Dissertation (Ph.D.)--University of South Florida, 2008. / Includes vita. Includes bibliographical references. Also available online.

Diss. (sammanfattning) Umeå : Univ., 2007. / Härtill 4 uppsatser.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Dissertation (Ph.D.)--University of South Florida, 2007. / Includes vita. Includes bibliographical references. Also available online.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Forkhead box (Fox) transcription factors have a conserved function in regulating lifespan and onset of age related disease in organisms from worms to mammals. Key functions in this process are the regulation of the cell cycle, oxidative stress response, and apoptosis. A complex post-translational code from nutrient, growth factor, and stress induced signals regulates Fox activity, target specificity, stability, and subcellular localization; however, many of the Fox mechanisms and targets responsible for regulating lifespan remain elusive. The budding yeast, Saccharomyces cerevisiae, is a powerful model for unravelling the genetic mechanism and pathways. Yeast encodes four Fox transcription factors, Fkh1, Fkh2, Fhl1 and Hcm1, and their roles in aging are only recently being examined. In this study, we utilized the chronological lifespan and oxidative stress assays, to explore evolutionary conservation of lifespan regulation in two of the yeast Fox orthologs, FKH1 and FKH2. We observed that deletion of both FKH genes in S. cerevisiae, impedes normal lifespan and stress resistance. Furthermore, fkh1Δ fkh2Δ cells were found to be non-responsive to caloric restriction, an intervention that extends lifespan from yeast to mammals. Conversely, increased expression of the FKHs leads to extended lifespan and improved stress resistance. Additionally, we show the Anaphase-Promoting Complex (APC) genetically interacts with the FKHs, likely functioning in a linear pathway under normal conditions, as fkh1Δ fkh2Δ post-mitotic survival defect is epistatic to that observed in apc5CA mutants. However, under stress conditions, post-mitotic survival is dramatically impaired in apc5CA fkh1Δ fkh2Δ beyond either apc5CA or fkh1Δ fkh2Δ. Finally, we observed that both the FKHs and APC genetically interact with nutrient-responsive lifespan-regulating kinase encoding genes SCH9 and TOR1. This study establishes that the yeast FKHs play a role as regulators of lifespan in yeast and identifies the APC as a novel component of this mechanism. We speculate this involves combined regulation of stress response, genomic stability, and cell cycle.

Dissertation (Ph.D.)--University of South Florida, 2007. / Title from PDF of title page. Document formatted into pages; contains 128 pages. Includes vita. Includes bibliographical references.

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.

Les protéines GILZ (Glucocorticoid-Induced Leucine Zipper) et TSC-22 (Transforming growth factor-beta Stimulated Clone-22) appartiennent à la famille de protéines TSC-22D (TSC-22 Domain). GILZ a été décrit précédemment comme étant induit au cours de la déprivation en interleukine-2 (IL-2) des lymphocytes de la lignée cellulaire CTLL-2, permettant ainsi de retarder leur apoptose. Le but de notre travail était de déterminer les rôles respectifs de GILZ et TSC-22 au cours de l’apoptose des cellules CTLL-2.Nos résultats ont permis de montrer que TSC-22 augmentait l’apoptose induite par la déprivation en IL-2 des cellules CTLL-2. Nous avons mis en évidence une augmentation de l’activation des caspases ainsi qu’une régulation positive de l’expression de BIM. Nous avons en outre montré que l’expression de GILZ, protéine anti-apoptotique, induite lors de la déprivation en IL-2, était régulée négativement en présence de TSC-22. Enfin, nous avons montré que l’expression de l’ARNm de gilz était régulée négativement par TSC-22, mais que la stabilité de son ARNm n’était pas modifiée.Notre travail a donc permis de montrer que TSC-22 accélère l’entrée en apoptose des lymphocytes T en régulant négativement l’expression de la protéine anti-apoptotique GILZ. / GILZ (Glucocorticoid-Induced Leucine Zipper) and TSC-22 (Transforming growth factor-beta Stimulated Clone-22) belong to the TSC-22D (TSC-22 Domain) family of proteins. GILZ has been previously shown to be induced upon interleukin-2 (IL-2) deprivation in the T-cell line CTLL-2, allowing cells to delay apoptosis. The aim of our study was to elucidate the respective roles of GILZ and TSC-22 during IL-2 deprivation-induced T-lymphocytes apoptosis.Our results demonstrated that TSC-22 increased CTLL-2 cells apoptosis induced upon IL-2 deprivation. We highlighted in TSC-22 expressing cells both an increase in caspases activation and BIM expression up-regulation. We also demonstrated that GILZ expression, an anti-apoptotic protein, known to be induced after IL-2 withdrawal, was down-regulated in the presence of TSC-22. Moreover, we showed that gilz mRNA expression was also significantly repressed, but gilz mRNA half-life was not modified.Altogether, these results suggest that, in T-cells, TSC-22 could behave as a repressor of GILZ expression, accelerating IL-2 deprivation-induced apoptosis.