Activation of PI3K is indispensable for interleukin 7-mediated viability, proliferation, glucose use, and growth of T cell acute lymphoblastic leukemia cells

Intracellular reactive oxygen species are essential for PI3K/Akt/mTOR-dependent IL-7-mediated viability of T-cell acute lymphoblastic leukemia cells

Interleukin-7 (IL-7) activates phosphoinositide 3-kinase/Akt/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway, thereby mediating viability, proliferation and growth of T-cell acute lymphoblastic leukemia (T-ALL) cells. Reactive oxygen species (ROS) can be upregulated by growth factors and are known to regulate proliferation and viability. Here, we show that IL-7 upregulates ROS in T-ALL cells in a manner that is dependent on PI3K/Akt/mTOR pathway activity and that relies on both NADPH oxidase and mitochondrial respiratory chain. Conversely, IL-7-induced activation of PI3K signaling pathway requires mitochondrial respiration and ROS. We have previously shown that IL-7-mediated activation of PI3K pathway drives the upregulation of the glucose transporter Glut1, promoting glucose uptake in T-ALL cells. Using phloretin to inhibit Glut function, we demonstrate that glucose uptake is mandatory for ROS upregulation in IL-7-treated T-ALL cells, suggesting that IL-7 stimulation leads to increased ROS via PI3K pathway activation and consequent upregulation of Glut1 and glucose uptake. Overall, our data reveal the existence of a critical crosstalk between PI3K/Akt signaling pathway and ROS that is essential for IL-7-mediated T-ALL cell survival, and that may constitute a novel target for therapeutic intervention.

Immunotherapeutic effects of IL-7 during a chronic viral infection in mice

Viral persistence during chronic viral infections is associated with a progressive loss of T-cell effector function called functional exhaustion. There is therefore a need to develop immunotherapies to remediate the functional deficits of T cells during these infections. We investigated the immunotherapeutic effects of IL-7 during chronic lymphocytic choriomeningitis virus infection in mice. Our results showed that the effects of IL-7 on T cells depend on the viral load, timing, and duration of treatment during the course of the infection. We document that the effectiveness of IL-7 was constrained by high viral load early in the infection, but treatment for at least 3 weeks during declining viral titers mitigated the programmed contraction of CD8 T cells, markedly enhanced the number of high-quality polyfunctional virus-specific CD8 T cells with a nonexhausted phenotype, and accelerated viral control. Mechanistically, the enhancement of CD8 T-cell responses by IL-7 was associated with increased proliferation and induction of Bcl-2, but not with altered levels of PD-1 or Cbl-b. In summary, our results strongly suggest that IL-7 therapy is a potential strategy to bolster the quality and quantity of T-cell responses in patients with chronic viral infections.

Highly specialized role of Forkhead box O transcription factors in the immune system

Recent studies have highlighted a fundamental role for Forkhead box O (Foxo) transcription factors in immune system homeostasis. Initial reports designed to dissect function of individual Foxo isoforms in the immune system were based on in vitro overexpression systems, and these experiments suggested that Foxo1 and Foxo3 are important for growth factor withdrawal-induced cell death. Moreover, Foxo factors importantly regulate basic cell cycle progression, and so the implication was that these factors may control lymphocyte homeostasis, including a critical function in the termination and resolution of an immune response. Most recently, cell-type-specific loss mutants for the different Foxo isoforms have revealed unexpected and highly specialized functions in the control of multiple cell types in the immune system, but they have yet to reveal a role in cell death or proliferation. This review will focus on the recent advances made in the understanding of the many ways that Foxo factors regulate the immune system, including a discussion of how the specialized versus redundant functions of Foxo transcription factors impact immune system homeostasis.

Metabolism, migration and memory in cytotoxic T cells

The transcriptional and metabolic programmes that control CD8(+) T cells are regulated by a diverse network of serine/threonine kinases. The view has been that the kinases AKT and mammalian target of rapamycin (mTOR) control T cell metabolism. Here, we challenge this paradigm and discuss an alternative role for these kinases in CD8(+) T cells, namely to control cell migration. Another emerging concept is that AMP-activated protein kinase (AMPK) family members control T cell metabolism and determine the effector versus memory fate of CD8(+) T cells. We speculate that one link between metabolism and immunological memory is provided by kinases that originally evolved to control T cell metabolism and have subsequently acquired the ability to control the expression of key transcription factors that regulate CD8(+) T cell effector function and migratory capacity.

Targeting of active mTOR inhibits primary leukemia T cells and synergizes with cytotoxic drugs and signaling inhibitors

OBJECTIVE

Rationally designed therapies aim at the specific disruption of critical signaling pathways activated by malignant transformation or signals from the tumor microenvironment. Because mammalian target of rapamycin (mTOR) is an important signal integrator and a key translational regulator, we evaluated its potential involvement in T-cell acute lymphoblastic leukemia (T-ALL) and whether mTOR blockade synergizes with chemotherapeutic agents or other signaling antagonists to inhibit primary leukemia T cells.

MATERIALS AND METHODS

mTOR signaling status was assessed using biochemical, immunostaining, and molecular regulation studies and functional assays performed to assess the impact of mTOR blockade on T-ALL proliferation, survival, and cell cycle.

RESULTS

We observed that mTOR signaling is highly activated in all T-ALL patients tested, with phosphorylation of its downstream substrates eIF4G and S6 ribosomal protein. mTOR activation was detected in vivo and was further increased in vitro by stimulation with interleukin-7, a potentially leukemogenic cytokine normally produced by the bone marrow microenvironment. In T-ALL cells, mTOR blockade was associated with accumulation of the cyclin-dependent kinase inhibitor p27(kip1), which preferentially adopted a nuclear localization. Functional studies using rapamycin or CCI-779 showed a dominant inhibitory effect of mTOR blockade on interleukin-7-induced proliferation, survival, and cell-cycle progression of T-ALL cells. Furthermore, mTOR blockade markedly potentiated the antileukemia effects of dexamethasone and doxorubicin, and showed highly synergistic interactions in combination with specific inhibitors of phosphatidylinositol 3-kinase/Akt and Janus kinase 3 signaling.

CONCLUSIONS

This study shows activation of mTOR signaling in primary T-ALL cells evolving in the leukemic bone marrow, and supports the inclusion of mTOR antagonists in current therapeutic regimens for this cancer.

Akt requires glucose metabolism to suppress puma expression and prevent apoptosis of leukemic T cells

The PI3K/Akt pathway is activated in stimulated cells and in many cancers to promote glucose metabolism and prevent cell death. Although inhibition of Akt-mediated cell survival may provide a means to eliminate cancer cells, this survival pathway remains incompletely understood. In particular, unlike anti-apoptotic Bcl-2 family proteins that prevent apoptosis independent of glucose, Akt requires glucose metabolism to inhibit cell death. This glucose dependence may occur in part through metabolic regulation of pro-apoptotic Bcl-2 family proteins. Here, we show that activated Akt relies on glycolysis to inhibit induction of Puma, which was uniquely sensitive to metabolic status among pro-apoptotic Bcl-2 family members and was rapidly up-regulated in glucose-deficient conditions. Importantly, preventing Puma expression was critical for Akt-mediated cell survival, as Puma deficiency protected cells from glucose deprivation and Akt could not readily block Puma-mediated apoptosis. In contrast, the pro-apoptotic Bcl-2 family protein Bim was induced normally even when constitutively active Akt was expressed, yet Akt could provide protection from Bim cytotoxicity. Up-regulation of Puma appeared mediated by decreased availability of mitochondrial metabolites rather than glycolysis itself, as alternative mitochondrial fuels could suppress Puma induction and apoptosis upon glucose deprivation. Metabolic regulation of Puma was mediated through combined p53-dependent transcriptional induction and control of Puma protein stability, with Puma degraded in nutrient-replete conditions and long lived in nutrient deficiency. Together, these data identify a key role for Bcl-2 family proteins in Akt-mediated cell survival that may be critical in normal immunity and in cancer through Akt-dependent stimulation of glycolysis to suppress Puma expression.

The impact of PTEN regulation by CK2 on PI3K-dependent signaling and leukemia cell survival

Gene alterations affecting elements of PI3K signaling pathway do not appear to be sufficient to explain the extremely high frequency of PI3K signaling hyperactivation in leukemia. It has been known for long that PTEN phosphorylation at the C-terminal tail, in particular by CK2, contributes to the stabilization and simultaneous inhibition of this critical tumor suppressor. However, direct evidence of the involvement of this mechanism in cancer has been gathered only recently. It is now known that CK2-mediated posttranslational, non-deleting, inactivation of PTEN occurs in T-ALL, CLL and probably other leukemias and solid tumors. To explore this knowledge for therapeutic purposes remains one of the challenges ahead.

IL-7 and lymphopenia

Interleukin-7 (IL-7) is a growth and anti-apoptotic factor for T-lymphocytes, with potential for clinical use in the treatment of immunodeficiencies due to loss of T-cells. Lymphopenia induced by disease (HIV infection, hemodialysis or Idiopathic CD4+ lymphopenia) or by treatment (high dose chemotherapy or depleting antibodies) for cancer or auto-immune diseases results in increased circulating levels of IL-7 which decline with T-cell recovery, however, the mechanism of such response remains to be elucidated. Furthermore, IL-7 is a major player in the regulation of peripheral T-cell homeostasis and as such is an important candidate cytokine for therapy aimed at improving T-cell reconstitution following lymphopenia. Anti- IL-7 is on the other hand proposed to treat conditions where IL-7 may play a more direct role in pathogenesis such as autoimmune disease like Rheumatoid Arthritis, Multiple Sclerosis or Inflammatory Bowel disease.

An overview of IL-7 biology and its use in immunotherapy

Interleukin (IL)-7 is required for T-cell development as well as for the survival and homeostasis of mature T-cells. In the thymus, the double negative (DN) CD4(-) CD8(-) thymocyte progenitor transition into double positive CD4+ CD8+ cells requires Notch and IL-7 signaling. Importantly, IL-7 seems to have a dose effect on T-cell development and, at high doses, DN progression is blocked. Naïve T-cells in the thymus, and after their exit to the periphery, are dependent on IL-7 and TCR signaling for survival. Upon antigen exposure, they proliferate and differentiate into memory T-cells. Because IL-7 intervenes at all stages of T-cell development and maintenance, it has been introduced recently into clinical trials as an immunotherapeutic agent for cancer patients (of particular note, those who had undergone T-cell depleting therapy) in an attempt to increase their population sizes of CD4+ and CD8+ cells overall, and specifically of CD8+ (CD45RA+)CCR7+ and/or CD27+), CD4+ (CD45RA+CD31+), and CD4+ central memory T-cells (CD45RA(-)CCR7+). Interestingly, IL-7 in humans induced a preferential expansion of naïve T-cells, resulting in a broader T-cell repertoire than before the treatment; this effect was independent of age. This suggests that IL-7 therapy could enhance immune responses in patients with limited naïve T-cell numbers as in aged patients or after disease-induced or iatrogenic T-cell depletion. This overview highlights the role of IL-7 on T-cells in mice and humans.

Interleukin-7 promotes the survival of human CD4+ effector/memory T cells by up-regulating Bcl-2 proteins and activating the JAK/STAT signalling pathway

SUMMARY

Interleukin-7 (IL-7) is a crucial cytokine involved in T-cell survival and development but its signalling in human T cells, particularly in effector/memory T cells, is poorly documented. In this study, we found that IL-7 protects human CD4(+) effector/memory T cells from apoptosis induced upon the absence of stimulation and cytokines. We show that IL-7 up-regulates not only Bcl-2 but also Bcl-xL and Mcl-1 as well. Interleukin-7-induced activation of the janus kinase/signal transducer and activator of transcription (JAK/STAT) signalling pathway is sufficient for cell survival and up-regulation of Bcl-2 proteins. In contrast to previous studies with naive T cells, we found that IL-7 is a weak activator of the phosphatidylinositol 3 kinase (PI3K)/AKT (also referred as protein kinase B) pathway and IL-7-mediated cell survival occurs independently from the PI3K/AKT pathway as well as from activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Considering the contribution of both IL-7 and CD4(+) effector/memory T cells to the pathogenesis of autoimmune diseases such as rheumatoid arthritis and colitis, our study suggests that IL-7 can contribute to these diseases by promoting cell survival. A further understanding of the mechanisms of IL-7 signalling in effector/memory T cells associated with autoimmune inflammatory diseases may lead to potential new therapeutic avenues.

Interleukin-7 mediates glucose utilization in lymphocytes through transcriptional regulation of the hexokinase II gene

The cytokine interleukin-7 (IL-7) has essential growth activities that maintain the homeostatic balance of the immune system. Little is known of the mechanism by which IL-7 signaling regulates metabolic activity in support of its vital function in lymphocytes. We observed that IL-7 deprivation caused a rapid decline in the metabolism of glucose that was attributable to loss of intracellular glucose retention. To identify the transducer of the IL-7 metabolic signal, we examined the expression of three important regulators of glucose metabolism, the glucose transporter GLUT-1 and two glycolytic enzymes, hexokinase II (HXKII) and phosphofructokinase-1 (PFK-1), using an IL-7-dependent T-cell line and primary lymphocytes. We found that in lymphocytes deprived of IL-7 loss of glucose uptake correlated with decreased expression of HXKII. Readdition of IL-7 to cytokine-deprived lymphocytes restored the transcription of the HXKII gene within 2 h, but not that of GLUT-1 or PFK-1. IL-7-mediated increases in HXKII, but not GLUT-1 or PFK-1, were also observed at the protein level. Inhibition of HXKII with 3-bromopyruvate or specific small-interfering RNA decreased glucose utilization, as well as ATP levels, in the presence of IL-7, whereas overexpression of HXKII, but not GLUT-1, restored glucose retention and increased ATP levels in the absence of IL-7. We conclude that IL-7 controls glucose utilization by regulating the gene expression of HXKII, suggesting a mechanism by which IL-7 supports bioenergetics that control cell fate decisions in lymphocytes.

IL-7 is essential for homeostatic control of T cell metabolism in vivo

It has become apparent that T cells require growth signals to maintain function and viability necessary to maintain proper immune homeostasis. One means by which cell extrinsic signals may mediate these effects is by sustaining sufficient basal cell metabolism to prevent cell atrophy. The role of metabolism and the specific growth factors essential to maintain metabolism of mature T cells in vivo, however, are poorly defined. As IL-7 is a nonredundant cytokine required for T cell development and survival and can regulate T cell metabolism in vitro, we hypothesized it may be essential to sustain metabolism of resting T cells in vivo. Thus, we generated a model for conditional expression of IL-7R in mature T cells. After IL-7R deletion in a generally normal lymphoid environment, T cells had reduced responses to IL-7, including abrogated signaling and maintenance of antiapoptotic Bcl-2 family expression that corresponded to decreased survival in vitro. T cell survival in vivo was also reduced after loss of the IL-7R in a T cell-intrinsic manner. Additionally, IL-7R deletion resulted in delayed growth and proliferation following stimulation. Importantly, in vivo excision of IL-7R led to T cell atrophy that was characterized by delayed mitogenesis and reduced glycolytic flux. These data are the first to identify an in vivo requirement for a specific cell extrinsic signal to sustain lymphocyte metabolism and suggest that control of glycolysis by IL-7R may contribute to the well-described roles of IL-7 in T cell development, homeostatic proliferation, and survival.

IL-7 induces rapid clathrin-mediated internalization and JAK3-dependent degradation of IL-7Ralpha in T cells

Interleukin-7 (IL-7) is an essential cytokine for T-cell development and homeostasis. It is well established that IL-7 promotes the transcriptional down-regulation of IL7RA, leading to decreased IL-7Ralpha surface expression. However, it is currently unknown whether IL-7 regulates the intracellular trafficking and early turnover of its receptor on ligand binding. Here, we show that, in steady-state T cells, IL-7Ralpha is slowly internalized and degraded while a significant fraction recycles back to the surface. On IL-7 stimulation, there is rapid IL-7Ralpha endocytosis via clathrin-coated pits, decreased receptor recycling, and accelerated lysosome and proteasome-dependent degradation. In accordance, the half-life of IL-7Ralpha decreases from 24 hours to approximately 3 hours after IL-7 treatment. Interestingly, we further demonstrate that clathrin-dependent endocytosis is necessary for efficient IL-7 signal transduction. In turn, pretreatment of T cells with JAK3 or pan-JAK inhibitors suggests that IL-7Ralpha degradation depends on the activation of the IL-7 signaling effector JAK3. Overall, our findings indicate that IL-7 triggers rapid IL-7Ralpha endocytosis, which is required for IL-7-mediated signaling and subsequent receptor degradation.

Metabolism in T cell activation and differentiation

When naïve or memory T cells encounter foreign antigen along with proper co-stimulation they undergo rapid and extensive clonal expansion. In mammals, this type of proliferation is fairly unique to cells of the adaptive immune system and requires a considerable expenditure of energy and cellular resources. While research has often focused on the roles of cytokines, antigenic signals, and co-stimulation in guiding T cell responses, data indicate that, at a fundamental level, it is cellular metabolism that regulates T cell function and differentiation and therefore influences the final outcome of the adaptive immune response. This review will focus on some earlier fundamental observations regarding T cell bioenergetics and its role in regulating cellular function, as well as recent work that suggests that manipulating the immune response by targeting lymphocyte metabolism could prove useful in treatments against infection and cancer.

Grb7 upregulation is a molecular adaptation to HER2 signaling inhibition due to removal of Akt-mediated gene repression

The efficacy of anti-HER2 therapeutics, such as lapatinib and trastuzumab, is limited by primary and acquired resistance. Cellular adaptations that allow breast cancer cell to survive prolonged HER2 inhibition include de-repression of the transcription factor FOXO3A with consequent estrogen receptor activation, and/or increased HER3 signaling. Here, we used low-density arrays, quantitative PCR, and western blotting to determine how HER2 signaling inhibition with lapatinib or PI3K inhibitors affects the expression of genes involved in breast cancer metastatic spread and overall prognosis. Retroviral transgenesis was used to express constitutively active forms of Akt in the HER2⁺ breast cancer cell line SKBR3, and Grb7 in MCF7 cells. Specific gene silencing was obtained by siRNAs transfection. A murine BT474 xenograft cancer model was used to assess the effect of lapatinib on gene expression in vivo. We found that lapatinib induces upregulation of Grb7, an adaptor protein involved in receptor tyrosine kinase signaling and promoting cell survival and cell migration. Grb7 upregulation induced by lapatinib was found to occur in cancer cells in vitro and in vivo. We demonstrate that Grb7 upregulation is recreated by PI3K inhibitors while being prevented by constitutively active Akt. Thus, Grb7 is repressed by PI3K signaling and lapatinib-mediated Akt inhibition is responsible for Grb7 de-repression. Finally, we show that Grb7 removal by RNA-interference reduces breast cancer cell viability and increases the activity of lapatinib. In conclusion, Grb7 upregulation is a potentially adverse consequence of HER2 signaling inhibition. Preventing Grb7 accumulation and/or its interaction with receptor tyrosine kinases may increase the benefit of HER2-targeting drugs.

Dual mechanism of impairment of interleukin-7 (IL-7) responses in human immunodeficiency virus infection: decreased IL-7 binding and abnormal activation of the JAK/STAT5 pathway

Interleukin-7 (IL-7) plays a central role in controlling the homeostasis of both naive and long-term-memory CD4(+) T cells. To better understand how human immunodeficiency virus (HIV) perturbs CD4(+) T-cell homeostasis, we performed a detailed analysis of IL-7R expression, IL-7 binding, and IL-7-dependent early and late signaling events in CD4(+) T-cell subsets from viremic and efficiently treated patients. HIV infection differentially affected the expression of IL-7 receptor (IL-7R) chains, with decreases in IL-7Ralpha/CD127 expression in the memory subset and increases in gammac/CD132 expression in all CD4(+) T cells. This resulted in preserved IL-7 binding in the naive compartment and decreased IL-7 binding in the memory compartment of viremic patients. Accordingly, the percentages of cells signaling in response to IL-7, as measured by pSTAT5 induction, were decreased in memory subsets, including conventional CD4(+) T cells and regulatory T cells. However, the levels of pSTAT5 induction per responding cell, as measured by pSTAT5 fluorescence intensity, were increased within all naive and memory CD4(+) T-cell subsets of viremic patients. The basal level of pSTAT5 was also increased, indicating a constitutive activation of the JAK/STAT5 pathway. IL-7 functional responses, as measured by Bcl-2, CD25, and Foxp3 induction, were impaired in viremic patient CD4(+) T cells, suggesting that chronic activation led to downstream defects in the STAT5 signaling pathway. Thus, HIV infection perturbs IL-7 responses at both receptor binding and signaling steps, which likely compromises the regenerative capacity of the CD4(+) T-cell pool and may contribute to CD4(+) T-cell depletion.

A Flt3- and Ras-dependent pathway primes B cell development by inducing a state of IL-7 responsiveness

Ras plays an important role in B cell development. However, the stage at which Ras governs B cell development remains unclear. Moreover, the upstream receptors and downstream effectors of Ras that govern B cell differentiation remain undefined. Using mice that express a dominant-negative form of Ras, we demonstrate that Ras-mediated signaling plays a critical role in the development of common lymphoid progenitors. This developmental block parallels that found in flt3(-/-) mice, suggesting that Flt3 is an important upstream activator of Ras in early B cell progenitors. Ras inhibition impaired proliferation of common lymphoid progenitors and pre-pro-B cells but not pro-B cells. Rather, Ras promotes STAT5-dependent pro-B cell differentiation by enhancing IL-7Ralpha levels and suppressing socs2 and socs3 expression. Our results suggest a model in which Flt3/Ras-dependent signals play a critical role in B cell development by priming early B cell progenitors for subsequent STAT5-dependent B cell differentiation.

Regulation of PTEN by CK2 and Notch1 in primary T-cell acute lymphoblastic leukemia: rationale for combined use of CK2- and gamma-secretase inhibitors

T-cell acute lymphoblastic leukemia (T-ALL) patients frequently display NOTCH1 activating mutations and Notch can transcriptionally down-regulate the tumor suppressor PTEN. However, it is not clear whether NOTCH1 mutations associate with decreased PTEN expression in primary T-ALL. Here, we compared patients with or without NOTCH1 mutations and report that the former presented higher MYC transcript levels and decreased PTEN mRNA expression. We recently showed that T-ALL cells frequently display CK2-mediated PTEN phosphorylation, resulting in PTEN protein stabilization and concomitant functional inactivation. Accordingly, the T-ALL samples analyzed, irrespectively of their NOTCH1 mutational status, expressed significantly higher PTEN protein levels than normal controls. To evaluate the integrated functional impact of Notch transcriptional and CK2 post-translational inactivation of PTEN, we treated T-ALL cells with both the gamma-secretase inhibitor DAPT and the CK2 inhibitors DRB/TBB. Our data suggest that combined use of gamma-secretase and CK2 inhibitors may have therapeutic potential in T-ALL.

Evidence of STAT5-dependent and -independent routes to CD8 memory formation and a preferential role for IL-7 over IL-15 in STAT5 activation

IL-7 and IL-15 have non-redundant roles in promoting development of memory CD8⁺ T cells. STAT5 is activated by receptors of both cytokines and has also been implicated as a requirement for generation of memory. To determine whether STAT5 activity was required for IL-7 and IL-15-mediated generation of memory, we expressed either wild type (WT) or constitutively active (CA) forms of STAT5a in normal effector cells and then observed their ability to form memory in cytokine replete or deficient hosts. Receptor independent CA-STAT5a significantly enhanced memory formation in the absence of either cytokine but did not mediate complete rescue. Interestingly, WT-STAT5a expression enhanced memory formation in a strictly IL-7 dependent manner, suggesting that IL-7 is a more potent activator of STAT5 than IL-15 in vivo. These data suggest that the non-redundant requirement for IL-7 and IL-15 is mediated through differential activation of both STAT5-dependent and STAT5-independent pathways.

The cunning little vixen: Foxo and the cycle of life and death

A screen for increased longevity in Caenorhabditis elegans has identified a transcription factor that programs cells for resistance to oxidative stress, DNA repair and cell cycle control. The mammalian orthologs of this factor are referred to as 'Foxo' for 'Forkhead box', with the second 'o' in the name denoting a subfamily of four members related by sequence. This family of factors is regulated by growth factors, oxidative stress or nutrient deprivation. Thus, it might readily control the inflammatory conflagration associated with infection-driven lymphocyte proliferation. Surprisingly, the first insights into Foxo-mediated immune regulation have instead revealed direct control of highly specialized genes of the adaptive immune system.

The CD8+ memory T-cell state of readiness is actively maintained and reversible

The ability of the adaptive immune system to respond rapidly and robustly upon repeated antigen exposure is known as immunologic memory, and it is thought that acquisition of memory T-cell function is an irreversible differentiation event. In this study, we report that many phenotypic and functional characteristics of antigen-specific CD8 memory T cells are lost when they are deprived of contact with dendritic cells. Under these circumstances, memory T cells reverted from G(1) to the G(0) cell-cycle state and responded to stimulation like naive T cells, as assessed by proliferation, dependence upon costimulation, and interferon-gamma production, without losing cell surface markers associated with memory. The memory state was maintained by signaling via members of the tumor necrosis factor receptor superfamily, CD27 and 4-1BB. Foxo1, a transcription factor involved in T-cell quiescence, was reduced in memory cells, and stimulation of naive CD8 cells via CD27 caused Foxo1 to be phosphorylated and emigrate from the nucleus in a phosphatidylinositol-3 kinase-dependent manner. Consistent with these results, maintenance of G(1) in vivo was compromised in antigen-specific memory T cells in vesicular stomatitis virus-infected CD27-deficient mice. Therefore, sustaining the functional phenotype of T memory cells requires active signaling and maintenance.

Highly active microbial phosphoantigen induces rapid yet sustained MEK/Erk- and PI-3K/Akt-mediated signal transduction in anti-tumor human gammadelta T-cells

Background

The unique responsiveness of Vγ9Vδ2 T-cells, the major γδ subset of human peripheral blood, to non-peptidic prenyl pyrophosphate antigens constitutes the basis of current γδ T-cell-based cancer immunotherapy strategies. However, the molecular mechanisms responsible for phosphoantigen-mediated activation of human γδ T-cells remain unclear. In particular, previous reports have described a very slow kinetics of activation of T-cell receptor (TCR)-associated signal transduction pathways by isopentenyl pyrophosphate and bromohydrin pyrophosphate, seemingly incompatible with direct binding of these antigens to the Vγ9Vδ2 TCR. Here we have studied the most potent natural phosphoantigen yet identified, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMB-PP), produced by Eubacteria and Protozoa, and examined its γδ T-cell activation and anti-tumor properties.

Methodology/Principal Findings

We have performed a comparative study between HMB-PP and the anti-CD3ε monoclonal antibody OKT3, used as a reference inducer of bona fide TCR signaling, and followed multiple cellular and molecular γδ T-cell activation events. We show that HMB-PP activates MEK/Erk and PI-3K/Akt pathways as rapidly as OKT3, and induces an almost identical transcriptional profile in Vγ9⁺ T-cells. Moreover, MEK/Erk and PI-3K/Akt activities are indispensable for the cellular effects of HMB-PP, including γδ T-cell activation, proliferation and anti-tumor cytotoxicity, which are also abolished upon antibody blockade of the Vγ9⁺ TCR Surprisingly, HMB-PP treatment does not induce down-modulation of surface TCR levels, and thereby sustains γδ T-cell activation upon re-stimulation. This ultimately translates in potent human γδ T-cell anti-tumor function both in vitro and in vivo upon transplantation of human leukemia cells into lymphopenic mice,

Conclusions/Significance

The development of efficient cancer immunotherapy strategies critically depends on our capacity to maximize anti-tumor effector T-cell responses. By characterizing the intracellular mechanisms of HMB-PP-mediated activation of the highly cytotoxic Vγ9⁺ T-cell subset, our data strongly support the usage of this microbial antigen in novel cancer clinical trials.

Transcription factor Foxo3 controls the magnitude of T cell immune responses by modulating the function of dendritic cells

Foxo transcription factors regulate cell cycle progression, survival, and DNA repair pathways. Here, we demonstrate that a deficiency in Foxo3 resulted in increased expansion of T cell populations after viral infection. This exaggerated expansion was not T cell intrinsic. Rather, it was caused by the enhanced capacity of Foxo3-deficient dendritic cells to sustain T cell viability by producing increased amounts of interleukin 6 (IL-6). CTLA-4-mediated stimulation of dendritic cells induced nuclear localization of Foxo3, which in turn inhibited IL-6 and tumor necrosis factor production. Thus, Foxo3 acts to constrain dendritic cell production of key inflammatory cytokines and control T cell survival.

The tumor suppressor function of mitochondria: translation into the clinics

Recently, the inevitable metabolic reprogramming experienced by cancer cells as a result of the onset of cellular proliferation has been added to the list of hallmarks of the cancer cell phenotype. Proliferation is bound to the synchronous fluctuation of cycles of an increased glycolysis concurrent with a restrained oxidative phosphorylation. Mitochondria are key players in the metabolic cycling experienced during proliferation because of their essential roles in the transduction of biological energy and in defining the life-death fate of the cell. These two activities are molecularly and functionally integrated and are both targets of commonly altered cancer genes. Moreover, energetic metabolism of the cancer cell also affords a target to develop new therapies because the activity of mitochondria has an unquestionable tumor suppressor function. In this review, we summarize most of these findings paying special attention to the opportunity that translation of energetic metabolism into the clinics could afford for the management of cancer patients. More specifically, we emphasize the role that mitochondrial beta-F1-ATPase has as a marker for the prognosis of different cancer patients as well as in predicting the tumor response to therapy.

Is cancer a disease of abnormal cellular metabolism? New angles on an old idea

In the 1920s, Otto Warburg observed that tumor cells consumed a large amount of glucose, much more than normal cells, and converted most of it to lactic acid. This phenomenon, now known as the "Warburg effect," is the foundation of one of the earliest general concepts of cancer: that a fundamental disturbance of cellular metabolic activity is at the root of tumor formation and growth. In the ensuing decades, as it became apparent that abnormalities in chromosomes and eventually individual genes caused cancer, the "metabolic" model of cancer lost a good deal of its appeal, even as emerging technologies were exploiting the Warburg effect clinically to detect tumors in vivo. We now know that tumor suppressors and proto-oncogenes influence metabolism, and that mutations in these genes can promote a metabolic phenotype supporting cell growth and proliferation. Thus, these advances have unified aspects of the metabolic and genetic models of cancer, and have stimulated a renewed interest in the role of cellular metabolism in tumorigenesis. This review reappraises the notion that dysregulated cellular metabolism is a key feature of cancer, and discusses some metabolic issues that have escaped scrutiny over the years and now deserve closer attention.

Foxo1 links homing and survival of naive T cells by regulating L-selectin, CCR7 and interleukin 7 receptor

Foxo transcription factors have a conserved role in the adaptation of cells and organisms to nutrient and growth factor availability. Here we show that Foxo1 has a crucial, nonredundant role in T cells. In naive T cells, Foxo1 controlled the expression of the adhesion molecule L-selectin, the chemokine receptor CCR7 and the transcription factor Klf2, and its deletion was sufficient to alter lymphocyte trafficking. Furthermore, Foxo1 deficiency resulted in a severe defect in interleukin 7 receptor alpha-chain (IL-7Ralpha) expression associated with its ability to bind an Il7r enhancer. Finally, growth factor withdrawal induced a Foxo1-dependent increase in Sell, Klf2 and Il7r expression. These data suggest that Foxo1 regulates the homeostasis and life span of naive T cells by sensing growth factor availability and regulating homing and survival signals.

Memory T-lymphocyte survival does not require T-cell receptor expression

The factors controlling memory T (Tm)-cell longevity are still poorly defined, and their identification is pivotal to the design of a vaccine conferring long-term protection against infection. Tm cells have the ability to survive in the absence of the T-cell receptor (TCR)-MHC interaction. This does not exclude a possible role for TCR-intrinsic ligand-independent constitutive signaling in Tm-cell homeostasis. Using a unique TCR tetracycline-inducible expression system, we show that the ablation of TCR expression, which abrogates any possible signaling via the TCR, did not influence the survival and self-renewal of antigen-specific CD8(+) Tm cells even when they have to compete with endogenous T cells for survival factors. Moreover, CD8(+) Tm-cell functionality was not altered even on prolonged maintenance in the absence of TCR-MHC interactions. Furthermore, our results show that a subset of CD4(+) Tm cells can survive in the absence of TCR expression in nonlymphopenic hosts.

IL-7 sustains CD31 expression in human naive CD4+ T cells and preferentially expands the CD31+ subset in a PI3K-dependent manner

The CD31(+) subset of human naive CD4(+) T cells is thought to contain the population of cells that have recently emigrated from the thymus, while their CD31(-) counterparts have been proposed to originate from CD31(+) cells after homeostatic cell division. Naive T-cell maintenance is known to involve homeostatic cytokines such as interleukin-7 (IL-7). It remains to be investigated what role this cytokine has in the homeostasis of naive CD4(+) T-cell subsets defined by CD31 expression. We provide evidence that IL-7 exerts a preferential proliferative effect on CD31(+) naive CD4(+) T cells from adult peripheral blood compared with the CD31(-) subset. IL-7-driven proliferation did not result in loss of CD31 expression, suggesting that CD31(+) naive CD4(+) T cells can undergo cytokine-driven homeostatic proliferation while preserving CD31. Furthermore, IL-7 sustained or increased CD31 expression even in nonproliferating cells. Both proliferation and CD31 maintenance were dependent on the activation of phosphoinositide 3-kinase (PI3K) signaling. Taken together, our data suggest that during adulthood CD31(+) naive CD4(+) T cells are maintained by IL-7 and that IL-7-based therapies may exert a preferential effect on this population.

The IKK-neutralizing compound Bay11 kills supereffector CD8 T cells by altering caspase-dependent activation-induced cell death

Antigen with dual costimulation through CD137 and CD134 induces powerful CD8 T cell responses. These effector T cells are endowed with an intrinsic survival program resulting in their accumulation in vivo, but the signaling components required for survival are unknown. We tested a cadre of pathway inhibitors and found one preclinical compound, Bay11-7082 (Bay11), which prevented survival. Even the gammac cytokine family members IL-2, -4, -7, and -15 could not block death, nor could pretreatment with IL-7. We found that dual costimulation caused loading of phosphorylated IkappaBalpha (p-IkappaBalpha) and high basal levels of NF-kappaB activity in the effector CD8 T cells. Bay11 trumped both events by reducing the presence of p-IkappaBalpha and ensuing NF-kappaB activity. Not all pathways were impacted to this degree, however, as mitogen-mediated ERK phosphorylation was evident during NF-kappaB inhibition. Nonetheless, Bay11 blocked TCR-stimulated cytokine synthesis by rapidly accentuating activation-induced cell death through elicitation of a caspase-independent pathway. Thus, in effector CD8 T cells, Bay11 forces a dominant caspase-independent death signal that cannot be overcome by an intrinsic survival program nor by survival-inducing cytokines. Therefore, Bay11 may be a useful tool to deliberately kill death-resistant effector T cells for therapeutic benefit.

PTEN posttranslational inactivation and hyperactivation of the PI3K/Akt pathway sustain primary T cell leukemia viability

Mutations in the phosphatase and tensin homolog (PTEN) gene leading to PTEN protein deletion and subsequent activation of the PI3K/Akt signaling pathway are common in cancer. Here we show that PTEN inactivation in human T cell acute lymphoblastic leukemia (T-ALL) cells is not always synonymous with PTEN gene lesions and diminished protein expression. Samples taken from patients with T-ALL at the time of diagnosis very frequently showed constitutive hyperactivation of the PI3K/Akt pathway. In contrast to immortalized cell lines, most primary T-ALL cells did not harbor PTEN gene alterations, displayed normal PTEN mRNA levels, and expressed higher PTEN protein levels than normal T cell precursors. However, PTEN overexpression was associated with decreased PTEN lipid phosphatase activity, resulting from casein kinase 2 (CK2) overexpression and hyperactivation. In addition, T-ALL cells had constitutively high levels of ROS, which can also downmodulate PTEN activity. Accordingly, both CK2 inhibitors and ROS scavengers restored PTEN activity and impaired PI3K/Akt signaling in T-ALL cells. Strikingly, inhibition of PI3K and/or CK2 promoted T-ALL cell death without affecting normal T cell precursors. Overall, our data indicate that T-ALL cells inactivate PTEN mostly in a nondeletional, posttranslational manner. Pharmacological manipulation of these mechanisms may open new avenues for T-ALL treatment.

IL-7 activates the phosphatidylinositol 3-kinase/AKT pathway in normal human thymocytes but not normal human B cell precursors

IL-7 signaling culminates in different biological outcomes in distinct lymphoid populations, but knowledge of the biochemical signaling pathways in normal lymphoid populations is incomplete. We analyzed CD127/IL-7Ralpha expression and function in normal (nontransformed) human thymocytes, and human CD19(+) B-lineage cells purified from xenogeneic cord blood stem cell/MS-5 murine stromal cell cultures, to further clarify the role of IL-7 in human B cell development. IL-7 stimulation of CD34(+) immature thymocytes led to phosphorylation (p-) of STAT5, ERK1/2, AKT, and glycogen synthase kinase-3 beta, and increased AKT enzymatic activity. In contrast, IL-7 stimulation of CD34(-) thymocytes (that included CD4(+)/CD8(+) double-positive, and CD4(+) and CD8(+) single-positive cells) only induced p-STAT5. IL-7 stimulation of CD19(+) cells led to robust induction of p-STAT5, but minimal induction of p-ERK1/2 and p-glycogen synthase kinase-3 beta. However, CD19(+) cells expressed endogenous p-ERK1/2, and when rested for several hours following removal from MS-5 underwent de-phosphorylation of ERK1/2. IL-7 stimulation of rested CD19(+) cells resulted in robust induction of p-ERK1/2, but no induction of AKT enzymatic activity. The use of a specific JAK3 antagonist demonstrated that all IL-7 signaling pathways in CD34(+) thymocytes and CD19(+) B-lineage cells were JAK3-dependent. We conclude that human CD34(+) thymocytes and CD19(+) B-lineage cells exhibit similarities in activation of STAT5 and ERK1/2, but differences in activation of the PI3K/AKT pathway. The different induction of PI3K/AKT may at least partially explain the different requirements for IL-7 during human T and B cell development.

The role of activin A and Akt/GSK signaling in ovarian tumor biology

Elevated activin A levels in serum, cyst fluid, and peritoneal fluid of ovarian cancer patients suggest a role for this peptide hormone in disease development. We hypothesize that activin A plays a role in ovarian tumor biology, and analyzed activin-mediated pro-oncogenic signaling in vitro and the expression of activin signaling pathway molecules in vivo. Activin A regulation of Akt and GSK, and the effects of repressing the activities of these molecules (with pharmacological inhibitors) on cellular proliferation were assessed in the cell line, OVCA429. Activin A activated Akt, which phosphorylated GSK, repressing GSK activity in vitro. Activin A stimulated cellular proliferation and repression of GSK augmented activin-regulated proliferation. To validate in vitro observations, immunostaining of the betaA-subunit of activin A and phospho-GSKalpha/beta (Ser9/21) was performed, and the correlation between immunoreactivity levels of these markers and survival was evaluated in benign serous cystadenoma, borderline tumor, and cystadenocarcinoma microarrays. Analysis of tissue microarrays revealed that betaA expression in epithelia did not correlate with survival or malignancy, but expression was elevated in stromal cells from carcinomas when compared with benign tumors. Phospho-GSKalpha/beta (Ser9/21) staining was more intense in mitotically active carcinoma cells and exhibited a polarized localization in benign neoplasms that was absent in carcinomas. Notably, lower phospho-GSKalpha/beta (Ser9/21) immunoreactivity correlated with better survival for carcinoma patients (P=0.046). Our data are consistent with a model in which activin A may mediate ovarian oncogenesis by activating Akt and repressing GSK to stimulate cellular proliferation.

Glucose metabolism in lymphocytes is a regulated process with significant effects on immune cell function and survival

Lymphocytes require glucose uptake and metabolism for normal survival and function. The signals that regulate the expression and localization of glucose transporter 1 (Glut1) to allow glucose uptake in T cells are now beginning to be understood. Resting T cells require extracellular signals, such as cytokines, hormones, and growth factors, or low-level TCR stimulation to take up adequate glucose to maintain housekeeping functions. In the absence of extrinsic signals, resting T cells internalize and degrade Glut1 and cannot maintain viability. Activated T cells have dramatically increased metabolic requirements to support the energy and biosynthetic needs necessary for growth, proliferation, and effector function. In particular, glucose metabolism and aerobic glycolysis fuel this demand. Therefore, activation of T cells causes a large increase in Glut1 expression and surface localization. If glucose uptake is limited, glycolytic flux decreases to a level that no longer sustains viability, and proapoptotic Bcl-2 family members become activated, promoting cell death. However, excessive glucose uptake can promote hyperactive immune responses and possible immune pathology. Tight regulation of glucose uptake is required to maintain immune homeostasis, and understanding of these metabolic pathways may lead to therapeutic strategies to target some forms of cancer or autoimmunity.

Cytosolic sequestration of Prep1 influences early stages of T cell development

Objective

Prep1 and Pbx2 are the main homeodomain DNA-binding proteins of the TALE (three amino acid loop extension) family expressed in the thymus. We previously reported reduced Pbx2 expression and defective thymocyte maturation in Prep1 hypomorphic mice. To further investigate the role of this homeodomain DNA-binding protein in T cell development, we generated transgenic mice expressing the N-terminal fragment of Pbx1 (Pbx1NT) under the control of the Lck proximal promoter.

Principal Findings

Pbx1NT causes Prep1 cytosolic sequestration, abolishes Prep1-dependent DNA-binding activity and results in reduced Pbx2 expression in developing thymocytes. Transgenic thymi reveal increased numbers of CD4⁻ CD8⁻ CD44⁻ (DN3 and DN4) thymocytes, due to a higher frequency of DN2 and DN4 Pbx1NT thymocytes in the S phase. Transgenic thymocytes however do not accumulate at later stages, as revealed by a normal representation of CD4/CD8 double positive and single positive thymocytes, due to a higher rate of apoptotic cell death of DN4 Pbx1NT thymocytes.

Conclusion

The results obtained by genetic (Prep1 hypomorphic) and functional (Pbx1NT transgenic) inactivation of Prep1 support nonredundant roles for this homeodomain protein during different stages of T cell development.

Aberrant signaling in T-cell acute lymphoblastic leukemia: biological and therapeutic implications

T-cell acute lymphoblastic leukemia (T-ALL) is a biologically heterogeneous disease with respect to phenotype, gene expression profile and activation of particular intracellular signaling pathways. Despite very significant improvements, current therapeutic regimens still fail to cure a portion of the patients and frequently implicate the use of aggressive protocols with long-term side effects. In this review, we focused on how deregulation of critical signaling pathways, in particular Notch, PI3K/Akt, MAPK, Jak/STAT and TGF-beta, may contribute to T-ALL. Identifying the alterations that affect intracellular pathways that regulate cell cycle and apoptosis is essential to understanding the biology of this malignancy, to define more effective markers for the correct stratification of patients into appropriate therapeutic regimens and to identify novel targets for the development of specific, less detrimental therapies for T-ALL.

Effects of IL-7 on memory CD8 T cell homeostasis are influenced by the timing of therapy in mice

IL-7 is integral to the generation and maintenance of CD8(+) T cell memory, and insufficient IL-7 is believed to limit survival and the persistence of memory CD8(+) T cells. Here, we show that during the mouse T cell response to lymphocytic choriomeningitis virus, IL-7 enhanced the number of memory CD8(+) T cells when its administration was restricted to the contraction phase of the response. Likewise, IL-7 administration during the contraction phase of the mouse T cell response to vaccinia virus or a DNA vaccine potentiated antigen-specific CD8(+) memory T cell proliferation and function. Qualitatively, CD8(+) T cells from IL-7-treated mice exhibited superior recall responses and improved viral control. IL-7 treatment during the memory phase stimulated a marked increase in the number of memory CD8(+) T cells, but the effects were transient. IL-7 therapy during contraction of the secondary CD8(+) T cell response also expanded the pool of memory CD8(+) T cells. Collectively, our studies show differential effects of IL-7 on memory CD8(+) T cell homeostasis and underscore the importance of the timing of IL-7 therapy to effectively improve CD8(+) T cell memory and protective immunity. These findings may have implications in the clinical use of IL-7 as an immunotherapeutic agent to bolster vaccine-induced CD8(+) T cell memory.

The biology of cancer: metabolic reprogramming fuels cell growth and proliferation

Cell proliferation requires nutrients, energy, and biosynthetic activity to duplicate all macromolecular components during each passage through the cell cycle. It is therefore not surprising that metabolic activities in proliferating cells are fundamentally different from those in nonproliferating cells. This review examines the idea that several core fluxes, including aerobic glycolysis, de novo lipid biosynthesis, and glutamine-dependent anaplerosis, form a stereotyped platform supporting proliferation of diverse cell types. We also consider regulation of these fluxes by cellular mediators of signal transduction and gene expression, including the phosphatidylinositol 3-kinase (PI3K)/Akt/mTOR system, hypoxia-inducible factor 1 (HIF-1), and Myc, during physiologic cell proliferation and tumorigenesis.

T-cell lymphomas in T-cell-specific Pten-deficient mice originate in the thymus

Phosphatase and tensin homolog deleted on chromosome 10 (Pten) is a tumor suppressor protein whose loss of lipid phosphatase activity is associated with lymphomagenesis. We made use of the Cre-loxP system to delete Pten expression in Lck- or CD4-expressing T-lineage cells. Mice initially showed modest thymic hyperplasia and subsequently developed expanding and infiltrating T-cell lymphomas, leading to a premature death within 5 to 23 weeks. Frequently, all thymocyte and peripheral T-cell populations displayed phenotypes characteristic for immature developing thymocyte precursors and shared elevated levels of clonally rearranged T-cell receptor (TCR) beta chains. In concert, CD2, CD5, CD3epsilon and CD44, proteins associated with increased expression and signaling capacity of both the immature pre-TCR and the mature alphabetaTCR, were more abundantly expressed, reflecting a constitutive state of activation. Although most T-cell lymphomas had acquired the capability to infiltrate the periphery, not all populations left the thymus and expanded clonally exclusively in the thymus. In line with this, only transplantation of thymocytes with infiltrating capacity gave rise to T-cell lymphoma in immunodeficient recipients. These results indicate that T-cell-specific Pten deletion during various stages of thymocyte development gives rise to clonally expanding T-cell lymphomas that frequently infiltrate the periphery, but originate in the thymus.

IL-7 promotes Glut1 trafficking and glucose uptake via STAT5-mediated activation of Akt to support T-cell survival

Lymphocyte homeostasis requires coordination of metabolic processes with cellular energetic and biosynthetic demands but mechanisms that regulate T-cell metabolism are uncertain. We show that interleukin-7 (IL-7) is a key regulator of glucose uptake in T lymphocytes. To determine how IL-7 affects glucose uptake, we analyzed IL-7 signaling mechanisms and regulation of the glucose transporter, Glut1. The IL-7 receptor (IL-7R) stimulated glucose uptake and cell-surface localization of Glut1 in a manner that required IL-7R Y449, which promoted rapid signal transducer and activator of transcription 5 (STAT5) activation and a delayed yet sustained activation of Akt. Each pathway was necessary for IL-7 to promote glucose uptake, as Akt1(-/-) T cells or PI3-kinase inhibition and RNAi of STAT5 led to defective glucose uptake in response to IL-7. STAT5 and Akt acted in a linear pathway, with STAT5-mediated transcription leading to Akt activation, which was necessary for STAT5 and IL-7 to promote glucose uptake and prevent cell death. Importantly, IL-7 required glucose uptake to promote cell survival. These data demonstrate that IL-7 promotes glucose uptake via a novel signaling mechanism in which STAT5 transcriptional activity promotes Akt activation to regulate Glut1 trafficking and glucose uptake that is critical for IL-7 to prevent T-cell death and maintain homeostasis.

Pten controls lung morphogenesis, bronchioalveolar stem cells, and onset of lung adenocarcinomas in mice

PTEN is a tumor suppressor gene mutated in many human cancers. We generated a bronchioalveolar epithelium-specific null mutation of Pten in mice [SP-C-rtTA/(tetO)(7)-Cre/Pten(flox/flox) (SOPten(flox/flox)) mice] that was under the control of doxycycline. Ninety percent of SOPten(flox/flox) mice that received doxycycline in utero [SOPten(flox/flox)(E10-16) mice] died of hypoxia soon after birth. Surviving SOPten(flox/flox)(E10-16) mice and mice that received doxycycline postnatally [SOPten(flox/flox)(P21-27) mice] developed spontaneous lung adenocarcinomas. Urethane treatment accelerated number and size of lung tumors developing in SOPten(flox/flox) mice of both ages. Histological and biochemical examinations of the lungs of SOPten(flox/flox)(E10-16) mice revealed hyperplasia of bronchioalveolar epithelial cells and myofibroblast precursors, enlarged alveolar epithelial cells, and impaired production of surfactant proteins. Numbers of bronchioalveolar stem cells (BASCs), putative initiators of lung adenocarcinomas, were increased. Lungs of SOPten(flox/flox)(E10-16) mice showed increased expression of Spry2, which inhibits the maturation of alveolar epithelial cells. Levels of Akt, c-Myc, Bcl-2, and Shh were also elevated in SOPten(flox/flox)(E10-16) and SOPten(flox/flox)(P21-27) lungs. Furthermore, K-ras was frequently mutated in adenocarcinomas observed in SOPten(flox/flox)(P21-27) lungs. These results indicate that Pten is essential for both normal lung morphogenesis and the prevention of lung carcinogenesis, possibly because this tumor suppressor is required for BASC homeostasis.

Proteomics Analysis of Interleukin (IL)-7-induced Signaling Effectors Shows Selective Changes in IL-7Rα449F Knock-in T Cell Progenitors

Interleukin (IL)-7 is a cytokine that plays a central role in the development, survival, and proliferation of T and B cell lymphocytes. Overexpression of IL-7 in mice (transgenic (Tg) IL-7) leads to both increased proliferation of early T and B cell progenitors and T and B cell lymphomas. Genetic evidence indicates that known IL-7 receptor (IL-7R)-dependent proteins, including prosurvival protein BCL-2, may not be solely responsible for the effects of IL-7. Other studies indicate that known IL-7-induced signaling proteins dock to a specific tyrosine (Tyr(449)) residue on the alpha-subunit of the IL-7R. We have previously shown in an IL-7Ralpha(449F) knock-in model that IL-7-induced lymphomas require Tyr(449) phosphorylation and that loss of this phosphorylation confers protection from disease. However, the mechanism by which this lymphoma protection occurs remains unclear. Using this genetic model, we aimed to identify novel prosurvival factors important for IL-7-mediated lymphocyte development and lymphomagenesis. An iTRAQ (isobaric tags for relative and absolute quantitation) proteomics analysis was performed comparing CD4(-)CD8(-) double negative T cell progenitors from mice overexpressing IL-7 (Tg IL-7) (lymphoma-prone) with Tg IL-7 mice with a mutated IL-7 receptor (Tg IL-7/IL-7Ralpha(449F)) (lymphoma-protected). Several proteins involved in survival, proliferation, and apoptosis were found to be differentially expressed between the two samples, and three proteins of particular interest, GIMAP4, BIT1, and FKBP51, were validated by immunoblot analysis.

Interlinking interleukin-7

The signaling processes that maintain the homeostatic proliferation of peripheral T-cells and result in their self-renewal largely remain to be elucidated. Much focus has been placed on the anti-apoptotic function of the cytokine, interleukin-7 (IL-7), during T-cell development. But a more critical role has been ascribed to IL-7 as a mediator of peripheral T-cell maintenance. The biological effects responsive to IL-7 signaling are transduced through only a few well-known pathways. In this review we will focus on the signals transduced by IL-7 and similar cytokines, examining how proliferative signals originate from cytokine receptors, are amplified and eventually alter gene expression. In this regard we will highlight the crosstalk between pathways that promote survival, drive cell cycle progression and most importantly provide the needed energy to sustain these critical cellular activities. Though this review showcases much of what has been learned about IL-7 proliferative signaling, it also reveals the significant gaps in our knowledge about cytokine signaling in the very relevant context of peripheral T-cell homeostasis.

Controlling cell growth and survival through regulated nutrient transporter expression

Although all cells depend upon nutrients they acquire from the extracellular space, surprisingly little is known about how nutrient uptake is regulated in mammalian cells. Most nutrients are brought into cells by means of specific transporter proteins. In yeast, the expression and trafficking of a wide variety of nutrient transporters is controlled by the TOR (target of rapamycin) kinase. Consistent with this, recent studies in mammalian cells have shown that mTOR (mammalian TOR) and the related protein, PI3K (phosphoinositide 3-kinase), play central roles in coupling nutrient transporter expression to the availability of extrinsic trophic and survival signals. In the case of lymphocytes, it has been particularly well established that these extrinsic signals stimulate cell growth and proliferation in part by regulating nutrient transporter expression. The ability of growth factors to control nutrient access may also play an important role in tumour suppression: the non-homoeostatic growth of tumour cells requires that nutrient transporter expression is uncoupled from trophic factor availability. Also supporting a link between nutrient transporter expression levels and oncogenesis, several recent studies demonstrate that nutrient transporter expression drives, rather than simply parallels, cellular metabolism. This review summarizes the evidence that regulated nutrient transporter expression plays a central role in cellular growth control and highlights the implications of these findings for human disease.

Expression of IL-7 receptor alpha is necessary but not sufficient for the formation of memory CD8 T cells during viral infection

During many acute viral and bacterial infections, IL-7 receptor alpha-chain (IL-7Ralpha) is expressed on a subset of effector CD8 T cells that preferentially develop into long-lived memory CD8 T cells. These cells functionally require IL-7Ralpha, but it is unclear whether IL-7Ralpha acts mainly to induce their differentiation into memory cells or to sustain their long-term survival. To examine this question, IL-7Ralpha was constitutively overexpressed on all antigen-specific effector CD8 T cells during viral infection. Constitutive IL-7Ralpha expression had minimal effects on the numbers or function of effector and memory CD8 T cells formed. This indicated that IL-7Ralpha expression is not sufficient to drive memory cell development. In particular, the forced IL-7Ralpha expression did not rescue the killer cell lectin-like receptor G1 (KLRG1)(hi) short-lived effector CD8 T cells from death, showing that the majority of effector CD8 T cells die in an IL-7Ralpha-independent manner. Moreover, we found that, regardless of the ectopic expression of IL-7Ralpha, the KLRG1(hi), but not the KLRG1(lo) effector CD8 T cells, were unable to proliferate well to IL-7, which may be due to increased amounts of p27(kip) in KLRG1(hi) cells. Because IL-7 can destabilize p27(kip), this result suggested that KLRG1(hi) and KLRG1(lo) effector CD8 T cells naturally differ in their ability to transmit IL-7 signals. Altogether, these results reveal that IL-7Ralpha expression is permissive, but not instructive, to the creation of memory CD8 T cells.

ERK1/2 phosphorylation is an independent predictor of complete remission in newly diagnosed adult acute lymphoblastic leukemia

Extracellular signal-regulated kinase-1/2 (ERK1/2) is frequently found constitutively activated (p-ERK1/2) in hematopoietic diseases, suggesting a role in leukemogenesis. The aim of this study was to assess the expression and clinical role of p-ERK1/2 in adult acute lymphoblastic leukemia (ALL). In 131 primary samples from adult de novo ALL patients enrolled in the Gruppo Italiano per le Malattie Ematologiche dell'Adulto (GIMEMA) Leucemia Acute Linfoide (LAL) 2000 protocol and evaluated by flow cytometry, constitutive ERK1/2 activation was found in 34.5% of cases; these results were significantly associated with higher white blood cell (WBC) values (P=.013). In a multivariate analysis, p-ERK1/2 expression was an independent predictor of complete remission achievement (P=.027). Effective approaches toward MEK inhibition need to be explored in order to evaluate whether this may represent a new therapeutic strategy for adult ALL patients.

Convergence of TCR and cytokine signaling leads to FOXO3a phosphorylation and drives the survival of CD4+ central memory T cells

The molecular events involved in the establishment and maintenance of CD4⁺ central memory and effector memory T cells (T_CM and T_EM, respectively) are poorly understood. In this study, we demonstrate that ex vivo isolated T_CM are more resistant to both spontaneous and Fas-induced apoptosis than T_EM and have an increased capacity to proliferate and persist in vitro. Using global gene expression profiling, single cell proteomics, and functional assays, we show that the survival of CD4⁺ T_CM depends, at least in part, on the activation and phosphorylation of signal transducer and activator of transcription 5a (STAT5a) and forkhead box O3a (FOXO3a). T_CM showed a significant increase in the levels of phosphorylation of STAT5a compared with T_EM in response to both IL-2 (P < 0.04) and IL-7 (P < 0.002); the latter is well known for its capacity to enhance T cell survival. Moreover, ex vivo T_CM express higher levels of the transcriptionally inactive phosphorylated forms of FOXO3a and concomitantly lower levels of the proapoptotic FOXO3a target, Bim. Experiments aimed at blocking FOXO3a phosphorylation confirmed the role of this phosphoprotein in protecting T_CM from apoptosis. Our results provide, for the first time in humans, an insight into molecular mechanisms that could be responsible for the longevity and persistence of CD4⁺ T_CM.

Molecular and functional evidence for activity of murine IL-7 on human lymphocytes

Although interleukin-7 (IL-7) is essential for human and murine lymphopoiesis and homeostasis, clear disparities between these species regarding the role of IL-7 during B-cell development suggest that other, subtler differences may exist. One basic unsolved issue of IL-7 biology concerns cross-species activity, because in contrast to the human ortholog, the ability of murine (m)IL-7 to stimulate human cells remains unresolved. Establishing whether two-way cross-species reactivity occurs is fundamental for evaluating the role of IL-7 in chimeric human-mouse models, which are the most versatile tools for studying human lymphoid development and disease in vivo. Here, we show that mIL-7 triggers the same signaling pathways as human (h)IL-7 in human T cells, promoting similar changes in viability, proliferation, size, and immunophenotype, even at low concentrations. This ability is not confined to T cells, because mIL-7 mediates cell growth and protects human B-cell precursors from dexamethasone-induced apoptosis. Importantly, endogenous mIL-7 produced in the mouse thymic microenvironment stimulates human T cells, because their expansion in chimeric fetal thymic organ cultures is inhibited by a mIL-7-specific neutralizing antibody. Our results demonstrate that mIL-7 affects human lymphocytes and indicate that mouse models of human lymphoid development and disease must integrate the biological effects of endogenous IL-7 on human cells.