Reciprocal regulation of mTORC1 signaling and ribosomal biosynthesis determines cell cycle progression in activated T cells

Ribosomal biosynthesis in nucleoli is an energy-demanding process driven by all RNA polymerases and hundreds of auxiliary proteins. We investigated how this process is regulated in activated T lymphocytes by T cell receptor (TCR) signals and the multiprotein complexes mTORC1 and mTORC2, both of which contain the kinase mTOR. Deficiency in mTORC1 slowed the proliferation of T cells, with further delays in each consecutive division, an effect not seen with deficiency in mTORC2. mTORC1 signaling was stimulated by components of conventional TCR signaling, and, reciprocally, TCR sensitivity was decreased by mTORC1 inhibition. The substantial increase in the amount of RNA per cell induced by TCR activation was reduced by 50% by deficiency in mTORC1, but not in mTORC2 or in S6 kinases 1 and 2, which are activated downstream of mTORC1. RNA-seq data showed that mTORC1 deficiency reduced the abundance of all RNA biotypes, although rRNA processing was largely intact in activated T cells. Imaging cytometry with FISH probes for nascent pre-rRNA revealed that deletion of mTORC1, but not that of mTORC2, reduced the number and expansion of nucleolar sites of active transcription. Protein translation was consequently decreased by 50% in the absence of mTORC1. Inhibiting RNA polymerase I blocked not only proliferation but also mTORC1 signaling. Our data show that TCR signaling, mTORC1 activity, and ribosomal biosynthesis in the nucleolus regulate each other during biomass production in clonally expanding T cells.

Mitogen signaling strength and duration can control cell cycle decisions

Decades ago, mitogen-promoted signaling duration and strength were observed to be sensed by the cell and to be critical for its decisions: to proliferate or differentiate. Landmark publications established the importance of mitogen signaling not only in the G1 cell cycle phase but also through the S and the G2/M transition. Despite these early milestones, how mitogen signal duration and strength, short and strong or weaker and sustained, control cell fate has been largely unheeded. Here, we center on cardinal signaling-related questions, including (i) how fluctuating mitogenic signals are converted into cell proliferation-differentiation decisions and (ii) why extended duration of weak signaling is associated with differentiation, while bursts of strong and short induce proliferation but, if too strong and long, induce irreversible senescence. Our innovative broad outlook harnesses cell biology and protein conformational ensembles, helping us to define signaling strength, clarify cell cycle decisions, and thus cell fate.

The immunosuppressive drug cyclosporin A has an immunostimulatory function in CD8+ T cells

Cyclosporin A is a well-established immunosuppressive drug used to treat or prevent graft-versus-host disease, the rejection of organ transplants, autoimmune disorders, and leukemia. It exerts its immunosuppressive effects by inhibiting calcineurin-mediated dephosphorylation of the nuclear factor of activated T cells (NFAT), thus preventing its nuclear entry and suppressing T cell activation. Here we report an unexpected immunostimulatory effect of cyclosporin A in activating the mammalian target of rapamycin complex 1 (mTORC1), a crucial metabolic hub required for T cell activation. Through screening a panel of tool compounds known to regulate mTORC1 activation, we found that cyclosporin A activated mTORC1 in CD8+ T cells in a 3-phosphoinositide-dependent protein kinase 1 (PDK1) and protein kinase B (PKB/AKT)-dependent manner. Mechanistically, cyclosporin A inhibited the calcineurin-mediated AKT dephosphorylation, thereby stabilizing mTORC1 signaling. Cyclosporin A synergized with mTORC1 pathway inhibitors, leading to potent suppression of proliferation and cytokine production in CD8+ T cells and an increase in the killing of acute T cell leukemia cells. Consequently, relying solely on CsA is insufficient to achieve optimal therapeutic outcomes. It is necessary to simultaneously target both the calcineurin-NFAT pathway and the mTORC1 pathway to maximize therapeutic efficacy.

NKG2D receptor signaling shapes T cell thymic education

The role of natural killer group 2D (NKG2D) in peripheral T cells as a costimulatory receptor is well established. However, its contribution to T cell thymic education and functional imprint is unknown. Here, we report significant changes in development, receptor signaling, transcriptional program, and function in T cells from mice lacking NKG2D signaling. In C57BL/6 (B6) and OT-I mice, we found that NKG2D deficiency results in Vβ chain usage changes and stagnation of the double-positive stage in thymic T cell development. We found that the expression of CD5 and CD45 in thymocytes from NKG2D deficient mice were reduced, indicating a direct influence of NKG2D on the strength of T cell receptor (TCR) signaling during the developmental stage of T cells. Depicting the functional consequences of NKG2D, peripheral OT-I NKG2D-deficient cells were unresponsive to ovalbumin peptide stimulation. Paradoxically, while αCD3/CD28 agonist antibodies led to phenotypic T cell activation, their ability to produce cytokines remained severely compromised. We found that OT-I NKG2D-deficient cells activate STAT5 in response to interleukin-15 but were unable to phosphorylate ERK or S6 upon TCR engagement, underpinning a defect in TCR signaling. Finally, we showed that NKG2D is expressed in mouse and human thymic T cells at the double-negative stage, suggesting an evolutionarily conserved function during T cell development. The data presented in this study indicate that NKG2D impacts thymic T cell development at a fundamental level by reducing the TCR threshold and affecting the functional imprint of the thymic progeny. In summary, understanding the impact of NKG2D on thymic T cell development and TCR signaling contributes to our knowledge of immune system regulation, immune dysregulation, and the design of immunotherapies.

Decoding mTOR signalling heterogeneity in the tumour microenvironment using multiplexed imaging and graph convolutional networks

Evaluating the contribution of the tumour microenvironment (TME) in tumour progression has proven a complex challenge due to the intricate interactions within the TME. Multiplexed imaging is an emerging technology that allows concurrent assessment of multiple of these components simultaneously. Here we utilise a highly multiplexed dataset of 61 markers across 746 colorectal tumours to investigate how complex mTOR signalling in different tissue compartments influences patient prognosis. We found that the signalling of mTOR pathway can have heterogeneous activation patterns in tumour and immune compartments which correlate with patient prognosis. Using graph neural networks, we determined the most predictive features of mTOR activity in immune cells and identified relevant cellular subpopulations. We validated our observations using spatial transcriptomics data analysis in an independent patient cohort. Our work provides a framework for studying complex cell signalling and reveals important insights for developing mTOR-based therapies.

Canagliflozin impairs T cell effector function via metabolic suppression in autoimmunity

Augmented T cell function leading to host damage in autoimmunity is supported by metabolic dysregulation, making targeting immunometabolism an attractive therapeutic avenue. Canagliflozin, a type 2 diabetes drug, is a sodium glucose co-transporter 2 (SGLT2) inhibitor with known off-target effects on glutamate dehydrogenase and complex I. However, the effects of SGLT2 inhibitors on human T cell function have not been extensively explored. Here, we show that canagliflozin-treated T cells are compromised in their ability to activate, proliferate, and initiate effector functions. Canagliflozin inhibits T cell receptor signaling, impacting on ERK and mTORC1 activity, concomitantly associated with reduced c-Myc. Compromised c-Myc levels were encapsulated by a failure to engage translational machinery resulting in impaired metabolic protein and solute carrier production among others. Importantly, canagliflozin-treated T cells derived from patients with autoimmune disorders impaired their effector function. Taken together, our work highlights a potential therapeutic avenue for repurposing canagliflozin as an intervention for T cell-mediated autoimmunity.

Protein phosphatase 2A propels follicular T helper cell development in lupus

Follicular helper T (Tfh) cells are important for generating humoral immune responses by helping B cells form germinal centers (GCs) and the production of high-affinity antibodies. However, aberrant Tfh cell expansion also contributes to the generation of self-reactive autoantibodies and promotes autoantibody-mediated autoimmune diseases such as systemic lupus erythematosus (SLE). Protein phosphatase 2A catalytic subunit alpha isoform (PP2A Cα) expression levels are elevated in peripheral T cells of SLE patients and positively correlate with autoantibody titers and disease activity. Here, we demonstrate a critical role of PP2A in Tfh differentiation by using T cell restricted PP2A Cα deficient mice. We observed impaired Tfh differentiation and GC response in two different classical Tfh induction models. Mechanistic studies revealed that downregulation of protein translation of the Tfh lineage transcription factor BCL6 in PP2A deficient T cells. Importantly, we found that PP2A deficiency by either gene knockout or chemical inhibition alleviated lupus severity in mice. Lastly, we confirmed a positive correlation between PP2A Cα and BCL6 protein levels in human CD4+ T cells from patients with SLE. In summary, our study revealed a critical role of PP2A in regulating Tfh cells and suggests it is a potential therapeutic target for lupus.

Slippy-Sloppy translation: a tale of programmed and induced-ribosomal frameshifting

Programmed ribosomal frameshifting (PRF) is a key mechanism that viruses use to generate essential proteins for replication, and as a means of regulating gene expression. PRF generally involves recoding signals or frameshift stimulators to elevate the occurrence of frameshifting at shift-prone 'slippery' sequences. Given its essential role in viral replication, targeting PRF was envisioned as an attractive tool to block viral infection. However, in contrast to controlled-PRF mechanisms, recent studies have shown that ribosomes of many human cancer cell types are prone to frameshifting upon amino acid shortage; thus, these cells are deemed to be sloppy. The resulting products of a sloppy frameshift at the 'hungry' codons are aberrant proteins the degradation and display of which at the cell surface can trigger T cell activation. In this review, we address recent discoveries in ribosomal frameshifting and their functional consequences for the proteome in human cancer cells.

HIF-1 stabilization in T cells hampers the control of Mycobacterium tuberculosis infection

The hypoxia-inducible factors (HIFs) regulate the main transcriptional pathway of response to hypoxia in T cells and are negatively regulated by von Hippel-Lindau factor (VHL). But the role of HIFs in the regulation of CD4 T cell responses during infection with M. tuberculosis isn’t well understood. Here we show that mice lacking VHL in T cells (Vhl cKO) are highly susceptible to infection with M. tuberculosis, which is associated with a low accumulation of mycobacteria-specific T cells in the lungs that display reduced proliferation, altered differentiation and enhanced expression of inhibitory receptors. In contrast, HIF-1 deficiency in T cells is redundant for M. tuberculosis control. Vhl cKO mice also show reduced responses to vaccination. Further, VHL promotes proper MYC-activation, cell-growth responses, DNA synthesis, proliferation and survival of CD4 T cells after TCR activation. The VHL-deficient T cell responses are rescued by the loss of HIF-1α, indicating that the increased susceptibility to M. tuberculosis infection and the impaired responses of Vhl-deficient T cells are HIF-1-dependent.

The role of hypoxia inducible factors in infection and immune response is unclear. Here, the authors study their impact on the regulation of T cells responses during Mycobacteria tuberculosis infection using transcriptomics, flow cytometry and in vivo infection.

TGFβ limits Myc-dependent TCR-induced metabolic reprogramming in CD8+ T cells

T cell activation is dependent upon the integration of antigenic, co-stimulatory and cytokine-derived signals and the availability and acquisition of nutrients from the environment. Furthermore, T cell activation is accompanied by reprogramming of cellular metabolism to provide the energy and building blocks for proliferation, differentiation and effector function. Transforming growth factor β (TGFβ) has pleiotropic effects on T cell populations, having both an essential role in the maintenance of immune tolerance but also context-dependent pro-inflammatory functions. We set out to define the mechanisms underpinning the suppressive effects of TGFβ on mouse CD8+ T cell activation. RNA-sequencing analysis of TCR-stimulated T cells determined that Myc-regulated genes were highly enriched within gene sets downregulated by TGFβ. Functional analysis demonstrated that TGFβ impeded TCR-induced upregulation of amino acid transporter expression, amino acid uptake and protein synthesis. Furthermore, TCR-induced upregulation of Myc-dependent glycolytic metabolism was substantially inhibited by TGFβ treatment with minimal effects on mitochondrial respiration. Thus, our data suggest that inhibition of Myc-dependent metabolic reprogramming represents a major mechanism underpinning the suppressive effects of TGFβ on CD8+ T cell activation.

Protein synthesis, degradation, and energy metabolism in T cell immunity

T cell activation, proliferation, and differentiation into effector and memory states involve massive remodeling of T cell size and molecular content and create a massive increase in demand for energy and amino acids. Protein synthesis is an energy- and resource-demanding process; as such, changes in T cell energy production are intrinsically linked to proteome remodeling. In this review, we discuss how protein synthesis and degradation change over the course of a T cell immune response and the crosstalk between these processes and T cell energy metabolism. We highlight how the use of high-resolution mass spectrometry to analyze T cell proteomes can improve our understanding of how these processes are regulated.

Disruption of STIM1-mediated Ca2+ sensing and energy metabolism in adult skeletal muscle compromises exercise tolerance, proteostasis, and lean mass

OBJECTIVE

Stromal interaction molecule 1 (STIM1) is a single-pass transmembrane endoplasmic/sarcoplasmic reticulum (E/SR) protein recognized for its role in a store operated Ca2+ entry (SOCE), an ancient and ubiquitous signaling pathway. Whereas STIM1 is known to be indispensable during development, its biological and metabolic functions in mature muscles remain unclear.

METHODS

Conditional and tamoxifen inducible muscle STIM1 knock-out mouse models were coupled with multi-omics tools and comprehensive physiology to understand the role of STIM1 in regulating SOCE, mitochondrial quality and bioenergetics, and whole-body energy homeostasis.

RESULTS

This study shows that STIM1 is abundant in adult skeletal muscle, upregulated by exercise, and is present at SR-mitochondria interfaces. Inducible tissue-specific deletion of STIM1 (iSTIM1 KO) in adult muscle led to diminished lean mass, reduced exercise capacity, and perturbed fuel selection in the settings of energetic stress, without affecting whole-body glucose tolerance. Proteomics and phospho-proteomics analyses of iSTIM1 KO muscles revealed molecular signatures of low-grade E/SR stress and broad activation of processes and signaling networks involved in proteostasis.

CONCLUSION

These results show that STIM1 regulates cellular and mitochondrial Ca2+ dynamics, energy metabolism and proteostasis in adult skeletal muscles. Furthermore, these findings provide insight into the pathophysiology of muscle diseases linked to disturbances in STIM1-dependent Ca2+ handling.

Dysregulated PI3K Signaling in B Cells of CVID Patients

The altered wiring of signaling pathways downstream of antigen receptors of T and B cells contributes to the dysregulation of the adaptive immune system, potentially causing immunodeficiency and autoimmunity. In humans, the investigation of such complex systems benefits from nature’s experiments in patients with genetically defined primary immunodeficiencies. Disturbed B-cell receptor (BCR) signaling in a subgroup of common variable immunodeficiency (CVID) patients with immune dysregulation and expanded T-bet^highCD21^low B cells in peripheral blood has been previously reported. Here, we investigate PI3K signaling and its targets as crucial regulators of survival, proliferation and metabolism by intracellular flow cytometry, imaging flow cytometry and RNAseq. We observed increased basal but disturbed BCR-induced PI3K signaling, especially in T-bet^highCD21^low B cells from CVID patients, translating into impaired activation of crucial downstream molecules and affecting proliferation, survival and the metabolic profile. In contrast to CVID, increased basal activity of PI3K in patients with a gain-of-function mutation in PIK3CD and activated PI3K delta syndrome (APDS) did not result in impaired BCR-induced AKT-mTOR-S6 phosphorylation, highlighting that signaling defects in B cells in CVID and APDS patients are fundamentally different and that assessing responses to BCR stimulation is an appropriate confirmative diagnostic test for APDS. The active PI3K signaling in vivo may render autoreactive T-bet^highCD21^low B cells in CVID at the same time to be more sensitive to mTOR or PI3K inhibition.

GSK3β Interacts With CRMP2 and Notch1 and Controls T-Cell Motility

The trafficking of T-cells through peripheral tissues and into afferent lymphatic vessels is essential for immune surveillance and an adaptive immune response. Glycogen synthase kinase 3β (GSK3β) is a serine/threonine kinase and regulates numerous cell/tissue-specific functions, including cell survival, metabolism, and differentiation. Here, we report a crucial involvement of GSK3β in T-cell motility. Inhibition of GSK3β by CHIR-99021 or siRNA-mediated knockdown augmented the migratory behavior of human T-lymphocytes stimulated via an engagement of the T-cell integrin LFA-1 with its ligand ICAM-1. Proteomics and protein network analysis revealed ongoing interactions among GSK3β, the surface receptor Notch1 and the cytoskeletal regulator CRMP2. LFA-1 stimulation in T-cells reduced Notch1-dependent GSK3β activity by inducing phosphorylation at Ser9 and its nuclear translocation accompanied by the cleaved Notch1 intracellular domain and decreased GSK3β-CRMP2 association. LFA-1-induced or pharmacologic inhibition of GSK3β in T-cells diminished CRMP2 phosphorylation at Thr514. Although substantial amounts of CRMP2 were localized to the microtubule-organizing center in resting T-cells, this colocalization of CRMP2 was lost following LFA-1 stimulation. Moreover, the migratory advantage conferred by GSK3β inhibition in T-cells by CHIR-99021 was lost when CRMP2 expression was knocked-down by siRNA-induced gene silencing. We therefore conclude that GSK3β controls T-cell motility through interactions with CRMP2 and Notch1, which has important implications in adaptive immunity, T-cell mediated diseases and LFA-1-targeted therapies.

Biomaterial-enabled induction of pancreatic-specific regulatory T cells through distinct signal transduction pathways

Autoimmune diseases-where the immune system mistakenly targets self-tissue-remain hindered by non-specific therapies. For example, even molecularly specific monoclonal antibodies fail to distinguish between healthy cells and self-reactive cells. An experimental therapeutic approach involves delivery of self-molecules targeted by autoimmunity, along with immune modulatory signals to produce regulatory T cells (TREG) that selectively stop attack of host tissue. Much has been done to increase the efficiency of signal delivery using biomaterials, including encapsulation in polymer microparticles (MPs) to allow for co-delivery and cargo protection. However, less research has compared particles encapsulating drugs that target different TREG inducing pathways. In this paper, we use poly (lactic-co-glycolide) (PLGA) to co-encapsulate type 1 diabetes (T1D)-relevant antigen and 3 distinct TREG-inducing molecules - rapamycin (Rapa), all-trans retinoic acid (atRA), and butyrate (Buty) - that target the mechanistic target of Rapa (mTOR), the retinoid pathway, and histone deacetylase (HDAC) inhibition, respectively. We show all formulations are effectively taken up by antigen presenting cells (APCs) and that antigen-containing formulations are able to induce proliferation in antigen-specific T cells. Further, atRA and Rapa MP formulations co-loaded with antigen decrease APC activation levels, induce TREG differentiation, and reduce inflammatory cytokines in pancreatic-reactive T cells.

Potentiating Therapeutic Effects of Epidermal Growth Factor Receptor Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subset of breast cancer with aggressive characteristics and few therapeutic options. The lack of an appropriate therapeutic target is a challenging issue in treating TNBC. Although a high level expression of epidermal growth factor receptor (EGFR) has been associated with a poor prognosis among patients with TNBC, targeted anti-EGFR therapies have demonstrated limited efficacy for TNBC treatment in both clinical and preclinical settings. However, with the advantage of a number of clinically approved EGFR inhibitors (EGFRis), combination strategies have been explored as a promising approach to overcome the intrinsic resistance of TNBC to EGFRis. In this review, we analyzed the literature on the combination of EGFRis with other molecularly targeted therapeutics or conventional chemotherapeutics to understand the current knowledge and to provide potential therapeutic options for TNBC treatment.

Fyn Kinase Controls Tau Aggregation In Vivo

Alzheimer's disease (AD) is a proteinopathy exhibiting aggregation of β-amyloid (Aβ) as amyloid plaques and tau as neurofibrillary tangles (NFTs), whereas primary tauopathies display only a tau pathology. Aβ toxicity is mediated by Fyn kinase in a tau-dependent process; however, whether Fyn controls tau pathology in diseases that lack Aβ pathology remains unexplored. To address this, we generate the Tg/Fyn^-/- mouse, which couples mutant tau overexpression with Fyn knockout. Surprisingly, Tg/Fyn^-/- mice exhibit a near-complete ablation of NFTs, alongside reduced tau hyperphosphorylation, altered tau solubility, and diminished synaptic tau accumulation. Furthermore, Tg/Fyn^-/- brain lysates elicit less tau seeding in tau biosensor cells. Lastly, the fibrillization of tau is boosted by its pseudophosphorylation at the Fyn epitope Y18. Together, this identifies Fyn as a key regulator of tau pathology independently of Aβ-induced toxicity and thereby represents a potentially valuable therapeutic target for not only AD but also tauopathies more generally.

Coordination of asparagine uptake and asparagine synthetase expression modulates CD8+ T cell activation

T cell receptor (TCR) triggering by antigen results in metabolic reprogramming that, in turn, facilitates the exit of T cells from quiescence. The increased nutrient requirements of activated lymphocytes are met, in part, by upregulation of cell surface transporters and enhanced uptake of amino acids, fatty acids, and glucose from the environment. However, the role of intracellular pathways of amino acid biosynthesis in T cell activation is relatively unexplored. Asparagine is a nonessential amino acid that can be synthesized intracellularly through the glutamine-hydrolyzing enzyme asparagine synthetase (ASNS). We set out to define the requirements for uptake of extracellular asparagine and ASNS activity in CD8+ T cell activation. At early time points of activation in vitro, CD8+ T cells expressed little or no ASNS, and, as a consequence, viability and TCR-stimulated growth, activation, and metabolic reprogramming were substantially impaired under conditions of asparagine deprivation. At later time points (more than 24 hours of activation), TCR-induced mTOR-dependent signals resulted in ASNS upregulation that endowed CD8+ T cells with the capacity to function independently of extracellular asparagine. Thus, our data suggest that the coordinated upregulation of ASNS expression and uptake of extracellular asparagine is involved in optimal T cell effector responses.

Cutting Edge: Tissue Antigen Expression Levels Fine-Tune T Cell Differentiation Decisions In Vivo

Immune homeostasis in peripheral tissues is, to a large degree, maintained by the differentiation and action of regulatory T cells (Treg) specific for tissue Ags. Using a novel mouse model, we have studied the differentiation of naive CD4⁺ T cells into Foxp3⁺ Treg in response to a cutaneous Ag (OVA). We found that expression of OVA resulted in fatal autoimmunity and in prevention of peripheral Treg generation. Inhibiting mTOR activity with rapamycin rescued the generation of Foxp3⁺ T cells. When we varied the level of Ag expression to modulate TCR signaling, we found that low Ag concentrations promoted the generation of Foxp3⁺ T cells, whereas high levels expanded effector T cells and caused severe autoimmunity. Our findings indicate that the expression level of tissue Ag is a key determinant of the balance between tissue-reactive effector and peripheral Foxp3⁺ T cells, which determines the choice between tolerance and autoimmunity.

Gab3 is required for IL-2- and IL-15-induced NK cell expansion and limits trophoblast invasion during pregnancy

The scaffolding protein Grb2-associated binding protein 3 (Gab3) is a member of the Gab family, whose functions have remained elusive. Here, we identify Gab3 as a key determinant of peripheral NK cell expansion. Loss of Gab3 resulted in impaired IL-2 and IL-15-induced NK cell priming and expansion due to a selective impairment in MAPK signaling but not STAT5 signaling. In vivo, we found that Gab3 is required for recognition and elimination of "missing-self" and tumor targets. Unexpectedly, our studies also revealed that Gab3 plays an important role during pregnancy. Gab3-deficient mice exhibited impaired uterine NK cell expansion associated with abnormal spiral artery remodeling and increased trophoblast invasion in the decidua basalis. This coincided with stillbirth, retained placenta, maternal hemorrhage, and undelivered fetoplacental units at term. Thus, Gab3 is a key component required for cytokine-mediated NK cell priming and expansion that is essential for antitumor responses and limits trophoblast cell invasion during pregnancy.

Stimulation strength controls the rate of initiation but not the molecular organisation of TCR-induced signalling

Millions of naïve T cells with different TCRs may interact with a peptide-MHC ligand, but very few will activate. Remarkably, this fine control is orchestrated using a limited set of intracellular machinery. It remains unclear whether changes in stimulation strength alter the programme of signalling events leading to T cell activation. Using mass cytometry to simultaneously measure multiple signalling pathways during activation of murine CD8+ T cells, we found a programme of distal signalling events that is shared, regardless of the strength of TCR stimulation. Moreover, the relationship between transcription of early response genes Nr4a1 and Irf8 and activation of the ribosomal protein S6 is also conserved across stimuli. Instead, we found that stimulation strength dictates the rate with which cells initiate signalling through this network. These data suggest that TCR-induced signalling results in a coordinated activation program, modulated in rate but not organization by stimulation strength.

Targeting ERK-Hippo Interplay in Cancer Therapy

Extracellular signal-regulated kinase (ERK) is a part of the mitogen-activated protein kinase (MAPK) signaling pathway which allows the transduction of various cellular signals to final effectors and regulation of elementary cellular processes. Deregulation of the MAPK signaling occurs under many pathological conditions including neurodegenerative disorders, metabolic syndromes and cancers. Targeted inhibition of individual kinases of the MAPK signaling pathway using synthetic compounds represents a promising way to effective anti-cancer therapy. Cross-talk of the MAPK signaling pathway with other proteins and signaling pathways have a crucial impact on clinical outcomes of targeted therapies and plays important role during development of drug resistance in cancers. We discuss cross-talk of the MAPK/ERK signaling pathway with other signaling pathways, in particular interplay with the Hippo/MST pathway. We demonstrate the mechanism of cell death induction shared between MAPK/ERK and Hippo/MST signaling pathways and discuss the potential of combination targeting of these pathways in the development of more effective anti-cancer therapies.

Receptor protein tyrosine phosphatases control Purkinje neuron firing

Spinocerebellar ataxias (SCA) are a genetically heterogeneous family of cerebellar neurodegenerative diseases characterized by abnormal firing of Purkinje neurons and degeneration. We recently demonstrated the slowed firing rates seen in several SCAs share a common etiology of hyper-activation of the Src family of non-receptor tyrosine kinases (SFKs). However, the lack of clinically available neuroactive SFK inhibitors lead us to investigate alternative mechanisms to modulate SFK activity. Previous studies demonstrate that SFK activity can be enhanced by the removal of inhibitory phospho-marks by receptor-protein-tyrosine phosphatases (RPTPs). In this Extra View we show that MTSS1 inhibits SFK activity through the binding and inhibition of a subset of the RPTP family members, and lowering RPTP activity in cerebellar slices with peptide inhibitors increases the suppressed Purkinje neuron basal firing rates seen in two different SCA models. Together these results identify RPTPs as novel effectors of Purkinje neuron basal firing, extending the MTSS1/SFK regulatory circuit we previously described and expanding the therapeutic targets for SCA patients.

DAPK1 (death associated protein kinase 1) mediates mTORC1 activation and antiviral activities in CD8+ T cells

Mechanistic target of rapamycin complex 1 (mTORC1) regulates CD8⁺ T-cell differentiation and function. Despite the links between PI3K-AKT and mTORC1 activation in CD8⁺ T cells, the molecular mechanism underlying mTORC1 activation remains unclear. Here, we show that both the kinase activity and the death domain of DAPK1 are required for maximal mTOR activation and CD8⁺ T-cell function. We found that TCR-induced activation of calcineurin activates DAPK1, which subsequently interacts with TSC2 via its death domain and phosphorylates TSC2 to mediate mTORC1 activation. Furthermore, both the kinase domain and death domain of DAPK1 are required for CD8⁺ T-cell antiviral responses in an LCMV infection model. Together, our data reveal a novel mechanism of mTORC1 activation that mediates optimal CD8⁺ T-cell function and antiviral activity.

NKG2D signaling certifies effector CD8 T cells for memory formation

BACKGROUND

The development of memory responses is an evolutionary function of the adaptive immune system. We propose that for the immune system to populate the memory compartment with the best-suited CD8 T cells it utilizes a process of certification or molecular accreditation mediated through Natural Killer Group 2D (NKG2D). This process of certification assures that the memory compartment is filled with CD8 T cells that have demonstrated their ability to kill their cognate targets through a two-step process that utilizes T cell receptor (TCR) and NKG2D signaling.

METHODS

One week after immunization with peptide-pulsed dendritic cells, NKG2D signaling was transiently blocked in vivo with a single injection of neutralizing antibodies. Under such conditions, we determined the importance of NKG2D signaling during the effector phase for memory formation without compromising NKG2D signaling at the memory phase. Both open (polyclonal) and closed (monoclonal) CD8 T cell repertoires were studied.

RESULTS

We show that signaling through NKG2D mediated this certification. Temporary blockade of NKG2D signaling during the effector phase resulted in the formation of highly defective memory CD8 T cells characterized by altered expression of the ribosomal protein S6 and epigenetic modifiers, suggesting modifications in the T cell translational machinery and epigenetic programming. Finally, these uncertified memory cells were not protective against a B16 tumor challenge.

CONCLUSION

Signaling through NKG2D during the effector phase (certification) favors the development of functional memory CD8 T cells, a previously undescribed role for NKG2D. Temporary blockade of NKG2D signaling during the effector phase results in the formation of highly defective memory CD8 T cells potentially by affecting the expression of the ribosomal protein S6 and epigenetic modifiers, suggesting alterations in T cell translational machinery and epigenetic programming.

The PI3K p110δ Isoform Inhibitor Idelalisib Preferentially Inhibits Human Regulatory T Cell Function

In chronic lymphocytic leukemia (CLL), signaling through several prosurvival B cell surface receptors activates the PI3K signaling pathway. Idelalisib is a highly selective PI3K (PI3Kδ) isoform-specific inhibitor effective in relapsed/refractory CLL and follicular lymphoma. However, severe autoimmune adverse effects in association with the use of idelalisib in the treatment of CLL, particularly as a first-line therapy, gave indications that idelalisib may preferentially target the suppressive function of regulatory T cells (Tregs). On this background, we examined the effect of idelalisib on the function of human Tregs ex vivo with respect to proliferation, TCR signaling, phenotype, and suppressive function. Our results show that human Tregs are highly susceptible to PI3Kδ inactivation using idelalisib compared with CD4⁺ and CD8⁺ effector T cells (Teffs) as evident from effects on anti-CD3/CD28/CD2-induced proliferation (order of susceptibility [IC₅₀]: Treg [.5 μM] > CD4⁺ Teff [2.0 μM] > CD8⁺ Teff [6.5 μM]) and acting at the level of AKT and NF-κB phosphorylation. Moreover, idelalisib treatment of Tregs altered their phenotype and reduced their suppressive function against CD4⁺ and CD8⁺ Teffs. Phenotyping Tregs from CLL patients treated with idelalisib supported our in vitro findings. Collectively, our data show that human Tregs are more dependent on PI3Kδ-mediated signaling compared with CD4⁺ and CD8⁺ Teffs. This Treg-preferential effect could explain why idelalisib produces adverse autoimmune effects by breaking Treg-mediated tolerance. However, balancing effects on Treg sensitivity versus CD8⁺ Teff insensitivity to idelalisib could still potentially be exploited to enhance inherent antitumor immune responses in patients.

Eradication of Established Tumors by Chemically Self-Assembled Nanoring Labeled T Cells

Our laboratory has developed chemically self-assembled nanorings (CSANs) as prosthetic antigen receptors (PARs) for the nongenetic modification of T cell surfaces. PARs have been successfully employed in vitro to activate T cells for the selective killing of leukemia cells. However, PAR efficacy has yet to be evaluated in vivo or against solid tumors. Therefore, we developed bispecific PARs that selectively target the human CD3 receptor and human epithelial cell adhesion molecule (EpCAM), which is overexpressed on multiple carcinomas and cancer stem cells. The αEpCAM/αCD3 PARs were found to stably bind T cells for >4 days, and treating EpCAM⁺ MCF-7 breast cancer cells with αEpCAM/αCD3 PAR-functionalized T cells resulted in the induction of IL-2, IFN-γ, and MCF-7 cytotoxicity. Furthermore, an orthotopic breast cancer model validated the ability of αEpCAM/αCD3 PAR therapy to direct T cell lytic activity toward EpCAM⁺ breast cancer cells in vivo, leading to tumor eradication. In vivo biodistribution studies demonstrated that PAR-T cells were formed in vivo and persist for over 48 h with rapid accumulation in tumor tissue. Following PAR treatment, the production of IL-2, IFN-γ, IL-6, and TNF-α could be significantly reduced by an infusion of clinically relevant concentrations of the FDA-approved antibiotic, trimethoprim, signaling pharmacologic PAR deactivation. Importantly, CSANs did not induce naïve T cell activation and thus exhibit a limited potential to induce naïve T cell anergy. In addition, murine immunogenicity studies demonstrated that CSANs do not induce a significant antibody response nor do they activate splenic cells. Collectively, our results demonstrate that bispecific CSANs are able to nongenetically generate reversibly modified T cells that are capable of eradicating targeted solid tumors.

IQ Domain-Containing GTPase-Activating Protein 1 Regulates Cytoskeletal Reorganization and Facilitates NKG2D-Mediated Mechanistic Target of Rapamycin Complex 1 Activation and Cytokine Gene Translation in Natural Killer Cells

Natural killer (NK) cells are innate lymphocytes that play essential roles in mediating antitumor immunity. NK cells respond to various inflammatory stimuli including cytokines and stress-induced cellular ligands which activate germline-encoded activation receptors (NKRs), such as NKG2D. The signaling molecules activated downstream of NKRs are well defined; however, the mechanisms that regulate these pathways are not fully understood. IQ domain-containing GTPase-activating protein 1 (IQGAP1) is a ubiquitously expressed scaffold protein. It regulates diverse cellular signaling programs in various physiological contexts, including immune cell activation and function. Therefore, we sought to investigate the role of IQGAP1 in NK cells. Development and maturation of NK cells from mice lacking IQGAP1 (Iqgap1^-/- ) were mostly intact; however, the absolute number of splenic NK cells was significantly reduced. Phenotypic and functional characterization revealed a significant reduction in the egression of NK cells from the bone marrow of Iqagp1^-/- mice altering their peripheral homeostasis. Lack of IQGAP1 resulted in reduced NK cell motility and their ability to mediate antitumor immunity in vivo. Activation of Iqgap1^-/- NK cells via NKRs, including NKG2D, resulted in significantly reduced levels of inflammatory cytokines compared with wild-type (WT). This reduction in Iqgap1^-/- NK cells is neither due to an impaired membrane proximal signaling nor a defect in gene transcription. The levels of Ifng transcripts were comparable between WT and Iqgap1^-/- , suggesting that IQGAP1-dependent regulation of cytokine production is regulated by a post-transcriptional mechanism. To this end, Iqgap1^-/- NK cells failed to fully induce S6 phosphorylation and showed significantly reduced protein translation following NKG2D-mediated activation, revealing a previously undefined regulatory function of IQGAP1 via the mechanistic target of rapamycin complex 1. Together, these results implicate IQGAP1 as an essential scaffold for NK cell homeostasis and function and provide novel mechanistic insights to the post-transcriptional regulation of inflammatory cytokine production.

An investigation of the anti-inflammatory effects and a potential biomarker of PI3Kδ inhibition in COPD T cells

Lymphocyte numbers are increased in the lungs of chronic obstructive pulmonary disease (COPD) patients. Phosphatidylinositol-3-kinase delta (PI3Kδ) is involved in lymphocyte activation. We investigated the effect of PI3Kδ inhibition on cytokine release from COPD lymphocytes. We also evaluated phosphorylated ribosomal S6 protein (rS6) as a potential biomarker of PI3Kδ activation. Peripheral blood mononuclear cells (PBMCs) and bronchoalveolar lavage (BAL) cells isolated from healthy never smokers (HNS), smokers (S) and COPD patients were stimulated to induce a T cell receptor response. The effects of a PI3Kδ specific inhibitor (GSK045) on cytokine release and rS6 phosphorylation were measured by Luminex and flow cytometry respectively. The effects of GSK045 on cytokine production from PHA stimulated chopped lung samples were investigated. GSK045 reduced cytokine release from PBMCs, BAL cells and chopped lung. Inhibition was greatest in the chopped lung model, with approximately 80% inhibition of interferon (IFN) γ, interleukin (IL)-2, IL-17 and IL-10. PI3Kδ inhibition suppressed rS6 phosphorylation in unstimulated airway T-lymphocytes by up to 60%. Inhibition of PI3Kδ suppressed T cell cytokine production in COPD patients. rS6 phosphorylation shows potential as a biomarker to assess PI3Kδ activity.

Prior acetaminophen consumption impacts the early adaptive cellular response of human skeletal muscle to resistance exercise

Resistance exercise (RE) is a powerful stimulus for skeletal muscle adaptation. Previous data demonstrate that cyclooxygenase (COX)-inhibiting drugs alter the cellular mechanisms regulating the adaptive response of skeletal muscle. The purpose of this study was to determine whether prior consumption of the COX inhibitor acetaminophen (APAP) alters the immediate adaptive cellular response in human skeletal muscle after RE. In a double-blinded, randomized, crossover design, healthy young men ( n = 8, 25 ± 1 yr) performed two trials of unilateral knee extension RE (8 sets, 10 reps, 65% max strength). Subjects ingested either APAP (1,000 mg/6 h) or placebo (PLA) for 24 h before RE (final dose consumed immediately after RE). Muscle biopsies (vastus lateralis) were collected at rest and 1 h and 3 h after exercise. Mammalian target of rapamycin (mTOR) complex 1 signaling was assessed through immunoblot and immunohistochemistry, and mRNA expression of myogenic genes was examined via RT-qPCR. At 1 h p-rpS6Ser240/244 was increased in both groups but to a greater extent in PLA. At 3 h p-S6K1Thr389 was elevated only in PLA. Furthermore, localization of mTOR to the lysosome (LAMP2) in myosin heavy chain (MHC) II fibers increased 3 h after exercise only in PLA. mTOR-LAMP2 colocalization in MHC I fibers was greater in PLA vs. APAP 1 h after exercise. Myostatin mRNA expression was reduced 1 h after exercise only in PLA. MYF6 mRNA expression was increased 1 h and 3 h after exercise only in APAP. APAP consumption appears to alter the early adaptive cellular response of skeletal muscle to RE. These findings further highlight the mechanisms through which COX-inhibiting drugs impact the adaptive response of skeletal muscle to exercise.

NEW & NOTEWORTHY The extent to which the cellular reaction to acetaminophen impacts the mechanisms regulating the adaptive response of human skeletal muscle to resistance exercise is not well understood. Consumption of acetaminophen before resistance exercise appears to suppress the early response of mTORC1 activity to acute resistance exercise. These data also demonstrate, for the first time, that resistance exercise elicits fiber type-specific changes in the intracellular colocalization of mTOR with the lysosome in human skeletal muscle.

Annexin A1: Uncovering the Many Talents of an Old Protein

Annexin A1 (ANXA1) has long been classed as an anti-inflammatory protein due to its control over leukocyte-mediated immune responses. However, it is now recognized that ANXA1 has widespread effects beyond the immune system with implications in maintaining the homeostatic environment within the entire body due to its ability to affect cellular signalling, hormonal secretion, foetal development, the aging process and development of disease. In this review, we aim to provide a global overview of the role of ANXA1 covering aspects of peripheral and central inflammation, immune repair and endocrine control with focus on the prognostic, diagnostic and therapeutic potential of the molecule in cancer, neurodegeneration and inflammatory-based disorders.

Inhibition of 5-Hydroxytryptamine Receptor 2B Reduced Vascular Restenosis and Mitigated the β-Arrestin2-Mammalian Target of Rapamycin/p70S6K Pathway

BACKGROUND

As a monoamine neurotransmitter, 5-hydroxytryptamine (5-HT) or serotonin modulates mood, appetite, and sleep. Besides, 5-HT also has important peripheral functions. 5-HT receptor 2B (5-HT2BR) plays a key role in cardiovascular diseases, such as pulmonary arterial hypertension and cardiac valve disease. Percutaneous intervention has been used to restore blood flow in occlusive vascular disease. However, restenosis remains a significant problem. Herein, we investigated the role of 5-HT2BR in neointimal hyperplasia, a key pathological process in restenosis.

METHODS AND RESULTS

The expression of 5-HT2BR was upregulated in wire-injured mouse femoral arteries. In addition, BW723C86, a selective 5-HT2BR agonist, promoted the injury response during restenosis. 5-HT and BW723C86 stimulated migration and proliferation of rat aortic smooth muscle cells. Conversely, LY272015, a selective antagonist, attenuated the 5-HT-induced smooth muscle cell migration and proliferation. In vitro study showed that the promigratory effects of 5-HT2BR were mediated through the activation of mammalian target of rapamycin (mTOR)/p70S6K signaling in a β-arrestin2-dependent manner. Inhibition of mammalian target of rapamycin or p70S6K mitigated 5-HT2BR-mediated smooth muscle cell migration. Mice with deficiency of 5-HT2BR showed significantly reduced neointimal formation in wire-injured arteries.

CONCLUSIONS

These results demonstrated that activation of 5-HT2BR and β-arrestin2-biased downstream signaling are key pathological processes in neointimal formation, and 5-HT2BR may be a potential target for the therapeutic intervention of vascular restenosis.

Expression of LLT1 and its receptor CD161 in lung cancer is associated with better clinical outcome

Co-stimulatory and inhibitory receptors expressed by immune cells in the tumor microenvironment modulate the immune response and cancer progression. Their expression and regulation are still not fully characterized and a better understanding of these mechanisms is needed to improve current immunotherapies. Our previous work has identified a novel ligand/receptor pair, LLT1/CD161, that modulates immune responses. Here, we extensively characterize its expression in non-small cell lung cancer (NSCLC). We show that LLT1 expression is restricted to germinal center (GC) B cells within tertiary lymphoid structures (TLS), representing a new hallmark of the presence of active TLS in the tumor microenvironment. CD161-expressing immune cells are found at the vicinity of these structures, with a global enrichment of NSCLC tumors in CD161+ CD4+ and CD8+ T cells as compared to normal distant lung and peripheral blood. CD161+ CD4+ T cells are more activated and produce Th1-cytokines at a higher frequency than their matched CD161-negative counterparts. Interestingly, CD161+ CD4+ T cells highly express OX40 co-stimulatory receptor, less frequently 4-1BB, and display an activated but not completely exhausted PD-1-positive Tim-3-negative phenotype. Finally, a meta-analysis revealed a positive association of CLEC2D (coding for LLT1) and KLRB1 (coding for CD161) gene expression with favorable outcome in NSCLC, independently of the size of T and B cell infiltrates. These data are consistent with a positive impact of LLT1/CD161 on NSCLC patient survival, and make CD161-expressing CD4+ T cells ideal candidates for efficient anti-tumor recall responses.

Novel multi‑kinase inhibitor, T03 inhibits Taxol‑resistant breast cancer

Activation of kinase-associated signaling pathways is one of the leading causes of various malignant phenotypes in breast tumors. Strategies of drug discovery and development have investigated approaches to target the inhibition of protein kinase signaling. In the current study, the anti‑tumor activities of a novel multi‑kinase inhibitor, T03 were evaluated in breast cancer. T03 inhibited Taxol‑resistant breast cancer cell proliferation and induced cell cycle arrest and apoptosis in vitro and in vivo. The current results demonstrated that T03 downregulated c‑Raf, platelet‑derived growth factor receptor‑β and other kinases, thus inhibited Raf/mitogen‑activated protein kinase kinase/extracellular signal‑regulated kinase and Akt/mechanistic target of rapamycin survival pathways in MCF‑7 and MCF‑7/Taxol xenograft tumors. At a dose of 100 mg/kg, T03 inhibited tumor growth by 62.90 and 59.98% in tumor weight in MX‑1 and MX‑1/T xenograft models, respectively and by 62.60 and 60.22% in MCF‑7 and MCF‑7/T tumors, respectively. These data indicate that the novel multi‑kinase inhibitor, T03, may present as a potential compound to develop novel treatments against breast cancer and Taxol‑resistant breast tumors.

TIM-3 Engagement Promotes Effector Memory T Cell Differentiation of Human Antigen-Specific CD8 T Cells by Activating mTORC1

T cell expression of TIM-3 following Ag encounter has been associated with a continuum of functional states ranging from effector memory T cells to exhaustion. We have designed an in vitro culture system to specifically address the impact of anti-TIM-3/TIM-3 engagement on human Ag-specific CD8 T cells during a normal response to Ag and found that anti-TIM-3 treatment enhances T cell function. In our in vitro T cell culture system, MART1-specific CD8 T cells were expanded from healthy donors using artificial APCs. To ensure that the T cells were the only source of TIM-3, cells were rechallenged with peptide-loaded artificial APCs in the presence of anti-TIM-3 Ab. In these conditions, anti-TIM-3 treatment promotes generation of effector T cells as shown by acquisition of an activated phenotype, increased cytokine production, enhanced proliferation, and a transcription program associated with T cell differentiation. Activation of mTORC1 has been previously demonstrated to enhance CD8 T cell effector function and differentiation. Anti-TIM-3 drives CD8 T cell differentiation through activation of the mTORC1 as evidenced by increased levels of phosphorylated S6 protein and rhebl1 transcript. Altogether these findings suggest that anti-TIM-3, together with Ag, drives differentiation in favor of effector T cells via the activation of mTOR pathway. To our knowledge, this is the first report demonstrating that TIM-3 engagement during Ag stimulation directly influences T cell differentiation through mTORC1.

Somatodendritic accumulation of Tau in Alzheimer's disease is promoted by Fyn-mediated local protein translation

The cause of protein accumulation in neurodegenerative disease is incompletely understood. In Alzheimer's disease (AD), the axonally enriched protein Tau forms hyperphosphorylated aggregates in the somatodendritic domain. Consequently, a process of subcellular relocalization driven by Tau phosphorylation and detachment from microtubules has been proposed. Here, we reveal an alternative mechanism of de novo protein synthesis of Tau and its hyperphosphorylation in the somatodendritic domain, induced by oligomeric amyloid-β (Aβ) and mediated by the kinase Fyn that activates the ERK/S6 signaling pathway. Activation of this pathway is demonstrated in a range of cellular systems, and in vivo in brains from Aβ-depositing, Aβ-injected, and Fyn-overexpressing mice with Tau accumulation. Both pharmacological inhibition and genetic deletion of Fyn abolish the Aβ-induced Tau overexpression via ERK/S6 suppression. Together, these findings present a more cogent mechanism of Tau aggregation in disease. They identify a prominent role for neuronal Fyn in integrating signal transduction pathways that lead to the somatodendritic accumulation of Tau in AD.

The PI3K Pathway in Human Disease

Phosphoinositide 3-kinase (PI3K) activity is stimulated by diverse oncogenes and growth factor receptors, and elevated PI3K signaling is considered a hallmark of cancer. Many PI3K pathway-targeted therapies have been tested in oncology trials, resulting in regulatory approval of one isoform-selective inhibitor (idelalisib) for treatment of certain blood cancers and a variety of other agents at different stages of development. In parallel to PI3K research by cancer biologists, investigations in other fields have uncovered exciting and often unpredicted roles for PI3K catalytic and regulatory subunits in normal cell function and in disease. Many of these functions impinge upon oncology by influencing the efficacy and toxicity of PI3K-targeted therapies. Here we provide a perspective on the roles of class I PI3Ks in the regulation of cellular metabolism and in immune system functions, two topics closely intertwined with cancer biology. We also discuss recent progress developing PI3K-targeted therapies for treatment of cancer and other diseases.

Influence of the RPL34 gene on the growth and metastasis of oral squamous cell carcinoma cells

BACKGROUND

Oral squamous cell carcinoma (OSCC) accounts for almost 3% of all malignant tumors all over the world. This study aims to investigate the correlation of RPL34 with the cell growth and metastasis of oral squamous cell carcinoma (OSCC) as well as its clinical prognosis.

METHOD

Quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemistry were conducted to determine the RPL34 expression in 85 OSCC tissues and 30 normal oral mucosa tissues. Besides, OSCC cell lines SCC-4 were divided into blank group, negative control (NC) group and RPL34-shRNA group. The qRT-PCR and western blot were performed to measure RPL34 expression, CCK-8 and flow cytometry to observe cell growth and apoptosis, and wound healing and transwell to detect cell migration and invasion.

RESULTS

The RPL34 gene expression was up-regulated in OSCC tissues and cells. The RPL34 expression was significantly correlated with differentiation degree, TNM stage and lymph node metastasis. Patients with positive RPL34 expression had a poorer prognosis. After inhibition of RPL34 expression, the proliferation of SCC-4 cells was slowed down at 24h, 48h, 72h and 96h respectively, and both the migration distance and the number of invasive cells were reduced, while there was an increase in the ratio of cells at G0/G1 stage and cell apoptosis.

CONCLUSION

The RPL34 gene was highly expressed in OSCC, while silencing RPL34 could block cell proliferation and metastasis, but promote cell apoptosis, suggesting the RPL34 gene to be a new promising clinical target for OSCC therapy.

Essential Role of mTORC1 in Self-Renewal of Murine Alveolar Macrophages

Alveolar macrophages (AMϕ) have the capacity of local self-renewal through adult life; however, mechanisms that regulate AMϕ self-renewal remain poorly understood. We found that myeloid-specific deletion of Raptor, an essential component of the mammalian/mechanistic target of rapamycin complex (mTORC)1, resulted in a marked decrease of this population of cells accompanying altered phenotypic features and impaired phagocytosis activity. We demonstrated further that Raptor/mTORC1 deficiency did not affect AMϕ development, but compromised its proliferative activity at cell cycle entry in the steady-state as well as in the context of repopulation in irradiation chimeras. Mechanically, mTORC1 confers AMϕ optimal responsiveness to GM-CSF-induced proliferation. Thus, our results demonstrate an essential role of mTORC1 for AMϕ homeostasis by regulating proliferative renewal.

Selective Sparing of Human Tregs by Pharmacologic Inhibitors of the Phosphatidylinositol 3-Kinase and MEK Pathways

Phosphatidylinositol 3-kinase (PI3K) and mitogen-activated protein kinase/extracellular signal-regulated (MEK) signaling are central to the survival and proliferation of many cell types. Multiple lines of investigation in murine models have shown that control of the PI3K pathway is particularly important for regulatory T cell (Treg) stability and function. PI3K and MEK inhibitors are being introduced into the clinic, and we hypothesized that pharmacologic inhibition of PI3K, and possibly MEK, in mixed cultures of human mononuclear cells would preferentially affect CD4(+) and CD8(+) lymphocytes compared with Tregs. We tested this hypothesis using four readouts: proliferation, activation, functional suppression, and signaling. Results showed that Tregs were less susceptible to inhibition by both δ and α isoform-specific PI3K inhibitors and by an MEK inhibitor compared with their conventional CD4(+) and CD8(+) counterparts. These studies suggest less functional reliance on PI3K and MEK signaling in Tregs compared with conventional CD4(+) and CD8(+) lymphocytes. Therefore, the PI3K and MEK pathways are attractive pharmacologic targets for transplantation and treatment of autoimmunity.

Early changes in the metabolic profile of activated CD8(+) T cells

Background

Antigenic stimulation of the T cell receptor (TCR) initiates a change from a resting state into an activated one, which ultimately results in proliferation and the acquisition of effector functions. To accomplish this task, T cells require dramatic changes in metabolism. Therefore, we investigated changes of metabolic intermediates indicating for crucial metabolic pathways reflecting the status of T cells. Moreover we analyzed possible regulatory molecules required for the initiation of the metabolic changes.

Results

We found that proliferation inducing conditions result in an increase in key glycolytic metabolites, whereas the citric acid cycle remains unaffected. The upregulation of glycolysis led to a strong lactate production, which depends upon AKT/PKB, but not mTOR. The observed upregulation of lactate dehydrogenase results in increased lactate production, which we found to be dependent on IL-2 and to be required for proliferation. Additionally we observed upregulation of Glucose-transporter 1 (GLUT1) and glucose uptake upon stimulation, which were surprisingly not influenced by AKT inhibition.

Conclusions

Our findings suggest that AKT plays a central role in upregulating glycolysis via induction of lactate dehydrogenase expression, but has no impact on glucose uptake of T cells. Furthermore, under apoptosis inducing conditions, T cells are not able to upregulate glycolysis and induce lactate production. In addition maintaining high glycolytic rates strongly depends on IL-2 production.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-016-0104-x) contains supplementary material, which is available to authorized users.

Performance of a phosphoflow assay to determine phosphorylation of S6 ribosomal protein as a pharmacodynamic read out for mTOR inhibition

OBJECTIVES

The S6 ribosomal protein (S6RP) is phosphorylated by the mammalian target of rapamycin (mTOR). The objective of this study was to assess the analytical suitability of a commercial kit-based phosphoflow cytometry protocol using whole blood (WBS) to measure the level of phosphorylated S6RP (p-S6RP) in T-cell subsets to study the pharmacodynamic effects of mTOR inhibitors (mTORi).

DESIGN AND METHODS

A kit was used for fixation and permeabilization of mitogen-stimulated cells, and p-S6RP was assessed separately in CD3+CD4+ and CD3+CD8+ cells by employing an anti-phospho-Ser235/236 antibody. Specificity, linearity, within-run precision and stability were investigated in either WBS spiked with everolimus and non-mTORi immunosuppressants or in WBS from patients on immunosuppressive therapy (n=56). In addition, healthy controls (n=10) and patients without immunosuppression (n=10) were included. A comparison (n=15) with an established western blot method based on anti-phospho p70S6 kinase (Thr389) was made by splitting WBS.

RESULTS

Everolimus decreased p-S6RP in vitro concentration dependently (0.00-27.4μg/L). This effect was also confirmed in vivo after a single dose of everolimus to healthy volunteers (n=3). However, spiking WBS with 500μg/L cyclosporine also decreased p-S6RP. The within-run coefficient of variation was <18% in transplant patients and <27% in healthy controls for both cell subsets. Sample stability for p-S6RP analysis was limited (<24h). p-S6RP was significantly decreased in CD3+CD8+ cells of patients treated with sirolimus (p=0.02) but not with everolimus. No significant correlation between the phosphoflow- and western blot method was noted.

CONCLUSION

The phosphoflow assay of p-S6RP performed well analytically, but sample stability, specificity, and method comparison results question its fitness for clinical purposes.

Regulators of Glucose Metabolism in CD4+ and CD8+ T Cells

Much like cancer cells, activated T cells undergo various metabolic changes that allow them to grow and proliferate rapidly. By adopting aerobic glycolysis upon activation, T cells effectively prioritize efficiency in biosynthesis over energy generation. There are distinct differences in the way CD4⁺ and CD8⁺ T cells process activation signals. CD8⁺ effector T cells are less dependent on Glut1 and oxygen levels compared to their CD4⁺ counterparts. Similarly the downstream signaling by TCR also differs in both effector T cell types. Recent studies have explored PI3K/Akt, mTORC, HIF1α, p70S6K and Bcl-6 signaling in depth providing definition of the crucial roles of these regulators in glucose metabolism. These new insights may allow improved therapeutic manipulation against inflammatory conditions that are associated with dysfunctional T-cell metabolism such as autoimmune disorders, metabolic syndrome, HIV, and cancers.

Asparagine deprivation mediated by Salmonella asparaginase causes suppression of activation-induced T cell metabolic reprogramming

Salmonellae are pathogenic bacteria that induce immunosuppression by mechanisms that remain largely unknown. Previously, we showed that a putative type II l-asparaginase produced by Salmonella Typhimurium inhibits T cell responses and mediates virulence in a murine model of infection. Here, we report that this putative L-asparaginase exhibits L-asparagine hydrolase activity required for Salmonella Typhimurium to inhibit T cells. We show that L-asparagine is a nutrient important for T cell activation and that L-asparagine deprivation, such as that mediated by the Salmonella Typhimurium L-asparaginase, causes suppression of activation-induced mammalian target of rapamycin signaling, autophagy, Myc expression, and L-lactate secretion. We also show that L-asparagine deprivation mediated by the Salmonella Typhimurium L-asparaginase causes suppression of cellular processes and pathways involved in protein synthesis, metabolism, and immune response. Our results advance knowledge of a mechanism used by Salmonella Typhimurium to inhibit T cell responses and mediate virulence, and provide new insights into the prerequisites of T cell activation. We propose a model in which l-asparagine deprivation inhibits T cell exit from quiescence by causing suppression of activation-induced metabolic reprogramming.

Hyperphosphorylation of ribosomal protein S6 predicts unfavorable clinical survival in non-small cell lung cancer

Background

Ribosomal protein S6 (rpS6), a component of the 40S ribosomal subunit, is involved in multiple cellular bioactivities. However, its clinicopathological significance in non-small cell lung cancer (NSCLC) is poorly understood.

Methods

Expressions of total rpS6 (t-rpS6) and phosphorylated rpS6 (Ser235/236, p-rpS6) were detected immunohistochemically in 316 NSCLC tissues and 82 adjacent controls, followed by statistical evaluation of the relationship between proteins expressions and patients’ survivals to identify their prognostic values. Cytological experiments with overexpressing or silencing rpS6 by lentivirus in human bronchial epithelial (HBE) and NSCLC cell lines were performed to explore potential mechanisms by which rpS6 affects the clinical development of NSCLC. Additionally, specific RNA interference for Akt1, Akt2, Akt3, Akt inhibitor and subsequent cellular bioactivity tests were employed as well to investigate the upstream regulation of rpS6.

Results

Positive rates of t-rpS6 and p-rpS6 were both significantly increased in NSCLC tissues, compared with controls (82.91 vs 62.20 % for t-rpS6; 52.22 vs 21.95 % for p-rpS6; both P < 0.001). However, only hyperphosphorylation of rpS6, expressed as either elevated p-rpS6 alone or the ratio of p-rpS6 to t-rpS6 (p-rpS6/t-rpS6) no less than 0.67, was greatly associated with the unfavorable survival of NSCLC patients, especially for cases at stage I (all P < 0.001). The independent adverse prognostic value of hyperphosphorylated rpS6 was confirmed by multivariate Cox regression analysis (hazard ratios for elevated p-rpS6 alone and p-rpS6/t-rpS6 no less than 0.67 were 2.403, 4.311 respectively, both P < 0.001). Overexpression or knockdown of rpS6, along with parallel alterations of p-rpS6, led to increased or decreased cells proliferations respectively, which were dependent on redistributions of cell cycles (all P < 0.05). Cells migration and invasion also changed with rpS6 interference (all P < 0.05). Furthermore, upstream overexpression or knockdown of Akt2 or Akt2 phosphorylation inhibition, rather than Akt1 or Akt3, resulted in striking hyperphosphorylation or dephosphorylation of mTOR, p70S6K and rpS6 (all P < 0.05), without any change in total proteins expressions. Further tests showed markedly accompanied variation of cells proliferation, cell cycle distribution and invasion (all P < 0.05).

Conclusion

Hyperphosphorylation of rpS6, probably regulated by the Akt2/mTOR/p70S6K signaling pathway, is closely relevant to the progression of NSCLC and it might be served as a promising therapeutic target for NSCLC treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0239-1) contains supplementary material, which is available to authorized users.

Mechanistic Target of Rapamycin Complex 1/S6 Kinase 1 Signals Influence T Cell Activation Independently of Ribosomal Protein S6 Phosphorylation

Ag-dependent activation of naive T cells induces dramatic changes in cellular metabolism that are essential for cell growth, division, and differentiation. In recent years, the serine/threonine kinase mechanistic target of rapamycin (mTOR) has emerged as a key integrator of signaling pathways that regulate these metabolic processes. However, the role of specific downstream effectors of mTOR function in T cells is poorly understood. Ribosomal protein S6 (rpS6) is an essential component of the ribosome and is inducibly phosphorylated following mTOR activation in eukaryotic cells. In the current work, we addressed the role of phosphorylation of rpS6 as an effector of mTOR function in T cell development, growth, proliferation, and differentiation using knockin and TCR transgenic mice. Surprisingly, we demonstrate that rpS6 phosphorylation is not required for any of these processes either in vitro or in vivo. Indeed, rpS6 knockin mice are completely sensitive to the inhibitory effects of rapamycin and an S6 kinase 1 (S6K1)–specific inhibitor on T cell activation and proliferation. These results place the mTOR complex 1-S6K1 axis as a crucial determinant of T cell activation independently of its ability to regulate rpS6 phosphorylation.

Protein phosphorylation profiling identifies potential mechanisms for direct immunotoxicity

Signaling networks are essential elements that are involved in diverse cellular processes. One group of fundamental components in various signaling pathways concerns protein tyrosine kinases (PTK). Various toxicants have been demonstrated to exert their toxicity via modulation of tyrosine kinase activity. The present study aimed to identify common cellular signaling pathways that are involved in chemical-induced direct immunotoxicity. To this end, an antibody array-based profiling approach was applied to assess effects of five immunotoxicants, two immunosuppressive drugs and two non-immunotoxic control chemicals on the phosphorylation of 28 receptor tyrosine kinases and 11 crucial signaling nodes in Jurkat T-cells. The phosphorylation of ribosomal protein S6 (RPS6) and of kinases Akt, Src and p44/42 were found to be commonly regulated by immunotoxicants and/or immunosuppressive drugs (at least three compounds), with the largest effect observed upon RPS6. Flow cytometry and Western blotting were used to further examine the effect of the model immunotoxicant TBTO on the components of the mTOR-p70S6K-RPS6 pathway. These analyses revealed that both TBTO and the mTOR inhibitor rapamycin inactivate RPS6, but via different mechanisms. Finally, a comparison of the protein phosphorylation data to previously obtained transcriptome data of TBTO-treated Jurkat cells resulted in a good correlation at the pathway level and indicated that TBTO affects ribosome biogenesis and leukocyte migration. The effect of TBTO on the latter process was confirmed using a CXCL12 chemotaxis assay.

PI3Kδ Regulates the Magnitude of CD8+ T Cell Responses after Challenge with Listeria monocytogenes

PI3Ks regulate diverse immune cell functions by transmitting intracellular signals from Ag, costimulatory receptors, and cytokine receptors to control cell division, differentiation, survival, and migration. In this study, we report the effect of inhibiting the p110δ subunit of PI3Kδ on CD8(+) T cell responses to infection with the intracellular bacteria Listeria monocytogenes. A strong dependency on PI3Kδ for IFN-γ production by CD8(+) T cells in vitro was not recapitulated after Listeria infection in vivo. Inactivation of PI3Kδ resulted in enhanced bacterial elimination by the innate immune system. However, the magnitudes of the primary and secondary CD8 +: T cell responses were reduced. Moreover, PI3Kδ activity was required for CD8(+) T cells to provide help to other responding CD8(+) cells. These findings identify PI3Kδ as a key regulator of CD8(+) T cell responses that integrates extrinsic cues, including those from other responding cells, to determine the collective behavior of CD8(+) T cell populations responding to infection.