An in vivo BSL-2 model for henipavirus infection based on bioluminescence imaging of recombinant Cedar virus replication in mice

Henipaviruses are enveloped single-stranded, negative-sense RNA viruses of the paramyxovirus family. Two henipaviruses, Nipah virus and Hendra virus, cause a systemic respiratory and/or neurological disease in humans and ten additional species of mammals, with a high fatality rate. Because of their highly pathogenic nature, Nipah virus and Hendra virus are categorized as BSL-4 pathogens, which limits the number and scope of translational research studies on these important human pathogens. To begin to address this limitation, we are developing a BSL-2 model of authentic henipavirus infection in mice, using the non-pathogenic henipavirus, Cedar virus. Notably, wild-type mice are highly resistant to Hendra virus and Nipah virus infection. However, previous work has shown that mice lacking expression of the type I interferon receptor (IFNAR-KO mice) are susceptible to both viruses. Here, we show that luciferase-expressing recombinant Cedar virus (rCedV-luc) is also able to replicate and establish a transient infection in IFNAR-KO mice, but not in wild-type mice. Using longitudinal bioluminescence imaging (BLI) of luciferase expression, we detected rCedV-luc replication as early as 10 h post-infection. Viral replication peaks between days 1 and 3 post-infection, and declines to levels undetectable by BLI by 7 days post-infection. Immunohistochemistry is consistent with viral infection and replication in endothelial cells and other non-immune cell types within tissue parenchyma. Serology analyses demonstrate significant IgG responses to the Cedar virus surface glycoprotein with potent neutralizing activity in IFNAR-KO mice, whereas antibody responses in wild-type animals were non-significant. Overall, these data suggest that rCedV-luc infection of IFNAR-KO mice represents a viable platform for the study of in vivo henipavirus replication, anti-henipavirus host responses and henipavirus-directed therapeutics.

mAb therapy controls CNS-resident lyssavirus infection via a CD4 T cell-dependent mechanism

Infections with rabies virus (RABV) and related lyssaviruses are uniformly fatal once virus accesses the central nervous system (CNS) and causes disease signs. Current immunotherapies are thus focused on the early, pre-symptomatic stage of disease, with the goal of peripheral neutralization of virus to prevent CNS infection. Here, we evaluated the therapeutic efficacy of F11, an anti-lyssavirus human monoclonal antibody (mAb), on established lyssavirus infections. We show that a single dose of F11 limits viral load in the brain and reverses disease signs following infection with a lethal dose of lyssavirus, even when administered after initiation of robust virus replication in the CNS. Importantly, we found that F11-dependent neutralization is not sufficient to protect animals from mortality, and a CD4 T cell-dependent adaptive immune response is required for successful control of infection. F11 significantly changes the spectrum of leukocyte populations in the brain, and the FcRγ-binding function of F11 contributes to therapeutic efficacy. Thus, mAb therapy can drive potent neutralization-independent T cell-mediated effects, even against an established CNS infection by a lethal neurotropic virus.

Genomic Surveillance of Rabies Virus in Georgian Canines

Rabies is a fatal zoonosis that is considered a re-emerging infectious disease. Although rabies remains endemic in canines throughout much of the world, vaccination programs have essentially eliminated dog rabies in the Americas and much of Europe. However, despite the goal of eliminating dog rabies in the European Union by 2020, sporadic cases of dog rabies still occur in Eastern Europe, including Georgia. To assess the genetic diversity of the strains recently circulating in Georgia, we sequenced seventy-eight RABV-positive samples from the brain tissues of rabid dogs and jackals using Illumina short-read sequencing of total RNA shotgun libraries. Seventy-seven RABV genomes were successfully assembled and annotated, with seventy-four of them reaching the coding-complete status. Phylogenetic analyses of the nucleoprotein (N) and attachment glycoprotein (G) genes placed all the assembled genomes into the Cosmopolitan clade, consistent with the Georgian origin of the samples. An amino acid alignment of the G glycoprotein ectodomain identified twelve different sequences for this domain among the samples. Only one of the ectodomain groups contained a residue change in an antigenic site, an R264H change in the G5 antigenic site. Three isolates were cultured, and these were found to be efficiently neutralized by the human monoclonal antibody A6. Overall, our data show that recently circulating RABV isolates from Georgian canines are predominantly closely related phylogroup I viruses of the Cosmopolitan clade. Current human rabies vaccines should offer protection against infection by Georgian canine RABVs. The genomes have been deposited in GenBank (accessions: OQ603609-OQ603685).

Control of established, CNS-resident lyssavirus infection by an adaptive immune response stimulated by single-dose monoclonal antibody therapy

Rabies virus and related lyssaviruses cause uniformly fatal disease, once the infection progresses to the central nervous system. Current lyssavirus immunotherapies are directed toward peripheral neutralization of virus to prevent CNS infection during the pre-symptomatic stage of disease. In this study, using an anti-lyssavirus human monoclonal antibody (mAb), F11, we evaluated the efficacy of immunotherapy on established lyssavirus infections in mice. Remarkably, using luminescence-based longitudinal tracing of virus infection in a mouse model of lethal disease, we found that a single dose of F11 reverses clinical signs of disease and protects animals from lethality following lyssavirus infection, even when administered after initiation of virus replication in the CNS. Investigation of the mechanisms of F11 efficacy revealed that F11-dependent neutralization is insufficient to protect animals from mortality. Control of infection requires an intact adaptive immune response, particularly CD4 T cells. Additionally, in vivo analysis of the F11-N297G mutant, which has defective FcRγ binding, showed a transiently increased viral load and increased morbidity when compared to F11 treated mice. Despite long-term survival and absence of clinical signs of disease in F11-treated animals, we found that lyssavirus infection persists chronically, concomitant with elevated expression of cellular immune response genes. These findings demonstrate that single-dose mAb therapy can stimulate an adaptive, T cell-dependent response that is durable and highly effective against an established CNS infection by a lethal neurotropic virus.

Supported by grants from the National Institute of Health (U01GM109887, R01AI125552), and a USU Program Project Grant (MIC-732515) and a USU Center for Global Health Engagement grant (HU00011920118)

Longitudinal Tracing of Lyssavirus Infection in Mice via In Vivo Bioluminescence Imaging

Bioluminescence imaging (BLI) is a technique that can be employed to quantify biological processes in living cells. When used in small animal models such as mice, BLI can provide both longitudinal and positional information regarding the biological process under investigation. Although perhaps best known for its utility in non-invasively quantifying tumor burden over time in experimental animals, BLI has also been applied in many pathogenesis models to track pathogen burden and responses to therapeutic interventions. In this chapter, we present a BLI-based method for tracing anatomical progression of lyssavirus infection in a mouse model. We also include validation methods to ensure that semiquantitative BLI data correlate well with viral load. Due to the longitudinal nature of this approach, lyssavirus pathogenesis and therapeutic intervention studies can be performed with far fewer animals than more traditional approaches, which typically require euthanasia of large animal groups at every data collection time point.

Genetic targeting of Card19 is linked to disrupted NINJ1 expression, impaired cell lysis, and increased susceptibility to Yersinia infection

Cell death plays a critical role in inflammatory responses. During pyroptosis, inflammatory caspases cleave Gasdermin D (GSDMD) to release an N-terminal fragment that generates plasma membrane pores that mediate cell lysis and IL-1 cytokine release. Terminal cell lysis and IL-1β release following caspase activation can be uncoupled in certain cell types or in response to particular stimuli, a state termed hyperactivation. However, the factors and mechanisms that regulate terminal cell lysis downstream of GSDMD cleavage remain poorly understood. In the course of studies to define regulation of pyroptosis during Yersinia infection, we identified a line of Card19-deficient mice (Card19lxcn) whose macrophages were protected from cell lysis and showed reduced apoptosis and pyroptosis, yet had wild-type levels of caspase activation, IL-1 secretion, and GSDMD cleavage. Unexpectedly, CARD19, a mitochondrial CARD-containing protein, was not directly responsible for this, as an independently-generated CRISPR/Cas9 Card19 knockout mouse line (Card19Null) showed no defect in macrophage cell lysis. Notably, Card19 is located on chromosome 13, immediately adjacent to Ninj1, which was recently found to regulate cell lysis downstream of GSDMD activation. RNA-seq and western blotting revealed that Card19lxcn BMDMs have significantly reduced NINJ1 expression, and reconstitution of Ninj1 in Card19lxcn immortalized BMDMs restored their ability to undergo cell lysis in response to caspase-dependent cell death stimuli. Card19lxcn mice exhibited increased susceptibility to Yersinia infection, whereas independently-generated Card19Null mice did not, demonstrating that cell lysis itself plays a key role in protection against bacterial infection, and that the increased infection susceptibility of Card19lxcn mice is attributable to loss of NINJ1. Our findings identify genetic targeting of Card19 being responsible for off-target effects on the adjacent gene Ninj1, disrupting the ability of macrophages to undergo plasma membrane rupture downstream of gasdermin cleavage and impacting host survival and bacterial control during Yersinia infection.

Signaling through polymerization and degradation: Analysis and simulations of T cell activation mediated by Bcl10

The adaptive immune system serves as a potent and highly specific defense mechanism against pathogen infection. One component of this system, the effector T cell, facilitates pathogen clearance upon detection of specific antigens by the T cell receptor (TCR). A critical process in effector T cell activation is transmission of signals from the TCR to a key transcriptional regulator, NF-κB. The transmission of this signal involves a highly dynamic process in which helical filaments of Bcl10, a key protein constituent of the TCR signaling cascade, undergo competing processes of polymeric assembly and macroautophagy-dependent degradation. Through computational analysis of three-dimensional, super-resolution optical micrographs, we quantitatively characterize TCR-stimulated Bcl10 filament assembly and length dynamics, and demonstrate that filaments become shorter over time. Additionally, we develop an image-based, bootstrap-like resampling method that demonstrates the preferred association between autophagosomes and both Bcl10-filament ends and punctate-Bcl10 structures, implying that autophagosome-driven macroautophagy is directly responsible for Bcl10 filament shortening. We probe Bcl10 polymerization-depolymerization dynamics with a stochastic Monte-Carlo simulation of nucleation-limited filament assembly and degradation, and we show that high probabilities of filament nucleation in response to TCR engagement could provide the observed robust, homogeneous, and tunable response dynamic. Furthermore, we demonstrate that the speed of filament disassembly preferentially at filament ends provides effective regulatory control. Taken together, these data suggest that Bcl10 filament growth and degradation act as an excitable system that provides a digital response mechanism and the reliable timing critical for T cell activation and regulatory processes.

The immune system serves to protect organisms against pathogen-mediated disease. While a strong immune response is needed to eliminate pathogens in host organisms, immune responses that are too robust or too persistent can trigger autoimmune disorders, cancer, and a variety of additional serious human pathologies. Thus, a careful balance of activating and inhibitory mechanisms is necessary to prevent detrimental health outcomes of immune responses. For example, activated effector T cells marshal the immune response and direct killing of pathogen-infected cells; however, effector T cells that are chronically activated can damage and destroy healthy tissue. Here, we study an important internal activation pathway in effector T cells that involves the growth and counterbalancing disassembly (involving a process called macroautophagy) of filamentous cytoplasmic signaling structures. We utilize image analysis of 3-D super-resolution images and Monte Carlo simulations to study a key signal-transduction protein, Bcl10. We found that the speed of filament disassembly has the greatest effect on the magnitude and duration of the response, implying that pharmaceutical interventions aimed at macroautophagy may have substantial impact on effector T cell function. Given that filamentous structures are utilized in numerous immune signaling pathways, our analysis methods could have broad applicability in the signal transduction field.

Bcl10 is associated with actin dynamics at the T cell immune synapse

T cell responses to antigen are initiated by engagement of the T cell receptor (TCR)¹, leading to activation of diverse signaling cascades, including an incompletely defined pathway that triggers rapid remodeling of the actin cytoskeleton. Defects in the control of actin dynamics and organization are associated with several human immunodeficiency diseases, emphasizing the importance of cytoskeletal remodeling in the functioning of the adaptive immune system. Here, we investigate the role of the adaptor protein Bcl10² in the control of actin dynamics. Although Bcl10 is primarily known as a component of the pathway connecting the TCR to activation of the NF-κB³ transcription factor, a few studies have implicated Bcl10 in antigen receptor-dependent control of actin polymerization and F-actin-dependent functional responses. However, the role of Bcl10 in the regulation of cytoskeletal dynamics remains largely undefined. To investigate the contribution of Bcl10 in the regulation of TCR-dependent cytoskeletal dynamics, we monitored actin dynamics at the immune synapse of primary murine CD8 effector T cells. Quantification of these dynamics reveals two distinct temporal phases distinguished by differences in speed and directionality. Our results indicate that effector CD8 T cells lacking Bcl10 display faster actin flows and more dynamic lamellipodia, compared to wild-type cells. These studies define a role for Bcl10 in TCR-dependent actin dynamics, emphasizing that Bcl10 has important cytoskeleton-directed functions that are likely independent of its role in transmission of NF-κB -activating signals.

CARD19, the protein formerly known as BinCARD, is a mitochondrial protein that does not regulate Bcl10-dependent NF-κB activation after TCR engagement

After T cell receptor (TCR) engagement, the CARD11-Bcl10-Malt1 (CBM) complex oligomerizes to transduce NF-κB activating signals. Bcl10 is then degraded to limit NF-κB activation. The cDNA AK057716 (BinCARD-1) was reported to encode a novel CARD protein that interacts with Bcl10 and modestly inhibits NF-κB activation. In a later study, a second isoform, BinCARD-2, was identified. Here, we report that the cDNA AK057716 (BinCARD-1) is an incompletely spliced derivative of the gene product of C9orf89, whereas CARD19 (BinCARD-2) represents the properly spliced isoform, with conservation across diverse species. Immunoblotting revealed expression of CARD19 in T cells, but no evidence of BinCARD-1 expression, and microscopy demonstrated that endogenous CARD19 localizes to mitochondria. Although we confirmed that both BinCARD-1 and CARD19 can inhibit NF-κB activation and promote Bcl10 degradation when transiently overexpressed in HEK293T cells, loss of endogenous CARD19 expression had little effect on Bcl10-dependent NF-κB activation, activation of Malt1 protease function, or Bcl10 degradation after TCR engagement in primary murine CD8 T cells. Together, these data indicate that the only detectable translated product of C9orf89 is the mitochondrial protein CARD19, which does not play a discernible role in TCR-dependent, Bcl10-mediated signal transduction to Malt1 or NF-κB.

Establishment of a longitudinal pre-clinical model of lyssavirus infection

Traditional mouse models of lyssavirus pathogenesis rely on euthanizing large groups of animals at various time points post-infection, processing infected tissues, and performing histological and molecular analyses to determine anatomical sites of infection. While powerful by some measures, this approach is limited by the inability to monitor disease progression in the same mice over time. In this study, we established a novel non-invasive mouse model of lyssavirus pathogenesis, which consists of longitudinal imaging of a luciferase-expressing Australian bat lyssavirus (ABLV) reporter virus. In vivo bioluminescence imaging (BLI) in mice revealed viral spread from a peripheral site of inoculation into the central nervous system (CNS), with kinetically and spatially distinct foci of replication in the footpad, spinal cord, and hindbrain. Detection of virus within the CNS was associated with onset of clinical disease. Quantification of virus-derived luminescent signal in the brain was found to be a reliable measure of viral replication, when compared to traditional molecular methods. Furthermore, we demonstrate that in vivo imaging of ABLV infection is not restricted to the use of albino strains of mice, but rather strong BLI signal output can be achieved by shaving the hair from the heads and spines of pigmented strains, such as C57BL/6. Overall, our data show that in vivo BLI can be used to rapidly and non-invasively identify sites of lyssavirus replication and to semi-quantitatively determine viral load without the need to sacrifice mice at multiple time points.

CARD19 interacts with MICOS complex proteins and protects against mitochondrial dysfunction in macrophages

CARD19 is a mitochondrial protein of unknown function; gene expression databases indicate that CARD19 is highly expressed in myeloid cells. We have observed that Card19 −/− mice injected with LPS display elevated levels of some pro-inflammatory cytokines relative to Card19 +/+ mice. Because CARD19 is a mitochondrial protein and mitochondrial dysfunction is frequently associated with immune dysregulation and chronic inflammation, we sought to identify the function of CARD19 in macrophages. We demonstrated via super resolution microscopy that endogenous CARD19 colocalizes with mitochondrial markers in bone marrow derived macrophages (BMDMs) and has a punctate distribution. Through immunoprecipitation and mass spectrometry analyses, we determined that CARD19 interacts with MIC19 and other components of the mitochondrial contact site and cristae organizing system (MICOS) complex. We further demonstrated that CARD19 colocalizes with MIC19 in mitochondrial sub-domains via super resolution microscopy. We then measured outcomes of mitochondrial stress in BMDMs. Consistent with previous reports of MICOS deficiencies, we found that Card19 −/− BMDMs have a modestly decreased oxygen consumption rate (OCR) measured by a Seahorse extracellular flux analyzer relative to Card19 +/+ BMDMs. Additionally, Card19 −/− BMDMs display elevated levels of mitochondrial reaction oxygen species (mROS) and a population of mitochondria with a decreased mitochondrial membrane potential, as measured by flow cytometry. Based on these data, we propose that CARD19 may be a previously unknown regulator of MICOS function which potentially links this complex to other mitochondrial and/or non-mitochondrial CARD proteins in macrophages.

CARD19: a mitochondrial caspase recruitment domain protein with a role in regulating pro-inflammatory innate immune responses

CARD19 is a ubiquitously expressed protein of unknown function. This protein was originally named BinCARD, and early data suggested that it interacts with Bcl10 and inhibits NF-κB activation in T cells. However, these early data were based on overexpression studies, and we are aware of no in vivo data that support this proposed function. Additionally, the cellular localization of CARD19 remains uncharacterized. We sought to address these gaps in knowledge by examining macrophages, thymocytes, and splenocytes from Card19 +/+ and Card19 −/− mice using superresolution microscopy and flow cytometry; we also compared secretion of TNF-alpha, IL-6, and MCP-1 in Card19 +/+ and Card19 −/− mice injected with LPS. Superresolution microscopy revealed that CARD19 is localized to the outer mitochondrial membrane, with no evidence of co-localization with BCL10. Deletion of the predicted transmembrane domain resulted in nuclear and cytosolic distribution, while a partial deletion of the C-terminus resulted in localization in the endoplasmic reticulum. Data to date do not indicate significant differences between Card19 +/+ and Card19 −/− thymocytes and splenocytes in development, activation, or effector function. Interestingly, Card19 −/− mice displayed higher plasma concentrations of TNF-alpha, IL-6, and MCP-1 relative to Card19 +/+ mice in response to LPS. We conclude that CARD19 does not measurably impact BCL10 function in vivo, and we suggest that CARD19 is likely involved in regulation of a mitochondrial function that affects pro-inflammatory innate immune responses via a mechanism independent of BCL10.

Immortalization of splenic and peripheral blood macrophages using a multi-cistronic v-Raf/v-Myc lentivirus

We have created an improved system for immortalizing mature macrophages by modifying the original v-raf/v-myc (J2) virus. Previously, these J2 viruses required a producer co-culture condition and maintained replicating virus. This provided more complexity, reagents, and biosafety risks. Our improved virus is replication deficient. Its lentiviral genome contains the v-raf/v-myc oncogenes and a thy1.1 surface marker, each of which is separated by a self-cleaving peptide. This virus, therefore, eliminates the issues described above. We transduced our modified virus into total murine PBMC isolated from murine peripheral blood or spleen. We found the transduction and successful cell line production can be done with as few as 1×105 PBMC. The resulting cytokine independent macrophage cell line from both spleen and blood expressed mature macrophage markers (F4-80+CD11b+) but lacked early myeloid progenitor markers (Sca1−c-kit−). In addition, we found these macrophages were functional as demonstrated by their ability to undergo phagocytosis and ability to upregulate MHCII in response to IFNγ. These findings demonstrate that the v-raf and v-myc oncogenes in our new system can immortalize macrophages from spleen but uniquely, and perhaps more importantly, can immortalize macrophages from blood. This advance provides a non-invasive method to obtain the starting tissue needed to make these macrophage cell lines. Having the v-raf/v-myc oncogenes in a lentivirus means it is likely this method will work on blood from humans and other species. Additionally, the cytokine independence associated with cell lines made with our virus make it ideal for creating macrophage cell lines from mammals without commercially available growth factors.

A transient Malt1 aggresome sustains T cell receptor signaling to NF-κB

The T cell receptor (TCR) to NF-κB signaling pathway is crucial for T cell activation and differentiation. Upon engagement of the TCR with cognate antigen, a series of events leads to the formation of the Carma1-Bcl10-Malt1 (CBM) complex, increasingly recognized as vital to a properly functioning immune response. We have demonstrated that in effector T cells, the CBM complex gives rise to a polymeric, filamentous signalosome called POLKADOTS that directs terminal activation of NF-κB. POLKADOTS consist of the core protein Bcl10, its constitutive binding partner Malt1, and their recruited signaling partners. We have previously shown that Bcl10 is degraded via selective autophagy following T cell activation. Here, we show that Malt1, which serves both as an adaptor transmitting signals to NF-κB and as a protease which cleaves a variety of substrates, is not concurrently degraded. Instead, Malt1-containing POLKADOTS coalesce via microtubule transport to a canonical aggresome. Aggresomes are thought to be depots of misfolded protein destined for degradation via macroautophagy; however, the Malt1 aggresome promotes late stage NF-κB activation through prolonging pIKK-Malt1 interactions. Additionally, this aggresome enhances the proteolysis of a subset of Malt1 targets. These results establish a mechanism for sustaining cytoplasmic signals from the TCR. More broadly, our findings demonstrate that aggresomes can serve as a stable platform for signal transduction.

T Cell Receptor Activation of NF-κB in Effector T Cells: Visualizing Signaling Events Within and Beyond the Cytoplasmic Domain of the Immunological Synapse

The T cell receptor (TCR) to NF-κB signaling pathway plays a critical role in regulation of proliferation and effector T cell differentiation and function. In naïve T cells, data suggest that most or all key cytoplasmic NF-κB signaling occurs in a TCR-proximal manner at the immunological synapse (IS). However, the subcellular organization of cytoplasmic NF-κB-activating complexes in effector T cells is more complex, involving signaling molecules and regulatory mechanisms beyond those operative in naïve cells. Additionally, in effector T cells, much signaling occurs at cytoplasmic locations distant from the IS. Visualization of these cytoplasmic signaling complexes has provided key insights into the complex and dynamic regulation of NF-κB signal transduction in effector T cells. In this chapter, we provide in-depth protocols for activating and preparing effector T cells for fluorescence imaging, as well as a discussion of the effective application of distinct imaging methodologies, including confocal and super-resolution microscopy and imaging flow cytometry.

Abstract 4000: Establishing the natural history of the immunosuppressive myeloid microenvironment in an inducible model of lung adenocarcinoma

Tumorigenesis is accompanied by broad changes to the surrounding tissue microenvironment in a tumor- and patient-specific manner. Phenotype shifts in tissue-resident immune cells promote cancer progression by establishing a proliferative inflammatory environment, activating angiogenesis, stimulating tumor cell invasion and suppressing anti-tumor immunity. While the former mechanisms are well appreciated and often targeted by current cancer therapeutics, the nature of the mechanisms controlling establishment of the local immunosuppressive state that contribute to a failure of anti-tumor immunity are less clearly defined. Blockade of tumor antigen-specific T cell killing is clearly a major contributor to the failure to control tumorigenesis. However, evidence suggests that phenotypic shifts in innate immune cell populations also contribute to the failure of anti-tumor immunity. We hypothesize that the emergence of early lung adenocarcinomas is accompanied by a shift in myeloid phenotypes, rapidly establishing a microenvironment favorable to tumor growth, survival and vascularization, and hostile to cell-mediated anti-tumor immune responses. Through the utilization of a Cre-inducible mouse model of p53-null, Kras-G12D+ lung adenocarcinoma, we have begun to define the natural history of the myeloid component of the tumor microenvironment, from tumor initiation to a point equivalent to human stage I adenocarcinoma. Histological, flow cytometry and real-time PCR approaches collectively demonstrate that tumor-associated myeloid phenotypes emerge at a very early stage of disease. These data are consistent with our hypothesis that the myeloid component of the tumor microenvironment plays a crucial role in establishing an immunosuppressive state during early tumorigenesis. Implications of these findings for current and emerging immunotherapies will be discussed.

Citation Format: Mouna Lagraoui, Clifton L. Dalgard, Gauthaman Sukumar, Celeste Huaman, Thomas Summers, Corey A. Carter, Brian C. Schaefer. Establishing the natural history of the immunosuppressive myeloid microenvironment in an inducible model of lung adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4000. doi:10.1158/1538-7445.AM2017-4000

Abstract 2939: Tumor associated myeloid cell transcriptome signatures in an inducible Kras-positive lung adenocarcinoma murine model

Tumorigenesis is modified by dynamic activities in the tumor microenvironment and mechanisms driving these alterations during tumor progression may be tumor- and patient-specific. Of well-established functions for tumor-associated stromal cells (e.g. angiogenesis, chemotaxis) immune system regulation by the tumor microenvironment is less well understood in their mechanism and effects. However, diminished activity of antigen-specific T cell lymphocytes tumor cytotoxicity is tumor promoting and recent cancer immunotherapy have targeted immune inhibitory checkpoints (e.g. anti-PD-L1) to restore T cell activity. Recent studies suggest that tumor-associated myeloid cells play a role in immunosuppression in several human cancers, including lung cancer. We hypothesize that early tumors of the lung promote changes in the phenotype of tumor-proximal myeloid cells, establishing an immunosuppressive microenvironment. As a component to observe this immunosuppressive role for myeloid cells, we performed specific transcriptome profiling of myeloid cells by immunomagnetic selection of CD11b-positive cells from lung tumors of a murine inducible Kras-positive, p53-negative cancer model. RNA sequencing of isolated myeloid cells as a function of tumorigenesis duration (3-18 weeks) establishes the kinetics of gene expression changes associated with tumor-supporting and immune-suppressing functions. Genome-wide expression analysis of myeloid cells between tumor-inducing adenovirus-Cre injected and normal control subjects resulted in identifying 1,883 genes with differential expression. Gene set enrichment analysis resulted in the stratification of samples by well-established gene signatures and tumor-promoting activity for angiogenesis (32 genes), lung tissue remodeling (47 genes) and cell survival (11 genes). Interestingly, a significant downregulated gene signature was observed in tumor-associated myeloid cells for immune cell chemotaxis (12 genes) and positive regulation of immune system activation (12 genes). These non-canonical gene signatures may identify a myeloid phenotype for immunosuppressive function with altered expression of genes such as L-selectin (Sell), C-C chemokine receptor type 7 (Ccr7), C-C motif chemokine (Ccl20) and CMRF35-like molecule 7 (CD300lb). The results shown are first steps in our tasks to define the phenotypes and mechanisms linking myeloid cells to tumor-associated immunosuppression in lung cancer.

Citation Format: Clifton L. Dalgard, Mouna Lagraoui, Gauthaman Sukumar, Celeste Huaman, Corey A. Carter, Brian C. Schaefer. Tumor associated myeloid cell transcriptome signatures in an inducible Kras-positive lung adenocarcinoma murine model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2939. doi:10.1158/1538-7445.AM2017-2939

Coalescence of Nanoscale Cytoplasmic Signalosomes Contributes to T Cell Receptor Signaling to NF-κB

T cell receptor (TCR) activation of the transcription factor NF-κB is a crucial determinant of effector T lymphocyte function. The complex regulatory network surrounding this pathway remains poorly understood, particularly at time periods further removed from initial TCR triggering. We have previously demonstrated that following activation of the TCR, the proteins p62, Bcl10, and Malt1 rapidly combine to form a cytoplasmic filamentous signalosome called POLKADOTS, which recruits further signaling proteins and initiates the terminal steps in activation of NF-κB. Here, we examine the fate of POLKADOTS signalosomes following initial activation of NF-κB. We demonstrate via super-resolution and confocal microscopy techniques that POLKADOTS filaments converge on the microtubule-organizing center via microtubule transport, aggregating in a peri-nuclear aggresomal structure. Aggresomes are poorly understood structures thought to be depots of misfolded protein destined for degradation; however, our data suggest that the aggresomal accumulations of POLKADOTS continue to promote T cell activation. We show that the formation and maintenance of this aggresome corresponds with a secondary increase in NF-κB translocation. Additionally, the aggresomal structure prolongs phosphorylation of IKK and promotes the proteolytic activity of Malt1. Together, these results demonstrate that TCR signaling to NF-κB directs the orchestrated assembly, transport, and stable coalescence of nanoscale cytoplasmic signaling complexes. More broadly, our findings provide evidence that aggresomes can serve as stable platforms of signal transduction, thereby proposing a new role for these little understood structures.

Salsalate treatment following traumatic brain injury reduces inflammation and promotes a neuroprotective and neurogenic transcriptional response with concomitant functional recovery

Neuroinflammation plays a critical role in the pathogenesis of traumatic brain injury (TBI). TBI induces rapid activation of astrocytes and microglia, infiltration of peripheral leukocytes, and secretion of inflammatory cytokines. In the context of modest or severe TBI, such inflammation contributes to tissue destruction and permanent brain damage. However, it is clear that the inflammatory response is also necessary to promote post-injury healing. To date, anti-inflammatory therapies, including the broad class of non-steroidal anti-inflammatory drugs (NSAIDs), have met with little success in treatment of TBI, perhaps because these drugs have inhibited both the tissue-damaging and repair-promoting aspects of the inflammatory response, or because inhibition of inflammation alone is insufficient to yield therapeutic benefit. Salsalate is an unacetylated salicylate with long history of use in limiting inflammation. This drug is known to block activation of NF-κB, and recent data suggest that salsalate has a number of additional biological activities, which may also contribute to its efficacy in treatment of human disease. Here, we show that salsalate potently blocks pro-inflammatory gene expression and nitrite secretion by microglia in vitro. Using the controlled cortical impact (CCI) model in mice, we find that salsalate has a broad anti-inflammatory effect on in vivo TBI-induced gene expression, when administered post-injury. Interestingly, salsalate also elevates expression of genes associated with neuroprotection and neurogenesis, including the neuropeptides, oxytocin and thyrotropin releasing hormone. Histological analysis reveals salsalate-dependent decreases in numbers and activation-associated morphological changes in microglia/macrophages, proximal to the injury site. Flow cytometry data show that salsalate changes the kinetics of CCI-induced accumulation of various populations of CD11b-positive myeloid cells in the injured brain. Behavioral assays demonstrate that salsalate treatment promotes significant recovery of function following CCI. These pre-clinical data suggest that salsalate may show promise as a TBI therapy with a multifactorial mechanism of action to enhance functional recovery.

Intrinsic Differences in Donor CD4 T Cell IL-2 Production Influence Severity of Parent-into-F1 Murine Lupus by Skewing the Immune Response Either toward Help for B Cells and a Sustained Autoantibody Response or toward Help for CD8 T Cells and a Downregulatory Th1 Response

Using the parent-into-F1 model of induced lupus and (C57BL/6 × DBA2) F1 mice as hosts, we compared the inherent lupus-inducing properties of the two parental strain CD4 T cells. To control for donor CD4 recognition of alloantigen, we used H-2(d) identical DBA/2 and B10.D2 donor T cells. We demonstrate that these two normal, nonlupus-prone parental strains exhibit two different T cell activation pathways in vivo. B10.D2 CD4 T cells induce a strong Th1/CMI pathway that is characterized by IL-2/IFN-γ expression, help for CD8 CTLs, and skewing of dendritic cell (DC) subsets toward CD8a DCs, coupled with reduced CD4 T follicular helper cells and transient B cell help. In contrast, DBA/2 CD4 T cells exhibit a reciprocal, lupus-inducing pathway that is characterized by poor IL-2/IFN-γ expression, poor help for CD8 CTLs, and skewing of DC subsets toward plasmacytoid DCs, coupled with greater CD4 T follicular helper cells, prolonged B cell activation, autoantibody formation, and lupus-like renal disease. Additionally, two distinct in vivo splenic gene-expression signatures were induced. In vitro analysis of TCR signaling revealed defective DBA CD4 T cell induction of NF-κB, reduced degradation of IκBα, and increased expression of the NF-κB regulator A20. Thus, attenuated NF-κB signaling may lead to diminished IL-2 production by DBA CD4 T cells. These results indicate that intrinsic differences in donor CD4 IL-2 production and subsequent immune skewing could contribute to lupus susceptibility in humans. Therapeutic efforts to skew immune function away from excessive help for B cells and toward help for CTLs may be beneficial.

Visualizing TCR-induced POLKADOTS formation and NF-κB activation in the D10 T-cell clone and mouse primary effector T cells

T cells are an immune cell lineage that play a central role in protection against pathogen infection. Antigen, in the form of pathogen-derived peptides, stimulates the T-cell receptor (TCR), leading to activation of the transcription factor, nuclear factor kappa B (NF-κB). The subsequent NF-κB-dependent gene expression program drives expansion and effector differentiation of antigen-specific T cells, leading to the adaptive anti-pathogen immune response. The cell surface TCR transmits activating signals to cytosolic NF-κB by a complex signaling cascade, in which the adapter protein Bcl10 plays a key role. We have previously demonstrated that TCR engagement leads to the formation of cytosolic Bcl10 clusters, called POLKADOTS, that provide a platform for the assembly of the terminal signaling complex that ultimately mediates NF-κB activation. In this chapter, we describe the methods utilized to visualize the formation of TCR-induced POLKADOTS and to study the temporal association between POLKADOTS formation and nuclear translocation of the NF-κB subunit, RelA/p65.

T cell receptor signals to NF-κB are transmitted by a cytosolic p62-Bcl10-Malt1-IKK signalosome

Antigen-mediated stimulation of the T cell receptor (TCR) triggers activation of nuclear factor κB (NF-κB), a key transcriptional regulator of T cell proliferation and effector cell differentiation. TCR signaling to NF-κB requires both the Carma1-Bcl10-Malt1 (CBM) complex and the inhibitor of κB (IκB) kinase (IKK) complex; however, the molecular mechanisms connecting the CBM complex to activation of IKK are incompletely defined. We found that the active IKK complex is a component of a TCR-dependent cytosolic Bcl10-Malt1 signalosome containing the adaptor protein p62, which forms in effector T cells. Phosphorylated IκBα and NF-κB were transiently recruited to this signalosome before NF-κB translocated to the nucleus. Inhibiting the activity of the kinase TAK1 or IKK blocked the phosphorylation of IKK, but not the formation of p62-Bcl10-Malt1 clusters, suggesting that activation of IKK occurs after signalosome assembly. Furthermore, analysis of T cells from p62-deficient mice demonstrated that the p62-dependent clustering of signaling components stimulated activation of NF-κB in effector T cells. Thus, TCR-stimulated activation of NF-κB requires the assembly of cytosolic p62-Bcl10-Malt1-IKK signalosomes, which may ensure highly regulated activation of NF-κB in response to TCR engagement.

A new look at T cell receptor signaling to nuclear factor-κB

Antigen stimulation of T cell receptor (TCR) signaling to nuclear factor (NF)-κB is required for T cell proliferation and differentiation of effector cells. The TCR-to-NF-κB pathway is generally viewed as a linear sequence of events in which TCR engagement triggers a cytoplasmic cascade of protein-protein interactions and post-translational modifications, ultimately culminating in the nuclear translocation of NF-κB. However, recent findings suggest a more complex picture in which distinct signalosomes, previously unrecognized proteins, and newly identified regulatory mechanisms play key roles in signal transmission. In this review, we evaluate recent data and suggest areas of future emphasis in the study of this important pathway.

Controlled cortical impact and craniotomy induce strikingly similar profiles of inflammatory gene expression, but with distinct kinetics

An immediate consequence of traumatic brain injury (TBI) is the induction of an inflammatory response. Mounting data suggest that inflammation is a major contributor to TBI-induced brain damage. However, much remains unknown regarding the induction and regulation of the inflammatory response to TBI. In this study we compared the TBI-induced inflammatory response to severe parenchymal injury (controlled cortical impact) vs. mild brain injury (craniotomy) over a 21-day period. Our data show that both severe and mild brain injury induce a qualitatively similar inflammatory response, involving highly overlapping sets of effector molecules. However, kinetic analysis revealed that the inflammatory response to mild brain injury is of much shorter duration than the response to severe TBI. Specifically, the inflammatory response to severe brain injury persists for at least 21 days, whereas the response to mild brain injury returns to near baseline values within 10 days post-injury. Our data therefore imply that the development of accurate diagnostic tests of TBI severity that are based on imaging or biomarker analysis of the inflammatory response may require repeated measures over at least a 10-day period, post-injury.

Selective autophagy regulates T cell activation

T cells are essential for defense of the host against invading pathogens. Antigen activation of the T cell receptor (TCR) is required for generation of an adaptive immune response. Several groups have observed that blocking autophagy augments T cell activation, but the molecular basis of this finding has remained elusive. The adaptor protein BCL10 transmits activating signals from the TCR to NFKB1-RELA/NFκB, a transcription factor that is critical for T cell proliferation and function. We recently reported that a TCR-dependent autophagy mechanism selectively targets and degrades BCL10. We found that BCL10 autophagy requires BCL10 K63-polyubiquitination and subsequent binding to the autophagy adaptor SQSTM1/p62. Blocking either one of these processes inhibits BCL10 degradation. Protecting BCL10 from autophagic degradation, either by pharmacological or genetic inhibition of autophagy, results in increased activation of NFKB1-RELA. By demonstrating the mechanism of autophagic uptake and degradation of BCL10, our study has revealed a key mechanism by which selective autophagy controls T cell activation. Here, we discuss the implications of our findings and explore possible directions for future research.

Selective autophagy of the adaptor protein Bcl10 modulates T cell receptor activation of NF-κB

The adaptor protein Bcl10 is a critically important mediator of T cell receptor (TCR)-to-NF-κB signaling. Bcl10 degradation is a poorly understood biological phenomenon suggested to reduce TCR activation of NF-κB. Here we have shown that TCR engagement triggers the degradation of Bcl10 in primary effector T cells but not in naive T cells. TCR engagement promoted K63 polyubiquitination of Bcl10, causing Bcl10 association with the autophagy adaptor p62. Paradoxically, p62 binding was required for both Bcl10 signaling to NF-κB and gradual degradation of Bcl10 by autophagy. Bcl10 autophagy was highly selective, as shown by the fact that it spared Malt1, a direct Bcl10 binding partner. Blockade of Bcl10 autophagy enhanced TCR activation of NF-κB. Together, these data demonstrate that selective autophagy of Bcl10 is a pathway-intrinsic homeostatic mechanism that modulates TCR signaling to NF-κB in effector T cells. This homeostatic process may protect T cells from adverse consequences of unrestrained NF-κB activation, such as cellular senescence.

An active kinase domain is required for retention of PKCθ at the T cell immunological synapse

Protein kinase Cθ (PKCθ) is a serine/threonine kinase that plays an essential role in antigen-regulated responses of T lymphocytes. Upon antigen stimulation, PKCθ is rapidly recruited to the immunological synapse (IS), the region of contact between the T cell and antigen-presenting cell. This behavior is unique among T cell PKC isoforms. To define domains of PKCθ required for retention at the IS, we generated deletion and point mutants of PKCθ. We used quantitative imaging analysis to assess IS retention of PKCθ mutants in antigen-stimulated T cell clones. Deletion of the kinase domain or site-directed mutation of a subset of known PKCθ phosphorylation sites abrogated or significantly reduced IS retention, respectively. IS retention did not correlate with phosphorylation of specific PKCθ residues but rather with kinase function. Thus PKCθ catalytic competence is essential for stable IS retention.

Cutting edge: TCR ligation triggers digital activation of NF-kappaB

TCR-mediated activation of the transcription factor NF-κB is required for T cell proliferation, survival, and effector differentiation. Although this pathway is the subject of intense study, it is not known whether TCR signaling to NF-κB is digital (switch-like) or analog in nature. Through analysis of the phosphorylation and degradation of IκBα and the nuclear translocation and phosphorylation of the NF-κB subunit RelA, we show that TCR-directed NF-κB activation is digital. Furthermore, digitization occurs well upstream of the IκB kinase complex, as protein kinase C translocation to the immunologic synapse and activation-associated aggregation of Bcl10 and Malt1 also demonstrate both digital behavior and high correlation with RelA nuclear translocation. Thus, similar to the TCR-to-MAPK signaling cascade, analog Ag inputs are converted to digital activation outputs to NF-κB at an early step downstream of TCR ligation.

Blood fluke exploitation of non-cognate CD4+ T cell help to facilitate parasite development

Schistosoma blood flukes, which infect over 200 million people globally, co-opt CD4⁺ T cell-dependent mechanisms to facilitate parasite development and egg excretion. The latter requires Th2 responses, while the mechanism underpinning the former has remained obscure. Using mice that are either defective in T cell receptor (TCR) signaling or that lack TCRs that can respond to schistosomes, we show that naïve CD4⁺ T cells facilitate schistosome development in the absence of T cell receptor signaling. Concurrently, the presence of naïve CD4⁺ T cells correlates with both steady-state changes in the expression of genes that are critical for the development of monocytes and macrophages and with significant changes in the composition of peripheral mononuclear phagocyte populations. Finally, we show that direct stimulation of the mononuclear phagocyte system restores blood fluke development in the absence of CD4⁺ T cells. Thus we conclude that schistosomes co-opt innate immune signals to facilitate their development and that the role of CD4⁺ T cells in this process may be limited to the provision of non-cognate help for mononuclear phagocyte function. Our findings have significance for understanding interactions between schistosomiasis and other co-infections, such as bacterial infections and human immunodeficiency virus infection, which potently stimulate innate responses or interfere with T cell help, respectively. An understanding of immunological factors that either promote or inhibit schistosome development may be valuable in guiding the development of efficacious new therapies and vaccines for schistosomiasis.

Schistosomes, or blood flukes, cause a debilitating illness in millions of people worldwide, which manifests when inflammation develops in response to parasite eggs that become trapped in the liver and other organs. Paradoxically, schistosomes require signals from the host's immune system in order to develop fully into egg-producing adults. Previously, we showed that CD4⁺ T cells facilitate schistosome development. Here, we show that the mere presence of CD4⁺ T cells is sufficient for schistosome development to proceed. There is no requirement for these cells to respond to the parasite, or to exhibit any typical “effector” response. Two pieces of data suggest this effect on parasite development is mediated by antigen-presenting cells of the innate immune system such as monocytes and macrophages, which interact with CD4⁺ T cells by expressing MHC class II molecules. First, the presence of naïve CD4⁺ T cells correlates with baseline changes in the development of monocyte/macrophage populations. Second, direct stimulation of the monocyte-macrophage system restores parasite development, bypassing the requirement for CD4⁺ T cells in schistosome development. Understanding the mechanisms that promote or inhibit blood fluke infection may facilitate the development of new treatments and vaccines for schistosomiasis.

Expanding the multicolor capabilities of basic confocal microscopes by employing red and near-infrared quantum dot conjugates

Background

Confocal microscopy is a widely employed methodology in cellular biology, commonly used for investigating biological organization at the cellular and sub-cellular level. Most basic confocal microscopes are equipped to cleanly discriminate no more than four fluorophores in a given sample, limiting the utility of this method for co-localization, co-expression, and other multi-parameter analyses. In this study, we evaluated the use of red and near-infrared emitting quantum dot staining reagents to expand the multi-parameter capabilities of basic confocal microscopes.

Results

We modified a three-laser Zeiss Pascal confocal microscope by the addition of two band-pass filters and one long-pass filter for the detection of three different red to near-infrared quantum dot conjugates. We then performed direct comparisons between organic dye- and quantum dot-labeled detection reagents for the detection of subcellular structures. We found that the quality of staining was generally indistinguishable, although quantum dot reagents do have certain limitations, relative to organic dye conjugates. Using the modified Pascal system, three quantum dot conjugates, two organic dye conjugates, and one fluorescent protein, we demonstrated clean discrimination of six distinct fluorescent labels in a single sample.

Conclusion

Our data demonstrate that nearly any basic confocal microscope can be modified by the simple addition of appropriate emission filters, allowing the detection of red and near-infrared quantum dot conjugates. Additionally, quantum dot- and organic dye-based secondary reagents can be successfully combined in complex intracellular staining experiments. Substantial expansion of the multi-parameter capabilities of basic confocal instruments can be achieved with a financial investment that is minimal in comparison to instrument replacement or upgrade with additional lasers.

Loss of protein kinase C theta, Bcl10, or Malt1 selectively impairs proliferation and NF-kappa B activation in the CD4+ T cell subset

The cytosolic proteins protein kinase Ctheta (PKCtheta), Bcl10, and Malt1 play critical roles in TCR signaling to the transcription factor NF-kappaB. Our data confirm that CD4(+) T cells from PKCtheta, Bcl10, and Malt1 knockout mice show severe impairment of proliferation in response to TCR stimulation. Unexpectedly, we find that knockout CD8(+) T cells proliferate to a similar extent as wild-type cells in response to strong TCR signals, although a survival defect prevents their accumulation. Both CD4(+) and CD8(+) knockout T cells express activation markers, including CD25, following TCR stimulation. Addition of exogenous IL-2 rescues survival of knockout CD4(+) and CD8(+) T cells, but fails to overcome the proliferation defect of CD4(+) T cells. CD4(+) T cells from knockout mice are extremely deficient in TCR-induced NF-kappaB activation, whereas NF-kappaB activation is only partially impaired in CD8(+) T cells. Overall, our results suggest that defects in TCR signaling through PKCtheta, Bcl10, and Malt1 predominantly impair NF-kappaB activation and downstream functional responses of CD4(+) T cells. In contrast, CD8(+) T cells maintain substantial NF-kappaB signaling, implying the existence of a significant TCR-regulated NF-kappaB activation pathway in CD8(+) T cells that is independent of PKCtheta, Bcl10, and Malt1.

Multiple protein domains mediate interaction between Bcl10 and MALT1

Bcl10 and MALT1 are essential mediators of NF-kappaB activation in response to the triggering of a diverse array of transmembrane receptors, including antigen receptors. Additionally, both proteins are translocation targets in MALT lymphoma. Thus, a detailed understanding of the interaction between these mediators is of considerable biological importance. Previous studies have indicated that a 13-amino acid region downstream of the Bcl10 caspase recruitment domain (CARD) is responsible for interacting with the immunoglobulin-like domains of MALT1. We now provide evidence that the death domain of MALT1 and the CARD of Bcl10 also contribute to Bcl10-MALT1 interactions. Although a direct interaction between the MALT1 death domain and Bcl10 cannot be detected via immunoprecipitation, FRET data strongly suggest that the death domain of MALT1 contributes significantly to the association between Bcl10 and MALT1 in T cells in vivo. Furthermore, analysis of point mutants of conserved residues of Bcl10 shows that the Bcl10 CARD is essential for interaction with the MALT1 N terminus. Mutations that disrupt proper folding of the Bcl10 CARD strongly impair Bcl10-MALT1 interactions. Molecular modeling and functional analyses of Bcl10 point mutants suggest that residues Asp(80) and Glu(84) of helix 5 of the Bcl10 CARD directly contact MALT1. Together, these data demonstrate that the association between Bcl10 and MALT1 involves a complex interaction between multiple protein domains. Moreover, the Bcl10-MALT1 interaction is the second reported example of interactions between a CARD and a non-CARD protein region, which suggests that many signaling cascades may utilize CARD interactions with non-CARD domains.

Analysis of tumor-associated stromal cells using SCID GFP transgenic mice: contribution of local and bone marrow-derived host cells

The green fluorescence protein (GFP) from the UBI-GFP/BL6 transgenic line was bred into C57BL/6J-scid and C.B-17-scid mice for investigating host-tumor cell interactions. These mice express high levels of GFP under the control of the ubiquitin promoter in virtually all cells examined. In tumor tissue generated by implanting tumor cells in the GFP transgenic SCID mice, the tumor cells and tumor-associated murine host cells were clearly distinguished by GFP expression. A population of cells expressing the endothelial cell marker VEGFR-2/Flk-1, and the progenitor markers c-Kit and Sca-1, were incorporated into tumor tissue. The majority of the Flk-1-positive cells were hematopoietic-derived cells that coexpressed CD45. To investigate the contribution of bone marrow-derived cells to the formation of tumor vessels and stroma, tumor cells were implanted in nontransgenic SCID mice that received a bone marrow transplant from GFP-expressing SCID mice. Although GFP-positive cells were readily detected by histology in tumors taken from bone marrow transplanted animals, they were spatially isolated and lacked organization. In contrast, if tumors were implanted in nontransgenic SCID mice adjacent to a patch of transplanted GFP-expressing skin, these tumors recruited GFP-positive cells that organized into tumor vessels. The results demonstrate that hematopoietic-derived cells, including Flk-1+/CD45+ cells, readily colonized the tumor stroma but were minimally incorporated in the tumor vasculature. The majority of the tumor vessels were instead recruited from tissue adjacent to the tumor. The expression of Flk-1 on nonendothelial, tumor-associated host cells raises the possibility that VEGF antagonists, such as Avastin, could inhibit tumor growth by a mechanism involving hematopoietic-derived CD45+/Flk-1+ cells, in addition to direct suppression of endothelial cell function.

POLKADOTS are foci of functional interactions in T-Cell receptor-mediated signaling to NF-kappaB

Stimulation of the T-cell receptor (TCR) results in the activation of several transcription factors, including NF-kappaB, that are crucial for T-cell proliferation and gain of effector functions. On TCR engagement, several proteins within the TCR-directed NF-kappaB signaling pathway undergo dynamic spatial redistribution, but the significance of these redistribution events is largely unknown. We have previously described TCR-induced cytoplasmic structures called POLKADOTS (punctate and oligomeric killing or activating domains transducing signals) that are enriched in the NF-kappaB signaling intermediate, Bcl10. We now show that these structures are formed only under conditions that promote efficient NF-kappaB activation. Furthermore, POLKADOTS formation is dependent on functional domains of specific NF-kappaB signal transducers. Through use of a photoactivatable GFP, we demonstrate that POLKADOTS contain both a highly stable and a rapidly equilibrating protein component. FRET analyses show that POLKADOTS are sites of enriched interactions between Bcl10 and partner signaling proteins. These observations strongly suggest that POLKADOTS are focal sites of dynamic information exchange between cytosolic intermediates in the process of TCR activation of NF-kappaB.

Constitutive association of the proapoptotic protein Bim with Bcl-2-related proteins on mitochondria in T cells

Apoptosis in activated T cells in vivo requires the proapoptotic Bcl-2 family member Bim. We show here that, despite its ability to bind LC8, a component of the microtubule dynein motor complex, most of the Bim in both healthy and apoptotic T cells is associated with mitochondria, not microtubules. In healthy resting T cells Bim is bound to the antiapoptotic proteins Bcl-2 and Bcl-x(L). In activated T cells, levels of Bcl-2 fall, and Bim is associated more with Bcl-x(L) and less with Bcl-2. Our results indicate that, in T cells, Bim function is regulated by interaction with Bcl-2 family members on mitochondria rather than by sequestration to the microtubules.

Complex and dynamic redistribution of NF-kappaB signaling intermediates in response to T cell receptor stimulation

The central zone of the supramolecular activation cluster (c-SMAC) is a zone of T cell receptor (TCR) enrichment that forms at a T cell/antigen-presenting cell (APC) junction in response to antigen stimulation. We demonstrate that there is a surprisingly complex relocalization process that brings PKC and Bcl10, two intermediates in TCR activation of NF-kappaB, to the cytoplasmic face of the c-SMAC. TCR activation causes enrichment of PKC at the c-SMAC, followed by Bcl10 relocalization to punctate cytoplasmic structures, often at sites distant from the c-SMAC. These Bcl10 structures then undergo further relocalization, becoming enriched at the c-SMAC. TCR activation of NF-kappaB therefore involves the dynamic relocalization of multiple signaling intermediates, with distinct phases proximal to and distant from the c-SMAC.

Cell surface expression of the HIV-1 envelope glycoproteins is directed from intracellular CTLA-4-containing regulated secretory granules

The envelope glycoprotein (Env) of HIV-1 is incorporated into virions that bud from the cell surface of infected T cells. With immunofluorescence microscopy and subcellular membrane fractionation techniques, the intracellular fate of Env in the secretory pathway of HIV-1-infected T cells was evaluated. Rather than trafficking constitutively from the Golgi to the cell surface, Env is directed to intracellular CTLA-4-containing granules, whose recruitment to the cell surface is regulated. The use of the regulated pathway for intracellular Env storage before virion assembly holds implications for the staging of Env exposure at the cell surface of infected cells and of coordinating HIV virion assembly.

T cells down-modulate peptide-MHC complexes on APCs in vivo

T cells compete in the response to antigen in vivo and this competition may drive the affinity maturation of a secondary T cell response. Here we show that high-affinity T cells out-competed lower affinity T cells during a response to antigenic challenge in vivo. Although competition between T cells specific for different peptide-major histocompatibility complexes (MHC) occurred, it was less efficient than competition between T cells of the same peptide-MHC specificity. In addition, high-affinity T cells efficiently induced antigen loss from the surface of antigen-presenting cells. Thus T cells that responded to the same peptide-MHC competed with each other by lowering the amount of ligand with which the cells could react. As a result, the activation of high-affinity cells was favored. This provides a mechanism for the affinity maturation of a secondary T cell response.

Observation of antigen-dependent CD8+ T-cell/ dendritic cell interactions in vivo

In order to track hematopoetic cells of all lineages unambiguously at all stages of development, we have developed C57BL/6 mice that express a transgene coding for green fluorescent protein (GFP) under control of the human ubiquitin C promoter. These mice, called UBI-GFP/BL6, express GFP in all tissues examined, with high levels of GFP expression observed in hematopoetic cells. UBI-GFP/BL6 mice are unique in that B cells, T cells, and dendritic cells have distinct levels of GFP fluorescence. In cell transfer experiments, leukocytes from UBI-GFP/BL6 mice are readily identified by FACS or fluorescence microscopy. We demonstrate that transplanted UBI-GFP/BL6 dendritic cells are easily identified in secondary lymphoid tissues. Direct interactions between individual dendritic cells and multiple naïve CD8+ T cells are observed in lymph nodes within 12 h of cell transfer and require loading of the dendritic cells with the appropriate peptide antigen. Dendritic cells undergo specific morphologic changes following interactions with antigen-specific T cells.

A novel family of retroviral vectors for the rapid production of complex stable cell lines

The production of stable cell lines is an important technique in cell biology, and it is often the rate-limiting step in studies involving the characterization of the function of novel genes or gene mutations. To facilitate this process, a novel family of retroviral vectors, the pE vector family, has been generated. The retroviral sequences in the pE vectors have been taken from the Moloney murine leukemia virus (MMLV) vector pMFG, which has been shown to express cDNA inserts more consistently and at higher levels than earlier generations of MMLV vectors. These vectors contain four different internal ribosome entry site-selectable markers, allowing high-efficiency selection of transductants expressing the desired cDNA. The pE vectors have an episomal design to allow long-term production of high-titer virus without the need for subcloning the producer line. Using a strategy of combinatorial infection followed by combinatorial drug selection, we demonstrate that the pE vectors can be used to generate stable, polyclonal cell lines expressing at least three novel cDNAs in less than 2 weeks. The use of these vectors will thus dramatically accelerate the production of complex stable cell lines.

Immunological adjuvants promote activated T cell survival via induction of Bcl-3

Injection of soluble protein antigen into animals causes abortive proliferation of the responding T cells. Immunological adjuvants boost T cell responses at least in part by increasing the survival of activated T cells during and after the initial proliferative phase of their clonal expansion. To understand how adjuvants promote T cell survival, we used gene microarrays to analyze gene expression in T cells activated either with antigen alone or in the presence of two different adjuvants. Among the genes whose expression was increased by both adjuvants was the IkappaB family member Bcl-3. Retroviral infection experiments showed that expression of Bcl-3 increased survival of activated T cells in vitro and in vivo. Adjuvants may therefore improve survival of activated T cells via induction of Bcl-3.

MEKK2 associates with the adapter protein Lad/RIBP and regulates the MEK5-BMK1/ERK5 pathway

MEKK2 and MEKK3 are two closely related mitogen-activated protein kinase (MAPK) kinase kinases. The kinase domains of MEKK2 and MEKK3 are nearly identical, although their N-terminal regulatory domains are significantly divergent. By yeast two-hybrid library screening, we have identified MEK5, the MAPK kinase in the big mitogen-activated protein kinase 1 (BMK1)/ERK5 pathway, as a binding partner for MEKK2. MEKK2 expression stimulates BMK1/ERK5 activity, the downstream substrate for MEK5. Compared with MEKK3, MEKK2 activated BMK1/ERK5 to a greater extent, which might correlate with a higher affinity MEKK2-MEK5 interaction. A dominant negative form of MEK5 blocked the activation of BMK1/ERK5 by MEKK2, whereas activation of c-Jun N-terminal kinase (JNK) was unaffected, showing that MEK5 is a specific downstream effector of MEKK2 in the BMK1/ERK5 pathway. Activation of BMK1/ERK5 by epidermal growth factor and H2O2 in Cos7 and HEK293 cells was completely blocked by a kinase-inactive MEKK3 (MEKK3kin(-)), whereas MEKK2kin(-) had no effect. However, in D10 T cells, expression of MEKK2kin(-) but not MEKK3kin(-) inhibited BMK1/ERK5 activity. Two-hybrid screening also identified Lck-associated adapter/Rlk- and Itk-binding protein (Lad/RIBP), a T cell adapter protein, as a binding partner for MEKK2. MEKK2 and Lad/RIBP colocalize at the T cell contact site with antigen-loaded presenting cells, demonstrating cotranslocation of MEKK2 and Lad/RIBP during T cell activation. MEKK3 neither binds Lad/RIBP nor is recruited to the T cell contact with antigen presenting cell. MEKK2 and MEKK3 are differentially associated with signaling from specific upstream receptor systems, whereas both activate the MEK5-BMK1/ERK5 pathway.

Homeostasis of alpha beta TCR+ T cells

Cytokines contribute to T cell homeostasis at all stages of T cell existence. However, the particular cytokine involved varies as T cells progress from a naïve through an activated to a memory state. In many cases the important cytokines are members of the interleukin 2 subfamily of the short-chain type I cytokines. A case is made for the idea that the evolutionary divergence of the short-chain family allowed for concurrent divergence in leukocytes.

Genomic-scale analysis of gene expression in resting and activated T cells

Recent advances in gene array technology and isolation of lymphocytes now allow comprehensive analysis of gene expression in many different types of T cells. So far only a few sets of results have been published. However it is already clear that these analyses provide accurate measurements of gene expression in T cells. This technology offers the first opportunity to examine global and subtle changes in gene expression in response to specific stimuli.

Activation-induced inhibition of interleukin 6-mediated T cell survival and signal transducer and activator of transcription 1 signaling

The cytokines interleukin (IL)-2, IL-4, IL-6, IL-7, and IL-15 have all previously been shown to inhibit resting T cell death in vitro. We have found a difference in the response of T cells to IL-6, depending on the activation status of the cells. IL-6 inhibited the death of naive T cells, but had no effect on the death of either superantigen-activated T cells, or T cells bearing memory markers. This was true even when the resting and activated T cells were isolated from the same animal; thus, the determining factor for IL-6 insensitivity was the activation status or activation history of the cell, and not the milieu in the animal from which the cells were isolated. Activated T cells expressed lower levels of IL-6 receptors on their surfaces, yet there were sufficient levels of receptors for signaling, as we observed similar levels of signal transducer and activator of transcription (Stat)3 phosphorylation in resting and activated T cells treated with IL-6. However, there was profound inhibition of IL-6-induced Stat1 phosphorylation in activated T cells compared with resting T cells. These data suggest that there is activation-induced inhibition of IL-6 receptor signaling in T cells. This inhibition appears to be specific for some but not all of the IL-6-mediated signaling cascades in these cells.

Activation changes the spectrum but not the diversity of genes expressed by T cells

During activation T cells are thought to change their patterns of gene expression dramatically. To find out whether this is true for T cells activated in animals, the patterns of genes expressed in resting T cells and T cells 8 and 48 hr after activation were examined by using Affymetrix gene arrays. Gene arrays gave accurate comparisons of gene expression in the different cell types because the expression of genes known to vary during activation changed as expected. Of the approximately 6,300 genes assessed by the arrays, about one-third were expressed to appreciable extents in any of the T cells tested. Thus, resting T cells express a surprisingly large diversity of genes. The patterns of gene expression changed considerably within 8 hr of T cell activation but returned to a disposition more like that of resting T cells within 48 hr of exposure to antigen. Not unexpectedly, the activated T cells expressed genes associated with cell division at higher levels than resting T cells. The resting T cells expressed a number of cytokine receptor genes and some genes thought to suppress cell division, suggesting that the state of resting T cells is not a passive failure to respond to extant external stimuli.

Live cell fluorescence imaging of T cell MEKK2: redistribution and activation in response to antigen stimulation of the T cell receptor

T cell activation requires engagement of the T cell receptor (TCR) at the interface of conjugates formed with antigen-presenting cells. TCR engagement is accompanied by a redistribution of specific signaling molecules to the cytoplasmic region of the TCR complex. In this study, immunocytochemistry and live cell fluorescence imaging demonstrate that T cell MEK kinase 2 (MEKK2) is translocated to the T cell/antigen-presenting cell interface in response to antigen activation. MEKK2 translocation occurs more rapidly as the antigen concentration is increased. Biochemical activation of MEKK2 follows TCR stimulation, and expression of a dominant-negative MEKK2 inhibits TCR-mediated conjugate stabilization and ERK and p38 MAP kinase phosphorylation. Live cell fluorescence imaging thus enables characterization of signal transducers that are dynamically translocated following TCR engagement.

Constitutive activation of Epstein-Barr virus (EBV) nuclear antigen 1 gene transcription by IRF1 and IRF2 during restricted EBV latency

The Epstein-Barr virus (EBV) EBNA1 gene promoter active in the type I program of restricted viral latency was recently identified and shown to reside in the viral BamHI Q fragment. This promoter, Qp, is active in a wide variety of cell lines and has an architecture reminiscent of eukaryotic housekeeping gene promoters (B. C. Schaefer, J. L. Strominger, and S. H. Speck, Proc. Natl. Acad. Sci. USA 92:10565-10569, 1995; B. C. Schaefer, J. L. Strominger, and S. H. Speck, Mol. Cell. Biol. 17:364-377, 1997). Here we demonstrate by deletion analysis that the important cis-acting elements regulating Qp are clustered in a relatively small region (ca. 80 bp) surrounding the site of transcription initiation. Immediately upstream of the site of initiation is a region which is protected from DNase I digestion by crude nuclear extracts. Electrophoretic mobility shift analyses (EMSA) employing probes spanning this region demonstrated the presence of two major protein complexes. Deletion analysis of Qp demonstrated that at least one of these complexes plays an important role in Qp activity. Evidence that interferon response factor 2 (IRF2) is a major constituent of the most prominent EMSA complex and that IRF1 may be a minor component of this complex is presented. Transfections into IRF1-/-, IRF2-/-, and IRF1,2-/- fibroblasts demonstrated that absence of both IRF1 and IRF2 reduced Qp activity to approximately the same extent as mutation of the IRF-binding site in Qp, strongly implicating IRF2, and perhaps IRF1, in the regulation of Qp activity. Notably, transcription from Qp was not inducible by either alpha or gamma interferon in EBV-negative B cells but rather was shown to be constitutively activated by IRF1 and IRF2. This observation suggests that IRF1 and IRF2 have a previously unrecognized role as constitutive activators of specific genes. Additionally, data presented indicate that a protein complex containing the nonhistone architectural protein HMG-I(Y) binds to the region identified as the major transcription initiation site for Qp. This observation raises the possibility that HMG-I(Y)-induced DNA bending plays a role in the initiation of transcription from Qp.