Analysis of antigen receptor signalling using mouse gene targeting

Distinct Roles of Vav Family Members in Adaptive and Innate Immune Models of Arthritis

Genetic evidence suggests that three members of the VAV family (VAV1, VAV2 and VAV3) of signal transduction proteins could play important roles in rheumatoid arthritis. However, it is not known currently whether the inhibition of these proteins protects against this disease and, if so, the number of family members that must be eliminated to get a therapeutic impact. To address this issue, we have used a collection of single and compound Vav family knockout mice in experimental models for antigen-dependent (methylated bovine serum albumin injections) and neutrophil-dependent (Zymosan A injections) rheumatoid arthritis in mice. We show here that the specific elimination of Vav1 is sufficient to block the development of antigen-induced arthritis. This protection is likely associated with the roles of this Vav family member in the development and selection of immature T cells within the thymus as well as in the subsequent proliferation and differentiation of effector T cells. By contrast, we have found that depletion of Vav2 reduces the number of neutrophils present in the joints of Zymosan A-treated mice. Despite this, the elimination of Vav2 does not protect against the joint degeneration triggered by this experimental model. These findings indicate that Vav1 is the most important pharmacological target within this family, although its main role is limited to the protection against antigen-induced rheumatoid arthritis. They also indicate that the three Vav family proteins do not play redundant roles in these pathobiological processes.

CD3γ/δ in sea bass (Dicentrarchus labrax): Molecular characterization and expression analysis

The CD3 complex is the common marker on the surface of both αβ and γδ T cells and is essential for formation of the T-cell receptor complex and for T-cell activation. In this paper, we report the gene cloning and molecular characterization of a CD3γ/δ homologue in sea bass (Dicentrarchus labrax), the analysis of transcription levels in lymphoid and non-lymphoid organs and the gene regulation after in vitro stimulation with LPS and PHA. Four cysteine residues in the extracellular domain, involved in the constitution of immunoglobulin-like domain, are present in sea bass CD3γ/δ sequence and they are conserved both in number and position from mammals to teleost sequences. Similar to other known CD3γ/δs, in sea bass CD3γ/δ there is also a conserved immunoreceptor tyrosine-based activation ITAM motif that could be responsible for its individual signal transduction capacity. The real time RT-PCR basal analysis shows the highest level of CD3γ/δ mRNA in thymus, followed by peripheral blood leucocytes, spleen, gills, gut, liver, head kidney, brain and muscle. The expression analysis under stimuli condition reveals a significant decrease of CD3γ/δ expression after LPS stimulation and a significant increase after PHA-L stimulation, in agreement with mammals results. In conclusion, these data allow us to affirm that sea bass CD3γ/δ can be used as a T cell marker and will help in adding new insight on the immune response mechanisms of sea bass.

CD22 EXON 12 deletion as a pathogenic mechanism of human B-precursor leukemia

Here, we report that primary leukemic cells from infants with newly diagnosed B-precursor leukemia express a truncated and functionally defective CD22 coreceptor protein that is unable to transmit apoptotic signals because it lacks most of the intracellular domain, including the key regulatory signal transduction elements and all of the cytoplasmic tyrosine residues. Expression of this structurally and functionally abnormal CD22 protein is associated with a very aggressive in vivo growth of patients' primary leukemia cells causing disseminated overt leukemia in SCID mice. The abnormal CD22 coreceptor is encoded by a profoundly aberrant mRNA arising from a splicing defect that causes the deletion of exon 12 (c.2208-c.2327) (CD22ΔE12) and results in a truncating frameshift mutation. The splicing defect is associated with multiple homozygous mutations within a 132-bp segment of the intronic sequence between exons 12 and 13. These mutations cause marked changes in the predicted secondary structures of the mutant CD22 pre-mRNA sequences that affect the target motifs for the splicing factors hnRNP-L, PTB, and PCBP that are up-regulated in infant leukemia cells. Forced expression of the mutant CD22ΔE12 protein in transgenic mice perturbs B-cell development, as evidenced by B-precursor/B-cell hyperplasia, and corrupts the regulation of gene expression, causing reduced expression levels of several genes with a tumor suppressor function. We further show that CD22ΔE12-associated unique gene expression signature is a discriminating feature of newly diagnosed infant leukemia patients. These striking findings implicate CD22ΔE12 as a previously undescribed pathogenic mechanism in human B-precursor leukemia.

Molecular cloning and characterization of common carp (Cyprinus carpio L.) TCRgamma and CD3gamma/delta chains

Partial cDNA sequences of TCRgamma and CD3gamma/delta were isolated from the thymus of common carp (Cyprinus carpio L.) by the method of suppression subtractive hybridization (SSH). Subsequently the full length cDNAs of carp TCRgamma and CD3gamma/delta were obtained by means of 3' RACE and 5' RACE, respectively. The full length of carp TCRgamma chain is 1368bp and encodes 326 amino acids including a signal peptide region of 19 amino acids and a transmembrane region of 23 amino acids at the C-terminal region from aa 291 to 313. The V region of carp TCRgamma contains 109 amino acids, the core motif FGXG in J segment was also found in carp TCRgamma. The C region of carp TCRgamma contains the characteristic CX6PX6WX45C motif. The CP region of carp TCR Cgamma contains 37 amino acids. The full length of carp CD3gamma/delta is 790bp and encodes 175 amino acids including a signal peptide region of 17 amino acids and a transmembrane region of 23 amino acids from aa 93 to 115. Similar to other known CD3gamma/deltas, four cysteine residues in the extracellular domain and an immunoreceptor tyrosine-based activation motif ITAM (YxxL/Ix6-8YxxL/I) in the intracellular domain are also included in carp CD3gamma/delta. Differing from other known CD3gamma/deltas, carp CD3gamma/delta lacks the CXXCXE motif in the extracellular domain. RT-PCR analysis demonstrated that the expression of TCRgamma gene was mainly in the thymus and gill of 6-month carp, but in 18-month carp, TCRgamma gene was detected in all the examined tissues. The expression of CD3gamma/delta gene was detected in all examined tissues of 6 and 18-month carp; among them, the highest expression level was in the thymus of 6-month carp. In situ hybridization showed that CD3gamma/delta-expressing cells were widely distributed in the head kidney, spleen and kidney of carp, whereas in the thymus, they were densely distributed in the lymphoid outer zone and scattered in the epithelioid inner zone.

Requirement for Abl kinases in T cell receptor signaling

BACKGROUND

The c-Abl and Arg proteins comprise a unique family of nonreceptor tyrosine kinases that have been implicated in the regulation of cell proliferation and survival, cytoskeletal reorganization, cell migration, and the response to oxidative stress and DNA damage. Targeted deletion or mutation of c-Abl in mice results in a variety of immune system phenotypes, including splenic and thymic atrophy, lymphopenia, and an increased susceptibility to infection. However, despite the generation of these mice over a decade ago, little is known regarding the mechanisms responsible for these phenotypes or the immune-related consequences of ablation of both the c-Abl and Arg kinases, which are coexpressed in lymphoid tissues.

RESULTS

Here, we report that T cell receptor (TCR) stimulation results in activation of the endogenous Abl kinases. We demonstrate that Zap70 and the transmembrane adaptor linker for activation of T cells (LAT) are targets of the Abl kinases, and that loss of Abl kinase activity reduces TCR-induced Zap70 phosphorylation at tyrosine 319. This correlates with diminished LAT tyrosine phosphorylation, as well as reduced tyrosine phosphorylation and recruitment of phospholipase Cgamma1 to LAT. Significantly, we show that Abl kinase activity is required for maximal signaling leading to transcription of the IL-2 promoter, as well as TCR-induced IL-2 production and proliferation of primary T cells.

CONCLUSIONS

We conclude that the Abl kinases have a role in the regulation of TCR-mediated signal transduction leading to IL-2 production and cell proliferation.

Contributions of the T cell receptor-associated CD3gamma-ITAM to thymocyte selection

The immunoreceptor tyrosine-based activation motifs (ITAMs) in the CD3 chains associated with the T cell receptor (TCR) are crucial for TCR signaling. To probe the role of the CD3gamma-ITAM in T cell development, we created knock-in mice in which the CD3gamma chain of the TCR complex is replaced by a mutant signaling-deficient CD3gamma chain, lacking the CD3gamma-ITAM. This mutation results in considerable impairment in positive selection in the polyclonal TCR repertoire. When CD3gamma-deltaITAM mice are crossed to mice expressing transgenic F5 TCRs, their thymocytes are completely unable to perform positive selection in vivo in response to intrathymic ligands. Also, the in vitro positive selection response of double-positive (DP) thymocytes with F5-CD3gamma-deltaITAM mutant receptors to their agonist ligand and many of its variants is severely impaired or abrogated. Yet, the binding and dissociation constants of agonist ligands for the F5 receptor are not affected by the CD3gamma-deltaITAM mutation. Furthermore, DP thymocytes with mutant receptors can respond to agonist ligand with normal antigen sensitivity and to normal levels, as shown by their ability to induce CD69 up-regulation, TCR down-regulation, negative selection, and ZAP70 and c-Jun NH2-terminal kinase activation. In sharp contrast, induction of extracellular signal-regulated kinase (ERK) activation and linker for activation of T cells (LAT) phosphorylation are severely impaired in these cells. Together, these findings underscore that intrinsic properties of the TCR-CD3 complex regulate selection at the DP checkpoint. More importantly, this analysis provides the first direct genetic evidence for a role of the CD3gamma-ITAM in TCR-driven thymocyte selection.

Comparative study on the effect of phosphorylated TCR zeta chain ITAM sequences on early activation events in Jurkat T cells

One of the main dilemma in T cell receptor (TCR) signal transduction is whether the presence of multiple Immunoreceptor Tyrosine-based Activation Motifs (ITAMs) within the TCR signaling module serves for signal amplification or signal distribution. To contribute to answer this question, we analyzed the effect of synthetic oligopeptides representing the three bi-phosphorylated zeta chain-ITAMs on the early signaling events in permeabilized leukemia T cells. Our main observations were as follows: 1/Stimulation of the cells with the bi-phosphorylated membrane proximal and central ITAMs (zeta (1)y(p)y(p) and zeta (2)y(p)y(p), respectively) resulted in a strong phosphorylation of proteins with a similar pattern. In contrast, the membrane distal ITAM, zeta (3)y(p)y(p) had a reduced ability to promote tyrosine phosphorylation and failed to induce the phosphorylation of a number of proteins. 2/ The phospho-peptide induced tyrosine phosphorylation events were at least partially mediated by p56(lck) and Syk/ZAP70 protein tyrosine kinases as it was shown in p56(lck) and Syk/ZAP70 deficient Jurkat variants. 3/The patterns of the association of the adaptor protein, Grb2 with tyrosine phosphorylated proteins following cell stimulation with the bi-phosphorylated membrane proximal or the central ITAMs were similar, while the membrane distal ITAM was unable to induce any of these associations. Our data provide additional evidence that the three zetaITAMs differ in their capacity to induce tyrosine phosphorylation of intracellular proteins in permeabilized T cells, depending to their primary sequence. The first and second ITAM sequences of the zeta chain may have similar but not totally overlapping functions. This conclusion results from their similar but not identical abilities to induce tyrosine phosphorylation and association of Grb-2 with intracellular phosphoproteins. In contrast, the third ITAM (zeta3) may have distinct functions since this peptide fails to induce tyrosine phosphorylation of a number of proteins compared to the other two ITAMs, and it is unable to induce either new association or the increase in the amount of Grb-2 associated phosphoproteins.

Tyrosine kinase activation in the decision between growth, differentiation, and death responses initiated from the B cell antigen receptor

Immunoglobulin-containing receptors expressed on B lineage lymphocytes play critical roles in the development and function of the humoral arm of the immune system. The preB cell antigen receptor (preBCR) contains the immunoglobulin mu heavy chain (Ig mu) and signals to the preB cell that heavy chain rearrangement has been successful, a process termed heavy chain selection. The B cell antigen receptor (BCR) contains both Ig heavy and light chains and is expressed on immature and mature B cells before and after antigen encounter. Both receptor types from a complex with the Ig alpha and Ig beta proteins that link the predominantly extracellular Ig with intracellular signal transduction pathways. Signaling through the BCR induces different cellular responses depending on the nature of the signaling agent and the development stage of the target cell. These responses include clonal anergy and apoptotic deletion in immature B cells and survival, proliferation, and differentiation in mature B and preB cells. Several protein tyrosine kinases are activated rapidly following engagement of the BCR/preBCR complexes, including members of the Src family (Lyn and Blk), the Syk/ZAP70 family (Syk), and the Tec family (Btk). In this review, we discuss possible mechanisms by which engagement of these similar receptor complexes can give rise to different cellular responses and the role that these kinases play in this process.

A redundant role of the CD3 gamma-immunoreceptor tyrosine-based activation motif in mature T cell function

At least four different CD3 polypeptide chains are contained within the mature TCR complex, each encompassing one (CD3gamma, CD3delta, and CD3epsilon) or three (CD3zeta) immunoreceptor tyrosine-based activation motifs (ITAMs) within their cytoplasmic domains. Why so many ITAMs are required is unresolved: it has been speculated that the different ITAMs function in signal specification, but they may also serve in signal amplification. Because the CD3zeta chains do not contribute unique signaling functions to the TCR, and because the ITAMs of the CD3-gammadeltaepsilon module alone can endow the TCR with normal signaling capacity, it thus becomes important to examine how the CD3gamma-, delta-, and epsilon-ITAMs regulate TCR signaling. We here report on the role of the CD3gamma chain and the CD3gamma-ITAM in peripheral T cell activation and differentiation to effector function. All T cell responses were reduced or abrogated in T cells derived from CD3gamma null-mutant mice, probably because of decreased expression levels of the mature TCR complex lacking CD3gamma. Consistent with this explanation, T cell responses proceed undisturbed in the absence of a functional CD3gamma-ITAM. Loss of integrity of the CD3gamma-ITAM only slightly impaired the regulation of expression of activation markers, suggesting a quantitative contribution of the CD3gamma-ITAM in this process. Nevertheless, the induction of an in vivo T cell response in influenza A virus-infected CD3gamma-ITAM-deficient mice proceeds normally. Therefore, if ITAMs can function in signal specification, it is likely that either the CD3delta and/or the CD3epsilon chains endow the TCR with qualitatively unique signaling functions.

Determination of transgenic loci by expression FISH

DNA targeting by homologous recombination in mouse embryonic stem (ES) cells has become a widely used method for manipulating the mouse genome and for studying the role of specific genes in mammalian development. For certain studies, it is necessary to target two or more DNA sequences residing on a particular chromosome. In these situations, it would be important to distinguish whether two sequential gene targeting events in the ES cells have occurred in cis or in trans. We report here a new application of fluorescence in situ hybridization to RNA molecules present at sites of transcription that allows the identification of cis and trans gene targeting events in ES cells. The method is based on detection of transcripts from commonly used selectable marker genes inserted during homologous recombination. Transcripts are detected in interphase nuclei, making the preparation of mitotic cells unnecessary and obviating the necessity for the more technically demanding DNA detection of genes. The method is applicable to any chromosomal locus, and compared with other methods (e.g., genetic linkage testing in chimeric mice), it will greatly shorten the time required for distinguishing cis and trans gene targeting events in ES cells. The method also may be useful for detecting changes in ploidy of individual chromosomes and loss of heterozygosity of genes in single cells in culture and also in animals, for example, during processes such as tumorigenesis.

Impaired CD40-signalling in CD19-deficient mice selectively affects Th2-dependent isotype switching

Activation of B lymphocytes involves binding of antigen to the specific receptor and signalling through several membrane coreceptors, of which CD19 has been found to play a pivotal role as a response regulator. Although previous studies in CD19 gene knockout mice have demonstrated that antibody responses to T-cell-dependent antigens are strongly impaired in the absence of this coreceptor, little is known about the consequences of CD19 deficiency for the interaction between T and B cells. Here we report that Th2 co-ordinated B-cell differentiation is selectively impaired in CD19-deficient mice in response to mucosal or systemic immunizations or following an intestinal infection with Nippostrongylus brasiliensis. Whereas immunoglobulin (Ig)G1 or IgE antibody responses were low or absent, IgG2a responses were normal. The selective defect was not caused by a poor Th2-development or interleukin (IL)-4 responsiveness in CD19-deficient mice. Rather, it was the result of an impaired Th2-B cell interaction, owing to a substantially reduced ability to signal via CD40 in CD19-deficient B cells. Thus, our study in CD19-deficient mice suggests that CD40L-CD40-interactions are more important for Th2 than for Th1 co-ordinated B-cell differentiation.

Early growth response (Egr)-1 gene induction in the thymus in response to TCR ligation during early steps in positive selection is not required for CD8 lineage commitment

The early growth response gene 1 (Egr-1) is induced during positive selection in the thymus and has been implicated in the differentiation of CD4+ thymocytes. Here, we show that signals that specifically direct CD8 lineage commitment also induce Egr-1 DNA-binding activity in the nucleus. However, we find that pharmacological inhibition of mitogen-activated protein kinase/extracellular signal-related kinase kinase activity potently inhibits Egr-1 DNA-binding function at concentrations that promote differentiation of CD8+ thymocytes, suggesting Egr-1 activity is not essential for CD8 commitment. To further determine the role of Egr-1 in thymocyte development, we compare steady-state Egr-1 DNA-binding activity in thymocytes from mice with defined defects in positive selection. The data indicate that the appearance of functional Egr-1 is downstream of signals induced by TCR/MHC engagement, whereas it is less sensitive to alterations in Lck-mediated signals, and does not correlate directly with proficient positive selection. Egr-1 is one of the earliest transcription factors induced upon TCR ligation on immature thymocytes, and plays a potential role in the transcription of genes involved in thymocyte selection.

B-cell-receptor-dependent positive and negative selection in immature B cells

This review touches on only a small part of the complex biology of B cells, but serves to illustrate the point that the antigen receptor is the most important of many cell-surface receptors affecting cell-fate decisions. Receptor expression is necessary, but not sufficient, for cell survival. It is also essential that a B cell's antigen-receptor specificity be appropriate for its environment. The need to balance reactivity with self tolerance has resulted in an intricate feedback control (affected by both the recombinase and cell survival) that regulates independent selection events at the level of the receptor and the cell.

The oncogenic 70Z Cbl mutation blocks the phosphotyrosine binding domain-dependent negative regulation of ZAP-70 by c-Cbl in Jurkat T cells

T-cell receptor (TCR) engagement results in the activation of Src family (Lck and Fyn) and ZAP-70 protein tyrosine kinases, leading to tyrosine phosphorylation of multiple cellular substrates including the complex adapter protein c-Cbl. Moreover, Cbl is tyrosine phosphorylated upon engagement of growth factor receptors, cytokine receptors, and immunoreceptors and functions as a negative regulator of tyrosine kinase signalling pathways. Cbl associates via its phosphotyrosine binding (PTB) domain to the ZAP-70 pY292 negative regulatory phosphotyrosine. We recently demonstrated that the oncogenic Cbl mutant, 70Z Cbl, requires its PTB domain to upregulate NFAT in unstimulated Jurkat T cells. Here, we demonstrate that kinase-dead but not wild-type forms of Fyn, Lck, and ZAP-70 block 70Z Cbl-mediated NFAT activation. Moreover, 70Z Cbl does not upregulate NFAT in the ZAP-70-deficient P116 Jurkat T-cell line. The requirement for Fyn, Lck, and ZAP-70 is not due to tyrosine phosphorylation of 70Z Cbl, as mutation of all tyrosines in, or deletion of, the C-terminal region of 70Z Cbl (amino acids 655 to 906) blocks 70Z Cbl tyrosine phosphorylation but enhances 70Z Cbl-mediated NFAT activation. Further, 70Z Cbl does not cooperate with ZAP-70 Y292F to upregulate NFAT, indicating that 70Z Cbl and ZAP-70 do not activate parallel signalling pathways. Finally, the upregulation of NFAT observed upon ZAP-70 overexpression is blocked by Cbl in a PTB domain-dependent manner. We conclude that oncogenic 70Z Cbl acts as a dominant negative to block the PTB domain-dependent negative regulatory role of endogenous Cbl on ZAP-70, leading to constitutive ZAP-70 signalling and activation of transcription factors.

Pre-TCR signaling and inactivation of p53 induces crucial cell survival pathways in pre-T cells

Signaling through the pre-TCR is essential for early T cell development and is severely impaired in mice lacking the CD3 gamma chain of the pre-TCR. We here address the molecular mechanisms underlying this defect. Impaired pre-TCR signaling is shown to be associated with a profound increase in the number of apoptotic CD4- CD8- (DN) thymocytes. Introduction of p53 deficiency into CD3 gamma-deficient mice completely reverses the cell survival defect in CD3 gamma-deficient DN thymocytes and rescues the block in pre-T cell differentiation. In addition, the CD4+ CD8+ (DP) compartment is expanded to its normal size. These findings suggest that the pre-TCR regulates progression through the DNA-damage checkpoint of the DN to DP transition by inactivating p53.

T cell antigen-receptor signal transduction

During the past year, major progress has been made in understanding proximal TCR signal-transduction events. Cbl has been identified as a negative regulator of kinases from the ZAP-70/Syk family. Studies on LAT, SLP-76, Itk and Vav have revealed their role in the activation of Ras and phospholipase-Cgamma1-Ca2+ signalling pathways. TCR-induced cytoskeletal changes involve signalling through SLP-76-Vav-Nck to activate effectors of the Rho-family of GTPases. Finally, glycolipid-enriched microdomains play a crucial role in T cell activation.