The TCR ADAPts to integrin-mediated cell adhesion

Enhanced Susceptibility of ADAP-Deficient Mice to Listeria monocytogenes Infection Is Associated With an Altered Phagocyte Phenotype and Function

The adhesion and degranulation-promoting adaptor protein (ADAP) serves as a multifunctional scaffold and is involved in the formation of immune signaling complexes. To date, only limited data exist regarding the role of ADAP in pathogen-specific immunity during in vivo infection, and its contribution in phagocyte-mediated antibacterial immunity remains elusive. Here, we show that mice lacking ADAP (ADAPko) are highly susceptible to the infection with the intracellular pathogen Listeria monocytogenes (Lm) by showing enhanced immunopathology in infected tissues together with increased morbidity, mortality, and excessive infiltration of neutrophils and monocytes. Despite high phagocyte numbers in the spleen and liver, ADAPko mice only inefficiently controlled pathogen growth, hinting at a functional impairment of infection-primed phagocytes in the ADAP-deficient host. Flow cytometric analysis of hallmark pro-inflammatory mediators and unbiased whole genome transcriptional profiling of neutrophils and inflammatory monocytes uncovered broad molecular alterations in the inflammatory program in both phagocyte subsets following their activation in the ADAP-deficient host. Strikingly, ex vivo phagocytosis assay revealed impaired phagocytic capacity of neutrophils derived from Lm-infected ADAPko mice. Together, our data suggest that an alternative priming of phagocytes in ADAP-deficient mice during Lm infection induces marked alterations in the inflammatory profile of neutrophils and inflammatory monocytes that contribute to enhanced immunopathology while limiting their capacity to eliminate the pathogen and to prevent the fatal outcome of the infection.

ADAP Promotes Degranulation and Migration of NK Cells Primed During in vivo Listeria monocytogenes Infection in Mice

The adhesion and degranulation-promoting adaptor protein (ADAP) serves as a multifunctional scaffold and is involved in the formation of immune signaling complexes. To date only limited and moreover conflicting data exist regarding the role of ADAP in NK cells. To extend existing knowledge we investigated ADAP-dependency of NK cells in the context of in vivo infection with the intracellular pathogen Listeria monocytogenes (Lm). Ex vivo analysis of infection-primed NK cells revealed impaired cytotoxic capacity in NK cells lacking ADAP as indicated by reduced CD107a surface expression and inefficient perforin production. However, ADAP-deficiency had no global effect on NK cell morphology or intracellular distribution of CD107a-containing vesicles. Proteomic definition of ADAPko and wild type NK cells did not uncover obvious differences in protein composition during the steady state and moreover, similar early response patterns were induced in NK cells upon infection independent of the genotype. In line with protein network analyses that suggested an altered migration phenotype in naïve ADAPko NK cells, in vitro migration assays uncovered significantly reduced migration of both naïve as well as infection-primed ADAPko NK cells compared to wild type NK cells. Notably, this migration defect was associated with a significantly reduced expression of the integrin CD11a on the surface of splenic ADAP-deficient NK cells 1 day post-Lm infection. We propose that ADAP-dependent alterations in integrin expression might account at least in part for the fact that during in vivo infection significantly lower numbers of ADAPko NK cells accumulate in the spleen i.e., the site of infection. In conclusion, we show here that during systemic Lm infection in mice ADAP is essential for efficient cytotoxic capacity and migration of NK cells.

Immune Cell-Type Specific Ablation of Adapter Protein ADAP Differentially Modulates EAE

The cytosolic adhesion and degranulation-promoting adapter protein ADAP is expressed in various hematopoietic cells including T cells, NK cells, myeloid cells, and platelets but absent in mature B cells. The role of ADAP in T cell activation, proliferation and integrin activation is well-accepted. We previously demonstrated that conventional ADAP knockout mice show a significantly attenuated course of experimental autoimmune encephalomyelitis (EAE). To dissect the impact of different ADAP expressing cell populations on the reduced EAE severity, here, we generated lineage-specific conditional knockout mice. ADAP was deleted in T cells, myeloid cells, NK cells and platelets, respectively. Specific loss of ADAP was confirmed on the protein level. Detailed immunophenotyping was performed to assess the consequence of deletion of ADAP with regard to the maturation and distribution of immune cells in primary and secondary lymphoid organs. The analysis showed equivalent results as for conventional ADAP knockout mice: impaired thymocyte development in ADAP^fl/fl Lck-Cre mice, normal NK cell and myeloid cell distribution in ADAP^fl/fl NKp46-Cre mice and ADAP^fl/fl LysM-Cre mice, respectively as well as thrombocytopenia in ADAP^fl/fl PF4-Cre mice. Active EAE was induced in these animals by immunization with the myelin oligodendrocyte glycoprotein₃₅₋₅₅ peptide. The clinical course of EAE was significantly milder in mice with loss of ADAP in T cells, myeloid cells and NK cells compared to ADAP-sufficient control littermates. Surprisingly, specific deletion of ADAP in platelets resulted in a more exacerbated disease. These data show that T cell-independent as well as T cell-dependent mechanisms are responsible for the complex phenotype observed in conventional ADAP knockout mice.

Far-infrared radiation stimulates platelet-derived growth factor mediated skeletal muscle cell migration through extracellular matrix-integrin signaling

Despite increased evidence of bio-activity following far-infrared (FIR) radiation, susceptibility of cell signaling to FIR radiation-induced homeostasis is poorly understood. To observe the effects of FIR radiation, FIR-radiated materials-coated fabric was put on experimental rats or applied to L6 cells, and microarray analysis, quantitative real-time polymerase chain reaction, and wound healing assays were performed. Microarray analysis revealed that messenger RNA expressions of rat muscle were stimulated by FIR radiation in a dose-dependent manner in amount of 10% and 30% materials-coated. In 30% group, 1,473 differentially expressed genes were identified (fold change [FC] > 1.5), and 218 genes were significantly regulated (FC > 1.5 and p < 0.05). Microarray analysis showed that extracellular matrix (ECM)-receptor interaction, focal adhesion, and cell migration-related pathways were significantly stimulated in rat muscle. ECM and platelet-derived growth factor (PDGF)-mediated cell migration-related genes were increased. And, results showed that the relative gene expression of actin beta was increased. FIR radiation also stimulated actin subunit and actin-related genes. We observed that wound healing was certainly promoted by FIR radiation over 48 h in L6 cells. Therefore, we suggest that FIR radiation can penetrate the body and stimulate PDGF-mediated cell migration through ECM-integrin signaling in rats.

ADAP is an upstream regulator that precedes SLP-76 at sites of TCR engagement and stabilizes signaling microclusters

Antigen recognition by the T cell receptor (TCR) directs the assembly of essential signaling complexes known as SLP-76 (also known as LCP2) microclusters. Here, we show that the interaction of the adhesion and degranulation-promoting adaptor protein (ADAP; also known as FYB1) with SLP-76 enables the formation of persistent microclusters and the stabilization of T cell contacts, promotes integrin-independent adhesion and enables the upregulation of CD69. By analyzing point mutants and using a novel phospho-specific antibody, we show that Y595 is essential for normal ADAP function, that virtually all tyrosine phosphorylation of ADAP is restricted to a Y595-phosphorylated (pY595) pool, and that multivalent interactions between the SLP-76 SH2 domain and its binding sites in ADAP are required to sustain ADAP phosphorylation. Although pY595 ADAP enters SLP-76 microclusters, non-phosphorylated ADAP is enriched in protrusive actin-rich structures. The pre-positioning of ADAP at the contact sites generated by these structures favors the retention of nascent SLP-76 oligomers and their assembly into persistent microclusters. Although ADAP is frequently depicted as an effector of SLP-76, our findings reveal that ADAP acts upstream of SLP-76 to convert labile, Ca2+-competent microclusters into stable adhesive junctions with enhanced signaling potential.

Integrin Activation Through the Hematopoietic Adapter Molecule ADAP Regulates Dendritic Development of Hippocampal Neurons

Integrin-mediated cell adhesion and signaling is of critical importance for neuronal differentiation. Recent evidence suggests that an “inside-out” activation of β1-integrin, similar to that observed in hematopoietic cells, contributes to the growth and branching of dendrites. In this study, we investigated the role of the hematopoietic adaptor protein adhesion and degranulation promoting adapter protein (ADAP) in these processes. We demonstrate the expression of ADAP in the developing and adult nervous hippocampus, and in outgrowing dendrites of primary hippocampal neurons. We further show that ADAP occurs in a complex with another adaptor protein signal-transducing kinase-associated phosphoprotein-homolog (SKAP-HOM), with the Rap1 effector protein RAPL and the Hippo kinase macrophage-stimulating 1 (MST1), resembling an ADAP/SKAP module that has been previously described in T-cells and is critically involved in “inside-out” activation of integrins. Knock down of ADAP resulted in reduced expression of activated β1-integrin on dendrites. It furthermore reduced the differentiation of developing neurons, as indicated by reduced dendrite growth and decreased expression of the dendritic marker microtubule-associated protein 2 (MAP2). Our data suggest that an ADAP-dependent integrin-activation similar to that described in hematopoietic cells contributes to the differentiation of neuronal cells.

Cell-cell communication via extracellular membrane vesicles and its role in the immune response

The host immune response involves a variety of cell types, including specialized immune and non-immune cells. The delicate coordination among these cells via close communication is central for the proper operation of immune system. Cell-cell communication is mediated by a complex network that includes soluble factors such as cytokines, chemokines, and metabolites exported from cells, as well as membrane-bound receptors and their ligands. Cell-cell communication is also mediated by membrane vesicles (e.g., exosomes, ectosomes), which are either shed by distant cells or exchanged by cells that are making direct contact. Intercellular communication via extracellular membrane vesicles has drawn much attention recently, as they have been shown to carry various biomolecules that modulate the activities of recipient cells. In this review, I will discuss current views on cell-cell communication via extra-cellular membrane vesicles, especially shedded membrane vesicles, and their effects on the control of the immune system.

TM4SF10 and ADAP interaction in podocytes: role in Fyn activity and nephrin phosphorylation

TM4SF10 [transmembrane tetra(4)-span family 10] is a claudin-like cell junction protein that is transiently expressed during podocyte development where its expression is downregulated in differentiating podocytes coincident with the appearance of nephrin at the slit diaphragm. In a yeast two-hybrid screen, we identified adhesion and degranulation-promoting adaptor protein (ADAP), a well-known Fyn substrate and Fyn binding partner, as a TM4SF10 interacting protein in mouse kidney. Using coimmunoprecipitation and immunohistochemistry experiments in cultured human podocytes, we show that TM4SF10 colocalizes with Fyn and ADAP but does not form a stable complex with Fyn. Cytoskeletal changes and phosphorylation events mediated by Fyn activity were reversed by TM4SF10 overexpression, including a decrease in the activating tyrosine phosphorylation of Fyn (Y(421)), suggesting TM4SF10 may have a regulatory role in suppressing Fyn activity. In addition, TM4SF10 was reexpressed following podocyte injury by puromycin aminonucleoside treatment, and its expression enhanced the abundance of high-molecular-weight forms of nephrin indicating it may participate in a mechanism controlling nephrin's appearance at the plasma membrane. Therefore, these studies have identified ADAP as another Fyn adapter protein expressed in podocytes, and that TM4SF10, possibly through ADAP, may regulate Fyn activity. Since TM4SF10 expression is temporally regulated during kidney development, these studies may help define a mechanism by which the slit diaphragm matures as a highly specialized cell junction during podocyte differentiation.

Functional cooperation between the proteins Nck and ADAP is fundamental for actin reorganization

T cell antigen receptor (TCR) activation triggers profound changes in the actin cytoskeleton. In addition to controlling cellular shape and polarity, this process regulates vital T cell responses, such as T cell adhesion, motility, and proliferation. These depend on the recruitment of the signaling proteins Nck and Wiskott-Aldrich syndrome protein (WASp) to the site of TCR activation and on the functional properties of the adapter proteins linker for activation of T cells (LAT) and SH2-domain-containing leukocyte protein of 76 kDa (SLP76). We now demonstrate that Nck is necessary but insufficient for the recruitment of WASp. We show that two pathways lead to SLP76-dependent actin rearrangement. One requires the SLP76 acidic domain, crucial to association with the Nck SH2 domain, and another requires the SLP76 SH2 domain, essential for interaction with the adhesion- and degranulation-promoting adapter protein ADAP. Functional cooperation between Nck and ADAP mediates SLP76-WASp interactions and actin rearrangement. We also reveal the molecular mechanism linking ADAP to actin reorganization.

The adapter protein Nck: role of individual SH3 and SH2 binding modules for protein interactions in T lymphocytes

Nck is a ubiquitously expressed, primarily cytosolic adapter protein consisting of one SH2 domain and three SH3 domains. It links receptor and nonreceptor tyrosine kinases to actin cytoskeleton reorganizing proteins. In T lymphocytes, Nck is a crucial component of signaling pathways for T cell activation and effector function. It recruits actin remodeling proteins to T cell receptor (TCR)-associated activation clusters and thereby initiates changes in cell polarity and morphology. Moreover, Nck is crucial for the TCR-induced mobilization of secretory vesicles to the cytotoxic immunological synapse. To identify the interactome of Nck in human T cells, we performed a systematic screen for interaction partners in untreated or pervanadate-treated cells. We used GST fusion proteins containing full length Nck, the combined SH3 domains or the individual SH3 and SH2 domains to precipitate putative Nck interactors from cellular lysates. Protein bands were excised from gels, processed by tryptic in-gel digestion and analyzed by mass spectrometry. Using this approach, we confirmed previously established interactions (e.g., with Slp76, CD3 epsilon, WASP, and WIPF1) and identified several novel putative Nck-binding proteins. We subsequently verified the SH2 domain binding to the actin-binding protein HIP55 and to FYB/ADAP, and the SH3-mediated binding to the nuclear proteins SFPQ/NONO. Using laser scanning microscopy, we provide new evidence for a nuclear localization of Nck in human T cells. Our data highlight the fundamental role of Nck in the TCR-to-cytoskeleton crosstalk and point to yet unknown nuclear functions of Nck also in T lymphocytes.

Functional genomic analysis of peripheral blood during early acute renal allograft rejection

BACKGROUND

Acute graft rejection is an important clinical problem in renal transplantation and an adverse predictor for long-term graft survival. Peripheral blood biomarkers that provide evidence of early graft rejection may offer an important option for posttransplant monitoring, optimize the utility of graft biopsy, and permit timely and effective therapeutic intervention to minimize the graft damage.

METHODS

In this feasibility study (n=58), we have used gene expression profiling in a case-control design to compare whole blood samples between normal subjects (n=20) and patients with (n=11) or without (n=22) biopsy-confirmed acute rejection (BCAR) or borderline changes (n=5).

RESULTS

A total of 183 probe sets representing 160 genes were differentially expressed (false discovery rate [FDR] <0.01) between subjects with or without BCAR, from which linear discriminant analysis and cross-validation identified an initial gene signature of 24 probe sets, and a more refined set of 11 probe sets found to classify subject samples correctly. Cross-validation suggested an out-of-sample sensitivity of 73% and specificity of 91% for identification of samples with or without BCAR. An increase in classifier gene expression correlated closely with acute rejection during the first 3 months posttransplant. Biological evaluation indicated that the differentially expressed genes encompassed processes related to immune response, signal transduction, and cytoskeletal reorganization.

CONCLUSION

Preliminary evidence indicates that gene expression in the peripheral blood may yield a relevant measure for the occurrence of BCAR and offer a potential tool for immunologic monitoring. These results now require confirmation in a larger cohort.

Role for ADAP in shear flow-induced platelet mechanotransduction

Binding of platelets to fibrinogen via integrin alphaIIbbeta3 stimulates cytoskeletal reorganization and spreading. These responses depend on tyrosine phosphorylation of multiple proteins by Src family members and Syk. Among Src substrates in platelets is adhesion- and degranulation-promoting adapter protein (ADAP), an adapter with potential binding partners: SLP-76, VASP, and SKAP-HOM. During studies of platelet function under shear flow, we discovered that ADAP(-/-) mouse platelets, unlike ADAP+/+ platelets, formed unstable thrombi in response to carotid artery injury. Moreover, fibrinogen-adherent ADAP(-/-) platelets in shear flow ex vivo showed reduced spreading and smaller zones of contact with the matrix. These abnormalities were not observed under static conditions, and they could not be rescued by stimulating platelets with a PAR4 receptor agonist or by direct alphaIIbbeta3 activation with MnCl2, consistent with a defect in outside-in alphaIIbbeta3 signaling. ADAP+/+ platelets subjected to shear flow assembled F-actin-rich structures that colocalized with SLP-76 and the Rac1 exchange factor, phospho-Vav1. In contrast, platelets deficient in ADAP, but not those deficient in VASP or SKAP-HOM, failed to form these structures. These results establish that ADAP is an essential component of alphaIIbbeta3-mediated platelet mechanotransduction that promotes F-actin assembly and enables platelet spreading and thrombus stabilization under fluid shear stress.

Differential gene expression in chronic inflammatory demyelinating polyneuropathy (CIDP) skin biopsies

Gene expression analysis previously identified molecular markers that are up-regulated in sural nerve biopsies from patients with chronic inflammatory demyelinating polyneuropathy (CIDP). To determine whether the same or additional genes are also up-regulated in skin, we applied gene microarray profiling and quantitative real-time PCR (qPCR) analysis to skin punch biopsies from patients with CIDP and controls. Five genes, allograft inflammatory factor 1 (AIF-1), lymphatic hyaluronan receptor (LYVE-1/XLKD1), FYN binding protein (FYB), P2RY1 (purinergic receptor P2Y, G-protein-coupled, 1), and MLLT3 (myeloid/lymphoid or mixed-lineage leukemia translocated to, 3), all associated with immune cells or inflammatory processes, were elevated in punch skin biopsies from patients with CIDP as compared to normal subjects or patients with Charcot-Marie-Tooth Type 1 (CMT1). The average fold change of the 5 genes over normal expression, as determined by qPCR, was significantly elevated in skin biopsies from patients with CIDP in comparison to CMT1 or diabetic neuropathy, and similar to that seen in Lyme disease. The findings indicate the presence of inflammatory changes in the skin of patients with CIDP.

The T-cell-specific adapter protein family: TSAd, ALX, and SH2D4A/SH2D4B

Adapter proteins play key roles in intracellular signal transduction through complex formation with catalytically active signaling molecules. In T lymphocytes, the role of several different types of adapter proteins in T-cell antigen receptor signal transduction is well established. An exception to this is the family of T-cell-specific adapter (TSAd) proteins comprising of TSAd, adapter protein of unknown function (ALX), SH2D4A, and SH2D4B. Only recently has the function of these adapters in T-cell signal transduction been explored. Here, we discuss advances in our understanding of the role of this family of adapter proteins in T cells. Their function as regulators of signal transduction in other cell types is also discussed.

Identification of SH3 domain interaction partners of human FasL (CD178) by phage display screening

BACKGROUND

Fas ligand is a cytotoxic effector molecule of T and NK cells which is characterized by an intracellular N-terminal polyproline region that serves as a docking site for SH3 and WW domain proteins. Several previously described Fas ligand-interacting SH3 domain proteins turned out to be crucial for the regulation of storage, expression and function of the death factor. Recent observations, however, indicate that Fas ligand is also subject to posttranslational modifications including shedding and intramembrane proteolysis. This results in the generation of short intracellular fragments that might either be degraded or translocate to the nucleus to influence transcription. So far, protein-protein interactions that specifically regulate the fate of the intracellular fragments have not been identified.

RESULTS

In order to further define the SH3 domain interactome of the intracellular region of Fas ligand, we now screened a human SH3 domain phage display library. In addition to known SH3 domains mediating binding to the Fas ligand proline-rich domain, we were able to identify a number of additional SH3 domains that might also associate with FasL. Potential functional implications of the new binding proteins for the death factor's biology are discussed. For Tec kinases and sorting nexins, the observed interactions were verified in cellular systems by pulldown experiments.

CONCLUSION

We provide an extended list of putative Fas ligand interaction partners, confirming previously identified interactions, but also introducing several novel SH3 domain proteins that might be important regulators of Fas ligand function.

Distinct regulation of integrin-dependent T cell conjugate formation and NF-kappa B 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.

Defective positive selection results in T cell lymphopenia and increased autoimmune diabetes in ADAP-deficient BDC2.5-C57BL/6 mice

Adhesion and degranulation promoting adapter protein (ADAP), a positive regulator of T cell receptor (TCR) signaling, is required for thymocyte development and T cell homeostasis. To investigate the role of ADAP in a T cell-driven autoimmune response, we generated ADAP-deficient, BDC2.5 TCR transgenic, diabetes-prone (C57BL/6) mice (BDC/B6). We observed a striking enhancement of diabetes incidence in ADAP-deficient mice, both in animals homozygous for I-Ag7, and in mice carrying one I-Ab allele (BDC/B6g7/b). Increased disease correlates with significantly reduced numbers of pathological CD4(+) T cells in the mice. Consistent with a state of functional lymphopenia in ADAP-deficient BDC/B6g7/b mice, T cells display increased homeostatic proliferation. Transfer of syngeneic lymphocytes or T cells both blocks ADAP-dependent diabetes and relieves exaggerated homeostatic T cell proliferation observed in ADAP-deficient mice. Marked attenuation in cellularity of the CD4+ single-positive thymocyte compartment in ADAP-deficient BDC/B6g7/b animals suggests a mechanism for induction of the lymphopenia. We conclude that inefficient positive selection in ADAP deficiency results in lymphopenia that leads to enhanced autoimmune diabetes in the BDC/B6g7/b model. Our findings support the notion that ineffective thymic T cell output can be a powerful causative factor in lymphopenia-driven autoimmune diabetes.

Compartmentalization of ITAM and integrin signaling by adapter molecules

Adapters are multidomain molecules that recruit effector proteins during signal transduction by immunoreceptors and integrins. The absence of these scaffolding molecules profoundly affects development and function of various hematopoietic lineages, underscoring their importance as regulators of signaling cascades. An emerging aspect of the mechanism by which engaged immunoreceptors and integrins transmit signals within the cell is by differential usage of various adapters that function to nucleate formation of distinct signaling complexes in a specific location within the cell. In this review, we discuss the mechanisms by which adapter proteins coordinate signal transduction with an emphasis on the role of subcellular compartmentalization in adapter function.

Integrin Regulation of Lymphocyte Trafficking: Lessons from Structural and Signaling Studies

High trafficking capability of lymphocytes is crucial in immune surveillance and antigen responses. Central to this regulatory process is a dynamic control of lymphocyte adhesion behavior regulated by chemokines and adhesion receptors such as integrins. Modulation of lymphocyte adhesive responses occurs in a wide range of time window from less than a second to hours, enabling rolling lymphocyte to attach to and migrate through endothelium and interact with antigen-presenting cells. While there has been a rapid progress in the understanding of integrin structure, elucidation of signaling events to relay extracellular signaling to integrins in physiological contexts has recently emerged from studies using gene-targeting and gene-silencing technique. Regulatory molecules critical for integrin activity control distribution of integrins, polarized cell morphology and motility, suggesting a signaling network that coordinates integrin function with lymphocyte migration. Here, I review recent studies of integrin structural changes and intracellular signal molecules that trigger integrin activation (inside-out signals), and discuss molecular mechanisms that control lymphocyte integrins and how inside-out signals coordinately modulate adhesive reactions and cell shape and migration.

Membrane-proximal signaling events in beta-2 integrin activation

In the immune system, integrins have essential roles in leukocyte trafficking and function. These include immune cell attachment to endothelial and antigen-presenting cells, cytotoxicity, and extravasation into tissues. The integrin leukocyte function-associated antigen-1 (LFA-1), which is exclusively expressed on hematopoietic cells, has been intensely studied since this receptor is important for many functions of the immune system. LFA-1 is involved in a) the interaction between T-cells and antigen presenting cells, b) the adhesion of cells to post-capillary high endothelial venules or to activated endothelium at sites of inflammation (extravasation), c) the control of cell differentiation and proliferation, and d) the regulation of T-cell effector functions. Therefore, a precise understanding of the spatial and temporal control of LFA-1 interaction with its cellular counter-receptors, the intercellular adhesion molecules (ICAM) -1, -2 and -3, in the various contexts, is of high interest. LFA-1 mediated adhesion is induced by several extracellular stimuli in different cell types. In T-cells, LFA-1 becomes activated upon signaling from the T-cell receptor (TCR), and upon cytokine and chemokine sensing. Adhesion of monocytes to ICAM-1 is induced by lipopolysaccharide (LPS), a component of the bacterial cell wall. To investigate the regulation of LFA-1 adhesiveness, research has focused on the identification of interaction partners of the intracellular portions of the integrin alpha and beta subunits. This review will highlight recent developments on transmembrane and intracellular signaling proteins, which have been implicated in beta-2 integrin activation.

Ets-1 expression promotes epithelial cell transformation by inducing migration, invasion and anchorage-independent growth

Ets-1 is the prototype of the family of ETS transcription factors. In human tumors, Ets-1 is expressed in endothelial cells and fibroblasts of the tumor stroma and is proposed to play a role in tumor vascularization and invasion by upregulating expression of matrix-degrading proteases. In human carcinomas, Ets-1 is also expressed by neoplastic cells, but little is known about the functional implications of this observation. We have addressed the role of Ets-1 in epithelial HeLa tumor cells by selecting stably Ets-1 over and underexpressing HeLa cells. Ets-1 expression increases the transformed phenotype of HeLa cells, by promoting cell migration, invasion and anchorage-independent growth, while Ets-1 downregulation reduces cell attachment. In correlation with these results, Ets-1 upregulation increases integrinbeta2 expression but not that of other integrins. These results suggest that, in addition to its role in the tumor stroma, Ets-1 may also promote tumor development and progression by increasing neoplastic transformation.

Physical and Functional Association of c-Src and Adhesion and Degranulation Promoting Adaptor Protein (ADAP) in Osteoclastogenesis in Vitro

c-Src plays a crucial role in osteoclastogenesis. In this study, we searched for c-Src-binding proteins using a combination of pull-down assays and mass spectrometric analysis, and identified the association of adhesion and degranulation promoting adaptor protein (ADAP) with c-Src in RAW264 cells and osteoclast precursors prepared from bone marrow cells. The kinase activity and the SH2 domain of c-Src were required for this association and Tyr807 in the extreme carboxyl terminus of ADAP was identified as a major recognition site. ADAP was found to be expressed in cells at the prefusion stage and localized mainly in the leading edge of lamellipodia and in pseudopodia. Tyrosine phosphorylation of ADAP was induced in an integrin-dependent manner, and the level was Src kinase-dependent. ADAP-knockdown RAW264 cells showed retarded migration and formed few multinucleated cells. Cas, known to be phosphorylated by c-Src, was identified as a major tyrosine-phosphorylated protein in differentiating RAW264 cells and the phosphorylation appeared to be decreased in ADAP-knockdown cells. ADAP thus may play an important role as a partner of c-Src for cell migration and progression to the multinucleated cell stage in osteoclastogenesis in vitro.

Intracellular signalling controlling integrin activation in lymphocytes

Since the discovery that integrins at the surface of lymphocytes undergo dynamic changes in their adhesive activity after stimulation through the T-cell receptor or stimulation with chemokines, intensive research has been carried out in an attempt to clarify the signalling events that lead to the activation of integrins. Whereas structural studies have provided us with a vivid picture of the conformational flexibility of integrins, the signalling pathways that regulate these conformational changes (known as inside-out signalling) have been elusive. However, as I discuss here, recent studies have provided new insight into the pathways that control the regulation of integrin activity and the coordination of complex cellular functions, such as the homing of lymphocytes and the formation of an immunological synapse.

Receptor-stimulated oxidation of SHP-2 promotes T-cell adhesion through SLP-76-ADAP

Receptor-stimulated generation of intracellular reactive oxygen species (ROS) modulates signal transduction, although the mechanism(s) is unclear. One potential basis is the reversible oxidation of the active site cysteine of protein tyrosine phosphatases (PTPs). Here, we show that activation of the antigen receptor of T cells (TCR), which induces production of ROS, induces transient inactivation of the SH2 domain-containing PTP, SHP-2, but not the homologous SHP-1. SHP-2 is recruited to the LAT-Gads-SLP-76 complex and directly regulates the phosphorylation of key signaling proteins Vav1 and ADAP. Furthermore, the association of ADAP with the adapter SLP-76 is regulated by SHP-2 in a redox-dependent manner. The data indicate that TCR-mediated ROS generation leads to SHP-2 oxidation, which promotes T-cell adhesion through effects on an SLP-76-dependent signaling pathway to integrin activation.

Deficiency of ADAP/Fyb/SLAP-130 destabilizes SKAP55 in Jurkat T cells

ADAP (adhesion and degranulation-promoting adaptor protein) and SKAP55 (Src kinase-associated phosphoprotein of 55 kDa) are T cell adaptors that mediate inside-out signaling from the T cell antigen receptor to integrins, giving rise to increased integrin affinity/avidity and formation of the immunological synapse between the T cell and the antigen-presenting cell. These two proteins are tightly and constitutively associated with one another, and their ability to interact is required for inside-out signaling. Here we show in an ADAP-deficient Jurkat T cell line that the co-dependence of ADAP and SKAP55 extends beyond their functional and physical interactions and show that SKAP55 protein is unstable in the absence of ADAP. Restoration of ADAP to the ADAP-deficient Jurkat T cell line restores SKAP55 expression by causing a 5-fold decrease in the rate of SKAP55 proteolysis. Inactivation of the Src homology 3 domain of SKAP55, which mediates the association between SKAP55 with ADAP, blocks the protective effect of ADAP. The half-life of SKAP55, in the absence of ADAP, is approximately 15-20 min, increasing to 90 min in the presence of ADAP. This is a remarkably rapid rate of turnover for a signaling protein and suggests the possibility that stimuli that signal for the stabilization of SKAP55 may play an important role in T cell adhesion and conjugate formation.

PRAM-1 potentiates arsenic trioxide-induced JNK activation

The promyelocytic leukemia RARalpha target gene encoding an adaptor molecule-1 (PRAM-1) is involved in a signaling pathway induced by retinoic acid in acute promyelocytic leukemia (APL) cells. To better understand the function of PRAM-1, we have undertaken the identification of its partners through a yeast two-hybrid screen. Here, we show that the proline-rich domain of PRAM-1 interacted with the Src homology 3 (SH3) domain of hematopoietic progenitor kinase 1 (HPK-1)-interacting protein of 55 kDa (HIP-55, also called SH3P7 and Abp1) known to stimulate the activity of HPK-1 and c-Jun N-terminal kinase (JNK). Overexpression of PRAM-1 in the NB4 APL cell line increased arsenic trioxide-induced JNK activation through a caspase 3-like-dependent activity. Dissociation of the SH3 domain from the rest of the HIP-55 protein was observed in the NB4 APL cell line treated with arsenic trioxide due to specific cleavage by caspase 3-like enzymes. The cleavage of HIP-55 correlated with the induction of PRAM-1 mRNA and protein expression. Taken together, our results suggest that the caspase 3-cleaved SH3 domain of HIP-55 is likely involved in PRAM-1-mediated JNK activation upon arsenic trioxide-induced differentiation of NB4 cells.

Cellular mechanisms of bacterial internalization counteracted by Yersinia

Upon host-cell contact, human pathogenic Yersinia species inject Yop virulence effectors into the host through a Type III secretion-and-translocation system. These virulence effectors cause a block in phagocytosis (YopE, YopT, YpkA, and YopH) and suppression of inflammatory mediators (YopJ). The Yops that block phagocytosis either interfere with the host cell actin regulation of Rho GTPases (YopE, YopT, and YpkA) or specifically and rapidly inactivate host proteins involved in signaling from the receptor to actin (YopH). The block in uptake has been shown to be activated following binding to Fc, Complement, and beta1-integrin receptors in virtually any kind of host cell. Thus, the use of Yersinia as a model system to study Yersinia-host cell interactions provides a good tool to explore signaling pathways involved in phagocytosis.

The Immunological Synapse and Rho GTPases

Rho GTPases are molecular switches controlling a broad range of cellular processes including lymphocyte activation. Not surprisingly, Rho GTPases are now recognized as pivotal regulators of antigen-specific T cell activation by APCs and immunological synapse formation. This review summarizes recent advances in our understanding of how Rho GTPase-dependent pathways control T lymphocyte motility, polarization and activation.

Molecular classification of human endometrial cycle stages by transcriptional profiling

Endometrium is a dynamic tissue that undergoes cyclic changes each month, under the overall control of estrogen and progesterone. The aims of this study were to investigate the changing global gene expression profile of human endometrium during the menstrual cycle using microarray technology and to determine the correlation between histopathological evaluation and molecular profile of the samples. Standard two-colour cDNA microarrays were performed on the 43 samples against a common reference, using a 10.5 K cDNA glass slide microarray. The results were validated using real-time PCR. Analysis of expression data was carried out using parametric analysis of variance with Benjamini-Hochberg correction. Hierarchical clustering reveals a strong relationship between histopathology and transcriptional profile of the samples. The study identified 1452 genes that showed significant changes in expression (P< or =0.05) across the menstrual cycle, with 425 genes having changes that are at least 2-fold. The data were also independently analysed by a CSIRO algorithm called GeneRaVE that identified a small subset of genes whose expression profiles could be used to classify nearly all the biopsies into their correct cycle stage. We also identified and validated three genes [(natural cytotoxicity triggering receptor (NCR)3, fucosyl transferase (FUT)4 and Fyn-binding protein (FYB)] that had not been shown to have significant cyclic changes in the human endometrium, previously. We have shown for the first time that endometrial cycle stage prediction is possible based on global gene expression profile.