G protein-coupled receptors (GPCRs) are the major group of cell-surface receptors that transmit extracellular signals via classical, G protein-dependent pathways into the cell. Although GPCRs were long assumed to signal exclusively from the cell-surface, recent investigations have demonstrated a possibly completely new paradigm. In this new view, GPCR continues signaling via 3´,5´-cyclic adenosine monophosphate (cAMP) after their agonist-induced internalization of ligand/receptor complexes into an intracellular compartment, causing persistent cAMP elevation and apparently specific signaling outcomes. The thyroid stimulating hormone (TSH) receptor is one of the first GPCRs, which has been reported to show persistent signaling after ligand removal (Calebiro et al., 2009). In the meantime, signaling by internalized GPCR become a highly investigated topic and has been shown for several GPCRs, including the parathyroid hormone receptor (Ferrandon et al., 2009), D1 dopamine receptor (Kotowski et al., 2011) and beta2-adrenergic receptor (Irannejad et al., 2013). A recent study on the beta2-adrenergic receptor revealed that internalized receptor not only participates in cAMP signaling, but is also involved in gene transcription (Tsvetanova and von Zastrow, 2014). However, a biological effect of GPCR signaling at intracellular sites, which would demonstrate its physiological relevance, still remained to be shown. To investigate GPCR signaling from intracellular compartment under physiological condition, two different cellular models were utilized in the present study: intact ovarian follicles expressing luteinizing hormone (LH) receptors and primary thyroid cells expressing TSH receptors. Intact ovarian follicles were obtained from a transgenic mouse expressing, a Förster/Fluorescence Resonance Energy Transfer (FRET) sensor for cAMP to monitor cAMP/LH receptor signaling. This study provides the first accurate spatiotemporal characterization of cAMP signaling, which is derived from different cell layers of an intact ovarian follicle. Additionally, it could be shown that cAMP diffusion via gap junctions is implicated in spreading the LH-induced cAMP signals from one the outermost (mural granulosa) to the innermost (cumulus oophorus) cell layer of an ovarian follicle. Interestingly, LH receptor stimulation was associated with persistent cAMP signaling after LH removal and negligible desensitization of the cAMP signal. Interfering with receptor internalization with a dynamin inhibitor dynasore did not only prevent persistent LH-induced cAMP signaling, but also impaired the resumption of meiosis in follicle-enclosed oocytes, a key biological effect of LH. In order to investigate the downstream activation of protein kinase A (PKA) in primary thyroid cells, FRET sensors with different subcellular localization (plasma membrane, cytosol and nucleus) were transiently transfected into primary thyroid cells of wild-type mice via electroporation. Interestingly, TSH stimulation causes at least two distinct phases of PKA activation in the global primary thyroid cell, which are temporally separated by approximately 2 min. In addition, PKA activation in different subcellular compartments are characterized by dissimilar kinetics and amplitudes. Pharmacological inhibition of TSH receptor internalization largely prevented the second (i.e. late) phase of PKA activation as well as the subsequent TSH-dependent phosphorylation of CREB and TSH-dependent induction of early genes. These results suggest that PKA activation and nuclear signaling require internalization of the TSH receptor. Taken together, the data of the present study provide strong evidence that GPCR signaling at intracellular sites is distinct from the one occurring at the cell-surface and is highly physiologically relevant. / G-Protein-gekoppelte Rezeptoren (GPCR) umfassen die größte Gruppe von Rezeptoren in der Zellmembran und übermitteln extrazelluläre Signale via G-Protein-abhängige Signalwege in das Zellinnere. Obwohl lange Zeit die Wissenschaft davon ausging, das GPCR ausschließlich an der Zelloberfläche Signale weiterleiten, zeigen Studien der letzten Jahre eine vollkommen neuartige Signalweiterleitung aus dem Zellinneren. In dieser neuen Sichtweise, vermitteln GPCR nach Agonist-induzierter Internalisierung des Liganden/Rezeptor-Komplexes in das Zellinnere weiterhin zyklische Adenosin-3´,5´-monophosphat (cAMP)-Signale, was zu einer dauerhaften cAMP-Erhöhung und einem spezifischen Ergebnis der Signaltransduktion führt. Einer der ersten GPCR, für den gezeigt wurde, dass Signale aus dem Zelleninneren übertragen werden können, war der Thyreoidea-stimulierendes Hormon (TSH) Rezeptor. In der Zwischenzeit wurde die Signalübertagung von bereits internalisierten Rezeptoren für weitere GPCR gezeigt, inklusive des beta2-adrenergen Rezeptors. Vor kurzem demonstrierte eine Studie des beta2-adrenerge Rezeptors, dass die intrazellulare GPCR-Signalübertragung nicht nur an der cAMP-Weiterleitung sondern auch an der Gentranskription beteiligt ist. Bis jetzt konnte jedoch noch kein Zusammenhang zwischen der GPCR-Signaltransduktion aus dem Zellinneren und einem biologischen Effekt mit physiologischer Relevanz hergestellt werden. Um GPCR-Signaltransduktion im Zellinneren unter physiologischen Bedingungen zu untersuchen, wurden in der aktuellen Arbeit zwei unterschiedliche zelluläre Modelle verwendet: Intakte Follikel eines Ovars, welche luteinisierende Hormon (LH) Rezeptoren exprimieren und TSH-Rezeptoren-exprimierende primäre Schilddrüsenzellen. Die Follikel wurden aus einer transgenen Maus, die einen Förster/Fluoreszenz Resonanz Energie Transfer (FRET) Sensor für cAMP exprimiert, gewonnen, um cAMP/LH-Signaltransduktion zu messen. Diese Arbeit zeigt die erste exakte, zeitliche und räumliche Charakterisierung der LH- induzierten cAMP-Signaltransduktion in intakten Follikeln des Ovars. Des Weiteren konnte gezeigt werden, dass die Diffusion von cAMP via Gap Junctions ein wichtiger Bestandteil bei der Übermittlung des LH-induzierten cAMP-Signals von der äußeren (Mural granulosa) zur inneren (Cumulus oophorus) Zellebene eines Follikels darstellt. Interessanterweise ergab die LH- Rezeptor Stimulation nach Entfernung des Liganden LH ein anhaltendes cAMP-Signal sowie eine unwesentliche Desensitization des cAMP-Signals. Die Inhibition der Rezeptorendozytose mit Dynasore verhinderte nicht nur das LH-induzierte anhaltende cAMP-Signal sondern beeinflusste auch die Wiederaufnahme der Meiose durch die Follikel-eingeschlossene Oozyte, einer der wichtigsten biologischen Aufgaben von LH. Um den Einfluss der TSH-Rezeptorinternalisierung auf die PKA-Aktivität zu untersuchen, wurden primäre Schilddrüsenzellen von FVB-Mäusen, mit FRET-basierenden Protein Kinase A (PKA) Sensor exprimiert werden, via Elektroporation transfiziert. Die Ergebnisse zeigen, dass eine TSH- vermittelte Stimulation des Rezeptors mindestens zwei kinetisch und räumlich unterschiedliche PKA-Signale in Schilddrüsenzellen auslöst, die zeitlich voneinander getrennt sind. Durch die Inhibierung des TSH-Rezeptorinternalisierung konnte gezeigt werden, dass das zweite PKA-Signal sowie die darauffolgende TSH-abhängige Phosphorylierung des Trankriptionsfaktors CREB und die TSH-abhängige Regulierung von Gen Expression vermindert ist. Diese Befunde geben Aufschluss über die Notwendigkeit der Internalisierung des Rezeptors in das Zellinnere für eine effektive PKA- und Zellkern-Signaltransduktion. Zusammenfassend lässt sich sagen, dass die Ergebnisse dieser Arbeit neue, und wichtige Erkenntnisse über den Mechanismus der GPCR-Signalweiterleitung im Zellinneren und erstmals einen Einblick über die biologische Relevanz der Rezeptorinternalisierung liefern.

Nuclear receptors (NR’s) comprise a large, ancient, superfamily of eukaryotic transcription factors that govern a wide range of metabolic, homeostatic, and developmental pathways, and which have been implicated in disease states including cancer, inflammation, and diabetes. The ability of NRs to activate or repress gene transcription is modulated through direct binding of small lipophilic ligands which induce conformational changes in their cognate receptor. These changes are structural in nature and lead to the recruitment of coactivator or corepressor complexes, ultimately regulating the expression of target genes to whose response elements NRs are bound. In Drosophila 18 NRs have been identified which have representative members belonging to each of the six major NR subfamilies, and which show a high degree of homology to their vertebrate counterparts. This fact, in addition to the power and ease of genetic manipulation, make Drosophila an excellent model system in which to study NR function. When I began my project, 17 of the 18 NRs in Drosophila were ‘orphan’ receptors for which no cognate ligand had been identified. As a first step in an effort to identify potential ligands for these 17 receptors I first set out to determine how, where and when nuclear receptors are regulated by small chemical ligands and/or their protein partners. In order to do so I contributed to developing a ‘ligand sensor’ system to visualize spatial activity patterns for each of the 18 Drosophila nuclear receptors in live, developing animals. This system is based upon transgenic lines that express the ligand binding domain of each Drosophila NR fused to the DNA-binding domain of yeast GAL4. When combined with a GAL4-responsive reporter gene, these fusion proteins show tissue- and stage-specific patterns of activation. Analysis using this system has revealed the stage and tissue specificity of NR activation for each of the fly NRs. The amnioserosa, yolk, midgut and fat body, which play major roles in lipid storage, metabolism and developmental timing, were identified as frequent sites of nuclear receptor activity. Dynamic changes in activation that are indicative of sweeping changes in ligand and/or co-factor production are also a prominent feature that has been revealed using this approach. In addition, I went on to characterize the ligand regulated function of a single Drosophila nuclear receptor, Ecdysone inducible protein 75 (E75). Previous work from our lab has demonstrated that E75 binds to heme, and that its function as a transcriptional repressor is regulated in vitro by binding of the small diatomic gases nitric oxide (NO) and carbon monoxide (CO) to its heme moiety. In an effort to validate and to further understand the in vivo relevance of E75 regulation by NO I used gain and loss of function transgenes, as well as tissues manipulated in culture to show that NO acts directly on the Drosophila nuclear receptor E75, reversing its ability to block the activity of its heterodimer partner Drosophila Hormone Receptor 3 (DHR3). By specifically focusing on the Drosophila larval ring gland, the principal endocrine organ responsible for the production of the metamorphosis-inducing hormone, ecdysone, I have shown that failure to produce NO and to inactivate E75 results in failure to recognize the signals that normally trigger metamorphosis.

Nuclear receptors (NR’s) comprise a large, ancient, superfamily of eukaryotic transcription factors that govern a wide range of metabolic, homeostatic, and developmental pathways, and which have been implicated in disease states including cancer, inflammation, and diabetes. The ability of NRs to activate or repress gene transcription is modulated through direct binding of small lipophilic ligands which induce conformational changes in their cognate receptor. These changes are structural in nature and lead to the recruitment of coactivator or corepressor complexes, ultimately regulating the expression of target genes to whose response elements NRs are bound. In Drosophila 18 NRs have been identified which have representative members belonging to each of the six major NR subfamilies, and which show a high degree of homology to their vertebrate counterparts. This fact, in addition to the power and ease of genetic manipulation, make Drosophila an excellent model system in which to study NR function. When I began my project, 17 of the 18 NRs in Drosophila were ‘orphan’ receptors for which no cognate ligand had been identified. As a first step in an effort to identify potential ligands for these 17 receptors I first set out to determine how, where and when nuclear receptors are regulated by small chemical ligands and/or their protein partners. In order to do so I contributed to developing a ‘ligand sensor’ system to visualize spatial activity patterns for each of the 18 Drosophila nuclear receptors in live, developing animals. This system is based upon transgenic lines that express the ligand binding domain of each Drosophila NR fused to the DNA-binding domain of yeast GAL4. When combined with a GAL4-responsive reporter gene, these fusion proteins show tissue- and stage-specific patterns of activation. Analysis using this system has revealed the stage and tissue specificity of NR activation for each of the fly NRs. The amnioserosa, yolk, midgut and fat body, which play major roles in lipid storage, metabolism and developmental timing, were identified as frequent sites of nuclear receptor activity. Dynamic changes in activation that are indicative of sweeping changes in ligand and/or co-factor production are also a prominent feature that has been revealed using this approach. In addition, I went on to characterize the ligand regulated function of a single Drosophila nuclear receptor, Ecdysone inducible protein 75 (E75). Previous work from our lab has demonstrated that E75 binds to heme, and that its function as a transcriptional repressor is regulated in vitro by binding of the small diatomic gases nitric oxide (NO) and carbon monoxide (CO) to its heme moiety. In an effort to validate and to further understand the in vivo relevance of E75 regulation by NO I used gain and loss of function transgenes, as well as tissues manipulated in culture to show that NO acts directly on the Drosophila nuclear receptor E75, reversing its ability to block the activity of its heterodimer partner Drosophila Hormone Receptor 3 (DHR3). By specifically focusing on the Drosophila larval ring gland, the principal endocrine organ responsible for the production of the metamorphosis-inducing hormone, ecdysone, I have shown that failure to produce NO and to inactivate E75 results in failure to recognize the signals that normally trigger metamorphosis.

<p><p>LAT is a transmembrane adaptor protein that is critical for the emanation of signals downstream of the TCR. Following TCR engagement, LAT is phosphorylated on multiple tyrosine residues, allowing it to serve as a scaffold for a multi-protein signaling complex. Mutation of tyrosine 136 on LAT abrogates binding of PLC-&#947;1. The disruption of this interaction has severe consequences on TCR-mediated calcium signaling and MAPK activation. Mice harboring a mutation at this tyrosine, LATY136F (LAT<super>m/m</super>) mice, have drastically impaired thymocyte development; however, CD4<super>+</super> T cells in the periphery rapidly expand and instigate a fatal lymphoproliferative syndrome. In order to bypass the severe developmental defects exhibited in LAT<super>m/m</super> mice, our laboratory previously developed a conditional knock-in mouse line in which the mutated LAT allele is expressed in mature T cells following deletion of a floxed wildtype LAT allele (ERCre<super>+</super>LAT<super>f/m</super> mice). LAT<super>f/m</super> mice develop a similar lymphoproliferative syndrome as LAT<super>m/m</super> mice. We used both of these mouse models to analyze the contribution of two other proteins that are essential for TCR-mediated signaling, RasGRP1 and Gads, in LAT-mediated autoimmunity. </p><p><p>Analysis of LAT<super>m/m</super>RasGRP1<super>-/-</super> mice demonstrated that the additional deletion of RasGRP1 increased the thymocyte development block and, as a result, young mice contained markedly reduced T cell populations. However, by four months of age, a lymphoproliferative disease had developed in these mice. To bypass the severe developmental block, we analyzed LAT<super>f/m</super>RasGRP1<super>-/-</super> mice and observed that they developed disease similarly to LAT<super>f/m</super> mice. We also assessed the effect of Gads deletion in both mouse models of LAT disease. LAT<super>m/m</super>Gads<super>-/-</super> mice had an even more dramatic block in the DN stage of thymocyte development compared to LAT<super>m/m</super> controls, although by four months of age CD4<super>+</super> T cells had expanded. Following deletion of the wildtype LAT allele, LAT<super>f/m</super>Gads<super>-/-</super> mice also developed disease. Our results indicated that LAT-mediated autoimmunity can occur independently of the critical T cell signaling components RasGRP1 and Gads. </p><p><p>In addition, we more closely examined RasGRP1-mediated Erk activation in T cells. RasGRP1 is a Ras-guanyl nucleotide exchange factor that is required for positive selection of thymocytes, activation of T cells, and control of T cell mediated-autoimmunity. While the importance of various RasGRP1 structural domains has previously been explored, RasGRP1 also contains a tail domain of unknown function. To elucidate the physiological role of this domain, we generated knock-in mice expressing RasGRP1 without the tail domain, RasGRP1<super>d/d</super> mice. Analysis of these mice demonstrated that deletion of the tail domain led to impaired T cell development but, with age, CD4<super>+</super> T cells expanded and auto-antibodies were produced. RasGRP1<super>d/d</super> thymocytes were unable to activate Erk and underwent aberrant thymic selection processes. Mechanistically, the tail-deleted form of RasGRP1 was not able to traffic to the cell membrane following stimulation, indicating a potential reason for its inability to activate Erk. While the DAG-binding C1 domain of RasGRP1 has long been recognized as an important factor mediating Erk activation, our data revealed the physiological relevance of the tail domain of RasGRP1 in the control of Erk signaling.</p> / Dissertation

The PIM family kinases promote growth and survival of tumor cells and are expressed in a wide variety of human cancers. Their potential as therapeutic targets, however, is complicated by overlapping activities with multiple other pathways and remains poorly defined in most clinical scenarios. Here we explore activity of the new pan-PIM inhibitor PIM447 in a variety of lymphoid-derived tumors. We find strong activity in cell lines derived from the activated B-cell subtype of diffuse large B-cell lymphoma (ABC-DLBCL). Sensitive lines show lost activation of the mTORC1 signaling complex and subsequent lost activation of cap-dependent protein translation. In addition, we characterize recurrent PIM1 protein-coding mutations found in DLBCL clinical samples and find most preserve the wild-type protein's ability to protect cells from apoptosis but do not bypass activity of PIM447. Pan-PIM inhibition therefore may have an important role to play in the therapy of selected ABC-DLBCL cases.

Glycodelin is a 162 amino acid secreted glycoprotein classified as a member of the lipocalin (carriers of small hydrophobic molecules) superfamily based on the presence of lipocalin signature motifs in its primary sequence. The protein has several isoforms which are expressed by various primate tissues, predominantly reproductive tissues. These isoforms are products of the same gene and hence have the same primary sequence; however, they are differentially glycosylated depending on tissue origin. The individual glycodelin isoforms perform very varied functions, which are largely dictated or modulated by the specific glycans on the molecule. Glycodelin A (GdA) is the major glycodelin isoform of the female reproductive tract; and is subclassified as an immunocalin (lipocalins with immunological function) due to its ability to modulate immune responses. Diverse activities have been associated with GdA; pertaining to determination of cell fate, tissue differentiation and significantly, immunomodulation towards fetal-allograft tolerance. The fetus expresses paternal allo-antigens and would be regarded as non-self or foreign by the maternal immune system. However, several synergistic mechanisms of immunomodulation at the fetal-maternal interface establish tolerance towards fetal antigens, protecting it from rejection. GdA is secreted by the uterine endometrium under progesterone induction, and is therefore the most abundant progesterone-regulated secretory glycoprotein of the uterus at the time of implantation and early pregnancy. GdA has been shown to have immunomodulatory activity targeting innate, humoral and cellular responses. It is inhibitory to T cell and B cell proliferation, and NK cell activity. It stimulates the Th2-type cytokine profile, and inhibits interleukins IL-2 and IL-1 production from mitogenically stimulated lymphocytes and mononuclear cell cultures. It has been reported from our laboratory that GdA induces apoptosis in activated T cells. GdA has also been shown to be inhibitory to B cells and monocytes. Clinical studies correlate subnormal levels of GdA with implantation Synopsis failure, habitual abortion and recurrent miscarriage. Due to its pleiotropic nature namely its diverse activities on different immune cell types; its spatio-temporal restriction of expression by progesterone; and its indispensable requirement for successful pregnancy; GdA is being increasingly recognized as a mechanism towards fetal allograft tolerance. Our laboratory has focused on the T cell inhibitory activity of GdA, with particular emphasis on T cell apoptosis. This study was aimed at delineating the molecular mechanism of GdA-induced apoptosis in activated T cells. Previous results from our laboratory have revealed that GdA-induced apoptosis is caspase dependent; and is not initiated by the extrinsic pathway involving Fas/death receptor signailing or initiator caspase 8. In this thesis, we present evidence that GdA triggers the intrinsic apoptotic program in T cells. Characterization of the apoptotic program initiated by GdA is presented in Chapter 1. We observe that GdA treatment triggers a stress response leading to decrease in mitochondrial transmembrane potential, which indicates mitochondrial membrane permeabilization (MMP). GdA-induced apoptosis can also be blocked by inhibition of caspase 9, the initiator caspase for the intrinsic program. The kinetics of mitochondrial depolarization precede onset of DNA fragmentation in both peripheral blood T cells and Jurkat cells treated with GdA. We also observe caspase 2 activation downstream of the mitochondria. Overexpression of the antiapoptotic protein Bcl-2 is sufficient to protect from GdA-induced cellular stress indicating that the apoptotic program can be reversed upstream of the mitochondria. Further, our studies reveal that stress signaling by GdA is not mediated by any of the canonical second messengers of stress signaling, namely, reactive oxygen species; the stress activated protein kinases JNK, p38 MAPK and ERK; intracellular calcium or ceramide. It has been reported that GdA desensitizes T cell receptor (TCR) signaling by decreasing the stability of TCR-triggered phosphoproteins, probably by its association ith the transmembrane tyrosine phosphatase CD45. TCR-desensitization would result in decreased proliferation and cytokine secretion, and has been postulated as the mechanism of T cell-inhibition by GdA. We have tested this theory and Chapter 2 provides evidence that the apoptogenic activity of GdA is not a consequence of its ability to blunt TCR-signaling. Further, GdA-induced apoptosis does not depend on components of the TCR signal cascade namely CD45, the kinase Lck and CTLA4, molecules that are proven transducers of apoptotic signals to the mitochondria in response to diverse stress stimuli. GdA triggers apoptosis in the CD45 deficient cell line J45.01 with similar kinetics of MMP and DNA fragmentation as with Synopsis wildtype cells, demonstrating that CD45 is not the determinant receptor for apoptosis on cells. We also observe that GdA is inhibitory to T cells stimulated with phorbol ester and calcium ionophore, which bypasses TCR-proximal signaling events; and that GdA treatment does not interfere with early T cell activation as evidenced from induction of the activation marker CD69. Thus, GdA initiates mitochondrial stress mediated apoptosis in T cells by a pathway that is distinct and independent from the TCR-coupled signaling pathway. This study presents a novel mode of immunosuppression for GdA and highlights the ability of GdA to suppress the immune response by more than one mechanism. Cell surface glycoproteins undergo alterations in their carbohydrate profiles upon T cell activation and differentiation, and this has a significant role to play in lymphocyte fate and function. One such global alteration in cell surface glycans is a difference in sialylation upon T cell activation and differentiation. While activated T cell have a lesser degree of sialylated surface glycoproteins as compared to naïve T cells, memory T cells are sialylated to a higher extent, and Th2 cells have more cell surface sialic acids than Th1 cells. As GdA is capable of triggering apoptosis in activated T cells, we investigated the requirement of cell surface glycans for differential recognition of T cell subsets by GdA, the results for which are detailed in Chapter 3. We observe that the activity of GdA could be competed out by asialofetuin and not fetuin, suggesting that GdA recognizes terminal galactose residues on asialofetuin glycans, which would be masked by sialic acids in case of fetuin glycans. This assumption was confirmed as the free sugars lactose and galactose, but not annose, could also competitively inhibit GdA activity. We also demonstrate that the lectin-activity of dA is calcium independent, typical of mammalian galectins. Thus, our results reveal GdA to be a novel galactose-specific lectin of the female reproductive tract. This carbohydrate specificity of GdA is responsible for its apoptotic activity on T cells. The selectivity of GdA towards activated T cells is a result of increased exposure of terminal galactose residues on activated T cell surface receptors, as demonstrated by staining of naïve and stimulated T cells with Fluorescent lectin-conjugates of different carbohydrate specificities. We also demonstrate hat GdA shows specificity towards N-liked glycans on cell surface glycoproteins. This is evident from the use of glycan processing inhibitors, which prevent addition of galactose to the core glycan on the nascent polypeptide chain. We observe that inhibition of processing of N-glycans, and not O-glycans, render cells resistant to GdA. Incidentally, we observe that another property of GdA, namely its ability to induce Synopsis epithelial differentiation and apoptosis in the breast cancer cell line MCF-7, is also due to ts galactose-specific lectin activity. It is therefore probable that the diverse functions ssociated with GdA are a consequence of its ability to recognize different glycoprotein receptors on different cell types. We can thus draw a comparison for GdA with the galectins, which are the prototype beta-galactoside binding mammalian lectins with diverse roles in determining cell fate and apoptosis, especially in the immune system. In fact, the immune-related activities of GdA are almost identical to the effects of galectin-1 on the immune system. Galectin-1 has also very recently been shown to play a significant role in fetal-tolerance. This raises a strong possibility of shared receptors for GdA and galectin-1 on the T cell surface, resulting from a shared calcium-independent recognition property for complex glycans with terminal galactose residues. Two predominant galectin-1 receptors on T cells are the glycoproteins CD45 and CD7. We have already observed that though GdA may recognize CD45, this association does not mediate its apoptotic activity. We therefore examined the possibility of the activation-induced glycoprotein CD7 as receptor for GdA. Our experiments reveal that the apoptotic activity of GdA on different T cell lines is dependent on the degree of CD7 expression by these cell lines. Notably, the CD7 negative lymphoma cell line HuT78 was completely resistant to GdA. To confirm CD7 as receptor, we obtained a cell line HuT78.7 in which CD7 expression has been restored by stable transfection. We observed that these CD7 positive cells now responded to GdA comparable to Jurkat cells, and GdA-induced apoptosis in these cells could be completely competed out with asialofetuin, not fetuin. To summarize, our study identifies GdA as a novel pregnancy-related galectin-like lectin of the female reproductive tract, which triggers mitochondrial stress and apoptosis in activated T cells. GdA shares receptors on T cells with galectin-1 due a common carbohydrate recognition property. We identify CD7 as a molecular target for GdA on activated T cells, capable of mediating the apoptotic signal. However, it is likely that GdA also recognizes other galectin receptors on T cells, as it is capable of inhibition by more than one mechanism. This underscores the requirement for redundant mechanisms indispensable for establishment and maintenance of successful pregnancy.

Thesis (Ph. D.)--Cornell University, August, 2007. / Vita. Includes bibliographical references (leaves 196-214).

Adenosine is a ubiquitous metabolite with multiple physiological functions in organisms. In this thesis, I studied the effect of extracellular adenosine on Huntington´s disease (HD) model Drosophila melanogaster. I show that extracellular Adenosine signaling mitigates HD pathology by observing three main types of symptoms of the disease in Drosophila. The results suggest that the mechanism involves Drosophila melanogaster adenosine receptor signaling.

The strength of peptide:MHC interactions with the T cell receptor (TCR) is correlated with the time to first cell division, the relative scale of the effector cell response, and the graded expression of activation-induced proteins. The TCR proximal tyrosine kinase ITK simultaneously influences many biochemically separate signaling cascades. T cells lacking ITK exhibit selective impairments in effector T cell responses after activation, but under the strongest signaling conditions ITK activity is dispensable. To gain insight into whether TCR signal strength and ITK activity tune observed graded gene expression through unequal activation of disparate signaling pathways, I examined NFAT, NF-κB and MAP kinase pathways during early activation of individual naïve OT-I CD8+ T cells using peptide-loaded antigen presenting cells. Utilizing both measurement of transcription factor translocation in single T cell nuclei and conventional phospho-flow cytometry, I observed digital activation of Erk-MAPK and NFAT1 at all peptide doses and avidities. However, NF-κB activation showed a graded response to variation in TCR signal strength and was more sensitive to treatment with an ITK inhibitor. Inhibitor-treated cells showed poor induction of AP-1 factors Fos and Fosb, NF-κB response gene transcripts, and survival factor Il2 transcripts. ATAC-seq analysis revealed genomic regions most sensitive to ITK inhibition are enriched for NF-κB and AP-1 motifs. Together, these data indicate a key role for ITK in orchestrating optimal activation of separate TCR downstream pathways, specifically aiding NF-κB activation. More broadly, I describe a mechanism by which variation in TCR signal strength can produce patterns of graded gene expression in activated T cells.

The T cell receptor (TCR) activation induced signaling cascade is a major driver of T cell effector responses such as cytokine production and actin cytoskeletal rearrangement. Characterizing chemical modulators of this pathway has the benefits of both revealing basic science knowledge about these signaling processes and providing foundation for development of novel therapeutics. Glycerol Monolaurate (GML) is a naturally occurring fatty acid monoester that is found as a monoglyceride in human breast milk and coconut oil. It is widely utilized in food, cosmetics, and homeopathic supplements. GML is a potent antimicrobial agent that targets a wide range of bacteria, fungi, and enveloped viruses. Because of this, GML has been developed as a preventative for menstrual associated Toxic Shock Syndrome, and is being tested to prevent HIV transmission and superficial skin infections. Interestingly, GML suppresses mitogen induced lymphocyte proliferation and inositol triphosphate production, suggesting that GML has immunomodulatory functions. This thesis mechanistically examined how GML affects human primary T cells. Chapter III describes how GML potently altered order and disorder dynamics in the plasma membrane that resulted in reduced membrane-localized clustering of the proteins LAT, PLC-γ, and AKT, events integral for proper TCR signal propagation. Altered membrane signaling events induced selective inhibition of TCR-induced signaling events. Specifically GML reduced the phosphorylation of the regulatory P85 subunit of PI3K, and AKT and abrogated calcium influx. Functionally, GML treatment potently reduced TCR-induced production of the cytokines IL-2, IFN-γ, TNF-α, and IL-10. Chapter V shows that GML causes the mis-localization of the ARPC3 subunit of the Arp2/3 complex that leads to the formation of abnormal filopodia structures, and reduced cellular adhesion. Chapter V shows that human serum albumin binds directly to GML on the 12 carbon acyl chain. This interaction reverses GML induced suppression of TCR-induced formation of LAT, PLC-γ1, and AKT microclusters at the plasma membrane, AKT phosphorylation, and cytokine production. These findings establish GML as a T cell suppressive agent in addition to an antimicrobial agent. This observation reveals the potential role of naturally occurring GML in human breast milk in the formation of microbiota and immune tolerance in the infant gastrointestinal tract. It also allows for optimization of the current applications of GML in various commercial products and therapeutic strategies. Finally this information provides the rationale to investigate GML in new remedial avenues as a topical agent to treat excessive inflammation in the skin, and vaginal and gut mucosal regions.