AMP-activated protein kinase is necessary for Treg cell functional adaptation to microenvironmental stress

CD4+FOXP3+ regulatory T (Treg) cells maintain self-tolerance, suppress the immune response to cancer, and protect against tissue injury in the lung and other organs. Treg cells require mitochondrial metabolism to exert their function, but how Treg cells adapt their metabolic programs to sustain and optimize their function during an immune response occurring in a metabolically stressed microenvironment remains unclear. Here, we tested whether Treg cells require the energy homeostasis-maintaining enzyme AMP-activated protein kinase (AMPK) to adapt to metabolically aberrant microenvironments caused by malignancy or lung injury, finding that AMPK is dispensable for Treg cell immune-homeostatic function but is necessary for full Treg cell function in B16 melanoma tumors and during acute lung injury caused by influenza virus pneumonia. AMPK-deficient Treg cells had lower mitochondrial mass and exhibited an impaired ability to maximize aerobic respiration. Mechanistically, we found that AMPK regulates DNA methyltransferase 1 to promote transcriptional programs associated with mitochondrial function in the tumor microenvironment. In the lung during viral pneumonia, we found that AMPK sustains metabolic homeostasis and mitochondrial activity. Induction of DNA hypomethylation was sufficient to rescue mitochondrial mass in AMPK-deficient Treg cells, linking DNA methylation with AMPK function and mitochondrial metabolism. These results define AMPK as a determinant of Treg cell adaptation to metabolic stress and offer potential therapeutic targets in cancer and tissue injury.

Differential roles of regulatory T cells in acute respiratory infections

Acute respiratory infections trigger an inflammatory immune response with the goal of pathogen clearance; however, overexuberant inflammation causes tissue damage and impairs pulmonary function. CD4+FOXP3+ regulatory T cells (Tregs) interact with cells of both the innate and the adaptive immune system to limit acute pulmonary inflammation and promote its resolution. Tregs also provide tissue protection and coordinate lung tissue repair, facilitating a return to homeostatic pulmonary function. Here, we review Treg-mediated modulation of the host response to respiratory pathogens, focusing on mechanisms underlying how Tregs promote resolution of inflammation and repair of acute lung injury. We also discuss potential strategies to harness and optimize Tregs as a cellular therapy for patients with severe acute respiratory infection and discuss open questions in the field.

TRAF3 regulates the oncogenic proteins Pim2 and c-Myc to restrain survival in normal and malignant B cells

TRAF3 is a versatile intracellular adapter protein with multiple context-specific roles. Uniquely in B cells, TRAF3 deficiency enhances survival and increases the risk of transformation, as loss of TRAF3 is observed in several types of B cell cancers. Here, we report a new mechanism for TRAF3 in the restraint of B cell survival. We found that TRAF3 deficiency was associated with induction of the pro-survival kinase Pim2 in mouse primary B cells and human malignant B cell lines. The increase in Pim2 was independent of NF-κB2 activation but was ameliorated with inhibition of STAT3 expression or function. TRAF3 deficiency also led to a Pim2-dependent increase in c-Myc protein levels and was associated with reduced c-Myc ubiquitination. TRAF3-deficient primary B cells were less sensitive to cell death induced by the Pim inhibitors SGI-1776 and TP-3654. Interestingly, human malignant B cell lines with low expression of TRAF3 were more sensitive to Pim inhibition-induced cell death. Combination treatment of TRAF3-deficient B cells and B cell tumor lines with c-Myc inhibitors enhanced their sensitivity to Pim inhibition, suggesting a possible therapeutic strategy. TRAF3 thus suppresses a Pim2-mediated B cell survival axis, which can be a potential target for treatment of B cell malignancies.

TRAF3 regulates Pim2 and c-Myc-mediated B cell survival

Tumor necrosis factor receptor associated factor 3 (TRAF3) is an adaptor protein that plays an important role in B cell homeostasis. TRAF3 deletions or inactivating mutations are common in human B cell malignancies. In human and mouse B cells, TRAF3 negatively regulates signaling of several receptors important for B cell homeostasis (including BAFFR, CD40, and IL-6R). B cell specific TRAF3-deficient (B-Traf3−/−) mice have enlarged spleens and lymph nodes and an increased frequency of B cell tumors as they age. B cells from B-Traf3−/− mice have markedly increased survival and autoantibody production. The mechanisms by which TRAF3 regulates B cell survival are not yet well defined. We found that TRAF3-deficient mouse B cells and human multiple myeloma cell lines with low expression of TRAF3 had increased RNA and protein expression of the pro-survival kinase Pim2. Additionally, TRAF3-deficient mouse B cells had increased phosphorylation of Pim2 targets BAD, p70S6K, and 4E-BP1. TRAF3-deficient B cells showed increased survival relative to TRAF3-sufficient B cells after treatment with the Pim inhibitors SGI-1776 and TP-3654. Pim2 can promote survival by phosphorylating and stabilizing the oncogenic transcription factor c-Myc. Loss of TRAF3 led to transcription-independent c-Myc protein elevation that was dependent on Pim2. K48 polyubiquitination of c-Myc was decreased in the absence of TRAF3, consistent with increased c-myc protein stability. TRAF3 deficiency correlated with B cell resistance to apoptosis mediated by the c-Myc transcription inhibitor JQ1. Our results show that TRAF3 promotes B cell survival by regulating expression of and interaction between Pim2 and c-Myc.

The lymphomagenic molecule LMP1 sequesters TRAF3 to induce enhanced B cell survival

The human TRAF3 gene is frequently mutated in multiple myeloma and lymphoma. TRAF3 restrains homeostatic B cell survival. B cell TRAF3 deficiency promotes enhanced viability and over-expression of the anti-apoptotic molecules NIK, Mcl1 and Pim2, enhanced nuclear CREB, and increased pSTAT3 in response to IL6 signaling. We assessed TRAF3 protein expression in human lymphoma samples. The number of TRAF3low DLBCL was higher than predicted based on genetic loss, so we speculated that cellular TRAF3 can be depleted through other means. The oncogenic Epstein Barr virus protein LMP1 binds TRAF3 with much higher avidity than do CD40 or BAFF receptors, so we hypothesized that LMP1-sequesters TRAF3, causing functional depletion. We found evidence of induction of survival pathways in TRAF3 sufficient B cells expressing LMP1 consistent with those in B cells genetically lacking TRAF3.

B lymphoma cell lines stably transfected with inducible LMP1 were stimulated via CD40 or BAFFR. TRAF3 binding was studied via CD40/BAFFR immunoprecipitation and Western blotting. We also examined levels of cellular NIK, and used confocal fluorescence microscopy to assess nuclear CREB expression. We found LMP1 expression sequesters cellular and nuclear TRAF3, decreasing its availability to CD40 and BAFFR, and increases survival-promoting NIK, CREB and pSTAT3. LMP1 mutated at the major TRAF binding site only marginally induced TRAF3 sequestration and NIK. Thus, B cell LMP1 expression can enhance survival by functionally reducing TRAF3 availability.

TRAF3 deficiency promotes metabolic reprogramming in B cells

The adaptor protein TNF receptor-associated factor 3 (TRAF3) is a critical regulator of B lymphocyte survival. B cell-specific TRAF3 deficiency results in enhanced viability and is associated with development of lymphoma and multiple myeloma. We show that TRAF3 deficiency led to induction of two proteins important for glucose metabolism, Glut1 and Hexokinase 2 (HXK2). This was associated with increased glucose uptake. In the absence of TRAF3, anaerobic glycolysis and oxidative phosphorylation were increased in B cells without changes in mitochondrial mass or reactive oxygen species. Chemical inhibition of glucose metabolism or glucose deprivation substantially attenuated the enhanced survival of TRAF3-deficient B cells, with a decrease in the pro-survival protein Mcl-1. Changes in Glut1 and Mcl-1 levels, glucose uptake and B cell number in the absence of TRAF3 were all dependent upon NF-κB inducing kinase (NIK). These results indicate that TRAF3 deficiency suffices to metabolically reprogram B cells, a finding that improves our understanding of the role of TRAF3 as a tumor suppressor, and suggests potential therapeutic strategies.

Loss of TRAF3 Promotes a Premalignant Metabolic State in B cells

TRAF3 is a signaling protein that acts as a tumor suppressor in B cells. B cell conditional TRAF3−/− mice display a remarkable expansion of B cell compartments and parenchymal B cell infiltration, attributed to enhanced B cell survival without increased proliferation. When aged, these mice develop lymphomas, and TRAF3 mutations are common in human B cell lymphoma and multiple myeloma. The mechanism of how loss of TRAF3 promotes B cell survival phenotype is not well understood; this particular role for TRAF3 is not seen in other immune cell types. We find that loss of TRAF3 leads to increased uptake of glucose in B cells in vitro and in vivo. This is accompanied by increased oxidative phosphorylation and glycolysis. In the absence of TRAF3, expression of Glut1 and Hexokinase II, two molecules important for glucose metabolism, is increased. Treatment of B cells with Glut1 inhibitor or the competitive glycolysis inhibitor 2-DG attenuates cell survival, and B cell viability is also substantially reduced in a glucose-free environment. Mechanistically, loss of TRAF3 leads to the induction of Pim2 kinase. Pim2 in turn promotes the protein stability of the oncogenic transcription factor c-Myc, known to drive expression of glycolytic genes. Our study shows that B cell deficiency of TRAF3 is sufficient for altered metabolic programming, consistent with a premalignant abnormal survival phenotype.

HABP2 is a Novel Regulator of Hyaluronan-Mediated Human Lung Cancer Progression

Background

Lung cancer is a devastating disease with limited treatment options. Many lung cancers have changes in their microenvironment including upregulation of the extracellular matrix glycosaminoglycan, hyaluronan (HA), which we have previously demonstrated can regulate the activity of the extracellular serine protease, hyaluronan binding protein 2 (HABP2). This study examined the functional role of HABP2 on HA-mediated human lung cancer dynamics.

Methods

Immunohistochemical analysis was performed on lung cancer patient samples using anti-HABP2 antibody. Stable control, shRNA, and HABP2 overexpressing human lung adenocarcinoma cells were evaluated using immunoblot analysis, migration, extravasation, and urokinase plasminogen activator (uPA) activation assays with or without high-molecular weight HA or low-molecular weight HA (LMW-HA). In human lung cancer xenograft models, primary tumor growth rates and lung metastasis were analyzed using consecutive tumor volume measurements and nestin immunoreactivity in nude mouse lungs.

Results

We provide evidence that HABP2 is an important regulator of lung cancer progression. HABP2 expression was increased in several subtypes of patient non-small cell lung cancer samples. Further, HABP2 overexpression increased LMW-HA-induced uPA activation, migration, and extravasation in human lung adenocarcinoma cells. In vivo, overexpression of HABP2 in human lung adenocarcinoma cells increased primary tumor growth rates in nude mice by ~2-fold and lung metastasis by ~10-fold compared to vector control cells (n = 5/condition).

Conclusion

Our data suggest a possible direct effect of HABP2 on uPA activation and lung cancer progression. Our observations suggest that exploration of HABP2 in non-small cell lung carcinoma merits further study both as a diagnostic and therapeutic option.

Nuclear TRAF3 Inhibits CREB-mediated survival and metabolic reprogramming in B lymphocytes (TUM10P.1045)

TRAF3 is an adaptor protein that negatively regulates signaling through CD40 and BAFF receptor in B lymphocytes. B cells isolated from B cell conditional TRAF3-/- mice display a remarkable pro-survival phenotype compared to wild type B cells, but the mechanism for this abnormal survival is poorly understood. We find that CREB protein expression and activity - but not mRNA - were increased in TRAF3-/- B cells. Inhibition of activity of CREB and its co-activator molecule CBP attenuated the survival of TRAF3-/- B cells. Immune precipitation revealed that TRAF3 associated with both CREB and CBP preferentially in the nucleus in B cells. The TRAF-C domain was identified as necessary and sufficient for TRAF3 nuclear localization. The human TRAF3 mutant LP1 isolated from a myeloma tumor and lacking a TRAF-C domain, failed to localize to the nucleus or associate with CREB. Guided by results of microarray analysis, we found that the proteins Glut1 and Hexokinase II, two CREB targets important for glucose metabolism, were elevated in TRAF3-/- B cells and associated with enhanced glucose uptake and broad metabolic reprogramming in Seahorse extracellular flux analysis. We are currently investigating the importance of TRAF3-regulated metabolic changes to B cell survival.

Transactivation of the receptor-tyrosine kinase ephrin receptor A2 is required for the low molecular weight hyaluronan-mediated angiogenesis that is implicated in tumor progression

Angiogenesis or the formation of new blood vessels is important in the growth and metastatic potential of various cancers. Therefore, understanding the mechanism(s) by which angiogenesis occurs can have important therapeutic implications in numerous malignancies. We and others have demonstrated that low molecular weight hyaluronan (LMW-HA, ∼2500 Da) promotes endothelial cell (EC) barrier disruption and angiogenesis. However, the mechanism(s) by which this occurs is poorly defined. Our data indicate that treatment of human EC with LMW-HA induced CD44v10 association with the receptor-tyrosine kinase, EphA2, transactivation (tyrosine phosphorylation) of EphA2, and recruitment of the PDZ domain scaffolding protein, PATJ, to the cell periphery. Silencing (siRNA) CD44, EphA2, PATJ, or Dbs (RhoGEF) expression blocked LMW-HA-mediated angiogenesis (EC proliferation, migration, and tubule formation). In addition, silencing EphA2, PATJ, Src, or Dbs expression blocked LMW-HA-mediated RhoA activation. To translate our in vitro findings, we utilized a novel anginex/liposomal targeting of murine angiogenic endothelium with either CD44 or EphA2 siRNA and observed inhibition of LMW-HA-induced angiogenesis in implanted Matrigel plugs. Taken together, these results indicate LMW-HA-mediated transactivation of EphA2 is required for PATJ and Dbs membrane recruitment and subsequent RhoA activation required for angiogenesis. These results suggest that targeting downstream effectors of LMW-HA could be a useful therapeutic intervention for angiogenesis-associated diseases including tumor progression.

The role of TRAF3 in B cell specific regulation of survival and malignancy (P1112)

TNF-receptor associated factor 3 (TRAF3), a negative regulator of CD40 and BAFF-receptor- mediated signaling pathways, also serves as a potentially important tumor suppressor in B cell malignancies. Deletion or loss of function mutations of the traf3 gene are highly associated with multiple myeloma (MM) and different subtypes of B cell lymphoma. Current dogma has attributed TRAF3’s role of restraining cell survival to its negative regulatory role in activating the non-canonical NF-κB2 pathway. However, studying cell-type-specific TRAF3-deficient mouse strains we produced, we found that TRAF3 deletion in B cells, T cells or dendritic cells all results in constitutive NF-κB2 activation, while enhanced cell survival is unique to TRAF3 deficient B cells. This indicates that TRAF3 must negatively regulate additional survival or anti-apoptotic pathways in a B-cell-specific manner. Our recent results show that TRAF3 deficient B cells, but not other TRAF3-deficient cell types, highly express the pro-survival kinase Pim2. Pim2 expression levels also correlate with copy number and loss of function mutations in the traf3 gene in human MM cell lines. TRAF3 deficient B cells also display higher basal levels of the activated form of the B cell-specific kinase Btk, a kinase implicated in MM pathogenesis. These findings reveal B cell-specific mechanisms by which TRAF3 can exert its cell-specific impact on regulation of survival, and are being further explored in ongoing work.

The novel role of the mu opioid receptor in lung cancer progression: a laboratory investigation

BACKGROUND

The possibility that μ opioid agonists can influence cancer recurrence is a subject of recent interest. Epidemiologic studies suggested that there were differences in cancer recurrence in breast and prostate cancer contingent on anesthetic regimens. In this study, we identify a possible mechanism for these epidemiologic findings on the basis of μ opioid receptor (MOR) regulation of Lewis lung carcinoma (LLC) tumorigenicity in cell and animal models.

METHODS

We used human lung tissue and human non-small cell lung cancer (NSCLC) cell lines and evaluated MOR expression using immunoblot and immunohistochemical analysis. LLC cells were treated with the peripheral opioid antagonist methylnaltrexone (MNTX) or MOR shRNA and evaluated for proliferation, invasion, and soft agar colony formation in vitro and primary tumor growth and lung metastasis in C57BL/6 and MOR knockout mice using VisEn fluorescence mediated tomography imaging and immunohistochemical analysis.

RESULTS

We provide several lines of evidence that the MOR may be a potential target for lung cancer, a disease with high mortality and few treatment options. We first observed that there is ∼5- to 10-fold increase in MOR expression in lung samples from patients with NSCLC and in several human NSCLC cell lines. The MOR agonists morphine and [D-Ala(2), N-MePhe(4), Gly-ol]-enkephalin (DAMGO) increased in vitro LLC cell growth. Treatment with MNTX or silencing MOR expression inhibited LLC invasion and anchorage-independent growth by 50%-80%. Injection of MOR silenced LLC lead to a ∼65% reduction in mouse lung metastasis. In addition, MOR knockout mice do not develop significant tumors when injected with LLC in comparison with wild-type controls. Finally, continuous infusion of the peripheral opioid antagonist MNTX attenuates primary LLC tumor growth and reduces lung metastasis.

CONCLUSIONS

Taken together, our data suggest a possible direct effect of opiates on lung cancer progression, and provide a plausible explanation for the epidemiologic findings. Our observations further suggest a possible therapeutic role for opioid antagonists.

High-molecular-weight hyaluronan is a novel inhibitor of pulmonary vascular leakiness

Endothelial cell (EC) barrier dysfunction results in increased vascular permeability, a perturbation observed in inflammatory states, tumor angiogenesis, atherosclerosis, and both sepsis and acute lung injury. Therefore, agents that enhance EC barrier integrity have important therapeutic implications. We observed that binding of high-molecular-weight hyaluronan (HMW-HA) to its cognate receptor CD44 within caveolin-enriched microdomains (CEM) enhances human pulmonary EC barrier function. Immunocytochemical analysis indicated that HMW-HA promotes redistribution of a significant population of CEM to areas of cell-cell contact. Quantitative proteomic analysis of CEM isolated from human EC demonstrated HMW-HA-mediated recruitment of cytoskeletal regulatory proteins (annexin A2, protein S100-A10, and filamin A/B). Inhibition of CEM formation [caveolin-1 small interfering RNA (siRNA) and cholesterol depletion] or silencing (siRNA) of CD44, annexin A2, protein S100-A10, or filamin A/B expression abolished HMW-HA-induced actin cytoskeletal reorganization and EC barrier enhancement. To confirm our in vitro results in an in vivo model of inflammatory lung injury with vascular hyperpermeability, we observed that the protective effects of HMW-HA on LPS-induced pulmonary vascular leakiness were blocked in caveolin-1 knockout mice. Furthermore, targeted inhibition of CD44 expression in the mouse pulmonary vasculature significantly reduced HMW-HA-mediated protection from LPS-induced hyperpermeability. These data suggest that HMW-HA, via CD44-mediated CEM signaling events, represents a potentially useful therapeutic agent for syndromes of increased vascular permeability.

Hyaluronic Acid binding protein 2 is a novel regulator of vascular integrity

OBJECTIVE

The disruption of the endothelial cell barrier is a critical feature of inflammation and an important contributing factor to acute lung injury (ALI), an inflammatory condition that is a major cause of morbidity and mortality in critically ill patients. We evaluated the role of the extracellular serine protease, hyaluronic acid binding protein 2 (HABP2), in vascular barrier regulation.

METHODS AND RESULTS

By using immunoblot and immunohistochemical analysis, we observed that lipopolysaccharide (LPS) induces HABP2 expression in murine lung endothelium in vivo and in human pulmonary microvascular endothelial cells (ECs) in vitro. High-molecular-weight hyaluronan (HMW-HA, approximately 1x10(6) Da) decreased HABP2 protein expression in human pulmonary microvascular ECs and decreased purified HABP2 enzymatic activity, whereas low-molecular-weight HA (LMW-HA, approximately 2500 Da) increased these activities. The effects of LMW-HA, but not HMW-HA, on HABP2 activity were inhibited with a peptide of the polyanion-binding domain of HABP2. Silencing (small interfering RNA) HABP2 expression augmented HMW-HA-induced EC barrier enhancement and inhibited LPS and LMW-HA-mediated EC barrier disruption, results that were reversed with overexpression of HABP2. Silencing protease-activated receptor 1 and 3, RhoA, or Rho kinase expression attenuated LPS-, LMW-HA-, and HABP2-mediated EC barrier disruption. By using murine models of acute lung injury, we observed that LPS- and ventilator-induced pulmonary vascular hyperpermeability was significantly reduced with vascular silencing (small interfering RNA) of HABP2.

CONCLUSIONS

HABP2 negatively regulates vascular integrity via activation of protease-activated receptor/RhoA/Rho kinase signaling and represents a potentially useful therapeutic target for syndromes of increased vascular permeability.

Methylnaltrexone potentiates the anti-angiogenic effects of mTOR inhibitors

Background

Recent cancer therapies include drugs that target both tumor growth and angiogenesis including mammalian target of rapamycin (mTOR) inhibitors. Since mTOR inhibitor therapy is associated with significant side effects, we examined potential agents that can reduce the therapeutic dose.

Methods

Methylnaltrexone (MNTX), a peripheral mu opioid receptor (MOR) antagonist, in combination with the mTOR inhibitors temsirolimus and/or rapamycin, was evaluated for inhibition of VEGF-induced human pulmonary microvascular endothelial cell (EC) proliferation and migration as well as in vivo angiogenesis (mouse Matrigel plug assay).

Results

MNTX inhibited VEGF-induced EC proliferation and migration with an IC50 of ~100 nM. Adding 10 nM MNTX to EC shifted the IC50 of temsirolimus inhibition of VEGF-induced proliferation and migration from ~10 nM to ~1 nM and from ~50 to ~10 nM respectively. We observed similar effects with rapamycin. On a mechanistic level, we observed that MNTX increased EC plasma membrane-associated tyrosine phosphate activity. Inhibition of tyrosine phosphatase activity (3,4-dephostatin) blocked the synergy between MNTX and temsirolimus and increased VEGF-induced tyrosine phosphorylation of Src with enhanced PI3 kinase and mTOR Complex 2-dependent phosphorylation of Akt and subsequent activation of mTOR Complex 1 (rapamycin and temsirolimus target), while silencing Src, Akt or mTOR complex 2 components blocked VEGF-induced angiogenic events.

Conclusions

Our data indicate that MNTX exerts a synergistic effect with rapamycin and temsirolimus on inhibition of VEGF-induced human EC proliferation and migration and in vivo angiogenesis. Therefore, addition of MNTX could potentially lower the dose of mTOR inhibitors which could improve therapeutic index.

Dynamin 2 and c-Abl are novel regulators of hyperoxia-mediated NADPH oxidase activation and reactive oxygen species production in caveolin-enriched microdomains of the endothelium

Reactive oxygen species (ROS) generation, particularly by the endothelial NADPH oxidase family of proteins, plays a major role in the pathophysiology associated with lung inflammation, ischemia/reperfusion injury, sepsis, hyperoxia, and ventilator-associated lung injury. We examined potential regulators of ROS production and discovered that hyperoxia treatment of human pulmonary artery endothelial cells induced recruitment of the vesicular regulator, dynamin 2, the non-receptor tyrosine kinase, c-Abl, and the NADPH oxidase subunit, p47(phox), to caveolin-enriched microdomains (CEMs). Silencing caveolin-1 (which blocks CEM formation) and/or c-Abl expression with small interference RNA inhibited hyperoxia-mediated tyrosine phosphorylation and association of dynamin 2 with p47(phox) and ROS production. In addition, treatment of human pulmonary artery endothelial cells with dynamin 2 small interfering RNA or the dynamin GTPase inhibitor, Dynasore, attenuated hyperoxia-mediated ROS production and p47(phox) recruitment to CEMs. Using purified recombinant proteins, we observed that c-Abl tyrosine-phosphorylated dynamin 2, and this phosphorylation increased p47(phox)/dynamin 2 association (change in the dissociation constant (K(d)) from 85.8 to 6.9 nm). Furthermore, exposure of mice to hyperoxia increased ROS production, c-Abl activation, dynamin 2 association with p47(phox), and pulmonary leak, events that were attenuated in the caveolin-1 knock-out mouse confirming a role for CEMs in ROS generation. These results suggest that hyperoxia induces c-Abl-mediated dynamin 2 phosphorylation required for recruitment of p47(phox) to CEMs and subsequent ROS production in lung endothelium.