T cell-specific loss of Pten leads to defects in central and peripheral tolerance

An in vitro system to characterize prostate cancer progression identified signaling required for self-renewal

Mutations in RB and PTEN are linked to castration resistance and poor prognosis in prostate cancer. Identification of genes that are regulated by these tumor suppressors in a context that recapitulates cancer progression may be beneficial for discovering novel therapeutic targets. Although various genetically engineered mice thus far provided tumor models with various pathological stages, they are not ideal for detecting dynamic changes in gene transcription. Additionally, it is difficult to achieve an effect specific to tumor progression via gain of functions of these genes. In this study, we developed an in vitro model to help identify RB- and PTEN-loss signatures during the malignant progression of prostate cancers. Trp53^-/- ; Rb^f/f , Trp53^-/- ; Pten^f/f , and Trp53^-/- ; Rb^f/f ; Pten^f/f prostate epithelial cells were infected with AD-LacZ or AD-Cre. We found that deletion of Rb, Pten or both stimulated prostasphere formation and tumor development in immune-compromised mice. The GO analysis of genes affected by the deletion of Rb or Pten in Trp53^-/- prostate epithelial cells identified a number of genes encoding cytokines, chemokines and extracellular matrix remodeling factors, but only few genes related to cell cycle progression. Two genes (Il-6 and Lox) were further analyzed. Blockade of Il-6 signaling and depletion of Lox significantly attenuated prostasphere formation in 3D culture, and in the case of IL-6, strongly suppressed tumor growth in vivo. These findings suggest that our in vitro model may be instrumental in identifying novel therapeutic targets of prostate cancer progression, and further underscore IL-6 and LOX as promising therapeutic targets. © 2015 Wiley Periodicals, Inc.

Oncogenic PTEN functions and models in T-cell malignancies

PTEN is a protein phosphatase that is crucial to prevent the malignant transformation of T-cells. Although a numerous mechanisms regulate its expression and function, they are often altered in T-cell acute lymphoblastic leukaemias and T-cell lymphomas. As such, PTEN inactivation frequently occurs in these malignancies, where it can be associated with chemotherapy resistance and poor prognosis. Different Pten knockout models recapitulated the development of T-cell leukaemia/lymphoma, demonstrating that PTEN loss is at the center of a complex oncogenic network that sustains and drives tumorigenesis via the activation of multiple signalling pathways. These aspects and their therapeutic implications are discussed in this review.

Elevation of ω-3 Polyunsaturated Fatty Acids Attenuates PTEN-deficiency Induced Endometrial Cancer Development through Regulation of COX-2 and PGE2 Production

Endometrial cancer is one of the most common gynecologic malignancies. Phosphatase and tensin homologue (PTEN)-mutation is frequently identified in endometrial cancer patients. Although high dietary intake of ω-3 polyunsaturated fatty acids (PUFAs) has been associated with reduced risk of endometrial cancer, the underlying mechanisms is still unknown. To this end, we evaluated the impact of ω-3 PUFAs using several endometrial cancer cellular and animal models. While ~27% and 40% of heterozygotic PTEN mutant mice developed endometrial cancer and atypical complex hyperplasia, respectively, none of the PTEN(+/-) mice developed cancer when we overexpressed an mfat-1 transgene, which allowed endogenous production of ω-3 PUFAs. Fish oil-enriched diet or expression of mfat-1 transgene significantly inhibited the growth of xenograft tumor derived from RL95-2 cells bearing a PTEN null mutation. At cellular level, ω-3 PUFAs treatment decreased the viability of RL95-2 cells, AKT phosphorylation, and cyclin D1 expression. These molecular events are primarily mediated through reduction of cyclooxygenase-2 (COX-2) expression and prostaglandin E2 (PGE2) production. Exogenous PGE2 treatment completely blunted the impact of ω-3 PUFAs on endometrial cancer. Thus, we revealed the direct inhibitory effects of ω-3 PUFAs on endometrial cancer development and the underlying mechanisms involving reduction of COX-2 and PGE2.

TCR-induced sumoylation of the kinase PKC-θ controls T cell synapse organization and T cell activation

Sumoylation regulates many cellular processes, but its role in signaling via the T cell antigen receptor (TCR) remains unknown. We found that the kinase PKC-θ was sumoylated upon costimulation with antigen or via the TCR plus the coreceptor CD28, with Lys325 and Lys506 being the main sumoylation sites. We identified the SUMO E3 ligase PIASxβ as a ligase for PKC-θ. Analysis of primary mouse and human T cells revealed that sumoylation of PKC-θ was essential for T cell activation. Desumoylation did not affect the catalytic activity of PKC-θ but inhibited the association of CD28 with PKC-θ and filamin A and impaired the assembly of a mature immunological synapse and central co-accumulation of PKC-θ and CD28. Our findings demonstrate that sumoylation controls TCR-proximal signaling and that sumoylation of PKC-θ is essential for the formation of a mature immunological synapse and T cell activation.

Phosphatase and Tensin Homologue: Novel Regulation by Developmental Signaling

Phosphatase and tensin homologue (PTEN) is a critical cell endogenous inhibitor of phosphoinositide signaling in mammalian cells. PTEN dephosphorylates phosphoinositide trisphosphate (PIP3), and by so doing PTEN has the function of negative regulation of Akt, thereby inhibiting this key intracellular signal transduction pathway. In numerous cell types, PTEN loss-of-function mutations result in unopposed Akt signaling, producing numerous effects on cells. Numerous reports exist regarding mutations in PTEN leading to unregulated Akt and human disease, most notably cancer. However, less is commonly known about nonmutational regulation of PTEN. This review focuses on an emerging literature on the regulation of PTEN at the transcriptional, posttranscriptional, translational, and posttranslational levels. Specifically, a focus is placed on the role developmental signaling pathways play in PTEN regulation; this includes insulin-like growth factor, NOTCH, transforming growth factor, bone morphogenetic protein, wnt, and hedgehog signaling. The regulation of PTEN by developmental mediators affects critical biological processes including neuronal and organ development, stem cell maintenance, cell cycle regulation, inflammation, response to hypoxia, repair and recovery, and cell death and survival. Perturbations of PTEN regulation consequently lead to human diseases such as cancer, chronic inflammatory syndromes, developmental abnormalities, diabetes, and neurodegeneration.

PTEN mediates Notch-dependent stalk cell arrest in angiogenesis

Coordinated activity of VEGF and Notch signals guides the endothelial cell (EC) specification into tip and stalk cells during angiogenesis. Notch activation in stalk cells leads to proliferation arrest via an unknown mechanism. By using gain- and loss-of-function gene-targeting approaches, here we show that PTEN is crucial for blocking stalk cell proliferation downstream of Notch, and this is critical for mouse vessel development. Endothelial deletion of PTEN results in vascular hyperplasia due to a failure to mediate Notch-induced proliferation arrest. Conversely, overexpression of PTEN reduces vascular density and abrogates the increase in EC proliferation induced by Notch blockade. PTEN is a lipid/protein phosphatase that also has nuclear phosphatase-independent functions. We show that both the catalytic and non-catalytic APC/C-Fzr1/Cdh1-mediated activities of PTEN are required for stalk cells' proliferative arrest. These findings define a Notch–PTEN signalling axis as an orchestrator of vessel density and implicate the PTEN-APC/C-Fzr1/Cdh1 hub in angiogenesis.

During the formation of vascular sprouts, Notch activation inhibits proliferation of the stalk ECs via unknown mechanism. Here the authors show that PTEN represents a critical mediator of Notch anti-proliferative response in stalk cells via its phosphatase-dependent and -independent activity.

1,8-Cineole Ameliorates Steatosis of Pten Liver Specific KO Mice via Akt Inactivation

Hepatocyte-specific Phosphatase and tensin homolog (Pten)-knockout (KO) mice exhibit hepatic lesions analogous to non-alcoholic steatohepatitis (NASH). 1,8-cineole is a monoterpene oxide and it has several biological effects including hepatoprotective effects. In this study we revealed that 1,8-cineole ameliorates NASH of Pten KO mice. Pten KO mice were assigned to a control group without any medication or to a 1,8-cineole group injected with 50 mg/kg i.p. twice per week for eight weeks. At eight weeks, livers from each group were processed to measure triglyceride (TG) content, gene expression analysis, western blot analysis, and histological examination including Oil red O staining. 1,8-cineole ameliorated hepatic steatosis in Pten KO mice, revealed by TG content and Oil red O staining. Moreover, 1,8-cineole downregulated collagen 1a1 expression and improved liver fibrosis. Thus, 1,8-cineole has potential as a candidate to treat NASH by inactivating the Akt/PI3-kinase pathway.

The parvalbumin/somatostatin ratio is increased in Pten mutant mice and by human PTEN ASD alleles

Mutations in the phosphatase PTEN are strongly implicated in autism spectrum disorder (ASD). Here, we investigate the function of Pten in cortical GABAergic neurons using conditional mutagenesis in mice. Loss of Pten results in a preferential loss of SST(+) interneurons, which increases the ratio of parvalbumin/somatostatin (PV/SST) interneurons, ectopic PV(+) projections in layer I, and inhibition onto glutamatergic cortical neurons. Pten mutant mice exhibit deficits in social behavior and changes in electroencephalogram (EEG) power. Using medial ganglionic eminence (MGE) transplantation, we test for cell-autonomous functional differences between human PTEN wild-type (WT) and ASD alleles. The PTEN ASD alleles are hypomorphic in regulating cell size and the PV/SST ratio in comparison to WT PTEN. This MGE transplantation/complementation assay is efficient and is generally applicable for functional testing of ASD alleles in vivo.

Signals and pathways controlling regulatory T cells

Induction of specific immune tolerance to grafts remains the sought-after standard following transplantation. Defined by expression of the Foxp3 (forkhead box protein 3) transcription factor, the regulatory T-cell (Treg) lineage has been noted to exert potent immunoregulatory functions that contribute to specific graft tolerance. In this review, we discuss the known signals and pathways which govern Treg development, both in the thymus and in peripheral sites, as well as lineage maintenance and homeostasis. In particular, we highlight the roles of T-cell receptor signaling, CD28 costimulation, and signals through phosphatidyl inositol 3-kinase (PI3K) and related metabolic pathways in multiple aspects of Treg biology.

Akt1 signaling coordinates BMP signaling and β-catenin activity to regulate second heart field progenitor development

Second heart field (SHF) progenitors exhibit continued proliferation and delayed differentiation, which are modulated by FGF4/8/10, BMP and canonical Wnt/β-catenin signaling. PTEN-Akt signaling regulates the stem cell/progenitor cell homeostasis in several systems, such as hematopoietic stem cells, intestinal stem cells and neural progenitor cells. To address whether PTEN-Akt signaling is involved in regulating cardiac progenitors, we deleted Pten in SHF progenitors. Deletion of Pten caused SHF expansion and increased the size of the SHF derivatives, the right ventricle and the outflow tract. Cell proliferation of cardiac progenitors was enhanced, whereas cardiac differentiation was unaffected by Pten deletion. Removal of Akt1 rescued the phenotype and early lethality of Pten deletion mice, suggesting that Akt1 was the key downstream target that was negatively regulated by PTEN in cardiac progenitors. Furthermore, we found that inhibition of FOXO by Akt1 suppressed the expression of the gene encoding the BMP ligand (BMP7), leading to dampened BMP signaling in the hearts of Pten deletion mice. Cardiac activation of Akt also increased the Ser552 phosphorylation of β-catenin, thus enhancing its activity. Reducing β-catenin levels could partially rescue heart defects of Pten deletion mice. We conclude that Akt signaling regulates the cell proliferation of SHF progenitors through coordination of BMP signaling and β-catenin activity.

PTEN is a negative regulator of NK cell cytolytic function

Human NK cells are characterized by their ability to initiate an immediate and direct cytolytic response to virally infected or malignantly transformed cells. Within human peripheral blood, the more mature CD56(dim) NK cell efficiently kills malignant targets at rest, whereas the less mature CD56(bright) NK cells cannot. In this study, we show that resting CD56(bright) NK cells express significantly more phosphatase and tensin homolog deleted on chromosome 10 (PTEN) protein when compared with CD56(dim) NK cells. Consistent with this, forced overexpression of PTEN in NK cells resulted in decreased cytolytic activity, and loss of PTEN in CD56(bright) NK cells resulted in elevated cytolytic activity. Comparable studies in mice showed PTEN overexpression did not alter NK cell development or NK cell-activating and inhibitory receptor expression yet, as in humans, did decrease expression of downstream NK activation targets MAPK and AKT during early cytolysis of tumor target cells. Confocal microscopy revealed that PTEN overexpression disrupts the NK cell's ability to organize immunological synapse components including decreases in actin accumulation, polarization of the microtubule organizing center, and the convergence of cytolytic granules. In summary, our data suggest that PTEN normally works to limit the NK cell's PI3K/AKT and MAPK pathway activation and the consequent mobilization of cytolytic mediators toward the target cell and suggest that PTEN is among the active regulatory components prior to human NK cells transitioning from the noncytolytic CD56(bright) NK cell to the cytolytic CD56(dim) NK cells.

PTEN-inhibition by zinc ions augments interleukin-2-mediated Akt phosphorylation

Free zinc ions (Zn(2+)) participate in several signaling pathways. The aim of the present study was to investigate a potential involvement of Zn(2+) in the PI3K/Akt pathway of interleukin (IL)-2 signaling in T-cells. The IL-2 receptor triggers three major pathways, ERK1/2, JAK/STAT5, and PI3K/Akt. We have previously shown that an IL-2-mediated release of lysosomal Zn(2+) into the cytoplasm activates ERK1/2, but not STAT5. In the present study, Akt phosphorylation in response to IL-2 was abrogated by the Zn(2+) chelator N,N,N',N'-tetrakis-2(pyridyl-methyl)ethylenediamine, and was induced by treatment with Zn(2+) and the ionophore pyrithione. The latter were ineffective in cells that were treated with siRNA against the phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a phosphatase that degrades the lipid second messenger PI(3,4,5)P3, which is produced by PI3K and leads to activation of Akt. Inhibition of recombinant PTEN by Zn(2+)in vitro yielded an IC50 of 0.59 nM. Considering a resting free cytoplasmic Zn(2+) level of 0.2 nM in the T-cell line CTLL-2, this seems ideally suited for dynamic regulation by cellular Zn(2+). Oxidation with H2O2 and supplementation with Zn(2+) led to similar changes in the CD spectrum of PTEN. Moreover, Zn(2+) partially prevented the oxidation of cysteines 71 and 124. Hence, we hypothesize that zinc signals affect the IL-2-dependent PI3K/Akt pathway by inhibiting the negative regulator PTEN through binding with a sub-nanomolar affinity to cysteine residues that are essential for its catalytic activity.

Hedgehog/GLI and PI3K signaling in the initiation and maintenance of chronic lymphocytic leukemia

The initiation and maintenance of a malignant phenotype requires complex and synergistic interactions of multiple oncogenic signals. The Hedgehog (HH)/GLI pathway has been implicated in a variety of cancer entities and targeted pathway inhibition is of therapeutic relevance. Signal cross-talk with other cancer pathways including PI3K/AKT modulates HH/GLI signal strength and its oncogenicity. In this study, we addressed the role of HH/GLI and its putative interaction with the PI3K/AKT cascade in the initiation and maintenance of chronic lymphocytic leukemia (CLL). Using transgenic mouse models, we show that B-cell-specific constitutive activation of HH/GLI signaling either at the level of the HH effector and drug target Smoothened or at the level of the GLI transcription factors does not suffice to initiate a CLL-like phenotype characterized by the accumulation of CD5⁺ B cells in the lymphatic system and peripheral blood. Furthermore, Hh/Gli activation in Pten-deficient B cells with activated Pi3K/Akt signaling failed to enhance the expansion of leukemic CD5⁺ B cells, suggesting that genetic or epigenetic alterations leading to aberrant HH/GLI signaling in B cells do not suffice to elicit a CLL-like phenotype in mice. By contrast, we identify a critical role of GLI and PI3K signaling for the survival of human primary CLL cells. We show that combined targeting of GLI and PI3K/AKT/mTOR signaling can have a synergistic therapeutic effect in cells from a subgroup of CLL patients, thereby providing a basis for the evaluation of future combination therapies targeting HH/GLI and PI3K signaling in this common hematopoietic malignancy.

Control of PI(3) kinase in Treg cells maintains homeostasis and lineage stability

Foxp3(+) regulatory T cells (Treg cells) are required for immunological homeostasis. One notable distinction between conventional T cells (Tconv cells) and Treg cells is differences in the activity of phosphatidylinositol-3-OH kinase (PI(3)K); only Tconv cells downregulate PTEN, the main negative regulator of PI(3)K, upon activation. Here we found that control of PI(3)K in Treg cells was essential for lineage homeostasis and stability. Mice lacking Pten in Treg cells developed an autoimmune-lymphoproliferative disease characterized by excessive T helper type 1 (TH1) responses and B cell activation. Diminished control of PI(3)K activity in Treg cells led to reduced expression of the interleukin-2 (IL-2) receptor α subunit CD25, accumulation of Foxp3(+)CD25(-) cells and, ultimately, loss of expression of the transcription factor Foxp3 in these cells. Collectively, our data demonstrate that control of PI(3)K signaling by PTEN in Treg cells is critical for maintaining their homeostasis, function and stability.

mTOR Links Environmental Signals to T Cell Fate Decisions

T cell fate decisions play an integral role in maintaining the health of organisms under homeostatic and inflammatory conditions. The localized microenvironment in which developing and mature T cells reside provides signals that serve essential functions in shaping these fate decisions. These signals are derived from the immune compartment, including antigens, co-stimulation, and cytokines, and other factors, including growth factors and nutrients. The mechanistic target of rapamycin (mTOR), a vital sensor of signals within the immune microenvironment, is a central regulator of T cell biology. In this review, we discuss how various environmental cues tune mTOR activity in T cells, and summarize how mTOR integrates these signals to influence multiple aspects of T cell biology.

Treg cells require the phosphatase PTEN to restrain TH1 and TFH cell responses

The interplay between effector and regulatory T (T_reg) cells is crucial for adaptive immunity, but how T_reg control diverse effector responses is elusive. We found that the phosphatase PTEN links T_reg stability to repression of T_H1 and T_FH (follicular helper) responses. Depletion of PTEN in T_reg resulted in excessive T_FH and germinal center responses and spontaneous inflammatory disease. These defects are considerably blocked by deletion of Interferon-γ, indicating coordinated control of T_H1 and T_FH responses. Mechanistically, PTEN maintains T_reg stability and metabolic balance between glycolysis and mitochondrial fitness. Moreover, PTEN deficiency upregulates mTORC2-Akt activity, and loss of this activity restores PTEN-deficient T_reg function. Our studies establish a PTEN-mTORC2 axis that maintains T_reg stability and coordinates T_reg-mediated control of effector responses.

Modeling cancer using genetically engineered mice

Genetically engineered mouse (GEM) models have proven to be a powerful tool to study tumorigenesis. The mouse is the preferred complex organism used in cancer studies due to the high number and versatility of genetic tools available for this species. GEM models can mimic point mutations, gene amplifications, short and large deletions, translocations, etc.; thus, most of the genetic aberrations found in human tumors can be modeled in GEM, making GEM models a very attractive system. Furthermore, recent developments in mouse genetics may facilitate the generation of GEM models with increased mutational complexity, therefore resembling human tumors better. Within this review, we will discuss the different possibilities of modeling tumorigenesis using GEM and the future developments within the field.

Suppression of T-cell lymphomagenesis in mice requires PTEN phosphatase activity

Mice with T-cell-specific loss of the tumor suppressor gene PTEN early in T-cell ontogeny develop thymic lymphomas that invariably harbor a reciprocal translocation involving the T-cell receptor α/δ locus and c-myc, t(14;15). In addition to its known function as a lipid phosphatase opposing PI3K signaling, PTEN has also been described as playing a prominent role in promoting genomic stability. As a result, it has been uncertain which one(s) of these 2 separable features were required to block the development of lymphoma. Here, using a conditional model in which T cells selectively express 1 phosphatase-dead PTEN mutant (C124S) and maintain 1 null allele, we show that PTEN phosphatase activity is required for preventing the emergence of a malignant T-cell population harboring t(14;15), thus constituting a critical function of PTEN in preventing lymphomagenesis.

A microRNA upregulated in asthma airway T cells promotes TH2 cytokine production

MicroRNAs (miRNAs) exert powerful effects on immunological function by tuning networks of target genes that orchestrate cell activity. We sought to identify miRNAs and miRNA-regulated pathways that control the type 2 helper T cell (TH2 cell) responses that drive pathogenic inflammation in asthma. Profiling miRNA expression in human airway-infiltrating T cells revealed elevated expression of the miRNA miR-19a in asthma. Modulating miR-19 activity altered TH2 cytokine production in both human and mouse T cells, and TH2 cell responses were markedly impaired in cells lacking the entire miR-17∼92 cluster. miR-19 promoted TH2 cytokine production and amplified inflammatory signaling by direct targeting of the inositol phosphatase PTEN, the signaling inhibitor SOCS1 and the deubiquitinase A20. Thus, upregulation of miR-19a in asthma may be an indicator and a cause of increased TH2 cytokine production in the airways.

PTEN knockdown alters dendritic spine/protrusion morphology, not density

Mutations in phosphatase and tensin homolog deleted on chromosome 10 (PTEN) are implicated in neuropsychiatric disorders including autism. Previous studies report that PTEN knockdown in neurons in vivo leads to increased spine density and synaptic activity. To better characterize synaptic changes in neurons lacking PTEN, we examined the effects of shRNA knockdown of PTEN in basolateral amygdala neurons on synaptic spine density and morphology by using fluorescent dye confocal imaging. Contrary to previous studies in the dentate gyrus, we find that knockdown of PTEN in basolateral amygdala leads to a significant decrease in total spine density in distal dendrites. Curiously, this decreased spine density is associated with increased miniature excitatory postsynaptic current frequency and amplitude, suggesting an increase in number and function of mature spines. These seemingly contradictory findings were reconciled by spine morphology analysis demonstrating increased mushroom spine density and size with correspondingly decreased thin protrusion density at more distal segments. The same analysis of PTEN conditional deletion in the dentate gyrus demonstrated that loss of PTEN does not significantly alter total density of dendritic protrusions in the dentate gyrus, but does decrease thin protrusion density and increases density of more mature mushroom spines. These findings suggest that, contrary to previous reports, PTEN knockdown may not induce de novo spinogenesis, but instead may increase synaptic activity by inducing morphological and functional maturation of spines. Furthermore, behavioral analysis of basolateral amygdala PTEN knockdown suggests that these changes limited only to the basolateral amygdala complex may not be sufficient to induce increased anxiety-related behaviors.

Ghrelin relieves cancer cachexia associated with the development of lung adenocarcinoma in mice

Cancer cachexia is a multifactorial, critical illness syndrome characterized by an ongoing loss of skeletal muscle and adipose tissue. The reductions in body weight and skeletal muscle mass are important prognostic indicators for cancer patients that are refractory to current therapies. Ghrelin, an endogenous ligand for the growth hormone secretagogue receptor, is produced in the stomach, stimulates food intake and growth hormone secretion, suppresses inflammation, and prevents muscle catabolism. We investigated the pharmacological potential of ghrelin in the treatment of cancer cachexia by using urethane-treated, bronchioalveolar epithelium-specific Pten-deficient mice that developed lung adenocarcinomas. Ghrelin or phosphate-buffered saline was given to mice daily for four weeks beginning at five months after urethane injection, which corresponded to the time point of lung adenocarcinoma formation. Ghrelin inhibited the inductions of C-reactive protein, tumor necrosis factor-α, interleukin-1β, and interleukin-6, mitigated the reduction of food intake and fat mass, and consequently ameliorated body weight loss in the mouse model of lung adenocarcinoma. We also demonstrated that skeletal muscle mass and muscle contraction force in both fast-twitch muscle and slow-twitch muscle were retained in ghrelin-treated mice in conjunction with an upregulation of local insulin-like growth factor 1/Akt signaling. In addition, ghrelin administration reduced the expressions of phosphorylated-p38 mitogen-activated protein kinase, phosphorylated-nuclear factor-kappa B, Forkhead box protein O1, muscle RING-finger protein-1, and F-Box protein 32 in the lysates of skeletal muscle in the tumor-bearing state. Our results indicate that ghrelin administration exerts a protective effect against cancer cachexia by ameliorating skeletal muscle wasting and regulating systemic inflammation.

The PTEN/PI3K/AKT Pathway in vivo, Cancer Mouse Models

When PI3K (phosphatidylinositol-3 kinase) is activated by receptor tyrosine kinases, it phosphorylates PIP2 to generate PIP3 and activates the signaling pathway. Phosphatase and tensin homolog deleted on chromosome 10 dephosphorylates PIP3 to PIP2, and thus, negatively regulates the pathway. AKT (v-akt murine thymoma viral oncogene homolog; protein kinase B) is activated downstream of PIP3 and mediates physiological processes. Furthermore, substantial crosstalk exists with other signaling networks at all levels of the PI3K pathway. Because of its diverse array, gene mutations, and amplifications and also as a consequence of its central role in several signal transduction pathways, the PI3K-dependent axis is frequently activated in many tumors and is an attractive therapeutic target. The preclinical testing and analysis of these novel therapies requires appropriate and well-tailored systems. Mouse models in which this pathway has been genetically modified have been essential in understanding the role that this pathway plays in the tumorigenesis process. Here, we review cancer mouse models in which the PI3K/AKT pathway has been genetically modified.

Macrophage PTEN regulates expression and secretion of arginase I modulating innate and adaptive immune responses

The activation of innate immune cells triggers numerous intracellular signaling pathways, which require tight control to mount an adequate immune response. The PI3K signaling pathway is intricately involved in innate immunity, and its activation dampens the expression and release of proinflammatory cytokines in myeloid cells. These signaling processes are strictly regulated by the PI3K antagonist, the lipid phosphatase, PTEN, a known tumor suppressor. Importantly, PTEN is responsible for the elevated production of cytokines such as IL-6 in response to TLR agonists, and deletion of PTEN results in diminished inflammatory responses. However, the mechanisms by which PI3K negatively regulates TLR signaling are only partially resolved. We observed that Arginase I expression and secretion were markedly induced by PTEN deletion, suggesting PTEN(-/-) macrophages were alternatively activated. This was mediated by increased expression and activation of the transcription factors C/EBPβ and STAT3. Genetic and pharmacologic experimental approaches in vitro, as well as in vivo autoimmunity models, provide convincing evidence that PI3K/PTEN-regulated extracellular Arginase I acts as a paracrine regulator of inflammation and immunity.

Androgen deprivation induces phenotypic plasticity and promotes resistance to molecular targeted therapy in a PTEN-deficient mouse model of prostate cancer

The transformation to castration-resistant prostate cancer drives cell plasticity that promotes intra-tumor heterogeneity and contributes to therapeutic resistance.

Castration-resistant prostate cancer is an incurable heterogeneous disease that is characterized by a complex multistep process involving different cellular and biochemical changes brought on by genetic and epigenetic alterations. These changes lead to the activation or overexpression of key survival pathways that also serve as potential therapeutic targets. Despite promising preclinical results, molecular targeted therapies aimed at such signaling pathways have so far been dismal. In the present study, we used a PTEN-deficient mouse model of prostate cancer to show that plasticity in castration-resistant tumors promotes therapeutic escape. Unlike castration-naïve tumors which depend on androgen receptor and PI3K/AKT signal activation for growth and survival, castration-resistant tumors undergo phenotypic plasticity leading to increased intratumoral heterogeneity. These tumors attain highly heterogeneous phenotypes that are characterized by cancer cells relying on alternate signal transduction pathways for growth and survival, such as mitogen-activated protein kinase and janus kinase/signal transducer and activator of transcription, and losing their dependence on PI3K signaling. These features thus enabled castration-resistant tumors to become insensitive to the therapeutic effects of PI3K/AKT targeted therapy. Overall, our findings provide evidence that androgen deprivation drives phenotypic plasticity in prostate cancer cells and implicate it as a crucial contributor to therapeutic resistance in castration-resistant prostate cancer. Therefore, incorporating intratumoral heterogeneity in a dynamic tumor model as a part of preclinical efficacy determination could improve prediction for response and provide better rationale for the development of more effective therapies.

Unraveling natalizumab effects on deregulated miR-17 expression in CD4+ T cells of patients with relapsing-remitting multiple sclerosis

MicroRNAs (miRNAs) are a family of noncoding RNAs that play critical roles in the posttranscriptional regulation of gene expression. Accumulating evidence supports their involvement in the pathogenesis of multiple sclerosis (MS). Here, we compare miR-17 expressions in CD4+ T cells from relapsing-remitting (RR) MS patients treated with natalizumab versus untreated patients. miR-17 was downregulated under natalizumab treatment and upregulated during relapse, therefore supporting a possible role of miR-17 in MS immunopathogenesis. Downregulation of miR-17 was associated with upregulation of PTEN, BIM, E2F1, and p21 target genes. In vitro miR-17 inhibition was associated with upregulation of the same targets and resulted in impaired CD4+ T cell activation and proliferation. We further describe deregulated TGFBR2 expression in untreated patients versus healthy volunteers (HVs) and confirm in vitro the link between miR-17 and TGFBR2 expressions. These findings support an effect of natalizumab on expression of specific miRNA and subsequent expression of genes involved in proliferation and control of the cell cycle.

PTEN in smooth muscle cells is essential for colonic immune homeostasis

Colonic immune homeostasis is essential for normal gastrointestinal tract functioning. In this study, we report that specific gene targeting of phosphatase and tensin homolog (PTEN) in smooth muscle cells caused age-related colonic lymphoid hyperplasia followed by global immune activation in mice. Beginning at 5 weeks of age, these mutant mice displayed massive neutrophil infiltration in the colonic lamina propria. The gene expression levels of pro-inflammatory cytokines and chemokines, including those code for monocyte chemotactic protein-1 (Mcp-1), stromal cell-derived factor 1α (Sdf-1α), and chemokine (C-C motif) ligand 28 (Ccl-28), were upregulated in the colon. Accordingly, permeability and proliferation of the colonic epithelium was compromised. These abnormalities were alleviated to a great extent when the mutants were crossed with Akt1-null mice, indicating that the pathogenesis was mediated by Akt1 signaling. Our results suggest that in smooth muscle cells, PTEN is crucial for maintaining colonic immune homeostasis.

PTEN action in leukaemia dictated by the tissue microenvironment

PTEN encodes a lipid phosphatase that is underexpressed in many cancers owing to deletions, mutations or gene silencing^1–3. PTEN dephosphorylates phosphatidylinositol 3,4,5-triphosphate (PIP₃), thereby opposing the activity of class I phosphatidylinositol 3-kinases (PI3Ks) that mediate growth and survival factors signaling through PI3K effectors such as AKT and mTOR². To determine whether continued PTEN inactivation is required to maintain malignancy, we generated an RNAi-based transgenic mouse model that allows tetracycline-dependent regulation of PTEN in a time- and tissue-specific manner. Postnatal PTEN knockdown in the hematopoietic compartment produced highly disseminated T-cell leukemia (T-ALL). Surprisingly, reactivation of PTEN mainly reduced T-ALL dissemination but had little effect on tumor load in hematopoietic organs. Leukemia infiltration into the intestine was dependent on CCR9 G-protein coupled receptor (GPCR) signaling, which was amplified by PTEN loss. Our results suggest that in the absence of PTEN, GPCRs may play an unanticipated role in driving tumor growth and invasion in an unsupportive environment. They further reveal that the role of PTEN loss in tumor maintenance is not invariant and can be influenced by the tissue microenvironment, thereby producing a form of intratumoral heterogeneity that is independent of cancer genotype.

Premalignant PTEN-deficient thymocytes activate microRNAs miR-146a and miR-146b as a cellular defense against malignant transformation

Cancer develops by a multistep process during which cells acquire characteristics that allow them to evade apoptosis and proliferate unchecked. Sequential acquisition of genetic alterations drives this process but also causes cellular stress, frequently prompting cells to enter a premalignant period during which they mount a defense against transformation. T cell-specific deletion of the tumor suppressor PTEN in mice induces premalignancy in the thymus and development of CD4(+) T-cell lymphomas in the periphery. Here we sought to identify factors mediating the cellular defense against transformation during the premalignant period. We identified several microRNAs upregulated specifically in premalignant thymocytes, including miR-146a, miR-146b, and the miR-183/96/182 cluster. CD4-driven T cell-specific transgenic overexpression of mir-146a and mir-146b significantly delayed PTEN-deficient lymphomagenesis and delayed c-myc oncogene induction, a key driver of transformation in PTEN-deficient T-cell malignancies. We found that miR-146a and miR-146b targeting of Traf6 attenuates TCR signaling in the thymus and inhibits downstream NF-κB-dependent induction of c-myc. Additionally, c-myc repression in mature CD4 T cells by miR-146b impaired TCR-mediated proliferation. Hence, we have identified 2 miRNAs that are upregulated as part of the cellular response against transformation that, when overrepresented, can effectively inhibit progression to malignancy in the context of PTEN deficiency.

HF, Paschal BM, Wotton D. Prostate cancer induced by loss of Apc is restrained by TGFβ signaling

Recent work with mouse models of prostate cancer (CaP) has shown that inactivation of TGFβ signaling in prostate epithelium can cooperate with deletion of the Pten tumor suppressor to drive locally aggressive cancer and metastatic disease. Here, we show that inactivating the TGFβ pathway by deleting the gene encoding the TGFβ type II receptor (Tgfbr2) in combination with a deletion of the Apc tumor suppressor gene specifically in mouse prostate epithelium, results in the rapid onset of invasive CaP. Micro-metastases were observed in the lymph nodes and lungs of a proportion of the double mutant mice, whereas no metastases were observed in Apc single mutant mice. Prostate-specific Apc;Tgfbr2 mutants had a lower frequency of metastasis and survived significantly longer than Pten;Tgfbr2 double mutants. However, all Apc;Tgfbr2 mutants developed invasive cancer by 30 weeks of age, whereas invasive cancer was rarely observed in Apc single mutant animals, even by one year of age. Further comparison of the Pten and Apc models of CaP revealed additional differences, including adenosquamous carcinoma in the Apc;Tgfbr2 mutants that was not seen in the Pten model, and a lack of robust induction of the TGFβ pathway in Apc null prostate. In addition to causing high-grade prostate intra-epithelial neoplasia (HGPIN), deletion of either Pten or Apc induced senescence in affected prostate ducts, and this restraint was overcome by loss of Tgfbr2. In summary, this work demonstrates that TGFβ signaling restrains the progression of CaP induced by different tumor suppressor mutations, suggesting that TGFβ signaling exerts a general tumor suppressive effect in prostate.

PTEN loss and KRAS activation leads to the formation of serrated adenomas and metastatic carcinoma in the mouse intestine

Mutation or loss of the genes PTEN and KRAS have been implicated in human colorectal cancer (CRC), and have been shown to co-occur despite both playing a role in the PI3' kinase (PI3'K) pathway. We investigated the role of these genes in intestinal tumour progression in vivo, using genetically engineered mouse models, with the aim of generating more representative models of human CRC. Intestinal-specific deletion of Pten and activation of an oncogenic allele of Kras was induced in wild-type (WT) mice and mice with a predisposition to adenoma development (Apc(fl/+) ). The animals were euthanized when they became symptomatic of a high tumour burden. Histopathological examination of the tissues was carried out, and immunohistochemistry used to characterize signalling pathway activation. Mutation of Pten and Kras resulted in a significant life-span reduction of mice predisposed to adenomas. Invasive adenocarcinoma was observed in these animals, with evidence of activation of the PI3'K pathway but no metastasis. However, mutation of Pten and Kras in WT animals not predisposed to adenomas led to perturbed homeostasis of the intestinal epithelium and the development of hyperplastic polyps, dysplastic sessile serrated adenomas and metastasizing adenocarcinomas with serrated features. These studies demonstrate synergism between Pten and Kras mutations in intestinal tumour progression, in an autochthonous and immunocompetent murine model, with potential application to preclinical drug testing. In particular, they show that Pten and Kras mutations alone predispose mice to the spectrum of serrated lesions that reflect the serrated pathway of CRC progression in humans.

Cadmium selectively induces MIP-2 and COX-2 through PTEN-mediated Akt activation in RAW264.7 cells

Increasing evidence demonstrates that cadmium (Cd) induces inflammation, but its mechanisms remain obscure. The present study showed that treatment with CdCl₂ selectively upregulates macrophage inflammatory protein (MIP)-2 and cyclooxygenase (COX)-2 in RAW264.7 cells. Concomitantly, Cd²⁺ markedly elevated the level of phosphorylated Akt in dose- and time-dependent manners. LY294002, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K), blocked Cd²⁺-evoked Akt phosphorylation. Correspondingly, LY294002 significantly repressed Cd²⁺-induced upregulation of MIP-2 and COX-2 in RAW264.7 cells. Further experiments showed that treatment with Cd²⁺ significantly reduced the level of PTEN protein in RAW264.7 cells. MG132, a specific proteasome inhibitor, blocked Cd²⁺-induced reduction in PTEN protein as well as Akt phosphorylation, implicating the involvement of proteasome-mediated PTEN degradation. Of interest, Cd²⁺-induced degradation of PTEN protein appears to be associated with PTEN ubiquitination. N-acetylcysteine, a glutathione (GSH) precursor, blocked Cd²⁺-evoked PTEN degradation as well as Akt phosphorylation. By contrast, L-buthionine-S,R-sulfoximine, an inhibitor of cellular GSH synthesis, exacerbated Cd²⁺-induced PTEN degradation and Akt phosphorylation. Alpha-phenyl-N-tert-butylnitrone and vitamin C, two antioxidants, did not prevent from Cd²⁺-induced PTEN degradation and Akt phosphorylation. In conclusion, Cd²⁺ selectively induces MIP-2 and COX-2 through PTEN-mediated PI3K/Akt activation. Cellular GSH depletion mediates Cd²⁺-induced PTEN degradation and subsequent PI3K/Akt activation in macrophages.

Dominant-activating germline mutations in the gene encoding the PI(3)K catalytic subunit p110δ result in T cell senescence and human immunodeficiency

The p110δ subunit of phosphatidylinositol-3-OH kinase (PI(3)K) is selectively expressed in leukocytes and is critical for lymphocyte biology. Here we report fourteen patients from seven families who were heterozygous for three different germline, gain-of-function mutations in PIK3CD (which encodes p110δ). These patients presented with sinopulmonary infections, lymphadenopathy, nodular lymphoid hyperplasia and viremia due to cytomegalovirus (CMV) and/or Epstein-Barr virus (EBV). Strikingly, they had a substantial deficiency in naive T cells but an over-representation of senescent effector T cells. In vitro, T cells from patients exhibited increased phosphorylation of the kinase Akt and hyperactivation of the metabolic checkpoint kinase mTOR, enhanced glucose uptake and terminal effector differentiation. Notably, treatment with rapamycin to inhibit mTOR activity in vivo partially restored the abundance of naive T cells, largely 'rescued' the in vitro T cell defects and improved the clinical course.

Premature terminal differentiation protects from deregulated lymphocyte activation by ITK-Syk

The development of hematopoietic neoplasms is often associated with mutations, altered gene expression or chromosomal translocations. Recently, the t(5, 9)(q33;q22) translocation was found in a subset of peripheral T cell lymphomas and was shown to result in an IL-2-inducible kinase-spleen tyrosine kinase (ITK-Syk) fusion transcript. In this study, we show that T cell-specific expression of the ITK-Syk oncogene in mice leads to an early onset and aggressive polyclonal T cell lymphoproliferation with concomitant B cell expansion and systemic inflammation by 7-9 wk of age. Because this phenotype is strikingly different from previous work showing that ITK-Syk expression causes clonal T cell lymphoma by 20-27 wk of age, we investigated the underlying molecular mechanism in more detail. We show that the reason for the severe phenotype is the lack of B-lymphocyte-induced maturation protein-1 (Blimp-1) induction by low ITK-Syk expression. In contrast, high ITK-Syk oncogene expression induces terminal T cell differentiation in the thymus by activating Blimp-1, thereby leading to elimination of oncogene-expressing cells early in development. Our data suggest that terminal differentiation is an important mechanism to prevent oncogene-expressing cells from malignant transformation, as high ITK-Syk oncogene activity induces cell elimination. Accordingly, for transformation, a specific amount of oncogene is required, or alternatively, the induction of terminal differentiation is defective.

PTEN, Longevity and Age-Related Diseases

Since the discovery of PTEN, this protein has been shown to be an effective suppressor of cancer and a contributor to longevity. This report will review, in depth, the associations between PTEN and other molecules, its mutations and regulations in order to present how PTEN can be used to increase longevity. This report will collect recent research of PTEN and use this to discuss PTEN’s role in caloric restriction, antioxidative defense of DNA-damage and the role it plays in suppressing tumors. The report will also discuss that variety of ways that PTEN can be compromised, through mutations, complete loss of alleles and its main antagonist, the PI3K/AKT pathway.

Activation of PI3K/Akt/mTOR signaling pathway triggered by PTEN downregulation in the pathogenesis of Crohn's disease

OBJECTIVE

We aimed to investigate the role of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway and its negative feedback factor, phosphatase and tensin homolog (PTEN), in the pathogenesis of Crohn's disease (CD).

METHODS

Peripheral blood was collected from patients with CD and healthy controls while colon tissue samples were collected from CD patients and those complaining of constipation but with normal endoscopic results. CD4⁺ T-cells were isolated from peripheral blood. The expression of PI3K/Akt/mTOR pathway components and PTEN was evaluated in the peripheral CD4⁺ T-cells using polymerase chain reaction and Western blot, and in intestinal mucosal lymphocytes using immunohistochemistry.

RESULTS

mRNA expressions of PI3K, Akt, mTOR, 4E-binding protein 1 (4E-BP1) and phosphate-ribosomal protein S6 kinase (p70S6K) in peripheral CD4⁺ T-cells were upregulated in CD patients compared with healthy controls . However, the differences were not significant (P > 0.05). Western blot showed that the ratios of phospho-Akt: Akt, phosphorylated-4E-BP1: 4E-BP1 and phospho-p70S6K: p70S6K in peripheral CD4⁺ T-cells were higher in CD patients (P < 0.05). The composite staining score of phospho-Akt and phospho-mTOR in intestinal mucosal lymphocytes also increased in patients with CD compared with those with constipation. Both PTEN mRNA and protein expressions in either peripheral CD4⁺ T-cells or mucosal lymphocytes were lower in patients with CD than in the healthy controls and those with constipation.

CONCLUSIONS

The PI3K/Akt/mTOR signaling pathway was activated in CD. The activation of the PI3K/Akt/mTOR pathway caused by PTEN downregulation may be involved in the pathogenesis of CD.

AKT activation promotes PTEN hamartoma tumor syndrome-associated cataract development

Mutations in the human phosphatase and tensin homolog (PTEN) gene cause PTEN hamartoma tumor syndrome (PHTS), which includes cataract development among its diverse clinical pathologies. Currently, it is not known whether cataract formation in PHTS patients is secondary to other systemic problems, or the result of the loss of a critical function of PTEN within the lens. We generated a mouse line with a lens-specific deletion of Pten (PTEN KO) and identified a regulatory function for PTEN in lens ion transport. Specific loss of PTEN in the lens resulted in cataract. PTEN KO lenses exhibited a progressive age-related increase in intracellular hydrostatic pressure, along with, increased intracellular sodium concentrations, and reduced Na+/K+-ATPase activity. Collectively, these defects lead to lens swelling, opacities and ultimately organ rupture. Activation of AKT was highly elevated in PTEN KO lenses compared to WT mice. Additionally, pharmacological inhibition of AKT restored normal Na+/K+-ATPase activity in primary cultured lens cells and reduced lens pressure in intact lenses from PTEN KO animals. These findings identify a direct role for PTEN in the regulation of lens ion transport through an AKT-dependent modulation of Na+/K+-ATPase activity, and provide a new animal model to investigate cataract development in PHTS patients.

Role of the PTEN signaling pathway in autism spectrum disorder

Autism is an etiologically heterogeneous group of neurodevelopmental disorders, diagnosed mostly by the clinical behavioral phenotypes. The concept that the tumor-related gene PTEN plays a critical role in autism spectrum disorder has emerged over the last decade. In this review, we focus on the essential role of the PTEN signaling pathway in neuronal differentiation and the formation of neural circuitry, as well as genetic mouse models with Pten manipulations. Particularly, accumulated data suggest that the effect of PTEN on neural stem-cell development contributes significantly to the pathophysiology of autism spectrum disorders.

Evolutionary etiology of high-grade astrocytomas

Glioblastoma (GBM), the most common brain malignancy, remains fatal with no effective treatment. Analyses of common aberrations in GBM suggest major regulatory pathways associated with disease etiology. However, 90% of GBMs are diagnosed at an advanced stage (primary GBMs), providing no access to early disease stages for assessing disease progression events. As such, both understanding of disease mechanisms and the development of biomarkers and therapeutics for effective disease management are limited. Here, we describe an adult-inducible astrocyte-specific system in genetically engineered mice that queries causation in disease evolution of regulatory networks perturbed in human GBM. Events yielding disease, both engineered and spontaneous, indicate ordered grade-specific perturbations that yield high-grade astrocytomas (anaplastic astrocytomas and GBMs). Impaired retinoblastoma protein RB tumor suppression yields grade II histopathology. Additional activation of v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (KRAS) network drives progression to grade III disease, and further inactivation of phosphatase and tensin homolog (PTEN) yields GBM. Spontaneous missense mutation of tumor suppressor Trp53 arises subsequent to KRAS activation, but before grade III progression. The stochastic appearance of mutations identical to those observed in humans, particularly the same spectrum of p53 amino acid changes, supports the validity of engineered lesions and the ensuing interpretations of etiology. Absence of isocitrate dehydrogenase 1 (IDH1) mutation, asymptomatic low grade disease, and rapid emergence of GBM combined with a mesenchymal transcriptome signature reflect characteristics of primary GBM and provide insight into causal relationships.

The Ras GTPase-activating protein neurofibromin 1 promotes the positive selection of thymocytes

TCR-mediated activation of the Ras signaling pathway is critical for T cell development in the thymus and function in the periphery. However, which members of a family of Ras GTPase-activating proteins (RasGAPs) negatively regulate Ras activation in T cells is unknown. In this study we examined a potential function for the neurofibromin 1 (NF1) RasGAP in the T cell lineage with the use of T cell-specific NF1-deficient mice. Surprisingly, on an MHC class I-restricted TCR transgenic background, NF1 was found to promote thymocyte positive selection. By contrast, NF1 neither promoted nor inhibited the negative selection of thymocytes. In the periphery, NF1 was found to be necessary for the maintenance of normal numbers of naïve CD4⁺ and CD8⁺ T cells but was dispensable as a regulator of TCR-induced Ras activation, cytokine synthesis, proliferation and differentiation and death. These findings point to a novel unexpected role for NF1 in T cell development as well as a regulator of T cell homeostasis.

Role of inositol poly-phosphatases and their targets in T cell biology

T lymphocytes play a critical role in host defense in all anatomical sites including mucosal surfaces. This not only includes the effector arm of the immune system, but also regulation of immune responses in order to prevent autoimmunity. Genetic targeting of PI3K isoforms suggests that generation of PI(3,4,5)P3 by PI3K plays a critical role in promoting effector T cell responses. Consequently, the 5'- and 3'-inositol poly-phosphatases SHIP1, SHIP2, and phosphatase and tensin homolog capable of targeting PI(3,4,5)P3 are potential genetic determinants of T cell effector functions in vivo. In addition, the 5'-inositol poly-phosphatases SHIP1 and 2 can shunt PI(3,4,5)P3 to the rare but potent signaling phosphoinositide species PI(3,4)P2 and thus these SHIP1/2, and the INPP4A/B enzymes that deplete PI(3,4)P2 may have precise roles in T cell biology to amplify or inhibit effectors of PI3K signaling that are selectively recruited to and activated by PI(3,4)P2. Here we summarize recent genetic and chemical evidence that indicates the inositol poly-phosphatases have important roles in both the effector and regulatory functions of the T cell compartment. In addition, we will discuss future genetic studies that might be undertaken to further elaborate the role of these enzymes in T cell biology as well as potential pharmaceutical manipulation of these enzymes for therapeutic purposes in disease settings where T cell function is a key in vivo target.

Activation of Akt signaling in prostate induces a TGFβ-mediated restraint on cancer progression and metastasis

Mutations in the PTEN tumor suppressor gene are found in a high proportion of human prostate cancers, and in mice, Pten deletion induces high-grade prostate intra-epithelial neoplasia (HGPIN). However, progression from HGPIN to invasive cancer occurs slowly, suggesting that tumorigenesis is subject to restraint. We show that Pten deletion, or constitutive activation of the downstream kinase AKT, activates the transforming growth factor (TGF) β pathway in prostate epithelial cells. TGFβ signaling is known to play a tumor suppressive role in many cancer types, and reduced expression of TGFβ receptors correlates with advanced human prostate cancer. We demonstrate that in combination either with loss of Pten, or expression of constitutively active AKT1, inactivation of TGFβ signaling by deletion of the TGFβ type II receptor gene relieves a restraint on tumorigenesis. This results in rapid progession to lethal prostate cancer, including metastasis to lymph node and lung. In prostate epithelium, inactivation of TGFβ signaling alone is insufficient to initiate tumorigenesis, but greatly accelerates cancer progression. The activation of TGFβ signaling by Pten loss or AKT activation suggests that the same signaling events that play key roles in tumor initiation also induce the activity of a pathway that restrains disease progression.

β-Catenin activation synergizes with Pten loss and Myc overexpression in Notch-independent T-ALL

Wnt activation, Pten loss, and Myc translocation synergize to define a novel subset of murine Notch-independent T-ALL.

The microRNA cluster miR-17∼92 promotes TFH cell differentiation and represses subset-inappropriate gene expression

Follicular helper T cells (TFH cells) are the prototypic helper T cell subset specialized to enable B cells to form germinal centers (GCs) and produce high-affinity antibodies. We found that expression of microRNAs (miRNAs) by T cells was essential for TFH cell differentiation. More specifically, we show that after immunization of mice with protein, the miRNA cluster miR-17∼92 was critical for robust differentiation and function of TFH cells in a cell-intrinsic manner that occurred regardless of changes in proliferation. In a viral infection model, miR-17∼92 restrained the expression of genes 'inappropriate' to the TFH cell subset, including the direct miR-17∼92 target Rora. Removal of one Rora allele partially 'rescued' the inappropriate gene signature in miR-17∼92-deficient TFH cells. Our results identify the miR-17∼92 cluster as a critical regulator of T cell-dependent antibody responses, TFH cell differentiation and the fidelity of the TFH cell gene-expression program.

Disruption of TSC1/2 signaling complex reveals a checkpoint governing thymic CD4+ CD25+ Foxp3+ regulatory T-cell development in mice

Thymic-derived CD4(+)CD25(+)Foxp3(+) natural regulatory T (nTreg) cells are essential for the maintenance of peripheral immune tolerance. Signaling pathways that drive immature thymic progenitors to differentiate into CD4(+)CD25(+)Foxp3(+) nTreg cells need to be elucidated. The precise role of the TSC1/2 complex, a critical negative regulator of mammalian target of rapamycin (mTOR), in thymic CD4(+)CD25(+)Foxp3(+) nTreg-cell development remains elusive. In the present study, we found that the percentage and cell number of thymic CD4(+)CD25(+)Foxp3(+) nTreg cells were significantly increased in T-cell-specific TSC1-knockout (TSC1KO) mice. Nevertheless, the levels of CD4(+)CD25(+)Foxp3(-) nTreg precursors in TSC1KO thymus were indistinguishable from those in wild-type mice. TSC1KO CD4(+)CD25(+)Foxp3(+) nTreg cells showed normal cell death but enhanced proliferative response to IL-2 in a STAT5-dependent manner. Rapamycin (Rapa) treatment failed to rescue but rather increased the frequency of CD4(+)CD25(+)Foxp3(+) nTreg cells in TSC1KO and RictorKO mice. The percentage and cell number of thymic CD4(+)CD25(+)Foxp3(+) nTreg cells were significantly increased in T-cell-specific RictorKO mice but not in PtenKO mice. Collectively, our studies suggest that TSC1 plays an important role in regulating thymic CD4(+)CD25(+)Foxp3(+) nTreg-cell development via a Rapa-resistant and mTORC2-dependent signaling pathway.

microRNA-17-92 regulates IL-10 production by regulatory T cells and control of experimental autoimmune encephalomyelitis

microRNAs (miRNA) are essential for regulatory T cell (Treg) function but little is known about the functional relevance of individual miRNA loci. We identified the miR-17-92 cluster as CD28 costimulation dependent, suggesting that it may be key for Treg development and function. Although overall immune homeostasis was maintained in mice with miR-17-92-deficient Tregs, expression of the miR-17-92 miRNA cluster was critical for Treg accumulation and function during an acute organ-specific autoimmune disease in vivo. Treg-specific loss of miR-17-92 expression resulted in exacerbated experimental autoimmune encephalitis and failure to establish clinical remission. Using peptide-MHC tetramers, we demonstrate that the miR-17-92 cluster was specifically required for the accumulation of activated Ag-specific Treg and for differentiation into IL-10-producing effector Treg.

Conditional deletion of PTEN in peripheral T cells augments TCR-mediated activation but does not abrogate CD28 dependency or prevent anergy induction

PTEN is thought to play a critical role in T cell activation by negatively regulating the PI3K signaling pathway important for cellular activation, growth, and proliferation. To directly eliminate PTEN in postthymic T cells for studies of functional effects, we used CAR transgenic × PTEN(flox/flox) mice, which enabled gene deletion using a Cre adenovirus in vitro. These mice were also immunized to generate stable Th1 clones that could have PTEN deleted when desired. PTEN-deleted T cells exhibited enhanced IL-2 production, proliferation, and Akt phosphorylation upon TCR/CD28 engagement, whereas T cell survival was not potentiated. Gene expression profiling revealed a small subset of induced genes that were augmented upon PTEN deletion. However, PTEN-deficient T cells still required CD28 costimulation for IL-2 production and remained susceptible to anti-CD3-induced anergy. The absence of PTEN within the CD8 T cell compartment led to markedly increased cytolytic activity following an allogeneic MLR in vitro, without increasing autologous MLR activity. Our results indicate that deletion of PTEN can augment the activation of postthymic T cells but does not mediate CD28 independence or anergy resistance. Nonetheless, PTEN inhibition may be a viable target for immune potentiation owing to increased cytokine production by activated CD4(+) cells and increased cytotoxicity by CD8(+) T cells.

The miR-183∼96∼182 cluster promotes tumorigenesis in a mouse model of medulloblastoma

Medulloblastoma is the most common malignant pediatric brain tumor. Some are thought to originate from cerebellar granule neuron progenitors (CGNPs) that fail to undergo normal cell cycle exit and differentiation. The contribution of microRNAs to the initiation and progression of medulloblastoma remains poorly understood. Increased expression of the miR-183∼96∼182 cluster of microRNAs has been noted in several aggressive subgroups. We identified that expression of miR-183∼96∼182 was higher in medulloblastomas with Pten gene loss in the background of the activated sonic hedgehog (Shh) signaling pathway. Ectopic miR-183∼96∼182 expression in CGNPs synergized with exogenous Shh to increase proliferation and its role depended on hedgehog signaling activation. Our findings suggest a new microRNA cluster, the miR-183∼96∼182, functionally collaborates with the Shh signaling pathway in the development of medulloblastomas in mice.