Exploring the action of immunological effector IFNγ in the biology of neuronal cells and the interaction of CIITA and KLF4 transcription factors during regulation of MHC class II gene expression (Doctoral thesis)

Ξαγαρά, Αναστασία

n recent years, a multifaceted synergy between the nervous and the immune systems has emerged. This synergy is accomplished by mechanisms that have not been fully elucidated. It is well known that all processes that are integral to adult neurogenesis (proliferation, differentiation, cell migration) are influenced by immunological effectors, for example interferon-gamma (IFNγ). However, the way by which these two systems interact remains a fascinating unanswered question. The aim of this dissertation was to investigate the impact of IFNγ, a pleiotropic cytokine of the immune system, in neuronal cell biology.The results of this study demonstrated an explicit influence of IFNγ in key properties of neural cells, such as proliferation and differentiation. Using as models human neuroblastoma cell lines we observed that IFNγ reduces the proliferation of the cells by delaying their progression through the S phase of the cell cycle, and at the same time it promotes the onset of early neuronal differentiation markers. Its continuous presence alters the program of retinoic acid (RA)-induced neuronal differentiation and modifies the response of the cells to neurotrophic factors. The neuroblastoma is characterized by high cellular heterogeneity that is systematically used in clinical practice to classify the stages of the disease. There are at least three different cell types present, which are characterized by their ability to interconvert from one type to another with mechanisms which are not yet known (trans- differentiation). We found that IFNγ favors the differentiation of N-type cells, which constitute the tumorigenic population of neuroblastoma, into S-type cells. As a result, the enrichment with S-type cells reduces the ability of the treated cells to form tumors after injection in mice, indicating that IFNγ may enhance the therapeutic effects of RA by promoting the trans-differentiation toward a non-tumorigenic lineage. We also studied the influence of IFNγ in the biology of normal neural progenitor cells isolated from rat hippocampus. The presence of IFNγ resulted in decreased multipotency and accelerated differentiation towards the neuronal lineage whereas the differentiation to glial lineages was not affected.By analyzing the actions of IFNγ in the neuroblastoma cells we found that in addition to altering the cell type composition as well as their cell fate, this cytokinewas also capable to induce the expression of CIITA, the master regulator of the MHC class II genes as well as that of KLF4, a factor with a critical role in many cellular processes, from proliferation and differentiation to tissue homeostasis, inflammation and oncogenesis. We therefore explored for the first time, the potential interplay of these two transcription factors that are concomitantly induced by IFNγ in the neuronal milieu. In particular, we questioned whether the increase of KLF4 by IFNγ contributes to the induction of MHC class II gene expression. We discovered that KLF4 indeed affects the transactivation potential of CIITA, thereby increasing the expression of MHC II molecules in the neural cell environment. This effect is accompanied by cell type-specific changes in the mobility of CIITA in the nucleus as revealed by FRAP experiments, as well as in the stability of the protein through the proteasome pathway. We further showed that these alterations are caused by the direct interaction of KLF4 with the CIITA amino acid residues 174-330. Interestingly, in a recent report, that coincided with the completion of this dissertation, it was shown that the N-terminal domain of CIITA plays an important role in the rapid turnover of the protein, which is directly linked to its transactivation properties, by favoring a more efficient interaction with the components of the basal transcription machinery.
Institution and School/Department of submitter: Πανεπιστήμιο Ιωαννίνων. Σχολή Επιστημών Υγείας. Τμήμα Βιολογικών Εφαρμογών και Τεχνολογιών
Subject classification: Νευρικό σύστημα
Keywords: Νευροβλάστωμα,Νευρικά κύτταρα,Neuroblastoma,Neuronal cells,IFNγ,MHC II,CIITA,KLF4
URI: http://olympias.lib.uoi.gr/jspui/handle/123456789/29219
Appears in Collections:Διδακτορικές Διατριβές

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