Engagement of p75/AIRM1 or CD33 inhibits the proliferation of normal or leukemic myeloid cells

P75/AIRM1 is a recently identified surface molecule that belongs to the sialoadhesin family and displays homology with the myeloid cell antigen CD33. In lymphoid cells, p75/AIRM1 is confined to natural killer cells and mediates inhibition of their cytolytic activity. In this study, we show that p75/AIRM1 is also expressed by cells of the myelomonocytic cell lineage, in which it appears at a later stage as compared with CD33. In vitro proliferation and differentiation of cord blood-derived CD34+ cells (induced by stem cell factor and granulocyte–macrophage colony-stimulating factor) were consistently inhibited by the addition of anti-p75/AIRM1 mAb. Engagement of CD33 led to inhibition in some experiments. A sharp decrease of cell proliferation/survival was detected in all three p75/AIRM1+ chronic myeloid leukemias analyzed when cultured in the presence of either anti-p75/AIRM1 or anti-CD33 mAbs. Thus, the present study suggests that p75/AIRM1 and CD33 may play a regulatory role in normal myelopoiesis and may be viewed as suitable target molecules to counteract the proliferation/survival of chronic myeloid leukemias.

Cytoskeletal Reorganization Induced by Engagement of the NG2 Proteoglycan Leads to Cell Spreading and Migration

Cells expressing the NG2 proteoglycan can attach, spread, and migrate on surfaces coated with NG2 mAbs, demonstrating that engagement of NG2 can trigger the cytoskeletal rearrangements necessary for changes in cell morphology and motility. Engagement of different epitopes of the proteoglycan results in distinct forms of actin reorganization. On mAb D120, the cells contain radial actin spikes characteristic of filopodial extension, whereas on mAb N143, the cells contain cortical actin bundles characteristic of lamellipodia. Cells that express NG2 variants lacking the transmembrane and cytoplasmic domains are unable to spread or migrate on NG2 mAb-coated surfaces, indicating that these portions of the molecule are essential for NG2-mediated signal transduction. Cells expressing an NG2 variant lacking the C-terminal half of the cytoplasmic domain can still spread normally on mAbs D120 and N143, suggesting that the membrane-proximal cytoplasmic segment is responsible for this process. In contrast, this variant migrates poorly on mAb D120 and exhibits abnormal arrays of radial actin filaments decorated with fascin during spreading on this mAb. The C-terminal portion of the NG2 cytoplasmic domain, therefore, may be involved in regulating molecular events that are crucial for cell motility.

Posttranscriptional regulation of urokinase plasminogen activator receptor messenger RNA levels by leukocyte integrin engagement

As an adhesion receptor, the β2 integrin lymphocyte function-associated antigen-1 (LFA-1) contributes a strong adhesive force to promote T lymphocyte recirculation and interaction with antigen-presenting cells. As a signaling molecule, LFA-1-mediates transmembrane signaling, which leads to the generation of second messengers and costimulation resulting in T cell activation. We recently have demonstrated that, in costimulatory fashion, LFA-1 activation promotes the induction of T cell membrane urokinase plasminogen activator receptor (uPAR) and that this induced uPAR is functional. To investigate the mechanism(s) of this induction, we used the RNA polymerase II inhibitor 5,6-dichloro-1-β-d-ribobenzimidazole and determined that uPAR mRNA degradation is delayed by LFA-1 activation. Cloning of the wild-type, deleted and mutated 3′-untranslated region of the uPAR cDNA into a serum-inducible rabbit β-globin cDNA reporter construct revealed that the AU-rich elements and, in particular the nonameric UUAUUUAUU sequence, are crucial cis-acting elements in uPAR mRNA degradation. Experiments in which Jurkat T cells were transfected with reporter constructs demonstrated that LFA-1 engagement was able to stabilize the unstable reporter mRNA containing the uPAR 3′-untranslated region. Our study reveals a consequence of adhesion receptor-mediated signaling in T cells, which is potentially important in the regulation of T cell activation, including production of cytokines and expression of proto-oncogenes, many of which are controlled through 3′ AU-rich elements.

Surface expression and function of p75/AIRM-1 or CD33 in acute myeloid leukemias: Engagement of CD33 induces apoptosis of leukemic cells

p75/AIRM-1 is a recently identified inhibitory receptor expressed by natural killer and myeloid cells displaying high homology with CD33. Crosslinking of p75/AIRM-1 or CD33 has been shown to sharply inhibit the in vitro proliferation of both normal myeloid cells and chronic myeloid leukemias. In this study, we analyzed acute myeloid leukemic cells for the expression of p75/AIRM-1. p75/AIRM-1 marked the M5 (11/12) and M4 (2/2) but not the M1, M2, and M3 subtypes according to the French–American–British classification. Cell samples from 12 acute myeloid leukemias were cultured in the presence of granulocyte/macrophage colony-stimulating factor. Addition to these cultures of anti-CD33 antibody resulted in ≈70% inhibition of cell proliferation as assessed by [3H]thymidine uptake or by the recovery of viable cells. Anti-p75/AIRM-1 antibody exerted a strong inhibitory effect only in two cases characterized by a high in vitro proliferation rate. After crosslinking of CD33 (but not of p75/AIRM-1), leukemic cells bound Annexin V and displayed changes in their light-scattering properties and nucleosomal DNA fragmentation, thus providing evidence for the occurrence of apoptotic cell death. Remarkably, when anti-CD33 antibody was used in combination with concentrations of etoposide insufficient to induce apoptosis when used alone, a synergistic effect could be detected in the induction of leukemic cell death. These studies provide the rationale for new therapeutic approaches in myeloid leukemias by using both chemotherapy and apoptosis-inducing mAbs.

Integrin engagement mediates tyrosine dephosphorylation on platelet-endothelial cell adhesion molecule 1.

Platelet-endothelial cell adhesion molecule 1 (PECAM-1, CD31) is a 130-kDa member of the immunoglobulin gene superfamily expressed on endothelial cells, platelets, neutrophils, and monocytes and plays a role during endothelial cell migration. Phosphoamino acid analysis and Western blot analysis with anti-phosphotyrosine antibody show that endothelial PECAM-1 is tyrosine-phosphorylated. Phosphorylation is decreased with endothelial cell migration on fibronectin and collagen and with cell spreading on fibronectin but not on plastic. Cell adhesion on anti-integrin antibodies is also able to specifically induce PECAM-1 dephosphorylation while concurrently inducing pp125 focal adhesion kinase phosphorylation. Inhibition of dephosphorylation with sodium orthovanadate suggests that this effect is at least partially mediated by phosphatase activity. Tyr-663 and Tyr-686 are identified as potential phosphorylation sites and mutated to phenylalanine. When expressed, both mutants show reduced PECAM-1 phosphorylation but Phe-686 mutants also show significant reversal of PECAM-1-mediated inhibition of cell migration and do not localize PECAM-1 to cell borders. Our results suggest that beta 1-integrin engagement can signal to dephosphorylate PECAM-1 and that this signaling pathway may play a role during endothelial cell migration.

Antibody-induced engagement of beta 2 integrins on adherent human neutrophils triggers activation of p21ras through tyrosine phosphorylation of the protooncogene product Vav.

It is known that beta 2 integrins are crucial for leukocyte cell-cell and cell-matrix interactions, and accumulating evidence now suggests that integrins serve not only as a structural link but also as a signal-transducing unit that controls adhesion-induced changes in cell functions. In the present study, we plated human neutrophils on surface-bound anti-beta 2 (CD18) antibodies and found that the small GTP-binding protein p21ras is activated by beta 2 integrins. Pretreatment of the cells with genistein, a tyrosine kinase inhibitor, led to a complete block of p21ras activation, an effect that was not achieved with either U73122, which abolishes the beta 2 integrin-induced Ca2+ signal, or wortmannin, which totally inhibits the phosphatidylinositol 3-kinase activity. Western blot analysis revealed that antibody-induced engagement of beta 2 integrins causes tyrosine phosphorylation of several proteins in the cells. One of these tyrosine-phosphorylated proteins had an apparent molecular mass of 95 kDa and was identified as the protooncogene product Vav, a p21ras guanine nucleotide exchange factor that is specifically expressed in cells of hematopoietic lineage. A role for Vav in the activation of p21ras is supported by the observations that antibody-induced engagement of beta 2 integrins causes an association of Vav with p21ras and that the effect of genistein on p21ras activation coincided with its ability to inhibit both the tyrosine phosphorylation of Vav and the Vav-p21ras association. Taken together, these results indicate that antibody-induced engagement of beta 2 integrins on neutrophils triggers tyrosine phosphorylation of Vav and, possibly through its association, a downstream activation of p21ras.

Regulation of CD45 engagement by the B-cell receptor CD22.

The B-cell receptor CD22 binds sialic acid linked alpha-2-6 to terminal galactose residues on N-linked oligosaccharides associated with several cell-surface glycoproteins. The first of these sialoglycoproteins to be identified was the receptor-linked phosphotyrosine phosphatase CD45, which is required for antigen/CD3-induced T-cell activation. In the present work, we examine the effect of interaction between the extracellular domain of CD45 and CD22 on T-cell activation. Using soluble CD22-immunoglobulin fusion proteins and T cells expressing wild-type and chimeric CD45 forms, we show that engagement of CD45 by soluble CD22 can modulate early T-cell signals in antigen receptor/CD3-mediated stimulation. We also show that addition of sialic acid by beta-galactoside alpha-2,6-sialyltransferase to the CD22 molecule abrogates interactions between CD22 and its ligands. Together, these observations provide direct evidence for a functional role of the interaction between the extracellular domain of CD45 and a natural ligand and suggest another regulatory mechanism for CD22-mediated ligand engagement.

Volunteer Engagement: Does Engagement Predict the Degree of Satisfaction among New Volunteers and the Commitment of Those who have been Active Longer?

This study examines the concept of engagement in samples of volunteers from different non-profit organisations. Study 1 analyzes the psychometric properties of the abbreviated version of the Utrecht Work Engagement Scale (UWES) (Schaufeli, Bakker, & Salanova, 2006a). Two factorial structures are examined: one-dimensional and three-dimensional structures. Based on the Three-Stage Model of Volunteers’ Duration of Service (Chacón, Vecina, & Dávila, 2007), Study 2 investigates the relationship between engagement, volunteer satisfaction, and intention to remain in a sample of new volunteers and the relationship between engagement, organisational commitment, and intention to remain in a sample of veteran volunteers. Moderated mediation analysis is provided using duration of service as a moderator in order to set a splitting point between new and veteran volunteers. The results of the confirmatory factor analysis suggest that the three-factor model fits better to the data. Regarding the structural models, the first one shows that engagement is crucial to volunteer satisfaction during the first stage, while volunteer satisfaction is the key variable in explaining intention to continue. The second structural model shows that engagement reinforces the participant’s commitment to the organisation, while organizational commitment predicts intention to continue. Both models demonstrate a notable decline when samples are changed.

Comprehensive Validation Of A Measure Of Student School Engagement: A Pilot Study Of Middle School Students

Although it may sound reasonable that American education continues to be more effective at sending high school students to college, in a study conducted in 2009, The Council of the Great City Schools states that "slightly more than half of entering ninth grade students arrive performing below grade level in reading and math, while one in five entering ninth grade students is more than two years behind grade level...[and] 25% received support in the form of remedial literacy instruction or interventions" (Council of the Great City Schools, 2009). Students are distracted with technology (Lei & Zhao, 2005), family (Xu & Corno, 2003), medical illnesses (Nielson, 2009), learning disabilities and perhaps the most detrimental to academic success, the very lack of interest in school (Ruch, 1963). In a Johns Hopkins research study, Building a Graduation Nation - Colorado (Balfanz, 2008), warning signs were apparent years before the student dropped out of high school. The ninth grade was often referenced as a critical point that indicated success or failure to graduate high school. The research conducted by Johns Hopkins illustrates the problem: students who become disengaged from school have a much greater chance of dropping out of high school and not graduating. The first purpose of this study was to compare different measurement models of the Student School Engagement (SSE) using Factor Analysis to verify model fit with student engagement. The second purpose was to determine the extent to which the SSE instrument measures student school engagement by investigating convergent validity (via the SSE and Appleton, Christenson, Kim and Reschly's instrument and Fredricks, Blumenfeld, Friedel and Paris's instrument), discriminant validity (via Huebner's Student Life Satisfaction Survey) and criterion-related validity (via the sub-latent variables of Aspirations, Belonging and Productivity and student outcome measures such as achievement, attendance and discipline). Discriminant validity was established between the SSE and the Appleton, Christenson, Kim and Reschly's model and Fredricks, Blumenfeld, Friedel and Paris's (2005) Student Engagement Instruments (SEI). When confirming discriminant validity, the SSE's correlations were weak and statistically not significant, thus establishing discriminant validity with the SLSS. Criterion-related validity was established through structural equation modeling when the SSE was found to be a significant predictor of student outcome measures when both risk score and CSAP scores were used. The third purpose of this study was to assess the factorial invariance of the SSE instrument across gender to ensure the instrument is measuring the intended construct across different groups. Conclusively, configural, weak and metric invariances were established for the SSE as a non-significant change in chi-square indicating that all parameters including the error variances were invariant across groups of gender. Engagement is not a clearly defined psychological construct; it requires more research in order to fully comprehend its complexity. Hopefully, with parental and teacher involvement and a sense of community, student engagement can be nurtured to result in a meaningful attachment to school and academic success.

Risk for engagement in nonsuicidal self-injury in children and adolescents

Although NSSI engagement is a growing public health concern, little research has documented the developmental precursors to NSSI in longitudinal studies using youth samples. This study aimed to expand upon previous research on groups of NSSI engagement in a population-based sample of youth using multi-wave data. Moreover, this study examined whether chronic peer and romantic stress, the serotonin transporter gene (5-HTTLPR), parenting behaviors, and negative attributional style predicted the NSSI group membership as well as the role of sex and grade. Participants were 549 youth in beginning in the 3rd, 6th, and 9th grades at the baseline assessment. NSSI was assessed across 7 waves of data. Chronic peer and romantic stress, 5-HTTLPR, parenting behaviors, and negative attributional style were assessed at baseline. Growth mixture models, conducted to test the latent trajectory of NSSI groups did not converge. Three NSSI groups were manually created according to classifications that were determined a priori. NSSI groups included: no NSSI (85.1%), episodic NSSI (8.5%), and repeated NSSI (6.4%). Chronic peer and romantic stress, sex, and grade differentiated the no NSSI vs. repeated NSSI groups and the episodic NSSI vs. repeated NSSI groups. Specifically, higher levels of stress, being female, and being in higher grades related to repeated NSSI. 5-HTTLPR differentiated the no NSSI vs. repeated NSSI groups, such that carrying the short allele of 5-HTTLPR related to repeated NSSI. Exploratory analyses revealed that the relationship between attributional style and NSSI group was moderated by grade. This study suggests chronic interpersonal peer and romantic stress is an important factor placing youth at greater risk for repeatedly engaging in NSSI.

Fostering Teaching Staff's Engagement in Continuous Assessment

Among the factors that affect the convergence towards the European Higher Education Area, university teaching staff's motivation is fundamental, and consequently, it is crucial to empirically know what this motivation depends on. In this context, one of the most relevant changes in the teacher-student relationship is assessment. In fact, the transition from a static assessment -focused on only one temporal point (final exam)- to a dynamic assessment, will require changes in thought and action, both on the part of teachers and students. In this line, the objective of this paper is to analyze the determinants of teaching staff's predisposition to the continuous assessment method. Specifically, we consider the following explanatory dimensions: teaching method used (which measures their degree of involvement with the ongoing adaptation process), type of subject (core, compulsory and optional), and teacher's personal characteristics (professional status and gender). The empirical application carried out at the University of Alicante uses Logit Models with Random Coefficients to capture heterogeneity, and shows that "cooperative learning" is a clear-cut determinant of "continuous assessment" as well as "continuous assessment plus final examination". Also, a conspicuous result, which in turn becomes a thought-provoking finding, is that professional status is highly relevant as a teacher's engagement is closely related to prospects of stability. Consequently, the most relevant implications from the results revolve around the way academic institutions can propose and implement inducement for their teaching staff.

Examining Adolescent Sport Dropout and Prolonged Engagement from a Developmental Perspective

This study examined youth sport dropout and prolonged engagement from a developmental perspective focusing on physical and psychosocial factors. Twenty-five dropout and 25 engaged adolescent swimmers, matched on key demographic variables, participated in a retrospective interview. Results indicated that dropouts were involved in fewer extra-curricular activities, less unstructured swimming play, and received less one-on-one coaching throughout development. Dropouts reached several developmental milestones (i.e., started training camps, started dry land training, and were top in club) earlier than engaged athletes. Dropouts were more likely to have had parents who were high-level athletes in their youth, were more likely to be the youngest in their training group, and were less likely to have a best friend at swimming. Findings are discussed in relation to past research; future directions and implications for researchers, sport programmers, coaches, and parents are suggested.

Understanding Dropout and Prolonged Engagement in Adolescent Competitive Sport

Objectives: The purpose of this study is to gain understanding of training patterns and roles of significant others (i.e. coaches, parents, peers, and siblings) in adolescent swimmers’ sport participation patterns. Design: The developmental model of sport participation [Côté, J., Baker, J., & Abernethy, B. (2003). From play to practice: A developmental framework for the acquisition of expertise in team sport. In J. Starkes, & K. A. Ericsson (Eds.), Recent advances in research on sport expertise (pp. 89–114). Champaign, IL: Human Kinetics; Côté, J., & Fraser-Thomas, J. (2007). Youth involvement in sport. In P. R. E. Crocker (Ed.), Introduction to sport psychology: A Canadian perspective (pp. 266–294). Toronto: Pearson Prentice Hall] was used as a framework. Method: Ten dropout and 10 engaged swimmers, matched on key demographic variables participated in a semi-structured qualitative interview. Results: Groups had many similar experiences (e.g. early training, supportive and unsupportive coaches, involved parents). However, only dropouts spoke of early peak performances, limited one-on-one coaching, pressuring parents during adolescence, lack of swimming peers during adolescence, and sibling rivalries. In contrast, only engaged athletes spoke of clubs’ developmental philosophies, coaches’ and parents’ open communication, school friends’ support, and siblings’ general positive influences. Conclusions: Findings highlight the importance of appropriately structured programs and the fragility of athletes’ relationships with significant others during the adolescent years. Implications for sport programmers, coaches, and parents are discussed.

No more compulsory engagement. The emancipation of German security policy. OSW Commentary no. 57, 2011-07-18

Germany’s stance on Libya at the UN Security Council and its later decision not to take part in the military intervention gave rise to heated controversy both in Germany and abroad. At home, this was criticised as “an enormous mistake of historic impact”1; while abroad this raised questions about Germany’s willingness to co-operate with its key Western allies. With its decision on Libya, Germany sealed the process of making its security policy independent from the stances of the US and France. It thus ceased to feel any compulsion to provide not only military engagement but also political support for overseas operations initiated by its key allies, even if these are legitimised by the UN Security Council. Germany’s stance, apart from finishing off a certain process, is also setting a starting point for a discussion inside Germany about its military engagement in international security policy. This will bring about a more assertive and selective approach to cooperation with NATO and the EU’s Common Security and Defence Policy.