LFA-1 Function Research Articles

Chronic stimulation desensitizes β2-adrenergic receptor responses in natural killer cells.

Adrenergic receptors (ARs) are preferentially expressed by innate lymphocytes such as natural killer (NK) cells. Here, we study the effect of epinephrine-mediated stimulation of the β2-adrenergic receptor (β2AR) on the function of human NK cells. Epinephrine stimulation inhibited early NK cell signaling events and blocked the function of the integrin LFA-1. This reduced the adhesion of NK cells to ICAM-1, explaining how NK cells are mobilized into the peripheral blood upon epinephrine release during acute stress or exercise. Additionally, epinephrine stimulation transiently reduced NK cell degranulation, serial killing, and cytokine production and affected metabolic changes upon NK cell activation via the cAMP-protein kinase A (PKA) pathway. Repeated exposure to β2AR agonists resulted in the desensitization of the β2AR via a PKA feedback loop-initiated G-protein switch. Therefore, acute epinephrine stimulation of chronically β2AR stimulated NK cells no longer resulted in inhibited signaling and reduced LFA-1 activity. Sustained stimulation by long-acting β2-agonists (LABA) not only inhibited NK cell functions but also resulted in desensitization of the β2AR. However, peripheral NK cells from LABA-treated asthma patients still reacted unchanged to epinephrine stimulation, demonstrating that local LABA administration does not result in detectable systemic effects on NK cells.

Different states of integrin LFA-1 aggregation are controlled through its association with tetraspanin CD9

The tetraspanin CD9 has been shown to interact with different members of the β1 and β3 subfamilies of integrins, regulating through these interactions cell adhesion, migration and signaling. Based on confocal microscopy co-localization and on co-immunoprecipitation results, we report here that CD9 associates with the β2 integrin LFA-1 in different types of leukocytes including T, B and monocytic cells. This association is resistant to stringent solubilization conditions which, together with data from chemical crosslinking, in situ Proximity Ligation Assays and pull-down experiments, suggest a primary/direct type of interaction mediated by the Large Extracellular Loop of the tetraspanin. CD9 exerts inhibitory effects on the adhesive function of LFA-1 and on LFA-1-dependent leukocyte cytotoxic activity. The mechanism responsible for this negative regulation exerted by CD9 on LFA-1 adhesion does not involve changes in the affinity state of this integrin but seems to be related to alterations in its state of aggregation.

Structure and Dynamics of the Integrin LFA-1 I-Domain in the Inactive State Underlie its Inside-Out/Outside-In Signaling and Allosteric Mechanisms

SummaryLymphocyte function-associated antigen 1 (LFA-1) is an integrin that transmits information in two directions across the plasma membrane of leukocytes, in so-called outside-in and inside-out signaling mechanisms. To investigate the structural basis of these mechanisms, we studied the conformational space of the apo I-domain using replica-averaged metadynamics simulations in combination with nuclear magnetic resonance chemical shifts. We thus obtained a free energy landscape that reveals the existence of three conformational substates of this domain. The three substates include conformations similar to existing crystallographic structures of the low-affinity I-domain, the inactive I-domain with an allosteric antagonist inhibitor bound underneath α helix 7, and an intermediate affinity state of the I-domain. The multiple substates were validated with residual dipolar coupling measurements. These results suggest that the presence of three substates in the apo I-domain enables the precise regulation of the binding process that is essential for the physiological function of LFA-1.

FRET detection of lymphocyte function-associated antigen-1 conformational extension.

Lymphocyte function-associated antigen 1 (LFA-1, CD11a/CD18, αLβ2-integrin) and its ligands are essential for adhesion between T-cells and antigen-presenting cells, formation of the immunological synapse, and other immune cell interactions. LFA-1 function is regulated through conformational changes that include the modulation of ligand binding affinity and molecular extension. However, the relationship between molecular conformation and function is unclear. Here fluorescence resonance energy transfer (FRET) with new LFA-1-specific fluorescent probes showed that triggering of the pathway used for T-cell activation induced rapid unquenching of the FRET signal consistent with extension of the molecule. Analysis of the FRET quenching at rest revealed an unexpected result that can be interpreted as a previously unknown LFA-1 conformation.

Ly6C supports preferential homing of central memory CD8+ T cells into lymph nodes

Ly6C is a murine cell-surface antigen expressed by plasma cells, subsets of myeloid cells and many T cells, including memory T cells. We previously documented that Ly6C crosslinking induces LFA-1 clustering on naïve CD8(+) T cells. Here, we show that in vitro and in vivo differentiation of naïve CD8(+) T cells into central (Tcm) but not effector (Tem) memory T cells enhances Ly6C expression, and its crosslinking induces strong LFA-1 clustering on Tcm. Blocking Ly6C function inhibits in vivo Tcm homing to LNs as efficiently as blocking L-selectin but it does not potentiate the inhibition provided by blocking either L-selectin or LFA-1 function. Thus, Ly6C, L-selectin and LFA-1 all appear to be part of a common homing pathway. In vitro, Ly6C crosslinking enhances Tcm adherence to ICAM-1 in the presence of CCL21. In summary, Tcm homing involves Ly6C, in addition to L-selectin and LFA-1, and appears to potentiate firm adhesion of Tcm to ICAM-1 in synergy with a chemokine. We propose that Ly6C augments Tcm compartmentalization into LNs during their homing.

LFA-1 gene polymorphisms are associated with the sporadic infiltrative duct breast carcinoma in Chinese Han women of Heilongjiang Province

The infiltrative duct carcinoma (IDC) is the most common malignant breast cancer in females and genetic factors appear to play a significant role in the susceptibility of IDC. The LFA-1 is a crucial co-stimulatory molecule in immune system and may affect the development of breast IDC. In order to clarify the association of LFA-1 polymorphisms with IDC, a case-control study was conducted in women from Heilongjiang Province, Northeast of China. We scrutinized four genetic polymorphisms in LFA-1 gene, which may influence the activity and function of LFA-1. Our research subjects consist of 537 cases with IDC and 577 age-matched healthy controls. Genotypes were determined by PCR-RFLP. Data were analyzed using the χ(2) test by SPSS 13.0 and Haploview 4.1 softwares. The association between LFA-1 polymorphisms and the clinical features of IDC was analyzed. In rs2230433, the frequency of GG genotype and G allele was lower in cases than in controls (P = 0.0316 and 0.0480). And rs2230433, CG genotype was higher in cases (P = 0.0397). In rs8058823, the frequency of AA genotype and A allele was lower in cases than in controls (P = 0.00000418 and 0.00000267). And rs8058823, AG genotype was higher in cases (P = 0.00000747). The frequency of haplotype CCGA was lower in patients. Significant association was shown between the four SNPs of LFA-1 gene and estrogen receptor (ER), progesterone receptor (PR), C-erbB-2, and P53 statuses. In addition, no association was found between LFA-1 gene polymorphisms and tumor size, and neither was it between LFA-1 gene polymorphisms and lymph node metastasis. Our results primarily suggested that LFA-1 gene polymorphisms may predict the sporadic breast IDC risk and prognosis factors in Chinese Han women in Heilongjiang Province.

Calpain 4 is not necessary for LFA-1-mediated function in CD4+ T cells.

BackgroundT cell activation and immune synapse formation require the appropriate activation and clustering of the integrin, LFA-1. Previous work has reported that the calpain family of calcium-dependent proteases are important regulators of integrin activation and modulate T cell adhesion and migration. However, these studies have been limited by the use of calpain inhibitors, which have known off-target effects.Methodology/Principal FindingsHere, we used a LoxP/CRE system to specifically deplete calpain 4, a small regulatory calpain subunit required for expression and activity of ubiquitously expressed calpains 1 and 2, in CD4+ T cells. CD4+ and CD8+ T cells developed normally in Capn4F/F:CD4-CRE mice and had severely diminished expression of Calpain 1 and 2, diminished talin proteolysis and impaired casein degradation. Calpain 4-deficient T cells showed no difference in adhesion or migration on the LFA-1 ligand ICAM-1 compared to control T cells. Moreover, there was no impairment in conjugation between Capn4F/F:CD4-CRE T cells and antigen presenting cells, and the conjugates were still capable of polarizing LFA-1, PKC-theta and actin to the immune synapse. Furthermore, T cells from Capn4F/F:CD4-CRE mice showed normal proliferation in response to either anti-CD3/CD28 coated beads or cognate antigen-loaded splenocytes. Finally, there were no differences in the rates of apoptosis following extrinsic and intrinsic apoptotic stimuli.Conclusion/SignificanceOur findings demonstrate that calpain 4 is not necessary for LFA-1-mediated adhesion, conjugation or migration. These results challenge previous reports that implicate a central role for calpains in the regulation of T cell LFA-1 function.

Genome-wide transcription profiling identifies the mechanisms of LFA-1 contributing to CD8+ T Cell Activation and immune signal network (50.26)

Abstract Our previous data demonstrated that the function of LFA-1 is to enhance TCR signaling through the immunological synapse and deliver distinct signal in CD8+ T cell activation. However, the detailed molecular pathways that regulate these processes and global impact on immune functions are poorly defined. The purpose of this genomic study is to explore and understand the LFA-1 and TCR signaling network with CD8+ T cell transcription profiling. CD8+ T cells from C57BL/6 mice and LFA-1-KO mice before and after stimulation were applied to the Mouse Whole Genome Oligo Microarray. Statistic analysis identified a list of LFA-1-associated genes differentially expressed in activated LFA-1-KO CD8+ T cells. Pathway analysis indicated that most of these genes are enriched in IL-10 signaling/ p38 MAPK signaling/ cell cycle regulation/ notch signaling/ NK signaling/ chemokine signaling. Furthermore, biological function analysis implicated these genes enriched in the functions of antigen presentation/ cell-mediated immune response/ inflammatory response/ cellular development/ cell-to-cell signaling and interaction/ immune cell trafficking/ cellular growth and proliferation/ inflammatory disease/ lymphoid tissue structure and development. Our results indicated that LFA-1 plays an important role in the immune signal network and has a global impact on immune system, and provided a complete genome-wide database to further characterize the molecular mechanisms of LFA-1 during T cell activation.

Gene Related to Anergy in Lymphocytes (GRAIL) Expression in CD4+ T Cells Impairs Actin Cytoskeletal Organization during T Cell/Antigen-presenting Cell Interactions

GRAIL (gene related to anergy in lymphocytes), is an E3 ubiquitin ligase with increased expression in anergic CD4+ T cells. The expression of GRAIL has been shown to be both necessary and sufficient for the induction of T cell (T) anergy. To date, several subsets of anergic T cells have demonstrated altered interactions with antigen-presenting cells (APC) and perturbed TCR-mediated signaling. The role of GRAIL in mediating these aspects of T cell anergy remains unclear. We used flow cytometry and confocal microscopy to examine T/APC interactions in GRAIL-expressing T cells. Increased GRAIL expression resulted in reduced T/APC conjugation efficiency as assessed by flow cytometry. Examination of single T/APC conjugates by confocal microscopy revealed altered polarization of polymerized actin and LFA-1 to the T/APC interface. When GRAIL expression was knocked down, actin polarization to the T/APC interface was restored, demonstrating that GRAIL is necessary for alteration of actin cytoskeletal rearrangement under anergizing conditions. Interestingly, proximal TCR signaling including calcium flux and phosphorylation of Vav were not disrupted by expression of GRAIL in CD4+ T cells. In contrast, interrogation of distal signaling events demonstrated significantly decreased JNK phosphorylation in GRAIL-expressing T cells. In sum, GRAIL expression in CD4+ T cells mediates alterations in the actin cytoskeleton during T/APC interactions. Moreover, in this model, our data dissociates proximal T cell signaling events from functional unresponsiveness. These data demonstrate a novel role for GRAIL in modulating T/APC interactions and provide further insight into the cell biology of anergic T cells.

LFA-1 Regulates CD8 + T Cell Activation and Immune Signal Network.

Abstract 1641Poster Board I-667LFA-1 regulates T cell activation and signal transduction through the immunological synapse. TCR stimulation rapidly activates LFA-1, which provides unique LFA-1-dependent signals to promote T cell activation. We found LFA-1 directly participates in Erk1/2 signaling upon TCR stimulation in CD8+ T cells. The presence of LFA-1, not ligand binding, is required for the TCR-mediated Erk1/2 signal pathway. LFA-1-KO T cells have defects in sustained Erk1/2 signaling and TCR/CD3 clustering, which subsequently prevents MTOC re-orientation, cell-cycle progression and mitosis. LFA-1 regulates the TCR-mediated Erk1/2 signal pathway in the context of immunological synapse for recruitment and amplification of Erk1/2 signal. In addition, LFA-1 ligation with ICAM-1 generates an additional Erk1/2 signal, which synergizes with the existing TCR-mediated Erk1/2 signal to enhance T cell activation. We demonstrated that the function of LFA-1 is to enhance TCR signaling through the immunological synapse and deliver distinct signal in CD8+ T cell activation.Based on our results, we proposed a model of TCR-mediated and LFA-1-mediated Erk1/2 signal pathways in CD8+ T cell activation. However, the detailed molecular pathways that regulate these processes and global impact on immune functions are poorly defined. With the launching of The Immunological Genome Project, we have generated data with CD8+ T cell expression array to explore and understand the LFA-1 and TCR signaling network. GeneChip hybridization and analysis CD8+ T cells from C57BL/6 mice and LFA-1-KO mice were collected before and after stimulation. Microarray experiments were carried out using the “ Mouse Whole Genome Oligo Microarray Kit” from Agilent. Differentially expressed gene lists between samples were considered significant if their p values were <0.0001 and their fold-change >1.8. The results are summarized below: 1) 641 genes were up-regulated and 174 were down-regulated in unstimulated LFA-1-KO CD8+ T cells comparing to these in unstimulated WT CD8+ T cells; 2)1036 genes were up-regulated and 406 were down-regulated in activated LFA-1-KO CD8+ T cells comparing to these in activated WT CD8+ T cells after 1 hours stimulation with unstimulated CD8+ T cells as control; 3)636 genes were up-regulated and 354 were down-regulated in activated LFA-1-KO CD8+ T cells comparing to these in activated WT CD8+ T cells after 8 hours stimulation with unstimulated CD8+ T cells as control.To estimate which pathways are significantly enriched among the genes that are differentially expressed, we used a database IPA (Ingenuity Pathways Analysis) software. Signaling pathways enriched by the genes differentially expressed in activated LFA-1-KO CD8+ T cells vs WT CD8+ T cells after 8 hours stimulation generated the most highly enriched differentially expressed genes in signaling pathways displayed below: 1) Pattern Recognition Receptors in Recognition of Bacteria and Viruses; 2) Activation of IRF by Cytosolic Pattern Recognition Receptors; 3) Aryl Hydrocarbon Receptor Signaling; 4) IL-10 Signaling; p38 MAPK Signaling; 5) LPS/IL-1 Mediated Inhibition of RXR Function; Cell Cycle: G2/M DNA Damage Checkpoint Regulation; 6) Notch Signaling; Natural Killer Cell Signaling; 7) Cell Cycle: G1/S Checkpoint Regulation and Chemokine Signaling. Furthermore, we examined the biological functions enriched by the genes differentially expressed in activated LFA-1-KO CD8+ T cells vs WT CD8+ T cells. The LFA-1-KO CD8+ T cells vs WT CD8+ T cells after 8 hours stimulation generated the most highly enriched differentially expressed genes in following biological functions: Immunological Disease; Antigen Presentation; Cell-mediated Immune Response; Humoral Immune Response; Inflammatory Response; Cellular Development; Cell-To-Cell Signaling and Interaction; Hematological System Development and Function; Immune Cell Trafficking; Cellular Growth and Proliferation; Inflammatory Disease; Cellular Movement; Hematopoiesis Cell Death; Hematological Disease; Lymphoid Tissue Structure and Development; Infectious Disease; Tissue Development and Cancer. Our results indicate that LFA-1 plays an important role in the immune signal network and has a global impact on immune system. DisclosuresNo relevant conflicts of interest to declare.

LFA-1 Regulates CD8+ T Cell Activation via T Cell Receptor-mediated and LFA-1-mediated Erk1/2 Signal Pathways

LFA-1 regulates T cell activation and signal transduction through the immunological synapse. T cell receptor (TCR) stimulation rapidly activates LFA-1, which provides unique LFA-1-dependent signals to promote T cell activation. However, the detailed molecular pathways that regulate these processes and the precise mechanism by which LFA-1 contributes to TCR activation remain unclear. We found LFA-1 directly participates in Erk1/2 signaling upon TCR stimulation in CD8+ T cells. The presence of LFA-1, not ligand binding, is required for the TCR-mediated Erk1/2 signal pathway. LFA-1-deficient T cells have defects in sustained Erk1/2 signaling and TCR/CD3 clustering, which subsequently prevents MTOC reorientation, cell cycle progression, and mitosis. LFA-1 regulates the TCR-mediated Erk1/2 signal pathway in the context of immunological synapse for recruitment and amplification of the Erk1/2 signal. In addition, LFA-1 ligation with ICAM-1 generates an additional Erk1/2 signal, which synergizes with the existing TCR-mediated Erk1/2 signal to enhance T cell activation. Thus, LFA-1 contributes to CD8+ T cell activation through two distinct signal pathways. We demonstrated that the function of LFA-1 is to enhance TCR signaling through the immunological synapse and deliver distinct signals in CD8+ T cell activation.

Simvastatin does not prevent acute cardiac allograft rejection in CD28-deficient mice

Heterotopic cardiac transplantation in mice was used to determine whether complementary immunomodulation by statins prevents lymphocyte function-associated antigen (LFA)-1-dependent acute allograft rejection in vivo. Hearts from BalbC mice were transplanted to the cervical vessels of either C57BL/6, CD11a(-/-), CD28(-/-) or double-deficient animals lacking expression of both LFA-1 and CD28. Allografts were rejected at days 7.2 +/- 0.7, 9.1 +/- 0.6 and 10.3 +/- 1.2 in C57BL/6, CD11a(-/-) and CD28(-/-) recipients, respectively. In contrast, mean allograft survival time in double-deficient animals was 27.2 +/- 2.9 days, indicating that acute allograft rejection in CD28(-/-) recipients was critically dependent on LFA-1 function. Allograft rejection was not delayed in CD28(-/-) recipients treated daily with 1 or 40 mg/kg simvastatin, graft survival was 9.6 +/- 0.2 and 10.3 +/- 0.3 days in these animals. Histology revealed that all rejected allografts uniformly presented with high-grade parenchymal rejection. Targeting of both LFA-1 and CD28 may provide efficient inhibition of co-stimulation and thus prolong experimental cardiac allograft survival. Simvastatin is not effective to blunt LFA-1-dependent acute cardiac allograft rejection in CD28(-/-) mice. Thus, pharmacological antagonism of LFA-1 function by oral treatment with statin compounds has to be considered an unsatisfactory means to improve the outcome after cardiac transplantation.

Dual requirement for adapters SKAP55 and ADAP in controlling T cell receptor dependent LFA-1 function (35.22)

Abstract T cell antigen receptor (TCR) engagement by an antigen-presenting cell (APC) promotes rapid activation of T cell LFA-1 integrins and stable T:APC conjugate formation. The T cell cytoplasmic adapter proteins ADAP and SKAP55 are critical intermediates for efficient LFA-1 function, but their specific contributions are unclear. Constitutive interaction between the N-terminal proline-rich domain of ADAP and the SKAP55 C-terminal SH3 domain is required for SKAP55 stability, resulting in loss of SKAP55 protein from ADAP-/- mice. To identify minimal requirement(s) for SKAP55 and/or ADAP in controlling LFA-1 function, we used adenovirus to express fragments or chimeras of SKAP55 and ADAP in naïve D011.10/hCAR/ADAP-/- T cells and monitored T:APC conjugate formation. Expression of the N-terminus of SKAP55 and/or the C-terminus of ADAP was insufficient to rescue T:APC conjugate formation. In contrast, a construct fusing these SKAP55 and ADAP fragments into a single chimera restores adhesion in ADAP-/- T cells independent of endogenous SKAP55. Surprisingly, a chimera fusing the Rap1 effector RIAM directly to ADAP failed to rescue adhesion, suggesting a key role for SKAP55. Further mutation of the SKAP/ADAP chimera indicates that tyrosine residues in SKAP55 are not required for conjugate formation, but that tyrosine residues in the ADAP C-terminus may be important for recruiting the Rap1 exchange factor C3G/CrkL complex to ADAP. NIH-R01AI038474 and AHA-0725934Z.

LFA-1 regulates CD8+ T cell activation through both TCR-mediated and LFA-1-mediated Erk1/2 signal pathways (35.16)

Abstract LFA-1 regulates T cell activation and signal transduction through the immunological synapse. TCR stimulation rapidly activates LFA-1, which provides unique LFA-1-dependent signals to promote T cell activation. However, the detailed molecular pathway and the precise mechanism by which LFA-1 contributes to TCR activation remain unclear. Herein, we report that LFA-1 directly participates in Erk1/2 signaling upon TCR stimulation in CD8+ T cells. The presence of LFA-1, not ligand binding, is required for the TCR-mediated Erk1/2 signal pathway. LFA-1-deficient CD8+ T cells have defects in sustained Erk1/2 signaling and TCR/CD3 clustering, which subsequently prevents MTOC re-orientation, cell-cycle progression and mitosis. LFA-1 regulates the TCR-mediated Erk1/2 signal pathway in the context of immunological synapse for recruitment and amplification of Erk1/2 signal. Furthermore, LFA-1 ligation with ICAM-1 generates an additional Erk1/2 signal, which synergizes with the existing TCR-mediated Erk1/2 signal to enhance T cell activation. The LFA-1-mediated Erk1/2 signal pathway is independent of ZAP-70 and PI3K but partially depends on Lck. Thus, LFA-1 contributes to CD8+ T cell activation through two distinct signal pathways. The function of LFA-1 is to enhance TCR signaling through the immunological synapse and deliver distinct signal in CD8+ T cell activation.

Reduced notch activity is associated with an impaired marginal zone B cell development and function in Sly1 mutant mice

MZ B cells represent a distinct lineage of naive B lymphocytes, apart from FO B cells and peritoneal B1 cells, and mediate humoral immune responses against blood-borne type 2 T-independent antigens. Regulation of MZ B cell development involves the Notch receptor signaling, the intensity of B cell receptor signals, and cell compartmentalization by adhesion and chemokine receptors. Our previous work showed that gene-targeted mice expressing a truncated form of the putative signaling adapter protein SLy1 exhibit reduced numbers of a splenic B cell population enriched in MZ B cells. Here, we demonstrate that Sly1 d/d mice exhibit a partial, but selective, block in the transition from pre-MZ to mature MZ B cells. Development of both T1 and T2 precursor subsets and FO B cells was normal in Sly1 d/d mice. Consistent with the loss of MZ B cells, the production of antigen-specific IgM antibodies following immunization with pneumococcal polysaccharides was severely impaired in Sly1 d/d mice. Importantly, expression of the Notch signaling mediator RBP-J and the Notch target genes Hes-1 and Hes-5 was markedly reduced in MZ but not FO B cells of Sly1 d/d mice. In contrast, B cell receptor signaling, expression and function of LFA-1 and α4-integrins, and expression of chemokine receptors appeared intact in Sly1 d/d cells. Collectively, these results provide strong evidence that SLy1 is important for the generation and function of MZ B cells and suggest a novel link between SLy1 and the activity of the Notch pathway in the development of MZ B cells.

Distinct Regulation of Integrin-Dependent T Cell Conjugate Formation and NF-κB Activation by the Adapter Protein ADAP

Following TCR stimulation, T cells utilize the hematopoietic specific adhesion and degranulation-promoting adapter protein (ADAP) to control both integrin adhesive function and NF-kappaB transcription factor activation. We have investigated the molecular basis by which ADAP controls these events in primary murine ADAP(-/-) T cells. Naive DO11.10/ADAP(-/-) T cells show impaired adhesion to OVAp (OVA aa 323-339)-bearing APCs that is restored following reconstitution with wild-type ADAP. Mutational analysis demonstrates that the central proline-rich domain and the C-terminal domain of ADAP are required for rescue of T:APC conjugate formation. The ADAP proline-rich domain is sufficient to bind and stabilize the expression of SKAP55 (Src kinase-associated phosphoprotein of 55 kDa), which is otherwise absent from ADAP(-/-) T cells. Interestingly, forced expression of SKAP55 in the absence of ADAP is insufficient to drive T:APC conjugate formation, demonstrating that both ADAP and SKAP55 are required for optimal LFA-1 function. Additionally, the ADAP proline-rich domain is required for optimal Ag-induced activation of CD69, CD25, and Bcl-x(L), but is not required for assembly of the CARMA1/Bcl10/Malt1 (caspase-recruitment domain (CARD) membrane-associated guanylate kinase (MAGUK) protein 1/B-cell CLL-lymphoma 10/mucosa-associated lymphoid tissue lymphoma translocation protein 1) signaling complex and subsequent TCR-dependent NF-kappaB activity. Our results indicate that ADAP is used downstream of TCR engagement to delineate two distinct molecular programs in which the ADAP/SKAP55 module is required for control of T:APC conjugate formation and functions independently of ADAP/CARMA1-mediated NF-kappaB activation.

Differential Regulation of Neutrophil CD18 Integrin Function by Di- and Tri-Valent Cations: Manganese vs. Gadolinium

Affinity regulation of integrin function plays an important role during both leukocyte-endothelial and leukocyte-leukocyte interactions. We compared the roles of Mn(2+) (Manganese) and Gd(3+) (Gadolinium) in regulating leukocyte CD18-integrin function. We observed that: (i) Both cations prolonged neutrophil homotypic aggregation following chemoattractant IL-8 stimulation, with Gd(3+) being effective at doses two orders of magnitude (10 microM range) lower that Mn(2+). (ii) While both Gd(3+) and Mn(2+) mediate homotypic cell aggregation via L: -selectin and CD18 integrins, their effects on the integrin subunits, LFA-1 (CD11a/CD18) and Mac-1 (CD11b/CD18), was different. Gd(3+) altered both LFA-1 and Mac-1 function, while the dominant effect of Mn(2+) was on Mac-1. This effect of Gd(3+) on LFA-1 function was confirmed in cell-free studies that measured the binding of recombinant ICAM-1 to LFA-1 immobilized on beads. (iii) Both ions augmented the binding of 327C, an antibody that recognizes active CD18 on human neutrophils, both in the presence and absence of exogenous IL-8. The effects of Mn(2+) was more pronounced since it caused 3-4-fold increase in mAb 327C binding to neutrophils compared to Gd(3+) which increased antibody binding by only approximately 80%. 327C binding was partially reduced by Ca(2+). Further, 327C binding induced by Mn(2+) did not correlate tightly with cell adhesion function. (iv) In studies that monitored intracellular Ca(2+) ([Ca(2+)](i)), the addition of Mn(2+) but not Gd(3+) to neutrophils altered [Ca(2+)](i) levels. Overall, while both Gd(3+) and Mn(2+) stabilize high affinity CD18 mediated cell adhesion, Gd(3+) affects integrin conformation while Mn(2+) may also trigger other effects.

BCR-ABL1 Disrupts SDF-1-Dependent Hematopoietic Cell Migration and Adhesion through the LFA-1 Integrin-Mediated Mechanism.

Stromal-derived factor-1 (SDF-1) and its receptor, CXCR4, are essential for normal stem/progenitor cell movement, adherence, and retention within the bone marrow environment. Two mechanisms through which BCR-ABL1 are thought to disrupt CXCR4-mediated chemotactic responses have been described in leukemia:1.the inhibition of CXCR4 expression (Geay et al. 2005, Cancer Res.) and2.intra-cellular signaling defects without modification of CXCR4 expression (Salgia et al. 1999, Blood; Ptasznik et al. 2002, J. Exp. Med.).These opposing mechanisms suggest that the actual situation is more complex and that new signaling paradigms are needed. To address this, we studied the effects of BCR-ABL1 on SDF-1-dependent, integrin-mediated, migration and adhesion of hematopoietic precursors. Stimulation of BCR-ABL1(−) hematopoietic cells with SDF-1 showed reduced cell adherence to surfaces coated with ICAM-1 (a ligand for the LFA-1 integrin), which was associated with down-regulated expression of activation-dependent epitopes of the β2 integrin, LFA-1, on hematopoietic cells. Inhibition of Lyn expression with siRNA prevented the SDF-1-triggered down-regulation of LFA-1 and cell adherence, indicating that CXCR4 inhibited the function of LFA-1 through Lyn. Expression of BCR-ABL1 in these cells resulted in increased expression of activation-dependent epitopes of LFA-1 and prevented SDF-1-dependent regulatory effects on both LFA-1 affinity and ICAM-1 adherence. Also, expression of BCR-ABL1 prevented Lyn-mediated regulation of cell adhesion to ICAM-1 as well as Lyn-mediated regulation of LFA-1 affinity. These results indicate that BCR-ABL1 constitutively increases the affinity of the LFA-1 integrin to its ligand ICAM-1, locking the integrin into an “active” conformation. The net result is the loss of responsiveness of LFA-1 to SDF-1-induced ‘inside-out' signaling involving CXCR4 and Lyn kinase. Because in our experiments BCR-ABL1 had no significant effect on the expression of CXCR4 in Mo7e cells, transfected with low and high amounts of p210-BCR-ABL, or in primary BCR-ABL(+) cells from CML blast crisis patients (n=3), we conclude that BCR-ABL1 inhibits CXCR4-triggered ‘inside-out' integrin signaling rather than CXCR4 expression. Taken together, we propose that BCR-ABL1 disrupts the signaling link between the chemokine receptor, CXCR4 and the β2 integrin LFA-1 so as to inhibit normal SDF-1-mediated chemotaxis and adhesion in hematopoietic cells.

Talin-Deficient NK Cells Reveal a Critical Role for Talin in LFA-1-Mediated Actin Cytoskeletal Rearrangement (91.4)

Abstract The purpose of this study is to elucidate the role that the cytoskeletal adaptor protein talin1 plays in the regulation of LFA-1 in natural killer (NK) cells. It has been proposed that LFA-1 not only mediates adhesion of NK cells to target cells, but may be an important activating receptor for NK cell cytotoxicity. Talin is known to act as a link between integrins and the actin cytoskeleton and to regulate ligand-binding function of LFA-1. To study the role of talin, we generated NK cells in vitro from talin1−/− ES cells and tested the effects of talin deficiency on LFA-1-mediated functions of these NK cells. Our results showed that talin is required for both adhesion of NK cells to ICAM-1 and for LFA-1-mediated activation signal leading to the re-organization of the actin cytoskeleton. Nevertheless, talin-deficient NK cells still killed some target cells in an LFA-1-independent manner, suggesting an alternative pathway of NK cytotoxicity independent of LFA-1 and talin. Thus we have shown that talin plays a critical role in LFA-1 mediated actin cytoskeletal reorganization in NK cells.

Intraluminal crawling of neutrophils to emigration sites: a molecularly distinct process from adhesion in the recruitment cascade

The prevailing view is that the β2-integrins Mac-1 (αMβ2, CD11b/CD18) and LFA-1 (αLβ2, CD11a/CD18) serve similar biological functions, namely adhesion, in the leukocyte recruitment cascade. Using real-time and time-lapse intravital video-microscopy and confocal microscopy within inflamed microvessels, we systematically evaluated the function of Mac-1 and LFA-1 in the recruitment paradigm. The chemokine macrophage inflammatory protein-2 induced equivalent amounts of adhesion in wild-type and Mac-1−/− mice but very little adhesion in LFA-1−/− mice. Time-lapse video-microscopy within the postcapillary venules revealed that immediately upon adhesion, there is significant intraluminal crawling of all neutrophils to distant emigration sites in wild-type mice. In dramatic contrast, very few Mac-1−/− neutrophils crawled with a 10-fold decrease in displacement and a 95% reduction in velocity. Therefore, Mac-1−/− neutrophils initiated transmigration closer to the initial site of adhesion, which in turn led to delayed transmigration due to movement through nonoptimal emigration sites. Interestingly, the few LFA-1−/− cells that did adhere crawled similarly to wild-type neutrophils. Intercellular adhesion molecule-1 but not intercellular adhesion molecule-2 mediated the Mac-1–dependent crawling. These in vivo results clearly delineate two fundamentally different molecular mechanisms for LFA-1 and Mac-1 in vivo, i.e., LFA-1–dependent adhesion followed by Mac-1–dependent crawling, and both steps ultimately contribute to efficient emigration out of the vasculature.