I develop three models that are designed to aid in the analysis of environments in which agents i) benefit from interacting with others, and ii) optimally choose their characteristics mindful of the fact that such choices will influence the quality of interaction that they can expect. Of central interest is the ways in which a concern for interaction affects the efficiency with which agents choose their characteristics. The first two models contrast with previous work in that each agents' relevant characteristics are both unobserved and endogenously determined. The first model provides an explanation for credentialism in the labour market, and demonstrates how a concern for interaction can lead to over-investment in the relevant characteristic. The second model is motivated by human capital development in the presence of peer effects, and demonstrates how a concern for interaction can exacerbate an inherent under-investment problem. The third model retains the feature of unobserved characteristics, and contrasts with previous work by embedding frictions in the process by which agents compete for partners. The model is set in a labour market and demonstrates that outcomes of interest (equilibrium matching patterns, income, inequality and welfare) are generally not monotonic in the level of frictions. / Arts, Faculty of / Vancouver School of Economics / Graduate

The Notch receptor is part of a highly conserved signaling pathway shared in Drosophila, C. elegans and mammals. Extensive studies of Notch signaling have revealed its participation in the development of diverse organ systems including brain, blood cells, blood vessels, gut, and skin. Many genetic modifiers of the Notch signaling pathway have been identified, including some which act at the membrane and others in the nucleus. One such member is Deltex, an E3 ubiquitin ligase, which was originally identified as a modifier of Notch in a Drosophila genetic screen. In early lymphoid development, Deltex has been demonstrated functionally to antagonize Notch signaling but the precise molecular mechanism for this functional antagonism between Notch and Deltex is not understood. However, in Drosophila, recent data supports the formation of a trimeric complex between Deltex, Kurtz and Notch that promotes Notch ubiquitin-mediated proteosomal degradation. Beta-arrestin1 is one of the closest mammalian homologues of Kurtz and functions as an adaptor protein in a variety of cellular processes such as endocytosis, ubiquitination and nuclear shuttling. We hypothesize that a similar interaction occurs in mammalian cells between Notch, beta-arrestin1 and Deltex to negatively modulate the Notch signaling pathway. Our data reveal a physical interaction between beta-arrestin1 and the Notch receptor. We could not, however, detect an interaction between Deltex and beta-arrestin1 by co-immunoprecipitation. We also demonstrate that Notch and beta-arrestin1 physically associate with both a membrane-bound form of activated Notch, as well as the intracellular form of Notch after membrane cleavage. Using RNA interference, as well as overexpression of beta-arrestin1, we demonstrate that beta-arrestin1 negatively regulates a Notch/CSL dependant reporter assay. We also show that the presence of Deltex enhances the negative modulation of the Notch signaling pathway mediated by beta-arrestin1. Therefore, we reveal a new Notch interacting protein and a novel role for beta-arrestin1 in the Notch signaling pathway. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

The short form of dopamine D2 receptor (D2S) functions as a presynaptic autoreceptor on dopamine neurons and has an inhibitory effect on dopaminergic tone. D2-MAPKs pathway is involved in many physiological events like production of prolactin and tyrosine hydroxylase (TH) expression. However, the effect of D2S receptor signalling on MAPKs is cell type specific, and is not fully understood.A recent study in our lab has identified a Gαi-interacting ras-MAPK inhibitor RASA3. Here, we showed that RASA3 is the key effector in D2-induced inhibition of MAPK by knockdown of endogenous RASA3 in the GH4 cell using RASA3 siRNA. We have also transfected a dominant negative RASA3 to compete with the endogenous RASA3 for the binding site on Ras. Both RASA3-siRNA and dominant negative RASA3 blocked D2S-induced inhibition of MAPK activation, clearly implicating that RASA3 is a key effector in Gαi3-dependent D2S mediated MAPKs inhibition To determine whether RASA3’s inhibitory effect could be reconstituted in fibroblast cells, the effect of RASA3 on D2-mediated ERK1/2 activation in COS7 cells was tested. Our results show that both active Gαi2 (or Gαi3) and active RASA3 are required for optimal inhibition of ERK1/2 activation in fibroblast COS7 cells.

The transient response of one-dimensional nonuniform dispersive media is studied through the use of numerical techniques for the inversion of the Laplace transforms of the transient signals. The media considered are those in which the permittivity varies in one spatial dimension only and for which an analytical or numerical solution of the wave equation can be obtained. Two numerical techniques for the inversion of Laplace transforms are used, one in which the inverse transform is obtained in terms of a series of generalized Laguerre polynomials and the other in which the inverse is obtained by direct numerical integration of the complex inversion integral. Responses are calculated for the following cases; (a) a uniform isotropic plasma, (b) dielectric media with a piecewise linear variation in permittivity and (c) isotropic cold plasmas with a piecewise linear variation in electron density, for step-modulated and rectangular-pulse-modulated carrier input signals. It is shown that the results for case (a) compare favorably with the known exact solution, for a unit-step-modulated carrier input signal. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

archives@tulane.edu / G protein-coupled receptors (GPCRs) constitute the largest family of human proteins with approximately around 800 genes and, are therapeutic targets for more than 35% of the FDA-approved drugs with around 180 billion dollars in sales. The therapeutic potential of GPCRs is still not completely utilized. Structure-guided drug discovery will definitely aid in identifying novel compounds with therapeutic responses while minimizing adverse effects in patients. Multiple protein engineering strategies including deletions, truncations, insertion of stable soluble protein or thermostabilizing mutations have been utilized to obtain the structural information of these membrane proteins. Yet to date, the high-resolution structure of only 63 GPCRs have been determined, with only a few of these structures being of active protein. Heterologous expression of most GPCRs results in low yields of active receptors and additional strategies are required to improve active receptor yields for these “hard-to-express” GPCRs. Yeast provides a unique heterologous expression platform to produce mammalian GPCRs, as it also allows us to measure downstream signaling activity with an easy and inexpensive high-throughput assay via its MAPK response pathway. The adenosine A2A receptor (A2AR) shows exceptional expression and trafficking to the plasma membrane in yeast; however, this is not the case for other adenosine receptors. A2AR has a longer C-terminus than the other adenosine receptor subtypes, which may contribute to its exceptional trafficking to the plasma membrane. To test the possibility to improve trafficking of the adenosine A1 receptor (A1R), chimeric receptors containing the seven transmembrane domains of A1R and the full-length or truncated A2AR C-terminus were constructed. The chimeric receptor showed improved localization to the plasma membrane and was capable of binding radioligand with native-like A1R affinity. Functionally active A1R receptor variants were produced at a theoretical yield of 95 pmol/mg total membrane protein, estimated using radioligand binding data, which is greater than three-fold higher than previously reported yields from other heterologous expression systems, and should facilitate biophysical characterization and drug discovery efforts. Recent efforts to determine the high-resolution crystal structures for the adenosine A1 and A2A receptors have utilized modifications to the native receptors in order to facilitate receptor crystallization and structure determination. One common modification is a truncation of the unstructured C-terminus, which has been employed for all the adenosine crystal structures obtained to date. Here, the presence of the full-length C-terminus is shown to affect downstream signaling using a yeast MAPK response-based fluorescence assay. Upon ligand binding, the A1d291R or A2Ad316R variants were unable to couple to human-yeast chimeric G-protein chimeras to generate a downstream signal in yeast, though full-length receptors showed native-like G-protein coupling. Further, constructs transfected into HEK-293 cells showed similar behavior – i.e. the variants with C-terminal truncations lacked cAMP-linked signaling compared to the full-length receptors. Although the C-terminus was essential for Ga protein- associated signaling, chimeras of A1R with a C-terminus of A2AR coupled to the A1R-specific Ga (i.e. Gai1 versus Gas). This surprising result suggests that the C-terminus is important in signaling, but not specificity, for the interaction with Ga protein. Based on these results for chimeric A1R variants, chimeric variants for adenosine A3R and tachykinin 2 receptor (NK2R) were constructed. The A3/A2AR variant was constructed using an approach similar to that for A1/A2AR; the resulting construct showed a two-fold increased expression as compared to the wild-type A3R. This chimeric variant showed native-like signaling activity in engineered yeast strains with a modified MAPK pathway, whereas the wild-type receptor showed no activity. In order to improve the functional expression of human NK2R required for high-resolution structural studies, NK2R chimeras utilizing sequences from rat NK2R previously shown to have a higher functional expression in yeast than human NK2R were utilized. Herein, we show that NK2R chimeras incorporating the rat NK2R C-terminus demonstrated improved expression, ligand binding, and downstream signaling in engineered yeast strains. Taken together, these results highlight the utility of the chimeric receptor engineering strategy to facilitate the expression of active receptors. / 0 / Abhinav Rabindra Jain

No description available.

In S. cerevisiae, the accumulation of dysfunctional mitochondria activates a retrograde signal that is mediated through multiple cytosolic regulators. Central to activation is the cytosolic regulator Rtg2p which through its interaction with Mks1p, promotes the nuclear translocation of Rtg1p/3p. Nuclear localized Rtg1p/3p promotes transcription of target genes. Prior work has shown Rtg2p interaction with Mks1p is required for downstream signaling, however the Mks1p binding site within Rtg2p is unknown. To identify this motif, random mutations were generated in RTG2 and a red-white screening strategy was used to assess 14,001 clones. Sequence analysis identified four mutants with amino acid mutations in the carboxy-terminus of Rtg2p that gave rise to defects in CIT2 transcription and loss of Mks1p interaction. Relative to RTG2, all mutants had reduced Rtg2p protein half-lives. Together these results suggest that the carboxy-terminal domain of Rtg2p is essential for retrograde signaling as it may contain the Mks1p binding site.

Acute myeloid leukemia (AML) is a clonal malignant disease characterized by a blockage in the differentiation of myeloid cells resulting in the accumulation of highly proliferating immature blast cells. With the success of All Trans Retinoic acid (ATRA) in acute promyelocytic leukemia (AML3), differentiation therapy has become a very attractive treatment option. Ligation of CD44 (a cell surface antigen) with anti-CD44 monoclonal antibodies (mAbs) is reported to reverse the blockage of differentiation and suppress the proliferation of blasts derived from most AML subtypes. However, the molecular mechanisms underlying this apparent ‘normalization’ (reversal) of AML cells induced by CD44 have not been fully elucidated. To expand our understanding of the cellular regulation and circuitry involved, we aimed to apply a quantitative phosphoproteomic approach using Stable Isotope Labeling with Amino acids in Cell culture (SILAC) to monitor dynamic changes of phosphorylation states in HL60 cells following treatment with CD44-mAbs. Phosphoproteomic analysis identified differentially phosphorylated proteins among CD44-mAb treated and control HL60 cells that are involved in a number of major signaling pathways as determined by the Ingenuity Pathway analysis (IPA®) platform. Among others, Rho signaling emerged as a major pathway significantly changed by CD44-mAb treatment. Rho GTPases are well-recognized regulators of the actin cytoskeleton but have also been implicated in diverse cellular events such as cell polarity, microtubule dynamics, membrane trafficking, transcriptional regulation, cell growth control and development. An interesting Rho family member, PAK2 was identified in our search. PAK2 is a ubiquitously expressed serine/threonine protein kinase, which is a direct target for small GTPases and has been identified as a switch between cell survival and cell death signaling depending on its mode of activation. Western-blot analyses of cell lysates of CD44-mAb treated and control HL60 cells confirmed that the phosphorylation of PAK2 ,as well as protein level,were altered as early as 5 minutes following treatment. PAK2 knockdown decreased the effect of CD44-mAb induction of proliferation and inhibition of proliferation proving its importance for mediating it’s signaling transduction. PAK1, a structural homologue of PAK2 had the opposite effect of augmenting CD44-mAb effects suggesting a different mechanism involved. This specificity is attributed to the specific mode of activation that PAK2 exhibits which is not shared with the rest of PAK group I members. Caspase-mediated cleavage of PAK2 producing pro-apoptotic fragments is hypothesized to be the signaling transduction mediated by CD44-mAb. In-Vivo experiments show that PAK2 is essential for leukemic cell migration to the spleen. Additionally, it proved essential for CD44-mAb inhibition of leukemic cells migration to the spleen. Further validation and characterization of PAK2’s activation mode, phosphorylation dynamics, subcellular localization as well as its role in invivo migration are essential in understanding its role in AML.

EDCs are commonly thought to bind or interfere with estrogen, androgen, progesterone, thyroid, and retinoid receptors. Oxybenzone is considered to be an endocrine-disrupting chemical and approximately 97% of people in the United States were found to have BP3 in their urine. This thesis will address how BP3 affects the innate immune system, in particular myeloid cells. My Master’s thesis aims to address two main overarching questions. Does BP3 alter macrophage polarization, cytokine/chemokine secretion, the viability in vitro? Does exposure to BP3 in vivo during pregnancy/lactation affect the RNA expression of cytokines and immunosuppressant factors associated with the myeloid population? It is unknown how BP3 impacts immune subpopulations in a neoplastic setting. Additionally, it is important to consider how these effects may contribute to malignant behaviors. My thesis evaluates the effects of BP3 on the Raw 264.7 cell lines as well as tumor tissues from mice exposed to BP3 during pregnancy and lactation. We hypothesized that BP3 exposures induce changes in myeloid cell interactions in the immune system through ER-mediated mechanisms. We anticipated that BP3 would increase the growth and migration of 4T1 cells through indirect signals imparted by myeloid cell populations. We also hypothesized that there will be a decrease in T cell proliferation following BP3 exposure and an alteration in gene expression consistent with a shift from Th1 to Th2. Finally, we expected that BP3 exposure would increase the number of myeloid cells in mouse tumors. Our research shows that oxybenzone appears to enhance the pro-inflammatory state of RAW264.7 cells and may result in the release of unidentified factors that can impact 4T1 cell anchorage-independent cell growth in these pro-inflammatory conditions. BP3 may also impact the metabolic activity of recovering RAW264.7 cells following LPS-induced activity. Additionally, BP3 may impact the release of factors from macrophages that control T cell activation-induced proliferation. By using the p53-/- mouse tumors we found that exposure to 3mg/kg/day BP3 during pregnancy and lactation did alter IDO1 RNA expression but this was not associated with markers of immunosuppressive cell types.

Since the 1970s, dividends have not only become less common (Fama and French, 2001), they have become less sticky, too. Today, it is not uncommon for a firm to cease dividend payments within three years of initiation. I examine the differences between firms that continue to pay dividends for a long period of time after initiation and those that do not. Although investors do not distinguish between the two groups at the time of the dividend initiation announcement, the firms that pay over a long period of time experience superior operating performance in subsequent years. I construct a model that predicts, at the time of the initiation announcement, whether a firm is likely to pay dividends well into the future. My predictions also extend to performance; the firms that I predict to pay for a long period of time also outperform those whose payments I predict to be temporary. Thus, it appears that the relationship between dividend stickiness and long-run performance is not fully reflected in stock returns surrounding the announcements of dividend initiations. / Ph. D.