affect identification of protein complexes in a complicated manner in dual-binding assays like Prox-seq. These effects are difficult to explore with experiments, yet important for accurate quantification of protein complexes. Here, we introduce a physical model of Prox-seq and computationally evaluate several different methods for reducing background noise when quantifying protein complexes. Furthermore, we developed an improved method for analysis of Prox-seq data, which resulted in more accurate and robust quantification of protein complexes. Finally, our Prox-seq model offers a simple way to investigate the behavior of Prox-seq data under various biological conditions and guide users toward selecting the best analysis method for their data.

Complementary CRISPR screen highlights the contrasting role of membrane-bound and soluble ICAM-1 in regulating antigen-specific tumor cell killing by cytotoxic T cells

Cytotoxic CD8 +T lymphocytes (CTLs) are key players of adaptive anti-tumor immunity based on their ability to specifically recognize and destroy tumor cells. Many cancer immunotherapies rely on unleashing CTL function. However, tumors can evade killing through strategies which are not yet fully elucidated. To provide deeper insight into tumor evasion mechanisms in an antigen-dependent manner, we established a human co-culture system composed of tumor and primary immune cells. Using this system, we systematically investigated intrinsic regulators of tumor resistance by conducting a complementary CRISPR screen approach. By harnessing CRISPR activation (CRISPRa) and CRISPR knockout (KO) technology in parallel, we investigated gene gain-of-function as well as loss-of-function across genes with annotated function in a colon carcinoma cell line. CRISPRa and CRISPR KO screens uncovered 187 and 704 hits, respectively, with 60 gene hits overlapping between both. These data confirmed the role of interferon-γ (IFN-γ), tumor necrosis factor α (TNF-α) and autophagy pathways and uncovered novel genes implicated in tumor resistance to killing. Notably, we discovered that ILKAP encoding the integrin-linked kinase-associated serine/threonine phosphatase 2 C, a gene previously unknown to play a role in antigen specific CTL-mediated killing, mediate tumor resistance independently from regulating antigen presentation, IFN-γ or TNF-α responsiveness. Moreover, our work describes the contrasting role of soluble and membrane-bound ICAM-1 in regulating tumor cell killing. The deficiency of membrane-bound ICAM-1 (mICAM-1) or the overexpression of soluble ICAM-1 (sICAM-1) induced resistance to CTL killing, whereas PD-L1 overexpression had no impact. These results highlight the essential role of ICAM-1 at the immunological synapse between tumor and CTL and the antagonist function of sICAM-1.

Computational prediction of protein interactions on single cells by proximity sequencing

Proximity sequencing (Prox-seq) measures gene expression, protein expression, and protein complexes at the single cell level, using information from dual-antibody binding events and a single cell sequencing readout. Prox-seq provides multi-dimensional phenotyping of single cells and was recently used to track the formation of receptor complexes during inflammatory signaling in macrophages and to discover a new interaction between CD9/CD8 proteins on naïve T cells. The distribution of protein abundance affects identification of protein complexes in a complicated manner in dual-binding assays like Prox-seq. These effects are difficult to explore with experiments, yet important for accurate quantification of protein complexes. Here, we introduce a physical model for protein dimer formation on single cells and computationally evaluate several different methods for reducing background noise when quantifying protein complexes. Furthermore, we developed an improved method for analysis of Prox-seq single-cell data, which resulted in more accurate and robust quantification of protein complexes. Finally, our model offers a simple way to investigate the behavior of Prox-seq under various biological conditions and guide users toward selecting the best analysis method for their data.

Intercellular Adhesion Molecule 1: More than a Leukocyte Adhesion Molecule

Intercellular adhesion molecule 1 (ICAM-1) is a transmembrane protein in the immunoglobulin superfamily expressed on the surface of multiple cell populations and upregulated by inflammatory stimuli. It mediates cellular adhesive interactions by binding to the β2 integrins macrophage antigen 1 and leukocyte function-associated antigen 1, as well as other ligands. It has important roles in the immune system, including in leukocyte adhesion to the endothelium and transendothelial migration, and at the immunological synapse formed between lymphocytes and antigen-presenting cells. ICAM-1 has also been implicated in the pathophysiology of diverse diseases from cardiovascular diseases to autoimmune disorders, certain infections, and cancer. In this review, we summarize the current understanding of the structure and regulation of the ICAM1 gene and the ICAM-1 protein. We discuss the roles of ICAM-1 in the normal immune system and a selection of diseases to highlight the breadth and often double-edged nature of its functions. Finally, we discuss current therapeutics and opportunities for advancements.

Quantitative imaging of vesicle-protein interactions reveals close cooperation among proteins

Membrane-bound vesicles such as extracellular vesicles (EVs) can function as biochemical effectors on target cells. Docking of the vesicles onto recipient plasma membranes depends on their interaction with cell-surface proteins, but a generalizable technique that can quantitatively observe these vesicle-protein interactions (VPIs) is lacking. Here, we describe a fluorescence microscopy that measures VPIs between single vesicles and cell-surface proteins, either in a surface-tethered or in a membrane-embedded state. By employing cell-derived vesicles (CDVs) and intercellular adhesion molecule-1 (ICAM-1) as a model system, we found that integrin-driven VPIs exhibit distinct modes of affinity depending on vesicle origin. Controlling the surface density of proteins also revealed a strong support from a tetraspanin protein CD9, with a critical dependence on molecular proximity. An adsorption model accounting for multiple protein molecules was developed and captured the features of density-dependent cooperativity. We expect that VPI imaging will be a useful tool to dissect the molecular mechanisms of vesicle adhesion and uptake, and to guide the development of therapeutic vesicles.

The magnitude of LFA-1/ICAM-1 forces fine-tune TCR-triggered T cell activation

T cells defend against cancer and viral infections by rapidly scanning the surface of target cells seeking specific peptide antigens. This key process in adaptive immunity is sparked upon T cell receptor (TCR) binding of antigens within cell-cell junctions stabilized by integrin (LFA-1)/intercellular adhesion molecule-1 (ICAM-1) complexes. A long-standing question in this area is whether the forces transmitted through the LFA-1/ICAM-1 complex tune T cell signaling. Here, we use spectrally encoded DNA tension probes to reveal the first maps of LFA-1 and TCR forces generated by the T cell cytoskeleton upon antigen recognition. DNA probes that control the magnitude of LFA-1 force show that F>12 pN potentiates antigen-dependent T cell activation by enhancing T cell-substrate engagement. LFA-1/ICAM-1 mechanical events with F>12 pN also enhance the discriminatory power of the TCR when presented with near cognate antigens. Overall, our results show that T cells integrate multiple channels of mechanical information through different ligand-receptor pairs to tune function.

Gene regulation of intracellular adhesion molecule-1 (ICAM-1): A molecule with multiple functions

Intracellular adhesion molecule 1 (ICAM-1) is one of the most extensively studied inducible cell adhesion molecules which is responsible for several immune functions like T cell activation, extravasation, inflammation, etc. The molecule is constitutively expressed over the cell surface and is regulated up / down in response to inflammatory mediators like cellular stress, proinflammatory cytokines, viral infection. These stimuli modulate the expression of ICAM-1 primarily through regulating the ICAM-1 gene transcription. On account of the presence of various binding sites for NF-κB, AP-1, SP-1, and many other transcription factors, the architecture of the ICAM-1 promoter become complex. Transcription factors in union with other transcription factors, coactivators, and suppressors promote their assembly in a stereospecific manner on ICAM-1 promoter which mediates ICAM-1 regulation in response to different stimuli. Along with transcriptional regulation, epigenetic modifications also play a pivotal role in controlling ICAM-1 expression on different cell types. In this review, we summarize the regulation of ICAM-1 expression both at the transcriptional as well as post-transcriptional level with an emphasis on transcription factors and signaling pathways involved.

Time-Resolved and Comprehensive Analysis of Surface Glycoproteins Reveals Distinct Responses of Monocytes and Macrophages to Bacterial Infection

Glycoproteins on the surface of immune cells play extremely important roles in response to pathogens. Yet, a systematic and time-resolved investigation of surface glycoproteins during the immune response remains to be explored. Integrating selective enrichment of surface glycoproteins with multiplexed proteomics, we globally and site-specifically quantified the dynamics of surface glycoproteins on THP-1 monocytes and macrophages in response to bacterial infection and during the monocyte-to-macrophage differentiation. The time-resolved analysis reveals transient changes and differential remodeling of surface glycoproteins on both cell types, and potential upstream regulators and downstream effects of the regulated glycoproteins. Besides, we identified novel surface glycoproteins participating in the immune response such as APMAP, and site-specific changes of glycoproteins. This study provides unprecedented information to deepen our understanding of glycoproteins and cellular activities.

Time-Resolved and Comprehensive Analysis of Surface Glycoproteins Reveals Distinct Responses of Monocytes and Macrophages to Bacterial Infection

Glycoproteins on the surface of immune cells play extremely important roles in response to pathogens. Yet, a systematic and time-resolved investigation of surface glycoproteins during the immune response remains to be explored. Integrating selective enrichment of surface glycoproteins with multiplexed proteomics, we globally and site-specifically quantified the dynamics of surface glycoproteins on THP-1 monocytes and macrophages in response to bacterial infection and during the monocyte-to-macrophage differentiation. The time-resolved analysis reveals transient changes and differential remodeling of surface glycoproteins on both cell types, and potential upstream regulators and downstream effects of the regulated glycoproteins. Besides, we identified novel surface glycoproteins participating in the immune response such as APMAP, and site-specific changes of glycoproteins. This study provides unprecedented information to deepen our understanding of glycoproteins and cellular activities.

Structure basis for AA98 inhibition on the activation of endothelial cells mediated by CD146

CD146 is an adhesion molecule that plays important roles in angiogenesis, cancer metastasis, and immune response. It exists as a monomer or dimer on the cell surface. AA98 is a monoclonal antibody that binds to CD146, which abrogates the activation of CD146-mediated signaling pathways and shows inhibitory effects on tumor growth. However, how AA98 inhibits the function of CD146 remains unclear. Here, we describe a crystal structure of the CD146/AA98 Fab complex at a resolution of 2.8 Å. Monomeric CD146 is stabilized by AA98 Fab binding to the junction region of CD146 domains 4 and 5. A higher-affinity AA98 variant (here named HA98) was thus rationally designed. Better binding to CD146 and prominent inhibition on cell migration were achieved with HA98. Further experiments on xenografted melanoma in mice with HA98 revealed superior inhibitory effects on tumor growth to those of AA98, which suggested future applications of this antibody in cancer therapy.

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Structural analysis elucidated how mAb AA98 inhibited CD146-mediated EC activation

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AA98-stabilized CD146 in monomer thus inhibited activation of EC

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Higher affinity monoclonal antibody HA98 was rationally designed for cancer treatment

CX3CL1 homo-oligomerization drives cell-to-cell adherence

During inflammatory response, blood leukocytes adhere to the endothelium. This process involves numerous adhesion molecules, including a transmembrane chemokine, CX3CL1, which behaves as a molecular cluster. How this cluster assembles and whether this association has a functional role remain unknown. The analysis of CX3CL1 clusters using native electrophoresis and single molecule fluorescence kinetics shows that CX3CL1 is a homo-oligomer of 3 to 7 monomers. Fluorescence recovery after photobleaching assays reveal that the CX3CL1-transmembrane domain peptide self-associates in both cellular and acellular lipid environments, while its random counterpart (i.e. peptide with the same residues in a different order) does not. This strongly indicates that CX3CL1 oligomerization is driven by its intrinsic properties. According to the molecular modeling, CX3CL1 does not associate in compact bundles but rather with monomers linearly assembled side by side. Finally, the CX3CL1 transmembrane peptide inhibits both the CX3CL1 oligomerization and the adhesive function, while its random counterpart does not. This demonstrates that CX3CL1 oligomerization is mandatory for its adhesive potency. Our results provide a new direction to control CX3CL1-dependent cellular adherence in key immune processes.

Omentin-1 Ameliorated Free Fatty Acid-Induced Impairment in Proliferation, Migration, and Inflammatory States of HUVECs

Objectives

Endothelial cell injury is a critical pathological change during the development of atherosclerosis. Here, we explored the effect of omentin-1 on free fatty acid- (FFA-) induced endothelial cell injury.

Methods

An FFA-induced endothelial cell injury model was established to investigate the role of omentin-1 in this process. Cell proliferation was analyzed with the Cell Counting Kit assay and flow cytometry. Scratch and transwell assays were used to evaluate cell migration. Factors secreted by endothelial cells after injury were detected by western blotting, reverse-transcription quantitative polymerase chain reaction, and cellular fluorescence assay.

Results

Omentin-1 rescued the FFA-induced impaired proliferation and migration capabilities of human umbilical vein endothelial cells (HUVECs). It decreased the number of THP-1 cells attached to HUVECs in response to injury and inhibited the FFA-induced proinflammatory state of HUVECs.

Conclusion

Omentin-1 could partly ameliorate FFA-induced endothelial cell injury.

ICAM-1: A master regulator of cellular responses in inflammation, injury resolution, and tumorigenesis

ICAM-1 is a cell surface glycoprotein and an adhesion receptor that is best known for regulating leukocyte recruitment from circulation to sites of inflammation. However, in addition to vascular endothelial cells, ICAM-1 expression is also robustly induced on epithelial and immune cells in response to inflammatory stimulation. Importantly, ICAM-1 serves as a biosensor to transduce outside-in-signaling via association of its cytoplasmic domain with the actin cytoskeleton following ligand engagement of the extracellular domain. Thus, ICAM-1 has emerged as a master regulator of many essential cellular functions both at the onset and at the resolution of pathologic conditions. Because the role of ICAM-1 in driving inflammatory responses is well recognized, this review will mainly focus on newly emerging roles of ICAM-1 in epithelial injury-resolution responses, as well as immune cell effector function in inflammation and tumorigenesis. ICAM-1 has been of clinical and therapeutic interest for some time now; however, several attempts at inhibiting its function to improve injury resolution have failed. Perhaps, better understanding of its beneficial roles in resolution of inflammation or its emerging function in tumorigenesis will spark new interest in revisiting the clinical value of ICAM-1 as a potential therapeutic target.

Association between K469E polymorphism of ICAM‐1 gene and susceptibility of ischemic stroke: An updated meta‐analysis

Background

The intercellular adhesion molecule‐1 (ICAM‐1)/leukocyte function associated antigen‐1 (LFA‐1) adhesion system regulates leukocyte interactions, migration, and adhesion, and appears to play an important role in atherosclerosis and thrombosis. Therefore, single nucleotide polymorphisms (SNPs) of the ICAM‐1 gene may strongly influence the expression and biological activity of ICAM‐1 and play a potentially important role in the pathogenesis of ischemic stroke. In the current meta‐analysis, we investigated the relationship between the ICAM‐1 gene K469E SNP and the risk of ischemic stroke.

Methods

Two investigators independently searched PubMed, Web of Science, Google Scholar, WANFANG, China National Knowledge Infrastructure (CNKI) and J‐STAGE for studies published from January 2000 to February 2019 without language restriction. The association of K469E polymorphism and ischemic stroke in three genetic models (allelic, recessive, and dominant) were evaluated using Pooled odds ratios (ORs) with 95% confidence intervals (CIs).

Results

Our study included 20 studies from four continents and four different countries, including 3,137 cases and 15,382 controls. Meta‐analysis results did not show a significant association between K469E polymorphism of ICAM‐1 gene and ischemic stroke when assuming allelic model (OR: 1.12; 95% CI: 0.8 to 1.55; p = 0.51; I² = 93%) or recessive model (OR: 1.28; 95% CI: 0.89 to 1.84; p = 0.18; I² = 82%) or dominant model (OR: 1.20; 95% CI: 0.92 to 1.56; p = 0.17; I² = 85%). However, in all three genetic models, subgroup analysis revealed that the K469E polymorphism of the ICAM‐1 gene is associated with ischemic stroke in the Caucasian population.

Conclusion

K469E polymorphism of ICAM‐1 gene might be a risk factor for ischemic stroke in Caucasians, which suggested that K469E polymorphism might help in early identification of those at risk and help in primary prevention of ischemic stroke.

Integrated proteomic analysis of tumor necrosis factor α and interleukin 1β-induced endothelial inflammation

The vascular endothelium provides a unique interaction plane for plasma proteins and leukocytes in inflammation. The pro-inflammatory cytokines Tumor Necrosis Factor α (TNFα) and interleukin 1β (IL-1β) have a profound effect on endothelial cells, which includes increased levels of adhesion molecules and a disrupted barrier function. To assess the endothelial response to these cytokines at the protein level, we evaluated changes in the whole proteome, cell surface proteome and phosphoproteome after 24 h of cytokine treatment. The effects of TNFα and IL-1β on endothelial cells were strikingly similar and included changes in proteins not previously associated with endothelial inflammation. Temporal profiling revealed time-dependent proteomic changes, including a limited number of early responsive proteins such as adhesion receptors ICAM1 and SELE. In addition, this approach uncovered a greater number of late responsive proteins, including proteins related to self-antigen peptide presentation, and a transient increase in ferritin. Peptide-based cell surface proteomics revealed extensive changes at the cell surface, which were in agreement with the whole proteome. In addition, site-specific changes within ITGA5 and ICAM1 were detected. Combined, our integrated proteomic data provide detailed information on endothelial inflammation, emphasize the role of the extracellular matrix therein, and include potential targets for therapeutic intervention. SIGNIFICANCE: Pro-inflammatory cytokines induce the expression of cell adhesion molecules in vascular endothelial cells. These molecules mediate the adhesion and migration of immune cells across the vessel wall, which is a key process to resolve infections in the underlying tissue. Dysregulation of endothelial inflammation can contribute to vascular diseases and the vascular endothelium is therefore an attractive target to control inflammation. Current strategies targeting endothelial adhesion molecules, including PECAM, CD99, ICAM1 and VCAM1 do not completely prevent transmigration. To identify additional therapeutic targets, we mapped the endothelial proteome after pro-inflammatory cytokine treatment. In addition to the whole proteome, we assessed the surface proteome to focus on cell adhesion molecules, and the phosphoproteome to uncover protein activation states. Here, we present an integrated overview of affected processes which further improves our understanding of endothelial inflammation and may eventually aid in therapeutic intervention of imbalanced inflammation.

Ligand-specific binding forces of LFA-1 and Mac-1 in neutrophil adhesion and crawling

The force spectra for various LFA-1/Mac-1–ligand bonds were compared and their functions tested in mediating PMN recruitment under flow. Multiple endothelial ligands present distinct bond rupture forces and lifetimes, which correlate well with their biological phenotypes. In addition to ICAM, JAM or RAGE is also crucial in cell adhesion and crawling.

Lymphocyte function–associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1) and their counterreceptors such as intercellular cell adhesion molecules (ICAM-1 and ICAM-2), junctional adhesion molecules (JAM-A, JAM-C), and receptors for advanced glycation end products (RAGE) are crucial for promoting polymorphonuclear leukocyte (neutrophil, PMN) recruitment. The underlying mechanisms of ligand-specific bindings in this cascade remain incompletely known. We compared the dynamic force spectra for various LFA-1/Mac-1–ligand bonds using single-molecule atomic force microscopy (AFM) and tested their functions in mediating PMN recruitment under in vitro shear flow. Distinct features of bond rupture forces and lifetimes were uncovered for these ligands, implying their diverse roles in regulating PMN adhesion on endothelium. LFA-1 dominates PMN adhesion on ICAM-1 and ICAM-2, while Mac-1 mediates PMN adhesion on RAGE, JAM-A, and JAM-C, which is consistent with their bond strength. All ligands can trigger PMN spreading and polarization, in which Mac-1 seems to induce outside-in signaling more effectively. LFA-1–ICAM-1 and LFA-1/Mac-1–JAM-C bonds can accelerate PMN crawling under high shear stress, presumably due to their high mechanical strength. This work provides new insight into basic molecular mechanisms of physiological ligands of β2 integrins in PMN recruitment.

Breast cancer cells compete with hematopoietic stem and progenitor cells for intercellular adhesion molecule 1-mediated binding to the bone marrow microenvironment

Adhesion-based cellular interactions involved in breast cancer metastasis to the bone marrow remain elusive. We identified that breast cancer cells directly compete with hematopoietic stem and progenitor cells (HSPCs) for retention in the bone marrow microenvironment. To this end, we established two models of competitive cell adhesion-simultaneous and sequential-to study a potential competition for homing to the niche and displacement of the endogenous HSPCs upon invasion by tumor cells. In both models, breast cancer cells but not non-tumorigenic cells competitively reduced adhesion of HSPCs to bone marrow-derived mesenchymal stromal cells (MSCs) in a tumor cell number-dependent manner. Higher adhesive force between breast cancer cells and MSCs, as compared with HSPCs, assessed by quantitative atomic force microscopy-based single-cell force spectroscopy could partially account for tumor cell mediated reduction in HSPC adhesion to MSCs. Genetic inactivation and blockade studies revealed that homophilic interactions between intercellular adhesion molecule 1 (ICAM-1) expressed on tumor cells and MSCs, respectively, regulate the competition between tumor cells and HSPCs for binding to MSCs. Moreover, tumor cell-secreted soluble ICAM-1(sICAM-1) also impaired HSPC adhesion via blocking CD18-ICAM-1 binding between HSPCs and MSCs. Xenotransplantation studies in NOD.Cg-Prkdc(scid) Il2rg(tm1Wjl)/SzJ mice revealed reduction of human HSPCs in the bone marrow via metastatic breast cancer cells. These findings point to a direct competitive interaction between disseminated breast cancer cells and HSPCs within the bone marrow micro environment. This interaction might also have implications on niche-based tumor support. Therefore, targeting this cross talk may represent a novel therapeutic strategy.

Polymorphism rs5498 of the ICAM-1 gene affects the progression of carotid atherosclerosis in patients with type 2 diabetes mellitus

Background

Adhesion molecules are involved in the development of atherosclerosis. An increased level of the ICAM 1 molecule is associated with numerous inflammatory diseases including atherosclerosis of carotid arteries. The rs5498 (K469E) polymorphism of the ICAM-1 gene leads to an increase in the level of serum ICAM. We investigated the association between the rs5498 (K469E) polymorphism of the ICAM-1 gene and the progression of carotid atherosclerosis in subjects with type 2 diabetes mellitus (T2DM).

Methods

The study included 595 patients with T2DM and 200 subjects in the control group without T2DM. The control examination was made 3.8 years after the initial examination. Indicators of atherosclerosis (carotid intima-media thickness (CIMT), total plaque sum and sum of the plaques thickness) were detected by ultrasound examination. Genetic analyses of the polymorphism rs5498 of the ICAM-1 gene were made by RT-PCR.

Results

The distribution of genotypes and frequencies of rs5498 polymorphism was not significantly different between the group with type 2 diabetes ( T2DM) and the control group. Genotype EE K469E polymorphism is associated with a statistically significant annual plaques growth.

Conclusion

The EE genotype of the rs5498 of the ICAM-1 gene was associated with a more rapid progression of carotid atherosclerosis in patients with T2DM in comparison with other genotypes.

The regulation of transendothelial migration: new knowledge and new questions

Leucocyte transendothelial migration (TEM) involves a co-operative series of interactions between surface molecules on the leucocyte and cognate counter-ligands on the endothelial cell. These interactions set up a cascade of signalling events inside the endothelial cell that both allow for the junctions to loosen and for membrane to be recruited from the lateral border recycling compartment (LBRC). The LBRC is thought to provide an increased surface area and unligated receptors to the leucocyte to continue the process. The relative importance of the individual adhesion/signalling molecules that promote transmigration may vary depending on the type of leucocyte, the vascular bed, the inflammatory stimulus, and the stage of the inflammatory response. However, the molecular interactions between leucocyte and endothelial cell activate signalling pathways that disengage the adherens and tight junctions and recruit the LBRC to the site of transmigration. With the exception of disengaging the junctions, similar molecules and mechanisms promote transcellular migration as paracellular migration of leucocytes. This review will discuss the molecular interactions and signalling pathways that regulate transmigration, and the common themes that emerge from studying TEM of different leucocyte subsets under different inflammatory conditions. We will also raise some unanswered questions in need of future research.

MUC1-mediated motility in breast cancer: a review highlighting the role of the MUC1/ICAM-1/Src signaling triad

Breast cancer is the most common cancer in women with the leading cause of death being metastasis, the spread of cancer to distant organs. For those patients with high-risk estrogen receptor positive (ER+) breast cancer, an increased expression of the glycoprotein MUC1 is associated with resistance to anti-hormonal therapy, metastasis and death. Tumor cells may use MUC1 to metastasize by exploiting the vascular adhesion pathways used by leukocytes during the inflammatory response. MUC1 is a type 1 transmembrane protein whose cytoplasmic tail acts as a scaffold for several signaling pathways including the non-receptor kinase Src, a signaling molecule involved in cell differentiation, proliferation, adhesion and motility. This review will highlight our current knowledge of how MUC1/ICAM-1 binding can lead to the recruitment and activation of Src and propose a novel role for lipid raft microdomains in this promigratory signaling. Improved understanding of the mechanism of metastases and the underlying signaling cascade is a prerequisite to the discovery of therapeutic targets to prevent metastasis and death in ER+ breast cancer patients.

The dendritic cell cytoskeleton promotes T cell adhesion and activation by constraining ICAM-1 mobility

Integrity of the dendritic cell (DC) actin cytoskeleton is essential for T cell priming, but the underlying mechanisms are poorly understood. We show that the DC F-actin network regulates the lateral mobility of intracellular cell adhesion molecule 1 (ICAM-1), but not MHCII. ICAM-1 mobility and clustering are regulated by maturation-induced changes in the expression and activation of moesin and α-actinin-1, which associate with actin filaments and the ICAM-1 cytoplasmic domain. Constrained ICAM-1 mobility is important for DC function, as DCs expressing a high-mobility ICAM-1 mutant lacking the cytoplasmic domain exhibit diminished antigen-dependent conjugate formation and T cell priming. These defects are associated with inefficient induction of leukocyte functional antigen 1 (LFA-1) affinity maturation, which is consistent with a model in which constrained ICAM-1 mobility opposes forces on LFA-1 exerted by the T cell cytoskeleton, whereas ICAM-1 clustering enhances valency and further promotes ligand-dependent LFA-1 activation. Our results reveal an important new mechanism through which the DC cytoskeleton regulates receptor activation at the immunological synapse.

Getting leukocytes to the site of inflammation

There is no "response" in either the innate or adaptive immune response unless leukocytes cross blood vessels. They do this through the process of diapedesis, in which the leukocyte moves in ameboid fashion through tightly apposed endothelial borders (paracellular transmigration) and in some cases through the endothelial cell itself (transcellular migration). This review summarizes the steps leading up to diapedesis, then focuses on the molecules and mechanisms responsible for transendothelial migration. Surprisingly, many of the same molecules and mechanisms that regulate paracellular migration also control transcellular migration, including a major role for membrane from the recently described lateral border recycling compartment. A hypothesis that integrates the various known mechanisms of transmigration is proposed.

Relationship between adhesion molecules and virological response to pegylated interferon-alpha-2a treatment in patients with chronic hepatitis B: A pilot study

AIM

We performed a clinical study to investigate potential association between serum levels of soluble adhesion molecules and virological response to pegylated interferon-alpha-2a (PEG IFN-α-2a) treatment in patients with chronic hepatitis B (CHB).

METHODS

Thirty-two patients with chronic hepatitis B virus genotype B were recruited in this study, who were treated with PEG IFN-α-2a 180 μg every week and then followed up for 24 weeks. Thirty healthy control subjects were recruited from volunteer blood donors. Serum concentrations of soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), soluble E-selectin (sE-selectin), soluble L-selectin (sL-selectin) in patients were investigated by enzyme-linked immunoassay before and after treatment.

RESULTS

Serum concentrations of sICAM-1, sVCAM-1, sE-selectin and sL-selectin in CHB patients were significantly higher compared to the control group before treatment (P < 0.00001, respectively). In CHB patients responding to the PEG IFN-α-2a treatment, serum levels of sICAM-1, sVCAM-1, sE-selectin and sL-selectin were higher than those in non-responders before treatment (PI  = 0.001, PV  = 0.002, PE  = 0.02, PL  = 0.004). The levels of sICAM-1, sVCAM-1, sE-selectin and sL-selectin decreased in virological responders of treatment at 12 and 24 weeks (PI  = 0.0001, PV  = 0.00004, PE  = 0.002, PL  = 0.0004; PI  = 0.00007, PV  = 0.00001, PE  = 0.0003, PL  = 0.00003), while no obvious changes were observed in non-responders (P > 0.05, respectively).

CONCLUSION

Results obtained indicated increased levels of sICAM-1, sVCAM-1, sE-selectin and sL-selectin could be related to virological response to PEG IFN-α-2a treatment in CHB patients, and have a prognostic effect on virological response.

Intercellular adhesion molecule-1 expression by skeletal muscle cells augments myogenesis

We previously demonstrated that the expression of intercellular adhesion molecule-1 (ICAM-1) by skeletal muscle cells after muscle overload contributes to ensuing regenerative and hypertrophic processes in skeletal muscle. The objective of the present study is to reveal mechanisms through which skeletal muscle cell expression of ICAM-1 augments regenerative and hypertrophic processes of myogenesis. This was accomplished by genetically engineering C2C12 myoblasts to stably express ICAM-1, and by inhibiting the adhesive and signaling functions of ICAM-1 through the use of a neutralizing antibody or cell penetrating peptide, respectively. Expression of ICAM-1 by cultured skeletal muscle cells augmented myoblast-myoblast adhesion, myotube formation, myonuclear number, myotube alignment, myotube-myotube fusion, and myotube size without influencing the ability of myoblasts to proliferate or differentiate. ICAM-1 augmented myotube formation, myonuclear accretion, and myotube alignment through a mechanism involving adhesion-induced activation of ICAM-1 signaling, as these dependent measures were reduced via antibody and peptide inhibition of ICAM-1. The adhesive and signaling functions of ICAM-1 also facilitated myotube hypertrophy through a mechanism involving myotube-myotube fusion, protein synthesis, and Akt/p70s6k signaling. Our findings demonstrate that ICAM-1 expression by skeletal muscle cells augments myogenesis, and establish a novel mechanism through which the inflammatory response facilitates growth processes in skeletal muscle.

Association of ICAM-1 K469E polymorphism with neurocysticercosis

Neurocysticercosis (NCC), a central nervous system (CNS) disease is caused by the larval stage of Taenia solium. The disease is heterogeneous in clinical presentation; some infected individuals develop symptoms and others may remain symptom free. Impaired blood brain barrier allows recruitment of immune cells in the CNS during infection and soluble intercellular adhesion molecule-1 (sICAM-1) plays an important role in the recruitment of immune cells. We studied ICAM-1 K469E polymorphism among symptomatic and asymptomatic NCC patients. The study revealed that individuals with variant (EE) genotype were more susceptible to symptomatic NCC and also had an elevated level of sICAM-1.

ICAM-1: isoforms and phenotypes

ICAM-1 plays an important role in leukocyte trafficking, immunological synapse formation, and numerous cellular immune responses. Although considered a single glycoprotein, there are multiple membrane-bound and soluble ICAM-1 isoforms that arise from alternative splicing and proteolytic cleavage during inflammatory responses. The function and expression of these isoforms on various cell types are poorly understood. In the generation of ICAM-1-deficient mice, two isoform-deficient ICAM-1 mutants were inadvertently produced as a result of alternative splicing. These mice, along with true ICAM-1-deficient mice and newly generated ICAM-1-transgenic mice, have provided the opportunity to begin examining the role of ICAM-1 isoforms (singly or in combination) in various disease settings. In this review, we highlight the sharply contrasting disease phenotypes using ICAM-1 isoform mutant mice. These studies demonstrate that ICAM-1 immunobiology is highly complex but that individual isoforms, aside from the full-length molecule, make significant contributions to disease development and pathogenesis.

Methylene blue modulates transendothelial migration of peripheral blood cells

Vasoplegia is a severe complication after cardiac surgery. Within the last years the administration of nitric oxide synthase inhibitor methylene blue (MB) became a new therapeutic strategy. Our aim was to investigate the role of MB on transendothelial migration of circulating blood cells, the potential role of cyclic cGMP, eNOS and iNOS in this process, and the influence of MB on endothelial cell apoptosis. Human vascular endothelial cells (HuMEC-1) were treated for 30 minutes or 2 hours with different concentrations of MB. Inflammation was mimicked by LPS stimulation prior and after MB. Transmigration of PBMCs and T-Lymphocytes through the treated endothelial cells was investigated. The influence of MB upon the different subsets of PBMCs (Granulocytes, T- and B-Lymphocytes, and Monocytes) was assessed after transmigration by means of flow-cytometry. The effect of MB on cell apoptosis was evaluated using Annexin-V and Propidium Iodide stainings. Analyses of the expression of cyclic cGMP, eNOS and iNOS were performed by means of RT-PCR and Western Blot. Results were analyzed using unpaired Students T-test. Analysis of endothelial cell apoptosis by MB indicated a dose-dependent increase of apoptotic cells. We observed time- and dose-dependent effects of MB on transendothelial migration of PBMCs. The prophylactic administration of MB led to an increase of transendothelial migration of PBMCs but not Jurkat cells. Furthermore, HuMEC-1 secretion of cGMP correlated with iNOS expression after MB administration but not with eNOS expression. Expression of these molecules was reduced after MB administration at protein level. This study clearly reveals that endothelial response to MB is dose- and especially time-dependent. MB shows different effects on circulating blood cell-subtypes, and modifies the release patterns of eNOS, iNOS, and cGMP. The transendothelial migration is modulated after treatment with MB. Furthermore, MB provokes apoptosis of endothelial cells in a dose/time-dependent manner.

Tyrosine phosphorylation of CD13 regulates inflammatory cell-cell adhesion and monocyte trafficking

CD13 is a large cell surface peptidase expressed on the monocytes and activated endothelial cells that is important for homing to and resolving the damaged tissue at sites of injury. We showed previously that cross-linking of human monocytic CD13 with activating Abs induces strong adhesion to endothelial cells in a tyrosine kinase- and microtubule-dependent manner. In the current study, we examined the molecular mechanisms underlying these observations in vitro and in vivo. We found that cross-linking of CD13 on U937 monocytic cells induced phosphorylation of a number of proteins, including Src, FAK, and ERK, and inhibition of these abrogated CD13-dependent adhesion. We found that CD13 itself was phosphorylated in a Src-dependent manner, which was an unexpected finding because its 7-aa cytoplasmic tail was assumed to be inert. Furthermore, CD13 was constitutively associated with the scaffolding protein IQGAP1, and CD13 cross-linking induced complex formation with the actin-binding protein α-actinin, linking membrane-bound CD13 to the cytoskeleton, further supporting CD13 as an inflammatory adhesion molecule. Mechanistically, mutation of the conserved CD13 cytoplasmic tyrosine to phenylalanine abrogated adhesion; Src, FAK, and ERK phosphorylation; and cytoskeletal alterations upon Ab cross-linking. Finally, CD13 was phosphorylated in isolated murine inflammatory peritoneal exudate cells, and adoptive transfer of monocytic cell lines engineered to express the mutant CD13 were severely impaired in their ability to migrate into the inflamed peritoneum, confirming that CD13 phosphorylation is relevant to inflammatory cell trafficking in vivo. Therefore, this study identifies CD13 as a novel, direct activator of intracellular signaling pathways in pathophysiological conditions.

Intracellular adhesion molecule-1 K469E gene polymorphism and risk of diabetic microvascular complications: a meta-analysis

BACKGROUND

A number of studies evaluated the association of intracellular adhesion molecule-1 (ICAM-1) K469E (rs5498, A/G) gene polymorphism with diabetic microvascular complications (DMI) including diabetic nephropathy (DN) and diabetic retinopathy (DR) in different populations. However, the results of individual studies remain conflicting.

METHODS

A comprehensive search was conducted to identify all eligible studies of the above-mentioned associations. The pooled odds ratios (ORs) and 95% confidence intervals (CIs) were assessed using the fixed or random effect model.

RESULTS

Seven studies involving 3411 subjects were included. Overall, the meta-analysis showed a significant association of the A allele with increased risk of DMI susceptibility in a recessive model (OR = 1.37, 95% CI 1.04-1.80, P = 0.02). In the subgroup analysis stratified by ethnicity, significant association was found in Asians but not in Caucasians (OR = 1.78, 95% CI 1.13-2.81, P = 0.01; OR = 1.10, 95% CI 0.79-1.54, P = 0.58, respectively). Moreover, it showed a significant association between the A allele and risk of DN in a recessive model (OR = 1.25, 95% CI 1.02-1.55, P = 0.04).

CONCLUSIONS

This meta-analysis suggested that the K469E polymorphism in ICAM-1 gene might affect individual susceptibility to DMI and showed a discrepancy in different ethnicities. Further investigations are needed to validate the association.

Molecular architecture of a complex between an adhesion protein from the malaria parasite and intracellular adhesion molecule 1

The adhesion of Plasmodium falciparum-infected erythrocytes to human tissues or endothelium is central to the pathology caused by the parasite during malaria. It contributes to the avoidance of parasite clearance by the spleen and to the specific pathologies of cerebral and placental malaria. The PfEMP1 family of adhesive proteins is responsible for this sequestration by mediating interactions with diverse human ligands. In addition, as the primary targets of acquired, protective immunity, the PfEMP1s are potential vaccine candidates. PfEMP1s contain large extracellular ectodomains made from CIDR (cysteine-rich interdomain regions) and DBL (Duffy-binding-like) domains and show extensive variation in sequence, size, and domain organization. Here we use biophysical methods to characterize the entire ∼300-kDa ectodomain from IT4VAR13, a protein that interacts with the host receptor, intercellular adhesion molecule-1 (ICAM-1). We show through small angle x-ray scattering that IT4VAR13 is rigid, elongated, and monomeric. We also show that it interacts with ICAM-1 through the DBLβ domain alone, forming a 1:1 complex. These studies provide a first low resolution structural view of a PfEMP1 ectodomain in complex with its ligand. They show that it combines a modular domain arrangement consisting of individual ligand binding domains, with a defined higher order architecture that exposes the ICAM-1 binding surface to allow adhesion.

Intercellular adhesion molecules (ICAMs) and spermatogenesis

BACKGROUND

During the seminiferous epithelial cycle, restructuring takes places at the Sertoli-Sertoli and Sertoli-germ cell interface to accommodate spermatogonia/spermatogonial stem cell renewal via mitosis, cell cycle progression and meiosis, spermiogenesis and spermiation since developing germ cells, in particular spermatids, move 'up and down' the seminiferous epithelium. Furthermore, preleptotene spermatocytes differentiated from type B spermatogonia residing at the basal compartment must traverse the blood-testis barrier (BTB) to enter the adluminal compartment to prepare for meiosis at Stage VIII of the epithelial cycle, a process also accompanied by the release of sperm at spermiation. These cellular events that take place at the opposite ends of the epithelium are co-ordinated by a functional axis designated the apical ectoplasmic specialization (ES)-BTB-basement membrane. However, the regulatory molecules that co-ordinate cellular events in this axis are not known.

METHODS

Literature was searched at http://www.pubmed.org and http://scholar.google.com to identify published findings regarding intercellular adhesion molecules (ICAMs) and the regulation of this axis.

RESULTS

Members of the ICAM family, namely ICAM-1 and ICAM-2, and the biologically active soluble ICAM-1 (sICAM-1) are the likely regulatory molecules that co-ordinate these events. sICAM-1 and ICAM-1 have antagonistic effects on the Sertoli cell tight junction-permeability barrier, involved in Sertoli cell BTB restructuring, whereas ICAM-2 is restricted to the apical ES, regulating spermatid adhesion during the epithelial cycle. Studies in other epithelia/endothelia on the role of the ICAM family in regulating cell movement are discussed and this information has been evaluated and integrated into studies of these proteins in the testis to create a hypothetical model, depicting how ICAMs regulate junction restructuring events during spermatogenesis.

CONCLUSIONS

ICAMs are crucial regulatory molecules of spermatogenesis. The proposed hypothetical model serves as a framework in designing functional experiments for future studies.

On the roles of polyvalent binding in immune recognition: perspectives in the nanoscience of immunology and the immune response to nanomedicines

Immunology often conveys the image of large molecules, either in the soluble state or in the membrane of leukocytes, forming multiple contacts with a target for actions of the immune system. Avidity names the ability of a polyvalent molecule to form multiple connections of the same kind with ligands tethered to the same surface. Polyvalent interactions are vastly stronger than their monovalent equivalent. In the present review, the functional consequences of polyvalent interactions are explored in a perspective of recent theoretical advances in understanding the thermodynamics of such binding. From insights on the structural biology of soluble pattern recognition molecules as well as adhesion molecules in the cell membranes or in their proteolytically shed form, this review documents the prominent role of polyvalent interactions in making the immune system a formidable barrier to microbial infection as well as constituting a significant challenge to the application of nanomedicines.

Quantitative modeling assesses the contribution of bond strengthening, rebinding and force sharing to the avidity of biomolecule interactions

Cell adhesion is mediated by numerous membrane receptors. It is desirable to derive the outcome of a cell-surface encounter from the molecular properties of interacting receptors and ligands. However, conventional parameters such as affinity or kinetic constants are often insufficient to account for receptor efficiency. Avidity is a qualitative concept frequently used to describe biomolecule interactions: this includes incompletely defined properties such as the capacity to form multivalent attachments. The aim of this study is to produce a working description of monovalent attachments formed by a model system, then to measure and interpret the behavior of divalent attachments under force. We investigated attachments between antibody-coated microspheres and surfaces coated with sparse monomeric or dimeric ligands. When bonds were subjected to a pulling force, they exhibited both a force-dependent dissociation consistent with Bell’s empirical formula and a force- and time-dependent strengthening well described by a single parameter. Divalent attachments were stronger and less dependent on forces than monovalent ones. The proportion of divalent attachments resisting a force of 30 piconewtons for at least 5 s was 3.7 fold higher than that of monovalent attachments. Quantitative modeling showed that this required rebinding, i.e. additional bond formation between surfaces linked by divalent receptors forming only one bond. Further, experimental data were compatible with but did not require stress sharing between bonds within divalent attachments. Thus many ligand-receptor interactions do not behave as single-step reactions in the millisecond to second timescale. Rather, they exhibit progressive stabilization. This explains the high efficiency of multimerized or clustered receptors even when bonds are only subjected to moderate forces. Our approach provides a quantitative way of relating binding avidity to measurable parameters including bond maturation, rebinding and force sharing, provided these parameters have been determined. Also, this provides a quantitative description of the phenomenon of bond strengthening.

Febrile-range hyperthermia modifies endothelial and neutrophilic functions to promote extravasation

Acute respiratory distress syndrome (ARDS) is a neutrophil (polymorphonuclear leukocyte; PMN)-driven lung injury that is associated with fever and heat-stroke, and involves approximately 40% mortality. In murine models of acute lung injury (ALI), febrile-range hyperthermia (FRH) enhanced PMN accumulation, vascular permeability, and epithelial injury, in part by augmenting pulmonary cysteine-x-cysteine (CXC) chemokine expression. To determine whether FRH increases chemokine responsiveness within the lung, we used in vivo and in vitro models that bypass the endogenous generation of chemokines. We measured PMN transalveolar migration (TAM) in mice after intratracheal instillations of the human CXC chemokine IL-8 in vivo, and of IL-8-directed PMN transendothelial migration (TEM) through human lung microvascular endothelial cell (HMVEC-L) monolayers in vitro. Pre-exposure to FRH increased in vivo IL-8-directed PMN TAM by 23.5-fold and in vitro TEM by 7-fold. Adoptive PMN transfer demonstrated that enhanced PMN TAM required both PMN donors and recipients to be exposed to FRH, suggesting interdependent effects on PMNs and endothelium. FRH exposure caused the activation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase in lung homogenates and circulating PMNs, with an associated increase in HSP27 phosphorylation and stress-fiber formation. The inhibition of these signaling pathways with U0126 and SB203580 blocked the effects of FRH on PMN extravasation in vivo and in vitro. Collectively, these results (1) demonstrate that FRH augments chemokine-directed PMN extravasation through direct effects on endothelium and PMNs, (2) identify ERK and p38 signaling pathways in the effect, and (3) underscore the complex effects of physiologic temperature change on innate immune function and its potential consequences for lung injury.

ICAM-1 K469E polymorphism is a genetic determinant for the clinical risk factors of T2D subjects with retinopathy in Indians: a population-based case-control study

OBJECTIVE

Elevated levels of intercellular adhesion molecule-1 (ICAM-1) are demonstrated in diabetes complications. The current study aims to understand association of K469E (rs5498) in ICAM-1 gene, in type 2 diabetic (T2D) subjects with retinopathy.

DESIGN

Case-control study.

SETTING

Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetic Study, an epidemiology study (on prevalence of diabetic retinopathy in T2D subjects (T2DR) from south India) and outpatient department of Sankara Nethralaya, a tertiary care hospital, in Chennai, India.

PARTICIPANTS

A total of 356 T2D subjects of >15 years of diabetes duration, with (n=199) and without (n=157) retinopathy.

METHODS

The rs5498 polymorphism was genotyped by direct sequencing. Multivariate analysis for various clinical covariates was done using SPSS V.14. Comparative assessment of structure stability, folding rate of the variants were assessed using bioinformatics tools like STRIDE, MuPro, ModellerV97, fold rate server, etc.

RESULTS

The AA genotype of rs5498 was seen at a higher frequency in the retinopathy group (p=0.012). The risk for diabetic retinopathy (DR) increased in the presence of AA genotype (OR=1.89-4.82) after the sequential addition of various clinical covariates. Multivariate logistic regression analysis showed 8.26 times high risk for developing DR in the AG genotype (p=0.003). Structural superimposition of ICAM-1 wild type (K469) and variant (E469) showed 0.943 Å of backbone root mean square deviation as calculated by PYMOL software. A difference in the fold rate time was also observed between the wild type (5.4/s) and variant (3.3/s).

CONCLUSIONS

This study shows that allele A of rs5498 in ICAM-1 is a putative risk predisposing allele for T2D retinopathy and its clinical covariates in Indian population. The folding rate of the protein decreases for the A allele implicating a potential effect on the structure and function of ICAM-1.

Procalcitonin, C-reactive protein, interleukin-6, and soluble intercellular adhesion molecule-1 as markers of postoperative orthopaedic joint prosthesis infections

There is a universally recognized need to identify new, reliable markers of inflammation that can aid in the rapid diagnosis of orthopaedic joint prosthesis infections (OJP-Is). Since prompt diagnosis is key to timely intervention in the course of infection, different molecules have been studied. In this study, we examined three groups of patients: those with prosthesis infection, those without infection, and a third group with previous infection in whom the infection had been cleared. Four presumed markers of infection were tested: procalcitonin (PCT); C-reactive protein (CRP); interleukin-6 (IL-6); and soluble intercellular adhesion molecule-1 (sICAM-1). The results showed that PCT cannot be considered as a good marker of periprosthetic infection as no statistically significant difference in serum PCT levels emerged between patients with infection and controls or patients without infection. In contrast, both sICAM-1 and CRP may be considered as good markers of infection, as measurement of their levels allowed us to distinguish between patients with and without infection, and between patients with infection and those with previous infection, since marker levels quickly returned to baseline values after clearance of the infection. IL-6 was found to be a good marker for inflammation, as it distinguished between patients with infection and the other groups. In the patients with previous infection, the IL-6 values remained high versus the controls but lower and with a statistically significant difference versus the patients with infection. Further studies are needed to determine the cut-off value of IL-6 between patients with infection and those with previous infection.

Determining beta2-integrin and intercellular adhesion molecule 1 binding kinetics in tumor cell adhesion to leukocytes and endothelial cells by a gas-driven micropipette assay

Interactions between polymorphonuclear neutrophils (PMNs) and tumor cells have been reported to facilitate the adhesion and subsequent extravasation of tumor cells through the endothelium under blood flow, both of which are mediated by binding β(2)-integrin to intercellular adhesion molecule 1 (ICAM-1). Here the adhesions between human WM9 metastatic melanoma cells, PMNs, and human pulmonary microvascular endothelial cells (HPMECs) were quantified by a gas-driven micropipette aspiration technique (GDMAT). Our data indicated that the cellular binding affinity of PMN-WM9 pair was 3.9-fold higher than that of the PMN-HPMEC pair. However, the effective binding affinities per molecular pair were comparable between the two cell pairs no matter whether WM9 cells or HPMECs were quiescent or cytokine-activated, indicating that the stronger adhesion between PMN-WM9 pair is mainly attributed to the high expression of ICAM-1 on WM9 cells. These results proposed an alternative mechanism, where WM9 melanoma cells adhere first with PMNs near vessel-wall regions and then bind to endothelial cells via PMNs under blood flow. In contrast, the adhesions between human MDA-MB-231 metastatic breast carcinoma cells and PMNs showed a comparable cellular binding affinity to PMN-HPMEC pair because the ICAM-1 expressions on MDA-MB-231 cells and HPMECs are similar. Furthermore, differences were observed in the intrinsic forward and reverse rates of the β(2)-integrin-ICAM-1 bond between PMN-TC and PMN-EC pairs. This GDMAT assay enables us to quantify the binding kinetics of cell adhesion molecules physiologically expressed on nucleated cells. The findings also further the understanding of leukocyte-facilitated tumor cell adhesion from the viewpoint of molecular binding kinetics.

Lack of association between intercellular adhesion molecule-1 (ICAM-1) polymorphisms and polycystic ovary syndrome

PURPOSE

This study examined the possible association of G241R and K469E single nucleotide polymorphisms (SNPs) of ICAM-1 gene with the occurrence and clinical/biochemical characteristics of polycystic ovary syndrome (PCOS).

METHODS

G241R and K469E SNPs in DNA from peripheral blood leukocytes of 169 PCOS and 259 healthy control women were investigated by real-time PCR combined with melting curve analysis using fluorescence-labeled hybridization probes.

RESULTS

We did not find significant differences in the distributions of G241R and K469E polymorphisms, nor in the haplotype frequencies between PCOS and control women. None of the studied polymorphisms were found to affect insulin resistance indices significantly.

CONCLUSIONS

These preliminary results suggest that the 241 and 469 SNPs of ICAM-1 gene may not be risk factors for PCOS. Further studies with a larger cohort, analyzing other ICAM-1 polymorphisms are necessary to support our observations before any statement can be made about the relationship between PCOS and ICAM-1 polymorphisms.

Leukocyte rolling and adhesion both contribute to regulation of microvascular permeability to albumin via ligation of ICAM-1

Activated neutrophils interacting with the vessel wall can alter vascular permeability to macromolecules such as albumin via release of various secretion products that induce changes in the endothelial monolayer. In the current work we used cremaster microvessels of anesthetized mice to show that, in addition to this paracrine mechanism, leukocyte ligation of endothelial ICAM-1 directly activates endothelial cell (EC) signaling, altering EC permeability to albumin [i.e., solute permeability (P(s))]. We show that antibody cross-linking of surface ICAM-1 in intact microvessels is sufficient to increase P(s) even in the absence of interacting leukocytes. Unstimulated arterioles do not support leukocyte-EC interactions, but despite this, antibody ligation of ICAM-1 in these vessels induced a twofold increase in P(s). Similarly, in venules that were depleted of interacting neutrophils, P(s) was decreased to below resting levels and was restored by ligation of ICAM-1. Use of function-blocking antibodies to separately block leukocyte rolling or adhesion under unstimulated or TNF-α-activated conditions established that both rolling and adhered leukocytes contribute to P(s) regulation in situ. Both rolling and adhesion activated EC-dependent signaling mechanisms that increased P(s). ICAM-1 ligation with primary antibody alone or primary followed by secondary antibodies showed that regulation of P(s) is directly dependent on the degree of ICAM-1 clustering. Under physiological versus inflamed conditions, respectively, this ICAM-1 clustering-dependent regulation of P(s) switches from PKC dependent and Src independent to Src dependent and PKC independent. This study thus identifies a new mechanism by which antiadhesion treatment may constitute a potential therapy for tissue edema.

Migrational guidance of neutrophils is mechanotransduced via high-affinity LFA-1 and calcium flux

Acute inflammation triggers the innate immune response of neutrophils that efficiently traffic from the bloodstream to concentrate at high numbers at the site of tissue infection or wounding. A gatekeeper in this process is activation of β(2) integrins, which form bond clusters with ICAM-1 on the endothelial surface. These bond clusters serve dual functions of providing adhesive strength to anchor neutrophils under the shear forces of blood flow and directional guidance for cell polarization and subsequent transmigration on inflamed endothelium. We hypothesized that shear forces transmitted through high-affinity LFA-1 facilitates the cooperation with the calcium release-activated channel Orai1 in directing localized cytoskeletal activation and directed migration. By using vascular mimetic microfluidic channels, we observed neutrophil arrest on a substrate of either ICAM-1 or allosteric Abs that stabilize a high- or low-affinity conformation of LFA-1. Neutrophils captured via low-affinity LFA-1 did not exhibit intracellular calcium flux, F-actin polymerization, cell polarization, or directional migration under shear flow. In contrast, high-affinity LFA-1 provided orientation along a uropod-pseudopod axis that required calcium flux through Orai1. We demonstrate how the shear stress of blood flow can transduce distinct outside-in signals at focal sites of high-affinity LFA-1 that provide contact-mediated guidance for neutrophil emigration.

Mechanisms of leukocyte transendothelial migration

Neither the innate nor adaptive immune system "responds" unless leukocytes cross blood vessels. This process occurs through diapedesis, in which the leukocyte moves in an ameboid fashion through tightly apposed endothelial borders and, in some cases, through the endothelial cell itself. This review focuses on the active role of the endothelial cell in diapedesis. Several mechanisms play a critical role in transendothelial migration, including signals derived from clustering of apically disposed intercellular adhesion molecule 1 and vascular cell adhesion molecule 1, disruption or loosening of adherens junctions, and targeted recycling of platelet/endothelial cell adhesion molecule and other molecules from the recently described lateral border recycling compartment. Surprisingly, many of the same molecules and mechanisms that regulate paracellular migration also control transcellular migration. A hypothesis that integrates the various known mechanisms of transmigration is proposed.

Src phosphorylation of endothelial cell surface intercellular adhesion molecule-1 mediates neutrophil adhesion and contributes to the mechanism of lung inflammation

OBJECTIVE

The goal of this study was to determine whether tumor necrosis factor α (TNFα)-induced Src activation and intercellular adhesion molecule-1 (ICAM-1) phosphorylation rapidly increase endothelial cell adhesivity and polymorphonuclear leukocyte (PMN) sequestration independently of de novo ICAM-1 synthesis.

METHODS AND RESULTS

TNFα exposure of mouse lungs for 5 minutes produced a 3-fold increase in (125)I-anti-ICAM-1 monoclonal antibody (mAb) binding and (111)In oxine-labeled PMN sequestration, as well as Src activation, ICAM-1 Tyr518 phosphorylation, and phospho- Tyr518-ICAM-1 coimmunoprecipitation with actin. The response was absent in Nox2(-/-) lungs or following Src inhibition. In COS-7 cells transfected with wild-type (WT), phospho-defective (Tyr518Phe), or phospho-mimicking (Tyr518Asp) mouse ICAM-1 cDNA constructs, TNFα increased the B(max) of YN1/1.7.4 anti-ICAM-1 mAb binding to WT-ICAM-1 but not to Tyr518Phe-ICAM-1, indicating increased binding avidity secondary to ICAM-1 phosphorylation. This effect was mimicked by expression of the Tyr518Asp-ICAM-1 mutant. TNFα also increased the staining intensity and cell surface clustering of YN1/1.7.4 mAb-labeled WT-ICAM-1 that colocalized with F-actin, which was not observed with Tyr518Phe-ICAM-1 but was recapitulated with Tyr518Asp-ICAM-1. Finally, overexpression of ICAM-1 in mouse lungs significantly increased lipopolysaccharide-induced transvascular albumin leakage and bronchoalveolar lavage PMN counts at 2 and 24 hours after lipopolysaccharide inhalation compared with lungs expressing the Tyr518Phe ICAM-1 mutant.

CONCLUSION

Src-dependent phosphorylation of endothelial cell ICAM-1 Tyr518 induces PMN adhesion by promoting ICAM-1 clustering, which we propose mediates rapid-phase lung vascular accumulation of PMNs during inflammation.

Constitutive expression and enzymatic cleavage of ICAM-1 in the spontaneously hypertensive rat

BACKGROUND/AIMS

Leukocyte adhesion to the endothelium is abnormal in hypertension. We have recently shown that spontaneously hypertensive rats (SHRs) have circulating leukocytes with enhanced CD18 receptor cleavage. In the current study, we investigate expression levels of its counter receptor, intercellular adhesion molecule (ICAM-1), and its possible proteolytic cleavage in the SHR and control Wistar rat.

METHODS

ICAM-1 was labeled on tissue sections with two antibodies targeting its extracellular and intracellular domains and evaluated by light absorption measurements. The in situ cleavage of ICAM-1 was assessed by treating vessel sections with matrix metalloproteinase (MMP)-7, MMP-9 and elastase.

RESULTS

SHRs showed a significant increase in ICAM-1 expression in liver and kidney compared with Wistar rats. The liver and kidney glomeruli exhibit a discrepancy in label density between intra- and extracellular antibodies, which suggests that enzymatic cleavage may be a factor determining ICAM-1 distribution. MMP-7 and MMP-9, which are elevated in SHR plasma, and elastase, which has elevated activity in SHR neutrophils, cleave the extracellular domain of ICAM-1 when applied to the tissue.

CONCLUSION

ICAM-1 expression in SHRs is upregulated in a tissue-specific manner. Proteolytic cleavage of the extracellular domain of ICAM-1 and accumulation in kidney glomeruli may play a role in the renal involvement of inflammation.

Rolling cell adhesion

Rolling adhesion on vascular surfaces is the first step in recruiting circulating leukocytes, hematopoietic progenitors, or platelets to specific organs or to sites of infection or injury. Rolling requires the rapid yet balanced formation and dissociation of adhesive bonds in the challenging environment of blood flow. This review explores how structurally distinct adhesion receptors interact through mechanically regulated kinetics with their ligands to meet these challenges. Remarkably, increasing force applied to adhesive bonds first prolongs their lifetimes (catch bonds) and then shortens their lifetimes (slip bonds). Catch bonds mediate the counterintuitive phenomenon of flow-enhanced rolling adhesion. Force-regulated disruptions of receptor interdomain or intradomain interactions remote from the ligand-binding surface generate catch bonds. Adhesion receptor dimerization, clustering in membrane domains, and interactions with the cytoskeleton modulate the forces applied to bonds. Both inside-out and outside-in cell signals regulate these processes.