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Nancy Hogg

Publications and source records attributed to Nancy Hogg.

15 recordsLinked to original sources
PubMed2004

How T cells use LFA-1 to attach and migrate.

The T lymphocyte (or T cell) has classically been perceived to be a passive circular cell attaching to other cells or fibrils of the extracellular matrix when its integrins become activated. We now understand that the modus operandi of the T cell is migration. These cells are proving to be impressively fast migrators, clocking up basal speeds of approximately 10-15 microm/min which makes them amongst the fastest movers recorded to date. Therefore, migration is the business of the T cell and in this review we will discuss how its motility is regulated and what functions this activity makes possible.

Animals↗
PubMed2003

T-cell integrins: more than just sticking points.

T cells use integrins in essentially all of their functions. They use integrins to migrate in and out of lymph nodes and, following infection, to migrate into other tissues. At the beginning of an immune response, integrins also participate in the immunological synapse formed between T cells and antigen-presenting cells. Because the ligands for integrins are widely expressed, integrin activity on T cells must be tightly controlled. Integrins become active following signalling through other membrane receptors, which cause both affinity alteration and an increase in integrin clustering. Lipid raft localization may increase integrin activity. Signalling pathways involving ADAP, Vav-1 and SKAP-55, as well as Rap1 and RAPL, cause clustering of leukocyte function-associated antigen-1 (LFA-1; integrin alphaLbeta2). T-cell integrins can also signal, and the pathways dedicated to the migratory activity of T cells have been the most investigated so far. Active LFA-1 causes T-cell attachment and lamellipodial movement induced by myosin light chain kinase at the leading edge, whereas RhoA and ROCK cause T-cell detachment at the trailing edge. Another important signalling pathway acts through CasL/Crk, which might regulate the activity of the GTPases Rac and Rap1 that have important roles in T-cell migration.

Adaptor Proteins, Signal Transducing↗
PubMed2003

LFA-1-induced T cell migration on ICAM-1 involves regulation of MLCK-mediated attachment and ROCK-dependent detachment.

This study analyzes signaling events initiated through binding of the leukocyte integrin LFA-1 to ICAM-1, which leads to T cell attachment, polarization and random migration. These events are critically dependent on dynamic changes in the acto-myosin cytoskeleton under the regulation of myosin light chain kinase and ROCK (Rho kinase). A key finding is that the activity of these two kinases is spatially segregated. Myosin light chain kinase (MLCK) must operate at the leading edge of the T cell because blocking its activity causes the polarized T cell to retract from the front of the cell. These activities are mirrored by inhibiting calmodulin, the activator of MLCK. In contrast inhibition of ROCK (and RhoA) has the effect of preventing detachment of the T cell trailing edge, showing that this kinase operates at the rear of the cell. This compartmentalized activity of the two kinases is reflected in their localization within the T cell. Myosin light chain kinase is concentrated at the leading edge, overlapping F-actin, whereas ROCK is more widely distributed in the trailing edge of the T cell. Thus these two kinases perform two different functions in the migrating T cell, with myosin light chain kinase activity important for attachment and movement at the leading edge and ROCK activity required for the detachment of the trailing edge. These two actomyosin-dependent processes operate coordinately to cause forward migration of a T cell.

Cell Adhesion↗
PubMed2003

SKAP-55 regulates integrin adhesion and formation of T cell-APC conjugates.

Src kinase-associated phosphoprotein of 55 kDa (SKAP-55; encoded by SCAP1) is a T cell adaptor protein of unknown function that contains a pleckstrin homology and an SH3 domain. Here we show that SKAP-55 regulates integrin-mediated adhesion and conjugate formation between T cells and antigen-presenting cells (APCs). SKAP-55 enhances adhesion to fibronectin and intercellular adhesion molecule-1 (ICAM-1), colocalizes with actin at the T cell-APC synapse and promotes the clustering of lymphocyte-associated antigen-1 (LFA-1). Enhanced conjugation is comparable to that induced by adhesion and degranulation-promoting adaptor protein (ADAP), a binding partner of SKAP-55, and is abrogated by deletion of the SKAP-55 SH3 domain. Conjugate formation is accompanied by the translocation of SKAP-55 to membrane rafts, an event that is regulated by both LFA-1 and T cell receptor ligation. Our findings identify a mechanism by which SKAP-55 modulates T cell responses to antigen.

Animals↗
PubMed2003

Rapid recruitment of inflammatory monocytes is independent of neutrophil migration.

Early neutrophil entry into an inflammatory site is thought to mediate a chemokine switch, inducing subsequent monocyte recruitment through the regulation of monocyte chemoattractant protein-1 (MCP-1) release. As the murine monocyte is poorly characterized and difficult to identify, there has been little examination of either its early recruitment in inflammatory models or of the factors that influence its early migration. The phenotyping of rapidly recruited inflammatory leukocytes with 7/4 and Gr-1 monoclonal antibodies (mAbs) identifies 2 distinct populations, which we characterize as murine monocytes and neutrophils. Monocytes migrate in the first 2 hours of inflammation making use of alpha4beta1 but not of Mac-1 or lymphocyte function-associated antigen-1 (LFA-1) integrins. Early migration is dependent on MCP-1, but neither MCP-1 release nor monocyte recruitment is affected by the reduced neutrophil migration seen in LFA-1-/- mice. Endogenous peritoneal macrophages and mesothelial cells lining the peritoneum contain MCP-1, which is released following thioglycollate stimulation. The murine monocyte therefore responds rapidly to chemokines produced in situ by tissue cells at the site of inflammation with no requirement for prior influx of neutrophils.

Animals↗
PubMed2003

Vav1 transduces TCR signals required for LFA-1 function and cell polarization at the immunological synapse.

Activation of T lineage cells through the TCR by peptide-MHC complexes on APC is critically dependent on rearrangement of the actin cytoskeleton. Vav1 is a guanine nucleotide exchange factor for members of the Rho/Rac family of GTPases which is activated following TCR stimulation, suggesting that it may transduce TCR signals to the activation of some or all actin-controlled processes. We show that Vav1-deficient double-positive thymocytes are less efficient at forming conjugates with APC presenting agonist peptide than wild-type cells are. Furthermore we demonstrate that Vav1 is required for TCR-induced activation of the integrin LFA-1, which is likely to explain the defect in conjugate formation. However, once Vav1-deficient cells form a conjugate, the assembly of proteins into an immunological synapse at the conjugate interface is normal. In contrast, thymocyte polarization is defective in the absence of Vav1, as judged by the relocalization of the microtubule-organizing center. These data demonstrate that Vav1 transduces signals to only a subset of cytoskeleton-dependent events at the immunological synapse.

Antigen-Presenting Cells↗
PubMed2003

Myeloid cell function in MRP-14 (S100A9) null mice.

Myeloid-related protein 14 (MRP-14) and its heterodimeric partner, MRP-8, are cytosolic calcium-binding proteins, highly expressed in neutrophils and monocytes. To understand the function of MRP-14, we performed targeted disruption of the MRP-14 gene in mice. MRP-14(-/-) mice showed no obvious phenotype and were fertile. MRP-8 mRNA but not protein is present in the myeloid cells of these mice, suggesting that the stability of MRP-8 protein is dependent on MRP-14 expression. A compensatory increase in other proteins was not detected in cells lacking MRP-8 and MRP-14. Although the morphology of MRP-14(-/-) myeloid cells was not altered, they were significantly less dense. When Ca(2+) responses were investigated, there was no change in the maximal response to the chemokine MIP-2. At lower concentrations, however, there was reduced responsiveness in MRP-14(-/-) compared with MRP-14(+/+) neutrophils. This alteration in the ability to flux Ca(2+) did not impair the ability of the MRP-14(-/-) neutrophils to respond chemotactically to MIP-2. In addition, the myeloid cell functions of phagocytosis, superoxide burst, and apoptosis were unaffected in MRP-14(-/-) cells. In an in vivo model of peritonitis, MRP-14(-/-) mice showed no difference from wild-type mice in induced inflammatory response. The data indicate that MRP-14 and MRP-8 are dispensable for many myeloid cell functions.

Animals↗
PubMed2003

A novel form of integrin dysfunction involving beta1, beta2, and beta3 integrins.

The adhesion receptors known as integrins perform key functions for hematopoietic cells. The platelet integrin alphaIIbbeta3 is critical in hemostasis, and the beta1 and beta2 integrins on leukocytes have many roles in cell-mediated immunity. Mutations in the beta2 subunit lead to integrin nonexpression and to an immune deficiency, leukocyte adhesion deficiency-1. Mutations in either the alpha or beta subunit of alphaIIbbeta3 usually lead to integrin nonexpression and a bleeding tendency termed Glanzmann thrombasthenia. Here we describe a unique patient with clinical features of both Glanzmann thrombasthenia and leukocyte adhesion deficiency-1. The patient has normal expression of beta1, beta2, and beta3 integrins, but all are dysfunctional. The key findings are that "inside-out" signaling pathways leading to integrin activation are defective and that this is associated with abnormal integrin clustering. The integrins themselves are intact and capable of function following extracellular stimulation. T cell motility is normal, as are the expression levels and electrophoretic characteristics of all cytoskeletal and signaling proteins tested, except PKC-alpha, which has enhanced expression in the patient's cells. To our knowledge, this is the first description of a dysfunction affecting three classes of integrins. We propose that it is caused by a lesion in an intracellular factor or signaling pathway essential for integrin activation in hematopoietic cells and results in lack of regulation of clustering, an essential component of integrin-mediated adhesion.

Blood Platelets↗
PubMed2002

Signaling through integrin LFA-1 leads to filamentous actin polymerization and remodeling, resulting in enhanced T cell adhesion.

The integrins can activate signaling pathways, but the final downstream outcome of these pathways is often unclear. This study analyzes the consequences of signaling events initiated by the interaction of the leukocyte integrin LFA-1 with its ligand, dimeric ICAM-1. We show that the active form of LFA-1 regulates its own function on primary human T cells by directing the remodeling of the F-actin cytoskeleton to strengthen T cell adhesion to ICAM-1. Confocal microscopy revealed that both F-actin bundling and overall levels of F-actin are increased in the ICAM-1-adhering T cells. This increase in F-actin levels and change in F-actin distribution was quantitated for large numbers of T cells using the technique of laser scanning cytometry and was found to be significant. The study went on to show that clustering of conformationally altered LFA-1 is essential for the changes in F-actin, and a model is proposed in which clustered, high-avidity T cell LFA-1, interacting with multivalent ICAM-1, causes LFA-1 signaling, which results in F-actin polymerization and higher-order F-actin bundling. The findings demonstrate that LFA-1 acts not only as an adhesion receptor but also as a signaling receptor by actively initiating the F-actin reorganization that is essential for many T cell-dependent processes.

Actin Cytoskeleton↗
PubMed2002

The involvement of lipid rafts in the regulation of integrin function.

Integrin activity on cells such as T lymphocytes is tightly controlled. Here we demonstrate a key role for lipid rafts in regulating integrin function. Without stimulation integrin LFA-1 is excluded from lipid rafts, but following activation LFA-1 is mobilised to the lipid raft compartment. An LFA-1 construct from which the I domain has been deleted mimics activated integrin and is constitutively found in lipid rafts. This correlation between integrin activation and raft localisation extends to a second integrin, alpha4beta1, and the clustering of alpha4beta1 is also raft dependent. Both LFA-1 and alpha4beta1-mediated adhesion is dependent upon intact lipid rafts providing proof of the functional relevance of the lipid raft localisation. Finally we find that non-raft integrins are excluded from the rafts by cytoskeletal constraints. The presence of integrin in lipid rafts under stimulating conditions that activate these receptors strongly indicates that the rafts have a key role in positively regulating integrin activity.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2002

The role of the CPNKEKEC sequence in the beta(2) subunit I domain in regulation of integrin alpha(L)beta(2) (LFA-1).

The alpha(L) I (inserted or interactive) domain of integrin alpha(L)beta(2) undergoes conformational changes upon activation. Recent studies show that the isolated, activated alpha(L) I domain is sufficient for strong ligand binding, suggesting the beta(2) subunit to be only indirectly involved. It has been unclear whether the activity of the alpha(L) I domain is regulated by the beta(2) subunit. In this study, we demonstrate that swapping the disulfide-linked CPNKEKEC sequence (residues 169-176) in the beta(2) I domain with a corresponding beta(3) sequence, or mutating Lys(174) to Thr, constitutively activates alpha(L)beta(2) binding to ICAM-1. These mutants do not require Mn(2+) for ICAM-1 binding and are insensitive to the inhibitory effect of Ca(2+). We have also localized a component of the mAb 24 epitope (a reporter of beta(2) integrin activation) in the CPNKEKEC sequence. Glu(173) and Glu(175) of the beta(2) I domain are identified as critical for mAb 24 binding. Because the epitope is highly expressed upon beta(2) integrin activation, it is likely that the CPNKEKEC sequence is exposed or undergoes conformational changes upon activation. Deletion of the alpha(L) I domain did not eliminate the mAb 24 epitope. This confirms that the alpha(L) I domain is not critical for mAb 24 binding, and indicates that mAb 24 detects a change expressed in part in the beta(2) subunit I domain. These results suggest that the CPNKEKEC sequence of the beta(2) I domain is involved in regulating the alpha(L) I domain.

Amino Acid Sequence↗
PubMed2002

Rap1A positively regulates T cells via integrin activation rather than inhibiting lymphocyte signaling.

T cell receptor (TCR) stimulation activates the small GTPase Rap1A, which is reported to antagonize Ras signaling and induces T cell anergy. To address its role in vivo, we generated transgenic mice that constitutively expressed active Rap1A within the T cell lineage. We found that active Rap1A did not interfere with the Ras signaling pathway or antagonize T cell activation. Instead of anergy, the T lymphocytes that constitutively expressed active Rap1A showed enhanced TCR-mediated responses, both in thymocytes and mature T cells. In addition, Rap1A activation was sufficient to induce strong activation of the beta1 and beta2 integrins via an avidity-modulation mechanism. This shows that, far from playing an inhibitory role during T cell activation, Rap1A positively influences T cells by augmenting lymphocyte responses and directing integrin activation.

Animals↗
PubMed2002

Mechanisms contributing to the activity of integrins on leukocytes.

Understanding how the integrins on leukocytes operate is important because these receptors control the activity of leukocytes in all phases of their lives. Thus integrins control leukocyte development and maturation in bone marrow, the circulation of naive cells in secondary lymphoid tissue, e.g. the lymph nodes, and leukocyte responses to inflammatory signals emanating from injured tissues. Using as an example LFA-1, which is expressed by all leukocytes, we outline how the activity of this integrin is modified to meet the challenges posed by these leukocyte activities. Briefly, we discuss three means by which LFA-1 is adapted to bind more efficiently to its chief ligand, ICAM-1. LFA-1 can undergo changes in conformation leading to increased affinity, can be clustered on the membrane and, finally, when activated can move into the lipid raft compartment of the membrane. The study of humans with the beta2 deficiency syndrome termed leukocyte adhesion deficiency (LAD)-1 and analysis of LFA-1 null mice has given further insight into integrin activation mechanisms and the in vivo roles of LFA-1 and other leukocyte integrins.

Animals↗
PubMed2001

The S100 family heterodimer, MRP-8/14, binds with high affinity to heparin and heparan sulfate glycosaminoglycans on endothelial cells.

The S100 family proteins MRP-8 (S100A8) and MRP-14 (S100A9) form a heterodimer that is abundantly expressed in neutrophils, monocytes, and some secretory epithelia. In inflamed tissues, the MRP-8/14 complex is deposited onto the endothelium of venules associated with extravasating leukocytes. To explore the receptor interactions of MRP-8/14, we use a model system in which the purified MRP-8/14 complex binds to the cell surface of an endothelial cell line, HMEC-1. This interaction is mediated by the MRP-14 subunit and is mirrored by recombinant MRP-14 alone. The cell surface binding of MRP-14 was blocked by heparin, heparan sulfate, and chondroitin sulfate B, and the binding sites were sensitive to heparinase I and trypsin treatment but not to chondroitinase ABC. Furthermore MRP-8/14 and MRP-14 did not bind to a glycosaminoglycan-minus cell line. MRP-14 has a high affinity for heparin (K(d) = 6.1 +/- 3.4 nm), and this interaction mimicked that with the endothelial cells. We therefore conclude that the MRP-8/14 complex binds to endothelial cells via the MRP-14 subunit interacting chiefly with heparan sulfate proteoglycans. CD36 and RAGE, two other putative receptors for MRP-8/14, were not expressed by HMEC-1 cells. This binding activity may explain the immobilization of the MRP-8/14 complex on endothelium that is observed in vivo.

Animals↗