Duration of calcineurin and Erk signals regulates CD4/CD8 lineage commitment of thymocytes

MicroRNA-7 overexpression positively regulates the CD8+ SP cell development via targeting PIK3R1

microRNA-7 (miR-7), a distinct miRNA family member, has been reported to be involved in the biological functions of immune cells. However, the potential role of miR-7 in the CD8⁺ T cell development remains to be elucidated. In this study, we estimated the potential effects of miR-7 overexpression in the thymic CD8⁺ SP cell development using miR-7 overexpression mice. Our results showed that compared with those in control wild type (WT) mice, the volume, weight and total cell numbers of thymus in miR-7 overexpression (OE) mice increased significantly. The absolute cell number of CD8⁺ SP cells in miR-7 OE mice increased and its ability of activation and proliferation enhanced. Futhermore, we clarified that miR-7 overexpression had an intrinsic promote role in CD8⁺ SP cell development by adoptive cell transfer assay. Mechanistically, the expression level of PIK3R1, a target of miR-7, decreased significantly in CD8⁺ SP cells of miR-7 OE mice. Moreover, the expression level of phosphorylated (p)-AKT and p-ERK changed inversely and indicating that miR-7 overexpression impaired the balance of AKE and ERK pathways. In summary, our work reveals an essential role of miR-7 in promoting CD8⁺ SP cell development through the regulation of PIK3R1 and balance of AKT and ERK pathways.

Thy-1 stimulation of mouse T cells induces a delayed T cell receptor-like signal that results in Ca2+‑independent cytotoxicity

Antibody-mediated crosslinking of Thy-1 [also known as cluster of differentiation (CD)90], results in a T cell receptor (TcR)‑like signal; however, the impact of Thy‑1 stimulation in comparison to TcR stimulation on T cell activation and effector function has yet to be fully elucidated. In the present study, the outcome of Thy‑1‑ and TcR‑induced stimulation of T cells was investigated in mice, using fragment crystalizable (Fc) receptor‑bound antibodies and costimulatory signals provided by syngeneic lipopolysaccharide‑matured bone marrow‑derived dendritic cells. Compared with TcR signaling, Thy‑1 signaling initiated a less robust proliferative response in T cells, as determined by tritiated‑thymidine incorporation. In addition, enzyme‑linked immunosorbent assays revealed that interleukin‑2 production was reduced, and the expression of CD25 and cyclin D3 was weaker in Thy‑1‑stimulated cells, as determined by western blotting; however, the expression of cyclin‑dependent kinase 6 was similar to that in TcR‑induced T cells. Furthermore, western blotting demonstrated that the phosphorylation of ζ-chain‑associated protein kinase 70 and extracellular signal‑regulated kinase 1/2 was delayed following Thy‑1 stimulation. DNA fragmentation assays revealed that cytotoxic effector function was also slower to develop in Thy‑1‑stimulated T cells, required more time to be effective and was largely Ca2+‑independent; these findings suggested that Fas ligand rather than granule‑associated perforin was involved in T cell effector function. In conclusion, the present results suggested that Thy‑1 signaling may contribute to the regulation of T cell homeostasis and the development of non‑specific T cell‑mediated cytotoxicity. However, further studies are required to elucidate the exact physiological roles of TcR‑like signals that result from Thy‑1 crosslinking and to investigate the molecular mechanisms that are involved.

Digital signaling decouples activation probability and population heterogeneity

Digital signaling enhances robustness of cellular decisions in noisy environments, but it is unclear how digital systems transmit temporal information about a stimulus. To understand how temporal input information is encoded and decoded by the NF-κB system, we studied transcription factor dynamics and gene regulation under dose- and duration-modulated inflammatory inputs. Mathematical modeling predicted and microfluidic single-cell experiments confirmed that integral of the stimulus (or area, concentration × duration) controls the fraction of cells that activate NF-κB in the population. However, stimulus temporal profile determined NF-κB dynamics, cell-to-cell variability, and gene expression phenotype. A sustained, weak stimulation lead to heterogeneous activation and delayed timing that is transmitted to gene expression. In contrast, a transient, strong stimulus with the same area caused rapid and uniform dynamics. These results show that digital NF-κB signaling enables multidimensional control of cellular phenotype via input profile, allowing parallel and independent control of single-cell activation probability and population heterogeneity.

Role of retinoic acid and platelet-derived growth factor receptor cross talk in the regulation of neonatal gonocyte and embryonal carcinoma cell differentiation

Neonatal gonocytes are direct precursors of spermatogonial stem cells, the cell pool that supports spermatogenesis. Although unipotent in vivo, gonocytes express pluripotency genes common with embryonic stem cells. Previously, we found that all-trans retinoic acid (RA) induced the expression of differentiation markers and a truncated form of platelet-derived growth factor receptor (PDGFR)β in rat gonocytes, as well as in F9 mouse embryonal carcinoma cells, an embryonic stem cell-surrogate that expresses somatic lineage markers in response to RA. The present study is focused on identifying the signaling pathways involved in RA-induced gonocyte and F9 cell differentiation. Mitogen-activated protein kinase kinase (MEK) 1/2 activation was required during F9 cell differentiation towards somatic lineage, whereas its inhibition potentiated RA-induced Stra8 expression, suggesting that MEK1/2 acts as a lineage specification switch in F9 cells. In both cell types, RA increased the expression of the spermatogonial/premeiotic marker Stra8, which is in line with F9 cells being at a stage before somatic-germline lineage specification. Inhibiting PDGFR kinase activity reduced RA-induced Stra8 expression. Interestingly, RA increased the expression of PDGFRα variant forms in both cell types. Together, these results suggest a potential cross talk between RA and PDGFR signaling pathways in cell differentiation. RA receptor-α inhibition partially reduced RA effects on Stra8 in gonocytes, indicating that RA acts in part via RA receptor-α. RA-induced gonocyte differentiation was significantly reduced by inhibiting SRC (v-src avian sarcoma [Schmidt-Ruppin A-2] viral oncogene) and JAK2/STAT5 (Janus kinase 2/signal transducer and activator of transcription 5) activities, implying that these signaling molecules play a role in gonocyte differentiation. These results suggest that gonocyte and F9 cell differentiation is regulated via cross talk between RA and PDGFRs using different downstream pathways.

T cell receptor (TCR)-induced tyrosine phosphorylation dynamics identifies THEMIS as a new TCR signalosome component

Stimulation of the T cell antigen receptor (TCR) induces formation of a phosphorylation-dependent signaling network via multiprotein complexes, whose compositions and dynamics are incompletely understood. Using stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomics, we investigated the kinetics of signal propagation after TCR-induced protein tyrosine phosphorylation. We confidently assigned 77 proteins (of 758 identified) as a direct or indirect consequence of tyrosine phosphorylation that proceeds in successive "signaling waves" revealing the temporal pace at which tyrosine kinases activate cellular functions. The first wave includes thymocyte-expressed molecule involved in selection (THEMIS), a protein recently implicated in thymocyte development but whose signaling role is unclear. We found that tyrosine phosphorylation of THEMIS depends on the presence of the scaffold proteins Linker for activation of T cells (LAT) and SH2 domain-containing lymphocyte protein of 76 kDa (SLP-76). THEMIS associates with LAT, presumably via the adapter growth factor receptor-bound protein 2 (Grb2) and with phospholipase Cγ1 (PLC-γ1). RNAi-mediated THEMIS knock-down inhibited TCR-induced IL-2 gene expression due to reduced ERK and nuclear factor of activated T cells (NFAT)/activator protein 1 (AP-1) signaling, whereas JNK, p38, or nuclear factor κB (NF-κB) activation were unaffected. Our study reveals the dynamics of TCR-dependent signaling networks and suggests a specific role for THEMIS in early TCR signalosome function.

Kinase suppressor of Ras 1 is required for full ERK activation in thymocytes but not for thymocyte selection

The scaffold protein kinase suppressor of Ras 1 (KSR1) is critical for efficient activation of ERK in a number of cell types. Consistent with this, we observed a defect in ERK activation in thymocytes that lack KSR1. Interestingly, we found that the defect was much greater after PMA stimulation than by CD3 activation. Since ERK activation is believed to be important for thymocyte development, we analyzed thymocyte selection in KSR1-deficient (KSR1(-/-) ) mice. We found that positive selection in two different TCR transgenic models, HY and AND, was normal. On the other hand, negative selection in the HY model was slightly impaired in KSR1(-/-) mice. However, a defect in negative selection was not apparent in the AND TCR model system or in an endogenous superantigen-mediated model of negative selection. These results suggest that, despite a requirement for KSR1 for full ERK activation in thymocytes, full and efficient ERK activation is not essential for the majority of thymocyte selection events.

Prosurvival and proapoptotic functions of ERK1/2 activation in murine thymocytes in vitro

The extracellular signal-regulated kinases 1/2 (ERK1/2) are serine/threonine-selective protein kinases involved in proliferation and differentiation of cells, including thymocytes. The requirement of ERK1/2 for thymocyte differentiation and maturation has been well established; however, their role in regulating thymocyte survival and apoptosis has not been resolved. Here, we asked whether ERK1/2 affected thymocyte survival in vitro in response to apoptotic stimuli. The results show that phorbol 12-myristate 13-acetate (PMA) treatment (with or without ionomycin) and serum starvation (s/s) induced sustained ERK1/2 activation in murine thymocytes. Importantly, pharmacological treatment of thymocytes with the MEK inhibitor UO126 revealed that PMA-induced ERK1/2 activation was proapoptotic, whereas serum starvation-induced ERK1/2 activation inhibited apoptosis and promoted cell survival. While basal MEK activity was required for both s/s- and PMA-induced ERK1/2 activation, MEK activity increased only in response to PMA. The results show that the suppression of ERK1/2 phosphatases was responsible for s/s-induced sustained ERK1/2 activation. Unexpectedly, neither s/s-induced proapoptotic nor PMA-induced anti-apoptotic functions of ERK1/2 depended on the Bcl-2 family phosphoprotein Bim(EL), which was previously implicated in thymocyte apoptosis. Lastly, etoposide treatment of immature thymocytes induced both p53 and ERK1/2 activation, but ERK1/2 activity did not affect the phosphorylation and stabilization of p53. Thus, ERK1/2 has a dual role in promoting cell survival and cell death in thymocytes in the context of different stimuli.

Induction of S100A4, S100A6, and galectin-1 during the lineage commitment of CD4+CD8+ thymocyte cell line is suppressed by 2,3,7,8-tetrachlorodibenzo-p-dioxin

To study the mechanisms underlying the linage commitment of CD4+CD8+ thymocytes and the skewed differentiation of CD4+CD8+ into CD4-CD8+ thymocytes induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we stimulated with antigen DPK cells, a CD4+CD8+ thymic lymphoma cell line which can differentiate into CD4+CD8- thymocytes and performed a comparative proteomic analysis of DPK cells stimulated with antigen or not. Among the 10 up-regulated or induced proteins upon antigenic stimulation, S100A4, S100A6, and galectin-1 were highly up-regulated. Kinetic studies revealed that expression of S100A4, S100A6, and galectin-1 was dramatically increased as early as 10min after antigen stimulation, similar to that of cKrox and Runx3, transcription factors intimately associated with the lineage commitment. Among four thymocyte subpopulations of the thymus examined, S100A4, S1006, and galectin-1 were most prominently expressed in CD4+CD8+ thymocytes, but not at all in CD4-CD8+ and CD4-CD8- thymocytes. In the spleen, expression of S100A4, S1006, and galectin-1 was greater in CD4 than in CD8 splenocytes. When TCDD was added to antigen-stimulated DPK cells, antigen-induced up-regulation of S100A4, S1006, and galectin-1 were remarkably inhibited, probably partly accounting for the skewed differentiation of CD4+CD8+ into CD4-CD8+ thymocytes induced by TCDD.

Dopamine, vesicular transporters and dopamine receptor expression and localization in rat thymus and spleen

The localization of dopamine stores and the expression and localization of vesicular monoamine transporter (VMAT) type-1 and 2 and of dopamine D1-like and D2-like receptor subtypes were investigated in rat thymus and spleen by immunohistochemical, immunochemical techniques and by RT-PCR. In the thymus dopamine immunoreactivity was developed in the cortico-medullary junction and in the medulla, but not in the thymic cortex. In the spleen, dopamine stores were found in reticular structures in the white pulp border and in the white pulp, but not in the red one. Both thymus and spleen expressed VMAT-1 and VMAT-2 immunoreactivity as well as dopamine D1, D2, D3, D4 and D5 receptor immunoreactivity. Immunohistochemistry revealed VMAT-1, VMAT-2 and dopamine D1, D2, D3, D4 and D5 receptor immunoreactivity primarily in the thymic cortical-medulla transitional zone and to a lesser extent in the medulla but not in the cortex. In the spleen, VMAT-1, VMAT-2 and dopamine D1, D2, D3, D4 and D5 receptor immunoreactivity was located primarily in the white pulp border and to a lesser extent in the white pulp. These findings indicate that both thymus and spleen express a dopaminergic system characterized by the presence of dopamine, vesicular monoamine transporters and the five subtypes of dopamine receptors. The presence of these dopaminergic markers suggests that dopamine likely originating from immune cells and/or from sympathetic neuroeffector plexus is released in the lymphoid microenvironment. Based on the microanatomical localization of dopaminergic markers investigated, a role of dopamine in maturation and selection of lymphocytes and activation of immune responses is suggested.

Impact of IFNalpha2b upon pSTAT3 and the MEK/ERK MAPK pathway in melanoma

PURPOSE

High-dose IFNalpha2b (HDI) was established as the first effective adjuvant therapy for patients with high-risk resected melanoma more than a decade ago, but its fundamental molecular mechanism of action remains unclear. STAT3 and the mitogen activated protein kinases (MAPKs), especially ERK (extracellular signal-regulating kinase) and MEK (MAPK/ERK kinase), play roles in melanoma progression and host immunity. We have therefore evaluated STAT3 and MEK/ERK MAP kinases in patients with regional lymph node metastasis (stage IIIB) of melanoma in the context of a prospective neoadjuvant trial of HDI (UPCI 00-008).

PATIENTS AND METHODS

In the context of this trial, HDI was administered daily for 20 doses following diagnostic biopsy, and prior to definitive surgery. Immunohistochemistry for pSTAT3, phospho-MEK1/2, phospho-ERK1/2, and EGFR was performed on paired fixed (nine patients) biopsies.

RESULTS

HDI was found to down-regulate pSTAT3 (P = 0.008) and phospho-MEK1/2 (P = 0.008) levels significantly in tumor cells. Phospho-ERK1/2 was down-regulated by HDI in tumor cells (P = 0.015), but not in lymphoid cells. HDI down-regulated EGFR (P = 0.013), but pSTAT3 activation appeared not to be associated with EGFR expression and the MEK/ERK MAPK pathway.

CONCLUSION

We conclude that HDI regulates MAPK signaling differentially in melanoma tumor cells and host lymphoid cells in vivo. STAT3 activation is independent of the EGFR/MEK/ERK signaling pathway.

Clinorotation differentially inhibits T-lymphocyte transcription factor activation

T lymphocytes cultured under the low-shear stress environment of modeled microgravity demonstrate an inhibition of activation in response to T-cell receptor (TCR)-mediated signaling. Modeled microgravity culture-induced inhibition mimics the inhibition observed during spaceflight. This work investigates the molecular signaling events of interleukin 2 transcription activation in modeled microgravity as generated with clinorotation. Under normal conditions, NFAT (nuclear factor of activated T cells) is dephosphorylated and activated with sustained calcium (Ca++) influx and calcineurin activity, whereas AP-1 is activated by protein kinase C (PKC) and Ras-mediated pathways. Purified human T lymphocytes are shown to exhibit differential inhibition of transcription factor activation in modeled microgravity. Activation of AP-1 is blocked with clinorotation, whereas NFAT dephosphorylation occurs. This work supports the theory that modeled microgravity differentially blocks the activation of distinct signaling mechanism.

RasGRP1 Transmits Prodifferentiation TCR Signaling That Is Crucial for CD4 T Cell Development

TCR signaling plays a governing role in both the survival and differentiation of bipotent double-positive thymocytes into the CD4(+) and CD8(+) single-positive T cell lineages. A central mediator of this developmental program is the small GTPase Ras, emitting cytoplasmic signals through downstream MAPK pathways and eventually affecting gene expression. TCR signal transduction orchestrates the activation of Ras by integrating at least two Ras-guanyl nucleotide exchange factors, RasGRP1 and Sos. In this study, we have characterized the relationship between RasGRP1 function and its potential roles in promoting ERK activity, cell survival, maturation, and lineage commitment. Investigations on RasGRP1(-/-) mice expressing a transgenic (Tg) MHC class II-restricted TCR revealed that the development of CD4 T cells expressing this Tg TCR is completely dependent on RasGRP1. Unexpectedly, a small number of functional CD8 single-positive thymocytes expressing the Tg MHC class II-restricted TCR exists in mutant mice. In addition, RasGRP1(-/-) double-positive thymocytes exhibit marked deficits in TCR-stimulated up-regulation of the positive selection marker CD69 and the antiapoptotic protein Bcl-2, whereas CD5 induction is unaffected. To evaluate the role of RasGRP1 in providing cellular survival signaling, we enforced Bcl-2 expression in RasGRP1(-/-) thymocytes. These studies demonstrate that RasGRP1 function cannot be fully complemented by Tg Bcl-2 expression. Therefore, we propose that RasGRP1 transmits differentiation signaling critically required for CD4 T cell development.

Commitment issues: linking positive selection signals and lineage diversification in the thymus

The thymus is responsible for the production of CD4+ helper and CD8+ cytotoxic T cells, which constitute the cellular arm of the immune system. These cell types derive from common precursors that interact with thymic stroma in a T-cell receptor (TCR)-specific fashion, generating intracellular signals that are translated into function-specific changes in gene expression. This overall process is termed positive selection, but it encompasses a number of temporally distinct and possibly mechanistically distinct cellular changes, including rescue from apoptosis, initiation of cell differentiation, and commitment to the CD4+ or CD8+ T-cell lineage. One of the puzzling features of positive selection is how specificity of the TCR controls lineage commitment, as both helper and cytolytic T cells utilize the same antigen-receptor components, with the exception of the CD4 or CD8 coreceptors themselves. In this review, we focus on the signals required for positive selection, particularly as they relate to lineage commitment. Identification of genes encoding transcriptional regulators that play a role in T-cell development has led to significant recent advances in the field. We also provide an overview of nuclear factors in this context and, where known, how their regulation is linked to the same TCR signals that have been implicated in initiating and regulating positive selection.

Real-time measurement of signaling and motility during T cell development in the thymus

Intracellular signals arising from interactions of immature thymocytes with distinct populations of stromal cells in the thymus are central to T cell development. The characteristics of these signals and the mechanisms underlying thymocyte migration between stromal cell compartments have been difficult to identify from static measurements of fixed tissue. Recent advances in two-photon microscopy and the development of three-dimensional models for real-time studies of T cell development have shed light on how single cells navigate the thymus. These studies reveal crosstalk between thymocyte signaling and motility that may integrate the search for potentially rare self-antigens with the requirement for sustained signaling in T cell maturation.

The role of erk1 and erk2 in multiple stages of T cell development

Activation of extracellular-signal-regulated protein kinase (Erk) is central to growth-factor-receptor-mediated signaling including that originating from the T cell antigen receptor. It integrates cytoplasmic signals to effect changes in transcription associated with differentiation, proliferation, and survival. In this report, we present an analysis of mice with targeted deletions in Erk1 and Erk2 to assess the relationship between Erk activity and cell-cycle progression, thymocyte development, and lineage commitment. These studies show that Erk is selectively retained during beta selection-driven proliferation, and yet Erk1/2 are not required to complete differentiation to CD4+CD8+ preselection stage of development. Erk activity is essential for the process of positive selection, and it differentially affects CD4 and CD8 T cell maturation; yet, diminished expression itself is not sufficient to alter lineage commitment.

Cathepsin-L influences the expression of extracellular matrix in lymphoid organs and plays a role in the regulation of thymic output and of peripheral T cell number

Nackt mice, which are deficient in cathepsin-L (CTSL), show an early impairment during positive selection in the context of class II MHC molecules and as a consequence, the percentage and absolute number of CD4(+) thymocytes are significantly decreased. In this study, we show that lymph nodes from nackt mice are hypertrophied, showing normal absolute numbers of CD4(+) T cells and marked increases in the number of CD8(+) T lymphocytes. Basal proliferative levels are increased in the CD4(+) but not in the CD8(+) population. Lymph node T cells show increases in the expression of alpha(5), alpha(6), and beta(1) integrin chains. These alterations correlate with increases in the expression of extracellular matrix (ECM) components in lymph nodes. Interestingly, laminin, fibronectin, and collagen I and IV are markedly decreased in nackt thymus which shows an augmented output of CD8(+) cells. These results demonstrate that a mutation in the Ctsl gene influences the levels of ECM components in lymphoid organs, the thymic output, and the number of T cells in the periphery. They further raise the possibility that, by regulating the level of expression of ECM components in lymphoid organs, CTSL is able to broadly affect the immune system.

Receptor signals and nuclear events in CD4 and CD8 T cell lineage commitment

MHC specificity in positive selection is a major determinant in the CD4/CD8 T cell lineage decision. Previous studies support the view that quantitative differences in T cell receptor (TCR) signaling in immature CD4+CD8+ double positive thymocytes leads to an instructive bias in CD4/CD8 T cell lineage commitment that must be re-inforced in subsequent selection steps to ensure that MHC-restricted antigen recognition is linked to appropriate effector functions in mature T cells. Recent work has further defined the TCR signaling pathways involved in this process, but a major effort has been made to identify transcription factors and other regulators of CD4 and CD8 T cell lineage commitment. Methods and screens for detecting changes in gene expression, associated with TCR signaling in positive selection and lineage determination, are starting to provide a better understanding of these complex developmental processes.

Neurotensin and EGF induce synergistic stimulation of DNA synthesis by increasing the duration of ERK signaling in ductal pancreatic cancer cells

Neurotensin (NT) and epidermal growth factor (EGF) induced rapid extracellular-regulated protein kinase (ERK) activation through different signaling pathways in the K-Ras mutated human pancreatic carcinoma cell lines PANC-1 and MIA PaCa-2. NT stimulated ERK activation via a protein kinase C (PKC)-dependent (but EGF receptor-independent) pathway in PANC-1 and MIA PaCa-2 cells, whereas EGF promoted ERK activation through a PKC-independent pathway in these cells. Concomitant stimulation of these cells with NT and EGF induced a striking increase in the duration of ERK pathway activation as compared with that obtained in cells treated with each agonist alone. Stimulation with NT + EGF promoted synergistic stimulation of DNA synthesis and anchorage-independent growth. Addition of the MEK inhibitor U0126, either prior to stimulation with NT + EGF or 2 h after stimulation with NT + EGF prevented the synergistic increase in DNA synthesis and suppressed the sustained phase of ERK activation. Furthermore, treatment with the selective PKC inhibitor GF-1 converted the sustained ERK activation in response to NT and EGF into a transient signal and also abrogated the synergistic increase in DNA synthesis. Collectively, our results suggest that the sustained phase of ERK signaling mediates the synergistic effects of NT and EGF on DNA synthesis in pancreatic cancer cells.

Calcium oscillations regulate thymocyte motility during positive selection in the three-dimensional thymic environment

The three-dimensional thymic microenvironment and calcium signaling pathways are essential for driving positive selection of developing T cells. However, the nature of calcium signals and the diversity of their effects in the thymus are unknown. We describe here a thymic slice preparation for visualizing thymocyte motility and signaling in real time with two-photon microscopy. Naive thymocytes were highly motile at low intracellular calcium concentrations, but during positive selection cells became immobile and showed sustained calcium concentration oscillations. Increased intracellular calcium was necessary and sufficient to arrest thymocyte motility. The calcium dependence of motility acts to prolong thymocyte interactions with antigen-bearing stromal cells, promoting sustained signaling that may enhance the expression of genes underlying positive selection.

A Toll-interleukin 1 repeat protein at the synapse specifies asymmetric odorant receptor expression via ASK1 MAPKKK signaling

A stochastic lateral signaling interaction between two developing Caenorhabditis elegans AWC olfactory neurons causes them to take on asymmetric patterns of odorant receptor expression, called AWC(OFF) and AWC(ON). Here we show that the AWC lateral signaling gene tir-1 (previously known as nsy-2) encodes a conserved post-synaptic protein that specifies the choice between AWC(OFF) and AWC(ON). Genetic evidence suggests that tir-1 acts downstream of a voltage-gated calcium channel and CaMKII (UNC-43) to regulate AWC asymmetry via the NSY-1(ASK1) p38/JNK MAP (mitogen-activated protein) kinase cascade. TIR-1 localizes NSY-1 to post-synaptic regions of AWC, and TIR-1 binds UNC-43, suggesting that it assembles a synaptic signaling complex that regulates odorant receptor expression. Temperature-shift experiments indicate that tir-1 affects AWC during a critical period late in embryogenesis, near the time of AWC synapse formation. TIR-1 is a multidomain protein with a TIR (Toll-interleukin-1 receptor) domain that activates signaling, SAM repeats that mediate localization to post-synaptic regions of axons, and an N-terminal inhibitory domain. TIR-1 and other TIR proteins are implicated in vertebrate and invertebrate innate immunity, as are NSY-1/ASK1 kinases, so this pathway may also have a conserved function in immune signaling.

The Regulated Expression of a Diverse Set of Genes during Thymocyte Positive Selection In Vivo

A signal initiated by the newly formed Ag receptor is integrated with microenvironmental cues during T cell development to ensure positive selection of CD4+CD8+ progenitors into functionally mature CD4+ or CD8+ T lymphocytes. During this transition, a survival program is initiated, TCR gene recombination ceases, cells migrate into a new thymic microenvironment, the responsiveness of the Ag receptor is tuned, and the cells commit to a specific T lineage. To determine potential regulators of these processes, we used mRNA microarray analysis to compare gene expression changes in CD4+CD8+ thymocytes from TCR transgenic mice that have received a TCR selection signal with those that had not received a signal. We found 129 genes with expression that changed significantly during positive selection, the majority of which were not previously appreciated. A large number of these changes were confirmed by real-time PCR or flow cytometry. We have combined our findings with gene changes reported in the literature to provide a comprehensive report of the genes regulated during positive selection, and we attempted to assign these genes to positive selection process categories.

TOX provides a link between calcineurin activation and CD8 lineage commitment

T cell development is dependent on the integration of multiple signaling pathways, although few links between signaling cascades and downstream nuclear factors that play a role in thymocyte differentiation have been identified. We show here that expression of the HMG box protein TOX is sufficient to induce changes in coreceptor gene expression associated with β-selection, including CD8 gene demethylation. TOX expression is also sufficient to initiate positive selection to the CD8 lineage in the absence of MHC–TCR interactions. TOX-mediated positive selection is associated with up-regulation of Runx3, implicating CD4 silencing in the process. Interestingly, a strong T cell receptor–mediated signal can modify this cell fate. We further demonstrate that up-regulation of TOX in double positive thymocytes is calcineurin dependent, linking this critical signaling pathway to nuclear changes during positive selection.

Protein kinase D potentiates DNA synthesis induced by Gq-coupled receptors by increasing the duration of ERK signaling in swiss 3T3 cells

Protein kinase D (PKD) potentiates cellular DNA synthesis in response to G protein-coupled receptor (GPCR) agonists but the mechanism(s) involved has not been elucidated. Here, we examined whether PKD overexpression in Swiss 3T3 cells regulates the activation/inactivation kinetics of the extracellular-regulated protein kinase (ERK) in response to the mitogenic GPCR agonists bombesin and vasopressin. Addition of bombesin or vasopressin to Swiss 3T3 cells overexpressing PKD induced a striking increase in the duration of MEK/ERK/RSK activation as compared with cultures of either control Swiss 3T3 cells or Swiss 3T3 cells expressing a kinase-inactive PKD mutant. In contrast, the duration of ERK activation in response to epidermal growth factor, which acts via protein kinase C/PKD-independent pathways, was not increased. Furthermore, bombesin or vasopressin promoted a striking increase in phosphorylation (at Ser-374) and accumulation of c-Fos (the c-fos proto-oncogene product) in Swiss 3T3 cells overexpressing wild-type (but not kinase-inactive) PKD. Inhibition of the sustained phase of ERK/RSK activation abrogated the increase in c-Fos accumulation and DNA synthesis induced by bombesin or vasopressin in PKD-overexpressing cells. Our results demonstrate that PKD selectively potentiates mitogenesis induced by bombesin or vasopressin in Swiss 3T3 cells by increasing the duration of MEK/ERK/RSK signaling.

The Ras/MAPK cascade and the control of positive selection

Immature double positive (DP) thymocytes bearing a T cell receptor (TCR) that interacts with self-major histocompatibility complex (MHC) molecules receive signals that induce either their differentiation (positive selection) or apoptosis (negative selection). Furthermore, those cells that are positively selected develop into two different lineages, CD4 or CD8, depending on whether their TCRs bind to MHC class II or I, respectively. Positive selection therefore involves rescue from the default fate (death), lineage commitment, and progression to the single positive (SP) stage. These are probably temporally distinct events that may require both unique and overlapping signals. Work in the past several years has started to unravel the signaling networks that control these processes. One of the first pathways identified as important for positive selection was Ras and its downstream effector, the Erk mitogen-activated protein kinase (MAPK) cascade. In this review we examine the factors that connect the TCR to the Ras/Erk cascade in DP thymocytes, as well as what we know about the downstream effectors of the Ras/Erk cascade important for positive selection. We also consider the possible role of this cascade in CD4/CD8 lineage development, and the possible interactions of the Ras/Erk cascade with Notch during these cell fate determination processes.