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

Onco-Circuit Addiction and Onco-Nutrient mTORC1 Signaling Vulnerability in a Model of Aggressive T Cell Malignancy

How genetic lesions drive cell transformation and whether they can be circumvented without compromising function of non-transformed cells are enduring questions in oncology. Here we show that in mature T cells-in which physiologic clonal proliferation is a cardinal feature- constitutive MYC transcription and Tsc1 loss in mice modeled aggressive human malignancy by reinforcing each other's oncogenic programs. This cooperation was supported by MYC-induced large neutral amino acid transporter chaperone SLC3A2 and dietary leucine, which in synergy with Tsc1 deletion overstimulated mTORC1 to promote mitochondrial fitness and MYC protein overexpression in a positive feedback circuit. A low leucine diet was therapeutic even in late-stage disease but did not hinder T cell immunity to infectious challenge, nor impede T cell transformation driven by constitutive nutrient mTORC1 signaling via Depdc5 loss. Thus, mTORC1 signaling hypersensitivity to leucine as an onco-nutrient enables an onco-circuit, decoupling pathologic from physiologic utilization of nutrient acquisition pathways.

PTEN directs developmental and metabolic signaling for innate-like T cell fate and tissue homeostasis

Phosphatase and tensin homologue (PTEN) is frequently mutated in human cancer, but its roles in lymphopoiesis and tissue homeostasis remain poorly defined. Here we show that PTEN orchestrates a two-step developmental process linking antigen receptor and IL-23-Stat3 signalling to type-17 innate-like T cell generation. Loss of PTEN leads to pronounced accumulation of mature IL-17-producing innate-like T cells in the thymus. IL-23 is essential for their accumulation, and ablation of IL-23 or IL-17 signalling rectifies the reduced survival of female PTEN-haploinsufficient mice that model human patients with PTEN mutations. Single-cell transcriptome and network analyses revealed the dynamic regulation of PTEN, mTOR and metabolic activities that accompanied type-17 cell programming. Furthermore, deletion of mTORC1 or mTORC2 blocks PTEN loss-driven type-17 cell accumulation, and this is further shaped by the Foxo1 and Stat3 pathways. Collectively, our study establishes developmental and metabolic signalling networks underpinning type-17 cell fate decisions and their functional effects at coordinating PTEN-dependent tissue homeostasis.

Large-scale multiplexed mosaic CRISPR perturbation in the whole organism

Here, we report inducible mosaic animal for perturbation (iMAP), a transgenic platform enabling in situ CRISPR targeting of at least 100 genes in parallel throughout the mouse body. iMAP combines Cre-loxP and CRISPR-Cas9 technologies and utilizes a germline-transmitted transgene carrying a large array of individually floxed, tandemly linked gRNA-coding units. Cre-mediated recombination triggers expression of all the gRNAs in the array but only one of them per cell, converting the mice to mosaic organisms suitable for phenotypic characterization and also for high-throughput derivation of conventional single-gene perturbation lines via breeding. Using gRNA representation as a readout, we mapped a miniature Perturb-Atlas cataloging the perturbations of 90 genes across 39 tissues, which yields rich insights into context-dependent gene functions and provides a glimpse of the potential of iMAP in genome decoding.

Calcium Signaling Is Impaired in PTEN-Deficient T Cell Acute Lymphoblastic Leukemia

PTEN (Phosphatase and TENsin homolog) is a well-known tumor suppressor involved in numerous types of cancer, including T-cell acute lymphoblastic leukemia (T-ALL). In human, loss-of-function mutations of PTEN are correlated to mature T-ALL expressing a T-cell receptor (TCR) at their cell surface. In accordance with human T-ALL, inactivation of Pten gene in mouse thymocytes induces TCRαβ⁺ T-ALL development. Herein, we explored the functional interaction between TCRαβ signaling and PTEN. First, we performed single-cell RNA sequencing (scRNAseq) of PTEN-deficient and PTEN-proficient thymocytes. Bioinformatic analysis of our scRNAseq data showed that pathological Pten^del thymocytes express, as expected, Myc transcript, whereas inference of pathway activity revealed that these Pten^del thymocytes display a lower calcium pathway activity score compared to their physiological counterparts. We confirmed this result using ex vivo calcium flux assay and showed that upon TCR activation tumor Pten^del blasts were unable to release calcium ions (Ca²⁺) from the endoplasmic reticulum to the cytosol. In order to understand such phenomena, we constructed a mathematical model centered on the mechanisms controlling the calcium flux, integrating TCR signal strength and PTEN interactions. This qualitative model displays a dynamical behavior coherent with the dynamics reported in the literature, it also predicts that PTEN affects positively IP3 (inositol 1,4,5-trisphosphate) receptors (ITPR). Hence, we analyzed Itpr expression and unraveled that ITPR proteins levels are reduced in PTEN-deficient tumor cells compared to physiological and leukemic PTEN-proficient cells. However, calcium flux and ITPR proteins expression are not defective in non-leukemic PTEN-deficient T cells indicating that beyond PTEN loss an additional alteration is required. Altogether, our study shows that ITPR/Calcium flux is a part of the oncogenic landscape shaped by PTEN loss and pinpoints a putative role of PTEN in the regulation of ITPR proteins in thymocytes, which remains to be characterized.

Metabolic adaptation of lymphocytes in immunity and disease

Adaptive immune responses mediated by T cells and B cells are crucial for protective immunity against pathogens and tumors. Differentiation and function of immune cells require dynamic reprogramming of cellular metabolism. Metabolic inputs, pathways, and enzymes display remarkable flexibility and heterogeneity, especially in vivo. How metabolic plasticity and adaptation dictate functional specialization of immune cells is fundamental to our understanding and therapeutic modulation of the immune system. Extensive progress has been made in characterizing the effects of metabolic networks on immune cell fate and function in discrete microenvironments or immunological contexts. In this review, we summarize how rewiring of cellular metabolism determines the outcome of adaptive immunity in vivo, with a focus on how metabolites, nutrients, and driver genes in immunometabolism instruct cellular programming and immune responses during infection, inflammation, and cancer in mice and humans. Understanding context-dependent metabolic remodeling will manifest legitimate opportunities for therapeutic intervention of human disease.

Challenging Cutaneous T-Cell Lymphoma: What Animal Models Tell us So Far

Cutaneous T-cell lymphomas are characterized by heterogeneity of clinical variants, further complicated by genomic and microenvironmental variables. Furthermore, in vitro experiments are hampered by the low culture efficiency of these malignant cells. Animal models are essential for understanding the pathogenetic mechanisms underlying malignancy and for discovering new anticancer treatments. They are divided into two main categories: those in which tumors arise in the host owing to genetic modifications and those that use tumor cell transplantation. In this review, we summarize the attempts to decipher the complexity of the pathogenesis of cutaneous T-cell lymphoma by exploiting genetically modified and xenograft models.

The requirement for pyruvate dehydrogenase in leukemogenesis depends on cell lineage

Cancer cells are metabolically similar to their corresponding normal tissues. Differences between cancers and normal tissues may reflect reprogramming during transformation or maintenance of the metabolism of the specific normal cell type that originated the cancer. Here, we compare glucose metabolism in hematopoiesis and leukemia. Thymus T cell progenitors were glucose avid and oxidized more glucose in the tricarboxylic acid cycle through pyruvate dehydrogenase (PDH) as compared with other hematopoietic cells. PDH deletion decreased double-positive T cell progenitor cells but had no effect on hematopoietic stem cells, myeloid progenitors, or other hematopoietic cells. PDH deletion blocked the development of Pten-deficient T cell leukemia, but not the development of a Pten-deficient myeloid neoplasm. Therefore, the requirement for PDH in leukemia reflected the metabolism of the normal cell of origin independently of the driver genetic lesion. PDH was required to prevent pyruvate accumulation and maintain glutathione levels and redox homeostasis.

New Drug Repositioning Candidates for T-ALL Identified Via Human/Murine Gene Signature Comparison

T-cell Acute Lymphoblastic Leukemia (T-ALL) is an aggressive subtype of leukemia for which important progress in treatment efficiency have been made in the past decades to reach a cure rate of 75%-80% nowadays. It is nevertheless mandatory to find new targets and active molecules for innovative therapeutic strategies as relapse is associated with a very dismal outcome. We designed an experimental workflow to highlight the conserved core pathways associated with leukemogenesis by confronting the gene expression profiles (GEPs) of human T-ALL cases to the GEP of a murine T-ALL representative model, generated by the conditional deletion of the PTEN tumor suppressor gene in T cell precursors (tPTEN-/-). We identified 844 differentially expressed genes, common GEPs (cGEP) that were conserved between human T-ALL and murine signatures, and also similarly differentially expressed, compared to normal T cells. Using bioinformatic tools we highlighted in cGEPan upregulation of E2F, MYC and mTORC1. Next, using Connectivity Map (CMAP) and CMAPViz a visualization procedure for CMAP data that we developed, we selected in silico three FDA-approved, bioactive molecule candidates: α-estradiol (α-E), nordihydroguaiaretic acid (NDGA) and prochlorperazine dimaleate (PCZ). At a biological level, we showed that the three drugs triggered an apoptotic cell death in a panel of T-ALL cell lines, activated a DNA damage response and interfered with constitutive mTORC1 activation and c-MYC expression. This analysis shows that the investigation of conserved leukemogenesis pathways could be a strategy to reveal new avenues for pharmacological intervention.

PTEN in Regulating Hematopoiesis and Leukemogenesis

PTEN is one of the most frequently mutated tumor suppressor genes in human cancers. By counteracting the PI3K/AKT/mTOR pathway, PTEN plays an essential role in regulating hematopoietic stem cells (HSCs) self-renewal, migration, lineage commitment, and differentiation. PTEN also plays important roles in suppressing leukemogenesis, especially T-cell acute lymphoblastic leukemia (T-ALL). Herein, we will review the function of PTEN in regulating hematopoiesis and leukemogenesis and discuss potential therapeutic approaches against leukemia with PTEN mutations.

The Genetics and Mechanisms of T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy derived from early T-cell progenitors. The recognition of clinical, genetic, transcriptional, and biological heterogeneity in this disease has already translated into new prognostic biomarkers, improved leukemia animal models, and emerging targeted therapies. This work reviews our current understanding of the molecular mechanisms of T-ALL.

HSF1-Mediated Control of Cellular Energy Metabolism and mTORC1 Activation Drive Acute T-Cell Lymphoblastic Leukemia Progression

Deregulated oncogenic signaling linked to PI3K/AKT and mTORC1 pathway activation is a hallmark of human T-cell acute leukemia (T-ALL) pathogenesis and contributes to leukemic cell resistance and adverse prognosis. Notably, although the multiagent chemotherapy of leukemia leads to a high rate of complete remission, options for salvage therapy for relapsed/refractory disease are limited due to the serious side effects of augmenting cytotoxic chemotherapy. We report that ablation of HSF1, a key transcriptional regulator of the chaperone response and cellular bioenergetics, from mouse T-ALL tumors driven by PTEN loss or human T-ALL cell lines, has significant therapeutic effects in reducing tumor burden and sensitizing malignant cell death. From a mechanistic perspective, the enhanced sensitivity of T-ALLs to HSF1 depletion resides in the reduced MAPK-ERK signaling and metabolic and ATP-producing capacity of malignant cells lacking HSF1 activity. Impaired mitochondrial ATP production and decreased intracellular amino acid content in HSF1-deficient T-ALL cells trigger an energy-saving adaptive response featured by attenuation of the mTORC1 activity, which is coregulated by ATP, and its downstream target proteins (p70S6K and 4E-BP). This leads to protein translation attenuation that diminishes oncogenic signals and malignant cell growth. Collectively, these metabolic alterations in the absence of HSF1 activity reveal cancer cell liabilities and have a profound negative impact on T-ALL progression. IMPLICATIONS: Targeting HSF1 and HSF1-dependent cancer-specific anabolic and protein homeostasis programs has a significant therapeutic potential for T-ALL and may prevent progression of relapsed/refractory disease.

A unique mutator phenotype reveals complementary oncogenic lesions leading to acute leukemia

Mice homozygous for a hypomorphic allele of DNA replication factor minichromosome maintenance protein 2 (designated Mcm2cre/cre) develop precursor T cell lymphoblastic leukemia/lymphoma (pre-T LBL) with 4-32 small interstitial deletions per tumor. Mice that express a NUP98-HOXD13 (NHD13) transgene develop multiple types of leukemia, including myeloid and T and B lymphocyte. All Mcm2cre/cre NHD13+ mice develop pre-T LBL, and 26% develop an unrelated, concurrent B cell precursor acute lymphoblastic leukemia (BCP-ALL). Copy number alteration (CNA) analysis demonstrated that pre-T LBLs were characterized by homozygous deletions of Pten and Tcf3 and partial deletions of Notch1 leading to Notch1 activation. In contrast, BCP-ALLs were characterized by recurrent deletions involving Pax5 and Ptpn1 and copy number gain of Abl1 and Nup214 resulting in a Nup214-Abl1 fusion. We present a model in which Mcm2 deficiency leads to replicative stress, DNA double strand breaks (DSBs), and resultant CNAs due to errors in DNA DSB repair. CNAs that involve critical oncogenic pathways are then selected in vivo as malignant lymphoblasts because of a fitness advantage. Some CNAs, such as those involving Abl1 and Notch1, represent attractive targets for therapy.

Beyond the Cell Surface: Targeting Intracellular Negative Regulators to Enhance T cell Anti-Tumor Activity

It is well established that extracellular proteins that negatively regulate T cell function, such as Cytotoxic T-Lymphocyte-Associated protein 4 (CTLA-4) and Programmed Cell Death protein 1 (PD-1), can be effectively targeted to enhance cancer immunotherapies and Chimeric Antigen Receptor T cells (CAR-T cells). Intracellular proteins that inhibit T cell receptor (TCR) signal transduction, though less well studied, are also potentially useful therapeutic targets to enhance T cell activity against tumor. Four major classes of enzymes that attenuate TCR signaling include E3 ubiquitin kinases such as the Casitas B-lineage lymphoma proteins (Cbl-b and c-Cbl), and Itchy (Itch), inhibitory tyrosine phosphatases, such as Src homology region 2 domain-containing phosphatases (SHP-1 and SHP-2), inhibitory protein kinases, such as C-terminal Src kinase (Csk), and inhibitory lipid kinases such as Src homology 2 (SH2) domain-containing inositol polyphosphate 5-phosphatase (SHIP) and Diacylglycerol kinases (DGKs). This review describes the mechanism of action of eighteen intracellular inhibitory regulatory proteins in T cells within these four classes, and assesses their potential value as clinical targets to enhance the anti-tumor activity of endogenous T cells and CAR-T cells.

The strange case of AMPK and cancer: Dr Jekyll or Mr Hyde? †

The AMP-activated protein kinase (AMPK) acts as a cellular energy sensor. Once switched on by increases in cellular AMP : ATP ratios, it acts to restore energy homeostasis by switching on catabolic pathways while switching off cell growth and proliferation. The canonical AMP-dependent mechanism of activation requires the upstream kinase LKB1, which was identified genetically to be a tumour suppressor. AMPK can also be switched on by increases in intracellular Ca2+, by glucose starvation and by DNA damage via non-canonical, AMP-independent pathways. Genetic studies of the role of AMPK in mouse cancer suggest that, before disease arises, AMPK acts as a tumour suppressor that protects against cancer, with this protection being further enhanced by AMPK activators such as the biguanide phenformin. However, once cancer has occurred, AMPK switches to being a tumour promoter instead, enhancing cancer cell survival by protecting against metabolic, oxidative and genotoxic stresses. Studies of genetic changes in human cancer also suggest diverging roles for genes encoding subunit isoforms, with some being frequently amplified, while others are mutated.

The Key Roles of PTEN in T-Cell Acute Lymphoblastic Leukemia Development, Progression, and Therapeutic Response

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive blood cancer that comprises 10–15% of pediatric and ~25% of adult ALL cases. Although the curative rates have significantly improved over the past 10 years, especially in pediatric patients, T-ALL remains a challenge from a therapeutic point of view, due to the high number of early relapses that are for the most part resistant to further treatment. Considerable advances in the understanding of the genes, signaling networks, and mechanisms that play crucial roles in the pathobiology of T-ALL have led to the identification of the key drivers of the disease, thereby paving the way for new therapeutic approaches. PTEN is critical to prevent the malignant transformation of T-cells. However, its expression and functions are altered in human T-ALL. PTEN is frequently deleted or mutated, while PTEN protein is often phosphorylated and functionally inactivated by casein kinase 2. Different murine knockout models recapitulating the development of T-ALL have demonstrated that PTEN abnormalities are at the hub of an intricate oncogenic network sustaining and driving leukemia development by activating several signaling cascades associated with drug-resistance and poor outcome. These aspects and their possible therapeutic implications are highlighted in this review.

Phenformin, But Not Metformin, Delays Development of T Cell Acute Lymphoblastic Leukemia/Lymphoma via Cell-Autonomous AMPK Activation

AMPK acts downstream of the tumor suppressor LKB1, yet its role in cancer has been controversial. AMPK is activated by biguanides, such as metformin and phenformin, and metformin use in diabetics has been associated with reduced cancer risk. However, whether this is mediated by cell-autonomous AMPK activation within tumor progenitor cells has been unclear. We report that T-cell-specific loss of AMPK-α1 caused accelerated growth of T cell acute lymphoblastic leukemia/lymphoma (T-ALL) induced by PTEN loss in thymic T cell progenitors. Oral administration of phenformin, but not metformin, delayed onset and growth of lymphomas, but only when T cells expressed AMPK-α1. This differential effect of biguanides correlated with detection of phenformin, but not metformin, in thymus. Phenformin also enhanced apoptosis in T-ALL cells both in vivo and in vitro. Thus, AMPK-α1 can be a cell-autonomous tumor suppressor in the context of T-ALL, and phenformin may have potential for the prevention of some cancers.

Fit αβ T-cell receptor suppresses leukemogenesis of Pten-deficient thymocytes

Signaling through the αβT cell receptor (TCR) is a crucial determinant of T-cell fate and can induce two opposite outcomes during thymocyte development: cell death or survival and differentiation. To date, the role played by T-cell receptor in the oncogenic transformation of developing T cells remains unclear. Here we show that human primary T-cell acute lymphoblastic leukemias expressing an αβT cell receptor are frequently deficient for phosphatase and tensin homolog protein (PTEN), and fail to respond strongly to T-cell receptor activation. Using Pten-deficient T-cell acute lymphoblastic leukemia mouse models, we confirm that T-cell receptor signaling is involved in leukemogenesis. We show that abrogation of T-cell receptor expression accelerated tumor onset, while enforced expression of a fit transgenic T-cell receptor led to the development of T-cell receptor-negative lymphoma and delayed tumorigenesis. We further demonstrate that pre-tumoral Pten-deficient thymocytes harboring fit T-cell receptors undergo early clonal deletion, thus preventing their malignant transformation, while cells with unfit T-cell receptors that should normally be deleted during positive selection, pass selection and develop T-cell acute lymphoblastic leukemias. Altogether, our data show that fit T-cell receptor signaling suppresses tumor development mediated by Pten loss-of-function and point towards a role of Pten in positive selection.

Analysis of the expression level and methylation of tumor protein p53, phosphatase and tensin homolog and mutS homolog 2 in N-methyl-N-nitrosourea-induced thymic lymphoma in C57BL/6 mice

Tumorigenesis is often caused by somatic mutation or epigenetic changes in genes that regulate aspects of cell death, proliferation and survival. Although the functions of multiple tumor suppressor genes have been well studied in isolation, how these genes cooperate during the progression of a single tumor remains unclear in numerous cases. The present study used N-methyl-N-nitrosourea (MNU), one of the most potent mutagenic nitrosourea compounds, to induce thymic lymphoma in C57BL/6J mice. Subsequently, the protein expression levels of phosphatase and tensin homolog (PTEN), transformation protein 53 and mutS homolog 2 (MSH2) were evaluated concomitantly in the thymus, liver, kidney and spleen of MNU-treated mice by western blotting. To determine whether changes in expression level were due to aberrant epigenetic regulation, the present study further examined the methylation status of each gene by MassARRAY analysis. During the tumorigenesis process of an MNU-induced single thymic lymphoma, the expression level of PTEN was revealed to be reduced in thymic lymphoma samples but not in normal or non-tumor thymus tissue samples. Furthermore, a marked reduction of P53 expression levels were demonstrated in thymic lymphomas and spleens with a metastatic tumor. Conversely, MSH2 upregulation was identified only in liver, kidney, and spleen samples that were infiltrated by thymic lymphoma cells. Furthermore, the present study revealed that a number of 5'-C-phosphate-G-3' sites located in the promoter of aberrantly expressed genes had significantly altered methylation statuses. These results improve the understanding of the course of mutagen-induced cancer, and highlight that epigenetic regulation may serve an important function in cancer.

Control of amino acid transport coordinates metabolic reprogramming in T-cell malignancy

This study explores the regulation and importance of System L amino acid transport in a murine model of T-cell acute lymphoblastic leukemia (T-ALL) caused by deletion of phosphatase and tensin homolog deleted on chromosome 10 (PTEN). There has been a strong focus on glucose transport in leukemias but the present data show that primary T-ALL cells have increased transport of multiple nutrients. Specifically, increased leucine transport in T-ALL fuels mammalian target of rapamycin complex 1 (mTORC1) activity which then sustains expression of hypoxia inducible factor-1α (HIF1α) and c-Myc; drivers of glucose metabolism in T cells. A key finding is that PTEN deletion and phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P₃) accumulation is insufficient to initiate leucine uptake, mTORC1 activity, HIF1α or c-Myc expression in T cells and hence cannot drive T-ALL metabolic reprogramming. Instead, a key regulator for leucine transport in T-ALL is identified as NOTCH. Mass spectrometry based proteomics identifies SLC7A5 as the predominant amino acid transporter in primary PTEN^−/− T-ALL cells. Importantly, expression of SLC7A5 is critical for the malignant transformation induced by PTEN deletion. These data reveal the importance of regulated amino acid transport for T-cell malignancies, highlighting how a single amino acid transporter can have a key role.

Microenvironmental cues for T-cell acute lymphoblastic leukemia development

Intensive chemotherapy regimens have led to a substantial improvement in the cure rate of patients suffering from T-cell acute lymphoblastic leukemia (T-ALL). Despite this progress, about 15% and 50% of pediatric and adult cases, respectively, show resistance to treatment or relapse with dismal prognosis, calling for further therapeutic investigations. T-ALL is an heterogeneous disease, which presents intrinsic alterations leading to aberrant expression of transcription factors normally involved in hematopoietic stem/progenitor cell development and mutations in genes implicated in the regulation of cell cycle progression, apoptosis, and T-cell development. Gene expression profiling allowed the classification of T-ALL into defined molecular subgroups that mostly reflects the stage of their differentiation arrest. So far this knowledge has not translated into novel, targeted therapy. Recent evidence points to the importance of extrinsic signaling cues in controlling the ability of T-ALL to home, survive, and proliferate, thus offering the perspective of new therapeutic options. This review summarizes the present understanding of the interactions between hematopoietic cells and bone marrow/thymic niches during normal hematopoiesis, describes the main signaling pathways implicated in this dialog, and finally highlights how malignant T cells rely on specific niches to maintain their ability to sustain and propagate leukemia.

Ndrg1b and fam49ab modulate the PTEN pathway to control T-cell lymphopoiesis in the zebrafish

During hematopoiesis, the balance between proliferation, differentiation, and apoptosis is tightly regulated in order to maintain homeostasis. Failure in these processes can ultimately lead to uncontrolled proliferation and leukemia. Phosphatase and tensin homolog (PTEN) is one of the molecular pathways involved in this balance. By opposing PI3-kinases, PTEN inhibits proliferation and promotes differentiation and is thus considered a tumor suppressor. Indeed, PTEN is frequently mutated in many cancers, including leukemias. Loss of PTEN often leads to lymphoid cancers. However, little is known about the molecular events that regulate PTEN signaling during lymphopoiesis. In this study, we used zebrafish to address this. We report that N-myc downstream-regulated gene 1b (ndrg1b) rescues lymphoid differentiation after PTEN inhibition. We also show that a previously uncharacterized gene, fam49ab, inhibits T-cell differentiation, a phenotype that can be rescued by ndrg1b We propose that ndrg1b and fam49ab are 2 new modulators of PTEN signaling that control lymphoid differentiation in the zebrafish thymus.

Iron chelation: an adjuvant therapy to target metabolism, growth and survival of murine PTEN-deficient T lymphoma and human T lymphoblastic leukemia/lymphoma

Iron is an essential nutrient, acting as a catalyst for metabolic reactions that are fundamental to cell survival and proliferation. Iron complexed to transferrin is delivered to the metabolism after endocytosis via the CD71 surface receptor. We found that transformed cells from a murine PTEN-deficient T-cell lymphoma model and from T-cell acute lymphoblastic leukemia/lymphoma (T-ALL/T-LL) cell lines overexpress CD71. As a consequence, the cells developed an addiction toward iron whose chelation by deferoxamine (DFO) dramatically affected their survival to induce apoptosis. Interestingly, DFO displayed synergistic activity with three ALL-specific drugs: dexamethasone, doxorubicin, and L-asparaginase. DFO appeared to act through a reactive oxygen species-dependent DNA damage response and potentiated the action of an inhibitor of the PARP pathway of DNA repair. Our results demonstrate that targeting iron metabolism could be an interesting adjuvant therapy for acute lymphoblastic leukemia.

Structure-function insights reveal the human ribosome as a cancer target for antibiotics

Many antibiotics in clinical use target the bacterial ribosome by interfering with the protein synthesis machinery. However, targeting the human ribosome in the case of protein synthesis deregulations such as in highly proliferating cancer cells has not been investigated at the molecular level up to now. Here we report the structure of the human 80S ribosome with a eukaryote-specific antibiotic and show its anti-proliferative effect on several cancer cell lines. The structure provides insights into the detailed interactions in a ligand-binding pocket of the human ribosome that are required for structure-assisted drug design. Furthermore, anti-proliferative dose response in leukaemic cells and interference with synthesis of c-myc and mcl-1 short-lived protein markers reveals specificity of a series of eukaryote-specific antibiotics towards cytosolic rather than mitochondrial ribosomes, uncovering the human ribosome as a promising cancer target.

The ribosome of bacteria and other unicellular pathogens is a common target for antibiotic drugs. Here the authors determine a structure of the human ribosome bound to the translation inhibitor cycloheximide, and provide evidence that targeting the ribosome is a promising avenue for cancer therapy.

Challenging perspectives on the cellular origins of lymphoma

Both B and T lymphocytes have signature traits that set them apart from other cell types. They actively and repeatedly rearrange their DNA in order to produce a unique and functional antigen receptor, they have potential for massive clonal expansion upon encountering antigen via this receptor or its precursor, and they have the capacity to be extremely long lived as ‘memory’ cells. All three of these traits are fundamental to their ability to function as the adaptive immune response to infectious agents, but concurrently render these cells vulnerable to transformation. Thus, it is classically considered that lymphomas arise at a relatively late stage in a lymphocyte's development during the process of modifying diversity within antigen receptors, and when the cell is capable of responding to stimulus via its receptor. Attempts to understand the aetiology of lymphoma have reinforced this notion, as the most notable advances to date have shown chronic stimulation of the antigen receptor by infectious agents or self-antigens to be key drivers of these diseases. Despite this, there is still uncertainty about the cell of origin in some lymphomas, and increasing evidence that a subset arises in a more immature cell. Specifically, a recent study indicates that T-cell lymphoma, in particular nucleophosmin-anaplastic lymphoma kinase-driven anaplastic large cell lymphoma, may originate in T-cell progenitors in the thymus.

Glucose and glutamine fuel protein O-GlcNAcylation to control T cell self-renewal and malignancy

Sustained glucose and glutamine transport are essential for activated T lymphocytes to support ATP and macromolecule biosynthesis. We now show that glutamine and glucose also fuel an indispensible dynamic regulation of intracellular protein O-GlcNAcylation at key stages of T cell development, transformation and differentiation. Glucose and glutamine are precursors of UDP-GlcNAc, a substrate for cellular glycosyltransferases. Immune activated T cells contained higher concentrations of UDP-GlcNAc and increased intracellular protein O-GlcNAcylation controlled by the enzyme O-GlcNAc glycosyltransferase as compared to naïve cells. We identified Notch, the T cell antigen receptor and c-Myc as key controllers of T cell protein O-GlcNAcylation, via regulation of glucose and glutamine transport. Loss of O-GlcNAc transferase blocked T cell progenitor renewal, malignant transformation, and peripheral T cell clonal expansion. Nutrient-dependent signaling pathways regulated by O-GlcNAc glycosyltransferase are thus fundamental for T cell biology.

A three-signal model of T-cell lymphoma pathogenesis

T-cell lymphoma pathogenesis and classification have, until recently, remained enigmatic. Recently performed whole-exome sequencing and gene-expression profiling studies have significant implications for their classification and treatment. Recurrent genetic modifications in antigen ("signal 1"), costimulatory ("signal 2"), or cytokine receptors ("signal 3"), and the tyrosine kinases and other signaling proteins they activate, have emerged as important therapeutic targets in these lymphomas. Many of these genetic modifications do not function in a cell-autonomous manner, but require the provision of ligand(s) by constituents of the tumor microenvironment, further supporting the long-appreciated view that these lymphomas are dependent upon and driven by their microenvironment. Therefore, the seemingly disparate fields of genomics and immunology are converging. A unifying "3 signal model" for T-cell lymphoma pathogenesis that integrates these findings will be presented, and its therapeutic implications briefly reviewed.

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.

A PI3K p110β-Rac signalling loop mediates Pten-loss-induced perturbation of haematopoiesis and leukaemogenesis

The tumour suppressor PTEN, which antagonizes PI3K signalling, is frequently inactivated in haematologic malignancies. In mice, deletion of PTEN in haematopoietic stem cells (HSCs) causes perturbed haematopoiesis, myeloproliferative neoplasia (MPN) and leukaemia. Although the roles of the PI3K isoforms have been studied in PTEN-deficient tumours, their individual roles in PTEN-deficient HSCs are unknown. Here we show that when we delete PTEN in HSCs using the Mx1–Cre system, p110β ablation prevents MPN, improves HSC function and suppresses leukaemia initiation. Pharmacologic inhibition of p110β in PTEN-deficient mice recapitulates these genetic findings, but suggests involvement of both Akt-dependent and -independent pathways. Further investigation reveals that a p110β–Rac signalling loop plays a critical role in PTEN-deficient HSCs. Together, these data suggest that myeloid neoplasia driven by PTEN loss is dependent on p110β via p110β–Rac-positive-feedback loop, and that disruption of this loop may offer a new and effective therapeutic strategy for PTEN-deficient leukaemia.

The tumor suppressor PTEN antagonizes the PI3K signalling pathway and is frequently inactivated in haematological malignancies. Here, the authors unravel the main contribution of the PI3K isoform p110ß to leukemic transformation driven by PTEN-loss.

L-type amino-acid transporter 1 (LAT1): a therapeutic target supporting growth and survival of T-cell lymphoblastic lymphoma/T-cell acute lymphoblastic leukemia

The altered metabolism of cancer cells is a treasure trove to discover new antitumoral strategies. The gene (SLC7A5) encoding system L amino-acid transporter 1 (LAT1) is overexpressed in murine lymphoma cells generated via T-cell deletion of the pten tumor suppressor, and also in human T-cell acute lymphoblastic leukemia (T-ALL)/lymphoma (T-LL) cells. We show here that a potent and LAT1 selective inhibitor (JPH203) decreased leukemic cell viability and proliferation, and induced transient autophagy followed by apoptosis. JPH203 could also alter the in vivo growth of luciferase-expressing-tPTEN-/- cells xenografted into nude mice. In contrast, JPH203 was nontoxic to normal murine thymocytes and human peripheral blood lymphocytes. JPH203 interfered with constitutive activation of mTORC1 and Akt, decreased expression of c-myc and triggered an unfolded protein response mediated by the C/EBP homologous protein (CHOP) transcription factor associated with cell death. A JPH203-resistant tPTEN-/-clone appeared CHOP induction deficient. We also demonstrate that targeting LAT1 may be an efficient broad spectrum adjuvant approach to treat deadly T-cell malignancies as the molecule synergized with rapamycin, dexamethasone, doxorubicin, velcade and l-asparaginase to alter leukemic cell viability.

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.

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.

Models for mature T-cell lymphomas--a critical appraisal of experimental systems and their contribution to current T-cell tumorigenic concepts

Mature T-cell lymphomas/leukemias (MTCL) have been understudied lymphoid neoplasms that currently receive growing attention. Our historically rudimentary molecular understanding and dissatisfactory interventional success in this complex and for the most part poor-prognostic group of tumors is only slightly improving. A major limiting aspect in further progress in these rare neoplasms is the lack of suitable model systems that would substantially facilitate pathogenic studies and pre-clinical drug evaluations. Such representations of MTCL have thus far not been systematically appraised. We therefore provide an overview on existing models and point out their particular advantages and limitations in the context of the specific scientific questions. After addressing issues of species-specific differences and classifications, we summarize data on MTCL cell lines of human as well as murine origin, on murine strain predispositions to MTCL, on available models of genetically engineered mice, and on transplant systems. From an in-silico meta-analysis of available primary data of gene expression profiles on human MTCL we cross-reference genes reported to transform T-cells in mice and reflect on their general vs entity-restricted relevance and on target-promoter influences. Overall, we identify the urgent need for new models of higher fidelity to human MTCL with respect to their increasingly recognized diversity and to predictions of drug response.

Deletion of Snai2 and Snai3 results in impaired physical development compounded by lymphocyte deficiency

The Snail family of transcriptional regulators consists of three highly conserved members. These proteins regulate (repress) transcription via the recruitment of histone deacetylases to target gene promoters that possess the appropriate E-box binding sequences. Murine Snai1 is required for mouse development while Snai2 deficient animals survive with some anomalies. Less is known about the third member of the family, Snai3. To investigate the function of Snai3, we generated a conditional knockin mouse. Utilizing Cre-mediated deletion to facilitate the ablation of Snai3 in T cells or the entire animal, we found little to no effect of the loss of Snai3 in the entire animal or in T cell lineages. This finding provided the hypothesis that absence of Snai3 was mitigated, in part, by the presence of Snai2. To test this hypothesis we created Snai2/Snai3 double deficient mice. The developmental consequences of lacking both of these proteins was manifested in stunted growth, a paucity of offspring including a dramatic deficiency of female mice, and impaired immune cell development within the lymphoid lineages.

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 metabolic perturbators metformin, phenformin and AICAR interfere with the growth and survival of murine PTEN-deficient T cell lymphomas and human T-ALL/T-LL cancer cells

We show here that the antidiabetic agents metformin and phenformin and the AMPK activator AICAR exert strong anti-tumoural effects on tPTEN-/- lymphoma cells and on human T-ALL cell lines and primary samples. The compounds act by inhibiting tumour metabolism and proliferation and by inducing apoptosis in parallel with an activation of AMPK and an inhibition of constitutive mTOR. In tPTEN-/- cells, the drugs potentiated the anti-leukaemic effects of dexamethasone, and metformin and phenformin synergised with 2-deoxyglucose (2DG) to impair tumour cell survival. In vivo, metformin and AICAR strongly decreased the growth of luciferase-expressing tPTEN-/- cells xenografted in Nude mice, demonstrating that metabolism targeting could be a potent adjuvant strategy for lymphoma/leukaemia treatment.

Regulation of glucose metabolism in T cells: new insight into the role of Phosphoinositide 3-kinases

Naïve T cells are relatively quiescent cells that only require energy to prevent atrophy and for survival and migration. However, in response to developmental or extrinsic cues T cells can engage in rapid growth and robust proliferation, produce of a range of effector molecules and migrate through peripheral tissues. To meet the significantly increased metabolic demands of these activities, T cells switch from primarily metabolizing glucose to carbon dioxide through oxidative phosphorylation to utilizing glycolysis to convert glucose to lactate (termed aerobic glycolysis). This metabolic switch allows glucose to be used as a source of carbon to generate biosynthetic precursors for the production of protein, DNA, and phospholipids, and is crucial for T cells to meet metabolic demands. Phosphoinositide 3-kinases (PI3K) are a family of inositol lipid kinases linked with a broad range of cellular functions in T lymphocytes that include cell growth, proliferation, metabolism, differentiation, survival, and migration. Initial research described a critical role for PI3K signaling through Akt (also called protein kinase B) for the increased glucose uptake and glycolysis that accompanies T cell activation. This review article relates this original research with more recent data and discusses the evidence for and against a role for PI3K in regulating the metabolic switch to aerobic glycolysis in T cells.

Regulation of T cell homeostasis and responses by pten

The generation of lipid products catalyzed by PI3K is critical for normal T cell homeostasis and a productive immune response. PI3K can be activated in response to antigen receptor, co-stimulatory, cytokine, and chemokine signals. Moreover, dysregulation of this pathway frequently occurs in T cell lymphomas and is implicated in lymphoproliferative autoimmune disease. Akt acts as a central mediator of PI3K signals, downstream of which is the mTOR pathway, controlling cell growth and metabolism. Members of the Foxo family of transcription factors are also regulated by Akt, thus linking control over homing and migration of T cells, as well cell cycle entry, apoptosis, and DNA damage and oxidative stress responses, to PI3K signaling. PTEN, first identified as a tumor suppressor gene, encodes a lipid phosphatase that, by catalyzing the reverse of the PI3K “reaction,” directly opposes PI3K signaling. However, PTEN may have other functions as well, and recent reports have suggested roles for PTEN as a tumor suppressor independent of its effects on PI3K signaling. Through the use of models in which Pten is deleted specifically in T cells, it is becoming increasingly clear that control over autoimmunity and lymphomagenesis by PTEN involves multi-faceted functions of this molecule at multiple stages within the T cell compartment.

Pten loss in CD4 T cells enhances their helper function but does not lead to autoimmunity or lymphoma

PTEN, one of the most commonly mutated or lost tumor suppressors in human cancers, antagonizes signaling by the PI3K pathway. Mice with thymocyte-specific deletion of Pten rapidly develop peripheral lymphomas and autoimmunity, which may be caused by failed negative selection of thymocytes or from dysregulation of postthymic T cells. We induced conditional deletion of Pten from CD4 Th cells using a Cre knocked into the Tnfrsf4 (OX40) locus to generate OX40(Cre)Pten(f) mice. Pten-deficient Th cells proliferated more and produced greater concentrations of cytokines. The OX40(Cre)Pten(f) mice had a general increase in the number of lymphocytes in the lymph nodes, but not in the spleen. When transferred into wild-type (WT) mice, Pten-deficient Th cells enhanced anti-Listeria responses and the clearance of tumors under conditions in which WT T cells had no effect. Moreover, inflammatory responses were exaggerated and resolved later in OX40(Cre)Pten(f) mice than in WT mice. However, in contrast with models of thymocyte-specific Pten deletion, lymphomas and autoimmunity were not observed, even in older OX40(Cre)Pten(f) mice. Hence loss of Pten enhances Th cell function without obvious deleterious effects.

Regulation and function of mTOR signalling in T cell fate decisions

The evolutionarily conserved kinase mTOR (mammalian target of rapamycin) couples cell growth and metabolism to environmental inputs in eukaryotes. T cells depend on mTOR signalling to integrate immune signals and metabolic cues for their proper maintenance and activation. Under steady-state conditions, mTOR is actively controlled by multiple inhibitory mechanisms, and this enforces normal T cell homeostasis. Antigen recognition by naive CD4(+) and CD8(+) T cells triggers mTOR activation, which in turn programmes the differentiation of these cells into functionally distinct lineages. This Review focuses on the signalling mechanisms of mTOR in T cell homeostatic and functional fates, and discusses the therapeutic implications of targeting mTOR in T cells.

Targeting nonclassical oncogenes for therapy in T-ALL

Constitutive phosphoinositide 3-kinase (PI3K)/Akt activation is common in T cell acute lymphoblastic leukemia (T-ALL). Although four distinct class I PI3K isoforms (α, β, γ, δ) could participate in T-ALL pathogenesis, none has been implicated in this process. We report that in the absence of PTEN phosphatase tumor suppressor function, PI3Kγ or PI3Kδ alone can support leukemogenesis, whereas inactivation of both isoforms suppressed tumor formation. The reliance of PTEN null T-ALL on the combined activities of PI3Kγ/δ was further demonstrated by the ability of a dual inhibitor to reduce disease burden and prolong survival in mice as well as prevent proliferation and promote activation of proapoptotic pathways in human tumors. These results support combined inhibition of PI3Kγ/δ as therapy for T-ALL.

The PTEN and Myotubularin phosphoinositide 3-phosphatases: linking lipid signalling to human disease

Two classes of lipid phosphatases selectively dephosphorylate the 3 position of the inositol ring of phosphoinositide signaling molecules: the PTEN and the Myotubularin families. PTEN dephosphorylates PtdIns(3,4,5)P(3), acting in direct opposition to the Class I PI3K enzymes in the regulation of cell growth, proliferation and polarity and is an important tumor suppressor. Although there are several PTEN-related proteins encoded by the human genome, none of these appear to fulfill the same functions. In contrast, the Myotubularins dephosphorylate both PtdIns(3)P and PtdIns(3,5)P(2), making them antagonists of the Class II and Class III PI 3-kinases and regulators of membrane traffic. Both phosphatase groups were originally identified through their causal mutation in human disease. Mutations in specific myotubularins result in myotubular myopathy and Charcot-Marie-Tooth peripheral neuropathy; and loss of PTEN function through mutation and other mechanisms is evident in as many as a third of all human tumors. This chapter will discuss these two classes of phosphatases, covering what is known about their biochemistry, their functions at the cellular and whole body level and their influence on human health.

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.

Phosphatidylinositol 3-kinase signaling in thymocytes: the need for stringent control

The thymus serves as the primary site for the lifelong formation of new T lymphocytes; hence, it is essential for the maintenance of an effective immune system. Although thymocyte development has been widely studied, the mechanisms involved are incompletely defined. A comprehensive understanding of the molecular events that control regular thymocyte development will not only shed light on the physiological control of T cell differentiation but also probably provide insight into the pathophysiology of T cell immunodeficiencies, the molecular basis that underpins autoimmunity, and the mechanisms that instigate the formation of T cell lymphomas. Phosphatidylinositol 3-kinases (PI3Ks) play a critical role in thymocyte development, although not all of their downstream mediators have yet been identified. Here, we discuss experimental evidence that argues for a critical role of the PI3K-phosphoinositide-dependent protein kinase (PDK1)-protein kinase B (PKB) signaling pathway in the development of both normal and malignant thymocytes, and we highlight molecules that can potentially be targeted therapeutically.