Antigen-presenting cells control T cell proliferation by regulating amino acid availability

Orchestration of mesenchymal plasticity and immune evasiveness via rewiring of the metabolic program in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is the most fatal cancer in humans, due to its difficulty of early detection and its high metastatic ability. The occurrence of epithelial to mesenchymal transition in preinvasive pancreatic lesions has been implicated in the early dissemination, drug resistance, and cancer stemness of PDAC. PDAC cells also have a reprogrammed metabolism, regulated by driver mutation-mediated pathways, a desmoplastic tumor microenvironment (TME), and interactions with stromal cells, including pancreatic stellate cells, fibroblasts, endothelial cells, and immune cells. Such metabolic reprogramming and its functional metabolites lead to enhanced mesenchymal plasticity, and creates an acidic and immunosuppressive TME, resulting in the augmentation of protumor immunity via cancer-associated inflammation. In this review, we summarize our recent understanding of how PDAC cells acquire and augment mesenchymal features via metabolic and immunological changes during tumor progression, and how mesenchymal malignancies induce metabolic network rewiring and facilitate an immune evasive TME. In addition, we also present our recent findings on the interesting relevance of the small G protein ADP-ribosylation factor 6-based signaling pathway driven by KRAS/TP53 mutations, inflammatory amplification signals mediated by the proinflammatory cytokine interleukin 6 and RNA-binding protein ARID5A on PDAC metabolic reprogramming and immune evasion, and finally discuss potential therapeutic strategies for the quasi-mesenchymal subtype of PDAC.

Roles of RNA-binding proteins in immune diseases and cancer

Genetic information that is transcribed from DNA to mRNA, and then translated from mRNA to protein, is regulated by complex and sophisticated post-transcriptional mechanisms. Recently, it has become clear that mRNA degradation not only acts to remove unnecessary mRNA, but is also closely associated with the regulation of translation initiation, and is essential for maintaining cellular homeostasis. Various RNA-binding proteins (RBPs) have been reported to play central roles in the mechanisms of mRNA stability and translation initiation through various signal transduction pathways, and to modulate gene expression faster than the transcription process via post-transcriptional modifications in response to intracellular and extracellular stimuli, without de novo protein synthesis. On the other hand, inflammation is necessary for the elimination of pathogens associated with infection, and is tightly controlled to avoid the overexpression of inflammatory cytokines, such as interleukin 6 (IL-6) and tumor necrosis factor (TNF). It is increasingly becoming clear that RBPs play important roles in the post-transcriptional regulation of these immune responses. Furthermore, it has been shown that the aberrant regulation of RBPs leads to chronic inflammation and autoimmune diseases. Although it has been recognized since the time of Rudolf Virchow in the 19th century that cancer-associated inflammation contributes to tumor onset and progression, involvement of the disruption of the balance between anti-tumor immunity via the immune surveillance system and pro-tumor immunity by cancer-associated inflammation in the malignant transformation of cancer remains elusive. Recently, the dysregulated expression and activation of representative RBPs involved in regulation of the production of pro-inflammatory cytokines have been shown to be involved in tumor progression. In this review, we summarize the recent progress in our understanding of the functional roles of these RBPs in several types of immune responses, and the involvement of RBP dysregulation in the pathogenesis of immune diseases and cancer, and discuss possible therapeutic strategies against cancer by targeting RBPs, coupled with immunotherapy.

Glutathione deficiency in the pathogenesis of SARS-CoV-2 infection and its effects upon the host immune response in severe COVID-19 disease

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 19 (COVID-19) has numerous risk factors leading to severe disease with high mortality rate. Oxidative stress with excessive production of reactive oxygen species (ROS) that lower glutathione (GSH) levels seems to be a common pathway associated with the high COVID-19 mortality. GSH is a unique small but powerful molecule paramount for life. It sustains adequate redox cell signaling since a physiologic level of oxidative stress is fundamental for controlling life processes via redox signaling, but excessive oxidation causes cell and tissue damage. The water-soluble GSH tripeptide (γ-L-glutamyl-L-cysteinyl-glycine) is present in the cytoplasm of all cells. GSH is at 1–10 mM concentrations in all mammalian tissues (highest concentration in liver) as the most abundant non-protein thiol that protects against excessive oxidative stress. Oxidative stress also activates the Kelch-like ECH-associated protein 1 (Keap1)-Nuclear factor erythroid 2-related factor 2 (Nrf2)-antioxidant response element (ARE) redox regulator pathway, releasing Nrf2 to regulate the expression of genes that control antioxidant, inflammatory and immune system responses, facilitating GSH activity. GSH exists in the thiol-reduced and disulfide-oxidized (GSSG) forms. Reduced GSH is the prevailing form accounting for >98% of total GSH. The concentrations of GSH and GSSG and their molar ratio are indicators of the functionality of the cell and its alteration is related to various human pathological processes including COVID-19. Oxidative stress plays a prominent role in SARS-CoV-2 infection following recognition of the viral S-protein by angiotensin converting enzyme-2 receptor and pattern recognition receptors like toll-like receptors 2 and 4, and activation of transcription factors like nuclear factor kappa B, that subsequently activate nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) expression succeeded by ROS production. GSH depletion may have a fundamental role in COVID-19 pathophysiology, host immune response and disease severity and mortality. Therapies enhancing GSH could become a cornerstone to reduce severity and fatal outcomes of COVID-19 disease and increasing GSH levels may prevent and subdue the disease. The life value of GSH makes for a paramount research field in biology and medicine and may be key against SARS-CoV-2 infection and COVID-19 disease.

Central Roles of STAT3-Mediated Signals in Onset and Development of Cancers: Tumorigenesis and Immunosurveillance

Since the time of Rudolf Virchow in the 19th century, it has been well-known that cancer-associated inflammation contributes to tumor initiation and progression. However, it remains unclear whether a collapse of the balance between the antitumor immune response via the immunological surveillance system and protumor immunity due to cancer-related inflammation is responsible for cancer malignancy. The majority of inflammatory signals affect tumorigenesis by activating signal transducer and activation of transcription 3 (STAT3) and nuclear factor-κB. Persistent STAT3 activation in malignant cancer cells mediates extremely widespread functions, including cell growth, survival, angiogenesis, and invasion and contributes to an increase in inflammation-associated tumorigenesis. In addition, intracellular STAT3 activation in immune cells causes suppressive effects on antitumor immunity and leads to the differentiation and mobilization of immature myeloid-derived cells and tumor-associated macrophages. In many cancer types, STAT3 does not directly rely on its activation by oncogenic mutations but has important oncogenic and malignant transformation-associated functions in both cancer and stromal cells in the tumor microenvironment (TME). We have reported a series of studies aiming towards understanding the molecular mechanisms underlying the proliferation of various types of tumors involving signal-transducing adaptor protein-2 as an adaptor molecule that modulates STAT3 activity, and we recently found that AT-rich interactive domain-containing protein 5a functions as an mRNA stabilizer that orchestrates an immunosuppressive TME in malignant mesenchymal tumors. In this review, we summarize recent advances in our understanding of the functional role of STAT3 in tumor progression and introduce novel molecular mechanisms of cancer development and malignant transformation involving STAT3 activation that we have identified to date. Finally, we discuss potential therapeutic strategies for cancer that target the signaling pathway to augment STAT3 activity.

Thioredoxin-1: A Promising Target for the Treatment of Allergic Diseases

Thioredoxin-1 (Trx1) is an important regulator of cellular redox homeostasis that comprises a redox-active dithiol. Trx1 is induced in response to various stress conditions, such as oxidative damage, infection or inflammation, metabolic dysfunction, irradiation, and chemical exposure. It has shown excellent anti-inflammatory and immunomodulatory effects in the treatment of various human inflammatory disorders in animal models. This review focused on the protective roles and mechanisms of Trx1 in allergic diseases, such as allergic asthma, contact dermatitis, food allergies, allergic rhinitis, and drug allergies. Trx1 plays an important role in allergic diseases through processes, such as antioxidation, inhibiting macrophage migration inhibitory factor (MIF), regulating Th1/Th2 immune balance, modulating allergic inflammatory cells, and suppressing complement activation. The regulatory mechanism of Trx1 differs from that of glucocorticoids that regulates the inflammatory reactions associated with immune response suppression. Furthermore, Trx1 exerts a beneficial effect on glucocorticoid resistance of allergic inflammation by inhibiting the production and internalization of MIF. Our results suggest that Trx1 has the potential for future success in translational research.

PI3K-AKT Pathway Modulation by Thymoquinone Limits Tumor Growth and Glycolytic Metabolism in Colorectal Cancer

Colorectal cancer (CRC) is the third leading cause of death in men and the fourth in women worldwide and is characterized by deranged cellular energetics. Thymoquinone, an active component from Nigella sativa, has been extensively studied against cancer, however, its role in affecting deregulated cancer metabolism is largely unknown. Further, the phosphoinositide 3-kinase (PI3K) pathway is one of the most activated pathways in cancer and its activation is central to most deregulated metabolic pathways for supporting the anabolic needs of growing cancer cells. Herein, we provide evidence that thymoquinone inhibits glycolytic metabolism (Warburg effect) in colorectal cancer cell lines. Further, we show that such an abrogation of deranged cell metabolism was due, at least in part, to the inhibition of the rate-limiting glycolytic enzyme, Hexokinase 2 (HK2), via modulating the PI3/AKT axis. While overexpression of HK2 showed that it is essential for fueling glycolytic metabolism as well as sustaining tumorigenicity, its pharmacologic and/or genetic inhibition led to a reduction in the observed effects. The results decipher HK2 mediated inhibitory effects of thymoquinone in modulating its glycolytic metabolism and antitumor effects. In conclusion, we provide evidence of metabolic perturbation by thymoquinone in CRC cells, highlighting its potential to be used/repurposed as an antimetabolite drug, though the latter needs further validation utilizing other suitable cell and/or preclinical animal models.

Toxoplasma gondii, Suicidal Behavior, and Intermediate Phenotypes for Suicidal Behavior

Within the general literature on infections and suicidal behavior, studies on Toxoplasma gondii (T. gondii) occupy a central position. This is related to the parasite's neurotropism, high prevalence of chronic infection, as well as specific and non-specific behavioral alterations in rodents that lead to increased risk taking, which are recapitulated in humans by T. gondii's associations with suicidal behavior, as well as trait impulsivity and aggression, mental illness and traffic accidents. This paper is a detailed review of the associations between T. gondii serology and suicidal behavior, a field of study that started 15 years ago with our publication of associations between T. gondii IgG serology and suicidal behavior in persons with mood disorders. This "legacy" article presents, chronologically, our primary studies in individuals with mood disorders and schizophrenia in Germany, recent attempters in Sweden, and in a large cohort of mothers in Denmark. Then, it reviews findings from all three meta-analyses published to date, confirming our reported associations and overall consistent in effect size [ranging between 39 and 57% elevation of odds of suicide attempt in T. gondii immunoglobulin (IgG) positives]. Finally, the article introduces certain links between T. gondii and biomarkers previously associated with suicidal behavior (kynurenines, phenylalanine/tyrosine), intermediate phenotypes of suicidal behavior (impulsivity, aggression) and state-dependent suicide risk factors (hopelessness/dysphoria, sleep impairment). In sum, an abundance of evidence supports a positive link between suicide attempts (but not suicidal ideation) and T. gondii IgG (but not IgM) seropositivity and serointensity. Trait impulsivity and aggression, endophenotypes of suicidal behavior have also been positively associated with T. gondii seropositivity in both the psychiatrically healthy as well as in patients with Intermittent Explosive Disorder. Yet, causality has not been demonstrated. Thus, randomized interventional studies are necessary to advance causal inferences and, if causality is confirmed, to provide hope that an etiological treatment for a distinct subgroup of individuals at an increased risk for suicide could emerge.

Potential alteration of tumor microenvironments by β-mercaptoethanol

The therapeutic effectiveness of immune checkpoint inhibitors in cancer patients is quite profound. However, it is generally accepted that further progress is curtailed by accompanying adverse events and by low cure rates linked to the tumor microenvironment. The multitudes of immune processes altered by low-molecular-weight thiols published over the past decades suggest they have potential to alter tumor microenvironment processes which could result in an increase in immune checkpoint inhibitor survival rates. Based on one of the most studied and most potent low-molecular-weight thiols, β-mercaptoethanol (BME), it is proposed that clinical assessment be undertaken to identify any BME benefits with relevance for proliferation/differentiation of immune cells, lymphocyte exhaustion, immunogenicity of tumor antigens and inactivation of suppressor cells/factors. The BME alterations projected to be most effective are: maintenance/replacement of glutathione in lymphocytes via facilitation of cysteine uptake, inhibition of suppressor cells/soluble factors and inactivation of free-radical, reactive oxygen species.

Tumor Infiltrating Regulatory T Cells in Sporadic and Colitis-Associated Colorectal Cancer: The Red Little Riding Hood and the Wolf

Regulatory T cells represent a class of specialized T lymphocytes that suppress unwanted immune responses and size the activation of the immune system whereby limiting collateral damages in tissues involved by inflammation. In cancer, the accumulation of Tregs is generally associated with poor prognosis. Many lines of evidence indicate that Tregs accumulation in the tumor microenvironment (TME) suppresses the immune response against tumor-associated antigens (TAA), thus promoting tumor progression in non-small cell lung carcinoma (NSLC), breast carcinoma and melanoma. In colorectal cancer (CRC) the effect of Tregs accumulation is debated. Some reports describe the association of high number of Tregs in CRC stroma with a better prognosis while others failed to find any association. These discordant results stem from the heterogeneity of the immune environment generated in CRC in which anticancer immune response may coexists with tumor promoting inflammation. Moreover, different subsets of Tregs have been identified that may exert different effects on cancer progression depending on tumor stage and their location within the tumor mass. Finally, Tregs phenotypic plasticity may be induced by cytokines released in the TME by dysplastic and other tumor-infiltrating cells thus affecting their functional role in the tumor. Here, we reviewed the recent literature about the role of Tregs in CRC and in colitis-associated colorectal cancer (CAC), where inflammation is the main driver of tumor initiation and progression. We tried to explain when and how Tregs can be considered to be the “good” or the “bad” in the colon carcinogenesis process on the basis of the available data concluding that the final effect of Tregs on sporadic CRC and CAC depends on their localization within the tumor, the subtype of Tregs involved and their phenotypic plasticity.

Complementary α-arrestin-ubiquitin ligase complexes control nutrient transporter endocytosis in response to amino acids

How cells adjust nutrient transport across their membranes is incompletely understood. Previously, we have shown that S. cerevisiae broadly re-configures the nutrient transporters at the plasma membrane in response to amino acid availability, through endocytosis of sugar- and amino acid transporters (AATs) (Müller et al., 2015). A genome-wide screen now revealed that the selective endocytosis of four AATs during starvation required the α-arrestin family protein Art2/Ecm21, an adaptor for the ubiquitin ligase Rsp5, and its induction through the general amino acid control pathway. Art2 uses a basic patch to recognize C-terminal acidic sorting motifs in AATs and thereby instructs Rsp5 to ubiquitinate proximal lysine residues. When amino acids are in excess, Rsp5 instead uses TORC1-activated Art1 to detect N-terminal acidic sorting motifs within the same AATs, which initiates exclusive substrate-induced endocytosis. Thus, amino acid excess or starvation activate complementary α-arrestin-Rsp5-complexes to control selective endocytosis and adapt nutrient acquisition.

Regulatory T cells: Master thieves of the immune system

Treg cells are the immune system's in-house combatants against pathological immune activation. Because they are vital to maintenance of peripheral tolerance, it is important to understand how they perform their functions. To this end, various mechanisms have been proposed for Treg-mediated immune inhibition. A major group of mechanisms picture Treg cells as skilled thieves stealing a plethora of molecules that would otherwise promote immune effector functions. This suggests that several million years of evolution have endowed Treg cells with efficient ways to deprive immune effectors of activating stimuli to prevent immunopathology for survival of the host. Although we are still long way from deciphering their complete set of tricks, this review will focus on the types of "crimes" committed by these master thieves in both secondary lymphoid organs and non-lymphoid tissue.

The PI3K-AKT network at the interface of oncogenic signalling and cancer metabolism

The altered metabolic programme of cancer cells facilitates their cell-autonomous proliferation and survival. In normal cells, signal transduction pathways control core cellular functions, including metabolism, to couple the signals from exogenous growth factors, cytokines or hormones to adaptive changes in cell physiology. The ubiquitous, growth factor-regulated phosphoinositide 3-kinase (PI3K)-AKT signalling network has diverse downstream effects on cellular metabolism, through either direct regulation of nutrient transporters and metabolic enzymes or the control of transcription factors that regulate the expression of key components of metabolic pathways. Aberrant activation of this signalling network is one of the most frequent events in human cancer and serves to disconnect the control of cell growth, survival and metabolism from exogenous growth stimuli. Here we discuss our current understanding of the molecular events controlling cellular metabolism downstream of PI3K and AKT and of how these events couple two major hallmarks of cancer: growth factor independence through oncogenic signalling and metabolic reprogramming to support cell survival and proliferation.

Modulation of cancer-specific immune responses by amino acid degrading enzymes

To evade immune destruction, tumors exploit a wide range of immune escape mechanisms, including the induction of an immunosuppressive tumor microenvironment. This is mediated, in part, by amino acid degrading enzymes indoleamine 2,3-dioxygenase, tryptophan 2,3-dioxygenase, arginase 1 and arginase 2, which have emerged as key players in the regulation of tumor-induced immune tolerance. Here we describe how the expression of tryptophan- and arginine-degrading enzymes by tumor and tumor-infiltrating cells can hamper cancer-specific immune responses, and discuss how this knowledge is being exploited to develop new strategies for cancer immunotherapy.

Increased expression of IDO associates with poor postoperative clinical outcome of patients with gastric adenocarcinoma

Clinical significance of 2,3-dioxygenase (IDO) has been studied in types of tumors, but the role that IDO played in gastric adenocarcinoma (GAC) is still unclear. Here, we aim to investigate the prognostic value of IDO expression in patients with GAC. We examined intratumoral IDO expression in retrospectively enrolled 357 patients with GAC undergoing gastrectomy at Zhongshan Hospital of Fudan University in 2008 by immunohistochemical staining. The Kaplan-Meier method and Cox regression models were used to evaluate the prognostic value of IDO expression and its association with clinical pathological factors. We generated a predictive nomogram by integrating IDO expression with the TNM staging system for overall survival of GAC patients. High expression of intratumoral IDO predicted a dismal outcome. Intratumoral IDO expression gave a further discrimination for the prognosis of GAC patients. By Cox multivariate analysis, IDO expression was defined as an independent prognosticator. The generated nomogram performed well in predicting the 3- and 5-year overall survival of GAC patients. Conclusively, IDO is a potential prognostic biomarker for overall survival of patients with GAC after gastrectomy.

Lysosomal signaling in control of degradation pathways

Autophagy mediates the (non-)selective bulk degradation of cytoplasm, protein aggregates, damaged organelles and certain pathogens. The endosomal membrane system uses multivesicular bodies (MVBs) to selectively deliver ubiquitinated membrane proteins together with extracellular components into lysosomes. Microautophagy (MA) and chaperone-mediated autophagy (CMA) additionally contribute to the selective delivery of cargo into lysosomes. The coordinated function of these lysosomal degradation pathways is essential to maintain cellular homeostasis. Their activity is controlled by mTOR (mammalian target of rapamycin) signaling and thus coupled to metabolic processes during cell growth. Here, we will discuss how TORC1 on lysosomes and TORC2 at the plasma membrane coordinate the different membrane biogenesis pathways with cargo selection, vesicle transport and fusion with lysosomes in response to intracellular and extracellular cues.

Combined Toxoplasma gondii seropositivity and high blood kynurenine--Linked with nonfatal suicidal self-directed violence in patients with schizophrenia

Toxoplasma gondii (T. gondii) chronic infection and elevated kynurenine (KYN) levels have been individually associated with non-fatal suicidal self-directed violence (NF-SSDV). We aimed to test the hypothesis that the association between T. gondii seropositivity and history of NF-SSDV would be stronger in schizophrenia patients with high plasma KYN levels than in those with lower KYN levels. We measured anti-T. gondii IgG antibodies and plasma KYN in 950 patients with schizophrenia, and used logistic regression to evaluate the relationship between NF-SSDV and KYN in patients who were either seropositive or seronegative for T. gondii. For those with KYN levels in the upper 25th percentile, the unadjusted odds ratio for the association between NF-SSDV history and KYN in T. gondii seropositive patients was 1.63 (95% CI 1.01 to 2.66), p = 0.048; the adjusted odds ratio was 1.95 (95% CI 1.15 to 3.30), p = 0.014. Plasma KYN was not associated with a history of NF-SSDV in T. gondii seronegative patients. The results suggest that T. gondii and KYN may have a nonlinear cumulative effect on the risk of NF-SSDV among those with schizophrenia. If confirmed by future longitudinal studies, this result is expected to have both theoretical and clinical implications for the prevention and treatment of suicidal behavior.

Exploratory Clinical Investigation of (4S)-4-(3-18F-Fluoropropyl)-L-Glutamate PET of Inflammatory and Infectious Lesions

We explored system [Formula: see text] transporter activity and the detection of inflammatory or infectious lesions using (4S)-4-(3-(18)F-fluoropropyl)-l-glutamate ((18)F-FSPG) PET.

METHODS

In 10 patients with various inflammatory or infectious diseases, as many as 5 of the largest lesions were selected as reference lesions. (18)F-FSPG images were assessed visually and quantitatively. Expression levels of xCT, CD44, and surface markers of inflammatory cells were evaluated by immunohistochemistry.

RESULTS

(18)F-FSPG PET detected all reference lesions. (18)F-FSPG uptake in sarcoidosis was significantly higher than that in nonsarcoidosis. The lesion-to-blood-pool SUV ratio for (18)F-FSPG was comparable to that for (18)F-FDG in sarcoidosis. In nonsarcoidosis, however, it was significantly lower. In 5 patients with available tissue samples, the SUVmax for (18)F-FSPG and CD163 were negatively correlated (ρ = -0.872, P = 0.054).

CONCLUSION

(18)F-FSPG PET may detect inflammatory lesions when activated macrophages or monocytes are present, such as in sarcoidosis.

Targeting cancer metabolism at the plasma membrane by limiting amino acid access through SLC6A14

Rapidly proliferating cancer cells increase flux through anabolic pathways to build the mass necessary to support cell division. Imported amino acids and glucose lie at the apex of the anabolic pyramid. Consistent with this, elevated expression of nutrient transporter proteins is characteristic of aggressive and highly malignant cancers. Because tumour cells are more dependent than their normal neighbours on accelerated nutrient import, these up-regulated transporters could be excellent targets for selective anti-cancer therapies. A study by Babu et al. in a recent issue of the Biochemical Journal definitively shows that SLC6A14 (where SLC is solute carrier) is one such cancer-specific amino acid transporter. Although mice completely lacking SLC6A14 are viable and exhibit normal mammary gland development, these animals are highly resistant to mammary tumour initiation and progression driven by potent oncogenes. Because SLC6A14 is essential for tumour growth yet dispensable for normal development and tissue maintenance, small molecules that block amino acid import through this transporter could be effective and selective anti-cancer agents, particularly as components of rational drug combinations.

Loss of Nrf2 in bone marrow-derived macrophages impairs antigen-driven CD8(+) T cell function by limiting GSH and Cys availability

NF-E2-related factor 2 (Nrf2), known to protect against reactive oxygen species, has recently been reported to resolve acute inflammatory responses in activated macrophages. Consequently, disruption of Nrf2 promotes a proinflammatory macrophage phenotype. In the current study, we addressed the impact of this macrophage phenotype on CD8(+) T cell activation by using an antigen-driven coculture model consisting of Nrf2(-/-) and Nrf2(+/+) bone marrow-derived macrophages (BMDMΦ) and transgenic OT-1 CD8(+) T cells. OT-1 CD8(+) T cells encode a T cell receptor that specifically recognizes MHC class I-presented ovalbumin OVA(257-264) peptide, thereby causing a downstream T cell activation. Interestingly, coculture of OVA(257-264)-pulsed Nrf2(-/-) BMDMΦ with transgenic OT-1 CD8(+) T cells attenuated CD8(+) T cell activation, proliferation, and cytotoxic function. Since the provision of low-molecular-weight thiols such as glutathione (GSH) or cysteine (Cys) by macrophages limits antigen-driven CD8(+) T cell activation, we quantified the amounts of intracellular and extracellular GSH and Cys in both cocultures. Indeed, GSH levels were strongly decreased in Nrf2(-/-) cocultures compared to wild-type counterparts. Supplementation of thiols in Nrf2(-/-) cocultures via addition of glutathione ester, N-acetylcysteine, β-mercaptoethanol, or cysteine itself restored T cell proliferation as well as cytotoxicity by increasing intracellular GSH. Mechanistically, we identified two potential Nrf2-regulated genes involved in thiol synthesis in BMDMΦ: the cystine transporter subunit xCT and the modulatory subunit of the GSH-synthesizing enzyme γ-GCS (GCLM). Pharmacological inhibition of γ-GCS-dependent GSH synthesis as well as knockdown of the cystine antiporter xCT in Nrf2(+/+) BMDMΦ mimicked the effect of Nrf2(-/-) BMDMΦ on CD8(+) T cell function. Our findings demonstrate that reduced levels of GCLM as well as xCT in Nrf2(-/-) BMDMΦ limit GSH availability, thereby inhibiting antigen-induced CD8(+) T cell function.

Amino acids and immune response: a role for cysteine, glutamine, phenylalanine, tryptophan and arginine in T-cell function and cancer?

While proteins are critical for immunity, T-cells constitute a critical component of adaptive immunity by clearing cancerous cells among other abnormal cells. However, cancer cells exhibit a potential to escape T-cell control by employing mechanisms not completely delineated. Interesting work has investigated how certain amino acids affect the proliferation rate of T-cells as well as their effectiveness in clearing tumors. The role of amino acids cysteine, glutamine, phenylalanine, tryptophan and arginine in immunomodulation and particularly regarding T-cell proliferation and activation is discussed. The redox balance is reported to affect T-cell proliferation via modulation of cysteine availability. In addition antigen presenting cells (APCs), similar to myeloid cells determine the availability of amino acids in the extracellular microenvironment affecting T-cell proliferation and activation. A better mechanistic understanding of T-cell function modulation via amino acid signaling or metabolic properties may be helpful towards optimization of adaptive immunity with implications for cancer prognosis and treatment.

Changing the energy of an immune response

The breakdown of nutrients into the critical energy source ATP is the general purpose of cellular metabolism and is essential for sustaining life. Similarly, the immune system is composed of different cell subsets that are indispensable for defending the host against pathogens and disease. The interplay between metabolic pathways and immune cells leads to a plethora of different signaling pathways as well as cellular activities. The activation of T cells via glycolysis-mediated upregulation of surface markers, for example, is necessary for an appropriate effector response against an infection. However, tight regulation of immune cell metabolism is required for protecting the host and resuming homeostasis. An imbalance of immunological metabolic function and/or metabolic byproducts (reactive oxygen species) can oftentimes lead to diseases. In the case of cancer, overactive glucose metabolism can lead to hyperproliferation of cells and subsequent decreases in cytotoxic T cell activity, which attack and destroy the tumor. For this reason and many more, targeting metabolism in immune cells may be a novel therapeutic strategy for treatment of disease. The metabolic pathways of immune cells and the possibilities of immunometabolic therapies will be discussed.

Back to the future: oral targeted therapy for RA and other autoimmune diseases

The molecular biology revolution coupled with the development of monoclonal antibody technology enabled remarkable progress in rheumatology therapy, comprising an array of highly effective biologic agents. With advances in understanding of the molecular nature of immune cell receptors came elucidation of intracellular signalling pathways downstream of these receptors. These discoveries raise the question of whether selective targeting of key intracellular factors with small molecules would add to the rheumatologic armamentarium. In this Review, we discuss several examples of this therapeutic strategy that seem to be successful, and consider their implications for the future of immune-targeted treatments. We focus on kinase inhibitors, primarily those targeting Janus kinase family members and spleen tyrosine kinase, given their advanced status in clinical development and application. We also summarize other targets involved in signalling pathways that might offer promise for therapeutic intervention in the future.

Metabolic switching and fuel choice during T-cell differentiation and memory development

Clearance or control of pathogens or tumors usually requires T-cell-mediated immunity. As such, understanding the mechanisms that govern the function, maintenance, and persistence of T cells will likely lead to new treatments for controlling disease. During an immune response, T-cell development is marked by striking changes in metabolism. There is a growing appreciation that these metabolic changes underlie the capacity of T cells to perform particular functions, and this has led to a recent focus on the idea that the manipulation of cellular metabolism can be used to shape adaptive immune responses. Although interest in this area has grown in the last few years, a full understanding of the metabolic control of T-cell functions, particularly during an immune response in vivo, is still lacking. In this review, we first provide a basic overview of metabolism in T cells, and then we focus on recent studies providing new or updated insights into the regulation of metabolic pathways and how they underpin T-cell differentiation and memory T-cell development.

Metabolic reprogramming and metabolic dependency in T cells

Upon activation, quiescent naive T cells undergo a growth phase followed by massive clonal expansion and differentiation that are essential for appropriate immune defense and regulation. Accumulation of cell biomass during the initial growth and rapid proliferation during the expansion phase is associated with dramatically increased bioenergetic and biosynthetic demands. This not only requires a metabolic rewiring during the transition between resting and activation but also 'addicts' active T cells to certain metabolic pathways in ways that naive and memory T cells are not. We consider such addiction in terms of the biological effects of deprivation of metabolic substrates or inhibition of specific pathways in T cells. In this review, we illustrate the relevant metabolic pathways revealed by recent metabolic flux analysis and discuss the consequences of metabolic intervention on specific metabolic pathways in T lymphocytes.

(4S)-4-(3-18F-fluoropropyl)-L-glutamate for imaging of xC transporter activity in hepatocellular carcinoma using PET: preclinical and exploratory clinical studies

(4S)-4-(3-(18)F-fluoropropyl)-l-glutamate ((18)F-FSPG, or BAY 94-9392) is a new tracer to assess system x(C)(¯) transporter activity with PET. The aim of this study was to explore the tumor detection rate of (18)F-FSPG, compared with that of (18)F-FDG, in patients with hepatocellular carcinoma (HCC).

METHODS

Preclinically, in vivo HCC models of orthotopically implanted Huh7 and MH3924a cancer cells were studied with (18)F-FSPG in Naval Medical Research Institute nude mice (n = 3) and August-Copenhagen Irish rats (n = 4), respectively. Clinically, 5 patients with HCC who had hyper- or isometabolic lesions on (18)F-FDG PET were enrolled for evaluation of the tracer. Dynamic whole-body PET images with (18)F-FSPG were acquired for up to 120 min after injection of approximately 300 MBq of (18)F-FSPG. Immunohistochemical expression levels of the xCT subunit of the system x(C)(¯) and CD44 of HCC were studied in 4 patients with HCC.

RESULTS

Strong tumor uptake and low background from nontarget tissue allowed excellent tumor visualization in animal models with orthotopically implanted liver tumors. (18)F-FSPG PET procedures were well tolerated in all patients. (18)F-FSPG PET and (18)F-FDG detected lesions in 5 of 5 and 3 of 5 patients, respectively. The maximal standardized uptake values (SUV) were comparable ((18)F-FSPG, 4.7 ± 3.2; (18)F-FDG, 6.1 ± 2.9). The ratios of maximal SUV of the tumor to mean SUV of normal liver were also comparable ((18)F-FSPG, 3.6 ± 2.2; (18)F-FDG, 2.7 ± 1.3), but the mean SUV of normal liver of (18)F-FSPG was significantly lower than that of (18)F-FDG (P < 0.05). Two patients with HCC who showed both xCT and CD44 expression had moderate or intense accumulation of (18)F-FSPG, but the remaining 2 patients with negative CD44 expression showed mild uptake.

CONCLUSION

(18)F-FSPG was successfully translated from preclinical evaluation into patients with HCC. (18)F-FSPG may be a promising tumor PET agent with a high cancer detection rate in patients with HCC.

Cysteine catabolism and cysteine desulfhydrase (CdsH/STM0458) in Salmonella enterica serovar typhimurium

Cysteine is potentially toxic and can affect diverse functions such as oxidative stress, antibiotic resistance, and swarming motility. The contribution of cysteine catabolism in modulating responses to cysteine has not been examined, in part because the genes have not been identified and mutants lacking these genes have not been isolated or characterized. We identified the gene for a previously described cysteine desulfhydrase, which we designated cdsH (formerly STM0458). We also identified a divergently transcribed gene that regulates cdsH expression, which we designated cutR (formerly ybaO, or STM0459). CdsH appears to be the major cysteine-degrading and sulfide-producing enzyme aerobically but not anaerobically. Mutants with deletions of cdsH and ybaO exhibited increased sensitivity to cysteine toxicity and altered swarming motility but unaltered cysteine-enhanced antibiotic resistance and survival in macrophages.

Cancer-stromal interactions: role in cell survival, metabolism and drug sensitivity

It has been known for a long time that the interaction between cancer cells and tissue microenvironment plays a major role in cancer development, progression and metastasis. The biochemical aspect of cancer-stromal interactions, however, is less appreciated. This short review article first provides a brief summary of the communications between cancer cells and the tissue microenvironment by direct cell-cell interactions and by soluble factors, and then describes several biochemical pathways that are important for the interaction between stromal and cancer cells with respect to energy metabolism, redox balance, cell survival and drug resistance. The potential therapeutic implications of abolishing stromal protective mechanisms to overcome drug resistance are also discussed.

Ncf1 (p47phox) is essential for direct regulatory T cell mediated suppression of CD4+ effector T cells

Background

Multiple mechanisms have been advanced to account for CD4+FOXP3+ regulatory T cell (Treg)-mediated suppression of CD4+ effector T cells (Teffs) but none appear to completely explain suppression. Previous data indicates that Tregs may affect the microenvironment redox state. Given the inherent redox sensitivity of T cells, we tested the hypothesis that oxidants may mediate the direct suppression of Teffs by Tregs.

Methodology/Principal Findings

Tregs and Teffs were isolated from the spleens of wild type (WT) C57BL/6 mice or Ncf1(p47phox)-deficient C57BL/6 mice which lack NADPH oxidase function. Teffs were labeled with CFSE and co-cultured with unlabeled Tregs at varying Treg:Teff ratios in the presence of anti-CD3/CD28 coated beads for 3 days in suppression assays. Treg-mediated suppression was quantified by flow cytometric analysis of CFSE dilution in Teffs. The presence of the antioxidants n-acetylcysteine (NAC) or 2-mercaptoethanol or inhibitors of NADPH oxidase (diphenyleneiodonium and VAS-2870) resulted in reduced WT Treg-mediated suppression. The observed suppression was in part dependent upon TGFβ as it was partially blocked with neutralizing antibodies. The suppression of Teff proliferation induced by exogenous TGFβ treatment could be overcome with NAC. Ncf1-deficient Teff were slightly but significantly less sensitive than WT Teff to suppression by exogenous TGFβ. Ncf1-deficient Tregs suppressed Ncf1-deficient Teff very poorly compared to wild type controls. There was partial but incomplete reconstitution of suppression in assays with WT Tregs and Ncf1-deficient Teff.

Conclusions/Significance

We present evidence that NADPH oxidase derived ROS plays a role in the direct Treg mediated suppression of CD4+ effector T cells in a process that is blocked by thiol-containing antioxidants, NADPH oxidase inhibitors or a lack of Ncf1 expression in Tregs and Teffs. Oxidants may represent a potential new target for therapeutic modulation of Treg function.

Aryl hydrocarbon receptor negatively regulates dendritic cell immunogenicity via a kynurenine-dependent mechanism

Although an immunoregulatory role of aryl hydrocarbon receptor (Ahr) has been demonstrated in T cells and macrophages, little is known about its function in dendritic cells (DC). Here, we show that lipopolysaccharide (LPS) and CpG stimulate Ahr expression in bone marrow-derived dendritic cells (BMDC). Furthermore, we found that Ahr is required to induce indoleamine 2,3-dioxygenase (IDO) expression, an immunosuppressive enzyme that catabolizes tryptophan into kynurenine (Kyn) and other metabolites in DC. In the presence of LPS or CpG, Ahr-deficient (Ahr(-/-)) mature BMDC induced immune responses characterized by reduced Kyn and IL-10 production compared with results observed with tolerogenic mature WT BMDC. In a coculture system with LPS- or CpG-stimulated BMDC and naive T cells, Ahr(-/-) BMDC inhibited naive T-cell differentiation into regulatory T (Treg) cells, which likely facilitated Th17 cell development and promoted naive T-cell proliferation. Addition of synthetic L-Kyn to the coculture system skewed the differentiation of naive T cells to Treg cells rather than Th17 cells. Taken together, our results demonstrate a previously unknown negatively regulatory role for Ahr in DC-mediated immunogenesis in the presence of LPS or CpG, which, in turn, alters the Kyn-dependent generation of Treg cells and Th17 cells from naive T cells.

Reciprocal relationship between cytosolic NADH and ENOX2 inhibition triggers sphingolipid-induced apoptosis in HeLa cells

ENOX2 (tNOX), a tumor-associated cell surface ubiquinol (NADH) oxidase, functions as an alternative terminal oxidase for plasma membrane electron transport. Ubiquitous in all cancer cell lines studied thus far, ENOX2 expression correlates with the abnormal growth and division associated with the malignant phenotype. ENOX2 has been proposed as the cellular target for various quinone site inhibitors that demonstrate anticancer activity such as the green tea constituent epigallocatechin-3-gallate (EGCg) and the isoflavone phenoxodiol (PXD). Here we present a possible mechanism that explains how these substances result in apoptosis in cancer cells by ENOX2-mediated alterations of cytosolic amounts of NAD(+) and NADH. When ENOX2 is inhibited, plasma membrane electron transport is diminished, and cytosolic NADH accumulates. We show in HeLa cells that NADH levels modulate the activities of two pivotal enzymes of sphingolipid metabolism: sphingosine kinase 1 (SK1) and neutral sphingomyelinase (nSMase). Their respective products sphingosine 1-phosphate (S1P) and ceramide (Cer) are key determinants of cell fate. S1P promotes cell survival and Cer promotes apoptosis. Using plasma membranes isolated from cervical adenocarcinoma (HeLa) cells as well as purified proteins of both bacterial and human origin, we demonstrate that NADH inhibits SK1 and stimulates nSMase, while NAD(+) inhibits nSMase and has no effect on SK1. Additionally, intact HeLa cells treated with ENOX2 inhibitors exhibit an increase in Cer and a decrease in S1P. Treatments that stimulate cytosolic NADH production potentiate the antiproliferative effects of ENOX2 inhibitors while those that attenuate NADH production or stimulate plasma membrane electron transport confer a survival advantage.

Extracellular/microenvironmental redox state

Extracellular redox (reduction-oxidation) state is a factor that serves as an important regulator of cell-microenvironmental interactions and is determined by several known variables; including redox-modulating proteins that are located on the plasma membrane or outside of cells, extracellular thiol/disulfide couples, and reactive oxygen species (ROS)/reactive nitrogen species (RNS) that are capable of traveling across plasma membranes into the extracellular space. The extracellular redox state works in concert with the intracellular redox state to control both the influx and efflux of ROS/RNS that may serve to modulate redox signaling or to perturb normal cellular processes or both. Under physiologic conditions, the extracellular space is known to have a relatively more-oxidized redox state than the interior of the cell. During pathologic conditions, such as cancer, the extracellular redox state may be altered, causing specific proteins such as proteases, soluble factors, or the extracellular matrix to have altered functions or activities. Recent studies have strongly supported an important relation between the extracellular redox state and cancer cell aggressiveness. The purpose of this review is to identify redox buffer networks in extracellular spaces and to emphasize the possible roles of the extracellular redox state in cancer, knowledge that may contribute to potential therapeutic interventions.

Redox remodeling as an immunoregulatory strategy

Activation and proliferation of T cells require a reducing extracellular microenvironment in the immune synapse that is provided by antigen presenting cells, especially dendritic cells. Stimulation of dendritic cells by T cells activates the NF-kappaB pathway in dendritic cells and induces an antioxidant response. It also enhances system x(c)(-)-dependent cystine uptake, leading to enhanced glutathione synthesis, export, and, finally, degradation to cysteine outside the cell. Accumulation of extracellular cysteine supports glutathione synthesis in T cells while also leading to a more reducing redox potential that is needed for T cell proliferation. Naturally occurring regulatory T cells, a suppressor subpopulation of T cells, prevent autoimmune diseases and maintain peripheral tolerance by suppressing self-reactive effector T cells. They also suppress beneficial immune responses to parasites, viruses, and tumors. However, their mechanism of suppression is still not fully understood. Recently, we have found that inhibition by regulatory T cells of dendritic cell-induced extracellular redox remodeling is a component of the regulatory T cell suppression mechanism. In this review, we describe recent advances in our understanding of redox regulation and signaling in the adaptive immune system with a focus on T cell activation by dendritic cells. The role of regulatory T cells in perturbing redox remodeling by dendritic cells and its implications as a general regulatory T cell suppression mechanism are discussed.

Metabolism in T cell activation and differentiation

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

Myeloid-derived suppressor cells inhibit T-cell activation by depleting cystine and cysteine

Myeloid-derived suppressor cells (MDSC) are present in most cancer patients and are potent inhibitors of T-cell-mediated antitumor immunity. Their inhibitory activity is attributed to production of arginase, reactive oxygen species, inducible nitric oxide synthase, and interleukin-10. Here we show that MDSCs also block T-cell activation by sequestering cystine and limiting the availability of cysteine. Cysteine is an essential amino acid for T-cell activation because T cells lack cystathionase, which converts methionine to cysteine, and because they do not have an intact xc- transporter and therefore cannot import cystine and reduce it intracellularly to cysteine. T cells depend on antigen-presenting cells (APC), such as macrophages and dendritic cells, to export cysteine, which is imported by T cells via their ASC neutral amino acid transporter. MDSCs express the xc- transporter and import cystine; however, they do not express the ASC transporter and do not export cysteine. MDSCs compete with APC for extracellular cystine, and in the presence of MDSCs, APC release of cysteine is reduced, thereby limiting the extracellular pool of cysteine. In summary, MDSCs consume cystine and do not return cysteine to their microenvironment, thereby depriving T cells of the cysteine they require for activation and function.

Burn injury induces the expression of cystine/glutamate transporter (x(c)(-)) in mouse T cells

System x(c)(-) transporter, formed by the association of CD98 and xCT proteins, regulates the import of cystine into cells and is poorly expressed in T lymphocytes. Thermal injury is associated with high oxidative stress, decreased levels of glutathione (GSH) and protein deficiency, all described as promoters of xCT expression and system x(c)(-) activity. T cell dysfunction is a consequence of thermal injury and has been related to oxidative stress. In order to evaluate if thermal injury induced system x(c)(-) expression in splenic T lymphocytes, cells were isolated from sham- and burn-injured mice at day 10 post-burn and cultured in 2-mercaptoethanol (2-ME)-rich and -free media. Isolated splenic T cells were stimulated and cell proliferation, system x(c)(-) expression and cystine transport activity were measured. Our results demonstrate that only burn-injured T cells express xCT and proliferate in (2-ME)-free media. In these cells, viability and CD25 expression was higher than control T cells. x(c)(-) system expression was responsible for significantly higher (14)C-cystine uptake by burn-injured T cells and its inhibition by sulfasalazine (SASP) decreased significantly their proliferation. Overall, these results demonstrate that xCT expression is induced by thermal injury in T lymphocytes and that cystine import by x(c)(-) leads to T cell dysfunction.

The xc- cystine/glutamate antiporter as a potential therapeutic target for small-cell lung cancer: use of sulfasalazine

PURPOSE

To determine whether the xc- cystine transporter could be a useful therapeutic target for small-cell lung cancer (SCLC).

METHODS

Human SCLC cell cultures were examined for growth dependence on extracellular cystine, xc- expression, glutathione levels and response to highly specific xc- inhibitors, i.e., monosodium glutamate (MSG) and the anti-inflammatory drug, sulfasalazine (SASP). In studying tumor growth inhibition by SASP, use was also made of a novel SCLC tissue xenograft model, LU6-SCLC, derived from a chemoresistant patient's SCLC specimen.

RESULTS

Growth of NCI-H69 and NCI-H82 SCLC cells greatly depended on xc- -mediated uptake of cystine. SASP substantially reduced their glutathione levels (>70%; 0.3 mM SASP; 24 h) and growth (72 h) with IC(50)s of 0.21 and 0.13 mM, respectively; MSG also inhibited growth markedly. Both SASP- and MSG-induced growth arrests were largely prevented by cystine uptake-enhancing 2-mercaptoethanol (66 approximately microM) indicating they were primarily due to cystine starvation. Without major side-effects, SASP (i.p.) restrained growth of NCI-H69 cell xenografts (approximately 50%) and, importantly, substantially inhibited growth of the clinically more relevant LU6-SCLC tissue xenografts (approximately 70% by stereological analysis), reducing tumor glutathione contents.

CONCLUSIONS

The xc- cystine/glutamate antiporter is potentially useful as a target for therapy of SCLC based on glutathione depletion. Sulfasalazine may be readily used for this approach, especially in combination chemotherapy.

Anti-inflammatory effects of mesenchymal stem cells: novel concept for future therapies

BACKGROUND

Mesenchymal stem cells (MSC) are multipotent cells that can be isolated from the bone marrow and expanded in culture relatively easily. Culture-expanded MSC have been used in clinical settings to enhance hematopoietic stem cell engraftment in bone marrow transplant patients and in tissue regeneration therapy. More recently, the anti-inflammatory effects of MSC have generated a great deal of interest.

OBJECTIVE/METHODS

In this review we describe in vitro assays that have demonstrated how MSC regulate immune cell proliferation, differentiation and phenotype. We also highlight effector molecules produced by MSC that drive this function. In addition, we focus on animal models of lung injury, in which administration of MSC attenuates inflammation, and injury revealing a central role for MSC in mitigating pro-inflammatory networks and amplifying anti-inflammatory signals.

CONCLUSIONS

The discoveries described herein have contributed to the novel concept of MSC as a therapeutic modality in inflammatory diseases, including acute lung injury.

The x(c)- cystine/glutamate antiporter: a potential target for therapy of cancer and other diseases

The x(c) (-) cystine/glutamate antiporter is a major plasma membrane transporter for the cellular uptake of cystine in exchange for intracellular glutamate. Its main functions in the body are mediation of cellular cystine uptake for synthesis of glutathione essential for cellular protection from oxidative stress and maintenance of a cystine:cysteine redox balance in the extracellular compartment. In the past decade it has become evident that the x(c) (-) transporter plays an important role in various aspects of cancer, including: (i) growth and progression of cancers that have a critical growth requirement for extracellular cystine/cysteine, (ii) glutathione-based drug resistance, (iii) excitotoxicity due to excessive release of glutamate, and (iv) uptake of herpesvirus 8, a causative agent of Kaposi's sarcoma. The x(c) (-) transporter also plays a role in certain CNS and eye diseases. This review focuses on the expression and function of the x(c) (-) transporter in cells and tissues with particular emphasis on its role in disease pathogenesis. The potential use of x(c) (-) inhibitors (e.g., sulfasalazine) for arresting tumor growth and/or sensitizing cancers is discussed.

Patulin influences the expression of Th1/Th2 cytokines by activated peripheral blood mononuclear cells and T cells through depletion of intracellular glutathione

Patulin is a mold toxin secreted mainly by fungi of the Penicillium species. Exposure generally results from consumption of moldy fruits and fruit products. Since recent studies identified mold exposure as a risk factor for allergic diseases, we examined the effects of patulin on human peripheral blood mononuclear cells (PBMC) prepared from buffy coats of healthy donors. Cells were stimulated with CD3- and CD28-specific antibodies in the presence or absence of patulin. Effects of patulin on PBMCs were evaluated by proliferation, viability assays, and cytokine ELISAs. The presence of 50 ng/mL patulin strongly decreased the amounts of several cytokines in the supernatant of stimulated PBMCs. This decrease in cytokine secretion was not due to cytotoxic effects of patulin. Moreover, the extent of the reduction of cytokine amounts was cytokine specific, affecting some (IL-4, IL-13, IFNgamma, and IL-10), but not others (IL-8, IL-5). We show that all effects could be abolished by adding thiol containing compounds. A depletion of intracellular GSH could be measured after incubation of cells with patulin. Taken together, our data indicate that patulin modulates the functional activation of PBMCs with respect to proliferation and cytokine secretion patterns by depletion of intracellular GSH. The depletion of intracellular glutathione may influence the balance between Th1 and Th2 cells and have implications for allergic diseases.

Induction of IFN-gamma gene expression by thioredoxin: positive feed-back regulation of Th1 response by thioredoxin and IFN-gamma

T cell differentiation, which leads to the generation of Th cells with a characteristic cytokine expression pattern, is regulated by diverse factors. In addition to the cytokine environment, the cellular redox status often serves as an important factor in survival and differentiation of Th cells. Thioredoxin, an intracellular redox sensor protein, has been suggested in the induction of Th1 response through the production of IL-12 by monocytes. Here we report that thioredoxin expression is up-regulated by IFN-gamma and other Th1 type cytokines in human primary immune cells, and that the overexpression of thioredoxin resulted in a specific increase in the mRNA level and promoter activity of IFN-gamma in mitogen-stimulated Jurkat T cells. Using the active site mutant (C32S/C35S) of thioredoxin, we demonstrate that such IFN-gamma-inducing capacity of thioredoxin is dependent on the redox-sensing activity of thioredoxin and involves the activation of transcription factors such as NF-kappaB and Stat1. Together, the results of the present study suggest that thioredoxin is a direct stimulator of IFN-gamma gene expression in human T cells and that there is a positive feed-back circuit by IFN-gamma and thioredoxin in the regulation of Th1 immune response.

Tolerance signaling molecules and pregnancy: IDO, galectins, and the renaissance of regulatory T cells

PROBLEM

Is the concept of maternal tolerance preventing rejection of the semi-allogeneic 'fetal allograft' still valid?

METHOD OF STUDY

Compilation of expert reviews of literature and recent advances in research on indoleamine-2,3 dioxygenase (IDO), regulatory T cells and galectin-1.

RESULTS AND CONCLUSION

A role for IDO in pregnancy success remains speculative, but solid data exist to support a role for Treg cells, and for galectin-1 in induction and action of Treg cells. Just as several signals may need to be simultaneously present to induce Th1 cytokine-triggered abortions, more than 1 signal may need to be simultaneously present to prevent rejection and ensure success. Both complement and coagulation pathways appear necessary for embryo execution.

Rheumatoid arthritis: the role of reactive oxygen species in disease development and therapeutic strategies

Autoimmune diseases such as rheumatoid arthritis (RA) are chronic diseases that cannot be prevented or cured If the pathologic basis of such disease would be known, it might be easier to develop new drugs interfering with critical pathway. Genetic analysis of animal models for autoimmune diseases can result in discovery of proteins and pathways that play key function in pathogenesis, which may provide rationales for new therapeutic strategies. Currently, only the MHC class II is clearly associated with human RA and animal models for RA. However, recent data from rats and mice with a polymorphism in Ncf1, a member of the NADPH oxidase complex, indicate a role for oxidative burst in protection from arthritis. Oxidative burst-activating substances can treat and prevent arthritis in rats, as efficiently as clinically applied drugs, suggesting a novel pathway to a therapeutic target in human RA. Here, the authors discuss the role of oxygen radicals in regulating the immune system and autoimmune disease. It is proposed that reactive oxygen species set the threshold for T cell activation and thereby regulate chronic autoimmune inflammatory diseases like RA. In the light of this new hypothesis, new possibilities for preventive and therapeutic treatment of chronic inflammatory diseases are discussed.

Controlling cell growth and survival through regulated nutrient transporter expression

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