Syk deficiency--a knockout for B-cell development

CEACAM1 induces B-cell survival and is essential for protective antiviral antibody production

B cells are essential for antiviral immune defence because they produce neutralizing antibodies, present antigen and maintain the lymphoid architecture. Here we show that intrinsic signalling of CEACAM1 is essential for generating efficient B-cell responses. Although CEACAM1 exerts limited influence on the proliferation of B cells, expression of CEACAM1 induces survival of proliferating B cells via the BTK/Syk/NF-κB-axis. The absence of this signalling cascade in naive Ceacam1^−/− mice limits the survival of B cells. During systemic infection with cytopathic vesicular stomatitis virus, Ceacam1^−/− mice can barely induce neutralizing antibody responses and die early after infection. We find, therefore, that CEACAM1 is a crucial regulator of B-cell survival, influencing B-cell numbers and protective antiviral antibody responses.

Antibody responses are regulated by selective survival of B cells with proper antigen specificity. Here the authors show that CEACAM1 is critical for B-cell survival during homeostasis and antiviral responses.

Spleen tyrosine kinase is overexpressed and represents a potential therapeutic target in chronic lymphocytic leukemia

B-cell receptor signaling contributes to apoptosis resistance in chronic lymphocytic leukemia (CLL), limiting the efficacy of current therapeutic approaches. In this study, we investigated the expression of spleen tyrosine kinase (SYK), a key component of the B-cell receptor signaling pathway, in CLL and its role in apoptosis. Gene expression profiling identified enhanced expression of SYK and downstream pathways in CLL compared with healthy B cells. Immunoblotting showed increased expression and phosphorylation of SYK, PLCgamma(2), signal transducers and activators of transcription 3, and extracellular signal regulated kinase 1/2 in CLL compared with healthy B cells, suggesting enhanced activation of these mediators in CLL. SYK inhibitors reduced phosphorylation of SYK downstream targets and induced apoptosis in primary CLL cells. With respect to prognostic factors, SYK inhibitors exerted stronger cytotoxic effects in unmutated and ZAP70(+) cases. Cytotoxic effects of SYK inhibitors also associated with SYK protein expression, potentially predicting response to therapy. Combination of fludarabine with SYK Inhibitor II or R406 increased cytotoxicity compared with fludarabine therapy alone. We observed no stroma-contact-mediated drug resistance for SYK inhibitors as described for fludarabine treatment. CD40 ligation further enhanced efficacy of SYK inhibition. Our data provide mechanistic insight into the recently observed therapeutic effects of the SYK inhibitor R406 in CLL. Combination of SYK inhibitors with fludarabine might be a novel treatment option particularly for CLL patients with poor prognosis and should be further evaluated in clinical trials.

Syk tyrosine kinase mediates Epstein-Barr virus latent membrane protein 2A-induced cell migration in epithelial cells

Although spleen tyrosine kinase (Syk) is known to be important in hematopoietic cell development, the roles of Syk in epithelial cells have not been well studied. Limited data suggest that Syk plays alternate roles in carcinogenesis under different circumstances. In breast cancer, Syk has been suggested to be a tumor suppressor. In contrast, Syk is essential for murine mammary tumor virus-mediated transformation. However, the roles of Syk in tumor migration are still largely unknown. Nasopharyngeal carcinoma, an unusually highly metastatic tumor, expresses Epstein-Barr virus LMP2A (latent membrane protein 2A) in most clinical specimens. Previously, we demonstrated LMP2A triggers epithelial cell migration. LMP2A contains an immunoreceptor tyrosine-based activation motif, which is important for Syk kinase activation in B cells. In this study, we explored whether Syk is important for LMP2A-mediated epithelial cell migration. We demonstrate that LMP2A expression can activate endogenous Syk activity. The activation requires the tyrosine residues in LMP2A ITAM but not YEEA motif, which is important for Syk activation by Lyn in B cells. LMP2A interacts with Syk as demonstrated by coimmunoprecipitation and confocal microscopy. Furthermore, LMP2A-induced cell migration is inhibited by a Syk inhibitor and short interfering RNA. Tyrosines 74 and 85 in the LMP2A immunoreceptor tyrosine-based activation motif are essential for both Syk activation and LMP2A-mediated cell migration, indicating the involvement of Syk in LMP2A-triggered cell migration. The LMP2A-Syk pathway may provide suitable drug targets for treatment of nasopharyngeal carcinoma.

The c-Rel transcription factor and B-cell proliferation: a deal with the devil

Activation of the Rel/NF-kappaB signal transduction pathway has been associated with a variety of animal and human malignancies. However, among the Rel/NF-kappaB family members, only c-Rel has been consistently shown to be able to malignantly transform cells in culture. In addition, c-rel has been activated by a retroviral promoter insertion in an avian B-cell lymphoma, and amplifications of REL (human c-rel) are frequently seen in Hodgkin's lymphomas and diffuse large B-cell lymphomas, and in some follicular and mediastinal B-cell lymphomas. Phenotypic analysis of c-rel knockout mice demonstrates that c-Rel has a normal role in B-cell proliferation and survival; moreover, c-Rel nuclear activity is required for B-cell development. Few mammalian model systems are available to study the role of c-Rel in oncogenesis, and it is still not clear what features of c-Rel endow it with its unique oncogenic activity among the Rel/NF-kappaB family. In any event, REL may provide an appropriate therapeutic target for certain human lymphoid cell malignancies.

G(s)alpha repression of adipogenesis via Syk

G(s)alpha regulates the differentiation of 3T3-L1 mouse embryonic fibroblasts to adipocytes, a process termed adipogenesis. Inducers of adipogenesis lead to a loss of G(s)alpha and derepress differentiation to adipocytes. The broad spectrum tyrosine kinase inhibitor genistein is shown to block induction of adipogenesis, suggesting an early role of tyrosine phosphorylation in adipogenesis. Staining of phosphotyrosine identified prominent staining of a approximately 70-kDa protein, hypothesized to be the tyrosine kinase Syk. Reverse transcription and polymerase chain reaction amplification established the expression of Syk mRNA in these embryonic fibroblasts. Immunoprecipitations with Syk-specific antibodies demonstrated the presence of Syk in fibroblasts and a rapid increase in the amount of phospho-Syk, peaking at 24 h post induction. Clones constitutively expressing G(s)alpha, which can no longer be induced to differentiate, no longer display increased phospho-Syk levels in response to inducers. The linkage between G(s)alpha and Syk was probed by immunoprecipitations revealing association of Syk with G(s)alpha in the absence of induction. Upon induction of adipogenesis, G(s)alpha levels decline and phospho-Syk levels as well as Syk kinase activity increase. Expression of wild-type Syk both potentiates the ability of inducers to act as well as induces adipogenesis itself. Expression of the kinase-deficient Syk had no such effects on adipogenesis. These data provide a new insight into the control of adipogenesis, suggesting that G(s)alpha represses adipogenesis via Syk. Treatment with the inducers promotes a decline in G(s)alpha, increases in levels of phospho-Syk, and adipogenesis.

Cellular and molecular basis of immunodeficiencies: their consequences for the development and induction of the immune response

This review lists primary immunodeficiencies which essentially involve mutations in genes coding for functionally important molecules, membrane antigens (e.g., MHC), chains of lymphokine receptors, protein kinases of the signal cascade, transcription factors, and important regulators of cellular metabolism. Mutations and subsequent immunodeficiencies occur as early as during embryogenesis (lymphopoiesis-I) as well as during induction of the immune response by antigen (ligand) binding to cell receptors, TCR and BCR (immunopoiesis-II). Immunodeficiencies are classified according the developmental stages in which they occur most markedly, even in clinical terms. Some early mutations are immediately lethal, some express themselves by blocking embryonic lymphopoiesis, while other mutations do not become demonstrable until after cell stimulation by antigens (see the Tables).

Effect of protein kinase inhibitors on primary antibody induction in tissue cultures

The effects of protein-kinase-inhibitors (PKIs) on protein kinase C (PKCs) i.e., staurosporin, calphostin C, H-7, H-8, H-9, on phosphatidyl inositol 3-proteinkinase (PI3-K) i.e., wortmannin, and on protein tyrosine kinase (PTKs) i.e., genistein, herbimycin A, sanguinarin, lavendustin A and B were tested on the induction phase of the primary Ab-response in vitro. The inhibitory action of PKIs was the highest with herbimycin A, sanguinarin, H-9 and wortmannin. Although wortmannin inhibits the function of T-lymphocytes (Taub et al., 1997, Shi et al., 1997), we believe that this communication is the first report of PKIs immunosuppressive action on the inductive steps of Ab-formation.