Beta 1-integrin-mediated cell signaling in T lymphocytes

β1 Integrin induces adhesion and migration of human Th17 cells via Pyk2-dependent activation of P2X4 receptor

Integrin-mediated T-cell adhesion and migration is a crucial step in immune response and autoimmune diseases. However, the underlying signalling mechanisms are not fully elucidated. In this study, we examined the implication of purinergic signalling, which has been associated with T-cell activation, in the adhesion and migration of human Th17 cells across fibronectin, a major matrix protein associated with inflammatory diseases. We showed that the adhesion of human Th17 cells to fibronectin induces, via β1 integrin, a sustained release of adenosine triphosphate (ATP) from the mitochondria through the pannexin-1 hemichannels. Inhibition of ATP release or its degradation with apyrase impaired the capacity of the cells to attach and migrate across fibronectin. Inhibition studies identified a major role for the purinergic receptor P2X4 in T-cell adhesion and migration but not for P2X7 or P2Y₁₁ receptors. Blockade of P2X4 but not P2X7 or P2Y₁₁ receptors reduced cell adhesion and migration by inhibiting activation of β1 integrins, which is essential for ligand binding. Furthermore, we found that β1 integrin-induced ATP release, P2X4 receptor transactivation, cell adhesion and migration were dependent on the focal adhesion kinase Pyk2 but not FAK. Finally, P2X4 receptor inhibition also blocked fibronectin-induced Pyk2 activation suggesting the existence of a positive feedback loop of activation between β1 integrin/Pyk2 and P2X4 purinergic signalling pathways. Our findings uncovered an unrecognized link between β1 integrin and P2X4 receptor signalling pathways for promoting T-cell adhesion and migration across the extracellular matrix.

Dynamic transcriptome analysis unveils key proresolving factors of chronic inflammatory arthritis

Despite recent advances in understanding chronic inflammation remission, global analyses have not been explored to systematically discover genes or pathways underlying the resolution dynamics of chronic inflammatory diseases. Here, we performed time-course gene expression profiling of mouse synovial tissues along progression and resolution of collagen-induced arthritis (CIA) and identified genes associated with inflammation resolution. Through network analysis of these genes, we predicted 3 key secretory factors responsible for the resolution of CIA: Itgb1, Rps3, and Ywhaz. These factors were predominantly expressed by Tregs and antiinflammatory M2 macrophages, suppressing production of proinflammatory cytokines. In particular, Ywhaz was elevated in the sera of mice with arthritis resolution and in the urine of rheumatoid arthritis (RA) patients with good therapeutic responses. Moreover, adenovirus-mediated transfer of the Ywhaz gene to the affected joints substantially inhibited arthritis progression in mice with CIA and suppressed expression of proinflammatory cytokines in joint tissues, lymph nodes, and spleens, suggesting Ywhaz is an excellent target for RA therapy. Therefore, our comprehensive analysis of dynamic synovial transcriptomes provides previously unidentified antiarthritic genes, Itgb1, Rps3, and Ywhaz, which can serve as molecular markers to predict disease remission, as well as therapeutic targets for chronic inflammatory arthritis.

Staphylococcal Superantigens Use LAMA2 as a Coreceptor To Activate T Cells

Canonical Ag-dependent TCR signaling relies on activation of the src-family tyrosine kinase LCK. However, staphylococcal superantigens can trigger TCR signaling by activating an alternative pathway that is independent of LCK and utilizes a Gα11-containing G protein-coupled receptor (GPCR) leading to PLCβ activation. The molecules linking the superantigen to GPCR signaling are unknown. Using the ligand-receptor capture technology LRC-TriCEPS, we identified LAMA2, the α2 subunit of the extracellular matrix protein laminin, as the coreceptor for staphylococcal superantigens. Complementary binding assays (ELISA, pull-downs, and surface plasmon resonance) provided direct evidence of the interaction between staphylococcal enterotoxin E and LAMA2. Through its G4 domain, LAMA2 mediated the LCK-independent T cell activation by these toxins. Such a coreceptor role of LAMA2 involved a GPCR of the calcium-sensing receptor type because the selective antagonist NPS 2143 inhibited superantigen-induced T cell activation in vitro and delayed the effects of toxic shock syndrome in vivo. Collectively, our data identify LAMA2 as a target of antagonists of staphylococcal superantigens to treat toxic shock syndrome.

Reinforcement of integrin-mediated T-Lymphocyte adhesion by TNF-induced Inside-out Signaling

Integrin-mediated leukocyte adhesion to endothelial cells is a crucial step in immunity against pathogens. Whereas the outside-in signaling pathway in response to the pro-inflammatory cytokine tumour necrosis factor (TNF) has already been studied in detail, little knowledge exists about a supposed TNF-mediated inside-out signaling pathway. In contrast to the outside-in signaling pathway, which relies on the TNF-induced upregulation of surface molecules on endothelium, inside-out signaling should also be present in an endothelium-free environment. Using single-cell force spectroscopy, we show here that stimulating Jurkat cells with TNF significantly reinforces their adhesion to fibronectin in a biomimetic in vitro assay for cell-surface contact times of about 1.5 seconds, whereas for larger contact times the effect disappears. Analysis of single-molecule ruptures further demonstrates that TNF strengthens sub-cellular single rupture events at short cell-surface contact times. Hence, our results provide quantitative evidence for the significant impact of TNF-induced inside-out signaling in the T-lymphocyte initial adhesion machinery.

The Role of Crk Adaptor Proteins in T-Cell Adhesion and Migration

Crk adaptor proteins are key players in signal transduction from a variety of cell surface receptors. They are involved in early steps of lymphocyte activation through their SH2-mediated transient interaction with signal transducing effector molecules, such as Cbl, ZAP-70, CasL, and STAT5. In addition, they constitutively associate, via their SH3 domain, with effector molecules, such as C3G, that mediate cell adhesion and regulate lymphocyte extravasation and recruitment to sites of inflammation. Recent studies demonstrated that the conformation and function of CrkII is subjected to a regulation by immunophilins, which also affect CrkII-dependent T-cell adhesion to fibronectin and migration toward chemokines. This article addresses mechanisms that regulate CrkII conformation and function, in general, and emphasizes the role of Crk proteins in receptor-coupled signaling pathways that control T-lymphocyte adhesion and migration to inflammatory sites.

The role of Cas-L/NEDD9 as a regulator of collagen-induced arthritis in a murine model

Cas-L/NEDD9 is a cytoplasmic docking protein downstream of β1 integrin-mediated signaling pathway and is essential for cellular migration and β1 integrin-mediated costimulation of T cells. We previously found that increased number of Cas-L positive leukocytes migrated into the inflamed joints of HTLV-I tax transgenic mice which spontaneously develop polyarthritis, suggesting a role of Cas-L in rheumatoid arthritis (RA) pathophysiology. Our current study expanded these findings on the role of Cas-L/NEDD9 in the development of RA by analyzing the pathophysiological changes in a Nedd9(-/-) mouse collagen-induced arthritis (CIA) model. Nedd9(-/-) mice exhibited a decrease in arthritis severity as compared to Nedd9(+/+) mice. In addition, as being conducted bone marrow transplantation experiments with a CIA model, Nedd9(-/-)→Nedd9(+/+) transplant showed a decrease in the incidence and severity score of arthritis, compared to those of Nedd9(+/+)→Nedd9(-/-) transplant. For analysis of serum levels of various cytokines, IL-1β, IL-6, IL-17, TNF-α, IFN-γ and anti-collagen antibody were decreased, while IL-4 and IL-10 levels were increased, in Nedd9(-/-) mice as compared to those in Nedd9(+/+) mice. Furthermore, collagen-mediated cellular responses of lymphocytes isolated from spleen or affected lymph nodes of Nedd9(-/-) mice were reduced. Our results strongly suggest that Cas-L/NEDD9 plays a pivotal role in the pathophysiology of CIA, and that Cas-L/NEDD9 may be a potential molecular target for the treatment of RA.

Functions of the FAK family kinases in T cells: beyond actin cytoskeletal rearrangement

T cells control the focus and extent of adaptive immunity in infectious and pathological diseases. The activation of T cells occurs when the T cell antigen receptor (TCR) and costimulatory and/or adhesion receptors are engaged by their ligands. This process drives signaling that promotes cytoskeletal rearrangement and transcription factor activation, both of which regulate the quality and magnitude of the T cell response. However, it is not fully understood how different receptor-induced signals combine to alter T cell activation. The related non-receptor tyrosine kinases focal adhesion kinase (FAK) and proline-rich tyrosine kinase 2 (Pyk2) are phosphorylated downstream of the TCR and several costimulatory and adhesion receptors. FAK family proteins integrate receptor-mediated signals that influence actin cytoskeletal rearrangement and effector T cell responses. In this review, we summarize the receptor-specific roles that FAK and Pyk2 control to influence T cell development and activation.

Sequestosome1/p62: a regulator of redox-sensitive voltage-activated potassium channels, arterial remodeling, inflammation, and neurite outgrowth

Sequestosome1/p62 (SQSTM1) is an oxidative stress-inducible protein regulated by the redox-sensitive transcription factor Nrf2. It is not an antioxidant but known as a multifunctional regulator of cell signaling with an ability to modulate targeted or selective degradation of proteins through autophagy. SQSTM1 implements these functions through physical interactions with different types of proteins including atypical PKCs, nonreceptor-type tyrosine kinase p56(Lck) (Lck), polyubiquitin, and autophagosomal factor LC3. One of the notable physiological functions of SQSTM1 is the regulation of redox-sensitive voltage-gated potassium (Kv) channels which are composed of α and β subunits: (Kvα)4 (Kvβ)4. Previous studies have established that SQSTM1 scaffolds PKCζ, enhancing phosphorylation of Kvβ which induces inhibition of pulmonary arterial Kv1.5 channels under acute hypoxia. Recent studies reveal that Lck indirectly interacts with Kv1.3 α subunits and plays a key role in acute hypoxia-induced Kv1.3 channel inhibition in T lymphocytes. Kv1.3 channels provide a signaling platform to modulate the migration and proliferation of arterial smooth muscle cells and activation of T lymphocytes, and hence have been recognized as a therapeutic target for treatment of restenosis and autoimmune diseases. In this review, we focus on the functional interactions of SQSTM1 with Kv channels through two key partners aPKCs and Lck. Furthermore, we provide molecular insights into the functions of SQSTM1 in suppression of proliferation of arterial smooth muscle cells and neointimal hyperplasia following carotid artery ligation, in T lymphocyte differentiation and activation, and in NGF-induced neurite outgrowth in PC12 cells.

Differential expression of FAK and Pyk2 in metastatic and non-metastatic EL4 lymphoma cell lines

The murine EL4 lymphoma cell line exists in variants that are either sensitive or resistant to phorbol 12-myristate 13-acetate (PMA). In sensitive cells, PMA causes Erk MAPK activation and Erk-mediated growth arrest. In resistant cells, PMA induces a low level of Erk activation, without growth arrest. A relatively unexplored aspect of the phenotypes is that resistant cells are more adherent to culture substrate than are sensitive cells. In this study, the roles of the protein tyrosine kinases FAK and Pyk2 in EL4 phenotype were examined, with a particular emphasis on the role of these proteins in metastasis. FAK is expressed only in PMA-resistant (or intermediate phenotype) EL4 cells, correlating with enhanced cell-substrate adherence, while Pyk2 is more highly expressed in non-adherent PMA-sensitive cells. PMA treatment causes modulation of mRNA for FAK (up-regulation) and Pyk2 (down-regulation) in PMA-sensitive but not PMA-resistant EL4 cells. The increase in Pyk2 mRNA is correlated with an increase in Pyk2 protein expression. The roles of FAK in cell phenotype were further explored using transfection and knockdown experiments. The results showed that FAK does not play a major role in modulating PMA-induced Erk activation in EL4 cells. However, the knockdown studies demonstrated that FAK expression is required for proliferation and migration of PMA-resistant cells. In an experimental metastasis model using syngeneic mice, only FAK-expressing (PMA-resistant) EL4 cells form liver tumors. Taken together, these studies suggest that FAK expression promotes metastasis of EL4 lymphoma cells.

Molecular basis for HEF1/NEDD9/Cas-L action as a multifunctional co-ordinator of invasion, apoptosis and cell cycle

Upregulation of the scaffolding protein HEF1, also known as NEDD9 and Cas-L, has recently been identified as a pro-metastatic stimulus in a number of different solid tumors, and has also been strongly associated with pathogenesis of BCR-Abl-dependent tumors. As the evidence mounts for HEF1/NEDD9/Cas-L as a key player in metastatic cancer, it is timely to review the molecular regulation of HEF1/NEDD9/Cas-L. Most of the mortality associated with cancer arises from uncontrolled metastases, thus a better understanding of the properties of proteins specifically associated with promotion of this process may yield insights that improve cancer diagnosis and treatment. In this review, we summarize the extensive literature regarding HEF1/NEDD9/Cas-L expression and function in signaling relevant to cell attachment, migration, invasion, cell cycle, apoptosis, and oncogenic signal transduction. The complex function of HEF1/NEDD9/Cas-L revealed by this analysis leads us to propose a model in which alleviation of cell cycle checkpoints and acquired resistance to apoptosis is permissive for a HEF1/NEDD9/Cas-L-promoted pro-metastatic phenotype.

Collagen-mediated survival signaling is modulated by CD45 in Jurkat T cells

T cell activation is a critical step in the development of a proper immune response to infection and inflammation. This dynamic process requires efficient T cell receptor signaling, which in turn is modulated by integrin receptor activation and the actin cytoskeleton. CD45 is a key player in T cell receptor mediated signal transduction. However, its exact role in integrin mediated signaling in T cells remains to be elucidated. The present study addresses the relationship between CD45 and beta1-integrin mediated survival signaling in the human T leukemic cell line Jurkat, in which collagen receptors alpha1 beta1 and alpha2 beta1 integrins are localized. Wild type (WT)-Jurkat T cells treated with collagen demonstrated increased cell proliferation and survival. Monitoring the intracellular signaling pathways activated by collagen in WT-Jurkat cells revealed increased focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK) activation. Moreover, examination of the actin cytoskeleton of WT-Jurkat T cells treated with collagen demonstrated the presence of an organized cortical actin structure, reminiscent of the survival phenotype. This is in contrast to CD45-deficient J45.01 T cells, where collagen treatment failed to enhance cell proliferation/survival and was unable to stimulate FAK and ERK activity. In addition, the actin cytoskeleton of collagen treated J45.01 T cells was disorganized with cortical actin aggregates present throughout. The importance of an organized actin cytoskeleton to proper cell signaling and survival was further demonstrated by the inability of collagen treated WT-Jurkat cells to activate the FAK and ERK survival pathway in the presence of cytochalasin D, a cytoskeleton-disrupting drug. Consistently, addition of the CD45 specific inhibitor abolished collagen-stimulated FAK and ERK activation in WT-Jurkat cells, further depicting CD45 as the key mediator. Furthermore, collagen-mediated T cell signaling alone was able to activate IL-2 gene transcription devoid of concomitant T cell receptor activation. Taken together, these results are the first to demonstrate that CD45 is important in promoting cell survival by modulating integrin-mediated FAK/ERK signaling in Jurkat T cells and is involved in a distinct signal transduction pathway, separate from T cell receptor signaling, influencing T cell immune responses. Hence, this study will help further our knowledge about beta1-integrin mediated signaling in T cells, which may prove to be essential for the regulation of various T cell mediated immune responses.

Alpha2 beta1 integrin signaling augments T cell receptor-dependent production of interferon-gamma in human T cells

The mechanisms by which beta1 integrins modulate T cell costimulation are still poorly defined. In this study, we examined the role of collagen-binding integrins alpha1 beta1 and alpha2 beta1 in the regulation of interferon-gamma (IFN-gamma). We demonstrated that ligation of alpha2 beta1 integrin with Collagen type I (Coll I) but not alpha1 beta1 integrin with Collagen IV (Coll IV) significantly augmented T cell receptor (TCR)-dependent expression and production of IFN-gamma by effector T cells. The effect of Coll I was not due to cell adhesion as soluble Coll I also augmented TCR-dependent production of IFN-gamma. Inhibition studies indicated that activation of ERK and JNK MAPKs and PI3K/AKT are necessary for both TCR- and TCR+alpha2 beta1 integrin-dependent IFN-gamma production and that Coll I increases TCR-dependent activation of ERK and JNK MAPKs, and AKT. In addition, our results showed that Coll IV is less potent than Coll I in augmenting TCR-dependent activation of JNK/MAPK, which may explain the differential effect of collagen matrices on TCR-dependent IFN-gamma production. Together, these results indicate that the costimulatory effect of Coll I on IFN-gamma expression is integrated at the levels of ERK and JNK MAPKs and PI3K/AKT signaling pathways and suggest JNK/MAPK as a major signaling pathway of Coll I costimulation. Thus, our study identifies alpha2 beta1 integrin as an important regulatory pathway of IFN-gamma expression and provides novel insights into the signaling mechanisms of integrin costimulation in T cells. As such, this study further supports the functional importance that Coll I interactions may have on the control of T cell-dependent Th1 inflammatory diseases.

The hematopoietic isoform of Cas-Hef1-associated signal transducer regulates chemokine-induced inside-out signaling and T cell trafficking

Leukocyte migration and trafficking is dynamically regulated by various chemokine and adhesion molecules and is vital to the proper function of the immune system. We describe a role for the Cas and Hef-1-associated signal transducer in hematopoietic cells (Chat-H) as a critical regulator of T lymphocyte migration, by using lentivirus-mediated RNA interference (RNAi). Impaired migration of Chat-H-depleted cells coincided with defective inside-out signaling shown by diminished chemokine-induced activation of the Rap-1 GTPase and integrin-mediated adhesion. Localization of Chat-H to the plasma membrane, association with its binding partner Crk-associated substrate in lymphocytes (CasL), and Chat-H-mediated CasL serine-threonine phosphorylation were required for T cell migration. These results identify Chat-H as a critical signaling intermediate acting upstream of Rap1 to regulate chemokine-induced adhesion and migration.

Collagen type I signaling reduces the expression and the function of human receptor activator of nuclear factor-kappa B ligand (RANKL) in T lymphocytes

The mechanisms by which beta1 integrins modulate T cell functions are still poorly defined. We have previously reported that signaling via the collagen type I (Coll I) receptor, alpha2beta1 integrin, inhibited FasL expression and protected Jurkat T cells from activation-induced cell death (AICD). In this study, we examined whether Coll I signaling in T cells also modulates the expression of the human receptor activator of nuclear factor-kappaB ligand (RANKL), a recently identified TNF family member which has important functions in osteoclastogenesis, cell survival and apoptosis. Our results show that in both Jurkat T cells and human primary T cells, Coll I signaling significantly reduces activation-induced RANKL expression by 50-60%. We also found that RANKL is not involved in AICD but participates in doxorubicin-induced apoptosis of leukemia T cell lines including Jurkat, CEM and HSB-2. In this respect, Coll I protected leukemia T cell lines from doxorubicin-induced apoptosis by inhibiting doxorubicin-induced RANKL expression. Together, our results suggest that by limiting the production of RANKL, Coll I signaling may contribute to the resistance of leukemia T cells to chemotherapy. Our study also emphasizes the importance Coll I signaling may have in the control of RANKL-associated T cell functions.

Cell Adhesion Regulates CDC25A Expression and Proliferation in Acute Myeloid Leukemia

The effects of cell adhesion on leukemia cell proliferation remain poorly documented and somehow controversial. In this work, we investigated the effect of adhesion to fibronectin on the proliferation of acute myeloid leukemia (AML) cell lines (U937 and KG1a) and CD34+ normal or leukemic primary cells. We observed an increased rate of proliferation of AML cells when adhered to fibronectin, concomitant with accelerated S-phase entry and accumulation of CDC25A. Conversely, normal CD34+ cell proliferation was decreased by adhesion to fibronectin with a concomitant drop in CDC25A expression. Importantly, we showed that both small interfering RNA (siRNA)-mediated CDC25A down-regulation and a recently developed CDC25 pharmacologic inhibitor impaired this adhesion-dependent proliferation, establishing a functional link between CDC25A accumulation and adhesion-dependent proliferation in leukemic cells. CDC25A accumulation was found only slightly dependent on transcriptional regulation and essentially due to modifications of the proteasomal degradation of the protein as shown using proteasome inhibitors and reverse transcription-PCR. Interestingly, CDC25A regulation was Chk1 dependent in these cells as suggested by siRNA-mediated down-regulation of this protein. Finally, we identified activation of the phosphatidylinositol 3-kinase/Akt pathway as an adhesion-dependent regulation mechanism of CDC25A protein expression. Altogether, our data show that in leukemic cells adhesion to fibronectin increases CDC25A expression through proteasome- and Chk1-dependent mechanisms, resulting in enhanced proliferation. They also suggest that these adhesion-dependent proliferation properties of hematopoietic cells may be modified during leukemogenesis.

Semaphorin 7A is a negative regulator of T cell responses

Semaphorins play an essential role in axonal guidance, and emerging evidence points to diverse functions of several Semaphorin family members in the immune system. Semaphorin 7A (Sema7A) promotes axonal growth in the central nervous system. Here, we show that Sema7A also plays a critical role in negative regulation of T cell activation and function. T cells deficient in Sema7A exhibit enhanced homeostatic and antigen-induced proliferative response. Moreover, autoreactive Sema7A-deficient T cells mediate aggressive autoimmune disease. The deficiency in Sema7A leads to defective TCR downmodulation and T cell hyperresponsiveness. These results demonstrate an important role of Sema7A in limiting autoimmune responses and add to growing evidence of shared signaling pathways used by the immune and nervous systems.

Collagen type I-mediated activation of ERK/MAP Kinase is dependent on Ras, Raf-1 and protein phosphatase 2A in Jurkat T cells

Growing evidence indicates that interactions of T cells with extracellular matrix through beta1 integrins are important for the regulation of T cell-mediated immune responses and diseases. In this regard, we have recently demonstrated that collagen I (Coll I) through alpha2beta1 integrin inhibited Fas-induced apoptosis of T cells by activating a protein phosphatase 2A (PP2A)-dependent ERK/MAP Kinase pathway. As survival of T cells is critical for their functions, we further investigated the mechanisms underlying the activation of this pathway. Inhibition studies demonstrated that Coll I activates the ERK/MAP Kinase pathway in Jurkat T cells through the activation of Ras and Raf-1. Activation of PP2A was not necessary for the binding of Coll I to Jurkat T cells, but is required for the activation of Raf-1. In accordance, activation of Ras, Raf-1 and PP2A were also required for the ability of Coll I to protect Jurkat T cells from Fas-induced apoptosis. In contrast and despite its capacity to activate Ras, fibronectin (Fbn) failed to activate PP2A and Raf-1. These results might explain, at least in part, the weak ability of Fbn to activate ERK in T cells, supporting thus the differential signaling of beta1 integrin members in these cells. This study provides novel insights into the mechanisms by which beta1 integrins activate the ERK/MAP Kinase pathway in T cells, and is the first report to provide a role for PP2A in integrin-mediated ERK/MAP Kinase activation.

Protein kinase D1 and the beta 1 integrin cytoplasmic domain control beta 1 integrin function via regulation of Rap1 activation

The functional activity of integrins is dynamically regulated by T cell receptor stimulation and by protein kinase C (PKC). We report a novel function for the PKC effector protein kinase D1 (PKD1) in integrin activation. Constitutively active and kinase-inactive PKD1 mutants lacking the PKD1 pleckstrin homology (PH) domain block phorbol ester- and TCR-mediated activation and clustering of beta1 integrins. The PH domain of PKD1 mediates the association of PKD1 with the GTPase Rap1 and is central to Rap1 activation and membrane translocation in T cells. Furthermore, PKD1 and Rap1 associate with beta1 integrins in a manner that is dependent on the carboxy-terminal end of the beta1 integrin subunit cytoplasmic domain. beta1 integrin expression is required for Rap1 activation and membrane localization of the PKD1-Rap1 complex. Therefore, PKD1 promotes integrin activation in T cells by regulating Rap1 activation and membrane translocation via interactions with the beta1 integrin subunit cytoplasmic domain.

Involvement of crk adapter proteins in regulation of lymphoid cell functions

The Crk adapter proteins consist of Src homology 2 (SH2) SH2 and SH3 domains, which bind tyrosine-phosphorylated peptides and polyproline-rich motives, respectively. They are linked to multiple signaling pathways in different cell types, including lymphocytes, and because of their lack of catalytic activity, many studies on Crk were aimed at the identification of their binding partners and determination of the physiologic meaning of these interactions. Crk proteins were found to be involved in the early steps of lymphocyte activation through their SH2-mediated transient interaction with signal-transducing molecules, such as Cbl, ZAP-70, CasL, and STAT5. In addition, Crk proteins are constitutively associated with effector molecules that mediate cell adhesion and thereby regulate lymphocyte extravasation and recruitment to sites of inflammation. This article describes selected studies of Crk, performed predominantly in lymphocytes, and discusses their potential relevance to the role of Crk in the regulation of lymphocyte functions.

Integrin alpha2beta1 inhibits Fas-mediated apoptosis in T lymphocytes by protein phosphatase 2A-dependent activation of the MAPK/ERK pathway

The mechanisms by which T lymphocytes escape apoptosis during their activation are still poorly defined. In this study, we elucidated the intracellular signaling pathways through which beta1 integrins modulate Fas-mediated apoptosis in T lymphocytes. In experiments done in Jurkat T cells and activated peripheral blood T lymphocytes, engagement of alpha2beta1 integrin with collagen type I (Coll I) was found to significantly reduce Fas-induced apoptosis and caspase-8 activation; Annexin V binding and DNA fragmentation were reduced by approximately 42 and 38%, respectively. We demonstrated that the protective action of Coll I does not require new protein synthesis but was dependent on the activation of the MAPK/Erk pathway. Furthermore, we found that activation of protein phosphatase 2A (PP2A) by Coll I was required for both Coll I-mediated activation of Erk, and inhibition of Fas-induced caspase-8 activation and apoptosis. Other ligands of beta1 integrins, fibronectin (Fbn), and laminin (Lam), did not sustain significant Erk activation and had no effect on Fas-induced apoptosis. Taken together, these results provide the first evidence of a PP2A-dependent activation of the MAPK/Erk pathway downstream of alpha2beta1 integrin, which has a functional role in regulating Fas-mediated apoptosis in T lymphocytes. As such, this study emphasizes the potential importance that Coll I interactions may have on the control of T lymphocyte homeostasis and their persistence in chronic inflammatory diseases.

Occurrence of an activated, profibrotic pattern of gene expression in lung CD8+ T cells from scleroderma patients

OBJECTIVE

Pulmonary fibrosis is a major cause of death in scleroderma patients. Previous studies have shown an increase in CD8+ T cells in the lungs of scleroderma patients. In the present study, we sought to determine whether activated CD8+ T cells contribute to pulmonary fibrosis in scleroderma patients through the production and activation of profibrotic mediators.

METHODS

CD8+ cells were isolated from bronchoalveolar lavage fluid obtained from 19 scleroderma patients and 7 healthy subjects. The phenotype of these cells was determined using DNA array technology. Expression of selected genes was confirmed in real-time polymerase chain reaction and enzyme-linked immunosorbent assay experiments.

RESULTS

Hierarchical clustering of gene expression profiles revealed 2 groups of subjects. Group 1 consisted of 11 patients (8 with and 3 without lung inflammation). Group 2 consisted of 15 subjects (7 healthy controls and 2 patients with and 6 without lung inflammation). Gene expression in group 1 indicated T cell activation, a type 2 phenotype, production of profibrotic factors and matrix metalloproteinases, and reduced activation-induced cell death. Increased expression of beta6 integrin messenger RNA by CD8+ T cells in group 1 suggested the possibility that these T cells might induce cell-contact-dependent activation of latent transforming growth factor beta (TGFbeta).

CONCLUSION

A subset of scleroderma patients at higher risk of progressive lung disease have activated, long-lived CD8+ T cells in their lungs that could promote fibrosis directly, through production of profibrotic factors such as interleukin-4 and oncostatin M, as well as indirectly, through activation of TGFbeta.

The beta1 and beta3 integrins promote T cell receptor-mediated cytotoxic T lymphocyte activation

Recognition by CD8+ cytotoxic T lymphocytes (CTLs) of antigenic peptides bound to major histocompatibility class (MHC) I molecules on target cells leads to sustained calcium mobilization and CTL degranulation resulting in perforin-dependent killing. We report that beta1 and beta3 integrin-mediated adhesion to extracellular matrix proteins on target cells and/or surfaces dramatically promotes CTL degranulation. CTLs, when adhered to fibronectin but not CTL in suspension, efficiently degranulate upon exposure to soluble MHC.peptide complexes, even monomeric ones. This adhesion induces recruitment and activation of the focal adhesion kinase Pyk2, the cytoskeleton linker paxillin, and the Src kinases Lck and Fyn in the contact site. The T cell receptor, by association with Pyk2, becomes part of this adhesion-induced activation cluster, which greatly increases its signaling.

Sin: good or bad? A T lymphocyte perspective

Stimulation of T cells through their antigen receptor induces a multitude of signaling networks that regulate T cell activation in the form of cytokine production and T cell proliferation. Multiple signal integration sites exist along these pathways in the form of multiprotein signaling complexes, the formation of which is facilitated by adapter and scaffold molecules. In recent years a number of adapter and scaffold molecules have been described in T cells and shown to play an integral part in T cell function. Among these molecules are proteins that function as positive or negative regulators of T cell activation downstream of the activated T cell receptor (TCR). Here, we discuss the role of a small family of multiadapter proteins on T cell activation, the p130Cas family, with emphasis on one of its members, Sin (Src-interacting protein). Our results suggest that Sin inhibits thymocyte development and T cell activation and is a novel negative regulator of T lymphocyte function.

Epstein-Barr virus infection of polarized tongue and nasopharyngeal epithelial cells

Epstein-Barr virus (EBV) initially enters the body through the oropharyngeal mucosa and subsequently infects B lymphocytes through their CD21 (CR2) complement receptor. Mechanisms of EBV entry into and release from epithelial cells are poorly understood. To study EBV infection in mucosal oropharyngeal epithelial cells, we established human polarized tongue and pharyngeal epithelial cells in culture. We show that EBV enters these cells through three CD21-independent pathways: (i) by direct cell-to-cell contact of apical cell membranes with EBV-infected lymphocytes; (ii) by entry of cell-free virions through basolateral membranes, mediated in part through an interaction between beta1 or alpha5beta1 integrins and the EBV BMRF-2 protein; and (iii) after initial infection, by virus spread directly across lateral membranes to adjacent epithelial cells. Release of progeny virions from polarized cells occurs from both their apical and basolateral membranes. These data indicate that multiple approaches to prevention of epithelial infection with EBV will be necessary.

Cellular localization of integrin isoforms in phenylephrine-induced hypertrophic cardiac myocytes

Cardiac hypertrophy is characterized by remodeling of the extracellular matrix (ECM). Integrins are cell-surface molecules that link the ECM to the cellular cytoskeleton where they play roles as signaling molecules and transducers of mechanical force. To clarify the possible roles of integrins in cardiac myocyte hypertrophy, we investigated the cellular localization and expression of ECM proteins and integrins in both normal cardiac myocytes and phenylephrine-induced hypertrophic myocytes. Addition of phenylephrine (PE) to cultured neonatal cardiac myocytes induced sarcomeric organization, increase in cell size, and synthesis of the hypertrophic marker, atrial natriuretic factor (ANF). In particular, fibronectin and collagen underwent dramatic localization changes during PE-induced cardiac hypertrophy. Significant changes were noted in the cellular localization of the respective collagen and fibronectin receptors, integrin alpha1 and alpha5, from diffuse to a sarcomeric banding pattern. Expression levels of integrins were also increased during hypertrophy. Treatment with okadaic acid (OA), an inhibitor of protein phosphatase 2A (PP2A), resulted in inhibition of hypertrophic response. These results suggest that dephosphorylation of integrin beta1 may be important in the induction of cardiac hypertrophy.

Defective thymocyte maturation by transgenic expression of a truncated form of the T lymphocyte adapter molecule and Fyn substrate, Sin

Adapter molecules that promote protein-protein interactions play a central role in T lymphocyte differentiation and activation. In this study, we examined the role of the T lymphocyte-expressed adapter protein and Src kinase substrate, Sin, on thymocyte function using transgenic mice expressing an activated, truncated allele of Sin (SinDeltaC). We found that SinDeltaC expression led to reduced numbers of CD4(+) and CD8(+) single-positive cells and reduced thymic cellularity due to increased thymocyte apoptosis. Because the adapter properties of Sin are mediated by tyrosine-based motifs and given that Sin is a substrate for Src tyrosine kinases, we examined the involvement of these kinases in the inhibitory effects of SinDeltaC. We found that in transgenic thymocytes, SinDeltaC was constitutively phosphorylated by the Src kinase Fyn, but not by the related kinase Lck. Using SinDeltaC and fyn(-/-) animals, we also found that the expression of Fyn was required for the inhibitory effect of SinDeltaC on thymocyte apoptosis but not for SinDeltaC-mediated inhibition of T cell maturation. The inhibitory effect of SinDeltaC on thymocyte maturation correlated with defective activation of the mitogen-activated protein kinase extracellular signal-regulated kinase. Our results suggest that the Sin mutant inhibits thymocyte differentiation through Fyn-dependent and -independent mechanisms and that endogenous Sin may be an important regulator of thymocyte development.

EBV-expressing AGS gastric carcinoma cell sublines present increased motility and invasiveness

Tumor invasion marks a critical point in cancer progression; it is a harbinger of morbidity and mortality. Thus, the cellular events that enable the invasive phenotype are under intense investigation. Epstein-Barr virus (EBV) is associated with a number of cancers, including Burkitt lymphoma (BL) and nasopharyngeal carcinoma (NPC) and is suspected to contribute to their tumorigenesis. On average, 8% of gastric carcinomas have been shown to carry this virus. To explore whether the presence of EBV in gastric carcinoma contributes to tumor progression in this predominantly invasive carcinoma, we examined a panel of 2 in vitro EBV-infected human gastric cancer cell line sublines and their mock-infected AGS parental control line. We found EBV infection caused a marked increase in transmigration of a Matrigel barrier (415% and 303%, p < 0.05, for the 2 infected lines). This correlated with increased motility of these sublines (233% and 140%, p < 0.05). As this pattern of increased motility leading to a more pronounced enhancement of invasion has been noted in other tumor cells, we explored the roles of autocrine signaling pathways previously implicated in carcinoma motility and invasion. Inhibitors to the epidermal growth factor receptor (EGFR) (PD153035), phospholipase C (PLC) (U73122), extracellular-signal regulated kinase (ERK)/mitogen-activated protein kinase (MAPK) (PD089035) and PI-3 kinase (Wortmannin) were not informative. These data suggest that EBV increases migration of AGS cells by a mechanism independent of these autocrine growth factor-induced pathways. Instead, we found that the EBV-infected cells presented increased focal adhesion kinase (FAK) phosphorylation. These findings suggest a role for integrin-mediated signaling in promoting EBV-associated invasiveness.

Lymphocyte binding to MAdCAM-1 via alpha4beta7 integrin activates a signal transduction pathway involving tyrosine phosphorylation of paxillin and p105(Cas-L)

Alpha4beta7 integrin mediates lymphocyte trafficking to mucosal lymphoid organs by interacting with the mucosal vascular addressin MAdCAM-1. While the structural basis for the alpha4beta7 integrin-MAdCAM-1 interaction has been well characterized, less is known about the signal transduction pathways that regulate the alpha4beta7 integrin-mediated lymphocyte interaction with MAdCAM-1-expressing endothelial cells. Here we demonstrate that ligation of alpha4beta7 integrin with MAdCAM-1 induces a prominent tyrosine phosphorylation of paxillin and a 105-kDa protein (p105) that is reactive with an anti-p130(Cas) antibody, in the mouse T-cell line TK-1. Cloning and expression of a full-length cDNA encoding the mouse p105(Cas-L) revealed that the p105 molecule is a mouse ortholog of p105(Cas-L). We also demonstrated that crosslinking of alpha4beta7 integrin with MAdCAM-1 induces the rapid tyrosine phosphorylation of paxillin and p105(Cas-L) in normal lymphocytes and that PMA stimulation enhances the tyrosine phosphorylation of p105(Cas-L) but not of paxillin. These results suggest that intracellular signals initiated by alpha4beta7 integrin involve the tyrosine phosphorylation of paxillin and p105(Cas-L), which are differentially regulated, at least in part, by mechanisms that are PMA-sensitive or -insensitive.

Signalling pathways induced by protease-activated receptors and integrins in T cells

Recent characterization of the thrombin receptor indicates that it plays a role in T-cell signalling pathways. However, little is known regarding the signalling events following stimulation of additional members of the protease-activated receptor (PAR) family, i.e. PAR2 and PAR3. Most of the postligand cascades are largely unknown. Here, we illustrate that in Jurkat T-leukaemic cells, activation of PAR1, PAR2 and PAR3 induce tyrosine phosphorylation of Vav1. This response was impaired in Jurkat T cells deficient in p56lck (JCaM1.6). Activation of PARs also led to an increase in tyrosine phosphorylation of ZAP-70 and SLP-76, two key proteins in T-cell receptor (TCR) signalling. We also demonstrated that p56lck is meaningful for integrin signalling. Thus, JCaM1.6 cells exhibited a marked reduction in their adherence to fibronectin-coated plates, as compared to the level of adherence of Jurkat T cells. While the phosphorylation of Vav1 in T cells is augmented following adhesion, no additional increase was noted following treatment of the adhered cells with PARs. Altogether, we have identified key components in the postligand-signalling cascade of PARs and integrins. Furthermore, we have identified Lck as a critical and possibly upstream component of PAR-induced Vav1 phosphorylation, as well as integrin activation, in Jurkat T cells.