Protein kinase B (Akt) regulation and function in T lymphocytes

Illuminating the Dark Cancer Phosphoproteome Through a Machine-Learned Co-Regulation Map of 26,280 Phosphosites

Mass spectrometry-based phosphoproteomics offers a comprehensive view of protein phosphorylation, but limited knowledge about the regulation and function of most phosphosites restricts our ability to extract meaningful biological insights from phosphoproteomics data. To address this, we combine machine learning and phosphoproteomic data from 1,195 tumor specimens spanning 11 cancer types to construct CoPheeMap, a network mapping the co-regulation of 26,280 phosphosites. Integrating network features from CoPheeMap into a machine learning model, CoPheeKSA, we achieve superior performance in predicting kinase-substrate associations. CoPheeKSA reveals 24,015 associations between 9,399 phosphosites and 104 serine/threonine kinases, including many unannotated phosphosites and under-studied kinases. We validate the accuracy of these predictions using experimentally determined kinase-substrate specificities. By applying CoPheeMap and CoPheeKSA to phosphosites with high computationally predicted functional significance and cancer-associated phosphosites, we demonstrate the effectiveness of these tools in systematically illuminating phosphosites of interest, revealing dysregulated signaling processes in human cancer, and identifying under-studied kinases as putative therapeutic targets.

Mechanistic insight of interleukin-9 induced osteoclastogenesis

Interleukin (IL)-9 is an emerging player in the pathogenesis of various chronic inflammatory diseases including bone disorders like rheumatoid arthritis (RA) and psoriatic arthritis. Recently, IL-9 was shown to enhance the osteoclast formation and their function in RA. However, the mechanisms by which IL-9 influences osteoclastogenesis are not known. Therefore, in this study we aimed to unravel the direct and indirect ways by which IL-9 can influence osteoclast formation. We used mouse bone marrow precursor cells for checking the effect of IL-9 on osteoclast differentiation and its function. Next, IL-9 induced signalling pathway were checked in the process of osteoclastogenesis. T cells play an important role in enhancing osteoclastogenesis in inflammatory conditions. We used splenic T cells to understand the impact of IL-9 on the functions of T effector (Teff) and regulatory T (Treg) cells. Furthermore, the effect of IL-9 mediated modulation of the T cell response on osteoclasts was checked using a coculture model of T cells with osteoclast precursors. We showed that IL-9 enhanced osteoclast formation and its function. We found that IL-9 activates STAT3, P38 MAPK, ERK1/2, NFκB and we hypothesize that it mediates the effect on osteoclastogenesis by accelerating mitochondrial biogenesis. Additionally, IL-9 was observed to facilitate the functions of pro-osteoclastogenic IL-17 producing T cells, but inhibits the function of anti-osteoclastogenic Treg cells. Our observations suggest that IL-9 can influence osteoclastogenesis directly by modulating the signalling cascade in the precursor cells; indirectly by enhancing IL-17 producing T cells and by reducing the functions of Treg cells.

Akt isoforms in the immune system

Akt is a PI3K-activated serine-threonine kinase that exists in three distinct isoforms. Akt's expression in most immune cells, either at baseline or upon activation, reflects its importance in the immune system. While Akt is most highly expressed in innate immune cells, it plays crucial roles in both innate and adaptive immune cell development and/or effector functions. In this review, we explore what's known about the role of Akt in innate and adaptive immune cells. Wherever possible, we discuss the overlapping and distinct role of the three Akt isoforms, namely Akt1, Akt2, and Akt3, in immune cells.

Protein S-Nitrosation: Biochemistry, Identification, Molecular Mechanisms, and Therapeutic Applications

Protein S-nitrosation (SNO), a posttranslational modification (PTM) of cysteine (Cys) residues elicited by nitric oxide (NO), regulates a wide range of protein functions. As a crucial form of redox-based signaling by NO, SNO contributes significantly to the modulation of physiological functions, and SNO imbalance is closely linked to pathophysiological processes. Site-specific identification of the SNO protein is critical for understanding the underlying molecular mechanisms of protein function regulation. Although careful verification is needed, SNO modification data containing numerous functional proteins are a potential research direction for druggable target identification and drug discovery. Undoubtedly, SNO-related research is meaningful not only for the development of NO donor drugs but also for classic target-based drug design. Herein, we provide a comprehensive summary of SNO, including its origin and transport, identification, function, and potential contribution to drug discovery. Importantly, we propose new views to develop novel therapies based on potential protein SNO-sourced targets.

Mitochondrial Disruption Is Involved in the Effect of Nuclear Factor of Activated T cells, Cytoplasmic 4 on Aggravating Cardiomyocyte Hypertrophy

ABSTRACT

Nuclear factor of activated T cells, cytoplasmic 4 (NFATc4), a nuclear transcription factor, has been implicated in cardiac hypertrophy through the enhancement of hypertrophic gene expression. However, the role of NFATc4 in mitochondrial modulation is mostly unknown. The current study aimed to investigate the role of NFATc4 in regulating mitochondrial function during phenylephrine (PE)-induced cardiac hypertrophy. Our results showed that overexpression of NFATc4 aggravated the PE-induced decrease in mitochondrial genesis, membrane potential, and mitochondrial gene expression as well as impaired mitochondrial respiration. However, knockdown of NFATc4 relieved PE-induced perturbations in mitochondria and cardiomyocyte hypertrophy. Mechanistically, by activating phosphoinositide-dependent kinase 1 and promoting a combination of AKT and phosphoinositide-dependent kinase 1, phosphorylation and sequential acetylation of PGC-1α were aggravated by NFATc4 and suppressed the activity of PGC-1α. In conclusion, NFATc4-regulated factors were shown to be associated with mitochondrial function and exacerbated PE-induced mitochondrial dysfunction. These findings revealed new roles of NFATc4 in cardiac hypertrophy.

Boosting Akt Pathway by Rupatadine Modulates Th17/Tregs Balance for Attenuation of Isoproterenol-Induced Heart Failure in Rats

Disruption of Th17/Tregs homeostasis plays a crucial role in governing the immune response during myocardial fibrosis and its progression to heart failure. The present study aimed to assess for the first time the possible protection afforded by rupatadine against isoproterenol-induced heart failure in rats. It also explored the role of PI3k/Akt as a possible mechanistic pathway, through which rupatadine could modulate Th17/Tregs balance to display its effect. Isoproterenol (85 and 170 mg/kg/day) was injected subcutaneously for 2 successive days, respectively and rupatadine (4 mg/kg/day) was then given orally for 14 days with or without wortmannin (PI3K/Akt inhibitor). Rupatadine succeeded to completely ameliorate isoproterenol-induced cardiac dysfunction as demonstrated by improvements of electrocardiographic and echocardiographic measurements. Moreover, rupatadine prevented the marked elevation of PAF and oxidative stress in addition to Th17 promoting cytokines (IL-6, IL-23, and TGF-β). Accordingly, rupatadine prevented Th17 stimulation or expansion as indicated by increased Foxp3/RORγt ratio and decreased production of its pro-inflammatory cytokine (IL-17). Rupatadine treatment mitigated isoproterenol-induced activation of STAT-3 signaling and the imbalance in p-Akt/total Akt ratio affording marked decrease in atrogin-1 and apoptotic biomarkers. Finally, this therapy was effective in averting cardiac troponin loss and reverting the histological alterations as assessed by myocardial fibrosis and hypertrophy grading. Contrariwise, co-administration of wortmannin mostly attenuated the protective effects of rupatadine affording more or less similar results to that of isoproterenol-untreated rats. In conclusion, rupatadine could be an effective therapy against the development of isoproterenol-induced heart failure where PI3K/Akt pathway seems to play a crucial role in its protective effect.

Akt3-Mediated Protection Against Inflammatory Demyelinating Disease

Akt is a serine/threonine protein kinase that plays a major role in regulating multiple cellular processes. While the isoforms Akt1 and Akt2 are involved in apoptosis and insulin signaling, respectively, the role for Akt3 remains uncertain. Akt3 is predominantly expressed in the brain, and total deletion of Akt3 in mice results in a reduction in brain size and neurodegeneration following injury. Previously, we found that Akt3-/- mice have a significantly worse clinical course during myelin-oligodendrocyte glycoprotein (MOG)-induced experimental autoimmune encephalomyelitis (EAE), an animal model in which autoreactive immune cells enter the CNS, resulting in inflammation, demyelination, and axonal injury. Spinal cords of Akt3-/- mice are severely demyelinated and have increased inflammation compared to WT, suggesting a neuroprotective role for Akt3 during EAE. To specifically address the role of Akt3 in neuroinflammation and maintaining neuronal integrity, we used several mouse strains with different manipulations to Akt3. During EAE, Akt3 Nmf350 mice (with enhanced Akt3 kinase activity) had lower clinical scores, a lag in disease onset, a delay in the influx of inflammatory cells into the CNS, and less axonal damage compared to WT mice. A significant increased efficiency of differentiation toward FOXP3 expressing iTregs was also observed in Akt3 Nmf350 mice relative to WT. Mice with a conditional deletion of Akt3 in CD4+ T-cells had an earlier onset of EAE symptoms, increased inflammation in the spinal cord and brain, and had fewer FOXP3+ cells and FOXP3 mRNA expression. No difference in EAE outcome was observed when Akt3 expression was deleted in neurons (Syn1-CKO). These results indicate that Akt3 signaling in T-cells and not neurons is necessary for maintaining CNS integrity during an inflammatory demyelinating disease.

CD55 Is Essential for CD103+ Dendritic Cell Tolerogenic Responses that Protect against Autoimmunity

Recent studies traced inflammatory bowel disease in some patients to deficiency of CD55 [decay-accelerating factor (DAF)], but the mechanism underlying the linkage remained unclear. Herein, we studied the importance of DAF in enabling processes that program tolerance in the gut and the eye, two immune-privileged sites where immunosuppressive responses are continuously elicited. Unlike oral feeding or ocular injection of ovalbumin in wild-type (WT) mice, which induced dominant immune tolerance, identical treatment of DAF^-/- mice or DAF^-/- to WT bone marrow chimeras did not. While 10% to 30% of mesenteric and submandibular lymph node CD4⁺ cells became robust T-regulatory cells (Tregs) in WT forkhead box P3 (Foxp3)-green fluorescent protein mice, few in either site became Tregs with little suppressor activity in DAF^-/- Foxp3-green fluorescent protein mice. Phenotyping of CD103⁺ dendritic cells (DCs) from the ovalbumin-fed DAF^-/- mice showed impaired expression of inducer of costimulation (ICOS) ligand, programmed death receptor 1-ligand 1 (PD1-L1), CxxxC chemokine receptor 1 (Cx3CR1), CCR7, and CCR9. Analyses of elicited DAF^-/- Foxp3⁺ Tregs showed reduced expression of interferon regulatory factor 8 (IRF-8)/aldehyde dehydrogenase 1 family member A2 (Aldh1a2) and glycoprotein A repetitions predominant/latency-associated protein associated with Treg transforming growth factor-β production and presentation, as well as integrin β6/integrin β8 associated with Treg and CD103⁺ DC transforming growth factor-β release. Thus, DAF is required for the properties of CD103⁺ DCs and their naïve CD4⁺ cell partners that together program tolerance.

Toxoplasma gondii excreted-secreted antigens suppress Foxp3 via PI3K-AKT-mTOR signaling pathway

Toxoplasma gondii excreted-secreted antigens (ESA) cause spontaneous abortion or fetal teratogenesis during the pregnancy in mice, especially in the early stage. Those adverse pregnancy outcomes are due to the deficit in regulatory T cells (Tregs). Forkhead box P3 (Foxp3), a critical transcription factor, modulates Tregs differentiation and its function. Besides, phosphatidylinositol 3-kinase-protein kinase B-mammalian target of rapamycin (PI3K-AKT-mTOR) signaling network is implicated in interfering with Foxp3 induction. We previously demonstrated that ESA diminished the number of Tregs and inhibited its function. And ESA suppressed Foxp3 expression via the attenuation of transforming growth factor β RII/Smad2/Smad3/Smad4 pathway. The current study aimed to investigate whether the PI3K-AKT-mTOR signaling network is involved in Foxp3 downregulation induced by ESA. We found that ESA upregulated PI3K, P-AKT, mTOR, and P-mTOR. Knockdown of PI3K cooperated with ESA to restore Foxp3 expression mediated by ESA. This suppressive role of ESA on Foxp3 expression was abrogated by AKT inhibitor. In addition, neutralization of Toll-like receptor 4 could restore the expression of Foxp3, PI3K, and its downstream effectors induced by ESA. Collectively, the findings indicated that ESA inhibited Foxp3 expression via the upregulation of PI3K-AKT-mTOR signaling pathway.

GSNOR modulates hyperhomocysteinemia-induced T cell activation and atherosclerosis by switching Akt S-nitrosylation to phosphorylation

The adaptive immune system plays a critical role in hyperhomocysteinemia (HHcy)-accelerated atherosclerosis. Recent studies suggest that HHcy aggravates atherosclerosis with elevated oxidative stress and reduced S-nitrosylation level of redox-sensitive protein residues in the vasculature. However, whether and how S-nitrosylation contributes to T-cell-driven atherosclerosis remain unclear. In the present study, we report that HHcy reduced the level of protein S-nitrosylation in T cells by inducing S-nitrosoglutathione reductase (GSNOR), the key denitrosylase that catalyzes S-nitrosoglutathione (GSNO), which is the main restored form of nitric oxide in vivo. Consequently, secretion of inflammatory cytokines [interferon-γ (IFN-γ) and interleukin-2] and proliferation of T cells were increased. GSNOR knockout or GSNO stimulation rectified HHcy-induced inflammatory cytokine secretion and T-cell proliferation. Site-directed mutagenesis of Akt at Cys224 revealed that S-nitrosylation at this site was pivotal for the reduced phosphorylation at Akt Ser473, which led to impaired Akt signaling. Furthermore, on HHcy challenge, as compared with GSNOR^+/+ApoE^-/- littermate controls, GSNOR^-/-ApoE^-/- double knockout mice showed reduced T-cell activation with concurrent reduction of atherosclerosis. Adoptive transfer of GSNOR^-/- T cells to ApoE^-/- mice fed homocysteine (Hcy) decreased atherosclerosis, with fewer infiltrated T cells and macrophages in plaques. In patients with HHcy and coronary artery disease, the level of plasma Hcy was positively correlated with Gsnor expression in peripheral blood mononuclear cells and IFN-γ⁺ T cells but inversely correlated with the S-nitrosylation level in T cells. These data reveal that T cells are activated, in part via GSNOR-dependent Akt denitrosylation during HHcy-induced atherosclerosis. Thus, suppression of GSNOR in T cells may reduce the risk of atherosclerosis.

Crucial role of carbonic anhydrase IX in tumorigenicity of xenotransplanted adult T-cell leukemia-derived cells

Carbonic anhydrase IX (CA9) is a membrane‐associated carbonic anhydrase that regulates cellular pH, is upregulated in various solid tumors, and is considered to be a therapeutic target. Here, we describe the essential role of CA9 in the tumorigenicity of cells derived from human adult T‐cell leukemia/lymphoma (ATL). We previously established the highly tumorigenic ST1‐N6 subline from the ATL‐derived ST1 cell line by serial xenotransplantation in NOG mice. In the present study, we first show that CA9 expression is strongly enhanced in ST1‐N6 cells. We then sorted ST1 cells by high or low CA9 expression and established ST1‐CA9^high and ST1‐CA9^low sublines. ST1‐CA9^high cells, like ST1‐N6 cells, were more strongly tumorigenic than ST1‐CA9^low or parental ST1 cells when injected into NOG mice. Knockdown of CA9 with shRNAs suppressed the ability of ST1‐CA9^high cells to initiate tumors, and the tumorigenicity of ST1 cells was significantly enhanced by introducing wild‐type CA9 or a CA9 mutant with deletion of an intracytoplasmic domain. However, a CA9 with point mutations in the catalytic site did not increase the tumorigenicity of ST1 cells. Furthermore, we detected a small population of CA9⁺CD25⁺ cells in lymph nodes of ATL patients. These findings suggest that CA9, and particularly its carbonic anhydrase activity, promotes the tumorigenicity of ATL‐derived cells and may be involved in malignant development of lymphoma‐type ATL.

BACH2 regulates CD8(+) T cell differentiation by controlling access of AP-1 factors to enhancers

T cell antigen receptor (TCR) signaling drives distinct responses depending upon the differentiation state and context of CD8⁺ T cells. We hypothesized that access of signal-dependent transcription factors (TFs) to enhancers is dynamically regulated to shape transcriptional responses to TCR signaling. We found that the TF BACH2 restrains terminal differentiation to enable generation of long-lived memory cells and protective immunity following viral infection. BACH2 was recruited to enhancers where it limited expression of TCR-driven genes by attenuating the availability of activator protein 1 (AP-1) sites to Jun family signal-dependent TFs. In naïve cells, this prevented TCR-driven induction of genes associated with terminal differentiation. Upon effector differentiation, reduced expression of BACH2 and its phosphorylation enabled unrestrained induction of TCR-driven effector programs.

Feeding an army: The metabolism of T cells in activation, anergy, and exhaustion

Through the direct control of infection or by providing cytokine signals to other cellular players, T cells play a central role in the orchestration of the immune response. However, in many disease states, T cells are rendered dysfunctional, unable to carry out their effector functions. As T cell activation is bioenergetically demanding, some T cell dysfunction can have metabolic underpinnings. In this review, we will discuss how T cells are programmed to fuel their effector response, and how programmed or pathologic changes can disrupt their ability to generate the energy needed to proliferate and carry out their critical functions.

Total velvet-antler polypeptide extract from Cervus nippon Temminck induces cell proliferation and activation of the PI3K–Akt signalling pathway in human peripheral blood lymphocytes

Velvet antler (VA) has been used for centuries as a traditional medicine to treat a wide range of health problems. VA was first recorded in the Chinese medical classics Shen Nong Ben Cao Jing 2000 years ago. VA has been extensively used to strengthen bones and muscles, promote blood flow and increase immune function. In the present study, we used VA (Cervus nippon Temminck) protein extract (VAPE) to induce cell proliferation and differentiation in human peripheral blood lymphocyte cell line 1301 cells. The results showed that 100 µg/mL of VAPE could significantly induce 1301-cell proliferation (151.3%), increase the population of S-phase cells and increase the expression of CDK4. In addition, VAPE could effectively increase the expression levels of PI3K and Akt and activate PI3K–Akt signal pathway. These findings have provided novel insights into the further understanding of the molecular and signalling pathway mechanisms of VAPE in promoting proliferation of human peripheral blood lymphocyte cells.

Over-expressing Akt in T cells to resist tumor immunosuppression and increase anti-tumor activity

BACKGROUND

Tumor employs various means to escape immunosurveillance and inhibit immune attack, and strategies have been developed to counteract the inhibitory signals. However, due to the complex suppressive mechanisms in the tumor microenvironment, blocking one or a few inhibitory signals has only limited effects on therapeutic efficacy. Instead of targeting tumor immunosuppression, we considered from another point of view, and hypothesized that manipulating T cells to make them resist any known or unknown suppressive mechanism may be more effective for cancer treatment.

METHODS

We used OT-1 cells transduced with retroviruses encoding Akt and human peripheral blood lymphocytes (PBLs) transduced with retroviruses encoding both Akt and a chimeric antigen receptor (CAR) specific for tumor antigen EpCAM to examine the effect of over-expressing Akt on tumor specific T cells in tumor environment.

RESULTS

We show that Akt activity of T cells in the tumor environment was inhibited, and over-expressing Akt in OT-1 cells increased the cytokine production and cell proliferation in the presence of B16-OVA tumor cells. What's more, adoptive transfer of OT-1 cells over-expressing Akt inhibited B16-OVA tumor growth and prolonged mouse survival. To examine if over-expressing Akt could increase the anti-tumor activity of T cells in human cancer, PBLs co-expressing EpCAM specific CAR and Akt were cultured with EpCAM-expressing human prostate cancer cells PC3M, and less inhibition on cell proliferation and less apoptosis were observed. In addition, adoptive transfer of PC3M specific T cells over-expressing Akt resulted in more dramatic tumor inhibitory effects in PC3M bearing NOD/SCID mice.

CONCLUSIONS

These data indicates that over-expressing Akt in tumor specific T cells increases T cell proliferation and activity in the tumor environment, and enhances anti-tumor effects of adoptively transferred T cells. Our study provides a new strategy to improve the efficacy of adoptive T cell therapy, and serves as an important foundation for clinical translation.

A central role for Notch in effector CD8(+) T cell differentiation

Activated CD8⁺ T cells choose between terminal effector cell (TEC) or memory precursor cell (MPC) fates. We show that Notch controls this choice. Notch promoted differentiation of immediately protective TECs and was correspondingly required for clearance of an acute influenza virus infection. Notch activated a major portion of the TEC-specific gene expression program and suppressed the MPC-specific program. Expression of Notch receptors was induced on naïve CD8⁺ T cells by inflammatory mediators and interleukin 2 (IL-2) via mTOR and T-bet dependent pathways. These pathways were subsequently amplified downstream of Notch, creating a positive feedback loop. Notch thus functions as a central hub where information from different sources converges to match effector T cell differentiation to the demands of the infection.

Enhanced activity of Akt in Teff cells from children with lupus nephritis is associated with reduced induction of tumor necrosis factor receptor-associated factor 6 and increased OX40 expression

OBJECTIVE

The breakdown of peripheral tolerance mechanisms is central to the pathogenesis of systemic lupus erythematosus (SLE). Although true Treg cells in patients with SLE exhibit intact suppressive activity, Teff cells are resistant to suppression. The underlying mechanisms are incompletely understood. This study was undertaken to examine the Akt signaling pathway and molecules that may alter its activity in T cells in lupus patients.

METHODS

The Akt pathway and its regulators were analyzed in Teff and Treg cells from children with lupus nephritis and controls using flow cytometry and real-time quantitative polymerase chain reaction. T cell proliferation was assessed by analysis of 5,6-carboxyfluorescein succinimidyl ester dilution.

RESULTS

CD4+CD45RA-FoxP3(low) and FoxP3- Teff cells from children with lupus nephritis expressed high levels of activated Akt, resulting in the down-regulation of the proapoptotic protein Bim and an enhanced proliferative response. The induction of tumor necrosis factor receptor-associated factor 6 (TRAF6) was impaired, and TRAF6 levels inversely correlated with Akt activity. Although the expression of OX40 was enhanced on Teff cells from children with lupus nephritis compared to controls, OX40 stimulation failed to significantly increase TRAF6 expression in cells from patients, in contrast to those from healthy controls, but resulted in further increased Akt activation that was reversed by blockade of OX40 signaling. Moreover, inhibition of Akt signaling markedly decreased the proliferation of Teff cells from lupus patients.

CONCLUSION

Our findings indicate that hyperactivation of the Akt pathway in Teff cells from children with lupus nephritis is associated with reduced induction of TRAF6 and up-regulation of OX40, which may cause Teff cell resistance to Treg cell-mediated suppression.

High CD74 expression correlates with ZAP70 expression in B cell chronic lymphocytic leukemia patients

Chronic lymphocytic leukemia (CLL) is the most common leukemia in adults in Western countries. It is characterized by heterogeneous clinical course of the disease and new prognostic factors are still needed. CD74 plays an important role in signal transduction in B cell proliferation and survival pathway. CD74 expression has been shown in solid tumors and has been connected with poor prognosis and tumor progression. The aim of the study was to evaluate the expression of CD74 in chronic lymphocytic leukemia patients with combination with other known prognostic factors. Expression of CD74 was determined in 90 patients and 28 healthy controls. CD74 expression was significantly higher in CLL group than in controls. There was positive correlation between CD74 and ZAP70 expression (p = 0.008). High expression of CD74 was positively correlated with more advanced stage of the disease (p = 0.02). No correlation was shown between CD74 and sex, mutational status IgVH and time to first treatment.

The regulating function of heterotrimeric G proteins in the immune system

Heterotrimeric guanine nucleotide-binding proteins (G proteins), which consist of an α-, a β- and a γ-subunit, have crucial roles as molecular switches in the regulation of the downstream effector molecules of multiple G protein-coupled receptor signalling pathways, such as phospholipase C and adenylyl cyclase. According to the structural and functional similarities of their α-subunits, G proteins can be divided into four subfamilies: Gαs, Gαi/o, Gαq/11 and Gα12/13. Most of the α- and the βγ-subunits are abundantly expressed on the surface of immune cells. Recent studies have demonstrated that G proteins are a group of important immunomodulatory factors that regulate the migration, activation, survival, proliferation, differentiation and cytokine secretion of immune cells. In this review, we summarise the recent findings on the functions of G proteins in immune regulation and autoimmunity.

Melanoma brain metastasis: overview of current management and emerging targeted therapies

The high rate of brain metastasis in patients with advanced melanoma has been a clinical challenge for oncologists. Despite considerable progress made in the management of advanced melanoma over the past two decades, improvement in overall survival has been elusive. This is due to the high incidence of CNS metastases, which progress relentlessly and which are only anecdotally responsive to systemic therapies. Surgery, stereotactic radiosurgery and whole-brain radiotherapy with or without cytotoxic chemotherapy remain the mainstay of treatment. However, new drugs have been developed based on our improved understanding of the molecular signaling mechanisms responsible for host immune tolerance and for melanoma growth. In 2011, the US FDA approved two agents, one antagonizing each of these processes, for the treatment of advanced melanoma. The first is ipilimumab, an anti-CTLA-4 monoclonal antibody that enhances cellular immunity and reduces tolerance to tumor-associated antigens. The second is vemurafenib, an inhibitor that blocks the abnormal signaling for melanoma cellular growth in tumors that carry the BRAF(V600E) mutation. Both drugs have anecdotal clinical activity for brain metastasis and are being evaluated in clinical trial settings. Additional clinical trials of newer agents involving these pathways are also showing promise. Therefore, targeted therapies must be incorporated into the multimodality management of melanoma brain metastasis.

Suppression of inflammatory responses during myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis is regulated by AKT3 signaling

AKT3, a member of the serine/threonine kinase AKT family, is involved in a variety of biologic processes. AKT3 is expressed in immune cells and is the major AKT isoform in the CNS representing 30% of the total AKT expressed in spinal cord, and 50% in the brain. Myelin-oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis (EAE) is a mouse model in which lymphocytes and monocytes enter the CNS, resulting in inflammation, demyelination, and axonal injury. We hypothesized that during EAE, deletion of AKT3 would negatively affect the CNS of AKT3(-/-) mice, making them more susceptible to CNS damage. During acute EAE, AKT3(-/-)mice were more severely affected than wild type (WT) mice. Evaluation of spinal cords showed that during acute and chronic disease, AKT3(-/-) spinal cords had more demyelination compared with WT spinal cords. Quantitative RT-PCR determined higher levels of IL-2, IL-17, and IFN-γ mRNA in spinal cords from AKT3(-/-) mice than WT. Experiments using bone marrow chimeras demonstrated that AKT3(-/-) mice receiving AKT3-deficient bone marrow cells had elevated clinical scores relative to control WT mice reconstituted with WT cells, indicating that altered function of both CNS cells and bone marrow-derived immune cells contributed to the phenotype. Immunohistochemical analysis revealed decreased numbers of Foxp3(+) regulatory T cells in the spinal cord of AKT3(-/-) mice compared with WT mice, whereas in vitro suppression assays showed that AKT3-deficient Th cells were less susceptible to regulatory T cell-mediated suppression than their WT counterparts. These results indicate that AKT3 signaling contributes to the protection of mice against EAE.

The tetraspanin CD37 orchestrates the α(4)β(1) integrin-Akt signaling axis and supports long-lived plasma cell survival

Signaling by the serine and threonine kinase Akt (also known as protein kinase B), a pathway that is common to all eukaryotic cells, is central to cell survival, proliferation, and gene induction. We sought to elucidate the mechanisms underlying regulation of the kinase activity of Akt in the immune system. We found that the four-transmembrane protein CD37 was essential for B cell survival and long-lived protective immunity. CD37-deficient (Cd37(-/-)) mice had reduced numbers of immunoglobulin G (IgG)-secreting plasma cells in lymphoid organs compared to those in wild-type mice, which we attributed to increased apoptosis of plasma cells in the germinal centers of the spleen, areas in which B cells proliferate and are selected. CD37 was required for the survival of IgG-secreting plasma cells in response to binding of vascular cell adhesion molecule 1 to the α(4)β(1) integrin. Impaired α(4)β(1) integrin-dependent Akt signaling in Cd37(-/-) IgG-secreting plasma cells was the underlying cause responsible for impaired cell survival. CD37 was required for the mobility and clustering of α(4)β(1) integrins in the plasma membrane, thus regulating the membrane distribution of α(4)β(1) integrin necessary for activation of the Akt survival pathway in the immune system.

All PI3Kinase signaling is not mTOR: dissecting mTOR-dependent and independent signaling pathways in T cells

The mechanistic target of rapamycin (mTOR) is emerging as playing a central role in regulating T cell activation, differentiation, and function. mTOR integrates diverse signals from the immune microenvironment to shape the outcome of T cell receptor (TCR) antigen recognition. Phosphatidylinositol 3-kinase (PI3K) enzymes are critical mediators of T cell activation through their generation of the second messenger phosphatidylinositol (3,4,5) triphosphate (PIP3). Indeed, PIP3 generation results in the activation of Protein Kinase B (PKB, also known as AKT), a key activator of mTOR. However, recent genetic studies have demonstrated inconsistencies between PI3K disruption and loss of mTOR expression with regard to the regulation of effector and regulatory T cell homeostasis and function. In this review, we focus on how PI3K activation directs mature CD4 T cell activation and effector function by pathways dependent on and independent of mTOR signaling. Importantly, what has become clear is that targeting both mTOR-dependent and mTOR-independent PI3K-induced signaling distally affords the opportunity for more selective regulation of T cell differentiation and function.

Functional human regulatory T cells fail to control autoimmune inflammation due to PKB/c-akt hyperactivation in effector cells

During the last decade research has focused on the application of FOXP3(+) regulatory T cells (Tregs) in the treatment of autoimmune disease. However, thorough functional characterization of these cells in patients with chronic autoimmune disease, especially at the site of inflammation, is still missing. Here we studied Treg function in patients with juvenile idiopathic arthritis (JIA) and observed that Tregs from the peripheral blood as well as the inflamed joints are fully functional. Nevertheless, Treg-mediated suppression of cell proliferation and cytokine production by effector cells from the site of inflammation was severely impaired, because of resistance to suppression. This resistance to suppression was not caused by a memory phenotype of effector T cells or activation status of antigen presenting cells. Instead, activation of protein kinase B (PKB)/c-akt was enhanced in inflammatory effector cells, at least partially in response to TNFα and IL-6, and inhibition of this kinase restored responsiveness to suppression. We are the first to show that PKB/c-akt hyperactivation causes resistance of effector cells to suppression in human autoimmune disease. Furthermore, these findings suggest that for a Treg enhancing strategy to be successful in the treatment of autoimmune inflammation, resistance because of PKB/c-akt hyperactivation should be targeted as well.

Differentiation of human peripheral blood Vδ1+ T cells expressing the natural cytotoxicity receptor NKp30 for recognition of lymphoid leukemia cells

The success of cancer immunotherapy depends on productive tumor cell recognition by killer lymphocytes. γδ T cells are a population of innate-like lymphocytes endowed with strong, MHC-unrestricted cytotoxicity against tumor cells. This notwithstanding, we recently showed that a large proportion of human hematologic tumors is resistant to γδ peripheral blood lymphocytes (PBLs) activated with specific agonists to the highly prevalent Vγ9Vδ2 TCR. Although this probably constitutes an important limitation to current γδ T cell–mediated immunotherapy strategies, we describe here the differentiation of a novel subset of Vδ2− Vδ1+ PBLs expressing natural cytotoxicity receptors (NCRs) that directly mediate killing of leukemia cell lines and chronic lymphocytic leukemia patient neoplastic cells. We show that Vδ1+ T cells can be selectively induced to express NKp30, NKp44 and NKp46, through a process that requires functional phosphatidylinositol 3-kinase (PI-3K)/AKT signaling on stimulation with γc cytokines and TCR agonists. The stable expression of NCRs is associated with high levels of granzyme B and enhanced cytotoxicity against lymphoid leukemia cells. Specific gain-of-function and loss-of-function experiments demonstrated that NKp30 makes the most important contribution to TCR-independent leukemia cell recognition. Thus, NKp30+ Vδ1+ T cells constitute a novel, inducible and specialized killer lymphocyte population with high potential for immunotherapy of human cancer.

OX40 complexes with phosphoinositide 3-kinase and protein kinase B (PKB) to augment TCR-dependent PKB signaling

T lymphocyte activation requires signal 1 from the TCR and signal 2 from costimulatory receptors. For long-lasting immunity, growth and survival signals imparted through the Akt/protein kinase B (PKB) pathway in activated or effector T cells are important, and these can be strongly influenced by signaling from OX40 (CD134), a member of the TNFR superfamily. In the absence of OX40, T cells do not expand efficiently to Ag, and memory formation is impaired. How most costimulatory receptors integrate their signals with those from Ag through the TCR is not clear, including whether OX40 directly recruits PKB or molecules that regulate PKB. We show that OX40 after ligation by OX40L assembled a signaling complex that contained the adapter TNFR-associated factor 2 as well as PKB and its upstream activator phosphoinositide 3-kinase (PI3K). Recruitment of PKB and PI3K were dependent on TNFR-associated factor 2 and on translocation of OX40 into detergent-insoluble membrane lipid microdomains but independent of TCR engagement. However, OX40 only resulted in strong phosphorylation and functional activation of the PI3K-PKB pathway when Ag was recognized. Therefore, OX40 primarily functions to augment PKB signaling in T cells by enhancing the amount of PI3K and PKB available to the TCR. This highlights a quantitative role of this TNFR family second signal to supplement signal 1.

Ivabradine reduces chemokine-induced CD4-positive lymphocyte migration

AIMS

Migration of CD4-positive lymphocytes into the vessel wall is a critical step in atherogenesis. Recent data suggest that ivabradine, a selective I(f)-channel blocker, reduces atherosclerotic plaque formation in apolipoprotein E-deficient mice, hitherto nothing is known about the mechanism by which ivabradine modulates plaque formation. Therefore, the present study investigated whether ivabradine regulates chemokine-induced migration of lymphocytes.

METHODS AND RESULTS

Stimulation of CD4-positive lymphocytes with SDF-1 leads to a 2.0 ± 0.1 fold increase in cell migration (P < .01; n = 7). Pretreatment of cells with ivabradine reduces this effect to a maximal 1.2 ± 0.1 fold induction at 0.1 µmol/L ivabradine (P < .01 compared to SDF-1-treated cells, n = 7). The effect of ivabradine on CD4-positive lymphocyte migration was mediated through an early inhibition of chemokine-induced PI-3 kinase activity as determined by PI-3 kinase activity assays. Downstream, ivabradine inhibits activation of the small GTPase Rac and phosphorylation of the Myosin Light Chain (MLC). Moreover, ivabradine treatment reduces f-actin formation as well as ICAM3 translocation to the uropod of the cell, thus interfering with two important steps in T cell migration.

CONCLUSION

Ivabradine inhibits chemokine-induced migration of CD4-positive lymphocytes. Given the crucial importance of chemokine-induced T-cell migration in early atherogenesis, ivabradine may be a promising tool to modulate this effect.

Effects of Salmonella on spatial-temporal processes of jejunal development in chickens

To study effects of Salmonella enteritidis on morphological and functional changes in chicken jejunal development, we analysed gene expression profiles at seven points post-infection in 1-21 day-old broiler chickens. Nine clusters with different gene expression patterns were identified, and the genes in each cluster were further analyzed by a functional annotation clustering method (DAVID). Functional and morphological developmental processes dominated in all the nine clusters. Salmonella infection caused delays in several intestinal-morphological processes, whereas functional metabolic processes occurred in a similar spatial-temporal frame compared to normal jejunum development. A clear difference between normal developing- and Salmonella disturbed jejunum was the higher expression of genes involved in cell turn-over at early stages in the infected jejunum. Surprisingly, we found no clustered immune related processes in the infected birds. To compare the immunological processes between control and Salmonella infected chickens, the gene expression data was superimposed on known immunological KEGG pathways. Furthermore an in-depth analysis on the immune gene level was performed. As expected, we did find immunological processes in the Salmonella infected jejunum. Several of these processes could be verified by immunohistochemistry measurements of different immunological cell types. However, the well-ordered spatial-temporal development of the immune system, as observed in control non-infected animals, was completely abolished in the infected animals. Several immunological processes started much earlier in time, whereas other processes are disorganised. These data indicate that normal morphological and immunological development of jejunum is changed dramatically by a disturbance due to Salmonella infection. Due to the disturbance, the well-organized spatial-temporal development of morphological processes are delayed, those of the immunological development are scattered, whereas metabolic functional processes are almost not affected. This demonstrates the flexibility of developmental processes in the broiler chicken intestine.

Cbl-b in T-cell activation

Peripheral activation of antigen-specific T cells is stringently controlled to prevent immune responses against self-antigens. Only after a T cell is presented with two signals, an antigen and a co-stimulatory signal, can they be fully activated. In case antigen presentation occurs without co-stimulation, T-cell receptor (TCR) signaling pathways are regulated to prevent T-cell activation and induce T-cell tolerance. Thus, for a productive T-cell response to occur, co-stimulatory receptors need to serve the dual role of amplifying the TCR signaling while concomitantly releasing T cells from suppression. Biochemical and genetic studies during the last 10 years have documented the critical role of the E3 ubiquitin-ligase Cbl-b in this fundamental two-signal modulation of T-cell responses. In this review, we will discuss our current understanding on how Cbl-b controls T-cell activation and tolerance, its in vivo implications, as well as mechanisms for tuning T-cell-mediated immune responses by this essential E3 ligase.

Protein kinase B/Akt signals impair Th17 differentiation and support natural regulatory T cell function and induced regulatory T cell formation

Protein kinase B (PKB)/Akt signals control T cell proliferation and differentiation but their effect on the generation and function of regulatory T cells (Treg) and Th17 cells is not well understood. In this study, we show that elevated PKB signals antagonize the immunosuppressive effect of TGF-beta1 on cell size, CD25 and CD98 expression, and proliferation of CD3-stimulated naive CD4(+) T cells from wild-type and CD28-deficient mice. Conventional CD4(+) T cells expressing active PKB are less susceptible to suppression by natural regulatory T cells. Although PKB signals do not affect the development of natural regulatory T cells, they enhance their suppressor capacity. Upon TCR triggering and TGF-beta1 costimulation, wild-type and CD28-deficient CD4(+) T cells transgenic for PKB readily express Foxp3, thereby acquiring suppressor capacity. These effects of elevated PKB signals on T cell function involve a marked and sustained activation of STAT5 and Foxp3 and reduction in nuclear NFATc1 levels. In contrast, PKB signals impair TGF-beta1/IL-6-mediated differentiation of naive CD4(+) T cells into the Th17 lineage. This correlates with an increased signaling of ERK, STAT5, and STAT6. Finally, elevated PKB signals reduced the severity of experimental autoimmune encephalomyelitis in wild-type mice but induced experimental autoimmune encephalomyelitis in mice deficient for CD28. Altogether, these data indicate an important role of PKB signals on control of TGF-beta1-mediated T cell responses and, thereby, on tolerizing and inflammatory immune processes.

PPARalpha ligands cause lymphocyte depletion and cell cycle block and this is associated with augmented TRB3 and reduced Cyclin B1 expression

PPARalpha ligands are medications used clinically to prevent cardiovascular events, however studies have shown that these agents are also anti-inflammatory. Our previous studies have shown that PPARalpha ligands induce lymphocyte depletion. PPARalpha ligands also potently upregulate TRB3, a protein that has been associated with cell cycle arrest. Therefore the following studies were undertaken to determine the mechanisms associated with lymphocyte depletion. Our studies demonstrate that WY14,643, a PPARalpha ligand, decreases the amount of lymphocytes recovered after stimulation and reduces cellular divisions. Cells treated with WY14,643 also accumulate in the G2/S phase of the cell cycle. TRB3 has been shown to inhibit the phosphorylation of AKT/Protein Kinase B, and reduced activation of AKT has been associated with decreased cellular divisions and survival. However in lymphocytes, TRB3 did not reduce the phosphorylation of AKT, and WY14,643 treatment was associated with enhanced activation of AKT. Drosophila tribbles (TRB3 homolog) causes G2 arrest by decreasing the expression of a Cdc25c homolog. Lymphocytes stimulated and treated with WY14,643 have reduced expression of Cdc25c, however this is not associated with enhanced expression of phosphorylated-Cdc2 which induces G2 arrest. Instead we observed that WY14,643 consistently reduces the protein and mRNA expression of Cyclin B1. Moreover, TRB3 inhibits activation of a Cyclin B1 promoter construct. In summary, we propose that PPARalpha ligands may reduce cellular number by augmenting TRB3 expression, which in turn induces cell cycle arrest by reducing the expression of Cyclin B1. Reduced cellular divisions and cell cycle arrest may be responsible for some of the immunomodulatory effects of these agents that have been consistently observed in human trials.

The Interleukin (IL)‐2 Family Cytokines: Survival and Proliferation Signaling Pathways in T Lymphocytes

Lymphocyte populations in the immune system are maintained by a well-organized balance between cellular proliferation, cellular survival and programmed cell death (apoptosis). One of the primary functions of many cytokines is to coordinate these processes. In particular, the interleukin (IL)-2 family of cytokines, which consists of six cytokines (IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21) that all share a common receptor subunit (gammac), plays a major role in promoting and maintaining T lymphocyte populations. The details of the molecular signaling pathways mediated by these cytokines have not been fully elucidated. However, the three major pathways clearly involved include the JAK/STAT, MAPK and phosphatidylinositol 3-kinase (P13K) pathways. The details of these pathways as they apply to the IL-2 family of cytokines is discussed, with a focus on their roles in proliferation and survival signaling.

IL-15 renders conventional lymphocytes resistant to suppressive functions of regulatory T cells through activation of the phosphatidylinositol 3-kinase pathway

IL-15 drives chronic inflammation in several human diseases. We have recently shown that IL-15 inhibits the immunosuppressive effects of TGF-beta through blockage of the Smad3-signaling pathway. Data pointing to reciprocal interactions between TGF-beta and CD4(+) regulatory T cells led us to investigate the impact of IL-15 on the de novo generation and function of regulatory T cells in humans. Our data indicate that IL-15 does not counteract, but rather promotes the effect of TGF-beta on the de novo generation of regulatory T cells (Treg). Thus, in the presence of TGF-beta, IL-15 enhanced the acquisition of regulatory functions by CD4(+)CD25(-) T cells stimulated by anti-CD3 and anti-CD28 Abs. In contrast, IL-15 impaired the functions of Tregs by acting on effector CD4 and CD8 T cells. Accordingly, in the presence of IL-15, proliferation and IFN-gamma production by peripheral CD4 and CD8 T cells could not be efficiently inhibited by Tregs. IL-15-induced resistance of effector T cells to Tregs resulted from activation of the PI3K signaling pathway but did not involve the rescue of effector T cells from apoptosis. Altogether, these data point to the ambiguous role of IL-15 in the control of Treg functions. This dual role may be instrumental to mount rapid but transient proinflammatory immune responses against pathogens but may become deleterious in situations associated with protracted IL-15 over-expression.

Two pathways of costimulation through CD28

CD28 is recognized as the primary costimulatory molecule involved in the activation of naïve T cells. However, the biochemical signaling pathways that are activated by CD28 and how these pathways are integrated with TCR signaling are still not understood. We have recently shown that there are at least two independent activation pathways induced by CD28 costimulation. One is integrated with TCR signaling in the context of the immunological synapse and is mediated through transcriptional enhancement and the second is mediated through the induction of mRNA stability. Here, we review the immunological consequences and biochemical mechanisms associated with CD28 costimulation and discuss the major questions that need to be resolved to understand the molecular mechanisms that transduce CD28 costimulation.

TLR9-activating DNA up-regulates ZAP70 via sustained PKB induction in IgM+ B cells

In the past, ZAP70 was considered a T cell-specific kinase, and its aberrant expression in B-CLL cells was interpreted as a sign of malignant transformation and dedifferentiation. It was only recently that ZAP70 was detected in normal human B cells. In this study, we show that TLR9-activated B cells resemble B-cell chronic lymphocytic leukemia cells with regard to CD5, CD23, CD25, and heat shock protein 90 expression. Furthermore, stimulatory CpG and GpC DNA oligonucleotides target CD27(+)IgM(+) and CD27(-)IgM(+) B cells (but not IgM(-) B cells) and enhance ZAP70 expression predominantly in the IgM(+)CD27(+) B cell subset. ZAP70 is induced via activation of TLR-7 or -9 in a MyD88-dependent manner, depends on protein kinase B (PKB)/mammalian target of rapamycin signaling and is rapamycin sensitive. Furthermore, ZAP70 expression levels correlate with induction of cyclin A2, prolonged B cell proliferation, and sustained induction of PKB. These events are not observed upon CD40 ligation. However, this deficit can be overcome by the expression of constitutively active PKB, given that CD40 ligation of PKB-transgenic B cells induces B cell proliferation and ZAP70 expression. These results highlight a major difference between CD40- and TLR-7/9-mediated B cell activation and suggest that ZAP70 expression levels in B cells give an estimate of the proliferative potential and the associated PKB availability.

Antigen-mediated T cell expansion regulated by parallel pathways of death

T cells enigmatically require caspase-8, an inducer of apoptosis, for antigen-driven expansion and effective antiviral responses, and yet the pathways responsible for this effect have been elusive. A defect in caspase-8 expression does not affect progression through the cell cycle but causes an abnormally high rate of cell death that is distinct from apoptosis and does not involve a loss of NFkappaB activation. Instead, antigen or mitogen activated Casp8-deficient T cells exhibit an alternative type of cell death similar to programmed necrosis that depends on receptor interacting protein (Ripk1). The selective genetic ablation of caspase-8, NFkappaB, and Ripk1, reveals two forms of cell death that can regulate virus-specific T cell expansion.

Combinatorial Signal Transduction Responses Mediated by Interleukin-2 and -4 Receptors in a Helper TH2 Cell Line

The cytokines interleukin (IL)-2 and IL-4 are important regulators of the adaptive immune response, due in part to their effects on clonal expansion and differentiation of T cells. When IL-2 and IL-4 are administered together, both antagonistic and synergistic effects have been reported, but little is known in general concerning the mechanisms underlying such combinatorial effects. We found evidence for both effects in the proliferation responses of the IL-2 and IL-4 responsive T cell line, HT-2; IL-4 delays the onset of cell growth yet ultimately allows a higher cell density to be achieved in static culture. At the level of signal transduction pathways, we found that IL-4 partially inhibits IL-2 receptor-mediated pathways (PI3K/Akt, Ras/Erk, and STAT5a/b) and does not prolong their transient kinetics. This mode of antagonism, but not the effects on cell proliferation, is overcome at higher concentrations of IL-2 that are sufficient to saturate the signaling responses. By comparison, IL-4-stimulated activation of STAT6 is unaffected by IL-2 and shows sustained kinetics, and we speculate that this or another IL-4 receptor-specific pathway is responsible for the effects of IL-4 on IL-2-stimulated proliferation. A possibly related observation is that IL-4 induces a dramatic cell adhesion phenotype.

Nuclear export of NF90 to stabilize IL-2 mRNA is mediated by AKT-dependent phosphorylation at Ser647 in response to CD28 costimulation

IL-2 is one of the most important cytokines required for T cell-mediated immune responses. Costimulation of CD28 in T cells up-regulates IL-2 mRNA levels via transcription activation and mRNA stabilization. Upon T cell activation, NF90, an AU-rich element (ARE)-binding protein, translocates from the nucleus into the cytoplasm, where it binds to the ARE-containing 3' untranslated regions of IL-2 mRNA and slows down degradation of IL-2 mRNA. The translocation of NF90 is mediated through a nuclear export signal at its N terminus, but how it is triggered is still unclear. Phosphorylation of ARE-binding proteins has been reported as a signal transduction pathway to stabilize ARE-containing transcripts. In this study, we demonstrate that AKT phosphorylates NF90 on Ser647 upon CD28 costimulation. This phosphorylation is necessary for nuclear export of NF90 and IL-2 mRNA stabilization by this protein, because a mutation at Ser647 abolished both functions. We observed that treatment of cells with CD28 costimulation induced distinct increase in phosphorylation of AKT and NF90 at Ser647 concomitantly. Phosphorylation at Ser647 of NF90 up-regulated IL-2 production in response to CD28 costimulation. In vivo and in vitro data support a model in which CD28 costimulation activates AKT to phosphorylate NF90 at Ser647 and phosphorylation triggers NF90 to relocate to the cytoplasm and stabilize IL-2 mRNA.

The AKT-mTOR axis regulates de novo differentiation of CD4+Foxp3+ cells

CD4(+)Foxp3(+) regulatory T (T reg) cells play an essential role in maintaining immunological tolerance via their suppressive function on conventional CD4(+) T (Tconv) cells. Repertoire studies suggest that distinct T cell receptor signaling pathways lead to T reg differentiation, but the signals that regulate T reg specification are largely unknown. We identify AKT as a strong repressor of entry into the T reg phenotype in vitro and in vivo. A constitutively active allele of AKT substantially diminished TGF-beta-induced Foxp3 expression in a kinase-dependent manner and via a rapamycin-sensitive pathway, implicating the AKT-mammalian target of rapamycin axis. The observed impairment in Foxp3 induction was part of a broad dampening of the typical T reg transcriptional signature. Expression of active AKT at a stage before Foxp3 turn on during normal T reg differentiation in the thymus selectively impaired differentiation of CD4(+)Foxp3(+) cells without any alteration in the positive selection of Tconv. Activated AKT, in contrast, did not affect established Foxp3 expression in T reg cells. These results place AKT at a nexus of signaling pathways whose proper activation has a strong and broad impact on the onset of T reg specification.

A human CD4 monoclonal antibody for the treatment of T-cell lymphoma combines inhibition of T-cell signaling by a dual mechanism with potent Fc-dependent effector activity

Zanolimumab is a human IgG1 antibody against CD4, which is in clinical development for the treatment of cutaneous and nodal T-cell lymphomas. Here, we report on its mechanisms of action. Zanolimumab was found to inhibit CD4+ T cells by combining signaling inhibition with the induction of Fc-dependent effector mechanisms. First, T-cell receptor (TCR) signal transduction is inhibited by zanolimumab through a fast, dual mechanism, which is activated within minutes. Ligation of CD4 by zanolimumab effectively inhibits early TCR signaling events but, interestingly, activates signaling through the CD4-associated tyrosine kinase p56lck. An uncoupling of p56lck from the TCR by anti-CD4 allows the kinase to transmit direct inhibitory signals via the inhibitory adaptor molecules Dok-1 and SHIP-1. Second, CD4+ T cells are killed by induction of antibody-dependent cell-mediated cytotoxicity, to which CD45RO+ cells are more sensitive than CD45RA+ cells. Finally, zanolimumab induces down-modulation of CD4 from cell surfaces via a slow Fc-dependent mechanism. In conclusion, zanolimumab rapidly inhibits T-cell signaling via a dual mechanism of action combined with potent Fc-dependent lysis of CD4+ T cells and may act long-term by down-regulating CD4.

Macrophage migration inhibitory factor induces B cell survival by activation of a CD74-CD44 receptor complex

Macrophage migration inhibitory factor (MIF) is an upstream activator of innate immunity that regulates subsequent adaptive responses. It was previously shown that in macrophages, MIF binds to a complex of CD74 and CD44, resulting in initiation of a signaling pathway. In the current study, we investigated the role of MIF in B cell survival. We show that in B lymphocytes, MIF initiates a signaling cascade that involves Syk and Akt, leading to NF-kappaB activation, proliferation, and survival in a CD74- and CD44-dependent manner. Thus, MIF regulates the adaptive immune response by maintaining the mature B cell population.

3-phosphoinositide-dependent kinase 1 deficiency perturbs Toll-like receptor signaling events and actin cytoskeleton dynamics in dendritic cells

The adaptive immune response depends on dendritic cell (DC) activation by microbial products that signal via pattern recognition receptors and activate mitogen-activated protein kinases, NFkappaB and PI3K. The contribution of the AGC kinase family, including protein kinase B, protein kinase C, p90kDa ribosomal S6 kinase, and S6 kinase, has been little investigated because the probable redundancy among their isoforms makes their study difficult. We took advantage of the fact that all these kinases are regulated by the upstream master kinase 3-phosphoinositide-dependent kinase 1 (PDK1). Here we analyze various properties of DC from mice expressing approximately 10% of normal PDK1 (PDK1(fl/-)). DC populations in lymphoid and nonlymphoid tissues appeared normal in PDK1(fl/-) mice, and some in vitro responses to lipopolysaccharide (LPS) such as cytokine production were normal in cultured bone marrow DC. However, LPS-induced expression of class II major histocompatibility complex and CD86 were elevated in PDK1(fl/-) BMDC and PDK1(fl/-) spleen DC produced more interleukin-10 and -12, implying an attenuating role for PDK1. Unexpectedly, PDK1(fl/-) DC had a significantly reduced capacity for LPS-stimulated macropinocytosis and phagocytosis that correlated with a lowered F-actin/G-actin ratio, apparently because of increased actin depolymerization. Several PDK1-regulated kinases, some of which feed into actin regulators, showed reduced activation in PDK1(fl/-) DC. Reintroduction of PDK1 restored S6 kinase activity, increased levels of F-actin, and boosted macropinocytosis thus linking PDK1 and its downstream effectors to the unusual phenotype of PDK1(fl/-) DC.

Differential impact of mammalian target of rapamycin inhibition on CD4+CD25+Foxp3+ regulatory T cells compared with conventional CD4+ T cells

Based on their ability to control T-cell homeostasis, Foxp3(+)CD4(+)CD25(+) regulatory T cells (Tregs) are being considered for treatment of autoimmune disorders and acute graft-versus-host disease (aGVHD). When combining Tregs with the immunosuppressant rapamycin (RAPA), we observed reduced alloreactive conventional T-cell (Tconv) expansion and aGVHD lethality compared with each treatment alone. This synergistic in vivo protection was paralleled by intact expansion of polyclonal Tregs with conserved high FoxP3 expression. In contrast to Tconv, activation of Tregs with alloantigen and interleukin-2 preferentially led to signal transducer and activator of transcription 5 (STAT5) phosphorylation and not phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway activity. Expression of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a negative regulator of the PI3K/Akt/mTOR pathway, remained high in Tregs but not Tconv during stimulation. Conversely, targeted deletion of PTEN increased susceptibility of Tregs to mTOR inhibition by RAPA. Differential impact of RAPA as a result of reduced usage of the mTOR pathway in Tregs compared with conventional T cells explains the synergistic effect of RAPA and Tregs in aGVHD protection, which has important implications for clinical trials using Tregs.

gamma(c) cytokines provide multiple homeostatic signals to naive CD4(+) T cells

Cytokines signaling through receptors sharing the common gamma chain (gamma(c)), including IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21, are critical for the generation and peripheral homeostasis of B, T and NK cells. To identify unique or redundant roles for gamma(c) cytokines in naive CD4(+) T cells, we compared monoclonal populations of CD4(+) T cells from TCR-Tg mice that were gamma(c) (+), gamma(c) (-), CD127(-/-) or CD122(-/-). We found that gamma(c) (-) naive CD4(+) T cells failed to accumulate in the peripheral lymphoid organs and the few remaining cells were characterized by small size, decreased expression of MHC class I and enhanced apoptosis. By over-expressing human Bcl-2, peripheral naive CD4(+) T cells that lack gamma(c) could be rescued. Bcl-2(+) gamma(c) (-) CD4(+) T cells demonstrated enhanced survival characteristics in vivo and in vitro, and could proliferate normally in vitro in response to antigen. Nevertheless, Bcl-2(+) gamma(c) (-) CD4(+) T cells remained small in size, and this phenotype was not corrected by enforced expression of an activated protein kinase B. We conclude that gamma(c) cytokines (primarily but not exclusively IL-7) provide Bcl-2-dependent as well as Bcl-2-independent signals to maintain the phenotype and homeostasis of the peripheral naive CD4(+) T cell pool.