Adaptive immunity requires T cell responses to foreign pathogens to be counterbalanced with the need to limit collateral destruction of the host’s own tissues. Further, the presence of a substantial pool of lymphocytes capable of recognizing selfantigen in the periphery poses a threat to the maintenance of peripheral tolerance and prevention of autoimmunity. Regulatory T cells (Treg) that can suppress potentially self-reactive T cells are critical regulators of peripheral tolerance as well as initiation of immune responses. Treg cells employ several context-dependent mechanisms to establish regulation. In this thesis, we describe two distinct pathways of regulation used by Treg cells involving negative costimulation by CTLA-4 and immunomodulation by the morphogen, TGFβ. CTLA-4 is a co-inhibitory receptor on T cells essential for maintaining T cell homeostasis and tolerance to self. CTLA-4 expression is induced in conventional T cells following activation, whereas it is constitutively expressed in regulatory FOXP3+CD4+ regulatory T cells. Mice lacking CTLA-4 develop an early onset, fatal breakdown in T cell tolerance. Whether this autoimmune disease occurs because of the loss of CTLA-4 function in regulatory T cells, conventional T cells, or both, is not known. We present evidence here that in addition to a critical CTLA-4 function in regulatory T cells, CTLA-4 in conventional T cells is also necessary for controlling the consequences of abnormal T cell activation. CTLA-4 expression in activated conventional T cells only in vivois unable to compensate for the impaired function of CTLA-4-less regulatory T cells that results in systemic lymphoproliferation, but it can prevent the aberrantly activated T cells from infiltrating and fatally damaging non-lymphoid tissues. These results demonstrate that CTLA-4 has a dual function in maintaining T cell homeostasis: CTLA-4 in regulatory T cells inhibits inappropriate naïve T cell activation and CTLA-4 in conventional T cells can prevent the harmful accumulation of inappropriately activated pathogenic T cells in vital organs. In addition, we have identified Disabled-2 (Dab2), a TGFβ signaling intermediate, as a FOXP3 target gene that is expressed exclusively in Treg cells and is critical for in vitro and in vivo regulation by Treg cells. During T cell development, DAB2 is also expressed in a Foxp3-independent manner in thymic precursor cells, and acts as a sensor of TGFβ signals that is required for programming normal TGFβ responsiveness in T cell progenies. Naïve CD4+ T cells that differentiate from Dab2-deficient precursors favor Th17 cell generation at the expense of FOXP3+ Treg cells as a result of altered sensitivity to TGFβ. Importantly, retinoic acid can restore TGFβ signaling capacity of naïve CD4+ T cells generated from Dab2-deficient precursors, emphasizing the cooperative nature of retinoic acid and TGFβ signaling pathways in promoting Treg cell development and maintenance.

No description available.

No description available.

Hao, Yan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 98-115). / Abstracts in English and Chinese. / Acknowledgement --- p.i / Abstract --- p.iii / 摘要 --- p.v / List of Abbreviations --- p.vii / List of Figures --- p.x / List of Tables --- p.xi / List of Primers --- p.xii / Publications arising from this study --- p.xiii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Alzheimer's disease --- p.1 / Chapter 1.2 --- APP and its functions --- p.4 / Chapter 1.2.1 --- APP processing --- p.7 / Chapter 1.3 --- APPc-interacting proteins --- p.10 / Chapter 1.3.1 --- FE65 --- p.10 / Chapter 1.3.2 --- Xllα and Xl1β --- p.12 / Chapter 1.3.3 --- JIP-1 --- p.13 / Chapter 1.3.4 --- Dabl and Dab2 --- p.15 / Chapter 1.3.5 --- SNX17 --- p.15 / Chapter 1.3.6 --- Numb --- p.15 / Chapter 1.3.7 --- AIDA-1 --- p.16 / Chapter 1.4 --- Objectives of the project --- p.18 / Chapter 1.4.1 --- Engulfment adaptor protein 1 (GULP1) --- p.19 / Chapter 1.4.2 --- Specific aims of my study --- p.20 / Chapter Chapter 2 --- General Methodology --- p.22 / Chapter 2.1 --- Bacterial culture --- p.22 / Chapter 2.2 --- Mini-preparation/Midi-preparation of plasmid DNA --- p.22 / Chapter 2.3 --- Spectrophotometric analysis of DNA --- p.22 / Chapter 2.4 --- Agarose gel electrophoresis for DNA --- p.23 / Chapter 2.5 --- Preparation of competent E. coli --- p.23 / Chapter 2.6 --- Transformation of competent E. coli --- p.24 / Chapter 2.7 --- Molecular cloning --- p.24 / Chapter 2.7.1 --- Preparation of the cloning vector and insert --- p.25 / Chapter 2.7.2 --- Isolation of DNA from agarose gel --- p.25 / Chapter 2.7.3 --- DNA ligation and transformation --- p.25 / Chapter 2.7.4 --- Rapid screening for ligated plasmid --- p.26 / Chapter 2.8 --- Site-directed mutagenesis --- p.26 / Chapter 2.9 --- Cell culture and transfection --- p.27 / Chapter 2.10 --- Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS/PAGE) --- p.28 / Chapter 2.11 --- Western blotting --- p.29 / Chapter Chapter 3 --- Investigation of the GULP1-APP interaction and the effect of GULP1 on APP processing --- p.31 / Chapter 3.1 --- Introduction --- p.31 / Chapter 3.2 --- Materials and methods --- p.34 / Chapter 3.2.1 --- DNA constructs --- p.34 / Chapter 3.2.2 --- Antibodies --- p.34 / Chapter 3.2.3 --- GST pull-down assays --- p.35 / Chapter 3.2.4 --- Rat tissues preparation --- p.36 / Chapter 3.2.5 --- Immunostaining --- p.36 / Chapter 3.2.6 --- "siRNA knockdown of GULPl in CHO, HEK293 and SHSY5Y cells" --- p.37 / Chapter 3.2.7 --- Luciferase assays --- p.37 / Chapter 3.2.9 --- Tricine-SDS/PAGE analysis for APP CTFs --- p.38 / Chapter 3.2.9 --- Aβ enzyme-linked immunosorbent assay (ELISA) --- p.39 / Chapter 3.2.10 --- Statistical analysis --- p.40 / Chapter 3.3 --- Results --- p.40 / Chapter 3.3.1 --- GULP1 F145V mutant abandons the GULP1-APP interaction --- p.40 / Chapter 3.3.2 --- GULP1 and APP colocalize in neurons --- p.45 / Chapter 3.3.3 --- "siRNA mediated knockdown of GULPl in CHO, HEK293 and SHSY5Y cells" --- p.48 / Chapter 3.3.4 --- GULP1 enhances the cleavage of APP in APP-GAL4 cleavage system --- p.49 / Chapter 3.3.5 --- GULP1 alters APP processing by increasing the secretion of APP CTFs --- p.52 / Chapter 3.3.6 --- GULP1 stimulates Aβ secretion --- p.55 / Chapter 3.4 --- Discussion --- p.57 / Chapter Chapter 4 --- Identification and characterization of GULPl phosphorylation sites --- p.60 / Chapter 4.1 --- Introduction --- p.60 / Chapter 4.2 --- Materials and Methods --- p.60 / Chapter 4.2.1 --- DNA constructs --- p.61 / Chapter 4.2.2 --- Antibodies --- p.61 / Chapter 4.2.3 --- Expression and purification of GST fusion proteins --- p.61 / Chapter 4.2.4 --- In vitro phosphorylation of GULP1 by cdk5/p35 --- p.62 / Chapter 4.3 --- Results --- p.62 / Chapter 4.3.1 --- GULP1 Ser223 can be phosphorylated by cdk5/p35 in vivo --- p.62 / Chapter 4.3.2 --- The phosphorylation ofGULPl Thr35 completely abolished the GULP1-APP interaction --- p.67 / Chapter 4.4 --- Discussion --- p.70 / Chapter Chapter 5 --- Crystallization of the PTB domains of GULPl and GULP1t35d…… --- p.72 / Chapter 5.1 --- Introduction --- p.72 / Chapter 5.2 --- Materials and Methods --- p.72 / Chapter 5.2.1 --- DNA constructs --- p.72 / Chapter 5.2.2 --- Small-scale protein expression and purification --- p.73 / Chapter 5.2.3 --- Large-scale protein expression and purification --- p.73 / Chapter 5.2.4 --- Dynamic light scattering measurement --- p.76 / Chapter 5.2.5 --- Crystallization screening GULP1-PTB --- p.76 / Chapter 5.2.6 --- Optimization of GULP1-PTB crystals by grid screen --- p.76 / Chapter 5.2.7 --- Optimization of GULPl -PTB crystals by additive screen and detergent screen --- p.79 / Chapter 5.3 --- Results --- p.79 / Chapter 5.3.1 --- Large-scale expression and purification of GULP 1-PTB --- p.79 / Chapter 5.3.2 --- Small-scale expression and purification of GULP1T35d-PTB --- p.86 / Chapter 5.3.3 --- Crystallization screening and optimization --- p.88 / Chapter 5.4 --- Discussion --- p.91 / Chapter Chapter 6 --- Conclusion and future perspective --- p.94 / Chapter 6.1 --- Conclusion --- p.94 / Chapter 6.2 --- Future perspective --- p.95 / References --- p.98

Thesis (Ph.D. in Pharmacology) -- University of Colorado Denver, 2008. / Typescript. Includes bibliographical references (leaves 117-147). Free to UCD Anschutz Medical Campus. Online version available via ProQuest Digital Dissertations;

Over the last decade, the innate immune system has been the subject of extensive research. Often overlooked by the robustness and specificity of the adaptive immune system, the innate immune system is proving to be just as complex. The identification of several families of pattern recognition receptors (PRRs) has revealed an ancient yet multifaceted system of proteins that are responsible for initiating host defense. A wide array of pathogens, from virus to bacteria, is detected using this assortment of receptors. One such family, the Toll-like receptors (TLRs), has been at the forefront of this research. To date, 10 TLRs have been described in the human genome. Activation of TLRs leads to the induction of immune-related genes that ultimately control the response of the host. However, the signaling pathways emanating from activated TLRs and other PRRs are not fully understood. In particular, the pathway leading to the activation of interferon regulatory factor 3 (IRF3), a transcription factor crucial for the induction of type I interferon, remains undefined. IRF3 activation occurs as the consequence of viral infection and through the activation of TLRs 3 and 4 by dsRNA and lipopolysaccharide (LPS), respectively. The focus of this research is to describe components of the IRF3 activation pathway, partly through the analysis of TLR signal transduction. IRF3 normally resides in the cytoplasm of cells. Upon infection with certain viruses and bacteria, IRF3 is activated though phosphorylation at its C-terminus. Phosphorylated IRF3 homodimerizes and associates with co-activators CBP-p300. After translocating to the nucleus, the activate IRF3 complex induces the activation of type 1 interferon and interferon related genes. Little is known about the pathways that lead to the activation of IRF3, especially the kinases involved. In this study we report that the non-canonical IкB kinase homologues, IкB kinase epsilon (IKKε) and TANK-binding kinase-1 (TBK1), which were previously implicated in NF-кB activation, are also essential components of the IRF3 signaling pathway. In particular, mouse embryonic fibroblasts from TBK1 deficient mice fail to activate IRF3 in response to both viral infection and stimulation with LPS or poly (IC), a dsRNA analog. Thus, both IKKε and TBK1 play a critical role in innate immunity and host defense. In addition to viral infection, IRF3 activation also occurs via the activation of TLR3 and 4. TLRs signal through a subfamily of Toll-IL-1-Resistance (TIR) domain containing adapter molecules. One such adapter, MyD88, is crucial for all TLRs, with the exception of TLR3. MyD88 participates in a signal transduction pathway culminating in the activation of the transcription factor NF-кB. Studies from MyD88-deficient mice reveal that both TLR3 and 4 still are capable of activating NF-кB, although with slightly delayed kinetics. Another aspect of the MyD88-independent signal transduction pathway is the activation of IRF3. A second TIR domain containing adapter molecule called Mal/Tirap was discovered and originally thought to mediate the MyD88-independent pathway. However, Mal-deficient mice were found to be defective in both TLR2 and 4 mediated NF-кB activation. We hypothesized that other TIR domain containing adapters could mediate this MyD88-independent pathway of TLR3 and 4 leading to the activation of IRF3. Two additional TIR adapters were discovered, TRIF and TRAM. TRIF was shown to mediate TLR3 signal transduction. In this study, we report that both TRIF and TRAM mediate the activation of the MyD88-independent pathway in response to LPS/TLR4 activation. Unlike any of the other known TIR domain containing adapters, TRAM appears to be restricted to the LPS/TLR4 activation pathway while TRIF plays a role in both TLR3 and TLR4 pathways leading to IRF3 target gene expression. Our studies revealed that TRAM could be acting upstream of TRIF in the LPS/TLR4 pathway. To this end, we sought to determine the localization of TRAM within the cell. We found that TRAM localizes to the plasma membrane. TRAM localization is the result of myristoylation since mutation of the predicted myristoylation site (G2A) resulted in the re-distribution of TRAM from the membrane into the cytoplasm. Reconstitution of TRAM-deficient macrophages with TRAM G2A is unable to rescue LPS/TLR4 signal transduction. Thus, myristoylation and membrane association of TRAM are critical for LPS/TLR4 signal transduction. The data generated in this dissertation extends our understanding of the signaling pathways of the innate immune system. Indeed, the molecules and pathways described herein could prove to be beneficial targets for ameliorating symptoms of disease, both autoimmune and pathogen-associated. Finally, the research described here will spur further insight into the complex signaling pathways of a once ignored arm of the immune system.

Crucial to a cell’s ability to migrate is the organization of its plasma membrane and associated proteins in a polarized manner to interact with and respond to its surrounding environment. Cells interact with the extracellular matrix (ECM) through specialized contact sites, including podosomes and invadopodia. Tumor cells use F-actin-rich invadopodia to degrade ECM and invade tissues; related structures, termed podosomes, are sites of dynamic ECM interaction and degradation. We show here that supervillin (SV), a peripheral membrane protein that binds F-actin and myosin II,reorganizes the actin cytoskeleton and potentiates invadopodial function. Overexpressed SV increases the number of F-actin punctae, which are highly dynamic and co-localize with markers of podosomes and invadopodia. Endogenous SV localizes to the cores of Src-generated podosomes in COS-7 cells and with invadopodia in MDA-MB-231 cells. EGFP-SV overexpression increases the average amount of matrix degradation; RNAi-mediated downregulation of SV decreases degradation. Cortactin, an essential component of both podosomes and invadopodia, binds SV sequences in vitro and contributes to the formation of EGFP-SV induced punctae. Additionally, SV affects cortactin localization,which could provide a mechanism for SV action at invadopodia. The formation of cholesterol-rich membrane rafts is one method of plasma membrane organization. A property of membrane rafts is resistance to extraction with cold Triton X-100 and subsequent flotation to low buoyant densities. The actin cytoskeleton has been implicated in many signaling events localized to membrane rafts, but interactions between actin and raft components are not well characterized. Our laboratory isolated a heavy detergent resistant membrane fraction from neutrophils, called DRM-H, that contains at least 23 plasma membrane proteins. DRM-H is rich in cytoskeletal proteins, including fodrin, actin, myosin II, as well as supervillin. DRM-H also contains proteins implicated in both raft organization and membrane-mediated signaling. DRM-H complexes exhibit a higher buoyant density than do most DRMs (referred to as DRM-L), which are deficient in cytoskeletal proteins. By using similar purification methods, I find that COS-7 cells also contain cytoskeleton-associated DRMs. In addition, when transfected into COS-7 cells, estrogen receptor (ER)α associates with DRM-H, while ERβ is seen in both DRM-L and DRM-H populations, suggesting a role for DRM-H in nongenomic estrogen signaling. Thus, the cytoskeleton-associated DRM-H not limited to hematopoietic cells and could constitute a scaffold for membrane raftcytoskeleton signaling events in many cells. Taken together, our results show that SV is a component of cytoskeleton-associated membrane rafts as well as podosomes and invadopodia, and that SV plays a role in invadopodial function. SV, with its connections to both membrane rafts and the cytoskeleton, is well situated to mediate cortactin localization, activation state, and/or dynamics of matrix metalloproteases at the ventral cell surface for proper matrix degradation through invadopodia. The molecular dissection of invadopodia formation and function may contribute to a greater understanding of in vivo invasion, and thus, tumor cell metastasis.

Innate immunity is the first line of defense against invading pathogens. It functions to eliminate pathogens and also to control infections. The innate immune response is also important for the development of pathogen-specific adaptive immune responses. As a result, the study of innate immune signaling pathways is crucial for understanding the interactions between host and pathogen. Unlike mammals, insects lack a classical adaptive immune response and rely mostly on innate immune responses. Innate immune mechanisms have been widely studied in the fruit fly, Drosophila melanogaster. The genetic and molecular tools available in the Drosophila system make it an excellent model system for studying immunity. Furthermore, the innate immune signaling pathways used by Drosophila show strong homology to those of vertebrates making them ideal for studying these pathways. Drosophila immunity relies on cellular and humoral innate immune responses to fight pathogens. The hallmark of the Drosophilahumoral immune response is the rapid induction of antimicrobial peptide genes in the fat body. The production of these antimicrobial peptides is regulated by two immune signaling pathways-Toll and Immune Deficency (IMD) pathways. The Toll pathway responds to many Gram-positive bacterial and fungal infections , while the IMD pathway is potently activated by DAP-type peptidoglycan (PGN) from Gram-negative bacteria and certain Gram-positive bacteria. Two receptors, PGRP-LC and PGRP-LE, are able to recognize DAP-type PGN at the cell surface or in the cytosol, respectively, and trigger the IMD pathway. Upon binding DAP-type PGN, both PGRP-LC and PGRP-LE dimerize/ multimerize and signal to the downstream components of IMD pathway. It is unclear how the receptor activates its downstream components. My work has focused on understanding the molecular events that take place at the receptors following there activation. In these studies I have identified a common motif in the N-terminal domains of both the receptors, known as the RHIM-like domain. The RHIM-like domain is critical for signaling by either receptor, but the mechanism(s) involved remain unclear. IMD, a downstream component of the pathway, associates with both PGRP-LC and -LE but the interaction of PGRP-LC with IMD is not mediated through its RHIM-like domain. Also, mutations affecting the PGRP-LC RHIM-like motif are defective in all known downstream signaling events. However, the RHIM-like mutant receptors are capable of serving as a platform for the assembly of all known components of a receptor proximal signaling complex. These results suggest that another, unidentified component of the IMD signaling pathway may function to mediate interaction with the RHIM-like motif. I performed a yeast two-hybrid screen to identify proteins that might interact with the receptor PGRP-LC through its RHIM- like domain. With this approach, two new components of the IMD pathway were identified. The first component I characterized is called Rudra and it is a critical feedback inhibitor of peptidoglycan receptor signaling. The other factor is known as RYBP, it includes a highly conserved ubiquitin binding motif (NZF), and RNAi studies suggest it is a critical component of the IMD pathway. The identification and characterization of these two new components of the IMD pathway has provided a new insight into the molecular events that take place proximal to the receptor.

No description available.

Recent evidence from cancer research indicates that lactate exerts a suppressive effect on innate immune responses in cancer. This study investigated the mechanisms by which lactate suppresses macrophage pro-inflammatory responses. Macrophages [Raw 264.7 and bone marrow derived macrophages (BMDMs)] were treated with LPS in the presence or absence of lactate. Pro-inflammatory cytokines, NF-κB and YAP activation and nuclear translocation were examined. Our results show that lactate significantly attenuates LPS stimulated macrophage TNF-α and IL-6 production. Lactate also suppresses LPS stimulated macrophage NF-κB and YAP activation and nuclear translocation in macrophages. Interestingly, YAP activation and nuclear translocation are required for LPS stimulated macrophage NF-κB activation and TNFα production. Importantly, lactate suppressed YAP activation and nuclear translocation is mediated by GPR81 dependent AMKP and LATS activation which phosphorylates YAP, resulting in YAP inactivation. Finally, we demonstrated that LPS stimulation induces an interaction between YAP and NF-κB subunit p65, while lactate decreases the interaction of YAP and NF-κB, thus suppressing LPS induced pro-inflammatory cytokine production. Our study demonstrates that lactate exerts a previously unknown role in the suppression of macrophage pro-inflammatory cytokine production via GPR81 mediated YAP inactivation, resulting in disruption of YAP and NF-κB interaction and nuclear translocation in macrophages.